JP4263302B2 - High weather resistant black electrodeposition coating composition - Google Patents

Description

【００３３】
樹脂のＳＰ値δは次式によって与えられる。
【００３４】
【表２】
δ＝（Ｖ_ml ^1/2δ_ml＋Ｖ_mh ^1/2δ_mh）／（Ｖ_ml ^1/2＋Ｖ_mh ^1/2）
Ｖ_m＝Ｖ₁Ｖ₂／（φ₁Ｖ₂＋φ₂Ｖ₁）
δ_m＝φ₁δ₁＋φ₂δ₂
Ｖ_i：溶媒の分子容（ｍｌ／ｍｏｌ）
φ_i：濁点における各溶媒の体積分率
δ_i：溶媒のＳＰ値
ｍｌ：低ＳＰ貧溶媒混合系
ｍｈ：高ＳＰ貧溶媒混合系
【００３５】
アミノ基含有アクリル樹脂は１０〜１５０ｍｅｑ／ｇのアミン価を有することが好ましい。また、５０〜１２０ｍｇＫＯＨ／ｇの水酸基価を有することが好ましい。アミン価および水酸基価がこのような範囲となるようにモノマー組成を構成することは当業者に周知の方法で行うことができる。
【００３６】
アミノ基含有アクリル樹脂はバインダー成分中３０〜６５重量％、好ましくは４１〜５５重量％を占める量で電着塗料組成物に含有される。アミノ基含有アクリル樹脂の含有量が３０重量％を下回ると得られる塗膜の耐候性が低下し、６５重量％を上回ると防食性が低下する。
【００３７】
脂肪族ブロックポリイソシアネート
硬化剤塗料分野においてバインダー樹脂の硬化剤としてブロックポリイソシアネートを使用することは周知である。本発明では脂肪族ブロックポリイソシアネートを用いることが好ましい。中でも、ＩＰＤＩ、水添ＭＤＩ、ＮＢＤＩ（ノルボルナンジイソシアネート）、それらの二量体および三量体、およびトリメチロールプロパンなどの脂肪族多価アルコールとの付加物など、脂環式ポリイソシアネートがより好ましい。これらで得られる塗膜は、耐食性および非黄変性に優れるからである。
【００３８】
ブロック剤も先にハーフブロックジイソシアネートに関して述べた任意のブロック剤でよいが、低温硬化（１６０℃）を望む場合はラクタム類およびオキシム類を使用するのがよい。
【００３９】
脂肪族ブロックポリイソシアネートはバインダー成分中２０〜３０重量％を占める量で電着塗料組成物に含有される。脂肪族ブロックポリイソシアネートの含有量が２０重量％を下回ると得られる塗膜の防食性が低下し、３０重量％を上回ると耐候性が低下する。
【００４０】
第２アクリル樹脂
本発明の電着塗料組成物には、バインダー成分中に更にアクリル樹脂を含有させることが好ましい。このアクリル樹脂は、必ずしもアミノ基を持たなくても良いこと、およびＳＰ値が上記アミノ基含有アクリル樹脂よりも低いことを除き、上記アミノ基含有アクリル樹脂と同じ特性を有する共重合体でよい（以下「第２アクリル樹脂」という。）。具体的には、第２アクリル樹脂のＳＰ値はアミノ基含有アクリル樹脂のＳＰ値よりも少なくとも０．５、好ましくは０．５〜２．０程度低いことが好ましい。
【００４１】
このように、アミノ基含有エポキシ樹脂と、アミノ基含有エポキシ樹脂よりＳＰ値が低いアミノ基含有アクリル樹脂と、アミノ基含有アクリル樹脂よりＳＰ値が低い第２アクリル樹脂とを併用すれば、本発明の電着塗料組成物は、電着後焼付け時にアミノ基含有エポキシ樹脂が金属基材側に移行して防食性の層を形成し、その上にアミノ基含有アクリル樹脂が密着性に優れた中間層を形成し、第２アクリル樹脂が塗膜表面側に移行して耐候性の層を形成すると思われる。
【００４２】
また、かかる本発明の電着塗料組成物では、アミノ基含有エポキシ樹脂と、第２アクリル樹脂との中間のＳＰ値を有するアミノ基含有アクリル樹脂が存在するため、塗料組成物全体の分散安定性は、相対的に差が小さいアミノ基含有アクリル樹脂と第２アクリル樹脂との間のＳＰ値差に主して依存し、相対的に差が大きいアミノ基含有エポキシ樹脂と第２アクリル樹脂との間のＳＰ値差に直接依存しない。その結果、分散安定性に悪影響することなく耐候性を実現するのに十分な量の第２アクリル樹脂をブレンドすることができるようになる。
【００４３】
さらに最も低いＳＰ値を有する第２アクリル樹脂の濃度勾配は塗膜表面近くで最も高くなると考えられ、それによって耐候性向上に寄与すると同時に、ハジキやへこみ等の外観異常を抑制する効果も発揮する。その結果、本発明の電着塗料組成物では、その上に上塗塗装しなくても、防食性および耐候性が更に優れた硬化塗膜を与えることになる。
【００４４】
第２アクリル樹脂の調製は、一般には、水酸基含有アクリルモノマーと、それ以外のエチレン性不飽和モノマーを必須モノマーとし、アミノ基を含有する場合はアミノ基含有アクリルモノマーを共重合するか、またはエポキシ基含有アクリルモノマーを共重合後アミンと反応させることによってアミノ基を導入する。
【００４５】
しかしながら第２アクリル樹脂はアミノ基含有アクリル樹脂成分より低いＳＰ値を持たなければならないので、モノマー組成として、ｔ−ブチル（メタ）アクリレート、２ーエチルヘキシル（メタ）アクリレート、ラウリル（メタ）アクリレート、ステアリル（メタ）アクリレート等、ホモポリマーのＳＰ値が低いモノマーを相対的に多くするか、または反対に高ＳＰモノマーの割合を減らして所望ＳＰ値範囲に設計する必要がある。
【００４６】
第２アクリル樹脂は、アミノ基含有アクリル樹脂と同様ハーフブロックジイソシアネートを付加して使用することもできる。
【００４７】
第２アクリル樹脂は塗膜の表面付近においてその濃度勾配が最大になることが意図されるので、ハジキ、へこみなどの外観異常が発生し難いことが望ましい。そのため、重合時使用する他のエチレン性不飽和モノマーの一部として、エーテル部分を有するアクリルモノマーを使用するのが有効である。
【００４８】
そのようなアクリルモノマーの例は、２−メトキシエチル（メタ）アクリレート、４−メトキシブチル（メタ）アクリレート、ナトラヒドロフルフリル（メタ）アクリレート、２−エトキシエチル（メタ）アクリレート、２−ブロポキシエチル（メタ）アクリレート、４−２−エチルヘキシルオキシ）ブチル（メタ）アクリレート、フルフリル（メタ）アクリレート等である。
【００４９】
第２アクリル樹脂を更に含有する本発明の好ましい態様では、黒色電着塗料組成物のバインダー成分は、固形分合計１００重量％中、（ａ）アミノ基含有エポキシ樹脂５〜３５重量％、好ましくは１３〜２７重量％；（ｂ）該アミノ基含有エポキシ樹脂よりもＳＰ値が０．５以上低いアミノ基含有アクリル樹脂２０〜６４重量％、好ましくは２４〜５５重量％；（ｃ）脂肪族ブロックポリイソシアネート２０〜３０重量％、好ましくは２４〜２７重量％；および（ｄ）該アミノ基含有アクリル樹脂よりもＳＰ値が低い第２アクリル樹脂１〜１０重量％、好ましくは５〜１０重量％；で構成される（成分（ａ）〜（ｄ）の合計は１００重量％である。）。
【００５０】
バインダー成分中、第２アクリル樹脂の量が１重量％を下回ると得られる塗膜の耐候性が低下し、塗膜にハジキやヘコミが発生し易くなり、１０重量％を上回ると塗膜の防食性が低下する。
【００５１】
顔料
本発明の黒色電着塗料組成物には、種々の黒色顔料を含有させることができる。黒色顔料の例は、カーボンブラック、黒色酸化鉄、銅クロムブラック、銅鉄マンガンブラック等である。
【００５２】
好ましい黒色顔料はカーボンブラックである。隠蔽力および着色力に優れるからである。粒子径１５ｎｍ以下、特に１３ｎｍ以下のカーボンブラックが好ましい。用いるカーボンブラックの粒子径が１５ｎｍを上回ると得られる塗膜の隠蔽性及び黒色度が低下する。
【００５３】
