JPH0796576A - Organic-coated steel plate superior in press molding, continuous welding, and conductive properties - Google Patents

Abstract

PURPOSE:To provide a steel plate coated with antireflection resin, which is improved in compression moldability, spot-weldability and conductivity. CONSTITUTION:An organic-coated steel plate has chromate films on both surfaces of a zinc-or zinc alloy-plated steel plate, and thermosetting resin composition layer on the chromate film. The resin composition contains a resin, a curing agent, a lubricant, and a silica as essential components. The resin in the composition is prepared by blending a polyol having a glass transition temperature from -30 deg.C to below 30 deg.C with a polyol having a Tg from 30 to and including 90 deg.C in a solid content ratio of 10/90-90/10 by weight is used as the resin contained in the thermosetting resin composition layer. The coating weight of the resin composition layer on each surface is 0.1-1.0g/m<2> in a dried state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organically coated surface-treated steel sheet used for automobiles, home appliances, building products, etc., which is excellent in press formability, continuous weldability and electrical conductivity, and a lubricated steel sheet.

[0002]

2. Description of the Related Art Steel sheets used for automobiles, home appliances, building products, etc., especially plated steel sheets such as zinc or zinc-based alloy plated steel sheets, are used unpainted or painted. On the street, and in the meantime, it is left unpainted for a very long time. Therefore, there are problems that rust is generated during that period, and various substances are adsorbed and adhered to the surface of the plated steel sheet, which deteriorates the adhesion of the paint.

Therefore, a chromate treatment is performed as a primary rust preventive treatment until the plated steel sheet is used by a consumer. However, the corrosion resistance of this chromate treatment is generally
It takes about 24 to 48 hours at most in the salt spray test, and 100 to 20 in the salt spray test even with the coating type chromate treatment which is a special chromate treatment containing silica sol.
Only 0 hours of corrosion resistance can be obtained. Therefore, products that are used in a severely corrosive environment for a long time have insufficient corrosion resistance.

Considering the case where the product is used in a severely corrosive environment, there is a method of preventing corrosion by applying a phosphate treatment instead of the chromate treatment and then applying a coating of about 20 μm thickness. However, when such a thick coating is applied, when the steel sheet is subjected to press working or the like, peeling or cracking of the coating film occurs, and local corrosion resistance is reduced at that portion. Also, with painted boards, spot welding, grounding, etc.
The weld requires pre-removal of the coating because the performance associated with conductivity is reduced or otherwise impractical. Further, there is a problem that the thicker the coating film, the more paint is consumed, resulting in an increase in cost. Therefore, it is desired to develop a surface-treated steel sheet having excellent corrosion resistance by itself without using a paint.

When press-forming a steel sheet,
Lubricating oil is applied to the surface of the steel sheet, but since this work involves a degreasing step, it is desired to develop a surface-treated steel sheet that can be pressed without using lubricating oil or the like at the time of working.

On the other hand, the thin film type resin steel plate may require grounding when used for electronic and electric appliances for household appliances. When it is used as a steel plate for automobiles or a part of steel plates for home appliances, spot weldability and electrodeposition coatability may be required, and in any case conductivity may be required.

[0007] Against this background, the following is disclosed as a prior art. (1) A urethane-modified epoxy resin having a chromate coating on a zinc-based plated steel sheet, which further contains a composite aluminum phosphate, a chromium-based rust preventive pigment, and a polyolefin wax, molybdenum disulfide, or silicone as a lubricant. A two-layer chromate-treated steel sheet having excellent corrosion resistance and lubricity (Japanese Patent Publication No. 62-24505) characterized by having 1 to 10 g / m ^{2 of} layers.

(2) Chromate coating is provided on a zinc-plated steel sheet, and a urethane-containing epoxy ester resin layer containing silica powder, hydrophilic polyamide resin and polyethylene wax as a lubricant is further formed thereon in a thickness of 0.3 to 5 μm. An organic composite steel sheet excellent in cation electrodeposition coating property (Japanese Patent Laid-Open No. 63-35798).

