JP4463371B2 - Formation method of multilayer coating film - Google Patents

Description

【００１７】
（式中、ＶＨ はｎ−ヘキサンの容積分率、ＶＤ は脱イオン水の容積分率、δＨ はｎ−ヘキサンのＳＰ値、δＤ は脱イオン水のＳＰ値を示す）
濁点滴定では、乾燥したビニル樹脂０．５ｇ（固形分）をアセトン１０ｍｌに溶解した中に、ｎ−ヘキサンを徐々に加え、濁点での滴定量Ｈ（ｍｌ）を読み、同様にアセトン溶液中に脱イオン水を加えての濁点における滴定量Ｄ（ｍｌ）を読んで、これらを下記式に適用しＶＨ 、ＶＤ 、δＨ 、δＤ を算出する。なお、各溶剤のＳＰ値はアセトン：９．７５、ｎ−ヘキサン：７．２４、脱イオン水：２３．４３である。
【００１８】
ＶＨ ＝Ｈ／（１０＋Ｈ）
ＶＤ ＝Ｄ／（１０＋Ｄ）
δＨ ＝９．７５×１０／（１０＋Ｈ）＋７．２４×Ｈ／（１０＋Ｈ）
δＤ ＝９．７５×１０／（１０＋Ｄ）＋２３．４３×Ｄ／（１０＋Ｄ）
ＳＰ値が９．６未満、好ましくは９．０〜９．６未満のビニル樹脂は、例えば、下記に列挙する重合性単量体から選ばれた１種又は２種以上を重合せしめることによって得られる。ＳＰ値の調整は、単量体の組成や比率などによって容易に行うことができる。
【００１９】
１）メチルアクリレート、メチルメタクリレート、エチルアクリレート、エチルメタクリレート、プロピルアクリレート、プロピルメタクリレート、ブチルアクリレート、ブチルメタアクリレート、２−エチルヘキシルアクリレート、２−エチルヘキシルメタクリレート、オクチルアクリレート、オクチルメタクリレート、ステアリルアクリレート、ステアリルメタクリレートなどのアクリル酸又はメタクリル酸と炭素数１〜２４のモノアルコ−ルとのモノエステル化物。
【００２０】
２）パーフルオロブチルエチルアクリレート、パーフルオロブチルエチルメタクリレート、パーフルオロイソノニルエチルアクリレート、パーフルオロイソノニルエチルメタクリレート等のアクリル酸又はメタクリル酸のフッ素含有エステル類。
【００２１】
３）シクロヘキシルアクリレート、シクロヘキシルメタクリレート等のアクリル酸又はメタクリル酸のシクロアルキルエステル類。
【００２２】
４）スチレン等の芳香族化合物類。
【００２３】
５）アクリロニトリル、塩化ビニル、酢酸ビニル。
【００２４】
６）グリシジルアクリレート、グリシジルメタクリレートなどのエポキシ基含有単量体。
【００２５】
７）２−ヒドロキシエチルアクリレート、２−ヒドロキシエチルメタクリレート、３−ヒドロキシブチルアクリレート、３−ヒドロキシブチルメタクリレート、ポリエチレングリコールモノアクリレート、ポリエチレングリコールモノメタクリレート、カプロラクトン変性ヒドロキシエチルアクリレ−ト、カプロラクトン変性ヒドロキシエチルメタクリレ−トなどの水酸基含有重合性単量体。
【００２６】
８）無水マレイン酸、無水イタコン酸なの酸無水基含有重合性単量体、この酸無水基含有重合性単量体を低分子量モノアルコールでハーフエステル化してなる単量体、アクリル酸、メタクリル酸、マレイン酸、フマル酸、イタコン酸、メサコン酸、シトラコン酸、塩素化マレイン酸などの遊離カルボキシル基含有単量体、マレイン酸、フマル酸、イタコン酸、メサコン酸、シトラコン酸、塩素化マレイン酸などの遊離カルボキシル基を２個以上含有する重合性単量体を低分子量モノアルコールでハーフエステル化してなる重合性単量体などのカルボキシル基含有重合性単量体。
【００２７】
（ｂ）成分は、ＳＰ値を調整しながら、上記の重合性単量体から選ばれた１種又は２種以上を重合せしめることによって得られ、その数平均分子量は３０００〜３００００、特に５０００〜２００００の範囲内にあることが好ましく、さらにその分子中にはエポキシ基、カルボキシル基、水酸基などの官能基を有していても差支えない。ＳＰ値の調整は、単量体の組成や比率などによって容易に行うことができる
（ｃ）成分：溶解性パラメ−タ値が９．６未満のポリアルキレングリコ−ル
これは、グリコ−ル類のポリエ−テル化物であって、例えば、エチレングリコ−ル、プロピレングリコ−ル、ブチレングリコ−ル、ヘキシレングリコ−ル、ペンタジオ−ル、ヘキサンジオ−ル、ジエチレングリコ−ル、ジプロピレングリコ−ル、トリエチレングリコ−ルなどから選ばれた１種又は２種以上のグリコ−ル類が使用できる。かかるポリアルキレングリコ−ルのＳＰ値は９．６未満、特に９．０〜９．６未満が好ましく、これはグリコ−ル類の組成と比率などによって容易に調整することができる。（ｃ）成分の数平均分子量は１０００〜１００００、特に１５００〜５０００の範囲内が適している。
【００２８】
（ｄ）成分：平均粒径が０．５μｍ以下に調整してなる顔料成分
具体的には、通常の塗料用顔料を使用することができ、例えば、チタン白、カ−ボンブラック、モリブデ−トオレンジ、べんがら、アゾ顔料、アントラキノン系、チオインジゴ系、ペリレン系、キナクリドン系、黄鉛、チタンイエロ−、モノアゾ系、ジスアゾ系、金属錯体系、クロムグリ−ン、フタロシアニングリ−ン、群青、コバルトブル−、フタロシアニンブル−などの着色顔料、亜鉛末、ジンククロメ−ト、ストロンチウムクロメ−ト、塩基性クロム酸鉛、塩基性硫酸鉛、りん酸塩系防錆顔料などの防錆顔料、炭酸カルシウム、カオリン、クレ−、ケイ藻土、含水微粉ケイ酸、タルク、硫酸バリウム、炭酸バリウム、ケイ砂などの体質顔料などが使用できる。
【００２９】
（ｄ）成分としての顔料は、塗料中で分散後のその平均粒径が０．５μｍ以下、好ましくは０．４μｍ以下に調整されていることが好ましい。平均粒径がこの範囲より大きくなると本発明の目的が達成できないので好ましくない。ここで、平均粒径とは、粒度分布曲線（通常は正規分布曲線が多い）における平均値のことである。
【００３０】
また、上記した顔料のうち、タルクやクレ−のようなりん片状顔料が混入されていてもよいが、塗料中に含まれる樹脂１００重量部（固形分）あたりのりん片状顔料の総吸油量が４００以下の範囲で含有することが好ましい。吸油量は顔料を液体と機械的に湿潤混合させて堅いペ−スト状にするために必要な油の量のことであり、具体的には、顔料１００に対する精製あまに油のｍｌで表される。例えば、樹脂１００重量部（固形分）あたり、吸油量が５０のりん片状顔料Ａを２重量部、吸油量が４０のりん片状顔料Ｂを５重量部を使用した系での総吸油量は３００となって、上記の要件を満たしている。かかる、要件を満たすりん片状顔料を、上記の平均粒径の範囲内に調整してから使用することが好ましい。
