JP2004050461A

JP2004050461A - Clear coated metal plate showing sharp hue

Info

Publication number: JP2004050461A
Application number: JP2002207766A
Authority: JP
Inventors: Kenichi Okubo; 大久保　謙一; Shuichi Sugita; 杉田　修一; Kazumi Matsubara; 松原　和美; Koji Mori; 森　浩治
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2002-07-17
Filing date: 2002-07-17
Publication date: 2004-02-19
Anticipated expiration: 2022-07-17
Also published as: JP3430170B1

Abstract

<P>PROBLEM TO BE SOLVED: To provide a clear coating metal plate wherein the hue developed by a color forming pigment 7 is adjusted by the brightness of a lower clear coating film 2 and rich in high grade filling. <P>SOLUTION: The clear coated metal plate is obtained by providing a lower layer clear coating film 2, of which the brightness L valve is adjusted to 25-60 by a translucent pigment 6, on the surface of the metal plate 1 being a substrate and forming an upper surface coating film 3, in which a color pigment 7 is dispersed, on the coating film 3. By this constitution, the developed hue is not scarcely diluted by the reflected light L<SB>3</SB>from the metal plate 1 being the substrate and the light quantity of the reflected light itself from the metal plate 1 is reduced. Therefore, a sharp mild hue is shown. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【産業上の利用分野】
本発明は、光の干渉作用で発現する色調を鮮明にしたクリア塗装金属板に関する。
【０００２】
【従来の技術】
家電製品，ＯＡ機器等の表装材として、クリア塗装を施した塗装金属板が使用され始めている。クリア塗装金属板は、金属光沢を活用した外観を呈することから、従来の着色塗装金属板では得られない雰囲気を醸し出す。
クリア塗装金属板は、着色剤を配合したクリア塗料を塗装原板表面に塗布し、焼付け乾燥することによって製造される。着色剤に染料を使用すると焼付け時に変色しやすく色調が安定しないので、有機顔料を通常使用している。
【０００３】
有機顔料を配合したカラークリア塗膜では、塗膜に入射した光の特定波長成分が有機顔料に吸収され、残りの入射光が下地金属板の表面で反射され、吸収波長成分を除く反射光により特定の色調が発現する。カラークリア塗膜を透過した入射光が有機顔料に吸収される光量は塗膜の厚みによって異なり、厚い塗膜ほど吸収量が大きく、薄い塗膜ほど吸収量が少ない。そのため、発現する色調の膜厚依存性が高く、僅かな膜厚変動によっても色調が微妙に変動しやすい。色調の変動は、製造ロットの異なるクリア塗装金属板を突き合わせて施工する場合に色ムラとして強調される。
有機顔料による色調付与は、下地金属板の金属光沢を損ない、明度Ｌ値が低く黒味がかった冷たい感じの色調を与えやすい。艶消し処理で明度Ｌ値の低下を防止できるが、艶消しによって塗膜の透明感が損なわれ、鮮映性も低くなって高級感がなくなる。
【０００４】
【発明が解決しようとする課題】
本発明者等は、膜厚に応じた色調の変動を抑制するため、有機顔料に代えて発色顔料をクリア塗膜に分散させることを特願２００１−３７６８９３号で提案した。発色顔料は、鱗片状無機基質に透明な金属酸化物皮膜を設けたものであり、塗膜に入射した光が鱗片状無機基質及び金属酸化物皮膜の表面で反射する。鱗片状無機基質，金属酸化物皮膜からの反射光に光路差が生じ、光路差に応じた光の干渉作用によって干渉色が発現する。
【０００５】
発色顔料で色調を発現させるカラークリア塗膜では、有機顔料のような光吸収物質がクリア塗膜に存在せず、基材・金属板，鱗片状無機基質，金属酸化物皮膜それぞれの表面で反射する光の合計が入射光の光量にほぼ等しい。そのため、発色した色調は、クリア塗膜の膜厚に影響されず、明度の低下もない。
本発明者等は、発色顔料を分散させたカラークリア塗膜を種々調査・検討する過程で、色調の鮮明度が基材の色調に大きく影響されることを見出した。具体的には、明度の高い基材を使用すると、発色顔料で発現させた干渉色が不鮮明になりやすい。逆に明度が低すぎる基材を使用すると、基材・金属板の色調が隠蔽されてしまい、クリア塗装金属板特有の透明感が損なわれる。
【０００６】
【課題を解決するための手段】
本発明は、このような知見をベースに完成されたものであり、明度が調節されたクリア塗膜を介在させることにより、発色顔料で発現させた干渉色を強調し、透明感を損なうことなく鮮明度の高い色調を呈するクリア塗装金属板を提供することを目的とする。
【０００７】
本発明のクリア塗装金属板は、その目的を達成するため、基材・金属板の表面に、半透明顔料の分散によって明度Ｌ値を２５〜６０の範囲に調整した下層クリア塗膜を介し、鱗片状無機基質を透明の金属酸化物で被覆した透明又は半透明の発色顔料を分散させた上層クリア塗膜が形成されていることを特徴とする。
【０００８】
下層クリア塗膜に分散させる半透明顔料としては、光透過率が１５〜９０％の範囲にあり、カーボンブラック，グラファイト，金属酸化物，金属硫化物の１種又は２種以上から選ばれたフレークが好ましい。半透明顔料の光透過率は、可視光域の光（たとえば波長５００ｎｍ）に対する値を示し、フレークの厚みやクリア塗料の顔料配合量によって所定範囲に収めることができる。
【０００９】
【実施の形態】
本発明に従ったクリア塗装金属板は、基材・金属板１に下層クリア塗膜２，上層クリア塗膜３を積層した構造（図１）を基本構成としている。基材・金属板１と下層クリア塗膜２との間に、塗膜の密着性を向上させるため顔料無添加のクリア塗膜４を設けても良い。上層クリア塗膜３の上にトップクリア塗膜５を形成すると、塗膜の表面性状が改善され、高級感に富む色調が得られる。
【００１０】
基材・金属板１としては、光沢のある金属表面が観察される製品形態で使用されることから、ステンレス鋼，各種めっき鋼板，アルミニウム，アルミニウム合金，銅，銅合金，マグネシウム，マグネシウム合金等が使用される。基材・金属板１には、クリア塗膜の形成に先立って脱脂・酸洗，クロメート処理，リン酸塩処理，クロムフリー処理等、適宜の塗装前処理が施される。
下層クリア塗膜２を形成するためのクリア塗料は、塗料種に特段の制約が加わるものではないが、透明度の高いアクリル系，ポリエステル系，ウレタン系，ポリオレフィン系，フッ素系，エポキシ系，酢酸ビニル系，クロロプレン系等の有機樹脂，無機系ポリマーを配合した有機樹脂も使用できる。
【００１１】
下層用クリア塗料には、下層クリア塗膜２の明度を調整するため半透明顔料６を配合している。半透明顔料６の他に、透明感の高いパールマイカ，ブルーマイカ，レッドマイカ等の発色顔料や、下層クリア塗膜２の透明性を損なわない範囲で防錆顔料，着色顔料，染料等を必要に応じて添加しても良い。
半透明顔料６には、カーボンブラック，グラファイト，金属酸化物，金属硫化物等のフレークが使用される。たとえば、カーボンブラックやグラファイトは、光吸収物質として通常扱われているが、厚みが２μｍ以下（好ましくは、１μｍ以下）のフレークにすると半透明になる。同様に薄いフレークで半透明を呈する金属酸化物にはＣｒＯ，Ｃｏ_２Ｏ_３，Ｃｏ_３Ｏ_４，ＣｕＯ，ＭｎＯ，Ｍｎ_２Ｏ_３，Ｍｎ_３Ｏ_４，ＳｎＯ，ＭｏＯ_３，ＭｏＯ_４等があり、金属硫化物にはＣｒＳ，Ｃｒ_２Ｓ_３，ＣｏＳ，ＣｏＳ_２，Ｃｏ_２Ｓ_３，ＣｕＳ，ＭｎＳ_２，ＭｏＳ_２，ＳｎＳ，ＣｕＳ，Ｃｕ_２Ｓ，ＦｅＳ等がある。
【００１２】
鱗片状の半透明顔料６を使用しているため、粒状の着色顔料を配合して基材・金属板１全体の明度Ｌ値を調整する方法に比較し、少量の配合量で基材・金属板１の金属感を損なうことなく明度Ｌ値が容易に調整される。しかも、半透明であるため、粒状着色顔料に比較して弱い隠蔽力が却って膜厚変動時の色調変化が小さくなる。
