Analysis of Factors Influencing the Uniformity of Impregnation Coating on Reconstituted Tobacco Sheets and Corresponding Control Strategies

Analysis of Factors Influencing the Uniformity of Impregnation Coating on Reconstituted Tobacco Sheets and Corresponding Control Strategies | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Analysis of Factors Influencing the Uniformity of Impregnation Coating on Reconstituted Tobacco Sheets and Corresponding Control Strategies Shuiming WANG, Pengfei LI, Jie LING, Dongdong LEI, Jian WANG, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9501440/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract To address the large fluctuations in coating weight and the poor coating uniformity encountered during the impregnation coating of reconstituted tobacco sheets, a custom-built prototype coating machine capable of simulating actual production conditions was developed. The effects of coating liquid level, coating speed, roller pressure, and roller material on the coating weight of reconstituted tobacco sheets were systematically investigated. Based on the findings, strategies for improving the impregnation coating performance of tobacco sheets were proposed, and the feasibility of an automatic control model for mitigating fluctuations in coating weight was explored. The optimal impregnation coating conditions determined were: use of a felt roller, a coating liquid level of 30 mm, a machine speed of 1.25 m/min, and a roller pressure of 0.14 MPa. impregnation coating reconstituted tobacco sheets coating weight coating uniformity influencing factors Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1 Introduction Reconstituted tobacco, also referred to as tobacco sheet, is a regenerated product manufactured from by-products of cigarette production—such as tobacco fines, stems, and broken leaf pieces—that are otherwise difficult to utilize directly[ 1 ]. Typically used as a cigarette filler, the incorporation of an appropriate proportion of reconstituted tobacco sheet not only enhances the overall utilization efficiency of raw tobacco materials and lowers production costs, but also helps to adjust and improve the physical properties and chemical composition of cigarettes, thereby contributing to better smoking quality[ 2 ]. Consequently, the use of reconstituted tobacco represents an important technical approach for reducing undesirable constituents in cigarette smoke [ 3 ]. Current industrial production methods for reconstituted tobacco sheets primarily include the slurry process, the roller-pressing process, and the paper-making process [ 4 , 5 ]. The present study focuses on the paper-making process and investigates the factors influencing coating uniformity and the corresponding control strategies[ 6 , 7 ]. The paper-making process employs conventional paper-making technology and equipment[ 8 ]. In this process, the tobacco raw material is first extracted with a solvent to separate soluble components from the fibrous and insoluble fractions. The fibrous material is then refined and formed into a base sheet using a paper machine[ 9 – 10 ]. Meanwhile, the soluble extract is concentrated and subsequently reapplied as a coating onto the formed base sheet. After drying, the coated sheet is cut to obtain the final reconstituted tobacco product [ 11 – 13 ]. Coating is a critical step in the paper-making process, and both the coating weight and coating uniformity have a pronounced effect on the quality of the final tobacco sheet[ 14 ]. Currently, problems such as poor coating uniformity and fluctuations in coating weight are frequently encountered in industrial coating operations, which significantly compromise product quality [ 15 – 18 ]. Previous studies have identified several factors that influence the coating weight of reconstituted tobacco sheets, including coating roller material, roller pressure, base sheet basis weight and uniformity, soaking time (governed by coating liquid level and machine speed), coating liquid viscosity, and solid content [ 19 – 20 ]. It has been reported that coating weight generally increases with higher coating liquid concentration and longer contact time; increases initially and then decreases with rising coating liquid temperature; and decreases with increasing roller pressure [ 21 ]. Roller coating is a widely adopted method for applying coatings in the paper-making production of reconstituted tobacco sheets. This technique employs a rotating roller to transfer the coating liquid onto the substrate, enabling straightforward application and making it adaptable to a variety of base materials, including paper, cardboard, plastic films, foils, metal sheets, glass plates, and wooden panels[ 22 ]. Coating rollers are generally classified into two types based on the surface material: steel rollers and rubber rollers. The steel roller functions both as the carrier of the coating liquid and as the rigid backing reference for the substrate and the rubber roller. As the core component of the coating system, its dimensional tolerances, rigidity, surface quality, temperature uniformity, and thermal deformation behavior all directly influence the final coating weight and coating uniformity. In the current paper-making production line for reconstituted tobacco sheets, the basis weight and uniformity of the base sheet are predetermined by the forming section, while the physicochemical properties of the coating liquid (e.g., viscosity and solid content) are fixed during the coating liquid preparation stage. These parameters remain non-adjustable during the coating operation itself and thus constitute inherent factors influencing the system. In contrast, the coating roller material, roller pressure, machine speed, and coating liquid level are all operational variables that can be regulated to control the final coating weight and coating uniformity. Consequently, a systematic investigation into the effects of these adjustable variables is essential for guiding improvements in coating quality. In this study, we first analyze the relationship between the identified variables and coating weight/uniformity. We then conduct controlled coating trials to evaluate the impact of each variable on coating performance. Finally, we examine the feasibility of an automatic control model for dynamic regulation of coating weight and refine the relevant model parameters through experimentation. The overarching goal is to achieve online monitoring of coating liquid physical properties and implement dynamic PID control of coating weight, thereby enhancing the coating quality of paper-making reconstituted tobacco sheets and improving overall product consistency. 2 Materials and methods This study primarily investigates the effects of coating liquid level, machine speed, roller pressure, and roller material (specifically steel versus felt rollers) on the coating weight and uniformity of reconstituted tobacco sheets, and further explores the influence of an automatic control system on coating stability. Single-factor experiments were conducted to evaluate the individual impact of each variable on coating weight, with the aim of identifying optimal process parameters. Subsequently, a PID control system was implemented, and comparative trials were performed under the identified optimal conditions to verify the effectiveness of the automatic control strategy in regulating coating weight—both in scenarios with a predefined target weight and in those without. Finally, the performance of steel rollers and felt rollers was directly compared in terms of their effects on coating weight and uniformity. 2.1 Experimental materials and equipment The coating liquid and base sheets used in this study were supplied by Hubei Xinye Tobacco Development Co., Ltd. The steel roller and felt roller were designed and fabricated in-house, and a laboratory-scale coating apparatus was constructed. The testing and characterization instruments employed included an OUMDL-III intelligent near-infrared coating weight monitoring system, an air compressor, an electrical proportional valve, a forced-air drying oven, and an analytical balance, among others. 