JP2004269595A - Cation electrodeposition coating composition having excellent thin film corrosion resistance - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、自動車鋼板などの各種鋼板に塗装して、１０μｍ未満の薄膜厚で優れた耐穴あき錆性を発揮するカチオン電着塗料組成物に関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
カチオン電着塗料は防食性や塗面平滑性に優れた塗膜を形成することができるため、自動車車体・部品などの防錆塗装などに広く利用されている。しかし、カチオン電着塗料といえども１０μｍ未満の薄膜になると著しく防錆性が低下する傾向が見られるが、この原因は必ずしも判っていなかった。
一般に、薄膜になると腐食促進物質である水や酸素に対する透過阻止能および防錆顔料に基づくインヒビター能が膜厚に比例して低下することは当然であると考えられるが、通常考えられる対策として塗膜の架橋密度を上げたり防錆顔料を増量したりしても、余り効果が大きくないうえ、仕上がり性の低下や塗料のコストアップを招くため有効な解決策とはならなかった。
また、最大粒径が２μｍ以下である酸化ビスマスの水和物を含有することによって長期防食性を向上する発明（例えば、特許文献１参照）があるが、これだけでは１０μｍ未満の薄膜における防錆性の著しい低下傾向を防ぐには到底不十分であった。
【特許文献１】特開２００１−３５４９１０号公報参照
【０００３】
【課題を解決するための手段】
従来から塩素イオンが大きな腐食促進作用を持つこと、及び塗膜抵抗による防食性能に対して塩素イオンの透過性が関係することは公知であるものの、カチオン電着塗膜が１０μｍ未満の薄膜になると塩素イオンの透過性が著しく増大すること、塩素イオン透過阻止能を向上することによって１０μｍ未満の薄膜での防錆性を改良できることは、従来においては知られていなかった。
そこで本発明者らは、塩素イオン透過阻止能向上による１０μｍ未満の薄膜防錆性の改良について鋭意検討を重ねた結果、エポキシ樹脂の変性剤として芳香族炭化水素―ホルムアルデヒド樹脂を樹脂中に平均して５〜２５重量％の割合で含有するアミン付加エポキシ樹脂、及びブロックポリイソシアネート硬化剤を樹脂成分とするカチオン電着塗料組成物を用いて、膜厚１０μｍにおける塩素イオン透過性を７．０×１０−６ｇ／ｃｍ−２／ｄａｙ（５％食塩水、５０℃×２４時間）以下とし、さらには顔料成分の最大粒子径が１．５μｍ以下であるカチオン電着塗料組成物を用いることにより、容易に各種鋼板の耐穴あき錆性を向上させ得ることを見出し、本発明を完成するに至った。
すなわち、本発明は、
１．カチオン電着塗料組成物の樹脂成分として、 エポキシ樹脂の変性剤として芳香族炭化水素―ホルムアルデヒド樹脂を樹脂中に平均して５〜２５重量％の割合で含むアミン付加エポキシ樹脂、及びブロックポリイソシアネート硬化剤を含有し、膜厚１０μｍにおける塩素イオン透過性が７．０×１０−６ｇ／ｃｍ−２／ｄａｙ（５％食塩水、５０℃×２４時間）以下であることを特徴とする薄膜耐食性に優れたカチオン電着塗料組成物、
２．芳香族炭化水素が、ｍ−キシレンである１項に記載の薄膜耐食性に優れたカチオン電着塗料組成物、
３．顔料成分の最大粒子径が１．５μｍ以下である１項又は２項に記載の薄膜耐食性に優れたカチオン電着塗料組成物、
４．最大粒子径が１．５μｍ以下である酸化ビスマス水和物を、樹脂成分の固形分合計１００重量部に対して、２〜５重量部含有する１項乃至３項のいずれか１項に記載の薄膜耐食性に優れたカチオン電着塗料組成物、に関する。
【０００４】
【発明の実施の形態】
本発明のカチオン電着塗料組成物の樹脂成分と顔料成分について、以下に詳細に説明する。
樹脂成分：
１０μｍ未満の薄膜厚で耐穴あき錆性向上に効果を発揮するには、 樹脂成分として、芳香族炭化水素―ホルムアルデヒド樹脂を樹脂中に平均して５〜２５重量％の割合で含有するアミン付加エポキシ樹脂、及びブロックポリイソシアネート硬化剤を含有するカチオン電着塗料組成物を用いて、膜厚１０μｍにおいて塩素イオン透過性を７．０×１０−６ｇ／ｃｍ−２／ｄａｙ（５％食塩水、５０℃×２４時間）以下とする必要がある。
従来からのカチオン電着塗料の樹脂成分として用いているアミン付加エポキシ樹脂は、電着塗膜の造膜性、平滑性、可とう性を付与するためエポキシ樹脂骨格を一部変性する。
本発明の狙いである１０μｍ未満の薄膜厚で優れた耐穴あき錆性を得るためには、この変性剤の役割が極めて重要であり、塗膜に造膜性、平滑性、可とう性を付与するとともに、特に、塩素イオンに対して透過阻止能を向上させることが必要である。
そのような変性剤として、下記の式（１）で表されるアルキル置換フェニル骨格がメチレン鎖及び／又はオキシメチレン鎖で結合した構造を有する芳香族炭化水素―ホルムアルデヒド樹脂が効果があることを見出した。
【０００５】
【化１】
（ 式（１）中、Ｒ１は炭素原子数１〜３のアルキル基、Ｒ２は水素原子または炭素原子数１〜３のアルキル基、ｍは０又は１、ｎは２〜２０の整数）
上記のアルキル置換フェニル骨格がメチレン鎖及び／又はオキシメチレン鎖で結合した構造を有する変性剤は、具体的には、ｍ−キシレンとホルマリン、又はパラホルムアルデヒド、又はトリオキサン等のホルムアルデヒドを発生する化合物などを酸性触媒の存在下に縮合反応させることにより製造することができる。上記の変性剤の使用割合は、塗料組成物の用途等に応じて適宜変えることができるが、アミン付加エポキシ樹脂の固形分を基準にして５〜２５重量％、好ましくは１０〜２０重量％の範囲内が適当である。
上記アミン付加エポキシ樹脂には、通常、ポリフェノール化合物とエピクロルヒドリンとの反応により得られるエポキシ樹脂が原料として用いられる。
中でも、ビスフェノールＡから誘導される下記式
【０００７】
【化２】
（ｎ＝０〜８で示されるものが好適である）
【０００９】
エポキシ樹脂は、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。
