A polyurethane automotive topcoat and a method of making the same

Abstract

The application discloses a polyurethane automobile finish and a preparation method thereof, and relates to the field of automobile finishes. In the preparation of the polyurethane automobile finish, titanium white powder, 3-buten-1, 2-diol and 6-bromo-3-(4-bromophenyl)-2, 4-dihydro-1, 3-benzoxazine are uniformly mixed to prepare modified titanium white powder; microcrystalline cellulose is aldehyde-based after being grafted with n-butyric acid, acetic anhydride and 2-aminopiperazine to obtain modified cellulose; 1, 3, 5, 7-tetramethylcyclotetrasiloxane and vinyl pentamethyl disiloxane are reacted to obtain a single-end vinyl hydrogen-containing silicone oil; acrylic acid, methyl acrylate, hydroxypropyl methacrylate and the single-end vinyl hydrogen-containing silicone oil are copolymerized to obtain modified acrylic resin; and the modified acrylic resin, the modified cellulose, the modified titanium white powder and various additives are uniformly mixed to prepare the polyurethane automobile finish. The polyurethane automobile finish prepared by the application has excellent quick-drying property, impact resistance and anti-aging property.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of automobile finish, in particular to a polyurethane automobile finish and a preparation method thereof. BACKGROUND

[0002] Traditional automobile finishes face many challenges in industrial production, with the most prominent problem being low drying efficiency. Due to the insufficient volatility of the solvent system of existing coatings and the limitation of resin cross-linking characteristics on fast curing ability, the finish requires a long air-drying and baking time, which seriously affects the coating production efficiency. In addition, the performance of such finishes in terms of weather resistance, impact resistance and chemical stability cannot meet the stringent requirements of modern automobile industry on the durability and protection of the paint film, directly affecting the appearance maintenance and service life of the automobile.

[0003] Polyurethane automobile finishes have become the mainstream choice in the field of automobile coating due to their excellent comprehensive performance, including excellent weather resistance, outstanding impact resistance, good chemical corrosion resistance and excellent decorative effect. However, the currently marketed polyurethane finishes still have obvious process defects: slow solvent release speed, which is difficult to adapt to modern high-speed baking process; surface closure phenomenon during film formation, which hinders the volatilization of inner layer solvent; and too long curing time, which cannot meet the demand of high-efficiency assembly line operation. In view of these technical bottlenecks, the present application develops a polyurethane automobile finish with good quick-drying property, which greatly improves the drying efficiency by optimizing the cross-linking network, while maintaining the excellent performance of traditional polyurethane coatings, providing a more efficient solution for automobile coating process. SUMMARY

[0004] The present application aims to provide a polyurethane automobile finish and a preparation method thereof to solve the problems in the prior art.

[0005] To solve the above technical problems, the present application provides the following technical solution: a polyurethane automobile finish, which is prepared by uniformly mixing modified acrylic resin, modified cellulose, modified titanium dioxide and various additives.

[0006] As an optimization, the modified acrylic resin is prepared by copolymerization of acrylic acid, methyl acrylate, hydroxypropyl methacrylate and single-end vinyl hydrogen-containing silicone oil.

[0007] As an optimization, the end-vinyl hydrogen-containing silicone oil is obtained by reaction of 1,3,5,7-tetramethylcyclotetrasiloxane and vinyl pentamethyl disiloxane.

[0008] As an optimization, the modified cellulose is obtained by grafting n-butyl acid, acetic anhydride and 2-aminopiperazine after aldehyde group modification of microcrystalline cellulose.

[0009] As optimization, the microcrystalline cellulose is 200 mesh from Shandong Shouhua Chemical Co., Ltd.

[0010] As optimization, the modified titanium dioxide is prepared by mixing titanium dioxide, 3-butene-1,2-diol and 6-bromo-3-(4-bromophenyl)-2,4-dihydro-1,3-benzoxazine.

[0011] As optimization, the titanium dioxide is THR-218 from Hebei Kuoou Chemical Technology Co., Ltd.

[0012] As optimization, the various additives include dispersants, wetting agents, leveling agents, curing agents and diluents.

[0013] As optimization, the dispersant is BYK-110 from Shanghai Kaijin Chemical Co., Ltd.

[0014] As optimization, the wetting agent is BYK-220S from Jining Fangyi Chemical Co., Ltd.

[0015] As optimization, the leveling agent is EFKA-3600 from Guangzhou Haoliangda International Trade Co., Ltd.

[0016] As optimization, the curing agent is N3390BA / SN from Dongguan Tison New Material Co., Ltd.

[0017] As optimization, the diluent is obtained by mixing 40-50 parts of butyl acetate, 20-30 parts of xylene, 10-15 parts of propylene glycol methyl ether acetate and 3-5 parts of nylon acid methyl ester.

