Epoxy resin for cathodic electrophoretic primer and preparation method therefor, and cathodic electrophoretic primer

Abstract

The present invention provides an epoxy resin for a cathodic electrophoretic primer, and a cathodic electrophoretic primer. The cathodic electrophoretic primer comprises the following components in percentages by mass: 10-25 wt% of a small-molecule epoxy resin, 0.5-1 wt% of a chain extender, 0.5-1 wt% of a molecular weight regulator, 1-2 wt% of a first catalyst, 0.5-5 wt% of an amine compound, 5-25 wt% of an isocyanate curing agent, 10-25 wt% of a hyperbranched polyester, 0.01-0.05 wt% of an organic solvent, 5-15 wt% of an auxiliary agent, 0.5-1 wt% of a neutralizing agent, and 40-60 wt% of deionized water. The hyperbranched polyester comprises the following components in percentages by mass: 10-15 wt% of a mixed solvent, 15-30 wt% of a long-chain fatty acid, 10-20 wt% of a polyol, 20-40 wt% of an anhydride, and 0.5-3 wt% of a second catalyst. By replacing high-boiling-point solvents and plasticizers required in electrophoretic coatings with the hyperbranched polyester, the formed electrophoretic composition can be subjected to electrophoresis on a conductive surface, and can form a uniform electrophoretic film after curing, thereby reducing volatile organic components in the coating.

Description

Epoxy resin for cathodic electrophoretic primer and preparation method thereof, and cathodic electrophoretic primer TECHNICAL FIELD

[0001] The present application relates to the technical field of electrophoretic primer, in particular to an epoxy resin for cathodic electrophoretic primer and a preparation method thereof, and a cathodic electrophoretic primer. BACKGROUND

[0002] In existing industrial electrophoretic coating, cathodic electrophoretic paint is generally used as a primer coating. By using the excellent substrate adhesion and corrosion resistance of epoxy resin, a matching topcoat and topcoat are used to achieve dual protection of corrosion resistance and weather resistance. Cathodic electrophoretic paint with acrylic resin as the main film-forming material has excellent light stability and weather resistance.

[0003] However, most of the film-forming aids used in current cathodic electrophoretic materials are volatile organic solvents or heat-volatile plasticizers. Therefore, even though the dispersion medium of the electrophoretic working solution is mostly deionized water, it still contains 2-5% organic solvent volatilization. This not only poses a certain risk to the health of the operators, but also poses a potential risk to the subsequent use of the product. Therefore, it is of great significance to find a new type of film-forming aid.

[0004] SUMMARY

[0005] In view of the defects in the prior art, the purpose of the present application is to provide an epoxy resin for cathodic electrophoretic primer and a preparation method thereof, and a cathodic electrophoretic primer. The use of hyperbranched polyester replaces the high-boiling solvent and plasticizer required in electrophoretic paint. The electrophoretic composition formed can be electrophoretic on a conductive surface, and after curing, a uniform electrophoretic coating film is formed, reducing the volatile organic components in the coating.

[0006] The present application provides an epoxy resin for cathodic electrophoretic primer, comprising the following components calculated in terms of mass percentage: 10-25wt% of small molecule epoxy resin, 0.5-1wt% of chain extender, 0.5-1wt% of molecular weight regulator, 1-2wt% of first catalyst, 0.5-5wt% of amine compound, 5-25wt% of isocyanate curing agent, 10-25wt% of hyperbranched polyester, 0.01-0.05wt% of organic solvent, 5-15wt% of additive, 0.5-1wt% of neutralizing agent, and 40-60wt% of deionized water.

[0007] The hyperbranched polyester comprises the following components calculated in terms of mass percentage: 10-15wt% of mixed solvent, 15-30wt% of long-chain fatty acid, 10-20wt% of polyol, 20-40wt% of acid anhydride, and 0.5-3wt% of second catalyst.

[0008] In an embodiment, the small molecule epoxy resin is one or more of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, phenolic epoxy resin, polyether epoxy resin.

[0009] In an embodiment, the chain extender is one or more of bisphenol A chain extender, bisphenol A chain extender derivative;

[0010] The molecular weight regulator is one or more of monocarboxylic acid, monohydric phenol;

[0011] The first catalyst is one or more of dimethylbenzylamine, triethylamine, dimethylethanolamine, triphenylphosphine.

[0012] In an embodiment, the amine compound is one or more of methylethanolamine, diethanolamine, dimethylaminopropylamine, ketimine of ethanolamine, diethylenetriamine, triethylenetetramine, ketimine of polyethylene polyamine.

