Photopolymerization self-initiated polyimide electrophoretic paint and preparation method thereof

Abstract

The application belongs to the technical field of paint. The application relates to a kind of photo-polymerization self-initiation polyimide electrophoretic paint and a preparation method thereof, which comprises the following raw materials by weight: polyimide solution 25-35 parts; neutralizing agent 0.5-1.0 parts; alcohol or ketone 5.0-10.0 parts; water 70-85 parts; wherein, the polyimide contains a photo-polymerization self-initiation group. The above raw materials are mixed and stirred to prepare paint by paint preparation process, which can effectively solve the problem of corrosion caused by shrinkage and exposure to bottom when existing electrophoretic paint is used to coat complex metal components and is cured by high-temperature baking due to the reduction of resin viscosity, and has great application prospect.

Description

Technical Field

[0001] This invention relates to a photopolymerization self-initiated polyimide electrophoretic paint and its preparation method. This invention belongs to the field of coating technology. Background Technology

[0002] In fields such as automotive manufacturing and precision machinery, complex-shaped metal workpieces (such as automotive parts and mechanical structural components) inevitably develop special structures like sharp edges and corners during the processing and forming process. When these workpieces are coated with traditional electrophoretic coatings, although the coating has good coverage at the edges and corners before curing, the resin viscosity decreases significantly with increasing temperature during the subsequent high-temperature baking and curing stage. Under the influence of surface tension, the coating at the edges shrinks towards the center of the workpiece, resulting in a significant reduction in the film thickness at sharp corners and edges, and even exposure of the substrate. This problem directly leads to the failure of corrosion protection at the edges and corners, making the workpiece prone to rust starting from the edges and corners during use, seriously affecting the product's service life and safety. This has become a core pain point restricting the application of electrophoretic coating technology on complex metal parts.

[0003] To address the issue of poor coverage caused by edge shrinkage, the industry has explored relevant technologies. Conventional methods include optimizing the resin system of electrophoretic coatings by adjusting the curing agent ratio and adding leveling agents to reduce surface tension differences at high temperatures; or improving coating process parameters, such as reducing the baking heating rate and controlling the curing temperature in stages, to delay the flow and shrinkage of the coating. In addition, some solutions attempt to use high-solids coatings to increase the initial viscosity and suppress shrinkage. However, these methods only alleviate the problem to a certain extent and cannot fundamentally prevent the shrinkage behavior caused by the decrease in resin viscosity at high temperatures. Issues such as exposed substrate at edges and uneven film thickness are still difficult to completely avoid. Summary of the Invention

[0004] The purpose of this invention is to address the problem in existing technologies where, during the high-temperature baking and curing of electrophoretic coatings on complex metal components, shrinkage and exposure of the substrate due to reduced resin viscosity lead to corrosion. This invention provides a photopolymerization-initiated polyimide electrophoretic paint and its preparation method. The photopolymerization-initiated polyimide electrophoretic paint used in this invention undergoes pre-crosslinking under light irradiation to fix the coating structure before baking, effectively solving the aforementioned problem. The technical solution adopted by this invention to solve its technical problem is as follows: This invention provides a photopolymerization self-initiated polyimide electrophoretic paint, comprising the following raw materials in parts by weight: 25-35 parts of polyimide solution; Neutralizing agent 0.5-1.0 parts; 5.0-10.0 parts of alcohols or ketones; 70-85 parts water; The polyimide contains photopolymerizable self-initiating groups.

[0005] Furthermore, The preparation method of the polyimide solution is as follows: The entire process is carried out in the dark. S1, 4,4'-dihydroxybenzophenone, paraformaldehyde, and an alkanolamine undergo the Mannich reaction; ready for use. The molar ratio of 4,4'-dihydroxybenzophenone, paraformaldehyde, and alkanolamine is 1:(4.4-4.8):(2.2-2.4). S2, the product of S1 undergoes a nucleophilic substitution reaction with acryloyl chloride; ready for use. The molar ratio of the S1 product to acryloyl chloride is 1:(2.2-2.4). S3, after dissolving polyetherimide ULTEM 1000 in a solvent, it undergoes a ring-opening grafting reaction with a diamine; ready for use. The weight ratio of the polyetherimide ULTEM 1000 to the diamine is (4-6):1; S4, the product of S3 and the product of S2 are subjected to a Maillard addition reaction to obtain the target product; The amount of the S2 product used is equimolar with that of the diamine.

[0006] Furthermore, The alkanolamine is selected from ethanolamine or diethylene glycolamine; and The secondary amine is selected from piperazine, N,N'-dimethylethylenediamine, N,N'-dimethyl-1,3-propanediamine or N,N'-diethylethylenediamine.

