JP2004225095A - Method for forming coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a coating film by using cation electrodeposition coating excellent in deposition property, suitability of the electrodeposition coating to corrosion preventive steel sheet (g material coating property) and corrosion resistance in the electrodeposition coating for a short time. <P>SOLUTION: The method for forming the coating film uses a cation electrodeposition coating comprising a base resin prepared by reacting an epoxy resin (a<SB>1</SB>) with at least one of modifier selected among polyhydric polyols (a<SB>2</SB>), epoxy compounds (a<SB>3</SB>) of polyhydric polyol and cyclic ester compounds (a<SB>4</SB>), a polyphenol compound (a<SB>5</SB>) and an amino group-containing compound (a<SB>6</SB>) and a curing agent prepared by reacting at least one of block agent (b<SB>2</SB>)selected among oxime base compounds, aliphatic alcohols, aromatic alkyl alcohols and ether alcohols with at least one of polyisocyanate compound (b<SB>1</SB>) selected from aromatic polyisosyanate compounds and alicyclic polyisosyanate compounds. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２２】
ここでｎ＝０〜８で示されるものが好適である。
【００２３】
エポキシ樹脂（ｉ）は、一般に１８０〜２，５００、好ましくは２００〜２，０００であり、さらに好ましくは４００〜１，５００の範囲内のエポキシ当量を有することができ、また、一般に少なくとも２００、特に４００〜４，０００、さらに特に８００〜２，５００の範囲内の数平均分子量を有するものが適している。
【００２４】
かかるエポキシ樹脂の市販品としては、例えば、ジャパンエポキシレジン（株）からエピコート８２８ＥＬ、同左１００２、同左１００４、同左１００７なる商品名で販売されているものが挙げられる。
【００２５】
変性剤：
変性剤として用いる多価ポリオール（ａ_２）は、例えば、１分子中に少なくとも２個のアルコール性水酸基を含有する化合物であり、具体的には、例えば、エチレングリコール、プロピレングリコール、１，３−ブチレングリコール、１，４−ブタンジオール、１，６−ヘキサンジオール、ジエチレングリコール、ジプロピレングリコール、シクロヘキサン−１，４−ジメチロール、ネオペンチルグリコール、ポリプロピレングリコール、ポリエチレングリコール、トリエチレングリコール、水素化ビスフェノールＡなどのジオール類；グリセリン、トリメチロールエタン、トリメチロールプロパンなどのトリオール類；ペンタエリスリトール、α−メチルグルコキシドなどのテトロール類；ソルビトール、ジペンタエリスリトールなどのヘキソール類；シュークロースなどのオクトール類が挙げられる。
変性剤としては、上記の多価ポリオール（ａ_２）にエピクロルヒドリンを反応させて得られる多価ポリオールのエポキシ化合物（ａ_３）も用いることができる。
【００２６】
さらにプロピレンオキシド変性ビスフェノールＡジグリシジル、エチレングリコールオキシド変性ビスフェノールＡジグリシジル等も変性剤として用いることができる。変性剤として用いる環状エステル化合物（ａ_４）は、下記の式 （１）
【００２７】
【化２】

式（１）
（式中、Ｒ＝ＨまたはＣＨ_３、ｎは３〜６）で示され、具体的には、例えば、δ−バレロラクトン、ε−カプロラクトン、ζ−エナラクトン、η−カプリロラクトン、γ−バレロラクトン、δ−カプロラクトン、ε−エナラクトン、ξ−カプリロラクトンが挙げられ、特に好ましくはε−カプロラクトンである。
【００２８】
上記付加反応において、式（１）の環状エステル化合物（ａ_４）は開環し、エポキシ樹脂中の２級水酸基と反応し、１級水酸基を付与するとともに、ラクトンに基因するメチレン鎖部分はエポキシ樹脂に可塑性を付与する。
【００２９】
エポキシ樹脂（ａ_１）と反応させる変性剤の量、即ち、多価ポリオール（ａ_２）、多価ポリオールのエポキシ化合物（ａ_３）、環状エステル化合物（ａ_４）から選ばれる少なくとも１種類の変性剤の量は、厳密に制限されるものではないが、アミン付加エポキシ樹脂（Ａ）中に、多価ポリオール（ａ_２）と多価ポリオールのエポキシ化合物（ａ_３）と環状エステル化合物（ａ_４）から選ばれる少なくとも１種類ノ変性剤が５〜４０重量％、好ましくは１０〜３５重量％を占めるように調節するのが好ましい。
【００３０】
次に、ポリフェノール化合物（ａ_５）は、例えば、フェノール、クレゾール類、パラ−オクチルフェノール、ノニルフェノール、ビスフェノールプロパン、ビスフェノールメタン、レゾルシン、ピロカテコール、ハイドロキノン、パラ−ｔｅｒｔ−ブチルフェノール、ビスフェノールスルホン、ビスフェノールエーテル、パラ−フェニルフェノール等、ビス（４−ヒドロキシフェニル）−２，２−プロパン、ビス（４−ヒドロキシフェニル）−１，１−エタン、ビス（４−ヒドロキシフェニル）−１，１−イソブタン、４，４′−ジヒドロキシベンゾフェノン、ビス（４−ヒドロキシ−３−ｔ−ブチルフェニル）−２，２プロパン、ビス（２−ヒドロキシナフチル）メタン、１，５−ジヒドロキシナフタレンが挙げられ、これらはそれぞれ単独で又は２種以上の組合せて用いることができる。
【００３１】
製造方法は、反応釜にエポキシ樹脂（ａ_１）、多価ポリオール（ａ_２）と多価ポリオールのエポキシ化合物（ａ_３）と環状エステル化合物（ａ_４）から選ばれる少なくとも１種類ノ変性剤、ポリフェノール化合物（ａ_５）を配合した後、さらに有機溶剤、ジメチルベンジルアミン、トリブチルアミン、トリエチルアミンなどの塩基性アミノ化合物触媒、及びテトラエチルアンモニュウムブロマイド、テトラブチルアンモニュウムブロマイド、テトラエチルアンモニュウムヒドロキシド、トリフェニルエチルホスホニュウムアイオダイドなどを加えて変性エポキシ樹脂を作成する。
【００３２】
変性エポキシ樹脂を製造するにおける触媒量としては、エポキシ樹脂（ａ_１）、多価ポリオール（ａ_２）と多価ポリオールのエポキシ化合物（ａ_３）と環状エステル化合物（ａ_４）から選ばれる少なくとも１種類ノ変性剤、及びポリフェノール化合物（ａ_５）の固形分合計に基づいて、１〜１０，０００ｐｐｍ配合し、約５０℃〜約２００℃の温度で約３０分〜約１０時間加熱することによって行うことができる。
【００３３】
次に、上記の変性エポキシ樹脂にアミノ基含有化合物（ａ_６）を付加してアミン付加エポキシ樹脂（Ａ）が製造される。
【００３４】
前記の変性エポキシ樹脂に反応するアミノ基含有化合物（ａ_６）は、エポキシ樹脂にアミノ基を導入して、該エポキシ樹脂をカチオン化するためのカチオン性付与成分であり、エポキシ樹脂と反応する活性水素を少なくとも１個含有するものが用いられる。
【００３５】
上記のアミノ基含有化合物（ａ_６）としては、モノメチルアミン、ジメチルアミン、モノエチルアミン、ジエチルアミン、モノイソプロピルアミン、トリイソプロピルアミン、モノブチルアミン、ジブチルアミンなどのモノ−もしくはジ−アルキルアミン；
モノエタノールアミン、ジエタノールアミン、モノ（２−ヒドロキシプロピル）アミン、ジ（２−ヒドロキシプロピル）アミン、トリ（２−ヒドロキシプロピル）アミン、モノメチルアミノエタノール、モノエチルアミノエタノールなどのアルカノールアミン；エチレンジアミン、プロピレンジアミン、ブチレンジアミン、ヘキサメチレンジアミン、テトラエチレンペンタミン、ペンタエチレンヘキサミン、ジエチルアミノプロピルアミン、ジエチレントリアミン、トリエチレンテトラミンなどのアルキレンポリアミン及びこれらのポリアミンのケチミン化物；エチレンイミン、プロピレンイミンなどのアルキレンイミン；ピペラジン、モルホリン、ピラジンなどの環状アミンなどが挙げられる。
【００３６】
これらのアミノ基含有化合物（ａ_６）は、変性エポキシ樹脂のエポキシ基と、約３０℃〜約１５０℃の温度で３０分〜１５０分間程度の条件下で反応させてもよいが、一般には、上記のアミンのうち第１級アミンやＮ−ヒドロキシアルキル第２級アミンを使用する場合には、このものをあらかじめケトン、アルデヒドもしくはカルボン酸と、１００〜２３０℃程度で加熱反応させてアルジミン、ケチミン、オキサゾリンもしくはイミダゾリンに変性し、このものを変性エポキシ樹脂中のエポキシ基と、約８０℃〜約２００℃の温度で約１時間〜約５時間反応させることが好ましい。
【００３７】
また、これらのアミノ基含有化合物（ａ_６）の使用量は、アミン付加エポキシ樹脂（Ａ）のアミン価が２０〜８０ｍｇＫＯＨ／ｇ、好ましくは２５〜７０ｍｇＫＯＨ／ｇとなるような範囲内が好ましい。また、アミン付加エポキシ樹脂（Ａ）の重量平均分子量は約１，０００〜約１０，０００の範囲内にあることが好ましい。
【００３８】
また、上記のようにして得られたアミン付加エポキシ樹脂（Ａ）のガラス転移温度は−１０〜６０℃の範囲である。
