A water-based self-crosslinking composition, its preparation method and application

Abstract

This invention relates to an aqueous self-crosslinking composition, its preparation method, and its application, belonging to the technical field of aqueous compositions. The aqueous self-crosslinking composition of this invention comprises blocked isocyanate A, oxazoline polymer B, and water; the blocked isocyanate A contains isocyanate groups with carboxyl groups and terminal isocyanate groups; the oxazoline polymer B contains oxazoline groups and hydroxyl groups; in the solids portion of the aqueous self-crosslinking composition, the concentration of carboxyl groups is 0.2-1.0 mmol / g, the concentration of terminal isocyanate groups is 1.2-2.0 mmol / g, the concentration of oxazoline groups is 0.2-1.2 mmol / g, and the concentration of hydroxyl groups is 1.2-2.8 mmol / g. The aqueous self-crosslinking composition exhibits high crosslinking density after baking, and possesses excellent impact resistance, pencil hardness, MEK abrasion resistance, and adhesion after boiling water, making it highly suitable for use in aqueous single-component baking coatings.

Description

Technical Field

[0001] This invention relates to the field of aqueous composition technology, and in particular to an aqueous self-crosslinking composition, its preparation method, and its application. Background Technology

[0002] In recent years, with the continuous advancement and improvement of environmental regulations, the coatings industry has increasingly restricted the release of volatile organic compounds (VOCs) during coating application, leading to the widespread application of environmentally friendly water-based coatings that use water as a dilution medium. However, coatings prepared from traditional thermoplastic waterborne acrylic and waterborne polyurethane polymers lack crosslinking, resulting in significant differences in water resistance, chemical resistance, gloss, and adhesion compared to solvent-based coatings, thus limiting their further use and promotion. Furthermore, while waterborne two-component polyurethane coatings using hydroxyl-containing waterborne resins and water-dispersible isocyanate crosslinking agents can rival solvent-based coatings in various properties, they also suffer from issues such as low film thickness and short usable time.

[0003] Self-crosslinking aqueous polymers can be stored stably as single components for a long time without any usability issues. Post-film formation self-crosslinking can improve coating performance, thus becoming a research hotspot. CN101959915B reports the preparation of a polyhydroxy compound via levulinic acid and epoxidized vegetable oil, followed by reaction with isocyanates and other raw materials to prepare an aqueous polyurethane dispersion. An acylhydrazine compound capable of self-crosslinking with ketone groups was then added. After drying and forming a film, the polymer undergoes self-crosslinking reactions of ketone and acylhydrazine groups at room temperature. CN101208367B reports a polyurethane dispersion containing end-capped polyisocyanates and hydroxyl groups. Under high-temperature baking, the end-capped polyisocyanates can be decapsulated into free polyisocyanates, which undergo urethane reaction with hydroxyl groups, resulting in a coating with a high-crosslinking density self-crosslinking network. The coating exhibits excellent appearance, hardness, and solvent resistance. However, the above technical solutions still have certain shortcomings, particularly in impact resistance, pencil hardness, MEK abrasion resistance, and adhesion after boiling water treatment, which still do not meet the requirements. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide an aqueous self-crosslinking composition, its preparation method and application, wherein the aqueous self-crosslinking composition has excellent impact resistance, pencil hardness, MEK abrasion resistance and adhesion after boiling water, and is very suitable for use in aqueous single-component baking coatings.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides an aqueous self-crosslinking composition comprising blocked isocyanate A, oxazoline polymer B, and water; wherein the blocked isocyanate A contains isocyanate groups with carboxyl groups and terminal isocyanate groups, the isocyanate groups with carboxyl groups are obtained by reacting the isocyanate groups with a carboxylic acid compound containing hydroxyl or amino groups, and the terminal isocyanate groups are obtained by reacting the isocyanate groups with a blocking agent (it is known to those skilled in the art that the terminal isocyanate groups will deblock and release the original isocyanate groups under high temperature conditions such as baking); in the solids of the aqueous self-crosslinking composition: the concentration of carboxyl groups is 0.2-1.0 mmol / g, the concentration of terminal isocyanate groups is 1.2-2.0 mmol / g, the concentration of oxazoline groups is 0.2-1.2 mmol / g, and the concentration of hydroxyl groups is 1.2-2.8 mmol / g.

[0007] Through repeated research, this invention has discovered that the aqueous self-crosslinking composition of this invention can undergo a dual self-crosslinking reaction under baking conditions: 1) the isocyanate groups released after baking and unsealing of the terminal isocyanate groups in the blocked isocyanate A undergo an amino esterification reaction with the hydroxyl groups in the oxazoline polymer B; 2) the ring-opening reaction between the oxazoline groups in the oxazoline polymer B and the carboxyl groups in the carboxyl-containing isocyanate groups in the blocked isocyanate A. The coating film formed by the aqueous self-crosslinking composition after baking has a high crosslinking density and exhibits excellent impact resistance, pencil hardness, MEK abrasion resistance, and adhesion after boiling water. If the blocked isocyanate A does not contain carboxyl groups (or does not contain isocyanate groups containing carboxyl groups), or if the oxazoline polymer B does not contain oxazoline groups or hydroxyl groups, the effects of this invention cannot be achieved.

