JP2004275965A - Method for forming coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a laminated coating film which has an excellent resistance to chipping by a 3-coat 1-bake method. <P>SOLUTION: A laminated coating film is formed by the 3-coat 1-bake method using a 5% to 30% by weight of a urethane-modified polyester resin (a) having a number-average molecular weight between 1,500 and 3,000, which is obtained by causing a hydroxy group-containing polyester resin being obtained by polycondensation between an acid component containing isophthalic acid of 80 mol% or more and a polyhydric alcohol and having a glass transition temperature (Tg) ranging from 40°C to 80°C to react with an aliphatic isocyanate compound, a 30% to 60% by weight of polyolefin elastmer (b) having an acid group and/or a hydroxy group, and an intermediate coat (c) containing a 10% to 30% by weight of a block isocyanate compound. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３０】
エチレン性不飽和基を有する酸無水物としては、例えば、無水マレイン酸、無水イタコン酸、無水コハク酸等が挙げられる。これらのうち、無水マレイン酸を使用するのが特に好ましい。
【００３１】
水酸基を有するポリオレフィンとエチレン性不飽和基を有する酸又は酸無水物との反応は、当業者に知られた方法で行うことができる。
【００３２】
ポリオレフィン系マクロマーは、水酸基を有するポリオレフィンとジイソシアネート化合物とエチレン性不飽和基を有するアルコールとを反応させて得てもよい。エチレン性不飽和基を有するアルコールとして、例えば水酸基含有アクリルモノマーを挙げることができる。
【００３３】
ジイソシアネート化合物としては、ウレタン変性ポリエステル樹脂の調製に使用した脂肪族ジイソシアネートを用いることができる。特に好ましくはイソホロンジイソシアネートである。
【００３４】
水酸基含有アクリルモノマーとしては、例えば、ヒドロキシエチルメタクリレート（ＨＥＭＡ）、ヒドロキシエチルアクリレート（ＨＥＡ）、ヒドロキシプロピルメタクリレート（ＨＰＭＡ）、ヒドロキシプロピルアクリレート（ＨＰＡ）、ヒドロキシブチルアクリレート（ＨＢＡ）などを用いることができる。これらは単独でもしくは二種以上を混合して用いることができる。これらの水酸基含有アクリルモノマーのうち、特に好ましくはヒドロキシエチル（メタ）アクリレートが用いられる。
【００３５】
水酸基を有するポリオレフィンとジイソシアネート化合物とエチレン性不飽和基を有するアルコールとの反応は、当業者に知られた方法で行うことができる。
【００３６】
ポリオレフィン系マクロマーと共重合されるエチレン性不飽和化合物には、エチレン性不飽和モノマー、不飽和アクリル樹脂、及び不飽和ポリエステル樹脂等が含まれる。
【００３７】
エチレン性不飽和モノマーとしては、例えば、アクリルモノマーを挙げることができ、具体的には、メチルアクリレート、メチルメタクリレート、アクリル酸、メタクリル酸、ヒドロキシエチルアクリレート、ヒドロキシエチルメタクリレート、ｎ−ブチルアクリレート、ｎ−ブチルメタクリレートなどの一般的なアクリルモノマーを用いることができる。これらのアクリルモノマーは単独で用いてもよいし、二種以上を混合して用いてもよい。さらには、スチレンや酢酸ビニルなどのこれらのアクリルモノマーと共重合可能な他のモノマーを併用してもよい。
【００３８】
不飽和アクリル樹脂は、アクリル樹脂に不飽和結合を導入したものである。例えばアクリル樹脂のカルボキシル基にグリシジルメタクリレートを付加することにより、アクリル樹脂のヒドロキシル基に不飽和結合を有する酸無水物を付加することにより、あるいはアクリル樹脂のオキシラン基に不飽和結合を有するカルボン酸を付加することにより得ることができる。
【００３９】
不飽和アクリル樹脂としては、酸価が０〜２００ｍｇＫＯＨ／ｇ、さらに好ましくは０〜１５０ｍｇＫＯＨ／ｇであり、水酸基価が１０〜３００、さらに好ましくは１０〜２００であり、数平均分子量が１０００〜５００００、さらに好ましくは２０００〜５０００であり、ヨウ素価が０．５〜１００、さらに好ましくは０．５〜７０であるものが好ましい。
【００４０】
不飽和ポリエステル樹脂は、一般的な方法により得ることができ、例えば、ポリオール化合物と不飽和基を有する多塩基酸化合物との反応により得ることができる。
【００４１】
不飽和ポリエステル樹脂としては、酸価が０〜２００ｍｇＫＯＨ／ｇ、さらに好ましくは０〜１５０ｍｇＫＯＨ／ｇであり、水酸基価が１０〜３００、さらに好ましくは１０〜２００であり、数平均分子量が１０００〜５００００、さらに好ましくは１０００〜４０００であり、ヨウ素価が０．５〜１００、さらに好ましくは０．５〜７０であるものが好ましい。
【００４２】
ポリオレフィン系マクロマーとエチレン性不飽和化合物との共重合は、当業者に知られた方法で行うことができる。例えば、溶液重合法によれば、ポリオレフィン系マクロマーを適当な溶媒に溶解し、昇温した後、撹拌下にエチレン性不飽和化合物を適当な重合開始剤と共に滴下すればよい。
【００４３】
反応に使用するのに適当な溶媒の例としては、白灯油、エチルシクロヘキサンおよびシェルゾールＴＨ（商品名、シェルジャパン社製）のような脂肪族炭化水素、トルエン、キシレンおよびスワゾール１００（商品名、丸善石油化学社製）のような芳香族炭化水素、酢酸ブチルおよびユーカエステルＥＥＰ（商品名、ユニオンカーバイド社製）のようなエステル、ブタノール、イソブタノールおよびエチレングリコールモノブチルエーテルのようなアルコール等が挙げられる。
【００４４】
重合開始剤の例としては、ｔ−ブチルパーオキシ−２−エチルヘキサノエート、ベンゾイルパーオキサイドおよびジフタルパーオキサイドのような過酸化物、アゾビスイソブチロニトリルおよび２，２’−アゾビス（２，４−ジメチルバレロニトリル）のようなアゾ系開始剤等が挙げられる。
【００４５】
反応温度は一般に６０〜１６０℃、好ましくは８０〜１４０℃に調節される。反応の終点は反応溶液の粘度が定常になることによって決定される。
【００４６】
得られるポリオレフィンエラストマーは、数平均分子量が３０００〜２０００００、好ましくは１００００〜１０００００である。数平均分子量が３０００より小さいと積層塗膜の外観が不良となる。また、２０００００を超えるとポリオレフィンエラストマーの溶剤溶解性が不良となる。
【００４７】
さらに、ポリオレフィンエラストマーが水酸基および／またはカルボキシル基を有するのが好ましい。より好ましくは、ポリオレフィンエラストマーが水酸基およびカルボキシル基の両方を有する。これらの官能基を１種以上含むポリオレフィンエラストマーを使用することによって、得られる積層塗膜の物性および耐チッピング性をさらに向上させることができる。
【００４８】
ポリオレフィンエラストマーの酸価は、好ましくは１〜５０ｍｇＫＯＨ／ｇ、より好ましくは５〜３０ｍｇＫＯＨ／ｇである。酸価が５０ｍｇＫＯＨ／ｇを超えると、得られる積層塗膜の耐水性が低下する。また、ポリオレフィンエラストマーの水酸基価は、好ましくは１〜２００、より好ましくは５０〜１５０である。水酸基価が２００を超えると、得られる積層塗膜の耐水性が低下する。
【００４９】
中塗り塗料に含まれるポリオレフィンエラストマー（ｂ）の量は、樹脂固形分重量を基準にして３０〜６０重量％、好ましくは３０〜４０重量％である。含有量が３０％を下回ると得られる積層塗膜の物性値および塗膜外観の向上がみられない。含有量が６０％を上回ると塗料の相溶性が低下して不均一な塗膜となる。
【００５０】
中塗り塗料の成分としてポリオレフィンエラストマーを含有させることで、塗膜の伸び率が向上し、塗膜の耐チッピング性も向上する。また、中塗り塗膜と上塗り塗膜の相溶性が低下してウェット状態の中塗り塗膜にベース塗膜やクリヤー塗膜が浸透し難くなるため混相が防止され、仕上がり外観、特に艶感が向上する。
【００５１】
ブロックイソシアネート化合物（ｃ）は、ウレタン変性ポリエステル樹脂（ａ）およびポリオレフィンエラストマー（ｂ）を硬化させるための成分である。
【００５２】
ブロックイソシアネート化合物は、脂肪族イソシアネート又はそれらの誘導体にブロック剤を付加させて得ることができる。ブロックイソシアネート化合物は、加熱されるとブロック剤が解離してイソシアネート基が発生し、ウレタン変性ポリエステル樹脂中の水酸基と反応し硬化させる。
【００５３】
脂肪族イソシアネート及び誘導体の例には、ウレタン変性ポリエステル樹脂を調製する際に使用した化合物が挙げられる。ブロック剤の例には、アセチルアセトン、アセト酢酸エチル、マロン酸エチルなどの活性メチレン基を有する化合物が挙げられる。かかるブロック剤を使用することで、塗膜の弾性が向上し、塗膜の耐チッピング性も向上する。
【００５４】
このようなブロックイソシアネート化合物は、例えば、旭化成社より、活性メチレン型ブロックイソシアネート「デュラネートＭＦ−Ｋ６０Ｘ」として市販されている。
【００５５】
中塗り塗料に含まれるブロックイソシアネート化合物（ｃ）の量は、樹脂固形分重量を基準にして１０〜３０重量％、好ましくは１５〜２５重量％である。含有量が１０重量％を下回ると硬化性が不十分となり、３０重量％を上回ると硬化膜が堅くなりすぎ脆くなる。
【００５６】
メラミン樹脂（ｄ）は、特に限定されるものではなく、メチル化メラミン樹脂、ブチル化メラミン樹脂あるいはメチル、ブチル混合型メラミン樹脂を用いることができる。例えば三井東圧株式会社から市販されている「サイメル−３０３」、「サイメル２５４」、「ユーバン１２８」、「ユーバン２０Ｎ６０」、住友化学工業株式会社から市販されている「スミマールシリーズ」等が挙げられる。
【００５７】
中塗り塗料に含まれるメラミン樹脂（ｄ）の量は樹脂固形分重量を基準にして最大２０重量％、より好ましくは、５〜１５重量％である。メラミン樹脂の含有量が２０重量％を上回ると硬化膜が堅くなりすぎ脆くなる。
【００５８】
コアシェル構造を有する非水デイスパージョン樹脂（ｅ）は、分散安定樹脂と有機溶剤との混合液中で、重合性単量体を共重合させることにより、この混合液に不溶な非架橋樹脂粒子として調製することができる。非架橋樹脂粒子を得るため分散安定樹脂の存在下で共重合させる単量体は、ラジカル重合性の不飽和単量体であれば特に制限されない。
【００５９】
但し、上記分散安定樹脂及び非水ディスパージョンを合成するためには、官能基を有する重合性単量体を用いることが好ましい。官能基を有する非水ディスパージョンは官能基を含有せしめた分散安定樹脂と共に後記硬化剤と反応して三次元に架橋した塗膜を形成することができるからである。
【００６０】
上記分散安定樹脂は、非水ディスパージョンを有機溶剤中で安定に合成できるものであれば特に限定されるものではない。具体的には、水酸基価が１０〜２５０、好ましくは２０〜１８０であり、酸価が０〜１００ｍｇＫＯＨ／ｇ、好ましくは０〜５０ｍｇＫＯＨ／ｇ、数平均分子量が８００〜１０００００、好ましくは１０００〜２００００であるアクリル樹脂、ポリエステル樹脂、ポリエーテル樹脂、ポリカーボネート樹脂、ポリウレタン樹脂等を用いることが好ましい。上限を越えると、樹脂のハンドリング性が低下し、非水ディスパージョン自身のハンドリングも低下する。下限を下回ると塗膜にした場合に樹脂が脱離したり、粒子の安定性が低下する恐れがある。
【００６１】
上記分散安定樹脂の合成方法は、特に限定されるものではないが、ラジカル重合開始剤の存在下でラジカル重合により得る方法、縮合反応や付加反応により得る方法等が好ましいものとして挙げられる。更に、上記分散安定樹脂を得るために用いられる単量体としては、樹脂の特性に応じて適宜選択され得るが、後述する非水ディスパージョンを合成するために用いられる重合性単量体が有するような、水酸基、酸基等の官能基を有するものを用いることが好ましく、更に必要に応じて、グリシジル基、イソシアネート基等の官能基を有するものを用いてもよい。
【００６２】
また、上記分散安定樹脂と上記重合性単量体との構成比率は目的に応じて任意に選択できるが、例えば、該両成分の合計重量に基いて分散安定樹脂は３〜８０重量％、特に５〜６０重量％、重合性単量体は９７〜２０重量％、特に９５〜４０重量％が好ましい。さらに有機溶剤中における分散安定樹脂と重合性単量体との合計濃度は合計重量を基準に、３０〜８０重量％、特に４０〜６０重量％が好ましい。
【００６３】
