JP3674938B2 - Coating composition and method for producing the same - Google Patents

Description

【００４０】
〔塗料の評価〕
応用実施例１
表２に示す原料で塗料を配合し、ペイントシェイカーにて１時間分散させて、塗料を調製した。分散メディアはガラスビーズを用いた。メディアの量は、塗料と同量である。得られた塗料をドライで５０μになるように鋼板に塗布し、２０℃・６５ＲＨ％・１週間の条件下で静置後、各種塗膜性能評価試験を行った。結果を表２に示す。
塗料配合条件
イソシアネート基／水酸基＝１／１（モル比）
顔料：酸化チタン
総固形分＝４０％
使用溶剤：酢酸ブチル／酢酸エチル／トルエン／ＰＭＡ
＝１／１／１／１（重量比）
ＰＭＡ：プロピレングリコールモノメチルエーテルアセテート
【００４１】
応用比較例１〜４
表２に示す原料を用い、配合条件は応用実施例１と同様にして塗料を調製し、応用実施例１と同様にして評価した。結果を表２に示す。
【００４２】
【表２】

【００４３】
表２における硬化剤は以下の通り。
Ａ：イソホロンジイソシアネートのイソシアヌレート変性ポリイソシアネート の酢酸ブチル溶液
商品名；Ｔ−１８９０Ｅ（独ヒュルス社製）
イソシアネート含量＝１２％（溶剤込み）
固形分＝７０％
Ｂ：ヘキサメチレンジイソシアネートのイソシアヌレート変性ポリイソシアネ ート（日本ポリウレタン工業社製）
イソシアネート含量＝２１％
固形分＝１００％
【００４４】
塗膜測定方法については、以下の通り。
鉛筆硬度試験 ：ＪＩＳ Ｓ−６００６で規定した鉛筆の先端を、４５度の角 度で押し出すようにして塗膜が破れない最高の硬さの鉛筆の 硬度を塗膜の硬度とした。
鏡面光沢度測定：ＪＩＳ Ｋ５４００に規定される方法にて測定した。なお入 射角は６０°とした。
碁盤目剥離試験：塗膜にカッターガイドをそえたカッターナイフを用いて１ｍ ｍ四方の１００個のマス目状の切れ込みを入れ、その上から セロハンテープを圧着し、その後瞬間的に剥がし、塗膜の剥 がれ状態を見た。
○：１０％未満が剥離
△：１０％以上〜５０％未満が剥離
×：５０％以上が剥離
耐屈曲性試験 ：ＪＩＳ Ｋ５４００に準じて測定した。
○：変化無し
×：割れ、はがれが認められる
促進耐候性試験：ＪＩＳ Ｋ５４００のサンシャインカーボンアーク灯式に準 じて測定した。なお、暴露期間は２０００時間とした。
○：塗膜に変化がほとんど認められない
×：光沢低下、変色、割れ、はがれが認められる[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a urethane prepolymer, a method for producing the same, and a coating composition using the same. More specifically, the present invention relates to a urethane prepolymer excellent in adhesion and weather resistance, a production method thereof, and a coating composition using the same and a polyisocyanate.
[0002]
[Prior art]
Urethane two-component curable paints are widely used due to their excellent performance. For example, Japanese Patent Laid-Open No. 3-41173 describes a two-component curable paint using a hydroxyl group-terminated urethane prepolymer of a polyol mainly composed of a polyester polyol using neopentyl glycol. Japanese Patent Application Laid-Open No. 6-143332 discloses a two-component curable paint using a urethane resin composed of polycarbonate polyol and polyisocyanate as a main ingredient. Further, those using polyester polyol or polycarbonate polyol itself as a main component of a two-component curable coating are also widely used.
[0003]
However, since the main agent in the paint described in JP-A-3-41173 is a polyester base, it has poor hydrolysis resistance and the like. Moreover, since the coating material described in JP-A-6-143332 has a large molecular weight of the main agent, the crosslinking density is low, and thus sufficient coating strength cannot be obtained. In the two-component curable paint using polyester polyol as the main agent as it is, the hydrolysis resistance is insufficient, and the polycarbonate polyol used as the main agent is often bifunctional and the coating strength is insufficient. .
[0004]
[Problems to be solved by the invention]
An object of the present invention is to provide a urethane prepolymer excellent in various physical properties such as water resistance, flexibility and adhesion, which are particularly required performances as a paint.
