Electrophoresis-non-electrophoresis composite coating and preparation method thereof

Abstract

The invention relates to the technical field of electrophoresis coatings, in particular to an electrophoresis-non-electrophoresis composite coating and a preparation method thereof. The invention provides an electrophoresis-non-electrophoresis composite coating. The composite coating comprises an electrophoresis coating and a non-electrophoresis coating compounded on the surface of the electrophoresis coating, the component of the electrophoretic coating comprises polyimide; the component of the non-electrophoretic coating comprises macromolecular resin; the absolute value of the difference between solubility parameters of the polymer resin and the polyimide is less than 1.3 (J / cm < 3 >) 1 / 2; according to the prepared electrophoresis-non-electrophoresis composite coating, the excellent adhesiveness between an electrophoresis coating and a non-electrophoresis coating can be guaranteed, and the comprehensive performance, such as insulativity, scratch resistance, cohesiveness, corona resistance and / or PDIV, of the composite coating can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrophoretic coatings, and in particular to an electrophoretic-non-electrophoretic composite coating and a preparation method thereof. Background Art

[0002] Electrophoretic coating is a modern surface treatment technology that utilizes the principles of electrodeposition and flow to deposit charged paint particles onto charged metal workpieces, thereby achieving coating, corrosion protection, and insulation. Electrophoretic coating is widely used in the automotive, home appliance, construction, aerospace, and other fields. With the continuous advancement of science and technology, the quality and performance requirements of electrophoretic coatings are also constantly increasing.

[0003] Polyimide (hereinafter referred to as "PI") electrophoretic coatings have excellent properties such as high insulation, high heat resistance and high chemical resistance and are gradually being recognized by the market. They are particularly suitable for various application scenarios such as new energy vehicles that have high requirements for insulation, heat resistance and chemical resistance of special-shaped metal workpieces. However, due to various factors such as the limited design of PI molecular structure, the difficulty in arbitrarily controlling the electrophoretic process, the poor surface condition of metal workpieces and the diversity of metal workpiece shapes, the optimization and expansion of other comprehensive properties of PI electrophoretic coatings, except for insulation, heat resistance and chemical resistance, are greatly restricted, such as many insulation defects, poor scratch resistance, poor adhesion, poor corona resistance and / or low partial discharge inception voltage (PDIV). Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide an electrophoretic-non-electrophoretic composite coating and a preparation method thereof, which can effectively solve the technical problems of traditional PI electrophoretic coatings such as many defects, poor scratch resistance, poor adhesion, poor corona resistance, and low PDIV.

[0005] The present invention provides an electrophoretic-non-electrophoretic composite coating, wherein the composite coating comprises an electrophoretic coating and a non-electrophoretic coating composited on the surface of the electrophoretic coating;

[0006] The components of the electrophoretic coating include polyimide;

[0007] The components of the non-electrophoretic coating include polymer resin;

[0008] The absolute value of the difference in solubility parameters between the polymer resin and the polyimide is less than 1.3 (J / cm 3 ) 1 / 2 .

[0009] Preferably, the polymer resin includes at least one of polyimide, polyester, polyurethane, polyesterimide, polyetherimide, polyamide, polyamideimide, and acetal.

[0010] The present invention also provides a method for preparing the electrophoretic-non-electrophoretic composite coating described above, comprising the following steps:

[0011] A) compounding the non-electrophoretic coating slurry on the surface of a metal workpiece having an electrophoretic coating through a coating process to obtain a semi-finished metal workpiece;

[0012] The non-electrophoretic coating slurry includes components of the non-electrophoretic coating;

[0013] B) rotating, drying, and solidifying the semi-finished metal workpiece to obtain an electrophoretic-non-electrophoretic composite coating.

