JP5773848B2 - Two-part clear coating composition - Google Patents

Description

The present invention relates to a two-part clear coating composition.

A coating film forming method in which a clear layer is formed on a base layer by wet-on-wet and baked and cured is used in many technical fields such as automobile coating and plastic coating. Conventionally, the composition of the clear paint has been adjusted to the composition of the base paint. This is because the use of a clear coating material corresponding to the composition of the base coating material improves the familiarity of the base layer and the clear layer and improves the adhesion of the multilayer coating film. However, according to such a method, a clear paint suitable for the base paint to be used is required, which is not preferable from the viewpoint of increasing the labor of painting, storage load, and the like.

On the other hand, in the formation of a multilayer coating film composed of a base layer and a top coat layer, by adjusting the composition of the top coat layer, the penetration of the curing agent component into the base layer is promoted, and water resistance, weather resistance, It describes that performance such as solvent resistance is imparted (see, for example, Patent Document 1). However, in the conventional combination, depending on the type of resin used for the topcoat layer, the penetration was insufficient and the performance could not be expressed.

In Patent Document 2, a low-viscosity polyisocyanate preparation is studied. Although it discloses the improvement of the surface quality when used as a lacquer, it is not for promoting the transfer of the curing agent component to the base layer and improving the adhesion.

Patent Document 3 discloses a low-viscosity polyisocyanate containing an iminooxadiazinedione group obtained by trimerization of isocyanate. Such polyisocyanates are disclosed as being usable as crosslinkers in coating compositions, but do not mention properties relating to migration to the base layer.

JP 2008-200587 A Special table 2009-523151 JP 9-268212 A

An object of the present invention is to provide a highly versatile two-component clear paint capable of exhibiting good adhesion to a base layer having any composition from the above viewpoint. is there.

The present invention is a two-part clear coating composition comprising a main component containing a hydroxyl group-containing resin (A) and a curing agent solution containing a polyisocyanate compound (B), wherein the hydroxyl group-containing resin (A) is a primary and The ratio of secondary hydroxyl groups is primary hydroxyl group / secondary hydroxyl group = 50/50 to 20/80 on the basis of hydroxyl value.
The polyisocyanate compound (B) is represented by the following formula (1)

(R ¹ , R ² and R ³ are the same or different from each other, and represent a group obtained by removing an isocyanate group from an aliphatic, alicyclic, aromatic isocyanate and / or oligomer thereof)
Having an iminooxadiazinedione group represented by:
The equivalent ratio (NCO / OH) of the hydroxyl group of the hydroxyl group-containing resin (A) to the isocyanate group of the polyisocyanate compound (B) is 0.8 to 1.5 ,
Of all the polyisocyanate compounds contained in the curing agent solution, 50 to 100% by weight is the polyisocyanate compound (B),
A two-part clear coating composition characterized by being an organic solvent type .
The polyisocyanate compound (B) preferably has a viscosity at 23 ° C. of 200 to 800 m · Pas.
The present invention consists of three layers of primer coating-base coating-clear coating, or color base coating-base coating-clear coating, or four layers of primer coating-color base coating-mica base coating-clear coating. A painting method that is a painting system,
It is also a method for forming a multilayer coating film, wherein the clear coating is performed by the above-described two-part clear coating composition.

According to the present invention, it is possible to provide a two-part clear coating composition that exhibits excellent adhesion and the like regardless of the composition of the base coating.

Hereinafter, the present invention will be described in detail.
The present invention is a two-part clear paint having a specific composition. Thereby, a part of the components (particularly the polyisocyanate compound (B)) in the clear layer permeates into the base layer, whereby the base layer is crosslinked and excellent adhesion can be obtained. In addition, since the clear layer and the base layer are firmly bonded, the properties such as water resistance and weather resistance are improved, and the base layer obtains sufficient cross-linking, thereby deteriorating the properties such as long-term durability and weather resistance. It is estimated that it will not occur.

