JP3902716B2 - Droplet ejection head, inkjet recording apparatus, image forming apparatus, and apparatus for ejecting droplets - Google Patents

Description

【００４１】
ここで、実効的なギャップ距離ｄとは、（２）式のような関係を意味し、振動板１０と対向電極１５ａ、１５ｂとの間に空気以外の誘電率を有する物質が介在する場合には、ｄは（２）式のように表わされる。但し、（２）式において、ｄ_aは振動板１０と対向電極１５ａ、１５ｂとの間に存在する空隙の距離、ｄ_εは振動板１０と対向電極１５ａ、１５ｂとの間に存在する誘電絶縁層１７の厚み、ε_rは誘電絶縁層１７の比誘電率を表わす。
【００４２】
【数２】

【００４３】
すなわち、振動板１０と対向電極１５ａ、１５ｂとの間に、ある誘電率を有する物質を介在させると、（２）式のように、その介在させた誘電物質の厚みｄ_εとその誘電物質が有する比誘電率ε_rを変化させることによって、振動板１０と対向電極１５ａ、１５ｂとの間に発生する電界強度Ｅ（すなわちＥ＝Ｖ／ｄ）と、それによって生じる静電吸引力Ｐの大きさが変化するということである。したがって、（１）式に示されるように静電吸引力Ｐは、振動板１０と対向電極１５ａ、１５ｂとの間の実効的なギャップ距離ｄが小さいほど振動板１０に大きな静電引力が働くこととなる。
【００４４】
そこで、このインクジェットヘッドを駆動するときには、図４に示すように、振動板１０が対向する対向電極１５ａ、１５ｂ方向へ撓み、最終的には振動板１０が凹（段）部１４内に配置され、振動板１０と同電位である接触対向部１８に接触するまで変形変位する駆動波形を印加する。
【００４５】
従来のインクジェットヘッドにあっては、この振動板が駆動電圧Ｖの印加されている対向電極へ接触した瞬間に、振動板と対向電極との間に発生している電位差が主たる原因で残留電荷が発生していることが、実験上、判明した。そこで、本発明では、振動板１０が凹（段）部１４内で主に接触する部分に予め接触対向部１８を配置し、その接触対向部１８を予め電気的に振動板１０側の電位と同電位となるように構成しておくことにより、本質的に残留電荷の発生を未然に防止することができる。
【００４６】
次に、対向電極１５ａ、１５ｂへのパルス電圧の印加をＯＦＦすると、上記のようにして撓んだ振動板１０が復元し、吐出室６内の圧力が急激に上昇するため、ノズル４よりインク液滴が形成され、記録紙に向けてインク吐出が行われる。そして、さらに、再び、対向電極１５ａ、１５ｂへパルス電圧をＯＮすると、振動板１０が再び対向する対向電極１５ａ、１５ｂ、及び接触対向部１８の方向へ撓むので、インクが共通液室８より流体抵抗部７を通じて吐出室６内に補給されるようになる。
【００４７】
このように、振動板１０が変形して対向する対向電極１５ａ、１５ｂ側へ接触する際、予め第２基板２の凹（段）部１４内に振動板１０の接触対向部１８を配置し、また、その接触対向部１８を予め振動板１０側の電位と電気的に同電位としておくことにより、残留電荷の発生を未然に防止することができ、また、残留電荷の発生が無いため片方の極性の駆動電圧のみでもインク滴吐出不良の無い安定したインク滴吐出動作を行うことができるようになる。
【００４８】
なお、この場合、駆動電圧が印加される対向電極１５ａ、１５ｂと振動板１０の接触対向部１８との間でも電位差が発生するので、対向電極１５ａ、１５ｂと振動板１０の接触対向部１８との間で電界放出等による放電や短絡等が生じないよう十分な電気的な絶縁処理を施している。
【００４９】
これを確認するため、上記構成のインクジェットヘッドを使用し、第１基板１の上側にステンレス製の第３基板３をエポキシ系接着剤にて接合し、ドライバＩＣ２０等を接続して対向電極１５ａ、１５ｂにパルス状のプラス（正）電圧のみの片極性の電圧を印加して、作製したインクジェットヘッドの印字試験を行った。同様に、比較例として、接触対向部１８を持たないインクジェットヘッドも製作して同様の印字試験を行った。
【００５０】
この試験結果によると、従来の接触対向部１８を持たないインクジェットヘッドにあっては、振動板１０と対向電極との間で僅か数分の間に徐々に残留電荷が蓄積し、インク滴の吐出不良等が発生して極めてインク滴吐出状態が不安定であったのに対し、上記第１実施形態のインクジェットヘッドでは、片極性のプラス（正）電圧のみで数時間以上もの間、繰り返し安定してインク吐出することが可能となり、印字品質が安定することが確認された。
【００５１】
また、片極性のプラス（正）電圧のみでインク滴吐出駆動することが可能となったことから、従来に比較して駆動回路の装置構成がより簡易で小型となり、また、回路コストも３０％以上も安価にすることができた。
【００５２】
次に、本発明の第２実施形態に係るインクジェットヘッドについて図５を参照して説明する。なお、同図は図４と同様な振動板変形時の振動板短手方向の要部拡大説明図である。
【００５３】
このインクジェットヘッドでは、前述したような振動板１０の接触対向部として、第２基板２の凹（段）部１４内に二ヵ所に接触対向部１８ａ、１８ｂを配置し、また、駆動電圧を印加するための対向電極として、凹部１４内に三ヶ所に接触対向部１８ａ、１８ｂを振動板短手方向で挟んで対向電極１５ａ、１５ｂ、１５ｃを配置している。
【００５４】
そして、電極を保護するためのＳｉＯ２等の誘電絶縁層１７の厚みを接触対向部１８ａ、１８ｂ上と対向電極１５ａ、１５ｂ、１５ｃ上とで異ならせて、接触対向部１８ａ、１８ｂ上の方が厚くなるように形成している。また、接触対向部１８ａ、１８ｂを予め振動板１０側の電位と電気的に同電位としていることは前記実施形態と同様である。
【００５５】
この構成のインクジェットヘッドにおいても、上記のとおり接触対向部１８ａ、１８ｂを予め振動板１０側の電位と電気的に同電位としているので、振動板１０が接触対向部１８ａ、１８ｂに接触することで、本質的に残留電荷の発生を未然に防止することができる。
【００５６】
これに加えて、本実施形態の場合、第１実施形態のヘッドに比べて振動板１０からの接触対向部１８ａ、１８ｂまでの距離の方が電圧印加される対向電極１５ａ、１５ｂ、１５ｃまでの距離よりも、より短くなっているため、振動板１０が電圧印加される対向電極１５ａ、１５ｂ、１５ｃにより確実に接触し難くなっており、結果としてより確実に残留電荷の発生を防止でき、より信頼性の高い安定したインク滴吐出動作を行うことができる。
【００５７】
これを確認するため、このインクジェットヘッドを使用し、第１基板１の上側にステンレス製の第３基板３をエポキシ系接着剤にて接合し、ドライバＩＣ２０等を接続して対向電極１５ａ、１５ｂ、１５ｃにパルス状のプラス（正）電圧のみの片極性の電圧を印加して、作製したインクジェットヘッドの印字試験を行った。
【００５８】
この試験結果によれば、第１実施形態のヘッドにおいては、時折、残留電荷の発生のためにインク滴吐出不良が生じるヘッドがあったのに対し、この第２実施形態のインクジェットヘッドでは、残留電荷によるインク滴吐出不良となるヘッドの発生はなく、歩留まりが向上し、より安定したインク吐出駆動をすることが可能となることを確認できた。
【００５９】
次に、本発明の第３実施形態に係るインクジェットヘッドについて図６を参照して説明する。なお、同図も図４と同様な振動板変形時の振動板短手方向の要部拡大説明図である。
【００６０】
このインクジェットヘッドでも、前述したような振動板１０の接触対向部として、第２基板２の凹（段）部１４内に二ヵ所に接触対向部１８ａ、１８ｂを配置し、また、駆動電圧を印加するための対向電極として、凹部１４内に三ヶ所に接触対向部１８ａ、１８ｂを振動板短手方向で挟んで対向電極１５ａ、１５ｂ、１５ｃを配置している。
【００６１】
そして、第２実施形態と同じく振動板１０からの接触対向部１８ａ、１８ｂまでの距離の方を振動板１０から電圧印加される対向電極１５ａ、１５ｂ、１５ｃまでの距離よりもより短くするために、凹（段）部１４内に凸部１４ａ、１４ｂを二ヵ所に形成し、この凸部１４ａ、１４ｂ上に上記振動板１０が接する接触対向部１８ａ、１８ｂを設けている。ここで、接触対向部１８ａ、１８ｂの表面側の材質としては、電極となるような電気的伝導性を有する材質（金属等）のもので形成している。
