KR20050067781A - Method of preparing acrylic resin and high solid transparent paint - Google Patents

Abstract

A method for producing a high solid acrylic resin and a high solid transparent paint suitable for automobile repair transparent paint and excellent in high gloss, lightness, and acid resistance is disclosed. The high solid transparent paint is 40 to 60 parts by weight of a high solid acrylic resin, 30 to 50 parts by weight of SGO (Solid Grade Oligomer) resin, 5 to 20 parts by weight of an organic solvent, 0.02 to 0.1 parts by weight of a reaction catalyst, and 1.5 to 3 parts by weight of an additive. It forms by mixing reaction of a part. Such a high solid transparent paint is not only excellent in acid resistance, scratch resistance, high glossiness, and sensibility, but also can form a transparent coating film having quick drying property.

Description

Method of preparing acrylic resin and high solid transparent paint

The present invention relates to a manufacturing method of a high solid acrylic resin and a high solid transparent paint, and more particularly, a manufacturing method of a high solid acrylic resin applied to forming a transparent paint for automobile repair and a high solid transparent paint for preparing the paint. It relates to a method for producing.

Recently, due to the development of the organic chemical industry, the global environment such as air pollution, global warming, ozone layer destruction is rapidly deteriorating. In order to prevent such environmental destruction, the use of volatile organic compounds should be suppressed to the maximum. A high solid resin may be applied as a method of reducing such volatile organic compounds.

However, the above-mentioned high solid resin has a problem in that the resin is not only slow in drying but also significantly lower in workability as compared with the conventional medium transparent paint. This is because when the low molecular weight resin is used to increase the nonvolatile content of the high solid resin, the reactivity of the resin is low, and the drying phenomenon and the flow of the coating film are slower than those of the medium solid paint.

In addition, the low molecular weight acrylic resin used to prepare the high solid resin has a wide molecular weight distribution and low crosslinking density, resulting in deterioration of coating performance such as scratch resistance and acid resistance. In addition, it is difficult to apply to the painting work because it shows a poor state in the lightness and glossiness that determines the appearance quality of the coating film.

Therefore, an object of the present invention for solving the above problems is to manufacture a high-solid acrylic resin that is applied to form a paint having a high drying resistance and excellent acid resistance, scratch resistance, glossiness and stiffness by applying a high viscosity resin of low viscosity To provide a method.

In addition, another object of the present invention for solving the above-mentioned problems is to provide a method for producing a high solid transparent paint that is quick to dry the paint and excellent in acid resistance, scratch resistance, gloss and stiffness.

The method for producing a high solid acrylic resin for achieving the above object of the present invention is 5 to 20 parts by weight of a vinyl monomer having an aromatic group, 15 to 50 parts by weight of a vinyl monomer having a hydroxyl group, and a vinyl monomer having an organic acid group. And mixing 1 to 5 parts by weight with 20 to 40 parts by weight of a vinyl monomer having an aliphatic group to form a mixture, and then adding 2 to 5 parts by weight of a radical polymerization initiator to the mixture to form a high solid acrylic resin. .

In addition, a method for producing a high solid transparent paint for achieving another object of the present invention described above, 5 to 20 parts by weight of a vinyl monomer having an aromatic group, 15 to 50 parts by weight of a vinyl monomer having a hydroxyl group, and an organic acid group 1 to 5 parts by weight of a vinyl monomer having 20 to 40 parts by weight of a vinyl monomer having an aliphatic group are mixed, and 2 to 5 parts by weight of a radical polymerization initiator is added to the mixture to form a high solid acrylic resin. 40 to 60 parts by weight of the acrylic resin, 30 to 50 parts by weight of the SOG (Solid Grade Oligomer) resin, 5 to 20 parts by weight of the organic solvent, 0.02 to 0.1 parts by weight of the reaction catalyst, 1.5 to 3 parts by weight of the additives to form a high solid transparent paint To form.

The high solid transparent paint formed by applying the above-described high solid acrylic resin is not only excellent in acid resistance, scratch resistance, high glossiness, and sensibility, but also can form a transparent coating film having quick drying property.

Hereinafter, the manufacturing method of the high solid acrylic resin and high solid transparent paint of this invention is demonstrated in detail.

