Weather-resistant water-based varnish and preparation method thereof

Abstract

The invention discloses a weather-resistant water-based varnish and a preparation method thereof, and belongs to the technical field of paints.The weather-resistant water-based varnish is characterized by being prepared from, by weight, 70-80 parts of modified water-based resin, 10-15 parts of water-based auxiliaries and 10-15 parts of deionized water; the modified water-based resin is obtained by modifying water-based acrylic resin through an ultraviolet light absorber, and the ultraviolet light absorber is grafted to the water-based acrylic resin, so that the migration and leaching possibility of the ultraviolet light absorber is greatly reduced, and the weather resistance of the water-based varnish is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of coatings, in particular to a weather-resistant water-based varnish and a preparation method thereof. Background Art

[0002] The coatings industry is currently undergoing profound transformation and development. With growing environmental awareness and increasingly robust national environmental regulations, the coatings industry is placing increasing emphasis on research into low-solvent and solvent-free binders. Water-based coatings, a promising new type of coating, have emerged. Using water as a solvent or dispersion medium, they are rapidly gaining market share thanks to their excellent environmental compatibility and protective properties. Against the backdrop of strict national controls on VOC emissions, the development of environmentally friendly water-based coatings has become a growing industry trend, garnering widespread attention from coatings professionals across the industry.

[0003] In the past, manufacturers have adopted a variety of conventional approaches to developing highly weatherable water-based clearcoats. Some have attempted to improve the performance of clearcoats by optimizing the formulation of traditional resins, adjusting the ratios of various components in the resin in the hope of enhancing the clearcoat's water and weather resistance. Others have focused on the selection and use of additives, attempting to leverage the properties of specific additives to enhance the clearcoat's performance. Still others have dedicated themselves to improving production processes, precisely controlling parameters such as temperature and pressure during the production process in order to achieve highly weatherable water-based clearcoats with even better performance.

[0004] However, these existing conventional methods have significant drawbacks. The high-weather-resistant water-based varnishes currently developed by various manufacturers have less than ideal water resistance (blistering after 240 hours) and weather resistance (around 1000 hours), far from meeting the requirements of practical applications. This makes existing high-weather-resistant water-based varnishes difficult to use in some scenarios with high water resistance and weather resistance requirements, limiting their wider application. Summary of the Invention

[0005] In order to solve the problems in the prior art, the present invention provides a weather-resistant water-based varnish and a preparation method thereof. The present application greatly reduces the possibility of migration and leaching of the ultraviolet absorber by grafting the ultraviolet absorber onto the water-based acrylic resin, thereby improving the weather resistance of the water-based varnish.

[0006] The first aspect of the present invention is to provide a weather-resistant water-based varnish, which adopts the following technical solution: A weather-resistant water-based varnish comprises the following components in parts by weight: 70-80 parts of a modified water-based resin, 10-15 parts of a water-based auxiliary agent, and 10-15 parts of deionized water. The modified water-based resin is obtained by modifying a water-based acrylic resin with an ultraviolet absorber.

[0007] Preferably, the modified water-based resin comprises the following components in parts by weight: 94-96 parts of water-based acrylic resin, 3-4 parts of ultraviolet light absorber, and 1-2 parts of catalyst.

[0008] Preferably, the modified water-based resin is obtained by the following preparation method: adding a catalyst and an ultraviolet light absorber to a water-based acrylic resin, stirring the mixture evenly, and reacting the mixture at 100-120° C. for 2-3 hours to obtain the modified water-based resin.

[0009] By adopting the above technical solution, the present invention carries out a polymerization reaction between the ultraviolet light absorber and the water-based acrylic resin under the action of a catalyst, and then the ultraviolet light absorber is grafted onto the molecular chain of the water-based acrylic resin in the form of a covalent bond through a chemical reaction, becoming a part of the structure of the water-based acrylic resin itself. Compared with physical mixing (i.e., the water-based acrylic resin and the ultraviolet light absorber are co-dispersed in a water system), the ultraviolet light absorber grafted onto the molecular chain of the water-based acrylic resin in the form of a covalent bond greatly reduces the possibility of its migration and leaching. Even if exposed to a harsh environment, the stabilizer can still play a role for a long time, thereby improving the long-lasting weather resistance of the water-based varnish. In addition, the inventors have also found that when the water-based acrylic resin is subjected to ultraviolet light, the ultraviolet light absorber can be grafted onto the molecular chain of the water-based acrylic resin in the form of a covalent bond. After the absorber is modified, the water resistance of the water-based varnish is greatly improved. The reason is that after the UV absorber is fixed to the resin skeleton with a covalent bond, the risk of migration and precipitation of small molecule additives in a humid environment is avoided, and the problem of decreased water resistance due to loss of additives is reduced. At the same time, the water-based acrylic resin may increase the cross-linking density of the water-based acrylic resin through the grafting reaction with the UV absorber, reduce the exposure of hydrophilic groups, and reduce the penetration path of water molecules, thereby further improving the water resistance of the water-based varnish. In addition, a curing agent needs to be added to the water-based varnish when used. The curing agent reacts with the hydrophilic groups of the modified water-based acrylic resin during film formation to increase the cross-linking density of the system and improve the water resistance of the water-based varnish.