【００６２】
このインクジェットヘッドでは、前記第１、第２実施形態のヘッドに比べてその接触対向部１８ａ、１８ｂの表面側に前記のような誘電絶縁層１７が無く、金属等の電気的伝導性を有する材質のもので形成されている。
【００６３】
したがって、例えば、ヘッドの製造途中で何らかの原因により初めから誘電絶縁層１７上に電荷が初期帯電するような場合でも、このヘッドであれば、接触対向部１８ａ、１８ｂが予め比較的抵抗の低い電気伝導性を有する材質のもので形成されているので、接触対向部１８ａ、１８ｂ上に初めから電荷が帯電しているようなことは発生しない。また、残留電荷に対してもより確実に効果的に発生の防止をすることができる。
【００６４】
次に、本発明の第４実施形態に係るインクジェットヘッドについて図７を参照して説明する。なお、同図も図４と同様な振動板変形時の振動板短手方向の要部拡大説明図である。
【００６５】
このインクジェットヘッドでも、前述したような振動板１０の接触対向部として、第２基板２の凹（段）部１４内に二ヵ所に接触対向部１８ａ、１８ｂを配置し、また、駆動電圧を印加するための対向電極として、凹部１４内に三ヶ所に接触対向部１８ａ、１８ｂを振動板短手方向で挟んで対向電極１５ａ、１５ｂ、１５ｃを配置している。
【００６６】
そして、第３実施形態と同じく振動板１０からの接触対向部１８ａ、１８ｂまでの距離の方を振動板１０から電圧印加される対向電極１５ａ、１５ｂ、１５ｃまでの距離よりもより短くするために、接触対向部１８ａ、１８ｂそれ自体の全体を金属等の前記電気的伝導性を有する材質のもので構成し、その厚み自体を電圧印加される対向電極１５ａ、１５ｂ、１５ｃの厚みよりも厚くするように形成している。
【００６７】
したがって、このインクジェットヘッドでは、第３実施形態のヘッドに比べて構成が簡易となり、容易に作製可能な構成で第３実施形態と同様な効果が得られる。
【００６８】
このインクジェットヘッドを使用し、第１基板１の上側にステンレス製の第３基板３をエポキシ系接着剤にて接合し、ドライバＩＣ２０等を接続して対向電極１５ａ、１５ｂ、１５ｃにパルス状のプラス（正）電圧のみの片極性の電圧を印加して、作製したインクジェットヘッドの印字試験を行った。
【００６９】
この試験結果によれば、第２実施形態のヘッドにおいては、製造途中での初期帯電によるインク滴吐出不良となるヘッドが発生していたのに対し、この第４実施形態のインクジェットヘッドでは、製造途中での初期帯電によるインク滴吐出不良となるヘッドの発生はなく、歩留まりが向上し、より安定したインクジェットヘッドの製作が可能になることを確認できた。また、ヘッド構成がより簡易となり、容易に作製可能となったので、ヘッドの生産効率が向上するようになった。
【００７０】
次に、本発明の第５実施形態に係るインクジェットヘッドについて図８を参照して説明する。なお、同図も図４と同様な振動板変形時の振動板短手方向の要部拡大説明図である。
【００７１】
このインクジェットヘッドでは、前記第１実施形態と同様に、振動板１０の接触対向部１８を第２基板２の凹（段）部１４内で振動板短手方向略中央部に設け、また、駆動電圧を印加するための対向電極として、凹部１４内に二ヶ所に接触対向部１８を振動板短手方向で挟んで対向電極１５ａ、１５ｂを配置している。
【００７２】
さらに、第２実施形態と同様に、振動板１０と接触対向部１８までの距離の方を振動板１０と電圧印加される対向電極１５ａ、１５ｂまでの距離よりも短くするため、接触対向部１８を保護するための誘電絶縁層１７の厚みを接触対向部１８上の方が対向電極１５ａ、１５ｂ上の絶縁層１７より厚くなるように形成している。
【００７３】
このように構成した場合、第２、第３実施形態のヘッドに比べてより簡易な構成で確実に安定して残留電荷の発生を未然に防止する効果が十分得られる。
【００７４】
次に、本発明の第６実施形態に係るインクジェットヘッドについて図９を参照して説明する。なお、同図も図４と同様な振動板変形時の振動板短手方向の要部拡大説明図である。
【００７５】
このインクジェットヘッドでも、前記第１実施形態と同様に、振動板１０の接触対向部１８を第２基板２の凹（段）部１４内で振動板短手方向略中央部に設け、また、駆動電圧を印加するための対向電極として、凹部１４内に二ヶ所に接触対向部１８を振動板短手方向で挟んで対向電極１５ａ、１５ｂを配置している。そして、振動板１０の接触対向部１８表面側に誘電絶縁層１７を形成している。
【００７６】
このように構成した場合、第２、第３実施形態のヘッドに比べてより簡易な構成で確実に安定して残留電荷の発生を未然に防止する効果が十分得られる。
【００７７】
次に、本発明の第７実施形態に係るインクジェットヘッドについて図１０を参照して説明する。なお、同図も図４と同様な振動板変形時の振動板短手方向の要部拡大説明図である。
【００７８】
このインクジェットヘッドでも、前記第１実施形態と同様に、振動板１０の接触対向部１８を第２基板２の凹（段）部１４内で振動板短手方向略中央部に設け、また、駆動電圧を印加するための対向電極として、凹部１４内に二ヶ所に接触対向部１８を振動板短手方向で挟んで対向電極１５ａ、１５ｂを配置している。
【００７９】
さらに、第３実施形態と同様に、振動板１０と接触対向部１８までの距離の方を振動板１０と電圧印加される対向電極１５ａ、１５ｂまでの距離よりも短くするため、振動板１０と接触対向部１８との間の距離の方を振動板１０と電圧印加される対向電極１５ａ、１５ｂとの間の距離よりもより短くするため、凹（段）部１４内に凸部１４ａを一ヵ所設け、その凸部１４ａ上に金属等の電気的伝導性を有する材質の接触対向部１８を形成している。
【００８０】
このように構成した場合、第２、第３実施形態のヘッドに比べてより簡易な構成で確実に安定して残留電荷の発生を未然に防止する効果が十分得られる。
【００８１】
これらの各実施形態において、複数のノズルのヘッドの対向電極１５ａ、１５ｂと振動板１０の接触対向部１８とを第２基板２上に配置する場合には、図１１に示すように各ヘッドの対向電極１５ａ、１５ｂと振動板１０の接触対向部１８を第２基板２上に図のようにパターン形成し、各接触対向部１８を同図に示すようにパターン形成された配線４０で結線することにより、複数のノズルにおいても残留電荷の発生を防止しながら、安定したインク吐出駆動を行うことが可能となる。
【００８２】
次に、本発明の第８実施形態に係るインクジェットヘッドについて図１２を参照して説明する。なお、同図も図４と同様な振動板変形時の振動板短手方向の要部拡大説明図である。
【００８３】
このインクジェットヘッドでは、振動板１０が接触する接触対向部１８を第２基板２の凹（段）部１４内において図示のように駆動電圧を印加するための対向電極１５の表面上に誘電絶縁層１７を介して設置している。また、前記と同様に接触対向部１８は振動板１０の振動板短辺方向に対してほぼ中央部に一ヵ所設けている。この場合、振動板１０の接触対向部１８は対向電極１５表面上に誘電絶縁層１７を介して形成するので、必然的に振動板１０と接触対向部１８との間の距離の方が振動板１０と電圧印加される対向電極１５との間の距離よりも短くなる。
【００８４】
このように構成した場合、前記第２、第３実施形態のヘッドに比べてより簡易な構成で容易に作製可能となり、また、より確実に安定して残留電荷の発生を未然に防止する効果が得られる。
【００８５】
このインクジェットヘッドを使用し、第１基板１の上側にステンレス製の第３基板３をエポキシ系接着剤にて接合し、ドライバＩＣ２０等を接続して対向電極１５にパルス状のプラス（正）電圧のみの片極性の電圧を印加して、作製したインクジェットヘッドの印字試験を行った。
【００８６】
この試験結果によれば、第２、第３実施形態のヘッドにおいては、製造途中においてヘッド不良によりＮＧとなるヘッドが発生していたのに対し、この実施形態のヘッドでは、ヘッド不良によるＮＧが減少し、ヘッドの歩留まりがより向上し、より安定したインクジェットヘッドを得ることができた。また、ヘッド構成がより簡易となり、より容易に作製可能となったため、ヘッドの生産効率が向上するようになった。
【００８７】
