JP4673938B1 - Clear paint composition - Google Patents

Abstract

Provided is a coating composition having scratch recovery properties superior to those of conventional coating compositions, and having performance equivalent to that of conventional coating compositions in terms of finished appearance, weather resistance, and water resistance.
A clear coating composition comprising a polycarbonate diol compound (A), a hydroxyl group-containing acrylic resin (B), a polycaprolactone polyol (C) having 3 to 5 branches and a hydroxyl group equivalent of 170 to 1600 and a curing agent (D).
[Selection figure] None

Description

The present invention relates to a clear coating composition.

An automobile body, automobile parts, and the like are overcoated for the purpose of imparting acid resistance, solvent resistance, weather resistance, and the like. In such a top coat film, in recent years, scratches on the paint film that occur during traveling, use of a car wash machine, and the like are regarded as a problem, and a paint film having scratch resistance has been demanded.

As a coating composition capable of forming a coating film having excellent scratch resistance, a urethane crosslinking system using a hydroxyl group-containing resin such as an acrylic resin as a base resin and a polyisocyanate compound as a crosslinking agent is widely used. In recent years, it has been studied to use polycarbonate diol in such urethane cross-linked paints (Patent Documents 1, 2, and 3).

Patent Document 1 describes a coating composition in which a polycarbonate diol is used in combination with a polyol compound and a polyisocyanate compound as a clear coating composition for improving scratch resistance. However, the polycarbonate diol has a problem that the physical properties of the coating film are liable to deteriorate because the compatibility with other resin components, particularly acrylic polyol, is not good. Further, when a large amount of polycarbonate diol is blended, the crosslink density is lowered, and physical properties such as weather resistance and solvent resistance become insufficient.

Patent Document 2 describes a polyurethane resin coating agent using acrylate polyol and acrylic polyol in combination. However, the coating agent described in the cited document 2 is a coating agent containing a urethanized resin. For this reason, sufficient crosslinking density cannot be obtained, and it cannot be used as a paint for automobiles.

In Patent Document 3, a coating composition using a polycarbonate diol and a polyisocyanate compound in combination is described. However, such a coating composition is a soft-feel coating and cannot obtain performances such as acid resistance, solvent resistance, and weather resistance that are used in automobile coating.

In order to improve such problems, Patent Document 4 discloses a coating composition containing a polycarbonate diol-modified polymer and a polyisocyanate compound. However, such a coating composition has a complicated composition and therefore requires a large amount of labor in synthesis, which causes an increase in cost.

WO2007 / 119305 JP 2006-182904 A JP 2008-3395 A JP 2009-149825 A

In view of the above situation, the present invention has better scratch recovery than conventional coating compositions, and also has the same performance as conventional coating compositions in terms of finished appearance, weather resistance, and water resistance. It aims at providing the coating composition which has.

The present invention comprises a polycarbonate diol compound (A), a hydroxyl group-containing acrylic resin (B), a polycaprolactone polyol (C) having 3 to 5 branches and a hydroxyl group equivalent of 170 to 1600, and a curing agent (D). The clear coating composition.

The polycarbonate diol compound (A) preferably has a hydroxyl group equivalent of 320 to 2000.
The hydroxyl group-containing acrylic resin (B) preferably has a hydroxyl group equivalent of 200 to 600 and the number of hydroxyl groups in one molecule of 4.0 to 30.
The hydroxyl group-containing acrylic resin (B) preferably has a glass transition temperature of -20 to 60 ° C.

The compounding ratio ((A) / (B) + (C)) of the polycarbonate diol compound (A), the hydroxyl group-containing acrylic resin (B) and the polycaprolactone polyol (C) is 90/10 to 10/90. Is preferred.
The compounding ratio of the hydroxyl group-containing acrylic resin (B) and the polycaprolactone polyol (C) is preferably (B) / (C) = 10/90 to 90/10.

The clear coating composition of the present invention can provide a coating film having excellent scratch recovery properties and having a finished appearance, water resistance, weather resistance and the like that can be sufficiently used as an automotive coating.

Hereinafter, the present invention will be described in detail.
The present invention uses a polycarbonate-based diol compound (A), a hydroxyl group-containing acrylic resin (B), and a polycaprolactone polyol (C) in combination to provide a coating film having excellent finished appearance, water resistance, weather resistance, stain resistance, and the like. It has both physical properties and scratch resistance recovery. That is, the problem of deterioration in compatibility that occurs when the polycarbonate diol compound (A) and the hydroxyl group-containing acrylic resin (B) are used in combination is solved by using the polycaprolactone polyol (C) having specific properties in combination. .

That is, since the polycaprolactone polyol (C) used in the present invention is a resin having affinity for both the polycarbonate diol compound (A) and the hydroxyl group-containing acrylic resin (B), the compatibility thereof is increased. Has an effect. By improving the compatibility of each component in the paint by such a method, it is possible to sufficiently exhibit performance such as scratch recovery, finished appearance, water resistance, and weather resistance, and a coating film with excellent performance can be obtained. Obtainable.

