JP2010106203A - Coating composition, coating finishing method, and coated article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a clear coating composition for obtaining a coating film excellently resistant to scratches, to weather, and in particular, to water stain, and to provide a coated article. <P>SOLUTION: The clear coating composition comprises an acrylic resin and an isocyanate compound. In the molecule of the acrylic resin, structural units (A) based on ε-caprolactone and structural units (B) based on a radical-polymerizable monomer having a ring structure are contained, and a content percentage of the structural units (A) is 15 mass% or more, while a mass ratio (A)/(B) of the structural units (A) to the structural units (B) ranges from 1/1 to 1/0.5. In a cured coating film obtained from the clear coating composition, a breaking elongation rate at 20°C is 20-40%, and molecular weight between cross-link points is 300-400 g/mol. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a coating composition used in a field where a coating film excellent in scratch resistance and weather resistance and particularly excellent in water resistance is required, and a coated article thereof.

In the automotive coating field, clear coatings in particular are required to have weather resistance, acid rain resistance, and car wash scratch resistance. In recent years, there has been a demand for preventing and suppressing the generation of scratches caused by car wash machines and having excellent water resistance in natural exposure.

As a coating composition for obtaining a coating film excellent in car wash machine scratch resistance, mud stain resistance, and weather resistance, (A) a component unit of ε-caprolactone is contained in the resin solid content in an amount of 35 to 50% by mass, and the hydroxyl value Is a coating composition containing an acrylic copolymer having a weight average molecular weight of 5,000 to 15,000 and (B) a non-yellowing polyisocyanate compound, wherein component (A) The isocyanate group of the component (B) is contained at a ratio of 0.5 to 2 equivalents with respect to 1 equivalent of the hydroxyl group, and the Young's modulus of the cured coating film obtained from the coating composition is 1.5 Pa or less, the molecular weight between crosslinks ( A clear coating composition having a Mc) of 350 g / mol or less and a glass transition temperature (Tg) of a cured coating film of 65 ° C. or more is known (for example, see Patent Document 1). However, this coating composition has a problem that the acid rain resistance is inferior because it contains a large amount of ε-caprolactone constituent units in the resin solids.

Moreover, as a coating composition from which a coating film excellent in scratch resistance, acid resistance, durability, and stain resistance is obtained, the base resin has a hydroxyl value of (A) 50 to 400 mgKOH / g and is based on a lactone compound. A hydroxyl group-containing lactone-modified resin containing 20 to 70% by mass of a structural unit, and (B) 10 to 80% of a structural unit based on a radical polymerizable monomer having a hydroxyl value of 50 to 150 mgKOH / g and having a ring structure. % Of a hydroxyl group and a ring structure-containing acrylic resin, and the crosslinking resin is an isocyanate compound, the resin solid content mass ratio of (A) / (B) is 95 / 5-5 A 20/80 thermosetting coating composition is known (see, for example, Patent Document 2).

However, this coating composition can have excellent scratch resistance and acid rain resistance, but in pursuing higher cost and lower productivity and higher quality by producing two different resins, The difficulty in design due to the failure of combination has been a problem.

In addition, as a coating composition from which scratch resistance, acid resistance, stain resistance, finish and an excellent coating film can be obtained, a specific ratio of (a) alicyclic hydrocarbon group-containing polymerizability having 3 to 20 carbon atoms. An unsaturated monomer, (b) styrene, (c) a hydroxyl group-containing polymerizable unsaturated monomer, (d) a hydrocarbon group-containing polymerizable unsaturated monomer having a branched structure having 8 to 22 carbon atoms, and (E) The weight average molecular weight obtained by copolymerizing a monomer mixture comprising other polymerizable unsaturated monomers is 1,500 to 30,000, and the hydroxyl value thereof is 120 to 180 mgKOH / g. A coating composition containing a hydroxyl group-containing resin for coating, and the coating resin (A) and a specific aliphatic polyisocyanate compound (B) is known (for example, Patent Documents). 3). However, this coating composition is insufficient in versatility because it uses a specific aliphatic polyisocyanate compound.