次に、本発明に係る液滴吐出ヘッドから液滴を吐出する装置を含む、本発明に係る画像形成装置としてのインクジェット記録装置の機構部の概要について図１３を参照して簡単に説明する。このインクジェット記録装置は、両側の側板５１，５２間に主支持ガイドロッド５３及び従支持ガイドロッド５４を略水平な位置関係で横架し、これらの主支持ガイドロッド５３及び従支持ガイドロッド５４でキャリッジ５５を主走査方向に摺動自在に支持している。
【００８８】
キャリッジ８には、それぞれイエロー（Ｙ）インク、マゼンタ（Ｍ）インク、シアン（Ｃ）インク、ブラック（Ｂｋ）インクをそれぞれ吐出する４個の本発明に係るインクジェットヘッドからなるヘッド５６ｙ，５６ｍ，５６ｃ，５６ｋを、その吐出面（ノズル面）を下方に向けて搭載し、またキャリッジ５５にはヘッド５６（符号「５６」は、「５６ｙ，５６ｍ，５６ｃ，５６ｋ」のいずれか又は総称である。）の上側に４個のヘッド５６に各々インクを供給するための各色のインク供給体である４個のインクカートリッジ５７（符号「５７」は、「５７ｙ，５７ｍ，５７ｃ，５７ｋ」のいずれか又は総称）を交換可能に搭載している。
【００８９】
そして、キャリッジ５５は主走査モータ５８で回転される駆動プーリ（駆動タイミングプーリ）５９と従動プーリ（アイドラプーリ）６０との間に張装したタイミングベルト６１に連結して、主走査モータ５８を駆動制御することによってキャリッジ５５、即ち４個のヘッド５６を主走査方向に移動するようにしている。
【００９０】
また、側板５１，５２をつなぐ底板６２上にサブフレーム６３，６４を立設し、このサブフレーム６３，６４間に用紙６６を主走査方向と直交する副走査方向に送るための搬送ローラ６５を回転自在に保持している。そして、サブフレーム６４側方に副走査モータ６７を配設し、この副走査モータ６７の回転を搬送ローラ６５に伝達するために、副走査モータ６７の回転軸に固定したギヤ６８と搬送ローラ６５の軸に固定したギヤ６９とを備えている。
【００９１】
さらに、側板５１とサブフレーム６２との間には、ヘッド５６の信頼性維持回復機構（以下、「サブシステム」という。）７１を配置している。サブシステム７１は、各ヘッド５６の吐出面をキャッピングする４個のキャップ手段７２をホルダ７３で保持し、このホルダ７３をリンク部材７４で揺動可能に保持して、キャリッジ５５の主走査方向の移動でホルダ７３に設けた係合部７５にキャリッジ５５が接触することで、キャリッジ５５の移動に従ってホルダ７３がリフトアップしてキャップ手段７２でヘッド５６の吐出面をキャッピングし、キャリッジ５５が印写領域側へ移動することで、キャリッジ５５の移動に従ってホルダ７３がリフトダウンしてキャップ手段７２がヘッド５６の吐出面から離れるようにしている。
【００９２】
なお、キャップ手段７２は、それぞれ吸引チューブ７６を介して吸引ポンプ７７に接続すると共に、大気開放口を形成して、大気開放チューブ及び大気開放バルブを介して大気に連通している。また、吸引ポンプ７７は吸引した廃液（廃インク）をドレインチューブ等を介して廃液貯留槽に排出する。
【００９３】
さらに、ホルダ７３の側方には、ヘッド５６の吐出面５６ａをワイピングする繊維部材、発泡部材或いはゴム等の弾性部材からなるワイピング手段であるワイパブレード８０をブレードアーム８１に取付け、このブレードアーム８１は揺動可能に軸支し、図示しない駆動手段で回動されるカムの回転によって揺動させるようにしている。
【００９４】
このように構成したこの記録装置では、ヘッド５６（キャリッジ５５）を主走査方向に移動走査させながら、用紙６６を副走査方向に搬送して、各ヘッドのノズルから所要の色のインク滴を吐出させることによって、用紙６６上に所要のカラー画像（モノクロ画像を含む。）を記録する。
【００９５】
このとき、前述したように本発明に係るインクジェットヘッドは、残留電荷の発生がなく、安定したインク滴吐出動作を行うことができるとともに、片極性の駆動波形でインク滴吐出動作を行うことができるので、駆動回路の構成が簡単になり、装置構成が簡易で、小型化を図れる。
【００９６】
なお、上記実施例においては、本発明を振動板変位方向とインク滴吐出方向が同じになるサイドシュータ方式のインクジェットヘッドに適用したが、振動板変位方向とインク滴吐出方向と直交するエッジシュータ方式のインクジェットヘッドにも同様に適用することができる。さらに、インクジェットヘッドだけでなく液体レジスト等を吐出させる液滴吐出ヘッドなどにも適用できる。また、前述したようにプリンタ、ファクシミリ、プロッタ等の画像形成装置及び液滴を吐出する装置にも本発明を適用することができる。
【００９７】
【発明の効果】
以上説明したように、本発明に係る液滴吐出ヘッドによれば、振動板が変形したときに振動板が接する接触対向部を有し、この接触対向部は振動板と同電位であるので、残留電荷が発生せず、安定した滴吐出動作を行うことができる。
【００９８】
ここで、接触対向部の表面とその接触対向部に接する振動板の表面とは電気的伝導性を有していることで、片極性の駆動波形でもより確実に残留電荷の発生を防止することができ、ヘッドの歩留まりが向上し、より安定したヘッドの製作が可能になる。
【００９９】
また、振動板と接触対向部との間の距離を振動板と対向電極との間の距離より短くすることで、片極性の駆動波形でもより確実に残留電荷の発生を防止することができ、より信頼性を向上できる。この場合、接触対向部の高さを対向電極の高さよりも高くすることで、より容易に残留電荷の発生を防止したヘッドを得ることができる。さらに、接触対向部は振動板短手方向の略中央部に設けることで、より容易に残留電荷の発生を防止したヘッドを得ることができる。
【０１００】
また、対向電極の表面側に絶縁層を設け、この絶縁層上に振動板が接する接触対向部を設けることで、より簡易な構成で確実に残留電荷の発生を防止でき、安定したヘッドを効率的に製作することが可能になる。この場合、接触対向部は対向電極の振動板短手方向の略中央部に設けることで、より簡易な構成で確実に残留電荷の発生を防止できる。
【０１０１】
本発明に係るインクジェット記録装置によれば、インク滴を吐出するインクジェットヘッドに本発明に係る液滴吐出ヘッドを用いたので、安定した画像品質を得ることができ、装置の構成も簡単になる。また、本発明に係る画像形成装置、液滴を吐出する装置によれば、本発明に係る液滴吐出ヘッドを用いたので、安定した画像品質を得ることができ、装置の構成も簡単になる。
【図面の簡単な説明】
【図１】本発明の第１実施形態に係るインク滴吐出ヘッドの分解斜視説明図
【図２】同ヘッドの振動板長手方向の断面説明図
【図３】同ヘッドの振動板短手方向の要部拡大断面図
【図４】同ヘッドの振動板変形時の振動板短手方向の要部拡大説明図
【図５】本発明の第２実施形態に係るインク滴吐出ヘッドの振動板変形時の振動板短手方向の要部拡大説明図
【図６】本発明の第３実施形態に係るインク滴吐出ヘッドの振動板変形時の振動板短手方向の要部拡大説明図
【図７】本発明の第３実施形態に係るインク滴吐出ヘッドの振動板変形時の振動板短手方向の要部拡大説明図
【図８】本発明の第４実施形態に係るインク滴吐出ヘッドの振動板変形時の振動板短手方向の要部拡大説明図
【図９】本発明の第５実施形態に係るインク滴吐出ヘッドの振動板変形時の振動板短手方向の要部拡大説明図
【図１０】本発明の第５実施形態に係るインク滴吐出ヘッドの振動板変形時の振動板短手方向の要部拡大説明図
【図１１】上記各実施形態における複数のノズル間の配線構造を説明する平面説明図
【図１２】本発明の第６実施形態に係るインク滴吐出ヘッドの振動板変形時の振動板短手方向の要部拡大説明図
【図１３】本発明に係るインクジェット記録装置の機構部の概略説明図
【符号の説明】
１…振動板／液室基板、２…電極基板、３…ノズル板、４…ノズル、６…吐出室、７…流体抵抗部、８…共通液室、１０…振動板、１４…凹部、１４ａ、１４ｂ…凸部、１５、１５ａ、１５ｂ、１５ｃ…対向電極、１７…絶縁膜、１８、１８ａ、１８ｂ…接触対向部、１９…配線、２０…ドライバＩＣ、５５…キャリッジ、５６…ヘッド。[0001]
[Industrial application fields]
  The present inventionDropletDischarge head and inkjet recording apparatus, Image forming apparatus, and apparatus for ejecting liquid dropletsAbout.
