JPS6123766A - Plated steel sheet having composite coating - Google Patents

Abstract

PURPOSE:To obtain a surface treated steel sheet capable of satisfying each of rustproof treatment and prime-coating treatment by making the second layer a cured film of specified silane compd. in a plated steel sheet consisting of a chromate-treated film and an organic resin film. CONSTITUTION:A chromate-treated film is formed as the first layer on the surface of a plate steel sheet. A cured film having the following siloxane bond as a skelton is formed as the second layer wherein the siloxane bond is formed by coating and baking a soln. contg. one or more kinds of monomer of oligomer of di- or trialkoxysilane which has alkyl groups having the organic functional groups. In the film of the second layer, the silane compd. in itself is a film forming component and the cured film consisting of the siloxane skelton obtained by baking the silane compds. has not hydrophilic nature and also is sufficiently bonded to the chromatetreated film of the lower layer. Therefore, the corrosion resistance of the plated steel plate is remarkably increased and the electrodeposited painting properties are not throughly degraded within the limitation of the coating build-up of the second layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides two
This invention relates to a composite coated plated steel sheet having a layer coating.

More specifically, the present invention relates to a composite coated plated steel plate having a two-layer coating on the surface of the plated steel plate consisting of a chromate treatment coating and a silicone-based organic resin coating.

(Prior art) Chromate treatment has been commonly used as a rust preventive or painting base treatment for galvanized steel sheets and other galvanized steel sheets. A treatment for primary rust prevention,
Its corrosion resistance was only at the level required for primary rust prevention, for example, at a level that caused white rust to occur during a 24 to 48 hour salt spray test. Therefore, in recent years, composite coated plated steel sheets having a two-layer structure have been proposed for the purpose of improving corrosion resistance. For example, Special Publication No. 49-1986, No. 49-1986,
No. 4166, No. 49-36100" and No. 50-1
No. 8455, the first layer is a chromate-treated film, the second layer is a chromate-treated film;
It is described that an organic resin film is formed as a layer.

(Problem to be Solved by the Invention) However, even with such a composite coating, since a hydrophilic resin is used as the second layer organic resin in consideration of adhesion with the chromate treatment film, this resin It is difficult to say that sufficient corrosion resistance can be obtained because it easily absorbs water. To overcome this drawback, Japanese Patent Laid-Open No. 57-108292 discloses the use of a composite silicate resin film as a second layer in which silica sol and a hydrophilic organic resin are crosslinked in the presence of a silane compound. As described above, even if this organic composite silicate resin film is used as the second layer, although it is improved compared to the conventional technology due to the presence of silica sol, it is not necessarily sufficient because the water resistance of the organic resin is not sufficient. It cannot be said that it has corrosion resistance and paint base properties. Although a silane compound is used as one component in this organic composite silicate resin, film formation in this composite resin is mainly performed by organic resin (e.g., acrylic, epoxy resin, etc.), and the function of the silane compound is , acts as a catalyst for the compositing of the main component silica and organic resin, as well as a crosslinking agent between these image components and a crosslinking agent for the chromate treatment film of No. It is a small amount, about 0.5 to 15% of the total amount.

In addition, if the sole purpose is corrosion resistance, it may be possible to increase the film thickness, but when applying electrodeposition coating to a plated steel sheet that has undergone surface treatment, the film thickness must be controlled to be sufficiently thin or it will stick to the surface. An electrodeposited coating film with good properties cannot be obtained.

An object of the present invention is to provide a surface-treated steel sheet that has both good corrosion resistance and paint base properties that can be used both as a rust preventive treatment for a plated steel sheet and as a paint base treatment.

Another object of the present invention is to provide a surface-treated steel sheet having good electrodeposition coating properties and spot weldability.

