Medium powder coating for vacuum plating as well as preparation method and application of medium powder coating

Abstract

The invention discloses a medium powder coating for vacuum plating as well as a preparation method and application thereof, and relates to the technical field of coatings. The powder coating disclosed by the invention is prepared from the following components in parts by mass: 100 to 150 parts of isocyanate-terminated polyether modified epoxy resin, 50 to 100 parts of hydroxyl-terminated phenol curing agent, 5 to 15 parts of dicyandiamide curing agent and 4 to 15 parts of auxiliary agent. A coating prepared from the powder coating provided by the invention has the advantages of high gloss, high fullness, high brilliance, high leveling, high corrosion resistance, high mechanical property and the like, meanwhile, the coating hardly has appearance defects such as pinholes, shrinkage cavities and the like, can meet the requirements of PVD vacuum plating dielectric layers, and is particularly suitable for PVD vacuum plating of hubs.

Description

Technical Field

[0001] The invention relates to the technical field of coatings, and in particular to a dielectric powder coating for vacuum electroplating and a preparation method and application thereof. Background Art

[0002] PVD (Physical Vapor Deposition) is physical vapor deposition technology. Compared with traditional electroplating process, PVD vacuum plating has the advantages of good material adaptability, low process temperature, fast film forming speed, dense coating structure, strong bonding with the substrate, and low pollution. Therefore, it is widely used in machinery, electronics, communications, automobiles and other fields.

[0003] The wheel hub obtained by electroplating with the PVD vacuum electroplating process has an obvious metal decorative effect, so it is quite popular among mid-to-high-end car users. However, since the coating obtained by vacuum electroplating is thin, it cannot provide good protection, and the uneven surface of the workpiece leads to unsatisfactory effect after electroplating, so a multi-layer spraying process is required before vacuum electroplating. The current common electroplating coating process is "substrate + base powder layer + dielectric layer + electroplating layer + transparent powder layer", in which the dielectric layer is currently mostly solvent-based coatings, but due to the high VOC emissions of solvent-based coatings, it is gradually not adapted to the country's increasingly stringent environmental protection policies, so the need for "paint to powder" is also increasingly strong. The development of powder coatings that can replace solvent-based coatings is conducive to the further development of PVD vacuum electroplating technology. Summary of the invention

[0004] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the purpose of the present invention is to provide a powder coating, which utilizes the synergy of the terminal isocyanate polyether modified epoxy resin and various components to improve the comprehensive performance of the powder coating, and can well replace the solvent-based medium coating.

[0005] A second aspect of the present invention is to provide a method for preparing a powder coating.

[0006] The third aspect of the present invention provides a use of a powder coating.

[0007] A fourth aspect of the present invention is to provide a wheel hub.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] The first aspect of the present invention is to provide a powder coating, which comprises the following components in parts by mass:

[0010] 100-150 parts of isocyanate-terminated polyether-modified epoxy resin,

[0011] 50-100 parts of hydroxyl-terminated phenol curing agent,

[0012] 5-15 parts of dicyandiamide curing agent,

[0013] 4 to 15 parts of additives.

[0014] The powder coating of the present invention is a dielectric powder coating, which can be used as dielectric powder of a dielectric layer in a vacuum electroplating process. An isocyanate-terminated polyether-modified epoxy resin is used as a matrix resin, and the epoxy resin is modified by using the isocyanate-terminated polyether. The isocyanate group reacts chemically with the hydroxyl group in the epoxy resin to form a chemical bond, and the polyether segment is grafted onto the side chain of the epoxy resin. The flexibility of the obtained isocyanate-terminated polyether-modified epoxy resin is improved. At the same time, the introduction of the isocyanate-terminated polyether segment increases the crosslinking degree between resin molecules and reduces the distance between molecules. Therefore, the molecules of the isocyanate-terminated polyether-modified epoxy resin are closer together. The coating formed by the coating using the isocyanate-terminated polyether-modified epoxy resin as the matrix resin has more excellent mechanical properties and corrosion resistance.

[0015] In addition, the powder coating formula of the present invention simultaneously adds a hydroxyl-terminated phenol curing agent and a dicyandiamide curing agent, which is beneficial to improving the curing performance of the powder coating and achieving rapid curing at low temperatures. After curing, the coating has good properties such as distinctness of image, leveling, and mechanical properties.

[0016] Preferably, the powder coating comprises the following components by mass:

[0017] 110-130 parts of isocyanate-terminated polyether-modified epoxy resin,

[0018] 60-75 parts of hydroxyl-terminated phenol curing agent,

[0019] 7-12 parts of dicyandiamide curing agent,

[0020] 6 to 11.5 parts of additives.