[0008] In the solids portion of the aqueous self-crosslinking composition of the present invention, the concentration of carboxyl groups is 0.2-1.0 mmol / g, the concentration of terminal isocyanate groups is 1.2-2.0 mmol / g, the concentration of oxazoline groups is 0.2-1.2 mmol / g, and the concentration of hydroxyl groups is 1.2-2.8 mmol / g. If the concentration of carboxyl groups in the solids portion of the aqueous self-crosslinking composition is too low, the crosslinking between carboxyl and oxazoline groups will decrease, reducing the crosslinking density of the coating film. Furthermore, the hydrophilicity of the aqueous self-crosslinking composition will decrease, leading to poor storage stability in water. Conversely, if the concentration of carboxyl groups in the solids portion of the aqueous self-crosslinking composition is too high, the water solubility of the aqueous self-crosslinking composition will be too strong, resulting in a low solids content. If the concentration of the end-capped isocyanate groups in the solids of the aqueous self-crosslinking composition is too low, the crosslinking between the isocyanate groups released after baking and decapsulation and the hydroxyl groups will be reduced, thus decreasing the crosslinking density of the coating film. If the concentration of the end-capped isocyanate groups in the solids of the aqueous self-crosslinking composition is too high, the concentration of carboxyl groups (or the concentration of isocyanate groups with carboxyl groups) in the blocked isocyanate A will be correspondingly reduced, affecting crosslinking. If the concentration of oxazoline groups in the solids of the aqueous self-crosslinking composition is too low, the crosslinking between the oxazoline groups and carboxyl groups will be reduced, thus decreasing the crosslinking density. If the concentration of oxazoline groups in the solids of the aqueous self-crosslinking composition is too high, the concentration of hydroxyl groups in the oxazoline polymer B will be correspondingly reduced, affecting crosslinking. If the concentration of hydroxyl groups in the solids of the aqueous self-crosslinking composition is too low, the crosslinking between hydroxyl groups and end-capped isocyanate groups will decrease, reducing the crosslinking density. If the concentration of hydroxyl groups in the solids of the aqueous self-crosslinking composition is too high, the concentration of oxazoline groups in oxazoline polymer B will be correspondingly reduced, affecting crosslinking.

[0009] Further, the carboxylic acid compound containing a hydroxyl or amino group is at least one selected from hydroxypentanoic acid, lactic acid, 6-hydroxyhexanoic acid, dimethylolpropionic acid, dimethylolbutyric acid, malic acid, 6-aminohexanoic acid, and ethylenediamine propionic acid. Particularly preferred are at least one selected from hydroxypentanoic acid and dimethylolpropionic acid. The above-mentioned carboxylic acid compound containing a hydroxyl or amino group can react with an isocyanate group to yield a corresponding isocyanate group with a carboxyl group.

[0010] Furthermore, the blocked isocyanate A has an aliphatic diisocyanate monomer unit and / or an aromatic diisocyanate monomer unit.

[0011] As a preferred embodiment of the present invention, the precursor isocyanate compound of the blocked isocyanate A is an aliphatic isocyanate compound or its derivative, and is at least one of hexamethylene diisocyanate, pentamethylene diisocyanate, 4,4-dicyclohexylmethane diisocyanate, norbornene diisocyanate, isophorone diisocyanate, diisocyanate adducts, urea-formate modified compounds, biuret modified compounds, isocyanurate modified compounds, carbodiimide modified compounds, and polyurethane prepolymers. The isocyanate group in the above-mentioned precursor isocyanate can react with a carboxylic acid compound containing a hydroxyl or amino group to obtain the isocyanate group with a carboxyl group, or can be end-capped with a blocking agent to obtain the end-capped isocyanate group.

[0012] Further, the blocking agent in the terminated isocyanate group is a substance containing an active hydrogen atom that can react with the isocyanate group, including at least one of pyrazole compounds, imidazole compounds, ketoxime compounds, and dialkyl malonate. Preferably, it is at least one of pyrazole compounds and ketoxime compounds. Particularly preferred is at least one of 3,5-dimethylpyrazole and methyl ethyl ketone oxime. The above-mentioned blocking agent can end-cap the isocyanate group to obtain the terminated isocyanate group; and the terminated isocyanate group will decapsulate and release the original isocyanate group under high-temperature conditions such as baking.

[0013] Further, the blocked isocyanate A or the aqueous self-crosslinking composition is neutralized by a neutralizing agent, which is at least one of an organic amine neutralizing agent and an inorganic base neutralizing agent, wherein the neutralizing agent has a degree of neutralization of 80-200 mol% relative to the carboxyl group. By using a neutralizing agent to neutralize the blocked isocyanate A or the aqueous self-crosslinking composition, the present invention can improve the storage stability and water resistance of the aqueous self-crosslinking composition. If the neutralizing agent has too low a degree of neutralization relative to the carboxyl group, the storage stability of the aqueous self-crosslinking composition will be reduced. If an organic amine neutralizing agent is used, an excessively high degree of neutralization will result in a high odor; if an inorganic base neutralizing agent is used, an excessively high degree of neutralization will result in poor water resistance. The neutralizing agent has a preferred degree of neutralization of 100-150% relative to the carboxyl group, and the neutralizing agent is preferably an organic amine neutralizing agent, particularly preferably one of N,N-dimethylethanolamine and triethylamine.

