JPH0476392B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a coating composition for rust-proofing steel plates, and more specifically, it relates to a coating composition for rust-proofing steel plates, and more specifically, it has excellent electrodeposition coating properties, high corrosion resistance, high processing adhesion, and can provide a coating film that can be spot welded. The present invention relates to a coating composition for rusted steel plates. Prior Art In recent years, coated steel plates have been increasingly adopted to improve productivity in the automobile, fixtures, home appliances, etc. industries, and various paint compositions for anti-corrosion coated steel plates have been developed to meet this demand in the paint field. Ta. However, conventional coating compositions do not sufficiently satisfy various quality requirements for coated steel sheets, such as those required for press working, electrodeposition coating, spot welding, and the like. In other words, Special Public Service 1972-24230
Although the zinc-rich paints proposed in Japanese Patent Publication No. 47-6882, etc., are capable of electrodeposition coating, their press workability is insufficient and their corrosion resistance and weldability are not sufficient. Japanese Patent Publication No. 58-138758
Paints containing conductive pigments proposed in Japanese Patent Application Laid-open No. 51-79138 and Japanese Patent Publication No. 58-19706 have significantly improved corrosion resistance and weldability on galvanized steel sheets, etc. However, since it contains relatively large pigment particles such as metal powder, metal carbide, and metal phosphide, the surface of the electrodeposited film is extremely uneven, lacks film smoothness, and has insufficient press formability, resulting in damage to the application area. Japanese Patent Application Laid-Open No. 60-197773 made it possible to perform electrodeposition coating with a thin film of 0.3 to 3μ without containing conductive pigments.
No. 60-199074, No. 58-224174, No. 60-
Although the organic composite silicate film proposed in No. 174879 and other papers and steel sheets coated with it have been improved in terms of high corrosion resistance, weldability, press formability, etc., there are problems with the unevenness of the electrodeposited surface, especially in the organic composite silicate film. There remains the problem that the surface of the electrodeposited film changes greatly in response to minute changes in the film thickness, making it impossible to obtain a smooth electrodeposited film. As described above, all of the techniques proposed in the past are insufficient in terms of the quality required for today's coated steel sheets, and problems arise particularly in terms of adhesion and smoothness of electrodeposition coatings in humid and corrosive environments. There are many. Problems to be Solved by the Invention Therefore, the present invention provides a coating composition for rust-preventing steel plates, which has excellent electrodeposition coating properties (electrodeposition film adhesion and smoothness) without using conductive pigments, has high anticorrosion ability, and has high pressability. If we can propose a paint composition that can be spot welded, it would be extremely useful as a paint for painted steel sheets because it would meet the quality requirements in the automobile, fixtures, and home appliance industries. This is the main purpose of the invention. Another object of the present invention is to provide a coating composition for a coated steel plate that exhibits small quality changes due to variations in coating film thickness of the coating composition for a rust-preventing steel plate in electrodeposition coating, and has excellent productivity. Means for Solving the Problems According to the present invention, the above-mentioned purpose is achieved by (a) epoxy resin containing 50% by weight or more of phenol in the molecule, the epoxy resin in the presence of an amine catalyst or in the absence of an amine catalyst; An epoxy ester resin having a number average molecular weight of 300 to 100,000 selected from the group consisting of an epoxy ester resin obtained by reacting a dicarboxylic acid in the presence of the epoxy ester resin and a urethanized epoxy ester resin obtained by reacting the epoxy ester resin with a partially blocked isocyanate compound. 30 to 90% by weight of binder resin (-CH ₂ - and/or =CH-)/(-
CONH-) ratio of 7/1 to 0/1 and a degree of polymerization of 5 to 40% by weight of a hydrophilic polyamide resin (c) 5 to 40% of silica particles with an average particle diameter of 1 to 100 mμ
This can be achieved by providing a solvent-based rust-preventing coating composition for steel sheets, characterized in that it contains % by weight. As mentioned above, the present invention is characterized by a combination of a highly water-resistant epoxy resin, a hydrophilic polyamide resin, and fine silica, and the hydrophilic polyamide resin is necessary for the smoothness of the electrodeposited film. However, the combination of hydrophilic polyamide resin, flexible resin and high hardness particles of fine silica gives good results for the lubricity of the film, but electrodeposition This was completed based on the knowledge that a highly water-resistant epoxy resin binder was required due to insufficient adhesion to the film. The epoxy binder resin used in the present invention is an organic solvent-soluble type with excellent corrosion resistance, water resistance, adhesion, chemical resistance, hardening properties, etc., contains 50% by weight or more of phenol, and has a number average molecular weight. is 300~
100000, preferably 1000-20000 epoxy resin
a ₁ Among these, bisphenol type epoxy resin, resorcinol type epoxy resin, or a mixed resin thereof is used. If the number average molecular weight is less than 300, the durability of the film formed will be insufficient, and if it exceeds 100,000, the viscosity of the paint will increase and a uniform coating film will not be formed, making it impossible to obtain the desired quality. For example, the expression (In the formula, R is H or CH ₃ ; -A- is >C
( _CH3 ) ₂ , _-CH2- , -O-,

[Formula], or -S-; n is 0 or an integer of 1 to 14) Resin represented by the following may be used, and specific examples thereof include the product name "Epotote" manufactured by Toto Kasei Co., Ltd.