[0018] A preparation method of a polyurethane automobile topcoat, comprising the following preparation steps:

[0019] (1) mixing and reacting titanium dioxide, 3-butene-1,2-diol, 6-bromo-3-(4-bromophenyl)-2,4-dihydro-1,3-benzoxazine, anhydrous potassium carbonate and N,N-dimethylformamide to obtain modified titanium dioxide;

[0020] (2) reacting microcrystalline cellulose and sodium periodate to obtain aldehyde-based cellulose;

[0021] (3) mixing and reacting aldehyde-based cellulose, n-butyric acid, acetic anhydride and sulfuric acid solution to obtain pre-modified cellulose; reacting the pre-modified cellulose and 2-aminopiperazine to obtain modified cellulose;

[0022] (4) reacting 1,3,5,7-tetramethylcyclotetrasiloxane and vinyl pentamethyl disiloxane to obtain a single-end vinyl hydrogen-containing silicone oil;

[0023] (5) mixing acrylic acid, methyl acrylate, hydroxypropyl methacrylate, monovinyl group containing hydrogen silicone oil, azobis isobutyronitrile, propylene glycol methyl ether acetate and N, N-dimethyl ethanolamine uniformly and reacting to obtain modified acrylic resin;

[0024] (6) mixing modified acrylic resin, dispersant, wetting agent, modified cellulose, butyl acetate, propylene glycol methyl ether acetate, modified titanium dioxide, leveling agent, curing agent, diluent and chloroplatinic acid uniformly and reacting to obtain polyurethane automobile topcoat.

[0025] As optimization, the preparation process of the modified titanium dioxide in step (1) is as follows: mixing titanium dioxide, 3-buten-1, 2-diol, 6-bromo-3-(4-bromophenyl)-2, 4-dihydro-1, 3-benzoxazine, anhydrous potassium carbonate and N, N-dimethyl formamide uniformly according to the mass ratio of 1: (0.3~0.5): (1.6~1.8): (0.85~0.95): (20~30), refluxing at 153~155℃, 100~300rpm for 9~11h to obtain modified titanium dioxide.

[0026] As optimization, the reaction equation of the modified titanium dioxide in step (1) is as follows: .

[0027] As optimization, the preparation process of the aldehyde group modified cellulose in step (2) is as follows: mixing microcrystalline cellulose and sodium periodate uniformly according to the mass ratio of 1: (0.9~1.1), reacting in hydrochloric acid aqueous solution with pH of 2~4 at 25~35℃ in dark for 7~9h to obtain aldehyde group modified cellulose.

[0028] As optimization, the preparation process of the modified cellulose in step (3) is as follows: mixing pre-modified cellulose and 2-aminopiperazine uniformly according to the mass ratio of 1: (1.2~1.4), reacting in phosphate buffer solution with pH of 7.1~7.3 at 36~38℃ for 3~5h to obtain modified cellulose.

[0029] As optimization, the preparation process of the pre-modified cellulose is as follows: mixing aldehyde group modified cellulose, n-butanoic acid and acetic anhydride according to the mass ratio of 1: (6.5~6.7): (1~3), adding 200~400mL of zirconium oxide balls, ball milling in sulfuric acid solution with mass fraction of 97%~99% at 65~75℃ for 55~65min to obtain pre-modified cellulose.

[0030] As optimization, the reaction equation of the modified cellulose in step (3) is as follows: ; wherein R is or .

[0031] As optimization, the preparation process of the single-end vinyl hydrogen-containing silicone oil in step (4) is as follows: 1,3,5,7-tetramethylcyclotetrasiloxane, vinyl pentamethyldisiloxane and trifluoromethyl sulfonic acid are uniformly mixed in a mass ratio of 1:(0.3-0.4):(0.01-0.02), reacted at 65-75℃ for 5-7h, the pH is adjusted to 6-7, and then distilled at 105-115℃, 0.1-0.3MPa for 1-2h to obtain the single-end vinyl hydrogen-containing silicone oil.

[0032] As optimization, the preparation process of the modified acrylic resin in step (5) is as follows: acrylic acid, methyl acrylate, hydroxypropyl methacrylate, single-end vinyl hydrogen-containing silicone oil, azobis isobutyronitrile and propylene glycol methyl ether acetate are uniformly mixed in a mass ratio of 1:(0.7-0.8):(1-3):(0.4-0.6):(0.1-0.2):(7-9), reacted at 85-95℃ for 4-8h, cooled to 55-65℃, and the pH is adjusted to 7-8 to obtain the modified acrylic resin.

[0033] As optimization, the reaction equation of the modified acrylic resin in step (5) is as follows: .

