JP2002086053A - Double-layered coating film formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve chipping resistance, acid resistance, water-proofness, a finishing appearance (smoothness and glossy impression), and interlayer adhesion between coating films by forming the double-layered coating film by applying a cationic electrodeposition coating material and an aqueous innercoating material in a wet-on-wet manner and curing or cross-linking both coating films by heating. SOLUTION: The method for forming a coating film with a double-layered structure comprises the steps of applying a cationic electrodeposition coating material (A) containing a block polyissocyanate compound as a cross-linking agent; applying an aqueous intermediate coating material (B) containing substrate resin containing hydroxyl group and carboxyl group, a block polyisocyanate cross-linking agent, and an alicyclic epoxy compound to from an intercoating film on the electrodeposition coating film without curing the coating film; and curing both the coating films together by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for applying a cationic electrodeposition coating and an aqueous intermediate coating by wet-on-wet,
Then, in a method of forming a multi-layer coating by a so-called two-coat one-bake method (2C1B) in which both the coatings are cross-linked and cured together by heating, the chipping resistance, water resistance, and finish of the formed multi-layer coating are formed. The present invention relates to improving appearance (such as glossiness), adhesion between layers, and the like.

[0002]

2. Description of the Related Art Heretofore, cationic electrodeposition coating compositions containing a block polyisocyanate compound as a cross-linking agent, and polyester resins and block polyisocyanate have been applied to conductive substrates such as automobile outer panels. It is already known to apply a water-based intermediate coating containing a compound to form a multilayer coating film with 2C1B.

[0003] However, the multi-layer coating film does not have a sufficient finished appearance such as glossiness, and it has been difficult to eliminate this drawback even if a top coat is applied. Moreover,
When a pebble or the like is flipped up during running, there is a problem that chipping peeling (pilling) easily occurs between the layers of the two coating films. Further, the water resistance of the multilayer coating film was not sufficient.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in a multilayer coating film formed by applying a cationic electrodeposition coating and an aqueous intermediate coating with 2C1B.
An object of the present invention is to provide a method for forming a multilayer coating film having excellent finished appearance, chipping resistance, water resistance and the like. This time, the purpose was to use cationic electrodeposition paint and water-based intermediate paint as 2C1B
Can be achieved by using, as an aqueous intermediate coating, an aqueous coating containing a base resin having a hydroxyl group and a carboxyl group, a block polyisocyanate crosslinking agent and an alicyclic epoxy compound. Heading, the present invention has been completed.

That is, the present invention provides a method of applying a cationic electrodeposition coating composition (A) containing a blocked polyisocyanate compound as a crosslinking agent and curing the formed electrodeposition coating film without curing the electrodeposition coating film. Aqueous intermediate coating (B) containing a base resin having a hydroxyl group and a carboxyl group, a block polyisocyanate crosslinking agent and an alicyclic epoxy compound
To form an intermediate coating film, and then heat to cure both the coating films together (hereinafter referred to as the present method).

In particular, in the present method, it is necessary to preliminarily adjust the cross-linking and curing reaction of the coating film of the cationic electrodeposition coating material (A) to start earlier than the cross-linking and curing reaction of the coating film of the aqueous intermediate coating material (B). However, it is more preferable to achieve the above object.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present method, the timing of the start of crosslinking and curing of the coating film of the cationic electrodeposition coating material (A) and the aqueous intermediate coating material (B) was measured by a pendulum type viscoelasticity meter (manufactured by Toyo Boldwin Co., Ltd.). , Reovibron DDV-OPA type). Specifically, the weight is 22 g, and the moment of inertia 8 is
Using a pendulum of 50 g · cm ² , the film thickness becomes 30 μm after curing.
m, the pendulum is placed on an uncured coating film coated on a steel sheet, and heated at a predetermined temperature (for example, 140 to 180 ° C.) for crosslinking and curing the coating film while vibrating the pendulum. The time when the value of the logarithmic decay rate of the pendulum starts to increase is referred to as “crosslinking hardening start time”. The time required from the start of heating to the start of crosslinking and curing is referred to as “curing start time”, and a shorter time means “crosslinking and curing reaction starts earlier”. The comparison between the timings of initiation of crosslinking and curing of both coating films is performed based on the results measured at the same temperature.

Hereinafter, the method for forming a multilayer coating film according to the present method will be described in more detail.

[0009] Cationic electrodeposition coating (A) : The cationic electrodeposition coating (A) used in the present method contains a block polyisocyanate compound as a crosslinking agent, and preferably has a hydroxyl group and a cationic group. Base resin (A-
This is a cationic electrodeposition paint containing 1) and a block polyisocyanate compound (A-2).

In the base resin (A-1), the hydroxyl group is involved in a crosslinking reaction with the block polyisocyanate compound, and the cationic group is for forming a stable aqueous dispersion. Examples of (A-1) include the following.

(I): A reaction product of a polyepoxy resin and a cationizing agent.

(Ii): A polycondensate of a polycarboxylic acid and a polyamine (see US Pat. No. 2,450,940) protonated with an acid.

(Iii): Polyisocyanate compounds and polyadducts of polyols with mono- or polyamines, which are protonated with an acid.

(Iv): A copolymer of an acrylic or vinyl monomer having a hydroxyl group and an amino group, which is protonated with an acid (JP-B-45-12395, JP-B-45-19545)
-12396).

(V): A product obtained by protonating an adduct of a polycarboxylic acid resin and an alkyleneimine with an acid (see US Pat. No. 3,403,088).

Specific examples and production methods of these cationic resins are described, for example, in JP-B-45-12395, JP-B-45-12396, and JP-B-49-23.
No. 087, U.S. Pat. No. 2,450,940, U.S. Pat. No. 3,403,088, U.S. Pat.
No. 529, U.S. Pat. No. 3,963,663, and the like.

Particularly preferred as the base resin (A-1) is a cation which is contained in the epoxy group of the polyepoxide resin, which is included in the above (i) and is excellent in anticorrosion obtained by the reaction between the polyphenol compound and epichlorohydrin. It is a product obtained by reacting an agent.

