JPH05147154A - Organic composite coated steel sheet with excellent front and back discrimination - Google Patents

Abstract

(57) [Summary] [Purpose] Not only is it excellent in press workability, cationic electrodeposition paintability, spot weldability, corrosion resistance, etc., but also powdering resistance, slidability, chromium elution resistance, secondary water resistance. (EN) Provided is an organic composite-coated steel sheet which is free from deterioration in adhesiveness and the like, and which does not contaminate a degreasing liquid by elution of a coloring pigment during degreasing with alkali, and which has excellent front and back distinguishability. [Composition] An organic composite-coated steel sheet having a chromate film on both surfaces of a zinc or zinc alloy plated steel sheet, and having a resin layer mainly composed of silica and an organic polymer resin on the upper layer of the chromate film. At least one kind of condensed polycyclic pigment is mixed in the resin layer on one side of the steel sheet in an amount of 1 to 10% by weight per one side, and the color tone of the resin layer is different between the front and back sides of the steel sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an organic composite coated steel sheet which is excellent in press workability, cationic electrodeposition coating property, spot weldability, corrosion resistance and the like, and which is excellent in front and back distinguishability as a steel sheet for automobile bodies.

[0002]

2. Description of the Related Art In response to the strong social demand for higher corrosion resistance of automobile bodies, the application of surface-treated steel sheets having zinc or zinc-based alloy plating on the surface of cold-rolled steel sheets has been expanding in recent years. ..

Examples of these surface-treated steel sheets include hot-dip galvanized steel sheets, galvannealed steel sheets, electrogalvanized steel sheets, and electrogalvanized alloy-plated steel sheets. However, even higher corrosion resistance has been required in the bag structure portion and the bending portion (hemming portion) of the inner plate of the vehicle body where the coating performed after the vehicle body assembly is not sufficiently spread. Steel sheets for automobiles that are suitable for such applications are disclosed in, for example, Japanese Patent Laid-Open Nos. 57-108292 and 58-2241.
No. 74 and Japanese Patent Laid-Open No. 63-22637 propose an organic composite-coated steel sheet in which a chromate and an organic polymer resin layer are applied on a zinc or zinc-based alloy plated steel sheet. Many proposals have been made even today regarding the improvement of press workability, cationic electrodeposition coatability, spot weldability, corrosion resistance, and the like of these organic composite-coated steel sheets.

Up to now, most of the organic composite coated steel sheets have had chromate and organic polymer only on the inner surface of the steel sheet when used as a vehicle body outer plate, even if both surfaces of the steel sheet are plated with zinc and a zinc alloy. Although a resin layer has been applied, the present inventors have proposed in Japanese Patent Application No. 2-133541 a method of improving the corrosion resistance by applying an organic composite coating also on the outer surface of the vehicle body.

By the way, in a processing and assembly line of an automobile manufacturing plant, a surface-treated steel sheet such as an organic composite coated steel sheet, a cold-rolled steel sheet, or even a surface-treated steel sheet having a different coating weight is used depending on the use site or destination. It is normal to use a mixture of these. Therefore, using the steel sheet as designed without confusion leads to important quality control. For this purpose, the use of a photoelectric sensor utilizing the difference in light reflection intensity between a cold-rolled steel sheet and a surface-treated steel sheet such as an organic composite coated steel sheet has been put into practical use as an automatic identification means. If only two types of steel plates having different light reflection intensities are mixed, the purpose can be achieved by using a relatively inexpensive photoelectric sensor. However, in the case where only the coating weight is different in the same type of surface-treated steel sheet, the light reflection intensity does not change, so
The above method cannot be applied.

Further, as described above, when the double-sided organic composite coated steel sheets having different adhesion amounts on the front and back are used as the vehicle body outer plate, or the organic composite coated steel sheets having different coating weights on the front and back are used, the front and back of the steel sheet are misused Doing becomes a big problem.

Therefore, it is proposed in JP-A-2-214653 to provide a color difference between the front and back surfaces of a steel sheet by chromate-treating a zinc-based plated steel sheet and providing a resin film having a coloring pigment added on at least one side thereof. Has been done.
However, in the above-mentioned publication, inorganic pigments such as iron oxide yellow specifically disclosed as a pigment to be added to provide a color difference, and phthalocyanine-based organic pigments have heat resistance, alkali resistance, acid resistance, solvent resistance, and water resistance. However, not all of the performances such as coloring power that a steel sheet for an automobile should have at the same time are satisfied.

