JPH0511515B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an organic composite steel sheet that has excellent corrosion resistance, weldability, workability, and excellent image clarity. That is, the present invention applies chromate treatment to various galvanized steel sheets, and then coats a special organic resin containing colloid (sol) with a specific fine particle size in a specific proportion. This is a method for manufacturing an organic composite steel sheet in which baking and drying are performed in a temperature range. [Prior Art] As is well known, electrogalvanized steel sheets, hot-dip galvanized steel sheets, and various alloy-plated steel sheets are widely used in automobiles, home appliances, building materials, and the like. Under these circumstances, in recent years, there has been an increasingly strong demand for surface-treated materials with particularly excellent corrosion resistance, and the demand for such steel sheets is likely to increase further in the future. For example, in the home appliance industry, there is a demand for a steel plate with excellent corrosion resistance that can be used bare and omit painting from the viewpoint of process and cost savings. In addition, recent environmental changes in the automobile industry include corrosion caused by rock salt, which is sprayed to prevent roads from freezing in winter in North America and Northern Europe, and corrosion caused by acid rain caused by the generation of SO ₂ gas in industrial areas. Vehicle bodies are exposed to severe corrosive environments, and from a safety standpoint, there is a strong demand for surface-treated steel sheets with excellent corrosion resistance. In order to solve these problems, various studies have been made and many products have been developed. Until now, galvanizing has been carried out to improve the corrosion resistance of steel sheets. Galvanized steel sheets prevent corrosion of the steel sheet through the sacrificial anticorrosive action of zinc, and in order to obtain corrosion resistance, the amount of zinc deposited must be increased. For this reason, there are several problems such as an increase in the cost of the required amount of zinc and a decrease in workability, weldability, and productivity. Additionally, galvanized steel sheets generally have poor paint adhesion. As a method for improving the corrosion resistance of such galvanized steel sheets, various alloy-plated steel sheets have been developed. For example, these alloy-plated steel sheets include
Zn-Ni series, Zn-Ni-Co series, Zn-Ni-Cr series, Zn
-Fe system, Zn-Co system, Zn-Mn system, etc. can be mentioned. It is recognized that these alloy platings improve the corrosion resistance of bare steel sheets by about 3 to 5 times compared to ordinary galvanized steel sheets. However, the problem is that white rust or red rust is likely to occur if left outdoors for a long period of time or if water or salt water is sprayed on it. There is also a method of applying chromate treatment after plating to improve corrosion resistance, which is quite effective, but in high temperature, high humidity or salt-containing atmospheres,
White rust occurs after 150 hours. In order to further improve corrosion resistance, various resins are applied to the chromate-treated zinc-plated steel sheets.
So-called simple pre-coated steel sheets (hereinafter referred to as organic composite steel sheets) have been developed and some are commercially available. An example is listed below. JP-A No. 58-210190 JP-A No. 58-210192 A chromate treatment is applied to a zinc-based alloy single-layer plating or double-layer plating, and conductive substances (Zn,
A weldable painted steel plate coated with a resin paint containing (Al, Sn, Fe, Ni, Co, Cr, Mn) for the purpose of improving weldability, paint film adhesion, and corrosion resistance. JP-A-58- Publication No. 224174 A method for manufacturing a highly corrosion-resistant rust-preventing coated steel sheet, in which the surface of a zinc alloy-plated steel sheet is subjected to paint-type chromate treatment, and then treated with a composite organic silicate resin solution without washing with water, with the aim of improving corrosion resistance. JP-A-59-116397 A steel plate has a highly corrosion-resistant electroplated layer such as Ni-Zn or Fe-Zn as the first layer on both sides, and a thin electroplated layer such as Fe-Zn on one side as the second layer. The coating layer is made of a highly corrosion-resistant and rust-preventing steel plate that has a resin containing conductive pigments or a resin film with a thickness of 0.5 to 3.0μ on the other side, and the outer side has corrosion resistance and paint adhesion, and the inner side has spot weldability. , for the purpose of imparting workability Patent Publication No. 61-36587 Electrogalvanized steel sheet in which a chromate film is formed on the surface of the galvanized steel sheet, and then a special resin aqueous solution containing colloidal silica is applied and dried. A surface treatment method for plated steel sheets that improves fingerprint resistance, paint adhesion, hardness,
