JP2004358743A - High gloss precoated metal sheet having excellent corrosion resistance in processed part - Google Patents
High gloss precoated metal sheet having excellent corrosion resistance in processed part Download PDFInfo
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- JP2004358743A JP2004358743A JP2003158168A JP2003158168A JP2004358743A JP 2004358743 A JP2004358743 A JP 2004358743A JP 2003158168 A JP2003158168 A JP 2003158168A JP 2003158168 A JP2003158168 A JP 2003158168A JP 2004358743 A JP2004358743 A JP 2004358743A
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- 229910052751 metal Inorganic materials 0.000 title claims abstract description 101
- 239000002184 metal Substances 0.000 title claims abstract description 101
- 230000007797 corrosion Effects 0.000 title claims abstract description 33
- 238000005260 corrosion Methods 0.000 title claims abstract description 33
- 239000000049 pigment Substances 0.000 claims abstract description 70
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 56
- 229920005989 resin Polymers 0.000 claims abstract description 54
- 239000011347 resin Substances 0.000 claims abstract description 54
- 238000011282 treatment Methods 0.000 claims abstract description 44
- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 claims abstract description 36
- 239000011230 binding agent Substances 0.000 claims abstract description 31
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 28
- 239000000126 substance Substances 0.000 claims abstract description 25
- ILRRQNADMUWWFW-UHFFFAOYSA-K aluminium phosphate Chemical compound O1[Al]2OP1(=O)O2 ILRRQNADMUWWFW-UHFFFAOYSA-K 0.000 claims abstract description 23
- 239000007787 solid Substances 0.000 claims abstract description 18
- 238000006243 chemical reaction Methods 0.000 claims abstract description 15
- 239000011247 coating layer Substances 0.000 claims description 26
- 229920000642 polymer Polymers 0.000 claims description 15
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims description 13
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- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical group [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 claims description 4
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- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 4
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- 229910000990 Ni alloy Inorganic materials 0.000 description 4
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- RRAMGCGOFNQTLD-UHFFFAOYSA-N hexamethylene diisocyanate Chemical compound O=C=NCCCCCCN=C=O RRAMGCGOFNQTLD-UHFFFAOYSA-N 0.000 description 4
- 150000002513 isocyanates Chemical class 0.000 description 4
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- RTTZISZSHSCFRH-UHFFFAOYSA-N 1,3-bis(isocyanatomethyl)benzene Chemical compound O=C=NCC1=CC=CC(CN=C=O)=C1 RTTZISZSHSCFRH-UHFFFAOYSA-N 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 239000004593 Epoxy Substances 0.000 description 2
- JOYRKODLDBILNP-UHFFFAOYSA-N Ethyl urethane Chemical compound CCOC(N)=O JOYRKODLDBILNP-UHFFFAOYSA-N 0.000 description 2
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
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- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 2
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 229920003180 amino resin Polymers 0.000 description 2
- 239000011668 ascorbic acid Substances 0.000 description 2
- TZCXTZWJZNENPQ-UHFFFAOYSA-L barium sulfate Chemical compound [Ba+2].[O-]S([O-])(=O)=O TZCXTZWJZNENPQ-UHFFFAOYSA-L 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
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- NAQMVNRVTILPCV-UHFFFAOYSA-N hexane-1,6-diamine Chemical compound NCCCCCCN NAQMVNRVTILPCV-UHFFFAOYSA-N 0.000 description 2
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- FVCSARBUZVPSQF-UHFFFAOYSA-N 5-(2,4-dioxooxolan-3-yl)-7-methyl-3a,4,5,7a-tetrahydro-2-benzofuran-1,3-dione Chemical compound C1C(C(OC2=O)=O)C2C(C)=CC1C1C(=O)COC1=O FVCSARBUZVPSQF-UHFFFAOYSA-N 0.000 description 1
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- KSPIHGBHKVISFI-UHFFFAOYSA-N Diphenylcarbazide Chemical compound C=1C=CC=CC=1NNC(=O)NNC1=CC=CC=C1 KSPIHGBHKVISFI-UHFFFAOYSA-N 0.000 description 1
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、プレス成形後の耐食性に優れた表面処理金属板に関するものであり、家電用、建材用、土木用、機械用、自動車用、家具用、容器用等において、特に環境上問題があるとされている６価クロムを用いずに、プレス成形時の塗膜密着性と防錆効果を発揮することを特徴とする。
【０００２】
【従来の技術】
家電用、建材用、自動車用等に、従来の加工後塗装されていたポスト塗装製品に代わって、着色した塗膜を被覆したプレコート金属板が使用されるようになってきている。この金属板は、金属用前処理を施した金属板に塗料を被覆したもので、塗料を塗装した後に切断しプレス成形されて使用されることが一般的である。そのため、塗膜が被覆されていない金属が露出する切断端面部の耐食性とプレス加工時の塗膜剥離がプレコート金属板の問題点となっていたが、金属用前処理としてクロメート処理を施し、且つ塗膜中に６価クロム系の防錆顔料を含有することでこれらの問題点が解決され、現在では汎用的に使用されている。しかし、６価クロムは環境負荷物質であるため、６価クロムを排除する動きが近年盛んである。
【０００３】
化成処理の技術としては、特開平９−８２８２９１号公報、特開平１０−２５１５０９号公報、特開平１０−３３７５３０号公報、特開２０００−１７４６６号公報、特開２０００−２４８３８５号公報、特開２０００−２７３６５９号公報、特開２０００−２８２２５２号公報、特開２０００−２６５２８２号公報、特開２０００−１６７４８２号公報等が開示されている。
【０００４】
一方、特開平９−１２９３１号公報では、６価クロム系防錆顔料の代わりにリン酸系防錆顔料とイオン交換シリカ系防錆顔料とを併用したポリエステル系並びにエポキシ系の塗料により切断端面部の耐食性に優れたプレコート鋼板を提供する技術が開示されている。
【０００５】
その一方で、プレコート鋼板の性能として、光沢や鮮映性の高い塗膜が要求される。前述の特開平９−１２９３１号公報の実施例に例示されているプレコート鋼板では、高光沢のプレコート鋼板を得ることは困難であり、更には、加工部の耐食性に劣る。特開昭６２−１１６１３８号公報、特開平２−２０５２０１号公報、特開平７−１５０３２６号公報、特開昭５８−６１２９２号公報等では、粗度調整した圧延ロールにてプレコート鋼板やその原板を圧延加工することで、プレコート鋼板の塗装後鮮映性を向上させる技術が開示されている。しかし、プレコート鋼板やその原板粗度を圧延ロールにて調整すると、製造工程が増えることによるコストアップや作業効率の低下の問題が発生する。
