JP3292810B2 - Metallic material surface coating structure and method of forming the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating structure on a metal material surface and a coating forming method.

[0002]

2. Description of the Related Art Typical coating methods known as coating methods for improving appearance and improving corrosion resistance are as follows. 1. Epoxy powder primer + solvent colored paint + solvent clear 2. Polyester powder primer + solvent colored paint + solvent clear 3. Epoxy / polyester hybrid powder primer + solvent colored paint + solvent clear 4. In above 1.2.3. Solvent clear powder (polyester, epoxy, acrylic) clear Solvent paint overcoat (solvent colored paint + solvent clear as in 1., 2., 3. above) is widely used However, since the quality is slightly deteriorated in appearance, the coating system of the above item 4 using powder has come to be used due to the recent tendency for high-grade commerciality. Judging from the viewpoint of coating performance among the coating systems in 4. above, those using epoxy, polyester, or epoxy-polyester hybrid powder coating for the top coat show generation of thread rust and weather resistance. Has difficulties. In addition, those using epoxy or polyester for the powder coating used as a primer are not necessarily sufficient in adhesion and corrosion resistance, and the most reliable coating system using powder coating at present is 4 ' It is said that this is an epoxy / polyester hybrid powder primer + acrylic solvent colored paint + acrylic powder clear (for example, Japanese Patent Application Laid-Open No. H5-220231).
No. 9, JP-A-5-209140, JP-A-5-209140
209141). As the conventional pretreatment for aluminum wheel powdering (aluminum base treatment), the following forms are generally adopted as disclosed in the above-listed gazettes. Rinsing → Degreasing → Rinsing → Chemical conversion treatment → Rinsing The chemicals used for degreasing are mainly silicate-based weak alkaline detergents. The chemical conversion treatment is generally a chromate treatment with chromic acid.

[0003]

However, the method 4 'still has the following problem. In other words, when applied to objects with strict appearance requirements such as aluminum wheels for automobiles, the acrylic powder paint as a top coat is sprayed by air or electrostatic coating, If the paint spilled into the booth does not adhere to the booth and is collected and reused, dust and bumps easily occur. Thus, spilled paint is typically discarded, reducing paint yield. Significant capital investment is required for a system that does not mix garbage and dust. Further, the following problem also exists in the pre-base processing. That is, in the pretreatment, the most important point is the amount of chromium adhered to the aluminum surface, but it has been confirmed that the amount of chromium adhered to the conventional underlayer varies. The cause is that surface uniformity is not always obtained in the degreasing stage, and that many impurities are brought into the chromate treatment solution, and the original performance of the chromate treatment is not exhibited. An object of the present invention is to provide a metal material surface coating structure and a method for forming the same, which can improve the yield of the coating while maintaining high coating reliability. Another object of the present invention is to improve the coating performance by stabilizing the base treatment, in addition to the above objects.

[0004]

The present invention to achieve the above object is as follows. (1) A primer layer formed of an acrylic powder coating formed on a metal substrate, a base coat layer formed of a colored solvent-based coating formed on the primer layer, and an acrylic formed on the base coat layer Metallic material surface coating structure consisting of a top coat layer composed of a system powder clear paint. (2) a step of forming a primer layer made of an acrylic powder coating on a metal substrate; a step of forming a base coat layer made of a colored solvent-based coating on the primer layer; Forming a top coat layer made of an acrylic powder clear paint, and a method of forming a metal material surface coating structure. (3) Before the step of forming the primer layer, a base treatment step of a base material of a metal material is provided, and the base treatment step includes a chromate conversion treatment step and an acid washing step performed before the chemical conversion treatment step. (2) The method for forming a metal material surface coating structure according to (2).

