JP2003201584A - Surface-treated steel sheet having excellent coatability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated steel sheet in which the removability of a lubricating film in an alkali degreasing process as treatment prior to a coating process is effectively improved, and which has improved appearance quality after coating. <P>SOLUTION: The solid lubricating film to be formed on the surface of a galvanized steel sheet is the nonreactive type one essentially consisting of the fine particles of zinc phosphate with a mean particle diameter of 0.5 to 3.0 μm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet having excellent coatability, and more particularly, to an advantageous improvement of the film-removing property of a lubricating film in the alkaline degreasing step which is a pretreatment of the coating step and the surface appearance after coating. It is intended.

[0002]

2. Description of the Related Art Galvanized steel sheets such as hot-dip galvanized steel sheets and electrogalvanized steel sheets have excellent corrosion resistance, but are inferior in press formability to cold-rolled steel sheets. Therefore, various proposals have hitherto been made on methods for improving the press formability of galvanized steel sheets.

For example, iron-based hard plating is applied to the upper layer of the zinc plating layer to increase the hardness of the surface.
A method for preventing galling of plating and dies has been proposed (for example, Patent Document 1). In addition, a method of improving slidability by forming a film of a P or B oxyacid salt and a metal oxide on the surface of the plating layer has been proposed (for example, Patent Document 2). However, in the above-described conventional technique, it is necessary to separately install a dedicated post-treatment facility after the normal galvanizing line, which causes a problem that the manufacturing cost of the steel sheet increases.

In addition, a zinc-based plated steel sheet coated with a zinc phosphate film is known as a lubricated steel sheet having excellent lubricity and easy to press. According to the method using the zinc phosphate coating (pre-foss treatment), the coating can be formed by commonly using general-purpose equipment such as the dipping method and the coating method, and the slidability improving effect is great. However, such a zinc phosphate coating is inferior in the film removal property (removability) in the alkaline degreasing step, which is a pretreatment of the coating step, and as a result, the chemical conversion coating becomes nonuniform, which in turn results in There was a problem that the appearance quality deteriorates.

[0005]

[Patent Document 1] JP-A-62-192597 (Claims)

[Patent Document 2] Japanese Patent Laid-Open No. 4-176878 (claims)

[0006]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems by effectively improving the film removal property of a lubricating film in an alkaline degreasing process, which is a pretreatment of the coating process, and coating the same. It is an object of the present invention to propose a surface-treated steel sheet having improved paint quality and excellent in paintability.

[0007]

That is, the present invention is a zinc-based plated steel sheet having a solid lubricating coating on the surface,
The solid lubricating film has an average particle size of 0.5 μm or more and 3.0 μm.
It is a surface-treated steel sheet having excellent coatability, which is characterized by comprising a solid lubricating film mainly containing fine particles of zinc phosphate having a size of m or less.

Further, the present invention is a zinc-based plated steel sheet having a solid lubricating film on the surface thereof, wherein the solid lubricating film has an average particle size of 0.5 μm or more and 3.0 μm or less, and the cumulative frequency from the smaller diameter side. It consists of a solid lubricant film consisting mainly of zinc phosphate fine particles having a particle size distribution of 0.3 μm or more when the distribution is 5% and 5.0 μm or less when the distribution is 95%. It is a surface-treated steel sheet with excellent coating properties.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. It is known that when a zinc-based plated steel sheet is pressed, it tends to cause adhesion to a mold due to the softness of zinc and has a high sliding resistance, so that galling may occur depending on conditions. Generally, the use of press oil results in a considerable improvement in formability. However, when forming a large-sized part or processing a difficult-to-form part, a partial oil film breakage may occur and press cracking may occur.

Solid lubricating coatings, such as zinc phosphate coatings,
Originally, it was considered to be effective against the partial increase in sliding resistance due to the oil film breakage as described above, and it was thought that the formability could be improved by using it in combination with an appropriate press oil. However, in the conventional zinc phosphate treatment, a phosphoric acid is prepared by mixing a soluble zinc compound or a reaction accelerator with an acidic solution containing phosphoric acid as a main component and dissolving a part of the base plating layer on the surface of the plating layer. Since a zinc film is formed, a reaction layer is inevitably present at the interface between the formed film and the plating layer.

