JP3292819B2 - 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 poor weather resistance. There are 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 and removal → Degreasing → Rinsing → Chemical treatment → Rinsing And the chemicals used for degreasing are mainly silicate 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. One cause is that in the degreasing step, the oil, dust, and contaminant adsorbed substances from the atmosphere in the previous step (for example, the cutting step) are not completely removed. 2
The problem is that the adhesion of chromium to the surface of the aluminum wheel is impeded by the coating of the oxide on the surface of the aluminum wheel or the introduction of miscellaneous ions into the chromate treatment solution, and the original performance of the chromate treatment is not sufficiently exhibited. In order to solve the above problems, the applicant first, a primer layer formed of an acrylic powder coating formed on a metal substrate, and a base coat layer formed of a colored solvent-based coating formed on the primer layer And a top coat layer formed of an acrylic powder clear coating formed on the base coat layer, and a method for forming the metal surface film structure and a method of forming the same have been developed and filed (Japanese Patent Application No. 8-274585, Unpublished). This metal material surface film structure and its formation method have been highly evaluated for the reliability of coating, but new requirements include reduction of coating cost, improvement of chipping resistance of the top coat layer, and further improvement of appearance quality. Improvement has been desired. However, on the premise that a powder coating is used for the top coat layer, it has been difficult to meet these requirements. SUMMARY OF THE INVENTION 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 chipping resistance and appearance quality at low cost 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 A metal material surface coating structure comprising a top coat layer made of a system solvent 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 solvent 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 is performed in the order of a degreasing treatment step, a pickling treatment step, and a chromate conversion treatment step. The method of forming a metal material surface coating structure. (4) Prior to the step of forming the primer layer, a base treatment of the base material of the metal material is provided, and the base treatment is performed in the order of a degreasing treatment with an pickling effect and a chromate conversion treatment (2). A method for forming a metal material surface coating structure according to the above).

In the method of forming the metal material surface coating structure of (1) and the coating structure of (2), an acrylic solvent clear coating is used for forming the top coat layer without using an expensive powder coating. By doing so, not only can the cost be significantly reduced, but also the chipping resistance and appearance quality of the topcoat layer can be improved. 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. In the above method (4), since the degreasing treatment with the pickling effect is performed, the pickling step can be omitted, and equipment costs and processing costs can be reduced.

[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 solvent clear paint formed on the top coat layer 3. The metal material base 1 is an arbitrary 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).

The thickness of the primer layer 2 made of an acrylic powder coating is about 80 to 100 μm (1 μm is 10 ⁻⁶ m). This is preferably about 80 μm or more in order to prevent the casting surface of the base 1 and prevent rust and to fill the unevenness of the base to make it a flat surface.
This is because the thickness is preferably about 0 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.

As the acrylic solvent clear coating for the top coat layer 4, a low solid or high solid coating is used, and the thickness of the top coat layer 4 is preferably about 10 to 30 μm. This is because even if the thickness is larger than about 30 μm, the protection function increases or it takes time to form, and if the thickness is smaller than about 10 μm, the protection function becomes insufficient. The top coat layer 4 is formed by spray-coating an acrylic clear resin paint with a spray gun.

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 solvent 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.

In the undercoating step, it is desirable to perform the following pickling treatment before the chemical conversion treatment in order to stably and uniformly adhere chromium. The base treatment step is performed in the order of (1) degreasing treatment → water washing treatment → pickling treatment → water washing treatment → chemical conversion treatment → water washing treatment, or (2) degreasing treatment with acid washing treatment → water washing treatment It is performed in any of the order of → chemical conversion treatment → water washing treatment. Next, the primer layer 2 is formed by electrostatic powder coating (air blowing may be used). In the step of forming the primer layer 2, in the case of electrostatic powder coating, a high DC voltage (30 to 90 kV) is applied between the grounded coating object (metallic material base 1) and the electrode of the gun. , Acrylic clear powder coating (particle size is about 3
６6 μm) from the gun by air 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. Primer layer 2
Is formed to a thickness of about 80 to 100 μm. After coating, bake and dry in a furnace at about 150 to 200 ° C. 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) Is preferably applied on the primer layer 2 to a thickness of about 10 to 30 μm, and then baked at 120 to 160 ° C.

