Preparation method of gradient color leather and gradient color leather

Abstract

The present invention provides a method for preparing a gradient leather, comprising the following steps: preparing a first primary color pigment, a second primary color pigment and a coating, and formulating them into M parts of finishing agents T1 to T M , such that the percentage of the color saturation and transparency of the first primary color of the M parts of finishing agents T1 to T M decreases in an equal difference from one hundred to zero, and formulating them into N parts of finishing agents L1 to L N , such that the percentage of the color saturation and transparency of the second primary color of the N parts of finishing agents L1 to L N decreases in an equal difference from one hundred to zero, where N = M + 1; feeding into a spraying device, and sequentially spraying the corresponding finishing agents T1 to T from the first sub-unit area to the Mth sub-unit area M ; re-dividing the gradient spraying area into N sub-unit areas along the second direction, and sequentially spraying the corresponding finishing agents L1 to L from the first sub-unit area to the Nth sub-unit area N ; continuously applying a pre-tensile force to the leather during spraying until the spraying is completed.

Description

Technical Field

[0001] The present invention relates to a method for coloring leather, and in particular to a method for preparing a gradient-color leather and the gradient-color leather, belonging to the technical field of leather processing. Background Art

[0002] Leather, due to its delicate handfeel and soft elasticity, is a main material for automotive steering wheel covering ornaments. With the improvement of users' aesthetic requirements, there are higher requirements for the surface color variability of the steering wheel covering ornaments. Users prefer leather with gradient colors as the steering wheel covering ornaments rather than the previous leather with a single color on the surface. Therefore, the research on leather coating with gradient colors has gradually received attention.

[0003] The gradient-color coating of leather can be achieved by various methods, such as roller coating, spraying, UV spraying, etc. Among them, spraying has advantages in terms of uniformity, production controllability, process flexibility, and resource utilization rate. However, due to the influence of the characteristics of leather itself, the existing leather gradient-color spraying methods still have aspects to be improved.

[0004] First, due to the surface characteristics of leather, especially genuine leather, the pores and textures on its surface will have a certain impact on the visual effect of the sprayed gradient color. One method of gradient-color spraying is to control the single-color spraying amount to achieve single-color gradient, and then reverse-stack another color by controlling the spraying amount to achieve two-color gradient; another method is to mix two colors in different proportions to form multiple transitional colors with stepped gradients, and then directly spray out the two-color gradient effect along the set direction in a uniform spraying manner. For the visual effect of the gradient color sprayed by the above two methods, there will be a certain degree of boundary at the adjacent boundaries of different color spraying areas. It may not be easily noticed on the surface of a conventional substrate, but when applied to the leather surface spraying, due to the scatter effect of the pores on the leather surface, the originally smooth color blocks show more obvious granularity, thus magnifying the boundary sense at the junction of different color spraying areas. Therefore, users are prone to notice the obvious stepwise change in the color of the leather surface. In other words, the visual effect of the gradient color on the leather surface presents a stepped change in color rather than a smooth transition.

[0005] Second, during the spraying operation, control errors in the spraying amount and penetration time are likely to cause the coating agent to not fully infiltrate some parts of the leather surface, thereby reducing the fastness of the film formed after coating and slightly affecting the color uniformity of the leather surface. Especially during gradient-color spraying, slight differences in color uniformity will cause irregular boundaries in the transitional change of the gradient color, thereby deepening the boundary sense in the color junction area. Summary of the Invention

[0006] Based on the above background, the object of the present invention is to provide a method for preparing a gradient leather, so that the gradient color on the leather surface presents a visual effect of smooth color transition, and the gradient color coating on the leather surface has good coating fastness.