[0010] Preferably, the ultraviolet light absorber is a triazine light stabilizer, and the reaction formula is as follows: Preferably, the catalyst is an acid catalyst.

[0011] Preferably, the aqueous additive includes a dispersant, a defoamer, a leveling agent, a wetting agent and a thickener.

[0012] Preferably, the weight ratio of the dispersant, defoamer, leveling agent, wetting agent and thickener is 6:1:1:1.5:0.5.

[0013] The water-based additives in weather-resistant water-based varnishes include dispersants, defoamers, leveling agents, wetting agents, and thickeners. These enhance dispersion, reduce bubble formation, improve leveling, enhance wettability, and adjust viscosity, contributing to the production of a weather-resistant water-based varnish with superior performance. Combined with the specific ratios of modified water-based resin and deionized water mentioned in the independent claims, the varnish possesses excellent weather resistance and, due to its water-based solvent, is environmentally friendly.

[0014] The second aspect of the present invention is to provide a method for preparing the weather-resistant water-based varnish as described above, comprising the following preparation steps: adding a modified water-based resin to deionized water, stirring at high speed to disperse evenly, then reducing the speed and adding a water-based additive while stirring, and dispersing evenly to obtain a weather-resistant water-based varnish.

[0015] Preferably, the rotation speed of the high-speed stirring is 1000-1200 r / min, and the stirring time is 15-20 min. The reduced rotation speed is 600-800 r / min, and the time is 15-20 min.

[0016] In summary, the present invention has the following beneficial effects: 1. The modified water-based resin obtained by the polymerization reaction of an ultraviolet absorber and a water-based acrylic resin under the action of a catalyst has excellent water resistance, excellent weather resistance, and chemical stability. In addition, since the modified water-based resin contains a large number of polar groups, it has good wetting and leveling properties. In addition, the varnish obtained by the present invention does not contain any solvent components and is an environmentally friendly product that meets modern environmental protection requirements. Most of the additives currently available on the market have defects such as repulsion and incompatibility with water-based resins. The present invention utilizes water-based acrylic resin to react under the action of a catalyst, which can improve the rheological properties and brightness without the effect of co-solvents, and greatly reduce the use of other additives, eliminating the drawbacks of repulsion, incompatibility, and uneven surface, and has excellent anti-settling properties during storage and construction.

[0017] 2. The water-based varnish obtained by the present invention has good construction performance and can be applied by various methods such as brushing and spraying, and has a high drying speed, thereby improving construction efficiency; due to the excellent water resistance of the resin itself, it can resist water erosion for a long time; it has strong resistance to natural environmental factors such as ultraviolet rays, wind and rain, cold and heat, and can maintain gloss and color after long-term exposure, and is not easy to powder and crack, meeting the requirements of modern green building materials. Compared with traditional water-based varnishes, the use of highly weather-resistant water-based varnishes can extend the use of paint and improve the economic benefits of the product.

[0018] 3. The performance of the highly weather-resistant water-based varnish prepared by the present invention meets the coating process requirements of automotive metal products. No benzene-containing solvents are added, so it is environmentally friendly. In addition, its preparation process is simple and suitable for industrial production. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below with reference to the examples. All reagents without manufacturer's indication are conventional reagents that can be purchased commercially.

[0020] Waterborne acrylic resin was purchased from Novista Group, UV absorber was purchased from BASF, and catalyst was purchased from Guangzhou Meicheng New Material Technology Co., Ltd.

[0021] The dispersant is BYK192, purchased from BYK Chemicals; the defoamer is BYK022, purchased from BYK Chemicals; the leveling agent is BYK345, purchased from BYK Chemicals; the wetting agent is Twin4100, purchased from Digo Company; the thickener is a non-ionic polyurethane associative thickener, purchased from Hemmings, model RHEOLATE 299.