半透明顔料６の光透過率は、次式に従って求められる値であり、可視光域にある５００ｎｍの光に対する透過率が１５〜９０％の範囲にあることが好ましい。
Ｅ＝−ｌｏｇＴ＝ｌｏｇ（Ｉ_０／Ｉ）
ただし、Ｅ：吸光度，Ｔ：透過率（透光度），
Ｉ_０：入射光強度，Ｉ：透過光強度
１５％以下の光透過率では、基材・金属板１に対する隠蔽力が強くなりすぎ、金属感がなくなる。逆に９０％を超える光透過率では、上層クリア塗膜３における光の干渉作用で発色した色調の鮮明度を向上させる半透明顔料６の作用が弱くなる。半透明顔料６には、下層用クリア塗料への配合に先立って分散性，樹脂密着性を改善する適宜の前処理が必要に応じて施される。
【００１３】
半透明顔料６は、下層クリア塗膜２の明度Ｌ値が２５〜６０の範囲となる配合割合で下層用クリア塗料に添加される。半透明顔料６の配合割合は、半透明顔料の材質，光透過率，下層用クリア塗料の樹脂種，下層用クリア塗料に添加する他の添加材等によって変わり、一概に定めることはできない。しかし、下層クリア塗膜２の明度Ｌ値が２５〜６０の範囲に維持される限り、干渉色が適度に強調された鮮明度の高い色調が発現する。
半透明顔料６を配合した下層用クリア塗料を基材・金属板１に塗布した後、クリア塗料の樹脂種や塗布量にもよるが２００〜４００℃で３０〜１２０秒加熱することによって下層クリア塗膜２が基材・金属板１に焼き付けられる。下層クリア塗膜２は、所定の明度Ｌ値を確保し、且つ基材・金属板１の金属光沢を損なわないように５〜２０μｍの膜厚で形成することが好ましい。
【００１４】
上層クリア塗膜３を形成するためのクリア塗料には、下層用クリア塗料と同様な透明度の高い塗料が使用され、必要に応じて防錆顔料，着色顔料，染料等が配合される。
クリア塗料に配合される発色顔料７は、マイカ，ガラスフレーク，アルミナフレーク，シリカフレーク等の鱗片状無機基質７ａに湿式法，ＣＶＤ法，粉末スパッタリング法等で単層又は複層の金属酸化物皮膜７ｂを形成することにより製造される（図２）。基材・金属板１の表面に沿った方向に鱗片状無機基質７ａを配向させるほど発色顔料７の表面で入射光Ｌ_ｉｎが反射する確率が高くなるので、鱗片状無機基質７ａのアスペクト比（厚みに対する最大径の比率）が大きなものほど好ましい。具体的には、アスペクト比が６０以上になると、大半の鱗片状無機基質７ａが基材・金属板１の表面と平行又はほぼ平行な配向性をもって上層クリア塗膜３に分散し、透明の金属酸化物皮膜７ｂの干渉色が強く発現して鮮やかな色調になる。
【００１５】
マイカを鱗片状無機基質７ａとして使用し、湿式法でＴｉＯ_２被覆する場合、種々の方法を採用できる。たとえば、希薄なチタン酸水溶液にマイカを懸濁させて７０〜１００℃に加温し、チタン塩の加水分解生成物である水和酸化チタン粒子をマイカ表面に析出させた後、７００〜１０００℃で高温焼成することによりＴｉＯ_２被覆が形成される。ＴｉＯ_２被覆の膜厚は、チタン塩の濃度，懸濁液の温度，処理時間等の処理条件によって制御できる。
粉末スパッタリング法で発色顔料７を製造する場合、マイカ，ガラスフレーク等の鱗片状無機基質７ａを回転ドラムに入れ、Ｔｉをターゲットとする反応性雰囲気下でスパッタリングすることにより、鱗片状無機基質７ａの表面にＴｉＯ_２被覆が形成される。
【００１６】
何れの方法による場合でも、金属酸化物皮膜７ｂの膜厚調整により、発色させようとする色調が得られる。たとえば、マイカをＴｉＯ_２で被覆した発色顔料７を分散させた上層クリア塗膜３では、ＴｉＯ_２が厚膜になるに従ってシルバー，ゴールド，レッド，カッパー，ライラック，ブルー，グリーンに色調が変わる。ＴｉＯ_２皮膜の上に更にＦｅ_２Ｏ_３皮膜を積層すると鮮やかなゴールド色調でパール光沢感に富む発色顔料，ＦｅＴｉＯ_３皮膜を積層すると鮮やかなグレー系の色調でパール光沢感に富む発色顔料，ＣｏＴｉＯ_３皮膜を積層すると鮮やかなグリーン系の色調でパール光沢感に富む発色顔料が得られる。
【００１７】
透明な金属酸化物皮膜７ｂで鱗片状無機基質７ａを被覆した発色顔料７は、そのままでクリア塗料用樹脂に添加することも可能であるが、必要に応じて適宜の表面処理を施すことができる。表面処理では、クロム酸系，リン酸系，アルミナ系，ジルコニア系，セリウム系等の無機質表面処理剤や各種シランカップリング剤，チタネートカップリング剤，有機モノマー系等の有機質表面処理剤が使用される。表面処理により、クリア塗料用樹脂に対する発色顔料７の分散性及び隣接樹脂層との層間密着性が改善される。
【００１８】
上層クリア塗膜３は、下層クリア塗膜２と同様な塗布・焼付け条件で形成され、所定の色調を安定して発現させるため好ましくは５〜２０μｍの膜厚に調整される。
上層クリア塗膜３を最表層とするクリア塗装金属板では、製品形状に加工されることもあるので、基材・金属板１，下層クリア塗膜２に対する密着性，塗膜自体の柔軟性に富むことが要求される。また、柔軟性に相反する機能として耐疵付き性が要求されることもある。このような目的に応じた特性を考慮して上層用クリア塗料の樹脂系が選択され、たとえばメラミン，イソシアネート等の硬化剤を適宜配合して上層クリア塗膜３を形成することも可能である。
【００１９】
基材・金属板１と下層クリア塗膜２との間に、基材・金属板１に対するクリア塗膜の密着性を高めるため発色顔料７を含まないプライマクリア塗膜４を設けても良い。プライマクリア塗膜４形成用のプライマ塗料は、塗料種に特段の制約が加わるものではないが、エポキシ樹脂，エポキシ変性ポリエステル樹脂，ウレタン樹脂，ウレタン変性ポリエステル樹脂等が使用される。プライマクリア塗膜４によって、塗装前処理した基材・金属板１と半透明顔料６を分散させた下層クリア塗膜２との密着性が一層向上する。プライマクリア塗膜４を形成する場合、プライマクリア塗膜４の膜厚を１〜１０μｍの範囲にすることが好ましい。
【００２０】
上層クリア塗膜３の上に、更にトップクリア塗膜５を積層しても良い。トップクリア塗膜５形成用のクリア塗料は、特に限定されるものではないが、発色顔料７を分散させたクリア塗膜２，３と同種又は類似の塗料が好ましい。具体的には、透明度の高いアクリル系，ポリエステル系，ウレタン系，ポリオレフィン系，フッ素系，エポキシ系，酢酸ビニル系，クロロプレン系等の有機樹脂や無機系ポリマーを配合した有機樹脂も使用できる。透明性を損なわない範囲で、防錆顔料，着色顔料，染料等を必要に応じてクリア塗料に添加しても良い。
【００２１】
トップクリア塗膜５は、上層クリア塗膜３から突出しがちな発色顔料７を覆い、塗膜表面の平滑度を向上させると共に、発色顔料７での光反射を均一化することにより光の干渉作用で発色した色調を安定化させる。その結果、濁りのない鮮明な干渉色が発現し、高級感のある色調が付与される。しかも、トップクリア塗膜５による平滑化も図られ、表面性状の良好なクリア塗装金属板が得られる。
【００２２】
【作用】
明度Ｌ値が２５〜６０の範囲にある下層クリア塗膜２は、上層クリア塗膜３に分散している発色顔料７による光の干渉作用で発現する色調を鮮明化する。下層クリア塗膜２の明度が色調の鮮明化に及ぼす影響は次のように推察される。
入射光Ｌ_ｉｎは、発色顔料７の鱗片状無機基質７ａ，金属酸化物皮膜７ｂで反射し、反射光Ｌ_１，Ｌ_２の間に光路差ΔＬが生じる（図２）。光路差ΔＬによる干渉作用で発色するが、上層クリア塗膜３を透過する入射光Ｌ_ｉｎもある。透過した入射光Ｌ_ｉｎは、基材・金属板１の表面で反射する。基材・金属板１の表面からの反射光Ｌ_３が強いと、光の干渉作用により発現した色調が希釈され、鮮明度が低下する。
【００２３】
これに対し、基材・金属板１と上層クリア塗膜３との間に下層クリア塗膜２を介在させると、上層クリア塗膜３を透過した入射光Ｌ_ｉｎの一部が半透明顔料６で吸収され、基材・金属板１の表面からの反射光Ｌ_３が弱くなる（図３）。その結果、光の干渉作用により発現した色調の反射光Ｌ_３による希釈が抑制され、色調の鮮明度が向上する。しかも、半透明顔料６の表面で反射する光Ｌ_４もあり、基材・金属板１の到達して反射する入射光Ｌ_ｉｎの光量が低下するので、金属表面のギラギラ感が抑えられ、マイルドな色調をもつ塗膜表面になる。また、膜厚変動が色調に及ぼす影響も抑制される。
下層クリア塗膜２に配合した半透明顔料６により基材・金属板１の表面からの反射光が適度に抑えられ、光の干渉作用で発色した色調が鮮明化する。色調の鮮明度は彩度（ａ値，ｂ値）による影響が大きいことから、均等色空間における透明度面内の２座標間の色刺激を色差として表面するクロマティクネス指数で鮮明度を表すことができる。クロマティクネス指数は、（ａ^２＋ｂ^２）^１／２として算出される。
【００２４】
【実施例１】
板厚０．４ｍｍのＳＵＳ４３０ステンレス鋼板を塗装原板に使用した。塗装原板を２％塩酸で酸洗し、酸系の表面処理を施した後、クロム換算付着量２０ｍｇ／ｍ^２の塗布型クロメート処理を施した。
下層用クリア塗料として、高分子ポリエステル系クリア樹脂塗料（ＰＭ５０００：日本ペイント株式会社製）に半透明顔料を配合したクリア塗料を用意した。半透明顔料には、（ａ）〜（ｄ）のフレークを使用した。なお、各フレークの光透過率は、ダブルビーム，ダイノードフィードバックによるダイレクトレシオ方式の分光光度計を用い、半透明顔料６を適量配合した膜厚５μｍのクリア塗膜に波長５００ｎｍの可視光を照射したときの透過光を測定し、式：Ｅ＝−ｌｏｇＴ＝ｌｏｇ（Ｉ_０／Ｉ）に従って算出された値で示す。
【００２５】