[0013] In an embodiment, the isocyanate curing agent is prepared by the following method: reacting isocyanate monomer with blocking agent at 60-100°C until the characteristic peak of -NCO group in infrared spectrum disappears completely;

[0014] The isocyanate monomer is one or more of aliphatic isocyanate, aromatic isocyanate;

[0015] The blocking agent is one or more of alcohol ether, small molecule alcohol, ketoxime, small molecule amine, amide, heterocyclic pyridine.

[0016] In an embodiment, the organic solvent is one or more of alcohol ether, small molecule alcohol, ketone;

[0017] The auxiliary agent is one or more of acetal-based substrate wetting agent, polysiloxane-based anti-cratering agent, polyether polyol-based leveling agent;

[0018] The neutralizing agent is one or more of organic acid and its derivative, inorganic acid and its derivative.

[0019] In an embodiment, the mixed solvent is one or more of toluene, xylene, methyl isobutyl ketone, N-methyl pyrrolidone;

[0020] The long-chain fatty acid is one or more of palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid;

[0021] The polyhydric alcohol is one or more of ethylene glycol, propylene glycol, glycerol, pentaerythritol;

[0022] The acid anhydride is one or more of phthalic anhydride, hexahydrophthalic anhydride, trimellitic anhydride;

[0023] The second catalyst is one or more of stannous octoate, stannous oxalate, dibutyltin dilaurate.

[0024] In one embodiment, the hyperbranched polyester is prepared by the following method: esterification of the polyol and the long chain fatty acid under the catalysis of the second catalyst in a nitrogen atmosphere at 140-200℃ for 4-8 hours to obtain a hyperbranched polyester prepolymer with terminal hydroxyl groups; cooling the hyperbranched polyester prepolymer to 120℃, adding the acid anhydride dissolved in the mixed solvent, the amount of the acid anhydride being 8-16% of the hyperbranched polyester prepolymer; reacting at 120-200℃ until the acid value is constant, and removing the solvent to obtain the hyperbranched resin for cathodic electrophoresis.

[0025] The second aspect of the present application also provides a preparation method of the above-mentioned epoxy resin for cathodic electrophoresis primer, comprising the following steps:

[0026] adding the small molecule epoxy resin, the chain extender, the molecular weight regulator and the first catalyst in a reaction container, and performing reaction chain extension at a temperature of 100-170℃ to obtain a macromolecular epoxy resin with an epoxy equivalent weight of 600-1100; continuing to react at a temperature of 110-140℃ after adding the amine compound under stirring to obtain an amine-modified macromolecular epoxy substance; adding the isocyanate curing agent, the hyperbranched polyester and the auxiliary agent in the amine-modified macromolecular epoxy substance to obtain an epoxy base resin; preheating the epoxy base resin to 70-90℃, and adding the neutralizing agent and deionized water for dilution to obtain the epoxy resin with a solid content of 34-38%.

[0027] The third aspect of the present application also provides a cathodic electrophoresis primer, comprising the following components in terms of mass percentage: 60-80wt% of the above-mentioned epoxy resin, 10-20wt% of pigment paste, and 0-30wt% of deionized water.

[0028] The preparation method of the cathodic electrophoresis primer comprises the following steps: adding the epoxy resin aqueous solution and deionized water into a dispersion container, controlling the stirring speed at 800rpm, and then adding the pigment paste, and stirring for 2 hours to obtain the cathodic electrophoresis primer.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] The composition of the epoxy resin for the cathodic electrophoretic primer provided by the present application selects the hyperbranched polyester to replace the volatile organic solvent or the heat-volatile plasticizer, and the film-forming aid has a brand-new selection. The hyperbranched polyester has good film-forming performance and will not crack into small-molecule organic volatile substances in the process of electrophoresis baking and coating, so that the cathodic electrophoretic primer has fluidity, and the coating film thickness, mechanical property, thermal property and electrical property of the final product can be improved. In addition, in the preparation method of the epoxy resin for the cathodic electrophoretic primer provided by the present application, the raw materials are widely sourced, the cost is low, the production process is simplified, and the production efficiency is improved. DETAILED DESCRIPTION

[0031] The present application will be described in detail below in combination with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be pointed out that those skilled in the art can make several changes and improvements without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0032] The present application first provides an epoxy resin for a cathodic electrophoretic primer, which comprises the following components calculated in percentage by mass: 10-25wt% of a small-molecule epoxy resin, 0.5-1wt% of a chain extender, 0.5-1wt% of a molecular weight regulator, 1-2wt% of a first catalyst, 0.5-5wt% of an amine compound, 5-25wt% of an isocyanate curing agent, 10-25wt% of a hyperbranched polyester, 0.01-0.05wt% of an organic solvent, 5-15wt% of an aid, 0.5-1wt% of a neutralizing agent, and 40-60wt% of deionized water, wherein the hyperbranched polyester comprises the following components calculated in percentage by mass: 10-15wt% of a mixed solvent, 15-30wt% of a long-chain fatty acid, 10-20wt% of a polyol, 20-40wt% of an acid anhydride, and 0.5-3wt% of a second catalyst.

