JP2831118B2 - Method for forming composite coating used for preparing electrodeposition coating base of aluminum or aluminum alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of joining a steel plate or a galvanized steel plate (hereinafter simply referred to as a steel plate or the like) by a welding, bonding, bolting method, or the like, and combining them. The present invention relates to a method of forming a composite film used for preparing an electrodeposition coating base in advance on an aluminum plate material used as the same structure made of a composite material.

[Prior art] Conventionally, as a surface treatment method of aluminum and aluminum alloy, a phosphoric acid chromate treatment method of treating with an aqueous solution containing chromic acid, phosphoric acid, hydrofluoric acid, or the like, or chromic acid, nitric acid, hydrofluoric acid, etc. The chromate chromate treatment method of treating with an aqueous solution containing, or the zinc phosphate treatment method of treating with an aqueous solution containing zinc ions, phosphate ions, fluorine ions, oxidizing agents, etc., improves corrosion resistance and coating adhesion. It is done for the purpose.

In recent years, aluminum plate materials have begun to be used for some parts of the vehicle body to reduce the weight of automobiles, and the amount of use has tended to increase year by year. Many of them have been joined to steel plates by welding, bonding, joining methods such as bolts, etc. Used in combination.

Conventionally, the surface of a steel plate or the like constituting an automobile body is degreased or treated as a pre-coating process (a process of creating an electrodeposition coating base).
Quality of corrosion resistance, coating adhesion, coating appearance, etc. required for automobile body by applying electrodeposition coating after applying zinc phosphate coating by water washing, surface conditioning, zinc phosphate treatment, water washing process It corresponds to.

Even when an aluminum plate material is applied to a part of an automobile body, the above-mentioned quality is naturally required. Therefore, various surface treatment methods have been proposed.

As a general method, an automobile body structure made of an aluminum plate material and a steel plate is subjected to the above-described pretreatment, and a zinc phosphate-based film is simultaneously formed on the surface of the aluminum plate material and the steel plate to form an electrodeposition coating. According to this method, aluminum ions naturally mix and accumulate in the zinc phosphate treatment solution. It is known to become inhibitory.

As a method for solving this problem, a method has been proposed in which an automobile body component part made of an aluminum plate material is separately pretreated separately from components made of other steel plates or the like. However, two sets are required, and equipment cost increases, which is economically disadvantageous.

On the other hand, Japanese Patent Application Laid-Open No. 61-96074 discloses a method of solving the above-mentioned drawbacks in which a component made of an aluminum plate is preliminarily subjected to a chromate treatment, and is then joined to a component such as a steel plate by welding, bonding, bolting or the like. A method is disclosed in which an automobile body is formed by joining and combining, and a coating pretreatment for forming a zinc phosphate-based coating is performed to prevent elution of aluminum ions into a zinc phosphate-based treatment solution. However, in this method, chromium ions are eluted from the chromate film in the zinc phosphate-based treatment solution, which accumulates in the zinc phosphate-based treatment solution and forms a normal zinc phosphate-based film on the surface of a steel plate or the like. The problem of hindering
It is pointed out that wastewater treatment requires new management and costs.

[Problems to be Solved by the Invention] The present invention relates to a method of forming a zinc phosphate-based coating on an aluminum plate material or a structure obtained by combining a steel plate or the like and an aluminum plate material to form a zinc phosphate-based coating to form an electrodeposition coating base. The method of treating aluminum sheet materials is excellent in aluminum phosphate and chromium leaching resistance to zinc phosphate-based treatment baths, and provides an electrodeposition coating base with excellent corrosion resistance, coating adhesion, and coating appearance. Provision is an issue.

[Means for Solving the Problems] The present invention relates to a method for forming a composite film of an aluminum plate material, and more specifically, used as a component of an automobile body alone in combination with or without a steel plate or the like. It relates to an aluminum plate, and before being processed by press molding or the like, an aqueous solution containing 5 to 90 g / m as total chromium ions is applied to the surface of the aluminum plate in advance, and then dried and dried to 10 to 150 mg / m in terms of metal chromium. to form a ^second chromate film layer and then the solid content ratio average particle diameter on said coating an organic polymer resin a silica sol 10～500Emumyu (weight)
In 0.2 to 1.2 after coating the organic polymer resin composition containing, a method of forming a composite coating film by coating weight is to perform organic polymer resin composition film layer of 0.2-5 g / m ² by dry It is about. The aluminum plate material with such a composite coating is subjected to processing such as press molding, or combined with a steel plate or the like without processing, or constitutes an automobile body without combining with a steel plate or the like. It is not affected by the alkaline washing of the process, and prevents the elution of aluminum ions and chromium ions into the zinc phosphate treatment bath. The purpose is to impart excellent corrosion resistance, paintability, and other performances to the constructed vehicle body.