[0014] Preferably, in step A), the method for preparing a metal workpiece containing an electrophoretic coating comprises the following steps:

[0015] a) Pre-processing of metal workpieces;

[0016] b) immersing the metal workpiece treated in step a) in an electrophoretic solution, and performing electrophoretic deposition under an external voltage to obtain a coating on the surface of the metal workpiece;

[0017] c) drying the metal workpiece after the electrophoretic deposition in step b) to obtain a metal workpiece containing an electrophoretic coating.

[0018] Preferably, in step a), the pretreatment includes at least one of leveling, degreasing, rust removal, oxidation, and neutralization of the surface of the metal workpiece.

[0019] Preferably, the leveling of the metal workpiece surface includes at least one of grinding, mechanical polishing, electrolytic polishing and chemical polishing of the metal workpiece; the degreasing includes at least one of organic solvent degreasing, chemical degreasing and electrochemical degreasing; the rust removal includes at least one of chemical etching rust removal and electrochemical etching rust removal; the oxidation includes at least one of chemical oxidation and electrochemical oxidation.

[0020] Preferably, in step A), the non-electrophoretic coating slurry further comprises an additive, and the additive comprises at least one of a solvent, a leveling agent, a color paste and a filler.

[0021] Preferably, in step A), the solid content of the polymer resin in the non-electrophoretic coating slurry is 5% to 30%.

[0022] Preferably, in step B), the rotation speed of the rotary drying is 5 to 25 r / min, and the inclination angle is 15° to 45°.

[0023] Preferably, in step B), the temperature of the rotary drying and curing is 80-260° C., and the time is 30-90 minutes.

[0024] The present invention provides an electrophoretic-non-electrophoretic composite coating, wherein the composite coating comprises an electrophoretic coating and a non-electrophoretic coating composited on the surface of the electrophoretic coating; the electrophoretic coating comprises a component of polyimide; the non-electrophoretic coating comprises a polymer resin; the absolute value of the difference in solubility parameter between the polymer resin and the polyimide is less than 1.3 (J / cm 3 ) 1 / 2 ; The electrophoretic-non-electrophoretic composite coating prepared by the present invention can not only ensure excellent adhesion between the electrophoretic coating and the non-electrophoretic coating, but also effectively improve the comprehensive performance of the composite coating, such as insulation, scratch resistance, adhesion, corona resistance and / or PDIV. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] The present invention provides an electrophoretic-non-electrophoretic composite coating, which comprises an electrophoretic coating and a non-electrophoretic coating composited on the surface of the electrophoretic coating.

[0027] The components of the electrophoretic coating include polyimide;

[0028] The components of the non-electrophoretic coating and polyimide have the characteristic of "like dissolves like".

[0029] In some embodiments of the present invention, the component of the non-electrophoretic coating layer includes a polymer resin, and the polymer resin includes at least one of polyimide, polyester, polyurethane, polyesterimide, polyetherimide, polyamide, polyamideimide, and acetal. The absolute value of the difference in solubility parameter between the polymer resin and the polyimide is less than 1.3 (J / cm 3 ) 1 / 2 ; For example, 0.4 (J / cm 3 ) 1 / 2 、0.5(J / cm 3 ) 1 / 2 , 0, 0.7(J / cm 3 ) 1 / 2 、0.6(J / cm 3 ) 1 / 2 、1.0(J / cm 3 ) 1 / 2 .

[0030] In some embodiments of the present invention, the thickness of the electrophoretic coating is 20 to 80 μm, such as 40 to 45 μm; the thickness of the non-electrophoretic coating is 10 to 40 μm, such as 10 to 12 μm, 16 to 18 μm, 20 to 22 μm, 17 to 19 μm, 13 to 15 μm, 11 to 13 μm, 25 to 28 μm, and 22 to 24 μm.

[0031] The present invention provides a method for preparing the electrophoretic-non-electrophoretic composite coating described above, which mainly forms a non-electrophoretic coating on the surface of the electrophoretic coating, comprising the following steps:

[0032] A) compounding the non-electrophoretic coating slurry on the surface of a metal workpiece having an electrophoretic coating through a coating process to obtain a semi-finished metal workpiece;

[0033] The non-electrophoretic coating slurry includes components of the non-electrophoretic coating;

[0034] B) rotating, drying, and solidifying the semi-finished metal workpiece to obtain an electrophoretic-non-electrophoretic composite coating.