【００３９】
本発明でのガラス転移温度は、示差熱分析装置（セイコー電子工業社製熱分析装置”ＤＳＣ−５２００型”により昇温速度１０℃／分で測定）により実測した値である。
【００４０】
ブロック化ポリイソシアネート（Ｂ）
本発明において、架橋剤として使用されるブロック化ポリイソシアネート（Ｂ）は、ポリイソシアネート種としては、芳香族ポリイソシアネート化合物又は脂環式ポリイソシアネート化合物のポリイソシアネート化合物（ｂ_１）に、ブロック剤としては、オキシム系化合物、脂肪族アルコール類、芳香族アルキルアルコール類、エーテルアルコール類の中から選ばれる少なくとも１種類のブロック剤（ｂ_２）を反応させてなるブロック化ポリイソシアネート硬化剤（Ｂ）である。
【００４１】
芳香族ジイソシアネート化合物は、例えば、１，３−および／または１，４−フェニレンジイソシアネート、２，４−および／または２，６−トリレンジイソシアネート（ＴＤＩ）、粗製ＴＤＩ、２，４’−および／または４，４’−ジフェニルメタンジイソシアネート（通常、「ＭＤＩ」と呼ばれる）、４，４’−ジイソシアナトビフェニル、３，３’−ジメチル−４，４’−ジイソシアナトビフェニル、３，３’−ジメチル−４，４’−ジイソシアナトジフェニルメタン、クルードＭＤＩ、１，５−ナフチレンジイソシアネート、４，４’，４”−トリフェニルメタントリイソシアネート、ｍ−およびｐ−イソシアナトフェニルスルホニルイソシアネートなどが挙げられる。
【００４２】
なかでもジフェニルメタン−２，４’−ジイソシアネート、ジフェニルメタン−４，４’−ジイソシアネート（通常、「ＭＤＩ」と呼ばれる）、クルードＭＤＩが好適である。
【００４３】
クルードＭＤＩは、ジフェニルメタン−４，４’−ジイソシアネートとジフェニルメタン−２，４’−ジイソシアネートとポリメチレンポリフェニルポリイソシアネートとを主成分とする混合物であり、市販品として、コスモネートＭ−５０、同Ｍ−２００、同Ｍ−１００、同Ｍ−３００等（以上、いずれも三井化学社製）；スミジュール４４Ｖ１０、同４４Ｖ２０、同４４Ｖ４０等（以上、いずれも住友バイエルウレタン社製）；ルプラネートＭ−１２、同Ｍ−１２Ｓ、同Ｍ−２０、同Ｍ−２０Ｓ等（以上、いずれもドイツ国、ＢＡＳＦ社製）；モンデュアＭＲ（ＬＩＧＨＴ）等（バイエル社製）などを挙げることができる。
【００４４】
脂環式ポリイソシアネート化合物は、イソホロンジイソシアネート（ＩＰＤＩ）、ジシクロヘキシルメタン−４，４’−ジイソシアネート（水添ＭＤＩ）、シクロヘキシレンジイソシアネート、メチルシクロヘキシレンジイソシアネート（水添ＴＤＩ）、ビス（２−イソシアナトエチル）−４−シクロヘキセン−１，２−ジカルボキシレート、２，５−及び／又は２，６−ノルボルナンジイソシアネートなどが挙げられる。
【００４５】
他に、上記のポリイソシアネート化合物の変性物には、変性ＭＤＩ（ウレタン変性ＭＤＩ、カルボジイミド変性ＭＤＩ、トリヒドロカルビルホスフェート変性ＭＤＩ）、ウレタン変性ＴＤＩ、ビウレット変性ＨＤＩ、イソシアヌレート変性ＨＤＩ、イソシアヌレート変性ＩＰＤＩなどのポリイソシアネートの変性物；およびこれらの２種以上の混合物［たとえば変性ＭＤＩとウレタン変性ＴＤＩ（イソシアネート基含有プレポリマー）との併用］が含まれる。
【００４６】
ブロック化剤は、ポリイソシアネート化合物のイソシアネート基に付加してブロックするものであり、そして付加によって生成するブロックポリイソシアネート化合物は常温において安定で且つ約１００〜２００℃、好ましくは１２０〜１５０℃に加熱した際、ブロック剤を解離して遊離のイソシアネート基を再生しうるものであることが望ましい。また解離するブロック剤としては分子量が小さい程、形成した加熱減量が少なく、またそのことにより乾燥炉の低ヤニ・ススに寄与する。
【００４７】
このようなブロック剤は、例えば、メチルエチルケトオキシム、シクロヘキサノンオキシムなどのオキシム系化合物；ｎ−ブタノール、２−エチルヘキサノールなどの脂肪族アルコール類；フェニルカルビノール、メチルフェニルカルビノールなどの芳香族アルキルアルコール類；エチレングリコールモノプロピルエーテル、エチレングリコールモノブチルエーテル、ジエチレングリコールモノエチルエーテルなどのエーテルアルコール類；ε−カプロラクタム、γ−ブチロラクタムなどのラクタム化合物；フェノール、パラ−ｔ−ブチルフェノール、クレゾールなどのフェノール系化合物；ｎ−メチルアセトアミド、ｎ−エチルアセトアミド、ｎ−メチルプロピオンアミド、ｎ−メチルホルムアミドなどの低分子量アミド化合物等が挙げられる。
【００４８】
なかでもオキシム系化合物、脂肪族アルコール類、芳香族アルキルアルコール類、エーテルアルコール類が、つきまわり性と防錆鋼板の電着適性の面から、本発明の目的とするカチオン電着塗料には好ましい。
上記のブロック剤の配合量としては、イソシアネートのＮＣＯ基に対して１：１〜１：１．３で反応させることが好ましい。比率が１．３を越えるとブロック剤が残存して塗膜の防食性を低下させ、１．０未満ではＮＣＯ基が残存して塗料組成物の安定性を損なうので好ましくない。
【００４９】
本発明の塗膜形成方法に用いるカチオン電着塗料のブロック化ポリイソシアネート硬化剤（Ｂ）には、ポリイソシアネート化合物として、芳香族ポリイソシアネート化合物、又は脂環式ポリイソシアネート化合物のポリイソシアネート化合物から選ばれる少なくとも１種類と、ブロック剤として、オキシム系化合物、脂肪族アルコール系、芳香族アルキルアルコール系、エーテルアルコール類の中から選ばれる少なくとも１種類の組み合わせが好ましく、そのことによってブロック化ポリイソシアネート硬化剤（Ｂ）のガラス転移温度を４５〜６５℃の範囲とすることができる。
【００５０】
上記のカチオン電着塗料は、アミン付加エポキシ樹脂（Ａ）及びブロック化ポリイソシアネート硬化剤（Ｂ）を必須成分として含有するものであり、さらに必要に応じて、有機錫化合物、着色顔料、体質顔料、防錆顔料、有機溶剤、水、中和剤、顔料分散剤、塗面調整剤などの塗料添加物を含有することができる。
【００５１】
上記有機錫化合物は、ブロック化ポリイソシアネート（Ｂ）のブロック化剤の解離を促進し硬化触媒として働くものであり、例えば、ジブチル錫オキサイド、ジオクチル錫オキサイドなどの有機錫酸化物；ジブチル錫ジラウレート、ジオクチル錫ジラウレート、ジブチル錫ジアセテート、ジオクチル錫ジベンゾエート、ジブチル錫ジベンゾエートなどのジアルキル錫の脂肪酸または芳香族カルボン酸塩等を挙げることができ、なかでも低温硬化性の点からジアルキル錫芳香族カルボン酸塩が好適である。
有機錫化合物の含有量は、厳密に規定されるものではなく、塗料組成物に要求される性能等に応じて広範囲にわたって変えることができるが、通常、塗料組成物中の樹脂固形分１００重量部あたり０〜８重量部、好ましくは０．０５〜５重量部の範囲内となるようにするのが好適である。
【００５２】
カチオン電着塗料は、電着塗装によって所望の基材表面に塗装することができる。電着塗装は、一般には、固形分濃度が約５〜４０重量％となるように脱イオン水などで希釈し、さらにｐＨを５．０〜９．０の範囲内に調整した電着浴を、通常、浴温１５〜３５℃に調整し、負荷電圧１００〜４００Ｖの条件で被塗物を陰極として、通電時間は３０秒間〜５分、極面積比（Ａ／Ｃ）：８／１〜１／８、極間距離は１０ｃｍ〜３００ｃｍで通電することによって行うことができる。
電着塗膜の膜厚は、特に制限されるものではないが、一般的には、１０〜４０μｍ、好ましくは１５〜３０μｍの範囲内とすることができる。また、塗膜の焼き付け硬化温度は、一般に約１００〜約２００℃、好ましくは約１２０〜約１７０℃の範囲内が適している。
【００５３】
本発明の特定の基体樹脂と特定の硬化剤を用いたカチオン電着塗料による塗膜形成方法は、電着塗装時において、通電開始から１分後の塗膜抵抗値を４００ｋΩ・ｃｍ^２〜８５０ｋΩ・ｃｍ^２、好ましくはを４８０ｋΩ・ｃｍ^２〜６５０ｋΩ・ｃｍ^２の範囲とすることが容易であり、そのことによって通電時間が９０秒間〜１５０秒間の短時間での電着塗装にて、袋構造や内板部の膜厚が得られる高いつきまわり性と、防錆鋼板の電着適性（ｇ材塗装性）の両立が可能となった。
【００５４】
【発明の効果】本発明によれば、特定の基体樹脂と特定の硬化剤を用い、好ましくは、両成分のガラス転移温度を一定の範囲内とした樹脂成分を用いたカチオン電着塗料によって、短時間（９０秒間〜１５０秒間）の電着塗装において高つきまわり性と、防錆鋼板の電着適性（ｇ材塗装性）、及び防食性に優れる塗装物品が得られる。
さらに上記のカチオン電着塗料の電着塗装において通電開始から１分後の塗膜抵抗値を４００ｋΩ・ｃｍ^２〜８５０ｋΩ・ｃｍ^２の範囲とすれば、容易に高つきまわり性と、防錆鋼板の電着適性（ｇ材塗装性）の両立が可能となる。
理由としては、カチオン電着塗料の構成成分であるエマルションは、エマルションのコア部（中心部分）に硬化剤が、シェル部（表層部分）に基体樹脂の成分となって、基体樹脂のアミノ基を中和することによってエマルションの粒子を形成している。ここで特定の基体樹脂と特定の硬化剤を用いて、好ましくはガラス転移温度が一定の範囲とすることによって、１．通電開始から早い時間に塗膜抵抗が形成されるため、外板に費やされた電流が内板の塗膜形成に費やすことができ、つきまわり性が向上する。２．コア部（中心部分）に硬化剤が、通電時のスパークに耐えうる硬さを有しており、塗膜破壊を起しにくく、またガス穴が発生しても、シェル部（表層部分）の軟らかさがピンホールを補修することから、防錆鋼板の電着適性（ｇ材塗装性）に優れる。と考えられる。
上記の塗膜形成方法によると、短時間電着塗装が可能であるため生産性の向上、ラインの省スペース化、省エネルギー性にも優れ、かつ高つきまわり性であることから、袋部や内板部では防食性に優れ、かつ外板面では防錆鋼板のピンホール発生のない、仕上り性に優れた塗装物品を得ることができる。
【００５５】
【実施例】以下、実施例を挙げて本発明をさらに具体的に説明するが、本発明の範囲はこれら実施例のみに限定されるものではない。以下、「％」は「重量％」を意味するものとする。
【００５６】
