Insulating coating composition suitable for electrodeposition coating, preparation method and coating preparation method

Abstract

The invention discloses an insulating coating composition suitable for electrodeposition coating, a preparation method and a coating preparation method, wherein the coating composition is prepared by the following method: step S1, preparing a carboxyl-containing polystyrene prepolymer: mixing ethylene glycol butyl ether with an initiator di-tert-amyl peroxide to obtain a first mixture, and heating; under the protection of nitrogen, uniformly mixing styrene, methacrylic acid, butyl acrylate and di-tert-amyl peroxide and dripping into the first mixture; after the dripping is completed, adding the initiator di-tert-amyl peroxide to continue the reaction; step S2, preparing a polystyrene-modified epoxy multi-branched polymer; step S3, heating and mixing a polystyrene-modified epoxy multi-branched polymer, a blocked isocyanate curing agent and a film-forming aid, then adding an organic acid for protonation, and finally adding pure water to dilute under stirring, thereby obtaining an insulating coating composition. The insulating composition has excellent insulation, corrosion resistance and moisture and heat resistance.

Description

Technical Field

[0001] The invention relates to the technical field of coatings, and in particular to an insulating coating composition suitable for electrodeposition coating, a preparation method and a coating preparation method. Background Art

[0002] At present, the insulation protection of new energy power battery packs and energy storage cells is mainly PET blue film and insulating powder coating. However, with the continuous development of battery technology, the continuous improvement of energy density, and the continuous optimization of battery module structure, including battery cells, high-voltage connectors, wiring harnesses, module structural parts, etc., the structure is complex and there are many types of parts. The traditional PET blue film and powder insulating coating can no longer fully meet the market demand due to the limitations of film pasting and spraying processes. Electrodeposition coating is very suitable for coating parts with porous, multilateral structures and complex structures in the inner cavity of battery packs. Its coating method is to form a film by electrodeposition under the action of a high-voltage electric field. The coating has better density than powder coating, and its corrosion resistance, voltage resistance and production efficiency are higher than those of insulating powder coating. However, the film thickness of traditional epoxy resin system electrodeposition coating does not exceed 60μm, which cannot effectively cover and protect the defects of the substrate. Therefore, the voltage resistance performance of traditional electrodeposition coating films on the market can generally only reach about 1200V, which cannot meet the high voltage resistance requirements of power battery packs and energy storage cells. Summary of the invention

[0003] The object of the present invention is to provide an insulating coating composition suitable for electrodeposition coating, a preparation method and a coating preparation method, so as to solve one or more of the above-mentioned prior art problems.

[0004] In the first aspect, the present invention provides a method for preparing an insulating coating composition suitable for electrodeposition coating, which is prepared by the following method:

[0005] Step S1, preparing a carboxyl-containing polystyrene prepolymer: firstly, mixing ethylene glycol butyl ether with an initiator di-tert-amyl peroxide to obtain a first mixture, and heating the first mixture; under the protection of nitrogen, uniformly mixing styrene, methacrylic acid, butyl acrylate and di-tert-amyl peroxide, and then dropwise adding the mixture to the first mixture; after the dropwise addition is completed, adding an initiator di-tert-amyl peroxide, continuing the reaction, and testing the acid value and number average molecular weight distribution;

[0006] Step S2, preparing a polystyrene-modified epoxy multi-branched polymer;

[0007] Step S3, heating and mixing the polystyrene-modified epoxy multi-branched polymer, the blocked isocyanate curing agent and the film-forming aid, then adding an organic acid for protonation, and finally adding pure water for dilution under high-speed stirring to obtain the insulating coating composition.

[0008] In certain embodiments, in step S1: the heating temperature of the first mixture is 140°C; under the protection of nitrogen, styrene, methacrylic acid, butyl acrylate and di-tert-amyl peroxide are mixed evenly and then added dropwise to the first mixture, and the temperature is maintained at 140-142°C during the reaction process; after the addition is completed, the temperature is continued to be maintained at 140-142°C, and the reaction time is controlled to 2h; after the initiator di-tert-amyl peroxide is added, the temperature is continued to be maintained at 140-142°C, and the reaction time is controlled to 2h.