[0007] To achieve the above object of the invention, the present invention provides the following technical solutions:

[0008] A method for preparing a gradient leather, the method comprising the following steps:

[0009] Determine the first main color and the second main color of the gradient color of the leather, and determine the pre-stretching force value during spraying;

[0010] Prepare the first main color pigment, the second main color pigment and the coating material, and mix the first main color pigment and the coating material in different proportions into M portions of finishing agents T1 to T M , so that the percentage of the color saturation and transparency of the first main color of the M portions of finishing agents T1 to T M decreases by an equal difference from one hundred to zero, and mix the second main color pigment and the coating material in different proportions into N portions of finishing agents L1 to L N , so that the percentage of the color saturation and transparency of the second main color of the N portions of finishing agents L1 to L N decreases by an equal difference from one hundred to zero, where N = M + 1;

[0011] Feed the leather into the spraying equipment, determine the gradient spraying area of the leather, divide the gradient spraying area into M sub-unit areas along the first direction, wherein the widths of the areas from the second sub-unit area to the M-1th sub-unit area are equal, and spray through multiple nozzles of the spraying equipment, and sequentially spray the corresponding finishing agents T1 to T from the first sub-unit area to the Mth sub-unit area M ;

[0012] Redivide the gradient spraying area into N sub-unit areas along the second direction, wherein the second direction is opposite to the first direction, the widths of the areas from the second sub-unit area to the N-1th sub-unit area are equal, and spray through multiple nozzles of the spraying equipment, and sequentially spray the corresponding finishing agents L i ~L N ;

[0013] Wherein, during spraying, a pre-stretching force is continuously applied to the leather according to the pre-stretching force value until spraying is completed.

[0014] The preparation method of the gradient-color leather colors the leather by spraying finishing agents with different color saturations and transparencies. First, the first main color is sprayed on the leather surface in a way that the color saturation and transparency decrease along the first direction, forming a gradient change of the first main color along the first direction. Then, the second main color is sprayed on the leather surface in a way that the color saturation and transparency decrease along the second direction, forming a gradient change of the second main color along the second direction. The superimposed effect of the reverse gradient changes between the first main color and the second main color realizes the visual effect of the gradient color from the first main color to the second main color. Due to the difference between the values of N and M, the gradient change boundaries of the two main colors do not overlap in the same area but are staggered. That is to say, any first main color sub-unit area overlaps with two second main color sub-unit areas in space, and any second main color sub-unit area overlaps with two first main color sub-unit areas in space. Thus, the color gradient boundary between two adjacent sub-unit areas is weakened, and the granularity presented by the color blocks in the adjacent areas is reduced, making the gradient color on the leather surface show a smooth transition change of colors. Moreover, during the spraying process, a pre-tensile force is continuously applied to the leather, so that the fiber structure and pores on the leather surface are relaxed, increasing the contact area between the finishing agent and the leather surface and enhancing the capillary effect of the leather, facilitating the penetration of the finishing agent, enhancing the coloring uniformity, reducing the color boundary sense of adjacent areas caused by uneven colors, and the better penetration conditions of the finishing agent effectively improve the coating adhesion, making the gradient-color coating after film formation have better coating fastness.

[0015] Preferably, the determination of the pre-tensile force value during spraying includes: substituting the independent variable into a pre-constructed multiple linear regression model to obtain the pre-tensile force value during spraying; wherein, the construction of the multiple linear regression model includes:

[0016] Defining variables, defining the leather parameters and color difference parameters as independent variables, and positioning the pre-tensile force value as the dependent variable;

[0017] Establishing a multiple linear regression model and introducing the influencing factors of each independent variable;

[0018] Collecting multiple groups of sample data sets, dividing them into a training data set and a verification data set, performing multiple linear regression analysis on the training data set, and determining the values of each influencing factor in the multiple linear regression model;

[0019] Substituting the verification data set into the multiple linear regression model, verifying the model accuracy, and iteratively optimizing it until the model accuracy meets the standard.