<Method for producing high solid acrylic resin>

In order to manufacture paints with excellent acid resistance, scratch resistance, high glossiness, and sensibility, it is necessary to apply high-solid acrylic resin.

The high solid acrylic resin is formed by a radical polymerization method using a vinyl monomer having an aromatic group, a vinyl monomer having a hydroxyl group, a vinyl monomer having an organic acid group, a vinyl monomer having an aliphatic group, and a thermal decomposition initiator.

Examples of the vinyl monomer having an aromatic group used to prepare the high solid acrylic resin of the present invention include styrene or vinyltoluene, or a mixture thereof. Here, when the usage-amount of the vinyl-type monomer which has the said aromatic group is less than 20 weight part, gloss and sensation property fall, and when it exceeds 40 weight part, scratch resistance and durability will fall.

Therefore, the vinyl monomer having the aromatic group is preferably used within the range of 20 parts by weight to 40 parts by weight.

In addition, the vinyl monomer having an organic acid group used to prepare a high solid acrylic resin may be acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, and the like, and these may be used alone or in combination of two or more. .

At this time, when the amount of the vinyl monomer having the organic acid group is less than 1 part by weight or more than 5 parts by weight, a problem arises that the crosslinking density does not increase due to the role of an internal catalyst when reacting with an isocyanate or it is difficult to delay a rapid reaction of a urethane bond. There is a problem that the pot life is shortened.

Therefore, the vinyl monomer having an organic acid group is preferably used within the range of 1 part by weight to 5 parts by weight.

Moreover, as a vinyl monomer which has a hydroxyl group used for manufacturing the said high solid acrylic resin, in addition to general monomers, such as 2-hydroxy ethyl methacrylate, 2-hydroxy ethyl acrylate, and 4-hydroxy butyl acrylate, The ring-opening addition compound of (epsilon) -caprolactone is mentioned. Examples of the ring-opening addition compound of [epsilon] -caprolactone include Fraxel FM-1, Fraxel FM-2, and Fraxel FA-1 manufactured by Daicel Chemical Industries, Ltd., and the like. The monomers having these hydroxyl groups may be used alone or in combination of two or more thereof.

If the amount of the vinyl monomer having a hydroxyl group is less than 15 parts by weight, the chemical resistance and mechanical properties are lowered, and if it exceeds 50 parts by weight, there is a problem that the drying is delayed.

In addition, examples of the vinyl monomer having an aliphatic group include ethyl acrylate, normal butyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, 2-ethylhexyl acrylate, and Usyl methacrylate etc. are mentioned. These can be used individually or in mixture of 2 or more.

If the amount of the vinyl-based monomer having an aliphatic group is less than 20 parts by weight, the mechanical properties and durability are lowered, and if it exceeds 40 parts by weight, the gloss and clarity are poor.

In addition, examples of the radical polymerization initiator used to prepare the high solid acrylic resin include benzoyl peroxide, azoisobutyronitrile, t-butyl peroxyoctoate and the like. At this time, the amount of the radical polymerization initiator should be used within the range of 2 to 5 parts by weight.

Here, looking at the method for producing the high solid acrylic resin of the present invention using the radical polymerization initiator, first, a vinyl monomer having an aromatic group, a vinyl monomer having a hydroxyl group, a vinyl monomer having an organic acid group and an aliphatic group 100 to 65% of the radical polymerization initiator is added and reacted for 3 to 7 hours under the reaction temperature range of 110 to 150 to 100% of the radical polymerization initiator. Subsequently, a radical polymerization initiator having a remaining amount of 25 to 35% is added to the reactant produced by the reaction to react for 2 hours or more to form a high solid acrylic resin.

The high solid acrylic resin formed by the above-described method has an acid value of 5 to 30 mgKOH / g, a hydroxyl content of 2 to 7%, and a glass transition temperature of -15 to 30. In addition, it has non-volatile content of 70 to 80%, Gardner viscosity of Z to Z3, number average molecular weight of 2,000 to 10,000, and molecular weight distribution of 3 or less.

If the acid value of the resin is 5 mgKOH / g or less, sufficient crosslinking reaction cannot be performed with the crosslinking agent, so that the scratch resistance is weakened, solubility coefficient and thixotropic value are lowered, and the selectivity at the vertical coating site is inferior. If the acid value is 30 mgKOH / g or more, the polarity of the resin is excessive, and the solidification of the resin becomes difficult due to the increase of the viscosity. Therefore, the high solid acrylic resin preferably has an acid value of 5 to 30 mgKOH / g.

