Quantitative prediction method for leveling time of coating wet film

Abstract

The invention discloses a quantitative prediction method for leveling time of a coating wet film, and belongs to the technical field of surface coating of metal plates. The method aims at solving the problems that the leveling time is difficult to accurately estimate due to the change of physical characteristics of the coating, and the adjustment of a production process depends on experience. The method comprises the following steps: firstly, acquiring roller coating process parameters, coating physical attribute parameters and wet film initial surface topography parameters; secondly, the average thickness of the wet film is calculated through a preset wet film thickness theoretical model; and finally, substituting the calculated thickness and other parameters into a preset leveling time theoretical model so as to quantitatively predict the time required for leveling. By establishing the parameterized mathematical model, a quantitative basis is provided for setting and optimizing production process parameters, so that the control precision and efficiency of coating iron production are improved.

Description

Technical Field

[0001] This invention relates to the field of metal sheet surface coating technology, specifically to a quantitative prediction method for the wet film leveling time of coatings. Background Technology

[0002] In the metal packaging industry, coated iron, a mainstream product, is generally coated onto the metal substrate using a roller coating process. However, in response to increasingly stringent environmental regulations, traditional coatings containing large amounts of organic solvents are being replaced by new environmentally friendly coatings with high solids content and low volatility. These new coatings have higher viscosity, causing them to not level instantly after roller coating like traditional coatings, resulting in a significantly increased leveling time. Therefore, a dedicated leveling process must be added after the roller coating process. Leveling time is a key factor in determining the length of this process and the production line speed. If the leveling time is too long, extremely long horizontal conveyor equipment will be required, which is difficult to implement in modern factories. Using inclined conveyors to save space will cause gravity-induced sagging, which will also compromise the uniformity of the coating.

[0003] Currently, in industrial production, adjustments to process parameters such as roller coating, leveling, and sagging mainly rely on the experience of on-site engineers, lacking precise and reliable theoretical models for guidance. This "trial and error" approach to machine adjustment is inefficient, wasteful of materials, and makes it difficult to guarantee product quality stability when facing new coatings and substrates.

[0004] Although the academic community has studied the leveling phenomenon of coatings, the existing theories are mostly qualitative or semi-quantitative models that do not fully consider the dynamic characteristics of the roller coating process, the elastic deformation of the coating roller, the boundary slip effect of the coating, and other actual industrial factors. This results in a large deviation between the calculation results and the actual working conditions, making it difficult to directly guide high-precision industrial production.

[0005] Therefore, there is an urgent need in this field for a method that can comprehensively consider various actual process parameters to accurately and quantitatively predict the wet film leveling time of coatings, providing a scientific basis for the automated and intelligent control of process parameters, and solving the pain points in current production. Summary of the Invention

[0006] To overcome the existing problems and shortcomings, this invention proposes a quantitative prediction method for coating wet film leveling time, comprising the following steps:

[0007] S1. Obtain initial parameters, including at least the roller coating process parameters, coating physical property parameters, and wet film initial surface morphology parameters;

[0008] S2. Calculate the wet film average thickness, which is calculated by a preset wet film thickness theoretical model based on the roll coating process parameters and the coating physical property parameters;

[0009] S3. Calculate the leveling time, which is calculated by a preset leveling time theoretical model based on the wet film average thickness, the coating physical property parameters and the wet film initial surface topography parameters:

[0010] ;

[0011] wherein t is the leveling time, λ is the initial wavelength, η is the coating viscosity, a0 is the initial wave height, a t is the preset leveling target wave height, σ is the surface tension, and h is the wet film average thickness.

[0012] Further, the roll coating process parameters include the line pressure between the rollers, the roller radius and the rotation speed; the coating physical property parameters include the coating viscosity and the surface tension; and the wet film initial surface topography parameters include the initial wave height and the initial wavelength.

[0013] Further, the wet film thickness theoretical model in step two is a roll gap material balance model based on the relationship between the coating transfer and the coating split.

[0014] Further, the wet film average thickness is determined based on the rotation speed ratio of the rollers, the feed gap width and the preset coating transfer ratio.