基体樹脂の製造例
製造例１
温度計、撹拌機、還流冷却器、窒素ガス吹込口を取り付けた反応容器に、窒素ガス吹込下でプロピレンオキシド変性ビスフエノールＡジグリシジルエーテル（注１）５２５部、ビスフエノールＡ ３４２部、及び有効成分８０％のモノエタノールアミンとメチルイソブチルケトンとのケチミンのメチルイソブチルケトン溶液３６部を仕込み、１６０℃でエポキシ基が消失するまで反応させた。
さらに、このものにエポキシ当量が約１９０のビスフエノールジグリシジルエーテル ６６５部及び有効成分８０％のモノエタノールアミンとメチルイソブチルケトンとのケチミンのメチルイソブチルケトン溶液２３２部を加え、１４０℃でエポキシ基濃度が０．２７ミリモル／ｇになるまで反応させた。これによって数平均分子量約１５００のエポキシ樹脂液が得られた。
次にエチレングリコールモノブチルエーテル３６５部で希釈冷却し、１００℃になったところで有効成分８０％のジエチレントリアミンのメチルイソブチルケトンジケチミンのメチルイソブチルケトン溶液１６７部を加え、１００℃で粘度上昇が停止するまで反応させ、固形分が８０％の基体樹脂Ｎｏ．１を得た。基体樹脂Ｎｏ．１のガラス転移温度は、２３℃であった。
（注１） プロピレンオキシド変性ビスフエノールＡジグリシジルエーテル（三洋化成社製、商品名、グリシエールＢＰＰ−３５０、エポキシ当量約３４０）。
【００５７】
製造例２
製造例１と同様な反応装置に窒素ガス吹込下でエポキシ当量約３００のエチレンオキシド変性ビスフエノールＡジグリシジルエーテル（注２）４５０部、及びビスフエノールＡ ３４２部、及び有効成分８０％のモノエタノールアミンのメチルイソブチルケトンケチミン（メチルイソブチルケトン溶液）３６部を仕込み、１６０℃でエポキシ基が消失するまで反応させた。
さらに、このものにエポキシ当量が約１９０のビスフエノールＡジグリシジルエーテル６６５部、及び有効成分８０％のモノエタノールアミンとメチルイソブチルケトンとのケチミンのメチルイソブチルケトン溶液２３２部を仕込み、１４０℃でエポキシ基濃度が０．２９ミリモル／ｇになるまで反応させた。これによつて数平均分子量約１，５００のエポキシ樹脂液が得られた。
次にこのものをエチレングリコールモノブチルエーテル３５０部で希釈冷却し、１００℃になつたところで有効成分８０％のジエチレントリアミンのメチルイソブチルケトンジケチミンのメチルイソブチルケトン１６７部を加え、１００℃の粘度上昇が停止するまで反応させ、固形分が８０％の基体樹脂Ｎｏ．２を得た。基体樹脂Ｎｏ．２のガラス転移温度は、２８℃であった。
（注２） エチレンオキシド変性ビスフエノールＡジグリシジルエーテル［三洋化成社製、商品名：グリシエールＢＰＥ−３００、エポキシ当量約３００］。
【００５８】
製造例３
攪拌機、温度計、窒素導入管および還流冷却器を取りつけたフラスコに、ビスフェノールＡとエピクロルヒドリンとの反応によって得られた数平均分子量３７０、エポキシ当量１８５のエポキシ樹脂５１８部を仕込み、ビスフェノールＡ ５７部、及びジメチルベンジルアミン０．２部を加え、１２０℃でエポキシ当量が２５０となるまで反応させた。
ついでε−カプロラクトン２１３部、及びテトラブトキシチタン０．０３部を加え、１７０℃に昇温し、この温度を保ちながら経時でサンプリングを行ない、赤外吸収スペクトル測定にて未反応ε−カプロラクトン量を追跡し、反応率が９８％以上になった時点でビスフェノールＡ １４８部とジメチルベンジルアミン０．４部をさらに加え、１３０℃でエポキシ当量９３６となるまで反応させた。ついでメチルイソブチルケトン２５７．４部、ジエチルアミン２５．６部、ジエタノールアミン６８．３部を加え８０℃で２時間反応後、メチルエチルケトンで希釈し、固形分が８０％の基体樹脂Ｎｏ．３を得た。基体樹脂Ｎｏ．３のガラス転移温度は、３８℃であった。
【００５９】
製造例４
反応容器にイソホロンジイソシアネート２２２部を仕込み反応温度を外部冷却により３０〜４０℃に保ちながら、メチルエチルケトオキシム１１３．１部を徐々に滴下して部分ブロックポリイソシアネートを合成した。
次に、製造例３で得た基体樹脂Ｎｏ．３ ５００部に、上記の部分ブロックイソシアネート８３．７部加え、窒素気流下に１００℃で赤外吸収スペクトル測定にてイソシアネート基の吸収がなくなるまで反応させた後、ジエチレングリコールモノブチルエーテルで希釈し、固形分が８０％の基体樹脂Ｎｏ．４を得た。基体樹脂Ｎｏ．４のガラス転移温度は、４４℃であった。
【００６０】
製造例５
エピコート８２８ＥＬ（ジャパンエポキシレジン（株）製、商品名、エポキシ樹脂）１０１０ｇに、ビスフェノールＡ ３９０ｇ及びジメチルベンジルアミン０．２ｇを加え、１３０℃でエポキシ当量８００になるまで反応させた。次に、ジエタノールアミン１６０ｇ及びジエチレントリアミンのケチミン化物６５ｇを加え、１２０℃で４時間反応させた後、ブチルセロソルブ３５５ｇを加え、アミン価６７、固形分が８０％の基体樹脂Ｎｏ．５を得た。基体樹脂Ｎｏ．５のガラス転移温度は、９０ ℃であった。
【００６１】
硬化剤の製造
製造例６
反応容器中に、コスモネートＭ−２００（注３） ２７０部及びメチルイソブチルケトン２５部を加え７０℃に昇温した。この中に２，２−ジメチロールブタン酸１５部を徐々に添加し、ついでエチレングリコールモノブチルエーテル１１８部を滴下して加え、７０℃で１時間反応させた後、６０℃に冷却し、プロピレングリコール１５２部を添加した。この温度を保ちながら、経時でサンプリングし、赤外線吸収スペクトル測定にて未反応のイソシアナト基の吸収がなくなったことを確認し、固形分が８０％の硬化剤Ｎｏ．１溶液を得た。ガラス転移温度は、５ ℃であった。（注３）コスモネートＭ−２００ ：商品名、三井化学社製、クルードＭＤＩ
【００６２】
製造例７
反応容器中に、トリレンジイソシアネート１７４部を加え７０℃に昇温した。この中に２，２−ジメチロールブタン酸１５部を徐々に添加し、ついでエチレングリコールモノブチルエーテル１１８部を滴下して加え、７０℃で１時間反応させた後、６０℃に冷却し、プロピレングリコール１５２部を添加した。この温度を保ちながら、経時でサンプリングし、赤外線吸収スペクトル測定にて未反応のイソシアナト基の吸収がなくなったことを確認し、固形分が８０％の硬化剤Ｎｏ．２を得た。ガラス転移温度は、１０ ℃であった。
【００６３】
製造例８
反応容器中に、イソホロンジイソシアネート２２２部及びメチルイソブチルケトン９９部を加え、５０℃に昇温した。この中にメチルエチルケトキシム１７４部をゆっくり加えた後、６０℃に昇温した。この温度を保ちながら、経時でサンプリングし、赤外線吸収スペクトル測定にて未反応のイソシアネートの吸収がなくったことを確認し、有機溶剤にて固形分を調整し、固形分８０％の硬化剤Ｎｏ．３を得た。ガラス転移温度は、８ ℃であった。
【００６４】
製造例９
ヘキサメチレンジイソシアネート５０部に、メチルケトオキシム３０部及びトリメチロールプロパン１０部を４０〜６０℃で滴下した後、８０℃で１時間加熱し、この温度を保ちながら、経時でサンプリングし、赤外線吸収スペクトル測定にて未反応のイソシアネートの吸収がなくったことを確認し、有機溶剤にて固形分を調整し、固形分８０％の硬化剤Ｎｏ．４を得た。ガラス転移温度は、−１９℃であった。
【００６５】
カチオン電着塗料用のエマルションの製造例
製造例１０ ＥＭ Ｎｏ．１
基体樹脂Ｎｏ．１ ８７．５部（樹脂固形分で７０部）、硬化剤Ｎｏ．１ を３７．５ｇ（樹脂固形分で３０ｇ）、及び１０％酢酸を１３部を配合し、均一に攪拌した後、脱イオン水を強く攪拌しながら約１５分間を要して滴下し、カチオン電着塗料用のエマルションである固形分３４％のＥＭ Ｎｏ．１を得た。
【００６６】
製造例１１〜１８ ＥＭ Ｎｏ．２〜Ｎｏ．９
表１の配合内容として、製造例１０と同様の操作にてカチオン電着塗料用のエマルションである固形分３４％のＥＭ Ｎｏ．２〜Ｎｏ．９を得た。
【００６７】
【表１】

【００６８】
顔料分散ペーストの製造
製造例１９
固形分６０％のエポキシ系４級アンモニウム型分散用樹脂 ５．８３部（固形分３．５部）、酸化チタン１４．５部、精製クレー７．０部、水酸化ビスマス １．０部、有機錫１．０部、カーボンブラック０．４部、脱イオン水２０．１部を加え、ボールミルにて２０時間分散したあと取出し、固形分５５％の顔料分散ペースト（固形分 ２７．４部）を得た。
【００６９】
実施例及び比較例
実施例１
エマルションＮｏ．１（基体樹脂Ｎｏ．１、硬化剤Ｎｏ．１） ２９４部（固形分１００部）に、顔料分散ペーストＮｏ．１を４９．８部（固形分２７．４部）、脱イオン水 ２９３．２部を加え、固形分２０％のカチオン電着塗料Ｎｏ．１（固形分 １２７．４）を製造した。
【００７０】
実施例２〜６
表２の配合内容とする以外は、実施例１と同様にしてカチオン電着塗料Ｎｏ．２〜Ｎｏ．６を得た。
【００７１】
比較例１〜３
表３の配合内容とする以外は、実施例１と同様にしてカチオン電着塗料Ｎｏ．７〜Ｎｏ．９を得た。
【００７２】
塗装試験
上記実施例及び比較例で得た各カチオン電着塗料中に、パルボンド＃３０２０（日本パーカラジジング社製、商品名、リン酸亜鉛処理剤）で化成処理した、０．８×１５０×７０ｍｍの冷延鋼板、亜鉛メッキ鋼板を用いて、下記の試験内容に従って、塗膜試験に供した。
【００７３】
カチオン電着塗料Ｎｏ．１〜Ｎｏ．６（実施例）の塗料配合、塗料特性、試験結果を表２に示す。
【００７４】
【表２】

【００７５】
カチオン電着塗料Ｎｏ．７〜Ｎｏ．９（比較例）の塗料配合、塗料特性、試験結果を表３に示す。
【００７６】
【表３】

【００７７】
（注４）つきまわり性：冷延鋼板（化成処理）によって図１のような４枚ボックス法つきまわり性試験の治具を作成し、図２のような配線にて、浴温２８℃で、表中の電圧にて９０分間、又は１５０秒間、電着塗装を行った。その後、１７０℃−２０分間の焼付け乾燥を行い、外板（Ａ面）膜厚、内板（Ｇ面）膜厚、Ｇ面膜厚／Ａ面膜厚（％）を評価した。
【００７８】
（注５）防錆鋼板の電着適性（ｇ材塗装性）：亜鉛メッキ鋼板（化成処理）を電着浴のカソードとして浸漬し、浴温度２８℃で、表中の電圧にて、９０分間、又は１５０秒間電着塗装した。その後、１７０℃−２０分間の焼付け乾燥を行い、試験板１０×１０ｃｍ中のピンホールの数をかぞえる。
