JPH0829295B2 - Coating film formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention can form a coating film having a high degree of appearance, weather resistance and chipping resistance in a shortened process. In particular, the present invention relates to a coating film forming method suitable for coating automobile outer panels.

[Prior Art] Generally, the coating of metal materials such as automobile outer panels and home appliances is performed by the steps of first applying electrodeposition coating, baking the formed coating, and then applying intermediate coating and top coating. However, recently, from the viewpoint of energy saving, resource saving, and labor saving, studies are being made on the application of wet-on-wet coating, which eliminates the baking process during electrodeposition coating.

In this case, 2 to 10 is applied to the electrodeposition-coated film before baking and drying.
The water-based type is more preferable than the solvent type as the coating material to be coated on the upper portion because it contains about% of water. However, since most of the volatile components of water-based paints are water, they have the drawback that they tend to drip during painting and that pinholes tend to occur during baking, which is a problem in terms of coating workability compared to solvent-based paints. .

In order to solve the above problems, we will manage the temperature and humidity of the booth,
Although improvement measures from the aspect of process such as extension of setting zone and addition of preheat treatment have been proposed, workability comparable to that of solvent type paint has not been obtained yet.

Against this background, the solvent composition of the solvent-based paint to be subjected to wet-on-wet was adjusted, and 20% by weight of all the organic solvents in the solvent-based paint was replaced with a hydrophilic organic solvent capable of dissolving 5% by weight or more in water. A coating method using a paint has been developed by the present applicant (Japanese Patent Laid-Open No. 60-193568).

[Problems to be Solved by the Invention]

By using the above-mentioned special solvent type paint, it is possible to reduce defects such as wrinkles, cracks, curing distortion, lack of gloss, lack of image clarity, insufficient adhesion, dents and cissing that occur when using a normal solvent type paint. It becomes possible. Therefore, a high-performance coating film can be formed by a process that omits the baking step during electrodeposition coating.

However, in the case of this method, there are still insufficient surfaces to effectively eliminate the above-mentioned defect phenomenon, and especially for the purpose of coating automobile outer panels, which require the highest level of coating performance and coating film appearance. There was room for improvement.

As a result of repeated studies on the conditions of wet-on-wet coating, the present inventors have found that an electrodeposition coating having a lower coating film curing start temperature than the conventional one or a specific amount of internally crosslinked fine resin particles and / or non-gelling When using an electrodeposition paint containing a polymer resin and applying a limited amount of the on-wet paint containing a specific amount of a hydrophilic solvent and a ketone solvent, the phenomenon of defects in the formed coating film, especially wrinkles, is observed. , Crack,
The inventors of the present invention have developed the present invention by clarifying that curing distortion, poor gloss, image clarity, and lack of adhesion, and further that dents in the mist portion and cissing are extremely effectively reduced.

Therefore, an object of the present invention is to provide a coating film forming method which gives an appearance and coating film performance which are particularly suitable for automobile outer panel coating by a shortening process.

[Means for solving the problem]

The first coating film forming method according to the present invention for achieving the above object is characterized in that the following steps are sequentially performed.

(1) A first step of applying an electrodeposition coating material having a coating film curing start temperature of 100 to 140 ° C. to an object to be coated.

(2) In a state where the electrodeposition coating film by the first step is uncured,
The second step of applying a paint having a maximum content of 15 to 100% by weight of a hydrophilic solvent and a ketone solvent with respect to the total amount of solvent at the time of coating, which is 10% by weight.

(3) A third step of simultaneously curing the electrodeposition coating film of the first step and the coating film of the second step.

A second method for forming a coating film according to the present invention has the second step and the third step of the first invention in common, and the first step is applied to an object to be coated, and a coating film forming resin solid content is 100 parts by weight. On the other hand, it should be replaced with a process mode in which 1-60 parts by weight of internally crosslinked fine resin particles and / or non-gelling polymer resin is contained as a solid content, and a coating film curing start temperature is 100-140. Is the summary of the structure.

The overall coating process on which the present invention is based includes: electrodeposition coating-intermediate coating-baking-overcoat-baking, electrodeposition coating-intermediate coating (A) -baking- (polishing) -intermediate coating (B) -baking-topcoat-baking, Or, it is a conventional process such as electrodeposition coating-top coating-baking. Therefore, in the wet-on-wet coating of the second step,
In some cases, not only the middle coat but the top coat is applied directly.

Hereinafter, the conditions of each step, the components used, and the like will be described in detail.

In the present invention, the uncured electrodeposition coating film state is measured by a detection method such as measuring the temperature of an inflection point at which the logarithmic decrement of the coating film starts to increase from the minimum value with a pendulum type viscoelasticity measuring device. .

The reason for selecting and using an electrodeposition paint having a coating film curing start temperature of 100 to 140 ° C in the first step of the first coating film forming method is that the coating film curing start temperature is less than 100 ° C and the intermediate coating of the second step is applied. Overbaking occurs after baking after coating, which causes problems such as poor coating film performance, yellowing, and poor paint stability.
If it exceeds the above, curing distortion occurs due to the difference in the curing start temperature of the commonly used intermediate coating or top coating in the second step, and defects such as shrinkage, lack of clarity and interlayer adhesion are effective. This is because it cannot be prevented. Therefore, by setting the curing start temperature of the electrodeposition coating film to 100-140 ° C, the occurrence of the defect phenomenon can be effectively prevented, and at the same time, it is possible to reduce the baking time and the baking temperature after the intermediate coating. Becomes

As such a means, it is effective to use a resin having a coating film curing initiation temperature in the range of 100 to 140 ° C. (hereinafter referred to as “main component resin”) as a main component constituting the coating film.

The main component resin of the coating material may be an anion type resin system or a cation type resin system, and may be a water-soluble type or a dispersion type. For example, α, β-ethylenically unsaturated dibasic acids or anhydride adducts of liquid rubbers such as drying oils or polybutadienes, optionally with an epoxidized resin as the main skeleton, and modified derivatives thereof, as examples. Maleated oil resin, maleated polybutadiene resin, amine-modified epoxidized polybutadiene resin, etc .; those having a fatty acid ester of resinous polyol as the main skeleton and its modified derivatives, such as epoxy resin, esterified resin, etc .; alkyd resin as the main skeleton Examples thereof include those having an acrylic resin as a main skeleton.