黒色顔料としてカーボンブラックを用いる場合、その使用量は、塗料ＰＶＣとして１〜７％、特に２．５〜５．５％であることが好ましい。カーボンブラックの使用量がＰＶＣ１％を下回ると得られる塗膜の隠蔽性および黒色度が低下し、ＰＶＣ７％を上回ると得られる塗膜の耐候性が低下する。尚、ＰＶＣとは、塗膜中の顔料体積率のことをいう。
【００５４】
中和剤
ここで使用する中和剤は、塩酸、硝酸、リン酸、ギ酸、酢酸、ヒドロキシ酢酸、スルファミン酸、乳酸のような無機酸または有機酸である。中和剤の量は、少なくとも２０％、好ましくは３０〜６０％の中和率を達成する量であればよい。
【００５５】
水性媒体
水性媒体としては、水並びに種々の有機溶剤であってよい。本発明での使用に適した溶剤の例としては、炭化水素類（例えば、キシレンまたはトルエン）、アルコール類（例えば、メチルアルコール、ｎ−ブチルアルコール、イソプロピルアルコール、２−エチルヘキシルアルコール、エチレングリコール、プロピレングリコール）、エーテル類（例えば、エチレングリコールモノエチルエーテル、エチレングリコールモノブチルエーテル、エチレングリコールモノヘキシルエーテル、プロピレングリコールモノエチルエーテル、３−メチル−３−メトキシブタノール、ジエチレングリコールモノエチルエーテル、ジエチレングリコールモノブチルエーテル）、ケトン類（例えば、メチルイソブチルケトン、シクロヘキサノン、イソホロン、アセチルアセトン）、エステル類（例えば、エチレングリコールモノエチルエーテルアセテート、エチレングリコールモノブチルエーテルアセテート）、並びにそれらの混合物が挙げられる。これらの溶剤の使用量は塗料全体に対して約０．０１〜２５重量％、好ましくは０．０５〜１５重量％である。
【００５６】
顔料分散ペースト
電着塗料組成物のような、水性媒体中に分散されたバインダー成分と顔料成分とを含む水性塗料組成物を製造する場合、粉体である顔料と水性媒体中に分散されたバインダー成分とを直接混合すると、顔料は一般に疎水性であるため水性媒体中に均一に分散しない。従って、通常は、顔料を水性媒体中に高濃度で均一に分散させて顔料分散ペーストを調製し、これを水性媒体中に分散されたバインダー成分を用いて希釈することにより水性塗料組成物とする。
【００５７】
本発明の電着塗料組成物においても、水性媒体中に分散されたバインダー成分と顔料成分とを混合するために、予め顔料分散ペーストを調製する。顔料分散ペーストは、顔料と顔料分散剤と水性媒体とを含有する。
【００５８】
顔料と顔料分散剤と水性媒体とを混合することにより、顔料分散ペーストが調製される。一般に、顔料分散ペーストは固形分３５〜７０重量％、好ましくは４０〜６５重量％に調製される。固形分中、顔料は３５〜７５重量％、好ましくは４０〜７０重量％を占め、顔料分散剤は２５〜６５重量％、好ましくは３０〜６０重量％を占める。
【００５９】
電着塗料組成物
一般に電着塗料組成物は、最初バインダー成分を中和剤を含む水性媒体中に分散してメインエマルションをつくり、これへ顔料分散ペーストを添加し、混合して調製される。本発明においてはバインダー樹脂としてアミノ基含有エポキシ樹脂、アミノ基含有アクリル樹脂、および必要に応じて第２アクリル樹脂を使用するのでこれらのブレンド方法はいく通りかが存在する。具体的には、特願平９−１１４２４２号第００３６〜００３７段落に記載の方法によりメインエマルションを調製することが好ましい。
【００６０】
添加する顔料分散ペーストの量は、塗料全体に含まれる顔料の量に依存して適宜調節することができる。一般には、メインエマルションに含まれるバインダー成分１００重量部に対して顔料成分が２〜１３重量部、好ましくは３〜６重量部となる量で添加される。
【００６１】
電着塗料組成物は、ジラウリン酸ジブチルスズ、ジブチルスズオキサイドのようなスズ化合物や、通常のウレタン開裂触媒を含むことができる。その量は脂肪族ブロックポリイソシアネートの０．１〜１０重量％が通常である。
【００６２】
電着塗料は、水混和性有機溶剤、界面活性剤、酸化防止剤、紫外線吸収剤などの常用の塗料用添加剤を含むことができる。
【００６３】
本発明の電着塗料組成物は、鉛系防錆顔料を実質上含有しない。「鉛系防錆顔料を実質上含有しない」とは、鉛系顔料を全く使用しないか、または使用しても希釈塗料（電着浴へ加える際のカチオン電着塗料組成物の状態）における鉛イオン濃度が５００ｐｐｍ以下、好ましくは２００ｐｐｍ以下となるような量であることをいう。鉛イオン濃度が高いと環境に有害であるばかりでなく、平滑性が低下し得る。
【００６４】
本発明の電着塗料組成物で得られる塗膜は耐食性に優れ、塗装面として十分な美感性および耐候性を有する。従って、本発明の電着塗料組成物は、中塗工程および上塗工程を省略して下塗り工程のみで金属基材の塗装を完了させる１コート塗装方法に用いることができる。具体的には、
電着塗装方法により金属基材の被塗面に本発明の電着塗料組成物の塗膜を形成する工程；及び
電着塗料組成物の塗膜を焼付け硬化させる工程；
を包含する方法で金属基材の塗装を行うことができる。
【００６５】
【実施例】
以下の実施例により本発明を更に詳細に説明するが、本発明はこれらに限定されない。実施例中、「％」及び「部」は特に断らない限り重量基準である。
【００６６】
製造例１〜３
製造例１〜３では顔料分散ペーストの調製について説明する。
【００６７】
製造例１
撹拌機、冷却機、窒素注入管、温度計および滴下ロートを取り付けたフラスコを用意した。このフラスコにイソホロンジイソシアネート２２２．０部を加え、メチルイソブチルケトン３９．１部で希釈した後にジブチルスズジラウレート０．２部を加えた。５０℃に昇温後、２−エチルヘキサノール１３１．５部を窒素をバブリングしながら撹拌しているところに滴下ロートから２時間かけて滴下した。適宜冷却することにより、この間の反応温度を５０℃に維持した。その結果、２−エチルヘキサノールハーフブロック化イソホロンジイソシアネートを得た（固形分９０％）。
【００６８】
撹拌機、窒素注入管、冷却管を備えた反応容器にエポン８２８（シェル化学社製エポキシ樹脂、エポキシ当量：１９０）３５１．６部およびビスフェノールＡ９９．２部を仕込み、窒素雰囲気下１３０℃まで加熱し、ベンジルジメチルアミン１．４１部を添加し、１７０℃で約１時間反応させることにより、エポキシ当量４５０のビスフェノールＡ型エポキシ樹脂を得た。
【００６９】
次いで、反応溶液を１４０℃まで冷却した後、上で調製した２−エチルヘキサノールハーフブロック化イソホロンジイソシアネート２１８．３部（固形分量１９６．５部）を加え、１４０℃に１時間保った。ここにジプロピレングリコールモノブチルエーテル１７２．３部を加えて希釈し、反応溶液を１００℃に冷却し、１−（２−ヒドロキシエチルチオ）−２−プロパノール（三洋化成社製「ＳＨＰ−１００」）４０８．０部（固形分量１３６．０部）、ジメチロールプロピオン酸１３４．０部および脱イオン水１４４．０部を加え、７０〜７５℃で酸価３．０以下になるまで反応させた。
【００７０】
３級スルホニウム化率７０．６％の３級オニウム基含有エポキシ樹脂を得た。これをジプロピレングリコールモノブチルエーテル３２４．８部およびイオン交換水１２０４．８部で希釈し、エポキシ系３級オニウム塩型顔料分散用樹脂を得た（樹脂固形分３０％）。
【００７１】
得られたエポキシ系３級オニウム塩型顔料分散樹脂（固形分３０％）８３部、カーボンブラック（三菱化成社製「Ｍ−２６００」、平均粒径１３ｎｍ）１７部を混合し、サンドグラインドミルで粒度１０μｍ以下まで粉砕して顔料分散ペースト（固形分４２％）を調製した。
【００７２】
製造例２