YD-017”, “YD-014”, “YD-011”, “YD-011”, “YD-014”, “YD-011”,
Commercial products such as "YD-128" and "Epiclon 4050" manufactured by Dainippon Ink and Chemicals Co., Ltd. are listed.
100,000 polyalkylene glycol glycidyl ether, etc.). When the above substitution rate exceeds 50% by weight, corrosion resistance, water resistance, adhesion, chemical resistance, hardenability, etc. tend to decrease. The present invention also provides _an epoxy ester resin ( _{A 1}
or A ₁ ′) can also be used as a binder resin. Examples of dicarboxylic acids _a2 used in this case include polymethylene dicarboxylic acids (adipic acid, azelaic acid, sebacic acid, etc.), aromatic dicarboxylic acids (phthalic anhydride, phthalic acid, isophthalic acid, terephthalic acid, etc.), dimer Examples include dicarboxylic acids having a molecular weight of 5000 or less, such as acid, polybutadiene dicarboxylic acid, and polyester dicarboxylic acid, and one or more of these can be used. In particular, polymethylene dicarboxylic acid is preferred from the viewpoint of processability, solubility, and compatibility, and azelaic acid is most preferred. It also takes a molecular weight of _two components
Trivalent carboxylic acids having a value of 5,000 or less may be used in combination within the same weight as the dicarboxylic acid. By reacting the dicarboxylic acid with the epoxy resin, the epoxy ring opens and the acid is incorporated into the resin through an ester bond. On this occasion,
For example, it is preferable to use an amine catalyst, and in the present invention, a secondary amine _a3 having a primary hydroxyl group is particularly preferably used, and the amine itself is incorporated into the resin along with the catalytic action to form a primary hydroxyl group. will give. This epoxy ester resin having a primary hydroxyl group is designated as [A ₁ ]. Examples of the secondary amines that can be used include dialkanolamines (diethanolamine, dipropanolamine, dibutanolamine, etc.), alkylalkanolamines (ethylethanolamine, etc.), and one or more of these can be used. put it into use. Particularly preferred are dialkanolamines, with diethanolamine being most suitable. Furthermore, tertiary amines (triethylamine, tributylamine, etc.) or quaternary amines (tetramethylammonium chloride, tetrabutylammonium chloride, etc.) can also be used as amine catalysts.
In this case, the primary hydroxyl group derived from the amine described above is not introduced as in the case where no amine catalyst is used, but the desired epoxy ester resin is obtained, which is designated as [A ₁ ']. The reaction is carried out by melting the epoxy resin or dissolving it in a suitable non-reactive solvent, then adding the dicarboxylic acid component and the amine catalyst component, and if necessary under _N2 gas.