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。
アミン化合物は、エポキシ基と反応する活性水素を少なくとも１個含有し、該エポキシ樹脂をカチオン化できるものであれば種類を問わないが、特に１級アミノ基を導入できるものを使用することが好ましい。
上記の１級アミノ基を導入できるアミン化合物としては、モノエタノールアミン、プロパノールアミン、ヒドロキシエチルアミノエチレンジアミン、ヒドロキシ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、テトラエチレンペンタミン、ペンタエチレンヘキサミンなどのケチミン化物が挙げられる。
上記１級アミンと併用できるアミン化合物としては、従来からエポキシ樹脂のカチオン化に用いられるものが使用できるが、特に２級アミンが好ましい。例としてジエチルアミン、ジイソプロピルアミン、ジエタノールアミン、ジ（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が挙げられる。
このような付加アミンの量としては、アミン価として３０〜７０ｍｇＫＯＨ／ｇ樹脂固形分の範囲、さらには４０〜６０ｍｇＫＯＨ／ｇ樹脂固形分とすることが好ましい。かくして得られた、エポキシ樹脂の変性剤として芳香族炭化水素―ホルムアルデヒド樹脂を用いたアミン付加エポキシ樹脂は、一般に、１０００〜１００００、特に２００〜５０００の範囲内の数平均分子量、および一般に１００〜５０００、特に２００〜２５００の範囲内の水酸基当量を有していることが好ましい。
【００１０】
このエポキシ樹脂の変性剤として芳香族炭化水素―ホルムアルデヒド樹脂を樹脂中に平均して５〜２５重量％の割合で含有するアミン付加エポキシ樹脂の効果としては、焼付け乾燥後の塗膜が高い均一性・疎水性・ガラス転移点を保ち、１０μｍ未満の薄膜厚における塩素イオンに対する透過阻止能が向上することが考えられ、その結果、薄膜での耐穴あき錆性が向上するものと思われる。
上記変性剤の含有量が５重量％未満であると塗膜に造膜性、平滑性、可とう性を付与する効果が不足し、また２５重量％を越えると耐穴あき錆性の向上に対しての効果が少ないばかりかカチオン電着塗料のコストが上がる。
本発明の樹脂成分として、アミン付加エポキシ樹脂以外に、耐候性、耐チッピング性、上塗りとの密着性などの要求に応じて、アクリル系、ポリウレタン系、ポリエステル系などの添加樹脂も併用することができる。
【００１１】
ブロックポリイソシアネート硬化剤はポリイソシアネート化合物とブロック剤との付加反応生成物であり、ポリイソシアネート化合物としては、トリレンジイソシアネート、キシリレンジイソシアネート、フェニレンジイソシアネート、ジフェニルメタンジイソシアネート、ビス（イソシアネートメチル）シクロヘキサン、テトラメチレンジイソシアネート、ヘキサメチレンジイソシアネート、メチレンジイソシアネート、イソホロンジイソシアネートなどの芳香族、脂環族または脂肪族のジイソシアネート化合物、およびこれらのトリイソシアヌレート化合物、あるいはこれらのイソシアネート化合物の過剰量にエチレングリコール、プロピレングリコール、トリメチロールプロパン、ヘキサントリオールなどの低分子活性水素含有化合物を反応させて得られる末端イソシアネート含有化合物などが挙げられる。
一方、前記ブロック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、常温において安定で、且つ約１２０〜１８０℃の加熱時、速やかに解離して遊離のイソシアネート基を再生しうるものが使用される。
このようなブロック剤としては、例えば、ε−カプロラクタム、γ−ブチロラクタムなどのラクタム系化合物；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；エチレングリコールモノブチルエーテルなどのエーテルアルコール系化合物が挙げられる。
アミン付加エポキシ樹脂、及びブロックポリイソシアネート硬化剤からなる樹脂成分は、通常、ギ酸、酢酸、乳酸などの水溶性有機酸で中和して水分散化することによりカチオン電着塗料用のエマルションとして使用される。
【００１２】
顔料成分：
１０μｍ未満の薄膜厚で耐穴あき錆性に効果を発揮するには、カチオン電着塗料組成物中の顔料成分の最大粒子径（注１）を１．５μｍ以下とすること、さらに、最大粒子径が１．５μｍ以下である酸化ビスマス水和物を樹脂成分の固形分合計１００重量部に対して２〜５重量部含有させることが極めて有効である。
（注１）最大粒子径：ＬＡ−５００（堀場製作所製、商品名、動的光散乱式粒径分布測定装置）を用いた。
具体的には、分散用樹脂、酸化ビスマス水和物などの防錆顔料を含む顔料、中和剤、脱イオン水、場合によっては界面活性剤を加えて混合し、最大粒子径が１．５μｍ以下となるまで分散することによって得られた顔料分散ペーストをカチオン電着塗料組成物中に添加することにより達成される。
上記顔料分散ペーストに使用される分散用樹脂は特に限定されないが、アミノ基含有エポキシ樹脂、４級アンモニウム塩型エポキシ樹脂、スルホニウム塩型エポキシ樹脂などのエポキシ樹脂系が好ましい。アミノ基含有エポキシ樹脂の場合は、酢酸、ギ酸、乳酸、プロピオン酸、ヒドロキシ酢酸、メトキシ酢酸、などの水溶性有機酸で中和して使用し、中和当量としては樹脂中のアミノ基に対し０．５〜１．２当量、好ましくは０．７〜１．０当量が良い。
酸化ビスマス水和物などの防錆顔料を含む顔料としては酸化ビスマス水和物、リンモリブデン酸アルミニウム、トリポリリン酸アルミニウム等の防錆顔料以外に、酸化チタン、カーボンブラック、ベンガラなどの着色顔料、クレー、マイカ、バリタ、タルク、炭酸カルシウム、シリカなどの体質顔料を含むことができる。
顔料分散ペーストの製造方法は、例えば、分散用樹脂、酸化ビスマス水和物などの防錆顔料を含む顔料、中和剤、脱イオン水、及び必要に応じてジブチル錫オキサイド（ＤＢＴＯ）、ジオクチル錫オキサイド（ＤＯＴＯ）等の有機錫化合物等を前練り混合後、分散機として、ボールミル、ペブルミル、サンドミル、シェイカー等、従来から用いられている分散機を用いて行うことができる。