【００３１】
カチオン電着塗料組成物（Ａ）は、上記した（ａ）成分、（ｂ）成分、（ｃ）成分及び（ｄ）成分を含有してなり、これらの各成分の構成比率は目的に応じて任意に選択できるが、例えば、固形分比で、（ａ）成分１００重量部あたり、（ｂ）成分は０．５〜１０重量部、特に１〜５重量部、（ｃ）成分は０．１〜１０重量部、特に０．５〜５重量部が好ましい。また、（ｄ）成分は、（ａ）成分１００重量部（固形分）あたり、顔料の総量で５〜５０重量部、特に１０〜３０重量部の範囲内が適している。
【００３２】
カチオン電着塗料組成物（Ａ）には、さらに、硬化剤、消泡剤、ハジキ防止剤、沈降防止剤、硬化触媒、有機溶剤などを適宜配合することができる。
【００３３】
このうち硬化剤として、ブロックポリイソシアネ−ト化合物が好適に使用することができる。具体的には、１分子中に２個以上の遊離のイソシアネ−ト基を有するポリイソシアネ−ト化合物のイソシアネ−ト基をブロック剤で封鎖してなる化合物があげられる。ポリイソシアネ−ト化合物として、例えば、トリレンジイソシアネ−ト、ジフェニルメタンジイソシアネ−ト、キシリレンジイソシアネ−ト、ナフタレンジイソシアネ−トなどの芳香族ジイソシアネ−ト；テトラメチレンジイソシアネ−ト、ヘキサメチレンジイソシアネ−ト、ダイマ−酸ジイソシアネ−ト、リジンジイソシアネ−トなどの脂肪族ジイソシアネ−ト；メチレンビス（シクロヘキシルイソシアネ−ト）、イソホロンジイソシアネ−ト、メチルシクロヘキサンジイソシアネ−ト、シクロヘキサンジイソシアネ−ト、シクロペンタンジイソシアネ−トなどの脂環族ジイソシアネ−ト；該ポリイソシアネ−ト化合物のビユ−レットタイプ付加物、イソシアヌル環タイプ付加物；これらのポリイソシアネ−ト化合物と低分子量又は高分子量のポリ−ル類とをイソシアネ−ト基過剰で反応させてなる遊離イソシアネ−ト基含有プレポリマ−などがあげられる。ブロック剤として、例えば、フェノ−ル類、オキシム類、ラクタム類、活性メチレン系、アルコ−ル類、酸アミド系、イミド系、アミン系、イミダゾ−ル系、尿素系、カルバミン酸系、イミン系、メルカプタン類などのそれ自体既知のブロック剤が使用できる。ブロックポリイソシアネ−ト化合物の数平均分子量は２００〜１００００のが好ましい。かかるブロックポリイソシアネ−ト化合物の配合量は、上記（Ａ）成分１００重量部（固形分）あたり、１００重量部以下、特に１０〜７０重量部が好ましい。
【００３４】
カチオン電着塗料組成物（Ａ）の固形分含有率を約５〜４０重量％になるように脱イオン水などを加え、さらにｐＨ５．５〜９．０の電着浴とし、浴温度１５〜３５℃、負荷電圧１００〜４００Ｖの条件で、被塗物を陰極として浸漬し通電することによって電着塗装が行なわれる。塗装膜厚は硬化塗膜を基準に、１０〜４０μｍの範囲が適している。通電後、電着浴から引き上げ水洗してから、１００〜２００℃で、１０〜４０分程度加熱することにより硬化せしめる。
【００３５】
本発明の方法は、被塗物に電着塗料（Ａ）を塗装し、その塗膜を加熱硬化させてから、その電着塗膜面に、中塗り塗料（Ｂ）、上塗りベース塗料（Ｃ）及びクリヤ塗料（Ｄ）をウエットオンウエットで塗装した後、加熱してこれらの３層塗膜を同時に硬化せしめて複層塗膜を形成する。
【００３６】
中塗り塗料（Ｂ）は、加熱硬化した中塗り塗膜面に塗装する塗料であって、それ自体既知のものが使用でき、例えば、基体樹脂、架橋剤、顔料及び有機溶剤を含有する熱硬化性塗料があげられる。基体樹脂としては、水酸基などの架橋性官能基を有するポリエステル樹脂、アクリル樹脂、アルキド樹脂などがあげられ、架橋剤としては上記の架橋性官能基と反応しうるメラミン樹脂や（ブロック）ポリイソシアネ−ト化合物があげられる。顔料としては、通常の無機系又は有機系のソリッドカラ−顔料が使用できる。中塗り塗料（Ｂ）はこれらの基体樹脂、架橋剤、顔料を有機溶剤に混合し溶解又は分散せしめることにより調製できる。その塗膜の色調は特に制限されないが、白〜灰色が好ましい。
【００３７】
中塗り塗料（Ｂ）は、塗装時の固形分含有率を１０〜６０重量％、粘度を１０〜５０秒／フォ−ドカップ＃４／２０℃に調整し、静電方式、スプレ−方式などにより、電着塗膜面に、硬化塗膜で５〜４０μｍになるように塗装することが好ましい。
【００３８】
本発明では、この中塗り塗膜を架橋硬化させることなく、未硬化の塗面に上塗りベース塗料（Ｃ）を塗装する。
【００３９】
上塗りベース塗料（Ｃ）は、複層塗膜に色彩的な美粧性を付与するためのものであって、例えば、基体樹脂、架橋剤、顔料及び有機溶剤を含有する熱硬化性塗料が使用でき、その塗膜の色調は、ソリッドカラ−調、メタリック調、光干渉調のいずれでも適用できる。基体樹脂としては、水酸基などの架橋性官能基を有するポリエステル樹脂、アクリル樹脂、アルキド樹脂などがあげられ、架橋剤としては上記の架橋性官能基と反応しうるメラミン樹脂や（ブロック）ポリイソシアネ−ト化合物があげられる。顔料としては、通常の無機系又は有機系のソリッドカラ−顔料、アルミニウムフレ−クなどのメタリック顔料、金属酸化物で被覆された雲母などの光干渉性顔料などが使用できる。上塗りベース塗料（Ｃ）はこれらの基体樹脂、架橋剤、顔料を有機溶剤に混合し溶解又は分散せしめることにより調製でき、塗装時の固形分含有率を１０〜６０重量％、粘度を１０〜５０秒／フォ−ドカップ＃４／２０℃に調整しておくことが好ましく、静電方式、スプレ−方式などにより、中塗り塗料（Ｂ）の未硬化塗面に、硬化塗膜で５〜４０μｍになるように塗装することが好ましい。
【００４０】
本発明では、この上塗りベース塗料（Ｃ）の塗膜を架橋硬化させることなく、未硬化の塗面にクリヤ塗料（Ｄ）を塗装する。
【００４１】
クリヤ塗料（Ｄ）は、無色透明又は有色透明の塗膜を形成することができ、具体的には、基体樹脂、架橋剤及び有機溶剤を含有する熱硬化性塗料が使用できる。基体樹脂としては、水酸基、カルボキシル基、エポキシ基などの架橋性官能基を有するポリエステル樹脂、アクリル樹脂、アルキド樹脂などがあげられ、架橋剤としては上記の架橋性官能基と反応しうるメラミン樹脂、（ブロック）ポリイソシアネ−ト化合物、エポキシ基含有化合物、カルボキシル基含有化合物があげられる。また、クリヤ塗料（Ｄ）には、その塗膜の透明性を阻害しない程度に、無機系又は有機系のソリッドカラ−顔料、アルミニウムフレ−クなどのメタリック顔料、金属酸化物で被覆された雲母などの光干渉性顔料などを含有せしめることができる。クリヤ塗料（Ｄ）はこれらの成分を有機溶剤に混合し溶解又は分散せしめることにより調製でき、塗装時の固形分含有率を１０〜６０重量％、粘度を１０〜５０秒／フォ−ドカップ＃４／２０℃に調整しておくことが好ましく、静電方式、スプレ−方式などにより、未硬化の上塗りベース塗料（Ｃ）の塗膜面に、硬化塗膜で５〜４０μｍになるように塗装することが好ましい。