[0015] Further, the wet film thickness theoretical model in step two is a comprehensive contact model taking into account the elastic deformation of the rubber-covered roller and the boundary slip effect of the coating on the roller surface.

[0016] Further, the wet film average thickness is determined based on the line pressure between the rollers, the elastic modulus and the Poisson's ratio of the roller material and the coating viscosity.

[0017] Further, the leveling time theoretical model in step three further comprises a correction factor for compensating for the dynamic changes of the physical parameters, which is a function representing the non-ideal dynamic changes of the coating viscosity or the elastic modulus of the rubber layer of the rubber-covered roller during the leveling process.

[0018] Further, the wet film initial surface topography parameters are determined by applying an initial disturbance with a specific geometric profile on the wet film.

[0019] Beneficial effects:

[0020] The application discloses a method for quantitatively predicting a wet film leveling time of paint, and provides accurate input parameters for calculation of the leveling time by constructing a wet film thickness theoretical model, and then establishes a function relationship of the leveling time covering physical properties of paint, roll coating process parameters and initial surface topography parameters of the wet film. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0022] Figure 1 The application scenario of the present application is a typical four-roll reverse roll coating process, and the mechanism principle thereof is shown in Fig. 1.

[0023] Figure 2 Fig. 4 is a curve graph of the relationship between the average thickness of the wet film and the line pressure.

[0024] Figure 3 Fig. 5 is a schematic diagram of a wet film thickness and wavelength jig for generating different initial wave peaks and wavelengths in the experiment.

[0025] Figure 4 Fig. 6 is a graph of the relationship between the leveling time and the wavelength under different jig conditions (i.e. different initial wave peaks). DETAILED DESCRIPTION

[0026] The present application will be described below in combination with specific embodiments.

[0027] In order to enable those skilled in the art to better understand the technical solutions of the present application, the present application will be described in detail below in combination with the drawings and specific embodiments.

[0028] The application scenario of the present application is a typical four-roll reverse roll coating process, and the mechanism principle thereof is shown in Fig. 1. Figure 1The coating is pumped from the storage bin into the V-shaped area between the feed roller and the uniformizing roller. The feed roller rotates to bring the coating to the uniformizing roller. By adjusting the width of the feed gap and the speed ratio of the two rollers, the preliminary control of the feed amount is realized. Subsequently, the uniformizing roller and the coating roller rotate in opposite directions to shear, extrude and homogenize the coating at the uniformizing gap, forming a coating film with uniform thickness and transferring to the surface of the coating roller. Finally, the coating gap between the coating roller and the pressure roller accurately coats the coating on the surface of the TFS substrate supported by the pressure roller to form a wet film. Before entering the subsequent baking and curing unit, the wet film needs to go through a leveling process section to eliminate the micro ripples or streaks that may be generated during the roller coating process, and form a smooth surface.

[0029] The core of the present application is to provide a method for quantitatively predicting the time required for the leveling process. The method first needs to obtain a series of initial parameters, including: roller coating process parameters such as the radius, speed and inter-roller pressure of each roller; coating physical property parameters such as the viscosity, surface tension, solid content of the coating and the slip characteristics of the coating on different surfaces; and the initial surface topography parameters of the wet film such as the initial wave height and wavelength of the wet film surface. These parameters can be measured by experiment, for example, using a rheometer, a surface tension meter, a laser thickness meter, a surface profiler, or by consulting equipment and material manuals, or provided by the supplier.

[0030] After obtaining the parameters, the average thickness of the wet film is calculated by a preset theoretical model, and the required time is finally calculated by substituting the leveling time theoretical model. The following two examples will detail the process.

[0031] Example 1:

[0032] This example provides a method for establishing a wet film thickness model based on the relationship between material transfer and distribution, and further solving the leveling time.

