JPH04153281A - Corrosion resistant paint composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a coating composition capable of forming a coating film having excellent corrosion resistance, cationic electrodeposition coating properties, etc. on a steel plate.

<Prior art and problems to be solved> In recent years, surface-treated steel sheets with good corrosion resistance have come into widespread use as steel sheets used for various purposes such as automobile bodies and home appliances. Galvanized steel sheets can be cited as a typical example of such surface-treated steel sheets, but for example, when used for automobile body panels, bag structures, and hemming parts, they cannot sufficiently meet the required performance. Therefore, a method has been adopted in which an organic coating film or an organic-inorganic composite coating film is applied on the plated steel plate, and a cationic electrodeposition coating film is further applied to improve the corrosion resistance. Therefore, surface-treated steel sheets are required not only to have high corrosion resistance but also to have good cationic electrodeposition coating properties.

However, a practical surface-treated steel sheet that satisfies both of these properties has not yet been developed.

For example, Special Publication No. 45-24230, Special Publication No. 47-68
The surface-treated steel sheet coated with a coating containing a large amount of zinc powder described in Publication No. 82 had a problem in corrosion resistance because the coating was easily peeled off during press working.

Also, JP-A-57-108292, JP-A-60-50
No. 179, JP-A-60-50180, JP-A-54-3
The surface-treated steel sheet described in publications such as No. 4406, in which an organic-inorganic composite coating is applied to a zinc alloy plated steel sheet, is not suitable for cationic electrodeposition coating because the electrical conductivity of the coating film required for cationic electrodeposition coating is uneven. There was a problem that gas pinholes, craters, and other coating film defects were likely to occur in the film.

Also, JP-A-61-60766, JP-A-63-831
Surface-treated steel sheets coated with coatings containing large amounts of conductive substances such as zinc, carbon black, and aluminum described in publications such as No. 72 and Japanese Patent Publication No. 63-2310 have good electrical conductivity, so they are coated with cationic electrodeposition. However, the appearance of the paint film is poor due to poor smoothness when thin S is applied, and furthermore, the paint film becomes #JI due to processing. There was a problem with corrosion resistance because L easily formed.

Also, as described in publications such as JP-A No. 63-357798,
Surface-treated steel sheets, in which a coating film containing hydrophilic polyamide resin is applied to a zinc alloy plated steel sheet to improve cationic electrodeposition coating properties, have problems in corrosion resistance because the coating film easily peels off during the alkali treatment in the pre-electrodeposition treatment. In addition, in order to improve the cationic electrodeposition coating properties of a surface-treated steel sheet with a thin coating, as described in publications such as JP-A No. 62-11733, cracks were formed in the coating using a roll skin pass or the like. This method not only increases the number of processing steps, but also has problems with corrosion resistance because it forms a crank.

<Object of the Invention> In view of the current situation, an object of the present invention is to provide a coating composition for obtaining a surface-treated steel sheet having excellent corrosion resistance and cationic electrodeposition coating properties.

Means for Solving the Problems In order to achieve the above object, the present inventors have made extensive studies and found that the following components: CI) An epoxy resin having at least a bisphenol A skeleton, a bisphenol F skeleton, and a bisphenol S skeleton in the resin. A high molecular weight epoxy resin (b) obtained by polymerizing the resin (al) or the epoxy resin with a polyfunctional compound that is reactive with the epoxy group or hydroxyl group in the resin.
The present invention was achieved by discovering that the above object can be achieved by a coating composition containing a modified epoxy resin modified with a basic nitrogen compound or a carboxyl group-containing compound and (I[) silica particles.

The present invention will be explained in detail below.

Modified epoxy resin constituting the coating composition of the present invention [■]
The epoxy resin (a) before being modified with a basic nitrogen compound and a carboxyl group-containing compound contains a bisphenol component consisting of bisphenol A, bisphenol F, and bisphenol S, and an epichlorohydrin component (the "epichlorohydrin component" in the present invention refers to methyl (contains derivatives such as epichlorohydrin) according to a conventional method; epoxy resin mixture (a2) consisting of bisphenol A-based epoxy resin, bisphenol F-based epoxy resin, and bisphenol S-based epoxy resin; Or 1 of bisphenol A epoxy resin, bisphenol F epoxy resin and bisphenol S epoxy resin.
species or two or more epoxy resins and bisphenol A
An epoxy resin (a3) having at least a bisphenol A skeleton, a bisphenol F skeleton, and a bisphenol S skeleton in the resin obtained by reaction with one or more bisphenol components of bisphenol F and bisphenol S (a3) can be used.