○：ピンホールの発生なく良好な仕上がり性、
△：ピンホールが３〜５個発生、
×：１０個以上発生した
【００７９】
（注６）防食性：冷延鋼板（化成処理）を用いてカチオン電着塗装を行った試験板に、素地に達するようにナイフでクロスカット傷を入れ、これをＪＩＳ Ｚ−２３７１に準じて８４０時間耐塩水噴霧試験を行った。ナイフ傷からの傷、フクレ幅によって以下の基準で評価した。
◎：錆、フクレの最大幅がカット部より２ｍｍ未満（片側）、
○：錆、フクレの最大幅がカット部より３ｍｍ未満（片側）、
△：錆、フクレの最大幅がカット部より３〜４ｍｍ（片側）、
×：錆、フクレの最大幅がカット部より４ｍｍ以上
【００８０】
【図面の簡単な説明】
【図１】４枚ボックスつきまわり性の塗装試験に用いる治具である。
【図２】４枚ボックスつきまわり性の塗装試験の結線図である。
【符号の説明】
１０．Ｈ面
１１．Ａ面
１２．Ｃ面
１３．Ｅ面
１４．Ｇ面
１５．８ｍｍφの穴を空ける
２０．浴槽
２１．カチオン電着塗料
２２．陽極[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coating film using a cationic electrodeposition paint containing a specific base resin and a specific blocked polyisocyanate curing agent. In a short time of electrodeposition coating, it is possible to obtain a coated article excellent in throwing power, electrodeposition suitability of a rust-proof steel plate (g material coating property), and corrosion resistance.
[0002]
[Prior art and problems]
[Patent Document 1] 2001-19878
[Patent Document 2] Japanese Patent Application Publication No. 2002-275690
[Patent Document 3] JP-A-2002-60680
Cationic electrodeposition paints are widely used as undercoat paints for conductive metal products, such as automobile bodies, which require these properties, because of excellent coating workability and good corrosion protection of the formed coating film. However, in recent years, in order to enhance the strength of the automobile body from the viewpoint of improving collision safety, the structure in which the reinforcing members are superimposed one on the other is difficult to conduct electricity, and the current density is reduced, so the coating film is difficult to deposit and it is not painted. It causes the deterioration of corrosion prevention. Therefore, it is conceivable to increase the coating voltage to give a film thickness to the inner plate portion.
[0003]
In addition, a galvanized steel plate (g material) is often used as a rust-preventive steel plate from the viewpoint of reducing the cost of an automobile body. In addition, electrodeposition coating in a short time (90 seconds to 150 seconds) has been required from the viewpoint of energy saving, space saving, and improvement in productivity of a coating line.
[0004]
In consideration of the above problems, electrodeposition coating at high voltage is inevitable in order to obtain high throwing power on the bag part and the inner plate surface of the coated object. Sparks generated at the time of electrodeposition coating of a steel plate (g material) sometimes remain as pinholes after baking of the coating film, resulting in a decrease in finish.
[0005]
According to the conventional invention, a method of preparing a cationic electrodeposition paint that suppresses the generation of gas pinholes on a galvanized steel sheet and obtains a coating film having high throwing power is performed. A method for forming an electrodeposition coating film using a cationic electrodeposition coating material whose conductivity during coating is adjusted to 1000 to 1500 μS / cm within ± 5 ° C. of the preset coating temperature and performing electrodeposition coating at the above-mentioned preset electrodeposition coating temperature. Invention related to
[Patent Document 1].
[0006]
A cationic electrodeposition paint having uniform coating properties that can secure the thickness of the inner plate (μm) without increasing the thickness of the outer plate (μm), and also has excellent finish of galvanized steel sheet. In the cationic electrodeposition coating, the polarization resistance value (a) per unit film thickness is 120 to 300 kΩ · cm.²/ Cm and a cationic electrodeposition paint having a paint deposition amount per unit amount of electricity (b) in the range of 50 to 150 mg / C, and coating at an effective voltage (V) of 230 V or less. Invention on method
[Patent Document 2]. A cationic electrodeposition coating composition having improved throwing power and gas pin resistance, comprising a resin component containing an amine-modified epoxy resin and a blocked polyisocyanate curing agent, wherein a metal salt of an organic acid and an organic acid is used as a neutralizing agent. And an invention relating to a cationic electrodeposition coating composition in which the total amount of organic acids contained as a neutralizing agent and the equivalent ratio of organic acids to metal salts of organic acids are adjusted
[Patent Document 3]. And the like.
