JP2004209720A

JP2004209720A - Coated metal plate excellent in processability and scratch resistance

Info

Publication number: JP2004209720A
Application number: JP2002379928A
Authority: JP
Inventors: Kenji Sakado; 健二坂戸; Keimei Mori; 啓明森; Hiroshi Tsuburaya; 浩圓谷
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2002-12-27
Filing date: 2002-12-27
Publication date: 2004-07-29
Anticipated expiration: 2022-12-27
Also published as: JP4090031B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated metal plate made excellent in both conflicting processability and scratch resistance by dispersing hard thermosetting organic resin particles in the resin coating film formed on the surface of a metal plate. <P>SOLUTION: In the coated metal plate wherein spherical thermosetting organic resin particles P harder than the resin coating film R are dispersed in the organic resin coating film R with a pencil hardness of HB or less formed on the surface of the metal plate M, the maximum particle size of the thermosetting organic resin particles P is below three times the average film thickness (h) of the resin coating film R and 2-20 mass % of the thermosetting organic resin particles P having a particle size larger than the average film thickness of the resin coating film R are dispersed in the resin coating film R. The protruded parts of the thermosetting organic resin particles P dispersed in the resin coating film R are covered with the thin film of the resin coating film R. The processability of the coated metal plate is charged with the soft base resin coating film R and the abrasion resistance and scratch resistance thereof are charged with the hard particles P in the coating film to obtain the coated metal plate having both characteristics. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【産業上の利用分野】
本発明は、外装建材，内装建材，表装材，器物外板等に使用される、加工性および耐傷付き性に優れた塗装金属板に関する。
【０００２】
【従来の技術】
塗装金属板、特に塗装鋼板は、目標形状に成形加工されて外装建材，内装建材，表装材，器物外板等に使用されている。
従来の塗装金属板は、その用途に応じて塗膜構成や有機樹脂塗膜の成分を設定している。使用態様に応じて、あるいは所望意匠を得るために、樹脂塗膜に対して種々の改良を施している。加工性能が必要とされる場合には塗膜の硬さを抑え、加工による塗膜の割れを防止する工夫が施されている。また、塗膜の傷付きや摩耗に対しては、逆に塗膜を硬くすることもある。さらには、艶消し調の外観や耐摩耗性を付与するために各種骨材を添加・分散させたりしている。そして、この種の骨材としては、シリカ，ガラスビーズ，ガラス繊維等の無機質粒子や、ポリエチレンビーズ，アクリルビーズ，ナイロンビーズ，尿素樹脂ビーズ等の有機質粒子が使用されている。
【０００３】
【発明が解決しようとする課題】
ところで、塗膜を軟らかくすると耐摩耗性が低下し、傷が付きやすくなる。逆に硬くすると加工性が低下する。例えば、特開２００２−１７８４４８号公報では、上塗り塗膜と下塗り塗膜の軟化開始温度を規定することにより、加工性の良い上塗り塗膜で加工性を付与し、比較的硬い下塗り塗膜で耐傷付き性を付与している。しかしながら、一層の塗膜で両方の性能を付与することは容易でなない。また、樹脂塗膜に骨材粒子を分散させた塗装金属板を製品形状に成形加工しようとすると、樹脂と骨材粒子の硬度差が大きすぎるため骨材粒子周辺に応力が集中し、骨材周辺を起点にした亀裂が発生しやすい。このため骨材粒子を分散させた塗装金属板は加工性が低くなる。