上記非水ディスパージョンは、分散安定樹脂の存在下でラジカル重合性の単量体を重合させることによって得ることができる。この非水ディスパージョンとしては、水酸基価が５０〜４００、好ましくは１００〜３００であり、酸価が０〜２００ｍｇＫＯＨ／ｇ、好ましくは０〜５０ｍｇＫＯＨ／ｇ、平均粒径（Ｄ_５０）が０．０５〜１０μｍ、好ましくは０．１〜２μｍであるものが好ましい。下限を越えると粒子形状を維持できず、上限を越えると塗料に分散した場合の安定性が低下する。
【００６４】
上記非水ディスパージョンを合成するために用いられる官能基を有する重合性単量体としてその代表的なものは以下のとおりである。水酸基を有するものとして、例えば、（メタ）アクリル酸ヒドロキシエチル、（メタ）アクリル酸ヒドロキシプロピル、（メタ）アクリル酸ヒドロキシブチル、メタクリル酸ヒドロキシメチル、アリルアルコール、（メタ）メタクリル酸ヒドロキシエチルとε−カプロラクトンとの付加物等が挙げられる。
【００６５】
一方、酸性基を有するものとしては、カルボキシル基、スルホン酸基等を有する重合性単量体が挙げられる。カルボキシル基を有するものの例としては、（メタ）アクリル酸、クロトン酸、エタアクリル酸、プロピルアクリル酸、イソプロピルアクリル酸、イタコン酸、無水マレイン酸、フマール酸等が挙げられる。スルホン酸基を有する重合性単量体の例としては、ｔ−ブチルアクリルアミドスルホン酸等が挙げられる。酸性基を有する重合性単量体を用いる場合は、酸性基の一部はカルボキシル基であることが好ましい。
【００６６】
また、（メタ）アクリル酸グリシジル等のグリシジル基含有不飽和単量体、ｍ−イソプロペニル−α，α−ジメチルベンジルイソシアネート、アクリル酸イソシアナトエチル等のイソシアネート基含有不飽和単量体等が官能基を有する重合性単量体として挙げられる。
【００６７】
この他の重合性単量体としては、例えば、（メタ）アクリル酸メチル、（メタ）アクリル酸エチル、（メタ）アクリル酸イソプロピル、（メタ）アクリル酸ｎ−プロピル、（メタ）アクリル酸ｎ−ブチル、（メタ）アクリル酸ｔ−ブチル、（メタ）アクリル酸イソブチル、（メタ）アクリル酸２−エチルヘキシル、（メタ）アクリル酸ｎ−オクチル、（メタ）アクリル酸ラウリル、（メタ）アクリル酸ステアリル、メタクリル酸トリデシル等の（メタ）アクリル酸アルキルエステル、油脂肪酸とオキシラン構造を有するアクリル酸またはメタクリル酸エステルモノマーとの付加反応物（例えば、ステアリン酸とグリシジルメタクリレートの付加反応物等）、Ｃ_３以上のアルキル基を含むオキシラン化合物とアクリル酸またはメタクリル酸との付加反応物、スチレン、α−メチルスチレン、ο−メチルスチレン、ｍ−メチルスチレン、ｐ−メチルスチレン、ｐ−ｔ−ブチルスチレン、（メタ）アクリル酸ベンジル、イタコン酸エステル（イタコン酸ジメチルなど）、マレイン酸エステル（マイレン酸ジメチルなど）、フマール酸エステル（フマール酸ジメチルなど）、その他に、アクリロニトリル、メタクリロニトリル、メチルイソプロペニルケトン、酢酸ビニル、ベオバモノマー（シェル化学社製、商品名）、ビニルプロピオネート、ビニルピバレート、エチレン、プロピレン、ブタジエン、Ｎ，Ｎ−ジメチルアミノエチルアクリレート、Ｎ，Ｎ−ジメチルアミノエチルメタクリレート、アクリルアミド、ビニルピリジン等の重合性単量体が挙げられる。
【００６８】
上記非水ディスパージョンを得るための重合反応は、ラジカル重合開始剤の存在下で行うことが好ましい。ラジカル重合開始剤としては、例えば２，２’−アゾビスイソブチロニトリル、２，２’−アゾビス（２，４−ジメチルバレロニトリル）等のアゾ系開始剤、ベンゾイルパーオキサイド、ラウリルパーオキサイド、ｔ−ブチルパーオクトエート等が挙げられる。これらの開始剤の使用量は重合性単量体合計１００重量部あたり０．２〜１０重量部、好ましくは０．５〜５重量部が望ましい。分散安定樹脂を含有する有機溶剤中での非水ディスパージョンを得るための重合反応は、一般に６０〜１６０℃程度の温度範囲で約１〜１５時間行うことが好ましい。
【００６９】
また、上記非水ディスパージョンは架橋重合体微粒子と異なり、塗料中においては粒子成分であるが、塗膜においては粒子構造を形成しない特徴を有する。つまり非水ディスパージョンは粒子内に架橋部位が存在しないため、焼き付け過程で粒子形状が変化し、樹脂成分となり得る点が架橋重合体微粒子とは異なる。
【００７０】
更に、例えば色材、４８巻（１９７５）第２８頁〜第３４頁中に記載されているＮＡＤ塗料に用いられるＮＡＤ（Ｎｏｎ Ａｑｕｅｏｕｓ Ｄｉｓｐｅｒｓｉｏｎ、非水系重合体分散液）と言われる樹脂粒子も使用することができる。
【００７１】
中塗り塗料中に含まれる非水デイスパージョン樹脂（ｅ）の量は、樹脂固形分重量を基準にして最大１５重量％、好ましくは５〜１２重量％である。含有量が１５重量％を上回ると耐チッピング性能が低下する。
【００７２】
非水デイスパージョン樹脂（ｅ）を使用することで塗膜の界面制御が容易になり、仕上がり外観が向上する。
【００７３】
偏平顔料（ｆ）としては、マイカ、アルミナ、タルク及びシリカ等を用いることができるが、タルクを用いることがチッピング性能の観点から好ましい。
【００７４】
扁平顔料（ｆ）の寸法は、長径が１〜１０μｍであり、数平均粒径が２〜６μｍであることが好ましい。長径が上記範囲外であると塗膜外観が劣ったり、十分な耐チッピング性能が出なくなり、数平均粒径が上記範囲外であると同様に塗膜外観が劣ったり、十分な耐チッピング性能が出なくなる。
【００７５】
扁平顔料（ｆ）の含有量は、塗料中の樹脂固形分重量を１００重量部として、０．４〜２重量部である。０．５〜１．５重量部であることが更に好ましい。上記範囲外では、下地塗膜との付着性が低下するので十分なチッピング性能を得られない。
【００７６】
上記その他に含有させることができる樹脂としては、特に限定されるものではなく、アクリル樹脂、ポリエステル樹脂、アルキド樹脂、エポキシ樹脂等を挙げることができ、１種または２種以上を併用して用いることができる。
【００７７】
また着色顔料として、例えば有機系のアゾキレート系顔料、不溶性アゾ系顔料、縮合アゾ系顔料、フタロシアニン系顔料、インジゴ顔料、ペリノン系顔料、ペリレン系顔料、ジオキサン系顔料、キナクリドン系顔料、イソインドリノン系顔料、金属錯体顔料等が挙げられ、無機系では黄鉛、黄色酸化鉄、ベンガラ、カーボンブラック、二酸化チタン等を用いることができる。また、体質顔料として、炭酸カルシウム、硫酸バリウム、アルミニウム粉、カオリン等が用いることができる。
【００７８】
標準的には、カーボンブラックと二酸化チタンとを主要顔料としたグレー系のものが用いられる。更に、上塗りとの色相を合わせたものや各種の着色顔料を組み合わせたものを用いることもできる。
【００７９】
また、上記中塗り塗料には、上塗り塗膜とのなじみ防止、塗装作業性を確保するために、粘性制御剤を添加することができる。粘性制御剤としては、一般にチクソトロピー性を示すものを含有でき、例えば、脂肪酸アマイドの膨潤分散体、アマイド系脂肪酸、長鎖ポリアミノアマイドの燐酸塩等のポリアマイド系のもの、酸化ポリエチレンのコロイド状膨潤分散体等のポリエチレン系等のもの、有機酸スメクタイト粘土、モンモリロナイト等の有機ベントナイト系のもの、ケイ酸アルミ、硫酸バリウム等の無機顔料、顔料の形状により粘性が発現する扁平顔料、架橋樹脂粒子等を粘性制御剤として挙げることができる。
【００８０】
本発明で用いられる中塗り塗料の塗装時の全固形分量は、２０〜８０重量％であり、好ましくは２５〜６５重量％である。この範囲外では塗料安定性が低下する。また上限を越えると、粘性が高すぎて塗膜外観が低下し、下限を下回ると粘性が低すぎてなじみやムラ等の外観不良が発生する。
【００８１】
本発明に用いられる中塗り塗料中には、上記成分の他に塗料に通常添加される添加剤、例えば、表面調整剤、酸化防止剤、消泡剤等を配合してもよい。これらの配合量は当業者の公知の範囲である。
【００８２】
また、ウレタン変性ポリエステル樹脂その他に別の樹脂を含有させることもできる。このような樹脂としては、特に限定されるものではなく、アクリル樹脂、ポリエステル樹脂、アルキド樹脂、エポキシ樹脂等を挙げることができ、１種または２種以上を併用して用いることができる。
【００８３】
本発明に用いられる塗料組成物の製造方法は、後述するものを含めて、特に限定されず、顔料等の配合物をニーダーまたはロール、ＳＧミル等を用いて混練、分散する等の当業者に周知の全ての方法を用い得る。
【００８４】
ベース塗膜
本発明の塗膜形成方法において用いられるベース塗料は、クリヤー塗料と共に上塗り塗膜を構成するために用いるものである。このベース塗料には、塗膜形成性樹脂、硬化剤、着色顔料、必要に応じて光輝性顔料等が含まれる。
【００８５】
上記ベース塗料に含有される塗膜形成性樹脂としては、特に限定されるものではなく、アクリル樹脂、ポリエステル樹脂、アルキド樹脂、エポキシ樹脂、ウレタン樹脂等を好ましいものとして挙げることができ、１種または２種以上を併用して用いることができる。
【００８６】
上記塗膜形成性樹脂は、硬化剤と組み合わせて用いることができるが、得られた塗膜の諸性能、コストの点からアミノ樹脂および／またはブロックイソシアネート樹脂が好ましいものとして用いられる。
【００８７】
上記硬化剤の含有量は、塗膜形成性樹脂の固形分重量に対して２０〜６０重量％とすることが好ましく、更に好ましくは３０〜５０重量％である。含有量が２０重量％を下回ると硬化性が不十分となり、６０重量％を上回ると硬化膜が堅くなりすぎ脆くなる。
【００８８】
また、上記着色顔料としては、例えば、上述の中塗り塗料についての記載で挙げたもの等を含有することができる。
【００８９】
上記ベース塗料に必要に応じて含まれる光輝性顔料としては、形状は特に限定されず、更に着色されていても良いが、例えば、平均粒径（Ｄ_５０）が２〜５０μｍであり、且つ厚さが０．１〜５μｍであるものが好ましい。また、平均粒径が１０〜３５μｍの範囲のものが光輝感に優れ、更に好適に用いられる。光輝性顔料の、上記塗料中の顔料濃度（ＰＷＣ）は、一般的に２０．０％重量以下である。好ましくは、０．０１〜１８．０重量％であり、より好ましくは、０．１〜１５．０重量％である。光輝剤の含有量が２０．０重量％を超えると、塗膜外観が低下する。
【００９０】
上記光輝性顔料としては、アルミニウム、銅、亜鉛、鉄、ニッケル、スズ、酸化アルミニウム等の金属または合金等の無着色あるいは着色された金属製光輝剤及びその混合物が挙げられる。更に、干渉マイカ顔料、ホワイトマイカ顔料、グラファイト顔料その他の着色、有色扁平顔料等を併用しても良い。
【００９１】
上記光輝性顔料およびその他の全ての顔料を含めた塗料中の全顔料濃度（ＰＷＣ）としては、０．１〜５０重量％であり、好ましくは、０．５〜４０重量％であり、より好ましくは、１．０〜３０重量％である。上限を越えると塗膜外観が低下する。
【００９２】
更に、上記ベース塗料には、上述の中塗り塗料同様に、塗装作業性を確保するために、粘性制御剤を添加することが好ましい。粘性制御剤は、ムラ及びたれのない塗膜を良好に形成するために用いられるのであり、一般にチクソトロピー性を示すものを含有できる。このようなものとして、例えば、上述の中塗り塗料についての記載で挙げたものを含有することができる。
【００９３】
本発明に用いられるベース塗料中には、上記成分の他に塗料に通常添加される添加剤、例えば、表面調整剤、増粘剤、酸化防止剤、紫外線防止剤、消泡剤等を配合してもよい。これらの配合量は当業者の公知の範囲である。
【００９４】
本発明で用いられるベース塗料の塗装時の全固形分量は、１０〜６０重量％であり、好ましくは１５〜５０重量％である。上限および下限を越えると塗料安定性が低下する。上限を越えると、粘性が高すぎて塗膜外観が低下し、下限を下回ると粘性が低すぎてなじみやムラ等の外観不良が発生する。
【００９５】
クリヤー塗膜
上記クリヤー塗膜の形成にはクリヤー塗料が用いられる。このクリヤー塗料は、特に限定されず、塗膜形成性熱硬化性樹脂および硬化剤等を含有するものを利用できる。このクリヤー塗料の形態としては、溶剤型、水性型および粉体型のものが挙げられる。
【００９６】
上記溶剤型クリヤー塗料の好ましい例としては、透明性あるいは耐酸エッチング性等の点から、アクリル樹脂および／またはポリエステル樹脂とアミノ樹脂との組合わせ、アクリル樹脂および／またはポリエステル樹脂とイソシアネート化合物との組合わせ、あるいはカルボン酸・エポキシ硬化系を有するアクリル樹脂および／またはポリエステル樹脂等が挙げられる。
【００９７】
また、上記水性型クリヤー塗料の例としては、上記溶剤型クリヤー塗料の例として挙げたものに含有される塗膜形成性樹脂を、塩基で中和して水性化した樹脂を含有するものが挙げることができる。この中和は重合の前又は後に、ジメチルエタノールアミンおよびトリエチルアミンのような３級アミンを添加することにより行うことができる。
【００９８】
一方、粉体型クリヤー塗料としては、熱可塑性および熱硬化性粉体塗料のような通常の粉体塗料を用い得ることができる。良好な物性の塗膜が得られるため、熱硬化性粉体塗料が好ましい。熱硬化性粉体塗料の具体的なものとしては、エポキシ系、アクリル系およびポリエステル樹脂系の粉体クリヤー塗料等が挙げられるが、耐候性が良好なアクリル系粉体クリヤー塗料が特に好ましい。
【００９９】
本発明に用いる粉体型クリヤー塗料として、硬化時の揮散物が無く、良好な外観が得られ、そして黄変が少ないことから、エポキシ含有アクリル樹脂／多価カルボン酸の系の粉体塗料が特に好ましい。
【０１００】
更に、上記クリヤー塗料には、上述の中塗り塗料同様に、塗装作業性を確保するために、粘性制御剤を添加されていることが好ましい。粘性制御剤は、一般にチクソトロピー性を示すものを含有できる。このようなものとして、例えば、上述の中塗り塗料についての記載で挙げたものを含有することができる。また必要により、硬化触媒、表面調整剤等を含むことができる。
