Aluminum hub finishing powder coating capable of improving corner coverage rate and preparation method of aluminum hub finishing powder coating

Abstract

The invention discloses an aluminum hub finishing powder coating capable of increasing the corner coverage rate. The aluminum hub finishing powder coating is prepared from the following raw materials in parts by mass: 80 parts of acrylic resin, 17 parts of a curing agent, 1.2 parts of a flatting agent, 0.3 part of benzoin and 0.2-0.8 part of fumed silica. The invention also discloses a preparation method of the aluminum hub finishing powder coating, which comprises the following steps: step S1, according to the raw material ratio, firstly adding the acrylic resin A, then adding the curing agent, the flatting agent, the benzoin and the fumed silica, and finally adding the acrylic resin B, and uniformly stirring; step S2, putting the stirred mixed raw materials into an extruder, crushing, carrying out compression roller and extruding a screw rod, and starting to extrude; and S3, the powder passes through a rotary screen of 200-220 meshes, the particle size D50 is made to be 30-35 microns, 0.05-0.1% of powder flowing drying agent is evenly mixed in the powder grinding process, and the powder coating is obtained. According to the aluminum hub finishing powder coating and the preparation method thereof, under the condition that transparency and leveling are not changed, the corner coverage rate of the powder coating on a workpiece can be increased.

Description

Technical Field

[0001] This invention relates to the field of aluminum wheel hub cover powder coating technology, and in particular to an aluminum wheel hub cover powder coating with improved edge and corner coverage and its preparation method. Background Technology

[0002] Aluminum wheel hub clear powder coating is a high-performance powder coating specifically designed for coating the surface of aluminum wheels. It is primarily used to improve the appearance, corrosion resistance, wear resistance, and UV resistance of aluminum wheels.

[0003] The factors affecting the coverage of aluminum wheel hub powder coatings are as follows:

[0004] (1) Characteristics of powder coatings

[0005] The particle size of powder coatings affects their flowability and covering power. Particles that are too small can lead to uneven fluidization, while those that are too large may result in incomplete coverage. Good flowability contributes to uniform coverage, while poor flowability can lead to uneven coating or missed areas.

[0006] (2) Spraying process

[0007] The voltage and current settings in electrostatic spraying affect powder adsorption; improper settings can lead to uneven coverage. Spraying too close a distance can result in an overly thick coating, while spraying too far a distance can lead to incomplete coverage. An improper spraying angle can also result in insufficient coverage in certain areas.

[0008] (3) Workpiece shape

[0009] The complex shape of aluminum wheels may make it difficult to cover certain areas evenly, requiring adjustments to spraying parameters or the use of auxiliary tools.

[0010] (4) Pretreatment

[0011] Surface oil or oxide layers can affect powder adsorption, leading to uneven coverage. Phosphating can enhance powder adhesion, but improper treatment can affect coverage.

[0012] (5) Curing process

[0013] Insufficient or excessive curing will affect the uniformity and adhesion of the coating.

[0014] (6) Environmental factors

[0015] High humidity or unsuitable temperature may affect powder flowability and adsorption efficiency.

[0016] The powder coating for aluminum wheel hubs is primarily acrylic-based, offering significant advantages in leveling, transparency, weather resistance, and corrosion resistance compared to other systems. However, this pursuit of high leveling results in excessive powder coating loss at the edges and corners of the workpiece during the melting and curing process, leading to low corner coverage. Currently, the corner coverage of existing aluminum wheel hub powder coatings is less than 20%. This low corner coverage, coupled with an overall coating thickness below the required upper limit, makes it prone to failing filiform corrosion tests. In practical applications, the coating at the wheel hub edges and corners is easily damaged, compromising both aesthetics and protective function. Summary of the Invention

[0017] To address the aforementioned technical problems, this invention provides an aluminum wheel hub cover powder coating with improved edge and corner coverage and its preparation method, which can increase the edge and corner coverage of the powder coating on the workpiece without changing the transparency and leveling.

[0018] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0019] A powder coating for improving edge and corner coverage of aluminum wheel hubs is prepared from the following raw materials in parts by weight: 80 parts acrylic resin, 17 parts curing agent, 1.2 parts leveling agent, 0.3 parts benzoin, and 0.2 to 0.8 parts fumed silica.

[0020] A further improvement to the above technical solution is as follows:

[0021] Preferably, the acrylic resin has an epoxy equivalent of 510-560 g / eq, volatile matter <0.5%, clear transparency, color <2, and insoluble matter <15 ppm.