さらに、骨材粒子の分散により耐摩耗性は向上しても、鋭利な硬質物が当たったときには目立つ傷が発生し、耐傷付き性という観点からは十分ではなかった。
本発明は、このような問題を解消すべく案出されたものであり、金属板表面に形成された樹脂塗膜に硬質の熱硬化型有機樹脂粒子を分散させることにより、相反する加工性と耐傷付き性の両方の特性に優れた塗装金属板を提供すること目的とする。
【０００４】
【課題を解決するための手段】
本発明の加工性および耐傷付き性に優れた塗装金属板は、その目的を達成するため、金属板表面に形成された鉛筆硬度ＨＢ以下の樹脂塗膜に該樹脂塗膜より硬い球状の熱硬化型有機樹脂粒子が分散した塗装金属板であって、前記熱硬化型有機樹脂粒子はその最大粒子径が前記樹脂塗膜の平均膜厚の３倍未満で、樹脂塗膜の平均膜厚よりも大径の熱硬化型有機樹脂粒子が塗膜量に対して２〜２０質量％で、しかも全熱硬化性有機樹脂粒子が塗膜量に対して２０質量％以下配合されており、有機樹脂塗膜中に分散している熱硬化型有機樹脂粒子の隆起部が塗膜を構成する有機樹脂の薄い皮膜で覆われていることを特徴とする。
【０００５】
【作用】
前記したように、有機樹脂塗装金属板は、一般的に塗膜を軟らかくすると耐摩耗性が低下して傷が付きやすく、硬くすると加工性が低下する。
本発明者等は、有機樹脂塗膜を形成した金属板に、優れた加工性および耐傷付き性を併せて持たせる手法について、鋭意検討を重ねてきた。その結果、金属板を被覆した有機樹脂塗膜中に硬質の有機樹脂粒子を分散させ、その加工性をベース樹脂塗膜に負わせ、耐摩耗性乃至耐傷付き性を塗膜中の硬質粒子に負わせることで、上記両特性を併せもつ塗装金属板が得られた。
【０００６】
そのメカニズムを、本発明塗装金属板の塗膜断面を示す図１に基づいて説明する。
ベース樹脂に目標とする平均膜厚ｈ以上の径を有する熱硬化型有機樹脂粒子Ｐを配合し、塗装すると、表面に凹凸を有した樹脂塗膜Ｒが形成される。平均膜厚ｈ以上の径の熱硬化型有機樹脂粒子Ｐは、表面がベース樹脂の薄い皮膜で覆われ、平均膜厚ｈ未満の径の熱硬化型有機樹脂粒子Ｐは塗膜表面の凹凸に影響することなく塗膜中に分散している。粒子の形状としては、真球状で径が大きいものほど塗膜表面に凹凸を与えることができる。樹脂塗膜中に分散された有機樹脂粒子Ｐは、ベース樹脂塗料との濡れ性がよく、塗膜形成時に粒子表面は薄い皮膜で覆われることとなり、加工やスクラッチを受けても脱落することはない。
そして塗膜の加工性は、ベース樹脂の硬度によって決定されるので、硬度の低い樹脂を選択することによって加工性を付与することができる。
【０００７】
ところで、硬度が低い樹脂塗膜Ｒを、硬質物質、例えば硬貨ＣによってスクラッチＳした場合、図２（ａ）に示すように、傷付き面積が広く、連続的に傷Ｗが付くために塗膜表面に線状の傷が入る。しかしながら、熱硬化型有機樹脂粒子Ｐを添加して表面に凹凸を付けた樹脂塗膜ＲをスクラッチＳした場合、図２（ｂ）に示すように、硬貨Ｃが熱硬化型有機樹脂粒子Ｐによる凸部にのみ接触するため、傷付き面積が少なくなり、しかも連続した傷Ｗとならないために目立つ傷とはならない。
さらに、塗膜中に分散された熱硬化型有機樹脂粒子Ｐは、ベース樹脂Ｒに対して濡れ性が良いために、塗膜形成時に粒子表面にもベース樹脂の薄い皮膜が形成され、粒子は容易には脱落しない。また有機樹脂粒子は無機質粒子ほど硬質ではなく、弾力性があるので、緩衝材的な作用も有している。
【０００８】
【実施の態様】
本発明の塗装金属板に使用されるベース樹脂としては、塗装金属板の加工性が塗膜樹脂の硬さに影響されるので、塗膜硬度の低い樹脂、具体的には塗膜の鉛筆硬度がＨＢ以下のものが使用される。塗膜鉛筆硬度がＨＢを超えるものは加工性が低下するため、本発明の塗膜形成には適さない。この条件を満たすものであれば、熱硬化或いは熱可塑の限定はない。
熱硬化型樹脂塗料としては、ウレタン樹脂系塗料，高分子ポリエステル樹脂系塗料，ポリエステル樹脂系塗料等が使用される。熱可塑性樹脂塗料としては塩化ビニール，アクリルゾル，フッ素樹脂系塗料等が使用される。本発明による塗装金属板を、耐候性が要求されるが外装建材として使用する場合には、耐候性に優れるウレタン樹脂系塗料を、内装・器物等に用いられる場合には、高分子ポリエステル樹脂系塗料を用いることが好ましい。ウレタン樹脂系塗膜に比べて高分子ポリエステル樹脂系塗膜は一般的に耐候性が低く、耐候性を向上させようとすると加工性が低下するため、加工性と耐候性の両立が難しい。
【０００９】
ベース樹脂塗膜中分散させる熱硬化型有機樹脂粒子としては、ベース樹脂塗膜よりも硬い樹脂を素材としたものを用いる。熱可塑性の有機樹脂粒子を用いると、塗料の焼付け時に樹脂が軟化し、塗料の硬化による収縮とともに粒子の変形が起こりやすく、塗膜表面に所望の凹凸が形成され難い。熱硬化型の架橋粒子であれば、塗料焼付け時に変形することがなく、塗膜表面に粒径に応じた凹凸を形成することができる。
ベース樹脂塗膜よりも硬い熱硬化型有機樹脂としては、ポリアクリロニトリル，アクリル，ウレタン，尿素樹脂等が使用される。これらの有機樹脂の粒子を、後述するような方法で数十μｍ程度の大きさで製造すると、その硬度はビッカース硬度（Ｈｖ）で５〜３０程度になっている。なお、この有機樹脂粒子の硬度は微小ビッカース硬度計にて測定される。具体的には、有機樹脂粒子をエポキシ系有機樹脂に埋め込み、耐水研磨紙を用いて研磨し、その断面で、圧痕が粒子径の１／３程度に収まる程度の測定荷重を掛けて測定することができる。ところで、ベース樹脂塗膜は軟らかすぎてビッカースによる圧痕が回復してしまうため、上記ビッカース硬度は測定できない。
【００１０】
粒子形状としては、球状であり、より真球度の高いものを用いることが好ましい。粒子形状はより真球に近い方が、配合する粒径に応じた凹凸が得られるため、塗膜表面に形成される凹凸の状態を予測しやすい。また形状が偏平である場合は凹凸が得られ難く、楕円形の場合でも塗装時に粒子が横になりやすい。鋭利な角をもった形状の場合は、粒子表面に薄い皮膜が付きにくくなることや、傷付き時に引っ掛かりができて耐傷付き性が得られなくなる。