[0022] Preparation Example 1 A method for preparing a modified waterborne resin comprises adding 0.2 kg of an acid catalyst to 9.4 kg of a waterborne acrylic resin, slowly adding 0.4 kg of an ultraviolet light absorber (triazine light stabilizer UV1577), stirring the mixture, and reacting the mixture at 100° C. for 3 hours to obtain the modified waterborne resin. The reaction process is as follows: Preparation Example 2 A method for preparing a modified waterborne resin comprises the following steps: adding 0.1 kg of an acid catalyst to 9.6 kg of a waterborne acrylic resin, slowly adding 0.3 kg of an ultraviolet light absorber (triazine light stabilizer UV1577), stirring the mixture, and carrying out a heat-insulating reaction at 120° C. for 2 hours to obtain the modified waterborne resin.

[0023] Preparation Example 3 A method for preparing a modified waterborne resin comprises the following steps: adding 0.2 kg of an acid catalyst to 9.3 kg of a waterborne acrylic resin, slowly adding 0.5 kg of an ultraviolet light absorber (triazine light stabilizer UV1577), stirring the mixture, and reacting the mixture at 120° C. for 2 hours to obtain the modified waterborne resin.

[0024] Example 1 A method for preparing a weather-resistant water-based varnish comprises the following steps: 7 kg of the modified water-based resin obtained in Preparation Example 1 was added to 1.5 kg of deionized water, and the mixture was stirred at a high speed of 1000 r / min for 20 min. The speed was then reduced to 600 r / min, and 1.5 kg of water-based additives was added while stirring. After dispersion for 20 min, a weather-resistant water-based varnish was obtained; the water-based additives were composed of BYK192 dispersant, BYK022 defoamer, BYK345 leveling agent, Twin4100 wetting agent and non-ionic polyurethane associative thickener in a weight ratio of 6:1:1:1.5:0.5.

[0025] Example 2 A method for preparing a weather-resistant water-based varnish comprises the following steps: 7.5 kg of the modified water-based resin obtained in Preparation Example 1 was added to 1.0 kg of deionized water, and the mixture was stirred at a high speed of 1100 r / min for 20 min. The speed was then reduced to 700 r / min, and 1.5 kg of water-based additives was added while stirring. After dispersion for 20 min, a weather-resistant water-based varnish was obtained; the water-based additives were composed of BYK192 dispersant, BYK022 defoamer, BYK345 leveling agent, Twin4100 wetting agent and non-ionic polyurethane associative thickener in a weight ratio of 6:1:1:1.5:0.5.

[0026] Example 3 A method for preparing a weather-resistant water-based varnish comprises the following steps: 8 kg of the modified water-based resin obtained in Preparation Example 1 was added to 1.0 kg of deionized water, and the mixture was stirred at a high speed of 1200 r / min for 15 min. The speed was then reduced to 800 r / min, and 1.0 kg of water-based additives was added while stirring. After dispersion for 15 min, a weather-resistant water-based varnish was obtained; the water-based additives were composed of BYK192 dispersant, BYK022 defoamer, BYK345 leveling agent, Twin4100 wetting agent, and non-ionic polyurethane associative thickener in a weight ratio of 6:1:1:1.5:0.5.

[0027] Example 4 A method for preparing a weather-resistant water-based varnish is different from Example 1 in that the modified water-based resin adopts the modified water-based resin obtained in Preparation Example 2, and the rest is the same as Example 1.

[0028] Example 5 A method for preparing a weather-resistant water-based varnish is different from Example 1 in that the modified water-based resin adopts the modified water-based resin obtained in Preparation Example 3, and the rest is the same as Example 1.

[0029] Comparative Example 1 A method for preparing a weather-resistant water-based varnish is disclosed, which differs from Example 1 in that 7 kg of water-based acrylic resin is added to 1.3 kg of deionized water, and the mixture is stirred at a high speed of 1000 r / min for 20 minutes. The speed is then reduced to 600 r / min, and 1.5 kg of a water-based auxiliary agent and 0.2 kg of a triazine light stabilizer UV1577 are added while stirring. The mixture is dispersed for 20 minutes to obtain a weather-resistant water-based varnish. Other conditions are the same as in Example 1.

