JPH0414191B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for significantly improving various coating properties of an organic coating in the production of an organic composite steel sheet in which an organic coating is present on a galvanized steel sheet. That is, the present invention involves adjusting the colloidal sol of a specific fine particle size to a specific ratio in a bath of a specific organic resin to be applied to a chromate-coated plated steel sheet that has undergone chromate treatment, and improving the corrosion resistance and weldability of the formed film. It increases the product value by significantly improving the product value. The galvanized steel sheet referred to here refers to zinc, aluminum, tin, copper, etc. on the steel sheet.
A steel plate plated with chromium or nickel, or an alloy plated with one or more metals, and refers to electroplated steel plates or hot-dip galvanized steel plates. <Prior Art> Electrogalvanized steel sheets, hot-dip galvanized steel sheets, and various alloy-plated steel sheets have been manufactured so far, and have been widely used in home appliances, automobiles, 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 have also occurred in the automobile industry, such as corrosion caused by rock salt sprinkled on winter roads to prevent freezing in North America and Northern Europe, and corrosion caused by acid rain caused by the generation of SO ₂ gas in industrial areas. There is a strong demand for surface-treated steel sheets that are exposed to corrosive environments and have excellent corrosion resistance from a safety standpoint. In order to solve these problems, various studies have been made and many products have been developed. Until now, galvanizing has been used 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. Various alloy-plated steel sheets have been developed as a method for improving the corrosion resistance of such galvanized steel sheets. These alloy-plated steel sheets include, for example, Zn−
Ni series, Zn-Ni-Co series, Zn-Ni-Cr series, Zn-Fe
Examples include Zn-Co, Zn-Mn, and the like. It is recognized that these alloy platings improve the bare corrosion resistance by 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. Furthermore, in order to improve corrosion resistance, a so-called simple pre-coated steel sheet (hereinafter referred to as an organic composite steel sheet in the present invention), which is a zinc-plated steel sheet coated with a chromate material and a special resin, has been developed and some are commercially available. For example, Japanese Patent Publication No. 58-177476 (Japanese Patent Publication No. 61-36587),
JP-A-60-149786, JP-A-58-210192, JP-A-58-210190, JP-A-59-116397
Publications, etc. can be mentioned. These consist of applying 0.3 to 5 g/m ² of a special resin onto the steel plate, which significantly improves, in particular, the bare corrosion resistance. <Problems to be solved by the invention> However, even in these cases, the corrosion resistance cannot necessarily be said to be sufficient in a severe corrosive environment, and
If the coating thickness is increased in order to ensure corrosion resistance, welding becomes difficult, making it virtually impossible to use it for automobile steel plates and the like. As mentioned above, organic composite steel sheets with coatings that have both excellent corrosion resistance and weldability are still lacking. In contrast, the present invention aims to improve the adhesion of the organic film applied to the chromate-coated plated steel plate to the plated steel plate when producing an organic composite steel plate, the adhesion with the top coat, fingerprint resistance, scratch resistance, and moldability. , which significantly improves various coating film properties, especially corrosion resistance and weldability. <Means for solving the problems> The present invention involves adding a polymerizable ethylenically unsaturated compound to a dispersion of an ethylene and α,β unsaturated carboxylic acid copolymer, carrying out emulsion polymerization, and crosslinking after completion of the polymerization. SiO ₂ , Cr ₂ O ₃ , Fe 2 O ₃ , Fe ₃ O ₄ , MgO, having _a particle size of 2 mμ to 12 mμ is added to the obtained aqueous resin.