(Means for Solving the Problems) As a result of repeated research in order to overcome the drawbacks of the conventional composite coated plated steel sheets described above, the present inventors have discovered that baking and hardening of coating films of silane compounds of various types are possible. It has been found that a plated steel sheet with good corrosion resistance and coating base properties can be obtained by using the cured film having a skeleton of siloxane bonds formed by the method as a 2N organic resin film.

Here, the present invention provides a solution containing one or more monomers or oligomers of di- or trialkoxylan having an alkyl group having an organic functional group and a (81 chromate treatment film) on the surface of a plated steel sheet. A composite coated plated steel sheet characterized by having a two-layer coating consisting of a hardened coating having a skeleton of siloxane bonds formed by coating and baking.

The present invention will be explained in detail below.

The plated steel plate used as the plate in the present invention is of this type.
Commonly used coated steel sheets, such as galvanized steel sheets, zinc alloy-plated steel sheets such as zinc-iron, zinc-nickel, and zinc-aluminum, aluminum-plated steel sheets, and composite plated steel sheets with multiple layers of these platings. can be mentioned.

The chromate treatment film formed as a first layer on the surface of the plated steel sheet may be formed by either the generally used reaction type or coating type chromate treatment. Although there is no particular strict limit to the amount of chromium deposited, it is generally preferable that the amount of Cr be in the range of 10 to 300 mB'/rrr.

If it is less than 10 mg/n, sufficient corrosion resistance cannot be obtained, while if it exceeds 300 mg/n, workability deteriorates and it is also disadvantageous in terms of cost.

When the surface-treated steel sheet of the present invention is used for electrodeposition coating, in order to improve the surface condition of the electrodeposition coating, iron phosphide (Pe2P
) powder may be included. This Fe2P powder preferably has an average particle size of about 1 to 5 microns, and the amount added is preferably about 20 times the molar amount of chromic acid. If the particle size is too large or the amount added is too large, it will be difficult to uniformly disperse the Fe2P powder in the chromate treatment solution.
Difficult to coat evenly. A more preferable addition amount is 1 to 10 times the molar amount of chromic acid.

The chromate treatment solution and treatment method, both the coating type and the reaction type, are well known to those skilled in the art, so further explanation will be omitted. In addition, in order to remove components that may interfere with the formation of the second layer film, the formed chromate-treated film may be washed with water, dried, etc. as appropriate.

The structure of the monomer or oligomer of di- or trialkoxysilane (hereinafter referred to as silane compound) having an alkyl group having an organic functional group used for forming the second layer is represented by the following formula: In the above formula, R1 : Alkyl group such as methyl, edyl, propyl, butyl; R2: Alkyl group or aryl group (in case of dialkoxysilane), or alkoxy group, i.e. OR1 (in case of 1-dialkoxysilane); R3: Organic functional group an alkyl group (examples of organic functional groups are vinyl, amino, chloro, epoxy, hydroxyl, carboxyl, methacryloxy, etc.); n: 0 (for monomers), or an integer greater than or equal to 1 and usually less than or equal to 6 (for oligomers); ).

Examples of such silane compounds include vinyltriethoxysilane, r-methacryloxypropyl 1-rimethoxysilane, γ-aminopropyltriethoxylane, T-
Glycidoxyprobyltrimethoxysilane, β-(3,
Examples include so-called silane coupling agents such as 4-epoxycyclohexyl)ethyltrimethoxysilane, N-β-(aminoethyl)-T-aminopropyltrimethoxysilane, and γ-chloropropyltrimethoxysilane.
Some of these are available as commercial products. Also included are reaction products of these silane compounds and organic resins.

Unlike the second layer film described in JP-A-57-108292, the present invention uses a silane compound alone as a film-forming component, and a hardened film consisting of a silane skeleton obtained by baking this is used as the second layer. However, such a hardened film is not hydrophilic and also bonds well with the underlying chromate-treated film, greatly improving the corrosion resistance of the plated steel sheet.Moreover, the electrodeposition coating property is also comparable to that of the second N. It has been found that as long as the coating amount is limited to a certain level or less, a composite coated plated steel sheet that is not damaged and exhibits good coating base properties can be obtained.