[0033] After obtaining the roller coating process parameters such as the radius, speed and linear pressure F of each roller, the coating physical property parameters such as the viscosity η and surface tension σ, and the initial surface topography parameters of the wet film such as the initial wave height a0 and wavelength λ, the leveling time can be calculated. The calculation of the leveling time in this example is based on the basic model describing the attenuation law of the surface ripples of the liquid film:

[0034]

[0035] Wherein:

[0036] a0 is the initial wave height; at is the wave height after t time; λ is the wavelength mm; σ is the surface tension; η is the viscosity; h is the average thickness of wet film. λ and a0 can be measured by a measuring tool, at is a boundary condition directly given, σ and η are properties of the paint, given by the paint manufacturer, while the average thickness of wet film h in the model is an undetermined variable, which cannot directly reflect the regulation process of the roller coating process.

[0037] The average thickness of wet film h in the embodiment is determined based on the material transfer and distribution relationship, and the specific formula is as follows:

[0038] h=

[0039] Wherein:

[0040] The average thickness of wet film h is brought into the leveling time calculation basic model to obtain:

[0041]

[0042] Further introduce the following formula:

[0043] Vi +(1-c)VII +(1-a)VI =VI

[0044]

[0045]

[0046]

[0047] The above formulas are respectively the material conservation relationship describing the balance of the roller system material volume flow rate, the paint flow rate relationship containing the correction coefficient μ, the wet film thickness relationship and the paint transfer ratio formula optimized through experiments, wherein:

[0048] The leveling time calculation is as follows:

[0049]

[0050] In order to make the prediction result reach the highest accuracy, to adapt to the dynamic change of material properties in real working conditions, the embodiment introduces the elastic modulus correction factor g* of the rubber layer for correcting the material properties of the rubber roller and the viscosity correction factor d* for compensating the dynamic change of the paint viscosity in the leveling process, which are brought into the above formula to obtain:

[0051]

[0052] Wherein:

[0053] L is the effective roll coating length; F is the linear pressure 1; R1 is the metering roll radius; Re is the equivalent radius; μ1 is the metering roll steel Poisson's ratio; E1 is the metering roll elastic modulus; μ2 is the rubber-covered roll Poisson's ratio; E2 is the rubber-covered roll elastic modulus of the rubber layer; g* is the correction factor of the elastic modulus of the rubber layer; d* is the correction factor of the coating viscosity; and r1 is the metering roll speed.

[0054] The above formula is a flow leveling time prediction model provided by the embodiment, which can comprehensively and accurately reflect the comprehensive influence of a plurality of parameters on the flow leveling time in a complex roll coating process, including the inter-roll pressure, the roll speed ratio, the material transfer characteristics, the roll body material characteristics, and the change of the coating itself attributes. Accordingly, the production personnel can input the actual process parameters to perform accurate flow leveling time prediction and process optimization according to the model.

[0055] Embodiment 2:

[0056] The embodiment provides an alternative construction method of a flow leveling time prediction model. The calculation basis model of the flow leveling time is the same as that in Embodiment 1, and the average thickness h of the wet film is still an intermediate variable that needs to be determined by specific process parameters. In order to establish a connection between the flow leveling time and the specific roll coating process parameters, the embodiment adopts a comprehensive wet film thickness model based on the boundary slip theory and the Hertz contact theory. In the model, the viscosity of the coating is assumed to be constant, and the viscosity of the wet film changes continuously after roll coating. In the embodiment, the high viscosity and constant temperature working condition is assumed, the viscosity change range is small, and the viscosity can be considered as constant. The correction factor d* is introduced, and the following model can be obtained on the calculation basis model of the flow leveling time:

[0057]

[0058] When the output material volume speed of the roll coating equipment is constant, the average thickness of the wet film is calculated, and the new flow leveling time theoretical model can be obtained by comprehensively using the above formula:

[0059]

[0060] The comprehensive wet film thickness model based on the boundary slip theory and the Hertz contact theory in the embodiment is as follows:

[0061]

[0062] The model directly establishes a function relationship between the wet film thickness h and a series of complex physical parameters such as the linear pressure (F), the equivalent radius (Re), the roll body material elastic modulus (E1, E2), the Poisson's ratio (μ1, μ2), and the slip length. The slip theory flow leveling time can be solved by introducing the model into the above new flow leveling time theoretical model.