【０１０１】
基材
本発明の塗膜形成方法は、種々の基材、例えば金属、プラスチック、発泡体等、特に金属表面、および鋳造物に有利に用い得るが、カチオン電着塗装可能な金属製品に対し、特に好適に使用できる。
【０１０２】
上記金属製品としては、例えば、鉄、銅、アルミニウム、スズ、亜鉛等およびこれらの金属を含む合金が挙げられる。具体的には、乗用車、トラック、オートバイ、バス等の自動車車体および部品が挙げられる。これらの金属は予めリン酸塩、クロム酸塩等で化成処理されたものが特に好ましい。
【０１０３】
また、本発明のメタリック塗膜形成方法に用いられる基材には、化成処理された鋼板上に電着塗膜が形成されていても良い。電着塗膜を形成する電着塗料としては、カチオン型及びアニオン型を使用できるが、カチオン型電着塗料組成物が防食性において優れた積層塗膜を与えるため好ましい。
【０１０４】
塗膜形成方法
本発明の塗膜形成方法では、基材上に、中塗り塗料により中塗り塗膜、ベース塗料によりベース塗膜及びクリヤー塗料によりクリヤー塗膜を、順次ウエット・オン・ウエットで形成する。
【０１０５】
本発明で中塗り塗料を自動車車体に塗装する場合は、外観を高めるために、エアー静電スプレー塗装による多ステージ塗装、好ましくは２ステージで塗装するか、或いは、エアー静電スプレー塗装と、通称「μμ（マイクロマイクロ）ベル」、「μ（マイクロ）ベル」あるいは「メタベル」等と言われる回転霧化式の静電塗装機とを組み合わせた塗装方法等により塗膜を形成することができる。
【０１０６】
本発明における、中塗り塗料による乾燥塗膜の膜厚は所望の用途により変化するが、多くの場合１０〜６０μｍが有用である。上限を越えると、鮮映性が低下したり、塗装時にムラあるいは流れ等の不具合が起こることがあり、下限を下回ると、下地が隠蔽できず膜切れが発生する。
【０１０７】
本発明の塗膜形成方法では更に、未硬化の中塗り塗膜の上に、ベース塗料、およびクリヤー塗料をウエット・オン・ウエットで塗布し、ベース塗膜、およびクリヤー塗膜を形成する。
【０１０８】
本発明の方法におけるベース塗膜を形成する為に用いるベース塗料は、上記中塗り塗料と同様に、エアー静電スプレー塗装あるいはメタベル、μμベル、μベル等の回転霧化式の静電塗装機により塗装することができ、その塗膜の乾燥膜厚は５〜３５μｍに設定することができ、好ましくは７〜２５μｍである。ベース塗膜の膜厚が３５μｍを超えると、鮮映性が低下したり、塗膜にムラまたは流れが生じることがあり、５μｍ未満であると、下地隠蔽性が不充分となり、膜切れ（塗膜が不連続な状態）が生じることがあるため、いずれも好ましくない。
【０１０９】
本発明の塗膜形成方法において、上記ベース塗膜を形成した後に塗装されるクリヤー塗膜は、上記ベース塗膜に起因する凹凸、光輝性顔料が含まれる場合に、これに起因して生じる微細な突起等を隠蔽し、保護するために形成される。塗装方法として具体的には、先に述べたμμベル、μベル等の回転霧化式の静電塗装機により塗膜形成することが好ましい。
【０１１０】
上記クリヤー塗料により形成されるクリヤー塗膜の乾燥膜厚は、一般に１０〜８０μｍ程度が好ましく、より好ましくは２０〜６０μｍ程度である。上限を越えると、塗装時にワキあるいはタレ等の不具合が起こることもあり、下限を下回ると、鮮映性が低下する。
【０１１１】
上述のようにして得られた積層された塗膜は、同時に硬化させる、いわゆる３コート１ベークによって塗膜形成を行う。この場合、焼き付け乾燥炉を省略することができ、経済性及び環境面からも好ましい。但し、一般にプレヒートといわれる、形成されたウェット塗膜内に内在する揮発分を、熱や風を利用して強制的に除く工程を、塗装工程間で実施することができる。例えば、４０〜１００℃で１〜５分程度の熱を加えることができる。
【０１１２】
上記積層塗膜を硬化させる硬化温度を１００〜１８０℃、好ましくは１３０〜１６０℃に設定することで高い架橋度の硬化塗膜が得られる。上限を越えると、塗膜が固く脆くなり、下限未満では硬化が充分でない。硬化時間は硬化温度により変化するが、１３０℃〜１６０℃で１０〜３０分が適当である。
【０１１３】
本発明で形成される積層塗膜の膜厚は、多くの場合３０〜３００μｍであり、好ましくは５０〜２５０μｍである。上限を越えると、冷熱サイクル等の膜物性が低下し、下限を下回ると膜自体の強度が低下する。
【０１１４】
【発明の効果】
本発明により、中塗り塗膜、ベース塗膜及びクリヤー塗膜を、順次ウエット・オン・ウエットで形成し、その後１度に硬化させる、３コート１ベーク法により積層塗膜を形成しても、耐チッピング性及び塗膜外観に優れた積層塗膜を得ることができる。
【０１１５】
本発明において、中塗り塗料の組成を上記のものにすることで、塗膜にチッピング時の衝撃に対する反発力と、衝撃エネルギーを熱エネルギーに変換する能力を付与することができる。こうして、本発明により得られる積層塗膜は、チッピングを受けた場合にも外観上剥離面積が小さい上、剥離頻度も少ない、耐チッピング性に優れた塗膜となる。
【０１１６】
本発明の、中塗り塗膜にベース塗膜及びクリヤー塗膜を順次ウエット・オン・ウエットで形成する積層塗膜の形成方法は、中塗り用の焼付け乾燥炉工程が省略されることにより経済性及び環境面において優れている。本発明によって、得られる積層塗膜の、耐チッピング性、積層塗膜の物性および外観を向上させることができ、かかる利点を有する積層塗膜を工業的に提供することができる。
【０１１７】
【実施例】
以下、具体的な実施例を挙げて本発明を詳細に説明するが、本発明は以下の実施例により限定されるものではない。尚、以下に於いて「部」及び「％」は重量基準である。
【０１１８】
製造例１
ウレタン変性ポリエステル樹脂（ａ）の製造
窒素導入管、撹拌機、温度調節機、滴下ロートおよびデカンターを備えた冷却管を取り付けた２Ｌの反応容器にイソフタル酸４４０部、ヘキサヒドロフタル酸２０部、アゼライン酸４０部、トリメチロールプロパン３００部及びネオペンチルグリコール２００部とを仕込み、加熱により原料が溶解し撹拌可能となったところで、ジブチル錫オキサイド０．２部を投入し、撹拌を開始し、反応層温度を１８０から２２０℃まで３時間かけて徐々に昇温した。生成する縮合水は系外へ留去した。２２０℃に達したところで、１時間保温し、反応層内にキシレン２０部を徐々に添加し、溶剤存在化で縮合反応を進行させた。樹脂酸価が１０ｍｇＫＯＨ／ｇに達したところで、１００℃に冷却し、ヘキサメチレンジイソシアネート１００部を３０分間かけて徐々に添加した。更に、１時間保持後、キシレン２００部および酢酸ブチル２００部を加え、固形分７０％、数平均分子量２０００、酸価８ｍｇＫＯＨ／ｇ、水酸基価１２０、樹脂Ｔｇ６０℃のウレタン変性ポリエステル樹脂を得た。
【０１１９】
製造例２
ポリオレフィンエラストマー（ｂ−１）の製造
温度計、攪拌機、冷却管、窒素導入管、滴下ロートを備えた適当な反応容器に、日本曹達社製のα，ω−水添ポリブタジエングリコール「ＧＩ−１０００」６５０部及びトルエン６５０部を入れ、５０℃まで昇温した。この反応容器に、イソホロンジイソシアネート９６部及びトルエン９６部でなる溶液を１時間かけて滴下し、５０℃に１時間保持した。次いで、反応容器を８５℃に昇温し、ヒドロキシエチルメタクリレート５６部及びトルエン５６部でなる溶液を１時間かけて滴下し、８５℃に１時間保持した後、冷却し、ポリオレフィン系マクロマー溶液（固形分含有量５０％）を得た。
【０１２０】
適当な反応容器にポリオレフィン系マクロマー溶液２５．６部及びトルエン８３．２部を仕込み、１１０℃に昇温した。別途、ブチルアクリレート２０．０部、ブチルメタクリレート２９．０部、ヒドロキシブチルメタクリレート２．２部、及びｔ−ブチルパーオキシ−２−エチルヘキサノエート１．５部を混合して溶液を作製し、内部を撹拌しながら反応容器に３時間かけて滴下した。その後、反応容器を３０分間１１０℃に保持した。ここに、ｔ−ブチルパーオキシ−２−エチルヘキサノエート０．５部、トルエン５．０部でなる溶液を３０分間かけて滴下した。９０分間撹拌を続けた後、冷却してポリオレフィンエラストマー（ｂ−１）溶液を得た（固形分４０％）。
【０１２１】
得られたポリオレフィンエラストマー（ｂ−１）の特性値は、数平均分子量２万、及び水酸基価２０であった。
【０１２２】
製造例３
ポリオレフィンエラストマー（ｂ−２）の製造
温度計、攪拌機、冷却管、窒素導入管、滴下ロートを備えた適当な反応容器に、日本曹達社製のα，ω−水添ポリブタジエングリコール「ＧＩ−１０００」６５０部及びトルエン６９２．１部、及び無水マレイン酸４２．１部を入れた。反応容器を加圧して１３０℃まで昇温した。ＦＴ−ＩＲで酸無水物のピーク（１７８０ｃｍ^−１）が消失するまで温度を保持し、消失時点で冷却し、ポリオレフィン系マクロマー溶液（固形分含有量５０％）を得た。
【０１２３】
適当な反応容器にポリオレフィン系マクロマー１０２．９部及びトルエン１０３．０部を仕込み、１１０℃に昇温した。別途、ブチルアクリレート９．３部、ブチルメタクリレート１０．０部、マレイン酸１０．０部、ヒドロキシエチルアクリレート９．０部、ヒドロキシブチルメタクリレート１０．０部、メタクリル酸３．２部、及びｔ−ブチルパーオキシ−２−エチルヘキサノエート１．５部を混合して溶液を作製し、反応溶液を撹拌しながら３時間かけて滴下した。その後、反応容器を３０分間１１０℃に保持した。ここに、ｔ−ブチルパーオキシ−２−エチルヘキサノエート０．５部、トルエン５．０部でなる溶液を３０分間かけて滴下した。９０分間撹拌を続けた後、冷却してポリオレフィンエラストマー（ｂ−２）溶液を得た（固形分４０％）。
【０１２４】
得られたポリオレフィンエラストマー（ｂ−２）の特性値は、数平均分子量４万、水酸基価１００、及び酸価２０ｍｇＫＯＨ／ｇであった。
【０１２５】
製造例４
非水ディスパージョンの製造
（ａ）分散安定樹脂の製造
攪拌機、温度制御装置、還流冷却器を備えた容器に酢酸ブチル９０部を仕込んだ。次に下記組成の溶液
【０１２６】
【表２】

【０１２７】
の内２０部を加え、攪拌しながら加熱し、温度を上昇させた。１１０℃で上記混合溶液の残り８５部を３時間で滴下し、次いでアゾビスイソブチロニトリル０．５部と酢酸ブチル１０部からなる溶液を３０分間で滴下した。反応溶液をさらに２時間攪拌還流させて樹脂への変化率を上昇させた後、反応を終了させ、固形分５０％、数平均分子量５６００及びＳＰ値９．５のアクリル樹脂を得た。
【０１２８】
（ｂ）非水ディスパージョンの製造
攪拌機、冷却器、温度制御装置を備えた容器に酢酸ブチル９０部、上記の（ａ）分散安定樹脂の製造で得たアクリル樹脂６０部を仕込んだ。次に下記組成の溶液
【０１２９】
【表３】

【０１３０】
を１００℃で３時間で滴下し、次いでアゾビスイソブチロニトリル０．１部と酢酸ブチル１部からなる溶液を３０分間で滴下した。反応溶液をさらに１時間攪拌を続けたところ、固形分６０％、粒子径１８０ｎｍのエマルジョンを得た。このエマルジョンを酢酸ブチルで希釈し、粘度３００ｃｐｓ（２５℃）、粒子径１８０ｎｍの非水ディスパージョン含量４０％のコアシェル型酢酸ブチル分散体を得た。この非水ディスパージョン樹脂のＴｇは２３℃、水酸基価は１６２及びＳＰ値は１１．８であり、この非水ディスパージョン樹脂全体とコア部とのＳＰ値の差は２．３であった。
【０１３１】
実施例１
中塗り塗料１
１Ｌのベッセルに、先の製造例１で得られたウレタン変性ポリエステル樹脂１４．３部、ＢＯＲ−９０４（坂井化学工業（株）社製ポリオレフィンエラストマー、エチレン／プロピレン共重合体、固形分１０％、酸価４ｍｇＫＯＨ／ｇ）５００部、デュラネートＭＦ−Ｋ６０Ｘ（旭化成社製ブロックイソシアネート、固形分６０％）６６．７部、ＣＲ−９７（石原産業社製酸化チタン）９５部、ＭＡ−１００（三菱化学社製カーボンブラック顔料）５部、ディスパロン４２００−２０（楠本化成社製沈降防止剤）０．１部、を入れてディスパーで混合した後、混合物の重量と同量のＧＢ５０３Ｍ（粒径１．６ｍｍガラスビーズ）を加え、卓上ＳＧミルを用いて室温で２時間分散した。グラインドゲージによる分散終了時の粒度は５μｍ以下であった。ガラスビーズを濾過して中塗り塗料を得た。この塗料に、トルエン／スワゾール−１００（エクソン社製芳香族炭化水素溶剤）＝１／１の混合溶剤で、Ｎｏ．４フォードカップを用いて２０秒／２０℃に希釈調整した。希釈した塗料の固形分は２５％、顔料濃度（ＰＷＣ）は５０％であった。
【０１３２】
ベース塗料
日本ペイント社製アクリルメラミン系メタリックベース塗料「オルガＴＯ Ｈ６００ １８Ｊ グリーンメタリック」を用い、エトキシエチルプロピオネート／Ｓ−１００（エクソン社製芳香族炭化水素溶剤）／トルエン＝１／１／２の混合溶剤で、Ｎｏ．３フォードカップを用いて１７秒／２０℃に希釈調整した。塗布時の塗料不揮発分は３１％であった。塗着時の不揮発分は６５％であった。
【０１３３】
クリヤー塗料
日本ペイント社製酸エポキシ硬化系クリヤー塗料「マック Ｏ−１６００ クリヤー」を用い、エトキシエチルプロピオネート／Ｓ−１００（エクソン社製芳香族炭化水素溶剤）＝１／１の混合溶剤で、Ｎｏ．４フォードカップを用いて２６秒／２０℃に希釈調整した。塗布時の塗料不揮発分は５０％であった。また塗着時の不揮発分は６１％であった。
【０１３４】
塗膜形成方法
厚さ０．８ｍｍ、縦３０ｃｍ、横１０ｃｍのリン酸亜鉛処理したＳＰＣ鋼板に、カチオン電着塗料「パワートップＶ−２０」（日本ペイント社製）を、乾燥膜厚が２０μｍとなるように電着塗装し、１６０℃で３０分間焼き付けた塗板を用意した。次に、移動体に貼着し、移動させながら先の中塗り塗料を乾燥膜厚が２０μｍとなるように「マイクロベル」（回転霧化型静電塗装機）で塗装し、塗布後に１０分間のインターバルをとり、セッティングを行った。
