JP4296849B2

JP4296849B2 - Powder coating method and powder coating apparatus

Info

Publication number: JP4296849B2
Application number: JP2003158944A
Authority: JP
Inventors: 隆久蟹江; 健児井尾
Original assignee: Aisin Seiki Co Ltd; Aisin Corp
Current assignee: Aisin Corp
Priority date: 2003-06-04
Filing date: 2003-06-04
Publication date: 2009-07-15
Anticipated expiration: 2023-06-04
Also published as: JP2004358337A

Description

【０００１】
【発明の属する技術分野】
本発明は粉体塗装方法および粉体塗装装置に関する。
【０００２】
【従来の技術】
地球環境への影響と環境意識の高まりから近年、溶剤塗装から粉体塗装への移行が急速に進められている。従来、一般的に平均粒子径が３５〜５０μｍの粉体塗料が使用されているが、溶剤塗装と比較して平滑性がかなり劣っていた。溶剤塗装なみの外観を要求される製品も多く、粉体塗装への移行を広げ、環境改善を進めるために平滑性が優れた粉体塗装を実現することが求められている。
【０００３】
その目的のために平均粒子径が２５μｍ以下の粉体塗料が使用され始めてきている。例えば、特許文献１のように平均粒子径が５〜２０μｍの粉体を使用する粉体流動層を用いる静電粉体塗装方法が提案されている。
【０００４】
【特許文献１】
特開平１０−１２０９４５号公報（［００１２］）
【０００５】
【発明が解決しようとする課題】
しかしながら、特許文献１のような平均粒子径が小さい粉体塗料を使用しても十分な平滑性が得られない問題点があった。平均粒子径が小さすぎる場合には逆に平滑性が悪くなる問題点があった。
【０００６】
本発明は上記課題を解決したもので、平滑性に優れた塗膜が形成できる粉体塗装方法および粉体塗装装置を提供する。
【０００７】
上記技術的課題を解決するために、本発明の請求項１において講じた技術的手段（以下、第１の技術的手段と称する。）は、第１粉体塗料を被塗物に粉体塗装する第１塗装工程と、該第１塗装工程で前記第１粉体塗料が塗装された前記被塗物に前記第１粉体塗料より小さい平均粒子径を有する第２粉体塗料を粉体塗装する第２塗装工程が設けられ、第１塗装工程および第２塗装工程は粉体塗料を帯電させ被塗物に向かって吐出させて粉体塗装する静電粉体塗装であり、第１粉体塗料の吐出量が第２粉体塗料の吐出量以下であることを特徴とする粉体塗装方法である。
【０００８】
上記第１の技術的手段による効果は、以下のようである。
【０００９】
上記第１の技術的手段による効果は、以下のようである。すなわち、第１塗装工程で平均粒子径の大きい粉体塗料を粉体塗装し、その上に第２塗装工程で平均粒子径の小さい粉体塗料を粉体塗装するので、平滑性に優れた塗膜が形成でき、第１粉体塗料の吐出量が第２粉体塗料の吐出量以下であるので、より平滑性に優れた塗膜を形成できる。
【００１０】
上記技術的課題を解決するために、本発明の請求項２において講じた技術的手段（以下、第２の技術的手段と称する。）は、前記第１塗装工程および前記第２塗装工程は粉体塗料を帯電させて粉体塗装する静電粉体塗装であり、前記第１粉体塗料の帯電印加電圧が前記第２粉体塗料の帯電印加電圧より低いことを特徴とする請求項１記載の粉体塗装方法である。
【００１１】
上記第２の技術的手段による効果は、以下のようである。
【００１２】
すなわち、第１粉体塗料の帯電印加電圧が第２粉体塗料の帯電印加電圧より低いので、第１粉体塗料の塗膜の帯電密度（単位面積当たりの帯電量）が小さく、かつその塗膜の上に大きな静電力により第２粉体塗料が塗装されるので、より平滑性に優れた塗膜を形成できる。
【００１３】
上記技術的課題を解決するために、本発明の請求項３において講じた技術的手段（以下、第３の技術的手段と称する。）は、前記第１塗装工程および前記第２塗装工程は粉体塗料を帯電させ前記被塗物に向かって吐出させて粉体塗装する静電粉体塗装であり、前記第１粉体塗料の吐出量が前記第２粉体塗料の吐出量以下であることを特徴とする請求項１記載の粉体塗装方法である。
【００２２】
【発明の実施の形態】
本発明者は平均粒子径が小さい粉体塗料を使用しても塗膜の平滑性が十分に向上しない原因を考察した。粉体塗料は、粒子径が異なる粒子が集合している。粉体塗装の際に、粒子径の大きい粒子から付着し、粒子径の小さい粒子は付着しにくい現象が見られる。これが平滑性が十分に向上できない原因と推察された。また静電粉体塗装方法や電界流動浸漬法のように静電気を使用した塗装方法では、平均粒子径が小さい粒子を使用すると、塗膜で静電反発が強くなり、塗面にゆず肌が生じ塗膜の平滑性を悪化させていた。粒子径が小さい粒子は比表面積が大きく、粒子の体積当たりの帯電量が大きいためと推察された。本発明者は、これらの推察をもとに鋭意研究し本発明に至った。
【００２３】