ボールミルを用いた場合、前練り混合物にメジアを適量加えた後、分散時間として２４〜２４０時間、好ましくは４８〜１２０時間をかけて分散することにより、顔料成分の最大粒子径が１．５μｍ以下である顔料分散ペーストを得ることができる。
上記、最大粒子径が１．５μｍ以下である顔料成分の配合割合は、樹脂成分の固形分合計１００重量部に対して、顔料成分の配合量が固形分換算で３〜３０重量部、最大粒子径が１．５μｍ以下である酸化ビスマス水和物を２〜５重量部含有することが好ましい。
酸化ビスマス水和物の配合割合が２重量部未満では耐穴あき錆性の向上に効果が少なく、５重量部を越えるとカチオン電着塗料組成物のコストが上がり好ましくない。
【００１３】
カチオン電着塗料組成物：
本発明のカチオン電着塗料組成物は、以上に述べたような樹脂成分を含有するエマルション、酸化ビスマス水和物等の顔料成分を含有し、最大粒子径が１．５μｍ以下となるように分散して得られる顔料分散ペーストを配合し、ｐＨを５．５〜９．０の範囲内、固形分濃度が約５〜４０重量％、好ましくは１５〜２５重量％となるように脱イオン水などで希釈して使用される。
カチオン電着塗料組成物の塗装は、一般には、浴温１５〜３５℃、負荷電圧１００〜４００Ｖの条件で行うことができる。焼き付け温度は、一般に１４０〜２００℃、好ましくは１５０〜１８０℃の範囲、焼き付け時間は５分間〜９０分間、好ましくは１０分間〜４０分間とするのがよい。焼き付け後の塗膜の膜厚は３０μｍ以下、好ましくは２０μｍ以下の範囲内とすることができる。
【００１４】
【発明の効果】
以下の内容のカチオン電着塗料組成物によって、電着塗装を施した自動車の各種鋼板における１０μｍ未満の薄膜厚で、耐穴あき錆性の向上を図ることができる。
エポキシ樹脂の変性剤として芳香族炭化水素―ホルムアルデヒド樹脂を樹脂中に平均して５〜２５重量％の割合で含有するアミン付加エポキシ樹脂、及びブロックポリイソシアネート硬化剤を樹脂成分とし、膜厚１０μｍにおける塩素イオン透過性が７．０×１０−６ｇ／ｃｍ−２／ｄａｙ（５％食塩水、５０℃×２４時間）以下であるカチオン電着塗料組成物。
かつ顔料成分の最大粒子径が１．５μｍ以下であり、さらには酸化ビスマス水和物を含有し、該成分の最大粒子径が１．５μｍ以下であるカチオン電着塗料組成物であることが好ましい。
本発明のカチオン電着塗料組成物が、１０μｍ未満の薄膜厚で耐穴あき錆性向上に効果を発揮する理由としては、次のように考えられる。
（１）樹脂成分の面から：芳香族炭化水素―ホルムアルデヒド樹脂を樹脂中に平均して５〜２５重量％の割合で含有するアミン付加エポキシ樹脂によって、１０μｍ未満の薄膜厚において均一で平滑な塗面が得られ、かつ疎水性であること、塗膜のガラス転移点（Ｔｇ）が高いことから塗膜に温度がかかった場合でも、腐食促進物質である塩素イオンが鋼板と塗膜との間の界面に到達するのを防ぐ作用（透過阻止能）が向上する。
さらに（２）顔料成分の面から：酸化ビスマス水和物などの防錆顔料を含む顔料成分の最大粒子径を１．５μｍ以下に分散することにより防錆顔料の表面積が飛躍的に大きくなるため、塩素イオンが鋼板と塗膜との間の界面に到達するのを防ぐ作用（透過阻止能）が一層向上する。
【００１５】
【実施例】
以下、実施例を挙げて本発明をさらに詳細に説明する。但し、本発明はこれによって制限されるものではない。
製造例１ アミン付加エポキシ樹脂Ｎｏ．１の製造
フラスコに、エピコート８２８ＥＬ（ジャパンエポキシレジン社製エポキシ樹脂 、エポキシ当量１９０）１０００部、ビスフェノールＡ ４００部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、ニカノールＬ（商品名、三菱ガス化学製、キシレンーホルムアルデヒド樹脂）を３００部、ジエタノールアミンを１４０部及びジエチレントリアミンのケチミン化物６５部を加え１２０℃で４時間反応させた後、ブチルセロソルブ４７５部を加え、アミン価５２ｍｇＫＯＨ／ｇ、樹脂固形分８０％のアミン付加エポキシ樹脂Ｎｏ．１を得た。
【００１６】
製造例２ アミン付加エポキシ樹脂Ｎｏ．２の製造
エピコート８２８ＥＬ（商品名、ジャパンエポキシレジン社製、エポキシ樹脂）１０００部、ビスフェノールＡ ３９０部、ジメチルベンジルアミノ０．２部を加え、１３０℃でエポキシ当量７５５になるまで反応させた。
次にε−カプロラクトン２６０部、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い赤外吸収スペクトル測定において未反応のε−カプロラクトン量を追跡し、反応率が９８質量％以上になった時点で１２０℃に温度を下げた。
次にジエタノールアミン１６０部、ジエチレントリアミンのメチルイソブチルジケチミン化物６５部を加え、１２０℃で４時間反応させ、ブチルセルソルブ４７０部を加え、アミン価５７ｍｇＫＯＨ／ｇ、樹脂固形分８０質量％のアミン付加エポキシ樹脂Ｎｏ．２を得た。
【００１７】
製造例３ カチオン電着用のエマルションＮｏ．１の製造
上記、製造例１で得られたアミン付加エポキシ樹脂Ｎｏ．１を８７．５部（樹脂固形分で７０ｇ）、硬化剤としてメチルエチルケトオキシムでブロックしたヘキサメチレンジイソシアネートトリイソヌレート２２．２部 （樹脂固形分で２０部）、及びエチレングリコールモノブチルエーテルでブロックしたジフェニルメタンジイソシアネート１１．１部（樹脂固形分で１０部）と良く混合し、中和剤として酢酸１．５部（中和価１４に相当）を配合し、強く攪拌しながら脱イオン水 １７０．７部を約１５分かけて滴下し、固形分３４％のカチオン電着用のエマルションＮｏ．１を得た。
【００１８】
製造例４〜５
表１の配合内容にて、カチオン電着用のエマルションＮｏ．２〜３を得た。
【００１９】
【表１】
（注２）サンニックスＰＰ−１０００：商品名、三洋化成株式会社製、表面調整剤
【００２１】
製造例６ ４級アンモニウム塩型エポキシ系顔料分散用樹脂の製造
フラスコにトリレンジイシシアネート（ＴＤＩ）６９６部、メチルイソブチルケトオキシム（ＭＩＢＫ） ３０４部 を加えて６０℃に昇温し、２エチルヘキシルアルコール５２０部を滴下し、ＮＣＯ価１１０．５になるまで反応させ、樹脂固形分８０％の部分ブロックイソシアネートＡを得た。
