JP2788362B2 - Organic composite coated steel sheet with excellent discrimination - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic composite coated steel sheet having excellent press workability, cationic electrodeposition coating property, spot weldability, corrosion resistance, etc., and excellent discriminability, mainly as a steel sheet for an automobile body.

[0002]

2. Description of the Related Art In response to strong social demands for higher corrosion resistance of automobile bodies, the use of surface-treated steel sheets in which zinc or a zinc-based alloy plating is applied to the surface of a cold-rolled steel sheet has been increasing in recent years. .

[0003] Examples of these surface-treated steel sheets include hot-dip galvanized steel sheets, galvannealed steel sheets, electro-galvanized steel sheets, and electro-zinc alloy-coated steel sheets. However, a higher degree of corrosion resistance has been required in a bag structure portion or a bent portion (hemming portion) of a body inner plate in which coating performed after the body assembly is not sufficiently distributed. As a steel sheet for an automobile corresponding to such an application, for example, Japanese Patent Application Laid-Open No. 57-108292 and Japanese Patent Application Laid-Open No. 58-2241
Japanese Patent Application Laid-Open No. 74-22637 and Japanese Patent Application Laid-Open No. Sho 63-22637 propose an organic composite coated steel sheet in which a chromate and an organic polymer resin layer are provided on a zinc or zinc-based alloy-plated steel sheet. Regarding these organic composite coated steel sheets, many proposals have been made today for further improvement of press workability, cationic electrodeposition coating property, spot weldability, corrosion resistance and the like.

[0004] By the way, in the processing and assembly line of an automobile manufacturing plant, depending on the use site and the destination, surface-treated steel sheets such as organic composite coated steel sheets, cold-rolled steel sheets, and even surface-treated steel sheets having different plating weights. It is normal that these are used together. Therefore, using a 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 surface-treated steel sheets such as a cold-rolled steel sheet and an organic composite coated steel sheet has been put to practical use as an automatic identification means. If only two types of steel plates having different light reflection intensities coexist, the purpose can be achieved even by using a relatively inexpensive photoelectric sensor. However, if only the basis weight of plating is different in the same type of surface-treated steel sheet, since the light reflection intensity does not change,
The above method cannot be applied. A method of positively changing the glossiness of an organic composite coated steel sheet by blending an additive in an organic resin layer is disclosed in Japanese Patent Application No. 1-26221.
Although it is proposed in Japanese Patent Publication No. 2 (1994), when the type of plating to be used is increased, the discrimination is insufficient with only the light reflection intensity.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems in the prior art.
For example, if there is a difference in the color tone of the organic composite coated steel sheet according to the type of plating or the difference in the basis weight of the plating, it becomes possible to automatically identify the organic composite coated steel sheet using a color sensor. In addition, even when judged by a human, there is an advantage that confusion such as a mistake in the applied steel plate due to a distinct color difference can be prevented.

The present invention has been made to give a color tone to an organic composite coated steel sheet from such a viewpoint. However, the organic composite coated steel sheet as a steel sheet for an automobile body has a press workability and a cationic electrodeposition coating property. In addition to being excellent in spot weldability, corrosion resistance, etc., even if a coloring pigment is added, there is no deterioration in powdering resistance, sliding property, chromium elution resistance, water secondary adhesion, etc., and It is an object of the present invention to provide an organic composite coated steel sheet having excellent discriminability without dissolving a coloring pigment during alkaline degreasing and contaminating the degreasing solution.

[0007]

In order to achieve the above-mentioned object, the present invention relates to a method for producing a steel sheet comprising zinc or zinc-based alloy-coated steel sheet, wherein Cr ⁶⁺ is 70% or less of the total amount of Cr and C
An organic composite coated steel sheet having a chromate film of 5 to 500 mg / m ^{2 in} terms of r, and having a resin composite layer mainly containing silica, a coloring pigment and an organic polymer resin as an upper layer of the chromate film, The silica has an average primary particle diameter of 5 to 60 nm, and the silica is agglomerated in the resin layer composite in an average thickness of 0.2 to 2 μm and an average diameter of 5 to 300 μm. Agglomerates are distributed almost uniformly on the steel plate surface,
And the color pigment is one or more condensed polycyclic pigments, and the amount of the resin composite layer attached is 0.1% by dry weight.
The present invention provides an organic composite coated steel sheet having excellent discriminability, characterized in that the steel sheet has a weight of up to ³ g / m ² .