[0020] Preferably, the leather parameters include leather material indexes, leather thickness, and leather moisture content, and the mathematical expression of the multiple linear regression model is:

[0021]

[0022] In the formula, F represents the pre-tension force value, P represents the leather material index, T represents the leather thickness, M represents the leather moisture content, ΔE represents the color difference parameter, and the color difference parameter is used to reflect the smoothness of the gradient color on the leather surface in the visual effect. α1 to α5 represent the influence factors of each independent variable. Among them, the leather material index uses numerical values to represent the indexes of different leather materials with increasing hardness. 1 is calfskin, 2 is cowhide, 3 is sheepskin, 4 is goatskin, and 5 is pigskin.

[0023] Preferably, when collecting multiple groups of sample data sets, the method for obtaining the color difference parameter includes:

[0024] In the gradient color spraying area of the leather, sample at a set interval along the first direction or the second direction, and use a colorimeter to measure the color brightness L, the color red-green chromaticity a, and the color yellow-blue chromaticity b at multiple points.

[0025] The following formula is used to calculate the color difference parameter between adjacent points.

[0026]

[0027] In the formula, ΔE represents the color difference parameter, ΔL represents the difference in color brightness between adjacent points, Δa represents the difference in color red-green chromaticity between adjacent points, and Δb represents the difference in color yellow-blue chromaticity between adjacent points.

[0028] Preferably, the independent variable further includes the coating thickness uniformity, and the mathematical expression of the multiple linear regression model is:

[0029]

[0030] In the formula, F represents the pre-tension force value, P represents the leather material index, r represents the leather thickness, M represents the leather moisture content, ΔE represents the color difference parameter, and the color difference parameter is used to reflect the smoothness of the gradient color on the leather surface in the visual effect. H represents the coating thickness uniformity, and the coating thickness uniformity is used to reflect the uniformity of the coating thickness of the gradient color on the leather surface. α1 to α7 represent the influence factors of each independent variable. Among them, the leather material index uses numerical values to represent the indexes of different leather materials with increasing hardness. 1 is calfskin, 2 is cowhide, 3 is sheepskin, 4 is goatskin, and 5 is pigskin.

[0031] Preferably, when collecting multiple groups of sample data sets, the method for obtaining the coating thickness uniformity includes:

[0032] Use an instrument to perform cross-sectional measurements on multiple parts of the leather, select multiple measurement points at different positions of each cross-section, and read the coating thickness at each point.

[0033] Calculate the standard deviation or coefficient of variation of the coating thickness data at each point.

[0034] Using the above standard deviation or coefficient of variation as the coating thickness uniformity value, the smaller the value, the better the coating thickness uniformity.

[0035] Preferably, during spraying, the nozzles for spraying different finishing agents adopt a cross-spraying method, so that each finishing agent covers the corresponding sub-unit area, and each finishing agent also covers a 15% - 25% width area of the adjacent sub-unit area.

[0036] Preferably, when adopting the cross-spraying method, after one nozzle finishes spraying the finishing agent for one sub-unit area, the other nozzle starts to spray the finishing agent for another adjacent sub-unit area.

[0037] A gradient leather is obtained by the preparation method of the gradient leather described in any one of the above.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] The preparation method of a gradient leather of the present invention weakens the color gradient boundary between two adjacent sub-unit areas, and continuously applies a pre-stretching force to the leather during spraying, weakening the granularity presented by the color blocks in the adjacent areas. When spraying, the fiber structure and pores on the leather surface are relaxed, increasing the contact area between the finishing agent and the leather surface and enhancing the capillary effect of the leather, facilitating the penetration of the finishing agent, enhancing the coloring uniformity, and making the gradient color on the leather surface present a smooth transition effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0041] Figure 1 It is a flow schematic diagram of the preparation method of a gradient leather of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The following will further specifically illustrate the technical solutions of the present invention through specific embodiments and in combination with the drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and / or change made to the present invention will fall within the protection scope of the present invention.

[0043] In the present invention, unless otherwise specified, all parts and percentages are in weight units, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are conventional methods in the art unless otherwise specified. The components or equipment in the following embodiments are general standard components or components known to those skilled in the art unless otherwise specified, and their structures and principles can all be known by those skilled in the art through technical manuals or by conventional experimental methods.

