Matt clear coating for automobile wheel hub and preparation method and application thereof

Abstract

The application discloses a matt varnish for automobile hub coating and a preparation method and application thereof. In the matt varnish, the raw materials for forming the varnish comprise the following components according to 100 parts of total weight: 42-55 parts of polyester resin, 5-10 parts of acrylic resin, 15-25 parts of amino resin, 3-5 parts of blocked isocyanate, 1.2-8 parts of auxiliary agent, 2-6 parts of matting powder and 20-30 parts of organic solvent. The varnish can be used for coating of automobile hub, especially for recoating of automobile hub, and when used for recoating of automobile hub, the obtained coating film has good recoating adhesion and hardness above HB level, and also has excellent appearance, fullness, car washing resistance, impact resistance, adhesion, salt spray resistance, water resistance and weather resistance and the like.

Description

Technical Field

[0001] This invention relates to the field of clear varnish technology for wheel hub coating. More specifically, it relates to a matte clear varnish for automotive wheel hub coating, its preparation method, and its application. Background Technology

[0002] As people's demands for car appearance continue to rise, the appearance and performance of car wheels are also becoming increasingly important factors. Matte finishes, in particular, are gaining popularity among consumers due to their unique color. However, the manufacturing process for matte finishes is extremely complex. A typical single-coat product requires four layers: base coat, color coat, transparent coat, and matte clear coat, resulting in a total film thickness of 220-260μm. If defects are found, recoating is necessary. The recoating process involves repeatedly spraying the color coat, transparent coat, and matte clear coat onto the matte clear coat. This not only increases the total film thickness to approximately 400μm, but also requires the underlying matte clear coat to be baked at temperatures exceeding 180℃, far exceeding the acceptable baking temperature for conventional clear coats. Therefore, the adhesion of the recoating process is a significant challenge, and the adhesion problem of the matte clear coat recoating process has always been a major obstacle to achieving matte finishes on wheels.

[0003] In existing technologies, conventional acrylic clear coats are commonly used for coating automotive bodies and other fields. However, since the matte clear coat needs to be baked at a high temperature of 180-200℃ when baking the transparent powder during the recoating process, the adhesion of the matte clear coat is prone to problems. The conventional solution is to reduce the reactivity of the clear coat, that is, to use hydroxyl or amino resins with milder reactions to soften the hardness of the matte clear coat. This can improve the adhesion of the recoating, but the hardness cannot meet the requirements of customers who need to achieve HB or higher. Summary of the Invention

[0004] Based on the above facts, the purpose of this invention is to provide a matte clear varnish for automotive wheel rim coating, its preparation method, and its application. This clear varnish can be used for coating automotive wheel rims, especially for recoating automotive wheel rims. When used in recoating automotive wheel rims, the resulting coating film exhibits good recoating adhesion and a hardness of HB level or higher. It also possesses excellent appearance, fullness, wash resistance, impact resistance, adhesion, salt spray resistance, water resistance, and weather resistance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A matte clear coat for automotive wheel rims, comprising, by weight 100 parts, the raw materials forming the clear coat contain the following components:

[0007] 42-55 parts polyester resin, 5-10 parts acrylic resin, 15-25 parts amino resin, 3-5 parts blocked isocyanate, 1.2-8 parts additives, 2-6 parts matting agent and 20-30 parts organic solvent.

[0008] Furthermore, the polyester resin has a non-volatile content of 59-61 wt%, an acid value of 3.5-6.1 mg KOH / g, and a viscosity of 1.1-1.8 Pa·s.

[0009] Furthermore, the acrylic resin has a non-volatile content of 68-72 wt%, a viscosity of 60-100 s (25°C, Gear tube), and an acid value of 9-13 mg KOH / g (based on solid resin).

[0010] Furthermore, the amino resin is a partially methylated amino resin with a degree of methylation of 60-70%, a non-volatile content of 78-82 wt%, and a viscosity of M-Q.

[0011] Furthermore, the non-volatile content of the blocked isocyanate is 73-77 wt%, and the viscosity is 2900-3700 mPa·s.

[0012] Furthermore, the blocked NCO content of the blocked isocyanate is 10-15%.