【０１３５】
次いで、先のベース塗料を、乾燥膜厚１５μｍとなるように「マイクロベル」と「メタベル」で２ステージ塗装した。２回の塗布の間に、２．５分間のインターバルを行った。２回目の塗布後、８分間セッティングを行った。次に、先のクリヤー塗料を、乾燥膜厚３５μｍとなるように「マイクロベル」により、１ステージ塗装し、７分間セッティングした。ついで、得られた塗装板を乾燥機で１４０℃で３０分間焼き付けを行った。
【０１３６】
塗膜評価方法
得られた塗装板について、積層塗膜の仕上がり外観の評価を、ＷＳ−ＤＯＩ（ビックケミー社製塗膜外観測定器）を用いて行なった。ＷＳ−ＤＯＩでは、塗膜仕上がりの外観の評価、特にツヤ感の評価をＷａ値で表すことができる。ここでＷａ値が小さいほど、ツヤ感があり仕上がり外観が良好である。
【０１３７】
また更に、得られた塗板の耐チッピング性の評価を以下のようにして行った。グラベロテスター試験機（スガ試験機社製）を用いて、７号砕石３００個を３５ｃｍの距離から３．０ｋｇｆ／ｃｍ^２の空気圧で、塗膜に４５°の角度で衝突させた。水洗乾燥後、ニチバン社製工業用ガムテープを用いて剥離テストを行い、その後、塗膜のはがれの程度を、剥離径と件数とに分け、目視により観察し評価した。
【０１３８】
中塗り塗膜の伸び率の評価を以下のようにして行なった。厚さ３ミリのポリプロピレン板に中塗り塗料を、乾燥膜厚が４０〜６０μｍとなるように塗装し、約２０分間セッティングした後、１４０℃にて２５分間焼付け乾燥した。得られた塗膜を有効部分が長さ５ｃｍ×幅１ｃｍになるようにカッティングし、ポリプロピレン板から引き剥がして、支持体を有さないフリーフィルムを得た。このフリーフィルムについて、引張り試験機（東洋ボールドウイン社製、「テンシロン」）にて、２０℃の環境下、引張り速度１０ｍｍ／分で伸び率を測定した。
【０１３９】
以上の結果を表４に示した。
【０１４０】
実施例２
中塗り塗料２
１Ｌのベッセルに、先の製造例１で得られたウレタン変性ポリエステル樹脂２８．６部、ＰＰ−２００１（三井化学社製ポリプロピレン系エラストマー、固形分２７％、酸価６．６ｍｇＫＯＨ／ｇ、水酸基価１３．６）１４８部、Ｕ−１２８（三井サイテック社製メラミン樹脂、固形分６０％）１６．７部、ＭＦ−Ｋ６０Ｘ（旭化成社製活性メチレン型ブロックイソシアネート、固形分６０％）３３．３部、先の製造例４で得られた非水ディスパージョン２５部、ＣＲ−９７（石原産業社製酸化チタン）３９．２部、ＭＡ−１００（三菱化学社製カーボンブラック顔料）２．９部、ディスパロン４２００−２０（楠本化成社製沈降防止剤）０．１部、ＬＭＳ−３００（富士タルク社製タルク）０．８部を入れてディスパーで混合した後、混合物の重量と同量のＧＢ５０３Ｍ（粒径１．６ｍｍガラスビーズ）を加え、卓上ＳＧミルを用いて室温で２時間分散した。グラインドゲージによる分散終了時の粒度は５μｍ以下であった。ガラスビーズを濾過して中塗り塗料を得た。この塗料に、トルエン／スワゾール−１００（エクソン社製芳香族炭化水素溶剤）＝１／１の混合溶剤で、Ｎｏ．４フォードカップを用いて２０秒／２０℃に希釈調整した。希釈した塗料の固形分は４６％、塗料中の顔料濃度（ＰＷＣ）は３０％であった。
【０１４１】
中塗り塗料１の代わりに上記の中塗り塗料２を用いること以外は実施例１と同様に積層塗膜を作製し、同様の評価をおこなった。結果を表４に示した。
【０１４２】
実施例３
中塗り塗料３
１Ｌのベッセルに、先の製造例１で得られたウレタン変性ポリエステル樹脂１４．３部、先の製造例２で得られたポリオレフィンエラストマー（ｂ−１）１２５部、ＭＦ−Ｋ６０Ｘ（旭化成社製ブロックイソシアネート、固形分６０％）６６．７部、ＣＲ−９７（石原産業社製酸化チタン）９５部、ＭＡ−１００（三菱化学社製カーボンブラック顔料）５部、ディスパロン４２００−２０（楠本化成社製沈降防止剤）０．１部を用いて、実施例１の中塗り塗料１と同様に調製した。得られた、希釈した塗料の固形分は５１％、塗料中の顔料濃度（ＰＷＣ）は５０％であった。
【０１４３】
中塗り塗料１の代わりに上記の中塗り塗料３を用いること以外は実施例１と同様に積層塗膜を作製し、同様の評価をおこなった。結果を表４に示した。
【０１４４】
実施例４
中塗り塗料４
１Ｌのベッセルに、先の製造例１で得られたウレタン変性ポリエステル樹脂２８．６部、先の製造例３で得られたポリオレフィンエラストマー（ｂ−２）９９．９部、Ｕ−１２８（三井サイテック社製メラミン樹脂、固形分６０％）１６．７部、ＭＦ−Ｋ６０Ｘ（旭化成社製活性メチレン型ブロックイソシアネート、固形分６０％）３３．３部、先の製造例４で得られた非水ディスパージョン２５部、ＣＲ−９７（石原産業社製酸化チタン）３９．２部、ＭＡ−１００（三菱化学社製カーボンブラック顔料）２．９部、ディスパロン４２００−２０（楠本化成社製沈降防止剤）０．１部、ＬＭＳ−３００（富士タルク社製タルク）０．８部を用いて、実施例２の中塗り塗料２と同様に調製した。得られた、希釈した塗料の固形分は４５％、塗料中の顔料濃度（ＰＷＣ）は３０％であった。
【０１４５】
中塗り塗料１の代わりに上記の中塗り塗料４を用いること以外は実施例１と同様に積層塗膜を作製し、同様の評価をおこなった。結果を表４に示した。
【０１４６】
比較例１
中塗り塗料５
１Ｌのベッセルに、先の製造例１で得られたウレタン変性ポリエステル樹脂ワニス１０７部、ＣＲ−９７（石原産業社製酸化チタン）２８０部、ＭＡ−１００（三菱化学社製カーボンブラック顔料）１３部、ＬＭＳ−１００（富士タルク社製鱗片状タルク）７部、酢酸ブチル４７部およびキシレン４７部を入れてディスパーで混合した後、混合物の重量と同量のＧＢ５０３Ｍ（粒径１．６ｍｍガラスビーズ）を加え、卓上ＳＧミルを用いて室温で３時間分散し、灰色の顔料ペーストとした。グラインドゲージによる分散終了時の粒度は５μｍ以下であった。ガラスビーズを濾過して顔料ペーストを得た。この顔料ペースト１００部に、製造例１のウレタン変性ポリエステル樹脂（ａ）２４部、ＭＦ−Ｋ６０Ｘ（旭化成社製活性メチレン型ブロックイソシアネート、固形分６０％）２４部、およびＵ−２０Ｎ−６０（三井サイテック社製メラミン樹脂、固形分６０％）２４部を加えた。ここに、エトキシエチルプロピオネート／Ｓ−１００（エクソン社製芳香族炭化水素溶剤）＝１／１の混合溶剤を加えて、Ｎｏ．４フォードカップを用いて１９秒／２０℃になるように希釈調整した。希釈した塗料の固形分４９％、塗料中の顔料濃度（ＰＷＣ）は３０％であった。
【０１４７】
中塗り塗料１の代わりに上記の中塗り塗料５を用いること以外は実施例１と同様に積層塗膜を作製し、同様の評価をおこなった。結果を表４に示した。
【０１４８】
比較例２
電着塗装し焼き付け硬化した鋼板に、比較例１で用いた中塗り塗料５を用いて塗膜を形成する前に、ＣＰ−１０１（日本ペイント社製チッピングプライマー）を膜厚が５μｍとなるようにスプレー塗装した。５分間セッティングした後、比較例１に記載の中塗り塗料５を用いて中塗り塗膜を形成した。次いで、実施例１記載のベース塗料及びクリヤー塗料を用いて実施例１と同様に積層塗膜を作製し、同様の評価をおこなった。結果を表４に示した。
【０１４９】
【表４】

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for forming a laminated coating film, and particularly to a method for forming a laminated coating film by a three-coat one-bake method.
[0002]
[Prior art]
As a method of forming a laminated coating film, there are a method of baking and hardening each time a plurality of paints are applied, and a method of simultaneously curing after coating each paint. For example, the two-coat one-bake method is generally performed to form a metallic coating film. Further, as disclosed in JP-A-11-114489 (Patent Document 1), In order to enhance the film quality, a method for forming a coating film in which a color base coating film, a metallic base coating film, and a clear coating film are sequentially formed, and three layers are baked and cured simultaneously has already been proposed.
[0003]
When forming an intermediate coating film, a base coating film, and a clear coating film by the three-coat one-bake method, a baking drying oven for the intermediate coating can be omitted. Therefore, the energy consumption and the coating process time can be reduced, and there are great economical and environmental advantages. However, the three-coat one-bake method has the following problems, for example.
[0004]
When a vehicle travels or the like, the pebbles are flipped up and collide with the coating film, that is, so-called chipping may cause peeling of the coating film. In a conventional method of forming a laminated coating film such as baking each time each paint is applied or a two-coat one-bake method, the undercoating film and the intermediate coating film are each baked and cured. Therefore, it was possible to take measures against chipping, such as providing a chipping-resistant coating film on or under the intermediate coating film, or matching the brightness with the top coating film, and providing an intermediate coating film with inconspicuous chipping. .
[0005]
For example, JP-A-2002-249699 (Patent Document 2) and JP-A-9-208882 (Patent Document 3) disclose a chipping primer coating composition or a chipping-resistant coating film formed between laminated coating films. It is described.
[0006]
Japanese Patent Application Laid-Open No. 6-256714 (Patent Document 4) or Japanese Patent Application Laid-Open No. 6-254482 (Patent Document 5) discusses an improvement in chipping resistance from the viewpoint of the composition of an intermediate coating composition. The level of improvement is insufficient for use in the one-bake method.
[0007]
Further, there are many irregularities on an automobile body, and when the entire surface is coated by a three-coat one-bake method, there is a problem that poor appearance such as a wrinkle and conformity is likely to occur depending on a part.
