A pyrolysis-resistant electrophoretic paint and a method of making the same

Abstract

The application discloses a heat-resistant electrophoretic paint, which comprises the following components in percentage by weight: 12.0%-16.0% of epoxy resin, 1.6%-2.4% of bismaleimide, 2.6%-4.8% of polyether amine, 2.0%-2.5% of small-molecule amine, 10.0%-12.0% of polyurethane crosslinking agent, 0.4%-0.6% of organic acid, 3.0%-5.0% of solvent and 62.0%-66.0% of pure water. The bismaleimide is chain-extended through Michael addition reaction by reacting with the polyether amine, so that a toughened BMI resin is obtained. The excess polyether amine brings primary amine and secondary amine, which can further react with the epoxy resin, so that the bismaleimide is successfully introduced into the structure of the epoxy resin. Therefore, the bismaleimide-modified epoxy resin and the cathode electrophoretic paint prepared by further processing the bismaleimide-modified epoxy resin have good heat-resistant performance.

Description

Technical Field

[0001] This invention relates to the field of electrophoretic coating technology, specifically to a pyrolysis-resistant electrophoretic coating and its preparation method. Background Technology

[0002] Electrophoretic coatings, as a new type of low-pollution, energy-saving, resource-saving, protective, and corrosion-resistant coating, feature smooth film, good water and chemical resistance, and are easily mechanized and automated in the coating industry. They are suitable for coating complex-shaped workpieces with edges, corners, and cavities, and are widely used in the coating of hardware parts in automobiles, construction machinery, electromechanical products, and home appliances. Currently, the most widely used electrophoretic coatings are epoxy cathodic electrophoretic coatings and acrylic cathodic electrophoretic coatings. However, epoxy resins begin to undergo thermal oxidative decomposition at 180℃ in the presence of oxygen, and the performance of acrylic coatings deteriorates significantly above 150℃. Therefore, these limitations restrict the application of electrophoretic coatings in high-temperature thermal fields.

[0003] Bismaleimide (BMI) possesses excellent heat resistance in its cured form due to the presence of benzene rings, imide heterocycles, and a high crosslinking density. Its heat resistance (Tg) is generally greater than 250℃, decomposition temperature is >420℃, and long-term service temperature is around 260-270℃. BMI is widely used in aerospace, machinery, and electronics industries as a resin matrix for advanced composite materials, a high-temperature insulating material, and an adhesive due to its excellent high-temperature resistance, radiation resistance, resistance to damp heat, low moisture absorption, and low coefficient of thermal expansion. However, the high rigidity of the bismaleimide resin molecular chain leads to poor impact resistance, low elongation at break, and low fracture toughness. Furthermore, the lack of directly reactive groups between BMI and epoxy resins limits its application in the epoxy resin field. Summary of the Invention

[0004] The purpose of this invention is to provide a pyrolytic electrophoretic coating and its preparation method, thereby solving one or more of the problems in the prior art.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] A water-soluble, electrodepositable cathodic electrophoretic coating was prepared using epoxy resin, polyurethane, and bismaleimide as raw materials, small molecule amines and polyether amines as chain extenders, and organic acids as neutralizing agents.

[0007] On one hand, the present invention provides a pyrolysis-resistant electrophoretic coating comprising the following components by weight percentage:

[0008]

[0009] In some embodiments, the epoxy resin is selected from one or a mixture of more than one of glycidyl ether bisphenol A type, bisphenol F type epoxy resin, glycidyl ester epoxy resin, aliphatic epoxy resin, and alicyclic epoxy resin. The molecular weight is preferably between 500 and 200.

[0010] In some embodiments, the bismaleimide is selected from one or a mixture of more than one of N,N'-(4,4'-methylenediphenyl)bismaleimide, N,N'-m-phenylenebismaleimide, N,N'-(4-methyl-1,3-phenylene)-bismaleimide, aliphatic bismaleimide of 2,2,4-trimethyl-1,6-hexanediamine, and 2,2-bis[4-(4-cis-butenediimidephenoxy)phenyl]propane.

[0011] In some embodiments, the polyetheramine contains repeating propylene oxide units on its main chain, and the polyetheramine is selected from one or a mixture of more than one of D-230, D-400, D2000, T-403, and T-5000.

[0012] In some embodiments, the small molecule amine is selected from one or more of diethanolamine, diisopropanolamine, N-methylethanolamine, diethylenetriamine, and ketoimines of diethylenetriamine.