(3) By containing a conductive substance (carbon black, graphite, metal powder, semiconductor oxide, iron phosphide) in the resin, the electric resistance of the resin film is lowered, and a lubricant (polyethylene wax, A fatty acid amide type, metal soap, metal sulfide, black fluoride, boron nitride, grease, alkali metal sulfate, etc. are contained to obtain a weldable rust-preventive lubricity coating forming composition ( JP-A-63-83172).

[0010]

The above-mentioned prior art has the following problems. In (1), excellent corrosion resistance is exhibited due to the effects of the composite aluminum phosphate, the chromium-based rust preventive pigment, and the urethane-modified epoxy resin, and the excellent press moldability due to the effects of molybdenum disulfide, silicone, and the urethane-modified epoxy resin. Is expressed.
However, when the adhesion amount is 1 to 10 g / m ² , the electric resistance of the coating film is high, and it is difficult to improve the conductivity, grounding property, and spot weldability.

In (2), by adding the hydrophilic polyamide resin to the resin, the electrodeposition resin solution permeates into the resin of the steel plate during electrodeposition coating, and the electric resistance of the coating film of the resin steel plate is lowered. Therefore, the electrodeposition coatability is improved. However, with this method, the electrical conductivity of the resin steel sheet in a normal state cannot be increased, and the groundability and spot weldability are not improved.

Further, in (3), since the inorganic pigment is used as the conductive pigment, the particle diameter of the pigment is large, and the resin film thickness is generally inevitably large. The powdering property is generally poor. Also,
The groundability and spot weldability do not improve as expected.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a lubricating resin-treated steel sheet having excellent press formability, spot weldability and conductivity.

[0014]

[Means for Solving the Problems] As seen in the above-mentioned prior art, by improving the corrosion resistance and lubricity of zinc or zinc-based plated steel sheet by forming a lubricating resin-based coating after chromate treatment on the steel sheet surface. Can be made.

The inventors of the present invention have diligently studied organic resin coatings having good lubricity even under high-speed press molding while taking advantage of the advantages of these prior arts. As a result, resins, curing agents, lubricants,
When a film having silica as a basic skeleton is formed, if the resin is a blend of two kinds of polymers having different glass transition temperatures (Tg) and the curing agent is reactively cured with the resin, lubricity under high speed press molding is obtained. To improve the performance related to electrical conductivity such as earthing property, spot weldability, and conductivity by improving the resin composition and controlling the amount of the resin composition deposited in the range of 0.1 to 1.0 g / m ^2. The inventors have found that the above can be achieved and have reached the present invention.

That is, according to the present invention, a thermosetting resin composition having a chromate film on both surfaces of a zinc or zinc-based alloy plated steel sheet and further having a resin, a curing agent, a lubricant and silica as essential components on the upper layer thereof. In an organic coated steel sheet having a layer, the resin in the thermosetting resin composition layer has a temperature of −30 ° C.
The polyol having a glass transition temperature (hereinafter abbreviated as Tg) of 30 ° C. or more and less than 30 ° C. and the polyol having a Tg of 30 ° C. or more and 90 ° C. or less in solid content weight ratio are 10/90 to 90/10.
Blended in the range of 0.1 to 1.0 g / m ² in terms of dry weight per side of the resin composition layer, press formability, continuous weldability,
It is intended to provide an organic coated steel sheet having excellent conductivity.

In the present invention, the polyol is preferably at least one selected from the group consisting of polyester polyols, urethane polyols, and acrylic polyols, and the curing agent is various amine compounds, amino resins, and isocyanates. The lubricant is preferably at least one selected from the group consisting of compounds, the lubricant is preferably polyethylene wax having a melting point of 70 ° C. or higher and 130 ° C. or lower, and the amount of the chromate coating attached is one side in terms of metallic chromium. 5-30mg per
/ M ² is preferred.

The polyester polyol, urethane polyol and acrylic polyol in the present invention are
Means having two or more OH groups in polyester resin, urethane resin, and acrylic resin, respectively, and COOH
It may have other functional groups such as groups.