In addition, as a coating composition having high scratch resistance, an acrylic resin (A) containing a short side chain hydroxy group (a1) and a long side chain hydroxy group (a2) and a polyisocyanate prepolymer (C) are essential. If necessary, the polylactone polyol (B) is also included, the content ratio of the short side chain hydroxy group (a1) and the long side chain hydroxy group (a2), the short side chain hydroxy group (a1) and the long side chain hydroxy group A coating composition characterized in that the total hydroxyl number of (a2), the solid content ratio of the acrylic resin (A) and the polylactone polyol (B), and the blending amount of the polyisocyanate prepolymer (C) are in specific ranges, respectively. It is known (for example, refer to Patent Document 4). However, since this coating composition does not contain a structural unit based on a radically polymerizable monomer having a ring structure, there is a problem that water resistance is poor.

JP 2007-023069 A JP 2006-348172 A Republished WO2006 / 028130 JP 2007-31690 A

An object of the present invention is to provide a clear coating composition and a coated article thereof that can provide a coating film having good scratch resistance and weather resistance, and particularly excellent in water resistance.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that a structural unit (A) based on a specific amount of ε-caprolactone and a structural unit based on a radical polymerizable monomer having a ring structure in the resin molecule. Using a clear coating composition containing an acrylic resin and an isocyanate compound in a specific mass ratio range, and the elongation at break at 20 ° C. of a cured coating film obtained from the clear coating composition is 20 to 40%. The inventors have found that the purpose can be achieved by setting the molecular weight between crosslinks in the range of 300 to 400 g / mol, and the present invention has been completed based on these findings.

That is, the present invention has a structural unit (A) based on ε-caprolactone and a structural unit (B) based on a radical polymerizable monomer having a ring structure in the resin molecule. The content ratio of the structural unit (A) based is 15% by mass or more, and is the mass ratio of the structural unit (A) based on ε-caprolactone to the structural unit (B) based on the radical polymerizable monomer having a ring structure. A clear coating composition containing an acrylic resin and an isocyanate compound in which (A) / (B) is in a range of 1/1 to 1 / 0.5, and a cured coating film obtained from the clear coating composition A clear coating composition having a breaking elongation at 20 ° C. of 20 to 40% and a molecular weight between crosslinks in the range of 300 to 400 g / mol is provided.

Further, the present invention provides the coating composition, wherein the radical polymerizable monomer having a ring structure is at least one selected from styrene, cyclohexyl acrylate, cyclohexyl methacrylate, tert-butylcyclohexyl acrylate, and tert-butylcyclohexyl methacrylate. A coating composition that is a monomer is provided.
Furthermore, this invention provides the coating finishing method characterized by apply | coating said coating composition as a top coating material, and the coated article obtained by the coating finishing method.

The clear coating composition of the present invention has good scratch resistance and weather resistance, and can provide a coating film particularly excellent in water stain resistance.

The acrylic resin used in the present invention has a structural unit (A) based on ε-caprolactone in the resin molecule. Examples of the structural unit (A) include a structural unit based on ε-caprolactone ring-added to a hydroxyl group-containing radical polymerizable monomer. The structural unit (A) based on ε-caprolactone usually has a hydroxyl group at the tip of ε-caprolactone after ring opening addition.

The structural unit (A) based on ε-caprolactone does not indicate the entire structural unit of the radical polymerizable monomer to which ε-caprolactone has been subjected to ring-opening addition, but represents only ε-caprolactone that has undergone ring-opening addition. is there.
Specific examples of the structural unit (A) include structural units based on ε-caprolactone ring-opened and added to the following hydroxyl group-containing radical polymerizable monomer.

As the hydroxyl group-containing radical polymerizable monomer, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, polyethylene glycol mono (Meth) acrylate, polypropylene glycol mono (meth) acrylate, neopentyl glycol mono (meth) acrylate, glycerin mono (meth) acrylate and the like. A hydroxyl-containing radically polymerizable monomer may be used individually by 1 type, and may be used in combination of 2 or more type.
The structural unit (A) based on ε-caprolactone is a caprolactone modified by ring-opening addition of ε-caprolactone such as a caprolactone-modified radical polymerizable monomer obtained by ring-opening addition of ε-caprolactone to the hydroxyl group-containing radical polymerizable monomer. By copolymerizing a radically polymerizable monomer, it can be contained as a structural unit in the acrylic resin molecule.

