WO1999012660A1

WO1999012660A1 - Method of forming multilayered coating film

Info

Publication number: WO1999012660A1
Application number: PCT/JP1998/004099
Authority: WO
Inventors: Tetsuya Yokoyama; Akira Kasari; Takeshi Yawata; Tadayoshi Hiraki; Yasuhiro Tomisaki
Original assignee: Kansai Paint Co., Ltd.
Priority date: 1997-09-11
Filing date: 1998-09-11
Publication date: 1999-03-18
Also published as: EP1027938A4; EP1027938A1; CA2303027A1

Abstract

A method of forming a multilayered coating film by applying a cationic electrodeposition coating material containing a blocked polyisocyanate compound as a cross-linking agent, applying a water-based intercoating material containing a blocked polyisocyanate compound as a cross-linking agent on the electrodeposited coating film to form an intercoating film without curing the electrodeposited coating film, and heating the two coating films to simultaneously cure both, characterized by regulating the coating materials so that the cross-linking curing reaction of the electrodeposited coating film begins earlier than that of the intercoating film. This method can give a multilayered coating film improved in finish appearance (smothness, gloss, etc.), interlaminar adhesion between the coating films, etc.

Description

Specification

Multilayer coating method

Technical field

The present invention is formed in a method of forming a multilayer coating film by coating a cationic electrodeposition coating material and an aqueous intermediate coating material with an “et-on-et” coating, and then heating and cross-linking and curing both coating films together. Finish appearance of multi-layer coatings (smoothness, gloss, etc.) ゃ Improving the interlayer adhesion of both coatings.

Background art

Until now, automotive exterior panels and the like have been coated with a cationic electrodeposition paint using a block polyisocyanate compound as a cross-linking agent and an aqueous intermediate coating containing polyester resin and amino resin, etc. It is already known to heat and cure both coatings together to form a multilayer coating.

However, this multi-layer coating film has insufficient finished appearance such as smoothness and luster, and it has been difficult to eliminate this defect even by applying a top coat. In addition, there is a problem in that if pebbles or the like that are flipped up during traveling hits, chipping peeling (peeling) easily occurs between the layers of the two coating films.

An object of the present invention is to solve the above-mentioned problems in a multilayer coating film composed of a cationic electrodeposition coating film and an aqueous intermediate coating film, and to provide a method for forming a multilayer coating film having excellent finished appearance and interlayer adhesion. To provide. The purpose of this study was to use a block polyisocyanate compound as a cross-linking agent for both cationic electrodeposition coatings and aqueous intermediate coatings, and to cross-link and cure electrodeposition coatings. It can be achieved by adjusting the reaction so that it starts earlier than the intermediate coating film. As a result, the finished appearance of the multilayer coating film (smoothness, gloss, etc.) Are found to be improved, and the present invention

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Disclosure of the invention

The present invention relates to a method of applying a cationic electrodeposition coating composition (A) containing a block polyisocyanate compound as a cross-linking agent and curing the formed electrodeposition coating film without curing the electrodeposition coating film. An aqueous intermediate coating (B) containing a polyisocyanate compound as a crosslinking agent is applied to form an intermediate coating, and then heated to cure both coatings together to form a multilayer coating. A method for forming a multilayer coating film, characterized in that the crosslinking and curing reaction of the electrodeposition coating film is adjusted to start earlier than the crosslinking and curing reaction of the intermediate coating film. In the present specification, the measurement of the time of the initiation of crosslinking and curing of the coating film of the cationic electrodeposition coating material (A) and the aqueous intermediate coating material (B) is performed using a pendulum-type viscoelasticity measuring device (manufactured by Toyo Ball Douin, Leo Vibron DDV-OPA type) This is performed using In concrete terms, the weight 2 2 g, using a pendulum inertia Mome down bets 8 5 0 g · cm ^2, thickness 3 0 / painted on the steel sheet so as to zm uncured film after curing The pendulum is placed on a plate and heated at a predetermined temperature (for example, 140 to 180 ° C) for crosslinking and curing the coating film while vibrating the pendulum, and the value of the logarithmic decay rate of the pendulum is applied. The time when the temperature begins to rise is referred to as the “crosslinking and curing start time”. The time required from the start of heating to the time of the start of crosslinking and curing is referred to as “curing start time”. The shorter the time, the faster the crosslinking and curing reaction starts. The comparison of the timing of cross-linking curing of both coatings is based on the results measured at the same temperature. Embodiment of the Invention

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

Cationic electrodeposition paint (A):

The cationic electrodeposition paint (A) used in the method of the present invention contains a block poly isocyanate compound as a crosslinking agent, and preferably has a base resin (A-1) having a hydroxyl group and a cationic group. It is a cationic electrodeposition coating composition containing a block poly isocyanate compound (A-2). In the base resin (A-1), the hydroxyl group participates in a crosslinking reaction with the block polyisocynate compound, and the cationic group contributes to form a stable aqueous dispersion. Examples of (A-1) include the following.

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

(ii) Polycondensates of polycarboxylic acids and polyamines (see US Pat. No. 2,450,940) which are protonated with acids.

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

(iv) A copolymer of an acrylic or vinyl monomer containing a hydroxyl group and an amino group, which is protonated with an acid (Japanese Patent Publication No. 45-12395, Japanese Patent Publication No. 45-1-1) See Japanese Patent Application Publication No. 23996.

(V) A product obtained by converting an adduct of a polycarboxylic acid resin and an alkyleneimine into a proton with an acid (see US Pat. No. 3,430,888).