2.2 Coating weight measurement and influencing factors All coating trials were performed using the impregnation coating method. The coating weight was determined by both the oven-drying gravimetric method and a near-infrared coating weight monitoring instrument. It should be noted that the monitoring instrument requires recalibration whenever its installation position is altered. 2.2.1 Effect of coating liquid level For this series of experiments, a felt roller was selected as the coating applicator. To minimize the influence of initial adsorption fluctuations on the experimental results, the roller was first brought into full contact with the coating liquid, and measurements were commenced only after the adsorption behavior had stabilized (i.e., approached saturation). A single-factor experimental design was employed, with coating liquid level as the independent variable while all other process parameters were held constant. Specifically, the machine speed was maintained at 1.8 m/min, the roller pressure at 0.15 MPa, and the ambient temperature at 26.5°C. The coating liquid level was set to 5 mm, 30 mm, and 50 mm, thereby adjusting the immersion depth and immersion time of the felt roller (corresponding to immersion times ranging from approximately 0 to 1.3 s). This allowed for the analysis of the effect of liquid level variation on coating weight. The parameter settings for each experimental condition are summarized in Table 1 . Table 1 Experimental design for coating liquid level Experiment number Spindle speed (m/min) Roll pressure (MPa) Temperature (℃) Liquid level (mm) 1 1.8 0.15 26.5 5 2 1.8 0.15 26.5 30 3 1.8 0.15 26.5 50 2.2.2 Effect of machine speed In this set of experiments, machine speed was selected as the independent variable to evaluate its influence on coating weight. Throughout the trials, roller pressure (0.15 MPa), ambient temperature (26.1°C), and coating liquid level (30 mm) were held constant. The machine speed was varied at levels of 0.5, 1.0, 1.2, 1.5, and 1.8 m/min, which directly altered the contact time between the felt roller and the coating liquid. Since the liquid level remained fixed at 30 mm, each change in speed corresponded to a specific immersion time, yielding immersion times of approximately 3.6, 1.8, 1.5, 1.2, and 1.0 s, respectively. The coating weight was measured under each speed condition to investigate the effect of contact time (as governed by machine speed) on the coating process. The detailed experimental parameters are presented in Table 2 . Table 2 Experimental design for spindle speed Experiment number Spindle speed (m/min) Roll pressure (MPa) Temperature (℃) Liquid level (mm) 1 0.5 0.15 26.1 30 2 1 0.15 26.1 30 3 1.2 0.15 26.1 30 4 1.5 0.15 26.1 30 5 1.8 0.15 26.1 30 2.2.3 Effect of roller pressure During the coating process, the uptake of coating liquid by the base sheet occurs primarily through two mechanisms: first, penetration driven by wetting and capillary action at the sheet surface; and second, structural compression of the sheet under an external load, which alters the pore structure and thereby enhances or suppresses volumetric absorption. As a key process parameter, roller pressure significantly influences the adsorption and transfer of the coating liquid by modifying the degree of compaction and, consequently, the pore structure of the sheet. To quantitatively evaluate the effect of roller pressure on coating weight, a single-factor experiment was conducted with all other process parameters held constant. Specifically, the machine speed was maintained at 1.8 m/min, the coating liquid level at 30 mm, and the ambient temperature at 26.2°C. The roller pressure was varied at graded levels within the range of 0.10 to 0.35 MPa. The coating weight was measured under each pressure condition to determine the relationship between roller pressure and coating behavior. The detailed experimental parameters are presented in Table 3 . Table 3 Experimental design for coating roll pressure Experiment number Spindle speed (m/min) Roll pressure (MPa) Temperature (℃) Liquid level (mm) 1 1.8 0.10 26.2 30 2 1.8 0.11 26.2 30 3 1.8 0.12 26.2 30 4 1.8 0.14 26.2 30 5 1.8 0.15 26.2 30 6 1.8 0.16 26.2 30 7 1.8 0.17 26.2 30 8 1.8 0.18 26.2 30 9 1.8 0.22 26.2 30 10 1.8 0.24 26.2 30 11 1.8 0.25 26.2 30 12 1.8 0.26 26.2 30 13 1.8 0.30 26.2 30 14 1.8 0.35 26.2 30 2.2.4 Effect of coating liquid viscosity The viscosity of the coating liquid is an important physical property that influences the coating process. Variations in viscosity directly affect the wetting behavior of the coating liquid on the substrate surface and its ability to penetrate the pore structure, thereby significantly impacting the coating weight. Since temperature is a primary factor governing coating liquid viscosity—with viscosity generally decreasing as temperature increases, thereby enhancing fluidity and permeability—temperature was employed as an indirect control variable to adjust viscosity. Specifically, the coating liquid temperature was set to three levels: 26°C, 35°C, and 45°C. Throughout the experiments, the machine speed (1.2 m/min), roller pressure (0.15 MPa), and coating liquid level (30 mm) were held constant. The coating weight was measured under each temperature condition to evaluate the influence of viscosity variations on coating behavior. The detailed experimental parameters are presented in Table 4 . Table 4 Experimental design for coating liquid viscosity Experiment number Spindle speed (m/min) Roll pressure (MPa) Temperature (℃) Liquid level (mm) 1 1.2 0.15 26 30 2 1.2 0.15 35 30 3 1.2 0.15 45 30 2.2.5 Experiment on automatic control of coating weight The procedure for the automatic coating weight control experiment is illustrated in Fig. 1 . A felt roller was employed as the coating applicator, and the contact pressure at which the passive roller began to rotate was taken as the initial system pressure. By adjusting the roller pressure and simultaneously monitoring the coating weight response in real time, the dynamic characteristics of the coating process were obtained. Analysis of the coating weight response curve as a function of roller pressure enabled identification of the pressure range within which coating weight responds sensitively and approximately linearly to pressure changes. Within this linear response region, the coating weight exhibits favorable controllability and predictability with respect to roller pressure adjustments. Consequently, the effective adjustment range of roller pressure can be established based on this linear region, and the corresponding input range for coating weight can be defined, thereby providing a foundation for subsequent experiments and control strategy development. It should be noted that, owing to variations in structural parameters and initial resistance, different coating systems exhibit distinct relationships between coating weight and roller pressure, particularly with regard to the location and extent of the linear response region. Therefore, for practical applications, preliminary experimental calibration should be performed for each specific system to determine its appropriate roller pressure adjustment range, ensuring the accuracy and stability of automatic coating weight control. 