High gloss electrophoretic coating process

Abstract

A high-gloss electrophoretic coating process includes a conductive coating layer forming step and an electrophoresis step. The conductive coating layer forming step forms a conductive coating layer composed of a conductive paint on at least a part of the surface of a substrate by coating to form a semi-finished product, and the resistivity of the surface of the conductive coating layer is not greater than 500 Ω·m. The electrophoresis step immerses a conductive sheet and the semi-finished product as electrodes in an electrophoretic solution containing charged colloidal particles, and applies a voltage of 60 V to 120 V to form an electrophoretic coating layer with a thickness of not greater than 30 μm coated on the conductive coating layer. The surface resistivity is reduced by the conductive coating layer, so that the subsequent electrophoresis step can be performed within a specific voltage range, the process time is reduced, the occurrence of orange peel phenomenon is reduced, and the appearance of the product is improved.

Description

Technical Field

[0001] This invention relates to a coating process, and more particularly to an electrophoretic coating process. Background Technology

[0002] Lightweight metals such as magnesium or aluminum alloys are frequently used to manufacture the casings of portable electronic products due to their good mechanical strength and low specific gravity. To meet users' demands for product appearance, such as color and metallic luster, the industry typically performs surface processing on magnesium or aluminum alloy casings to alter their appearance, color, and gloss.

[0003] Generally speaking, common surface treatment methods in the industry involve directly adding dyes or pigments to an electrophoretic solution and then electrophoretically forming an electrophoretic coating layer of a specific color on the surface of the metal substrate. This allows the surface of the metal substrate to exhibit a specific color and maintain gloss. However, this electrophoretic process needs to be carried out under low voltage (no more than 60V) to avoid electrolytic reactions on the metal substrate. Furthermore, to achieve the desired gloss level, the electrophoretic coating layer needs to have a certain thickness (generally, to achieve a gloss level of 85GU, a film thickness of approximately 20μm to 25μm is required). However, since this method is carried out under low voltage, a long processing time is required to achieve the desired thickness. Additionally, the addition of dyes or pigments changes the surface tension of the electrophoretic solution, and an excessively long processing time can easily cause an orange peel effect in the electrophoretic coating layer, resulting in a visually unappealing surface.

[0004] Another common processing method involves pre-anodizing the metal substrate to form a porous oxide passivation film on its surface, preventing corrosion caused by reactions with moisture or chemical agents. This porous oxide passivation film is then dyed using a dip-coating method, followed by electrophoresis to form a transparent electrophoretic coating layer, thus enhancing surface gloss. However, because the porous oxide passivation film provides insulation to the metal substrate surface, this electrophoresis process requires a high voltage (above 180V). Excessive voltage can cause the electrophoretic coating layer on the metal substrate surface to develop an orange-peel effect, resulting in poor aesthetics. Furthermore, this processing method requires the electrophoretic coating layer to be thicker than 50μm to achieve the desired gloss, leading to higher production costs.

[0005] Therefore, adjusting the process to improve various technical problems encountered in metal surface processing, such as excessively long process time, excessively high applied voltage, and orange peel texture, is one of the directions that relevant industry players are striving for. Summary of the Invention

[0006] The purpose of this invention is to provide a high-gloss electrophoretic coating process.

[0007] The high-gloss electrophoretic coating process of the present invention includes a conductive coating layer formation step and multiple electrophoretic steps.

[0008] The conductive coating layer forming step involves coating a conductive coating layer made of conductive paint onto at least a portion of the surface of a substrate to form a semi-finished product, wherein the surface resistivity of the conductive coating layer is not greater than 500 Ω·m.

[0009] The electrophoresis step involves immersing a conductive sheet and the semi-finished product as electrodes in an electrophoretic solution containing charged colloidal particles. A voltage is applied to either the conductive sheet or the semi-finished product, creating an electric field between the conductive sheet, the conductive coating layer, and the electrophoretic solution to form a conductive circuit. This causes some of the colloidal particles to move along the direction of the electric field toward the semi-finished product, forming an electrophoretic coating layer with a thickness not exceeding 30 μm on the conductive coating layer. The voltage is between 60V and 120V.

[0010] Preferably, in the high-gloss electrophoretic coating process of the present invention, the total thickness of the conductive coating layer and the electrophoretic coating layer is not greater than 50 μm.

