A high-solid, low-viscosity acrylic polyurethane topcoat and preparation method thereof

Abstract

The invention relates to the technical field of coatings, and proposes a high-solid and low-viscosity acrylic polyurethane topcoat and a preparation method thereof, wherein the acrylic polyurethane topcoat comprises an A component and a B component, wherein the A component comprises a hyperbranched acrylic resin, a pigment filler, a mixed organic solvent, a dispersant and a defoamer, and the B component comprises an isocyanate curing agent; the hyperbranched acrylic resin is obtained by copolymerizing an acrylate monomer, ethoxylated trimethylolpropane triacrylate and 2-thiol benzoimidazole. In the hyperbranched acrylic resin of the invention, ethoxylated trimethylolpropane triacrylate introduces a flexible segment through its ethoxylated structure, and the combination of ethoxylated trimethylolpropane triacrylate and a highly reactive group (thiol group) can improve the crosslinking density, and the synergistic effect of the three solves the steric hindrance problem of the hyperbranched acrylic resin to a certain extent, improves the crosslinking density of the hyperbranched acrylic resin, and further improves the comprehensive performance of the coating.

Description

Technical Field

[0001] The invention relates to the technical field of coatings, and in particular to a high-solid and low-viscosity acrylic polyurethane topcoat and a preparation method thereof. Background Art

[0002] High-solid, low-viscosity acrylic polyurethane topcoat is widely used in the fields of automobile, aviation, shipbuilding and construction due to its excellent wear resistance, chemical resistance and weather resistance. Its high solid content (usually above 60%) means higher coating efficiency and lower VOC emissions, which not only improves the thickness and protective performance of the coating, but also responds to the trend of green environmental protection; the low viscosity property ensures good construction performance, enables it to form a uniform and smooth paint film during the spraying process, and reduces the occurrence of sagging and orange peel. The use of this coating improves the appearance quality and service life of the product, and has become an important direction for the development of modern coating technology.

[0003] In the prior art, low-viscosity resins and hyperbranched resins are usually used to achieve the purpose of high solid and low viscosity. Since low-viscosity resins usually have a small molecular weight, they will lead to poor curing effect and insufficient flexibility of the topcoat; the highly branched structure of the hyperbranched resin will increase the steric hindrance within and between molecules, making it impossible for certain reaction sites to effectively participate in the reaction, thereby leading to technical problems such as reduced resin crosslinking density, reduced hardness of the coating, and poor aging resistance. Therefore, it is necessary to develop a high-solid and low-viscosity acrylic polyurethane topcoat with small steric hindrance and high crosslinking density. Summary of the invention

[0004] In view of this, the present invention provides a high-solid and low-viscosity acrylic polyurethane topcoat with small steric hindrance and high crosslinking density and a preparation method thereof.

[0005] The technical solution of the present invention is achieved as follows: On the one hand, the present invention provides a high-solid and low-viscosity acrylic polyurethane topcoat, comprising component A and component B, wherein the component A comprises a hyperbranched acrylic resin, a pigment filler, a mixed organic solvent, a reactive diluent, a dispersant and a defoamer, and the component B comprises an isocyanate curing agent;

[0006] The hyperbranched acrylic resin is obtained by copolymerizing acrylic ester monomer, ethoxylated trimethylolpropane triacrylate and 2-thiol benzoimidazole.

[0007] Hyperbranched acrylic resin obtained by copolymerization of acrylate monomer, ethoxylated trimethylolpropane triacrylate and 2-thiol benzoimidazole can solve the steric hindrance problem to a certain extent and improve the coating performance. The principle is: the ethoxylated structure of ethoxylated trimethylolpropane triacrylate introduces a flexible chain segment, which helps to reduce steric hindrance. In addition, the high reactivity of 2-thiol benzoimidazole can also overcome some steric hindrance effects. The combination of multifunctional monomer (ethoxylated trimethylolpropane triacrylate) and highly reactive group (thiol group) can increase the crosslinking density. The high crosslinking density and benzoimidazole structure can further increase the hardness of the coating. Both the acrylic skeleton and the benzoimidazole structure help to improve weather resistance and chemical resistance. The ethoxylated structure further reduces the interaction between molecules and helps to maintain the low viscosity characteristics of the hyperbranched structure.

