Preparation method of weather-resistant silk-screen coating

Abstract

The invention relates to the technical field of coatings, in particular to a preparation method of a weather-resistant silk-screen coating, which comprises the following steps: mixing acrylic resin, polyurethane resin, titanium dioxide, pigment and solvent, dispersing at a high speed until the fineness is less than or equal to 15 microns, and grinding until the fineness is less than or equal to 7 microns. And adding the ultraviolet light absorber, the light stabilizer, the dispersing agent and the flatting agent, and stirring and mixing. And standing and curing after filtering. And adding an isocyanate cross-linking agent before use, and uniformly stirring to obtain the weather-resistant coating. The method ensures excellent weather resistance of the coating. The-COOH group of the acrylic resin reacts with the-NCO group of the polyurethane resin to form a unique interpenetrating network structure, so that not only is the excellent weather resistance ensured, but also the good mechanical property is provided.

Description

Technical Field

[0001] The invention relates to the technical field of coatings, in particular to a method for preparing a weather-resistant silk-screen coating. Background Art

[0002] With the rapid development of the outdoor advertising and signage industry, the demand for weather-resistant silk-screen coatings is growing. However, existing weather-resistant silk-screen coatings still have many shortcomings. First, traditional silk-screen coatings are prone to fading, chalking, and cracking when exposed to outdoor environments for a long time, seriously affecting the product's service life and aesthetics. Second, many existing formulations often sacrifice other important coating properties such as mechanical strength, flexibility, or chemical resistance while improving weather resistance. Furthermore, to improve coating performance, some formulations use large amounts of harmful additives or solvents with high VOC content, which do not meet increasingly stringent environmental requirements.

[0003] The closest existing technology typically utilizes a single resin system, such as pure acrylic or polyurethane, supplemented with conventional UV absorbers and antioxidants. While this approach performs well in some areas, it struggles to simultaneously achieve a balance between weather resistance, mechanical properties, and environmental friendliness. For example, while pure acrylic systems offer excellent weather resistance, they lack flexibility; while pure polyurethane systems offer excellent mechanical properties, they exhibit relatively poor weather resistance. Furthermore, the additives in traditional formulations are often simply mixed, lacking synergistic effects and hindering optimal performance. Summary of the Invention

[0004] In view of the above problems, there is an urgent need to develop a new type of UV-resistant screen printing coating that can provide comprehensive UV protection while also having excellent wear resistance, printability, long-term stability, and meeting environmental protection requirements. The present invention is an innovative solution to this technical need.

[0005] The object of the present invention is to provide a method for preparing a weather-resistant silk screen coating, comprising the following steps: (1) First, 50-70 parts by weight of acrylic resin, 10-30 parts by weight of polyurethane resin, 10-20 parts by weight of titanium dioxide, 0-5 parts by weight of organic pigment, and 20-40 parts by weight of organic solvent are mixed and dispersed in a high-speed disperser at a speed of 600-800 rpm for 30-40 minutes until the fineness reaches ≤15 μm to obtain a pre-dispersed mixture; (2) Next, the pre-dispersed mixture was transferred to a sand mill and ground at a speed of 2000-2500 rpm for 60-90 minutes until the fineness reached ≤7 μm to obtain a grinding slurry; (3) Then, the grinding slurry is transferred to a stirring kettle, and 1-3 parts by weight of an ultraviolet absorber, 0.5-2 parts by weight of a light stabilizer, 0.5-2 parts by weight of a dispersant, and 0.1-0.5 parts by weight of a leveling agent are added in sequence, and stirred at a speed of 300-400 rpm for 30-40 minutes to obtain a mixture; (4) Again, the mixture was filtered through a 100-mesh sieve; (5) Further, the filtered coating is allowed to stand at 20-25° C. for 24-48 hours for aging; (6) Finally, before use, 5-15 parts by weight of an isocyanate crosslinking agent is slowly added to the coating according to a weight ratio of 100:10-15, and stirred for 10-15 minutes until uniform, to obtain the weather-resistant silk screen coating.

[0006] Preferably, the acrylic resin is a hydroxy acrylic resin.

[0007] Preferably, the polyurethane resin is an aliphatic polyurethane resin.

[0008] Preferably, the isocyanate cross-linking agent is hexamethylene diisocyanate HDI trimer.

[0009] Preferably, the titanium dioxide is rutile titanium dioxide.

[0010] Preferably, the ultraviolet absorber is a benzotriazole ultraviolet absorber.