[0007] Furthermore, the solvent is a mixture of a water-soluble polar organic solvent and a ketone solvent.

[0008] Furthermore, the neutralizing agent is an organic acid.

[0009] Another object of the present invention is to provide a method for preparing a photopolymerization self-initiated polyimide electrophoretic paint, comprising the following steps: (1) After stirring and mixing the polyimide solution and neutralizing agent, add alcohol or ketone substances dropwise, stir and mix to obtain polyimide electrophoretic paint intermediate; The neutralizing agent is diluted with water to a concentration of 40-60 wt% and then mixed. (2) Mix the polyimide electrophoretic paint intermediate and the remaining water to obtain the polyimide electrophoretic paint.

[0010] Another object of the present invention is to provide the application of the above-mentioned electrophoretic paint in insulated wires, aluminum products or copper products.

[0011] The beneficial effects of this invention are: (1) The present invention provides a photopolymerization self-initiated polyimide electrophoretic paint, wherein the modified polyimide resin has the function of self-initiated photopolymerization, and can be pre-cured and cross-linked to improve the wet film viscosity and ensure the coating effect.

[0012] (2) This invention provides a photopolymerization self-initiated polyimide electrophoretic paint, which contains a modified polyimide resin, specifically polyetherimide as the macromolecular backbone and acryloyloxy, benzophenone, and tertiary amine structures as side chains. First, the polyetherimide backbone structure provides the main performance; second, the acryloyloxy, benzophenone, and tertiary amine structures of the side chains are a combination of hydrogen-abstracting photoinitiators and polymerizable groups, which can perform self-initiated photopolymerization pre-crosslinking; third, the benzophenone and tertiary amine (actually benzoxazine structures) in the side chains can undergo ring-opening reactions during the baking process, which can increase the crosslinking density and thus improve the overall performance of the coating.

[0013] (3) The present invention provides a method for preparing a photopolymerization self-initiated polyimide electrophoretic paint. The polyimide resin is modified with a secondary amine and then neutralized with an organic acid, which can improve the water solubility and storage stability of the resin. Detailed Implementation

[0014] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0015] The purpose of this invention is to address the problem in existing electrophoretic coatings for complex metal components where the resin viscosity decreases during the high-temperature baking and curing stage, leading to edge shrinkage, substrate exposure, and corrosion. To address this, a photopolymerization-initiated polyimide electrophoretic paint has been developed. The approach is as follows: Since traditional electrophoretic paints cannot lock the coating structure before high-temperature curing, this invention uses polyetherimide ULTEM1000 as the macromolecular backbone. Through Mannich reaction, nucleophilic substitution reaction, ring-opening grafting reaction, and Mileck addition reaction, acryloyloxy, benzophenone, and tertiary amine structures are introduced into the side chains, enabling the modified polyimide to simultaneously possess self-initiated photopolymerization capabilities. Pre-crosslinking and shaping under light irradiation increases the wet film viscosity, thus solving the problem of edge shrinkage and substrate exposure. Furthermore, since the benzophenone / tertiary amine structure is designed as a benzoxazine structure, it possesses multiple curing functions. In addition, considering the influence of the water solubility and storage stability of polyimide on electrophoretic performance, ring-opening grafting modification with a diamine and neutralization with an organic acid are performed, while alcohols / ketones are introduced to optimize system compatibility, further improving the physical properties and storage stability of the electrophoretic paint. Examples of the present invention are as follows: This invention provides a photopolymerization self-initiated polyimide electrophoretic paint, comprising the following raw materials in parts by weight: 25-35 parts of polyimide solution; Neutralizing agent 0.5-1.0 parts; 5.0-10.0 parts of alcohols or ketones; 70-85 parts water; The polyimide contains photopolymerizable self-initiating groups.

[0016] The preparation method of the polyimide solution is as follows: The entire process is carried out in the dark. S1. Paraformaldehyde, alkanolamine, and 1,4-dioxane A were added to a reaction vessel and stirred at room temperature for 0.5 h. 4,4'-dihydroxybenzophenone was dissolved in 1,4-dioxane B and added dropwise to the reaction vessel. The mixture was heated under reflux for 8-12 h. After the reaction was completed, the mixture was filtered, and the filtrate was distilled under reduced pressure. The concentrate was dissolved in chloroform. The concentrate was washed three times with 0.1 mol / L NaOH aqueous solution and deionized water, respectively. The oil phase was collected, dried with anhydrous sodium sulfate, filtered, and the filtrate was collected. Chloroform was removed by rotary evaporation, and the concentrate was dried under vacuum at 60 °C for 8 h. The ratio of the amounts of paraformaldehyde, alkanolamine, 1,4-dioxane A, 4,4'-dihydroxybenzophenone, 1,4-dioxane B, chloroform, NaOH aqueous solution, deionized water, and anhydrous sodium sulfate is 0.44-0.48 mol: 0.22-0.24 mol: 200 mL: 0.1 mol: 100 mL: 300 mL: 200 mL: 200 mL: 5.0 g.

