Water-based paint for leather and preparation method of water-based paint

Abstract

The invention discloses a water-based coating for leather and a preparation method, and belongs to the technical field of surface treating agents for leather, the water-based coating for leather comprises waterborne polyurethane resin, wax emulsion, water, matting powder, fluff powder, a thickening agent, a wetting agent, a hand feeling agent and a water-based closed curing agent. The water-based closed curing agent is added into a water-based paint system, so that the film-forming ability of the paint can be greatly improved, the coating is prevented from falling off and cracking after being used for a long time, meanwhile, the chemical bonding between resin molecules and hydroxyl and amino on the surface of leather can be enhanced, the adhesive force of the coating is further improved, and the service life of a leather product is prolonged. The waterborne polyurethane resin compounded by PU-6140 and PU-608 is adopted, so that the stiffness of the coating can be properly improved, the convex part of the leather texture is clearer in touch feeling, the concave part of the leather texture is milder and moist in touch feeling, the soft and hard alternate touch texture is formed, and the visual contrast of the texture can be enhanced.

Description

Technical Field

[0001] This invention relates to the field of surface treatment agents for leather, and more particularly to a water-based coating for leather and its preparation method. Background Technology

[0002] Crazy Horse leather is a vintage-style leather made from top-grain cowhide. Its core characteristics are a soft, waxy feel, a natural vintage texture, and a color-changing effect that varies in depth after rubbing or bending. It is commonly used to make leather shoes, bags, sofas, and other leather goods, combining practicality with vintage aesthetics. Water-based polyurethane coatings for leather use water as a solvent or dispersion medium, making them environmentally friendly and safe. However, water-based polyurethane coatings have weak film-forming properties, leading to coating peeling after prolonged use. Furthermore, existing water-based polyurethane coatings for leather often result in poor texture and fail to create a distinct natural vintage look.

[0003] It is evident that existing technologies need improvement and enhancement. Summary of the Invention

[0004] The purpose of this invention is to provide a water-based coating for leather and a method for its preparation, aiming to solve the problems of weak film-forming properties and poor texture of existing water-based polyurethane coatings.

[0005] The first aspect of this invention provides a water-based coating for leather, comprising, by weight, the following raw materials: 30-60 parts water-based polyurethane resin, 24-40 parts wax emulsion, 20-40 parts water, 4-10 parts matting agent, 3-6 parts velvet powder, 2-5 parts thickener, 2-3.5 parts wetting agent, 1.5 parts hand feel agent, and 0.5-1 parts water-based blocking curing agent; wherein the water-based polyurethane resin is a mixture of PU-6140 and PU-608.

[0006] Optionally, the ratio of PU-6140 and PU-608 by weight is 0.8:(1 to 1.2).

[0007] Optionally, the wax emulsion is a mixture of color-changing wax emulsion, tactile wax emulsion, and polyethylene hard wax emulsion.

[0008] Optionally, the color-changing wax emulsion, the hand-feel wax emulsion, and the polyethylene hard wax emulsion are mixed in a weight ratio of (2.8-4):1:1.

[0009] Optionally, the waterborne blocked curing agent is an aliphatic waterborne blocked isocyanate.

[0010] Optionally, the matting agent is silicon dioxide.

[0011] Optionally, the thickener is an aqueous polyurethane thickener.

[0012] Optionally, the wetting agent is an organosilicon wetting agent; the hand feel agent is an organosilicon hand feel agent.

[0013] A second aspect of the present invention provides a method for preparing a water-based coating for leather, comprising the following steps: Step S001: Add matting powder to water and stir to disperse it into a matting powder dispersion; Step S002: Add waterborne polyurethane resin to the reactor, and while stirring, slowly add matting powder dispersion and wax emulsion in sequence. After stirring for 15-20 minutes, add waterborne blocking curing agent, wetting agent, hand feel agent and thickener. Step S003: After the viscosity of the coating is adjusted to 1500-2000 CPS, add a pH adjuster to the reaction vessel to adjust the pH value of the coating to 7.5-8.5.

