JP2000281943A - High weatherability electrodeposition coating composition and coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide undercoats which have weatherability while retaining corrosion resistance similar to that of conventional ones and have a surface almost free from deterioration even without an intercoat and, in addition, is excellent in adhesion to a topcoat, and electrodeposition coating compositions capable of forming such undercoats. SOLUTION: An electrodeposition coating composition comprising a binder component and a pigment component dispersed in an aqueous medium containing a neutralizing agent, wherein the binder component is constituted by (a) 40-75 wt.% amino group-containing epoxy resin; (b) 10-30 wt.% amino group-containing acrylic resin; and (c) 15-30 wt.% aliphatic block polyisocyanate (provided that the sum of component (a) to component (c) is 100 wt.%), and the pigment component contains, as the major component, titanium oxide coated with zirconium and the amount of the entire pigment component as the coating PVC is 3.0-7.5%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly weather-resistant electrodeposition coating composition, and more particularly to an electrodeposition coating composition excellent in weather resistance and corrosion resistance and a coating method.

[0002]

BACKGROUND OF THE INVENTION Metal substrates, such as automobile bodies, are generally provided with a primer coat, mainly for rust prevention, on which a base color is concealed, the surface to be coated is smoothed, and a primer coat is formed. And a top coat to adhere to each other and to form a middle coat having a high ultraviolet shielding effect, and then a top coat for imparting color and gloss. In other words, usually when coating a metal substrate, the undercoating film having corrosion resistance and the topcoat film having weather resistance, and the intermediate coating film that adheres both of them are formed by overlapping to form a coated surface from corrosion. The purpose of the coating, which is to protect and maintain its aesthetics during use, is achieved.

However, in recent years, there has been a demand for simplification of the coating process in order to save resources and labor. In the field of coating metal substrates, the conventional undercoating, intermediate coating, and from the coating method of overcoating, omit the intermediate coating process,
There is a strong demand for a coating method that completes coating only in the undercoating step and the topcoating step.

[0004] On the other hand, if the formation of the intermediate coating film is simply omitted and the top coating film is formed directly on the undercoat coating film, there arises a problem that the adhesion between the undercoat coating film and the top coating film is reduced. The undercoat film generally has poor weather resistance, and its surface is easily deteriorated when irradiated with sunlight. Therefore, the interface between the undercoat film and the topcoat film is deteriorated in a short period of time, the adhesion between the two is lost, and there is a fear that the appearance may be abnormal and the topcoat film may fall off during use.

[0005] Therefore, the undercoat film which has the same corrosion resistance as the conventional one, has weather resistance on the other hand, does not easily degrade the surface even without intermediate coating, and has excellent adhesion to the top coat film. An undercoat paint capable of forming such an undercoat film is desired.

[0006] When undercoating a metal substrate, an electrodeposition coating method is widely used. As a paint used for the electrodeposition coating method, an electrodeposition paint containing a binder component and a pigment component dispersed in an aqueous medium containing a neutralizing agent is well known. The binder component is generally a resin component containing a cationic resin and a curing agent. In the electrodeposition coating method, a coating component is electrodeposited on the surface of a metal substrate to form a coating film of an electrodeposition coating composition. Thereafter, this coating film is heated to cure the binder component, and the undercoat coating film is obtained by solidifying the pigment component with a resin.

[0007] As the cationic resin used for the electrodeposition paint, an amine-modified epoxy resin, an amine-modified acrylic resin and the like are known. Among them, the amine-modified epoxy resin has excellent corrosion resistance, and the amine-modified acrylic resin has excellent weather resistance.

In general, the amine-modified epoxy resin and the amine-modified acrylic resin are used properly depending on the application, or when both corrosion resistance and weather resistance are required, both resins are blended and used. .

For example, JP-A-62-174277, JP-A-63-51470, and JP-A-2-330
No. 69, JP-A-2-160876 and the like, an amine-modified epoxy resin layer having excellent corrosion resistance is formed on the metal substrate side, and an amine-modified acrylic resin layer having excellent weather resistance is formed on the surface side. Describes an epoxy / acrylic blend-based binder component that separates into two layers.

However, even in an electrodeposition coating composition using such an epoxy / acrylic blend binder component, depending on the pigment used in combination with the binder component, the weather resistance of the surface of the undercoat film and the adhesion to the topcoat film are reduced. It is difficult to increase to a practically satisfactory level.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. It is an object of the present invention to maintain the corrosion resistance in the same manner as the conventional one, and on the other hand, have the weather resistance, It is an object of the present invention to provide an undercoat film in which the surface is not easily degraded even without the above and which has excellent adhesion to the overcoat film, and an electrodeposition coating composition capable of forming such an undercoat film.

[0012]

According to the present invention, there is provided an electrodeposition coating composition comprising a binder component and a pigment component dispersed in an aqueous medium containing a neutralizing agent, wherein the binder component comprises a) 40 to 75% by weight of an amino group-containing epoxy resin; b) 10 to 30% by weight of an amino group-containing acrylic resin; and c) 15 to 30% by weight of an aliphatic blocked polyisocyanate (components (a) to (c)). Is 100% by weight
It is. The present invention provides an electrodeposition coating composition wherein the pigment component contains titanium oxide coated with zirconium as a main component, and the total amount of the pigment component is 3.0 to 7.5% as a coating PVC. Thereby, the above object is achieved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Amino group-containing epoxy resin As the amino group-containing epoxy resin, an amine-modified epoxy resin well-known in the field of electrodeposition coatings can be used. In general,
These are produced by opening the epoxy group of an epoxy resin by reaction with a primary amine, secondary amine or tertiary amine salt.