The polyepoxide resin has one epoxy group.
It is a low or high molecular weight compound having two or more in the molecule, and at least 200 or more, preferably 400 to
Those having a number average molecular weight in the range of 4000, more preferably in the range of 800 to 2000 are suitable. As such a polyepoxide resin, those known per se can be used.For example, polyglycidyl of a polyphenol compound which can be produced by reacting a polyphenol compound with epichlorohydrin in the presence of an alkali can be used. Ethers are included. Here, as the polyphenol compound, for example, bis (4-hydroxyphenyl) -2,2-propane, 4,4′-dihydroxybenzophenone, bis (4-hydroxyphenyl)-
1,1-ethane, bis- (4-hydroxyphenyl)-
1,1-isobutane, bis (4-hydroxy-tert
-Butyl-phenyl) -2,2-propane, bis (2-
Hydroxybutyl) methane, 1,5-dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4-hydroxyphenyl) -1,1,2,2
2-ethane, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenylsulfone, phenol novolak, cresol novolak and the like.

Among these polyepoxide resins, those particularly suitable for producing the base resin (A-1) have a number average molecular weight of at least about 380, preferably from about 800 to about 200.
0 and an epoxy equivalent of 190-2000, preferably 4
It is a polyglycidyl ether of a polyphenol compound having a molecular weight of 00 to 1000. This includes those partially reacted with polyols, polyether polyols, polyester polyols, polyamidoamines, polycarboxylic acids, polyisocyanate compounds, etc., and further includes ε-caprolactone, acrylic Those obtained by graft polymerization of monomers or the like may be used.

The reaction product (i) of the polyepoxy resin and the cationizing agent is obtained by reacting most or all of the epoxy groups of the polyepoxide resin with the cationizing agent.

As the cationizing agent, for example, amine compounds such as primary amines, secondary amines, tertiary amines and polyamines can be used, which are reacted with epoxy groups by a method known per se. A cationic group-containing resin can be obtained by introducing a cationic group such as a secondary amino group, a tertiary amino group, and a quaternary ammonium base into the epoxy resin.

The primary amine compounds include, for example, methylamine, ethylamine, n-propylamine, isopropylamine, monoethanolamine, n-propano-
Examples of secondary amine compounds such as dimethylamine, isopropanolamine and the like include tertiary amines such as diethylamine, diethanolamine, di-n-propanolamine, diisopropanolamine, N-methylethanolamine and N-ethylethanolamine. Examples of the compound include triethylamine, triethanolamine, N, N-dimethylethanolamine, N-methyldiethanolamine, N, N-diethylethanolamine, and N-ethyldiethanolamine. Examples of the polyamine include ethylenediamine and diethylenetriamine. , Hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine, dimethylaminoethylamine, dimethylaminopropylamine and the like.

A basic compound other than these amine compounds, such as ammonia, hydroxyamine, hydrazine, hydroxyethylhydrazine, N-hydroxyethylimidazoline, is used as a cationizing agent and reacted with the epoxy group of the polyepoxy resin. May be protonated with an acid to form a cationic group. As the acid that can be used, a water-soluble organic carboxylic acid such as formic acid, acetic acid, glycolic acid, and lactic acid is preferable.

The hydroxyl groups of these cationic resins include, for example, a reaction with an alkanolamine in the above-mentioned cationizing agent, a ring-opened product of caprolactone which may be introduced into a polyepoxide resin, and a compound with a polyol. A primary hydroxyl group introduced by a reaction or the like; a secondary hydroxyl group originally contained in an epoxy resin. this house,
The primary hydroxyl group introduced by the reaction with the alkanolamine is a block polyisocyanate compound (crosslinking agent)
Is preferred because of its excellent cross-linking reactivity. As the alkanolamine, those exemplified above as the cationizing agent are preferable.

The content of hydroxyl groups in the base resin (A-1) is from 20 to 5000, particularly from 60 to 300, in terms of hydroxyl equivalents.
0, more preferably in the range of 100 to 1000 mg KOH / g, and especially the primary hydroxyl group equivalent is 20.
It is preferably in the range of 0 to 1000 mgKOH / g. The content of the cationic group is preferably at least the minimum necessary to stably disperse the base resin in water, and is generally 3 to 200 in terms of KOH (mg / g solid content) (amine value). , Especially 5-150, more particularly 10-
It is preferably in the range of 80.

It is desirable that the base resin (A-1) does not contain free epoxy groups in principle.

On the other hand, a block polyisocyanate compound (A-2) used as a crosslinking agent for a cationic electrodeposition coating composition
Is a volatile active hydrogen compound (blocking agent) in which substantially all of the isocyanate groups of the polyisocyanate compound are volatile.
The reaction is closed at room temperature and made inactive at normal temperature.
When heated above a predetermined temperature, the blocking agent is dissociated and the original isocyanate group is regenerated to participate in a crosslinking reaction with the base resin (A-1).

The polyisocyanate compound is a compound having two or more free isocyanate groups in one molecule,
For example, hexamethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate,
Aliphatic diisocyanates such as dimer acid diisocyanate and lysine diisocyanate; isophorone diisocyanate, methylene bis (cyclohexyl isocyanate)
A) alicyclic diisocyanates such as methylcyclohexane diisocyanate, cyclohexane diisocyanate, and cyclopentane diisocyanate; xylylene diisocyanate, tolylene diisocyanate, and diphenylmethane diamine. Isocyanate, naphthalene diisocyanate,
Aromatic diisocyanate such as toluidine diisocyanate
G; these urethanized adducts, biuret type adducts, isocyanuric ring type adducts and the like.

The isocyanate of the polyisocyanate compound
Examples of the blocking agent used for temporarily blocking the hydroxyl group include phenol-based blocking agents, alcohol-based blocking agents, active methylene-based blocking agents, mercaptan-based blocking agents, acid amide-based blocking agents, Imide blocking agents, amine blocking agents, imidazole blocking agents,
Examples include urea-based blocking agents, carbamic acid-based blocking agents, imine-based blocking agents, oxime-based blocking agents, sulfite-based blocking agents, and lactam-based blocking agents.

The block polyisocyanate compound (A-
The reaction between the polyisocyanate compound and the active hydrogen compound (blocking agent) for preparing 2) can be carried out by a method known per se, and the obtained blocked polyisocyanate compound is substantially free. It preferably does not contain an isocyanate group.

In the cationic electrodeposition paint (A), the base resin (A-1) and the block polyisocyanate compound (A
The composition ratio of the base resin (A-1) to the base resin (A-1) is generally 40 to 90%, preferably 50 to 80%, and more preferably 50 to 80%, based on the total solid weight of both components. Isocyanate compound (A-2) is 60 to 10
%, Particularly preferably in the range of 50 to 20%.

The cationic electrodeposition coating material (A) is made of a base resin (A
-1) The cationic group in -1) can be neutralized with an acidic compound such as acetic acid, formic acid, lactic acid, or phosphoric acid, and dispersed and mixed in water together with the block polyisocyanate compound (A-2).
The pH of the aqueous dispersion is preferably in the range of 3 to 9, particularly 5 to 7, and the resin solid content is suitably in the range of 5 to 30% by weight.