次にこの部分ブロックイソシアネートＡ ３８０部を取り、７０℃でジメチルエタノールアミン８９部を滴下し、実質的にＮＣＯが無くなるまで反応させ、ブチルセロソルブ３４．７５部で希釈した後、９０％の乳酸１００部で中和して８０％の乳酸中和アミノ基含有ブロックイソシアネートＢを得た。
別のフラスコに、エピコート８２８ＥＬ（ジャパンエポキシレジン社製エポキシ樹脂 、エポキシ当量１８８）１１２５部、ビスフェノールＡ ４５６部及びトリフェニルホスホニュウムアイオダイト１．１ 部を加え、１７０℃でエポキシ当量７９０になるまで反応させたのち、ＭＩＢＫ２７９部で希釈し、ついで上記部分ブロックイソシアネートＡ７６０部を加え実質的にＮＣＯが無くなるまで１００℃で反応させた。
次いでブチルセロソルブ６３０部を加えて８０℃まで冷却し、８０％の乳酸中和アミノ基含有ブロックイソシアネートＢ８６０部を加え、酸価が１ｍｇＫＯＨ／ｇ以下になるまで反応させ、樹脂固形分７０％の４級アンモニウム塩型エポキシ系顔料分散用樹脂を得た。
【００２２】
製造例７ 顔料分散ペーストＮｏ．１の製造
製造例６で得た４級アンモニウム塩型エポキシ系顔料分散用樹脂 ５．０部（固形分３．５部）、酸化チタン１４．５部、酸化ビスマス水和物 ３．０部、トリポリリン酸アルミニウム ３部、精製クレー ７．０部、カーボンブラック０．５部、ジブチル錫オキサイド２．０部、１０％酢酸 ２．３８部、脱イオン水 ２８．６２部をボールミルにて１２０時間分散したあと排出し、最大粒子径が１．５μｍで固形分５５％の顔料分散ペーストＮｏ．１を得た。
【００２３】
製造例８ 顔料分散ペースト Ｎｏ．２の製造
表２に示す配合、及び分散時間にて、最大粒子径が１．５μｍの顔料分散ペーストＮｏ．２を得た。
【００２４】
製造例９ 顔料分散ペーストＮｏ．３の製造
表２に示す配合、及び分散時間にて、最大粒子径が２．０μｍの顔料分散ペーストＮｏ．３を得た。
【００２５】
製造例１０ 顔料分散ペーストＮｏ．４の製造
表２に示す配合、及び分散時間にて、最大粒子径が３．０μｍの顔料分散ペーストＮｏ．４を得た。
【００２６】
【表２】
実施例１
カチオン電着塗料用のエマルションＮｏ．１ ２９４部（固形分１００部）に、顔料分散ペーストＮｏ．１を６５部（固形分３２．５部）、脱イオン水 ３０３．５部を加え、固形分２０％のカチオン電着塗料Ｎｏ．１を得た。
【００２８】
実施例２、比較例１〜３
実施例１と同様にして、実施例２、比較例１〜３の固形分２０％のカチオン電着塗料Ｎｏ．２〜Ｎｏ．５を得た。
上記、実施例１〜２、比較例１〜３の配合について表３に示す。
【００２９】
【表３】
試験板の作成
実施例、及び比較例で得られたカチオン電着塗料Ｎｏ．１〜Ｎｏ．５を用いて、被塗物としてパルボンド＃３０２０（日本パーカライジング社製、商品名、りん酸亜鉛処理剤）で化成処理を施した亜鉛メッキ鋼板（７０×１５０×０．８ｍｍ）を用いて、膜厚が７μｍ、及び１０μｍの２水準、焼き付け温度は１５０℃で、焼き付け時間を２０分間（保持時間）として試験板を作成した。
試験内容は、下記の条件にて塗膜試験に供した。その結果を表４に示す。
【００３１】
【表４】
（注３）穴あき耐食性：周り１０ｍｍと裏面のマスキングを施した試験板を用いて、表面の半分に模擬泥（ＮａＣｌ／Ｎａ２ＳＯ４／ＣａＣｌ２／カオリン／蒸留水からなる）を塗布した後、水平から６０度の角度にて、以下のサイクル条件にて１２０サイクルを施した後、塗膜膨れ（注４）、赤錆発生（注５）、板厚減少量（注６）を評価した。
サイクル条件：１サイクル［３５℃ 塩水噴霧試験 （ＪＩＳ Ｚ ２３７１による）６時間−乾燥（温度５０℃ 、相対湿度２０〜４０％ ）３時間− 湿潤（温度５０℃、 相対湿度９５％以上）１４時間−冷気送風（室温）１時間 ］
（注４）塗膜膨れ：試験板から模擬泥を水道水で洗いながら刷毛で落とし、室温にて乾燥させた後、以下の式から塗膜膨れ発生率（％）を算出し評価した。
塗膜膨れ発生率（％）＝塗膜膨れ面積／全評価面積
◎：塗膜膨れが３０％以下
○：塗膜膨れが５０％以下
△：塗膜膨れが７０％以下
×：塗膜膨れが７０％を越えるもの
（注５）赤錆発生：試験板から模擬泥を水道水で洗いながら刷毛で落とし、室温にて乾燥させた後、以下の式から赤錆発生率（％）を算出して評価した。
赤錆発生率（％）＝錆発生面積／全評価面積
◎：赤錆発生率が１０％以下
○：赤錆発生率が２０％以下
△：赤錆発生率が３０％以下
×：赤錆発生率が３０％を越えるもの
（注６）板厚減少量：試験後の試験板から赤錆を除去した後、リムーバーで塗膜を除去する。ピンポイントマイクロメーターを用いて鋼板の厚みの減少（錆の深さ）を測定する。
◎：鋼板の厚みの減少が０．３ｍｍ以下
○：鋼板の厚みの減少が０．４ｍｍ以下
△：鋼板の厚みの減少が０．５ｍｍ以下
×：鋼板の厚みの減少が０．５ｍｍを越えるもの
（注７）塩素イオン透過性：ブリキ板に塗装した１０μｍの塗膜をアマルガム法によって剥離し、Ｋ−３１６フィルム酸素透過率計（ツクバリカセイキ株式会社製、製科研式酸素透過率計）のセル（図１の１）に塗膜（図１の３）をつける。セル内に脱イオン水を加え、５％ＮａＣｌ水５００ｍｌ中に浸漬し、塗膜を通過する塩素イオンの濃度を、ＪＩＳ Ｋ０１０１に記載のチオシアン酸水銀（ＩＩ）吸光度法によって求めた。試験時間は２４時間、温度は５０℃で行った。
【図面の簡単な説明】
【図１】フィルム酸素透過率計のモデル図である。
【符号の説明】
１．脱イオン水（１０ｍｌ）
２．セル（内径１８０ｍｍ）
３．塗膜
４．５％ＮａＣｌ（５００ｍｌ）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cationic electrodeposition coating composition which is applied to various steel sheets such as an automobile steel sheet and exhibits excellent rust resistance perforated at a thin film thickness of less than 10 μm.