[0030] Comparative Example 2 A method for preparing a weather-resistant water-based varnish is disclosed, which differs from Example 1 in that 7 kg of water-based acrylic resin is added to 1.25 kg of deionized water, and the mixture is stirred at a high speed of 1000 r / min for 20 minutes. The speed is then reduced to 600 r / min, and 1.5 kg of a water-based auxiliary agent and 0.25 kg of a triazine light stabilizer UV1577 are added while stirring. The mixture is dispersed for 20 minutes to obtain a weather-resistant water-based varnish. Other conditions are the same as in Example 1.

[0031] Performance testing The water-clear varnish obtained in the above embodiment and comparative example was used for automobile painting. The specific preparation was as follows: the weather-resistant water-based varnish and the curing agent (the curing agent consisted of Covestro N3900 and propylene glycol diacetate in a weight ratio of 65:35) were mixed and stirred in a weight ratio of 2:1, diluted with deionized water, and the viscosity was adjusted to 25-30S (tested according to the T-4 cup method). Then, it was sprayed on the surface of the 1K paint or metallic paint after the surface was dried. The spraying pressure was 0.4 MPa, the paint film thickness was controlled at 60-80 μm, and the leveling was carried out for 10-15 minutes. The sprayed board was placed in an oven at 80°C and baked for 1 hour. Then, the adhesion, impact resistance, hardness, water resistance, weather resistance, salt spray resistance, acid and alkali resistance, gasoline resistance, etc. were tested. The test results are shown in Table 1.

[0032] Among them, adhesion is tested using the 100-grid method, with level 0 being the best and level 5 being the worst; hardness is tested using a Chinese pencil.

[0033] Weather resistance test is based on ISO4892-3:2016, using a xenon lamp aging instrument with an irradiation intensity of 0.51W / m 2 (340nm), blackboard temperature is 60℃, cycle is 102 minutes of light + 18 minutes of spraying, key indicators (powdering, cracking and adhesion) are tested every 120-250h. When the powdering level is ≥3 (according to ISO4628-6 standard, use tape to stick to the paint film surface and observe the powder adhered by the tape, the powdering level is 3, which means a clear powder layer can be seen with the naked eye, and there is powder residue when wiping with fingers) or cracking occurs (crack density > 10 / cm 2 The test was stopped when the peeling area was greater than 5%) or the adhesion dropped to level 3 or higher, and the test duration was recorded.

[0034] The salt spray resistance test is carried out using 5% NaCl solution for 500 hours. After 500 hours, if there are no bubbles, peeling or obvious rust spots on the surface of the paint film, it is qualified; otherwise, it is unqualified.

[0035] The water resistance test is based on GB / T5209-1985. Immerse 2 / 3 of the sample area in running water and test in 40℃ running water for 360 hours. Take it out after 360 hours and dry it with filter paper. If there is no bubble, peeling or rust on the surface of the paint film, it is qualified. Otherwise, it is unqualified.

[0036] The acid resistance test is to immerse 2 / 3 of the sample area in 0.05mol / L sulfuric acid solution for 72 hours, then take it out and dry it with filter paper. If there are no bubbles, peeling, or substrate rust on the paint film surface, it is qualified; otherwise it is unqualified.

[0037] For the alkali resistance test, 2 / 3 of the sample area is immersed in 0.1 mol / L sodium hydroxide solution for 72 hours, then taken out and dried with filter paper. If there are no bubbles, wrinkles or dissolution on the surface of the paint film, it is qualified; otherwise, it is unqualified.

[0038] For gasoline resistance test, immerse the sample into 90# gasoline to a depth of 2 / 3, let it stand at room temperature for 72 hours, then take it out and drain it for 10 minutes. If there are no bubbles, wrinkles, or stickiness on the surface of the paint film, and there is no dissolution or discoloration when wiped, it is qualified; otherwise it is unqualified.

[0039] The anti-sagging performance is tested according to the relevant provisions of GB / T9264-2012.

[0040] Mobility test: The sample was immersed in an ethanol solution (50% v / v) for 24 hours, and the content of the ultraviolet absorber dissolved in the ethanol solution was detected by HPLC.

[0041] Table 1. Test results of paint films of examples and comparative examples As can be seen from Table 1: The paint film surfaces of the weather-resistant water-based varnishes obtained in Examples 1-5 and Comparative Examples 1-2 of the present application are plump and smooth. The adhesion of the water-based varnishes obtained in Examples 1-5 is all level 0, the hardness is 2H, the impact resistance is qualified, the salt spray resistance is qualified at 500h, and the acid and alkali resistance and gasoline resistance tests are qualified at 72h. When the weight proportion of the ultraviolet light absorber reaches 5%, the weather resistance of the water-based varnish obtained in Example 5 decreases by 200h compared with that in Example 1, and the water resistance is also reduced. It can be seen that when the amount of the ultraviolet light absorber is within the range of 3-4%, the weather resistance and water resistance of the water-based varnish can be guaranteed.

