A water-based polyurethane coating for labels and a method for preparing the same

Abstract

The present application relates to the technical field of water-based polyurethane coating, in particular to a kind of water-based polyurethane coating for label and preparation method thereof, by mass parts, consisting of following components: core resin component 30-50 parts, film-forming aid 3-8 parts, pigment and filler 5-15 parts, wetting dispersant 0.5-1.5 parts, defoaming agent 0.3-0.8 parts, leveling agent 0.2-0.7 parts, thickening agent 0.1-0.5 parts, crosslinking agent 1-4.5 parts, deionized water 18-30 parts;The water-based polyurethane coating for label and preparation method thereof provided by the present application solve a plurality of technical shortcomings of the existing water-based polyurethane coating for label, realize the comprehensive performance of product to improve, have significant technical advantage and application value.

Description

Technical Field

[0001] This invention relates to the field of waterborne polyurethane coating technology, and more specifically to a waterborne polyurethane coating for labels and its preparation method. Background Technology

[0002] Waterborne polyurethane coatings, with their advantages of low volatility and environmental friendliness, have become an important alternative to traditional solvent-based coatings in the label industry, and their application in coating various label substrates is becoming increasingly widespread. However, the current industry still faces many technical shortcomings in waterborne polyurethane coatings for labels, and a comprehensive solution that adapts performance to different application scenarios has not yet been developed.

[0003] Existing products suffer from simplistic resin system designs, often employing ordinary waterborne polyurethane or single modified components. This makes it difficult to balance adhesion, flexibility, and environmental friendliness of the coating film, leading to issues like film peeling and poor adhesion on inert substrates. Core performance characteristics are significantly weak; abrasion resistance, weather resistance, and water resistance cannot be simultaneously met. Some products exhibit color differences and chalking after aging tests, and the coating film easily exposes the substrate after friction, failing to meet the long-term use requirements of labels. Furthermore, the additive formulation lacks synergistic design, and improper pigment and filler dispersion processes can lead to agglomeration, resulting in insufficient film hiding power. Inappropriate crosslinking agent ratios can affect film density, thereby reducing water resistance.

[0004] The existing manufacturing processes mostly employ a one-time feeding and room-temperature stirring method, lacking a targeted design for step-by-step temperature control and orderly feeding. This results in poor product performance stability and insufficient batch-to-batch consistency. Furthermore, existing products lack adaptability to specific application scenarios, exhibit poor film-forming effects during low-temperature application, and fail to meet stringent environmental standards for food labeling products. Additionally, the applicable range of raw material ratios is narrow, and there is a lack of verification of limiting parameters, severely restricting their large-scale application and scenario expansion. Summary of the Invention

[0005] The primary objective of this invention is to provide a water-based polyurethane coating for labels and a method for preparing the same.

[0006] A further objective of this invention is to provide a water-based polyurethane coating for labels, comprising, by weight, the following components: 30-50 parts of core resin component, 3-8 parts of film-forming aid, 5-15 parts of pigments and fillers, 0.5-1.5 parts of wetting and dispersing agent, 0.3-0.8 parts of defoamer, 0.2-0.7 parts of leveling agent, 0.1-0.5 parts of thickener, 1-4.5 parts of crosslinking agent, and 18-30 parts of deionized water;

[0007] The core resin component is an epoxy-modified waterborne polyurethane dispersion, or a bio-based waterborne polyurethane dispersion, or a compound of an epoxy-modified waterborne polyurethane dispersion and a bio-based waterborne polyurethane dispersion. The epoxy-modified waterborne polyurethane dispersion is prepared by emulsification after mixing and reacting propylene oxide, isocyanate, chain extender, and neutralizer. The bio-based waterborne polyurethane dispersion uses castor oil-based polyol as raw material. The crosslinking agent is a blocked isocyanate compounded with HDI and IPDI, and its n-NCO / n-OH ratio is 1.2-1.5. The wetting and dispersing agent is a polycarboxylate, the defoamer is a polyether-modified silicone, the leveling agent is an acrylic acid, and the thickener is hydroxyethyl cellulose.

[0008] Preferably, when the core resin component is a compound of epoxy-modified waterborne polyurethane dispersion and bio-based waterborne polyurethane dispersion, the epoxy-modified waterborne polyurethane dispersion comprises 15-25 parts by mass and the bio-based waterborne polyurethane dispersion comprises 30-35 parts by mass.

[0009] Preferably, the adhesive further includes 0.5-3 parts by weight of an adhesion promoter, wherein the adhesion promoter is one of a silane coupling agent, an epoxy polyether modified silane, or a pentaerythritol tetra-mercaptopropionate.

[0010] Preferably, the product also includes a weather-resistant component, which is a compound of benzotriazole ultraviolet absorber and hindered amine light stabilizer; by weight, the benzotriazole ultraviolet absorber is 0.6-1.2 parts and the hindered amine light stabilizer is 0.4-0.6 parts.

[0011] Preferably, the pigment or filler is titanium dioxide, or a mixture of titanium dioxide and talc, or a mixture of titanium dioxide and calcium carbonate, or barium sulfate; the particle size of the pigment or filler is 1500 mesh to 3000 mesh.

[0012] Preferably, the film-forming aid is propylene glycol methyl ether acetate, or a mixture of propylene glycol methyl ether acetate and dodecyl alcohol ester, or hexanediol butyl ether acetate.

[0013] A method for preparing the waterborne polyurethane coating for the label includes the following steps: (1) Pre-dispersion: Deionized water, wetting and dispersing agent and defoamer are added to a stirring device and mixed to obtain a pre-dispersion liquid; (2) Pigment and filler dispersion: Add pigments and fillers to the pre-dispersion liquid and stir to disperse them to obtain a pigment and filler dispersion; (3) Main mixture: Add the core resin component to the pigment and filler dispersion and stir to mix. Then add the film-forming aid and leveling agent and continue stirring to obtain the main mixture. (4) Modification and adjustment: Add crosslinking agent to the main mixture and stir to disperse. Add adhesion promoter and weather-resistant component as needed and stir to disperse. Then add thickener and stir to adjust the viscosity of the coating to obtain modified mixture. (5) Post-treatment: The modified mixture is filtered, then kept warm, and cooled to room temperature to obtain the waterborne polyurethane coating for the label.