As a commercial product of a caprolactone-modified radical polymerizable monomer obtained by ring-opening addition of ε-caprolactone, a commercially available radical polymerizable monomer obtained by ring-opening addition of ε-caprolactone to a hydroxyl group-containing (meth) acrylic acid ester. Goods. Specific examples of this commercially available product include Plaxel FA-1 (trade name, manufactured by Daicel Chemical Industries, Ltd., a monomer obtained by ring-opening addition of 1 mol of ε-caprolactone to 1 mol of 2-hydroxyethyl acrylate), Plaxel FM -1D, Plaxel FM-2D, Plaxel FM-3, Plaxel FM-4 (all trade names, manufactured by Daicel Chemical Industries, Ltd., 1 mol, 2 mol of ε-caprolactone in 1 mol of 2-hydroxyethyl methacrylate, And a monomer obtained by ring-opening addition of 3 mol and 4 mol, respectively. These may be used individually by 1 type and may be used in combination of 2 or more type.

The structural unit (A) based on ε-caprolactone is contained in an acrylic resin molecule in an amount of 15% by mass or more. When the content of the structural unit (A) based on ε-caprolactone is less than 15% by mass, the elongation percentage of the coating film is small and the scratch resistance is poor. The content of the structural unit (A) based on ε-caprolactone is more preferably 15 to 30% by mass in the acrylic resin molecule. When it exceeds 30 mass%, it is inferior to acid rain resistance. The content of the structural unit (A) based on ε-caprolactone is particularly preferably 18 to 27% by mass in the acrylic resin molecule.

The acrylic resin used in the present invention has a structural unit (B) based on a radical polymerizable monomer having a ring structure in the resin molecule.
The structural unit (B) can be contained as a structural unit in the acrylic resin molecule by copolymerizing a radical polymerizable monomer having a ring structure.

Preferred examples of the radically polymerizable monomer having a ring structure include styrene, cyclohexyl acrylate, cyclohexyl methacrylate, tert-butylcyclohexyl acrylate and tert-butylcyclohexyl methacrylate, and these may be used alone or in combination of two kinds. A combination of the above may also be used. Particularly preferred are styrene, cyclohexyl acrylate and cyclohexyl methacrylate.

The acrylic resin used in the present invention is a mass ratio of the structural unit (A) based on ε-caprolactone to the structural unit (B) based on the radical polymerizable monomer having a ring structure (A) / (B). Is in the range of 1/1 to 1 / 0.5. When the mass ratio of (A) / (B) in the acrylic resin is larger than 1 / 0.5, that is, when the number of structural units (B) based on the radically polymerizable monomer having a ring structure is small, water stain resistance Inferior to acid rain resistance. When the mass ratio of (A) / (B) in the acrylic resin is smaller than 1/1, that is, when there are many structural units (B) based on a radical polymerizable monomer having a ring structure, the elongation percentage of the coating film Is small and inferior in scratch resistance.

The acrylic resin used in the present invention may have structural units based on other radical polymerizable monomers in the resin molecule.
The content of the structural unit based on the other radical polymerizable monomer is preferably 40 to 77.5% by mass in the resin molecule, more preferably 45 to 75% by mass, and still more preferably 50 to 70% by mass.
Examples of the other radical polymerizable monomer include a hydroxyl group-containing radical polymerizable monomer to which ε-caprolactone is not subjected to ring-opening addition, other vinyl monomers that can be copolymerized, and the like.

Examples of the hydroxyl group-containing radical polymerizable monomer to which ε-caprolactone is not subjected to ring-opening addition are the same as those described above for the hydroxyl group-containing radical polymerizable monomer. A hydroxyl-containing radically polymerizable monomer may be used individually by 1 type, and may be used in combination of 2 or more type.
The content ratio of the structural unit based on the hydroxyl group-containing radical polymerizable monomer to which ε-caprolactone is not subjected to ring-opening addition is preferably 1 to 15% by mass, more preferably 2 to 10% by mass, in the resin molecule. More preferred is mass%.

