A high-strength aqueous acrylic resin and a method of preparation

Abstract

This invention relates to the field of acrylic resin coating technology, and discloses a high-strength waterborne acrylic resin and its preparation method. The high-strength waterborne acrylic resin of this invention comprises 100 parts by weight of waterborne hydroxyl acrylic resin emulsion, 5-15 parts by weight of 4-carboxybenzoxazine-1,2-propanediol, and 17-23 parts by weight of curing agent, etc. 4-Carboxybenzoxazine-1,2-propanediol contains two hydroxyl groups. During the baking and curing process, it undergoes cross-linking polymerization with the hydroxyl groups of the acrylic resin through a polyisocyanate curing agent, forming a continuous cured cross-linked network. Simultaneously, during the high-temperature heat curing process, benzoxazine itself undergoes a ring-opening cross-linking curing reaction, thereby forming a stable double chemical cross-linked network. This significantly improves the resin's cohesive strength and dimensional stability, significantly enhances pencil hardness and tensile strength, and improves heat resistance, making it well-suited for practical applications in high-strength, high-temperature resistant, high-performance coatings.

Description

Technical Field

[0001] This invention relates to the field of acrylic resin coating technology, specifically to a high-strength waterborne acrylic resin and its preparation method. Background Technology

[0002] Waterborne acrylic resins are low in VOCs, environmentally friendly, have good film-forming properties, high flexibility, and excellent weather resistance. They can be used as wood coatings, floor coatings, and interior and exterior wall coatings, and have wide applications in the construction industry, automobile manufacturing, and industrial corrosion protection. Although acrylic resins have high flexibility, their tensile strength and other mechanical properties are relatively low, and their high-temperature resistance is poor, which limits their practical applications.

[0003] Benzoxazine is a thermosetting resin that undergoes ring-opening cross-linking and curing at high temperatures, exhibiting excellent mechanical strength and heat resistance. It has important applications in materials such as acrylic and epoxy resins. Patent CN108359312B discloses inks prepared from phenolic epoxy resin, UV-curable acrylic resin, and benzoxazine resin, which possess good high-temperature resistance and hardness. However, traditional benzoxazine resins have poor water solubility, making them difficult to apply in water-based acrylic resins. Summary of the Invention

[0004] This invention solves the problem of low strength and heat resistance of acrylic resin.

[0005] The technical solution of this invention is: a high-strength waterborne acrylic resin and its preparation method.

[0006] (1) Add 4-hydroxybenzoic acid, 3-amino-1,2-propanediol and paraformaldehyde to the reaction solvent, stir to carry out the reaction, remove the solvent by vacuum distillation, wash the product with petroleum ether, dry it and add it to water, heat to evaporate, cool to crystallize, and obtain 4-carboxybenzoxazine-1,2-propanediol.

[0007] (2) Add 4-carboxybenzoxazine-1,2-propanediol, defoamer, and leveling agent to the waterborne hydroxy acrylic resin emulsion, stir and disperse, and finally add a diluent solution containing polyisocyanate curing agent, stir and mix well to obtain high-strength waterborne acrylic resin.

[0008] Furthermore, in (1), the amount of 4-hydroxybenzoic acid is 100 parts by weight, 3-amino-1,2-propanediol is 66-72 parts by weight, and paraformaldehyde is 46-52 parts by weight.

[0009] Furthermore, in (1), the reaction temperature is 80-100℃ and the reaction time is 10-16h.

[0010] Furthermore, (2) the amount of waterborne hydroxyl acrylic resin emulsion is 100 parts by weight, 4-carboxybenzoxazine-1,2-propanediol is 5-15 parts by weight, defoamer is 0.2-0.4 parts by weight, leveling agent is 0.1-0.25 parts by weight, curing agent is 17-23 parts by weight, and diluent is 8-10 parts by weight.

[0011] Furthermore, (2) contains a polyisocyanate curing agent.

[0012] Furthermore, the diluents in (2) include propylene glycol methyl ether acetate and N-methylpyrrolidone.

[0013] Furthermore, the reaction solvents in (1) include toluene and 14-dioxane.

[0014] Furthermore, the curing method for high-strength waterborne acrylic resin is as follows: spray the high-strength waterborne acrylic resin onto the substrate surface, bake it at 70-85℃ for 30-40 minutes, then cure it at 130-140℃ for 4-5 hours, and finally heat-cure it at 170-180℃ for 3-4 hours.

[0015] The beneficial technical effects of this invention are as follows: This invention combines waterborne hydroxyl acrylic resin emulsion, 4-carboxybenzoxazine-1,2-propanediol, polyisocyanate curing agent, etc., to obtain a high-strength waterborne acrylic resin. 4-Carboxybenzoxazine-1,2-propanediol contains hydrophilic carboxyl groups and multiple hydroxyl groups. When added to the waterborne acrylic resin, it exhibits excellent water solubility and dispersibility, produces no precipitates, and does not affect the storage stability and mechanical properties of the waterborne acrylic resin.