Usually, the reaction may be carried out by heating at 80 to 200°C for 1 to 15 hours. Esterification improves coating film flexibility. In the present invention, a resin [A ₂ ] obtained by urethanizing the above-mentioned epoxy ester resin is also used as a binder resin in order to further improve the adhesion to the substrate. In this case, the above first
A partially blocked polyisocyanate compound [B] is reacted with an epoxy Esthes resin [A ₁ ] having a class hydroxyl group, and this compound [B] is a mixture of a polyisocyanate compound b ₁ and an isocyanate protecting agent b ₂ , b Number of ₁ isocyanate groups/
It is obtained by reacting at a ratio such that the ratio of the number of active hydrogen groups in b ₂ is 5/1 to 5/4. This reaction is usually carried out without a solvent or in a hot reaction solvent at _a temperature between room temperature and 150 _° C. It is preferable to carry out the reaction while dropping a solution with a non-reactive solvent, from the viewpoint of the quality of the product [B] and reaction control. Examples of the polyisocyanate compound b ₁ include aliphatic or alicyclic diisocyanate compounds (hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, etc.), and aromatic diisocyanate compounds. (Tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, etc.) Triisocyanate compound (adduct of 1 mol of trimethylolpropane and 3 mol of the above diisocyanate,
trimers of diisocyanates such as hexamethylene diisocyanate and tolylene diisocyanate), and one or more of these may be used. Particularly suitable are aliphatic or alicyclic diisocyanate compounds from the viewpoint of solubility, compatibility and processability of the thermosetting resin. The isocyanate protecting agent b ₂ is such that the adduct formed by adding it to the isocyanate group of component b ₁ is stable at room temperature and dissociates when heated to 140 to 250°C to regenerate free isocyanate groups. It must be something that does that. Examples of such protective agents include lactam-based protective agents (ε-caprolactam, γ-butyrolactam, etc.), oxime-based protective agents (methyl ethyl ketoxime, cyclohexanone oxime, etc.), alcohol-based protective agents (methanol, ethanol, isobutyl alcohol, etc.),
Examples include phenolic protective agents (phenol, paratertiary butylphenol, cresol, etc.). The urethanized epoxy ester resin [A ₂ ] can be produced very conveniently by reacting the above product [A ₁ ] with [B]. In this case, _the reaction rate is
The ratio of the number of class hydroxyl groups/the number of free isocyanate groups contained in the product [B] is 10/1 to 10/
8, preferably in the range of 10/1 to 10/6. This is because the above ratio is
This is because when the ratio is greater than 10/1, the hardenability of the coating film decreases, and when this ratio is less than 10/8, it tends to cause gelation during paint production. The reaction is usually carried out at a temperature of 50-150<0>C, optionally under _N2 gas, until substantially no isocyanate groups are present. In some cases, even if isocyanate groups remain, once the molecular weight reaches the desired value,
For example, the reaction may be stopped by adding a primary alcohol. The number average molecular weight of the urethanized epoxy ester resin [A ₂ ] produced in this way is 6000~
100000 is appropriate. This molecular weight is mainly controlled by the molecular weight of the epoxy ester main chain, and the ratio of g equivalent of glycidyl group of epoxy resin a ₁ / g equivalent of carboxyl group of polyvalent carboxylic acid a ₂ is 1.1 to 1.
1.4, preferably 1.15 to 1.25, and the acid value of the reaction product of a ₁ and a ₂ is 2 (KOHmg/g)
Hereinafter, it is preferable to complete the reaction so that the concentration becomes preferably 1 (KOHmg/g) or less. Such thermosetting resins contribute to the provision of paints with excellent adhesion, processability, corrosion resistance, water resistance, and chemical resistance, which have been conventionally required. In addition, taking into account epoxy resins with relatively low molecular weights and epoxy ester resins with relatively large molecular weights, the number average molecular weight of the epoxy binder resin is within the range of 300 to 100,000, and such resin has a content of 30 to 90% of the non-volatile content of the paint. Makes up % by weight. If the amount of the resin is less than 30% by weight, the adhesion and processability of the electrodeposited film will deteriorate, which is not preferable. In the present invention, a hydrophilic polyamide resin is used as a second resin component together with the binder resin in an amount of 5 to 40% by weight based on the nonvolatile content of the paint. This polyamide resin has (−CH ₂ − and/or
Or the ratio of =CH-)/(-CONH-) is 7/1
~0/1, and the degree of polymerization is 50 to 1000. Various types of polyamide resins having acid amide bonds in the molecule are known, such as nylon 6, nylon 66, and nylon, which are aliphatic polyamides obtained by ring-opening polymerization of lactam or polycondensation of alkylene diamine and dibasic acid. 610, or copolymers of these and other nylons; polyether polyol-modified nylons from lactams and polyols, polybutadiene polyol-modified nylons, polyester polyol-modified nylons (e.g., JP-A-61-12729, JP-A-61-12728) Alternatively, aromatic polyamides such as polymetaphenylene isophthalamide and polyparaphenylene terephthalamide are known, and in the present invention, among these known polyamide resins, -CH ₂ - groups and/or Or the ratio of the total number of =CH- groups including aromatic ones to the number of -CONH- groups is in the large range of 7/1 to 0/1, and the degree of polymerization is 50 to 0/1.