Aiming to improve corrosion resistance JP-A-60-149786 A treatment method that is the same as the above-mentioned JP-B No. 61-36587, but the base plating is limited to zinc-based alloy, and it is different from JP-A-61-36587. This is a surface treatment method using a different resin, which adds even more corrosion resistance and solvent resistance to the above. JP-A-61-167545 Chromate treatment is applied on the zinc-based alloy plating layer. Highly corrosion-resistant weldable coated steel plate coated with one or two of hard metal powder, hard carbonized powder, and zinc powder, for the purpose of improving corrosion resistance and weldability. All of these are called organic composite steel sheets, and they have improved properties. [Problems to be solved by the invention] However, ED coating (electrodeposition coating) on organic composite steel sheets
When applying the ED coating, the formed ED coating is greatly influenced by the underlying organic film, and generally the sharpness of the ED coating and
Cratering resistance is considerably inferior to that of ordinary chemically treated cold-rolled steel sheets or matted steel sheets. In contrast, the present invention provides an organic composite steel sheet with excellent image clarity and cratering resistance after ED. [Means for solving the problems] The present invention includes fine particles of SiO ₂ in an aqueous resin dispersion.
_Cr2O3 , _{Fe2O3 , Fe3O4 ,} MgO, _ZrO2 , _{SnO2 ,}
By containing one or more types of colloids (sols) of Al ₂ O ₃ and Sb ₂ O ₅ in a specific proportion, applying it to a chromate-coated steel plate and heating it to a specific temperature (baking-drying). This significantly improves the image clarity and cratering resistance of organic films after ED. The excellent characteristics of the present invention can only be obtained by adding a specific amount of fine colloid (sol) with a specific particle size or less to the aqueous resin dispersion, and heating the organic resin to a specific temperature when drying. As a result of detailed study, the present inventors found that the colloid (sol) must meet the following conditions. Particle size of colloid (sol): 1 mμ to 12 mμ Amount of colloid (sol) added: 5 to 100 parts (parts by weight) per 100 parts of coexisting resin A bath that satisfies the above conditions is applied onto the plated steel plate.
It was confirmed that by heating and baking at 100-150°C, it was possible to produce an organic composite steel sheet with extremely excellent image clarity and cratering resistance after ED. A method for significantly improving the post-ED image clarity and cratering resistance of the organic resin film of the present invention will be specifically explained. Figures 1 and 2 show acrylic resin: collodyl silica = 100:20 on a Zn-Ni alloy plated steel plate that has been chromate treated to give a chromium adhesion amount of 75mg/ ^m2 .
(solid content weight ratio), and collodyl silica (SiO ₂ )
Apply an aqueous solution with different particle sizes and heat to 120℃.
This figure shows how the sharpness and cratering resistance change after ED when the coating is applied to a film thickness of 1 μm after drying. Figures 3 and 4 show that the amount of chromium deposited is 75mg/
A layer of colloidal silica ⁴ to 6
Using particles with a particle size of mμ, a bath with a different blending ratio of acrylic resin and colloidal silica (SiO ₂ ) was applied, heated to 120℃, and the film after baking and drying was 1μ.
This figure shows how the image clarity and cratering resistance change after ED. Figures 5 and 6 also show the amount of chromium deposited.
Zn− chromated to 75mg/ ^m2
Using colloidal silica with a particle size of 4 to 6 mμ on a Ni-based alloy plated steel plate, acrylic resin: colloidal silica = 100:20
(solid content weight ratio) After drying the aqueous liquid, the film thickness is
This figure shows how the sharpness and cratering resistance after ED change when the coating is applied to a thickness of 1.0μ and the baking-drying temperature is changed. Here, the image clarity was determined using a commercially available cationic ED paint.