The condensation reaction between the bisphenol component and the epichlorohydrin component of the epoxy resin (a1) can be carried out by mixing bisphenol A, bisphenol F, and bisphenol S, and reacting them with the epichlorohydrin component at the same time;
A method of mixing bisphenol A and bisphenol F, reacting it with an epichlorohydrin component, and then adding and reacting bisphenol S; mixing bisphenol A and bisphenol S, reacting it with an epichlorohydrin component, and then adding bisphenol F. , a method of reacting; a method of reacting bisphenol A and an epichlorohydrin component, and then adding bisphenol F and bisphenol S simultaneously or sequentially;
A method of mixing bisphenol F and bisphenol S, reacting it with an epichlorohydrin component, and further adding bisphenol A to react; reacting bisphenol F and an epichlorohydrin component, and then reacting bisphenol A and bisphenol S simultaneously or sequentially. Alternatively, bisphenol S and epichlorohydrin components are reacted, and bisphenol A and bisphenol F are added simultaneously or sequentially.
This is carried out by a reaction method, etc.

In addition, the reaction between the epoxy resin and the bisphenol component of the epoxy resin (a3) can be performed using a quaternary ammonium salt compound such as tetramethylammonium chloride, a lithium compound such as lithium chloride or lithium bromide, an imidazole compound such as butylimidazole, or a sodium chloride compound. Acetate, sodium phenol, 1,8-diazabicyclo(5,4゜0)-7-undecene, sodium hydroxide,
The reaction can be carried out in the presence of a reaction catalyst such as potassium hydroxide or in the presence of other compounds that promote the reaction.

The high molecular weight epoxy resin (bl is the epoxy resin fal) and a polyfunctional compound that is reactive with the epoxy group or hydroxyl group in the resin at 10 to 250°C, preferably 5°C.
It is made into a polymer by reacting at 0 to 190°C and reacting between epoxy resins (81 and 81) via a polyfunctional compound.

The polyfunctional compounds include amines such as m-xylylene diamine, diaminodiphenylmethane, diaminodiphenylsulfone, 4,4'-diamino 3,3'-diethyldiphenylmethane, and toluidine amine; hexamethylene diisocyanate, tolylene diamine, and the like; Isocyanate, 4゜4'-diphenylmethane diisocyanate, xylene diisocyanate, m-xylene diisocyanate, lysine diisocyanate, 4.4'-methylenebis(cyclohexyl isocyanate), methylcyclohexane-2,4(2,6) diisocyanate, 1.3-(
Typical examples include isocyanate 11 such as (methyl isocyanate) cyclohexane, isophorone diisocyanate, and trimethylhexamethylene diisocyanate, but are not limited thereto. The epoxy resin (al, high molecular weight epoxy resin (b)) thus obtained is a resin having an epoxy group, preferably having an epoxy equivalent of 250 to 60,000 and a molecular weight of about 500 to 100,000.

By the way, bisphenol A is the only bisphenol component that has been traditionally used.
The resulting coating film of epoxy resin has excellent water resistance, chemical resistance, etc., and has excellent adhesion to steel plates and top coats, but the coating film is hard and has poor flexibility. Also, since it was electrically insulating, its cationic electrodeposition coating properties were somewhat poor.

Therefore, the epoxy resin (a) having a bisphenol A skeleton, a bisphenol F skeleton, and a bisphenol S skeleton
Alternatively, when using a high-molecular weight epoxy resin ('b), which is a polymerized version of epoxy resin, it has unexpected flexibility, and greatly improves corrosion resistance, adhesion, and cationic electrodeposition coating properties. Furthermore, it was found that heat resistance etc. were also improved.

In other words, as a bisphenol component, bisphenol A
By using bisphenol F in combination with bisphenol A, corrosion resistance and cationic electrodeposition coating properties are improved compared to the case of bisphenol A alone, but when bisphenol S is used in combination with this, the above-mentioned performance is further improved, and heat resistance is also improved. There was found.

In this way, due to the synergistic effect of the three types of bisphenol components, an excellent coating film as described above can be obtained.