3. Results and analysis 3.1 Effect of coating liquid level on coating performance Both machine speed and coating liquid level influence the contact time between the coating liquid and the base sheet during the impregnation coating process. From experimental observations, it was noted that approximately 10 to 15 seconds were required for the coating liquid to penetrate from one side of the base sheet to the other (as illustrated in Fig. 2 ). In contrast, under typical production conditions, the production line operates at a machine speed of approximately 100 m/min with a coating liquid level of around 15 cm, yielding a contact time of only about 0.09 s. Based on this marked discrepancy, it can be inferred that under actual manufacturing conditions, coating liquid uptake is largely confined to the surface of the base sheet, while any internal liquid absorption is primarily driven by the elastic deformation of the sheet structure rather than by prolonged capillary infiltration. The variation in coating weight as the liquid level was increased from zero to the maximum level was systematically measured in the experiments described below. As illustrated in Fig. 3 , the coating weight exhibits a stepwise increase as the coating liquid level is raised from zero to its maximum. As discussed above, the rapid initial infiltration rate leads to a swift, step-like change in coating weight over a very short time interval. Coating trials were performed at liquid levels of 5 mm, 30 mm, and 50 mm, corresponding to contact times of 0.16 s, 0.1 s, and 1.7 s, respectively. The results of these trials are presented in Fig. 4 . At a constant machine speed—where the contact time remains far shorter than the time required for complete penetration—the coating weight evolves in two distinct stages as the liquid level increases, provided that sufficient coating liquid is available to supply the absorption driven by elastic deformation of the sheet. In the initial step stage, the coating weight rises extremely rapidly (on the order of milliseconds). In the subsequent gradual increase stage, the rate of weight gain progressively diminishes with further increases in liquid level. Given that the contact time on a typical production line is approximately 0.09 s, the influence of liquid level variation on coating weight is confined predominantly to the initial step stage. While liquid level clearly exerts a substantial influence on coating weight, the precise quantitative nature of this effect within the step stage warrants further investigation. 3.2 Effect of machine speed on coating performance As shown in Fig. 5 , the coating weight initially increased and then decreased with increasing machine speed. For a given combination of machine speed and liquid level, the contact time between the base sheet and the coating liquid is fixed. When this contact time is far shorter than the time required for complete liquid penetration, the coating weight becomes highly sensitive to variations in machine speed. This sensitivity arises because machine speed modulates the elastic deformation behavior of the base sheet, and a portion of the coating liquid is taken up via this elastic deformation mechanism. As observed in the liquid level experiments, the coating weight exhibits an initial step-like increase that occurs on a millisecond timescale. In contrast, the contact times corresponding to the machine speeds employed in the present experiments were all greater than one second. Consequently, under the pilot-scale conditions investigated here, the coating weight displayed an overall trend of first increasing and then decreasing as the machine speed was raised. 3.3 Effect of roller pressure on coating performance As shown in Fig. 6 , within the roller pressure range of 0.14 MPa to 0.2 MPa, the coating weight exhibited an approximately linear relationship with roller pressure, decreasing notably as the pressure increased. When the roller pressure exceeded 0.2 MPa, the coating weight tended to stabilize at a comparatively low level with minimal further variation. Based on these observations, the effective adjustment range of roller pressure for subsequent experiments was established as 0.14–0.2 MPa, corresponding to a coating weight range of approximately 37–40 g/m² (equivalent to a coating pick-up of 35%–40% relative to the base sheet weight). Analysis of the relationship between roller pressure and coating weight during the coating process indicates that the total uptake of coating liquid by the base sheet can be divided into two distinct contributions. The first contribution arises from liquid penetration driven by capillary action and infiltration into the base sheet. This portion diminishes as the contact time is reduced, and its magnitude can be quantified under zero liquid level conditions. The second contribution stems from liquid absorption associated with volume deformation of the base sheet. The amount of coating liquid taken up via this mechanism is directly related to the extent of sheet deformation. During the elastic deformation regime, the liquid uptake exhibits an approximately linear dependence on deformation. In contrast, when the base sheet undergoes plastic deformation, the corresponding coating liquid uptake decreases accordingly, as illustrated in Fig. 7 . 3.4 Effect of coating liquid viscosity on coating weight The viscosity of the coating liquid (at a fixed solid content of 38.5%) was measured at various temperatures to establish the relationship between viscosity and temperature, as shown in Fig. 8 . It was noted that the coating liquid employed in this study tended to concentrate upon standing; therefore, the solid content was adjusted to 38.5% by dilution prior to testing. As illustrated in Fig. 8 , the viscosity of the coating liquid decreased with increasing temperature, and the rate of change became progressively smaller at elevated temperatures. Coating trials were subsequently conducted with the coating liquid conditioned at different temperatures, and the corresponding coating weight was determined. The results are presented in Fig. 9 . The coating weight was found to increase with rising temperature (i.e., with decreasing viscosity). A model relating the mean coating weight to temperature (and thus to viscosity) was constructed, as depicted in Fig. 10 . This model enables the quantitative correlation between coating weight and viscosity to be established, thereby providing a correction factor for the output of the automatic control system. Owing to the limited quantity of coating liquid samples available, additional coating trials at higher temperatures (lower viscosities) may be pursued in future work. 3.5 Automatic adjustment of coating weight The system was configured to achieve the target coating weight and to enable automatic adjustment of roller pressure. The resulting control performance is illustrated in Fig. 11 . When a target coating weight was preset, the system performed satisfactorily. Specifically, whenever the real-time coating weight deviated from the set value beyond the allowable tolerance, the system adjusted the roller pressure to restore the coating weight to the predetermined range. This closed-loop control strategy effectively suppressed the large fluctuations in coating weight that commonly occur during production, leading to improved product uniformity. 3.6 Feedback of roller pressure system in the production line during shutdown The output of the electrical proportional valve from the pilot-scale device was connected to the air inlet of the pressurizing buffer tank on the production line coating machine, enabling adjustment of the roller pressure over the range of 0.10 MPa to 0.16 MPa in increments of 0.01 MPa. The response time of the coating roller pressure and the pressure variation of the pressurizing system were monitored. Based on observations of the air drum and pressurizing system pressure, the pressure response of the air drum and pressurizing system was found to be delayed by approximately 15–20 s, a delay attributed to the water level in the buffer tank and the output flow rate of the electrical proportional valve. Under actual production line conditions, the PID parameters should be retuned according to the specific delay time encountered. 3.7 Effect of roller material on coating performance Figure 12 compares the coating performance of the steel roller and the felt roller. The felt roller produces more pronounced edge effects during coating but yields better overall coating uniformity. 