[0014] Optionally, in step S003, the pH adjuster is at least one of triethanolamine and trimethylethanolamine.

[0015] The beneficial effects of this invention are: The first aspect of this invention provides a water-based coating for leather. By adding a water-based sealing curing agent to the water-based coating system, the film-forming ability of the coating can be significantly improved, preventing the coating from peeling and cracking after long-term use. Simultaneously, it can enhance the chemical bonding between resin molecules and the hydroxyl and amino groups on the leather surface, further improving the adhesion of the coating and thus extending the service life of leather products. Furthermore, by using a water-based polyurethane resin compounded with PU-6140 and PU-608, the stiffness of the coating can be moderately improved, making the raised parts of the leather texture more distinct and the recessed parts more smooth, forming a texture with alternating softness and hardness. It can also enhance the visual contrast of the texture. Combined with the synergistic effects of suede powder, wax emulsion, matting agent, wetting agent, and hand-feeling agent, it can give the leather surface excellent three-dimensionality of the crazy horse pattern, abrasion resistance, and softness, further enhancing the retro texture. This allows the coating to meet the needs of retro-style leathers such as crazy horse leather, balancing practicality and decoration.

[0016] The second aspect of this invention provides a method for preparing a water-based coating for leather. This method involves first dispersing a matting powder separately in water to form a dispersion, which avoids the problem of agglomeration of the matting powder when added to the water-based polyurethane resin, ensuring its uniform distribution in the water-based coating system and guaranteeing that the coating forms a uniform waxy finish on the leather surface. Slowly adding the matting powder dispersion and wax emulsion, and using an appropriate rotation speed, avoids high-speed shearing that could damage the resin molecular structure and cause the wax emulsion to demulsify. Adjusting the pH of the coating to 7.5–8.5 maintains the stability of the water-based polyurethane resin and various additives, preventing acidic environments from causing resin demulsification or excessive alkalinity from affecting coating adhesion. The preparation method provided by this invention requires no complex equipment, is simple and controllable to operate, and can mass-produce coatings that are uniformly dispersed, have stable performance, and are suitable for the needs of Crazy Horse leather, effectively balancing production efficiency and product quality. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing a water-based coating for leather provided by the present invention.

[0018] Figure 2 The image shows a crazy horse leather product coated with the water-based coating provided by this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] The first aspect of this invention provides a water-based coating for leather, wherein the leather may be crazy horse leather. The water-based coating for leather, by weight, comprises the following raw materials: 30-60 parts of water-based polyurethane resin, 24-40 parts of wax emulsion, 20-40 parts of water, 4-10 parts of matting agent, 3-6 parts of nap powder, 2-5 parts of thickener, 2-3.5 parts of wetting agent, 1.5 parts of hand feel agent, and 0.5-1 parts of water-based sealing curing agent.

[0021] In the above composition, waterborne polyurethane resin serves as the film-forming substrate for the coating. Through cross-linking of resin molecules, a dense film layer can be formed, allowing the waterborne coating for leather to adhere to the crazy horse leather, thus imparting an excellent three-dimensional effect to the leather surface. The wax emulsion can be compounded with various types of wax emulsions to give the leather a vintage color-changing effect after friction and bending, matching the style of crazy horse leather. It also enhances the tactile texture of the coating and increases its hardness, scratch resistance, and water resistance, extending the lifespan of the crazy horse leather. Water, as a solvent and dispersion medium, dilutes the coating to a suitable viscosity, facilitating stirring, spraying, and other application operations. It also dissolves some additives, ensuring uniform dispersion of all raw materials and improving the storage stability of the coating. The thickener adjusts the viscosity of the coating to a suitable range for application, preventing dripping and missed areas during application. It also improves the thixotropy of the coating, allowing the wet film to maintain its shape during drying, thereby improving film smoothness.