【０００６】
特開平１−３０４９３４号公報では、金属板上に数平均分子量５０００〜７００００のエポキシ変成ポリエステル樹脂にアミノ樹脂を配合した下塗り塗料と数平均分子量２０００〜１００００のポリエステル樹脂に架橋速度の異なる２種以上のアミノ樹脂を配合した上塗り塗料を形成させることで高鮮映性を得る技術が開示されている。しかし、上塗り塗料に分子量の低い塗料を適用すると、密着曲げや深絞り成形等の厳しい加工性が施されると塗膜にクラックが入り易く、更にはこの塗膜のクラック部から腐食が発生し易いため、加工部耐食性が劣る。
【０００７】
特開平１０−６６９３１号公報には、金属板に有機塗料を塗布し、更にその上にクリヤー樹脂を含む溶液を塗布することで塗膜に鮮映性を付与する技術が開示されている。しかし、この様に乾燥前の塗料上にクリヤー樹脂を含む溶液を均一に且つ安定的に塗布することは困難である。その一方で、乾燥後の塗膜上にクリヤー塗料等を塗布乾燥させることは容易であるが、この場合、外観意匠性と耐食性を両立するために防錆力を付与した下塗り塗装、着色を施した中塗り塗装、上塗りであるクリヤー塗装と３層以上の塗装を施さなければならない。しかし、プレコート鋼板を製造する連続塗装ラインでは、２回塗装２回焼付（一般に２コート２ベイクと呼ばれる）が一般的であり、３層以上の塗装を施すことは困難である。２コート２ベイク方式で上塗りクリヤータイプの塗装を施す場合は、防錆塗膜層を省略して、着色を施した下塗り塗装として、上塗り塗装にトップクリヤーを施すことが一般的であるが、防錆塗膜層を省力しているために耐食性に劣る。このようなタイプの場合、着色層に防錆顔料を添加することが一般的であるが、従来の６価クロム系防錆顔料は黄色系であるため、塗膜中に着色顔料と共に添加すると、目的の色がでにくい欠点を有していた。
【０００８】
【特許文献１】
特開平９−８２８２９１号公報
【特許文献２】
特開平１０−２５１５０９号公報
【特許文献３】
特開平１０−３３７５３０号公報
【特許文献４】
特開２０００−１７４６６号公報
【特許文献５】
特開２０００−２４８３８５号公報
【特許文献６】
特開２０００−２７３６５９号公報
【特許文献７】
特開２０００−２８２２５２号公報
【特許文献８】
特開２０００−２６５２８２号公報
【特許文献９】
特開２０００−１６７４８２号
【特許文献１０】
特開平９−１２９３１号公報
【特許文献１１】
特開昭６２−１１６１３８号公報
【特許文献１２】
特開平２−２０５２０１号公報
【特許文献１３】
特開平７−１５０３２６号公報
【特許文献１４】
特開昭５８−６１２９２号公報
【特許文献１５】
特開平１−３０４９３４号公報
【特許文献１６】
特開平１０−６６９３１号公報
【０００９】
【発明が解決しようとする課題】
本発明は、従来技術における上記問題点を解決し、６価クロムを含まなくても加工部耐食性に優れ、さらに、高光沢高鮮映性を有する２コート２ベークのプレコート金属板を提供することをその課題としている。
【００１０】
【課題を解決するための手段】
発明者らは、６価クロムを含まない化成処理を施した金属板上に、リン酸アルミ系顔料とシリカ系防錆顔料と着色顔料とを含むベース塗膜層を施し、更にその上にクリヤー塗膜層を施すことで、加工性（特にプレスによる深絞り加工性）に優れ、且つ、６価クロムを用いずに加工部耐食性に優れた高光沢プレコート金属板を得ることができることを見出した。本発明は、かかる知見を基に完成させたものであって、本発明がその要旨とするところは、以下の通りである。
（１） 金属板の片面もしくは両面上に、６価のクロムを含まない化成処理層、その上に、バインダー樹脂と（ａ）着色顔料を必須成分として含み、且つ（ｂ）リン酸アルミ系顔料又は（ｃ）シリカ系防錆顔料の一方又は双方を含むベース塗膜層、更にその上にクリヤー塗膜層を有するプレコート金属板であって、前記ベース塗膜層中のバインダー樹脂固形分１００質量部に対し、（ｂ）の添加量が０〜５０質量部、（ｃ）の添加量が０〜５０質量部、且つ（ｂ）と（ｃ）の合計添加量が１〜５０質量部であると共に、（ａ）、（ｂ）、（ｃ）の合計添加量がバインダー樹脂固形分１００質量部に対し１質量部超３００質量部以下であることを特徴とする加工部耐食性に優れた高光沢プレコート金属板。
（２） 前記ベース塗膜層中に含まれるリン酸アルミ系顔料がトリポリリン酸二水素アルミニウムである（１）記載の高光沢プレコート金属板。
（３） 前記ベース塗膜層中に含まれるシリカ系防錆顔料がカルシウムイオン交換シリカである（１）記載の高光沢プレコート金属板。
（４） 前記ベース塗膜層のバインダー樹脂又はクリヤー塗膜層の樹脂の一方又は双方が、両端に官能基を有する直鎖状重合体である樹脂と２官能化合物からなる塗料組成物を加熱によって直鎖上重合体の更なる直鎖状重合反応を促進させて成膜させてなる樹脂である（１）記載の高光沢プレコート金属板。
（５） 前記金属板の表面粗度Ｒａが１．０以下である（１）記載の高光沢プレコート金属板。
【００１１】
【発明の実施の形態】
本発明は、金属板の片面もしくは両面上に、６価のクロムを含まない化成処理層、その上に、バインダー樹脂と（ａ）着色顔料を必須成分として含み、且つ（ｂ）リン酸アルミ系顔料又は（ｃ）シリカ系防錆顔料の一方又は双方を含むベース塗膜層、更にその上にクリヤー塗膜層を有するプレコート金属板であって、前記ベース塗膜層中のバインダー樹脂固形分１００質量部に対し、（ｂ）の添加量が０〜５０質量部、（ｃ）の添加量が０〜５０質量部、且つ（ｂ）と（ｃ）の合計添加量が１〜５０質量部であると共に、（ａ）、（ｂ）、（ｃ）の合計添加量がバインダー樹脂固形分１００質量部に対し１質量部超３００質量部以下であることを特徴とする加工部耐食性に優れた高光沢プレコート金属板によって達せられる。
【００１２】
本発明に用いる金属板は、一般に公知の金属材料を用いることができる。金属材料が合金材料であってもよい。例えば、鋼板、ステンレス鋼板、アルミ板、アルミ合金板、チタン板、銅板等が挙げられる。これらの材料の表面にはめっきが施されていてもよい。
【００１３】
めっきの種類としては、亜鉛めっき、アルミめっき、銅めっき、ニッケルめっき等が挙げられる。これらの合金めっきであってもよい。鋼板の場合は、溶融亜鉛めっき鋼板、電気亜鉛めっき鋼板、亜鉛−ニッケル合金めっき鋼板、溶融合金化亜鉛めっき鋼板、アルミめっき鋼板、アルミ−亜鉛合金化めっき鋼板、ステンレス鋼板等、一般に公知の鋼板及びめっき鋼板を適用できる。
【００１４】
特に、アルミめっきを施した金属板（例えばアルミめっき鋼板）、亜鉛めっきを施した金属板（例えば亜鉛めっき鋼板）、ニッケルめっきを施した金属板（例えばニッケルめっき鋼板）、ニッケルを含む合金めっきを施した金属板（例えば亜鉛−ニッケル合金めっき鋼板）、アルミを含む合金めっきを施した金属板（例えば５５％アルミ−亜鉛めっき鋼板）は、熱反射性に優れより好適である。
【００１５】
中でも、特に亜鉛−ニッケル合金めっき鋼板は、加工部の耐食性に優れるためより好適である。亜鉛−ニッケル合金めっき鋼板とは、めっき層にニッケルを１〜３０質量％、好ましくは５〜１５質量％含む亜鉛系合金めっき鋼板のことであり、新日本製鐵社製の「ジンクライト」（新日本製鐵の登録商標）等を使用することができる。
【００１６】
更に、本発明に用いる金属板の表面粗度Ｒａが１．０以下であると、プレコート金属板の塗装後鮮映性が向上するためより好適である。金属板の表面粗度は、表面粗度を調整した調質圧延ロールにて金属板を圧延することや、金属板にめっきを施した後に表面粗度を調整した調質圧延ロールにて圧延する、もしくは、めっきを施す前の金属板原板に表面粗度を調整した調質圧延ロールにて圧延した後にめっきすることで、粗度を調整することができる。ここで、Ｒａとは、ＪＩＳ．Ｂ．０６０１．３に記載された算術平均粗さ（Ｒａ）のことである。
【００１７】
金属板上に処理する化成処理は、６価クロム含まないものであることを特徴とする。６価クロムは、環境負荷物質であるため、これを含むものは不適である。６価クロムを含まない化成処理としては、一般に公知のもの、電解クロメート処理、反応クロメート処理、リン酸亜鉛系処理、ジルコニア系処理、チタニア系処理、シランカップリング系処理を使用することができ、具体例としては、特開平９−８２８２９１号公報、特開平１０−２５１５０９号公報、特開平１０−３３７５３０号公報、特開２０００−１７４６６号公報、特開２０００−２４８３８５号公報、特開２０００−２７３６５９号公報、特開２０００−２８２２５２号公報、特開２０００−２６５２８２号公報、特開２００００−１６７４８２号公報、等に記載された技術や、日本パーカライジング社製のクロムを含まない化成処理「ＣＴ−Ｅ３００」や「ＣＴ−Ｅ２００」、日本ペイント社製の３価クロム型化成処理「サーフコートＮＲＣ１０００」等を使用することができる。なお、電解クロメート処理や反応クロメート処理は、処理過程において６価クロムを含む処理液を用いるが、処理過程で行われる還元反応において、全ての６価クロムが３価クロムとなるため、これを施したプレコート金属板には最終的に６価クロムが含まれないため、本発明ではこれらも６価クロムを含まない化成処理と言える。
【００１８】
本発明のプレコート金属板は、化成処理を施した金属板上に、バインダー樹脂とリン酸アルミ系顔料、シリカ系防錆顔料、着色顔料を含むベース塗膜層を形成することを特徴とする。
【００１９】
本発明のベース塗膜層は、バインダー樹脂として一般に公知のプレコート金属板用塗料に、リン酸アルミ系顔料、シリカ系防錆顔料、着色顔料を添加したものを成膜させることで形成できる。
【００２０】
本発明のベース塗膜層中に含まれるリン酸アルミ系顔料は、一般に公知のリン酸アルミ系顔料を使用することができ、トリポリリン酸二水素アルミニウムが特に好適である。リン酸アルミ系顔料を含まないと塗膜密着性が劣り、プレス加工時に塗膜がプレス金型によって擦り取られる（一般に型かじりとも呼ばれる）恐れがある。さらに、リン酸アルミ系顔料は薄い白色であるため、ベース塗膜を着色顔料で色付けする際に色調に悪影響を及ぼさないため好適である。リン酸アルミ系顔料の添加量は塗膜のバインダー樹脂固形分１００質量部に対し０〜５０質量部にする必要があり、５０質量部超ではベース塗膜の色調が調整できなくなるため、不適である。
【００２１】
本発明のベース塗膜層中に含まれるシリカ系防錆顔料は、一般に公知のシリカ系防錆顔料を使用することができ、カルシウムイオン交換シリカが特に好適である。カルシウムイオン交換シリカは、シリカ表面にカルシウムイオンを吸着したようなタイプのもので、グレイス社製の「シールデックス」（グレイス社の登録商標）等を使用することができる。シリカ系防錆顔料は、耐食性に優れる上、薄い白色であるため、ベース塗膜を着色顔料で色付けする際に色調に悪影響を及ぼさないため好適である。シリカ系防錆顔料の添加量は、バインダー樹脂固形分１００質量部に対し０〜５０質量部にする必要があり、５０質量部超ではベース塗膜の色調が調整できなくなるため不適である。
【００２２】
更に、リン酸アルミ系顔料とシリカ系防錆顔料との合計の添加量が塗膜のバインダー樹脂固形分１００質量部に対し１〜５０質量部にする必要がある。１質量部未満では、耐食性や密着性が劣り、５０質量部超ではベース塗膜の色調が調整できなくなるため不適である。
【００２３】
本発明のベース塗膜中には前記リン酸アルミ系顔料とシリカ系防錆顔料については、どちらか一方が含まれていれば良いが、リン酸アルミ系顔料とシリカ系防錆顔料の双方が含まれていると、耐食性や加工性密着性がより向上し、より好適である。
【００２４】
本発明のベース塗膜層中に含まれる着色顔料は、一般に公知の着色顔料を使用することができる。例えば、酸化チタン（ＴｉＯ２）、酸化亜鉛（ＺｎＯ）、酸化ジルコニウム（ＺｒＯ２）、炭酸カルシウム（ＣａＣＯ３）、硫酸バリウム（ＢａＳＯ４）、アルミナ（Ａｌ２Ｏ３）、カオリンクレー、カーボンブラック、酸化鉄（Ｆｅ２Ｏ３、Ｆｅ３Ｏ４）等の無機顔料や、有機顔料等を使用することができる。着色顔料の添加量は、特に規定するものではなく、求める色調を得るのに必要な量を添加できる。しかし、リン酸アルミ系顔料とシリカ系防錆顔料と全着色顔料との合計は、塗膜のバインダー樹脂固形分１００質量部に対し１質量部超３００質量部以下にする必要がある。１質量部以下では、耐食性や密着性が劣り、３００質量部超では塗膜の加工性が劣るため不適である。