【００４２】
本発明の方法は、被塗物に電着塗料（Ａ）を塗装し、その塗膜を加熱硬化させてから、中塗り塗料（Ｂ）、上塗りベース塗料（Ｃ）及びクリヤ塗料（Ｄ）を上記のようにウエットオンウエットで塗装した後、１００〜１８０℃、好ましくは１２０〜１６０℃で、１０〜４０分間加熱してこれらの３層塗膜を同時に硬化せしめて複層塗膜を形成せしめることのより達成される。
【００４３】
【発明の効果】
被塗物に塗装した電着塗料の硬化塗面に、中塗り塗料、上塗りベース塗料及びクリヤ塗料を３Ｃ１Ｂで塗装して複層塗膜を形成するにあたり、電着塗料として、上記した（ａ）ビスフェノ−ル型エポキシ樹脂の水酸基に環状エステル化合物を反応させてなる樹脂、（ｂ）溶解性パラメ−タ値が９．６未満のビニル樹脂、（ｃ）溶解性パラメ−タ値が９．６未満のポリアルキレングリコ−ル及び（ｄ）平均粒径が０．５μｍ以下に調整してなる顔料成分を含有するカチオン電着塗料を使用することにより、複層塗膜の平滑性などの仕上がり外観及び耐チッピング性などを改良することができた。
【００４４】
【実施例】
以下に、本発明に関する実施例及び比較例について説明する。部及び％はいずれも重量に基づいている。また、塗膜の厚さは硬化塗膜についてである。
【００４５】
１．カチオン電着塗料（Ａ）の調製
１）（ａ）成分
ｉ）：ε−カプロラクトン変性ビスフェノ−ルＡ型エポキシ樹脂にジエタノ−ルアミン反応させて、ついでギ酸で中和してなる樹脂。ε−カプロラクトンの含有率は、（ａ）成分（固形分）を基準に２０％である。数平均分子量は約３５０００。
【００４６】
ｉｉ）：ビスフェノ−ルＡ型エポキシ樹脂にジエタノ−ルアミン反応させて、ついでギ酸で中和してなる樹脂。ε−カプロラクトンで変性していない。数平均分子量は約３５０００。
【００４７】
２）（ｂ）成分
ｉ）：イソブチルアクリレ−ト、ヒドロキシエチルメタクリレ−ト及びジメチルアミノエチルメタクリレ−トを使用してなるアクリル樹脂で、ＳＰ値を９．３に調整した。数平均分子量は７０００。
【００４８】
ｉｉ）：イソブチルアクリレ−ト、ヒドロキシエチルメタクリレ−ト及びジメチルアミノエチルメタクリレ−トを使用してなるアクリル樹脂で、ＳＰ値を９．８に調整した。数平均分子量は７０００。
【００４９】
３）（ｃ）成分
ｉ）：ポリプロピレングリコ−ルで、ＳＰ値を９．１に調整した。数平均分子量は３０００。
【００５０】
ｉｉ）：ポリテトタメチレングリコ−ルで、ＳＰ値を９．７に調整した。数平均分子量は３０００。
【００５１】
４）顔料成分
ｉ）：上記の（ａ）ｉ）成分５部（固形分）に、平均粒径が０．４μｍに調整されたチタン白顔料１５部、カ−ボンブラック０．３部、ケイ酸鉛２部及びジオクチル錫オキサイド（触媒）２部を混合分散した。
【００５２】
ｉｉ）：上記の（ａ）ｉｉ）成分５部（固形分）に、平均粒径が１．０μｍに調整されたチタン白顔料１５部、カ−ボンブラック０．３部、ケイ酸鉛２部及びジオクチル錫オキサイド（触媒）２部を混合分散した。
【００５３】
５）硬化剤
ｉ）：「デュラネ−トＴＰＡ−１００」（旭化成社製、商品名、ヘキサメチレンジイソシアネ−ト系のポリイソシアネ−ト化合物）のイソシアネ−ト基を、メチルエチルケトオキシムでブロックしたもの。
【００５４】
６）カチオン電着塗料（Ａ）
イ）：（ａ）成分ｉ）１００部（固形分）、硬化剤ｉ）３０部（固形分）、（ｂ）成分ｉ）２部（固形分）、（ｃ）成分ｉ）１部（固形分）、顔料成分ｉ）２４．３部（固形分）を混合し、水を加えて、固形分含有率１５％のカチオン電着塗料を得た。（実施例用）
ロ）：（ａ）成分ｉ）１００部（固形分）、硬化剤ｉ）３０部（固形分）、（ｂ）成分ｉ）５部（固形分）、顔料成分ｉ）２４．３部（固形分）を混合し、水を加えて、固形分含有率２０％のカチオン電着塗料を得た。（比較例用）
ハ）：（ａ）成分ｉ）１００部（固形分）、硬化剤ｉ）３０部（固形分）、（ｃ）成分ｉ）２部（固形分）、顔料成分ｉ）２４．３部（固形分）を混合し、水を加えて、固形分含有率２０％のカチオン電着塗料を得た。（比較例用）
ニ）：（ａ）成分ｉ）１００部（固形分）、硬化剤ｉ）３０部（固形分）、（ｂ）成分ｉｉ）２部（固形分）、（ｃ）成分ｉｉ）１部（固形分）、顔料成分ｉ）２４．３部（固形分）を混合し、水を加えて、固形分含有率２０％のカチオン電着塗料を得た。（比較例用）
ホ）：（ａ）成分ｉｉ）１００部（固形分）、硬化剤ｉ）３０部（固形分）、（ｂ）成分ｉ）２部（固形分）、（ｃ）成分ｉ）１部（固形分）、顔料成分ｉ）２４．３部（固形分）を混合し、水を加えて、固形分含有率２０％のカチオン電着塗料を得た。（比較例用）
ヘ）：（ａ）成分ｉ）１００部（固形分）、硬化剤ｉ）３０部（固形分）、（ｂ）成分ｉ）２部（固形分）、（ｃ）成分ｉ）１部（固形分）、顔料成分ｉｉ）２４．３部（固形分）を混合し、水を加えて、固形分含有率２０％のカチオン電着塗料を得た。（比較例用）
２．実施例及び比較例
カチオン電着塗料（Ａ）の浴温度を２８℃に調整し、「ＰＢ−Ｌ３０８０」（日本パ−カライジング社製、商品名）で表面処理を行ったＳＰＣダル鋼板を陰極として浸漬し、膜厚２０μｍの塗膜が形成するように２５０Ｖで通電した後、引き上げて水洗を行なってから、電着板を１７０℃で２０分間焼き付けてその塗膜を硬化させた。
【００５５】
ついで、この電着塗面に中塗り塗料（Ｂ）（「ＴＰ６５グレ−」、関西ペイント社製、商品名、有機溶剤系）を膜厚３０μｍになるように塗装し、室温で２分間放置してから、メタリック塗料（Ｃ）（「マジクロンシルバー」、関西ペイント社製、商品名、有機溶剤系）を膜厚１５μｍになるように塗装し、室温で３分間放置してから、さらにクリヤ塗料（Ｄ）（「マジクロンクリヤ」、関西ペイント社製、商品名、有機溶剤系）を膜厚３５μｍになるように塗装し、室温で３分間放置してから、１４０℃で３０分間焼き付けて３層塗膜を同時に架橋硬化させた。
【００５６】
このようにして得た塗膜について性能試験を行なった。その結果を表１に示した。
【００５７】
【表１】

試験方法は下記のとおりである。
【００５８】