Any polyamide resin can be suitably used as long as it is within the range of 1000. Such resins have traditionally been used for curing epoxy resins.
Unlike polyamide resin, which has a CH ₂ −/−CONH− ratio of 10/1 to 20/1 and a degree of polymerization of about 5 to 20, it has a large number of acid amide bonds and is highly hydrophilic and highly hygroscopic.
It also has the characteristics of a high degree of polymerization and an extremely high molecular weight. The present inventors have found that by using such a hydrophilic polyamide resin, the electrodeposition liquid penetrates into the coating film during electrodeposition coating, the electrical resistance value of the coating film decreases, good electrodeposition properties are produced, and the electrodeposition film appearance was found to be significantly improved, and this became one of the important basis of the present invention. If the ratio of (-CH ₂ - and/or =CH-)/(-CONH-) in the polyamide skeleton is greater than 7/1, there will be insufficient hydrophilic groups and no improvement in electrodepositivity will be observed. Furthermore, the high molecular weight of the polyamide resin is useful for surface treatment and prevention of resin dissolution during electrodeposition. In other words, the degree of polymerization is 50~
1000, preferably 50 to 500. If the degree of polymerization is less than 50, the coating film will dissolve during electrodeposition and uniform electrodeposition will not be obtained, and a decrease in acid resistance will be observed.
If it exceeds this amount, the polymer is too high and is inappropriate for the purpose of the invention. Incorporation of polyamide resin is also desirable for imparting flexibility and high processability. Regarding the amount of the polyamide resin blended into the paint, the above polyamide resin has a content of 5 to 50% of the non-volatile content of the paint.
It is selected within the range of 40% by weight, preferably from 5 to 25% by weight. This is because if it is less than 5% by weight, there is no effect of improving electrodepositivity, and if it exceeds 40% by weight,
This is because, on the contrary, a decrease in the adhesion of the electrodeposited film is observed. Next, in the present invention, finely divided silica having an average particle size of 1 to 100 mμ is used in an amount of 5 to 40% by weight based on the nonvolatile content of the paint for the purpose of improving corrosion resistance. If the primary particle size of the silica particles is less than 1 mμ, the alkali resistance will deteriorate, which is undesirable, and if it exceeds 100 mμ, there will be no effect of improving corrosion resistance, and the smoothness of the electrodeposited film will also deteriorate. Therefore, the average particle size of silica particles is 1~
Must be in the range of 100mμ, especially 5-50mμ
Preferably, the range is . Examples of such silica particles include fumed silica and colloidal silica, and among them, fumed silica is preferably used. Colloidal silica contains ammonium ions and alkali metal ions for colloidal stabilization, and these ions tend to reduce membrane anticorrosion ability. The amount of silica particles added is 5 to 40% by weight, preferably 10 to 20% by weight based on the nonvolatile content of the paint.
If it is less than 5% by weight, there is no effect of improving corrosion resistance.