[0044] The following will make a detailed description of the embodiments of the present invention with reference to the accompanying drawings. In the following detailed description, for the sake of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, one or more embodiments can also be implemented by those skilled in the art without these specific details.

[0045] As Figure 1 shown, the embodiments of the present invention disclose a method for preparing a gradient leather, and the method includes the following steps:

[0046] S1. Determine the first main color and the second main color of the leather gradient color, and determine the pre-stretching force value during spraying;

[0047] S2. Prepare the first main color pigment, the second main color pigment and the coating material, and mix the first main color pigment and the coating material in different proportions into M parts of finishing agents T1 to T M , so that the percentage of the color saturation and transparency of the first main color of the M parts of finishing agents T1 to T M decreases in equal differences from one hundred to zero, and mix the second main color pigment and the coating material in different proportions into N parts of finishing agents L i to L N , so that the percentage of the color saturation and transparency of the second main color of the N parts of finishing agents L i to L N decreases in equal differences from one hundred to zero, where N = M + 1;

[0048] S3. Feed the leather into the spraying equipment, determine the gradient spraying area of the leather, divide the gradient spraying area into M sub-unit areas along the first direction. Among them, the widths of the areas from the second sub-unit area to the M - 1 sub-unit area are equal, and spray through multiple nozzles of the spraying equipment, and sequentially spray the corresponding finishing agents T i to T M from the first sub-unit area to the M sub-unit area;

[0049] S4. Re-divide the gradient color spraying area into N sub-unit areas along the second direction, where the second direction is opposite to the first direction, and the widths of the areas from the 2nd sub-unit area to the N-1th sub-unit area are equal. Spray through multiple nozzles of the spraying device, and sequentially spray the corresponding finishing agents L1 to L from the 1st sub-unit area to the Nth sub-unit area. N 。

[0050] Wherein, during the spraying in step S3 and step S4, a pre-tensile force is continuously applied to the leather according to the pre-tensile force value until the spraying is completed.

[0051] The preparation method of the gradient color leather colors the leather by spraying finishing agents with different color saturations and transparencies. First, spray the first main color on the leather surface in a way that the color saturation and transparency decrease along the first direction, forming a gradient change of the first main color along the first direction. Then, spray the second main color on the leather surface in a way that the color saturation and transparency decrease along the second direction, forming a gradient change of the second main color along the second direction. The superimposed effect of the reverse gradient changes between the first main color and the second main color realizes the visual effect of the gradient color from the first main color to the second main color.

[0052] Due to the difference in the values of N and M, the gradient change boundaries of the two main colors do not overlap in the same area but are staggered. That is to say, any first main color sub-unit area overlaps with two second main color sub-unit areas in space, and any second main color sub-unit area overlaps with two first main color sub-unit areas in space. Thus, the color gradient boundary between two adjacent sub-unit areas is weakened, the granularity presented by the color blocks in the adjacent areas is reduced, and the gradient color on the leather surface shows a smooth transition change of colors.

[0053] Moreover, during the spraying, a pre-tensile force is continuously applied to the leather, so that the fiber structure and pores on the leather surface are relaxed, the contact area between the finishing agent and the leather surface is increased, and the capillary effect of the leather is enhanced, which is beneficial to the penetration of the finishing agent, enhances the coloring uniformity, reduces the color boundary sense of adjacent areas caused by uneven colors, and the good penetration conditions of the finishing agent effectively improve the coating adhesion, making the gradient color coating after film formation have good coating fastness.

[0054] Taking the preparation of a two-color gradient color leather with a gradient from red to yellow as an example, each step of this method will be described in detail below.

[0055] Step S1, determine that the first main color is red and the second main color is yellow; and determine the pre-tensile force value during spraying.

[0056] The pre-tensile force value during spraying is determined by the following method: substitute the independent variable into the pre-constructed multiple linear regression model to obtain the pre-tensile force value during spraying.