The film was treated at 220V to a film thickness of 20μ, and after baking at 165℃, the reflectance passing through a 2mm slit was measured using a commercially available image clarity measuring device. It was evaluated by ◎ is the best. ◎: Reflectance of 50% or more ○: 〃 40-50% △: 〃 30-40% ×: 〃 20-30% Check the number of cratering ◎, ○, △, ×, ××
It is evaluated on a five-point scale, with ◎ being the best. ◎: Number of crater rings: 0 pieces/dm ² ○: 〃 0-1 pieces/dm ² △: 〃 1-10 pieces/dm ² ×: Number of crater rings: 10-50 pieces/dm ² ××: 〃 50 pieces/dm ² or more As is clear from Figure 1, the sharpness of the paint film after ED coating changes depending on the particle size of colloidal silica.
It shows excellent image clarity with a particle size of 1 mμ to 12 mμ, and
When it becomes less than mμ or more than 12 mμ, image clarity tends to decrease. As is clear from Figure 2, the cratering resistance of the ED coating changes depending on the particle size of the colloidal silica, with particle sizes of 1 mμ to 12 mμ showing excellent cratering resistance, and particles with a particle size of 1 mμ or less decreasing slightly.
When the value exceeds mμ, the cratering resistance tends to decrease rapidly. As is clear from Figure 3, the sharpness of the coating film after ED coating changes depending on the amount of colloidal silica added, and excellent sharpness is shown when the added amount is 5 parts to 100 parts (by weight). , when the number of copies is less than 5 or more than 100, the sharpness tends to decrease. As is clear from Figure 4, the cratering resistance of the paint film after ED coating changes depending on the amount of colloidal silica added, and the amount added ranges from 5 parts to 100 parts (parts by weight).
It shows excellent cratering resistance at 5 parts or less and at 100 parts or more, the cratering resistance tends to decrease rapidly. As is clear from Figure 5, the sharpness of the paint film after ED coating changes depending on the heating temperature of the organic film, and excellent sharpness is exhibited at a heating (baking) temperature of 100 to 150°C.
Below 100℃, it decreases slightly as the temperature decreases,
When the temperature exceeds 150°C, image sharpness deteriorates rapidly. As is clear from Figure 6, the cratering resistance of the paint film after ED coating changes depending on the heating (baking) temperature of the organic film, and it shows excellent cratering resistance at a heating temperature of 100 to 150°C. , below 100°C, the cratering resistance decreases slightly as the temperature decreases, and above 150°C, the cratering resistance suddenly deteriorates. The above results showed the results using colloidal silica (SiO ₂ ) as the colloid (sol), but instead of colloidal silica, Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ ,
Similar results were obtained using colloids (sols) of MgO, ZrO ₂ , SnO ₂ , Al ₂ O ₃ and Sb ₂ O ₅ . Similar results were also obtained when two or more of the above colloids (sols) were contained. In addition, although the above results showed the results using acrylic resin as the resin, the resins used were ethylene-acrylic acid copolymer resin, polyacrylic acid and its copolymer resin, polymethacrylic acid and its copolymer resin. Any water-based resin may be used, including water-based resin dispersions of resin, polyacrylic acid ester and its copolymer resin, polymethacrylic acid ester and its copolymer resin, and in either case, the particle size of the colloid (sol) and the addition regulate the amount, and
By regulating the heating (baking) temperature of the organic film and applying ED coating to the formed organic film, the image clarity and cratering resistance after ED coating can be greatly improved, and almost the same results can be obtained. The above results indicate that the amount of Cr deposited on the plated steel sheet is 75 mg/m ²
Figure 7 shows that the amount of chromium deposited on a Zn-Ni alloy-plated steel plate is changed and acrylic resin is applied.
1.0μ (solid content) of an aqueous solution prepared by mixing 100 parts (weight parts) with 30 parts (weight parts) of 4-6 mμ colloidal silica.