[0008]
[Patent Document 1]
JP-A-11-114489
[Patent Document 2]
JP-A-2002-249699
[Patent Document 3]
JP-A-9-208882
[Patent Document 4]
JP-A-6-256714
[Patent Document 5]
JP-A-6-254482
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for forming a laminated coating film having excellent chipping resistance by a three-coat one-bake method.
[0010]
[Means for Solving the Problems]
The present invention provides a step of sequentially applying an intermediate coating, a base coating and a clear coating on a base material on which an electrodeposition coating film is formed by wet-on-wet, and baking the three coated layers at once. Curing, comprising:
The intermediate coating, based on the resin solids,
(A) a hydroxyl group-containing polyester resin obtained by polycondensation of an acid component containing 80% by mole or more of isophthalic acid with a polyhydric alcohol and having a glass transition point (Tg) of 40 to 80 ° C and an aliphatic isocyanate compound; 5 to 30% by weight of a urethane-modified polyester resin having a number average molecular weight of 1500 to 3000 obtained by the reaction,
(B) 30 to 60% by weight of a polyolefin elastomer having an acid group and / or a hydroxyl group, and
(C) 10 to 30% by weight of a blocked isocyanate compound
The present invention provides a coating film forming and coating method, which achieves the above object.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Intermediate coating film
In the method for forming a coating film of the present invention, the intermediate coating material used for forming the intermediate coating film contains a urethane-modified polyester resin (a), a polyolefin elastomer (b), and a blocked isocyanate compound (c). The intermediate coating may further contain a melamine resin (d), a non-aqueous dispersion resin (e) having a core-shell structure, a flat pigment (f), and the like, if necessary.
[0012]
The urethane-modified polyester resin (a) can be obtained by reacting a hydroxyl group-containing polyester resin with an aliphatic isocyanate compound.
[0013]
Generally, a polyester resin can be produced by polycondensing an acid component such as a carboxylic acid, an acid anhydride or an acid chloride with a monohydric or polyhydric alcohol. The hydroxyl group-containing polyester resin used in the present invention contains 80% by mole or more of isophthalic acid in the acid component used for the polycondensation reaction, based on the total number of moles of the acid component. If the amount of isophthalic acid in the acid component is less than 80 mol%, the glass transition point (Tg) of the obtained hydroxyl group-containing polyester resin becomes lower than a desired range, which is not preferable.
[0014]
Acid components other than isophthalic acid include, for example, phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahydrophthalic acid, methyltetrahydrophthalic anhydride, Acid, trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, terephthalic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride Acid, dodecenyl succinic acid, dodecenyl succinic anhydride and the like. Further, as the acid component, an acid other than the polyvalent carboxylic acid and the acid anhydride which is usually used in the production of the polyester resin may be included. Such acids include, for example, monocarboxylic acids and hydroxycarboxylic acids. As the acid component used for producing the hydroxyl group-containing polyester resin, isophthalic acid may be used alone, or isophthalic acid and another acid may be used as a mixture.
[0015]
Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, and 1,4-butanediol. , 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypro Pionate, 2,2,4-trimethyl-1,3-pentanediol, polytetramethylene ether glycol, polycaprolactone polyol, glycerin, sorbitol, annitol, trimethylolethane, trimethylolpropane Trimethylol butane, hexanetriol, pentaerythritol, dipentaerythritol and the like.
[0016]
In the production of the hydroxyl group-containing polyester resin, apart from the acid component and the polyhydric alcohol, other components that can react with these components may be used. Examples of such other components include acid derivatives such as acid chlorides and lactones, epoxide compounds, and drying oils, anti-drying oils, and fatty acid derivatives thereof. Lactones can form a graft chain by ring opening addition of polyhydric carboxylic acids and polyhydric alcohols to polyester resins. As lactones, for example, β-propiolaclone, dimethylpropiolactone, butyllactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-caprolactone, crotlactone, δ-valerolactone, δ-caprolactone, and the like Among them, ε-caprolactone is most preferred. Specifically, there are, for example, monoepoxide compounds such as Kadura E (manufactured by Shell Chemical Company) and lactones.
[0017]
The hydroxyl group-containing polyester resin has a glass transition point (Tg) of 40 to 80C, preferably 45 to 75C. When the glass transition point (Tg) is lower than 40 ° C., the hardness of the coating film decreases, and when it exceeds 80 ° C., the chipping resistance decreases.
[0018]
Examples of the aliphatic isocyanate compound include hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4-diisocyanate, methylcyclohexane diisocyanate, and isophorone diisocyanate.
[0019]
Among them, it is preferable to use hexamethylene diisocyanate and trimethylhexamethylene diisocyanate from the viewpoints of chipping resistance and weather resistance of the coating film. These burettes, isocyanurates, and adducts may be used.
[0020]
The reaction between the hydroxyl group-containing polyester resin and the aliphatic isocyanate compound can be performed by a method known to those skilled in the art.
[0021]
The urethane-modified polyester resin (a) has a number average molecular weight (Mn) of 1500 to 3000, preferably 1700 to 2500. If it is smaller than 1500, the workability and curability are not sufficient, and if it exceeds 3000, the non-volatile content at the time of coating becomes too low, and the workability worsens. In this specification, the number average molecular weight is determined by a GPC method using polystyrene as a standard.
[0022]
The urethane-modified polyester resin (a) preferably has a hydroxyl value (OHV) of 30 to 180, and more preferably has a hydroxyl value of 40 to 160. When the hydroxyl value exceeds 180, the water resistance of the coating film decreases, and when it is less than 30, the curability of the coating film decreases. Further, it preferably has an acid value (AV) of 3 to 30 mgKOH / g, more preferably 5 to 25 mgKOH / g. When the acid value exceeds 30 mgKOH / g, the water resistance of the coating film decreases, and when it is less than 3 mgKOH / g, the curability of the coating film decreases.
[0023]
The amount of the urethane-modified polyester resin (a) contained in the intermediate coating is 5 to 30% by weight, preferably 10 to 30% by weight, based on the weight of the resin solids. If the content is less than 5% by weight, the chipping resistance becomes insufficient, and if it exceeds 30% by weight, the hardness of the coating film decreases.
[0024]
It is considered that by including a urethane-modified polyester resin as a component of the intermediate coating, the elasticity of the coating film is improved and the chipping resistance of the coating film is also improved.
[0025]
The polyolefin elastomer (b) is generally a polyolefin-based graft polymer. The polyolefin elastomer (b) is prepared, for example, by copolymerizing a polyolefin-based macromer and an ethylenically unsaturated compound.
[0026]
The polyolefin-based macromer refers to a high molecular weight monomer having a polyolefin chain and an ethylenically unsaturated group at its terminal. The polyolefin-based macromer is obtained, for example, by reacting a polyolefin having a hydroxyl group with an acid or acid anhydride having an ethylenically unsaturated group.
[0027]
Examples of the polyolefin having a hydroxyl group include polyolefin resins such as polyethylene, polypropylene, polybutadiene, hydrogenated polybutadiene, polyisoprene, hydrogenated polyisoprene, and EPDM, and resins having hydroxyl groups at both ends. Those having a number average molecular weight of 200 to 5000 are preferable, and those having Mn of 500 to 4000 are more preferable.
[0028]
Examples of commercially available polyolefins having a hydroxyl group include those described below.
[0029]
[Table 1]

[0030]
Examples of the acid anhydride having an ethylenically unsaturated group include maleic anhydride, itaconic anhydride, and succinic anhydride. Of these, the use of maleic anhydride is particularly preferred.
[0031]
The reaction between the polyolefin having a hydroxyl group and the acid or acid anhydride having an ethylenically unsaturated group can be carried out by a method known to those skilled in the art.
[0032]
The polyolefin-based macromer may be obtained by reacting a polyolefin having a hydroxyl group with a diisocyanate compound and an alcohol having an ethylenically unsaturated group. Examples of the alcohol having an ethylenically unsaturated group include a hydroxyl group-containing acrylic monomer.
[0033]
As the diisocyanate compound, the aliphatic diisocyanate used for preparing the urethane-modified polyester resin can be used. Particularly preferred is isophorone diisocyanate.
[0034]
As the hydroxyl group-containing acrylic monomer, for example, hydroxyethyl methacrylate (HEMA), hydroxyethyl acrylate (HEA), hydroxypropyl methacrylate (HPMA), hydroxypropyl acrylate (HPA), hydroxybutyl acrylate (HBA) and the like can be used. These can be used alone or in combination of two or more. Of these hydroxyl group-containing acrylic monomers, hydroxyethyl (meth) acrylate is particularly preferably used.
[0035]
The reaction between the polyolefin having a hydroxyl group, the diisocyanate compound and the alcohol having an ethylenically unsaturated group can be carried out by a method known to those skilled in the art.
[0036]
Ethylenically unsaturated compounds copolymerized with the polyolefin-based macromer include ethylenically unsaturated monomers, unsaturated acrylic resins, unsaturated polyester resins, and the like.
[0037]
Examples of the ethylenically unsaturated monomer include, for example, an acrylic monomer. Specifically, methyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, n-butyl acrylate, n- General acrylic monomers such as butyl methacrylate can be used. These acrylic monomers may be used alone or as a mixture of two or more. Further, other monomers copolymerizable with these acrylic monomers such as styrene and vinyl acetate may be used in combination.
[0038]
The unsaturated acrylic resin is obtained by introducing an unsaturated bond into the acrylic resin. For example, by adding glycidyl methacrylate to the carboxyl group of the acrylic resin, by adding an acid anhydride having an unsaturated bond to the hydroxyl group of the acrylic resin, or by adding a carboxylic acid having an unsaturated bond to the oxirane group of the acrylic resin. It can be obtained by adding.
[0039]
The unsaturated acrylic resin has an acid value of 0 to 200 mgKOH / g, more preferably 0 to 150 mgKOH / g, a hydroxyl value of 10 to 300, more preferably 10 to 200, and a number average molecular weight of 1,000 to 50,000. More preferably, it is 2000-5000, and the thing whose iodine value is 0.5-100, More preferably, it is 0.5-70.
[0040]
The unsaturated polyester resin can be obtained by a general method, for example, by reacting a polyol compound with a polybasic acid compound having an unsaturated group.
[0041]
The unsaturated polyester resin has an acid value of 0 to 200 mgKOH / g, more preferably 0 to 150 mgKOH / g, a hydroxyl value of 10 to 300, more preferably 10 to 200, and a number average molecular weight of 1,000 to 50,000. More preferably, it is 1000-4000, and the thing whose iodine value is 0.5-100, More preferably, it is 0.5-70.
[0042]
The copolymerization of the polyolefin-based macromer and the ethylenically unsaturated compound can be performed by a method known to those skilled in the art. For example, according to the solution polymerization method, a polyolefin-based macromer may be dissolved in an appropriate solvent, heated, and then the ethylenically unsaturated compound may be added dropwise with an appropriate polymerization initiator with stirring.
[0043]
Examples of suitable solvents for use in the reaction include white kerosene, aliphatic hydrocarbons such as ethylcyclohexane and Shellsol TH (trade name, manufactured by Shell Japan), toluene, xylene and swazole 100 (trade name, Aromatic hydrocarbons such as Maruzen Petrochemical Co., Ltd., esters such as butyl acetate and Eukaester EEP (trade name, manufactured by Union Carbide), alcohols such as butanol, isobutanol and ethylene glycol monobutyl ether. Can be
[0044]
Examples of polymerization initiators include peroxides such as t-butylperoxy-2-ethylhexanoate, benzoyl peroxide and diphthal peroxide, azobisisobutyronitrile and 2,2′-azobis ( Azo-based initiators such as 2,4-dimethylvaleronitrile).
[0045]
The reaction temperature is generally adjusted to 60-160C, preferably 80-140C. The end point of the reaction is determined when the viscosity of the reaction solution becomes steady.
[0046]
The obtained polyolefin elastomer has a number average molecular weight of 3,000 to 200,000, preferably 10,000 to 100,000. If the number average molecular weight is smaller than 3000, the appearance of the laminated coating film becomes poor. If it exceeds 200,000, the solvent solubility of the polyolefin elastomer becomes poor.
[0047]
Further, it is preferable that the polyolefin elastomer has a hydroxyl group and / or a carboxyl group. More preferably, the polyolefin elastomer has both hydroxyl and carboxyl groups. By using a polyolefin elastomer containing one or more of these functional groups, the physical properties and chipping resistance of the obtained laminated coating film can be further improved.
[0048]
The acid value of the polyolefin elastomer is preferably 1 to 50 mgKOH / g, more preferably 5 to 30 mgKOH / g. When the acid value exceeds 50 mgKOH / g, the water resistance of the obtained laminated coating film decreases. Further, the hydroxyl value of the polyolefin elastomer is preferably from 1 to 200, more preferably from 50 to 150. When the hydroxyl value exceeds 200, the water resistance of the obtained laminated coating film decreases.
[0049]
The amount of the polyolefin elastomer (b) contained in the intermediate coating composition is 30 to 60% by weight, preferably 30 to 40% by weight, based on the weight of the resin solids. If the content is less than 30%, no improvement in the physical property values and appearance of the coated film is obtained. If the content is more than 60%, the compatibility of the coating material is reduced, resulting in a non-uniform coating film.
[0050]
By including a polyolefin elastomer as a component of the intermediate coating, the elongation of the coating film is improved and the chipping resistance of the coating film is also improved. In addition, the compatibility between the intermediate coating film and the top coating film decreases, and the base coating film and the clear coating film hardly penetrate into the wet intermediate coating film, thereby preventing phase mixing and improving the finished appearance, particularly the glossiness. improves.
[0051]
The blocked isocyanate compound (c) is a component for curing the urethane-modified polyester resin (a) and the polyolefin elastomer (b).
[0052]
The blocked isocyanate compound can be obtained by adding a blocking agent to an aliphatic isocyanate or a derivative thereof. When heated, the blocked isocyanate compound dissociates the blocking agent to generate an isocyanate group, and reacts with a hydroxyl group in the urethane-modified polyester resin to be cured.