【００２６】
上層用クリア塗料には、同じ高分子ポリエステル系クリア樹脂塗料に発色顔料を配合したクリア塗料を用意した。発色顔料としては、膜厚９０ｎｍのＴｉＯ_２被覆を形成したアスペクト比１５０，中心粒径３０μｍのカッパー色マイカフレークを使用した。
塗装前処理した塗装原板に下層用クリア塗料を塗布し、到達板温２３０℃で６０秒加熱することにより乾燥膜厚５μｍの下層クリア塗膜２を形成した。形成された下層クリア塗膜２の明度Ｌ値を測定したところ、クリア塗膜Ａ〜Ｄの明度Ｌ値は配合した半透明顔料６に応じて異なっていた。
【００２７】
下層クリア塗膜２の上に更に上層用クリア塗料を塗布し、同様な焼付け条件下で膜厚１０μｍの上層クリア塗膜３を形成した。
得られた各クリア塗装金属板の色調を測定し、色調の鮮明度に及ぼす下層クリア塗膜の影響を調査した。なお、色調の鮮明度は、クロマティクネス指数により評価した。比較のため、下層クリア塗膜２を形成しない他は同じ条件下で上層クリア塗膜３を形成したクリア塗装金属板についても、色調及び色調の鮮明度を調査した。
【００２８】
表２の調査結果にみられるように、基材・金属板１と上層クリア塗膜３との間に下層クリア塗膜２を介在させることにより、発色顔料７で発色させた色調ではａ値が１．５〜３．５倍も高くなっていることが確認される。他方、下層クリア塗膜２を介在させない比較例５〜８では、発色顔料７を１０％配合（約４０％の増量に相当する）した場合でもａ値の増加が小さく、鮮明度の向上も１０％程度に過ぎなかった。
【００２９】