[0034] As optimization, the preparation process of the polyurethane automobile topcoat in step (6) is as follows: 90-110 parts of the modified acrylic resin, 3-6 parts of a dispersing agent, 3-6 parts of a wetting agent, 6-14 parts of a modified cellulose, 14-28 parts of butyl acetate, 14-28 parts of propylene glycol methyl ether acetate and 80-90 parts of modified titanium white powder are ground to pass through a 4-10μm sieve at 55-65℃ and 15-17L / min, 3-6 parts of a leveling agent, 40-60 parts of a curing agent, 5-15 parts of a diluent and 1-3 parts of chloroplatinic acid are uniformly mixed, sieved to pass through a 100-200 mesh sieve, and then placed for 10-20min, sprayed to a thickness of 40-50μm, flash dried at 40-60℃ for 3-5min, dried at 70-80℃ for 55-65min to obtain the polyurethane automobile topcoat.

[0035] As optimization, the process parameters of the spraying are as follows: spraying temperature 20-30℃, spraying pressure 2-2.5kg / cm 2 , spraying gun caliber 1.3-1.5mm, and spraying gun distance 15-25cm.

[0036] Compared with the prior art, the present application has the beneficial effects that: in the preparation of the polyurethane automobile finish, the titanium white powder, 3-butene-1, 2-diol and 6-bromo-3-(4-bromophenyl)-2, 4-dihydro-1, 3-benzoxazine are uniformly mixed to prepare modified titanium white powder; the microcrystalline cellulose is aldehyde-based after grafting n-butyric acid, acetic anhydride and 2-aminopiperazine to obtain modified cellulose; 1, 3, 5, 7-tetramethylcyclotetrasiloxane and vinyl pentamethyl disiloxane are reacted to obtain a single-end vinyl hydrogen-containing silicone oil; acrylic acid, methyl acrylate, hydroxypropyl methacrylate and the single-end vinyl hydrogen-containing silicone oil are copolymerized to obtain modified acrylic resin; and the modified acrylic resin, the modified cellulose, the modified titanium white powder and various additives are uniformly mixed to prepare the polyurethane automobile finish.

[0037] Firstly, the titanium white powder, 3-butene-1, 2-diol and 6-bromo-3-(4-bromophenyl)-2, 4-dihydro-1, 3-benzoxazine are uniformly mixed to prepare modified titanium white powder; the microcrystalline cellulose is aldehyde-based after grafting n-butyric acid, acetic anhydride and 2-aminopiperazine to obtain modified cellulose; the benzoxazine ring and carbon-carbon double bond are introduced on the surface of the titanium white powder by polymerization of 3-butene-1, 2-diol and 6-bromo-3-(4-bromophenyl)-2, 4-dihydro-1, 3-benzoxazine, the benzoxazine can undergo thermal ring-opening polymerization to generate a structure similar to phenolic resin, the crosslinking network is optimized, the drying speed is accelerated, and the free radicals can also be captured to improve the quick-drying property, impact resistance and anti-aging property of the polyurethane automobile finish; the carbon-carbon double bond can undergo addition reaction with the silicon-hydrogen bond on the modified acrylic resin to optimize the crosslinking network and further improve the quick-drying property and impact resistance of the polyurethane automobile finish; by grafting n-butyric acid and acetic anhydride after aldehyde-based modification of the cellulose, butyric acid and acetic groups are introduced to form hydrogen bonds with solvent molecules in the paint film, the release of the solvent in the paint film forming process is promoted, and the quick-drying property of the polyurethane automobile finish is improved; by grafting 2-aminopiperazine through Schiff base reaction, the piperazine and the isocyanate group in the curing agent undergo amide reaction to generate a structure similar to hindered amine, the crosslinking network is formed, and the oxidative free radicals are also removed, and the quick-drying property and anti-aging property of the polyurethane automobile finish are further improved.

[0038] Secondly, 1, 3, 5, 7-tetramethylcyclotetrasiloxane and vinyl pentamethyl disiloxane are reacted to obtain a single-end vinyl hydrogen-containing silicone oil; acrylic acid, methyl acrylate, hydroxypropyl methacrylate and the single-end vinyl hydrogen-containing silicone oil are copolymerized to obtain modified acrylic resin; the modified acrylic resin, the modified cellulose, the modified titanium white powder and various additives are uniformly mixed to prepare the polyurethane automobile finish; by copolymerization, the long-chain organic silicon is introduced into the acrylic resin to reduce the surface tension of the resin, improve the defoaming property and reduce the addition amount of functional additives; the carboxyl groups in the polyacrylic acid resin are neutralized by N, N-dimethylethanolamine to reduce the charge repulsion between the polymer chains, so that the polymer chains are more easily entangled with each other, and the impact resistance of the polyurethane automobile finish is improved. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0040] The raw materials used in the following examples and comparative examples are all commercially available: the microcrystalline cellulose is 200 mesh from Shandong Shuhua Chemical Co., Ltd.; the titanium dioxide is THR-218 from Hebei Koyou Chemical Technology Co., Ltd.; the dispersing agent is BYK-110 from Shanghai Kaixin Chemical Co., Ltd.; the wetting agent is BYK-220S from Jining Fangyu Chemical Co., Ltd.; the leveling agent is EFKA-3600 from Guangzhou Haoliangda International Trade Co., Ltd.; and the curing agent is N3390BA / SN from Dongguan Tison New Material Co., Ltd.