[0014] Preferably, in step (1), the stirring speed is 200-300 r / min and the stirring temperature is 25-28℃; in step (2), the stirring speed is 500-700 r / min and the stirring temperature is 35-40℃; in step (3), the stirring speed is 500-550 r / min and the stirring temperature is 45-55℃; and in step (4), after adding the thickener, the stirring speed is 300-350 r / min and the stirring temperature is 35-38℃.

[0015] Preferably, a 150-200 mesh filter is used for filtration in step (5); the temperature of the heat preservation treatment is 25-55℃ and the heat preservation treatment time is 45-120 minutes.

[0016] Preferably, when the core resin component is a compound of epoxy-modified waterborne polyurethane dispersion and bio-based waterborne polyurethane dispersion, the epoxy-modified waterborne polyurethane dispersion and the bio-based waterborne polyurethane dispersion are mixed evenly before the main body mixing in step (3).

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention optimizes and blends resin systems to combine the advantages of epoxy modification and bio-based waterborne polyurethane, taking into account the adhesion, flexibility and environmental friendliness of the paint film. With the use of adhesion promoters, it significantly improves the adhesion of the coating on inert substrates and solves the problem of easy paint film peeling from the root.

[0018] 2. This invention achieves synergistic improvement of various properties through the synergistic combination and precise control of additives. The compound use of weather-resistant components effectively delays the aging of the paint film. The reasonable combination of pigments and fillers and the dispersion process significantly improve the wear resistance and hiding power of the paint film. The scientific control of the crosslinking agent ratio enhances the density and water resistance of the paint film, so that the core performance of the coating reaches the industry's excellent level.

[0019] 3. The preparation process of this invention adopts a step-by-step temperature control and orderly feeding method, which effectively improves the stability of product performance and batch-to-batch consistency. The process operation is simple and controllable, requiring no complex production equipment and reducing the difficulty of production management. The product has excellent environmental performance, with low volatile organic compound content, and can meet the stringent environmental requirements of food labels. At the same time, the formula and process have been specifically optimized for low-temperature construction scenarios, making it compatible with various label substrates such as coated paper, plastic, and tinplate, and applicable to a wide range of scenarios.

[0020] 4. The raw material ratio design of this invention has been verified by extreme parameters and can still meet the usage requirements. It has a wide range of applications and the overall preparation scheme has good potential for large-scale production. It can provide a new solution for high-performance, multi-scenario adaptable environmentally friendly water-based coatings for the labeling field and has good market application prospects. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: This embodiment uses an epoxy-modified waterborne polyurethane dispersion as the core resin component. The epoxy-modified waterborne polyurethane dispersion has a solid content of 40% and is made by mixing propylene oxide, isocyanate, chain extender, and neutralizer in a certain proportion, reacting at 50-80°C for 2-4 hours, and then adding deionized water for emulsification. This can improve the adhesion between the coating and the substrate, as well as the hardness and chemical resistance of the paint film.

[0023] Specific raw material ratios (parts by weight): The mixture contains 50 parts epoxy-modified waterborne polyurethane dispersion, 5 parts film-forming aid (propylene glycol methyl ether acetate), 10 parts pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part wetting and dispersing agent (polycarboxylate), 0.5 parts defoamer (polyether-modified silicone), 0.5 parts leveling agent (acrylic), 0.4 parts thickener (hydroxyethyl cellulose), 3 parts crosslinking agent (blocked isocyanate of HDI and IPDI, n-NCO / n-OH=1.4), and 20 parts deionized water.

[0024] Specific preparation process: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 300 r / min and the temperature is 28℃. The mixture is mixed for 15 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. Add the pigment and filler to the pre-dispersion liquid, adjust the stirring speed to 650 r / min and the temperature to 40℃, and stir for 45 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step is to mix the main body. Add the epoxy-modified waterborne polyurethane dispersion to the pigment and filler dispersion, maintain the stirring speed at 550 r / min and the temperature at 50℃, and stir for 30 minutes to mix evenly. Then add the film-forming aid and leveling agent, and continue stirring for 20 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. Add the crosslinking agent and stir for 15 minutes to ensure uniform dispersion. Then add the thickener, adjust the stirring speed to 350 r / min and the temperature to 38℃, and stir for 12 minutes to adjust the viscosity of the coating to 35s. The fifth step is post-processing. The above mixture is filtered through a 150-mesh filter to remove impurities and undispersed particles. Then, it is kept at 45°C for 60 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0025] Example 2: This embodiment uses a bio-based waterborne polyurethane dispersion instead of the epoxy-modified waterborne polyurethane dispersion in Example 1 to optimize environmental friendliness and flexibility. This bio-based waterborne polyurethane dispersion uses castor oil-based polyols as raw materials, with a bio-based content of 65% and a solid content of 45%, balancing environmental friendliness and film-forming properties.

[0026] Specific raw material ratios (parts by weight): The composition includes 50 parts of bio-based waterborne polyurethane dispersion, 5 parts of film-forming aid (propylene glycol methyl ether acetate), 10 parts of pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part of wetting and dispersing agent (polycarboxylate), 0.5 parts of defoamer (polyether modified silicone), 0.5 parts of leveling agent (acrylic acid), 0.4 parts of thickener (hydroxyethyl cellulose), 3 parts of crosslinking agent (blocked isocyanate of HDI and IPDI, n-NCO / n-OH=1.4), and 20 parts of deionized water.

