JP4370793B2 - Powder paint and coating method using the same - Google Patents

Description

（式（１）中、Ｒ_１〜Ｒ_４はそれぞれ水素を示す。）
【化４】

（式（２）中、Ｒ_５は水素原子またはメチル基であり、Ｒ_６はアルキレン基であり、Ｒ_７〜Ｒ_９はそれぞれアルキル基である。）
また、結着樹脂１００質量部に対して、摩擦帯電付与剤が０．１〜１０質量部配合されていることが好ましい。
本発明の塗装方法は、前記粉体塗料を、摩擦帯電方式により帯電させて、被塗物に吹き付ける工程を有することを特徴とする。
【０００７】
【発明の実施の形態】
以下、本発明を詳細に説明する。
本発明の粉体塗料は、少なくとも下記式（１）で示される化合物を含有する摩擦帯電付与剤と、結着樹脂とを含有する。
【化５】

式（１）中、Ｒ_１〜Ｒ_４はそれぞれ水素、アルキル基、アルコキシル基、水酸基、ニトロ基からなる群より選ばれるいずれかを示す。
【０００８】
式（１）で示される化合物の具体例としては、パラニトロ安息香酸、３−メチル−パラニトロ安息香酸、３，４−ジニトロ安息香酸、４−ニトロサリチル酸などが挙げられる。
このような化合物は、帯電力に優れるとともに初期帯電立ち上がり性も良好であるので、粉体塗料の塗着効率を向上させることができる。また、このような化合物は透明性を備えているので、粉体塗料に使用しても、その色相に影響を与えることがなく、任意の着色剤とともに使用することができる。また、式（１）の化合物は、樹脂との相溶性、分散性も良好であるので、粉体塗料のマトリクス成分である結着樹脂中に容易かつ均一に分散し、安定した帯電力を発現できるとともに、平滑性、強度に優れた塗膜を形成することもできる。
【０００９】
式（１）で示される化合物は単独で摩擦帯電付与剤として粉体塗料に使用することができるが、他の摩擦帯電付与剤と併用してもよい。
他の摩擦帯電付与剤としては特に制限はないが、好ましい例として、４級アンモニウム塩基含有共重合体からなる摩擦帯電付与剤が挙げられる。
４級アンモニウム塩基含有共重合体は、４級アンモニウム塩基含有単位と、その他の単位とから構成されるものであって、好ましい４級アンモニウム塩基含有単位としては、ジアルキルアミノアルキル（メタ）アクリレートから後述する方法で第４級化の工程を経て誘導される、下記式（２）で示される単位が挙げられる。
【化６】

式（２）中、Ｒ_５は水素原子またはメチル基であり、Ｒ_６はアルキレン基であり、Ｒ_７〜Ｒ_９はそれぞれアルキル基である。
【００１０】
ジアルキルアミノアルキル（メタ）アクリレートとしては、例えば、ジメチルアミノエチル（メタ）アクリレート、ジエチルアミノエチル（メタ）アクリレート、ジプロピルアミノエチル（メタ）アクリレート、ジブチルアミノエチル（メタ）アクリレートなどのジ（低級アルキル）アミノエチル（メタ）アクリレートが好適である。
【００１１】
一方、その他の単位としては、４級アンモニウム塩基含有単位とともに共重合体を構成できるものであれば特に制限はないが、スチレン系単量体および／または（メタ）アクリル系単量体から主に構成される単位が好ましい。
スチレン系単量体としては、スチレン、α−メチルスチレンなどが挙げられ、（メタ）アクリル系単量体としては、（メタ）アクリル酸の他、（メタ）アクリル酸メチル、（メタ）アクリル酸エチル、（メタ）アクリル酸プロピル、（メタ）アクリル酸ブチルなどの（メタ）アクリル酸エステルなどが挙げられる。これらの単量体については、１種単独で使用しても、２種以上を併用してもよいが、少なくともスチレン系単量体を使用すると、得られる４級アンモニウム塩基含有共重合体の透明性が高く、また、結着樹脂への相溶性も優れるため好ましい。
【００１２】
また、その他の単位としては、スチレン系単量体および／または（メタ）アクリル系単量体から構成される単位とともに、下記式（３）で示される単位を含んでいてもよい。式（３）で示される単位は、その他の単位中、好ましくは２０質量％以下、より好ましくは１５質量％以下、さらに好ましくは１０〜１５質量％の範囲である。このような範囲で式（３）の単位が含まれると、４級アンモニウム塩基含有共重合体を式（１）で示される化合物とともに摩擦帯電付与剤として粉体塗料に含有させた場合、結着樹脂への相溶性が一層向上する。
【化７】