Examples of other copolymerizable vinyl monomers include (meth) acrylic acid and alkyl substituted products thereof; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) ) Acrylates, alkyl (meth) acrylates such as lauryl (meth) acrylate, stearyl (meth) acrylate; esters of dibasic acids such as itaconic acid, maleic acid, fumaric acid; (meth) acrylonitrile, (meth) acrylamide, vinyl acetate , And vinyl chloride. Of these, (meth) acrylic acid and alkyl-substituted products thereof, and alkyl (meth) acrylate are preferable. Other vinyl monomers that can be copolymerized may be used singly or in combination of two or more.

  The content ratio of the structural unit based on (meth) acrylic acid and its alkyl-substituted product is preferably 0.1 to 3% by mass, more preferably 0.2 to 2.5% by mass, and 0.3 to 2% in the resin molecule. More preferred is mass%. Moreover, 5-50 mass% is preferable in a resin molecule, as for the content rate of the structural unit based on an alkyl (meth) acrylate, 10-40 mass% is more preferable, and 12-35 mass% is further more preferable.

  The acrylic resin used in the present invention includes (1) a caprolactone-modified radical polymerizable monomer obtained by ring-opening addition of ε-caprolactone to a hydroxyl group-containing radical polymerizable monomer, and a radical having a ring structure. A method of copolymerizing a polymerizable monomer and, if necessary, another vinyl monomer; and (2) a hydroxyl group-containing radical polymerizable monomer and a radical polymerizable monomer having a ring structure, In addition, a method of ring-opening addition of ε-caprolactone during or after the copolymerization reaction when other vinyl monomers are copolymerized as necessary may be mentioned. In the above method, it is not necessary for all the hydroxyl groups of the hydroxyl group-containing radical polymerizable monomer to undergo ring-opening addition of ε-caprolactone. For example, in the method (1), ε-caprolactone is not subjected to ring-opening addition. A hydroxyl group-containing radical polymerizable monomer may be copolymerized, and in the method (2), there is a structural unit based on a hydroxyl group-containing radical polymerizable monomer to which ε-caprolactone is not subjected to ring-opening addition. You may let them.

When manufacturing an acrylic resin, a polymerization initiator is usually used. Examples of the polymerization initiator include organic peroxide polymerization initiators and azo polymerization initiators. Although the usage-amount of a polymerization initiator does not have a restriction | limiting in particular, 0.5-15 mass% is preferable with respect to the total amount of a monomer normally.
Suitable examples of organic solvents used in the production of the acrylic resin used in the present invention include alicyclic hydrocarbons such as cyclohexane and ethylcyclohexane, and aromatic carbonization such as toluene, xylene, ethylbenzene and aromatic naphtha. Ketone solvents such as hydrogen solvents, acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, cyclohexanone, isophorone, ethyl acetate, n-butyl acetate, isobutyl acetate, 3-methoxybutyl acetate, bis (2-ethylhexyl) adipate Such as ester solvents such as dibutyl ether, tetrahydrofuran, 1,4-dioxane, 1,3,5-trioxane, acetonitrile, valeronitrile, N, N-dimethylformamide, N, N-diethylformamide, etc. Nitrogen-containing system Agents. The organic solvent may be one kind alone or may be two or more kinds of mixed solvents. At this time, the solid content concentration of the hydroxyl group-containing resin can be arbitrarily selected within a range not impairing the dispersion stability of the resin, but is usually 10 to 70% by mass in terms of solid content concentration.

  As the isocyanate compound used in the clear coating composition of the present invention, aliphatic and alicyclic polyisocyanate compounds are preferably used. Typical examples include a reaction product of hexamethylene diisocyanate and / or isophorone diisocyanate with a polyhydric alcohol and / or a low molecular weight polyester polyol, an isocyanurate body which is a polymer of hexamethylene diisocyanate and / or isophorone diisocyanate, Examples include a burette body obtained by further reacting with a urethane bond.