If the hydroxyl group of the resin is less than 2%, there is a problem that the physical properties of the coating film is weakened due to the decrease in the crosslinking density, and if the hydroxyl group content is more than 7%, the compatibility with the crosslinking agent and the nonpolar solvent is poor, and excellent appearance quality can be expected. Not only that, but also shortening the pot life and delay in painting workability results in deterioration. Therefore, the high solid acrylic resin preferably has a hydroxyl value in the range of 2 to 7%.

In addition, when the glass transition temperature of the resin is less than -15, the coating film hardness is weakened. When the glass transition temperature is more than 30, the viscosity rise and the scratch resistance are weakened. Therefore, the high solid acrylic resin preferably has a glass transition temperature in the range of -15 to 30.

<Method for producing high solid transparent paint>

The high solid transparent paint having excellent acid resistance, scratch resistance, high glossiness, and stiffness is 5 to 20 parts by weight of a vinyl monomer having an aromatic group, 15 to 50 parts by weight of a vinyl monomer having a hydroxyl group, and a vinyl having an organic acid group. 1-5 parts by weight of the monomer and 20-40 parts by weight of the vinyl monomer having an aliphatic group are mixed to form a mixture, and then 2-5 parts by weight of a radical polymerization initiator is added to the mixture to react with the high-solid acrylic resin and the high-solid acrylic It is formed by mixing 40 to 60 parts by weight of a resin, 30 to 50 parts by weight of a solid grade oligomer (SGO) resin, 5 to 20 parts by weight of an organic solvent, 0.02 to 0.1 parts by weight of a reaction catalyst, and 1.5 to 3 parts by weight of an additive. At this time, it can be formed by further adding a curing agent to the resultant.

Since the high solid acrylic resin and its manufacturing method have been described in detail above, it will be omitted to avoid duplication.

The SGO resin is a polyol designed to have a molecular weight distribution of less than 1.7 by SGO (Solid Grade Oligomer) process, it is possible to design a paint having a fast drying property of a low-solid resin of high viscosity when using SGO resin.

If the amount of SGO resin is less than 30 parts by weight, it is difficult to expect as much drying as desired, and if it exceeds 50 parts by weight, there is a limit to high solidification.

When the amount of dibutyltin laurate which is the reaction catalyst is less than 0.02 parts by weight, the reactivity decreases, and the drying is slowed. When the amount of dibutyltin laurate used is less than 0.1 parts by weight, the appearance and gloss are lowered and the weather resistance is poor.

In addition, the additives are surface modifiers and ultraviolet absorbers, and if the amount of the additive is less than 1.5 parts by weight, it is difficult to obtain a good surface state, and if the amount is more than 3 parts by weight, adverse effects may occur.

The curing agent is prepared by mixing 30 to 70 parts by weight of hexamethylene diisocyanate derivative, 20 to 60 parts by weight of isopron diisocyanate derivative, and 30 to 50 parts by weight of xylene. Lengthened.

The mixture of the transparent paint and the curing agent prepared above was mixed to have a hydroxy equivalent and an isocyanate equivalent of 1: 1 so as to be 15 to 20 seconds at 25 ° C. with a Pood Cup # 4 viscometer.

And the resultant and the curing agent must be mixed so that the hydroxyl equivalent and the isocyanate equivalent is 1: 1.

The high solid transparent paint formed by the above-described method has a nonvolatile content of 55% or more and a viscosity range of 15 to 20 seconds at 25 ° C. with a Pood Cup # 4 viscometer.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples. However, the present invention is not limited by the following examples, and it will be understood that various modifications and applications may be made within the spirit and scope of the present invention based on the detailed description and the claims of the present invention.

Example 1-1

25 parts by weight of butyl acetate, 12 parts by weight of styrene, 3% methacrylic acid, 15 parts by weight of 2-hydroxyethyl acrylate, 2-hydroxyethyl meth arc in a four-necked flask equipped with a thermometer, a condenser, a dropping vessel, and a stirrer. 10 parts by weight of rate, 30 parts by weight of normal butyl acrylate and 5 parts by weight of normal butyl methacrylate were mixed together, and 2.5 parts by weight of t-butyl peroxyoctoate was added dropwise at a constant rate over 110 hours at 110 to 150 ° C. Subsequently, after the dropwise addition was maintained for 1 hour, 0.5 parts by weight of t-butyl peroxyoctoate was added and reacted for 2 hours to obtain a high solid acrylic resin.