Colloidal sol of ZrO ₂ , SnO ₂ , Al ₂ O ₃ , Sb ₂ O ₅
An aqueous liquid containing 5 to 100 parts by weight of the solid content of one or more species based on 100 parts by weight of the solid content of the water-based resin is applied to the surface of a chromate-coated galvanized steel sheet with a chromium deposition amount of 5 to 200 mg/ ^m2 . This is a method for surface treatment of steel sheets, which is characterized by coating the surface of the steel plate with a dry coating and forming a dry film. The base of the aqueous resin used in the present invention is a copolymer consisting of ethylene and α,β unsaturated carboxylic acid. Water can be dispersed by neutralizing the acid groups contained in this resin with a basic substance. The ratio of ethylene to α,β unsaturated carboxylic acid is ethylene 97-40
% by weight and α,β unsaturated carboxylic acid from 3 to 60% by weight. The base required for neutralization is lithium hydroxide,
Examples include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, morpholine, triethylamine, and dimethylethanolamine, and ammonia and lower amines are suitable for the present invention. The production of an aqueous dispersion of an ethylene, α,β-unsaturated carboxylic acid copolymer is generally carried out in hot water at about 60 to 200°C with stirring for 1 to 8 hours. Next, a polymerizable ethylenically unsaturated compound is introduced into this system and emulsion polymerization is performed. This operation may be carried out by a method commonly used as emulsion polymerization, but the compounds used include ethylenically unsaturated compounds containing carboxyl groups, such as maleic acid, acrylic acid, methacrylic acid, croton, etc., in order to carry out the crosslinking reaction. Acids etc. are used alone or in combination. Furthermore, styrene, aminostyrene, methylstyrene, acrolein, acrylonitrile, methyl methacrylate, acrylamide, dihydroxyethyl acrylate, isopropyl methacrylate, ethyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate, hexyl acrylate. , methoxypolyethylene glycol acrylate, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl oleate, vinyl sulfonic acid, Beova 10 (Ciel Chemicals), etc., singly or in combination with ethylenically unsaturated compounds that do not contain carboxyl groups. is preferably used in combination with the ethylenically unsaturated compound containing a carboxyl group. Polyfunctional (meth)acrylates such as glycidyl methacrylate, ethylene glycol dimethacrylate, and glycerin trimethacrylate are used so that a slight polymerization reaction occurs during the emulsion polymerization.
If necessary, reactive acrylates such as acrylates may be used in combination. In the emulsion polymerization method, a surfactant, a surfactant, and
This is carried out using a polymerization initiator, a PH adjuster, etc., and protective colloids, a solvent, etc. can be used in combination as necessary. In the present invention, the weight ratio of the ethylene, α, β-unsaturated carboxylic acid copolymer and the polymerizable ethylenically unsaturated compound used for emulsion polymerization is 90/90/1, respectively.
You can achieve your goal in 10-10/90. During the above emulsion polymerization, it is mixed at the molecular level,
Although the grafting and the reaction type acrylate further proceed with some reactions under the polymer, in the present invention, after the emulsion polymerization is completed, crosslinking is further performed using a crosslinking agent. Crosslinking agents are methylolmelamines that have a hydroxyl group as a reactive group, epoxy compounds that have an epoxy group as a reactive group, imines and aziridines that have a cyclic secondary amine as a reactive group that can react with two or more carboxy groups. Compounds having groups can be used alone or in combination. The crosslinking agent used is added to the emulsion after the emulsion polymerization is completed in an amount of 0.01 to 1.4 equivalents per equivalent of carboxyl group in the resin.
The crosslinking agent used usually has two or more functional groups, and the
If it is less than 0.01 equivalent, it will not be effective, and if it is more than 1.4 equivalent, it will lack stability and will further reduce adhesion, making it impractical. The crosslinking reaction is usually carried out at a reaction temperature of 120° C. or lower and takes several hours. This crosslinking reaction produces a resin having a crosslinked structure that prevents the dry film from dissolving from the emulsion. As shown below, an ethylenically unsaturated compound is graft-polymerized onto a copolymer of ethylene and an α,β-unsaturated carboxylic acid, and a crosslinking reaction is further introduced to form a single body at the molecular level.
mμ to 12mμ SiO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ ,
One or more colloidal sols of MgO, ZrO ₂ , SnO ₂ , Al ₂ O ₃ , Sb ₂ O ₅ as solid content
Water solubility can be obtained by adding 100 parts by weight. <Function> The excellent characteristics of the present invention depend on the particle size and amount of the colloidal sol added to the water-based resin, and the use of fine colloidal sol with a specific particle size or less, and
It can only be obtained by limiting the amount added. As a result of detailed study, the present inventors found that the colloidal sol must meet the following conditions. Particle size of colloidal sol: 2 mμ to 12 mμ Amount of colloidal sol added: 5 to 100 parts by weight per 100 parts of coexisting resin A bath that satisfies the above conditions is applied onto a plated steel plate, and when it dries, it improves corrosion resistance and weldability. It was confirmed that an extremely excellent film was formed and that an excellent organic composite steel sheet could be manufactured. When the particle size of the colloid is 2 mμ or less, the adhesion of the dry coating film to the chromate-coated plated steel plate, the adhesion with the top coat, the fingerprint resistance, the scratch resistance, the molding process, etc. Although the properties are good, corrosion resistance and weldability are reduced, and the stability of aqueous liquids is poor, making it unsuitable. Moreover, if it is 12 mμ or more, there is no problem with the stability of the aqueous liquid, but there is no significant improvement in corrosion resistance or weldability among the above coating properties, which is unsuitable. Regarding the amount of colloid added, if the solid content ratio is less than 5 parts by weight with respect to 100 parts by weight of the solid content of the water-based resin, the corrosion resistance will be poor, and even if it is added more than 100 parts by weight, the corrosion resistance will not improve. Furthermore, it is difficult to form a continuous organic film, and therefore the forming processability such as drawing workability is mainly poor, making it unsuitable. Colloidal silica for types of colloids
SiO ₂ is economically advantageous, but Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ ,
Similar results can be obtained using colloidal sols of MgO, ZrO ₂ , SnO ₂ , Al ₂ O ₃ , and Sb ₂ O ₅ .