Moreover, if it exceeds 40% by weight, a decrease in processability is observed, which is insufficient for the purpose of the invention. In the present invention, each of the above components is dissolved or dispersed in an organic solvent to obtain a coating composition. The organic solvent is appropriately selected from various solvents commonly used for paints, such as various hydrocarbons, esters, ketones, alcohols, and amides, but it is also possible to select one that dissolves both epoxy resin and polyamide resin. Alternatively, you can use a combination of various solvents, such as dissolving the epoxy resin in a mixed system of xylene, methyl ethyl ketone, cellosolve acetate, isopropyl alcohol, etc., dissolving the polyamide in a mixed solvent of alcohol and hydrocarbon, and mixing the two. The polyamide resin may be directly dispersed and contained in the epoxy resin varnish. However, when the polyamide resin is used in a dispersed manner, the particle size is preferably 5 mμ or less. 5mμ
If it exceeds this, the smoothness of the electrodeposited film will decrease. The preparation of the paint is carried out in accordance with the preparation of ordinary solvent-based paints, and no special techniques are required. As described above, the coating composition of the present invention contains specific amounts of an epoxy binder resin, a hydrophilic polyamide resin, and particulate silica as nonvolatile components, and the combination of these three components additively improves the electrodeposition coating properties. It has high corrosion resistance, high workability, excellent adhesion, and can provide a smooth, spot-weldable coating. Regarding processability, the coating composition of the present invention contains lubricants such as polyolefins, carboxylic esters, carboxylic acid metal salts, and polyalkylene glycols, as well as lubricant powders such as molybdenum disulfide, silicone compounds, and fluorine compounds. For non-volatile content
It is preferable to add 20% by weight or less, preferably 1 to 10% by weight, to further improve processability. Particularly preferred lubricants have a density of 0.94 or more and a molecular weight of 1000 or more.
10,000, a polyethylene wax with an acid value of 15KOHmg/g or less. However, when adding a lubricant,
The maximum amount added should be up to 20% by weight; if it exceeds this amount, the adhesion of the electrodeposited film will deteriorate, which is not desirable. Furthermore, in the coating composition of the present invention, a curing agent such as a melamine resin, a resol type phenolic resin, or a polyisocyanate is added to the epoxy resin at a solid weight ratio of curing agent/epoxy resin = 0.1/9.9/~4/.
It can be contained in a ratio of 6 to 6 and thermally cured. Particularly preferable resol type phenolic resins have the formula (In the formula, n is 0 to 4; W is -CH ₂ - or -CH ₂ -
O-CH ₂ -; R is CH ₃ , H or

It is a resol type phenol resin represented by the following formula. The coating composition of the present invention is extremely useful as a coating composition for anti-rust coated steel sheets used in automobiles, fixtures, and electrical appliances, and can be used as a base material for hot-dip galvanized steel sheets, hot-dip galvanized aluminized steel sheets, and electrogalvanized steel sheets. , electrolytic zinc/nickel or electrolytic zinc/iron alloy plated steel sheets, electrolytic zinc/iron double-layer plated steel sheets, cold rolled steel sheets, etc. The coating composition of the present invention is applied to these substrates after the surfaces thereof have been cleaned, such as by alkaline degreasing, if necessary, and after these substrates have been directly or subjected to conventional pre-painting treatment. As this pre-painting treatment, chromate chemical conversion treatment and phosphate chemical conversion treatment are used; the former includes electrolytic chromate, coating-type chromate, and reactive chromate treatment, and the latter includes zinc phosphate treatment. The coating composition of the present invention is applied by a suitable coating method such as spraying, roll coating, shower coating, etc., and dried to form a coating film. Preferably
Baking drying is performed at 100-250°C. A steel plate coated with the coating composition of the present invention to a dry film thickness of about 0.3 to 3 microns exhibits excellent corrosion resistance, excellent lubricity, good press workability, and can be spot welded. Furthermore, the particularly excellent characteristics of the steel plate coated with this coating composition are the smoothness of the electrodeposited film formed by the electrodeposition coating,
The coating composition of the present invention exhibits extremely good quality in terms of uniformity and adhesion. Therefore, the coating composition of the present invention is a coating for rust-proofing steel sheets that can meet the high quality requirements in various fields such as automobile fixtures and home appliance industries. It is extremely useful as a composition. The present invention will be explained below with reference to Examples. Parts and percentages are by weight unless otherwise specified. Production Example 1 Method for producing urethanized epoxy ester resin varnish After dissolving 475 parts of epoxy resin (trade name: "Epotote YD-014" manufactured by Toto Kasei Co., Ltd., epoxy equivalent: 950) in 95 parts of xylol and 119 parts of cellosolve acetate, 39.2 parts of azelaic acid was dissolved. and 8.3 parts of diethanolamine were added, and the reaction was carried out at 145°C for 6 hours. When the acid value of the resin solid content reached 1.1 KOHmg/g, 209 parts of xylol and 130 parts of methyl ethyl ketone were added.