製造例１で得たエポキシ系３級オニウム塩型顔料分散樹脂（固形分３０％）８３部、カーボンブラック（コロンビアカーボン社製「ラーベン４１０」、平均粒径７０ｎｍ）１７部を混合し、サンドグラインドミルで粒度１０μｍ以下まで粉砕して顔料分散ペースト（固形分４２％）を調製した。
【００７３】
製造例３
製造例１で得たエポキシ系３級オニウム塩型顔料分散樹脂（固形分３０％）８３部、カーボンブラック（三菱化成社製「ＭＡ−１００」、平均粒径２２ｎｍ）１７部を混合し、サンドグラインドミルで粒度１０μｍ以下まで粉砕して顔料分散ペースト（固形分４２％）を調製した。
【００７４】
製造例４
アミノ基含有エポキシ樹脂（ａ）の調製
撹拌装置、窒素導入管、冷却管および温度計を備えた反応容器にエポキシ当量が９５０のビスフェノールＡ型エポキシ樹脂（東都化成社製エポトートＹＤ−０１４）９５０部を入れ、メチルイソブチルケトン２３７．５部と共に１００℃に加熱し完全に溶解させた。次いで、Ｎ−メチルエタノールアミン６０部、ジエチレントリアミンのメチルイソブチルケチミン７３％メチルイソブチルケトン溶液７３部を添加した。
【００７５】
この混合物を１２０℃で１時間保温し、ＳＰ値１１．４のアミノ基含有エポキシ樹脂の溶液を得た。
【００７６】
製造例５
脂肪族ブロックポリイソシアネート（ｃ）の調製
撹拌装置、温度計、冷却管及び窒素導入管を備えた反応容器にイソホロンジイソシアネート２２２部を入れ、メチルイソブチルケトン５６部を加えて希釈した後ジブチル錫ジラウレート０．２部を加えた。その後、５０℃に昇温し、メチルエチルケトオキシム１７４部を樹脂温度が７０℃を超えないように加えた。赤外線吸収スペクトルによりイソシアネート基の吸収が実質上消滅するまで７０℃で１時間保持し、その後、ｎ−ブタノール４３部を加えて希釈して脂肪族ブロックポリイソシアネートの溶液を得た。
【００７７】
製造例６
第２アクリル樹脂（ｄ）の調製
撹拌機、温度計、デカンター、環流冷却器、窒素導入管及び滴下ロートを備えた反応容器にメチルイソブチルケトン１５５０部を仕込み、窒素ガスを導入しつつ１２０℃に昇温し、メタクリル酸メチル６２７部、メタクリル酸ラウリル１９１部、アクリル酸−４−ヒドロキシブチル１８２部、アクリル酸−２−メトキシエチル３００部、メタクリル酸ブチル２００部およびｔ−ブチルパーオキシ−２−エチルヘキサノエート５０部の混合物を３時間かけて等速滴下した。滴下終了後３時間さらに１２０℃で反応後冷却し、ＳＰ値９．７の第２アクリル樹脂の溶液を得た。
【００７８】
製造例７
アミノ基含有エポキシ樹脂（ａ）と脂肪族ブロックポリイソシアネート（ｃ）とを含むエマルションの調製
製造例４で得たアミノ基含有エポキシ樹脂の溶液１２０．４部、及び製造例５で得た脂肪族ブロックポリイソシアネートの溶液５６．２部を加えて混合した後、窒素雰囲気下６０℃で３０分間保持し、酢酸２．０部を加え、十分撹拌しながらイオン交換水２１５．６部を徐々に加え、アミノ基含有エポキシ樹脂と脂肪族ブロックポリイソシアネートとを含むエマルションを得た。エマルションの固形分は３６％であった。
【００７９】
製造例８
アミノ基含有アクリル樹脂（ｂ）と脂肪族ブロックポリイソシアネート（ｃ）と第２アクリル樹脂（ｄ）とを含むエマルションの調製
環流冷却器、撹拌機、滴下ロートおよび窒素導入管を備えた５つ口フラスコに、メチルイソブチルケトン５６．３部を仕込み、窒素雰囲気下１１５℃に加熱保持した。これへ、グリシジルメタクリレート１６．０部、２−ヒドロキシエチルメタクリレート４．２部、２−ヒドロキシプロピルメタクリレート１４．８部、ｎ−ブチルメタクリレート５８．１部、ｔ−ブチルメタクリレート６．９部、およびｔ−ブチルパーオクトエート４．０部の混合物を滴下ロートから３時間かけて滴下した。滴下終了後１１５℃に約１時間保持した後、ｔ−ブチルパーオクトエート０．５部を滴下し、１１５℃で約３０分保持し、固形分６５％のアクリル樹脂の溶液を得た。数平均分子量（Ｍｎ）は６０００であった。
【００８０】
冷却後これへＮ−メチルエタノールアミン８．５部を加え、窒素雰囲気下１２０℃で２時間反応させ、樹脂ＳＰ１０．３および固形分約６７％のアミノ基含有アクリル樹脂の溶液を得た。
【００８１】
この溶液に製造例５で得た脂肪族ブロックポリイソシアネート４４．６部、製造例６で得た第２アクリル樹脂の溶液３３．６部及び酢酸２．６部を加え、窒素雰囲気下で７０℃で３０分保持し、十分撹拌しながらイオン交換水３０１．２部を徐々に加え、アミノ基含有アクリル樹脂を含むエマルションを得た。エマルションの固形分は３０％であった。
【００８２】
実施例１〜５及び比較例１〜６
黒色電着塗料組成物の調製
表３に示す塗料成分の配合量に従って、製造例１〜３で得られた顔料分散ペーストと製造例７および８で得られたエマルションとを混合し、得られた混合物にイオン交換水を加えて固形分を２０％とし、電着塗料組成物を得た。
【００８３】
【表３】

【００８４】
これらの電着塗料組成物を用いてリン酸亜鉛処理鋼板（０．８×７０×１５０ｍｍ）に対して電着塗装を施し、１７０℃（被膜物）で２０分間焼付を行った。焼き付け後の膜厚は２０μｍとなるようにした。
【００８５】
得られた電着塗膜の外観及び性能を以下の様にして評価した。結果を表４及び５に示す。
【００８６】
塗膜の外観
(1)色相
スガ試験機社製ＳＭ−４型カラーコンピューターにて、黒色標準板（現行上塗板）と比較して、硬化塗膜の色差（黒色度の差）ΔＬを測定した。
評価基準
良好：ΔＬ≦３
不良：ΔＬ＞３
【００８７】
(2)平滑性（Ｒａ）
表面粗さ測定機（ミツトヨ社製「Ｓｕｒｆｔｅｓｔ２１１」）を用いて硬化塗膜のＲａ（μｍ）を測定した。
評価基準
良好：Ｒａ≦０．３
不良：Ｒａ＞０．３
【００８８】
(3)へこみ
電着塗板（厚み０．７ｍｍ）面積７０×１５０ｍｍ当たりのあわ粒からあずき粒大のへこみの発生個数を数えた。
評価基準
良好：０
不良：１≦
【００８９】
塗膜の性能
(1)耐候性
電着塗装した亜鉛処理鋼板をサンシャインウェザオメーター（ＪＩＳ Ｂ ７７５３（サンシャインカーボンアーク燈式耐候性試験機）に規定されるもの）に取り付け、４００時間照射した。その後、電着塗膜表面の６０°グロスを測定し、初期６０°グロスに対するグロス保持率を求めた。
評価基準
良好：グロス保持率≧８０％
不良：グロス保持率＜８０％
【００９０】
(2)耐塩水噴霧性
電着塗装した亜鉛処理鋼板の塗膜に小型カッター（例えば、ＮＴカッター）を用いて、交差する対角線状に、素地に達するクロスカットを入れた。ＪＩＳ Ｚ２３７１に規定する塩水噴霧試験器に規定時間入れ、クロスカット部のさび（ふくれ）幅を測定した。
評価基準
良好：カット線からの最大さび（ふくれ）幅（片側）≦２ｍｍ
不良：カット線からの最大さび（ふくれ）幅（片側）＞２ｍｍ
【００９１】
【表４】

【００９２】
【表５】

【００９３】
【発明の効果】
従来と同様に耐食性を保持していながら、その上に上塗塗装しなくても、塗装面として十分な美感性および耐候性を有する下塗塗膜を形成できる、黒色電着塗料組成物が提供された。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a highly weather-resistant black electrodeposition coating composition, and more particularly to a black electrodeposition coating composition having excellent weather resistance and corrosion resistance, and high concealability and blackness.