[0005]
[Means for Solving the Problems]
The present invention includes the following (1) to (3).
(1) At least the following (A) polyol, (B) polyisocyanate , and (C) chain extender, the molar ratio of (A) to (C) is (C) / (I) = 0.3 to 5. A coating composition comprising a urethane prepolymer as a main ingredient , which is obtained by reacting with No. 5 and has a hydroxyl value of 100 to 250 mg KOH / g.
(I) Polyol:
A polyol mainly composed of a polycarbonate polyol having a hydroxyl value of 20 to 350 mgKOH / g and an average number of functional groups of 2 to 4.
(B) Polyisocyanate:
An isocyanurate-modified polyisocyanate of isophorone diisocyanate having an isocyanate content of 10 to 40% by weight and an average functional group number of 2.5 to 6.
(C) Chain extender
A mixture of 3-methyl-1,5-pentanediol and trimethylolpropane .
[0006]
(2) At least the following (A) polyol, (B) polyisocyanate , and (C) chain extender, the molar ratio of (A) to (C) is (C) / (I) = 0.3 to 5. A method for producing a coating composition comprising a urethane prepolymer as a main component, which is obtained by reacting in step 5 and has a hydroxyl value of 100 to 250 mgKOH / g.
(I) Polyol:
A polyol mainly composed of a polycarbonate polyol having a hydroxyl value of 20 to 350 mgKOH / g and an average number of functional groups of 2 to 4.
(B) Polyisocyanate:
An isocyanurate-modified polyisocyanate of isophorone diisocyanate having an isocyanate content of 10 to 40% by weight and an average functional group number of 2.5 to 6.
(C) Chain extender
A mixture of 3-methyl-1,5-pentanediol and trimethylolpropane .
[0007]
(3) A coating composition using the urethane prepolymer according to (1) and an isocyanurate-modified polyisocyanate of isophorone diisocyanate .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
First, the raw materials used in the present invention are described.
The polyol (a) used in the present invention is mainly composed of a polycarbonate polyol having a hydroxyl value of 20 to 350 mgKOH / g and an average functional group number of 2 to 4, and the amount used is 50 to The amount is 100% by weight.
Particularly preferred (a) polyol in the present invention is a polyol mainly composed of a polycarbonate polyol having a hydroxyl value of 30 to 250 mgKOH / g and an average functional group number of 2.
[0009]
As the polycarbonate polyol, a dealcoholization reaction between a polyhydric alcohol and ethylene carbonate, dimethyl carbonate, diethyl carbonate, diphenyl carbonate, or the like, or a phenol exchange reaction of a high molecular weight polycarbonate polyol with a polyhydric alcohol. can get. Examples of the polyhydric alcohol include low molecular diols and low molecular polyols having a number average molecular weight of 62 to 300, such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, and 1,2-butanediol. 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 2-ethyl-2- n-butyl-1,3-propanediol, 1,8-octanediol, 1,9-nonanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, bisphenol A, ethylene oxide, propylene oxide, etc. Low molecular diols such as adducts of alkylene oxides , Trimethylolmethane, trimethylolethane, trimethylolpropane, trimethylolbutane, glycerin, 1,2,6-hexanetriol, triethanolamine, cyclohexane-1,2,3-trimethanol, cyclohexane-1,2,4 -Trimethanol, cyclohexane-1,3,5-trimethanol, reaction products of monoethanolamine and glycidol, low molecular triols such as pentaerythritol, low molecular tetraols, and the like.
In the above polyhydric alcohol, 1,6-hexanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-ethyl-2-n-butyl-1,3-propanediol, trimethylolpropane, Low molecular diols and low molecular triols having 5 to 20 carbon atoms such as 1,2,6-hexane are preferable, and low molecular diols and low molecular triols having 5 to 10 carbon atoms are particularly preferable.
[0010]
Moreover, the transesterification product of the above-mentioned polycarbonate polyol and polyester polyol and the transesterification product of polycarbonate polyol and polylactone polyol can also be used suitably. This transesterification product has a hydroxyl value of 20 to 350 mgKOH / g, an average functional group number of 2 to 4, and the weight ratio of polycarbonate polyol to polyester polyol or polylactone polyol is 50 to 100% by weight of polycarbonate polyol. Is the amount.
[0011]
In the present invention, a polyol other than the above-described polycarbonate polyol having a hydroxyl value of 20 to 350 mgKOH / g and an average functional group number of 2 to 4 can be used in combination, polyester polyol, polyesteramide polyol, polyether polyol, polyolefin polyol, Examples include animal and vegetable oil-based polyols and copolyols thereof. These polyols may be used alone or in admixture of two or more.