[0022] Preferably, the acrylic resin comprises acrylic resin A and acrylic resin B, wherein, according to the total raw material mass parts: 40 parts of acrylic resin A and 40 parts of acrylic resin B.

[0023] Preferably, the acrylic resin A has a melt viscosity of 39-47P, a molecular weight of 7800-8900Mw, and a Tg of 42-46℃.

[0024] Preferably, the acrylic resin A is an acrylic-based polymer material.

[0025] Preferably, the acrylic resin B has a melt viscosity of 53-57P, a molecular weight of 11000-15000Mw, and a Tg of 55-85℃.

[0026] Preferably, the acrylic resin B is an acrylic-based polymer material.

[0027] This invention also discloses a method for preparing a powder coating for aluminum wheel hubs, comprising the following steps:

[0028] Step S1, Premixing:

[0029] According to the raw material ratio, first add acrylic resin A, then add curing agent, leveling agent, benzoin and fumed silica, and finally add acrylic resin B, and stir evenly.

[0030] Step S2, Extrusion:

[0031] The mixed raw materials are put into the extruder, and the crushing, pressure roller, extrusion screw and feeding screw are turned on in sequence to start extrusion;

[0032] Step S3, grinding:

[0033] The extruded and crushed flakes are ground in a grinding mill and passed through a 200-220 mesh rotary sieve to achieve a particle size D50 of 30-35 micrometers. During the grinding process, 0.05-0.1% of powder flow desiccant is mixed in to obtain powder coating.

[0034] The aluminum wheel hub cover powder coating with improved edge and corner coverage and its preparation method provided by the present invention have the following advantages compared with the prior art:

[0035] The present invention relates to an aluminum wheel hub clear powder coating and its preparation method for improving edge and corner coverage. The addition of a thixotropic agent—fumed silica—changes the fluidity of the aluminum wheel hub clear powder coating during melting, preventing too much powder coating from flowing away from the edges and corners of the workpiece, thereby improving the edge and corner coverage.

[0036] The present invention relates to an aluminum wheel hub clear powder coating with improved edge and corner coverage and its preparation method. The edge and corner coverage is ≥30%. Even when the coating thickness is at the lower limit of the required index, the filamentous corrosion test can be passed smoothly. In practical applications, the coating film at the edge and corner of the aluminum wheel hub is not easily damaged, and the aesthetic and protective effects last longer. Detailed Implementation

[0037] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0038] The aluminum wheel hub clear powder coating of this invention, which improves edge and corner coverage, incorporates a thixotropic agent—fumed silica—to alter the fluidity of the aluminum wheel hub clear powder coating during melting. This prevents excessive powder coating from flowing away from the edges and corners of the workpiece, thereby improving edge and corner coverage. Among all thixotropic agents (such as precipitated silica, organobentonite, asbestos, kaolin, etc.), fumed silica is characterized by requiring a small dosage and exhibiting excellent thixotropic effects. It can increase the edge and corner coverage of the powder coating on the workpiece without altering transparency and leveling.

[0039] If precipitated silica is used to achieve the same edge coverage, the amount added will increase to more than 1%. With a larger amount added, the transparency will decrease. Organic bentonite, asbestos, kaolin, etc. have an even more serious impact on transparency.

[0040] Another way to improve the edge coverage of powder coatings is to add a catalyst to allow the powder coating to cure quickly, but this method will affect the leveling properties of the powder coating.

[0041] The method for preparing the aluminum wheel hub cover powder coating with improved edge and corner coverage according to the present invention includes the following steps:

[0042] Step S1, Premixing

[0043] According to the raw material ratio, first add acrylic resin A, then add curing agent, leveling agent, benzoin, and fumed silica, and finally add acrylic resin B, and stir evenly; set the mixer to slow speed for 3 minutes and fast speed for 60 seconds, with a speed frequency of 20Hz for slow speed and 40Hz for fast speed. Acrylic resin A is ALMATEX PD 7610, and acrylic resin B is WK6550.

[0044] Step S2, extrusion

[0045] S2-1, preheat the extruder 30 minutes before use to prevent the formation of gelled particles. At startup, set the temperatures of each zone as follows: Zone I: 40℃, Zone II: 80℃, Zone III: 100℃, Zone IV: 100℃, Zone V: 100℃, Zone VI: 100℃. During machine operation, set the temperatures of each zone as follows: Zone I: 40℃, Zone II: 80℃, Zone III: 80℃, Zone IV: 80℃, Zone V: 80℃, Zone VI: 80℃.