[0002]
[Prior art]
In general, metal substrates such as automobile bodies are mainly coated with an undercoating film for rust prevention, an intermediate coating film for concealing the ground color and smoothing the coated surface, It is painted by forming a top coat film to give gloss. In other words, when a metal base material is usually applied, the surface to be coated is protected from corrosion by maintaining an undercoat film having corrosion resistance and a topcoat film having weather resistance, and the aesthetic feeling is maintained during the period of use. The purpose of painting is achieved.
[0003]
However, in recent years, there has been a demand for simplification of the painting process in order to save resources and labor. Also in the field of metal base coating, there is a strong demand for a coating method in which the intermediate coating process and by extension, the top coating process are omitted, and the coating process is completed only by the base coating process, rather than the conventional coating method of undercoating, intermediate coating, and overcoating. . On the other hand, if the formation of the top coat film is simply omitted, the coated surface is inferior in weather resistance, and the important function of coating for maintaining its aesthetics during use is impaired.
[0004]
Accordingly, there are provided a primer coating film having sufficient aesthetics and weather resistance as a coating surface, and a primer coating film capable of forming such a primer coating film, while maintaining corrosion resistance as in the past, and without applying a coating on the other side. It is desired.
[0005]
By the way, the electrodeposition coating method is widely used for the undercoating of the metal substrate. As a paint used in the electrodeposition coating method, an electrodeposition paint containing a binder component and a pigment component dispersed in an aqueous medium containing a neutralizing agent is well known. The binder component is generally a resin component containing a cationic resin and a curing agent. In the electrodeposition coating method, a paint component is electrodeposited on the surface of a metal substrate, and then heated to cure the binder component, thereby forming an undercoat film in which the pigment component is hardened with a resin.
[0006]
As cationic resins used for electrodeposition coatings, amine-modified epoxy resins, amine-modified acrylic resins and the like are known. Among them, the amine-modified epoxy resin is excellent in corrosion resistance, and the amine-modified acrylic resin is excellent in weather resistance.
[0007]
In general, the amine-modified epoxy resin and the amine-modified acrylic resin are properly used depending on the application, or when both corrosion resistance and weather resistance are required, both resins are blended and used.
[0008]
For example, in JP-A-62-174277, JP-A-63-51470, JP-A-2-33069, and JP-A-2-160876, an amine modification excellent in corrosion resistance on the metal substrate side is disclosed. An epoxy / acryl blend binder component that separates into two layers is described so that an epoxy resin layer is formed and an amine-modified acrylic resin layer having excellent weather resistance is formed on the surface side.
[0009]
However, even in an electrodeposition coating composition using such an epoxy / acrylic blend binder component, depending on the pigment used in combination with the binder component, it is possible to increase the aesthetics and weather resistance of the painted surface to a level that is practically satisfactory. Have difficulty.
[0010]
For example, when forming a black paint film, it is necessary to increase the concealability and blackness of the paint film in order to achieve a practically satisfactory level of aesthetics on the painted surface. Need to be increased considerably. However, when the pigment concentration is increased to a level sufficient to realize the aesthetics of the painted surface, the physical strength of the coating film decreases, and as a result, the weather resistance of the coating film decreases. .
[0011]
[Problems to be solved by the invention]
The present invention solves the above-mentioned conventional problems, and the object of the present invention is to maintain sufficient corrosion resistance as in the prior art, and to provide sufficient aesthetics as a coated surface even without overcoating on it. An object of the present invention is to provide a black electrodeposition coating composition capable of forming an undercoat film having weather resistance.
[0012]
[Means for Solving the Problems]
The present invention is a black electrodeposition coating composition containing a binder component and a pigment component dispersed in an aqueous medium containing a neutralizing agent,
The binder component is
a) 5 to 35% by weight of an amino group-containing epoxy resin;
b) 30 to 65% by weight of an amino group-containing acrylic resin; and
c) 20-30% by weight of aliphatic blocked polyisocyanate;
(The sum of components (a) to (c) is 100% by weight),
The pigment component is carbon black having a particle diameter of 15 nm or less, and the amount thereof is 1 to 7% as a coating PVC, thereby providing the black electrodeposition coating composition, thereby achieving the above object.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Amino group-containing epoxy resin
As the amino group-containing epoxy resin, an amine-modified epoxy resin well known in the field of electrodeposition coating can be used. In general, they are produced by ring opening of epoxy groups of epoxy resins by reaction with primary amines, secondary amines or tertiary amine salts.
[0014]
The amino group-containing epoxy resin constituting the binder component needs to be dispersed in an aqueous medium containing a neutralizing agent. Therefore, they must not be water soluble. The molecular weight of the epoxy resin used to prepare the amine-modified epoxy resin, the amount of amino groups introduced into the epoxy resin, and the like can be appropriately adjusted so as to have good dispersibility as a binder for electrodeposition coatings.
[0015]
A typical epoxy resin used for preparing an amino group-containing epoxy resin is a polyphenol which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak and epichlorohydrin. Polyglycidyl ether type epoxy resin.
[0016]
The epoxy resin may be chain extended using a bifunctional polyester polyol, polyether polyol, bisphenol, dibasic carboxylic acid or the like before reacting with the amine. Alternatively, before reacting with an amine, some epoxy groups may have a mono group such as 2-ethylhexanoic acid, 2-ethylhexanol, nonylphenol, ethylene glycol mono-2-ethylhexyl ether, propylene glycol mono-2-ethylhexyl ether. Carboxylic acids or monohydroxy compounds may be added to adjust molecular weight or amine equivalent and improve heat flow.
[0017]
The amine to be reacted with the epoxy resin is primary such as butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine acid salt, N, N-dimethylethanolamine acid salt. Secondary or tertiary amine salts. Ketimine-blocked primary amino group-containing secondary amines such as aminoethylethanolamine methyl isobutyl ketimine are often used. It is preferable that the amine is reacted in an approximately equivalent amount with respect to the epoxy group.