[0019]

The following is a detailed description of the lubricating resin-treated steel sheet of the present invention, which is excellent in press formability, continuous weld spotting property and conductivity. Examples of the material of the lubricating resin-treated steel sheet targeted by the present invention include various galvanized steel sheets such as electrogalvanized steel sheet, electrogalvanized-nickel plated steel sheet, hot-dip galvanized steel sheet, 5% aluminum-zinc hot-dip galvanized steel sheet. You can

The chromate coating on the zinc or zinc-based plated steel sheet may be a known ordinary coating, for example, an aqueous solution containing chromic anhydride, chromate salt, dichromic acid or the like as a main component, or a colloidal solution of the above aqueous solution. This is a coating film mainly composed of a hydrated chromium oxide obtained by treating a zinc or zinc-based plated steel sheet with a treatment liquid mixed with silica or the like by a known ordinary method.

The amount of deposited chromium is preferably 5 to 30 mg / m ^{2 on} one side in terms of metallic chromium, and the reason is as follows. That is, when the amount is less than 5 mg / m ² , not only the adhesiveness between the steel sheet surface and the resin is insufficient and the press formability is lowered, but also the corrosion resistance is insufficient. Also, 30 mg
If it exceeds / m ² , the electric resistance of the coating film increases, and the performance related to energization, such as continuous welding point property, conductivity, and grounding property, deteriorates.

The combination of the resin and the curing agent in the thermosetting composition provided on the upper layer of the chromate is a polyol resin, particularly at least one resin selected from polyester polyol, urethane polyol and acrylic polyol, and various amine compounds and amino resins. And a combination of at least one of the isocyanate compounds are preferable. In addition, the polyester polyol, urethane polyol, and acrylic polyol in the present invention refer to two or more O in a polyester resin, a urethane resin, and an acrylic resin, respectively.
It means a substance having an H group, and may have other functional groups such as a COOH group.

As for the resin, since a relatively wide range of low Tg resin and high Tg resin are blended as shown below, it is a general-purpose resin whose Tg can be easily changed and which has a hydroxyl group capable of reacting with the other at the terminal or branch. The reason for selection is that the curing agent has reactivity with the above resin, and the coil coating cures under conditions such that the final reached plate temperature is 150 to 250 ° C. for 20 to 60 seconds. It is preferable that it can be obtained. Further, the compounding amount of the curing agent is preferably 1 to 40 parts by weight based on 100 parts by weight (solid content) of the low Tg resin and the high Tg resin.

Further, the above resins are those having a Tg of −30 ° C. or more and less than 30 ° C. and those having a Tg of 30 ° C. or more and 90 ° C. or less, and the blending ratio thereof is 10/90 by weight.
The reason for the range of 90/10 will be described.

When press molding is continuously performed at a high speed, the temperature of the mold gradually rises. When a resin coating film having a low Tg is used, the initial press moldability is excellent, but the performance is not sustained. . When a resin coating film having a high Tg is used, initial press cracking occurs, but the molding height (molding height up to cracking) increases while press molding continues, and finally molding becomes possible. That is, when the sample temperature during press molding is in the transition region near Tg of the resin coating film, the press moldability is good. Considering that the product temperature rises from room temperature to around 120 ° C. in continuous press molding, the resin transition region must be wide in order to provide excellent moldability from the initial stage of pressing. Achieving only with one type of resin is insufficient. Therefore, it was considered that blending resins having different Tg can improve high-speed, continuous press moldability.

The continuous press formability refers to the press formability in a state where the die has accumulated heat at about 120 ° C. when continuously (about 500 pieces or more) is pressed by high speed press forming. .