[0008]

The present invention has been made to solve these problems in the prior art. For example, if there is a difference in color tone of the organic composite coated steel sheet due to the difference in the type of plating, the difference in coating weight, the difference in the amount of resin on the front and back surfaces, etc., it will be possible to automatically identify using a color sensor. .. Further, even when a person discriminates, there is an advantage that it is possible to prevent confusion such as an error in the applied steel sheet due to a clear difference in color tone. Further, it also sufficiently satisfies various performances required for a steel sheet for automobiles.

From the above viewpoint, the present invention is mainly aimed at giving a color tone to the organic composite coated steel sheet, but as an organic composite coated steel sheet as a steel sheet for automobile bodies, press workability, cationic electrodeposition coating In addition to excellent properties, spot weldability, corrosion resistance, etc., even if a coloring pigment is added, there is no deterioration in powdering resistance, slidability, chromium elution resistance, water secondary adhesion, etc. Another object of the present invention is to provide an organic composite-coated steel sheet which is excellent in front and back distinctiveness, in which a coloring pigment is not eluted during alkali degreasing to contaminate the degreasing liquid.

[0010]

In order to achieve the above object, according to the present invention, a zinc or zinc-based alloy-plated steel sheet has a chromate film on both surfaces, and silica and An organic composite-coated steel sheet having a resin layer formed by blending an organic polymer resin, wherein 1 to 10% by weight of one or more condensed polycyclic pigments is blended per one side in at least the resin layer on one side of the steel sheet, Provided is an organic composite-coated steel sheet excellent in front and back distinctiveness, characterized in that the color tone of the resin layer is different between the front and back of the steel sheet.

It is preferable to use quinacridone red and / or quinophthalone yellow as the condensed polycyclic pigment.

As the silica constituting the resin layer, it is preferable to use an organic solvent-dispersed silica sol having cohesive properties or hydrophobic fumed silica.

The dry weight ratio of silica to organic resin in the resin layer is 10 to 100 parts by weight of the silica.
It is preferably 100 parts by weight.

The present invention will be described in more detail below. Book
In the invention, the material is zinc or zinc-based alloy plating.
Use a steel plate. As the type of plating applied to steel sheets
Is pure Zn plating, Zn-Ni alloy plating, Zn-Fe
Binary alloys such as alloy plating and Zn-Cr alloy plating
Plating, Zn-Ni-Cr alloy plating, Zn-Co-Cr
It is possible to use ternary alloy plating such as alloy plating
Yes, and Zn-SiO₂Plating, Zn-Co-Cr-
Al₂O ₃It is also possible to use composite dispersion plating such as plating.
it can. These plating methods are electroplating and hot dipping
Method or vapor-phase plating method.

Chromate treatment is performed on these zinc or zinc alloy plated steel sheets in order to improve the adhesion with the resin layer described later and to impart high corrosion resistance. The chromate deposition amount 5 to 500 mg / m ² of Cr terms, preferably in the range of 10-150 mg / m ^2. Such chromate treatment may be carried out by any of a coating type chromate method using a roll coater, an electrolytic chromate method, a reactive chromate method and the like.

On the upper layer of such a chromate film, a composite film made of silica and an organic polymer resin is applied. The organic polymer resin used in the present invention is not particularly limited, but an epoxy resin, an acrylic resin, a polyethylene resin, an alkyd resin, a urethane resin, or the like can be exemplified, and particularly, JP-A-2-258335 and JP-A-3-25835. From the viewpoint of toughness and corrosion resistance, it is more preferable to use a resin composition based on an epichlorohydrin-bisphenol A type epoxy resin having a number average molecular weight of 2000 or more proposed in JP-A-130141.

Next, the condensed polycyclic pigment will be described.
Color pigments are roughly classified into inorganic pigments and organic pigments. Inorganic pigments generally have a large particle size and inferior coloring power, so a large amount of pigment must be added for coloring. Since the film thickness of the thin film type organic composite coated steel sheet aimed at by the present invention is usually 2 μm or less, if the average particle diameter of the pigment exceeds this, there is a problem that powdering resistance and press workability are deteriorated.