平均粒子径が異なる２種類の粉体塗料を用意し、はじめに第１塗装工程で平均粒子径の大きい粉体塗料を粉体塗装し、次に第２塗装工程で、第１塗装工程で形成された塗膜上に平均粒子径の小さい粉体塗料を粉体塗装する。こうすることによって、平均粒子径の大きい粉体塗料と小さい粉体塗料を別々に粉体塗装するので、粒子径の小さい粒子が大きい粒子に妨げられた付着しにくい現象をなくすことができる。また第１塗装工程で大きい粒子で形成された塗膜の凹凸すなわち大きい粒子の隙間が第２塗装工程の小さな粒子で埋まるように塗装するため、効果的に小さな粒子を付着させることができ、平滑性に優れた塗膜が形成できる。さらに第１塗装工程では大きな粒子により塗膜が形成されるため、形成された塗膜の帯電密度が低いので、静電反発が少なく、ゆず肌の発生がなくなり平滑性に優れた塗膜が形成できる。
【００２４】
第１塗装工程と第２塗装工程が分かれているので、平均粒子径が大きい粉体塗料を塗装する場合と、平均粒子径が大きい粉体塗料を塗装する場合で、それぞれに適した粉体塗装条件を設定できる。特に第２塗装工程において、粉体塗料の帯電量を制御することにより、静電反発を減少させ、ゆず肌の発生をなくすことができる。
【００２５】
以下、本発明の実施形態について、図面に基づいて説明する。図１は実施形態の粉体塗装装置を説明する説明図である。この粉体塗装装置は、粉体塗料を帯電させ被塗物に向かって吐出させて粉体塗装する静電粉体塗装装置である。原料粉体塗料タンク１、サイクロン式分級器（分級装置）２、粗粉粉体塗装部１０、微粉粉体塗装部２０、粉体塗料回収装置４、塗装ブース３などから構成されている。
【００２６】
粗粉粉体塗装部１０は、粗粉粉体塗料タンク１１、エジェクタ１２、高電圧発生装置１３、静電スプレーガン１４などから構成されている。エジェクタ１２は粗粉粉体塗料タンク１１に連結されており、粗粉粉体塗料タンク１１内の粉体塗料を粉体塗料輸送管路１５を介して塗装ブース３内に設けられた静電スプレーガン１４に輸送するものである。高電圧発生装置１３は静電スプレーガン１４と高圧電線１６を介して連結されている。
【００２７】
同様に、微粉粉体塗装部２０は、微粉粉体塗料タンク２１、エジェクタ２２、高電圧発生装置２３、静電スプレーガン２４などから構成されている。エジェクタ２２は微粉粉体塗料タンク２１に連結されており、微粉粉体塗料タンク２１内の粉体塗料を粉体塗料輸送管路２５を介して塗装ブース３内に設けられた静電スプレーガン２４に輸送するものである。高電圧発生装置２３は静電スプレーガン２４と高圧電線２６を介して連結されている。
【００２８】
原料粉体塗料タンク１にはサイクロン式分級器２が連結されている。サイクロン式分級器２は粉体塗料輸送管路５を介して粗粉粉体塗料タンク１１に連結され、粉体塗料輸送管路６を介して微粉粉体塗料タンク２１に連結されている。
【００２９】
塗装ブース３内の被塗物に付着しなかった余剰の粉体塗料が粉体回収管路７を介して粉体塗料回収装置４に送られるように構成されている。粉体塗料回収装置４は粉体回収管路８を介して粉体塗料タンク１に連結されている。
【００３０】
９ａ、９ｂは被塗物であり、それぞれ塗装ブース３内にアースされて設置され、被塗物９ａの位置から被塗物９ｂの位置に順次移動するようになっている。
【００３１】
原料粉体塗料タンク１内の原料粉体塗料はサイクロン式分級器２に送られ、平均粒子径が大きい粗粉粉体塗料（第１粉体塗料）と平均粒子径が小さい微粉粉体塗料（第２粉体塗料）に分級される。分級された粗粉粉体塗料は粉体塗料輸送管路５を介して粗粉粉体塗料タンク１１に輸送され貯蔵され、微粉粉体塗料は粉体塗料輸送管路６を介して微粉粉体塗料タンク２１に輸送され貯蔵される。
【００３２】
粗粉粉体塗料タンク１１に貯蔵されている粗粉粉体塗料はエジェクタ１２により静電スプレーガン１４に供給される。静電スプレーガン１４に供給された粗粉粉体塗料は高電圧発生装置１３により負に荷電され被塗物６ａに向かってスプレーされる。スプレーされた粗粉粉体塗料は、接地されている被塗物６ａに付着し、塗膜を形成する。
【００３３】
同様に、微粉粉体塗料タンク２１に貯蔵されている微粉粉体塗料はエジェクタ２２により静電スプレーガン２４に供給される。静電スプレーガン２４に供給された微粉粉体塗料は高電圧発生装置２３により負に荷電され被塗物６ｂに向かってスプレーされる。スプレーされた微粉粉体塗料は、接地されている被塗物６ｂに付着し、塗膜を形成する。
【００３４】
被塗物は、はじめに被塗物６ａの位置に移動され粗粉粉体塗料が静電粉体塗装される（第１塗装工程）。次に被塗物は被塗物６ｂの位置に移動され微粉粉体塗料が静電粉体塗装される（第２塗装工程）。
【００３５】
第１塗装工程、第２塗装工程で被塗物に付着しなかった粉体塗料は、粉体回収管路７を介して粉体塗料回収装置４に回収され、粉体回収管路８を介して原料粉体塗料タンク１に戻される。
【００３６】
この粉体塗装装置を使用して、以下の粉体塗装試験を実施した。
【００３７】
（試験例１）
被塗物としてアルミテストパネル（日本テストパネル株式会社製アルミ材Ａ１０５０縦１５０ｍｍ、横７０ｍｍ、厚さ０．８ｍｍ）の一方面をスプレー側に向けて塗装した。粉体塗料としてポリエステル樹脂粉体塗料を使用した。以下のすべての試験例で、同様の被塗物を使用し、同じ材質の粉体塗料を使用した。
【００３８】
第１塗装工程では平均粒子径４０μｍの粉体塗料を使用し、吐出量６０ｇ／分、印加電圧４０ｋＶの条件で静電粉体塗装を５秒間行った。第２塗装工程では平均粒子径１５μｍの粉体塗料を使用し、吐出量６０ｇ／分、印加電圧４０ｋＶの条件で静電粉体塗装を５秒間行った。平均粒子径は、株式会社島津製作所製のレーザー回析式粒度分布測定器ＳＡＬＤ−２０００Ｊで粒度分布を測定し、ふるい下積算体積百分率が５０％の粒子径Ｄ_ｐ５０で表している。
【００３９】