The high-solid acryl resin obtained by the above-described method has characteristics of Gardner viscosity Z1, nonvolatile content 75%, glass transition temperature -7 ° C, hydroxyl content 4.1%, acid value 21mg KOH / g, number average molecular weight 6,200 and molecular weight distribution 2.0. .

Example 1-2

15 parts by weight of butyl acetate, 10 parts by weight of xylene, 20 parts by weight of styrene, 5 parts by weight of methacrylic acid, 15 parts by weight of 2-hydroxyethyl acetic acid in a four-necked flask equipped with a thermometer, a condenser, a dropping vessel and a stirrer. 10 parts by weight of hydroxyethyl methacrylate and 25 parts by weight of normal butyl acetate were mixed, and 3.5 parts by weight of azoisobutyronitrile was added dropwise at a constant rate over 5 hours at 110 to 150 ° C. Subsequently, after the dropwise addition was maintained for 1 hour, 0.5 parts by weight of azoisobutyronitrile was added and reacted for 2 hours to obtain a high solid acrylic resin.

The high solid acryl resin obtained by the above-described method has the characteristics of Gardner viscosity Z2, nonvolatile content 75%, glass transition temperature 0 ° C, hydroxyl content 4.1%, acid value 24mg KOH / g, number average molecular weight 8,500 and molecular weight distribution 2.3.

Example 2-1

83 parts by weight of the high solid acrylic resin obtained in Example 1-1, 5 parts by weight of butyl acetate, 10 parts by weight of xylene, 0.05 parts by weight of dibutyl tin laurate, 1.5 parts by weight of an ultraviolet absorber, and 0.045 parts by weight of a surface modifier. A high solid transparent paint was prepared.

Example 2-2

83 parts by weight of the high solid acrylic resin obtained in Example 1-2, 5 parts by weight of butyl acetate, 10 parts by weight of xylene, 0.05 parts by weight of dibutyl tin laurate, 1.5 parts by weight of an ultraviolet absorber, and 0.045 parts by weight of a surface modifier. A high solid transparent paint was prepared.

Example 3-1

50 parts by weight of the high solid acrylic resin obtained in Example 1-1, 30 parts by weight of SGO polyol, 5 parts by weight of butyl acetate, 10 parts by weight of xylene, 0.05 parts by weight of dibutyltin laurate, 1.5 parts by weight of an ultraviolet absorber, 0.5 parts by weight of the surface modifier was mixed to prepare a high solid transparent paint.

Example 3-2

50 parts by weight of the high solid acrylic resin obtained in Example 1-2, 30 parts by weight of SGO polyol, 5 parts by weight of butyl acetate, 10 parts by weight of xylene, 0.05 parts by weight of dibutyltin laurate, 1.5 parts by weight of a UV absorber, surface 0.5 parts by weight of the modifier was mixed to prepare a high solid transparent paint.

Comparative Example 1

30 parts by weight of butyl acetate, 20 parts by weight of cyclohexamethacrylate, 20 parts by weight of isobornyl methacrylate, 12 parts by weight of butyl acrylate in a four-necked flask equipped with a thermometer, a condenser, a dropping vessel, and a stirrer. 17 parts by weight of ethyl acrylate and 1.5 parts by weight of methacrylic acid were mixed together, and 3.0 parts by weight of t-butyl peroxyoctoate was added dropwise at a constant rate over 5 hours while maintaining a reaction temperature of 110 to 150. Subsequently, after the dropwise addition was maintained for 1 hour, 0.5 parts by weight of t-butyl peroxyoctoate was added and reacted for 2 hours to obtain a resin.

Subsequently, 83 weight part of obtained resin, 5 weight part of butyl acetate, 10 weight part of xylene, 0.05 weight part of dibutyl tin laurate, 1.5 weight part of ultraviolet absorbers, and 0.045 weight part of surface modifiers were mixed, and the coating material was prepared.