In addition, epoxy resin (a), high molecular weight epoxy resin (b)
The weight ratio of bisphenol A skeleton, bisphenol F skeleton, and bisphenol S skeleton in l is not particularly limited, but is preferably (10 to 97): (2 to 89): (1
~88) are suitable.

The modified epoxy resin constituting the coating composition of the present invention (N is the epoxy group of the above-mentioned epoxy resin (a) or (b) modified with a basic nitrogen compound or a carboxyl group-containing compound; By using a modified epoxy resin, the alkali resistance, water resistance, secondary adhesion, etc. of the resulting coating film are improved compared to when an unmodified epoxy resin is used.

The modified epoxy resin (1) is suitably a bisphenol-type epoxy resin in which 5 to 100% of the epoxy groups are modified with a basic nitrogen compound or a carboxyl group-containing compound, and if the modification rate is less than the above range, the alkali resistance etc. The improvement effect tends to decrease.

Examples of basic nitrogen compounds include n-propylamine, 1so-propylamine, n-butylamine, 5ec
-butylamine, tert-butylamine, diethylamine, ethylenediamine, diethylenetriamine, triethylenediamine, tetraethylenediamine, propylenediamine, N-methylpiperazine, ethanolamine, jetanolamine, N-methylethanolamine,
iso-propaturamine, diisopropaturamine, n-propaturamine, ethylethanolamine, 3-methanolpiperidine, histidine, 3,5-dimethylpyrazole, 1-hydroxy-hencitriazole, 3-amino-1,2 , 4-triazole, 4-amino-1,2,4-triazole and the like are representative examples, but the present invention is not limited thereto. Examples of carboxyl group-containing compounds include acetic acid, propionic acid,
Typical examples include monocarboxylic acids such as lactic acid and methionine, and dicarboxylic acids such as succinic acid, phthalic acid, isophthalic acid, adipic acid, maleic acid, tetrahydrophthalic acid, citric acid, and thioglyconic acid, but are limited to these. It is not something that will be done.

Note that the modification with the basic nitrogen compound can be carried out without a catalyst, for example, preferably at a temperature of 50 to 150°C.

Modification with a carboxyl group-containing compound can be carried out using alkaline hydroxides such as lithium hydroxide, tertiary amines such as triethylamine or their hydrochlorides, quaternary ammonium salts such as tetramethylammonium chloride, imidazole compounds, and In the presence of a catalyst such as an acidic phosphorus compound such as phenylphosphine, an alkali salt of an organic carboxylic acid such as calcium acetate, a Lewis acid such as titanium tetrachloride, a sulfonium salt, or a phosphonium salt, preferably at a temperature of 80 to 250°C. It can be reacted with.

The silica particles (II) constituting the coating composition of the present invention are:
It is blended to further impart high corrosion resistance, and representative examples include organic solvent-dispersed colloidal silica and powdered fumed silica with a particle size of 1 mμ to 500 mμ.

Organic solvent-dispersed colloidal silica is methyl alcohol,
Colloidal alcohol dispersed in an organic solvent such as ethyl alcohol, propyl alcohol, butyl alcohol, ethyl cellosolve, ethylene glycol, dimethylacetamide, dimethylformamide, etc., and commercially available products such as 05CAL 1132.1232.1332.143
2.1532.1622.1722.1724 (the above are product names manufactured by Catalysts & Chemicals Co., Ltd.)
PA-3T, NBA-3T, IB^-5T, E
G-5T, MiTC-3TS DMAC-3T
.

DMF-3T (the above is a trade name manufactured by Nichikagaku Kogyo Co., Ltd.), and the like.

For example, R97 is a commercially available powdered fumed silicone product.
4, R811, R812, R97' 2, R805, T
805, R202, RX200, RY200, RY30
0, RY380, RY180.0X50 (all trade names manufactured by Nippon Aerosil Co., Ltd.), and the like.

When a coating film is formed by blending silica particles, hydrogen bonds occur between the silanol groups on the surface of the silica particles and the steel plate surface and top coat, and when the coating film is baked, a dehydration condensation reaction of the silanol groups occurs. occurs, the top coat and liquor steel sheet are integrated, and corrosion resistance is significantly improved.

