JPH0459350B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to surface-treated steel materials with excellent corrosion resistance.
In detail, the corrosion resistance of so-called zinc-rich coated steel,
In particular, it relates to surface-treated steel materials that have significantly improved corrosion resistance in areas where the paint film is damaged. Various types of rust-preventing steel plates have been proposed and used in highly corrosive environments.For example, in recent years, rust-preventing steel plates for automobiles have Combined with demand, extremely strict conditions are being imposed. To give an example, painted steel sheets commonly known as zinc chrome metal are used to prevent corrosion of automobile bodies caused by salts in cold regions such as North America. It is a painted steel plate coated with a second layer of zinc-rich paint containing powder, and has good corrosion resistance.
Spot welding, which is a requirement for automotive steel plates,
Electrodeposition coating can be performed. However, zinc-rich coating materials are not without problems, and the following issues remain to be improved. Generally, in order to ensure sufficient rust prevention effect, the paint must contain at least 80% by weight, more preferably 95% by weight.
It is said that Zn powder must be contained in the above amount, but when the metal content increases like this, the elongation of the coating film and the adhesion to steel materials deteriorate.
When a painted steel plate is bent or press-formed, the coating film may crack or peel easily.
Once cracks or peeling occur, corrosion will begin to progress from that area. If the paint film is damaged during use as a product, corrosion progresses starting from the damaged area, similar to the above, and causes the paint film to peel off. Ideally, the anti-corrosion coating should be strong enough to be resistant to damage, but this is not possible in practice, so the next best option is to prevent this damage even if the anti-rust coating is damaged. It is desirable to be able to prevent the rapid progression of corrosion starting from the damaged area by forming a product with a high antirust effect on the damaged area. The inventors of the present invention have focused on these circumstances, and have developed a method to stop corrosion in the damaged area and reliably prevent corrosion from progressing, even if the anti-rust coating is locally damaged. Various research efforts have been made in an effort to establish technologies that will enable this. The present invention was completed as a result of such research, and its composition is as follows: Synthetic resin paint vehicle: 2 to 55% by weight Metallic zinc powder: 40 to 97.5% by weight Metal phosphate or metal molybdate: 0.5 to 55% by weight 20
% by weight is formed on the surface of steel material. The characteristics of the present invention will be clarified by clarifying the functions and grounds for setting the content of each coating component in the present invention. Synthetic resin paint vehicle: 2 to 55% by weight Synthetic resin paint vehicle is an essential component for forming a paint film, and if it is less than 2% by weight, the physical properties of the paint film will deteriorate and the adhesion to the steel surface will be insufficient. Peeling or cracking of the coating film is likely to occur during forming processes such as bending and pressing, making it impossible to take advantage of its original characteristics as a rust-preventing coating film. On the other hand, if it exceeds 60% by weight, the absolute amount of Zn powder becomes insufficient, resulting in poor weldability and electrodeposition coating properties, and
The sacrificial anticorrosion effect due to corrosion will no longer be effectively exerted.
As the vehicle, all known conventional zinc-rich paint vehicles can be used, but the most suitable examples include acrylic, vinyl, polyester, epoxy, and phthalic paint vehicles. type, styrene type, butadiene type, melamine type, alkyl silicate type,
Examples include organic silicate composite film systems. Zn powder: 40-97.5% by weight Zn powder is an indispensable main component for improving the weldability and electrocoatability of coated steel sheets and exhibiting sacrificial corrosion protection effects, and these effects are effective at less than 40% by weight. It becomes less effective. while 97.5% by weight
If it exceeds this amount, the absolute amount of the synthetic resin paint vehicle will be insufficient, and the elongation of the paint film and its adhesion to the steel surface will deteriorate, resulting in significant peeling and cracking. Metal phosphate or metal molybdate: 0.5-20
Weight% This component is the most characteristic component of the present invention, and even if the anti-rust coating is locally damaged, it has the effect of stopping oxidative corrosion only in that area and preventing the spread of corrosion to the surrounding area. However, if the amount is less than 0.5% by weight, these effects will not be exhibited effectively. However, if it exceeds 20% by weight, the elongation and adhesion of the coating film will be poor. The metals constituting the metal phosphate or metal molybdate include Mg, Ni, Al, Cr, Co,
Examples include Mn and Ca. Although it is not necessarily clear why the coexistence of the metal phosphate or metal molybdate prevents corrosion from spreading from the damaged part of the paint film, it is possible to form an anticorrosive film in the damaged part of the paint film. This is thought to be due to the following. The metal phosphate and the metal molybdate may be used alone or in combination of two or more. The above-mentioned anti-rust coating exhibits sufficient anti-corrosion function even when applied directly to the surface of a steel plate that has been subjected to alkaline degreasing treatment, etc. However, in addition to this, there are other coatings such as Zn plating or single-layer or multi-layer Zn alloy plating on the steel plate surface. The above-mentioned anti-corrosion paint may be applied after the steel surface has been subjected to chromate treatment or phosphoric acid treatment, or the above-mentioned anti-corrosion paint may be applied after the steel surface has been subjected to chromate treatment or phosphoric acid treatment. It is also effective to further enhance the anticorrosive effect by applying a treatment such as applying the anticorrosive paint after applying a chromate treatment or phosphoric acid treatment to the surface. The preparation method and coating method for the above-mentioned anticorrosive paint are not particularly special, and the above-mentioned synthetic resin is dissolved in a suitable solvent to prepare a synthetic resin paint vehicle, and Zn powder and metal phosphate or metal are added to the vehicle. The molybdate may be uniformly dispersed and applied to the surface of the steel material (or surface-treated steel material as described above) using a known method such as a brush, roller, or spray. The thickness of the anti-corrosion coating may be determined appropriately by taking into consideration the required properties (formability, weldability, corrosion resistance), but in order to ensure satisfactory corrosion resistance, the thickness must be at least 1 μm.
A thickness of about 20 μm is required. After painting, a strong anticorrosion coating is formed by natural drying or forced drying, but it is also effective to further perform a baking treatment to improve coating performance. The present invention is constructed as described above, but the key point is that by containing an appropriate amount of metal phosphate or metal molybdate together with the vehicle and Zn powder, the progress of corrosion starting from the damaged part of the paint film is inhibited. As a result, the lifespan of anti-corrosion-treated steel materials can be significantly extended. Next, experimental examples will be given to further clarify the effects of the present invention. Experimental Example 1 After applying chromate treatment to the surface of a cold-rolled steel sheet [treatment agent: Acomet C (manufactured by Kansai Paint Co., Ltd.) Cr surface adhesion amount: approximately 50 mg/m ² ], a zinc-rich paint shown in Table 1 was applied. The surface-coated steel sheet was obtained by heating and drying at 340°C for 0.5 minutes. The paint vehicle may be an epoxy resin manufactured by Dainippon Ink Co., Ltd. (trade name: Epicron, Lactucamide as a hardening agent) or a special water-based resin (water-soluble acrylic resin manufactured by Teikoku Kagaku Sangyo Co., Ltd.).
80 parts + 20 parts of ethyl silicate). After cross-cutting the surface of each of the obtained surface-coated steel sheets with a cutter knife, the following corrosion resistance test was conducted to examine the performance. Salt spray test: 5% NaCl, 35°C, 600 hours Salt water immersion test: 5% NaCl, 20°C, 600 hours Combined cycle test: Salt spray (5 hours) - Dry (1 hour at room temperature) - Wet (2 hours at room temperature) time) repeated 50 cycles. Immersion cycle test: salt water immersion (10 minutes) - wet (15 minutes)
minutes)-drying (5 minutes) for 1000 cycles. The results are shown in Table 2.

