JP3540885B2 - Painting method - Google Patents

Description

【０００１】
【発明の属する技術分野】
本発明は新規な塗装方法に係わる。
【０００２】
【従来の技術】
従来、自動車ボデ−等の金属被塗物には下塗り電着塗装、水洗、焼付け、研磨、水洗、乾燥、中塗り塗装、焼付け、上塗り塗装、焼付けをおこなって下塗り〜上塗り塗膜が形成されている。しかしながら、該塗装工程において下塗り電着塗装を行った後焼付け、研磨、水洗、乾燥後中塗りが塗装されるために該焼付け〜乾燥工程の設備、設置及び運転等に掛かる費用が高くなるとともにゴミ、ブツ等のコンタミが入り易くなり塗膜外観が低下する。このために自動車等の分野からこれらの塗装工程の改善が要求されているのが実情である。また、従来から中塗り塗装として有機溶剤形塗料が使用されており、該塗料は塗装作業中に有機溶剤を発生するため環境衛生上好ましくないといった問題点がある。
【０００３】
【発明が解決しようとする課題】
本発明は従来からの塗装工程の短縮をはかるとともに有機溶剤を含まない塗装系の開発を目的とする。
【０００４】
【課題を解決するための手段】
本発明者等は、上記した問題点を解決するために鋭意研究を重ねた結果、含水率が５重量％以下の未硬化電着塗膜の表面に特定の粉体塗料を塗装することにより従来からの問題点が改善できる方法であることを見出だし、本発明を完成するに至った。
【０００５】
即ち、本発明は、金属被塗物に熱硬化性カチオン電着塗料を塗装して下塗り電着塗膜を形成した後、
▲１▼該電着塗膜を水洗し、
▲２▼次いで、水切り乾燥をおこなって、含水率が５重量％以下の未硬化電着塗膜を形成し、
▲３▼該未硬化電着塗膜の硬化開始時間よりも遅く且つ未硬化電着塗膜の表面張力よりも小さい熱硬化性粉体塗料を静電粉体塗装して粉体塗膜を形成した後、
▲４▼焼付けをおこなって電着塗膜及び粉体塗膜を同時に硬化させる
ことを特徴とする塗装方法に係わる。
【０００６】
【発明の実施の形態】
本発明塗装方法において使用される金属被塗物は、従来から自動車ボデ−、部品等の塗装に使用される金属被塗物が特に制限なしに使用でき、具体的には、アルミニウム、アルマイト、鉄鋼等の金属素材及び該金属素材表面に亜鉛、スズ、クロム、アルミニウム等をメッキした金属素材あるいはこれらの金属素材表面をクロム酸、燐酸等で化成処理したもの等の広範囲な金属素材が挙げられる。
【０００７】
本発明塗装方法において使用されるカチオン電着塗料としては、従来から公知のカチオン電着塗料が使用でき、特にエポキシ樹脂をベ−ス樹脂として含有する電着塗料が好適に使用できる。該カチオン電着塗料としては、例えば、アミン付加エポキシ樹脂やアミン付加ポリエステル変性エポキシ樹脂をベ−ス樹脂としてこのものにプロックポリイソシアネ−トの架橋剤を配合もしくは付加したものを中和、水分散したものが使用できる。カチオン電着塗料には、必要に応じて顔料、有機溶剤、硬化触媒、界面活性剤等を配合することができる。
【０００８】
カチオン電着塗装方法としては、従来から公知の塗装方法で行うことができる。例えば、カチオン電着塗料を電着浴とし、金属被塗物を陰極とし金属溶出のない素材（炭素板等）を陽極として通電することにより行うことができる。通電条件は電着塗装膜厚が約１０〜４０ミクロン、好ましくは約１５〜３０ミクロンの範囲で行うことが望ましい。また、電着塗装後、ウルトラフィルトレ−シヨン濾過液、限外濾過液、上水などにより水洗が行われる。
【０００９】
