JPH09169078A - Resin coated steel panel excellent in electrodeposition coating properties and press moldability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an electrodeposition coating film excellent in appearance after coating and to obtain excellent press moldability by adding a specific amt. of a silane coupling agent to a resin film as a solid along with a urethane resin, a lubricant and an inorg. colloid compd. and setting the adhesion amt. of a resin to a specific value. SOLUTION: A resin coated steel panel is coated with a resin film. The resin film contains 0.1-20wt.% of a silane coupling agent as a solid along with a urethane resin, a lubricant and an inorg. colloid compd. The silane coupling agent is one or more kind of a compd. having a group having one or more functional group selected from a (meth)acryloyl group, a vinyl group and an epoxy group and three alkoxy groups directly bonded to an Si atom. The resin coated steel panel is produced by applying a coating soln. containing the urethane resin, the lubricant, the inorg. colloid compd. and the silane coupling agent as essential components to the surface of a raw steel panel by an arbitrary method and drying the coated steel panel.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to household electric appliances,
The present invention relates to a resin-coated steel sheet that is excellent in electrodeposition paintability and press formability and is used in building materials, furniture, automobile members and the like.

[0002]

2. Description of the Related Art Home appliance manufacturers and automobile manufacturers have widely used resin-coated steel sheets having a resin film formed on the surface of the steel sheet in order to improve the corrosion resistance of zinc- or zinc-based steel sheets. However, it has been conventionally pointed out that these resin-coated steel sheets suffer from defects such as pinholes and concavities and convexities when subjected to electrodeposition coating, which significantly reduces the value of the product. That is, since the resin film has low electrical conductivity and high electric resistance, during electrodeposition coating, electric current concentrates on a portion having a small electric resistance, such as a defective portion of the resin film, and a spark occurs,
The heat generated by the spark deteriorates the electrodeposition coating film, so that a smooth electrodeposition coating film cannot be obtained.

To solve this problem, resin-coated steel sheets using various compositions of organic resins or organic / inorganic composite type resins as resin coating compositions have been proposed. For example, a coating composition containing a urethanized epoxy resin, a hydrophilic polyamide resin, silica particles and the like (Japanese Patent Publication No. 3-32).
No. 638), polyamide, polyamine, polyimine resin, and silica agglomerated particles mixed with an epoxy resin as a binder (Japanese Patent Laid-Open No. 7-76585).
No.) and the like. With these proposals, it is only necessary to form a relatively thin electrodeposition coating because intermediate coating and topcoating are performed after electrodeposition coating.In the epoxy-based cationic electrodeposition coating process, defects such as pinholes and surface irregularities are generated. Has come to be suppressed to some extent. However, in the case of acrylic-based cationic electrodeposition coating that has good weather resistance and other properties and is used to form a thick coating with one coat (only electrodeposition coating), pinholes cannot be suppressed and users can be satisfied. The appearance after painting is still not obtained.

On the other hand, resin-coated steel sheets can exhibit good press workability without the use of press oil. Therefore, products which are particularly strongly worked for the purpose of improving environmental deterioration due to splash of press oil during press working. It is applied to products that do not require degreasing after processing. As a material for such a resin film that emphasizes press workability, a urethane modified polyolefin resin to which fluorine resin particles and silica particles are added as solid lubricants by the same applicant (Japanese Patent Laid-Open No. 03-17189). No.), a urethane resin to which spherical wax particles and silica particles are added (JP-A-6-29).
No. 2859), a urethane resin to which spherical wax particles and chain silica are added (JP-A-7-171498).
Have been proposed, and resin-coated steel sheets coated with these resins are widely used. However, when electrodeposition coating is applied to these resin-coated steel sheets, problems such as coating film defects such as pinholes and cissing of the coating material still occur, so improvement has been strongly demanded.

[0005]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a resin-coated steel sheet capable of forming an electrodeposition coating film having an excellent appearance after coating and having excellent press formability. It is what

[0006]

A resin-coated steel sheet excellent in electrodeposition coatability and press formability according to the present invention is a resin-coated steel sheet coated with a resin film, and the resin film is a urethane resin, The solid content of the silane coupling agent is 1.0 to 20% by weight together with the lubricant and the inorganic colloid compound, and the amount of the resin film adhered is 0.1 to 20% by weight.
The gist is that it is 1.5 g / m ² .