[0021] Preferably, the mass ratio of the isocyanate-terminated polyether-modified epoxy resin, the hydroxyl-terminated phenol curing agent and the dicyandiamide curing agent is 100:(33-50):(3-10).

[0022] More preferably, the mass ratio of the isocyanate-terminated polyether-modified epoxy resin, the hydroxyl-terminated phenol curing agent and the dicyandiamide curing agent is 100:(40-45):(5-8).

[0023] Preferably, the mass percentage of the polyether segment in the isocyanate-terminated polyether-modified epoxy resin is 16-24%.

[0024] Further preferably, the mass percentage of the polyether segment in the isocyanate-terminated polyether-modified epoxy resin is 16.7-23.1%.

[0025] More preferably, the mass percentage of the polyether segment in the isocyanate-terminated polyether-modified epoxy resin is 20-23%.

[0026] Preferably, the mass percentage of isocyanate groups in the isocyanate-terminated polyether-modified epoxy resin is 57-63%.

[0027] Further preferably, the mass percentage of isocyanate groups in the isocyanate-terminated polyether-modified epoxy resin is 57.1-62.5%.

[0028] Preferably, the epoxy equivalent of the isocyanate-terminated polyether-modified epoxy resin is 450 to 750 g / eq.

[0029] More preferably, the epoxy equivalent of the isocyanate-terminated polyether-modified epoxy resin is 470 to 730 g / eq.

[0030] The epoxy equivalent range of the isocyanate-terminated polyether-modified epoxy resin will affect the performance of the coating formed by the powder coating of the present invention. For example, when the epoxy equivalent is large, the crosslinking density of the coating is low, and the mechanical properties and anti-corrosion properties are relatively poor; and when the epoxy equivalent is small, the resin reaction activity is large, and the coating appearance flatness is poor.

[0031] Preferably, the hydroxyl value of the hydroxyl-terminated phenol curing agent is 0.3 to 0.6 eq / 100g.

[0032] More preferably, the hydroxyl value of the hydroxyl-terminated phenol curing agent is 0.38 to 0.51 eq / 100 g.

[0033] More preferably, the hydroxyl value of the hydroxyl-terminated phenol curing agent is 0.4 to 0.5 eq / 100g.

[0034] Although a high hydroxyl value will accelerate the curing rate of the epoxy resin and increase the crosslinking density, the toughness of the formed coating is reduced. A low hydroxyl value can provide better flexibility and thermal stability, but the curing rate will be affected. Therefore, by adjusting the hydroxyl value of the hydroxyl-terminated curing agent, it is beneficial to optimize the coating performance while ensuring the curing rate.

[0035] Preferably, the auxiliary agent includes a leveling agent, a breathable agent and a promoter; the breathable agent includes benzoin and modified polyamide wax.

[0036] Further preferably, the mass fractions of the leveling agent, the air permeability agent and the accelerator are respectively:

[0037] 2 to 5 parts of leveling agent,

[0038] 1 to 5 parts of breathable agent,

[0039] 1 to 5 parts of accelerator.

[0040] More preferably, the powder coating comprises the following components by mass:

[0041] 110-130 parts of isocyanate-terminated polyether-modified epoxy resin,

[0042] 60-75 parts of hydroxyl-terminated phenol curing agent,

[0043] 7-12 parts of dicyandiamide curing agent,

[0044] 2-3.5 parts of leveling agent,

[0045] 2 to 4 parts of breathable agent,

[0046] 2 to 4 parts of accelerator.

[0047] More preferably, the mass ratio of benzoin to modified polyamide wax is 1:(3-4).

[0048] By further controlling the ratio of benzoin and modified polyamide wax as air permeating agents, pinholes of the coating formed by the coating can be effectively eliminated without the need to add excessive amount of air permeating agent.

[0049] More preferably, the mass ratio of benzoin to modified polyamide wax is 1:(3-3.5).

[0050] Preferably, in the isocyanate-terminated polyether-modified epoxy resin, the epoxy resin includes at least one of GESR-602, GESR-603, GESR-901, GESR-903, GESR-903H and GESR-904; more preferably GESR-901, GESR-903 or GESR-904.

[0051] Preferably, the hydroxyl-terminated phenol curing agent includes at least one of V-209, V-2081, and V-2081W produced by Shaanxi Jinchen Yongyue New Materials Co., Ltd.; more preferably V-209 or V-2081W.