[0027] The specific preparation process is exactly the same as in Example 1: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 300 r / min and the temperature is 28℃. The mixture is mixed for 15 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. Add the pigment and filler to the pre-dispersion liquid, adjust the stirring speed to 650 r / min and the temperature to 40℃, and stir for 45 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step involves mixing the main body. The bio-based waterborne polyurethane dispersion is added to the pigment and filler dispersion. The stirring speed is maintained at 550 r / min and the temperature at 50℃. After stirring for 30 minutes to mix evenly, the film-forming aid and leveling agent are added. Stirring is continued for 20 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. Add the crosslinking agent and stir for 15 minutes to ensure uniform dispersion. Then add the thickener, adjust the stirring speed to 350 r / min and the temperature to 38℃, and stir for 12 minutes to adjust the viscosity of the coating to 35s. The fifth step is post-processing. The above mixture is filtered through a 150-mesh filter to remove impurities and undispersed particles. Then, it is kept at 45°C for 60 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0028] Example 3: This embodiment employs a compound system of bio-based and epoxy-modified waterborne polyurethane dispersions, with the addition of an adhesion promoter to optimize adhesion to inert substrates. The bio-based waterborne polyurethane dispersion uses castor oil-based polyols as raw materials, with a bio-based content of 65% and a solid content of 45%. The epoxy-modified waterborne polyurethane dispersion has a solid content of 40% and is prepared by emulsifying a mixture of propylene oxide, isocyanate, chain extender, and neutralizer in a specific ratio. The adhesion promoter selected is a silane coupling agent, which can improve the bonding strength between the coating and the inert substrate.

[0029] Specific raw material ratios (parts by weight): 30 parts of bio-based waterborne polyurethane dispersion, 20 parts of epoxy-modified waterborne polyurethane dispersion, 5 parts of film-forming aid (propylene glycol methyl ether acetate), 10 parts of pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part of wetting and dispersing agent (polycarboxylate), 0.5 parts of defoamer (polyether-modified silicone), 0.5 parts of leveling agent (acrylic acid), 0.4 parts of thickener (hydroxyethyl cellulose), 2 parts of adhesion promoter (silane coupling agent), 3 parts of crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n—NCO / n—OH=1.4), and 20 parts of deionized water.

[0030] The specific preparation process is exactly the same as in Example 1: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 300 r / min and the temperature is 28℃. The mixture is mixed for 15 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. Add the pigment and filler to the pre-dispersion liquid, adjust the stirring speed to 650 r / min and the temperature to 40℃, and stir for 45 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step is the main body mixing. First, the bio-based and epoxy-modified waterborne polyurethane dispersions are mixed evenly. Then, the pigment and filler dispersion is added. The stirring speed is maintained at 550 r / min and the temperature is 50℃. After stirring for 30 minutes to mix evenly, the film-forming aid and leveling agent are added. Stirring is continued for 20 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. Add adhesion promoter and crosslinking agent, stir for 15 minutes to ensure uniform dispersion, then add thickener, adjust the stirring speed to 350 r / min and temperature to 38℃, stir for 12 minutes, and adjust the viscosity of the coating to 35s. The fifth step is post-processing. The above mixture is filtered through a 150-mesh filter to remove impurities and undispersed particles. Then, it is kept at 45°C for 60 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0031] Example 4: This embodiment is based on Example 3, but the amount and ratio of crosslinking agent are adjusted, and an ultraviolet absorber is added to optimize weather resistance and water resistance. The raw materials used are basically the same as those in Example 3, except that the ultraviolet absorber is a benzotriazole, which can absorb ultraviolet rays and delay the aging of the paint film; the crosslinking agent is adjusted to 4 parts, and n—NCO / n—OH=1.5, which can improve the density of the paint film.

[0032] Specific raw material ratios (parts by weight): 30 parts of bio-based waterborne polyurethane dispersion, 20 parts of epoxy-modified waterborne polyurethane dispersion, 5 parts of film-forming aid (propylene glycol methyl ether acetate), 10 parts of pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part of wetting and dispersing agent (polycarboxylate), 0.5 parts of defoamer (polyether-modified silicone), 0.5 parts of leveling agent (acrylic acid), 0.4 parts of thickener (hydroxyethyl cellulose), 2 parts of adhesion promoter (silane coupling agent), 0.8 parts of ultraviolet absorber (benzotriazole), 4 parts of crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n—NCO / n—OH=1.5), and 20 parts of deionized water.

[0033] The specific preparation process is exactly the same as in Example 1: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 300 r / min and the temperature is 28℃. The mixture is mixed for 15 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. Add the pigment and filler to the pre-dispersion liquid, adjust the stirring speed to 650 r / min and the temperature to 40℃, and stir for 45 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step is the main body mixing. First, the bio-based and epoxy-modified waterborne polyurethane dispersions are mixed evenly. Then, the pigment and filler dispersion is added. The stirring speed is maintained at 550 r / min and the temperature is 50℃. After stirring for 30 minutes to mix evenly, the film-forming aid and leveling agent are added. Stirring is continued for 20 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. Add adhesion promoter, UV absorber and crosslinking agent, stir for 15 minutes to ensure uniform dispersion, then add thickener, adjust the stirring speed to 350 r / min and temperature to 38℃, stir for 12 minutes, and adjust the viscosity of the coating to 35s. The fifth step is post-processing. The above mixture is filtered through a 150-mesh filter to remove impurities and undispersed particles. Then, it is kept at 45°C for 60 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0034] Example 5: This embodiment, based on Example 4, adjusts the amount, type, particle size of pigments and fillers, and the amount of wetting and dispersing agent to optimize hiding power and abrasion resistance. The amount of pigments and fillers used is adjusted to 15 parts, including 8 parts of titanium dioxide and 7 parts of talc, with a particle size of 1500 mesh, which can improve hiding power and abrasion resistance; the amount of wetting and dispersing agent is adjusted to 1.5 parts to accommodate the increase in the amount of pigments and fillers and avoid pigment and filler agglomeration.

[0035] Specific raw material ratios (parts by weight): 30 parts of bio-based waterborne polyurethane dispersion, 20 parts of epoxy-modified waterborne polyurethane dispersion, 5 parts of film-forming aid (propylene glycol methyl ether acetate), 15 parts of pigments and fillers (8 parts titanium dioxide, 7 parts talc, particle size 1500 mesh), 1.5 parts of wetting and dispersing agent (polycarboxylate), 0.5 parts of defoamer (polyether-modified silicone), 0.5 parts of leveling agent (acrylic acid), 0.4 parts of thickener (hydroxyethyl cellulose), 2 parts of adhesion promoter (silane coupling agent), 0.8 parts of ultraviolet absorber (benzotriazole), 4 parts of crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n—NCO / n—OH=1.5), and 20 parts of deionized water.