In addition, Nlica particles (n) are the modified epoxy resin (1)
It is appropriate to mix 5 to 400 parts by weight (in terms of solid content) per 100 parts by weight; if it is less than the above range, corrosion resistance tends to decrease, and if it is added in excess, it will affect processability, alkali resistance, and top coat. Adhesion to the film tends to decrease.

The coating composition of the present invention comprises the modified epoxy resin (
It is a paint containing I) and silica particles (II) as essential components, preferably with a solid content of 10 to 60% by weight.

As other components, conventionally known components that are appropriately blended as necessary are blended. Specifically, curing agents such as amino resins, resol-type phenolic resins, and polyisocyanates; organic cutting agents such as various hydrocarbons, esters, ketones, alcohols, and amide types; organic or inorganic pigments; dispersants; Additives such as anti-settling agents and leveling agents or various modified resins can be added.

The coating composition of the present invention is applied to hot-dip galvanized steel sheets, hot-dip zinc-aluminum alloy plated steel sheets, electrolytic galvanized steel sheets, electrolytic zinc-nickel alloy plated steel sheets, electrolytic zinc-iron alloy plated steel sheets, etc. used in automobiles, home appliances, building materials, etc. It can be suitably used as an undercoat paint for various steel plates such as steel plates, electrolytic zinc-iron double-layer plated steel plates, and cold-rolled steel plates, or pretreated steel plates such as chromate chemical conversion treatment and phosphate chemical conversion treatment, but is limited to these coated objects. It is not something that will be done.

The coating composition of the present invention is applied to these steel plates by means such as spraying, roll coating, shower coating, etc.
It can be cured at a temperature of 300°C, preferably 100-240°C. It should be noted that although a thin film having a thickness of several μm can exhibit sufficient performance, it is not prohibited to make the film even thicker.

<Effects of the Invention> The surface-treated steel sheet coated with the coating composition of the present invention has high corrosion resistance and alkali resistance, and is flexible and has good workability. It has good properties such as durability and heat resistance, and can be said to be a paint with high practical value.

Hereinafter, the present invention will be explained in more detail with reference to Examples. In the examples, "parts" and "%" are expressed on a weight basis.

[Preparation of modified epoxy resin solution (a)] Bisphenol A-based epoxy ma “Epicote 82SEL,
(Product name manufactured by Yuka Shell Epoxy Co., Ltd.), epoxy equivalent: 18
7] 380, 5 parts, Bisphere/-A 197.6 parts,
Bisphenol FI L, 0 parts, bisphenol 5
11.0 parts, reaction catalyst (lithium chloride) 0.2 parts, propylene glycol monomethyl ether acetate 408
．． 1 part and stirred while introducing nitrogen gas for 15 minutes.
The reaction was carried out at 0°C, and the precondensate (weight average molecular weight 600
, number average molecular weight 3,400) solution was obtained.

Then propylene glycol monomethyl ether acetate)218. OR and hexamethylene diisocyanate)
14.0 parts were added and reacted at 65° C. with stirring to obtain a high molecular weight epoxy resin solution. The end point of the reaction was determined by the absorption of incyanate group (2270 am-') using an infrared spectrophotometer.
) disappears.

Then propylene glycol monomethyl ether acetate 127.3R and diisopropanolamine 3.9
of amine-modified epoxy resin (weight average molecular weight 25.600, number average molecular weight 55
00) Solution (a) was prepared.

Note that the solution (A) had a viscosity of Z1 and a solid content of 45.1%.

[Preparation of modified epoxy resin solution (b)] Bisphenol A epoxy resin "Epicoat 828ELJ300.0"
Part, Bisphenol F-based epoxy resin ["Evicron 8"
30J (trade name manufactured by Dainippon Ink and Chemicals), epoxy equivalent 175] 37.5 parts, bisphenol S-based epoxy resin [Epiclon EXA-1514J (trade name manufactured by Dainippon Ink and Chemicals), epoxy equivalent 310]
11.3 parts, bisphenol A 197.6 parts, bisphenol Fil. 0 parts of bisphenol, 311.0 parts of bisphenol, 0.2 parts of a reaction catalyst (lithium bromide), and 257.5 parts of ethylene glycol monomethyl ether acetate were added, and the mixture was reacted at 156°C with stirring while introducing nitrogen gas. Methylene diisocyanate 14.0 parts, ethylene glycol monomethyl ether acetate 218.0 parts
1 part and reacted in the same manner as the solution (a) to obtain a high molecular weight epoxy resin solution.