[0052] Preferably, the dicyandiamide curing agent includes at least one of Epikure 107FF and Epikure 108FF produced by Shell Chemical Company, and DEH40 and DEH41 produced by Dow Chemical.

[0053] Preferably, the leveling agent includes an acrylic leveling agent.

[0054] Further preferably, the leveling agent includes at least one of polyethyl acrylate, polybutyl acrylate, poly-2-ethylhexyl acrylate, and butyl acrylate-ethyl acrylate copolymer.

[0055] Preferably, the accelerator comprises an imidazole accelerator.

[0056] Further preferably, the accelerator includes at least one of 2-phenylimidazole, 2-ethylimidazole, 2,4-dimethylimidazole, 2-methylimidazole, imidazole epoxy adduct, and imidazole isocyanate adduct; more preferably, it is at least one of 2-phenylimidazole, 2-ethylimidazole, and 2-methylimidazole.

[0057] Preferably, the D of the powder coating is 50 The particle size is 25~50μm.

[0058] Further preferably, the D of the powder coating is 50 The particle size is 30~35μm.

[0059] It is understandable that the particle size mainly affects the appearance of the coating, and there is no obvious difference in the appearance performance within the range of 25 to 50 μm, so it can be adjusted within the range as needed.

[0060] The second aspect of the present invention provides a method for preparing the powder coating according to the first aspect of the present invention, comprising the following steps:

[0061] The isocyanate-terminated polyether-modified epoxy resin and the hydroxyl-terminated phenol curing agent are mixed, extruded and crushed to obtain the first material; the first material is mixed with a dicyandiamide curing agent and an auxiliary agent, extruded and crushed to obtain the powder coating.

[0062] Preferably, the isocyanate-terminated polyether-modified epoxy resin is prepared by a preparation method comprising the following steps:

[0063] The epoxy resin, the isocyanate-terminated polyether and the organic solvent are mixed and reacted in an inert atmosphere to obtain the isocyanate-terminated polyether-modified epoxy resin; the reaction temperature is 70-95°C.

[0064] More preferably, the organic solvent includes at least one of xylene, toluene and n-butanol.

[0065] More preferably, the reaction temperature is 80-90°C.

[0066] More preferably, the reaction time is 2 to 5 hours.

[0067] More preferably, the reaction time is 3 to 4 hours.

[0068] More preferably, the mass ratio of the epoxy resin, the isocyanate-terminated polyether and xylene is 1:(0.3-0.5):(0.4-0.7).

[0069] More preferably, the mass ratio of the epoxy resin, the isocyanate-terminated polyether and xylene is 1:(0.35-0.4):(0.5-0.6).

[0070] Further preferably, the isocyanate-terminated polyether is prepared by a preparation method comprising the following steps:

[0071] Diethylene glycol monobutyl ether, diphenylmethane diisocyanate (MDI) and cyclohexane are stirred and mixed under an inert atmosphere; the temperature of the reaction system is raised to 60-80° C. and the reaction is carried out for 1-4 hours; the temperature is then raised to 80-90° C. and the reaction is continued for 1-3 hours; the reaction is rapidly cooled to room temperature and the solvent cyclohexane is removed under vacuum conditions to obtain a terminal isocyanate polyether.

[0072] More preferably, the mass ratio of diethylene glycol monobutyl ether, diphenylmethane diisocyanate (MDI) and cyclohexane is (2.5-3.5):(3.5-4.5):(6.5-7.5).

[0073] More preferably, the reaction system is first heated to 70-75° C. and reacted for 2-3 h; then heated to 80-85° C. and reacted for 2.5-3 h.

[0074] Preferably, the extrusion is performed using a twin-screw extruder; during the extrusion process, the heating temperature of the first zone of the twin-screw extruder is 90-100°C, and the heating temperature of the second zone is 95-110°C.

[0075] The third aspect of the present invention provides an application of the powder coating described in the first aspect of the present invention in a PVD vacuum plating process.

[0076] Preferably, the powder coating forms dielectric powder in a PVD vacuum plating process, forming a dielectric layer in a coating of a PVD vacuum plating product.

[0077] A fourth aspect of the present invention provides a wheel hub, comprising a coating formed by the powder coating according to the first aspect of the present invention.

[0078] Preferably, the wheel hub is an aluminum wheel hub.