[0005] In the method of forming the metal material surface coating structure of (1) and the coating structure of (2), the acrylic powder coating used for the top coat can also be used for the primer. By using the spilled acrylic powder paint as it is as a primer, a paint yield of about 100% can be achieved and the cost can be reduced. In addition, it was confirmed that the coating performance when the acrylic powder coating was used as the primer was higher than the coating system using the epoxy / polyester hybrid powder primer, which is considered to be the most reliable at present. In addition, a sufficiently smooth surface can be obtained by the primer, and the appearance quality is high. In the above method (3), in addition to the effect of the above (2), since the pickling step is performed before the chromate treatment step, the chromium coating amount is formed uniformly and stably in the chromate treatment. The formed coating film is stable.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The metal material surface coating structure of the present invention comprises:
As shown in FIG. 1, a primer layer 2 made of an acrylic powder coating formed on a base material 1 of a metal material, a base coat layer 3 made of a colored solvent-based coating formed on the primer layer 2, and a base coat layer And a top coat layer 4 formed of an acrylic powder clear coating formed on the top coat layer 3. Metal material base 1 is any member made of a metal such as an aluminum alloy, a magnesium alloy, and iron, and is made of, for example, an aluminum alloy wheel (aluminum wheel).

As the acrylic powder paint of the primer layer 2, it is desirable to use the same powder paint as the acrylic powder clear paint of the top coat layer 4. This is because the paint spilled into the booth during the formation of the top coat layer 4 is collected and reused for the acrylic powder paint for the primer layer 2. The thickness of the primer layer 2 made of an acrylic powder coating is about 20 to 40 μm (1 μm is 10 ⁻⁶ m). This is preferably about 20 μm or more in order to prevent the casting surface of the substrate 1 and to prevent rust and to fill the unevenness of the substrate to make it a flat surface.
This is because the thickness is preferably about μm or less. In powder coating, the size of the paint particles is usually about 3 to 6 μm, and a layer having a required thickness can be formed quickly.

[0008] Colored solvent-based paints for the base coat layer 3 include:
In order to reduce the amount of solvent so as not to cause environmental problems, high solids (solid content of 40% by weight or more) and metallic paint (aluminum fine powder has an average diameter of 5 to 15 μm)
It is desirable to use an acrylic high solid metallic paint in order to have a good appearance (a glossy metallic feeling) with a good scaly appearance. The thickness of the base coat layer 3 is about 10 to 30 μm. This is because at least about 10 μm is required to suppress the protrusion of the aluminum fine powder to the surface, and about 30 μm or less from the viewpoint of reducing the consumption of the paint amount. The color of the base coat layer 3 is the same as the color required for the metal material surface coating structure because the top coat layer 4 is clear (transparent) and the color of the base coat layer 3 is visible from the outside.

The acrylic powder clear coating of the top coat layer 4 is mainly composed of a thermosetting acrylic resin. The thermosetting acrylic resin is a chain copolymer of acrylic acid, methacrylic acid ester, styrene, and an acrylic monomer having various active functional groups. Glycidyl acrylate, glycidyl methacrylate, β-
Acrylic glycidyl resins such as methyl glycidyl acrylate, β-methyl glycidyl methacrylate, and triglycidyl isocyanurate acrylate are included in the thermosetting acrylic resin. These prepolymers are used alone or mixed with a co-reaction resin (amino resin, epoxy resin, alkyd resin, polyamine, dibasic acid anhydride, etc.) to form a coating film main element. By heating (baking), the acrylic resin is cross-linked and polymerized with the co-reactive resin to form a stitch structure coating film. The thickness of the top coat layer 4 is 10 to 5
About 0 μm is desirable. This is because even if the thickness is more than about 50 μm, the protection function increases or it takes time to form, and if the thickness is less than about 10 μm, the protection function becomes insufficient. The top coat layer 4 is formed by applying an acrylic resin paint electrostatically (or air spray paint).