[0007]
As described above, in the cationic electrodeposition paint, there are many techniques for achieving both the throwing power and the electrodeposition suitability of a rust-preventive steel sheet (galvanized steel sheet). There was no invention which was able to achieve both the throwing power and the electrodeposition suitability of a rust-preventive steel sheet, and which had good anti-corrosion properties.
[0008]
Means for Solving the Problems The present inventors have conducted intensive studies in order to meet these problems, and as a result, have found that the object can be achieved by the following means, and have completed the present invention.
[0009]
That is, the present invention
1. A coating film forming method using a cationic electrodeposition paint containing the following amine-added epoxy resin (A) and blocked polyisocyanate curing agent (B),
Amine-added epoxy resin (A): epoxy resin (a₁) Has a polyhydric polyol (a₂) And an epoxy compound of a polyhydric polyol (a₃) And a cyclic ester compound (a₄), A polyphenol compound (a₅) And an amino group-containing compound (a₆) Base resin
Blocked polyisocyanate curing agent (B): at least one polyisocyanate compound selected from aromatic polyisocyanate compounds and alicyclic polyisocyanate compounds (b)₁), As a blocking agent, at least one blocking agent selected from oxime compounds, aliphatic alcohols, aromatic alkyl alcohols, and ether alcohols (b₂)
2. The glass transition temperature of the amine-added epoxy resin (A) is in the range of -10 to 60C, and the glass transition temperature of the blocked polyisocyanate curing agent (B) is in the range of -10 to 50C. Coating film forming method according to,
3. Further, a coating film forming method using the cationic electrodeposition coating composition according to claim 1 or 2, which contains a bismuth compound as a rust inhibitor,
4. At the time of electrodeposition coating, the coating film resistance value after 1 minute from the start of energization is 400 kΩ · cm²~ 850kΩcm²The method for forming a coating film according to any one of Items 1 to 3, wherein the cationic electrodeposition coating material is
5. A coated article coated by the method for forming a coating film according to any one of the items 1 to 4.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION The present invention uses a specific base resin and a specific curing agent, and preferably, a cationic electrodeposition paint having a glass transition temperature of both components within a certain range, for a short time (from 90 seconds to 90 seconds). (150 seconds) electrodeposition coating, high throwing power to easily attach film thickness to bag structure and inner plate, electrodeposition suitability of rustproof steel plate (g material coating property), and corrosion resistance And found a method of forming a coating film having excellent properties.
[0011]
Furthermore, the above-mentioned cationic electrodeposition paint has a coating resistance value of 400 kΩ · cm one minute after the start of energization in the electrodeposition coating.²~ 850kΩcm², Preferably 480 kΩ · cm²~ 650kΩcm²Within this range, it is possible to easily achieve both high throwing power and electrodeposition suitability (g-material coatability) of the rustproof steel sheet.
[0012]
The throwing power is evaluated by a four-box method. That is, as shown in FIG. 1, a box in which four zinc phosphate-treated cold-rolled steel sheets are arranged in parallel at intervals of 20 mm is used. The steel plates AB to EF other than the GH steel plate are provided with 8 mmφ holes at the bottom. Electrodeposition coating is performed using a wiring diagram as shown in FIG.
[0013]
According to the coating film forming method of the present invention, in the electrodeposition coating in which the energization time is 90 seconds to 150 seconds in the electrodeposition coating, the G-plane film thickness (μm) / A-plane film thickness (μm) = 30 to 100%, preferably G It is possible to obtain a throwing power of surface film thickness (μm) / A surface film thickness (μm) = 50 to 100%.
[0014]
Regarding the electrodeposition suitability (g material coatability) of the rust-preventive steel sheet, a voltage at which the above throwing power is obtained, for example, a voltage of 200 V or more, preferably 250 V or more, more preferably 300 V or more is applied to the object to be coated. No pinholes occur on the painted surface.
[0015]
As described above, in order to obtain throwing power and electrodeposition suitability of a rust-proof steel sheet, it is essential that a cationic electrodeposition paint using a specific base resin and a specific curing agent be used. In the agent, the glass transition temperature falls within a specific range, and more preferably, the coating resistance value after one minute from the start of energization of the cationic electrodeposition paint falls within a certain range, so that throwing power and rust prevention can be improved. It has been found that the electrodeposition suitability of the steel sheet is further improved.
[0016]
Hereinafter, the amine-added epoxy resin (A) used as a specific base resin used in the cationic electrodeposition coating and the blocked polyisocyanate curing agent (B) used as a curing agent will be described.
[0017]
Amine-added epoxy resin (A):
Epoxy resin (a₁) Has a polyhydric polyol (a₂) And an epoxy compound of a polyhydric polyol (a₃) And a cyclic ester compound (a₄), A polyphenol compound (a₅) And an amino group-containing compound (a₆) Is a base resin obtained by reacting
[0018]
Epoxy resin (a₁From the viewpoint of the anti-corrosion property of the coating film, in particular, an epoxy resin obtained by reacting a polyphenol compound with an epihalohydrin, for example, epichlorohydrin, is preferable.
[0019]
As the polyphenol compound that can be used for forming the epoxy resin, the same ones as those used in the related art can be used, and bis (4-hydroxyphenyl) -2,2-propane (bisphenol A), 4,4-dihydroxybenzophenone , Bis (4-hydroxyphenyl) methane (bisphenol F), bis (4-hydroxyphenyl) -1,1-ethane, bis (4-hydroxyphenyl) -1,1-isobutane, bis (4-hydroxy-tert- Butyl-phenyl) -2,2-propane, bis (2-hydroxynaphthyl) methane, tetra (4-hydroxyphenyl) -1,1,2,2-ethane, 4,4-dihydroxydiphenylsulfone (bisphenol S), Phenol novolak, cresol novolak and the like can be mentioned.
[0020]
The epoxy resin obtained by the reaction of the polyphenol compound with epichlorohydrin includes, among others, the following formula derived from bisphenol A:
[0021]
Embedded image

[0022]
Here, those represented by n = 0 to 8 are preferable.
[0023]
The epoxy resin (i) can generally have an epoxy equivalent in the range of 180 to 2,500, preferably 200 to 2,000, more preferably 400 to 1,500, and generally has an epoxy equivalent of at least 200, Those having a number average molecular weight in the range of 400 to 4,000, more preferably 800 to 2,500 are particularly suitable.
[0024]
Examples of commercially available epoxy resins include those sold by Japan Epoxy Resin Co., Ltd. under the trade names Epicoat 828EL, left 1002, left 1004, and left 1007.
[0025]
Modifier:
Polyhydric polyol used as a modifier (a₂) Is, for example, a compound containing at least two alcoholic hydroxyl groups in one molecule, and specifically, for example, ethylene glycol, propylene glycol, 1,3-butylene glycol, 1,4-butanediol, Diols such as 1,6-hexanediol, diethylene glycol, dipropylene glycol, cyclohexane-1,4-dimethylol, neopentyl glycol, polypropylene glycol, polyethylene glycol, triethylene glycol, hydrogenated bisphenol A; glycerin, trimethylolethane, Triols such as trimethylolpropane; tetrols such as pentaerythritol and α-methylglucoxide; hexols such as sorbitol and dipentaerythritol; Le acids and the like.
As the modifier, the above-mentioned polyhydric polyol (a₂) Is reacted with epichlorohydrin to obtain a polyhydric polyol epoxy compound (a)₃) Can also be used.
[0026]
Further, propylene oxide-modified bisphenol A diglycidyl, ethylene glycol oxide-modified bisphenol A diglycidyl, and the like can also be used as a modifier. Cyclic ester compound (a₄) Is the following equation (1)
[0027]
Embedded image

Equation (1)
(Wherein R = H or CH₃, N is 3 to 6), and specifically, for example, δ-valerolactone, ε-caprolactone, ζ-enalactone, η-caprylolactone, γ-valerolactone, δ-caprolactone, ε-enalactone, ξ-Caprolactone is preferred, and ε-caprolactone is particularly preferred.
[0028]
In the above addition reaction, the cyclic ester compound (a) of the formula (1)₄) Is ring-opened and reacts with a secondary hydroxyl group in the epoxy resin to give a primary hydroxyl group, and a methylene chain portion derived from lactone gives plasticity to the epoxy resin.
[0029]
Epoxy resin (a₁), The amount of the modifier, ie, the polyhydric polyol (a₂), An epoxy compound of a polyhydric polyol (a₃), Cyclic ester compound (a₄The amount of at least one modifier selected from the above) is not strictly limited, but the polyhydric polyol (a) is contained in the amine-added epoxy resin (A).₂) And an epoxy compound of a polyhydric polyol (a₃) And a cyclic ester compound (a₄It is preferable to adjust so that at least one kind of modifier selected from the above) accounts for 5 to 40% by weight, preferably 10 to 35% by weight.
