JPH0645774B2 - Corrosion resistant coating composition - Google Patents

Description

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

<Prior Art and Problems to be Solved> In recent years, a surface-treated steel sheet having good corrosion resistance has been widely used as a steel sheet used for various applications such as automobile bodies and home electric appliances. A typical example of such a surface-treated steel sheet is a galvanized steel sheet, but when it is applied to, for example, an inner plate of an automobile body, a bag structure portion, or a hemming portion, it can sufficiently meet the required performance. Instead, a method of improving the corrosion resistance by applying an organic coating film or an organic-inorganic composite coating film on a plated steel sheet and further applying a cationic electrodeposition coating film has been adopted. Therefore, the surface-treated steel sheet is required to have high corrosion resistance as well as good cationic electrodeposition coating property.

However, a practical surface-treated steel sheet satisfying both of these characteristics has not yet been developed.

For example, a surface-treated steel sheet coated with a coating containing a large amount of zinc powder described in JP-B-45-24230 and JP-B-47-6882 has a problem that the coating is easily peeled off by press working, which causes a problem in corrosion resistance. was there.

Further, JP-A-57-108292, JP-A-60-50179, and JP-A-6-
The surface-treated steel sheet obtained by applying an organic-inorganic composite coating film to a zinc alloy-plated steel sheet described in Japanese Patent Publication No. 0-50180, Japanese Patent Publication No. 54-34406, etc., has the electrical conductivity of the coating film necessary for cationic electrodeposition coating property. Due to the non-uniformity, there is a problem that the cationic electrodeposition coating film is apt to be caused by coating film defects such as gas pinholes and craters.

Further, JP-A-61-60766, JP-A-63-83172, JP-B-63
The surface-treated steel sheet coated with a large amount of a conductive substance such as zinc, carbon black, and aluminum described in the publication No. -2310 and the like has excellent electroconductivity, but has excellent cationic electrodeposition coatability. However, the appearance of the coating film is poor due to poor smoothness when applied in a thin film, and the coating film is likely to peel off due to processing, which causes a problem in corrosion resistance.

Further, as disclosed in JP-A-63-357798, surface-treated steel sheet obtained by applying a coating film containing a hydrophilic polyamide resin to a zinc alloy-plated steel sheet for improving cationic electrodeposition coating property is a pre-electrodeposition treatment. The coating is easy to peel off with the alkali treatment in
There was a problem in corrosion resistance.

Further, as described in JP-A-62-11733 and the like, a method of forming a crack in the coating film by a roll skin pass or the like in order to improve the cationic electrodeposition coating property on the surface-treated steel sheet coated with a thin film is However, not only the number of processing steps is increased, but also cracks are formed, which causes a problem in corrosion resistance.

<Object of the Invention> In view of such a 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 property.

<Means for Solving the Problems> The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, the following components: [I] The resin has at least a bisphenol A skeleton, a bisphenol F skeleton and a bisphenol S skeleton. Epoxy resin (a), or a high molecular weight epoxy resin (b) obtained by polymerizing the epoxy resin with an epoxy resin in the resin or a polyfunctional compound having reactivity with a hydroxyl group, containing a basic nitrogen compound or a carboxyl group. The present invention has been achieved by finding that the above objects can be achieved by a coating composition containing a modified epoxy resin modified with a compound and [II] silica particles.

The present invention will be described in detail below.

Modified epoxy resin [I] constituting the coating composition of the present invention
The basic nitrogen compound and the epoxy resin (a) before being modified with a carboxyl group-containing compound are bisphenol components consisting of bisphenol A, bisphenol F and bisphenol S and an epichlorohydrin component (the "epichlorohydrin component" in the present invention is Methyl epichlorohydrin and other derivatives) and an epoxy resin (a1) which has been subjected to a condensation reaction according to a conventional method; an epoxy resin mixture (a2) consisting of a bisphenol A epoxy resin, a bisphenol F epoxy resin and a bisphenol S epoxy resin (a2); Or 1 of bisphenol A type epoxy resin, bisphenol F type epoxy resin and bisphenol S type epoxy resin
At least a bisphenol A skeleton, a bisphenol F skeleton and a bisphenol S skeleton in a resin obtained by reacting one or more epoxy resins with one or more bisphenol components of bisphenol A, bisphenol F and bisphenol S The epoxy resin (a3) etc. which it has can be used.