[0057] Among them, constructing a multiple linear regression model includes the following steps:

[0058] Define variables, define leather parameters and color difference parameters as independent variables. The leather parameters include leather material indexes, leather thickness and leather moisture content, and define the pre-stretching force value as the dependent variable;

[0059] Establish a multiple linear regression model, introduce the influencing factors of each independent variable. The mathematical expression of the multiple linear regression model is:

[0060]

[0061] In the formula, F represents the pre-stretching force value, P represents the leather material index, T represents the leather thickness, M represents the leather moisture content, ΔE represents the color difference parameter, and the color difference parameter is used to reflect the smoothness of the gradient color on the leather surface in the visual effect. α1 to α5 represent the influencing factors of each independent variable; among them, the leather material index is represented by a numerical value indicating the indexes of different leather materials with increasing hardness. 1 is calfskin, 2 is cowhide, 3 is sheepskin, 4 is goatskin, and 5 is pigskin;

[0062] Collect multiple groups of sample data sets, divide them into training data sets and validation data sets, perform multiple linear regression analysis on the training data sets, and determine the numerical values of each influencing factor in the multiple linear regression model. Among them, when collecting multiple groups of sample data sets, the method for obtaining the color difference parameter includes:

[0063] In the gradient color spraying area of the leather, sample at a set interval along the first direction or the second direction, and use a colorimeter to measure the color brightness L, color red-green chromaticity a, and color yellow-blue chromaticity b at multiple points;

[0064] Use the following formula to calculate the color difference parameter between adjacent points

[0065]

[0066] In the formula, ΔE represents the color difference parameter, ΔL represents the color brightness difference between adjacent points, Δa represents the color red-green chromaticity difference between adjacent points, and Δb represents the color yellow-blue chromaticity difference between adjacent points;

[0067] Substitute the validation data set into the multiple linear regression model, verify the model accuracy, and iterate and optimize it until the model accuracy meets the standard.

[0068] The above-mentioned multiple linear regression model is composed of a linear combination of multiple independent variables. There are no high-order terms in the model, and the number of influencing factors is controlled within five, which is convenient for performing multiple regression fitting and solution based on experimental data in practical applications. Among them, considering the interactive effect between the moisture content of leather and the leather thickness, under the condition of the same moisture content, thinner leather requires a smaller pre-tension force. Under the condition of the same leather thickness, the pre-tension force of leather with a higher moisture content can be smaller, that is, the softening effect of a higher leather moisture content on thinner leather is more obvious. Therefore, the cross-term variable T / M is introduced into this multiple linear regression model to describe their interactive effect. In order to correct the model results, a color difference parameter reflecting the smoothness of the gradual color change on the leather surface in the visual effect is also introduced into the model, so that the pre-tension force value calculated according to this model can lead to an ideal smooth effect of the gradual color change as much as possible.

[0069] Step S2: Prepare red pigment, yellow pigment, and coating. The coating is the general term for the film-forming agent, solvent, and additives that make up the finishing agent.

[0070] The red pigment and the coating are mixed in different proportions to prepare 5 finishing agents T1 - T5, so that the percentages of the red saturation and transparency of the 5 finishing agents T1 - T5 decrease in equal differences from one hundred to zero, that is, the red saturation and transparency of finishing agent T1 are 100%, those of finishing agent T2 are 75%, those of finishing agent T3 are 50%, those of finishing agent T4 are 25%, decreasing in turn, and the red saturation and transparency of finishing agent T5 are 0, that is, a transparent finishing agent.

[0071] The yellow pigment and the coating are mixed in different proportions to prepare 6 finishing agents L1 - L6, so that the percentages of the yellow saturation and transparency of the 6 finishing agents L1 - L6 decrease in equal differences from one hundred to zero, that is, the red saturation and transparency of finishing agent L1 are 100%, those of finishing agent L2 are 80%, those of finishing agent L3 are 60%, those of finishing agent L4 are 40%, those of finishing agent L5 are 20%, decreasing in turn, and the yellow saturation and transparency of finishing agent L6 are 0, that is, a transparent finishing agent.