式（３）中、Ｒ_１０は水素原子またはメチル基であり、Ｒ_１１はアルキル基、好ましくはメチル基、エチル基、ｎ−またはｉｓｏ−プロピル基、ｎ−またはｉｓｏ−ブチル基、２−エチルヘキシル基のいずれかである。
【００１３】
好ましい４級アンモニウム塩基含有共重合体としては、４級アンモニウム塩基含有単位０．５〜３５質量％と、その他の単位９９．５〜６５質量％とからなるものが挙げられる。４級アンモニウム塩基含有単位が０．５質量％未満では、この共重合体を式（１）で示される化合物とともに摩擦帯電付与剤として使用して粉体塗料に含有させた場合、結着樹脂への相溶性は向上するものの、摩擦帯電付与剤としての帯電性が不十分となる傾向がある。一方、３５質量％を超えると、結着樹脂への相溶性が低下するとともに、耐湿性も不十分となる傾向がある。より好ましい４級アンモニウム塩基含有単位の含有量は２〜２０質量％である。
【００１４】
４級アンモニウム塩基含有共重合体を製造する方法としては、ジアルキルアミノアルキル（メタ）アクリレートと、スチレン系単量体などその他の単位を構成する単量体とを、重合開始剤の存在下に共重合させ、生成した共重合体を、パラトルエンスルホン酸メチル、パラトルエンスルホン酸エチル、パラトルエンスルホン酸プロピルなどのパラトルエンスルホン酸アルキルエステルで第４級化する方法がある。この方法によれば、ハロゲン化水素の副生が少なく好ましい。
また、その他の方法としては、ジアルキルアミノアルキル（メタ）アクリレートを常法にしたがって、あらかじめメチルクロライド、メチルブロマイド、エチルクロライド、エチルブロマイド、プロピルクロライド、プロピルブロマイド、ブチルクロライド、ブチルブロマイドなどのアルキルハライドで第４級アンモニウムハライドに変え、得られた第４級アンモニウムハライドとその他の単位を構成する単量体と共重合させ、生成した共重合体をパラトルエンスルホン酸と反応させる方法でもよい。
【００１５】
ここで共重合に使用する重合開始剤としては、例えばアゾビスイソブチロニトリル、アゾビスジメチルバレロニトリル、アゾビス（２，４−ジメチル−４−メトキシバレロニトリル）、２−フェニルアゾ（２，４−ジメチル−４−メトキシバレロニトリル）などのアゾ系開始剤が挙げられる。重合開始剤は、使用する単量体の混合物の合計質量を１００質量部とした時、これに対して、０．５〜１０質量部の範囲で用いるのが好ましい。
また、共重合法としては、溶液重合、懸濁重合、塊状重合、乳化重合など、いずれの方法を用いてもよく、制限はないが、得られる共重合体の質量平均分子量の制御が比較的容易であること、また、得られた共重合体をパラトルエンスルホン酸またはそのアルキルエステルと反応させる操作が容易であることなどから、ベンゼン、トルエン、キシレン、ジオキサン、プロピレングリコールモノメチルエーテル、エチレングリコールモノメチルエーテル、酢酸エチル、酢酸イソプロピル、メチルエチルケトン、ジエチルケトン、イソブチルケトンなどの有機溶剤、または、これら有機溶剤とメタノール、エタノール、プロパノール、イソプロパノール、ブタノールなどの低級アルコールとの混合溶剤中で、単量体の混合物を共重合させる溶液重合法が特に好ましい。
【００１６】
生成した共重合体とパラトルエンスルホン酸アルキルエステルまたはパラトルエンスルホン酸との反応は、共重合体の溶液にパラトルエンスルホン酸アルキルエステルまたはパラトルエンスルホン酸を加え、６５〜９５℃の温度に加熱することにより進行し、その結果、４級アンモニウム塩基含有共重合体が得られる。パラトルエンスルホン酸アルキルエステルまたはパラトルエンスルホン酸の使用量は、これと反応させる共重合体中に含まれるジアルキルアミノアルキル（メタ）アクリレートまたはその第４級アンモニウムハライドの単位１モル当り、通常０．８〜１モル、好ましくは０．９〜１モルの範囲とする。
【００１７】
また、４級アンモニウム塩基含有共重合体は、質量平均分子量が１５００〜１００００００の範囲内であることが好ましい。このような範囲であると、高湿度環境下であっても帯電性が低下しにくい。また、結着樹脂との相溶性、分散性がより良好となる。４級アンモニウム塩基含有共重合体のより好ましい質量平均分子量は、５０００〜１０００００である。
さらに、４級アンモニウム塩基含有共重合体は、そのガラス転移温度が５０〜１００℃であると、粉体塗料としての定着性を維持したまま、高温での保存安定性が良好となる。
【００１８】
以上説明したように、式（１）で示される化合物は単独で、または、上述の４級アンモニウム塩基含有共重合体などと任意の質量比で組み合わせて、摩擦帯電付与剤として、粉体塗料に使用することができる。具体的には、式（１）の化合物を単独で使用すると、その使用量が少なくても高い帯電力が得られ、一方、４級アンモニウム塩基含有共重合体と併用すると、高い帯電力が得られることはもちろん、耐湿性などその他の性能もバランスよく備えるものとなる。
【００１９】
この摩擦帯電付与剤を、結着樹脂に対して、必要に応じて着色剤、硬化剤、充填材、流展剤、発泡防止剤などの添加剤とともに配合して、例えば平均粒径２〜８０μｍ程度の粒子にすることによって、帯電性、帯電立ち上がり性に優れ、塗着効率の良好な粉体塗料とすることができる。
ここで、摩擦帯電付与剤の好ましい配合量は、摩擦帯電付与剤中における式（１）の化合物の含有量などにもよるが、通常、結着樹脂１００質量部に対して０．１〜１０質量部である。
ここで、０．１質量部未満であると、十分な帯電性が得られにくく塗着効率を上げることに寄与しにくくなる傾向があり、一方、１０質量部を超えると、粉体塗料から形成された塗膜の強度が低下する可能性がある。
【００２０】
結着樹脂としては、アクリル樹脂、ポリエステル樹脂、エポキシ樹脂、フェノール樹脂、キシレン樹脂、ユリア樹脂、メラミン樹脂などが好ましく、１種単独で、または、２種以上を組み合わせて使用できる。
【００２１】
着色剤としては特に制限はなく、酸化チタン、酸化クロム、酸化鉄、カーボンブラックなどが使用でき、これらを１種単独で、または、２種以上組み合わせて使用できる。
【００２２】
硬化剤としては、ドデカン二酸、（ポリ）イソシアネート、アミン、ポリアミド、酸無水物、ポリスルフィド、三フッ化ホウ素酸、酸ジヒドラジド、イミダゾール、ジシアンジアミドなどを使用できる。
充填剤としては、硫酸バリウム、炭酸カルシウム、酸化アルミニウム、ケイ酸カルシウムなどが、流展剤としては、アクリルオリゴマー、シリコーンなどが、発泡防止剤としてはベンゾインなどが使用できる。
【００２３】
粉体塗料の製造には、まず、上述した各成分を、スーパーミキサー、ヘンシェルミキサー、ボールミルなどの混合機にて充分に混合した後、加熱ロール、ニーダー、エクストルーダーなどの熱混練機中で溶融混練し、冷却固化する。ついで、ハンマーミル、ジェットミルなどの粉砕機で粉砕し、得られた粉砕物を分級して、平均粒径が好ましくは２〜８０μｍの粒子を回収することにより調製できる。
その他には、各成分が溶融または分散している有機溶媒溶液を噴霧乾燥法などで、２００℃以下の条件で乾燥する方法、結着樹脂を構成する単量体の混合物中に他の各成分を混合して乳化懸濁液とし、これを共重合する方法などによっても調製できる。
【００２４】
また、このようにして得られた粉体塗料の表面に、必要に応じて、シリカ、アルミナ、酸化チタンなどの無機微粒子を付着させてもよい。無機微粒子の付着には、ヘンシェルミキサーなどの混合機を使用して、粉体塗料と無機微粒子とを撹拌混合すればよい。
【００２５】
こうして得られた粉体塗料は、摩擦帯電方式などのスプレーガンにより摩擦帯電されて被塗物に吹き付けられ、帯電性により塗装物に付着する。そして、この粉体塗料が付着した状態の被塗物を焼付炉などで焼き付けることにより、塗膜を形成することができる。
【００２６】
以上説明したように式（１）で示される化合物は、結着樹脂との相溶性、分散性が良好であって、帯電力と初期帯電立ち上がり性に優れる。よって、摩擦帯電付与剤として粉体塗料に配合する際に大量に使用しなくても、優れた帯電性および帯電立ち上がり性を付与することができ、塗装時にスプレーガンとして摩擦帯電方式のものを使用する場合であっても十分な帯電性が得られる。また、結着樹脂に均一に分散されるので、形成される塗膜の平滑性、強度なども良好なる。さらに、式（１）で示される化合物は透明性を備えているので、任意の着色剤とともに使用して、所望の色相の粉体塗料とすることができる。