[0011] Preferably, in the high-gloss electrophoretic coating process of the present invention, the conductive paint has a base material and a conductive substance, wherein the base material is selected from epoxy resin or acrylic resin, and the conductive substance is selected from modified titanium dioxide, metal, nano-carbon material, graphite or graphene.

[0012] Preferably, in the high-gloss electrophoretic coating process of the present invention, the conductive paint further comprises a colorant, wherein the colorant is selected from inorganic pigments or organic dyes.

[0013] Preferably, in the high-gloss electrophoretic coating process of the present invention, the substrate is selected from magnesium, aluminum, magnesium alloy, aluminum alloy, aluminum-magnesium alloy, or magnesium-aluminum alloy.

[0014] Preferably, in the high-gloss electrophoretic coating process of the present invention, the colloidal particles of the electrophoretic solution are selected from aqueous resins.

[0015] Preferably, in the high-gloss electrophoretic coating process of the present invention, the applied voltage of the electrophoretic step is between 80V and 120V.

[0016] Preferably, in the high-gloss electrophoretic coating process of the present invention, the applied voltage of the electrophoretic step is between 80V and 100V.

[0017] The beneficial effects of the present invention are as follows: by first forming the conductive coating layer on the surface of the substrate to reduce the resistivity of the substrate surface, the electrophoretic coating layer covering the conductive coating layer can be formed on the surface of the semi-finished product by the electrophoretic step within a specific voltage range (between 60V and 120V), which can make the finished product after coating have good gloss and less prone to orange peel phenomenon, thereby improving the aesthetics of the product and shortening the process time at the same time. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating an embodiment of the high-gloss electrophoretic coating process of the present invention;

[0019] Figure 2 This is a side view schematic diagram illustrating the metal component produced by the electrophoretic coating process.

[0020] Figure 3 This is a diagram, for illustrative purposes only. Figure 1 The electrophoretic steps of the electrophoretic coating process are described. Detailed Implementation

[0021] Before the invention is described in detail, it should be noted that similar elements are represented by the same numbers in the following description.

[0022] See Figure 1 and Figure 2 The present invention relates to a high-gloss electrophoretic coating process for forming a high-gloss electrophoretic coating as described above. Figure 2 The metal component 3 shown. The electrophoretic coating process includes a conductive coating layer formation step 21 and an electrophoresis step 22.

[0023] The conductive coating layer forming step 21 involves forming a conductive coating layer 32 composed of conductive paint from at least a portion of the surface of the substrate 31, thereby forming a semi-finished product 30.

[0024] In detail, the substrate 31 is made of a lightweight and easily processed light metal material, such as magnesium, aluminum, magnesium alloy, aluminum alloy, magnesium-aluminum alloy, or aluminum-magnesium alloy. The conductive coating layer 32 is applied to the surface of the substrate 31 by coating, with a thickness between 10 μm and 20 μm and a surface resistivity of no more than 500 Ω·m. It provides conductivity and prevents the substrate 31 from being corroded by contact with moisture or chemical agents during subsequent electrophoresis processes.

[0025] Specifically, the conductive coating layer 32 is composed of conductive paint, which includes a base material, a conductive substance, and a colorant. The base material is selected from epoxy resin or acrylic resin, and acts as a dispersant for the conductive substance and the colorant, ensuring their uniform distribution within the conductive paint. This results in a uniform color of the conductive coating layer 32 and increases the adhesion between the conductive coating layer 32 and the substrate 31, allowing it to adhere tightly to the surface of the substrate 31. The conductive substance is selected from modified titanium dioxide, metal-doped modified titanium dioxide (e.g., silver-doped modified titanium dioxide), metals, carbon nanomaterials, graphite, or graphene, reducing the resistivity of the conductive coating layer 32 and providing good conductivity. The colorant is selected from inorganic pigments or organic dyes, enabling the conductive coating layer 32 to exhibit specific colors and providing a wider range of color choices.

[0026] The conductive coating layer 32 can be formed on the surface of the substrate 31 by spraying, roller coating, or dip coating. In this embodiment, the conductive coating layer forming step 21 involves applying the conductive paint to one surface of the substrate 31 by spraying (see...). Figure 2 The conductive coating layer 32, with a thickness of 20 μm and a surface resistivity between 200 Ω·m and 400 Ω·m, is cured and solidified as an example. Specifically, in this embodiment, the conductive paint is thoroughly mixed with an organic solvent (e.g., isobutanol, toluene, etc.) to adjust to an appropriate viscosity, then sprayed onto the surface of the substrate 31, and dried to form the conductive coating layer 32. The ratio of the conductive paint (including the base material, conductive substance, and colorant) to the organic solvent is between 3:7 and 4:6. However, in actual implementation, the ratio of the conductive paint to the organic solvent can be adjusted according to process requirements and is not limited to this.