該カチオン電着塗膜は上記水洗を行った後、水切り乾燥を行ってカチオン電着塗膜の含水率が５重量％以下、好ましくは３重量％以下になるように水分の調整を行う。該カチオン電着塗膜の含水率が５重量％を越えると電着塗膜層から揮発、拡散した水分は粉体塗膜とは相溶性がないために電着塗膜及び粉体塗膜との界面で多く存在するようになり、その結果として粉体塗膜の外観や付着性等の性能を低下させたり、また該水分は粉体塗膜を透過し難いために塗膜中に泡として残り易くなりワキ、ピンホ−ル等の塗膜外観を低下させたりするといった欠点がある。また、水切り乾燥後のカチオン電着塗膜は未硬化塗膜である。未硬化塗膜は一部硬化塗膜であっても差支えない。該未硬化塗膜はゲル分率（塗膜を剥しとり３００メッシュのステンレススチ−ル製の網状容器に入れソックスレ−抽出器でアセトン溶媒を用いて還流温度で２時間抽出させた後、式 ゲル分率＝（抽出後の試料の重量／抽出前の試料の重量）×１００）が約１０重量％以下、好ましくは約５重量％以下の範囲である。
【００１０】
水切り乾燥後のカチオン塗膜として硬化したものを使用した場合にはカチオン電着塗膜と粉体塗膜との付着性、粉体塗膜の平滑性、光沢等の塗膜外観が低下すると共に焼付け硬化工程が増えるため好ましくない。上記水切り乾燥条件は金属被塗物の大きさ、熱容量、材質等や乾燥機の風量等に応じて電着塗膜の含水率が５重量％以下で塗膜の硬化が始まらない条件を適宜決めれば良いが、通常、約４０〜１２０℃、好ましくは約５０〜１００℃で約５〜３０分間、好ましくは約５〜２０分間の範囲である。
【００１１】
本発明塗装方法において使用される粉体塗料は、その粉体塗料の硬化開始時間（電着塗膜と同一の焼付け温度条件）が上記水切り乾燥後のカチオン電着塗膜の硬化開始時間よりも遅く、且つ粉体塗料の表面張力がカチオン電着塗膜の表面張力よりも小さいことが必要である。粉体塗料の硬化開始時間がカチオン電着塗膜の硬化開始時間と同一もしくは粉体塗料の方がカチオン電着塗膜よりも早く（短く）なると粉体塗膜の外観（平滑性、チヂミ等）が悪くなるので好ましくない。該粉体塗料の硬化開始時間は、例えば約１４０〜１８０℃の焼付け温度範囲で粉体塗料の硬化開始時間がカチオン電着塗膜と比較して、特に約１０秒間〜２０分間、特に約２０秒間〜１５分間長いことが好ましい。粉体塗料及び電着塗膜の硬化開始時間は、例えば、使用する樹脂組成、架橋剤、触媒等によって調整することができる。
【００１２】
粉体塗料及びカチオン電着塗膜の硬化開始時間は、剛体振り子型粘弾性測定装置［例えば、ポリファイル．Ｖｏｌ３１．Ｎｏ３６２（１９９４）２６〜２８頁に記載の最近の表面・界面の評価技術、色材協会誌．５１巻（１９７８）４０３〜４０９頁に記載の剛体振り子の自由減衰振動による塗膜形成過程の粘弾性型測定及び実開平６−５６７５７号記載の熱及び時間的に粘弾性変化を生じる塗料の粘弾性測定］を用いて、その熱（焼付け温度に相当）による時間（焼付け時間に相当）と塗膜の振り子の振動周期（粘弾性）を測定し、該振動周期の変曲点（時間）により硬化開始時間を求めることができる。
【００１３】
また、上記した塗料の表面張力において、粉体塗料（粉体塗膜）の表面張力がカチオン電着塗膜と同一もしくは粉体塗料の方がカチオン電着塗膜よりも大きくなると粉体塗膜の外観（平滑性、ハジキ、ヘコミ、塗膜表面光沢等）が悪くなるので好ましくない。粉体塗料の表面張力は、粉体塗膜として、通常、２５〜４５ダイン／ｃｍ、好ましくは２５〜４０ダイン／ｃｍの範囲であり、カチオン電着塗膜の表面張力は、通常、３０〜５０ダイン／ｃｍ、好ましくは３５〜４５ダイン／ｃｍの範囲であり、そしてその粉体塗料と電着塗膜との表面張力の差は、粉体塗料が電着塗膜と比較して約５ダイン／ｃｍより小さく、特に約７〜３０ダイン／ｃｍ小さいことが好ましい。粉体塗料及び電着塗膜の表面張力は、例えば、使用する基体樹脂、架橋剤、添加剤等により調整することができる。
【００１４】