【００２７】
【実施例】
以下、本発明について実施例を挙げて具体的に説明する。
［摩擦帯電付与剤１］
市販の第４級アンモニウム塩基含有共重合体アクリベースＦＣＡ−２０１−ＰＳ（藤倉化成（株）製）１００質量部に対して、パラニトロ安息香酸１質量部を添加したものをメチルエチルケトンに溶解して、均一な溶液を得た。これを１３０℃で加熱乾燥したものを摩擦帯電付与剤１とした。この摩擦帯電付与剤１は透明性を備えた淡黄色であった。
なお、使用した市販の第４級アンモニウム塩基含有共重合体アクリベースＦＣＡ−２０１−ＰＳ（藤倉化成（株）製）は、粒子状であって、４級アンモニウム塩基含有単位としては、式（２）中のＲ_５がメチル基であり、Ｒ_６は−ＣＨ_２−ＣＨ_２−であり、Ｒ_７〜Ｒ_９はそれぞれエチル基、メチル基、エチル基であるものを含有し、その他の単位としてはスチレンとブチルアクリレート単量体から構成される単位を含有している。そして、４級アンモニウム塩基含有共重合体における４級アンモニウム塩基含有単位の含有率は、１５質量％となっている。また、質量平均分子量は１２０００、ガラス転移温度は６７℃である。
【００２８】
［摩擦帯電付与剤２］
市販の第４級アンモニウム塩基含有共重合体アクリベースＦＣＡ−２０１−ＰＳ（藤倉化成（株）製）１００質量部に対して、パラニトロ安息香酸１質量部を添加したものをメチルエチルケトンに溶解して、均一な溶液を得た。これを１３０℃で加熱乾燥したものを摩擦帯電付与剤２とした。この摩擦帯電付与剤２は透明性を備えた淡黄色であった。
【００２９】
［摩擦帯電付与剤３］
パラニトロ安息香酸を摩擦帯電付与剤３として使用した。この摩擦帯電付与剤３は透明性を備えた淡黄色であった。
【００３０】
［実施例１］
結着樹脂であるアクリル樹脂（大日本インキ化学工業社製 Ａ−２５３）７７質量部に対して、硬化剤（ドデカン二酸、宇部興産社製 ＤＤＡ）１６．５質量部、流展剤（アクリル系コポリマー、ＢＡＳＦ社製 アクロナール４Ｆ）１．０質量部、発泡防止剤（ベンゾイン、みどり化学社製）０．５質量部、着色剤（カーボンブラック、三菱化学社製 ＭＡ−１００）５部と、上記の摩擦帯電付与剤１を２質量部配合し、スーパーミキサ−で混合し、加圧ニーダーにより１２０℃で熱溶融混練し、冷却固化後、ジェットミルで粉砕した。
その後、得られた粉砕物を乾式気流分級機で分級して、平均粒径が２２μｍの粒子を回収し、これを粉体塗料とした。
【００３１】
（塗着効率）
得られた粉体塗料を、摩擦帯電式スプレーガンを使用して被塗物に吹き付け、塗着効率（％）を求めた。結果を表１に示す。
１）塗着条件
スプレーガンとしては松尾産業社製Ｔ−１ａを使用し、被塗物としては、１０００ｍｍ四方の鉄板の中央に固定された３００ｍｍ四方の鉄板を使用した。詳細条件は以下のとおりである。
レシプロストローク：上下に１ｍ
レシプロ速度：２０ｍ／ｍｉｎ．
被塗物移動速度（コンベア速度）：２ｍ／ｍｉｎ．
スプレーガンの粉体塗料吐出量：１００ｇ／ｍｉｎ．
スプレーガン先端と被塗物との距離：１８０ｍｍ
塗装環境：２５℃／５０％ＲＨ
２）塗着効率（％）の算出
被塗物の上をスプレーガンが移動するのに要した時間（ｍｉｎ．）を算出し、この時間（ｍｉｎ．）にスプレーガンの粉体塗料吐出量（ｇ／ｍｉｎ．）を乗じた値を理論吐出量とした。ついで、１）のように粉体塗料が塗着される前後の被塗物の質量から、被塗物に塗着した粉体塗料の質量を求め、この質量の理論吐出量に対する百分率（％）を求め、塗着効率とした。
【００３２】
（塗膜強度）
得られた粉体塗料を、日本テストパネル社製のテストパネル（ＰＢ−１３７Ｍ）に膜厚４０μｍとなるように上記スプレーガンで塗布し、１８０℃で２０分焼き付けて、塗膜を形成した。
この塗膜の強度をＪＩＳ Ｋ５４００（８．１）に規定された耐屈曲性試験で心棒の直径を３ｍｍとして測定したところ、塗膜の割れもなく十分な機械的強度を備えていた。
【００３３】
［実施例２］
摩擦帯電付与剤１の代わりに摩擦帯電付与剤２を使用した以外は、実施例１と同様にして粉体塗料を得て、塗着効率を求めた。結果を表１に示す。また、実施例１と同様にして塗膜を形成し、この塗膜の強度を測定したところ、塗膜の割れもなく十分な機械的強度を備えていた。
【００３４】
［実施例３］
摩擦帯電付与剤１の代わりに摩擦帯電付与剤３を使用した以外は、実施例１と同様にして粉体塗料を得て、塗着効率を求めた。結果を表１に示す。また、実施例１と同様にして塗膜を形成し、この塗膜の強度を測定したところ、塗膜の割れもなく十分な機械的強度を備えていた。
【００３５】
［比較例１］
摩擦帯電付与剤を使用しない以外は実施例１と同様にして粉体塗料を得て、塗着効率を求めた。結果を表１に示す。
【００３６】
［実施例４］
結着樹脂としてポリエステル樹脂（日本エステル社製 ＥＲ−８１５５）３５質量部とエポキシ樹脂（東京化成社製 ＹＤ−０１４）６６質量部を使用し、これに対して、硬化剤（トリフェニルフォスフィン、ケイアイ化成社製ＰＰ−３６０）２．５質量部、流展剤（アクリル系コポリマー、ＢＡＳＦ社製 アクロナール４Ｆ）１．０質量部、発泡防止剤（ベンゾイン、みどり化学社製）０．５質量部、着色剤（カーボンブラック、三菱化学社製 ＭＡ−１００）５部と、上記の摩擦帯電付与剤２を２質量部配合し、スーパーミキサ−で混合し、加圧ニーダーにより１２０℃で熱溶融混練し、冷却固化後、ジェットミルで粉砕した。
その後、得られた粉砕物を乾式気流分級機で分級して、平均粒径が２２μｍの粒子を回収し、これを粉体塗料とした。また、これについて実施例１と同様にして塗着効率を求めた。結果を表１に示す。また、実施例１と同様にして塗膜を形成し、この塗膜の強度を測定したところ、塗膜の割れもなく十分な機械的強度を備えていた。
【００３７】
［比較例２］
摩擦帯電付与剤を使用しない以外は実施例４と同様にして粉体塗料を得て、塗着効率を求めた。結果を表１に示す。
【００３８】
［実施例５］
結着樹脂であるポリエステル樹脂（日本エステル社製 ＥＲ−６６８０）８０質量部に対して、硬化剤（ポリイソシアネート、ヒュルス社製 ＢＦ−１５４０）１３．５質量部、流展剤（アクリル系コポリマー、ＢＡＳＦ社製 アクロナール４Ｆ）１．０質量部、発泡防止剤（ベンゾイン、みどり化学社製）０．５質量部、着色剤（カーボンブラック、三菱化学社製 ＭＡ−１００）５部と、上記の摩擦帯電付与剤２を２質量部配合し、スーパーミキサ−で混合し、加圧ニーダーにより１２０℃で熱溶融混練し、冷却固化後、ジェットミルで粉砕した。
その後、得られた粉砕物を乾式気流分級機で分級して、平均粒径が２２μｍの粒子を回収し、これを粉体塗料とした。また、これについて実施例１と同様にして塗着効率を求めた。結果を表１に示す。また、実施例１と同様にして塗膜を形成し、この塗膜の強度を測定したところ、塗膜の割れもなく十分な機械的強度を備えていた。
【００３９】
［比較例３］
摩擦帯電付与剤を使用しない以外は実施例５と同様にして粉体塗料を得て、塗着効率を求めた。結果を表１に示す。
【００４０】
［実施例６］
結着樹脂であるエポキシ樹脂（油化シェルエポキシ化学社製 エピコート１００４）８８．５質量部に対して、硬化剤（ジシアンジアミド）５質量部、流展剤（アクリル系コポリマー、ＢＡＳＦ社製 アクロナール４Ｆ）１．０質量部、発泡防止剤（ベンゾイン、みどり化学社製）０．５質量部、着色剤（カーボンブラック、三菱化学社製 ＭＡ−１００）５部と、上記の摩擦帯電付与剤２を２質量部配合し、スーパーミキサ−で混合し、加圧ニーダーにより１２０℃で熱溶融混練し、冷却固化後、ジェットミルで粉砕した。
その後、得られた粉砕物を乾式気流分級機で分級して、平均粒径が２２μｍの粒子を回収し、これを粉体塗料とした。また、これについて実施例１と同様にして塗着効率を求めた。結果を表１に示す。また、実施例１と同様にして塗膜を形成し、この塗膜の強度を測定したところ、塗膜の割れもなく十分な機械的強度を備えていた。
【００４１】
［比較例４］
摩擦帯電付与剤を使用しない以外は実施例６と同様にして粉体塗料を得て、塗着効率を求めた。結果を表１に示す。
【００４２】
【表１】