[0033] In an embodiment, the small-molecule epoxy resin is one or more of a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a bisphenol S type epoxy resin, a phenolic epoxy resin, and a polyether epoxy resin.

[0034] In an embodiment, the chain extender is one or more of a bisphenol A type chain extender and a bisphenol A type chain extender derivative. The phenolic hydroxyl group of the bisphenol A type chain extender and the epoxy resin are dehydrated and condensed with each other, so as to control the molecular weight and distribution of the final resin product.

[0035] The molecular weight regulator is one or more of a monobasic carboxylic acid and a monohydric phenol. The monobasic carboxylic acid or the monohydric phenol acts as a reaction terminator to effectively control the molecular weight of the chain extension product, so as to make the resin have good fluidity.

[0036] The first catalyst is one or more of dimethyl benzyl amine, triethyl amine, dimethyl ethanol amine, triphenyl phosphine, and the addition of the catalyst can accelerate the reaction rate of the chain extender with the epoxy resin, and the polymerization completed resin is obtained more quickly.

[0037] In an embodiment, the amine compound is one or more of methyl ethanol amine, diethanol amine, dimethyl amino propyl amine, ketimine of ethanol amine, diethylene triamine, triethylene tetramine, and ketimine of polyethylene polyamine, and the amine compound can open the ring of the epoxy resin to obtain an amine modified cationic resin, and the performance of the resin is improved.

[0038] In an embodiment, the isocyanate curing agent is prepared by the following method: the isocyanate monomer is reacted with a blocking agent at 60-100°C until the characteristic peak of the -NCO group in the infrared spectrum disappears completely.

[0039] The isocyanate monomer is one or more of aliphatic isocyanate and aromatic isocyanate.

[0040] The blocking agent is one or more of alcohol ethers, small molecule alcohols, ketoxime, small molecule amines, amides, and heterocyclic pyridines.

[0041] In an embodiment, the organic solvent is one or more of alcohol ethers, small molecule alcohols, and ketones, and the addition of the organic solvent in the production process can flush the materials remaining in the pipeline, so that the feeding is more accurate and precise.

[0042] The auxiliary agent is one or more of acetal base substrate wetting agent, polysiloxane anti-porosity agent, and polyether polyol leveling agent.

[0043] The neutralizing agent is one or more of organic acids and derivatives thereof and inorganic acids and derivatives thereof, and the neutralizing agent can neutralize the amine compound in the resin to generate a water-soluble cationic resin, and the performance of the final resin product is improved.

[0044] In an embodiment, the mixed solvent is one or more of toluene, xylene, methyl isobutyl ketone, and N-methyl pyrrolidone.

[0045] The long-chain fatty acid is one or more of palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid, and the long-chain fatty acid can adjust the film forming property of the hyperbranched polyester to ensure the mechanical property.

[0046] The polyhydric alcohol is one or more of ethylene glycol, propylene glycol, glycerol, and pentaerythritol, and the polyhydric alcohol adjusts the branching degree of the hyperbranched polyester to reduce the heating loss of the resin.

[0047] The anhydride is one or more of phthalic anhydride, hexahydrophthalic anhydride, trimellitic anhydride, and the addition of the anhydride not only promotes the film-forming property of the hyperbranched polyester, but also adjusts the molecular weight and distribution thereof.

[0048] The second catalyst is one or more of stannous octoate, stannous oxalate, and dibutyltin dilaurate.

[0049] In an embodiment, the hyperbranched polyester is prepared by the following method: esterification of the polyol and the long-chain fatty acid under the catalysis of the second catalyst in a nitrogen atmosphere at 140-200°C for 4-8 hours to obtain a hyperbranched polyester prepolymer with terminal hydroxyl groups; cooling the hyperbranched polyester prepolymer with terminal hydroxyl groups to 120°C, adding the anhydride dissolved in the mixed solvent, and the amount of the anhydride is 8-16% of the hyperbranched polyester prepolymer with terminal hydroxyl groups; reacting at 120-200°C until the acid value is constant, and then removing the solvent to obtain the hyperbranched resin for cathodic electrophoresis.

[0050] The application further provides a preparation method of the epoxy resin for the cathodic electrophoresis primer.