Furthermore, since the polycaprolactone polyol (C) has 3 to 5 branches, the crosslinking density can be increased. Thus, even when the polycarbonate diol compound (A) which is a diol component is used, the crosslinking density does not decrease. For this reason, performance, such as water resistance and a weather resistance, can be improved. Furthermore, by using the polycaprolactone polyol (C) having a hydroxyl group equivalent of 170 to 1600, the balance between the hydrophilization and the hydrophobization degree is achieved, whereby the polycarbonate diol compound (A) and the hydroxyl group-containing acrylic resin (B )) And a particularly uniform effect can be obtained by forming a more uniform coating film.

Since the compatibility can be improved by using the polycaprolactone polyol (C), various actions and effects expected by using the polycarbonate-based diol compound (A) excellent in hydrolysis resistance can be maximized. And improved functions such as excellent scratch recovery, finished appearance, water resistance, and weather resistance. As a result, a paint having a well-balanced balance of all physical properties required in the clear paint composition is completed.

The polycarbonate diol compound (A) is a component for imparting scratch recovery properties. Furthermore, by using together with the hydroxyl group-containing acrylic resin (B), both a network structure having a high crosslink density and a low molecular weight between crosslinks and a large network structure can be formed in the cured coating film. At the same time, excellent physical properties as a coating film can be obtained. Furthermore, since the polycarbonate diol compound (A) is a polycarbonate diol compound (A) having excellent hydrolysis resistance, it has excellent performance in water resistance and weather resistance.

The polycarbonate diol compound (A) is represented by the following general formula (1);

It is represented by the general formula of
In the formula, the structure of R is determined by the diol component used in the production of the polycarbonate diol. Examples of the diol component include divalent alcohols having 2 to 10 carbon atoms, preferably 4 to 8 carbon atoms. Specifically, for example, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1 , 7-heptanediol, 1,8-octanediol, 2-ethyl-1,6-hexanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, etc. Aliphatic systems such as 1,3-cyclohexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and the like; aromatic systems such as p-xylenediol and p-tetrachloroxylenediol; Examples thereof include diols such as diethylene glycol and dipropylene glycol. These diols can be used alone or in combination of two or more. The polycarbonate diol can be obtained by reacting the diol with a carbonylating agent such as phosgene.

In the polycarbonate diol compound (A) used in the present invention, R in the general formula (1) is preferably a linear alkyl group. The polycarbonate diol compound (A) in which R is a linear alkyl group has the following general formula (2);

(In the formula, n = 2 to 40, m = 2 to 20). Among these, from the viewpoint of obtaining scratch resistance while maintaining durability and hardness, those obtained by polycondensation of a diol component containing 1,6-hexanediol and a carbonylating agent are preferable.

Particularly preferred is a combination of two or more diol components using 1,6-hexanediol as an essential diol component, and a combination of 1,6-hexanediol and 1,5-pentanediol, 1,6 -A polycarbonate diol obtained by polycondensation of a diol component such as a combination of hexanediol and 1,4-butanediol or a combination of 1,6-hexanediol and 1,4-dimethylolcyclohexane and a carbonylating agent. Can do.

Especially, it is a combination of the above 1,6-hexanediol and 1,5-pentanediol, and 1,6-hexanediol / 1,5-pentanediol = 80/20 to 20/80 (molar ratio) Is preferred. Thus, what used 2 or more types together is preferable at the point that the transparency of a clear coating film is favorable.

As said carbonylating agent, 1 type, or 2 or more types, such as a normally used alkylene carbonate, dialkyl carbonate, diallyl carbonate, and phosgene, can be used, for example. Among these, preferred are ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, and diphenyl carbonate.

The polycarbonate diol compound (A) preferably has a hydroxyl group equivalent of 320 to 2000. If the hydroxyl equivalent is less than 320, the crosslink density becomes too high, and there is a possibility that the scratch recovery property is deteriorated. When the hydroxyl equivalent exceeds 2000, the stain resistance and water resistance may be deteriorated. The hydroxyl group equivalent is more preferably 350 to 1000.

A commercial item can be used as said polycarbonate diol. Examples of commercially available products include T-5650J, T-5651, T-5651 (diol components: 1,6-hexanediol and 1,5-pentanediol) and T-4671 (diol component: 1) manufactured by Asahi Kasei Chemicals Corporation. , 6-hexanediol and 1,4-butanediol); ETERNACOLL UM-90 (1/1, 1/3) manufactured by Ube Industries, Ltd. (diol components: 1,6-hexanediol and 1,4-dimethylolcyclohexane) And the like.

The hydroxyl group-containing acrylic resin (B) used in the present invention is a component that imparts water resistance, weather resistance and the like. The hydroxyl group-containing acrylic resin (B) is not particularly limited as long as it is a polymer in which a structural unit derived from the acrylic monomer (a) having a hydroxyl group is essential, and appropriately, an acrylic monomer having a carboxyl group. (B), single monomers such as acrylic monomers (c) having ester groups copolymerizable with the acrylic monomers (a) and (b), and other vinyl monomers (d) The copolymer may further include a structural unit derived from the body, and the type of the structural unit constituting the polymer is not particularly limited.