【００４３】
表１に示すように、実施例で得られた粉体塗料は、十分な帯電性を有するために塗着効率が優れていた。
【００４４】
【発明の効果】
以上説明したように本発明では、式（１）で示される化合物を含有する摩擦帯電付与剤を使用するので、塗装時にスプレーガンとして摩擦帯電方式のものを使用する場合であっても十分な帯電性が得られ塗着効率に優れ、形成される塗膜の平滑性、強度なども良好である。また、式（１）で示される化合物は透明性を備えているので、任意の着色剤とともに使用して、所望の色の粉体塗料とすることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a powder coating material suitably used for electrostatic coating and a coating method using the same.
[0002]
[Prior art]
Since the powder coating is a solvent-free coating that does not contain an organic solvent, it is very useful from the viewpoints of environment and safety. In addition, there is an advantage that the powder coating material that has not adhered to the object to be coated can be recovered and reused, which is a preferable coating material from the viewpoint of cost as well as the environment. As a method for applying powder paint, spray the powder paint charged with a spray gun to the work carried in the conveyor in the painting booth, and electrostatically attach the powder paint to the work. A method of baking a powder paint on an object to be coated in a baking furnace or the like is common. Therefore, the powder coating material is often mixed with a charge imparting agent for improving the chargeability (see, for example, Patent Document 1 or 2).
[0003]
[Patent Document 1]
JP-A-8-176469 [Patent Document 2]
JP-A-8-199091 [0004]
[Problems to be solved by the invention]
However, the conventional charge imparting agent cannot impart sufficient chargeability to the powder paint, and the powder paint sprayed with a spray gun is difficult to adhere to the object to be coated, so that the coating efficiency is insufficient. Met. In recent years, the use of friction charging spray guns, which can form a uniform coating even on uneven surfaces, is increasing in place of conventional corona charging spray guns. In the spray gun, the powder coating is charged only by friction, so the chargeability tends to be insufficient.
[0005]
The present invention has been made in view of the above circumstances, and even when a friction charging spray gun is used, sufficient charging property and initial charge rising property can be imparted, coating efficiency is excellent, and transparency is provided. In addition, a powder coating that does not adversely affect the hue of the powder coating, has good compatibility with the binder resin, has good dispersibility, and is excellent in the smoothness and strength of the formed coating film. It is an object to provide a painting method.
[0006]
[Means for Solving the Problems]
The powder coating material of the present invention is a powder coating material containing at least a friction charge imparting agent containing a compound represented by the following formula (1) and a binder resin, and the friction charge imparting agent is quaternary. A quaternary ammonium base-containing copolymer composed of an ammonium base-containing unit and other units is further contained, and the other units are mainly composed of a styrene monomer and / or a (meth) acrylic monomer. The quaternary ammonium base-containing unit is represented by the following formula (2), and the quaternary ammonium base-containing copolymer contains 0.5 to 35% by mass of the quaternary ammonium base-containing unit. characterized in that it.
[Chemical 3]

