JPH0693228A - Method for forming coating film - Google Patents

Abstract

PURPOSE:To form a coating film having excellent chipping resistance, impact resistance, solvent resistance, etc., in a process for coating a middle coating compound and a top coating compound, by using a coating compound consisting essentially of a specific self-cross-linkable resin as the middle coating compound. CONSTITUTION:A self-cross-linkable resin containing both a block isocyanate group and an OH group in one molecule obtained by bonding a vinyl polymer containing a block isocyanate group in one molecule to a polyester resin containing an OH group in one molecule through a urethane group, such as a self-cross-likable resin obtained by reacting part of the liberated isocyanate group of a vinyl polymer containing two or more liberated isocyanate groups in one molecule with part of the OH group in a polyester resin containing two or more OH groups in one molecule and reacting the whole remaining liberated isocyanate group with a blocking agent. The self-cross-linkable resin is used as a main component to give a coating compound, which is used as a middle coating compound in a process consisting of a middle coating process and a top coating process to form a coating film having excellent chipping resistance, etc.

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 coating film having improved chipping resistance, impact resistance, solvent resistance, smoothness and sharpness.

[0002]

2. Description of the Related Art Conventionally, an outer panel of an automobile or the like is coated with a multi-layer coating film consisting of an undercoat coating film, an intermediate coating film and an overcoat coating film for the purpose of protection and imparting beauty.
Among these, the intermediate coating film is important for improving the smoothness and chipping resistance of the top coating film. That is, the intermediate coating film eliminates fine irregularities on the surface to be coated after the undercoat coating to improve the smoothness of the top coating film, and the coating film remains even if pebbles or the like hit the coating film while the automobile is running. It is very important because it has a function of preventing breakage and not lowering cosmetic properties and anticorrosion properties, and improving so-called chipping resistance.

Particularly in cold regions such as North America and Northern Europe,
In order to prevent the occurrence of traffic accidents due to road surface freezes in winter,
It is common practice to pebble the road surface, and the anti-chipping performance of a vehicle traveling at high speed on the road surface has become more and more important in recent years.

In order to improve the smoothness and chipping resistance of the above-mentioned top coating film, an intermediate coating composition using a soft polyester resin as a base resin and a melamine resin as a curing agent is widely used, but it is insufficient. there were. Further, when the melamine resin is replaced with a polyisocyanate compound, a urethane bond is formed by a curing reaction, and thus the physical properties such as chipping resistance and impact resistance of the coating film are improved, but the smoothness is not sufficient, and further It has been pointed out that it has the drawbacks described in 1.

First, when a polyisocyanate compound having a free isocyanate group is used as a curing agent,
Since the cross-linking reaction with the base resin proceeds rapidly even at room temperature, it becomes a two-component type paint in which both components are mixed immediately before use.
Therefore, in addition to requiring special coating equipment, there are serious defects in the workability of coating, such as the difficulty of cleaning the coating equipment.

On the other hand, if a blocked polyisocyanate compound is used, a one-pack type intermediate coating composition having good storage stability can be obtained. However, since the blocking agent has a high dissociation temperature, it is difficult to cure the coating film. Normally, a baking temperature of 150 ° C. or higher is required, and the low temperature curability is inferior to that of the above melamine resin curable coating which can be baked and cured at 120 ° C. to 140 ° C. In addition, since the block polyisocyanate compound does not have sufficient compatibility with the base resin, the curability of the intermediate coating film is not sufficient, and the image clarity, smoothness, impact resistance, solvent resistance and chipping resistance are based on that. It also has a defect that the property and the like are deteriorated.

[0007]

DISCLOSURE OF THE INVENTION The present invention is intended to eliminate the above-mentioned defects by using a polyisocyanate compound or a blocked polyisocyanate compound as a curing agent. 1
An intermediate coating composition containing a specific self-crosslinking resin in which a blocked isocyanate group and a hydroxyl group, which are complementary reactive groups, coexist in the molecule, is used. As a result, the intermediate coating film can be cured at a low temperature to the same extent as or higher than the melamine resin-curable coating material, and since a specific self-crosslinking resin is used, the compatibility with the crosslinking agent is high. All the above defects due to insufficiency are eliminated,
The curability, sharpness, smoothness, impact resistance, solvent resistance and chipping resistance could be improved. Therefore, when the topcoat paint is applied to the surface of the intermediate coating film, a topcoat film having excellent image clarity, smoothness, impact resistance and chipping resistance is formed.

That is, according to the present invention, a vinyl polymer having a blocked isocyanate group in one molecule and a hydroxyl group in one molecule are used as the intermediate coating material in the step of applying the intermediate coating material and the top coating material to the substrate. A method for forming a coating film, which comprises using an intermediate coating composition containing, as a main component, a self-crosslinking resin in which a blocked isocyanate group and a hydroxyl group coexist in one molecule formed by bonding a polyester resin through a urethane group. Pertain to.

In the present invention, the self-crosslinking resin in which a blocked isocyanate group and a hydroxyl group coexist in one molecule used will be described.

The self-crosslinking resin is a resin in which a vinyl polymer having a blocked isocyanate group in one molecule and a polyester resin having a hydroxyl group in one molecule are bonded via a urethane group. The resin is, for example, (I) a polyester resin having two or more hydroxyl groups in one molecule in a part of the free isocyanate groups of the vinyl polymer (A) having two or more free isocyanate groups in one molecule ( B)
A part of the hydroxyl groups therein and then reacting all the remaining free isocyanate groups with a blocking agent, or (II) a vinyl polymer having a free isocyanate group and a blocked isocyanate group in one molecule. It can be obtained by reacting a part of the hydroxyl groups in the polyester resin (B) having two or more hydroxyl groups in one molecule with all the free isocyanate groups in the polymer (C).