【００３０】
【実施例２】
明度Ｌ値を種々変化させた膜厚５μｍの下層クリア塗膜２を形成する以外には、実施例１と同様に発色顔料７を７％配合した上層クリア塗膜３を形成した。本実施例では、下層用クリア塗料に配合する半透明顔料６として厚み（ひいては、光透過率）が異なる鱗片状ＭｏＳ_２を使用することにより、下層クリア塗膜２の明度Ｌ値を変えた。
鱗片状ＭｏＳ_２を３質量％配合した下層用クリア塗料から形成された下層クリア塗膜２の明度Ｌ値は、鱗片状ＭｏＳ_２の厚みに応じて表３に示すように変化していた。
【００３１】

【００３２】
得られた各クリア塗装金属板について、色調を測定し、色調の鮮明度及び金属素地の外観に及ぼす下層クリア塗膜２の影響を調査した。金属素地の外観は、金属素地が良好に観察されたものを○，金属素地が観察可能なものを△，金属素地が観察できなかったものを×と評価した。
表４の調査結果にみられるように、基材・金属板１／上層クリア塗膜３間の下層クリア塗膜２に鱗片状ＭｏＳ_２を分散させることによって、発色顔料７で発色させた色調の鮮明度が改善されていることが判る。なかでも、光透過率が１５〜９０％の範囲に収まる厚みの鱗片状ＭｏＳ_２を分散させた下層クリア塗膜２を設けたクリア塗装金属板では、鱗片状ＭｏＳ_２が分散していない比較例５に比べて色調の鮮明度が格段に改善されていた。しかし、厚すぎる鱗片状ＭｏＳ_２を分散させた比較例６，７では、光透過率が１５％以下となったため金属素地を観察できず、目標とするクリア塗装金属板が得られなかった。
【００３３】