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

The above-mentioned condensed polycyclic pigment is contained in the resin composite in an amount of from 1 to 3.
Preferably, it is contained at 10% by weight.

The silica content in the resin layer is 10 to 5
It is preferably 0% by weight.

The organic polymer resin has a number average molecular weight of 2
More than 000 epichlorhydrin-bisphenol A
It is preferable to use an organic polymer resin based on a type epoxy resin.

It is preferable to use an organic solvent-dispersed silica sol or a hydrophobic fumed silica having an average agglomerated particle size of 0.05 to 2 μm as the silica to be constituted.

Hereinafter, the present invention will be described in more detail. Book
In the invention, the material is zinc or zinc-based alloy
Use a steel plate. Types of plating applied to steel sheets
Are pure Zn plating, Zn-Ni alloy plating, Zn-Fe
For binary alloys such as alloy plating and Zn-Cr alloy plating
, Zn-Ni-Cr alloy plating, Zn-Co-Cr
Use of ternary alloy plating such as alloy plating
And Zn-SiO_Two Plating, Zn-Co-Cr-
Al_Two 0 _Three Composite dispersion plating such as plating can also be used.
it can. These plating is electroplating, hot-dip plating
Or vapor phase plating.

[0014] These zinc or zinc-based alloy coated steel sheets
To improve the adhesion to the resin composite layer described below,
Chromate treatment to impart high corrosion resistance. K
5 to 500 mg / m in terms of Cr^Two ,
Preferably 10 to 150 mg / m ^Two Range. like this
Chromate treatment is a coating type using a roll coater etc.
Chromate method, electrolytic chromate method, reactive chromate method
Any of these methods may be used. Surface treatment of the present invention
5mg / m chromate adhesion on steel plate^Two Less than good
High corrosion resistance and water-resistant secondary adhesion cannot be obtained. Ma
500mg / m^TwoChromium is eluted when the temperature exceeds
Not preferred.

The Cr ⁶⁺ ratio in the chromate is
It is desirably 70% or less based on the amount. If the content of Cr ⁶⁺ exceeds 70%, the elution resistance of chromium during alkaline degreasing deteriorates, which is not preferable.

On the upper layer of such a chromate film, a resin composite film composed of silica, a coloring pigment and an organic polymer resin is applied. The organic resin used in the present invention is not particularly limited, but examples thereof include an epoxy resin, an acrylic resin, a polyethylene resin, an alkyd resin, and a urethane resin.
No. 5 and Japanese Patent Application No. 2-29973, the epichlorohydrin having a number average molecular weight of 2,000 or more.
It is more desirable to use a resin composition based on a bisphenol A type epoxy resin from the viewpoint of toughness and corrosion resistance.

Next, the color pigment will be described. Color pigments are roughly classified into inorganic pigments and organic pigments. Inorganic pigments
Generally, since the particle diameter is large and the coloring power is inferior, a large amount of pigment must be added for coloring. Since most of the film thickness of the thin film type organic composite coated steel sheet aimed at by the present invention is 2 μm or less, if the average particle diameter of the pigment is more than this, there arises a problem that the powdering resistance and the press workability deteriorate.

On the other hand, since organic pigments have a smaller particle size and higher coloring power than inorganic pigments, they can be colored with a small amount, and are advantageous in terms of powdering resistance and press workability. However, azo pigments, which are widely used as organic pigments, have poor heat resistance as can be inferred from their chemical structures,
When the resin layer is used for baking at a high temperature of about 160 ° C. as in the present invention, it is difficult to perform stable identification using a color sensor. Further, lake pigments are poor in water resistance and alkali resistance, and when used in applications where alkali degreasing is performed, decolorization of the steel sheet and elution of the pigment into the degreasing solution occur, which is also unsuitable.

As described above, the performance of the organic pigment greatly changes 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, coloring power, etc. from the purpose of use, and condensed polycyclic pigments are suitable for this purpose. Applied to Fused polycyclic pigments have very good performance due to their high electron density and chemical stabilization due to the presence of a highly conjugated π-electron system. Therefore, as the condensed polycyclic pigment, quinacridone pigments, quinophthalone pigments, anthraquinone pigments, perylene pigments, perinone pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, and the like,
From these, a pigment having a desired hue can be selected. For example, quinacridone red and the like can be mentioned as pigments having red discrimination, and quinophthalone yellow and the like can be mentioned as pigments having yellow discrimination.