4 Conclusion This study investigated the effects of coating liquid level, machine speed, roller pressure, and coating liquid temperature on the coating weight of reconstituted tobacco sheets. Analysis of the experimental results revealed the following key findings: (1) as the coating liquid level was increased from zero to its maximum, the coating weight exhibited a distinct stepwise increase; (2) with increasing machine speed, the coating weight initially rose sharply and then declined gradually; (3) as roller pressure increased, the coating weight first increased and then decreased; (4) elevated temperature reduced the viscosity of the coating liquid, thereby leading to an increase in coating weight; and (5) compared with the steel roller, the felt roller produced more pronounced edge effects but delivered superior overall coating uniformity. The optimal process conditions determined from the experiments were as follows: use of a felt roller, a coating liquid level of 30 mm, a machine speed of 1.25 m/min, and a roller pressure of 0.14 MPa. It should be noted that these optimal parameters may require further refinement and adjustment during actual production trials to accommodate specific equipment configurations and production requirements. Following PID tuning, the automatic control system for coating weight demonstrated satisfactory performance in maintaining the target coating weight. Declarations Funding Declaration The authors declare that no financial support or funding from any institution, organization, or agency was received for the research, authorship, and/or publication of this article. Author contributions WANG Shuiming and LI Pengfei conceived and designed the experiments, analyzed the data, and wrote the main manuscript text. LING Jie performed the single‑factor coating experiments and contributed to data interpretation. LEI Dongdong, WANG Jian, and XIA Zhigang participated in the construction of the pilot coating machine and the automatic control system setup. ZHANG Yi and XU Long prepared figures 1–10, performed the literature review, and revised the manuscript. All authors reviewed and approved the final manuscript. Data Availability All data supporting the findings of this study are available within the paper. Experimental design for coating liquid level, spindle speed and coating roll pressure are provided in Supplementary Table 1, 2, 3. References Chen Z, Cai B, Wang J, et al. Comparison between domestic and foreign paper-process tobacco sheets. Tobacco Science & Technology, 2002(02): 4-10. Liu W, Liu G, Che J, et al. Present status of preparation technology of reconstituted tobacco. China Pulp & Paper, 2009, 28(07): 55-60. Hui J, Li H, Wei Q, et al. Influence of coatings coverage rate on comprehensive quality of reconstituted tobacco. Chinese Journal of Spectroscopy Laboratory, 2012, 29(03): 1729-1733. Qiu Y. Development research report on China's paper-process tobacco sheet. Scientific Research Monthly (Hong Kong), 2006(12): 186-188. 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Journal of Yunnan University (Natural Sciences Edition), 2014, 36(S1): 130-134. He L, Wu L, Liu Y, et al. Technology for coating calcium carbonate on surface of paper-making process reconstituted tobacco. Tobacco Science & Technology, 2013(12): 5-8. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9501440","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":632844029,"identity":"75be3e0e-1d53-45aa-8d66-dc26f85c5771","order_by":0,"name":"Shuiming WANG","email":"","orcid":"","institution":"China Tobacco Hubei Industrial","correspondingAuthor":false,"prefix":"","firstName":"Shuiming","middleName":"","lastName":"WANG","suffix":""},{"id":632844031,"identity":"fa699329-7cb6-463f-93bd-45ad21eccdef","order_by":1,"name":"Pengfei 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LEI","email":"","orcid":"","institution":"China Tobacco Hubei Industrial","correspondingAuthor":false,"prefix":"","firstName":"Dongdong","middleName":"","lastName":"LEI","suffix":""},{"id":632844038,"identity":"11c23dfa-9624-429f-a7c4-f16bc9dbfa22","order_by":4,"name":"Jian WANG","email":"","orcid":"","institution":"China Tobacco Hubei Industrial","correspondingAuthor":false,"prefix":"","firstName":"Jian","middleName":"","lastName":"WANG","suffix":""},{"id":632844040,"identity":"36398c6b-b25b-45cf-9069-bb98edba15af","order_by":5,"name":"Zhigang XIA","email":"","orcid":"","institution":"China Tobacco Hubei Industrial","correspondingAuthor":false,"prefix":"","firstName":"Zhigang","middleName":"","lastName":"XIA","suffix":""},{"id":632844041,"identity":"bee0476e-56f3-416f-94a7-940b8b402a72","order_by":6,"name":"Yi ZHANG","email":"","orcid":"","institution":"China Tobacco Hubei Industrial","correspondingAuthor":false,"prefix":"","firstName":"Yi","middleName":"","lastName":"ZHANG","suffix":""},{"id":632844042,"identity":"84aec39c-e86e-44dd-8f5e-9557bfcd34fa","order_by":7,"name":"Long XU","email":"","orcid":"","institution":"China Tobacco Hubei Industrial","correspondingAuthor":false,"prefix":"","firstName":"Long","middleName":"","lastName":"XU","suffix":""}],"badges":[],"createdAt":"2026-04-23 02:38:56","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9501440/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9501440/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108806580,"identity":"1da10c87-14f0-4b44-80c0-a793c70c0032","added_by":"auto","created_at":"2026-05-08 15:28:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":240831,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart of automatic coating weight adjustment\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/bfc798dfdc8ca0f2f8ffde29.png"},{"id":108733943,"identity":"741330b0-20b8-45df-803e-778f45f829bd","added_by":"auto","created_at":"2026-05-07 19:44:42","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":162539,"visible":true,"origin":"","legend":"\u003cp\u003eSubstrates with dipping times of 0, 10 s, 60 s, and 90 s\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/a5d54d7d869fb1482c2457d7.jpeg"},{"id":108733944,"identity":"485dcb14-0971-467d-aa8e-affc4d097cde","added_by":"auto","created_at":"2026-05-07 19:44:42","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":74880,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between coating weight and coating liquid level\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/883ffc4a47e977227554f327.png"},{"id":108806162,"identity":"6ba23e7f-c528-4a94-af3d-2dec46178505","added_by":"auto","created_at":"2026-05-08 15:27:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":64239,"visible":true,"origin":"","legend":"\u003cp\u003eCurve of coating weight versus coating liquid level\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/ad54b2b8149d510993c79ab2.png"},{"id":108977115,"identity":"e3d92b87-cdb4-4190-854e-36b96372a56c","added_by":"auto","created_at":"2026-05-11 11:30:26","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":79383,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of machine speed variation on coating weight\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/d76ef3a843a94acc6b74bf55.png"},{"id":108733946,"identity":"08329c9b-1e47-4dbb-b841-225013248d56","added_by":"auto","created_at":"2026-05-07 19:44:42","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":83595,"visible":true,"origin":"","legend":"\u003cp\u003eCoating weight as a function of roller pressure\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/8c900f4b685fb398be738884.png"},{"id":108807052,"identity":"adc8c9db-9492-4499-9600-5aa3b915b8c8","added_by":"auto","created_at":"2026-05-08 15:30:01","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":95149,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of base sheet deformation and coating liquid uptake during the coating process\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/0b9c1ef69ed05dd1f32b3494.png"},{"id":109221575,"identity":"3739833c-f235-4d51-a9b8-e6e615054d16","added_by":"auto","created_at":"2026-05-13 20:46:39","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":66404,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of coating liquid viscosity with temperature\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/b6e319175f7b02087080cdb7.png"},{"id":108733951,"identity":"105b4ee0-6179-4104-b098-158bdfd378d8","added_by":"auto","created_at":"2026-05-07 19:44:42","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":185105,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of coating liquid temperature on coating weight\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/0b87a5b56b704fa874a003e6.png"},{"id":108806536,"identity":"e66c6f3c-ab88-42ca-ba56-5d37a1ce3c0f","added_by":"auto","created_at":"2026-05-08 15:28:52","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":68882,"visible":true,"origin":"","legend":"\u003cp\u003eFitted curve of coating weight versus temperature\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/86576fd19d1ef2c96a2e1285.png"},{"id":108733953,"identity":"f0c994f7-6e3b-4950-a750-b892e403f35e","added_by":"auto","created_at":"2026-05-07 19:44:42","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":129651,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in coating weight under automatic control modes: without a preset target versus with a preset target\u003c/p\u003e\n\u003cp\u003ePID tuning parameters: setpoint = 37%; proportional gain = 3; integral time = 0.1 min; derivative time = 1 min.