Similar results can also be obtained by containing two or more of the above colloids. <Example> Production example of water-based resin Production example-1 In a pressurized reaction tank, 200 g of Dow Chemical's product Primacol 5983, which is an α,β unsaturated carboxylic acid copolymer of ethylene, 18 g of 28% ammonia water, and 600 g of water
After charging with _N2 , the temperature was raised while stirring. After keeping the temperature under stirring at 140°-150°C for 3 hours,
It was cooled to obtain an ethylene dispersion. To this dispersion, 2 g of potassium persulfate was added to water while stirring.
The solution dissolved in 210 g was added and the temperature was raised to 80°C again. A mixture of 20 g of methyl methacrylate, 18 g of butyl methacrylate, and 4 g of methacrylic acid was added dropwise over 1 hour while stirring, and at the same time a solution of 2 g of potassium persulfate dissolved in 50 g of water was added dropwise. 20 minutes after the dropwise addition was completed, 20 g of the crosslinking agent Epicote 256 was added under stirring, and a crosslinking reaction was carried out at 80-85°C for 3 hours. The resulting emulsion had a non-volatile content of 22% and a pH of
It was 9.2. Production Examples 2, 3, 4 Examples produced using the same procedure are shown in the table below.

【table】

[Table] Comparative Production Examples 1 and 2 are the dispersions of ethylene and α,β-unsaturated carboxylic acid copolymers produced in Production Examples 1 and 2, and the polymerizable ethylene-based unsaturated copolymer dispersions produced in Production Examples 1 and 2. Comparative Examples 1 and 2 are obtained by emulsion polymerizing and mixing a saturated compound alone, and Comparative Examples 1 and 2 are those of Production Example 1,
This is a liquid mixture corresponding to 2. Example 1 A Zn-Ni alloy plated steel sheet (Ni = 11.2%) with a plating weight of 20 g/m ² was treated with chromate so that the Cr coating weight was 60 mg/m ² , and the water-based coating shown in Production Example 1 was prepared. An aqueous solution of colloidal silica with a particle size of 5 to 6 mμ adjusted to 20 parts by weight per 100 parts by weight of the solid content is applied onto the resin, and dried.
A film was formed at a density of 1.0 g/m ² . Example 2 For the steel plate shown in Example 1, an aqueous liquid prepared by adding colloidal silica having a particle size of 5 to 6 mμ to 100 parts by weight of the aqueous resin solid content shown in Production Example 2 so that the solid content was 20 parts by weight was prepared. on it, dry it and
A film was formed to have a weight of 1.2 g/m ² . Example 3 A Zn-Ni-Co alloy plated steel sheet (Ni = 11.3%, Co = 0.3%) with a plating weight of 20 g/m ² was chromate-treated so that the Cr coating weight was 80 mg/m ² . Cr ₃ O ₃ with a particle size of 8 to 10 mμ is added to the aqueous resin shown in Production Example 1.
An aqueous solution prepared by adjusting the sol to 30 parts by weight (solid content) per 100 parts by weight (solid content) of the resin is applied on top of the sol, and a film is formed so that it dries to 1.0 g/ ^m2 . Formed. Example 4 A Zn-Fe alloy coated steel plate with a plating weight of 20 g/m ² was treated with chromate so that the Cr adhesion was 50 mg/m ² , and the water-based resin shown in Production Example 3 was coated with a particle size of 3. An aqueous solution containing ~5 mμ Al ₂ O ₃ sol adjusted to 50 parts by weight (solid content) per 100 parts by weight (solid content) of the water-based resin was applied on top of the aqueous solution and dried.