[0013] Furthermore, the blocked isocyanate has a blocked NCO content of 11%.

[0014] Furthermore, the organic solvent is selected from ether solvents and / or aromatic solvents.

[0015] Furthermore, the ether solvent is selected from one or more of ethylene glycol butyl ether, diethylene glycol monobutyl ether, and diethylene glycol butyl ether acetate; the aromatic solvent is one or a combination of 100# and / or 150# solvents.

[0016] Furthermore, by weight, the organic solvent comprises 8 to 11 parts of ether solvent and 15 to 20 parts of aromatic solvent, and the total weight of the two organic solvents is 23 to 30 parts.

[0017] Furthermore, the additive is selected from one or more of ultraviolet absorbers, light stabilizers, leveling agents, defoamers, and substrate wetting and dispersing agents.

[0018] Furthermore, the leveling agent is an organosilicon-based leveling agent.

[0019] Further, by weight, the additives comprise:

[0020] 0.2–0.4 parts UV absorber, 0.4–0.8 parts light stabilizer, 0.2–0.4 parts leveling agent, 0.1–0.5 parts defoamer and 0.2–0.5 parts substrate wetting and dispersing agent.

[0021] In another aspect, the present invention provides a method for preparing the matte clear coat for automotive wheel rims as described above, the method comprising the following steps:

[0022] Polyester resin, acrylic resin and amino resin were mixed under stirring conditions of 400 to 600 r / min for 10 to 15 min.

[0023] Under these stirring conditions, first add the blocked isocyanate and stir for 10-15 minutes; then add a portion of the organic solvent and stir for 10-15 minutes; then add the additives and stir until homogeneous.

[0024] Adjust the stirring speed to 1500-2000 r / min, add matting powder, and disperse until the fineness is ≤10μm;

[0025] Add the remaining organic solvent, mix well, and adjust to the appropriate viscosity to obtain the matte varnish.

[0026] In another aspect, the present invention provides the application of the matte clear varnish for automotive wheel rims as described above in the coating of automotive wheel rims.

[0027] Furthermore, the matte clear varnish is used in the recoating process of automobile wheel hubs.

[0028] Furthermore, the application includes the following steps:

[0029] The matte clear varnish is applied to the wheel hub base;

[0030] Furthermore, the coating conditions are as follows: a primer is sprayed onto the wheel hub base and baked; then a color paint is sprayed and baked; next, a transparent coating is sprayed, and finally the matte clear coat is sprayed.

[0031] The beneficial effects of this invention are as follows:

[0032] The matte clear varnish provided by this invention uses polyester resin as the main hydroxyl resin, combined with a small amount of acrylic resin and amino resin as the base resin, and an appropriate amount of blocked isocyanate to improve crosslinking density and flexibility. Suitable additives, solvents, and matting agents are also added. The resulting matte clear varnish, after drying, has a pencil hardness of up to F, a spray solids content >45%, a spray viscosity range of 18-24 seconds / 20℃*Ford cup 4, and exhibits good recoating adhesion, fullness, weather resistance, car wash resistance, and chemical resistance. The clear varnish composition provided by this invention can be well applied to the topcoat coating of automotive original equipment manufacturer (OEM) paints (body) and automotive wheel rims. Detailed Implementation

[0033] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0034] To address the challenge of achieving excellent recoating adhesion and hardness in automotive wheel recoating processes, where the resulting coating exhibits superior washability, weather resistance, and appearance, one specific embodiment of the present invention provides a matte clear coat for automotive wheel coating. The clear coat, based on 100 parts by weight, comprises the following components:

[0035] 42-55 parts polyester resin, 5-10 parts acrylic resin, 15-25 parts amino resin, 3-5 parts blocked isocyanate, 1.2-8 parts additives, 2-6 parts matting agent and 20-30 parts organic solvent.

[0036] Unlike ordinary clear varnishes for wheel coatings that are mainly based on acrylic resin, the clear varnish (solvent-based matte clear varnish) in this embodiment uses polyester resin as the main film-forming resin, combined with blocked isocyanate and amino resin, and a small amount of weather-resistant amino resin to improve aging resistance. It is suitable for wheel recoating processes and can ensure good recoating adhesion (grade 0) and hardness of the paint film. At the same time, it also has excellent appearance, fullness, car wash resistance, impact resistance (≥40cm), adhesion, salt spray resistance, water resistance and weather resistance.