The vinyl polymer (A) is a vinyl polymer having two or more free isocyanate groups in the molecule,
Specifically, a polymer obtained by using an isocyanate group-containing vinyl monomer (hereinafter abbreviated as “NCO group-containing monomer”) as an essential component, and further using other vinyl monomer as necessary. Yes, it is mainly composed of a linear polymer having an isocyanate group at the terminal and / or side chain.

The NCO group-containing monomer is a compound having at least one unblocked free isocyanate group and at least one radically polymerizable double bond in one molecule, and examples thereof include methacryloyl isocyanate and 2-isocyanatoethyl. One or two selected from methacrylate, m- or p-isopropenyl-α, α'-dimethylbenzyl isocyanate, a 1: 1 (molar ratio) adduct of a hydroxyl group-containing vinyl monomer and a diisocyanate compound, and the like.
More than one seed is used.

The hydroxyl group-containing vinyl monomer used in the preparation of the NCO group-containing monomer is a compound having at least one hydroxyl group and at least one radically polymerizable double bond in one molecule, for example 2-hydroxyethyl ( Examples thereof include (meth) acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl acrylate, 2,3-dihydroxypropyl acrylate, 2-hydroxy-3-phenoxyethyl acrylate, and 2-hydroxy-3-ethoxyethyl acrylate. Further, an equimolar addition product of acrylic acid or methacrylic acid and glycol (having 2 to 20 carbon atoms) may, for example, be mentioned.

The diisocyanate compound used in the preparation of the NCO group-containing monomer has two isocyanate groups in one molecule. For example, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylene diisocyanate, Hexamethylene diisocyanate, lysine diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4 (2,6) -diisocyanate, isophorone diisocyanate, trimethylhexane diisocyanate, and other aliphatic, aromatic and alicyclic systems The diisocyanate compound of is mentioned.

Preferred among the above as the NCO group-containing monomer are 2-isocyanate ethyl methacrylate,
Examples include m-isopropenyl-α, α'-dimethylbenzyl isocyanate, an equimolar addition product of 2-hydroxyethyl acrylate and isophorone diisocyanate, and the like.

The vinyl polymer (A) is obtained by polymerizing only the above NCO group-containing monomer or by copolymerizing this with another vinyl monomer.

Further, the other vinyl monomer is preferably a compound having a radically polymerizable double bond in one molecule and not having active hydrogen capable of reacting with an isocyanate group, specifically, styrene and α. -Aromatic vinyl monomers such as methylstyrene and vinyltoluene; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
(Meth) acrylic acid esters such as lauryl (meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, and benzyl (meth) acrylate; viscose 3F (Osaka Organic Chemical Co., Ltd., product Name, the same meanings below), 3MF, 8F, 8MF, perfluorocyclohexyl (meth) acrylate, N-2-propylperfluorooctane sulfonic acid amide (meth) acrylate, vinyl fluoride, vinylidene fluoride. Fluorine-containing vinyl monomers such as N, N'-diethylaminoethyl (meth) acrylate, N, N'-diethylaminoethyl (meth) acrylate, N, N'-diethylaminoethyl (meth) acrylate, N, N ' -Diethyl (meth) acry Nitrogen-containing vinyl monomers such as amides; vinyl ether monomers such as vinyl ethyl ether and vinyl butyl ether; and glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, aryl glycidyl ether, methylol Alkyl ether compound of acrylamide, (meth) acrylamide, (meth) acrylic acid chloride,
Examples thereof include vinyl chloride, vinylidene chloride, (meth) acrylonitrile, and γ-methacryloxyalkyltrimethoxysilane. These may be used alone or in combination of two or more.

The ratio of the NCO group-containing monomer to the other vinyl monomer is not particularly limited as long as it has two or more free isocyanate groups in one molecule of the polymer (A).
100 / 0-1 / 99, preferably 65 / 35-, based on NCO group-containing monomer / other vinyl monomer (weight ratio)
A range of 30/70 is suitable.

The polymerization reaction of the NCO group-containing monomer alone or with the other vinyl monomer is preferably carried out in an inert organic solvent which does not normally have active hydrogen capable of reacting with an isocyanate group. . As such an inert organic solvent, for example, hexane, heptane, an aliphatic hydrocarbon such as octane, an aromatic solvent such as benzene, toluene, xylene, an ester solvent, a single solvent such as a ketone solvent, or a mixed solvent is used. To be Since these solvents may contain water, it is preferable to dehydrate them if necessary.

These polymerization reactions are usually carried out at 50 to 180.
It is carried out at a temperature of ° C using a radical polymerization initiator, and the molecular weight of the polymer (A) can be adjusted by the reaction concentration, the amount of the initiator and the like. The reaction concentration is 20 to 80% by weight as a polymer. In particular, in order to increase the polymerization rate, a peroxide type or carbonate type initiator is used, and the reaction temperature is 10
It is preferably carried out at 0 ° C or higher. More preferably, when an acrylate-based monomer is used in combination, a polymer having a high polymerization rate can be easily obtained. The concentration of the polymerization initiator is 0.01-1 of all monomers.
It can be used in the range of 5% by weight, but preferably in the range of 0.1-10% by weight.

Further, instead of using the polymerization initiator, the polymerization can be carried out by using an electron beam, an ultraviolet ray or the like.

In addition to radical polymerization, ionic polymerization or group transfer polymerization method can also be used.

The weight average molecular weight of the polymer (A) used in the present invention is 1,000 to 100,000, particularly 3,000 to
The range of 30,000 is preferable. A resin having an isocyanate value of 30 to 200 g / 1000 g is suitable.

The polymer (A) has two or more free isocyanate groups in one molecule, but preferably has no active hydrogen capable of reacting with the isocyanate groups.