[0014] Furthermore, the method for preparing the blocked isocyanate A includes the following steps: adding an organic solvent, a precursor isocyanate compound, a carboxylic acid compound containing hydroxyl or amino groups, and a blocking agent to a first reaction vessel for reaction until the NCO value is detected as 0, and then neutralizing with a neutralizing agent to obtain the blocked isocyanate A.

[0015] In the preparation method of the blocked isocyanate A of the present invention, a portion of the isocyanate group in the precursor isocyanate compound reacts with a carboxylic acid compound containing hydroxyl or amino groups to generate the isocyanate group with a carboxyl group; the remaining portion is end-capped by a blocking agent, i.e., the NCO value is detected as 0. Furthermore, by neutralizing the blocked isocyanate A using a neutralizing agent, the storage stability and water resistance of the aqueous self-crosslinking composition can be improved.

[0016] Further, the monomers of the oxazoline polymer B comprise:

[0017] At least one hydroxyl-containing olefinic unsaturated monomer b;

[0018] At least one olefinic unsaturated monomer c, wherein the olefinic unsaturated monomer c comprises an oxazoline group;

[0019] The hydroxyl-containing olefinic unsaturated monomer b accounts for 45-70 wt% of the total polymer monomers, and the olefinic unsaturated monomer c accounts for 9-34 wt% of the total polymer monomers.

[0020] The oxazoline polymer B is polymerized by means of the hydroxyl-containing olefinic unsaturated monomer b and the olefinic unsaturated monomer c, thereby introducing oxazoline groups and hydroxyl groups.

[0021] Furthermore, the monomers of the oxazoline polymer B further comprise:

[0022] At least one monomer a selected from hydroxyl-free C1-20 alkyl esters of (meth)acrylate and hydroxyl-free C8-20 vinyl aromatic compounds;

[0023] The hydroxyl-containing olefinic unsaturated monomer b accounts for 45-70 wt% of the total amount of monomer a, the hydroxyl-containing olefinic unsaturated monomer b, and the olefinic unsaturated monomer c, and the olefinic unsaturated monomer c accounts for 9-34 wt% of the total amount of monomer a, the hydroxyl-containing olefinic unsaturated monomer b, and the olefinic unsaturated monomer c.

[0024] The oxazoline polymer B of the present invention may or may not contain monomer a, preferably monomer a. The addition of monomer a can reduce costs, and by controlling the content of hydroxyl-containing olefinic unsaturated monomer b to be 45-70 wt% and the content of olefinic unsaturated monomer c to be 9-34 wt%, the crosslinking density of the final coating film can be guaranteed.

[0025] In a preferred embodiment of the present invention, monomer a is at least one selected from methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, sec-butyl methacrylate, 2-ethylhexyl methacrylate, tridecyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, n-dodecyl methacrylate, benzyl methacrylate, styrene, α-methylstyrene, and vinyltoluene. Particularly preferred are at least one selected from methyl methacrylate and ethyl methacrylate.

[0026] In a preferred embodiment of the present invention, the hydroxyl-containing olefinic unsaturated monomer b is at least one selected from 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate. Particularly preferred is at least one selected from 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate.

[0027] As a preferred embodiment of the present invention, the olefinically unsaturated monomer C is 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-vinyl-4-ethyl-2-oxazoline, 2-vinyl-4,4-dimethyl-2-oxazoline, 2-vinyl-5,5-dimethyl-2-oxazoline, 2-vinyl-4,4,5,5-tetramethyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-4-ethyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2-isopropenyl-4,4-dimethyl ...5-ethyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, 2-isopropenyl-5-ethyl- At least one of 5-dimethyl-2-oxazoline and 2-isopropenyl-4,4,5,5-tetramethyl-2-oxazoline. Particularly preferred is at least one of 2-isopropyl-2-oxazoline and 2-vinyl-2-oxazoline.

[0028] Further, the preparation method of the oxazoline polymer B includes the following steps: adding an organic solvent to a second reaction vessel, heating to 60-120°C, and dropwise adding a mixture of the monomers of the oxazoline polymer B and an initiator to polymerize and obtain the oxazoline polymer B. By polymerizing each monomer under the action of an initiator, the obtained oxazoline polymer B contains oxazoline groups and hydroxyl groups.

[0029] Furthermore, the solid content of the aqueous self-crosslinking composition is 30-50 wt%. If the solid content of the aqueous self-crosslinking composition is too high, it may result in a high viscosity; if the solid content of the aqueous self-crosslinking composition is too low, it may result in a low content of the effective components, making construction inconvenient.

[0030] The present invention also provides a method for preparing any of the above-described aqueous self-crosslinking compositions, comprising the following steps: mixing the blocked isocyanate A and the oxazoline polymer B uniformly at 30-50°C, adding water for dispersion, and obtaining the aqueous self-crosslinking composition.

[0031] Furthermore, in the preparation method of the aqueous self-crosslinking composition, after dispersing with water, the method further includes vacuum removal of low-boiling-point organic solvents to obtain the aqueous self-crosslinking composition. By vacuum removal of the low-boiling-point organic solvents carried by the blocked isocyanate A and the oxazoline polymer B, the content of volatile organic compounds (VOCs) in the aqueous self-crosslinking composition can be further reduced.