平滑性：中塗り塗料及び上塗り着色塗料を塗装する前の硬化せしめた電着塗膜について、表面粗度計（東京精密社製、商品名、「サ−フコム５５０Ａ」）を使用して、表面粗度Ｒａを測定した。○は０．２μｍ未満、△は０．２μｍ〜０．２５μｍ未満、×は０．２５μｍ以上を示す。
【００５９】
耐ハジキ性：未硬化の電着塗膜面に、油（日本パ−カ−社製、ＮｏｘＲｕｓｔ８８０Ｐ）を１〜２滴付着させてから、１７０℃で２０分間焼き付けてその塗膜を硬化した後の塗面を調べた。○はハジキ発生全くなし、△は直径１ｍｍ未満の微小ハジキが発生した、×は直径１ｍｍ以上のハジキが発生したことを示す。
【００６０】
耐チッッピング性：−２０℃において、７号砕石５０ｇを４ｋｇ／ｃｍ２ の圧力で、塗面に対し４５度の角度で、上塗り着色塗料を塗装し硬化せしめた塗面に吹き付けた後の塗面を観察した。○は砕石の吹き付けによる塗膜のハガレた部分の直径が１ｍｍ未満である、△は同様に１ｍｍ以上・２ｍｍ未満、×は同様に２ｍｍ以上のハガレが発生したことを示す。
【００６１】
鮮映性：複層塗膜表面の鮮映性を目視で評価した。○は鮮映性良好、△は鮮映性少し劣る、×は鮮映性非常に劣ることを示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to improving the finished appearance such as smoothness of a multilayer coating film formed by applying an electrodeposition coating, an intermediate coating, a top coating base and a clear coating, and chipping resistance.
[0002]
[Prior art and its problems]
Cationic electrodeposition paint is applied to automobile bodies, etc. After heat-curing, intermediate paint, topcoat base paint, and clear paint are applied by 3 coat 1 bake method (3C1B) or 3 coat 2 bake method (3C2B). Forming a layer coating is widely performed. However, 3C1B is suitable for energy saving because the heating and curing process of the coating film is one time. However, 3C2B has a defect that the finished appearance of the multilayer coating film is not sufficient. The chipping resistance and interlayer adhesion of the film are inferior, and energy saving is not preferable.
[0003]
[Means for Solving the Problems]
The object of the present invention is to eliminate the above-mentioned defects, apply a cationic electrodeposition coating, heat cure, and then apply the intermediate coating, top coating base and clear coating with 3C1B to obtain a finished appearance, resistance to resistance. It is to improve the chipping property, interlayer adhesion and the like. As a result of intensive studies, it was found that the object can be achieved by using a cationic electrodeposition paint having a specific composition, and the present invention has been completed.
[0004]
That is, in the present invention, the electrodeposition paint (A) is applied to the object to be coated and the coating film is heated and cured, and then the intermediate paint (B), the top coat base paint (C) and the clear paint (D) are applied. In the method of coating by wet-on-wet and heating to form a multilayer coating film by simultaneously curing these three-layer coating films, (a) a bisphenol type epoxy resin A resin obtained by reacting a cyclic ester compound with a hydroxyl group, (b) a vinyl resin having a solubility parameter value of less than 9.6, and (c) a polyalkylene glycol having a solubility parameter value of less than 9.6. And (d) a method for forming a multilayer coating film, wherein a cationic electrodeposition paint containing a pigment component having an average particle size adjusted to 0.5 μm or less is used.