[0002]
Problems to be solved by the prior art and the invention
Cationic electrodeposition paints are widely used for anti-rust coating of automobile bodies and parts because they can form a coating film having excellent anticorrosion properties and smoothness of the coated surface. However, even for cationic electrodeposition paints, when the thickness is reduced to less than 10 μm, the rust prevention property tends to be remarkably reduced, but the cause has not been known.
In general, it is considered that when a thin film is formed, the ability to inhibit the penetration of water and oxygen, which are corrosion-promoting substances, and the inhibitor ability based on the rust-preventive pigment decrease in proportion to the film thickness. Increasing the cross-linking density of the film or increasing the amount of the rust-preventive pigment was not an effective solution because the effect was not so large, and the finishability was lowered and the cost of the paint was increased.
In addition, there is an invention that improves the long-term corrosion resistance by containing a hydrate of bismuth oxide having a maximum particle size of 2 μm or less (for example, see Patent Document 1). It was not enough to prevent a remarkable downward trend.
[Patent Document 1] See JP-A-2001-354910
[Means for Solving the Problems]
Conventionally, it is known that chloride ions have a large corrosion promoting action, and that chloride ion permeability is related to the anticorrosion performance due to coating resistance, but when the cationic electrodeposition coating film becomes a thin film of less than 10 μm. It has not been conventionally known that the permeability of chloride ions is remarkably increased, and that the rust-preventive property of a thin film having a thickness of less than 10 μm can be improved by improving the ability to inhibit the penetration of chloride ions.
Accordingly, the present inventors have conducted intensive studies on the improvement of the anticorrosion property of a thin film having a thickness of less than 10 μm by improving the ability to prevent chloride ion permeation. As a result, an aromatic hydrocarbon-formaldehyde resin was used as an epoxy resin modifier in the resin. Chloride ion permeability at a film thickness of 10 μm using a cationic electrodeposition coating composition containing an amine-added epoxy resin containing 5 to 25% by weight of a resin and a blocked polyisocyanate curing agent as a resin component. By using a cationic electrodeposition coating composition having a particle size of 10 −6 g / cm −2 / day (5% saline, 50 ° C. × 24 hours) or less, and further having a maximum particle diameter of the pigment component of 1.5 μm or less. The present inventors have found that the rust resistance of various steel sheets can be easily improved, and have completed the present invention.
That is, the present invention
1. As a resin component of the cationic electrodeposition coating composition, an amine-added epoxy resin containing an aromatic hydrocarbon-formaldehyde resin as an epoxy resin modifier at an average ratio of 5 to 25% by weight in the resin, and a cured block polyisocyanate Thin film corrosion resistance characterized by having a chloride ion permeability at a film thickness of 10 μm of 7.0 × 10 −6 g / cm −2 / day (5% saline, 50 ° C. × 24 hours). Excellent cationic electrodeposition coating composition,
2. 4. The cationic electrodeposition coating composition according to
3. 3. The cationic electrodeposition coating composition having excellent thin film corrosion resistance according to
4. The bismuth oxide hydrate having a maximum particle size of 1.5 μm or less according to any one of
[0004]
BEST MODE FOR CARRYING OUT THE INVENTION
The resin component and the pigment component of the cationic electrodeposition coating composition of the present invention will be described in detail below.
Resin component:
In order to exhibit the effect of improving pitting rust resistance with a thin film thickness of less than 10 μm, an amine containing an aromatic hydrocarbon-formaldehyde resin as a resin component at an average ratio of 5 to 25% by weight in the resin is added. Using a cationic electrodeposition coating composition containing an epoxy resin and a blocked polyisocyanate curing agent, a chloride ion permeability of 7.0 × 10 −6 g / cm −2 / day (5% saline) at a film thickness of 10 μm was used. , 50 ° C. × 24 hours).
The amine-added epoxy resin used as a resin component of the conventional cationic electrodeposition paint partially modifies the epoxy resin skeleton in order to impart film forming properties, smoothness, and flexibility of the electrodeposition coating film.
In order to obtain excellent rust resistance against perforation with a thin film thickness of less than 10 μm, which is the object of the present invention, the role of this modifier is extremely important, and the film is required to have film forming properties, smoothness, and flexibility. It is necessary to improve the ability to prevent permeation of chloride ions, in addition to the addition.
As such a modifier, an aromatic hydrocarbon-formaldehyde resin having a structure in which an alkyl-substituted phenyl skeleton represented by the following formula (1) is bonded by a methylene chain and / or an oxymethylene chain has been found to be effective. Was.
[0005]
Embedded image
(In the formula (1), R 1 is an alkyl group having 1 to 3 carbon atoms, R 2 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, m is 0 or 1, and n is an integer of 2 to 20)
Specific examples of the modifier having a structure in which the alkyl-substituted phenyl skeleton is bonded with a methylene chain and / or an oxymethylene chain include compounds that generate formaldehyde such as m-xylene and formalin, or paraformaldehyde, or trioxane. Can be produced by a condensation reaction in the presence of an acidic catalyst. The use ratio of the above modifier can be appropriately changed depending on the use of the coating composition and the like, but is 5 to 25% by weight, preferably 10 to 20% by weight based on the solid content of the amine-added epoxy resin. The range is appropriate.
As the amine-added epoxy resin, an epoxy resin obtained by a reaction between a polyphenol compound and epichlorohydrin is usually used as a raw material.
In particular, the following formula derived from bisphenol A
Embedded image
(Those represented by n = 0 to 8 are preferable.)
[0009]
The epoxy resin can generally have an epoxy equivalent weight in the range of 180 to 2,500, preferably 200 to 2,000, more preferably 400 to 1,500, and generally has at least 200, especially 400 to 2,500. Those having a number average molecular weight in the range of 4,000, more particularly 800 to 2,500 are suitable.
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.
The amine compound is not particularly limited as long as it contains at least one active hydrogen that reacts with an epoxy group and can cationize the epoxy resin, but it is particularly preferable to use one that can introduce a primary amino group. .