[0002]
[Prior art]
In general, as an inkjet head that is a droplet ejection head in an inkjet recording apparatus used in an image recording apparatus (including an image forming apparatus) such as a printer, a facsimile machine, a copying apparatus, and a plotter, a nozzle that ejects ink droplets and the nozzle An ink channel (also referred to as an ink chamber, a pressure chamber, a discharge chamber, a pressurizing chamber, a pressurized liquid chamber, etc.) communicating with the diaphragm, and a diaphragm that also serves as a first electrode that forms the wall surface of the ink channel There is known an electrostatic force type ink jet head that includes a counter electrode (second electrode) opposite to this, and deforms and displaces the diaphragm with electrostatic force to eject ink droplets from the nozzle.
[0003]
Here, in the conventional electrostatic force type ink jet head, in order to stabilize the ink discharge amount per one time discharged from each nozzle and to stabilize the print quality, the vibration plate and the counter electrode are disposed between the diaphragm and the counter electrode. Although the dimensional accuracy of the minute gap (gap) must be made high and the displacement of the diaphragm must be controlled accurately and constant, it is extremely difficult with the current technology.
[0004]
In addition, the electrostatic force type that deforms and displaces the diaphragm using electrostatic force has a much lower discharge pressure that can be generated at the same voltage than the piezoelectric type that deforms and displaces the diaphragm using a piezoelectric element. Moreover, since the generated pressure is proportional to the square of the reciprocal of the distance, in order to obtain a discharge pressure equivalent to that of the piezoelectric type, a very high driving voltage that is twice or more that of the piezoelectric type is required, and the head cost increases.
[0005]
Therefore, in the electrostatic force type ink jet head, it is preferable to make the gap between the diaphragm and the counter electrode smaller in order to perform low voltage driving. However, if the gap is made smaller, stronger electrostatic Because the attractive force works, the deformed diaphragm comes into contact with the counter electrode, and a large discharge current due to gas breakdown or field emission flows instantaneously in the gap, causing the counter electrode to melt or the counter electrode and diaphragm May cause a short circuit and destroy the head.
[0006]
Therefore, as described in Japanese Patent Laid-Open No. 7-214769, an insulating film such as an oxide film or a nitride film is provided on the surface side facing the counter electrode on the diaphragm side, and an oxidation film made of ITO is used as the counter electrode. By using a conductive material and bringing the diaphragm into contact with the counter electrode through an insulating film, the displacement of the diaphragm is stabilized to a constant level, and head destruction due to a short circuit at the gap is avoided. Yes.
[0007]
However, in such a head, when a voltage is applied between the diaphragm and the counter electrode and the diaphragm is brought into contact with the counter electrode via the insulating film, the insulating film on the diaphragm side and the counter electrode Electric charges remain in the dielectric on the side, and the relative displacement between the diaphragm and the counter electrode decreases due to the electric field created by the residual charges. This decrease in the relative displacement amount causes a drop in the ink droplet ejection amount and the ink droplet ejection speed, and causes ejection failure. For example, the print quality is poor such as print density and pixel shift, and reliability such as pixel omission is lost. It has the problem of causing a drop.
[0008]
Therefore, as described in the same publication, in order to perform ink ejection while removing the residual charge, drive voltages having different polarities are alternately applied to the counter electrode for each ink ejection operation. It is composed. That is, by alternately applying driving voltages having different polarities to the counter electrode, it is possible to cancel out residual charges generated between the diaphragm and the counter electrode with voltages of each polarity. The amount of relative displacement with the counter electrode can be kept constant, and a stable ink droplet ejection operation can be maintained.
[0009]
[Problems to be solved by the invention]
However, in the above-described conventional electrostatic force type ink jet head, in order to remove residual charges and perform stable ink ejection, it is necessary to separately provide driving voltage sources having different polarities, so that the apparatus becomes large. Also, as the withstand voltage of other elements used in the drive circuit, it is necessary to withstand the voltage for both polarities, so use elements with a withstand voltage twice that of the drive voltage for ejecting ink. There is a problem that the cost on the drive circuit side becomes high.
[0010]
Furthermore, the residual charges are merely canceled out by alternately applying drive voltages having different polarities to the counter electrode, and the residual charges are not essentially in a non-generated state.
[0011]
Therefore, for example, the drive voltage signal applied to the counter electrode is applied according to the image signal. However, depending on the image signal, there is an image pattern that can be printed only with the drive voltage of one polarity. In this case, the amount of accumulated residual charge at each polarity voltage is different, and the relative displacement amount between the diaphragm and the counter electrode at each voltage polarity is gradually decreased to be different. As described above, it is difficult to perform a stable ink discharge operation, and there is a problem that a print quality defect occurs.
[0012]
  The present invention has been made in view of the above points, and is stable.DropsCan perform discharge operationDropletInk jet recording apparatus having a stable discharge head and image quality and a simple apparatus configuration, Image forming apparatus, and apparatus for ejecting liquid dropletsThe purpose is to provide.
[0013]
[Means for Solving the Problems]
  In order to solve the above problems, the present invention relates toDropletThe ejection head has a contact facing portion that contacts the diaphragm when the diaphragm is deformed, and the contact facing portion has the same potential as the diaphragm. The “diaphragm” means a vibrating part, and includes a case where the diaphragm also serves as the first electrode, and includes a diaphragm separately formed from the first electrode.
[0014]
Here, it is preferable that the surface of the contact facing portion and the surface of the diaphragm in contact with the contact facing portion have electrical conductivity. Moreover, it is preferable that the distance between the diaphragm and the contact facing portion is shorter than the distance between the diaphragm and the counter electrode. In this case, the height of the contact facing portion can be made higher than the height of the counter electrode. Furthermore, it is preferable that the contact facing portion is provided at a substantially central portion in the diaphragm lateral direction.
[0015]
Moreover, an insulating layer can be provided on the surface side of the counter electrode, and a contact facing portion with which the diaphragm contacts can be provided on the insulating layer. In this case, it is preferable to provide the contact facing portion at a substantially central portion of the counter electrode in the lateral direction of the diaphragm.
[0016]
  An ink jet recording apparatus according to the present invention includes:DropletAccording to the present invention as an inkjet head for discharging inkDropletA discharge head is used.
  The image forming apparatus and the apparatus for ejecting droplets according to the present invention include the droplet ejection head according to the present invention.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 relates to a first embodiment of the present invention.DropletFIG. 2 is an exploded perspective view of the inkjet head, which is an ejection head, FIG. 2 is a sectional view of the head in the longitudinal direction of the diaphragm, and FIG. 3 is an enlarged sectional view of the main part of the head in the lateral direction of the diaphragm.
[0018]
The inkjet head includes a diaphragm / liquid chamber substrate 1 that is a first substrate using a silicon substrate such as a single crystal silicon substrate, a polycrystalline silicon substrate, or an SOI substrate, and a lower side of the diaphragm / liquid chamber substrate 1. An electrode substrate 2 that is a second substrate using a silicon substrate, a Pyrex glass substrate, a ceramic substrate, and the like provided on the substrate, and a nozzle plate 3 that is a third substrate provided on the upper side of the vibration plate / liquid chamber substrate 1, A plurality of nozzles 4 that discharge ink droplets, a discharge chamber 6 that is an ink flow path communicating with each nozzle 4, a common liquid chamber 8 that communicates with each discharge chamber 6 via a fluid resistance portion 7 that also serves as an ink supply path, and the like Is forming.
[0019]
The vibration plate / liquid chamber substrate 1 is provided with a plurality of discharge chambers 6 with which the nozzles 4 communicate with each other, and concave portions that form a vibration plate 10 (also serving as an electrode) that forms the bottom of the wall of the discharge chamber 6. The plate 3 is provided with a hole for forming the nozzle 4 and a groove for forming the fluid resistance portion 7, and the diaphragm / liquid chamber substrate 1 and the electrode substrate 2 are formed with a through portion for forming the common liquid chamber 8. .
[0020]
Here, when the diaphragm / liquid chamber substrate 1 is, for example, a single crystal silicon substrate, boron is previously implanted into the diaphragm thickness to form a high-concentration boron layer serving as an etching stop layer. After the bonding, the concave portion that becomes the discharge chamber 6 is anisotropically etched using an etching solution such as a KOH aqueous solution, and at this time, the high-concentration boron layer becomes an etching stop layer, and the diaphragm 10 is formed with high accuracy. The Further, when the diaphragm 10 is formed of a polycrystalline silicon substrate, a method of forming a polycrystalline silicon thin film to be a diaphragm on the liquid chamber substrate, or the electrode substrate 2 is previously planarized with a sacrificial material and formed thereon After the polycrystalline silicon thin film is formed, it can be formed by removing the sacrificial material.
[0021]
In addition, an electrode film serving as a first electrode may be separately formed on the vibration plate 10, but as described above, the vibration plate also serves as an electrode by diffusion of impurities or the like. An insulating film can also be formed on the surface of the vibration plate 10 on the electrode substrate 2 side. This insulating film is SiO₂Oxide-based insulating film such as Si_ThreeN_FourNitride-based insulating films such as those can be used. The insulating film can be formed by thermally oxidizing the vibration plate surface to form an oxide film or using a film forming method.