The morphology of this reaction layer is not always completely clear, but in many cases
The presence of Hopeite (hovite: zinc phosphate tetrahydrate) is confirmed by X-ray diffraction analysis. In the case of a film formed by the dipping method, scaly zinc phosphate crystals of 5 to 10 μm are often observed. These crystalline particles and the reaction layer are dissolved in the alkaline degreasing liquid to some extent and partially removed, but they are not completely removed. If the chemical conversion treatment is carried out in this state, the chemical conversion film becomes non-uniform and the subsequent coating appearance is deteriorated.

Therefore, the inventors have tried to solve the above-mentioned problems by applying a solid lubricating coating mainly composed of zinc phosphate fine particles. That is, when forming a solid lubricating film, an aqueous treatment liquid containing zinc phosphate fine particles that have been reacted and formed in advance and an organic film forming aid is applied and dried on a steel plate by, for example, a roll coater to form a film. The coating liquid did not contain a component such as phosphoric acid that causes a chemical reaction with the plating layer. According to the above treatment, crystalline particles and a reaction layer are not formed at the interface between the coating and the plating layer. Therefore, the organic film-forming aid water-soluble polymer binder (organic film-forming aid) dissolves to form the film. Are easily removed.

However, such a non-reactive solid lubricating film has a poor film removal property in the alkaline degreasing process which is a pretreatment of the coating process, which may adversely affect the subsequent chemical conversion processability and paintability. found. That is, for example, when a solid lubricating film mainly composed of zinc phosphate fine particles as described above is formed on the surface of a plating layer having fine irregularities on the surface, such as an alloyed hot-dip galvanized layer, it is deep in the recess. It was found that the fine particles that entered were not completely removed in the alkali degreasing step, and that this resulted in deterioration of chemical conversion treatment property and paintability. It has also been found that such a tendency is likely to occur when the alkaline degreasing liquid used in the pretreatment for coating is deteriorated.

Therefore, as a result of intensive studies to solve this problem, the inventors of the present invention regulated the particle size distribution of the zinc phosphate fine particles, which is the raw material, within a predetermined range so that even the deteriorated degreasing liquid was used. Even in such a case, it was found that the intended purpose can be achieved advantageously.

That is, the inventors have conducted numerous experiments and studies on the relationship between the particle size distribution of zinc phosphate fine particles and the film-removing property in the alkaline degreasing process, and the subsequent chemical conversion treatment property and paintability. By using zinc phosphate fine particles having an average particle size in the range of 0.5 μm or more and 3.0 μm or less, the film removal property in the alkaline degreasing step, and by extension, the subsequent chemical conversion treatment property and paintability are effectively improved. It turned out that

The average particle size may be measured by using a commercially available particle size distribution measuring device, for example, a laser diffraction / scattering type particle size distribution measuring device. At this time, the particle diameter when the cumulative frequency distribution from the smaller diameter side is 50% is the average particle diameter.

Further, after satisfying the above-mentioned average particle diameter range, as shown in FIG. 1, when the cumulative frequency distribution from the small diameter side is 5%, the particle diameter is 0.3 μm or more and 95%. It was found that even more results can be obtained by using zinc phosphate fine particles having a particle size distribution satisfying a particle size of 5.0 μm or less.

Here, the cumulative frequency distribution from the small diameter side is 5%.
The particle size at the time of was set to 0.3 μm or more in order to reduce the proportion of fine particles and reduce the adverse effects caused by such fine particles entering the recesses of the plating layer. The particle size when the cumulative frequency distribution is 95% is 5.0 μm
The reason for this is that if the proportion of coarse particles increases, the adhesion with the undercoat plating layer will decrease.

In the present invention, a solid lubricating film is formed by using a mixture of zinc phosphate fine particles having the above-described particle size distribution with an organic film forming aid as a processing liquid. Here, the mixing ratio of the zinc phosphate fine particles and the organic film forming aid is preferably about 3 to 50 parts by weight based on 100 parts by weight of zinc phosphate fine particles.

As the organic film-forming aid, for example, water-soluble polymers such as methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyethylene glycol, xanthan gum and guar gum, their derivatives, and salts thereof are suitable. . Further, if necessary, a surfactant as a dispersion stabilizer of zinc phosphate fine particles may be contained. Considering the application as a steel sheet for automobiles, which is generally used by applying a complexing oil or a cleaning oil on the steel sheet, the above film-forming aids are stable against rust-preventing oil and cleaning oil. It is also important to have sex.