\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/5d325090338deace6657c0f0.png"},{"id":108806578,"identity":"eb062769-e62c-4cb1-be21-3fa01337a761","added_by":"auto","created_at":"2026-05-08 15:28:57","extension":"jpeg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":525131,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of coating performance between steel roller (left) and felt roller (right)\u003c/p\u003e","description":"","filename":"floatimage12.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/8ad19969bee6f76d3f61203b.jpeg"},{"id":109252355,"identity":"6c217827-d698-4b49-9485-94fee0cf3ca9","added_by":"auto","created_at":"2026-05-14 09:25:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1838478,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9501440/v1/06dad97a-aebd-45d7-822b-81f49bdee526.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Analysis of Factors Influencing the Uniformity of Impregnation Coating on Reconstituted Tobacco Sheets and Corresponding Control Strategies","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eReconstituted tobacco, also referred to as tobacco sheet, is a regenerated product manufactured from by-products of cigarette production\u0026mdash;such as tobacco fines, stems, and broken leaf pieces\u0026mdash;that are otherwise difficult to utilize directly[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Typically used as a cigarette filler, the incorporation of an appropriate proportion of reconstituted tobacco sheet not only enhances the overall utilization efficiency of raw tobacco materials and lowers production costs, but also helps to adjust and improve the physical properties and chemical composition of cigarettes, thereby contributing to better smoking quality[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Consequently, the use of reconstituted tobacco represents an important technical approach for reducing undesirable constituents in cigarette smoke [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCurrent industrial production methods for reconstituted tobacco sheets primarily include the slurry process, the roller-pressing process, and the paper-making process [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The present study focuses on the paper-making process and investigates the factors influencing coating uniformity and the corresponding control strategies[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The paper-making process employs conventional paper-making technology and equipment[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In this process, the tobacco raw material is first extracted with a solvent to separate soluble components from the fibrous and insoluble fractions. The fibrous material is then refined and formed into a base sheet using a paper machine[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Meanwhile, the soluble extract is concentrated and subsequently reapplied as a coating onto the formed base sheet. After drying, the coated sheet is cut to obtain the final reconstituted tobacco product [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Coating is a critical step in the paper-making process, and both the coating weight and coating uniformity have a pronounced effect on the quality of the final tobacco sheet[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Currently, problems such as poor coating uniformity and fluctuations in coating weight are frequently encountered in industrial coating operations, which significantly compromise product quality [\u003cspan additionalcitationids=\"CR16 CR17\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Previous studies have identified several factors that influence the coating weight of reconstituted tobacco sheets, including coating roller material, roller pressure, base sheet basis weight and uniformity, soaking time (governed by coating liquid level and machine speed), coating liquid viscosity, and solid content [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. It has been reported that coating weight generally increases with higher coating liquid concentration and longer contact time; increases initially and then decreases with rising coating liquid temperature; and decreases with increasing roller pressure [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRoller coating is a widely adopted method for applying coatings in the paper-making production of reconstituted tobacco sheets. This technique employs a rotating roller to transfer the coating liquid onto the substrate, enabling straightforward application and making it adaptable to a variety of base materials, including paper, cardboard, plastic films, foils, metal sheets, glass plates, and wooden panels[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Coating rollers are generally classified into two types based on the surface material: steel rollers and rubber rollers. The steel roller functions both as the carrier of the coating liquid and as the rigid backing reference for the substrate and the rubber roller. As the core component of the coating system, its dimensional tolerances, rigidity, surface quality, temperature uniformity, and thermal deformation behavior all directly influence the final coating weight and coating uniformity.\u003c/p\u003e \u003cp\u003eIn the current paper-making production line for reconstituted tobacco sheets, the basis weight and uniformity of the base sheet are predetermined by the forming section, while the physicochemical properties of the coating liquid (e.g., viscosity and solid content) are fixed during the coating liquid preparation stage. These parameters remain non-adjustable during the coating operation itself and thus constitute inherent factors influencing the system. In contrast, the coating roller material, roller pressure, machine speed, and coating liquid level are all operational variables that can be regulated to control the final coating weight and coating uniformity. Consequently, a systematic investigation into the effects of these adjustable variables is essential for guiding improvements in coating quality. In this study, we first analyze the relationship between the identified variables and coating weight/uniformity. We then conduct controlled coating trials to evaluate the impact of each variable on coating performance. Finally, we examine the feasibility of an automatic control model for dynamic regulation of coating weight and refine the relevant model parameters through experimentation. The overarching goal is to achieve online monitoring of coating liquid physical properties and implement dynamic PID control of coating weight, thereby enhancing the coating quality of paper-making reconstituted tobacco sheets and improving overall product consistency.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cp\u003eThis study primarily investigates the effects of coating liquid level, machine speed, roller pressure, and roller material (specifically steel versus felt rollers) on the coating weight and uniformity of reconstituted tobacco sheets, and further explores the influence of an automatic control system on coating stability. Single-factor experiments were conducted to evaluate the individual impact of each variable on coating weight, with the aim of identifying optimal process parameters. Subsequently, a PID control system was implemented, and comparative trials were performed under the identified optimal conditions to verify the effectiveness of the automatic control strategy in regulating coating weight\u0026mdash;both in scenarios with a predefined target weight and in those without. Finally, the performance of steel rollers and felt rollers was directly compared in terms of their effects on coating weight and uniformity.