[0035] In step A):

[0036] Compounding the non-electrophoretic coating slurry on the surface of the metal workpiece containing the electrophoretic coating through a coating process to obtain a semi-finished metal workpiece;

[0037] The non-electrophoretic coating slurry includes components of a non-electrophoretic coating.

[0038] In some embodiments of the present invention, the coating process comprises printing, spraying or dipping.

[0039] In some embodiments of the present invention, the method for preparing a metal workpiece containing an electrophoretic coating comprises the following steps:

[0040] a) Pre-processing of metal workpieces;

[0041] b) immersing the metal workpiece treated in step a) in an electrophoretic solution, and performing electrophoretic deposition under an external voltage to obtain a coating on the surface of the metal workpiece;

[0042] c) drying the metal workpiece after the electrophoretic deposition in step b) to obtain a metal workpiece containing an electrophoretic coating.

[0043] In step a):

[0044] Pre-processing of metal workpieces.

[0045] The material of the metal workpiece includes at least one of aluminum, copper, titanium, magnesium, or alloys thereof, preferably aluminum or an alloy thereof.

[0046] The pre-treatment includes but is not limited to leveling, degreasing, rust removal, oxidation, neutralization, etc. of the metal workpiece surface;

[0047] The surface leveling of the metal workpiece includes, but is not limited to, grinding, mechanical polishing, electrolytic polishing, chemical polishing, and combinations thereof; the degreasing includes, but is not limited to, organic solvent degreasing, chemical degreasing, electrochemical degreasing, and combinations thereof; the rust removal includes, but is not limited to, chemical etching, electrochemical etching, and combinations thereof; the oxidation includes at least one of chemical oxidation and electrochemical oxidation; the neutralization includes treating the surface of the metal workpiece with a pickling solution; the pickling solution includes sulfuric acid and a surfactant; the mass concentration of sulfuric acid in the pickling solution is 5% to 15%, such as 10%, and the mass concentration of the surfactant is 0.05% to 0.15%, such as 0.1%; the surfactant may be sodium lauryl sulfate. The purpose is to remove burrs, pits, oil stains, oxides, rust, passivation films, and the like from the surface of the metal workpiece.

[0048] In step b):

[0049] The metal workpiece treated in step a) is immersed in an electrophoretic solution, and electrophoretic deposition is performed under an external voltage condition to obtain a coating on the surface of the metal workpiece.

[0050] The electrophoresis fluid is a polyimide solution, specifically comprising polyimide and an organic solvent; the organic solvent comprises N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), or dimethyl sulfoxide (DMSO), preferably NMP. The mass concentration of the electrophoresis fluid is 4% to 8%, preferably 4.5% to 6.5%, such as 6%.

[0051] The temperature of the electrophoretic deposition is 20-40°C, preferably 25-35°C, such as 25°C; the voltage is 20-400V, preferably 30-200V, such as 100V; the time is 5-50min, preferably 5-20min. The electrophoretic time is reasonably controlled according to the target thickness. For example, the electrophoretic deposition time is 12min, and the thickness of the obtained electrophoretic coating is 40-45um.

[0052] In step c):

[0053] The metal workpiece after the electrophoretic deposition in step b) is dried to obtain a metal workpiece containing an electrophoretic coating.

[0054] The drying temperature is 40-120° C., such as 80° C., and the drying time is 10-30 minutes, such as 30 minutes.

[0055] After the metal workpiece containing the electrophoretic coating is obtained, the non-electrophoretic coating slurry is compounded on the surface of the metal workpiece containing the electrophoretic coating through a coating process to obtain a semi-finished metal workpiece.