[0051] The small-molecule epoxy resin, the chain extender, the molecular weight regulator, and the first catalyst are added to a reaction container, and the reaction is carried out at a temperature of 100-170°C to obtain a macromolecular epoxy resin with an epoxy equivalent weight of 600-1100; the amine compound is added under stirring, and the reaction is continued at a temperature of 110-140°C to obtain an amine-modified macromolecular epoxy substance; the isocyanate curing agent, the hyperbranched polyester, and the auxiliary agent are added to the amine-modified macromolecular epoxy substance to obtain an epoxy base resin; the epoxy base resin is preheated to 70-90°C, and then the neutralizing agent and deionized water are added to dilute the epoxy base resin to obtain the epoxy resin with a solid content of 34-38%.

[0052] The application further provides a cathodic electrophoresis primer, which comprises the following components in terms of mass percentage: 60-80 wt% of the epoxy resin, 10-20 wt% of pigment paste, and 0-30 wt% of deionized water.

[0053] The preparation method of the cathodic electrophoresis primer comprises the following steps: adding the epoxy resin aqueous solution and deionized water to a dispersion container, controlling the stirring speed at 800 rpm, and then adding the pigment paste, and stirring for 2 hours to obtain the cathodic electrophoresis primer.

[0054] The application is further described below by way of examples:

[0055] Example 1

[0056] The embodiment provides an epoxy resin for a cathodic electrophoretic primer, a cathodic electrophoretic primer comprising the epoxy resin and a preparation method of both.

[0057] The epoxy resin comprises the following components in parts by mass: 25wt% of epoxy resin, 10wt% of bisphenol A, 1wt% of phenol, 0.2wt% of dimethyl benzyl amine, 1.5wt% of diethanol amine, 20wt% of isocyanate curing agent, 20wt% of hyperbranched polyester A, 0.1wt% of polysiloxane, 2wt% of polyether polyol, 1wt% of acetic acid and 60wt% of deionized water, wherein the hyperbranched polyester A comprises the following components in percentage: 15wt% of dimethylbenzene / methyl isobutyl ketone, 15wt% of long-chain fatty acid, 20wt% of polyol, 30wt% of trimellitic anhydride and 0.5wt% of stannous octoate.

[0058] The cathodic electrophoretic primer comprises the following components in parts by mass: 60wt% of epoxy resin, 20wt% of pigment paste and 20wt% of deionized water.

[0059] The preparation method of the epoxy resin comprises the following steps: adding the epoxy resin, bisphenol A, phenol and dimethyl benzyl amine in a reaction container, performing reaction chain extension at a temperature of 134 DEG C to obtain a macromolecular epoxy resin with an epoxy equivalent weight of 1050; continuing to react at a temperature of 119 DEG C after stirring and adding diethanol amine to obtain an amine-modified macromolecular epoxy substance; adding an isocyanate curing agent, a hyperbranched polyester and a polyether polyol in the amine-modified macromolecular epoxy substance to obtain an epoxy main body resin; preheating the epoxy main body resin to 90 DEG C, adding acetic acid and deionized water to dilute to obtain an epoxy resin with a solid content of 30%; wherein the preparation method of the hyperbranched polyester is as follows: performing esterification reaction at 198 DEG C for 2 hours to obtain a hyperbranched polyester prepolymer with terminal hydroxyl groups; cooling the hyperbranched polyester prepolymer with terminal hydroxyl groups to 120 DEG C, adding trimellitic anhydride dissolved in dimethylbenzene / methyl isobutyl ketone, and the amount of the trimellitic anhydride is 33% of the hyperbranched polyester prepolymer with terminal hydroxyl groups; reacting at 120 DEG C until the acid value does not change, and removing the solvent to obtain a hyperbranched resin for cathodic electrophoresis; and the isocyanate curing agent is prepared by the following method: reacting isocyanate monomer and a blocking agent at 68 DEG C until the characteristic peak of -NCO group in the infrared spectrum disappears completely.

[0060] The preparation method of the cathodic electrophoretic primer comprises the following steps: adding the epoxy resin and deionized water into a dispersion container, controlling the stirring speed at 800 rpm, and then adding the pigment paste, and stirring for 2 hours to obtain the cathodic electrophoretic primer.

[0061] Test of the cathodic electrophoretic primer: the low volatile organic compound content (VOC) of the cathodic electrophoretic primer prepared in the embodiment was determined according to the Technical Requirements for Low Volatile Organic Compound Content Coating Products (GB / T 38597-2020); the electrophoretic paint was coated on the cold-rolled steel sheet treated by film pretreatment through a direct current power supply, and the electrophoretic plate was obtained after drying; the film thickness of the cathodic electrophoretic primer was measured by a QNIX7500 handheld film thickness meter; the impact was measured by a paint film impact tester; the appearance and leveling state was observed by visual observation; the cross test was carried out according to the ASTM B117 standard, using a neutral salt spray chamber, and the one-side blistering and corrosion state was observed; the 60° gloss of the cathodic electrophoretic primer was measured by a BYK gloss meter, and all the test data are shown in Table 1.

