JPS6334793B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a manufacturing method for improving the blister resistance of a baked-coated steel plate using an aluminized steel plate as a base metal plate. In general, in painted steel sheets that use galvanized steel sheets or aluminized steel sheets as the base metal, zinc and aluminum exhibit a base potential compared to the underlying iron, so zinc and aluminum are selectively eluted due to the so-called sacrificial corrosion protection effect, and the steel Protect the substrate. In the case of a coated steel plate, in which a steel plate plated with zinc or aluminum is used as the base metal and a coating is applied on top of the base metal, the coating film may be damaged by hydrogen gas generated as the zinc or aluminum elutes or water vapor that permeates through the coating film from the outside world. Internal pressure is generated between the paint and the underlying metal surface, pushing up the paint film and causing so-called blisters. Naturally, such blisters create a space between the paint film and the underlying metal surface, and moisture or various ions enter this space, promoting corrosion. Similarly, when moisture enters from defective parts of the coating film or from the end faces, blisters occur from the surrounding areas and corrosion is accelerated. This tendency is greater for zinc, and aluminum should have better blister resistance, but since impurities such as silicon segregate in the surface layer of painted steel sheets that are made of ordinary aluminized steel sheets as the base metal. , or due to plating defects on the plating surface, an optimal treatment method has not yet been proposed.
Therefore, the adhesion of the coating film is not sufficient, and furthermore, the blister property cannot be said to be good. As pre-painting treatments for aluminized steel sheets, methods such as anodic oxidation, chromate treatment, and phosphoric acid film treatment have been proposed. However, chromate treatment has pollution problems such as chromium wastewater treatment,
Regarding phosphoric acid film treatment, there is a problem with sludge treatment. Therefore, the present inventors applied aminosilane, which is water-based and has excellent long-term stability, to a pre-painting treatment of aluminized steel sheets, thereby improving the adhesion between the aluminized steel sheets and the paint, the water resistance as a chemical conversion coating, and the interface with the paint. The researchers discovered a method that works well as a curing agent for paints and is also suitable from the perspective of preventing pollution. The present invention proposes an improvement in the blister resistance of a coated steel plate whose base metal is an aluminized steel plate and which is sent after being painted and baked. That is, the present invention provides (1) that the base metal is limited to an aluminized steel plate, (2) that it is treated with aqueous aminosilane, and (3) that the pH of the aminosilane aqueous solution is adjusted to be slightly alkaline in the range of 8 to 10. (4) forming a silane film by heating before painting, (5) painting and baking a thermosetting paint on the top surface, etc. The present invention relates to a method for producing a coated aluminized steel sheet with excellent properties. Next, these requirements will be explained in detail. First, the aluminized steel sheet used in the present invention may be manufactured by hot-dip plating, vapor deposition plating, or any other method. The paints used are mainly epoxy/
Thermosetting paints are used like hardener systems. In the present invention, the coating system includes bisphenol A type epoxy, epoxy-polyester, and epoxy-polyester.
Paints based on modified epoxy or polyester such as acrylic or epoxy-urethane, or a combination of a modified polyester and a curing agent are preferred from the viewpoint of reactivity with the silane coupling agent. The mechanism of action of the silane coupling agent is well known, but when the silane coupling agent is expressed as RSiX ₃ , it is hydrolyzed by moisture on the surface of the inorganic material, RSiX ₃ +3H ₂ O→RSi(OH) ₃ +3HX, and the surface of the inorganic material becomes It is adsorbed to form a film of siloxane bonds, resulting in a dense water-resistant film. In addition, the organic functional group R reacts with the polymer of the paint,
Contributes to improved adhesion. On the other hand, if a non-polluting water-based treatment can be used as a pre-painting treatment, no pollution treatment or anti-aircraft equipment will be necessary. However, conventionally, water-based treatment of silane coupling agents has not been very effective, but the present invention is significant in that it uses aminosilane, which is originally water-based, and explores its preferred conditions. That is, instead of the conventionally known method of adding a non-aqueous vehicle and a silane coupling agent to a pigment to form an anchor material, the present invention uses a film-like method formed using an aqueous aminosilane between the coating film and the underlying metal. The two techniques are fundamentally different, as they are characterized by the intervention of objects. Therefore, aminopropyl-trihydroxysilane having the following structure is suitable as the aminosilane. NH ₂ ―CH ₂ ―CH ₂ ―CH ₂ Si(OH) ₃ This means that it exists stably in an aqueous solution due to aqueous bonding, can be stably mixed with water at any ratio, and does not need to be treated as a dangerous substance during storage. It can also be stored optionally diluted with water. In addition, for paints, as mentioned above, the amino group having active hydrogen acts as a curing agent for the paint, so that strong adhesion can be obtained between the paint film and the base metal. The concentration of water-soluble aminopropyltrihydroxysilane, which is a type of water-based aminosilane used in the present invention, is related to the amount of film after coating and drying on an aluminized steel plate. The concentration of the treated aqueous solution is 0.1 to 10% by weight as it may be destroyed or the effect may become saturated.
It is necessary to control the processing time within the range of 10 to 20 seconds. Further, the pH of the treatment liquid needs to be in the range of 8 to 10 in order to lightly alkaline clean the steel plate surface. As mentioned above, the hydroxyl group of aminosilane is adsorbed on the surface of the aluminized steel plate, and when heated, it forms a dense water-resistant film of siloxane bonds. After applying an aqueous solution of aminosilane for reasons such as the appearance of wrinkles during baking,
Must be dried at 150°C. The present invention is a method for manufacturing painted metal sheets using aluminized steel sheets as a base material, which has a simple treatment process and does not require pollution treatment.It has improved blister resistance compared to conventional chromate treatment, and has improved corrosion resistance. Since improvements can be expected, it is considered to have high industrial value. EXAMPLES Next, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 Aluminized steel sheets with aluminized thicknesses of 8, 20, and 30μ on one side, respectively, were degreased with alkali and treated with 1% by weight of aminopropyltrihydroxysilane (PH
8.5), 5% by weight (PH9.1), and 10% by weight (PH10.0) for 10 seconds, and then squeezed with a roller.
This treated plate was heat treated at 100°C for 60 seconds. Next, a coated steel plate was prepared by applying 5μ of epoxy paint as a primer and 15μ of polyester paint as a primer to the aluminized steel sheet that had undergone the above treatment, and 2coat-2bake to create a coated steel sheet, and tests were conducted on the adhesion, corrosion resistance, moisture resistance, etc. of the paint film. Summer. The adhesion of the paint film was tested under three levels of conditions as shown in the table. Corrosion resistance was based on the salt spray test of JIS Z2371, and moisture resistance was based on the wet test of JIS K2246. Evaluations were made based on various test items and test methods. The evaluation criteria are shown outside the table. Goban Erichsen test: In accordance with JIS K 5400 6.15, a 1 mm square square was cut into the painted test piece using a cutter to reach the steel substrate, extruded using an Erichsen testing machine specified in JIS B7729, and cellophane tape was applied to the area. was applied and rapidly peeled off, and the degree of abnormality on the painted surface was observed. Impact deformation test (DuPont impact deformation test): Compliant with JIS G3312 8.5, diameter 12.7mm
(1/2 inch), a weight weighing 1 kg was dropped from a height of 50 cm, cellophane tape was applied and rapidly peeled off, and the degree of abnormality on the painted surface was observed. 180 degree bending test: Based on JIS G3312 8.3, painted test piece
It was bent 180 degrees, a predetermined number of boards of the same thickness were sandwiched inside and tightened, and cellophane tape was pasted on the bend and rapidly peeled off to observe the degree of abnormality on the painted surface. Erichsen extrusion test: In accordance with JIS K6744 8.2, a painted test piece was extruded by 6 mm using an Erichsen extruder specified in JIS B7729, cellophane tape was applied and rapidly peeled off, and the degree of abnormality on the painted surface was observed. Exps 1 to 3, 10 to 12, and 19 to 21 in the table are respectively Example 1, and Exps 9, 18, and 27 are conventional chromate treated materials, respectively.