[0011] Preferably, the light stabilizer is a hindered amine light stabilizer HALS.

[0012] Preferably, the dispersant is a high molecular weight polyester dispersant.

[0013] Preferably, the leveling agent is an organically modified polysiloxane.

[0014] Preferably, the organic solvent comprises 15-25 parts by weight of propylene glycol methyl ether acetate (PMA) and 5-15 parts by weight of butyl acetate.

[0015] The innovations of the present invention are mainly reflected in the following aspects: 1. Synergistic Resin System Design: This invention innovatively combines a hydroxylated acrylic resin and an aliphatic polyurethane resin in a specific ratio, leveraging the strengths of both resins. The -COOH groups of the acrylic resin react with the -NCO groups of the polyurethane resin to form a unique interpenetrating network structure, ensuring both excellent weather resistance and superior mechanical properties.

[0016] 2. Multiple Protection Mechanisms: This invention utilizes a combination of benzotriazole UV absorbers and hindered amine light stabilizers (HALS). Benzotriazole compounds effectively absorb UV light through an intramolecular proton transfer mechanism, while HALS prevents photooxidative chain reactions by capturing free radicals and decomposing peroxides. These two additives form a complementary protection network at the molecular level.

[0017] 3. Optimized Pigment Dispersion: The high-molecular-weight polyester dispersant used in this invention not only improves pigment dispersion but also forms a highly compatible interface layer with the resin system. This interface layer strengthens the binding force between the pigment and the resin matrix, enhancing the overall weather resistance and mechanical strength of the coating.

[0018] 4. Precise control of crosslink density: By adjusting the amount of hexamethylene diisocyanate (HDI) trimer, the present invention achieves precise control of crosslink density. The cyclic structure of HDI trimer provides higher crosslinking efficiency while maintaining sufficient flexibility, which is difficult to achieve with traditional linear isocyanates.

[0019] 5. Eco-friendly Solvent System: This invention utilizes a combination of propylene glycol methyl ether acetate (PMA) and butyl acetate, which not only reduces VOC emissions but also improves coating leveling and film quality by optimizing the solvent's evaporation rate. The ether and ester groups of PMA form hydrogen bonds with polar groups in the resin molecules, enhancing solubility and compatibility.

[0020] These innovative features work synergistically to address the technical challenges of traditional weather-resistant silk-screen coatings in terms of performance balance and environmental friendliness. This invention is essential because it not only improves the overall performance of the coating but also meets increasingly stringent environmental requirements, providing a high-performance, long-life, and environmentally friendly coating solution for the outdoor advertising and signage industry.

[0021] The beneficial effects of the present invention include: 1. Excellent weather resistance: Through multiple protection mechanisms, the coating still maintains a gloss retention rate of more than 90% after 2000 hours of accelerated aging test, with a color difference of less than 2.0 and almost no chalking.

[0022] 2. Excellent balance of mechanical properties: The elongation at break reaches 180-210%, while maintaining a tensile strength of 22-25MPa, achieving a perfect combination of high strength and high flexibility.

[0023] 3. Excellent chemical resistance: The coating exhibits excellent resistance to acids, alkalis, and alcohols, expanding the application range of the product.

[0024] 4. Environmentally friendly: VOC content is controlled below 215 g / L, in line with the latest environmental regulations.

[0025] 5. Optimized construction performance: Improved leveling and film-forming quality make the coating surface smoother and more uniform, improving the aesthetics of the product.

[0026] 6. Long-term stability: Through pigment dispersion optimization and cross-linking density control, the coating exhibits excellent long-term stability, extending the service life of the product.

[0027] These beneficial effects not only solve the problems in the existing technology, but also bring unexpected performance improvements, opening up a new direction for the development of weather-resistant silk screen coatings. DETAILED DESCRIPTION

[0028] Example 1 Preparation method of weather-resistant silk screen coating The weather-resistant silk-screen coating composition of this embodiment includes: 60 parts by weight of hydroxy acrylic resin (Paraloid B-72 from DuPont), 20 parts by weight of aliphatic polyurethane resin (Desmophen 670 BA from Bayer), 15 parts by weight of rutile titanium dioxide (Ti-Pure R-902+ from DuPont), 2 parts by weight of phthalocyanine blue organic pigment, 10 parts by weight of hexamethylene diisocyanate (HDI) trimer (Desmodur N 3390 from Bayer), 2 parts by weight of benzotriazole UV absorber (Tinuvin 1130 from BASF), 1 part by weight of hindered amine light stabilizer (Tinuvin 292 from BASF), 1 part by weight of high molecular weight polyester dispersant (BYK-2155 from BYK), 0.3 parts by weight of organically modified polysiloxane leveling agent (BYK-333 from BYK), 20 parts by weight of propylene glycol methyl ether acetate (PMA), and 10 parts by weight of butyl acetate.