[0053]
Examples of the aliphatic isocyanates and derivatives include the compounds used in preparing the urethane-modified polyester resin. Examples of the blocking agent include compounds having an active methylene group such as acetylacetone, ethyl acetoacetate, and ethyl malonate. By using such a blocking agent, the elasticity of the coating film is improved, and the chipping resistance of the coating film is also improved.
[0054]
Such a blocked isocyanate compound is commercially available, for example, from Asahi Kasei Corporation as an active methylene-type blocked isocyanate “Duranate MF-K60X”.
[0055]
The amount of the blocked isocyanate compound (c) contained in the intermediate coating is from 10 to 30% by weight, preferably from 15 to 25% by weight, based on the weight of the resin solids. If the content is less than 10% by weight, the curability becomes insufficient, and if it exceeds 30% by weight, the cured film becomes too hard and brittle.
[0056]
The melamine resin (d) is not particularly limited, and a methylated melamine resin, a butylated melamine resin, or a mixed melamine resin of methyl and butyl can be used. For example, "Symer-303", "Symel 254", "U-Van 128", "U-Van 20N60" available from Mitsui Toatsu Co., Ltd., and "Sumimar Series" available from Sumitomo Chemical Co., Ltd., etc. Can be
[0057]
The amount of the melamine resin (d) contained in the intermediate coating is at most 20% by weight, more preferably 5 to 15% by weight, based on the weight of the resin solids. If the content of the melamine resin exceeds 20% by weight, the cured film becomes too hard and brittle.
[0058]
The non-aqueous dispersion resin (e) having a core-shell structure is obtained by copolymerizing a polymerizable monomer in a mixed solution of a dispersion-stable resin and an organic solvent, thereby forming non-crosslinked resin particles insoluble in the mixed solution. Can be prepared as The monomer to be copolymerized in the presence of a dispersion-stable resin to obtain non-crosslinked resin particles is not particularly limited as long as it is a radically polymerizable unsaturated monomer.
[0059]
However, in order to synthesize the dispersion stable resin and the non-aqueous dispersion, it is preferable to use a polymerizable monomer having a functional group. This is because the non-aqueous dispersion having a functional group can form a three-dimensionally crosslinked coating film by reacting with a later-described curing agent together with the dispersion-stable resin containing the functional group.
[0060]
The dispersion-stable resin is not particularly limited as long as it can stably synthesize a non-aqueous dispersion in an organic solvent. Specifically, the hydroxyl value is 10 to 250, preferably 20 to 180, the acid value is 0 to 100 mgKOH / g, preferably 0 to 50 mgKOH / g, and the number average molecular weight is 800 to 100,000, preferably 1,000 to 20,000. It is preferable to use acrylic resin, polyester resin, polyether resin, polycarbonate resin, polyurethane resin or the like. If the upper limit is exceeded, the handleability of the resin will decrease, and the handling of the non-aqueous dispersion itself will also decrease. If the ratio is below the lower limit, the resin may be detached when the coating film is formed, or the stability of the particles may be reduced.
[0061]
The method for synthesizing the dispersion-stable resin is not particularly limited, but a method obtained by radical polymerization in the presence of a radical polymerization initiator, a method obtained by a condensation reaction or an addition reaction, and the like are preferred. Further, the monomer used to obtain the dispersion-stable resin may be appropriately selected according to the characteristics of the resin, and has a polymerizable monomer used to synthesize a nonaqueous dispersion described below. It is preferable to use such a compound having a functional group such as a hydroxyl group or an acid group. If necessary, a compound having a functional group such as a glycidyl group or an isocyanate group may be used.
[0062]
The composition ratio of the dispersion-stable resin and the polymerizable monomer can be arbitrarily selected according to the purpose. For example, the dispersion-stable resin is 3 to 80% by weight based on the total weight of the two components, and particularly, 5 to 60% by weight, and the polymerizable monomer is preferably 97 to 20% by weight, particularly preferably 95 to 40% by weight. Further, the total concentration of the dispersion-stable resin and the polymerizable monomer in the organic solvent is preferably from 30 to 80% by weight, particularly preferably from 40 to 60% by weight based on the total weight.
[0063]
The non-aqueous dispersion can be obtained by polymerizing a radically polymerizable monomer in the presence of a dispersion stable resin. The non-aqueous dispersion has a hydroxyl value of 50 to 400, preferably 100 to 300, an acid value of 0 to 200 mgKOH / g, preferably 0 to 50 mgKOH / g, and an average particle diameter (D₅₀) Is 0.05 to 10 μm, preferably 0.1 to 2 μm. If the ratio is below the lower limit, the particle shape cannot be maintained. If the ratio exceeds the upper limit, the stability when dispersed in the coating material is reduced.
[0064]
Typical examples of the polymerizable monomer having a functional group used for synthesizing the non-aqueous dispersion are as follows. Examples of those having a hydroxyl group include, for example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxymethyl methacrylate, allyl alcohol, hydroxyethyl (meth) methacrylate and ε- And adducts with caprolactone.
[0065]
On the other hand, those having an acidic group include polymerizable monomers having a carboxyl group, a sulfonic acid group, and the like. Examples of those having a carboxyl group include (meth) acrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride, fumaric acid, and the like. Examples of the polymerizable monomer having a sulfonic acid group include t-butylacrylamide sulfonic acid. When a polymerizable monomer having an acidic group is used, a part of the acidic group is preferably a carboxyl group.
[0066]
Glycidyl group-containing unsaturated monomers such as glycidyl (meth) acrylate, and isocyanate group-containing unsaturated monomers such as m-isopropenyl-α, α-dimethylbenzyl isocyanate and isocyanatoethyl acrylate are functional. Examples thereof include a polymerizable monomer having a group.
[0067]
Examples of the other polymerizable monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, and n- (meth) acrylate. Butyl, t-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, Alkyl (meth) acrylates such as tridecyl methacrylate, addition products of oil fatty acids and acrylic acid or methacrylate monomers having an oxirane structure (for example, addition products of stearic acid and glycidyl methacrylate), C₃An addition reaction product of the above oxirane compound containing an alkyl group with acrylic acid or methacrylic acid, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, pt-butylstyrene, ( Benzyl meth) acrylate, itaconic acid ester (dimethyl itaconate, etc.), maleic acid ester (dimethyl dimethyl maleate, etc.), fumaric acid ester (dimethyl fumarate, etc.), acrylonitrile, methacrylonitrile, methyl isopropenyl ketone, Vinyl acetate, Beoba monomer (trade name, manufactured by Shell Chemical Co., Ltd.), vinyl propionate, vinyl pivalate, ethylene, propylene, butadiene, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, acrylamide And polymerizable monomers such as vinylpyridine.
[0068]
The polymerization reaction for obtaining the non-aqueous dispersion is preferably performed in the presence of a radical polymerization initiator. Examples of the radical polymerization initiator include azo initiators such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile), benzoyl peroxide, lauryl peroxide, and the like. t-butyl peroctoate and the like. The amount of these initiators used is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, per 100 parts by weight of the total of polymerizable monomers. The polymerization reaction for obtaining a non-aqueous dispersion in an organic solvent containing a dispersion-stable resin is generally preferably performed in a temperature range of about 60 to 160 ° C. for about 1 to 15 hours.
[0069]
Further, the non-aqueous dispersion is different from the crosslinked polymer fine particles in that it is a particle component in a coating material, but has a characteristic that it does not form a particle structure in a coating film. That is, the non-aqueous dispersion is different from the crosslinked polymer fine particles in that the crosslinked portion does not exist in the particles, and thus the particle shape changes during the baking process and can be a resin component.
[0070]
Further, for example, resin particles called NAD (Non Aqueous Dispersion, non-aqueous polymer dispersion) used in a NAD paint described in Coloring Material, Vol. 48 (1975) pp. 28-34 are also used. be able to.
[0071]
The amount of the non-aqueous dispersion resin (e) contained in the intermediate coating is up to 15% by weight, preferably 5 to 12% by weight, based on the weight of the resin solids. If the content exceeds 15% by weight, the chipping resistance is reduced.
[0072]
By using the non-aqueous dispersion resin (e), interface control of the coating film is facilitated, and the finished appearance is improved.
[0073]
As the flat pigment (f), mica, alumina, talc, silica and the like can be used, but talc is preferable from the viewpoint of chipping performance.
[0074]
The flat pigment (f) preferably has a major axis of 1 to 10 μm and a number average particle diameter of 2 to 6 μm. If the major axis is outside the above range, the appearance of the coating film is inferior, or sufficient chipping resistance cannot be obtained. Will not come out.
[0075]
The content of the flat pigment (f) is 0.4 to 2 parts by weight based on 100 parts by weight of the resin solid content in the paint. More preferably, it is 0.5 to 1.5 parts by weight. Outside the above range, sufficient chipping performance cannot be obtained because the adhesion to the undercoat film is reduced.
[0076]
The resin that can be contained in the above and other components is not particularly limited, and examples thereof include an acrylic resin, a polyester resin, an alkyd resin, and an epoxy resin. One or more of them may be used in combination. Can be.
[0077]
Examples of color pigments include, for example, organic azo chelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, quinacridone pigments, and isoindolinone pigments. Pigments, metal complex pigments and the like can be mentioned. In the case of inorganic materials, it is possible to use, for example, graphite, yellow iron oxide, red iron oxide, carbon black, titanium dioxide and the like. Calcium carbonate, barium sulfate, aluminum powder, kaolin, etc. can be used as the extender pigment.
[0078]
As a standard, a gray pigment containing carbon black and titanium dioxide as main pigments is used. Further, a combination of a hue with the top coat and a combination of various coloring pigments can also be used.
[0079]
In addition, a viscosity control agent can be added to the above-mentioned intermediate coating material in order to prevent adaptation to the top coating film and to ensure coating workability. As the viscosity control agent, those which generally show thixotropic properties can be contained, for example, swelling dispersions of fatty acid amides, amide-based fatty acids, polyamide-based ones such as long-chain polyaminoamide phosphates, and colloidal swelling dispersions of polyethylene oxide Body, such as polyethylene-based, organic acid smectite clay, organic bentonite-based such as montmorillonite, inorganic pigments such as aluminum silicate and barium sulfate, flat pigments that exhibit viscosity depending on the shape of the pigment, crosslinked resin particles, etc. It can be mentioned as a viscosity control agent.
[0080]
The total solid content of the intermediate coating used in the present invention at the time of application is 20 to 80% by weight, preferably 25 to 65% by weight. Outside this range, the paint stability decreases. On the other hand, if the upper limit is exceeded, the viscosity is too high and the appearance of the coating film deteriorates, and if it is lower than the lower limit, the viscosity is too low and poor appearance such as adaptability and unevenness occurs.
[0081]
The intermediate coating used in the present invention may contain, in addition to the above components, additives usually added to the coating, such as a surface conditioner, an antioxidant and an antifoaming agent. These amounts are within the range known to those skilled in the art.
[0082]
Further, another resin may be contained in the urethane-modified polyester resin or the like. Such a resin is not particularly limited, and examples thereof include an acrylic resin, a polyester resin, an alkyd resin, and an epoxy resin, and one or more of them can be used in combination.
[0083]
The method for producing the coating composition used in the present invention is not particularly limited, including those described below, and is known to those skilled in the art of kneading and dispersing a compound such as a pigment using a kneader or a roll, an SG mill or the like. All known methods can be used.
[0084]
Base coating
The base paint used in the coating film forming method of the present invention is used for forming a top coat together with the clear paint. The base paint contains a film-forming resin, a curing agent, a coloring pigment, and, if necessary, a bright pigment.
[0085]
The film-forming resin contained in the base paint is not particularly limited, and preferred examples include acrylic resin, polyester resin, alkyd resin, epoxy resin, and urethane resin. Two or more can be used in combination.
[0086]
The above-mentioned film-forming resin can be used in combination with a curing agent, but an amino resin and / or a blocked isocyanate resin are preferably used in view of various properties and cost of the obtained coating film.
[0087]
The content of the curing agent is preferably 20 to 60% by weight, more preferably 30 to 50% by weight, based on the solid content of the film-forming resin. If the content is less than 20% by weight, the curability becomes insufficient, and if it exceeds 60% by weight, the cured film becomes too hard and brittle.
[0088]
Further, as the above-mentioned coloring pigment, for example, those mentioned in the description of the above-mentioned intermediate coating material and the like can be contained.
[0089]
The glitter pigment contained in the base paint as required is not particularly limited in its shape, and may be further colored.₅₀) Is 2 to 50 μm and the thickness is preferably 0.1 to 5 μm. Those having an average particle size in the range of 10 to 35 μm are excellent in glitter and are more preferably used. The pigment concentration (PWC) of the brilliant pigment in the paint is generally 20.0% by weight or less. Preferably, it is 0.01 to 18.0% by weight, more preferably 0.1 to 15.0% by weight. When the content of the glittering agent exceeds 20.0% by weight, the appearance of the coating film is deteriorated.
[0090]
Examples of the glitter pigment include non-colored or colored metal glitters such as metals or alloys such as aluminum, copper, zinc, iron, nickel, tin and aluminum oxide, and mixtures thereof. Further, interference mica pigments, white mica pigments, graphite pigments and other colored or colored flat pigments may be used in combination.
[0091]
The total pigment concentration (PWC) in the paint including the glitter pigment and all other pigments is 0.1 to 50% by weight, preferably 0.5 to 40% by weight, more preferably Is 1.0 to 30% by weight. If it exceeds the upper limit, the appearance of the coating film will be reduced.