In the condensation reaction of the bisphenol component and the epichlorohydrin component of the epoxy resin (a1), bisphenol A, bisphenol F and bisphenol S are mixed,
Method of reacting with epichlorohydrin component at the same time; method of mixing bisphenol A and bisphenol F, reacting with epichlorohydrin component and further adding bisphenol S to react; mixing bisphenol A and bisphenol S, and mixing it with epichlorohydrin component Method of reacting and further adding bisphenol F; reacting: bisphenol A and epichlorohydrin component are reacted, and further bisphenol F and bisphenol S
And bisphenol F and bisphenol S are mixed at the same time or sequentially to react with each other; bisphenol F and bisphenol S are mixed and reacted with epichlorohydrin component; and bisphenol A is further added and reacted; bisphenol F and epichlorohydrin component are reacted, Furthermore, bisphenol A and bisphenol S are added simultaneously or sequentially,
A method of reacting; or a method of reacting bisphenol S with an epichlorohydrin component, and then adding bisphenol A and bisphenol F simultaneously or sequentially and reacting them.

The reaction of the epoxy resin with the bisphenol component of the epoxy resin (a3) is performed by quaternary ammonium salt compounds such as tetramethylammonium chloride, lithium compounds such as lithium chloride and lithium bromide, imidazole compounds such as butylimidazole, sodium. 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 a compound that accelerates the reaction.
The high molecular weight epoxy resin (b) is the epoxy resin (a)
With a polyfunctional compound having reactivity with an epoxy group or a hydroxyl group in the resin, and 10 to 250 ° C., preferably 50 to 1
Polymerization is carried out by reacting at 90 ° C. and reacting the epoxy resin (a) through a polyfunctional compound.

As the polyfunctional compound, amines such as m-xylylenediamine, ciaminodiphenylmethane, diaminodiphenylsulfone, 4,4′-diamino-3,3′-diethyldiphenylmethane and toluidineamine; hexamethylene diisocyanate, Tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate,
Xylene diisocyanate, m-xylene diisocyanate, lysine diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4 (2,6) diisocyanate, 1,3-
Representative examples thereof include isocyanates such as (isocyanatomethyl) cyclohexane, isophorone diisocyanate, and trimethylhexamethylene diisocyanate, but are not limited thereto. The epoxy resin (a) and the high molecular weight epoxy resin (b) thus obtained are resins having an epoxy group, and preferably have an epoxy equivalent of 250 to 60,000 and a molecular weight of about 500 to 10.
It is 0,000 resin.

By the way, as the bisphenol component that has been conventionally used, only bisphenol A can be obtained.
The epoxy-based epoxy resin has excellent water resistance, chemical resistance, etc., adhesion to steel sheets, and adhesion to the top coating film, while the coating film is hard and inferior in flexibility. Moreover, since it is electrically insulating, the cationic electrodeposition coating property was slightly inferior.

Therefore, the epoxy resin (a) having a bisphenol A skeleton, a bisphenol F skeleton and a bisphenol S skeleton
Alternatively, when a high molecular weight epoxy resin (b) obtained by further polymerizing it is used, it is unexpectedly flexible,
In addition, it was found that the cationic electrodeposition coating property as well as the corrosion resistance and the adhesiveness were greatly improved, and the heat resistance and the like were also improved.

That is, as the bisphenol component, bisphenol A
By using bisphenol F together with bisphenol A, the corrosion resistance and the cationic electrodeposition coating property are improved as compared with the case of using bisphenol A alone, but when bisphenol S is further used in combination with the above, the above-mentioned performance is further improved and the heat resistance is also improved. There was found. In this way, the synergistic effect of the three kinds of bisphenol components provides the excellent coating film as described above.