This shows the adhesion of the film when applied and baked and dried at 120°C. As is clear from the figure, the amount of Cr deposited is
If the amount is less than 10 mg/m ² or more than 150 mg/m ² , the adhesion of the film tends to decrease somewhat. To test the adhesion of the film, the coated test piece was boiled for 30 minutes, and then the film was cut into 2 mm squares, peeled off with tape, and evaluated by the peeled area. ◎: Peeling area 0% ○: 〃 0-1% △: 〃 1-10% ×: 〃 10-50%
The baking temperature of solvent-based organic resins is generally 160 to 220°C. In contrast,
In the present invention, a water-based resin is used, and by heating it to 100 to 150°C, the resin is finely cured by interaction with ultrafine colloid (sol), and
It was found that the reactive groups in the film were uniformly dispersed. It was found that when a finely cured resin is coated with ED, a current flows uniformly throughout the film, and a uniform and flat film is formed in the initial stage of ED coating deposition. As a result, it was found that the image clarity and cratering resistance after ED coating were significantly improved. Based on the above results, in the present invention, when manufacturing an organic composite steel sheet by applying an aqueous liquid to a plated steel sheet,
For 100 parts by weight of the solid content of the ^aqueous resin dispersion,
SiO ₂ , Cr ₂ O ₃ having a particle size of 1 mμ to 12 mμ,
Fe ₂ O ₃ , Fe ₃ O ₄ , MgO, ZrO ₂ , SnO ₂ , Al ₂ O ₃ ,
A steel plate characterized in that it is coated with an aqueous solution containing 5 to 100 parts by weight of one or more colloids (sols) of Sb ₂ O ₅ as a solid content, and baked and dried at 100 to 150°C. It is a surface treatment method, and the formed film
This greatly improves the clarity and cratering resistance of ED coatings. [Example] Examples will be described below. Example 1 Zn-Ni alloy plating (Ni: 11.5%) with a plating amount of 20 g/m ² was treated with chromate so that the Cr adhesion amount was 65 mg/m ² , and ethylene-acrylic acid copolymer was applied. Colloidal silica with a particle size of 3 to 4 mμ is applied to the resin, and an aqueous solution prepared in a ratio of ethylene-acrylic acid copolymer resin: colloidal silica = 100:20 (parts by weight) is applied on top of the resin.
The film was baked and dried at 120°C to form a film having a density of 1.0 g/m ² . Example 2 A Zn-Ni-Co alloy plated steel sheet (Ni: 12.5%, Co: 0.6%) with a plating weight of 20 g/m2 was chromate-treated so that the Cr coating weight was 90 mg/ ^{m2 .} , a Cr ₂ O ₃ sol with a particle size of 1 to 2 mμ was applied to a polyacrylic acid resin, and an aqueous solution adjusted so that the ratio of polyacrylic acid resin: Cr ₂ O ₃ = 100:40 (parts by weight) was applied thereon. ,
A film was formed by baking and drying at 145°C to give a weight of 1.2 g/m ² . Example 3 A Zn-Fe alloy plated steel sheet with a plating weight of 20 g/m ² was chromate-treated so that the Cr adhesion was 60 mg/m ² , and a polyacrylate copolymer resin with a particle size of 7-9 mμ Al ₂ O ₃ sol Polyacrylic acid ester copolymer resin: Al ₂ O ₃
Apply an aqueous solution adjusted so that the sol = 100:60 (parts by weight) on top of it,
A film was formed by baking and drying at 110°C to a weight of 0.8 g/m ² . Example 4 A Zn-Ni-Cr alloy coated steel sheet (Ni: 11.8%, Cr: 1.0%) with a plating weight of 20 g/ ^m2 was chromate treated so that the Cr coating weight was 55 mg/ ^m2 . , polymethacrylic acid ester with a particle size of 10 to 12 mμ
Fe ₃ O ₄ sol Polymethacrylic acid ester: Fe ₃ O ₄ = 100:70
(parts by weight) Apply an aqueous solution adjusted to
The film was baked and dried at 130°C to form a film having a weight of 1.2 g/m ² . Example 5 A Zn-Mn alloy plated steel sheet (Mn: 35%) with a plating weight of 20 g/m ² was treated with chromate so that the Cr adhesion was 70 mg/m ² , and a polymethacrylic acid ester copolymer was applied. SnO ₂ with a particle size of 8 to 11 mμ is added to the combined resin.