第１塗装工程後、第２塗装工程後それぞれで塗装膜厚を電磁式膜厚計（Ｋｅｔｔ社製ＬＺ−３３０Ｊ）によって測定した。第２塗装工程後の塗装膜厚は塗装総膜厚であり、第２塗装工程の塗装膜厚は塗装総膜厚と第１塗装工程の塗装膜厚の差を計算して求めた。
【００４０】
形成された塗膜の平滑性について、表面粗さ計ＴＡＹＬＯＲＨＯＢＳＯＮ（ＦｏｒｍＴａｌｙｓｕｒｆＳｅｒｉｅｓ）を用い、測定長さ１５ｍｍ、縦倍率１万倍で測定した表面形状の振幅の５点平均値を計算したうねり振幅で評価した。
【００４１】
（試験例２）
第１塗装工程で平均粒子径３６μｍの粉体塗料を使用し、第２塗装工程では平均粒子径２１μｍの粉体塗料を使用した以外は、試験例１と同じ条件で静電粉体塗装した。膜厚の測定や平滑性の評価も試験例１と同様に行った。
【００４２】
（試験例３）
第１塗装工程、第２塗装工程とも平均粒子径２５μｍの粉体塗料を使用した以外は、試験例１と同じ条件で静電粉体塗装した。膜厚の測定や平滑性の評価も試験例１と同様に行った。試験例３では原料粉体塗料タンク１内の原料粉体塗料を分級せずに使用した。試験例１、２では、この原料粉体塗料をサイクロン式分級器２で分級して使用している。
【００４３】
（試験例４）
平均粒子径２５μｍの粉体塗料を使用し第１塗装工程のみで試験例１と同様の条件で静電粉体塗装した。ただし、塗装総膜厚が上記した試験例と同じになるように塗装時間を１０秒間にした。以下の試験例５、６でも同じ塗装時間である。膜厚の測定や平滑性の評価は試験例１と同様に行った。
【００４４】
（試験例５）
サイクロン式分級器２で分級された平均粒子径１５μｍの粉体塗料を使用し、微粉粉体塗装部２０を使用して試験例４と同様の条件で静電粉体塗装した。膜厚の測定や平滑性の評価は試験例１と同様に行った。
【００４５】
（試験例６）
サイクロン式分級器２で分級された平均粒子径４０μｍの粉体塗料を使用し、粗粉粉体塗装部１０を使用して試験例４と同様の条件で静電粉体塗装した。膜厚の測定や平滑性の評価は試験例１と同様に行った。
【００４６】
（試験結果１）
表１に試験例１〜試験例６の評価結果を示す。
【表１】

試験例４〜試験例６は、一度に塗膜を形成する従来の静電粉体塗装方法を用いた試験例である。平均粒子径４０μｍ（試験例６）から平均粒子径２５μｍ（試験例４）に平均粒子径が小さくなるとうねり振幅も小さくなっている。しかし平均粒子径がさらに小さい１５μｍ（試験例５）になると、逆にうねり振幅が大きくなっている。これは静電反発による肌荒れ発生のためである。すなわち、平均粒子径を小さくするだけでは平滑性向上には限界があることを示している。
【００４７】
試験例３では第１塗装工程と第２塗装工程で静電粉体塗装しているが、いずれも同じ平均粒子径の粉体塗料を使用している。試験例４の平均粒子径と同じであり、吐出量・印加電圧とも同じ条件であるが、試験例３の方がうねり振幅が小さくなっている。静電塗装工程を２回に分割するだけでも平滑性が高くなる可能性があることを示している。
【００４８】
試験例１と試験例２では、第２粉体塗料の平均粒子径が第１粉体塗料の平均粒子径より小さい場合の試験例である。いずれも、試験例３〜試験例６に比べてうねり振幅が非常に小さく、優れた平滑性の塗膜が得られている。特に、第１粉体塗料と第２粉体塗料の平均粒子径の差が大きい試験例１の平滑性が優れている。すなわち、第１塗装工程で平均粒子径の大きい粉体塗料を粉体塗装し、その上に第２塗装工程で平均粒子径の小さい粉体塗料を粉体塗装することにより、平滑性に優れた塗膜が形成できる。
【００４９】
次に粉体塗料の吐出量の影響について試験した。吐出量とは単位時間当たりに吐出される粉体塗料の重量を表している。
【００５０】
（試験例７）
第１粉体塗料、第２粉体塗料として試験例１と同じ平均粒子径４０μｍ、１５μｍの粉体塗料をそれぞれ使用した。第１塗装工程では吐出量３０ｇ／分、印加電圧３０ｋＶの条件で静電粉体塗装を７秒間行った。第２塗装工程では吐出量７０ｇ／分、印加電圧３０ｋＶの条件で静電粉体塗装を４秒間行った。膜厚の測定や平滑性の評価も試験例１と同様に行った。
【００５１】
（試験例８）
第１塗装工程の吐出量を７０ｇ／分にし、その粉体塗装時間を４秒間にした以外は試験例７と同様の条件で静電粉体塗装した。膜厚の測定や平滑性の評価も試験例１と同様に行った。
【００５２】
（試験例９）
第２塗装工程の吐出量を３０ｇ／分にし、その粉体塗装時間を７秒間にした以外は試験例８と同様の条件で静電粉体塗装した。膜厚の測定や平滑性の評価も試験例１と同様に行った。
【００５３】
（試験結果２）
表２に試験例７〜試験例９の評価結果を示す。
【表２】

第２粉体塗料の吐出量が第１粉体塗料の吐出量より小さい試験例９では、うねり振幅が大きくなっている。これは第２粉体塗料が第１粉体塗料で形成された第１塗膜上に供給される速度が小さいため、第１塗膜の第１粉体塗料粒子間の隙間に十分密に入っていかなかったためと推察される。第２粉体塗料が第１塗膜の第１粉体塗料粒子間の隙間に密に入り込んでいないと、後に被塗物温度を上げ粉体塗料を溶融するときに、第２粉体塗料が第１粉体塗料粒子間の隙間に流れ込み、最終的な塗膜の平滑性が悪くなってしまうためである。したがって、第１粉体塗料の吐出量が第２粉体塗料の吐出量に等しいか、小さいと塗膜の平滑性を向上できる。
【００５４】
次に静電粉体塗装の印加電圧の影響について試験した。
【００５５】
（試験例１０）
第１粉体塗料、第２粉体塗料として試験例１と同じ平均粒子径４０μｍ、１５μｍの粉体塗料をそれぞれ使用した。第１塗装工程では吐出量３０ｇ／分、印加電圧３０ｋＶの条件で静電粉体塗装を７秒間行った。第２塗装工程では吐出量７０ｇ／分、印加電圧６０ｋＶの条件で静電粉体塗装を４秒間行った。膜厚の測定や平滑性の評価も試験例１と同様に行った。