[0022]
Further, a Pyrex glass (borosilicate glass) substrate is used as the electrode substrate 2, and a concave portion 14 is formed in the Pyrex glass substrate, and counter electrodes 15 a and 15 b facing the diaphragm 10 are provided on the bottom surface of the concave portion 14. A gap 16 is formed between the diaphragm 10 and the counter electrodes 15a and 15b, and the diaphragm 10 and the counter electrodes 15a and 15b constitute an actuator part (energy generating means). At this time, the depth of the recess 14 defines the length of the gap 16. In addition, a ceramic substrate, a silicon substrate, etc. can also be used for the electrode substrate 2, and when an electroconductive silicon substrate is used, an oxide layer is formed and the recessed part 14 is formed in this oxide layer.
[0023]
The surface of the counter electrode 15a, 15b is SiO₂Oxide-based insulating films such as films, Si_ThreeN_FourA dielectric insulating film 17 made of a nitride insulating film such as a film is formed. As described above, an insulating film can be formed on the diaphragm 10 side without forming the insulating film 17 on the surfaces of the counter electrodes 15a and 15b.
[0024]
Further, as the counter electrodes 15a and 15b of the electrode substrate 2, gold or a metal material such as Al, Cr, or Ni generally used in a process for forming a semiconductor element, or a high melting point such as Ti, TiN, or W is used. A metal or a polycrystalline silicon material whose resistance is reduced by an impurity can be used.
[0025]
Further, in the concave portion 14 of the electrode substrate 2, as shown in FIG. 3, when the diaphragm 10 is deformed between the counter electrode 15 a and the electrode 15 b at a substantially central portion in the diaphragm short-side direction. A contact facing portion 18 is provided. The contact facing portion 18 is formed on the bottom surface of the recess 14 in the same process as the counter electrodes 15a and 15b. A dielectric insulating film 17 is also formed on the surface of the contact facing portion 18.
[0026]
Further, when the contact facing portion 18 and the diaphragm 10 of the diaphragm / liquid chamber substrate 1 are in contact with each other, they are connected to each other by wiring 19 so that the diaphragm 10 side is electrically connected to GND (grounding). ) The wiring 19 is grounded so as to have a potential. However, as long as the contact opposing portion 18 and the vibration plate 10 of the vibration plate / liquid chamber substrate 1 come into contact with each other, the same potential is not necessary, and they may be connected to a certain potential.
[0027]
The diaphragm / liquid chamber substrate 1 and the electrode substrate 2 are joined by anodic bonding. In anodic bonding, precise bonding can be performed at a relatively low temperature (300 ° C. to 400 ° C.) by applying a voltage (about −300 V to −500 V) between the substrates.
[0028]
In order to reliably perform such anodic bonding, either the vibration plate / liquid chamber substrate (first substrate 1) or the electrode substrate (second substrate) 2 is used so that the substrates are covalently bonded at the bonding interface of the substrates. Must be a substrate that contains a large amount of alkali ions, and when bonding, select a material whose coefficients of thermal expansion are relatively the same so that distortion between the substrates due to thermal stress is reduced It is preferable to do.
[0029]
Here, as described above, a single crystal silicon substrate is used for the first substrate 1, and the second substrate 2 contains a large amount of alkali ions such as Na, and Pyrex glass (boron having a relatively high thermal expansion coefficient with that of the silicon substrate. Since a (silicate glass) substrate is used, reliable bonding with little thermal distortion between the substrates can be obtained.
[0030]
In addition, when the electrode substrate 2 is formed of silicon, a direct bonding method through an oxide film can be used. This direct bonding is performed at a high temperature of about 1000 ° C. Further, when the electrode substrate 2 is formed of silicon and anodic bonding is performed, Pyrex glass is formed between the electrode substrate 2 and the diaphragm / liquid chamber substrate 1, and the anodic bonding is performed through this film. It can also be done. Further, the diaphragm / liquid chamber substrate 1 and the electrode substrate 2 can be bonded by eutectic bonding using a silicon substrate with a binder such as gold interposed on the bonding surface.
[0031]
In the nozzle plate 3, a large number of nozzles 4 are formed, and a groove portion for forming a fluid resistance portion 7 for communicating the common liquid chamber 8 and the discharge chamber 6 is formed. Here, a water-repellent film is formed on the ink ejection surface (nozzle surface side). This nozzle plate 3 uses a stainless steel substrate, but in addition to this, a nickel plated film by electroforming (electroforming) method, excimer laser processing on a resin such as polyimide, and punching a metal plate by pressing. It can also be used.
[0032]
The water-repellent film can be formed by a plating film by electrolytic or electroless nickel eutectoid plating (PTFE-Ni eutectoid plating) in which polytetrafluoroethylene fine particles, which are fluororesin fine particles, are dispersed.
[0033]
In this ink jet head, two rows of nozzles 4 are arranged, and two rows of discharge chambers 6, diaphragms 10, counter electrodes 15, etc. are arranged corresponding to each nozzle 4, and a common liquid chamber 8 is arranged at the center of each nozzle row. A configuration is adopted in which ink is supplied to the left and right ejection chambers 6. Thus, a multi-nozzle head having a large number of nozzles can be configured with a simple head configuration.
[0034]
The counter electrode 15a is extended to the outside to form a connection portion (electrode pad portion) 15A, and a driver IC 20 as a head drive circuit is mounted on the FPC cable 21 by flip chip bonding, and the FPC cable 21 The inkjet head is connected via an anisotropic conductive film or the like. At this time, the gap between the electrode substrate 2 and the nozzle plate 3 (gap 16 inlet) is hermetically sealed with a gap sealant 22 using an adhesive such as epoxy resin, and moisture enters the gap 16 and vibrates. The plate 10 is prevented from being displaced.
[0035]
Further, the entire inkjet head is bonded onto the frame member 25 with an adhesive. An ink supply hole 26 for supplying ink from the outside to the common liquid chamber 8 of the ink jet head is formed in the frame member 25, and the FPC cable 21 and the like are accommodated in a hole portion 27 formed in the frame member 25. The
[0036]
The frame member 25 and the nozzle plate 3 are sealed with a gap sealant 28 using an adhesive such as an epoxy resin, and the ink on the surface of the nozzle plate 3 having water repellency is transferred to the electrode substrate 2 or the FPC cable 21. To prevent it from going around.
[0037]
A joint member 30 with an ink cartridge is connected to the frame member 25 of the head, and ink is supplied from the ink cartridge to the common liquid chamber 8 through the ink supply hole 26 through a filter 31 thermally fused to the frame member 25. Supplied.
[0038]
Next, the operation of the ink jet head configured as described above will be described with reference to FIG.
When a positive pulse voltage (driving waveform) is applied to the counter electrodes 15a and 15b of the inkjet head by the driver IC 20, the surfaces of the counter electrodes 15a and 15b are charged to a positive potential, and the lower surface of the corresponding diaphragm 10 is set to a negative potential. Charge. Therefore, the diaphragm 10 bends downward (on the side of the counter electrodes 15a and 15b) due to electrostatic attraction.
[0039]
Here, the magnitude P of the electrostatic attraction force generated in the vibration plate 10 is expressed as in equation (1). Where ε is the dielectric constant of the air existing between the diaphragm 10 and the counter electrodes 15a and 15b, S is the effective area of the electrostatic force acting between the diaphragm 10 and the counter electrodes 15a and 15b, and V is the counter electrode The drive voltage applied to 15a and 15b, d represents the effective gap distance between the diaphragm 10 and the counter electrodes 15a and 15b.
[0040]
[Expression 1]

[0041]
Here, the effective gap distance d means a relationship such as the expression (2), and when a substance having a dielectric constant other than air is interposed between the diaphragm 10 and the counter electrodes 15a and 15b. Is expressed by the following equation (2). However, in equation (2), d_aIs the distance of the air gap existing between the diaphragm 10 and the counter electrodes 15a, 15b, d_εIs the thickness of the dielectric insulating layer 17 existing between the diaphragm 10 and the counter electrodes 15a, 15b, ε_rRepresents the relative dielectric constant of the dielectric insulating layer 17.
[0042]
[Expression 2]

[0043]
That is, when a substance having a certain dielectric constant is interposed between the diaphragm 10 and the counter electrodes 15a and 15b, the thickness d of the interposed dielectric substance is expressed by the equation (2)._εAnd the dielectric constant ε of the dielectric material_rBy changing the electric field strength E (that is, E = V / d) generated between the diaphragm 10 and the counter electrodes 15a and 15b and the magnitude of the electrostatic attraction force P generated thereby. It is. Therefore, as shown in the equation (1), the electrostatic attractive force P has a larger electrostatic attractive force on the diaphragm 10 as the effective gap distance d between the diaphragm 10 and the counter electrodes 15a and 15b is smaller. It will be.