[0041] The diluents used in the following examples and comparative examples are all obtained by uniformly mixing 45 parts of butyl acetate, 25 parts of xylene, 12.5 parts of propylene glycol methyl ether acetate and 4 parts of nylon acid methyl ester by mass fraction.

[0042] Example 1:

[0043] A preparation method of a polyurethane automobile topcoat, the preparation method of the polyurethane automobile topcoat comprising the following preparation steps:

[0044] (1) uniformly mixing titanium dioxide, 3-buten-1,2-diol, 6-bromo-3-(4-bromophenyl)-2,4-dihydro-1,3-benzoxazine, anhydrous potassium carbonate and N,N-dimethylformamide in a mass ratio of 1:0.3:1.6:0.85:20, refluxing at 153℃ and 100rpm for 11h, naturally cooling to room temperature, centrifuging, washing with anhydrous ethanol and deionized water for 3 times respectively, and drying at 55℃ for 25h to obtain modified titanium dioxide;

[0045] (2) uniformly mixing microcrystalline cellulose and deionized water in a mass ratio of 1:55, adding hydrochloric acid to adjust the pH to 2, stirring at 25℃ and 100rpm in the dark for 65min, adding sodium periodate in an amount of 0.9 times the mass of the microcrystalline cellulose, continuing to stir for 9h, filtering, washing with deionized water for 3 times, freeze-drying for 11h, grinding and sieving to 200 mesh to obtain aldehyde-modified cellulose;

[0046] (3) mixing aldehyde group cellulose, n-butanoic acid, acetic anhydride and a 97% mass fraction sulfuric acid solution according to a mass ratio of 1:6.5:1:0.01, adding 200 mL zirconium oxide balls, separating after ball milling at 65 °C and 200 r / min for 65 min, washing with deionized water for 3 times, and drying at 50 °C for 13 h to obtain pre-modified cellulose; mixing the pre-modified cellulose, 2-aminopiperazine and a phosphate buffer solution with a pH of 7.1 according to a mass ratio of 1:1.2:120, centrifuging after stirring at 36 °C and 100 rpm for 5 h, washing with deionized water for 3 times, and freeze-drying to obtain modified cellulose;

[0047] (4) mixing 1,3,5,7-tetramethylcyclotetrasiloxane and vinyl pentamethyldisiloxane according to a mass ratio of 1:0.3, stirring at 65 °C and 100 rpm for 20 min, adding trifluoromethyl sulfonic acid with a mass of 0.01 times that of 1,3,5,7-tetramethylcyclotetrasiloxane, continuing to stir for 7 h, filtering after adding anhydrous sodium carbonate to adjust the pH to 6, and distilling at 105 °C and 0.1 MPa for 2 h to obtain a single-end vinyl hydrogen-containing silicone oil;

[0048] (5) mixing acrylic acid, methyl acrylate, hydroxypropyl methacrylate, a single-end vinyl hydrogen-containing silicone oil, azobis isobutyl cyanide and propylene glycol methyl ether acetate according to a mass ratio of 1:0.7:1:0.45:0.1:7, stirring at 85 °C and 100 rpm for 8 h, cooling to 55 °C, and adding N,N-dimethyl ethanolamine to adjust the pH to 7 to obtain a modified acrylic resin;

[0049] (6) mixing the modified acrylic resin, a dispersant, a wetting agent, modified cellulose, butyl acetate and propylene glycol methyl ether acetate according to a mass ratio of 1:0.03:0.03:0.06:0.14:0.14, stirring at 20 °C and 500 rpm for 30 min, adding modified titanium white powder with a mass of 0.8 times that of the modified acrylic resin, continuing to stir for 10 min, grinding and sieving at 55 °C and 15-17 L / min to 4 μm, adding a leveling agent with a mass of 0.03 times that of the modified acrylic resin and a curing agent with a mass of 0.4 times that of the modified acrylic resin, stirring at 450 rpm for 3 min, adding a diluent with a mass of 0.05 times that of the modified acrylic resin and chloroplatinic acid with a mass of 0.01 times that of the modified acrylic resin, continuing to stir for 3 min, sieving to 100 meshes, standing for 20 min, and spraying at 20 °C, a spraying pressure of 2 kg / cm 2 , a spraying gun caliber of 1.3 mm, a spraying gun distance of 15 cm, to a thickness of 40 μm, flash drying at 40 °C for 5 min, and drying at 70 °C for 65 min to obtain a polyurethane automobile topcoat.