On the other hand, since the organic pigment has a smaller particle size and a larger coloring power than the inorganic pigment, it can be colored in a small amount and is advantageous in powdering resistance and press workability. However, azo pigments that are widely used as organic pigments have poor heat resistance, as can be inferred from their chemical structure,
When the resin layer is used for baking at a high temperature of about 160 ° C. as in the present invention, stable identification by a color sensor becomes difficult. Further, the lake pigment is inferior in water resistance and alkali resistance, and when it is used for an application in which alkaline degreasing or the like is performed, decolorization of a steel sheet and elution of the pigment into a degreasing liquid occur, which is also not suitable.

As described above, the performance of the organic pigment varies greatly depending on the chemical structure. The organic pigment used in the present invention is required to have excellent heat resistance, alkali resistance, acid resistance, solvent resistance, water resistance, tinting strength and the like from the purpose of use, and a condensed polycyclic pigment is suitable for this purpose. Applied to. Fused polycyclic pigments have very good performance because of their high electron density and chemical stabilization due to the presence of highly conjugated π-electron systems. Therefore, examples of condensed polycyclic pigments include quinacridone pigments, quinophthalone pigments, anthraquinone pigments, perylene pigments, perinone pigments, isoindolinone pigments, dioxazine pigments, and thioindigo pigments.
A pigment having a hue suitable for the purpose can be selected from these. For example, quinacridone red or the like can be used as the pigment having red distinguishability, and quinophthalone yellow or the like can be used as the pigment having yellow distinguishability.

Description will be made based on concrete experimental facts. Zn-Ni alloy plating (12 wt% Ni) with a basis weight of 20 g / m ² was applied on a low carbon steel plate, and then 50 mg / m of coating type chromate with a Cr ⁶⁺ ratio of 50% was applied using a roll coater.
² (Cr equivalent) was applied and baked at a maximum plate temperature of 130 ° C. Next, from 9% by weight of an epoxy resin having a number average molecular weight of 3750 (Epicoat 1009 manufactured by Shell Chemical Co., Ltd.) and 6% by weight of silica sol dispersed in ethyl cellosolve (average primary particle diameter 10 nm, average aggregate particle diameter 0.4 μm). The resulting coating composition was applied by a roll coater so that the dry weight was 0.7 g / m ² , baked at the maximum plate temperature of 160 ° C., and immediately cooled with water and dried. At this time, the added amount of quinacridone red in the paint is 0 to 0 as the dry weight ratio in the resin layer.
It was changed to 15% by weight.

FIG. 1 shows the results of evaluation of the red color distinguishability of the organic composite coated steel sheet thus produced using a color sensor HCS1080 manufactured by HOYA-SCHOTT. When the blended amount of quinacridone red in the resin layer was 1% by weight or more, the output value required for red color discrimination could be obtained. This is the reason why the lower limit of the amount of the red pigment quinacridone red compounded in the resin layer is set to 1% by weight. From this viewpoint, the higher the blended amount, the higher the output value, but the blended amount of quinacridone red is 10% by weight.
When it exceeded, deterioration in adhesion to the electrodeposition paint was confirmed, so this was made the upper limit.

Zn-N having a basis weight of 20 g / m ² on a low carbon steel plate
i alloy plating (12 wt% Ni) is applied, then 50 mg / m ² (Cr conversion) of a coating type chromate with a Cr ⁶⁺ ratio of 50% is coated using a roll coater, and the maximum attainable plate temperature is 130 ° C.
Burned in. Next, from 9% by weight of an epoxy resin having a number average molecular weight of 3750 (Epicoat 1009 manufactured by Shell Chemical Co., Ltd.) and 6% by weight of silica sol dispersed in ethyl cellosolve (average primary particle diameter 10 nm, average aggregate particle diameter 0.4 μm). The resulting coating composition was applied by a roll coater so that the dry weight was 0.7 g / m ² , baked at the maximum plate temperature of 160 ° C., and immediately cooled with water and dried. At this time, the amount of yellow pigment quinophthalone yellow added in the paint was changed to 0 to 15% by weight as a dry weight ratio in the resin layer.