[0009] In certain embodiments, in step S1: the molar ratio of butyl acrylate to styrene in the carboxyl-containing polystyrene prepolymer is 1:3-9;

[0010] The molar ratio of the total amount of the mixture of styrene, methacrylic acid and butyl acrylate in the carboxyl-containing polystyrene prepolymer to the initiator di-tert-amyl peroxide is 15-30:1;

[0011] The acid value of the carboxyl-containing polystyrene prepolymer is 25-50 mgKOH / g; the number average molecular weight Mn distribution is 1500-3000, accounting for 50-65%, and 2500-4000, accounting for 25-40%.

[0012] In certain embodiments, the molar ratio of butyl acrylate to styrene in the carboxyl-containing polystyrene prepolymer is 1:5-7;

[0013] The molar ratio of the total amount of the mixture of styrene, methacrylic acid and butyl acrylate in the carboxyl-containing polystyrene prepolymer to the initiator di-tert-amyl peroxide is 15-20:1;

[0014] The acid value of the carboxyl-containing polystyrene prepolymer is 35-45 mgKOH / g.

[0015] In certain embodiments, step S2 is specifically:

[0016] Mix carboxyl-containing polystyrene prepolymer, epoxy resin, chain extender, end-capping agent and solvent, add catalyst triphenylphosphine when the temperature is raised to 110-120°C, continue to raise the temperature to 140-150°C and react for 2.5 hours, and control the epoxy equivalent at 800-1200; add solvent and cool to below 90°C, add small molecule organic amine, raise the temperature to 120-130°C and react for 2.5 hours, and after the reaction, cool to 90°C for discharge.

[0017] In certain embodiments, the epoxy resin is a bisphenol A epoxy resin having an epoxy equivalent of 180-540 g / mol; the chain extender is bisphenol A, bisphenol F, bisphenol A polyether polyol, polyester polyol or polyacid, which has two active functional groups and a molecular weight of 50-1000; the end capping agent is a mixture of one or more monophenols and monoacids, and the end capping agent is phenol, dodecylphenol, monooleic acid, or isooctanoic acid; the small molecule organic amine is an organic amine with a molecular weight of 70-300, and its molecule contains a primary amine, a secondary amine or a ketimine structure, and may also contain a ketimine structure at the same time, and the small molecule organic amine is monoethanolamine, diethanolamine, N-methylethanolamine, 3-dimethylamino-1-propylamine or methyl isobutyl ketimine.

[0018] In certain embodiments, in step S3: the heating temperature is 60-70°C.

[0019] In certain embodiments, the emulsion amount of the film-forming aid is 1% to 4%.

[0020] In certain embodiments, the film-forming aid is an alcohol ether having a C4-14 alkyl carbon chain structure, such as ethylene glycol isooctyl ether, ethylene glycol hexyl ether, diethylene glycol butyl ether, and the like.

[0021] In certain embodiments, the insulating coating composition has a solids content of 33-37%.

[0022] In certain embodiments, the preparation steps of the blocked isocyanate curing agent are:

[0023] Trimethylolpropane and diisocyanate are reacted under nitrogen protection with a catalyst, and a chain extension reaction is carried out at a temperature of 70-80°C. The reaction consumes 50% of the NCO groups. After the NCO value is tested to be qualified, a small molecule alcohol ether is added, and the temperature is raised to 90°C and the reaction is continued for 2 hours until the NCO value is less than 1.

[0024] In certain embodiments, the diisocyanate is an aromatic isocyanate or an alicyclic isocyanate containing two isocyanate groups, preferably toluene diisocyanate, diphenylmethane diisocyanate, or dicyclohexylmethane-4,4'-diisocyanate.

[0025] In certain embodiments, small molecule alcohol ether refers to alcohol ether containing 4-20 carbon atoms and a molecular weight between 90-300, including ethanol, ethylene glycol monobutyl ether, ethylene glycol ethyl ether, ethylene glycol hexyl ether, diethylene glycol monobutyl ether, propylene glycol methyl ether, etc.