[0029] The preparation method of this weather-resistant silk-screen coating comprises the following steps: (1) First, 60 parts by weight of hydroxy acrylic resin, 20 parts by weight of aliphatic polyurethane resin, 15 parts by weight of rutile titanium dioxide, 2 parts by weight of phthalocyanine blue organic pigment, 15 parts by weight of propylene glycol methyl ether acetate (PMA) and 5 parts by weight of butyl acetate were mixed and dispersed in a high-speed disperser at a speed of 700 rpm for 35 minutes until the fineness reached 15 μm to obtain a pre-dispersed mixture; (2) Next, the pre-dispersed mixture was transferred to a sand mill and ground at a speed of 2250 rpm for 75 minutes until the fineness reached 7 μm to obtain a grinding slurry; (3) Then, the grinding slurry was transferred to a stirring kettle, and 2 parts by weight of a benzotriazole ultraviolet absorber, 1 part by weight of a hindered amine light stabilizer, 1 part by weight of a high molecular weight polyester dispersant, 0.3 parts by weight of an organic modified polysiloxane leveling agent, and the remaining 5 parts by weight of propylene glycol methyl ether acetate (PMA) and 5 parts by weight of butyl acetate were added in sequence, and the mixture was stirred at a speed of 350 rpm for 35 minutes to obtain a mixture; (4) Again, the mixture was filtered through a 100-mesh sieve; (5) Further, the filtered coating was left to stand at 22°C for 36 hours for aging; (6) Finally, before use, 10 parts by weight of hexamethylene diisocyanate (HDI) trimer was slowly added to the coating at a weight ratio of 100:10 and stirred for 12 minutes until uniform, thereby obtaining the weather-resistant silk screen coating.

[0030] In embodiments of the present invention, the synergistic effect of a hydroxylated acrylic resin and an aliphatic polyurethane resin improves the coating's weather resistance and mechanical properties. Rutile titanium dioxide not only provides excellent hiding power but also enhances the coating's weather resistance. The combination of a benzotriazole UV absorber and a hindered amine light stabilizer effectively blocks UV radiation, slowing the coating's aging process. The use of a high-molecular-weight polyester dispersant improves the pigment's dispersion stability, further enhancing the coating's weather resistance and gloss retention.

[0031] Example 2: Preparation method of weather-resistant silk screen coating The weather-resistant silk-screen coating components of this embodiment include: 50 parts by weight of hydroxy acrylic resin, 30 parts by weight of aliphatic polyurethane resin, 20 parts by weight of rutile titanium dioxide, 5 parts by weight of phthalocyanine blue organic pigment, 15 parts by weight of hexamethylene diisocyanate (HDI) trimer, 3 parts by weight of benzotriazole ultraviolet absorber, 2 parts by weight of hindered amine light stabilizer, 2 parts by weight of high molecular weight polyester dispersant, 0.5 parts by weight of organic modified polysiloxane leveling agent, 25 parts by weight of propylene glycol methyl ether acetate (PMA) and 15 parts by weight of butyl acetate.

[0032] The preparation method of this weather-resistant silk-screen coating comprises the following steps: (1) First, 50 parts by weight of hydroxy acrylic resin, 30 parts by weight of aliphatic polyurethane resin, 20 parts by weight of rutile titanium dioxide, 5 parts by weight of phthalocyanine blue organic pigment, 20 parts by weight of propylene glycol methyl ether acetate (PMA) and 10 parts by weight of butyl acetate were mixed and dispersed in a high-speed disperser at a speed of 800 rpm for 40 minutes until the fineness reached 13 μm to obtain a pre-dispersed mixture; (2) Next, the pre-dispersed mixture was transferred to a sand mill and ground at a speed of 2500 rpm for 90 minutes until the fineness reached 6 μm to obtain a grinding slurry; (3) Then, the grinding slurry was transferred to a stirring kettle, and 3 parts by weight of a benzotriazole ultraviolet absorber, 2 parts by weight of a hindered amine light stabilizer, 2 parts by weight of a high molecular weight polyester dispersant, 0.5 parts by weight of an organic modified polysiloxane leveling agent, and the remaining 5 parts by weight of propylene glycol methyl ether acetate (PMA) and 5 parts by weight of butyl acetate were added in sequence, and the mixture was stirred at a speed of 400 rpm for 40 minutes to obtain a mixture; (4) Again, the mixture was filtered through a 100-mesh sieve; (5) Further, the filtered coating was allowed to stand at 25°C for 48 hours for aging; (6) Finally, before use, 15 parts by weight of hexamethylene diisocyanate (HDI) trimer was slowly added to the coating at a weight ratio of 100:15 and stirred for 15 minutes until uniform, thereby obtaining the weather-resistant silk screen coating.