As the silane coupling agent, a group having at least one functional group selected from the group consisting of (meth) acryloyl group, vinyl group, amino group and epoxy group;
It is a preferred embodiment of the present invention for improving the electrodeposition coating property to use one kind or two or more kinds of compounds having three alkoxy groups directly bonded to the i atom.

The lubricant is 0.5 to 20% by weight, and the inorganic colloid compound is 1 to 1 in terms of solid content in the resin film.
When it is contained in an amount of 30% by weight, more excellent press moldability can be obtained. Examples of the lubricant include waxes such as polyethylene wax and paraffin wax; lubricating resins such as fluororesin and vinyl chloride resin; metal soaps such as zinc stearate and calcium stearate; graphite;
It is recommended to use one or more solid lubricants having cleavability such as molybdenum disulfide, boron nitride, melamine / cyanuric acid adduct (for example, "MCA" manufactured by Mitsubishi Petrochemical). As the inorganic colloid compound, it is preferable to use one or more of silica sol, alumina sol, titania sol, zirconium sol and the like.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, for the resin-coated steel sheet of the present invention which is excellent in electrodeposition coatability and press formability, a combination of urethane resin and silane coupling agent is selected as the resin film. Furthermore, the greatest point lies in finding the optimum amount of adhesion of this resin film. By adopting this configuration in the present invention, it is possible to perform press working without using press oil, high-performance resin coating that does not require degreasing or phosphate treatment before electrodeposition coating, and has an excellent appearance after electrodeposition coating. Succeeded in providing steel sheet. Hereinafter, the present invention will be described in detail.

In the resin-coated steel sheet of the present invention, a urethane resin is used as a resin component which is the main constituent of the resin film. This is because the obtained resin film is superior in physical properties (adhesion, impact resistance, processability) and the like as compared with acrylic resins and polyester resins. The urethane-based resin is not particularly limited, and any of those commercially available as urethane-based paints, those synthesized with an isocyanate monomer and various polyols, and the like can be used, and in particular, the Shore D hardness of the obtained resin film. (Measured according to JIS-K7215)
Is 30 to 70, and a pencil hardness of H or more is preferably used from the viewpoint of press workability and corrosion resistance.
The urethane-based resin component may be one that has been subjected to various modifications within a range not impairing press workability and corrosion resistance.

In the present invention, it was found that the addition of the silane coupling agent dramatically improves the electrodeposition coatability of the resin-coated steel sheet. Therefore, the silane coupling agent is contained in the resin film in an amount of 1 to 20% by weight. It was made mandatory to include it. The addition of the silane coupling agent improves the adhesion between the electrodeposition coating film and the resin film and the adhesion between the resin film and the steel plate, and the coated steel plate obtained has high performance. this is,
The organic functional group in the silane coupling agent chemically bonds the urethane resin and the steel sheet surface to improve adhesion, and the functional group of the silane coupling agent acts as a crosslinking agent to form a dense film. And the hydrophilic silanol groups produced by the hydrolysis of the silane coupling agent in the presence of water increase the affinity with the water-based electrodeposition coating, and the resin film surface and the electrodeposition coating It is considered to be due to a synergistic effect such as an action of improving wettability.

The addition of the silane coupling agent makes the appearance of the electrodeposition coating film very beautiful. The addition of the silane coupling agent produces fine irregularities on the surface of the resin film. It is presumed that this concave portion can serve as an energization point.

As the silane coupling agent in the present invention, any silane compound having a hydrolyzable group such as an alkoxy group or chlorine and a functional group can be used without particular limitation. Among them, those which can be preferably used in the present invention are (meth) acryloyl group, vinyl group, amino which are excellent in reactivity with the functional group itself or with the functional group in the urethane-based resin (for example, carboxyl group or hydroxyl group). A compound having a group having at least one functional group selected from the group consisting of a group and an epoxy group, and three alkoxy groups (methoxy group and / or ethoxy group) directly bonded to a Si atom. Specific examples of the most preferable silane coupling agent that has good compatibility with the urethane resin and has good liquid stability include γ- (methacryloxypropyl) trimethoxysilane and β- (3,4-epoxycyclohexyl) ethyl. Examples thereof include trimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and vinyltrimethoxysilane, and one or more of these can be used.