[0018]
The amino group-containing epoxy resin is contained in the electrodeposition coating composition in an amount occupying 5 to 35% by weight, preferably 13 to 27% by weight, in the binder component. When the content of the amino group-containing epoxy resin is more than 35% by weight, the weather resistance of the resulting coating film is lowered, and when it is less than 5% by weight, the corrosion resistance is lowered.
[0019]
Amino group-containing acrylic resin
The amino group-containing acrylic resin is obtained by copolymerization of (i) an amino group-containing acrylic monomer, (ii) a hydroxyl group-containing acrylic monomer, and (iii) other ethylenically unsaturated monomers. Furthermore, instead of the amino group-containing acrylic monomer, an epoxy group-containing acrylic monomer is copolymerized with a hydroxyl group-containing acrylic monomer and other ethylenically unsaturated monomers, and the epoxy group of the obtained copolymer is ring-opened with an amine. You can also.
[0020]
Examples of the amino group-containing acrylic monomer (i) are N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylate, N, N -Diethylaminopropyl (meth) acrylate and the like.
[0021]
Examples of the hydroxyl group-containing acrylic monomer (ii) are 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, polypropylene glycol mono Mono (meth) acrylates of alkylene diols such as (meth) acrylate and 1,6-hexanediol mono (meth) acrylate are preferred.
[0022]
In addition, (meth) acrylamides such as N-hydroxyethyl (meth) acrylamide, N-hydroxypropyl (meth) acrylamide and the like are also preferable, and a reaction product of hydroxyalkyl mono (meth) acrylate and ε-caprolactone or A reaction product of a hydroxyalkyl mono (meth) acrylate and a six-membered ring carbonate can also be suitably used as the hydroxyl group-containing acrylic monomer (ii).
[0023]
Examples of other ethylenically unsaturated monomers (iii) are methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl ( Examples thereof include meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, styrene, vinyltoluene, α-methylstyrene, (meth) acrylonitrile, (meth) acrylamide, and vinyl acetate.
[0024]
As an alternative method for preparing an amino group-containing acrylic resin, after copolymerizing an acrylic monomer having a hydroxyl group and other ethylenically unsaturated monomers and a monomer having an epoxy group such as glycidyl (meth) acrylate, You may make a secondary amine react with an epoxy group. Secondary amines that can be used for the reaction with epoxy groups are diethylamine, dibutylamine, dicyclohexylamine, morpholine, diethanolamine, N-methylethanolamine, and the like, and particularly amines having a hydroxyl group and a secondary amino group in the molecule. Is preferred. In addition, methyl isobutyl ketone diketiminate of diethylenetriamine and methyl isobutyl ketone monoketiminate of 2- (2-aminoethylamino) ethanol can be used.
[0025]
The polymerization can be performed by a conventional method such as a solution polymerization method. The number average molecular weight of the copolymer is in the range of 1000 to 50000, preferably 2000 to 20000. In some cases, the degree of polymerization is adjusted using a chain transfer agent such as dodecyl mercaptan or 2-ethylhexyl thioglycolate.
[0026]
A half-block diisocyanate may be added to the amino group-containing acrylic polymer by a urethane bond to give self-crosslinking properties. In this case, the diisocyanate is preferably an alicyclic diisocyanate such as isophorone diisocyanate (IPDI), 4,4'-methylenebis (cyclohexyl isocyanate) (hydrogenated MDI), norbornane diisocyanate (NBDI).
[0027]
A known blocking agent can be used to block one isocyanate group of the diisocyanate to form a half-blocked diisocyanate. Examples of the blocking agent include alcohols such as n-butanol, 2-ethylhexanol, ethylene glycol monobutyl ether, and cyclohexanol; phenols such as phenol, nitrophenol, cresol, and nonylphenol; dimethyl ketoxime, methyl ethyl ketoxime, and methyl isobutyl Oximes such as ketoxime and lactams such as ε-caprolactam can be used.
[0028]
The amino group-containing acrylic resin preferably has a lower SP value than the amino group-containing epoxy resin. Specifically, the SP value of the amino group-containing acrylic resin is preferably at least 0.5, preferably about 0.5 to 2.0 lower than the SP value of the amino group-containing epoxy resin.
[0029]
Thus, when the amino group-containing epoxy resin and the amino group-containing acrylic resin having a lower SP value than the amino group-containing epoxy resin are used in combination, the electrodeposition coating composition of the present invention has an amino group-containing during baking after electrodeposition. It is considered that the epoxy resin migrates to the metal substrate side to form an anticorrosive layer, and the amino group-containing acrylic resin migrates to the coating surface side to form a weather resistant layer. Even without coating, a cured coating film having further excellent corrosion resistance and weather resistance is provided.
[0030]
In general, the SP value of the copolymer can be estimated by calculation based on the SP value of the homopolymer of the constituent monomer and the weight fraction of each constituent monomer in the monomer mixture, so that the SP of the amino group-containing epoxy resin can be estimated. If the value is known by actual measurement by a known method, an amino group-containing acrylic copolymer having a desired SP value can be designed.
[0031]
For example, the SP value can be measured by the following method [references: SUH, CLARKE, J. et al. P. S. A-1, 5, 1671-1681 (1967)].
[0032]
[Table 1]

[0033]
The SP value δ of the resin is given by the following equation.
[0034]
[Table 2]
δ = (V_ml ^1/2δ_ml+ V_mh ^1/2δ_mh) / (V_ml ^1/2+ V_mh ^1/2)
V_m= V₁V₂/ (Φ₁V₂+ Φ₂V₁)
δ_m= Φ₁δ₁+ Φ₂δ₂
V_i: Molecular volume of solvent (ml / mol)
φ_i: Volume fraction of each solvent at cloud point
δ_i: SP value of solvent
ml: Low SP poor solvent mixed system
mh: High SP poor solvent mixed system
[0035]
The amino group-containing acrylic resin preferably has an amine value of 10 to 150 meq / g. Further, it preferably has a hydroxyl value of 50 to 120 mgKOH / g. Constructing the monomer composition so that the amine value and the hydroxyl value fall within such ranges can be performed by methods well known to those skilled in the art.
[0036]
The amino group-containing acrylic resin is contained in the electrodeposition coating composition in an amount of 30 to 65% by weight, preferably 41 to 55% by weight, in the binder component. When the content of the amino group-containing acrylic resin is less than 30% by weight, the weather resistance of the resulting coating film is lowered, and when it exceeds 65% by weight, the corrosion resistance is lowered.
[0037]
Aliphatic block polyisocyanate
It is well known to use block polyisocyanates as curing agents for binder resins in the field of curing agent coatings. In the present invention, it is preferable to use an aliphatic blocked polyisocyanate. Among them, alicyclic polyisocyanates such as IPDI, hydrogenated MDI, NBDI (norbornane diisocyanate), dimers and trimers thereof, and adducts with aliphatic polyhydric alcohols such as trimethylolpropane are more preferable. It is because the coating film obtained by these is excellent in corrosion resistance and non-yellowing.
[0038]
The blocking agent may be any blocking agent described above for the half-blocked diisocyanate, but lactams and oximes may be used if low temperature curing (160 ° C.) is desired.
[0039]
The aliphatic block polyisocyanate is contained in the electrodeposition coating composition in an amount accounting for 20 to 30% by weight in the binder component. When the content of the aliphatic block polyisocyanate is less than 20% by weight, the corrosion resistance of the resulting coating film is lowered, and when it exceeds 30% by weight, the weather resistance is lowered.