[0056] The non-electrophoretic coating slurry includes a polymer resin and additives;

[0057] The absolute value of the difference in solubility parameters between the polymer resin and the polyimide is less than 1.3 (J / cm 3 ) 1 / 2 ;

[0058] The polymer resin includes at least one of polyimide, polyester, polyurethane, polyesterimide, polyetherimide, polyamide, polyamideimide, and acetal.

[0059] The additives include at least one of a solvent, a leveling agent, a color paste and a filler.

[0060] In some embodiments of the present invention, the non-electrophoretic coating slurry comprises a polymer resin and a solvent; the solvent comprises at least one of NMP, DMF, DMAC and DMSO.

[0061] In some embodiments of the present invention, the solid content of the polymer resin in the non-electrophoretic coating slurry is 5% to 30%, such as 6%, 22%, 30%, 12%, 25%, and 15%; the viscosity is 6.5 to 65cp, such as 8cp and 65cp.

[0062] In step B):

[0063] The semi-finished metal workpiece is rotated, dried and solidified to obtain an electrophoretic-non-electrophoretic composite coating.

[0064] In some embodiments of the present invention, before the semi-finished metal workpiece is spin-dried in step B), the method further comprises:

[0065] The excess non-electrophoretic coating slurry on the surface of the semi-finished metal workpiece is dripped back into the tank.

[0066] In some embodiments of the present invention, the spin drying and curing is performed at a rotation speed of 5 to 25 rpm, such as 15 rpm; an inclination angle of 15° to 45°, such as 35°; a temperature of 80° to 260°C, such as 80°C or 230°C; and a time of 30 to 90 minutes, such as 30 minutes. The spin drying and curing is performed in an oven.

[0067] In some embodiments of the present invention, after the spin drying and curing, the further step includes: inverting and baking the spin-dried metal workpiece to obtain an electrophoretic-non-electrophoretic composite coating. The inverted baking temperature is 80 to 260°C, for example, 205°C, and the time is 30 to 90 minutes, for example, 60 minutes.

[0068] The present invention has no particular limitation on the sources of the raw materials used above, and they can be generally commercially available.

[0069] The post-processing method provided by the present invention has a simple construction process and can be implemented through various construction methods such as printing, spraying or dipping according to the shape and size of the metal workpiece.

[0070] The present invention significantly improves the bonding properties of the electrophoretic coating. Measured by the shear strength of the bond, the shear strength is increased from 3.4 MPa to 12.6 MPa, which is much greater than the required standard of >9 MPa by customers in the power battery industry.

[0071] At the same time, the preparation method of the electrophoretic-non-electrophoretic composite coating provided by the present invention effectively covers and repairs the defective points of the electrophoretic coating, thereby significantly improving the overall insulation performance of the metal workpiece.

[0072] In order to further illustrate the present invention, an electrophoretic-non-electrophoretic composite coating and a preparation method thereof provided by the present invention are described in detail below in conjunction with examples, but they should not be construed as limiting the scope of protection of the present invention.

[0073] The polyimide mentioned in the following examples is a polyimide varnish with the model number Q-VR-1688.

[0074] The reagents used in the following examples are all commercially available.

[0075] Example 1

[0076] 1) A metal workpiece containing an electrophoretic coating is prepared according to the following method:

[0077] 1-1) A 35 g / L alkaline degreasing agent (G-0927) solution was prepared with deionized water and degreased on the surface of an aluminum metal workpiece at 55°C;

[0078] 1-2) preparing an acid wash solution: mixing a certain amount of sulfuric acid and a surfactant, sodium lauryl sulfate, with deionized water to obtain an acid wash solution; wherein the mass concentration of the sulfuric acid in the acid wash solution is 10% and the mass concentration of the surfactant is 0.1%;

[0079] Using the pickling solution to neutralize the surface of the aluminum metal workpiece treated in step 1-1);

[0080] 1-3) Immersing the aluminum metal workpiece treated in step 1-2) in a 6% polyimide electrophoretic solution (solvent: NMP) for electrophoretic deposition at 100 V and 25° C. for 12 minutes;

[0081] 1-4) The sample obtained in step 1-3) was placed in an oven and baked at 80° C. for 30 min to obtain an aluminum metal workpiece containing an electrophoretic coating, wherein the thickness of the electrophoretic coating was 40 to 45 μm.