The silane coupling agent should be contained in the resin film in an amount of 1.0 to 20% by weight. 1.0% by weight
When the amount is less than the above, the energizing point of the resin film cannot be secured, and the penetrability of the electrodeposition coating material into the resin film is insufficient, and the electrodeposition coating property is not improved. Further, since the resin film is not formed densely, the corrosion resistance and the scratch resistance during processing are inferior. On the other hand, when it exceeds 20% by weight, the irregularities on the surface of the resin film become too large, impairing the appearance of the electrodeposition coating film, and the corrosion resistance deteriorates. The more preferable amount of the silane coupling agent is 5 to 20% by weight.

In the present invention, in addition to the urethane resin and the silane coupling agent, a lubricant and an inorganic colloid compound are essentially contained in the resin film. The lubricant is a component necessary for improving press moldability. During press molding, the resin-coated steel sheet is severely slid between the die and the die, but a resin coating consisting only of the urethane-based resin and the silane coupling agent causes too much surface friction. For this reason, the sliding portion between the die and the steel plate locally becomes a high temperature exceeding 200 ° C., and a part of the film is softened / decomposed to cause flaws. By adding the lubricant, the friction coefficient of the surface of the resin film is reduced and the lubricity is improved, so that the scratch resistance and the press moldability are improved.

The type of the lubricant is not particularly limited, but waxes such as polyethylene wax and paraffin wax; lubricating resins such as fluororesin and vinyl chloride resin; metallic soaps such as zinc stearate and calcium stearate; graphite and nickel. Molybdenum sulfide, boron nitride, melamine
It is recommended to use one or more solid lubricants having a cleavage property such as a cyanuric acid adduct (for example, "MCA" manufactured by Mitsubishi Petrochemical).

The content of the lubricant is 0.5 to 2 in the resin film.
It is preferably 0% by weight (solid content). When the amount of the lubricant is less than 0.5% by weight, it is not possible to sufficiently improve the lubricity and press formability of the obtained resin film.
If it exceeds 0% by weight, there is no particular problem in terms of lubrication performance, but the adhesion between the resin film obtained and the steel sheet deteriorates, and the film peels off during press working and adheres to the mold. Is not preferable because A more preferable lubricant content is 1 to 10% by weight.

Next, the inorganic colloid compound used in the present invention will be described. As the inorganic colloid compound, one or more of silica sol, alumina sol, titania sol and zirconium sol can be used. By including an inorganic colloidal compound in the resin film, it reacts with the hydrolyzable groups of the silane coupling agent to form a denser film, improving corrosion resistance and suppressing flaws in the resin film during press molding. To do.

The inorganic colloid compound is contained in the resin film in an amount of 1 to 3
It is preferable to contain 0% by weight (solid content). If it is less than 1% by weight, the corrosion resistance of the resulting coating and the scratch resistance during press molding will be insufficient, and if it exceeds 30% by weight, the inorganic colloid compound will act as a lubricant and the friction of the coating will increase. The coefficient may be increased to reduce lubricity, and as a result, the appearance after processing may be deteriorated. In particular, in order to maximize the effect of the inorganic colloid compound, it is recommended that the content be in the range of 5 to 20% by weight.

In the present invention, when a resin film comprising the above various components is provided on the surface of a steel sheet, the amount of the resin film deposited is set to 0.
It should be 1 to 1.5 g / m ² . When the amount of adhesion to the steel sheet is less than 0.1 g / m ² , the desired lubrication effect cannot be obtained, and the coating film has large flaws during press working. Also, the corrosion resistance is not sufficient. On the other hand, when the adhesion amount is more than 1.5 g / m ² , the press workability and the corrosion resistance are good, but pinholes are generated during electrodeposition coating, the appearance is deteriorated, and the adhesion of the electrodeposition coating film is deteriorated. Therefore,
In order to achieve a good balance of all properties of electrodeposition paintability, press formability, and corrosion resistance, the amount of resin film deposited is 0.1.
It was determined to be ~ 1.5 g / m ² .