[0072] Step S3, feed the leather into the spraying equipment, the spraying equipment is the prior art, and the spraying equipment with multiple nozzles can be used. Determine the gradient color spraying area of the leather, and divide the gradient color spraying area into 5 sub-unit areas along the first direction, wherein the widths of the areas from the 2nd sub-unit area to the 4th sub-unit area are equal, and the 1st sub-unit area and the 5th sub-unit area are close to the red pure color area and the yellow pure color area respectively, so the area widths of the two are set to be equal, but there may be a difference with the widths of the remaining 3 sub-unit areas. Area width refers to the shortest straight-line distance between the boundaries of adjacent sub-unit areas along the first direction. Spraying is performed through multiple nozzles of the spraying equipment, and the corresponding finishing agents T1 to T5 are sprayed in sequence from the 1st sub-unit area to the 5th sub-unit area. Measured in terms of RGB values, the RGB values from the first sub-unit area to the fifth sub-unit area are (255, 0, 0), (204, 51, 51), (153, 102, 102), (102, 153, 153), and (255, 255, 255), gradually changing from red to transparent. At this point, the red gradient color spraying is completed.

[0073] Step S4, re-divide the gradient color spraying area into 6 sub-unit areas along the second direction, wherein the second direction is opposite to the first direction, and the widths of the areas from the 2nd sub-unit area to the 5th sub-unit area are equal, and the 1st sub-unit area and the 6th sub-unit area are respectively close to the yellow pure color area and the red pure color area, so the area widths of the two are set to be equal, but there may be a difference with the widths of the remaining 4 sub-unit areas. Spraying is performed through multiple nozzles of the spraying equipment, and the corresponding finishing agents L1 to L6 are sprayed in sequence from the 1st sub-unit area to the 6th sub-unit area. In terms of RGB values, the RGB values from the 1st sub-unit area to the 6th sub-unit area are (255, 255, 0), (255, 255, 42), (255, 255, 84), (255, 255, 126), (255, 255, 168), (255, 255, 255), and gradually change from yellow to transparent.

[0074] The color boundaries of each red gradient sub-unit area formed in step S3, after the yellow gradient sub-unit area is sprayed in step S4, since the number of yellow gradient sub-unit areas is greater than the number of red gradient sub-unit areas, the areas on both sides of the color boundary of each red gradient sub-unit area are mixed with different yellow gradient colors respectively, thereby diluting the visual effect of the color boundary of this part and weakening the step presentation effect of the color display.

[0075] During the spraying in steps S3 and S4, a pre-stretching force is continuously applied to the leather according to the pre-stretching force value determined in step S1 until the spraying is completed. The pre-stretching force is provided by a plurality of stretching components arranged at the edge of the spraying area of the spraying equipment. The stretching components have a clamping function and uniformly stretch the leather from multiple parts. The stretching force is controlled by a control component through a motor. The stretching components are conventional components in the prior art.

[0076] Due to the spray fan surface of the nozzle of the spraying equipment, in each sub-unit area of the spraying, the middle part of the area is directly below the nozzle while the edge of the area is slightly farther away from the nozzle. The spraying amount in the middle part of the area is higher than that in the edge of the area, which may cause uneven coating. Therefore, during the spraying, the nozzles spraying different finishing agents adopt a cross-spraying method, so that each finishing agent covers the corresponding sub-unit area and each finishing agent also covers a 15% - 25% width area of the adjacent sub-unit area. In this way, at the edge of a sub-unit area, the reduced spraying amounts of the two nozzles due to the spray fan surface are superimposed, reaching an approximate spraying amount to that in the middle part of the area, making the coating more uniform and keeping the color presentation effect at the edge of the sub-unit area consistent with that in the middle part of the area.