【００５６】
（試験例１１）
第１塗装工程の印加電圧を６０ｋＶ以外は試験例１０と同様の条件で静電粉体塗装した。膜厚の測定や平滑性の評価も試験例１と同様に行った。
【００５７】
（試験例１２）
第２塗装工程の印加電圧を３０ｋＶ以外は試験例１１と同様の条件で静電粉体塗装した。膜厚の測定や平滑性の評価も試験例１と同様に行った。
【００５８】
（試験結果３）
表３に試験例１０〜試験例１２の評価結果を示す。
【表３】

第２塗装工程の印加電圧が第１塗装工程の印加電圧より低い試験例１２では、うねり振幅が大きくなっている。第１塗装工程の印加電圧と第２塗装工程の印加電圧が等しい試験例１１では試験例１２よりうねり振幅が小さくなっている。第１塗装工程の印加電圧が第２塗装工程の印加電圧より低い試験例１０では、うねり振幅が非常に小さく、非常に優れた平滑性を有する塗膜が得られている。
【００５９】
以上の試験例の結果は、下記のようにまとめられる。
【００６０】
・第１塗装工程で平均粒子径の大きい粉体塗料を粉体塗装し、その上に第２塗装工程で平均粒子径の小さい粉体塗料を粉体塗装することにより、平滑性に優れた塗膜が形成できる。これにより、従来、粉体塗装で用いられることが少なかった自動車車両、車両部品、船舶、家庭用電化製品、塗装鋼鈑等の塗膜形成方法およびその装置として使用できる。試験例では静電スプレーガンを用いて帯電した粉体塗料を被塗物に向かって吐出させる静電粉体塗装で示したが、流動浸漬法でも粉体流動層を用いる静電塗装方法でも同様の効果を奏する。
【００６１】
・静電スプレーガンを用いて帯電した粉体塗料を被塗物に向かって吐出させる静電粉体塗装の場合には、第１粉体塗料の吐出量が第２粉体塗料の吐出量以下であれば、より平滑性に優れた塗膜を形成できる。
【００６２】
・静電粉体塗装の場合、第１粉体塗料の帯電印加電圧が第２粉体塗料の帯電印加電圧より低ければ、より平滑性に優れた塗膜を形成できる。試験例では静電スプレーガンを用いて帯電した粉体塗料を被塗物に向かって吐出させる静電粉体塗装で示したが、粉体流動層を用いる静電塗装方法でも同様の効果を奏する。粉体塗料の帯電印加電圧の大小は、被塗物に対する粉体塗料の帯電電圧の絶対値で比較している。一般的には、被塗物がアースされ、粉体塗料が負に帯電して静電塗装される。この場合には粉体塗料の帯電印加電圧の絶対値で比較される。仮に粉体塗料を正に帯電して静電塗装する場合には、粉体塗料の帯電印加電圧をそのまま比較できる。また被塗物がアースされず、アースに対して電位を有する場合には、被塗物に対する粉体塗料の電位差の絶対値で比較される。
【００６３】
・第１塗装工程と第２塗装工程に分けて粉体塗装することによって、平均粒子径の異なる粉体塗料ごとに適した塗装条件を設定することが可能となり、同じ膜厚で静電反発のない塗装外観にすることができる。また粒子径の大きい粉体塗料が先に消費され、平均粒子径の小さい粉体塗料の使用効率が悪く、粉体塗料の歩留まりが悪い問題も解決され、粉体塗料の使用効率が向上し、廃棄物を低減することができる。
【００６４】
実施形態のように分級装置によって平均粒子径の大きい粉体塗料と小さい粉体塗料に分級すれば、粒度分布の大きな市販の粉体塗料が使用でき、かつ被塗物や粉体塗料等に適した平均粒子径に分級して使用でき、より平滑性に優れた塗膜を得ることができる。また第１塗装工程と第２塗装工程を同じブース内で塗装しても、被塗物に付着しなかった粉体塗料を回収し、再び使用することができ、廃棄物をより低減できる。
【００６５】
図２は別の実施形態の粉体塗装装置を説明する説明図である。図１と同様の部位には同じ符号を付し説明は省略する。この粉体塗装装置では分級装置は設けられておらず、別に分級した第１粉体塗料が粗粉粉体塗料タンク１１に入れられ、第１粉体塗料より小さい平均粒子径を有する第２粉体塗料が微粉粉体塗料タンク２１にに入れられている。この実施形態でも第１塗装工程と第２塗装工程を同じブース内で塗装しているが、第１塗装工程と第２塗装工程の塗装ブースを仕切り、それぞれの塗装ブースで被塗物に付着しなかった粉体塗料を回収し、それぞれの粉体塗料タンクに戻して再使用してもよい。
【００６６】
【発明の効果】
以上のように、本発明は、第１粉体塗料を被塗物に粉体塗装する第１塗装工程と、該第１塗装工程で前記第１粉体塗料が塗装された前記被塗物に前記第１粉体塗料より小さい平均粒子径を有する第２粉体塗料を粉体塗装する第２塗装工程が設けられていることを特徴とする粉体塗装方法または第１粉体塗料を被塗物に粉体塗装する粗粉粉体塗装部と、前記第１粉体塗料より小さい平均粒子径を有する第２粉体塗料を前記被塗物に粉体塗装する微粉粉体塗装部が設けられていることを特徴とする粉体塗装装置であるので、平滑性に優れた塗膜が形成できる。
【図面の簡単な説明】
【図１】実施形態の静電粉体塗装装置を説明する説明図
【図２】別の実施形態の粉体塗装装置を説明する説明図
【符号の説明】
２…サイクロン式分級器（分級装置）
９ａ、９ｂ…被塗物
１０…粗粉粉体塗装部
１１…粗粉粉体塗料タンク
１３…高電圧発生装置
１４…静電スプレーガン
２０…微粉粉体塗装部
２１…微粉粉体塗料タンク
２３…高電圧発生装置
２４…静電スプレーガン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a powder coating method and a powder coating apparatus.