FIG. 2 shows the results of evaluation of the yellow color distinguishability of the organic composite-coated steel sheet thus produced using the color sensor HCS1080 manufactured by HOYA-SCHOTT.

When the compounding amount of quinophthalone yellow in the resin layer was 1% by weight or more, the output value required for yellow discrimination could be obtained. This is the reason why the lower limit of the compounding amount of the coloring pigment quinophthalone yellow in the resin layer is set to 1% by weight. From this point of view, the larger the blending amount, the higher the output value, but when the blending amount of quinophthalone yellow exceeds 10% by weight, deterioration in the adhesiveness with the electrodeposition coating material was confirmed, so this was made the upper limit. It should be noted that the condensed polycyclic pigments other than the quinacridone red and the quinophthalone yellow are preferably mixed in an amount of 1 to 10% by weight for the same reason.

In the above-mentioned example, the organic solvent-dispersed silica sol having cohesive property was used as the silica constituting the resin layer. As silica in the coating material, silica sol which has no cohesive property and is uniformly dispersed in ethyl cellosolve (average primary particle diameter 10 n
The result of the same experiment using m) was also plotted in FIG. 1, but the output value was significantly reduced. Even in this case, when observed with the naked eye, a clear red color tone was recognized, but it was difficult to detect with a color sensor. When the cause of this was examined, when the uniformly dispersed silica sol was used, the glossiness of the resin layer surface was high, so the specular reflection light from the resin layer surface reflected light from the chromate layer (the light transmitted through the resin layer was signaled. It was found that it is difficult to detect information regarding the color tone inside the resin layer.

When an organic solvent-dispersed silica sol having a cohesive property is used as the silica constituting the resin layer, the glossiness of the resin layer surface is low and the specular reflection light from the resin layer surface is weak. The reflected light from the chromate layer containing the transmitted light as a signal becomes relatively strong, and the information regarding the color tone inside the resin layer can be easily detected.

For the same purpose, when hydrophobic fumed silica was used as the silica constituting the resin layer, aggregation in the resin layer was clearly observed, and a cohesive organic solvent-dispersed silica sol was used. It was possible to detect almost the same signal as in the case.

The dry weight ratio of the organic resin and silica in the resin layer is 10 to 1 with respect to 100 parts by weight of the resin.
It is preferably 00 parts by weight. When the amount of silica is less than 10 parts by weight, the ability to stably hold the Zn-based corrosion product formed in the coating when exposed to a corrosive environment is insufficient, and high corrosion resistance cannot be obtained. Further, if the amount of silica exceeds 100 parts by weight, the compatibility with the resin composition decreases and it becomes difficult to apply it as a paint on a steel sheet, which is not preferable.

[0029]

EXAMPLES The present invention will be specifically described below based on examples.

Example 1 Zn-Ni alloy plating (12 wt% Ni) having a basis weight of 20 g / m ² was applied on a low carbon steel plate having a plate thickness of 0.8 mm, and then Cr ⁶⁺ was applied using a roll coater.
50 mg / m ² of coating type chromate with a ratio of 50% (Cr conversion)
It was applied and baked at a maximum plate temperature of 130 ° C. Next, on one surface of the steel sheet, 9% by weight of an epoxy resin having a number average molecular weight of 3750 (Epicoat 1009 manufactured by Shell Chemical Co., Ltd.) and silica sol dispersed in ethyl cellosolve (average primary particle diameter 10 nm, average aggregate particle diameter 0.4 μm) ) 6% by weight and 1% by weight of quinacridone red (6.25% by weight as a dry weight ratio in the resin layer), a dry weight of 1 g /
It is coated with a roll coater so that the dry weight is 0.4 g / m ² without adding a coloring pigment to the other surface so that the m ² becomes, and the plate is baked at the maximum reaching plate temperature of 160 ° C. and immediately cooled with water. After drying, it was confirmed that silica in the organic resin layer aggregated in a flat plate shape and was distributed almost uniformly on the steel plate surface. The following tests were conducted to evaluate the coating performance on the colored surface side of this organic composite-coated steel sheet.