The polyester resin (B) has 2 in one molecule.
It is a polyester resin having one or more hydroxyl groups. The polyester resin (B) requires a polybasic acid (B-1) having two or more carboxyl groups in one molecule and a polyhydric alcohol (B-2) having two or more hydroxyl groups in one molecule. It can be obtained by esterification or transesterification reaction using a fatty acid and / or fatty acid methyl ester (B-3) as a raw material as a component and containing a free hydroxyl group.

Examples of the polybasic acid (B-1) include (anhydrous) phthalic acid, terephthalic acid, isophthalic acid, tetrahydro (anhydrous) phthalic acid, hexahydro (anhydrous) phthalic acid, 4-methylhexahydro (anhydrous). Phthalic acid, 3-
Methyl hexahydro (anhydrous) phthalic acid, 3-methyl tetrahydro (anhydrous) phthalic acid, (anhydrous) trimellitic acid,
(Anhydrous) pyromellitic acid, (anhydrous) hettic acid, (anhydrous)
Examples thereof include hymic acid, adipic acid, sebacic acid, azelaic acid, succinic anhydride, maleic anhydride, fumaric acid, itaconic acid, dimethyl isophthalate and dimethyl terephthalate. Of these, an aliphatic dibasic acid such as adipic acid is used in the acid component of the polyester component in an amount of 15 to
It is preferable to contain 50 mol%.

The polyhydric alcohol (B-2) is a compound having two or more alcoholic or phenolic hydroxyl groups in one molecule, and specific examples thereof include ethylene glycol, diethylene glycol, triethylene glycol and polyethylene. Glycol, 1,6-hexanediol, pentanediol, cyclohexanone dimethanol, propylene glycol, butylene glycol, butylene diglycol, trimethylolethane, trimethylolpropane, glycerin, neopentyl glycol,
Examples thereof include sorbitol, tris (2-hydroxyethyl) isocyanurate, diethanolamine, diisopropanolamine, bisphenol A and bisphenol F. Of these, aliphatic diols such as 1,6-hexanediol are preferred.

Examples of (B-3) include safflower oil fatty acid, linseed oil fatty acid, soybean oil fatty acid, eno oil fatty acid, corn oil fatty acid, tall oil fatty acid, sunflower oil fatty acid, cottonseed oil fatty acid, tung oil fatty acid and the like. (Half)
Dry oil fatty acid, coconut oil fatty acid, olive oil fatty acid, palm oil fatty acid and the like can be used. Among these, (semi) drying oil fatty acid is preferably used from the viewpoint of improving coating film performance.

In the present invention, the polyester resin (B)
Generally has an acid value (mgKOH / g resin) in the range of 200 or less and a hydroxyl value (mgKOH / g resin) in the range of about 5 to 400, preferably about 20 to about 250. . If the hydroxyl value is less than about 5, the curability of the coating film tends to decrease, and the coating performance such as hardness and bending resistance tends to decrease. On the other hand, if the hydroxyl value exceeds about 400, water resistance, corrosion resistance, etc. It is not so preferable because the coating film performance is deteriorated.

The introduction of a hydroxyl group into the polyester resin (B) is preferably carried out, for example, by using a compound having 3 or more hydroxyl groups in one molecule in combination as the polyhydric alcohol (B-2).

The polyester resin (B) generally has a weight average molecular weight of about 500 to about 50,000, preferably about 1,000 to about 30,000 and a softening point of 1.
Desirably, it is below 50 ° C, preferably below about 115 ° C.

The esterification reaction with the above-mentioned components for producing the polyester resin (B) is preferably carried out in the presence of an organic solvent. The organic solvent used for this esterification reaction is preferably an inert organic solvent which does not have active hydrogen capable of reacting with an isocyanate group in consideration of introduction of a urethane bond based on a urethane reaction with the vinyl polymer A. Specifically, those exemplified in the production of the polymer (A) are preferable, and hydrophilic or water-soluble solvents having no active hydrogen are also preferable, and for example, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether and the like are preferable.

On the other hand, when the hydroxyl group-containing polyester resin (B) is synthesized in an organic solvent having active hydrogen, the organic solvent is removed under reduced pressure or the like, or concentrated or spray-dried to remove the polymer ( It can be used for the urethane reaction with A). Further, as the polyester resin (B), a ring-opening polymer of ε-caprolactone can also be used, and specific examples thereof include Placcel 208, 240, 305 and 308 manufactured by Daicel Chemical Industries Ltd.

In the production of the self-crosslinking resin (I), the vinyl polymer (A) and the hydroxyl group-containing polyester resin (B)
The reaction with is a urethanization reaction of an isocyanate group and a hydroxyl group, specifically, the hydroxyl group-containing polyester resin (B) is blended in an organic solution of the vinyl polymer (A), and usually 20 to 100 ° C., preferably Undergoes a urethanization reaction at a temperature of 25 to 60 ° C. The reaction is controlled by the reduction amount of isocyanate groups, that is, the isocyanate value. In this reaction, a tin-based catalyst may be used if necessary. The amount of the hydroxyl group-containing polyester resin (B) to be blended is 0.1 to 10.0, preferably based on the functional group ratio of the vinyl polymer (A) and the hydroxyl group containing polyester resin (B), that is, the NCO / OH ratio. The range of 0.5 to 5.0 is suitable, and the vinyl polymer (A) is 1 to 99% by weight, preferably 10 to 7 based on the total weight of both.
0 wt% and hydroxyl group-containing polyester resin (B) 1-9
9% by weight, preferably 30 to 90% by weight. The weight average molecular weight of the vinyl polymer (A) is 500 to 5
It may be blended so that at least 0.1 urethane bonds can be introduced per 1 molecule of 0000, and preferably 0.5 to 1 per 1 molecule of vinyl polymer (A) having a weight average molecular weight of 500 to 30000. It is preferable that 0.5 urethane bonds are introduced, and most preferably, 1 urethane bond is introduced per 1 molecule of the vinyl polymer (A).