[0082] 2) Post-treatment of electrophoretic coating:

[0083] 2-1) The sample obtained in step 1-4) was immersed in a post-treatment solution (non-electrophoretic coating slurry) at room temperature, wherein the post-treatment solution consisted of polyamide-imide and NMP, wherein the solid content of the polyamide-imide was 6%, and the viscosity of the post-treatment solution was 8 cp; the absolute value of the difference in solubility parameter between the polyamide-imide and the polyimide was 0.4 (J / cm 3 ) 1 / 2 .

[0084] 2-2) dripping the excess post-treatment solution on the surface of the sample obtained in step 2-1) back into the tank, then placing the obtained sample on a fixed device and placing it in an oven, maintaining the metal workpiece at an inclination angle of 35° and a rotation speed of 15 r / min, and baking at 80°C under rotating conditions for 30 min;

[0085] 2-3) The metal workpiece treated in step 2-2) is taken out, placed upside down in an oven, and baked at 205° C. for 60 minutes to obtain a non-electrophoretic coating having a thickness of 10 to 12 μm.

[0086] Example 2

[0087] The difference from Example 1 is that in step 2-1), the post-treatment solution is composed of polyesterimide and NMP, wherein: the solid content of polyesterimide is 22%, the viscosity of the post-treatment solution is 8cp; the absolute value of the difference in solubility parameters between the polyesterimide and the polyimide is 0.5 (J / cm 3 ) 1 / 2 .

[0088] The thickness of the final non-electrophoretic coating is 16 to 18 μm.

[0089] Example 3

[0090] The difference from Example 1 is that in step 2-1), the post-treatment solution consists of polyimide and NMP, wherein the solid content of the polyimide is 30% and the viscosity of the post-treatment solution is 8 cp.

[0091] The thickness of the final non-electrophoretic coating is 20 to 22 μm.

[0092] Example 4

[0093] The difference from Example 1 is that in step 2-1), the post-treatment solution consists of polyurethane and DMF, wherein the solid content of polyurethane is 25%, the viscosity of the post-treatment solution is 8cp, and the absolute value of the difference in solubility parameters between the polyesterimide and the polyimide is 0.7 (J / cm 3 ) 1 / 2 ;

[0094] The baking temperature in step 2-3) is 155°C.

[0095] The thickness of the final non-electrophoretic coating is 17 to 19 μm.

[0096] Example 5

[0097] The difference from Example 1 is that in step 2-1), the post-treatment solution is composed of polyetherimide and NMP, wherein the solid content of polyetherimide is 15%, the viscosity of the post-treatment solution is 8cp; the absolute value of the difference in solubility parameters between the polyetherimide and the polyimide is 0.6 (J / cm 3 ) 1 / 2 .

[0098] The thickness of the final non-electrophoretic coating is 13 to 15 μm.

[0099] Example 6

[0100] The difference from Example 1 is that in step 2-1), the post-treatment solution consists of polyamide and NMP, wherein the solid content of polyamide is 8%, the viscosity of the post-treatment solution is 8cp, and the absolute value of the difference in solubility parameters between the polyamide and polyimide is 1.0 (J / cm 3 ) 1 / 2 .

[0101] The thickness of the final non-electrophoretic coating is 11 to 13 μm.

[0102] Example 7

[0103] The difference from Example 1 is that a non-electrophoretic coating is further applied to the surface of the sample obtained in step 2-2) of Example 1. The composition of the non-electrophoretic coating is the same as that described in Example 2.

[0104] 2-3) The metal workpiece treated in step 2-2) is taken out, placed upside down in an oven, and baked at 180° C. for 60 minutes to obtain a non-electrophoretic coating having a thickness of 25 to 28 μm.