The two-part clear coating is composed of a main agent containing a hydroxyl group-containing resin (A) and a curing agent solution containing a polyisocyanate compound (B). The hydroxyl group-containing resin (A) has the property that the ratio of primary and secondary hydroxyl groups is primary hydroxyl group / secondary hydroxyl group = 50/50 to 20/80 on the basis of hydroxyl value. The hydroxyl group-containing resin is cured by reacting with a polyisocyanate compound. As curing proceeds, the transition of the polyisocyanate compound (B) to the base coat layer is inhibited, but the reaction with the polyisocyanate compound can be slowed by specifying the substance of the hydroxyl group-containing resin as described above. . Thereby, the adhesion can be enhanced by increasing the amount of the polyisocyanate compound penetrating into the base coat layer.

Furthermore, the adhesiveness is also improved by using a polyisocyanate compound (B) containing an iminooxadiazinedione group. Since the polyisocyanate compound containing an iminooxadiazinedione group has a low viscosity, it has a property that penetration into the base layer is likely to occur. Also by this, the penetration amount of the polyisocyanate compound into the base coat layer can be increased, and the adhesion can be improved.

The primary hydroxyl group has a relatively high reactivity with the polyisocyanate compound, and the secondary hydroxyl group has a relatively low reactivity with the polyisocyanate compound. For this reason, the content ratio of the primary and secondary hydroxyl groups greatly affects the degree of migration of the polyisocyanate compound to the base layer. More specifically, when a large amount of primary hydroxyl groups having high reactivity are present, the hydroxyl group-containing resin (A) and the polyisocyanate compound (B) are more likely to penetrate than the polyisocyanate compound (B) penetrates into the base layer. Since the reaction proceeds quickly, the transition is less likely to occur. In order to obtain the above-described effect of the present invention, it is necessary to use a hydroxyl group-containing resin (A) having both a primary hydroxyl group and a secondary hydroxyl group within the range of the ratio described above.

Therefore, when the content ratio of the primary hydroxyl group is less than 20/80, the polyisocyanate compound (B) tends to migrate to the base layer, but the clear layer is not sufficiently cured, and the solvent resistance of the multilayer coating film Decreases. On the other hand, when the content ratio of the primary hydroxyl group exceeds 50/50, curing in the clear layer is sufficient but difficult to migrate, and the water resistance of the multilayer coating film is lowered.

The glass transition temperature (Tg) of the hydroxyl group-containing resin (A) is preferably -20 to 50 ° C. When the temperature is −20 ° C. or lower, the stain resistance of the clear coating film is decreased, and when the temperature is 50 ° C. or higher, the flexibility of the coating film may be decreased.

It is preferable that the weight average molecular weights of the said hydroxyl-containing resin (A) are 2000-20000. If it is less than 2000, the film performance required for the clear layer such as solvent resistance and appearance cannot be exhibited. If it exceeds 20000, the viscosity of the paint becomes high, and in such a high viscosity state, the coating operation becomes difficult. The appearance will be worse. It is possible to reduce the viscosity by reducing the proportion of non-volatile components in the paint using a volatile organic solvent, but in this case, there arises a problem of environmental pollution due to the organic solvent. In the present specification, the weight average molecular weight is a polystyrene equivalent weight average molecular weight measured by GPC (gel permeation chromatography).

The hydroxyl value of the hydroxyl group-containing resin (A) is preferably 80 to 230 KOHmg / g, and more preferably 120 to 200 KOHmg / g. If it is less than 80 KOHmg / g, the crosslink density of the clear layer becomes insufficient, and the solvent resistance and weather resistance of the multilayer film are lowered. If it exceeds 230 KOHmg / g, the compatibility with the curing agent is lowered, and tack remains after baking. Or the initial hardness is insufficient.