Examples of the acrylic monomer (a) having a hydroxyl group include 1-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and (meth) acrylic. Examples include 4-hydroxybutyl acid, 2-hydroxyethyl (meth) acrylate, and these ε-caprolactone adducts, and only one kind or two or more kinds may be used in combination as required. . Of these, it is preferable to use 1-hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, or 3-hydroxypropyl (meth) acrylate that does not contain alkyl having 4 or more carbon atoms in the molecule. . By using an acrylic monomer having a hydroxyl group (a) having an alkyl group having 1 to 3 carbon atoms, a site having a small network structure is formed. This is preferable from the viewpoint of forming a portion having a large network structure and a portion having a small network structure, and forming a coating film having a plurality of performances as described above.

Examples of the acrylic monomer (b) having a carboxyl group include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and anhydrides thereof. You may use 2 or more types together only with a seed | species or as needed.

Examples of the acrylic monomer (c) having an ester group include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, and t-butyl (meth) acrylate. , N-amyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (Meth) acrylate, cyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meta Acrylate, dicyclopentenyl can be mentioned oxyethyl (meth) acrylate, alone, or may be used in combination of two or more as necessary.

Examples of the other vinyl monomers (d) include acrylamide monomers such as acrylamide, methacrylamide, N-methylol acrylamide, N, N-dimethylacrylamide, diacetone acrylamide, and the like. You may use 2 or more types together only with a seed | species or as needed. The hydroxyl group-containing acrylic resin can be obtained by appropriately selecting a monomer from the acrylic monomers (a) to (c) and the vinyl monomer (d) and polymerizing them.

Although there is no limitation in particular about the hydroxyl equivalent of the said hydroxyl-containing acrylic resin (B), it is preferable that it is 200-600, and it is more preferable that it is 300-500. If the hydroxyl equivalent is less than 200, the crosslink density becomes too high, and there is a possibility that the scratch recovery property is deteriorated. Moreover, when 600 is exceeded, stain resistance and water resistance may deteriorate.

The hydroxyl group-containing acrylic resin (B) preferably has 4.0 to 30 hydroxyl groups in one molecule. If the number of hydroxyl groups is less than 4.0, there is a possibility that the coating film strength is lowered, and if it exceeds 30, there is a possibility that the scratch recovery property is lowered.

Although the glass transition temperature of the said hydroxyl-containing acrylic resin (B) is not specifically limited, It is preferable that it is -20-60 degreeC, and it is more preferable that it is 0 degreeC-40 degreeC. If it is less than −20 ° C., the stain resistance may be deteriorated, and if it exceeds 60 ° C., scratch recovery may be deteriorated.

Although there is no limitation in particular about the number average molecular weight of the said hydroxyl-containing acrylic resin (B), it is preferable that it is 1000-20000, and it is more preferable that it is 1500-10000. If it is less than 1000, the resulting clear coating composition may have a large variation in hue. If it exceeds 20000, the finished appearance may be poor and the film thickness may be reduced.

The SP value (solubility parameter) of the hydroxyl group-containing acrylic resin (B) is not particularly limited, but is preferably 10.0 to 11.5, and more preferably 10.3 to 11.0. . If it is less than 10.0, peeling may occur at the interface with the base coating film. If it exceeds 11.5, familiarity may occur at the interface with the base coating film, and the coating film appearance may deteriorate.

The polycaprolactone polyol (C) used in the present invention has the following general formula (3):

It is preferable that it has a structure represented by these. R in the general formula (3) represents a branched alkyl group. The polycaprolactone polyol (C) has 3 to 5 branches. The number of branches refers to the number of terminal groups present in the molecule, and is indicated as p in the general formula (3). When the number of branches of the polycaprolactone polyol (C) is less than 3, the weather resistance tends to decrease and the stain resistance tends to deteriorate. On the other hand, when the number of branches of the polycaprolactone polyol (C) exceeds 5, The force becomes insufficient, the dent produced by the impact cannot be returned to the original coating film surface state, and the scratch resistance may be lowered.

The polycaprolactone polyol (C) is preferably obtained by reacting caprolactone with a compound having 3 to 5 hydroxyl groups in one molecule. Examples of the compound having 3 to 5 hydroxyl groups in one molecule include trimethylolpropane, pentaerythritol, ditrimethylolpropane, trimethylolethane, and glycerin.

The polycaprolactone polyol (C) preferably has a hydroxyl group equivalent of 170 to 1600. When the hydroxyl group equivalent is outside the range of 170 to 1600, the compatibility of the polycarbonate diol compound (A) and the hydroxyl group-containing acrylic resin (B) is insufficient, and the coating film performance is lowered. The hydroxyl group equivalent is 200 to 1500. It is more preferable that

Commercially available polycaprolactone polyols can also be used. Examples of commercially available polycaprolactone polyols include Placel 305 (3 branches, hydroxyl equivalent 183) Plaxel 308 (3 branches, hydroxyl equivalent 283), Plaxel 312 (3 branches, hydroxyl equivalent 417), manufactured by Daicel Chemical Industries, Ltd. be able to.

In the clear coating composition of the present invention, the mixing ratio of the polycarbonate-based diol compound (A), the hydroxyl group-containing acrylic resin (B) and the polycaprolactone polyol (C) ((A) / ((B) + (C))) Is preferably 90/10 to 10/90, more preferably 80/20 to 20/80 in terms of solid content mass ratio. If it exceeds 90/10, the water resistance and stain resistance may deteriorate. If it is less than 10/90, the scratch recovery property may not be sufficient.