1 part and cooled to obtain product A. Separately, 222 parts of isophorodiisocyanate is dissolved in 222 parts of cellosolve acetate, heated to 80°C, and then a solution of 113 parts of ε-caprolactam and 113 parts of cellosolve acetate is added dropwise over 1 hour to react. After completion of the dropwise addition, the reaction was completed while keeping the temperature at 80° C. for another 3 hours to obtain Product B having an isocyanate equivalent of 670 g. Next, 55.9 parts of product B and 118 parts of cellosolve acetate were added to the above product A, and after reacting at 100°C for 3 hours, 102 parts of isopropyl alcohol was added and cooled to obtain a urethanized epoxy ester resin varnish. Production Example 2 Process for producing polypropylene glycol-modified nylon-6 A mixture of 70% by weight of substantially anhydrous ε-caprolactam and 30% by weight of polypropylene glycol having a molecular weight of 4000 was melted and held at 80°C, and sodium caprolactamate was added thereto. After adding 1 mol% of ε-caprolactam and 2 mol% of pyridine dicarbonyl biscaprolactam prepared by the method of Reference Example (*) to ε-caprolactam and uniformly blending, the mixture was immediately heated to 140°C. It was injected into a mold that was held and polymerization was carried out at the same temperature. Polymerization was completed in about 6 minutes. *Reference example: In a flask equipped with a stirrer and a nitrogen introduction tube, 1
mol of pyridine-2,6-dicarboxylic acid dichloride, 6 mol of ε-caprolactam, and pyridine as a hydrogen chloride scavenger were charged, and the mixture was heated under a nitrogen atmosphere.
The reaction was carried out at 120°C for 1 hour. Next, the reaction mixture was poured into a large amount of cold water to precipitate the reaction product, which was separated by filtration, washed sequentially with pure water and methanol, and dried in vacuum to produce pyridine dicarbonyl biscaprolactam as an off-white powder. Obtained. Example 1 To 48 parts of the urethanized epoxy ester resin varnish (in terms of solid content weight) obtained in Production Example 1, 12 parts of resol type phenol resin (in terms of solid content weight) was added, and then to the polypropylene glycol-modified nylon 6 obtained in Production Example 2 (solid content weight equivalent) 20 parts varnish obtained by dissolving 20 parts (solid content weight equivalent) in N-methyl-2-pyrrolidone to a concentration of 20% by weight, 15 parts fumed silica with a particle size of 8 mμ, and polyethylene powder (Hoechst Co., Ltd.) , Product name Seridust 3620, Density 0.95~
0.97, molecular weight 2000, acid value 0) and were uniformly stirred and mixed to obtain a coating composition whose nonvolatile content concentration was adjusted to 20% by weight with N-methyl-2-pyrrolidone. Examples 2 to 10 and Comparative Examples 1 to 7 Coating compositions having a non-volatile concentration of 20% by weight were obtained in the same manner as in Example 1, but using the raw materials listed in Table 1. The resins used in these Examples and Comparative Examples are as follows. Epoxy resin: Epotote YD017 (bisphenol A type epoxy resin, Toto Kasei) Nylon 12: -CH ₂ -/-CONH = 11/1 Degree of polymerization 200 (not inventive) Nylon 6: -CH ₂ -/-CONH = 5/ 1 Degree of polymerization 200 Fatty acid polyamide: -CH ₂ -/-CONH=16/
1 degree of polymerization 10 Polymetaphenylene isophthalamide: -CH ₂
-/-CONH=6/1 degree of polymerization 150 (not inventive) Resol type phenol resin: BKS-316 (manufactured by Showa Kobunshi KK)

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[Table] Zn/
Ni electroplating (Ni content 11%, area weight 20g/m ² )
Electrolytic chromate treatment (fabric weight 40mgCr/
^m2 ) was coated with each coating composition obtained in the above Examples and Comparative Examples, and heated at 200°C.
A painted steel sheet with a coating film of the indicated dry film thickness was produced by baking for 30 seconds. The following tests were conducted on this painted steel plate. (A) Corrosion resistance Spray 5% NaCl on painted steel plate at 35℃ for 4 hours,
After drying at 60°C for 2 hours, at 50°C, relative humidity.
