JP5058933B2 - LAMINATED COATING FORMATION METHOD AND COATED PRODUCT - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the appearance of a coating film in a method of forming a coating film which applies an intermediate coating composition, a base coating composition and a clear coating composition in this order to burn and cure the formed three layers at once. <P>SOLUTION: The method of forming the laminated coating film includes a step of applying the intermediate coating composition, the base coating composition and the clear coating composition successively in a wet-on-wet manner, and a step of firing and curing the formed three layers at the same time. The base coating composition is a solvent-type base coating composition which includes an acrylic resin (a), a melamine resin (b), an organic bentonite (c), a maleic acid monoalkyl ester (d), and a brilliant pigment (e). <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention is obtained by a method of applying a coating composition such as an intermediate coating composition, a base coating composition, and a clear coating composition to an object to be coated such as an automobile body in order by wet-on-wet and a coating method. The present invention relates to a coated product having a laminated coating film.

  A laminated coating film such as an automobile body has a method of baking and curing each time a coating film is formed, and a method of simultaneously curing a plurality of laminated coating films. Among these, the method of simultaneously curing a plurality of laminated coating films has an advantage that the baking and drying step can be omitted. For example, Japanese Patent Laid-Open No. 2001-302964 (Patent Document 1) discloses a 3-coat 1-bake method in which an intermediate coating film, a base coating film, and a clear coating film are sequentially formed by wet-on-wet coating. .

  JP 2002-153805 (Patent Document 2) discloses an intermediate coating composition containing an amide group-containing acrylic resin, an amino resin and a block isocyanate as a curing agent in a 3-coat 1-bake method. A method of controlling the conformity and reversal at the interface between the respective coating film layers by using the coating film and forming a laminated coating film having excellent coating film properties, particularly chipping resistance, is disclosed.

In the case of forming a laminated coating film by the 3-coat 1-bake method, the baking step of the intermediate coating composition and the base coating composition can be omitted. Therefore, there is an economic advantage, and further, there is an advantage that CO ₂ emission can be reduced. On the other hand, when a laminated coating film is formed by a three-coat one-bake method, there is a tendency that a coating film defect called “waki”, in which innumerable minute holes are formed in the coating film after baking, tends to occur. This phenomenon of “waki” originates from the formation of a hole when the solvent in the coating film evaporates and escapes during baking and curing. In the 3-coat 1-bake method, a plurality of uncured coating films having different compositions are baked and cured at a time, and thus a laminate obtained by a 3-coat 3-bake method in which each coating composition is baked and cured each time. Compared with the coating film, “Waki” coating film defects tend to occur.

  In addition, the laminated coating film obtained by the 3-coat 1-bake method has a lower smoothness of the coating film than the laminated coating film obtained by the 3-coat 3-bake method, which is baked and cured each time after coating each coating composition, For this reason, there is a problem that glossiness is inferior. In general, it can be said that it is an important factor that a smooth coating film has a mirror-like glossiness as a role of a coating film that gives a sense of quality to an object. In particular, in the field of automobile painting and the like, the level required for the appearance of such a coating film is increasing year by year.

JP 2007-75791 A (Patent Document 3) describes a crosslinked polymer fine particle having an average particle diameter (D ₅₀ ) of 0.01 to 1 μm and a core-shell structure having an average particle diameter (D ₅₀ ) of 0.05 to 10 μm. A method for forming a multilayer coating film by three coats and one bake using a solvent-based base coating composition containing polymer fine particles containing a non-aqueous dispersion resin is described. The solvent-based base coating composition used in this method is an invention that differs from the present invention in that it uses two kinds of polymer particles, that is, a crosslinked polymer particle and a non-aqueous dispersion resin as described above.

JP 2001-302964 A JP 2002-153805 A JP 2007-75791 A

  The present invention includes a step of sequentially applying an intermediate coating composition, a base coating composition, and a clear coating composition on an electrodeposited substrate, and baking and curing the three coated layers at once. In the coating film formation method which consists of a process, it makes it a subject to improve a coating-film external appearance.

  The present invention includes a step of sequentially applying an intermediate coating composition, a base coating composition and a clear coating composition on an electrodeposited substrate in a wet-on-wet manner, and simultaneously baking and curing the three coated layers. In the method for forming a laminated coating film comprising the step of forming the coating film, the present invention has been made to solve the problems of improving the coating film appearance, in particular, preventing the occurrence of “flakes” and improving the smoothness of the coating film. As a result of intensive investigations, the inventors have determined that the base coating composition contains both organic bentonite and maleic acid monoalkyl ester in specific amounts, whereby a specific intermediate coating composition, base coating composition, and clear coating composition are prepared. It has been found that the above-mentioned problems can be solved in a 3-coat 1-bake method using a coating composition.

That is, the present invention
An intermediate coating composition, a base coating composition, and a clear coating composition are sequentially applied on a substrate on which an electrodeposition coating film is formed by wet-on-wet, and three uncoated three layers are applied. A step of baking and curing the coating film simultaneously,
A method for forming a laminated coating film comprising:
This intermediate coating composition comprises the following components:
A hydroxyl group-containing polyester resin obtained by polycondensation of an acid component containing 80 mol% or more of isophthalic acid and a polyhydric alcohol and having a glass transition point (Tg) of 40 to 80 ° C. is reacted with an aliphatic diisocyanate compound. The urethane-modified polyester resin (a) having a number average molecular weight (Mn) of 1200 to 3000, obtained by 40 to 56% by mass;
Melamine resin (b) 10-30% by mass;
Block isocyanate compound (c) 15 to 30% by mass, in which an isocyanate compound obtained by reacting with hexamethylene diisocyanate or hexamethylene diisocyanate and a compound that reacts with it is blocked with a compound having an active methylene group;
Non-aqueous dispersion resin (d) having a core-shell structure 4 to 15% by mass;
However, the amount of (a) to (d) is based on the solid content mass of the coating resin; and the flat pigment (e) 0.4 to 2 having a major axis of 1 to 10 μm and a number average particle size of 2 to 6 μm Parts by weight, wherein the part by weight of (e) is the amount relative to 100 parts by weight of the solid content of the coating resin;
A solvent-type intermediate coating composition containing, and
This base coating composition has the following components:
Acrylic resin (A) having a number average molecular weight (Mn) of 1000 to 20000, a hydroxyl value of 10 to 200, and an acid value of 1 to 80 mgKOH / g;
Melamine resin (I) 5 to 60% by mass;
Organic bentonite (U) 0.1-10% by mass;
Maleic acid monoalkyl ester (d) 0.2-4% by mass;
However, the amounts of (a) to (d) are based on the solid content mass of the paint resin; and the glitter pigment (e) pigment concentration (PWC) is 1 to 23.0 mass%, but based on the solid mass of the paint ;
A solvent-based base coating composition, and the clear coating composition contains a carboxyl group-containing acrylic resin (A), a carboxyl group-containing polyester resin (B), and an epoxy group-containing acrylic resin (C). A solvent-based clear coating composition,
A method for forming a laminated coating film is provided, whereby the above object is achieved.

  The present invention further provides a coated product having a multilayer coating film obtained by the above-described method for forming a multilayer coating film.

  A laminated coating film obtained by a three-coat one-bake method in which a specific intermediate coating composition, base coating composition, and clear coating composition, which are the methods of the present invention, are sequentially applied by wet on wet, It has the characteristics that it is not accompanied by “flakes” that cause a decrease, and the resulting laminated coating film has high smoothness and excellent gloss.

In the 3-coat 1-bake method, the baking and drying furnace for the intermediate coating composition and the base coating composition can be omitted, which is excellent in economic efficiency and can reduce CO ₂ emission to the environment. This has the advantage that the load of According to the present invention, it is possible to form a laminated coating film by a three-coat one-bake method without deteriorating the coating film appearance or the coating film properties. By the method for forming a multilayer coating film of the present invention, a multilayer coating film having an excellent coating film appearance can be formed by an industrially excellent method.

Process leading to the present invention First, the process leading to the present invention will be described. As a technique for improving the coating film appearance of a multilayer coating film obtained by a 3-coat 1-bake method in which an intermediate coating composition, a base coating composition, and a clear coating composition are sequentially applied by wet-on-wet, Studies are underway to control the cure rate. For example, assembling the coating composition so that the curing rate during baking of the intermediate coating composition, the base coating composition and the clear coating composition is set so that the intermediate coating composition is fastest and the clear coating composition is cured most slowly. Thus, it is considered that curing occurs from the lower layer coating film, and this can prevent the occurrence of “waks” in which countless minute holes are formed in the coating film after baking.

  However, in the case of using a solvent-based base coating composition containing an acrylic resin and a melamine resin and a clear coating composition containing a carboxyl group-containing acrylic resin, a carboxyl group-containing polyester resin and an epoxy group-containing acrylic resin as in the present invention. As described above, it has been found that even when the coating composition is assembled so as to be cured from the base coating composition constituting the lower layer coating film, a problem of occurrence of cracks occurs. The present inventors have found that the occurrence of this crack is a phenomenon that occurs characteristically when the above-mentioned specific solvent-based base coating composition and clear coating composition are used.

  Specifically, the solvent-based base coating composition containing an acrylic resin and a melamine resin, and a clear coating composition containing a carboxyl group-containing acrylic resin, a carboxyl group-containing polyester resin, and an epoxy group-containing acrylic resin, used in the present invention, Their paint curing systems are very different. Here, in the 3-coat 1-bake method, the uncured base coating film constituted by the solvent-based base coating composition comes into contact with the uncured clear coating film constituted by the clear coating composition. Then, when the uncured base coating film and the clear coating film, which have greatly different coating curing systems, come into contact with each other, a mixed layer of the solvent-based base coating composition and the clear coating composition is generated. The resulting mixed layer of the solvent-based base coating composition and the clear coating composition has its own curing rate due to the great difference in their coating curing systems, and the mixed layer It has been found by experiments by the present inventors that the curing rate of the above may exceed the curing rate of the solvent-based base coating composition as the lower layer.

  In the three-coat one-bake method using the solvent-based base coating composition and the clear coating composition in which a mixed layer having such a curing rate is generated, the curing rate of the clear coating composition is set as the curing rate of the base coating composition. Even if the coating material is designed so as to be slower, the mixed layer is hardened quickly, making it difficult to prevent the occurrence of cracks. On the other hand, if the curing system of the solvent-based base coating composition is greatly changed, there is a possibility that an adverse effect is caused on the adhesion and / or compatibility with the intermediate coating film. In response to such a problem, the present inventors added a specific component to the solvent-based base coating composition in the 3-coat 1-bake method using the solvent-based base coating composition and the clear coating composition. I found that I could solve the problem of the armpit.

  In the method for forming a laminated coating film of the present invention, a specific intermediate coating composition, a solvent-based base coating composition and a clear coating composition are used. Hereinafter, each coating composition will be described.