In addition, blocked isocyanates in which the isocyanate groups in these polymers are masked with a compound having a hydroxyl group are also preferably used. Various non-yellowing polyisocyanate compounds such as polymers of diisocyanate compounds other than the above can also be used. An isocyanate compound may be used individually by 1 type, and may be used in combination of 2 or more type.

In the present invention, the content ratio of the acrylic copolymer and the isocyanate compound is 0.2 to 2 equivalents of the isocyanate group of the isocyanate compound component, preferably 0.5 to 1 with respect to 1 equivalent of the hydroxyl group of the acrylic copolymer. .5 equivalents, particularly preferably 0.6 to 1.2 equivalents. If the isocyanate group of the isocyanate compound is less than 0.5 equivalent to 1 equivalent of the hydroxyl group of the acrylic copolymer, the curability is insufficient, and if it exceeds 2 equivalent, the scratch resistance is lowered.

The clear coating composition of the present invention contains the above components or, if necessary, an organic solvent, various additives such as an ultraviolet absorber, a light stabilizer, an antioxidant, a surfactant, a surface conditioner, A curing reaction catalyst, an antistatic agent, a fragrance, a dehydrating agent, a rheology adjusting agent such as polyethylene wax, polyamide wax, and internally crosslinked resin fine particles can be added and used.

In the clear coating composition of the present invention, the elongation at break at 20 ° C. of the cured coating film obtained from the clear coating composition is 20 to 40%, preferably 20 to 35%, particularly preferably 20 to 30%. The said component is adjusted so that it may become the range whose molecular weight between bridge | crosslinking is 300-400 g / mol, Preferably it is 330-380 g / mol. When the elongation at break of the cured coating film is less than 20%, the scratch resistance is poor. Moreover, when the breaking elongation rate of a cured coating film exceeds 40%, it is inferior to a weather resistance and a water-stain resistance. When the molecular weight between crosslinks of the cured coating is less than 300, the scratch resistance is poor, and when the molecular weight between crosslinks of the cured coating exceeds 400, the weather resistance and acid rain resistance are poor.

The measuring method of the elongation at break in the present invention is that the isolated coating film is sampled at 20 ° C. per minute with a tensile tester (trade name “Tensilon / UTM-III-200” manufactured by Toyo Baldwin Co., Ltd.). The test was conducted at a tensile rate of 10% of the length, and the elongation when the coating film was broken was calculated.
The molecular weight between crosslinks (Mc) of the cured coating film in the present invention is determined using a forced stretching vibration type viscoelasticity measuring apparatus (trade name “Leo Vibron DDV-II-EA” manufactured by Toyo Baldwin Co., Ltd.). , A value obtained from the dynamic rigidity in the rubber region measured at a frequency of 110 Hertz and a temperature increase rate of 2 ° C./min, and is represented by the following equation.

Mc = 293 × ρ / (log ₁₀ G′−7)
Here, Mc is the molecular weight (g / mol) between crosslinks, ρ is the coating film density (g / cm ³ ), and G ′ is the dynamic rigidity (E ′ / 3 (10 ⁻⁹ N) in the rubber region. / M ² )) and E ′ is the dynamic modulus of elasticity in the rubber region (10 ⁻⁹ N / m ² ).

The coating finishing method of the present invention is a coating finishing method characterized in that the clear coating composition of the present invention is applied as a top coating.
Specific examples of the paint finishing method of the present invention include, for example, a two-coat one-bake paint finishing method in which a colored base coat paint is applied onto a substrate and the clear paint composition is applied as a clear paint in an uncrosslinked state, or Examples include an overcoat coating finishing method in which a colored base coat paint is applied on a substrate, a clear paint is applied in an uncrosslinked state, and baked at the same time, and then the clear paint composition is applied and baked as an overcoat clear paint. Further, in the above overcoat paint finishing method, in order to ensure adhesion with the undercoat clear coat film, a transparent primer paint is applied, and the clear paint composition is applied as an overcoat clear paint in an uncrosslinked state. A method etc. can also be mentioned.