[0036] The specific preparation process is exactly the same as in Example 1: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 300 r / min and the temperature is 28℃. The mixture is mixed for 15 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. After the titanium dioxide and talc are mixed evenly, they are added to the pre-dispersion liquid. The stirring speed is adjusted to 650 r / min and the temperature is 40℃. Stir for 45 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step is the main body mixing. First, the bio-based and epoxy-modified waterborne polyurethane dispersions are mixed evenly. Then, the pigment and filler dispersion is added. The stirring speed is maintained at 550 r / min and the temperature is 50℃. After stirring for 30 minutes to mix evenly, the film-forming aid and leveling agent are added. Stirring is continued for 20 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. Add adhesion promoter, UV absorber and crosslinking agent, stir for 15 minutes to ensure uniform dispersion, then add thickener, adjust the stirring speed to 350 r / min and temperature to 38℃, stir for 12 minutes, and adjust the viscosity of the coating to 35s. The fifth step is post-processing. The above mixture is filtered through a 150-mesh filter to remove impurities and undispersed particles. Then, it is kept at 45°C for 60 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0037] Example 6: This embodiment, based on Example 5, adjusts the type and dosage of film-forming aids and the process temperature to optimize drying speed and film-forming performance. The film-forming aid is adjusted to 6 parts, including 3 parts of propylene glycol methyl ether acetate and 3 parts of dodecyl alcohol ester, which can improve film-forming efficiency and accelerate drying speed; the main mixing temperature and post-treatment holding temperature are adjusted to further optimize the film-forming effect.

[0038] Specific raw material ratios (parts by weight): 30 parts of bio-based waterborne polyurethane dispersion, 20 parts of epoxy-modified waterborne polyurethane dispersion, 6 parts of film-forming aid (3 parts of propylene glycol methyl ether acetate and 3 parts of twelfth alcohol ester), 15 parts of pigments and fillers (8 parts of titanium dioxide and 7 parts of talc, particle size 1500 mesh), 1.5 parts of wetting and dispersing agent (polycarboxylate), 0.5 parts of defoamer (polyether-modified silicone), 0.5 parts of leveling agent (acrylic acid), 0.4 parts of thickener (hydroxyethyl cellulose), 2 parts of adhesion promoter (silane coupling agent), 0.8 parts of ultraviolet absorber (benzotriazole), 4 parts of crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n-NCO / n-OH=1.5), and 20 parts of deionized water.

[0039] Specific preparation process: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 300 r / min and the temperature is 28℃. The mixture is mixed for 15 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. After the titanium dioxide and talc are mixed evenly, they are added to the pre-dispersion liquid. The stirring speed is adjusted to 650 r / min and the temperature is 40℃. Stir for 45 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step involves mixing the main components. First, the bio-based and epoxy-modified waterborne polyurethane dispersions are mixed evenly. Then, the pigment and filler dispersion is added. The stirring speed is maintained at 550 r / min and the temperature at 55℃. After stirring for 30 minutes to mix evenly, the film-forming aid and leveling agent are added. Stirring is continued for 20 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. Add adhesion promoter, UV absorber and crosslinking agent, stir for 15 minutes to ensure uniform dispersion, then add thickener, adjust the stirring speed to 350 r / min and temperature to 38℃, stir for 12 minutes, and adjust the viscosity of the coating to 35s. The fifth step is post-processing. The above mixture is filtered through a 150-mesh filter to remove impurities and undispersed particles. Then, it is kept at 50°C for 45 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0040] Example 7: This embodiment, based on Example 6, adds a hindered amine light stabilizer and adjusts the amount of ultraviolet absorber to enhance weather resistance. The ultraviolet absorber is adjusted to 1 part, and 0.5 parts of hindered amine light stabilizer are added. The combination of the two can synergistically improve weather resistance and delay the aging rate of the paint film.

[0041] Specific raw material ratios (parts by weight): 30 parts of bio-based waterborne polyurethane dispersion, 20 parts of epoxy-modified waterborne polyurethane dispersion, 6 parts of film-forming aid (3 parts of propylene glycol methyl ether acetate and 3 parts of twelfth alcohol ester), 15 parts of pigments and fillers (8 parts of titanium dioxide and 7 parts of talc, particle size 1500 mesh), 1.5 parts of wetting and dispersing agent (polycarboxylate), 0.5 parts of defoamer (polyether-modified silicone), 0.5 parts of leveling agent (acrylic acid), 0.4 parts of thickener (hydroxyethyl cellulose), 2 parts of adhesion promoter (silane coupling agent), 1 part of ultraviolet absorber (benzotriazole), 0.5 parts of hindered amine light stabilizer, 4 parts of crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n-NCO / n-OH=1.5), and 20 parts of deionized water.

[0042] The specific preparation process is exactly the same as in Example 6: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 300 r / min and the temperature is 28℃. The mixture is mixed for 15 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. After the titanium dioxide and talc are mixed evenly, they are added to the pre-dispersion liquid. The stirring speed is adjusted to 650 r / min and the temperature is 40℃. Stir for 45 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step involves mixing the main components. First, the bio-based and epoxy-modified waterborne polyurethane dispersions are mixed evenly. Then, the pigment and filler dispersion is added. The stirring speed is maintained at 550 r / min and the temperature at 55℃. After stirring for 30 minutes to mix evenly, the film-forming aid and leveling agent are added. Stirring is continued for 20 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. First, mix the UV absorber and hindered amine light stabilizer evenly, then add the adhesion promoter and crosslinking agent, stir for 15 minutes to ensure uniform dispersion, then add the thickener, adjust the stirring speed to 350 r / min and the temperature to 38℃, stir for 12 minutes, and adjust the viscosity of the coating to 35s. The fifth step is post-processing. The above mixture is filtered through a 150-mesh filter to remove impurities and undispersed particles. Then, it is kept at 50°C for 45 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0043] Example 8: This embodiment, based on Example 1, uses the extreme values ​​of raw material ratios and process parameters for verification, expanding the scope of application and verifying the rationality of the ratios and process parameter settings of this technical solution. The epoxy-modified waterborne polyurethane dispersion used has a solid content of 30%, barium sulfate is selected as the pigment and filler with a particle size of 3000 mesh, hexanediol butyl ether acetate is selected as the film-forming aid, and silane coupling agent is selected as the adhesion promoter. All raw material ratios and process parameters are selected from reasonable extreme values.