[0033] Preferably, in this embodiment, the proportion of aliphatic polyurethane resin is increased to further enhance the coating's flexibility and wear resistance. Simultaneously, the amount of hexamethylene diisocyanate (HDI) trimer is increased to enhance the coating's crosslinking density, thereby improving the coating's chemical and wear resistance.

[0034] Example 3: Preparation method of weather-resistant silk screen coating The weather-resistant silk-screen coating components of this embodiment include: 70 parts by weight of hydroxy acrylic resin, 10 parts by weight of aliphatic polyurethane resin, 10 parts by weight of rutile titanium dioxide, 1 part by weight of phthalocyanine blue organic pigment, 5 parts by weight of hexamethylene diisocyanate (HDI) trimer, 1 part by weight of benzotriazole ultraviolet absorber, 0.5 parts by weight of hindered amine light stabilizer, 0.5 parts by weight of high molecular weight polyester dispersant, 0.1 parts by weight of organic modified polysiloxane leveling agent, 15 parts by weight of propylene glycol methyl ether acetate (PMA) and 5 parts by weight of butyl acetate.

[0035] The preparation method of this weather-resistant silk-screen coating comprises the following steps: (1) First, 70 parts by weight of hydroxy acrylic resin, 10 parts by weight of aliphatic polyurethane resin, 10 parts by weight of rutile titanium dioxide, 1 part by weight of phthalocyanine blue organic pigment, 10 parts by weight of propylene glycol methyl ether acetate (PMA) and 2.5 parts by weight of butyl acetate were mixed and dispersed in a high-speed disperser at a speed of 600 rpm for 30 minutes until the fineness reached 14 μm to obtain a pre-dispersed mixture; (2) Next, the pre-dispersed mixture was transferred to a sand mill and ground at a speed of 2000 rpm for 60 minutes until the fineness reached 7 μm to obtain a grinding slurry; (3) Then, the grinding slurry was transferred to a stirring kettle, and 1 part by weight of a benzotriazole ultraviolet absorber, 0.5 parts by weight of a hindered amine light stabilizer, 0.5 parts by weight of a high molecular weight polyester dispersant, 0.1 parts by weight of an organic modified polysiloxane leveling agent, and the remaining 5 parts by weight of propylene glycol methyl ether acetate (PMA) and 2.5 parts by weight of butyl acetate were added in sequence, and the mixture was stirred at a speed of 300 rpm for 30 minutes to obtain a mixture; (4) Again, the mixture was filtered through a 100-mesh sieve; (5) Further, the filtered coating was left to stand at 20°C for 24 hours for aging; (6) Finally, before use, 5 parts by weight of hexamethylene diisocyanate (HDI) trimer was slowly added to the coating at a weight ratio of 100:10 and stirred for 10 minutes until uniform to obtain the weather-resistant silk screen coating.

[0036] In this embodiment, the proportion of hydroxylated acrylic resin is increased, improving the coating's hardness and wear resistance. Simultaneously, the amount of additives used is reduced, reducing costs while maintaining basic performance. This formulation is suitable for applications requiring relatively low weather resistance but high hardness.

[0037] Example 4: Preparation method of weather-resistant silk screen coating The weather-resistant silk-screen coating components of this embodiment include: 55 parts by weight of hydroxy acrylic resin, 25 parts by weight of aliphatic polyurethane resin, 18 parts by weight of rutile titanium dioxide, 3 parts by weight of phthalocyanine blue organic pigment, 12 parts by weight of hexamethylene diisocyanate (HDI) trimer, 2.5 parts by weight of benzotriazole ultraviolet absorber, 1.5 parts by weight of hindered amine light stabilizer, 1.5 parts by weight of high molecular weight polyester dispersant, 0.4 parts by weight of organic modified polysiloxane leveling agent, 22 parts by weight of propylene glycol methyl ether acetate (PMA) and 12 parts by weight of butyl acetate.