The amino group-containing epoxy resin constituting the binder component needs to be dispersed in an aqueous medium containing a neutralizing agent. Therefore, they must not be water-soluble.
The molecular weight of the epoxy resin used for preparing the amino group-containing epoxy resin, the amount of the amino group introduced into the epoxy resin, and the like can be appropriately adjusted so as to have good dispersibility as a binder for an electrodeposition paint.

Typical epoxy resins used to prepare amino-containing epoxy resins include bisphenol A,
It is a polyphenol polyglycidyl ether type epoxy resin which is a reaction product of a polycyclic phenol compound such as bisphenol F, bisphenol S, phenol novolak, cresol novolak and epichlorohydrin.

The epoxy resin may be chain-extended using a bifunctional polyester polyol, polyether polyol, bisphenol, dibasic carboxylic acid or the like before reacting with the amine. Alternatively, before reacting with an amine, some epoxy groups may have 2-ethylhexanoic acid,
A monocarboxylic acid or a monohydroxy compound such as ethylhexanol, nonylphenol, ethylene glycol mono-2-ethylhexyl ether, propylene glycol mono-2-ethylhexyl ether is added to adjust the molecular weight or the amine equivalent to improve the heat flow property. May be improved.

The amine to be reacted with the epoxy resin is butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine,
Primary, secondary or tertiary amine salts such as diethanolamine, N-methylethanolamine, triethylamine, N, N-dimethylethanolamine.
Secondary amines containing ketimine-blocked primary amino groups, such as aminoethylethanolamine methyl isobutyl ketimine, are also often used. The amine is preferably reacted in approximately equivalent amounts to the epoxy groups.

The amino group-containing epoxy resin is contained in the electrodeposition coating composition in an amount occupying 40 to 75% by weight, preferably 50 to 60% by weight of the binder component. When the content of the amino group-containing epoxy resin exceeds 75% by weight, the weather resistance of the undercoat film decreases, and the adhesion to the overcoat film is impaired. When the content is less than 40% by weight, the corrosion resistance becomes abnormal. Becomes

Amino group-containing acrylic resin The amino group-containing acrylic resin is obtained by copolymerizing (i) an amino group-containing acrylic monomer, (ii) a hydroxyl group-containing acrylic monomer, and (iii) other ethylenically unsaturated monomers. Furthermore, instead of the amino group-containing acrylic monomer, an epoxy group-containing acrylic monomer is copolymerized with a hydroxyl group-containing acrylic monomer and other ethylenically unsaturated monomers, and the epoxy group of the obtained copolymer is obtained by ring opening with an amine. You can also.

Examples of the amino group-containing acrylic monomer (i) include N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate and the like.

Examples of the hydroxyl group-containing acrylic monomer (ii) include 2-hydroxyethyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate.
Alkylene such as hydroxypropyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, polypropylene glycol mono (meth) acrylate, 1,6-hexanediol mono (meth) acrylate Diol mono (meth) acrylates are preferred.

(Meth) acrylamides such as N-hydroxyethyl (meth) acrylamide and N-hydroxypropyl (meth) acrylamide are also preferable, and furthermore, the reaction of hydroxyalkyl mono (meth) acrylate with ε-caprolactone. The product or the reaction product of the hydroxyalkyl mono (meth) acrylate and the six-membered ring carbonate is also a hydroxyl group-containing acrylic monomer (i
It can be suitably used as i).

Other ethylenically unsaturated monomers (ii
Examples of i) are methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, cyclohexyl (meth) Examples include acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, styrene, vinyl toluene, α-methylstyrene, (meth) acrylonitrile, (meth) acrylamide, and vinyl acetate.

As another method for preparing an amino group-containing acrylic resin, an acrylic monomer having a hydroxyl group and other ethylenically unsaturated monomers are copolymerized with a monomer having an epoxy group such as glycidyl (meth) acrylate. After that, a secondary amine may be reacted with the epoxy group. Secondary amines that can be used for the reaction with the epoxy group include diethylamine, dibutylamine, dicyclohexylamine, morpholine, diethanolamine, N-methylethanolamine, and the like. Particularly, amines having a hydroxyl group and a secondary amino group in the molecule. Is preferred. Also, methyl isobutyl ketone diketimine of diethylenetriamine and methyl isobutyl ketone monoketimine of 2- (2-aminoethylamino) ethanol can be used.

The polymerization can be carried out by a conventional method such as a solution polymerization method. The number average molecular weight of the copolymer is 1000 to 5
The polymerization degree is controlled using a chain transfer agent such as dodecyl mercaptan or 2-ethylhexyl thioglycolate.

A half-blocked diisocyanate may be added to the amino group-containing acrylic polymer through a urethane bond to provide self-crosslinking properties. In that case, the diisocyanate is isophorone diisocyanate (IPDI), 4,
4'-methylenebis (cyclohexyl isocyanate)
(Hydrogenated MDI), norbornane diisocyanate (NB
It is preferred to use cycloaliphatic diisocyanates such as DI).

A known blocking agent can be used to block one of the isocyanate groups of the diisocyanate to form a half-blocked diisocyanate. Examples of the blocking agent include alcohols such as n-butanol, 2-ethylhexanol, ethylene glycol monobutyl ether and cyclohexanol; phenol, nitrophenol,
Phenols such as cresol and nonylphenol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime and methyl isobutyl ketoxime; lactams such as ε-caprolactam can be used.