In the production of the self-crosslinking resin (I), a vinyl polymer containing, as the vinyl polymer (A), m-isopropenyl-α, α'-dimethylbenzyl isocyanate having a tertiary isocyanate group. The use of (A) is particularly preferable because it prevents gelation in the reaction with the hydroxyl group-containing polyester resin (B) and enables low-temperature curability of the coating film.

Next, as described above, the hydroxyl group-containing polyester resin (B) is reacted to introduce a urethane bond, and the hydroxyl group-containing polyester resin (B) is added to the residual free polymer contained in the vinyl polymer (A). A self-crosslinking resin (I) is obtained by reacting an isocyanate group with a blocking agent and completely blocking it. Examples of the blocking agent include phenol, cresol, xylenol, p-ethylphenol, o-isopropylphenol, p-tert-butylphenol, p-tert-.
Octylphenol, thymol, p-naphthol, p-
Phenols such as nitrophenol and p-chlorophenol; alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol, methyl cellosolve, butyl cellosolve, methyl carbitol, benzyl alcohol, phenyl cellosolve, furfuryl alcohol, cyclohexanol: malon Dimethyl acid,
Active methylene type such as ethyl acetoacetate; Mercaptan type such as butyl mercaptan, thiophenol, tert-dodecyl mercaptan; Acid amide type such as acetanilide, acetaniside, acetic acid amide, benzamide; Imide type such as succinimide, maleic acid imide; Amine-based compounds such as diphenylamine, phenylnaphthylamine, aniline and carbazole; imidazole-based compounds such as imidazole and 2-ethylimidazole; urea-based compounds such as urea, thiourea and ethyleneurea; phenyl N-phenylcarbamate.
Carbamates such as 2-oxazolidone: Imines such as ethyleneimine; oximes such as formaldoxime, acetaldoxime, acetoxime, methylethylketoxime, methylisobutylketoxime, cyclohexanoneoxime; sodium bisulfite, potassium bisulfite And sulfites such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propiolactam, and the like. Of these,
Phenol-based, lactam-based, alcohol-based, and oxime-based are preferable, but low temperature baking (120
When it is required to be (° C. Or lower), an oxime-based blocking agent is most preferable.

In principle, the blocking agent is preferably incorporated in an amount necessary to react with all the remaining free isocyanate groups.

The reaction between the polymer (A) to which the hydroxyl group-containing polyester resin (B) is added and the blocking agent is usually 20 to
It is carried out at a temperature of 100 ° C. Moreover, you may use a tin-type catalyst etc. as needed.

The self-crosslinking resin (II) has two hydroxyl groups in one molecule for all the free isocyanate groups in the vinyl polymer (C) in which a free isocyanate group and a blocked isocyanate group coexist in one molecule. It is a self-crosslinking resin in which a blocked isocyanate group and a hydroxyl group coexist in one molecule obtained by reacting a part of the hydroxyl group in the polyester resin (B).

The vinyl polymer (C) is a vinyl polymer in which a free isocyanate group and a blocked isocyanate group coexist in one molecule, and specifically, the free isocyanate group contained in the vinyl polymer (A). It is obtained by reacting a part of the blocking agent with a blocking agent. Regarding the vinyl polymer (A) used for preparing the vinyl polymer (C), those described above can be used as the NCO group-containing monomer, and particularly preferred are 2-isocyanate ethyl methacrylate and m-. A vinyl polymer (A) obtained by using isopropenyl-α, α'-dimethylbenzyl isocyanate, an equimolar addition product of 2-hydroxyethyl acrylate and isophorone diisocyanate, and the like.

The amount of the blocking agent added to the polymer (A) is
If the amount required to leave free isocyanate groups so that the amount of urethane bonds introduced based on the reaction with the hydroxyl group-containing polyester resin (B) in the next step becomes similar to that of the self-crosslinking resin (I), Well, it is particularly preferable that the amount of the blocking agent required to completely block the remaining free isocyanate groups by allowing one urethane bond to be introduced per molecule of the polymer (A). It is preferable to mix and react.

Then, a part of the hydroxyl groups in the hydroxyl group-containing polyester resin (B) is reacted with all the remaining free isocyanate groups in the polymer (C) obtained by reacting the polymer (A) with the blocking agent. As a result, the self-crosslinking resin (II) is obtained. That is, it is necessary that the number of hydroxyl groups in the resin (B) is greater than that of the above residual free isocyanate groups.

The reaction with the blocking agent and the reaction between the polymer (A) and the resin (B) for obtaining the self-crosslinking resin (II) are the same as those described for the self-crosslinking resin (I). Done.

The self-crosslinking resins (I) and (II) are composed of a blocked isocyanate group-containing resin molecule and a hydroxyl group-containing polyester resin molecule bonded via a urethane bond formed by a reaction between an isocyanate group and a hydroxyl group. . Therefore, it can be said that it is a graft polymer of both resin molecules.

The self-crosslinking resins (I) and (II) thus obtained have at least one blocked isocyanate group and at least one hydroxyl group, and the weight average molecular weight thereof is about 1000 to 120,000, particularly 5000.
It is preferably about 50,000. The self-crosslinking resin used in the present invention has the highest degree of crosslinking as a self-crosslinking coating film if the amounts of the blocked isocyanate group and the hydroxyl group are equal in one molecule. Considering the adhesion to the base material and the top coating film, it is preferable that the hydroxyl groups are excessive. Hydroxyl value of the resin (mgK
OH / g resin) is 30 to 200, isocyanate value (g
/ 1000g resin) is 15 to 150, acid value (mgKOH
/ G resin) is suitably in the range of 200 or less.