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Experimental materials and equipment\u003c/h2\u003e \u003cp\u003eThe coating liquid and base sheets used in this study were supplied by Hubei Xinye Tobacco Development Co., Ltd. The steel roller and felt roller were designed and fabricated in-house, and a laboratory-scale coating apparatus was constructed. The testing and characterization instruments employed included an OUMDL-III intelligent near-infrared coating weight monitoring system, an air compressor, an electrical proportional valve, a forced-air drying oven, and an analytical balance, among others.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Coating weight measurement and influencing factors\u003c/h2\u003e \u003cp\u003eAll coating trials were performed using the impregnation coating method. The coating weight was determined by both the oven-drying gravimetric method and a near-infrared coating weight monitoring instrument. It should be noted that the monitoring instrument requires recalibration whenever its installation position is altered.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Effect of coating liquid level\u003c/h2\u003e \u003cp\u003eFor this series of experiments, a felt roller was selected as the coating applicator. To minimize the influence of initial adsorption fluctuations on the experimental results, the roller was first brought into full contact with the coating liquid, and measurements were commenced only after the adsorption behavior had stabilized (i.e., approached saturation). A single-factor experimental design was employed, with coating liquid level as the independent variable while all other process parameters were held constant. Specifically, the machine speed was maintained at 1.8 m/min, the roller pressure at 0.15 MPa, and the ambient temperature at 26.5\u0026deg;C. The coating liquid level was set to 5 mm, 30 mm, and 50 mm, thereby adjusting the immersion depth and immersion time of the felt roller (corresponding to immersion times ranging from approximately 0 to 1.3 s). This allowed for the analysis of the effect of liquid level variation on coating weight. The parameter settings for each experimental condition are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental design for coating liquid level\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExperiment number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpindle speed\u003c/p\u003e \u003cp\u003e(m/min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRoll pressure\u003c/p\u003e \u003cp\u003e(MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTemperature\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLiquid level\u003c/p\u003e \u003cp\u003e(mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Effect of machine speed\u003c/h2\u003e \u003cp\u003eIn this set of experiments, machine speed was selected as the independent variable to evaluate its influence on coating weight. Throughout the trials, roller pressure (0.15 MPa), ambient temperature (26.1\u0026deg;C), and coating liquid level (30 mm) were held constant. The machine speed was varied at levels of 0.5, 1.0, 1.2, 1.5, and 1.8 m/min, which directly altered the contact time between the felt roller and the coating liquid. Since the liquid level remained fixed at 30 mm, each change in speed corresponded to a specific immersion time, yielding immersion times of approximately 3.6, 1.8, 1.5, 1.2, and 1.0 s, respectively. The coating weight was measured under each speed condition to investigate the effect of contact time (as governed by machine speed) on the coating process. The detailed experimental parameters are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental design for spindle speed\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExperiment number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpindle speed\u003c/p\u003e \u003cp\u003e(m/min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRoll pressure\u003c/p\u003e \u003cp\u003e(MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTemperature\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLiquid level (mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.2.3 Effect of roller pressure\u003c/h2\u003e \u003cp\u003eDuring the coating process, the uptake of coating liquid by the base sheet occurs primarily through two mechanisms: first, penetration driven by wetting and capillary action at the sheet surface; and second, structural compression of the sheet under an external load, which alters the pore structure and thereby enhances or suppresses volumetric absorption. As a key process parameter, roller pressure significantly influences the adsorption and transfer of the coating liquid by modifying the degree of compaction and, consequently, the pore structure of the sheet.\u003c/p\u003e \u003cp\u003eTo quantitatively evaluate the effect of roller pressure on coating weight, a single-factor experiment was conducted with all other process parameters held constant. Specifically, the machine speed was maintained at 1.8 m/min, the coating liquid level at 30 mm, and the ambient temperature at 26.2\u0026deg;C. The roller pressure was varied at graded levels within the range of 0.10 to 0.35 MPa. The coating weight was measured under each pressure condition to determine the relationship between roller pressure and coating behavior. The detailed experimental parameters are presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental design for coating roll pressure\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExperiment number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpindle speed\u003c/p\u003e \u003cp\u003e(m/min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRoll pressure\u003c/p\u003e \u003cp\u003e(MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTemperature\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLiquid level (mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.2.4 Effect of coating liquid viscosity\u003c/h2\u003e \u003cp\u003eThe viscosity of the coating liquid is an important physical property that influences the coating process. Variations in viscosity directly affect the wetting behavior of the coating liquid on the substrate surface and its ability to penetrate the pore structure, thereby significantly impacting the coating weight. Since temperature is a primary factor governing coating liquid viscosity\u0026mdash;with viscosity generally decreasing as temperature increases, thereby enhancing fluidity and permeability\u0026mdash;temperature was employed as an indirect control variable to adjust viscosity. Specifically, the coating liquid temperature was set to three levels: 26\u0026deg;C, 35\u0026deg;C, and 45\u0026deg;C. Throughout the experiments, the machine speed (1.2 m/min), roller pressure (0.15 MPa), and coating liquid level (30 mm) were held constant. The coating weight was measured under each temperature condition to evaluate the influence of viscosity variations on coating behavior. The detailed experimental parameters are presented in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental design for coating liquid viscosity\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExperiment number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpindle speed\u003c/p\u003e \u003cp\u003e(m/min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRoll pressure\u003c/p\u003e \u003cp\u003e(MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTemperature\u003c/p\u003e \u003cp\u003e(℃)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLiquid level\u003c/p\u003e \u003cp\u003e(mm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.2.5 Experiment on automatic control of coating weight\u003c/h2\u003e \u003cp\u003eThe procedure for the automatic coating weight control experiment is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A felt roller was employed as the coating applicator, and the contact pressure at which the passive roller began to rotate was taken as the initial system pressure. By adjusting the roller pressure and simultaneously monitoring the coating weight response in real time, the dynamic characteristics of the coating process were obtained. Analysis of the coating weight response curve as a function of roller pressure enabled identification of the pressure range within which coating weight responds sensitively and approximately linearly to pressure changes. Within this linear response region, the coating weight exhibits favorable controllability and predictability with respect to roller pressure adjustments. Consequently, the effective adjustment range of roller pressure can be established based on this linear region, and the corresponding input range for coating weight can be defined, thereby providing a foundation for subsequent experiments and control strategy development.