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

Modified epoxy resin (I) constituting the coating composition of the present invention
Is an epoxy group of the above-mentioned epoxy resin (a) or (b) is modified with a basic nitrogen compound or a carboxyl group-containing compound, by using the modified epoxy resin, unmodified epoxy resin It is characterized in that the obtained coating film has improved alkali resistance, water-resistant secondary adhesion, etc., as compared with the case of using.

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

Examples of the basic nitrogen compound include n-propylamine, iso-propylamine, n-butylamine, sec-butylamine, tert-butylamine, diethylamine, ethylenediamine, diethylenetriamine, triethylenediamine, tetraethylenediamine, propylenediamine, N-methylpiperazine, Ethanolamine, diethanolamine, N-methylethanolamine, iso-propanolamine, diisopropanolamine, n-propanolamine, ethylethanolamine, 3-methanolpiperidine, histidine, 3,5-dimethylpyrazole, 1-hydroxy-benzotriazole, 3-amino-1,2,4-triazole, 4-amino-1,
Typical examples thereof include 2,4-triazole and the like, but the invention is not limited thereto. Examples of the carboxyl group-containing compound include monocarboxylic acids such as acetic acid, propionic acid, lactic acid, and methionine, and dicarboxylic acids such as succinic acid, phthalic acid, isophthalic acid, adipic acid, maleic acid, tetrahydrophthalic acid, citric acid, and thioglycolic acid. As a typical example, the present invention is not limited to this.

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.

In addition, modification with a carboxyl group-containing compound is carried out by alkaline hydroxides such as lithium hydroxide, tertiary amines such as triethylamine or their hydrochlorides, quaternary ammonium salts such as tetramethylammonium chloride, imidazole compounds, triamines, and the like. 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, for example, preferably at a temperature of 80 to 250 ° C. Can be reacted with.

The silica particles (II) constituting the coating composition of the present invention are added to further impart high corrosion resistance,
Specific examples thereof include organic solvent-dispersed colloidac silica having a particle size of 1 mμ to 500 mμ and powdered fumed silica. Organic solvent dispersed colloidal silica is methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, ethyl cellosolve, ethylene glycol, dimethylacetamide, colloidal silica dispersed in an organic solvent such as dimethylformamide, as a commercial product, for example, OSCAL 1132, 1232, 1332, 1432, 15
32, 1622, 1722, 1724 (above, trade name by Catalysts & Chemicals Industry Co., Ltd.); MA-ST, IPA-ST, NBA-ST, IBA-ST, EG-ST, ETC-ST, DMAC
-ST, DMF-ST (above, trade name of Nissan Chemical Industries, Ltd.) and the like.

Examples of commercially available powdered fumed silica include R97
4, R811, R812, R972, R805, T80
5, R202, RX200, RY200, RY300,
RY380, RY180, OX50 (above, trade name by Nihon Aerosil Co., Ltd.) and the like can be mentioned.

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 sheet surface and the top coating film, and when the coating film is baked, the silanol group dehydration condensation reaction occurs. Then, the top coat film-silica-steel plate is integrated, and the corrosion resistance is remarkably improved.

The silica particles (II) are the modified epoxy resin (I).
It is appropriate to add 5 to 400 parts by weight (solid content conversion) to 100 parts by weight, and if it is less than the above range, the corrosion resistance tends to decrease, while if it is excessively added, processability,
Alkali resistance and adhesion to the top coating film tend to decrease.

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

As other components, conventionally known components which are appropriately blended as necessary are blended. Specifically, curing agents such as amino resins, resol-type phenol resins, polyisocyanates; various hydrocarbon-based, ester-based, ketone-based, alcohol-based, amide-based organic solvents; organic or inorganic pigments; dispersants; sedimentation It is possible to add additives such as inhibitors and leveling agents or various modified resins.