[0032] The present invention also provides the application of any of the above-described waterborne self-crosslinking compositions in waterborne single-component baking coatings. The waterborne self-crosslinking compositions of the present invention can be used in waterborne single-component baking coatings and exhibit excellent impact resistance, pencil hardness, MEK abrasion resistance, and adhesion after boiling in water. Detailed Implementation

[0033] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0034] The following examples or comparative examples use the following raw materials:

[0035] Blocked isocyanate A:

[0036] (1) Blocked isocyanate A1:

[0037] Blocked isocyanate A1 contains an isocyanate group with a carboxyl group and a capped isocyanate group; wherein the isocyanate group with a carboxyl group is obtained by reacting the isocyanate group with a carboxylic acid compound containing a hydroxyl or amino group, and the capped isocyanate group is obtained by capping the isocyanate group with a blocking agent.

[0038] A method for preparing blocked isocyanate A1 includes the following steps:

[0039] In a four-necked flask, add 478.1 g of acetone, 668.0 g of Wannate HT-100 (HDI trimer, NCO value: 22.0%), and 118.1 g of hydroxypentanoic acid. Purge with nitrogen and heat to 60-65°C, maintaining the temperature for 4 hours. Cool to below 50°C, then add 240.2 g of 3,5-dimethylpyrazole in portions, heating to 60-65°C and maintaining the temperature until the NCO value is zero. Add 89.1 g of N,N-dimethylethanolamine, stir until homogeneous, and cool to obtain blocked isocyanate A1.

[0040] (2) Blocked isocyanate A2:

[0041] Blocked isocyanate A2 contains isocyanate groups with carboxyl groups and capped isocyanate groups; wherein the isocyanate groups with carboxyl groups are obtained by reacting isocyanate groups with carboxylic acid compounds containing hydroxyl or amino groups, and the capped isocyanate groups are obtained by capping isocyanate groups with a blocking agent.

[0042] A method for preparing blocked isocyanate A2 includes the following steps:

[0043] Add 435.8 g of acetone, 668.0 g of Wannate HT-100 (HDI trimer, NCO value: 22.0%), and 53.7 g of dimethylolpropionic acid to a four-necked flask. Purge with nitrogen and heat to 60-65 °C, maintaining the temperature for 4 hours. Cool to below 50 °C, then add 259.5 g of 3,5-dimethylpyrazole in portions, heating to 60-65 °C and maintaining the temperature until the NCO value is zero. Add 35.7 g of N,N-dimethylethanolamine, stir until homogeneous, and cool to obtain blocked isocyanate A2.

[0044] (3) Blocked isocyanate A3:

[0045] Blocked isocyanate A3 contains isocyanate groups with carboxyl groups and capped isocyanate groups; wherein the isocyanate groups with carboxyl groups are obtained by reacting isocyanate groups with carboxylic acid compounds containing hydroxyl or amino groups, and the capped isocyanate groups are obtained by capping isocyanate groups with a blocking agent.

[0046] A method for preparing blocked isocyanate A3 includes the following steps:

[0047] In a four-necked flask, add 490.4 g of acetone, 668.0 g of Wannate HT-100 (HDI trimer, NCO value: 22.0%), and 177.2 g of hydroxypentanoic acid. Purge with nitrogen and heat to 60-65°C, maintaining the temperature for 4 hours. Cool to below 50°C, then add 192.2 g of 3,5-dimethylpyrazole in portions, heating to 60-65°C and maintaining the temperature until the NCO value is zero. Add 107.0 g of N,N-dimethylethanolamine, stir until homogeneous, and cool to obtain blocked isocyanate A3.

[0048] (4) Blocked isocyanate A4:

[0049] Blocked isocyanate A4 contains isocyanate groups with carboxyl groups and capped isocyanate groups; wherein the isocyanate groups with carboxyl groups are obtained by reacting isocyanate groups with carboxylic acid compounds containing hydroxyl or amino groups, and the capped isocyanate groups are obtained by capping isocyanate groups with a blocking agent.

[0050] A method for preparing blocked isocyanate A4 includes the following steps:

[0051] In a four-necked flask, add 468.4 g of acetone, 668.0 g of Wannate HT-100 (HDI trimer, NCO value: 22.0%), and 118.1 g of hydroxypentanoic acid. Purge with nitrogen and heat to 60-65°C, maintaining the temperature for 4 hours. Cool to below 50°C, then add 217.7 g of methyl ethyl ketone oxime in portions, heating to 60-65°C and maintaining the temperature until the NCO value is zero. Add 89.1 g of N,N-dimethylethanolamine, stir until homogeneous, and cool to obtain blocked isocyanate A4.

[0052] Capped isocyanate C:

[0053] (1) Blocked isocyanate C1:

[0054] Blocked isocyanate C1 contains a capped isocyanate group, which is obtained by capping the isocyanate group using a blocking agent. Blocked isocyanate C1 does not contain an isocyanate group with a carboxyl group.