[0044] Specific raw material ratios (parts by weight): The composition includes 40 parts epoxy-modified waterborne polyurethane dispersion, 3 parts film-forming aid (hexanediol butyl ether acetate), 5 parts pigments and fillers (barium sulfate, 3000 mesh particle size), 0.5 parts wetting and dispersing agent (polycarboxylate), 0.3 parts defoamer (polyether-modified silicone), 0.2 parts leveling agent (acrylic acid), 0.1 parts thickener (hydroxyethyl cellulose), 1 part adhesion promoter (silane coupling agent), 1 part crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n—NCO / n—OH=1.2), and 30 parts deionized water.

[0045] Specific preparation process: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 200 r / min and the temperature is 25℃. The mixture is mixed for 20 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. Add the pigment and filler to the pre-dispersion liquid, adjust the stirring speed to 500 r / min and the temperature to 35℃, and stir for 60 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step is to mix the main body. Add the epoxy-modified waterborne polyurethane dispersion to the pigment and filler dispersion, maintain the stirring speed at 500 r / min and the temperature at 45℃, and stir for 40 minutes to mix evenly. Then add the film-forming aid and leveling agent, and continue stirring for 20 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. Add adhesion promoter and crosslinking agent, stir for 15 minutes to ensure uniform dispersion, then add thickener, adjust the stirring speed to 300 r / min and temperature to 35℃, stir for 10 minutes, and adjust the viscosity of the coating to 20s. The fifth step is post-processing. The above mixture is filtered through a 200-mesh filter to remove impurities and undispersed particles. Then, it is kept at 25°C for 120 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0046] Example 9: This embodiment, based on Embodiment 7, adjusts the raw material ratio and process parameters to adapt to low-temperature construction scenarios, further expanding its applicability. The amount of film-forming aid is increased, and the resin ratio and adhesion promoter dosage are adjusted to optimize the low-temperature film-forming effect; process parameters are also adjusted to adapt to low-temperature construction environments.

[0047] Specific raw material ratios (parts by weight): 35 parts of bio-based waterborne polyurethane dispersion, 25 parts of epoxy-modified waterborne polyurethane dispersion, 8 parts of film-forming aid (4 parts of propylene glycol methyl ether acetate and 4 parts of twelfth alcohol ester), 12 parts of pigments and fillers (6 parts of titanium dioxide and 6 parts of calcium carbonate, particle size 2000 mesh), 1.2 parts of wetting and dispersing agent (polycarboxylate), 0.8 parts of defoamer (polyether-modified silicone), 0.7 parts of leveling agent (acrylic acid), 0.5 parts of thickener (hydroxyethyl cellulose), 3 parts of adhesion promoter (epoxy polyether-modified silane), 1.2 parts of ultraviolet absorber (benzotriazole), 0.6 parts of hindered amine light stabilizer, 4.5 parts of crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n-NCO / n-OH=1.5), and 18 parts of deionized water.

[0048] Specific preparation process: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 300 r / min and the temperature is 25℃. The mixture is mixed for 18 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. After the titanium dioxide and calcium carbonate are mixed evenly, they are added to the pre-dispersion liquid. The stirring speed is adjusted to 700 r / min and the temperature is 40℃. Stir for 50 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step is to mix the main body. First, mix the bio-based and epoxy-modified waterborne polyurethane dispersion evenly, then add the pigment and filler dispersion. Keep the stirring speed at 550 r / min and the temperature at 50℃. Stir for 35 minutes to mix evenly, then add the film-forming aid and leveling agent, and continue stirring for 25 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. First, mix the UV absorber and hindered amine light stabilizer evenly, then add the adhesion promoter and crosslinking agent, stir for 18 minutes to ensure uniform dispersion, then add the thickener, adjust the stirring speed to 350 r / min and the temperature to 38℃, stir for 13 minutes, and adjust the viscosity of the coating to 40s. The fifth step is post-processing. The above mixture is filtered through a 180-mesh filter to remove impurities and undispersed particles. Then, it is kept at 55°C for 50 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0049] Example 10: This embodiment, based on Embodiment 7, adjusts the ratio of pigments, fillers, and additives to suit food labeling scenarios and expand its high-end application range. It reduces the amount of pigments and fillers used, selects a single titanium dioxide, lowers VOC content, optimizes environmental performance, and meets the stringent requirements of food labeling.

[0050] Specific raw material ratios (parts by weight): 40 parts of bio-based waterborne polyurethane dispersion, 15 parts of epoxy-modified waterborne polyurethane dispersion, 4 parts of film-forming aid (4 parts of propylene glycol methyl ether acetate), 8 parts of pigments and fillers (titanium dioxide, particle size 2500 mesh), 0.8 parts of wetting and dispersing agent (polycarboxylate), 0.4 parts of defoamer (polyether-modified silicone), 0.4 parts of leveling agent (acrylic acid), 0.3 parts of thickener (hydroxyethyl cellulose), 1.5 parts of adhesion promoter (pentaerythritol tetra-3-mercaptopropionate), 0.6 parts of ultraviolet absorber (benzotriazole), 0.4 parts of hindered amine light stabilizer, 3.5 parts of crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n-NCO / n-OH=1.4), and 22 parts of deionized water.