[0079] Compared with the prior art, the present invention has the following beneficial effects:

[0080] (1) The powder coating provided by the present invention is modified by grafting epoxy resin with terminal isocyanate polyether, which significantly improves the leveling, gloss, brightness and mechanical properties of the coating formed by the powder coating, and has excellent comprehensive performance. In addition, combined with hydroxyl-terminated phenol curing agent and dicyandiamide curing agent, low-temperature rapid curing can be achieved. The coating made of the powder coating has the advantages of high gloss, high fullness, high brightness, high leveling, high corrosion resistance, high mechanical properties, etc. At the same time, the coating has almost no appearance defects such as pinholes and shrinkage cavities, can play a good coating role, and is suitable for large-scale industrial applications.

[0081] (2) The present invention further adds benzoin and modified polyamide wax as air permeants, thereby effectively avoiding the occurrence of pinholes and shrinkage holes in the coating and greatly improving the appearance of the coating.

[0082] (3) The preparation method of the present invention extrude the terminal isocyanate polyether modified epoxy resin and the hydroxyl-terminated phenol curing agent with the other components in two times, which can improve the appearance of the coating formed by the coating, and the preparation process is simple and suitable for large-scale production.

[0083] (4) The powder coating provided by the present invention can well replace solvent-based medium coatings, has excellent comprehensive performance, can meet the requirements of PVD vacuum plating medium layer, and is particularly suitable for PVD vacuum plating of wheel hubs. DETAILED DESCRIPTION

[0084] The present invention is further described in detail below by specific examples. Unless otherwise specified, the raw materials, reagents or devices used in the examples and comparative examples can be obtained from conventional commercial sources or can be obtained by prior art methods. Unless otherwise specified, the experiments or test methods are conventional methods in the art.

[0085] Some of the raw materials and equipment used in the following examples and comparative examples of the present invention are described as follows:

[0086] Epoxy resin: GESR-903, Zhuhai Hongchang Electronic Materials Co., Ltd., epoxy equivalent is 730 g / eq, softening point is 90°C; GESR-901, Zhuhai Hongchang Electronic Materials Co., Ltd., epoxy equivalent is 470 g / eq, softening point is 70°C.

[0087] Diethylene glycol monobutyl ether: Shandong Kejian Chemical Co., Ltd.

[0088] Diphenylmethane diisocyanate: Jinan Hongwang Chemical Co., Ltd.

[0089] Hydroxyl-terminated phenol curing agent: V-209, Shaanxi Jinchen Yongyue New Materials Co., Ltd., hydroxyl value 0.45eq / 100g, softening point 88°C.

[0090] Dicyandiamide curing agent: Epikure 107FF, Shell Chemicals.

[0091] Leveling agent: BYK 360P, BYK Chemical.

[0092] Accelerator: 2-methylimidazole, Hubei Changyao Biotechnology Co., Ltd.

[0093] Breathable agent: benzoin: MIWON BENZOIN; modified polyamide wax: T-961, Shanghai Suoshi Chemical Co., Ltd.

[0094] Twin-screw extruder: JFY-30 crawler-type twin-screw extruder.

[0095] The following is a detailed description with reference to different embodiments and comparative examples.

[0096] Example 1

[0097] This embodiment provides a dielectric powder coating for vacuum plating, the formula of which is shown in Table 1 below:

[0098] Table 1 Powder coating formula of Example 1

[0099] Components Mass Isocyanate-terminated polyether modified epoxy resin GESR-903 120 Hydroxyl terminated phenol curing agent V-209 60 Dicyandiamide curing agent Epikure 107FF 8 BYK 360P 3 Benzoin 1 Modified polyamide wax T-961 3 2-Methylimidazole 2

[0100] The preparation method of the isocyanate-terminated polyether-modified epoxy resin GESR-903 comprises the following steps:

[0101] S01. Weigh diethylene glycol monobutyl ether, diphenylmethane diisocyanate (MDI) and cyclohexane in a mass ratio of 2:4:7 and add them into a reaction bottle, and stir and mix under nitrogen protection;

[0102] S02. The reaction system temperature was raised to 70 ° C and reacted for 2 hours; then the temperature was slowly raised to 80 ° C, the reaction was continued for 2.5 hours, and then rapidly cooled to room temperature, and the solvent cyclohexane was removed under vacuum to obtain an isocyanate-terminated polyether;

[0103] S03. The epoxy resin GESR-903, the terminal isocyanate polyether and the xylene are mixed in a mass ratio of 1:0.4:0.5 and added into a reactor. The reaction temperature is raised to 85°C under nitrogen protection and the reaction is carried out for 3 hours to obtain the terminal isocyanate polyether modified epoxy resin GESR-903, in which the mass percentage of the polyether segment is 21.3%.