[0017] The alcoholamine is selected from ethanolamine or diethylene glycolamine.

[0018] S2: Weigh triethylamine and the product of S1 and add them to dichloromethane A. Dissolve acryloyl chloride in dichloromethane B and add it dropwise to the above reaction solution. Stir in an ice-water bath for 6-10 hours and filter. Wash the filtrate three times each with saturated sodium bicarbonate solution and deionized water. Take the oil phase, add anhydrous sodium sulfate powder, and let it stand overnight. Filter, take the oil phase, concentrate by rotary evaporation, and dry under vacuum at 40°C for 12 hours for later use. The ratio of triethylamine, S1 product, dichloromethane A, acryloyl chloride, dichloromethane B, sodium bicarbonate solution, deionized water, and anhydrous sodium sulfate is: 0.23-0.25 mol : 0.1 mol : 200 mL : 0.22-0.24 mol : 100 mL : 250 mL : 250 mL : 5.0 g.

[0019] Under S3 and N2 protection, add polyetherimide ULTEM1000 to the solvent, heat to 80-90℃ and stir to dissolve; after complete dissolution, add acetophenone solution containing diamine in batches over 2 hours; after the addition is complete, heat to 105-115℃ and stir for 2-3 hours, then set aside for use. The ratio of polyetherimide ULTEM1000, solvent, diamine, and acetophenone is 4-6g:12g:1g:4g; The solvent is a mixture of a water-soluble polar organic solvent and a ketone solvent in a mass ratio of 8 / 1.

[0020] The water-soluble polar organic solvent may include N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone, γ-valerolactone, and sulfolane. The ketone solvent can be phenyl ketone; it can be benzophenone, acetophenone, etc.

[0021] The secondary amine is selected from piperazine, N,N'-dimethylethylenediamine, N,N'-dimethyl-1,3-propanediamine or N,N'-diethylethylenediamine.

[0022] S4. At room temperature, the product of S2 is added to the solution of product S3 and stirred for 24 hours to obtain the target product.

[0023] The amount of the S2 product used is equimolar with that of the diamine.

[0024] In step S3 of the above-mentioned method for preparing polyimide solution in this invention, the diamine is a small molecule with a symmetrical structure, and the two secondary amino groups have the same activity. Theoretically, they can simultaneously carry out ring-opening grafting reactions on polyetherimide ULTEM1000. However, due to the large molecular weight of polyetherimide ULTEM1000, the diamine is a small molecule with a small number of carbon atoms. When one of the secondary amino groups undergoes ring-opening grafting, its diffusion activity is limited by the large molecular chain, which causes the reactivity of the other secondary amino group to decrease instantaneously, resulting in a reaction dominated by one secondary amino group.

[0025] Similarly, in step S4 of this invention, the product of S2 is a small molecule of diacrylate with a symmetrical structure. Its carbon-carbon double bond has the same activity. When one of the carbon-carbon double bonds undergoes a Michael addition reaction with the secondary amino group on the polyetherimide ULTEM1000, its diffusion activity is limited by the macromolecular chain, which causes the reactivity of the other carbon-carbon double bond to decrease instantaneously, forming a situation in which one carbon-carbon double bond participates in the Michael reaction and the other carbon-carbon double bond is exposed.

[0026] In this invention, the polyimide contains photopolymerizable self-initiating groups, and the reaction process is as follows (ethanolamine and piperazine are selected as intermediate raw materials for illustration): The polyimide in this invention, through molecular structure design, contains benzophenone, a tertiary amine (piperazine and oxazine rings), and an acrylate structure as side groups. Since the tertiary amine needs to be neutralized with organic acids to form salts to improve water solubility, the molecular structure design further incorporates a tertiary amine structure (benzoxazine ring) to ensure high self-initiation efficiency. Furthermore, the benzoxazine in this invention undergoes a ring-opening reaction during the electrophoretic paint thermosetting process, improving the density and performance of the paint film.

[0027] The neutralizing agent is an organic acid; it can be lactic acid, acetic acid, or citric acid, etc.

[0028] The alcohols mentioned are benzyl alcohol, 4-methylbenzyl alcohol, 4-methoxybenzyl alcohol, ethylene glycol monophenyl ether, phenoxy-2-ethanol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, propylene glycol methyl ether, isopropanol, n-butanol, or diethylene glycol, etc. The ketone substance is a phenyl ketone; it can be benzophenone, acetophenone, etc.