The amino group-containing acrylic resin preferably has a lower SP value than the amino group-containing epoxy resin.
Specifically, the SP value of the amino group-containing acrylic resin is preferably about 0.1 to 2.0 lower than the SP value of the amino group-containing epoxy resin.

As described above, when an amino group-containing epoxy resin and an amino group-containing acrylic resin having an SP value lower than that of the amino group-containing epoxy resin are used in combination, the electrodeposition coating composition of the present invention can be used at the time of baking after electrodeposition. The group-containing epoxy resin migrates to the metal substrate side to form an anticorrosive layer, and the amino group-containing acrylic resin migrates to the coating film surface side to form a weather-resistant layer. As a result, a cured coating film having even more excellent anticorrosion properties and weather resistance can be provided without overcoating.

Generally, the SP value of a copolymer can be estimated by calculation based on the SP value of a homopolymer of constituent monomers and the weight fraction of each constituent monomer in a monomer mixture. If the SP value of the resin is known by actual measurement using a known method, the desired SP value can be obtained.
It is possible to design an amino group-containing acrylic copolymer having a certain value.

For example, the SP value can be measured by the following method [references: SUH, CLARKE,
J. P. S. A-1, 5, 1671-1681 (196
7)].

[0032]

[Table 1]

The SP value δ of the resin is given by the following equation.

[0034]

Δ = (V _ml ^1/2 δ _ml + V _mh ^1/2 δ _mh ) / (V _ml
^1/2 + V _mh ^1/2 ) V _m = V ₁ V ₂ / (φ ₁ V ₂ + φ ₂ V ₁ ) δ _m = φ ₁ δ ₁ + φ ₂ δ ₂

[0035] In the formula, V _i is the solvent of molecular volume (ml / mo
l), φ _i is the volume fraction of each solvent at the cloud point, δ _i is the SP value of the solvent, ml indicates a low SP poor solvent mixture, and mh indicates a high SP poor solvent mixture. . ]

The amino group-containing acrylic resin is 10 to 150
It preferably has an amine value of meq / g. Also,
It preferably has a hydroxyl value of 50 to 150 mgKOH / g. Constructing the monomer composition so that the amine value and the hydroxyl value fall within such ranges can be performed by a method well known to those skilled in the art.

The amino group-containing acrylic resin is contained in the electrodeposition coating composition in an amount occupying 10 to 30% by weight, preferably 15 to 25% by weight of the binder component. When the content of the amino group-containing acrylic resin is less than 10% by weight, the two-layer separation function is greatly reduced, and the expected weather resistance cannot be obtained. The rust prevention of the mold will be reduced.

The use of blocked polyisocyanates as curing agents for binder resins in the field of aliphatic blocked polyisocyanate thermosetting coatings is well known. In the present invention, it is preferable to use an aliphatic blocked polyisocyanate. Among them, HMDI, IPDI,
Hydrogenated MDI, NBDI, their dimers and trimers,
Alicyclic polyisocyanates such as adducts with aliphatic polyhydric alcohols such as trimethylolpropane and the like are more preferred. This is because the coating films obtained therefrom are excellent in corrosion resistance and non-yellowing.

The blocking agent may be any of the blocking agents described above for the half-blocked diisocyanates, but if low temperature curing (160 ° C.) is desired, lactams and oximes are preferred.

The aliphatic blocked polyisocyanate accounts for 15 to 30% by weight, preferably 18 to 25% by weight of the binder component.
It is contained in the electrodeposition coating composition in an amount occupying the weight%. When the content of the aliphatic blocked polyisocyanate is less than 15% by weight, the crosslink density is reduced and the physical properties of the coating film are significantly reduced. That is, the rust prevention of the coating film is reduced, and the coating film swells due to the solvent contained in the top coating when the top coating is applied. If it exceeds 30% by weight, the dry-wet circulation type rust-preventive properties such as those found in exposure and the like will be reduced.

Second Acrylic Resin The electrodeposition coating composition of the present invention preferably further contains an acrylic resin in the binder component. This acrylic resin does not necessarily have to have an amino group,
And a copolymer having the same properties as the amino group-containing acrylic resin except that the SP value is lower than that of the amino group-containing acrylic resin (hereinafter, “second acrylic resin”).
That. ). Specifically, the SP value of the second acrylic resin is 0.5 to 2.
It is preferably about 0 lower.

As described above, the amino group-containing epoxy resin, the amino group-containing acrylic resin having a lower SP value than the amino group-containing epoxy resin, and the second acrylic resin having a lower SP value than the amino group-containing acrylic resin are used in combination. Thus, the electrodeposition coating composition of the present invention, when baking after electrodeposition, the amino group-containing epoxy resin migrates to the metal substrate side to form a corrosion-resistant layer, on which the amino group-containing acrylic resin has weather resistance It is considered that an intermediate layer having excellent adhesion is formed, and the second acrylic resin migrates to the coating film surface side to form a weather-resistant layer.

In the electrodeposition coating composition of the present invention, the amino group-containing epoxy resin and the amino group-containing acrylic resin having an intermediate SP value between the second acrylic resin and the amino group-containing epoxy resin are present. The dispersion stability mainly depends on the SP value difference between the relatively small difference between the amino group-containing acrylic resin and the second acrylic resin, and the relatively large difference between the amino group-containing epoxy resin and the second acrylic resin. It does not directly depend on the SP value difference with the resin. As a result, a sufficient amount of the second acrylic resin can be blended to achieve weather resistance without adversely affecting the dispersion stability of the main emulsion.