[0104] The preparation method of the powder coating of this embodiment comprises the following steps:

[0105] S1. According to the formula, the isocyanate-terminated polyether-modified epoxy resin and the hydroxyl-terminated phenol curing agent were weighed and added to the mixing tank, stirred and crushed for 8 minutes, and then the resulting mixture was fed into a twin-screw extruder for extrusion. The heating temperature of the first zone was 120 ° C, and the heating temperature of the second zone was 125 ° C. After extrusion, tableting, cooling, and coarse grinding, a first material was obtained;

[0106] S2. Then weigh the dicyandiamide curing agent, leveling agent, breathable agent and accelerator according to the formula, and add them together with the first material obtained in step S1 into the mixing tank, crush for 8 minutes, and then send the obtained mixture into a twin-screw extruder for extrusion. The heating temperature of the first zone is 95°C and the heating temperature of the second zone is 100°C. After extrusion, tableting, cooling, crushing and screening, a powder coating (D 50 The particle size is 33 μm).

[0107] Example 2

[0108] This embodiment provides a dielectric powder coating for vacuum plating, the formula of which is shown in Table 2 below:

[0109] Table 2 Powder coating formula of Example 2

[0110] Components Mass Isocyanate-terminated polyether modified epoxy resin GESR-903 130 Hydroxyl terminated phenol curing agent V-209 70 Dicyandiamide curing agent Epikure 107FF 7 BYK 360P 3 Benzoin 0.7 Modified polyamide wax T-961 2.1 2-Methylimidazole 2.5

[0111] The preparation method of the isocyanate-terminated polyether-modified epoxy resin GESR-903 is the same as that in Example 1; and the preparation method of the powder coating is the same as that in Example 1.

[0112] Example 3

[0113] This embodiment provides a dielectric powder coating for vacuum plating, the formula of which is shown in Table 3 below:

[0114] Table 3 Powder coating formula of Example 3

[0115] Components Mass Isocyanate-terminated polyether modified epoxy resin GESR-903 80 Isocyanate-terminated polyether modified epoxy resin GESR-901 40 Hydroxyl terminated phenol curing agent V-209 75 Dicyandiamide curing agent Epikure 107FF 8 BYK 360P 3 Benzoin 0.9 Modified polyamide wax T-961 2.7 2-Methylimidazole 2

[0116] Wherein, the preparation method of the isocyanate-terminated polyether-modified epoxy resin GESR-903 is the same as that of Example 1;

[0117] The preparation method of the isocyanate-terminated polyether-modified epoxy resin GESR-901 comprises the following steps:

[0118] S01. Weigh diethylene glycol monobutyl ether, diphenylmethane diisocyanate (MDI) and cyclohexane in a mass ratio of 2:4:7 and add them into a reaction bottle, and stir and mix under nitrogen protection;

[0119] S02. The reaction system temperature was raised to 70 ° C and reacted for 2 hours; then the temperature was slowly raised to 80 ° C, the reaction was continued for 2.5 hours, and then rapidly cooled to room temperature, and the solvent cyclohexane was removed under vacuum to obtain an isocyanate-terminated polyether;

[0120] S03. The epoxy resin GESR-901, the terminal isocyanate polyether and the xylene are mixed in a mass ratio of 1:0.45:0.6 and added into a reactor. The reaction temperature is raised to 85°C under nitrogen protection and the reaction is carried out for 3 hours to obtain the terminal isocyanate polyether modified epoxy resin GESR-901, in which the mass percentage of the polyether segment is 20-22%.

[0121] The preparation method of the powder coating is the same as that of Example 1.

[0122] Comparative Example 1

[0123] Comparative Example 1 provides a powder coating, the formula of which is shown in Table 4 below:

[0124] Table 4 Powder coating formula of comparative example 1

[0125] Components Mass Epoxy resin GESR-903 120 Hydroxyl terminated phenol curing agent V-209 70 Dicyandiamide curing agent Epikure 107FF 7 BYK 360P 3 Benzoin 0.7 Modified polyamide wax T-961 2.1 2-Methylimidazole 2.5

[0126] Among them, the epoxy resin GESR-903 has not been modified.

[0127] The preparation method of the powder coating of Comparative Example 1 is the same as that of Example 1.