粒子の表面状態としては、滑らかであるよりも細かな凹凸がある方がベース樹脂との密着性がよくなる。粒子と樹脂の密着性が良くないと、加工等によって樹脂塗膜が伸ばされたときに粒子と樹脂の界面に隙間が発生し、樹脂塗膜の加工性を低下させる。したがって、熱硬化型有機樹脂粒子としては、表面に微細な凹凸があるものを使用することが好ましい。
このような熱硬化型有機樹脂粒子は、水系沈殿重合法等で製造される。ポリアクリロニトリルビーズの製造法に関しては、特願２００２−３２１４２６号の明細書中で紹介している。
【００１１】
粒子の大きさとしては、最大粒子径がベース樹脂塗膜平均膜厚の３倍未満のものを使用する。粒子径が塗膜平均膜厚の３倍以上のものが分散されていると、粒子表面に薄い皮膜を形成でき難くなる。同時に塗装が困難になり、皮膜を形成できても脱落しやすくなって、塗膜の表面性状を悪化させることになる。
そして、ベース樹脂塗膜平均膜厚よりも大きな径の有機樹脂粒子量は、塗膜量に対して２〜２０質量％とし、かつ有機樹脂粒子全体量に対しては２０質量％以下とする。平均膜厚よりも大きな径の有機樹脂粒子量が２質量％に満たないと、塗膜表面の凹凸が少なく、耐傷付き性が得られない。有機樹脂粒子全体量が２０質量％を超えると、ベース樹脂本来の加工性が得られず、塗膜の加工性が低下する。有機樹脂粒子量の絶対量を抑えるためには小径の有機樹脂粒子の割合が少ない方が好ましい。
【００１２】
ベース樹脂塗料に、上記熱硬化型の有機樹脂粒子を配合する。
ベース樹脂塗料には、有機樹脂粒子の他に、必要に応じて顔料，ワックス，分散剤，レベリング剤等が配合される。
ベース樹脂塗料に熱硬化型有機樹脂粒子やその他の添加剤を混合・分散させる際、粒子の凝集がなく、分散性が良い場合には従来の攪拌で分散が可能である。粒子が凝集している場合や分散性が悪い場合、塗膜中で粒子が凝集し、加工性の低下や耐傷付き性の低下につながるので、３本ロールを用いる等で十分に分散させることが好ましい。
【００１３】
本発明の塗装金属板に使用される金属板には、材質的な制約は受けることなく、種々の金属板が使用できる。例えば、冷延鋼板，溶融Ｚｎめっき鋼板，電気Ｚｎめっき鋼板，溶融Ａｌ−Ｚｎ合金めっき鋼板，溶融Ａｌ−Ｚｎ−Ｍｇ合金めっき鋼板，溶融Ａｌめっき鋼板，ステンレス鋼板，アルミニウム合金板，銅板，銅合金板等が使用できる。
塗装に先立って、耐食性や塗膜密着性を向上させるために、通常の脱脂・酸洗や表面調整、及びクロメート処理，リン酸塩処理，クロムフリー処理等の塗装前処理を必要に応じて下地金属板に施すこともできる。
【００１４】
塗装前処理された下地金属板に前記有機樹脂粒子分散塗料を塗布し、乾燥・焼付けすることによって樹脂塗膜が形成される。
有機樹脂粒子分散塗膜を形成する前に、下塗り塗膜を形成しても良い。下塗り塗装には、防錆顔料を配合したエポキシ樹脂系あるいはポリエステル樹脂系の塗料を用いることが好ましい。
下塗り塗膜，有機樹脂粒子分散樹脂塗膜の形成は、通常の塗膜形成法と同様に、塗料をロールコータ，カーテンコータ等で下地金属板上に塗布した後、２００〜２５０℃×１分程度の乾燥・焼付けで行われる。
【００１５】
【実施例】
実施例１：
片面当りめっき付着量７５ｇ／ｍ²の、Ａｌ：５５質量％を含むＡｌ−Ｚｎ合金めっき層が形成された板厚０．５ｍｍの溶融Ａｌ−Ｚｎ合金めっき鋼板をゼンジミア方式の連続溶融めっきラインで製造した。
Ａｌ−Ｚｎ合金めっき鋼板をアルカリ脱脂処理した後、湯洗，水洗により洗浄し、乾燥した。次いで、塗布型クロメート処理液をロールコーターで塗布し、１００℃で乾燥させ、全Ｃｒ付着量４０ｍｇ／ｍ²のクロメート皮膜を形成した。
クロメート皮膜の上に、クロム酸ストロンチウムを不揮発分にして２５質量％を配合したエポキシ系樹脂の下塗り塗料を塗装・焼付けすることにより、プライマー塗膜を形成した。
プライマー塗膜の上に鉛筆硬度ＨＢのウレタン系樹脂をベース樹脂として、各種熱硬化性有機樹脂粒子を１２．５質量％配合した塗料を乾燥平均膜厚として３５μｍとなるように塗装・焼付けをすることにより表面塗膜を形成し、平均膜厚以上の粒子配合量が２質量％以上のものを実施例１〜３、２質量％未満のものを比較例４，５、熱可塑性有機樹脂粒子を配合したものを比較例６、および熱硬化性有機樹脂粒子を配合していない塗膜を比較例７とした。
【００１６】
各塗装鋼板から試験片を切り出し、加工性試験および耐傷付き性試験に供した。
〔加工性試験〕
サイズ５０ｍｍ×５０ｍｍの試験片を使用し、試験片の圧延方向と直角に試験面を外にして直径２ｍｍの棒の回りに約１秒かけて１８０度折り曲げた。折り曲げに際し、曲げ部内側に試験片と同じ厚さの厚さの板を２枚挟み込み、万力を用いて急速に締め付けた。
曲げ部外側にある塗膜を倍率２０倍の視野で観察し、割れが検出できなかった塗膜を◎，微細な割れが発生した塗膜を○，中程度の割れが発生した塗膜を△，著しい割れが発生した塗膜を×として加工性を評価した。
【００１７】
〔耐傷つき性〕
サイズ１００ｍｍ×１００ｍｍの試験片を使用し、試験片の表面塗膜をスクラッチ方向に４５度傾けた１０円銅貨で圧延方向と平行にスクラッチした。試験装置として、新東科学株式会社製の連続荷重式表面性測定機トライボギアTYPE１８を用い、荷重４００ｇ，スクラッチ速度６００ｍ／ｍｉｎで５０ｍｍスクラッチした。
スクラッチした５０ｍｍの中の前後１０ｍｍを除いた部分を目視にて観察し、傷が観察されなかった塗膜を◎，部分的に傷が確認できた塗膜を○，中程度の傷が線状に連続して確認された塗膜を△，著しい傷が線状に連続して発生した塗膜を×として耐傷付き性を評価した。
【００１８】
各塗装鋼板表層塗膜の熱硬化性有機樹脂粒子の構成および配合量、ならびに試験結果を併せて表１に示す。
表１に示す結果にみられるように、本発明例１〜３の塗装鋼板は加工性および耐傷付き性に優れ、加工試験による塗膜割れや耐傷付き性試験による傷の発生は認められなかった。