[0012]
Examples of the polyester polyol and polyesteramide polyol include known succinic acid, adipic acid, sebacic acid, azelaic acid, terephthalic acid, isophthalic acid, orthophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, hexahydroorthophthalic acid, and naphthalene. One or more of polycarboxylic acids such as dicarboxylic acid and trimellitic acid, acid esters, or acid anhydrides, and one or more of the polyhydric alcohols used in the aforementioned polycarbonate polyol, or part of the polyhydric alcohol For replacement, polyamines such as hexamethylenediamine, xylylenediamine, and isophoronediamine, and amino alcohols such as monoethanolamine and diethanolamine are used, and those obtained by a dehydration condensation reaction or a dealcoholization condensation reaction can be used.
Further, lactone polyester polyols obtained by ring-opening polymerization of cyclic ester (lactone) monomers such as ε-caprolactone and γ-valerolactone using the low molecular polyol as an initiator can be mentioned.
[0013]
Examples of the polyether polyol include polyethylene glycol obtained by ring-opening polymerization of ethylene oxide, propylene oxide, tetrahydrofuran and the like, polypropylene glycol, polytetramethylene ether glycol and the like, and a polyether polyol copolymerized with these, and the above-described polyester polyol, Examples thereof include polyester ether polyols using polycarbonate polyol as an initiator.
[0014]
Examples of the polyolefin polyol include hydroxyl group-containing polybutadiene, hydrogenated hydroxyl group-containing polybutadiene, hydroxyl group-containing polyisoprene, hydrogenated hydroxyl group-containing polyisoprene, hydroxyl group-containing chlorinated polypropylene, and hydroxyl group-containing chlorinated polyethylene.
[0015]
Examples of animal and vegetable oil-based polyols include castor oil-based polyols and silk fibroin.
[0016]
Further, if the hydroxyl value is 20 to 350 mgKOH / g and the average number of functional groups is 2 to 4, in addition to dimer acid polyol and hydrogenated dimer acid polyol, epoxy resin, polyamide resin, polyester resin, acrylic resin, rosin resin Resins such as urea resin, melamine resin, phenol resin, coumarone resin, and polyvinyl alcohol can also be suitably used as the polyol.
[0017]
The (c) chain extender used in the present invention is a mixture of 3-methyl-1,5-pentanediol and trimethylolpropane. By using trimethylolpropane, an appropriate crosslinked structure can be introduced into the coating film. The amount of chain extender introduced is, in terms of molar ratio, chain extender / polyol = 0.3-5, and particularly preferably 0.5-4.5.
[0018]
The (b) polyisocyanate used in the present invention is an isocyanurate of an aliphatic and / or alicyclic diisocyanate having an isocyanate content in terms of solid content of 10 to 40% by weight and an average functional group number of 2.5 to 6. The modified polyisocyanate is a main component, and the amount used is 50 to 100% by weight based on the whole polyisocyanate.
The (b) polyisocyanate particularly preferred in the present invention is an aliphatic having an isocyanate content in terms of solid content of 15 to 35 wt%, an average functional group number of 2.5 to 5.5, and a free isocyanate monomer content of 1% or less. Or it is polyisocyanate which has the isocyanurate modified polyisocyanate of alicyclic diisocyanate as a main component.
[0019]
The isocyanurate-modified polyisocyanate used in the present invention is an isocyanurate-modified polyisocyanate of isophorone diisocyanate .
[0020]
In the present invention, a polyisocyanate other than the above isocyanurate-modified polyisocyanate can be used in combination with the polyisocyanate. For example, in addition to the above-mentioned aliphatic diisocyanate and alicyclic diisocyanate, 2,4-tolylene diisocyanate, 2, 6-tolylene diisocyanate, xylene-1,4-diisocyanate, xylene-1,3-diisocyanate, 4,4'-difelmethane diisocyanate, 2,4'-difelmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane dii Soshi Aromatic diisocyanates such as nate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3′-dimethoxydiphenyl-4,4′-diisocyanate, and the like Examples thereof include polymeric bodies, urethane-modified bodies, burette-modified bodies, carbodiimide-modified bodies, uretonimine-modified bodies, uretdione-modified bodies, and a mixture of two or more of these.