Usually, in the case of a single resin, the transition region is Tg ± 30 ° C.
, And good press moldability is secured in this range. Therefore, in order to secure a good press moldability in this range with the pressing temperature set to 0 to 120 ° C., the Tg of the low Tg resin is −30 ° C. or higher and lower than 30 ° C., and the Tg of the high Tg resin is Tg.
Was set to 30 ° C. or higher and 90 ° C. or lower. That is, low Tg
When the Tg of the resin is less than -30 ° C, the coating film becomes extremely soft at high temperatures, and metal contact with the mold is likely to occur during continuous press molding. Similarly, if the Tg is 30 ° C. or higher, it becomes hard at a low temperature and cracks occur in the initial stage of pressing. On the other hand, if the Tg of the high Tg resin is less than 30 ° C., the coating film becomes extremely soft at high temperature and easily causes metal contact, and if the Tg is more than 90 ° C., it becomes hard at low temperature and both are pressed. This is because it leads to defects. Further, regarding the blending ratio, if the low Tg resin and the high Tg resin are not contained at least 10%, the effect of expanding the transition region becomes small.

Examples of the lubricant include polyolefin waxes made of polymers of olefinic hydrocarbons such as polyethylene, polypropylene and polybutene, polytetrafluoroethylene resins, polyvinyl fluoride resins, polyvinylidene fluoride resins and polyfluoroethylene resins. Fluorine-based resins may be mentioned, and one of these may be used alone, or two or more thereof may be mixed and used. As the lubricant, polyolefin wax is preferable, and polyethylene wax is more preferable. The lubricant content is low Tg.
The total amount of the resin and the high Tg resin is 100 parts by weight (solid content), and preferably 1 to 40 parts by weight.

Polyethylene waxes having various melting points are known, but those having a melting point of 70 ° C. or higher and 130 ° C. or lower are particularly preferably used. Higher than 70 ° C,
The melt viscosity under continuous press molding becomes too low, the lubricating effect is small, and the press moldability is poor. On the other hand, if it is higher than 130 ° C., the melt viscosity becomes high, the melt does not melt sufficiently, the lubricating effect is small, and the press formability is poor.

Silica is added to improve the corrosion resistance of the lubricating resin-treated steel sheet. Colloidal silica, such as Snowtex-O and Snowtex-N (both manufactured by Nissan Chemical Co., Ltd.), organosilica sol, For example, ethyl cellosolve silica sol (manufactured by Nissan Chemical Co., Ltd.) or the like, silica powder, for example, vapor phase silica powder (manufactured by Aerosil Co., Ltd.), or the like, organic silicate, for example, ethyl silicate or the like may be used. The particle size of silica powder is 5 to 70 n
It is preferably m. Silica content is low Tg
The amount of the resin and the high Tg resin is preferably 10 to 80 parts by weight based on 100 parts by weight (solid content weight).

A silane coupling agent may be used as a reaction accelerator for the base resin and silica. Examples of the silane coupling agent include γ- (2-aminoethyl) aminopropyltrimethoxysilane and γ-glycidoxypropyltrimethoxysilane.

It is possible, and preferable, to add general additives such as a reaction accelerator, a stabilizer, and a dispersant to the base resin as long as they do not impair the gist of the present invention.

Further, the amount of such a lubricating coating deposited is preferably 0.1 to 1.0 g / m ² in dry weight per one side. When the adhesion amount is less than 0.1 g / m ² , the unevenness on the surface of the steel sheet cannot be completely filled, and the effect of improving press formability is small. ^{On the other hand} , when it exceeds 1.0 g / m ² , the press formability is improved, but the performance related to energization such as continuous welding point property, conductivity, and grounding property is remarkably reduced.

Next, a brief description will be made on a method for producing a lubricating resin-treated steel sheet having excellent corrosion resistance according to the present invention. Examples of the material of the lubricating resin treated steel sheet targeted by the present invention include various galvanized steel sheets such as electrogalvanized steel sheet, electrogalvanized-nickel plated steel sheet, hot-dip galvanized steel sheet, 5% aluminum-zinc hot-dip galvanized steel sheet. be able to.