[0105] Example 8

[0106] The difference from Example 1 is that in step 2-1), the solid content of the polyamide-imide is 12%, and the viscosity of the post-treatment solution is 65 cp.

[0107] The thickness of the final non-electrophoretic coating is 22 to 24 μm.

[0108] Comparative Example 1

[0109] The difference from Example 1 is that step 2) is not included.

[0110] Comparative Example 2

[0111] The difference from Example 1 is:

[0112] In step 2-1), the solid content of polyamide-imide in the post-treatment solution is 20%, and the viscosity of the post-treatment solution is 220 cp.

[0113] The thickness of the final non-electrophoretic coating is 38 to 42 μm.

[0114] Comparative Example 3

[0115] The difference from Example 1 is that in step 2-1), the post-treatment solution is composed of polyacrylonitrile and NMP, wherein the solid content of polyacrylonitrile is 16%, the viscosity of the post-treatment solution is 8cp, and the absolute value of the difference in solubility parameters between the polyacrylonitrile and the polyimide is 5.2 (J / cm 3 ) 1 / 2 .

[0116] The thickness of the final non-electrophoretic coating is 18 to 20 μm.

[0117] Comparative Example 4

[0118] The difference from Example 1 is that in step 2-1), the post-treatment solution is composed of polyvinyl acetate and NMP, wherein the solid content of polyvinyl acetate is 11%, the viscosity of the post-treatment solution is 8cp; the absolute value of the difference in solubility parameters between polyvinyl acetate and polyimide is 1.6 (J / cm 3 ) 1 / 2 .

[0119] The thickness of the final non-electrophoretic coating is 12 to 14 μm.

[0120] Comparative Example 5

[0121] (1) Pretreatment of metal workpieces: Degrease with 20 g / L sodium hydroxide solution, then surface condition the workpiece with 50 g / L trisodium phosphate, then place it in a phosphating agent with an acidity of 20 Pt, a free acidity of 0.6 Pt, and an accelerator of 5 Pt for phosphating, and finally passivate with a strong oxidant, chromic acid;

[0122] (2) Electrophoresis: Using cathodic electrophoresis, place the metal workpiece after the above treatment in epoxy resin electrophoretic paint, control the electrophoresis time, and obtain a coating with a thickness of 20 to 25 μm;

[0123] (3) Middle coating and top coating: a polyurethane middle coating with a thickness of 30 μm is applied on the surface of the electrophoretic paint in step (2) by spraying, and then a layer of acrylic resin top coating with a thickness of 40 to 45 μm is applied on the surface;

[0124] (4) Drying: The above samples were placed in an oven at 160°C for 60 min.

[0125] The properties of the coatings after treatment in Examples 1 to 8 and Comparative Examples 1 to 5 were tested, and the results are shown in Table 1.

[0126] The bonding property of the coating is measured by the shear strength of the bond. The sample to be tested is mounted on a shear tester and then a shear force is applied until the coating peels off from the substrate. The test is repeated three times and the unit is MPa or N / mm 2 .

[0127] Method for testing the voltage resistance of the coating: test the insulation performance of the sample in a voltage breakdown tester.

[0128] Testing method for the scratch resistance of the coating: According to ASTM D4060 standard testing, a Taber abrasion tester is used for friction testing. The indicators considered are wear and withstand voltage. The reduction in coating thickness is required to be less than 20%.

[0129] The test method of the corona resistance of the coating is as follows: the sample to be tested is placed under the conditions of a frequency of 20.0kHz and a pulse voltage of 3000V. The high-frequency pulse voltage resistance time of at least four samples out of five samples should be not less than 200 minutes;

[0130] PDIV test method for coatings: wipe the sample to be tested clean, then paint the middle part of the sample with a graphite brush (the coating length is about 5 cm), and then blow dry with a hair dryer. Place the dried sample in a drying oven to heat it, and test the relative dielectric loss value through temperature changes. The value is intuitively reflected on the computer screen in the form of a curve.