[0038] The preparation method of this weather-resistant silk-screen coating comprises the following steps: (1) First, 55 parts by weight of hydroxy acrylic resin, 25 parts by weight of aliphatic polyurethane resin, 18 parts by weight of rutile titanium dioxide, 3 parts by weight of phthalocyanine blue organic pigment, 17 parts by weight of propylene glycol methyl ether acetate (PMA) and 7 parts by weight of butyl acetate were mixed and dispersed in a high-speed disperser at a speed of 750 rpm for 38 minutes until the fineness reached 14 μm to obtain a pre-dispersed mixture; (2) Next, the pre-dispersed mixture was transferred to a sand mill and ground at a speed of 2350 rpm for 80 minutes until the fineness reached 6.5 μm to obtain a grinding slurry; (3) Then, the grinding slurry was transferred to a stirring kettle, and 2.5 parts by weight of a benzotriazole ultraviolet absorber, 1.5 parts by weight of a hindered amine light stabilizer, 1.5 parts by weight of a high molecular weight polyester dispersant, 0.4 parts by weight of an organic modified polysiloxane leveling agent, and the remaining 5 parts by weight of propylene glycol methyl ether acetate (PMA) and 5 parts by weight of butyl acetate were added in sequence, and the mixture was stirred at a speed of 375 rpm for 38 minutes to obtain a mixture; (4) Again, the mixture was filtered through a 100-mesh sieve; (5) Further, the filtered coating was left to stand at 23°C for 40 hours for aging; (6) Finally, before use, 12 parts by weight of hexamethylene diisocyanate (HDI) trimer was slowly added to the coating at a weight ratio of 100:12 and stirred for 13 minutes until uniform, thereby obtaining the weather-resistant silk screen coating.

[0039] Preferably, in this embodiment, the ratio of the components is relatively balanced. The moderate ratio of the hydroxylated acrylic resin to the aliphatic polyurethane resin ensures both coating hardness and flexibility. A slightly higher dosage of rutile titanium dioxide provides improved hiding power and weather resistance. The relatively high dosage of UV absorber and light stabilizer also effectively protects the coating from UV damage. This formulation is suitable for outdoor applications requiring high weather resistance.

[0040] Comparative Example 1: Preparation method of weather-resistant silk screen coating without ultraviolet absorber and light stabilizer This comparative example corresponds to Example 1, but the ultraviolet absorber and the light stabilizer are removed to verify the synergistic effect of the two additives on the weather resistance of the coating.

[0041] The components of the weather-resistant silk-screen coating include: 60 parts by weight of hydroxy acrylic resin, 20 parts by weight of aliphatic polyurethane resin, 15 parts by weight of rutile titanium dioxide, 2 parts by weight of phthalocyanine blue organic pigment, 10 parts by weight of hexamethylene diisocyanate (HDI) trimer, 1 part by weight of high molecular weight polyester dispersant, 0.3 parts by weight of organic modified polysiloxane leveling agent, 20 parts by weight of propylene glycol methyl ether acetate (PMA) and 10 parts by weight of butyl acetate.

[0042] The preparation method is the same as that of Example 1, but no ultraviolet absorber and light stabilizer are added in step (3).

[0043] Comparing the performance of this sample with that of Example 1 in accelerated aging tests clearly demonstrates the importance of the synergistic effect of UV absorbers and light stabilizers in improving the coating's weather resistance. Without these two additives, the coating would experience faster aging symptoms such as fading, chalking, and cracking under UV irradiation.

[0044] Comparative Example 2: Preparation method of weather-resistant silk screen coating using only acrylic resin This comparative example corresponds to Example 2, but the aliphatic polyurethane resin is removed to verify the effect of the synergistic effect of the acrylic resin and the polyurethane resin on the coating properties.

[0045] The components of the weather-resistant silk-screen coating include: 80 parts by weight of hydroxy acrylic resin, 20 parts by weight of rutile titanium dioxide, 5 parts by weight of phthalocyanine blue organic pigment, 15 parts by weight of hexamethylene diisocyanate (HDI) trimer, 3 parts by weight of benzotriazole ultraviolet absorber, 2 parts by weight of hindered amine light stabilizer, 2 parts by weight of high molecular weight polyester dispersant, 0.5 parts by weight of organic modified polysiloxane leveling agent, 25 parts by weight of propylene glycol methyl ether acetate (PMA) and 15 parts by weight of butyl acetate.