【００３４】
【発明の効果】
以上に説明したように、光の干渉作用で色調を発現する発色顔料を分散させたクリア塗膜と基材・金属板との間に明度Ｌ値が調整された下層クリア塗膜を介在させるとき、発色した色調が基材・金属板からの反射光で希釈されることが少なくなり、金属板からの反射光自体の光量も減少するので、鮮明でマイルドな色調を呈するクリア塗装金属板が得られる。光の干渉作用による発色で色調を付与しているため、クリア塗膜の膜厚変動による影響が少なく、発現した色調も安定する。このような特性を活用し、家電機器，ＯＡ機器，厨房機器等の広範な分野で表装材，内装材として使用可能なクリア塗装金属板が提供される。
【図面の簡単な説明】
【図１】本発明に従ったクリア塗装金属板の塗膜構成を示す断面図
【図２】上層クリア塗膜に分散させた発色顔料で光の干渉作用が生じることを示す説明図
【図３】上層クリア塗膜を透過した入射光の一部が下層クリア塗膜で吸収され、残りが基材・金属板１で反射されることを示す説明図
【符号の説明】
１：基材・金属板　　２：下層クリア塗膜　　３：上層クリア塗膜　　４：顔料無添加のクリア塗膜　　５：トップクリア塗膜　　６：半透明顔料　　７：発色顔料
Ｌ_ｉｎ：入射光　　Ｌ_ｏｕｔ：反射光
Ｌ_１：発色顔料７の鱗片状無機基質７ａで反射した光
Ｌ_２：発色顔料７の金属酸化物皮膜７ｂで反射した光
Ｌ_３：基材・金属板１の表面で反射した光
Ｌ_４：下層クリア塗膜２の半透明顔料６で反射した光[0001]
[Industrial applications]
The present invention relates to a clear painted metal plate in which the color tone developed by the interference of light is sharpened.
[0002]
[Prior art]
As a surface material for home electric appliances, OA equipment, and the like, a coated metal plate with a clear coating has begun to be used. Since the clear painted metal plate has an appearance utilizing metallic luster, it creates an atmosphere that cannot be obtained with a conventional colored painted metal plate.
The clear-painted metal plate is manufactured by applying a clear paint containing a coloring agent to the surface of the original paint plate and baking and drying. When a dye is used as a colorant, an organic pigment is usually used because the color tends to be discolored at the time of baking and the color tone is not stable.
[0003]
In a color clear coating film containing an organic pigment, the specific wavelength component of the light incident on the coating film is absorbed by the organic pigment, and the remaining incident light is reflected by the surface of the base metal plate, and the reflected light excluding the absorption wavelength component A specific color tone appears. The amount of incident light transmitted through the color clear coating film and absorbed by the organic pigment differs depending on the thickness of the coating film. The thicker the coating film, the larger the absorption amount, and the thinner the coating film, the smaller the absorption amount. Therefore, the color tone to be developed is highly dependent on the film thickness, and the color tone is liable to change slightly even with a slight change in the film thickness. Variations in color tone are emphasized as color unevenness when clear coating metal plates of different production lots are put together.
The use of an organic pigment to impart a color tone impairs the metallic luster of the underlying metal plate, and tends to give a low-value L value and a blackish, cool color tone. The matting treatment can prevent a decrease in the lightness L value, but the matting impairs the transparency of the coating film, lowers the sharpness, and eliminates the luxury.
[0004]
[Problems to be solved by the invention]
The present inventors have proposed in Japanese Patent Application No. 2001-376893 to disperse a coloring pigment instead of an organic pigment in a clear coating film in order to suppress a change in color tone according to the film thickness. The coloring pigment is a scaly inorganic substrate provided with a transparent metal oxide film, and light incident on the coating film is reflected on the surface of the scaly inorganic substrate and the metal oxide film. An optical path difference is generated in the reflected light from the scaly inorganic substrate and the metal oxide film, and an interference color is generated by an interference action of light according to the optical path difference.
[0005]
In the color clear coating film that expresses the color tone with the coloring pigment, the light absorbing substance such as the organic pigment does not exist in the clear coating film and is reflected on the surface of the base material, metal plate, flaky inorganic substrate, and metal oxide film. The total amount of incident light is substantially equal to the amount of incident light. Therefore, the developed color tone is not affected by the thickness of the clear coating film, and there is no decrease in lightness.
The present inventors have found in the course of various investigations and examinations of a color clear coating film in which a coloring pigment is dispersed, that the sharpness of the color tone is greatly affected by the color tone of the substrate. Specifically, when a base material having high brightness is used, the interference color expressed by the coloring pigment tends to be unclear. Conversely, if a base material having too low a brightness is used, the color tone of the base material / metal plate will be concealed, and the transparency characteristic of the clear coated metal plate will be impaired.
[0006]
[Means for Solving the Problems]
The present invention has been completed on the basis of such findings, by interposing a clear coating film whose brightness has been adjusted, enhances the interference color expressed by the coloring pigment, without impairing the transparency. It is an object of the present invention to provide a clear painted metal plate exhibiting a high color tone.
[0007]
The clear coated metal plate of the present invention, in order to achieve the object, on the surface of the base metal plate, through a lower clear coating film whose lightness L value is adjusted to a range of 25 to 60 by dispersion of a translucent pigment, An upper clear coating film in which a transparent or translucent color pigment in which a scaly inorganic substrate is coated with a transparent metal oxide is dispersed is formed.
[0008]
The semi-transparent pigment dispersed in the lower clear coating film has a light transmittance in the range of 15 to 90%, and is a flake selected from one or more of carbon black, graphite, metal oxide, and metal sulfide. Is preferred. The light transmittance of the translucent pigment indicates a value with respect to light in the visible light range (for example, a wavelength of 500 nm), and can be within a predetermined range depending on the thickness of the flakes and the amount of the pigment in the clear paint.
[0009]
Embodiment
The clear coated metal plate according to the present invention has a basic structure in which a lower clear coating film 2 and an upper clear coating film 3 are laminated on a substrate / metal plate 1 (FIG. 1). A pigment-free clear coating film 4 may be provided between the base material / metal plate 1 and the lower clear coating film 2 in order to improve the adhesion of the coating film. When the top clear coating film 5 is formed on the upper clear coating film 3, the surface properties of the coating film are improved, and a high-grade color tone is obtained.
[0010]
The base material / metal plate 1 is used in a product form in which a glossy metal surface is observed, and thus stainless steel, various plated steel plates, aluminum, aluminum alloy, copper, copper alloy, magnesium, magnesium alloy and the like are used. used. Prior to the formation of the clear coating film, the base material / metal plate 1 is subjected to an appropriate pre-coating treatment such as degreasing, pickling, chromate treatment, phosphate treatment, and chromium-free treatment.
The clear paint for forming the lower clear coating film 2 is not particularly limited in the kind of the paint, but has high transparency acrylic, polyester, urethane, polyolefin, fluorine, epoxy, vinyl acetate. Organic resins such as those based on chloroprene and chloroprene, and organic resins containing an inorganic polymer can also be used.
[0011]
The clear paint for the lower layer contains a translucent pigment 6 for adjusting the brightness of the lower clear coating film 2. In addition to the translucent pigment 6, a coloring pigment such as pearl mica, blue mica, red mica or the like having a high transparency, or a rust-preventive pigment, a coloring pigment, a dye, etc. are required as long as the transparency of the lower clear coating film 2 is not impaired. May be added according to the conditions.
As the translucent pigment 6, flakes such as carbon black, graphite, metal oxide, and metal sulfide are used. For example, carbon black and graphite are usually treated as light absorbing substances, but when they are made into flakes having a thickness of 2 μm or less (preferably 1 μm or less), they become translucent. Similarly, metal oxides exhibiting translucency with thin flakes include CrO, Co ₂ O ₃ , Co ₃ O ₄ , CuO, MnO, Mn ₂ O ₃ , Mn ₃ O ₄ , SnO, MoO ₃ , MoO _{4 and the} like. , the metal sulfide is _{_{_{_{CrS, Cr 2 S 3, CoS}}}} , CoS 2, Co 2 S 3, CuS, MnS 2, MoS 2, SnS, CuS, Cu 2 S, is FeS or the like.