Next, 127.3 parts of propylene glycol monomethyl ether acetate and 3.9 parts of diisopropanolamine
A solution (b) of an amine-modified epoxy resin (weight average molecular weight: 20,000, number average molecular weight: 4,800) was prepared in the same manner as in the solution (a). Note that the solution (
B) had a viscosity of Z3 and a solid content of 49.3%.

[Preparation of modified epoxy resin solution (c)] Bisphenol A-based epoxy resin [Epicote 828EL
J280.0 parts, bisphenol F-based epoxy resin "Epicron 830140.0 parts, bisphenol S-based epoxy resin "Epiclon EXA-1514" 80 parts, bisphenol A 299.9 parts, reaction catalyst (1,8-diazabicyclo(5,4, 730.3 parts of O'3-7-undece, ethylene glycol monomethyl ether acetate)
419.7 parts of the precondensate (weight average molecular weight 81
00, number average molecular weight 3200) solution was obtained.

Next, 235.0 parts of ethylene glycol monomethyl ether acetate and xylylene diisocyanate) 25.
2 parts were added and reacted at 65° C. with stirring to obtain a high molecular weight epoxy resin solution. (The end point of the reaction is the same as in solution (a) above.) Next, 51.7 parts of propylene glycol monomethyl ether acetate, 22 parts of (2-benzothiazolylthio)-succinic acid, and 3.3 parts of a catalyst (triethylamine) were added. The reaction was carried out at 120°C with stirring, and a carboxyl-modified epoxy resin (weight average molecular weight 28,000, number average molecular weight 6
000) solution (c) was prepared. Note that the solution (c) had a viscosity ZI and a solid content of 51.5%.

[Preparation of modified epoxy resin solution (d)] Bisphenol A-based epoxy resin [Epicote 828ELJ305.6
Part, bisphenol F-based engineered boxy resin [[Epicron 8
30J 100.0 parts, bisphenol S epoxy resin "Epiclon EXA-1514J 70.0 parts, bisphenol A 137.2 parts, bisphenol F 68.6 parts
An amine-modified epoxy resin ( Weight average molecular weight 40,000, number average molecular weight 6.30
0) Solution (d) was prepared.

Note that the solution (d) had a viscosity of ZS and a solid content of 37.2%.

[Preparation of modified epoxy resin solution (e)] Bisphenol A 60.2%, bisphenol Fl 9.9% in a four-way flask equipped with a reflux condenser, thermometer, and stirrer.
Epoxy resin (epoxy equivalent: 3100) obtained by reacting bisphenol consisting of 9.9% of bisphenol S L and epichlorohydrin (epoxy equivalent: 3100) 2
00 parts, 138.7 parts of ethylene glycol monomethyl ether acetate, 62.5 parts of bisphenol A, and 0.5 part of a reaction catalyst (butylimidazole) were added, and the mixture was reacted at 156°C with stirring while introducing nitrogen gas to form a precondensate (
A solution with a weight average molecular weight of 11,000 and a number average molecular weight of 3,800 was obtained.

140.1N of propylene glycol monomethyl ether acetate and 8.3N of tolylene diisocyanate
C) and reacted at 65°C with stirring to obtain a high molecular weight epoxy resin solution.
) Next, 63.6 parts of propylene glycol monomethyl ether acetate and 1.3 parts of jetanolamine were added and reacted at 80°C with stirring to form an amine-modified epoxy resin (
Weight average molecular weight 30.100, number average molecular weight 6100)
A solution (e) was prepared. The solution (e) had a viscosity of Z3 and a solid content of 44.3%.

[Preparation of modified epoxy resin solution] Epoxy resin (epoxy equivalent 1100) 300 parts of propylene glycol monomethyl ether acetate 384.
1 part and 14.3 parts of jetanolamine were added and reacted at 80° C. with stirring to prepare an amine-modified epoxy resin solution (weight average molecular weight 2400, number average molecular weight 1400). The solution (to) has a viscosity of V and a solid content of 45.0%.
Met.