[0008] In summary, the copolymerization of acrylate monomer, ethoxylated trimethylolpropane triacrylate and 2-mercaptobenzoimidazole can alleviate the steric hindrance problem of hyperbranched resin to a certain extent and improve the crosslinking density and coating performance.

[0009] On the basis of the above technical solution, preferably, calculated by weight, the component A includes 40-60 parts of hyperbranched acrylic resin, 25-40 parts of pigments and fillers, 1-5 parts of mixed organic solvents, 3-5 parts of active diluents, 0.1-1 parts of dispersants and 0.1-0.5 parts of defoamers; the component B includes isocyanate curing agent and γ-mercaptopropylmethyldimethoxysilane

[0010] The mass ratio of the acrylate monomer: ethoxylated trimethylolpropane triacrylate: 2-mercaptobenzoimidazole is 50-60: 15-20: 5-10;

[0011] The mass ratio of component A to component B is 6-10:1.

[0012] On the basis of the above technical solution, preferably, the preparation method of the hyperbranched acrylic resin is:

[0013] S1, acrylate monomer, ethoxylated trimethylolpropane triacrylate and 2-mercaptobenzoimidazole are mixed to obtain a monomer mixture;

[0014] S2, taking 10%-30% of the weight of the monomer mixture and adding it into the reactor, dissolving 10%-20% by weight of the initiator and adding it into the reactor, and reacting at 150-170°C and 2-5Bar for 2-3h;

[0015] S3, after the reaction is completed, the remaining monomer mixture and the initiator solution are mixed evenly, and then slowly added dropwise to the reaction solution for 3-4 hours, and the reaction is carried out at 150-170°C and 2-5Bar for 4-6 hours to obtain a hyperbranched acrylic resin.

[0016] Specifically, by adopting a step-by-step polymerization method to gradually increase the molecular weight and cross-linking density, it is possible to avoid generating too many branches at one time and to reduce steric hindrance to a certain extent.

[0017] On the basis of the above technical solution, preferably, the organic solvent is one or more of dimethyl sulfoxide, dimethylformamide and N-methylpyrrolidone.

[0018] On the basis of the above technical solution, preferably, the initiator is 1%-3% of the mass of the monomer mixture.

[0019] On the basis of the above technical solution, preferably, the component B also includes γ-mercaptopropylmethyldimethoxysilane.

[0020] Specifically, γ-mercaptopropylmethyldimethoxysilane has a thiol group and a silane group, which can react with the isocyanate group in isocyanate to form multiple crosslinking points, which helps to increase the crosslinking density of the coating. In addition, the silane coupling agent can also form a bridge between the organic and inorganic phases, increase the overall crosslinking density, enhance the hardness and durability of the coating, and make up for the shortcomings of hyperbranched resins in this regard.

[0021] On the basis of the above technical solution, preferably, the mass of the γ-mercaptopropylmethyldimethoxysilane is 1 / 10-1 / 8 of the mass of the isocyanate curing agent.

[0022] On the basis of the above technical solution, preferably, the acrylate monomer is one or more combinations of butyl methacrylate, isooctyl acrylate, isobornyl acrylate, ethyl methacrylate and hydroxypropyl methacrylate;

[0023] The active diluent is one of trimethylolpropane glycidyl ether, ethylene glycol glycidyl ether and tert-carbonic acid glycidyl ether;

[0024] The dispersant is one of alkyl polyglucoside, fatty alcohol polyoxyethylene ether, and fatty acid methyl ester ethoxylate;

[0025] The defoamer is a polyether defoamer or a silicone defoamer;

[0026] The initiator is one of tert-butyl hydroperoxide, cyclohexanone peroxide and tert-amyl peroxypivalate;

[0027] The pigment and filler is one or more of mica powder, talc powder, titanium dioxide, carbon black and precipitated barium sulfate;

[0028] The mixed organic solvent is a mixture of toluene, ethyl acetate, methyl ethyl ketone, diethyl carbonate and acetone.