[0027] In some embodiments, the conductive coating layer 32 may completely cover the entire surface of the substrate 31 as needed, or may only be formed on a portion of the surface of the substrate 31, as long as it does not affect the subsequent electrophoresis step 22, and is not limited to the form of this embodiment.

[0028] In some embodiments, when the conductive material added to the conductive paint itself has a strong color, the conductive coating layer 32 can also exhibit color through the conductive material. In this case, the conductive paint may only have a base material and a conductive material, without the need to add colorants. For example, when the conductive material is selected from modified titanium dioxide, the conductive coating layer 32 can exhibit the color of modified titanium dioxide and become white; if the conductive material is selected from nano-carbon materials, graphite, or graphene, the conductive coating layer 32 can display black.

[0029] See also Figure 3The electrophoresis step 22 involves immersing the conductive sheet 4 and the semi-finished product 30 as electrodes into an electrophoretic solution 5 containing charged colloidal particles 51, and applying a voltage between 60V and 120V from one of the conductive sheet 4 and the semi-finished product 30 to establish an electric field between the conductive sheet 4, the conductive coating layer 32 and the electrophoretic solution 5 to form a conductive circuit. This causes some of the colloidal particles 51 to move along the direction of the electric field toward the semi-finished product 30, thereby forming an electrophoretic coating layer 33 on the conductive coating layer 32.

[0030] In some embodiments, the applied voltage of the electrophoresis step 22 is between 60V and 100V.

[0031] In some embodiments, the applied voltage of the electrophoresis step 22 is between 80V and 100V.

[0032] It should be noted that the colloidal particles 51 of the electrophoretic solution 5 can be selected from waterborne resin, and pure water is used as the solvent. The semi-finished product 30 is selected as the positive or negative electrode according to the charge properties of the colloidal particles in the electrophoretic solution to be deposited on the surface of the semi-finished product 30, so as to generate an electric field in a predetermined direction, causing the colloidal particles 51 in the electrophoretic solution 5 to move along the direction of the electric field according to their own charge properties, and deposit and adhere to the semi-finished product 30 to form the electrophoretic coating layer 33.

[0033] To avoid orange peel effect caused by excessively high voltage and excessively long process time due to excessively low voltage during the film formation process, preferably, the voltage applied in the electrophoresis step 22 is between 80V and 120V, and the thickness of the electrophoretic coating layer 33 is not greater than the thickness of the conductive coating layer 32.

[0034] In some embodiments, the total thickness of the conductive coating layer 32 and the electrophoretic coating layer 33 is no greater than 50 μm. Preferably, the thickness of the electrophoretic coating layer 33 is no greater than 30 μm. More preferably, the thickness of the electrophoretic coating layer 33 is between 20 μm and 25 μm. In this embodiment, the voltage applied in the electrophoresis step 22 is 80V, and the thickness of the electrophoretic coating layer 33 is 25 μm, for example.

[0035] In this embodiment, the colloidal particles 51 of the electrophoretic solution 5 are selected from water-based acrylic resin, and pure water is used as the solvent. The conductive sheet 4 and the semi-finished product 30 serve as the anode and cathode, respectively. An 80V positive voltage is applied to the conductive sheet 4 to cause the colloidal particles 51 to move toward the semi-finished product 30, forming an electrophoretic coating layer 33 that is transparent to light and coated on the conductive coating layer 32, thereby obtaining the metal element 3. The gloss of the surface of the metal element 3 is not less than 100 GU (gloss unit), wherein the gloss is measured at a gloss measurement angle of 60 degrees.