Sol Polymethacrylate copolymer resin:
An aqueous solution adjusted so that SnO ₂ sol = 100:30 (parts by weight) is applied on top of it.
A film was formed to a dry weight of 1.3 g/m ² . Example 6 A Zn-Mn-Cr alloy plated steel sheet (Mn = 20%, Cr = 2%) with a plating weight of 20 g/ ^m2 was chromate-treated so that the Cr coating weight was 55 mg/ ^m2 . , Sb ₂ O ₅ with a particle size of 10 to 12 mμ in polyacrylic ester
Sol Polyacrylic acid ester: Sb ₂ O ₅ sol = 100:
Apply an aqueous solution adjusted to 50 (parts by weight) on top of it,
A film was formed by baking and drying at 110°C to a weight of 0.9 g/m ² . Example 7 A Zn-Ni alloy plated steel sheet (Ni: 11.5%) with a plating weight of 20 g/m ² was chromate-treated so that the Cr coating weight was 75 mg/m ² , and then treated with ethylene-acrylic acid copolymer. Colloidal silica (SiO ₂ ) with a particle size of 5 to 7 mμ and CrO ₃ colloid (sol) with a particle size of 3 to 4 mμ are added to the combined resin Ethylene-acrylic acid copolymer resin: SiO ₂ :
Apply an aqueous solution adjusted to have a ratio of Cr ₂ O ₃ = 100:20:10 (parts by weight) on top of it,
The film was baked and dried at 120°C to form a film having a weight of 1.2 g/m ² . Example 8 A Zn-Ni- ^Co alloy coated steel sheet (Ni: 11.2%, Co: 0.5%) with a plating weight of 20 g/m2 was chromate treated so that the Cr coating weight was 70 mg/ ^m2 . , polyacrylic acid ester copolymer resin has a particle size of 7~
9 mμ Fe ₂ O ₃ colloid (sol) 5-7 mμ
ZrO ₂ colloid (sol), 3-4 mμ Sb ₂ O ₅ colloid (sol) Polyacrylic ester copolymer resin:
An aqueous solution adjusted so that Fe ₂ O ₃ : ZrO ₂ : Sb ₂ O ₅ = 100:10:10:20 (parts by weight) is applied on top.
The film was baked and dried at 130°C to form a film having a weight of 1.1 g/m ² . Comparative Example 1 A Zn-Ni alloy plated (Ni: 11.5%) steel plate with a coating weight of 20 g/m ² was chemically treated using a commercially available chemical conversion bath. Comparative Example 2 A Zn-Ni alloy plated steel plate (Ni: 11.5%) with a plating weight of 20 g/m ² was chromate-treated to have a Cr coating weight of 70 mg/m ² . Comparative Example 3 A Zn-Ni alloy plated steel sheet (Ni: 11.5%) with a plating weight of 20 g/m ² was chromate treated so that the Cr adhesion was 70 mg/m ² , and then melamine resin was applied on top of it. Coat and bake at 120℃ - dry to 1.2g/m ²
A film was formed so that Comparative Example 4 A Zn-Ni alloy plated steel sheet (Ni: 11.5%) with a plating weight of 20 g/m ² was chromate-treated so that the Cr adhesion was 70 mg/m ² , and the particle size of the melamine resin was 15 mμ of Al ₂ O ₃ sol was coated with an aqueous solution adjusted so that the ratio of melamine resin: Al ₂ O ₃ sol = 100:30 (parts by weight) was applied.