[0029] On the other hand, the present invention also provides a method for preparing a high-solid and low-viscosity acrylic polyurethane topcoat, comprising the following steps:

[0030] S1, adding a hyperbranched acrylic resin, an organic solvent, a reactive diluent, a dispersant and a defoamer into a reaction kettle, mixing and stirring evenly, then adding a pigment and a filler, stirring evenly again and filtering to obtain a component A;

[0031] S2, mixing component A and component B, stirring evenly, and then filtering to obtain a high-solid, low-viscosity acrylic polyurethane topcoat.

[0032] On the basis of the above technical solution, preferably, the stirring speed is 1000-2000 r / min and the stirring time is 0.5-1 h.

[0033] The high-solid and low-viscosity acrylic polyurethane topcoat and the preparation method thereof of the present invention have the following beneficial effects compared with the prior art:

[0034] (1) The hyperbranched acrylic resin of the present invention is obtained by copolymerizing an acrylic ester monomer, ethoxylated trimethylolpropane triacrylate and 2-thiol benzoimidazole, wherein the ethoxylated trimethylolpropane triacrylate introduces a flexible segment through its ethoxylated structure, and the combination of a multifunctional monomer (ethoxylated trimethylolpropane triacrylate) and a highly reactive group (thiol group) can improve the crosslinking density. The synergistic effect of the three can solve the steric hindrance problem of the hyperbranched acrylic resin to a certain extent, improve the crosslinking density of the hyperbranched acrylic resin, and further improve the coating performance.

[0035] (2) The step-by-step polymerization method is used in the preparation of hyperbranched acrylic resin, which can gradually increase the molecular weight and cross-linking density, avoid the generation of too many branches at one time, and reduce steric hindrance to a certain extent.

[0036] (3) The γ-mercaptopropylmethyldimethoxysilane in the curing agent has a thiol group and a silane group, which can react with the isocyanate group in the isocyanate to form multiple cross-linking points, which helps to further increase the cross-linking density of the coating. In addition, the silane coupling agent can also form a bridge between the organic and inorganic phases, increase the overall cross-linking density, enhance the adhesion, hardness and durability of the coating, and make up for the shortcomings of hyperbranched resins in this regard. DETAILED DESCRIPTION

[0037] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The materials used in the present invention are all purchased from the market, among which the isocyanate curing agent is TDI adduct, model SC-75LT, purchased from Shanghai (Guangzhou) Haoyi Chemical Technology Co., Ltd. The silicone defoamer (models MY-220, MY-230, MY-208) and polyether defoamer (models P-20, P-12, P-06) are purchased from Shandong Meiyu Chemical Co., Ltd. Ethoxylated trimethylolpropane triacrylate and 2-mercaptobenzoimidazole are purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0039] Example 1

[0040] The high-solid, low-viscosity acrylic polyurethane topcoat of this embodiment includes component A and component B, component A: 55g of hyperbranched acrylic resin, 15g of mica powder, 15g of titanium dioxide, 3g of mixed organic solvent (mixed in equal volumes of toluene, ethyl acetate, methyl ethyl ketone, diethyl carbonate and acetone), 4g of trimethylolpropane glycidyl ether, 0.6g of alkyl polyglucoside and 0.3g of polyether defoamer P-20; component B: 11.61g of isocyanate curing agent, and the mass ratio of component A: component B is 8:1.

[0041] The preparation method of hyperbranched acrylic resin is:

[0042] S1, weigh 40g of butyl methacrylate, 15g of isobornyl acrylate, 18g of ethoxylated trimethylolpropane triacrylate and 8g of 2-mercaptobenzoimidazole and mix them to obtain 81g of a monomer mixture; dissolve 1.62g of tert-butyl hydroperoxide in 18g of dimethyl sulfoxide to obtain a tert-butyl hydroperoxide solution.