The cationic electrodeposition paint (A) may include aluminum, nickel, zinc, strontium,
Curing catalysts having rust-preventive properties such as hydroxides, oxides, organic acid salts and inorganic acid salts of metals selected from zirconium, molybdenum, tin, antimony, tungsten, etc .; extender pigments; coloring pigments; anti-settling agents And the like.

Further, in order to promote a crosslinking reaction between the base resin (A-1) and the block polyisocyanate compound (A-2), tin octoate, dibutyltin dilaurate, a manganese-containing compound, a cobalt-containing compound, Lead-containing compound, zirconium octoate, zinc octoate, dibutyltin-bis-O-phenylphenylene, dibutyltin-S, S-dibutyldithio-carbonate, triphenylantimony chloride, dibutyltin maleate, dibutyltin diacetate, dibutyltin dilaurate A curing catalyst such as mercaptide, triethylenediamine, dimethyltin dichloride and the like can be blended. The compounding amount is based on 100 parts by weight of the total of the base resin (A-1) and the block polyisocyanate compound (A-2).
Generally, a range of 0.1 to 10 parts by weight, particularly 0.5 to 2 parts by weight is suitable.

In particular, in the present method, in addition to the aforementioned base resin (A-1) and the block polyisocyanate compound (A-2), the bismuth-containing compound (A) It is preferable to use a lead-free cationic electrodeposition paint containing -3). This makes it possible to form an electrodeposition coating film having excellent anticorrosion properties and curability without using a lead compound which poses a problem in environmental hygiene.

Examples of the bismuth-containing compound that can be blended with the cationic electrodeposition coating composition (A) include bismuth oxides, hydroxides, salts with inorganic or organic acids, and examples thereof include bismuth hydroxide and bismuth trioxide. , Bismuth nitrate,
Examples include bismuth benzoate, bismuth citrate, bismuth oxycarbonate, bismuth silicate, and the like, with bismuth hydroxide being preferred. These bismuth-containing compounds (A
-3) is generally 0.1 to 10 parts by weight, particularly 0.15 to 7 parts by weight, per 100 parts by weight of the total solid content of the base resin (A-1) and the block polyisocyanate compound (A-2). .
5 parts by weight, more preferably 0.2 to 5 parts by weight.

As the bismuth-containing compound (A-3), a water-insoluble bismuth compound and a compound represented by the formula R ₁ C (H) (OR
₂ ) (CH ₂ ) nCOOH wherein R ₁ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ₂ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n is 0 or 1. The aliphatic carboxylic acid shown is obtained by mixing and dispersing in an aqueous medium in the presence of a dispersant, if necessary, so that the “aliphatic carboxylic acid-modified bismuth compound” is uniformly and stably dispersed in a water-insoluble state. Bismuth aqueous dispersion pastes can be used.

The water-dispersible paste containing the water-insoluble aliphatic carboxylic acid-modified bismuth compound (hereinafter, referred to as bismuth water-dispersed paste or simply water-dispersed paste) which can be blended with the cationic electrodeposition coating composition (A) is as follows: It can be produced by mixing and dispersing the water-insoluble bismuth compound and the aliphatic carboxylic acid represented by the above formula in an aqueous medium in the presence of a dispersant. In this case, the aliphatic carboxylic acid is used in such a ratio that a water-insoluble aliphatic carboxylic acid-modified bismuth compound is mainly produced. Thus, a water-dispersed paste of bismuth in which the resulting aliphatic carboxylic acid-modified bismuth compound is uniformly and stably dispersed in a water-insoluble state is obtained, and this water-dispersed paste is mixed with the cationic electrodeposition paint (A). Thereby, the curability and anticorrosion properties can be remarkably improved without impairing the throwing power and finish of the electrodeposition coating film.

The content of the water-soluble bismuth compound present in the supernatant obtained by subjecting the aqueous dispersion paste to centrifugation (12,000 rpm for 30 minutes) is converted into the amount of water used as a raw material in terms of metal bismuth weight. It is desirable that the total amount of the insoluble bismuth compound is about 40% by weight or less, particularly about 30% by weight or less, and more particularly about 20% by weight or less.

Examples of the water-insoluble bismuth compound used for preparing such an aqueous paste of bismuth include, for example, bismuth oxide, bismuth hydroxide, and tribasic bismuth carbonate having a solubility in water at 20 ° C. of 0.00
A bismuth compound of 1 g / 100 g or less;
Among them, bismuth oxide is preferred.

The aliphatic carboxylic acid represented by the above formula is used for the purpose of converting the above water-insoluble bismuth compound into a sufficiently uniform dispersion in an aqueous medium. Aliphatic hydroxycarboxylic acids such as acetic acid, lactic acid, hydroxypropionic acid;
Examples thereof include aliphatic alkoxycarboxylic acids such as methoxyacetic acid, ethoxyacetic acid, and 3-methoxypropionic acid. Of these, lactic acid, particularly L-lactic acid and methoxyacetic acid, are preferred. These can be used alone or in combination of two or more. These aliphatic carboxylic acids may be used in combination with other organic acids, for example, acetic acid.

The amount of the aliphatic carboxylic acid used is within a range in which the obtained aliphatic carboxylic acid-modified bismuth compound may be in a water-insoluble state, and varies depending on the type of the aliphatic carboxylic acid used. For lactic acid, the molar ratio to the amount of bismuth in the water-insoluble bismuth compound is usually in the range of 0.5 to 1.7, preferably 0.75 to 1.3, and for methoxyacetic acid, the bismuth in the water-insoluble bismuth compound is 0.25 to 2.5 in molar ratio to the amount,
Preferably, it can be in the range of 0.5 to 1.3.

Further, as the bismuth-containing compound, bismuth lactate using lactic acid containing 80% or more of the L-form among the optical isomers can also be used effectively. Specifically, an aqueous bismuth lactate solution obtained by reacting lactic acid containing 80% or more of the L-form with 1 mol of bismuth oxide in the presence of water at a ratio of 2 to 10 mol is preferable. The compounding amount of bismuth lactate is preferably 0.1 to 10 parts by weight, particularly preferably 0.2 to 5 parts by weight, per 100 parts by weight of the electrodeposition coating resin solids.