[0016] The 4-carboxybenzoxazine-1,2-propanediol of this invention contains two hydroxyl groups. During the baking and curing process, it undergoes cross-linking polymerization with the hydroxyl groups of the acrylic resin through a polyisocyanate curing agent to form a continuous cured cross-linking network. At the same time, benzoxazine itself undergoes a ring-opening cross-linking curing reaction during the high-temperature thermosetting process, thereby forming a stable double chemical cross-linking network, which significantly improves the cohesiveness and dimensional stability of the resin, and significantly improves the pencil hardness and tensile strength.

[0017] The benzoxazine of the present invention has excellent high temperature resistance. The chemical crosslinking introduced into the molecular chain of acrylic resin significantly improves the initial thermal decomposition temperature and heat resistance of the paint film, and has good practical applications in high-strength, high-temperature resistant high-performance coatings. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0019] Example 1:

[0020] (1) Add 10g of 4-hydroxybenzoic acid, 6.6g of 3-amino-1,2-propanediol, and 5.2g of paraformaldehyde to 100mL of toluene. Heat to 100℃, stir, reflux for 12h, remove solvent by vacuum distillation, wash the product with petroleum ether, dry, add to water, heat to evaporate, cool to crystallize, and obtain 4-carboxybenzoxazine-1,2-propanediol with a yield of 12.8g. The reaction formula is:

[0021] .

[0022] (2) Add 10g of 4-carboxybenzoxazine-1,2-propanediol, 0.7g of defoamer (Haimingside Qian DAPROAP7010, the same below) and 0.2g of leveling agent (BYK348, the same below) to 200g of waterborne hydroxyl acrylic resin emulsion (model Changzhou Jien New Material JE-6190, solid content about 45%), stir and disperse, and finally add N-methylpyrrolidone (16mL) solution containing 34g of polyisocyanate curing agent (model Suzhou Xinshengwang Plastic Basonat HW 2100 CN, the same below), stir and mix well to obtain high-strength waterborne acrylic resin, spray it on the surface of the substrate, bake it at 75℃ for 40min, then cure it at 140℃ for 4h, and finally heat cure it at 175℃ for 3h to make a high-strength acrylic resin paint film.

[0023] Example 2:

[0024] (1) Add 10g of 4-hydroxybenzoic acid, 7.2g of 3-amino-1,2-propanediol and 4.8g of paraformaldehyde to 120mL of toluene, heat to 100℃, stir and reflux for 10h, remove solvent by vacuum distillation, wash product with petroleum ether, dry and add to water, heat to evaporate, cool and crystallize to obtain 4-carboxybenzoxazine-1,2-propanediol, yield 9.6g.

[0025] (2) Add 20g of 4-carboxybenzoxazine-1,2-propanediol, 0.4g of defoamer and 0.5g of leveling agent to 200g of waterborne hydroxy acrylic resin emulsion, stir and disperse, and finally add propylene glycol methyl ether acetate (21mL) solution containing 42g of polyisocyanate curing agent, stir and mix well to obtain high-strength waterborne acrylic resin, spray it on the surface of the substrate, bake it at 70℃ for 40min, then cure it at 130℃ for 5h, and finally heat cure it at 180℃ for 3h to make a high-strength acrylic resin paint film.

[0026] Example 3:

[0027] (1) Add 10g of 4-hydroxybenzoic acid, 6.9g of 3-amino-1,2-propanediol and 4.6g of paraformaldehyde to 120mL of 14-dioxane, heat to 80℃, stir and react for 16h, remove the solvent by vacuum distillation, wash the product with petroleum ether, dry it and add it to water, heat to evaporate, cool and crystallize to obtain 4-carboxybenzoxazine-1,2-propanediol, yield 11.5g.

[0028] (2) Add 30g of 4-carboxybenzoxazine-1,2-propanediol, 0.8g of defoamer and 0.2g of leveling agent to 200g of waterborne hydroxy acrylic resin emulsion, stir and disperse, and finally add N-methylpyrrolidone (16mL) solution containing 46g of polyisocyanate curing agent, stir and mix well to obtain high-strength waterborne acrylic resin, spray it on the surface of the substrate, bake it at 85℃ for 30min, then cure it at 130℃ for 5h, and finally heat cure it at 170℃ for 4h to make a high-strength acrylic resin paint film.