In the present invention, first, a chromate film is formed on the surface of an aluminum plate at 10 to 150 mg / m ^{2 in} terms of metal chromium. Not have sufficient corrosion resistance in the chromate film is less than 10 mg / m ² reckoned as metal chromium, not only corrosion resistance is saturated at 150 mg / m ^2, greater than chromium in the formation of the zinc phosphate coating of the pretreatment step of the coating The amount of elution increases, which is not preferable. As the chromate treatment liquid used for forming the present chromate film, an aqueous solution containing 5 to 90 g / total chromium ions can be used.
When the total chromium ion is less than 5g /, it is 1 in terms of metallic chromium
0 mg / formation of m ² or more chromate film is difficult, 90 g /
If the amount is more than 150 mg / m ^{2 in} terms of chromium metal, it is difficult to form a chromate film. Next, as a chromium ion contained in the chromate treatment liquid, a chromate treatment liquid having a trivalent chromium ion / 6 chromium ion ratio of 0.25 to 1.5 (weight ratio) can be used. If the ratio of trivalent / 6-valent chromium ions is less than 0.25 (weight ratio), the chromium elution resistance in the process of forming the zinc phosphate coating is not sufficient, and the ratio of trivalent / 6-valent chromium ions is 1.
If it exceeds 5 (weight ratio), the corrosion resistance is insufficient. In order to make the total chromium ion 5g / ~ 90g /, and to make the trivalent / 6valent chromium ion ratio 0.25 ~ 1.5 (weight ratio), 3 ~ 50g as hexavalent chromium ion / It is reasonable to use 2 to 40 g /.

Further, the treatment liquid for forming the chromate film preferably contains 1 to 100 g / as phosphate ions, and the weight ratio of phosphate ions to all chromium ions is 0.1 to 1.2, so that chromium-resistant elution is more effectively performed. Can be improved.

In addition, the chromate treatment liquid preferably contains silica sol, and its content is adjusted to 0.1 to 1.2 in terms of a weight ratio with respect to all chromium ions, whereby the adhesion of the film to the base metal surface can be further improved. .

Next, an organic polymer resin composition containing 0.2 to 1.2 of silica sol at a solid content ratio (weight) to the organic polymer resin is applied on the chromate film, and then dried, whereby the organic polymer resin composition is dried. To form a coating layer having a coating weight of 0.2 to 5 g / m ² . Examples of the organic polymer resin include acrylic polymers mainly composed of acrylic acid, acrylic esters, methacrylic acid, and methacrylic esters, polyols having two or more hydroxyl groups in a molecule, and two polymers in a molecule. Urethane resin, epoxy resin based on epichlorohydrin and bisphenol A, alkyd resin, etc. dissolved or dispersed in water to form a water-based resin liquid by reaction with polyisocyanates having isocyanate group of An organic solvent-based resin solution dissolved or dispersed in an organic solvent that can be dissolved or dispersed can be used, but is not specified.

Next, as the silica sol, an average particle diameter of 10 to 500 mμ can be used.If the average particle diameter is less than 10 mμ, the corrosion resistance of the film formed by the organic polymer resin composition is not sufficient. It is difficult to form a film by the method. Specific examples of the silica sol that can be used include, for example, Aerosil # 200, # 300, # 380 (manufactured by Nippon Aerosil),
Snowtex-O, -N, -C (manufactured by Nissan Chemical Industries) and the like can be used.

If the content of silica sol is less than 0.2 in terms of solid content ratio (weight) to the organic polymer resin, it is difficult to form a normal electrodeposition coating film, and if it exceeds 1.2, the formed film becomes brittle and the workability deteriorates. If the coating weight is less than 0.2 g / m ² , the elution of chromium in the step of preparing a zinc phosphate coating which is a pretreatment for coating is insufficient, and the corrosion resistance is also deteriorated. If it exceeds 5 g / m ² , the cost increases, which is not only economically disadvantageous, but also makes it difficult to form a normal electrodeposition coating film.

Since the aluminum sheet material with the composite surface treatment film in this way has good workability, it is excellent in press moldability as a component of an automobile body, and is subjected to pre-coating treatment in combination with a part made of other steel sheets and the like. Also, aluminum ions and chromium ions do not accumulate in the zinc phosphate treatment bath, so they do not impede the pre-painting property of the parts such as steel sheets, and the corrosion resistance, paintability, It provides excellent performance such as paint adhesion.

Hereinafter, the effects of the present invention will be specifically described with reference to examples and comparative examples.

Example A composite surface treatment was performed in the following step using an aluminum alloy plate (material: A5082, H32) as a material.

(1) (2) Chemicals used and conditions Alkaline degreaser: Fine cleaner # 359 (manufactured by Nippon Parkerizing), 20 g /, 60 ° C., 30 seconds, spray.