[0037] For example, the polyester resin has a non-volatile content of 59-61 wt%, an acid value of 3.5-6.1 mg KOH / g, and a viscosity of 1.1-1.8 Pa·s.

[0038] The preferred use of the polyester resin imparts properties such as good adhesion and flexibility to the matte varnish after recoating. Exemplary polyester resins include, but are not limited to, SETAL 173VS-60 and SETAL 1703XX-75 resins from Zhanxin. Exemplary amounts of the polyester resin added to the raw materials include, but are not limited to, 42-50 parts, 42-45 parts, and 42-44 parts.

[0039] For example, the acrylic resin has a non-volatile content of 68-72 wt%, a viscosity of 60-100 s (25°C, Gear tube), and an acid value of 9-13 mg KOH / g (based on solid resin).

[0040] Exemplary acrylic resins include, but are not limited to, SWK 337 from Sanwang Resin. In this embodiment, based on the formulation described above, only a small amount of acrylic resin needs to be added to ensure good recoating adhesion and hardness of the paint film.

[0041] For example, the amount of acrylic resin added in the raw materials includes, but is not limited to, 5-8 parts, 5-6 parts, etc.

[0042] For example, the amino resin is a partially methyl etherified amino resin with a degree of methyl etherification of 60-70%, a non-volatile content of 78-82 wt%, and a Grignard viscosity of M-Q; or, the amino resin has a non-volatile content of 86.0-90.0% and a viscosity of 1400-6900 mPa·s. Exemplary amino resins include, but are not limited to, Resimene 741 and Changchun Chemical's M-40ST. Compared to other amino resins such as fully methyl etherified amino resins, using this amino resin can impart better flexibility and recoating adhesion to the coating film while meeting hardness requirements.

[0043] For example, the amount of amino resin added in the raw materials includes, but is not limited to, 15-20 parts, 16-20 parts, etc.

[0044] For example, the blocked isocyanate has a non-volatile content of 73-77 wt% and a viscosity of 2900-3700 mPa·s. For example, the blocked NCO content of the blocked isocyanate is 10-15%, preferably 11%. Examples of blocked isocyanates include, but are not limited to, those containing... BL 3175SN, BL 3575SN, etc. The addition of blocked isocyanates can increase the crosslinking density of the paint film, improve flexibility, and enhance the recoating adhesion of the coating.

[0045] For example, the matting agent is selected from SYLYSIA 350 pigment. One or a combination of E-1011. In a preferred embodiment of the present invention, the amount of matting agent added to the raw materials includes, but is not limited to, 2-5 parts, 3-5 parts, 3-4 parts, etc.

[0046] For example, the organic solvent is selected from ether solvents and / or aromatic solvents.

[0047] For example, the ether solvent is selected from one or more of ethylene glycol butyl ether, diethylene glycol monobutyl ether, and diethylene glycol butyl ether acetate; the aromatic solvent is one or a combination of 100# and / or 150# solvents. Ether solvents and aromatic solvents possess excellent hydrophilicity, solubility, slow drying, and leveling properties, enabling them to efficiently dissolve resins and additives, achieve better leveling, and prevent scabbing during varnish baking.

[0048] For example, by weight, the organic solvent comprises 8 to 11 parts of ether solvent and 15 to 20 parts of aromatic solvent, and the total weight of the two organic solvents is 23 to 30 parts.

[0049] For example, the additive is selected from one or more of ultraviolet absorbers, light stabilizers, leveling agents, defoamers, and substrate wetting and dispersing agents.

[0050] For example, the leveling agent is an organosilicon leveling agent.

[0051] For example, the adjuvant comprises, by weight:

[0052] 0.2–0.4 parts UV absorber, 0.4–0.8 parts light stabilizer, 0.2–0.4 parts leveling agent, 0.1–0.5 parts defoamer and 0.2–0.5 parts substrate wetting and dispersing agent.