The distinctiveness of these pigments will be explained based on specific experimental facts. After degreasing and pickling the cold-rolled steel sheet, average N
Zn-Ni plating with an i content of 12 wt% and a basis weight of 20 g / m ² was performed to produce a plated steel sheet. A chromate treatment liquid having a chromium reduction ratio of about 50% was applied to the surface of the plated steel sheet produced in this manner by a roll coater, and then baked at a maximum temperature of 130 ° C. in an electric furnace to perform a chromate treatment. The amount of attached chromate was 50 mg / m ² . Further, on this upper layer, an epoxy resin having a number average molecular weight of 3750, silica sol dispersed in ethyl cellosolve (average primary particle diameter 10 nm, average secondary particle diameter 0.4 μm
) And a coloring pigment (quinacridone red or quinophthalone yellow), the silica ratio in the solid content is fixed at 40% by weight, the coloring pigment is changed from 1% to 15% by weight, and the remainder becomes resin. Further, a coating prepared by diluting with an organic solvent so that the solid content in the coating was 15% by weight was applied by a bar coater, and then baked in an electric furnace so that the maximum temperature reached 160 ° C.
The coating amount of the resin composite layer was 0.7 g / m ² in a dry state.

In the resin composite film of the obtained organic composite coated steel sheet, silica is aggregated in a planar shape having an average thickness of 0.2 to 2 μm and an average diameter of 5 to 300 μm. It was distributed almost uniformly on the surface. The distinctiveness of the organic composite coated steel sheet prepared in this way was determined by HOYA
-Color sensor HCS1080 manufactured by SCHOTT Corporation
Was evaluated using FIG. 1 shows red discrimination when quinacridone red was added. FIG. 2 shows the yellow discrimination when quinophthalone yellow was added. When the amount of quinacridone red in the resin composite layer was 1% by weight or more, an output value necessary for red color identification could be obtained.
When the amount of quinophthalone yellow in the resin composite layer was 1% by weight or more, an output value required for yellow identification could be obtained. This is the reason why the lower limit of the color pigment in the resin composite layer is set to 1% by weight. From this viewpoint, the output value increases as the blending amount increases, but when the blending amount of the coloring pigment exceeds 10% by weight, deterioration in the adhesion to the electrodeposition paint has been confirmed. did.

In the above-described example, an organic solvent-dispersed silica sol having cohesiveness was used as silica constituting the resin composite layer. The same experiment was performed using silica sol (average primary particle diameter: 10 nm) having no cohesiveness and uniformly dispersed in n-propyl cellosolve as the silica in the coating. , The output value was significantly reduced. Even in this case, when observed with the naked eye, a clear red or yellow color tone is recognized, but it is difficult to detect with a color sensor. When the cause was examined, when the homogeneously dispersed silica sol was used, the specular reflection light from the resin composite layer surface reflected light from the chromate layer (resin composite resin) due to the high glossiness of the resin composite layer surface. (Including the transmitted light of the layer as a signal)
It was found that it was difficult to detect information on the color tone inside the resin composite layer.

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

For the same purpose, when hydrophobic fumed silica was used as the silica constituting the resin composite layer, aggregation inside the resin composite layer was clearly observed, and the organic solvent dispersion having a cohesive property was observed. A signal almost equivalent to that when silica sol was used could be detected.

From the above results, the content of the coloring pigment in the dried coating film is set to 1 to 10% by weight. If the content of the color pigment is less than 1% by weight, sufficient discrimination cannot be obtained, and if it exceeds 10% by weight, the adhesion after coating is undesirably reduced.

The silica has an average primary particle diameter of 5 to 60 nm, and the silica is agglomerated in an organic coating film in a plane having an average thickness of 0.2 to 2 μm and an average diameter of 5 to 300 μm, The silica planar aggregate must be distributed almost uniformly on the surface of the steel sheet. Any silica having such a configuration is applicable. As silica having such a configuration, an average aggregated particle diameter of 0.05 to 2 μm
Organic solvent-dispersed silica sol and hydrophobic fumed silica are preferred.