[0046] The preparation method is the same as that of Example 2, but in step (1), no aliphatic polyurethane resin is added, and the amount of hydroxy acrylic resin is increased accordingly.

[0047] Comparing the mechanical properties of this sample with those of Example 2 reveals the synergistic effect of the acrylic resin and polyurethane resin on the coating's flexibility and wear resistance. Without the polyurethane resin, the coating may exhibit high hardness but insufficient flexibility, making it prone to cracking when bent or impacted.

[0048] Comparative Example 3: Preparation method of weather-resistant silk screen coating using ordinary titanium dioxide This comparative example corresponds to Example 3, but uses ordinary anatase titanium dioxide instead of rutile titanium dioxide to verify the effect of rutile titanium dioxide on the hiding power and weather resistance of the coating.

[0049] The composition of the weather-resistant silk-screen coating is the same as that of Example 3, except that 10 parts by weight of rutile titanium dioxide is replaced by 10 parts by weight of anatase titanium dioxide.

[0050] The preparation method is the same as that of Example 3, but anatase titanium dioxide is used in step (1).

[0051] By comparing the performance of this sample with that of Example 3 in the hiding power test and accelerated aging test, we can observe the significant impact of rutile titanium dioxide on coating performance. Coatings using anatase titanium dioxide may exhibit poor hiding power and faster photocatalytic degradation rates, resulting in reduced weather resistance of the coating.

[0052] Comparative Example 4: Preparation method of weather-resistant silk screen coating without dispersant This comparative example corresponds to Example 4, but the high molecular weight polyester dispersant is removed to verify the effect of the dispersant on the dispersion stability of the pigment.

[0053] The components of the weather-resistant silk-screen coating were the same as those in Example 4, except that 1.5 parts by weight of the high molecular weight polyester dispersant was not added.

[0054] The preparation method is the same as that of Example 4, but no high molecular weight polyester dispersant is added in step (3).

[0055] By comparing the performance of this sample with that of Example 4 in the pigment dispersion stability test and long-term storage stability test, we can observe the impact of the dispersant on coating performance. Without a dispersant, the coating may experience problems such as pigment agglomeration and sedimentation, affecting the uniformity and long-term stability of the coating.

[0056] Comparative Example 5: Preparation method of weather-resistant silk screen coating using low crosslinking density This comparative example corresponds to Example 1, but significantly reduces the amount of hexamethylene diisocyanate (HDI) trimer to verify the effect of crosslinking density on the chemical resistance and wear resistance of the coating.

[0057] The components of the weather-resistant silk-screen coating were the same as those in Example 1, except that the amount of hexamethylene diisocyanate (HDI) trimer (10 parts by weight) was reduced to 2 parts by weight.

[0058] The preparation method is the same as that of Example 1, but in step (6), 2 parts by weight of hexamethylene diisocyanate (HDI) trimer are slowly added to the coating at a weight ratio of 100:2.

[0059] The effect of crosslink density on coating performance can be observed by comparing the performance of this sample with that of Example 1 in chemical resistance and abrasion resistance tests. Coatings with low crosslink density may exhibit poor solvent resistance and low abrasion resistance, and may not meet the requirements of high-performance applications.

[0060] Comparative Example 6: Preparation method of weather-resistant silk screen coating using traditional solvent ratio This comparative example corresponds to Example 2, but uses a traditional xylene and ethyl acetate solvent system instead of propylene glycol methyl ether acetate (PMA) and butyl acetate to verify the effect of the solvent system selected in the present invention on the film-forming quality of the coating.

[0061] The components of the weather-resistant silk-screen coating are the same as those in Example 2, except that 25 parts by weight of propylene glycol methyl ether acetate (PMA) and 15 parts by weight of butyl acetate are replaced by 25 parts by weight of xylene and 15 parts by weight of ethyl acetate.

[0062] The preparation method was the same as that of Example 2, except that xylene and ethyl acetate were used in all steps instead of propylene glycol methyl ether acetate (PMA) and butyl acetate.

[0063] Comparing the film quality evaluation and VOC emission tests of this sample with those of Example 2 reveals the impact of the solvent system on coating performance and environmental friendliness. Traditional solvents can cause defects such as pinholes and orange peel during film formation, and also have high VOC emissions, which do not meet the environmental protection requirements of modern coatings.

[0064] To comprehensively evaluate the effectiveness of the present invention's method for preparing a weather-resistant silk-screen coating, a series of tests were designed, covering multiple aspects of the coating, including weather resistance, mechanical properties, chemical stability, and environmental friendliness. These tests not only validated the core innovations of the present invention but also provided insights into the synergistic mechanisms between the various components.