Experimental Example 1

After coating the surface treated with zinc phosphate, the Puraima Surfacer (Dipai Product Name; PS-550) for automobile repair was applied to have a thickness of 50 to 60 μm, dried at 70 ° C. for 20 minutes, and then polished with # 400 abrasive paper. . Subsequently, the base coat color paint (Dipiai product name; Hi-Q Base) was applied to a thickness of 15 to 20 μm, and 10 minutes later, each of the paints obtained in Examples 2-1, 2-2 and Comparative Example 1 was coated with a thick film. After spray coating twice to 50 to 60 μm, the coating film was cured and dried at 70 ° C. for 40 minutes to evaluate the performance of each coating film.

Table 1 shows the evaluation results of the physical properties of the coating films formed of the respective paints.

Physical property evaluation result of coating Property Item Example 2-1 Example 2-2 Comparative Example 1 Remarks Viscosity (Topics / Hardeners) 17'62 17'24 18'61 F.C # 4,25 ℃  Solid content (%) 56.5 56.2 47.5 Housework time 3 hours 3 hours 2 hours Forced drying 2B- 3B + 3B 70 degrees Celsius * 30 minutes Natural dry 4B- / 2B- / B- 4B- / 2B- / B- 4B- / 4B + / 2B Pencil hardness (1/2/3 days) Glossy (20/60 °) 89.3 / 97.5 89.8 / 97.6 91.1 / 98.0 Bewaikei-Gardner Acid resistant ○ (3 hours) ○ (3 hours) ○ (30 minutes) 24 hours immersion in 20% H ₂ SO ₄ solution Alkali resistance ○ ○ ○ NaOH undiluted solution for 24 hours Scratch resistance 1.07 / 98% 1.10 / 98% 1.48 / 97% ΔL (25 °) / GR (20 °) Impact resistance 40 cm 40 cm 30 cm 500g × 1/2 " Weathering resistance QUV 3.8 4.2 6.2 2000hrs W-O-M 98 98 98 2000hrs

Experimental results of the paints obtained in Examples 2-1 and 2-2 showed very good acid and scratch resistance, and the drying performance was faster than that of the general high solid resin composition of Comparative Example 1. Could.

Experimental Example 2

The paints obtained in Examples 3-1 and 3-2 and MS-2002 in the same manner as in Experiment 1 except for the paints obtained in Examples 2-1, 2-2 and Comparative Example 1. (Dipiai product) paint was applied. MS-2002 (Dipiai) is a transparent paint of medium solid for automobile repair.

The evaluation results of the physical properties of the coating films formed of the respective paints are shown in Table 2 below.

 Coating property evaluation result Property Item Example 3-1 Example 3-2 MS-2002 Remarks Viscosity (Topics / Hardeners) 18'32 17'82 14'10 F.C # 4,25 ℃  Solid content (%) 56.2 56.2 42 Housework time 3 hours 3 hours 5 hours Forced drying 2B- 2B 2B + 70 degrees Celsius * 30 minutes Pendulum hardness 42 40 45 Konig, 70 ℃ × 30 minutes Natural dry 4B / HB 4B / HB 4B- / B 1/3 day Glossy (20/60 °) 89.5 / 97.8 90.1 / 97.8 89.4 / 97.6 Acid resistant ○ ○ ○ 24 hours immersion in 20% H ₂ SO ₄ solution Alkali resistance ○ ○ ○ NaOH solution 24 hours dropping Scratch resistance 1.08 / 98% 1.10 / 98% 1.07 / 98% ΔL (25 °) / GR (20 °) Impact resistance 40 cm 40 cm 40 cm 500g × 1/2 " Promote weather resistance QUV 4.2 4.3 5.2 2000hrs W-O-M 98 98 98 2000hrs

As can be seen from the evaluation of the physical properties, the high solid transparent paints obtained in Examples 3-1 and 3-2 are similar to medium solid transparent paints, but have excellent acid resistance and scratch resistance.

Note 1) Solid content: After adjusting the viscosity to be sprayed by mixing the main material and the curing agent, 1 ~ 3g sample is taken and heated at 150 ℃ for 2 hours, and then the solid content is measured.

Note 2) Pot life: Shows the time required for the viscosity to reach 2 times based on the spray viscosity.