Further, the concentration gradient of the second acrylic resin having the lowest SP value becomes highest near the coating film surface, thereby contributing to the improvement of weather resistance and at the same time exerting the effect of suppressing appearance abnormality such as cissing and dents. It is thought that. As a result, the electrodeposition coating composition of the present invention provides an excellent cured coating film which does not cause poor adhesion to the top coating film due to weather deterioration of the undercoat film even without intermediate coating.

The second acrylic resin is generally prepared by using a hydroxyl group-containing acrylic monomer and other ethylenically unsaturated monomers as essential monomers and, when containing an amino group, copolymerizing the amino group-containing acrylic monomer. ,
Alternatively, an amino group is introduced by reacting an epoxy group-containing acrylic monomer with an amine after copolymerization.

However, since the second acrylic resin must have a lower SP value than the amino group-containing acrylic resin component, the monomer composition is t-butyl (meth)
Acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, etc., have relatively low homopolymer SP monomers, or conversely reduce the proportion of high SP monomers. It is necessary to design in a desired SP value range.

The second acrylic resin can be used by adding a half-block diisocyanate, similarly to the amino group-containing acrylic resin.

Since it is intended that the concentration gradient of the second acrylic resin is maximized near the surface of the coating film, it is desirable that appearance defects such as repelling and dents hardly occur. Therefore, it is effective to use an acrylic monomer having an ether moiety as a part of another ethylenically unsaturated monomer used at the time of polymerization.

An example of such an acrylic monomer is 2-
Methoxyethyl (meth) acrylate, 4-methoxybutyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2-propoxyethyl (meth) acrylate, 4-2-ethylhexyloxy) Butyl (meth) acrylate, furfuryl (meth) acrylate and the like.

In a preferred embodiment of the present invention further comprising a second acrylic resin, the binder component of the electrodeposition coating composition comprises (a) 40 to 75% by weight, preferably 50 to 70% by weight, of an amino group-containing epoxy resin; (B) 10-30% by weight, preferably 15-25% by weight of an amino group-containing acrylic resin having a lower SP value than the amino group-containing epoxy resin.
(C) aliphatic blocked polyisocyanate 15
(D) a second acrylic resin having an SP value lower than that of the amino group-containing acrylic resin, 1 to 10% by weight, preferably 1 to 5% by weight; (The total of components (a) to (d) is 10
0% by weight. ).

When the amount of the second acrylic resin in the binder component is less than 1% by weight, the dispersion stability of the main emulsion decreases, and the surface condition of the coating film also decreases.
Even if it exceeds 10% by weight, the dispersion stability of the main emulsion will be reduced.

Pigment The electrodeposition coating composition of the present invention contains various black pigments and white pigments. In the present invention, zirconium-coated titanium dioxide is used as the white pigment. This is because such titanium dioxide has a property of capturing radicals generated by light irradiation, preventing deterioration of a resin containing the same, and as a result, increasing the weather resistance of the coating film.

With titanium dioxide coated with zirconium
For example, it is described in JP-B-59-37305.
Weight of this substrate on the surface of the titanium dioxide substrate particles, such as
SnO based on quantity_TwoOxidation of tin from 0.1 to 3% by weight
And ZrO_Two0.1-5% of zirconium water
Inner coating with hydrated oxide and Al based on the weight of the substrate
_TwoO_Three0.3 to 8% of aluminum hydrated oxide
Having an external coating of the same can be used.

The white pigments may be used as a mixture of two or more kinds. Examples of white pigments that can be used are titanium dioxide, barium sulfate and the like. Precipitable barium sulfate is also preferred as a white pigment. A preferred combination for use in combination is a combination of zirconium-coated titanium dioxide and precipitated barium sulfate.

When a gray coating film is formed, a black pigment and a white pigment are mixed and used in an appropriate amount. Examples of the black pigment include carbon black, black iron oxide, copper chrome black, copper iron manganese black, and the like.

The preferred black pigment is carbon black. This is because they have excellent hiding power and coloring power. Carbon black having an average particle diameter of 30 nm or less, particularly 25 nm or less, is preferred. The particle size of the carbon black used is 30 n
If it exceeds m, the desired ultraviolet absorbing ability will not be exhibited, and the weather resistance will decrease.

The amount of the pigment used was 3.0 as a paint PVC.
-7.5%, particularly preferably 3.0-5.0%. When the amount of the pigment is less than 3.0% of PVC, the concealing property and color density of the obtained coating film are reduced, and when the amount of the pigment is more than 7.5% of PVC, the weather resistance of the obtained coating film is reduced. In addition, PVC
The term “volume ratio” of the pigment in the coating film is used.

Neutralizing agent The neutralizing agent used here is hydrochloric acid, nitric acid, phosphoric acid, formic acid,
Inorganic or organic acids such as acetic acid, hydroxyacetic acid, sulfamic acid, lactic acid. The amount of the neutralizing agent may be an amount that achieves a neutralization ratio of at least 20%, preferably 30 to 60%.

Aqueous Medium The aqueous medium may be water or various organic solvents. Examples of solvents suitable for use in the present invention include hydrocarbons (eg, xylene or toluene), alcohols (eg, methyl alcohol, n-butyl alcohol, isopropyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, propylene) Glycol), ethers (eg, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monoethyl ether, 3-methyl-3-
Methoxybutanol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether), ketones (eg, methyl isobutyl ketone, cyclohexanone, isophorone, acetylacetone), esters (eg, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate), and the like And mixtures thereof.
The amount of these solvents used is about 0.01 to
It is 25% by weight, preferably 0.05 to 15% by weight.