[0026] In a second aspect, the present invention provides an insulating coating composition suitable for electrodeposition coating, which is prepared by the following preparation method, specifically:

[0027] Step S1, preparing a carboxyl-containing polystyrene prepolymer: firstly, mixing ethylene glycol butyl ether with an initiator di-tert-amyl peroxide to obtain a first mixture, and heating the first mixture; under the protection of nitrogen, uniformly mixing styrene, methacrylic acid, butyl acrylate and di-tert-amyl peroxide, and then dropwise adding the mixture to the first mixture; after the dropwise addition is completed, adding an initiator di-tert-amyl peroxide, continuing the reaction, and testing the acid value and number average molecular weight distribution;

[0028] Step S2, preparing a polystyrene-modified epoxy multi-branched polymer;

[0029] Step S3, heating and mixing the polystyrene-modified epoxy multi-branched polymer, the blocked isocyanate curing agent and the film-forming aid, then adding an organic acid for protonation, and finally adding pure water for dilution under high-speed stirring to obtain the insulating coating composition.

[0030] In a third aspect, the present invention provides a method for preparing an insulating coating, comprising the following steps:

[0031] A1. Dilute the above insulating coating composition with deionized water to a tank solution with a solid content of 10-15%, place the object to be coated in the tank solution, and perform the first electrodeposition coating. The coating adopts two voltage stages, the first stage adopts a low voltage of 60V-100V, and the second stage adopts a high voltage of 160V-200V. After the electrodeposition is completed, the floating paint on the coating surface is rinsed clean with deionized water;

[0032] A2. The coating object that has completed the first electrodeposition coating is placed in the tank liquid again, and the second electrodeposition coating is carried out. The coating adopts two voltages, wherein the second voltage value is higher than the first voltage value, and both voltages are higher than the highest voltage of the first electrodeposition coating; after the electrodeposition is completed, the floating paint on the coating surface is washed off with deionized water;

[0033] A3. The coating is baked to form an insulating coating at a temperature of 180°C to 200°C for 15 minutes to 30 minutes.

[0034] Among them: segmented voltage and secondary electrophoresis are used for electrodeposition coating. Many components in the new energy battery system are composed of aluminum and galvanized materials. The materials are highly active. The electrodeposition reaction is relatively violent during electrodeposition, and a large amount of hydrogen is easily produced, which leads to the deterioration of the density of the paint film on the surface of the substrate. Many invisible micropores are formed inside the paint film, resulting in a decrease in insulation performance and a low product qualification rate. In order to reduce the impact of the violent electrodeposition reaction, it is necessary to use a segmented voltage from low voltage to high voltage for electrodeposition. The secondary electrophoresis method is adopted, that is, pure water rinsing is performed after the first electrophoresis is completed, and the second electrophoresis operation is performed again after the rinsing is completed. The second electrophoresis can repair the micropore defects caused by the first electrophoresis, which is beneficial to improve the density of the coating, form a defect-free paint film, and improve the insulation performance and voltage resistance qualification rate of the coating.

[0035] Beneficial effects: The present invention prepares a polystyrene prepolymer containing carboxyl groups on the molecular chain through polymerization reaction of styrene, methacrylic acid and butyl acrylate, which has a suitable acid value and molecular weight distribution. The carboxyl-containing polystyrene prepolymer is further reacted with epoxy resin to prepare a polystyrene-modified epoxy resin, which is further reacted with a small molecule organic amine to prepare a polystyrene-modified epoxy multi-branched polymer. If the acid value and molecular weight of polystyrene are too large, it is easy to cause the molecular weight of the polymer to be too large, affecting the ionized water solubility and electrodeposition stability, and in severe cases causing the polymer to gel; if the acid value and molecular weight of polystyrene are too small, it is not conducive to improving the dielectric properties and cross-linking density, resulting in a decrease in the insulating properties of the coating after cross-linking. The polystyrene-modified epoxy resin has a suitable epoxy equivalent, can further react with a small molecule organic amine, introduces an ionizable amino group on the main chain of the polymer molecule, and has good water solubility and electrodeposition stability after acid neutralization. Fully blocked isocyanate is used as a curing agent for the polymer. It undergoes a cross-linking reaction with the polymer to form a coating with a high cross-linking density. After curing, the coating has excellent insulation, corrosion resistance, and moisture and heat resistance. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below through embodiments.