In producing the lubricating resin-treated steel sheet having excellent formability according to the present invention, the chromate treatment applied to the plated steel sheet may be carried out according to a known ordinary treatment method, for example, chromic anhydride, chromate salt, heavy metal salt. Immersion chromate treatment, electrolytic chromate treatment may be performed in an aqueous solution containing chromic acid as a main component, and a coating type chromate treatment for applying a treatment liquid obtained by mixing colloidal silica or the like to the above aqueous solution onto a plated steel sheet is performed. Thus, a coating film mainly composed of chromium hydrate may be formed. After treating the plated steel sheet with a chromate treatment liquid, a chromate film is formed on both sides of the steel sheet through a step of squeezing with a flat rubber roll or the like and a drying step such as hot air drying.

Subsequently, an organic resin film made of the above resin composition is formed on the chromate film as follows. Prepare a prescribed amount of each compounding ingredient and mix them.
The resin composition is dispersed to form a physically uniform resin composition. The resin composition is applied by a known ordinary method such as roll coating, spray coating, dip coating, and brush coating so as to have a predetermined thickness, and usually dried at 50 to 180 ° C. for usually 3 to 90 seconds, Allow the coating to dry and cure. In this way
A lubricating resin-treated steel sheet having excellent press formability, continuous welding spotting property, and conductivity according to the present invention is produced.

[0037]

EXAMPLES Next, the present invention will be described more specifically based on examples. The glass transition temperature (Tg) of the resin is a value measured by the DSC method. (Example) Under the following conditions, the test piece No. of the lubricating resin-treated steel sheet of the present invention was obtained. 1 to 13, and No. 1 as a comparative material. 14
~ 22 was created.

(1) Kind of plated steel sheet A. Electrogalvanized steel sheet Thickness 0.8 mm Zinc coating amount 20 g / m ² B. Electrolytic zinc-nickel plated steel sheet 0.8 mm thickness Zinc-nickel plating adhesion amount 20 g / m ² Nickel content 12% C.I. Hot-dip galvanized steel sheet Thickness 0.8mm Zinc coating amount 60g / m ²

(2) Chromate A chromate treatment liquid having a composition of 20 g / l of CrO _{3 and 4} g / l of Na ₃ AlF ₆ .

(3) Resin Polyurethane polyol resin (manufactured by Toyobo Co., Ltd.) Product name UR1400 Number average molecular weight 40,000 Tg 83 ° C UR3200 Number average molecular weight 40,000 Tg -3 ° C UR3400 Number average molecular weight 35,000 Tg -33 ° C UR1200 number average molecular weight 15,000 Tg 59 ° C UR2300 number average molecular weight 32,000 Tg 18 ° C

(4) Curing agent Isocyanate compound (Nippon Polyurethane Industry Co., Ltd.)
Product name: Coronate 2513

(5) Polyethylene wax (Mitsui Petrochemical Industry Co., Ltd.) Trade name Mitsui High Wax 210P Melting point * 114 ° C. Melt viscosity at 140 ° C. 80 cps Number average molecular weight 2,000 * Brookfield viscometer

(6) Silica sol (Nippon Aerosil Co., Ltd.)
Product name: AEROSIL200 Average particle size 20nm

Both sides of the plated steel sheet shown in (1) are degreased with an alkali, and then the chromate treatment solution shown in (2) is applied onto the zinc or zinc alloy plated steel sheet by a roll coating method, followed by heating, After drying, a chromate film having a predetermined thickness in terms of metal chromium was formed. further,
A paint prepared by blending the paint constituents (3) to (6) in the ratios shown in Table 1 was applied onto the chromate film formed on both surfaces of the plated steel sheet by a roll coating method. Then, in the hot air drying oven, the reached plate temperature after 60 seconds was 200.
The resin coating film having a predetermined thickness was formed by heating under the condition that the temperature became ℃.

Each of the above-described steel sheet of the present invention and the comparative steel sheet was evaluated for press formability, continuous weld spotting property, and conductivity by the performance test described below. The evaluation results are shown in Table 2.