[0013] In some embodiments, the polyurethane crosslinking agent is a fully blocked polyisocyanate; the polyisocyanate includes, but is not limited to, aliphatic diisocyanates and aromatic diisocyanates; the aliphatic diisocyanate includes hexamethylene diisocyanate or isophorone diisocyanate, and the aromatic diisocyanate includes toluene diisocyanate or 4,4′-diphenylmethane diisocyanate; the blocking agent includes small molecule alcohols, alcohol ether solvents, or methyl ethyl ketone oxime blocking agents, the small molecule alcohols include n-butanol, methanol, or propylene glycol; the alcohol ether solvents include ethylene glycol butyl ether, diethylene glycol butyl ether, or propylene glycol methyl ether.

[0014] In some embodiments, the organic acid is selected from one or more of formic acid, acetic acid, and lactic acid.

[0015] In some embodiments, the solvent refers to all solvents in the emulsion, including N-methylpyrrolidone and ethylene glycol butyl ether.

[0016] On the other hand, the method for producing a pyrolytic electrophoretic coating provided by the present invention includes the following steps:

[0017] Step (1): Preparation of amine-terminated bismaleimide: Using bismaleimide as raw material, it is dissolved in N-methylpyrrolidone, and one or more polyetheramines are added; the primary amine group undergoes a Michael addition reaction with the unsaturated double bond, which extends and toughens the bismaleimide chain; the molar ratio of polyetheramine to bismaleimide is 2.0-1.0:1.0, and finally the polyetheramine is used for end capping;

[0018] Step (2): After the epoxy resin and the small molecule amine react at 80-100℃ for 2 hours, the above-mentioned terminal amine maleimide is added for further amination reaction to obtain bismaleimide modified epoxy resin polymer.

[0019] Step (3): Use a blocking agent to block polyisocyanate to prepare a fully blocked polyurethane crosslinking agent, then blend it with the above-mentioned bismaleimide modified epoxy resin polymer, add organic acid to neutralize to obtain a protonable resin, add water to emulsify to form a water-soluble electrodeposition cathodic electrophoretic coating.

[0020] The reaction equations for steps (1) and (2) above are as follows:

[0021]

[0022] The present invention significantly improves the pyrolysis resistance and corrosion resistance of the electrophoretic coating by modifying epoxy resin with bismaleimide, and has good long-term stability.

[0023] In some implementations, step (2) specifically includes:

[0024] After dissolving the epoxy resin in ethylene glycol butyl ether, the temperature was raised to 80°C; a small molecule amine was added dropwise and reacted at 80-100°C for 2 hours; the above-mentioned terminal amine maleimide was added, and the temperature was further raised to 100-110°C and held for 2 hours to obtain a bismaleimide modified epoxy resin polymer.

[0025] In some implementations, step (3) specifically includes:

[0026] A fully enclosed polyurethane crosslinking agent is added to the above-mentioned bismaleimide modified epoxy resin polymer, and the mixture is blended at 80-90℃ for more than 30 minutes. An organic acid is added for neutralization, and after stirring for 30 minutes, pure water is added for emulsification to obtain the pyrolysis-resistant electrophoretic coating.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] This invention utilizes the reaction between polyetheramine and bismaleimide, followed by Michael addition reaction to extend the chain of bismaleimide, resulting in a toughened BMI resin. Excess polyetheramine introduces primary and secondary amines, which can further react with epoxy resin, successfully incorporating bismaleimide into the epoxy resin's three-dimensional structure. Therefore, the bismaleimide-modified epoxy resin, further used to prepare cathodic electrophoretic coatings, exhibits excellent pyrolysis resistance, making it particularly suitable for applications requiring heat resistance, such as new energy battery packs, high-power semiconductors, and heat sinks. Detailed Implementation

[0029] The technical solution of the present invention will be described in detail below with reference to various embodiments.

[0030] Example 1

[0031] Synthesis of terminal amino group bismaleimide A1:

[0032] Using N,N'-(4,4'-methylenediphenyl)bismaleimide (MBMI) as a starting material, dissolved in N-methylpyrrolidone (NMP), and then polyetheramine D-230 was added, resulting in Michael addition. This led to chain extension of the bismaleimide, ultimately ending with primary amine groups. The molar ratio of polyetheramine D-230 to BMI was 1.2:1, and the reaction was carried out at a relatively low temperature.

[0033] Example 2

[0034] Synthesis of terminal amino group bismaleimide A2:

[0035] Using N,N'-(4,4'-methylenediphenyl)bismaleimide (MBMI) as a starting material, dissolved in N-methylpyrrolidone (NMP), polyetheramine D-400 was added, resulting in Michael addition, chain extension of the bismaleimide, and final capping with primary amine groups. The molar ratio of polyetheramine D-400 to BMI was 1.6:1, and the reaction was carried out at a relatively low temperature.

[0036] Example 3

[0037] Synthesis of terminal amino group bismaleimide A3:

[0038] Using N,N'-(4,4'-methylenediphenyl)bismaleimide (MBMI) as a starting material, dissolved in N-methylpyrrolidone (NMP), polyetheramine D-2000 was added, resulting in Michael addition, which extended the chain of the bismaleimide, ultimately ending it with a primary amine group. The molar ratio of polyetheramine D-2000 to BMI was 2.0:1, and the reaction was carried out at a relatively low temperature.