[0030]
Next, a polyphenol compound (a₅) Is, for example, phenol, cresols, para-octylphenol, nonylphenol, bisphenolpropane, bisphenolmethane, resorcin, pyrocatechol, hydroquinone, para-tert-butylphenol, bisphenolsulfone, bisphenolether, para-phenylphenol, etc. -Hydroxyphenyl) -2,2-propane, bis (4-hydroxyphenyl) -1,1-ethane, bis (4-hydroxyphenyl) -1,1-isobutane, 4,4'-dihydroxybenzophenone, bis (4 -Hydroxy-3-t-butylphenyl) -2,2 propane, bis (2-hydroxynaphthyl) methane and 1,5-dihydroxynaphthalene, each of which is used alone or in combination of two or more. Door can be.
[0031]
The production method is such that an epoxy resin (a₁), Polyhydric polyol (a₂) And an epoxy compound of a polyhydric polyol (a₃) And a cyclic ester compound (a₄), A polyphenol compound (a₅), An organic solvent, a basic amino compound catalyst such as dimethylbenzylamine, tributylamine and triethylamine, and tetraethylammonium bromide, tetrabutylammonium bromide, tetraethylammonium hydroxide and triphenylethylphosphonium iodide. To create a modified epoxy resin.
[0032]
The amount of the catalyst in the production of the modified epoxy resin may be an epoxy resin (a₁), Polyhydric polyol (a₂) And an epoxy compound of a polyhydric polyol (a₃) And a cyclic ester compound (a₄), And a polyphenol compound (a₅1) to 10,000 ppm based on the total solid content of the above) and heating at a temperature of about 50 ° C. to about 200 ° C. for about 30 minutes to about 10 hours.
[0033]
Next, an amino group-containing compound (a₆) Is added to produce an amine-added epoxy resin (A).
[0034]
Amino group-containing compound (a) which reacts with the modified epoxy resin₆) Is a cationicity-imparting component for introducing an amino group into the epoxy resin to cationize the epoxy resin, and a component containing at least one active hydrogen that reacts with the epoxy resin is used.
[0035]
The above amino group-containing compound (a₆) Includes mono- or di-alkylamines such as monomethylamine, dimethylamine, monoethylamine, diethylamine, monoisopropylamine, triisopropylamine, monobutylamine and dibutylamine;
Alkanolamines such as monoethanolamine, diethanolamine, mono (2-hydroxypropyl) amine, di (2-hydroxypropyl) amine, tri (2-hydroxypropyl) amine, monomethylaminoethanol and monoethylaminoethanol; ethylenediamine, propylenediamine Alkylenepolyamines such as butylenediamine, hexamethylenediamine, tetraethylenepentamine, pentaethylenehexamine, diethylaminopropylamine, diethylenetriamine, and triethylenetetramine; and ketimines of these polyamines; alkyleneimines such as ethyleneimine and propyleneimine; piperazine; And cyclic amines such as morpholine and pyrazine.
[0036]
These amino group-containing compounds (a₆) May be reacted with an epoxy group of the modified epoxy resin at a temperature of about 30 ° C. to about 150 ° C. for about 30 minutes to 150 minutes, but in general, primary amines among the above amines When an N-hydroxyalkyl secondary amine is used, it is previously reacted with a ketone, an aldehyde or a carboxylic acid at about 100 to 230 ° C. to modify it into an aldimine, ketimine, oxazoline or imidazoline. It is preferred to react the epoxy resin with the epoxy group in the modified epoxy resin at a temperature of about 80C to about 200C for about 1 hour to about 5 hours.
[0037]
In addition, these amino group-containing compounds (a₆) Is preferably used in such a range that the amine value of the amine-added epoxy resin (A) is 20 to 80 mgKOH / g, preferably 25 to 70 mgKOH / g. Further, the weight average molecular weight of the amine-added epoxy resin (A) is preferably in the range of about 1,000 to about 10,000.
[0038]
The glass transition temperature of the amine-added epoxy resin (A) obtained as described above is in the range of -10 to 60C.
[0039]
The glass transition temperature in the present invention is a value actually measured by a differential thermal analyzer (measured at a heating rate of 10 ° C./min using a thermal analyzer “DSC-5200” manufactured by Seiko Instruments Inc.).
[0040]
Blocked polyisocyanate (B)
In the present invention, the blocked polyisocyanate (B) used as a cross-linking agent includes, as a polyisocyanate species, a polyisocyanate compound (b) of an aromatic polyisocyanate compound or an alicyclic polyisocyanate compound.₁), As the blocking agent, at least one blocking agent selected from oxime compounds, aliphatic alcohols, aromatic alkyl alcohols, and ether alcohols (b₂) Is a blocked polyisocyanate curing agent (B).
[0041]
Aromatic diisocyanate compounds include, for example, 1,3- and / or 1,4-phenylene diisocyanate, 2,4- and / or 2,6-tolylene diisocyanate (TDI), crude TDI, 2,4′- and / or Or 4,4′-diphenylmethane diisocyanate (usually called “MDI”), 4,4′-diisocyanatobiphenyl, 3,3′-dimethyl-4,4′-diisocyanatobiphenyl, 3,3′- Dimethyl-4,4'-diisocyanatodiphenylmethane, crude MDI, 1,5-naphthylene diisocyanate, 4,4 ', 4 "-triphenylmethane triisocyanate, m- and p-isocyanatophenylsulfonyl isocyanate, and the like. Can be
[0042]
Among them, diphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate (usually called "MDI") and crude MDI are preferred.
[0043]
Crude MDI is a mixture containing diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate and polymethylenepolyphenylpolyisocyanate as main components, and commercially available products such as Cosmonate M-50 and Cosmonate M-50. -200, M-100, M-300, etc. (all, manufactured by Mitsui Chemicals, Inc.); Sumidur 44V10, 44V20, 44V40, etc. (all, manufactured by Sumitomo Bayer Urethane Co., Ltd.); Luplanate M-12 , M-12S, M-20, M-20S, etc. (all, manufactured by BASF, Germany); Mondur MR (LIGHT), etc. (manufactured by Bayer).
[0044]
Alicyclic polyisocyanate compounds include isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), bis (2-isocyanatoethyl). ) -4-cyclohexene-1,2-dicarboxylate, 2,5- and / or 2,6-norbornane diisocyanate.
[0045]
In addition, modified MDIs (urethane-modified MDI, carbodiimide-modified MDI, trihydrocarbylphosphate-modified MDI), urethane-modified TDI, biuret-modified HDI, isocyanurate-modified HDI, isocyanurate-modified IPDI, etc. And mixtures of two or more of these [for example, a combination of modified MDI and urethane-modified TDI (isocyanate group-containing prepolymer)].
[0046]
The blocking agent is one that blocks by adding to the isocyanate group of the polyisocyanate compound, and the blocked polyisocyanate compound formed by the addition is stable at room temperature and heated to about 100 to 200 ° C, preferably 120 to 150 ° C. In this case, it is desirable that the blocking agent be dissociated to regenerate a free isocyanate group. Also, as the molecular weight of the dissociating blocking agent is smaller, the formed heating loss is smaller, and this contributes to lowering the soot and soot of the drying furnace.
[0047]
Such blocking agents include, for example, oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime; aliphatic alcohols such as n-butanol and 2-ethylhexanol; and aromatic alkyl alcohols such as phenylcarbinol and methylphenylcarbinol. Ether alcohols such as ethylene glycol monopropyl ether, ethylene glycol monobutyl ether and diethylene glycol monoethyl ether; lactam compounds such as ε-caprolactam and γ-butyrolactam; phenol compounds such as phenol, para-t-butylphenol and cresol; Low-molecular-weight amide compounds such as -methylacetamide, n-ethylacetamide, n-methylpropionamide, and n-methylformamide. You.
[0048]
Among them, oxime compounds, aliphatic alcohols, aromatic alkyl alcohols, and ether alcohols are preferred for the cationic electrodeposition coating intended for the present invention from the viewpoint of throwing power and electrodeposition suitability of a rustproof steel plate. .
As the compounding amount of the above-mentioned blocking agent, it is preferable to react the NCO group of the isocyanate in a ratio of 1: 1 to 1: 1.3. If the ratio exceeds 1.3, the blocking agent remains to reduce the corrosion resistance of the coating film, and if the ratio is less than 1.0, NCO groups remain to impair the stability of the coating composition, which is not preferable.
[0049]
The blocked polyisocyanate curing agent (B) of the cationic electrodeposition paint used in the coating film forming method of the present invention is selected from aromatic polyisocyanate compounds and polyisocyanate compounds of alicyclic polyisocyanate compounds as the polyisocyanate compound. And at least one combination selected from oxime compounds, aliphatic alcohols, aromatic alkyl alcohols, and ether alcohols as the blocking agent, whereby the blocked polyisocyanate curing agent is used. The glass transition temperature of (B) can be in the range of 45 to 65 ° C.
[0050]
The above cationic electrodeposition coating composition contains an amine-added epoxy resin (A) and a blocked polyisocyanate curing agent (B) as essential components, and further, if necessary, an organotin compound, a coloring pigment, and an extender pigment. And paint additives such as rust preventive pigments, organic solvents, water, neutralizers, pigment dispersants, and coating surface adjusters.
