JP4296668B2 - Reversible image display method - Google Patents

Description

【０２２５】
【表２】

【０２２６】
図１３は非画像部面積の割合（非画像部面積／媒体単位面積）と反射濃度比との関係を示すグラフである。
【０２２７】
このように実施例４〜実施例８の画像表示媒体によると、画像ムラがなく、高コントラストを示す画像が得られた。実施例９の画像表示媒体では、非画像部の面積割合が高くなるため、コントラストがやや悪くなるが、実用上許容できる。
【０２２８】
比較例媒体Ｅ３では、非画像部の割合があまりにも少なくなるため、シート間ギャップが保持できなくなって画像ムラが生じ、黒色部の反射濃度の低下、白色部の反射濃度の増加が観察された。
【０２２９】
比較例媒体Ｅ４では、非画像部の割合があまりにも大きいため、十分なコントラストが得られなかった。その原因は、黒色表示において黒ベタが黒白の縞状に表示されるために反射濃度が低下する一方、白色表示において非画像領域の反射濃度が大きいために白ベタの反射濃度が増加したためである。
次に可逆性画像表示媒体において、各シートの厚みを５μｍ〜１００μｍ、両シート間のギャップを２０μｍ〜３００μｍ、全体の厚みを３０μｍ〜５００μｍとすること、媒体の２枚のシートのうち一方のシートの外表面の表面抵抗率を１０¹⁰Ω／□〜１０¹⁶Ω／□、他方のシートの外表面の表面抵抗率を１０⁷ Ω／□以下とすることが好ましいことを示す実施例媒体（実施例１０〜２１）及び比較例媒体Ｅ５〜Ｅ１２について説明する。
（実施例１０〜１４、比較例媒体Ｅ５〜Ｅ８）
実施例２の媒体において、各シートの厚みは２５μｍ、シート間ギャップは１００μｍのままとして第１シート１２１の表面抵抗率及び第２シート１２２の表面抵抗率を種々変えた画像表示媒体。シート表面抵抗率を種々変更した以外は実施例２の媒体と同様である。
【０２３０】
なお、これら媒体のほか、このあと説明する実施例１５〜２１の媒体等についても、第１シート１２１の表面抵抗率はシート表面に界面活性剤を塗布することで調整した。第２シート１２２の表面抵抗率は第２シートに導電性カーボンを含有させ、その含有量を変化させることで調整した。また表面抵抗率は測定法ＡＳＴＭ Ｄ−２５７に準じて、６５％ＲＨ環境下で測定した。
【０２３１】
実施例１０〜１４の媒体及び比較例媒体Ｅ５〜Ｅ８を表３にまとめて示す。
（実施例１５）
実施例３の媒体（第２シートにＡｌ蒸着膜を有する媒体）において、第１シート１２１の表面抵抗率を１．２０×１０¹⁵Ω／□とし、第２シート１２２の表面抵抗率を８．５０×１０^-1Ω／□とした媒体。その他は実施例３の媒体と同様である。
（実施例１６〜２１、比較例媒体Ｅ９〜Ｅ１２）
実施例１５の媒体において、各シートの表面抵抗率はそのままとして各シートの厚み、シート間ギャップを種々変化させた媒体。その他は実施例１５の媒体と同様である。
【０２３２】
実施例１６〜２１の媒体及び比較例媒体Ｅ９〜Ｅ１２を表３にまとめて示す。
【０２３３】
【表３】

【０２３４】
前記実施例媒体（実施例１０〜２１）及び比較例媒体Ｅ５〜Ｅ１２のそれぞれにつき、図１６（Ａ）及び図１６（Ｂ）に示す画像形成装置を用いて図１３に示すような画像を形成し、画像コントラストについて評価した。なお、図１６に示す画像形成装置は、イオンフロー型の直接静電潜像形成装置を利用した画像形成装置である。これについては後ほど説明する。
【０２３５】
評価は、ここでは、黒色部、白色部のいずれについても、最大反射濃度、最小反射濃度を測定し、これらに基づいて黒色部Ｂｋ、白色部Ｗの各平均反射濃度を求め、これら平均反射濃度から反射濃度比を求めることで行った。この場合も反射濃度比が１０．０以上を良（○）、１０．０より小さいときを不良（×）とした。
【０２３６】
また、画像ムラについても評価した。画像ムラ評価は黒色部の画像濃度を反射濃度計（コニカ社製：SAKURA DENSITOMETER PDA −65）を用いて測定し、画像濃度の最大値と最小値との差を求め、画像濃度差が０．２以下を良（○）、それより大きいときを不良（×）として行った。
【０２３７】
これらの評価結果を表４にまとめて示す。なお、表４にはコントラスト不良のものについても不良マークを記してある。
【０２３８】
【表４】

【０２３９】
この評価結果から、各シートの厚みを５μｍ〜１００μｍ、両シート間のギャップを２０μｍ〜３００μｍ、全体の厚みを３０μｍ〜５００μｍとすること、媒体の２枚のシートのうち一方のシートの外表面の表面抵抗率を１０¹⁰Ω／□〜１０¹⁶Ω／□、他方のシートの外表面の表面抵抗率を１０⁷ Ω／□以下とすることが好ましいことが分かる。
【０２４０】
さて、図１６（Ａ）及び図１６（Ｂ）に示す画像形成装置は、図１４や図１５に原理を示す画像形成装置を発展させたものである。
【０２４１】
図１４に示す画像形成装置は、図１２の媒体１３のように、一方のシートが導電性膜を備えた電極無しのタイプの画像表示媒体に適している。
【０２４２】
図１４の画像形成装置は、イオンフロー型の直接静電潜像形成装置ＣＲ１を備えている。装置ＣＲ１は、コロナイオンを発生させるコロナイオン発生部ｃ１と、該発生部で発生するコロナイオンをシート１２１表面へ導くための書き込み電極ｅ１と、正又は負のコロナイオンを表示しようとする画像に応じてシート１２１表面の画素対応部分へ導くための電圧を書き込み電極ｅ１へ印加する書き込み電極制御回路ｆ１とを含んでいる。電極制御回路ｆ１には、図示を省略した制御電源及びバイアス電源が含まれる。
【０２４３】
コロナイオン発生部ｃ１はシールドケースｃ１１内に、それには限定されないが、例えば６０〜１２０μｍ径の金メッキタングステン線を張設してコロナワイヤｃ１２とし、このワイヤに電源Ｐｃ１から正極性又は負極性の電圧（例えば４ｋＶ〜１０ｋＶ）を印加してコロナイオンを発生させるものである。
【０２４４】
書き込み電極ｅ１は、媒体（例えば媒体１３）の第１シート１２１に向けられたシールドケースｃ１１の部分に臨設されており、中央に設けられた透孔をコロナイオン流が通過できる。
【０２４５】
電極制御回路ｆ１は媒体１３へ向け導出しようとするイオンの正、負に応じたイオン引出し電圧を電極ｅ１に印加できる。
【０２４６】
かくして媒体１３をその第２シート１２２を接地電位として（或いは潜像極性と同極性で且つ潜像電位より小さい値のバイアス電圧を印加して）装置ＣＲ１に対し相対的に移動させつつ、表示しようとする画像に応じて、シート１２１表面の画素対応部分へ正又は負のコロナイオンを導き、これにより第１シート１２１表面に静電潜像電荷を付与し、これと同時的に静電場を形成して媒体１３における各セル内の現像粒子を移動させて画像表示させることができる。
【０２４７】
図１５の画像形成装置は、図８等に示す媒体１２のように、一方のシートに導電性膜を備えない、電極無しのタイプの画像表示媒体に適している。図１５の画像形成装置は、静電潜像を形成する側のシート１２１とは反対側のシート１２２に接触する電極Ｅａを有している。図１４の場合と同様に電極Ｅａにはバイアス電圧を印加してもよい。それ以外の点は図１４の装置と同様である。
【０２４８】
前記評価実験に用いた図１６（Ａ）及び図１６（Ｂ）の画像形成装置は、イオンフロー型の直接静電潜像形成装置ＣＲ２を含んでいる。装置ＣＲ２は、コロナイオンを発生させるコロナイオン発生部ｃ２と、該発生部で発生するコロナイオンをシート１２１表面へ導くための書き込み電極ｅ２と、正（又は負）のコロナイオンを表示しようとする画像に応じてシート１２１表面の画素対応部分へ導くための電圧を書き込み電極ｅ２へ印加する書き込み電極制御回路ｆ２とを含んでいる。
【０２４９】
コロナイオン発生部ｃ２はシールドケースｃ２１内に図１４に示す装置ＣＲ１におけると同様のコロナワイヤｃ２２を張設し、このワイヤに電源Ｐｃ２からプラス（又はマイナス）の電圧を印加してコロナイオンを発生させるものである。
【０２５０】
書き込み電極ｅ２は、媒体１２、１３のタイプの媒体（図には媒体１２を代表例として示す）の第１シート１２１に向けられたシールドケースｃ２１の部分に臨設されており、上部電極ｅ２１と下部電極ｅ２２とからなり、それらの中央の透孔をコロナイオン流が通過できる。
【０２５１】
電極制御回路ｆ２は、制御電源Ｐｃ２１、バイアス電源Ｐｃ２２及び制御部ｆ２１を含んでおり、制御部ｆ２１は、媒体１２へ向け導出しようとするイオンの極性に応じたイオン引出し電圧を電極ｅ２１、ｅ２２に印加できる。
【０２５２】
ここでは制御部ｆ２１の指示のもとに、上部電極ｅ２１に正電圧を、下部電極ｅ２１に負電圧を印加すると、正コロナイオンを媒体へ導くことができる（図１６（Ａ））。上部電極ｅ２１に負電圧を、下部電極ｅ２１に正電圧を印加すると、正コロナイオンを閉じ込めておくことができる（図１６（Ｂ））。
【０２５３】
また書き込み電極ｅ２に対向させて電極ローラＲ１を設け、これに電源ＰＷ１からここでは正のバイアス電圧を印加する。ローラＲ１は回転駆動される磁極ローラＲ２を内蔵している。
【０２５４】
かくして媒体１２を装置ＣＲ２に対し相対的に移動させつつ、且つ、電極ローラＲ１を媒体送り方向に、磁極ローラＲ２を反対方向に回転させつつ、表示しようとする画像に応じて、制御部ｆ２１の指示のもとに、第１シート１２１表面の複数の画素対応部分のうち表示しようとする画像に応じた所定の画素対応部分については図１６（Ａ）に示すように正コロナイオンを導き、他の画素については図１６（Ｂ）に示すようにイオンの流出を阻止する。
【０２５５】
前記画像評価実験では、第１シート１２１表面の複数の画素対応部分のうち表示しようとする画像に応じた所定の画素対応部分に正コロナイオンを導き、その部分を＋５００Ｖ〜＋６００Ｖに帯電させ、他の画素についてはバイアス電圧＋２５０Ｖだけを印加した。これにより正コロナイオンが乗った部分は負帯電性の白色現像粒子ＷＰにより白く表示され、正コロナイオンが乗らなかった部分は正帯電性の黒色現像粒子ＢＰにより黒く表示され、かくして画像表示がなされた。
【０２５６】
なお、装置ＣＲ１やＣＲ２における放電ワイヤｃ１２、ｃ２２は固体放電素子に代えることもできる。
【０２５７】
また図１４から図１６に示す静電潜像形成装置ＣＲ１、ＣＲ２は放電現象を利用したものであるが、これら装置の他、各種放電型静電潜像形成装置を利用できる。
【０２５８】
また図１４から図１６に示す画像形成装置に代えて図１７や図１８に示す画像形成装置を採用しても画像表示できる。
【０２５９】
図１７の画像形成装置は、マルチスタイラス方式の直接静電潜像形成装置ＣＲ３を備えている。装置ＣＲ３は、例えば媒体１３に対する主走査方向に配列されて第１シート１２１に近接配置される複数の電極ｅ３を有するマルチスタイラスヘッドＨ３を含んでいる。各電極ｅ３に表示しょうとする画像に応じて第１シート１２１表面の画素対応部分に静電潜像電荷を付与すべく信号電圧が印加される。媒体１３は、反対側の第２シート１２２に例えばバイアスを印加して、該ヘッドＨ３に対し相対的に搬送され、これにより画像表示される。
【０２６０】
図１８に示す画像形成装置は電荷注入型の直接静電潜像形成装置ＣＲ４を含んでいる。装置ＣＲ４は媒体に対する主走査方向に複数の記録電極ｅ４を配列するとともに記録電極ｅ４に隣り合わせて隣接制御電極ｅ４１を配列した静電記録ヘッドＨ４を有するマルチスタイラス型装置である。このヘッドを例えば媒体１３に近接配置し、ヘッドＨ４の制御電極ｅ４１に画像記録に必要な電圧（記録電圧）の約１／２の電圧を順次シーケンシヤルに印加し、記録電極ｅ４に記録電圧の約１／２の画信号電圧を印加することにより、記録電極直下に位置する媒体に静電潜像を形成することができる。
【０２６１】
ここで潜像形成を行うことが有利であることを、図１１に示すような外部静電潜像形成装置を備えた画像形成装置を例にとって説明する。
【０２６２】
該装置の等価回路を図１９（Ａ）から（Ｄ）に示す。これら図において、感光体ドラムのような静電潜像担持体、画像表示媒体及びその間の空気層の静電容量をそれぞれＣ１、Ｃ２、Ｃ０とする。
【０２６３】
静電潜像担持体（以下「像担持体」という）は帯電チャージャ、画像露光装置によって潜像電荷Ｑ（その時の電位Ｖ）が印加されているとする。
【０２６４】
図１９（Ａ）は像担持体と画像表示媒体とが離間している状態の等価回路を示し、Ｃ１、Ｃ２がＣ０に比べてて非常に大きいため、電荷Ｑは移動せず、媒体は静電潜像の影響を受けない。
【０２６５】
この状態から、像担持体と媒体が接近すると、Ｃ０が大きくなり、Ｃ１及びＣ２に充電されていた電荷が静電誘導によって誘起されて、図１９（Ｂ）の状態となる。図１９（Ｂ）は像担持体を画像表示媒体に近接させて静電誘導させた状態の等価回路である。
【０２６６】
図１９（Ｂ）の状態で、誘起電荷によって、像担持体、媒体、空気層に誘起される電位差Ｖ１、Ｖ２、Ｖ０は以下の式（１）、式（２）、式（３）のように表せる。
【０２６７】
【数１】

【０２６８】
【数２】

【０２６９】
【数３】

【０２７０】
ここでＶは像担持体の潜像表面電位、Ｖｂはバイアス値である。
【０２７１】
媒体には現像剤が内包されている。電界下において現像剤粒子が電荷を搬送するため、現像剤層は見かけ上、導電層に近似する。つまり、媒体の静電容量Ｃ２は、上下２枚の樹脂シートの合成容量と近似する。
【０２７２】
ここで、像担持体の潜像電荷が媒体に転写するためには、空気層が絶縁破壊を起こし、電荷移動する必要がある。もし、絶縁破壊が発生しなければ、像担持体と媒体が離間すると、再び図１９（Ａ）の状態に戻り、潜像転写は行われない。
【０２７３】
つまり、例えばＶ０が小さい場合は、誘導による静電界で粒子の移動が発生するが、潜像が転写されない。
【０２７４】
例えばギャップ１０μｍの空気層が絶縁破壊を発生するためには、パッシェン則よりＶ０は約３７０Ｖ以上必要である。
【０２７５】
ここでバイアス値Ｖｂ＝一１０００Ｖに設定し、Ｖ＝１０００Ｖ、各々の静電容量の比をＣ１：Ｃ２：Ｃ０＝１８：５：１２とした場合、Ｖ０（空気層の電位差）＝４８０Ｖとなり、絶縁破壊が発生して潜像が転写される。
（但し、像担持体は通常の有機系感光体、媒体は前記構成の合成容量、空気層は絶縁破壊が生じやすい間隙約１０μｍを想定し、各々の静電容量の比を考えている。）
このように、Ｖ−Ｖｂが約１５００Ｖ以上の条件において、潜像が転写されることとなる。逆にこの条件以外では、像担持体と媒体が近接している状態で静電誘導はされるが、潜像転写しないこととなる。
【０２７６】
像担持体上の静電潜像において、帯電部▲１▼は媒体との間で電荷移動が発生し、非帯電部（露光部）▲２▼では電荷移動が発生しない。このため、媒体上の表面電位に差が生じる。帯電部▲１▼の電荷移動が行われた後の媒体の表面電位は次の式（４）で、非帯電部▲２▼のそれは前式（３）で表される。
【０２７７】
図１９（Ｃ）は絶縁破壊により電荷移動が生じた状態の等価回路を示しているるが、このように絶縁破壊により電荷移動が生じた状態では次式（４）が成立する。
【０２７８】
【数４】

【０２７９】
式（４）においてＶ’０は放電可能な最小電位差、Ｖ１、Ｖ２は前式（２）、（３）である。
【０２８０】
例えば、前記設定条件において、媒体上の表面電位は、帯電部に相当する領域▲１▼は約＋２６５Ｖ、非帯電部に相当する領域▲２▼は約−３４０Ｖとなる。
【０２８１】
ここで、対向電極ローラに任意のバイアス（あるいは接地）を印加すると、帯電部▲１▼及び非帯電部▲２▼の領域は互いに逆向きの電界が形成され、現像粒子がその電界に沿って移動して画像を形成することができる。
【０２８２】
その後、像担持体と媒体が離間すると、誘導電荷に移動が生じて、媒体の表面電位は変化する。▲１▼部は約＋２７５Ｖに、▲２▼部は略０Ｖに復帰し、媒体に潜像を形成することができる。
【０２８３】
以上は静電潜像担持体が感光体ドラム（光導電体）である場合を説明したが、誘電体ドラムを用いてもよい。静電潜像の極性は負極性でもよい。現像粒子の帯電極性は逆でもよい。
【０２８４】
このように媒体に潜像を近接させるだけでなく、静電潜像を転写、直接形成等にて媒体上に形成することによって、静電潜像担持体と対向電極の対向領域を通過後も、現像剤粒子と可逆性画像表示媒体に静電的吸着力が発生するため、画像保持性が良好となることがわかる。要するに静電潜像を媒体上に形成することが有利である。特に流動性の高い現像剤や、画像表示に先立って現像剤攪拌処理により流動性が高められる現像剤を用いる場合に画像保持の点で有利である。
【０２８５】
次に現像剤に含まれる現像粒子の粒径は非導電性現像粒子については体積平均粒径１μｍ〜５０μｍが、磁性現像粒子については体積平均粒径１μｍ〜１００μｍが好ましいことを示す実施例媒体（実施例２２〜３０）及び比較例媒体Ｅ１３〜Ｅ２８について説明する。
【０２８６】
これら媒体はいずれも、実施例２の媒体において、隔壁１２３の高さｈを１５０μｍに、隣り合う仕切り壁１２３ａの間隔ｐｔを２５０μｍに変更し、各セル１２４に内包する現像粒子を種々変えた以外は実施例２の媒体と同じ構造の媒体である。
【０２８７】
これらについても画像コントラストの評価を行った。そのとき、図１１に示す画像形成装置を用いて図１３（Ａ）に示すように右側半分が黒色部（Ｂｋ）、左側半分が白色部（Ｗ）の画像を形成して評価した。
【０２８８】
なおここでのコントラスト評価は、反射濃度比（Ｂｋ／Ｗ）が９．０以上を非常に良好（◎）、９．０より小さく７．０以上を良好（○）、７．０より小さく５．０以上をやや不良（△）、５．０より小さいものを不良（×）とした。
【０２８９】
これら各媒体及び評価結果を表５にまとめて示す。表５においてＷＰ１〜ＷＰ５、ＢＰ１〜ＢＰ５はそれぞれ既述の粒径を有する非導電性の白色現像粒子、磁性の黒色現像粒子である。実施例２２〜３０では既述の現像剤ＤＬ１〜ＤＬ９を、比較例Ｅ１３〜Ｅ２８では既述の比較例現像剤Ｄｅ１〜Ｄｅ１６を採用した。
【０２９０】
また表５の実施例、比較例を示す各枡目中、右側の上段はコントラスト評価結果を、中段は反射画像濃度比を、下段は黒色画像部の反射濃度、その左側は白色画像部の反射濃度を示している。
【０２９１】
【表５】