本発明塗装方法において使用される粉体塗料は、上記した条件を満足するものであれば特に制限なしに従来から公知の熱硬化性粉体塗料を使用することができる。該熱硬化性粉体塗料としては、例えば、エポキシ樹脂、ポリエステル樹脂（水酸基、カルボキシル基等の官能基を含有したもの）、アクリル系樹脂（水酸基、カルボキシル基、エポキシ基等の官能基を含有したもの）を基体樹脂としこのものに架橋剤（水酸基と反応する架橋剤としてブロックポリイソシアネ−ト、テトラメトキシメチルグリコルリル等、カルボキシル基と反応する架橋剤としてポリエポキシド、β−ヒドロキシアルキルアミド等、エポキシ基と反応する架橋剤としてポリカルボン化合物、ポリカルボン酸ポリエステル樹脂、酸無水物、フェノ−ル樹脂、ジシアンジアミド、有機酸ジヒドラジッド、芳香族スルホニウム塩カチオン重合触媒等）を配合してなる熱硬化性粉体塗料が好適に使用できる。
【００１５】
熱硬化性粉体塗料において、上記した成分以外に、例えば、着色顔料、充填剤、流動性調整剤、ブロッキング防止剤、表面調整剤、ワキ防止剤、酸化防止剤、硬化促進剤、その他樹脂等のその他の配合物を必要に応じて配合できる。該粉体プライマ−は約１５０メッシュを透過したものが好適に使用できる。
【００１６】
熱硬化性粉体塗料は、従来から公知の熱硬化性粉体塗料の製造方法、例えば、基体樹脂、架橋剤及び必要に応じてその他の配合物を配合した後、ドライブレンドを行い、次ぎに溶融ブレンドを行った後、冷却、粗粉砕、微粉砕、濾過を行って製造することができる。
【００１７】
熱硬化性粉体塗料の塗装は、それ自体公知の静電粉体塗装方法、例えば、コロナ帯電式、摩擦帯電式等によって行うことができる。熱硬化性粉体塗料の膜厚は、通常、約２０〜１００ミクロン、好ましくは約３０〜６０ミクロンの範囲が好適である。熱硬化性粉体塗料の焼付けはカチオン電着塗膜と同時に硬化できる温度条件で焼付けを行うことができる、具体的には、例えば約１４０〜１８０℃で約２０〜４０分間の範囲が好ましい。
【００１８】
熱硬化性粉体塗膜が形成された塗膜表面には、粉体塗料、有機溶剤系塗料、非水分散系塗料等の硬化型上塗り塗料を塗装することができる。これらの塗料としては従来から自動車分野で使用されている塗料を特に制限なしに使用することができる。上塗り塗料は、例えばワンコ−トであっても２コ−ト１ベ−ク方式、２コ−ト２ベ−ク方式、３コ−ト２ベ−ク方式であっても差支えない。また、上塗り塗料は、例えばソリッド仕上げ、メタリック仕上げ、パ−ル仕上げのいずれの仕上げであっても差支えない。
【００１９】
【実施例】
以下、実施例を掲げて本発明を詳細に説明する。
【００２０】
実施例１
燐酸亜鉛化成処理を施した厚さ０．８×縦３００×横１００（ｍｍ）のダル鋼板にカチオン電着塗料（アミン付加エポキシ樹脂をベ−ス樹脂としてこのものにプロックポリイソシアネ−トの架橋剤及び錫触媒を配合したもの、硬化開始時間７２０秒“１６０℃”、表面張力４２ダイン／ｃｍ）を乾燥膜厚が約２０ミクロンになるようにカチオン電着塗装し、ウルトラフィルトレ−ション濾過液で水洗した後、１６０℃で約１０分間乾燥し、含水率が約３重量％の未硬化乾燥電着塗膜を得た。次いで該電着塗膜の表面にエポキシポリエステル熱硬化型樹脂粉体塗料（ファインデックＭ−８８６０“大日本インキ株式会社製、商品名、酸価３２の高酸価ポリエステル粉体樹脂”／エピコ−ト１００２“油化シェル株式会社製、商品名、ビスフェノ−ルＡタイプのエポキシ樹脂＝７０／３０重量比にポリｎ−ブチルアクリレ−ト“表面張力低下剤を配合したもの、硬化開始時間８４０秒“１６０℃”、表面張力３２ダイン／ｃｍ）を膜厚が約６０ミクロンになるように静電粉体塗装を行い１６０℃で３０分間焼付けて電着塗膜及び粉体塗膜を同時に硬化させ電着塗膜及び粉体塗膜を形成した。
【００２１】
実施例２〜４