In the clear coating composition of the present invention, the mixing ratio of the hydroxyl group-containing acrylic resin (B) and the polycaprolactone polyol (C) is (B) / (C) = 10/90 to 90/10 in terms of solid content mass ratio. It is preferable. If it is less than 10/90, there is a concern that the coating performance such as weather resistance is deteriorated. When it exceeds 90/10, the compatibility of the resin is lowered, the coating film becomes non-uniform, and there is a possibility that the coating film quality and the coating film appearance are deteriorated. The blending ratio is more preferably (B) / (C) = 90 / 10-30 / 70.

The clear coating composition of the present invention further contains a curing agent (D). The clear coating composition may be a two-pack type or a one-pack type, and in the case of a two-pack type, the polycarbonate diol compound (A), the hydroxyl group-containing acrylic resin (B), and the polycaprolactone polyol. It can be set as the coating composition which consists of a main ingredient containing (C) and a hardening | curing agent solution.

In the present invention, the curing agent (D) acts on the hydroxyl group contained in the polycarbonate diol compound (A), the hydroxyl group-containing acrylic resin (B) and the polycaprolactone polyol (C). In the case of the two-component type, examples of the curing agent (D) include polyisocyanate. The polyisocyanate is not particularly limited as long as it is a compound having two or more isocyanate groups in one molecule. For example, aliphatic, alicyclic, aromatic and aromatic-aliphatic Any of these may be used.

Specific examples of polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI), 2,2,4- C3-C12 aliphatic diisocyanates such as trimethylhexane diisocyanate and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI) Methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, and 1,3-diisocyanatomethyl cyclohexyl Carbon such as xane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate). Aliphatic diisocyanates having a number of 5 to 18; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); modified products of these diisocyanates (urethanes, carbodiimides, Uretdione, uretoimine, burette and / or isocyanurate modified product); and the like. These may be used alone or in combination of two or more.

When the clear coating composition is a one-pack type, examples of the curing agent (D) include a blocked isocyanate compound and a melamine resin. As said blocked isocyanate compound, the block polyisocyanate which blocked the isocyanate group of polyisocyanate can be mentioned. As the polyisocyanate, those described above can be used.

The blocking agent is added to a polyisocyanate group and is stable at ordinary temperature, but can regenerate a free isocyanate group when heated to a temperature higher than the dissociation temperature. As the blocking agent, those usually used such as ε-caprolactam and butyl cellosolve can be used. However, among these, many volatile blocking agents are regulated as targets of HAPs, and it is preferable that the amount used is minimized. Adducts or prepolymers obtained by reacting polyisocyanates with polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylolpropane and hexanetriol at an NCO / OH ratio of 2 or more may also be used as the block isocyanate curing agent.

When polyisocyanate or a block isocyanate compound is used as the curing agent (D), the total number of hydroxyl groups contained in the polycarbonate diol compound (A), the hydroxyl group-containing acrylic resin (B) and the polycaprolactone polyol (C) is 1 It is preferable to mix | blend a hardening | curing agent with respect to an isocyanate group in the range of 0.6-1.8. If the blending ratio is less than the lower limit, sufficient curing tends not to be obtained. If the blending ratio exceeds the upper limit, unreacted isocyanate groups react with moisture in the air, and the scratch resistance of the coating film tends to deteriorate.

Examples of the melamine resin include alkyl etherified melamines such as methyl etherified melamine, ethyl etherified melamine, and butyl etherified melamine, and only one kind or two or more kinds may be used in combination. Also good.

It is preferable that content of the said melamine resin is 10-40 mass% with respect to resin solid content of a clear coating composition. If the upper limit is exceeded, the coating film may be hard and brittle, and if it is less than the lower limit, the curability of the coating film may be reduced. The content of the melamine resin is more preferably 20 to 30% by mass.

The clear coating composition may have an organotin compound curing catalyst. The organotin compound curing catalyst is not particularly limited, and examples thereof include dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin dioctate. The blending amount of the curing catalyst is preferably a lower limit of 0.005% by mass and an upper limit of 0.05% by mass with respect to the resin solid content in the clear coating composition.

In the clear coating composition of the present invention, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, a crosslinked resin particle, a surface conditioner, an antifoaming agent, a film-forming aid and the like may be blended. When the crosslinked resin particles are used, it is preferable that the lower limit is 0.01% by mass and the upper limit is 10% by mass with respect to the resin solid content of the clear coating composition of the present invention. The lower limit is more preferably 0.1% by mass, and the upper limit is more preferably 5% by mass. When the added amount of the crosslinked resin particles exceeds 10% by mass, the appearance of the obtained coating film tends to deteriorate, and when it is less than 0.01% by mass, the rheology control effect tends to be not obtained.