More specifically, the hydroxyl group-containing resin (A) is preferably a copolymer mainly composed of an acrylic monomer. The monomer used for the polymerization of the hydroxyl group-containing resin (A), which is a copolymer mainly composed of the acrylic monomer, is not particularly limited. For example, acrylic acid, methacrylic acid, maleic acid, itaconic acid Ethylenically unsaturated carboxylic acid monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, (meth) acrylate-2-ethylhexyl, etc. Alicyclic esters of ethylenically unsaturated carboxylic acids such as carboxylic acid alkyl ester monomers, cyclohexyl (meth) acrylate, norbornyl (meth) acrylate; ethyl maleate, butyl maleate, ethyl itaconate, itaconic acid Monoester monomers of ethylenically unsaturated dicarboxylic acids such as butyl; (meth) acrylic acid-2-hydroxyethyl, acrylic Hydroxyl group-containing ethylenically unsaturated carboxylic acid ester monomer that is a primary hydroxyl group-containing monomer such as acid-4-hydroxybutyl, a reaction product of 2-hydroxyethyl (meth) acrylate and ε-caprolactone; Hydroxyl group-containing ethylenically unsaturated carboxylic acid ester monomers that are secondary hydroxyl group-containing monomers such as (meth) acrylic acid-2-hydroxypropyl; unsaturated fatty acid glycidyl ester monomers such as glycidyl acrylate and glycidyl methacrylate ; Vinyl cyanide monomers such as (meth) acrylonitrile and α-chloroacrylonitrile; saturated aliphatic carboxylic acid vinyl ester monomers such as vinyl acetate and vinyl propionate; styrene, α-methylstyrene, vinyltoluene, etc. Examples thereof include styrene monomers. The monomer mixture may be one that uses the monomer alone or may be a combination of two or more components.

The polymerization method for obtaining the acrylic resin is not particularly limited, and known methods such as solution polymerization, high pressure polymerization, and continuous polymerization can be used.

The said hardening | curing agent solution contains the said polyisocyanate compound (B). The polyisocyanate compound (B) in the present invention has the following general formula (1):

(R ¹ , R ² and R ³ are the same or different from each other, and represent a group obtained by removing an isocyanate group from an aliphatic, alicyclic, aromatic isocyanate and / or oligomer thereof)

Containing an iminooxazinedione group represented by: The polyisocyanate compound (B) having such a structure exhibits a lower viscosity than a polyisocyanate compound that has been conventionally used as a curing agent in a coating composition. Such a low-viscosity polyisocyanate compound (B) easily migrates to the base layer, and as a result, crosslinking in the base layer is promoted, and good adhesion, water resistance, and the like can be obtained.

Examples of the polyisocyanate compound used as a raw material for the compound having an iminooxazinedione group represented by R ¹ , R ² and R ³ in the above general formula include 1,6-hexane diisocyanate, lysine diisocyanate, isophorone diisocyanate, cyclohexane-1,4- Examples thereof include diisocyanate compounds such as diisocyanate, xylylene diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate, and polyfunctional isocyanate compounds such as adducts, burettes, and isocyanurates.

Although the said hardening | curing agent solution mainly consists of a polyisocyanate compound, it is more preferable that 50-100 weight% contains the said iminooxazine dione group in all the polyisocyanate compounds. More preferably, it is 70 to 90% by weight. Since the compound containing an iminooxazinedione group within such a range can have a low viscosity, it is presumed that it is preferable in terms of easy penetration into the lower layer when used in a multilayer coating film.

A method for producing such a compound having an iminooxazinedione group is not particularly limited, and examples thereof include a method described in JP-A-9-268212. Moreover, as a commercially available thing, Death Module N3900 (made by Sumika Bayer) etc. can be mentioned.

The viscosity of the isocyanate compound (B) is preferably 800 mPa · s or less at 23 ° C. The viscosity is measured according to JISK1603. The viscosity is more preferably 600 mPa · s or less. Although it does not specifically limit as a minimum, It is preferable that it is 200 mPa * s or more.

The curing agent solution may contain another polyisocyanate compound. The other polyisocyanate compound is not particularly limited, and examples thereof include aliphatic isocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate, and 1,3-cyclopentane. Aliphatic cyclic isocyanates such as diisocyanate, 1,4-cyclohexane diisocyanate, 1,2-cyclohexane diisocyanate, xylylene diisocyanate (XDI), 2,4-tolylene diisocyanate (TDI), 2,6-tolylene diisocyanate, etc. Alicyclic isocyanates such as aromatic isocyanate, isophorone diisocyanate (IPDI), norbornane diisocyanate methyl, Let body can include multimers of isocyanurate and the like, and mixtures.

In addition, the two-component clear coating composition may contain a base color pigment or a metallic pigment as long as it does not impair transparency. Furthermore, you may mix | blend a ultraviolet absorber, a hindered amine light stabilizer, antioxidant, a crosslinked resin particle, a surface conditioning agent, etc.