この結果から、鉛筆試験ＨＢ以下のベース樹脂に、該ベース樹脂よりも硬くしかもその平均膜厚以上の粒径の熱硬化型有機樹脂粒子を配合させることにより、加工性および耐傷付き性に優れることが確認できた。
他方、平均膜厚以上の大きさの熱硬化型有機樹脂粒子の配合量が２質量％未満の比較例４および５は、加工性には優れているが、耐傷付き性試験により線状に連続した傷が確認された。また、熱可塑性有機樹脂粒子を配合した比較例６は、塗膜焼付け時に粒子の変形が起こり、塗膜表面の凹凸が小さく、耐傷付き性試験により線状に連続した傷が確認された。さらに、熱硬化型有機樹脂粒子が配合されていない比較例７では著しい傷が発生していた。
【００１９】

【００２０】
実施例２：
実施例１と同じＡｌ−Ｚｎ合金めっき鋼板に、同じ処理を施して製造したプライマー塗膜形成めっき鋼板を使用した。
プライマー塗膜の上に鉛筆硬度ＨＢのウレタン系樹脂をベース樹脂として、ポリアクリロニトリル（ＰＡＮ）粒子の粒子径および配合量を変えて乾燥平均膜厚が３５μｍになるように表層塗膜を形成した。平均粒子径５０μｍおよび３５μｍのポリアクリロニトリル粒子を平均膜厚以上の粒子配合量が２質量％以上であり、全配合量が２０質量％以下の塗膜を本発明例１１〜１６とし、全配合量が１質量％および３０質量％の塗膜を比較例１７〜２０、最大粒子径が１２５μｍの塗膜を比較例２１とした。
【００２１】
各塗装鋼板から試験片を切り出し、実施例１と同じ加工性試験および耐傷付き性試験に供した。
各塗装鋼板表層塗膜の熱硬化性有機樹脂粒子の構成および配合量、ならびに試験結果を併せて表２に示す。
表２に示す結果にみられるように、本発明例１１〜１６の塗装鋼板は加工性および耐傷付き性に優れ、加工試験による塗膜割れや耐傷付き性試験による傷の発生は認められなかった。
この結果から、鉛筆試験ＨＢ以下のベース樹脂に、該ベース樹脂よりも硬くしかもその平均膜厚以上の粒径の熱硬化型有機樹脂粒子を２質量％以上、全粒子配合量２０質量％以下配合させることにより、加工性を維持したまま耐傷付き性が向上されることが確認できた。
他方、比較例１７〜２０にみられるように、平均膜厚以上の大きさの熱硬化型有機樹脂粒子配合量が２質量％に満たないと耐傷付き性に対して効果を示さず、全粒子量が２０質量％を超えると加工性の低下に繋がる。
また、比較例２１にみられるように、最大粒子径が塗膜平均膜厚の３倍を超えて大きすぎると塗装時に粒子による筋引きが起こり、健全な塗膜が形成されなくなる。
【００２２】

【００２３】
実施例３：
実施例１と同じＡｌ−Ｚｎ合金めっき鋼板に、同じ処理を施して製造したプライマー塗膜形成めっき鋼板を使用した。
プライマー塗膜の上に、ベース樹脂の異なる塗料に平均粒径３０μｍのＰＡＮ粒子を２．２および１１．１質量％配合し、乾燥平均膜厚が１５μｍになるように塗装・焼付けを行い表層塗膜を形成した。ベース樹脂の鉛筆硬度がＨＢ以下の塗膜を本発明例３１〜３４とし、ＨＢを超えるベース樹脂の塗膜を比較例３５〜３８とした。
【００２４】
各塗装鋼板から試験片を切り出し、実施例１と同じ加工性試験および耐傷付き性試験に供した。
各塗装鋼板表層塗膜のベース樹脂硬度およびPAN粒子の配合量、ならびに試験結果を併せて表３に示す。
表３に示す結果にみられるように、本発明例３１〜３４の塗装鋼板は加工性および耐傷付き性に優れ、加工試験による塗膜割れや耐傷付き性試験による傷の発生は認められなかった。
この結果から、鉛筆試験ＨＢ以下のベース樹脂に、該ベース樹脂よりも硬くしかもその平均膜厚以上の粒径の熱硬化型有機樹脂粒子を２質量％以上、全粒子配合量２０質量％以下配合させることにより、加工性を維持したまま耐傷付き性が向上されることが確認できた。
他方、比較例３５〜３８にみられるように、鉛筆試験がＨＢよりも硬いベース樹脂を用いた塗料では、熱硬化型のＰＡＮ粒子の配合により耐傷付き性の効果は認められたものの、ベース樹脂の加工性が劣るため、加工による塗膜の割れが確認された。加工性能としては、ベース樹脂の硬い方が著しい割れ発生しており、ベース樹脂の硬度が高ほど加工性が低下することがわかる。
【００２５】

【００２６】
【発明の効果】
以上に説明したように、本発明においては、金属板表面に形成された比較的軟らかい樹脂塗膜中に、この樹脂塗膜よりも硬い球状の熱硬化型有機樹脂粒子を分散させた塗装金属板であって、前記熱硬化型有機樹脂粒子の最大粒子径を前記樹脂塗膜の平均膜厚の３倍未満で、しかも樹脂塗膜の平均膜厚よりも大径の熱硬化型有機樹脂粒子を樹脂塗膜量に対して２〜２０質量％塗膜中に分散させ、前記熱硬化型有機樹脂粒子の隆起部を、塗膜を構成する有機樹脂の薄い皮膜で覆わせることにより、その加工性を軟らかい樹脂塗膜に負わせ、耐摩耗性乃至耐傷付き性を塗膜中の硬質有機樹脂粒子に負わせて、加工性と耐傷付き性の両特性に優れた塗装金属板を提供することができる。
したがって、本発明により、加工性に優れ、艶消し外観を長期にわたって維持できる塗装鋼板を低コストで製造することができる。
【図面の簡単な説明】
【図１】本発明塗装金属板の塗膜断面構造を説明する図
【図２】硬貨でスクラッチしたときの塗膜の傷付き状況を模式的に説明する図、（ａ）が有機樹脂粒子を分散していない塗膜で、（ｂ）が有機樹脂粒子を分散している塗膜[0001]
[Industrial applications]
The present invention relates to a painted metal sheet having excellent workability and scratch resistance, which is used for exterior building materials, interior building materials, surface covering materials, outer panels of equipment, and the like.