【０２９２】
表５から分かるように、現像剤に含まれる現像粒子の粒径は非導電性現像粒子（ここでは白色粒子）については体積平均粒径１μｍ〜５０μｍが、磁性現像粒子（ここでは黒色粒子）については体積平均粒径１μｍ〜１００μｍが好ましいと言える。
次に画像表示前に画像消去処理を施す画像表示方法について説明する。この画像表示方法の実施にあたっては前記実施例２の画像表示媒体（ここでは媒体１２と記す）を採用した。
【０２９３】
図２０から図２２のそれぞれはこの画像表示方法を実施する画像形成装置例を示している。特に画像消去装置を備えた画像形成装置を示している。
【０２９４】
図２０の画像形成装置は、図１１の画像形成装置（但し回転磁極ローラＲ２を備えていないもの）において、感光体ドラムＰＣと電極ローラＲ１との対向領域よりも、媒体１２の相対的搬送方向（図中直線矢印方向）において上流側に画像消去装置ＥＬ１を配置したものである。
【０２９５】
画像消去装置ＥＬ１は、上下一対の電極ローラＲ３、Ｒ４を含んでいる。上側電極ローラＲ３はバイアス電源ＰＷ３に接続される。電極ローラＲ３は接地してもよい。下側電極ローラＲ４はバイアス電源ＰＷ４に接続される。電極ローラＲ４は接地してもよい。
【０２９６】
この画像形成装置によると、画像表示に先立って画像消去装置ＥＬ１の電極ローラＲ３、Ｒ４にそれぞれ印加されるバイアスの電位差に応じた電界が媒体１２に対し形成され、これにより異なる帯電極性の現像粒子ＢＰ、ＷＰのうち一方の粒子ＢＰが一方のシート側に、他方の粒子ＷＰが他方のシート側に寄り集まり、これにより画像が消去される。媒体１２はかかる画像消去処理後に感光体ドラムＰＣと対向電極ローラＲ１との間に送りこまれ、新たな画像が表示される。
【０２９７】
図２０の装置を用いて次の条件で画像消去、画像形成の実験を行ってみた。
【０２９８】
すなわち、感光体ドラムＰＣ上の静電潜像の帯電部電位を−８００Ｖ、非帯電部（露光部）電位を−１００Ｖとし、対向電極ローラＲ１に印加するバイアスを−１００Ｖとした。消去装置ＥＬ１においては、電極ローラＲ４を接地し、電極ローラＲ３への印加バイアスを＋１０００Ｖとした。電極ローラＲ３、Ｒ４間を通過する際の電界で、現像剤はクーロンカを受ける。この場合、白色粒子ＷＰは負極性、黒色粒子ＢＰは正極性に帯電しているため、白色粒子は図中上側に、黒色粒子は図中下側に移動し、以前に表示された画像は全面にわたって消去される。このとき、媒体１２を図中上側から見ると、全面白色となっていた。
【０２９９】
その後全面画像消去された媒体１２は、感光体ドラムＰＣと電極ローラＲ１が対向する領域で、静電潜像に応じて電界が形成され、現像剤ＤＬはクーロンカを受ける。感光体ドラムＰＣ上の帯電部は、電極ローラＲ１のバイアスとの電位差によって、７００Ｖの図中上向きの電界が形成され、白色粒子が下向きに移動し、非帯電部は電位差がないため粒子が移動せず、白色粒子は上面に存在したままであった。このようにして形成された画像は、図中上側から見ると、帯電部相当領域は黒色部、非帯電部相当領域は白色部となった。
【０３００】
このように、帯電部に応じた現像粒子を移動させるだけで画像形成でき、このため現像粒子を移動させるための電界強度を大きくすることができる。
【０３０１】
また以下の条件でも実験した。すなわち、感光体ドラムＰＣの帯電部電位を−８００Ｖ、非帯電部（露光部）電位を−１００Ｖ、対向電極口一ラＲ１に印加するバイアスを−８００Ｖとした。また消去装置ＥＬ１においては、電極ローラＲ４のバイアスを＋１０００Ｖ、電極ローラＲ３は接地状態とした。
【０３０２】
この場合、媒体１２が電極ローラＲ４、Ｒ３間を通過した後、白色粒子は図中下側に、黒色粒子は図中上側に移動し、以前に表示された画像は全面にわたって消去された。このとき、媒体１２を図中上側から見ると、全面黒部となっていた。
【０３０３】
その後感光体ドラムＰＣの非帯電部について、対向電極ローラＲ１のバイアスとの電位差によって、７００Ｖの図中下向きの電界が形成され、白色粒子が上向きに移動し、帯電部は電位差がないため粒子が移動せず、白色粒子は下側に存在したままであった。このようにして形成された画像は、図中上側から見ると、帯電部応じた領域は黒色部、非帯電部に応じた領域は白色部となった。
【０３０４】
図２１の画像形成装置は、図１４に示すイオンフロー型の静電潜像形成装置ＣＲ１に対し電極ローラＲ１を対向させ、これらの対向領域の上流側に図２０に示すと同じ画像消去装置ＥＬ１を設けたものである。
【０３０５】
図２２に示す画像形成装置は図２０に示す画像形成装置において、消去装置ＥＬ１における下側電極ローラＲ４に回転磁極ローラＲ２を内蔵したものである。その他の点は図２０の装置と同様である。回転磁極ローラＲ２は一方向に回転駆動、或いは往復回転駆動され、振動磁場を媒体１２に対し形成する。これにより黒色の磁性現像粒子ＢＰに影響して現像剤ＤＬを攪拌する。この現像剤攪拌により、現像粒子の摩擦帯電量が増し、画像表示におけるクーロン力による移動速度が高まるとともに、現像粒子の流動性が向上し、現像粒子の移動効率が高まる。
【０３０６】
画像消去装置は図１５〜図１８に示す画像形成装置等にも適用できる。
次に画像表示にあたり、現像剤を攪拌する画像表示方法について説明する。この画像表示方法の実施にあたっても前記実施例２の画像表示媒体（ここでは媒体１２と記す）を採用した。
【０３０７】
図２３から図２９のそれぞれはこの画像表示方法を実施する画像形成装置例を示している。特に現像剤の攪拌装置を備えた画像形成装置を示している。図４に示す画像形成装置において回転磁極ローラＲ２を設けたり、図１１に示す画像形成装置において感光体ドラムＰＣに対向する現像電極ローラＲ１に回転磁極ローラＲ２を内蔵させたりして、該磁極ローラＲ２を一方向に回転駆動したり、往復回転駆動する場合も、該磁極ローラＲ２は現像剤攪拌装置として機能する。
【０３０８】
先ず図１１に示す画像形成装置を用いて現像剤の攪拌、画像表示を行った実験例について説明する。
【０３０９】
感光体ドラムＰＣの帯電部電位を＋５００Ｖ、非帯電部（露光部）電位を＋１００Ｖ、現像電極ローラＲ１に印加するバイアスを＋３００Ｖとした。また電極ローラＲ１内部の磁極ローラＲ２を、最大磁束密度４００ガウス、磁極数８、回転速度約１００ｒｐｍ、図中左方向（反時計回り）に回転させた。
【０３１０】
このような条件下で、帯電部位に対応する白色粒子ＷＰは電界の向きに逆らって図中上向きに、黒色粒子ＢＰは電界の向きに沿って図中下向きに力を受けると同時に、黒色粒子ＢＰが振動磁場によって撹乱されるため、現像粒子は効率よく移動した。
【０３１１】
図２３の画像形成装置は、図１４に示す画像形成装置においてイオンフロー型の静電潜像形成装置ＣＲ１に対向させて現像電極ローラＲ１を配置するとともに該ローラ内に回転磁極ローラＲ２を内蔵したものである。
【０３１２】
この装置において次の条件で現像剤攪拌及び画像表示の実験を行った。すなわち、媒体１２の帯電部電位を＋５００Ｖ、非帯電部（露光部）電位を約０Ｖ、電極ローラＲ１に印加するバイアスを＋３００Ｖとした。磁極ローラＲ２は、最大磁束密度４００ガウス、磁極数８、回転速度約１００ｒｐｍ、図中左方向（反時計回り）に回転させた。
【０３１３】
このような条件下で、帯電部位に対応する白色粒子ＷＰは電界の向きに逆らって図中上向きに、黒色粒子ＢＰは電界の向きに沿って図中下向きに力を受けると同時に、黒色粒子ＢＰが振動磁場によって攪拌されるため、現像粒子が効率よく移動した。
【０３１４】
以上説明した画像形成装置は、ひろく捉えれば、画像表示工程において形成する静電場を、前記可逆性画像表示媒体の２枚のシートのうちいずれかの外表面に表示しようとする画像に対応した静電潜像を形成して該静電潜像に基づいて該静電潜像形成と同時的に形成し、さらに該静電場形成と同時的に前記現像剤の攪拌を行う例である。
【０３１５】
次に説明する図２４、図２５のそれぞれに示す画像形成装置は、広く捉えれば、画像表示工程において形成する静電場を、可逆性画像表示媒体の２枚のシートのうちいずれかの外表面に表示しようとする画像に対応した静電潜像を形成した後に該静電潜像に基づいて形成し、現像剤の攪拌を静電潜像を形成した後、前記静電場形成と同時的に行うものである。
【０３１６】
図２４の画像形成装置は、図１１の画像形成装置において現像電極ローラＲ１のあった位置に静電潜像転写のための転写電極ローラＲ５を配置し、感光体ドラムＰＣと転写電極ローラＲ５との対向領域より下流側に静電場形成のための現像電極ローラＲ１とそれに内蔵された回転磁極ローラＲ２を配置したものである。
【０３１７】
転写電極ローラＲ５にはバイアス電源ＰＷ５が、電極ローラＲ１にバイアス電源ＰＷ１が接続されている。
【０３１８】
図２５の画像形成装置は、図２３の画像形成装置において現像電極ローラＲ１のあった位置に静電潜像転写のための対向電極ローラＲ５を配置し、静電潜像形成装置ＣＲ１と対向電極ローラＲ５との対向領域より下流側に静電場形成のための現像電極ローラＲ１とそれに内蔵された回転磁極ローラＲ２を配置したものである。
【０３１９】
対向電極ローラＲ５にはバイアス電源ＰＷ５が、電極ローラＲ１にバイアス電源ＰＷ１が接続されている。
【０３２０】
図２４、図２５の画像形成装置によると、感光体ドラムＰＣ又は静電潜像形成装置ＣＲ１と転写（対向）電極ローラＲ５とが対向する領域で媒体１２に静電潜像が形成されたのち、該媒体が現像電極ローラＲ１に接触することで、静電潜像に応じて画素ごとの静電場が形成され、これにより画像が表示される。そしてこのとき、磁極ローラＲ２が一方向に回転駆動されるか、又は往復回転駆動されることで振動磁場が発生し、この磁場の影響により現像粒子が攪拌されながら画像表示される。現像粒子の攪拌により現像粒子の帯電量が増すとともに、現像粒子の流動性が向上する。これらにより円滑、良好に画像表示される。
【０３２１】
なお、磁極ローラＲ２は電極ローラＲ１、Ｒ５間に配置してもよい。
【０３２２】
次に説明する図２６、図２７に示す画像形成装置は、広く捉えれば、画像表示工程において形成する静電場を、可逆性画像表示媒体の２枚のシートのうちいずれかの外表面に表示しようとする画像に対応した静電潜像を形成して該静電潜像に基づいて該静電潜像形成と同時的に又は該静電潜像形成後に形成し、現像剤の攪拌を静電潜像形成前に行う例である。
【０３２３】
図２６の画像形成装置は、図１１の画像形成装置において電極ローラＲ１には磁極ローラを内蔵せず、感光体ドラムＰＣと電極ローラＲ１との対向領域より上流側に回転磁極ローラＲ２を配置したものである。磁極ローラＲ２は一方向に回転駆動されるか、又は往復回転駆動され、これにより現像剤を攪拌する振動磁場が形成される。
【０３２４】
電極ローラＲ１にはバイアス電源ＰＷ１が接続されている。
【０３２５】
この画像形成装置において、感光体ドラムＰＣの帯電部電位を＋５００Ｖ、非帯電部（露光部）電位を＋１００Ｖ、現像電極ローラＲ１に印加するバイアスを＋３００Ｖとすると、帯電部に対応する白色粒子は電界の向きに逆らって図中上向きに、黒色粒子は電界の向きに沿って図中下向きに移動した。現像粒子は予め攪拌されているため帯電量が高められるとともに流動性が向上しており、効率よく移動した。
【０３２６】
図２７の画像形成装置は、図２４の画像形成装置において、感光体ドラムＰＣと電極ローラＲ５との対向領域より上流側に回転磁極ローラＲ２を配置したものである。磁極ローラＲ２は一方向に回転駆動されるか、又は往復回転駆動され
、これにより現像剤を攪拌する振動磁場が形成される。
【０３２７】
図２８に示す画像形成装置は、磁性現像粒子ＢＰが一つの磁極ローラＲ２による磁場のために現像剤収容セル中でいずれかへ偏るおそれがあるときに備えた画像形成装置である。この装置は、ひろく捉えれば、振動磁場を形成する現像剤攪拌装置を媒体搬送方向に沿って順次複数（ここでは２個）設けたものである。
【０３２８】
図２８に示す例では、図１１に示す画像形成装置において回転磁極ローラＲ２を内蔵した現像磁極ローラＲ１を二つ、感光体ドラムＰＣに対向配置したものである。ローラＲ１、Ｒ１には電源ＰＷ１、ＰＷ’が接続されている。二つの回転磁極ローラＲ２は互いに反対方向に回転駆動される。これにより磁性現像粒子（ここでは黒色粒子ＢＰ）のセル内での偏りを抑制できる。
【０３２９】
図２９に示す画像形成装置は、図２４に示す画像形成装置において現像電極ローラＲ１及び磁極ローラＲ２に代えて、Ｎ極、Ｓ極を交互に設けた磁石部材Ｍｇを感光体ドラムＰＣの下流側に、到来する媒体１２に接触するように配置し、且つ、該部材Ｍｇに現像バイアス電源ＰＷ１”を接続したものである。
【０３３０】
媒体１２が部材Ｍｇに対し相対的に移動することで媒体１２に対し振動磁場が形成される。
次に画像表示にあたり、画像表示媒体の表面（シート表面）に静電潜像を形成し、該静電潜像形成前に媒体表面を所定電位に一様に帯電させ、その帯電域に静電潜像を形成する画像表示方法について説明する。この画像表示方法の実施にあたっても前記実施例２の画像表示媒体（ここでは媒体１２と記す）を採用した。
【０３３１】
図３０、図３１のそれぞれはこの画像表示方法を実施する画像形成装置例を示している。特に静電潜像形成前に媒体表面を所定電位に一様に帯電させる帯電装置を備えた画像形成装置を示している。
【０３３２】
図３０に示す画像形成装置は、図１１に示す画像形成装置において現像電極ローラＲ１に磁極ローラＲ２を内蔵せず、感光体ドラムＰＣと電極ローラＲ１との対向領域より上流側に予備帯電装置２を備えたものである。帯電装置２は搬送される媒体１２の静電潜像形成側の表面に対向するチャージャ２１と媒体通路を挟んでこれに対向する接地電極２２とからなっている。なお、電極ローラＲ１は場合によっては接地してもよい。
【０３３３】
図３１の画像形成装置は、図２１の画像形成装置において、静電潜像形成装置ＣＲ１の上流側の画像消去装置ＥＬ１に代えて前記と同じ予備帯電装置２を備えたものである。なお、電極ローラＲ１は場合によっては接地してもよい。
【０３３４】
これらの画像形成装置では、媒体１２の表面が画像表示に先立って予備帯電装置により予め一様に帯電される。その後、図３０の例では該帯電域に感光体ドラムＰＣ上に形成された静電潜像が転写、書き込みされる。図３１の例では静電潜像形成装置ＣＲ１により静電潜像が書き込まれる。いずれの例も予め一様に帯電された領域と、後に静電潜像が書き込まれた領域は互いに逆極性である。電極ローラＲ１のバイアスを接地、或いは適当に電位設定することで、静電潜像が書き込まれた領域とそうでない領域とで電界の向きが異なり、これにより現像粒子を移動させて画像を形成することができる。
【０３３５】
図３０に示す例では、媒体１２の表面を後に形成される静電潜像の極性とは逆極性に一様に帯電させることで、媒体１２内部での絶縁破壊を防止でき、且つ、媒体１２に潜像を確実に転写できる。このように静電潜像が確実に転写されるので、画像保持性が良好となる。
【０３３６】
図３１に示す例では、静電潜像形成時に、画像部と非画像部の電位差を大きくすることができる。例えば、帯電装置２による予備帯電による負極性の一様帯電部を−１０００Ｖ、静電潜像書き込みによる正極性帯電部を＋１０００Ｖとし、電極ローラＲ１のバイアスを接地とすることで、画像部と非画像部は各々１０００Ｖの電位差が生じ、これにより現像粒子を駆動することができる。このように現像粒子駆動電界を大きくすることができ、現像粒子の移動速度を高めることができる。
【０３３７】
なお、予め一様に帯電された領域と、後に静電潜像が書き込まれた領域は同極性でもかまわない。この場合には、電極ローラＲ１のバイアスを静電潜像が書き込まれた領域とそうでない領域との中間電位に設定することで、両領域で電界の向きが異なり、画像を形成することができる。
【０３３８】
また、後に静電潜像が書き込まれた領域は０Ｖでもかまわない。この場合も、電極ローラＲ１のバイアスを静電潜像が書き込まれた領域とそうでない領域との中間電位に設定することで、両領域で電界の向きが異なり、画像を形成することができる。
【０３３９】
かくして媒体１２は、感光体ドラムＰＣ或いは静電潜像形成装置ＣＲ１と電極ローラＲ１との対向領域を通過後も、現像剤粒子と媒体のシート間に静電的吸着力が発生するため、画像保持性が良好となる。
【０３４０】
なお、形成する静電潜像の極性は負極性であってもよい。
【０３４１】
また白黒の現像粒子の帯電極性は逆であってもよい。
【０３４２】
また静電潜像形成装置は図３０、図３１に示すものに限定されず、先に説明した他の静電潜像形成装置も採用できる。
ここで、媒体表面への静電潜像形成前に媒体表面を一様に帯電させ、その帯電域に静電潜像を形成することが有利であることを、図１１に示すような外部静電潜像形成装置を備えた画像形成装置を例にとって説明する。
【０３４３】
該装置の等価回路を図３２（Ａ）から（Ｅ）に示す。これら図において、感光体ドラムのような静電潜像担持体、画像表示媒体及びその間の空気層の静電容量をそれぞれＣ１、Ｃ２、Ｃ０とする。
【０３４４】
静電潜像担持体（以下「像担持体」という）には帯電チャージャ、画像露光装置によって潜像電荷Ｑ（その時の電位Ｖ）が、媒体には予備帯電装置によって予め電荷Ｑ’（そのときの電位Ｖ’）が印加されているとする。
【０３４５】
図３２（Ａ）は像担持体と画像表示媒体とが離間している状態の等価回路を示し、Ｃ１、Ｃ２がＣ０に比べてて非常に大きいため、電荷Ｑは移動せず、媒体は静電潜像の影響を受けない。
【０３４６】
この状態から、像担持体と媒体が接近すると、Ｃ０が大きくなり、Ｃ１及びＣ２に充電されていた電荷が静電誘導によって誘起されて、図３２（Ｂ）の状態となる。図３２（Ｂ）は像担持体を画像表示媒体に近接させて静電誘導させた状態の等価回路である。
【０３４７】
図３２（Ｂ）の状態で、誘起電荷によって、像担持体、媒体、空気層に誘起される電位差Ｖ１、Ｖ２、Ｖ０は以下の式（５）、式（６）、式（７）のように表せる。ここではバイアスを印加しないで、接地した場合を考える。
【０３４８】
【数５】

【０３４９】
【数６】

【０３５０】
【数７】

【０３５１】
ここでＶは像担持体の潜像表面電位、Ｖ’は媒体の表面電位である。
【０３５２】
媒体には現像剤が内包されている。電界下において現像剤粒子が電荷を搬送するため、現像剤層は見かけ上、導電層に近似する。つまり、媒体の静電容量Ｃ２は、上下２枚の樹脂シートの合成容量と近似する。
【０３５３】
ここで、像担持体の潜像電荷が媒体に転写するためには、空気層が絶縁破壊を起こし、電荷移動する必要がある。もし、絶縁破壊が発生しなければ、像担持体と媒体が離間すると、再び図３２（Ａ）の状態に戻り、潜像転写は行われない。
【０３５４】
つまり、例えばＶ０が小さい場合は、誘導による静電界で粒子の移動が発生するが、潜像が転写されない。
【０３５５】
例えばギャップ１０μｍの空気層が絶縁破壊を発生するためには、パッシェン則よりＶ０は約３７０Ｖ以上必要である。
【０３５６】
ここでＶ＝１０００Ｖ、Ｖ’＝−１０００Ｖ、各々の静電容量の比をＣ１：Ｃ２：Ｃ０＝１８：５：１２とした場合、Ｖ０（空気層の電位差）＝４８０Ｖとなり、絶縁破壊が発生して潜像が転写される。また媒体にかかる電位差は約２００Ｖで、媒体内部での絶縁破壊は防止できる。（但し、像担持体は通常の有機系感光体、媒体は前記構成の合成容量、空気層は絶縁破壊が生じやすい間隙約１０μｍを想定し、各々の静電容量の比を考えている。）
像担持体上の静電潜像において、帯電部▲１▼は媒体との間で電荷移動が発生し、非帯電部（露光部）▲２▼では電荷移動が発生しない。このため、媒体上の表面電位に差が生じる。帯電部▲１▼の電荷移動が行われた後の媒体の表面電位は次の式（８）で、非帯電部▲２▼のそれは前式（７）で表される。
【０３５７】
図３２（Ｃ）は絶縁破壊により電荷移動が生じた状態の等価回路を示しているるが、このように絶縁破壊により電荷移動が生じた状態では次式（８）が成立する。
【０３５８】
【数８】