As lactic acid used for preparing bismuth lactate,
Of the optical isomers, L-form is 80% or more (that is, D-form is 20% or more).
%), Preferably 85% or more, more preferably 8% or more.
A material containing 0% or more is used. If the L-form is less than 80%, the water solubility may decrease. L-lactic acid is preferably produced by a fermentation method. As the bismuth compound used for preparing bismuth lactate, bismuth hydroxide, basic bismuth carbonate, and the like are also suitable in addition to bismuth oxide.

The reaction between the bismuth compound and lactic acid is suitably carried out at a ratio of 2 to 10 mol, particularly 3 to 8 mol, of lactic acid containing 80% or more of L-form per mol of bismuth compound. For example, in the presence of water, 2 to 10 mol, particularly 3 to 8 mol, of lactic acid containing 80% or more of the L-form per 1 mol of bismuth oxide is allowed to react at room temperature to 90 ° C. for about 1 to 30 hours to form a homogeneous solution. A bismuth lactate aqueous solution is obtained. If the amount of lactic acid is less than 2 mol, it is difficult to make water soluble, and if it exceeds 10 mol, the electrodeposition coatability may be reduced. When bismuth hydroxide is used, bismuth lactate can be obtained by reacting 1 to 5 mol, particularly 1.5 to 4 mol, of lactic acid containing 80% or more of the L-form per 1 mol of bismuth hydroxide. The concentration of these reaction solids is usually 0.1 to 8
0% by weight, preferably 0.5 to 70% by weight, more preferably 1 to 60% by weight is suitable.

The bismuth lactate aqueous solution may be blended before or after the cationic electrodeposition paint is dispersed in water. The solid content concentration at the time of mixing the bismuth lactate aqueous solution is not particularly limited before being dispersed in water, but when blended after being dispersed in water, it is suitably adjusted to 60% by weight or less. This is because bismuth lactate is uniformly dispersed in the electrodeposition coating composition,
Considering the ease of coating formulation, storage stability, etc., it is preferable to add the electrodeposition coating composition after dispersion.

As the above-mentioned dispersing agent, a cationic dispersing resin or a surfactant known per se in the field of cationic electrodeposition paint can be used without any limitation. It can be appropriately selected and used from those listed as the base resin for electrodeposition paint. For example, resins of tertiary amine type, quaternary ammonium salt type, tertiary sulfonium salt type and the like can be mentioned. As the surfactant, for example, HLB is 3 to 18,
Acetylene glyco- preferably in the range of 5 to 15
And nonionic surfactants such as polyethylene glycol, polyethylene glycol and polyhydric alcohol.

The amount of the dispersant used can be varied depending on the type thereof, the amount of the water-insoluble bismuth compound used, and the like. Usually, the amount is 1 to 150 parts by weight, especially 10 parts by weight, per 100 parts by weight of the water-insoluble bismuth compound. A range of from about 100 parts by weight to 100 parts by weight is preferred.

The production of a water-dispersed paste of bismuth using the water-insoluble bismuth compound, aliphatic carboxylic acid and dispersant described above is carried out in the same manner as the production of a pigment paste used in a cationic electrodeposition paint. Specifically, for example, by adding an aliphatic carboxylic acid and a water-insoluble bismuth compound to water containing a dispersant, and performing dispersion treatment in a dispersion mixer such as a ball mill or a sand mill, the water of bismuth can be obtained. A dispersion paste can be produced. The aqueous dispersion paste obtained is generally from 10 to 70% by weight, in particular from 30 to 70% by weight.
It may have a solids concentration of 60% by weight.

Further, the water-dispersed paste may be prepared as a pigment paste by adding a pigment used in a usual cationic electrodeposition paint. Specifically, for example, a pigment paste is prepared by mixing a pigment dispersing resin, a neutralizing agent, and pigments, and performing dispersion treatment in a dispersing mixer such as a ball mill or a sand mill. Bismuth aqueous dispersion paste can be added. As the neutralizing agent used for neutralizing the pigment dispersing resin, for example, organic acids such as acetic acid, formic acid, and lactic acid can be used.

As the pigment dispersing resin, for example, conventionally known resins can be used without any limitation. For example, the same cationic dispersing resin as used in preparing the bismuth dispersion paste can be used.

As the above-mentioned pigments, any pigment can be used without particular limitation as long as it is a pigment usually used in cationic electrodeposition paints. For example, titanium oxide, carbon black,
Coloring pigments such as red iron oxide; extender pigments such as clay, mica, barita, talc, calcium carbonate and silica; and rust preventive pigments such as aluminum phosphomolybdate and aluminum tripolyphosphate.

The aqueous dispersion paste of bismuth or the aqueous dispersion paste can be blended with the binder resin component of the cationic electrodeposition paint.

The bismuth dispersion paste is generally
The bismuth metal content is 0.1 to 10 parts by weight, preferably 0.1 to 100 parts by weight, per 100 parts by weight of the total solid content of the base resin (A-1) and the blocked polyisocyanate compound (A-2).
It can be blended with the cationic electrodeposition paint in such a ratio as to be in the range of 3 to 7 parts by weight, more preferably 0.5 to 5 parts by weight.

In the present method, the cationic electrodeposition paint (A)
It is preferable that the cross-linking curing reaction of the coating film starts earlier than that of the water-based intermediate coating (B) coating film located in the upper layer. For this purpose, for example, it is preferable to set the curing temperature of the coating film of the cationic electrodeposition coating material (A) to be lower than the curing temperature of the coating film of the intermediate coating material (B). For example, the difference between the curing temperatures of the two coating films is preferably in the range of 0 to 20 ° C, particularly 5 to 15 ° C. When the onset of the cross-linking curing reaction of the cationic electrodeposition coating (A) is later than that of the intermediate coating, generally,
It may be difficult to improve the finished appearance (smoothness, glossiness, etc.) of the multilayer coating film and the interlayer adhesion between the two coating films.

The start time of the crosslinking curing reaction of the coating film of the cationic electrodeposition paint (A) is, for example, a polyisocyanate compound,
It can be easily controlled by appropriately selecting the type and the amount of the blocking agent, the curing catalyst, and the like.

Regarding the coating film of the cationic electrodeposition paint (A), the “curing start time” from the start of heating to the start of crosslinking and curing is preferably 5 to 15 minutes in the coating step.

The coating of the cationic electrodeposition coating material (A) is carried out, for example, by using an object to be coated as a cathode, a carbon plate as an anode, and a bath temperature of 2%.
0 to 35 ° C, voltage 100 to 400 V, current density O. 01
It is preferable that the heating is performed at 5 to 5 A for 1 to 10 minutes. The coating film thickness can be about 10 to 40 μm for the cured coating film. Examples of the object to be coated include a substrate having a conductive metal surface, particularly an automobile body, an electric appliance and the like.