[0050] Example 2:

[0051] A preparation method of a polyurethane automobile topcoat, the preparation method of the polyurethane automobile topcoat comprising the following preparation steps:

[0052] (1) titanium white powder, 3-butene-1, 2-diol, 6-bromo-3-(4-bromophenyl)-2, 4-dihydro-1, 3-benzoxazine, anhydrous potassium carbonate and N, N-dimethylformamide were mixed in a mass ratio of 1:0.4:1.7:0.9:25, refluxed at 154℃ and 200rpm for 10h, naturally cooled to room temperature, centrifuged, washed with anhydrous ethanol and deionized water for 4 times respectively, and dried at 60℃ for 24h to obtain modified titanium white powder;

[0053] (2) microcrystalline cellulose and deionized water were mixed in a mass ratio of 1:60, hydrochloric acid was added to adjust the pH to 3, stirred at 30℃ and 200rpm for 60min in the dark, 1 times of microcrystalline cellulose of sodium periodate was added, and stirred for 8h, then filtered, washed with deionized water for 4 times, freeze-dried for 12h, and ground to 250 mesh to obtain aldehyde-based cellulose;

[0054] (3) aldehyde-based cellulose, n-butyric acid, acetic anhydride and 98% sulfuric acid solution were mixed in a mass ratio of 1:6.6:2:0.02, 300mL zirconium oxide balls were added, ball-milled at 70℃ and 300r / min for 60min, then separated, washed with deionized water for 4 times, and dried at 55℃ for 12h to obtain pre-modified cellulose; the pre-modified cellulose, 2-aminopiperazine and phosphate buffer solution with pH of 7.2 were mixed in a mass ratio of 1:1.3:125, stirred at 37℃ and 150rpm for 4h, then centrifuged, washed with deionized water for 4 times, and freeze-dried to obtain modified cellulose;

[0055] (4) 1, 3, 5, 7-tetramethylcyclotetrasiloxane and vinyl pentamethyl disiloxane were mixed in a mass ratio of 1:0.35, stirred at 70℃ and 150rpm for 15min, 0.015 times of 1, 3, 5, 7-tetramethylcyclotetrasiloxane of trifluoromethyl sulfonic acid was added, and stirred for 6h, then filtered after adjusting the pH to 6.5 with anhydrous sodium carbonate, and distilled at 110℃ and 0.2MPa for 1.5h to obtain a single-end vinyl hydrogen-containing silicone oil;

[0056] (5) acrylic acid, methyl acrylate, hydroxypropyl methacrylate, single-end vinyl hydrogen-containing silicone oil, azobis isobutyl cyanide and propylene glycol methyl ether acetate were mixed in a mass ratio of 1:0.75:2:0.5:0.15:8, stirred at 90℃ and 150rpm for 6h, cooled to 60℃, and N, N-dimethyl ethanolamine was added to adjust the pH to 7.5 to obtain a modified acrylic resin;

[0057] (6) mixing the modified acrylic resin, dispersant, wetting agent, modified cellulose, butyl acetate and propylene glycol methyl ether acetate in a mass ratio of 1:0.045:0.045:0.1:0.21:0.21, stirring at 25℃ and 550rpm for 25min, adding modified titanium white powder with a mass of 0.85 times that of the modified acrylic resin, continuing to stir for 15min, grinding and sieving at 60℃ and 15~17L / min to 7μm, adding leveling agent with a mass of 0.045 times that of the modified acrylic resin and curing agent with a mass of 0.5 times that of the modified acrylic resin, stirring at 500rpm for 2min, adding diluent with a mass of 0.1 times that of the modified acrylic resin and chloroplatinic acid with a mass of 0.02 times that of the modified acrylic resin, continuing to stir for 2min, sieving to 150mesh, standing for 15min, spraying at 25℃, spraying pressure 2.25kg / cm 2 , gun caliber 1.4mm, gun distance 20cm, to a thickness of 45μm, flash drying at 50℃ for 4min, drying at 75℃ for 60min, to obtain a polyurethane automobile topcoat.