[0051] The specific preparation process is exactly the same as in Example 7: The first step is pre-dispersion. Deionized water, wetting and dispersing agent, and defoamer are added to the stirring equipment. The stirring speed is controlled at 300 r / min and the temperature is 28℃. The mixture is mixed for 15 minutes to obtain a uniform pre-dispersion liquid. The second step is pigment and filler dispersion. Titanium dioxide is added to the pre-dispersion liquid, the stirring speed is adjusted to 650 r / min and the temperature is 40℃, and the mixture is stirred for 45 minutes to fully disperse the pigment and filler and avoid agglomeration, so as to obtain a uniform pigment and filler dispersion. The third step involves mixing the main components. First, the bio-based and epoxy-modified waterborne polyurethane dispersions are mixed evenly. Then, the pigment and filler dispersion is added. The stirring speed is maintained at 550 r / min and the temperature at 55℃. After stirring for 30 minutes to mix evenly, the film-forming aid and leveling agent are added. Stirring is continued for 20 minutes to fully integrate the film-forming aid with the main resin. The fourth step is modification and adjustment. First, mix the UV absorber and hindered amine light stabilizer evenly, then add the adhesion promoter and crosslinking agent, stir for 15 minutes to ensure uniform dispersion, then add the thickener, adjust the stirring speed to 350 r / min and the temperature to 38℃, stir for 12 minutes, and adjust the viscosity of the coating to 35s. The fifth step is post-processing. The above mixture is filtered through a 150-mesh filter to remove impurities and undispersed particles. Then, it is kept at 50°C for 45 minutes to promote the full cross-linking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0052] Comparative Example 1: This comparative example uses a common waterborne polyurethane dispersion instead of the epoxy-modified waterborne polyurethane dispersion in Example 1, and no resin system optimization was performed.

[0053] Specific raw material ratios (parts by weight): 50 parts of ordinary waterborne polyurethane dispersion (40% solid content), 5 parts of film-forming aid (propylene glycol methyl ether acetate), 10 parts of pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part of wetting and dispersing agent (polycarboxylate), 0.5 parts of defoamer (polyether modified silicone), 0.5 parts of leveling agent (acrylic), 0.4 parts of thickener (hydroxyethyl cellulose), 3 parts of crosslinking agent (blocked isocyanate of HDI and IPDI, n-NCO / n-OH=1.4), and 20 parts of deionized water.

[0054] The specific preparation process is completely consistent with that in Example 1.

[0055] Comparative Example 2: This comparative example uses a bio-based and epoxy-modified waterborne polyurethane dispersion compound system, but no adhesion promoter was added and no adhesion optimization was performed.

[0056] Specific raw material ratios (parts by weight): 30 parts of bio-based waterborne polyurethane dispersion (65% bio-based content, 45% solid content), 20 parts of epoxy-modified waterborne polyurethane dispersion (40% solid content), 5 parts of film-forming aid (propylene glycol methyl ether acetate), 10 parts of pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part of wetting and dispersing agent (polycarboxylate), 0.5 parts of defoamer (polyether-modified silicone), 0.5 parts of leveling agent (acrylic acid), 0.4 parts of thickener (hydroxyethyl cellulose), 3 parts of crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n—NCO / n—OH=1.4), and 20 parts of deionized water.

[0057] The specific preparation process is completely consistent with that in Example 1.

[0058] Comparative Example 3: This comparative study adjusted the amount and particle size of pigments and fillers, but did not optimize the dispersion of pigments and fillers. The amount of pigments and fillers exceeded the reasonable range and the particle size was too small, which easily led to agglomeration.

[0059] Specific raw material ratios (parts by weight): 50 parts epoxy-modified waterborne polyurethane dispersion (40% solid content), 5 parts film-forming aid (propylene glycol methyl ether acetate), 25 parts pigments and fillers (titanium dioxide, 800 mesh particle size), 1 part wetting and dispersing agent (polycarboxylate), 0.5 parts defoamer (polyether-modified silicone), 0.5 parts leveling agent (acrylic), 0.4 parts thickener (hydroxyethyl cellulose), 3 parts crosslinking agent (blocked isocyanate of HDI and IPDI, n-NCO / n-OH=1.4), and 20 parts deionized water.

[0060] The specific preparation process is completely consistent with that in Example 1.

[0061] Comparative Example 4: The raw material ratio of this comparative example is exactly the same as that of Example 1, but the process of step-by-step temperature control and orderly feeding is not adopted. Instead, a one-time feeding and room temperature stirring method is used, and no process optimization is performed.

[0062] Specific raw material ratios (parts by weight): 50 parts epoxy-modified waterborne polyurethane dispersion (40% solid content), 5 parts film-forming aid (propylene glycol methyl ether acetate), 10 parts pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part wetting and dispersing agent (polycarboxylate), 0.5 parts defoamer (polyether-modified silicone), 0.5 parts leveling agent (acrylic), 0.4 parts thickener (hydroxyethyl cellulose), 3 parts crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n-NCO / n-OH=1.4), and 20 parts deionized water.

[0063] Specific preparation process: All raw materials are added to the mixing equipment at one time and stirred for 60 minutes at room temperature (25°C). The mixture is then filtered through a 150-mesh filter to remove impurities and undispersed particles. The mixture is kept at 45°C for 60 minutes to promote the full crosslinking reaction. After cooling to room temperature, the water-based polyurethane coating for the label is obtained.

[0064] Comparative Example 5: The raw material ratio of this comparative example is exactly the same as that of Example 1, but the ratio of crosslinking agent is adjusted beyond the reasonable range, and the ratio of crosslinking agent has not been optimized.

[0065] Specific raw material ratios (parts by weight): 50 parts epoxy-modified waterborne polyurethane dispersion (40% solid content), 5 parts film-forming aid (propylene glycol methyl ether acetate), 10 parts pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part wetting and dispersing agent (polycarboxylate), 0.5 parts defoamer (polyether-modified silicone), 0.5 parts leveling agent (acrylic), 0.4 parts thickener (hydroxyethyl cellulose), 3 parts crosslinking agent (blocked isocyanate of HDI and IPDI, n-NCO / n-OH=1.7), and 20 parts deionized water.

[0066] The specific preparation process is completely consistent with that in Example 1.

[0067] Comparative Example 6: This comparative example uses a bio-based waterborne polyurethane dispersion, but the bio-based content did not meet the optimization requirements, and no environmental optimization was carried out.

[0068] Specific raw material ratios (parts by weight): 50 parts of bio-based waterborne polyurethane dispersion (50% bio-based content, 45% solid content), 5 parts of film-forming aid (propylene glycol methyl ether acetate), 10 parts of pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part of wetting and dispersing agent (polycarboxylate), 0.5 parts of defoamer (polyether modified silicone), 0.5 parts of leveling agent (acrylic acid), 0.4 parts of thickener (hydroxyethyl cellulose), 3 parts of crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n-NCO / n-OH=1.4), and 20 parts of deionized water.