[0037] Example 1

[0038] Preparation of carboxyl-containing polystyrene prepolymer:

[0039]

[0040] In a reaction bottle equipped with a thermometer, a stirrer and a reflux condenser, add the formulated amount of ethylene glycol butyl ether and di-tert-amyl peroxide, stir and heat the reaction system to 140°C. Styrene, methacrylic acid, butyl acrylate and di-tert-amyl peroxide are mixed evenly and then added dropwise to the reactor. The temperature of the reaction is maintained at 140°C-142°C during the addition process. After all the additions are completed, the temperature is 140°C-142°C and the reaction continues for 2 hours. A certain amount of initiator di-tert-amyl peroxide is added, and the temperature is 140°C-142°C and the reaction ends after the reaction continues for 2 hours. The acid value of the tested prepolymer is between 37.0 and 38.0, and the number average molecular weight Mn distribution is 1500-3000 accounting for 51-55%, and 2500-4000 accounting for 35-40%.

[0041] Example 2

[0042] The preparation process is the same as that in Example 1, except that the molar ratio of the initiator di-tert-amyl peroxide to the total amount of the mixture of styrene, methacrylic acid and butyl acrylate is 1:15 in Example 1, and 1:20 in Example 2. The acid value of the tested prepolymer is between 37.0 and 38.0, and the number average molecular weight Mn distribution is 1500-3000, accounting for 58-62%, and 2500-4000, accounting for 30-35%.

[0043] Example 3

[0044] The preparation process is the same as that in Example 1, except that the molar ratio of the initiator di-tert-amyl peroxide to the total amount of the mixture of styrene, methacrylic acid and butyl acrylate is 1:15 in Example 1, and 1:30 in Example 2. The acid value of the tested prepolymer is between 37.0 and 38.0, and the number average molecular weight Mn distribution is 1500-3000, accounting for 61-65%, and 2500-4000, accounting for 26-30%.

[0045] Example 4

[0046] The preparation process is the same as that of Example 2, except that the amount of methacrylic acid is adjusted, the acid value of the tested prepolymer is between 26 and 27, the number average molecular weight Mn distribution is 1500-3000 accounting for 58-62%, and 2500-4000 accounting for 30-35%.

[0047] Example 5

[0048] The preparation process is the same as that of Example 2, except that the amount of methacrylic acid is adjusted, the acid value of the tested prepolymer is between 45 and 46, the number average molecular weight Mn distribution is 1500-3000 accounting for 58-62%, and 2500-4000 accounting for 30-35%.

[0049] Example 6

[0050] The preparation process is the same as that of Example 2, except that the molar ratio of butyl acrylate to styrene in Example 2 is 1:5, while that in Example 6 is 1:5;

[0051] Example 7

[0052] The preparation process is the same as that of Example 6, except that the molar ratio of butyl acrylate to styrene is 1:7.

[0053] Example 8

[0054] Preparation of polystyrene modified epoxy multi-branched polymer:

[0055]

[0056] *Methyl isobutyl ketimine: It is prepared by the reaction of diethylenetriamine and methyl isobutyl ketone. The final product has a solid content of 70% and an amine value of 450-480 mgKOH / g.

[0057] In a reaction bottle equipped with a thermometer, a stirrer and a reflux condenser, nitrogen protection was passed through, and carboxyl-containing polystyrene prepolymer, epoxy resin, bisphenol A, dodecylphenol and methyl isobutyl ketone were added in sequence and mixed evenly. When the temperature was raised to 110°C-120°C, the catalyst triphenylphosphine was added, and the temperature was continued to rise to 140°C-150°C for reaction for 2.5 hours. The epoxy equivalent (solvent was not included in the calculation) was tested to reach 900-930. Ethylene glycol butyl ether was added and the temperature was lowered to below 90°C, and N-methylethanolamine, methyl isobutyl ketone imine and 3-dimethylamino-1-propylamine were quickly added. The temperature was raised to 120-130°C for reaction for 2.5 hours. After the reaction was completed, the temperature was lowered to 90°C for discharge.