【００２５】
バインダー樹脂としてのプレコート金属板用塗料とは、溶剤中にバインダー成分である有機物や無機物が溶解もしくは分散しているものであり、熱を加えて短時間（５〜４００秒）で成膜可能な塗料のことである。ベース塗膜に用いるバインダー樹脂成分は特に規定するものではなく、一般に塗料用バインダー樹脂として公知のもの、例えば、ポリエステル樹脂、アクリル樹脂、メラミン樹脂、エポキシ樹脂、フッ素樹脂、塩化ビニル樹脂等の一般に公知の塗料用樹脂等を使用することができる。これらの樹脂には、硬化剤としてイソシアネートやメラミン樹脂等を添加しても良い。
【００２６】
本発明者らがこれまでに得た知見によれば、メラミン硬化型ポリエスエル系、イソシアネート硬化型ポリエステル系の樹脂をバインダー成分として用いると、塗膜の加工性に優れ好適であり、特に、次のものが好適であるが、これらは一例であり、これらに限定されるものではない。
【００２７】
メラミン硬化型ポリエスエル系の場合、ポリエステル樹脂の分子量は、数平均分子量で２０００〜３００００が好適であり、ポリエステル樹脂のＴｇは−１０〜１３０℃が好適であり、メラミン樹脂の添加量は、ポリエステル樹脂１００質量部に対して５〜７０質量部が好適である。
【００２８】
ポリエステル樹脂の分子量が２０００未満では塗膜の加工性が低下し、３００００超では、樹脂が溶剤に溶解したときに粘度が高すぎるため塗装しにくくなる恐れがある。ポリエステル樹脂のＴｇが−１０℃未満では塗膜が成膜しない恐れがあり、１３０℃超では塗膜が硬すぎるため、加工性が低下する恐れがある。メラミン樹脂の添加量がポリエステル１００質量部に対して５質量部未満であると、塗膜が未硬化となる恐れがあり、７０質量部超では、塗膜が硬くなりすぎて加工性が低下する恐れがある。
【００２９】
使用するポリエステル樹脂は、一般に市販されているもの、例えば、東洋紡績社製の「バイロンＴＭ」や、住化バイエルウレタン社製「デスモフェンＴＭ」等を使用することができる。使用するメラミン樹脂も、一般に市販されているもの、例えば、三井サイテック社製「サイメルＴＭ」、「マイコートＴＭ」、大日本インキ化学工業社製「ベッカミンＴＭ」、「スーパーベッカミンＴＭ」等を使用することができる。
【００３０】
イソシアネート硬化型ポリエステル系の場合、ポリエステル樹脂の分子量は、数平均分子量で２０００〜３００００が好適であり、ポリエステル樹脂のＴｇは−１０〜７０℃が好適であり、イソシアネートの添加量は、［イソシアネートのＮＣＯ基当量］／［ポリエステル樹脂のＯＨ基当量］＝０．８〜１．２であると好適である。
【００３１】
［イソシアネートのＮＣＯ基当量］／［ポリエステル樹脂のＯＨ基当量］の値が０．８未満もしくは１．２超では、塗膜生成時に塗膜が未硬化となりやすい。ポリエステル樹脂の分子量が２０００未満では塗膜の加工性が低下し、３００００超では、樹脂が溶剤に溶解したときに粘度が高すぎるため、塗装しにくくなる恐れがある。ポリエステル樹脂のＴｇが−１０℃未満では、塗膜が成膜しない恐れがあり、７０℃超では塗膜が硬すぎるため、加工性が低下する恐れがある。
【００３２】
使用するポリエステル樹脂は、一般に市販されているもの、例えば、東洋紡績社製の「バイロンＴＭ」、住化バイエルウレタン社製「デスモフェンＴＭ」等を使用することができる。
【００３３】
使用するイソシアネートも、一般に市販されているもの、例えば、住化バイエルウレタン社製「スミジュールＴＭ」、「デスモジュールＴＭ」、三井武田ケミカル社製「タケネート」（三井武田ケミカル社の登録商標）等を使用することができる。
【００３４】
本発明プレコート金属板は、リン酸アルミ系顔料とシリカ系防錆顔料と着色顔料とを含むベース塗膜層上にクリヤー塗膜を形成することを特徴とする。クリヤー塗膜は、ベース塗膜と同様の一般に公知のプレコート金属板用塗料を使用することができる。一般には、有機樹脂のみを溶剤に溶融もしくは分散させ、成膜したときに透明となるものである。クリヤー塗膜に用いる有機樹脂は、ベース塗膜のバインダーとして例示したものを使用することができ、特にベース樹脂のバインダーとして例示したメラミン硬化型ポリエスエル系、イソシアネート硬化型ポリエステル系の樹脂であるとより好適である。また、成膜したとき透明性が担保できる範囲であれば、僅かな着色顔料や防錆顔料等を添加しても良い。クリヤー塗料中には、必要に応じて一般に公知の界面活性剤、ワックス、スリップ材、レベリング材、消胞剤等の添加剤を添加することができる。特にクリヤー塗膜層にワックスを添加すると、プレコート鋼板表面の摩擦係数が低くなり、プレス成形性が向上するためより好適である。塗膜の透明性については特に規定するものではなく、ベース塗膜の色彩が透けて見えなければならない。樹脂の種類や添加剤の種類や添加量によって透明性は異なるため、必要に応じてこれらを選定する必要がある。
【００３５】
また、本発明のプレコート金属板に塗装するベース塗膜層のバインダー樹脂又はクリヤー塗膜の樹脂が、両端に官能基を有する直鎖状重合体である樹脂と２官能化合物からなる塗料組成物を加熱によって直鎖上重合体の更なる直鎖状重合反応を促進させて成膜させるタイプのものであると、加工部の耐食性が向上し、更に好適である。このように焼付過程で直鎖状重合反応を促進させて成膜させた塗膜は、見かけ上、高分子の熱可塑型塗膜となる。そのため、これらの塗膜を被覆したプレコート鋼板を加工すると、加工部で塗膜樹脂中の分子鎖のズレが発生し、加工により伸張された塗膜の内部応力が架橋された熱硬化型塗膜と比べて緩和し易くなる。そのため、直鎖重合を促進させた塗膜を塗装したプレコート鋼板は加工部での塗膜内部応力が一般の熱硬化性塗膜の時と比べて小さくなるため、加工部の耐食性がより向上するものと推定される。
【００３６】
両端に官能基を有する２官能の直鎖状重合体は、一般に公知の直鎖状ポリエステル、直鎖状エポキシ、直鎖状アクリル等を使用することができる。例えば、直鎖状ポリエステルの場合、大日本インキ化学工業社製の「ベッコライトＴＭ Ｍ−６２０７−４０」、「ベッコライトＴＭ ５７−２０６−４０」、東洋紡社製の「バイロンＴＭ ６００」、「バイロンＴＭ ２９０」等を、直鎖状エポキシ樹脂の場合、大日本インキ化学工業社製の「エピクロンＴＭ ７０５０−４０Ｓ」、ジャパンエポキシレジン社製の「エピコート１００７」、「エピコート１００９」等を、直鎖状アクリル樹脂の場合、三菱レイヨン社製の「ＬＲ−６３５」や大日本インキ化学工業社製の「アクリディックＴＭ Ａ−４０５」等を使用することができる。
【００３７】
両端に官能基を有する直鎖状重合体と反応し得る２官能化合物としては、ジイソシアネート化合物、ジカルボキシル基化合物が挙げられる。ジイソシアネート化合物としては、キシレンジイソシアネート、トルエンジイソシアネート、ヘキサメチレンジイソシアネート等がある。また、ポリエステルポリオール、アクリルポリオールの両端を前述のジイソシアネート又はヘキサメチレンジアミン、ポリエステルポリオールジカルボン酸、グリシジル変性アクリル樹脂等で変性した樹脂等が挙げられる。ジイソシアネート化合物としては、ブロック化イソシアネート化合物でも良い。
【００３８】
両端に官能基を有する２官能の直鎖状重合体と２官能化合物との比率は、２官能化合物／直鎖状重合体の官能基比で０．５〜１０が好適である。０．５未満もしくは１０超であると、直鎖重合反応が促進しない恐れがある。両端に官能基を有する直鎖状重合体である樹脂と２官能化合物からなる塗料組成物については、特開２００２−２４９７２５号公報に記載の技術を使用することができる。
【００３９】
本発明のベース塗膜やクリヤー塗膜の塗装方法は、一般に公知の塗布方法、例えば、ロールコート、カーテンフローコート、ローラーカーテンコート、ダイコート、エアースプレー、エアーレススプレー、電着塗装、粉体塗装、浸漬、バーコート、刷毛塗りなどで行うことができる。ただし、ロールコートやカーテンフローコート、ローラーカーテンコートを完備した一般的コイルコーティングライン、シートコーティングラインと呼ばれる連続塗装ラインで塗装すると、塗装作業効率が良く大量生産が可能であるため、より好適である。塗料の乾燥焼付方法は、熱風オーブン、直火型オーブン、塩赤外線オーブン、誘導加熱型オーブン等の一般に公知の乾燥焼付方法を用いることができる。塗料が紫外線硬化型塗料の場合は一般に公知の紫外線照射装置、電子線硬化型塗料の場合は一般に公知の電子線照射装置を使用することができる。
【００４０】
本発明のプレコート金属板の塗膜厚は、特に限定するものではないが、ベース塗膜が乾燥膜厚にして１０μｍ以上、ベース塗膜と上塗りクリヤー塗膜との合計膜厚が２０μｍ以上であると、光沢や鮮映性、色調が向上し、より好適である。ベース塗膜の膜厚が１０μｍ未満であると、塗膜の隠蔽性が劣り、色調が悪くなる恐れがある。ベース塗膜と上塗りクリヤー塗膜との合計膜厚が２０μｍ未満であると、光沢や鮮映性が低下する恐れがある。これらの塗膜の上限は、特に規定するものではないが、膜厚が厚すぎると塗装焼付の工程でワキと呼ばれる塗装欠陥が発生したり、均一膜厚で塗装しにくい等の問題が発生する恐れがあるので、ベース塗膜及び上塗りクリヤー塗膜の各塗膜の膜厚は１００μｍ以下が好ましい。
【００４１】
また、本発明のプレコート金属板は、本発明の塗膜を両面に施しても良いし、片面に施しても良い。片面にのみ本発明の塗膜を施した場合、他方の面には一般に公知のプレコート鋼板用塗膜を被覆しても良い。
【００４２】
【実施例】
以下、実験に用いた供試材について詳細を説明する。
【００４３】
まず、次に示す２種類のクリヤー塗料を作製した。
クリヤー塗料 −１
東洋紡社製の非晶性ポリエステル樹脂である「バイロンＴＭ ２７０」を、有機溶剤（質量比でシクロヘキサノン：ソルベッソ１５０＝１：１に混合したものを使用）に、樹脂固形分濃度が３０質量％となるように溶解した。次に、硬化剤として三井サイテック社製のメラミン樹脂「サイメルＴＭ ３０３」を添加した。メラミン樹脂の添加量は、樹脂固形分の質量比で、ポリエステル樹脂固形分：メラミン樹脂固形分＝８５：１５となるように添加した。さらに、このポリエステル樹脂とメラミン樹脂の混合溶液に、三井サイテック社製の酸性触媒「キャタリストＴＭ ６００」を０．５質量％添加し、これらを攪拌することで、クリヤー塗料を得た。
クリヤー塗料 −２
東洋紡社製の直鎖型非晶性ポリエステル樹脂である「バイロンＴＭ ６００」を、有機溶剤（質量比でシクロヘキサノン：ソルベッソ１５０＝１：１に混合したものを使用）に、樹脂固形分濃度が３０質量％となるように溶解した。次に、２官能化合物である住化バイエルウレタン社製のヘキサメチレンジイソシアネート（ＨＤＩ）「スミジュールＴＭ ＢＬ３１７５」を、ＨＤＩのＮＣＯ基／ポリエステル樹脂のＯＨ基の比で１．０となるように添加した。更に、反応触媒として、三井武田ケミカル社製の「タケネートＴＫ−１」を添加し、攪拌することでクリヤー塗料を得た。
【００４４】
次に、ベース塗料の作製方法を示す。上記２種のクリヤー塗料を用いて、テイカ社製のトリポリリン酸二水素アルミニウム「Ｋ−ＷＨＩＴＥ＃１０５」（以下、リン酸アルミと称す）、グレイス社製のカルシウムイオン交換シリカ「シールデックスＣ３０３」（以下、Ｃａシリケートと称す）、石原産業社製の白色の着色顔料「タイペークＣＲ９５」（以下、着色顔料と称す）を添加し、攪拌することでベース塗料を得た。なお、作製した塗料の詳細を表１に記載する。
【００４５】
【表１】
また、比較として、次に示す市販のプレコート鋼板用塗料も使用した。
市販プライマー塗料
日本ファインコーティング社製プライマー塗料「ＦＬ６４１プライマー」（塗膜中にクロム酸ストロンチウムを１０質量％含むものを使用）
市販トップ塗料
日本ファインコーティング社製「ＦＬ１００ＨＱ」（酸化チタンのみにて白色に着色したもので、その他の添加顔料を含まないものを使用）
以下、実験に用いたプレコート金属板について詳細を説明する。
【００４７】
新日本株式会社製の亜鉛−ニッケル合金めっき鋼板「ジンクライト」（以下、ＺＬと称す）を原板として準備した。板厚は０．６ｍｍのものを使用した。また、電気めっきラインにてめっきする前の工程にて、焼鈍した冷延鋼板に表面の粗度を調整した圧延ロールにて調質圧延を施すことで、亜鉛−ニッケル合金めっき鋼板の表面粗度を変えた材料も準備した。本実験で用いた亜鉛−ニッケル合金めっき鋼板のめっき付着量は片面２０ｇ／ｍ２、めっき層中のニッケル量は１２％であった。