[0128] Comparative Example 2

[0129] Comparative Example 2 provides a powder coating, the formula of which is shown in Table 5 below:

[0130] Table 5 Powder coating formula of comparative example 2

[0131]

[0132]

[0133] The preparation method of the isocyanate-terminated polyether-modified epoxy resin GESR-903 is the same as that of Example 1; the preparation method of the powder coating of Comparative Example 2 is as follows:

[0134] All components were added into the mixing tank according to the proportion, fully mixed and crushed for 8 minutes, and then the obtained mixture was sent to the twin-screw extruder for extrusion. The heating temperature of the first zone of the twin-screw extruder was 95°C and the heating temperature of the second zone was 105°C. The extruded material was then sent to the tablet press for tableting, and then cooled, crushed, sieved and packaged to obtain the powder coating (D 50 The particle size is 37 μm).

[0135] Comparative Example 3

[0136] Comparative Example 3 provides a powder coating, the formula of which is shown in Table 6 below:

[0137] Table 6 Powder coating formula of comparative example 3

[0138] Components Mass Isocyanate-terminated polyether modified epoxy resin GESR-903 120 Hydroxyl terminated phenol curing agent V-209 60 Dicyandiamide curing agent Epikure 107FF 8 BYK 360P 3 Benzoin 1 2-Methylimidazole 2

[0139] The preparation method of the isocyanate-terminated polyether-modified epoxy resin GESR-903 is the same as that in Example 1; and the preparation method of the powder coating is the same as that in Example 1.

[0140] Comparative Example 4

[0141] Comparative Example 4 provides a powder coating, the formula of which is shown in Table 7 below:

[0142] Table 7 Powder coating formula of comparative example 4

[0143] Components Mass Isocyanate-terminated polyether modified epoxy resin GESR-903 130 Hydroxyl terminated phenol curing agent V-209 70 Dicyandiamide curing agent Epikure 107FF 7 BYK 360P 3 Modified polyamide wax T-961 3 2-Methylimidazole 2.5

[0144] The preparation method of the isocyanate-terminated polyether-modified epoxy resin GESR-903 is the same as that in Example 1; and the preparation method of the powder coating is the same as that in Example 1.

[0145] Comparative Example 5

[0146] Comparative Example 5 provides a powder coating, the formula of which is shown in Table 8 below:

[0147] Table 8 Powder coating formula of comparative example 5

[0148] Components Mass Isocyanate-terminated polyether modified epoxy resin GESR-903 120 Hydroxyl terminated phenol curing agent V-209 60 Dicyandiamide curing agent Epikure 107FF 8 BYK 360P 3 Benzoin 1 Modified polyamide wax T-961 3 2-Methylimidazole 2

[0149] The preparation method of the isocyanate-terminated polyether-modified epoxy resin GESR-903 is the same as that of Example 1; and the preparation method of the powder coating is as follows:

[0150] All components were added into the mixing tank according to the proportion, fully mixed and crushed for 8 minutes, and then the obtained mixture was sent to the twin-screw extruder for extrusion. The heating temperature of the first zone of the twin-screw extruder was 95°C and the heating temperature of the second zone was 105°C. The extruded material was then sent to the tablet press for tableting, and then cooled, crushed, sieved and packaged to obtain the powder coating (D 50 The particle size is 33 μm).

[0151] Comparative Example 6

[0152] Comparative Example 6 provides a powder coating, the formula of which is shown in Table 9 below:

[0153] Table 9 Powder coating formula of comparative example 6

[0154] Components Mass Isocyanate-terminated epoxy resin GESR-903 120 Hydroxyl terminated phenol curing agent V-209 60 Dicyandiamide curing agent Epikure 107FF 8 BYK 360P 3 Benzoin 1 Modified polyamide wax T-961 3 2-Methylimidazole 2

[0155] The preparation method of the terminal isocyanate modified epoxy resin GESR-903 is as follows:

[0156] The epoxy resin GESR-903, diphenylmethane diisocyanate (MDI) and xylene were mixed in a mass ratio of 1:0.4:0.5 and added into a reactor. The reaction temperature was raised to 85°C under nitrogen protection and reacted for 3 hours to obtain terminal isocyanate modified epoxy resin GESR-903.

[0157] The preparation method of the powder coating of Comparative Example 6 is the same as that of Example 1.

[0158] Performance Testing

[0159] The powder coating obtained in the above embodiments and comparative examples is sprayed on the surface of the wheel hub. In the following test, the curing condition of the powder coating is 170℃ / 15min, the coating thickness is 100-120μm, and relevant performance tests are carried out after curing. It should be noted that the above powder coating is used as a medium powder, and therefore a base powder (Qingtian base powder JW-A1701C) is sprayed on the surface of the aluminum wheel hub before spraying the powder coating. The same base powder is used in the following test, the base powder curing condition is 180℃ / 20min, and the base powder layer coating film thickness is 100-120μm.