[0058] Example 9

[0059] The preparation process is the same as that of Example 8, except that the carboxyl-containing polystyrene prepolymer of Example 1 is used instead of the carboxyl-containing polystyrene prepolymer of Example 2.

[0060] Example 10

[0061] The preparation process is the same as that of Example 8, except that the carboxyl-containing polystyrene prepolymer of Example 3 is used instead of the carboxyl-containing polystyrene prepolymer of Example 2.

[0062] Embodiment 11

[0063] Preparation of polystyrene modified epoxy multi-branched polymer:

[0064]

[0065] In a reaction bottle equipped with a thermometer, a stirrer and a reflux condenser, nitrogen protection was passed through, and carboxyl-containing polystyrene prepolymer, epoxy resin, bisphenol A, dodecylphenol and methyl isobutyl ketone were added in sequence and mixed evenly. When the temperature was raised to 110°C-120°C, the catalyst triphenylphosphine was added, and the temperature was continued to rise to 140°C-150°C for reaction for 2.5 hours. The epoxy equivalent (solvent was not included in the calculation) was tested to reach 900-930. Ethylene glycol butyl ether was added and the temperature was lowered to below 90°C, and N-methylethanolamine, methyl isobutyl ketone imine and 3-dimethylamino-1-propylamine were quickly added. The temperature was raised to 120-130°C for reaction for 2.5 hours. After the reaction was completed, the temperature was lowered to 90°C for discharge.

[0066] Example 12

[0067] Preparation of polystyrene modified epoxy multi-branched polymer:

[0068]

[0069] In a reaction bottle equipped with a thermometer, a stirrer and a reflux condenser, nitrogen protection was passed through, and carboxyl-containing polystyrene prepolymer, epoxy resin, bisphenol A, dodecylphenol and methyl isobutyl ketone were added in sequence and mixed evenly. When the temperature was raised to 110°C-120°C, the catalyst triphenylphosphine was added, and the temperature was continued to rise to 140°C-150°C for reaction for 2.5 hours. The epoxy equivalent (solvent was not included in the calculation) was tested to reach 900-930. Ethylene glycol butyl ether was added and the temperature was lowered to below 90°C, and N-methylethanolamine, methyl isobutyl ketone imine and 3-dimethylamino-1-propylamine were quickly added. The temperature was raised to 120-130°C for reaction for 2.5 hours. After the reaction was completed, the temperature was lowered to 90°C for discharge.

[0070] Embodiment 13

[0071] The preparation process is the same as that of Example 8, except that the carboxyl-containing polystyrene prepolymer of Example 6 is used instead of the carboxyl-containing polystyrene prepolymer of Example 2.

[0072] Embodiment 14

[0073] The preparation process is the same as that of Example 8, except that the carboxyl-containing polystyrene prepolymer of Example 7 is used instead of the carboxyl-containing polystyrene prepolymer of Example 2.

[0074] Embodiment 15

[0075] Preparation of polystyrene modified epoxy multi-branched polymer:

[0076]

[0077] *Methyl isobutyl ketimine: It is prepared by the reaction of diethylenetriamine and methyl isobutyl ketone. The final product has a solid content of 70% and an amine value of 450-480 mgKOH / g.

[0078] In a reaction bottle equipped with a thermometer, a stirrer and a reflux condenser, nitrogen protection was passed through, and carboxyl-containing polystyrene prepolymer, epoxy resin, bisphenol A, dodecylphenol and methyl isobutyl ketone were added in sequence and mixed evenly. When the temperature reached 110°C-120°C, the catalyst triphenylphosphine was added, and the temperature was continued to rise to 140°C-150°C for reaction for 2.5 hours. The epoxy equivalent (solvent was not included in the calculation) was tested to reach 1100-1130. Ethylene glycol butyl ether was added and the temperature was lowered to below 90°C, and N-methylethanolamine, methyl isobutyl ketone imine and 3-dimethylamino-1-propylamine were quickly added. The temperature was raised to 120-130°C for reaction for 2.5 hours. After the reaction was completed, the temperature was lowered to 90°C for discharge.