[0022] In the above composition, the velvet powder forms a tiny velvety layer on the coating surface, giving the leather a soft, velvety feel and improving its tactile comfort. It also enhances the coating's coverage, mitigates uneven surface texture, strengthens the vintage feel, and improves the coating's abrasion resistance and scratch resistance. The matte powder adjusts the coating's gloss on the leather substrate, giving it a high level of waxy sheen, but not limited to this. The wetting agent reduces the surface tension of the coating, promoting even spreading of the coating on the leather substrate surface and avoiding defects such as pinholes and fisheyes. It is particularly suitable for textured substrates like crazy horse leather, ensuring uniform coating coverage. The feel agent optimizes the coating's tactile feel, enhancing its smoothness and delicacy. In synergy with the wax emulsion, it improves the feel of the finished leather product, preventing the coating from becoming rough or stiff.

[0023] In the above composition, the water-based blocked curing agent can coexist stably with water-based polyurethane resin at room temperature for a long time. During heat treatment processes such as coating drying, the water-based blocked curing agent can react with the hydrophilic groups in the polyurethane resin to form stable chemical bonds. Therefore, it can crosslink and bind the dispersed resin molecules to form a denser three-dimensional network structure, thereby improving the film-forming ability of the coating and preventing the coating from peeling and cracking after long-term use. Moreover, by introducing the water-based blocked curing agent into the coating system, the chemical bonding between the resin molecules and the hydroxyl and amino groups on the leather surface can be enhanced, further improving the adhesion of the coating.

[0024] In the above composition, the waterborne polyurethane resin is a mixture of PU-6140 and PU-608. PU-6140, after film formation, has moderate flexibility, allowing it to conform to the uneven texture of the leather surface, thus preserving the basic outline of the original leather texture. PU-608 possesses a certain degree of gloss adjustment capability; after film formation, it creates a slight gloss difference between the raised and recessed areas of the leather texture, thereby enhancing the visual contrast of the texture. Furthermore, the molecular chain density of PU-608 is slightly higher than that of PU-6140. When combined with PU-6140, the stiffness of the coating can be moderately increased, making the raised areas of the leather texture more clearly defined, while the recessed areas, due to the slightly thicker coating, feel smoother, creating a textured feel that alternates between soft and hard.

[0025] In an optional embodiment, the weight ratio of PU-6140 and PU-608 is 0.8:(1~1.2). When PU-6140 and PU-608 are compounded in the above ratio, they can enhance the abrasion resistance of the coating, protect the texture additives (wax emulsion, velvet powder) from being easily worn, and at the same time buffer the stress when the leather is bent, avoid the coating from cracking and causing the texture to break, and ensure that the texture is clear for a long time.

[0026] In an optional embodiment, the wax emulsion is a mixture of color-changing wax emulsion, hand-feel wax emulsion, and polyethylene hard wax emulsion. In this embodiment, the wax emulsion is a mixture of color-changing wax emulsion, hand-feel wax emulsion, and polyethylene hard wax emulsion. Through the synergistic function of the three wax emulsions, the requirements of leather (especially crazy horse leather) for appearance texture, touch feel, and durability can be simultaneously met. Specifically, color-changing wax emulsions can impart a vintage color-changing effect to leather after friction and bending, thereby enhancing the visual depth of the natural texture. Meanwhile, hand-feel wax emulsions optimize the tactile experience of the coating, compensating for the potential dryness issues caused by color-changing wax emulsions and polyethylene hard wax emulsions, thus improving the comfort of using the leather. Polyethylene hard wax emulsions enhance the coating's hardness and scratch and abrasion resistance, reducing the wear and tear on the texture during daily use. Furthermore, the three components, when mixed, can be evenly dispersed in water-based coating systems, forming a compatibility with water-based polyurethane resin, velvet powder, matting powder, wetting agents, and hand-feel agents. This avoids the limitations of a single wax emulsion in terms of leather performance, and through subsequent application, it creates a comprehensive coating with a long-lasting color-changing effect, a delicate feel, and wear and scratch resistance. Therefore, it can meet the needs of Crazy Horse leather for a combination of decoration, comfort, and practicality.