[0058] Example 3:

[0059] A preparation method of a polyurethane automobile topcoat, the preparation method of the polyurethane automobile topcoat comprising the following preparation steps:

[0060] (1) mixing titanium white powder, 3-buten-1,2-diol, 6-bromo-3-(4-bromophenyl)-2,4-dihydro-1,3-benzoxazine, anhydrous potassium carbonate and N,N-dimethylformamide in a mass ratio of 1:0.5:1.8:0.95:30, refluxing at 155℃ and 300rpm for 9h, centrifuging after natural cooling to room temperature, washing with anhydrous ethanol and deionized water for 5 times respectively, drying at 65℃ for 23h, to obtain modified titanium white powder;

[0061] (2) mixing microcrystalline cellulose and deionized water in a mass ratio of 1:65, adding hydrochloric acid to adjust pH to 4, stirring at 35℃ and 300rpm for 65min in the dark, adding sodium periodate with a mass of 1.1 times that of the microcrystalline cellulose, continuing to stir for 7h, filtering, washing with deionized water for 5 times, freeze-drying for 13h, grinding and sieving to 300mesh, to obtain aldehyde-modified cellulose;

[0062] (3) mixing aldehyde-based cellulose, n-butanoic acid, acetic anhydride and a 99% mass fraction of sulfuric acid solution according to a mass ratio of 1:6.7:3:0.03, adding 400 mL of zirconium oxide balls, separating after ball milling at 75 °C and 400 r / min for 55 min, washing with deionized water for 5 times, and drying at 60 °C for 11 h to obtain pre-modified cellulose; mixing the pre-modified cellulose, 2-aminopiperazine and a phosphate buffer solution with a pH of 7.3 according to a mass ratio of 1:1.4:130, centrifuging after stirring at 38 °C and 200 rpm for 3 h, washing with deionized water for 5 times, and freeze-drying to obtain modified cellulose;

[0063] (4) mixing 1,3,5,7-tetramethylcyclotetrasiloxane and vinyl pentamethyl disiloxane according to a mass ratio of 1:0.4, stirring at 75 °C and 200 rpm for 10 min, adding trifluoromethyl sulfonic acid with a mass of 0.02 times of 1,3,5,7-tetramethylcyclotetrasiloxane, continuing to stir for 5 h, filtering after adding anhydrous sodium carbonate to adjust the pH to 7, and distilling at 115 °C and 0.3 MPa for 1 h to obtain a single-end vinyl hydrogen-containing silicone oil;

[0064] (5) mixing acrylic acid, methyl acrylate, hydroxypropyl methacrylate, single-end vinyl hydrogen-containing silicone oil, azobis isobutyl cyanide and propylene glycol methyl ether acetate according to a mass ratio of 1:0.8:3:0.6:0.2:9, stirring at 95 °C and 200 rpm for 8 h, cooling to 65 °C, and adding N,N-dimethyl ethanolamine to adjust the pH to 8 to obtain a modified acrylic resin;

[0065] (6) mixing the modified acrylic resin, a dispersant, a wetting agent, the modified cellulose, butyl acetate and propylene glycol methyl ether acetate according to a mass ratio of 1:0.06:0.06:0.14:0.28:0.28, stirring at 30 °C and 600 rpm for 20 min, adding modified titanium white powder with a mass of 0.9 times of the modified acrylic resin, continuing to stir for 10 min, grinding and sieving at 65 °C and 15-17 L / min with a mesh size of 10 μm, adding a leveling agent with a mass of 0.06 times of the modified acrylic resin and a curing agent with a mass of 0.6 times of the modified acrylic resin, stirring at 550 rpm for 1 min, adding a diluent with a mass of 0.15 times of the modified acrylic resin and chloroplatinic acid with a mass of 0.03 times of the modified acrylic resin, continuing to stir for 1 min, sieving to 200 mesh, standing for 10 min, and spraying at 30 °C with a spraying pressure of 2.5 kg / cm 2 , a spraying gun caliber of 1.5 mm, a spraying gun distance of 25 cm, to a thickness of 50 μm, flash drying at 60 °C for 3 min, and drying at 80 °C for 55 min to obtain a polyurethane automobile topcoat.

[0066] Comparative Example 1:

[0067] The preparation method of the polyurethane automotive topcoat of Comparative Example 1 is different from that of Example 2 only in that step (1) is omitted. The modified titanium dioxide of step (6) is modified to titanium dioxide. The remaining steps are the same as those of Example 2.

[0068] Comparative Example 2:

[0069] The preparation method of the polyurethane automotive topcoat of Comparative Example 2 is different from that of Example 2 only in that step (3) is modified to: the aldehyde group-modified cellulose, n-butyric acid, acetic anhydride and a mass fraction of 98% sulfuric acid solution are uniformly mixed in a mass ratio of 1:6.6:2:0.02, 300 mL of zirconium oxide balls are added, and after ball milling at 70°C and 300 r / min for 60 min, the modified cellulose is separated, washed with deionized water 4 times, and dried at 55°C for 12 h. The remaining steps are the same as those of Example 2.

[0070] Comparative Example 3:

[0071] The preparation method of the polyurethane automotive topcoat of Comparative Example 3 is different from that of Example 2 only in that step (3) is modified to: the aldehyde group-modified cellulose, 2-aminopiperazine and a phosphate buffer solution with a pH of 7.2 are uniformly mixed in a mass ratio of 1:1.3:125, and after stirring at 37°C and 150 rpm for 4 h, the modified cellulose is centrifuged, washed with deionized water 4 times, and freeze-dried. The remaining steps are the same as those of Example 2.