The intermediate coating used in the present invention contains the above-mentioned self-crosslinking resin and pigment as main components, and further contains a pigment dispersant, a curing catalyst, an antioxidant, a surface conditioner, etc., if necessary. Can be used as a one-pack type coating material prepared by mixing with an organic solvent and / or water. Further, other polyester polyols, reactive diluents, epoxy resins, and melamine resins as other cross-linking agents can also be blended. However, the content of the self-crosslinking resin is preferably 30 to 100% by weight based on the total solid content of the resin in order to obtain good chipping resistance.

Examples of pigments include chromatic inorganic pigments such as titanium white, red iron oxide, and carbon black, quinacridone red,
Coloring organic pigments such as phthalocyanine blue and extender pigments such as barium sulfate, talc and clay can be used alone or in combination of several kinds. The concentration of the pigment is not particularly limited as long as it is a concentration capable of imparting the hiding power so that the underlying color cannot be seen through. However, in order to secure the finished appearance after the topcoat coating, it is 20% relative to the resin solid content. ~ 120% by weight
Is preferred.

Examples of the curing catalyst include tetraisopropyl titanate, tetrabutyl titanate, lithium acetate, iron (III) acetylacetone, zinc 2-ethylhexonate, copper acetate, vanadium trichloride, tin octylate, dibutyltin diacetate, dibutyl. Tin dioctoate, dibutyltin dilaurate, dibutyltin dimaleate, tetrabutyltin, dibutyltin oxide, tetra-n-butyl-
1,3-diacetyloxydistannoxane, tetra-n
Examples thereof include metal catalysts such as -propyl-1,3-diacetyloxydistannoxane and tetra-n-butyl-1,3-dilauryloxydistannoxane. You may use these metal catalysts individually or as a mixture of 2 or more types. Furthermore, for example, 3 such as trimethylamine, triethylamine, dimethylcyclohexylamine, N-tetramethylhexane-1,6-diamine, N-pentamethyldiethylenetriamine, 2-methyl-1,4-diazabicyclo [2,2,2] octane. A primary amine can also be preferably used as a curing catalyst. In particular, organic tin compounds such as tin octylate, dibutyltin diacetate, dibutyltin dilaurate and distannoxane are preferable. The amount of the curing catalyst varies depending on its type, but is usually about 0 to 5% by weight.

In the method for forming a coating film of the present invention, in the step of applying an intermediate coating composition and a top coating composition to a substrate, a coating composition containing a self-crosslinking resin having the above-mentioned specific composition as a main component is used as the intermediate coating composition. Is characterized by.

Examples of the substrate include the article to be coated itself and the article to be coated with an undercoat paint. As the article to be coated, for example, metals and plastics used for outer panels of automobiles, household electric appliances and office equipment are preferable, and these are preferably surface-treated in advance by a known method. Further, as the above-mentioned undercoating material, conventionally known ones can be used, and for example, a cationic electrodeposition coating material is suitable for metal.

In the present invention, such a base material is coated with an intermediate coating composition containing the above-mentioned specific composition of the self-crosslinking resin as a main component. The coating of the intermediate coating material is not particularly limited and can be carried out by a conventionally known means, but preferably electrostatic coating (bell type,
(REA type, etc.), air spray coating, or the like. The coating film thickness is usually about 10 to 10 as a dry film thickness.
A range of 0 μm, preferably about 25-50 μm is suitable. The coating film is hardened by baking, and the baking condition is, for example, about 110 ° C to 160 ° C, preferably about 1 ° C.
Suitably it is carried out at a temperature between 20 ° C and 140 ° C.

A topcoat paint can be applied to the intermediate coating surface thus formed. As the top-coat paint, known ones can be used, and for example, one or more base resins selected from acrylic resin, polyester resin, alkyd resin, fluororesin, etc. and a curing agent such as melamine resin or blocked isocyanate compound are the main components. A thermosetting coating composition is preferred. Examples of top-coat paints containing these as the main components include solid color paints containing color pigments, metallic paints containing metallic pigments, and clear paints containing no such pigments in principle. Using these paints, a top coat film can be formed by a 1-coat 1-bake system, a 2-coat 2-bake system, or the like.

[0053]

【The invention's effect】

(1) The smoothness, sharpness, chipping resistance, and the like after the top coating is improved as compared with the conventional intermediate coating.

(2) Since the intermediate coating material used in the present invention is a one-pack type, weighing of each component, mixing operation, restriction of pot life and maintenance of the coating apparatus immediately before use in the two-pack type, etc. All the complicated problems of were solved.

(3) Various defects based on the compatibility with the curing agent in the one-pack type intermediate coating composition using the blocked polyisocyanate compound, such as curability, sharpness, smoothness, impact resistance and resistance Solvent resistance, chemical resistance, chipping resistance, etc. were all eliminated in the present invention.

(4) The intermediate coating composition used in the present invention has excellent low-temperature curability, and even if a melamine resin is used together, the curing reaction temperature can be carried out within the same temperature range, and uniform curing is possible. It was

[0057]

The present invention will be further described below with reference to examples, but the present invention is not limited thereto. All parts and% in the examples and comparative examples are based on weight.

Sample 1 Base material: Elektron HB-2000 (manufactured by Kansai Paint Co., Ltd.) on a surface-treated steel sheet having a size of 15 × 7 cm and a thickness of 0.8 mm.
Cation electrodeposition paint) based on the cured coating film thickness is 25μ
A primer-coated steel sheet that is electrodeposited to a m and baked at 160 ° C for 30 minutes to cure.

2 Topcoat Paint 2-1 Metallic Paint Magicron TB-500 Silver Metallic (Kansai Paint Co., Ltd., acrylic / melamine base coat, aluminum concentration 12.5 PHR).

2-2 Clear paint Magicron TC-50 clear (Kansai Paint Co., Ltd., acrylic / melamine clear coat).