【００４８】
更に、原板として新日本製鐵株式会社製の溶融亜鉛めっき鋼板「シルバージンク」（以降、ＧＩと称す）とも準備した。「シルバージンク」（新日本製鐵の登録商標）は、板厚０．６ｍｍ、亜鉛付着量Ｚ０８（片面２０ｇ／ｍ２）のものを用いた。化成処理は施していない未処理材を用いた。また、必要に応じて、既にめっきを施したＧＩを調整した圧延ロールにて調質圧延を施すことで、ＧＩの表面粗度を変えた材料も準備した。
【００４９】
次に、準備した原板を必要に応じてＦＣ−４３３６（日本パ−カライジング製）の２質量％濃度、５０℃温度の水溶液にてスプレー脱脂し、水洗後、乾燥した後に電解クロメート処理、ノンクロメート処理、３価クロム処理、６価クロム処理を行った。電解クロメート処理は、クロム酸５０ｇ／Ｌ、硫酸０．３ｇ／Ｌの浴中で、電流密度１０Ａ／ｄｍ２で所定の電気量を通電して、電解型クロメート処理を施し、水洗した後、熱風乾燥炉を用いて到達板温８０℃で乾燥することで、処理した。電解クロメート処理の付着量はクロム付着量で１５ｍｇ／ｍ２とした。また、ノンクロメート処理、３価クロム処理、６価クロム処理は、それぞれの処理液をロールコーターにて塗布し、熱風オーブンにて乾燥させた。熱風オーブンでの乾燥条件は、鋼板の到達板温で６０℃とした。
【００５０】
なお、ノンクロメート処理液は日本パーカライジング社製の「ＣＴ−Ｅ３００」を使用し、全固形分付着量として５０ｍｇ／ｍ２となるように塗布した。３価クロム処理液は日本ペイント社製の「サーフコートＮＲＣ１０００」を使用し、クロム付着量として５０ｍｇ／ｍ２となるように、６価クロム処理液は日本パーカライジング社製の「ＺＭ１３００ＡＮ」を使用し、クロム付着量として５０ｍｇ／ｍ２となるようにした。
【００５１】
次に、化成処理を施した金属板の片方の面にベース塗料を（以降こちらの面を表面と称す）、他方の面に裏面塗料を（以降、こちらの面を裏面と称す）ロールコーターにて塗装し、熱風を吹き込んだ誘導加熱炉にて金属板の到達板温が２１０℃となる条件で乾燥硬化することでベース塗膜層を得た。そして乾燥焼付後に、塗装された金属板へ水をスプレーにて拭きかけ、水冷した。更に、表面のベース塗膜層の上に、クリヤー塗料をローラーカーテンコーターにて塗装し、熱風を吹き込んだ誘導加熱炉にて金属板の到達板温が２３０℃となる条件で乾燥硬化させることでクリヤー塗膜層を得た。そして、乾燥焼付後に、塗装された金属板へ水をスプレーにて吹きかけ、水冷することで、プレコート金属板サンプルを得た。また、比較材として、６価クロム処理を施した金属板上に市販プライマー塗料を前記ベース塗料と同条件で塗装焼き付けし、更にその上に、市販トップ塗料と表１中の塗料−１３をトップ塗料としてクリヤー塗料と同条件で塗装焼付したプレコート金属板も作製した。
【００５２】
なお、表２に、作製したプレコート金属板の詳細を記載する。また、裏面塗料は、全てのサンプルにおいて日本ペイント社製の「ＦＬ１００ＨＱ」（グレー色に着色したもの）を乾燥膜厚にして５μｍ塗装した。
【００５３】
【表２】
以下、作製したプレコート金属板の評価方法の詳細を記載する。
１． 光沢測定
ＪＩＳ．Ｋ．５４００．７．６に準じて作製したプレコート金属板の表面の光沢度を測定した。測定条件は入射角及び受光角を２０°とした。更に、測定した値が８０％のものを○、６０％以上８０％未満のものを△、６０％未満のものを×と評価した。
２． 鮮映性測定
携帯用鮮明度光沢度計「ＰＧＤ」（東京光電社製）にてＧｄ値を測定した。更に、測定したＧｄ値が０．３以上のものを○、０．１以上０．３未満のものを△、０．１未満のものを×と評価した。
３． 色調測定
ＪＩＳ．Ｋ．５４００．７．４．２に準じて色の計測を行った。本実験では、全てのプレコート金属板サンプルを白色に着色しているため、白色度の指標であるＬ値に着目し、Ｌ値が９０以上のものを○、７０以上９０未満のものを△、７０未満のものを×と評価した。
４． 塗膜加工密着性試験
作製したプレコート金属板を、１８０°折り曲げ加工（密着曲げ加工）し、加工部の塗膜を目視で観察し、塗膜の割れの有無を調べた。なお、１８０°折り曲げを行う際には、プレコート金属板の表面が曲げの外側となるように折り曲げ、さらに曲げの内側にはプレコート金属板と同じ板厚のスペーサーを２枚挟んだ状態で密着曲げを行った（一般に２Ｔ曲げとして知られている）。また、加工部に粘着テープを貼り付け、これを勢い良く剥離したときの塗膜の残存状態を目視にて観察した。
【００５５】
塗膜割れ及び剥離の評価は、塗膜割れや剥離の全くない時を○、塗膜に僅かな亀裂や剥離が認められる時を△、塗膜に明確な大きな割れや剥離がある時を×として評価した。
５． ビードによる塗膜かじり試験
プレコート金属板をプレス成形したときに、プレス金型でプレコート金属板の塗膜をかじることによって発生する塗膜の剥離を再現する試験方法である「ビードによる塗膜かじり試験法」（公開技報９５−１０７８）を実施した。まず、作製したプレコート金属板を３０ｍｍ（幅）×３００ｍｍ（長さ）の試験片に切り出し、この試験片を平面の金型と半径４ｍｍＲのビードを設けた金型とで挟み込む。この際に試験片の表面（評価面）に金型のビードが押し付けられるように挟み込み、さらに１ｔの荷重を加えて金型のビード部をプレコート金属板の評価面に押し付けた。この状態で、プレコート金属板を２００ｍｍ／ｍｉｎの速度で引き抜き、ビードにて擦られたプレコート金属板の評価面の塗膜剥離状態を目視にて観察し、評価した。
【００５６】
評価は、塗膜が全く剥離していない場合を◎、極部分的に剥離している場合を○、ビードで擦られた部分の面積率にして２０％程度以上が剥離している場合を△、全面剥離している場合を×とした。
６． 耐食性試験
作製したプレコート金属板を油圧式エリクセンタイプの２０ｔプレス加工試験機を用いて円筒絞り試験した。円筒絞り試験は、ポンチ径φ５０ｍｍ、ポンチ肩Ｒ３ｍｍ、ポンチコーナーＲ３ｍｍ、ダイス肩Ｒ３ｍｍ、絞り比２．０、しわ押さえ圧１ｔの条件で行い、金属板が金型から絞り抜けるまで加工を行った。なお、本試験においては、市販の潤滑油を金属板に塗布した条件でプレス加工を行い、また、加工材カップの外側が表面となるように加工した。さらに、これら絞り加工を施したプレコート鋼板加工材をＪＩＳ．Ｚ．２３７１に準じて塩水を１２０時間噴霧した。なお、プレス加工されたサンプルの切断端面は特にシール等はせずに、切断端面が露出する状態で腐食試験を行った。また、塩水は加工材のカップ外側に噴霧した。耐食性試験後の加工サンプル表面の端面部からの腐食程度を観察し、評価した。端面部の評価基準は、加工端面からの最大赤錆発生幅及び最大膨れ幅が２ｍｍ以下の場合◎、２ｍｍ超３ｍｍ以下の場合○、３ｍｍ超４ｍｍ以下の場合○△、４ｍｍ超５ｍｍ以下の場合△、５ｍｍ超の場合×と評価した。
７． ６価クロム含有量の測定
作成したプレコート金属板に６価クロムが含まれるか否かを判定するために、次の方法にて評価を行った。
【００５７】
まず、作製したプレコート金属を５０ｍｍ×５０ｍｍサイズに切断し、試験片を作製した。次に、ビーカーにイオン交換水を５００ｍｌ入れ、ヒーターにて沸騰させ、この沸騰水中に試験片を３０分間浸漬した。そして、試験片を取り出した残溶液中に含まれるクロム濃度をＪＩＳ．Ｋ．０１０２のジフェニルカルバジド吸光光度法に準じて測定した。そして、得られたクロム濃度から、作製した試験片から沸騰水中に溶出したクロムトータル量を算出し、これを試験片に含まれるトータル６価クロム量とした。更に、算出したトータル６価クロム量を試験片の面積（２５００ｍｍ２）で割ることで、作製したプレコート金属板の面積当たりに含まれる６価クロム量を算出し、そして、この６価クロム含有量が０．３ｍｇ／ｍ２以下の場合は○（６価クロムを含まない）と評価し、０．３ｍｇ／ｍ２超の場合は×（６価クロムを含む）と評価した。
【００５８】
【表３】
以下、評価結果について詳細を記載する。表３に作製したプレコート金属板の評価結果を示す。本発明のプレコート金属板（本発明例Ｎｏ．１〜２２）は、高光沢、鮮映性、色調に優れ、更には加工性、加工後の耐食性に優れる。更に、プレコート金属板に塗装した塗膜のバインダー樹脂又はクリヤー塗膜の樹脂が、両端に官能基を有する直鎖状重合体である樹脂と２官能化合物からなる塗料組成物を加熱によって直鎖状重合体の更なる直鎖状重合反応を促進させて成膜させたものであると、加工部の耐食性が更に向上し、より好適である（本発明例Ｎｏ．１、１３、１４と本発明例Ｎｏ．８、１６、１７との比較）。この直鎖重合体の直鎖重合反応を促進させたタイプの皮膜は、ベース塗膜、クリヤー塗膜のいずれか一方への適用で、加工部耐食性に効果を発揮するが、ベース塗膜、クリヤー塗膜の双方に適用すると加工部耐食性が更に向上するため、より好適である（本発明例Ｎｏ．１、１３、１４と本発明例Ｎｏ．８、１６、１７と本発明例Ｎｏ．２１、２２との比較）。また、本発明のプレコート金属板の原板に用いる金属板の表面粗度Ｒａが１．０超のもの（本発明例Ｎｏ．１０、１８）は光沢や鮮映性が少し低下するため、原板に用いる金属板の粗度Ｒａは１．０以下がより好適である。更に、本発明に用いる金属板が亜鉛−ニッケル合金めっき鋼板であると、耐食性が更に向上し、より好適である（本発明例Ｎｏ．１、９、１０と本発明例Ｎｏ．１７、１８との比較）。また、本発明のプレコート金属板で、下塗り塗膜の膜厚を８μｍとし、且つ下塗り塗膜と上塗り塗膜との合計膜厚を１８μｍとしたもの（本発明例Ｎｏ．１２）は、若干光沢、鮮映性、色調が劣るため、下塗り塗膜の膜厚を１０μｍ以上とし、且つ下塗り塗膜と上塗り塗膜との合計膜厚を２０μｍ以上とすることがより好ましい。
【００６０】
プレコート金属板のベース塗膜中にリン酸アルミ系顔料又はシリカ系防錆顔料のどちらか一方しか添加されていないもの（本発明例Ｎｏ．１９、２０）は、ビードカジリ性や耐食性が低下するため、リン酸アルミ系顔料とシリカ系顔料の双方を含むものの方がより好ましい。
【００６１】
プレコート金属板のベース塗膜中に含まれるリン酸アルミ系顔料の添加量や、シリカ系防錆顔料のどちらか一方の添加量もしくは両方の合計添加量が、ベース塗膜のバインダー樹脂１００質量部に対して５０質量部超のもの（比較例Ｎｏ．２２、２３、２４）は、色調に劣るため不適である。プレコート金属板のベース塗膜中に含まれるリン酸アルミ系顔料とシリカ系防錆顔料と着色顔料との合計添加量がベース塗膜のバインダー樹脂１００質量部に対して３００質量部超のもの（比較例Ｎｏ．２５）は、加工性に劣るため不適である。また、６価クロムを含む化成処理を用いたプレコート金属板は、環境負荷物質であるクロムが溶出し易いため、不適である。なお、６価クロムを含まない化成処理であれば、ノンクロメート化成処理、３価クロム化成処理、電解クロメート化成処理のいずれでも良く、光沢、鮮映性、色調、加工性、ビードかじり性、加工部耐食性等の諸性能は好適である（本発明例Ｎｏ．１とＮｏ．１３とＮｏ．１４との比較、もしくは本発明例Ｎｏ．８とＮｏ．１５とＮｏ．１６との比較）。
【００６２】
【発明の効果】
本発明により、環境上の影響が懸念される６価クロムを使用せずに、高光沢、高鮮映性を有し、且つ、塗膜の加工密着性、耐食性に優れ、プレス成形に非常に適した高意匠性プレコート金属板を提供することが可能となった。従って、本発明は工業的価値の極めて高い発明であるといえる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface-treated metal sheet having excellent corrosion resistance after press forming, and particularly has environmental problems in household appliances, building materials, civil engineering, machinery, automobiles, furniture, containers, and the like. It is characterized by exhibiting coating film adhesion during press molding and rust prevention effect without using hexavalent chromium.