[0002]
[Prior art]
BACKGROUND ART Painted metal plates, especially painted steel plates, are formed into target shapes and used for exterior building materials, interior building materials, surface covering materials, outer plates of equipment, and the like.
In a conventional coated metal plate, the composition of the coating film and the components of the organic resin coating film are set according to the application. Various improvements have been made to the resin coating according to the mode of use or to obtain the desired design. When processing performance is required, measures are taken to reduce the hardness of the coating film and prevent cracking of the coating film due to processing. On the other hand, the coating film may be hardened to prevent the coating film from being damaged or worn. Further, various aggregates are added and dispersed to impart a matte appearance and abrasion resistance. As this type of aggregate, inorganic particles such as silica, glass beads, and glass fibers, and organic particles such as polyethylene beads, acrylic beads, nylon beads, and urea resin beads are used.
[0003]
[Problems to be solved by the invention]
By the way, when the coating film is softened, the abrasion resistance is reduced and the coating is easily scratched. Conversely, if it is hard, workability decreases. For example, in Japanese Patent Application Laid-Open No. 2002-178448, by defining the softening start temperature of the overcoat film and the undercoat film, the workability is imparted with an overcoat film having good workability, and the relatively hard undercoat film is scratch-resistant. Gives stickiness. However, it is not easy to provide both properties with a single coating film. Also, when trying to form a coated metal plate in which aggregate particles are dispersed in a resin coating film into a product shape, stress is concentrated around the aggregate particles because the hardness difference between the resin and the aggregate particles is too large. Cracks originating from the periphery are likely to occur. Therefore, the coated metal plate in which the aggregate particles are dispersed has low workability.
Furthermore, even if the wear resistance is improved by the dispersion of the aggregate particles, noticeable scratches occur when hit by a sharp hard material, which is not sufficient from the viewpoint of scratch resistance.
The present invention has been devised to solve such a problem, and by dispersing hard thermosetting organic resin particles in a resin coating film formed on the surface of a metal plate, contradictory workability is achieved. It is an object of the present invention to provide a coated metal sheet excellent in both properties of scratch resistance.
[0004]
[Means for Solving the Problems]
In order to achieve the object, the coated metal sheet having excellent workability and scratch resistance according to the present invention is formed on a resin coating film having a pencil hardness of HB or less on the surface of the metal plate. A coated metal plate in which type organic resin particles are dispersed, wherein the thermosetting organic resin particles have a maximum particle diameter of less than three times the average film thickness of the resin coating film, and are smaller than the average film thickness of the resin coating film. The thermosetting organic resin particles having a large diameter are contained in an amount of 2 to 20% by mass based on the coating amount, and the total thermosetting organic resin particles are blended in an amount of 20% by mass or less based on the coating amount. It is characterized in that the raised portions of the thermosetting organic resin particles dispersed in the film are covered with a thin film of the organic resin constituting the coating film.
[0005]
[Action]
As described above, in the case of an organic resin-coated metal plate, generally, when the coating film is soft, the abrasion resistance is reduced and the film is easily damaged, and when the coating film is hard, the workability is reduced.
The present inventors have intensively studied a technique for imparting excellent workability and scratch resistance to a metal plate having an organic resin coating film formed thereon. As a result, the hard organic resin particles are dispersed in the organic resin coating film coated on the metal plate, the workability is imposed on the base resin coating film, and the wear resistance or scratch resistance is reduced to the hard particles in the coating film. As a result, a coated metal plate having both of the above characteristics was obtained.
[0006]
The mechanism will be described with reference to FIG. 1 showing a cross section of a coating film of the coated metal sheet of the present invention.
When the thermosetting organic resin particles P having a diameter equal to or more than the target average film thickness h are blended into the base resin and coated, a resin coating film R having irregularities on the surface is formed. The thermosetting organic resin particles P having a diameter of not less than the average film thickness h are covered with a thin film of the base resin, and the thermosetting organic resin particles P having a diameter less than the average film thickness h have irregularities on the coating film surface. It is dispersed in the coating without any effect. Regarding the shape of the particles, the more spherical and the larger the diameter, the more unevenness can be given to the coating film surface. The organic resin particles P dispersed in the resin coating film have good wettability with the base resin coating, and the particle surface is covered with a thin film at the time of forming the coating film. Absent.