[0044]
Therefore, when driving the inkjet head, as shown in FIG. 4, the diaphragm 10 bends in the direction of the opposing electrodes 15 a and 15 b, and finally the diaphragm 10 is disposed in the concave (step) portion 14. Then, a drive waveform that is deformed and displaced until it contacts the contact facing portion 18 that has the same potential as the diaphragm 10 is applied.
[0045]
In the conventional ink jet head, the residual charge is generated mainly due to the potential difference generated between the diaphragm and the counter electrode at the moment when the diaphragm contacts the counter electrode to which the drive voltage V is applied. It has been experimentally found that this occurs. Therefore, in the present invention, the contact facing portion 18 is disposed in advance in a portion where the diaphragm 10 mainly contacts within the concave (step) portion 14, and the contact facing portion 18 is electrically connected to the potential on the diaphragm 10 side in advance. By configuring the same potential, it is possible to essentially prevent the generation of residual charges.
[0046]
Next, when the application of the pulse voltage to the counter electrodes 15a and 15b is turned off, the vibration plate 10 bent as described above is restored, and the pressure in the discharge chamber 6 rapidly increases. Droplets are formed and ink is ejected toward the recording paper. Further, when the pulse voltage is turned ON again to the counter electrodes 15a and 15b, the diaphragm 10 is bent again in the direction of the counter electrodes 15a and 15b and the contact facing portion 18 facing each other, so that the ink is transferred from the common liquid chamber 8. The discharge chamber 6 is supplied through the fluid resistance portion 7.
[0047]
As described above, when the diaphragm 10 is deformed and contacts the opposing counter electrodes 15a and 15b, the contact facing portion 18 of the diaphragm 10 is disposed in the concave (step) portion 14 of the second substrate 2 in advance. In addition, by setting the contact facing portion 18 to be electrically the same as the potential on the diaphragm 10 side in advance, it is possible to prevent the generation of residual charges, and there is no generation of residual charges. A stable ink droplet ejection operation without ink droplet ejection failure can be performed even with only a polar driving voltage.
[0048]
In this case, since a potential difference also occurs between the counter electrodes 15a and 15b to which the driving voltage is applied and the contact facing portion 18 of the diaphragm 10, the counter electrodes 15a and 15b and the contact facing portion 18 of the diaphragm 10 Sufficient electrical insulation treatment is applied so as not to cause a discharge or a short circuit due to field emission or the like.
[0049]
In order to confirm this, the inkjet head having the above configuration is used, the third substrate 3 made of stainless steel is bonded to the upper side of the first substrate 1 with an epoxy adhesive, the driver IC 20 or the like is connected, and the counter electrode 15a, A printing test of the manufactured inkjet head was performed by applying a unipolar voltage of only a pulsed positive (positive) voltage to 15b. Similarly, as a comparative example, an ink jet head without the contact facing portion 18 was also manufactured, and a similar printing test was performed.
[0050]
According to this test result, in the conventional inkjet head that does not have the contact facing portion 18, residual charges are gradually accumulated between the diaphragm 10 and the counter electrode in only a few minutes, and ink droplets are ejected. While the ink droplet ejection state was extremely unstable due to the occurrence of a defect or the like, the inkjet head of the first embodiment was repeatedly stable for several hours or more with only a unipolar positive voltage. It was confirmed that the ink could be discharged and the print quality was stable.
[0051]
In addition, since it is possible to perform ink droplet ejection driving with only a positive (positive) voltage of one polarity, the device configuration of the driving circuit is simpler and smaller than before, and the circuit cost is also 30%. The above could also be made cheaper.
[0052]
Next, an inkjet head according to a second embodiment of the present invention will be described with reference to FIG. This figure is an enlarged explanatory view of the main part in the lateral direction of the diaphragm when the diaphragm is deformed, similar to FIG.
[0053]
In this ink jet head, the contact facing portions 18a and 18b are arranged at two locations in the concave (step) portion 14 of the second substrate 2 as the contact facing portions of the diaphragm 10 as described above, and a drive voltage is applied. As counter electrodes for this purpose, counter electrodes 15a, 15b, and 15c are arranged in three positions in the recess 14 with the contact facing portions 18a and 18b sandwiched in the lateral direction of the diaphragm.
[0054]
Then, the thickness of the dielectric insulating layer 17 such as SiO2 for protecting the electrode is made different between the contact facing portions 18a, 18b and the counter electrodes 15a, 15b, 15c. It is formed to be thick. Further, as in the above-described embodiment, the contact facing portions 18a and 18b are set to have the same electrical potential as the potential on the diaphragm 10 side in advance.
[0055]
Also in the ink jet head having this configuration, the contact facing portions 18a and 18b are set to have the same electric potential as the potential on the diaphragm 10 side in advance as described above, so that the diaphragm 10 comes into contact with the contact facing portions 18a and 18b. In essence, generation of residual charges can be prevented in advance.
[0056]
In addition to this, in the case of the present embodiment, the distance from the diaphragm 10 to the contact facing portions 18a, 18b from the head of the first embodiment is closer to the counter electrodes 15a, 15b, 15c to which voltage is applied. Since it is shorter than the distance, it is difficult for the diaphragm 10 to be reliably contacted by the counter electrodes 15a, 15b, 15c to which a voltage is applied, and as a result, the generation of residual charges can be prevented more reliably, and more A highly reliable and stable ink droplet ejection operation can be performed.
[0057]
In order to confirm this, using this inkjet head, the third substrate 3 made of stainless steel is bonded to the upper side of the first substrate 1 with an epoxy adhesive, and the driver IC 20 or the like is connected to the counter electrodes 15a, 15b, A printing test of the manufactured inkjet head was performed by applying a unipolar voltage having only a pulsed positive (positive) voltage to 15c.
[0058]
According to this test result, in the head of the first embodiment, there was a head that occasionally caused an ink droplet ejection failure due to the generation of residual charge, whereas in the ink jet head of the second embodiment, the residual was It was confirmed that there was no occurrence of a head that caused ink droplet ejection failure due to electric charge, yield was improved, and more stable ink ejection driving was possible.
[0059]
Next, an inkjet head according to a third embodiment of the present invention will be described with reference to FIG. This figure is also an enlarged explanatory view of the main part in the lateral direction of the diaphragm when the diaphragm is deformed, similar to FIG.
[0060]
Also in this ink jet head, the contact facing portions 18a and 18b are arranged at two locations in the concave (step) portion 14 of the second substrate 2 as the contact facing portions of the diaphragm 10 as described above, and a drive voltage is applied. As counter electrodes for this purpose, counter electrodes 15a, 15b, and 15c are arranged in three positions in the recess 14 with the contact facing portions 18a and 18b sandwiched in the lateral direction of the diaphragm.
[0061]
And in order to make the distance from the diaphragm 10 to the contact facing portions 18a, 18b shorter than the distance from the diaphragm 10 to the counter electrodes 15a, 15b, 15c to which voltage is applied, as in the second embodiment. Convex portions 14a and 14b are formed in two locations in the concave (step) portion 14, and contact facing portions 18a and 18b with which the diaphragm 10 contacts are provided on the convex portions 14a and 14b. Here, the material on the surface side of the contact facing portions 18a and 18b is made of a material (metal or the like) having electrical conductivity to be an electrode.
[0062]
In this ink jet head, compared to the heads of the first and second embodiments, there is no dielectric insulating layer 17 on the surface side of the contact facing portions 18a and 18b, and a material having electrical conductivity such as metal. Is formed of things.
[0063]
Therefore, for example, even when the charge is initially charged on the dielectric insulating layer 17 from the beginning for some reason during the manufacture of the head, the contact facing portions 18a and 18b have an electrical resistance with a relatively low resistance in advance. Since it is made of a conductive material, it does not occur that charges are initially charged on the contact facing portions 18a and 18b. In addition, it is possible to prevent the occurrence of residual charges more reliably and effectively.
[0064]
Next, an inkjet head according to a fourth embodiment of the present invention will be described with reference to FIG. This figure is also an enlarged explanatory view of the main part in the lateral direction of the diaphragm when the diaphragm is deformed, similar to FIG.
[0065]
Also in this ink jet head, the contact facing portions 18a and 18b are arranged at two locations in the concave (step) portion 14 of the second substrate 2 as the contact facing portions of the diaphragm 10 as described above, and a drive voltage is applied. As counter electrodes for this purpose, counter electrodes 15a, 15b, and 15c are arranged in three positions in the recess 14 with the contact facing portions 18a and 18b sandwiched in the lateral direction of the diaphragm.
[0066]
And, in order to make the distance from the diaphragm 10 to the contact facing portions 18a, 18b shorter than the distance from the diaphragm 10 to the counter electrodes 15a, 15b, 15c to which voltage is applied, as in the third embodiment. The contact facing portions 18a and 18b themselves are made of a material having electrical conductivity such as metal, and the thickness itself is made thicker than the thickness of the counter electrodes 15a, 15b and 15c to which voltage is applied. It is formed as follows.