【０３５９】
式（８）においてｖ０は放電可能な最小電位差、Ｖ１、Ｖ２は前式（６）、（７）である。
【０３６０】
例えば、前記設定条件において、媒体上の表面電位は、帯電部に相当する領域▲１▼は約＋２６０Ｖ、非帯電部に相当する領域▲２▼は約−３４０Ｖとなる。
【０３６１】
ここで、対向電極ローラを接地すると、帯電部▲１▼及び非帯電部▲２▼の領域には互いに逆向きの電界が形成され、現像粒子がその電界に沿って移動して画像を形成することができる。
【０３６２】
その後、像担持体と媒体が離間すると、誘導電荷に移動が生じて、媒体の表面電位は変化する。▲１▼部は約−７２０Ｖに、▲２▼部は約−１０００Ｖに復帰し、媒体に潜像を形成することができる（図３２（Ｄ）参照）。
【０３６３】
以上は対向電極ローラＲ１を接地状態にして説明したが、該ローラに適当なバイアスを印加することもできる。この場合はＶ’をＶ’＋Ｖｂに置き換えて考えればよい。図３２（Ｅ）はこの場合の等価回路を示している。
【０３６４】
また、静電潜像担持体が感光体ドラム（光導電体）である場合を説明したが、誘電体ドラムを用いてもよい。静電潜像の極性は負極性でもよい。現像粒子の帯電極性は逆でもよい。
【０３６５】
このように静電潜像担持体と媒体との間で絶縁破壊を発生させて潜像を転写する前に、予め媒体表面を所定電位に一様に帯電させることで、媒体内部の電位差を抑制することができ、これにより画像保持性が良好となる。
次に可逆性画像表示媒体のさらに他の例について図３３、図３４を参照して説明する。
【０３６６】
図３３に示す可逆性画像表示媒体１４は電気泳動型の媒体例である。
【０３６７】
この媒体１４は、透明支持基板１４６に支持された電界発色層１４０を備えている。電界発色層１４０は帯電着色粒子１４１を絶縁性液体１４２中に分散させた液体層１４３を透明導電層１４４と絶縁層１４５の間に密封したものである。絶縁性の液体１４２は、高純度石油（エッソ社 商品名アイソパー）に、イオン性界面活性剤及び染料を含有した有機物を混合したものである。このイオン性界面活性剤が顔料を含有した有機物着色粒子１４１に吸着して該粒子が電気化学的に安定的に帯電する。この帯電着色粒子１４１が液１４２中に分散して電気泳動の性質を示す。
【０３６８】
この媒体１４は、電界が加わらないか、所定の電界とは逆電界が加わっているときは、絶縁性液体１４２中の染料の色が見えているが、静電潜像が書き込まれると、帯電着色粒子１４１が透明導電層１４４の方へ移動し、その顔料が見える。
【０３６９】
この媒体１４による画像表示についても、例えば図３０や図３１に示す画像形成装置を用いて、画像表示に先立って、媒体１４の表面を予め一様に所定電位に帯電させ、帯電した媒体表面に静電潜像ＥＩを形成し、該静電潜像に基づいて媒体内の絶縁性液体１４２に分散している帯電現像粒子（ここでは帯電着色粒子）１４１に対し表示しょうとする画像に対応する画素ごとに所定の静電場を形成することで画像表示させることができる。
【０３７０】
このように静電潜像形成に先立って予め媒体１４表面を帯電させ、その帯電域に静電潜像を形成することで、従来の電気泳動型画像表示媒体による画像表示のように、予備帯電しないで画像形成する場合に比べると、画像保持性が良好となる。
【０３７１】
図３４に示す可逆性画像表示媒体１５は、回転粒子球型表示媒体例である。
【０３７２】
この媒体１５は、透明支持基板１５６に支持された電界発色層１５０を有している。電界発色層１５０は、片面に着色１５１ａした片面着色球１５１を絶縁性液体１５２で囲繞し、該液体ごと絶縁性保持媒質１５３に埋め込み、該媒質１５３の片面に透明導電層１５４を、反対側面に絶縁層１５５を形成したものである。
【０３７３】
片面着色球１５１は、例えばＴｉＯ₂ を主成分とするガラスの白色球を適当な台上に一様に配置し上面からクロム等を蒸着することで作製される。その大きさは３０μｍ〜１００μｍの範囲でよいが、１０μｍ以下とすれば、より解像度が高くなる。
【０３７４】
この片面着色球１５１を、例えばエラストマーのような絶縁性保持媒質１５３中に分散させ、この媒質１５３をトルエン等の有機溶媒にイオン性界面活性剤を溶かした溶液に浸たすことにより膨潤させ、それにより片面着色球１５１の周囲に絶縁性液体１５２を溜まらせる。かくして片面着色球１５１は絶縁性液体層１５２で囲繞され、回転可能な状態で該液体ごと絶縁性保持媒質１５３に埋め込まれた状態が得られる。
【０３７５】
片面着色球１５１は一方の半球面と他方の半球面とが性質が異なるため、これら両面においてイオンの吸着の量が異なる。よって媒体１５に電界をかけると、電界の方向により片面着色粒子１５１の面の向きが変化する。従つて片面着色球１５１の着色面が見えたり、着色していない面が見えたりすることで画像表示される。
【０３７６】
この媒体１５による画像表示についても、例えば図３０や図３１に示す画像形成装置を用いて、画像表示に先立って、媒体１５の表面を予め一様に所定電位に帯電させ、帯電した媒体表面に静電潜像ＥＩを形成し、該静電潜像に基づいて媒体内の絶縁性液体１５２に浮遊している片面着色球１５１に対し表示しょうとする画像に対応する画素ごとに所定の静電場を形成することで画像表示させることができる。これにより画像保持性良好に画像表示できる。
【０３７７】
媒体１４、１５についても画像表示、画像消去を繰り返すことができる。
【０３７８】
なお媒体１４、１５は、良好に画像表示できるのであれば、先に説明した他の画像形成装置によって画像形成してもかまわない。
【０３７９】
【発明の効果】
以上説明したように本発明によると、次の利点を有する可逆性画像表示方法及び可逆性画像表示媒体を提供することができる。
（１）画像表示、画像消去を繰り返し行うことができ、よって従来の画像表示に関係する紙等の画像表示媒体、現像剤、インク等の消耗品の使用を低減することができ、それだけ今日の環境負荷低減に応えることができる。
（２）コントラストに優れ、高解像度で高品質な画像を長期にわたり安定的に表示できる。
（３）残像が発生しにくく、従って良好な可逆性を示し、この点でも高品質な画像を表示できる。
【０３８０】
特に、本発明に係る可逆性画像表示方法よると、画像表示にあたり、画像表示媒体表面を予め一様に所定電位に帯電させてから、該帯電域に静電潜像を書き込むようにしているから、画像保持性が良好となり、この点で一層コントラストに優れた高品質の画像を長期にわたり安定的に表示できる。
【図面の簡単な説明】
【図１】図（Ａ）から図（Ｉ）のそれぞれは現像剤収容セルの形状例を示す図である。
【図２】図（Ａ）から図（Ｈ）はそれぞれ現像剤移動抑制部材の形状及び配列の例を示す図である。図（Ｉ）は媒体単位面積Ｓｂとその中のセルによる画像部面積Ｓａの１例を示す図である。
【図３】電極付きの可逆性画像表示媒体の１例の画像表示前の断面図である。
【図４】図３に示す媒体の画像表示状態の断面図である。
【図５】図３に示す媒体における第２シートとこれに形成された格子状隔壁等の斜視図である。
【図６】図３に示す媒体における第２シートとこれに形成された個別電極の平面図である。
【図７】図３に示す媒体の画像表示例を示す図である。
【図８】可逆性画像表示媒体の他の例の断面図である。図８（Ａ）は可逆性画像表示媒体の画像表示前の断面図であり、図８（Ｂ）は画像表示時の１例の断面図である。
【図９】図８に示す媒体の一部を切り欠いて示す平面図である。
【図１０】図８に示す媒体の画像表示例を示す図である。
【図１１】外部静電潜像形成装置を備えている画像形成装置例の概略構成を示す図である。
【図１２】本発明に係る可逆性画像表示媒体のさらに他の例の断面図である。
【図１３】図（Ａ）は画像表示のさらに他の例を示す平面図であり、図（Ｂ）は非画像部面積の割合（非画像部面積／媒体単位面積）と反射濃度比との関係を示すグラフである。
【図１４】イオンフロー方式の直接静電潜像形成装置を備えている画像形成装置例の概略構成を示す図である。
【図１５】イオンフロー方式の直接静電潜像形成装置を備えてい画像形成装置の他の例の概略構成を示す図である。
【図１６】イオンフロー方式の直接静電潜像形成装置を備えている画像形成装置のさらに他の例の概略構成を示す図である。
【図１７】マルチスタイラス方式の直接静電潜像形成装置を備えている画像形成装置例の概略構成を示す図である。
【図１８】隣接制御電極を有するマルチスタイラス型静電潜像形成装置を備えている画像形成装置例の概略構成を示す図である。
【図１９】外部静電潜像形成装置を備えた画像形成装置の等価回路を示す図である。図（Ａ）は像担持体と画像表示媒体とが離間している状態の等価回路、図（Ｂ）は像担持体を画像表示媒体に近接させて静電誘導させた状態の等価回路、図（Ｃ）は絶縁破壊により電荷移動が生じた状態の等価回路、図（Ｄ）は電荷移動後に像担持体と媒体が離間した状態の等価回路である。
【図２０】画像消去装置を備えた画像形成装置例の概略構成を示す図である。
【図２１】画像消去装置を備えた画像形成装置の他の例の概略構成を示す図である。
【図２２】画像消去装置を備えた画像形成装置のさらに他の例の概略構成を示す図である。
【図２３】現像剤攪拌装置を備えた画像形成装置例の概略構成を示す図である。
【図２４】現像剤攪拌装置を備えた画像形成装置の他の例の概略構成を示す図である。
【図２５】現像剤攪拌装置を備えた画像形成装置のさらに他の例の概略構成を示す図である。
【図２６】現像剤攪拌装置を備えた画像形成装置のさらに他の例の概略構成を示す図である。
【図２７】現像剤攪拌装置を備えた画像形成装置のさらに他の例の概略構成を示す図である。
【図２８】現像剤攪拌装置を備えた画像形成装置のさらに他の例の概略構成を示す図である。
【図２９】現像剤攪拌装置を備えた画像形成装置のさらに他の例の概略構成を示す図である。
【図３０】予備帯電装置を備えた画像形成装置の１例の概略構成を示す図である。
【図３１】予備帯電装置を備えた画像形成装置の他の例の概略構成を示す図である。
【図３２】外部静電潜像形成装置を備えた画像形成装置において静電潜像形成前に媒体を帯電させる場合の等価回路を示す図である。図（Ａ）は像担持体と画像表示媒体とが離間している状態の等価回路、図（Ｂ）は像担持体を画像表示媒体に近接させて静電誘導させた状態の等価回路、図（Ｃ）は絶縁破壊により電荷移動が生じた状態の等価回路、図（Ｄ）は電荷移動後に像担持体と媒体が離間した状態の等価回路、図（Ｅ）は対向電極ローラを接地した場合の等価回路である。
【図３３】可逆性画像表示媒体のさらに他の例の一部の断面図である。
【図３４】可逆性画像表示媒体のさらに他の例の一部の断面図である。
【符号の説明】
ＣＥ１ 連続溝形状の現像剤収容セル
ｗ１ 仕切り壁
Ｓ 画像表示媒体
ＣＥ２ 独立タイプのセル
α 仕切り壁の厚さ
ｐｔ 隣り合う仕切り壁間隔
ｈ 仕切り壁の高さ
ＣＬ１、ＣＬ２、ＣＬ３、ＣＬ４ 現像剤移動抑制部材
β１、β２ 柱状現像剤移動抑制部材の縦横の寸法
γ１、γ２ 画像表示領域の一つの単位の縦横の寸法
ＤＬ、ＤＬｏ 現像剤
ＷＰ 白色現像粒子
ＢＰ 黒色現像粒子
１１ 可逆性画像表示媒体
１１１ 第１シート
１１２ 第２シート
１１３ 隔壁
１１４ 第１電極
１１５ 第２電極
１１５ａ 個別電極（画素電極）
１１６ 現像剤収容セル
１１０ リ一ド部
１１７ 電極選択回路
１１８ａ 正駆動電圧発生回路
１１８ｂ 負駆動電圧発生回路
１１９ 表示データ制御部
Ｂｋ 黒色表示部分
Ｗ 白色表示部分
１２ 可逆性画像表示媒体
１２１ 第１シート
１２２ 第２シート
１２３ 隔壁
１２３ａ 縦仕切り壁
１２４ 現像剤収容セル
１２０ 封止部
１２０ａ 封止部１２０の部分
ＰＣ 感光体ドラム
ＣＨ スコロトロン帯電器
ＥＸ レーザー画像露光装置
ＩＲ イレーサランプ
Ｒ１ 電極ローラ
Ｒ２ 回転磁極ローラ
ＰＷ１ バイアス電源
１３ 可逆性画像表示媒体
１２２Ａ 導電性膜
ＣＲ１ イオンフロー型の直接静電潜像形成装置
ｃ１ コロナイオン発生部
ｃ１１ シールドケース
ｃ１２ コロナワイヤ
ｅ１ 書き込み電極
ｆ１ 書き込み電極制御回路
Ｅａ 接地電極
ＣＲ２ イオンフロー型の直接静電潜像形成装置
ｃ２ コロナイオン発生部
ｅ２ 書き込み電極
ｆ２ 書き込み電極制御回路
ｃ２１ シールドケース
ｃ２２ コロナワイヤ
Ｐｃ２ 電源
ｅ２１ 上部電極
ｅ２２ 下部電極
Ｐｃ２１ 制御電源
Ｐｃ２２ バイアス電源
ｆ２１ 制御部
Ｒ３ 電極ローラ
ＰＣ２０ 電源
ＣＲ３ マルチスタイラス方式の直接静電潜像形成装置
ｅ３ 電極
Ｈ３ マルチスタイラスヘッド
ＣＲ４ 隣接制御電極を有するマルチスタイラス型静電潜像形成装置
ｅ４ 記録電極
ｅ４１ 制御電極
Ｈ４ 静電記録ヘッド
ＥＬ１、ＥＬ２ 画像消去装置
Ｒ５ 転写電極ローラ
ＰＷ５ 電源
Ｍｇ Ｎ極、Ｓ極を交互に設けた部材
ＰＷ１’ 現像バイアス電源
２ 予備帯電装置
２１ チャージャ
２２ 接地電極
１４ 電気泳動型可逆性画像表示媒体
１４０ 電界発色層
１４１ 帯電着色粒子
１４２ 絶縁性液体
１４３ 液体層
１４４ 透明導電層
１４５ 絶縁層
１４６ 支持基板
１５ 回転粒子球型可逆性画像表示媒体
１５０ 電界発色層
１５１ 片面着色球
１５１ａ 着色
１５２ 絶縁性液体
１５３ 絶縁性保持媒質
１５４ 透明導電性層
１５５ 絶縁層
１５６ 支持基板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image display method and an image display medium. In particular, the present invention relates to a reversible image display method and a reversible image display medium capable of repeatedly performing image display and image erasure.
[0002]
[Prior art]
Today's image display uses a pencil, pen, paint, etc. to manually write characters, figures, etc. on an image display medium such as paper, or a document, figure, etc. created by a computer, word processor, etc., such as a CRT display Or by displaying it on a medium such as paper with a printer.
[0003]
Also, manually create documents and graphics on paper and other media such as paper, and documents and graphics on paper and other media that have been output to a printer on another paper or other media using a copier, etc. Alternatively, it is transmitted by a facsimile machine or the like, and is copied and output on a medium such as paper at the transmission destination.
[0004]
[Problems to be solved by the invention]
  Among these image displays, image display for displaying characters, figures, etc. on an image display medium such as paper using a pencil, pen, etc., printers, copiers, facsimiles using electrophotography, ink spraying, thermal transfer, etc. In image display in which characters and figures are displayed on an image display medium such as paper by an image forming apparatus such as a machine, the image can be clearly displayed at a high resolution and the image can be viewed.InThe image is kind to human eyes.
[0005]
However, image display and image erasure cannot be repeated on an image display medium such as paper. When writing a character using a pencil, the character can be erased to some extent by using an eraser. However, if the character is thinly written, it is completely erased when written at a normal density. It is difficult to leave, and it is difficult to reuse a medium such as paper once image-displayed, except for the case where an image is also displayed on the back side of the medium that has not yet been image-displayed.
[0006]
For this reason, media such as paper on which images are displayed are discarded or incinerated after they are used up, and many resources are consumed. In printers and copiers, consumables such as toner and ink are also consumed. Further, in order to obtain a display medium such as new paper, toner, ink, and the like, resources such as a medium and production energy of the medium are required. This is contrary to the reduction in environmental load that is required today.
[0007]
In this respect, image display and image erasure can be repeated in image display by a display such as a CRT display. However, an image displayed on a display has a lower resolution than an image displayed on a paper or the like by a printer or the like, and there is a limit in obtaining a clear and fine image. In addition, the eyes are very tiring when viewing for a long time due to the relatively low resolution and the light emission from the display.
[0008]
An electrophoretic display has been proposed as an image display method capable of repeating image display and image deletion. In this display method, two substrates, at least one of which is transparent, are arranged to face each other with a gap between them to form a sealed space, in which electrophoretic particles are dispersed in different colors. A display liquid dispersed in a medium is filled, and an image is displayed in the color of the particles or the color of the dispersion medium by applying an electrostatic field and causing the particles in the display liquid to migrate.
[0009]
Such a display liquid usually comprises an isoparaffin-based dispersion medium, particles such as titanium dioxide, a dye for imparting a color contrast with the particles, a dispersant such as a surfactant, and an additive such as a charge imparting agent.
[0010]
  However, in this electrophoretic display, since the contrast display between the high refractive index particles such as titanium dioxide and the insulating colored liquid, the degree of concealment of the colored liquid by the particles (the degree to which the colored liquid can be hidden by the particles) The contrast is low. In addition, the specific gravity difference between the particles and the dispersion medium in the display liquid is very large,AgglomerationTherefore, the display contrast is likely to be lowered, and it is difficult to display images stably for a long period of time, and the previous display afterimage is likely to occur. Furthermore, the charging of the particles in the liquid varies greatly with time, and the image display stability is also inferior in this respect.
[0011]
  Therefore, the present invention has the following advantages.Reversible image display methodThe issue is to provide. (1) Image display and image erasure can be performed repeatedly. Therefore, it is possible to reduce the use of image display media such as paper, developer, ink and other consumables related to conventional image display. It can respond to the environmental load reduction.
(2) An image with excellent contrast, high resolution and high quality can be stably displayed over a long period of time.
(3) Afterimages are unlikely to occur, thus exhibiting good reversibility, and a high-quality image can also be displayed in this respect.
[0012]
[Means for Solving the Problems]
  The present invention provides the followingA first type of reversible image display method is provided. The second and third types of reversible image display methods and reversible image display media described after the first type of reversible image display method are shown for reference.
(A) First type reversible image display method
  Two sheets facing each other with a predetermined gap, at least one of which is light transmissive,
  One or more developer containing cells formed between the two sheets and surrounded by a partition wall;
  A dry developer contained in each cell;
  Have
  The dry developer contains at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities.
  A reversible image display medium,
  Preparing a reversible image display medium in which at least two types of dry developer particles constituting the dry developer in the developer containing cell are frictionally charged to different charging polarities;
  A charging step of uniformly charging the sheet surface of the reversible image display medium to a predetermined potential;
  An electrostatic latent image corresponding to the image to be displayed is formed on the surface of the sheet charged in the charging step, and an image to be displayed on the developer particles in the developer containing cell is formed based on the electrostatic latent image. A step of displaying the image by moving the developing particles by forming a predetermined electrostatic field for each corresponding pixel;
  A reversible image display method comprising:
[0013]
In this reversible image display method, the sheet surface of the reversible image display medium is uniformly charged to a predetermined potential prior to image display.
[0014]
Thereafter, an electrostatic latent image corresponding to the image to be displayed is formed on the surface of the charged sheet, and an image to be displayed on the developer particles in the developer containing cell is supported based on the electrostatic latent image. Thus, a predetermined electrostatic field is formed for each pixel. The formation of the electrostatic field may be performed simultaneously with the formation of the electrostatic latent image, or may be performed by applying a bias voltage to the medium after forming the electrostatic latent image or grounding the medium. Development is performed by moving the developing particles by the Coulomb force generated by the electrostatic field, and an image is displayed.
(B) A second type reversible image display method.
[0015]
Charged charged developer particles having a color different from the color of the liquid are dispersed in an insulating liquid of a predetermined color, and the insulating liquid and the charged developer particles are opposed to each other with a predetermined gap, at least one of which is light transmissive Providing a reversible image display medium sealed between two sheets having:
A charging step of uniformly charging the sheet surface of the reversible image display medium to a predetermined potential;
An electrostatic latent image corresponding to the image to be displayed is formed on the surface of the sheet charged in the charging step, and for each pixel corresponding to the image to be displayed on the charged developing particles based on the electrostatic latent image. A step of displaying the image by moving the charged developing particles by forming a predetermined electrostatic field;
A reversible image display method comprising:
[0016]
Also in this reversible image display method, the sheet surface of the reversible image display medium is uniformly charged to a predetermined potential prior to image display.
[0017]
Then, for each pixel corresponding to the image to be displayed on the charged developing particles dispersed in the insulating liquid in the medium by forming an electrostatic latent image corresponding to the image to be displayed on the charged sheet surface. A predetermined electrostatic field is formed. The formation of the electrostatic field may be performed simultaneously with the formation of the electrostatic latent image, or may be performed by applying a bias voltage to the medium after forming the electrostatic latent image or grounding the medium. Development is performed by moving the charged developer particles by the Coulomb force generated by the electrostatic field, and an image is displayed.
(C) A third type reversible image display method.
[0018]
Among the outer surfaces, the other half of the surface opposite to the half is different in color and the spherical developer particles different in ion adsorption amount are surrounded by an insulating liquid layer in the insulating holding medium. Preparing an embedded reversible image display medium;
A charging step for uniformly charging the surface of the reversible image display medium to a predetermined potential;
An electrostatic latent image corresponding to the image to be displayed is formed on the surface of the medium charged in the charging step, and for each pixel corresponding to the image to be displayed on the spherical developing particles based on the electrostatic latent image. Controlling the orientation of the differently colored surfaces of the spherical developer particles by forming a predetermined electrostatic field and displaying an image;
A reversible image display method comprising:
[0019]
Also in this reversible image display method, the surface of the reversible image display medium is uniformly charged to a predetermined potential prior to image display.
[0020]
After that, an electrostatic latent image corresponding to the image to be displayed is formed on the surface of the charged medium, and a predetermined electrostatic field is formed for each pixel corresponding to the image to be displayed on the spherical developing particles in the medium. . The formation of the electrostatic field may be performed simultaneously with the formation of the electrostatic latent image, or may be performed by applying a bias voltage to the medium after forming the electrostatic latent image or grounding the medium.
[0021]
Due to the influence of the electrostatic field, the spherical developer particles which are surrounded by the insulating liquid layer and can be rotated are inverted, and an image is displayed. The reversal of the spherical developer particles is that the other half of the outer surface of the spherical developer particles is different from the other half in terms of the amount of ion adsorption, and therefore the direction of the surface changes depending on the direction of the electric field. Occur. In addition, since half of the outer surface of the spherical developer particle is opposite in color to the other half, the image can be displayed.
(D) A reversible image display medium.
[0022]
Among the outer surfaces, the other half of the surface opposite to the half is different in color and the spherical developer particles different in ion adsorption amount are surrounded by an insulating liquid layer in the insulating holding medium. Embedded reversible image display medium.
[0023]
This medium can display an image by reversing the particles by forming a predetermined electrostatic field for each pixel corresponding to the image to be displayed on the spherical developing particles. Of course, the image can be displayed by the image display method of the item (C).
[0024]
In any type of image display method, the electrostatic latent image on the medium is formed directly on the surface of the medium charged in the charging step, for example, or outside the reversible image display medium. The electrostatic latent image formed corresponding to the image to be displayed on the image carrier can be formed by transferring and forming it on the surface of the medium charged in the charging step.
[0025]
In both types of image display methods, the electrostatic polarity of the area of the electrostatic latent image formed on the medium is determined by charging the charged area by uniform charging of the medium surface prior to the formation of the electrostatic latent image. It may be the same polarity as the polarity, a different polarity, or 0 [V].
In both types of image display methods, the surface of the image display medium is uniformly charged to a predetermined potential in advance, and the electrostatic latent image is written in the charged area. In this method, the developing particles can be moved, and in the third type method, the spherical developing particles can be reversed. Further, an electrostatic field sufficient to hold the moved developer particles and the inverted developer particles at the position is formed. In other words, when the surface of the image display medium is uniformly charged to a predetermined potential in advance and then an electrostatic latent image is written in the charged area, the image retention is improved. In particular, it is advantageous in terms of image retention when a developer having high fluidity or a developer whose fluidity is enhanced by a developer stirring process prior to image display is used. As a result, high-quality images with excellent contrast can be stably displayed over a long period of time.
[0026]
The reversible image display medium (D) can also be displayed by the third type image display method, so that a high-quality image with excellent contrast can be stably displayed over a long period of time. .
[0027]
  Also,AboveIn any reversible image display method or reversible image display medium, a different electrostatic field is formed after an image is displayed once, or an alternating electric field or an oscillating magnetic field (developing particles contain a magnetic material as described in detail later). The image can be erased by forming a case), or the image can be rewritten by forming a different electrostatic latent image. Therefore, it is not necessary to discard the image display medium once displayed. Further, the developer is included in the image display medium and is not consumed, and it is not necessary to supply the developer from the outside. As a result, the use of conventional image display media such as paper and image consumables such as developer can be greatly reduced.
[0028]
In addition, it is not necessary to melt and fix toner on a sheet of paper or the like as in conventional electrophotographic image formation, and the image forming energy required for this type of conventional image formation is not required. You can save most.
[0029]
Thus, today's environmental burden can be reduced.
[0030]
In the first type of image display method using a reversible image display medium containing a dry developer in a developer containing cell, the developer contained in the cell has a different optical reflection density (another In other words, it contains at least two types of developing particles having different contrasts or different colors, and the developing particles are dry-type developing particles, and the other type by one type of developing particles. Since the degree of hiding of the developed particles is good, an image can be displayed with good contrast in this respect.
[0031]
The developer contained in the cell contains at least two types of chargeable dry developing particles that are mutually triboelectrically chargeable, each having a different charge polarity. Since it moves under the Coulomb force, an image can be displayed with good contrast at this point, and an afterimage of the previous display hardly occurs.
[0032]
  The dry developing particles, for example, settled because no liquid intervenes compared to the conductive toner in the display liquid used for conventional electrophoretic image display.AgglomerationIn this respect, the contrast of the image display is hardly lowered, and stable image display can be performed over a long period of time. Settling of developer particles,AgglomerationIs less likely to occur, and the afterimage of the previous display is also unlikely to occur. Further, since the dry developing particles have less change with time in the charging performance as compared with the toner in the liquid, stable image display can be performed for a long time also in this respect.
[0033]
  Also,AnyEven in the reversible image display method and the reversible image display medium, the electrostatic latent image on the surface of the medium can be formed with a high resolution. Easy to display images.
[0034]
  in this wayAboveAccording to the reversible image display medium and the reversible image display method, high-resolution and high-quality images can be stably displayed over a long period of time with good contrast. In addition, afterimages are unlikely to occur, and therefore show good reversibility, and a high-quality image can also be displayed in this respect.
[0035]
  AboveAccording to the reversible image display medium and the reversible image display method, it is possible to display an image with display characteristics close to the display characteristics of a paper medium. Compared with an electrophoretic display (EPD), the contrast can be made higher.
[0036]
The electrostatic latent image may be directly formed on the surface of the medium using, for example, a direct electrostatic latent image forming apparatus, or an electrostatic latent image formed outside the medium using an external electrostatic latent image forming apparatus. The image may be formed by transferring it to the medium surface.
[0037]
As a direct electrostatic latent image forming apparatus, various discharge type electrostatic latent image forming apparatuses that discharge the surface of the medium according to an image to be displayed and put an electrostatic latent image charge on the image to be displayed. Accordingly, various types of charge injection type electrostatic latent image forming devices that inject charges onto the surface of the medium to place electrostatic latent image charges can be exemplified. Examples of the former include an ion flow type apparatus and a multi-stylus type apparatus having an electrostatic recording head in which recording electrodes are arranged in a predetermined direction (for example, a main scanning direction when a sheet is scanned by the apparatus). As an example of the latter, a multi-stylus type apparatus having an electrostatic recording head in which recording electrodes are arranged in a predetermined direction (for example, main scanning direction when a sheet is scanned by the apparatus) and adjacent control electrodes are arranged adjacent to the recording electrodes. Can be mentioned.
[0038]
As an external electrostatic latent image forming apparatus, an electrostatic latent image corresponding to an image to be displayed is formed on an electrostatic latent image carrier, and the electrostatic latent image on the electrostatic latent image carrier is transferred to the sheet. What is transferred to the surface can be exemplified. Furthermore, an electrostatic latent image corresponding to an image to be displayed on a photoconductor such as a photoconductor is formed, and the electrostatic latent image on the photoconductor is transferred to the sheet surface, For example, an electrostatic latent image corresponding to an image to be displayed on a dielectric is formed, and the electrostatic latent image on the dielectric is transferred to the sheet surface.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0040]
A reversible image display medium according to a preferred embodiment of the present invention basically has the following configuration.
[0041]
That is, one or two or more developments formed between two sheets facing each other with a predetermined gap, at least one of which is light transmissive, and surrounded by a partition wall It is a reversible image display medium having an agent storage cell and a dry developer contained in each cell. The dry developer contains at least two types of dry developer particles having triboelectric charging properties having different charging polarities and different optical reflection densities.
[0042]
A reversible image display method according to a preferred embodiment of the present invention uses the reversible image display medium and is basically the following method.
[0043]
That is, a step of preparing the reversible image display medium, wherein the at least two types of developer particles in the dry developer are frictionally charged to different charging polarities, and the inclusion in each cell. A step of moving the developed particles to display an image by forming a predetermined electrostatic field for each pixel in correspondence with an image to be displayed on the developed particles in a state in which the developed particles are frictionally charged; Is a reversible image display method.
[0044]
According to these reversible image display media and a reversible image display method using the same, an image to be displayed on the developer particles in a state where the developer particles contained in each cell of the image display medium are frictionally charged. By forming a predetermined electrostatic field for each pixel in correspondence with each other, development is performed by moving the developing particles with a Coulomb force acting between the electrostatic field and the charged developing particles, and an image is displayed with a predetermined contrast. can do.
[0045]
The electrostatic field can be formed based on the electrostatic latent image by forming an electrostatic latent image on the outer surface of one of the two sheets, for example. The electrostatic field may be formed simultaneously with the formation of the electrostatic latent image or after the formation of the electrostatic latent image. Such an electrostatic field is used for forming an electrostatic field by applying a bias voltage to the sheet opposite to the sheet on which the electrostatic latent image is formed or by grounding the opposite sheet. May be set to a predetermined potential.
[0046]
The reversible image display medium may include an electrode.
[0047]
That is, a transparent electrode may be formed on the inner surface of one of the sheets having light permeability, and an electrode facing the transparent electrode may be provided on the inner surface of the other sheet.
[0048]
In a reversible image display medium provided with an electrode and a reversible image display method using the same, a voltage is applied between the two electrodes in a state where developer particles included in each cell of the medium are frictionally charged. By developing a predetermined electrostatic field for each pixel corresponding to the image to be displayed between both electrodes, the developing particles are moved by the Coulomb force acting between the electrostatic field and the charged developing particles for development. The image can be displayed with a predetermined contrast.
[0049]
The electrode on the inner surface of the other sheet may consist of a group of individual electrodes formed for each pixel.
[0050]
In any type of the reversible image display medium (including the display medium employed in the reversible image display method), in order to obtain a state in which the developer particles contained in the cell are triboelectrically charged, the developer particles are placed in the cell. Prior to encapsulating, it is triboelectrically charged by mixing and stirring, etc., and then encapsulated in the cell, or after encapsulating the developer particles in the cell and mixing and stirring in the cell by applying some energy, triboelectrically charged, or both What is necessary is just to carry out friction charging.
[0051]
Specific examples of the mixing and stirring of the developing particles include mixing and stirring by applying an alternating electric field (for example, AC electric field), mixing and stirring by magnetic force when at least one of the developing particles is a magnetic particle, ultrasonic irradiation, and mechanical vibration application. Mixing stirring, mixing stirring by a combination of two or more of these, and the like can be mentioned.
[0052]
By further mixing and stirring the developer particles and charging them, the contrast can be further improved and the driving voltage can be further reduced.
[0053]
In any type of the reversible image display medium (including the display medium employed in the reversible image display method), each of the two sheets has a larger area than the thickness and has a wide area. It can be made of various materials such as synthetic resin and glass, and can be any of a flexible material, a flexible material, a glass plate with poor flexibility, etc. It suffices that at least one of the sheets (sheet on the image observation side) has light transmittance so that the image can be visually recognized. Both sheets may have optical transparency.
[0054]
Further, a developer movement suppressing member for suppressing the lateral movement of the dry developer in the developer containing cell may be provided between the two sheets. As a matter of course, the partition walls forming the cells also suppress the lateral movement of the developer.
[0055]
Further, the partition wall forming the developer containing cell and / or the developer movement suppressing member may also serve as a spacer for maintaining the gap between the two sheets at a predetermined gap. A dedicated spacer for maintaining the gap between the two sheets at a predetermined gap may be provided separately from the partition wall and the developer movement suppressing member.
[0056]
By providing such a developer movement suppressing member, unevenness of the developing particles in the cell is suppressed, and a high-quality image with less image unevenness can be displayed. Further, since the gap between the two sheets is maintained at a predetermined value by the spacer, it is possible to display an image with little image unevenness. The shape of the developer movement suppressing member is arbitrary such as a columnar member or a wall member.
[0057]
Regardless of the presence or absence of electrodes, the number, size, shape, distribution, arrangement (regular, irregular), etc. of the developer containing cells in the reversible image display medium are not particularly limited as long as the image can be displayed. The same applies to the developer movement suppressing member and the dedicated spacer.
[0058]
Each of the partition wall, the developer movement suppressing member, and the dedicated spacer can be integrally formed by, for example, bonding and fixing at least a part to at least one of the two sheets by bonding or the like, or by forming the sheet and the like. . However, each of the partition wall, the developer movement suppressing member, and the dedicated spacer is not bonded and fixed to one or both of the two sheets, or formed integrally with the sheet, and between the two sheets, It may be arranged so as not to move with respect to at least one sheet.
[0059]
The shape of the developer containing cell can be roughly classified into a continuous groove type and an independent type. The continuous groove type cell CEl is a cell in which each partition wall w1 extends without intersecting with another partition wall w1 as illustrated in FIGS. 1A, 1B, and 1C. For example, it is a cell formed by extending between the sealing portions cw on the periphery of the medium S facing each other. In this case, the sealing part cw can also serve as a partition wall forming the cell. The continuous groove type cell CE1 may extend in parallel with the two parallel sides of the medium S (FIG. 1A) or may extend in a direction intersecting with each side of the medium S (FIG. 1B). It may extend in a wave shape (FIG. 1C) or may extend in another manner.
[0060]
The independent type cell CE2 has, for example, a grid pattern (FIG. 1 (D)), a brick fence shape (FIG. 1 (E)), a honeycomb shape (FIG. 1 (F)), and a mode in which triangles are connected (FIG. 1 (G)). ), An embodiment in which corrugated sections are connected (FIG. 1H), an embodiment in which continuous grooves each surrounded by a partition wall are connected (FIG. 1I), and the like.