[Preparation of modified epoxy resin solution (g)] Bisphenol A epoxy resin (epoxy equivalent 1120) 150.0
parts, bisphenol F-based epoxy resin (epoxy equivalent: 1
206) 100.0 parts, bisphenol S-based epoxy resin (epoxy equivalent: 1155) 50.0 parts, propylene glycol monomethyl ether acetate 384.4 parts,
1.8 parts of catalyst (triethylamine) and 12.7 parts of (2-benzothiazolylthio)-succinic acid were mixed with stirring at 120
React at ℃, carboxyl-modified epoxy resin (weight average molecular weight 2500, number average molecular weight 1400) solution (T)
was prepared. The solution (g) has a viscosity of V and a solid content of 45.0.
%Met.

[Preparation of modified epoxy resin solution (H)] Bisphenol A-based epoxy resin (epoxy equivalent: 187) 2 was placed in a four-eye flask equipped with a stirrer, nitrogen gas introduction device, and thermometer.
37.8 parts, bisphenol F 137.2 parts, reaction catalyst (tetramethylammonium bromide) 0.1 part, ethylene glycol monomethyl ether acetate 258 parts
．． Add 4 parts and heat to 156℃ while stirring while introducing nitrogen gas.
to form a precondensate (weight average molecular weight 10,100,
A solution with a number average molecular weight of 4000 was obtained.

Next, 213.5 parts of ethylene glycol monomethyl ether acetate and 1 part of hexamethylene diisocyanate were added.
1.1 parts were added and reacted at 65° C. with stirring to obtain a high molecular weight epoxy resin solution. (The end point of the reaction is the solution (
(Same as b)) Then 3-amino-1,2,4-1-riazole 3,0
parts, propylene glycol monomethyl ether 3.7
of amine-modified epoxy resin (weight average molecular weight 23,400, number average molecular weight 56
00) Solution (H) was prepared.

Note that solution (H) had a viscosity of Z1 and a solid content of 45.0%.

(Preparation of modified epoxy resin solution (H)) Said solution (H)
In a reactor similar to the above, 235.6 parts of bisphenol A-based epoxy resin (epoxy equivalent: 187), 125.5 parts of bisphenol A, 314.0 parts of bisphenol, a reaction catalyst (1 part of lithium chloride LO, propylene glycol monomethyl ether acetate) were added. -1-275, 1 part was added and reacted at 150°C with stirring while introducing nitrogen gas, and the precondensate (weight average molecular weight 12,500, number average molecular weight 33
o (a solution was obtained.

Next, 194.4 parts of propylene glycol monomethyl ether acetate and 9 parts of hexamethylene diisocyanate were added.
．． 0 part was added and reacted at 65° C. with stirring to obtain a high molecular weight epoxy resin solution. (The end point of the reaction is the same as in solution (a) above.) Next, 2.9 parts of n-butylamine and 3.5 parts of propylene glycol monomethyl ether acetate were added, and the reaction was carried out at 6°C with stirring. Average molecular weight 28600, number average molecular weight 6000
) Solution (January) was prepared.The solution had a viscosity of 2 and a solid content of 45.0%.

[Preparation of epoxy resin solution (nu)]

To the high molecular weight epoxy resin solution obtained during the preparation of the solution (a), 1.24.5 parts of propylene glycol monomethyl ether acetate was added, and the epoxy resin (
A solution (nu) with a weight average molecular weight of 25,400 and a number average molecular weight of 5,500 was prepared. Note that the solution (N) had a viscosity of Z1 and a solid content of 45.0%.

[Preparation of modified epoxy resin solution (1)] Epoxy resin 2 with a weight average molecular weight of 11,000 obtained by reacting bisphenol A and epichlorohydrin in a conventional manner.
138.7 parts of ethylene glycol methyl ether acetate, 62.5 parts of bisphenol A and 0.3 parts of a reaction catalyst (lithium bromide) were added to 0.00 parts, and the mixture was reacted at 156°C with stirring while introducing nitrogen gas. A solution of condensate (weight average molecular weight: 11,500, number average molecular weight: 3,900) was obtained.

Then 140.1 parts of propylene glycol monomethyl ether acetate and tolylene diisocyanate) 8.3
The mixture was reacted at 65° C. with stirring to obtain a high molecular weight epoxy resin solution. (Note that the end point of the reaction is the same as the above solution (a)) Next, propylene methyl ether acetate 63.
6 parts of diisopropanol amine and 1.3 parts of diisopropanolamine were added thereto and reacted at 80° C. with stirring to prepare an amine-modified epoxy resin solution (weight average molecular weight: 26,000, number average molecular weight: 5,000). The solution (L) has a viscosity of Z1 and a solid content of 4.
It was 4.3%.