Since the workability of the coating film is determined by the hardness of the base resin, the workability can be imparted by selecting a resin having a low hardness.
[0007]
By the way, when the resin coating film R having a low hardness is scratched with a hard material, for example, a coin C, as shown in FIG. Linear scratches on the surface. However, when the resin coating film R having the uneven surface formed by adding the thermosetting organic resin particles P is scratched, the coin C is formed by the thermosetting organic resin particles P as shown in FIG. Since it comes into contact only with the convex portion, the scratched area is reduced, and furthermore, it does not become a conspicuous scratch because it does not become a continuous scratch W.
Further, since the thermosetting organic resin particles P dispersed in the coating film have good wettability with respect to the base resin R, a thin film of the base resin is also formed on the particle surface when the coating film is formed. Does not fall off easily. In addition, since the organic resin particles are not as hard as the inorganic particles and have elasticity, they also have a function as a buffer material.
[0008]
Embodiment
As the base resin used in the coated metal plate of the present invention, since the workability of the coated metal plate is affected by the hardness of the coating film resin, a resin having a low coating film hardness, specifically, the pencil hardness of the coating film Are HB or less. Those having a coating film pencil hardness exceeding HB are not suitable for forming the coating film of the present invention because the processability is reduced. There is no limitation on thermosetting or thermoplastic as long as this condition is satisfied.
As the thermosetting resin paint, urethane resin paint, polymer polyester resin paint, polyester resin paint and the like are used. As the thermoplastic resin paint, vinyl chloride, acrylic sol, fluororesin paint and the like are used. When the coated metal sheet according to the present invention is required to have weather resistance but is used as an exterior building material, a urethane resin-based coating having excellent weather resistance is used, and when used for interiors and articles, a high-molecular polyester resin-based resin is used. It is preferable to use a paint. Compared with a urethane resin-based coating film, a high-molecular polyester resin-based coating film generally has low weather resistance, and if the weather resistance is to be improved, the workability is reduced. Therefore, it is difficult to achieve both workability and weather resistance.
[0009]
As the thermosetting organic resin particles to be dispersed in the base resin coating film, those made of a resin harder than the base resin coating film are used. When thermoplastic organic resin particles are used, the resin is softened at the time of baking of the paint, the particles are likely to be deformed together with shrinkage due to the curing of the paint, and desired unevenness is hardly formed on the surface of the coating film. If the thermosetting type crosslinked particles are used, they will not be deformed at the time of baking the paint, and irregularities corresponding to the particle size can be formed on the surface of the coating film.
As the thermosetting organic resin harder than the base resin coating film, polyacrylonitrile, acryl, urethane, urea resin or the like is used. When these organic resin particles are manufactured to have a size of about several tens of μm by a method described later, the hardness is about 5 to 30 in Vickers hardness (Hv). The hardness of the organic resin particles is measured with a micro Vickers hardness meter. Specifically, the organic resin particles are embedded in an epoxy-based organic resin, polished using a water-resistant abrasive paper, and measured by applying a measurement load on the cross section such that the indentation is about 1/3 of the particle diameter. Can be. By the way, the Vickers hardness cannot be measured because the base resin coating is too soft and the indentation due to Vickers recovers.
[0010]
It is preferable to use a particle having a spherical shape and a higher sphericity. When the particle shape is closer to a true sphere, irregularities corresponding to the particle size to be blended can be obtained, so that the state of the irregularities formed on the coating film surface can be easily predicted. Further, when the shape is flat, it is difficult to obtain irregularities, and even when the shape is elliptical, the particles tend to lie down during painting. In the case of a shape having sharp corners, it is difficult to form a thin film on the surface of the particles, and when the particles are scratched, they are caught and scratch resistance cannot be obtained.
Regarding the surface state of the particles, the finer the unevenness is, the better the adhesion to the base resin is than the smoothness is. If the adhesion between the particles and the resin is not good, a gap is generated at the interface between the particles and the resin when the resin coating is stretched by processing or the like, and the workability of the resin coating decreases. Therefore, it is preferable to use thermosetting organic resin particles having fine irregularities on the surface.
Such thermosetting organic resin particles are produced by an aqueous precipitation polymerization method or the like. The method for producing polyacrylonitrile beads is introduced in the specification of Japanese Patent Application No. 2002-321426.
[0011]
As the size of the particles, those having a maximum particle size of less than three times the average thickness of the base resin coating film are used. If a particle having a particle diameter of three times or more the average thickness of the coating film is dispersed, it becomes difficult to form a thin film on the particle surface. At the same time, coating becomes difficult, and even if a film can be formed, the film tends to fall off, deteriorating the surface properties of the coating film.
The amount of the organic resin particles having a diameter larger than the average thickness of the base resin coating film is set to 2 to 20% by mass with respect to the coating amount and to 20% by mass or less with respect to the total amount of the organic resin particles. If the amount of the organic resin particles having a diameter larger than the average film thickness is less than 2% by mass, the surface of the coating film has few irregularities and scratch resistance cannot be obtained. When the total amount of the organic resin particles exceeds 20% by mass, the original processability of the base resin cannot be obtained, and the processability of the coating film decreases. In order to suppress the absolute amount of the organic resin particles, it is preferable that the ratio of the small-diameter organic resin particles is small.
[0012]
The thermosetting organic resin particles are mixed with the base resin paint.
In addition to the organic resin particles, pigments, waxes, dispersants, leveling agents, and the like are added to the base resin paint as needed.