These resins, according to the mechanism of their curing reaction,
There are a self-crosslinking type that is cured by the resin itself by radical polymerization or oxidative polymerization, and a curing agent type that is cured by a curing agent, for example, a curing agent such as a melamine resin or a block polyisocyanate compound, or a type that uses both together.
In these cases, a metal compound such as manganese, cobalt, nickel, lead or tin can be used as a catalyst.

Of these, specific examples of the main component resin as an anion type resin system can be listed below.

(1) Introduced by reacting a diisocyanate compound half-blocked with hydroxycarboxylic acid by reacting with a reactive hydrogen compound containing a side chain bonding block and at least one of terminal epoxy groups capable of reacting with the epoxy group. A modified epoxy resin having a carboxyl group at the end of the main chain (JP-A-1-236224).

(2) Sorbic acid, maleic anhydride, number average molecular weight 500
A resin obtained by condensing the above-mentioned epoxy resin, unsaturated resin acid and a monovalent to trivalent organic acid with a monovalent to tetravalent alcohol (JP-A-60-81261).

(3) a free carboxylic acid group on the side chain and / or the main chain,
A resin obtained by modifying either a drying oil having a conjugated diene-bonded α, β-unsaturated monocarboxylic acid residue or a conjugated diene polymer or copolymer (JP-A-1-146971).

(4) 0.1 to 10% by weight based on the total amount of the acrylic copolymer (I) containing a carboxyl group and a hydroxyl group and / or an alkoxyalkyl group bonded to a nitrogen atom, and the aminoplast resin (II). Electrodeposition coating composition comprising sulfonic acid group-containing polymer (III) (JP-A-62-53383)
Issue).

Further, examples of the cation-type resin-based main component resin include the following.

(1) Functional group capable of reacting with cationic group and isocyanate group (for example, hydroxyl group, amino group, imino group, etc.)
A mixture of a cationic substrate resin having γ and a blocked polyisocyanate blocked with a blocking agent that dissociates at a temperature of 70 to 140 ° C.

(2) Iodine value 50-500, basic group 30 per 100g of solid content
~ 300 mmol and a number average molecular weight of 500 to 5000 (A), at least 2 benzene nuclei and at least 1 ethylenic vinyl group in one molecule, and 5 acidic groups per 100 g of solid content. To 350 mmol and a resin (B) having a number average molecular weight of 500 to 5000 at a ratio of 0.03 to 0.5 mol of the acidic group of the component (B) to 1 mol of the basic group of the component (A), and at least one. A cathodic electrocoating composition containing a part of which is neutralized with an acid (JP-A-1-271467).

(3) The ester group-containing compound (B) capable of performing a micr addition reaction comprises a micul addition reaction product (A) obtained by subjecting a compound (C) containing at least two double bonds capable of a micul addition reaction to a micul addition reaction. In a curable component for synthetic resins containing groups forming amides or esters with carboxylic acids, the reaction product (A) has on average at least one polymerizable double bond and at least two transesterifications per molecule. Compound having a possible or amido-exchangeable ester group and compound (B) is (b1) CH--
A paint preparation using the above-mentioned curable component for synthetic resin, which is a reaction product consisting of an active alkyl ester and (b2) polyisocyanate (JP-A-62-192463).
Issue).

(4) (i) sulfonium group or phosphonium group (i
i) a moiety capable of cross-linking with (i) and (iii) (i) and (i
An aqueous cationic electrodeposition coating composition having a film-forming electrodeposition source having a moiety capable of catalyzing the crosslinking reaction with i) (Japanese Patent Laid-Open No. 63-179983).

(5) A coating composition containing an onium group-containing polymer and an aminoplast curing agent (JP-A-60-1265).

Among these, (1) is the most desirable. The (1)
There are known epoxy resin-based resins and acrylic resin-based resins for forming the cationic base resin. Specific examples of such a cationic base resin include those having active hydrogen and containing an amino group. Resins may be mentioned.

The epoxy resin is a compound having one or more epoxy groups per molecule on average, and an epoxy resin having two epoxy groups is particularly preferable. Examples of useful epoxy resins include epoxy resins obtained from bisphenol A and epichlorohydrin, polyglycidyl ethers obtained from bisphenol F and epichlorohydrin, or hydrogenated bisphenol A and epichlorohydrin. Epoxy resins obtained by reacting bisphenol A with epichlorohydrin are particularly preferred.

In addition, an acrylic polymer having an epoxy group may be used. Such polymers include unsaturated epoxy group-containing monomers such as glycidyl (meth) acrylate and 1
Alternatively, it can be obtained by polymerization with other polymerizable ethylenically unsaturated monomers. Examples of such polymers are disclosed in U.S. Pat. No. 4,001,156 at col. 3, line 59 to col. 5, line 60.

The basic amino compound used in the amino group-containing epoxy resin as the cationizing agent may be a primary amine, a secondary amine, a tertiary amine, a polyamine, or an alkanolamine. Preferred basic amino compounds include diethylamine, dipropylamine, N-methylethanolamine, diethanolamine, ethylenediamine, diethylenetriamine, dimethylcyclohexylamine, dimethylethanolamine and diethylenetriamine. When a polyamine such as diethylenetriamine is used, its primary amine group is preferably a ketimine derivative obtained by previously reacting it with a ketone such as acetone, methyl ethyl ketone or methyl isobutyl ketone. The ketimine formation reaction proceeds easily by heating above 100 ° C. and distilling off the produced water. When a tertiary amine having no active hydrogen is used, it is replaced with an acid such as boric acid, phosphoric acid, sulfuric acid, acetic acid or lactic acid to use as an acid amine salt.

With respect to the amounts of the amino compound and the epoxy resin which react with each other, their relative amounts vary based on the amount of cationic salt, for example the amount of the desired cationic base formed, and also on the molecular weight of the epoxy resin. The amount of cationic base formed and the molecular weight of the reaction product are selected so that the resulting cationic polymer forms a stable dispersion when mixed with an aqueous medium.

The reaction between the basic amino compound and the epoxy resin generally occurs only by mixing at room temperature, but in order to complete the reaction, it is heated at about 20 to 200 ° C, preferably 50 to 150 ° C for about 1 to 5 hours. Preferably.

The above reaction and reaction products are described, for example, in JP-A-51-1031.
35, Japanese Patent Publication No. 55-32385, Japanese Unexamined Patent Publication No. 53-65327, Japanese Unexamined Patent Publication No. 53-65328, Japanese Unexamined Patent Publication No. 52-87498 and the like.

The blocked polyisocyanate to be used with these cationic base resins is obtained by adding a blocking agent to polyisocyanate, and the blocking agent is dissociated within the temperature range of 100 ° C. or higher and 140 ° C. or lower to generate an isocyanate group. It cures by reacting with the functional groups in the resin.

As the blocked polyisocyanate, all polyisocyanates that have been conventionally used as a vehicle component for electrodeposition coatings can be used, but it is necessary to select a blocking agent in low temperature curing. Representative polyisocyanates are exemplified below. Trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,2-
Propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, ethylidene diisocyanate,
Aliphatic compounds such as butylidene diisocyanate, 1,3
-Cyclopentane diisocyanate, 1,4-cyclohexane diisocyanate, aliphatic cyclic compounds such as 1,2-cyclohexane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,
Aromatic compounds such as 4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4- or 2,6-toluene diisocyanate or mixtures thereof, 4 , 4'-Toluidine diisocyanate, aliphatic-aromatic compounds such as 1,4-xylene diisocyanate, dianisidine diisocyanate, 4,
4'-diphenyl ether diisocyanate, nuclear-substituted aromatic compounds such as chlorodiphenyl diisocyanate,
Triphenylmethane-4,4 ', 4 "-triisocyanate, 1,3,5-triisocyanate benzene, 2,4,6-triisocyanate Toluene and other triisocyanates, 4,
There are tetraisocyanates such as 4'-diphenyl-dimethylmethane-2,2 ', 5,5'-tetraisocyanate, and polymerized polyisocyanates such as toluene diisocyanate dimer and toluene diisocyanate trimer.

The blocking agent that dissociates at a temperature of 100 to 140 ° C. may be in the presence of a catalyst. As such a blocking agent, for example, in the case of an aromatic polyisocyanate,
1-chloro-2-propanol, halogenated hydrocarbons such as ethylene chlorohydrin, n-propanol, furfuryl alcohol, aliphatic or heterocyclic alcohols such as alkyl group-substituted furfuryl alcohol, phenol, m-cresol, Phenols such as p-nitrophenol, p-chlorophenol, nonylphenol,
Methyl ethyl ketone oxime, methyl isobutyl ketone oxime, oximes such as acetone oxime, cyclohexane oxime, acetylacetone, ethyl acetoacetate, active methylene compounds such as ethyl malonate, and others, such as caprolactam can be mentioned, particularly preferable oximes, Among the alcohols, furfuryl alcohol and alkyl-substituted furfuryl alcohol. In the case of aliphatic polyisocyanate, phenols and oxyls are preferable among the above.

In addition, the blocking agent which dissociates at 100 to 140 ° C. (hereinafter referred to as “blocking agent” (a)) can be used by mixing with another blocking agent (b). The blocking agent (b) preferably has a dissociation temperature of less than 160 ° C., for example, aliphatic alcohols such as methanol, ethanol and isopropanol, aromatic alcohols such as benzyl alcohol, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether. Ethers such as ethylene glycol monobutyl ether and diethylene glycol monomethyl ether. As a method for mixing the blocking agent (b), the polyisocyanate is blocked with the blocking agents (a) and (b) at a constant ratio, or the blocked polyisocyanate blocked with the blocking agent (a) and the blocking agent (b) are mixed. A method in which a blocked polyisocyanate blocked by is mixed and used at a constant ratio is used. The mixing ratio of the blocking agent (a) and the blocking agent (b) is an equivalent ratio of (a) :( b) = 10: 0.
It is desirable to set in the range of ~ 10: 5.

As the dissociation catalyst for the blocking agent, organic tin compounds such as dibutyltin laurate, dibutyltin oxide and dioctyltin, amines such as N-methylmorpholine, and metal salts such as lead acetate can be used. The concentration of the catalyst is usually 0.3 to 5% by weight based on the solid content of the coating film forming resin in the cationic electrodeposition coating composition.

In the first step in the second coating film production method of the present invention,
As described above, the coating film curing start temperature is 100 to 140 ° C.,
In addition, an electrodeposition paint containing 1 to 60 parts by weight of internally crosslinked fine resin particles and / or non-gelling polymer resin as a solid content with respect to 100 parts by weight of the coating film-forming resin solid content should be applied to the object to be coated. Is a requirement, and by applying this process, it becomes possible to form a coating film having higher appearance, high weather resistance and high chipping property in a shortening step.

The inclusion of the internally crosslinked fine resin particles and the non-gelling polymer resin in the electrodeposition coating alone or in combination increases the melt viscosity at the time of curing the electrodeposition coating film to smoothly perform the coating in the uncured state. This is because. For this purpose, for example, a method of adding a pigment component in a weight ratio of 35% or more based on the total solid content of the resin in the electrodeposition coating bath is also effective, but in this case, the smoothness of the coating film, the coating There is a problem with stability.

As means for producing internally crosslinked fine resin particles to be used, for example, recovered from a fine resin particle dispersion liquid obtained by suspension-polymerizing or emulsion-polymerizing an ethylenically unsaturated monomer and a crosslinkable copolymerizable monomer in an aqueous medium. Method, a low-SP organic solvent such as an aliphatic hydrocarbon or a high-SP organic solvent such as an ester, a ketone, or an alcohol dissolves a monomer but does not dissolve a polymer. Copolymerize the monomer and the crosslinkable copolymerization monomer,
A method called a NAD method or a precipitation method in which the generated internally crosslinked fine resin particles are dispersed can be applied.

Examples of the ethylenically unsaturated monomer used in the above method include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, and (meth) acrylic. Alkyl esters of acrylic acid or methacrylic acid such as 2-ethylhexyl acid and other monomers having an ethylenically unsaturated bond capable of copolymerizing the same, such as styrene and α-methylstyrene,
Examples include vinyltoluene, t-butylstyrene, ethylene, propylene, vinyl acetate, vinyl propionate, (meth) acrylonitrile, and dimethylaminoethyl (meth) acrylate. Two or more kinds of these monomers may be used. The crosslinkable copolymerizable monomer is a monomer having two or more radically polymerizable ethylenically unsaturated bonds in the molecule and / or two kinds of ethylenically unsaturated monomers each carrying a group capable of reacting with each other. Including a group-containing monomer.

Examples of the monomer having two or more radically polymerizable ethylenically unsaturated groups in the molecule include polyhydric alcohol polymerizable unsaturated monocarboxylic acid esters, polybasic acid polymerizable unsaturated alcohol esters, and 2 There are aromatic compounds substituted with one or more vinyl groups, and examples thereof include the following compounds.

Ethylene glycol di (meth) acrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane tri (meth) acrylate, 1,4-butanediol diacrylate, neopentyl glycol Diacrylate, 1,6-hexanediol diacrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, pentaerythritol dimethacrylate, glycerol di (meth) acrylate, glycerol ant Roxydimethacrylate, 1,1,1-trishydroxymethylethanedi (meth) acrylate, 1,1,
1-trishydroxymethylethane tri (meth) acrylate, 1,1,1-trishydroxymethylpropane di (meth) acrylate, 1,1,1-trishydroxymethylpropane tri (meth) acrylate, triallyl cyanurate, tri Allyl isocyanurate, triallyl trimellitate, diallyl terephthalate, diallyl phthalate and divinylbenzene.

Examples of the monomer having two kinds of ethylenically unsaturated groups each carrying a group capable of reacting with each other include an epoxy group-containing ethylenically unsaturated monomer such as glycidyl (meth) acrylate and (meth ) Acrylic acid, crotonic acid, and other carboxyl group-containing ethylenically unsaturated monomers are the most typical, but the mutually reactive groups are not limited to these, and examples include amines, carbonyls, and epoxides. Various substances such as carboxylic acid anhydrides, carboxylic acid anhydrides, amines and carboxylic acid chlorides, alkyleneimines and carbonyls, organoalkoxysilanes and carboxyls, hydroxyls and isocyanates have been proposed, and the present invention includes these.

For the fine resin particles produced in an aqueous medium or a non-aqueous organic medium, the internally crosslinked fine resin particles are isolated by a method such as filtration, spray drying or freeze drying, and pulverized to a suitable particle size as it is or using a mill. Can be used as it is, or the synthesized dispersion liquid can be used as it is, or the medium can be replaced by solvent replacement.

As a method for producing internally crosslinked fine resin particles different from the above, a film-forming water-based resin (A) that is electrically chargeable in water,
A self-crosslinking and / or water-insoluble crosslinking agent (B) capable of crosslinking with the aqueous resin (A) is emulsified in an aqueous medium, and the obtained emulsion is heated at a temperature equal to or higher than the crosslinking temperature of the crosslinking agent (B). In the case of the chargeable gel fine particles containing a pigment in the core portion, the method for producing by the method, the pigment is dispersed in the crosslinking agent (B), and then the aqueous resin (A) is added to emulsify it in an aqueous medium, There is a method of obtaining the obtained emulsion by heat treatment as described above.

Film-forming aqueous resin (A) used in this method
Examples of typical substances include anionic type maleic oil or maleic polybutadiene half ester and anionic acrylic resin, and cationic type aminated polybutadiene and aminated epoxy resin.

The water-insoluble thermosetting crosslinking agent (B) that self-crosslinks and / or crosslinks with the above-mentioned aqueous resin (A) by condensation or addition reaction is a melamine resin, methylolphenols or etherification for anionic aqueous resin. There are methylolphenols and the like, and etherified methylolphenols can be used for the cationic aqueous resin, and tetrabromobisphenol A can also be used as the crosslinking agent when the cationic aqueous resin is an aminated polybutadiene resin.

The pigment contained in the core portion is a pigment substance usually used in electrodeposition paints such as iron oxide, lead oxide, strontium chromate, silica, carbon black, titanium dioxide, talc, aluminum silicate, precipitated barium sulfate, and basic silicic acid. In addition to lead and aluminum phosphomolybdate, there are metallic pigments such as zinc dust and other extender pigments.

It is preferable that the internally crosslinked fine resin particles themselves have an ionizable group having the same polarity as the main component resin in order to maintain a stable dispersed state in the coating material and the electrodeposition bath. That is, it is preferable to carry an anionic group such as a carboxyl group and a sulfonic acid group for anionic electrodeposition, and to carry an anionic group such as an amino group or a quaternary ammonium group for cationic electrodeposition. Become. To achieve this,
In the case of carrying an anionic group, a monomer having an ethylenically unsaturated bond and a carboxyl group, such as (meth) acrylic acid, or in the case of carrying a cationic group, an ethylenically unsaturated bond and a basic group A monomer having, for example, dimethylaminoethyl (meth) acrylate, vinyl pyridines, etc. is added to the monomer mixture during the synthesis of the internally crosslinked fine resin particles, or for the synthesis of the internally crosslinked fine resin particles,
There is a method of polymerizing the monomer mixture using an initiator which gives a cationic end.

When the polymer itself that constitutes the internally crosslinked fine resin particles is non-polar, the internally crosslinked fine resin particles may be prepared by using an appropriate emulsifier during synthesis of the internally crosslinked fine resin particles, particularly oligosoap, polysoap or reactive emulsifier having a zwitterionic group. The resin particles can also be stably dispersed.

Next, the non-gelling polymer resin will be described. The non-gelling polymer resin applied to the present invention is required to have a function of increasing melt viscosity when the coating film is cured. This function is the minimum logarithmic decay rate (relative viscosity index) when non-gelling polymer resin is used in the vibration type viscoelasticity measurement method.
Can be specifically verified by the fact that the value increases compared to when it is not used.

Examples of the non-gelling polymer resin include various resin systems such as epoxy resin, acrylic resin, polybutadiene resin, polyester resin and polyether resin.
These cannot be limited by the molecular weight value, and differ depending on the resin system and composition, the polymer structure, the type of functional group, the main resin system of the electrodeposition coating to be applied, and the like.

Typical examples are EP-bis type epoxy resins such as polyether polyol, polyester polyol, polyether polyol modified polyisocyanate, monoalcohol, carboxylic acid ester-containing diol, carboxyl group-containing butadiene-acrylic copolymer, terminal carboxyl group-containing butadiene- Chain extension using an acrylonitrile copolymer, long-chain dibasic acid, polyamine, polyoxyalkylene polyamine, polyurethane polyamine, ε-caprolactone ring-opening polymer, etc. In the case of using a coating composition, in the case of a terminal carboxyl group-containing butadiene-acrylonitrile copolymer, for example, a number average molecular weight of 3500
As described above, the polyoxyalkylene polyamine has a number average molecular weight of 10,000 or more. When using a non-crosslinked acrylic polymer obtained by emulsion polymerization in an acrylic resin-based electrodeposition coating, generally a number average molecular weight of 50,000 or more, an epoxidized polybutadiene added with an amine and unsaturated fatty acid When used in an epoxy resin-based cationic electrodeposition coating, at least a number average molecular weight of 2200 or more is selected.When used in a polybutadiene-based cationic electrodeposition coating, at least a number average molecular weight of 2500 or more is selected. It

The non-gelling polymer resin may be water-soluble or water-insoluble, and is either directly mixed with the electrodeposition coating film-forming resin or directly mixed with the aqueous dispersion of the film-forming resin. Alternatively, it is contained by a method of adding and mixing to the electrodeposition paint bath. When it is water-insoluble, it may be dispersed using a surfactant or a solvent. When it is water-soluble, the stability of the coating is better when it has an ionizable group having the same polarity as that of the electrodeposition coating film-forming resin.

Internally crosslinked fine resin particles to be contained in electrodeposition paint and /
Or, the amount of non-gelling polymer resin is the solid content of the film-forming resin.
The solid content is set to 1 to 60 parts by weight, preferably 2 to 40 parts by weight, relative to 100 parts by weight. If the content is less than 1 part by weight, the melt viscosity hardly increases, so that the effect of preventing dents, cissing and the like due to the overcoat mist of the intermediate coating is not exhibited, and the corrosion resistance of the end surface of the steel sheet is deteriorated. On the other hand, if it exceeds 60 parts by weight, melt viscosity is excessively increased during curing of the electrodeposition coating film, resulting in problems such as deterioration of smoothness of the coating film.

Furthermore, in addition to water as a medium, the following additives, solvents and pigments can be used in the electrodeposition coating as required.

Additives: As additives used when dispersing the coating film-forming resin in an aqueous medium, for example, acids such as formic acid, acetic acid, lactic acid, sulfamic acid in the case of a cationic resin, ammonia and amine in the case of an anionic resin. , Bases such as inorganic alkali and surfactants. Generally, the concentration of the additive is preferably in the range of 0.1 to 15% by weight based on the solid content of the coating film forming resin in the electrodeposition coating material.

Solvent: A solvent component used for the purpose of dissolving the resin, adjusting the viscosity of the coating film, adjusting the coating material, for example, hydrocarbons such as xylene and toluene, ethyl alcohol, n-butyl alcohol, isopropyl alcohol, 2-ethylhexyl alcohol. , Alcohols such as ethylene glycol and propylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,
Ethers such as ethylene glycol monohexyl ether, propylene glycol monoethyl ether, 3-methyl 3-methoxybutanol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ketones such as methyl isobutyl ketone, cyclohexanone, isophorone and acetylacetone, ethylene glycol monoethyl ether Esters such as ethyl ether acetate and ethylene glycol monobutyl ether acetate, either alone or as a mixture. In this case, the solvent concentration for the electrodeposition paint is about 0.01 to 25% by weight, preferably 0.05 to
It is about 15% by weight.

Pigments: For example, carbon black, graphite, titanium oxide,
Coloring pigments such as zinc white, extender pigments such as aluminum silicate and kaolin, and rust preventive pigments such as strontium chromate, basic lead silicate, basic lead sulfate and aluminum phosphomolybdate alone or in a mixture.

The electrodeposition coating carried out in the first step of the present invention is the coating bath temperature.
The temperature is 20 to 40 ° C., the applied voltage is 50 to 500 V, and the energization time is 30 seconds to 10 minutes while the object is completely immersed in the coating bath, which is a conventionally used condition. The required thickness of the electrodeposition coating film is 5 to 50 μm as a baked coating film, preferably 10 to
35 μm.

After performing electrodeposition coating, usually, a washing process is performed to remove excess paint, but if the drainage after washing is insufficient, dents, repelling, uneven finish etc. occur during painting in the second step. It is desirable to perform sufficient draining and air blowing, as this will cause

The article to be coated that has been subjected to the electrodeposition coating in the first step is transferred to the second step coating by wet-on-wet while the electrodeposition coating film is uncured. Usually, the coating of the second step is carried out as an intermediate coating, and like the general coating for automobile outer panels, for example, a polyester-based, alkyd-based, urethane-modified, polyester-based, acrylic-based resin material and curing of melamine resin, blocked isocyanate, etc. It is performed using a paint whose main component is an agent.

In the present invention, as a paint used for the intermediate coating or top coating of the second step, the maximum content is 10 wt% in the case of containing a ketone solvent in an amount of 15 to 100 wt% with respect to the total solvent at the time of painting. It is a requirement to select and use a solvent composition having a percentage of%. If the hydrophilic solvent is less than the above range, the coating film becomes rough and foaming appears. If the amount of the ketone solvent exceeds 10%, the mist becomes dented.

As the hydrophilic solvent, methyl alcohol, ethyl alcohol, isopropyl alcohol, tertiary butyl alcohol, regular propyl alcohol, secondary butyl alcohol, isobutyl alcohol, regular butyl alcohol, active amyl alcohol, isoamyl alcohol, regular amyl alcohol, regular hexyl alcohol. Alcohols such as benzyl alcohol; propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, 3-methoxybutanol, ethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, diethylene glycol diethyl ether, Diethylene glycol monomethyl ether, diethylene glycol Ether alcohols and ethers such as monoethyl ether, diethylene glycol monobutyl ether, dioxane; methyl acetate, ethylene acetate monomethyl ether acetate, ethyl lactate, ethylene glycol monoethyl ether acetate, butyl lactate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl acetate Esters such as ethers and ether esters; hydrophilic ketones such as acetone, methyl ethyl ketone, diethyl ketone, cyclohexanone, methoxymethyl, pentanol, diacetone alcohol and the like.

As a ketone solvent with a maximum content of 10% by weight,
Acetone, methyl ethyl ketone, diethyl ketone, cyclohexane, methoxymethyl pentanol, diacetone alcohol, methyl isobutyl ketone, methyl amyl ketone, anone, diisobutyl ketone, isophorone, cyclohexane and the like can be mentioned.

For the coating in the second step, the conventional conditions of intermediate coating or top coating can be applied as they are, and after the coating, the bake hardening treatment is performed simultaneously with the electrodeposition coating film in the first step.

When a particularly high appearance is required, a coating process in which the surface of the intermediate coating film is polished and then a secondary intermediate coating treatment is performed is adopted. Also for this secondary intermediate coating, the conditions generally used in the conventional intermediate coating process for automobile outer panels can be applied as they are.

In addition, the conditions for applying the top coat directly or through the middle coat can also be achieved by air spray, electrostatic air spray, bell type electrostatic paint, etc. using metallic paint, clear paint or colored paint excluding metallic as in the conventional method. You can do it.

[Work]

According to the coating film forming method of the present invention, the coating film curing start temperature is
By taking the first step using the electrodeposition coating at 100-140 ℃, the simultaneous baking temperature after electrodeposition coating and intermediate coating can be lowered, so that the conventional intermediate coating step can be applied and various problems due to overbaking of the intermediate coating surface. Can be prevented. In addition, the fuel cost can be reduced.

In addition, in the second coating film forming method of the present invention, in addition to the low coating film curing start temperature, a specific amount of internally crosslinked fine resin particles and / or non-gelling polymer resin is added to the electrodeposition coating material. The coating composition is always controlled to a melt viscosity suitable for wet-on-wet coating, and wrinkles, cracks, curing distortion, lack of gloss, lack of sharpness, insufficient adhesion of the formed coating film, as well as dents in the mist, cissing, etc. Performs the function of effectively preventing the occurrence of the phenomenon. Therefore, the coating in the second step proceeds smoothly without causing any inconvenient phenomenon.

The selective adjustment of the solvent composition of the paint used in the second step reduces the effect of the solvent component on the electrodeposition coating film surface during coating, and cooperates with the viscosity adjusting action of the electrodeposition coating material described above to improve the coating composition. It works effectively to prevent the occurrence of dents and pinholes.

Combined with such effects, it becomes possible to always form a high-performance coating film having a high degree of appearance, weather resistance and chipping resistance.

Furthermore, if the present invention is applied, the baking process after electrodeposition coating is omitted, so that, for example, conventional 3c3b (3 coatings, 3 bakings)
3c2b and 4c3b high appearance coating of 4c4b
Therefore, it is possible to significantly reduce the number of painting steps.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

Examples 1 to 17 and Comparative Examples 1 to 6 Preparation of test piece As a first step, zinc phosphate treatment was performed to a thickness of 0.8 mm.
Electroplating paint (~ / Table 1) on the dull steel plate of
Electrodeposition was performed under the conditions of an applied voltage of 250 V and an energization time of 3 minutes to obtain an electrodeposition coating film having a dry film thickness of about 25 μm.

Next, after washing the coating film with water, it is blown with compressed air with an air pressure of about 4 kg / cm ² , and 2 minutes later, the intermediate coating material is air sprayed with a viscosity of 20 seconds (No. 4 Ford cup) to give a dry film thickness of about 40 μm.
The second step was applied so that

The coating films of the first step and the second step were baked and cured at the same time, but they were set at room temperature for 10 minutes before the baking step.

The following examples and comparative examples are based on the above basic process, and the coating is performed by changing the properties and coating conditions of the electrodeposition coating, the properties and coating conditions of the intermediate coating, and the addition of secondary intermediate coating and top coating. The obtained coating film was subjected to appearance inspection and water resistance test. The results are summarized in Table 3.

In Comparative Example 4, the electrodeposition coating film was baked and dried at 160 ° C. for 10 minutes and then subjected to intermediate coating.

Manufacture of internally crosslinked fine resin particles [A] Stirrer, nitrogen introduction pipe, temperature control device, condenser,
Into 2 Kolben equipped with a decanter, 100 parts by weight of ethylene glycol monomethyl ether was charged, and the temperature was raised to 100 ° C. and maintained. Prepare two dropping funnels, and put 100 parts by weight of ethylene glycol monomethyl ether into one of them and add N-methyl-N- (vinylbenzyl) taurine into it.
75 parts by weight dissolved. At this time, a small amount of dimethylethanolamine was added as a solubilizing agent.

Further, 50 parts by weight of 2-hydroxyethyl acrylate, 10 parts by weight of acrylic acid, 110 parts by weight of methyl methacrylate, 110 parts by weight of styrene, 145 parts by weight of n-butyl acrylate and 10 parts by weight of ularyl mercaptan were mixed into one dropping funnel, 10 parts by weight of azobisisobutyronitotyl was dissolved.

The contents of the two dropping funnels were added dropwise over 120 minutes, after which the temperature was maintained at 100 ° C and stirring was continued for 60 minutes. Then, the solvent of this resin solution was removed by a rotary evaporator to obtain an acrylic resin having a resin solid content of 96% and a number average molecular weight of 4,500.

After stirring, charge 306 parts by weight of deionized water, 18 parts by weight of the acrylic resin obtained in the above step, 2.6 parts by weight of dimethylethanolamine into one reaction vessel equipped with a cooling tube and a temperature control device, and stir to 80 ° C. The temperature was raised. After the contents were dissolved, the temperature was maintained at 80 ° C. with stirring, and an aqueous solution containing 4.8 parts by weight of azobiscyanovaleric acid, 4.56 parts by weight of dimethylethanolamine and 48 parts by weight of deionized water was charged. Next, styrene 26.6 parts by weight, methyl methacrylate 79.8 parts by weight, n-butyl acrylate
53.2 parts by weight, ethylene glycol dimethacrylate 53.2
By weight, a mixed solution of 53.2 parts by weight of ethyl acrylate and 16.0 parts by weight of diethylaminoethyl acrylate was added dropwise over 60 minutes. After dropping, at the same temperature, 1.2 parts by weight of azobiscyanovaleric acid and 1.1 of dimethylethanolamine were further added.
Add a mixed aqueous solution consisting of 4 parts by weight and 12 parts by weight of deionized water and continue stirring for 60 minutes to obtain a particle size of 146 nm and a degree of crosslinking.
Cationic internally crosslinked fine resin particles with 0.9532 mmol / g and a non-volatile content of 45% were obtained.

Production of Internally Crosslinked Micro Resin Particles [B] As a monomer mixture liquid, styrene 74.7 parts by weight, methyl methacrylate 74.7 parts by weight, n-butyl acrylate 9
Except that 9.6 parts by weight, 30 parts by weight of 2-hydroxyethyl acrylate and 3 parts by weight of ethylene glycol dimethacrylate were used, the same procedure as in Production Example [A] was used to obtain a particle size of 132 nm, a degree of crosslinking of 0.054 mmol / g, and a nonvolatile content. 45% of anionic internally crosslinked fine resin particles were obtained.

Manufacture of non-gelling polymer resin "Jeffamine D-2000" [Jefferson Chemical Company with a molecular weight of 2000]
Polyoxypropylenediamine] of 1000 parts by weight was charged into a reaction vessel in a nitrogen gas filled state, heated to 90 ° C., and then “DE
R-723 "(a polypropylene glycol diepoxy resin having a number average molecular weight of about 752 commercially available from Dow Chemical Company) 285 parts by weight and 100 parts by weight of ethylene glycol monoethyl ether were added.
The mixture was heated to 10 ° C. and kept for 2 hours, and then mixed with 25 parts by weight of acetic acid and 2870 parts by weight of deionized water to obtain a non-gelling polymer resin having a nonvolatile content of 30%.

Production of cationic base resin (a) Dissolve 1000 parts by weight of diglycidyl ether of bisphenol A (epoxy equivalent 910) in 463 parts by weight of ethylene glycol monoethyl ether with stirring, and further add 80.3 parts by weight of diethylamine. Was added and reacted at 100 ° C. for 2 hours to obtain a cationic base resin (a).

Production of block polyisocyanate (b) Toluene diisocyanate (2,4
-Toluene diisocyanate / 2,6-toluene diisocyanate 80/20 mixture: TDI) 174 parts by weight of methyl ethyl ketone oxime 87 parts by weight, the reaction temperature by external cooling 50
While keeping the temperature below ℃, it was gradually dropped to obtain a half-blocked isocyanate. Then trimethylolpropane
45 parts by weight and 0.05 part by weight of dibutyltin dilaurate were added and reacted at 120 ° C. for 90 minutes. The obtained reaction product was diluted with 131 parts by weight of ethylene glycol monoethyl ether to obtain a blocked polyisocyanate (II).

Production of block polyisocyanate (C) Toluene diisocyanate (2,4
-Toluene diisocyanate / 2,6-toluene diisocyanate 80/20 mixture) To 174 parts by weight, 30.5 parts by weight of methyl ethyl ketone oxime is gradually added dropwise while keeping the reaction temperature at 50 ° C or less by external cooling, and the reaction is continued. Then, 60.9 parts by weight of furfuryl alcohol was completely reacted in the same manner, and further 35.4 parts by weight of ethylene glycol monobutyl ether were similarly reacted to obtain a half-blocked isocyanate. Then trimethylolpropane 45
Parts by weight and 0.05 parts by weight of dibutyltin dilaurate were added and reacted at 120 ° C. for 90 minutes. The obtained reaction product was diluted with 148 parts by weight of ethylene glycol monoethyl ether to obtain a blocked polyisocyanate (c).

Production of block polyisocyanate (d) Toluene diisocyanate (2,4
-Toluene diisocyanate / 2,6-toluene diisocyanate 80/20 mixture: TDI) To 174 parts by weight, 130 parts by weight of 2-ethylhexyl alcohol is gradually added dropwise while maintaining the reaction temperature at 50 ° C or lower by external cooling. A blocked isocyanate was obtained. Then, 45 parts by weight of trimethylolpropane and 0.05 parts by weight of dibutyltin dilaurate were added, and the mixture was reacted at 120 ° C. for 90 minutes. The obtained reaction product was diluted with 150 parts by weight of ethylene glycol monoethyl ether to obtain a blocked polyisocyanate (d).

Manufacture of pigment paste Cationic base resin (a) 150 parts by weight Glacial acetic acid 6.4 〃 Deionized water 278.6 〃 Carbon black 20 〃 Titanium oxide 122 〃 Kaolin 40 〃 Basic lead silicate 28 〃Dibutyltin oxide 15 〃 Based on the cationic base resin (a), glacial acetic acid and deionized water were added and dissolved, and then the pigment and dibutyltin oxide were added and stirred with a disper for about 1 hour. Glass beads were added to this mixture and dispersed to 20 μm or less by a sand mill, and the glass beads were separated by filtration. The obtained pigment paste had a nonvolatile content of 50%.

Composition for cationic electrodeposition coating A component resin consisting of 220 parts by weight of a cationic base resin (a) and 146 parts by weight of a blocked polyisocyanate (b) was neutralized with 4.8 parts by weight of glacial acetic acid, and then 271.2 parts by weight of deionized water was added. It was diluted with to obtain a resin composition having a nonvolatile content of about 40% by weight.

Next, 275 parts by weight of pigment paste and 1189 deionized water.
The composition for cationic electrodeposition coating composition was prepared by gradually adding parts by weight with stirring at room temperature.

Cationic electrodeposition coating composition ~, ~, carried out according to the above except that the block polyisocyanate (b) and the internally crosslinked fine resin particles [A] and / or the non-gelling polymer resin with different amounts added are added. The composition for cationic electrodeposition coating of Examples ~ and the compositions for cationic electrodeposition coating of Comparative Examples ~ and were prepared.