[0063] In summary, the present application provides two parallel technical solutions for constructing a wet film leveling time prediction model, based on the material balance theory of Example 1 and the boundary slip theory of Example 2, respectively, to cope with different process conditions. The effectiveness of the two solutions is verified by a specially built high-precision leveling experiment platform.

[0064] During the verification process, it is first necessary to ensure the accuracy of the wet film thickness theory. The experiment adjusts the hand wheel to change the line pressure F and compares it with the theoretical calculation value, as shown in Figure 2 The theoretical value of the wet film thickness is in good agreement with the experimental value, proving the reliability of the thickness model. The wet film thickness and the wavelength jig as shown in Figure 3 The wet film with a specific initial corrugation is manufactured, and its actual leveling time is recorded.

[0065] Finally, the experimental data are compared with the theoretical prediction values of the two models. As shown in a series of graphs Figure 4 It is clear that under different initial conditions, the leveling time calculated by the two theoretical models is highly consistent with the experimental measurement value. The results show that the material balance leveling time model constructed in Example 1 is more suitable for larger line pressure and thinner wet film roller coating conditions. The slip theory leveling time model constructed in Example 2 can better explain the physical phenomena when lower line pressure and thicker wet film roller coating are performed. This series of experimental results strongly confirm the correctness and effectiveness of the two models within their respective applicable ranges, and can provide accurate theoretical guidance for process optimization in actual production.

[0066] It should be noted that the above examples can be combined and adjusted as needed. Improvements and refinements can be made without departing from the principles of the present application, and are considered within the scope of protection. The embodiments are described in a progressive manner, and the same or similar parts can be referred to each other.

[0067] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts can be referred to each other.

Claims

1. A quantitative prediction method for the wet film leveling time of a coating, characterized in that, Includes the following steps: S1. Obtain initial parameters, including at least the roller coating process parameters, coating physical property parameters, and wet film initial surface morphology parameters; S2. Calculate the average wet film thickness, which is based on the roller coating process parameters and the physical property parameters of the coating material, and is calculated using a preset wet film thickness theoretical model. S3. Calculate the leveling time by substituting the average wet film thickness, coating physical property parameters, and initial surface morphology parameters of the wet film into the following preset leveling time theoretical model: ； Where t is the leveling time, λ is the initial wavelength, η is the coating viscosity, a0 is the initial peak height, and a t σ is the preset leveling target peak height, h is the surface tension, and h is the average wet film thickness.

2. The method according to claim 1, characterized in that, The roller coating process parameters include the linear pressure between the rollers, the roller radius, and the rotation speed; the physical property parameters of the coating include the coating viscosity and surface tension; and the initial surface morphology parameters of the wet film include the initial peak height and the initial wavelength.

3. The method according to claim 1 or 2, characterized in that, The theoretical model for wet film thickness in step two is a material balance model between roll gaps based on the relationship between coating transfer and splitting.

4. The method according to claim 3, characterized in that, The average thickness of the wet film is determined based on the rotational speed ratio of each roller, the feed gap width, and the preset coating transfer ratio.

5. The method according to claim 1 or 2, characterized in that, The theoretical model for wet film thickness in step two is a comprehensive contact model that takes into account the elastic deformation of the coating roller and the boundary slip effect of the coating on the roller surface.

6. The method according to claim 5, characterized in that, The average thickness of the wet film is determined based on the linear pressure between the rollers, the elastic modulus and Poisson's ratio of the roller material, and the viscosity of the coating.

7. The method according to claim 1, characterized in that, The leveling time theoretical model in step three further includes a correction factor to compensate for dynamic changes in physical parameters. This correction factor is a function that characterizes the non-ideal dynamic changes in the viscosity of the coating or the elastic modulus of the rubber layer on the coating roller during the leveling process.

8. The method according to claim 1, characterized in that, The initial surface morphology parameters of the wet film are determined by applying an initial perturbation with a specific geometric profile to the wet film.

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