The type of steel sheet used in the present invention is
There is no particular limitation. Suitably, for example, a zinc-based plated steel sheet (pure Zn plating, Zn-Ni plating, Zn-Fe plating, Zn-Cr plating, etc.) produced by a manufacturing method such as a hot dipping method, an electroplating method, and a vapor deposition plating method, Alternatively, those subjected to surface treatment such as chromate treatment may be mentioned.

Next, a method of manufacturing the resin-coated steel sheet according to the present invention will be described. Resin-coated steel sheet is a raw steel sheet (zinc-based plated steel sheet or chromate-treated zinc-based plated steel sheet) prepared by applying a coating solution containing urethane resin, lubricant, inorganic colloid compound and silane coupling agent as essential components by any coating method. It may be produced by coating the surface of the same) and drying. The coating method is not limited at all, and examples thereof include a method of coating the surface of a zinc-based plated steel sheet whose surface has been cleaned or chromated by using a roll coater method, a spray method, a curtain flow coater method, or the like. . Considering the uniformity of coating film thickness, processing cost, coating efficiency, etc., the most practically preferable method is a coating method using a roll coater. Note that the resin-coated steel sheet of the present invention includes both a steel sheet having only one surface and a resin coating formed on both surfaces thereof.

The coating liquid may be either a solution type or an emulsion type, and is a pigment, a partial cross-linking agent, or a diluting agent as long as it does not significantly change the electrodeposition coatability and press formability of a urethane resin-coated steel sheet. You may add various additives, such as a solvent, a surfactant, a defoaming agent, a penetrating agent, a film-forming auxiliary, and a thickener.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which do not limit the present invention.
Modifications and alterations that do not depart from the spirit described below are all included in the technical scope of the present invention.

Example 1 Investigation of Resin System First, a resin system was examined in order to select an optimum base resin. As a base plate for resin coating, electrogalvanized steel plate (zinc adhesion amount: 20 g / m ² ) is chromated (C
r Adhesion amount: 20 mg / m ² ) was used. On the other hand, as the base resin used in the resin film-forming composition (resin coating liquid), a urethane resin having a Shore D hardness of 51 (Superflex manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), an acrylic resin (Boncoat manufactured by Dainippon Ink and Chemicals, Inc.) ) And a polyester resin (Almatex manufactured by Mitsui Toatsu Chemicals, Inc.) were selected. Each resin coating liquid contained γ-glycidoxypropyltrimethoxysilane as a silane coupling agent:
10% by weight, polyethylene wax as lubricant: 10
% By weight, and 10% by weight of colloidal silica as an inorganic colloid compound as SiO ₂ . The resin coating liquid was well stirred and uniformly mixed and dispersed, and then applied to the surface of the original plate with a squeezing roll so that the amount of the adhered coating after drying was 1 g / m ² . This was dried at 80 ° C. to form a resin film, and a resin-coated steel plate was obtained.

The resin coated steel sheet thus obtained was divided into test materials for evaluation of dynamic friction coefficient, press performance (scratches, blackening) and corrosion resistance, and test materials for electrodeposition coating process. The electrodeposition coating conditions are as follows. Electrodeposition paint: Acrylic cation electrodeposition paint "Aqua 4800" manufactured by NOF CORPORATION Bath temperature: 28 ° C Energization time: 2 minutes Energization voltage: 160-230V Coating film thickness: 25 μm Energization method: Docan method Water washing: Water spray spray washing Baking conditions: 180 ° C x 20 minutes

After the electrodeposition coating, the appearance, adhesion and impact resistance were evaluated. Table 1 shows the performance evaluation results of the resin-coated steel sheet and the resin / electrodeposition-coated steel sheet. The measurement / evaluation methods are as follows. (1) Measurement of dynamic friction coefficient Applied pressure 1 against resin coated steel sheet using a sliding tester
Sliding was performed at 50 kg, and the dynamic friction coefficient was determined from the load. The dynamic friction coefficient was measured simultaneously on both sides, and the measurement result was displayed as an average of both sides. (2) Press Performance (Scratch, Blackening) After resin-molded steel sheet was press-molded using a single-shot press tester, scratches and blackening of the sliding surface of the molded product were evaluated.