[0062] Example 2

[0063] The embodiment provides an epoxy resin for a cathodic electrophoretic primer, a cathodic electrophoretic primer comprising the foregoing epoxy resin, and a preparation method of both.

[0064] The epoxy resin comprises the following components calculated by mass parts: epoxy resin 25wt%, bisphenol A 10wt%, phenol 1wt%, dimethyl benzyl amine 0.2wt%, diethanol amine 1.5wt%, isocyanate curing agent 20wt%, hyperbranched polyester B 20wt%, polysiloxane 0.1wt%, polyether polyol 2wt%, acetic acid 1wt%, deionized water 60wt%, wherein the hyperbranched polyester B comprises the following components calculated by percentage: dimethylbenzene / methyl isobutyl ketone mixed solvent 15wt%, long-chain fatty acid 30wt%, polyol 10wt%, hexahydrophthalic anhydride 15wt%, phthalic anhydride 15wt%, stannous octoate 0.5wt%.

[0065] The cathodic electrophoretic primer comprises the following components calculated by mass percentage: epoxy resin 60wt%, pigment paste 20wt%, deionized water 20wt%.

[0066] The preparation method of the epoxy resin comprises the following steps: adding the epoxy resin, bisphenol A, phenol and dimethyl benzylamine in a reaction container, and performing a reaction chain extension at a temperature of 134 DEG C to obtain a macromolecular epoxy resin with an epoxy equivalent weight of 1050; continuing the reaction at a temperature of 119 DEG C after adding diethanolamine under stirring to obtain an amine-modified macromolecular epoxy substance; adding an isocyanate curing agent, a hyperbranched polyester B and a polyether polyol in the amine-modified macromolecular epoxy substance to obtain an epoxy base resin; preheating the epoxy base resin to 90 DEG C, and then adding acetic acid and deionized water for dilution to obtain an epoxy resin with a solid content of 30%; wherein the preparation method of the hyperbranched polyester B is as follows: performing an esterification reaction at 198 DEG C for 2 hours to obtain a hyperbranched polyester prepolymer with terminal hydroxyl groups; cooling the hyperbranched polyester prepolymer with terminal hydroxyl groups to 120 DEG C, and then adding hexahydrophthalic anhydride and phthalic anhydride dissolved in a dimethylbenzene / methyl isobutyl ketone mixed solvent, wherein the amount of the anhydride is 33% of the hyperbranched polyester prepolymer with terminal hydroxyl groups; reacting at 120 DEG C until the acid value does not change, and then removing the solvent to obtain the hyperbranched resin B for cathodic electrophoresis; and the isocyanate curing agent is prepared by the following method: reacting the isocyanate monomer with a blocking agent at 68 DEG C until the characteristic peak of the -NCO group in the infrared spectrum disappears completely.

[0067] The preparation method of the cathodic electrophoretic primer comprises the following steps: adding the epoxy resin and deionized water into a dispersion container, controlling the stirring speed at 800 rpm, then adding the pigment paste, and stirring for 2 hours to obtain the cathodic electrophoretic primer.

[0068] Test of the cathodic electrophoretic primer: the low volatile organic compound content (VOC) of the cathodic electrophoretic primer prepared in this embodiment is determined according to the Technical Requirements for Low Volatile Organic Compound Content Coating Products (GB / T 38597-2020); the electrophoretic paint is coated on a cold-rolled steel sheet subjected to a film pretreatment by a direct current power supply, and an electrophoretic plate is obtained after drying; the film thickness of the cathodic electrophoretic primer is measured by a QNIX7500 handheld film thickness meter; the impact is measured by a paint film impact tester; the appearance and leveling state is observed by visual observation; the single-side blistering and corrosion state is observed by a cross test according to ASTM B117 standard, using a neutral salt spray chamber; and the 60 DEG gloss of the cathodic electrophoretic primer is measured by a BYK gloss meter, and all the test data are shown in Table 1.

[0069] Example 3

[0070] The present embodiment provides an epoxy resin for a cathodic electrophoretic primer, a cathodic electrophoretic primer comprising the aforementioned epoxy resin, and preparation methods of both.

[0071] The epoxy resin comprises the following components by mass parts: epoxy resin 25wt%, bisphenol A 10wt%, phenol 1wt%, dimethyl benzyl amine 0.2wt%, diethanol amine 1.5wt%, isocyanate curing agent 20wt%, hyperbranched polyester C 20wt%, polysiloxane 0.1wt%, polyether polyol 2wt%, acetic acid 1wt%, deionized water 60wt%, wherein the hyperbranched polyester C comprises the following components by percentage: dimethylbenzene / methyl isobutyl ketone mixed solvent 15wt%, long-chain fatty acid 17.5wt%, polyol 15wt%, hexahydrophthalic anhydride 20wt%, trimellitic anhydride 20wt%, stannous octoate 0.5wt%.