A film was formed to have a weight of 1.2 g/m ² . Example 5 A Zn-Mn alloy plated steel plate (Mn=41%) with a plating weight of 20 g/m ² was treated with chromate so that the Cr coating weight was 60 mg/m ² and the water-based coating shown in Production Example 3 was prepared. 100 parts by weight (solid content) of resin with a particle size of 3 to 5 mμ
An aqueous solution of SnO ₂ sol adjusted to 30 parts by weight (solid content) was applied on top of it and dried to give 0.9 g/
A film was formed to have an area of m ² . Comparative Example 1 In place of colloidal silica in Example 1, the particle size was
A film was formed in the same manner as in the example except that colloidal silica of 15 to 20 mμ was used. Comparative Example 2 Colloidal silica with a particle size of 5 to 6 mμ was prepared in the same manner as in Example 1 to a resin solid content of 100% as shown in Example 1.
Based on the weight part, 150 parts by weight (solid content) was added to form a film. Comparative Example 3 Colloidal silica with a particle size of 5 to 6 mμ was added to the resin solid content shown in Example 1 in the same manner as in Example 1.
Add 2 parts by weight (solid content) to 100 parts by weight,
A film was formed. Comparative Example 4 Manufactured using the chromate-treated plated steel plate shown in Example 1. Colloidal silica with a particle size of 5 to 6 mμ was adjusted to 20 parts by weight in solid content of the aqueous resin shown in Comparative Example 1 to 100 parts by weight. 1.0 in aqueous liquid
A film of g/m ² was formed. Comparative Example 5 A film was formed in the same manner as in Comparative Example 4 except that the aqueous resin shown in Manufacture Comparative Example 2 was used. Examples 1, 2, 3, 4, 5 and comparative example 1,
Table 1 shows the results of various tests conducted on the surface-treated steel sheets obtained in steps 2, 3, and 4. Various test conditions are as follows. (1) Corrosion Resistance The incidence of white rust (%) after 1500 hours and the incidence of red rust (%) after 4000 hours were determined by a salt spray test in accordance with JIS-Z-2321. (2) Paint adhesion The paint and evaluation method are as follows. Paint adhesion is melamine-based (baking condition 280℃ x
The paint adhesion evaluation method uses baking paint (60 seconds).
Drawn according to JIS-5400, Eriksen's eyes,
Impact and 2T bending tests were conducted, and judgments were made based on the overall evaluation of these tests. Evaluation is ◎, ○,
Perform the test in five stages: △, ×, and XX, with ◎ being the best. ◎: Paint film peeling area 0% ○: 〃 0~1% △: 〃 1~10% ×: 〃 10~50% ××: 〃 50% or more (3) Spot welding method In the continuous welding test, the nugget diameter was 4 mmφ The evaluation was based on the number of consecutive hits until . ◎: 5,000 points or more ○: 4,500 to 5,000 points △: 4,000 to 4,500 points ×: 3,500 to 4,000 points XX: 3,500 points or less (4) Film adhesion After cross-cutting, 7 mm of Erichsen was extruded, and then cellophane tape was peeled off. In addition, after the 2T bending test, the tape was peeled off and a comprehensive evaluation of both was performed. (5) Alkali resistance Commercially available alkaline degreasing liquid (PH10.0-10.5, 60℃
Judgment was made based on the weight loss after immersion (immersion for 2 minutes). Evaluation is ◎: weight loss 0%, ○: weight loss 1% or less, △: weight loss 1-5%, ×: weight loss 5-10%,
XX: Evaluated on a five-point scale with weight loss of 10% or more. (6) Solvent resistance Judgment was made by weight loss after immersion in trichloroethane solution for 2 minutes. (7) Pencil hardness Determined by pencil hardness. (8) Processability After drawing a cylinder of 40φ for 25 hours, the cellophane tape was peeled off from the side wall.

[Table] (8) Processability ◎ ◎ ◎
◎ ◎ ◎ × ○ ○ ×

Claims (1)

[Claims] 1. A water-based resin obtained by adding a polymerizable ethylenically unsaturated compound to a dispersion of an ethylene and α,β unsaturated carboxylic acid copolymer, carrying out emulsion polymerization, and further crosslinking after completion of the polymerization. , SiO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , MgO, ZrO ₂ with a particle size of 2 mμ to 12 mμ,
One or more colloidal sols of SnO ₂ , Al ₂ O ₃ , and Sb ₂ O ₅ are added in a solid content of 5 to 100 parts per 100 parts by weight of the solid content of the water-based resin.
A method for surface treatment of a steel sheet, which comprises applying an aqueous liquid containing parts by weight to the surface of a chromate-coated galvanized steel sheet having a chromium adhesion amount of 5 to 200 mg/m ² to form a dry film.