[0002]
[Prior art]
For home appliances, building materials, automobiles, and the like, pre-coated metal sheets coated with a colored coating have come to be used instead of post-painted products that have been coated after conventional processing. This metal plate is obtained by coating a metal plate that has been subjected to a metal pretreatment with a paint, and is generally used after being coated with the paint and cut and press-molded. Therefore, the corrosion resistance of the cut end surface where the metal not coated with the coating film is exposed and the coating film peeling at the time of press working have been problems of the precoated metal plate, but a chromate treatment is performed as a pretreatment for the metal, and These problems have been solved by including a hexavalent chromium-based rust-preventive pigment in the coating film, and are now widely used. However, since hexavalent chromium is an environmentally hazardous substance, movement to eliminate hexavalent chromium has been active in recent years.
[0003]
As the chemical conversion treatment technology, JP-A-9-828291, JP-A-10-251509, JP-A-10-337530, JP-A-2000-17466, JP-A-2000-248385, and JP-A-2000-248385 JP-A-273659, JP-A-2000-282252, JP-A-2000-265282, JP-A-2000-167482 and the like are disclosed.
[0004]
On the other hand, in Japanese Patent Application Laid-Open No. 9-12931, the cut end face is coated with a polyester-based or epoxy-based paint using a phosphoric acid-based rust preventive pigment and an ion-exchange silica-based rust preventive pigment in place of the hexavalent chromium-based rust preventive pigment. A technique for providing a precoated steel sheet having excellent corrosion resistance is disclosed.
[0005]
On the other hand, as a performance of the precoated steel sheet, a coating film having high gloss and sharpness is required. In the case of the precoated steel sheet exemplified in the above-mentioned JP-A-9-12931, it is difficult to obtain a high-gloss precoated steel sheet, and furthermore, the corrosion resistance of the processed portion is poor. JP-A-62-116138, JP-A-2-205201, JP-A-7-150326, JP-A-58-61292, etc. disclose a pre-coated steel sheet or its original sheet with a roll having adjusted roughness. A technique for improving the sharpness after painting of a precoated steel sheet by rolling is disclosed. However, if the roughness of the precoated steel sheet or the original sheet is adjusted by a rolling roll, problems such as an increase in cost and a decrease in work efficiency due to an increase in the number of manufacturing steps occur.
[0006]
In JP-A-1-304934, two or more different types of cross-linking rates are used for an undercoat paint obtained by mixing an amino resin with an epoxy-modified polyester resin having a number average molecular weight of 5,000 to 70,000 on a metal plate and a polyester resin having a number average molecular weight of 2,000 to 10,000. A technique for obtaining high definition by forming a top coat containing the above amino resin is disclosed. However, when a low molecular weight paint is applied to the top coat, cracks tend to occur in the paint film if severe workability such as close bending and deep drawing is applied, and furthermore, corrosion occurs from cracks in this paint film. Because it is easy, the corrosion resistance of the processed part is inferior.
[0007]
Japanese Patent Application Laid-Open No. 10-66931 discloses a technique in which an organic coating material is applied to a metal plate and a solution containing a clear resin is further applied thereon to impart sharpness to the coating film. However, it is difficult to uniformly and stably apply the solution containing the clear resin on the paint before drying. On the other hand, it is easy to apply a clear paint or the like on the coating film after drying, and in this case, in this case, in order to achieve both appearance design and corrosion resistance, an undercoating and a rust-proofing coating are applied. It is necessary to apply three or more layers of intermediate coating, clear coating which is the top coating. However, in a continuous coating line for producing precoated steel sheets, two coatings and two bakings (generally called two coatings and two baking) are common, and it is difficult to apply three or more coatings. When a top coat clear type coating is applied by a two-coat two-bake method, it is common to omit the rust-preventive coating layer and apply a top clear to the top coat as a colored undercoat. Poor corrosion resistance due to labor saving of rust coating layer. In the case of such a type, it is common to add a rust-preventive pigment to the colored layer, but since the conventional hexavalent chromium-based rust-preventive pigment is yellow, when added together with the color pigment in the coating film, There was a drawback that the desired color was hardly produced.
[0008]
[Patent Document 1]
JP-A-9-828291
[Patent Document 2]
JP-A-10-251509
[Patent Document 3]
JP-A-10-337530
[Patent Document 4]
JP 2000-17466 A
[Patent Document 5]
JP 2000-248385 A
[Patent Document 6]
JP 2000-273659 A
[Patent Document 7]
JP 2000-282252 A
[Patent Document 8]
JP 2000-265282A
[Patent Document 9]
JP-A-2000-167482
[Patent Document 10]
JP-A-9-12931
[Patent Document 11]
JP-A-62-116138
[Patent Document 12]
JP-A-2-205201
[Patent Document 13]
JP-A-7-150326
[Patent Document 14]
JP-A-58-61292
[Patent Document 15]
JP-A-1-304934
[Patent Document 16]
JP-A-10-66931
[0009]
[Problems to be solved by the invention]
The present invention solves the above-mentioned problems in the prior art, and provides a two-coat two-bake pre-coated metal plate that has excellent corrosion resistance in a processed part without containing hexavalent chromium and has high gloss and sharpness. Is the subject.
[0010]
[Means for Solving the Problems]
The inventors applied a base coating layer containing an aluminum phosphate-based pigment, a silica-based rust-preventive pigment, and a coloring pigment on a metal plate that had been subjected to a chemical conversion treatment containing no hexavalent chromium, and further applied a clear coating thereon. By applying the coating layer, it has been found that a high gloss precoated metal sheet having excellent workability (particularly, deep drawing workability by pressing) and excellent corrosion resistance in a processed portion can be obtained without using hexavalent chromium. . The present invention has been completed based on such findings, and the gist of the present invention is as follows.
(1) A chemical conversion treatment layer containing no hexavalent chromium on one or both surfaces of a metal plate, on which a binder resin and (a) a color pigment are contained as essential components, and (b) an aluminum phosphate pigment Or (c) a base coating layer containing one or both of silica-based rust preventive pigments, and a precoated metal plate further having a clear coating layer thereon, wherein the solid content of the binder resin in the base coating layer is 100% by mass. Parts, the addition amount of (b) is 0 to 50 parts by mass, the addition amount of (c) is 0 to 50 parts by mass, and the total addition amount of (b) and (c) is 1 to 50 parts by mass. And high gloss having excellent corrosion resistance in the processed part, wherein the total amount of (a), (b) and (c) is more than 1 part by mass and 300 parts by mass or less based on 100 parts by mass of the solid content of the binder resin. Pre-coated metal plate.
(2) The high-gloss precoated metal plate according to (1), wherein the aluminum phosphate-based pigment contained in the base coating layer is aluminum dihydrogen tripolyphosphate.
(3) The high gloss precoated metal sheet according to (1), wherein the silica-based rust-preventive pigment contained in the base coating layer is calcium ion exchange silica.
(4) One or both of the binder resin of the base coating layer and the resin of the clear coating layer are heated by heating a coating composition comprising a resin which is a linear polymer having a functional group at both ends and a bifunctional compound. The high-gloss precoated metal sheet according to (1), which is a resin formed by forming a film by promoting a further linear polymerization reaction of a linear polymer.
(5) The high gloss precoated metal plate according to (1), wherein the metal plate has a surface roughness Ra of 1.0 or less.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention provides a chemical conversion treatment layer containing no hexavalent chromium on one or both surfaces of a metal plate, and further comprises a binder resin and (a) a color pigment as essential components, and (b) an aluminum phosphate-based material. A base coat layer containing one or both of a pigment and (c) a silica-based rust-preventive pigment, and a pre-coated metal plate further having a clear coat layer thereon, wherein the solid content of the binder resin in the base coat layer is 100%. The addition amount of (b) is 0 to 50 parts by mass, the addition amount of (c) is 0 to 50 parts by mass, and the total addition amount of (b) and (c) is 1 to 50 parts by mass with respect to parts by mass. And a total addition amount of (a), (b) and (c) is more than 1 part by mass and not more than 300 parts by mass with respect to 100 parts by mass of the solid content of the binder resin. Achieved by glossy pre-coated metal sheets.
[0012]
As the metal plate used in the present invention, a generally known metal material can be used. The metal material may be an alloy material. Examples include a steel plate, a stainless steel plate, an aluminum plate, an aluminum alloy plate, a titanium plate, a copper plate and the like. The surfaces of these materials may be plated.