[0043] S2, add 20% by weight of the monomer mixture (16.2 g) and 15% by weight of tert-butyl hydroperoxide solution into a reactor, and react at 160°C and 3 Bar for 3 hours;

[0044] S3, after the reaction is completed, the remaining monomer mixture and tert-butyl hydroperoxide solution are mixed evenly, and slowly added dropwise to the reaction solution of step S2 for 4 hours, and then reacted at 160° C. 4 Bar for 5 hours to obtain a hyperbranched acrylic resin.

[0045] The preparation method of the high-solid and low-viscosity acrylic polyurethane topcoat of this embodiment comprises the following steps:

[0046] S1, adding hyperbranched acrylic resin, mixed organic solvent, trimethylolpropane glycidyl ether, alkyl polyglucoside and polyether defoamer P-20 into a reaction kettle, stirring at 2000 r / min for 1 hour, then adding mica powder and titanium dioxide, stirring again and filtering to obtain component A;

[0047] S2, adding isocyanate curing agent to component A, stirring at 1000 r / min for 0.5 h, and then filtering to obtain a high-solid and low-viscosity acrylic polyurethane topcoat.

[0048] Example 2

[0049] Example 2 Compared with Example 1, component B adds γ-mercaptopropylmethyldimethoxysilane, as follows:

[0050] The high-solid, low-viscosity acrylic polyurethane topcoat of this embodiment includes component A and component B, component A: 55g of hyperbranched acrylic resin, 15g of mica powder, 15g of titanium dioxide, 3g of mixed organic solvent (mixed in equal volumes of toluene, ethyl acetate, methyl ethyl ketone, diethyl carbonate and acetone), 4g of trimethylolpropane glycidyl ether, 0.6g of alkyl polyglucoside and 0.3g of polyether defoamer P-20; component B: 11.61g of isocyanate curing agent and 1.22g of γ-mercaptopropylmethyldimethoxysilane, and the mass ratio of component A: component B is 7.24:1.

[0051] The preparation method of the hyperbranched acrylic resin is the same as that in Example 1.

[0052] The preparation method of the high-solid and low-viscosity acrylic polyurethane topcoat of this embodiment comprises the following steps:

[0053] S1, adding a hyperbranched acrylic resin, 80% by weight of a mixed organic solvent, trimethylolpropane glycidyl ether, alkyl polyglucoside and polyether defoamer P-20 into a reaction kettle, stirring at 2000 r / min for 1 h, then adding mica powder and titanium dioxide, stirring again and filtering to obtain component A;

[0054] S2, mixing the isocyanate curing agent, γ-mercaptopropylmethyldimethoxysilane and the remaining mixed organic solvent, stirring at 1000 r / min for 0.5 h to obtain component B, then mixing component A and component B, stirring at 1000 r / min for 0.5 h, and then filtering to obtain a high-solid, low-viscosity acrylic polyurethane topcoat.

[0055] Example 3

[0056] The high-solid, low-viscosity acrylic polyurethane topcoat of this embodiment includes component A and component B, component A: 40g of hyperbranched acrylic resin, 10g of talcum powder, 15g of carbon black, 1g of mixed organic solvent (mixed in equal volumes of toluene, ethyl acetate, methyl ethyl ketone, diethyl carbonate and acetone), 3g of ethylene glycol glycidyl ether, 0.1g of fatty alcohol polyoxyethylene ether and 0.1g of silicone defoamer MY-2200; component B: 6.30g of isocyanate curing agent and 0.63g of γ-mercaptopropylmethyldimethoxysilane, and the mass ratio of component A: component B is 10:1.

[0057] The preparation method of hyperbranched acrylic resin is:

[0058] S1, weigh 30g of isooctyl acrylate, 20g of hydroxypropyl methacrylate, 20g of ethoxylated trimethylolpropane triacrylate and 6g of 2-mercaptobenzoimidazole and mix to obtain 76g of a monomer mixture; dissolve 0.76g of cyclohexanone peroxide in 20g of dimethylformamide to obtain a cyclohexanone peroxide solution;

[0059] S2, adding 25% by weight of the monomer mixture and 10% by weight of the cyclohexanone peroxide solution into a reaction kettle, and reacting at 160° C. 2 Bar for 5 hours;

[0060] S3, after the reaction is completed, the remaining monomer mixture and cyclohexanone peroxide solution are mixed evenly, and slowly added dropwise to the reaction solution of step S2 for 4 hours, and then reacted at 170° C. 5 Bar for 4 hours to obtain a hyperbranched acrylic resin.