Example 1 200 parts of modified epoxy resin solution (A), 400 parts of colloidal silica CrETC-3T (trade name manufactured by Nichikagaku Kogyo Co., Ltd.), ethylene glycol monoethyl ether dispersion type, solid content 20%), and ethylene glycol monoethyl ether 418 parts were mixed and dissolved to prepare a paint.

The obtained paint was applied to various steel plates shown in Table 2 with a dry film thickness of 3 μm.
Roll coated to achieve a maximum board temperature of 30 m.
Baked to 150℃ in seconds, corrosion resistance, cationic electrodeposition paintability, topcoat adhesion, water resistance, secondary adhesion, alkali resistance,
Heat resistance tests were conducted and the results are shown in the lower column of Table 2.

Examples 2 to 10 and Comparative Examples 1 to 5 A mixture of (modified) epoxy resin solution and silica particles (and curing agent) in the proportions shown in Table 1 was mixed with ethylene glycol monoethyl in an amount such that the solid content was 20%. A paint was prepared by dissolving it in ether.

The obtained paint was subjected to various tests in the same manner as in Example 1,
The results are shown in the lower column of Table 2.

As is clear from Table 2, Examples 1 to 10 using the coating composition of the present invention were all excellent in corrosion resistance, cationic electrodeposition coating properties, adhesion, alkali resistance, and heat resistance.

Comparative Example 1, which used an epoxy resin that does not contain the 14-bisphenol S skeleton, had a low glass transition temperature, and also had lower corrosion resistance and water resistant secondary adhesion than the paint of the present invention. Furthermore, in Comparative Example 2, which used an epoxy resin that does not contain a bisphenol F skeleton, corrosion resistance, cationic electrodeposition paintability, topcoat adhesion, and water resistant secondary adhesion were lower than those of the paint of the present invention.

Furthermore, Comparative Example 3, which used an epoxy resin that was not modified with a basic nitrogen compound or a carboxyl group-containing compound, had poor secondary waterproof adhesion.

Comparative Example 4, which used an epoxy resin containing neither bisphenol F skeleton nor bisphenol S skeleton, had poor cationic electrodeposition coating properties.

Comparative Example 5, which did not contain silica particles, had poor corrosion resistance, cationic electrodeposition coating properties, and water resistant secondary adhesion.

Claims (3)

[Claims] (1) [I] (a1) An epoxy resin obtained by reacting a bisphenol component consisting of bisphenol A, bisphenol F, and bisphenol S with an epichlorohydrin component, or (b1) the epoxy resin (a1), A corrosion-resistant paint composition containing a modified epoxy resin obtained by modifying a high-molecular-weight epoxy resin polymerized with a polyfunctional compound that is reactive with groups or hydroxyl groups with a basic nitrogen compound or a carboxyl group-containing compound, and [II] silica particles. thing. (2) [I] (a2) An epoxy resin mixture consisting of a bisphenol A epoxy resin, a bisphenol F epoxy resin, and a bisphenol S epoxy resin; Or a modified epoxy resin obtained by modifying a high molecular weight epoxy resin polymerized with a polyfunctional compound that is reactive with hydroxyl groups with a basic nitrogen compound or a carboxyl group-containing compound, and [II] a corrosion-resistant coating composition containing silica particles. . (3) [I] (a3) One or two of bisphenol A epoxy resin, bisphenol F epoxy resin, and bisphenol S epoxy resin
An epoxy resin having at least a bisphenol A skeleton, a bisphenol F skeleton, and a bisphenol S skeleton in the resin obtained by reacting one or more types of epoxy resin with one or more types of bisphenol components of bisphenol A, bisphenol F, and bisphenol S. or (b3) A high molecular weight epoxy resin obtained by polymerizing the epoxy resin (a3) with a polyfunctional compound that is reactive with the epoxy group or hydroxyl group in the resin with a basic nitrogen compound or a carboxyl group-containing compound. A corrosion-resistant paint composition containing a modified epoxy resin and [II] silica particles.