[0013]
Examples of the type of plating include zinc plating, aluminum plating, copper plating, and nickel plating. These alloy platings may be used. In the case of steel sheets, generally known steel sheets such as hot-dip galvanized steel sheets, electro-galvanized steel sheets, zinc-nickel alloy-coated steel sheets, hot-dip galvanized steel sheets, aluminum-coated steel sheets, aluminum-zinc alloy-coated steel sheets, stainless steel sheets, and the like Plated steel sheet can be applied.
[0014]
In particular, aluminum-plated metal plates (for example, aluminum-plated steel plates), zinc-plated metal plates (for example, galvanized steel plates), nickel-plated metal plates (for example, nickel-plated steel plates), and alloy plating containing nickel A metal plate (for example, a zinc-nickel alloy-plated steel plate) or a metal plate (for example, a 55% aluminum-zinc-plated steel plate) that has been subjected to alloy plating containing aluminum has excellent heat reflectivity and is more preferable.
[0015]
Among them, a zinc-nickel alloy-plated steel sheet is particularly preferable because of excellent corrosion resistance of the processed portion. Zinc-nickel alloy-plated steel sheet is a zinc-based alloy-plated steel sheet containing 1 to 30% by mass, preferably 5 to 15% by mass of nickel in a plating layer, and is “Zinclite” (manufactured by Nippon Steel Corporation). Nippon Steel's registered trademark) can be used.
[0016]
Further, it is more preferable that the surface roughness Ra of the metal plate used in the present invention is 1.0 or less, because the sharpness after painting of the precoated metal plate is improved. The surface roughness of the metal plate is obtained by rolling the metal plate with a temper rolling roll whose surface roughness has been adjusted, or rolling it with a temper rolling roll whose surface roughness has been adjusted after plating the metal plate. Alternatively, the roughness can be adjusted by rolling the original metal sheet before plating with a temper roll having adjusted surface roughness and then plating. Here, Ra is JIS. B. It refers to the arithmetic average roughness (Ra) described in 0601.3.
[0017]
The chemical conversion treatment performed on a metal plate is characterized in that hexavalent chromium is not included. Hexavalent chromium is an unfavorable substance because it is an environmentally hazardous substance. As the chemical conversion treatment not containing hexavalent chromium, generally known ones, electrolytic chromate treatment, reaction chromate treatment, zinc phosphate treatment, zirconia treatment, titania treatment, and silane coupling treatment can be used. Specific examples include JP-A-9-828291, JP-A-10-251509, JP-A-10-337530, JP-A-2000-17466, JP-A-2000-248385, and JP-A-2000-27359. JP, JP-A-2000-282252, JP-A-2000-265282, JP-A-2000-167482, and the like, and a chromium-free chemical treatment "CT-E300" manufactured by Nippon Parkerizing Co., Ltd. ”And“ CT-E200 ”, and Nippon Paint Co., Ltd. It can be used over door NRC1000 "and the like. In the electrolytic chromate treatment and the reaction chromate treatment, a treatment solution containing hexavalent chromium is used in the treatment process. However, in the reduction reaction performed in the treatment process, all hexavalent chromium becomes trivalent chromium. Since the pre-coated metal plate finally does not contain hexavalent chromium, it can be said that these are chemical conversion treatments which do not contain hexavalent chromium in the present invention.
[0018]
The pre-coated metal plate of the present invention is characterized in that a base coating layer containing a binder resin, an aluminum phosphate-based pigment, a silica-based rust-preventive pigment, and a coloring pigment is formed on a metal plate subjected to a chemical conversion treatment.
[0019]
The base coating film layer of the present invention can be formed by forming a film obtained by adding an aluminum phosphate-based pigment, a silica-based rust-preventive pigment, and a coloring pigment to a paint for a pre-coated metal plate generally known as a binder resin.
[0020]
As the aluminum phosphate-based pigment contained in the base coating layer of the present invention, generally known aluminum phosphate-based pigments can be used, and aluminum dihydrogen tripolyphosphate is particularly preferred. When the aluminum phosphate-based pigment is not contained, the adhesion of the coating film is inferior, and the coating film may be rubbed off by a press mold during press working (generally referred to as mold galling). Further, since the aluminum phosphate pigment is light white, it is preferable because the color tone is not adversely affected when the base coating film is colored with the coloring pigment. The addition amount of the aluminum phosphate pigment must be 0 to 50 parts by mass based on 100 parts by mass of the binder resin solid content of the coating film. If the amount exceeds 50 parts by mass, the color tone of the base coating film cannot be adjusted. is there.
[0021]
As the silica-based rust preventive pigment contained in the base coating film layer of the present invention, generally known silica-based rust preventive pigments can be used, and calcium ion-exchanged silica is particularly preferred. The calcium ion-exchanged silica is of a type in which calcium ions are adsorbed on the silica surface, and “Sealdex” manufactured by Grace (registered trademark of Grace) can be used. Silica-based rust preventive pigments are suitable because they have excellent corrosion resistance and are light white, and do not adversely affect the color tone when coloring the base coating film with the coloring pigment. The amount of the silica-based rust-preventive pigment to be added must be 0 to 50 parts by mass with respect to 100 parts by mass of the solid content of the binder resin, and if it exceeds 50 parts by mass, the color tone of the base coating film cannot be adjusted.
[0022]
Further, the total amount of the aluminum phosphate-based pigment and the silica-based rust-preventive pigment needs to be 1 to 50 parts by mass based on 100 parts by mass of the binder resin solid content of the coating film. If the amount is less than 1 part by mass, the corrosion resistance and adhesion are inferior. If the amount is more than 50 parts by mass, the color tone of the base coating film cannot be adjusted.
[0023]
The aluminum phosphate-based pigment and the silica-based rust-preventive pigment may be contained in the base coating film of the present invention. When it is contained, the corrosion resistance and the workability and adhesion are further improved, which is more preferable.
[0024]
As the coloring pigment contained in the base coating layer of the present invention, generally known coloring pigments can be used. For example, titanium oxide (TiO)2), Zinc oxide (ZnO), zirconium oxide (ZrO)2), Calcium carbonate (CaCO3), Barium sulfate (BaSO)4), Alumina (Al2O3), Kaolin clay, carbon black, iron oxide (Fe2O3, Fe3O4) And organic pigments. The amount of the color pigment to be added is not particularly limited, but may be an amount necessary to obtain a desired color tone. However, the total of the aluminum phosphate-based pigment, the silica-based rust-preventive pigment, and all the color pigments needs to be more than 1 part by mass and 300 parts by mass or less based on 100 parts by mass of the binder resin solid content of the coating film. If the amount is less than 1 part by mass, the corrosion resistance and the adhesion are inferior.
[0025]
The precoat metal sheet paint as a binder resin is a solvent in which an organic or inorganic substance as a binder component is dissolved or dispersed in a solvent, and can be formed into a film in a short time (5 to 400 seconds) by applying heat. It is paint. The binder resin component used in the base coating film is not particularly limited, and is generally known as a binder resin for coating, for example, generally known polyester resins, acrylic resins, melamine resins, epoxy resins, fluororesins, vinyl chloride resins, and the like. Paint resin and the like can be used. An isocyanate or a melamine resin may be added as a curing agent to these resins.
[0026]
According to the findings obtained by the present inventors so far, the use of a melamine-curable polyester-based resin and an isocyanate-curable polyester-based resin as the binder component is excellent in the processability of the coating film, and is particularly preferable. Although those are preferable, these are only examples and the present invention is not limited to these.
[0027]
In the case of a melamine-curable polyester, the molecular weight of the polyester resin is preferably from 2,000 to 30,000 in terms of number average molecular weight, the Tg of the polyester resin is preferably from -10 to 130 ° C, and the amount of the melamine resin added is 5 to 70 parts by mass is suitable for 100 parts by mass.
[0028]
If the molecular weight of the polyester resin is less than 2,000, the processability of the coating film is reduced. If the molecular weight is more than 30,000, the viscosity may be too high when the resin is dissolved in a solvent, which may make the coating difficult. If the Tg of the polyester resin is lower than −10 ° C., the coating film may not be formed, and if the Tg is higher than 130 ° C., the coating film is too hard, and thus the processability may be reduced. If the amount of the melamine resin is less than 5 parts by mass with respect to 100 parts by mass of the polyester, the coating film may be uncured, and if it is more than 70 parts by mass, the coating film becomes too hard and the processability decreases. There is fear.
[0029]
The polyester resin used is generally commercially available, for example, "Byron" manufactured by Toyobo Co., Ltd.TMAnd Sumika Bayer Urethane Co., Ltd.TMEtc. can be used. The melamine resin to be used is also generally available on the market, for example, “SymelTM"," My CourtTM, Dainippon Ink and Chemicals, Inc.TM”,“ Super BeckamineTMEtc. can be used.
[0030]
In the case of an isocyanate-curable polyester system, the molecular weight of the polyester resin is preferably from 2,000 to 30,000 in terms of number average molecular weight, the Tg of the polyester resin is preferably from -10 to 70 ° C, and the amount of isocyanate added is It is preferable that NCO group equivalent] / [OH group equivalent of polyester resin] = 0.8 to 1.2.
[0031]
If the value of [NCO group equivalent of isocyanate] / [OH group equivalent of polyester resin] is less than 0.8 or more than 1.2, the coating film tends to be uncured when the coating film is formed. If the molecular weight of the polyester resin is less than 2,000, the processability of the coating film is reduced. If the molecular weight is more than 30,000, the viscosity may be too high when the resin is dissolved in a solvent, which may make the coating difficult. If the Tg of the polyester resin is lower than −10 ° C., the coating film may not be formed, and if the Tg is higher than 70 ° C., the coating film is too hard, and the workability may be reduced.
[0032]
The polyester resin used is generally commercially available, for example, "Byron" manufactured by Toyobo Co., Ltd.TM”, Sumika Bayer Urethane“ Desmophen ”TMEtc. can be used.
[0033]
The isocyanate to be used is also generally available on the market, for example, "Sumidule" manufactured by Sumika Bayer Urethane Co., Ltd.TM"," Death moduleTMAnd "Takenate" (registered trademark of Mitsui Takeda Chemical Co., Ltd.) manufactured by Mitsui Takeda Chemical Co., Ltd. can be used.
[0034]
The precoated metal plate of the present invention is characterized in that a clear coating film is formed on a base coating film layer containing an aluminum phosphate pigment, a silica rust preventive pigment, and a coloring pigment. As the clear coating film, a generally known precoated metal plate paint similar to the base coating film can be used. Generally, only organic resins are transparent or melted or dispersed in a solvent to form a film. As the organic resin used for the clear coating film, those exemplified as a binder for the base coating film can be used, and in particular, a melamine-curable polyester-based resin exemplified as a binder for the base resin, and an isocyanate-curable polyester-based resin are more preferable. It is suitable. Also, as long as the transparency can be ensured when the film is formed, a slight amount of a coloring pigment or a rust-preventive pigment may be added. Additives such as generally known surfactants, waxes, slip materials, leveling materials, and defoamers can be added to the clear paint as needed. In particular, when wax is added to the clear coating layer, the friction coefficient of the surface of the precoated steel sheet is reduced, and press formability is improved, which is more preferable. The transparency of the coating film is not particularly specified, and the color of the base coating film must be visible. Since the transparency varies depending on the type of the resin, the type and the amount of the additive, it is necessary to select these as necessary.