[0021]
The isocyanurate-modified polyisocyanate used in the present invention can be obtained by a known reaction. For example, an isocyanurate-forming catalyst such as a tertiary amine, an alkyl-substituted ethyleneimine, a tertiary alkylphosphine, an acetylacetone metal salt, a metal salt of various organic acids, etc. may be used alone or in combination with an isocyanate compound, If necessary, a co-catalyst such as a phenolic hydroxyl group-containing compound or an alcoholic hydroxyl group-containing compound is used, usually in the absence of a solvent at a reaction temperature of 0 to 120 ° C., preferably 20 to 100 ° C. or polyurethane industry Conventional solvents, for example, aromatic hydrocarbon solvents such as toluene and xylene, aliphatic hydrocarbon solvents such as pentane, hexane, and octane, alicyclic hydrocarbon solvents such as cyclopentane, cyclohexane, and methylcyclohexane, Acetone, methyl ethyl ketone, methyl butyl ketone, methyl isobuty Ketone solvents such as ketone, diisobutyl ketone, cyclohexanone, methylcyclohexanone, ether solvents such as diethyl ether, 1,4-dioxane, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol dimethyl ether, propylene glycol monomethyl ether acetate Such as cellosolve solvent such as ester solvent such as ethyl acetate and butyl acetate, polar solvent such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, etc. In a plasticizer. After the reaction, the catalyst may be deactivated to stop the reaction by using, for example, phosphoric acid, methyl paratoluenesulfonate, sulfur or the like which is a stopper.
[0022]
The urethane prepolymer of the present invention may be dissolved in an organic solvent for the purpose of adjusting the viscosity. When dissolving in an organic solvent,
(1) The raw materials are dissolved in an organic solvent and then reacted to form a solution.
(2) It is made into a urethane prepolymer and then dissolved in an organic solvent.
However, the method (1) is preferable because it does not require any special process or apparatus.
[0023]
As the organic solvent, in addition to the organic solvent described above, an alcohol solvent such as methanol, ethanol or isopropanol can be used depending on the reaction conditions.
[0024]
Next, a method for producing the urethane prepolymer of the present invention will be described.
The urethane prepolymer of the present invention can be obtained by a known method, for example, a solution reaction method in which a raw material is dissolved in a single or mixed solvent and then reacted, a solventless mixture in which each raw material is sufficiently mixed and reacted. Reaction method etc. are mentioned.
Moreover, the additive normally used for manufacture of polyurethane resins, such as a catalyst and a stabilizer, can be used at the time of reaction of a urethane prepolymer. Examples of such a catalyst include tertiary amines such as triethylamine and triethylenediamine, metal salts such as potassium acetate and zinc stearate, and organometallic compounds such as dibutyltin laurate and dibutyltin oxide. Examples of the stabilizer include a stabilizer against ultraviolet rays such as substituted benzotriazoles, a stabilizer against thermal oxidation such as a phenol derivative, and the like.
The reaction temperature at this time is 0-120 degreeC, Preferably it is 20-100 degreeC.
[0025]
When synthesizing the urethane prepolymer, considering the average number of functional groups of the organic polyisocyanate and the average number of functional groups of active hydrogen compounds such as polyols, and the (number average) molecular weight of the resulting prepolymer It is important to determine and blend each raw material so as to satisfy such conditions. The blending ratio at which gelation does not occur is described in “J. P. Although the gelation theory calculated theoretically by Flory, Khun, etc. is followed, the reaction is actually carried out at a compounding ratio that takes into consideration the reactivity ratio of the reactive groups contained in each molecule of the active hydrogen compound and the organic polyisocyanate. Thus, the urethane prepolymer can be produced without gelation. Usually, the specific molar ratio of the isocyanate group and the active hydrogen group in the reaction is isocyanate group / active hydrogen group = 0.1 / 1 to 0.9 / 1 (molar ratio), preferably 0.00. The active hydrogen group excess condition is 2/1 to 0.8 / 1 (molar ratio).
[0026]
The urethane prepolymer thus obtained contains a hydroxyl group, and the hydroxyl value is 100 to 250 mgKOH / g, preferably 105 to 245 mgKOH / g (converted to 100% solid content). The average number of functional groups is 2.5 to 5, preferably 3 to 4.5. Furthermore, when this urethane prepolymer is made into a butyl acetate solution having a solid content of 80%, the viscosity is 100 to 100,000 mPa · s / 25 ° C, preferably 150 to 80,000 mPa · s / 25 ° C. The average number of functional groups is calculated from the hydroxyl value and the number average molecular weight determined by gel permeation chromatography.