[0069] The specific preparation process is completely consistent with that in Example 1.

[0070] Comparative Example 7: This comparative example uses an epoxy-modified waterborne polyurethane dispersion with added UV absorbers, but no adhesion promoters were added, and no adhesion optimization was performed, making it difficult to adapt to inert substrates.

[0071] Specific raw material ratios (parts by weight): 50 parts epoxy-modified waterborne polyurethane dispersion (40% solid content), 5 parts film-forming aid (propylene glycol methyl ether acetate), 10 parts pigments and fillers (titanium dioxide, 1500 mesh particle size), 1 part wetting and dispersing agent (polycarboxylate), 0.5 parts defoamer (polyether-modified silicone), 0.5 parts leveling agent (acrylic), 0.4 parts thickener (hydroxyethyl cellulose), 0.8 parts ultraviolet absorber (benzotriazole), 3 parts crosslinking agent (blocked isocyanate compounded with HDI and IPDI, n—NCO / n—OH=1.4), and 20 parts deionized water.

[0072] The specific preparation process is completely consistent with that in Example 1.

[0073] Performance testing and results analysis: Test sample: The waterborne polyurethane coatings for labels prepared in Examples 1 to 10, Comparative Examples 1 to 7, and Prior Art Control Samples 1 to 3 were all coated with the same coating equipment and with the same wet film thickness (15 μm) onto three standard label substrates (coated paper, PET plastic, and tinplate). They were then placed in a constant temperature and humidity environment (temperature 25°C, humidity 50%RH) for natural drying for 24 hours to obtain standard test samples. All samples were left to stand for 48 hours before various performance tests were conducted to ensure that the test conditions were uniform and the data were comparable.

[0074] Test method: All items in this test were performed in accordance with the corresponding industry standards, with key steps clearly defined to ensure that the test is reproducible and has no publicly known vulnerabilities. The specific methods are as follows: (1) Adhesion: Refer to GB / T9286-1998, use the cross-cut test with a cross-cut spacing of 1mm and a cross-cut depth to the substrate surface. After pasting with 3M 600 tape, peel it off at a uniform speed and observe the paint film peeling. Rating is from 0 to 5 (0 is the best and 5 is the worst). (2) Abrasion resistance: Refer to GB / T1768-2021, use Martindale abrasion tester, load 500g, friction medium is standard cotton cloth, after 1000 abrasions, observe the paint film wear, exposure of the substrate, and evaluate whether it is qualified and the degree of wear. (3) Weather resistance: Refer to GB / T1865-2009, use a xenon lamp aging test chamber, irradiate for 480h (simulate outdoor natural aging for 1 year), and observe the color difference, chalking and cracking of the paint film after the test. The color difference ΔE≤2.0 is qualified. (4) Drying speed: Referring to GB / T1728-1979, the surface drying time and actual drying time of the sample under constant temperature and humidity environment were tested by the finger touch method, accurate to the minute; (5) Water resistance: Refer to GB / T1733-1993, use the immersion method, immerse the sample in 25℃ distilled water, soak for 24 hours, observe whether the paint film wrinkles, peels off, or turns white, and it is qualified if there is no obvious abnormality after wiping it dry; (6) Viscosity: Refer to GB / T2794-2013, use a Forte 4 viscometer, test at 25℃, accurate to 1s; (7) VOC content: According to GB / T23985-2009, the gas chromatography method was used for testing, accurate to 0.1g / L, which meets the relevant requirements of green packaging; (8) Hiding power: Refer to GB / T1726-1979 and use the black and white grid method to test the minimum thickness required for the paint film to completely cover the black and white grid, accurate to 1μm.

[0075] The performance test results are shown in Table 1 below: Table 1:

[0076] Based on the performance test data above, a comprehensive analysis was conducted on the performance of all tested samples to clarify the performance advantages of this technical solution and the effectiveness of each optimization measure. Simultaneously, the rationality of the raw material ratio and process parameter settings was verified to ensure there were no issues of insufficient disclosure. The test results show that the waterborne polyurethane coatings for labels prepared in Examples 1 to 10 all exhibit superior overall performance compared to Comparative Examples 1 to 7 and existing technology control samples 1 to 3, with a clear performance progression among the examples.

[0077] (1) Regarding adhesion, Example 1, using an epoxy-modified resin system, achieved an adhesion level of 1, which is superior to Comparative Example 1, which uses ordinary resin, and the existing technology control sample. In Example 3, after adding an adhesion promoter, the adhesion level was improved to 0, making it suitable for inert PET substrates. In contrast, Comparative Examples 2 and 7, which did not add an adhesion promoter, and the existing technology control sample, had adhesion levels of only 2-3, verifying the significant improvement effect of adhesion promoters and compound resin systems on adhesion. Regarding abrasion resistance, Example 5, after adjusting the amount and type of pigments and fillers and dispersants, achieved 1000 cycles of friction without wear, which is superior to Comparative Example 3, which had an unreasonable pigment and filler ratio, and Comparative Example 4, which had an unoptimized process. This indicates that a reasonable combination of pigments and fillers can effectively improve the abrasion resistance of the coating film.

[0078] (2) Regarding weather resistance, after adding an ultraviolet absorber in Example 4, the color difference ΔE decreased to 1.3 after 480 hours of xenon lamp aging. In Example 7, the addition of a hindered amine light stabilizer further reduced the color difference to 0.9, which is far superior to Comparative Example 1, Comparative Example 2, and the existing technology control sample without the addition of weather-resistant components, highlighting the synergistic effect of the combined use of weather-resistant components. After optimization for low-temperature construction scenarios, Example 9 still maintains excellent weather resistance and is suitable for different usage environments. Regarding drying speed, after adjusting the type, dosage, and process temperature of the film-forming aid in Example 6, the surface drying time was shortened to 22 minutes, which is significantly improved compared to Example 1, the comparative example, and the existing technology control sample, meeting the needs of high-efficiency production and verifying the effectiveness of the film-forming aid and process temperature optimization.