Intermediate coating composition In the method for forming a laminated coating film of the present invention, a solvent-type intermediate coating composition is used for forming the intermediate coating film. This intermediate coating composition contains a urethane-modified polyester resin (a), a melamine resin (b), a blocked isocyanate compound (c), a non-aqueous dispersion resin (d) having a core-shell structure, and a flat pigment (e). To do. The intermediate coating composition may further contain various organic or inorganic color pigments and extender pigments.

Urethane modified polyester resin (a)
The urethane-modified polyester resin (a) can be obtained by reacting a hydroxyl group-containing polyester resin with an aliphatic diisocyanate compound.

  The polyester resin can generally be produced by polycondensation of an acid component such as a polyvalent carboxylic acid and / or an acid anhydride and a polyhydric alcohol. The hydroxyl group-containing polyester resin used for the preparation of the urethane-modified polyester resin (a) is produced using an acid component containing 80 mol% or more of isophthalic acid in the acid component based on the total number of moles of the acid component. . When the amount of isophthalic acid in the acid component is less than 80 mol%, the glass transition point (Tg) of the resulting hydroxyl group-containing polyester resin is lowered, which is not preferable for use.

  The hydroxyl group-containing polyester resin has a glass transition point (Tg) of 40 to 80 ° C, preferably 45 to 75 ° C. When the glass transition point (Tg) is lower than the lower limit, the coating film hardness is lowered, and when the glass transition point (Tg) is higher than the upper limit, the chipping resistance may be lowered.

  The polyvalent carboxylic acid and / or acid anhydride other than isophthalic acid contained in the acid component used for the preparation of the hydroxyl group-containing polyester resin is not particularly limited. For example, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydro Phthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, hymic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, terephthalic acid, Examples thereof include maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, dodecenyl succinic acid, dodecenyl succinic anhydride and the like.

  The polyhydric alcohol used for the preparation of the hydroxyl group-containing polyester resin is not particularly limited. For example, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol. 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 2,2-dimethyl-3 -Hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, 2,2,4-trimethyl-1,3-pentanediol, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol An'nitoru, trimethylol ethane, trimethylol propane, trimethylol butane, hexanetriol, pentaerythritol, dipentaerythritol and the like.

  In the preparation of the hydroxyl group-containing polyester resin, other reaction components may be used in addition to the polyvalent carboxylic acid and / or acid anhydride and the polyhydric alcohol component. Examples of such other reaction components include monocarboxylic acid, hydroxycarboxylic acid, and lactone. Moreover, you may use drying oil, semi-drying oil, and those fatty acids. Specific examples include monoepoxide compounds such as Cardura E (manufactured by Shell Chemical Co.) and lactones. The lactones can be subjected to ring-opening addition to polyesters of polyvalent carboxylic acids and polyhydric alcohols to form graft chains. For example, β-propiolaclone, dimethylpropiolactone, butyllactone, γ- Examples include valerolactone, ε-caprolactone, γ-caprolactone, γ-caprolactone, crotolactone, δ-valerolactone, and δ-caprolactone, among which ε-caprolactone is most preferable.

  The urethane-modified polyester resin (a) is prepared by reacting the hydroxyl group-containing polyester resin thus obtained with an aliphatic diisocyanate compound. Specific examples of such aliphatic diisocyanate compounds include hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, and methylcyclohexane diisocyanate. . Of these, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and their burettes, nurate bodies, and adduct bodies are preferably used from the viewpoints of chipping resistance and weather resistance.

  In the preparation of the urethane-modified polyester resin (a), it is preferable to react 5 to 15 parts by mass of an aliphatic diisocyanate compound with respect to 100 parts by mass of the hydroxyl group-containing polyester resin. The number average molecular weight of the urethane-modified polyester resin (a) is preferably 1200 to 3000, and more preferably 1500 to 2500. Below the lower limit, the coating workability and curability may be insufficient. On the other hand, when the upper limit is exceeded, the non-volatile content at the time of painting becomes too low, and the workability becomes worse. In the present specification, the number average molecular weight is determined by a GPC method using a styrene polymer as a standard.

  The urethane-modified polyester resin (a) preferably has a hydroxyl value (solid content) of 30 to 180, more preferably a hydroxyl value (solid content) of 40 to 160. If the upper limit is exceeded, the water resistance in the case of a coating film may be reduced, and if the lower limit is exceeded, the curability of the coating film may be reduced. Moreover, it is preferable that the acid value of urethane-modified polyester resin (a) is 3-30 mgKOH / g (solid content), More preferably, it is 5-25 mgKOH / g. If it exceeds the upper limit, the water resistance of the coating film may be lowered, and if it is less than the lower limit, the curability of the coating film may be lowered.

  Content of the said urethane-modified polyester resin (a) in the intermediate coating composition of this invention is 40-56 mass% on the basis of coating resin solid content mass. If the content of the urethane-modified polyester resin (a) is less than 40% by mass, the chipping resistance in the case of forming a coating film may be insufficient. Moreover, when content exceeds 56 mass%, when it is set as a coating film, there exists a possibility that hardness may fall. The content is preferably 43 to 50% by mass.

Melamine resin (b)
The melamine resin is not particularly limited, and a methylated melamine resin, a butylated melamine resin, or a methyl / butyl mixed melamine resin can be used. For example, “Cymel 303” and “Cymel 254” commercially available from Nippon Cytec Co., Ltd., “Uban 128” and “Uban 20N60” commercially available from Mitsui Chemicals, Inc., and commercially available from Sumitomo Chemical Co., Ltd. “Sumimar series” and the like.

  The melamine resin (b) is contained in an amount of 10 to 30% by mass based on the solid content mass of the coating resin. If the content is less than the lower limit, the curability may be insufficient, and if the content exceeds the upper limit, the cured film may be too hard and brittle. The content of the melamine resin (b) is preferably 15 to 25% by mass.

Block isocyanate compound (c)
The blocked isocyanate compound (c) has an active methylene group in hexamethylene diisocyanate or an isocyanate compound obtained by reacting with hexamethylene diisocyanate and a compound that reacts with it, for example, a multimer such as its nurate. What is obtained by adding a compound is mentioned. In this blocked isocyanate compound (c), the blocking agent is dissociated by heating to generate an isocyanate group, which reacts with the functional group in the urethane-modified polyester resin and cures. Examples of the compound having an active methylene group include active methylene compounds such as acetylacetone, ethyl acetoacetate, and ethyl malonate.

  Content of the said block isocyanate compound is 15-30 mass% on the basis of paint resin solid content mass. More preferably, it is 17-25 mass%. Outside the above range, curing may be insufficient. Specific examples include active methylene type blocked isocyanate “Duranate MF-K60X” manufactured by Asahi Kasei Corporation.

Non-aqueous dispersion resin (d)
The non-aqueous dispersion resin (d) having the core-shell structure is prepared as resin particles insoluble in the mixed solution by copolymerizing a polymerizable monomer in a mixed solution of a dispersion-stable resin and an organic solvent. can do. The “non-aqueous dispersion” means a non-aqueous dispersion type resin, and is obtained by dispersing and stabilizing a resin using an organic solvent as a medium.

  The resin particles in the non-aqueous dispersion resin (d) are preferably prepared as non-crosslinked resin particles. The monomer to be copolymerized in the presence of the dispersion-stable resin for obtaining non-crosslinked resin particles is not particularly limited as long as it is a radical polymerizable unsaturated monomer.

  However, it is preferable to use a polymerizable monomer having a functional group in the synthesis of the dispersion stabilizing resin and the non-aqueous dispersion resin (d). This is because the non-aqueous dispersion resin (d) having a functional group can react with a post-curing agent together with the dispersion stabilizing resin containing the functional group to form a three-dimensionally crosslinked coating film.

  The dispersion stable resin is not particularly limited as long as it can stably synthesize the non-aqueous dispersion resin (d) in an organic solvent. Specifically, as the dispersion stable resin, the hydroxyl value (solid content) is 10 to 250, preferably 20 to 180, and the acid value (solid content) is 0 to 100 mgKOH / g, preferably 0 to 50 mgKOH / g, It is preferable to use an acrylic resin, a polyester resin, a polyether resin, a polycarbonate resin or a polyurethane resin having a number average molecular weight of 800 to 100,000, preferably 1000 to 20,000. If these upper limits are exceeded, the handling properties of the resin may be reduced, and the handling of the non-aqueous dispersion itself may also be reduced. If the lower limit is not reached, the resin may be detached or the stability of the particles may be reduced when the coating film is formed.

  The method for synthesizing the dispersion stable resin is not particularly limited, and preferred examples include a method obtained by radical polymerization in the presence of a radical polymerization initiator, a method obtained by a condensation reaction or an addition reaction, and the like. Furthermore, the monomer used to obtain the dispersion-stable resin can be appropriately selected according to the properties of the resin, but has a polymerizable monomer used to synthesize a non-aqueous dispersion described later. It is preferable to use those having a functional group such as a hydroxyl group and an acid group, and if necessary, those having a functional group such as a glycidyl group and an isocyanate group may be used.

  The non-aqueous dispersion resin (d) can be obtained by polymerizing a polymerizable monomer in a mixed solution of a dispersion stable resin and an organic solvent. As the polymerizable monomer, a radical polymerizable monomer can be used. This organic solvent dissolves the dispersion stable resin but does not dissolve the resin particles obtained by polymerizing the polymerizable monomer, and can be appropriately selected from various organic solvents.

  As the polymerizable monomer used for the synthesis of the non-aqueous dispersion resin (d), a monomer having a functional group is preferably used. Typical examples of the polymerizable monomer having a functional group are as follows. Examples of the polymerizable monomer having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxymethyl methacrylate, allyl alcohol, and hydroxy (meth) methacrylate. Examples include adducts of ethyl and ε-caprolactone.

  On the other hand, the polymerizable monomer having an acidic group includes a polymerizable monomer having a carboxyl group, a sulfonic acid group, or the like. Examples of those having a carboxyl group include (meth) acrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride, fumaric acid and the like. Examples of the polymerizable monomer having a sulfonic acid group include t-butylacrylamide sulfonic acid. When using the polymerizable monomer which has an acidic group, it is preferable that a part of acidic group is a carboxyl group.

  In addition, glycidyl group-containing unsaturated monomers such as glycidyl (meth) acrylate, isocyanate group-containing unsaturated monomers such as m-isopropenyl-α, α-dimethylbenzyl isocyanate, isocyanatoethyl acrylate, etc. Is mentioned as a polymerizable monomer having a functional group.