In the case of producing an aqueous coating composition containing a binder component and a pigment component dispersed in an aqueous medium, such as a pigment dispersion paste electrodeposition coating composition, a pigment as a powder is dispersed in the aqueous medium. When the pigment component is directly mixed with the binder component, the pigment is generally not hydrophobic and thus is not uniformly dispersed in an aqueous medium. Therefore, usually, a pigment is uniformly dispersed at a high concentration in an aqueous medium to prepare a pigment dispersion paste, and this is diluted with a binder component dispersed in an aqueous medium to obtain an aqueous coating composition. .

In the electrodeposition coating composition of the present invention, a pigment-dispersed paste is prepared in advance in order to mix a binder component and a pigment component dispersed in an aqueous medium. The pigment dispersion paste contains a pigment, a pigment dispersant, and an aqueous medium.

The pigment dispersion paste is prepared by mixing the pigment, the pigment dispersant and the aqueous medium. In general,
The pigment dispersion paste is prepared to have a solid content of 40 to 70% by weight, preferably 50 to 65% by weight. 5% pigment in solids
0-90% by weight, preferably 65-85% by weight,
The pigment dispersant is 10 to 50% by weight, preferably 15 to 35%.
Accounts for% by weight.

Electrodeposition coating composition In general, an electrodeposition coating composition is prepared by first dispersing a binder component in an aqueous medium containing a neutralizing agent to form a main emulsion, adding a pigment dispersion paste thereto, and mixing. Is done. In the present invention, since an amino group-containing epoxy resin, an amino group-containing acrylic resin, and, if necessary, a second acrylic resin are used as the binder resin, there are several methods for blending these. Specifically, it is preferable to prepare the main emulsion by the method described in Japanese Patent Application No. 9-114242, paragraphs 0036 to 0037.

The amount of the pigment-dispersed paste to be added can be appropriately adjusted depending on the amount of the pigment contained in the whole paint. Generally, the pigment component is added in an amount of 10 to 35 parts by weight, preferably 10 to 20 parts by weight, based on 100 parts by weight of the binder component contained in the main emulsion.

The electrodeposition coating composition contains tin compounds such as dibutyltin dilaurate and dibutyltin oxide;
A conventional urethane cleavage catalyst can be included. The amount is usually 0.1 to 10% by weight of the aliphatic blocked polyisocyanate.

The electrodeposition paint may contain conventional paint additives such as a water-miscible organic solvent, a surfactant, an antioxidant and an ultraviolet absorber.

The electrodeposition coating composition of the present invention contains substantially no lead-based rust preventive pigment. "Substantially free of lead-based rust-preventive pigments" means that lead-based pigments are not used at all, or even if used, lead in diluted paint (the state of a cationic electrodeposition paint composition when added to an electrodeposition bath). It means that the ion concentration is 800 ppm or less, preferably 500 ppm or less. If the lead ion concentration is high, it is not only harmful to the environment but also the smoothness may be reduced.

Coating Method Using the electrodeposition coating composition of the present invention, a metal substrate can be undercoated by a usual electrodeposition coating method. The middle coat and the top coat may be applied on the formed undercoat film in the same manner as before, but the middle coat may be omitted. This is because the undercoat film formed from the electrodeposition coating composition of the present invention has weather resistance, the surface does not easily deteriorate even without intermediate coating, and has excellent adhesion to the overcoat film.

As the intermediate coating and the top coating, those usually used for the middle coating and the top coating of the electrodeposition coating film may be used.

In forming the overcoat film, it may be finished in one coat using a solid paint, or may be finished in two coats using a colored base paint and a clear paint.
When finishing with two coats, it is preferable to adopt a method in which each paint is coated on the undercoating film by wet-on-wet, and then both are baked and cured.

When a solid paint is used as the top coat and the surface to be coated is finished with one coat, (1) a film of the electrodeposition coating composition of the present invention is applied to the surface to be coated of the metal substrate by an electrodeposition coating method. (2) a step of baking and curing the coating film of the electrodeposition coating composition; (3) a step of forming a coating film of a solid coating thereon; and (4) a baking and curing of the coating film of the solid coating composition. The coating is preferably performed by a method including the following steps:

When a metallic base paint and a clear paint are used as the top coat and the coated surface is finished with two coats, (1) the electrodeposited paint composition of the present invention is applied to the coated surface of the metal substrate by the electrodeposition coating method. (2) a step of baking and curing a coating film of the electrodeposition coating composition; (3) a step of forming a metallic base coating film thereon; (4) a clear coat thereon The coating is preferably carried out by a method comprising the steps of: forming a paint film; and (5) baking and curing the paint film of the metallic base paint and the clear paint.

[0073]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Production Examples 1 to 9 Production Examples 1 to 9 explain the preparation of the pigment dispersion paste.

Production Example 1 34.1 parts of an epoxy tertiary onium salt type pigment-dispersed resin (solid content: 30%) produced by the method described in Production Example 4 of Japanese Patent Application No. 10-317883, zirconium-coated titanium dioxide ( Pigment dispersion paste obtained by dispersing a mixture of 47.8 parts of CR-97 (manufactured by Ishihara Sangyo Co., Ltd.), 1.0 part of basic lead silicate, and 18.1 parts of ion-exchanged water with a sand grind mill and pulverizing the mixture to a particle size of 10 μm or less. (Solid content 59%) was prepared.