(3) Corrosion resistance According to the method described in JIS Z 2371, the resin-coated steel sheet was subjected to a salt spray test to examine the corrosion resistance.
The measurement result shows the time when 1% of SST white rust was generated in the bare plate material. (4) Appearance of electrodeposition coating film Regarding the appearance of the coating film after electrodeposition coating, it was visually evaluated whether or not it had an orange skin appearance and whether pinholes were generated.

(5) Adhesion of coating film after electrodeposition coating-Cross-cut test After the electrodeposition coating, cross-cuts were provided on the surface of the steel plate with a cutter knife at 1 mm intervals, and a peeling test was performed using cellophane tape to confirm the coating film. The peeling condition was visually evaluated.・ Erichsen test Using the Erichsen tester, the steel plate after electrodeposition coating was tested.
After extrusion by 5 mm, the occurrence of cracks in the coating film was visually evaluated.

(6) Impact resistance test Using a DuPont impact tester, an impact test was conducted in which an impactor having a weight of 500 g and a punch diameter of 1/2 inch was dropped from a height of 300 mm. Moreover, the peeling state of the coating film after the cellophane tape was attached was evaluated.

[0031]

[Table 1]

From Table 1, it is clear that when a urethane resin is used as the base resin, it is superior to the acrylic resin and the polyester resin in the press performance, the corrosion resistance and the electrodeposition coating property.

Example 2 Examination of Addition Amount of Silane Coupling Agent Next, the addition amount of the silane coupling agent was examined. In the urethane resin coating liquid used in Example 1, polyethylene wax and colloidal silica were the same in type and amount,
The amount of the silane coupling agent (γ-glycidoxypropyltrimethoxysilane) was varied in the range of 0 to 20% by weight as shown in Table 2. Each resin coating solution was dried on a surface of the same original plate as in Example 1 by a squeezing roll so that the adhesion amount was 1
It was applied so as to be g / m ² and dried at 80 ° C. to form a resin film to obtain a resin-coated steel sheet. Electrodeposition coating was also performed under the same conditions as in Example 1, and the resin coated steel sheet and the resin / electrodeposition coated steel sheet were evaluated for performance in the same manner as in Example 1 and Table 2
The results are shown in. From Table 2, it was confirmed that when the silane coupling agent was 1.0 to 20.0% by weight, good pressing performance and electrodeposition coatability were obtained.

[0034]

[Table 2]

Example 3 Investigation of Addition Amount of Lubricant Next, the addition amount of the lubricant was examined. In the urethane resin coating liquid used in Example 1, the silane coupling agent (γ
-Glycidoxypropyltrimethoxysilane) and colloidal silica were not changed in type and amount, and the type and amount of lubricant were changed as shown in Tables 3 and 4. Each resin coating solution was applied to the same surface of the original plate as in Example 1 by a squeezing roll so that the amount of adhesion would be 1 g / m ² after drying, and dried at 80 ° C. to form a resin film. Got
Also, electrodeposition coating was performed under the same conditions as in Example 1. The obtained resin-coated steel sheet and resin / electrodeposition-coated steel sheet were evaluated for performance in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

[0036]

[Table 3]

[0037]

[Table 4]

From Tables 3 and 4, it can be seen that if the lubricant is not contained, the pressing performance tends to be poor, and if it is too large, the electrocoating property tends to deteriorate. In the examples of the present invention, excellent press characteristics and electrodeposition coatability were obtained with any lubricant.

Example 4 Examination of Addition Amount of Inorganic Colloid Compound Next, the addition amount of the inorganic colloid compound was examined. Example 1
In the urethane-based resin coating liquid used in step 1, the type and amount of the silane coupling agent and polyethylene wax were not changed, and the type and amount of the inorganic colloid compound were changed as shown in Tables 5 and 6. Each resin coating solution was dried on a surface of the same original plate as in Example 1 with a squeezing roll to have an adhesion amount of 1 g.
/ M ² and then dried at 80 ° C. to form a resin film to obtain a resin-coated steel sheet. Also, electrodeposition coating was performed under the same conditions as in Example 1. Obtained resin coated steel plate and resin
The performance of the electrodeposited coated steel sheet was evaluated in the same manner as in Example 1, and the results are shown in Tables 5 and 6.