Specific examples and production methods of these cationic resins are described in, for example, JP-B-45-12395, JP-B-45-123396, and JP-B-49-123. No. 087, U.S. Pat.No. 2,450,940, Described in U.S. Pat. No. 3,403,088, U.S. Pat. No. 3,891,5 29, U.S. Pat. No. 3,963,666 Therefore, these descriptions will be replaced with detailed explanations here.

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

The polyepoxide resin is a low molecular weight or high molecular weight compound having two or more epoxy groups in one molecule, and is at least 200, preferably 400 to 400, more preferably 800. Those having a number average molecular weight in the range of 2,000 to 2,000 are suitable. As such a polyepoxide resin, those known per se can be used, for example, a polyphenol compound which can be produced by reacting a polyphenol compound with epichlorohydrin in the presence of an alcohol. Of polyglycidyl ethers. Examples of the polyphenol compounds that can be used here include bis (4-hydroxyphenyl) 1-2,2-propane, 4,4'-dihydroxybenzobenzophenone, and bis (4-hydroxyphenyl). ) 1, 1-ethane, bis-1-(4-hydroxyphenyl) 1-1-isobutane, bis (4-hydroxy-tert-butyl-phenyl)-2,2-propane, bis (2-hydroxybutyl) methane, 1,5-dihydroxynaphthalene, bis (2,4dihydroxyphenyl) methane, tetra (4-hydroxyphenyl) 1-1,1,2,2-ethane, 4,4-dihydroxydiphenylether, 4, 4'—dihydroxydiphenylsulfone, phenol novolak, cresol novola, knock, etc. I can do it.

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 about 800 to about 200, And a polyglycidyl ether of a polyphenol compound having an epoxy equivalent of 190 to 200, preferably 40 to 100. This includes those partially reacted with polyols, polyether polyols, polyester polyols, polyamide amines, polycarboxylic acids, polyisocyanate compounds, etc., as well as ε-force products. Those obtained by graft polymerization of acrylonitrile and acrylic monomers may also be used. The reaction product (i) between the polyepoxy resin and the cationizing agent can be obtained by reacting most or all of the epoxy groups of the polyepoxide resin with the cationizing agent.

As the cationizing agent, for example, an amine compound such as a primary amine, a secondary amine, a tertiary amine, or a polyamine can be used. To form a cationic group-containing resin by introducing a cationic group such as a secondary amino group, a tertiary amino group, or a quaternary ammonium base into the polyepoxy resin. it can.

Examples of the primary amine compound include methylamine, ethylamine, n-propylamine, isopropylamine, monoethanolamine, n-propanolamine, and isopropanolamine. Examples of the secondary amine compound include getylamine, diethanolamine, di-n-propanolamine, diisopropanolamine, N-methylethanolamine, N-ethylethanolamine, and the like. But Examples of the tertiary amine compound include triethylamine, triethanolamine, N, N-dimethylethanolamine, N-methylethanolamine, N, N-ethylethylamine, and N-ethylethylamine. Examples of polyamines include ethylenediamine, diethylenetriamine, hydroxyxethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine, and dimethylamine. Noethylamine, dimethylaminopropylamine, and the like.

Other than these amine compounds, a basic compound such as ammonia, hydroxyamine, hydrazine, hydroxyshetyl hydrazine, N-hydroxyshetyl imidazoline is used as a cationizing agent, which is used as an epoxy group of the polyepoxy resin. The basic group formed by the reaction may be converted to a cationic group by protonation with an acid. Preferred acids that can be used are water-soluble organic carboxylic acids such as formic acid, acetic acid, glycolic acid, and lactic acid.

Examples of the hydroxyl group contained in these cationic group-containing resins include, for example, a reaction with alkanolamine as the above-mentioned cationizing agent, and ring opening of force prolactone which may be introduced into a polyepoxide resin. Primary hydroxyl group introduced by reaction with a product or a polyol; a secondary hydroxyl group originally contained in an epoxy resin; and the like. Of these, primary hydroxyl groups introduced by reaction with alkanolamine are preferred because of their excellent cross-linking reactivity with block polyisocyanate compounds (cross-linking agents). As such an alkanolamine, those exemplified above as the cationizing agent are preferable.

The content of the hydroxyl group in the base resin (A-1) is 20 equivalents in terms of hydroxyl equivalent. 5,000, especially 60 to 3,000, more preferably 100 to 1,000 mg KOHZg, and particularly, the primary hydroxyl group equivalent is in the range of 200 to 1,000 mg KOH / g. Is preferred. Further, the content of the cationic group is preferably at least the minimum necessary for stably dispersing the base resin in water, and is generally 3 to 3 in terms of KOH (mgZg solid content) (amine value). It is preferably in the range of 200, especially 5 to 150, more particularly 10 to 80.

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

On the other hand, the block polyisocyanate compound (A-2) used as a cross-linking agent in the cationic electrodeposition coating (A) is a compound in which substantially all of the isocyanate groups of the polyisocyanate compound are volatile active hydrogen compounds. (Blocking agent) reacts and blocks it and renders it inactive at room temperature. When heated to a predetermined temperature or higher, the blocking agent dissociates and the original isocyanate group is regenerated, and the base resin (A — Involves in crosslinking reaction with 1).

Polyisocyanate compounds are aliphatic, alicyclic, and aromatic compounds having two or more free isocyanate groups in one molecule, such as hexamethylene diisocyanate and trimethylene diisocyanate. Aliphatic diisocyanates such as sodium, tetramethylene diisocyanate, dimer monoacid diisocyanate, and lysine diisocyanate; isophorone diisocyanate, methylene bis (cyclohexyl isocyanate), methylcyclohexyl Alicyclic diisocyanates such as sandiisocyanate, cyclohexanediisocyanate, and cyclopentanediisocyanate; xylylene diisocyanate, tridiethylene isocyanate, diphenyl methane diisocyanate Aromatic diisocyanates such as polyisocyanate, naphthalene diisocyanate, and toluidine diisocyanate; and the like, such as perethane-modified adducts, buret-type adducts, and isocyanuric ring-type adducts of these polyisocyanate compounds. .

Examples of the blocking agent used for temporary blocking of the isocyanate group of the polyisocyanate compound include phenol, cresol, xylenol, p-ethylphenol, o-isopropylphenol, p-isopropylphenol — Tert —butylphenol, p-tert-octylpheno

-Phenol, thymol, p-naphthol, p-ditropanol, p-phenol-based blocking agents such as chlorophenol; methanol, ethanol, propanol, butanol, amyl alcohol, ethylene glycol, ethylene glycol monomethyl ether , Ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether, methyl sorb, butyl sorb, methyl carbitol, benzyl alcohol, phenyl sorb, furfuryla Alcohol-based blocking agents such as norecol, cyclohexanol, methyl glycolate, butyl glycolate, diacetone alcohol, methyl lactate, and ethyl lactate; Active methylene blocking agents such as tilacetone, dimethyl malonate, getyl malonate, and ethyl acetate; mercaptans such as butylmercaptan, hexylmethylcarbbutane, thiophenol, methylthiophenol, methylthiophenol, tert-dodecylmercaptan Blocking agents; acid amide blocking agents such as acetoanilide, acetonicide, amide amide and benzamide; imidic succinate, maleic acid, etc. Imid-based blocking agents; diphenylamine, xylidine, dibutylamine, phenylnaphthylamine, aniline, carbazole and other amine-based blocking agents; imidazole, 2-ethylimidazole, etc. Imidazole blocking agents; urea blocking agents such as urea, thiourea and ethylene urea; carbamate blocking agents such as phenyl N-phenylcarbamate and 2-oxazolidone; ethyleneimine, propyleneimidone Blocking agents such as imamidoxoxime, formaldoxime, acetoaldoxime, acetoxime, methylethylketoxime, diacetyl monooxime, cyclohexanone oxime, etc .; sodium bisulfite, potassium bisulfite Sulfite block such as Agents: ε-caprolactam, 5-valerolactam, abutyrolactam, β-prop. Lactam blocking agents such as piolactam;

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

In the cationic electrodeposition coating (Α), the mixing ratio of the base resin (A-1) and the block polysocyanate compound (Α-2) is not particularly limited, but is generally based on the total solid weight of both components. Thus, the base resin (Α-1) is 40 to 90%, particularly 50 to 80%, and the block polyisocyanate compound (Α-2) is 60 to 10%, particularly 50 to 20.0%. It is preferably within the range of 0%.

Cationic electrodeposition paint (Α) is used to remove the cationic groups in the base resin (Α-1). It can be prepared by neutralizing with acidic compounds such as acetic acid, formic acid, lactic acid, and phosphoric acid, and dispersing and mixing in water together with the block polyisocynate compound.The pH of the aqueous dispersion is 3 to 9, especially 5 to 5. It is preferably within the range of 7, and the resin solid content concentration is suitably within the range of 5 to 30% by weight.

The cationic electrodeposition paint (A) may include, if necessary, a hydroxide of a metal selected from aluminum, nickel, zinc, stotium, zirconium, molybdenum, tin, antimony, lanthanum, tungsten, etc. A curing catalyst having an anti-oxidation property such as an oxide, an organic acid salt, or an inorganic acid salt; an extender pigment; a coloring pigment; an anti-pigment pigment;

Furthermore, in order to accelerate the cross-linking reaction between the base resin (A-1) and the block polyisocyanate compound (A-12), tin octoate, dibutyltin dilaurate, a manganese-containing compound, and a cobalt-containing compound are used. Compounds, Lead-containing compounds, Zirconium octarate, Zinc octoate, Dibutyltin-bis-bisphenylphenylene, Dibutyltin-S, S, S-Dibutyldithiol-one-bonate, Triphenylantimony dichloride A curing catalyst such as dibutyltin maleate, dibutyltin diacetate, dibutyltin dilaurethmercaptide-triethylenediamine, and dimethyltin dichloride can be blended. The compounding amount is generally 0.1 to 10 parts by weight, particularly 0.5 to 2 parts by weight, per 100 parts by weight of the total of the base resin (A-1) and the block polyisocyanate compound (A-2). Within the range of parts is suitable. In particular, in the present invention, a bismuth-containing compound (A-3) is further used as the cationic electrodeposition coating material (A), in addition to the aforementioned base resin (A-1) and block polyisocyanate compound (A-2). It is desirable to use the lead-free cationic electrodeposition paint contained. As a result, environmental health It is possible to form an electrodeposition coating film having excellent anti-corrosion properties and curability without using a lead compound which is a problem. Examples of bismuth-containing compounds that can be added to the cationic electrodeposition coating (A) include bismuth oxides, hydroxides, salts with inorganic or organic acids, and include, for example, bismuth hydroxide, bismuth trioxide, and nitric acid. Bismuth, bismuth benzoate, bismuth citrate, bismuth oxycarbonate, bismuth gaylate and the like are mentioned, and among them, bismuth hydroxide is preferred. These bismuth-containing compounds are generally used in an amount of 0.1 to 10 parts by weight, especially 0.1 part by weight, per 100 parts by weight of the total of the base resin (A-1) and the block polyisocyanate compound (A-2). It can be blended in the range of 15 to 7.5 parts by weight, more particularly 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

H

I

R ¹ -C + CH ₂ ) rC00H

During 0- R ² formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms; R ² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; n is 0 or 1, in An aliphatic carboxylic acid-modified bismuth compound obtained by mixing and dispersing the aliphatic carboxylic acid shown in an aqueous medium in the presence of a dispersant, if necessary, disperses uniformly and stably in a water-insoluble form. Bismuth aqueous dispersion paste can be used. The water-insoluble aliphatic carboxylic acids described above that can be blended with the cationic electrodeposition paint (A) A water-dispersed paste containing a boronic acid-modified bismuth compound (hereinafter referred to as an aqueous dispersion paste of bismuth or simply a water-dispersed paste) is a method in which a water-insoluble bismuth compound and an aliphatic carboxylic acid represented by the above formula are dissolved in an aqueous medium. And by mixing and dispersing in the presence of a dispersant. At that time, the aliphatic carboxylic acid is used in such a ratio that the water-insoluble aliphatic carboxylic acid-modified bismuth compound is mainly produced. Thus, a water-dispersed paste of bismuth in which the aliphatic carboxylic acid-modified bismuth compound to be formed is uniformly and stably dispersed in a water-insoluble state is obtained, and this water-dispersed paste is mixed with the electrodeposition paint. As a result, the curability and corrosion resistance can be remarkably improved without impairing the throwing power and finish of the electrodeposition coating film.

The content of the water-soluble bismuth compound in the supernatant obtained by subjecting the aqueous dispersion of bismuth to centrifugal separation (at 1200 rpm for 30 minutes) is calculated as the weight of the metal bismuth, The total amount of the water-insoluble bismuth compound used in the above is preferably about 40% or less, particularly about 30% or less, and more preferably about 20% or less.

Examples of the water-insoluble bismuth compound used in the preparation of such an aqueous dispersion paste of bismuth include, for example, bismuth oxide, bismuth hydroxide, basic bismuth carbonate, and the like having a solubility in water at 20 ° C of 0.0. Bismuth compounds having a weight of 0.1 g or less are preferred, with bismuth oxide being particularly preferred.

The aliphatic carboxylic acid represented by the above formula is used for the purpose of converting the water-insoluble bismuth compound into a sufficiently uniform dispersion in an aqueous medium, and specifically, for example, Droxyacetic acid, lactic acid- Aliphatic hydroxycarboxylic acids such as hydroxypropionic acid; and 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. The aliphatic carboxylic acid may be used in combination with another organic acid, for example, acetic acid.

The amount of the above-mentioned aliphatic cationic acid to be 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 kind of the aliphatic carboxylic acid used. In the case of monolactic 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.In the case of methoxyacetic acid, the molar ratio is based on the amount of bismuth in the water-insoluble bismuth compound. The ratio can be generally in the range of 0.25 to 2.5, preferably 0.5 to 1.3.

As the dispersant, a cationic dispersing resin or a surfactant known per se in the field of cationic electrodeposition coatings can be used without any limitation. Examples of the cationic dispersing resin include those for electrodeposition coating described below. The base resin can be appropriately selected and used from those listed. For example, resins such as tertiary amine type, quaternary ammonium salt type, and tertiary sulfonium salt type are exemplified. Examples of the surfactant include nonionic surfactants such as acetylene glycol-based, polyethylene glycol-based, and polyhydric alcohol-based surfactants having an HLB in the range of 3 to 18, preferably 5 to 15. .

The amount of the dispersant used can vary depending on the type thereof, the amount of the water-insoluble bismuth compound used, and the like. It is preferably in the range of 1 to 150 parts by weight, particularly 10 to 100 parts by weight based on 0 parts by weight.

The production of the aqueous dispersion paste of bismuth using the water-insoluble bismuth compound, the aliphatic carboxylic acid and the dispersant described above can be performed in the same manner as the production of the pigment paste used in the cationic electrodeposition paint. Specifically, for example, an aliphatic carboxylic acid and a water-insoluble bismuth compound are added to water containing a dispersant, and the mixture is dispersed in a dispersing mixer such as a ball mill or a sand mill. Can be manufactured. The resulting water-dispersed pastes can generally have a solids concentration of 10 to 70% by weight, preferably 30 to 60% by weight.

Further, the aqueous dispersion paste of bismuth may be prepared as a pigment paste by adding pigments used in ordinary cationic electrodeposition paints. Specifically, for example, a pigment paste is prepared by blending a pigment dispersing resin, a neutralizing agent, and pigments, and performing a dispersion treatment in a dispersion mixer such as a ball mill or a sand mill, and then dispersing the bismuth in water. 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 above-mentioned pigment-dispersing resin, for example, a conventionally known pigment-dispersing resin can be used without any limitation. For example, a cation-type dispersing resin similar to that used for preparing the bismuth-dispersed paste can be used.

As the above-mentioned pigments, any pigment can be used without particular limitation as long as it is a pigment generally used in electrodeposition paints. For example, coloring pigments such as titanium oxide, carbon black, and red iron; , Talc, calcium carbonate, silica and other extenders; aluminum limolybdate, Waterproof pigments such as aluminum tripolyphosphate are mentioned.

An aqueous dispersion paste of bismuth or a pigment paste containing the aqueous dispersion paste can be blended with the binder-resin component of the cationic electrodeposition paint. In general, the bismuth dispersion base has a bismuth metal content of 0.1 per 100 parts by weight of the base resin (A-1) and the block polyisocyanate compound (A-2) in total. To 10 parts by weight, preferably 0.3 to 7 parts by weight, and more preferably 0.5 to 5 parts by weight.

In the present invention, the cross-linking and curing reaction of the cationic electrodeposition coating (A) coating film needs to start earlier than the cross-linking and curing reaction of the intermediate coating (B) coating film located in the upper layer. For example, it is preferable to set the curing temperature of the coating film of the cationic electrodeposition coating material (A) 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 5 to 20 ° C, particularly preferably in the range of 5 to 15 ° C. If the onset of the cross-linking curing reaction of the cationic electrodeposition coating (A) is later than that of the intermediate coating, the finished appearance of the multi-layer coating (smoothness, gloss, etc.) is generally observed. It becomes difficult to improve such.

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

Regarding the cationic electrodeposition paint (A) coating film, the “curing start time” from the start of heating to the start of cross-linking curing is suitably between 5 and 15 minutes in the coating process.

For the application of the cationic electrodeposition paint (A), for example, the object to be coated is a power source, carbon The plate is preferably used as an anode, with a bath temperature of 20 to 35 ° C, a voltage of 100 to 400 V, a current density of 0.01 to 5 A, and an energization time of 1 to 10 minutes. The coating film thickness can be about 10 to about a cured film. Examples of the object to be coated include a substrate having a conductive metal surface, in particular, an automobile body, an electric product and the like.

In the method of the present invention, after the cationic electrodeposition paint (A) is applied, the aqueous intermediate coating containing a block polyisocyanate compound as a cross-linking agent is applied to the coated surface without curing the coated film. Paint (B) is applied.

Waterborne intermediate paint (B):

The aqueous intermediate coating composition (B) is an aqueous coating composition containing a block polyisocyanate compound as a crosslinking agent, and is preferably a base resin having a functional group capable of undergoing a crosslinking reaction with an isocyanate group such as a hydroxyl group. This is a water-based paint containing (B-1) and a block polyisocyanate compound (B-2), which are mixed and dispersed in water.

Examples of the base resin (B-1) having a functional group capable of undergoing a crosslinking reaction with an isocyanate group such as a hydroxyl group in the aqueous intermediate coating material (B) include, for example, a polyester resin having two or more hydroxyl groups in one molecule. Acrylic resins are particularly preferred.

The hydroxyl group-containing polyester resin can be produced by subjecting a polybasic acid and a polyhydric alcohol to an esterification reaction by a method known per se, and has a number average molecular weight of 1,000 to 50,000, particularly 2,000 to 2,000, and a hydroxyl group. The value is preferably from 20 to 200 mg KOHZg, especially from 50 to 150 mg K〇H / g, and the acid value is preferably not more than 10 OmgKOHZg, especially from 10 to 70 mgK0HZg. A 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, azellanic acid, sebacic acid, tetrahydrophthalic acid, and hexakis Examples include phthalic acid, maleic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid and anhydrides thereof.

Polyhydric alcohols are compounds having two or more hydroxyl groups in one molecule, such as ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, Examples include hydrogenated bisphenol A, triethyleneglycol, glycerin, trimethylol-l-ethane, trimethyl-l-luppan, and pentaerythritol. A hydroxyl group-containing acrylic resin can be produced by copolymerizing a hydroxyl group-containing polymerizable monomer and a polymerizable monomer component containing an acryl-based monomer under ordinary conditions. The number average molecular weight is 1000 to 5000, especially 2000 to 20000, the hydroxyl value is 20 to 200 mg KOH / g, especially 50 to 150 mg KOH / g, and the acid value is 1 O Omg KOHZg or less, especially 20 to 7 Omg KOHZg. preferable. 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. Examples thereof include hydroxyxethyl (meta) acrylate, hydroxypropyl (meta). ) Monoesters of glycols having 2 to 20 carbon atoms and (meth) acrylic acid, such as acrylates and hydroxybutyl (meth) acrylates. Examples of the acryl monomer include monoesters of (meth) acrylic acid and a monohydric alcohol having 1 to 22 carbon atoms, such as methyl acrylate and methyl acrylate. Metal acrylate, ethyl acrylate, ethyl methacrylate, propanol acrylate, propyl methacrylate, butyl acrylate, butyno methacrylate, hexyl acrylate, hexyl methacrylate Relate, octyl acrylate, octyl methacrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, etc. .

In the production of the hydroxyl-containing acrylic resin, other polymerizable monomers other than these hydroxyl-containing polymerizable monomers and acryl-based monomers can be used in combination.

Other polymerizable monomers include, for example, C ₂ of (meta) allylic acid such as methoxybutyl acrylate, methoxybutyl methacrylate, methoxethyl acrylate, methoxyl ethyl methacrylate, and the like. -C _{1 8} § Turkey alkoxyalkyl ester; N, N-Jimechirua Mi Noechiruaku Li rate, N, N-Jimechirua Mi Noechirume Tak Li rate, N, N-Jechiru A Mi Noechiruaku Li rate, N, N-Jechirua Minoethyl methyl acrylate, N-t—Butylaminoethyl acrylate, N—t—Butylaminoethyl methacrylate, N, N-Dimethylaminopropyl acrylate, N, N-Dimethylaminopropyl methacrylate Amino (meta) acrylic monomers such as acrylates; acrylamide, methacrylic N-methylacrylamide, N-methylacrylamide, N-ethylacrylamide, N-ethylacrylamide, N-butylacrylamide, N-butylacrylamide, N-butylmethacrylamide (Meth) acrylamide monomers such as N, N-dimethylacrylamide and N-dimethylmethylacrylamide; acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaric acid, mesaconic acid You And compounds having at least one carboxyl group and at least one polymerizable unsaturated bond in one molecule such as anhydrides and half-esterified products thereof; glycidyl group-containing monomers such as glycidyl acrylate and glycidyl methacrylate Styrene, α-methylstyrene, vinyl toluene, acrylonitrile, vinyl acetate, vinyl chloride, etc.

The block polyisocyanate compound (Β-2) is a cross-linking agent for the base resin (Β-1), and has been specifically described as a cross-linking agent in the cationic electrodeposition paint (Α). One or more compounds selected from those exemplified as the block polyisocyanate compound (II-2) can be used. In the water-based intermediate coating (Β), the mixing ratio of the base resin (Β-1) and the block poly isocyanate compound (Β-2) is not particularly limited, but based on the total solid weight of both components. The base resin (Β-1) may be in the range of 40 to 90%, especially 50 to 80%, and the block polyisocyanate compound (Β-2) may be in the range of 60 to 10%, especially 50 to 20%. preferable. The aqueous intermediate coating (Β) is composed of a base resin (体 -1) and a block polyisocyanate compound (Β-2), and a curing catalyst, extender, It may contain a coloring pigment, a surface conditioner and the like. As the curing catalyst, one or more selected from those exemplified for the cationic electrodeposition coating (塗料) can be used. The compounding amounts thereof are based on the base resin (Β-1) and the block polyisocynate. It is generally suitable that the amount is in the range of 0.1 to 10 parts by weight, especially 0.5 to 2 parts by weight, per 100 parts by weight of the compound (Β-2).

In the present invention, the timing of the start of crosslinking and curing of the coating of the aqueous intermediate coating (中) is determined based on the timing of starting the crosslinking of the coating of the cationic electrodeposition coating (Α) located thereunder. More specifically, the cross-linking and curing reaction of the cationic electrodeposition paint (A) is started 0.5 to 10 minutes, especially 5 to 10 minutes later than the start of the cross-linking and curing reaction. Is preferred. In other words, the “curing start time” required from the start of heating of the coating film of the aqueous intermediate coating material (B) to the start of cross-linking curing is the “curing start time” of the coating film of the cationic electrodeposition paint (A). The difference is between 0.5 and 10 minutes, especially between 5 and 10 minutes. The timing of the start of crosslinking and curing of the coating film of the aqueous intermediate coating composition (B) can be easily controlled by, for example, appropriately selecting the type and the amount of the polyisocyanate compound, the blocking agent, the curing catalyst, and the like. The onset of the cross-linking and curing reaction of the coating of the aqueous intermediate coating (B) is later than the onset of the cross-linking and curing of the coating of the cationic electrodeposition coating (A). In 5.5 to 20 minutes, especially between 10 and 15 minutes is suitable.

The aqueous intermediate coating (B) is obtained by uniformly mixing and dispersing the base resin (B-1) and the block polyisocyanate compound (B-2) and optionally other additives in water. It is preferable that the solid content concentration is adjusted in the range of 20 to 70% by weight.

In the method of the present invention, the cationic electrodeposition coating (A) is applied and, if necessary, dried at a temperature of 120 ° C. or less without curing, and then the aqueous intermediate coating (B) is coated on the electrodeposition coating. After coating, both films are heated and crosslinked and cured together.

The aqueous intermediate coating (B) is applied by electrostatic coating, airless spraying, air spraying, etc., and its film thickness is about 5 to about 80 m, especially about 15 to about 35 m, based on the cured coating. A range of 〃 m is suitable. In addition, both cation electrodeposition coating (A) coating and waterborne intermediate coating (B) coating were applied. The heating temperature for curing the bridge is equal to or higher than the dissociation temperature of the block polyisocyanate compound contained in the coating film, but is usually about 130 to about 180 ° C. The coating film can be hardened by baking for a minute.

If necessary, a top coat such as a solid paint, a metallic paint, and a clear paint is coated on the multilayer coating film formed by the method of the present invention by a known method, for example, 1 coat 1 coat. Painted by wake-up method (1C1B), 2-coat 1-bake method (2C1B), 2-coat 2-bake method (2C2B), 3-coat 1-bake method (3C1B) can do.

Example

Hereinafter, the method of the present invention will be described more specifically with reference to Examples and Comparative Examples. All parts and percentages are based on weight.

In the examples and comparative examples, the measurement of the cross-linking start time of the electrodeposited coating film and the aqueous intermediate coating film was performed using a pendulum type viscoelasticity meter (Toyo Baldwin, Leo Vibron DDV-OPA type).

1. Sample preparation

1) Polyester resin (1):

756 parts of neopentyl glycol, 109 parts of trimethylolpropane, 370 parts of hexahydrophthalic acid, 292 parts of adipic acid and 398 parts of isophthalic acid are placed in a reaction vessel and reacted at 220 ° C for 6 hours. Toluic acid (45 parts) was added and reacted at 170 ° C for 30 minutes to obtain a polyester resin having a number average molecular weight of about 8000, an acid value of 20 mgKOHZg, and a hydroxyl value of 95 mgKOH / g.