  Other polymerizable monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, and n- (meth) acrylate. Butyl, t-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, (Meth) acrylic acid alkyl ester such as tridecyl methacrylate, addition reaction product of oil fatty acid and acrylic acid or methacrylic acid ester monomer having oxirane structure (for example, addition reaction product of stearic acid and glycidyl methacrylate), carbon number 3 Oxirane compounds containing the above alkyl groups and acrylic acid or methacrylic acid Addition reaction product of styrene, α-methyl styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, pt-butyl styrene, benzyl (meth) acrylate, itaconic acid ester (dimethyl itaconate, etc.) , Maleic acid esters (such as dimethyl maleate), fumaric acid esters (such as dimethyl fumarate), acrylonitrile, methacrylonitrile, methyl isopropenyl ketone, vinyl acetate, Veova monomer (made by Shell Chemical Co., Ltd., trade name), vinyl Examples thereof include polymerizable monomers such as propionate, vinyl pivalate, ethylene, propylene, butadiene, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, acrylamide, and vinyl pyridine.

  In the preparation of the non-aqueous dispersion resin (d), the constituent ratio of the dispersion stable resin and the polymerizable monomer can be arbitrarily selected according to the purpose. For example, the dispersion stable resin is based on the total mass of these two components. Is preferably 3 to 80% by mass, particularly 5 to 60% by mass, and the polymerizable monomer is preferably 97 to 20% by mass, and particularly preferably 95 to 40% by mass. Furthermore, the total concentration of the dispersion stabilizing resin and the polymerizable monomer in the organic solvent is preferably 30 to 80% by mass, particularly 40 to 60% by mass based on the total mass.

  The polymerization reaction for obtaining the non-aqueous dispersion is preferably performed in the presence of a radical polymerization initiator. Examples of the radical polymerization initiator include azo initiators such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile), benzoyl peroxide, lauryl peroxide, Examples include t-butyl peroctoate. These initiators are used in an amount of 0.2 to 10 parts by mass, preferably 0.5 to 5 parts by mass per 100 parts by mass of the polymerizable monomers. In general, the polymerization reaction for obtaining a non-aqueous dispersion in an organic solvent containing a dispersion-stable resin is preferably performed in a temperature range of about 60 to 160 ° C. for about 1 to 15 hours.

The non-aqueous dispersion resin (d) thus obtained has a hydroxyl value (solid content) of 50 to 400, preferably 100 to 300, and an acid value (solid content) of 0 to 200 mgKOH / g, preferably 0 to 50 mgKOH. / g, an average particle diameter _{(D 50)} 0.05 to 10 [mu] m, it is preferable preferably 0.1-2 .mu.m. If it is below the lower limit, the particle shape cannot be maintained, and if it exceeds the upper limit, the stability when dispersed in the coating composition is lowered. The average particle diameter (D ₅₀ ) can be measured by a dynamic light scattering method. Specifically, it can be measured using a nanotrack particle size distribution measuring apparatus UPA (manufactured by Nikkiso Co., Ltd.).

  Further, the non-aqueous dispersion is different from the crosslinked polymer fine particles, and is a particle component in the coating composition, but has a characteristic that a particle structure is not formed in the coating film. That is, the non-aqueous dispersion is different from the crosslinked polymer fine particles in that there are no cross-linked sites in the particles, so that the particle shape changes during the baking process and can become a resin component.

  Furthermore, for example, resin particles called NAD (Non Aqueous Dispersion) used in the NAD paint described in Color Material, Vol. 48 (1975), pages 28 to 34 are also used. be able to.

  The content of the non-aqueous dispersion resin (d) in the intermediate coating composition of the present invention is 4 to 15% by mass based on the mass of the coating resin solid content. If the content is below the lower limit, the overall coating film appearance may be insufficient, and if it exceeds the upper limit, the chipping resistance may be reduced. This content is preferably 5 to 12% by mass.

Flat pigment (e)
The flat pigment (e) is a pigment in which at least one surface of the pigment has a flat shape. Examples of the flat pigment (e) include mica, alumina, talc and silica. Of these, talc is preferably used. This is because the chipping performance of the coating film can be improved.

  The flat pigment preferably has a major axis of 1 to 10 μm and a number average particle diameter of 2 to 6 μm. Here, the major axis is the length of the diameter in the flat plane of the flat pigment. The number average particle diameter is an average particle diameter obtained by selecting a predetermined number of particles from a scanning electron micrograph and performing image analysis to obtain an average value of the equivalent circle diameter and its distribution. Here, the equivalent circle diameter refers to the value of the diameter when the pigment is converted into the diameter of a perfect circle having the same area. These diameters and number average particle diameters can be measured by using a scanning electron microscope or the like. When the long diameter of the flat pigment is outside the above range, the appearance of the coating film may be inferior or it may be difficult to develop sufficient chipping resistance. Further, when the number average particle size is outside the above range, the appearance of the coating film is similarly inferior, and it may be difficult to develop sufficient chipping resistance.

  The content of the flat pigment (e) is 0.4 to 2 parts by mass, where the resin solid content in the coating is 100 parts by mass. This content is more preferably 0.5 to 1.5 parts by mass. Outside the above range, the adhesion with the base coating film may be lowered, and there is a risk that sufficient chipping performance may not be obtained.

  The intermediate coating composition may further contain other components in addition to the components (a) to (e). Examples of other components include a resin component. The resin component that can be used is not particularly limited, and examples thereof include acrylic resins, polyester resins, alkyd resins, and epoxy resins. These may use only 1 type and may use 2 or more types together.

  As other components, a color pigment or the like can also be used. Color pigments include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, Examples include dioxane pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, and inorganic pigments such as yellow lead, yellow iron oxide, bengara, carbon black, and titanium dioxide. Furthermore, calcium carbonate, barium sulfate, aluminum powder, kaolin and the like can be used as extender pigments.

  In general, for the intermediate coating composition, a gray-based one containing carbon black and titanium dioxide as main pigments is used. In addition, a combination of hues with the top coat and a combination of various color pigments can be used.

  Furthermore, a viscosity control agent can be added to the intermediate coating composition. As a result, it is possible to prevent familiarity with the top coat film and to ensure coating workability. Viscosity control agents can generally include those exhibiting thixotropic properties, such as swelling dispersions of fatty acid amides, polyamides such as amide fatty acids, phosphates of long-chain polyaminoamides, colloidal swelling dispersion of oxidized polyethylene Such as polyethylene-based bodies, organic acid smectite clay, organic bentonite-based materials such as montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, flat pigments that develop viscosity depending on the shape of the pigment, crosslinked resin particles, etc. It can be mentioned as a viscosity control agent.

  The total solid content during coating of the intermediate coating composition used in the present invention is 30 to 80% by mass, preferably 35 to 65% by mass. Outside this range, the paint stability may be reduced. On the other hand, when the upper limit is exceeded, the viscosity is too high and the appearance of the coating film is lowered, and when below the lower limit, the viscosity is too low and appearance defects such as familiarity and unevenness may occur. In the intermediate coating composition used in the present invention, in addition to the above components, additives usually added to the coating, for example, a surface conditioner, an antioxidant, an antifoaming agent, and the like may be blended. These compounding amounts are within the range known to those skilled in the art.

  The method for producing the coating composition used in the present invention is not particularly limited, including those described later, and those skilled in the art such as kneading and dispersing a compound such as a pigment using a kneader or roll, a sand grinder mill, etc. Any of the known methods can be used.

Base coating composition The base coating composition used in the method for forming a laminated coating film of the present invention comprises an acrylic resin (A), a melamine resin (I), an organic bentonite (U), a maleic acid monoalkyl ester (D), and glitter. It is a solvent-type metallic base coating composition containing a pigment (e).

  The base coating composition of the present invention contains an acrylic resin (a). By including the acrylic resin (a), the physical properties of the base coating film can be improved, for example, by increasing fastness. The acrylic resin has a hydroxyl value (solid content) of 10 to 200. If it is less than 10, curing may be insufficient and physical properties of the coating film may be inferior. Moreover, when it exceeds 200, there exists a possibility that the flexibility and water resistance of a coating film may fall.

  The acrylic resin (a) in the present invention is prepared using one or more unsaturated monomers usually used for obtaining acrylic resins such as acrylic acid, methacrylic acid, and / or derivatives thereof. And a hydroxyl-containing monomer is also used as a monomer component used for preparation of an acrylic resin (a).

  The derivative of acrylic acid or methacrylic acid is not particularly limited. For example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n, i or t-butyl (meth) acrylate, 2-ethylhexyl. Alkyl esters such as (meth) acrylate, lauryl (meth) acrylate and glycidyl (meth) acrylate; hydroxyalkyl such as 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate Examples include esters; amides such as (meth) acrylamide; and nitriles such as (meth) acrylonitrile. The monomer component may further include styrenes such as styrene and α-methylstyrene; vinyl compounds such as vinyl acetate. Examples of the hydroxyl group-containing monomer include hydroxyl group-containing unsaturated monomers such as hydroxyethyl (meth) acrylate.

  The acrylic resin (a) has a number average molecular weight of 1000 to 20000. If it is less than 1000, the coating film properties such as weather resistance may be inferior. On the other hand, if it exceeds 20000, the viscosity of the resin increases and a large amount of solvent may be required. In addition, in this specification, a number average molecular weight is a number average molecular weight of polystyrene conversion measured by gel permeation chromatography (GPC).

  The acrylic resin (a) preferably has an acid value of 1 to 80 mgKOH / g (solid content). When it is less than 1 mgKOH / g, the physical properties of the coating film may be inferior, and when it exceeds 80 mgKOH / g, the water resistance of the coating film may be easily retreated. More preferably, it is 10-45 mgKOH / g.

  It does not specifically limit as a manufacturing method of the said acrylic resin (a), For example, it can carry out by solution polymerization etc., such as normal radical polymerization.

  The content of the acrylic resin (A) in the base coating composition is the total amount of acrylic resin (A), melamine resin (I), organic bentonite (U) and maleic acid monoalkyl ester (D) in the base coating composition. It is preferable that it is 10-90 mass% with respect to solid content. If it is less than 10% by mass, the physical properties of the coating film may be inferior, such as a decrease in fastness, and if it exceeds 90% by mass, the coating film becomes hard and brittle and the physical properties of the coating film such as chipping resistance may be inferior. is there.

  The melamine resin (I) contained in the base coating composition of the present invention is not particularly limited, and may be the same as or different from the melamine resin (b) contained in the intermediate coating. May be. As the melamine resin (A), for example, a methylated melamine resin, a butylated melamine resin, or a methyl / butyl mixed melamine resin can be used. Examples of commercially available melamine resins include “Cymel-303” and “Cymel 254” manufactured by Nippon Cytec Co., Ltd., “Uban 20N60” and “Uban 128” manufactured by Mitsui Chemicals, and “Sumimar Series” manufactured by Sumitomo Chemical Co., Ltd. Is mentioned.