[0029] Comparative Example 1:

[0030] (1) Add 0.7g of defoamer and 0.2g of leveling agent to 200g of waterborne hydroxyl acrylic resin emulsion, stir and disperse, and finally add N-methylpyrrolidone (16mL) solution containing 34g of polyisocyanate curing agent, stir and mix well to obtain waterborne acrylic resin, spray it on the surface of the substrate, bake at 75℃ for 40min, then cure at 140℃ for 4h, and finally heat cure at 175℃ for 3h to make a high-temperature acrylic resin paint film.

[0031] Comparative Example 2:

[0032] (1) Add 10g of 4-hydroxybenzoic acid, 3.5g of n-butylamine, and 5.2g of paraformaldehyde to 100mL of toluene. Heat to 100℃, stir, reflux for 12h, remove solvent by vacuum distillation, wash the product with petroleum ether, dry, add to water, heat to evaporate, cool to crystallize, and obtain 4-carboxybenzoxazine-1-butane with the structural formula: .

[0033] (2) Add 10g of 4-carboxybenzoxazine-1-butane, 0.7g of defoamer and 0.2g of leveling agent to 200g of waterborne hydroxy acrylic resin emulsion, stir and disperse, and finally add N-methylpyrrolidone (16mL) solution containing 34g of polyisocyanate curing agent, stir and mix well to obtain waterborne acrylic resin, spray it on the surface of the substrate, bake it at 75℃ for 40min, then cure it at 140℃ for 4h, and finally heat cure it at 175℃ for 3h to make an acrylic resin paint film.

[0034] Comparative Example 3:

[0035] (1) Add 6.8 g phenol, 6.6 g 3-amino-1,2-propanediol, and 5.2 g paraformaldehyde to 100 mL toluene. Heat to 100 °C, stir, reflux for 12 h, remove solvent by vacuum distillation, wash product with petroleum ether, dry, add to water, heat to evaporate, cool to crystallize, and obtain benzoxazine-1,2-propanediol with the structural formula: .

[0036] (2) Add 10g of benzoxazine-1,2-propanediol, 0.7g of defoamer and 0.2g of leveling agent to 200g of waterborne hydroxyl acrylic resin emulsion, stir and disperse, and finally add N-methylpyrrolidone (16mL) solution containing 34g of polyisocyanate curing agent, stir and mix well to obtain waterborne acrylic resin, spray it on the surface of the substrate, bake it at 75℃ for 40min, then cure it at 140℃ for 4h, and finally heat cure it at 175℃ for 3h to make an acrylic resin paint film.

[0037] Comparative Example 4:

[0038] (1) Add 10g of 4-hydroxybenzoic acid, 4.4g of ethanolamine, and 5.2g of paraformaldehyde to 100mL of toluene, heat to 100℃, stir and reflux for 12h, remove the solvent by vacuum distillation, wash the product with petroleum ether, dry it, add it to water, heat to evaporate, cool and crystallize to obtain 4-carboxybenzoxazine-1-ethanol, with the structural formula: .

[0039] (2) Add 10g of 4-carboxybenzoxazine-1-ethanol, 0.7g of defoamer and 0.2g of leveling agent to 200g of waterborne hydroxy acrylic resin emulsion, stir and disperse, and finally add N-methylpyrrolidone (16mL) solution containing 34g of polyisocyanate curing agent, stir and mix well to obtain waterborne acrylic resin, spray it on the surface of the substrate, bake it at 75℃ for 40min, then cure it at 140℃ for 4h, and finally heat cure it at 175℃ for 3h to make an acrylic resin paint film.

[0040] The water-based acrylic resin was left at room temperature for 30 days to observe its storage stability. The pencil hardness of the paint film was tested according to GB / T6739-2022 standard.

[0041] The thermal properties of the paint film were tested using a thermogravimetric analyzer in a nitrogen atmosphere at a heating rate of 5°C / min.

[0042] Acrylic resin is cast into a mold, baked and cured, and then heat-cured to form a casting sample. The tensile strength is tested according to GB / T2567-2021.

[0043] Table 1: Properties of acrylic resins

[0044] Storage stability Pencil hardness Tensile strength (MPa) Initial thermal decomposition temperature (°C) Example 1 No sediment 4H 7.62 294.1 Example 2 No sediment 5H 9.24 301.9 Example 3 No sediment 5H 7.38 307.6 Comparative Example 1 No sediment 2H 4.83 275.0 Comparative Example 2 There is obvious sediment. 2H 5.27 286.1 Comparative Example 3 There is a small amount of sediment. 3H 7.16 292.5 Comparative Example 4 There is a small amount of sediment. 3H 6.49 291.4