\u003c/p\u003e \u003cp\u003eIt should be noted that, owing to variations in structural parameters and initial resistance, different coating systems exhibit distinct relationships between coating weight and roller pressure, particularly with regard to the location and extent of the linear response region. Therefore, for practical applications, preliminary experimental calibration should be performed for each specific system to determine its appropriate roller pressure adjustment range, ensuring the accuracy and stability of automatic coating weight control.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and analysis","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Effect of coating liquid level on coating performance\u003c/h2\u003e\n \u003cp\u003eBoth machine speed and coating liquid level influence the contact time between the coating liquid and the base sheet during the impregnation coating process. From experimental observations, it was noted that approximately 10 to 15 seconds were required for the coating liquid to penetrate from one side of the base sheet to the other (as illustrated in Fig. \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In contrast, under typical production conditions, the production line operates at a machine speed of approximately 100 m/min with a coating liquid level of around 15 cm, yielding a contact time of only about 0.09 s. Based on this marked discrepancy, it can be inferred that under actual manufacturing conditions, coating liquid uptake is largely confined to the surface of the base sheet, while any internal liquid absorption is primarily driven by the elastic deformation of the sheet structure rather than by prolonged capillary infiltration. The variation in coating weight as the liquid level was increased from zero to the maximum level was systematically measured in the experiments described below.\u003c/p\u003e\n \u003cp\u003eAs illustrated in Fig. \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the coating weight exhibits a stepwise increase as the coating liquid level is raised from zero to its maximum. As discussed above, the rapid initial infiltration rate leads to a swift, step-like change in coating weight over a very short time interval. Coating trials were performed at liquid levels of 5 mm, 30 mm, and 50 mm, corresponding to contact times of 0.16 s, 0.1 s, and 1.7 s, respectively. The results of these trials are presented in Fig. \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. At a constant machine speed\u0026mdash;where the contact time remains far shorter than the time required for complete penetration\u0026mdash;the coating weight evolves in two distinct stages as the liquid level increases, provided that sufficient coating liquid is available to supply the absorption driven by elastic deformation of the sheet. In the initial step stage, the coating weight rises extremely rapidly (on the order of milliseconds). In the subsequent gradual increase stage, the rate of weight gain progressively diminishes with further increases in liquid level. Given that the contact time on a typical production line is approximately 0.09 s, the influence of liquid level variation on coating weight is confined predominantly to the initial step stage. While liquid level clearly exerts a substantial influence on coating weight, the precise quantitative nature of this effect within the step stage warrants further investigation.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Effect of machine speed on coating performance\u003c/h2\u003e\n \u003cp\u003eAs shown in Fig. \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the coating weight initially increased and then decreased with increasing machine speed. For a given combination of machine speed and liquid level, the contact time between the base sheet and the coating liquid is fixed. When this contact time is far shorter than the time required for complete liquid penetration, the coating weight becomes highly sensitive to variations in machine speed. This sensitivity arises because machine speed modulates the elastic deformation behavior of the base sheet, and a portion of the coating liquid is taken up via this elastic deformation mechanism. As observed in the liquid level experiments, the coating weight exhibits an initial step-like increase that occurs on a millisecond timescale. In contrast, the contact times corresponding to the machine speeds employed in the present experiments were all greater than one second. Consequently, under the pilot-scale conditions investigated here, the coating weight displayed an overall trend of first increasing and then decreasing as the machine speed was raised.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Effect of roller pressure on coating performance\u003c/h2\u003e\n \u003cp\u003eAs shown in Fig. \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, within the roller pressure range of 0.14 MPa to 0.2 MPa, the coating weight exhibited an approximately linear relationship with roller pressure, decreasing notably as the pressure increased. When the roller pressure exceeded 0.2 MPa, the coating weight tended to stabilize at a comparatively low level with minimal further variation. Based on these observations, the effective adjustment range of roller pressure for subsequent experiments was established as 0.14\u0026ndash;0.2 MPa, corresponding to a coating weight range of approximately 37\u0026ndash;40 g/m\u0026sup2; (equivalent to a coating pick-up of 35%\u0026ndash;40% relative to the base sheet weight).\u003c/p\u003e\n \u003cp\u003eAnalysis of the relationship between roller pressure and coating weight during the coating process indicates that the total uptake of coating liquid by the base sheet can be divided into two distinct contributions. The first contribution arises from liquid penetration driven by capillary action and infiltration into the base sheet. This portion diminishes as the contact time is reduced, and its magnitude can be quantified under zero liquid level conditions. The second contribution stems from liquid absorption associated with volume deformation of the base sheet. The amount of coating liquid taken up via this mechanism is directly related to the extent of sheet deformation. During the elastic deformation regime, the liquid uptake exhibits an approximately linear dependence on deformation. In contrast, when the base sheet undergoes plastic deformation, the corresponding coating liquid uptake decreases accordingly, as illustrated in Fig. \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Effect of coating liquid viscosity on coating weight\u003c/h2\u003e\n \u003cp\u003eThe viscosity of the coating liquid (at a fixed solid content of 38.5%) was measured at various temperatures to establish the relationship between viscosity and temperature, as shown in Fig. \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. It was noted that the coating liquid employed in this study tended to concentrate upon standing; therefore, the solid content was adjusted to 38.5% by dilution prior to testing. As illustrated in Fig. \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the viscosity of the coating liquid decreased with increasing temperature, and the rate of change became progressively smaller at elevated temperatures. Coating trials were subsequently conducted with the coating liquid conditioned at different temperatures, and the corresponding coating weight was determined. The results are presented in Fig. \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The coating weight was found to increase with rising temperature (i.e., with decreasing viscosity). A model relating the mean coating weight to temperature (and thus to viscosity) was constructed, as depicted in Fig. \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. This model enables the quantitative correlation between coating weight and viscosity to be established, thereby providing a correction factor for the output of the automatic control system. Owing to the limited quantity of coating liquid samples available, additional coating trials at higher temperatures (lower viscosities) may be pursued in future work.