(In formula (1), R _{1 to} R ₄ each represent hydrogen .)
[Formula 4]

(In Formula (2), R ₅ is a hydrogen atom or a methyl group, R ₆ is an alkylene group, and R _{7 to} R ₉ are each an alkyl group.)
Moreover, it is preferable that 0.1-10 mass parts of triboelectric charge imparting agents are mix | blended with respect to 100 mass parts of binder resin.
The coating method of the present invention includes a step of charging the powder coating material by a frictional charging method and spraying the powder coating material on an object to be coated.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The powder coating material of the present invention contains at least a triboelectric charge imparting agent containing a compound represented by the following formula (1) and a binder resin.
[Chemical formula 5]

In the formula (1), R _{1 to} R ₄ are each selected from the group consisting of hydrogen, an alkyl group, an alkoxyl group, a hydroxyl group, and a nitro group.
[0008]
Specific examples of the compound represented by the formula (1) include paranitrobenzoic acid, 3-methyl-paranitrobenzoic acid, 3,4-dinitrobenzoic acid, 4-nitrosalicylic acid and the like.
Since such a compound is excellent in the electric power and the initial charge rising property is also good, the application efficiency of the powder coating material can be improved. Moreover, since such a compound has transparency, even if it is used in a powder coating material, it does not affect its hue and can be used with any colorant. In addition, since the compound of formula (1) has good compatibility and dispersibility with the resin, it is easily and uniformly dispersed in the binder resin, which is a matrix component of the powder coating material, and exhibits a stable electric power. In addition, a coating film having excellent smoothness and strength can be formed.
[0009]
The compound represented by the formula (1) can be used alone as a triboelectric charge imparting agent in powder coatings, but may be used in combination with other triboelectric charge imparting agents.
Although there is no restriction | limiting in particular as another friction charge imparting agent, As a preferable example, the friction charge imparting agent which consists of a quaternary ammonium base containing copolymer is mentioned.
The quaternary ammonium base-containing copolymer is composed of a quaternary ammonium base-containing unit and other units. As a preferable quaternary ammonium base-containing unit, a dialkylaminoalkyl (meth) acrylate will be described later. The unit shown by following formula (2) induced | guided | derived through the process of quaternization by the method to do is mentioned.
[Chemical 6]

In formula (2), R ₅ is a hydrogen atom or a methyl group, R ₆ is an alkylene group, and R _{7 to} R ₉ are each an alkyl group.
[0010]
Examples of the dialkylaminoalkyl (meth) acrylate include di (lower alkyl) such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, and dibutylaminoethyl (meth) acrylate. Aminoethyl (meth) acrylate is preferred.
[0011]
On the other hand, the other unit is not particularly limited as long as it can constitute a copolymer with a quaternary ammonium base-containing unit, but is mainly composed of a styrene monomer and / or a (meth) acrylic monomer. Preferred are units that are composed.
Examples of the styrene monomer include styrene and α-methylstyrene. Examples of the (meth) acrylic monomer include (meth) acrylic acid, methyl (meth) acrylate, and (meth) acrylic acid. Examples include (meth) acrylic acid esters such as ethyl, propyl (meth) acrylate, and butyl (meth) acrylate. These monomers may be used alone or in combination of two or more. However, when at least a styrene monomer is used, the resulting quaternary ammonium base-containing copolymer is transparent. It is preferable because of its high compatibility and excellent compatibility with the binder resin.
[0012]
Moreover, as another unit, the unit shown by following formula (3) may be included with the unit comprised from a styrene-type monomer and / or a (meth) acrylic-type monomer. The unit represented by the formula (3) is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10 to 15% by mass in other units. When the unit of the formula (3) is contained within such a range, the binder is contained when the quaternary ammonium base-containing copolymer is contained in the powder coating material as a triboelectric charge imparting agent together with the compound represented by the formula (1). The compatibility with the resin is further improved.
[Chemical 7]