Production Example 2 Epoxy tertiary onium salt type pigment dispersion resin (solid content 30
%, The same as in Production Example 1) 34.1 parts, zirconium-coated titanium dioxide (CR-97, manufactured by Ishihara Sangyo Co., Ltd.) 47.0 parts
Part, carbon black (M # 260 manufactured by Mitsubishi Chemical Corporation)
0, average particle diameter 13 nm) 0.8 part, basic lead silicate
A mixture of 0 parts and 17.1 parts of ion-exchanged water was dispersed by a sand grind mill to prepare a pigment dispersion paste (solid content: 59%) pulverized to a particle size of 10 μm or less.

Production Example 3 Epoxy tertiary onium salt type pigment dispersion resin (solid content 30
%, The same as in Production Example 1) 34.1 parts, zirconium-coated titanium dioxide (CR-97, manufactured by Ishihara Sangyo Co., Ltd.) 23.5
Part, carbon black (M # 260 manufactured by Mitsubishi Chemical Corporation)
0) 0.8 part, basic lead silicate 1.0 part, barium sulfate (precipitable barium sulfate B-30, Sakai Chemical Co., Ltd.) 23.5
And a mixture of 17.1 parts of ion-exchanged water were dispersed in a sand grind mill to prepare a pigment dispersion paste (solid content: 59%) pulverized to a particle size of 10 μm or less.

Production Example 4 "MA # 10" manufactured by Mitsubishi Chemical Corporation as carbon black
A pigment-dispersed paste was prepared in the same manner as in Production Example 3 except that "0" (average particle size: 22 nm) was used.

Production Example 5 "MA # 10" manufactured by Mitsubishi Chemical Corporation as carbon black
A pigment-dispersed paste was prepared in the same manner as in Production Example 2 except that "0" (average particle size: 22 nm) was used.

Production Example 6 Instead of zirconium-coated titanium dioxide, ordinary Al _{2 was used.}
O ₃ coated titanium dioxide (CR-50 manufactured by Ishihara Sangyo Co., Ltd.)
A pigment dispersion paste was prepared in the same manner as in Production Example 5 except for using.

Production Example 7 Instead of zirconium-coated titanium dioxide, ordinary Al _{2 was used.}
O ₃ coated titanium dioxide (CR-50 manufactured by Ishihara Sangyo Co., Ltd.)
A pigment dispersion paste was prepared in the same manner as in Production Example 1 except that the above was used.

Production Example 8 A pigment-dispersed paste was prepared in the same manner as in Production Example 6, except that "Raben 410" (average particle size: 70 nm) manufactured by Columbia Carbon Co., Ltd. was used as carbon black.

[0083]

[Table 2]

Production Example 9 Preparation of Aliphatic Blocked Polyisocyanate (c) 222 parts of isophorone diisocyanate was placed in a reaction vessel equipped with a stirrer, a thermometer, a cooling tube and a nitrogen inlet tube, and 56 parts of methyl isobutyl ketone was added to dilute the mixture. After that, 0.2 parts of dibutyltin dilaurate was added. Thereafter, the temperature was raised to 50 ° C., and 174 parts of methyl ethyl ketoxime were added so that the resin temperature did not exceed 70 ° C. The mixture was kept at 70 ° C. for 1 hour until the absorption of isocyanate groups substantially disappeared by an infrared absorption spectrum, and then diluted with 43 parts of n-butanol.

Preparation Example 10 Preparation of Main Emulsion Containing Amino Group-Containing Epoxy Resin (a) and Aliphatic Blocked Polyisocyanate (c) Epoxy equivalent in a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a cooling tube and a thermometer. Is 950, a bisphenol A type epoxy resin (Epototo YD-014 manufactured by Toto Kasei) 9
50 parts were added, and the mixture was heated to 100 ° C. and completely dissolved with 237.5 parts of methyl isobutyl ketone. Then, N-
60 parts of methylethanolamine and 73 parts of a 73% solution of diethylenetriamine in methyl isobutyl ketimine in methyl isobutyl ketone were added.

The mixture was kept at 120 ° C. for 1 hour,
A solution of an amino group-containing epoxy resin having a P value of 11.4 was obtained.

To 1320 parts of this solution, 330 parts of the blocked polyisocyanate of Production Example 9 and 150 parts of ethylene glycol monohexyl ether were mixed, and 34 parts of glacial acetic acid were added.
After adding to a mixed solution of 479 parts of ion-exchanged water and sufficiently stirring, 2215 parts of ion-exchanged water was slowly added. Then, the organic solvent and water were removed under reduced pressure until the solid content became 36% to obtain a main emulsion containing an amino group-containing epoxy resin and an aliphatic blocked polyisocyanate.

Production Example 11 Preparation of Second Acrylic Resin (d) 1500 parts of methyl isobutyl ketone was charged into a reaction vessel equipped with a stirrer, thermometer, decanter, reflux condenser, nitrogen inlet tube and dropping funnel. 120 while introducing
C., 627 parts of methyl methacrylate, 191 parts of lauryl methacrylate, 182 parts of 4-hydroxybutyl acrylate, 300 parts of 2-methoxyethyl acrylate
Part of a mixture of 200 parts of butyl methacrylate and 50 parts of t-butylperoxy-2-ethylhexanoate.
It was dropped at a constant speed over time. 3 hours after dropping, 12 more
After the reaction at 0 ° C., the mixture was cooled, and the SP value was 9.7, the number average molecular weight (M
n) A solution of 10,000 second acrylic resin was obtained. The solids content of this solution was 50%.