[0061]
In these figures, α represents the thickness of the partition wall, and pt represents the interval between the adjacent partition walls.
[0062]
In any case, as shown in FIG. 1 (A) to FIG. 1 (I), each cell may be continuously formed in other cells so as to be adjacent to other cells, but apart from other cells. It may be formed. The cell arrangement may be regular or irregular. The number of cells may be one. Further, the partition wall w1 may also serve as a spacer for maintaining a predetermined gap between sheets.
[0063]
As for the pixels for image display, there may be one case where there is one pixel for one cell, when there are a plurality of pixels in one cell, and when there is one pixel for a plurality of cells. .
[0064]
The shape of the developer movement suppressing member may be any of a columnar shape (such as a cylinder, a quadrangular column, or a triangular column), a cone shape (such as a cone, a quadrangular pyramid, a truncated cone, or a quadrangular pyramid), or a wall shape. Various types of developer movement restraining members may be used. The arrangement may be regular or irregular. The columnar member is convenient for firmly bonding it to the sheet. A long wall-like member can be expected to have a large effect of suppressing developer movement. A thin plate-like member among the wall-like members is convenient for securing a desired developer capacity. The height of the developer movement suppressing member is arbitrary. Therefore, it may be arranged so as not to move to either one of the sheets. When it has a height that extends between two sheets, it may also serve as a spacer that maintains the gap between the sheets at a predetermined value.
[0065]
2A to 2H illustrate the shape and arrangement of the developer movement suppressing member.
[0066]
FIG. 2 (A) shows a state in which a plurality of member rows in which columnar suppressing members CL1 having a rectangular cross section are arranged at intervals in a predetermined direction are arranged in parallel. FIG. 2B shows a state in which the columnar suppressing members CL2 having a circular cross section are arranged in a distributed manner. FIG. 2C shows a state in which a plurality of thin plate-like (wall-like) suppression members CL3 are arranged in parallel. FIG. 2D shows a state in which the columnar suppressing members CL2 and the thin plate-like (wall-shaped) suppressing members CL3 having various lengths are irregularly distributed. FIG. 2E shows a state in which the columnar suppressing members CL2 and the thin plate-like (wall-shaped) suppressing members CL3 having the same length are regularly distributed to some extent. FIG. 2F shows a state in which a plurality of columnar suppressing members CL4 each having a rectangular cross section are arranged in an island shape in each of the continuous groove type cells CE1 shown in FIG. FIG. 2 (G) shows a state where one columnar suppressing member CL4 having a rectangular cross section is arranged in an island shape in each of the independent cells CE2 having a grid-like arrangement of the type shown in FIG. 1 (D). Each suppressing member CL1, CL2, CL3, CL4 can also serve as a spacer. In these drawings, β1 and β2 indicate vertical and horizontal dimensions of the columnar suppressing member. γ1 and γ2 indicate the vertical and horizontal dimensions of one unit of the image display area. In FIG. 2 (F), δ indicates an interval between adjacent members CL4.
By the way, in the image display medium, a non-image display area is generated by the partition wall, the developer movement suppressing member, the spacer and the like as described above. If the total area of the non-image display area is too large, it becomes difficult to display an image or the image quality deteriorates. On the other hand, if it is too small, the result is that the area where the spacers are provided is reduced, resulting in non-uniform gaps between the sheets and image unevenness.
[0067]
Therefore, the ratio Sn / So of the area Sn of the non-image part in the unit area So (for example, the region of γ1 × γ2 in FIGS. 2A and 2H) provided by the image display medium regardless of the presence or absence of electrodes. It is preferable to set it to 0.0001 or more and 0.5 or less. The unit area So can be set arbitrarily, but may be set so that both the area where the image can actually be displayed and the non-image part area are included. Further, for example, it may be set in a repeating unit in which both an area where an image can actually be displayed and a non-image area are included and repeatedly appear on the medium.
[0068]
Alternatively, an image display area provided by one developer containing cell (or a plurality of developer containing cells) in any one developer containing cell (or a plurality of successive developer containing cells). Is the area surrounded by the center line of the partition wall forming the outer contour of the one developer containing cell (or the partition forming the outer contour of the plurality of developer containing cell groups). When the area surrounded by the center line of the wall is Sb, the value of (1-Sa / Sb) relating to the one developer accommodating cell (or the plurality of developer accommodating cell groups) is 0.0001 or more and 0.00. 5 or less is preferable (see FIG. 2I).
[0069]
As a result, an image display area area that does not hinder image display can be secured and a high-quality image can be displayed with good contrast, while a spacer such as a spacer by a partition wall, a spacer by a developer movement restraining member, a dedicated spacer, etc. This area can be secured and the gap between the two sheets can be maintained at a predetermined value, thereby suppressing the occurrence of image unevenness.
[0070]
In addition, for an image display medium with an electrode, a lead is connected to the electrode, and the lead is preferably provided in a non-image display area such as a partition wall.
The material of the sheet, cell partition wall, developer movement suppressing member, spacer, etc. is not particularly limited. However, for example, when an electrostatic latent image is formed on the medium surface (sheet surface) for image display, at least the sheet on which the electrostatic latent image is formed is an insulating sheet. The sheet on the opposite side may or may not be an insulating sheet with or without electrodes. In the case where an insulating sheet is used, when it is necessary to apply a bias voltage to the ground potential, the insulating sheet may be left as it is. For example, a conductive film may be formed on the outer surface of the sheet, or the opposite sheet. The whole may be formed of a conductive material or a material containing a conductive material. In this way, if necessary, the sheet can be easily grounded to the ground potential, or a bias voltage can be applied to the sheet. In addition, when the opposite side sheet is an insulating sheet and a conductive film is formed on its outer surface, regardless of the presence or absence of electrodes, or when the opposite side sheet itself is a conductive sheet, Therefore, even when the image-displayed media are stacked, the image is not easily collapsed, and the image can be held stably.
[0071]
In the case of a medium without electrodes, if the gap between the sheets or the thickness of each sheet is too large, the electric field applied to the developer between the sheets becomes weak and developability deteriorates, resulting in a decrease in contrast and a decrease in resolution. On the other hand, if the gap between the sheets is too small, the amount of developer that can be contained in the developer containing cell is reduced, and it becomes difficult to obtain the necessary contrast. Further, if the thickness of each sheet, and thus the thickness of the entire medium based on the thickness of each sheet, is too small, the medium is likely to be bent, the uniformity of the gap between sheets cannot be obtained, and image unevenness is likely to occur.
[0072]
Therefore, in the reversible image display medium without electrodes, the thickness of each sheet is preferably 5 μm to 100 μm, the gap between the two sheets is preferably 20 μm to 300 μm, and the total thickness is preferably 30 μm to 500 μm. .
[0073]
Also for the reversible image display medium with electrodes, in order to secure the developer amount and maintain the uniformity of the gap between sheets, the thickness of each sheet is 5 μm to 100 μm, and the gap between both sheets is not limited thereto. May be 20 μm to 300 μm, and the total thickness may be 30 μm to 500 μm.
[0074]
In a reversible image display medium without electrodes, for example, when an electrostatic latent image is formed on the medium surface (sheet surface) and an electrostatic field is formed based on the electrostatic latent image, the surface resistance of the sheet When the value, particularly the surface resistance value of the sheet on the side where the electrostatic field is formed, is small, an electrostatic latent image is formed directly on the surface of the sheet to form an electrostatic field for image display, In any case where the electrostatic latent image is transferred to the surface of the sheet, the electrostatic latent image tends to collapse.
[0075]
Therefore, in the reversible image display medium without an electrode, the surface resistivity of the outer surface of at least one of the two sheets is 10.^TenΩ / □ -10¹⁶It is preferable to set to Ω / □.
[0076]
On the other hand, if the sheet surface resistance value, particularly the surface resistance value on the side opposite to the side on which the electrostatic field is formed, is too large, it will hinder image formation and retention. In particular, when an electrostatic latent image is directly formed on the sheet surface on the electrostatic field forming side, the latent image charge is difficult to be applied, and when an electrostatic latent image formed externally is transferred, it is difficult to obtain a uniform electric field. Image unevenness is likely to occur. Furthermore, when the media after image formation are overlapped, electrostatic shielding between adjacent media becomes difficult, and the image tends to collapse and is difficult to hold.
[0077]
Therefore, the surface resistivity of the outer surface of at least one of the two sheets is 10⁷Ω / □ or less (resistivity equivalent to or lower than that of paper) is preferable.
[0078]
From the above, in the electrodeless reversible image display medium, the surface resistivity of the outer surface of one of the two sheets is 10^TenΩ / □ -10¹⁶Ω / □, the surface resistivity of the outer surface of the other sheet is 10⁷It is recommended to be Ω / □ or less.
[0079]
The thickness of each sheet is 5 μm to 100 μm, the gap between both sheets is 20 μm to 300 μm, the total thickness is 30 μm to 500 μm, and the surface resistance of the outer surface of one of the two sheets is within the range without any problem. Rate is 10^TenΩ / □ -10¹⁶Ω / □, the surface resistivity of the outer surface of the other sheet is 10⁷It may be Ω / □ or less.
[0080]
The surface resistivity of each sheet can be adjusted, for example, by containing conductive materials (for example, conductive carbon) having different resistance values in the sheet, or by applying a surfactant to the sheet surface.
For both reversible image display media with and without electrodes, the developers contained in the developer containing cells have different charge polarities and different optical reflection densities (in other words, “contrast It is preferable that at least two types of dry developing particles are included. Representative examples include positively chargeable (or negatively chargeable) black particles having light absorptivity and negatively charged (or positively charged positive) white particles having light reflectivity.
[0081]
At least one of the at least two types of developing particles constituting the dry developer may be non-conductive particles. In this case, regardless of whether or not the image display medium has an electrode, the presence of such non-conductive particles makes it possible to easily and reliably frictionally charge the two kinds of developing particles, and thus to display a good image. Can be done.
[0082]
Further, at least one of the at least two kinds of developing particles constituting the dry developer may be magnetic particles. Regardless of whether the image display medium has electrodes or not, the presence of such magnetic particles allows the developer (development particles) to be stirred by a magnetic field, for example, an oscillating magnetic field, as will be described later. This agitation makes it possible to erase the previous image prior to image formation (image display) and to make the developer particles move easily in the electrostatic field for image display in the image display, and display the image as well.
[0083]
In any case, if the developing particles are too small, the adhesion force becomes very large, causing adhesion between the developing particles and a decrease in developing efficiency. If the developing particles are too small, the charge amount of the particles becomes very large, so that an electric field for moving the particles must be increased for image display, and thus a high driving voltage is required.
[0084]
If the developing particles are too large, triboelectric charging cannot be performed well, and a sufficient developing particle moving speed cannot be obtained in an electrostatic field for image display, or good contrast cannot be obtained.
[0085]
In light of these and materials for obtaining developing particles having predetermined characteristics, a particle size of 1 to 50 μm is suitable for non-conductive developing particles, and a particle size of 1 to 100 μm is suitable for magnetic developing particles.
[0086]
One type of developing particles may be non-conductive particles and magnetic particles.
[0087]
The developing particles can be formed from, for example, a binder resin, a colorant, or the like, or a colorant alone. What can be used for these is as follows.
・ Binder resin
There is no particular limitation as long as it can disperse a colorant, a magnetic material, and the like and is usually used as a binder. A typical example is a binder resin used in an electrophotographic toner.
[0088]
For example, polystyrene resin, poly (meth) acrylic resin, polyolefin resin, polyamide resin, polycarbonate resin, polyether resin, polysulfone resin, polyester resin, epoxy resin, urea resin, urethane resin, urea Resins, fluorine-based resins, silicon-based resins, copolymers thereof, block polymers, graft polymers, polymer blends, and the like can be used.
[0089]
The glass transition point Tg may be quite high and in some cases need not be a thermoplastic resin.
・ Coloring agent
As the colorant, various organic or inorganic pigments and dyes as shown below can be used.
[0090]
Examples of black pigments include carbon black, copper oxide, manganese dioxide, aniline black, and activated carbon.
[0091]
Yellow pigments include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, banza yellow G, banza yellow 10G, benzidine yellow G, benzidine yellow GR, There are quinoline ero lakes, permanent ero NCGs, tartarine rakes, etc.
[0092]
Examples of the orange pigment include red yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, indanthrene brilliant orange RK, benzidine orange G, and indanthrene brilliant orange GK.
[0093]
Examples of red pigments include bengara, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, risor red, pyrazolone red, watching red, calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, There are Alizarin Lake and Brilliant Carmine 3B.
[0094]
Examples of purple pigments include manganese purple, fast violet B, and methyl violet lake.
[0095]
Examples of blue pigments include bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, and induslen blue BC.
[0096]
Examples of green subjects include chrome green, chromium oxide, pigment green B, malachite green lake, final yellow green G, and the like.
[0097]
Examples of white pigments include zinc white, titanium oxide, antimony white, and zinc sulfide.
[0098]
Examples of extender pigments include barite powder, barium carbonate, clay, silica, white carbon, talc, and alumina white.
[0099]
Various dyes such as basic, acidic, disperse, and direct dyes include nigrosine, methylene blue, rose bengal, quinoline yellow, and ultramarine blue.
[0100]
These colorants can be used alone or in combination.
[0101]
Particularly in black and white display, carbon black is preferred as the black colorant and titanium dioxide is preferred as the white colorant.
[0102]
In particular, when a white pigment is kneaded with a melt binder resin (binder resin) to obtain developed particles from the kneaded product, the amount of white pigment used is a raw material monomer for white particles in order to obtain sufficient whiteness. 10 parts by weight or more, preferably 20 parts by weight or more with respect to 100 parts by weight. In order to ensure sufficient dispersibility of the white pigment, 60 parts by weight or less, preferably 50 parts by weight or less. It is desirable to be. When the white pigment exceeds 60 parts by weight, the binding property between the pigment and the binder resin and the dispersibility of the pigment deteriorate, and when the white pigment is less than 10 parts by weight, sufficient development particles of other colors can be obtained. Cannot be concealed.
[0103]
Carbon black is preferable as the black colorant. However, in the case where the developing particles are made magnetic, magnetic particles such as magnetite and ferrite and magnetic fine powders can be used as the colorant.
・ Other internal additives
Examples of the internal additive that is preferably used in addition to the binder resin and the colorant include a magnetic material, a charge control agent, and a resistance adjusting agent.
・ Charge control agent
The charge control agent is not particularly limited as long as it gives a charge to the developing particles by frictional charging.
[0104]
Examples of the positive charge control agent include nigrosine dyes, triphenylmethane compounds, quaternary ammonium salt compounds, polyamine resins, and imidazole derivatives.
[0105]
Examples of negative charge control agents include salicylic acid metal complexes, metal-containing azo dyes, metal-containing oil-soluble dyes (including metal ions and metal atoms), quaternary ammonium salt compounds, calixarene compounds, boron-containing compounds (benzylic acid). Boron complex), nitroimidazole derivatives and the like.
[0106]
In addition, metal oxides such as ultrafine silica, ultrafine titanium oxide, ultrafine alumina, nitrogen-containing cyclic compounds such as pyridine and derivatives and salts thereof, various organic pigments, resins containing fluorine, chlorine, nitrogen, etc. are also charged. It can be used as a control agent.
・ Magnetic material
Magnetic particles and magnetic fine powders can be used, such as ferromagnetic elements and alloys, compounds, etc. containing these, for example, iron such as magnetite, hematite, ferrite, cobalt, nickel, manganese, etc. It is sufficient that a conventionally known magnetic material such as an alloy, a compound, or another ferromagnetic alloy is contained. These magnetic powders have various shapes such as granular, needle-like, and flake-like shapes, and can be appropriately selected and used.
・ Resistance regulator
Examples of the resistance adjusting agent include those equivalent to the above-described magnetic powder and colorant, and various shapes of metal oxides such as flakes, fibers, and powders, graphite, and carbon black can be preferably used.
[0107]
Next, a production example of developing particles will be described.
[0108]
Necessary ones are selected from the binder resin, magnetic powder, colorant, charge control agent, resistance adjusting agent and other additives as described above, and after mixing them by a predetermined amount, a pressure kneader or 2 Heat kneading with a shaft kneader or the like, and after cooling, coarsely pulverize with a hammer mill, cutter mill or the like. Next, after further finely pulverizing with a jet mill, ang mill, etc., classification is performed using an air classifier or the like until a predetermined average particle diameter is obtained, whereby developer particles are obtained.
[0109]
A developer having a predetermined charge amount can be prepared by mixing and stirring the particles having different charge polarities and different contrasts (optical reflection densities) thus obtained at a predetermined ratio. At this time, a third component (particles) such as a fluidity improver may be added and mixed.
・ About such fluidizers
Examples of fluidity improvers include silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, silica sand, clay, mica, wollastonite, diatomaceous earth, chromium oxide. Cerium oxide, bengara, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride and the like.
[0110]
In particular, fine powders such as silica, aluminum oxide, titanium dioxide, and magnesium fluoride are preferable, and a fluidizing agent may be added alone or in combination.
Formation of an electrostatic field for developing particles for image display employing an electrodeless reversible image display medium is intended to be displayed on the surface of one of the two sheets (for example, the image observation side sheet), for example. An electrostatic latent image corresponding to the image to be formed can be formed and formed based on the electrostatic latent image. In this case, the electrostatic field may be formed simultaneously with the formation of the electrostatic latent image or after the electrostatic latent image is formed. The electrostatic field can be formed, for example, by setting a predetermined potential for forming the electrostatic field on a sheet opposite to the sheet on which the electrostatic latent image is formed. The predetermined potential can be set, for example, by applying a bias to the opposite sheet or grounding the sheet.
[0111]
The electrostatic latent image may be formed directly on the medium surface (sheet surface) using, for example, a direct electrostatic latent image forming apparatus, or may be formed outside the medium using an external electrostatic latent image forming apparatus. The image may be formed by transferring it to the medium surface (sheet surface).
[0112]
As a direct electrostatic latent image forming apparatus, various discharge-type electrostatic latent image forming apparatuses that discharge an electrostatic latent image charge on a medium surface according to an image to be displayed and put an electrostatic latent image charge on it, depending on the image to be displayed. Various types of charge injection type electrostatic latent image forming devices that inject charges onto the surface of the medium to place electrostatic latent image charges can be exemplified. Examples of the former include an ion flow type apparatus and a multi-stylus type apparatus having an electrostatic recording head in which recording electrodes are arranged in a predetermined direction (for example, a main scanning direction when a sheet is scanned by the apparatus). As an example of the latter, a multi-stylus type apparatus having an electrostatic recording head in which recording electrodes are arranged in a predetermined direction (for example, main scanning direction when a sheet is scanned by the apparatus) and adjacent control electrodes are arranged adjacent to the recording electrodes. Can be mentioned.
[0113]
As an external electrostatic latent image forming apparatus, an electrostatic latent image corresponding to an image to be displayed is formed on an electrostatic latent image carrier, and the electrostatic latent image on the electrostatic latent image carrier is transferred to the sheet. What is transferred to the surface can be exemplified. Furthermore, an electrostatic latent image corresponding to an image to be displayed on a photoconductor such as a photoconductor is formed, and the electrostatic latent image on the photoconductor is transferred to the sheet surface, For example, an electrostatic latent image corresponding to an image to be displayed on a dielectric is formed, and the electrostatic latent image on the dielectric is transferred to the sheet surface.
[0114]
For image display, an electric field forming device including any one of the electrostatic latent image forming devices can be employed.
[0115]
As described above, when an electrostatic latent image is formed on an image display medium, whether it is transfer or direct formation, image retention is improved as will be described in detail later. In particular, it is advantageous in terms of image retention when a developer having high fluidity or a developer whose fluidity is enhanced by a developer stirring process prior to image display is used.
[0116]
For a reversible image display medium having electrodes, an electrostatic field for image display can be formed by applying a voltage to the electrodes. An electric field forming apparatus for this medium will be exemplified later.
Regardless of whether any reversible image display medium with or without electrodes is used, an image erasing process for erasing the previously displayed image may be performed before displaying the image.
[0117]
The image erasing process can be performed by, for example, forming an electric field for moving the developer particles constituting the developer in the image display medium, applying a stirring force to the developer, or both. The stirring force can be applied by, for example, forming an alternating electric field on the developer, forming an oscillating magnetic field, irradiating ultrasonic waves, applying mechanical vibration, or a combination thereof.
[0118]
Accordingly, when displaying an image, the image erasing device includes, for example, an electric field forming device that forms an electric field for moving the developed particles, an image erasing device that includes an agitating device that applies a stirring force to the developed particles, What contains both the formation apparatus and the stirring apparatus etc. can be employ | adopted suitably.
[0119]
For example, while collecting developer particles having the same optical reflection density (in other words, “same contrast” or “same color”) of one of the two types of developer particles under an electric field to one sheet side, If the other developer particles having the same optical reflection density are collected on the other sheet side, the image can be erased, and when the next image is formed, it is only necessary to move the developer particles only in the image portion. Therefore, the image display is smooth, sure, and high quality.
[0120]
Further, for example, when the developer (development particles) is stirred, the image is erased, and the charge amount and fluidity of the development particles are improved. In this case, the next image display is smoothly, reliably and high quality. The
[0121]
Examples of such an electric field forming device include a device including a pair of electrodes (usually metal) or a dielectric disposed with a reversible image display medium therebetween, and a power supply device for applying a bias voltage thereto.
[0122]
In addition, various discharge type electric field forming devices that discharge an image display medium to form an electric field and various charge injection type electric field forming devices that form an electric field by injecting electric charge into a reversible image display medium can be exemplified. Examples of the former include a corona charging device, an ion flow type electric field forming device, and a multi-stylus type electric field forming device having a head in which electrodes are arranged in a predetermined direction, and examples of the latter include arranging electrodes in a predetermined direction. In addition, a multi-stylus type electric field forming apparatus having a head in which adjacent control electrodes are arranged adjacent to the electrodes can be exemplified.
[0123]
Moreover, the following can be illustrated as a stirring apparatus.
A device that forms an alternating electric field on a reversible image display medium.
[0124]
This apparatus can be used when at least one of the developer particles is insulative.
A device that generates an oscillating magnetic field for a reversible image display medium.
[0125]
This apparatus can be used when at least one of the developer particles contains a magnetic material.
A device that irradiates a reversible image display medium with ultrasonic waves.
A device that applies mechanical vibration to a reversible image display medium.
-A device combining two or more of the above devices.
As described above, when the developer (development particles) is stirred, the charge amount and fluidity of the development particles are improved, and the next image display is smoothly and reliably made high quality.
[0126]
In addition, when the developer is stirred prior to image display, the charge amount of the developer particles is stabilized, and in this respect, image display can be performed satisfactorily. Furthermore, there is an advantage that the allowable range of chargeability and fluidity of the developer is widened.
[0127]
Therefore, for image display, regardless of whether a reversible image display medium with or without electrodes is used, the developer is used together with the image erasing process or separately from the image erasing process. You may stir.
[0128]
When an image display medium without electrodes is adopted, for example, an electrostatic latent image corresponding to an image to be displayed on the surface (sheet surface) of the image display medium is formed, and the electrostatic latent image is based on the electrostatic latent image. An electrostatic field for image display is formed simultaneously with image formation or after formation of the electrostatic latent image, and the developer is agitated simultaneously with and / or before formation of the electrostatic field. That's fine.
[0129]
For an image display medium having electrodes, an electrostatic field is formed by applying a voltage between the electrodes, and the developer may be stirred before or simultaneously with the formation of the electrostatic field. Regardless of the presence or absence of electrodes, the developer agitation faces the image display medium conveyance path in the electrostatic field formation region by the electric field forming device or the upstream side in the relative conveyance direction of the image display medium with respect to the electric field forming device, for example. This can be done using a stirrer.
[0130]
As for the developer stirring method and the stirring device, the same method and apparatus as the stirring method and stirring device exemplified in connection with the image erasing process can be adopted.
[0131]
In this way, the contrast can be further improved and the driving voltage can be further lowered by stirring the developer for image display.
When an electrostatic latent image is formed on the surface (sheet surface) of the image display medium when displaying the image in the case of employing the reversible image display medium without electrodes, the surface of the medium is predetermined before the electrostatic latent image is formed. An electrostatic latent image corresponding to an image to be displayed in the charged area may be formed by charging the potential uniformly. Based on the electrostatic latent image, a predetermined electrostatic field is formed for each pixel corresponding to the image to be displayed on the developer particles in the developer containing cell, thereby moving the developer particles to display an image. Also good.
[0132]
Such an image display method is:
Charged charged developer particles having a color different from the color of the liquid are dispersed in an insulating liquid of a predetermined color, and the insulating liquid and the charged developer particles are opposed to each other with a predetermined gap, at least one of which is light transmissive The present invention can also be applied to a reversible image display medium sealed between two sheets having the above.
[0133]
That is, prior to image display, the surface of the image display medium is uniformly charged to a predetermined potential. Thereafter, an electrostatic latent image is formed on the surface of the charged medium, and each pixel corresponding to the image to be displayed on the charged developing particles dispersed in the insulating liquid in the medium based on the electrostatic latent image. A predetermined electrostatic field is formed on the surface.
[0134]
The image display method is as follows:
Among the outer surfaces, the other half of the surface opposite to the half is different in color and the spherical developer particles different in ion adsorption amount are surrounded by an insulating liquid layer in the insulating holding medium. The present invention can also be applied to an embedded reversible image display medium.
[0135]
That is, prior to image display, the surface of the image display medium is uniformly charged to a predetermined potential. Thereafter, an electrostatic latent image is formed on the surface of the charged medium, and a predetermined electrostatic field is formed for each pixel corresponding to an image to be displayed on the spherical developer particles based on the electrostatic latent image. An image is displayed by controlling the directions of the surfaces of the spherical developing particles having different colors. More specifically, the spherical developer particles that are surrounded by the insulating liquid layer and are rotatable are reversed by the influence of the electrostatic field, and an image is displayed. The reversal of the spherical developer particles is that the other half of the outer surface of the spherical developer particles is different from the other half in terms of the amount of ion adsorption, and therefore the direction of the surface changes depending on the direction of the electric field. Occur. In addition, since half of the outer surface of the spherical developer particle is opposite in color to the other half, the image can be displayed.
[0136]
The electrostatic latent image on the medium is directly formed on, for example, the surface of the medium charged in the charging step, regardless of whether the medium includes cell-encapsulated developer particles, developer particles in an insulating liquid, or rotatable spherical particles. Alternatively, the electrostatic latent image formed on the electrostatic latent image carrier outside the medium can be formed by transfer onto the surface of the medium charged in the charging step.
[0137]