[0077] Moreover, when adopting the cross-spraying method, after one nozzle sprays the finishing agent for a corresponding sub-unit area, the other nozzle starts to spray the finishing agent for another adjacent sub-unit area. In this way, the superposition interference of the spray fan surfaces of adjacent nozzles can be reduced, avoiding local accumulation of the finishing agent at the superimposed part at the edge of the sub-unit area and affecting the coating uniformity effect.

[0078] In another embodiment, considering the reflection of the calculation model of the pre-stretching force value on the correlation between the pre-stretching force and the coating thickness uniformity after spraying, when constructing the multiple linear regression model in step S1, the coating thickness uniformity is also introduced as an independent variable of the model. At this time, the mathematical expression of the multiple linear regression model is:

[0079]

[0080] In the formula, F represents the pre-stretching force value, P represents the leather material index, T represents the leather thickness, M represents the leather moisture content, ΔE represents the color difference parameter, and the color difference parameter is used to reflect the smoothness of the gradual color change on the leather surface in the visual effect. H represents the coating thickness uniformity, and the coating thickness uniformity is used to reflect the uniformity of the coating thickness of the gradual color change coating on the leather surface. α1 - α7 represent the influence factors of each independent variable. Among them, the leather material index uses numerical values to represent the indexes of different leather materials with increasing hardness. 1 is calfskin, 2 is cowhide, 3 is sheepskin, 4 is goatskin, and 5 is pigskin.

[0081] When collecting multiple groups of sample data sets, the method for obtaining the coating thickness uniformity includes:

[0082] Use an instrument to measure the cross-sections of multiple parts of the leather, select multiple measurement points at different positions of each cross-section, and read the coating thickness at each point;

[0083] Calculate the standard deviation or coefficient of variation of the coating thickness data at each point;

[0084] Use the above standard deviation or coefficient of variation as the coating thickness uniformity value. The smaller the value, the better the coating thickness uniformity.

[0085] The above multiple linear regression model not only further introduces the coating thickness uniformity, but also takes into account the interaction between the coating thickness uniformity and the moisture content of the leather. When the moisture content of the leather is high, the influence of the coating thickness uniformity on the pre-tensioning force will increase. Therefore, the cross-term HM is introduced.

[0086] The embodiments of the present invention also disclose a gradient leather, which is prepared according to the above-mentioned preparation method of the gradient leather.

[0087] Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A preparation method of gradient-color leather, characterized in that: The method comprises the following steps: Determine a first primary color and a second primary color of the leather gradient color, and determine the pre-stretching force value during spraying; Prepare the first primary color pigment, the second primary color pigment and the coating material, and mix the first primary color pigment and the coating material in different proportions to obtain M portions of finishing agents T1 to T M , such that the percentage of the color saturation and transparency of the first primary color of the M portions of finishing agents T1 to T M decreases by an equal difference from one hundred to zero. Mix the second primary color pigment and the coating material in different proportions to obtain N portions of finishing agents L1 to L N , such that the percentage of the color saturation and transparency of the second primary color of the N portions of finishing agents L1 to L N decreases by an equal difference from one hundred to zero, where N = M + 1; Feed the leather into a spraying device, determine the gradient color spraying area of the leather, divide the gradient color spraying area into M sub-unit areas along the first direction, where the widths of the areas from the second sub-unit area to the (M-1)-th sub-unit area are equal, spray through multiple nozzles of the spraying device, and spray the corresponding finishing agents T1 to T in sequence from the first sub-unit area to the M-th sub-unit area M ; The gradient color spraying area is re-divided into N sub-unit areas along the second direction, where the second direction is opposite to the first direction, and the widths of the areas from the second sub-unit area to the N-1th sub-unit area are equal. Spraying is carried out through multiple nozzles of the spraying device, and the corresponding finishing agents L1 to L are sprayed in sequence from the first sub-unit area to the Nth sub-unit area N ; Wherein, during spraying, a pre-stretching force is continuously applied to the leather according to the pre-stretching force value until the spraying is completed; The determination of the pre-stretching force value during spraying includes: substituting an independent variable into a pre-constructed multiple linear regression model to obtain the pre-stretching force value during spraying; wherein, the construction of the multiple linear regression model includes: Define variables, define leather parameters and color difference parameters as independent variables, and define the pre-stretching force value as a dependent variable. The leather parameters include leather material indexes, leather thickness and leather moisture content, and the color difference parameters are used to reflect the smoothness of the leather surface gradient color in the visual effect; Establish a multiple linear regression model and introduce the influencing factors of each independent variable; Collect multiple groups of sample data sets, divide them into a training data set and a validation data set, perform multiple linear regression analysis on the training data set, and determine the values of each influencing factor in the multiple linear regression model; Substitute the validation data set into the multiple linear regression model, verify the model accuracy, and iteratively optimize it until the model accuracy meets the standard.