[0005]
Below, the formation method of the multilayer coating film of this invention is demonstrated in detail.
[0006]
Object to be coated: It is a base material for forming a multi-layer coating film and is not particularly limited as long as it is a conductive metal product that can be subjected to cationic electrodeposition coating. The finished appearance, chipping resistance, interlayer adhesion, etc. are strong. The required automobile skin is particularly suitable. These objects to be coated are preferably subjected to a chemical conversion treatment in advance with zinc phosphate or the like prior to electrodeposition coating.
[0007]
Cationic electrodeposition coating (A): A water-based coating applied to an object as an undercoat prior to the intermediate coating (B). In the present invention, (a) a cyclic ester is added to the hydroxyl group of the bisphenol type epoxy resin. A resin obtained by reacting a compound, (b) a vinyl resin having a solubility parameter value of less than 9.6, (c) a polyalkylene glycol having a solubility parameter value of less than 9.6, and (d) A cationic electrodeposition paint containing a pigment component having an average particle size adjusted to 0.5 μm or less is used.
[0008]
(A) A resin obtained by reacting a cyclic ester compound with a hydroxyl group of a bisphenol type epoxy resin.
[0009]
First, the bisphenol type epoxy resin has both a hydroxyl group and an epoxy group in one molecule. Specifically, the average number of hydroxyl groups per molecule is 0.5 or more, especially 0.8-2. The number average molecular weight is preferably about 400 to about 1000, and more preferably about 450 to about 700. Examples of the epoxy resin include bis (4-hydroxyphenyl) -2,2-propane, bis (4-hydroxyphenyl) -1,1-ethane, bis (4-hydroxyphenyl) -methane, and 4,4′-. Examples thereof include glycidyl ethers of polyphenols such as dihydroxydiphenyl sulfone, phenol novolak and cresol novolak, and polymers thereof.
[0010]
Examples of the cyclic ester compound include δ-valerolactone, ε-caprolactone, ζ-enalactone, η-caprolactone, γ-valerolactone, δ-caprolactone, ε-enalactone, ξ-caprolactone, and the like.
[0011]
(A) component is obtained by carrying out ring-opening esterification reaction of the cyclic ester to the hydroxyl group of the bisphenol type epoxy resin. This reaction can be performed, for example, by heating both components at 100 to 250 ° C. for 1 to 15 hours. The amount of the cyclic ester compound used is preferably adjusted so that the content in the obtained component (a) is 5 to 40% by weight, particularly 10 to 35% by weight.
In order to promote the reaction, titanium compounds such as tetrabutoxy titanium and tetrapropoxy titanium, organotin compounds such as tin octylate, dibutyltin oxide and dibutyltin laurate, stannous chloride and the like can be used as a catalyst. The number average molecular weight of the component (a) thus obtained is preferably in the range of about 1000 to about 7000.
[0012]
By this ring-opening esterification reaction, a side chain having a large plasticizing ability having a primary hydroxyl group having excellent reactivity based on the ring-opening of the cyclic ester compound is introduced into the epoxy resin. It is estimated that the corrosion resistance, adhesion, impact resistance, chipping resistance, finish, etc. of the film could be improved.
[0013]
By reacting an amino compound with the epoxy group of component (a) and then neutralizing with an acid such as formic acid, acetic acid or lactic acid, it can be used as a cationic electrodeposition resin.
[0014]
Any amino compound may be used as long as it can react with an epoxy group to introduce a secondary amino group, a tertiary amino group or the like, and may be an aliphatic, alicyclic, or aromatic-aliphatic primary or secondary. Primary amines such as methylamine, ethylamine, n- or iso-propylamine, monoethanolamine, n- or isopropanolamine; diethylamine, diethanolamine, di-n. Or secondary monoamines such as iso-propanolamine, N-methylethanolamine, N-ethylethanolamine, ethylenediamine, diethylenetriamine, hydroxyethylaminoethylamine, ethylaminoethylamine, methylaminopropylamine, dimethylaminoethylamine, dimethylaminopropyl Amine Primary or secondary polyamines and the like. Of these amino group-containing compounds, primary amines and N-hydroxyalkyl secondary amines are preliminarily reacted with ketones, aldehydes or carboxylic acids to be modified into aldimine, ketimine, oxazoline or imidazoline, which are then converted to epoxy. It is preferred to react with a group. The amount of the amino group-containing compound used is preferably such that the amine value is generally in the range of 15 to 100, particularly 30 to 80.
[0015]
(B) Vinyl resin having a solubility parameter value of less than 9.6 The SP value of this vinyl resin can be measured by cloud point titration. W. SUH, J. et al. M.M. It can be calculated according to the CORBETT equation (Journal of Applied Polymer Science, 12, 2359, 1968).
[0016]
[Expression 1]

[0017]
(Where VH is the volume fraction of n-hexane, VD is the volume fraction of deionized water, δH is the SP value of n-hexane, and δD is the SP value of deionized water)
In the cloud point titration, 0.5 g (solid content) of the dried vinyl resin was dissolved in 10 ml of acetone, n-hexane was gradually added, and the titration amount H (ml) at the cloud point was read. The titration amount D (ml) at the turbidity point by adding deionized water is read and applied to the following formula to calculate VH, VD, δH, and δD. In addition, SP value of each solvent is acetone: 9.75, n-hexane: 7.24, deionized water: 23.43.
[0018]
VH = H / (10 + H)
VD = D / (10 + D)
δH = 9.75 × 10 / (10 + H) + 7.24 × H / (10 + H)
δD = 9.75 × 10 / (10 + D) + 23.43 × D / (10 + D)
A vinyl resin having an SP value of less than 9.6, preferably less than 9.0 to 9.6 is obtained, for example, by polymerizing one or more selected from the polymerizable monomers listed below. It is done. The SP value can be easily adjusted depending on the monomer composition and ratio.
[0019]
1) Methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, stearyl acrylate, stearyl methacrylate, etc. Monoesterified product of acrylic acid or methacrylic acid and monoalcohol having 1 to 24 carbon atoms.
[0020]
2) Fluorine-containing esters of acrylic acid or methacrylic acid such as perfluorobutylethyl acrylate, perfluorobutylethyl methacrylate, perfluoroisononylethyl acrylate, perfluoroisononylethyl methacrylate.
[0021]
3) Cycloalkyl esters of acrylic acid or methacrylic acid such as cyclohexyl acrylate and cyclohexyl methacrylate.
[0022]
4) Aromatic compounds such as styrene.
[0023]
5) Acrylonitrile, vinyl chloride, vinyl acetate.