The coating composition of the present invention is used in automobiles, home appliances, building materials, etc., hot dip galvanized steel sheet, hot dip galvanized-aluminum alloy plated steel sheet, galvanized galvanized steel sheet, galvanized zinc-nickel alloy plated steel sheet, galvanized zinc-iron alloy. It can be suitably applied as various steel sheets such as gold-plated steel sheets, electric zinc-iron double-layered steel sheets, cold-rolled steel sheets or pre-treated steel sheets that have undergone chromate conversion treatment, phosphate conversion treatment, etc. It is not limited.

The coating composition of the present invention is applied to these steel plates by means of 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 film thickness of about several μm exhibits sufficient performance, it does not prevent further increase in thickness.

<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 in the resulting coating film, and also has workability due to its flexibility, and is further subjected to cationic electrodeposition coating. It has good practicality and heat resistance, and can be said to have high practical value.

Hereinafter, the present invention will be described in more detail with reference to Examples. In the examples, "parts" and "%" are shown by weight.

[Preparation of modified epoxy resin solution (a)]

A four-necked flask equipped with a stirrer, a nitrogen gas introducing device, and a thermometer was added to a bisphenol A epoxy resin [“Epicoat 828EL” (trade name, manufactured by Yuka Shell Epoxy Co., Ltd.),
Epoxy equivalent 187] 380.5 parts, bisphenol A 197.6 parts, bisphenol F
11.0 parts, bisphenol S 11.0 parts, reaction catalyst (lithium chloride) 0.2 parts, and propylene glycol monomethyl ether acetate 408.1 parts were added and reacted at 150 ° C. with stirring while introducing nitrogen gas, and the precondensate (weight average) was added. A solution having a molecular weight of 9,600 and a number average molecular weight of 3,400) was obtained.

Next, 218.0 parts of propylene glycol monomethyl ether acetate and 14.0 parts of hexamethylene diisocyanate 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 defined as the point at which absorption of isocyanate groups (2270 cm ^-1 ) disappeared by an infrared spectrophotometer.

Next, 127.3 parts of propylene glycol monomethyl ether acetate and 3.9 parts of diisopropanolamine were added,
The reaction was carried out at 80 ° C. with stirring to prepare an amine-modified epoxy resin (weight average molecular weight 25,600, number average molecular weight 5500) solution (a). The solution (a) had a viscosity Z ₁ and a solid content of 45.1%.

[Preparation of modified epoxy resin solution (b)]

Bisphenol A epoxy resin "Epicoat 828E
L "300.0 parts, bisphenol F-based epoxy resin [" Epiclon 830 "(trade name, manufactured by Dainippon Ink and Chemicals, Inc., epoxy equivalent 175) 37.5 parts, bisphenol S
Epoxy resin ["Epiclon EXA-1514" (trade name of Dainippon Ink and Chemicals, Inc.), epoxy equivalent 31
0] 11.3 parts, bisphenol A 197.6 parts, bisphenol F 11.0 parts, bisphenol S 11.0 parts, reaction catalyst (lithium bromide) 0.2 parts, ethylene glycol monomethyl ether acetate 257.5 parts, while introducing nitrogen gas, The reaction was carried out at 156 ° C. with stirring, 14.0 parts of hexamethylene diisocyanate and 218.0 parts of ethylene glycol monomethyl ether acetate were further added, and the reaction was carried out 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 were added and reacted in the same manner as the solution (a) to prepare an amine-modified epoxy resin (weight average molecular weight 20000, number average molecular weight 4800) solution (b). . Solution (b)
Had a viscosity Z ₃ and a solid content of 49.3%.