When using a surface conditioner in the present invention, the surface conditioner to be blended is not particularly limited, but it is preferable to use a silicon-based surface conditioner, and in particular, use a polyester-modified silicon-based surface conditioner. Is more preferable. An acrylic copolymer surface conditioner can also be suitably used. These surface conditioners can be used alone or in combination of two or more. Such a surface conditioner is particularly preferable in terms of both the finished appearance (leveling property and repellency prevention property) and stain resistance. The blending amount of the surface conditioner is preferably blended at a lower limit of 0.01% by mass and an upper limit of 10% by mass with respect to the total solid content in the paint, and further the lower limit of 0.1% by mass and the upper limit of 5 More preferably, it is mass%. If the addition amount of the surface conditioner exceeds 10% by mass, the stain resistance of the resulting coating film tends to deteriorate, and if it is less than 0.01% by mass, rheology controllability may not be obtained.

The coating form of the clear coating composition of the present invention may be either an organic solvent type or an aqueous type (water-soluble, water-dispersible, emulsion). Examples of organic solvents include ester organic solvents such as ethyl acetate, butyl acetate, isobutyl acetate, and ethylene glycol monoethyl ether acetate; ether organic solvents such as methoxypropanol and ethoxypropanol; alcohol organics such as butanol, ethanol, and propyl alcohol Solvents; ketone organic solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aromatic organic solvents such as toluene and xylene. These may be used alone or in combination of two or more.

The method for obtaining the clear coating composition is not particularly limited, and all methods well known to those skilled in the art such as kneading various formulations using a kneader, roll, etc., and dispersing using a sand grind mill, disper, etc. Can be used.

The clear coating composition of the present invention can be used for any substrate, for example, wood, iron, copper, aluminum, tin, zinc, alloys containing these metals, glass, cloth, plastics, foams, and molded articles. In particular, it can be advantageously used for plastic and metal surfaces. That is, the clear coating composition of the present application can be suitably used for automobile parts such as automobile bodies and bumpers. In addition, it is possible to simultaneously coat a plurality of objects made of different materials such as a bumper and an automobile body.

When the base material is a steel plate, it is preferable that an undercoat coating film, an intermediate coating film and a base coating film are formed before applying the clear coating composition of the present invention.
Moreover, when a base material is a metal, what was chemically converted in advance with phosphate, chromate, etc. is especially preferable.

Examples of the method for forming the undercoat coating film include a method using an electrodeposition paint. As the electrodeposition paint, a cation type and an anion type can be used, but a cationic type electrodeposition paint composition is preferable in terms of anticorrosion.

The intermediate coating film is for concealing underlying defects, ensuring surface smoothness after coating with a clear coating (appearance improvement), and imparting coating film properties (impact resistance, chipping resistance, etc.). . In order to form the intermediate coating film, an intermediate coating is used, and the intermediate coating usually contains various organic and inorganic color pigments, extender pigments, a film-forming resin, a curing agent, and the like. It is a waste.

Examples of the film-forming resin and curing agent used in the intermediate coating composition include film-forming resins such as acrylic resins, polyester resins, alkyd resins, and fluorine resins, and amino resins and / or block polyisocyanate compounds. A curing agent such as is used. From the viewpoint of pigment dispersibility and workability, a combination of an alkyd resin and / or a polyester resin and an amino resin is preferable.

As the above intermediate coating material, a gray intermediate coating material mainly containing carbon black and titanium dioxide is used. Furthermore, a so-called color intermediate coating composition in which set gray or various colored pigments are combined can also be used.

After the intermediate coating material is applied onto the substrate on which the undercoat coating film is formed, it can be used even in an uncured state. However, when the intermediate coating film is cured, the curing temperature has a lower limit of 100. It is preferable that it is 0 degreeC and an upper limit is 180 degreeC. If it is less than 100 ° C, curing may not be sufficient, and if it exceeds 180 ° C, the coating film may be hard and brittle. The lower limit is more preferably 120 ° C., and the upper limit is more preferably 160 ° C. Thereby, a cured coating film having a high degree of crosslinking can be obtained. The curing time varies depending on the curing temperature, but 10 to 30 minutes at 120 to 160 ° C. is appropriate.

The base coating film is usually obtained from a base paint containing a color pigment, a coating film-forming resin and a curing agent, and additives as required.
Examples of the color pigments contained in the base paint include conventionally known color pigments such as organic azo lake pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, and perylene-based pigments. Examples thereof include pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, inorganic yellow lead, yellow iron oxide, bengara, carbon black, titanium dioxide, and the like. Further, flat pigments such as aluminum powder and graphite powder may be added. Further, extender pigments such as calcium carbonate, barium sulfate, clay and talc may be contained. Furthermore, you may contain bright materials, such as an interference mica pigment and an aluminum pigment, as needed.

Examples of the film-forming resin and curing agent for the base coating include curing of a film-forming resin such as an acrylic resin, a polyester resin, an alkyd resin, and a fluorine resin, and an amino resin and / or a block polyisocyanate compound An agent is used.

The total pigment concentration (PWC) in the base paint is preferably a lower limit of 3% by mass and an upper limit of 70% by mass. When it exceeds 70% by mass, the appearance of the coating film is deteriorated. The lower limit is more preferably 4% by mass, and still more preferably 5% by mass. The upper limit is more preferably 65% by mass, and still more preferably 60% by mass.

In general, the base paint is preferably a solution type, and may be any of an organic solvent type, an aqueous type (water-soluble, water-dispersible, and emulsion) or a non-aqueous dispersion type as long as it is a solution type.