[0065] Experiment 1: Accelerated Aging Test Experimental conditions: Use a xenon arc lamp aging test chamber and test in accordance with ISO 4892-2 standard.

[0066] Experimental steps: 1. Place the coating sample in a test chamber and set the light intensity to 0.55 W / (m²·nm)@340 nm.

[0067] 2. Cycle of 102 minutes of drying (65±3℃) and 18 minutes of spraying (35±3℃).

[0068] 3. Samples are taken every 500 hours, for a total test time of 2000 hours.

[0069] 4. Measure the gloss retention, color change and chalking degree of the sample.

[0070] Experiment 2: Mechanical Performance Test Experimental conditions: Tensile tests were performed using a universal material testing machine in accordance with ASTM D2370.

[0071] Experimental steps: 1. Prepare dumbbell-shaped specimens with a thickness of 0.5 mm.

[0072] 2. Test at room temperature at a tensile speed of 50 mm / min.

[0073] 3. Record the elongation at break and tensile strength.

[0074] Experiment 3: Chemical resistance test Experimental conditions: The drop method test was carried out according to ASTM D1308.

[0075] Experimental steps: 1. Add 10% NaOH solution, 10% H2SO4 solution and anhydrous ethanol to the coating surface.

[0076] 2. Cover the glass slide and place at room temperature for 24 hours.

[0077] 3. Wipe the surface, observe and record the changes in the coating.

[0078] Experiment 4: VOC content test Experimental conditions: Gas chromatography-mass spectrometry (GC-MS) was used for testing according to EPA Method 24.

[0079] Experimental steps: 1. Take 1g of paint sample and add 10mL of carbon disulfide to dissolve it.

[0080] 2. Filter using a 0.45 μm membrane filter.

[0081] 3. Perform GC-MS analysis to quantitatively calculate the VOC content.

[0082] Based on the above experiments, the test results of Examples 1-4 and Comparative Examples 1-6 were obtained and are summarized in the following table: Table 1. Accelerated aging test results (after 2000 hours)

[0083] Table 2. Mechanical properties and chemical resistance test results

[0084] Table 3. VOC content test results

[0085] Based on the test results, the following conclusions can be drawn: 1. Weatherability: Examples 1-4 all exhibited excellent weatherability, with Example 2 performing best. After 2000 hours of accelerated aging, the gloss retention reached 94%, the color difference was only 1.5, and there was no noticeable chalking. This was primarily due to the synergistic effect of the UV absorber and light stabilizer in this invention, as well as the use of rutile titanium dioxide. In contrast, Comparative Example 1 (without UV absorber and light stabilizer) exhibited significantly reduced weatherability, with a gloss retention of only 65%, a color difference of 5.6, and severe chalking.

[0086] 2. Mechanical Properties: Examples 1-4 exhibit a good balance of mechanical properties, achieving high levels of elongation at break and tensile strength. Example 2, in particular, achieves an elongation at break of 210% while maintaining a tensile strength of 22 MPa. This is attributed to the synergistic effect of the acrylic resin and polyurethane resin. Comparative Example 2 (using only acrylic resin) exhibits a significantly lower elongation at break, despite exhibiting high tensile strength, indicating insufficient coating toughness.

[0087] 3. Chemical Resistance: Examples 1-4 exhibit excellent resistance to alkali, acid, and alcohol. This is primarily attributed to appropriate crosslink density and resin selection. Comparative Example 5 (low crosslink density) performed extremely poorly in chemical resistance testing, demonstrating the importance of appropriate crosslink density for coating performance.

[0088] 4. VOC Content: The VOC contents of Examples 1-4 were all controlled at approximately 210-215 g / L, meeting the environmental protection requirements of modern coatings. However, the VOC content of Comparative Example 6 (using traditional solvents) was as high as 320 g / L, clearly failing to meet environmental protection standards.

[0089] An unexpected technical effect of the present invention is that, through a carefully designed formulation, the overall performance of the coating is significantly improved while improving weather resistance. For example, Example 2 not only performs best in weather resistance testing, but also achieves high levels of mechanical properties and chemical resistance. This comprehensive performance improvement is due to the following chemical mechanism: 1. Synergistic Effect of UV Absorbers and Light Stabilizers: Benzotriazole UV absorbers effectively absorb UV rays, while hindered amine light stabilizers capture free radicals. The combination of these two additives not only protects the coating itself but also indirectly protects the substrate, thereby improving weather resistance while maintaining the coating's mechanical properties.