In the formula (3), R ₁₀ is a hydrogen atom or a methyl group, and R ₁₁ is an alkyl group, preferably a methyl group, an ethyl group, an n- or iso-propyl group, an n- or iso-butyl group, or 2-ethylhexyl. One of the groups.
[0013]
Preferred quaternary ammonium base-containing copolymers include those comprising 0.5 to 35% by mass of quaternary ammonium base-containing units and 99.5 to 65% by mass of other units. When the quaternary ammonium base-containing unit is less than 0.5% by mass, when this copolymer is used as a triboelectric charge imparting agent together with the compound represented by the formula (1), it is converted into a binder resin. However, the chargeability as a frictional charge imparting agent tends to be insufficient. On the other hand, when it exceeds 35% by mass, the compatibility with the binder resin is lowered, and the moisture resistance tends to be insufficient. The content of the quaternary ammonium base-containing unit is more preferably 2 to 20% by mass.
[0014]
As a method for producing a quaternary ammonium base-containing copolymer, a dialkylaminoalkyl (meth) acrylate and a monomer constituting another unit such as a styrene monomer are copolymerized in the presence of a polymerization initiator. There is a method in which a copolymer obtained by polymerization is quaternized with a paratoluenesulfonic acid alkyl ester such as methyl paratoluenesulfonate, ethyl paratoluenesulfonate, or propyl paratoluenesulfonate. This method is preferable because there is little by-product of hydrogen halide.
In addition, as other methods, dialkylaminoalkyl (meth) acrylate can be prepared in advance according to a conventional method using alkyl halides such as methyl chloride, methyl bromide, ethyl chloride, ethyl bromide, propyl chloride, propyl bromide, butyl chloride, and butyl bromide. Instead of the quaternary ammonium halide, a method may be used in which the obtained quaternary ammonium halide is copolymerized with a monomer constituting another unit, and the resulting copolymer is reacted with paratoluenesulfonic acid.
[0015]
Examples of the polymerization initiator used for the copolymerization here include azobisisobutyronitrile, azobisdimethylvaleronitrile, azobis (2,4-dimethyl-4-methoxyvaleronitrile), 2-phenylazo (2,4- And azo initiators such as dimethyl-4-methoxyvaleronitrile). The polymerization initiator is preferably used in the range of 0.5 to 10 parts by mass with respect to the total mass of the monomer mixture used being 100 parts by mass.
As the copolymerization method, any method such as solution polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization may be used, and there is no limitation. However, the control of the mass average molecular weight of the obtained copolymer is relatively limited. Benzene, toluene, xylene, dioxane, propylene glycol monomethyl ether, ethylene glycol monomethyl ether, because it is easy and the operation of reacting the obtained copolymer with paratoluenesulfonic acid or its alkyl ester is easy. In an organic solvent such as ether, ethyl acetate, isopropyl acetate, methyl ethyl ketone, diethyl ketone, and isobutyl ketone, or in a mixed solvent of these organic solvents and lower alcohols such as methanol, ethanol, propanol, isopropanol, and butanol, Solution weight to copolymerize the mixture The law is particularly preferred.
[0016]
In the reaction of the produced copolymer with paratoluenesulfonic acid alkyl ester or paratoluenesulfonic acid, paratoluenesulfonic acid alkyl ester or paratoluenesulfonic acid is added to the copolymer solution and heated to a temperature of 65 to 95 ° C. As a result, a quaternary ammonium base-containing copolymer is obtained. The amount of paratoluenesulfonic acid alkyl ester or paratoluenesulfonic acid used is usually about 0.1 per mole of dialkylaminoalkyl (meth) acrylate or quaternary ammonium halide contained in the copolymer to be reacted therewith. The range is 8 to 1 mol, preferably 0.9 to 1 mol.
[0017]
The quaternary ammonium base-containing copolymer preferably has a mass average molecular weight in the range of 1500 to 1000000. Within such a range, the chargeability is unlikely to deteriorate even in a high humidity environment. Further, the compatibility with the binder resin and the dispersibility become better. A more preferable mass average molecular weight of the quaternary ammonium base-containing copolymer is 5,000 to 100,000.
Furthermore, when the glass transition temperature of the quaternary ammonium base-containing copolymer is 50 to 100 ° C., the storage stability at a high temperature becomes good while maintaining the fixability as a powder coating material.
[0018]
As described above, the compound represented by the formula (1) is used alone or in combination with the above-described quaternary ammonium base-containing copolymer or the like in an arbitrary mass ratio to form a powder paint as a frictional charge imparting agent. Can be used. Specifically, when the compound of the formula (1) is used alone, a high electric power can be obtained even if the amount used is small, while when used in combination with a quaternary ammonium base-containing copolymer, a high electric power is obtained. Of course, other performance such as moisture resistance is provided in a well-balanced manner.
[0019]
This frictional charge imparting agent is blended with additives such as a colorant, a curing agent, a filler, a flow agent, and an antifoaming agent as necessary with respect to the binder resin, for example, an average particle diameter of 2 to 80 μm. By making particles of a degree, it is possible to obtain a powder paint having excellent chargeability and charge rising property and good coating efficiency.
Here, the preferable blending amount of the triboelectric charge imparting agent depends on the content of the compound of the formula (1) in the triboelectric charge imparting agent, but usually 0.1 to 10 parts per 100 parts by mass of the binder resin. Part by mass.
Here, if it is less than 0.1 parts by mass, sufficient chargeability is hardly obtained, and it tends to be difficult to contribute to increasing the coating efficiency. On the other hand, if it exceeds 10 parts by mass, it is formed from a powder paint. The strength of the applied coating may be reduced.
[0020]
As the binder resin, an acrylic resin, a polyester resin, an epoxy resin, a phenol resin, a xylene resin, a urea resin, a melamine resin, and the like are preferable, and one kind can be used alone, or two or more kinds can be used in combination.
[0021]
There is no restriction | limiting in particular as a coloring agent, A titanium oxide, chromium oxide, iron oxide, carbon black etc. can be used, These can be used individually by 1 type or in combination of 2 or more types.
[0022]
As the curing agent, dodecanedioic acid, (poly) isocyanate, amine, polyamide, acid anhydride, polysulfide, boron trifluoride, acid dihydrazide, imidazole, dicyandiamide and the like can be used.
As the filler, barium sulfate, calcium carbonate, aluminum oxide, calcium silicate and the like can be used. As the flow agent, acrylic oligomer, silicone and the like can be used. As the antifoaming agent, benzoin and the like can be used.
[0023]
For the production of powder coating, first, the above-mentioned components are mixed thoroughly in a mixer such as a super mixer, a Henschel mixer, or a ball mill, and then melted in a heat kneader such as a heating roll, a kneader, or an extruder. Knead and cool and solidify. Subsequently, it can grind | pulverize with grinders, such as a hammer mill and a jet mill, the obtained ground material is classified, and it can prepare by collect | recovering particles with an average particle diameter of preferably 2-80 micrometers.
In addition, a method of drying an organic solvent solution in which each component is melted or dispersed by a spray drying method or the like at a temperature of 200 ° C. or less, and other components in the mixture of monomers constituting the binder resin Can be prepared by mixing them into an emulsion suspension and copolymerizing them.
[0024]
In addition, inorganic fine particles such as silica, alumina, titanium oxide and the like may be attached to the surface of the powder coating thus obtained, if necessary. For the adhesion of the inorganic fine particles, a powder coating and the inorganic fine particles may be mixed by stirring using a mixer such as a Henschel mixer.
[0025]
The powder coating obtained in this way is frictionally charged by a spray gun such as a frictional charging system and sprayed onto the object to be coated, and adheres to the object to be coated due to charging properties. And a coating film can be formed by baking the to-be-coated object in the state to which this powder coating material adhered in a baking furnace etc.
[0026]
As described above, the compound represented by the formula (1) has good compatibility and dispersibility with the binder resin, and is excellent in charged power and initial charge rising property. Therefore, it is possible to give excellent chargeability and charge start-up property without using a large amount when blended in powder paint as a friction charge imparting agent, and use a friction charge type spray gun at the time of painting In this case, sufficient chargeability can be obtained. Moreover, since it is uniformly disperse | distributed to binder resin, the smoothness of a coating film formed, intensity | strength, etc. become favorable. Furthermore, since the compound represented by the formula (1) has transparency, it can be used together with an arbitrary colorant to form a powder coating material having a desired hue.
[0027]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
[Friction charge imparting agent 1]