Examples of the amine compound into which the primary amino group can be introduced include ketimine compounds such as monoethanolamine, propanolamine, hydroxyethylaminoethylenediamine, hydroxyethylaminopropylamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine. Is mentioned.
As the amine compound that can be used in combination with the primary amine, those conventionally used for cationization of an epoxy resin can be used, and a secondary amine is particularly preferable. Examples include diethylamine, diisopropylamine, diethanolamine, di (2-hydroxypropyl) amine, monomethylaminoethanol, monoethylaminoethanol, and the like.
The amount of the added amine is preferably in the range of 30 to 70 mgKOH / g resin solids, more preferably 40 to 60 mgKOH / g resin solids, as an amine value. The thus obtained amine-added epoxy resin using an aromatic hydrocarbon-formaldehyde resin as a modifier for the epoxy resin generally has a number average molecular weight in the range of 1,000 to 10,000, particularly 200 to 5,000, and generally 100 to 5,000. In particular, it is preferable to have a hydroxyl equivalent within the range of 200 to 2500.
[0010]
The effect of the amine-added epoxy resin containing an aromatic hydrocarbon-formaldehyde resin in a proportion of 5 to 25% by weight on average as a modifier of the epoxy resin is as follows. It is conceivable that the hydrophobicity and the glass transition point are maintained, and the permeation inhibiting ability against chlorine ions at a thin film thickness of less than 10 μm is improved. As a result, it is considered that the rust resistance against perforation in the thin film is improved.
If the content of the modifier is less than 5% by weight, the effect of imparting film-forming properties, smoothness, and flexibility to the coating film is insufficient, and if it exceeds 25% by weight, the pitting resistance is improved. Not only is this less effective, but the cost of the cationic electrodeposition coating increases.
As the resin component of the present invention, in addition to the amine-added epoxy resin, according to requirements such as weather resistance, chipping resistance, and adhesion to the overcoat, an acrylic, polyurethane, or polyester-based additive resin may be used in combination. it can.
[0011]
The blocked polyisocyanate curing agent is an addition reaction product of a polyisocyanate compound and a blocking agent. Examples of the polyisocyanate compound include tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, diphenylmethane diisocyanate, bis (isocyanatomethyl) cyclohexane, and tetramethylene. Aromatic, cycloaliphatic or aliphatic diisocyanate compounds such as diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and isophorone diisocyanate, and their triisocyanurate compounds, or excess amounts of these isocyanate compounds, ethylene glycol, propylene glycol, Low molecular active hydrogen-containing compounds such as methylolpropane and hexanetriol Such terminal isocyanate-containing compounds obtained by reaction.
On the other hand, the blocking agent is one that blocks by adding to the isocyanate group of the polyisocyanate compound, is stable at normal temperature, and can be rapidly dissociated to regenerate a free isocyanate group when heated at about 120 to 180 ° C. Things are used.
Examples of such a blocking agent include lactam compounds such as ε-caprolactam and γ-butyrolactam; oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime; and ether alcohol compounds such as ethylene glycol monobutyl ether.
A resin component consisting of an amine-added epoxy resin and a blocked polyisocyanate curing agent is usually used as an emulsion for cationic electrodeposition coating by neutralizing with a water-soluble organic acid such as formic acid, acetic acid, or lactic acid and dispersing in water. Is done.
[0012]
Pigment component:
In order to exhibit an effect on perforated rust resistance at a thin film thickness of less than 10 μm, the maximum particle diameter (Note 1) of the pigment component in the cationic electrodeposition coating composition must be 1.5 μm or less, and further, the maximum particle size It is very effective to contain bismuth oxide hydrate having a diameter of 1.5 μm or less based on 100 parts by weight of the total solid content of the resin component.
(Note 1) Maximum particle diameter: LA-500 (trade name, manufactured by HORIBA, Ltd., dynamic light scattering particle size distribution analyzer) was used.
Specifically, a dispersion resin, a pigment containing a rust-preventive pigment such as bismuth oxide hydrate, a neutralizing agent, deionized water, and a surfactant are added and mixed, and the maximum particle diameter is 1.5 μm. This is achieved by adding a pigment-dispersed paste obtained by dispersing to the following to a cationic electrodeposition coating composition.
The dispersing resin used in the pigment dispersion paste is not particularly limited, but an epoxy resin such as an amino group-containing epoxy resin, a quaternary ammonium salt type epoxy resin, and a sulfonium salt type epoxy resin is preferable. In the case of an amino group-containing epoxy resin, acetic acid, formic acid, lactic acid, propionic acid, hydroxyacetic acid, methoxyacetic acid, and neutralized with a water-soluble organic acid, such as used, the neutralization equivalent to the amino group in the resin 0.5 to 1.2 equivalents, preferably 0.7 to 1.0 equivalents are good.
Examples of pigments containing rust preventive pigments such as bismuth oxide hydrate include rust preventive pigments such as bismuth oxide hydrate, aluminum phosphomolybdate, and aluminum tripolyphosphate, as well as coloring pigments such as titanium oxide, carbon black, red iron oxide, and clay. , Mica, barita, talc, calcium carbonate, silica and the like.
The method for producing the pigment dispersion paste includes, for example, a dispersing resin, a pigment containing a rust-preventive pigment such as bismuth oxide hydrate, a neutralizing agent, deionized water, and, if necessary, dibutyltin oxide (DBTO) and dioctyltin. After pre-kneading and mixing an organic tin compound such as oxide (DOTO), a conventional dispersing machine such as a ball mill, a pebble mill, a sand mill, and a shaker can be used.
When using a ball mill, after adding an appropriate amount of media to the pre-kneaded mixture, by dispersing for 24 to 240 hours as a dispersion time, preferably 48 to 120 hours, the maximum particle diameter of the pigment component is 1.5 μm or less Can be obtained.
The mixing ratio of the pigment component having a maximum particle size of 1.5 μm or less is such that the mixing amount of the pigment component is 3 to 30 parts by weight in terms of the solid content based on 100 parts by weight of the total solid content of the resin component. It is preferable to contain 2 to 5 parts by weight of bismuth oxide hydrate having a diameter of 1.5 μm or less.
If the blending ratio of bismuth oxide hydrate is less than 2 parts by weight, the effect of improving pitting rust resistance is small, and if it exceeds 5 parts by weight, the cost of the cationic electrodeposition coating composition increases, which is not preferable.