[0024]
6) Epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate.
[0025]
7) 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxybutyl acrylate, 3-hydroxybutyl methacrylate, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, caprolactone-modified hydroxyethyl acrylate, caprolactone-modified hydroxyethyl methacrylate Hydroxyl group-containing polymerizable monomers such as a rate.
[0026]
8) An acid anhydride group-containing polymerizable monomer such as maleic anhydride, itaconic anhydride, a monomer obtained by half-esterifying this acid anhydride group-containing polymerizable monomer with a low molecular weight monoalcohol, acrylic acid, methacrylic acid , Maleic acid, fumaric acid, itaconic acid, mesaconic acid, citraconic acid, free carboxyl group-containing monomers such as chlorinated maleic acid, maleic acid, fumaric acid, itaconic acid, mesaconic acid, citraconic acid, chlorinated maleic acid, etc. A carboxyl group-containing polymerizable monomer such as a polymerizable monomer obtained by half-esterifying a polymerizable monomer containing at least two free carboxyl groups with a low molecular weight monoalcohol.
[0027]
(B) A component is obtained by superposing | polymerizing 1 type (s) or 2 or more types chosen from said polymeric monomer, adjusting SP value, The number average molecular weight is 3000-30000, Especially 5000- It is preferably within the range of 20000, and the molecule may have a functional group such as an epoxy group, a carboxyl group, or a hydroxyl group. The SP value can be easily adjusted by the composition and ratio of the monomer (c) component: a polyalkylene glycol having a solubility parameter value of less than 9.6. For example, ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, pentadiol, hexanediol, diethylene glycol, dipropylene glycol, One or two or more glycols selected from triethylene glycol and the like can be used. The SP value of such polyalkylene glycol is preferably less than 9.6, particularly preferably less than 9.0 to 9.6, which can be easily adjusted by the composition and ratio of glycols. The number average molecular weight of the component (c) is suitably in the range of 1000 to 10,000, particularly 1500 to 5000.
[0028]
Component (d): Pigment component having an average particle diameter adjusted to 0.5 μm or less Specifically, ordinary pigments for paints can be used, such as titanium white, carbon black, molybdate. Orange, brown, azo pigment, anthraquinone, thioindigo, perylene, quinacridone, yellow lead, titanium yellow, monoazo, disazo, metal complex, chrome green, phthalocyanine green, ultramarine, cobalt blue Color pigments such as phthalocyanine blue, zinc dust, zinc chromate, strontium chromate, basic lead chromate, basic lead sulfate, phosphate anticorrosive pigments such as calcium carbonate, kaolin, For example, extender pigments such as clay, diatomaceous earth, hydrous finely divided silicic acid, talc, barium sulfate, barium carbonate, and silica sand can be used.
[0029]
The pigment as the component (d) is preferably adjusted so that the average particle size after dispersion in the paint is 0.5 μm or less, preferably 0.4 μm or less. If the average particle size is larger than this range, the object of the present invention cannot be achieved, which is not preferable. Here, the average particle diameter is an average value in a particle size distribution curve (usually, there are many normal distribution curves).
[0030]
Of the above-mentioned pigments, flaky pigments such as talc and clay may be mixed, but the total oil absorption of the flaky pigment per 100 parts by weight (solid content) of the resin contained in the paint. It is preferable to contain in the range whose quantity is 400 or less. The amount of oil absorption is the amount of oil required to mechanically wet mix the pigment with the liquid to form a firm paste, and is specifically expressed in milliliters of refined oil for the pigment 100. The For example, per 100 parts by weight (solid content) of resin, the total oil absorption in a system using 2 parts by weight of flake pigment A having an oil absorption of 50 and 5 parts by weight of flake pigment B having an oil absorption of 40 300, which satisfies the above requirements. It is preferable to use a flake pigment that satisfies the above requirements after adjusting it within the above average particle diameter range.
[0031]
The cationic electrodeposition coating composition (A) contains the above-described component (a), component (b), component (c) and component (d), and the composition ratio of these components depends on the purpose. Although it can be arbitrarily selected, for example, in terms of solid content ratio, per 100 parts by weight of component (a), component (b) is 0.5 to 10 parts by weight, particularly 1 to 5 parts by weight, and component (c) is 0.1 10 to 10 parts by weight, particularly 0.5 to 5 parts by weight is preferred. The component (d) is suitably in the range of 5 to 50 parts by weight, particularly 10 to 30 parts by weight in terms of the total amount of pigment per 100 parts by weight (solid content) of the component (a).
[0032]
In the cationic electrodeposition coating composition (A), a curing agent, an antifoaming agent, a repellency inhibitor, an anti-settling agent, a curing catalyst, an organic solvent, and the like can be appropriately blended.
[0033]
Among these, a block polyisocyanate compound can be suitably used as the curing agent. Specific examples include compounds formed by blocking isocyanate groups of polyisocyanate compounds having two or more free isocyanate groups in one molecule with a blocking agent. Examples of polyisocyanate compounds include aromatic diisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and naphthalene diisocyanate; tetramethylene diisocyanate Aliphatic diisocyanates such as hexamethylene diisocyanate, dimer acid diisocyanate, lysine diisocyanate; methylene bis (cyclohexyl isocyanate), isophorone diisocyanate, methylcyclohexane diisocyanate Alicyclic diisocyanates such as neat, cyclohexane diisocyanate, cyclopentane diisocyanate; biuret type adducts, isocyanuric ring type adducts of the polyisocyanate compounds; these polyisocyanates And low molecular weight or high molecular weight compounds Poly - isocyanate and Le acids - DOO group excess reacted and becomes free isocyanate - DOO group-containing prepolymer - and the like. Examples of blocking agents include phenols, oximes, lactams, active methylenes, alcohols, acid amides, imides, amines, imidazoles, ureas, carbamic acids, and imines. In addition, known blocking agents such as mercaptans can be used. The number average molecular weight of the block polyisocyanate compound is preferably 200 to 10,000. The blending amount of the block polyisocyanate compound is preferably 100 parts by weight or less, particularly 10 to 70 parts by weight, per 100 parts by weight (solid content) of the component (A).
[0034]
Deionized water or the like is added so that the solid content of the cationic electrodeposition coating composition (A) is about 5 to 40% by weight, and an electrodeposition bath having a pH of 5.5 to 9.0 is obtained. Electrodeposition coating is performed by immersing and energizing the object to be coated as a cathode under conditions of 35 ° C. and a load voltage of 100 to 400V. The coating film thickness is suitably in the range of 10 to 40 μm based on the cured coating film. After energization, the resin is pulled up from the electrodeposition bath and washed with water, and then cured by heating at 100 to 200 ° C. for about 10 to 40 minutes.