【table】

【table】

[Table] As is clear from the table, the degree of blister progression (degree of blister progression) in the salt spray test and wet test, that is, from the end face and cross cut part to the tip of the blister or rust progression at each aluminum plating thickness. The distance (mm) is the comparative example (No. 9, 18,
The examples of the present invention (Nos. 1 to 3, 10 to 12, and 19 to 21) treated with aminosilane are all smaller (the blistering progress is slower) than the 27), and have excellent blister resistance. I understand that. In addition, when the treatment concentration is 1 to 10% by weight, the results are better than the comparative example, and there is no difference within the scope of the present invention. Note that an improvement was also observed in heat adhesion. Example 2 An aluminized steel plate that had been alkaline-degreased in the same manner as in Example 1 was immersed in a 1% by weight aqueous solution of aminopropyltrihydroxysilane for 10 seconds, and after squeezing with a roller, various heating conditions were examined. i.e. 10 seconds and 30 seconds at 100℃; 10 seconds and 30 seconds at 150℃
Heat treatment was performed for 2 seconds and 60 seconds, respectively. Exps 4 to 8, 13 to 17, and 22 to 26 are Example 2 of the present invention, and Exps 9, 18, and 27 are similarly comparative examples. As in Example 1, the blister resistance is superior to the conventional material, but within the scope of the present invention, the more the heat treatment is sufficient, the more dense the layer is formed, so the blister resistance is improved. .

Claims (1)

[Claims] 1. A degreased aluminized steel plate with a pH of 8 to 10.
A method for producing a blister-resistant coated aluminized steel sheet, which comprises treating the steel sheet with aqueous aminosilane adjusted to the desired temperature, heating and drying, and then applying a baking coating. 2 The aqueous aminosilane is aminopropyltrihydroxysilane, and its treatment concentration is 0.1 to 10.
The method for producing a blister-resistant painted aluminized steel sheet according to claim 1, which is a wt % aqueous solution. 3. The method for producing a blister-resistant painted aluminized steel sheet according to claim 1 or 2, wherein the heating and drying conditions are 90 to 150°C for 10 to 60 seconds.