To evaluate the discriminating property, HOYA-SC
When a color sensor HCS1080 manufactured by HOTT Co., Ltd. was used and the measurement was performed at an extraction angle of 70 °, it was possible to obtain an output value sufficient for red color identification on the steel plate surface mixed with the color pigment.

In order to evaluate the corrosion resistance, a 5% NaCl aqueous solution spray (35 ° C.) for 4 hours, a drying (60 ° C.) for 2 hours and a wet environment (50 ° C.) for 2 hours were subjected to a combined cycle corrosion test. However, red rust did not occur even after exceeding 200 cycles.

In order to evaluate the chromium elution resistance, degreasing,
When four steps of washing with water, surface conditioning and chemical conversion treatment were performed, and the amount of deposited Cr before and after the treatment was measured by fluorescent X-ray analysis,
The elution amount was 1 mg / m ² or less.

In order to evaluate the electrodeposition coatability, the power
Put U-600 (manufactured by Nippon Paint Co., Ltd.) at 100V, 2
After 180 seconds treatment at 8 ℃, 170 ℃ for 2 seconds
The appearance was evaluated after baking for 0 minutes.
Almost 0 spins / cm ²And also the skin of the yuzu
No raw was found.

In order to evaluate the water-resistant secondary adhesion, 20 μm
After applying an m-thick electrodeposition coating film, a top coat paint (Luger Bake White, manufactured by Kansai Paint Co., Ltd.) is applied in a thickness of 35 μm, dried and then immersed in warm water (pure water) at 40 ° C. for 10 days, Next, 100 squares of 2 mm square were cut and the coating film residual rate after tape peeling was measured.
%, And peeling was not observed.

To evaluate the spot weldability, the tip 6
Using a welding tip made of Al ₂ O ₃ dispersed copper alloy of mmφ,
Pressure 200kgf, welding current 9kA, welding time 10Hz
The continuous welding was carried out at 4 and the number of continuous welding points until the nugget diameter fell below the reference diameter was 4200.

(Example 2) Zn-Ni alloy plating (12 wt% Ni) having a basis weight of 20 g / m ² was applied on a low carbon steel sheet having a plate thickness of 0.8 mm, and then chromate was applied in the same manner as in Example 1. Processed. Next, the number average molecular weight is 800 on one side of the steel sheet.
9% by weight of urethane-modified epoxy resin of 0, 6% by weight of hydrophobic fumed silica (specific surface area 150 m ² / g) and 0.6% by weight of quinophthalone yellow (3.85% by weight as a dry weight ratio in the resin layer) The coating composition is applied with a roll coater to a dry weight of 1.5 g / m ² and a dry weight of 0.5 g / m ² without blending a coloring pigment on the other side, and the maximum is reached. When baked at a plate temperature of 160 ° C. and immediately water-cooled and dried, it was confirmed that silica in the organic resin layer aggregated into a flat plate shape and was distributed almost uniformly on the steel plate surface. The following tests were conducted to evaluate the coating performance on the colored surface side of this organic composite-coated steel sheet.

In the evaluation of distinctiveness, an output value sufficient for yellowish discrimination could be obtained. In the corrosion resistance evaluation, red rust did not occur even after exceeding 200 cycles. In the evaluation of chromium elution resistance, the amount of Cr elution was 1 mg / m ² or less.
In the evaluation of electrodeposition coatability, almost no gas pins were generated / cm
^{It was 2} , and the occurrence of yuzu skin was not observed.

In the evaluation of the secondary adhesiveness against water, the residual rate of the coating film after peeling the tape was 100%, and peeling was not observed. In the evaluation of spot weldability, the number of continuous welding points until the nugget diameter fell below the reference diameter was 3,800.