When mixing and dispersing the thermosetting organic resin particles and other additives in the base resin paint, if there is no aggregation of the particles and the dispersibility is good, the dispersion can be performed by conventional stirring. When the particles are agglomerated or have poor dispersibility, the particles are agglomerated in the coating film, leading to a reduction in workability and a decrease in scratch resistance. preferable.
[0013]
Various metal plates can be used for the metal plate used for the coated metal plate of the present invention, without being restricted by the material. For example, cold-rolled steel sheet, hot-dip galvanized steel sheet, electric Zn-coated steel sheet, hot-dip Al-Zn alloy coated steel sheet, hot-dip Al-Zn-Mg alloy coated steel sheet, hot-dip Al-plated steel sheet, stainless steel sheet, aluminum alloy sheet, copper sheet, copper alloy A plate or the like can be used.
Prior to painting, in order to improve corrosion resistance and coating film adhesion, normal degreasing, pickling, surface conditioning, and pre-painting treatment such as chromate treatment, phosphate treatment, and chromium-free treatment are performed as necessary. It can also be applied to a metal plate.
[0014]
A resin coating film is formed by applying the organic resin particle-dispersed coating material to a base metal plate that has been pre-treated for coating, followed by drying and baking.
Before forming the organic resin particle dispersed coating film, an undercoat coating film may be formed. For undercoating, it is preferable to use an epoxy resin-based or polyester resin-based paint containing a rust preventive pigment.
The undercoating film and the organic resin particle-dispersed resin coating film are formed by applying the coating material on a base metal plate using a roll coater, a curtain coater or the like in the same manner as in a normal coating film forming method, and then at 200 to 250 ° C. × 1 minute. Drying and baking are performed to a degree.
[0015]
【Example】
Example 1
A hot-dip Al—Zn alloy plated steel sheet having a thickness of 0.5 mm on which an Al—Zn alloy plated layer containing 55% by mass of Al having a plating adhesion amount of 75 g / m ² per side is formed by a continuous hot-dip plating line of Sendzimir method. Manufactured.
After the Al-Zn alloy plated steel sheet was subjected to alkaline degreasing treatment, it was washed with hot water and water, and dried. Next, a coating type chromate treatment solution was applied by a roll coater and dried at 100 ° C. to form a chromate film having a total Cr adhesion amount of 40 mg / m ² .
On the chromate film, a primer coating film was formed by applying and baking an undercoat paint of epoxy resin containing 25% by mass of strontium chromate as a non-volatile content.
A paint containing 12.5% by mass of various thermosetting organic resin particles is coated and baked on the primer coating film using a urethane-based resin having a pencil hardness of HB as a base resin so as to have a dry average film thickness of 35 μm. By forming a surface coating film by the method described above, particles having an average film thickness of 2% by mass or more were used in Examples 1 to 3 and Comparative Examples 4 and 5 in which the amount was less than 2% by mass. The compounded composition was designated as Comparative Example 6, and the coating film containing no thermosetting organic resin particles was designated as Comparative Example 7.
[0016]
A test piece was cut out from each of the coated steel sheets and subjected to a workability test and a scratch resistance test.
(Workability test)
Using a test piece having a size of 50 mm × 50 mm, the test piece was bent 180 ° around a bar having a diameter of 2 mm for about 1 second, with the test surface out of the test piece at right angles to the rolling direction of the test piece. At the time of bending, two plates having the same thickness as the test piece were sandwiched inside the bent portion and fastened quickly using a vise.
The coating film on the outside of the bent portion was observed in a visual field of 20 times magnification. A coating film in which cracks could not be detected was indicated by ◎, a coating film in which fine cracks occurred was indicated by ○, and a coating film in which moderate cracks occurred was indicated by △ The workability was evaluated as “poor” for the coating film in which significant cracks occurred.
[0017]
[Scratch resistance]
A test piece having a size of 100 mm × 100 mm was used, and the surface coating film of the test piece was scratched in parallel with the rolling direction with a 10 yen copper coin inclined at 45 degrees in the scratch direction. As a test device, a continuous load type surface property measuring device Tribogear TYPE18 manufactured by Shinto Kagaku Co., Ltd. was used, and the load was 400 g, and the scratching speed was 600 m / min and the 50 mm scratch was performed.
A portion of the scratched 50 mm excluding the front and rear 10 mm was visually observed, and the coating where no scratch was observed was ◎, the coating where partial scratch was confirmed was ○, and the medium scratch was linear. The coating film which was confirmed continuously was evaluated as △, and the coating film in which remarkable damage was continuously generated linearly was evaluated as ×, and the scratch resistance was evaluated.
[0018]
Table 1 also shows the composition and blending amount of the thermosetting organic resin particles of the surface coating film of each coated steel sheet and the test results.
As can be seen from the results shown in Table 1, the coated steel sheets of Examples 1 to 3 of the present invention were excellent in workability and scratch resistance, and no cracks were found in the coating film in the processing test or in the scratch resistance test. .
From these results, it can be seen that by blending thermosetting organic resin particles having a particle size that is harder than the base resin and has a particle size greater than or equal to the average film thickness to a base resin having a pencil test of HB or less, the workability and scratch resistance are excellent. Was confirmed.
On the other hand, Comparative Examples 4 and 5, in which the compounding amount of the thermosetting organic resin particles having a size equal to or larger than the average film thickness is less than 2% by mass, are excellent in workability, but are continuous linearly in the scratch resistance test. Scratch was confirmed. In Comparative Example 6 in which the thermoplastic organic resin particles were blended, the particles were deformed at the time of baking of the coating film, the unevenness of the coating film surface was small, and a continuous scratch was confirmed by a scratch resistance test. Further, in Comparative Example 7 in which the thermosetting organic resin particles were not blended, remarkable scratches were generated.