[0036] The electrophoretic coating process of this invention utilizes a conductive coating layer 32 formed on the surface of the substrate 31 beforehand. Since the conductive coating layer 32 has good conductivity (i.e., surface resistivity not greater than 500 Ω·m), a conductive circuit can be formed between the conductive sheet 4, the conductive coating layer 32, and the electrophoretic solution 5 during the electrophoresis step 22. Therefore, an applied voltage not exceeding 180V is sufficient to establish a sufficiently strong electric field to drive the colloidal particles 51 in the electrophoretic solution 5 to uniformly adhere to the conductive coating layer 32, forming the electrophoretic coating layer 33, thus avoiding the orange peel phenomenon seen in conventional high-voltage plating. Furthermore, since the electrophoretic solution 5 does not contain dyes or pigments, the formed electrophoretic coating layer 33 can be maintained at a relatively thin thickness (not exceeding 30 μm), thus achieving good gloss. Simultaneously, it avoids the problem of orange peel phenomenon in electrophoretic coating layers caused by changes in surface tension due to the addition of dyes or pigments to the electrophoretic solution. Furthermore, the conductive coating layer 32 also provides protection to prevent the surface of the substrate 31 from directly contacting moisture or chemical agents (i.e., electrophoretic solution 5). Therefore, there is no need to perform the electrophoretic process under low voltage conditions to avoid electrolysis of the substrate 31, thus shortening the processing time of the electrophoretic coating layer 33. Since the color effect of the metal component 3 produced by the electrophoretic coating process of the present invention is provided by the conductive coating layer 32, and the electrophoretic layer (i.e., the electrophoretic coating layer 33) mainly serves as protection and provides gloss, the electrophoretic layer does not need to be too thick to give the metal component 3 a high gloss, resulting in a better visual appearance.

[0037] In summary, the high-gloss electrophoretic coating process of the present invention reduces the surface resistivity by first forming the conductive coating layer 32 on the surface of the substrate 31, allowing the electrophoresis step 22 to be performed at a voltage not exceeding 180V. This results in a metal component 3 with a high-gloss surface that is less prone to orange peel effect, thus improving the product's aesthetics. Furthermore, compared to conventional methods that change the surface color of the metal substrate by dyeing, the present invention presents color by coating the substrate 31 with the conductive coating layer 32, resulting in a better appearance of the metal component 3. The conductive coating layer 32 also provides protection to prevent the substrate 31 from electrolyzing in the subsequent electrophoresis step 22. Therefore, the electrophoresis step 22 does not need to be performed under low voltage conditions, thus shortening the process time and effectively achieving the objectives of the present invention.

Claims

1. A high-gloss electrophoretic coating process, characterized in that: Include: The conductive coating layer forming step involves spraying a conductive coating layer composed of conductive paint onto at least a portion of the surface of a substrate to form a semi-finished product. The substrate is composed of a light metal material selected from magnesium, aluminum, magnesium alloys, and aluminum alloys. The surface resistivity of the conductive coating layer is not greater than 500 Ω•m. The conductive paint comprises colorant, base material, and conductive substance. The base material is selected from epoxy resin or acrylic resin. and In the electrophoresis step, the conductive sheet and the semi-finished product are used as electrodes and immersed in an electrophoresis solution containing charged colloidal particles. A voltage is applied to one of the conductive sheet and the semi-finished product to establish an electric field between the conductive sheet, the conductive coating layer and the electrophoresis solution, forming a conductive circuit. This causes some of the colloidal particles to move along the direction of the electric field toward the semi-finished product, thus forming an electrophoretic coating layer with a thickness of no more than 30 μm on the conductive coating layer. The voltage is between 60V and 120V.

2. The high-gloss electrophoretic coating process according to claim 1, characterized in that: The total thickness of the conductive coating layer and the electrophoretic coating layer is no greater than 50 μm.

3. The high-gloss electrophoretic coating process according to claim 2, characterized in that: The conductive material is selected from modified titanium dioxide, metals, nano-carbon materials, or graphite.

4. The high-gloss electrophoretic coating process according to claim 3, characterized in that: The colorant is selected from inorganic pigments or organic dyes.

5. The high-gloss electrophoretic coating process according to claim 1, characterized in that: The colloidal particles in the electrophoretic solution are selected from aqueous resins.

6. The high-gloss electrophoretic coating process according to claim 1, characterized in that: The applied voltage for the electrophoresis step is between 80V and 120V.

7. The high-gloss electrophoretic coating process according to claim 6, characterized in that: The applied voltage for the electrophoresis step is between 80V and 100V.

8. The high-gloss electrophoretic coating process according to claim 2, characterized in that: The conductive paint contains a conductive material, which is graphene.

9. The high-gloss electrophoretic coating process according to claim 1, characterized in that: The substrate is an aluminum-magnesium alloy or a magnesium-aluminum alloy.

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