[0092]
Furthermore, it is preferable to add a viscosity control agent to the base paint, in order to ensure the workability of the coating, similarly to the above-mentioned intermediate paint. The viscosity controlling agent is used for favorably forming a coating film without unevenness and sagging, and generally contains a material having a thixotropic property. As such a material, for example, those described in the description of the intermediate coating material can be contained.
[0093]
In the base paint used in the present invention, in addition to the above components, additives usually added to the paint, for example, a surface conditioner, a thickener, an antioxidant, an ultraviolet ray inhibitor, an antifoaming agent and the like are compounded. You may. These amounts are within the range known to those skilled in the art.
[0094]
The total solid content of the base paint used in the present invention at the time of coating is 10 to 60% by weight, preferably 15 to 50% by weight. Exceeding the upper and lower limits lowers the paint stability. If it exceeds the upper limit, the viscosity is too high and the appearance of the coating film is reduced. If it is below the lower limit, the viscosity is too low and poor appearance such as adaptability and unevenness occurs.
[0095]
Clear coating
A clear paint is used for forming the clear coating film. The clear paint is not particularly limited, and a paint containing a film-forming thermosetting resin, a curing agent, and the like can be used. Examples of the form of the clear coating include a solvent type, an aqueous type and a powder type.
[0096]
Preferable examples of the solvent-type clear paint include a combination of an acrylic resin and / or a polyester resin and an amino resin, and a combination of an acrylic resin and / or a polyester resin and an isocyanate compound in terms of transparency or acid etching resistance. An acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system may be used.
[0097]
Examples of the water-based clear coating include those containing a resin which is a film-forming resin contained in those exemplified as the solvent-based clear coating and which is made aqueous by neutralizing with a base. be able to. This neutralization can be performed before or after polymerization by adding a tertiary amine such as dimethylethanolamine and triethylamine.
[0098]
On the other hand, as the powder type clear coating material, an ordinary powder coating material such as a thermoplastic and thermosetting powder coating material can be used. A thermosetting powder coating is preferred because a coating film having good physical properties can be obtained. Specific examples of the thermosetting powder coating include an epoxy-based, acrylic-based, and polyester resin-based powder clear coating, and an acrylic powder clear coating having good weather resistance is particularly preferable.
[0099]
As a powder type clear coating material used in the present invention, there is no volatile matter at the time of curing, a good appearance is obtained, and since there is little yellowing, an epoxy-containing acrylic resin / polycarboxylic acid type powder coating material is used. Particularly preferred.
[0100]
Further, it is preferable that a viscosity control agent is added to the clear coating material in order to ensure coating workability, similarly to the intermediate coating material described above. The viscosity controlling agent may contain a substance exhibiting thixotropic properties. As such a material, for example, those described in the description of the intermediate coating material can be contained. If necessary, a curing catalyst, a surface conditioner and the like can be included.
[0101]
Base material
The coating film forming method of the present invention can be advantageously used for various substrates, for example, metals, plastics, foams, etc., particularly metal surfaces, and castings, but is particularly suitable for cationic electrodeposition-coatable metal products. Can be used for
[0102]
Examples of the metal product include iron, copper, aluminum, tin, zinc, and the like, and alloys containing these metals. Specific examples include automobile bodies and parts such as passenger cars, trucks, motorcycles, and buses. It is particularly preferable that these metals have been previously subjected to a chemical conversion treatment with a phosphate, a chromate or the like.
[0103]
Further, the substrate used in the method for forming a metallic coating film of the present invention may have an electrodeposition coating film formed on a steel plate which has been subjected to a chemical conversion treatment. As the electrodeposition paint for forming the electrodeposition coating film, a cationic type and an anion type can be used, but a cationic type electrodeposition coating composition is preferable because it gives a laminated coating film having excellent corrosion resistance.
[0104]
Coating method
In the method for forming a coating film of the present invention, an intermediate coating film with an intermediate coating, a base coating with a base coating, and a clear coating with a clear coating are sequentially formed on a substrate in a wet-on-wet manner.
[0105]
When an intermediate coating is applied to an automobile body in the present invention, in order to enhance the appearance, multi-stage coating by air electrostatic spray coating, preferably two-stage coating, or air electrostatic spray coating, is commonly called. A coating film can be formed by a coating method or the like in combination with a rotary atomizing electrostatic coating machine called “μμ (micro micro) bell”, “μ (micro) bell”, or “metabell”.
[0106]
In the present invention, the thickness of the dried coating film of the intermediate coating varies depending on the desired use, but in most cases, 10 to 60 μm is useful. When the ratio exceeds the upper limit, sharpness may be deteriorated, or problems such as unevenness or flow may occur at the time of coating. When the ratio is below the lower limit, the substrate cannot be concealed and the film may be cut.
[0107]
Further, in the coating film forming method of the present invention, the base coating material and the clear coating material are applied on the uncured intermediate coating film in a wet-on-wet manner to form a base coating film and a clear coating film.
[0108]
The base paint used for forming the base coating film in the method of the present invention is, similarly to the above-mentioned intermediate coating, an air electrostatic spray coating or a rotary atomizing electrostatic coating machine such as a metabell, μμ bell, μ bell and the like. And the dry film thickness of the coating film can be set to 5 to 35 μm, preferably 7 to 25 μm. When the thickness of the base coating film is more than 35 μm, the sharpness may be deteriorated or unevenness or flow may occur in the coating film. Both of these are not preferable because a film may be discontinuous).
[0109]
In the coating film forming method of the present invention, the clear coating film applied after the formation of the base coating film has irregularities caused by the base coating film, and when a bright pigment is contained, fine coating caused by the fine pigment is caused. It is formed to cover and protect various projections and the like. Specifically, as a coating method, it is preferable to form a coating film by using a rotary atomizing electrostatic coating machine such as a μμ bell, μ bell or the like described above.
[0110]
The dry film thickness of the clear coating film formed by the clear coating is generally preferably about 10 to 80 μm, and more preferably about 20 to 60 μm. If the upper limit is exceeded, problems such as waking or sagging may occur at the time of coating, and if the lower limit is not reached, sharpness deteriorates.
[0111]
The laminated coating films obtained as described above are simultaneously cured to form a coating film by so-called three-coat one-bake. In this case, the baking / drying furnace can be omitted, which is preferable in terms of economy and environment. However, the step of forcibly removing volatile components present in the formed wet coating film by using heat or air, which is generally called preheating, can be performed between the coating steps. For example, heat can be applied at 40 to 100 ° C. for about 1 to 5 minutes.
[0112]
By setting the curing temperature for curing the laminated coating film at 100 to 180 ° C, preferably 130 to 160 ° C, a cured coating film having a high degree of crosslinking can be obtained. When the amount exceeds the upper limit, the coating film becomes hard and brittle, and when the amount is less than the lower limit, curing is not sufficient. Although the curing time varies depending on the curing temperature, it is suitably from 130 ° C. to 160 ° C. for 10 to 30 minutes.
[0113]
In many cases, the thickness of the laminated coating film formed in the present invention is 30 to 300 μm, and preferably 50 to 250 μm. If it exceeds the upper limit, the physical properties of the film such as a thermal cycle decrease, and if it falls below the lower limit, the strength of the film itself decreases.
[0114]
【The invention's effect】
According to the present invention, an intermediate coating film, a base coating film, and a clear coating film are sequentially formed on a wet-on-wet basis, and then cured at one time. A laminated coating film having excellent chipping resistance and coating film appearance can be obtained.
[0115]
In the present invention, by making the composition of the intermediate coating composition as described above, the coating film can be provided with a repulsive force against an impact at the time of chipping and an ability to convert impact energy into heat energy. Thus, the laminated coating film obtained by the present invention becomes a coating film having a small peeling area, a small peeling frequency, and excellent chipping resistance even when subjected to chipping.
[0116]
The method of forming a laminated coating film of the present invention, in which the base coating film and the clear coating film are sequentially formed on the intermediate coating film by wet-on-wet, is economical because the baking and drying furnace step for the intermediate coating is omitted. And environmentally friendly. According to the present invention, the chipping resistance of the obtained laminated coating film, the physical properties and appearance of the laminated coating film can be improved, and a laminated coating film having such advantages can be industrially provided.
[0117]
【Example】
Hereinafter, the present invention will be described in detail with reference to specific examples, but the present invention is not limited to the following examples. In the following, “parts” and “%” are based on weight.
[0118]
Production Example 1
Production of urethane-modified polyester resin (a)
In a 2 L reaction vessel equipped with a nitrogen inlet pipe, a stirrer, a temperature controller, a dropping funnel and a cooling pipe equipped with a decanter, 440 parts of isophthalic acid, 20 parts of hexahydrophthalic acid, 40 parts of azelaic acid, 300 parts of trimethylolpropane And 200 parts of neopentyl glycol, and the raw material was dissolved by heating, and when stirring became possible, 0.2 parts of dibutyltin oxide was added, stirring was started, and the temperature of the reaction layer was raised from 180 to 220 ° C. for 3 hours. And the temperature gradually increased. The condensed water generated was distilled out of the system. When the temperature reached 220 ° C., the temperature was maintained for 1 hour, 20 parts of xylene was gradually added into the reaction layer, and the condensation reaction was allowed to proceed in the presence of a solvent. When the resin acid value reached 10 mgKOH / g, the mixture was cooled to 100 ° C., and 100 parts of hexamethylene diisocyanate was gradually added over 30 minutes. After further holding for 1 hour, 200 parts of xylene and 200 parts of butyl acetate were added to obtain a urethane-modified polyester resin having a solid content of 70%, a number average molecular weight of 2,000, an acid value of 8 mgKOH / g, a hydroxyl value of 120 and a resin Tg of 60 ° C.
[0119]
Production Example 2
Production of polyolefin elastomer (b-1)
In a suitable reaction vessel equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, 650 parts of α, ω-hydrogenated polybutadiene glycol “GI-1000” manufactured by Nippon Soda Co., Ltd. and 650 parts of toluene were added. The temperature was raised to 50 ° C. A solution composed of 96 parts of isophorone diisocyanate and 96 parts of toluene was added dropwise to this reaction vessel over 1 hour, and the mixture was kept at 50 ° C. for 1 hour. Next, the temperature of the reaction vessel was raised to 85 ° C., a solution composed of 56 parts of hydroxyethyl methacrylate and 56 parts of toluene was added dropwise over 1 hour, and the mixture was kept at 85 ° C. for 1 hour, cooled, and cooled with a polyolefin-based macromer solution (solid Fraction content 50%).
[0120]
An appropriate reaction vessel was charged with 25.6 parts of a polyolefin-based macromer solution and 83.2 parts of toluene, and heated to 110 ° C. Separately, a solution was prepared by mixing 20.0 parts of butyl acrylate, 29.0 parts of butyl methacrylate, 2.2 parts of hydroxybutyl methacrylate, and 1.5 parts of t-butyl peroxy-2-ethylhexanoate, The mixture was dropped into the reaction vessel over 3 hours while stirring the inside. Thereafter, the reaction vessel was kept at 110 ° C. for 30 minutes. A solution consisting of 0.5 parts of t-butylperoxy-2-ethylhexanoate and 5.0 parts of toluene was added dropwise over 30 minutes. After stirring was continued for 90 minutes, the mixture was cooled to obtain a polyolefin elastomer (b-1) solution (solid content: 40%).
[0121]
The characteristic values of the obtained polyolefin elastomer (b-1) were a number average molecular weight of 20,000 and a hydroxyl value of 20.
[0122]
Production Example 3
Production of polyolefin elastomer (b-2)
In a suitable reaction vessel equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel, 650 parts of α, ω-hydrogenated polybutadiene glycol “GI-1000” manufactured by Nippon Soda Co., Ltd. and 692.1 parts of toluene were added. And 42.1 parts of maleic anhydride. The reactor was pressurized and heated to 130 ° C. Acid anhydride peak (1780 cm^-1) Was maintained until the disappearance, and cooled at the time of the disappearance to obtain a polyolefin-based macromer solution (solid content: 50%).
[0123]
A suitable reaction vessel was charged with 102.9 parts of a polyolefin-based macromer and 103.0 parts of toluene, and the temperature was raised to 110 ° C. Separately, 9.3 parts of butyl acrylate, 10.0 parts of butyl methacrylate, 10.0 parts of maleic acid, 9.0 parts of hydroxyethyl acrylate, 10.0 parts of hydroxybutyl methacrylate, 3.2 parts of methacrylic acid, and t-butyl A solution was prepared by mixing 1.5 parts of peroxy-2-ethylhexanoate, and the reaction solution was added dropwise over 3 hours while stirring. Thereafter, the reaction vessel was kept at 110 ° C. for 30 minutes. A solution consisting of 0.5 parts of t-butylperoxy-2-ethylhexanoate and 5.0 parts of toluene was added dropwise over 30 minutes. After stirring was continued for 90 minutes, the mixture was cooled to obtain a polyolefin elastomer (b-2) solution (solid content: 40%).
[0124]
The characteristic values of the obtained polyolefin elastomer (b-2) were a number average molecular weight of 40,000, a hydroxyl value of 100, and an acid value of 20 mgKOH / g.
[0125]
Production Example 4
Production of non-aqueous dispersion
(A) Production of dispersion stable resin
90 parts of butyl acetate was charged into a vessel equipped with a stirrer, a temperature controller and a reflux condenser. Next, a solution of the following composition
[0126]
[Table 2]

[0127]
Was added and heated with stirring to raise the temperature. At 110 ° C., the remaining 85 parts of the above mixed solution was added dropwise over 3 hours, and then a solution composed of 0.5 parts of azobisisobutyronitrile and 10 parts of butyl acetate was added dropwise over 30 minutes. The reaction solution was further stirred and refluxed for 2 hours to increase the conversion to resin, and then the reaction was terminated to obtain an acrylic resin having a solid content of 50%, a number average molecular weight of 5,600 and an SP value of 9.5.