Preparation Example 12 Preparation of Main Emulsion Containing Amino Group-Containing Epoxy Resin (a), Amino Group-Containing Acrylic Resin (b) and Aliphatic Block Polyisocyanate (c) Reflux cooler, stirrer, dropping funnel and nitrogen In a five-necked flask equipped with an inlet tube, add methyl isobutyl ketone 56.
Three parts were charged and heated and maintained at 115 ° C. in a nitrogen atmosphere.
To this, glycidyl methacrylate 16.0 parts, 2-hydroxyethyl methacrylate 4.2 parts, 2-hydroxypropyl methacrylate 14.8 parts, n-butyl methacrylate 58.1 parts, t-butyl methacrylate 6.
A mixture of 9 parts and 4.0 parts of t-butyl peroctoate was dropped from the dropping funnel over 3 hours. After the completion of the dropwise addition, the mixture was kept at 115 ° C. for about 1 hour, then 0.5 part of t-butyl peroctoate was added dropwise, and the mixture was kept at 115 ° C. for about 30 minutes to obtain an acrylic resin solution having a solid content of 65%. The SP value of this resin was 10.3, and the number average molecular weight (Mn) was 6000.

After cooling, 8.5 parts of N-methylethanolamine was added thereto and reacted at 120 ° C. for 2 hours under a nitrogen atmosphere to obtain a solution of an amino group-containing acrylic resin having a solid content of about 67%. The SP value of this resin was 11.2.

Next, this solution was kept at 60 ° C.
After adding and mixing 27.1 parts of the aliphatic block polyisocyanate obtained in the above, the mixture was kept at 50 ° C. for 30 minutes under a nitrogen atmosphere, 2.6 parts of acetic acid was added, and ion-exchanged water was gradually added with sufficient stirring. An emulsion containing an amino group-containing acrylic resin and an aliphatic blocked polyisocyanate was obtained. The solids content of the emulsion was 36%.

To 340 parts of the obtained emulsion, 660 parts of the emulsion containing the amino group-containing epoxy resin and the aliphatic block polyisocyanate obtained in Production Example 10 were added, and the amino group-containing epoxy resin and the amino group-containing acrylic resin were added. A main emulsion containing an aliphatic blocked polyisocyanate was prepared.

Preparation Example 13 Preparation of Main Emulsion Containing Amino Group-Containing Epoxy Resin (a), Amino Group-Containing Acrylic Resin (b), Aliphatic Block Polyisocyanate (c), and Second Acrylic Resin (d) Preparation Example 12 The same flask was charged with 56.3 parts of methyl isobutyl ketone, and heated and maintained at 115 ° C. under a nitrogen atmosphere. To this, 16.0 parts of glycidyl methacrylate,
4.2 parts of 2-hydroxyethyl methacrylate, 14.8 parts of 2-hydroxypropyl methacrylate, 58.1 parts of n-butyl methacrylate, 6.9 parts of t-butyl methacrylate, and 4.0 parts of t-butyl peroctoate
Part of the mixture was dropped from the dropping funnel over 3 hours. After the completion of the dropwise addition, the mixture was kept at 115 ° C. for about 1 hour, then 0.5 part of t-butyl peroctoate was added dropwise, and the mixture was kept at 115 ° C. for about 30 minutes to obtain an acrylic resin solution having a solid content of 65%. The SP value of this resin was 10.3, and the number average molecular weight (M
n) was 6000.

After cooling, 8.5 parts of N-methylethanolamine was added thereto and reacted at 120 ° C. for 2 hours in a nitrogen atmosphere to obtain a solution of an amino group-containing acrylic resin having a solid content of about 67%. The SP value of this resin was 11.2.

This solution was kept at 60 ° C., and 27.1 parts of the blocked polyisocyanate obtained in Production Example 9 and 47.5 parts of the second acrylic resin (d) obtained in Production Example 11 were added and mixed. The mixture was kept at 50 ° C. for 30 minutes in a nitrogen atmosphere, and 2.6 parts of acetic acid was added. While sufficiently stirring, ion-exchanged water was gradually added, and the mixture contained an amino group-containing acrylic resin, an aliphatic block polyisocyanate, and a second acrylic resin. I got an emulsion. The solids content of the emulsion was 36%.

To 340 parts of the obtained emulsion, 660 parts of the emulsion containing the amino group-containing epoxy resin and the aliphatic blocked polyisocyanate obtained in Production Example 10 were added, and the amino group-containing epoxy resin and the amino group-containing acrylic resin were added. A main emulsion containing an aliphatic blocked polyisocyanate and a second acrylic resin was obtained.

Examples 1 to 6 and Comparative Examples 1 to 5 In accordance with the coating components shown in Table 3, the PVC described in the table was used.
So that the pigment dispersion paste obtained in Production Examples 1 to 9 and the main emulsion obtained in Production Examples 13, 14 and 11 are mixed, and ion-exchanged water is added to the obtained mixture to obtain a solid content. The content was 20% to obtain an electrodeposition coating composition.

[0098]

[Table 3]

Using these electrodeposition coating compositions, a zinc phosphate treated steel sheet was subjected to electrodeposition coating, and baked at 170 ° C. (coating) for 20 minutes. The film thickness after baking is 20
μm.

The repellency and weather resistance of the obtained electrodeposition coating film were evaluated as follows. The results are shown in Tables 4 to 6.

[0102] resistance is at repellency were visually counted dent number in the coated plates both surfaces of the 7 × 15cm.