[0039] Example 4

[0040] Preparation of polyurethane crosslinking agent:

[0041] 4,4'-diphenylmethane diisocyanate and dibutyltin dilaurate were added to a reaction flask equipped with a thermometer, stirrer, and reflux condenser. After stirring and heating to 60°C, ethylene glycol monobutyl ether was added dropwise. During the dropwise addition, the temperature was cooled using a water bath and controlled to not exceed 65°C. After the dropwise addition was completed, the reaction was continued at 80°C for 2 hours. The content of the remaining isocyanate groups in the reaction system was analyzed by standard di-n-butylamine back titration. When the content of the remaining isocyanate groups was less than 0.2%, methyl isobutyl ketone was added for dilution to obtain a fully closed isocyanate crosslinking agent with a final solid content of 80%.

[0042] Example 5

[0043] Preparation of pyrolysis-resistant cathodic electrophoretic coating:

[0044] As per Table 1, epoxy resin Epikote 1001 was dissolved in ethylene glycol butyl ether, heated to 80°C, and diethanolamine was added dropwise. The mixture was then kept at 100°C for 2 hours. A1 from the example was added, and the temperature was raised to 100-110°C and kept at 100-110°C for 2 hours. After amination, a polyurethane crosslinking agent was added, and the mixture was blended at 80-90°C for at least 30 minutes. Glacial acetic acid was added for neutralization, and the mixture was stirred for 30 minutes. Pure water was then added for emulsification to obtain a coating with a solids content of 33%.

[0045] pH value: 5.5-6.0;

[0046] Electrical conductivity: 1000-1500 μs / cm.

[0047] Example 6

[0048] Preparation of pyrolysis-resistant cathodic electrophoretic coating:

[0049] As per Table 1, epoxy resin Epikote 1001 was dissolved in ethylene glycol butyl ether, heated to 80°C, and diethanolamine was added dropwise. The mixture was then kept at 100°C for 2 hours. A2 from the example was added, and the temperature was raised to 100-110°C and kept at 100-110°C for 2 hours. After amination, a polyurethane crosslinking agent was added, and the mixture was blended at 80-90°C for at least 30 minutes. Glacial acetic acid was added for neutralization, and the mixture was stirred for 30 minutes. Pure water was then added for emulsification to obtain a coating with a solids content of 33%.

[0050] pH value: 5.5-6.0;

[0051] Electrical conductivity: 1000-1500 μs / cm.

[0052] Example 7

[0053] Preparation of pyrolysis-resistant cathodic electrophoretic coating:

[0054] As per Table 1, epoxy resin Epikote 1001 was dissolved in ethylene glycol butyl ether, heated to 80°C, and diethanolamine was added dropwise. The mixture was then kept at 100°C for 2 hours. A3 from the example was added, and the temperature was raised to 100-110°C and kept at 100-110°C for 2 hours. After amination, a polyurethane crosslinking agent was added, and the mixture was blended at 80-90°C for at least 30 minutes. Glacial acetic acid was added for neutralization, and the mixture was stirred for 30 minutes. Pure water was then added for emulsification to obtain a coating with a solids content of 33%.

[0055] pH value: 5.5-6.0;

[0056] Electrical conductivity: 1000-1500 μs / cm.

[0057] Comparative Example 1

[0058] Preparation of electrodeposited cathodic electrophoretic coating:

[0059] According to the requirements of Table 1, in Comparative Example 1, epoxy resin Epikote 1001 was dissolved in ethylene glycol butyl ether, heated to 80°C, and then diethanolamine was added dropwise. The mixture was then kept at 100°C for 2 hours. Polyurethane crosslinking agent and polyamide 3155 were added, and the mixture was heated to 120°C and kept at 120°C for 2 hours. Glacial acetic acid was added below 90°C for neutralization, and pure water was added for emulsification to obtain a coating with a solid content of 33%.

[0060] pH value: 6.0-6.5;

[0061] Electrical conductivity: 1000-1500 μs / cm.

[0062] Table 1 Component content of each embodiment

[0063]

[0064]

[0065] Performance testing

[0066] The electrophoretic coatings of Examples 5-7 and Comparative Example 1 were subjected to performance tests, and the specific results are shown below:

[0067] Table 2 Performance of Each Example

[0068]

[0069] In summary, the pyrolysis-resistant electrophoretic coating of the present invention has the following advantages:

[0070] 1. The pyrolysis-resistant electrophoretic coating allows the workpiece to remain at 100℃ for 1000 hours without peeling or cracking, and the adhesion meets grade 0-1.