When the base paint is applied onto the substrate on which the undercoat film and the intermediate coat film are formed, the base paint film is formed by applying in the same manner as the method of applying the clear paint composition described later. be able to.

Although the film thickness of the coating film at the time of application | coating with the said base coating material changes with desired uses, in many cases, 10-30 micrometers is useful. If the thickness is less than 10 μm, the substrate may not be concealed and the film may be cut. If the thickness exceeds 30 μm, the sharpness may be deteriorated, or defects such as unevenness and flow may occur during painting. Moreover, the dry film thickness of a base coating film is 10-30 micrometers normally. When the thickness is less than 10 μm, the concealability is inferior, and when it exceeds 30 μm, the economical efficiency is insufficient.

The coating film formed from the base paint may be coated with the next clear paint composition as it is without being dried by heat, but may be dried at a temperature of 60 ° C to 120 ° C. In particular, in the case of a water-based paint, when the drying temperature is 60 ° C. or lower, the familiarity with the clear paint may occur and the appearance of the coating film may be deteriorated. If the temperature is too high, peeling may occur between the base coating and the clear coating. Although drying time changes with drying temperature, 1 minute-5 minutes are suitable for more preferable drying conditions at 80 to 100 degreeC.

The method for applying the clear coating composition of the present invention to the substrate is not particularly limited, and examples thereof include a spray coating method and an electrostatic coating method. Industrially, for example, an air electrostatic spray coating machine called “react gun” or a rotary atomizing electrostatic coating machine called “micro micro bell”, “micro bell”, “metallic bell” or the like is used. Can mention the method

As for the dry film thickness of the clear coating film formed with the said clear coating composition, generally a minimum of 10 micrometers and an upper limit of 70 micrometers are preferable. If the thickness is less than 10 μm, the unevenness of the base may not be concealed, and if it exceeds 70 μm, problems such as cracking and sagging may occur during coating. The lower limit is more preferably 20 μm, and the upper limit is more preferably 50 μm.

After the clear coating is applied, the curing temperature for curing the coating film is preferably a lower limit of 60 ° C. and an upper limit of 180 ° C. If it is less than 60 ° C, curing may not be sufficient, and if it exceeds 180 ° C, the coating film may become brittle. The lower limit is more preferably 80 ° C. Although hardening time changes with hardening temperature, 20 to 30 minutes are suitable at 80 to 160 degreeC.

When the clear coating is applied on a plastic substrate, it may be applied on a substrate having a known coating such as primer coating or base coating, if necessary.

EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these Examples. In addition, all% in the compounding quantity of a present Example is the mass% unless there is particular limitation.

Synthesis Example 1 Compound B-1 synthesis temperature controller, stirring blade, reflux tube, 1 L separable flask equipped with nitrogen inlet was charged with 200 g of xylene and 150 g of propylene glycol monomethyl ether acetate, and the temperature was raised to 130 ° C. , Kept constant. On the other hand, a mixed liquid of 80 g of styrene, 52 g of 2-ethylhexyl acrylate, 108 g of 2-ethylhexyl methacrylate, 156 g of hydroxyethyl methacrylate, 4 g of methacrylic acid, and 32 g of azobisisobutyronitrile was dropped into the dropping funnel over 3 hours. After continuing the reaction for another hour, a mixed solution of 50 g of propylene glycol monomethyl ether acetate and 3.2 g of azobisisobutyronitrile was added dropwise over 30 minutes, and the reaction was continued for another hour.

Synthesis Example 2 Synthesis of Compound B-2 A 1 L separable flask equipped with a temperature controller, a stirring blade, a reflux tube, and a nitrogen inlet was charged with 200 g of xylene and 150 g of butyl acetate, and the temperature was raised to 90 ° C. Kept. On the other hand, a mixed liquid of 100 g of styrene, 136 g of 2-ethylhexyl methacrylate, 160 g of hydroxyethyl methacrylate, 4 g of methacrylic acid, and 16 g of azobisisobutyronitrile was added dropwise to the dropping funnel over 3 hours. After the reaction was continued for another hour, a mixed solution of 50 g of butyl acetate and 1.6 g of azobisisobutyronitrile was added dropwise over 30 minutes, and the reaction was further continued for 1 hour.

Synthesis Example 3 Synthesis of Compound B-3 A 1 L separable flask equipped with a temperature controller, a stirring blade, a reflux tube and a nitrogen inlet was charged with 200 g of xylene and 150 g of propylene glycol monomethyl ether acetate, and the temperature was raised to 130 ° C. , Kept constant. On the other hand, a mixed solution of 100 g of styrene, 116 g of 2-ethylhexyl acrylate, 180 g of hydroxyethyl methacrylate, 4 g of methacrylic acid, and 30 g of azobisisobutyronitrile was put into a dropping funnel and dropped over 3 hours. After continuing the reaction for another hour, a mixed solution of 50 g of propylene glycol monomethyl ether acetate and 3.2 g of azobisisobutyronitrile was added dropwise over 30 minutes, and the reaction was continued for another hour.