  The content of the melamine resin (I) in the base coating composition is the total solids such as acrylic resin (A), melamine resin (I) organic bentonite (U) and maleic acid monoalkyl ester (d) in the base coating composition. The amount is preferably 5 to 60 parts by mass, more preferably 15 to 45% by mass based on the minute. If the amount used is less than the lower limit, the curability may be insufficient, and if it exceeds the upper limit, the cured film becomes stiff and the chipping property may be lowered when it is formed into a coating film.

The organic bentonite (u) contained in the base coating composition in the present invention is a component having a structure in which an organic ammonium salt is intercalated between bentonite layers having a crystal layer. While this organic bentonite does not swell in an aqueous system, it has the property of swelling with an organic solvent or the like and exhibiting thickening. As the organic ammonium salt is intercalated between the layers of bentonite, for example, an alkyl group having a carbon number of C ₁ -C _30, more preferably a quaternary ammonium having an alkyl group of C ₁ -C ₂₀ carbon atoms. Specific examples of such organic bentonite (U) include, for example, trade name “Benton 34” (dimethyl dioctadecyl ammonium bentonite / quaternary ammonia-18 bentonite, manufactured by National Red), trade name “Benton 38” ( Magnesium montmorillonite / quaternary ammonia-18 hectorite, manufactured by National Red Co., Ltd., trade name “Organite A” (complex of montmorillonite and trialkylbenzylammonium salt, manufactured by Nippon Organic Clay Co., Ltd.), and trade name “New D” Orben "(bentonite dimethyl C ₁₈ H ₃₇ N ⁺ , manufactured by Shiroishi Kogyo Co., Ltd.).

  The inclusion of organic bentonite (U) in the base coating composition is believed to provide structural viscosity to the base coating composition. By providing the base coating composition with a structural viscosity, a fine metallic feeling accompanying the atomization of the coating in the spraying device is imparted, and the appearance of the coating film is improved. Furthermore, color reversion due to a slight mixing (mixed layer) between the metallic base coating film and the clear coating film is suppressed.

  The blending amount of organic bentonite (U) is 0 with respect to the total solid content of acrylic resin (A), melamine resin (I), organic bentonite (U), maleic acid monoalkyl ester (D) and the like of the base coating composition. .1 to 10% by mass. When the content of the organic bentonite (U) is less than 0.1% by mass, the structural viscosity does not appear and the smoothness of the obtained multilayer coating film is inferior. On the other hand, when the content of the organic bentonite (U) exceeds 10% by mass, the adhesion with the intermediate coating film and the clear coating film is deteriorated.

The maleic acid monoalkyl ester (d) contained in the base coating composition in the present invention has a structure in which one of the carboxylic acid groups of maleic acid which is a dicarboxylic acid is an alkyl ester. Examples of the alkyl group constituting the maleic acid monoalkyl ester (d) include an alkyl group having C _{1 to} C ₁₀ carbon atoms, and more preferably an alkyl group having C _{1 to} C ₅ carbon atoms. When the maleic acid monoalkyl ester (d) has the above alkyl group, there is an advantage that compatibility with the coating material is improved, and a decrease in water resistance of the resulting laminated coating film can be prevented.

  By including the maleic acid monoalkyl ester (d) in the base coating composition in the present invention, it is possible to prevent the occurrence of cracks in the multilayer coating film, and thereby a multilayer coating film having a good coating film appearance. Will be obtained. In addition, the present inventors think that it is based on the following reasons that generation | occurrence | production of the crack in a laminated coating film can be prevented by including maleic acid monoalkylester (D) in a base coating composition. The base coating composition is a system that is cured by a reaction between a hydroxyl group contained in the acrylic resin (A) and the melamine resin (A). In this curing system, the acrylic resin is generally used as a curing catalyst by giving the acrylic resin a carboxyl group. In the method for forming a laminated coating film of the present invention, the curing start temperature of the base coating composition can be specifically lowered by including the maleic acid monoalkyl ester (D) in the base coating composition. When forming a multilayer coating film, the base coating film begins to harden due to the presence of the maleic acid monoalkyl ester (d), so that the solvent contained in the base coating film is smoothly stripped off. I think that the occurrence of armpits has been reduced.

  Furthermore, the inclusion of maleic acid monoalkyl ester (d) in the base coating composition results in the formation of a mixed layer of both coatings formed at the boundary between the resulting base coating and the clear coating. The problem can be solved. The clear coating composition is a system that cures by a reaction between a carboxyl group contained in the carboxyl group-containing acrylic resin (A) and the carboxyl group-containing polyester resin (B) and an epoxy group contained in the epoxy group-containing acrylic resin (C). It is. Here, in the above-mentioned mixed layer, the curing start temperature is lowered by the penetration of a resin having a large amount of carboxyl groups contained in the clear coating composition, and curing is performed before the solvent contained in the base coating film which is the lower layer is sufficiently volatilized. As a result, the occurrence of cracks in the laminated coating film was observed. However, since maleic acid monoalkyl ester (D) is contained in the base coating composition, the curing start temperature of the base coating composition is lowered, and even if the mixed layer is formed as described above, it is included in the base coating film. It is considered that the occurrence of cracks in the laminated coating film has been reduced because the solvent is cured after the volatilization of the solvent is smoothly performed.

  The content of the maleic acid monoalkyl ester (D) in the base coating composition is determined based on the acrylic resin (A), melamine resin (I), organic bentonite (U), and maleic acid monoalkyl ester (D) in the base coating composition. It is 0.2-4 mass% in paint solid content, such as. When the content of maleic acid monoalkyl ester (d) exceeds 4% by mass, the curing start temperature of the base coating composition will be too low, and the occurrence of cracks will occur due to a sudden increase in viscosity. Or the appearance may deteriorate. On the other hand, when the content of the maleic acid monoalkyl ester (D) is less than 0.2% by mass, the curing rate of the base coating composition is not sufficiently improved, and the occurrence of cracks cannot be effectively prevented.

The glitter pigment (e) contained in the base coating composition is not particularly limited in shape and may be further colored. For example, the average particle diameter (D ₅₀ ) is 2 to ₅₀ μm, A scaly thing having a thickness of 0.1 to 5 μm is preferred. Moreover, the thing with the average particle diameter of 10-35 micrometers has the advantage that it is excellent in a brightness, and is used more suitably. The pigment concentration (PWC) in the paint of the glitter pigment is generally 23.0% by mass or less. If the upper limit is exceeded, the coating film appearance may be reduced. Preferably, it is 1-20.0 mass%, More preferably, it is 1-18.0 mass%. In addition, this pigment density | concentration shows content (mass%) of the pigment on the basis of resin solid content mass.

  Examples of the glitter pigment include non-colored or colored metallic glitter materials such as metals or alloys and mixtures thereof, interference mica powder, colored mica powder, white mica powder, graphite, and colorless and colored flat pigments. . Non-colored or colored metallic glitters such as metals or alloys and mixtures thereof are preferred. Specific examples of the metal include aluminum, aluminum oxide, copper, zinc, iron, nickel, tin and the like. These are excellent in dispersibility, and by using these, a highly transparent coating film can be formed.

  The base coating composition of the present invention may further contain a color pigment and / or an extender pigment. Color pigments include organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, isoindolinone pigments And metal complex pigments, and inorganic inorganic materials include yellow lead, yellow iron oxide, bengara, carbon black, and titanium dioxide. Furthermore, calcium carbonate, barium sulfate, clay, talc and the like may be used in combination as extender pigments.

  The total pigment concentration (PWC) in the base coating composition including the glitter pigment and all other pigments is 1 to 50%, preferably 1% to 40%, more preferably, 1% to 30%. If the upper limit is exceeded, the coating film appearance may be reduced.

  The film-forming resin contained in the base coating composition may further include a resin other than those described above, for example, a film-forming resin such as a polyester resin, an alkyd resin, an epoxy resin, or a urethane resin. May be included. In addition, from the viewpoint of pigment dispersibility or workability, a combination of an acrylic resin (A) and / or a polyester resin and a melamine resin (A) is preferable.

  The solid content at the time of coating of the base coating composition used in the present invention is 15 to 70% by mass, and preferably 20 to 50% by mass. If the upper limit is exceeded, the viscosity may be too high and the appearance of the coating film may be lowered. If the lower limit is not reached, the viscosity may be too low and appearance defects such as familiarity and unevenness may occur. Further, outside the above range, the paint stability tends to decrease.

  The base coating composition is a solution type, and examples thereof include an organic solvent type and a non-aqueous dispersion type.

  The production of the coating composition used in the present invention is not particularly limited, including those described later, and all known to those skilled in the art such as kneading and dispersing a compound such as a pigment using a kneader or a roll. This method can be used.

Clear coating composition The clear coating composition used for forming the clear coating film in the laminated coating film forming method of the present invention comprises a carboxyl group-containing acrylic resin (A), a carboxyl group-containing polyester resin (B), and an epoxy group-containing acrylic resin. Resin (C) is included. This clear coating composition is crosslinked by forming an ester bond by a reaction between a carboxyl group and an epoxy group by heating.

  The carboxyl group-containing acrylic resin (A) contained in the clear coating composition has an average of two or more carboxyl groups in one molecule, and has an acid value of 5 to 300 mgKOH / g (solid content) and a number average molecular weight. The thing which is (Mn) 500-8000 is mentioned.

  As the carboxyl group-containing acrylic resin, (1) a carboxyl group containing a carboxyl group and a carboxylate group, obtained by reacting an acrylic polyanhydride and (2) a monoalcohol, is bonded to adjacent carbon. It is more desirable to use an acrylic resin.

  The above-mentioned (1) acrylic polyanhydride has an acid anhydride group-containing ethylenically unsaturated monomer of 15 to 40% by mass, preferably 15 to 35% by mass, and an ethylenically unsaturated monomer 60 having no acid anhydride group. It can be obtained by copolymerizing ˜85 mass%, preferably 65 to 85 mass%. If the amount of the acid anhydride group-containing ethylenically unsaturated monomer is less than the lower limit, the curability may be insufficient. If the amount exceeds the upper limit, the coating film becomes too brittle and the weather resistance may be insufficient.

  Examples of the acid anhydride group-containing ethylenically unsaturated monomer include itaconic anhydride, maleic anhydride, and citraconic anhydride.

  The ethylenically unsaturated monomer having no acid anhydride group is not particularly limited as long as it is an ethylenically unsaturated monomer that does not adversely affect the acid anhydride group, but has 3 to 3 carbon atoms having one ethylenically unsaturated bond. It is preferred to use 15, especially 3-12 monomers. It is also preferable to use two or more kinds of ethylenically unsaturated monomers having no acid anhydride group in order to improve the compatibility between the resins.