The charge polarity of the area of the electrostatic latent image formed on the medium has a different polarity even if it is the same polarity as the charge polarity of the charge area due to uniform charging of the medium surface prior to the formation of the electrostatic latent image. Or 0 [V].
[0138]
The formation of the electrostatic field may be performed simultaneously with the formation of the electrostatic latent image, or may be performed by applying a bias voltage to the medium after forming the electrostatic latent image or grounding the medium.
[0139]
As described above, when the surface of the image display medium is uniformly charged to a predetermined potential in advance and an electrostatic latent image is written in the charged area, the charged developer particles in the developer containing cells or The charged developing particles in the insulating liquid can be moved, or the spherical developing particles can be reversed. Further, an electrostatic field sufficient to hold the moved developer particles and the inverted developer particles at the position is formed. In other words, when the surface of the image display medium is uniformly charged to a predetermined potential in advance and then an electrostatic latent image is written in the charged area, the image retention is improved. In particular, it is advantageous in terms of image retention when a developer having high fluidity or a developer whose fluidity is enhanced by a developer stirring process prior to image display is used. As a result, high-quality images with excellent contrast can be stably displayed over a long period of time.
[0140]
It should be noted that the image can be erased by forming a different electrostatic field or forming an alternating electric field for both the medium in which the charged developer particles are dispersed in the insulating liquid and the medium containing the spherical developer particles. The image can be rewritten by forming an electrostatic latent image.
According to the various reversible image display media described above and the reversible image display method using the same, high-resolution and high-quality images can be stably displayed over a long period of time with good contrast. In addition, afterimages are unlikely to occur, and therefore show good reversibility, and a high-quality image can also be displayed in this respect. It is also possible to reduce the driving voltage. It is also possible to display an image with little image unevenness.
Hereinafter, specific examples of the developing particles and the developer will be described, and specific examples of the reversible image display medium, the reversible image display method, the image forming apparatus, and the like will be described with reference to the drawings.
<Development particles and developer>
・ White developer particles WP
100 parts by weight of thermoplastic polyester resin (softening point 121 ° C., glass transition point 67 ° C.), 40 parts by weight of titanium oxide (manufactured by Ishihara Sangyo Co., Ltd .: CR-50), zinc salicylate complex (Orient Chemical Co., Ltd.) as a negative charge control agent (Product: Bontron E-84) 5 parts by weight were sufficiently mixed with a Henschel mixer, then kneaded with a twin screw extruder and cooled. The kneaded material was coarsely pulverized, then pulverized by a jet pulverizer, and classified by wind to obtain a white fine powder. White fine powders having a volume average particle size of 0.7 μm, 2.1 μm, 10.1 μm, 46.2 μm, and 55.3 μm were obtained.
[0141]
Thereafter, 0.3 part by weight of hydrophobic silica particles (Aerosil R-972, manufactured by Nippon Aerosil Co., Ltd.) is added to the white fine powder of each particle size, and mixed with a Henschel mixer to obtain a white particle having substantially the following particle size. Developer particles WP (WP1 to WP5) were obtained.
[0142]
Particle WP1: Volume average particle diameter 0.7 μm
Particle WP2: Volume average particle diameter 2.1 μm
Particle WP3: Volume average particle diameter 10.1 μm
Particle WP4: Volume average particle diameter 46.2 μm
Particle WP5: Volume average particle diameter 55.3 μm
These white developing particles are non-conductive particles.
・ Black developer particles BP
100 parts by weight of a styrene-n-butyl methacrylate resin (softening point 132 ° C., glass transition point 65 ° C.), 4 parts by weight of carbon black (manufactured by Lion Oil & Fats, Ketjen Black EC), silica (manufactured by Nippon Aerosil Co., Ltd., # 200) ) And 500 parts by weight of magnetite-based magnetic powder (RB-BL Titanium Kogyo Co., Ltd.) were sufficiently mixed with a Henschel mixer and then kneaded with a bent biaxial kneader.
[0143]
The kneaded product was cooled, coarsely pulverized with a feather mill, then finely pulverized with a jet mill, and classified with an air classifier to obtain black particles BP (BPo, BP1 to BP5) having the following volume average particle diameter. .
[0144]
Particle BPo: Volume average particle diameter 25.0 μm
Particle BP1: Volume average particle diameter 0.8 μm
Particle BP2: Volume average particle diameter 3.0 μm
Particle BP3: Volume average particle diameter 25.1 μm
Particle BP4: Volume average particle diameter 87.7 μm
Particle BP5: Volume average particle diameter 121.0 μm
These black developing particles are magnetic particles.
・ Developer DL
The white particles WP3 (10.1 μm) and the black particles BPo (25.0 μm) are placed in a polyethylene bottle at a ratio of 20 g of white particles and 80 g of black particles, rotated on a ball mill stand and mixed for 30 minutes for development. Agent DL (DLo) was obtained.
[0145]
Further, white particles and black particles are combined in the following manner, and 20 g of white particles and 80 g of black particles are put in a polyethylene bottle, rotated on a ball mill base and mixed and stirred for 30 minutes. While making (DL1 to DL9), the following developers De1 to De16 were made as comparative developers.
[0146]
In any developer, white particles were negatively charged and black particles were positively charged.
[0147]
Developer DL1: WP2 (2.1 μm) + BP2 (3.0 μm)
Developer DL2: WP3 (10.1 μm) + BP2
Developer DL3: WP4 (46.2 μm) + BP2
Developer DL4: WP2 + BP3 (25.1 μm)
Developer DL5: WP3 + BP3
Developer DL6: WP4 + BP3
Developer DL7: WP2 + BP4 (87.7 μm)
Developer DL8: WP3 + BP4
Developer DL9: WP4 + BP4
Comparative Example Developer De1: WP1 (0.7 μm) + BP1 (0.8 μm)
Comparative Example Developer De2: WP2 (2.1 μm) + BP1
Comparative Example Developer De3: WP3 (10.1 μm) + BP1
Comparative Example Developer De4: WP4 (46.2 μm) + BP1
Comparative Example Developer De5: WP5 (55.3 μm) + BP1
Comparative Example Developer De6: WP1 (0.7 μm) + BP2 (3.0 μm)
Comparative Example Developer De7: WP5 (55.3 μm) + BP2
Comparative Example Developer De8: WP1 (0.7 μm) + BP3 (25.1 μm)
Comparative Example Developer De9: WP5 (55.3 μm) + BP3
Comparative Example Developer De10: WP1 (0.7 μm) + BP4 (87.7 μm)
Comparative Example Developer De11: WP5 (55.3 μm) + BP4
Comparative Example Developer De12: WP1 (0.7 μm) + BP5 (121 μm)
Comparative Example Developer De13: WP2 (2.1 μm) + BP5
Comparative developer De14: WP3 (10.1 μm) + BP5
Comparative Example Developer De15: WP4 (46.2 μm) + BP5
Comparative developer De16: WP5 (55.3 μm) + BP5
The following developer was also prepared as a comparative developer.
Comparative developer d1
1 g of Sudan Black X60 (trade name, manufactured by BASF) was added to 100 ml of isoparaffin hydrocarbon (trade name: Isopa G, manufactured by Exxon Chemical Co., Ltd.) and sufficiently dissolved and mixed to prepare a colored liquid.
[0148]
10 g of titanium dioxide particles (manufactured by Ishihara Sangyo Co., Ltd .: CR-50) and 70 g of an IP solvent 1620 solution of 0.5% by weight of Sulhol Ba-30N (barium sulfonate manufactured by Matsumura Oil Research Co., Ltd.) were mixed with this. , Sand grinder (manufactured by IGARASHI KIKAI SEIZO CO., Ltd.), 1 mm diameter glass beads (1500 cc) as media, 1/8 GL Bessel with water jacket, cooling water temperature 20 ° C., disk rotation speed Wet grinding was performed by treating at 2000 rpm for 15 hours.
[0149]
To 100 parts by weight of this concentrated liquid developer, 900 parts by weight of IP solvent 1620 was added for dilution. K. A developer d1 was obtained by carrying out a dispersion treatment at 10,000 rpm for 5 minutes using an auto homomixer type M (manufactured by Tokushu Kika Kogyo Co., Ltd.).
<Reversible image display medium>
・ Reversible image display medium 11
3 and 4 show an example of a reversible image display medium. The medium 11 shown in FIGS. 3 and 4 includes a first sheet 111 and a second sheet 112. These sheets 111 and 112 face each other with a predetermined gap therebetween. A partition wall 113 is provided between the sheets 111 and 112, and a gap between both sheets is secured by the partition wall 113. That is, the partition wall 113 also serves as a spacer between the sheets 111 and 112. Both sheets 111 and 112 are connected and fixed to each other by a partition wall 113.
[0150]
The first sheet 111 is formed of, for example, a light transmissive plate such as transparent glass, a transparent resin film, or the like. This sheet 111 is a sheet on the image observation side.
[0151]
A first electrode 114 is provided on the inner surface of the sheet facing the second sheet 112. The first electrode 114 is continuous over the entire image display area on the inner surface of the sheet 111. The first electrode 114 is a transparent electrode formed of indium tin oxide (ITO), for example.
[0152]
The second sheet 112 is not necessarily transparent, but is formed of, for example, a light transmissive plate such as transparent glass, a resin film, or the like.
[0153]
A second electrode 115 is formed on the inner surface of the second sheet 112 facing the first sheet 111. Here, the second electrode 115 is a plurality of individual electrodes 115a arranged in a grid pattern. Each individual electrode is not necessarily a transparent electrode, but is formed of, for example, a transparent ITO film.
[0154]
As shown in FIG. 5, the partition wall 113 is formed upright on the inner surface of the second sheet 112 in a lattice shape, and thereby, a plurality of developments each partitioned into a square shape with a part of the partition wall 113 as a partition wall. An agent storage cell 116 is formed, and one individual electrode 115 a is arranged in each of the cells 116. That is, here, one cell corresponds to one pixel.
[0155]
Further, a dry developer DL containing white developer particles WP and black developer particles BP that are frictionally charged with each other is contained in each cell.
[0156]
Each cell is sealed, and the developer DL does not leak from the cell.
[0157]
The gap between the sheets, the height of the partition wall 113, or the distance between the first electrode 114 and the second electrode 115 is not limited thereto, but is set to, for example, 20 μm to 1 mm.
[0158]
The individual electrodes 115a that lie along the second electrode 115 in the image display medium 11 have lead portions 110 connected to each other as shown in FIG. 6, and the electrodes as shown in FIG. Connected to the selection circuit 117. A positive drive voltage generation circuit 118a, a negative drive voltage generation circuit 118b, and a display data control unit 119 are connected to the electrode selection circuit 117. A drive voltage is applied to each of the individual electrodes 115a independently from the electrode selection circuit 117, and the display data control unit 119 displays display data output means (for example, a computer, a word processor, Display data is input from a facsimile machine or the like, and the electrode selection circuit 117 is controlled based on the display data. In other words, these electrode selection circuits and the like constitute one example of an electric field forming apparatus or an image forming apparatus for a reversible image display medium with electrodes.
[0159]
Thus, the first electrode 114 in the image display medium 11 is used as a ground electrode, and an electrode that is controlled so that a desired image display is performed by the display data control unit 119 between the electrode 114 and each individual electrode 115a. By applying a predetermined voltage from the positive drive voltage generation circuit 118a or the negative drive voltage generation circuit 118b via the selection circuit 117 and forming a predetermined electric field for each pixel, as shown in FIG. As shown in FIG. 4, the developer particles WP and BP move from the state where the developer particles are mixed in accordance with the electric field. Thus, an image can be displayed with a predetermined contrast. For example, an image can be displayed as shown in FIG. In FIG. 7, Bk is a black display portion, and W is a white display portion.
[0160]
The roller R2 shown in FIG. 4 will be described later.
-Reversible image display medium 12
8 and 9 show other examples of the image display medium. FIG. 8A is a cross-sectional view of the reversible image display medium 12 before image display, and FIG. 8B is a cross-sectional view of an example during image display. FIG. 9 is a plan view in which a part of the medium 12 is cut away.
[0161]
The image display medium 12 shown in FIGS. 8 and 9 is a rectangular medium as a whole, and includes a first sheet 121, a second sheet 122, and a partition wall 123 between these sheets.
[0162]
The first sheet 121 and the partition wall 123 are integrally formed by heat-molding a synthetic resin base material. At least the first sheet 121 is transparent and is a sheet on the image observation side. The second sheet 122 is also a synthetic resin sheet.
[0163]
The partition wall 123 is composed of a plurality of vertical partition walls 123a extending in parallel with the vertical side of the medium 12, and a developer containing cell 124 is provided between the adjacent vertical partition walls. Each cell 124 contains a developer DL containing white developer particles WP and black developer particles BP that are frictionally charged with each other.
[0164]
Both sheets 121 and 122 are heat-sealed at the peripheral edge of the medium 12 to form a sealing portion 120. Of the sealing portion 120, a portion 120 a connected to both ends in the longitudinal direction of the vertical partition wall 123 a and sealing both ends of each cell also serves as a partition wall forming the cell 124.
[0165]
Each partition wall 123a has a width α and a height h, and is formed with an interval between adjacent vertical partition walls 123a as pt.
[0166]
Each cell is sealed, and the developer DL does not leak from the cell.
[0167]
The partition wall 123 (partition wall 123a) also serves as a spacer that maintains a predetermined gap between the sheets 121 and 122.
[0168]
As described above, it is preferable that any of the sheets 121 and 122 is formed in the thickness range of 5 μm to 100 μm, and the height h of the partition wall 123a (in other words, the gap between the sheets) is preferably 20 μm to 300 μm. The thickness of the entire medium 12 is preferably 30 μm to 500 μm.
[0169]
The surface resistivity of the first sheet 121 that forms the electrostatic latent image is 10^TenΩ / □ -10¹⁶Ω / □, the surface resistivity of the second sheet 122 is 10⁷Ω / □ or less is preferable.
[0170]
The medium 12 can be displayed as an image by the image forming apparatus shown in FIG.
[0171]
The image forming apparatus shown in FIG. 11 includes a photosensitive drum PC that is rotationally driven in the direction of the arrow in the drawing. A scorotron charger CH, a laser image exposure apparatus EX, and an eraser lamp IR are disposed around the photosensitive drum PC. An electrode roller R1 that is rotationally driven is disposed below the photosensitive drum PC. The electrode roller R1 is a developing electrode roller for forming an electrostatic field for image display. A bias voltage can be applied to the roller R1 from the power supply PW1. The roller R1 may incorporate a rotating magnetic pole roller R2 that is driven to rotate in the opposite direction to the roller R1 (or that is driven to reciprocate).
[0172]
After the surface of the photosensitive drum PC is charged by the charger CH, an image is exposed to the charged area by the exposure apparatus EX to form an electrostatic latent image EI on the drum PC. On the other hand, a bias is applied to the electrode roller R1 from the power supply PW1.
[0173]
Then, in synchronization with the electrostatic latent image EI on the photosensitive drum PC, the medium 12 is fed between the drum and the electrode roller R1.
[0174]
Thus, a predetermined electrostatic field is formed for each pixel on the developer particles BP and WP of the developer DL contained in each cell 124 of the medium 12, and thereby, a Coulomb force acting between the electrostatic field and the charged developer particles. The developing particles move at. Then, as shown in FIG. 8A, the white particles WP and the black particles BP move in accordance with the electric field from the state where the black and white particles WP and BP are mixed in the developer DL as shown in FIG. 8B. To do. Thus, an image can be displayed with a predetermined contrast. For example, an image can be displayed as shown in FIG. In FIG. 10, Bk is a black display portion, and W is a white display portion.
[0175]
After the image display as described above, the charge on the surface of the photosensitive drum PC is erased by the eraser lamp IR in preparation for the next printing.
[0176]
In this image display, if the magnetic pole roller R2 is provided and rotated, the developer DL in each cell 124 is agitated and the developer particles BP and WP are easily moved, and a better image can be displayed. The drive voltage can be reduced.
[0177]
Such a rotating magnetic pole roller R2 can also be adopted for the medium 11 shown in FIG.
-Reversible image display medium 13
FIG. 12 shows a cross-sectional view of still another example of the reversible image display medium. The image display medium 13 shown in FIG. 12 is the same as the medium 12 except that a conductive film 122A is formed on the outer surface of the second sheet 122 of the medium 12 shown in FIG. The same parts as those of the medium 12 are denoted by the same reference numerals.
[0178]
The medium 13 can also be displayed with a predetermined contrast using, for example, the image forming apparatus shown in FIG. Instead of using the electrode roller R1, the conductive film 122A on the surface of the second sheet 122 may be grounded.
・ Other reversible image display media
The following are illustrated as another reversible image display medium.
a) A medium in which the developer containing cell has another shape selected from FIG. 1A to FIG.
b) A medium in which the developer movement suppressing member shown in any of FIGS. 2 (A) to 2 (H) is provided in the developer containing cell in the mediums 11 to 13;
c) A medium that employs a developer accommodating cell other than those employed in the mediums 11 to 13 and employs any developer movement suppressing member.
As described above, each image display medium described with reference to the drawings and the other medium just described can repeat image display and image erasure. Further, the developer particles WP and BP are contained in the cell, and it is not necessary to supply the developer from the outside. As a result, the use of conventional media such as paper and consumables such as developer can be significantly suppressed. In addition, the image forming energy can be reduced by not requiring the heat energy for fusing the toner to the medium unlike the conventional case. Therefore, today's environmental load can be reduced.
[0179]
Further, since each medium 11, 12, 13, etc. employs the dry developer DL containing developer particles WP, BP having different colors, the other developer particles BP (or WP) by one developer particle WP (or BP). ) Has a good concealment degree and can display an image with good contrast.
[0180]
Further, since the developing particles WP and BP contained in the cells are charged with different charging polarities, and accordingly can easily move by receiving the Coulomb force when displaying the image, the image can be displayed with good contrast in this respect, The previous afterimage is unlikely to occur.
[0181]
Further, since the dry developer DL is employed as the developer, the settling and aggregation of the developed particles are difficult to occur, and the contrast is not reduced much in the image display, and stable image display can be performed over a long period of time. Since settling and agglomeration of developing particles are unlikely to occur, an afterimage of the previous display image is also unlikely to occur. Since the dry developer DL has little change with time, a stable image display can be performed for a long time in this respect.
[0182]
In addition, since one pixel can be reduced, an image can be displayed with high resolution by doing so.
[0183]
As a result, it is possible to stably display an image with excellent contrast, high resolution and high quality over a long period of time.
Next, a specific example medium (example medium) of the reversible image display medium and image display using the medium will be described.
Example 1
A reversible image display medium with electrodes of the type shown in FIGS. 3 to 7 and formed as follows.
[0184]
That is, an ITO film as a first electrode 114 is formed on the entire surface of the first sheet 111 made of a transparent PET (polyethylene terephthalate) film having a thickness of 100 μm to a thickness of 500 mm by a sputtering method.
[0185]
Next, using a PET film with an AL deposition layer formed on the entire surface, applying a photoresist, patterning it by exposure, development, and etching, stripping and removing the photoresist layer, and two-dimensionally arranged individual pixels A second sheet 112 having a group of electrodes 115a is formed.
[0186]
The transparent individual pixel electrode group 151a formed in this way is in an arrangement state in which square electrodes of 5 mm in length and width are arranged in a grid pattern with an electrode interval of 0.5 mm as shown in FIG. 6, for example. The lead part 110 is patterned between the individual electrodes so that a voltage can be applied.
[0187]
A portion other than the individual electrodes on the second sheet 112 (a thick film resist was repeatedly applied between the individual electrodes and the surrounding area to form partition walls 113 having a height of 90 μm in a grid pattern (see FIG. 5). Each concave portion of the grid-like partition wall 113 is used as a space of the cell 116, and the developer DL is put up to a height of 90% in the developer 116. The developer DL is a developer DL (DLo) among several examples of the developer described above. Yes, it contains white developing particles WP (WP3 10.1 μm) and black developing particles BP (BPo 25.0 μm).
[0188]
Next, after thinly applying the photocurable adhesive 119a only on the partition wall 113, the first sheet 111 is brought into close contact, and the adhesive is cured by ultraviolet irradiation to adhere the sheet 111.
[0189]
Thereafter, the periphery of the first and second sheets 111 and 112 was sealed and sealed with an epoxy adhesive 119b as shown in FIG. 3 and the like, and the reversible image display medium of Example 1 was obtained.
[0190]
As a comparative example for the medium 11, a comparative medium E1 was also formed in the same manner as the medium 11 except that each cell space was filled with the developer dl so that no bubbles would enter.
[0191]
For the medium of Example 1 described above, +100 V was applied to the electrode corresponding to the pixel to be displayed in black among the individual electrodes 115a, and −100 V was applied to the electrode corresponding to the pixel to be displayed in white. In this way, a voltage corresponding to the display data was applied, and a desired image display could be performed as illustrated in FIG.
[0192]
Similarly to the medium of Example 1, voltages of +100 V and −100 V were applied to the image display medium E1 (not shown) to display an image, and the image contrast was evaluated together with the medium of Example 1.
[0193]
The contrast was evaluated by measuring the image density of the black part Bk and the white part W using a reflection densitometer (manufactured by Konica: SAKURA DENSITOMETER PDA-65) and evaluating the ratio (BK / W). A reflection density ratio of 10.0 or more was judged good (◎), 7.0 or more and less than 10.0 was acceptable (◯), and less than 7.0 was judged as bad (x). Note that the contrast evaluation method is the same in this specification unless otherwise specified.
[0194]
The evaluation results were as follows.
-Medium of Example 1
The reflection density (BK) of the black part was 1.5, the reflection density (W) of the white part was 0.1, and the reflection density ratio was 15.0 (good).
Comparative medium E1
The black portion had a reflection density of 0.6, the white portion had a reflection density of 0.1, and the reflection density ratio was 6.0, which was poor (×).
(Example 2)
An electrodeless reversible image display medium of the type shown in FIGS. 8 to 10 and formed as follows.
[0195]
A base material made of transparent PET was heated and stamped to integrally form a partition wall 123 composed of a plurality of partition walls 123a parallel to the first sheet 121 having an average thickness of 25 μm. Each partition wall 123a has a width α = 20 μm, a height h = 100 μm, and an interval between adjacent partition walls pt = 200 μm.
[0196]
The developer DL is put in a cell 124 provided between each adjacent partition wall 123a up to 90% of the space height, and then a photo-curable adhesive 123b is applied only to the upper part of the partition wall 123, and then on the top. A second sheet 122 having a thickness of 25 μm was adhered, and then the adhesive was cured by ultraviolet irradiation. The peripheral portions of the sheets 121 and 122 were heat-sealed to form a sealing portion 120. Thus, the reversible image display medium of Example 2 was formed.
[0197]
The developer DL is the developer DL (DLo) described above, and includes white developer particles WP (WP3 10.1 μm) and black developer particles BP (BPo 25.0 μm).
(Example 3)
In the medium 12 of the second embodiment, a conductive film 122A is formed on the outer surface of the second sheet 122 by aluminum deposition as shown in FIG. 12, and the other points are the same as those of the medium 12 of the second embodiment.
[0198]
The media of Examples 2 and 3 were displayed as follows using the image forming apparatus shown in FIG.
[0199]
The surface of the photosensitive drum PC is charged to +1000 V by the charger CH, and an image is exposed to the charged area to form an electrostatic latent image EI, while a bias +500 V is applied to the electrode roller R1, and the photosensitive drum PC and the electrode roller R1 are exposed. The medium 12 was passed between them. At this time, the ratio (peripheral speed ratio) θ between the peripheral speed of the photosensitive drum PC and the peripheral speed of the counter electrode roller R1 is constant at θ = 1.
[0200]
Thus, an image as shown in FIG. 10 could be displayed.
[0201]
As a comparative example for the media of Examples 2 and 3, a comparative example was made in the same manner as these media, except that each cell space of the media of Example 2 was filled with the developer dl so that no bubbles would enter. A medium E2 (not shown) was also formed.
[0202]
For the media of Examples 2 and 3 and the comparative example media E2, images were displayed using the image forming apparatus shown in FIG. 11, and the image contrast was evaluated.
[0203]
The evaluation results were as follows.
-Medium of Example 2
The reflection density (Bk) of the black part was 1.5, the reflection density (W) of the white part was 0.1, and the reflection density ratio was 15.0 (good).
-Medium of Example 3
The reflection density (Bk) of the black part was 1.6, the reflection density (W) of the white part was 0.1, and the reflection density ratio was 16.0, which was good (◎).
-Comparative example medium E2
The black portion had a reflection density of 0.6, the white portion had a reflection density of 0.1, and the reflection density ratio was 6.0, which was poor (×).
Next, the ratio Sn / So of the non-image area Sn in the unit area So provided by the image display medium is set to 0.0001 or more and 0.5 or less, or the value of (1-Sa / Sb) is set. Example media (Examples 4 to 9) and comparative example media E3 to E4, which show that it is preferably 0.0001 or more and 0.5 or less, will be described.
(Example 4)
In the medium of Example 2 (partition wall thickness α = 20 μm, adjacent partition wall interval pt = 200 μm), the medium has Sn / So of 0.091. This medium has substantially the same structure as the medium of Example 2.
[0204]
Evaluation of the image contrast was performed using the image forming apparatus shown in FIG. 11 and displaying an image of the black portion Bk on the right half and the white portion W on the left half as shown in FIG. 13A. . For image formation, the surface of the photosensitive drum PC is charged to +1000 V by the charger CH, and the electrostatic latent image EI is formed by exposing the charged area to the charged area, while a bias of +500 V is applied to the electrode roller R1, A medium was passed between the photosensitive drum PC and the electrode roller R1. At this time, the ratio (peripheral speed ratio) θ between the peripheral speed of the photosensitive drum PC and the peripheral speed of the counter electrode roller R1 is constant at θ = 1.
[0205]
As a result of the image contrast evaluation, the reflection density of the black part was 1.65, the reflection density of the white part was 0.133, and the reflection density ratio (Bk / W) was 12.4 (◎).
(Example 5)
In the medium of Example 2, the shape and arrangement of the developer containing cells are grid-like as shown in FIG. 1D, the thickness (width) α of the partition walls forming the cells is 20 μm, and the spacing between adjacent partition walls pt Is 200 μm (in other words, the cell size is 200 μm × 200 μm), and Sn / So is 0.174. Others are the same as the medium of Example 2.
[0206]
A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.
[0207]
As a result of image contrast evaluation, the reflection density of the black part was 1.52, the reflection density of the white part was 0.135, and the reflection density ratio (Bk / W) was 11.2 (（).
(Example 6)
In the electrode-attached medium of Example 1 (cells having a grid pattern), the spatial dimension of the cells 116 is 200 μm × 200 μm, the thickness (width) of the partition wall 113 also serving as the partition wall forming the cells is 20 μm, and Sn / So is a medium with 0.174. Others are the same as the medium of Example 1. .
[0208]
With respect to this medium, an image similar to that in FIG. 13A was formed using the same electric field forming apparatus and image forming conditions as those of the medium of Example 1.
[0209]
As a result of the image contrast evaluation, the reflection density of the black part was 1.59, the reflection density of the white part was 0.135, and the reflection density ratio (Bk / W) was 11.8 (◎).
(Example 7)
In the medium of Example 2, as shown in FIG. 2A, developer movement suppression column members having vertical and horizontal dimensions β1 × β2 = 60 μm × 10 μm are dispersedly erected and the medium unit area γ1 × γ2 = 1000 μm × A medium in which a pattern in which the suppression members are arranged one by one in 800 μm is repeated. Sn / So is 0.0008. Others are the same as the medium of Example 2.
[0210]
A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.
[0211]
As a result of the image contrast evaluation, the reflection density of the black part was 1.80, the reflection density of the white part was 0.130, and the reflection density ratio (Bk / W) was 13.8 (◎).
(Example 8)
In the medium of Example 2, as shown in FIG. 2F, a medium in which developer movement suppression column members having vertical and horizontal dimensions β1 × β2 = 60 μm × 10 μm are erected at intervals of δ = 1000 μm in each cell. Sn / So is 0.101. Others are the same as the medium of Example 2.
[0212]
A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.
[0213]
As a result of evaluating the image contrast, the reflection density of the black part was 1.63, the reflection density of the white part was 0.133, and the reflection density ratio (Bk / W) was 12.3 (◎).
Example 9
In the medium of Example 2, the shape and arrangement of the developer containing cells are grid-like as shown in FIG. 1D, the thickness (width) α of the partition walls forming the cells is 50 μm, and the spacing between adjacent partition walls pt Is a medium in which a developer movement suppression column member having vertical and horizontal dimensions β1 × β2 = 60 μm × 10 μm is set up one by one in each cell, in other words, the cell size is 150 μm × 150 μm. Sn / So is 0.468. Others are the same as the medium of Example 2.
[0214]
A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.
[0215]
As a result of the image contrast evaluation, the reflection density of the black part was 1.03, the reflection density of the white part was 0.144, and the reflection density ratio (Bk / W) was 7.2 (◯).
(Comparative Example Medium E3)
In the medium of Example 2, as shown in FIG. 2H, developer movement suppression column members having vertical and horizontal dimensions β1 × β2 = 20 μm × 20 μm are dispersedly erected, and the medium unit area γ1 × γ2 = 5000 μm × A medium in which a pattern in which the suppression members are arranged one by one in 2000 μm is repeated. Sn / So is 0.00004. Others are the same as the medium of Example 2.
[0216]
A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.
[0217]
As a result of image contrast evaluation, the reflection density of the black part was 0.90, the reflection density of the white part was 0.186, and the reflection density ratio (Bk / W) was 4.8, which was poor (×).
[0218]
Both the solid black image portion and the white solid image were images with uneven density.
(Comparative Example Medium E4)
In the medium of Example 2, the partition wall thickness α = 160 μm, the interval between adjacent partition walls pt = 140 μm, and Sn / So is 0.53. This medium has substantially the same structure as the medium of Example 2.
[0219]
A similar image was formed on this medium using the same image forming apparatus and image forming conditions as those of the medium of Example 4.
[0220]
As a result of image contrast evaluation, the reflection density of the black part was 0.84, the reflection density of the white part was 0.146, and the reflection density ratio (Bk / W) was 5.8, which was poor (×).
[0221]
The black solid image portion formed between the partition walls was obtained only in a stripe shape.
[0222]
The configurations of the media of Examples 4 to 9 described above are summarized in Table 1.
[0223]
Table 2 summarizes the image contrast evaluation results for the media of Examples 4 to 9 and the comparative media E3 and E4.
[0224]
[Table 1]