[0029] Another objective of this invention is to provide a method for preparing a photopolymerization self-initiated polyimide electrophoretic paint, comprising the following steps: (1) After stirring and mixing the polyimide solution and neutralizing agent, add alcohol or ketone substances dropwise, stir and mix to obtain polyimide electrophoretic paint intermediate; The neutralizing agent is diluted with water to a concentration of 40-60 wt% and then mixed. (2) Mix the polyimide electrophoretic paint intermediate and the remaining water to obtain the polyimide electrophoretic paint.

[0030] Another object of the present invention is to provide the application of the above-mentioned electrophoretic paint in insulated wires, aluminum products or copper products.

[0031] To further understand the present invention, the following detailed description of a photopolymerization self-initiated polyimide electrophoretic paint provided by the present invention is provided in conjunction with specific embodiments. The scope of protection of the present invention is not limited by the following embodiments. Example 1

[0032] A photopolymerization self-initiated polyimide electrophoretic paint comprises the following raw materials in parts by weight: 30 parts of polyimide solution; Lactic acid 0.75 parts; 7.0 parts of acetophenone; 78 parts water; The polyimide contains photopolymerizable self-initiating groups.

[0033] The preparation method of the polyimide solution is as follows: The entire process is carried out in the dark. S1, paraformaldehyde, ethanolamine, and 1,4-dioxane A were added to a reaction vessel and stirred at room temperature for 0.5 h. 4,4'-dihydroxybenzophenone was dissolved in 1,4-dioxane B and added dropwise to the reaction vessel. The mixture was heated under reflux for 10 h. After the reaction was complete, the mixture was filtered, and the filtrate was distilled under reduced pressure. The concentrate was dissolved in chloroform. The concentrate was washed three times with 0.1 mol / L NaOH aqueous solution and deionized water, respectively. The oil phase was collected, dried with anhydrous sodium sulfate, filtered, and the filtrate was collected. Chloroform was removed by rotary evaporation, and the concentrate was dried under vacuum at 60 °C for 8 h. The ratio of the amounts of paraformaldehyde, ethanolamine, 1,4-dioxane A, 4,4'-dihydroxybenzophenone, 1,4-dioxane B, chloroform, NaOH aqueous solution, deionized water, and anhydrous sodium sulfate is 0.46 mol: 0.23 mol: 200 mL: 0.1 mol: 100 mL: 300 mL: 200 mL: 200 mL: 5.0 g.

[0034] Its infrared data is as follows: -OH is present; , , : Benzene ring is present; -CN- exists; , -COC- exists; The oxazine ring is present.

[0035] S2: Weigh triethylamine and the product of S1 and add them to dichloromethane A. Dissolve acryloyl chloride in dichloromethane B and add it dropwise to the above reaction solution. Stir in an ice-water bath for 8 hours and filter. Wash the filtrate three times each with saturated sodium bicarbonate solution and deionized water. Take the oil phase, add anhydrous sodium sulfate powder, and let it stand overnight. Filter, take the oil phase, concentrate by rotary evaporation, and dry under vacuum at 40°C for 12 hours for later use. The ratio of triethylamine, S1 product, dichloromethane A, acryloyl chloride, dichloromethane B, sodium bicarbonate solution, deionized water, and anhydrous sodium sulfate is: 0.24 mol: 0.1 mol: 200 mL: 0.23 mol: 100 mL: 250 mL: 250 mL: 5.0 g.

[0036] Its infrared data is as follows: -OH does not exist; , , : Benzene ring is present; -CN- exists; , -COC- exists; The oxazine ring is present. The C=O (ester group) is present; , -C=C-exists.

[0037] Under S3 and N2 protection, polyetherimide ULTEM1000 is added to the solvent, heated to 85°C and stirred to dissolve; after complete dissolution, a piperazine-containing acetophenone solution is added in batches over 2 hours; after the addition is complete, the temperature is raised to 110°C and stirred for 2.5 hours, then it is ready for use. The ratio of polyetherimide ULTEM1000, solvent, piperazine, and acetophenone is 5g:12g:1g:4g; The solvent is a mixture of N-methylpyrrolidone and acetophenone at a mass ratio of 8 / 1.

[0038] Its infrared data is as follows: -NH- exists; , , : Benzene ring is present; , -C=O (imide ring) is present; -CN- (imide ring) is present; -C=O (amide) is present; -NH- (amide) is present.

[0039] S4. At room temperature, the product of S2 is added to the solution of product S3 and stirred for 24 hours to obtain the target product.