[0079] Example 16

[0080] Preparation of polystyrene modified epoxy multi-branched polymer:

[0081]

[0082] *Methyl isobutyl ketimine: It is prepared by the reaction of diethylenetriamine and methyl isobutyl ketone. The final product has a solid content of 70% and an amine value of 450-480 mgKOH / g.

[0083] In a reaction bottle equipped with a thermometer, a stirrer and a reflux condenser, nitrogen protection was passed through, and carboxyl-containing polystyrene prepolymer, epoxy resin, bisphenol A, dodecylphenol and methyl isobutyl ketone were added in sequence and mixed evenly. When the temperature was raised to 110°C-120°C, the catalyst triphenylphosphine was added, and the temperature was continued to rise to 140°C-150°C for reaction for 2.5 hours. The epoxy equivalent (solvent was not included in the calculation) was tested to reach 1210-1250. Ethylene glycol butyl ether was added and the temperature was lowered to below 90°C, and N-methylethanolamine, methyl isobutyl ketone imine and 3-dimethylamino-1-propylamine were quickly added. The temperature was raised to 120-130°C for reaction for 2.5 hours. After the reaction was completed, the temperature was lowered to 90°C for discharge.

[0084] Implementation 17

[0085] Preparation of blocked isocyanate curing agent:

[0086]

[0087] In a reaction bottle equipped with a thermometer, a stirrer and a reflux condenser, add the formulated amount of diphenylmethane diisocyanate and methyl isobutyl ketone in sequence. Stir in a nitrogen atmosphere to raise the temperature of the reaction system to 70-80°C, mix trimethylolpropane, methyl isobutyl ketone and dibutyltin dilaurate evenly, and then slowly drip into the reaction system containing diphenylmethane diisocyanate and methyl isobutyl ketone. The temperature of the reaction system is between 70-80°C during the dripping, and the dripping is completed in about 1-2 hours. After all the dripping is completed, the reaction is kept warm for 1 hour, and the NCO value is measured between 98 and 103. Ethylene glycol butyl ether is slowly dripped into the reaction system, and the dripping is completed in about 1-2 hours. After all the dripping is completed, the temperature is raised to 90°C and the reaction is kept warm for 2 hours. It is qualified when the NCO is less than 1.0.

[0088] Embodiment 18

[0089] Preparation of insulating coating emulsion:

[0090]

[0091] Add polystyrene modified epoxy multi-branched polymer, blocked isocyanate curing agent and ethylene glycol hexyl ether to a reactor equipped with a thermometer and a stirrer, heat to 60°C~70°C and stir and disperse for 1 hour, then add 20% methyl sulfonic acid for protonation, finally add pure water under high-speed stirring to dilute into an insulating coating emulsion, then perform decompression desolventizing and adjust the solid content to about 33-37%.

[0092] The preparation process of Examples 19 to 26 is the same as that of Example 18, except that the polystyrene-modified epoxy multi-branched polymers used are different, as shown in the following table:

[0093]

[0094] Example 27 is a commercially available epoxy electrodeposition coating POWERCRON RESIN CR681.

[0095] Example 28 is a commercially available epoxy insulating powder coating, Shinichi FA-0101.

[0096] Preparation of electrodeposition coating

[0097] Method 1: Add pure water to the insulating coating emulsions of Examples 18 to 26 above to prepare a coating bath with a solid content of about 13%. The bath temperature is 34 to 35°C. Immerse a 3 series aluminum battery cell in the coating bath. Connect the battery cell to the cathode and coat it by electrodeposition. The electrodeposition voltage / time is 160V / 60s+280V / 180s. After the electrodeposition is completed, the product is washed with water and baked at 180°C for 20 minutes to obtain a product with an insulating coating.