To 100 parts by mass of a commercially available quaternary ammonium base-containing copolymer acrylic base FCA-201-PS (manufactured by Fujikura Kasei Co., Ltd.), 1 part by mass of paranitrobenzoic acid is dissolved in methyl ethyl ketone, A homogeneous solution was obtained. This was heated and dried at 130 ° C. to obtain triboelectric charge imparting agent 1. This triboelectric charge imparting agent 1 was light yellow with transparency.
The commercially available quaternary ammonium base-containing copolymer acrylic base FCA-201-PS (manufactured by Fujikura Kasei Co., Ltd.) is in the form of particles, and the quaternary ammonium base-containing unit is represented by the formula (2 ) In which R ₅ is a methyl group, R ₆ is —CH ₂ —CH ₂ —, R _{7 to} R ₉ are each an ethyl group, a methyl group, and an ethyl group, Contains units composed of styrene and butyl acrylate monomers. And the content rate of the quaternary ammonium base containing unit in a quaternary ammonium base containing copolymer is 15 mass%. The mass average molecular weight is 12000, and the glass transition temperature is 67 ° C.
[0028]
[Friction charge imparting agent 2]
To 100 parts by mass of a commercially available quaternary ammonium base-containing copolymer acrylic base FCA-201-PS (manufactured by Fujikura Kasei Co., Ltd.), 1 part by mass of paranitrobenzoic acid is dissolved in methyl ethyl ketone, A homogeneous solution was obtained. This was heated and dried at 130 ° C. to obtain triboelectric charge imparting agent 2. This triboelectric charge imparting agent 2 was light yellow with transparency.
[0029]
[Friction charge imparting agent 3]
Paranitrobenzoic acid was used as triboelectric charge imparting agent 3. This triboelectric charge imparting agent 3 was light yellow with transparency.
[0030]
[Example 1]
17.7 parts by mass of a curing agent (dodecanedioic acid, DDA made by Ube Industries) and 77 parts by mass of an acrylic resin (A-253 manufactured by Dainippon Ink & Chemicals, Inc.), a binder resin, and an acrylic (acrylic) Copolymer, 1.0 part by mass of BASF's acronal 4F), 0.5 parts by mass of antifoaming agent (benzoin, manufactured by Midori Chemical Co., Ltd.), 5 parts of colorant (carbon black, MA-100, manufactured by Mitsubishi Chemical Corporation), 2 parts by mass of the above triboelectric charge imparting agent 1 was blended, mixed with a super mixer, hot melt kneaded at 120 ° C. with a pressure kneader, cooled and solidified, and then pulverized with a jet mill.
Thereafter, the obtained pulverized product was classified with a dry air classifier, and particles having an average particle size of 22 μm were collected, which was used as a powder coating material.
[0031]
(Coating efficiency)
The obtained powder coating was sprayed on the object to be coated using a frictional charging spray gun, and the coating efficiency (%) was determined. The results are shown in Table 1.
1) Coating conditions As a spray gun, T-1a manufactured by Matsuo Sangyo Co., Ltd. was used, and as an object to be coated, a 300 mm square iron plate fixed at the center of a 1000 mm square iron plate was used. Detailed conditions are as follows.
Reciprocating stroke: 1m up and down
Reciprocating speed: 20 m / min.
Workpiece moving speed (conveyor speed): 2 m / min.
Powder gun discharge rate of spray gun: 100 g / min.
Distance between spray gun tip and substrate: 180mm
Painting environment: 25 ° C / 50% RH
2) Calculation of coating efficiency (%) The time (min.) Required for the spray gun to move on the object to be coated is calculated. g / min.) was used as the theoretical discharge amount. Next, the mass of the powder coating material applied to the object to be coated is determined from the mass of the material to be coated before and after the powder coating is applied as in 1), and the percentage (%) of this mass with respect to the theoretical discharge amount. Was determined as the coating efficiency.
[0032]
(Coating strength)
The obtained powder coating material was applied to a test panel (PB-137M) manufactured by Japan Test Panel Co. with a spray gun so as to have a film thickness of 40 μm and baked at 180 ° C. for 20 minutes to form a coating film.
When the strength of the coating film was measured by a bending resistance test specified in JIS K5400 (8.1) with the diameter of the mandrel set to 3 mm, the coating film had sufficient mechanical strength without cracking.
[0033]
[Example 2]
A powder paint was obtained in the same manner as in Example 1 except that the friction charge imparting agent 2 was used instead of the friction charge imparting agent 1, and the coating efficiency was determined. The results are shown in Table 1. Moreover, when the coating film was formed like Example 1 and the intensity | strength of this coating film was measured, it was equipped with sufficient mechanical strength without the crack of a coating film.
[0034]
[Example 3]
A powder paint was obtained in the same manner as in Example 1 except that the friction charge imparting agent 3 was used instead of the friction charge imparting agent 1, and the coating efficiency was determined. The results are shown in Table 1. Moreover, when the coating film was formed like Example 1 and the intensity | strength of this coating film was measured, it was equipped with sufficient mechanical strength without the crack of a coating film.
[0035]
[Comparative Example 1]
A powder paint was obtained in the same manner as in Example 1 except that the frictional charge imparting agent was not used, and the coating efficiency was determined. The results are shown in Table 1.
[0036]
[Example 4]
As a binder resin, 35 parts by mass of a polyester resin (ER-8155 manufactured by Nihon Ester Co., Ltd.) and 66 parts by mass of an epoxy resin (YD-014 manufactured by Tokyo Chemical Industry Co., Ltd.) were used. On the other hand, a curing agent (triphenylphosphine, PP-360 manufactured by Keisei Kasei Co., Ltd. 2.5 parts by mass, 1.0 part by mass of a flow agent (acrylic copolymer, acronal 4F manufactured by BASF), 0.5 part by mass of an antifoaming agent (benzoin, manufactured by Midori Chemical Co., Ltd.) , 5 parts of a colorant (carbon black, MA-100 manufactured by Mitsubishi Chemical Corporation) and 2 parts by mass of the above triboelectric charge imparting agent 2 are mixed, mixed with a super mixer, and hot melt kneaded at 120 ° C. with a pressure kneader. After cooling and solidifying, the mixture was pulverized with a jet mill.
Thereafter, the obtained pulverized product was classified with a dry air classifier, and particles having an average particle size of 22 μm were collected, which was used as a powder coating material. In addition, the coating efficiency was determined in the same manner as in Example 1. The results are shown in Table 1. Moreover, when the coating film was formed like Example 1 and the intensity | strength of this coating film was measured, it was equipped with sufficient mechanical strength without the crack of a coating film.
[0037]
[Comparative Example 2]
A powder coating was obtained in the same manner as in Example 4 except that the frictional charge imparting agent was not used, and the coating efficiency was determined. The results are shown in Table 1.
[0038]
[Example 5]
13.5 parts by weight of a curing agent (polyisocyanate, BF-1540 from Huls) and 80 parts by weight of a polyester resin (ER-6680, manufactured by Nippon Ester Co., Ltd.), a flow agent (acrylic copolymer, BASF Acronal 4F) 1.0 part by mass, foam inhibitor (benzoin, Midori Chemical Co., Ltd.) 0.5 part by mass, colorant (carbon black, MA-100 manufactured by Mitsubishi Chemical Co., Ltd.) 5 parts, and the above friction 2 parts by mass of the charge imparting agent 2 was blended, mixed with a super mixer, hot melt kneaded at 120 ° C. with a pressure kneader, cooled and solidified, and then pulverized with a jet mill.
Thereafter, the obtained pulverized product was classified with a dry air classifier, and particles having an average particle size of 22 μm were collected, which was used as a powder coating material. In addition, the coating efficiency was determined in the same manner as in Example 1. The results are shown in Table 1. Moreover, when the coating film was formed like Example 1 and the intensity | strength of this coating film was measured, it was equipped with sufficient mechanical strength without the crack of a coating film.
[0039]
[Comparative Example 3]
A powder coating was obtained in the same manner as in Example 5 except that the frictional charge imparting agent was not used, and the coating efficiency was determined. The results are shown in Table 1.
[0040]
[Example 6]
Epoxy resin as a binder resin (Epicoat 1004 manufactured by Yuka Shell Epoxy Chemical Co., Ltd.), 88.5 parts by mass, 5 parts by mass of a curing agent (dicyandiamide), a flow agent (acrylic copolymer, Acronal 4F manufactured by BASF) 1.0 part by mass, 0.5 part by mass of an antifoaming agent (benzoin, manufactured by Midori Chemical Co., Ltd.), 5 parts of a colorant (carbon black, MA-100 manufactured by Mitsubishi Chemical Co., Ltd.), and 2 of the above triboelectric charge imparting agent 2 A part by mass was blended, mixed with a super mixer, hot melt kneaded at 120 ° C. with a pressure kneader, cooled and solidified, and then pulverized with a jet mill.
Thereafter, the obtained pulverized product was classified with a dry air classifier, and particles having an average particle size of 22 μm were collected, which was used as a powder coating material. In addition, the coating efficiency was determined in the same manner as in Example 1. The results are shown in Table 1. Moreover, when the coating film was formed like Example 1 and the intensity | strength of this coating film was measured, it was equipped with sufficient mechanical strength without the crack of a coating film.
[0041]
[Comparative Example 4]
A powder paint was obtained in the same manner as in Example 6 except that the frictional charge imparting agent was not used, and the coating efficiency was determined. The results are shown in Table 1.
[0042]
[Table 1]