[0051]
The organotin compound promotes the dissociation of the blocking agent of the blocked polyisocyanate (B) and functions as a curing catalyst. For example, organic tin oxides such as dibutyltin oxide and dioctyltin oxide; dibutyltin dilaurate; Dialkyltin fatty acids or aromatic carboxylate such as dioctyltin dilaurate, dibutyltin diacetate, dioctyltin dibenzoate, dibutyltin dibenzoate, etc., and among them, dialkyltin aromatic carboxylic acid from the viewpoint of low-temperature curability Acid salts are preferred.
The content of the organotin compound is not strictly defined, and can be varied over a wide range according to the performance and the like required for the coating composition. However, usually, the resin solid content in the coating composition is 100 parts by weight. It is suitable that the amount is in the range of 0 to 8 parts by weight, preferably 0.05 to 5 parts by weight.
[0052]
The cationic electrodeposition paint can be applied to a desired substrate surface by electrodeposition coating. In general, the electrodeposition coating is performed by diluting the electrodeposition bath with deionized water or the like so that the solid content concentration is about 5 to 40% by weight, and further adjusting the pH within a range of 5.0 to 9.0. Normally, the bath temperature is adjusted to 15 to 35 ° C., the load is set to 100 to 400 V, and the object to be coated is used as a cathode. The energization time is 30 seconds to 5 minutes, and the electrode area ratio (A / C): 8/1 to 1 It can be carried out by applying a current of 1/8, the distance between the electrodes being 10 cm to 300 cm.
Although the thickness of the electrodeposition coating film is not particularly limited, it can be generally in the range of 10 to 40 μm, preferably 15 to 30 μm. The bake curing temperature of the coating is generally in the range of about 100 to about 200C, preferably about 120 to about 170C.
[0053]
The method for forming a coating film using a cationic electrodeposition coating composition using a specific base resin and a specific curing agent according to the present invention is such that, during electrodeposition coating, the coating film resistance after one minute from the start of energization is 400 kΩ · cm.²~ 850kΩcm², Preferably 480 kΩ · cm²~ 650kΩcm²It is easy to be in the range of, and by the electrodeposition coating in a short time of energization time of 90 seconds to 150 seconds, high throwing power to obtain the bag structure and the film thickness of the inner plate portion, This makes it possible to achieve both electrodeposition suitability (g-material paintability) of rust-proof steel plates.
[0054]
According to the present invention, a cationic electrodeposition paint using a specific base resin and a specific curing agent, preferably a resin component having a glass transition temperature of both components within a certain range, In a short time (90 seconds to 150 seconds) electrodeposition coating, a coated article having high throwing power, electrodeposition suitability of a rustproof steel plate (g material coating property), and corrosion resistance is obtained.
Further, in the electrodeposition coating of the above cationic electrodeposition paint, the coating film resistance value one minute after the start of energization was set to 400 kΩ · cm.²~ 850kΩcm²Within this range, it is possible to easily achieve both high throwing power and electrodeposition suitability (g-material coatability) of the rustproof steel sheet.
The reason for this is that the emulsion, which is a component of the cationic electrodeposition coating composition, has a curing agent in the core part (center part) of the emulsion and a base resin component in the shell part (surface layer part). The emulsion particles are formed by neutralization. Here, by using a specific base resin and a specific curing agent, preferably by setting the glass transition temperature within a certain range, Since the coating film resistance is formed early from the start of energization, the current spent on the outer plate can be spent on forming the coating film on the inner plate, and the throwing power is improved. 2. The hardener in the core (central part) has a hardness that can withstand sparks when energized, hardly causes breakage of the coating film, and even if gas holes are generated, the shell part (surface layer part) Since the softness repairs the pinhole, the rust-proof steel plate is excellent in electrodeposition suitability (g material coating property). it is conceivable that.
According to the above-mentioned coating film forming method, it is possible to perform electrodeposition coating in a short time, thereby improving productivity, saving space in a line, being excellent in energy saving, and having high throwing power. It is possible to obtain a coated article having excellent corrosion resistance at the plate portion and no pinholes of the rust-preventive steel plate at the outer plate surface and having excellent finish.
[0055]
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the scope of the present invention is not limited to these examples. Hereinafter, “%” means “% by weight”.
[0056]
Production example of base resin
Production Example 1
In a reaction vessel equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen gas inlet, 525 parts of propylene oxide-modified bisphenol A diglycidyl ether (Note 1), 342 parts of bisphenol A, and effective under nitrogen gas injection. 36 parts of a solution of ketimine in 80% monoethanolamine and methyl isobutyl ketone in methyl isobutyl ketone was charged and reacted at 160 ° C. until the epoxy group disappeared.
Further, 665 parts of bisphenol diglycidyl ether having an epoxy equivalent of about 190 and 232 parts of a ketimine-methylisobutylketone solution of monoethanolamine and methylisobutylketone of 80% of the active ingredient were added thereto at 140 ° C. Was reduced to 0.27 mmol / g. As a result, an epoxy resin liquid having a number average molecular weight of about 1500 was obtained.
Then, the mixture was diluted with 365 parts of ethylene glycol monobutyl ether and cooled. When the temperature reached 100 ° C., 167 parts of a 80% active ingredient of a solution of methyl isobutyl ketone of diethylene triamine in methyl isobutyl ketone of diketimine was added, and the viscosity rise was stopped at 100 ° C. The base resin No. having a solid content of 80% was reacted. 1 was obtained. Substrate resin No. The glass transition temperature of 1 was 23 ° C.
(Note 1) Propylene oxide-modified bisphenol A diglycidyl ether (trade name, Glycier BPP-350, manufactured by Sanyo Chemical Co., Ltd., epoxy equivalent: about 340).
[0057]
Production Example 2
In a reaction apparatus similar to that of Production Example 1, 450 parts of ethylene oxide-modified bisphenol A diglycidyl ether (Note 2) having an epoxy equivalent of about 300 and 342 parts of bisphenol A, and monoethanolamine containing 80% of the active ingredient were injected under nitrogen gas injection. 36 parts of methyl isobutyl ketone ketimine (methyl isobutyl ketone solution) was added and reacted at 160 ° C. until the epoxy group disappeared.
Further, 665 parts of bisphenol A diglycidyl ether having an epoxy equivalent of about 190, and 232 parts of a ketimine-methylisobutylketone solution of monoethanolamine and methylisobutylketone of 80% of the active ingredient were charged into the mixture at 140 ° C. The reaction was continued until the group concentration reached 0.29 mmol / g. As a result, an epoxy resin liquid having a number average molecular weight of about 1,500 was obtained.
Next, this was diluted and cooled with 350 parts of ethylene glycol monobutyl ether, and when the temperature reached 100 ° C., 167 parts of methyl isobutyl ketone of methyl isobutyl ketone of 80% of active ingredient was added, and the increase in viscosity at 100 ° C. was stopped. Until the solid content of the base resin no. 2 was obtained. Substrate resin No. The glass transition temperature of 2 was 28 ° C.
(Note 2) Ethylene oxide-modified bisphenol A diglycidyl ether [manufactured by Sanyo Chemical Co., Ltd., trade name: Glycier BPE-300, epoxy equivalent: about 300].
[0058]
Production Example 3
A flask equipped with a stirrer, thermometer, nitrogen inlet tube and reflux condenser was charged with 518 parts of an epoxy resin having a number average molecular weight of 370 and an epoxy equivalent of 185 obtained by the reaction of bisphenol A with epichlorohydrin, and 57 parts of bisphenol A, And 0.2 parts of dimethylbenzylamine were added and reacted at 120 ° C. until the epoxy equivalent became 250.
Then, 213 parts of ε-caprolactone and 0.03 part of tetrabutoxytitanium were added, the temperature was raised to 170 ° C., sampling was performed over time while maintaining this temperature, and the amount of unreacted ε-caprolactone was measured by infrared absorption spectrum measurement. When the reaction rate reached 98% or more, 148 parts of bisphenol A and 0.4 part of dimethylbenzylamine were further added, and the mixture was reacted at 130 ° C. until the epoxy equivalent became 936. Then, 257.4 parts of methyl isobutyl ketone, 25.6 parts of diethylamine and 68.3 parts of diethanolamine were added, and the mixture was reacted at 80 ° C. for 2 hours. The mixture was diluted with methyl ethyl ketone to obtain a base resin having a solid content of 80%. 3 was obtained. Substrate resin No. The glass transition temperature of No. 3 was 38 ° C.
[0059]
Production Example 4
A reaction vessel was charged with 222 parts of isophorone diisocyanate, and 113.1 parts of methyl ethyl ketoxime was gradually dropped while maintaining the reaction temperature at 30 to 40 ° C. by external cooling to synthesize a partially blocked polyisocyanate.
Next, the base resin No. obtained in Production Example 3 was used. 3500 parts, 83.7 parts of the above partially blocked isocyanate was added, and reacted at 100 ° C. under a nitrogen stream until the absorption of isocyanate groups disappeared by infrared absorption spectrum measurement. The mixture was diluted with diethylene glycol monobutyl ether and solidified. Base resin no. 4 was obtained. Substrate resin No. The glass transition temperature of 4 was 44 ° C.