  Examples of the ethylenically unsaturated monomer having no acid anhydride group include styrene, α-methylstyrene, pt-butylstyrene, various (meth) acrylic acid esters, VeoVa-9 and VeoVa manufactured by Shell. And Versatic acid glycidyl ester such as -10. When using styrene or a styrene derivative, it is desirable to use in the range of 5-40 mass% in all the monomers.

  Further, as an ethylenically unsaturated monomer having no acid anhydride group, a monomer having a carboxyl group such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, and an ethylenically unsaturated monomer having a hydroxyl group and an acid anhydride group Adducts with contained compounds can also be used. Among them, it is particularly preferable to use a long-chain carboxyl group-containing monomer having a spacer portion of about 5 to 20 carbon atoms between the ethylenically unsaturated group and the carboxyl group, since the scratch resistance of the coating is improved. .

  (1) The number average molecular weight of the acrylic polyanhydride obtained by copolymerization of the acid anhydride group-containing ethylenically unsaturated monomer and the ethylenically unsaturated monomer having no acid anhydride group is 500 to 8000, 800 to 6000, particularly 1500 to 4000 is preferable. If the number average molecular weight exceeds the upper limit, the compatibility between the resins may decrease and the appearance quality of the coating film may decrease, and if it falls below the lower limit, the curability may become insufficient. Moreover, it is desirable that the obtained polymer has an average of at least 2, preferably 2 to 15, acid anhydride groups in one molecule. If the acid anhydride group is below the lower limit, the curability may be insufficient, and if it exceeds the upper limit, the coating film becomes too brittle and the weather resistance may be insufficient.

  As said (2) monoalcohol, it is preferable to use a C1-C12 thing, especially 1-8 thing. This is because alcohol easily volatilizes during the reaction with the acrylic polyanhydride described above, which is suitable for regenerating the acid anhydride group. As such (2) monoalcohol, methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, n-hexyl alcohol, lauryl alcohol, methyl cellosolve, ethyl cellosolve, methoxy Examples include propanol, ethoxypropanol, furfuryl alcohol, dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol, propargyl alcohol and the like.

  When synthesizing the carboxyl group-containing acrylic resin (A) by reacting the above (1) acrylic polyanhydride and (2) monoalcohol, the acid anhydride group and the hydroxyl group are in a molar ratio of 1/10 to 1 / 1, preferably 1/5 to 1/1, more preferably 1/2 to 1/1. If the molar ratio is below the lower limit, excess alcohol may cause cracking at the time of curing, and if it exceeds the upper limit, storage stability may be deteriorated due to residual unreacted acid anhydride groups.

  The carboxyl group-containing acrylic resin (A) having a carboxyl group and a carboxylic ester group obtained by the above reaction preferably has a solid content acid value of 5 to 300 mgKOH / g, particularly 50 to 250 mgKOH / g. If the acid value is below the lower limit, the curability may be insufficient, and if it exceeds the upper limit, the storage stability may be poor.

  The carboxyl group-containing acrylic resin (A) is used in an amount of 10 to 70 mass%, preferably 15 to 50 mass%, more preferably 20 to 45 mass%, based on the total nonvolatile content in the resin composition. If this blending amount is less than the lower limit, the weather resistance of the resulting coating film may be lowered, and if it exceeds the upper limit, the coating film may be too hard.

  As the carboxyl group-containing polyester resin (B) contained in the clear coating composition, an acid value of 50 obtained by reacting (1) a polyester polyol having 3 or more hydroxyl groups and (2) an acid anhydride. -350 mgKOH / g (solid content), number average molecular weight 400-3500, and a weight average molecular weight / number average molecular weight are 1.8 or less.

  The carboxyl group-containing polyester resin (B) can be obtained by (1) half-esterifying a polyester polyol having 3 or more hydroxyl groups and (2) an acid anhydride. Polyester polyol refers to a polyhydric alcohol having two or more ester bond chains, which reacts with an acid anhydride group and has two or more acid functionalities per molecule and the following characteristics.

  Such (1) polyester polyol is a low molecular polyhydric alcohol having 3 to 16 carbon atoms having at least three hydroxyl groups, or a chain obtained by adding a lactone compound such as ε-caprolactone to this low molecular polyhydric alcohol. It can also be synthesized by extending. By introducing a linear aliphatic group into the low-molecular polyhydric alcohol, flexibility is imparted to the resulting coating film and impact resistance is improved.

  Examples of the low molecular weight polyhydric alcohol used include trimethylolethane, trimethylolpropane, 1,2,4-butanetriol, ditrimethylolpropane, pentaerythritol, dipentaerythritol, glycerin and mixtures thereof.

  Examples of the low-molecular polyhydric alcohol preferably used include trimethylolpropane, ditrimethylolpropane, pentaerythritol, and an adduct of these with a lactone compound. Examples of the lactone compound include ε-caprolactone, γ-caprolactone, γ-valerolactone, δ-valerolactone, and γ-butyrolactone, and ε-caprolactone, γ-valerolactone, and γ-butyrolactone are preferable.

  Examples of the acid anhydride (2) include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methylhexahydrophthalic anhydride, trimellitic anhydride, and succinic anhydride.

  The half esterification reaction of the above (1) polyester polyol and (2) acid anhydride can be carried out under ordinary reaction conditions such as room temperature to 150 ° C. and normal pressure. However, it is not necessary to modify all the hydroxyl groups of the polyester polyol to carboxyl groups, and the hydroxyl groups may remain. According to the above-mentioned method, since the molecular weight distribution becomes sharp, further solidification is possible, and a coating film excellent in weather resistance and water resistance can be formed.

  The carboxyl group-containing polyester resin (B) obtained by the reaction described above has an acid value of 50 to 350 mgKOH / g (solid content), preferably 100 to 300 mgKOH / g (solid content), more preferably 150 to 250 mgKOH / g (solid content). Solid content), the number average molecular weight is 400-3500, preferably 500-2500, more preferably 700-2000, and the weight average molecular weight / number average molecular weight is 1.8 or less, preferably 1.5 or less, More preferably, it is 1.35 or less.

  If the acid value exceeds the upper limit, the resin viscosity becomes too high and the concentration of non-volatile components in the paint may be lowered. If the acid value is lower than the lower limit, the curability of the paint may be insufficient. If the molecular weight exceeds the upper limit, the resin viscosity becomes too high and the non-volatile content of the diluted paint diluted to the coating viscosity may be reduced. If the molecular weight is lower than the lower limit, the curability may be insufficient. Furthermore, when the weight average molecular weight / number average molecular weight exceeds the upper limit, the water resistance and weather resistance of the coating film may be lowered.

  Since the carboxyl group-containing polyester resin (B) has a hydroxyl group in the molecule, a carboxyl group and a hydroxyl group are simultaneously provided on the surface of the coating film, so that, for example, adhesion during recoating is improved. In this case, the hydroxyl value of the carboxyl group-containing polyester resin is 150 (solid content) or less, preferably 5 to 100 (solid content), more preferably 10 to 80 (solid content). When the hydroxyl value exceeds the upper limit, the water resistance decreases.

  Since the carboxyl group-containing polyester resin (B) having the hydroxyl group and the carboxyl group reacts with both the epoxy group-containing acrylic resin (C) and the carboxyl group-containing acrylic resin (A) described later, a stronger coating film is formed. Can be formed. Therefore, it is desirable that the carboxyl group-containing polyester resin (B) has an average of 0.1 or more hydroxyl groups in one molecule.

  In order to obtain such a carboxyl group-containing polyester resin, (1) the molar amount of the acid anhydride group of the acid anhydride relative to the molar amount of the hydroxyl group of the polyester polyol is 0.2 to 1.0 times, particularly 0. It is preferable to make it 0.5 to 0.9 times. If this ratio is below the lower limit, the curability of the paint may be insufficient.

  The carboxyl group-containing polyester resin (B) component is blended in an amount of 5 to 70% by mass, preferably 5 to 50% by mass, more preferably 10 to 40% by mass, based on the mass of the total nonvolatile content in the paint. be able to. If the amount of the carboxyl group-containing polyester resin (B) is less than the lower limit, the nonvolatile content concentration of the paint may be lowered, and if it exceeds the upper limit, the weather resistance of the coating film may be lowered.

  The epoxy group-containing acrylic resin (C) contained in the clear coating composition used in the present invention has an average of 2 or more, preferably 2 to 10, more preferably 3 to 8 epoxy groups in one molecule. It is an epoxy group-containing acrylic resin.

  The epoxy group-containing acrylic resin (C) is preferably (1) 10 to 60% by mass of an epoxy group-containing ethylenically unsaturated monomer, preferably 15 to 50% by mass, and (2) an ethylenic group having no epoxy group. An epoxy group-containing acrylic resin obtained by copolymerizing 40 to 90 mass%, preferably 10 to 60 mass% of an unsaturated monomer. If the epoxy group-containing ethylenically unsaturated monomer is below the lower limit, the curability is insufficient, and if it exceeds the upper limit, it becomes too hard and the weather resistance is insufficient.

  Examples of the (1) epoxy group-containing ethylenically unsaturated monomer include glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexanyl (meth) acrylate, and the like. In order to ensure balanced curability and storage stability, it is preferable to use glycidyl (meth) acrylate.

  As said (2) ethylenically unsaturated monomer which does not have an epoxy group, what does not influence an epoxy group among the ethylenically unsaturated monomers which do not have the above-mentioned acid anhydride group can be used similarly.

  Moreover, the hydroxyl group containing ethylenically unsaturated monomer shown to following formula (I) can also be used as (2) ethylenically unsaturated monomer which does not have an epoxy group.

(In the formula, R is a hydrogen atom or a methyl group, and X is an organic chain represented by the following formula (II) or formula (III).)

(In the formula, Y is a linear or branched alkylene group having 2 to 8 carbon atoms, n is an integer of 3 to 7, and q is an integer of 0 to 4.)

(In the formula, R ′ is a hydrogen atom or a methyl group, and m is an integer of 2 to 50.)

  Specific examples of the hydroxyl group-containing ethylenically unsaturated monomer represented by the formula (I) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, ( 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and their reaction products with ε-caprolactone, (meth) acrylic acid and a large excess of diol (eg, 1,4 butanediol, 1, Examples thereof include compounds obtained by esterifying 6-hexanediol, polyethylene glycol, or polypropylene glycol).

  As a hydroxyl-containing ethylenically unsaturated monomer used here, a C5-C23, especially 5-13 thing can be used preferably. This is because if the chain length of this monomer is too short, the flexibility in the vicinity of the crosslinking point is lost and it becomes too hard, and if it is too long, the molecular weight between the crosslinking points becomes too large.

  When the hydroxyl group-containing ethylenically unsaturated monomer is used, the adhesion and recoatability of the resulting coating film are improved. In addition, the epoxy group-containing acrylic resin having a hydroxyl group and a carboxyl group includes, as described later, a carboxyl group-containing acrylic resin (A) having a carboxyl group and a carboxylic ester group, and functional groups of both the hydroxyl group and the epoxy group. Since it reacts and bonds, a stronger coating film can be obtained.