When a solution containing one or more of the above-mentioned silane compound monomers or oligomers is applied to a chromate-treated plated steel sheet and then baked, the alkoxy groups of the silane compound are thermally decomposed to form 0 and Si. When siloxane bonds are formed by alternately bonding K, a cured film having siloxane bonds as a skeleton is obtained.゛If this baking or hardening is insufficient, the desired corrosion resistance cannot be obtained.
It is necessary to carry out sufficient curing, ie almost complete thermal decomposition of the alkoxy groups. Although it varies depending on the type of silane compound, the temperature of the steel plate is usually 150 to 35
It is necessary to heat to a temperature of 0°C. However, if the temperature is too high, the alkyl groups with organic functional groups that should originally remain in the film may be decomposed, so high temperatures of 400° C. or higher should generally be avoided. The heating time depends on the temperature,
Sh.

Although it depends on the type of orchid compound and the thickness of the coating film, it is generally about 30 seconds to 60 minutes.

For the purpose of the present invention, an alkyl group having an organic functional group is important not only for imparting corrosion resistance to the film but also for providing adhesion to the coating film as a coating base. For example, painting of an automobile body is usually carried out by processing a steel plate into a predetermined shape by press forming or the like and then applying electrodeposition coating, but the surface-treated plated steel plate according to the present invention
Due to the presence of this functional group, the adhesion with the electrodeposited coating is as good as an emergency. Further, even during processing before electrodeposition coating, such alkyl groups provide flexibility to the film, so that peeling of the film does not occur and good processability can be obtained.

Furthermore, in order to improve the performance of this film, rust inhibitors, inorganic fillers (e.g., colloidal silica, titanium dioxide, etc.), organic resins (e.g., epoxy resins, acrylic resins, polyester resins, urethane resins, etc.) are added as necessary. It is also possible to add resins, etc.). If the amount of these optionally added components is too large, it may have an adverse effect on the performance of the cured film of the silane compound, so it is usually kept within 50% by weight of the total solid content of the coating solution. , as already mentioned, the organic resin can also be present as a reactant with the silane compound.

There are no particular restrictions on the method of applying the silane compound solution to the chromate-treated plated steel sheet, and any conventional methods such as dipping, roll coating, and spray painting can be used. In order to obtain sufficient corrosion resistance, it is preferable that the amount of the coating film is 0.1 g/m or more, especially 1.0 g/lTr or more as a silane compound, but when it also serves as a base treatment for electrodeposition coating, If the amount of adhesion is too large, electrodeposition coating will be difficult, so 5
．． It is necessary to keep it below 0g/r/. The concentration of the coating solution, that is, the solid content, is adjusted appropriately depending on the amount of coating, but is usually about 1 to 50% by weight, including the concentration of the silane compound.

The solvent is appropriately selected from water and organic solvents depending on the solubility of the silane compound used.

The following examples further illustrate the invention.

Electrogalvanized steel sheet with a thickness of 0.8+a++ and zinc-
After degreasing, the chromate treatment solution shown in Table 1 was applied to the surface of a Ninokel alloy electroplated steel plate (the amount of chromium adhesion was 20 g/% on each side) to the indicated amount of Cr, and the steel plate was coated in 60 seconds. It was heated to a temperature of 130 to 140°C. After cooling, a xylene solution of various silane compounds shown in Table 1 was applied as a second layer by dip coating to the indicated amount, and baked by heating at 250° C. for 15 minutes. The concentration of the silane compound in the solution is 1.5% by weight when the coating weight is 0.3 g/nr, 5% by weight when the coating weight is 1.0g/nr, and 5% by weight when the coating weight is 3.0g/nr. 35 in the case of 15% by weight and a coating amount of 1.0g/rd.
% by weight.