[0035]
In the method of the present invention, an electrodeposition paint (A) is applied to an object to be coated, the coating film is heated and cured, and then an intermediate coating paint (B), a top coating base paint (C) is applied to the electrodeposition coating film surface. ) And clear paint (D) are applied by wet-on-wet and then heated to simultaneously cure these three-layer coating films to form a multilayer coating film.
[0036]
The intermediate coating (B) is a coating that is applied to the surface of the intermediate coating film that has been heat-cured and can be used as it is known, for example, thermal curing containing a base resin, a crosslinking agent, a pigment, and an organic solvent. Reactive paints. Examples of the base resin include a polyester resin having a crosslinkable functional group such as a hydroxyl group, an acrylic resin, and an alkyd resin. Examples of the crosslinker include a melamine resin capable of reacting with the crosslinkable functional group and a (block) polyisocyanate. Compounds. As the pigment, a normal inorganic or organic solid color pigment can be used. The intermediate coating (B) can be prepared by mixing these base resin, crosslinking agent, and pigment in an organic solvent and dissolving or dispersing them. The color tone of the coating film is not particularly limited, but white to gray is preferable.
[0037]
For the intermediate coating (B), the solid content at the time of coating is adjusted to 10 to 60% by weight and the viscosity is adjusted to 10 to 50 seconds / forward cup # 4/20 ° C. It is preferable to coat the electrodeposition coating film so as to have a cured coating film thickness of 5 to 40 μm.
[0038]
In the present invention, the top coating base paint (C) is applied to the uncured coating surface without crosslinking and curing the intermediate coating film.
[0039]
The top coat base coating (C) is for imparting a colorful cosmetic to the multilayer coating film. For example, a thermosetting coating containing a base resin, a crosslinking agent, a pigment and an organic solvent can be used. The color tone of the coating film can be applied to any of solid color tone, metallic tone, and light interference tone. Examples of the base resin include a polyester resin having a crosslinkable functional group such as a hydroxyl group, an acrylic resin, and an alkyd resin. Examples of the crosslinker include a melamine resin capable of reacting with the crosslinkable functional group and a (block) polyisocyanate. Compounds. Usable pigments include ordinary inorganic or organic solid color pigments, metallic pigments such as aluminum flakes, and light interference pigments such as mica coated with a metal oxide. The top coat base paint (C) can be prepared by mixing these base resin, cross-linking agent and pigment in an organic solvent and dissolving or dispersing them. The solid content during coating is 10 to 60% by weight and the viscosity is 10 to 50%. Second / Ford cup # 4/20 ° C. It is preferable to adjust the thickness to 5 to 40 μm on the uncured coating surface of the intermediate coating (B) by a static coating method or a spray coating method. It is preferable to paint so that it becomes.
[0040]
In the present invention, the clear coating (D) is applied to the uncured coating surface without crosslinking and curing the coating film of the top coat base coating (C).
[0041]
The clear coating (D) can form a colorless transparent or colored transparent coating, and specifically, a thermosetting coating containing a base resin, a crosslinking agent and an organic solvent can be used. Examples of the base resin include a polyester resin having a crosslinkable functional group such as a hydroxyl group, a carboxyl group, and an epoxy group, an acrylic resin, an alkyd resin, and the like. As the crosslinker, a melamine resin that can react with the above crosslinkable functional group, (Block) Polyisocyanate compound, epoxy group-containing compound, carboxyl group-containing compound. The clear paint (D) has a mica coated with an inorganic or organic solid color pigment, a metallic pigment such as an aluminum flake, or a metal oxide to such an extent that the transparency of the coating is not impaired. A light interference pigment such as can be contained. The clear paint (D) can be prepared by mixing these components in an organic solvent and dissolving or dispersing them. The solid content during coating is 10 to 60% by weight, the viscosity is 10 to 50 seconds / Ford cup # 4. It is preferable to adjust to / 20 ° C., and it is applied to the surface of the uncured topcoat base paint (C) by an electrostatic method, a spray method or the like so as to have a cured coating film thickness of 5 to 40 μm. It is preferable.
[0042]
In the method of the present invention, an electrodeposition paint (A) is applied to an object to be coated, the coating film is heated and cured, and then an intermediate paint (B), a top coat base paint (C) and a clear paint (D) are applied. After coating with wet-on-wet as described above, heating at 100 to 180 ° C., preferably 120 to 160 ° C. for 10 to 40 minutes, simultaneously curing these three-layer coating films to form a multilayer coating film More of that is achieved.
[0043]
【The invention's effect】
The above-mentioned electrodeposition paint (a) is used for forming a multilayer coating film by applying 3C1B to the cured coating surface of the electrodeposition paint applied to the object to be coated with 3C1B. A resin obtained by reacting a cyclic ester compound with a hydroxyl group of a bisphenol type epoxy resin, (b) a vinyl resin having a solubility parameter value of less than 9.6, and (c) a solubility parameter value of 9.6. By using a cationic electrodeposition paint containing a polyalkylene glycol of less than (d) and a pigment component having an average particle size adjusted to 0.5 μm or less, a finished appearance such as smoothness of a multilayer coating film is obtained. And chipping resistance could be improved.
[0044]
【Example】
Below, the Example and comparative example regarding this invention are described. Both parts and percentages are based on weight. Moreover, the thickness of a coating film is about a cured coating film.
[0045]
1. Preparation of Cationic Electrodeposition Paint (A) 1) (a) Component i): A resin obtained by subjecting an ε-caprolactone-modified bisphenol A type epoxy resin to a diethylamine reaction and then neutralizing with formic acid. The content of ε-caprolactone is 20% based on the component (a) (solid content). The number average molecular weight is about 35000.
[0046]
ii): A resin obtained by reacting a bisphenol A type epoxy resin with a ethanolamine and then neutralizing with formic acid. Not modified with ε-caprolactone. The number average molecular weight is about 35000.
[0047]
2) (b) Component i): An acrylic resin using isobutyl acrylate, hydroxyethyl methacrylate and dimethylaminoethyl methacrylate, and the SP value was adjusted to 9.3. The number average molecular weight is 7000.
[0048]
ii): An acrylic resin using isobutyl acrylate, hydroxyethyl methacrylate and dimethylaminoethyl methacrylate, and the SP value was adjusted to 9.8. The number average molecular weight is 7000.
[0049]
3) (c) Component i): SP value was adjusted to 9.1 with polypropylene glycol. The number average molecular weight is 3000.
[0050]
ii): SP value was adjusted to 9.7 with polytetotamethylene glycol. The number average molecular weight is 3000.