[0040] The amount of the S2 product used is equimolar with piperazine.

[0041] Its infrared data is as follows: -NH- is present (weakened); , , : Benzene ring is present; , , -C=O exists; -CN- exists; -NH- (amide) is present; , -COC- exists; The oxazine ring is present. , -C=C- exists and weakens.

[0042] A method for preparing a photopolymerization self-initiated polyimide electrophoretic paint includes the following steps: (1) After stirring and mixing the polyimide solution and neutralizing agent, add alcohol or ketone substances dropwise, stir and mix to obtain polyimide electrophoretic paint intermediate; The neutralizing agent is diluted with water to a concentration of 50 wt% and then mixed. (2) Mix the polyimide electrophoretic paint intermediate and the remaining water to obtain the polyimide electrophoretic paint. Example 2

[0043] A photopolymerization self-initiated polyimide electrophoretic paint comprises the following raw materials in parts by weight: 25 parts of polyimide solution; Acetic acid 0.5 parts; 5.0 parts of acetophenone; 70 parts water; The polyimide contains photopolymerizable self-initiating groups.

[0044] The preparation method of the polyimide solution is as follows: The entire process is carried out in the dark. S1, paraformaldehyde, ethanolamine, and 1,4-dioxane A were added to a reaction vessel and stirred at room temperature for 0.5 h. 4,4'-dihydroxybenzophenone was dissolved in 1,4-dioxane B and added dropwise to the reaction vessel. The mixture was heated under reflux for 12 h. After the reaction was complete, the mixture was filtered, and the filtrate was distilled under reduced pressure. The concentrate was dissolved in chloroform. The concentrate was washed three times with 0.1 mol / L NaOH aqueous solution and deionized water, respectively. The oil phase was collected, dried with anhydrous sodium sulfate, filtered, and the filtrate was collected. Chloroform was removed by rotary evaporation, and the concentrate was dried under vacuum at 60 °C for 8 h. The ratio of the amounts of paraformaldehyde, ethanolamine, 1,4-dioxane A, 4,4'-dihydroxybenzophenone, 1,4-dioxane B, chloroform, NaOH aqueous solution, deionized water, and anhydrous sodium sulfate is 0.44 mol: 0.22 mol: 200 mL: 0.1 mol: 100 mL: 300 mL: 200 mL: 200 mL: 5.0 g.

[0045] S2: Weigh triethylamine and the product of S1 and add them to dichloromethane A. Dissolve acryloyl chloride in dichloromethane B and add it dropwise to the above reaction solution. Stir in an ice-water bath for 8 hours and filter. Wash the filtrate three times each with saturated sodium bicarbonate solution and deionized water. Take the oil phase, add anhydrous sodium sulfate powder, and let it stand overnight. Filter, take the oil phase, concentrate by rotary evaporation, and dry under vacuum at 40°C for 12 hours for later use. The ratio of triethylamine, S1 product, dichloromethane A, acryloyl chloride, dichloromethane B, sodium bicarbonate solution, deionized water, and anhydrous sodium sulfate is: 0.23 mol: 0.1 mol: 200 mL: 0.22 mol: 100 mL: 250 mL: 250 mL: 5.0 g.

[0046] Under S3 and N2 protection, polyetherimide ULTEM1000 is added to the solvent, heated to 80°C and stirred to dissolve; after complete dissolution, an acetophenone solution containing N,N'-diethylethylenediamine is added in batches over 2 hours; after the addition is complete, the temperature is raised to 115°C and stirred for 2 hours, ready for use. The ratio of polyetherimide ULTEM1000, solvent, N,N'-diethylethylenediamine, and acetophenone is 6g:12g:1g:4g; The solvent is a mixture of N-methylpyrrolidone and acetophenone at a mass ratio of 8 / 1.

[0047] S4. At room temperature, the product of S2 is added to the solution of product S3 and stirred for 24 hours to obtain the target product.

[0048] The amount of the S2 product used is equimolar with that of N,N'-diethylethylenediamine.

[0049] A method for preparing a photopolymerization self-initiated polyimide electrophoretic paint includes the following steps: (1) After stirring and mixing the polyimide solution and neutralizing agent, add alcohol or ketone substances dropwise, stir and mix to obtain polyimide electrophoretic paint intermediate; The neutralizing agent is diluted with water to a concentration of 40 wt% and then mixed. (2) Mix the polyimide electrophoretic paint intermediate and the remaining water to obtain the polyimide electrophoretic paint. Example 3

[0050] A photopolymerization self-initiated polyimide electrophoretic paint comprises the following raw materials in parts by weight: 35 parts of polyimide solution; Citric acid 1.0 part; 10.0 parts of acetophenone; 85 parts water; The polyimide contains photopolymerizable self-initiating groups.