[0072] The cathodic electrophoretic primer comprises the following components by mass percentage: epoxy resin 60wt%, pigment paste 20wt%, deionized water 20wt%.

[0073] The preparation method of the epoxy resin comprises the following steps: adding epoxy resin, bisphenol A, phenol and dimethyl benzyl amine in a reaction container, and performing reaction chain extension at a temperature of 134℃ to obtain a macromolecular epoxy resin with an epoxy equivalent weight of 1050; after stirring and adding diethanol amine, continuing to react at a temperature of 119℃ to obtain an amine-modified macromolecular epoxy substance; after adding an isocyanate curing agent, hyperbranched polyester C and a polyether polyol in the amine-modified macromolecular epoxy substance, an epoxy main body resin is obtained; after preheating the epoxy main body resin to 90℃, adding acetic acid and deionized water for dilution, an epoxy resin with a solid content of 30% is obtained; wherein, the preparation method of the hyperbranched polyester C is: performing esterification reaction at 198℃ for 2 hours to obtain a hydroxyl-terminated hyperbranched polyester prepolymer; after cooling the hydroxyl-terminated hyperbranched polyester prepolymer to 120℃, adding hexahydrophthalic anhydride and trimellitic anhydride dissolved in dimethylbenzene / methyl isobutyl ketone mixed solvent, the amount of the anhydride is 33% of the hydroxyl-terminated hyperbranched polyester prepolymer; after reacting at 120℃ until the acid value does not change, removing the solvent to obtain a hyperbranched resin C for cathodic electrophoresis; the isocyanate curing agent is prepared by the following method: under the condition of 68℃, reacting isocyanate monomer with a blocking agent until the characteristic peak of -NCO group in the infrared spectrum disappears completely.

[0074] The preparation method of the cathodic electrophoretic primer comprises the following steps: adding epoxy resin and deionized water into a dispersion container, controlling the stirring speed at 800rpm, after adding pigment paste, stirring for 2 hours to obtain a cathodic electrophoretic primer.

[0075] Test of the cathodic electrophoretic primer: the low volatile organic compound content (VOC) of the cathodic electrophoretic primer prepared in the present example was determined according to the Technical Requirements for Low Volatile Organic Compound Content Coating Products (GB / T 38597-2020); the electrophoretic paint was coated on the cold-rolled steel sheet treated by film pretreatment through a direct current power supply, and the electrophoretic plate was obtained after drying; the film thickness of the cathodic electrophoretic primer was measured by a QNIX7500 handheld film thickness meter; the impact was measured by a paint film impact tester; the appearance and leveling state was observed by visual observation; the cross test was carried out according to the ASTM B117 standard, using a neutral salt spray chamber, and the one-side blistering and corrosion state was observed; the 60° gloss of the cathodic electrophoretic primer was measured by a BYK gloss meter, and all the test data are shown in Table 1.

[0076] Example 4

[0077] The present example provides an epoxy resin for a cathodic electrophoretic primer, a cathodic electrophoretic primer comprising the aforementioned epoxy resin, and a preparation method of both.

[0078] The epoxy resin comprises the following components calculated by mass parts: epoxy resin 25wt%, bisphenol A 10wt%, phenol 1wt%, dimethyl benzylamine 0.2wt%, diethanolamine 1.5wt%, isocyanate curing agent 20wt%, hyperbranched polyester D 20wt%, polysiloxane 0.1wt%, polyether polyol 2wt%, acetic acid 1wt%, deionized water 60wt%, wherein the hyperbranched polyester D comprises the following components calculated by percentage: dimethylbenzene / methyl isobutyl ketone mixed solvent 10wt%, long-chain fatty acid 20wt%, polyol 20wt%, hexahydrophthalic anhydride 10wt%, trimellitic anhydride 10wt%, stannous octoate 0.5wt%.

[0079] The cathodic electrophoretic primer comprises the following components calculated by mass percentage: epoxy resin 60wt%, pigment paste 20wt%, deionized water 20wt%.