[0131] Table 1 Performance test results of the coatings after treatment in Examples 1 to 8 and Comparative Examples 1 to 5

[0132]

[0133] As can be seen from Table 1, compared with Comparative Example 1, the embodiment adds a post-processing non-electrophoretic process, which greatly improves the product's voltage resistance, scratch resistance, corona resistance and PDIV, and also provides an effective solution for the complex electrophoretic process of the workpiece; compared with Comparative Example 2, although the increase in solid content and viscosity does not affect the relevant parameters, the high viscosity will cause obvious marks in the later baking process, and the baking time is long, which is not conducive to product cost reduction; compared with Comparative Examples 3 and 4, the present invention uses a specific polymer resin, and the comprehensive performance is significantly better; compared with Comparative Example 5, epoxy resin electrophoretic paint is used for insulation, and its insulation effect is poor. In addition, the thickness of the composite coating used is also greatly increased compared with the present invention, which is not conducive to the comprehensive utilization of the product.

[0134] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrophoretic-non-electrophoretic composite coating, characterized in that: The composite coating comprises an electrophoretic coating and a non-electrophoretic coating composited on the surface of the electrophoretic coating; The components of the electrophoretic coating include polyimide; The components of the non-electrophoretic coating include polymer resin; The absolute value of the difference in solubility parameters between the polymer resin and the polyimide is less than 1.3 (J / cm 3 ) 1 / 2 .

2. The electrophoretic-non-electrophoretic composite coating according to claim 1, characterized in that: The polymer resin includes at least one of polyimide, polyester, polyurethane, polyesterimide, polyetherimide, polyamide, polyamideimide, and acetal.

3. A method for preparing the electrophoretic-non-electrophoretic composite coating according to any one of claims 1 to 2, comprising the following steps: A) compounding the non-electrophoretic coating slurry on the surface of a metal workpiece having an electrophoretic coating through a coating process to obtain a semi-finished metal workpiece; The non-electrophoretic coating slurry includes components of the non-electrophoretic coating; B) rotating, drying, and solidifying the semi-finished metal workpiece to obtain an electrophoretic-non-electrophoretic composite coating.

4. The preparation method according to claim 3, characterized in that In step A), the method for preparing a metal workpiece containing an electrophoretic coating comprises the following steps: a) Pre-processing of metal workpieces; b) immersing the metal workpiece treated in step a) in an electrophoretic solution, and performing electrophoretic deposition under an external voltage to obtain a coating on the surface of the metal workpiece; c) drying the metal workpiece after the electrophoretic deposition in step b) to obtain a metal workpiece containing an electrophoretic coating.

5. The preparation method according to claim 4, characterized in that In step a), the pretreatment includes at least one of leveling, degreasing, rust removal, oxidation, and neutralization of the surface of the metal workpiece.

6. The preparation method according to claim 5, characterized in that The leveling of the metal workpiece surface includes at least one or more of grinding, mechanical polishing, electrolytic polishing and chemical polishing of the metal workpiece; the degreasing includes at least one of organic solvent degreasing, chemical degreasing and electrochemical degreasing; the rust removal includes at least one of chemical etching rust removal and electrochemical etching rust removal; the oxidation includes at least one of chemical oxidation and electrochemical oxidation.

7. The preparation method according to claim 3, characterized in that In step A), the non-electrophoretic coating slurry further comprises an additive, wherein the additive comprises at least one of a solvent, a leveling agent, a color paste and a filler.

8. The preparation method according to claim 3, characterized in that In step A), the solid content of the polymer resin in the non-electrophoretic coating slurry is 5% to 30%.

9. The preparation method according to claim 3, characterized in that In step B), the rotation speed of the rotary drying is 5 to 25 r / min, and the inclination angle is 15° to 45°.

10. The preparation method according to claim 3, characterized in that In step B), the temperature of the rotary drying and curing is 80-260° C., and the time is 30-90 minutes.

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