[0053] In some preferred examples, the amount of the above-mentioned adjuvant added is 1.2 to 2 parts.

[0054] In some preferred examples, the adjuvant comprises, by weight:

[0055] 0.2–0.3 parts ultraviolet absorber, 0.5–0.7 parts light stabilizer, 0.2–0.3 parts leveling agent, 0.1–0.3 parts defoamer, and 0.2–0.3 parts substrate wetting and dispersing agent;

[0056] The total weight of all the above components is 1.2 to 2 parts.

[0057] The use of appropriate additives solves the problems of easy settling, poor wetting, and poor weather resistance of matte varnish coatings. By selecting suitable solvents, the varnish composition has good workability while ensuring that other properties remain unchanged.

[0058] For example, the ultraviolet absorber is RIASORB UV-1130 (purchased from RIA Novosti).

[0059] For example, the light stabilizer is RIASORB UV-292 (purchased from RIA Novosti).

[0060] For example, the leveling agent is a silicone leveling agent; more specifically, the silicone leveling agent is selected from one or a combination of BYK 306 (purchased from BYK Company) and BYK 348 (purchased from BYK Company).

[0061] For example, the defoamer is BYK 011 (purchased from TEGO).

[0062] For example, the substrate wetting and dispersing agent is selected from one or a combination of BYK 392 (purchased from BYK Company), BYK 345 (purchased from BYK Company).

[0063] In this embodiment, specific amounts and solid contents of polyester resin, acrylic resin, and amino resin, along with specific types and amounts of blocked isocyanate, are used to solve the recoating adhesion problem in complex processes involving base powder, color paint, transparent powder, and matte clear coat. Simultaneously, the matte clear coat exhibits good hardness, flexibility, chemical resistance, and weather resistance. By using a blend of polyester and acrylic resins, the problem of brittle paint films and poor recoating adhesion due to excessively high Tg values ​​when using only acrylic resin is solved, as is the issue of slightly poor weather resistance when using only polyester resin. Furthermore, in this embodiment, the good combination of amino resin with polyester and acrylic resins, along with the use of specific types and amounts of blocked isocyanate, achieves cross-linking and curing, satisfying both the surface hardness and scratch resistance requirements of the matte clear coat and providing good flexibility and recoatability, thus solving the problem of the inability to recoat matte clear coats in complex wheel hub processes.

[0064] According to another specific embodiment of the present invention, a method for preparing the matte clear coat for automotive wheel rims as described above is provided, the method comprising the following steps:

[0065] Polyester resin, acrylic resin and amino resin were mixed under stirring conditions of 400 to 600 r / min for 10 to 15 min.

[0066] Under these stirring conditions, first add the blocked isocyanate and stir for 10-15 minutes; then add a portion of the organic solvent and stir for 10-15 minutes; then add the additives and stir until homogeneous.

[0067] Adjust the stirring speed to 1500-2000 r / min, add matting powder, and disperse until the fineness is ≤10μm;

[0068] Add the remaining organic solvent, mix well, and adjust to the appropriate viscosity to obtain the matte varnish.

[0069] In some specific examples, the preparation method of the matte varnish includes the following steps:

[0070] (1) Add polyester resin to a container, and then add acrylic resin and amino resin under stirring conditions of 400-600 r / min, and stir for 10-15 min;

[0071] (2) Add the blocked isocyanate under stirring conditions of 400-600 r / min and stir for 10-15 min;

[0072] (3) Under stirring conditions of 400-600 r / min, add part of the ether solvent and stir for 10-15 min;

[0073] (4) Under stirring conditions of 400-600 r / min, add ultraviolet absorber and light stabilizer, and stir for 5-10 min;

[0074] (5) Under stirring conditions of 400-600 r / min, add substrate wetting and dispersing agent, defoamer and leveling agent, and stir for 5-10 min;

[0075] (6) Add aromatic solvent under stirring conditions of 400-600 r / min and stir for 10-15 min;

[0076] (7) Under stirring conditions of 400-600 r / min, add matting powder, adjust the stirring speed to 1500-2000 r / min, and disperse at high speed for half an hour until the fineness is ≤10 μm;

[0077] (8) Under stirring conditions of 400-600 r / min, add the remaining ether solvent and adjust to the appropriate viscosity.