[0225]
[Table 2]

[0226]
FIG. 13 is a graph showing the relationship between the ratio of the non-image area (non-image area / medium unit area) and the reflection density ratio.
[0227]
As described above, according to the image display media of Examples 4 to 8, images having no image unevenness and high contrast were obtained. In the image display medium of Example 9, since the area ratio of the non-image part is high, the contrast is slightly deteriorated, but it is practically acceptable.
[0228]
In the comparative example medium E3, since the ratio of the non-image portion is too small, the gap between the sheets cannot be maintained, the image unevenness occurs, and the reflection density of the black portion is decreased and the reflection density of the white portion is increased. .
[0229]
In the comparative example medium E4, since the ratio of the non-image area is too large, sufficient contrast cannot be obtained. This is because the black solid is displayed in black and white stripes in the black display, and thus the reflection density is lowered. On the other hand, in the white display, the reflection density of the non-image area is large and the white solid has a high reflection density. .
Next, in the reversible image display medium, the thickness of each sheet is 5 μm to 100 μm, the gap between both sheets is 20 μm to 300 μm, the total thickness is 30 μm to 500 μm, one of the two sheets of the medium The surface resistivity of the outer surface is 10^TenΩ / □ -10¹⁶Ω / □, the surface resistivity of the outer surface of the other sheet is 10⁷Example media (Examples 10 to 21) and comparative example media E5 to E12 showing that it is preferable to set the resistance to Ω / □ or less will be described.
(Examples 10-14, Comparative Example Media E5-E8)
An image display medium in which the surface resistivity of the first sheet 121 and the surface resistivity of the second sheet 122 are variously changed while the thickness of each sheet is 25 μm and the gap between sheets is 100 μm. The medium is the same as that of Example 2 except that the sheet surface resistivity is variously changed.
[0230]
In addition to these media, the surface resistivity of the first sheet 121 was adjusted by applying a surfactant to the sheet surface for the media of Examples 15 to 21 to be described later. The surface resistivity of the second sheet 122 was adjusted by making the second sheet contain conductive carbon and changing its content. The surface resistivity was measured in a 65% RH environment according to the measurement method ASTM D-257.
[0231]
Table 3 shows the media of Examples 10 to 14 and the comparative media E5 to E8.
(Example 15)
In the medium of Example 3 (the medium having the Al deposited film on the second sheet), the surface resistivity of the first sheet 121 is 1.20 × 10.¹⁵Ω / □, and the surface resistivity of the second sheet 122 is 8.50 × 10^-1Medium with Ω / □. Others are the same as the medium of Example 3.
(Examples 16 to 21, Comparative Example Media E9 to E12)
In the medium of Example 15, the medium is obtained by changing the thickness of each sheet and the gap between sheets in various ways while keeping the surface resistivity of each sheet as it is. Others are the same as the medium of Example 15.
[0232]
The media of Examples 16 to 21 and the comparative media E9 to E12 are shown together in Table 3.
[0233]
[Table 3]