【table】

[Table] Experimental Example 2 Experimental examples (Nos. 16 to 18) in which the anticorrosive coating of the present invention was applied after chromate treatment to a cold rolled steel sheet having a corrosion-resistant plating layer, and cold rolled steel sheets without chemical conversion treatment. Tables 3 and 4 show an experimental example (No. 19) in which the anticorrosive coating of the present invention was directly coated, and an experimental example (No. 20 to 28) in which the coating was coated with a coating whose coating composition was outside the scope of the claims of the present invention. The amount of plating of the corrosion-resistant plating layer used was as shown below, and the other conditions were the same as in Example 1. Zn: 30 (g/m ² ) Zn-Ni: 30 (g/m ² ) Zn-Fe/Zn-Ni: 30 (g/m ² ) The film composition and corrosion test performance are shown in Tables 3 and 4.

【table】

【table】

[Table] As is clear from Tables 1 to 4, Examples (No. 1 to 12 and No. 16 to 19) that meet the specified requirements of the present invention
Good results have been obtained not only in salt spray tests and salt water immersion tests, but also in severe corrosion tests such as combined cycle and immersion cycle. On the other hand, in the comparative examples (No. 13 and No. 26 to 28) that do not contain phosphate or molybdate, and the comparative examples (No. 20 to 25) whose coating composition is outside the scope of the claims, the salt water immersion test However, the other test results were poor. Furthermore, "Zinchrome Metal" cited as a conventional example has a high rate of red rust at the cross cut portion in the salt spray test, and the results of the immersion cycle test are also poor compared to the examples of the present invention.

Claims (1)

[Scope of Claims] 1. A coating composition film consisting of a synthetic resin paint vehicle: 2 to 55% by weight, metal zinc powder: 40 to 97.5% by weight, metal phosphate or metal molybdenum hydrochloric acid: 0.5 to 20% by weight, A surface-treated steel material with excellent corrosion resistance that is formed on the surface of steel material. 2. The surface-treated steel material according to claim 1, wherein a corrosion-resistant base layer is formed under the coating composition film. 3 The metal constituting the metal phosphate or metal molybdate is Mg, Ni, Al, Cr, Co, Mn, Ca
The surface-treated steel material according to claim 1 or 2, which is one or more selected from the group consisting of: