JP2003145031A - Method of forming clear coating film and coating material used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating film forming method in finish coating by which acid resistance and scratch resistance are attained at the same time and a coating material used for the same. SOLUTION: A two-pack type urethane based coating material consisting essentially of an organic solvent dilution type hydroxy group-containing resin containing a curing agent for moisture curing and an isocyanate compound which can be blocked is applied on a material to be coated, cured by moisture and heated to cause curing by urethane reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a clear coating film which has both acid resistance and scratch resistance, and a two-pack type polyurethane coating material used therefor.

[0002]

2. Description of the Related Art Durability against erosion due to acid rain and scratches due to car wash machines is required for the top coating film of automobile outer panels, but it is difficult to satisfy both of these performances at the same time. Met.

Efforts have been made to develop such coating compositions. For example, in JP-A-2000-309745, a hydroxyl group-containing polymerizable unsaturated monomer and an acid anhydride group-containing compound are used to form an acid anhydride group of 1 to 1.5 per mole of the hydroxyl group.
Polymerizable unsaturated half-esterified product (a), acid anhydride group-containing polymerizable unsaturated monomer (b), and other polymerizable unsaturated monomer obtained by carrying out half-esterification reaction in a molar ratio Polymer (B) obtained by half-esterifying a monohydric alcohol with the acid anhydride group of the acid anhydride group-containing polymer (A) obtained by copolymerizing (c).
And a polymer (C) having both a hydroxyl group and an epoxy group in one molecule, capable of forming a coating film excellent in low temperature curability, acid resistance, and scratch resistance, and a thermosetting resin composition for coating. The thing is disclosed.

Japanese Patent Laid-Open No. 2001-26747 discloses that
It contains (A) a hydroxyl group-containing resin, (B) inorganic oxide colloidal fine particles, and (C) an optionally blocked polyisocyanate compound, and has an acid value of 0.1 based on the total solid content in the coating composition. An organic solvent-based coating composition that forms a coating film having excellent acid resistance and scratch resistance, which is up to 50 mgKOH / g, has been proposed.

However, since both of these compositions are applied as a single layer, the acid resistance and the scratch resistance have a negative correlation with each other. Therefore, if one property is improved, the other property is improved. There is a problem that the property is deteriorated.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a clear coating film and a paint used therefor, which simultaneously achieves acid resistance and scratch resistance.

[0007]

Means for Solving the Problems The present inventor has introduced a high surface cross-link density and an internal cross-link density by introducing a gradient function in which the cross-link density is increased from the inside to the outside in the clear coating film during finish coating. It was found that the elasticity and the scratch resistance are combined by the elasticity based on the low crosslink density.

That is, according to the present invention, a two-component polyurethane-based organic solvent-containing coating composition using a moisture-curing curing agent as a curing agent is applied, and after the solvent is substantially removed, the surface of the surface is removed from the inside due to the difference in the penetration of moisture. We propose a method for forming a clear coating film, which comprises curing a curing agent by external humidification so as to increase the crosslink density toward, and then heating it to cause a urethane curing reaction. The clear coating film obtained by this method exhibits excellent acid resistance and scratch resistance.

The two-component polyurethane-based organic solvent-containing paint used in the method for forming a clear coating film of the present invention is
A main component is (i) an organic solvent-dilutable hydroxyl group-containing resin containing a curing agent for moisture curing and (ii) an isocyanate compound which may be blocked. This paint is also an object of the present invention.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A moisture-curing curing agent used in the present invention is an oxazolidine compound which produces an OH group by hydrolysis in moisture and a ketimine which produces an amino group and a hydroxyl group by addition of moisture water. And the like, which are compounds that release a reactive group by water of moisture, and which act as a cross-linking agent before the curing reaction of polyurethane. Among them, oxazolidines and ketimines are particularly preferable. It is preferably included in component (i) in an amount of from 2 to 10% by weight thereof.

The polyurethane paint used in the present invention contains a hydroxyl group-containing resin and an optionally blocked polyisocyanate compound as main constituents.

The hydroxyl group-containing resin has a resin skeleton made of vinyl resin, polyester resin, or the like, and has a hydroxyl group introduced therein. The hydroxyl group content of these resins is preferably in the range of 10 to 260 mgKOH / g based on the hydroxyl value, and the number average molecular weight is suitably in the range of 1,000 to 60,000.

The hydroxyl group-containing resin whose resin skeleton is a vinyl resin can be produced, for example, by using a hydroxyl group-containing vinyl monomer in combination with other vinyl monomers and copolymerizing them by a usual method. The hydroxyl group-containing vinyl monomer is a compound having at least one hydroxyl group and at least one polymerizable unsaturated bond in one molecule, and is 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth). (Meth) acrylic acid such as acrylate and 2 to 10 carbon atoms
And a monoester compound with glycol. Furthermore, esterified products of these hydroxyl group-containing vinyl monomers and lactones can also be used as the hydroxyl group-containing vinyl monomer. As the other vinyl monomer, a compound having one or more polymerizable unsaturated bond in one molecule can be used. For example, a carboxyl group-containing vinyl monomer such as (meth) acrylic acid, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, and n- (meth) acrylate.
Butyl, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, decyl (meth) acrylate, (Meta)
Stearyl acrylate, lauryl (meth) acrylate,
C1-C24 alkyl or cycloalkyl ester of (meth) acrylic acid such as cyclohexyl (meth) acrylate; methoxybutyl (meth) acrylate,
2 to 2 carbon atoms of (meth) acrylic acid such as methoxyethyl (meth) acrylate and ethoxybutyl (meth) acrylate
18 alkoxyalkyl esters; aromatic monomers such as styrene and vinyltoluene; vinyl ethers; olefins; nitrogen-containing vinyl monomers; acid anhydrides such as hexahydrophthalic anhydride, succinic anhydride, tetrahydrosuccinic anhydride, methylhexahydro Half-esterified vinyl monomers of succinic anhydride and vinyl monomers containing hydroxyl groups; polymerizable anhydride monomers such as maleic anhydride, itaconic anhydride, hymic acid anhydride; polymerizable acid anhydrides and non-polymerizable monoalcohols (eg methanol , Ethanol, etc.) half-esterified vinyl monomer; glycidyl (meth) acrylate, methylglycidyl (meth)
Epoxy group-containing vinyl monomers such as acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate and allyl glycidyl ether; Fluorine-containing olefins such as vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene and chlorotrifluoroethylene Vinyl esters such as vinyl acetate, vinyl acetate, vinyl octylate, isopropenyl acetate, isopropenyl octylate; ω- (meth) acryloyl (oxy) alkyl acid phosphates, ω- (meth) acryloyl (oxy) alkyl acid phosphates and alcohols Examples thereof include a reaction product with and a hetero element-based oxygen-containing vinyl monomer such as a terminal sulfonic acid type (meth) acryloyl.

In producing the hydroxyl group-containing vinyl resin, it is preferable that the vinyl resin obtained has a hydroxyl value within the above range as a ratio of the hydroxyl group-containing vinyl monomer and the other vinyl monomer.

The hydroxyl group-containing resin whose resin skeleton is a polyester resin is a polyhydric alcohol having two or more hydroxyl groups in one molecule, a polybasic acid having two or more carboxyl groups in one molecule and an excess alcohol content. It can be obtained by an ester reaction by a known method. Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, hydrogenated bisphenol A, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol. Etc. are polybasic acids such as phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexahydrophthalic acid, het acid, hymic acid, maleic acid, fumaric acid. , Itaconic acid, trimellitic acid, and their anhydrides. The hydroxyl group-containing resin also includes a resin having an alkoxylsilyl group introduced, if necessary. The content of alkoxyl silyl groups is preferably 3.3 mmol or less per 1 g of resin.

The introduction of the alkoxysilyl group into the vinyl resin can be carried out, for example, by the above-mentioned vinyl monomer together with an alkoxysilyl group-containing vinyl monomer such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (methoxyethoxy) silane, γ- (. It can be carried out by copolymerization using (meth) acryloylpropyltrimethoxysilane, γ- (meth) acryloylpropyltriethoxysilane and the like in combination. The alkoxysilyl group can also be introduced by subjecting a vinyl resin or polyester resin having a hydroxyl group to a urethane reaction of an alkoxysilane compound having a terminal isocyanate group. This urethanization reaction is known.

The optionally blocked polyisocyanate compound acts as a cross-linking agent for forming a three-dimensionally cured coating film by cross-linking reaction with the hydroxyl group-containing resin.
Such a polyisocyanate compound is a polyisocyanate compound having two or more isocyanate groups in one molecule, and a blocked polyisocyanate in which some or all of the isocyanate groups are blocked.

Examples of polyisocyanates suitable for use are ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12 -Dodecane diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-1,3- and / or -1,4-diisocyanate, 1-isocyanate-2-isocyanate methylcyclopentane, 1-isocyanate-3,5,
5-trimethyl-5-isocyanate methylcyclohexane (isophorone diisocyanate or IPDI),
2,4- and / or 2,6-hexahydrotoluylene diisocyanate, 2,4′- and / or 4,
4'-dicyclohexylmethane diisocyanate, α,
α, α ′, α-tetramethyl-1,3- and / or -1,4-xylylene diisocyanate, 1,3- and 1,4-xylylene diisocyanate, 1-isocyanate-1-methyl-4 (3 ) -Isocyanate methyl-cyclohexane, 1,3- and 1,4-phenylene diisocyanate, 2,4- and / or 2,6-toluylene diisocyanate, diphenylmethane-2,4
-And / or -4,4'-diisocyanate, naphthalene-1,5-diisocyanate, triphenylmethane-4,4 ', 4 "-triisocyanate, condensation of aniline with formaldehyde and subsequent phosgenation (phosg
There are polyphenylpolymethylene polyisocyanates of the type obtained by enation) and mixtures of the abovementioned polyisocyanates.

Blocking agents for blocked polyisocyanates having blocked isocyanate groups include phenols, oximes, active methylenes, lactams, alcohols, mercaptans, acid amides, imides, amides, imidazoles and urea. , Carbamic acids, imines, etc.

The organic solvent used in the production of the component (i) is an organic solvent capable of dissolving the hydroxyl group-containing resin and the moisture-curing curing agent.

The paint of the present invention is a clear paint that forms a transparent coating film called a finish paint or a topcoat paint,
Directly on the coated object made of plastic or metal,
Alternatively, it is applied on an intermediate coating film made of metallic paint, solid color paint or the like. This paint may contain additives conventionally used in the paint industry such as an anti-flow agent, an ultraviolet stabilizer, a flame retardant and an antifouling agent, if necessary.

An example of the method for forming a coating film of the coating material of the present invention will be described below in detail: After applying a primer coating material and a metallic coating material as an intermediate coating material to a metal or plastic substrate, moisture curing Containing a curing agent (oxazolidine compound, ketimine compound, etc.) in a content of 2 to 10% by weight, viscosity 10 to 25 seconds Ford cup # 4/20
C., a polyurethane-based clear paint prepared by mixing an organic solvent-containing hydroxyl group-containing resin solution prepared to a solid content of 20 to 60% by weight with a polyisocyanate compound is applied onto the metallic paint by brush coating, roll coating, airless spraying,
Film thickness cured by air spray or electrostatic coating etc. 20
˜60 μm, then preheat dried to remove substantially any solvent, eg, up to 90%, subjected to a humidification step for moisture curing, and for urethane crosslinking reactions. It is cured at 80 to 150 ° C.

Since the coating film produced in this way is cured by moisture so that the crosslinking density increases from the inside toward the surface due to the difference in the degree of penetration of moisture, it has a low elasticity and a low crosslinking density. It has a cross-linking density that is inclined from the inside of the coating film to a surface portion with a high cross-linking density, and due to such a gradient function, it exhibits excellent acid resistance and scratch resistance. That is, the coating film surface portion that is directly exposed to moisture during the humidification step has its hardness increased by moisture curing and heat curing,
Since it has a high glass transition point, it exhibits high acid resistance. On the other hand, moisture does not penetrate into the inside of the coating film during the humidification process, so that moisture curing is not promoted and appropriate elasticity is maintained. Therefore, when an external force is applied to the surface of the coating film from a car washing machine or the like, the inside of the coating film is slightly bent, which prevents the surface from being scratched.