Composition for anionic electrodeposition coating composition Epoxy resin 520 having an epoxy equivalent of 250 and a number average molecular weight of 500 obtained by the reaction of pisphenol A and epichlorohydrin in a flask equipped with a stirrer, a thermometer, a nitrogen introducing tube and a reflux cooling tube. Charge 290 parts by weight, and add 289 parts by weight of methyl isoptyl ketone to dissolve it, and add 154 parts by weight of N-methylethanolamine under a nitrogen stream at 80 ° C.
After the reaction was carried out until the epoxy value became 0 at the reaction temperature of, 1087 parts by weight of 12-hydroxystearic acid half block isophorone diisocyanate (solid content) was added,
The reaction is carried out at ℃, until the absorption of isocyanate group disappears in the infrared spectrum, then 238 parts by weight of ε-caplacton and 1.0 part by weight of diptyltin oxide are added, and the reaction is carried out at 120 ° C. for 8 hours to give a nonvolatile content of 50.2%. , Acid number 5
7.2 α, ω-Sudare structure resin A of 7.2 was obtained.

On the other hand, pigment paste B was prepared by using 12.0 parts by weight of a dispersant (nonylphenol polyethylene edoxy-phosphate ester), 160 parts by weight of aluminum silicate, 220 parts by weight of rouge, 20 parts by weight of strontium chromate and 189 parts by weight of deionized water. Prepared. Next, resin A: 70 parts by weight (solid content)
And methylated melamine resin (number average molecular weight: 500, non-volatile content: 100% made by Nippon Paint Co., Ltd.): 30 parts by weight (solid content)
After removing the solvent, triethylamine is added so that the neutralization rate becomes 50%, 40 parts by weight (solid content) of pigment paste B is further added, and the mixture is stirred. Then, ion-exchanged water is added at a solid content concentration of 15%. To obtain an anionic electrodeposition coating composition.

Composition for Anion Electrodeposition Coating Compositions for anion electrodeposition coating compositions of Examples were obtained according to the above except that the internally crosslinked fine resin particles [B] were added.

Composition for anion electrodeposition coating Epoxy resin having an epoxy equivalent of 250 and a number average molecular weight of 500 obtained by the reaction of bisphenol A and epichlorohydrin in a flask equipped with a stirrer, a thermometer, a nitrogen introducing tube and a reflux cooling tube 1059 weight Parts were dissolved in 588 parts by weight of methyl isobutyl ketone and reacted with 314 parts by weight of N-methylethanolamine and 627 parts by weight of phthalic anhydride. This was diluted with 268 parts by weight of methyl isobutyl ketone to a nonvolatile content of 70% to obtain a resin a having an acid value of 82.8.

An anion electrodeposition coating composition was obtained in the same manner as described above except that the resin a was used in place of the α, ω-sudder structure resin A of the anion electrodeposition coating composition.

 Table 1 shows the composition of each electrodeposition paint prepared above.

The coating curing start temperature of each electrodeposition paint was 7.83 g with a pendulum viscoelasticity measuring instrument (manufactured by Sentech Co., Ltd., FDOM MODEL 001), a vibration cycle of 0.71 seconds, a pendulum length of 18 cm, and a heating rate of 20. It was determined as the temperature at the inflection point at which the logarithmic decrement of the coating film starts to increase from the minimum value when measured under the condition of ° C / min.

Intermediate coating The intermediate coating was performed under the conventional coating conditions using the coating composition shown in Table 2.

Topcoat coating The following coating was used.

(A) Acrylic melamine-based silver base coat (15μ
m) Acrylic melamine clear coat (30 μm) wet and wet after painting.

(B) Alkyd melamine black solid color (40
μm).

(C) Alkyd melamine white solid color (40
μm).

Evaluation method and evaluation criteria (1) Process reduction effect ○… Reduction effect ×… No reduction effect (2) Appearance of coating film (visual judgment) General surface: ◎… Very good ○… Good △… Slightly abnormal ×… Abnormal Yes Medium coat overspray part: ◎… Very good ○… Good △… Slightly dented ×… Vented (3) Water resistance Visual appearance and adhesion after immersion in 50 ° C. hot water for 10 days: ○… No abnormality × ... abnormal [Effects of the Invention] As described above, according to the method for forming a coating film of the present invention, it is possible to always form a high-performance coating film excellent in appearance, weather resistance and chipping resistance by the shortened wet-on-wet coating process. it can.

Therefore, it is extremely useful as a coating process for automobile outer panels that require a particularly high-quality coating film appearance.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Tsuneo Ukita 4-1-1-15 Minami-Shinagawa, Shinagawa-ku, Tokyo Inside Nippon Paint Co., Ltd. (72) Katsumi Murata 4-1-1 Minami-Shinagawa, Shinagawa-ku, Tokyo No. 15 Nippon Paint Co., Ltd. Tokyo office

Claims (2)

[Claims] 1. A method for forming a coating film, which comprises sequentially performing the following steps. (1) A first step of applying an electrodeposition coating material having a coating film curing start temperature of 100 to 140 ° C. to an object to be coated. (2) In a state where the electrodeposition coating film by the first step is uncured,
The second step of applying a coating material having a maximum content of hydrophilic solvent of 15 to 100% by weight and a ketone solvent of 10% by weight based on all the solvents at the time of application. (3) A third step of simultaneously curing the electrodeposition coating film of the first step and the coating film of the second step. 2. A method for forming a coating film, which comprises sequentially performing the following steps. (1) The coating object contains 1 to 60 parts by weight of internally crosslinked fine resin particles and / or non-gelling polymer resin as a solid content based on 100 parts by weight of the coating film forming resin solid content, and the coating film curing starts. The first step of applying an electrodeposition paint at a temperature of 100-140 ℃. (2) In a state where the electrodeposition coating film by the first step is uncured,
The second step of applying a paint having a maximum content of 15 to 100% by weight of a hydrophilic solvent and a ketone solvent with respect to all the solvents at the time of application. (3) A third step of simultaneously curing the electrodeposition coating film of the first step and the coating paint of the second step.