Examples of the base material on which the clear coating composition of the present invention is applied include organic materials and inorganic materials such as wood, glass, metal, cloth, plastic, foam, elastic body, paper, ceramic, concrete, and gypsum board. . These base materials may have been surface-treated in advance, or may have a coating film formed on the surface in advance.
Examples of the surface treatment include chemical conversion treatment such as zinc phosphate treatment. The coating film formed on the surface in advance is a coating film obtained by applying a cationic electrodeposition coating, a coating obtained by applying an intermediate coating, or a coating obtained by applying a cationic electrodeposition coating. On top of this, a coating film obtained by applying an intermediate coating is mentioned.

The cationic electrodeposition coating and intermediate coating used in the present invention are not particularly limited, and known water-based or solvent-based coatings can be used.
The colored base coat paint used in the present invention is not particularly limited, and a known water-based or solvent-based paint can be used.
As the resin component of the colored base coat paint used in the present invention, a base resin and a curing agent can be contained. The base resin is not particularly limited, and known water-based or solvent-based resin components can be used. For example, specific examples of the base resin of the resin component include resins such as urethane resin, polyester resin, and alkyd resin. These may be used alone or in combination of two or more.

Examples of the curing agent include melamine resins and blocked isocyanate compounds. These may be used alone or in combination of two or more.
The colored base coat paint contains at least one of various pigments such as inorganic pigments, organic pigments, aluminum pigments, pearl pigments and extender pigments. In addition, the colored base coat paint includes various additives such as surface conditioners, antifoaming agents, surfactants, film-forming aids, preservatives, ultraviolet absorbers, light stabilizers, antioxidants, various rheology control agents, You may contain 1 or more types, such as various organic solvents.

The dry film thickness of the colored base coat film is preferably 8 to 25 μm, more preferably 10 to 20 μm.
The colored base coat paint, clear paint, overcoat clear paint, and transparent primer paint are heated as necessary, adjusted to a desired viscosity by adding an organic solvent or a reactive diluent, and then air sprayed. The coating is performed using a commonly used coating machine such as an electrostatic air spray, a roll coater, a flow coater, a dipping type coating machine, or a brush, a bar coater, an applicator, or the like. Of these, spray coating is preferred.

The thickness of the coating film obtained by applying the clear coating composition of the present invention is not particularly limited, but usually the film thickness after drying is preferably 10 to 150 μm, more preferably 10 to 100 μm.
The baking temperature of the clear coat film layer may be appropriately selected in the range of usually 120 to 180 ° C., and the baking time may be appropriately selected in the range of usually 10 to 60 minutes.
The colored base coating layer may be baked under the same conditions as the clear coating layer, but usually it is not baked and cured, and often baked simultaneously with the clear coating layer by wet-on-wet.
Specific examples have been shown above, but the method for finishing the clear coating composition of the present invention is not limited by these.

Examples of the coated article obtained by applying the clear coating composition of the present invention include structures, wooden products, metal products, plastic products, rubber products, processed paper, ceramic products, and glass products. More specifically, automobiles, automotive parts (for example, parts such as bodies, bumpers, spoilers, mirrors, wheels, interior materials, etc., of various materials), metal plates such as steel plates, motorcycle parts, motorcycle parts , Road materials (eg guardrails, traffic signs, noise barriers, etc.), tunnel materials (eg side walls, etc.), ships, railway vehicles, aircraft, furniture, musical instruments, household appliances, building materials, containers, office supplies, Examples include sports equipment and toys.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The performance of the coating film obtained from the coating composition of the present invention was evaluated as follows. The elongation at break and the molecular weight between crosslinks were measured by the methods described in paragraph [0032] of the present specification.
(1) Scratch resistance The lightness of the surface of the clear film of the paint film test piece was measured with a variable angle color difference meter (manufactured by Suga Test Instruments Co., Ltd.) to determine L0. The lightness was measured with light incident perpendicular to the clear film measurement surface and the light receiving angle of the reflected light deviated from the light incident by 10 degrees. Use a pipette to drop 0.5 cc of test dust water (20% aqueous solution specified in JIS Z8901) on the clear film side of each test piece, and then apply the dust water to the entire clear film surface of the test piece using a brush. Spread (dust water application). Then, each test piece after applying dust water is placed on a horizontal base of a mini car wash machine (BASF Coatings Japan Co., Ltd.) with the clear film facing up, and water is put into the mini car wash machine at 4 liters / minute. The surface of each test piece (the surface of the clear coating film) was washed by running the mini car wash machine for 10 seconds with the rotation speed of the mini car wash machine set to 150 rpm. The test dust water application and the washing with the mini car wash machine were performed as one cycle, and after 5 cycles, the surface of the test piece was lightly wiped with absorbent cotton containing isopropyl alcohol. Then, the lightness (L1) of the clear film surface was measured with the same color difference meter used for L0 measurement after being left for 1 hour, and the lightness color difference from L0 before the test (
ΔL1 = L0−L1) was determined and evaluated according to the following criteria.
○: ΔL1 = 5 or less ×: ΔL1 = 6 or more