[0024]

【Example】Manufacturing example: A) Production of hydroxyl group-containing resin: 1) 30 parts by weight of butyl methacrylate, methyl methacrylate
Rate 40 parts by weight, hydroxyethyl methacrylate 2
A mixture of 0 parts by weight and 10 parts by weight of styrene,
50 parts by weight of xylene and 10 parts by weight of butanol
Copolymerize by heating to 125 ° C in a mixed solvent. About 61%
A resin solution having a solid content of is obtained. 2) 50 parts by weight of butyl methacrylate, methyl methacrylate
Rate 30 parts by weight, hydroxyethyl methacrylate 2
A mixture of 0 parts by weight was added to 45 parts by weight of xylene and pig.
Heat to 125 ° C in a mixed solvent consisting of 5 parts by weight of nol
And copolymerize. A resin solution with a solids content of about 57%
can get. B) Preparation of component (i): 1) 100 parts by weight of the solution of A1) is represented by the following formula
Add 8 parts by weight of the sazolidine compound.

[0025]

[Chemical 1]

[0026]Painting example: a) (Comparative example) Hydroxyl group-containing solution of the above Production Example A1) and hexamethylenedi
Isocyanate is mixed (NCO / OH-ratio: 1 /
1), Medium coated on a metal plate and dried by a conventionally known method
Spray to a dry coating thickness of 40 μm on the coating layer.
-Coat and heat at 140 ° C for 30 minutes to cure urethane
To respond. b) (Example) Hexamethylene diisocyanate is used as component (i) B) in the above Production Example.
Add anate (NCO / OH-ratio: 1/1) and mix
To do. An intermediate coating of this mixture on a metal plate and dried
Spray coating on the layer to a dry coating thickness of 40 μm
And preheat at 80 ° C for 10 minutes to substantially remove the solvent.
And then in a humid chamber (relative humidity 100%, room temperature) for 10 seconds
Moisture cure between. Finally in a drying oven at 140 ° C for 30 minutes
Urethane reacts and cures. c) (Comparative example) Hydroxyl group-containing solution of Production Example A2) and hexamethylene diiso
Cyanate and mixed (NCO / OH-ratio: 1/1),
An intermediate coating layer applied to a metal plate and dried by a conventionally known method
Spray coating on top of it to give a dry coating thickness of 40 μm
And then heat at 140 ° C. for 30 minutes.

Coating performance test results: A coating film performance test is carried out using the coated metal plates obtained in the above a) to c). The results are shown in Table 1.

[0028]

[Table 1]

Acid resistance: A 1% strength sulfuric acid aqueous solution was applied to the coated surface and gradually heated in a graduate oven to measure the temperature at which etching marks began to remain. ⊚ indicates that it was the best, ∘ indicates that it was relatively good, and Δ indicates that the etching occurred earliest.

Scratch resistance: A test coating film plate was attached to the outer surface of an automobile, and the gloss retention (GR) of the coated surface after washing at 20 ° C. in an automobile car was measured. ⊚ indicates that it was the best, ∘ indicates that it was relatively good, and Δ indicates that the etching was the worst.

From the results of this test, the coating according to the invention of b) is outstandingly superior in both scratch resistance and acid resistance to those of a) and b) not coated with the coating of the invention. I understand.

[0032]

According to the invention of claim 1, a clear coating film having both acid resistance and scratch resistance can be obtained.

According to the second aspect of the present invention, it is possible to provide a coating material capable of forming a coating film excellent in acid resistance and scratch resistance.

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Claims (2)

[Claims] 1. A two-component polyurethane-based organic solvent-containing paint using a moisture-curing curing agent as a curing agent is applied,
After the solvent is substantially removed, the curing agent is cured by external humidification so that the crosslinking density increases from the inside toward the surface due to the difference in the degree of penetration of moisture, and then the urethane curing reaction is performed by heating. A method for forming a clear coating film. 2. The two-component polyurethane coating composition according to claim 1, wherein the coating composition comprises (i) an organic solvent-dilutable hydroxyl group-containing resin containing a moisture-curing curing agent, and (ii) an optionally blocked isocyanate compound. The two-component polyurethane-based organic solvent-containing coating material, characterized in that