[0051]
4) Pigment component i): 5 parts (solid content) of the above (a) i) 15 parts of titanium white pigment with an average particle size adjusted to 0.4 μm, carbon black 0.3 part, silica 2 parts of lead acid and 2 parts of dioctyltin oxide (catalyst) were mixed and dispersed.
[0052]
ii): 5 parts (solid content) of the above (a) ii) 15 parts of titanium white pigment adjusted to an average particle size of 1.0 μm, 0.3 part of carbon black, 2 parts of lead silicate And 2 parts of dioctyltin oxide (catalyst) were mixed and dispersed.
[0053]
5) Curing agent i): "Duranet TPA-100" (trade name, hexamethylene diisocyanate polyisocyanate compound manufactured by Asahi Kasei Co., Ltd.) blocked with methyl ethyl ketoxime .
[0054]
6) Cationic electrodeposition paint (A)
A): (a) component i) 100 parts (solid content), curing agent i) 30 parts (solid content), (b) component i) 2 parts (solid content), (c) component i) 1 part (solid) And 24.3 parts (solid content) of pigment component i) were mixed and water was added to obtain a cationic electrodeposition paint having a solid content of 15%. (For example)
B): (a) component i) 100 parts (solid content), curing agent i) 30 parts (solid content), (b) component i) 5 parts (solid content), pigment component i) 24.3 parts (solid) Min) and water was added to obtain a cationic electrodeposition paint having a solid content of 20%. (For comparative example)
C): (a) component i) 100 parts (solid content), curing agent i) 30 parts (solid content), (c) component i) 2 parts (solid content), pigment component i) 24.3 parts (solid) Min) and water was added to obtain a cationic electrodeposition paint having a solid content of 20%. (For comparative example)
D): (a) component i) 100 parts (solid content), curing agent i) 30 parts (solid content), (b) component ii) 2 parts (solid content), (c) component ii) 1 part (solid) Min) and 24.3 parts (solid content) of pigment component i) were mixed and water was added to obtain a cationic electrodeposition paint having a solid content of 20%. (For comparative example)
E): (a) component ii) 100 parts (solid content), curing agent i) 30 parts (solid content), (b) component i) 2 parts (solid content), (c) component i) 1 part (solid) Min) and 24.3 parts (solid content) of pigment component i) were mixed and water was added to obtain a cationic electrodeposition paint having a solid content of 20%. (For comparative example)
F): (a) component i) 100 parts (solid content), curing agent i) 30 parts (solid content), (b) component i) 2 parts (solid content), (c) component i) 1 part (solid) And 24.3 parts (solid content) of pigment component ii) were mixed, and water was added to obtain a cationic electrodeposition paint having a solid content of 20%. (For comparative example)
2. Examples and Comparative Examples The bath temperature of the cationic electrodeposition coating material (A) was adjusted to 28 ° C., and an SPC dull steel plate surface-treated with “PB-L3080” (trade name, manufactured by Nippon Parkerizing Co., Ltd.) was used as the cathode. Then, the film was energized at 250 V so that a 20 μm-thick coating film was formed, and then pulled up and washed with water, and then the electrodeposition plate was baked at 170 ° C. for 20 minutes to cure the coating film.
[0055]
Next, an intermediate coating (B) ("TP65 Gray", trade name, organic solvent-based) manufactured by Kansai Paint Co., Ltd. was applied to the electrodeposited surface to a film thickness of 30 μm and left at room temperature for 2 minutes. After that, paint the metallic paint (C) ("Magiclon Silver", manufactured by Kansai Paint Co., Ltd., trade name, organic solvent type) to a film thickness of 15μm, leave it at room temperature for 3 minutes, and then further clear paint (D) (“Majiklon Kuriya”, manufactured by Kansai Paint Co., Ltd., trade name, organic solvent type) was applied to a film thickness of 35 μm, allowed to stand at room temperature for 3 minutes, and then baked at 140 ° C. for 30 minutes. The layer coating was simultaneously crosslinked and cured.
[0056]
A performance test was performed on the coating film thus obtained. The results are shown in Table 1.
[0057]
[Table 1]

The test method is as follows.
[0058]
Smoothness: The surface of the electrodeposition coating film cured before applying the intermediate coating and the top coating color coating was measured using a surface roughness meter (trade name, “Surfcom 550A”, manufactured by Tokyo Seimitsu Co., Ltd.). The roughness Ra was measured. ○ indicates less than 0.2 μm, Δ indicates 0.2 μm to less than 0.25 μm, and x indicates 0.25 μm or more.
[0059]
Repelling resistance: After 1 or 2 drops of oil (manufactured by Nihon Parker Co., NoxRust 880P) is attached to the uncured electrodeposition coating surface, the coating film is cured by baking at 170 ° C. for 20 minutes. The paint surface of was examined. ○ indicates that no repelling occurs, Δ indicates that a small repelling with a diameter of less than 1 mm has occurred, and x indicates that a repelling with a diameter of 1 mm or more has occurred.
[0060]
Chipping resistance: At −20 ° C., the coated surface after spraying 50 g of No. 7 crushed stone at a pressure of 4 kg / cm 2 at an angle of 45 degrees with respect to the coated surface and then applying the top-coated colored paint and curing it. Observed. ○ indicates that the diameter of the peeled portion of the coating film by spraying of crushed stone is less than 1 mm, Δ indicates that it is 1 mm or more and less than 2 mm, and × indicates that peeling of 2 mm or more is generated.
[0061]
Vividness: Vividness of the surface of the multilayer coating film was visually evaluated. ○ indicates good visibility, Δ indicates slightly poor clarity, and x indicates very poor clarity.

Claims (1)

  The electrodeposition paint (A) was applied to the object to be coated, and the coating film was heated and cured, and then the intermediate paint (B), the top coat base paint (C) and the clear paint (D) were applied wet-on-wet. Then, in a method of heating to form these multilayer coating films by simultaneously curing these three-layer coating films, as the electrodeposition paint (A), (a) a cyclic ester compound is reacted with the hydroxyl group of the bisphenol type epoxy resin. (B) a vinyl resin having a solubility parameter value of less than 9.6, (c) a polyalkylene glycol having a solubility parameter value of less than 9.6, and (d) an average particle size adjusted to 0.5 μm or less. The vinyl resin (b) is obtained by polymerizing isobutyl acrylate, hydroxyethyl methacrylate and dimethylaminoethyl methacrylate, and has a solubility parameter value of In the range of less than .0～9.6 method for forming a multilayer coating film having a number average molecular weight is characterized by the use of cationic electrocoating acrylic resin in the range of 5,000 to 20,000.