In the present method, after the cationic electrodeposition paint (A) is applied, the coating surface is applied to the coated surface without curing the coating film.
An aqueous intermediate coating composition (B) using a block polyisocyanate compound as a crosslinking agent is applied.

Aqueous intermediate coating (B) : The aqueous intermediate coating (B) comprises a base resin (B-1) having a hydroxyl group and a carboxyl group, a block polyisocyanate crosslinking agent (B-2) and an alicyclic ring. This is an aqueous paint containing the formula epoxy compound (B-3) and mixing and dispersing these in water.

As the base resin (B-1) containing a hydroxyl group and a carboxyl group in the aqueous intermediate coating composition (B), for example, a polyester resin or an acrylic resin having two or more hydroxyl groups and a carboxyl group in one molecule, respectively, is used. Particularly preferred.

Among them, the polyester resin can be produced by subjecting a polybasic acid and a polyhydric alcohol to an esterification reaction, and has a number average molecular weight of 1,000 to 5,
0000, especially 2000 to 20000, and the hydroxyl value is 20
~ 200 mgKOH / g, especially 50-150 mgKOH
/ G, acid value 3-100 mgKOH / g, especially 10-7
It is preferably in the range of 0 mgKOH / g.

The polybasic acid is a compound having two or more carboxyl groups in one molecule, for example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, Examples thereof include hexahydrophthalic acid, heptic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid and anhydrides thereof.

The polyhydric alcohol is a compound having two or more hydroxyl groups in one molecule.
Propylene glycol, diethylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, hydrogenated bisphenol A, triethylene glycol.
, Glycerin, trimethylol-ethane, trimethylo-
And propane and pentaerythritol.

The hydroxyl group and the carboxyl group are directly or indirectly bonded to the polyester resin skeleton. For example, a polybasic acid or a polyhydric alcohol having three or more carboxyl groups and hydroxyl groups in one molecule is used in combination. Can be introduced.

The acrylic resin can be produced by copolymerizing a polymerizable monomer component containing a hydroxyl group-containing polymerizable monomer, a carboxyl group-containing polymerizable monomer and an acrylic monomer under ordinary conditions. Has a number average molecular weight of 1
000-50,000, especially 2000-20,000, hydroxyl value 20-200 mgKOH / g, especially 50-150
mgKOH / g, and the acid value is preferably 3 to 100 mgKOH / g, particularly preferably 20 to 70 mgKOH / g.

The hydroxyl group-containing polymerizable monomer is a compound having at least one hydroxyl group and at least one polymerizable unsaturated bond in one molecule, for example, hydroxyethyl (meth) acrylic acid.
, Hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate and the like having 2 to 20 carbon atoms
And a monoesterified product of (meth) acrylic acid and the like. The carboxyl group-containing polymerizable monomer is a compound having one or more carboxyl groups and one or more polymerizable unsaturated bonds in one molecule, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaric acid, mesacon Acids and their anhydrides and half esters; The acrylic monomer is (meth)
Monoesters of acrylic acid and monovalent alcohols having 1 to 22 carbon atoms, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate and propyl Methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate, hexyl methacrylate, octyl acrylate, octyl methacrylate, lauryl acrylate, lauryl methacrylate And 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate and the like.

In the production of a hydroxyl- and carboxyl-containing acrylic resin, these hydroxyl-containing polymerizable monomers,
Other polymerizable monomers other than the carboxyl group-containing polymerizable monomer and the acrylic monomer can be used in combination.

As other monomers, for example, methoxybutyl acrylate, methoxybutyl methacrylate,
(Meth) acrylic acid such as methoxyethyl acrylate and methoxyethyl methacrylate and an alkoxyester having 2 to 18 carbon atoms; N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate Ray
N, N-diethylaminoethyl acrylate, N, N
N-diethylaminoethyl methacrylate, Nt-butylaminoethyl acrylate, Nt-butylaminoethyl methacrylate, N, N-dimethylaminopropyl acrylate, N, N-dimethyl Aminoacrylic monomers such as aminopropyl methacrylate; acrylamide, methacrylamide, N-methylacrylamide,
Acrylamide-based monomers such as N-methylmethacrylamide, N-ethylacrylamide, N-ethylmethacrylamide, N-butylacrylamide, N-butylmethacrylamide, N-dimethylacrylamide, N-dimethylmethacrylamide; And glycidyl group-containing monomers such as glycidyl methacrylate;
Styrene, α-methylstyrene, vinyltoluene, acrylonitrile, vinyl acetate, vinyl chloride and the like can be mentioned.

The block polyisocyanate cross-linking agent (B-2) is for cross-linking the base resin (B-1), and is, for example, used as a cross-linking agent in the above-mentioned cationic electrodeposition paint (A). One or more selected from the exemplified block polyisocyanate compounds (A-2) can be suitably used.

In the aqueous intermediate coating composition (B), the composition ratio of the base resin (B-1) and the crosslinking agent (B-2) is not particularly limited, but is based on the total solid weight of both components.
The base resin (B-1) accounts for 40 to 90%, particularly 50 to 80%.
%, The crosslinking agent (B-2) is 60 to 10%, particularly 50 to 20%.
% Is preferred.

The alicyclic epoxy compound (B-3) is a compound having one or more alicyclic epoxy groups in one molecule. Here, the alicyclic epoxy group means a functional group in which two adjacent carbon atoms and one oxygen atom constituting a ring of the alicyclic hydrocarbon skeleton constitute an epoxy group. . The alicyclic hydrocarbon skeleton may be a 4- to 10-membered, preferably 5- to 6-membered, saturated hydrocarbon ring, or a condensed hydrocarbon ring formed by condensing two or more such rings. The rings may form a bridged hydrocarbon ring linked by a bridge such as an alkylene group. Specific examples of such alicyclic compounds include compounds represented by the following formulas below.

Epoxidized tetrahydrobenzyl alcohol represented by the formula (1):

[0074]

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Formula (2) wherein m is an integer of 2 to 12,
n represents an integer of 1 to 20 (average)), a lactone-modified epoxidized tetrahydrobenzyl alcohol,

[0076]

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A cyclohexene oxide represented by the formula (3):

[0078]

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Α-pinene oxide represented by the formula (4):

[0080]

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A vinyl group-containing cyclohexene oxide represented by the formula (5).

[0082]

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Further, there may be mentioned compounds represented by the following formula.