[0067]
Therefore, this ink jet head has a simpler configuration than the head of the third embodiment, and the same effects as those of the third embodiment can be obtained with a configuration that can be easily manufactured.
[0068]
Using this inkjet head, a third substrate 3 made of stainless steel is bonded to the upper side of the first substrate 1 with an epoxy adhesive, and a driver IC 20 or the like is connected to the counter electrodes 15a, 15b, 15c in a pulse-like plus. A printing test of the produced inkjet head was performed by applying a unipolar voltage of only (positive) voltage.
[0069]
According to the test results, in the head of the second embodiment, there was a head that caused ink droplet ejection failure due to initial charging during the manufacturing, whereas in the inkjet head of the fourth embodiment, the head was manufactured. It was confirmed that there was no generation of a head that would cause ink droplet ejection failure due to initial charging during the process, yield was improved, and a more stable inkjet head could be manufactured. In addition, the head configuration becomes simpler and can be easily manufactured, so that the production efficiency of the head is improved.
[0070]
Next, an inkjet head according to a fifth embodiment of the invention will be described with reference to FIG. This figure is also an enlarged explanatory view of the main part in the lateral direction of the diaphragm when the diaphragm is deformed, similar to FIG.
[0071]
In this ink jet head, as in the first embodiment, the contact facing portion 18 of the vibration plate 10 is provided in the concave (step) portion 14 of the second substrate 2 at a substantially central portion in the short side direction of the vibration plate. As counter electrodes for applying a voltage, counter electrodes 15 a and 15 b are arranged at two locations in the recess 14 with the contact facing portions 18 sandwiched in the lateral direction of the diaphragm.
[0072]
Further, as in the second embodiment, the distance between the diaphragm 10 and the contact facing portion 18 is shorter than the distance between the diaphragm 10 and the counter electrodes 15a and 15b to which a voltage is applied. The thickness of the dielectric insulating layer 17 for protecting the electrode is formed so that the thickness on the contact facing portion 18 is thicker than the insulating layer 17 on the counter electrodes 15a and 15b.
[0073]
When configured in this way, it is possible to obtain a sufficient effect of reliably and stably preventing the generation of residual charges with a simpler configuration than the heads of the second and third embodiments.
[0074]
Next, an inkjet head according to a sixth embodiment of the present invention will be described with reference to FIG. This figure is also an enlarged explanatory view of the main part in the lateral direction of the diaphragm when the diaphragm is deformed, similar to FIG.
[0075]
Also in this ink jet head, as in the first embodiment, the contact facing portion 18 of the vibration plate 10 is provided in the concave (step) portion 14 of the second substrate 2 at a substantially central portion in the short side direction of the vibration plate, and is driven. As counter electrodes for applying a voltage, counter electrodes 15 a and 15 b are arranged at two locations in the recess 14 with the contact facing portions 18 sandwiched in the lateral direction of the diaphragm. A dielectric insulating layer 17 is formed on the surface side of the contact facing portion 18 of the diaphragm 10.
[0076]
When configured in this way, it is possible to obtain a sufficient effect of reliably and stably preventing the generation of residual charges with a simpler configuration than the heads of the second and third embodiments.
[0077]
Next, an inkjet head according to a seventh embodiment of the present invention will be described with reference to FIG. This figure is also an enlarged explanatory view of the main part in the lateral direction of the diaphragm when the diaphragm is deformed, similar to FIG.
[0078]
Also in this ink jet head, as in the first embodiment, the contact facing portion 18 of the vibration plate 10 is provided in the concave (step) portion 14 of the second substrate 2 at a substantially central portion in the short side direction of the vibration plate, and is driven. As counter electrodes for applying a voltage, counter electrodes 15 a and 15 b are arranged at two locations in the recess 14 with the contact facing portions 18 sandwiched in the lateral direction of the diaphragm.
[0079]
Further, as in the third embodiment, in order to make the distance between the diaphragm 10 and the contact facing portion 18 shorter than the distance between the diaphragm 10 and the counter electrodes 15a and 15b to which voltage is applied, In order to make the distance between the contact facing portion 18 shorter than the distance between the diaphragm 10 and the counter electrodes 15a and 15b to which a voltage is applied, the convex portion 14a is provided in the concave (step) portion 14. The contact facing portion 18 made of a material having electrical conductivity such as metal is formed on the convex portion 14a.
[0080]
When configured in this way, it is possible to obtain a sufficient effect of reliably and stably preventing the generation of residual charges with a simpler configuration than the heads of the second and third embodiments.
[0081]
In each of these embodiments, when the counter electrodes 15a, 15b of the heads of the plurality of nozzles and the contact facing portion 18 of the diaphragm 10 are arranged on the second substrate 2, as shown in FIG. The counter electrodes 15a and 15b and the contact facing portions 18 of the diaphragm 10 are patterned on the second substrate 2 as shown in the figure, and the respective contact facing portions 18 are connected by the wiring 40 patterned as shown in the figure. Accordingly, it is possible to perform stable ink ejection driving while preventing the generation of residual charges even in a plurality of nozzles.
[0082]
Next, an inkjet head according to an eighth embodiment of the invention will be described with reference to FIG. This figure is also an enlarged explanatory view of the main part in the lateral direction of the diaphragm when the diaphragm is deformed, similar to FIG.
[0083]
In this ink jet head, a dielectric insulating layer is formed on the surface of the counter electrode 15 for applying a driving voltage to the contact facing portion 18 with which the diaphragm 10 contacts within the concave (step) portion 14 of the second substrate 2 as shown in the figure. 17 is installed. Similarly to the above, the contact facing portion 18 is provided at substantially one central portion with respect to the diaphragm short side direction of the diaphragm 10. In this case, since the contact facing portion 18 of the diaphragm 10 is formed on the surface of the counter electrode 15 via the dielectric insulating layer 17, the distance between the diaphragm 10 and the contact facing portion 18 is inevitably larger. 10 and the distance between the counter electrode 15 to which a voltage is applied.
[0084]
When configured in this manner, the head can be easily manufactured with a simpler configuration than the heads of the second and third embodiments, and the effect of preventing the generation of residual charges in a more reliable and stable manner can be obtained. can get.
[0085]
Using this inkjet head, a third substrate 3 made of stainless steel is bonded to the upper side of the first substrate 1 with an epoxy adhesive, a driver IC 20 or the like is connected, and a pulsed positive voltage is applied to the counter electrode 15. A printing test was performed on the manufactured inkjet head by applying only one-polarity voltage.
[0086]
According to the test results, in the heads of the second and third embodiments, a head that becomes NG due to a head failure occurred during the manufacturing process, whereas in the head of this embodiment, NG due to the head failure was detected. As a result, the yield of the head was further improved, and a more stable inkjet head could be obtained. In addition, since the head configuration becomes simpler and can be more easily manufactured, the head production efficiency is improved.
[0087]
  Next, according to the present inventionAs an image forming apparatus according to the present invention, including an apparatus for discharging droplets from a droplet discharge headThe outline of the mechanism part of the ink jet recording apparatus will be briefly described with reference to FIG. In this ink jet recording apparatus, a main support guide rod 53 and a sub support guide rod 54 are horizontally mounted between side plates 51 and 52 on both sides in a substantially horizontal positional relationship, and the main support guide rod 53 and the sub support guide rod 54 are used. A carriage 55 is slidably supported in the main scanning direction.
[0088]
The carriage 8 includes heads 56y, 56m, and 56c each including four inkjet heads according to the present invention that respectively discharge yellow (Y) ink, magenta (M) ink, cyan (C) ink, and black (Bk) ink. , 56k are mounted with their discharge surfaces (nozzle surfaces) facing downward, and the head 56 (reference numeral “56” is one of “56y, 56m, 56c, 56k” or a generic name). ), Four ink cartridges 57 (reference numerals “57” are either “57y, 57m, 57c, 57k”) or ink supply bodies of respective colors for supplying ink to the four heads 56 respectively. (Generic name) is interchangeably mounted.
[0089]
The carriage 55 is connected to a timing belt 61 stretched between a drive pulley (drive timing pulley) 59 and a driven pulley (idler pulley) 60 that are rotated by the main scanning motor 58 to drive the main scanning motor 58. By controlling, the carriage 55, that is, the four heads 56 are moved in the main scanning direction.
[0090]
Further, sub frames 63 and 64 are erected on a bottom plate 62 connecting the side plates 51 and 52, and a conveying roller 65 for feeding the paper 66 in the sub scanning direction orthogonal to the main scanning direction is provided between the sub frames 63 and 64. Holds freely. A sub-scanning motor 67 is disposed on the side of the sub-frame 64, and a gear 68 fixed to the rotation shaft of the sub-scanning motor 67 and the transport roller 65 in order to transmit the rotation of the sub-scan motor 67 to the transport roller 65. And a gear 69 fixed to the shaft.