(2) Weather resistance (water stain resistance)
A test plate was attached to a black box exposure stand (south direction, angle 30 °) installed in Okinawa, and the appearance and water stain generation of the coating after one year of exposure were observed and evaluated according to the following criteria.
○: There is no water blot in the coating film.
X: Water-stain generation is remarkable in the coating film.

(3) Acid rain resistance 2 ml of 40% by mass sulfuric acid was spotted on the test plate, and after standing at 60 ° C. for 30 minutes, the abnormality of the coating film was visually determined.
○: There is no abnormality in the coating film △: There is a decrease in gloss x;

(Production Examples 1-10)
<Manufacture of acrylic copolymer resin A-1-10>
A four-necked flask equipped with a thermometer, a stirrer, a reflux condenser, and a dropping funnel was charged with the amount of xylene / methyl amyl ketone = 18 parts / 7 parts of the reaction solvent described in Tables 1 and 2 at 140 ° C. The temperature rose. Subsequently, a mixture of the monomer and the polymerization initiator described as the dropping component was dropped from the dropping funnel over 2 hours. After completion of dropping, the content was cooled to 100 ° C. while maintaining the reflux temperature for 1 hour. After cooling to 100 ° C., additional catalyst was added dropwise. Thereafter, when the temperature was maintained at 100 ° C. for 3 hours, the polymerization reaction was terminated, and a thinning solvent was added to obtain a solution of Resin A-1 to 10.
In the table, “Placcel FM-1” is a monomer in which 1 mol of ε-caprolactam is added to the hydroxyl group of hydroxyethyl methacrylate, and “Placcel FM-2” is ε-caprolactam to the hydroxyl group of hydroxyethyl methacrylate. Two moles are added monomers, both of which are commercially available from Daicel Chemical Industries.

(Production Examples 11 to 20)
<Manufacture of clear paint CC-1 to 10>
The raw materials listed in Table 3 were sequentially mixed and stirred uniformly to prepare clear paints CC-1 to 10.

≪Table notes≫
1) Desmodur N3300: trade name, manufactured by Sumika Bayer Urethane Co., Ltd., isocyanurate type resin of liquid hexamethylene diisocyanate (nonvolatile content: 100% by mass, NCO content: 21.8% by mass)
2) Tinuvin 900: trade name, manufactured by Ciba Specialty Chemicals Co., Ltd., UV absorber solution, 20 mass% xylene solution 3) Tinuvin 292: trade name, manufactured by Ciba Specialty Chemicals Co., Ltd., light stabilizer solution, 20 mass% xylene solution 4) BYK-300: trade name, manufactured by Big Chemie, surface conditioner solution, 10% by mass xylene solution 5) Solvesso 100: trade name, manufactured by Esso, aromatic petroleum naphtha