Note 3) Scratch resistance: Using LAB-SCALE CAR WASH APPARATUS designed by KISTLER of Germany, Warer Pressure is 3bar, Brush Speed is 110rpm, Wash Cycle is 10washings, Wash Mixture is 1.5g / liter quartz powder ( Average particle 16㎛), Water Temperature was tested at 20 to 25 ℃ and the gloss retention was measured at ΔL and 20 ° angle at 25 ° angle.

Note 4) Acid resistance: To observe the method of immersion in 20% H ₂ SO ₄ solution for 24 hours, and to check in more severe conditions, observe the point where the coating film is swelled with 0.1 ~ 1g drop of the stock solution by dropper with air. One value.

The high solid transparent paint formed by the invention according to the present invention has a fast drying due to the combination of a low viscosity high solid resin and a low molecular weight resin, and is excellent in acid resistance, scratch resistance and sunscreen, and gloss.

In addition, the high solid transparent paint of the present invention is very low in the content of volatile organic compounds can improve the working environment of the operator and prevent environmental pollution.

Claims (9)

(a) 5 to 20 parts by weight of a vinyl monomer having an aromatic group, 15 to 50 parts by weight of a vinyl monomer having a hydroxyl group, 1 to 5 parts by weight of a vinyl monomer having an organic acid group, and Mixing 20 to 40 parts by weight of a vinyl monomer having an aliphatic group to form a mixture; And (B) a method of producing a high solid acrylic resin comprising the addition of 2 to 5 parts by weight of a radical polymerization initiator to the mixture to form a high solid acrylic resin. The method of claim 1, wherein step (b) comprises: (1) adding 65 to 75% of the radical polymerization initiator to the mixture for 3 to 7 hours to form a reactant; And (2) A method of producing a high solid acrylic resin, comprising the step of reacting 25 to 35% of the radical polymerization initiator to the reactant. The high solid acrylic resin of claim 1, wherein the high solid acrylic resin has an acid value of 5 to 30 mgKOH / g, a hydroxyl group content of 2 to 7%, and a glass transition temperature of -15 to 30. Method of preparation. The high solid acrylic resin of claim 1, wherein the high solid acrylic resin has a nonvolatile content of 70 to 80%, a Gardner viscosity of Z to Z3, a number average molecular weight of 2,000 to 10,000, and a molecular weight distribution of 3 or less. Method for producing a resin. (a) 5 to 20 parts by weight of a vinyl monomer having an aromatic group, 15 to 50 parts by weight of a vinyl monomer having a hydroxyl group, 1 to 5 parts by weight of a vinyl monomer having an organic acid group, and 20 to 20 parts by weight of a vinyl monomer having an aliphatic group. Mixing 40 parts by weight to form a mixture; (b) adding 2 to 5 parts by weight of a radical polymerization initiator to the mixture to form a high solid acrylic resin; And (c) 40 to 60 parts by weight of the high solid acrylic resin, 30 to 50 parts by weight of SGO (Solid Grade Oligomer) resin, 5 to 20 parts by weight of an organic solvent, 0.02 to 0.1 parts by weight of a reaction catalyst, and 1.5 to 3 parts by weight of an additive Reacting to form a high solid transparent paint comprising the step of producing a high solid transparent paint. The method of claim 5, wherein the high solid acrylic resin has an acid value of 5 to 30 mgKOH / g, a hydroxyl content of 2 to 7%, a glass transition temperature of -15 to 30, a non-volatile content of 70 to 80%, Gardner viscosity is Z-Z3, the number average molecular weight is 2,000-10,000, and the molecular weight distribution is 3 or less, The manufacturing method of the high solid transparent coating material characterized by the above-mentioned. The method of claim 5, wherein the SGO resin is a resin having a molecular weight distribution of 1.7 or less by SGO (Solid Grade Oligomer) process. The method of claim 5, wherein after the step (c), the high solid transparent paint is obtained from 30 to 70 parts by weight of hexamethylene diisocyanate derivative, 20 to 60 parts by weight of isopron diisocyanate derivative and 30 to 50 parts by weight of xylene A method of producing a high solid transparent paint further comprising the step of mixing a curing agent. The method for producing a high solid transparent paint according to claim 8, wherein the high solid transparent paint and the curing agent are mixed so that the hydroxyl equivalent and the isocyanate equivalent are 1: 1.