[0013]
Cationic electrodeposition coating composition:
The cationic electrodeposition coating composition of the present invention contains an emulsion containing a resin component as described above, contains a pigment component such as bismuth oxide hydrate, and is dispersed so that the maximum particle size becomes 1.5 μm or less. And a deionized water such that the pH is in the range of 5.5 to 9.0 and the solid concentration is about 5 to 40% by weight, preferably 15 to 25% by weight. Used after dilution.
The coating of the cationic electrodeposition coating composition can be generally performed at a bath temperature of 15 to 35 ° C and a load voltage of 100 to 400V. The baking temperature is generally in the range of 140 to 200 ° C, preferably 150 to 180 ° C, and the baking time is 5 to 90 minutes, preferably 10 to 40 minutes. The film thickness of the coating film after baking can be set to 30 μm or less, preferably 20 μm or less.
[0014]
【The invention's effect】
The cationic electrodeposition coating composition having the following contents can improve pitting rust resistance with a thin film thickness of less than 10 μm in various steel plates of an automobile subjected to electrodeposition coating.
As an epoxy resin modifier, an amine-added epoxy resin containing an aromatic hydrocarbon-formaldehyde resin at an average ratio of 5 to 25% by weight in the resin, and a blocked polyisocyanate curing agent as a resin component. A cationic electrodeposition coating composition having a chloride ion permeability of 7.0 × 10 −6 g / cm −2 / day (5% saline, 50 ° C. × 24 hours).
And it is preferable that the maximum particle size of the pigment component is 1.5 μm or less, and further, it is a cationic electrodeposition coating composition containing bismuth oxide hydrate and having a maximum particle size of 1.5 μm or less. .
The reason why the cationic electrodeposition coating composition of the present invention exhibits an effect of improving the rust resistance perforated at a thin film thickness of less than 10 μm is considered as follows.
(1) From the viewpoint of the resin component: a uniform and smooth coating at a thin film thickness of less than 10 μm by an amine-added epoxy resin containing an aromatic hydrocarbon-formaldehyde resin in an average proportion of 5 to 25% by weight in the resin. Surface is obtained and hydrophobic, and the coating has a high glass transition point (Tg), so that even when the coating is heated, chlorine ions, which are corrosion-promoting substances, can be transferred between the steel sheet and the coating. The function of preventing the particles from reaching the interface (permeation blocking ability) is improved.
(2) From the viewpoint of the pigment component: The surface area of the rust-preventive pigment is dramatically increased by dispersing the maximum particle diameter of the pigment component containing the rust-preventive pigment such as bismuth oxide hydrate to 1.5 μm or less. The effect of preventing chlorine ions from reaching the interface between the steel sheet and the coating film (permeation blocking ability) is further improved.
[0015]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by this.
Production Example 1 Amine-added epoxy resin No. 1 To the production flask of No. 1, 1000 parts of Epicoat 828EL (epoxy resin manufactured by Japan Epoxy Resin Co., epoxy equivalent 190), 400 parts of bisphenol A and 0.2 g of dimethylbenzylamine were added and reacted at 130 ° C. until the epoxy equivalent became 800. .
Next, 300 parts of Nicanol L (trade name, manufactured by Mitsubishi Gas Chemical Company, xylene-formaldehyde resin), 140 parts of diethanolamine and 65 parts of a ketimine compound of diethylenetriamine were added, and the mixture was reacted at 120 ° C. for 4 hours. Then, 475 parts of butyl cellosolve was added. In addition, an amine-added epoxy resin No. having an amine value of 52 mgKOH / g and a resin solid content of 80% was used. 1 was obtained.
[0016]
Production Example 2 Amine-added epoxy resin No. Production of No. 2 Epicoat 828EL (trade name, manufactured by Japan Epoxy Resin Co., Ltd., epoxy resin) (1000 parts), bisphenol A (390 parts), and dimethylbenzylamino (0.2 part) were added and reacted at 130 ° C. until the epoxy equivalent reached 755.
Next, 260 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 traced by infrared absorption spectrum measurement. Then, when the conversion reached 98% by mass or more, the temperature was lowered to 120 ° C.
Next, 160 parts of diethanolamine and 65 parts of methyl isobutyl diketiminate of diethylenetriamine were added and reacted at 120 ° C. for 4 hours, 470 parts of butyl cellosolve was added, and an amine-added epoxy having an amine value of 57 mgKOH / g and a resin solid content of 80% by mass was added. Resin No. 2 was obtained.
[0017]
Production Example 3 Emulsion No. for cationic electrodeposition Production of amine-added epoxy resin No. 1 obtained in Production Example 1 above. 17.5 parts (70 g resin solids), 22.2 parts hexamethylene diisocyanate triisonurate blocked with methyl ethyl ketoxime as curing agent (20 parts resin solids), and diphenylmethane blocked with ethylene glycol monobutyl ether Mix well with 11.1 parts of diisocyanate (10 parts in resin solids), add 1.5 parts of acetic acid (corresponding to a neutralization number of 14) as a neutralizing agent, and add 170.7 parts of deionized water with vigorous stirring. Was added dropwise over about 15 minutes to give a cationic electrodeposition emulsion having a solid content of 34%. 1 was obtained.
[0018]
Production Examples 4 and 5
In the formulation of Table 1, the emulsion No. for cationic electrodeposition was used. 2-3 were obtained.
[0019]
[Table 1]
(Note 2) Sannix PP-1000: trade name, manufactured by Sanyo Chemical Co., Ltd., surface conditioner
Production Example 6 696 parts of tolylene diisocyanate (TDI) and 304 parts of methyl isobutyl ketoxime (MIBK) were added to a flask for preparing a quaternary ammonium salt type epoxy pigment dispersing resin, the temperature was raised to 60 ° C., and 2-ethylhexyl alcohol was added. 520 parts were added dropwise and reacted until the NCO value reached 110.5 to obtain a partially blocked isocyanate A having a resin solid content of 80%.
Next, 380 parts of this partially blocked isocyanate A was taken, 89 parts of dimethylethanolamine was added dropwise at 70 ° C., and the mixture was allowed to react until NCO substantially disappeared. After diluting with 34.75 parts of butyl cellosolve, 100 parts of 90% lactic acid was added. To give 80% lactic acid-neutralized amino group-containing blocked isocyanate B.
To another flask, 1125 parts of Epicoat 828EL (Epoxy resin manufactured by Japan Epoxy Resin Co., epoxy equivalent: 188), 456 parts of bisphenol A and 1.1 parts of triphenylphosphonium iodide are added, and the epoxy equivalent becomes 790 at 170 ° C. After the reaction, the mixture was diluted with 279 parts of MIBK, and 760 parts of the above partially blocked isocyanate A was added, and the mixture was reacted at 100 ° C. until NCO substantially disappeared.