A film was formed by baking and drying at 120°C to give a weight of 1.1 g/m ² . Comparative Example 5 A Zn-Ni alloy plated steel sheet (Ni: 11.5%) with a plating weight of 20 g/m ² was treated with chromate so that the Cr coating weight was 70 mg/m ² , and a polymethacrylate ester was coated with grains. Colloidal silica with a diameter of 17 mμ was coated with an aqueous solution prepared in a ratio of polymethacrylate: colloidal silica = 100:20 (parts by weight), and
The film was baked and dried at 80°C to form a film having a weight of 1.1 g/m ² . Table 1 shows the results of various tests conducted on the surface-treated steel sheets obtained in Examples 1, 2, 3, 4, 5, 6, 7, and 8 and Comparative Examples 1, 2, 3, 4, and 5. show. Various test conditions are as follows. (a) Image clarity after ED coating The evaluation method is the same as in Figure 1. (b) Cratering resistance after ED coating The evaluation method is the same as in Figure 2.

【table】

〔Effect of the invention〕

Conventionally, when applying ED coating to organic composite steel sheets, the formed ED coating is greatly affected by the underlying organic film, and generally the sharpness and cratering resistance of the ED coating are lower than those of ordinary chemically treated cold-rolled steel sheets. It is considerably inferior to steel plates and matted steel plates. In contrast, the surface-treated steel sheet obtained according to the present invention can significantly improve the image clarity and cratering resistance of the ED coating when the formed coating is applied with ED coating. Therefore, when coated on top of this, a coating film with significantly superior image clarity can be obtained, giving an extremely superior appearance to the outer panels of automobiles, and by applying the present invention, economical effects can also be achieved. It is extremely large.

[Brief explanation of the drawing]

Figures 1 and 2 show acrylic resin: colloidal silica = 100:20 on a Zn-Ni alloy plated steel sheet that has been chromate treated to give a chromium adhesion amount of 75mg/ ^m2 .
(solid content weight ratio), and colloidal silica (SiO ₂ )
Apply an aqueous solution with different particle sizes, heat to 120℃,
Figures 3 and 4 show how the sharpness and cratering resistance change after ED when the film is applied to a film thickness of 1μ after drying, and the amount of chromium deposited is 75mg. Colloidal silica with a particle size of 4 to 6 ^mμ was used on a Zn-Ni alloy-plated steel sheet that had been chromate-treated so that the ratio of acrylic resin and colloidal silica (SiO ₂ ) was varied. This figure shows how the sharpness and cratering resistance change after ED when the coating is coated with a hot bath and heated to 120℃ so that the film thickness after baking and drying is 1.0μ. Figures 5 and 6 show that colloidal silica with a grain size of 4 to 6 mμ is used on a Zn-Ni alloy plated steel sheet that has been chromate-treated so that the chromium adhesion amount is 75 mg/ ^m2 . System resin: Colloidal silica = 100:20
(solid content weight ratio) After drying the aqueous liquid, the film thickness is
Figure 7 shows how the sharpness and cratering resistance after ED change when the coating is applied to a thickness of 1.0μ and the baking-drying temperature is changed.
Varying the amount of chromium deposited on the Zn-Ni alloy plated steel plate, add 100 parts (by weight) of acrylic resin to 4 to 6
This is a diagram showing how the adhesion of the film changes when 1.0μ (solid content) of an aqueous solution mixed with 30 parts (parts by weight) of colloidal silica of mμ is applied and baked and dried at 120°C. .

Claims (1)

[Claims] 1. The solid content of the water-based resin dispersion is applied to a chromate-coated plated steel sheet with a chromium adhesion amount of 10 to 150 mg/ ^m2 .
SiO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , MgO, ZrO ₂ , having a particle size of 1 mμ to 12 mμ per 100 parts by weight;
Apply an aqueous solution containing 5 to 100 parts by weight of one or more colloids (sols) of SnO ₂ , Al ₂ O ₃ , and Sb ₂ O ₅ as a solid content, and bake and dry at 100 to 150°C. A method for manufacturing a surface-treated steel sheet with excellent image clarity and cratering resistance.