  The hydroxyl value of the epoxy group-containing acrylic resin (C) is 5 to 300 (solid content), preferably 10 to 200 (solid content), more preferably 15 to 150 (solid content). If the hydroxyl value exceeds the upper limit, the non-volatile content of the paint may decrease or the water resistance of the coating film may be insufficient. Below the lower limit, the adhesion may be inferior.

  The epoxy group-containing acrylic resin (C) comprises 5 to 70% by mass of a hydroxyl group-containing ethylenically unsaturated monomer having the structure represented by the above formula (I), and (1) an epoxy group-containing ethylenically unsaturated monomer 10 to 60%. It can be obtained by copolymerizing the mass% with 0 to 85 mass% of an ethylenically unsaturated monomer having neither a hydroxyl group nor an epoxy group as required. In this case, the epoxy group-containing acrylic resin (C) to be obtained has an average of 2 to 12, more preferably 3 to 10, and an average of 0.5 to 10 hydroxyl groups in one molecule, more preferably 0.5 to 10 hydroxyl groups. Have 1-8.

  The number average molecular weight of the epoxy group-containing acrylic resin (C) is preferably 500 to 10000, more preferably 1000 to 8000, and further preferably 1500 to 5000. If the number average molecular weight is below the lower limit, the curability of the paint may be insufficient, and if it exceeds the upper limit, the non-volatile content of the diluted paint diluted to the coating viscosity may be reduced. The epoxy equivalent is preferably 50 to 700, more preferably 80 to 600, and still more preferably 100 to 500. If the epoxy equivalent exceeds the upper limit, the curability of the coating may be insufficient. If the epoxy equivalent is less than the lower limit, the coating becomes brittle and the coating film becomes brittle.

  The epoxy group-containing acrylic resin (C) component is 10 to 80% by mass, preferably 20 to 70% by mass, more preferably 30 to 65% by mass, based on the total solid content in the curable resin composition. It can mix | blend in quantity. If the amount of the epoxy group-containing acrylic resin is below the lower limit, the curability may be lowered, and if it exceeds the upper limit, the yellowing resistance may be deteriorated.

  The clear coating composition used in the present invention can be produced by mixing a carboxyl group-containing acrylic resin (A), a carboxyl group-containing polyester resin (B), and an epoxy group-containing acrylic resin (C). In particular, when the carboxyl group-containing acrylic resin (A) having a carboxyl group and a carboxylic ester group is used, and the epoxy group-containing acrylic resin (C) having a hydroxyl group and an epoxy group is used, the acid resistance is particularly excellent. A clear coating composition that forms a coating film is obtained.

  In this case, the molar ratio of the carboxyl group contained in the carboxyl group-containing acrylic resin (A) and the carboxyl group-containing polyester resin (B) to the epoxy group contained in the epoxy group-containing acrylic resin (C) is 1 / 1.4 to 1 / 0.6, preferably 1 / 1.2 to 1 / 0.8, and the carbon adjacent to the carboxyl group or carboxyl group-bonded carbon contained in the carboxyl group-containing acrylic resin (A). The molar ratio of the carboxylic acid ester group to be bonded to the hydroxyl group contained in the carboxyl group-containing polyester resin (B) and the epoxy group-containing acrylic resin (C) is 1 / 2.0 to 1 / 0.5, more preferably 1. It is preferable to mix | blend in the quantity used as /1.5-1/0.7.

  When the molar ratio of the carboxyl group contained in the carboxyl group-containing acrylic resin (A) and the carboxyl group-containing polyester resin (B) and the epoxy group contained in the epoxy group-containing acrylic resin (C) exceeds the upper limit, There is a possibility that the curability of the resulting paint may be lowered, and when the content is below the lower limit, the coating film may be yellowed. In addition, the carboxyl group contained in the carboxyl group-containing acrylic resin (A) or the carboxylate ester group and carboxyl group-containing polyester resin (B) bonded to the carbon adjacent to the carboxyl group-bonded carbon and the epoxy group-containing acrylic resin (C) If the molar ratio with the hydroxyl group contained in the solvent exceeds the upper limit, the curability of the resulting coating may be reduced. If the mole ratio is lower than the lower limit, the hydroxyl group becomes excessive and the water resistance may decrease.

  The curing mechanism of the clear coating composition obtained in this way is as follows. First, the carboxyl group in the carboxyl group-containing acrylic resin (A) reacts with the carboxylate ester group by heating to cause the carboxyl group-containing acrylic resin (A) to react. An acid anhydride group is formed, and a free monoalcohol is formed. The produced monoalcohol is evaporated and removed out of the system. And the acid anhydride group produced | generated in carboxyl group-containing acrylic resin (A) forms a crosslinking point by reacting with the hydroxyl group contained in carboxyl group-containing polyester resin (B) and epoxy group-containing acrylic resin (C). Then, a carboxyl group is formed again. The carboxyl group and the carboxyl group present in the carboxyl group-containing polyester resin (B) react with the epoxy group present in the epoxy group-containing acrylic resin (C) to form a crosslinking point. In this way, the three types of polymers react with each other, so that curing proceeds and a coating film crosslinked at a high density is formed.

  The clear coating composition used in the present invention may contain a curing catalyst usually used in an esterification reaction between an acid such as a quaternary ammonium salt and an epoxy. Examples of the curing catalyst include benzyltriethylammonium chloride or bromide, tetrabutylammonium chloride or bromide, salicylate or glycolate, paratoluenesulfonate, and the like.

  The amount of the curing catalyst added is generally 0.01 to 3.0% by mass, preferably 0.1 to 1.5% by mass, more preferably 0.4 to 1.2%, based on the solid content of the resin composition. % By mass. If the amount of the curing catalyst is less than the lower limit, the added effect may not be obtained, and if it exceeds the upper limit, the storage stability may be lowered.

  Moreover, in the clear coating composition used in the present invention, a known tin-based compound described in JP-A-2-151651 can be mixed. Examples of such a tin-based catalyst include dimethyltin bis (methyl maleate), dimethyltin bis (ethyl maleate), dimethyltin bis (butyl maleate), dibutyltin bis (butyl maleate), and the like.

  The added amount of the tin-based catalyst is generally 0.05 to 6.0% by mass, preferably 0.1 to 4.0% by mass, and more preferably 0.2 to 2.% by mass with respect to the solid content of the resin composition. 0% by mass. If the amount of the tin-based catalyst is less than 0.05% by mass, the storage stability may be lowered, and if it exceeds 6.0% by mass, the weather resistance may be lowered. In addition, when using together a curing catalyst and a tin-type catalyst, it is preferable that the mass ratio of a curing catalyst and a tin-type catalyst shall be 1 / 4-1 / 0.2.

  A blocked isocyanate can be added to the clear coating composition used in the present invention in order to increase the crosslinking density and improve the water resistance. Moreover, you may add a well-known ultraviolet absorber, light stabilizer, antioxidant, etc. Furthermore, known rheology control agents and other surface conditioners may be added, and solvents such as alcohol solvents, aromatic hydrocarbon solvents, ester solvents and ketone solvents are used for viscosity adjustment and the like. You can also.

Substrate The method for forming a laminated coating film of the present invention can be advantageously used for various substrates such as metals, plastics, foams, etc., particularly metal surfaces, and castings. Especially, it can use especially suitably with respect to the metal product which can be cationic electrodeposition coating.

  Examples of the metal products include iron, copper, aluminum, tin, zinc and the like and alloys containing these metals. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. These metals are particularly preferably those subjected to chemical conversion treatment with phosphate, chromate or the like in advance.

  Moreover, the electrodeposition coating film may be formed in the base material used for the laminated coating film formation method of this invention on the steel plate by which chemical conversion treatment was carried out. As the electrodeposition paint for forming the electrodeposition coating film, a cation type and an anion type can be used. However, the cationic electrodeposition coating composition is preferable because it provides a laminated coating film excellent in corrosion resistance.

Laminated coating film forming method The laminated coating film forming method of the present invention comprises a method of forming an intermediate coating film by an intermediate coating composition, a base coating film by a base coating composition and a clear coating composition by a clear coating composition on a substrate. In this method, the layers are sequentially formed by wet-on-wet, and then these three kinds of coating films are baked and cured at once.

  In the present invention, when the intermediate coating composition is applied to an article to be coated such as an automobile body, it is applied by multistage coating by air electrostatic spray coating, preferably by two stages, or by air electrostatic spray coating. And a coating method using a combination of a rotary atomizing electrostatic coating machine called “μμ (micro micro) bell”, “μ (micro) bell” or “metabell”. Can do. By these coating methods, a coating film excellent in coating film appearance can be obtained.

  In the present invention, the film thickness of the dry coating film by the intermediate coating composition varies depending on the desired application, but in many cases, 10 to 60 μm is useful. If the upper limit is exceeded, sharpness may be reduced, or defects such as unevenness or flow may occur during painting. If the lower limit is exceeded, the substrate cannot be concealed and film breakage may occur.

  In the laminated coating film forming method of the present invention, the base coating composition and the clear coating composition are sequentially applied on the uncured intermediate coating film by wet-on-wet to form the base coating film and the clear coating film. To do.

  Similarly to the intermediate coating composition, the base coating composition of the present invention can be applied by air electrostatic spray coating or a rotary atomizing electrostatic coating machine such as Metabell, μμ Bell, μ Bell. The dry film thickness of a base coating film can be set to 5-35 micrometers, Preferably it is 7-25 micrometers. If the film thickness of the base coating film exceeds 35 μm, the sharpness may be deteriorated, or unevenness or flow may occur in the coating film. Neither of these is preferable because a discontinuous state of the film may occur.

  In the method for forming a laminated coating film according to the present invention, the clear coating film that is applied after the base coating film is formed smoothes irregularities resulting from the base coating film, flickering that occurs when a glitter pigment is included, Formed to protect. Specifically, as a coating method, it is preferable to form a coating film by the above-described rotary atomizing electrostatic coater such as μμ bell or μbell.

  The dry film thickness of the clear coating film formed from the clear coating composition is generally preferably about 10 to 80 μm, more preferably about 20 to 60 μm. If the upper limit is exceeded, defects such as armpits or sagging may occur. If the lower limit is not reached, the underlying irregularities may not be concealed.

  The three types of coating films thus obtained are cured by so-called three-coat one-bake, which is simultaneously baked and cured. This method can omit the baking and drying furnace for the intermediate coating film and the base coating film, and is preferable from the viewpoint of economy and environmental protection.

  A cured coating film having a high degree of crosslinking can be obtained by setting the curing temperature for curing the laminated coating film to, for example, 120 to 160 ° C. If the upper limit is exceeded, the coating film may become hard and brittle, and if the lower limit is not reached, sufficient curing may not be obtained. Although hardening time changes with hardening temperature, it is 10 to 60 minutes at 120 to 160 degreeC, for example.