(Examples 1-4)
Preparation of test piece and examination of coating film performance Cathode No. of cationic electrodeposition paint on mild steel sheet treated with zinc phosphate. 300 (trade name, manufactured by BASF Coatings Japan Co., Ltd.) was electrodeposited to a dry film thickness of 20 μm, baked at 175 ° C. for 25 minutes, and then an intermediate coating paint Aqua GX sealer (trade name, BASF Coatings Japan ( Co., Ltd.) was air spray coated to a dry film thickness of 30 μm and baked at 140 ° C. for 30 minutes. Next, Aqua BC-3 black (trade name, manufactured by BASF Coatings Japan Co., Ltd., paint color: black), which is a water-based colored base coat paint, is air sprayed to a dry film thickness of 12 μm and flashed at 80 ° C. for 3 minutes. After that, the clear paint was diluted with Solvesso 100 (trade name, manufactured by Esso Corporation, aromatic petroleum naphtha) to a coating viscosity (Ford Cup No. 4, 25 seconds at 20 ° C.). Then, each was sprayed with air spray to a dry film thickness of 40 μm and baked at 140 ° C. for 30 minutes to prepare test pieces.
The coating film performances of the examples are shown in Table 4. In each case, excellent car wash resistance, acid rain resistance, and water stain resistance were exhibited.

(Comparative Examples 1-6)
A test piece was prepared in the same manner as in the example except that the clear paint was changed to CC-5 to CC-10. The coating film performance is shown in Table 5.
Since Comparative Example 1 did not contain the radical polymerizable monomer (B) having a ring structure, the water stain resistance and acid rain resistance were insufficient. In Comparative Example 2, since the content of the structural unit (A) based on ε-caprolactone was small, the elongation percentage of the coating film was small and the scratch resistance was insufficient. Furthermore, since Comparative Example 3 did not contain the radical polymerizable monomer (B) having a ring structure as in Comparative Example 1, the water stain resistance and acid rain resistance were insufficient. In Comparative Example 4, the content of the radically polymerizable monomer (B) having a ring structure is a constituent unit (A) based on ε-caprolactone relative to the constituent unit (B) based on the radically polymerizable monomer having a ring structure. Therefore, the water stain resistance and acid rain resistance were insufficient because the mass ratio ((A) / (B)) was less than the range of 1/1 to 1 / 0.5.

In Comparative Example 5, the content of the radically polymerizable monomer (B) having a ring structure is different from that of the structural unit (A) based on ε-caprolactone relative to the structural unit (B) based on the radically polymerizable monomer having a ring structure. Since the mass ratio ((A) / (B)) was larger than the range of 1/1 to 1 / 0.5, the elongation percentage of the coating film was small, and the scratch resistance was insufficient. Further, Comparative Example 6 has a structural unit (B) based on a radically polymerizable monomer having a structural unit (A) based on ε-caprolactone in an acrylic resin solid content of 15% by mass or more and having a ring structure. And the mass ratio ((A) / (B)) of the structural unit (A) based on ε-caprolactone to the structural unit (B) based on the radical polymerizable monomer having a ring structure is 1/1 to 1 However, since the molecular weight between crosslinks in the cured coating film was 450 g / mol and the crosslink density was sparse, both scratch resistance, water stain resistance and acid rain resistance were insufficient.

Claims (4)

  The resin molecule has a structural unit (A) based on ε-caprolactone and a structural unit (B) based on a radical polymerizable monomer having a ring structure, and a structural unit (A) based on ε-caprolactone Is a mass ratio of the structural unit (A) based on ε-caprolactone to the structural unit (B) based on the radically polymerizable monomer having a ring structure. Is a clear coating composition containing an acrylic resin and an isocyanate compound in the range of 1/1 to 1 / 0.5, and the elongation at break at 20 ° C. of the cured coating film obtained from the clear coating composition The clear coating composition is characterized by having a molecular weight of 20 to 40% and a molecular weight between crosslinks of 300 to 400 g / mol. 2. The clear coating composition according to claim 1, wherein the radical polymerizable monomer having a ring structure is at least one monomer selected from styrene, cyclohexyl acrylate, cyclohexyl methacrylate, tert-butylcyclohexyl acrylate, and tert-butylcyclohexyl methacrylate. . 3. A coating finishing method, wherein the clear coating composition according to claim 1 is applied as a top coating. A coated article obtained by the paint finishing method according to claim 3.