[0098] The corresponding insulating coating products obtained by electrodeposition in Examples 18 to 26 were respectively recorded as F1 to F9, with a coating thickness of 60 to 70 microns and relatively orange leveling.

[0099] Method 2: Add pure water to the insulating coating emulsions of Examples 18 to 26 above to prepare a coating bath with a solid content of about 13%. The bath temperature is 34 to 35°C. Immerse the 3 series aluminum battery core in the coating bath, connect the battery core to the cathode, and coat it by electrodeposition. Carry out the first electrodeposition coating, the electrodeposition voltage / time is 80V / 45s+180V / 45s, and after the electrodeposition is completed, rinse the floating paint on the coating surface with deionized water. Place the coating again in the tank liquid, and carry out the second electrodeposition coating, the electrodeposition voltage / time is 230V / 60s+300V / 90s. After the electrodeposition is completed, the product is washed with water and baked at 180°C for 20 minutes to obtain a product with an insulating coating.

[0100] The corresponding insulating coating products obtained by electrodeposition in Examples 18 to 26 were respectively recorded as H1 to H9, with a coating thickness of 60 to 70 microns and good and fine leveling.

[0101] Implementation 27 was electro-deposited according to method 1, and the corresponding product was recorded as F10. The coating thickness was 50-55 μm, and the leveling was relatively orange.

[0102] The corresponding product of Example 28 was prepared by electrostatic spraying and was recorded as F11. The coating thickness was 150-180 μm and the leveling was good.

[0103] Performance Testing

[0104] 1. Insulation test (normal temperature insulation test):

[0105] Voltage withstand test conditions: room temperature 25℃, DC voltage 5KV, voltage withstand time 30s, leakage current less than 0.1mA. Each product provides 10 parallel cell samples with a size of 160mm*160mm*55mm for testing.

[0106]

[0107] In summary, the insulating composition has excellent insulation, corrosion resistance and moisture and heat resistance. The present invention adopts a secondary electrophoresis method, that is, pure water rinsing is performed after the first electrophoresis is completed, and the second electrophoresis operation is performed again after the rinsing is completed. The second electrophoresis can repair the micropore defects generated by the first electrophoresis, which is beneficial to improve the density of the coating, form a paint film without defects, and improve the insulation performance and voltage resistance qualified rate of the coating.

[0108] The above description is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the creative concept of the present invention, and these should also be regarded as within the scope of protection of the invention.

Claims

1. A method for preparing an insulating coating composition suitable for electrodeposition coating, characterized in that: Prepared by the following method: Step S1, preparing a carboxyl-containing polystyrene prepolymer: firstly, mixing ethylene glycol butyl ether with an initiator di-tert-amyl peroxide to obtain a first mixture, and heating the first mixture; under the protection of nitrogen, uniformly mixing styrene, methacrylic acid, butyl acrylate and an initiator di-tert-amyl peroxide, and then dropwise adding the mixture to the first mixture; after the dropwise addition is completed, adding an initiator di-tert-amyl peroxide, continuing the reaction, and testing the acid value and the number average molecular weight distribution; Step S2, preparing a polystyrene-modified epoxy multi-branched polymer; Step S3, heating and mixing the polystyrene-modified epoxy multi-branched polymer, the blocked isocyanate curing agent and the film-forming aid, then adding an organic acid for protonation, and finally adding pure water for dilution under high-speed stirring to obtain the insulating coating composition; Wherein: in step S1: the molar ratio of butyl acrylate to styrene is 1:3-9; The molar ratio of the total amount of the mixture of styrene, methacrylic acid and butyl acrylate to the initiator di-tert-amyl peroxide is 15-30:1; The acid value of the carboxyl-containing polystyrene prepolymer is 25-50 mgKOH / g; the number average molecular weight Mn distribution is 1500-3000 accounting for 50-65%, and 2500-4000 accounting for 25-40%; Step S2 is specifically as follows: Mix carboxyl-containing polystyrene prepolymer, epoxy resin, chain extender, end-capping agent and solvent, add catalyst triphenylphosphine when the temperature is raised to 110-120°C, continue to raise the temperature to 140-150°C for reaction for 2.5h, and control the epoxy equivalent to 800-1130; add solvent and cool to below 90°C, add small molecular organic amine, raise the temperature to 120-130°C for reaction for 2.5h, and cool to 90°C for discharge after the reaction; The epoxy resin is a bisphenol A type epoxy resin with an epoxy equivalent between 180 and 540 g / mol; the chain extender is bisphenol A, bisphenol F, bisphenol A type polyether polyol, polyester polyol or polyacid, which has two active functional groups and a molecular weight between 50 and 1000; the small molecule organic amine is an organic amine with a molecular weight between 70 and 300, and contains a primary amine, a secondary amine or a ketimine structure in its molecule.