[Preparation of modified epoxy resin solution (C)]

In a four-necked flask equipped with a stirrer, a nitrogen gas introducing device and a thermometer, 280.0 parts of bisphenol A epoxy resin "Epicoat 828EL", 40.0 parts of bisphenol F epoxy resin "Epiclon 830", bisphenol S
Epoxy resin "Epiclon EXA-1514" 80
Part, bisphenol A 299.9 parts, reaction catalyst (1,8-diazabicyclo [5,4,0] -7-undecene] 0.3
Part, ethylene glycol monomethyl ether acetate
Add 419.7 parts, and while introducing nitrogen gas, under stirring 15
The reaction is carried out at 6 ° C. and the precondensate (weight average molecular weight 810
0, number average molecular weight 3200) solution was obtained.

Next, 235.0 parts of ethylene glycol monomethyl ether acetate and 25.2 parts of xylylene diisocyanate were added and reacted at 65 ° C. under stirring to obtain a high molecular weight epoxy resin solution. (The end point of the reaction is the same as that of the solution (a).) Then, 51.7 parts of propylene glycol monomethyl ether acetate, 22 parts of (2-benzothiazolylthio) -succinic acid and 3.3 parts of catalyst (triethylamine) were added, and the mixture was stirred at 120 ° C. The carboxyl-modified epoxy resin (weight average molecular weight 28,000, number average molecular weight 600
0) A solution (C) was prepared. The solution (C) has a viscosity Z
_{1. The} solid content was 51.5%.

[Preparation of modified epoxy resin solution (d)]

Bisphenol A epoxy resin "Epicoat 828E
L "305.6 parts, bisphenol F-based epoxy resin [" Epiclon 830 "100.0 parts, bisphenol S-based epoxy resin" Epiclon EXA-1514 "70.0 parts, bisphenol A 137.2 parts, bisphenol F 68.6 parts, bisphenol S 68.6 parts, Amine-modified epoxy resin (weight average molecular weight 40,0%) was prepared in the same manner as in the above solution (a) except that 953.3 parts of propylene glycol monomethyl ether acetate and 0.3 part of a reaction catalyst (lithium bromide) were used as starting materials.
00, number average molecular weight 6,300) solution (d) was prepared.

[Preparation of modified epoxy resin solution (e)]

Bisphenol A 60.2%, bisphenol F 19.9% in a four-necked flask equipped with a reflux condenser, thermometer and stirrer.
And 200 parts of an epoxy resin (epoxy equivalent 3100) obtained by reacting bisphenol consisting of 19.9% of bisphenol S with epichlorohydrin by a conventional method, ethylene glycol monomethyl ether acetate 138.
7 parts, bisphenol A 62.5 parts reaction catalyst (butyl imidazole) 0.5 parts were added and reacted at 156 ° C. with stirring while introducing nitrogen gas. Precondensate (weight average molecular weight 110
00, number average molecular weight 3800) solution was obtained.

Next, 140.1 parts of propylene glycol monomethyl ether acetate and 8.3 parts of tolylene diisocyanate were added,
The reaction was carried out 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 the case of the solution (a)) Next, 63.6 parts of propylene glycol monomethyl ether acetate and 1.3 parts of diethanolamine were added, and the mixture was reacted at 80 ° C. with stirring to obtain an amine-modified epoxy resin (weight average molecular weight 30,100, number average molecular weight 30,100). 6100) solution (e) was prepared. The solution (e) had a viscosity Z ₃ and a solid content of 44.3%.

[Preparation of modified epoxy resin solution (f)]

Epoxy resin (epoxy equivalent 1100) obtained by reacting bisphenol consisting of bisphenol A 55.7%, bisphenol F 35.8% and bisphenol S 8.5% with epichlorohydrin by a conventional method was added to 300 parts of propylene glycol monoethyl ether acetate 384.1.
And 14.3 parts of diethanolamine are added, and the mixture is stirred at 80 ° C.
To prepare an amine-modified epoxy resin (weight average molecular weight 2400, number average molecular weight 1400) solution (f). The solution (f) had a viscosity V and a solid content of 45.0%.

[Preparation of modified epoxy resin solution (G)]

Bisphenol A epoxy resin (epoxy equivalent 112
0) 150.0 parts, bisphenol F epoxy resin (epoxy equivalent 1206) 100.0 parts, bisphenol S epoxy resin (epoxy equivalent 1155) 50.0 parts, propylene glycol monomethyl ether acetate 384.4 parts, catalyst (triethylamine) 1.8 parts and (2-benzo Thiazolylthio) -succinic acid (12.7 parts) was reacted with stirring at 120 ° C. to prepare a carboxyl-modified epoxy resin (weight average molecular weight 2500, number average molecular weight 1400) solution (g). The solution (g) had a viscosity V and a solid content of 45.0%.

[Preparation of modified epoxy resin solution (h)]

In a four-necked flask equipped with a stirrer, a nitrogen gas introducing device and a thermometer, 237.8 parts of bisphenol A epoxy resin (epoxy equivalent 187), 137.2 parts of bisphenol F, 0.1 part of reaction catalyst (tetramethylammonium bromide),
Ethylene glycol monomethyl ether acetate 258.
4 parts was added, and the reaction was carried out at 156 ° C. with stirring while introducing nitrogen gas to obtain a precondensate (weight average molecular weight 10100, number average molecular weight 4000) solution.

Next, 213.5 parts of ellalen glycol monomethyl ether acetate and 11.1 parts of hexamethylene diisocyanate were added and reacted at 65 ° C. under stirring to obtain a high molecular weight epoxy resin solution. (The end point of the reaction is the same as that of the above solution (a).) Then, 3.0 parts of 3-amino-1,2,4-triazole,
3.7 parts of propylene glycol monomethyl ether was added, and the mixture was reacted at 80 ° C. with stirring to give an amine-modified epoxy resin (weight average molecular weight 23400, number average molecular weight 5600).
A solution (H) was prepared. The solution (H) had a viscosity Z ₁ and a solid content of 45.0%.

[Preparation of modified epoxy resin solution (i)]

Add bisphenol A to the same reactor as the solution (H).
235.6 parts of epoxy resin (epoxy equivalent 187), 125.5 parts of bisphenol A, 14.0 parts of bisphenol S, 0.1 part of reaction catalyst (lithium chloride), 275.1 parts of propylene glycol monomethyl ether acetate are added, with stirring while introducing nitrogen gas. Precondensation product (weight average molecular weight 12500, number average molecular weight 3300)
A solution was obtained.

Next, 194.4 parts of propylene glycol monomethyl ether acetate and 9.0 parts of hexamethylene diisocyanate were added and reacted at 65 ° C. under stirring to obtain a high molecular weight epoxy resin solution. (The end point of the reaction is the same as in the case of the solution (a)) Then, 2.9 parts of n-butylamine and 3.5 parts of propylene glycol monomethyl ether acetate were added, and the mixture was reacted at 60 ° C. under stirring to give an amine-modified epoxy resin (weight average molecular weight 28600, number). A solution (i) having an average molecular weight of 6000) was prepared. The solution (i) had a viscosity Z ₁ and a solid content of 45.0%.

[Preparation of Epoxy Resin Solution (N)]

124.5 parts of propylene glycol monomethyl ether acetate was added to the high molecular weight epoxy resin solution obtained during the preparation of the solution (a) to prepare an epoxy resin (weight average molecular weight 25400, number average molecular weight 5500) solution (nu). did. The solution (nu) has a viscosity Z ₁ and a solid content.
It was 45.0%.

[Preparation of modified epoxy resin solution (L)]

200 parts of an epoxy resin having a weight average molecular weight of 11,000 obtained by reacting bisphenol A with epichlorohydrin by a conventional method, 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). In addition, while introducing nitrogen gas, the mixture was reacted at 156 ° C. with stirring to give a precondensate (weight average molecular weight 11500, number average molecular weight 3900).
A solution was obtained.