[0072] Test Example

[0073] 1. Anti-aging property

[0074] Test method: The polyurethane automotive topcoat obtained in each example and comparative example is tested for gloss loss after polishing according to GB / T1865.

[0075] 2. Quick-drying property

[0076] Test method: The polyurethane automotive topcoat obtained in each example and comparative example is tested for surface dry time by finger touch method and for real dry time by knife method according to GB / T1728.

[0077] 3. Impact resistance

[0078] Test method: The polyurethane automotive topcoat obtained in each example and comparative example is sprayed on a 0.3 mm thick tinplate sample, and a weight of 1000 g is used as a weight to be fixed at a distance of 50 cm from the sliding cylinder using a control device, and the weight is dropped onto the punch in free fall, and the test sample is taken out and observed under a magnifying glass to determine whether there are cracks, wrinkles and peeling, etc.

[0079] The following Table 1 gives the analysis results of the quick-drying property, impact resistance and aging resistance of the polyurethane automobile topcoat prepared by using the examples 1-3 and the comparative examples 1-3 of the present application.

[0080]

[0081] It can be found from the comparison of the experimental data of the examples 1-3 and the comparative examples 1-3 in Table 1 that the polyurethane automobile topcoat prepared by the present application has good quick-drying property, impact resistance and aging resistance.

[0082] The comparative example 1 does not polymerize and coat 3-butene-1,2-diol and 6-bromo-3-(4-bromophenyl)-2,4-dihydro-1,3-benzoxazine on the surface of titanium white; by comparison, the gloss loss rate after polishing, the surface dry time and the real dry time of the examples 1, 2 and 3 are lower than those of the comparative example 1, and there is obvious cracking after impact, which shows that by polymerizing 3-butene-1,2-diol and 6-bromo-3-(4-bromophenyl)-2,4-dihydro-1,3-benzoxazine, benzoxazine ring and carbon-carbon double bond are introduced on the surface of titanium white, benzoxazine can undergo thermal ring-opening polymerization to generate a structure similar to phenolic resin, optimize the crosslinking network, speed up the drying speed, and also can capture free radicals to improve the quick-drying property, impact resistance and aging resistance of the polyurethane automobile topcoat; the carbon-carbon double bond can undergo addition reaction with the silicon-hydrogen bond on the modified acrylic resin to optimize the crosslinking network and further improve the quick-drying property and impact resistance of the polyurethane automobile topcoat.

[0083] The comparative example 2 does not graft 2-aminopiperazine on cellulose; by comparison, the gloss loss rate after polishing, the surface dry time and the real dry time of the examples 1, 2 and 3 are lower than those of the comparative example 2, and there is slight cracking after impact, which shows that by grafting 2-aminopiperazine using Schiff base reaction, piperazine and isocyanate groups in the curing agent undergo amide reaction to generate a structure similar to hindered amine, form a three-dimensional crosslinking network, and also can remove oxidizing free radicals to further improve the quick-drying property, impact resistance and aging resistance of the polyurethane automobile topcoat.

[0084] The comparative example 3 does not graft n-butanoic acid and acetic anhydride on cellulose; by comparison, the surface dry time and the real dry time of the examples 1, 2 and 3 are shorter than those of the comparative example 3, which shows that by grafting n-butanoic acid and acetic anhydride after aldehyde group of cellulose, butyric acid and acetic acid groups are introduced to form hydrogen bonds with solvent molecules in the paint film, promote the release of solvent in the paint film formation process, and improve the quick-drying property of the polyurethane automobile topcoat.