[0055] The method for preparing blocked isocyanate C1 in this embodiment includes the following steps:

[0056] In a four-necked flask, add 482.4 g of acetone, 668.0 g of Wannate HT-100 (HDI trimer, NCO value: 22.0%), and 150.0 g of Ymer N 120 (Pastor, nonionic polyester diol, molecular weight 1000). Purge with nitrogen, heat to 60-65°C, and maintain the reaction temperature for 4 hours. Cool to below 50°C, then add 259.5 g of 3,5-dimethylpyrazole in portions, heat to 60-65°C, and maintain the reaction temperature until the NCO value is zero. Cool to obtain blocked isocyanate C1.

[0057] Oxazoline polymer B:

[0058] (1) Oxazoline polymer B1:

[0059] Oxazoline polymer B1 contains oxazoline and hydroxyl groups.

[0060] The preparation method of oxazoline polymer B1 includes the following steps:

[0061] 70.0 g of propylene glycol methyl ether was added to a four-necked flask, nitrogen gas was introduced, and the temperature was raised to 110 °C. A mixture of 58.0 g of 2-hydroxyethyl acrylate, 20.0 g of methyl methacrylate, 22.0 g of 2-isopropenyl-2-oxazoline, and 5.0 g of tert-butyl peroxide was added dropwise over 3 hours. The mixture was then kept at 110 °C for another 3 hours and cooled to obtain oxazoline polymer B1.

[0062] (2) Oxazoline polymer B2:

[0063] Oxazoline polymer B2 contains oxazoline and hydroxyl groups.

[0064] The preparation method of oxazoline polymer B2 includes the following steps:

[0065] 70.0 g of propylene glycol methyl ether was added to a four-necked flask, nitrogen gas was introduced, and the temperature was raised to 110 °C. A mixture of 70.1 g of 2-hydroxyethyl acrylate, 20.0 g of methyl methacrylate, 9.9 g of 2-isopropenyl-2-oxazoline, and 5.0 g of tert-butyl peroxide was added dropwise over 3 hours. The mixture was then kept at 110 °C for another 3 hours and cooled to obtain oxazoline polymer B2.

[0066] (3) Oxazoline polymer B3:

[0067] Oxazoline polymer B3 contains oxazoline and hydroxyl groups.

[0068] The preparation method of oxazoline polymer B3 includes the following steps:

[0069] 70.0 g of propylene glycol methyl ether was added to a four-necked flask, nitrogen gas was introduced, and the temperature was raised to 110 °C. A mixture of 46.5 g of 2-hydroxyethyl acrylate, 20.0 g of methyl methacrylate, 33.5 g of 2-isopropenyl-2-oxazoline, and 5.0 g of tert-butyl peroxide was added dropwise over 3 hours. The mixture was then kept at 110 °C for another 3 hours and cooled to obtain oxazoline polymer B3.

[0070] (4) Oxazoline polymer B4:

[0071] Oxazoline polymer B4 contains oxazoline and hydroxyl groups.

[0072] The preparation method of oxazoline polymer B4 includes the following steps:

[0073] 70.0 g of propylene glycol methyl ether was added to a four-necked flask, nitrogen gas was introduced, and the temperature was raised to 110 °C. A mixture of 46.5 g of 4-hydroxybutyl acrylate, 20.0 g of ethyl acrylate, 33.5 g of 2-vinyl-2-oxazoline, and 5.0 g of tert-butyl peroxide was added dropwise over 3 hours. The mixture was then kept at 110 °C for another 3 hours and cooled to obtain oxazoline polymer B4.

[0074] Polymer D:

[0075] (1) Polymer D1:

[0076] Polymer D1 contains an oxazoline group but no hydroxyl group.

[0077] The preparation method of polymer D1 includes the following steps:

[0078] Add 70.0 g of propylene glycol methyl ether to a four-necked flask, purge with nitrogen, heat to 110 °C, and dropwise add a mixture of 58.0 g of ethyl acrylate, 20.0 g of methyl methacrylate, 22.0 g of 2-isopropenyl-2-oxazoline, and 5.0 g of tert-butyl peroxide-2-ethylhexanoate. The addition is completed in 3 hours, and then the temperature is maintained at 110 °C for another 3 hours. After cooling, polymer D1, which contains oxazoline groups and does not contain hydroxyl groups, is obtained.

[0079] (2) Polymer D2:

[0080] Polymer D2 contains hydroxyl groups but not oxazoline groups.

[0081] The preparation method of polymer D2 includes the following steps:

[0082] Add 70.0g of propylene glycol methyl ether to a four-necked flask, purge with nitrogen, heat to 110℃, and dropwise add a mixture of 58.0g of 2-hydroxyethyl acrylate, 42.0g of methyl methacrylate, and 5.0g of tert-butyl peroxide-2-ethylhexanoate. The addition is completed in 3 hours, and then the temperature is maintained at 110℃ for another 3 hours. After cooling, polymer D2, which contains hydroxyl groups but does not contain oxazoline groups, is obtained.

[0083] Example 1

[0084] This embodiment provides an aqueous self-crosslinking composition comprising blocked isocyanate A1, oxazoline polymer B1, and deionized water. The specific amounts of each raw material are shown in Table 1.