[0042] The difference between Comparative Example 1 and Example 1 lies in weather resistance and water resistance. As can be seen from Table 1, the water resistance of the water-based varnish obtained in Comparative Example 1 was unqualified at 260h, while the weather resistance of Comparative Example 1 was 1500h. In Comparative Example 2, when the content of triazine light stabilizer UV1577 was increased, the weather resistance of Comparative Example 2 was 1000h and the water resistance was 220h, which were unqualified. The adhesion of the paint film was also Class 1. The reason may be that the excessive triazine light stabilizer UV1577 tends to aggregate together to form tiny particles or In the region, these aggregated UV absorber particles will not only increase the cohesion of the paint film and reduce the adhesion of the paint film, but will also interfere with the arrangement and cross-linking of the water-based acrylic resin molecules and destroy the continuous phase structure of the acrylic resin. Moreover, the aggregated UV absorber molecules may not be able to perform photothermal conversion as effectively as individual molecules. Instead, they may absorb more light energy, causing abnormal temperature increases in the local area. The temperature increase will greatly accelerate the oxidative degradation reaction of the acrylic resin itself, thereby reducing the weather resistance and water resistance of the paint film. After the UV absorber is grafted onto the water-based acrylic resin, the agglomeration of the UV absorber is effectively prevented, and the migration and exudation of the UV absorber can also be effectively avoided, thereby significantly improving the weather resistance and water resistance of the water-based varnish.

[0043] Moreover, compared with Example 1, the proportion of the ultraviolet light absorber in the water-based varnish in Example 1 of the present application is greater than the proportion of the ultraviolet light absorber in the water-based varnish in Comparative Example 2, but the weather resistance and water resistance in Example 1 are significantly higher than those in Comparative Example 2, and it can be seen from the migration rate of the ultraviolet light absorber that the mobility of the ultraviolet light absorber in the water-based varnish of Comparative Examples 1-2 is much higher than the mobility of the ultraviolet light absorber in the examples of the present application, indicating that after the ultraviolet light absorber is grafted with the water-based acrylic resin, the migration performance of the ultraviolet light absorber in the water-based varnish is effectively reduced, thereby improving the weather resistance and water resistance of the water-based varnish.

[0044] The embodiments of this specific implementation method are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A weather-resistant water-based varnish, characterized by: The invention comprises the following components in parts by weight: 70-80 parts of modified water-based resin, 10-15 parts of water-based auxiliary agent and 10-15 parts of deionized water. The modified water-based resin is obtained by modifying water-based acrylic resin with ultraviolet light absorber.

2. The weather-resistant water-based varnish according to claim 1, characterized in that: The modified water-based resin comprises the following components in parts by weight: 94-96 parts of water-based acrylic resin, 3-4 parts of ultraviolet light absorber, and 1-2 parts of catalyst.

3. The weather-resistant water-based varnish according to claim 2, characterized in that: The modified water-based resin is obtained by the following preparation method: adding a catalyst and an ultraviolet light absorber to a water-based acrylic resin, stirring the mixture evenly, and reacting the mixture at 100-120° C. for 2-3 hours to obtain the modified water-based resin.

4. The weather-resistant water-based varnish according to claim 2, characterized in that: The ultraviolet light absorber is a triazine light stabilizer.

5. The weather-resistant water-based varnish according to claim 2, characterized in that: The catalyst is an acid catalyst.

6. The weather-resistant water-based varnish according to claim 1, characterized in that: The aqueous additives include dispersants, defoamers, leveling agents, wetting agents and thickeners.

7. The weather-resistant water-based varnish according to claim 6, characterized in that: The weight ratio of the dispersant, defoamer, leveling agent, wetting agent and thickener is 6:1:1:1.5:0.

5.

8. A method for preparing the weather-resistant water-based varnish according to any one of claims 1 to 7, characterized in that: The method comprises the following preparation steps: adding modified water-based resin into deionized water, stirring at high speed to disperse uniformly, then reducing the speed while stirring and adding water-based additives, and dispersing uniformly to obtain weather-resistant water-based varnish.

9. The method for preparing a weather-resistant water-based varnish according to claim 8, characterized in that: The rotation speed of the high-speed stirring is 1000-1200 r / min, and the stirring time is 15-20 min. The reduced rotation speed is 600-800 r / min, and the time is 15-20 min.

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