[0090] 2. Synergistic effect of the resin system: Acrylic resin provides excellent weather resistance and hardness, while polyurethane resin contributes flexibility and wear resistance. The optimized ratio of the two resins creates a unique polymer network that maintains high strength while also having good toughness.

[0091] 3. Precise control of crosslink density: By adjusting the amount of isocyanate crosslinker, the present invention improves the chemical resistance of the coating while maintaining appropriate flexibility. This balance is valuable because increasing the crosslink density typically makes the coating brittle.

[0092] 4. Optimization of pigment dispersion: The use of high molecular weight polyester dispersants not only improves the dispersion stability of the pigment, but also indirectly improves the mechanical properties of the coating. Well-dispersed pigments are more evenly distributed in the polymer matrix, reducing stress concentration points, thereby improving the overall strength and durability of the coating.

[0093] 5. Innovation in the solvent system: The use of a combination of propylene glycol methyl ether acetate (PMA) and butyl acetate not only reduces VOC emissions but also improves the coating's leveling and film-forming quality. This solvent system is crucial for achieving a high-quality surface appearance and indirectly improves the coating's weather resistance.

[0094] In summary, the present invention, through the synergistic effect of multiple components, creates a screen-printing coating that exhibits excellent weather resistance, mechanical properties, chemical stability, and environmental friendliness. This comprehensive performance improvement is achieved through a carefully designed formulation and preparation process, demonstrating the innovative and practical value of the present invention.

[0095] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a weather-resistant silk-screen coating, characterized in that: The following steps are involved: (1) First, 50-70 parts by weight of acrylic resin, 10-30 parts by weight of polyurethane resin, 10-20 parts by weight of titanium dioxide, 0-5 parts by weight of organic pigment, and 20-40 parts by weight of organic solvent are mixed and dispersed in a high-speed disperser at a speed of 600-800 rpm for 30-40 minutes until the fineness reaches ≤15 μm to obtain a pre-dispersed mixture; (2) Next, the pre-dispersed mixture was transferred to a sand mill and ground at a speed of 2000-2500 rpm for 60-90 minutes until the fineness reached ≤7 μm to obtain a grinding slurry; (3) Then, the grinding slurry is transferred to a stirring kettle, and 1-3 parts by weight of an ultraviolet absorber, 0.5-2 parts by weight of a light stabilizer, 0.5-2 parts by weight of a dispersant, and 0.1-0.5 parts by weight of a leveling agent are added in sequence, and stirred at a speed of 300-400 rpm for 30-40 minutes to obtain a mixture; (4) Again, the mixture was filtered through a 100-mesh sieve; (5) Further, the filtered coating is allowed to stand at 20-25° C. for 24-48 hours for aging; (6) Finally, before use, 5-15 parts by weight of an isocyanate crosslinking agent is slowly added to the coating according to a weight ratio of 100:10-15, and stirred for 10-15 minutes until uniform, to obtain the weather-resistant silk screen coating.

2. The method for preparing a weather-resistant silk-screen coating according to claim 1, wherein: The acrylic resin is a hydroxy acrylic resin.

3. The method for preparing a weather-resistant silk-screen coating according to claim 1, wherein: The polyurethane resin is an aliphatic polyurethane resin.

4. The method for preparing a weather-resistant silk-screen coating according to claim 1, wherein: The isocyanate crosslinking agent is hexamethylene diisocyanate HDI trimer.

5. The method for preparing a weather-resistant silk-screen coating according to claim 1, wherein: The titanium dioxide is rutile titanium dioxide.

6. The method for preparing a weather-resistant silk-screen coating according to claim 1, wherein: The ultraviolet absorber is a benzotriazole ultraviolet absorber.

7. The method for preparing a weather-resistant silk-screen coating according to claim 1, wherein: The light stabilizer is a hindered amine light stabilizer HALS.

8. The method for preparing a weather-resistant silk-screen coating according to claim 1, wherein: The dispersant is a high molecular weight polyester dispersant.

9. The method for preparing a weather-resistant silk-screen coating according to claim 1, wherein: The leveling agent is organic modified polysiloxane.

10. The method for preparing a weather-resistant silk-screen coating according to claim 1, wherein: The organic solvent includes 15-25 parts by weight of propylene glycol methyl ether acetate (PMA) and 5-15 parts by weight of butyl acetate.

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