2) Acrylic resin (1): 210 parts of styrene, 294 parts of n-butyl methacrylate, 253 parts of hydroxybutyl acrylate, 200 parts of 2-ethylhexyl methacrylate, and 30 parts of acrylic acid are placed in a reaction vessel and placed at 5 ° C at 120 ° C. After reacting for an hour, an acryl resin having a number average molecular weight of about 20,000, an acid value of 25 mg KOHZg, and a hydroxyl value of 95 mg KOHZg was obtained.

3) Cationic electrodeposition paint (1):

Bisphenol A type epoxy resin with epoxy equivalent of 630 (Epico 1002 (trade name, manufactured by Shell Chemical Co., Ltd.)) 1,260 parts are dissolved in 450 parts of butyl ether solvent, 132 parts of ρ-nonylphenol and 105 parts of N-methylethanolamine Then, the mixture was heated to 140 ° C. and reacted at the same temperature to obtain an additional epoxy resin having a solid content of 77% and an amine value of 52. To 130 parts of this resin were added 30 parts of block polyisocyanate compound (curing agent) and 1.3 parts of polypropylene glycol (number average molecular weight 4000), and then 2.1 parts of acetic acid was added to make it water-soluble. 20% aqueous lead acetate solution 6.5 parts are added, then deionized water is gradually added and dispersed to obtain an emulsion having a solid content of 30%.

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

Next, the above-mentioned 30% solid content emulsion and the 55% solid content pigment paste were mixed, and diluted with deionized water to obtain an electrodeposition bath having a 19% solid content. 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 equivalent of 425 to 2-ethylhexyl alcohol monoether of ethylene glycol. (Blocking agent).

4) Cationic electrodeposition paint (2):

In the above cationic electrodeposition paint (1), except that 6.5 parts of a 20% aqueous lead acetate solution was omitted, and 3.0 parts of basic lead gayate of the pigment paste was replaced with 3.0 parts of bismuth hydroxide Were adjusted in the same manner as in the cationic electrodeposition paint (1).

5) Cationic electrodeposition paint (3):

Except that 6.5 parts of a 20% aqueous lead acetate solution in the above cationic electrodeposition paint (1) and 3.0 parts of basic lead gaite in the pigment paste were replaced with 1 part of bismuth dispersed paste (as the amount of metallic bismuth) Were all adjusted in the same manner as the cationic electrodeposition paint (1).

Here, the “dispersion paste of bismuth” was prepared as follows.

In a container, 133.3 parts of an epoxy-based tertiary amine pigment-dispersing resin having a solid content of 75% (amin value: 100) and 81.1 parts of methoxyacetic acid were blended and stirred to a uniform level. Thereafter, 233.5 parts of deionized water was added dropwise with vigorous stirring, and 111.5 parts of bismuth oxide was further added and mixed and dispersed with a ball mill for 20 hours to obtain a bismuth dispersion paste having a solid content of 50%. Get ο

6) Waterborne intermediate coating (1): Polyester resin (l) 1000 parts (as solid content, the same applies hereinafter), dimethylaminoethanol (Note 1) 40 parts, aliphatic hexafunctional block polyisocyanate compound (Note 2) 410 parts, titanium white pigment (Note 3) ) 1400 parts and carbon black (Note 4) 20 parts were mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating (1).

(Note 1) Dimethylaminoethanol: Nippon Emulsifier Co., Ltd., trade name,

"Amino alcohol 2Ma bs"

(Note 2) Aliphatic hexafunctional block polyisocyanate compound: A hexameric methylene diisocyanate trimer is blocked with methylethylketoxime.

(Note 3) Titanium white pigment: "Tika J R 806J (manufactured by Tika, trade name)" (Note 4) Riki Bon Black: "Mitsubishi Riki Bon Black M-100"

(Mitsubishi Chemical Corporation, trade name)

7) Waterborne intermediate coating (2):

Polyester resin (1) 1000 parts, Dimethylaminoethanol (Note 1) 40 parts, Aliphatic trifunctional block polyisocyanate compound (Note 5) 410 parts, Titanium white pigment (Note 3) 1400 parts And 20 parts of carbon black (Note 4) were mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating (2).

(Note 5) Aliphatic trifunctional block polyisocyanate compound: Hexamethylene diisocyanate trimer was blocked with methylethylketoxime.

8) Waterborne intermediate coating (3):

Acrylic resin (1) 1000 parts, dimethylaminoethanol (Note 1) Mix 40 parts, aliphatic trifunctional block polyisocyanate compound (Note 5) 410 parts, titanium white pigment (Note 3) 1400 parts and carbon black (Note 4) 20 parts with 1800 parts of deionized water It was dispersed to obtain an aqueous intermediate coating (3).

9) Waterborne intermediate paint (4) (for comparison):

Polyester resin (2) 1 00 parts, dimethylaminoethanol (Note 1) 40 parts, aliphatic trifunctional block polyisocyanate compound (Note 6) 410 parts, Titanium white pigment (Note 3) 1400 parts 20 parts were mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating (2).

(Note 6) Aliphatic trifunctional block polyisocyanate compound: A hexamethylene diisocyanate trimer was blocked with ethyl malonate.