[0002]
[Prior art]
In recent years, the transition from solvent coating to powder coating has been promoted rapidly due to the impact on the global environment and the increase in environmental awareness. Conventionally, a powder coating having an average particle diameter of 35 to 50 μm is generally used, but the smoothness is considerably inferior to solvent coating. Many products are required to have an appearance similar to that of solvent coating, and in order to expand the transition to powder coating and improve the environment, it is required to realize powder coating with excellent smoothness.
[0003]
For this purpose, powder coatings having an average particle size of 25 μm or less have begun to be used. For example, an electrostatic powder coating method using a powder fluidized bed using a powder having an average particle diameter of 5 to 20 μm as in Patent Document 1 has been proposed.
[0004]
[Patent Document 1]
JP-A-10-120945 ([0012])
[0005]
[Problems to be solved by the invention]
However, there is a problem in that sufficient smoothness cannot be obtained even if a powder coating material having a small average particle diameter as in Patent Document 1 is used. On the other hand, when the average particle size is too small, there is a problem that the smoothness deteriorates.
[0006]
This invention solves the said subject and provides the powder coating method and powder coating apparatus which can form the coating film excellent in smoothness.
[0007]
In order to solve the above technical problem, the technical means taken in claim 1 of the present invention (hereinafter referred to as the first technical means) is to apply the first powder coating to the object to be coated. A first coating step, and a powder coating of a second powder coating having an average particle size smaller than the first powder coating on the article coated with the first powder coating in the first coating step A second coating step is provided, and the first coating step and the second coating step are electrostatic powder coatings in which powder coating is charged and discharged toward the object to be coated, and powder coating is performed. The powder coating method is characterized in that the discharge amount of the paint is equal to or less than the discharge amount of the second powder paint .
[0008]
The effects of the first technical means are as follows.
[0009]
The effects of the first technical means are as follows. That is, a powder coating with a large average particle size is powder-coated in the first coating step, and a powder coating with a small average particle size is powder-coated thereon in the second coating step. film can in formation, because the discharge amount of the first powder coating is less than the discharge amount of the second powder coating can be formed smoother excellent in coating film.
[0010]
In order to solve the above technical problem, the technical means taken in claim 2 of the present invention (hereinafter referred to as second technical means) is that the first painting process and the second painting process are powder. 2. The electrostatic powder coating in which a body coating is charged to perform powder coating, wherein the charging application voltage of the first powder coating is lower than the charging application voltage of the second powder coating. This is a powder coating method.
[0011]
The effects of the second technical means are as follows.
[0012]
That is, since the charge application voltage of the first powder paint is lower than the charge application voltage of the second powder paint, the charge density (charge amount per unit area) of the coating film of the first powder paint is small, and the application Since the second powder coating is applied on the film by a large electrostatic force, a coating film with more excellent smoothness can be formed.
[0013]
In order to solve the above technical problem, the technical means taken in claim 3 of the present invention (hereinafter referred to as third technical means) is that the first painting process and the second painting process are powder. Electrostatic powder coating in which a body coating is charged and discharged toward the object to be coated, and the discharge amount of the first powder coating is less than or equal to the discharge amount of the second powder coating The powder coating method according to claim 1.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The present inventor has considered the reason why the smoothness of the coating film is not sufficiently improved even when a powder coating material having a small average particle diameter is used. The powder coating is a collection of particles having different particle sizes. During powder coating, a phenomenon is observed in which particles having a large particle diameter are attached and particles having a small particle diameter are difficult to adhere. This is presumed to be the reason why the smoothness cannot be sufficiently improved. Also, in electrostatic coating methods such as the electrostatic powder coating method and the electric field flow dipping method, if particles with a small average particle diameter are used, electrostatic repulsion will be strong in the coating film, and the skin will be distorted. The smoothness of the coating film was deteriorated. It was inferred that particles having a small particle size had a large specific surface area and a large charge amount per particle volume. The present inventor has intensively studied based on these inferences to arrive at the present invention.
[0023]
Two types of powder paints with different average particle sizes are prepared. First, powder paint with a large average particle size is powder-coated in the first coating process, and then formed in the first coating process in the second coating process. A powder coating with a small average particle size is powder coated on the coated film. By doing so, since the powder coating having a large average particle size and the powder coating having a small average particle size are separately powder-coated, the phenomenon that the particles having a small particle size are prevented from adhering to the large particles can be eliminated. In addition, since coating is performed so that the unevenness of the coating film formed with large particles in the first coating process, that is, the gap between large particles is filled with small particles in the second coating process, small particles can be effectively adhered and smooth. A coating film with excellent properties can be formed. Furthermore, since the coating film is formed with large particles in the first coating process, the charge density of the formed coating film is low, so there is little electrostatic repulsion, and there is no occurrence of distorted skin, and a coating film with excellent smoothness is formed. it can.
[0024]
Since the first painting process and the second painting process are separated, the powder coating suitable for the case of painting a powder paint with a large average particle diameter and the case of painting a powder paint with a large average particle diameter You can set conditions. In particular, in the second coating step, by controlling the amount of charge of the powder coating material, electrostatic repulsion can be reduced and the occurrence of distorted skin can be eliminated.