The method for forming a metal material surface coating structure according to the present invention comprises a step of forming a primer layer 2 made of an acrylic powder coating on a base material 1 of a metal material (for example, an aluminum wheel); A step of forming a base coat layer 3 made of a colored solvent-based paint (preferably a metallic paint), and a step of forming a top coat layer 4 made of an acrylic powder clear paint on the base coat layer 3;
Consists of Prior to the step of forming the primer layer 2, a base treatment step of the metal base 1 is provided. It is desirable to use the same resin paint for the top layer 4 as the resin paint for the primer layer 2. This is because the paint spilled into the booth during the formation of the top coat layer 4 is collected and reused for the acrylic powder paint for the primer layer 2.

In the step of forming the primer layer 2, first, the metal substrate 1 is degreased (oil and the like are removed by alkali degreasing).
Chemical conversion treatment (however, chemical conversion treatment is not required) and water washing are performed. Next, the primer layer 2 is formed by electrostatic powder coating (air blowing may be used). Primer layer 2
In the forming step, in the case of electrostatic powder coating, a DC high voltage (30 to 90 kV) is applied between a grounded coating object (metallic base material 1) and a gun electrode. A clear powder paint (having a particle size of about 3 to 6 μm) is sprayed from the gun by pneumatic force. The powder particles dispersed in the air collide with the ionized air generated by the corona discharge generated at the gun electrode and become charged.They move toward the coating object by the action of the electrostatic field between the gun and the coating object and the air flow, Adsorbs to the surface of the substrate by force. The thickness of the primer layer 2 is formed to be about 20 to 40 μm. After painting, in a furnace, about 150-200 ° C
And bake and dry for about 10 to 40 minutes. During baking, the paint crosslinks and polymerizes to form a stitched coating.

In the step of forming the base coat layer 3, the acrylic colored solvent paint (a metallic paint containing aluminum fine powder having an average diameter of 5 to 15 μm and a high solid paint having a solid component of about 40% by weight or more) (Preferably) is applied on the primer layer 2 to a thickness of about 10 to 30 μm and then baked at 130 to 190 ° C.

In the step of forming the top coat layer 4, an acrylic powder paint (same as the paint for the primer layer 2) is used in the booth to place the electrostatic powder on the base coat layer 3 of the article to be coated. By body painting (or air blowing)
Paint to a thickness of 20-50 μm. After that, 130-2
Bake at 00 ° C for 15-60 minutes. The top coat layer 4 thus formed functions as a protective layer for the base coat layer 3.

In the undercoat treatment step, it is desirable to add an acid pickling step as described below before the chemical conversion treatment in order to stabilize the chromate treatment to stabilize the chromium coating amount. If added, the underlying processing step is as follows. Water washing → degreasing → water washing → pickling → water washing → chemical conversion treatment → water washing The liquid used in the additional pickling step may be any of nitric acid, sulfuric acid, phosphoric acid, etc. . However, a chemical, a temperature, and a concentration that do not change the color tone and gloss of the surface are selected.

[0015]

EXAMPLE An acrylic powder primer layer (resin of the same type as the top coat layer), a solvent colored base coat layer, and an acrylic powder clear top coat layer formed in this order on an aluminum wheel base material for automobiles. Inventive product and a comparative product in which an epoxy / polyester hybrid powder primer layer, a solvent-colored base coat layer, and an acrylic powder clear top coat layer were formed in this order on an aluminum substrate, and a coating performance test was performed. (Weather resistance test, yarn rust test, appearance test) and paint yield were examined.

In the weather resistance test, an exposure test was conducted for 600 hours using a sunshine weatherometer, and thereafter, the sample was kept at 50 ° C. and a relative humidity of 98% for 240 hours, left standing for 24 hours, and then subjected to a grid test (1 mm × 1 mm grid) Eye 100
), And peeling and discoloration of each grid were examined. In the rust test, the surface was cut with a knife, sprayed with 5% by weight of salt water at 35 ° C. for 24 hours, and then kept at 40 ° C. and kept at 82% relative humidity for 240 hours, and the cycle was repeated three times. (Whether rust or blistering of the coating has occurred)
Was examined. In the appearance test, the smoothness of the surface of the top coat layer was visually examined. In the paint yield, the yield of the acrylic powder paint in the clear top coat layer was examined. Among the paints that spilled into the booth when the clear top coat layer was formed, those that were collected and used as the paint for the primer layer were counted as used paints (paints not discarded). The paint that spilled in the comparison product is
Since it cannot be used for the primer layer (because the type is different), it was discarded.