カチオン電着塗料の硬化開始時間（錫触媒の量で調整した）を表１とし、粉体塗料の表面張力（ポリｎ−ブチルアクリレ−トの量で調整した）を表１とした以外は実施例１と同様にして実施例２〜４の電着塗膜及び粉体塗膜を形成した。
【００２２】
実施例５
実施例１で得られた電着塗膜及び粉体塗膜の粉体塗膜表面に上塗り塗料ホワイト（マジクロン１０００、関西ペイント株式会社、商品名、熱硬化型アクリル樹脂塗料）を乾燥膜厚が約６０ミクロンになるようにスプレ−塗装し、約１４０℃で３０分間焼付けを行って上塗り塗膜を形成した。
【００２３】
比較例１〜４
電着塗膜の含水率及び電着塗膜と粉体塗料の硬化時及び表面張力を表１とした以外は実施例１、５と同様にして比較例１〜４の電着塗膜及び粉体塗膜を形成した。
【００２４】
実施例及び比較例の結果を表１に示す。
【００２５】
【表１】

【００２６】
表１において硬化開始時間、表面張力、塗膜外観及び塗膜性能は下記によるものである。
【００２７】
硬化開始時間：レオバイブロンＤＤＶ−ＯＰＡIII （（株）オリエンテック社製）の粘弾測定器を使用して測定した。実施例１の電着塗膜及び粉体塗料における硬化開始時間を図１に示す。図１は基準点における振り子の振動周期と加熱時間との関係を示し、図１において１６０℃での振り子の振動周期の変曲点から、電着塗膜約７２０秒（１２分）、粉体塗料約８４０秒（１４分）を求めた。実施例２〜５及び比較例１〜４の硬化開始時間は上記と同様の方法で求めた。なお、硬化開始時間の差において−は電着塗膜が粉体塗料よりも遅いことを示す。
【００２８】
表面張力：電着塗膜及び粉体塗料の表面張力を次ぎのようにして測定した。電着塗料及び粉体塗料の硬化塗膜（１６０℃で３０分間焼付け）表面に脱イオン水を滴下して接触角（θ）を測定した。次いで、ＳｅｌｌとＮｅｕｍａｎｎの実験式
【００２９】
【数１】

【００３０】
式中、γ_L ：水の表面張力（７２．８ダイン／ｃｍ）
γ_S ：電着塗膜又は粉体塗膜の表面張力（ダイン／ｃｍ）
により求めた。
【００３１】
なお、表面張力の差において−は電着塗膜が粉体塗料よりも小さいことを示す。
【００３２】
塗膜外観
ハジキ：塗膜表面のハジキを目視で評価した。○はハジキがなく良好なもの、△はハジキが発生し劣るもの、×はハジキが多く発生し著しく劣るもの
ワキ：塗膜表面のワキを目視で評価した。○はワキがなく良好なもの、△はワキが発生し劣るもの、×はワキが多く発生し著しく劣るもの
平滑性：塗膜表面の平滑性を目視で評価した。○は平滑性が良好なもの、△は平滑性が劣るもの、×は平滑性が著しく劣るもの
光沢：ＪＩＳ Ｋ５４００に記載の鏡面反射率を測定した。
【００３３】
塗膜性能
電着塗膜と粉体塗膜との層間付着性：ゴバン目カッタ−で塗面に２ｍｍマスを２５個作り、その表面にセロファンテ−プを密着させて、強く引き離した後、下記の基準で評価した。○は全く剥がれがないもの、△は剥離が若干認められるもの、×は剥離が多く認められるもの
粉体塗膜と上塗り塗膜との層間付着性：上記と同様の付着試験方法で試験した。
【００３４】
【発明の効果】
本発明塗装方法は従来の塗装系と比較して電着塗装後の焼付け、研磨、水洗、乾燥等の工程を省略することができる、更に電着塗膜表面に塗装する塗料として有機溶剤を含まない粉体塗料を使用しているので環境を汚染する恐れがない等の特徴がある。また、通常、電着水洗塗膜表面に粉体塗料を塗装しても塗膜仕上がり外観、性能等が悪くなるが本発明においてはこれらの外観及び性能は良好である。
【図面の簡単な説明】
【図１】本発明における実施例１の電着塗膜及び粉体塗料における硬化開始時間を示す。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a novel coating method.