[0040]
Second acrylic resin
The electrodeposition coating composition of the present invention preferably further contains an acrylic resin in the binder component. The acrylic resin may be a copolymer having the same characteristics as the amino group-containing acrylic resin except that it does not necessarily have an amino group and the SP value is lower than that of the amino group-containing acrylic resin ( Hereinafter referred to as “second acrylic resin”). Specifically, the SP value of the second acrylic resin is preferably at least 0.5, preferably about 0.5 to 2.0 lower than the SP value of the amino group-containing acrylic resin.
[0041]
Thus, if the amino group-containing epoxy resin, the amino group-containing acrylic resin whose SP value is lower than that of the amino group-containing epoxy resin, and the second acrylic resin whose SP value is lower than that of the amino group-containing acrylic resin are used in combination, the present invention In the electrodeposition coating composition, an amino group-containing epoxy resin migrates to the metal substrate side during baking after electrodeposition to form an anticorrosive layer, on which the amino group-containing acrylic resin has excellent adhesion. A layer is formed, and the second acrylic resin appears to move to the coating surface side to form a weather resistant layer.
[0042]
Further, in the electrodeposition coating composition of the present invention, since there is an amino group-containing acrylic resin having an intermediate SP value between the amino group-containing epoxy resin and the second acrylic resin, the dispersion stability of the entire coating composition Is mainly dependent on the SP value difference between the amino group-containing acrylic resin and the second acrylic resin having a relatively small difference between the amino group-containing epoxy resin and the second acrylic resin having a relatively large difference. It does not depend directly on the SP value difference between As a result, a sufficient amount of the second acrylic resin can be blended to achieve weather resistance without adversely affecting the dispersion stability.
[0043]
Further, the concentration gradient of the second acrylic resin having the lowest SP value is considered to be highest near the surface of the coating film, thereby contributing to the improvement of weather resistance and at the same time exhibiting the effect of suppressing appearance abnormalities such as repelling and dents. . As a result, in the electrodeposition coating composition of the present invention, a cured coating film having further excellent corrosion resistance and weather resistance can be provided without being overcoated thereon.
[0044]
In general, the second acrylic resin is prepared by using a hydroxyl group-containing acrylic monomer and another ethylenically unsaturated monomer as essential monomers, and copolymerizing the amino group-containing acrylic monomer when it contains an amino group, or epoxy. An amino group is introduced by reacting a group-containing acrylic monomer with an amine after copolymerization.
[0045]
However, since the second acrylic resin must have a lower SP value than the amino group-containing acrylic resin component, the monomer composition is t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl. It is necessary to relatively increase the number of monomers having a low SP value of homopolymers such as (meth) acrylate, or to reduce the proportion of high SP monomers to the desired SP value range.
[0046]
The second acrylic resin can also be used by adding a half-block diisocyanate in the same manner as the amino group-containing acrylic resin.
[0047]
Since the second acrylic resin is intended to have a maximum concentration gradient in the vicinity of the surface of the coating film, it is desirable that the appearance abnormality such as repellency and dent is difficult to occur. Therefore, it is effective to use an acrylic monomer having an ether moiety as a part of other ethylenically unsaturated monomers used during polymerization.
[0048]
Examples of such acrylic monomers are 2-methoxyethyl (meth) acrylate, 4-methoxybutyl (meth) acrylate, natrahydrofurfuryl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2-propoxyethyl (Meth) acrylate, 4-2-ethylhexyloxy) butyl (meth) acrylate, furfuryl (meth) acrylate, and the like.
[0049]
In a preferred embodiment of the present invention further containing a second acrylic resin, the binder component of the black electrodeposition coating composition is (a) an amino group-containing epoxy resin in an amount of 5 to 35% by weight, preferably in a total solid content of 100% by weight. 13 to 27% by weight; (b) 20 to 64% by weight, preferably 24 to 55% by weight, of an amino group-containing acrylic resin having an SP value lower than that of the amino group-containing epoxy resin by 0.5 or more; (c) aliphatic block 20 to 30% by weight of polyisocyanate, preferably 24 to 27% by weight; and (d) 1 to 10% by weight of a second acrylic resin having an SP value lower than that of the amino group-containing acrylic resin, preferably 5 to 10% by weight; (The sum of components (a) to (d) is 100% by weight).
[0050]
In the binder component, if the amount of the second acrylic resin is less than 1% by weight, the weather resistance of the resulting coating film is lowered, and repellency and dents are likely to occur in the coating film. Sex is reduced.
[0051]
Pigment
Various black pigments can be contained in the black electrodeposition coating composition of the present invention. Examples of black pigments are carbon black, black iron oxide, copper chrome black, copper iron manganese black and the like.
[0052]
A preferred black pigment is carbon black. It is because it is excellent in hiding power and coloring power. Carbon black having a particle size of 15 nm or less, particularly 13 nm or less is preferred. When the particle size of the carbon black used exceeds 15 nm, the concealability and blackness of the resulting coating film are reduced.
[0053]
When carbon black is used as the black pigment, the amount used is preferably 1 to 7%, particularly 2.5 to 5.5% as the coating PVC. When the amount of carbon black used is less than 1% of PVC, the concealability and blackness of the coating film obtained are lowered, and when it is more than 7% of PVC, the weather resistance of the obtained coating film is lowered. In addition, PVC means the pigment volume ratio in a coating film.
[0054]
Neutralizer
The neutralizing agent used here is inorganic acid or organic acid such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, hydroxyacetic acid, sulfamic acid, lactic acid. The amount of the neutralizing agent may be an amount that achieves a neutralization rate of at least 20%, preferably 30 to 60%.
[0055]
Aqueous medium
The aqueous medium may be water as well as various organic solvents. Examples of solvents suitable for use in the present invention include hydrocarbons (eg, xylene or toluene), alcohols (eg, methyl alcohol, n-butyl alcohol, isopropyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, propylene Glycol), ethers (for example, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monoethyl ether, 3-methyl-3-methoxybutanol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether), Ketones (eg, methyl isobutyl ketone, cyclohexanone, isophorone, acetylacetone), esters (eg, ethylene glycol Monoethyl ether acetate, ethylene glycol monobutyl ether acetate), and mixtures thereof. The amount of these solvents used is about 0.01 to 25% by weight, preferably 0.05 to 15% by weight, based on the entire coating material.
[0056]
Pigment dispersion paste
When producing an aqueous coating composition containing a binder component and a pigment component dispersed in an aqueous medium, such as an electrodeposition coating composition, a pigment as a powder and a binder component dispersed in an aqueous medium When mixed directly, the pigments are generally hydrophobic and do not disperse uniformly in the aqueous medium. Therefore, usually, a pigment dispersion paste is prepared by uniformly dispersing a pigment at a high concentration in an aqueous medium to prepare an aqueous coating composition by diluting it with a binder component dispersed in the aqueous medium. .
[0057]
Also in the electrodeposition coating composition of the present invention, a pigment dispersion paste is prepared in advance in order to mix the binder component and the pigment component dispersed in the aqueous medium. The pigment dispersion paste contains a pigment, a pigment dispersant, and an aqueous medium.
[0058]
A pigment dispersion paste is prepared by mixing a pigment, a pigment dispersant, and an aqueous medium. Generally, the pigment dispersion paste is prepared to a solid content of 35 to 70% by weight, preferably 40 to 65% by weight. In the solid content, the pigment accounts for 35 to 75% by weight, preferably 40 to 70% by weight, and the pigment dispersant accounts for 25 to 65% by weight, preferably 30 to 60% by weight.
[0059]
Electrodeposition coating composition
In general, an electrodeposition coating composition is prepared by first dispersing a binder component in an aqueous medium containing a neutralizing agent to form a main emulsion, adding a pigment dispersion paste thereto, and mixing them. In the present invention, an amino group-containing epoxy resin, an amino group-containing acrylic resin, and, if necessary, a second acrylic resin are used as the binder resin, so there are several blending methods. Specifically, it is preferable to prepare the main emulsion by the method described in Japanese Patent Application No. 9-114242, paragraphs 0036 to 0037.