[0084]

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[0085]

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(Wherein, n ′ is an integer of 1 to 8, k is 0 to 1)
Each of which represents an integer of 5).

Further, a compound having the following unit formula:

[0088]

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Wherein Y is an alicyclic epoxy residue;
X is

[0090]

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[0091] a and, R ₁ is C _{1 ~ 18} alkyl group or a cycloalkyl group, R ₂ is C _{1 ~ 6} alkylene group, q is 0 to 1
00 represents an integer, and p represents an integer of 1 to 100).

In the above unit formula, Y is

[0093]

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And an organic group having an alicyclic epoxy group.

Compounds having the above unit formula include those described in Japanese Patent Application No. 1-209667, for example,
3,4-epoxycyclohexylmethyl acrylate,
3,4-Epoxycyclohexyl acrylate, a polymerizable epoxy monomer such as "METHB" or "AETHB" (all trade names, manufactured by Daicel Chemical Industries, Ltd.) as a commercial product thereof, or a radical polymerizable monomer alone or with another radical polymerizable monomer What was done is given.

As the alicyclic epoxy compound (B-3),
A polymer obtained using a compound having an alicyclic epoxy group and a polymerizable unsaturated bond in the same molecule is also included. Examples of the compound having an alicyclic epoxy group and a polymerizable unsaturated bond in the same molecule include, for example, the following general formulas (6) to (1)
The polymerizable epoxy monomer represented by 7) is mentioned.

[0097]

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[0098]

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(Wherein R ₄ represents a hydrogen atom or a methyl group;
R ₅ represents a divalent aliphatic saturated hydrocarbon group having 1 to 6 carbon atoms,
R ₆ represents a divalent aliphatic saturated hydrocarbon group having 1 to 10 carbon atoms) As the divalent aliphatic saturated hydrocarbon group having 1 to 6 carbon atoms represented by R ₅ in the polymerizable epoxy monomer, ,
A linear or branched alkylene group, for example, methylene,
Examples include ethylene, propylene, tetramethylene, ethylethylene, pentamethylene, hexamethylene and the like. Examples of the divalent aliphatic saturated hydrocarbon group having 1 to 10 carbon atoms represented by R ₆ include methylene, ethylene, propylene, tetramethylene, ethylethylene, pentamethylene, hexamethylene, polymethylene,
Phenylene,

[0100]

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And the like.

Specific examples of the polymerizable epoxy monomers represented by the above general formulas (6) to (17) include 3,4-
Epoxycyclohexylmethyl acrylate, 3,4-
Epoxycyclohexylmethyl methacrylate and the like. "METHB", "AE
Examples thereof include those obtained by subjecting a polymerizable epoxy monomer such as “THB” (all manufactured by Daicel Chemical Industries, Ltd., trade name) to single or radical polymerization with another radical polymerizable monomer.
Further, 4-vinylcyclohexene oxide can be used as the polymerizable epoxy monomer.

The alicyclic epoxy compound (B-3) can be obtained by (co) polymerizing one or more monomers selected from these polymerizable epoxy monomers, and further copolymerized with other polymerizable monomers. What did (B-3)
Can be used as an ingredient. Other polymerizable monomers include those containing a hydroxyl group and a carboxyl group, as exemplified in the description of the acrylic resin having two or more hydroxyl groups and carboxyl groups in one molecule as one of the base resin (B-1) containing the hydroxyl group. Polymerizable monomers, carboxyl group-containing polymerizable monomers, acrylic monomers, other polymerizable monomers, and the like can be suitably used.

The ratio of the polymerizable epoxy monomer to the other polymerizable monomer is selected within a range having at least one, preferably at least two, alicyclic epoxy groups in one molecule of the component (B-3). For example, per 100 parts by weight of the total of the polymerizable epoxy monomer and the other polymerizable monomer constituting the component (B-3), the polymerizable epoxy monomer is 5 to 100% by weight, preferably 20 to 100% by weight, The other polymerizable monomer is suitably in the range of 95 to 0% by weight, preferably 80 to 0% by weight.

The above-mentioned alicyclic epoxy compound (B-3)
Has a number average molecular weight of 90 to 50,000, particularly 200 to 20.
000 is suitable, and this (B-3) component 1
The number of alicyclic epoxy groups in the molecule is one or more, especially 2 to 2
Within the range of 00 is preferred.

The above alicyclic epoxy compound (B-3)
When a compound or resin having another epoxy group is used instead of this, the storage stability of the aqueous intermediate coating composition becomes insufficient, and the chipping resistance and water resistance of the multilayer coating film are reduced. Not preferred.

The amount of the alicyclic epoxy compound (B-3) is based on 100 parts by weight of the total of the base resin (B-1) having a hydroxyl group and a carboxyl group and the crosslinking agent (B-2).
It is preferably in the range of 0.5 to 20 parts by weight, especially 1 to 15 parts by weight.

As a neutralizing agent for neutralizing the carboxyl group of the base resin (B-1) having a hydroxyl group and a carboxyl group to impart solubility or dispersibility with water, for example,
Ammonia, trimethylamine, triethylamine, dimethylethanolamine, triethanolamine, tetraethylammonium hydroxide, diethylaminoethanol and the like can be mentioned.

The aqueous intermediate coating (B) contains a base resin (B-1) having a hydroxyl group and a carboxyl group, a crosslinking agent (B-2) and an alicyclic epoxy compound (B-3). An aqueous paint mixed and dispersed in water, and further, a curing catalyst for accelerating a crosslinking reaction of the coating film,
An extender, a coloring pigment, and a surface conditioner can be blended. As the curing catalyst, the above-mentioned cationic electrodeposition paint (A)
And at least one compound selected from the group consisting of the base resin (B-1) and the crosslinking agent (B
-2), 0.1 to 10 parts by weight, especially 0.5 to 2 parts by weight, per 100 parts by weight in total.

In the present method, the time for starting the crosslinking and curing of the coating film of the aqueous intermediate coating material (B) is later than the time for starting the crosslinking and curing of the coating film of the cationic electrodeposition coating material (A) located thereunder. Specifically, it is preferable that the cross-linking curing reaction starts 0.5 to 10 minutes, particularly 1 to 5 minutes later than the start time of the cross-linking curing reaction of the coating film of the cationic electrodeposition coating composition (A). That is, the “curing start time” required from the start of heating of the coating film of the aqueous intermediate coating composition (B) to the start of crosslinking and curing is changed to the “curing start time” of the cationic electrodeposition coating (A) coating film. The difference is 0.5 to 10 minutes, especially 1 to 5 minutes.
Minutes are suitable.