Synthesis Example 4 Synthesis of Compound B-4 A 1 L separable flask equipped with a temperature controller, a stirring blade, a reflux tube, and a nitrogen inlet was charged with 200 g of xylene and 150 g of butyl acetate, and the temperature was raised to 110 ° C. to be constant. Kept. On the other hand, a mixed solution of 240 g of cyclohexyl methacrylate, 60 g of 2-ethylhexyl methacrylate, 100 g of hydroxyethyl acrylate, and 16 g of t-butylperoxy-2-ethylhexanoate was put in a dropping funnel and dropped over 3 hours. After continuing the reaction for another hour, a mixed solution of 50 g of butyl acetate and 1.6 g of t-butylperoxy-2-ethylhexanoate was added dropwise over 30 minutes, and the reaction was continued for another hour.

Table 1 below summarizes the special values of Compound B. Each numerical value was measured by the following method.
(1) Calculation of SP value The SP value can be measured by cloud point titration. W. SUH, J. et al. M.M. It is a value calculated by the following equation described in the CORBETT equation (Journal of Applied Polymer Science, 12, 2359, 1968).

(Where V _H is the volume fraction of n-hexane, V _D is the volume fraction of deionized water, δ _H is the SP value of n-hexane, and δ _D is the SP value of deionized water)
In the cloud point titration, 0.5 g of the dried resin composition (solid content) was dissolved in 10 ml of acetone, n-hexane was gradually added, and the titration amount H (ml) at the cloud point was read and the acetone solution was similarly obtained. The titration amount D (ml) at the turbidity point with deionized water added thereto is read and applied to the following formula to calculate V _H , V _D , δ _H and δ _D. In addition, SP value of each solvent is acetone: 9.75, n-hexane: 7.24, deionized water: 23.43.
V _H = H / (10 + H)
V _D = D / (10 + D)
δ _H = 9.75 × 10 / (10 + H) + 7.24 × H / (10 + H)
δ _D = 9.75 × 10 / (10 + D) + 23.43 × D / (10 + D)

(2) After removing the solvent of acrylic polyol obtained by glass transition polymerization by distillation under reduced pressure, the following steps were carried out with a differential scanning calorimeter (DSC) [thermal analyzer SSC / 5200H (manufactured by Seiko Denshi)]. It is the value actually measured. 1 step: 20 ° C. → 100 ° C. (temperature increase rate 10 ° C./min)
2 steps: 100 ° C. → −50 ° C. (temperature decrease rate 10 ° C./min)
3 steps: −50 ° C. → 100 ° C. (temperature increase rate 10 ° C./min)
The glass transition point was determined from the time of temperature increase in 3 steps.

(3) Calculated from the monomer composition during hydroxyl equivalent synthesis.

(4) Number average molecular weight Number average molecular weight in terms of polystyrene measured by GPC (gel permeation chromatography)

As compound A-1, polycarbonate diol T-5650 (hydroxyl equivalent 400) manufactured by Asahi Kasei Chemicals Corporation was used. As compound A-2, polycarbonate diol T-5651 manufactured by Asahi Kasei Chemicals Corporation was used. The hydroxyl equivalent of compound A-2 is 500. As compound A-3, polycarbonate boat diol T4672 manufactured by Asahi Kasei Chemicals Corporation was used. The hydroxyl equivalent of compound A-3 is 1000.

Synthesis Example 5 Synthesis of compound C-1 In a 1 L separable flask equipped with a temperature controller, a stirring blade, a reflux tube, and a nitrogen inlet, 36.8 g of trimethylolpropane, 563.2 g of ε-caprolactone, dibutyltin laurate 3 g was charged and the reaction was continued at 160 ° C. for 6 hours. The number of branches of the obtained resin was 3, and the hydroxyl equivalent was 730.

Synthesis Examples 6 to 11 Synthesis of Compounds C-2 to 7 Reactions were performed in the same manner as in Synthesis Example 5 using the raw materials shown in Table 2. Table 2 shows the number of branches and the OH equivalent of the obtained compound.

Example 1
In the proportions shown in Table 3, A-1, B-1, C-1, BYK310 0.6 g manufactured by Big Chemie Japan, Tinuvin 292 1.0 g manufactured by Ciba Specialty Chemicals, and Tinuvin 384 manufactured by Ciba Specialty Chemicals 2 2.1 g and 0.01 g of dibutyltin dilaurate were mixed, and butyl acetate was added to adjust the solid content rate to 30%. A clear coating composition was prepared by adding Sumidur N3300 manufactured by Sumika Bayer Urethane Co., Ltd. such that the molar ratio of hydroxyl group / isocyanate group was 1.0 / 1.2. In the table, Compound A-1, Compound B-1, and Compound C-1 each indicated a solid content ratio.

Examples 2-8, Comparative Examples 1-11
Each clear coating composition was prepared in the same manner as in Example 1 except that the resin solution was replaced as shown in Tables 3 and 4.