[0025]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view illustrating a powder coating apparatus according to an embodiment. This powder coating apparatus is an electrostatic powder coating apparatus that performs powder coating by charging a powder coating material and discharging it toward an object to be coated. A raw material powder coating tank 1, a cyclone classifier (classifying device) 2, a coarse powder coating unit 10, a fine powder coating unit 20, a powder coating collection device 4, a coating booth 3, and the like are included.
[0026]
The coarse powder coating unit 10 includes a coarse powder coating tank 11, an ejector 12, a high voltage generator 13, an electrostatic spray gun 14, and the like. The ejector 12 is connected to a coarse powder coating tank 11, and electrostatic spray is provided in the coating booth 3 through the powder coating transport line 15 for the powder coating in the coarse powder coating tank 11. It is transported to the gun 14. The high voltage generator 13 is connected to the electrostatic spray gun 14 via a high voltage electric wire 16.
[0027]
Similarly, the fine powder coating unit 20 includes a fine powder coating tank 21, an ejector 22, a high voltage generator 23, an electrostatic spray gun 24, and the like. The ejector 22 is connected to a fine powder paint tank 21, and an electrostatic spray gun 24 provided in the painting booth 3 through the powder paint transport line 25 for the powder paint in the fine powder paint tank 21. To be transported to. The high voltage generator 23 is connected to the electrostatic spray gun 24 via a high voltage electric wire 26.
[0028]
A cyclone classifier 2 is connected to the raw material powder coating tank 1. The cyclone classifier 2 is connected to a coarse powder coating tank 11 through a powder coating transport line 5, and is connected to a fine powder coating tank 21 through a powder coating transport line 6.
[0029]
Excess powder paint that has not adhered to the object to be coated in the painting booth 3 is sent to the powder paint collection device 4 via the powder collection pipe 7. The powder paint recovery device 4 is connected to the powder paint tank 1 through a powder recovery pipe line 8.
[0030]
Reference numerals 9a and 9b are objects to be coated, which are respectively grounded and installed in the painting booth 3, and sequentially move from the position of the object 9a to the position of the object 9b.
[0031]
The raw material powder paint in the raw material powder paint tank 1 is sent to a cyclone classifier 2, and a coarse powder paint (first powder paint) having a large average particle diameter and a fine powder paint (a small average particle diameter) ( Second powder coating). The classified coarse powder paint is transported and stored in the coarse powder paint tank 11 via the powder paint transport line 5, and the fine powder paint is fine powder via the powder paint transport pipe 6. It is transported and stored in the paint tank 21.
[0032]
The coarse powder paint stored in the coarse powder paint tank 11 is supplied to the electrostatic spray gun 14 by the ejector 12. The coarse powder coating material supplied to the electrostatic spray gun 14 is negatively charged by the high voltage generator 13 and sprayed toward the object 6a. The sprayed coarse powder coating material adheres to the grounded article 6a to form a coating film.
[0033]
Similarly, the fine powder paint stored in the fine powder paint tank 21 is supplied to the electrostatic spray gun 24 by the ejector 22. The fine powder coating material supplied to the electrostatic spray gun 24 is negatively charged by the high voltage generator 23 and sprayed toward the object 6b. The sprayed fine powder coating material adheres to the grounded object 6b to form a coating film.
[0034]
The object to be coated is first moved to the position of the object to be coated 6a, and the coarse powder coating is electrostatic powder coated (first coating process). Next, the object to be coated is moved to the position of the object to be coated 6b, and the fine powder coating material is electrostatically powder coated (second coating process).
[0035]
The powder paint that has not adhered to the object to be coated in the first painting process and the second painting process is collected by the powder paint collecting device 4 through the powder collecting pipe 7 and through the powder collecting pipe 8. And returned to the raw material powder coating tank 1.
[0036]
Using this powder coating apparatus, the following powder coating test was carried out.
[0037]
(Test Example 1)
As an object to be coated, one surface of an aluminum test panel (aluminum material A1050 manufactured by Nippon Test Panel Co., Ltd., length 150 mm, width 70 mm, thickness 0.8 mm) was applied toward the spray side. A polyester resin powder coating was used as the powder coating. In all the following test examples, the same coated material was used, and a powder coating material of the same material was used.
[0038]
In the first coating step, a powder coating having an average particle diameter of 40 μm was used, and electrostatic powder coating was performed for 5 seconds under the conditions of a discharge rate of 60 g / min and an applied voltage of 40 kV. In the second coating step, a powder coating material having an average particle diameter of 15 μm was used, and electrostatic powder coating was performed for 5 seconds under the conditions of a discharge rate of 60 g / min and an applied voltage of 40 kV. The average particle size, the particle size distribution measured with a laser diffraction particle size distribution measuring apparatus SALD-2000J manufactured by Shimadzu Corporation, minus sieve cumulative volume percentage is expressed in 50% of the particle diameter D _p50.
[0039]
After the first coating step and after the second coating step, the coating film thickness was measured by an electromagnetic film thickness meter (LZ-330J manufactured by Kett). The coating film thickness after the second coating process is the total coating film thickness, and the coating film thickness in the second coating process was obtained by calculating the difference between the coating total film thickness and the coating film thickness in the first coating process.
[0040]
For the smoothness of the formed coating film, a surface roughness meter TAYLOR HOBSON (Form Talysurf Series) was used to calculate a five-point average value of the amplitude of the surface shape measured at a measurement length of 15 mm and a vertical magnification of 10,000 times. The amplitude was evaluated.
[0041]
(Test Example 2)
Electrostatic powder coating was performed under the same conditions as in Test Example 1 except that a powder coating material having an average particle size of 36 μm was used in the first coating step and a powder coating material having an average particle size of 21 μm was used in the second coating step. Measurement of film thickness and evaluation of smoothness were also performed in the same manner as in Test Example 1.