2. The preparation method of a gradient leather according to claim 1, characterized in that: The mathematical expression of the multiple linear regression model is: ， In the formula, represents the pre-tensile force value, represents the leather material index, represents the leather thickness, represents the leather moisture content, represents the color difference parameter, ~ represent the influence factors of each independent variable; among them, the leather material index uses numerical values to represent the indexes of different leather materials with increasing hardness, 1 is calfskin, 2 is cowhide, 3 is sheepskin, 4 is goatskin, and 5 is pigskin.

3. The preparation method of a gradient leather according to claim 2, characterized in that: When collecting multiple groups of sample data sets, the method for obtaining the color difference parameters includes: In the gradient color spraying area of the leather, sample at set intervals along the first direction or the second direction, and use a colorimeter to measure the color brightness L, color red-green chromaticity a, and color yellow-blue chromaticity b at multiple points; Calculate the color difference parameters between adjacent points by using the following formula ， In the formula, represents the color difference parameter, represents the color brightness difference between adjacent points, represents the red-green chromaticity difference of the color between adjacent points, represents the yellow-blue chromaticity difference of the color between adjacent points.

4. The preparation method of a gradient leather according to claim 1, characterized in that: The independent variable also includes the coating thickness uniformity, and the mathematical expression of the multiple linear regression model is: ， Wherein, represents the pre-tension force value, represents the leather material index, represents the leather thickness, represents the leather moisture content, represents the color difference parameter, and the color difference parameter is used to reflect the smoothness of the gradient color on the leather surface in terms of visual effect, represents the coating thickness uniformity, and the coating thickness uniformity is used to reflect the uniformity of the coating thickness of the gradient color on the leather surface, ~ represent the influence factors of each independent variable; wherein, the leather material index uses numerical values to represent the indexes of different leather materials with increasing hardness, 1 is calfskin, 2 is cowhide, 3 is sheepskin, 4 is goatskin, and 5 is pigskin.

5. The preparation method of a gradient leather according to claim 4, characterized in that: When collecting multiple groups of sample data sets, the method for obtaining the coating thickness uniformity includes: Use an instrument to perform cross-sectional measurements on multiple parts of the leather, select multiple measurement points at different positions of each cross-section, and read the coating thickness at each point; Calculate the standard deviation or coefficient of variation of the coating thickness data at each point; Use the above standard deviation or coefficient of variation as the coating thickness uniformity value, and the smaller the value, the better the coating thickness uniformity.

6. The preparation method of a gradient leather according to claim 1, characterized in that: During spraying, the nozzles for spraying different finishing agents adopt a cross-spraying method, so that each finishing agent covers the corresponding sub-unit area, and each finishing agent also covers a 15% - 25% width area of the adjacent sub-unit area.

7. The preparation method of a gradient leather according to claim 6, characterized in that: When adopting the cross-spraying method, after one nozzle sprays the finishing agent corresponding to one sub-unit area, the other nozzle starts to spray the finishing agent corresponding to another adjacent sub-unit area.

8. A gradient leather, characterized in that: Prepared according to the method for preparing gradient-color leather according to any one of claims 1-7.

Images