[0012]
Since the scale-like translucent pigment 6 is used, compared with the method of adjusting the lightness L value of the entire base material / metal plate 1 by mixing a granular color pigment, the base material / metal The lightness L value can be easily adjusted without impairing the metallic feeling of the plate 1. In addition, since it is translucent, the hiding power is weaker than that of the granular color pigment, and the color tone change when the film thickness changes is rather small.
The light transmittance of the translucent pigment 6 is a value determined according to the following equation, and the transmittance for light of 500 nm in the visible light region is preferably in the range of 15 to 90%.
E = −logT = log (I ₀ / I)
Here, E: absorbance, T: transmittance (light transmittance),
At a light transmittance of I ₀ : incident light intensity and I: transmitted light intensity of 15% or less, the hiding power to the base material / metal plate 1 becomes too strong, and the metallic feeling disappears. Conversely, if the light transmittance exceeds 90%, the effect of the translucent pigment 6 for improving the sharpness of the color tone formed by the interference of light in the upper clear coating film 3 becomes weak. The translucent pigment 6 is optionally subjected to an appropriate pretreatment for improving dispersibility and resin adhesion prior to its incorporation into the lower layer clear paint.
[0013]
The translucent pigment 6 is added to the clear paint for the lower layer at a blending ratio such that the lightness L value of the lower clear coating film 2 is in the range of 25 to 60. The blending ratio of the translucent pigment 6 varies depending on the material of the translucent pigment, the light transmittance, the resin type of the clear paint for the lower layer, other additives added to the clear paint for the lower layer, and the like, and cannot be unconditionally determined. However, as long as the lightness L value of the lower clear coating film 2 is maintained in the range of 25 to 60, a high-definition color tone in which the interference color is appropriately emphasized is developed.
After applying the clear paint for the lower layer containing the translucent pigment 6 to the base material / metal plate 1, the lower layer is cleared by heating at 200 to 400 ° C. for 30 to 120 seconds, depending on the resin type and the amount of the clear paint. The coating film 2 is baked on the substrate / metal plate 1. The lower clear coating film 2 is preferably formed with a thickness of 5 to 20 μm so as to secure a predetermined lightness L value and not to impair the metallic luster of the substrate / metal plate 1.
[0014]
As the clear paint for forming the upper clear coating film 3, a paint having high transparency similar to the clear paint for the lower layer is used, and a rust preventive pigment, a coloring pigment, a dye, and the like are blended as necessary.
The coloring pigment 7 blended in the clear paint is a single-layer or multiple-layer metal oxide film formed on a scaly inorganic substrate 7a such as mica, glass flake, alumina flake, silica flake by a wet method, a CVD method, a powder sputtering method, or the like. 7b (FIG. 2). Since the probability of the incident light L _in the surface of the coloring pigment 7 enough to orient the scale-like inorganic substrates 7a in a direction along the surface of the substrate, the metal plate 1 is reflected increases, the aspect ratio of the scaly inorganic substrates 7a ( The larger the ratio of the maximum diameter to the thickness, the better. Specifically, when the aspect ratio becomes 60 or more, most of the flaky inorganic substrate 7a is dispersed in the upper clear coating film 3 with an orientation parallel or almost parallel to the surface of the substrate / metal plate 1, and the transparent metal The interference color of the oxide film 7b is strongly expressed and a vivid color tone is obtained.
[0015]
When mica is used as the scaly inorganic substrate 7a and coated with TiO ₂ by a wet method, various methods can be adopted. For example, mica is suspended in a dilute aqueous solution of titanic acid and heated to 70 to 100 ° C. to precipitate hydrated titanium oxide particles, which are hydrolysis products of titanium salts, on the mica surface. Baking at a high temperature to form a TiO ₂ coating. The thickness of the TiO ₂ coating can be controlled by processing conditions such as the concentration of the titanium salt, the temperature of the suspension, and the processing time.
In the case of producing the coloring pigment 7 by the powder sputtering method, the flaky inorganic substrate 7a such as mica, glass flake, etc. is put into a rotating drum and sputtered under a reactive atmosphere using Ti as a target. A TiO ₂ coating is formed on the surface.
[0016]
In any case, the color tone to be developed can be obtained by adjusting the thickness of the metal oxide film 7b. For example, in the upper clear coating film 3 in which the coloring pigment 7 in which mica is coated with TiO ₂ is dispersed, the color tone changes to silver, gold, red, copper, lilac, blue, and green as the TiO ₂ becomes thicker. When a Fe ₂ O ₃ film is further laminated on the TiO ₂ film, a vivid gold color and a pearly glossy color pigment are laminated. When a FeTiO ₃ film is laminated, a vivid grayish color and a pearly glossy color pigment, CoTiO. By laminating _three films, a color pigment having a bright green color tone and rich in pearl luster can be obtained.
[0017]
The coloring pigment 7 in which the flaky inorganic substrate 7a is coated with the transparent metal oxide film 7b can be added as it is to the resin for clear coating, but can be subjected to an appropriate surface treatment if necessary. . In the surface treatment, chromic acid-based, phosphoric acid-based, alumina-based, zirconia-based, cerium-based inorganic surface treatment agents, and various silane coupling agents, titanate coupling agents, and organic monomer-based organic surface treatment agents are used. You. By the surface treatment, the dispersibility of the coloring pigment 7 in the resin for the clear paint and the interlayer adhesion with the adjacent resin layer are improved.
[0018]
The upper clear coating film 3 is formed under the same coating and baking conditions as the lower clear coating film 2 and is preferably adjusted to a thickness of 5 to 20 μm in order to stably develop a predetermined color tone.
The clear coated metal plate having the upper clear coating film 3 as the outermost layer may be processed into a product shape, so that the adhesion to the base material / metal plate 1 and the lower clear coating film 2 and the flexibility of the coating film itself are reduced. It is required to be rich. In addition, scratch resistance may be required as a function contradictory to flexibility. The resin system of the clear paint for the upper layer is selected in consideration of such characteristics according to the purpose, and the clear clear coating film 3 can be formed by appropriately blending a curing agent such as melamine and isocyanate.
[0019]
A primer clear coating film 4 containing no coloring pigment 7 may be provided between the base material / metal plate 1 and the lower clear coating film 2 in order to enhance the adhesion of the clear coating film to the base material / metal plate 1. As the primer paint for forming the primer clear coating film 4, although there is no particular restriction on the kind of the paint, an epoxy resin, an epoxy-modified polyester resin, a urethane resin, a urethane-modified polyester resin or the like is used. The primer clear coating film 4 further improves the adhesion between the base material / metal plate 1 pre-treated for coating and the lower clear coating film 2 in which the translucent pigment 6 is dispersed. When the primer clear coating film 4 is formed, it is preferable that the thickness of the primer clear coating film 4 be in the range of 1 to 10 μm.
[0020]
A top clear coating film 5 may be further laminated on the upper clear coating film 3. The clear coating material for forming the top clear coating film 5 is not particularly limited, but is preferably the same or similar coating material as the