[0027] In an optional embodiment, the color-changing wax emulsion, the hand-feel wax emulsion, and the polyethylene hard wax emulsion are mixed in a weight ratio of (2.8-4):1:1. This ratio matches the priority requirements of Crazy Horse leather for vintage decoration, comfortable touch, and durability. Specifically, a higher proportion of color-changing wax emulsion ensures sufficient depth and light color-changing effects after leather friction and bending, enhancing the visual recognition of the vintage texture and preventing weakening of decoration due to insufficient proportion of color-changing wax emulsion. The hand-feel wax emulsion neutralizes the dry touch caused by the color-changing wax emulsion and the polyethylene hard wax emulsion, giving the coating a silky and warm touch experience. The polyethylene hard wax emulsion improves the scratch and abrasion resistance of the coating to reduce texture wear and decay. The equal proportion of the two avoids an imbalance where one property is too strong. For example, too much polyethylene hard wax emulsion results in a stiff feel, while too much hand-feel wax emulsion results in insufficient abrasion resistance.

[0028] In an optional embodiment, the waterborne blocked curing agent is an aliphatic waterborne blocked isocyanate. During the heat treatment of the coating, the aliphatic waterborne blocked isocyanate can release isocyanate groups and react with the hydrophilic groups in the polyurethane resin to form a cross-linked structure, thereby significantly improving the various properties of the coating.

[0029] In an optional embodiment, the matte powder is silicon dioxide. The silicon dioxide can be modified nano-silica, which can effectively reduce the gloss of the coating surface, forming a soft matte effect (such as a waxy effect), avoiding the plastic feel caused by high gloss, and giving the leather a more natural retro visual texture. At the same time, the particle shape of the matte powder can fill the tiny pores on the coating surface, enhancing the coating's wear resistance and scratch resistance, and reducing scratch damage during daily use.

[0030] In an optional embodiment, the thickener is a waterborne polyurethane thickener. Waterborne polyurethane thickeners have good compatibility with waterborne polyurethane resins, which can avoid defects such as coating delamination, demulsification, or pinholes after film formation caused by incompatibility between the thickener and the resin, thus ensuring the stability of the coating system.

[0031] In an optional embodiment, the wetting agent is an organosilicon wetting agent, which can effectively reduce the surface tension of the coating through the low surface energy characteristics of organosilicon molecules, quickly break the air film and fine oil stains on the leather surface, promote the uniform spreading of the coating and penetration into the gaps of the leather texture, avoid pinholes, fish eyes or local omissions in the coating caused by insufficient wetting of the coating, and ensure the full coverage of the coating on the leather substrate.

[0032] In an optional embodiment, the feel agent is an organosilicon feel agent. Due to the low surface area of ​​the organosilicon molecules in the feel agent, a smooth siloxane film can be formed on the coating surface, giving the leather a delicate and silky tactile experience, allowing products such as Crazy Horse leather to combine a vintage waxy feel with comfortable smoothness. Furthermore, the organosilicon feel agent has good compatibility with water-based polyurethane resins and organosilicon wetting agents, and will not cause coating delamination. In addition, the organosilicon feel agent exhibits excellent weather resistance after film formation; with long-term use, the coating's tactile feel will not diminish due to friction or changes in temperature and humidity. Moreover, it can slightly improve the coating's anti-blocking properties, preventing the coating from sticking together when leather products are stacked, without affecting the coating's flexibility and water resistance.

[0033] A second aspect of the present invention provides a method for preparing a water-based coating for leather, comprising the following steps: Step S001: Add matting powder to water and stir to disperse it into a matting powder dispersion; Step S002: Add waterborne polyurethane resin to the reactor, and slowly add matting powder dispersion and wax emulsion in sequence at a speed of 400-800 r / min. After stirring for 15-20 min, add waterborne blocked curing agent, wetting agent, hand feel agent and thickener. Step S003: After the viscosity of the coating is adjusted to 1500-2000 CPS, add a pH adjuster to the reaction vessel to adjust the pH value of the coating to 7.5-8.5.