The timing of the start of crosslinking and curing of the coating film of the aqueous intermediate coating (B) is determined, for example, by the type and amount of the crosslinking agent (B-2), the alicyclic epoxy compound (B-3), and the curing catalyst. It can be easily controlled by appropriate selection. The timing of the start of the cross-linking curing reaction of the coating of the aqueous intermediate coating (B) is later than the timing of the start of the cross-linking curing of the coating of the cationic electrodeposition coating (A). Suitably between 10 and 10 minutes, especially between 1 and 5 minutes.

The aqueous intermediate coating material (B) is a base resin (B-
1), a crosslinking agent (B-2) and an alicyclic epoxy compound (B
-3) and the like are uniformly mixed and dispersed in water, and the solid content concentration at the time of coating is preferably adjusted to a range of 20 to 70% by weight.

In this method, the cationic electrodeposition coating composition (A) is applied and, if necessary, dried at a temperature of 120 ° C. or less without curing, and then the aqueous intermediate coating composition ( This is achieved by applying B) and then heating to crosslink and cure both coatings together.

The aqueous intermediate coating (B) is applied by electrostatic coating, airless spraying, air spraying, etc., and its film thickness is about 5 to 80 μm, especially about 15 to 35 μm, based on the cured coating film. Is suitable. The heating temperature for crosslinking and curing both the cationic electrodeposition coating (A) coating and the aqueous intermediate coating (B) coating is usually from 130 to 1
80 ° C. is suitable, and the coating can be cured together by baking at this temperature for 10 to 40 minutes.

On the multilayer coating film formed by the present method,
If necessary, using a top coat such as solid color paint, metallic paint and clear paint, in a known manner,
1-coat 1-bake method (1C1B), 2-coat 1-bake method (2C1B), 2-coat 2-bake method (2C2
B) It can be coated by a three-coat one-bake method (3C1B) or the like.

[0116]

According to the present method, the following remarkable effects can be obtained.

[0117] 1. An aqueous intermediate coating (B) is applied to the uncured coating surface of the cationic electrodeposition coating (A), and the two coatings are cross-linked and cured together by heating. In addition, it was possible to improve the finished appearance (such as glossiness) and the adhesion between the layers of both coating films after water resistance.

[0118]

EXAMPLES Examples and comparative examples according to the present invention will be described below. All parts and percentages are based on weight. The thickness of the coating film is for the cured coating film.

In the examples and comparative examples, the timing of the start of crosslinking and curing of the cationic electrodeposition coating film and the aqueous intermediate coating film was measured using a pendulum type viscoelasticity meter (Ryovibron DDV-OPA type, manufactured by Toyo Boldwin). I went.

[0120] 1. Preparation of sample 1) Cathodic electrodeposition paint (A) (A-1): 1,260 parts of bisphenol A type epoxy resin having epoxy equivalent of 630 (trade name of “Epic Coat 1002”, manufactured by Shell Chemical Co., Ltd.) is butyl cellosolve 450 And 132 parts of p-nonylphenol and 105 parts of N-methylethanolamine. The mixture was heated to 140 ° C. and reacted at the same temperature to give a solid content of 77% and an amine value of 52.
Was obtained. To 130 parts of this resin, 30 parts of a blocked polyisocyanate compound (curing agent) and 1.3 parts of polypropylene glycol (number average molecular weight: 4000) were used.
After adding 2.1 parts of acetic acid, 2.1 parts of acetic acid was added to make water soluble, then 6.5 parts of a 20% aqueous lead acetate solution was added, and then deionized water was gradually added to disperse the emulsion. And

On the other hand, 4.7 parts of a 75% epoxy-based amine-type pigment dispersion resin was neutralized with 0.16 parts of a 88% aqueous formic acid solution, 22.2 parts of deionized water was added, and a titanium white pigment 15 Parts, 7 parts of clay, 0.3 parts of carbon black, 3.0 parts of basic lead silicate and 3 parts of dioctyltin oxide are dispersed in a ball mill to prepare a pigment-dispersed paste having a solid content of 55%.

Next, the above-mentioned emulsion having a solid content of 30% and the pigment dispersion paste having a solid content of 55% were mixed and diluted with deionized water to obtain an electrodeposition bath having a solid content of 19%.

The above block polyisocyanate compound is obtained by reacting 174 parts of 2,6-tolylene diisocyanate with 85 parts of polycaprolactone diol having a hydroxyl group equivalent of 425 to 2-ethylene glycol. It is obtained by reacting ethylhexyl alcohol monoether (blocking agent).

(A-2): Cationic electrodeposition paint (A-1)
In the above, except that 6.5 parts of a 20% aqueous lead acetate solution was omitted, and 3.0 parts of basic lead silicate in the pigment paste was replaced with 3.0 parts of bismuth hydroxide, all of the cationic electrodeposition paint (A) was used.
It was prepared in the same manner as in -1).

(A-3): Cationic electrodeposition paint (A-1)
All cationic cationic electrodeposition coatings were used except that 6.5 parts of a 20% aqueous lead acetate solution and 3.0 parts of a basic lead silicate of a pigment paste were replaced with 1 part of the following “bismuth dispersed paste” (as the amount of metallic bismuth). It was prepared in the same manner as in (A-1).

Here, the “dispersed paste of bismuth” was prepared as follows. 75% solids in the container
Epoxy Tertiary Amine Pigment Dispersion Resin (Amine Value 1
00) 133.3 parts and 81.1 parts of methoxyacetic acid were mixed and stirred so as to be uniform.
3.5 parts was added dropwise with vigorous stirring, and 111.5 parts of bismuth hydroxide was further added and mixed and dispersed in a ball mill for 20 hours to obtain a bismuth-dispersed paste having a solid content of 50%.

2) Aqueous intermediate coating (B) (Bi): 1000 parts of polyester resin (Note 1), 40 parts of dimethylaminoethanol (Note 2), aliphatic 6-functional block polyisocyanate Compound (Note 3) 410
, An alicyclic epoxy compound (Note 4), 100 parts of titanium white pigment, and 1400 parts of carbon black were mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating composition.

(Note 1) Polyester resin: 756 parts of neopentyl glycol, trimethylolpropane 109
Parts, hexahydrophthalic acid 370 parts, adipic acid 292
Parts and 398 parts of isophthalic acid are placed in a reaction vessel,
After reacting for 6 hours at 45 ° C., 45 parts of trimellitic anhydride was added and reacted at 170 ° C. for 30 minutes to obtain a number average molecular weight of about 8
000, acid value 20mgKOH / g, hydroxyl value 95mgK
An OH / g polyester resin was obtained.