[0035]
Further, the binder resin of the base coating layer or the resin of the clear coating film applied to the precoated metal sheet of the present invention is a coating composition comprising a resin which is a linear polymer having a functional group at both ends and a bifunctional compound. If the film is formed by heating to promote a further linear polymerization reaction of the linear polymer, the corrosion resistance of the processed portion is improved, which is more preferable. The coating film formed by accelerating the linear polymerization reaction in the baking process in this way becomes a polymer thermoplastic coating film in appearance. Therefore, when pre-coated steel sheets coated with these coatings are processed, the molecular chains in the coating resin are displaced in the processed part, and the internal stress of the coating stretched by the processing is crosslinked, so that thermosetting coating It is easier to relax than. Therefore, the pre-coated steel sheet coated with a coating film that promotes linear polymerization has a smaller coating internal stress in the processed portion than in the case of a general thermosetting coating film, so that the corrosion resistance of the processed portion is further improved. It is presumed that.
[0036]
As the bifunctional linear polymer having a functional group at both ends, generally known linear polyester, linear epoxy, linear acrylic, and the like can be used. For example, in the case of a linear polyester, "Beccolight" manufactured by Dainippon Ink and Chemicals, Inc.TM M-6207-40 "," BeccolightTM 57-206-40 "and" Byron "manufactured by ToyoboTM 600 "," ByronTM 290 ”and the like in the case of a linear epoxy resin,“ Epiclon ”manufactured by Dainippon Ink and Chemicals, Inc.TM 7050-40S "," Epicoat 1007 "and" Epicoat 1009 "manufactured by Japan Epoxy Resin Co., Ltd., and in the case of a linear acrylic resin," LR-635 "manufactured by Mitsubishi Rayon Co., Ltd. and Dainippon Ink & Chemicals, Inc. "AcridicTM A-405 "can be used.
[0037]
Examples of the bifunctional compound capable of reacting with a linear polymer having a functional group at both ends include a diisocyanate compound and a dicarboxyl group compound. Examples of the diisocyanate compound include xylene diisocyanate, toluene diisocyanate, and hexamethylene diisocyanate. In addition, resins obtained by modifying both ends of a polyester polyol or an acrylic polyol with the above-described diisocyanate or hexamethylenediamine, polyester polyol dicarboxylic acid, glycidyl-modified acrylic resin, and the like are included. As the diisocyanate compound, a blocked isocyanate compound may be used.
[0038]
The ratio of the bifunctional linear polymer having functional groups at both ends to the bifunctional compound is preferably 0.5 to 10 in terms of the functional group ratio of the bifunctional compound / linear polymer. If it is less than 0.5 or more than 10, the linear polymerization reaction may not be promoted. The technique described in JP-A-2002-249725 can be used for a coating composition comprising a resin which is a linear polymer having functional groups at both ends and a bifunctional compound.
[0039]
The coating method of the base coating film and the clear coating film of the present invention is a generally known coating method, for example, roll coating, curtain flow coating, roller curtain coating, die coating, air spray, airless spray, electrodeposition coating, powder coating. Immersion, bar coating, brush coating, and the like. However, it is more preferable to apply a continuous coating line called a general coil coating line or sheet coating line equipped with a roll coat, curtain flow coat, and roller curtain coat because the coating work efficiency is good and mass production is possible, . As a method of drying and baking the paint, a generally known dry baking method such as a hot air oven, a direct fire oven, a salt infrared oven, and an induction heating oven can be used. When the coating material is an ultraviolet-curable coating material, a generally known ultraviolet irradiation device can be used. When the coating material is an electron beam-curable coating material, a generally known electron beam irradiation device can be used.
[0040]
The coating thickness of the precoated metal sheet of the present invention is not particularly limited, but the base coating film has a dry film thickness of 10 μm or more, and the total film thickness of the base coating film and the top clear coating film is 20 μm or more. In addition, gloss, sharpness, and color tone are improved, which is more preferable. When the thickness of the base coating film is less than 10 μm, the concealing property of the coating film is inferior and the color tone may be deteriorated. If the total film thickness of the base coating film and the top clear coating film is less than 20 μm, gloss and sharpness may be reduced. The upper limits of these coatings are not particularly specified, but if the film thickness is too thick, problems such as coating defects called waki occur in the coating baking step and difficulty in coating with a uniform film thickness occur. Since there is a possibility that the thickness of each of the base coating film and the overcoating clear coating film is preferably 100 μm or less.
[0041]
In the precoated metal sheet of the present invention, the coating film of the present invention may be applied to both sides, or may be applied to one side. When the coating of the present invention is applied to only one surface, the other surface may be coated with a generally known coating for a precoated steel sheet.
[0042]
【Example】
Hereinafter, the test materials used in the experiment will be described in detail.
[0043]
First, the following two types of clear coatings were prepared.
Clear paint -1
Byron, an amorphous polyester resin manufactured by ToyoboTM 270 "was dissolved in an organic solvent (using a mixture of cyclohexanone: solvesso 150 = 1: 1 by mass ratio) so that the resin solid content concentration was 30% by mass. Next, as a curing agent, melamine resin “CymelTM 303 "was added. The melamine resin was added in such an amount that the polyester resin solid content: melamine resin solid content = 85: 15 in mass ratio of resin solid content. Furthermore, the mixed solution of the polyester resin and the melamine resin was added to an acidic catalyst “Catalyst” manufactured by Mitsui Cytec.TM By adding 0.5% by mass of “600” and stirring them, a clear paint was obtained.
Clear paint -2
Byron, a straight-chain amorphous polyester resin manufactured by ToyoboTM "600" was dissolved in an organic solvent (using a mixture of cyclohexanone: solvesso 150 = 1: 1 by mass) so that the resin solid content concentration was 30% by mass. Next, hexamethylene diisocyanate (HDI) "Sumidule" manufactured by Sumika Bayer Urethane, which is a bifunctional compound, is used.TM BL3175 "was added so that the ratio of NCO groups of HDI / OH groups of polyester resin was 1.0. Further, "Takenate TK-1" manufactured by Mitsui Takeda Chemical Co., Ltd. was added as a reaction catalyst and stirred to obtain a clear coating.
[0044]
Next, a method for preparing the base paint will be described. Using the above two types of clear paints, aluminum dihydrogen tripolyphosphate “K-WHITE # 105” (hereinafter, referred to as aluminum phosphate) manufactured by Teica, and calcium ion exchange silica “Sealdex C303” manufactured by Grace Co., Ltd. Hereinafter, it is referred to as Ca silicate), and a white color pigment “Taipeku CR95” (hereinafter, referred to as a color pigment) manufactured by Ishihara Sangyo Co., Ltd. was added and stirred to obtain a base paint. Table 1 shows details of the prepared paint.
[0045]
[Table 1]
For comparison, the following commercially available paint for a precoated steel sheet was also used.
Commercial primer paint
Primer paint "FL641 primer" manufactured by Nippon Fine Coating Co. (uses a paint film containing 10% by mass of strontium chromate)
Commercial top paint
"FL100HQ" manufactured by Nippon Fine Coatings Co., Ltd. (Used only with titanium oxide and colored white and without other added pigments)
Hereinafter, the precoated metal plate used in the experiment will be described in detail.
[0047]
A zinc-nickel alloy plated steel sheet “Zinclite” (hereinafter referred to as ZL) manufactured by Shin Nihon Co., Ltd. was prepared as an original sheet. The thickness was 0.6 mm. In addition, in a process before plating in the electroplating line, the annealed cold-rolled steel sheet is subjected to temper rolling with rolling rolls whose surface roughness is adjusted, whereby the surface roughness of the zinc-nickel alloy plated steel sheet is obtained. The material which changed was prepared. The zinc-nickel alloy plated steel sheet used in this experiment had a coating weight of 20 g / m on one side.2The nickel content in the plating layer was 12%.
[0048]
Further, a hot-dip galvanized steel sheet “Silver Zinc” (hereinafter referred to as GI) manufactured by Nippon Steel Corporation was also prepared as an original sheet. "Silver zinc" (registered trademark of Nippon Steel Corporation) has a thickness of 0.6 mm, a zinc adhesion amount Z08 (20 g / m2 on one side).2) Was used. An untreated material that had not been subjected to a chemical conversion treatment was used. Further, if necessary, a material in which the surface roughness of the GI was changed by subjecting the already-plated GI to a tempering roll using a prepared rolling roll was prepared.
[0049]
Next, if necessary, the prepared master plate is spray-degreased with an aqueous solution of FC-4336 (manufactured by Nippon Parkerizing Co., Ltd.) at a concentration of 2% by mass at a temperature of 50 ° C., washed with water, dried, and then subjected to electrolytic chromate treatment. Chromate treatment, trivalent chromium treatment, and hexavalent chromium treatment were performed. The electrolytic chromate treatment was carried out in a bath of chromic acid 50 g / L and sulfuric acid 0.3 g / L in a current density of 10 A / dm.2, A predetermined amount of electricity was supplied to perform electrolytic chromate treatment, washed with water, and then dried at a plate temperature of 80 ° C. using a hot-air drying furnace. The amount of deposit in the electrolytic chromate treatment is 15 mg / m in chromium deposit2And In the non-chromate treatment, the trivalent chromium treatment, and the hexavalent chromium treatment, the respective treatment liquids were applied by a roll coater and dried in a hot air oven. The drying condition in the hot air oven was set to 60 ° C. at the ultimate sheet temperature of the steel sheet.
[0050]
The non-chromate treatment liquid used was "CT-E300" manufactured by Nippon Parkerizing Co., Ltd., and the total solid content was 50 mg / m2.2It applied so that it might become. The trivalent chromium treatment solution uses "Surfcoat NRC1000" manufactured by Nippon Paint Co., and has a chromium adhesion amount of 50 mg / m2.2As the hexavalent chromium treatment liquid, "ZM1300AN" manufactured by Nippon Parkerizing Co., Ltd. was used, and the chromium adhesion amount was 50 mg / m2.2It was made to become.
[0051]
Next, a base paint (hereinafter, this surface is referred to as a front surface) is applied to one surface of the metal plate subjected to the chemical conversion treatment, and a back paint is applied to the other surface (hereinafter, this surface is referred to as a back surface). Then, the coating was dried and cured in an induction heating furnace into which hot air was blown under the condition that the ultimate plate temperature of the metal plate was 210 ° C. to obtain a base coating layer. Then, after drying and baking, the painted metal plate was sprayed with water with a spray and cooled with water. Further, on the base coating layer on the surface, a clear paint is applied by a roller curtain coater, and is dried and cured in an induction heating furnace in which hot air is blown under the condition that the reached plate temperature of the metal plate is 230 ° C. A clear coating layer was obtained. Then, after drying and baking, water was sprayed on the coated metal plate by spraying and cooled with water to obtain a pre-coated metal plate sample. As a comparative material, a commercially available primer paint was baked on a metal plate treated with hexavalent chromium under the same conditions as the base paint, and then a commercially available top paint and paint-13 in Table 1 were further topped. As a paint, a pre-coated metal plate which was baked under the same conditions as the clear paint was also prepared.