Comparative Example 1 Zn-Ni alloy plating (12 wt% Ni) having a basis weight of 20 g / m ² was applied on a low carbon steel plate having a plate thickness of 0.8 mm, and then Cr ⁶⁺ was applied using a roll coater.
50 mg / m ² of coating type chromate with a ratio of 50% (Cr conversion)
It was treated and baked at a maximum plate temperature of 130 ° C. Next, on one side of the steel sheet, 9% by weight of an epoxy resin having a number average molecular weight of 3750 (Epicoat 1009 manufactured by Shell Chemical Co., Ltd.), 6% by weight of silica sol (average primary particle diameter 10 nm) uniformly dispersed in ethyl cellosolve, and quinacridone. Red 0.1 wt% (0.67 as the dry weight ratio in the resin layer)
%) With a roll coater to a dry weight of 2.0 g / m ² and a dry weight of 0.5 g / m ² without any coloring pigment on the other side. After baking at the maximum plate temperature of 160 ° C. and immediately cooling with water and drying, it was confirmed that silica was evenly dispersed in the organic resin layer. The following tests were conducted to evaluate the coating performance on the colored surface side of this organic composite-coated steel sheet.

In the discrimination evaluation, the obtained output value was completely insufficient for red discrimination, and the difference between the front and the back could not be discriminated. In the evaluation of corrosion resistance, red rust did not occur even after exceeding 200 cycles. In the evaluation of chromium elution resistance, the amount of Cr elution was 1 mg / m ² or less. In the evaluation of the electrodeposition coating property, the generation of gas pins is about 10 pieces / cm.
² , and the occurrence of yuzu skin was partially observed. In the evaluation of the water-resistant secondary adhesion, the coating residual rate after tape peeling was 100%, and peeling was not observed. In the evaluation of spot weldability, the number of continuous welding points until the nugget diameter fell below the reference diameter was only 300 points.

In the above embodiment, only one side of the steel sheet was colored and the other side was kept colorless. However, a coloring pigment may be mixed in the resin layers on both sides of the steel sheet as long as the front and back sides can be identified. Needless to say.

[0043]

Since the present invention is constituted as described above, the organic composite coated steel sheet of the present invention has excellent coating properties such as corrosion resistance, spot weldability, electrodeposition coating property, and water resistant secondary adhesion. Since good front and back discrimination can be provided without damaging it, it can be used in a wide range of applications where similar quality characteristics are expected, including those for automobile bodies, and therefore is highly evaluated industrially.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a quinacridone red blending amount and red color identification.

FIG. 2 is a diagram showing a relationship between a quinophthalone yellow compounding amount and yellow discrimination.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ryoichi Mukai, 1st Kawasaki-cho, Chiba City, Chiba Prefecture, Technical Research Division, Kawasaki Steel Co., Ltd. (72) Nobuhiro Morito, 1st Kawasaki-machi, Chiba City, Chiba Prefecture Kawasaki Steel (72) Inventor Hiroyuki Tanabe 8-15 Asahi-cho, Nishinasuno-cho, Nasu-gun, Tochigi Prefecture 72-72 (72) Inventor Masanori Nagai 1926-9 Osawara, Tochigi Prefecture (72) Inventor Small Osamu Kawa, 3-1172-4 Shimonagata, Nishi-Nasu Town, Nasu District, Tochigi Prefecture

Claims (5)

[Claims] 1. An organic composite coated steel sheet having a chromate film on both surfaces of a zinc or zinc-based alloy plated steel sheet, and a resin layer mainly comprising silica and an organic polymer resin as an upper layer of the chromate film. At least one or more condensed polycyclic pigments are blended in the resin layer on at least one side of the steel plate in an amount of 1 to 10% by weight per one side, and the color tone of the resin layer is different between the front and back sides of the steel sheet. Organic composite coated steel sheet with excellent distinguishability. 2. The organic composite coated steel sheet excellent in front and back distinctiveness according to claim 1, wherein quinacridone red and / or quinophthalone yellow is used as the condensed polycyclic pigment. 3. The organic composite coated steel sheet excellent in front and back distinctiveness according to claim 1, wherein an organic solvent-dispersed silica sol having cohesiveness is used as silica constituting the resin layer. 4. The organic composite coated steel sheet excellent in front and back distinctiveness according to claim 1 or 2, wherein hydrophobic fumed silica is used as silica constituting the resin layer. 5. The front / back discrimination according to claim 1, wherein the dry weight ratio of silica to the organic polymer resin in the resin layer is 10 to 100 parts by weight of silica with respect to 100 parts by weight of the resin. Organic composite coated steel sheet with excellent properties.