[0079] (3) In terms of water resistance, viscosity, VOC content and hiding power, all examples showed excellent performance. The water resistance was normal, the viscosity was controlled within the range of 20-40s, which is suitable for coating process requirements, and the VOC content was lower than 40g / L, which is in line with the trend of green packaging. The hiding power was better than the comparative example and the existing technology control sample. Among them, after optimization for food labeling scenarios, the VOC content of Example 10 was reduced to 28.3g / L, and the environmental protection performance was further improved, which is suitable for high-end food labeling requirements. Example 8 was prepared using the raw material ratio and process parameter limit values, and all performance still met the usage requirements, which verified the rationality of the ratio and process parameter settings of this technical solution and the wide applicability.

[0080] (4) The shortcomings of the comparative examples and existing technology control samples further confirm the necessity of the optimization measures of this technical solution: Comparative Example 1 did not optimize the resin system, resulting in poor adhesion, abrasion resistance and weather resistance; Comparative Example 4 did not adopt the step-by-step temperature control and orderly feeding process, resulting in poor film stability and unsatisfactory performance; Comparative Example 5 had a crosslinking agent ratio that exceeded the reasonable range, resulting in slight cracking in water resistance; The existing technology control samples did not undergo multi-dimensional optimization, and their overall performance was far inferior to that of this technical solution.

[0081] (5) In summary, this technical solution effectively solves the performance shortcomings of existing waterborne polyurethane coatings for labels by optimizing the resin system, additives, and process parameters in multiple dimensions, improving the overall performance, adapting to a variety of label substrates and application scenarios, and the preparation process is simple and controllable, with good potential for large-scale production.

[0082] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A water-based polyurethane coating for labels, characterized in that, By weight, it consists of the following components: 30-50 parts core resin component, 3-8 parts film-forming aid, 5-15 parts pigments and fillers, 0.5-1.5 parts wetting and dispersing agent, 0.3-0.8 parts defoamer, 0.2-0.7 parts leveling agent, 0.1-0.5 parts thickener, 1-4.5 parts crosslinking agent, and 18-30 parts deionized water; The core resin component is an epoxy-modified waterborne polyurethane dispersion, or a bio-based waterborne polyurethane dispersion, or a compound of an epoxy-modified waterborne polyurethane dispersion and a bio-based waterborne polyurethane dispersion. The epoxy-modified waterborne polyurethane dispersion is prepared by emulsification after mixing and reacting propylene oxide, isocyanate, chain extender, and neutralizer. The bio-based waterborne polyurethane dispersion uses castor oil-based polyol as raw material. The crosslinking agent is a blocked isocyanate compounded with HDI and IPDI, and its n-NCO / n-OH ratio is 1.2-1.

5. The wetting and dispersing agent is a polycarboxylate, the defoamer is a polyether-modified silicone, the leveling agent is an acrylic acid, and the thickener is hydroxyethyl cellulose.

2. The water-based polyurethane coating for labels according to claim 1, characterized in that, When the core resin component is a compound of epoxy-modified waterborne polyurethane dispersion and bio-based waterborne polyurethane dispersion, the epoxy-modified waterborne polyurethane dispersion comprises 15-25 parts by mass, and the bio-based waterborne polyurethane dispersion comprises 30-35 parts.

3. The water-based polyurethane coating for labels according to claim 2, characterized in that, It also includes an adhesion promoter in the form of 0.5-3 parts by weight, wherein the adhesion promoter is one of a silane coupling agent, an epoxy polyether modified silane, or a pentaerythritol tetra-mercaptopropionate.

4. The water-based polyurethane coating for labels according to claim 2 or 3, characterized in that, It also includes a weather-resistant component, which is a compound of benzotriazole ultraviolet absorber and hindered amine light stabilizer; by weight, the benzotriazole ultraviolet absorber is 0.6-1.2 parts and the hindered amine light stabilizer is 0.4-0.6 parts.

5. The water-based polyurethane coating for labels according to claim 4, characterized in that, The pigments and fillers are titanium dioxide, or a mixture of titanium dioxide and talc, or a mixture of titanium dioxide and calcium carbonate, or barium sulfate; the particle size of the pigments and fillers is 1500 mesh to 3000 mesh.

6. The water-based polyurethane coating for labels according to claim 5, characterized in that, The film-forming aid is propylene glycol methyl ether acetate, or a mixture of propylene glycol methyl ether acetate and decyl alcohol ester, or hexanediol butyl ether acetate.

7. A method for preparing the water-based polyurethane coating for labels according to claim 1, characterized in that, Includes the following steps: (1) Pre-dispersion: Deionized water, wetting and dispersing agent and defoamer are added to a stirring device and mixed to obtain a pre-dispersion liquid; (2) Pigment and filler dispersion: Add pigments and fillers to the pre-dispersion liquid and stir to disperse them to obtain a pigment and filler dispersion; (3) Main mixture: Add the core resin component to the pigment and filler dispersion and stir to mix. Then add the film-forming aid and leveling agent and continue stirring to obtain the main mixture. (4) Modification and adjustment: Add crosslinking agent to the main mixture and stir to disperse. Add adhesion promoter and weather-resistant component as needed and stir to disperse. Then add thickener and stir to adjust the viscosity of the coating to obtain modified mixture. (5) Post-treatment: The modified mixture is filtered, then kept warm, and cooled to room temperature to obtain the waterborne polyurethane coating for the label.

8. The preparation method according to claim 7, characterized in that, In step (1), the stirring speed is 200-300 r / min and the stirring temperature is 25-28℃; in step (2), the stirring speed is 500-700 r / min and the stirring temperature is 35-40℃; in step (3), the stirring speed is 500-550 r / min and the stirring temperature is 45-55℃; in step (4), after adding the thickener, the stirring speed is 300-350 r / min and the stirring temperature is 35-38℃.

9. The preparation method according to claim 7, characterized in that, In step (5), a 150-200 mesh filter is used for filtration; the temperature of the heat preservation treatment is 25-55℃, and the heat preservation time is 45-120 minutes.

10. The preparation method according to claim 7, characterized in that, When the core resin component is a compound of epoxy-modified waterborne polyurethane dispersion and bio-based waterborne polyurethane dispersion, the epoxy-modified waterborne polyurethane dispersion and the bio-based waterborne polyurethane dispersion are mixed evenly before the main body mixing in step (3).

Images