[0034] The preparation method provided by this invention avoids the problem of agglomeration of matting powder when added to water-based polyurethane resin by first dispersing the matting powder separately in water to form a dispersion, ensuring uniform distribution in the water-based coating system and guaranteeing that the coating can form a uniform waxy effect on the leather surface. Slowly adding the matting powder dispersion and wax emulsion, and using an appropriate rotation speed, avoids high-speed shearing that could damage the resin molecular structure and cause wax emulsion demulsification. Adjusting the pH value of the coating to 7.5–8.5 maintains the stability of the water-based polyurethane resin and various additives, preventing resin demulsification due to an acidic environment or excessive alkalinity that could affect coating adhesion. The preparation method provided by this invention requires no complex equipment, is simple and controllable to operate, and can mass-produce coatings that are uniformly dispersed, stable in performance, and suitable for the needs of Crazy Horse leather, effectively balancing production efficiency and product quality.

[0035] In an optional embodiment, in step S003, the pH adjuster is at least one of triethanolamine and trimethylethanolamine. Compared to inorganic pH adjusters, the organic amine pH adjuster used in this embodiment is weakly alkaline, resulting in a mild reaction when adjusting the pH. It can control the pH value of the coating within the range of 7.5 to 8.5, avoiding sudden pH increases and decreases caused by excessive alkalinity of inorganic strong alkalis. This prevents demulsification and stratification of waterborne polyurethane resin due to drastic pH fluctuations. Furthermore, organic amine molecules contain polar groups such as hydroxyl and amino groups, which can form weak interactions with resin molecules and the surface of matting agents. This not only helps improve the dispersion uniformity of each component and reduces sedimentation and stratification during coating storage, but also synergistically improves the flexibility of the coating after film formation. In addition, triethanolamine and trimethylethanolamine have low volatility and no irritating odor during application.

[0036] The following examples and comparative examples further illustrate the present invention. The sources or types of some of the raw materials used in the following examples and comparative examples are as follows: PU-6140 (Guangdong Yinyang Resin), PU-608 (Guangdong Yinyang Resin), color-changing wax emulsion (BH-617), hand-feel wax emulsion (WAX5053), polyethylene wax emulsion (V-815A), wetting agent (TEGO245), hand-feel agent (AKN-108), aliphatic waterborne blocked isocyanate (Y-01).

[0037] Example 1 This embodiment provides a water-based coating for leather, comprising, by weight, the following raw materials: 30.6 parts water-based polyurethane resin, 24 parts wax emulsion, 20 parts water, 4 parts silica matting agent, 3 parts velvet powder, 2 parts water-based polyurethane thickener, 2 parts silicone wetting agent, 1.5 parts silicone hand feel agent, and 0.5 parts aliphatic water-based blocked isocyanate. The water-based polyurethane resin is a mixture of PU-6140 and PU-608; the weight ratio of PU-6140 to PU-608 is 0.8:1; the wax emulsion is a mixture of color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion; the weight ratio of the color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion is 2.8:1:1.

[0038] This embodiment also provides a method for preparing a water-based coating for leather, comprising the following steps: Step S001: Add matting powder to water and stir to disperse it into a matting powder dispersion; Step S002: Add waterborne polyurethane resin to the reactor, and slowly add matting powder dispersion and wax emulsion in sequence at a speed of 500 r / min. After stirring for 20 min, add waterborne blocked curing agent, wetting agent, hand feel agent and thickener. Step S003: After the viscosity of the coating is adjusted to 1500-2000 CPS, a pH adjuster is added to the reaction vessel to adjust the pH value of the coating to 7.5-8.5. The pH adjuster is triethanolamine.

[0039] Example 2 This embodiment provides a water-based coating for leather, comprising, by weight, the following raw materials: 60 parts water-based polyurethane resin, 40 parts wax emulsion, 40 parts water, 10 parts silica matting agent, 6 parts velvet powder, 5 parts water-based polyurethane thickener, 3.5 parts organosilicon wetting agent, 1.5 parts organosilicon hand feel agent, and 1 part aliphatic water-based blocked isocyanate; the water-based polyurethane resin is a mixture of PU-6140 and PU-608; the weight ratio of PU-6140 and PU-608 is 0.8:1.2; the wax emulsion is a mixture of color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion; the weight ratio of the color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion is 3:1:1.