[0045] The waterborne acrylic resin in Comparative Example 1 exhibited low pencil hardness and tensile strength, a low initial (5% mass loss) thermal decomposition temperature, and poor mechanical strength and heat resistance. In Examples 1-3, 4-carboxybenzoxazine-1,2-propanediol was added to the waterborne acrylic resin. Containing hydrophilic carboxyl groups and multiple hydroxyl groups, it exhibits excellent water solubility and dispersibility, produces no precipitates, and does not affect the storage stability or mechanical properties of the waterborne acrylic resin. Furthermore, containing two hydroxyl groups, it undergoes cross-linking polymerization with the hydroxyl groups of the acrylic resin during baking and curing via a polyisocyanate curing agent, forming a continuous cured cross-linked network. Simultaneously, benzoxazine itself undergoes a ring-opening cross-linking curing reaction during high-temperature thermal curing, thus forming a stable double chemical cross-linked network. This significantly improves the resin's cohesiveness and dimensional stability, resulting in a marked increase in pencil hardness and tensile strength. Benzoxazine also demonstrates excellent high-temperature resistance. The introduction of chemical cross-linking into the molecular chain of the acrylic resin significantly improves the initial thermal decomposition temperature and heat resistance of the coating film.

[0046] Compared with Example 1, the 4-carboxybenzoxazine-1-butane in Comparative Example 2 does not contain dihydroxyl groups, has poor water solubility, and is prone to producing precipitates in water-based acrylic resins, which affects its storage stability and mechanical properties. Furthermore, it cannot undergo cross-linking reaction with hydroxyl acrylic resins through isocyanate curing agents, resulting in lower pencil hardness, tensile strength, and initial thermal decomposition temperature of the cured paint film, as well as poor mechanical strength and heat resistance.

[0047] The benzoxazine-1,2-propanediol of Comparative Example 3 has the following structural formula: It does not contain carboxyl groups and has poor water solubility, which will affect the storage stability and mechanical properties of waterborne acrylic resins. The pencil hardness and tensile strength of the cured paint film are lower than those in Example 1.

[0048] The 4-carboxybenzoxazine-1-ethanol in Comparative Example 4 contains only one hydroxyl group, which has poor water solubility and will affect the storage stability and mechanical properties of the waterborne acrylic resin. In addition, since it contains only one hydroxyl group, it can only react with the hydroxyl group of the acrylic resin through isocyanate curing agent, making it difficult to form a continuous curing crosslinking network. As a result, the pencil hardness and tensile strength of the cured paint film are lower than those in Example 1.

[0049] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A high-strength aqueous acrylic resin, characterized by, The high-strength waterborne acrylic resin comprises 100 parts by weight of waterborne hydroxyl acrylic resin emulsion, 5-15 parts by weight of 4-carboxybenzoxazine-1,2-propanediol, 0.2-0.4 parts by weight of defoamer, 0.1-0.25 parts by weight of leveling agent, 17-23 parts by weight of curing agent, and 8-10 parts by weight of diluent. The structural formula of the 4-carboxybenzoxazine-1,2-propanediol is: ; The curing agent is a polyisocyanate curing agent.

2. The high-strength waterborne acrylic resin according to claim 1, characterized in that, The diluents include propylene glycol methyl ether acetate and N-methylpyrrolidone.

3. The high-strength waterborne acrylic resin according to claim 1, characterized in that, The 4-carboxybenzoxazine-1,2-propanediol was prepared as follows: 4-hydroxybenzoic acid, 3-amino-1,2-propanediol, and paraformaldehyde were added to the reaction solvent, and the mixture was stirred to carry out the reaction. The solvent was removed by vacuum distillation, the product was washed with petroleum ether, dried, added to water, heated to evaporate, and cooled to crystallize, thereby obtaining 4-carboxybenzoxazine-1,2-propanediol.

4. The high-strength waterborne acrylic resin according to claim 3, characterized in that, The reaction solvents include toluene and 14-dioxane.

5. The high-strength waterborne acrylic resin according to claim 3, characterized in that, The amount of 4-hydroxybenzoic acid is 100 parts by weight, 3-amino-1,2-propanediol is 66-72 parts by weight, and paraformaldehyde is 46-52 parts by weight.

6. The high-strength waterborne acrylic resin according to claim 3, characterized in that, The reaction temperature is 80-100℃, and the reaction time is 10-16h.

7. A method for preparing a high-strength waterborne acrylic resin as described in any one of claims 1-6, characterized in that, The preparation method includes: adding 4-carboxybenzoxazine-1,2-propanediol, defoamer, and leveling agent to an aqueous hydroxy acrylic resin emulsion, stirring and dispersing, and finally adding a diluent solution containing a polyisocyanate curing agent, stirring and mixing to obtain a high-strength aqueous acrylic resin.

8. A curing method for the high-strength waterborne acrylic resin obtained by the preparation method as described in claim 7, characterized in that, The curing method is as follows: high-strength water-based acrylic resin is sprayed onto the surface of the substrate, baked at 70-85℃ for 30-40 minutes, cured at 130-140℃ for 4-5 hours, and finally heat-cured at 170-180℃ for 3-4 hours.

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