  The film thickness of the laminated coating film formed in the present invention is often 30 to 300 μm, and preferably 50 to 250 μm. If the upper limit is exceeded, film physical properties such as a cooling cycle will decrease, and if it falls below the lower limit, the strength of the film itself may decrease.

  EXAMPLES Hereinafter, although a specific Example is given and this invention is demonstrated in detail, this invention is not limited by a following example. In the following description, “part” means “part by mass”.

Production Example 1 Production of urethane-modified polyester resin for intermediate coating composition 440 parts of isophthalic acid, hexahydro in a 2 L reaction vessel equipped with a nitrogen introducing tube, a stirrer, a temperature controller, a dropping funnel and a cooling tube equipped with a decanter 20 parts of phthalic acid, 40 parts of azelaic acid, 300 parts of trimethylolpropane and 200 parts of neopentyl glycol were charged. When the raw material was dissolved and stirred by heating, 0.2 part of dibutyltin oxide was added and stirred. The reaction layer temperature was gradually raised from 180 to 220 ° C. over 3 hours. The resulting condensed water was distilled out of the system. When the temperature reached 220 ° C., the temperature was kept for 1 hour, 20 parts of xylene was gradually added into the reaction layer, and the condensation reaction proceeded in the presence of a solvent. When the resin acid value reached 10 mg KOH / g (solid content), it was cooled to 100 ° C., and 100 parts of hexamethylene diisocyanate was gradually added over 30 minutes. Further, after holding for 1 hour, 200 parts of xylene and 200 parts of butyl acetate were added, and the solid content was 70%, the number average molecular weight was 2000, the acid value was 8 mgKOH / g (solid content), the hydroxyl value was 120 (solid content), and the resin Tg was 60 ° C. A urethane-modified polyester resin was obtained.

Production Example 2 Production of non-aqueous dispersion
(2-1) Production of Dispersion Stabilizing Resin 90 parts of butyl acetate was charged into a container equipped with a stirrer, a temperature controller, and a reflux condenser. Next, 20 parts of a solution composed of 38.9 parts of methyl methacrylate, 38.8 parts of stearyl methacrylate, 22.3 parts of 2-hydroxyethyl acrylate and 5.0 parts of azobisisobutyronitrile were added and stirred. While heating, the temperature was raised. The remaining 85 parts of the above mixed solution was added dropwise at 110 ° C. over 3 hours, and then a solution consisting of 0.5 parts of azobisisobutyronitrile and 10 parts of butyl acetate was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to increase the rate of conversion to resin, and then the reaction was terminated to obtain an acrylic resin having a solid content of 50%, a number average molecular weight of 5600 and an SP value of 9.5.

(2-2) Production of non-aqueous dispersion In a container equipped with a stirrer, a cooler, and a temperature control device, 90 parts of butyl acetate, 120 parts of acrylic resin obtained by the production of (2-1) dispersion-stable resin (solid 60 parts per minute). Next, 7.0 parts of styrene, 1.8 parts of methacrylic acid, 12.0 parts of methyl methacrylate, 8.5 parts of ethyl acrylate, 40.7 parts of 2-hydroxyethyl acrylate, and 1.4 parts of azobisisobutyronitrile. Then, a solution consisting of 0.1 parts of azobisisobutyronitrile and 1 part of butyl acetate was added dropwise over 30 minutes. When the reaction solution was further stirred for 1 hour, an emulsion having a solid content of 60% and a particle size of 180 nm was obtained. This emulsion was diluted with butyl acetate to obtain a core-shell type butyl acetate dispersion having a viscosity of 300 cps (25 ° C.) and a particle diameter of 180 nm and a non-aqueous dispersion content of 40% by mass. The non-aqueous dispersion resin had a Tg of 23 ° C. and a hydroxyl value (solid content) of 162.

Production Example 3 Production of Intermediate Coating Composition Into 1 L vessel, 107 parts of urethane-modified polyester resin varnish for intermediate coating composition obtained in Production Example 1 above, CR-97 (Ishihara Sangyo Co., Ltd. titanium oxide) 280 Parts, MA-100 (Mitsubishi Chemical Corporation carbon black pigment) 13 parts, LMS-100 (Fuji talc scale talc) 7 parts, butyl acetate 47 parts and xylene 47 parts, GB503M of the same amount as the charged mass (Glass beads having a particle size of 1.6 mm) were added and dispersed at room temperature for 3 hours using a tabletop sand grinder mill to obtain a gray pigment paste. The particle size at the end of dispersion by a grind gauge was 5 μm or less. The glass beads were filtered to obtain a pigment paste.

  To 100 parts of the pigment paste, 130 parts of the urethane-modified polyester resin for the intermediate coating composition, 53 parts of a non-aqueous dispersion for the intermediate coating composition of the above production example, Uban 128 (Melamine resin manufactured by Mitsui Chemicals, solid content) The intermediate coating composition was prepared by mixing 71 parts of 60%) and 71 parts of Duranate MF-K60X (active methylene type blocked isocyanate manufactured by Asahi Kasei Corporation, solid content 60%).

  Further, a mixed solvent of ethoxyethyl propionate / S-100 (Aromatic hydrocarbon solvent manufactured by Exxon) = 1/1. The dilution was adjusted to 19 seconds / 20 ° C. using a 4 Ford cup. The nonvolatile content at the time of application was 49%.

Production Example 4 Production of Acrylic Resin (A) 50 parts of xylene and 25 parts of n-butanol were charged into a container equipped with a stirrer, a temperature controller, and a reflux condenser. Next, 5.0 parts of solution styrene having the following composition, 1.5 parts of methacrylic acid, 20.0 parts of methyl methacrylate, 45.0 parts of ethyl acrylate, 6.6 parts of 2-hydroxyethyl acrylate, 5.0 of butoxymethylacrylamide Part, Plaxel FM-2 17.6 parts (Daicel Chemical Industries hydroxyl group-containing monomer) and azobisisobutyronitrile 7.0 parts were added and heated while stirring to raise the temperature. While refluxing, the remaining 87.7 parts of the mixed solution was added dropwise over 3 hours, and then a solution consisting of 0.2 parts of azobisisobutyronitrile and 8 parts of xylol was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 1 hour to increase the rate of conversion to resin, and then the reaction was terminated. The solid content was 55%, the number average molecular weight was 3800, the acid value was 9.8 mgKOH / g (solid content), the hydroxyl value. An acrylic resin varnish of 59.5 (solid content) was obtained.

Production Example 5 Production of Organic Bentonite Dispersed Paste (U-1) In a 2 L vessel, 512.7 parts of the acrylic resin (A) obtained from Production Example 4, 70.5 parts of Benton 38 (manufactured by RHEOX) and butyl acetate 416.8 parts were charged, and GB503M (glass beads having a particle diameter of 1.6 mm) having the same amount as the charged weight was charged and dispersed at room temperature for 1 hour using a tabletop sand grinder mill. The particle size at the end of dispersion by a grind gauge was 5 μm or less. The glass beads were filtered to obtain an organic bentonite dispersion paste (U-1).

Production Example 6 Production of Organic Bentonite Dispersed Paste (U-2) Instead of Benton 38 used in Production Example 5, Benton 27 (manufactured by RHEOX) 70.5 parts was used in the same manner as Production Example 5 Thus, an organic bentonite dispersion paste (U-2) was prepared.

Comparative Production Example 1 Production of crosslinked polymer fine particles
(Comparative Production Example 1-1) Production of polyester resin having amphoteric groups In 2 L Kolben equipped with a stirrer, nitrogen introduction tube, temperature controller, condenser, decanter, 134 parts of bishydroxyethyl taurine, 130 parts of neopentyl glycol Then, 236 parts of azelaic acid, 186 parts of phthalic anhydride and 27 parts of xylene were charged and the temperature was raised. The water produced by the reaction was removed by azeotropy with xylene. The temperature was raised to 190 ° C. over about 2 hours from the start of refluxing, and stirring and dehydration were continued until the acid value corresponding to carboxylic acid reached 145 mgKOH / g (solid content), and then cooled to 140 ° C. Subsequently, the temperature of 140 ° C. was maintained, and 314 parts of “Cardura E-10” (Versatic acid glycidyl ester manufactured by Shell) was dropped in 30 minutes, and then the stirring was continued for 2 hours to complete the reaction. The polyester resin thus obtained had an acid value of 59 mgKOH / g (solid content), a hydroxyl value of 90 (solid content), and a number average molecular weight of 1054.

(Comparative Production Example 1-2) Production of crosslinked polymer fine particles In production of a polyester resin having 232 parts of deionized water and the above amphoteric group in a 1 L reaction vessel equipped with a stirrer, a cooler, and a temperature control device. 10 parts of the obtained polyester resin and 0.75 parts of dimethylethanolamine were added and dissolved while maintaining the temperature at 80 ° C. with stirring, and 4.5 parts of azobiscyanovaleric acid was added to 45 parts of deionized water and dimethylethanolamine 4 .3 parts of the dissolved solution was added. Next, a mixed solution consisting of 130 parts of methyl methacrylate, 40 parts of styrene and 140 parts of ethylene glycol dimethacrylate was dropped over 60 minutes. After the dropwise addition, 1.5 parts of azobiscyanovaleric acid dissolved in 15 parts of deionized water and 1.4 parts of dimethylethanolamine were added and stirring was continued at 80 ° C. for 60 minutes. As a result, the solid content was 45%, pH 7 An emulsion having a viscosity of 92 cps (25 ° C.) and a particle size of 0.1 μm was obtained. This emulsion was replaced with a xylol solution using azeotropy to obtain a xylol dispersion having a crosslinked polymer fine particle diameter of 0.07 μm and a crosslinked polymer fine particle content of 20% by mass.

Example 1
Production of base coating composition In a stainless steel container, 127.3 parts of acrylic resin (A) of Production Example 4, 50.0 parts of Uban 20N60 (Mitsui Chemicals, 60% solids) which is melamine resin (I), organic 14.2 parts of organic bentonite dispersion paste (U-1) of Production Example 5 which is bentonite (U), 1 part of monobutyl maleate which is monoalkyl maleate (E), and aluminum paste which is glitter pigment (E) 21.0 parts of 91-0562 (aluminum pigment manufactured by Toyo Aluminum Co., Ltd.) were weighed and stirred with a desktop stirrer to prepare a metallic base coating composition.

Formation of a multilayer coating film A cationic electrodeposition paint “V-50” (manufactured by Nippon Paint Co., Ltd.) was applied on a 0.8 mm thick dull steel plate subjected to zinc phosphate conversion treatment so that the cured film thickness was about 20 μm. After coating and heating at 160 ° C. for 30 minutes to cure, the intermediate coating composition obtained in Production Example 3 is coated with METABEL (rotational atomization type static product manufactured by ABB Co. Painted with an electric coating machine).