[0040] This embodiment also provides a method for preparing a water-based coating for leather, which is the same as the preparation method provided in Example 1.

[0041] Example 3 This embodiment provides a water-based coating for leather, comprising, by weight, the following raw materials: 50 parts water-based polyurethane resin, 30 parts wax emulsion, 30 parts water, 8 parts silica matting agent, 5 parts suede powder, 3 parts water-based polyurethane thickener, 3 parts silicone wetting agent, 1.5 parts silicone hand feel agent, and 0.8 parts aliphatic water-based blocked isocyanate; the water-based polyurethane resin is a mixture of PU-6140 and PU-608; the weight ratio of PU-6140 and PU-608 is 0.8:1.2; the wax emulsion is a mixture of color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion; the weight ratio of the color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion is 4:1:1.

[0042] This embodiment also provides a method for preparing a water-based coating for leather, which is the same as the preparation method provided in Example 1.

[0043] Comparative Example 1 This comparative example provides a water-based coating for leather, comprising, by weight, the following raw materials: 30.6 parts water-based polyurethane resin, 24 parts wax emulsion, 20 parts water, 4 parts silica matting agent, 3 parts velvet powder, 2 parts water-based polyurethane thickener, 2 parts silicone wetting agent, and 1.5 parts silicone hand feel agent. The water-based polyurethane resin is a mixture of PU-6140 and PU-608; the weight ratio of PU-6140 to PU-608 is 0.8:1; the wax emulsion is a mixture of color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion; the weight ratio of the color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion is 2.8:1:1.

[0044] This comparative example also provides a method for preparing an aqueous coating for leather, which is the same as the method provided in Example 1.

[0045] Comparative Example 2 This comparative example provides a water-based coating for leather, comprising, by weight, the following raw materials: 30.6 parts water-based polyurethane resin, 24 parts wax emulsion, 20 parts water, 4 parts silica matting agent, 3 parts velvet powder, 2 parts water-based polyurethane thickener, 2 parts silicone wetting agent, 1.5 parts silicone hand feel agent, and 0.5 parts aliphatic water-based blocked isocyanate. The water-based polyurethane resin is a mixture of PU-6140 and PU-608; the weight ratio of PU-6140 to PU-608 is 0.5:1; the wax emulsion is a mixture of color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion; the weight ratio of the color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion is 2.8:1:1.

[0046] This comparative example also provides a method for preparing an aqueous coating for leather, which is the same as the method provided in Example 1.

[0047] Comparative Example 3 This comparative example provides a water-based coating for leather, comprising, by weight, the following raw materials: 30.6 parts water-based polyurethane resin, 24 parts wax emulsion, 20 parts water, 4 parts silica matting agent, 3 parts velvet powder, 2 parts water-based polyurethane thickener, 2 parts silicone wetting agent, 1.5 parts silicone hand feel agent, and 0.5 parts aliphatic water-based blocked isocyanate. The water-based polyurethane resin is a mixture of PU-6140 and PU-608; the weight ratio of PU-6140 to PU-608 is 0.8:1.7; the wax emulsion is a mixture of color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion; the weight ratio of the color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion is 2.8:1:1.

[0048] This comparative example also provides a method for preparing an aqueous coating for leather, which is the same as the method provided in Example 1.

[0049] Comparative Example 4 This comparative example provides a water-based coating for leather, comprising, by weight, the following raw materials: 30.6 parts water-based polyurethane resin, 24 parts wax emulsion, 20 parts water, 4 parts silica matting agent, 3 parts velvet powder, 2 parts water-based polyurethane thickener, 2 parts silicone wetting agent, 1.5 parts silicone hand feel agent, and 0.5 parts aliphatic water-based blocked isocyanate. The water-based polyurethane resin is a mixture of PU-6140 and PU-608; the weight ratio of PU-6140 to PU-608 is 0.8:1; the wax emulsion is a mixture of color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion; the weight ratio of the color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion is 2:1:1.

