JPH03223497A - Formation of film - Google Patents

Abstract

PURPOSE:To obtain a film excellent in smoothness by coating the material to be coated in cationic electro-coating paint by electrodeposition and then washing this material to be coated with water and thereafter treating the same with cationic aq. soln. while being intactly held in an unhardened state and successively baking it. CONSTITUTION:The material to be coated is coated by electrodeposition in a cationic electro-coating paint (A) incorporating cationic resin and block isocyanate compd. as an essential component. Then the material is washed with water and thereafter treated by cationic aqueous liquid (P) while being intactly held in an unhardened state and successively baked. Pigment and/or a gelled particulate polymer are incorporated in the paint (A). Cationic resin and block isocyanate compd. are incorporated into the aqueous liquid (B) as an essential component. Thereby a film excellent in rustproof properties for an edge and in weather resistance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for forming a coating film particularly excellent in smoothness, rust prevention, and weather resistance.

[Prior art and its problems] Conventionally, rust-proof steel plates have been used or anti-corrosion paint has been applied to the edges with a roller or brush to improve the rust-proofing properties of the edges. The disadvantages are that the cost is high and the number of steps is large. In addition, various attempts have been made to improve the rust prevention properties of the edges, such as adding a large amount of pigment to the electrodeposition paint or adding gelatinized fine particles, but these efforts have not improved smoothness and the coating film on the edges. This is incompatible with the formation properties, and a cationic electrolyte coating film that fully satisfies these smoothness and edge film formation properties has not been obtained.

In order to improve these drawbacks, the applicant proposed applying a water-based paint on top of the cationic electrodeposition coating. However, anionic resin paints are essentially used as the water-based paints, and since aggregation of anions and cations occurs at the interface of the paint film, it becomes difficult for the water-based paints to soak into the electrodeposited film. The reality is that it is still not possible to obtain coating films with excellent smoothness and corrosion resistance.

Conventionally, block isocyanate-curable cationic electrodeposition paints using bisphenol-epichlorohydrin type epoxy resin as a base resin have been widely used as undercoating paints for automobile bodies and the like. Painting systems for automobile bodies using such cationic 1i@ paints are generally cationic electrodeposition undercoat paints.
Previously, a 3-coat finish consisting of an intermediate coat and a top coat was used, but in recent years, in order to reduce painting costs, various ways to reduce the number of painting processes have been studied, and a 2-coat finish consisting of a cationic electrodeposition base coat and a top coat has been carried out. There is a strong demand for the development of a coating system that can provide coating performance (particularly weather resistance) and finishing properties (particularly smoothness) equivalent to those of conventional three-coat finishes.

The present invention was made with the object of providing a coating film with excellent smoothness and rust prevention properties.

In addition to the above-mentioned objectives, the present invention has also been made to provide a coating film that is excellent in smoothness, edge rust prevention, and weather resistance.

[Means for solving the problem] Therefore, the present inventors improved the rust prevention of the edge part, the smoothness of the coating surface,
As a result of intensive research aimed at developing a coating film with excellent weather resistance, we applied cationic electrodeposition paint and then left it uncured! It was discovered that a coating film that solved all of the above problems could be formed by treating the coating film with a cationic aqueous liquid, and the present invention was completed.

That is, in the present invention, an object to be coated is electrodeposited in a cationic electrodeposition paint (A) containing a cationic resin and a blocked isocyanate compound as essential components, and then the object to be coated is washed with water and then uncured. Treated as is with cationic aqueous solution (B),
The present invention relates to a method for forming a coating film, which is characterized by subsequent baking.

In the present invention, the electrodeposition paint (A) has an amino group and optionally a hydroxyl group as a functional group, and a cationic resin in which at least a part of the amine group is protonated with an acid, a blocked isocyanate compound, and optionally a cationic resin having an amino group and optionally a hydroxyl group as a functional group. It is a paint containing a catalyst (metal ion, tertiary amine, organometallic compound, etc.) as a cured resin composition.

The above-mentioned cationic resin is, for example, a polyepoxide resin reacted with an amine compound (for example, a primary amine, a secondary amine, a polyamine, a ketimine-blocked polyamine) to convert at least a portion of the amine group into an acid (for example, an organic carboxylic acid).
Examples include reaction products obtained by protonation with .

The polyepoxide resin is an epoxy group compound and generally has a molecular weight of at least 200, preferably from 400 to
Those having a number average molecular weight within the range of 50,000, more preferably 800 to 2,000 are suitable. As such epoxide compounds, those known per se can be used, and examples thereof include the following.

b) Includes polyglycidyl ethers of polyphenols that can be produced by reacting polyphenols with epichlorohydrin in the presence of an alkali.

Examples of the vine polyphenols used here include bis(4-hydroxyphenyl)-2,2-propane, 4-hydroxyphenyl
．． 4' dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-tert-butyl-phenyl) = 2. 2-propane, bis(2-hydroxynaphthyl)methane, 1.5-
Dihydroxynaphthalene, bis(2,4-dihydroxyphenyl)methane, tetra(4-hydroxyphenyl)
-1,1°2.2-ethane, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfone, phenol novolak, talesol novolak and the like.

(11) Polyepoxides obtained by epoxidizing natural oils such as linseed oil, tung oil, soybean oil, and dehydrated castor oil, or stand oil obtained by heat-treating these natural oils (e.g., JP-A-53-16048) (see official bulletin).

(■) Polymers of conjugated diolefins such as butadiene, isoprene, and piperylene and/or copolymers of these conjugated diolefins; vinyl having one or more of the above conjugated diolefins and an ethylenically unsaturated group Polyepoxides obtained by epoxidizing copolymers 1 and the like with monomers such as isobutylene, styrene, vinyltoluene, acrylonitrile, etc.
(see publication).

(IV) One or more of ethylenically unsaturated polymerizable epoxy group-containing monomers, such as butadiene monoepoxide, 4-vinylcyclohexene monoepoxide, etc., and the conjugated diolefin and/or vinyl having an ethylenically unsaturated group. Copolymers with monomers [e.g., JP-A-54-
(v) Epoxy cationic resin with a surface tension of 40 to 60 dyne/cm and a surface tension of 25 to 45 dyne/cm.
m nonionic resin is preferably contained within the range of epoxy cationic resin:nonionic resin = 60.40 to 98:2 (weight ratio), and the surface tension of the epoxy cationic resin is higher than the surface tension of the nonionic resin. Resin is also a big one (
For example, see Japanese Patent Application Laid-open No. 174277/1983).

In addition to the above, cationic unsaturated vinyl monomers (e.g. N,N-dimethylamine ethyl methacrylate, vinyl pyrrolidone), hydroxyl group-containing unsaturated vinyl monomers (e.g. hydroxyethyl methacrylate, hydroxyethyl acrylate) (vl) cationic vinyl copolymers obtained by copolymerization with other vinyl monomers (for example, see JP-A No. 61-293273) can be used.

Among the above, resins (1) to (IV) can be used to obtain a coating film with excellent rust prevention properties, and resins (V) and (vl) can be used to obtain a coating film with excellent weather resistance. There are advantages.

Examples of blocked isocyanate compounds used in combination with polyepoxide resins include aromatic, aliphatic, and alicyclic incyanate compounds, and free incyanate compounds such as caprolactams, oximes, phenols, and alcohols. Examples include those obtained by reacting so that no groups remain.

Desirably, the incyanate compound has 2 to 3 isocyanate groups as a whole and has a molecular weight in the range of 150 to 600. Representative examples of such polyisocyanates include aromatic inocyanates such as 4,4'-diphenylmethane diisocyanate. Cyanates: aliphatic diisocyanates such as hexamethylene diisocyanate and dimer acid diisocyanate; diisocyanates containing cycloalkylene rings such as l,4-dicyclohexylmethane diisoneanate and inphorone diisocyanate: n- or p
- Aromatic-aliphatic diisocyanates such as xylylene diisocyanate.

Among the above isocyanate compounds, the use of aromatic incyanate compounds has the advantage of providing a coating film with excellent rust prevention properties, and the use of aliphatic or alicyclic isocyanate compounds has the advantage that a coating film with excellent weather resistance can be obtained. . In addition, when the aromatic incyanate compound is combined with the polyepoxide resin of (1) to (1v) above, and the aliphatic or alicyclic isocyanate compound is combined with the polyepoxide resin of (V) or the vinyl copolymer (vl), Furthermore, a coating film with excellent rust prevention and weather resistance can be obtained.

The above-mentioned blocked isocyanate compound can be used in a mixture with a cationic resin, but it can be used by partially reacting a blocked isocyanate compound containing a portion of free incyanate groups with a cationic resin to form a block in the cationic resin. It is also possible to introduce isocyanate groups.

In the present invention, an electrodeposition coating material containing a pigment, a gelled fine particle polymer, etc. in addition to the cationic resin and blocked isocyanate compound can be used. Electrodeposition paints using this material can form coatings with excellent rust prevention properties, especially at the edges.

1 containing the above pigment! The coating material contains at least one pigment, and the pigment has an oil absorption of 10
The total oil absorption amount of the pigment is 1.000 to 10.0% per 100 parts by weight of the cationic resin and the blocked isocyanate compound.
000, preferably in the range of 3.000 to 7.000, can be suitably used.

As the silicon dioxide pigment having an oil absorption of 100 or more, for example, Nippon Aerosil Co., Ltd.'s product name [Erosil 200J
(oil absorption 143-183), Fuji Davison's product name "Thyroid 161" (oil absorption 128-135),
"Thyroid 244J (oil absorption 270-330),
"Thyroid 308J (oil absorption 170-220),
"Thyroid 404J (oil absorption 170-230),
Commercially available products such as Thyroid 978J (oil absorption 180-230) can be mentioned, and examples of carbon-based pigments include furnace-type or channel-type carbon black (usually used as a black pigment) (oil absorption 100-130). ) is used, for example, the product name [Carbon BAGJ, etc.] manufactured by Columbia Carbon Company, USA.

Pigments to be blended include, in addition to the above-mentioned pigments with an oil absorption of 100 or more, pigments commonly used in electrodeposition paints, such as inorganic color pigments such as red iron oxide and titanium white, strontium dichromate, and anti-corrosion pigments such as basic lead sulfate. Pigment: Extender pigments such as talc, clay, and calcium carbonate can be used in combination as long as the total oil absorption of the pigment is within the range of 1.000 to 10.000 per 100 parts by weight of the cationic resin and blocked isocyanate compound. .

The "oil absorption" and "total oil absorption" of pigments are based on JIS K5.
101-78 (pigment test method).

As the electrodeposition paint containing the gelled fine particle polymer, a coating containing a cationic 1i@ type gelled fine particle polymer preferably having the following composition can be suitably used.

These fine particle polymers have a particle size of 500 nm or less, preferably 1
0-300nm, more preferably 5O-100nrn
The average particle diameter can be within the range of . The blending ratio of the fine particle polymer can be selected as appropriate depending on the required performance, but is usually 5 to 4 parts by weight per 100 parts by weight (solid content) of the cationic resin and blocked isocyanate compound.
It can be selected within the range of 5 parts by weight, preferably 10 to 30 parts by weight.

Examples of the cationic electrodepositable gelling fine particle polymer include the following. These materials can be used alone or in combination of two or more.

■ Emulsion polymerization of a polymerizable monomer containing at least two radically polymerizable unsaturated groups in the molecule and a radically polymerizable unsaturated monomer other than the above using a reactive emulsifier containing an allyl group in the molecule. gelled fine particle polymer (as disclosed in JP-A No. 2-47107).

■ Using a cationic reactive emulsifier containing an allyl group in the molecule, as a first step, a polymerizable unsaturated vinyl silane monomer containing a vinyl double bond and a hydrolyzable alkoxysilane group, at least 2 Emulsion polymerization of monomer component (a) consisting of a polymerizable monomer containing a radically polymerizable unsaturated group, a polymerizable unsaturated monomer containing a vinyl double bond and a hydroxyl group, and other polymerizable unsaturated monomers is carried out. Then, in the presence of the aqueous gelled fine particle polymer obtained in the first step, as a second step,
Blocked mono- or polyisocyanates in which at least one isocyanate group in the molecule is blocked with a radically polymerizable monohydroxy compound, polymerizable unsaturated monomers containing a vinyl double bond and a hydroxyl group, and other polymerizable unsaturated monomers Gelled fine particle polymer (patent application No. 1-197929).

■ Polymerizable unsaturated vinyl silane monomer having a vinyl double bond and a hydrolyzable alkoxysilane group, block polyisocyanate in which at least two isocyanate groups are blocked with a radically polymerizable monohydroxy compound, a vinyl double bond and a hydroxyl group and other polymerizable unsaturated monomers using a cationic reactive emulsifier containing an allyl group in the molecule. 1
No. 97930).

■ Using a cationic reactive emulsifier containing an allyl group in the molecule, as a first step, a polymerizable unsaturated vinyl silane monomer containing a vinylic double bond and a hydrolyzable alkoxysilane group, at least 2 A monomer component (c) consisting of a polymerizable monomer containing a radically polymerizable unsaturated group, a polymerizable unsaturated monomer containing a vinyl double bond and a hydroxyl group, and other polymerizable unsaturated monomers is emulsion polymerized. Then, as a second step, in the presence of the aqueous gelled particulate polymer obtained in the first step,
Blocked mono- or polyisocyanate in which at least one isocyanate group in the molecule is blocked with a radically polymerizable monohydroxy compound, a polymerizable unsaturated monomer containing a vinyl double bond and a hydroxyl group, and an amino group in the molecule The core is a polymer of monomer component (c) obtained by emulsion polymerization of monomer component (d) consisting of a polymerizable unsaturated monomer and other polymerizable unsaturated monomers, and the polymer of monomer component (d) is Gelled fine particle polymer having a core-shell structure as a shell (Patent application No. 1-2)
65160).

■ A polymerizable unsaturated vinyl silane monomer containing a vinyl double bond and a hydrolyzable alkoxysilane group, a block polyisocyanate vinyl double bond in which at least two incyanate groups are blocked with a radically polymerizable monohydroxy compound; Emulsify a polymerizable unsaturated monomer containing a hydroxyl group, a polymerizable unsaturated monomer containing an amino group in the molecule, and other polymerizable unsaturated monomers using a cationic reactive emulsifier containing an allyl group in the molecule. Gelled fine particle polymer obtained by polymerization (Patent application No. 1-2)
66850).

Among the above-mentioned materials, it is preferable to use those described in (1) and (2).

In the one-part paint containing the gelled fine particle polymer, the above-mentioned coloring pigments, extender pigments, anticorrosion pigments, etc. can be used as necessary.

Further, in the present invention, the cationic aqueous liquid (B) has an epoxy group, an amino group, and optionally a hydroxyl group as a functional group, and at least a part of the amino group is protonated with an acid. It is an aqueous liquid containing an isocyanate compound and, if necessary, a catalyst (metal ion, tertiary amine, organometallic compound, etc.) as a cured resin composition. The aqueous liquid similar to the cationic electrodeposition paint described above can be used.

In the present invention, when a coating film with excellent weather resistance is desired, it is particularly preferable to use (V) or (vl) as the cationic resin and an aliphatic or alicyclic isocyanate compound as the isocyanate compound.

In the present invention, the method of electrodepositing the cationic electrodeposition paint (A) on the object to be coated is not particularly limited, but for example, the cationic electrodeposition paint (A) is coated with a solid content of about 5 to 40%. % by weight, preferably about 10 to 30% by weight, and further adjust the pH to about 5.5.
~9.0, preferably within the range of about 5.8 to 7.0, is used as an electrodeposition bath, and the bath temperature is adjusted to 15 to 35°C,
After the object to be coated is immersed in the bath, a voltage of 50 to 400 V is applied between the object to be coated and the counter electrode for about 1 to 5 minutes. This can be done by applying i@painting.

The film thickness of the electrodeposition coating is usually about 10 to 70-1, preferably about 15 to 50P (dry film thickness).

In the present invention, washing with water is performed after electrodeposition coating. Water washing is usually performed using deionized water, an ultrafiltrate of water-based paint, or a reverse osmosis filtrate.

Before the water-washed coating film is treated with the cationic aqueous liquid (B), it may be heated, for example, at about 80°C for about 30 minutes, or heated to the extent that water is forcibly removed using hot air, as necessary. You may do so.

The heating may be performed until a semi-cured state is reached.

In the present invention, if the bath paint is baked on the precipitated paint film without washing with water, the low neutralization and high concentration bath paint existing near the precipitated paint film will cause wrinkles and unevenness on the cured paint film. This is not desirable as it may cause

In the present invention, the method of treating the electrolyte coating film using the cationic aqueous liquid (B) is a method other than electrolyzing, usually by sinking,
(thick) by dipping, spraying, etc.

The cationic aqueous liquid (B) is not particularly limited, but has a solid content concentration of about 5 to 50% by weight, preferably 10 to 3% by weight.
An aqueous solution having a pH adjusted to about 5.5 to 9.0, preferably 5.7 to 7.0 can be used in the range of 0% by weight.

The coating film treated with the cationic aqueous liquid (B) is cured by baking at about 100 to about 180°C. The total paint film thickness is
The total film thickness of the above-mentioned electric 1iF paint film thickness and the paint film thickness above it can be, but from the viewpoint of economical efficiency etc.
This is the TOP range.

The paint film thus formed can be finished by further applying a top coat as necessary.

[Operation and Effects of the Invention] The coating film formed by the method of the present invention is obtained by electrocoating the object to be coated in a cationic electrodeposition coating as the first step, and washing the deposited coating film with water to form a porous coating film. is formed and the second
By applying a cationic aqueous liquid on this coating film in stages, this liquid easily impregnates the porous precipitated coating film of the first stage, and a uniform coating film without pores can be obtained. Since the porous precipitated coating film itself has poor melt flowability when heated, the edge portions are coated thickly, resulting in a coating film with excellent rust prevention properties. The cationic aqueous liquid can provide a coating film with excellent smoothness due to the melting and flow of the cationic aqueous liquid itself present in the surface layer of the coating film upon heating.

In the present invention, when applied to a cationic electrodeposition coating containing a flow control agent (pigment such as silicon dioxide, gelled fine particles, etc.) to improve the corrosion resistance of the edge part, the edge rust prevention property is particularly high. An excellent coating film can be formed.

In addition, in the present invention, when a cationic aqueous liquid containing an epoxy cationic resin and a nonionic resin as a resin component or a cationic aqueous liquid containing a vinyl copolymer as a resin component is used as the cationic aqueous liquid, a coating with particularly excellent weather resistance can be obtained. A film can be formed.

EXAMPLES The present invention will be specifically explained below with reference to Examples and Comparative Examples. "Parts" and "%" are "parts by weight" and "% by weight"
” means.

Example 1 The following cationic electrodeposition paint (paint 1) using a block isocyanate group-containing epoxy polyamine resin (*l) equivalent to Nireclone No. 9400 manufactured by Kansai Paint Co., Ltd. was electrodeposited under the conditions shown in Table 1. .

After that, the same paint l as above was adjusted to a solid content of 20%, 25%, and 30% on the uncured electrodeposited film, and was spray-painted under the conditions shown in Table 1, and baked and cured in an electric dryer at 170°C. A coating film was formed.

Paint 1 Umbrella Resin A blocked isocyanate group-containing epoxy polyamino resin with an amine value of 80 is neutralized with acetic acid at an equivalent weight of 055.
Dispersed in water.

Medium 2 Water-containing amorphous silicon dioxide pigment manufactured by Fuji Devison Co., Ltd., trade name "Syroid 244" Table 1 Example 2 The following cationic electrodeposition paint (Paint 2) was electrodeposited under the conditions shown in Table 1, then washed with water, Paint 2 with different solids content adjustment (20%, 25%, 30%) was applied on the cured coating under the conditions shown in Table 1, and baked in an electric dryer at 170'C to form a cured coating. formed.

Coating 42 Example 3 The above epoxy polyamino resin 1°I+ (solid content) 1
A 20% solid content cationic electronic sign paint (Paint 3) containing 20 parts of titanium oxide, 20 parts of titanium oxide, and 10 parts of the following gelatinized fine particle polymer (solid content) was electrodeposited under the conditions shown in Table 1, and then washed with water.
The above coating material 3 was coated on the uncured coating film under the conditions shown in Table 1, and a cured coating film was obtained by baking.

Gelation 11 Heavy Al 1 equipped with stirrer, thermometer, cooling tube and heating mantle
2 flask, add deionized water 3507 in the amount shown in Table-1.
and 80 parts of an emulsifier (-180, manufactured by Kao Corporation, 25% aqueous quaternary ammonium salt type allyl group-containing cationic reactive emulsifier) were added to the mixture, and the temperature was raised to 90° C. with stirring. To this, 12.5 parts of a polymerization initiator (VA-086, manufactured by Wako Tsumugi Co., Ltd., 2,2'-azobis[2-methyl-N-(2hydroxyethyl)-propionamide]) was added to 500 parts of deionized water. A dissolved aqueous solution was added. After 15 minutes, the monomer mixture (styrene/n-butyl acrylate/
1.6-hexanediol diacrylate = 470/4
70/60 parts) was added. Polymerization was carried out at 90° C. for 7 hours to obtain a gelled fine particle polymer having a solid content of 20% and an average particle diameter of 70 nm (measured with Coulter Counter Nanosizer N-4).

Example 4 A cationic electrodeposition paint material 4) with a solid content of 20% was produced in the same manner as in Example 3, except that the gelled fine particle polymer 1 in Example 3 was replaced with the gelled fine particle polymer 2 below, This product was used for electrodeposition coating under the conditions shown in Table 1, washed with water, and the above-mentioned coating material 4 was applied on the uncured coating film under the conditions shown in Table 1 to obtain a cured coating film.

Gelui 11 Heavy A2 Production example of incyanate compound 222 parts of isophorone diisocyanate and 50 parts of methyl isobutyl ketone were charged into a flask equipped with a stirrer, an air introduction tube, a cooling tube, and a temperature control device, and the mixture was stirred while blowing dry air into the liquid phase. The temperature was raised to 70°C. Add 0.3 parts of dibutyltin dilaurate to this, and then add 2-
116 parts of hydroxyethyl acrylate was added dropwise over 1 hour, and the temperature was maintained at 70°C for an additional hour after the addition was completed. Subsequently, 115 parts of methyl isobutyl ketoxime was added dropwise over 1 hour. After the completion of the first drop, the mixture was heated and kept at 70°C. The reaction mixture was collected over time and the absorption of -NCO was confirmed by IR.
The end point of the reaction was defined as the point at which GO absorption ceased. In this way, a 90% isophorone diisocyanate/2-hydroxyethyl acrylate/methyl isobutyl ketoxime block solution was obtained.

Production example of gelled particulate polymer 2 I equipped with a stirring device, thermometer, cooling tube and heating mantle
Into a J2 flask, add 700 parts of deionized water and 162 parts of -180 to the same lame as above, and add 90 parts of -180 while stirring.
The temperature was raised to ℃. To this was added an aqueous solution prepared by dissolving 2 parts of the same VA-086 as the polymerization initiator in 100 parts of deionized water. After 15 minutes, the following monomer mixture was added.

Styrene 32 parts n-butyl acrylate 32 parts 1,6-hexanediol 30 parts diacrylate 2-hydroxyethyl acrylate 4 parts KBM-
503×2 parts×γ-methacryloxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) Polymerization was carried out at 90° C. for 6 hours. Next, the following monomer mixture was added dropwise to this product.

Styrene 38 parts n-butyl acrylate 38 parts 2-hydroxyethyl acrylate 4 parts Isocyanate compound obtained in the production example 22 parts Polymerization was carried out at 90°C for 2 hours.

In this way, a gelled fine particle polymer 2 having a solid content of 20% and an average particle diameter of 74 nm (measured with Coulter Nanosizer N-4) was obtained.

Example 5 Paint l spray-painted on the electrodeposited film in Example 1
A cured coating film was obtained by painting and baking in the same manner as in Example 1, except that the following paint 5 was used instead of λ.

Paint 5 27 parts of n-butyl alcohol and 27 parts of isopropyl alcohol were placed in a reaction vessel and heated to 90°C.

Next, 25 parts of styrene, 35 parts of 2-ethylhexyl methacrylate, 25 parts of hydroxyethyl methacrylate, N
, 15 parts of N-dimethylaminoethyl acrylate, and 35 parts of azobisisobutyronitrile were added dropwise to this solution over about 2 hours. The reaction was carried out under nitrogen injection, and the reaction temperature was maintained at 90°C, and the reaction was further carried out for 4 hours to obtain a vinyl copolymer solution with a solid content of 65%.Next, 20 parts of titanium white was added to this solution. After blending and dispersing, 2.0 parts of acetic acid, 20 parts of isophorone diisocyanate compound diblocked with ε-caprolactam, and 2 parts of dibutyltin oxide were added, stirred thoroughly, and then deionized water was gradually added dropwise. A paint 5 having a solid content of 20% was obtained.

Example 6 Electrodeposition paint 1 (paint 6) described below was electrodeposited under the conditions shown in Table 1. Thereafter, paint 6 was spray coated on the uncured electrodeposited film under the conditions shown in Table 1, and a cured film was obtained by baking.

Paint 6 Surface tension 53 dyne/cm Cationic epoxy resin (resin E-1 described in JP-A-63-266097)
using a nonionic film-forming resin with a surface tension of 40 dyne/cm (using resin F-1 described in JP-A No. 63-266097) with a solid content of 20% cation i.
i@Paint (Paint 6) was electrodeposited under the conditions in Table 1, washed with water, and the above paint 6 was applied on the uncured coating under the conditions in Table 1 and baked to obtain a cured coating. .

Paint 6: Resin E-1 (solid content) 57.8 parts, Resin F-1
(Solid content) 248 parts, 5.0 parts of ethylene glycol mono-2-ethylhexyl ether diblock of 4.4'-diphenylmethane diisocyanate, 12.4 parts of methyl ethyl ketoxime block of isophorone diisocyanate
parts, 20 parts of titanium oxide and 7 parts of purified clay.

Comparative Example 1 Using paint 1 described in Example 1, N coating was applied under the conditions shown in Table 1, followed by washing with water and curing at 170°C.

Comparative Example 2 Using the coating material 1 described in Example 1, electrodeposition was applied under the conditions shown in Table 1, and the coating was cured by baking at 170° C. without washing with water.

Comparative Examples 3 to 6 Paints 2 to 4 and 6 shown in Table 2 were electrodeposited under the conditions shown in Table 1, washed with water, and baked and cured at 170°C.

Comparative Example 7 A baked cured coating was formed in the same manner as in Example 1, except that the paint sprayed on the electrodeposition coating in Example 1 was replaced with an anionic water-based paint equivalent to Asukabake MG500 manufactured by Kansai Paint Co., Ltd. Ta.

A table summarizing the results of coating film performance obtained in Examples and Comparative Examples.
Shown in 2.

*3 Poor surface smoothness] *4 Visibility The coated plates of the Examples and Comparative Examples were further coated with 35% of aminoalkyd resin paint, and baked at 140°C for 15 minutes.

Using this test plate, the sharpness measuring device rJCRI-GGD
-Measured using a 166-type Gd meter J (sold by Japan Color Research Institute). Measured with the angle fixed at 55°.

*545° edge rust prevention A SPC mild steel plate is processed to an angle of 45°, subjected to surface treatment Bonderite #3004 treatment, and subjected to prescribed electrodeposition coating, and used for the test. The rust prevention test was based on JIS 22371 salt spray test. The test continued for up to 720 hours. 240 hours during the test, Good, *7 Water resistance Immersed in tap water at 40°C. After cross-cutting the coating film, it was peeled off using cellophane tape, and adhesion deterioration was visually examined.

[0: good, ○, slightly good, △: poor, ×: markedly poor] *8 The coated plates of the accelerated weathering examples and comparative examples were further coated with 35μ of amino alkyd resin paint clear, and heated at 140°C for 15 minutes. Bake for a minute. This coated plate was subjected to a Sunshine Weather-Ometer for 20 hours, and after being immersed in water at 40°C for 20 hours, a cross cut was made on the coated plate and a peel test was performed using cellophane adhesive tape.This test was repeated and no peeling occurred. I checked the time.

Claims (1)

[Scope of Claims] [1] The object to be coated is electrocoated in a cationic electrodeposition paint (A) containing a cationic resin and a blocked isocyanate compound as essential components, and then the object to be coated is washed with water and then untreated. A method for forming a coating film, which comprises treating the cured state with a cationic aqueous liquid (B), followed by baking. [2] The coating film forming method according to claim 1, wherein the coating material (A) contains a pigment and/or a gelled fine particle polymer. [3] The cationic resin of the paint (A) has a surface tension of 40 to 60
dyne/cm epoxy cationic resin and surface tension 2
2. The coating film forming method according to claim 1, wherein the resin is a mixed resin with a nonionic resin of 5 to 45 dyne/cm, and the surface tension of the epoxy cationic resin is larger than the surface tension of the nonionic resin. [4] The method for forming a coating film according to claim 1, wherein the cationic resin of the coating material (A) is a cationic vinyl polymer. [5] The coating film forming method according to claim 1, wherein the aqueous liquid (B) contains a cationic resin and a blocked isocyanate compound as essential components. [6] The coating film forming method according to claim 5, wherein the cationic resin of the aqueous liquid (B) is a cationic vinyl polymer.