[0002]
[Prior art]
Conventionally, undercoat electrodeposition coating, washing with water, baking, polishing, washing with water, drying, intermediate coating, baking, overcoating, and baking are performed on a metal coating object such as an automobile body to form an undercoating to overcoating film. I have. However, since the intermediate coating is applied after baking, polishing, rinsing, and drying after the undercoating electrodeposition coating is performed in the coating process, the cost of equipment, installation, operation, and the like in the baking to drying process is increased, and the dust is increased. Contaminants such as dust and dirt easily enter, and the appearance of the coating film deteriorates. For this reason, the improvement of these coating processes is demanded from the field of automobiles and the like. Further, conventionally, an organic solvent type paint has been used as an intermediate coating, and the paint generates an organic solvent during the coating operation, and thus has a problem that it is not preferable in terms of environmental hygiene.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to shorten the conventional coating process and to develop a coating system containing no organic solvent.
[0004]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by applying a specific powder coating on the surface of an uncured electrodeposition coating film having a water content of 5% by weight or less. The present inventors have found that this is a method that can solve the problems described in (1), and have completed the present invention.
[0005]
That is, the present invention is to apply a thermosetting cationic electrodeposition coating on a metal substrate to form an undercoat electrodeposition coating,
(1) The electrodeposited film is washed with water,
{Circle around (2)} Next, draining and drying is performed to form an uncured electrodeposition coating film having a water content of 5% by weight or less,
{Circle around (3)} A powder coating is formed by applying a thermosetting powder coating which is later than the curing start time of the uncured electrodeposition coating film and smaller than the surface tension of the uncured electrodeposition coating film by electrostatic powder coating. After doing
(4) The present invention relates to a coating method characterized by baking to simultaneously cure an electrodeposition coating film and a powder coating film.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
As the metal coated object used in the coating method of the present invention, a metal coated object conventionally used for coating automobile bodies and parts can be used without any particular limitation. Specifically, aluminum, alumite, steel and the like can be used. And a metal material obtained by plating the surface of the metal material with zinc, tin, chromium, aluminum, or the like, or a metal material obtained by subjecting the surface of these metal materials to a chemical conversion treatment with chromic acid, phosphoric acid, or the like.
[0007]
As the cationic electrodeposition paint used in the coating method of the present invention, a conventionally known cationic electrodeposition paint can be used, and particularly, an electrodeposition paint containing an epoxy resin as a base resin can be suitably used. As the cationic electrodeposition paint, for example, an amine-added epoxy resin or an amine-added polyester-modified epoxy resin is used as a base resin, and a mixture obtained by blending or adding a cross-linking agent of block polyisocyanate to the resin is neutralized. Dispersed ones can be used. A pigment, an organic solvent, a curing catalyst, a surfactant and the like can be added to the cationic electrodeposition paint as needed.
[0008]
As the cationic electrodeposition coating method, a conventionally known coating method can be used. For example, it can be carried out by using a cationic electrodeposition paint as an electrodeposition bath, applying a metal-coated object as a cathode, and using a material (carbon plate or the like) having no metal elution as an anode. The energization conditions are desirably performed when the thickness of the electrodeposition coating is in the range of about 10 to 40 microns, preferably about 15 to 30 microns. After the electrodeposition coating, washing with an ultrafiltration filtrate, an ultrafiltrate, tap water or the like is performed.
[0009]
After the above-mentioned cation electrodeposition coating film is washed with water, it is drained and dried to adjust the water content so that the water content of the cation electrodeposition coating film is 5% by weight or less, preferably 3% by weight or less. If the water content of the cationic electrodeposition coating film exceeds 5% by weight, the water volatilized and diffused from the electrodeposition coating film layer is not compatible with the powder coating film, so that the water content of the cationic electrodeposition coating film and the powder coating film are not compatible. A large amount at the interface of the powder, and as a result, the performance such as the appearance and adhesion of the powder coating is reduced. There is a drawback that the film is apt to remain and deteriorates the appearance of the coating such as armpits and pinholes. Further, the cationic electrodeposition coating film after draining and drying is an uncured coating film. The uncured coating film may be a partially cured coating film. The uncured coating film was gel fraction (the coating film was peeled off, placed in a 300 mesh stainless steel net-like container, extracted with a Soxhlet extractor using an acetone solvent at reflux temperature for 2 hours, and then treated with a gel. Fraction = (weight of sample after extraction / weight of sample before extraction) × 100) is in the range of about 10% by weight or less, preferably about 5% by weight or less.