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5 Automatic adjustment of coating weight\u003c/h2\u003e\n \u003cp\u003eThe system was configured to achieve the target coating weight and to enable automatic adjustment of roller pressure. The resulting control performance is illustrated in Fig. \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. When a target coating weight was preset, the system performed satisfactorily. Specifically, whenever the real-time coating weight deviated from the set value beyond the allowable tolerance, the system adjusted the roller pressure to restore the coating weight to the predetermined range. This closed-loop control strategy effectively suppressed the large fluctuations in coating weight that commonly occur during production, leading to improved product uniformity.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e3.6 Feedback of roller pressure system in the production line during shutdown\u003c/h2\u003e\n \u003cp\u003eThe output of the electrical proportional valve from the pilot-scale device was connected to the air inlet of the pressurizing buffer tank on the production line coating machine, enabling adjustment of the roller pressure over the range of 0.10 MPa to 0.16 MPa in increments of 0.01 MPa. The response time of the coating roller pressure and the pressure variation of the pressurizing system were monitored.\u003c/p\u003e\n \u003cp\u003eBased on observations of the air drum and pressurizing system pressure, the pressure response of the air drum and pressurizing system was found to be delayed by approximately 15\u0026ndash;20 s, a delay attributed to the water level in the buffer tank and the output flow rate of the electrical proportional valve. Under actual production line conditions, the PID parameters should be retuned according to the specific delay time encountered.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003e3.7 Effect of roller material on coating performance\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e compares the coating performance of the steel roller and the felt roller. The felt roller produces more pronounced edge effects during coating but yields better overall coating uniformity.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eThis study investigated the effects of coating liquid level, machine speed, roller pressure, and coating liquid temperature on the coating weight of reconstituted tobacco sheets. Analysis of the experimental results revealed the following key findings: (1) as the coating liquid level was increased from zero to its maximum, the coating weight exhibited a distinct stepwise increase; (2) with increasing machine speed, the coating weight initially rose sharply and then declined gradually; (3) as roller pressure increased, the coating weight first increased and then decreased; (4) elevated temperature reduced the viscosity of the coating liquid, thereby leading to an increase in coating weight; and (5) compared with the steel roller, the felt roller produced more pronounced edge effects but delivered superior overall coating uniformity.\u003c/p\u003e \u003cp\u003eThe optimal process conditions determined from the experiments were as follows: use of a felt roller, a coating liquid level of 30 mm, a machine speed of 1.25 m/min, and a roller pressure of 0.14 MPa. It should be noted that these optimal parameters may require further refinement and adjustment during actual production trials to accommodate specific equipment configurations and production requirements. Following PID tuning, the automatic control system for coating weight demonstrated satisfactory performance in maintaining the target coating weight.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that no financial support or funding from any institution, organization, or agency was received for the research, authorship, and/or publication of this article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWANG Shuiming and LI Pengfei conceived and designed the experiments, analyzed the data, and wrote the main manuscript text. LING Jie performed the single‑factor coating experiments and contributed to data interpretation. LEI Dongdong, WANG Jian, and XIA Zhigang participated in the construction of the pilot coating machine and the automatic control system setup. ZHANG Yi and XU Long prepared figures 1\u0026ndash;10, performed the literature review, and revised the manuscript. All authors reviewed and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data supporting the findings of this study are available within the paper. Experimental design for coating liquid level, spindle speed and coating roll pressure are provided in Supplementary Table 1, 2, 3.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eChen Z, Cai B, Wang J, et al. Comparison between domestic and foreign paper-process tobacco sheets. Tobacco Science \u0026amp; Technology, 2002(02): 4-10.\u003c/li\u003e\n\u003cli\u003eLiu W, Liu G, Che J, et al. 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Tobacco Science \u0026amp; Technology, 2013(12): 5-8.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"impregnation coating, reconstituted tobacco sheets, coating weight, coating uniformity, influencing factors","lastPublishedDoi":"10.21203/rs.3.rs-9501440/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9501440/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTo address the large fluctuations in coating weight and the poor coating uniformity encountered during the impregnation coating of reconstituted tobacco sheets, a custom-built prototype coating machine capable of simulating actual production conditions was developed. The effects of coating liquid level, coating speed, roller pressure, and roller material on the coating weight of reconstituted tobacco sheets were systematically investigated. Based on the findings, strategies for improving the impregnation coating performance of tobacco sheets were proposed, and the feasibility of an automatic control model for mitigating fluctuations in coating weight was explored. The optimal impregnation coating conditions determined were: use of a felt roller, a coating liquid level of 30 mm, a machine speed of 1.25 m/min, and a roller pressure of 0.14 MPa.\u003c/p\u003e","manuscriptTitle":"Analysis of Factors Influencing the Uniformity of Impregnation Coating on Reconstituted Tobacco Sheets and Corresponding Control Strategies","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-07 19:44:37","doi":"10.21203/rs.3.rs-9501440/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0b76cf36-8373-469e-a70d-074ad897a4f4","owner":[],"postedDate":"May 7th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"317226726299520622073491072648974710479","date":"2026-05-15T06:36:36+00:00","index":13,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-07T19:44:37+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-07 19:44:37","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9501440","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9501440","identity":"rs-9501440","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}