[0042]
(Test Example 3)
Electrostatic powder coating was performed under the same conditions as in Test Example 1 except that a powder coating material having an average particle diameter of 25 μm was used in both the first coating process and the second coating process. Measurement of film thickness and evaluation of smoothness were also performed in the same manner as in Test Example 1. In Test Example 3, the raw material powder paint in the raw material powder paint tank 1 was used without being classified. In Test Examples 1 and 2, this raw material powder paint is classified by the cyclone classifier 2 and used.
[0043]
(Test Example 4)
A powder coating material having an average particle diameter of 25 μm was used, and electrostatic powder coating was performed under the same conditions as in Test Example 1 only in the first coating step. However, the coating time was set to 10 seconds so that the total coating thickness would be the same as in the above test example. The same coating time is used in the following Test Examples 5 and 6. Measurement of film thickness and evaluation of smoothness were performed in the same manner as in Test Example 1.
[0044]
(Test Example 5)
The powder coating material with an average particle diameter of 15 μm classified by the cyclone classifier 2 was used, and electrostatic powder coating was performed using the fine powder coating unit 20 under the same conditions as in Test Example 4. Measurement of film thickness and evaluation of smoothness were performed in the same manner as in Test Example 1.
[0045]
(Test Example 6)
The powder coating material with an average particle diameter of 40 μm classified by the cyclone classifier 2 was used, and the coarse powder coating portion 10 was used for electrostatic powder coating under the same conditions as in Test Example 4. Measurement of film thickness and evaluation of smoothness were performed in the same manner as in Test Example 1.
[0046]
(Test result 1)
Table 1 shows the evaluation results of Test Examples 1 to 6.
[Table 1]

Test Examples 4 to 6 are test examples using a conventional electrostatic powder coating method for forming a coating film at a time. As the average particle size decreases from the average particle size of 40 μm (Test Example 6) to the average particle size of 25 μm (Test Example 4), the swell amplitude also decreases. However, when the average particle diameter is 15 μm (Test Example 5), the undulation amplitude is increased. This is due to the occurrence of rough skin due to electrostatic repulsion. That is, it is shown that there is a limit to improving smoothness only by reducing the average particle size.
[0047]
In Test Example 3, electrostatic powder coating is performed in the first coating step and the second coating step, but both use a powder coating having the same average particle diameter. Although it is the same as the average particle diameter of Test Example 4 and the discharge amount and the applied voltage are the same, the swell amplitude is smaller in Test Example 3. It shows that even if the electrostatic coating process is divided only twice, smoothness may be increased.
[0048]
Test Example 1 and Test Example 2 are test examples when the average particle size of the second powder paint is smaller than the average particle size of the first powder paint. In any case, the swell amplitude was very small as compared with Test Examples 3 to 6, and a coating film having excellent smoothness was obtained. In particular, the smoothness of Test Example 1 having a large difference in average particle diameter between the first powder coating and the second powder coating is excellent. That is, by applying powder coating with a large average particle diameter in the first coating process and powder coating with powder coating with a small average particle diameter in the second coating process, excellent smoothness is achieved. A coating film can be formed.
[0049]
Next, the influence of the discharge amount of the powder paint was tested. The discharge amount represents the weight of the powder coating material discharged per unit time.
[0050]
(Test Example 7)
As the first powder coating material and the second powder coating material, the same powder coating materials having average particle diameters of 40 μm and 15 μm as in Test Example 1 were used. In the first coating step, electrostatic powder coating was performed for 7 seconds under the conditions of a discharge rate of 30 g / min and an applied voltage of 30 kV. In the second coating step, electrostatic powder coating was performed for 4 seconds under the conditions of a discharge rate of 70 g / min and an applied voltage of 30 kV. Measurement of film thickness and evaluation of smoothness were also performed in the same manner as in Test Example 1.
[0051]
(Test Example 8)
Electrostatic powder coating was performed under the same conditions as in Test Example 7 except that the discharge amount in the first coating step was 70 g / min and the powder coating time was 4 seconds. Measurement of film thickness and evaluation of smoothness were also performed in the same manner as in Test Example 1.
[0052]
(Test Example 9)
The electrostatic powder coating was performed under the same conditions as in Test Example 8 except that the discharge amount in the second coating step was 30 g / min and the powder coating time was 7 seconds. Measurement of film thickness and evaluation of smoothness were also performed in the same manner as in Test Example 1.
[0053]
(Test result 2)
Table 2 shows the evaluation results of Test Example 7 to Test Example 9.
[Table 2]

In Test Example 9 in which the discharge amount of the second powder paint is smaller than the discharge amount of the first powder paint, the undulation amplitude is large. This is because the speed at which the second powder coating material is supplied onto the first coating film formed by the first powder coating material is small, so that the gap between the first powder coating particles of the first coating film is sufficiently dense. It is inferred that this was not possible. If the second powder paint does not penetrate into the gaps between the first powder paint particles of the first coating film, the second powder paint will be used when the temperature of the object is increased later and the powder paint is melted. It is because it flows into the gaps between the first powder coating particles and the smoothness of the final coating film is deteriorated. Therefore, if the discharge amount of the first powder paint is equal to or smaller than the discharge amount of the second powder paint, the smoothness of the coating film can be improved.
[0054]
Next, the influence of the applied voltage of electrostatic powder coating was tested.
[0055]
(Test Example 10)
As the first powder coating material and the second powder coating material, the same powder coating materials having average particle diameters of 40 μm and 15 μm as in Test Example 1 were used. In the first coating step, electrostatic powder coating was performed for 7 seconds under the conditions of a discharge rate of 30 g / min and an applied voltage of 30 kV. In the second coating step, electrostatic powder coating was performed for 4 seconds under the conditions of a discharge rate of 70 g / min and an applied voltage of 60 kV. Measurement of film thickness and evaluation of smoothness were also performed in the same manner as in Test Example 1.