3 Intermediate coating 3-1 Intermediate coating (P-1) 1) Preparation of vinyl polymer (A-1) 65 parts of xylene was placed in a reactor equipped with a stirrer, a reflux condenser and a thermometer. The mixture was charged and kept at 130 [deg.] C., 50 parts of m-isopropenyl- [alpha], [alpha] '-dimethylbenzyl isocyanate, 30 parts of n-butyl acrylate, 20 parts of 2-ethylhexyl acrylate, and t-butyl peroxyisopropyl carbonate 4
Part of the mixture was added dropwise over 3 hours. Then, a mixed solution of 35 parts of xylene and 1.0 part of t-butylperoxyisopropyl carbonate was added dropwise over 1 hour and aged for 3 hours (this reaction solution is referred to as a vinyl polymer solution (A-1)). The obtained resin liquid was a colorless and transparent liquid having a solid content of 50%. The Gardner viscosity (Gardner foam viscometer, measured at 25 ° C., the same meanings below) is D, the weight average molecular weight is about 6000, and the isocyanate value is 1.
It was 00 g / 1000 g resin.

2) Preparation of polyester resin (B-1) In a reactor equipped with a stirrer, a reflux condenser, a rectification column and a thermometer, 36.5 parts of adipic acid, 58.1 parts of isophthalic acid,
Hexahydrophthalic anhydride 30.8 parts, trimethylolpropane 27.3 parts and neopentyl glycol 84.
160 parts of the mixture was stirred under a nitrogen gas atmosphere while stirring.
After reacting at ~ 230 ° C for 10 hours (dibasic acid ratio: 0.
8), acid value 8 mg KOH / 1 g resin, hydroxyl value 167 mg K
An OH / 1 g resin polyester resin was obtained. Next, the obtained polyester resin was dissolved in xylene to obtain a polyester resin liquid (B-1) having a solid content of 65%. The weight average molecular weight of this resin was about 4000.

3) Preparation of self-crosslinking resin (I-1) 2000 parts of vinyl polymer solution (A-1) and polyester resin solution (B-1) were placed in a reactor equipped with a stirrer, a reflux condenser and a thermometer. ) 1367 parts were added, and the mixture was added at room temperature (25 ° C) to 30
After stirring for a minute and measuring the isocyanate value of the mixture, it is 5
It was 2.9 (this was made into the initial isocyanate value). Then, the mixture was heated and maintained at 40 ° C. with stirring, the reaction was allowed to proceed for about 3 hours, and when the isocyanate value reached 50.0, 227 parts of methylethylketoxime was added,
The mixture was aged at 60 ° C for 2 hours to obtain a self-crosslinking resin liquid (I-1).

The resin solution (I-1) thus obtained had a solid content of 58% and a hydroxyl value of 69.5 mg KOH / 1 g resin,
The acid value was 3.4 mg KOH / 1 g resin, the NCO / OH ratio was 0.90, and the weight average molecular weight was about 11,000. Further, no thickening was observed even after this resin solution was stored at 30 ° C. for 6 months.

[0065] Was added to obtain an intermediate coating composition (P-1).

3-2 Intermediate Coating Paint (P-2 ) 292 parts of the above intermediate coating paint (P-1) is coated with Epicoat 82.
5.0 parts (trade name, epoxy resin, manufactured by Ciel Chemical Co., Ltd.) was added.

3-3 Intermediate Coating (P-3) 1) Preparation of Hydroxyl Group-Containing Polyester Resin (B-2) In a reactor equipped with a stirrer, a reflux condenser, a rectification column and a thermometer, isophthalic acid 66 A mixture of 4 parts, 38.5 parts of hexahydrophthalic anhydride, 36.5 parts of adipic acid, 27.3 parts of trimethylolpropane and 84 parts of neopentyl glycol while stirring under a nitrogen gas atmosphere at 160-23.
After reacting at 0 ° C. for 10 hours (dibasic acid ratio 0.9), acid value 8 mg KOH / 1 g resin, hydroxyl value 99.8 mg KOH / 1
A polyester resin of g resin was obtained. Next, the obtained polyester resin was dissolved in xylene to obtain a polyester resin liquid (B-2) having a solid content of 65%. The weight average molecular weight of the resin was about 6000.

2) Preparation of intermediate coating composition (P-3) 50 parts of TITON R-51N, 20 parts of barium sulfate B30, 40 parts of self-crosslinking resin liquid (I-1), 30 parts of xylene were used with a paint shaker for 1 hour. Dispersed, then 64.8 parts of self-crosslinking resin liquid (I-1), 46.2 parts of polyester resin liquid (B-2), Uban 20SE (Mitsui Toatsu, melamine resin, solid content 60%) 25 parts Dibutyltin dilaurate (0.6 part) and Disparlon L-1980 (0.2 part) were added to obtain an intermediate coating composition (P-3).

The self-crosslinking resin (I-1) in the resin solids of this coating was 55% and the melamine resin was 15%.

3-4 Intermediate Coating (P-4) 1) Preparation of Vinyl Polymer (A-2) A reactor equipped with a stirrer, a reflux condenser and a thermometer was charged with 65 parts of xylene and heated to 130 ° C. The mixture is heated and held at 40 parts of m-isopropenyl-α, α'-dimethylbenzyl isocyanate, 20 parts of styrene, 35 parts of n-butyl acrylate, 5 parts of methyl methacrylate, and 3 parts of t-butyl peroxyisopropyl carbonate.
Part of the mixture was added dropwise over 3 hours. Then, a mixed solution of 35 parts of xylene and 1.0 part of t-butylperoxyisopropyl carbonate was added dropwise over 1 hour and aged for 3 hours (this reaction solution is referred to as a vinyl polymer solution (A-2)). The obtained resin liquid has a solid content of 50%.
It was a colorless and transparent liquid. Gardner viscosity is F, weight average molecular weight is about 9000, and isocyanate value is 80 g /
It was 1000 g resin.