[0040]

[Table 5]

[0041]

[Table 6]

From Tables 5 and 6, it can be seen that the press performance and the corrosion resistance are poor even when the inorganic colloid compound is not contained or when the amount is too large. In the examples of the present invention, excellent press characteristics and electrodeposition coatability were obtained with any inorganic colloid compound.

Example 5: Examination of Resin Adhesion Amount of the urethane resin coating liquid used in Example 1 on the surface of the same original plate as in Example 1 was 0.05 to 2.0 g /
It was changed to m ² and coated with a squeeze roll. 8
A resin film was formed by drying at 0 ° C to produce a resin-coated steel sheet. Electrodeposition coating under the same conditions as in Example 1 (acrylic)
Then, epoxy-based electrodeposition coating was performed under the following conditions. Example 1 of the obtained resin coated steel sheet and resin / electrodeposition coated steel sheet
The performance was evaluated in the same manner as in, and the results are shown in Table 7. Electrodeposition paint: Epoxy cation electrodeposition paint "U-100" manufactured by Nippon Paint Co., Ltd. Bath temperature: 28 ° C Energizing time: 3 minutes Energizing voltage: 250V Coating film thickness: 20 μm Energizing method: Dokan method Washing: Water spray spray washing Baking Conditions: 170 ° C x 20 minutes, rising control for 30 seconds

[0044]

[Table 7]

From Table 7, the adhesion amount of the resin film is 0.1-0.1%.
It was confirmed that the press performance and the electrodeposition coatability were compatible with each other by setting the amount to 1.5 g / m ² . In addition, the epoxy electrodeposition coating gave better results than the acrylic electrodeposition coating. On the other hand, in Comparative Example 7, the effect of the resin film was not exhibited, only the appearance after electrodeposition coating was good, and all other items were inferior. In Comparative Example 8, since the resin film was thick, there was no particular problem with epoxy-based electrodeposition coating (20 μm), but with acrylic-based electrodeposition coating (25 μm) pinholes were generated in the electrodeposition coating film, resulting in appearance and adhesion. Became worse.

[0046]

The resin-coated steel sheet of the present invention has a coating containing a urethane resin, a silane coupling agent, a lubricant and an inorganic colloid compound formed on the surface of the steel sheet. Moreover, it is possible to form an electrodeposition coating film excellent in appearance and adhesion. The resin-coated steel sheet of the present invention is also excellent in press formability, and the work environment is improved because the oiling and degreasing work during press forming and the pretreatment for electrodeposition coating (phosphate treatment, etc.) can be omitted. At the same time, it has become possible to improve productivity and reduce costs by saving processes. Since this resin-coated steel sheet also has excellent corrosion resistance, it can be used in a wide range of applications, such as being used for audio chassis without painting.

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Claims (4)

[Claims] 1. A resin-coated steel sheet coated with a resin film, wherein the resin film contains a urethane-based resin, a lubricant, an inorganic colloid compound, and a silane coupling agent in a solid content of 1.0 to 20% by weight. A resin-coated steel sheet excellent in electrodeposition coatability and press formability, characterized in that the amount of the resin film deposited is 0.1 to 1.5 g / m ² . 2. The silane coupling agent comprises a group having at least one functional group selected from the group consisting of (meth) acryloyl group, vinyl group, amino group and epoxy group, and Si.
1 of compounds having 3 alkoxy groups directly bonded to atoms
The resin-coated steel sheet according to claim 1, which is one kind or two or more kinds. 3. A lubricant in a resin film, in terms of solid content, of 0.1.
The resin-coated steel sheet according to claim 1 or 2, containing 5 to 20% by weight. 4. The resin-coated steel sheet according to claim 1, wherein the resin coating contains the inorganic colloid compound in an amount of 1 to 30% by weight in terms of solid content.