[0085] The preparation method of the aqueous self-crosslinking composition in this embodiment includes the following steps:

[0086] According to the formulation in Table 1, all raw materials (blocked isocyanate A1 and oxazoline polymer B1) of the waterborne self-crosslinking composition except for deionized water are mixed at 35-45°C for 15 minutes until homogeneous. Deionized water is added according to the formulation in Table 1 under high-speed stirring, and the mixture is stirred for 30 minutes. Then, acetone is removed under vacuum at 40-45°C to obtain the waterborne self-crosslinking composition.

[0087] Example 2

[0088] This embodiment provides an aqueous self-crosslinking composition comprising blocked isocyanate A2, oxazoline polymer B2, and deionized water. The specific amounts of each raw material are shown in Table 1.

[0089] The preparation method of the aqueous self-crosslinking composition in this embodiment includes the following steps:

[0090] According to the formulation in Table 1, all raw materials (blocked isocyanate A2 and oxazoline polymer B2) of the waterborne self-crosslinking composition except for deionized water are mixed at 35-45°C for 15 minutes until homogeneous. Deionized water is added according to the formulation under high-speed stirring, and the mixture is stirred for 30 minutes. Then, acetone is removed under vacuum at 40-45°C to obtain the waterborne self-crosslinking composition.

[0091] Example 3

[0092] This embodiment provides an aqueous self-crosslinking composition comprising blocked isocyanate A3, oxazoline polymer B3, and deionized water. The specific amounts of each raw material are shown in Table 1.

[0093] The preparation method of the aqueous self-crosslinking composition in this embodiment includes the following steps:

[0094] According to the formulation in Table 1, all raw materials (blocked isocyanate A3 and oxazoline polymer B3) of the waterborne self-crosslinking composition except for deionized water are mixed at 35-45°C for 15 minutes until homogeneous. Deionized water is added according to the formulation under high-speed stirring, and the mixture is stirred for 30 minutes. Then, acetone is removed under vacuum at 40-45°C to obtain the waterborne self-crosslinking composition.

[0095] Example 4

[0096] This embodiment provides an aqueous self-crosslinking composition comprising blocked isocyanate A4, oxazoline polymer B4, and deionized water. The specific amounts of each raw material are shown in Table 1.

[0097] The preparation method of the aqueous self-crosslinking composition in this embodiment includes the following steps:

[0098] According to the formulation in Table 1, all raw materials (blocked isocyanate A4 and oxazoline polymer B4) of the waterborne self-crosslinking composition except for deionized water are mixed at 35-45°C for 15 minutes until homogeneous. Deionized water is added according to the formulation under high-speed stirring, and the mixture is stirred for 30 minutes. Then, acetone is removed under vacuum at 40-45°C to obtain the waterborne self-crosslinking composition.

[0099] Example 5

[0100] This embodiment provides an aqueous self-crosslinking composition comprising blocked isocyanate A1, oxazoline polymer B2, and deionized water. The specific amounts of each raw material are shown in Table 1.

[0101] The preparation method of the aqueous self-crosslinking composition in this embodiment includes the following steps:

[0102] According to the formulation in Table 1, all raw materials except deionized water (i.e., blocked isocyanate A1 and oxazoline polymer B2) in the waterborne self-crosslinking composition are mixed at 35-45℃ for 15 minutes until homogeneous. Deionized water is added according to the formulation under high-speed stirring, and the mixture is stirred for 30 minutes. Then, acetone is removed under vacuum at 40-45℃ to obtain the waterborne self-crosslinking composition.

[0103] Comparative Example 1

[0104] This comparative example provides an aqueous self-crosslinking composition comprising blocked isocyanate A1, polymer D1, and deionized water. The specific amounts of each raw material are shown in Table 1.

[0105] The preparation method of the comparative example aqueous self-crosslinking composition includes the following steps:

[0106] According to the formulation in Table 1, all raw materials except deionized water (i.e., blocked isocyanate A1 and polymer D1) in the waterborne self-crosslinking composition are mixed at 35-45℃ for 15 minutes until homogeneous. Deionized water is added according to the formulation under high-speed stirring, and the mixture is stirred for 30 minutes. Then, acetone is removed under vacuum at 40-45℃ to obtain the waterborne self-crosslinking composition.

[0107] Comparative Example 2

[0108] This comparative example provides an aqueous self-crosslinking composition comprising blocked isocyanate A1, polymer D2, and deionized water. The specific amounts of each raw material are shown in Table 1.

[0109] The preparation method of the comparative example aqueous self-crosslinking composition includes the following steps:

[0110] According to the formulation in Table 1, all raw materials except deionized water (i.e., blocked isocyanate A1 and polymer D2) in the waterborne self-crosslinking composition are mixed at 35-45°C for 15 minutes until homogeneous. Deionized water is added according to the formulation under high-speed stirring, and the mixture is stirred for 30 minutes. Then, acetone is removed under vacuum at 40-45°C to obtain the waterborne self-crosslinking composition.

[0111] Comparative Example 3

[0112] This comparative example provides an aqueous self-crosslinking composition comprising blocked isocyanate C1, oxazoline polymer B1, and deionized water. The specific amounts of each raw material are shown in Table 1.