2) Preparation of self-crosslinking resin (I-2) In a reactor equipped with a stirrer, a reflux condenser and a thermometer, 2104 parts of the vinyl polymer solution (A-2) and the polyester resin solution (B- Add 1538 parts of 2) and mix at room temperature (25 ° C) for 3
After stirring for 0 minutes, the isocyanate value was measured. The isocyanate value of the mixed varnish was 41.0 (this value was defined as the initial isocyanate value). Then, with stirring, 4
After heating and maintaining at 0 ° C and proceeding the reaction for about 3.5 hours, when the isocyanate value reached 37.8, 148 parts of acetoxime and 46.5 parts of xylene were added, and the mixture was heated at 60 ° C for 2 hours.
Aged for a period of time (this reaction solution was used as a self-crosslinking resin (I-2)
Called. ).

The obtained resin liquid was a slightly yellowish transparent liquid. The Gardner viscosity is V, the solid content of the obtained resin liquid is 57.0%, and the hydroxyl value is 55.2 mgK.
OH / 1g resin, acid value 1.8mgKOH / 1g resin, N
CO / OH ratio is 0.9, isocyanate value is 37.8g
/ 1000 g resin, weight average molecular weight was about 20,000. Further, no increase in viscosity was observed even after storage at 30 ° C. for 6 months.

3) Preparation of intermediate coating material (P-4) 50 parts of TITON R-51N, 20 parts of barium sulfate B30, 40 parts of self-crosslinking resin liquid (I-2), 30 parts of xylene were used for 1 hour on a paint shaker. After dispersion, 150.5 parts of the self-crosslinking resin liquid (I-2), 1.0 part of dibutyltin dilaurate and 0.2 part of Disparlon L-1980 were added to obtain an intermediate coating composition (P-4).

3-5 Intermediate Coating Paint (P-5) 1) Preparation of Vinyl Polymer (A-3) 65 parts of xylene was put into a reactor equipped with a stirrer, a reflux condenser and a thermometer, and 130 ° C. The mixture is heated and held at 60 parts of m-isopropenyl-α, α′-dimethylbenzyl isocyanate, 35 parts of n-butyl acrylate, 5 parts of styrene, and 4 parts of t-butyl peroxyisopropyl carbonate.
Part of the mixture was added dropwise over 3 hours. Then, a mixed solution of 35 parts of xylene and 1.0 part of t-butylperoxyisopropyl carbonate was added dropwise over 1 hour and aged for 3 hours (this reaction solution is referred to as a vinyl polymer solution (A-3)). The obtained resin liquid had a solid content of 50%, a Gardner viscosity of B, a weight average molecular weight of about 6000, and an isocyanate value of 120.0 g / 1000 g.

2) Preparation of polyester resin (B-3) In a reactor equipped with a stirrer, a reflux condenser, a rectification column and a thermometer, 45.45 parts of trimethylolpropane, 96.05 parts of cyclohexanedimethanol, A mixture of 57.28 parts of cyclohexanedicarboxylic acid, 33.6 parts of adipic acid, and 15.4 parts of hexahydrophthalic anhydride was reacted for 14 hours while stirring under a nitrogen gas atmosphere (dibasic acid ratio of 0.
666), acid value 0.2 mg KOH / 1 g resin, hydroxyl value 2
A polyester resin of 41 mg KOH / 1 g resin was obtained. Next, the obtained polyester resin was dissolved in xylene to obtain a polyester resin liquid (B-3) having a solid content of 70%. The weight average molecular weight of the resin was about 2600.

3) Preparation of self-crosslinking resin (II-1) 2706 parts of vinyl polymer solution (A-3) and 322 parts of methylethylketoxime were added to a reactor equipped with a stirrer, a reflux condenser and a thermometer. After heating and stirring at 60 ° C. for 2 hours [vinyl polymer (C-1)], 1428 parts of polyester resin liquid (B-3) was added and aged at 40 ° C. for 4 hours until the isocyanate value became 0. Then, 32.5 parts of methyl ethyl ketoxime and 45.4 parts of xylene were added (this reaction solution is referred to as self-crosslinking resin solution (II-1)).

The obtained resin liquid was a slightly yellowish transparent liquid. Gardner viscosity (Gardner foam viscometer,
(Measured at 25 ° C.) is U, the solid content of the obtained resin liquid is 59.0%, the hydroxyl value is 87.5 mg KOH / 1 g resin, the acid value is 0.07 mg KOH / g resin, and the isocyanate value is 60. The resin was 6 g / 1000 g, the NCO / OH ratio was 0.9, and the weight average molecular weight was about 10,000. Also,
No thickening was observed even after storage at 30 ° C. for 6 months.

4) Preparation of intermediate coating composition (P-5) 50 parts of TITON R-51N, 20 parts of barium sulfate B30, 40 parts of self-crosslinking resin liquid (II-1), 30 parts of xylene were used for 1 hour on a paint shaker. After being dispersed, 150.5 parts of the self-crosslinking resin liquid (II-1), 1.0 part of dibutyltin dilaurate and 0.2 part of Disparlon L-1980 were added to obtain an intermediate coating composition (P-5).

3-6 Intermediate coating (P-6) for comparison TITONE R51N 50 parts, barium sulfate B30
Disperse 20 parts, 40 parts of polyester resin (B-2) and 30 parts of xylene in a paint shaker for 1 hour,
Next, 67 parts of polyester resin (B-2), Uban 2
50 parts of 0SE (melamine resin) and Disparon L-1
980 0.2 parts was added to obtain an intermediate coating composition (P-6).