(Note 2) Dimethylaminoethanol: Nippon Emulsifier Co., Ltd., trade name “Amino Alcohol 2Mab”
s "(Note 3) Aliphatic hexafunctional block polyisocyanate compound: A hexameric diisocyanate trimer adduct was blocked with methyl ethyl ketoxime.

(Note 4) Alicyclic epoxy compound: "Celoxide 2021" (trade name, manufactured by Daicel Chemical Industries, Ltd., represented by the following structural formula)

[0131]

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(B-ii): Polyester resin (Note 1)
1000 parts, dimethylaminoethanol (Note 2) 40
Part, aliphatic trifunctional block polyisocyanate compound (Note 5) 410 parts, alicyclic epoxy compound (Note 6) 1
00 parts, 1400 parts of titanium white pigment and 20 parts of carbon black were mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating composition (B-ii).

(Note 5) Aliphatic trifunctional block polyisocyanate compound: A trimer of hexamethylene diisocyanate was blocked with methyl ethyl ketoxime.

(Note 6) Alicyclic epoxy compound: “ERL”
-4299 "(manufactured by Union Carbide, trade name, represented by the following structural formula)

[0135]

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(B-iii): Acrylic resin (Note 7) 1
000 parts, dimethylaminoethanol (Note 2) 40 parts,
410 parts of aliphatic trifunctional block polyisocyanate compound (Note 5), alicyclic epoxy compound (Note 8) 10
0 parts, 1400 parts of titanium white pigment (Note 3) and 20 parts of carbon black were mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating composition (B-iii).

(Note 7) Acrylic resin: styrene 210
Parts, 294 parts of n-butyl methacrylate, 253 parts of hydroxybutyl acrylate, 200 parts of 2-ethylhexyl methacrylate, and 30 parts of acrylic acid were placed in a reaction vessel, and reacted at 120 ° C. for 5 hours. Number average molecular weight about 20
000, acid value 25mgKOH / g, hydroxyl value 95mgK
An OH / g acrylic resin was obtained.

(* 8) Alicyclic epoxy compound: "Eporide GT-300" (trade name, manufactured by Daicel Chemical Industries, Ltd.)
(B-iv) (for comparison): The above-mentioned aqueous intermediate coating (B-iv)
An aqueous intermediate coating (B-iv) was obtained in the same manner as (B-i) except that the alicyclic epoxy compound (Note 4) in i) was not blended.

[0139] 2. Examples and Comparative Examples Dull steel sheets treated with zinc phosphate were immersed as cathodes in the electrodeposition baths of the cationic electrodeposition paints (A-1) to (A-3).
Electrodeposit at 200C for 3 minutes at 0 ° C (film thickness is 25
μm) and dried at 100 ° C. for 10 minutes, and then each of the aqueous intermediate coatings (Bi) to (B-iv) was applied by air spray (film thickness: 35 μm), and then heated at 170 ° C. for 30 minutes. Both coatings were crosslinked and cured.

The performance test of the thus obtained multilayer coating film was conducted. Table 1 shows the test results.

[0141]

[Table 1]

The test method is as follows.

Gloss: 60 ° specular reflectance.

Chipping resistance: QGR gravelomer
15 to 20 m in diameter using a tar (manufactured by Q Panel Co., Ltd.)
100 g of crushed stone with an air pressure of about 4 kg / cm ² ,
Spraying was performed at 0 ° C. at a spray angle of 90 ° to the coated surface. Thereafter, the state of the coated surface was visually evaluated. ○: slight impact flaw is observed on the intermediate coating surface, but no peeling of the electrodeposition coating film is observed. Δ: slight impact flaw is recognized on the intermediate coating surface, and slight peeling of the electrodeposition coating film is also observed. In the case of "x", many impact flaws were observed on the intermediate coated surface, and the electrodeposition coating film was considerably peeled off.

Water resistance: immersed in warm water of 80 ° C. for 24 hours,
The coated surface after washing with water and drying was visually observed. ○ indicates no abnormality, △ indicates slight gloss, and × indicates whitening of the coated surface.

Interlayer adhesion: After immersion in warm water under the same conditions as described above, cut with a cutter to reach the substrate, make 100 gobangs of size 1 mm x 1 mm, and paste an adhesive tape on the surface. The remaining number of the Gobang-like paint film after the coating and rapid peeling at 20 ° C. was examined.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C09D 7/12 C09D 7/12 175/04 175/04 C25D 13/00 307 C25D 13/00 307D 308 308C 13/06 13 / 06 EF term (reference) 4D075 AE12 BB26Z BB89X CA04 CA13 CA38 CA48 CB04 DA06 DA23 DB01 DC11 EA06 EA10 EB14 EB20 EB22 EB33 EB35 EB38 EB45 EB47 4J038 DG111 DG161 DG171 HA36 JA37 PA196 HA37

Claims (5)

[Claims] 1. A cationic electrodeposition coating composition (A) containing a blocked polyisocyanate compound as a cross-linking agent is applied, and a hydroxyl group and a carboxyl group are formed on the electrodeposition coating film without curing the formed electrodeposition coating film. A waterborne intermediate coating composition (B) containing a base resin having the above, a blocked polyisocyanate crosslinking agent and an alicyclic epoxy compound is applied to form an intermediate coating film, which is then heated to cure both coating films together. Forming a multilayer coating film. 2. The method according to claim 1, wherein the crosslinking and curing reaction of the coating of the cationic electrodeposition coating (A) is adjusted to start earlier than the crosslinking and curing of the coating of the aqueous intermediate coating (B). Layer coating method. 3. The method according to claim 1, wherein the cationic electrodeposition paint is a lead-free cationic electrodeposition paint further containing a bismuth-containing compound. 4. A bismuth-containing compound comprising: bismuth hydroxide;
4. The method according to claim 3, wherein the method is selected from bismuth trioxide, bismuth nitrate, bismuth benzoate, bismuth citrate, bismuth oxycarbonate, and bismuth silicate. 5. The bismuth-containing compound is a water-insoluble bismuth compound and R ₁ C (H) (OR ₂ ) (CH ₂ ) nCOO.
H wherein R ₁ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ₂ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms,
n is 0 or 1];
A water-dispersed paste obtained by mixing and dispersing in the presence of a dispersant in an aqueous medium, wherein the aliphatic carboxylic acid-modified bismuth compound is a water-dispersed paste in a water-insoluble state. 4. The method for forming a multilayer coating film according to claim 3.