[0051] The preparation method of the polyimide solution is as follows: The entire process is carried out in the dark. S1, paraformaldehyde, ethanolamine, and 1,4-dioxane A were added to a reaction vessel and stirred at room temperature for 0.5 h. 4,4'-dihydroxybenzophenone was dissolved in 1,4-dioxane B and added dropwise to the reaction vessel. The mixture was heated under reflux for 8 h. After the reaction was complete, the mixture was filtered, and the filtrate was distilled under reduced pressure. The concentrate was dissolved in chloroform. The concentrate was washed three times with 0.1 mol / L NaOH aqueous solution and deionized water, respectively. The oil phase was collected, dried with anhydrous sodium sulfate, filtered, and the filtrate was collected. Chloroform was removed by rotary evaporation, and the concentrate was dried under vacuum at 60 °C for 8 h. The ratio of the amounts of paraformaldehyde, ethanolamine, 1,4-dioxane A, 4,4'-dihydroxybenzophenone, 1,4-dioxane B, chloroform, NaOH aqueous solution, deionized water, and anhydrous sodium sulfate is 0.48 mol: 0.24 mol: 200 mL: 0.1 mol: 100 mL: 300 mL: 200 mL: 200 mL: 5.0 g.

[0052] S2: Weigh triethylamine and the product of S1 and add them to dichloromethane A. Dissolve acryloyl chloride in dichloromethane B and add it dropwise to the above reaction solution. Stir in an ice-water bath for 12 hours and filter. Wash the filtrate three times each with saturated sodium bicarbonate solution and deionized water. Take the oil phase, add anhydrous sodium sulfate powder, and let it stand overnight. Filter, take the oil phase, concentrate by rotary evaporation, and dry under vacuum at 40°C for 12 hours. Set aside for use. The ratio of triethylamine, S1 product, dichloromethane A, acryloyl chloride, dichloromethane B, sodium bicarbonate solution, deionized water, and anhydrous sodium sulfate is: 0.25 mol: 0.1 mol: 200 mL: 0.24 mol: 100 mL: 250 mL: 250 mL: 5.0 g.

[0053] Under S3 and N2 protection, polyetherimide ULTEM1000 is added to the solvent, heated to 90°C and stirred to dissolve; after complete dissolution, an acetophenone solution containing N,N'-dimethyl-1,3-propanediamine is added in batches over 2 hours; after the addition is complete, the temperature is raised to 105°C and stirred for 3 hours, ready for use. The ratio of polyetherimide ULTEM1000, solvent, N,N'-dimethyl-1,3-propanediamine, and acetophenone is 4g:12g:1g:4g. The solvent is a mixture of N-methylpyrrolidone and acetophenone at a mass ratio of 8 / 1.

[0054] S4. At room temperature, the product of S2 is added to the solution of product S3 and stirred for 24 hours to obtain the target product.

[0055] The amount of the S2 product used is equimolar with that of N,N'-dimethyl-1,3-propanediamine.

[0056] A method for preparing a photopolymerization self-initiated polyimide electrophoretic paint includes the following steps: (1) After stirring and mixing the polyimide solution and neutralizing agent, add alcohol or ketone substances dropwise, stir and mix to obtain polyimide electrophoretic paint intermediate; The neutralizing agent is diluted with water to a concentration of 60 wt% and then mixed. (2) Mix the polyimide electrophoretic paint intermediate and the remaining water to obtain the polyimide electrophoretic paint. Example 4

[0057] Everything else is the same as in Example 1, except that: In the preparation method S1 of the polyimide solution, the alcohol amine is diethylene glycolamine. Example 5

[0058] Everything else is the same as in Example 1, except that: In the preparation method S3 of the polyimide solution, the secondary amine is N,N'-dimethylethylenediamine.

[0059] The following comparative examples are all compared with Example 1: Comparative Example 1 Everything else is the same as in Example 1, except that: A photopolymerizable self-initiated polyimide electrophoretic paint, wherein the polyimide does not contain photopolymerizable self-initiated groups; specifically: the polyimide solution is a polyetherimide ULTEM1000 solution; that is, polyetherimide ULTEM1000 is dissolved in a mixed solvent (N-methylpyrrolidone and acetophenone are mixed at a mass ratio of 8 / 1) to prepare the solution.

[0060] Comparative Example 2 Everything else is the same as in Example 1, except that: A photopolymerizable self-initiated polyimide electrophoretic paint, wherein the polyimide does not contain photopolymerizable self-initiated groups; specifically, the polyimide solution is the product S3 in Example 1.