[0061] The preparation method of the high-solid and low-viscosity acrylic polyurethane topcoat of this embodiment comprises the following steps:

[0062] S1, adding hyperbranched acrylic resin, 80% by weight of mixed organic solvent, ethylene glycol glycidyl ether, fatty alcohol polyoxyethylene ether and silicone defoamer MY-220 into a reaction kettle, stirring at 1800 r / min for 1 h, then adding talcum powder and carbon black, stirring again and filtering to obtain component A;

[0063] S2, mixing the isocyanate curing agent, γ-mercaptopropylmethyldimethoxysilane and the remaining mixed organic solvent to obtain component B, then mixing component A and component B, stirring at 1500 r / min for 0.5 h, and then filtering to obtain a high-solid, low-viscosity acrylic polyurethane topcoat.

[0064] Example 4

[0065] The high-solid, low-viscosity acrylic polyurethane topcoat of this embodiment includes component A and component B, component A: 45g of hyperbranched acrylic resin, 20g of carbon black, 15g of precipitated barium sulfate, 2g of mixed organic solvent (mixed in equal volumes of toluene, ethyl acetate, methyl ethyl ketone, diethyl carbonate and acetone), 3.5g of tert-butyl glycidyl ether, 0.3g of fatty acid methyl ester ethoxylate and 0.2g of silicone defoamer MY-208; component B: 8.25g of isocyanate curing agent and 1.03g of γ-mercaptopropylmethyldimethoxysilane, and the mass ratio of component A to component B is 9.27:1.

[0066] The preparation method of hyperbranched acrylic resin is:

[0067] S1, weighing 30g of butyl methacrylate, 22g of ethyl methacrylate, 17g of ethoxylated trimethylolpropane triacrylate and 10g of 2-mercaptobenzoimidazole and mixing to obtain 79g of a monomer mixture; dissolving 1.185g of tert-amyl peroxypivalate in 20g of ‌N-methylpyrrolidone to obtain a tert-amyl peroxypivalate solution;

[0068] S2, adding 10% by weight of the monomer mixture and 15% by weight of tert-amyl peroxypivalate solution into a reaction kettle, and reacting at 160° C. 4 Bar for 2.5 h;

[0069] S3, after the reaction is completed, the remaining monomer mixture and tert-amyl peroxypivalate solution are mixed evenly, and then slowly added dropwise to the reaction solution for 3 hours, and the mixture is reacted at 165° C. and 4 Bar for 5 hours to obtain a hyperbranched acrylic resin.

[0070] The preparation method of the high-solid and low-viscosity acrylic polyurethane topcoat of this embodiment comprises the following steps:

[0071] S1, adding hyperbranched acrylic resin, 80% by weight of mixed organic solvent, tert-butyl glycidyl ether, fatty acid methyl ester ethoxylate and silicone defoamer MY-208 into a reaction kettle, stirring at 1500 r / min for 1 hour, then adding carbon black and precipitated barium sulfate, stirring again and filtering to obtain component A;

[0072] S2, mixing the isocyanate curing agent, γ-mercaptopropylmethyldimethoxysilane and the remaining mixed organic solvent to obtain component B, then mixing component A and component B, stirring at 1200 r / min for 1 hour, and then filtering to obtain a high-solid, low-viscosity acrylic polyurethane topcoat.

[0073] Example 5

[0074] The high-solid, low-viscosity acrylic polyurethane topcoat of this embodiment includes component A and component B, component A: 50g of hyperbranched acrylic resin, 10g of talcum powder, 25g of titanium dioxide, 4g of mixed organic solvent (mixed in equal volumes of toluene, ethyl acetate, methyl ethyl ketone, diethyl carbonate and acetone), 4.5g of trimethylolpropane glycidyl ether, 0.8g of fatty acid methyl ester ethoxylate and 0.4g of polyether defoamer P-12; component B: 11g of isocyanate curing agent and 1.1g of γ-mercaptopropylmethyldimethoxysilane, and the mass ratio of component A to component B is 7.83:1.