[0052]
Table 2 shows details of the prepared precoated metal sheet. In addition, as for the back surface paint, “FL100HQ” (colored in gray) manufactured by Nippon Paint Co., Ltd. was applied to all samples in a dry film thickness of 5 μm.
[0053]
[Table 2]
Hereinafter, the details of the evaluation method of the produced precoated metal plate will be described.
1. Gloss measurement
JIS. K. The glossiness of the surface of the precoated metal plate prepared according to 5400.7.6 was measured. The measurement conditions were an incident angle and a light receiving angle of 20 °. Furthermore, those with a measured value of 80% were evaluated as ○, those with 60% or more and less than 80% as Δ, and those with less than 60% as X.
2. Sharpness measurement
The Gd value was measured using a portable clarity gloss meter “PGD” (manufactured by Tokyo Kodensha). Furthermore, those having a measured Gd value of 0.3 or more were evaluated as ○, those having a measured Gd value of 0.1 or more and less than 0.3 were evaluated as Δ, and those measuring less than 0.1 were evaluated as x.
3. Color tone measurement
JIS. K. The color was measured according to 5400.7.4.2. In this experiment, since all the precoated metal plate samples were colored white, attention was paid to the L value, which is an index of whiteness. Those less than 70 were evaluated as x.
4. Coating process adhesion test
The prepared precoated metal plate was bent at 180 ° (close contact bending), and the coating film in the processed portion was visually observed to check for cracks in the coating film. When performing 180 ° bending, the precoated metal plate is bent so that the surface of the precoated metal plate is outside the bend, and two spacers having the same thickness as the precoated metal plate are sandwiched inside the bend. (Commonly known as 2T bending). Further, an adhesive tape was attached to the processed portion, and the remaining state of the coating film when the adhesive tape was vigorously peeled off was visually observed.
[0055]
The evaluation of coating film cracking and peeling was evaluated as follows: ○ when no coating film cracking or peeling was observed, Δ when slight cracking or peeling was observed in the coating film, × when clear large cracking or peeling was observed in the coating film. Was evaluated.
5. Bead galling test with beads
"Bead coating galling test method" is a test method that reproduces the peeling of the coating film that occurs when the precoated metal plate is press-molded and the coating film of the precoated metal plate is pressed with a press die (public technical report 95-1078). First, the prepared precoated metal plate is cut into a test piece of 30 mm (width) × 300 mm (length), and the test piece is sandwiched between a flat mold and a mold provided with a bead having a radius of 4 mmR. At this time, the bead of the mold was sandwiched so as to be pressed against the surface (evaluation surface) of the test piece, and a load of 1 t was applied to press the bead portion of the mold against the evaluation surface of the precoated metal plate. In this state, the precoated metal plate was pulled out at a speed of 200 mm / min, and the state of peeling of the coating film on the evaluation surface of the precoated metal plate rubbed with a bead was visually observed and evaluated.
[0056]
The evaluation was ◎ when the coating film was not completely peeled off, を when the coating film was partially peeled off, and △ when the area ratio of the portion rubbed with the bead was about 20% or more. And the case where the entire surface was peeled off was evaluated as x.
6. Corrosion resistance test
The produced precoated metal plate was subjected to a cylindrical drawing test using a hydraulic Eriksen type 20 t press working tester. The cylindrical drawing test was performed under the following conditions: punch diameter φ50 mm, punch shoulder R3 mm, punch corner R3 mm, die shoulder R3 mm, drawing ratio 2.0, wrinkle pressure 1 t, and worked until the metal plate was drawn out of the mold. In this test, press working was performed under the condition that a commercially available lubricating oil was applied to a metal plate, and processing was performed so that the outside of the work material cup became the surface. Furthermore, these drawn pre-processed steel sheet processed materials are referred to as JIS. Z. Brine was sprayed for 120 hours according to 2371. In addition, the cut end face of the pressed sample was not particularly sealed, and the corrosion test was performed in a state where the cut end face was exposed. The salt water was sprayed on the outside of the cup of the processed material. The degree of corrosion from the end surface of the processed sample surface after the corrosion resistance test was observed and evaluated. The evaluation criteria of the end face part are as follows: when the maximum width of red rust occurrence and the maximum swollen width from the processed end face are 2 mm or less; when it is more than 2 mm and 3 mm or less; when it is more than 3 mm and 4 mm or less; When it was more than 5 mm, it was evaluated as x.
7. Measurement of hexavalent chromium content
In order to determine whether the prepared precoated metal plate contains hexavalent chromium, evaluation was performed by the following method.
[0057]
First, the prepared precoated metal was cut into a size of 50 mm × 50 mm to prepare a test piece. Next, 500 ml of ion-exchanged water was put into a beaker, boiled by a heater, and the test piece was immersed in the boiling water for 30 minutes. Then, the chromium concentration contained in the residual solution from which the test piece was taken out was determined according to JIS. K. The measurement was performed according to the diphenylcarbazide absorption spectrophotometry of No. 0102. Then, from the obtained chromium concentration, the total amount of chromium eluted from the prepared test piece into the boiling water was calculated, and this was defined as the total hexavalent chromium amount contained in the test piece. Further, the calculated total amount of hexavalent chromium was measured using the area of the test piece (2500 mm2) To calculate the amount of hexavalent chromium contained per area of the prepared precoated metal plate, and the content of hexavalent chromium is 0.3 mg / m2In the following cases, it was evaluated as ○ (excluding hexavalent chromium), and 0.3 mg / m2In the case of exceeding, it was evaluated as x (including hexavalent chromium).
[0058]
[Table 3]
Hereinafter, the evaluation results will be described in detail. Table 3 shows the evaluation results of the prepared precoated metal sheets. The precoated metal plate (Examples Nos. 1 to 22) of the present invention is excellent in high gloss, sharpness and color tone, and further excellent in workability and corrosion resistance after processing. Further, the binder resin of the coating film applied on the pre-coated metal plate or the resin of the clear coating film is formed by heating a coating composition comprising a resin which is a linear polymer having a functional group at both ends and a bifunctional compound to form a linear composition. When the film is formed by further promoting the linear polymerization reaction of the polymer, the corrosion resistance of the processed portion is further improved, which is more preferable (Examples Nos. 1, 13 and 14 of the present invention and the present invention). Example No. 8, 16, 17). This type of film that promotes the linear polymerization reaction of this linear polymer has an effect on the corrosion resistance of the processed part when applied to either the base coating film or the clear coating film. When applied to both of the coating films, the corrosion resistance of the processed portion is further improved, so that it is more preferable (Examples of the present invention No. 1, 13, 14 and Examples of the present invention No. 8, 16, 17 and Example of the present invention No. 21, 22). In the case where the surface roughness Ra of the metal plate used as the original plate of the precoated metal plate of the present invention is more than 1.0 (Examples Nos. 10 and 18 of the present invention), the gloss and the sharpness are slightly reduced. The roughness Ra of the metal plate used is more preferably 1.0 or less. Furthermore, when the metal plate used in the present invention is a zinc-nickel alloy-plated steel plate, the corrosion resistance is further improved, which is more preferable (Examples Nos. 1, 9 and 10 of the present invention and Examples Nos. 17 and 18 of the present invention). comparison). The precoated metal sheet of the present invention having an undercoat film thickness of 8 μm and a total film thickness of the undercoat film and the overcoat film of 18 μm (Example No. 12 of the present invention) was slightly glossy. Inferior in image clarity and color tone, it is more preferable that the thickness of the undercoat film be 10 μm or more, and that the total film thickness of the undercoat film and the overcoat film be 20 μm or more.
[0060]
When only one of the aluminum phosphate-based pigment and the silica-based rust-preventive pigment is added to the base coating film of the precoated metal plate (Examples Nos. 19 and 20 of the present invention), bead galling property and corrosion resistance are reduced. Those containing both an aluminum phosphate pigment and a silica pigment are more preferred.
[0061]
The addition amount of the aluminum phosphate-based pigment contained in the base coating film of the precoated metal plate or the addition amount of either one or both of the silica-based anticorrosion pigments is 100 parts by mass of the binder resin of the base coating film. In contrast, those having more than 50 parts by mass (Comparative Examples Nos. 22, 23 and 24) are inadequate because of poor color tone. The total amount of the aluminum phosphate-based pigment, the silica-based rust-preventive pigment, and the coloring pigment contained in the base coating film of the precoated metal plate exceeds 300 parts by mass with respect to 100 parts by mass of the binder resin of the base coating film ( Comparative Example No. 25) is unsuitable because of poor workability. Further, a precoated metal plate using a chemical conversion treatment containing hexavalent chromium is not suitable because chromium, which is an environmentally harmful substance, is easily eluted. As long as the chemical treatment does not contain hexavalent chromium, any of non-chromate chemical treatment, trivalent chromium chemical treatment, and electrolytic chromate chemical treatment may be used, and gloss, sharpness, color tone, workability, bead galling, and processing can be used. Various properties such as corrosion resistance of the part are preferable (Comparison of Invention Examples No. 1, No. 13 and No. 14, or Comparison of Invention Examples No. 8, No. 15, and No. 16).
[0062]
【The invention's effect】
According to the present invention, without using hexavalent chromium, which is concerned about environmental impact, it has high gloss, high image clarity, excellent coating adhesion and corrosion resistance, and is very suitable for press molding. It has become possible to provide a suitable predesigned metal plate with high designability. Therefore, it can be said that the present invention is an invention having extremely high industrial value.
Claims (5)
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| JP2007119858A (en) * | 2005-10-28 | 2007-05-17 | Sumitomo Metal Ind Ltd | Chromium-free precoated steel plate |
| JP2007290294A (en) * | 2006-04-26 | 2007-11-08 | Nippon Steel Corp | Coated base material and its manufacturing method |
| JP2009503253A (en) * | 2005-07-25 | 2009-01-29 | ポスコ | Pre-shielded steel plate with excellent corrosion resistance and weldability and method for producing the same |
| JP2014177002A (en) * | 2013-03-14 | 2014-09-25 | Nisshin Steel Co Ltd | Coated steel plate and method for producing the same |
| WO2014175420A1 (en) * | 2013-04-26 | 2014-10-30 | 新日鐵住金株式会社 | Precoated steel sheet and method for producing same |
| JP2015116734A (en) * | 2013-12-18 | 2015-06-25 | 日新製鋼株式会社 | Coated steel plate |
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| JP2009503253A (en) * | 2005-07-25 | 2009-01-29 | ポスコ | Pre-shielded steel plate with excellent corrosion resistance and weldability and method for producing the same |
| JP4943432B2 (en) * | 2005-07-25 | 2012-05-30 | ポスコ | Pre-shielded steel plate with excellent corrosion resistance and weldability and method for producing the same |
| JP2007119858A (en) * | 2005-10-28 | 2007-05-17 | Sumitomo Metal Ind Ltd | Chromium-free precoated steel plate |
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| JP2014177002A (en) * | 2013-03-14 | 2014-09-25 | Nisshin Steel Co Ltd | Coated steel plate and method for producing the same |
| WO2014175420A1 (en) * | 2013-04-26 | 2014-10-30 | 新日鐵住金株式会社 | Precoated steel sheet and method for producing same |
| JP2015116734A (en) * | 2013-12-18 | 2015-06-25 | 日新製鋼株式会社 | Coated steel plate |
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