[0071] 2. This pyrolysis-resistant electrophoretic coating exhibits high long-term circulating stability of the bath solution and good uniformity of the electrophoretic coating film.

[0072] 3. This pyrolysis-resistant electrophoretic coating has a curing temperature of 160℃, is energy-saving and environmentally friendly, and can still form a film even when the working solvent content in the bath is below 1.5%. The coating film has good anti-corrosion performance, with a neutral salt spray resistance of over 1000 hours.

[0073] Those skilled in the art will appreciate that various modifications to the above embodiments can be made without departing from the overall spirit and concept of the present invention. All such modifications fall within the protection scope of the present invention. The protection scheme of the present invention is defined by the appended claims.

Claims

1. A pyrolysis resistant electrophoretic coating, characterized in that, Comprise the following components by weight percentage: The preparation method of the pyrolysis-resistant electrophoretic paint comprises the following steps: Step (1): preparation of terminal amine-based bismaleimide: using bismaleimide as raw material, dissolving in N-methyl pyrrolidone, adding polyether amine; Michael addition reaction occurs between primary amine group and unsaturated double bond, so as to chain extend and toughen the bismaleimide; wherein the molar ratio of polyether amine and bismaleimide is 2.0-1.0:1.0, and finally terminated with polyether amine; Step (2): after the epoxy resin and small molecule amine are reacted at 80-100℃ for 2 hours, the terminal amine-based bismaleimide is added for further amination reaction to obtain a bismaleimide modified epoxy resin polymer; Step (3): using a blocking agent to block the polyisocyanate to prepare a fully blocked polyurethane crosslinking agent, then blending with the above bismaleimide modified epoxy resin polymer, adding organic acid for neutralization to obtain a protonatable resin, and adding water for emulsification to form a water-soluble electrodeposition cathode electrophoretic paint, namely the pyrolysis-resistant electrophoretic paint; The small molecule amine is selected from one or more than one mixture of diethanolamine, diisopropanolamine, N-methylethanolamine, diethylene triamine, and ketimine of diethylene triamine.

2. A pyrolysis resistant electrophoretic paint according to claim 1, characterised in that, The epoxy resin is selected from one or more than one mixture of glycidyl ether type bisphenol A type epoxy resin, bisphenol F type epoxy resin, glycidyl ester epoxy resin, aliphatic epoxy resin, and alicyclic epoxy resin.

3. A pyrolysis resistant electrophoretic coating according to claim 1, wherein, The bismaleimide is selected from one or more than one mixture of N,N'-(4,4'-methylene diphenyl) bismaleimide, N,N'-m-phenylene bismaleimide, N,N'-(4-methyl-1,3-phenylene)-bismaleimide, aliphatic bismaleimide of 2,2,4-trimethyl-1,6-hexanediamine, and 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane.

4. The pyrolysis resistant electrophoretic paint of claim 1, wherein, The polyether amine is selected from one or more than one mixture of D-230, D-400, D2000, T-403, and T-5000.

5. A pyrolysis resistant electrophoretic coating according to claim 1, wherein, The polyurethane crosslinking agent is a fully blocked polyisocyanate; the polyisocyanate comprises aliphatic diisocyanate and aromatic diisocyanate; the aliphatic diisocyanate comprises hexamethylene diisocyanate or isophorone diisocyanate, and the aromatic diisocyanate comprises toluene diisocyanate or 4,4'-diphenylmethane diisocyanate; the blocking agent comprises small molecule alcohol, alcohol ether solvent, or methyl ethyl ketoxime blocking agent; the small molecule alcohol comprises n-butanol, methanol, or propylene glycol; and the alcohol ether solvent comprises ethylene glycol butyl ether, diethylene glycol butyl ether, or propylene glycol methyl ether.

6. A pyrolysis resistant electrophoretic coating according to claim 1, wherein, The organic acid is selected from one or more than one mixture of formic acid, acetic acid, and lactic acid.

7. A pyrolysis resistant electrophoretic coating according to claim 1, wherein, Step (2) is specifically: After the epoxy resin is dissolved using ethylene glycol butyl ether, the temperature is raised to 80℃; the small molecule amine is added dropwise and reacted at 80-100℃ for 2 hours; the terminal amine-based bismaleimide is added, the temperature is continuously raised to 100-110℃, and the reaction is maintained for 2 hours to obtain a bismaleimide modified epoxy resin polymer.

8. The pyrolysis resistant electrophoretic paint of claim 1, wherein, Step (3) is specifically: The heat-resistance electrophoretic paint is prepared by adding a full-enclosed polyurethane cross-linking agent into the above bismaleimide modified epoxy resin polymer, blending at 80-90 ℃ for more than 30 minutes, adding an organic acid for neutralization, stirring for 30 minutes, and then adding pure water for emulsification.

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