[0027]
The coating composition of the present invention comprises the urethane prepolymer of the present invention, pigments and dyes, organic solvents for adjusting solid content and viscosity, anti-blocking agents, dispersion stabilizers, thixotropic agents, antioxidants, UV absorbers. , An antifoaming agent, a thickener, a dispersant, a surfactant, a catalyst, a filler, a lubricant, an antistatic agent, an additive such as a plasticizer, and a ball mill, a sand grind mill, and the like. The obtained paint is applied using a brush, spray or the like. If necessary, a curing agent such as melamine or polyisocyanate may be added and used immediately before coating. Of these, polyisocyanate is preferred.
[0028]
The polyisocyanate as the curing agent is an isocyanurate-modified polyisocyanate of isophorone diisocyanate with an emphasis on weather resistance .
[0029]
The compounding ratio of this urethane prepolymer and polyisocyanate is such that the molar ratio of hydroxyl group and isocyanate group present in the system is hydroxyl group / isocyanate group = 3/7 to 7/3, preferably 4/6 to 6/4. . When the blending ratio is outside this range, the cross-linking density of the coating film becomes insufficient, and it is difficult to obtain necessary physical properties.
[0030]
A coating film made of a coating composition using the urethane prepolymer of the present invention has good adhesion and weather resistance, and thus is particularly useful as a coating having water in use.
[0031]
The urethane prepolymer of the present invention can be applied to adhesives, coating agents, sealants, repair agents, elastomers and the like in addition to paints.
[0032]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a urethane prepolymer excellent in water resistance and adhesion. This urethane prepolymer is useful as a paint.
[0033]
【Example】
The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited thereto. In Examples and Comparative Examples, “part” means “part by weight” and “%” means “% by weight”.
[0034]
[Production of urethane prepolymer]
The meanings of the abbreviations in Example 1 and Comparative Examples 1 to 4 and Table 1 are as follows.
Polyol A: Polycarbonate diol obtained from 1,6-hexanediol and diethyl carbonate
Hydroxyl value = 56.1 mgKOH / g
Average number of functional groups = 2
MPD: 3-methyl-1.5-pentanediol 1,6-HD: 1,6-hexanediol DPETT: dipentaerythritol PETT: pentaerythritol TMP: trimethylolpropane TBT: tetrabutyl titanate T-1890 / 100: isophorone Isocyanurate-modified polyisocyanate of diisocyanate (manufactured by Huls, Germany)
Isocyanate content = 17.3%
Solid content = 100%
[0035]
Example 1
A reactor equipped with a stirrer, a nitrogen introducing tube, and a cooling tube was charged with 489 parts of polyol A and 114 parts of MPD and mixed by heating. Next, 22 parts of TMP and 200 parts of butyl acetate were added and mixed uniformly, and then 176 parts of T-1890 / 100 was added and a urethanization reaction was performed at 80 to 85 ° C. Urethane prepolymer U-1 was obtained as the end of the reaction when the peak of the isocyanate group disappeared by infrared absorbance analysis. The solid content of U-1 was 80%, the hydroxyl value (including solvent) was 125 mgKOH / g, the number average molecular weight was 1460, the average number of functional groups was 3.4, and the viscosity was 4800 mPa · s / 25 ° C.
[0036]
Comparative Example 1
A reactor similar to Example 1 was charged with 797 parts of polyol A and 203 parts of DPETT, and subjected to a transesterification reaction at 180 to 190 ° C. for 3 hours to obtain polyol O-1 for coating. The hydroxyl value of O-1 was 312 mgKOH / g, the number average molecular weight was 850, and the average number of functional groups was 4.7.
[0037]
Comparative Examples 2 and 3
Using the raw materials shown in Table 1 , O-2 and 3 were obtained in the same manner as in Comparative Example 1.
[0038]
Comparative Example 4
A reactor similar to Example 1 was charged with 437 parts of DEC, 313 parts of TMP, and 250 parts of 1,6-HD, and subjected to deethanol reaction at 180 to 190 ° C. under normal pressure. When the ethanol distillation rate became slow, 0.01 part of TBT was charged, and then the pressure reduction was started to further proceed the reaction. The pressure was gradually reduced, and finally up to 5 Torr. When the terminal ethyl group could not be confirmed by NMR, the reaction was terminated to obtain paint polyol O-4. The hydroxyl value of O-4 was 330 mgKOH / g, the number average molecular weight was 880, and the average functional group number was 5.1.