[0078] According to another specific embodiment of the present invention, the application of the matte clear varnish for automotive wheel rims as described above in the coating of automotive wheel rims is provided.

[0079] For example, the matte clear coat is used in the recoating process of automobile wheels.

[0080] For example, the application includes the following steps:

[0081] The matte varnish is applied to the wheel hub base.

[0082] For example, the coating conditions are as follows: a primer is sprayed onto the wheel hub base and baked; then a color paint is sprayed and baked; next, a clear coat is sprayed, and finally a matte clear coat is sprayed.

[0083] The technical solution of the present invention will be described below with reference to some more specific embodiments:

[0084] Relevant raw material models and manufacturers' information:

[0085] Polyester resins: SETAL 173VS-60 resin, purchased from Zhanxin Resin; SETAL 1703XX-75, purchased from Zhanxin Resin; 1715VX-74, purchased from Zhanxin Resin;

[0086] Acrylic resin: SWK 337, purchased from Sanwang Resin;

[0087] Amino resins: M-40ST, purchased from Changchun Chemical; Resimene 741, purchased from INEOS.

[0088] Leveling agents: BYK 348, purchased from BYK Company; BYK 306, purchased from BYK Company;

[0089] Substrate wetting and dispersing agents: BYK 392, purchased from BYK; BYK 345, purchased from BYK Corporation;

[0090] Defoamer: BYK 011, purchased from BYK Corporation;

[0091] Blocked isocyanates: BL 3175SN, purchased from Covestro; BL 3575SN, purchased from Covestro;

[0092] Ultraviolet absorber: RIASORB UV-1130, purchased from RIA Novosti.

[0093] Light stabilizer: RIASORB UV-292, purchased from RIA Novosti.

[0094] Matting agent: SYLYSIA 350 pigment, purchased from Fuji Electric Co., Ltd., Japan; E-1011 was purchased from Tosoh Corporation of Japan.

[0095] Example 1

[0096] Matte clear varnish 1:

[0097] A matte varnish, the raw material formula of which is shown in Table 1 below.

[0098] The preparation of this matte varnish 1 includes the following steps:

[0099] (1) In a suitable container, add 47 parts of polyester resin SETAL 173VS-60, add 6 parts of acrylic resin SWK 337 and 18 parts of amino resin Resimene 741 while stirring at 400-600 r / min, and stir for 10-15 min.

[0100] (2) Under stirring conditions of 400-600 r / min, add 3.5 parts of blocked isocyanate. BL3175SN, stir for 10-15 minutes;

[0101] (3) Under stirring conditions of 400-600 r / min, add 5 parts of the ether solvent diethylene glycol monobutyl ether and stir for 10-15 min;

[0102] (4) Under stirring conditions of 400-600 r / min, add 0.3 parts of ultraviolet absorber RIASORB UV-1130 and 0.6 parts of light stabilizer RIASORB UV-292, and stir for 5-10 min.

[0103] (5) Under stirring conditions of 400-600 r / min, add 0.25 parts of substrate wetting and dispersing agent BYK 392, 0.15 parts of defoamer BYK 011, and 0.25 parts of leveling agent BYK 306, and stir for 5-10 min;

[0104] (6) Under stirring conditions of 400-600 r / min, add 19 parts of Solvent-150 and stir for 10-15 min;

[0105] (7) Under stirring conditions of 400-600 r / min, add 4 parts of matting powder SYLYSIA350 pigment, adjust the stirring speed to 1500-2000 r / min, and disperse at high speed for half an hour until the fineness is ≤10μm;

[0106] (8) Under stirring conditions of 400-600 r / min, add 3 parts of diethylene glycol butyl ether acetate solvent and adjust to the qualified viscosity to obtain matte varnish 1.

[0107] Table 1

[0108]

[0109] Examples 2-4

[0110] A matte varnish is prepared using the raw material formula shown in Table 1 above and the preparation method is the same as in Example 1.