  Seven minutes after applying the intermediate coating composition, the above-mentioned coated plate coated with the uncured intermediate coating composition was erected vertically. The base coating composition obtained above was subjected to No. 1 using a diluted thinner comprising 50 parts of Solvesso 150 (hydrocarbon solvent manufactured by Exxon Petroleum), 25 parts of ethyl acetate and 25 parts of toluene. The dilution was adjusted to 12.5 seconds / 20 ° C. with a 4 Ford cup. The obtained diluted base coating composition was coated with Metabell (rotary atomization type electrostatic coating machine manufactured by ABB Co., Ltd.) in two stages at intervals of 1.5 minutes so that the dry film thickness was 15 μm. A metallic base coating film was prepared by allowing to stand at room temperature for 10 minutes.

  Next, in advance, no. Clear coating "McFlow O-600" (manufactured by Nippon Paint Co., Ltd.) diluted to 25 seconds / 20 [deg.] C. with a 4 Ford cup, coated with an uncured intermediate coating and base coating formed vertically The product was coated once by Metabell so that the dry coating of the clear coating was 35 μm by wet-on-wet.

  The article on which the three-layer uncured coating film was formed was left standing in a vertical state at room temperature for 7 minutes, and then baked in a 160 ° C. dryer for 20 minutes in the vertical state. A laminated coating film by 3 coats and 1 bake was obtained. Usually, the baking temperature is often set to 140 ° C. as the center value. In this example, baking was performed at 160 ° C. in order to perform the harsh conditions in the appearance evaluation of the laminated coating film.

Example 2
The same procedure as in Example 1 except that 14.2 parts of the organic bentonite dispersion paste (U-2) of Production Example 6 was used instead of 14.2 parts of the organic bentonite dispersion paste (U-1) of Production Example 5. A base coating composition was prepared and painted as in Example 1.

Example 3
Implementation was performed except that the amount of the organic bentonite dispersed paste (U-1) in Production Example 5 was changed to 7.1 parts and 7.1 parts of the organic bentonite dispersed paste (U-2) in Production Example 6 was used. A base coating composition was prepared in the same manner as in Example 1 and painted in the same manner as in Example 1.

Example 4
A base coating composition was prepared in the same manner as in Example 3 except that 1 part of monoethyl maleate was used instead of 1 part of monobutyl maleate, and was applied in the same manner as in Example 1.

Comparative Example 1
A base coating composition was prepared in the same manner as in Example 1 except that organic bentonite dispersion paste (U-1) and monobutyl maleate were not used, but 25 parts of the crosslinked polymer fine particles of Comparative Production Example 1 were used. The coating was carried out in the same manner as in Example 1.

Comparative Example 2
A base coating composition was prepared in the same manner as in Example 1 except that 25 parts of the crosslinked polymer fine particles of Comparative Production Example 1 were used without using the organic bentonite dispersion paste (U-1). Painted in the same way.

Comparative Example 3
A base coating composition was prepared in the same manner as in Example 3 except that the amount of monobutyl maleate was changed to 0.1 part, and coated in the same manner as in Example 1.

Comparative Example 4
A base coating composition was prepared in the same manner as in Example 3 except that the amount of monobutyl maleate was changed to 5 parts, and was applied in the same manner as in Example 1.

Comparative Example 5
A base coating composition was prepared in the same manner as in Example 1 except that monobutyl maleate was not used, and was applied in the same manner as in Example 1.

Comparative Example 6
A base coating composition was prepared in the same manner as in Example 2 except that monobutyl maleate was not used, and was applied in the same manner as in Example 1.

Comparative Example 7
A base coating composition was prepared in the same manner as in Example 3 except that 1 part of succinic acid was used instead of 1 part of monobutyl maleate, and was applied in the same manner as in Example 1.

Comparative Example 8
A base coating composition was prepared in the same manner as in Example 3 except that 1 part of monomethyl phthalate was used in place of 1 part of monobutyl maleate, and coated in the same manner as in Example 1.

  The following evaluation tests were performed on the above examples and comparative examples.

Evaluation of armpit generation Electrodeposition coating of cationic electrodeposition paint “V-50” (manufactured by Nippon Paint Co., Ltd.) on a 10 × 30 cm dull steel plate that has been subjected to zinc phosphate conversion treatment so that the cured film thickness is about 20 μm. Then, after being cured by heating at 160 ° C. for 30 minutes, the intermediate coating composition obtained in Production Example 3 was applied with a metabell so that the cured film thickness was about 25 μm. Seven minutes after applying the intermediate coating composition, the above-mentioned coated plate coated with the uncured intermediate coating composition was erected vertically. The base coating composition of the example or comparative example was subjected to No. 1 using a thinner diluted with 50 parts of Solvesso 150 (hydrocarbon solvent manufactured by Exxon Petroleum), 25 parts of ethyl acetate and 25 parts of toluene. The dilution was adjusted to 12.5 seconds / 20 ° C. with a 4 Ford cup. The obtained diluted base coating composition was applied with a metabell on two stages at 1.5 minute intervals so that the dry film thickness was 15 μm.

  One minute after the base coating composition was applied, no. A clear paint “McFlow O-600” (manufactured by Nippon Paint Co., Ltd.) diluted to 25 seconds / 20 ° C. with a 4 Ford cup was sprayed from a place 5 m away from the coating plate for about 10 seconds. After allowing to stand at room temperature for 5 minutes, the clear coating was applied by a single application with a metabell so that the dry coating of the clear coating was 35 μm.

The coated plate on which the three-layer uncured coating film was formed was allowed to stand for 7 minutes in a vertical state at room temperature and then baked in a dryer at 160 ° C. for 20 minutes in the vertical state. The number of arms present on the laminated coating film thus obtained was counted and evaluated according to the following criteria. Usually, the baking temperature is often set to 140 ° C. as the center value. In this evaluation, baking was performed at 160 ° C. in order to perform the harsh conditions in the appearance evaluation of the laminated coating film.
5: No armpit 4: Armpit within 5 points 3: Armpit within 10 points 2: Armpit within 20 points 1: Armpit over 20 points

Appearance evaluation About the surface of the laminated coating film obtained from the said Example and the comparative example, the finished external appearance was evaluated by measuring W1 value and W4 value using "wave scan" by BYK-Gardner GmbH. The W1 value is an index for evaluating the skin swell (round) of the coating film, and the lower this value, the better the finished appearance. The W4 value is an index for evaluating the gloss and fine skin of the coating film, and the lower this value, the better the finished appearance.

  The composition and evaluation results of the above examples and comparative examples are summarized in the following table. In addition, each component compounding amount in the following table | surface shows the solid content mass of each component.

As can be seen from the above results, it was confirmed that the laminated coating films obtained by the examples had no occurrence of cracks, W1 and W4 were small, and the finished appearance was good.
On the other hand, Comparative Example 1 which did not contain maleic acid alkyl ester and used cross-linked polymer fine particles instead of organic bentonite had a lot of cracking, and W1 and W4 were large and the finished appearance was inferior.
In Comparative Example 2 in which crosslinked polymer fine particles were used instead of organic bentonite, there was a crack and W1 and W4 were large and the finished appearance was inferior.
In Comparative Example 3 in which the amount of maleic acid monoalkyl ester is small and Comparative Example 4 in which the amount of maleic acid monoalkyl ester is large, both exist, W1 and W4 are large, and the finished appearance is inferior.
In each of Comparative Examples 5 and 6 containing no maleic acid alkyl ester, the occurrence of cracks was large, and W1 and W4 were both large and the finished appearance was poor.
Comparative Example 7 using succinic acid instead of maleic acid monoalkyl ester and Comparative Example 8 using monomethyl phthalate also had armpits, and W1 and W4 were large and the finished appearance was poor.

  A laminated coating film obtained by a three-coat one-bake method in which a specific intermediate coating composition, base coating composition, and clear coating composition, which are the methods of the present invention, are sequentially applied by wet on wet, It has the characteristics that it is not accompanied by “flakes” that cause a decrease, and the resulting laminated coating film has high smoothness and excellent gloss. The method of the present invention is a method for forming a coating film by a 3-coat 1-bake system that is excellent in economic efficiency and has a low environmental impact. Thus, the method of the present invention is an industrially excellent method and can form a laminated coating film having an excellent coating film appearance.

Claims (2)

An intermediate coating composition, a base coating composition, and a clear coating composition are sequentially applied on a substrate on which an electrodeposition coating film is formed by wet-on-wet, and three uncoated three layers are applied. A step of baking and curing the coating film simultaneously,
A method for forming a laminated coating film comprising:
The intermediate coating composition has the following components:
A hydroxyl group-containing polyester resin obtained by polycondensation of an acid component containing 80 mol% or more of isophthalic acid and a polyhydric alcohol and having a glass transition point (Tg) of 40 to 80 ° C. is reacted with an aliphatic diisocyanate compound. The urethane-modified polyester resin (a) having a number average molecular weight (Mn) of 1200 to 3000, obtained by 40 to 56% by mass;
Melamine resin (b) 10-30% by mass;
Block isocyanate compound (c) 15 to 30% by mass, in which an isocyanate compound obtained by reacting with hexamethylene diisocyanate or hexamethylene diisocyanate and a compound that reacts with it is blocked with a compound having an active methylene group;
Non-aqueous dispersion resin (d) having a core-shell structure 4 to 15% by mass;
However, the amount of (a) to (d) is based on the solid content mass of the coating resin; and the flat pigment (e) 0.4 to 2 having a major axis of 1 to 10 μm and a number average particle size of 2 to 6 μm Parts by weight, wherein the part by weight of (e) is the amount relative to 100 parts by weight of the solid content of the coating resin;
A solvent-type intermediate coating composition containing, and
The base coating composition has the following components:
Acrylic resin (A) having a number average molecular weight (Mn) of 1000 to 20000, a hydroxyl value of 10 to 200, and an acid value of 1 to 80 mgKOH / g;
Melamine resin (I) 5 to 60% by mass;
Organic bentonite (U) 0.1-10% by mass;
Maleic acid monoalkyl ester (d) 0.2-4% by mass;
However, the amounts of (a) to (d) are based on the solid content mass of the paint resin; and the glitter pigment (e) pigment concentration (PWC) is 1 to 23.0 mass%, but based on the solid mass of the paint ;
A solvent-based base coating composition, and the clear coating composition contains a carboxyl group-containing acrylic resin (A), a carboxyl group-containing polyester resin (B), and an epoxy group-containing acrylic resin (C). A solvent-based clear coating composition,
Laminated coating film forming method.   A coated article having a multilayer coating film obtained by the method for forming a multilayer coating film according to claim 1.