[0050] This comparative example also provides a method for preparing an aqueous coating for leather, which is the same as the method provided in Example 1.

[0051] Comparative Example 5 This comparative example provides a water-based coating for leather, comprising, by weight, the following raw materials: 30.6 parts water-based polyurethane resin, 24 parts wax emulsion, 20 parts water, 4 parts silica matting agent, 3 parts velvet powder, 2 parts water-based polyurethane thickener, 2 parts silicone wetting agent, 1.5 parts silicone hand feel agent, and 0.5 parts aliphatic water-based blocked isocyanate. The water-based polyurethane resin is a mixture of PU-6140 and PU-608; the weight ratio of PU-6140 to PU-608 is 0.8:1; the wax emulsion is a mixture of color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion; the weight ratio of the color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion is 2.8:1.2:1.

[0052] This comparative example also provides a method for preparing an aqueous coating for leather, which is the same as the method provided in Example 1.

[0053] Comparative Example 6 This comparative example provides a water-based coating for leather, comprising, by weight, the following raw materials: 30.6 parts water-based polyurethane resin, 24 parts wax emulsion, 20 parts water, 4 parts silica matting agent, 3 parts velvet powder, 2 parts water-based polyurethane thickener, 2 parts silicone wetting agent, 1.5 parts silicone hand feel agent, and 0.5 parts aliphatic water-based blocked isocyanate. The water-based polyurethane resin is a mixture of PU-6140 and PU-608; the weight ratio of PU-6140 to PU-608 is 0.8:1; the wax emulsion is a mixture of color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion; the weight ratio of the color-changing wax emulsion, hand feel wax emulsion, and polyethylene hard wax emulsion is 2.8:1:1.2.

[0054] This comparative example also provides a method for preparing an aqueous coating for leather, which is the same as the method provided in Example 1.

[0055] The above embodiments and comparative examples were tested. Before testing, the water-based coatings obtained in each embodiment and comparative example were added to the water-based color paste and stirred for 15-20 minutes until the color paste and coating were completely mixed and uniform with no color difference. Then, the mixed color paste coating was applied to the substrate using a three-plate printing press with two coatings (the substrate used for coating was Crazy Horse leather, consistent with the actual application, and the coating thickness was controlled at 15-20 μm). After coating, the substrate was placed in a drying equipment and dried at 100-130℃ for 15-20 minutes. After drying, the substrate was placed in a texturing machine. After texturing was completed, the substrate was removed and cooled to room temperature, and then the performance of each coating was tested.

[0056] The tests included coating adhesion, coating hardness, abrasion resistance of the leather surface, and the vintage color-changing effect of the leather. The testing standard for coating adhesion was ASTM D3359 "Standard Test Methods for Measuring Adhesion by Tape Test"; the testing standard for coating hardness was GB / T 6739-2021 "Determination of Hardness of Paints and Varnishes by Pencil Method"; and the testing standard for abrasion resistance of the leather surface was GB / T 22895-2008 "Leather Physical and Mechanical Tests - Determination of Color Fastness to Abrasion". The vintage color-changing effect was determined by rubbing and bending the leather, recording the depth of the leather surface texture, the clarity of the color change, the texture layering, and the feel. The test results are shown in Tables 1, 2, and 3 below.

[0057] Table 1:

[0058] Table 2:

[0059] Table 3:

[0060] Comparing Comparative Example 1 with Examples 1-3, it was found that the coating adhesion and abrasion resistance of Comparative Example 1 decreased significantly, and the coating was prone to peeling and cracking. This is because the water-based coating for leather provided by Comparative Example 1 did not use a water-based closed curing agent, which resulted in the resin molecules being unable to form a dense network, and the resin film-forming properties were generally poor.