After processing a part of the obtained composite coated steel plate, a salt spray test was conducted. The results are shown in Table 1.

Further, the surface-treated steel sheet obtained above was subjected to the following electrodeposition coating for automobile bodies. The obtained coated plates were tested for coating film adhesion and corrosion resistance. The results are also shown in Table 1.

The operation of painting an automobile body is as follows. First, it was degreased with alkali, washed with deionized water, dried at 110° C. for 5 minutes, and then coated with Power Top U30 (trade name, manufactured by Kuchmoto Paint Co., Ltd.) to a thickness of 20 μm by cationic electrodeposition. Next, 552E Sealer (trade name,
(manufactured by Kuchimoto Paint Co., Ltd.) to a film thickness of 20 μm,
Baked at 40°C for 30 minutes. Finally, Olga G-26 (trade name, manufactured by Nippon Paint Co., Ltd.) was applied as a top coat to a thickness of 40 μm, and baked at 140° C. for 30 minutes.

(Effects of the Invention) As can be seen from the test results in Table 1, a composite film in which a chromate treatment film is formed as the first layer and a hardened film of a silane compound having a functional group is formed as the second layer on the surface of a plated steel sheet according to the present invention. The coated steel sheet not only exhibits generally good bare corrosion resistance in both the flat plate portion and the processed portion as it is, but also exhibits good paint adhesion and paint corrosion resistance when electrodeposition coating is applied thereon. However, the amount of silane compound attached is 5 g/
If it exceeds rd (Example 4), electrodeposition coating will not be possible, so for steel plates for electrodeposition coating, this coating amount should be 5 g.
/% or less. However, it is generally recognized that bare corrosion resistance is around 1, which is better as the amount of silane compound attached is larger, so such a high amount of silane compound attached is also useful as a corrosion-resistant steel sheet for purposes other than electrodeposition coating. Further, from a comparison between Examples 1 and 2, it can be seen that when Fe2P is added to the chromate treatment liquid, the electrodeposition coating properties are further improved.

On the other hand, if chromate treatment is not performed first (Comparative Example 1)
, the bare corrosion resistance cannot withstand the severe salt spray test of 400 hours, and the corrosion resistance of the coating also decreases. In addition, when the surface was treated with ethyl silicate (i.e., tetraethoxysilane) that does not have an alkyl group with an organic functional group (comparative example 2), all of the properties of bare corrosion resistance, paint adhesion, and corrosion resistance were performance is inferior in some respects. In the zinc phosphate treatment (Comparative Example 3), although the coating corrosion resistance was good to a certain degree, the bare corrosion resistance was extremely poor and the coating adhesion was not very good.

As is clear from the above, the composite coated plated steel sheet of the present invention exhibits good corrosion resistance as it is, and is therefore useful as a general corrosion-resistant steel sheet. In addition, if the amount of silane compound deposited in the second layer is limited to 5 g/m or less, the electrocoating properties will not deteriorate, so it is suitable as a base for coating, especially for electrocoating, which improves corrosion resistance and adhesion. An electrodeposited plate that is sharp in both properties can be obtained.

Moreover, this composite coated plated steel sheet has a good level of spot weldability when it is assembled by spot welding and then subjected to electrodeposition coating.

Applicant: Sumitomo Metal Industries, Ltd. (1 idiot) Agent: Patent attorney Do Hirose - (1 idiot) ζ □

Claims (2)

[Claims] (1) A solution containing (a) a chromate treatment film and (b) one or more di- or trialkoxylan monomers or oligomers having an alkyl group with an organic functional group is applied to the surface of a plated steel sheet. A composite coated plated steel sheet characterized by having a two-layer coating consisting of a hardened coating with a skeleton of siloxane bonds formed by coating and baking, and a hardened coating formed by coating and baking. (2) The composite coated plated steel sheet according to claim 1, wherein the chromate treatment film contains iron phosphide.