[0234]
For each of the example media (Examples 10 to 21) and the comparative example media E5 to E12, an image as shown in FIG. 13 is formed using the image forming apparatus shown in FIGS. 16 (A) and 16 (B). The image contrast was evaluated. Note that the image forming apparatus shown in FIG. 16 is an image forming apparatus using an ion flow type direct electrostatic latent image forming apparatus. This will be explained later.
[0235]
In this evaluation, the maximum reflection density and the minimum reflection density are measured for each of the black part and the white part, and the average reflection density of each of the black part Bk and the white part W is obtained based on these. From this, the reflection density ratio was obtained. Also in this case, when the reflection density ratio was 10.0 or more, it was judged as good (◯), and when it was smaller than 10.0, it was judged as defective (x).
[0236]
Also, image unevenness was evaluated. For the evaluation of image unevenness, the image density of the black portion is measured using a reflection densitometer (manufactured by Konica: SAKURA DENSITOMETER PDA-65), and the difference between the maximum value and the minimum value of the image density is obtained. A value of 2 or less was evaluated as good (◯), and a value larger than that was determined as defective (×).
[0237]
These evaluation results are summarized in Table 4. Table 4 also shows a defect mark for those with poor contrast.
[0238]
[Table 4]

[0239]
From this evaluation result, the thickness of each sheet is 5 μm to 100 μm, the gap between both sheets is 20 μm to 300 μm, the total thickness is 30 μm to 500 μm, and the outer surface of one of the two sheets of the medium is The surface resistivity is 10^TenΩ / □ -10¹⁶Ω / □, the surface resistivity of the outer surface of the other sheet is 10⁷It can be seen that the value is preferably Ω / □ or less.
[0240]
The image forming apparatus shown in FIGS. 16A and 16B is a development of the image forming apparatus whose principle is shown in FIGS.
[0241]
The image forming apparatus shown in FIG. 14 is suitable for an image display medium of an electrodeless type in which one sheet is provided with a conductive film like the medium 13 in FIG.
[0242]
The image forming apparatus of FIG. 14 includes an ion flow type direct electrostatic latent image forming apparatus CR1. The apparatus CR1 includes a corona ion generating part c1 for generating corona ions, a writing electrode e1 for guiding the corona ions generated in the generating part to the surface of the sheet 121, and an image for displaying positive or negative corona ions. Accordingly, it includes a write electrode control circuit f1 that applies a voltage to the write electrode e1 to guide the pixel 121 on the surface of the sheet 121. The electrode control circuit f1 includes a control power supply and a bias power supply (not shown).
[0243]
The corona ion generation part c1 is not limited to this in the shield case c11, but, for example, a gold-plated tungsten wire having a diameter of 60 to 120 μm is stretched to form a corona wire c12. (For example, 4 kV to 10 kV) is applied to generate corona ions.
[0244]
The write electrode e1 is provided adjacent to the portion of the shield case c11 facing the first sheet 121 of the medium (for example, the medium 13), and the corona ion flow can pass through the through hole provided in the center.
[0245]
The electrode control circuit f1 can apply to the electrode e1 an ion extraction voltage corresponding to positive and negative ions to be derived toward the medium 13.
[0246]
Thus, the medium 13 is displayed with the second sheet 122 as the ground potential (or by applying a bias voltage having the same polarity as the latent image polarity and smaller than the latent image potential) relative to the apparatus CR1. Depending on the image, the positive or negative corona ions are guided to the pixel-corresponding portion on the surface of the sheet 121, thereby applying an electrostatic latent image charge to the surface of the first sheet 121, and simultaneously forming an electrostatic field. Then, the developed particles in each cell of the medium 13 can be moved to display an image.
[0247]
The image forming apparatus shown in FIG. 15 is suitable for an image display medium having no electrode and having no conductive film on one sheet, like the medium 12 shown in FIG. The image forming apparatus of FIG. 15 includes an electrode Ea that contacts the sheet 122 on the side opposite to the sheet 121 on the side on which the electrostatic latent image is formed. Similarly to the case of FIG. 14, a bias voltage may be applied to the electrode Ea. The other points are the same as in the apparatus of FIG.
[0248]
The image forming apparatus shown in FIGS. 16A and 16B used in the evaluation experiment includes an ion flow type direct electrostatic latent image forming apparatus CR2. The device CR2 attempts to display a corona ion generating part c2 for generating corona ions, a writing electrode e2 for guiding the corona ions generated in the generating part to the surface of the sheet 121, and a positive (or negative) corona ion. And a write electrode control circuit f2 that applies a voltage to the write electrode e2 to guide the pixel 121 on the surface of the sheet 121 in accordance with the image.
[0249]
The corona ion generator c2 stretches a corona wire c22 similar to that in the apparatus CR1 shown in FIG. 14 in the shield case c21, and applies a positive (or negative) voltage from the power source Pc2 to the corona ion to generate corona ions. It is something to be made.
[0250]
The write electrode e2 is provided adjacent to the portion of the shield case c21 facing the first sheet 121 of the medium 12 or 13 type medium (the medium 12 is shown as a representative example in the figure). It consists of an electrode e22, and a corona ion stream can pass through the central through hole.
[0251]
The electrode control circuit f2 includes a control power source Pc21, a bias power source Pc22, and a control unit f21. The control unit f21 applies an ion extraction voltage to the electrodes e21 and e22 according to the polarity of ions to be derived toward the medium 12. Can be applied.
[0252]
Here, when a positive voltage is applied to the upper electrode e21 and a negative voltage is applied to the lower electrode e21 under the instruction of the control unit f21, positive corona ions can be guided to the medium (FIG. 16A). When a negative voltage is applied to the upper electrode e21 and a positive voltage is applied to the lower electrode e21, positive corona ions can be confined (FIG. 16B).
[0253]
Further, an electrode roller R1 is provided so as to face the writing electrode e2, and a positive bias voltage is applied thereto from the power source PW1. The roller R1 incorporates a magnetic pole roller R2 that is rotationally driven.
[0254]
Thus, according to the image to be displayed while moving the medium 12 relative to the apparatus CR2, and rotating the electrode roller R1 in the medium feeding direction and the magnetic pole roller R2 in the opposite direction, the control unit f21 Under the instruction, for a predetermined pixel corresponding portion corresponding to an image to be displayed among a plurality of pixel corresponding portions on the surface of the first sheet 121, as shown in FIG. As for the pixel of, the outflow of ions is prevented as shown in FIG.
[0255]
In the image evaluation experiment, a positive corona ion is led to a predetermined pixel corresponding portion corresponding to an image to be displayed among a plurality of pixel corresponding portions on the surface of the first sheet 121, the portion is charged to + 500V to + 600V, and the like. Only the bias voltage + 250V was applied to the pixels of. As a result, the portion where the positive corona ions are placed is displayed white by the negatively charged white developer particles WP, and the portion where the positive corona ions are not placed is displayed black by the positively charged black developer particles BP, thus displaying an image. It was.
[0256]
The discharge wires c12 and c22 in the devices CR1 and CR2 can be replaced with solid discharge elements.
[0257]
The electrostatic latent image forming apparatuses CR1 and CR2 shown in FIGS. 14 to 16 use the discharge phenomenon. In addition to these apparatuses, various discharge type electrostatic latent image forming apparatuses can be used.
[0258]
Further, the image can be displayed even if the image forming apparatus shown in FIGS. 17 and 18 is adopted instead of the image forming apparatus shown in FIGS.
[0259]
The image forming apparatus in FIG. 17 includes a multi-stylus type direct electrostatic latent image forming apparatus CR3. The apparatus CR3 includes, for example, a multi-stylus head H3 having a plurality of electrodes e3 arranged in the main scanning direction with respect to the medium 13 and arranged close to the first sheet 121. A signal voltage is applied to apply an electrostatic latent image charge to a pixel corresponding portion on the surface of the first sheet 121 according to an image to be displayed on each electrode e3. For example, a bias is applied to the second sheet 122 on the opposite side, and the medium 13 is conveyed relative to the head H3, whereby an image is displayed.
[0260]
The image forming apparatus shown in FIG. 18 includes a charge injection type direct electrostatic latent image forming apparatus CR4. The device CR4 is a multi-stylus type device having an electrostatic recording head H4 in which a plurality of recording electrodes e4 are arranged in the main scanning direction with respect to the medium and an adjacent control electrode e41 is arranged adjacent to the recording electrode e4. For example, this head is disposed close to the medium 13, and a voltage about half of the voltage (recording voltage) necessary for image recording (recording voltage) is sequentially applied to the control electrode e41 of the head H4, and the recording voltage about the recording voltage is applied to the recording electrode e4. By applying a half of the image signal voltage, an electrostatic latent image can be formed on the medium located immediately below the recording electrode.
[0261]
Here, it will be described that the latent image formation is advantageous by taking an image forming apparatus having an external electrostatic latent image forming apparatus as shown in FIG. 11 as an example.
[0262]
An equivalent circuit of the device is shown in FIGS. In these drawings, electrostatic capacitances of an electrostatic latent image carrier such as a photosensitive drum, an image display medium, and an air layer therebetween are denoted as C1, C2, and C0, respectively.
[0263]
Assume that an electrostatic latent image carrier (hereinafter referred to as “image carrier”) is applied with a latent image charge Q (potential V at that time) by a charging charger and an image exposure apparatus.
[0264]
FIG. 19A shows an equivalent circuit in a state where the image carrier and the image display medium are separated from each other. Since C1 and C2 are much larger than C0, the charge Q does not move, and the medium is static. Not affected by the electrostatic latent image.
[0265]
When the image carrier and the medium approach from this state, C0 increases, and the charges charged in C1 and C2 are induced by electrostatic induction, resulting in the state of FIG. FIG. 19B is an equivalent circuit in a state where the image carrier is brought close to the image display medium and electrostatically induced.
[0266]
In the state of FIG. 19B, the potential differences V1, V2, and V0 induced in the image carrier, the medium, and the air layer by the induced charges are expressed by the following equations (1), (2), and (3). It can be expressed as
[0267]
[Expression 1]

[0268]
[Expression 2]

[0269]
[Equation 3]

[0270]
Here, V is a latent image surface potential of the image carrier, and Vb is a bias value.
[0271]
A developer is included in the medium. Since the developer particles carry charge under an electric field, the developer layer apparently approximates a conductive layer. That is, the electrostatic capacity C2 of the medium approximates the combined capacity of the upper and lower resin sheets.
[0272]
Here, in order to transfer the latent image charge of the image carrier to the medium, it is necessary for the air layer to cause dielectric breakdown and to move the charge. If dielectric breakdown does not occur, when the image carrier and the medium are separated from each other, the state returns to the state shown in FIG. 19A and the latent image is not transferred.
[0273]
That is, for example, when V0 is small, particle movement occurs due to an induced electrostatic field, but the latent image is not transferred.
[0274]
For example, in order for an air layer having a gap of 10 μm to cause dielectric breakdown, V0 needs to be about 370 V or more according to Paschen's law.
[0275]
Here, when the bias value Vb = 11000V, V = 1000V, and the ratio of each capacitance is C1: C2: C0 = 18: 5: 12, V0 (potential difference of the air layer) = 480V, Dielectric breakdown occurs and the latent image is transferred.
(However, the ratio of the respective capacitances is considered assuming that the image carrier is a normal organic photoreceptor, the medium is the combined capacity of the above structure, and the air layer has a gap of about 10 μm where dielectric breakdown is likely to occur.)
Thus, the latent image is transferred under the condition that V-Vb is about 1500 V or more. Conversely, under these conditions, electrostatic induction is performed in a state where the image carrier and the medium are close to each other, but the latent image is not transferred.
[0276]
In the electrostatic latent image on the image bearing member, charge movement occurs between the charging portion (1) and the medium, and no charge movement occurs in the non-charging portion (exposure portion) (2). For this reason, a difference occurs in the surface potential on the medium. The surface potential of the medium after the charge transfer of the charging portion (1) is performed is expressed by the following equation (4), and that of the non-charging portion (2) is expressed by the preceding equation (3).
[0277]
FIG. 19C shows an equivalent circuit in a state where charge transfer occurs due to dielectric breakdown. In this state where charge transfer occurs due to dielectric breakdown, the following equation (4) holds.
[0278]
[Expression 4]

[0279]
In Expression (4), V′0 is the minimum potential difference that can be discharged, and V1 and V2 are Expressions (2) and (3).
[0280]
For example, under the set conditions, the surface potential on the medium is about + 265V in the region {circle around (1)} corresponding to the charged portion and about −340V in the region {circle around (2)} corresponding to the non-charged portion.
[0281]
Here, when an arbitrary bias (or ground) is applied to the counter electrode roller, electric fields in opposite directions are formed in the charged portion (1) and the non-charged portion (2), and the developer particles follow the electric field. It can be moved to form an image.
[0282]
Thereafter, when the image carrier and the medium are separated from each other, the induced charge is moved, and the surface potential of the medium is changed. The {circle around (1)} portion returns to about + 275V and the {circle around (2)} portion returns to approximately 0V, so that a latent image can be formed on the medium.
[0283]
The case where the electrostatic latent image carrier is a photosensitive drum (photoconductor) has been described above, but a dielectric drum may be used. The polarity of the electrostatic latent image may be negative. The charged polarity of the developer particles may be reversed.
[0284]
In this way, not only the latent image is brought close to the medium, but also the electrostatic latent image is formed on the medium by transfer, direct formation, etc., so that even after passing through the opposing area of the electrostatic latent image carrier and the counter electrode. It can be seen that image retention is improved because electrostatic attracting force is generated between the developer particles and the reversible image display medium. In short, it is advantageous to form an electrostatic latent image on the medium. In particular, it is advantageous in terms of image retention when a developer having high fluidity or a developer whose fluidity is enhanced by a developer stirring process prior to image display is used.
[0285]
Next, the particle size of the developer particles contained in the developer is preferably an example medium (volume average particle size 1 μm to 50 μm is preferable for non-conductive developer particles, and volume average particle size 1 μm to 100 μm is preferable for magnetic developer particles ( Examples 22 to 30) and comparative example media E13 to E28 will be described.
[0286]
All of these media are the same as those of Example 2, except that the height h of the partition wall 123 is changed to 150 μm, the interval pt between the adjacent partition walls 123a is changed to 250 μm, and the developer particles contained in each cell 124 are variously changed. Is a medium having the same structure as the medium of Example 2.
[0287]
These were also evaluated for image contrast. At that time, using the image forming apparatus shown in FIG. 11, as shown in FIG. 13 (A), an image in which the right half was a black portion (Bk) and the left half was a white portion (W) was formed and evaluated.
[0288]
The contrast evaluation here is very good (◎) when the reflection density ratio (Bk / W) is 9.0 or more, good (良好) when smaller than 9.0, or better than (7.0), smaller than 7.0. A value of .0 or higher was evaluated as slightly defective (.DELTA.), And a value smaller than 5.0 was determined as defective (x).
[0289]
These media and evaluation results are summarized in Table 5. In Table 5, WP1 to WP5 and BP1 to BP5 are non-conductive white developer particles and magnetic black developer particles having the above-described particle sizes, respectively. In Examples 22 to 30, the above-described developers DL1 to DL9 were used, and in Comparative Examples E13 to E28, the above-described comparative developers De1 to De16 were used.
[0290]
In each cell showing the examples and comparative examples in Table 5, the upper right side shows the contrast evaluation result, the middle side shows the reflection image density ratio, the lower side shows the reflection density of the black image portion, and the left side shows the reflection of the white image portion. The concentration is shown.
[0291]
[Table 5]

[0292]
As can be seen from Table 5, the developer particles contained in the developer have a volume average particle size of 1 μm to 50 μm for non-conductive developer particles (here, white particles) and magnetic developer particles (here, black particles). It can be said that the volume average particle diameter is preferably 1 μm to 100 μm.
Next, an image display method for performing image erasure processing before image display will be described. In implementing this image display method, the image display medium of Example 2 (herein referred to as medium 12) was employed.
[0293]
Each of FIG. 20 to FIG. 22 shows an example of an image forming apparatus that implements this image display method. In particular, an image forming apparatus provided with an image erasing apparatus is shown.
[0294]
The image forming apparatus shown in FIG. 20 is the same as the image forming apparatus shown in FIG. 11 (provided that the rotating magnetic pole roller R2 is not provided), but the relative conveyance direction of the medium 12 rather than the area where the photosensitive drum PC and the electrode roller R1 face each other. The image erasing apparatus EL1 is arranged on the upstream side (in the direction of the straight arrow in the figure).
[0295]
The image erasing device EL1 includes a pair of upper and lower electrode rollers R3 and R4. The upper electrode roller R3 is connected to a bias power source PW3. The electrode roller R3 may be grounded. The lower electrode roller R4 is connected to the bias power source PW4. The electrode roller R4 may be grounded.
[0296]
According to this image forming apparatus, an electric field corresponding to the potential difference of the bias applied to the electrode rollers R3 and R4 of the image erasing apparatus EL1 is formed on the medium 12 prior to image display, thereby developing particles having different charged polarities. Of the BP and WP, one particle BP gathers on one sheet side, and the other particle WP gathers on the other sheet side, thereby erasing the image. The medium 12 is fed between the photosensitive drum PC and the counter electrode roller R1 after the image erasing process, and a new image is displayed.
[0297]
An experiment of image erasure and image formation was performed using the apparatus of FIG. 20 under the following conditions.
[0298]
That is, the charged portion potential of the electrostatic latent image on the photosensitive drum PC was −800 V, the uncharged portion (exposed portion) potential was −100 V, and the bias applied to the counter electrode roller R1 was −100 V. In the erasing apparatus EL1, the electrode roller R4 is grounded, and the bias applied to the electrode roller R3 is + 1000V. The developer receives a coulomb at an electric field when passing between the electrode rollers R3 and R4. In this case, since the white particles WP are negatively charged and the black particles BP are positively charged, the white particles move to the upper side in the figure, the black particles move to the lower side in the figure, and the previously displayed image is the entire surface. Will be erased. At this time, when the medium 12 was viewed from the upper side in the figure, the entire surface was white.
[0299]
Thereafter, on the medium 12 on which the entire image has been erased, an electric field is formed in accordance with the electrostatic latent image in a region where the photosensitive drum PC and the electrode roller R1 face each other, and the developer DL receives a coulomb. The charged portion on the photoconductive drum PC generates a 700V upward electric field in the figure due to the potential difference from the bias of the electrode roller R1, the white particles move downward, and the non-charged portion has no potential difference, so the particles move. The white particles remained on the top surface. When the image formed in this way was viewed from the upper side in the figure, the area corresponding to the charged part was a black part, and the area corresponding to the non-charged part was a white part.
[0300]
In this way, an image can be formed simply by moving the developing particles according to the charging portion. For this reason, the electric field strength for moving the developing particles can be increased.
[0301]
The experiment was also performed under the following conditions. That is, the charged portion potential of the photosensitive drum PC was −800 V, the non-charged portion (exposed portion) potential was −100 V, and the bias applied to the counter electrode port R1 was −800 V. In the erasing apparatus EL1, the bias of the electrode roller R4 is +1000 V, and the electrode roller R3 is grounded.
[0302]
In this case, after the medium 12 passed between the electrode rollers R4 and R3, the white particles moved to the lower side in the figure and the black particles moved to the upper side in the figure, and the previously displayed image was erased over the entire surface. At this time, when the medium 12 was viewed from the upper side in the figure, the entire surface was black.
[0303]
Thereafter, a non-charged portion of the photosensitive drum PC forms a downward electric field of 700 V in the figure due to a potential difference from the bias of the counter electrode roller R1, and white particles move upward. It did not move and the white particles remained below. When the image formed in this way was viewed from the upper side in the figure, the region corresponding to the charged portion was a black portion, and the region corresponding to the non-charged portion was a white portion.
[0304]
In the image forming apparatus of FIG. 21, the electrode roller R1 is opposed to the ion flow type electrostatic latent image forming apparatus CR1 shown in FIG. 14, and the same image erasing apparatus EL1 as shown in FIG. Is provided.
[0305]
The image forming apparatus shown in FIG. 22 is the same as the image forming apparatus shown in FIG. 20, except that a rotating magnetic pole roller R2 is built in the lower electrode roller R4 of the erasing device EL1. The other points are the same as the apparatus of FIG. The rotating magnetic pole roller R2 is rotationally driven in one direction or reciprocally rotated to form an oscillating magnetic field with respect to the medium 12. As a result, the developer DL is agitated by affecting the black magnetic developer particles BP. By stirring the developer, the triboelectric charge amount of the developing particles is increased, the moving speed due to the Coulomb force in image display is increased, the flowability of the developing particles is improved, and the moving efficiency of the developing particles is increased.
[0306]
The image erasing apparatus can also be applied to the image forming apparatus shown in FIGS.
Next, an image display method for stirring the developer for image display will be described. In implementing this image display method, the image display medium of Example 2 (herein referred to as medium 12) was employed.
[0307]
Each of FIG. 23 to FIG. 29 shows an example of an image forming apparatus that implements this image display method. In particular, an image forming apparatus including a developer stirring device is shown. In the image forming apparatus shown in FIG. 4, the rotating magnetic pole roller R2 is provided. In the image forming apparatus shown in FIG. 11, the rotating magnetic pole roller R2 is built in the developing electrode roller R1 facing the photosensitive drum PC. The magnetic roller R2 also functions as a developer stirring device when the R2 is rotationally driven in one direction or reciprocally rotated.
[0308]
First, an experimental example in which the developer is stirred and an image is displayed using the image forming apparatus shown in FIG. 11 will be described.
[0309]
The charged portion potential of the photosensitive drum PC was + 500V, the non-charged portion (exposed portion) potential was + 100V, and the bias applied to the developing electrode roller R1 was + 300V. Further, the magnetic pole roller R2 inside the electrode roller R1 was rotated in the left direction (counterclockwise) in the drawing, with a maximum magnetic flux density of 400 gauss, a magnetic pole number of 8, and a rotational speed of about 100 rpm.
[0310]
Under such conditions, the white particles WP corresponding to the charged sites are subjected to a force upward in the figure against the direction of the electric field, and the black particles BP are subjected to a force downward in the figure along the direction of the electric field, and at the same time, the black particles BP Was disturbed by the oscillating magnetic field, and the developed particles moved efficiently.
[0311]
The image forming apparatus of FIG. 23 has a developing electrode roller R1 disposed opposite to the ion flow type electrostatic latent image forming apparatus CR1 in the image forming apparatus shown in FIG. 14, and a rotating magnetic pole roller R2 is incorporated in the roller. Is.
[0312]
In this apparatus, experiments of developer agitation and image display were performed under the following conditions. That is, the charged portion potential of the medium 12 was +500 V, the non-charged portion (exposed portion) potential was about 0 V, and the bias applied to the electrode roller R1 was +300 V. The magnetic pole roller R2 was rotated in the left direction (counterclockwise) in the drawing with a maximum magnetic flux density of 400 gauss, a magnetic pole number of 8, and a rotational speed of about 100 rpm.
[0313]
Under such conditions, the white particles WP corresponding to the charged portion receive a force upward in the figure against the direction of the electric field, and the black particles BP simultaneously receive a force downward in the figure along the direction of the electric field, and at the same time, the black particles BP Was stirred by the oscillating magnetic field, and the developed particles moved efficiently.
[0314]
The image forming apparatus described above can be broadly grasped as a static image corresponding to an image to be displayed on the outer surface of one of the two sheets of the reversible image display medium. In this example, an electrostatic latent image is formed and formed simultaneously with the formation of the electrostatic latent image based on the electrostatic latent image, and the developer is stirred simultaneously with the formation of the electrostatic field.
[0315]
The image forming apparatus shown in each of FIGS. 24 and 25 to be described next broadly captures the electrostatic field formed in the image display process on either outer surface of two sheets of the reversible image display medium. After forming an electrostatic latent image corresponding to the image to be displayed, the electrostatic latent image is formed based on the electrostatic latent image, and the developer is stirred to form the electrostatic latent image and then simultaneously with the electrostatic field formation. Is.
[0316]
In the image forming apparatus of FIG. 24, a transfer electrode roller R5 for transferring an electrostatic latent image is disposed at a position where the developing electrode roller R1 is located in the image forming apparatus of FIG. 11, and the photosensitive drum PC, the transfer electrode roller R5, and the like. A developing electrode roller R1 for forming an electrostatic field and a rotating magnetic pole roller R2 built in the developing electrode roller R2 are disposed downstream of the facing region.
[0317]
A bias power source PW5 is connected to the transfer electrode roller R5, and a bias power source PW1 is connected to the electrode roller R1.
[0318]
In the image forming apparatus of FIG. 25, the counter electrode roller R5 for transferring the electrostatic latent image is disposed at the position where the developing electrode roller R1 is located in the image forming apparatus of FIG. A developing electrode roller R1 for forming an electrostatic field and a rotating magnetic pole roller R2 incorporated in the developing electrode roller R2 are arranged downstream of the region facing the roller R5.
[0319]
A bias power source PW5 is connected to the counter electrode roller R5, and a bias power source PW1 is connected to the electrode roller R1.
[0320]
24 and 25, after the electrostatic latent image is formed on the medium 12 in the region where the photosensitive drum PC or the electrostatic latent image forming device CR1 and the transfer (counter) electrode roller R5 face each other. When the medium comes into contact with the developing electrode roller R1, an electrostatic field for each pixel is formed according to the electrostatic latent image, thereby displaying an image. At this time, the magnetic pole roller R2 is rotationally driven in one direction or reciprocally driven to generate an oscillating magnetic field, and an image is displayed while developing particles are stirred by the influence of the magnetic field. As the developer particles are stirred, the charge amount of the developer particles is increased, and the fluidity of the developer particles is improved. As a result, images are displayed smoothly and satisfactorily.
[0321]
The magnetic pole roller R2 may be disposed between the electrode rollers R1 and R5.
[0322]
The image forming apparatus shown in FIG. 26 and FIG. 27 to be described next will display the electrostatic field formed in the image display process on the outer surface of one of the two sheets of the reversible image display medium. An electrostatic latent image corresponding to the image to be formed is formed, and formed based on the electrostatic latent image simultaneously with the electrostatic latent image formation or after the electrostatic latent image formation. This is an example performed before forming a latent image.
[0323]
The image forming apparatus shown in FIG. 26 does not include a magnetic pole roller in the electrode roller R1 in the image forming apparatus shown in FIG. 11, and a rotating magnetic pole roller R2 is disposed upstream of the region where the photosensitive drum PC and the electrode roller R1 are opposed to each other. Is. The magnetic pole roller R2 is rotationally driven in one direction or reciprocally rotated, thereby forming an oscillating magnetic field for stirring the developer.
[0324]
A bias power supply PW1 is connected to the electrode roller R1.
[0325]
In this image forming apparatus, when the charged portion potential of the photosensitive drum PC is +500 V, the non-charged portion (exposure portion) potential is +100 V, and the bias applied to the developing electrode roller R1 is +300 V, the white particles corresponding to the charged portion have an electric field. The black particles moved upward along the direction of the electric field and downward along the direction of the electric field. Since the developing particles are agitated in advance, the charge amount is increased and the fluidity is improved, and the developer particles move efficiently.
[0326]
The image forming apparatus in FIG. 27 is the same as the image forming apparatus in FIG. 24 except that the rotating magnetic pole roller R2 is disposed upstream of the region where the photosensitive drum PC and the electrode roller R5 are opposed. The magnetic pole roller R2 is driven to rotate in one direction or is driven to reciprocate.
This creates an oscillating magnetic field that agitates the developer.
[0327]
The image forming apparatus shown in FIG. 28 is an image forming apparatus provided when there is a possibility that the magnetic developer particles BP may be biased to any one in the developer containing cell due to the magnetic field generated by one magnetic pole roller R2. If this apparatus is grasped extensively, a plurality (two in this case) of developer agitating devices that form an oscillating magnetic field are sequentially provided along the medium conveyance direction.
[0328]
In the example shown in FIG. 28, in the image forming apparatus shown in FIG. 11, two developing magnetic pole rollers R1 incorporating a rotating magnetic pole roller R2 are arranged opposite to the photosensitive drum PC. Power sources PW1, PW 'are connected to the rollers R1, R1. The two rotating magnetic pole rollers R2 are rotationally driven in opposite directions. Thereby, the bias | inclination in the cell of a magnetic developing particle (here black particle BP) can be suppressed.
[0329]
In the image forming apparatus shown in FIG. 29, in place of the developing electrode roller R1 and the magnetic pole roller R2 in the image forming apparatus shown in FIG. 24, a magnet member Mg provided with alternating N and S poles is provided downstream of the photosensitive drum PC. Further, it is arranged so as to be in contact with the incoming medium 12, and a developing bias power supply PW1 "is connected to the member Mg.
[0330]
As the medium 12 moves relative to the member Mg, an oscillating magnetic field is formed on the medium 12.
Next, when an image is displayed, an electrostatic latent image is formed on the surface (sheet surface) of the image display medium, and the surface of the medium is uniformly charged to a predetermined potential before the electrostatic latent image is formed. An image display method for forming a latent image will be described. In carrying out this image display method, the image display medium of Example 2 (herein referred to as medium 12) was employed.
[0331]
Each of FIG. 30 and FIG. 31 shows an example of an image forming apparatus that implements this image display method. In particular, an image forming apparatus including a charging device that uniformly charges a medium surface to a predetermined potential before forming an electrostatic latent image is shown.
[0332]
The image forming apparatus shown in FIG. 30 does not include the magnetic pole roller R2 in the developing electrode roller R1 in the image forming apparatus shown in FIG. 11, and the preliminary charging device 2 is located upstream from the region where the photosensitive drum PC and the electrode roller R1 face each other. It is equipped with. The charging device 2 includes a charger 21 facing the surface of the conveyed medium 12 on the electrostatic latent image forming side, and a ground electrode 22 facing the medium passage with the medium passage therebetween. The electrode roller R1 may be grounded depending on circumstances.
[0333]
The image forming apparatus shown in FIG. 31 is the same as the image forming apparatus shown in FIG. 21, except that the image erasing apparatus EL1 on the upstream side of the electrostatic latent image forming apparatus CR1 is provided with the same preliminary charging device 2 as described above. The electrode roller R1 may be grounded depending on circumstances.
[0334]
In these image forming apparatuses, the surface of the medium 12 is uniformly charged in advance by a preliminary charging device prior to image display. Thereafter, in the example of FIG. 30, the electrostatic latent image formed on the photosensitive drum PC is transferred and written in the charged area. In the example of FIG. 31, the electrostatic latent image is written by the electrostatic latent image forming apparatus CR1. In any example, the area charged uniformly in advance and the area where the electrostatic latent image is written later have opposite polarities. By setting the bias of the electrode roller R1 to the ground or appropriately setting the potential, the direction of the electric field differs between the area where the electrostatic latent image is written and the area where the electrostatic latent image is not written, thereby moving the developing particles to form an image. be able to.
[0335]
In the example shown in FIG. 30, the dielectric breakdown inside the medium 12 can be prevented by charging the surface of the medium 12 uniformly with a polarity opposite to the polarity of the electrostatic latent image formed later. The latent image can be transferred reliably. As described above, since the electrostatic latent image is reliably transferred, the image retention is improved.
[0336]
In the example shown in FIG. 31, the potential difference between the image portion and the non-image portion can be increased when forming the electrostatic latent image. For example, the negatively charged uniform charged portion by preliminary charging by the charging device 2 is set to -1000 V, the positive charged portion by electrostatic latent image writing is set to +1000 V, and the bias of the electrode roller R1 is grounded, thereby preventing the image portion from being non-imaged. Each image portion has a potential difference of 1000 V, which can drive the developing particles. Thus, the developing particle driving electric field can be increased, and the moving speed of the developing particles can be increased.
[0337]
It should be noted that the area charged uniformly in advance and the area where the electrostatic latent image is written later may have the same polarity. In this case, by setting the bias of the electrode roller R1 to an intermediate potential between the area where the electrostatic latent image is written and the area where the electrostatic latent image is not written, the direction of the electric field is different in both areas, and an image can be formed. .
[0338]
The area where the electrostatic latent image is written later may be 0V. Also in this case, by setting the bias of the electrode roller R1 to an intermediate potential between the area where the electrostatic latent image is written and the area where the electrostatic latent image is not written, the direction of the electric field is different in both areas, and an image can be formed.
[0339]
Thus, since the medium 12 passes through the photosensitive drum PC or the area where the electrostatic latent image forming apparatus CR1 and the electrode roller R1 face each other, an electrostatic attracting force is generated between the developer particles and the sheet of the medium. Good retention.
[0340]
Note that the polarity of the electrostatic latent image to be formed may be negative.
[0341]
The charging polarity of the black and white developing particles may be reversed.
[0342]
Further, the electrostatic latent image forming apparatus is not limited to the one shown in FIGS. 30 and 31, and the other electrostatic latent image forming apparatus described above can be adopted.
Here, it is advantageous to uniformly charge the surface of the medium before forming the electrostatic latent image on the surface of the medium and form an electrostatic latent image in the charged area, as shown in FIG. An image forming apparatus provided with an electrostatic latent image forming apparatus will be described as an example.
[0343]
An equivalent circuit of the device is shown in FIGS. In these drawings, electrostatic capacitances of an electrostatic latent image carrier such as a photosensitive drum, an image display medium, and an air layer therebetween are denoted as C1, C2, and C0, respectively.
[0344]
The electrostatic latent image carrier (hereinafter referred to as “image carrier”) is charged with a charging charger and an image exposure device, and the latent image charge Q (the potential V at that time) is preliminarily charged to the medium with a preliminary charging device. Is applied.
[0345]
FIG. 32A shows an equivalent circuit in which the image carrier and the image display medium are separated from each other. Since C1 and C2 are very large compared to C0, the charge Q does not move, and the medium is static. Not affected by the electrostatic latent image.
[0346]
When the image carrier and the medium approach from this state, C0 increases, and the charges charged in C1 and C2 are induced by electrostatic induction, resulting in the state of FIG. FIG. 32B is an equivalent circuit in a state where the image carrier is brought close to the image display medium and electrostatically induced.
[0347]
In the state of FIG. 32B, the potential differences V1, V2, and V0 induced in the image carrier, the medium, and the air layer by the induced charges are expressed by the following equations (5), (6), and (7). It can be expressed as Here, let us consider a case where a ground is applied without applying a bias.
[0348]
[Equation 5]