[0061] Implement Comparative Example 3 Everything else is the same as in Example 1, except that: A photopolymerization self-initiated polyimide electrophoretic paint, wherein the polyimide contains only self-initiating groups; specifically, in step S1 of the preparation method of the polyimide solution, 4,4'-dihydroxybenzophenone is replaced with 4-hydroxybenzophenone.

[0062] Comparative Example 4 Everything else is the same as in Example 1, except that: A photopolymerization self-initiated polyimide electrophoretic paint, wherein the polyimide contains only photopolymerization groups; specifically, in step S4 of the method for preparing the polyimide solution, the product of S2 is replaced with tripropylene glycol diacrylate.

[0063] Comparative Example 5 Everything else is the same as in Example 1, except that: A photopolymerization self-initiated polyimide electrophoretic paint, wherein the preparation method of the S2 product in the preparation step of the polyimide solution is as follows: Weigh triethylamine and 4,4'-dihydroxybenzophenone and add them to dichloromethane A. Dissolve acryloyl chloride in dichloromethane B and add it dropwise to the above reaction solution. Stir in an ice-water bath for 8 hours and filter. Wash the filtrate three times each with saturated sodium bicarbonate solution and deionized water. Take the oil phase, add anhydrous sodium sulfate powder, and let stand overnight. Filter, take the oil phase, concentrate by rotary evaporation, and dry under vacuum at 40°C for 12 hours for later use. The ratio of triethylamine, 4,4'-dihydroxybenzophenone, dichloromethane A, acryloyl chloride, dichloromethane B, sodium bicarbonate solution, deionized water, and anhydrous sodium sulfate is: 0.24 mol: 0.1 mol: 200 mL: 0.23 mol: 100 mL: 250 mL: 250 mL: 5.0 g.

[0064] Comparative Example 6 Everything else is the same as in Example 1, except that: A photopolymerization self-initiated polyimide electrophoretic paint, wherein the preparation method of the S2 product in the preparation step of the polyimide solution is as follows: Weigh triethylamine, 4,4'-dihydroxybenzophenone, and N-methyldiethanolamine and add them to dichloromethane A. Dissolve acryloyl chloride in dichloromethane B and add it dropwise to the above reaction solution. Stir in an ice-water bath for 8 hours and filter. Wash the obtained filtrate three times each with saturated sodium bicarbonate solution and deionized water. Take the oil phase, add anhydrous sodium sulfate powder, and let it stand overnight. Filter, take the oil phase, concentrate by rotary evaporation, and dry under vacuum at 40°C for 12 hours for later use. The ratio of triethylamine, 4,4'-dihydroxybenzophenone, N-methyldiethanolamine, dichloromethane A, acryloyl chloride, dichloromethane B, sodium bicarbonate solution, deionized water, and anhydrous sodium sulfate is: 0.24 mol: 0.05 mol: 0.05 mol: 200 mL: 0.23 mol: 100 mL: 250 mL: 250 mL: 5.0 g.

[0065] The photopolymerization self-initiated polyimide electrophoretic paints prepared in the above embodiments and comparative examples of the present invention were used to prepare electrophoretic paint films (thickness of...) according to the following methods. ): Polyimide electrophoretic paint was electrophoretically deposited on irregularly shaped aluminum parts to obtain a wet film. After drying at 80°C for 30 minutes, UV radiation pre-crosslinking was performed, followed by heat curing to obtain the electrophoretic paint film.

[0066] The electrophoretic deposition was performed at a voltage of 150V for 4 minutes.

[0067] The UV radiation pre-crosslinking: Radiation was applied for 3 minutes.

[0068] The thermosetting process includes drying at 150°C for 30 minutes, followed by heating to 210°C and drying for another 30 minutes.

[0069] The relevant physical properties of the electrophoretic coatings in the above examples and comparative examples were measured respectively, and the results are shown in Table 1.

[0070] Table 1 Physical test performance of each embodiment First, as can be seen from Examples 1-5 in Table 1, the photopolymerization self-initiated polyimide electrophoretic paint of the present invention has excellent coating effect; at the same time, the paint film has excellent physical properties; and the water solubility and storage stability of the electrophoretic paint are OK.