[0091]
Further, a reliability maintenance / recovery mechanism (hereinafter referred to as “subsystem”) 71 of the head 56 is disposed between the side plate 51 and the subframe 62. The sub-system 71 holds four cap means 72 for capping the ejection surface of each head 56 by a holder 73, holds the holder 73 by a link member 74 so as to be swingable, and moves the carriage 55 in the main scanning direction. When the carriage 55 comes into contact with the engaging portion 75 provided on the holder 73 by the movement, the holder 73 is lifted up according to the movement of the carriage 55, and the discharge surface of the head 56 is capped by the cap means 72. By moving to the region side, the holder 73 is lifted down as the carriage 55 moves, so that the cap means 72 is separated from the ejection surface of the head 56.
[0092]
The cap means 72 is connected to the suction pump 77 via the suction tube 76, forms an atmosphere opening, and communicates with the atmosphere via the atmosphere opening tube and the atmosphere opening valve. The suction pump 77 discharges the sucked waste liquid (waste ink) to a waste liquid storage tank through a drain tube or the like.
[0093]
Further, on the side of the holder 73, a wiper blade 80, which is a wiping means made of an elastic member such as a fiber member, a foam member, or rubber, for wiping the discharge surface 56a of the head 56 is attached to the blade arm 81. Is pivotally supported so that it can be swung by rotation of a cam that is rotated by a driving means (not shown).
[0094]
In this recording apparatus configured as described above, while the head 56 (carriage 55) is moved and scanned in the main scanning direction, the paper 66 is conveyed in the sub scanning direction, and ink droplets of a desired color are ejected from the nozzles of each head. By doing so, a required color image (including a monochrome image) is recorded on the paper 66.
[0095]
At this time, as described above, the ink jet head according to the present invention does not generate residual charges, can perform a stable ink droplet ejection operation, and can perform an ink droplet ejection operation with a unipolar drive waveform. Therefore, the configuration of the drive circuit is simplified, the device configuration is simple, and the size can be reduced.
[0096]
  In the above-described embodiment, the present invention is applied to the side shooter type inkjet head in which the vibration plate displacement direction and the ink droplet ejection direction are the same, but the edge shooter method orthogonal to the vibration plate displacement direction and the ink droplet ejection direction. The same can be applied to the inkjet head. Furthermore, the present invention can be applied not only to an ink jet head but also to a droplet discharge head that discharges a liquid resist or the like.Further, as described above, the present invention can also be applied to image forming apparatuses such as printers, facsimiles, and plotters, and apparatuses that eject droplets.
[0097]
【The invention's effect】
  As described above, according to the present inventionDropletAccording to the ejection head, the diaphragm has a contact facing portion that comes into contact with the diaphragm when the diaphragm is deformed, and the contact facing portion has the same potential as the diaphragm.DropsA discharge operation can be performed.
[0098]
Here, the surface of the contact facing portion and the surface of the diaphragm in contact with the contact facing portion have electrical conductivity, so that the generation of residual charges can be more reliably prevented even with a unipolar drive waveform. The head yield is improved, and a more stable head can be manufactured.
[0099]
In addition, by making the distance between the diaphragm and the contact facing portion shorter than the distance between the diaphragm and the counter electrode, it is possible to more reliably prevent the generation of residual charges even in a unipolar drive waveform, Reliability can be improved. In this case, by making the height of the contact facing portion higher than the height of the counter electrode, it is possible to obtain a head that can more easily prevent the generation of residual charges. Furthermore, by providing the contact facing portion at a substantially central portion in the diaphragm lateral direction, a head in which the generation of residual charges can be more easily prevented can be obtained.
[0100]
In addition, by providing an insulating layer on the surface side of the counter electrode and providing a contact facing portion on which the diaphragm is in contact, the generation of residual charges can be reliably prevented with a simpler structure, and a stable head can be efficiently used. Can be manufactured. In this case, by providing the contact facing portion at a substantially central portion of the counter electrode in the lateral direction of the diaphragm, it is possible to reliably prevent the generation of residual charges with a simpler configuration.
[0101]
  According to the ink jet recording apparatus according to the present invention, the ink jet head for ejecting ink droplets according to the present invention.DropletSince the discharge head is used, stable image quality can be obtained and the configuration of the apparatus is simplified.Further, according to the image forming apparatus and the apparatus for ejecting droplets according to the present invention, since the droplet ejection head according to the present invention is used, stable image quality can be obtained and the configuration of the apparatus is simplified. .
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of an ink droplet ejection head according to a first embodiment of the invention.
FIG. 2 is a cross-sectional explanatory view of the head in the longitudinal direction of the diaphragm.
FIG. 3 is an enlarged cross-sectional view of the main part of the head in the lateral direction of the diaphragm.
FIG. 4 is an enlarged explanatory view of the main part in the short direction of the diaphragm when the diaphragm of the head is deformed.
FIG. 5 is an enlarged explanatory view of a main part in a short side direction of the diaphragm when the diaphragm of the ink droplet discharge head according to the second embodiment of the present invention is deformed.
FIG. 6 is an enlarged explanatory view of the main part in the short side direction of the diaphragm when the diaphragm of the ink droplet discharge head according to the third embodiment of the present invention is deformed.
FIG. 7 is an enlarged explanatory view of a main part in the short side direction of the diaphragm when the diaphragm of the ink droplet discharge head according to the third embodiment of the present invention is deformed.
FIG. 8 is an enlarged explanatory view of a main part in the short side direction of the diaphragm when the diaphragm of the ink droplet discharge head according to the fourth embodiment of the present invention is deformed.
FIG. 9 is an enlarged explanatory view of a main part in the short side direction of the diaphragm when the diaphragm of the ink droplet discharge head according to the fifth embodiment of the invention is deformed.
FIG. 10 is an enlarged explanatory view of a main part in a short side direction of the diaphragm when the diaphragm of the ink droplet discharge head according to the fifth embodiment of the invention is deformed.
FIG. 11 is an explanatory plan view illustrating a wiring structure between a plurality of nozzles in each of the embodiments.
FIG. 12 is an enlarged explanatory view of the main part in the short side direction of the diaphragm when the diaphragm of the ink droplet discharge head according to the sixth embodiment of the present invention is deformed.
FIG. 13 is a schematic explanatory diagram of a mechanism portion of the ink jet recording apparatus according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Vibration plate / liquid chamber substrate, 2 ... Electrode substrate, 3 ... Nozzle plate, 4 ... Nozzle, 6 ... Discharge chamber, 7 ... Fluid resistance part, 8 ... Common liquid chamber, 10 ... Vibration plate, 14 ... Recessed part, 14a , 14b ... convex portions, 15, 15a, 15b, 15c ... counter electrode, 17 ... insulating film, 18, 18a, 18b ... contact opposing portion, 19 ... wiring, 20 ... driver IC, 55 ... carriage, 56 ... head.

Claims (10)

It has a nozzle that discharges droplets , a flow path that communicates with the nozzle, a diaphragm that forms the wall surface of the flow path , and a counter electrode that faces the diaphragm, and the diaphragm is deformed by electrostatic force in the droplet discharge head for discharging liquid droplets by the vibration plate and a contact face portion capable of contacting vibration plate is deformed, and characterized in that the contact face portion is at the same potential and the diaphragm Droplet discharge head. In the droplet discharge head according to claim 1, the droplet discharge head, wherein the contact facing portion of the surface and the diaphragm surface in contact with the contact face portion has an electrical conductivity. In the droplet discharge head according to claim 1 or 2, the liquid, wherein a distance between the vibrating plate and the contact face portion is shorter than the distance between the counter electrode and the diaphragm Drop ejection head. In the droplet discharge head according to claim 3, the droplet discharge head height of the contact facing portion may be higher than the height of the counter electrode. In the droplet discharge head according to any one of claims 1 to 4, wherein the contact face portion is droplet ejection head is characterized in that provided at the substantially central portion of the diaphragm lateral direction. 6. The liquid droplet ejection head according to claim 1, wherein an insulating layer is provided on a surface side of the counter electrode, and a contact facing portion in contact with the diaphragm is provided on the insulating layer. Droplet discharge head. In the droplet discharge head according to claim 6, wherein the contact face portion is droplet discharge head, characterized in that provided at the substantially central portion of the diaphragm lateral direction of the counter electrode. 8. An ink jet recording apparatus equipped with an ink jet head for ejecting ink droplets, wherein the ink jet head is the liquid droplet ejecting head according to any one of claims 1 to 7. 8. An image forming apparatus comprising a droplet discharge head, wherein the droplet discharge head is the droplet discharge head according to any one of claims 1 to 7. An apparatus for ejecting droplets from a droplet ejection head, wherein the droplet ejection head is the droplet ejection head according to any one of claims 1 to 7.

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