(Test / Evaluation Method) (1) High Speed Press Formability An oilless test piece was processed by an Erichsen cup drawing tester while changing the drawing ratio, and the limiting drawing ratio was determined. Further, the powdering property at that time was evaluated from the degree of the peeling powder adhering to the die, which was collected with cellophane tape. Press conditions ・ Wrinkle pressing pressure 2 tons ・ Punch diameter 33 mmΦ ・ Blank diameter 59 to 79 mmΦ ・ Drawing speed 500 mm / s Evaluation standard ◎: No die adhered ○: Die adhered slightly △: Die adhered somewhat ×: Die adhered a lot

(2) High-speed continuous press moldability Continuous press molding was carried out under the same conditions as in (1), and evaluation was made by the number immediately before cracking and the number by which the appearance was evaluated as x.

(3) Testing method for continuous spotting property during welding A single-phase AC spot welding machine was used. Welding conditions are RWMA
Refer to, use CF type 5mmΦ electrode, pressurize 190k
gf, current value at 13 cycles of energizing time, nugget diameter 5√
It was set so as to fall within the range from t to the occurrence of dust. The evaluation was performed based on the shear peel strength and the nugget diameter, and the limit number of continuous hit points was set until the nugget diameter of 4√t could not be obtained.

(4) Conductivity test method The surface resistance of the steel sheet was measured using a surface resistance measuring device manufactured by Mitsubishi Petrochemical Co., Ltd., Lorester (between electrode terminals: 10 mm, electrode terminal diameter: 2 mm).

As is clear from Table 2, the organic coated steel sheet of the present invention is excellent in high-speed press formability, high speed, continuous press formability, and excellent continuous spotting property during welding.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

EFFECTS OF THE INVENTION According to the present invention, since the lubricity at the time of high-speed continuous press molding is good, it is possible to perform press working as it is without using lubricating oil such as press oil during press working, and There is an effect that it is possible to provide an organic coated steel sheet having excellent weldability and conductivity and a method for producing the same. Furthermore, in order to improve the lubricity during press working, it is possible to omit the lubricating oil application work and the degreasing treatment which have been conventionally performed by the customer. Therefore, there is an effect that the cost can be reduced. Since it retains its properties, it has the effect of enabling spot welding.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Okuno Keizo 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Division (72) Inventor Yoshihiro Nase Chuo-ku, Chiba-shi, Chiba Kawasaki Town No. 1 Kawasaki Steel Corporation Technical Research Division

Claims (5)

[Claims] 1. An organic material having a chromate film on both surfaces of a zinc or zinc-based alloy plated steel sheet, and a thermosetting resin composition layer containing a resin, a curing agent, a lubricant and silica as essential components on the chromate film. In the coated steel sheet, as a resin in the thermosetting resin composition layer, a polyol having a glass transition temperature of -30 ° C or higher and lower than 30 ° C (hereinafter abbreviated as Tg) and a polyol having a Tg of 30 ° C or higher and 90 ° C or lower are solid. It is characterized by using a blend in a weight-weight ratio of 10/90 to 90/10, and the amount of the resin composition layer attached is 0.1 to 1.0 g / m ² in terms of dry weight per side. , Organically coated steel sheet with excellent press formability, continuous welding point and conductivity. 2. The organic material excellent in press formability, continuous welding point property, and conductivity according to claim 1, wherein the polyol is at least one selected from the group consisting of polyester polyol, urethane polyol, and acrylic polyol. Coated steel sheet. 3. The press moldability, continuous weldability, and conductivity according to claim 1 or 2, wherein the curing agent is at least one selected from the group consisting of various amine compounds, amino resins, and isocyanate compounds. Excellent organic coated steel sheet. 4. The lubricant is a polyethylene wax having a melting point of 70 ° C. or higher and 130 ° C. or lower.
2. An organic coated steel sheet excellent in press formability, continuous welding point property, and conductivity according to any one of 1. 5. The press coatability, continuous welding point property, and conductivity according to claim 1, wherein the amount of the chromate coating adhered is 5 to 30 mg / m ^{2 on} one side in terms of metal chromium. Organic coated steel sheet.