The amount of silica in the resin composite layer is 10
Preferably, it is about 50% by weight. When the amount of silica is less than 10% by weight, the ability to stably retain a Zn-based corrosion product formed when exposed to a corrosive environment is lacking, and high corrosion resistance cannot be obtained. On the other hand, if the amount of silica exceeds 50% by weight, the compatibility with the resin product is reduced, and it becomes difficult to apply the coating material on a steel sheet, which is not preferable.

[0028]

Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention. (Example) After degreasing and pickling a cold-rolled steel sheet, Zn-Ni plating with an average Ni content of 12 wt% and a basis weight of 20 g / m ² was performed to prepare a plated steel sheet.

A chromate treatment solution having a chromium reduction ratio of 50% was applied to the surface of the plated steel sheet produced in this manner by a roll coater, and then baked in an electric furnace at a maximum temperature of 130 ° C. to perform a chromate treatment. Table 4 shows the chromate adhesion amount. Further, the resin in Table 1, the silica in Table 2 and the coloring pigment in Table 3 were appropriately blended into the upper layer, dispersed in an organic solvent, and coated with a bar coater.
It was baked in an electric furnace so that the maximum temperature reached 160 ° C. Table 4 shows the silica content, the organic coating application amount, and the color pigment content of the organic coating layer. Silica dispersed organic solvent is n-
Propyl cellosolve.

(Observation of Surface Shape) Observation of the surface of the steel sheet coated with a paint containing silica E and silica F shown in Table 2 showed that silica had an average thickness of 0.2 to 2 μm and an average diameter of 5 μm.
It was aggregated in a plane of ~ 300 µm. On the surface of the steel sheet to which the coating material containing silica G shown in Table 2 was applied, silica was uniformly dispersed in the organic coating layer.

(Distinction) The evaluation of the discrimination by the color sensor was carried out at a take-out angle of 70 ° using a color sensor HCS1080 manufactured by HOYA-SCHOTT. The evaluation criteria are as follows. ◎: Stable identification possible △: Unstable identification ×: Unrecognizable

(Corrosion Resistance) Bare corrosion resistance was evaluated by the number of cycles in which red rust occurred in a combined cycle corrosion test in which the following conditions were defined as one cycle. Salt spray 4 hours 5% NaCl solution 35 ° C Drying 2 hours 60 ° C Wet 2 hours 95% RH 50 ° C

(Phosphate treatment, chromium elution resistance, decolorization) Normal alkali degreasing is performed, followed by phosphate treatment (Palbond 3020 manufactured by Nippon Parkerizing Co., Ltd.).
(Immersion for 0 seconds). The chromium elution amount of each sample obtained before and after the phosphate treatment step was measured. The amount of chromium attached was measured by X-ray fluorescence analysis, and the difference between before and after was evaluated as the amount of chromium eluted. The evaluation criteria are as follows. ◎: 1mg / m ² or less ○: 1-2 mg / m less than ² △: ^2~5mg / m ² less ×: 5mg / m ² or more

Further, the bleaching property at this time was evaluated. The evaluation criteria are as follows. ◎: No decolorization ：: Almost no decoloration Δ: Slight decolorization ×: Almost all decolorization The results are shown in Table 4.

(Water Resistance Secondary Adhesion Test) Power top U-600 (manufactured by Nippon Paint Co., Ltd.) was applied to the phosphate-treated sample at an electrodeposition voltage of 250 V, a bath temperature of 28 ° C. for 180 seconds, and a temperature of 170 ° C. Bake for 20 minutes.

The sample after electrodeposition coating was further spray-coated with a top coat for automobiles. Using each of the samples thus obtained, a water-resistant secondary adhesion test was performed. Each sample was immersed in warm water of 40 ° C. for 240 hours. After taking out each sample, 100
Each piece was scratched using a cutter knife, and a peeling test was performed using cellophane tape. The evaluation was performed by measuring the number of peeled pieces. ：: No peeling ○: Number of peeled 1 or less △: Number of peeled 2 to 10 ×: Number of peeled 11 or more The test results are shown in Table 4.