[0060]
The amount of the pigment dispersion paste to be added can be appropriately adjusted depending on the amount of the pigment contained in the entire paint. Generally, the pigment component is added in an amount of 2 to 13 parts by weight, preferably 3 to 6 parts by weight, based on 100 parts by weight of the binder component contained in the main emulsion.
[0061]
The electrodeposition coating composition can contain a tin compound such as dibutyltin dilaurate and dibutyltin oxide, and an ordinary urethane cleavage catalyst. The amount is usually 0.1 to 10% by weight of the aliphatic blocked polyisocyanate.
[0062]
The electrodeposition paint can contain conventional paint additives such as a water-miscible organic solvent, a surfactant, an antioxidant, and an ultraviolet absorber.
[0063]
The electrodeposition coating composition of the present invention contains substantially no lead-based anticorrosive pigment. “Substantially free of lead-based anticorrosive pigment” means that lead in diluted paint (cationic electrodeposition coating composition when added to electrodeposition bath) is used at all or no lead-based pigment is used. It means that the ion concentration is 500 ppm or less, preferably 200 ppm or less. A high lead ion concentration is not only harmful to the environment, but can also reduce smoothness.
[0064]
The coating film obtained with the electrodeposition coating composition of the present invention is excellent in corrosion resistance and has sufficient aesthetics and weather resistance as a coated surface. Therefore, the electrodeposition coating composition of the present invention can be used in a one-coat coating method in which the intermediate coating step and the top coating step are omitted and the coating of the metal substrate is completed only by the undercoating step. In particular,
Forming a coating film of the electrodeposition coating composition of the present invention on the coated surface of the metal substrate by an electrodeposition coating method; and
Baking and curing the coating film of the electrodeposition coating composition;
The metal substrate can be coated by a method including
[0065]
【Example】
The following examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof. In Examples, “%” and “part” are based on weight unless otherwise specified.
[0066]
Production Examples 1-3
In Production Examples 1 to 3, preparation of the pigment dispersion paste will be described.
[0067]
Production Example 1
A flask equipped with a stirrer, a cooler, a nitrogen injection tube, a thermometer, and a dropping funnel was prepared. To this flask, 222.0 parts of isophorone diisocyanate was added, diluted with 39.1 parts of methyl isobutyl ketone, and then 0.2 part of dibutyltin dilaurate was added. After raising the temperature to 50 ° C., 131.5 parts of 2-ethylhexanol was added dropwise over 2 hours from the dropping funnel while stirring while bubbling nitrogen. By appropriately cooling, the reaction temperature during this period was maintained at 50 ° C. As a result, 2-ethylhexanol half-blocked isophorone diisocyanate was obtained (solid content 90%).
[0068]
A reaction vessel equipped with a stirrer, a nitrogen injection tube, and a cooling tube was charged with 351.6 parts of Epon 828 (epoxy resin manufactured by Shell Chemical Co., Ltd., epoxy equivalent: 190) and 99.2 parts of bisphenol A, and heated to 130 ° C. in a nitrogen atmosphere. Then, 1.41 parts of benzyldimethylamine was added and reacted at 170 ° C. for about 1 hour to obtain a bisphenol A type epoxy resin having an epoxy equivalent of 450.
[0069]
Next, after the reaction solution was cooled to 140 ° C., 218.3 parts (solid content 196.5 parts) of 2-ethylhexanol half-blocked isophorone diisocyanate prepared above was added and kept at 140 ° C. for 1 hour. To this, 172.3 parts of dipropylene glycol monobutyl ether was added for dilution, and the reaction solution was cooled to 100 ° C. to give 1- (2-hydroxyethylthio) -2-propanol (“SHP-100” manufactured by Sanyo Chemical Co., Ltd.). 408.0 parts (solid content 136.0 parts), dimethylolpropionic acid 134.0 parts and deionized water 144.0 parts were added and reacted at 70-75 ° C. until the acid value was 3.0 or less.
[0070]
A tertiary onium group-containing epoxy resin having a tertiary sulfoniumation rate of 70.6% was obtained. This was diluted with 324.8 parts of dipropylene glycol monobutyl ether and 1204.8 parts of ion-exchanged water to obtain an epoxy-based tertiary onium salt type pigment dispersing resin (resin solid content 30%).
[0071]
83 parts of the obtained epoxy type tertiary onium salt type pigment dispersion resin (solid content 30%) and 17 parts of carbon black (“M-2600” manufactured by Mitsubishi Kasei Co., Ltd., average particle size 13 nm) were mixed and mixed with a sand grind mill. A pigment dispersion paste (solid content 42%) was prepared by pulverizing to a particle size of 10 μm or less.
[0072]
Production Example 2
83 parts of the epoxy-type tertiary onium salt type pigment dispersion resin (solid content 30%) obtained in Production Example 1 and 17 parts of carbon black (“Raben 410” manufactured by Columbia Carbon Co., Ltd., average particle size: 70 nm) are mixed and sand grind is mixed. A pigment dispersion paste (solid content 42%) was prepared by grinding to a particle size of 10 μm or less with a mill.
[0073]
Production Example 3
83 parts of the epoxy-based tertiary onium salt type pigment dispersion resin (solid content 30%) obtained in Production Example 1 and 17 parts of carbon black (“MA-100” manufactured by Mitsubishi Kasei Co., Ltd., average particle size 22 nm) are mixed, and sand is mixed. A pigment dispersion paste (solid content 42%) was prepared by grinding to a particle size of 10 μm or less with a grind mill.
[0074]
Production Example 4
Preparation of amino group-containing epoxy resin (a)
Into a reaction vessel equipped with a stirrer, a nitrogen introducing tube, a cooling tube, and a thermometer, 950 parts of bisphenol A type epoxy resin having an epoxy equivalent of 950 (Epototo YD-014 manufactured by Tohto Kasei Co., Ltd.) is placed, and 237.5 parts of methyl isobutyl ketone Together with heating to 100 ° C. to complete dissolution. Next, 60 parts of N-methylethanolamine and 73 parts of a methyl isobutyl ketimine 73% methyl isobutyl ketone solution of diethylenetriamine were added.
[0075]
This mixture was kept at 120 ° C. for 1 hour to obtain an amino group-containing epoxy resin solution having an SP value of 11.4.
[0076]
Production Example 5
Preparation of aliphatic blocked polyisocyanate (c)
In a reaction vessel equipped with a stirrer, a thermometer, a cooling tube and a nitrogen introduction tube, 222 parts of isophorone diisocyanate was placed, diluted by adding 56 parts of methyl isobutyl ketone, and then 0.2 part of dibutyltin dilaurate was added. Thereafter, the temperature was raised to 50 ° C., and 174 parts of methyl ethyl ketoxime was added so that the resin temperature did not exceed 70 ° C. It was kept at 70 ° C. for 1 hour until the absorption of isocyanate groups substantially disappeared by infrared absorption spectrum, and then diluted by adding 43 parts of n-butanol to obtain a solution of an aliphatic block polyisocyanate.
[0077]
Production Example 6
Preparation of second acrylic resin (d)
A reaction vessel equipped with a stirrer, thermometer, decanter, reflux condenser, nitrogen inlet tube and dropping funnel was charged with 1550 parts of methyl isobutyl ketone, heated to 120 ° C. while introducing nitrogen gas, and 627 parts of methyl methacrylate. , 191 parts lauryl methacrylate, 182 parts hydroxy-4-hydroxybutyl acrylate, 300 parts 2-methoxyethyl acrylate, 200 parts butyl methacrylate and 50 parts t-butylperoxy-2-ethylhexanoate. It was added dropwise at a constant rate over 3 hours. After the completion of dropping, the reaction was further carried out at 120 ° C. for 3 hours, followed by cooling to obtain a second acrylic resin solution having an SP value of 9.7.