[0010]
When a cured cationic coating is used after draining and drying, the adhesion between the cationic electrodeposition coating and the powder coating, the smoothness of the powder coating, and the appearance of the coating, such as gloss, decrease. It is not preferable because the baking hardening step increases. The above-mentioned draining drying conditions are appropriately determined according to the size, heat capacity, material, etc. of the metal coated object, and the conditions under which the water content of the electrodeposition coating film does not start to be cured when the water content of the electrodeposition coating film is 5% by weight or less depending on the air volume of the dryer. The temperature is usually about 40 to 120 ° C., preferably about 50 to 100 ° C., for about 5 to 30 minutes, preferably about 5 to 20 minutes.
[0011]
In the powder coating used in the coating method of the present invention, the curing start time of the powder coating (the same baking temperature condition as the electrodeposition coating film) is longer than the curing start time of the cationic electrodeposition coating film after draining and drying. It is necessary that the surface tension of the powder coating is slower than that of the cationic electrodeposition coating film. If the curing start time of the powder coating is the same as the curing start time of the cationic electrodeposition coating, or the powder coating is earlier (shorter) than the cationic electrodeposition coating, the appearance (smoothness, shrinkage, etc.) of the powder coating ) Is unfavorable. The curing start time of the powder coating is, for example, about 10 seconds to 20 minutes, particularly about 20 seconds, in the baking temperature range of about 140 to 180 ° C., as compared with the cationic electrodeposition coating film. Preferably, it is longer for seconds to 15 minutes. The curing start time of the powder coating and the electrodeposition coating film can be adjusted by, for example, a resin composition, a crosslinking agent, a catalyst, and the like to be used.
[0012]
The curing start time of the powder coating and the cationic electrodeposition coating film is determined by a rigid pendulum type viscoelasticity measuring device [for example, Polyfile. Vol31. No. 362 (1994), pages 26 to 28, recent surface / interface evaluation techniques, Journal of the Society of Color Materials. Vol. 51 (1978), pp. 403 to 409, viscoelasticity measurement of a coating film formation process by free damping vibration of a rigid pendulum, and viscoelasticity of a paint which causes a viscoelastic change with heat and time described in Japanese Utility Model Application Laid-Open No. 6-56757. Elasticity measurement], the time (corresponding to the baking time) due to the heat (corresponding to the baking temperature) and the vibration period (viscoelasticity) of the pendulum of the coating film are measured, and the inflection point (time) of the vibration period is measured. The curing start time can be determined.
[0013]
When the surface tension of the powder coating (powder coating) is the same as that of the cationic electrodeposition coating or the powder coating is larger than the cationic electrodeposition coating, (E.g., smoothness, cissing, dents, surface gloss of the coating film, etc.) are unfavorably deteriorated. The surface tension of the powder coating is usually in the range of 25 to 45 dynes / cm, preferably 25 to 40 dynes / cm as a powder coating, and the surface tension of the cationic electrodeposition coating is usually 30 to 40 dynes / cm. The difference in surface tension between the powder coating and the electrodeposited coating is about 50 dynes / cm, preferably 35-45 dynes / cm, and the difference between the surface tension of the powder coating and the electrodeposition coating is about 5 dynes / cm. It is preferably less than dynes / cm, especially about 7-30 dynes / cm. The surface tension of the powder coating and the electrodeposition coating film can be adjusted by, for example, the used base resin, cross-linking agent, additive and the like.
[0014]
As the powder coating used in the coating method of the present invention, a conventionally known thermosetting powder coating can be used without any particular limitation as long as the above conditions are satisfied. Examples of the thermosetting powder coating include epoxy resin, polyester resin (containing a functional group such as a hydroxyl group and a carboxyl group), and acrylic resin (containing a functional group such as a hydroxyl group, a carboxyl group and an epoxy group). ) As a base resin, and a crosslinking agent (block polyisocyanate, tetramethoxymethylglycolyl or the like as a crosslinking agent that reacts with a hydroxyl group), a polyepoxide or β-hydroxyalkylamide as a crosslinking agent that reacts with a carboxyl group. Thermosetting curable compounding a polycarboxylic compound, polycarboxylic acid polyester resin, acid anhydride, phenol resin, dicyandiamide, organic acid dihydrazide, aromatic sulfonium salt cationic polymerization catalyst, etc. as a crosslinking agent that reacts with the epoxy group Powder coatings can be suitably used.