[0019]

[0020]
Example 2:
A primer film-formed plated steel sheet produced by performing the same treatment on the same Al—Zn alloy plated steel sheet as in Example 1 was used.
A surface coating film was formed on the primer coating film using a urethane resin having a pencil hardness of HB as a base resin and changing the particle size and blending amount of polyacrylonitrile (PAN) particles so that the dry average film thickness was 35 μm. The polyacrylonitrile particles having an average particle diameter of 50 μm and 35 μm have an average film thickness of not less than 2% by mass, and the total coating amount is 20% by mass or less. Were 1% by mass and 30% by mass as Comparative Examples 17 to 20, and a film having a maximum particle size of 125 μm was Comparative Example 21.
[0021]
A test piece was cut out from each coated steel sheet and subjected to the same workability test and scratch resistance test as in Example 1.
Table 2 also shows the composition and amount of the thermosetting organic resin particles of the surface coating film of each coated steel sheet and the test results.
As can be seen from the results shown in Table 2, the coated steel sheets of Examples 11 to 16 of the present invention were excellent in workability and scratch resistance, and no cracks were found in the coating film in the processing test or in the scratch resistance test. .
From the results, it was found that thermosetting organic resin particles having a particle size of 2% by mass or more and a total particle size of 20% by mass or less were added to a base resin having a pencil test of HB or less and harder than the base resin and having a particle size not less than the average thickness. By doing so, it was confirmed that the scratch resistance was improved while maintaining the workability.
On the other hand, as seen in Comparative Examples 17 to 20, if the blending amount of the thermosetting organic resin particles having a size equal to or larger than the average film thickness is less than 2% by mass, no effect is exhibited on the scratch resistance, and all the particles have no effect. When the amount exceeds 20% by mass, workability is reduced.
Further, as seen in Comparative Example 21, if the maximum particle diameter is too large, which is more than three times the average film thickness of the coating film, streaks due to particles occur at the time of coating, and a sound coating film cannot be formed.
[0022]

[0023]
Example 3
A primer film-formed plated steel sheet produced by performing the same treatment on the same Al—Zn alloy plated steel sheet as in Example 1 was used.
2.2 and 11.1% by mass of PAN particles having an average particle size of 30 μm are mixed with a coating material having a different base resin on the primer coating film, and coated and baked so as to have a dry average film thickness of 15 μm. A film was formed. The coating films of the base resin having a pencil hardness of HB or less were defined as inventive examples 31 to 34, and the coating films of the base resin exceeding HB were defined as comparative examples 35 to 38.
[0024]
A test piece was cut out from each coated steel sheet and subjected to the same workability test and scratch resistance test as in Example 1.
Table 3 also shows the base resin hardness of the surface coating film of each coated steel sheet, the blending amount of PAN particles, and the test results.
As can be seen from the results shown in Table 3, the coated steel sheets of Examples 31 to 34 of the present invention were excellent in workability and scratch resistance, and no cracks were found in the coating film in the processing test and the scratches in the scratch resistance test. .
From the results, it was found that thermosetting organic resin particles having a particle size of 2% by mass or more and a total particle size of 20% by mass or less were added to a base resin having a pencil test of HB or less and harder than the base resin and having a particle size not less than the average film thickness. By doing so, it was confirmed that the scratch resistance was improved while maintaining the workability.
On the other hand, as shown in Comparative Examples 35 to 38, in the paint using a base resin harder than HB in the pencil test, although the effect of scratch resistance was recognized by the blending of thermosetting PAN particles, the base resin was used. Because of poor processability, cracking of the coating film due to the processing was confirmed. Regarding the processing performance, it is found that the harder of the base resin has a remarkable crack, and the higher the hardness of the base resin, the lower the workability.
[0025]

[0026]
【The invention's effect】
As described above, in the present invention, in a relatively soft resin coating formed on the surface of a metal plate, a coated metal plate in which spherical thermosetting organic resin particles harder than the resin coating are dispersed. The maximum particle diameter of the thermosetting organic resin particles is less than three times the average thickness of the resin coating, and moreover, the thermosetting organic resin particles having a diameter larger than the average thickness of the resin coating. By dispersing in the coating film in an amount of 2 to 20% by mass based on the amount of the resin coating film, the raised portions of the thermosetting organic resin particles are covered with a thin film of the organic resin constituting the coating film, thereby improving the processability. Can be applied to a soft resin coating film, and abrasion resistance or scratch resistance can be applied to hard organic resin particles in the coating film to provide a coated metal sheet excellent in both properties of workability and scratch resistance. it can.
Therefore, according to the present invention, a coated steel sheet having excellent workability and capable of maintaining a matte appearance for a long period of time can be manufactured at low cost.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a cross-sectional structure of a coating film of a coated metal sheet of the present invention. FIG. 2 is a diagram schematically illustrating a situation in which a coating film is damaged when scratched with a coin. (B) a coating film in which organic resin particles are dispersed in a non-dispersed coating film

Claims

A coated metal plate in which spherical thermosetting organic resin particles harder than the resin coating are dispersed in a resin coating having a pencil hardness of HB or less formed on the surface of the metal plate. The particle size is less than three times the average thickness of the resin coating, and the thermosetting organic resin particles having a diameter larger than the average thickness of the resin coating are 2 to 20% by mass based on the coating amount, and 20% by mass or less of the total thermosetting organic resin particles based on the amount of the coating film, and the raised portions of the thermosetting organic resin particles dispersed in the organic resin coating film constitute the coating film. A coated metal sheet with excellent workability and scratch resistance characterized by being covered with a thin film of.