[0043]
As shown in Table 1, the powder paint obtained in the examples had sufficient chargeability, and thus the coating efficiency was excellent.
[0044]
【The invention's effect】
As described above, in the present invention, since the triboelectric charge imparting agent containing the compound represented by the formula (1) is used, sufficient charging is possible even when using a triboelectric charging system as a spray gun during coating. Properties are obtained, the coating efficiency is excellent, and the smoothness and strength of the formed coating film are also good. Moreover, since the compound shown by Formula (1) is equipped with transparency, it can be used with an arbitrary colorant to form a powder coating material of a desired color.

Claims (3)

A powder paint containing at least a triboelectric charge imparting agent containing a compound represented by the following formula (1) and a binder resin ,
The triboelectric charge imparting agent further contains a quaternary ammonium base-containing copolymer composed of a quaternary ammonium base-containing unit and other units,
The other unit is mainly composed of a styrene monomer and / or a (meth) acrylic monomer, and the quaternary ammonium base-containing unit is represented by the following formula (2):
The quaternary ammonium base-containing copolymer contains 0.5 to 35% by mass of the quaternary ammonium base-containing unit .

(In formula (1), R _{1 to} R ₄ each represent hydrogen .)

(In Formula (2), R ₅ is a hydrogen atom or a methyl group, R ₆ is an alkylene group, and R _{7 to} R ₉ are each an alkyl group. ) The powder coating material according to claim 1, wherein 0.1 to 10 parts by mass of a frictional charge imparting agent is blended with respect to 100 parts by mass of the binder resin. A coating method comprising: charging the powder coating material according to claim 1 or 2 by a frictional charging method and spraying the powder coating material on an object to be coated.