[0015]
In the thermosetting powder coating, in addition to the above-mentioned components, for example, a coloring pigment, a filler, a fluidity modifier, an antiblocking agent, a surface modifier, an anti-bake agent, an antioxidant, a curing accelerator, and other resins Can be blended as required. As the powder primer, those that have passed about 150 mesh can be suitably used.
[0016]
Thermosetting powder coating is a conventionally known method for producing a thermosetting powder coating, for example, after blending a base resin, a cross-linking agent and other compounds as necessary, dry blending is performed, and then After performing melt blending, it can be manufactured by cooling, coarse pulverization, fine pulverization, and filtration.
[0017]
The thermosetting powder coating can be applied by a known electrostatic powder coating method, for example, a corona charging method, a friction charging method, or the like. The thickness of the thermosetting powder coating is generally in the range of about 20 to 100 microns, preferably about 30 to 60 microns. The baking of the thermosetting powder coating can be performed under a temperature condition that can be cured simultaneously with the cationic electrodeposition coating film. Specifically, for example, the baking is preferably performed at about 140 to 180 ° C. for about 20 to 40 minutes.
[0018]
A curable topcoat such as a powder coating, an organic solvent-based coating, or a non-aqueous dispersion coating can be applied to the surface of the coating on which the thermosetting powder coating is formed. As these paints, paints conventionally used in the field of automobiles can be used without any particular limitation. The top coat may be of a one-coat, two-coat one-bake, two-coat two-bake or three-coat two-bake system, for example. The top coat may be any of solid finish, metallic finish and pearl finish, for example.
[0019]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples.
[0020]
Example 1
A cationic electrodeposition coating (using an amine-added epoxy resin as a base resin) and a block polyisocyanate coating on a dull steel plate having a thickness of 0.8.times.300.times.100 (mm) treated with zinc phosphate chemical conversion treatment. A mixture of a crosslinking agent and a tin catalyst, a curing start time of 720 seconds "160 ° C", a surface tension of 42 dynes / cm), and a cationic electrodeposition coating to a dry film thickness of about 20 microns, and ultrafiltration. After washing with the filtrate, drying was performed at 160 ° C. for about 10 minutes to obtain an uncured dry electrodeposited coating film having a water content of about 3% by weight. Next, an epoxy polyester thermosetting resin powder coating (Finedec M-8860 “trade name, high acid value polyester powder resin with an acid value of 32, manufactured by Dainippon Ink Co., Ltd.”) / Epico- 1002 "Bisphenol A type epoxy resin manufactured by Yuka Shell Co., Ltd. = poly (n-butyl acrylate) blended with 70/30 weight ratio of surface tension reducing agent, curing start time 840 seconds" 160 ° C., a surface tension of 32 dynes / cm) is applied by electrostatic powder coating so that the film thickness becomes about 60 μm, and baked at 160 ° C. for 30 minutes to simultaneously cure the electrodeposition coating film and the powder coating film. A coating film and a powder coating film were formed.
[0021]
Examples 2 to 4
Example 1 except that the curing start time (adjusted by the amount of the tin catalyst) of the cationic electrodeposition paint is shown in Table 1, and the surface tension of the powder coating (adjusted by the amount of poly n-butyl acrylate) was shown in Table 1. In the same manner as in Example 1, electrodeposition coating films and powder coating films of Examples 2 to 4 were formed.
[0022]
Example 5
The top coat white (Magicron 1000, Kansai Paint Co., trade name, thermosetting acrylic resin paint) is applied to the surface of the powder coating of the electrodeposition coating film and the powder coating film obtained in Example 1 to have a dry film thickness. It was spray-coated to about 60 microns and baked at about 140 ° C. for 30 minutes to form a top coat.
[0023]
Comparative Examples 1-4
The electrodeposition coating films and powders of Comparative Examples 1 to 4 were prepared in the same manner as in Examples 1 and 5, except that the moisture content of the electrodeposition coating film and the curing time and surface tension of the electrodeposition coating film and the powder coating were set to Table 1. A body coating was formed.
[0024]
Table 1 shows the results of Examples and Comparative Examples.