Chromate treatment solution (A) Total chromium ion concentration = 40 g / hexavalent chromium ion concentration = 20 g / phosphate ion concentration = 16 g / trivalent / 6 chromium ion ratio = 1.0, phosphate ion / total chromium ion ratio = 0.4 ( B) Total chromium ion concentration = 40 g / hexavalent chromium ion concentration = 30 g / phosphate ion concentration = 40 g / silica sol concentration = 20 g / trivalent / 6valent chromium ion ratio = 0.33, phosphate / total chromium ion ratio = 1.0 Silica sol / total chromium ion ratio = 0.5 (C) Total chromium ion concentration = 50 g / hexavalent chromium ion concentration = 40 g / trivalent / 6 / valent chromium ion ratio = 0.25 Table 1 shows the composition of the organic polymer resin composition. Indicated.

(3) Performance test (a) Chromium elution resistance test An aluminum sheet material with a composite film was pre-coated under the conditions described in (d) below, and the amount of chromium adhering before and after the coating was determined by fluorescence X
It was measured with a line (mg / m ² ) and expressed as chromium elution resistance by the following formula. That is, the smaller the value of%, the better the chromium elution resistance, and the value of 0 indicates that the coating was not affected by the pretreatment at all in this test.

(B) Corrosion resistance test piece (composite film-formed aluminum plate, size 70mm × 150m
m) was extruded 6 mm with an Erichsen tester, and then JIS-Z-2
The salt spray test specified in 371 was performed for 500 hours, and the corrosion resistance was evaluated from the state of white rust occurrence on the entire area of the test piece.

◎: White rust occurrence area rate 0% ○: Same as above, less than 10% △: Same as above, 10% or more and less than 30% ×: Same as above, 30% or more (c) Appearance after ED coating Test piece (composite film-formed aluminum plate material, size 70mm × 150m)
m) was subjected to cationic electrodeposition coating for automobiles after coating pretreatment, and the appearance of the coating film was visually judged.

◎: No abnormality.

：: Some unevenness on the coating film surface.

Δ: Unevenness on the coating film surface.

×: There are countless irregularities on the coating film surface.

(D) Pretreatment for painting Condition, drug type; Degreasing; FC-L4460 (manufactured by Nippon Parkerizing), Agent A: 20 g /, Agent B: 12 g /, Spray: 43 ° C. × 2 minutes.

Surface adjustment; PL-ZN (manufactured by Nippon Parkerizing): 1 g / spray: 30 seconds.

Chemical formation; PB-L3020 (Zinc phosphate type film forming agent manufactured by Nippon Parkerizing Co., Ltd.), M agent: 48 g /, AD-4913: 5 g /, AD-4856: 17 g /, immersion, 43 ° C. × 2 minutes.

The performance test results of the examples according to the present invention are shown in Table 2 together with comparative examples.

As can be seen from Table 2, by forming the composite film according to the present invention, the material to be treated was excellent in chromium elution resistance, corrosion resistance, and formability of an electrodeposition coating base, and the effect of the present invention was confirmed.

[Effects of the Invention] When a pretreatment for coating is applied to the aluminum plate material according to the present invention or to a structure in which a steel plate or the like and the aluminum plate material according to the present invention are combined, the corrosion resistance, coating adhesion, and coating appearance are excellent. The electrodeposition coating base can be formed, and the aluminum elution resistance and the chromium elution resistance during coating pretreatment are excellent.

Continuation of the front page (56) References JP-A-3-39485 (JP, A) JP-A-62-152579 (JP, A) JP-A-60-50180 (JP, A) JP-A-61-60886 (JP, A) JP-A-55-152184 (JP, A) JP-A-62-202084 (JP, A) JP-A-3-63130 (JP, A) JP-A-4-191396 (JP, A) 57-108292 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 22/00-22/86 C23C 28/00-28/04 B32B 15/08

Claims (2)

(57) [Claims] 1. A method of forming a composite film in a process prior to preparing a zinc phosphate electrodeposition coating base of aluminum or an aluminum alloy, wherein the content of hexavalent chromium ions is 3 to 50 g /
A chromium component having a trivalent chromium ion content of 2 to 40 g /, a total chromium ion content of 5 to 90 g /, and a trivalent chromium ion / 6 chromium ion ratio of 0.25 to 1.5 (weight ratio) And a phosphoric acid component having a phosphate ion content of 1 to 100 g / and a phosphoric acid component having a weight ratio of phosphate ions to all chromium ions of 0.1 to 1.2 is applied to the surface of aluminum or an aluminum alloy. Then, after drying to form a chromate film layer of 10 to 150 mg / m ^{2 in} terms of metallic chromium, a silica sol having an average particle size of 10 to 500 mμ is coated on the film layer with a solid content ratio (weight )
In coating an organic polymer resin composition containing 0.2 to 1.2, and then dried, characterized in that to form a coating layer of 0.2-5 g / m ^2, an aluminum or zinc phosphate-based electrodeposition of aluminum alloy A method for forming a composite coating used to create a coating base. 2. The zinc phosphate-based electrodeposition coating base of aluminum or an aluminum alloy according to claim 1, wherein the chromate treatment solution further contains silica sol in a weight ratio of 0.1 to 1.2 with respect to all chromium ions. The method of forming the composite film used for making.