2. The method for preparing an insulating coating composition suitable for electrodeposition coating according to claim 1, characterized in that: In step S1: the heating temperature of the first mixture is 140° C.; under the protection of nitrogen, styrene, methacrylic acid, butyl acrylate and initiator di-tert-amyl peroxide are mixed evenly and then added dropwise to the first mixture, and the temperature is maintained at 140-142° C. during the reaction process; after the addition is completed, the temperature is continued to be maintained at 140-142° C., and the reaction time is controlled to be 2 hours; after the initiator di-tert-amyl peroxide is added, the temperature is continued to be maintained at 140-142° C., and the reaction time is controlled to be 2 hours.

3. The method for preparing an insulating coating composition suitable for electrodeposition coating according to claim 1, characterized in that: In step S1: the molar ratio of butyl acrylate to styrene is 1:5-7; The molar ratio of the total amount of the mixture of styrene, methacrylic acid and butyl acrylate to the initiator di-tert-amyl peroxide is 15-20:1; The acid value of the carboxyl-containing polystyrene prepolymer is 35-45 mgKOH / g.

4. The method for preparing an insulating coating composition suitable for electrodeposition coating according to claim 1, characterized in that: The end-capping agent is a mixture of one or more monophenols and monoacids.

5. The method for preparing an insulating coating composition suitable for electrodeposition coating according to claim 1, characterized in that: The end-capping agent is phenol, dodecylphenol, monooleic acid, isooctanoic acid; the small molecule organic amine is diethanolamine, N-methylethanolamine, 3-dimethylamino-1-propylamine or methyl isobutyl ketimine.

6. The method for preparing an insulating coating composition suitable for electrodeposition coating according to claim 1, characterized in that: In step S3: the heating temperature is 60-70°C.

7. The method for preparing an insulating coating composition suitable for electrodeposition coating according to claim 1, characterized in that: The preparation steps of blocked isocyanate curing agent are as follows: Trimethylolpropane and diisocyanate are reacted under nitrogen protection with a catalyst, and a chain extension reaction is carried out at a temperature of 70-80°C. The reaction consumes 50% of the NCO groups. After the NCO value is tested to be qualified, a small molecule alcohol ether is added, and the temperature is raised to 90°C and the reaction is continued for 2 hours until the NCO value is less than 1.

8. An insulating coating composition suitable for electrodeposition coating, characterized in that: Prepared by the preparation method described in any one of claims 1 to 7.

9. A method for preparing an insulating coating, characterized in that: The following steps are involved: A1. Dilute the insulating coating composition according to claim 8 with deionized water to a bath solution with a solid content of 10-15%, place the object to be coated in the bath solution, and perform the first electrodeposition coating. The coating adopts two voltage stages, the first stage adopts a low voltage of 60V-100V, and the second stage adopts a high voltage of 160V-200V. After the electrodeposition is completed, the floating paint on the coating surface is rinsed clean with deionized water; A2. Place the coating object that has completed the first electrodeposition coating in the tank again and implement the second electrodeposition coating. The coating adopts two voltages, wherein the second voltage value is higher than the first voltage value, and both voltages are higher than the highest voltage of the first electrodeposition coating; after the electrodeposition is completed, rinse the floating paint on the coating surface with deionized water; A3. The coating is baked to form an insulating coating at a temperature of 180°C to 200°C for 15 minutes to 30 minutes.

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