[0085] The above detailed description of the specific embodiments of the present application has been given to understand the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a polyurethane automotive topcoat, characterized in that, The preparation steps include the following: (1) Titanium dioxide, 3-buten-1,2-diol, 6-bromo-3-(4-bromophenyl)-2,4-dihydro-1,3-benzoxazine, anhydrous potassium carbonate and N,N-dimethylformamide were mixed and reacted to obtain modified titanium dioxide; The modified titanium dioxide is prepared by mixing titanium dioxide, 3-butene-1,2-diol, 6-bromo-3-(4-bromophenyl)-2,4-dihydro-1,3-benzoxazine, anhydrous potassium carbonate and N,N-dimethylformamide in a mass ratio of 1:(0.3~0.5):(1.6~1.8):(0.85~0.95):(20~30) and refluxing at 153~155℃ and 100~300rpm for 9~11h to obtain modified titanium dioxide. (2) Microcrystalline cellulose and sodium periodate were reacted to obtain aldehyde-modified cellulose; (3) Aldehyde-modified cellulose, butyric acid, acetic anhydride and sulfuric acid solution are mixed and reacted to obtain pre-modified cellulose; the pre-modified cellulose is reacted with 2-aminopiperazine to obtain modified cellulose; The modified cellulose is prepared by adding aldehyde-modified cellulose, butyric acid and acetic anhydride in a mass ratio of 1:(6.5~6.7):(1~3) to 200~400 mL of zirconium oxide balls, and ball milling the mixture in a 97%~99% sulfuric acid solution at 65~75℃ for 55~65 min to obtain pre-modified cellulose. Pre-modified cellulose and 2-aminopiperazine were mixed at a mass ratio of 1:(1.2~1.4) and reacted in phosphate buffer solution at pH 7.1~7.3 at 36~38℃ for 3~5 h to obtain modified cellulose; (4) React 1,3,5,7-tetramethylcyclotetrasiloxane and vinylpentamethyldisiloxane to obtain a single-end vinyl hydrogen-containing silicone oil; (5) Acrylic acid, methyl acrylate, hydroxypropyl methacrylate, monovinyl hydrogen-containing silicone oil, azobisisobutyric acid, propylene glycol methyl ether acetate and N,N-dimethylethanolamine are mixed and reacted to obtain modified acrylic resin. The modified acrylic resin is prepared by mixing acrylic acid, methyl acrylate, hydroxypropyl methacrylate, monovinyl hydrogen-containing silicone oil, azobisisobutyronitrile and propylene glycol methyl ether acetate in a mass ratio of 1:(0.7~0.8):(1~3):(0.4~0.6):(0.1~0.2):(7~9), reacting at 85~95℃ for 4~8h, cooling to 55~65℃, and adjusting the pH to 7~8 to obtain the modified acrylic resin. (6) The modified acrylic resin, dispersant, wetting agent, modified cellulose, butyl acetate, propylene glycol methyl ether acetate, modified titanium dioxide, leveling agent, curing agent, diluent and chloroplatinic acid are mixed and sprayed to obtain polyurethane automotive topcoat. The preparation process of the polyurethane automotive topcoat is as follows: 90-110 parts by weight of modified acrylic resin, 3-6 parts by dispersant, 3-6 parts by wetting agent, 6-14 parts by modified cellulose, 14-28 parts by butyl acetate, 14-28 parts by propylene glycol methyl ether acetate, and 80-90 parts by modified titanium dioxide are ground and sieved to a thickness of 4-10 μm at 55-65℃ and 15-17 L / min. 3-6 parts by weight of leveling agent, 40-60 parts by curing agent, 5-15 parts by diluent, and 1-3 parts by chloroplatinic acid are added and mixed. The mixture is then sieved to a mesh of 100-200, allowed to stand for 10-20 min, sprayed to a thickness of 40-50 μm, flash-dried at 40-60℃ for 3-5 min, and dried at 70-80℃ for 55-65 min to obtain the polyurethane automotive topcoat.

2. The method for preparing a polyurethane automotive topcoat according to claim 1, characterized in that, The preparation process of aldehyde-modified cellulose in step (2) is as follows: microcrystalline cellulose and sodium periodate are mixed at a mass ratio of 1:(0.9~1.1) and reacted in hydrochloric acid aqueous solution with pH 2~4 at 25~35℃ in the dark for 7~9h to obtain aldehyde-modified cellulose.

3. The method for preparing a polyurethane automotive topcoat according to claim 1, characterized in that, The preparation process of the single-end vinyl hydrogen-containing silicone oil in step (4) is as follows: 1,3,5,7-tetramethylcyclotetrasiloxane, vinylpentamethyldisiloxane and trifluoromethanesulfonic acid are mixed in a mass ratio of 1:(0.3~0.4):(0.01~0.02), reacted at 65~75℃ for 5~7h, the pH is adjusted to 6~7, and distilled at 105~115℃ and 0.1~0.3MPa for 1~2h to obtain the single-end vinyl hydrogen-containing silicone oil.

4. The method for preparing a polyurethane automotive topcoat according to claim 1, characterized in that, The spraying process parameters in step (6) are: spraying temperature 20~30℃, spraying pressure 2~2.5kg / cm. 2 The nozzle diameter of the spray gun is 1.3~1.5mm, and the distance between the spray gun and the nozzle is 15~25cm.

5. The method for preparing a polyurethane automotive topcoat according to claim 1, characterized in that, The diluent in step (6) is obtained by mixing 40-50 parts by weight of butyl acetate, 20-30 parts by weight of xylene, 10-15 parts by weight of propylene glycol methyl ether acetate and 3-5 parts by weight of methyl nylon.

6. A polyurethane automotive topcoat prepared by the method of preparing polyurethane automotive topcoat according to any one of claims 1 to 5.

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