[0060]
Production Example 5
390 g of bisphenol A and 0.2 g of dimethylbenzylamine were added to 1010 g of Epicoat 828EL (trade name, epoxy resin, manufactured by Japan Epoxy Resin Co., Ltd.), and reacted at 130 ° C. until the epoxy equivalent became 800. Next, 160 g of diethanolamine and 65 g of a ketiminated product of diethylenetriamine were added and reacted at 120 ° C. for 4 hours. Then, 355 g of butyl cellosolve was added, and a base resin No. having an amine value of 67 and a solid content of 80% was added. 5 was obtained. Substrate resin No. The glass transition temperature of 5 was 90 ° C.
[0061]
Manufacturing of curing agent
Production Example 6
In a reaction vessel, 270 parts of Cosmonate M-200 (Note 3) and 25 parts of methyl isobutyl ketone were added, and the temperature was raised to 70 ° C. 15 parts of 2,2-dimethylolbutanoic acid was gradually added thereto, and 118 parts of ethylene glycol monobutyl ether was added dropwise thereto. The mixture was reacted at 70 ° C. for 1 hour, cooled to 60 ° C. 152 parts were added. Sampling was performed over time while maintaining this temperature, and it was confirmed by infrared absorption spectrometry that the absorption of unreacted isocyanate groups had disappeared. One solution was obtained. The glass transition temperature was 5 ° C. (Note 3) Cosmonate M-200: trade name, manufactured by Mitsui Chemicals, Crude MDI
[0062]
Production Example 7
In a reaction vessel, 174 parts of tolylene diisocyanate was added and the temperature was raised to 70 ° C. 15 parts of 2,2-dimethylolbutanoic acid was gradually added thereto, and 118 parts of ethylene glycol monobutyl ether was added dropwise. The mixture was reacted at 70 ° C. for 1 hour. 152 parts were added. Sampling was conducted over time while maintaining this temperature, and it was confirmed by infrared absorption spectrometry that the absorption of unreacted isocyanate groups had disappeared. 2 was obtained. The glass transition temperature was 10 ° C.
[0063]
Production Example 8
In a reaction vessel, 222 parts of isophorone diisocyanate and 99 parts of methyl isobutyl ketone were added, and the temperature was raised to 50 ° C. After slowly adding 174 parts of methyl ethyl ketoxime, the temperature was raised to 60 ° C. Sampling was performed over time while maintaining this temperature, and it was confirmed by infrared absorption spectrometry that no unreacted isocyanate had been absorbed. The solid content was adjusted with an organic solvent, and the curing agent No. 1 having a solid content of 80% was used. 3 was obtained. The glass transition temperature was 8 ° C.
[0064]
Production Example 9
To 50 parts of hexamethylene diisocyanate, 30 parts of methyl ketoxime and 10 parts of trimethylolpropane were added dropwise at 40 to 60 ° C., and the mixture was heated at 80 ° C. for 1 hour. It was confirmed by measurement that no unreacted isocyanate was absorbed, and the solid content was adjusted with an organic solvent. 4 was obtained. The glass transition temperature was -19C.
[0065]
Production example of emulsion for cationic electrodeposition paint
Production Example 10 EM No. 1
Substrate resin No. No. 1 87.5 parts (70 parts by resin solid content), 1 in an amount of 37.5 g (resin solid content: 30 g) and 10% acetic acid in 13 parts were mixed and uniformly stirred, and then deionized water was added dropwise while stirring vigorously for about 15 minutes. EM No. having a solid content of 34%, which is an emulsion for a color coating material. 1 was obtained.
[0066]
Production Examples 11 to 18 EM No. 2-No. 9
As the content of Table 1, the EM No. having a solid content of 34%, which is an emulsion for a cationic electrodeposition paint, was manufactured in the same manner as in Production Example 10. 2-No. 9 was obtained.
[0067]
[Table 1]

[0068]
Manufacture of pigment dispersion paste
Production Example 19
5.83 parts (3.5 parts solid) of epoxy quaternary ammonium type dispersion resin having a solid content of 60%, titanium oxide 14.5 parts, purified clay 7.0 parts, bismuth hydroxide 1.0 part, organic 1.0 part of tin, 0.4 part of carbon black and 20.1 parts of deionized water were added, and the mixture was dispersed in a ball mill for 20 hours. The dispersion was taken out, and a pigment dispersion paste having a solid content of 55% (solid content: 27.4 parts) was obtained. Obtained.
[0069]
Examples and comparative examples
Example 1
Emulsion No. No. 1 (base resin No. 1, curing agent No. 1) Pigment dispersion paste No. 1 was added to 294 parts (solid content: 100 parts). 19.8 parts (solid content 27.4 parts) and deionized water 293.2 parts were added, and the cationic electrodeposition paint No. 20% solid content was added. 1 (solids 127.4).
[0070]
Examples 2 to 6
Except for having the composition shown in Table 2, the same procedure as in Example 1 was carried out for the cationic electrodeposition paint No. 2-No. 6 was obtained.
[0071]
Comparative Examples 1-3
Except for having the formulation shown in Table 3, the cationic electrodeposition paint No. 7-No. 9 was obtained.
[0072]
Painting test
Each of the cationic electrodeposition paints obtained in the above Examples and Comparative Examples was subjected to a chemical conversion treatment with Palbond # 3020 (trade name, manufactured by Nippon Parkerazing Co., Ltd., zinc phosphate treating agent), 0.8 × 150 × 70 mm. A cold-rolled steel sheet and a galvanized steel sheet were used for a coating film test according to the following test contents.
[0073]
Cationic electrodeposition paint No. 1 to No. Table 2 shows the coating composition, coating characteristics, and test results of No. 6 (Example).
[0074]
[Table 2]

[0075]
Cationic electrodeposition paint No. 7-No. Table 3 shows the paint formulation, paint properties, and test results of 9 (Comparative Example).
[0076]
[Table 3]

[0077]
(Note 4) Throwing power: A jig for a four-box method throwing power test as shown in FIG. 1 was prepared from a cold-rolled steel sheet (chemical conversion treatment), and wiring was used as shown in FIG. 2 at a bath temperature of 28 ° C. The electrodeposition coating was performed at the voltage shown in the table for 90 minutes or 150 seconds. Thereafter, baking drying was performed at 170 ° C. for 20 minutes, and the outer plate (A surface) film thickness, the inner plate (G surface) film thickness, and the G surface film thickness / A surface film thickness (%) were evaluated.
[0078]
(Note 5) Electrodeposition suitability of rust-preventive steel sheet (g material coating property): A galvanized steel sheet (chemical conversion treatment) was immersed as a cathode in an electrodeposition bath, at a bath temperature of 28 ° C. and a voltage shown in the table for 90 minutes. Or for 150 seconds. Thereafter, baking and drying is performed at 170 ° C. for 20 minutes, and the number of pinholes in a test plate of 10 × 10 cm is counted.
：: good finish without pinholes,
Δ: 3 to 5 pinholes occurred
×: 10 or more occurred
[0079]
(Note 6) Corrosion protection: A cross-cut wound was made with a knife on a test plate that had been subjected to cationic electrodeposition coating using a cold-rolled steel plate (chemical conversion treatment) so as to reach the substrate, and this was cut according to JIS Z-2371. A salt spray test was conducted for 840 hours. It was evaluated according to the following criteria by the scratches from the knife scratches and the blister width.
◎: The maximum width of rust and blisters is less than 2 mm from the cut part (one side),
○: The maximum width of rust and blisters is less than 3 mm from the cut part (one side),
△: The maximum width of rust and blisters is 3 to 4 mm (one side) from the cut part,
×: The maximum width of rust and blisters is 4 mm or more from the cut part
[0080]
[Brief description of the drawings]
FIG. 1 shows a jig used for a coating test with four boxes.
FIG. 2 is a connection diagram of a coating test with four boxes.
[Explanation of symbols]
10. H side
11. A side
12. C surface
13. E side
14． G side
Drill a hole of 15.8mmφ
20. Bathtub
21. Cationic electrodeposition paint
22. anode

Claims (5)

A coating film forming method using a cationic electrodeposition paint containing the following amine-added epoxy resin (A) and blocked polyisocyanate curing agent (B).
Amine-added epoxy resin (A): at least one selected from a polyhydric polyol (a ₂ ), an epoxy compound (a ₃ ) of a polyhydric polyol, and a cyclic ester compound (a ₄ ) in the epoxy resin (a ₁ ). Modifier, base resin blocked polyisocyanate curing agent (B) obtained by reacting polyphenol compound (a ₅ ) and amino group-containing compound (a ₆ ): aromatic polyisocyanate compound or alicyclic polyisocyanate compound As at least one kind of polyisocyanate compound (b ₁ ) selected from the group, as a blocking agent, at least one kind of blocking agent selected from oxime compounds, aliphatic alcohols, aromatic alkyl alcohols, and ether alcohols Curing agent obtained by reacting (b ₂ ) The glass transition temperature of the amine-added epoxy resin (A) is in the range of -10 to 60C, and the glass transition temperature of the blocked polyisocyanate curing agent (B) is in the range of -10 to 50C. 2. The coating film forming method according to 1. The method for forming a coating film using the cationic electrodeposition coating composition according to claim 1, further comprising a bismuth compound as a rust inhibitor. During electrodeposition coating, the coating according to any one of claims 1 to 3 using a cationic electrocoating paint film resistance after 1 minute from the start of energization is 400kΩ · cm ² ~850kΩ · cm ² Film formation method. A coated article coated by the method for forming a coating film according to claim 1.

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