When the crosslinked resin particles are used, it is preferable that the lower limit is 0.01% by weight and the upper limit is 10% by weight with respect to the resin solid content of the two-part clear coating composition of the present invention. The lower limit is more preferably 0.1% by weight, and the upper limit is more preferably 5% by weight. When the addition amount of the crosslinked resin particles exceeds 10% by weight, the appearance of the obtained coating film tends to deteriorate, and when it is less than 0.01% by weight, the rheology control effect tends to be not obtained.

In the present invention, when a surface conditioner is used, the surface conditioner to be blended is not particularly limited, but a silicon-based surface conditioner or an acrylic copolymer-based surface conditioner can 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 weight and an upper limit of 10% by weight with respect to the total solid content in the paint, and further, a lower limit of 0.1% by weight and an upper limit of 5%. More preferably, it is% by weight. When the amount of the surface modifier added exceeds 10% by weight, the stain resistance of the resulting coating film tends to deteriorate, and when it is less than 0.01% by weight, rheology controllability may not be obtained.

The coating form of the two-part clear coating composition of the present invention is preferably an organic solvent type. 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.

Examples of the two-component form include a coating composition obtained by adding a curing agent solution to a main agent and stirring and dispersing it. At the time of the mixing, the main agent and the curing agent solution are equivalent ratios (NCO) of the isocyanate group (NCO) contained in the polyisocyanate compound (B) and the hydroxyl group (OH) contained in the hydroxyl group-containing resin (A). / OH) may be mixed at a ratio such that 0.8 / 1.5. If it is out of the above range, the polyisocyanate compound (B) is hardly transferred from the clear layer to the base layer, and the water resistance of the multilayer coating film is lowered. Moreover, it is preferable that the equivalent ratio (NCO / OH) of the said isocyanate group (NCO) and a hydroxyl group (OH) is 0.8-1.2.

The method for obtaining the two-part clear coating composition is not particularly limited. For example, all methods well known to those skilled in the art, such as dispersing various blends using a disper or the like, 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. However, it can be advantageously used on the surface of a plastic material.

Examples of the plastic material include polyolefin materials such as polyethylene and polypropylene, ethylene-vinyl acetate copolymer, polyamide, polyacryl, polyester, ethylene polyvinyl alcohol copolymer, ABS resin, vinyl chloride resin, vinylidene chloride resin, polycarbonate, and polyurethane. Examples thereof include polymer alloys made of polycarbonate and polybutylene terephthalate, and plastic materials such as various FRPs. In particular, thermoplastic resin materials, among them, polyolefin materials, ABS resin materials, and polymer alloy materials made of polycarbonate and polybutylene terephthalate are preferable. Specific examples include interior and exterior parts such as automobile bumpers, moldings, grills, spoilers, dashboards, consoles, and audio grills. In particular, since the clear paint has excellent weather resistance, it can be suitably used for automobile exterior parts.

There are three types of plastic materials: primer coating-base coating-clear coating, or color base coating-base coating-clear coating, and primer coating-color base coating-mica base coating-clear coating. Examples include a coating system composed of layers. The two-part clear coating composition of the present invention can be suitably used in any coating system. Hereinafter, these coating systems will be described.

(Primer coating)
Although it does not specifically limit as said primer coating, It is preferable that it is what coats an aqueous primer. As a process of applying the aqueous primer to the substrate surface, for example, it can be applied by a technique such as spray coating or bell coating. You may wash | clean and degrease the said base material as needed.

The primer coating film is preferably 5 to 30 μm in dry film thickness. If the thickness is less than 5 μm, the hiding property is insufficient, and if it exceeds 30 μm, the cracks and sagging are likely to occur. Preferably it is 10-20 micrometers. The dry film thickness can be measured by using SDM-miniR manufactured by SANKO.

(Base paint)
Although it does not specifically limit as said base coating, Arbitrary base coating compositions etc. which are normally used can be used. For example, a coating composition containing a color pigment or extender pigment such as a film-forming resin, a curing agent, an organic type, an inorganic type, or a bright material can be exemplified. Especially, it is preferable to contain an acrylic polyol as a film-forming resin and a melamine compound as a curing agent.

The method for applying the base coating composition is not particularly limited, and examples thereof include air spray application and airless spray application. More specifically, there can be mentioned a coating method using a rotary atomization type electrostatic coating machine called micro-microbell or microbell. The coating thickness of the base coat paint is preferably in the range of a lower limit of 10 μm and an upper limit of 30 μm in terms of dry film thickness.