Then, 630 parts of butyl cellosolve was added and the mixture was cooled to 80 ° C., and 860 parts of 80% lactic acid-neutralized amino group-containing blocked isocyanate B was added and reacted until the acid value became 1 mgKOH / g or less. An ammonium salt type epoxy pigment dispersion resin was obtained.
[0022]
Production Example 7 Pigment dispersion paste No. Production of 1 5.0 parts of quaternary ammonium salt type epoxy pigment dispersing resin (solid content 3.5 parts) obtained in Production Example 6, titanium oxide 14.5 parts, bismuth oxide hydrate 3.0 parts, 3 parts of aluminum tripolyphosphate, 7.0 parts of purified clay, 0.5 part of carbon black, 2.0 parts of dibutyltin oxide, 2.38 parts of 10% acetic acid, and 28.62 parts of deionized water are dispersed in a ball mill for 120 hours. The pigment dispersion paste No. having a maximum particle size of 1.5 μm and a solid content of 55% was discharged. 1 was obtained.
[0023]
Production Example 8 Pigment Dispersion Paste Preparation of Pigment Dispersion Paste No. 2 having a maximum particle size of 1.5 μm with the composition and dispersion time shown in Production Table 2. 2 was obtained.
[0024]
Production Example 9 Pigment Dispersion Paste No. No. 3 according to the composition and the dispersion time shown in Table 2, the pigment dispersion paste No. 3 having a maximum particle size of 2.0 μm. 3 was obtained.
[0025]
Production Example 10 Pigment dispersion paste No. Pigment Dispersion Paste No. 4 having a maximum particle size of 3.0 μm with the composition and dispersion time shown in Production Table 2 of Production No. 4 4 was obtained.
[0026]
[Table 2]
Example 1
Emulsion No. for
[0028]
Example 2, Comparative Examples 1-3
In the same manner as in Example 1, the cationic electrodeposition paint No. having a solid content of 20% of Example 2 and Comparative Examples 1 to 3 was used. 2-No. 5 was obtained.
Table 3 shows the formulations of Examples 1 and 2 and Comparative Examples 1 to 3.
[0029]
[Table 3]
The cationic electrodeposition paint Nos. 1 to No. 5, a galvanized steel sheet (70 × 150 × 0.8 mm) treated with Palbond # 3020 (trade name, manufactured by Nippon Parkerizing Co., trade name, zinc phosphate treating agent) as an object to be coated. Test plates were prepared with two levels of thickness of 7 μm and 10 μm, a baking temperature of 150 ° C., and a baking time of 20 minutes (holding time).
The test contents were subjected to a coating film test under the following conditions. Table 4 shows the results.
[0031]
[Table 4]
(Note 3) Perforated corrosion resistance: Simulated mud (composed of NaCl / Na 2 SO 4 / CaCl 2 / kaolin / distilled water) was applied to half of the front surface using a test plate with a circumference of 10 mm and the back surface masked. Thereafter, 120 cycles were performed under the following cycle conditions at an angle of 60 degrees from the horizontal, and then the film swelling (Note 4), the occurrence of red rust (Note 5), and the thickness reduction (Note 6) were evaluated. .
Cycle conditions: 1 cycle [35 ° C salt spray test (according to JIS Z 2371) 6 hours-dry (temperature 50 ° C, relative humidity 20 to 40%) 3 hours-wet (temperature 50 ° C, relative humidity 95% or more) 14 hours -Cold air (room temperature) 1 hour]
(Note 4) Coating swelling: Simulated mud was dropped from a test plate with a brush while washing with tap water, dried at room temperature, and then the coating swelling rate (%) was calculated from the following formula and evaluated.
Coating swelling rate (%) = Coating swelling area / Total evaluation area ：: Coating swelling is 30% or less ：: Coating swelling is 50% or less Δ: Coating swelling is 70% or less ×: Coating swelling is More than 70% (Note 5) Red rust generation: After simulating mud was washed off from the test plate with tap water and brushed down and dried at room temperature, the red rust generation rate (%) was calculated from the following formula and evaluated. did.
Red rust occurrence rate (%) = rust occurrence area / total evaluation area ◎: Red rust occurrence rate is 10% or less ○: Red rust occurrence rate is 20% or less △: Red rust occurrence rate is 30% or less ×: Red rust occurrence rate is 30% Exceeding (Note 6) Reduction in thickness: After removing red rust from the test plate after the test, remove the coating film with a remover. The thickness reduction (rust depth) of the steel sheet is measured using a pinpoint micrometer.
◎: Reduction in thickness of steel sheet is 0.3 mm or less ：: Reduction in thickness of steel sheet is 0.4 mm or less △: Reduction in thickness of steel sheet is 0.5 mm or less X: Reduction in thickness of steel sheet exceeds 0.5 mm (Note 7) Chloride ion permeability: A 10-μm coating film applied to a tin plate was peeled off by an amalgam method, and a K-316 film oxygen permeability meter (manufactured by Tsukuba Riki Seiki Co., Ltd., Kakenhi type oxygen permeability meter) was used. A coating film (3 in FIG. 1) is applied to the cell (1 in FIG. 1). Deionized water was added into the cell, immersed in 500 ml of 5% NaCl water, and the concentration of chloride ions passing through the coating film was determined by the mercury (II) thiocyanate absorbance method described in JIS K0101. The test time was 24 hours and the temperature was 50 ° C.
[Brief description of the drawings]
FIG. 1 is a model diagram of a film oxygen permeability meter.
[Explanation of symbols]
1. Deionized water (10ml)
2. Cell (inner diameter 180mm)
3. Coating 4.5% NaCl (500ml)
Claims (4)
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Cited By (5)
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| JP2006169458A (en) * | 2004-12-20 | 2006-06-29 | Nippon Paint Co Ltd | Cation electrodeposition coating composition |
| JP2007197688A (en) * | 2005-12-27 | 2007-08-09 | Kansai Paint Co Ltd | Electrodeposition paint |
| US7625477B2 (en) | 2005-12-27 | 2009-12-01 | Kansai Paint Co., Ltd. | Electrodeposition paint |
| CN105176330A (en) * | 2015-10-21 | 2015-12-23 | 苏州赛斯德工程设备有限公司 | Epoxy water-base corrosion-resistance paint and preparation method thereof |
| KR101753761B1 (en) | 2014-04-24 | 2017-07-04 | 메이-화 엔터프라이즈 코포레이션 | Polymer particle and preparation method thereof |
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