From the test results, it was confirmed that the coating performance (weather resistance, suppression of yarn rust generation, appearance) of the product of the present invention was higher than the coating performance of the comparative product (good). In addition, the paint yield was about 80% or less in the comparative product, but it was confirmed that almost 100% was achieved in the product of the present invention. In addition, in the appearance test, it was confirmed that the product of the present invention can obtain a sufficient smooth surface (equivalent to the comparative product) by the primer layer.

Next, in order to see the effect of pickling in the undercoating treatment, in the case of the product of the present invention with and without pickling before chromate treatment, and in the case of the conventional product with pickling before chromate treatment ( Conventionally, pickling was not performed, so that a case with pickling is shown as a comparative example) and a test piece without pickling was prepared. Sunshine test (except for 1200 hours exposure and the same conditions as above), rust test (same as above, 3 cycle cross cut), complex corrosion test (salt spray 4 hours, 60 ° C 2 hours drying, 50 °) C, holding for 2 hours at a relative humidity of 95% was repeated for 10 cycles, and bulging around the cross cut and the length of rust were observed). Table 1 shows the results.

[0019]

[Table 1]

As is evident from Table 1, it was found that by adding an acid washing step and a water washing step before the chromate conversion treatment in the base treatment, the coating was stabilized, and rust generation and blistering were suppressed.

[0021]

According to the structure of the first aspect, since the primer layer is an acrylic powder coating layer, the same powder coating as the top coat layer can be used. The powder paint that has spilled can be collected and reused as the paint for the primer layer, and the material yield can be improved. Further, the coating performance is equal to or higher than that of a conventional primer layer formed from an epoxy / polyester hybrid powder coating. According to the method of the second aspect, since the method includes the step of forming the primer layer from the acrylic powder coating layer, the same effect as that of the first aspect is obtained. According to the method of claim 3, since the pickling step is provided before the chemical conversion treatment in the base substrate treatment step before the formation of the primer layer, the chromium coating amount can be formed stably by the chemical conversion treatment, Coating performance of the coating film can be improved.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a metal material surface coating structure according to an embodiment of the present invention.

[Explanation of symbols]

 1 Base of metal material 2 Primer layer 3 Base coat layer 4 Top coat layer

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C23C 28/00 C23C 28/00 C (56) References JP-A-60-203437 (JP, A) JP-A-5-146752 ( JP, A) JP-A-4-41565 (JP, A) JP-A-5-202319 (JP, A) JP-A-5-115843 (JP, A) JP-A-6-134393 (JP, A) Hei 5-209141 (JP, A) JP-B-59-29109 (JP, B2) JP-B-58-500314 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 15 / 08 B05D 7/14-7/24

Claims (3)

(57) [Claims] 1. A primer layer formed of an acrylic-based powder coating formed on a metal substrate, a base coat layer formed of a colored solvent-based coating formed on the primer layer, and formed on the base coat layer. Metallic material surface coating structure consisting of a top coat layer made of an acrylic powder clear paint. 2. A step of forming a primer layer made of an acrylic powder coating on a base material of a metal material, a step of forming a base coat layer made of a colored solvent-based coating on the primer layer, and Forming a top coat layer made of an acrylic powder clear paint thereon, and a method of forming a metal material surface coating structure. 3. A base treatment step for a base material of a metal material is provided before the step of forming the primer layer, and the base treatment step includes a chromate conversion treatment step and an acid washing step performed before the chemical conversion treatment step. The method for forming a surface coating structure of a metal material according to claim 2, comprising: