JP2003221546A - Method for forming a coating film using an intermediate coating and cationic electrodeposition coating composition - Google Patents

Abstract

(57) [Summary] [Problem] An intermediate coating that is excellent in corrosion resistance, solvent resistance and weather resistance even in two-coat coating, has excellent adhesion to a top coat, and can achieve the same coating appearance as three-coat coating. Provided is a method for forming a coating film using a cationic electrodeposition coating composition. SOLUTION: The acrylic resin (a1), the polyester resin (a2) and the blocked polyisocyanate (c1) dispersed in an aqueous medium are converted into an acrylic resin (a1).
And a shell part containing the blocked polyisocyanate (c1) and a core part containing the polyester resin (a2) and the blocked polyisocyanate (c1) to form emulsion particles having a core-shell structure. Electrodeposition coating is performed using an intermediate coating / cationic electrodeposition coating composition in which the epoxy resin (b) and the blocked polyisocyanate (c2) form emulsion particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cationic electrodeposition coating composition and a method for forming a coating film, and more particularly to an intermediate coating and cationic electrodeposition coating composition capable of forming an intermediate coating film at the same time as an undercoat coating film. The present invention relates to a coating film forming method used.

[0002]

2. Description of the Related Art In the paint industry, especially in the field of automobile body painting, in recent years, in order to solve the problems of resource saving, cost saving and reduction of environmental load (VOC, HAPS, etc.), shortening of the painting process has been strongly demanded. ing.

For example, as a coating finish procedure for automobiles,
Conventionally, three-coat coatings of electrodeposition primer coating, intermediate coating and top coating have been mainly performed. However, in recent years, it has been attempted to reduce the number of coating processes by the intermediate coating less (two-coat system) in which the top coating is directly applied after the electrodeposition primer coating. Of course, even with 2 coats, the same appearance as with 3 coats,
It is required to maintain adhesion with the topcoat, weather resistance, corrosion resistance and the like.

As a technique relating to a multi-layer electrodeposition coating film without intermediate coating, for example, Japanese Patent Application Laid-Open Nos. 2000-345394 and 2001-140097 describe a film using a two-layer separation type cationic electrodeposition coating composition. A method of forming is described.

The cationic electrodeposition coating composition described herein is
It contains a cationic acrylic resin, a cationic epoxy resin, a blocked polyisocyanate, and a pigment dispersed in an aqueous medium. Since the solubility parameter of the cationic epoxy resin is larger than that of the cationic acrylic resin by 1 or more, the two resins are not compatible with each other even if they flow by heating at the time of curing after electrodeposition coating, and the cationic epoxy resin layer A cationic acrylic resin layer is separated on the top of the base to form a coating film.

As described above, when the layer of the cation-modified epoxy resin is brought into direct contact with the conductive base material in forming the coating film, the corrosion resistance of the base material which is the object to be coated is improved. Further, when a layer of a cationic acrylic resin is formed thereon, the weather resistance and solvent resistance of the base material are improved, and the adhesion with the top coat film is also improved. Moreover, regarding the pigment concentration,
The appearance of the coating film is also improved by providing a gradient for each resin layer.

However, the surface smoothness of the coating film has not been improved by this technique, and the improvement of the coating film appearance is still insufficient. That is, in order to provide a coating film appearance equivalent to that of the three-coat coating by the two-coat coating, it is necessary to control the flow property of the electrodeposition coating film at the time of heating to dramatically improve the surface smoothness.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art.
An intermediate coating / cationic electrodeposition coating composition that is excellent in corrosion resistance, solvent resistance, and weather resistance even in coat coating, has excellent adhesion to the top coating film, and can achieve the same coating film appearance as in 3-coat coating, and the same. It is to provide a coating film forming method to be used.

[0009]

The present invention relates to a cationic acrylic resin (a1) having a number average molecular weight of 2000 to 20000 and a number average molecular weight of 1000 to 1000 dispersed in an aqueous medium.
3000 anionic polyester resin (a2), cation-modified epoxy resin (b), blocked polyisocyanate (c1), blocked polyisocyanate (c
2) and a cationic electrodeposition coating composition for intermediate coating containing at least pigment (d), the acrylic resin (a
1), the polyester resin (a2), and the blocked polyisocyanate (c1) are the shell portion containing the acrylic resin (a1) and the blocked polyisocyanate (c1), the polyester resin (a2), and the blocked polyisocyanate (c1). And a core portion containing, to form emulsion particles of core-shell structure, apart from this,
There is provided an electrodeposition coating composition characterized in that an epoxy resin (b) and a blocked polyisocyanate (c2) form emulsion particles.

In the present invention, the step of immersing an article to be coated in the above-mentioned cationic electrodeposition coating composition; electrodeposition coating is carried out using the article to be coated as a cathode to form an electrodeposition coating film on the surface of the article to be coated. The present invention provides a method for forming a coating film, which comprises a forming step; and a step of baking the electrodeposition coating film.

Further, the present invention comprises the step of immersing an article to be coated in the above cationic electrodeposition coating composition; performing electrodeposition coating using the above article as a cathode to form an electrodeposition coating film on the surface of the article to be coated. A step of forming; a step of baking the above electrodeposition coating film; a step of forming an overcoat coating film by applying a topcoat coating material on the cured electrodeposition coating film; and a step of baking the above topcoat coating film. A method for forming a coating film is provided.

The above objects are achieved by these means.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The cationic electrodeposition coating composition contains various additives such as a binder, a pigment, a solvent and a corrosion resistance-imparting agent in an aqueous medium. The binder is a thermosetting resin composition, and contains at least a cationic resin having a functional group and a curing agent that cures the cationic resin.

In the intermediate electrodeposition cationic electrodeposition coating composition used in the present invention, the cationic acrylic resin (a1), the anionic polyester resin (a2), the cation-modified epoxy resin (b), and these are used as the constituent components of the binder. Blocked polyisocyanate (c
1) and the blocked polyisocyanate (c2) are used.

Cationic acrylic resin (a1) Cationic acrylic resin (hereinafter referred to as "acrylic resin (a1
1) ”. ) Has a cationic group in the molecule. The cationic group is typically an amino group. The amount of amino groups is such that the amine value is in the range of 50 to 150, preferably 60 to
The amount is in the range of 130. If the acrylic resin (a1) has an amine value of less than 50, the resin cannot exhibit sufficient water dispersibility because the amine value is insufficient. Therefore, it becomes difficult to form an emulsion. Further, when it exceeds 150, the resin becomes extremely water-soluble, which is disadvantageous for emulsion formation. Moreover, since the hydrophilicity of the resin is too high, the water resistance of the coating film is insufficient, and the anticorrosion property is deteriorated.

The number average molecular weight of the acrylic resin (a1) is 2
000 to 20000, preferably 2500 to 15000
Adjust to. The number average molecular weight of the acrylic resin (a1) is 2
If it is less than 000, the stability of the emulsion will be insufficient and the storage stability of the paint will decrease. On the other hand, if it exceeds 20,000, the resin viscosity is too high, and thus handling such as emulsification operation becomes difficult.

Such a cationic acrylic resin can be synthesized by a ring-opening addition reaction of an acrylic resin containing a plurality of epoxy rings and a plurality of hydroxyl groups with an amine. In the ring-opening addition reaction, the epoxy ring of the acrylic resin is ring-opened by the reaction with a primary amine, a secondary amine or a tertiary amine acid salt to provide an acrylic resin (a1).

The acrylic resin containing an epoxy ring or the like includes glycidyl (meth) acrylate, an acrylic monomer containing a hydroxyl group, and other acrylic and / or
Alternatively, it can be obtained by copolymerizing with a non-acrylic monomer. Examples of the acrylic monomer containing a hydroxyl group include a hydroxyl group-containing (meth) acrylate such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or 2-hydroxyethyl (meth) acrylate, and ε-. Addition products with caprolactone and the like are included.

Examples of other acrylic monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate and isobutyl (meth). ) Acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
Examples include lauryl (meth) acrylate. Examples of non-acrylic monomers include styrene, vinyltoluene, α-methylstyrene, (meth) acrylonitrile, (meth) acrylamide and vinyl acetate.

Examples of amines for opening an epoxy group of an acrylic resin containing an epoxy ring to introduce an amino group include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine. Examples thereof include primary, secondary, or tertiary amine acid salts such as N-methylethanolamine, triethylamine acid salt, and N, N-dimethylethanolamine acid salt.

It is also possible to use a secondary amine containing a ketimine block primary amino group, such as aminoethylethanolamine methylisobutylketimine. These amines need to be reacted in at least an equivalent amount with respect to the epoxy ring in order to open all the epoxy rings.

The acrylic resin (a1) may be synthesized by copolymerizing an acrylic monomer having an amino group with another monomer. In this method, an amino group-containing acrylic monomer such as N, N-dimethylaminoethyl (meth) acrylate or N, N-di-t-butylaminoethyl (meth) acrylate is used instead of the above glycidyl (meth) acrylate. Then, the acrylic resin (a1) can be obtained by copolymerizing this with a hydroxyl group-containing acrylic monomer and another acrylic and / or non-acrylic monomer.

Acrylic resin (a1) thus obtained
Introduces a blocked isocyanate group by an addition reaction with a half-blocked diisocyanate compound, as described in JP-A-8-333528,
It can also be self-crosslinking.

Anionic polyester resin (a2) The anionic polyester resin (hereinafter referred to as "polyester resin (a2)") has an anionic group in the molecule. The anionic group is typically an acid group. The amount of this acid group is preferably such that the acid value is in the range of 3 to 20, preferably 5 to 15. Polyester resin (a
If the acid value of 2) is less than 3, the adhesion with the top coat film may be poor. On the other hand, when it exceeds 20, there is a possibility that when the blocked polyisocyanate is used as a curing agent, it may be difficult to cure or it may be difficult to form a pigment paste.

The hydroxyl value of the polyester resin (a2) is preferably in the range of 50 to 150. If the hydroxyl value is less than 50, the coating film will be poorly cured and, conversely, will be 150.
When it exceeds, as a result of excess hydroxyl groups remaining in the coating film after curing, the water resistance of the coating film may decrease.

The number average molecular weight of the polyester resin (a2) is preferably in the range of 1,000 to 10,000. When the number average molecular weight is less than 1000, the physical properties such as solvent resistance of the cured coating film are poor. On the other hand, when it exceeds 10,000, the viscosity of the resin solution is high, so that it is difficult to handle the obtained resin in terms of operations such as emulsion dispersion, and the film appearance of the obtained electrodeposition coating film is significantly deteriorated. There is.

The polyester resin (a2) is a polyol component such as neopentyl glycol, trimethylolpropane, ethylene glycol, diethylene glycol, propylene glycol, 1,6-hexanediol, glycerin, pentaerythritol; phthalic acid, isophthalic acid, trimellitate. Acids, terephthalic acid, pyromellitic acid, hexahydrophthalic acid, succinic acid, adipic acid, sebacic acid and other polybasic acids; and their anhydrides; lactones such as δ-butyrolactone and ε-caprolactone, if necessary; Further, as a modifier, various saturated and / or unsaturated fatty acids such as coconut oil fatty acid, tung oil fatty acid, soybean oil fatty acid, and linseed oil fatty acid; their mono-, di- or triglycerides; and Cardura E-10 (having 1 carbon atom).
It is produced by dehydration condensation of a monoepoxide having a branched alkyl group of 0, manufactured by Shell Kagaku Co., Ltd., etc. according to a conventional method.

Further, the polyester resin (a2) may partially contain an appropriate amount of urethane bond. The introduction of such a urethane bond is, for example, 4,4 ′ at both ends of a polyester polyol such as poly δ-butyrolactone or poly ε-caprolactone having a hydroxyl group at both ends of the molecular chain.
A diisocyanate such as diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate or isophorone diisocyanate may be urethane-bonded and partly chain-extended to be used as a part of the polyol component.

Further, the polyester resin (a2) preferably has a tertiary carboxyl group inside the molecule. The tertiary carboxyl group is a group in which no hydrogen is bonded to the carbon atom to which the carboxyl group is directly bonded. The tertiary carboxyl group has a low activity as an acid group, and the SP value can be easily adjusted by introducing this into the polyester resin (a2).

Further, since the polyester resin (a2) has a tertiary carboxyl group in the molecule, the interaction between the acidic groups in the resin is lowered and the heat flow property of the coating film is improved, so that the heat curing property at the time of heat curing is improved. Membrane smoothness is secured,
The coating film appearance can be improved.

The polyester resin (a2) having a tertiary carboxyl group in the molecule is a diol compound having a tertiary carboxyl group, such as 2,2'-dimethylolpropionic acid, 2,2'-dimethylolbutanoic acid, Two
It can be produced by using 2'-dimethylolhexanoic acid, 2,2'-dimethyloloctanoic acid or 2,2'-dimethyloldecanoic acid as a part of the polyol component. The diol compound having a tertiary carboxyl group is preferably used in such an amount that the above acid value, that is, the proportion of the tertiary carboxyl group in the total acid value of the polyester resin (a2) is 80% or more. It is more preferable to adjust so that

The polyester resin (a2) can also be made into a self-crosslinking type resin by carrying out an addition reaction with a half-blocked diisocyanate compound or a partial cocondensation of a melamine resin, if necessary. Such a self-crosslinking type is excellent in curing reactivity and thus is preferably used in the present invention.

Cation-modified epoxy resin (b) Cation-modified epoxy resin (hereinafter referred to as "epoxy resin (b)") is a resin that exhibits rust preventive property against a conductive base material in the field of cationic electrocoating. Well known. The epoxy resin (b) has a cationic group in the molecule. The cationic group is typically an amino group. The amount of the amino group is such that the amine value is in the range of 30 to 100, preferably 40 to 80. When the amine value of the epoxy resin (b) is less than 30, the resin cannot exhibit sufficient water dispersibility because the amine value is insufficient. Therefore, it becomes difficult to form an emulsion. Also, 100
If it exceeds, the resin exhibits high water solubility, which is disadvantageous for emulsion formation. In addition, since the hydrophilicity of the resin is too high, the water resistance of the coating film is insufficient and the rust resistance is reduced.

The number average molecular weight of the epoxy resin (b) is 15
It is preferable to adjust it in the range of 00 to 5000. When the number average molecular weight of the epoxy resin (b) is less than 1500, the cured coating film may have poor physical properties such as solvent resistance and corrosion resistance. On the other hand, when it exceeds 5,000, not only the viscosity control of the resin solution is difficult and the synthesis is difficult, but also the handling of the obtained resin may be difficult in terms of operation such as emulsion dispersion. Furthermore, because of its high viscosity, the flowability during heating / curing is poor and the appearance of the coating film may be significantly impaired.

The epoxy resin (b) is preferably molecularly designed so that the hydroxyl value is in the range of 50 to 250. When the hydroxyl value is less than 50, the coating film may be poorly cured. On the other hand, when it exceeds 250, excess hydroxyl groups may remain in the coating film after curing, resulting in a decrease in water resistance. Furthermore, the softening point of the epoxy resin (b) is set to 80 ° C. or higher, and more preferably 100 ° C. or higher to achieve compatibility of solvent resistance, weather resistance, corrosion resistance or high-dimensional appearance of the cured coating film. It is desirable to do.

Generally, the epoxy resin (b) is produced by ring-opening the epoxy ring in the raw material epoxy resin molecule by reaction with an amine such as a primary amine, a secondary amine or a tertiary amine acid salt. A typical example of the raw material epoxy resin is a polyphenol polyglycidyl ether type epoxy resin which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolac, and cresol novolac with epichlorohydrin.

As another example of the raw material epoxy resin, the oxazolidone ring-containing epoxy resin described in JP-A-5-306327 can be mentioned. This epoxy resin is obtained by reacting a diisocyanate compound or a bisurethane compound obtained by blocking the NCO group of the diisocyanate compound with a lower alcohol such as methanol or ethanol, and epichlorohydrin.

The raw material epoxy resin is a bifunctional polyester polyol, polyether polyol, bisphenol, or 2 before the ring-opening reaction of the epoxy ring with amines.
The chain can be extended and used with a basic carboxylic acid or the like. In addition, before the ring-opening reaction of the epoxy ring with amines, 2-ethylhexanol, nonylphenol, ethylene glycol monoester is added to some epoxy rings for the purpose of adjusting the molecular weight or amine equivalent and improving the heat flow property. A monohydroxy compound such as 2-ethylhexyl ether or propylene glycol mono-2-ethylhexyl ether can also be added and used.

As the amines for opening the epoxy ring of the raw material epoxy resin to introduce an amino group, those described in the cationic acrylic resin (a1) may be used in the same amount.

Blocked polyisocyanate (c1) and
The (c2) blocked polyisocyanate refers to a compound in which the isocyanate group of polyisocyanate is protected with a sealant. Examples of polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate (including trimer), tetramethylene diisocyanate and trimethylhexamethylene diisocyanate, and fats such as isophorone diisocyanate and 4,4′-methylenebis (cyclohexyl isocyanate). Cyclic polyisocyanate, 4,
Aromatic diisocyanates such as 4′-diphenylmethane diisocyanate, tolylene diisocyanate and xylylene diisocyanate are mentioned.

Examples of the above-mentioned sealing agent include monovalent alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, and methylphenyl carbinol. , Ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, etc., cellosolves, phenol, para-t-
Butylphenol, phenol such as cresol, dimethylketoxime, methylethylketoxime, methylisobutylketoxime, methylamylketoxime,
Oximes such as cyclohexanone oxime, and ε-
Lactams represented by caprolactam and γ-butyrolactam are preferably used. In particular, oxime and lactam sealing agents are suitable from the viewpoint of resin curability because they dissociate at low temperatures.

The above sealants may be used alone or in combination of two or more kinds. The blocking rate is preferably 100% in order to secure the storage stability of the coating material unless there is a purpose of reacting with the resin component (a1), (a2) or (b).

In the present invention, it is preferable to use at least two types of blocked polyisocyanates ((c1) component and (c2) component). The blocked polyisocyanates (c1) and (c2) are each independently selected so that their unique solubility parameters satisfy the compounding conditions described below.

Of the plurality of blocked polyisocyanates used, at least one (component (c1)) must satisfy the following solubility parameter conditions. That is, the SP of the blocked polyisocyanate (c1) is an intermediate value between the average value of the resin (a1) and the resin (a2) and the resin (b), that is, {(a1) + (a2)} / 2 ≦ (c1 ) ≦ (b) is preferable. By setting the solubility parameter of the blocked polyisocyanate in this way, it becomes possible to carry out distributive dissolution after separating the two layers, and to simultaneously cure the layer containing the resin components (a1) and (a2) and the resin component (b). It can be compatible. For the above-mentioned purpose, the blocked polyisocyanate (c1) is used as the core-shell type first emulsion of the present invention (mainly the resin (a1) and (a)).
It is preferably introduced inside).

Regarding the other blocked polyisocyanate (c2), the resin (b) is mainly used to adjust the crosslinkability of the layer in direct contact with the base material and mainly to improve the rust prevention property.
Is to be selectively cured. Therefore, the component (c2) needs to be dissolved in the resin (b). Therefore, the following solubility parameter conditions must be met. That is (c2)
It is preferable that − (b) ≦ ± 0.5. For the above purposes, blocked polyisocyanate (c2)
Is preferably introduced into the second emulsion of the present invention (mainly composed of the resin (b)) in advance.

The pigment (d) can be used without particular limitation as long as it is a pigment usually used in electrodeposition paints. Examples thereof include color pigments such as carbon black, titanium dioxide and graphite,
Examples include extender pigments such as kaolin, aluminum silicate (clay) and talc, and rust preventive pigments such as aluminum phosphomolybdate.

Of these, titanium dioxide, carbon black and aluminum silicate (clay) are particularly important.
And aluminum phosphomolybdate. In particular, titanium dioxide is suitable as an electrocoating film because it has a high hiding property as a color pigment and is inexpensive. Although the above pigments can be used alone, a plurality of pigments are generally used according to the purpose.

When the pigment is used as a component of the electrodeposition paint,
Generally, the pigment is previously dispersed in an aqueous medium at a high concentration to form a paste. This is because the pigment is in powder form, so it is difficult to disperse it in one step in a low-concentration uniform state used in an electrodeposition coating. Generally, such a paste is called a pigment dispersion paste.

The pigment dispersion paste is prepared by dispersing a pigment together with a pigment dispersion resin in an aqueous medium. As the pigment-dispersing resin, generally, a cationic polymer such as a cationic or nonionic low molecular weight surfactant or a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfonium group is used.

Cationic Electrodeposition Coating Composition Also Used for Intermediate Coating The cationic electrodeposition coating composition used in the present invention is prepared by a method in which the resin component is made into an aqueous emulsion and blended with the remaining components as usual. However, in the present invention, it is necessary to prepare two types of emulsions.

The first emulsion is an acrylic resin (a
1), a polyester resin (a2), and a blocked polyisocyanate (c1). FIG. 1 is a sectional view schematically showing the structure of the first emulsion particles. The particles of this resin emulsion have a core-shell structure in which the shell portion 1 containing the acrylic resin (a1) and the blocked polyisocyanate (c1) includes the core portion 2 containing the polyester resin (a2) and the blocked polyisocyanate (c1). Must have

By inserting the polyester resin (a2) as the core portion of the acrylic resin (a1), the heat flow property of the resin layer in contact with air is improved and the surface smoothness of the coating film is improved. . Therefore, the acrylic resin (a
It is preferable that 1) and the polyester resin (a2) have a relatively low melt viscosity.

The melt viscosity of the acrylic resin (a1) and the polyester resin (a2) may be lowered by adding another type of resin. As the resin added to the acrylic resin (a1) and the polyester resin (a2) for the purpose of lowering the melt viscosity, a polyether resin is preferable.

The polyether resin means a resin having an ether bond chain as the main chain. The polyether resin (a3) used in the present invention has the formula

[0055]

Embedded image H- [O- (CHR) _m ] _n -OR

[In the formula, each R is independently a hydrogen atom,
An alkyl group having 1 to 6 carbon atoms, or a phenyl group,
m is an integer of 2 to 4, and n is an integer of 4 to 70. ] It is a polyalkylene polyol of the structure shown by these.

The amount of terminal hydroxyl group is such that the hydroxyl value is 30 to 500.
, And preferably in the range of 100 to 350. If the hydroxyl value of the polyether resin is less than 30, the crosslinking reactivity at the time of curing the coating film is insufficient, and the crosslinking density is lowered, resulting in deterioration of the coating film physical properties and rust preventive properties. Also,
When it exceeds 500, the cross-linking reactivity is too high, so that curing strain of the surface layer of the coating film is caused, and the film appearance is impaired.

The polyether resin (a3) is prepared to have a number average molecular weight of 200 to 2000, preferably 400 to 1000. When the number average molecular weight of the polyether resin is less than 200, the boiling point is lowered, and as a result, it is dissipated in the air during baking of the coating film, and a sufficient leveling effect cannot be expected. Further, the dispersed polyether may become tar in the heating furnace and cause stains. On the other hand, when it exceeds 2000, the viscosity of the resin becomes high, so that the leveling effect of the film surface layer cannot be expected sufficiently.

Specific examples of the polyether resin (a3) include polyoxytetramethylene glycol, polyoxypropylene glycol, polyoxyethylene glycol, polyoxytetramethylene glycol phenyl ether, polyoxypropylene glycol phenyl ether and polyoxyethylene glycol phenyl. Ether, polyoxytetramethylene glycol butyl ether, polyoxypropylene glycol butyl ether, and polyoxyethylene glycol butyl ether.

Most preferred among these are polyoxypropylene glycol and its one-terminal alkyl or phenyl ethers. Since these are insoluble in cation-modified epoxy resin and compatible with cation-modified acrylic resin and anionic polyester resin, they selectively plasticize the resin layer in direct contact with air. This is advantageous because it has a high effect of improving the flowability of the surface layer. Further, recently, there is polyoxypropylene glycol in which hydroxyl groups at both ends are both primaryized by adding a diol to at least one end of the molecular structure. In the present invention, it is also preferably used. You can

The first emulsion was prepared by uniformly mixing acrylic resin (a1), polyester resin (a2), blocked polyisocyanate (c1) and, if necessary, polyether resin (a3) in an organic solvent. , Dispersed in an aqueous medium containing a neutralizing agent. As the neutralizing agent, inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid and formic acid, acetic acid, lactic acid,
Organic acids such as sulfamic acid and acetylglycinic acid can be used. Then, the organic solvent contained in the dispersion is evaporated to obtain the first emulsion.

The second emulsion is the epoxy resin (b)
And a blocked polyisocyanate (c2). The second emulsion can be prepared in the same manner as the first emulsion. Then, the first emulsion and the second emulsion are mixed to prepare the main emulsion of the electrodeposition coating composition.

Further, a part of the polyester resin (a2), which should otherwise be introduced into the first emulsion, may be introduced into the second emulsion. As long as the intended effect of the present invention is not impaired in this way, the partial composition of each emulsion may be changed.

Here, the solubility parameter of the acrylic resin (a1), the polyester resin (a2), the epoxy resin (b) and the blocked polyisocyanate (c1) is represented by the formula

[0065]

## EQU4 ## (b)-{(a1) + (a2)} / 2 ≧ ± 1.0 I (a1)-(a2) ≦ ± 0.2 II {(a1) + (a2)} / 2 ≦ (C1) ≦ (b) III (c2) − (b) ≦ ± 0.5 IV [wherein (a1), (a2), (b), (c1), and (c2) are the respective resin components. The value of the solubility parameter is shown. ]

It is preferable to satisfy the relationship of The acrylic resin (a1) and the polyester resin (a2) form a stable core-shell structure, and the blocked polyisocyanate (c1) is evenly contained in the core and shell parts of the first emulsion and the epoxy resin (b). This is to separate the layers of the acrylic resin (a1) and the polyester resin (a2) and the epoxy resin (b) layer during thermosetting. The blocked polyisocyanate (c2) needs to be dissolved in the resin (b) in order to achieve the purpose of selectively curing the resin (b).

The mixing ratio of each resin component is a solid content weight ratio,
formula

[0068]

[Formula 5] {(a1) + (a2)} / (b) = 3/7 to 7/3 V (a2) / {(a1) + (a2)} = 1/9 to 1/2 VI [Expression Inside, (a1), (a2), and (b) show the solid content weight of each resin component. ]

It is preferable to satisfy the relationship of When the value of formula V is less than 3/7 or exceeds 7/3, it becomes difficult to form a two-layer separated structure, and a sea-island structure (microdomain structure) in which a large amount of components are continuous phases (sea) is formed. Will be formed. If the value of formula VI is less than 1/9, sufficient flowability during curing cannot be secured. On the other hand, if it exceeds 1/2, it becomes difficult to emulsify and disperse, and it cannot be introduced into a coating material.

In the first emulsion, the blocked polyisocyanate (c1) is blended in such a manner that the acrylic resin (a1), the polyester resin (a2) and, if necessary, the polyether resin (a3) are cured as a coating film. Therefore, the amount may be determined by a person skilled in the art by a usual method. Usually, the active hydrogen-containing group (for example, hydroxyl group) contained in these resins and the isocyanate group of the blocked polyisocyanate (c) are in an equivalent relationship.

Similarly, the blending amount of the blocked polyisocyanate (c2) in the second emulsion may be an amount determined by a person skilled in the art by a usual method in order to cure the epoxy resin (b) as a coating film.

When the polyether resin (a3) is used, its compounding ratio is the solid content weight ratio,

[0073]

## EQU6 ## (a3) / {(a1) + (a2) + (a3)} ≦ 0.1 VII [wherein (a1), (a2), and (a3) are the solid weights of the resin components. Indicates. ]

It is preferable that the amount satisfy the following condition. Formula VI
This is because if the value of I exceeds 0.1, the physical properties of the film may deteriorate.

Next, the obtained main emulsion and the pigment dispersion paste are blended. The mixing ratio of both is such that the pigment accounts for 1 to 35% by weight of the total solids of the electrodeposition coating composition. Furthermore, conventional curing catalysts, plasticizers, surfactants,
An antioxidant, an ultraviolet absorber and the like may be blended as necessary to obtain the intermediate coating / cationic electrodeposition coating composition used in the present invention.

Method for forming a coating film In the electrodeposition coating, a bath for electrodeposition is filled with the above-mentioned cationic electrodeposition coating composition which also serves as an intermediate coating, and a voltage of 50 to 450 V is usually applied between an object to be coated as a cathode and an anode. Is applied. If the applied voltage is less than 50V, the electrodeposition will be insufficient and 450
When it exceeds V, power consumption increases, which is uneconomical.

When the above voltage is applied, the temperature of the bath liquid filled with the electrodeposition coating composition is usually preferably 10 to 45 ° C.

The electrodeposition process includes (i) a step of immersing an article to be coated in the electrodeposition coating composition, and (ii) a cathode of the article to be coated,
A process of applying a voltage between the anode and the electrode to deposit a coating film. Further, the time for applying the voltage varies depending on the electrodeposition conditions, but it can be generally set to 2 to 4 minutes.

The electrodeposition coating film obtained as described above is dried as it is or after being washed with water after the completion of the electrodeposition process. Here, when a particularly good finished appearance is required, the electrodeposition coating film may be preheated before the baking step. The preheating is performed by heating the electrodeposition coating film at 80 to 120 ° C. for 1 to 10 minutes. Then, the electrodeposition coating film is baked to complete the coating. Baking is carried out by heating the electrodeposition coating film at 140 to 260 ° C., preferably 160 to 220 ° C. for 10 to 30 minutes.

FIG. 2 is a cross-sectional view schematically showing an aspect in which the structure of the coating film changes before and after the baking treatment. Figure 2 (i)
Is an electrodeposition coating film before baking treatment. The cationic electrodeposition coating composition that also serves as an intermediate coating used in the present invention is an article to be coated (conductive substrate).
3 is electrodeposited to form an electrodeposited coating (wet coating in uncured state) 4. The object to be coated is not particularly limited as long as it has conductivity, and examples thereof include an iron plate, a copper plate, an aluminum plate, a surface-treated product thereof, and a molded product thereof.

FIG. 2 (ii) shows the coating film after the electrodeposition coating film has been baked. During the baking treatment, the emulsion resin particles are dissolved by heating and the resin flows. Here, the solubility parameter of each resin is controlled, and the acrylic resin (a1) and the polyester resin (a
2) is compatible with each other, but these are not compatible with the epoxy resin (b), and the cationic epoxy resin layer 5 is provided on the article (conductive substrate) 3 and the anionic polyester is provided thereon. The resin and the cationic acrylic resin layer 6 are separated to form a two-layer separation electrodeposition film 7.

Thereafter, heating is continued to continue the two-layer separation electrodeposition film 7
Completely cure. The thickness of the two-layer separation electrodeposition film 7 is 10 to
The thickness is preferably 30 μm. If the film thickness is less than 10 μm, the corrosion resistance of the coating film becomes insufficient, and if it exceeds 30 μm, the paint is wasted.

The article to be electrodeposited by the method of the present invention has excellent surface smoothness of the coating film and does not require intermediate coating. Therefore, usually, a necessary topcoating or the like is further applied depending on the purpose. Topcoat coating, by applying a topcoat paint on the cured electrodeposition coating film, to form a topcoat coating film,
This top coating film is baked and cured.

The type of topcoat paint used is not particularly limited, but a specific example thereof is Japanese Patent Laid-Open No. 2001-311043.
Water-based paints described in JP-A No. 2001-311035 and the like; and JP-A No. 2001-316630.
And functional topcoats described in JP 2001-240791 A, and more specifically, environmentally friendly water-based paints marketed by Nippon Paint Co., Ltd. under the trade name of "AR-2000" are recommended.

The coating and baking of the topcoat paint may be carried out by a commonly used method. As an automobile coating method, an atomization coating method is generally used for a top coating. For example, when the topcoat is a metallic paint composed of base and clear, the coating amount of the base part is adjusted so that the film thickness of the topcoat base coat after baking is 10 to 17 μm, preferably 13 to 15 μm. When the film thickness is less than 10 μm, the weather resistance of the coating film becomes insufficient, and when it exceeds 17 μm, the paint is wasted. Also, the suitable film thickness of clear paint is 25-
The thickness is 40 μm, preferably 30 to 35 μm. Film thickness is 2
If it is less than 5 μm, the weather resistance and appearance of the coating film will be poor, and if it exceeds 40 μm, the coating material will be wasted. Baking of the overcoat coating is generally carried out by heating the coating at 100 to 180 ° C, preferably 120 to 160 ° C for 20 to 60 minutes.

[0086]

EFFECT OF THE INVENTION The coating film formed by the cationic electrodeposition coating composition for intermediate coating and the coating film forming method of the present invention has excellent corrosion resistance, solvent resistance, weather resistance, and chipping resistance, and adheres to the top coating film. It has excellent properties, and even a two-coat coating without intermediate coating has the same coating appearance as the three-coat coating.

[0087]

EXAMPLES The present invention will be described in more detail below with reference to production examples, examples and comparative examples. In each example, "part" means "part by weight" and "%" means "% by weight".

Production Example 1 ( Production of Acrylic Resin (a1)) 50 parts of methyl isobutyl ketone was charged into a reaction vessel equipped with a stirrer, a cooler, a nitrogen introducing tube, a thermometer and a dropping funnel, and 110 ° C. under a nitrogen atmosphere. It was kept heated. Furthermore, 18.6 parts of 2-hydroxypropyl acrylate, 34.2 parts of 2-ethylhexyl methacrylate, 30 parts of N, N-dimethylaminoethyl methacrylate, n-butyl acrylate 2.
A mixture of 2 parts, 15 parts of styrene and 4 parts of t-butyl peroctoate was added dropwise from the dropping funnel over 3 hours,
Thereafter, 0.5 part of t-butyl peroctoate was further added dropwise and the mixture was kept at 110 ° C. for 1.5 hours.

The solid content of the obtained cation-modified acrylic resin solution was 65%, and the number average molecular weight of the resin was 74.
00, hydroxyl number 80, amine number 107, and solubility parameter (SP) of 10.0.

Production Example 2 ( Production of Acrylic Resin (a1)) 50 parts of methyl isobutyl ketone was charged into a reaction vessel equipped with a stirrer, a cooler, a nitrogen introducing tube, a thermometer and a dropping funnel, and the temperature was 110 ° C. under a nitrogen atmosphere. It was kept heated. 2-hydroxypropyl acrylate 18.6 parts, 2-ethylhexyl methacrylate 22.1 parts, N, N-dimethylaminoethyl methacrylate 30 parts, n-butyl acrylate 9.
A mixture of 5 parts, 4.8 parts of methyl methacrylate, 15 parts of styrene and 4 parts of t-butyl peroctoate was added dropwise from the dropping funnel over 3 hours, and then 0.5 part of t-butyl peroctoate was further added. At 110 ° C.
Hold for 5 hours.

The resulting cation-modified acrylic resin solution had a solid content of 65%, and the resin had a number average molecular weight of 73.
00, hydroxyl number 80, amine number 107, and solubility parameter (SP) 10.2.

Production Example 3 ( Production of Acrylic Resin (a1)) In a reaction vessel equipped with a stirrer, a cooler, a nitrogen introducing pipe, a thermometer and a dropping funnel, 50 parts of methyl isobutyl ketone was charged and the temperature was 110 ° C. under a nitrogen atmosphere. It was kept heated. 2-hydroxypropyl methacrylate 20.6 parts, 2-ethylhexyl methacrylate 22.1 parts, N, N-dimethylaminoethyl methacrylate 20 parts, n-butyl acrylate 8.2 parts, lauryl methacrylate 12.3 parts, styrene 20 parts. And a mixture of 4 parts of t-butyl peroctoate were added dropwise from the dropping funnel over 3 hours, and then 0.5 part of t-butyl peroctoate was further added dropwise to form 110.
Hold at 1.5 ° C for 1.5 hours.

The resulting cation-modified acrylic resin solution had a solid content of 65%, and the resin had a number average content of 74%.
00, hydroxyl number 80, amine number 71, and solubility parameter (SP) was 9.8.

Production Example 4 ( Production of Acrylic Resin (a1)) 50 parts of methyl isobutyl ketone was charged into a reaction vessel equipped with a stirrer, a cooler, a nitrogen introducing tube, a thermometer and a dropping funnel, and 110 ° C. under a nitrogen atmosphere. It was kept heated. Further, 28.6 parts of 2-hydroxypropyl acrylate, 22.1 parts of 2-ethylhexyl methacrylate, 30 parts of N, N-dimethylaminoethyl methacrylate, n-butyl acrylate 9.
A mixture of 5 parts, 4.8 parts of methyl methacrylate, 15 parts of styrene and 4 parts of t-butyl peroctoate was added dropwise from the dropping funnel over 3 hours, and then 0.5 part of t-butyl peroctoate was further added. At 110 ° C.
Hold for 5 hours.

The resulting cation-modified acrylic resin solution had a solid content of 65%, and the resin had a number average molecular weight of 75.
00, hydroxyl number 80, amine number 107, and solubility parameter (SP) 10.3.

Production Example 5 ( Production of Acrylic Resin (a1)) 50 parts of methyl isobutyl ketone was charged into a reaction vessel equipped with a stirrer, a cooler, a nitrogen introducing tube, a thermometer and a dropping funnel, and 110 ° C. under a nitrogen atmosphere. It was kept heated. 2-hydroxypropyl methacrylate 20.6 parts, 2-ethylhexyl methacrylate 20.5 parts, N, N-dimethylaminoethyl methacrylate 20 parts, n-butyl acrylate 1.8 parts, lauryl methacrylate 17.2 parts, styrene 20 parts. And a mixture of 4 parts of t-butyl peroctoate are added dropwise from the dropping funnel over 3 hours, and then 0.5 part of t-butyl peroctoate is further added dropwise to form 110.
Hold at 1.5 ° C for 1.5 hours.

The resulting cation-modified acrylic resin solution had a solid content of 65%, and the resin had a number average molecular weight of 74.
00, hydroxyl number 80, amine number 71, and solubility parameter (SP) was 9.7.

Production Example 6 ( Production of polyester resin (a2)) Stirrer, cooler,
Into a reaction vessel equipped with a decanter, a nitrogen introduction tube, a thermometer and a dropping funnel, neopentyl glycol 21.6
Parts, trimethylolpropane 95.2 parts, phthalic anhydride 328.5 parts, isophthalic acid 157.8 parts, 2,2′-
26.2 parts of dimethylolbutanoic acid, 0.6 part of dibutyltin oxide as a reaction catalyst and 60 parts of xylene as a reflux solvent were charged, and the mixture was heated and maintained at 150 ° C. in a nitrogen atmosphere. Further, Curdular E-10 (manufactured by Shell Chemical Co., monoepoxide having a branched alkyl (C-10) group)
598.5 parts was dropped from the dropping funnel over 30 minutes,
Thereafter, the temperature was raised to 230 ° C. in 210 to carry out the dehydration condensation reaction for about 5 hours. Then, 240 parts of methyl isobutyl ketone was added as a diluting solvent.

The solid content of the obtained anionic polyester resin solution was 80%, and the number average molecular weight of the resin was 1
The acid number was 600, the acid number was 8, the hydroxyl number was 70, and the solubility parameter (SP) was 10.0.

Production Example 7 ( Production of Epoxy Resin (b)) A reaction vessel equipped with a stirrer, a decanter, a nitrogen introducing tube, a thermometer and a dropping funnel was charged with a bisphenol A type epoxy resin having an epoxy equivalent of 188 (trade name DER-331J). , Manufactured by Dow Chemical Company)
2400 parts, 141 parts of methanol, 168 parts of methyl isobutyl ketone, and 0.5 parts of dibutyltin dilaurate were charged and stirred at 40 ° C. to uniformly dissolve them, and then 2,4- /
When 320 parts of 2,6-tolylene diisocyanate (80/20 weight ratio mixture) was added dropwise over 30 minutes, heat was generated and the temperature rose to 70 ° C. To this, 5 parts of N, N-dimethylbenzylamine was added, the temperature in the system was raised to 120 ° C., and the reaction was continued at 120 ° C. for 3 hours until the epoxy equivalent reached 500 while distilling methanol off. Furthermore, 644 parts of methyl isobutyl ketone, bisphenol A341
Part, and 413 parts of 2-ethylhexanoic acid were added, the temperature in the system was maintained at 120 ° C., the reaction was carried out until the epoxy equivalent became 1070, and then the temperature in the system was cooled to 110 ° C.

Then, diethylenetriamine diketimine (methyl isobutyl ketone solution having a solid content of 73%) 241
And 192 parts of N-methylethanolamine were added and reacted at 110 ° C. for 1 hour to obtain a cation-modified epoxy resin solution (solid content 81%). This resin had a number average molecular weight of 2,100, an amine value of 50, a hydroxyl value of 160, and a resin softening point of 130 ° C. measured according to JIS-K-5665. From the measurement of infrared absorption spectrum and the like, it was confirmed that the resin had an oxazolidone ring (absorption wave number; 1750 cm ⁻¹ ). The solubility parameter (SP) was 11.4.

Production Example 8 ( Production of Blocked Polyisocyanate (c1)) A hexamethylene diisocyanate trimer 199 was placed in a reaction vessel equipped with a stirrer, a nitrogen introducing tube, a cooling tube and a thermometer.
Part, and after diluting with 39 parts of methyl isobutyl ketone, 0.2 part of butyltin laurate was added, and after heating to 50 ° C., 44 parts of methyl ketoxime and 87 parts of ethylene glycol mono-2-ethylhexyl ether were added. It was added so that the temperature did not exceed 70 ° C. Then, the mixture was kept at 70 ° C. for 1 hour until the absorption of the isocyanate residue was substantially disappeared by the infrared absorption spectrum, and then n-butanol 4 was added.
The desired blocked polyisocyanate having a solid content of 80% by dilution with 3 parts (solubility parameter SP = 1
0.7) was obtained.

Production Example 9 ( Production of Blocked Polyisocyanate (c2)) 222 parts of isophorone diisocyanate was placed in a reaction vessel equipped with a stirrer, nitrogen introducing tube, cooling tube and thermometer, and diluted with 56 parts of methyl isobutyl ketone. After adding 0.2 part of butyltin laurate and raising the temperature to 50 ° C., 17 parts of methyl ethyl ketoxime were added so that the content temperature did not exceed 70 ° C. 1 at 70 ° C until the absorption of the isocyanate residue is substantially extinguished according to the infrared absorption spectrum
The mixture was kept warm for a period of time and then diluted with 43 parts of n-butanol to obtain a desired blocked polyisocyanate having a solid content of 70% (solubility parameter (SP) 11.8).

Production Example 10 ( Production of Pigment Dispersion Resin) Stirrer, cooling pipe, nitrogen introducing pipe,
A reaction vessel equipped with a thermometer was charged with 710 parts of a bisphenol A type epoxy resin (trade name Epon 829, manufactured by Shell Chemical Co., Ltd.) having an epoxy equivalent of 198, and bisphenol A 289.6 parts, and at 150 to 160 ° C. for 1 hour under a nitrogen atmosphere. After reacting and then cooling to 120 ° C., a solution of 2-ethylhexanolated half-blocked tolylene diisocyanate in methyl isobutyl ketone (solid content 95%) 406.
4 parts were added. The reaction mixture was kept at 110 to 120 ° C. for 1 hour, and then 1584.1 parts of ethylene glycol mono n-butyl ether was added. And it cooled to 85-95 degreeC and it homogenized.

In parallel with the production of the above reaction product, 384 parts of a solution of 2-ethylhexanolated half-blocked tolylene diisocyanate in methyl isobutyl ketone (solid content: 95%) was added to 384 parts of dimethylethanolamine.
The mixture to which 4.6 parts was added was stirred at 80 ° C. for 1 hour, then 141.1 parts of 75% lactic acid water was charged, and further mixed with 47.0 parts of ethylene glycol mono-n-butyl ether, and mixed.
After stirring for 0 minute, a quaternizing agent (solid content: 85%) was manufactured. Then, 620.46 parts of this quaternizing agent was added to the above reaction product and the mixture was kept at 85 to 95 ° C. until an acid value of 1 was reached, and a pigment dispersion resin varnish (resin solid content 56%, average molecular weight 2200, solubility) The parameter (SP) 11.3) was obtained.

Production Example 11 ( Production of Pigment Dispersion Paste) Using a sand mill, a pigment paste (solid content 50%) containing the pigment dispersion resin obtained in Production Example 10 was prepared.

[0107]

[Table 1] Formulation part Pigment dispersion resin varnish of Production Example 53.6 Ion-exchanged water 46.4 Titanium dioxide 88.0 Carbon black 2.0 Aluminum phosphomolybdate 10.0

Production Example 12 ( Production of core-shell type first emulsion) 108.2 parts of the acrylic resin (a1) solution obtained in Production Example 1 and 37.5 polyester resin (a2) solution obtained in Production Example 6
Parts and 46 parts of the blocked polyisocyanate (c1) solution obtained in Production Example 8 were added and bonded for 30 minutes. Then, ethylene glycol mono-n-butyl ether 10
And 3 parts of acetic acid were added, and the mixture was diluted with ion-exchanged water to a nonvolatile content of 32%, and then concentrated under reduced pressure to a nonvolatile content of 36% to obtain an aqueous emulsion mainly containing a cation-modified acrylic resin.

Production Example 13 ( Production of Core-shell First Emulsion) The compounding amount of the acrylic resin (a1) solution obtained in Production Example 1 was 139.1.
Part of the polyester resin (a2) obtained in Production Example 6
Production Example 12 except that the amount of the solution blended was 12.5 parts
An aqueous emulsion was obtained in the same manner as in.

Production Example 14 ( Production of core-shell type first emulsion) The amount of the acrylic resin (a1) solution obtained in Production Example 1 was 77.3 parts, and the polyester resin (a2) obtained in Production Example 6 was used. An aqueous emulsion was obtained in the same manner as in Production Example 12 except that the amount of the solution was 62.5 parts.

Production Example 15 ( Production of Core-Shell Type First Emulsion) Production Example except that the acrylic resin (a1) solution obtained in Production Example 1 was used in place of the acrylic resin (a1) solution obtained in Production Example 1. An aqueous emulsion was obtained in the same manner as in Example 12.

Production Example 16 ( Production of Core-Shell Type First Emulsion) Production Example except that the acrylic resin (a1) solution obtained in Production Example 1 was replaced with the acrylic resin (a1) solution obtained in Production Example 3. An aqueous emulsion was obtained in the same manner as in Example 12.

Production Example 17 ( Production of Core-Shell First Emulsion) 69.5 parts of the acrylic resin (a1) solution obtained in Production Example 1, Production Example 6
62.5 parts of the polyester resin (a2) solution obtained in
Polyoxypropylene glycol (number average molecular weight 40
0, hydroxyl value 280, Sanyo Kasei “New Pole PP-
400 ") and 5 parts of the blocked polyisocyanate (c1) solution obtained in Production Example 8 were added and stirred for 30 minutes. Then, 10 parts of ethylene glycol mono-n-butyl ether and 3 parts of acetic acid were added, and the mixture was diluted with ion-exchanged water to a nonvolatile content of 32%, and then concentrated under a reduced pressure to a nonvolatile content of 36% to obtain an aqueous solution mainly containing a cation-modified acrylic resin. An emulsion was obtained.

Production Example 18 ( Production of First Emulsion for Comparative Example) The amount of the acrylic resin (a1) solution obtained in Production Example 1 was adjusted to 154.5 parts, and the polyester resin (a2 obtained in Production Example 6 was used. ) An aqueous emulsion was obtained in the same manner as in Production Example 12 except that the solution was not used.

Production Example 19 ( Production of First Emulsion for Comparative Example) The acrylic resin (a1) solution obtained in Production Example 4 was used in place of the acrylic resin (a1) solution obtained in Production Example 1. An aqueous emulsion was obtained in the same manner as in Production Example 12.

Production Example 20 ( Production of First Emulsion for Comparative Example) The acrylic resin (a1) solution obtained in Production Example 5 was used in place of the acrylic resin (a1) solution obtained in Production Example 1. An aqueous emulsion was obtained in the same manner as in Production Example 12.

Production Example 21 ( Production of Second Emulsion) 1834 parts of the blocked polyisocyanate curing agent (c2) produced in Production Example 9 and 9 parts of acetic acid were added to the epoxy resin (b) solution obtained in Production Example 7.
After adding 0 parts, the mixture was diluted with ion-exchanged water to a nonvolatile content of 32%, and then concentrated under reduced pressure to a nonvolatile content of 36% to obtain an aqueous emulsion mainly containing a cation-modified epoxy resin.

Example 1 Core-shell type first emulsion 2 obtained in Production Example 12
78 parts, the second emulsion 270 obtained in Production Example 21
Part, 127 parts of the pigment dispersion paste obtained in Production Example 11,
2.6 parts of dibutyltin oxide and 64 ion-exchanged water
0.9 parts were mixed to obtain a cationic electrodeposition coating composition. The solid content of this cationic electrodeposition coating composition was 20%, the solid content blending weight ratio of the acrylic resin (a1) and the polyester resin (a2) was 70/30, and the SP difference between the two was 0.

The obtained cationic electrodeposition coating composition was electrodeposited on a zinc phosphate treated cold-rolled steel sheet at a voltage such that the thickness of the electrodeposited coating film after baking was 20 μm, and the temperature was maintained at 160 ° C.
And baked for 15 minutes. Various performance evaluations described below were performed on the obtained cured coating film. The results are shown in Table 2.

Coating Viscosity A film melt viscosity (Pas) of the uncured coating film at 160 ° C. was measured by using a liquid meter manufactured by UBM.

Observation of coating film cross-section The coating film cross-section was visually observed with a video microscope. If the coating film was transparent, it was uniform and judged as “◯”. If it was opaque, it was non-uniform and judged as “x”. The main resin that constitutes each layer separated into multiple layers is FTIR-ATR.
Identified by analysis.

Attach the SWH1000H coated plate to the sunshine weatherometer , and
After irradiation for 00 hours, 60-degree gloss was measured to determine the retention rate (%) with respect to the initial value.

A cross cut reaching the substrate was put into the SDT coated plate with a knife. This coated plate was immersed in salt water (5% saline, 50 ° C.) for 840 hours, then washed with water and dried. An adhesive tape (“Cellophane tape” manufactured by Nichiban Co., Ltd.) was firmly attached with a finger along the cut portion on the surface of the coating film, and was peeled off in a 90 ° direction with respect to the coated surface. The maximum width (mm) of the peeled coating film was used as the evaluation value.

Solvent resistance : The coated surface of the coated plate is 10
I rubbed back and forth. The sample having no change on the surface of the coating film was evaluated as “◯”, and the sample having dissolution, discoloration, scratches and the like was evaluated as “x”.

2-Coat Finishing Property A water-based metallic base paint (“AR-2000 / 199B silver” manufactured by Nippon Paint Co., Ltd.) and a clear paint (“MAC-O-180 manufactured by Nippon Paint Co., Ltd.”) are formed on the cured electrodeposition coating film.
0 W ”) is spray-coated in wet-on-wet so that the dry film thickness becomes 13 μm / 30 μm,
A two-coat coating film was obtained by baking at 140 ° C. for 20 minutes. The surface smoothness of the resulting coating film was determined by BYK-Gardner in Germany.
It was measured using "Wavescan-T" manufactured by the company. W1
And W3 as evaluation values, W1 is 10 or less, and W3
Was evaluated as “◯” (good) when it was 15 or less, and as “x” (poor) in other cases.

Topcoat cross-cut adhesion A water-based metallic base paint (“AR-2000 / 199B silver” manufactured by Nippon Paint Co., Ltd.) and a clear paint (“MAC-O-180 manufactured by Nippon Paint Co., Ltd.”) on the cured electrodeposition coating film.
0 W ”) is spray-coated in wet-on-wet so that the dry film thickness becomes 13 μm / 30 μm,
A two-coat coating film was obtained by baking at 140 ° C. for 20 minutes. 2mm x 2mm by making a cut in the obtained coating film with a knife
I made 100 squares. An adhesive tape (“Cellophane tape” manufactured by Nichiban Co., Ltd.) was firmly attached to the cross-cut portion with a finger and peeled off in a 90 ° direction with respect to the coated surface. After peeling off the adhesive tape, the number of cross-cuts left on the coated surface was taken as the evaluation value.

Example 2 Core-shell type first emulsion 2 obtained in Production Example 13
78 parts, the second emulsion 270 obtained in Production Example 21
Part, 127 parts of the pigment dispersion paste obtained in Production Example 11,
2.6 parts of dibutyltin oxide and 64 ion-exchanged water
0.9 parts were mixed to obtain a cationic electrodeposition coating composition. This cationic electrodeposition coating composition had a solid content of 20%, a solid content blending weight ratio of the acrylic resin (a1) and the polyester resin (a2) was 90/10, and the SP difference between the two was 0. The obtained cationic electrodeposition coating composition was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 3 Core-shell type first emulsion 2 obtained in Production Example 14
78 parts, the second emulsion 270 obtained in Production Example 21
Part, 127 parts of the pigment dispersion paste obtained in Production Example 11,
2.6 parts of dibutyltin oxide and 64 ion-exchanged water
0.9 parts were mixed to obtain a cationic electrodeposition coating composition. The solid content of this cationic electrodeposition coating composition was 20%, the solid content blending weight ratio of the acrylic resin (a1) and the polyester resin (a2) was 50/50, and the SP difference between the two was 0. The obtained cationic electrodeposition coating composition was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 4 Core-shell type first emulsion 2 obtained in Production Example 15
78 parts, the second emulsion 270 obtained in Production Example 21
Part, 127 parts of the pigment dispersion paste obtained in Production Example 11,
2.6 parts of dibutyltin oxide and 64 ion-exchanged water
0.9 parts were mixed to obtain a cationic electrodeposition coating composition. The solid content of this cationic electrodeposition coating composition was 20%, the solid content blending weight ratio of the acrylic resin (a1) and the polyester resin (a2) was 70/30, and the SP difference between the two ((a1)
-(A2)) was 0.2. The obtained cationic electrodeposition coating composition was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 5 Core-shell type first emulsion 2 obtained in Production Example 16
78 parts, the second emulsion 270 obtained in Production Example 21
Part, 127 parts of the pigment dispersion paste obtained in Production Example 11,
2.6 parts of dibutyltin oxide and 64 ion-exchanged water
0.9 parts were mixed to obtain a cationic electrodeposition coating composition. The solid content of this cationic electrodeposition coating composition was 20%, the solid content blending weight ratio of the acrylic resin (a1) and the polyester resin (a2) was 70/30, and the SP difference between the two ((a1)
-(A2)) was -0.2. The obtained cationic electrodeposition coating composition was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Example 6 Core-shell type first emulsion 2 obtained in Production Example 17
78 parts, the second emulsion 270 obtained in Production Example 21
Part, 127 parts of the pigment dispersion paste obtained in Production Example 11,
2.6 parts of dibutyltin oxide and 64 ion-exchanged water
0.9 parts were mixed to obtain a cationic electrodeposition coating composition. The solid content of the cationic electrodeposition coating composition was 20%, and the solid content mixing ratio of the acrylic resin (a1), the polyester resin (a2) and the polyether resin (a3) was 45/50 /.
5, and the SP difference between the acrylic resin (a1) and the polyester resin (a2) was 0. The obtained cationic electrodeposition coating composition was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 1 278 parts of the first emulsion obtained in Production Example 18, 270 parts of the second emulsion obtained in Production Example 21, Production Example 1
The cationic electrodeposition coating composition was obtained by mixing 127 parts of the pigment dispersion paste obtained in 1 above, 2.6 parts of dibutyltin oxide, and 640.9 parts of ion-exchanged water. The solid content of this cationic electrodeposition coating composition was 20%. The obtained cationic electrodeposition coating composition was evaluated in the same manner as in Example 1. The results are shown in Table 3.

Comparative Example 2 278 parts of the first emulsion obtained in Production Example 19, 270 parts of the second emulsion obtained in Production Example 21, Production Example 1
The cationic electrodeposition coating composition was obtained by mixing 127 parts of the pigment dispersion paste obtained in 1 above, 2.6 parts of dibutyltin oxide, and 640.9 parts of ion-exchanged water. The cationic electrodeposition coating composition has a solid content of 20%, and the acrylic resin (a1) and the polyester resin (a2) have a solid content mixing ratio of 70.
/ 30, and the SP difference between them ((a1)-(a2)) was 0.3. The obtained cationic electrodeposition coating composition was evaluated in the same manner as in Example 1. The results are shown in Table 3.

Comparative Example 3 278 parts of the first emulsion obtained in Production Example 20, 270 parts of the second emulsion obtained in Production Example 21, Production Example 1
The cationic electrodeposition coating composition was obtained by mixing 127 parts of the pigment dispersion paste obtained in 1 above, 2.6 parts of dibutyltin oxide, and 640.9 parts of ion-exchanged water. The cationic electrodeposition coating composition has a solid content of 20%, and the acrylic resin (a1) and the polyester resin (a2) have a solid content mixing ratio of 70.
/ 30, and the SP difference between them ((a1)-(a2)) was -0.3. The obtained cationic electrodeposition coating composition was evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0135]

[Table 2]

[0136]

[Table 3]

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing the structure of first emulsion particles.

FIG. 2 is a cross-sectional view schematically showing an aspect in which the structure of a coating film changes before and after baking treatment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Shell part of core-shell type 1st emulsion, 2 ... Core part of core-shell type 1st emulsion, 3 ... Coating object (electroconductive base material), 4 ... Electrodeposition coating film (wet coating film in an uncured state), 5 ... Cationic epoxy resin layer 6 ... Layer of anionic polyester resin and cationic acrylic resin, 7 ... Two-layer separation electrodeposition film.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C09D 167/00 C09D 167/00 171/00 171/00 175/04 175/04 (72) Inventor Seiji Yokoi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Satoshi Kodama 1 Toyota Town, Toyota City, Aichi Toyota Motor Corporation F Term (reference) 4D075 AE03 BB28Z CA13 CA32 CA33 CA48 DA23 DB03 DC12 EA07 EA19 EB22 EB33 EB35 EB38 EB52 EB56 4J038 CG001 CP001 DD002 DF002 DG262 DG302 MA08 MA10 MA14 PA04

Claims (9)

[Claims] 1. A cationic acrylic resin (a) having a number average molecular weight of 2000 to 20000 dispersed in an aqueous medium.
1), at least containing an anionic polyester resin (a2) having a number average molecular weight of 1000 to 3000, a cation-modified epoxy resin (b), a blocked polyisocyanate (c1), a blocked polyisocyanate (c2), and a pigment (d). A cationic electrodeposition coating composition that also serves as an intermediate coating, comprising an acrylic resin (a1), a polyester resin (a2), and a blocked polyisocyanate (c1)
Is a shell part containing an acrylic resin (a1) and a blocked polyisocyanate (c1) and a polyester resin (a
2) and a core portion containing the blocked polyisocyanate (c1) to form an emulsion particle having a core-shell structure. Separately from this, the epoxy resin (b) and the blocked polyisocyanate (c2) are emulsion particles. An electrodeposition coating composition, characterized in that 2. The solubility parameter of the resin component is represented by the following formula: (b)-{(a1) + (a2)} / 2 ≧ ± 1.0 I (a1) − (a2) ≦ ± 0. 2 II {(a1) + (a2)} / 2 ≦ (c1) ≦ (b) III (c2) − (b) ≦ ± 0.5 IV [wherein (a1), (a2), (b) , (C1), and (c2) show the value of the solubility parameter of each resin component. ] The cationic electrodeposition coating composition for intermediate coating according to claim 1, which satisfies the relationship 3. The acrylic resin (a1), the polyester resin (a2) and the epoxy resin (b) are mixed in a solid content weight ratio of the following formula: ((a1) + (a2)} / (b ) = 3/7 to 7/3 V (a2) / {(a1) + (a2)} = 1/9 to 1/2 VI [wherein (a1), (a2), and (b) are each The solid content weight of the resin component is shown. ] The cationic electrodeposition coating composition for intermediate coating according to claim 1, which satisfies the relationship 4. The acrylic resin (a1) is mainly 2
The cationic electrodeposition coating composition for intermediate coating according to claim 1, which has a primary hydroxyl group and has a hydroxyl value of 50 to 150. 5. The cationic electrodeposition coating composition for intermediate coating according to claim 1, wherein the emulsion particles having a core-shell structure further contain a polyether resin (a3) having a number average molecular weight of 200 to 2000. 6. The compounding ratio of acrylic resin (a1), polyester resin (a2) and polyether resin (a3) is
In terms of solid content weight ratio, the formula: (a3) / {(a1) + (a2) + (a3)} ≦ 0.1 VII [wherein (a1), (a2), and (a3) are The solid content weight of each resin component is shown. ] The cationic electrodeposition coating composition which also serves as an intermediate coat according to claim 5, which satisfies the relationship of 7. A step of immersing an article to be coated in the cationic electrodeposition coating composition according to claim 1, wherein the surface of the article to be coated is subjected to electrodeposition coating using the article to be coated as a cathode. Forming an electrodeposition coating film; and baking the electrodeposition coating film;
A method for forming a coating film, which comprises: 8. The coating film forming method according to claim 7, further comprising a step of preheating the electrodeposition coating film before the step of baking the electrodeposition coating film. 9. A step of immersing an article to be coated in the cationic electrodeposition coating composition according to claim 1, wherein the surface of the article to be coated is subjected to electrodeposition coating using the article to be coated as a cathode. A step of forming an electrodeposition coating film; a step of baking the electrodeposition coating film; applying a top coating material on the cured electrodeposition coating film,
A method for forming a coating film, which comprises a step of forming an overcoat coating film; and a step of baking the above-mentioned top coating film.