[0078]
Production Example 7
Preparation of emulsion containing amino group-containing epoxy resin (a) and aliphatic block polyisocyanate (c)
120.4 parts of the amino group-containing epoxy resin solution obtained in Production Example 4 and 56.2 parts of the aliphatic block polyisocyanate solution obtained in Production Example 5 were added and mixed, followed by 30 at 60 ° C. in a nitrogen atmosphere. The mixture was held for 2 minutes, 2.0 parts of acetic acid was added, and 215.6 parts of ion-exchanged water was gradually added with sufficient stirring to obtain an emulsion containing an amino group-containing epoxy resin and an aliphatic block polyisocyanate. The solid content of the emulsion was 36%.
[0079]
Production Example 8
Preparation of emulsion containing amino group-containing acrylic resin (b), aliphatic block polyisocyanate (c), and second acrylic resin (d)
Into a five-necked flask equipped with a reflux condenser, a stirrer, a dropping funnel and a nitrogen introduction tube, 56.3 parts of methyl isobutyl ketone was charged and heated to 115 ° C. in a nitrogen atmosphere. To this, 16.0 parts glycidyl methacrylate, 4.2 parts 2-hydroxyethyl methacrylate, 14.8 parts 2-hydroxypropyl methacrylate, 58.1 parts n-butyl methacrylate, 6.9 parts t-butyl methacrylate, and t -A mixture of 4.0 parts of butyl peroctoate was added dropwise from the dropping funnel over 3 hours. After the completion of dropping, the mixture was kept at 115 ° C. for about 1 hour, and then 0.5 part of t-butyl peroctoate was dropped and kept at 115 ° C. for about 30 minutes to obtain an acrylic resin solution having a solid content of 65%. The number average molecular weight (Mn) was 6000.
[0080]
After cooling, 8.5 parts of N-methylethanolamine was added thereto and reacted at 120 ° C. for 2 hours in a nitrogen atmosphere to obtain a solution of resin SP10.3 and an amino group-containing acrylic resin having a solid content of about 67%.
[0081]
To this solution was added 44.6 parts of the aliphatic blocked polyisocyanate obtained in Production Example 5, 33.6 parts of the second acrylic resin solution obtained in Production Example 6 and 2.6 parts of acetic acid, and 70 ° C. under a nitrogen atmosphere. For 30 minutes, and 301.2 parts of ion-exchanged water was gradually added with sufficient stirring to obtain an emulsion containing an amino group-containing acrylic resin. The solid content of the emulsion was 30%.
[0082]
Examples 1-5 and Comparative Examples 1-6
Preparation of black electrodeposition coating composition
According to the blending amounts of the paint components shown in Table 3, the pigment dispersion paste obtained in Production Examples 1 to 3 and the emulsion obtained in Production Examples 7 and 8 were mixed, and ion-exchanged water was added to the resulting mixture. The electrodeposition coating composition was obtained with a solid content of 20%.
[0083]
[Table 3]

[0084]
Using these electrodeposition coating compositions, electrodeposition coating was applied to a zinc phosphate-treated steel plate (0.8 × 70 × 150 mm) and baked at 170 ° C. (film) for 20 minutes. The film thickness after baking was set to 20 μm.
[0085]
The appearance and performance of the obtained electrodeposition coating film were evaluated as follows. The results are shown in Tables 4 and 5.
[0086]
Appearance of the coating
(1) Hue
With a SM-4 type color computer manufactured by Suga Test Instruments Co., Ltd., the color difference (difference in blackness) ΔL of the cured coating film was measured as compared with a black standard plate (current overcoat plate).
Evaluation criteria
Good: ΔL ≦ 3
Defect: ΔL> 3
[0087]
(2) Smoothness (Ra)
Ra (μm) of the cured coating film was measured using a surface roughness measuring machine (“Surftest 211” manufactured by Mitutoyo Corporation).
Evaluation criteria
Good: Ra ≦ 0.3
Defect: Ra> 0.3
[0088]
(3) dent
The number of occurrences of dents from the bubble grains to the size of azuki grains per 70 × 150 mm area of the electrodeposition coated plate (thickness 0.7 mm) was counted.
Evaluation criteria
Good: 0
Defect: 1 ≦
[0089]
Coating performance
(1) Weather resistance
The electrodeposited zinc-treated steel sheet was attached to a sunshine weatherometer (specified in JIS B 7753 (Sunshine Carbon Arc Weathering Tester)) and irradiated for 400 hours. Then, 60 degree gloss of the electrodeposition coating film surface was measured and the gloss retention with respect to initial 60 degree gloss was calculated | required.
Evaluation criteria
Good: Gloss retention ≧ 80%
Poor: gross retention <80%
[0090]
(2) Salt spray resistance
Using a small cutter (for example, an NT cutter), a crosscut reaching the substrate was put on the electrodeposited zinc-coated steel sheet using a small cutter (for example, NT cutter). The salt spray tester specified in JIS Z2371 was placed for a specified time, and the rust width of the cross-cut portion was measured.
Evaluation criteria
Good: Maximum rust (bulge) width from cut line (one side) ≤ 2 mm
Defect: Maximum rust (bulge) width from cut line (one side)> 2mm
[0091]
[Table 4]

[0092]
[Table 5]

[0093]
【The invention's effect】
Provided is a black electrodeposition coating composition that can form an undercoating film having sufficient aesthetics and weather resistance as a coated surface, while maintaining corrosion resistance as in the past, and without being overcoated thereon. .

Claims (7)

A black electrodeposition coating composition comprising a binder component and a pigment dispersion paste dispersed in an aqueous medium containing a neutralizing agent,
Those the binder component,
a) 5 to 35% by weight of an amino group-containing epoxy resin;
b) 30 to 65% by weight of an amino group-containing acrylic resin; and c) 20 to 30% by weight of an aliphatic blocked polyisocyanate;
(The sum of components (a) to (c) is 100% by weight),
The pigment dispersion paste is prepared by mixing carbon black, a pigment dispersant, and an aqueous medium, the pigment dispersant is an epoxy-based tertiary onium salt type pigment dispersion resin, and the carbon black has a particle diameter of 15 nm or less. A black electrodeposition coating composition which is black and whose amount is 35 to 75% by weight in the solid content of the pigment dispersion paste and 1 to 7% as a coating PVC.   The electrodeposition coating composition according to claim 1, wherein the amino group-containing acrylic resin has an SP value lower by 0.5 or more than the amino group-containing epoxy resin. The binder component is
a) 5 to 35% by weight of an amino group-containing epoxy resin;
b) 20 to 64% by weight of an amino group-containing acrylic resin having an SP value of 0.5 or more lower than that of the amino group-containing epoxy resin;
c) aliphatic blocked polyisocyanate 20 to 30% by weight; and d) 2nd acrylic resin 1 to 10% by weight lower than the amino group-containing acrylic resin by 0.5 or more;
(The total of component (a)-(d) is 100 weight%.) The black electrodeposition coating composition of Claim 1. 2. The black electrodeposition coating composition according to claim 1, wherein the epoxy-based tertiary onium salt pigment dispersion resin is a tertiary sulfoniumated resin. 2. The black electrodeposition coating composition according to claim 1, wherein the epoxy type tertiary onium salt type pigment dispersion resin is produced from a bisphenol full A type epoxy resin. The process of forming the coating film of the electrodeposition coating composition in any one of Claims 1-3 on the to-be-coated surface of a metal base material by an electrodeposition coating method; and the process of baking and hardening the coating film of an electrodeposition coating composition ;
A method for coating a metal substrate, comprising:   The black electrodeposition coating material composition for 1 coat coating methods including the black electrodeposition coating material composition in any one of Claims 1-3.