[0075] The preparation method of hyperbranched acrylic resin is:

[0076] S1, weighing 30g of butyl methacrylate, 27g of ethyl methacrylate, 19g of ethoxylated trimethylolpropane triacrylate and 5g of 2-mercaptobenzoimidazole and mixing them to obtain 81g of a monomer mixture; dissolving 2.025g of tert-butyl hydroperoxide in 15g of dimethylformamide to obtain a tert-butyl hydroperoxide solution;

[0077] S2, adding 15% by weight of the monomer mixture and 10% by weight of tert-butyl hydroperoxide solution into a reactor, and reacting at 150° C. and 4 Bar for 3 hours;

[0078] S3, after the reaction is completed, the remaining monomer mixture and tert-butyl hydroperoxide solution are mixed evenly, and then slowly added dropwise to the reaction solution for 4 hours, and the mixture is reacted at 160° C. and 4 Bar for 5 hours to obtain a hyperbranched acrylic resin.

[0079] The preparation method of the high-solid and low-viscosity acrylic polyurethane topcoat of this embodiment comprises the following steps:

[0080] S1, adding a hyperbranched acrylic resin, 80% by weight of a mixed organic solvent, trimethylolpropane glycidyl ether, fatty acid methyl ester ethoxylate and polyether defoamer P-12 into a reaction kettle, stirring at 1000 r / min for 1 h, then adding talcum powder and titanium dioxide, stirring again and filtering to obtain component A;

[0081] S2, mixing the isocyanate curing agent, γ-mercaptopropylmethyldimethoxysilane and the remaining mixed organic solvent to obtain component B, then mixing component A and component B, stirring at 1000 r / min for 1 hour, and then filtering to obtain a high-solid, low-viscosity acrylic polyurethane topcoat.

[0082] Example 6

[0083] The high-solid, low-viscosity acrylic polyurethane topcoat of this embodiment includes component A and component B, component A: 60g of hyperbranched acrylic resin, 35g of titanium dioxide, 5g of carbon black, 5g of mixed organic solvent (mixed in equal volumes of toluene, ethyl acetate, methyl ethyl ketone, diethyl carbonate and acetone), 1g of ethylene glycol glycidyl ether, 0.1g of alkyl polyglucoside and 0.5g of polyether defoamer P-06; component B: 16.50g of isocyanate curing agent and 2.06g of γ-mercaptopropylmethyldimethoxysilane, and the mass ratio of component A to component B is 6:1.

[0084] The preparation method of hyperbranched acrylic resin is:

[0085] S1, weigh 20g of isooctyl acrylate, 20g of isobornyl acrylate, 20g of ethyl methacrylate, 15g of ethoxylated trimethylolpropane triacrylate and 9g of 2-mercaptobenzoimidazole and mix to obtain 84g of a monomer mixture; dissolve 2.52g of cyclohexanone peroxide in 15g of ‌N-methylpyrrolidone to obtain a cyclohexanone peroxide solution;

[0086] S2, adding 30% by weight of the monomer mixture and 20% by weight of the cyclohexanone peroxide solution into a reaction kettle, and reacting at 170° C. 4 Bar for 3 hours;

[0087] S3, after the reaction is completed, the remaining monomer mixture and cyclohexanone peroxide solution are mixed evenly, and then slowly added dropwise to the reaction solution for 4 hours, and the reaction is carried out at 170° C. and 4 Bar for 5 hours to obtain a hyperbranched acrylic resin.

[0088] The preparation method of the high-solid and low-viscosity acrylic polyurethane topcoat of this embodiment comprises the following steps:

[0089] S1, adding hyperbranched acrylic resin, 80% by weight of mixed organic solvent, ethylene glycol glycidyl ether, alkyl polyglucoside and polyether defoamer P-06 into a reaction kettle, stirring at 2000 r / min for 0.5 h, then adding titanium dioxide and carbon black, stirring again and filtering to obtain component A;

[0090] S2, mixing the isocyanate curing agent, γ-mercaptopropylmethyldimethoxysilane and the remaining mixed organic solvent to obtain component B, then mixing component A and component B, stirring at 1500 r / min for 1 hour, and then filtering to obtain a high-solid, low-viscosity acrylic polyurethane topcoat.