Further, the coating amount of the treatment liquid is preferably such that the solid lubricant coating amount after coating and drying is about 0.05 to 2.0 g / m ^2, and an appropriate amount of the treatment liquid is applied. After that, it is dried at a temperature of about 60 to 120 ° C. The main component of the solid lubricating coating thus obtained is zinc phosphate fine particles, and the other components are an organic film forming aid and its derivative. And, the ratio of these after the film formation is preferably about 65 to 97 mass% of zinc phosphate fine particles and about 3 to 35 mass% of organic film forming aid and its derivative.

Further, in the present invention, the zinc-based plated layer includes a hot-dip galvanized layer, an alloyed hot-dip galvanized layer, an electrogalvanized layer, and one or more of Al, Mg, Si and the like. Means a hot dip galvanized layer, an electrogalvanized alloy plated layer containing one or more of Ni, Fe, Co and the like.

[0023]

[Example] As a zinc-based plated steel sheet as a material, an alloyed hot-dip galvanized steel sheet (plating base plate: 0.8 mm thick plain steel).
Plating layer composition Fe: 8 to 14 mass%, Al: 0.1 to 0.2 mass
%, Balance: zinc) to form a solid lubricating coating according to the present invention under the following conditions. As shown in Table 1, zinc phosphate fine particles with various changes in average particle size and cumulative frequency distribution: 5 to 20 mass% and water-soluble polymer binder (carboxymethyl cellulose sodium salt [polymerization degree 700]): 0.5
An aqueous solution containing ˜5.0 mass% was used as a treatment liquid, and an amount of 1.0 g / m ² (per one side) after application and drying was applied, followed by drying at 80 ° C. The results of an examination of the delamination resistance in the blank cleaning step, which is the pretreatment of the alkaline degreasing step of the alloyed hot dip galvanized steel sheet with the solid lubricating film thus obtained, and
It is also shown in Table 1.

The particle size distribution of the zinc phosphate fine particles is
The measurement was performed using a laser diffraction / scattering particle size distribution measuring device. The film removal property in the alkaline degreasing step was measured as follows. Alkaline degreasing liquid for chemical pretreatment FC44
60 (manufactured by Nippon Parkerizing) standard concentration (FC4460
A: 20 g / l, FC4460B: 12 g / l), adjust the pH to 10 by adding dry ice (carbon dioxide), and liquid temperature:
After dipping under the conditions of 40 ° C. and dipping time: 60 seconds, the film was washed with water and dried, and then the film adhesion amount was measured. If the film removal rate by this test is less than 80%, uneven appearance is likely to occur in the chemical conversion treatment unevenness and the subsequent coating process. Furthermore, regarding the peeling resistance in the blank cleaning process, after applying cleaning oil (Mitsubishi Nichiishi P1600) to the test piece, rub it 20 times with a polypropylene brush, degrease it with petroleum benzine, and attach it before and after it. The change was evaluated. The amount of peeling by this test
If it exceeds 20%, there is a great concern of causing slidability failure.

[0025]

[Table 1]

As shown in the table, when zinc phosphate fine particles having a particle size distribution according to the present invention are used, the film removal property in the alkaline degreasing process is high and the peeling resistance in the blank cleaning process is high. Is also excellent.

[0027]

As described above, according to the present invention, by using zinc phosphate fine particles, which are the material of the non-reactive solid lubricating coating, satisfying the predetermined particle size distribution, the film removing property in the alkaline degreasing step and the blank can be obtained. It is possible to stably obtain a surface-treated steel sheet having excellent peeling resistance in the cleaning process.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the particle size of zinc phosphate fine particles and the frequency and cumulative frequency.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoichi Toyama             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. (72) Inventor Chiaki Kato             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. F term (reference) 4K044 AA02 AB02 BA10 BB11 BC01                       BC04 CA53 CA64

Claims (2)

[Claims] 1. A zinc-based plated steel sheet having a solid lubricating film on the surface thereof, wherein the solid lubricating film has an average particle size of 0.5.
A surface-treated steel sheet excellent in coatability, which is characterized by comprising a solid lubricating film mainly containing fine particles of zinc phosphate having a size of at least μm and at most 3.0 μm. 2. A zinc-based plated steel sheet having a solid lubricating film on the surface thereof, wherein the solid lubricating film has an average particle size of 0.5.
When the cumulative frequency distribution from the smaller diameter side is 5% or more and 3.0 μm or less and the cumulative frequency distribution is 5%, the particle size is 0.3 μm or more and 95%.
A surface-treated steel sheet having excellent coatability, which is characterized by comprising a solid lubricating film mainly containing fine particles of zinc phosphate having a particle size distribution such that the particle size at the time is 5.0 μm or less.