[0046] S2-2, Take out a portion of the mixed raw material for testing. Take out about 5KG to test whether it is qualified. Put it into the feed hopper of the extruder, and then start the crusher, pressure roller, extrusion screw and feeder in sequence. Adjust the screw speed frequency to 40-45Hz and the feed screw speed frequency to 20-25Hz to start extrusion.

[0047] Step S3, grinding

[0048] Adjust the speed of the main and auxiliary mills, pass the powder through a 200-220 mesh rotary sieve to make the particle size D50 = 30-35 micrometers, mix 0.05-0.1% powder flow desiccant during the grinding process, and confirm that no gelling particles are generated; thus, obtain the powder coating.

[0049] In this embodiment, as shown in Table 1, different ratios of raw materials were used for testing.

[0050] Table 1 Raw Material Proportions

[0051] Formula number Formula 1 Formula 2 Formula 3 Formula 4 Acrylic resin A (ALMATEX PD 7610) 40 40 40 40 Acrylic resin B (WK6550) 40 40 40 40 Curing agent (DDDA) 17 17 17 17 Leveling agent (PL200A) 1 1 1 1 Degassing agent (benzoin) 0.4 0.4 0.4 0.4 Fumed silica (R-972) 0 0.2 0.8 1

[0052] The results of the edge coverage of powder coatings obtained from different proportions of raw materials are shown in Table 2.

[0053] Table 2 shows the edge coverage of powder coatings obtained from different proportions of raw materials.

[0054] Formula number Formula 1 Formula 2 Formula 3 Formula 4 Corner coverage 24％ 30％ 37％ 42％

[0055] The leveling grades of powder coatings obtained from different proportions of raw materials are shown in Table 3.

[0056] Table 3. Leveling grades of powder coatings obtained from different proportions of raw materials.

[0057] Formula number Formula 1 Formula 2 Formula 3 Formula 4 Leveling grade Level 9 Level 9 Level 9 8％

[0058] It can be seen that the powder coating of the present invention is superior to existing powder coatings in terms of both edge coverage and leveling grade.

[0059] The above embodiments are merely preferred examples of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A powder coating for improving edge and corner coverage of aluminum wheel hubs, characterized in that, It is formulated from the following raw materials in parts by weight: 65-80 parts acrylic resin, 16-20 parts curing agent, 1-1.5 parts leveling agent, 0.3-0.5 parts benzoin, and 0.2-0.8 parts fumed silica.

2. The aluminum wheel hub clear powder coating for improving edge and corner coverage according to claim 1, characterized in that, The acrylic resin has an epoxy equivalent of 510-560 g / eq, volatile matter <0.5%, transparency of clear, color <2, and insoluble matter <15 ppm.

3. The aluminum wheel hub clear powder coating for improving edge and corner coverage according to claim 2, characterized in that, The acrylic resin includes acrylic resin A and acrylic resin B, wherein, according to the total raw material mass parts: 40 parts of acrylic resin A and 40 parts of acrylic resin B.

4. The aluminum wheel hub clear powder coating for improving edge and corner coverage according to claim 3, characterized in that, The acrylic resin A has a melt viscosity of 39–47P, a molecular weight of 7800–8900Mw, and a Tg of 42–46℃.

5. The aluminum wheel hub clear powder coating for improving edge and corner coverage according to claim 4, characterized in that, The acrylic resin A is an acrylic-based polymer material.

6. The aluminum wheel hub clear powder coating for improving edge and corner coverage according to claim 4, characterized in that, The acrylic resin B has a melt viscosity of 53-57P, a molecular weight of 11000-15000Mw, and a Tg of 55-85℃.

7. The aluminum wheel hub clear powder coating for improving edge and corner coverage according to claim 6, characterized in that, The acrylic resin B is an acrylic-based polymer material.

8. A method for preparing a powder coating for improving edge and corner coverage of aluminum wheel hubs, characterized in that, The preparation of the aluminum wheel hub cover powder coating according to claim 7 comprises the following steps: Step S1, Premixing: According to the raw material ratio, first add acrylic resin A, then add curing agent, leveling agent, benzoin and fumed silica, and finally add acrylic resin B, and stir evenly. Step S2, Extrusion: The mixed raw materials are sequentially started by the crusher, pressure roller, extrusion screw and feeding screw to begin extrusion; Step S3, grinding: The extruded and crushed flakes are ground in a grinding mill and passed through a 200-220 mesh rotary sieve to achieve a particle size D50 of 30-35 micrometers. During the grinding process, 0.05-0.1% of powder flow desiccant is mixed in to obtain powder coating.