A composite corrosion test was conducted for 100 cycles in which the specimen was held in an atmosphere of 95% or higher for 2 hours, and the occurrence of rust on the flat surface was observed with the naked eye. (Evaluation criteria) ◎...No abnormalities ○...Less than 10% white rust △...10% or more white rust ×...Red rust (B) Lubricity (processing adhesion and deep drawability) Processing adhesion Punch the painted steel plate with a diameter of 50mmφ,
After cylindrical deep drawing at a drawing ratio of 1.9 and a wrinkle pressing pressure of 0.5 t, the adhesion of the coating film was examined and evaluated by peeling off the cylindrical side wall using cellophane adhesive tape. (Evaluation criteria) ◎...No peeling ○...Minute peeling △...Less than 50% peeling ×...50% or more peeling Deep drawability is based on rectangular cylinder crank press material (manufactured by Amada Seisakusho, 150t press material) Evaluation was made based on the aperture height using a 60 x 120 mm rectangular tube aperture. (Evaluation criteria) ◎...70 mm or more ○...50 to less than 70 mm △...30 to less than 50 mm ×...less than 30 mm Next, apply a voltage of 200 V to the painted steel plate using Power Top U-30, a cationic electrodeposition paint. , time 3 minutes,
Electrodeposition coating was carried out at a bath temperature of 28 to 30°C, and baking treatment was performed at 175°C for 30 minutes to produce an electrodeposition coating film with a dry film thickness of 20μ, and the following tests were conducted. (C) Appearance evaluation of electrodeposition coating The smoothness and uniformity of the electrodeposition coating was evaluated with the naked eye. (Evaluation criteria) ◎...Excellent ○...Good △...Yuzu skin ×...Unpainted areas (D) Electrodeposition coating corrosion resistance Sprayed with 5% NaCl at 35℃ for 4 hours, then heated to 60℃ for 2 hours.
After drying, a composite corrosion test was carried out for 2 hours at 50°C and a relative humidity of 95% or higher for 100 cycles, and the corrosion resistance was evaluated by the peeling width (one side, mm) of the coating film with cellophane adhesive tape at the cross cut part. (Evaluation criteria) ◎...0 to less than 1 mm ○...1 to less than 3 mm △...3 to less than 5 mm ×...5 mm or more (E) Secondary adhesion of electrodeposition coating The coated plate after the above composite corrosion test After immersing in pure water at 40℃ for 240 hours, it was left at room temperature for 24 hours.
100 square squares were cut with a knife and a peel test was performed using cellophane adhesive tape. (Evaluation criteria) ◎... No peeling ○... Peeling within 1/100 △... Peeling 2/100 to 10/100 ×... Peeling 11/100 or more The results of these tests are shown in Table 2.

Claims (1)

[Scope of Claims] 1. As a paint non-volatile component (a) an epoxy resin containing 50% by weight or more of phenol in the molecule, obtained by reacting the epoxy resin with a dicarboxylic acid in the presence or absence of an amine catalyst; and urethanized epoxy ester resins obtained by reacting the epoxy ester resin with a partially blocked isocyanate compound. ) (−CH ₂ − and/or =CH−)/(−
CONH-) ratio of 7/1 to 0/1 and a degree of polymerization of 5 to 40% by weight of a hydrophilic polyamide resin (c) 5 to 40% of silica particles with an average particle diameter of 1 to 100 mμ
A solvent-based antirust coating composition for steel plate, characterized in that it contains % by weight. 2. The composition according to claim 1, which contains a lubricant in an amount of 20% by weight or less in the nonvolatile content of the paint. 3 The lubricant has a density of 0.94 or more, a molecular weight of 1000 to 10000,
The composition according to claim 2, which is a polyethylene wax having an acid value of 15 KOH mg/g or less. 4 A curing agent selected from melamine resin, resol type phenolic resin, and polyisocyanate is added to the epoxy binder resin in terms of solid content weight ratio.
The composition according to claim 1, wherein the composition is contained in a ratio of 0.1/9.9 to 4/6. 5 Hydrophilic polyamide resin is a copolymer of nylon 6, nylon 66, and other nylons;
The composition according to claim 1, which is selected from polyether polyol-, polyester polyol-, polybutadiene polyol-modified nylon; aromatic polyamides such as polymetaphenylene isophthalamide and polyparaphenylene terephthalamide.