3-7 Intermediate coating (P-7) for comparison TITONE R51N 50 parts, barium sulfate B30
Disperse 20 parts, 40 parts of polyester resin (B-2) and 30 parts of xylene in a paint shaker for 1 hour,
Next, 113 parts of the polyester resin (B-2) and 0.25 part of Disparlon L-1980 were added to obtain a base material of the intermediate coating composition (P-7). Next, 30 parts of Duranate TPA-100 (manufactured by Sumitomo Bayer Urethane Co., Ltd., hexamethylene polyisocyanate) was added to this main agent to obtain a two-pack type intermediate coating composition (P-7).

3-8 Intermediate Coating (P-8) Comparative TITON R51N 50 Parts, Barium Sulfate B30
Disperse 20 parts, 40 parts of polyester resin (B-2) and 30 parts of xylene in a paint shaker for 1 hour,
Next, 113 parts of polyester resin (B-2), 0.25 part of Disparon L-1980, 60 parts of 75% dismodul BL3175 (manufactured by Sumitomo Bayer Urethane Co., complete block type hexamethylene polyisocyanate) and 1 part of dibutyltin dilaurate are blended. Then, an intermediate coating material (P-8) was obtained (NCO / OH = 0.9 / 1.0).

3-9 Intermediate coating (P-9) for comparison TITONE R51N 50 parts, barium sulfate B30
20 parts, 40 parts of polyester resin (B-1) and 30 parts of xylene were dispersed in a paint shaker for 1 hour, then 114 parts of polyester resin (B-1), 0.25 part of Disparlon L-1980, 75% dispersant. Addition of 89 parts of module BL3175 and intermediate paint (P-
9) was obtained (NCO / OH = 0.8 / 1.0).

Examples 1 to 5 and Comparative Examples 1 to 4 Solvesso # 100 (hydrocarbon solvent, manufactured by Cosmo Oil Co., Ltd., trade name) was applied to the base material coated with the cationic electrodeposition paint.
For 25 seconds / Ford cup # 4/20 ℃
The above-mentioned intermediate coating materials (P-1) to (P-9) adjusted to the above are spray-coated so as to have a film thickness of 35 μm based on the cured coating film (spray gun: wiper 70, spraying pressure 4.0 kg).
/ Cm ² , distance from the tip of the gun to the surface to be coated 30 cm), leave at room temperature for 10 minutes, and then at 120 ℃ or 140 ℃ for 30 minutes.
It was heated for a minute to cure the intermediate coating film. Using the coated steel sheet thus obtained, a performance test of the coating film was conducted, and the results are shown in Table 1.

Next, the metallic coating material was applied to the surface of the intermediate coating film so that the film thickness based on the cured coating film was 15 μm, and the clear coating material was similarly applied so as to have a thickness of 35 μm. The coating film was cured by heating for 30 minutes (2 coat 1 bake method). A test for chipping resistance of the coating film was conducted using the coated steel sheet thus coated with the top coating film, and the results are shown in Table 1.

[0085]

[Table 1]

Test method Storage stability: The intermediate coating composition whose viscosity was adjusted to 2.5 seconds was stored in a closed state at a temperature of 60 ° C. for 16 hours and then stored at 20 ° C.
After cooling to, measure viscosity again to check storage stability,
It was examined whether the increase in viscosity was within 10 seconds as compared with that before storage and there was no abnormality in the paint state.

Hardness: At 20 ° C., the hardness is the hardness of the hardest pencil with which the coating film is not scratched with a pencil for scratch value test (Mitsubishi Uni).

Impact resistance: Using a DuPont type impact tester,
The drop height (cm) of a weight that withstands an impact of ½ inch and 500 g is shown.

Xylene wiping property: The coated surface was rubbed 10 times with gauze soaked with xylene, and abnormalities such as scratches on the surface and deterioration of gloss were visually evaluated. O indicates that there is no abnormality, and X indicates that scratches, lower gloss, etc. have occurred.

Gloss: Specular glossiness was shown at an incident angle of 60 °.

Image clarity: Image clarity gloss meter (I
It was displayed by the numerical value measured by CH). The higher the number, the better.

Chipping resistance: 100 g of crushed stone of No. 7 was applied to a coated plate cooled to -20 ° C. at a pneumatic pressure of 4.0 kg / cm ² by a stepping stone tester manufactured by Suga Test Instruments, and the coated surface was hit at right angles to the coated plate. The size of the fracture scratch was evaluated visually according to the following criteria.

5: Very good with almost no scratches.

4: Slightly scratched, practical.

3: The coating film peeled off a little and was not practical.

2: A large amount of coating film peeled off.

1: Most of the coating film peeled off.

Claims (3)

[Claims] 1. In the step of applying an intermediate coating composition and a top coating composition to a substrate, a vinyl polymer having a blocked isocyanate group in one molecule and a polyester resin having a hydroxyl group in one molecule are used as the intermediate coating composition. A method for forming a coating film, which comprises using an intermediate coating composition containing, as a main component, a self-crosslinking resin in which a blocked isocyanate group and a hydroxyl group coexist in one molecule bonded through a urethane group. 2. A self-crosslinking resin is a vinyl polymer (A) having two or more free isocyanate groups in one molecule, wherein two or more hydroxyl groups are included in one molecule of the free isocyanate groups.
Self in which a blocked isocyanate group and a hydroxyl group coexist in one molecule obtained by reacting a part of the hydroxyl groups in the polyester resin (B) having at least one and then reacting all the remaining free isocyanate groups with a blocking agent The coating film forming method according to claim 1, which is a crosslinkable resin. 3. The self-crosslinking resin has two or more hydroxyl groups in one molecule in all of the free isocyanate groups in the vinyl polymer (C) in which a free isocyanate group and a blocked isocyanate group coexist in one molecule. The coating film formation according to claim 1, wherein the polyester resin (B) is a self-crosslinking resin in which a blocked isocyanate group and a hydroxyl group coexist in one molecule obtained by reacting a part of the hydroxyl group in the polyester resin (B). Method.