[0113] The preparation method of the comparative example aqueous self-crosslinking composition includes the following steps:

[0114] According to the formulation in Table 1, all raw materials except deionized water (i.e., blocked isocyanate C1 and oxazoline polymer B1) in the waterborne self-crosslinking composition are mixed at 35-45°C for 15 minutes until homogeneous. Deionized water is added according to the formulation under high-speed stirring, and the mixture is stirred for 30 minutes. Then, acetone is removed under vacuum at 40-45°C to obtain the waterborne self-crosslinking composition.

[0115] Table 1 Formulation of aqueous self-crosslinking compositions (parts by weight)

[0116]

[0117] Example 6

[0118] This embodiment provides an application of an aqueous self-crosslinking composition in an aqueous single-component baking coating.

[0119] The aqueous self-crosslinking compositions of Examples 1-5 were used in aqueous single-component baking coatings.

[0120] Performance testing

[0121] The properties of the aqueous self-crosslinking compositions provided in Examples 1-5 and Comparative Examples 1-3 were tested. The procedure is as follows:

[0122] The aqueous compositions provided in Examples 1-5 and Comparative Examples 1-3, as well as the acrylic resin / amino resin mixture (80wt% PA-4842, 20wt% Cymel 325), were formulated into aqueous one-component baking coatings according to the formulations in Table 2, and the relevant properties of the coating films were tested. In the aforementioned acrylic resin / amino resin mixture (80wt% PA-4842, 20wt% Cymel 325), PA-4842 is a secondary dispersion of hydroxyl acrylic acid from Guangzhou Guanzhi New Materials, with a solid content of 43wt% and a hydroxyl content of 3.3%; Cymel 325 is cyanoacrylate, a methyl etherified amino resin containing high imino groups, with a solid content of 80wt%.

[0123] Table 2. Formulations of water-based single-component baking coatings (parts by weight)

[0124]

[0125] Among them, the waterborne self-crosslinking compositions of Examples 1-5 were formulated into waterborne one-component baking coatings 1-5, the waterborne self-crosslinking compositions of Comparative Examples 1-3 were formulated into waterborne one-component baking coatings 6-8, and the waterborne one-component baking coating 9 was formulated into an acrylic resin / amino resin mixture (80wt% PA-4842 + 20wt% Cymel 325).

[0126] The relevant properties of the single-component baked coatings 1-9 formed on tinplate substrates were tested respectively:

[0127] Construction process: Grind the tinplate substrate, spray the coating to a dry film thickness of 20±2um, place at room temperature for 15 minutes after spraying, and then bake at 150℃ for 30 minutes.

[0128] Impact resistance test standard: conducted in accordance with GB / T 1732-2020, positive impact.

[0129] Pencil hardness test standard: conducted according to GB 6739-86, 500g weight.

[0130] MEK wiping resistance test standard: conducted in accordance with GB / T 9286-2021.

[0131] Adhesion test standard after boiling water: After the coating is immersed in boiling water for 2 hours, it is then tested according to GB / T 9286-2021.

[0132] Coating storage stability test standard: The prepared coating is placed in a 50℃ forced-air oven for 14 days and observed for gelation, precipitation or obvious thickening. If there is no gelation, the coating storage stability test is considered to have passed.

[0133] Table 3 Performance test results of water-based single-component baking coatings

[0134]

[0135] Based on the above results, we can conclude that:

[0136] The waterborne single-component baking coatings 1-5 formulated using the waterborne self-crosslinking compositions of Examples 1-5 of the present invention all exhibit excellent impact resistance, pencil hardness, MEK abrasion resistance, adhesion after boiling in water, and good storage stability.

[0137] The waterborne one-component baking coating 6 formulated using the waterborne self-crosslinking composition of Comparative Example 1 has a low crosslinking density because the polymer D1 in the waterborne self-crosslinking composition of Comparative Example 1 does not contain hydroxyl groups and cannot crosslink with the isocyanate groups generated after the end-capped isocyanate groups in the blocked isocyanate A1 are unblocked. As a result, the coating film formed by the waterborne one-component baking coating 6 exhibits poor pencil hardness, MEK abrasion resistance, and adhesion after boiling water.

[0138] The waterborne one-component baking coating 7 formulated using the waterborne self-crosslinking composition of Comparative Example 2 has poor adhesion to MEK abrasion and boiling water because the polymer D2 in the waterborne self-crosslinking composition of Comparative Example 2 does not contain oxazoline groups and cannot crosslink with the carboxyl groups in the blocked isocyanate A1. As a result, the coating film formed by the waterborne one-component baking coating 7 will have residual hydrophilic carboxyl groups and the crosslinking density of the coating film is low.

[0139] The waterborne one-component baking coating 8, prepared using the waterborne self-crosslinking composition of Comparative Example 3, has a low crosslinking density and exhibits poor adhesion after MEK wiping and boiling. This is because the blocked isocyanate C1 in the waterborne self-crosslinking composition of Comparative Example 3 only contains end-capped isocyanate groups and does not contain carboxyl groups (isocyanate groups with carboxyl groups), and therefore cannot crosslink with the oxazoline groups in the oxazoline polymer B1.

[0140] A water-based, one-component baking coating 9, formulated with an acrylic / amino resin mixture (80wt% PA-4842 + 20wt% Cymel 325), resulted in a coating film exhibiting poor impact resistance, MEK wiping resistance, and adhesion after boiling.