In the step of forming the top coat layer 4, a low solid or high solid acrylic clear solvent paint is used to coat the base coat layer 3 having a thickness of 1 μm.
Paint to 0-30 μm. Then 130-190 ° C
Bake for 15-25 minutes. The top coat layer 4 thus formed functions as a protective layer for the base coat layer 3.

The action of pickling in the undercoating step (1) or (2) means that oil, dust, adsorbed substances from the air, which are not completely removed only by degreasing in a preceding step (for example, a cutting step). This means that the removal of oxide films promotes the adhesion of chromium to the surface of aluminum wheels and maximizes the original performance of chromate treatment. And
(1) requires more equipment costs due to the acidic process compared to (2), but it is clear that high performance coating quality can be obtained by clearly separating the functions of degreasing and pickling. Was. However, a chemical, a temperature, a concentration, and the like are appropriately selected according to a need such as a color tone and a gloss of the surface of the aluminum wheel.

[0015]

EXAMPLE An acrylic powder primer layer, a solvent-colored base coat layer, and an acrylic solvent clear top coat layer were formed in this order on an aluminum wheel base material for automobiles, and an aluminum base material was formed on the aluminum base material. Epoxy ・
Polyester hybrid powder primer layer, solvent colored base coat layer, acrylic powder clear top coat layer and a comparative product were formed in this order to produce a coating performance test (weather resistance test, thread rust test, appearance test, Chipping test).

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 (2 mm × 2 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 pitting resistance test, a crushed stone of 500 g having a certain particle size was blown out and projected at a pressure of 4 kg / cm ² to examine the peeling state of the coating film.

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 the appearance test, the product of the present invention can obtain a sufficient smooth surface (equivalent to the comparative product) by the primer layer, and the surface property is improved because the top coat layer is formed by a thin solvent paint. It was confirmed that it was done. In addition, in the pitting resistance test, even when compared with the comparative product and the one using an acrylic powder coating for the top coat previously filed,
Significant improvement was achieved.

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 clear from Table 1, the amount of chromium coating in the chemical conversion treatment is increased by adding a pickling step and a water washing step before the chromate conversion treatment or by performing a degreasing step with an acid cleaning effect. It has been found that rust generation, blistering, and the like can be suppressed because they can be formed stably.

[0021]

According to the structure of the first aspect, the top coat layer is an inexpensive acrylic solvent paint layer. Not only can significant cost reduction be achieved, but also the film thickness can be reduced, so that chipping resistance and appearance quality can be improved. The coating performance is equal to or better than that of a conventional primer layer formed from an epoxy / polyester hybrid powder coating. According to the method of claim 2, since the step of forming the top coat layer from the acrylic solvent paint layer is provided, the same effect as that of claim 1 can be 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 stably formed by the chemical conversion treatment, and the chromium coating amount can be formed thereon. The performance of the coating film can be improved. According to the method of claim 4, before the chemical conversion treatment, the degreasing treatment with the pickling effect is performed. In other words, since the degreasing treatment step and the pickling treatment step are performed in one step, the efficiency of the step and the equipment cost are increased. Can be reduced.

[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-4-235773 (JP, A) JP-A-5-209141 (JP, A) JP-A-5-115584 (JP, A) Hei 6-134393 (JP, A) JP 59-29109 (JP, B2) JP 58-500314 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 15 / 08 B05D 7/14-7/24

Claims (4)

(57) [Claims] 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 formed on the base coat layer. And a top coat layer made of an acrylic solvent clear paint. 2. A step of forming a primer layer made of an acrylic powder paint on a metal substrate, a step of forming a base coat layer made of a colored solvent paint on the primer layer, and Forming a top coat layer made of an acrylic solvent clear paint thereon, and a method of forming a metal material surface coating structure. 3. The method according to claim 1, further comprising: providing a base treatment of the metal material before the step of forming the primer layer, wherein the base treatment is performed in the order of a degreasing treatment, a pickling treatment, and a chromate conversion treatment. 3. The method for forming a metal material surface coating structure according to item 2. 4. A base treatment step for a metal base material is provided before the step of forming the primer layer, and the base treatment step is performed in the order of a degreasing treatment step having an pickling effect and a chromate conversion treatment step. A method for forming a metal material surface coating structure according to claim 2.