[0128]
(B) Production of non-aqueous dispersion
A container equipped with a stirrer, a cooler and a temperature controller was charged with 90 parts of butyl acetate and 60 parts of the acrylic resin obtained in the above (a) Production of dispersion stable resin. Next, a solution of the following composition
[0129]
[Table 3]

[0130]
Was added dropwise at 100 ° C. for 3 hours, and then a solution consisting of 0.1 part of azobisisobutyronitrile and 1 part of butyl acetate was added dropwise for 30 minutes. When the reaction solution was further stirred for 1 hour, an emulsion having a solid content of 60% and a particle diameter of 180 nm was obtained. This emulsion was diluted with butyl acetate to obtain a core-shell butyl acetate dispersion having a viscosity of 300 cps (25 ° C.) and a particle diameter of 180 nm and a nonaqueous dispersion content of 40%. The Tg of this non-aqueous dispersion resin was 23 ° C., the hydroxyl value was 162, and the SP value was 11.8. The difference in SP value between the whole non-aqueous dispersion resin and the core was 2.3.
[0131]
Example 1
Intermediate paint 1
In a 1 L vessel, 14.3 parts of the urethane-modified polyester resin obtained in Production Example 1 above, BOR-904 (a polyolefin elastomer manufactured by Sakai Chemical Industry Co., Ltd., an ethylene / propylene copolymer, a solid content of 10%, 500 parts of acid value 4 mgKOH / g), 66.7 parts of duranate MF-K60X (block isocyanate manufactured by Asahi Kasei Corporation, solid content 60%), 95 parts of CR-97 (titanium oxide manufactured by Ishihara Sangyo), MA-100 (Mitsubishi Chemical) 5 parts of carbon black pigment (manufactured by K.K.) and 0.1 part of Disparon 4200-20 (settling inhibitor manufactured by Kusumoto Kasei Co., Ltd.) were mixed with a disper, and then mixed with the same amount of GB503M (particle size 1.6 mm) as the weight of the mixture. (Glass beads) and dispersed for 2 hours at room temperature using a desktop SG mill. The particle size at the end of dispersion by a grind gauge was 5 μm or less. The glass beads were filtered to obtain an intermediate coating. A No. 1 mixed solvent of toluene / Swazol-100 (an aromatic hydrocarbon solvent manufactured by Exxon) = 1/1 The dilution was adjusted to 20 seconds / 20 ° C. using a 4 Ford cup. The solid content of the diluted paint was 25%, and the pigment concentration (PWC) was 50%.
[0132]
Base paint
Mixing of ethoxyethyl propionate / S-100 (aromatic hydrocarbon solvent manufactured by Exxon) / toluene = 1/1/2 using acrylic melamine-based metallic base paint "OLGA TO H600 18J Green Metallic" manufactured by Nippon Paint Co., Ltd. No. The dilution was adjusted to 17 seconds / 20 ° C. using a 3 Ford cup. The nonvolatile content of the paint at the time of application was 31%. The non-volatile content at the time of coating was 65%.
[0133]
Clear paint
A mixed solvent of ethoxyethyl propionate / S-100 (an aromatic hydrocarbon solvent manufactured by Exxon) = 1/1 using an acid epoxy-curable clear paint "Mac O-1600 Clear" manufactured by Nippon Paint Co., Ltd. The dilution was adjusted to 26 seconds / 20 ° C. using a 4 Ford cup. The non-volatile content of the paint at the time of application was 50%. The nonvolatile content at the time of coating was 61%.
[0134]
Coating method
A cation electrodeposition paint “Power Top V-20” (manufactured by Nippon Paint Co., Ltd.) was applied to a zinc phosphate-treated SPC steel sheet having a thickness of 0.8 mm, a length of 30 cm and a width of 10 cm so as to have a dry film thickness of 20 μm. A coated plate which was coated and baked at 160 ° C. for 30 minutes was prepared. Next, it is applied to a moving body, and while being moved, the intermediate coating material is applied by a “microbell” (rotary atomizing electrostatic coating machine) so that the dry film thickness becomes 20 μm, and is applied for 10 minutes. Interval was set and setting was performed.
[0135]
Next, the above-mentioned base paint was applied in two stages using “Microbell” and “Metabell” so as to have a dry film thickness of 15 μm. There was a 2.5 minute interval between the two applications. After the second application, setting was performed for 8 minutes. Next, the above-mentioned clear paint was applied in one stage by a “microbell” so as to have a dry film thickness of 35 μm, and was set for 7 minutes. Next, the obtained coated plate was baked at 140 ° C. for 30 minutes using a dryer.
[0136]
Film evaluation method
With respect to the obtained coated plate, the finished appearance of the laminated coating film was evaluated using WS-DOI (by Big Chemie Co., Ltd.). In the WS-DOI, the evaluation of the appearance of the coating film finish, particularly the evaluation of the glossiness, can be represented by a Wa value. Here, the smaller the Wa value, the better the gloss and the finished appearance.
[0137]
Furthermore, the evaluation of chipping resistance of the obtained coated plate was performed as follows. Using a gravure tester tester (manufactured by Suga Test Instruments Co., Ltd.), 300 pieces of No. 7 crushed stones were 3.0 kgf / cm from a distance of 35 cm.²At an angle of 45 °. After washing and drying, a peeling test was performed using an industrial rubber tape manufactured by Nichiban Co., Ltd., and then the degree of peeling of the coating film was divided into a peeling diameter and the number of cases, and visually observed and evaluated.
[0138]
The elongation of the intermediate coating film was evaluated as follows. An intermediate coating was applied to a 3-mm-thick polypropylene plate so as to have a dry film thickness of 40 to 60 µm, set for about 20 minutes, and baked and dried at 140 ° C for 25 minutes. The obtained coating film was cut so that the effective portion was 5 cm in length × 1 cm in width, and peeled off from the polypropylene plate to obtain a free film having no support. The elongation of this free film was measured at a tensile speed of 10 mm / min in a 20 ° C. environment using a tensile tester (“Tensilon” manufactured by Toyo Baldwin Co., Ltd.).
[0139]
Table 4 shows the above results.
[0140]
Example 2
Intermediate paint 2
In a 1 L vessel, 28.6 parts of the urethane-modified polyester resin obtained in Production Example 1 above, PP-2001 (polypropylene elastomer manufactured by Mitsui Chemicals, Inc., solid content: 27%, acid value: 6.6 mgKOH / g, hydroxyl value: 13.6) 148 parts, U-128 (Melamine resin manufactured by Mitsui Cytec, solid content 60%) 16.7 parts, MF-K60X (Asahi Kasei Corporation active methylene block isocyanate, solid content 60%) 33.3 parts 25 parts of the non-aqueous dispersion obtained in Production Example 4 above, 39.2 parts of CR-97 (titanium oxide manufactured by Ishihara Sangyo), 2.9 parts of MA-100 (carbon black pigment manufactured by Mitsubishi Chemical Corporation), 0.1 part of Disparon 4200-20 (Anti-settling agent manufactured by Kusumoto Kasei Co., Ltd.) and 0.8 part of LMS-300 (Talc manufactured by Fuji Talc Co.) were added, mixed with a disper, and then mixed. Added weight and the same amount of GB503M (particle diameter 1.6mm glass beads) were dispersed for 2 hours at room temperature using a bench SG mill. The particle size at the end of dispersion by a grind gauge was 5 μm or less. The glass beads were filtered to obtain an intermediate coating. A No. 1 mixed solvent of toluene / Swazol-100 (an aromatic hydrocarbon solvent manufactured by Exxon) = 1/1 The dilution was adjusted to 20 seconds / 20 ° C. using a 4 Ford cup. The solid content of the diluted paint was 46%, and the pigment concentration (PWC) in the paint was 30%.
[0141]
A laminated coating film was prepared in the same manner as in Example 1 except that the intermediate coating material 2 was used instead of the intermediate coating material 1, and the same evaluation was performed. The results are shown in Table 4.
[0142]
Example 3
Intermediate paint 3
In a 1 L vessel, 14.3 parts of the urethane-modified polyester resin obtained in Production Example 1, 125 parts of the polyolefin elastomer (b-1) obtained in Production Example 2, and MF-K60X (a block manufactured by Asahi Kasei Corporation) 66.7 parts of isocyanate, solid content 60%), 95 parts of CR-97 (titanium oxide manufactured by Ishihara Sangyo), 5 parts of MA-100 (carbon black pigment manufactured by Mitsubishi Chemical Corporation), Dispalon 4200-20 (manufactured by Kusumoto Chemicals) Using 0.1 part of an anti-settling agent), it was prepared in the same manner as in the intermediate coating 1 of Example 1. The solid content of the obtained diluted paint was 51%, and the pigment concentration (PWC) in the paint was 50%.
[0143]
A laminated coating film was prepared in the same manner as in Example 1 except that the intermediate coating material 3 was used instead of the intermediate coating material 1, and the same evaluation was performed. The results are shown in Table 4.
[0144]
Example 4
Intermediate coating 4
In a 1 L vessel, 28.6 parts of the urethane-modified polyester resin obtained in Production Example 1, 99.9 parts of the polyolefin elastomer (b-2) obtained in Production Example 3, U-128 (Mitsui Cytec) 16.7 parts of melamine resin manufactured by Sharp Corporation, 33.3 parts of MF-K60X (active methylene block isocyanate manufactured by Asahi Kasei Corporation, solid content 60%), and the non-aqueous dispersion obtained in Production Example 4 above. John 25 parts, CR-97 (Ishihara Sangyo Co., Ltd. titanium oxide) 39.2 parts, MA-100 (Mitsubishi Chemical Co., Ltd. carbon black pigment) 2.9 parts, Dispalon 4200-20 (Kusumoto Kasei Co., Ltd. anti-settling agent) It prepared similarly to the intermediate coating material 2 of Example 2 using 0.1 part and 0.8 parts of LMS-300 (talc made by Fuji Talc). The solid content of the obtained diluted paint was 45%, and the pigment concentration (PWC) in the paint was 30%.
[0145]
A laminated coating film was prepared in the same manner as in Example 1 except that the intermediate coating material 4 was used instead of the intermediate coating material 1, and the same evaluation was performed. The results are shown in Table 4.
[0146]
Comparative Example 1
Intermediate coating 5
In a 1 L vessel, 107 parts of the urethane-modified polyester resin varnish obtained in Production Example 1 above, 280 parts of CR-97 (titanium oxide manufactured by Ishihara Sangyo), 13 parts of MA-100 (carbon black pigment manufactured by Mitsubishi Chemical Corporation) And 7 parts of LMS-100 (scale talc manufactured by Fuji Talc), 47 parts of butyl acetate and 47 parts of xylene were mixed by a disper and then mixed with GB503M (glass beads having a particle diameter of 1.6 mm) in the same amount as the weight of the mixture. Was added and dispersed at room temperature for 3 hours using a desktop SG mill to obtain a gray pigment paste. The particle size at the end of dispersion by a grind gauge was 5 μm or less. The glass beads were filtered to obtain a pigment paste. To 100 parts of the pigment paste, 24 parts of the urethane-modified polyester resin (a) of Production Example 1, 24 parts of MF-K60X (active methylene block isocyanate, solid content 60%, manufactured by Asahi Kasei Corporation), and U-20N-60 (Mitsui 24 parts of a melamine resin (60% solid content, manufactured by Scitech) were added. A mixed solvent of ethoxyethyl propionate / S-100 (an aromatic hydrocarbon solvent manufactured by Exxon) = 1/1 was added thereto. The dilution was adjusted to 19 sec / 20 ° C. using a 4 Ford cup. The solid content of the diluted paint was 49%, and the pigment concentration (PWC) in the paint was 30%.
[0147]
A laminated coating film was prepared in the same manner as in Example 1 except that the intermediate coating material 5 was used instead of the intermediate coating material 1, and the same evaluation was performed. The results are shown in Table 4.
[0148]
Comparative Example 2
Before forming a coating film on the steel plate which has been electrodeposition-coated and baked and cured by using the intermediate coating material 5 used in Comparative Example 1, CP-101 (Nippon Paint Co., Ltd. chipping primer) is formed to have a thickness of 5 μm. Was spray painted. After setting for 5 minutes, an intermediate coating film was formed using the intermediate coating material 5 described in Comparative Example 1. Next, using the base paint and the clear paint described in Example 1, a laminated coating film was prepared in the same manner as in Example 1, and the same evaluation was performed. The results are shown in Table 4.
[0149]
[Table 4]

Claims (5)

On the substrate on which the electrodeposition coating film is formed, a step of sequentially applying wet-on-wet an intermediate coating, a base coating, and a clear coating, and a step of baking and curing the three painted layers at once, A coating film forming method comprising:
The intermediate coating, based on the resin solids,
(A) A hydroxyl group-containing polyester resin obtained by polycondensation of an acid component containing 80% by mole or more of isophthalic acid with a polyhydric alcohol and having a glass transition point (Tg) of 40 to 80 ° C, and an aliphatic isocyanate compound. 5-30% by weight of a urethane-modified polyester resin having a number average molecular weight of 1500-3000 obtained by the reaction,
(B) 30 to 60% by weight of a polyolefin elastomer having an acid group and / or a hydroxyl group, and (c) 10 to 30% by weight of a blocked isocyanate compound
And a coating film forming coating method. The intermediate coating composition further comprises (d) a maximum of 20% by weight of the melamine resin based on the resin solid content.
The method of claim 1, comprising: The intermediate coating composition further comprises (e) a non-aqueous dispersion resin having a core-shell structure of up to 15% by weight based on the resin solid content.
The method according to claim 1, comprising: The method according to any one of claims 1 to 3, wherein the polyolefin elastomer (b) has an acid value of 1 to 50 mgKOH / g and / or a hydroxyl value of 1 to 200. The method according to claim 1, wherein the blocked isocyanate compound is a compound blocked with a compound having an active methylene group.