clear coating films

2 and 3 in which the coloring pigment 7 is dispersed. Specifically, an organic resin such as an acrylic, polyester, urethane, polyolefin, fluorine, epoxy, vinyl acetate, chloroprene, or other organic resin having a high degree of transparency and an inorganic polymer can be used. Rust-preventing pigments, coloring pigments, dyes and the like may be added to the clear paint as needed, as long as the transparency is not impaired.
[0021]
The top clear coating film 5 covers the coloring pigment 7 that tends to protrude from the upper clear coating film 3 to improve the smoothness of the coating film surface and to make the light reflection on the coloring pigment 7 uniform so that the light interference effect is obtained. Stabilizes the developed color tone. As a result, a clear interference color without turbidity is exhibited, and a high-grade color tone is provided. In addition, smoothing by the top clear coating film 5 is also achieved, and a clear coated metal plate having good surface properties can be obtained.
[0022]
[Action]
The lower clear coating film 2 having a lightness L value in the range of 25 to 60 sharpens the color tone developed by the light interference effect of the coloring pigment 7 dispersed in the upper clear coating film 3. The effect of the brightness of the lower clear coating film 2 on the sharpness of the color tone is presumed as follows.
The incident light _{L in} the scale-like inorganic substrates 7a of color pigments 7, reflected by the metal oxide film 7b, the optical path difference ΔL is generated between the reflected light _L 1, _{L 2} (FIG. 2). Colored, with interferences caused by the optical path difference ΔL, there is also the incident light L _in passing through the upper clear coating 3. The transmitted incident light L _in is reflected by the surface of the substrate, the metal plate 1. A strong reflected light L ₃ from the substrate-metal plate first surface, color tone expressed by the interference action of light is diluted, the sharpness decreases.
[0023]
In contrast, when an intervening lower clearcoats 2 between the substrate-metal plate 1 and the upper clear coating 3, the upper clear coating film 3 partially translucent pigments of the incident light L _in passing through the 6 in is absorbed, the reflected light L ₃ from the surface of the substrate, the metal plate 1 becomes weaker (Fig. 3). As a result, diluted by the reflected light L ₃ of the tone expressed by the interference effect of light can be suppressed, thus improving the sharpness of the color tone. Moreover, the light L ₄ reflected by the surface of the semi-transparent pigments 6 also has, since the amount of incident light L _in the reflection to reach the substrate, the metal plate 1 is lowered, is suppressed glittering feeling of the metal surface, mild The surface of the coating film has a rich color tone. Further, the effect of the variation in film thickness on the color tone is also suppressed.
The reflected light from the surface of the base material / metal plate 1 is appropriately suppressed by the translucent pigment 6 blended in the lower clear coating film 2, and the color tone generated by the interference of light is sharpened. Since the sharpness of the color tone is greatly affected by the saturation (a value, b value), the sharpness can be expressed by a chromaticness index which is a color difference between two coordinates on a transparency plane in a uniform color space. it can. The chromaticness index is calculated as (a ² + b ² ) ^1/2 .
[0024]
Embodiment 1
A SUS430 stainless steel plate having a thickness of 0.4 mm was used as a coating original plate. The coated base plate was pickled with 2% hydrochloric acid, subjected to an acid-based surface treatment, and then subjected to a coating type chromate treatment with a chromium equivalent adhesion amount of 20 mg / m ² .
As the lower layer clear coating, a clear coating prepared by blending a translucent pigment with a polymer polyester clear resin coating (PM5000: manufactured by Nippon Paint Co., Ltd.) was prepared. Flakes (a) to (d) were used as the translucent pigment. The light transmittance of each flake was measured using a direct-ratio spectrophotometer using double beam and dynode feedback, and a clear coating film having a thickness of 5 μm in which an appropriate amount of translucent pigment 6 was blended was irradiated with visible light having a wavelength of 500 nm. The transmitted light at that time is measured, and is represented by a value calculated according to the formula: E = −logT = log (I ₀ / I).
[0025]