[0080] The preparation method of the epoxy resin comprises the following steps: adding the epoxy resin, bisphenol A, phenol and dimethyl benzylamine in a reaction container, and performing reaction chain extension at a temperature of 134 DEG C to obtain a macromolecular epoxy resin with an epoxy equivalent weight of 1050; after stirring and adding diethanolamine, continuing to react at a temperature of 119 DEG C to obtain an amine-modified macromolecular epoxy substance; adding isocyanate curing agent, hyperbranched polyester D and polyether polyol in the amine-modified macromolecular epoxy substance to obtain an epoxy base resin; after preheating the epoxy base resin to 90 DEG C, adding acetic acid and deionized water to dilute to obtain an epoxy resin with a solid content of 30%; wherein, the preparation method of the hyperbranched polyester D is: performing esterification reaction at 198 DEG C for 2 hours to obtain a hyperbranched polyester prepolymer with terminal hydroxyl groups; cooling the hyperbranched polyester prepolymer with terminal hydroxyl groups to 120 DEG C, adding hexahydrophthalic anhydride and trimellitic anhydride dissolved in a mixed solvent of xylene / methyl isobutyl ketone, and the amount of the anhydride is 33% of the hyperbranched polyester prepolymer with terminal hydroxyl groups; reacting at 120 DEG C until the acid value does not change, and then removing the solvent to obtain a hyperbranched resin D for cathodic electrophoresis; the isocyanate curing agent is prepared by the following method: under the condition of 68 DEG C, the isocyanate monomer is reacted with the blocking agent until the characteristic peak of -NCO group in the infrared spectrum disappears completely.

[0081] The preparation method of the cathodic electrophoretic primer comprises the following steps: adding the epoxy resin and deionized water into a dispersion container, controlling the stirring speed at 800 rpm, then adding the pigment paste, and stirring for 2 hours to obtain the cathodic electrophoretic primer.

[0082] Test of the cathodic electrophoretic primer: the low volatile organic compound content (VOC) of the cathodic electrophoretic primer prepared in the embodiment is determined according to the Technical Requirements for Low Volatile Organic Compound Content Coating Products (GB / T 38597-2020); the electrophoretic paint is coated on the cold-rolled steel sheet after film pretreatment by a direct current power supply, and the electrophoretic plate is obtained after drying; the film thickness of the cathodic electrophoretic primer is measured by a QNIX7500 handheld film thickness meter; the impact is measured by a paint film impact tester; the appearance and leveling state is observed by visual observation; the single-side blistering and corrosion state is observed by using a neutral salt spray chamber for cross-cut test according to the ASTM B117 standard; the 60 DEG gloss of the cathodic electrophoretic primer is measured by a BYK gloss meter, and all the test data are shown in Table 1.

[0083] Comparative Example 1

[0084] The present comparative example provides an epoxy resin for a cathodic electrophoretic primer, a cathodic electrophoretic primer comprising the aforementioned epoxy resin, and preparation methods of the two.

[0085] Compared with Example 4, the present comparative example uses an organic solvent conducive to film formation in the composition of the epoxy resin, and the compositions, preparation methods and test methods of other parts remain consistent with Example 4, and the test results are shown in Table 1.

[0086] Comparative Example 2

[0087] The present comparative example provides an epoxy resin for cathodic electrophoretic primer, a cathodic electrophoretic primer comprising the aforementioned epoxy resin and a preparation method of both.

[0088] Compared with Example 4, the present comparative example uses more organic solvent conducive to film formation in the composition of the epoxy resin, and the compositions, preparation methods and test methods of other parts remain consistent with Example 4. The test results are shown in Table 1.

[0089] Table 1

[0090] Note 1: The electrophoretic paint coating construction condition is direct current 240V for 2 minutes;

[0091] Note 2: The electrophoretic paint coating construction condition is direct current 200V for 2 minutes;

[0092] Other notes on performance tests: except for VOC performance, the drying conditions for other performances are 170℃ for 20 minutes.

[0093] As can be seen from the above table, in Comparative Example 1, due to the addition of a part of film-forming aid ethylene glycol monohexyl ether, there are more free low-volatile organic solvents in the coating during VOC testing, which in turn causes the VOC content of the synthesized product to be higher, and at the same time, the film-forming ability of the electrophoretic composition is still poor, and the resin leveling property is insufficient. In Comparative Example 2, due to the increase of low-volatile solvent ethylene glycol monohexyl ether, the free low-volatile organic solvents in the coating increase, which in turn causes the VOC content of the synthesized product to increase, and at the same time, the film-forming ability of the electrophoretic composition is improved, and the resin leveling property is good.

[0094] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the present application. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be arbitrarily combined with each other.

Claims

1. An epoxy resin for use in cathodic electrophoretic primer, characterized in that, The composition comprises the following components in percentage by mass: 10-25wt% of small molecule epoxy resin, 0.5-1wt% of chain extender, 0.5-1wt% of molecular weight regulator, 1-2wt% of first catalyst, 0.5-5wt% of amine compound, 5-25wt% of isocyanate curing agent, 10-25wt% of hyperbranched polyester, 0.01-0.05wt% of organic solvent, 5-15wt% of auxiliary agent, 0.5-1wt% of neutralizing agent, and 40-60wt% of deionized water. The hyperbranched polyester comprises the following components in percentage by mass: 10-15wt% of mixed solvent, 15-30wt% of long-chain fatty acid, 10-20wt% of polyol, 20-40wt% of acid anhydride, and 0.5-3wt% of second catalyst.