[0111] Comparative Example 1

[0112] Matte Clear Coat C1:

[0113] Example 1 was repeated, except that the amount of solids such as commercially available Setal 1715VX-74 polyester resin was used to replace the polyester resin SETAL 173VS-60 in Example 1, while the amounts of other materials remained unchanged, and matte varnish C1 was prepared.

[0114] It should be noted that, compared with the polyester resin in Example 1, the polyester resin Setal1715VX-74 used in this comparative example is a commonly used resin in varnishes, with excellent mechanical properties, appearance fullness, and weather resistance; however, the use of this polyester resin will result in unsatisfactory recoating adhesion in the complex recoating process of matte varnishes.

[0115] Comparative Example 2

[0116] Matte Clear Coat C2:

[0117] Comparative Example 1 was repeated, except that commercially available amino resin CYMEL 303 and other solids were used to replace the amino resin Resimene 741 in Example 1, while the amounts of other materials remained unchanged, and matte varnish C2 was prepared.

[0118] It should be noted that the amino resin CYMEL 303 used in this comparative example is a fully methylated amino resin. This will result in a decrease in the hardness of the paint film.

[0119] Comparative Example 3

[0120] Matte Clear Coat C3:

[0121] Comparative Example 1 was repeated, except that commercially available amino resin CYMEL 325 and other solids were used to replace the amino resin Resimene 741 in Example 1, while the amounts of other materials remained unchanged, and matte varnish C3 was prepared.

[0122] It should be noted that in this comparative example, the amino resin CYMEL 325 used has a relatively high imino content and a low degree of methyl etherification.

[0123] In terms of paint film performance, it has better hardness than Comparative Example 1, but its flexibility and recoating adhesion are worse.

[0124] Comparative Example 4

[0125] Matte Clear Coat C4:

[0126] Example 1 was repeated, except that no blocked isocyanate was added. BL 3175SN, with other conditions unchanged, was used to prepare matte varnish C4.

[0127] Compared to Example 1, the crosslinking density of the paint film obtained in Comparative Example 4 decreases, and the recoating adhesion deteriorates.

[0128] Comparative Example 5

[0129] Matte Clear Coat C5:

[0130] Example 1 was repeated, except that instead of adding 6 parts of acrylic resin, polyester resin SETAL 173VS-60 and other solid components were used as substitutes, while the other conditions remained unchanged, and matte varnish C5 was prepared.

[0131] Comparative Example 6

[0132] Matte Clear Coat C6:

[0133] Example 1 was repeated, except that the amount of polyester resin SETAL 173VS-60 added was 42 parts, and the other conditions remained the same, to prepare matte varnish C6.

[0134] Comparative Example 7

[0135] Matte Clear Coat C7:

[0136] Example 1 was repeated, except that the amount of polyester resin SETAL 173VS-60 added was 6 parts and the amount of acrylic resin SWK 337 added was 47 parts, while the other conditions remained unchanged, and matte varnish C7 was prepared.

[0137] Performance testing:

[0138] The standard one-time product spraying process is as follows:

[0139] Wheel hub base material + base powder (baked at 180℃ / 30min) + color paint (baked at 140℃ / 30min) + transparent powder (baked at 180℃ / 30min) + matte clear varnish (baked at 140℃ / 30min).

[0140] The recoating process is as follows:

[0141] Wheel hub base material + base powder (baked at 180℃ / 30min) + color paint (baked at 140℃ / 30min) + transparent powder (baked at 180℃ / 30min) + matte clear varnish (baked at 140℃ / 30min) + color paint (baked at 140℃ / 30min) + transparent powder (baked at 180℃ / 30min) + matte clear varnish (baked at 140℃ / 30min).

[0142] The performance testing methods are shown in Table 2 below.

[0143] Table 2

[0144]

[0145] The varnish performance of the examples and comparative examples was tested using the above method, and the results are shown in Tables 3 and 4 below.

[0146] Table 3

[0147]

[0148]

[0149] Table 4

[0150]

[0151]

[0152] As can be seen from the table above, the matte varnish prepared in the examples meets the customer's requirements for the original paint indicators. When sprayed under standard construction conditions, the paint film has no abnormalities in appearance, good workability, and qualified mechanical properties, chemical resistance, and aging resistance.