[0026]
As the clear coating for the upper layer, a clear coating prepared by blending a coloring pigment with the same high molecular polyester clear resin coating was prepared. As the coloring pigment, a copper-colored mica flake having an aspect ratio of 150 and a central particle diameter of 30 μm, on which a TiO ₂ coating having a thickness of 90 nm was formed, was used.
The lower layer clear coating material 2 was formed by applying a lower layer clear coating material to the pretreated coating original plate and heating it at an ultimate plate temperature of 230 ° C. for 60 seconds. When the lightness L value of the formed lower clear coating film 2 was measured, the lightness L values of the clear coating films A to D differed depending on the blended translucent pigment 6.
[0027]
An upper clear coating was further applied on the lower clear coating 2 to form a 10 μm thick upper clear coating 3 under the same baking conditions.
The color tone of each of the obtained clear coated metal plates was measured, and the effect of the lower clear coating film on the sharpness of the color tone was investigated. The sharpness of the color tone was evaluated by a chromaticness index. For comparison, the color tone and the sharpness of the color tone were also examined for the clear coated metal plate on which the upper clear coating film 3 was formed under the same conditions except that the lower clear coating film 2 was not formed.
[0028]
As can be seen from the survey results in Table 2, by interposing the lower clear coating film 2 between the base material / metal plate 1 and the upper clear coating film 3, the a value was It is confirmed that it is 1.5 to 3.5 times higher. On the other hand, in Comparative Examples 5 to 8 in which the lower clear coating film 2 was not interposed, even when the coloring pigment 7 was blended at 10% (corresponding to an increase of about 40%), the increase in the a value was small, and the sharpness was improved by 10%. %.
[0029]

[0030]
Embodiment 2
An upper clear coating film 3 containing 7% of a coloring pigment 7 was formed in the same manner as in Example 1, except that a lower clear coating film 2 having a film thickness of 5 μm having variously changed lightness L values was formed. In this example, the lightness L value of the lower clear coating film 2 was changed by using flaky MoS ₂ having a different thickness (and, consequently, light transmittance) as the translucent pigment 6 to be mixed into the lower clear paint.
Lightness L value of the lower clearcoats 2 formed scaly MoS ₂ to 3 wt% compounded for lower layer clear paint was changed as shown in Table 3 according to the thickness of the scaly MoS _2.
[0031]

[0032]
The color tone of each of the obtained clear coated metal plates was measured, and the effect of the lower clear coating film 2 on the sharpness of the color tone and the appearance of the metal substrate was investigated. The appearance of the metal substrate was evaluated as ○ when the metal substrate was favorably observed, Δ when the metal substrate was observable, and × when the metal substrate was not observed.
As can be seen from the investigation results in Table 4, by dispersing the flaky MoS ₂ in the lower clear coating film 2 between the base material / metal plate 1 and the upper clear coating film 3, It can be seen that the definition has been improved. Above all, in the clear coated metal plate provided with the lower clear coating film 2 in which the flaky MoS ₂ having a light transmittance falling within the range of 15 to 90% is provided, a comparative example in which the flaky MoS ₂ is not dispersed. Compared with No. 5, the sharpness of the color tone was remarkably improved. However, in Comparative Examples 6 and 7 in which flake-like MoS ₂ that was too thick was dispersed, the light transmittance was 15% or less, so that the metal substrate could not be observed, and the target clear-coated metal plate could not be obtained.
[0033]

[0034]
【The invention's effect】
As described above, when interposing a lower clear coating film in which the lightness L value is adjusted between a clear coating film in which a color pigment that expresses a color tone due to light interference and a base material / metal plate are dispersed. Because the color tone that is developed is less diluted by the reflected light from the base material and metal plate, the amount of reflected light itself from the metal plate also decreases, resulting in a clear painted metal plate with a clear and mild color tone. Can be Since the color tone is given by the color development due to the interference of light, the influence of the variation in the thickness of the clear coating film is small, and the developed color tone is also stabilized. Utilizing such characteristics, a clear painted metal plate that can be used as a surface covering material or an interior material in a wide range of fields such as home appliances, OA appliances, kitchen appliances, and the like is provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a coating film configuration of a clear-coated metal plate according to the present invention. FIG. 2 is an explanatory diagram showing that light interference is caused by a coloring pigment dispersed in an upper clear coating film. Explanatory drawing showing that part of the incident light transmitted through the upper clear coating film is absorbed by the lower clear coating film, and the rest is reflected by the base material / metal plate 1.
1: Base material / metal plate 2: Lower clear coating film 3: Upper clear coating film 4: Clear coating film without pigments 5: Top clear coating film 6: Translucent pigment 7: Color pigment L _in : Incident light L _out : Reflected light L ₁ : Light L ₂ reflected by the flaky inorganic substrate 7 a of the color pigment 7: Light L ₃ reflected by the metal oxide film 7 b of the color pigment 7: Light reflected by the surface of the base material / metal plate 1 L ₄ : light reflected by translucent pigment 6 of lower clear coating film 2

Claims

On the surface of a base material / metal plate, a transparent or semi-transparent coating of a scaly inorganic substrate with a transparent metal oxide via a lower clear coating film whose lightness L value is adjusted to a range of 25 to 60 by dispersion of a translucent pigment. A clear coated metal plate having a clear color tone, wherein an upper clear coating film in which a transparent coloring pigment is dispersed is formed.

The clear coated metal sheet according to claim 1, wherein a translucent pigment having a light transmittance of 15 to 90% is dispersed in the lower clear coating film.

3. The clear-coated metal sheet according to claim 1, wherein one or more flakes of carbon black, graphite, metal oxide, and metal sulfide are formed into a thin film, and a translucent pigment having an adjusted light transmission amount is used.