[0025]
[Table 1]

[0026]
In Table 1, the curing start time, surface tension, coating appearance and coating performance are as follows.
[0027]
Curing start time: Measured using a viscoelasticity meter of Leo Vibron DDV-OPAIII (manufactured by Orientec Co., Ltd.) FIG. 1 shows the curing start time of the electrodeposition coating film and the powder coating material of Example 1. FIG. 1 shows the relationship between the oscillation period of the pendulum at the reference point and the heating time. In FIG. 1, from the inflection point of the oscillation period of the pendulum at 160 ° C., about 720 seconds (12 minutes) of the electrodeposition coating film, powder About 840 seconds (14 minutes) of paint was determined. The curing start times of Examples 2 to 5 and Comparative Examples 1 to 4 were determined by the same method as described above. In addition,-in the difference of the curing start time indicates that the electrodeposition coating film is slower than the powder coating.
[0028]
Surface tension: The surface tension of the electrodeposition coating film and the powder coating was measured as follows. Deionized water was dropped on the surface of the cured coating film (baked at 160 ° C. for 30 minutes) of the electrodeposition paint and the powder paint, and the contact angle (θ) was measured. Then, the empirical formula of Cell and Neumann is as follows.
(Equation 1)

[0030]
Where γ _L : surface tension of water (72.8 dynes / cm)
γ _S : Surface tension of electrodeposition coating film or powder coating film (dyne / cm)
Determined by
[0031]
In addition,-in the difference in surface tension indicates that the electrodeposition coating film is smaller than the powder coating material.
[0032]
Coating appearance cissing: The cissing on the coating film surface was visually evaluated.は: good without repelling, Δ: poor repelling, ×: remarkably poor repelling: Positiveness on the coating film surface was visually evaluated.は: good without a crack, Δ: poor cracking, x: markedly poor cracking: The smoothness of the coating film surface was visually evaluated.は: good smoothness, Δ: poor smoothness, ×: extremely poor smoothness Gloss: Specular reflectance described in JIS K5400 was measured.
[0033]
Coating performance Interlayer adhesion between electrodeposited coating and powder coating: After making 25 2mm squares on the coating surface with a goban cutter, adhere cellophane tape to the surface and strongly separate them. Evaluation was made according to the following criteria. ○: no peeling at all, Δ: slight peeling observed, ×: many peeling observed Interlayer adhesion between powder coating and top coat: tested by the same adhesion test method as described above.
[0034]
【The invention's effect】
The coating method of the present invention can omit the steps of baking, polishing, washing with water, drying and the like after electrodeposition coating as compared with the conventional coating system, and further includes an organic solvent as a coating applied to the surface of the electrodeposition coating film. There is such a feature that there is no risk of polluting the environment because no powder coating is used. Further, usually, even when a powder coating is applied to the surface of the electrodeposition-washed coating film, the finished appearance and performance of the coating film deteriorate, but in the present invention, these appearance and performance are good.
[Brief description of the drawings]
FIG. 1 shows the curing start time of an electrodeposition coating film and a powder coating material of Example 1 of the present invention.

Claims (1)

金属被塗物に熱硬化性カチオン電着塗料を塗装して下塗り電着塗膜を形成した後、
▲１▼該電着塗膜を水洗し、
▲２▼次いで、水切り乾燥をおこなって、含水率が５重量％以下の未硬化電着塗膜を形成し、
▲３▼該未硬化電着塗膜の硬化開始時間よりも遅く且つ未硬化電着塗膜の表面張力よりも小さい熱硬化性粉体塗料を静電粉体塗装して粉体塗膜を形成した後、
▲４▼焼付けをおこなって電着塗膜及び粉体塗膜を同時に硬化させる
ことを特徴とする塗装方法。After applying a thermosetting cationic electrodeposition paint to the metal coating to form an undercoat electrodeposition coating,
(1) The electrodeposited film is washed with water,
{Circle around (2)} Next, draining and drying is performed to form an uncured electrodeposition coating film having a water content of 5% by weight or less,
{Circle around (3)} A powder coating is formed by applying a thermosetting powder coating which is later than the curing start time of the uncured electrodeposition coating film and smaller than the surface tension of the uncured electrodeposition coating film by electrostatic powder coating. After doing
{Circle around (4)} A coating method characterized by baking to simultaneously cure the electrodeposition coating film and the powder coating film.

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