[0071] Secondly, it can be observed from Example 1 and Comparative Example 1 that the unmodified polyimide solution has water solubility issues, leading to subsequent failure to coat properly. From Example 1 and Comparative Example 2, it can be observed that the piperazine-modified polyimide solution, due to the presence of an active secondary amine structure, poses a risk of gelation during heat storage; furthermore, it cannot undergo UV pre-crosslinking, resulting in poor film surface performance and affecting overall performance. From Example 1 and Comparative Examples 3-4, it can be observed that modification with self-initiating and photopolymerizable groups, followed by UV pre-crosslinking treatment, can effectively improve film uniformity and enhance film surface performance. From Example 1 and Comparative Examples 5-6, it can be observed that the introduced tertiary amine structure serves two purposes: firstly, it forms salts with organic acids to improve water solubility; secondly, it serves for the self-initiation of the co-initiator (manifested as reduced initiation efficiency and the presence of orange peel); furthermore, the benzoxazine structure in the self-initiator and photopolymerizable groups can further improve film density (manifested as improved salt water resistance).

[0072] In summary, the photopolymerization self-initiated polyimide electrophoretic paint of the present invention can effectively solve the problem of corrosion caused by shrinkage and exposure of the substrate due to the decrease in resin viscosity after high-temperature baking and curing of complex metal components, and has great application prospects.

[0073] The testing method is as follows: (1) Water solubility: visual inspection. The electrophoretic paint in the above examples and comparative examples is adjusted with water to the same solid content (e.g., 10 wt%), and the appearance of the system is observed. If no precipitation is observed, the water solubility result is recorded as "OK"; if precipitation is observed, the water solubility result is recorded as "NG".

[0074] (2) Storage stability: visual inspection. After the electrophoretic paints in the above examples and comparative examples are placed at 70°C for 7 days, the appearance is observed. If no precipitation occurs, the storage stability result is recorded as "OK"; if layering or precipitation is observed, it is recorded as "NG".

[0075] (3) Film thickness: The film thickness was tested according to the method described in GB / T 13452.2-2008.

[0076] (4) Appearance: Visually inspect the paint film formed on the surface of the irregular aluminum parts and evaluate the appearance of the paint film.

[0077] (5) Adhesion: Tested in accordance with GB / T 1720-2020.

[0078] (6) Salt water resistance: Immerse the coating in 5wt% NaCl solution at 80℃ and allow it to corrode rapidly. Record the time it takes for corrosion spots to appear on the coating surface to evaluate its corrosion resistance.

[0079] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A photopolymerization self-initiated polyimide electrophoretic paint, characterized in that, Including the following parts by weight of raw materials: 25-35 parts of polyimide solution; Neutralizing agent 0.5-1.0 parts; 5.0-10.0 parts of alcohols or ketones; 70-85 parts water; The polyimide contains photopolymerizable self-initiating groups.

2. The photopolymerization self-initiated polyimide electrophoretic paint according to claim 1, characterized in that, The preparation method of the polyimide solution is as follows: The entire process is carried out in the dark. S1, 4,4'-dihydroxybenzophenone, paraformaldehyde, and an alkanolamine undergo the Mannich reaction; ready for use. The molar ratio of 4,4'-dihydroxybenzophenone, paraformaldehyde, and alkanolamine is 1:(4.4-4.8):(2.2-2.4). S2, the product of S1 undergoes a nucleophilic substitution reaction with acryloyl chloride; ready for use. The molar ratio of the S1 product to acryloyl chloride is 1:(2.2-2.4). S3, after dissolving polyetherimide ULTEM 1000 in a solvent, it undergoes a ring-opening grafting reaction with a diamine; ready for use. The weight ratio of the polyetherimide ULTEM 1000 to the diamine is (4-6):1; S4, the product of S3 and the product of S2 are subjected to a Maillard addition reaction to obtain the target product; The amount of the S2 product used is equimolar with that of the diamine.

3. The photopolymerization self-initiated polyimide electrophoretic paint according to claim 2, characterized in that, The alkanolamine is selected from ethanolamine or diethylene glycolamine; and The secondary amine is selected from piperazine, N,N'-dimethylethylenediamine, N,N'-dimethyl-1,3-propanediamine or N,N'-diethylethylenediamine.

4. The photopolymerization self-initiated polyimide electrophoretic paint according to claim 2, characterized in that, The solvent is a mixture of water-soluble polar organic solvent and ketone solvent.

5. The photopolymerization self-initiated polyimide electrophoretic paint according to claim 1, characterized in that, The neutralizing agent is an organic acid.

6. A method for preparing a photopolymerization self-initiated polyimide electrophoretic paint as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) After stirring and mixing the polyimide solution and neutralizing agent, add alcohol or ketone substances dropwise, stir and mix to obtain polyimide electrophoretic paint intermediate; The neutralizing agent is diluted with water to a concentration of 40-60 wt% and then mixed. (2) Mix the polyimide electrophoretic paint intermediate and the remaining water to obtain the polyimide electrophoretic paint.

7. The application of the electrophoretic paint according to any one of claims 1-5 in insulated wires, aluminum products or copper products.

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