[0141] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. An aqueous self-crosslinking composition, characterized in that: The water-based self-crosslinking composition comprises a blocked isocyanate A, an oxazoline polymer B, and water. The blocked isocyanate A contains isocyanate groups with carboxyl groups and blocked isocyanate groups, the isocyanate groups with carboxyl groups are obtained by reacting a carboxylic acid compound containing a hydroxyl group or an amino group with isocyanate groups, and the blocked isocyanate groups are obtained by end-capping reaction of isocyanate groups with a blocking agent; the NCO value of the blocked isocyanate A is 0. The oxazoline polymer B contains oxazoline groups and hydroxyl groups; the polymerized monomers of the oxazoline polymer B comprise: at least one hydroxyl-containing ethylenically unsaturated monomer b; the hydroxyl-containing ethylenically unsaturated monomer b is at least one of 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate; at least one ethylenically unsaturated monomer c containing an oxazoline group; The hydroxyl-containing ethylenically unsaturated monomer b accounts for 45-70 wt% of the total amount of polymerized monomers, and the ethylenically unsaturated monomer c accounts for 9-34 wt% of the total amount of polymerized monomers. In the solid content of the water-based self-crosslinking composition: the concentration of carboxyl groups is 0.2-1.0 mmol / g, the concentration of blocked isocyanate groups is 1.2-2.0 mmol / g, the concentration of oxazoline groups is 0.2-1.2 mmol / g, and the concentration of hydroxyl groups is 1.2-2.8 mmol / g.

2. The water-based self-crosslinking composition according to claim 1, characterized in that: The precursor isocyanate compound of the blocked isocyanate A is an aliphatic isocyanate compound or a derivative thereof, and the derivative is at least one of an addition product of diisocyanate, an allophanate-modified product, a biuret-modified product, an isocyanurate-modified product, a carbodiimide-modified product, and a polyurethane prepolymer; The carboxylic acid compound containing a hydroxyl group or an amino group is at least one of hydroxy-pentanoic acid, lactic acid, 6-hydroxyhexanoic acid, dimethylolpropionic acid, dimethylolbutyric acid, malic acid, and 6-aminohexanoic acid; The blocking agent is a substance containing one active hydrogen capable of reacting with isocyanate groups, and the blocking agent includes at least one of a pyrazole compound, an imidazole compound, a ketoxime compound, and a malonic acid dialkyl ester.

3. The aqueous self-crosslinking composition according to claim 2, characterized in that: The precursor isocyanate compound of the blocked isocyanate A is at least one of hexamethylene diisocyanate, pentamethylene diisocyanate, 4,4-dicyclohexylmethane diisocyanate, norbornane diisocyanate, and isophorone diisocyanate.

4. The aqueous self-crosslinking composition according to claim 1, characterized in that: The blocked isocyanate A or the water-based self-crosslinking composition is subjected to neutralization treatment with a neutralizing agent, and the neutralizing agent is at least one of an organic amine neutralizing agent and an inorganic base neutralizing agent, and the neutralizing degree of the neutralizing agent with respect to carboxyl groups is 80-200 mol%.

5. The aqueous self-crosslinking composition according to claim 1, characterized in that: The preparation method of the blocked isocyanate A comprises the following steps: In a first reaction container, an organic solvent, a precursor isocyanate compound, a carboxylic acid compound containing a hydroxyl group or an amino group, and a blocking agent are added and reacted until the NCO value is 0, and then a neutralizing agent is used for neutralization to obtain the blocked isocyanate A.

6. The aqueous self-crosslinking composition according to claim 1, characterized in that: The polymerized monomers of the oxazoline polymer B further comprise: at least one monomer a selected from the group consisting of C1-20 alkyl (meth)acrylate free of hydroxyl group and C8-20 vinyl aromatic compound free of hydroxyl group; the hydroxyl group-containing ethylenically unsaturated monomer b accounts for 45-70 wt% of the total amount of the monomer a, the hydroxyl group-containing ethylenically unsaturated monomer b and the ethylenically unsaturated monomer c, and the ethylenically unsaturated monomer c accounts for 9-34 wt% of the total amount of the monomer a, the hydroxyl group-containing ethylenically unsaturated monomer b and the ethylenically unsaturated monomer c.

7. The aqueous self-crosslinking composition according to claim 1 or 6, characterized in that: The preparation method of the oxazoline polymer B comprises the following steps: adding an organic solvent in a second reaction container, heating to 60-120℃, dropping the mixture of the polymerized monomers of the oxazoline polymer B and an initiator, and polymerizing to obtain the oxazoline polymer B.

8. The aqueous self-crosslinking composition according to claim 1, characterized in that: The solid content of the water-based self-crosslinking composition is 30-50 wt%.

9. A process for the preparation of an aqueous self-crosslinking composition according to any one of claims 1 to 8, characterized in that: The blocked isocyanate A and the oxazoline polymer B are mixed uniformly at 30-50℃, water is added for dispersion, and the water-based self-crosslinking composition is obtained.

10. The use of the water-based self-crosslinking composition according to any one of claims 1-8 in water-based one-component baking paint.

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