[0056]
(Test Example 11)
Electrostatic powder coating was performed under the same conditions as in Test Example 10 except that the applied voltage in the first coating step was 60 kV. Measurement of film thickness and evaluation of smoothness were also performed in the same manner as in Test Example 1.
[0057]
(Test Example 12)
Electrostatic powder coating was performed under the same conditions as in Test Example 11 except that the applied voltage in the second coating step was 30 kV. Measurement of film thickness and evaluation of smoothness were also performed in the same manner as in Test Example 1.
[0058]
(Test result 3)
Table 3 shows the evaluation results of Test Example 10 to Test Example 12.
[Table 3]

In Test Example 12 in which the applied voltage in the second painting process is lower than the applied voltage in the first painting process, the swell amplitude is large. In Test Example 11 in which the applied voltage in the first painting process and the applied voltage in the second painting process are equal, the undulation amplitude is smaller than in Test Example 12. In Test Example 10 where the applied voltage in the first coating process is lower than the applied voltage in the second coating process, a coating film having very small undulation amplitude and excellent smoothness is obtained.
[0059]
The results of the above test examples are summarized as follows.
[0060]
-Powder coating with a large average particle diameter is applied in the first coating process, and powder coating with a small average particle diameter is applied on the powder coating in the second coating process. A film can be formed. Thereby, it can be used as a coating film forming method and apparatus for automobile vehicles, vehicle parts, ships, household appliances, painted steel plates, etc., which have been rarely used in powder coating. In the test example, the electrostatic powder coating was used to discharge the charged powder coating toward the substrate by using an electrostatic spray gun, but the same applies to both the fluid immersion method and the electrostatic coating method using a powder fluidized bed. The effect of.
[0061]
-In the case of electrostatic powder coating in which a charged powder paint is discharged toward an object using an electrostatic spray gun, the discharge amount of the first powder paint is less than the discharge amount of the second powder paint. If it is, the coating film excellent in smoothness can be formed.
[0062]
In the case of electrostatic powder coating, if the charge application voltage of the first powder paint is lower than the charge application voltage of the second powder paint, a coating film with better smoothness can be formed. In the test example, the electrostatic powder coating was used to discharge the charged powder paint toward the workpiece using an electrostatic spray gun. However, the electrostatic coating method using a powder fluidized bed has the same effect. . The magnitude of the charging applied voltage of the powder coating is compared with the absolute value of the charging voltage of the powder coating with respect to the object to be coated. In general, the object to be coated is grounded, and the powder coating is negatively charged and electrostatically coated. In this case, the absolute value of the charging applied voltage of the powder coating is compared. If the powder coating is positively charged and electrostatically applied, the charging applied voltage of the powder coating can be compared as it is. When the object to be coated is not grounded and has a potential with respect to the ground, the absolute value of the potential difference of the powder coating material with respect to the object to be coated is compared.
[0063]
-By applying powder coating in the first coating process and the second coating process, it is possible to set suitable coating conditions for each powder coating material with different average particle diameters, and electrostatic repulsion can be achieved with the same film thickness. There can be no painted appearance. In addition, powder paint with a large particle size is consumed first, the use efficiency of powder paint with a small average particle size is poor, the problem of poor yield of powder paint is solved, the use efficiency of powder paint is improved, Waste can be reduced.
[0064]
By classifying into a powder paint with a large average particle size and a powder paint with a small average particle size using a classifier as in the embodiment, a commercially available powder paint with a large particle size distribution can be used and suitable for objects to be coated and powder paints. Thus, it is possible to obtain a coating film which is classified into an average particle diameter and is more excellent in smoothness. Even if the first painting process and the second painting process are applied in the same booth, the powder paint that has not adhered to the object can be collected and reused, and waste can be further reduced.
[0065]
FIG. 2 is an explanatory view illustrating a powder coating apparatus according to another embodiment. The same parts as those in FIG. In this powder coating apparatus, no classification device is provided, and the first powder paint classified separately is put in the coarse powder paint tank 11, and the second powder having an average particle size smaller than that of the first powder paint. Body paint is placed in a fine powder paint tank 21. In this embodiment, the first painting process and the second painting process are applied in the same booth, but the first and second painting processes are separated from each other. The powder coating that has not been collected may be collected and returned to the respective powder coating tank for reuse.
[0066]
【The invention's effect】
As described above, the present invention provides a first coating process in which a first powder coating is powder-coated on an object to be coated, and the coating on which the first powder coating is coated in the first coating process. A powder coating method or a first powder coating method is provided, wherein a second coating step of powder coating a second powder coating having an average particle size smaller than the first powder coating is provided. There are provided a coarse powder coating portion for powder coating on an object and a fine powder coating portion for powder coating a second powder coating having an average particle size smaller than that of the first powder coating on the object to be coated. Since the powder coating apparatus is characterized in that, a coating film having excellent smoothness can be formed.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating an electrostatic powder coating apparatus according to an embodiment. FIG. 2 is an explanatory diagram illustrating a powder coating apparatus according to another embodiment.
2. Cyclone classifier (classifier)
9a, 9b ... Coating object 10 ... Coarse powder coating part 11 ... Coarse powder coating tank 13 ... High voltage generator 14 ... Electrostatic spray gun 20 ... Fine powder coating part 21 ... Fine powder coating tank 23 ... High voltage generator 24 ... Electrostatic spray gun

Claims

A first coating step of powder-coating a first powder coating material to be coated;
A second coating step is provided in which a second powder coating having an average particle size smaller than that of the first powder coating is powder-coated on the object to be coated with the first powder coating in the first coating step. And
The first coating step and the second coating step are electrostatic powder coatings in which a powder coating is charged and discharged toward the object to be coated, and powder coating is performed.
A powder coating method, wherein a discharge amount of the first powder paint is equal to or less than a discharge amount of the second powder paint .

The first coating step and the second coating step are electrostatic powder coatings in which powder coating is charged and powder coating is performed, and a charging applied voltage of the first powder coating is charged by charging the second powder coating. The powder coating method according to claim 1, wherein the applied voltage is lower than the applied voltage.