Next, 140.1 parts of propylene glycol monomethyl ether acetate and 8.3 parts of tolylene diisocyanate were added,
The reaction was carried out 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 the case of the solution (a).) Then, propylene monomethyl ether acetate 63.6
And 1.3 parts of diisopropanolamine were added, and the mixture was stirred for 8 hours.
The reaction was carried out at 0 ° C. to prepare an amine-modified epoxy resin (weight average molecular weight 26000, number average molecular weight 5000) solution (L). The solution (L) had a viscosity Z ₁ and a solid content of 44.3%.
It was there.

Example 1 200 parts of modified epoxy resin solution (ii), 400 parts of colloidal silica [“ETC-ST (trade name, manufactured by Nissan Chemical Industries, Ltd., ethylene glycol monoethyl ether dispersion type, solid content 20%)” and ethylene glycol monoethyl. A paint was prepared by mixing and dissolving 418 parts of ether.

The resulting paint was applied to various steel plates shown in Table 2 and the dry film thickness was 3μ.
Roll coating is applied so that the maximum plate temperature is 30.
Baking to 150 ° C in seconds, corrosion resistance, cationic electrodeposition coating property, adhesion of topcoat, secondary adhesion of water resistance, alkali resistance,
Each heat resistance test was 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 a curing agent) blended in the proportions shown in Table 1 was used in an amount of ethylene glycol monoethyl having a solid content of 20%. A paint was prepared by dissolving with ether.

Each test is performed on the obtained coating material 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, all of Examples 1 to 10 using the coating composition of the present invention were excellent in corrosion resistance, cationic electrodeposition coating property, adhesion, alkali resistance, and heat resistance.

On the other hand, in Comparative Example 1 using the epoxy resin containing no bisphenol S skeleton, the glass transition temperature was low, and the corrosion resistance and the water resistant secondary adhesion were lower than those of the coating material of the present invention.
Further, in Comparative Example 2 in which the epoxy resin containing no bisphenol F skeleton was used, the corrosion resistance, the cationic electrodeposition coating property, the adhesion of the topcoat, and the secondary adhesion of water resistance were lower than those of the coating composition of the present invention.

Comparative Example 3 using an epoxy resin which was not modified with a basic nitrogen compound or a carboxyl group-containing compound
Had poor water-resistant secondary adhesion.

Further, Comparative Example 4 using an epoxy resin containing neither bisphenol F skeleton nor bisphenol S skeleton had a poor cationic electrodeposition coating property.

Comparative Example 5 containing no silica particles was poor in corrosion resistance, cationic electrodeposition coating property, 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) in the resin. Corrosion resistance including [II] silica particles and modified epoxy resin obtained by modifying a high-molecular-weight epoxy resin polymerized with a polyfunctional compound having reactivity with the epoxy group or hydroxyl group of the above, with a basic nitrogen compound or a compound containing a carboxyl group Coating composition. 2. An epoxy resin mixture [I] (a2) comprising a bisphenol A epoxy resin, a bisphenol F epoxy resin and a bisphenol S epoxy resin, or (b2) the epoxy resin mixture (a2) in the resin. Corrosion resistant paint containing [II] silica particles and modified epoxy resin obtained by modifying a high molecular weight epoxy resin polymerized with a polyfunctional compound having reactivity with an epoxy group or a hydroxyl group with a basic nitrogen compound or a compound containing a carboxyl group Composition. 3. [I] (a3) One or more epoxy resins of bisphenol A epoxy resin, bisphenol F epoxy resin and bisphenol S epoxy resin and one of bisphenol A, bisphenol F and bisphenol S Alternatively, an epoxy resin having at least a bisphenol A skeleton, a bisphenol F skeleton and a bisphenol S skeleton in a resin obtained by a reaction with two or more bisphenol components, or (b3) the epoxy resin (a3), which is an epoxy resin in the resin. Corrosion-resistant coating composition containing [II] silica particles and a modified epoxy resin obtained by modifying a high-molecular-weight epoxy resin polymerized with a polyfunctional compound reactive with a group or a hydroxyl group with a basic nitrogen compound or a compound containing a carboxyl group object.