Evaluation criteria A: 0 B: 2 B: 5 B: 6 or more

Weather Resistance (SWM Test) The electrodeposited steel sheet was attached to a sunshine weatherometer and irradiated for 200 hours. Thereafter, the 60 ° gloss of the surface of the electrodeposited coating film was measured, and the gloss retention relative to the initial 60 ° gloss was determined.

Evaluation criteria A: 70% or more B: 69 to 60% C: 59 to 50% X: 49% or less

Adhesion over time (SWM cycle test) A zinc phosphate treated steel sheet was newly subjected to electrodeposition coating.
Next, a metallic base paint (Superlac M-180 # 06 silver manufactured by Nippon Paint Co., Ltd.) was applied on the obtained electrodeposition coating film in an amount to give a dry film thickness of 8 μm, dried at room temperature for 5 minutes, and then placed thereon. A clear paint (Nippon Paint Super Lac O-80 Clear) was applied in an amount to give a dry film thickness of 30 μm, and dried at room temperature for 10 minutes. Next, the coated steel sheet is placed in an oven and heated at 140 ° C. (painted plate temperature) for 2 hours.
The coating of the metallic base paint and the clear paint was cured by heating for 0 minutes.

The adhesion with time of the metallic two-coat film to the electrodeposited film was evaluated by the following method. The results are shown in Tables 4 to 6.

A metallic two-coat coated steel sheet was attached to a sunshine weatherometer and irradiated for 300 hours.
Next, the coated plate was placed in an environment of 95% humidity and 50 ° C for 20 minutes.
Left for hours. This irradiation and standing process was defined as one cycle, and was repeated up to five consecutive cycles.

After that, the coating film was measured with a knife to a size of 2 mm × 2 m.
m cross cut to form 100 Goban eyes,
Adhesive tape on the surface (Nichiban “Cellotape”)
Was affixed with a finger and peeled off sharply in a direction perpendicular to the surface.
The adhesion of the coating film was evaluated based on the ratio of the peeled area within the square.

Evaluation criteria ◎: No peeling ○: Linear peeling of cut portion △: Less than 25% of total peeling area ×: 25% or more of total peeling area

[0110] Thereafter, the irradiation and standing steps were further repeated 5 times (total 10 cycles), and the adhesion of the coating film was similarly evaluated.

[0111]

[Table 4]

[0112]

[Table 5]

[0113]

[Table 6]

[0114]

According to the present invention, the undercoat film has the same corrosion resistance as the conventional one, but has weather resistance on the other hand, does not easily degrade the surface without intermediate coating, and has excellent adhesion to the overcoat film. And an electrodeposition coating composition capable of forming such an undercoat film.

──────────────────────────────────────────────────の Continued on the front page (51) Int. Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 5/00 C09D 5/00 D 17/00 17/00 175/04 175/04 (72) Inventor Shirakawa Shinsuke 19-17 Ikedanakamachi, Neyagawa-shi, Osaka Nippon Paint Co., Ltd. (72) Ryoichi Murakami 19-17 Ikedanakamachi, Neyagawa-shi, Osaka Japan F-term (reference) 4D075 BB26Z BB89Y CA13 CA32 CA33 DA06 DB02 DC12 EA43 EB22 EB33 EB38 EC02 EC13 4J037 AA09 AA22 CA09 EE03 4J038 DG161 DG192 DG301 DG302 HA096 HA216 HA336 HA376 HA416 JA37 JC09 KA08 KA15 KA16 KA18 MA08 MA10 NA03 NA12 PA04 PA14 PA19

Claims (7)

[Claims] An electrodeposition coating composition comprising a binder component and a pigment component dispersed in an aqueous medium containing a neutralizing agent, wherein the binder component comprises: a) an amino group-containing epoxy resin 40 to 75. B) 10 to 30% by weight of an amino group-containing acrylic resin; and c) 15 to 30% by weight of an aliphatic blocked polyisocyanate (the total of components (a) to (c) is 100% by weight).
It is. An electrodeposition coating composition wherein the pigment component contains titanium oxide coated with zirconium as a main component, and the total amount of the pigment component is 3.0 to 7.5% as a coating PVC. 2. The electrodeposition coating composition according to claim 1, wherein the amino group-containing acrylic resin has a lower SP value than the amino group-containing epoxy resin. 3. The electrodeposition coating composition according to claim 1, wherein the pigment component further contains precipitated barium sulfate. 4. The binder component comprises: a) 40 to 75% by weight of an amino-containing epoxy resin; b) 10 to 30% by weight of an amino-containing acrylic resin having a lower SP value than the amino-containing epoxy resin; c. 15 to 30% by weight of an aliphatic block polyisocyanate; and d) 1 to 10% by weight of a second acrylic resin having an SP value lower than that of the amino group-containing acrylic resin (components (a) to (d)). Is 100% by weight.) The electrodeposition coating composition according to claim 1. 5. The electrodeposition coating composition according to claim 4, wherein the SP value of the second acrylic resin is lower than the SP value of the amino group-containing acrylic resin by 0.5 or more. 6. A step of forming a coating film of the electrodeposition coating composition according to claim 1 on a surface to be coated of a metal substrate by an electrodeposition coating method; Baking and curing; forming a solid paint film thereon;
And baking and curing a coating film of a solid paint. 7. A step of forming a coating film of the electrodeposition coating composition according to any one of claims 1 to 5 on a surface to be coated of a metal substrate by an electrodeposition coating method; Baking and curing; forming a metallic base paint film thereon; forming a clear paint film thereon;
And baking and curing a coating film of a metallic base paint and a clear paint.