[0091] Comparative Example 1

[0092] Comparative Example 1 Compared with Example 1, the hyperbranched acrylic resin lacks ethoxylated trimethylolpropane triacrylate during preparation and is replaced by butyl methacrylate. The rest of the contents are the same as Example 1.

[0093] Comparative Example 2

[0094] Comparative Example 2 Compared with Example 1, the hyperbranched acrylic resin lacks 2-thiol benzoimidazole during preparation and is replaced by butyl methacrylate. The rest of the contents are the same as Example 1.

[0095] Comparative Example 3

[0096] Compared with Example 1, in Comparative Example 3, the monomer mixture and the initiator are added at one time during the preparation of the hyperbranched acrylic resin, and the rest of the contents are the same as in Example 1.

[0097] Comparative Example 4

[0098] Compared with Example 1, in Comparative Example 4, the amount of hyperbranched acrylic resin exceeded the limit, specifically 65 g, and the rest of the contents were the same as in Example 1.

[0099] Comparative Example 5

[0100] Compared with Example 1, the amount of ethoxylated trimethylolpropane triacrylate used in Comparative Example 5 exceeds the specified range, specifically 25 g, and the rest is the same as Example 1.

[0101] Comparative Example 6

[0102] Compared with Example 1, the amount of 2-thiolbenzoimidazole used in Comparative Example 6 exceeds the specified range, specifically 15 g, and the rest is the same as Example 1.

[0103] The topcoat prepared in the above embodiments and comparative examples was sprayed on a sample steel plate, and the sprayed paint film thickness was 80 μm. After drying, the topcoat performance was tested, wherein the pull-off adhesion test was in accordance with GB / T 5210, the pencil hardness test was in accordance with GB / T 6759, and the flexibility test was in accordance with GB / T 1731-1993. The coating film thickness was 20 ± 3 μm; the viscosity (coating -4 # The test of aging test (cup, 25℃) / s refers to GB / T 1723-93, the test of artificial accelerated aging test refers to GB / T 1865, the test of moisture and heat resistance refers to GB / T 1740. The measured technical indicators are shown in Table 1.

[0104] Table 1 Properties of high solid and low viscosity acrylic polyurethane topcoat

[0105]

[0106] It can be seen from Example 1 and Comparative Examples 1-2 that the introduction of the hyperbranched acrylic resin lacking ethoxylated trimethylolpropane triacrylate and 2-thiolbenzoimidazole reduces the steric hindrance of the hyperbranched resin, increases the crosslinking density, and thus improves the overall performance of the topcoat.

[0107] As shown in Comparative Example 3, when all monomers and initiators are added at one time, the polymerization reaction will be too fast, the polymer produced will be uneven, the formation of the hyperbranched structure and the performance of the final product will be affected, and the mechanical properties, solubility and other physical properties of the product will be unsatisfactory. In addition, some undesirable side reactions will be generated, which will affect the formation of the hyperbranched structure and increase the viscosity of the resin. Batch polymerization can avoid the occurrence of the above problems and reduce steric hindrance. As shown in Comparative Example 4, the amount of hyperbranched acrylic resin is too high, which will affect the curing performance of the paint film, because the highly branched structure of the hyperbranched resin will cause some reaction sites to be unable to effectively participate in the reaction. In addition, it will also affect the hardness and weather resistance of the coating film. As shown in Comparative Example 5, the amount of hyperbranched acrylic resin exceeds the limit range, which will lead to excessive crosslinking density and decreased flexibility; it will also affect the curing speed (drying time) and extend the curing time. From Comparative Example 6, it can be seen that if the content of 2-thiol benzoimidazole is too high, the curing speed will be too fast, affecting the construction performance and the flatness of the paint film; it will also affect the weather resistance of the paint film, because too many thiol groups will make the coating film more easily degraded under ultraviolet rays.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-solid, low-viscosity acrylic polyurethane topcoat, characterized in that: The invention comprises a component A and a component B. Calculated by weight, the component A comprises 40-60 parts of a hyperbranched acrylic resin, 25-40 parts of a pigment and filler, 1-5 parts of a mixed organic solvent, 3-5 parts of an active diluent, 0.1-1 parts of a dispersant and 0.1-0.5 parts of a defoamer. The component B comprises an isocyanate curing agent. The mass ratio of the component A to the component B is 6-10:

1. The hyperbranched acrylic resin is obtained by copolymerizing acrylate monomer, ethoxylated trimethylolpropane triacrylate and 2-thiol benzoimidazole; The acrylic acid ester monomer is one or more combinations of butyl methacrylate, isooctyl acrylate, isobornyl acrylate, ethyl methacrylate and hydroxypropyl methacrylate; The preparation method of the hyperbranched acrylic resin is: S1, acrylate monomer, ethoxylated trimethylolpropane triacrylate and 2-mercaptobenzoimidazole are mixed to obtain a monomer mixture; the mass ratio of the acrylate monomer: ethoxylated trimethylolpropane triacrylate: 2-mercaptobenzoimidazole is 50-60: 15-20: 5-10; S2, taking 10%-30% of the weight of the monomer mixture and adding it into the reactor, dissolving 10%-20% by weight of the initiator and adding it into the reactor, and reacting at 150-170°C and 2-5Bar for 2-3h; S3, after the reaction is completed, the remaining monomer mixture and the initiator solution are mixed evenly, and then slowly added dropwise to the reaction solution for 3-4 hours, and the reaction is carried out at 150-170°C and 2-5Bar for 4-6 hours to obtain a hyperbranched acrylic resin.

2. A high-solid, low-viscosity acrylic polyurethane topcoat as claimed in claim 1, characterized in that: The organic solvent is one or more of dimethyl sulfoxide, dimethylformamide and N-methylpyrrolidone.

3. A high-solid, low-viscosity acrylic polyurethane topcoat as claimed in claim 1, characterized in that: The initiator is 1%-3% of the mass of the monomer mixture.

4. The high-solid, low-viscosity acrylic polyurethane topcoat according to claim 1, characterized in that: The B component also includes γ-mercaptopropylmethyldimethoxysilane.

5. A high-solid, low-viscosity acrylic polyurethane topcoat as claimed in claim 4, characterized in that: The mass of the γ-mercaptopropylmethyldimethoxysilane is 1 / 10-1 / 8 of that of the isocyanate curing agent.

6. The high-solid, low-viscosity acrylic polyurethane topcoat according to claim 1, characterized in that: The active diluent is one of trimethylolpropane glycidyl ether, ethylene glycol glycidyl ether and tert-carbonic acid glycidyl ether; The dispersant is one of alkyl polyglucoside, fatty alcohol polyoxyethylene ether, and fatty acid methyl ester ethoxylate; The defoamer is a polyether defoamer or an organosilicon defoamer; The initiator is one of tert-butyl hydroperoxide, cyclohexanone peroxide and tert-amyl peroxypivalate; The pigment filler is one or more of mica powder, talcum powder, titanium dioxide, carbon black and precipitated barium sulfate; The mixed organic solvent is a mixture of toluene, ethyl acetate, methyl ethyl ketone, diethyl carbonate and acetone.

7. A method for preparing a high-solid, low-viscosity acrylic polyurethane topcoat as described in any one of claims 1 to 6, characterized in that: The following steps are involved: S1, adding a hyperbranched acrylic resin, an organic solvent, a reactive diluent, a dispersant and a defoamer into a reaction kettle, mixing and stirring evenly, then adding a pigment and a filler, stirring evenly again and filtering to obtain a component A; S2, mixing component A and component B, stirring evenly, and then filtering to obtain a high-solid, low-viscosity acrylic polyurethane topcoat.

8. The method for preparing a high-solid, low-viscosity acrylic polyurethane topcoat as claimed in claim 7, characterized in that: The stirring speed is 1000-2000r / min and the stirring time is 0.5-1h.

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