(Color base coating)
The color base coating is not particularly limited, and examples thereof include coating a color base coating composition containing a film-forming resin, a curing agent, and a pigment.

The base resin is not particularly limited, and examples thereof include water-soluble acrylic resins, water-dispersible acrylic resins, emulsion acrylic resins, water-soluble polyester resins, and water-dispersible polyester resins. Moreover, it is preferable to use together hardening agents, such as a melamine resin and a polyisocyanate compound.

Examples of the pigment contained in the color base coating composition include organic and inorganic color pigments and extender pigments. Examples of organic coloring pigments include azo lake pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, phthalocyanine pigments, indigo pigments, perinone pigments, and perylene pigments. Examples thereof include pigments, dioxazine pigments, quinacridone pigments, selenium pigments, isoindoline pigments, isoindolinone pigments, and metal complex pigments. Examples of inorganic coloring pigments include chrome yellow, zinc white, iron oxide, yellow iron oxide, bengara, carbon black, cadmium red, molybdenum red, chromium yellow, chromium oxide, Prussian blue, cobalt blue, and titanium oxide (for example, , Titanium dioxide) and the like. Examples of extender pigments include calcium carbonate, barium sulfate, calcined kaolin, magnesium silicate, clay, and talc. You may use the said pigment 1 type or in combination of 2 or more types.

In addition to the pigment, the film-forming resin, and the curing agent, which are essential components, the color base coating composition may contain an organic solvent (for example, an aromatic hydrocarbon, an aliphatic hydrocarbon, an ester, Alcohol solvents, etc.), thickeners (eg, crosslinked resin particles, organic bentonite, fatty acid polyamide, polyethylene wax, etc.), glittering materials (eg, aluminum foil, mica, tin foil, gold foil, metal titanium foil, nickel foil, etc.) An acid catalyst, an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant, a surface conditioner, a leveling agent, a pigment dispersant, a plasticizer, an antifoaming agent, and the like may be appropriately blended.

(Mica base paint)
It does not specifically limit as said mica base coating, What can apply | coat the well-known mica base coating composition containing resin for bases and a mica pigment can be mentioned.

The base resin is not particularly limited, and examples thereof include water-soluble acrylic resins, water-dispersible acrylic resins, emulsion acrylic resins, water-soluble polyester resins, and water-dispersible polyester resins. Moreover, it is preferable to use together hardening agents, such as a melamine resin and a polyisocyanate compound.

By blending the above mica pigment, it is possible to obtain a pearly glossy coating film that is more excellent in design and design. The mica pigment is not particularly limited, and examples of commercially available products include “Iriodin” and “Silary” manufactured by Merck. The content is preferably 1 to 20% by weight in the total solid content (resin solid content and other solid content such as pigment) in the paint.

As a method for applying the mica base coating composition, electrostatic coating is preferably used. The mica base coating film preferably has a dry film thickness of 5 to 20 μm, and more preferably 7 to 15 μm. If the dry film thickness is less than 5 μm, the target color may not be exhibited. On the other hand, when the thickness exceeds 20 μm, defects such as sagging and flares may occur.

(Clear paint)
In the clear coating, the two-part clear coating composition of the present invention is applied. A preheating step may be performed in each coating step except clear coating. In addition, what is necessary is just to set the heating temperature in the case of preheating suitably, but 40-100 degreeC is preferable and 40-90 degreeC is more preferable. There is no restriction | limiting in particular about the method of preheating, For example, what is necessary is just to employ | adopt well-known methods, such as a hot-air drying method and an infrared rays drying method.

The method for applying the two-part clear coating composition of the present invention 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 2 liquid clear coating composition, generally the minimum of 15 micrometers and the upper limit of 50 micrometers are preferable. If the thickness is less than 15 μm, the unevenness of the base may not be concealed, and if it exceeds 50 μm, defects such as cracking and sagging may occur during coating. The lower limit is more preferably 20 μm, and the upper limit is more preferably 45 μm.

After the application of the two-part clear coating composition, the curing temperature for curing the obtained multilayer coating film is preferably a lower limit of 100 ° C. and an upper limit of 140 ° C. If it is less than 100 ° C, curing may not be sufficient, and if it exceeds 140 ° C, the coating film may become brittle. The lower limit is more preferably 110 ° C. Although hardening time changes with hardening temperature, 20 to 40 minutes are suitable at 110 to 130 degreeC.

EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail, this invention is not limited only to these Examples. In the examples, “part” means “part by weight” unless otherwise specified, and “%” means “% by weight” unless otherwise specified.

(Production of hydroxyl group-containing resin (A))
With the formulation shown in Table 1, hydroxyl-containing resins AC-1 to AC-6 were obtained. The non-volatile content of the hydroxyl group-containing resin is not simply the non-volatile content of the monomer alone, but 70% by weight of the polymerization initiator t-butylperoxy-2-ethylhexanate reacts with the monomer and is non-volatile. It was a minute. That is, specifically, the ratio of the total amount of the monomer and 70% by weight of the amount of t-butylperoxy-2-ethylhexanate used was calculated as the weight of the non-volatile content.

Further, t-butylperoxy-2-ethylhexanate reacts with the monomer as described above to form a part of the hydroxyl group-containing resin. The hydroxyl group and acid group to be used were ignored in the calculation because they have little influence on the properties of the hydroxyl group-containing resin.

<Production of hydroxyl group-containing resin (AC-1)>
A reactor equipped with a stirring blade, thermometer, dripping device, temperature control device, nitrogen gas inlet and cooling tube was charged with 130 parts of butyl acetate as a solvent, and the temperature was raised to 125 ° C. with stirring while introducing nitrogen gas. did. Next, as a monomer, a mixture of 63 parts of 2-hydroxyethyl methacrylate, 126 parts of 2-hydroxypropyl methacrylate, 3.5 parts of methacrylic acid, 45 parts of styrene, 212.7 parts of 2-ethylhexyl methacrylate, and t- A solution prepared by dissolving 67.5 parts of butyl peroxy-2-ethylhexanate in 90 parts of butyl acetate was dropped into the reactor over 3 hours.
After completion of the dropping, the mixture was aged for 1 hour, and further 0.9 parts of a polymerization initiator t-butyl peroxy-2-ethylhexanate was dissolved in 10 parts of butyl acetate and dropped into the reactor over 1 hour. Thereafter, the mixture was aged for 2 hours while being kept at 125 ° C. and cooled to complete the reaction.
The weight average molecular weight of the obtained acrylic resin was 4000, OHV was 170, AV was 5, and the nonvolatile content was 70%.

Production of hydroxyl-containing resins (AC-2) to (AC-6) Hydroxyl-containing resins (AC-2) to (AC-6) were produced in the same manner as in the production of the hydroxyl group-containing resin (AC-1). . After polymerization, the nonvolatile content was adjusted using butyl acetate.

Table 1 below summarizes the special values of Compound B. Each numerical value was measured by the following method.
(1) Glass transition point The glass transition point was calculated from the literature value of Tg of each monomer.

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

(3) Weight average molecular weight GPC (gel permeation chromatography) was used to measure the polystyrene equivalent weight average molecular weight.

<Manufacture of clear paint (CL-1)>
A clear paint (CL-1) was obtained with the formulation shown in Table 2.
The NCO species used are A (Sumika Bayer Sumijour N3300) and B (Sumika Bayer Death Module N3900).

A container is charged with 30 parts of butyl acetate and 76.05 parts of AC-1 prepared in (Manufacturing of acrylic resin), and while stirring well, BYK-310 (manufactured by Big Chemie Japan) 0.54 parts, Tinuvin 292 (Ciba 0.25 parts by Japan) and 0.55 parts Tinuvin 384-2 (by Ciba Japan) were sequentially charged and stirred until they were uniform, and used as the main ingredients of the clear paint.
The curing agent was prepared by mixing 20 parts of butyl acetate and 30.4 parts of Desmodur N3900 (manufactured by Sumika Bayer Urethane Co., Ltd.) in a container. 107.39 parts of the main agent prepared above and 50.4 parts of a curing agent were mixed to obtain a clear paint CL-1.
At this time, the non-volatile content of the clear paint was 53.4%.

<Manufacture of clear paints (CL-2) to (CL-9)>
CL-2 to 9 were produced by the same method as CL-1.