10) Waterborne intermediate coating (5) (for comparison):

Polyester resin (1) 1000 parts, Dimethylaminoethanol (Note 1) 40 parts, Melamine resin (Note 7) 300 parts, Titanium white pigment (Note 3) 1 400 parts and Rikibon black (Note 4) 20 parts Was mixed and dispersed in 1800 parts of deionized water to obtain an aqueous intermediate coating composition (5).

(Note 7) Melamine resin: Cymel 303 (Mitsui Cyanamid Co., Ltd., trade name, methanol-modified melamine resin)

2. Examples 1 to 5 and Comparative Example:! ~ 2

Cathode dipped steel sheet treated with zinc phosphate is immersed in a cathodic electrodeposition paint (1) to (3) as a cathode, and electrodeposited at 30 ° C and 200 V for 3 minutes. 25 / m), dried at 100 ° C for 10 minutes, and then Each of the paints (1) to (5) was applied by air spray (thickness of the cured film is 30 to 35 ^ m), and then heated at 170 ° C for 30 minutes to crosslink and cure both films.

A performance test was performed on the multilayer coating film thus obtained. The test results are shown in Table 1.

The test method is as follows.

Gloss: 60 degree specular reflectance.

Sharpness: The result of measurement with an image clarity measuring device (IMAGE CLARITY METER, manufactured by Suga Test Instruments Co., Ltd.). The numbers in the table are ICM values, and take values in the range of 0 to 100. The larger the value, the better the sharpness (image clarity). If the ICM value is 80 or more, the sharpness is extremely good.

Chipping resistance: Using a Q-G-R gravelometer (Q Panel Co., Ltd.), 100 g of crushed stone with a diameter of 15 to 20 mm is applied with an air pressure of about 4 kg / c. m ^2, and the spraying with spray angle 9 0 ° to the coated surface in one 2 0 ° C. Thereafter, the state of the coated surface was visually evaluated. 〇 shows slight scratches on the intermediate coated surface but no peeling of the electrodeposited film. △ shows slight impact scratches on the intermediate coated surface and slight peeling of the electrodeposited film. X indicates that many impact scratches were observed on the intermediate coated surface, and that the electrodeposition coating film was considerably peeled off.

Impact resistance: Using a Dupont-type impact tester, drop a weight of 500 g with a striker core of 1 inch and 2 inches with the coating surface facing upward. No drop occurs on the coating film. Cm).

Moisture resistance: The test plate was allowed to stand for 72 hours under the conditions of 50 ° C and a humidity of 95%, and the appearance and adhesion of the coating film were examined. Appearance evaluation: Δ indicates no abnormality, Δ indicates slight blistering, and X indicates slight blistering. Adhesion is performed using a taper test (a 1m x 1mm gobber, 100 pieces) tape peeling test.

Claims

The scope of the claims

1. A cation electrodeposition paint containing a block polyisocyanate compound as a cross-linking agent is applied, and the block electrodeposition coating film is formed on the electrodeposition coating film without curing the formed electrodeposition coating film. A method of applying an aqueous intermediate coating containing a compound as a crosslinking agent to form an intermediate coating film, and then heating to cure the both coating films together to form a multilayer coating film. A method for forming a multilayer coating film, characterized in that the cross-linking and curing reaction of the electrodeposition coating film is adjusted to start earlier than the crosslinking and curing reaction of the intermediate coating film.

2. The method for forming a multilayer coating film according to claim 1, wherein the curing temperature of the coating film of the cationic electrodeposition coating material is set lower than the curing temperature of the coating film of the intermediate coating material.

3. The method according to claim 1, wherein the temperature difference between the curing temperature of the coating film of the cationic electrodeposition paint and the curing temperature of the coating film of the intermediate coating is in the range of 5 to 20 ° C. Layer coating method.

4. The method according to claim 1, wherein the temperature difference between the curing temperature of the coating film of the cationic electrodeposition coating material and the curing temperature of the coating film of the intermediate coating material is within a range of 5 to 15 ° C. Layer coating method.

5. The method for forming a multilayer coating film according to claim 1, wherein the curing start time of the coating film of the cationic electrodeposition paint is between 5 and 15 minutes.

6. The method according to claim 1, wherein the cationic electrodeposition paint is a lead-free cationic electrodeposition paint further comprising a bismuth-containing compound.

7. The multi-layer coating film according to claim 6, wherein the bismuth-containing compound is selected from bismuth hydroxide, bismuth trioxide, bismuth nitrate, bismuth benzoate, bismuth citrate, bismuth oxycarbonate and bismuth silicate. Law.

8. The bismuth-containing compound is a water-insoluble bismuth compound and a compound represented by the following general formula:

H

R ¹ -C + CH ₂ > TrC00H

I

0-R ²

In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and n is 0 or 1,

A water-dispersed paste obtained by mixing and dispersing an aliphatic carboxylic acid represented by in the presence of a dispersant in an aqueous medium, wherein the aliphatic carboxylic acid-modified bismuth compound is in a water-insoluble state. 7. The method for forming a multilayer coating film according to claim 6, wherein the method is a water-dispersed paste existing in the above.

9. A method for forming a multilayer coating film in which the difference between the curing start time of the coating film of the Kathyon electrodeposition paint and the curing start time of the coating film of the intermediate coating is 0.5 to 10 minutes.

10. The method according to claim 1, wherein the heat curing is performed at a temperature of about 130 to about 180 ° C.

11. The method for forming a multilayer coating film according to claim 1, wherein a top coating material is further applied on the coating film of the intermediate coating material.

12. An article having a multilayer coating formed by the method according to claim 1.