(Electrodeposition coating property) Power top U-600 (manufactured by Nippon Paint Co., Ltd.) was applied to the phosphate-treated sample.
Was applied for 180 seconds at an electrodeposition voltage of 90 V, a bath temperature of 28 ° C., and 17
After baking at 0 ° C for 20 minutes, the appearance (number of gas pinholes) was evaluated according to the following evaluation criteria. ◎: 0 pieces / cm ² ：: 1 to 6 pieces / cm ² Δ: 7 to 10 pieces / cm ² ×: 11 pieces / cm ² or more

(Weldability) Using a welding tip made of an Al ₂ O ₃ dispersed copper alloy having a tip of 6 mmφ, a continuous welding was performed at a pressure of 200 kgf, a welding current of 9 kA and a welding time of 10 cycles.
The number of continuous welding points until the nugget diameter became smaller than the reference diameter was measured. Evaluation was made according to the following evaluation criteria. ◎: 3000 points or more ○: 2000 to 2999 points △: 1000 to 1999 points ×: Less than 1000 points From the results shown in Table 4 above, according to the surface-treated steel sheet of the present invention, corrosion resistance, adhesion, paintability, welding It is possible to obtain discrimination with the color sensor without impairing the performance such as the performance.

[0039]

[0040]

[0041]

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

The surface-treated steel sheet of the present invention has excellent corrosion resistance,
It can provide good discrimination with a color sensor without impairing electrodeposition coating properties, water-resistant secondary adhesion, weldability, etc., so it can be widely used for automobile bodies and other products, and its industrial value is Extremely high.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of quinacridone red and red color identification.

FIG. 2 is a graph showing the relationship between the amount of quinophthalone yellow and the amount of yellow.

Continuing from the front page (72) Inventor Hideo Ogishi 1 Kawasaki-cho, Chiba-shi, Chiba Prefecture Kawasaki Steel Corporation Research and Technology Headquarters (72) Inventor Nobuyuki Morito 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Corp. (72) Inventor Hiroyasu Tanabe 8-15 Asahi-machi, Nishinasuno-machi, Nasu-gun, Tochigi Prefecture (72) Inventor Masanori Nagai 1926-9, Usaba, Otawara-shi, Tochigi (72) Inventor Small Osamu Kawagawa 3-1172-4 Shimonagata, Nishinasuno-machi, Nasu-gun, Tochigi Prefecture (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C 22/00-28/86 C23C 28/00 B32B 15/08

Claims (7)

(57) [Claims] 1. The method according to claim 1, wherein the amount of Cr ⁶⁺ on the surface of the zinc or zinc-based alloy plated steel sheet is 70% or less of the total amount of Cr, and
An organic composite coated steel sheet having a chromate film of 5 to 500 mg / m ^{2 in} terms of r, and having a resin composite layer mainly containing silica, a coloring pigment and an organic polymer resin as an upper layer of the chromate film, The silica has an average primary particle diameter of 5 to 60 nm, and the silica is aggregated in the resin composite layer in a plane having an average thickness of 0.2 to 2 μm and an average diameter of 5 to 300 μm. Agglomerates are distributed almost uniformly on the steel plate surface,
And the color pigment is one or more condensed polycyclic pigments, and the amount of the resin composite layer attached is 0.1% by dry weight.
An organic composite coated steel sheet excellent in discriminability, characterized in that the thickness is 3 g / m ^{2 or} less. 2. The organic composite coated steel sheet according to claim 1, wherein quinacridone red and / or quinophthalone yellow are used as the condensed polycyclic pigment. 3. The method according to claim 1, wherein the condensed polycyclic pigment is contained in a resin composite.
The organic composite coated steel sheet having excellent distinguishability according to claim 1 or 2, which is contained in an amount of from 10 to 10% by weight. 4. The organic composite coated steel sheet according to claim 1, wherein the resin composite layer contains 10 to 50% by weight of silica. 5. The organic polymer resin according to claim 1, wherein an organic polymer resin based on epichlorohydrin-bisphenol A type epoxy resin having a number average molecular weight of 2,000 or more is used as the organic polymer resin. Organic composite coated steel sheet with excellent discrimination. 6. The organic composite-coated steel sheet having excellent discrimination characteristics according to claim 1, wherein an organic solvent-dispersed silica sol having an average agglomerated particle size of 0.05 to 2 μm is used as the constituent silica. 7. The organic composite coated steel sheet according to claim 1, wherein hydrophobic fumed silica is used as the constituent silica.