[0039]
[Table 1]

[0040]
[Evaluation of paint]
Application Example 1
A paint was blended with the raw materials shown in Table 2, and dispersed for 1 hour with a paint shaker to prepare a paint. Glass beads were used as the dispersion media. The amount of media is the same as the paint. The obtained paint was applied to a steel plate to a dry thickness of 50 μm, and allowed to stand under conditions of 20 ° C., 65 RH%, 1 week, and then various coating film performance evaluation tests were performed. The results are shown in Table 2 .
Paint blending conditions Isocyanate group / Hydroxylol = 1/1 (Molar ratio)
Pigment: Titanium oxide Total solid content = 40%
Solvent used: butyl acetate / ethyl acetate / toluene / PMA
= 1/1/1/1 (weight ratio)
PMA: Propylene glycol monomethyl ether acetate
Application Comparative Examples 1-4
Using the raw materials shown in Table 2 , the coating conditions were prepared in the same manner as in Application Example 1 and the composition conditions were evaluated in the same manner as in Application Example 1. The results are shown in Table 2 .
[0042]
[Table 2]

[0043]
The curing agents in Table 2 are as follows.
A: Isophorone diisocyanate isocyanurate-modified polyisocyanate in butyl acetate solution Trade name; T-1890E (manufactured by Huls, Germany)
Isocyanate content = 12% (including solvent)
Solid content = 70%
B: isocyanurate-modified polyisocyanate over the city of hexamethylene diisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd.)
Isocyanate content = 21%
Solid content = 100%
[0044]
The coating film measurement method is as follows.
Pencil hardness test: The hardness of a pencil with the highest hardness at which the coating film cannot be broken by extruding the tip of the pencil specified in JIS S-6006 at an angle of 45 degrees was defined as the hardness of the coating film.
Specular gloss measurement: Measured by the method defined in JIS K5400. The incident angle was 60 °.
Cross-cut peel test: Using a cutter knife with a cutter guide on the paint film, make 100 square cuts of 1 mm square, press the cellophane tape on top of it, and then peel off instantaneously. I saw the state of peeling.
○: Less than 10% peeled
Δ: 10% to less than 50% peeled
X: 50% or more peeled Bending resistance test: Measured according to JIS K5400.
○: No change
X: Cracking and peeling are observed Accelerated weather resistance test: Measured according to JIS K5400 sunshine carbon arc lamp type. The exposure period was 2000 hours.
○: Almost no change in coating film
X: Gloss reduction, discoloration, cracking, peeling are recognized

Claims (3)

At least the following (A) polyol, (B) polyisocyanate , and (C) chain extender are reacted at a molar ratio of (A) to (C) of (C) / (I) = 0.3 to 5 A coating composition comprising a urethane prepolymer as a main ingredient, wherein the composition is obtained by the above-described process and has a hydroxyl value of 100 to 250 mgKOH / g.
(I) Polyol:
A polyol mainly composed of a polycarbonate polyol having a hydroxyl value of 20 to 350 mgKOH / g and an average number of functional groups of 2 to 4.
(B) Polyisocyanate:
An isocyanurate-modified polyisocyanate of isophorone diisocyanate having an isocyanate content of 10 to 40% by weight and an average functional group number of 2.5 to 6.
(C) Chain extender
A mixture of 3-methyl-1,5-pentanediol and trimethylolpropane . At least the following (A) polyol, (B) polyisocyanate , and (C) chain extender are reacted at a molar ratio of (A) to (C) of (C) / (I) = 0.3 to 5 A method for producing a coating composition comprising a urethane prepolymer as a main ingredient , wherein the hydroxyl value is 100 to 250 mgKOH / g.
(I) Polyol:
A polyol mainly composed of a polycarbonate polyol having a hydroxyl value of 20 to 350 mgKOH / g and an average number of functional groups of 2 to 4.
(B) Polyisocyanate:
An isocyanurate-modified polyisocyanate of isophorone diisocyanate having an isocyanate content of 10 to 40% by weight and an average functional group number of 2.5 to 6.
(C) Chain extender
A mixture of 3-methyl-1,5-pentanediol and trimethylolpropane . A coating composition using the urethane prepolymer according to claim 1 and an isocyanurate-modified polyisocyanate of isophorone diisocyanate .