[0153] The paint film obtained in Comparative Example 1 has better hardness and aging resistance, but the recoating adhesion is unqualified; the hardness of the paint film in Comparative Example 2 is unqualified; the flexibility and recoating adhesion of Comparative Example 3 are worse; the recoating adhesion of Comparative Example 4 is worse; the aging resistance of the paint film in Comparative Example 5 is worse; the paint film in Comparative Example 6 becomes brittle due to the reduction of polyester resin, and the recoating adhesion is worse; in Comparative Example 7, acrylic resin is the main film-forming resin, and the recoating adhesion of the paint film is worse.

[0154] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A matte clear coat for automotive wheel rim coating, characterized in that, The raw materials forming the varnish, based on a total weight of 100 parts, contain the following components: 42-55 parts polyester resin, 5-10 parts acrylic resin, 15-25 parts amino resin, 3-5 parts blocked isocyanate, 1.2-8 parts additives, 2-6 parts matting agent and 20-30 parts organic solvent.

2. The matte varnish according to claim 1, characterized in that, The polyester resin has a non-volatile content of 59-61 wt%, an acid value of 3.5-6.1 mg KOH / g, and a viscosity of 1.1-1.8 Pa·s.

3. The matte varnish according to claim 1, characterized in that, The acrylic resin has a non-volatile content of 68-72 wt%, a viscosity of 60-100 s (25°C, Gearbox), and an acid value of 9-13 mg KOH / g (based on solid resin).

4. The matte varnish according to claim 1, characterized in that, The amino resin is a partially methylated amino resin with a degree of methylation of 60-70%, a non-volatile content of 78-82 wt%, and a viscosity of M-Q.

5. The matte varnish according to claim 1, characterized in that, The blocked isocyanate has a non-volatile content of 73-77 wt%, a viscosity of 2900-3700 mPa·s, and the blocked NCO content is preferably 11%.

6. The matte varnish according to claim 1, characterized in that, The organic solvent is selected from ether solvents and / or aromatic solvents; Preferably, the ether solvent is selected from one or more of ethylene glycol butyl ether, diethylene glycol monobutyl ether, and diethylene glycol butyl ether acetate; the aromatic solvent is one or a combination of 100# and / or 150# solvents. More preferably, the organic solvent comprises 8 to 11 parts by weight of ether solvent and 15 to 20 parts by weight of aromatic solvent, and the total weight of the two organic solvents is 23 to 30 parts.

7. The matte varnish according to claim 1, characterized in that, The additives are selected from one or more of the following: ultraviolet absorbers, light stabilizers, leveling agents, defoamers, and substrate wetting and dispersing agents. Preferably, the leveling agent is an organosilicon leveling agent; More preferably, the adjuvant comprises, by weight: 0.2–0.4 parts UV absorber, 0.4–0.8 parts light stabilizer, 0.2–0.4 parts leveling agent, 0.1–0.5 parts defoamer and 0.2–0.5 parts substrate wetting and dispersing agent.

8. The method for preparing matte clear varnish for automotive wheel rim coating as described in any one of claims 1-7, characterized in that, Includes the following steps: Polyester resin, acrylic resin and amino resin were mixed under stirring conditions of 400 to 600 r / min for 10 to 15 min. Under these stirring conditions, first add the blocked isocyanate and stir for 10-15 minutes; then add a portion of the organic solvent and stir for 10-15 minutes; then add the additives and stir until homogeneous. Adjust the stirring speed to 1500-2000 r / min, add matting powder, and disperse until the fineness is ≤10μm; Add the remaining organic solvent, mix well, and adjust to the appropriate viscosity to obtain the matte varnish.

9. The application of the matte clear varnish for automotive wheel rims as described in any one of claims 1-7 in the coating of automotive wheel rims.

10. The application according to claim 9, characterized in that, Preferably, the matte clear varnish is used in the recoating process of automobile wheel hubs; Preferably, the application includes the following steps: The matte clear varnish is applied to the wheel hub base; Preferably, the coating conditions are as follows: spray primer onto the wheel hub base and bake; then spray color paint and bake; then spray transparent coating and finally spray the matte clear coat.

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