Examples 1-6, Comparative Examples 1-12
Conductive primer “WB-1200CD-4” by “Wider-71” (manufactured by Anest Iwata Co., Ltd.) under the environment of 25 ° C./70% RH on the surface of polypropylene material (70 mm × 150 mm × 3 mm) wiped with isopropyl alcohol ( Nippon Bee Chemical Co., Ltd.) was spray-coated (dry film thickness 20 μm) and dried at 80 ° C. for 5 minutes. Thereafter, the paint colors # 1F7 (silver) and # 040 of the aqueous base “AR-2000” (manufactured by Nippon Paint), “WBC-713T” (manufactured by Kansai Paint) and “TGB-W2700” (manufactured by DuPont), respectively. (White) Under the same environment, electrostatic coating (conditions, gun distance: 200 mm, gun speed: 900 mm / s, applied voltage: −60 kV, rotation speed: 35000 rpm) using a new cartridge bell (manufactured by ABB) (Shaving air pressure: 0.15 MPa, dry film thickness 30 μm) and dried at 80 ° C. for 5 minutes. On top of that, the clear paints (CL-1 to 9) shown in Table 3 were applied using Robobel 951 (manufactured by ABB), and electrostatic coating (conditions, gun distance: 200 mm, gun speed: 700 mm / s, applied voltage) : -60 kV, rotation speed: 25000 rpm, shaving air pressure: 0.07 MPa) The atomization coating (dry film thickness 15 μm) was performed. Then, after setting for 10 minutes, it dried for 35 minutes at 120 degreeC, the multilayer coating film was formed, and the final coating board was obtained.

The following test was done about the obtained coated plate. The results are shown in Table 3.
-The water-resistant final coated plate is immersed in warm water at 40 ° C for 240 hours, then dried at room temperature for 1 hour, and blister (swelling of the coating film due to water penetration) is visually evaluated based on ASTM D714, and JIS K5600 grid tape A peel test was performed.
○ When there is no abnormality in the appearance compared to before the test and there was no peeling
Those that are abnormal in appearance compared to before the test, or those that are slightly peeled ×
It was.
-Xylene rubbing resistance A load of 500 g was applied to the final coated plate with xylene, and an 8 reciprocating rubbing test was performed to evaluate the presence or absence of abnormalities such as tackiness, wrinkles, blistering, peeling. In the case where no abnormality was observed, it was marked as “◯”, and in the case where any abnormality was observed, it was marked as “X”.

By using the clear coating composition of the present invention, a multilayer coating film excellent in water resistance and xylene rubbing resistance could be obtained regardless of the type of base coating used.

The two-part clear coating composition of the present invention can obtain good adhesion regardless of the composition of the base layer. In particular, since it can be suitably used for coating a plastic material, excellent water resistance, weather resistance, adhesion and the like can be imparted to automotive exterior products such as bumpers.

Claims (3)

A two-part clear coating composition comprising a main agent containing a hydroxyl group-containing resin (A) and a curing agent solution containing a polyisocyanate compound (B),
In the hydroxyl group-containing resin (A), the ratio of primary and secondary hydroxyl groups is primary hydroxyl group / secondary hydroxyl group = 50/50 to 20/80 on the basis of hydroxyl value.
The polyisocyanate compound (B) is represented by the following formula (1).
(R ¹ , R ² and R ³ are the same or different from each other, and represent a group obtained by removing an isocyanate group from an aliphatic, alicyclic, aromatic isocyanate and / or oligomer thereof)
Having the iminooxadiazinedione group represented,
The equivalent ratio (NCO / OH) of the hydroxyl group of the hydroxyl group-containing resin (A) to the isocyanate group of the polyisocyanate compound (B) is 0.8 to 1.5 ,
Of all the polyisocyanate compounds contained in the curing agent solution, 50 to 100% by weight is the polyisocyanate compound (B),
A two-part clear coating composition characterized by being an organic solvent type . The two-component clear coating composition according to claim 1, wherein the polyisocyanate compound (B) has a viscosity at 23 ° C of 200 to 800 m · Pas. Primer paint-base paint-clear paint or color base paint-base paint-clear paint three-layer paint system or primer paint-color base paint-mica base paint-clear paint four-layer paint system Painting method,
A method for forming a multilayer coating film, wherein the clear coating is performed with the two-part clear coating composition according to claim 1 or 2.