2. The epoxy resin for cathodic electrophoretic primer according to claim 1, characterized by, The small molecule epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenolic epoxy resin, and polyether epoxy resin.

3. The epoxy resin for cathodic electrophoretic primer according to claim 1, characterized by, The chain extender is one or more of bisphenol A type chain extender and bisphenol A type chain extender derivative. The molecular weight regulator is one or more of monobasic carboxylic acid and monobasic phenol. The first catalyst is one or more of dimethylbenzylamine, triethylamine, dimethylethanolamine, and triphenylphosphine.

4. The epoxy resin for cathodic electrophoretic primer according to claim 1, characterized by, The amine compound is one or more of methyl ethanolamine, diethanolamine, dimethylaminopropylamine, ketimine of ethanolamine, diethylene triamine, triethylene tetramine, and ketimine of polyethylene polyamine.

5. The epoxy resin for cathodic electrophoretic primer according to claim 1, characterized by, The isocyanate curing agent is prepared by the following method: reacting isocyanate monomer with blocking agent at 60-100℃ until the characteristic peak of -NCO group in infrared spectrum disappears completely. The isocyanate monomer is one or more of aliphatic isocyanate and aromatic isocyanate. The blocking agent is one or more of alcohol ether, small molecule alcohol, ketoxime, small molecule amine, amide, and heterocyclic pyridine.

6. The epoxy resin for cathodic electrophoretic primer according to claim 1, characterized by, The organic solvent is one or more of alcohol ether, small molecule alcohol, and ketone. The auxiliary agent is one or more of acetal base substrate wetting agent, polysiloxane anti-porosity agent, and polyether polyol leveling agent. The neutralizing agent is one or more of organic acid and its derivative, and inorganic acid and its derivative.

7. The epoxy resin for cathodic electrophoretic primer according to claim 1, characterized by, The mixed solvent is one or more of toluene, xylene, methyl isobutyl ketone, and N-methyl pyrrolidone. The long-chain fatty acid is one or more of palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid. The polyol is one or more of ethylene glycol, propylene glycol, glycerol, and pentaerythritol. The acid anhydride is one or more of phthalic anhydride, hexahydrophthalic anhydride, and trimellitic anhydride. The second catalyst is one or more of stannous octoate, stannous oxalate, and dibutyltin dilaurate.

8. The epoxy resin for cathodic electrophoretic primer according to claim 7, characterized by, The hyperbranched polyester is prepared by the following method: esterification of the polyol and the long chain fatty acid under the catalysis of the second catalyst in a nitrogen atmosphere at 140-200℃ for 4-8 hours to obtain a hydroxyl-terminated hyperbranched polyester prepolymer; cooling the hydroxyl-terminated hyperbranched polyester prepolymer to 120℃, adding the acid anhydride dissolved in the mixed solvent, the amount of the acid anhydride being 8-16% of the hydroxyl-terminated hyperbranched polyester prepolymer; reacting at 120-200℃ until the acid value is constant, and removing the solvent to obtain the hyperbranched resin for cathodic electrophoresis.

9. A process for the preparation of an epoxy resin for cathodic electrophoretic primer according to claims 1-8, characterized by, The method comprises the following steps: adding the small molecule epoxy resin, the chain extender, the molecular weight regulator and the first catalyst in a reaction vessel, and performing chain extension at a temperature of 100-170℃ to obtain a macromolecular epoxy resin with an epoxy equivalent weight of 600-1100; adding the amine compound under stirring and continuing the reaction at a temperature of 110-140℃ to obtain an amine-modified macromolecular epoxy substance; adding the isocyanate curing agent, the hyperbranched polyester and the auxiliary agent in the amine-modified macromolecular epoxy substance to obtain an epoxy base resin; preheating the epoxy base resin to 70-90℃, and adding the neutralizing agent and deionized water for dilution to obtain the epoxy resin with a solid content of 34-38%.

10. A cathodic electrocoat primer characterized in that, The method comprises the following components by mass percentage: the epoxy resin of claims 1-9 60-80wt%, pigment paste 10-20wt%, deionized water 0-30wt%. The preparation method of the cathodic electrophoretic primer comprises the following steps: adding the epoxy resin aqueous solution and deionized water into a dispersion vessel, controlling the stirring speed at 800rpm, and then adding the pigment paste, and stirring for 2 hours to obtain the cathodic electrophoretic primer.

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