[0160] The coating appearance, transparency and leveling grade are tested by visual inspection;

[0161] The leveling grade is evaluated as follows:

[0162] Level 10: indicates the best leveling property, the coating surface is very smooth, and there is no obvious leveling defect;

[0163] Level 9: The coating surface is smooth, with only very minor leveling defects;

[0164] Level 8: The coating surface is relatively smooth with slight leveling defects;

[0165] Level 7: There are some leveling defects on the coating surface, but they do not affect the overall appearance;

[0166] Level 6: There are moderate leveling defects on the coating surface;

[0167] Level 5: There are obvious leveling defects on the coating surface, but it is still acceptable;

[0168] Level 4: There are large leveling defects on the coating surface, affecting the appearance;

[0169] Level 3: There are serious leveling defects on the coating surface, which significantly affects the appearance;

[0170] Level 2: The coating surface is very uneven and the leveling defects are very obvious;

[0171] Level 1: The coating surface is extremely uneven, the leveling property is the worst, and there are a large number of leveling defects.

[0172] Distinctness of Image (DOI): Tested according to ASTM D5767-17 and measured by Konica Minolta Rhopoint IQ-S instrument.

[0173] Gloss (60°): Tested in accordance with GB / T 9754-2007; this gloss test is the gloss test before vacuum plating.

[0174] Gloss after vacuum plating (60°): tested in accordance with GB / T 9754-2007; the test was conducted before spraying of clear paint and after vacuum plating. The vacuum plating process was a conventional vacuum plating process, including spraying of primer, spraying of powder coatings of the embodiments of the present invention and the comparative example, and vacuum plating.

[0175] Bending performance: Tested according to ASTM D1333-99.

[0176] Impact performance (50kg.cm): tested in accordance with GB / T 1732-2020.

[0177] Hardness: Tested in accordance with GB / T6739-2006.

[0178] Adhesion: Tested in accordance with GB / T 9286-2021.

[0179] CASS performance (copper salt accelerated acetic acid salt spray test, 240h): tested in accordance with GB / T 10125-2021. Neutral salt spray (1000h): tested in accordance with GB / T 1771-2007.

[0180] Water resistance (40℃, 240h): Tested in accordance with GB / T 1733-1993.

[0181] The test results are shown in Tables 10 and 11 below.

[0182] Table 10 Coating performance test results of the powder coating formed by the embodiment

[0183]

[0184] Table 11 Test results of coating properties formed by powder coatings of comparative examples

[0185]

[0186]

[0187] It can be seen from Table 10 and Table 11 that the powder coating of the present invention can be quickly cured at 170°C, and the formed coating has at least the following advantages: the coating has a good appearance, is smooth and flat, and has no pinholes and shrinkage cavities; has good transparency, is transparent and clear, and has no haze; has high distinctness of image, not less than 97; has excellent leveling, and the leveling grade is not less than grade 10; has high gloss at 60°, not less than 185; the coating after vacuum electroplating has an excellent electroplating mirror effect, and the gloss after electroplating is not less than 545; has excellent mechanical properties, the bending performance reaches 0T, and both the front and back sides pass the impact test; has high hardness, not less than 2H; has strong adhesion, reaching grade 0; has excellent corrosion resistance and water resistance, the maximum width of unilateral corrosion in CASS performance does not exceed 0.5mm, the maximum width of unilateral corrosion in the neutral salt spray test does not exceed 0.7mm, and the water resistance has no discoloration and blisters in the test. Therefore, the powder coating obtained by the present invention has excellent comprehensive performance, can be applied to PVD vacuum plating, can replace traditional solvent-based medium coatings, form a medium layer, and can meet the decoration and protection needs of aluminum wheels.

[0188] Compared with Example 1, the powder coating of Comparative Example 1 did not modify the epoxy resin with terminal isocyanate polyether, resulting in poor leveling, gloss, brightness, mechanical properties and corrosion resistance of the coating, and obvious haze. This is mainly because the isocyanate group in the terminal isocyanate polyether can react chemically with the hydroxyl group in the epoxy resin to form a chemical bond, and the polyether is grafted onto the side chain of the epoxy resin. This chemical grafting effect improves the flexibility of the epoxy resin and improves the curing processability. At the same time, the introduction of the terminal isocyanate polyether increases the crosslinking degree between molecules, reduces the distance between molecules, and makes the polymers closer, thereby affecting the mechanical properties and corrosion resistance of the coating.