[0061] Comparing Comparative Example 2 with Examples 1-3, it was found that the leather texture visual contrast of the water-based leather coating provided by Comparative Example 2 was poor. At the same time, the abrasion resistance decreased, affecting the retro texture and service life. This is because the proportion of PU-6140 in the water-based polyurethane resin used in Comparative Example 2 was relatively small, which enhances the visual contrast of the texture.

[0062] Comparing Comparative Example 3 with Examples 1-3, it was found that the leather using the water-based leather coating provided by Comparative Example 3 had reduced flexibility, was prone to cracking when bent, damaged the integrity of the texture, and had a poor feel. This was because the proportion of PU-608 in the water-based polyurethane resin used in Comparative Example 3 was too high, resulting in a harder coating.

[0063] Comparing Comparative Example 4 with Examples 1-3, it was found that Comparative Example 4 could not produce a significant retro color-changing effect, and the leather surface texture lacked a sense of layering. This was because the proportion of color-changing wax emulsion in the water-based leather coating provided by Comparative Example 4 was reduced compared to Examples 1-3.

[0064] Comparing Comparative Example 5 with Examples 1-3, it was found that the leather surface of Comparative Example 5 had a smooth feel, but the abrasion resistance and suede texture of the leather surface coating decreased. This is because the proportion of hand-feel wax emulsion in the water-based leather coating provided by Comparative Example 5 was increased compared with Examples 1-3, which reduced the abrasion resistance and suede texture of the coating.

[0065] Comparing Comparative Example 6 with Examples 1-3, it was found that the water-based leather coating provided by Comparative Example 6 had an excessively high proportion of polyethylene hard wax emulsion, which resulted in a decrease in coating hardness and flexibility, a dry feel, and affected the comfort and durability of the leather.

[0066] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A water-based coating for leather, characterized in that, The raw materials for its preparation, by weight, include: 30-60 parts of waterborne polyurethane resin, 24-40 parts of wax emulsion, 20-40 parts of water, 4-10 parts of matting agent, 3-6 parts of fluffing powder, 2-5 parts of thickener, 2-3.5 parts of wetting agent, 1.5 parts of hand feel agent, and 0.5-1 parts of waterborne blocked curing agent; wherein the waterborne polyurethane resin is a mixture of PU-6140 and PU-608.

2. The water-based coating for leather according to claim 1, characterized in that, The ratio of PU-6140 and PU-608 by weight is 0.8:(1~1.2).

3. The water-based coating for leather according to claim 1, characterized in that, The wax emulsion is a mixture of color-changing wax emulsion, hand-feel wax emulsion, and polyethylene hard wax emulsion.

4. The water-based coating for leather according to claim 3, characterized in that, The color-changing wax emulsion, the hand-feeling wax emulsion, and the polyethylene hard wax emulsion are mixed in a weight ratio of (2.8-4):1:

1.

5. The water-based coating for leather according to claim 1, characterized in that, The water-based blocked curing agent is an aliphatic water-based blocked isocyanate.

6. The water-based coating for leather according to claim 1, characterized in that, The matting agent is silicon dioxide.

7. The water-based coating for leather according to claim 1, characterized in that, The thickener is a water-based polyurethane thickener.

8. The water-based coating for leather according to claim 1, characterized in that, The wetting agent is an organosilicon wetting agent; the hand feel agent is an organosilicon hand feel agent.

9. A method for preparing an aqueous coating for leather as described in any one of claims 1-8, characterized in that, Includes the following steps: Step S001: Add matting powder to water and stir to disperse it into a matting powder dispersion; Step S002: Add waterborne polyurethane resin to the reactor, and while stirring, slowly add matting powder dispersion and wax emulsion in sequence. After stirring for 15-20 minutes, add waterborne blocking curing agent, wetting agent, hand feel agent and thickener. Step S003: After the viscosity of the coating is adjusted to 1500-2000 CPS, add a pH adjuster to the reaction vessel to adjust the pH value of the coating to 7.5-8.

5.

10. The method for preparing an aqueous coating for leather according to claim 9, characterized in that, In step S003, the pH adjuster is at least one of triethanolamine and trimethylethanolamine.

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