<Production example of multi-layer coating film test piece-painting on plastic material->
A method for producing a multilayer coating film test piece will be described. It was produced in a coating environment with a temperature of 20 ± 5 ° C. and a relative humidity of 78% or less.
With respect to 100 parts of each clear coating composition, it was diluted with a mixed solvent of ethyl acetate / 3-ethoxypropionate = 7/3 so that the viscosity of # 4 Ford cup was 15 to 20 seconds. Spray gun (“W-101-134G” manufactured by Anest Iwata Co., Ltd.) is used as a primer on polypropylene material (70 mm × 150 mm × 3 mm: JNB-117 manufactured by Topra Sangyo Co., Ltd.) as a primer. ) To a dry film thickness of 7 μm, left in the coating environment for 1 minute, and then “R-303N Black” manufactured by Nihon Bee Chemical Co., Ltd. as a base paint using the above spray gun. After coating so that the dried coating film becomes 15 μm, the film is left for 1 minute in the coating environment and immediately diluted with the above clear coating composition, and the dry film thickness is 30 μm with the spray gun. After leaving it to stand for 10 minutes in a coating environment, it is dried and cured in a 120 ° C temperature atmosphere for 20 minutes using a dryer. To obtain a coating material (multilayer coating film test piece).

The evaluation method in the Example of this invention is demonstrated. The evaluation results are shown in Tables 3 and 4.
Both the adhesion evaluation and the scratch recovery evaluation were performed in a test environment having a temperature of 20 ± 5 ° C. and a relative humidity of 73 ± 5%.
<Weather resistance evaluation method>
Using a xenon weather meter according to JIS K5600-7-7, each test piece was exposed for 775 hours, and then the state of the coating film was visually determined.
○: No water stain trace Δ: Slight trace of water stain observed X: Significant water stain trace observed

<Adhesion evaluation method>
A single blade cutting tool defined in JIS K5600-5-6 was vertically applied on the coating surface of the test piece, and 11 cutting lines reaching the substrate were drawn in parallel. Draw 11 parallel lines perpendicularly intersecting the parallel lines and make 100 square squares surrounded by 4 straight lines. The interval between the parallel lines was 2 mm. A transparent pressure-sensitive adhesive tape specified in JIS K5600-5-6 is closely attached to the grid area so as not to contain air bubbles between the coated surfaces, and the tape is applied at once in 0.5 to 1.0 seconds. It peeled off and the residual film peeling state of the grid part was evaluated visually.
○: No peeling at all Δ: Slight peeling can be observed along the grid-like cuts ×: The area of the peeling part exceeds 15% of the grid part

<Scratch recovery evaluation method>
On the coated surface of the test piece, a 4-line brass brush made by Industry Kowa was scratched in parallel with the handle at a load of 500 g, a stroke speed of 30 cm / second, and a stroke width of 15 cm. . After the scratch, the test piece was immersed in hot water at 80 ° C. for 2 seconds, and the degree of recovery of the scratch on the coated surface was visually evaluated.
○: All scratches recovered ×: Unrecovered scratches were observed. Also, leave the test piece with scratches under the same conditions as above in the test environment, and visually check the degree of recovery of the scratches. Evaluated.
◎: All wounds recovered within 5 minutes ○: All wounds recovered within 1 hour Δ: All wounds recovered within 24 hours ×: Unrecovered scratches observed after 24 hours thing

<Compatibility evaluation method>
50 g of a resin solution prepared by mixing (A) to (C) with a predetermined composition is put into a 100 ml glass bottle and stored at 40 ° C. for 30 days. After that, the resin solution that was transparent and matched was marked with ◯, and that with separation or turbidity confirmed was marked with ×. In the evaluation of the experiment, a resin solution in which only the components (A) to (C) were mixed at the ratios shown in Tables 3 and 4 was prepared, and the compatibility of the solution was evaluated. The results are shown in Tables 3 and 4.

It was shown that the coating film obtained by the clear coating composition of the present invention has sufficient water resistance and weather resistance and is excellent in scratch recovery. On the other hand, the coating film obtained with the clear coating composition of the comparative example was inferior in any of these performances.

The clear coating composition of the present invention does not cause deterioration of substances originally required in clear coatings such as sufficient water resistance and weather resistance, and has excellent scratch recovery, so that it can be used as a top coating for automobiles. It can be used suitably.

Claims (6)

A clear paint composition comprising a polycarbonate diol compound (A), a hydroxyl group-containing acrylic resin (B), a polycaprolactone polyol (C) having 3 to 5 branches and a hydroxyl group equivalent of 170 to 1600, and a curing agent (D). object. The clear coating composition according to claim 1, wherein the polycarbonate-based diol compound (A) has a hydroxyl group equivalent of 320 to 2,000. The clear coating composition according to claim 1 or 2, wherein the hydroxyl group-containing acrylic resin (B) has a hydroxyl group equivalent of 200 to 600 and the number of hydroxyl groups in one molecule is 4.0 to 30. The clear coating composition according to claim 1, 2 or 3, wherein the hydroxyl group-containing acrylic resin (B) has a glass transition temperature of -20 to 60 ° C. The compounding ratio ((A) / (B) + (C)) of the polycarbonate diol compound (A), the hydroxyl group-containing acrylic resin (B) and the polycaprolactone polyol (C) is 90/10 to 10/90 (solid content The clear coating composition according to claim 1, 2, 3 or 4. The compounding ratio of the hydroxyl group-containing acrylic resin (B) and the polycaprolactone polyol (C) is (B) / (C) = 10/90 to 90/10 (solid content mass ratio). 4. The clear coating composition according to 4 or 5.