[0189] Compared with Example 1, the powder coating of Comparative Example 2 does not add hydroxyl-terminated phenol curing agent V-209 and dicyandiamide curing agent Epikure 107FF at the same time, and it is difficult to achieve rapid curing at 170°C / 15min. Therefore, the coating performance is poor under this curing condition.

[0190] Compared with Example 1, the powder coatings of Comparative Examples 3 and 4 only added benzoin or modified polyamide wax, resulting in pinholes in the coating appearance, reducing the gloss and brightness of the coating, and further affecting the mirror effect after vacuum plating.

[0191] Compared with Example 1, the powder coating of Comparative Example 4 does not first extrude the terminal isocyanate polyether modified epoxy resin and the hydroxyl-terminated phenol curing agent separately at high temperature during the production process and then extrude it with the remaining components for a second time. Although some performances meet the requirements of the wheel hub coating, the coating still has pinholes and shrinkage holes in appearance.

[0192] Compared with Example 1, the powder coating of Comparative Example 6 uses only diphenylmethane diisocyanate to modify the epoxy resin, and the coating formed by the obtained powder coating has poor flexibility and impact resistance.

[0193] In summary, the present invention grafts and modifies epoxy resin by terminal isocyanate polyether, significantly improving the leveling, gloss, brightness and mechanical properties of the coating formed by the powder coating, and the overall performance is excellent. At the same time, combined with hydroxyl-terminated phenol curing agent and dicyandiamide curing agent, the powder coating is rapidly cured at low temperature at 170°C / 15min, which is suitable for heat-sensitive substrates, and the rapid curing property is conducive to improving production efficiency. In addition, by further adding benzoin and modified polyamide wax as a breathable agent, pinholes and shrinkage cavities in the coating are effectively avoided, greatly improving the appearance of the coating.

[0194] The coating formed by the powder coating provided by the present invention has the advantages of no pinholes and shrinkage cavities, excellent leveling, high gloss, excellent electroplating mirror effect, high mechanical properties, high hardness, high corrosion resistance and high water resistance, etc., can be used in PVD vacuum electroplating process, used as a medium powder coating, and is particularly suitable for PVD vacuum electroplating of wheel hubs, and can meet the decoration and protection requirements of wheel hubs, especially aluminum wheel hubs.

[0195] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A powder coating, characterized in that: Calculated by mass, it includes the following components: 100-150 parts of isocyanate-terminated polyether-modified epoxy resin, 50-100 parts of hydroxyl-terminated phenol curing agent, 5-15 parts of dicyandiamide curing agent, 4 to 15 parts of additives.

2. The powder coating according to claim 1, characterized in that The mass percentage of the polyether segment in the isocyanate-terminated polyether-modified epoxy resin is 16-24%; And / or, the mass percentage of isocyanate groups in the isocyanate-terminated polyether-modified epoxy resin is 57-63%; And / or, the epoxy equivalent of the isocyanate-terminated polyether-modified epoxy resin is 450 to 750 g / eq.

3. The powder coating according to claim 1, characterized in that The hydroxyl value of the hydroxyl-terminated phenol curing agent is 0.3 to 0.6 eq / 100g.

4. The powder coating according to claim 1, characterized in that The auxiliary agent comprises a leveling agent, a breathable agent and a promoter; the breathable agent comprises benzoin and modified polyamide wax.

5. The powder coating according to claim 4, characterized in that The mass ratio of the benzoin to the modified polyamide wax is 1:(3-4).

6. The powder coating according to claim 1, characterized in that The leveling agent includes an acrylic leveling agent; And / or, the accelerator includes an imidazole accelerator.

7. A method for preparing a powder coating according to any one of claims 1 to 6, characterized in that: The steps include: The isocyanate-terminated polyether-modified epoxy resin and the hydroxyl-terminated phenol curing agent are mixed, extruded and crushed to obtain the first material; the first material is mixed with a dicyandiamide curing agent and an auxiliary agent, extruded and crushed to obtain the powder coating.

8. The preparation method according to claim 7, characterized in that: The isocyanate-terminated polyether-modified epoxy resin is prepared by a preparation method comprising the following steps: The epoxy resin, the isocyanate-terminated polyether and the organic solvent are mixed and reacted in an inert atmosphere to obtain the isocyanate-terminated polyether-modified epoxy resin; the reaction temperature is 70-95°C.

9. Use of the powder coating according to any one of claims 1 to 6 in a PVD vacuum electroplating process.

10. A wheel hub, characterized in that: A coating layer formed from the powder coating according to any one of claims 1 to 6.

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