[0349]
[Formula 6]

[0350]
[Expression 7]

[0351]
Here, V is the latent image surface potential of the image carrier, and V 'is the surface potential of the medium.
[0352]
A developer is included in the medium. Since the developer particles carry charge under an electric field, the developer layer apparently approximates a conductive layer. That is, the electrostatic capacity C2 of the medium approximates the combined capacity of the upper and lower resin sheets.
[0353]
Here, in order to transfer the latent image charge of the image carrier to the medium, it is necessary for the air layer to cause dielectric breakdown and to move the charge. If dielectric breakdown does not occur, when the image carrier and the medium are separated from each other, the state returns to the state shown in FIG. 32A and the latent image is not transferred.
[0354]
That is, for example, when V0 is small, particle movement occurs due to an induced electrostatic field, but the latent image is not transferred.
[0355]
For example, in order for an air layer having a gap of 10 μm to cause dielectric breakdown, V0 needs to be about 370 V or more according to Paschen's law.
[0356]
Here, when V = 1000V, V ′ = − 1000V, and the ratio of the respective capacitances is C1: C2: C0 = 18: 5: 12, V0 (potential difference of the air layer) = 480 V, and dielectric breakdown occurs. Then, the latent image is transferred. Further, the potential difference applied to the medium is about 200 V, and dielectric breakdown inside the medium can be prevented. (However, the ratio of the respective capacitances is considered assuming that the image carrier is a normal organic photoreceptor, the medium is the combined capacity of the above structure, and the air layer has a gap of about 10 μm where dielectric breakdown is likely to occur.)
In the electrostatic latent image on the image bearing member, charge movement occurs between the charging portion (1) and the medium, and no charge movement occurs in the non-charging portion (exposure portion) (2). For this reason, a difference occurs in the surface potential on the medium. The surface potential of the medium after the charge transfer of the charging portion (1) is performed is expressed by the following equation (8), and that of the non-charging portion (2) is expressed by the preceding equation (7).
[0357]
FIG. 32C shows an equivalent circuit in a state where charge transfer occurs due to dielectric breakdown. In this state where charge transfer occurs due to dielectric breakdown, the following equation (8) holds.
[0358]
[Equation 8]

[0359]
In Equation (8), v0 is the minimum potential difference that can be discharged, and V1 and V2 are Equations (6) and (7).
[0360]
For example, under the set conditions, the surface potential on the medium is about +260 V in the region {circle around (1)} corresponding to the charged portion and about −340V in the region {circle around (2)} corresponding to the non-charged portion.
[0361]
Here, when the counter electrode roller is grounded, electric fields opposite to each other are formed in the areas of the charging portion (1) and the non-charging portion (2), and the developer particles move along the electric field to form an image. be able to.
[0362]
Thereafter, when the image carrier and the medium are separated from each other, the induced charge is moved, and the surface potential of the medium is changed. The {circle around (1)} portion returns to about −720V and the {circle around (2)} portion returns to about −1000 V, and a latent image can be formed on the medium (see FIG. 32D).
[0363]
Although the above description has been made with the counter electrode roller R1 in a grounded state, an appropriate bias can be applied to the roller. In this case, V ′ may be replaced with V ′ + Vb. FIG. 32E shows an equivalent circuit in this case.
[0364]
Further, although the case where the electrostatic latent image carrier is a photosensitive drum (photoconductor) has been described, a dielectric drum may be used. The polarity of the electrostatic latent image may be negative. The charged polarity of the developer particles may be reversed.
[0365]
In this way, before the latent image is transferred by causing dielectric breakdown between the electrostatic latent image carrier and the medium, the surface of the medium is uniformly charged to a predetermined potential in advance, thereby suppressing the potential difference inside the medium. This can improve the image retention.
Next, still another example of the reversible image display medium will be described with reference to FIGS. 33 and 34. FIG.
[0366]
A reversible image display medium 14 shown in FIG. 33 is an example of an electrophoretic medium.
[0367]
The medium 14 includes an electric field coloring layer 140 supported on a transparent support substrate 146. The electric field coloring layer 140 is obtained by sealing a liquid layer 143 in which charged colored particles 141 are dispersed in an insulating liquid 142 between the transparent conductive layer 144 and the insulating layer 145. The insulating liquid 142 is obtained by mixing an organic substance containing an ionic surfactant and a dye with high-purity petroleum (trade name Isopar, Esso). The ionic surfactant is adsorbed on the organic colored particles 141 containing the pigment, and the particles are stably charged electrochemically. The charged colored particles 141 are dispersed in the liquid 142 and exhibit electrophoretic properties.
[0368]
The medium 14 shows the color of the dye in the insulating liquid 142 when no electric field is applied or when an electric field opposite to the predetermined electric field is applied. However, when the electrostatic latent image is written, the medium 14 is charged. The colored particles 141 move toward the transparent conductive layer 144 and the pigment is visible.
[0369]
For the image display on the medium 14, for example, using the image forming apparatus shown in FIG. 30 or FIG. 31, the surface of the medium 14 is uniformly charged to a predetermined potential in advance before the image display. An electrostatic latent image EI is formed and corresponds to an image to be displayed on charged developing particles (here, charged colored particles) 141 dispersed in the insulating liquid 142 in the medium based on the electrostatic latent image. An image can be displayed by forming a predetermined electrostatic field for each pixel.
[0370]
In this way, the surface of the medium 14 is charged in advance prior to the formation of the electrostatic latent image, and the electrostatic latent image is formed in the charged region, so that the preliminary charging is performed as in the image display by the conventional electrophoretic image display medium. As compared with the case where the image is formed without the image retention, the image retention is improved.
[0371]
A reversible image display medium 15 shown in FIG. 34 is an example of a rotating particle sphere display medium.
[0372]
This medium 15 has an electric field coloring layer 150 supported by a transparent support substrate 156. The electric field coloring layer 150 surrounds a single-sided colored sphere 151 colored 151a on one side with an insulating liquid 152 and embeds the liquid together in an insulating holding medium 153, and a transparent conductive layer 154 on one side of the medium 153 and an opposite side. An insulating layer 155 is formed.
[0373]
One-side colored sphere 151 is, for example, TiO₂It is produced by uniformly arranging white spheres of glass mainly composed of and depositing chromium or the like from the upper surface. The size may be in the range of 30 μm to 100 μm, but if it is 10 μm or less, the resolution becomes higher.
[0374]
The single-sided colored sphere 151 is dispersed in an insulating holding medium 153 such as an elastomer, and the medium 153 is swollen by immersing it in a solution obtained by dissolving an ionic surfactant in an organic solvent such as toluene. Thereby, the insulating liquid 152 is accumulated around the single-sided colored sphere 151. Thus, the single-sided colored sphere 151 is surrounded by the insulating liquid layer 152, and a state where the liquid is embedded in the insulating holding medium 153 in a rotatable state is obtained.
[0375]
Since the single-sided colored sphere 151 has different properties on one hemispherical surface and the other hemispherical surface, the amount of ions adsorbed on both surfaces is different. Therefore, when an electric field is applied to the medium 15, the direction of the surface of the single-sided colored particle 151 changes depending on the direction of the electric field. Therefore, an image is displayed when the colored surface of the single-sided colored sphere 151 is seen or the uncolored surface is seen.
[0376]
For the image display using the medium 15, for example, using the image forming apparatus shown in FIGS. 30 and 31, the surface of the medium 15 is uniformly charged to a predetermined potential in advance before the image display. An electrostatic latent image EI is formed, and a predetermined electrostatic field is generated for each pixel corresponding to an image to be displayed on the single-sided colored sphere 151 floating in the insulating liquid 152 in the medium based on the electrostatic latent image. An image can be displayed by forming. As a result, the image can be displayed with good image retention.
[0377]
Image display and image deletion can be repeated for the media 14 and 15.
[0378]
Note that the mediums 14 and 15 may form images with the other image forming apparatuses described above as long as the images can be displayed satisfactorily.
[0379]
【The invention's effect】
As described above, according to the present invention, a reversible image display method and a reversible image display medium having the following advantages can be provided.
(1) Image display and image erasure can be performed repeatedly. Therefore, it is possible to reduce the use of image display media such as paper, developer, ink and other consumables related to conventional image display. It can respond to the environmental load reduction.
(2) An image with excellent contrast, high resolution and high quality can be stably displayed over a long period of time.
(3) Afterimages are unlikely to occur, thus exhibiting good reversibility, and a high-quality image can also be displayed in this respect.
[0380]
In particular, according to the reversible image display method according to the present invention, when displaying an image, the surface of the image display medium is uniformly charged to a predetermined potential in advance, and an electrostatic latent image is written in the charged area. The image retention is improved, and in this respect, a high-quality image having further excellent contrast can be stably displayed over a long period of time.
[Brief description of the drawings]
FIG. 1A to FIG. 1I are diagrams showing examples of the shape of a developer containing cell.
FIGS. 2A to 2H are diagrams showing examples of shapes and arrangements of developer movement suppressing members, respectively. FIG. (I) is a diagram showing an example of the medium unit area Sb and the image portion area Sa by the cells therein.
FIG. 3 is a cross-sectional view of an example of a reversible image display medium with electrodes before image display.
4 is a cross-sectional view of an image display state of the medium shown in FIG.
5 is a perspective view of a second sheet in the medium shown in FIG. 3 and a lattice-shaped partition wall formed on the second sheet. FIG.
6 is a plan view of a second sheet and individual electrodes formed thereon in the medium shown in FIG. 3;
7 is a diagram showing an image display example of the medium shown in FIG. 3; FIG.
FIG. 8 is a cross-sectional view of another example of a reversible image display medium. FIG. 8A is a cross-sectional view of the reversible image display medium before image display, and FIG. 8B is a cross-sectional view of an example during image display.
FIG. 9 is a plan view showing a part of the medium shown in FIG.
10 is a diagram showing an image display example of the medium shown in FIG. 8. FIG.
FIG. 11 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including an external electrostatic latent image forming apparatus.
FIG. 12 is a cross-sectional view of still another example of a reversible image display medium according to the present invention.
13A is a plan view showing still another example of image display, and FIG. 13B shows the ratio of the non-image area (non-image area / medium unit area) to the reflection density ratio. It is a graph which shows a relationship.
FIG. 14 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including an ion flow type direct electrostatic latent image forming apparatus.
FIG. 15 is a diagram showing a schematic configuration of another example of an image forming apparatus having an ion flow type direct electrostatic latent image forming apparatus.
FIG. 16 is a diagram showing a schematic configuration of still another example of an image forming apparatus including an ion flow type direct electrostatic latent image forming apparatus.
FIG. 17 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a multi-stylus type direct electrostatic latent image forming apparatus.
FIG. 18 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a multi-stylus type electrostatic latent image forming apparatus having adjacent control electrodes.
FIG. 19 is a diagram illustrating an equivalent circuit of an image forming apparatus including an external electrostatic latent image forming apparatus. FIG. (A) is an equivalent circuit in a state where the image carrier and the image display medium are separated from each other. FIG. (B) is an equivalent circuit in a state where the image carrier is brought close to the image display medium and electrostatically induced. (C) is an equivalent circuit in a state where charge transfer occurs due to dielectric breakdown, and FIG. (D) is an equivalent circuit in a state where the image carrier and the medium are separated after charge transfer.
FIG. 20 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including an image erasing apparatus.
FIG. 21 is a diagram illustrating a schematic configuration of another example of an image forming apparatus including an image erasing apparatus.
FIG. 22 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including an image erasing apparatus.
FIG. 23 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a developer stirring device.
FIG. 24 is a diagram illustrating a schematic configuration of another example of an image forming apparatus including a developer stirring device.
FIG. 25 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including a developer stirring device.
FIG. 26 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including a developer stirring device.
FIG. 27 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including a developer stirring device.
FIG. 28 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including a developer stirring device.
FIG. 29 is a diagram illustrating a schematic configuration of still another example of an image forming apparatus including a developer stirring device.
FIG. 30 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including a preliminary charging device.
FIG. 31 is a diagram illustrating a schematic configuration of another example of an image forming apparatus including a preliminary charging device.
FIG. 32 is a diagram illustrating an equivalent circuit in a case where a medium is charged before forming an electrostatic latent image in an image forming apparatus including an external electrostatic latent image forming apparatus. FIG. (A) is an equivalent circuit in a state where the image carrier and the image display medium are separated from each other. FIG. (B) is an equivalent circuit in a state where the image carrier is brought close to the image display medium and electrostatically induced. (C) is an equivalent circuit in a state where charge transfer occurs due to dielectric breakdown, FIG. (D) is an equivalent circuit in which the image carrier and the medium are separated after charge transfer, and FIG. (E) is a case where the counter electrode roller is grounded. Is an equivalent circuit.
FIG. 33 is a partial cross-sectional view of still another example of a reversible image display medium.
FIG. 34 is a partial cross-sectional view of still another example of a reversible image display medium.
[Explanation of symbols]
CE1 Developer groove containing continuous groove
w1 partition wall
S Image display medium
CE2 Independent type cell
α Partition wall thickness
pt Distance between adjacent partition walls
h Partition wall height
CL1, CL2, CL3, CL4 Developer movement restraining member
β1, β2 Vertical and horizontal dimensions of columnar developer movement suppression member
γ1, γ2 Vertical and horizontal dimensions of one unit of image display area
DL, DLo Developer
WP White developer particles
BP Black developer particles
11 Reversible image display medium
111 1st sheet
112 2nd sheet
113 Bulkhead
114 First electrode
115 Second electrode
115a Individual electrode (pixel electrode)
116 Developer storage cell
110 Lead part
117 Electrode selection circuit
118a Positive drive voltage generation circuit
118b Negative drive voltage generation circuit
119 Display data control unit
Bk black display part
W White display part
12 Reversible image display medium
121 1st sheet
122 2nd sheet
123 Bulkhead
123a Vertical partition wall
124 Developer storage cell
120 Sealing part
120a Sealing part 120 part
PC photoconductor drum
CH Scorotron charger
EX Laser image exposure equipment
IR eraser lamp
R1 electrode roller
R2 Rotating magnetic pole roller
PW1 Bias power supply
13 Reversible image display medium
122A conductive film
CR1 ion flow type direct electrostatic latent image forming device
c1 Corona ion generator
c11 Shield case
c12 corona wire
e1 Write electrode
f1 Write electrode control circuit
Ea Grounding electrode
CR2 ion flow type direct electrostatic latent image forming device
c2 Corona ion generator
e2 Write electrode
f2 Write electrode control circuit
c21 shield case
c22 corona wire
Pc2 power supply
e21 Upper electrode
e22 Lower electrode
Pc21 control power supply
Pc22 Bias power supply
f21 control unit
R3 electrode roller
PC20 power supply
CR3 Multi-stylus type direct electrostatic latent image forming apparatus
e3 electrode
H3 Multi-stylus head
Multi-stylus type electrostatic latent image forming apparatus having CR4 adjacent control electrode
e4 recording electrode
e41 Control electrode
H4 electrostatic recording head
EL1, EL2 Image erasing device
R5 transfer electrode roller
PW5 power supply
Member with Mg N pole and S pole alternately
PW1 'Development bias power supply
2 Preliminary charging device
21 Charger
22 Ground electrode
14 Electrophoretic reversible image display medium
140 Electric field coloring layer
141 charged colored particles
142 Insulating liquid
143 liquid layer
144 Transparent conductive layer
145 Insulating layer
146 Support substrate
15 Rotating particle sphere type reversible image display medium
150 Electric field coloring layer
151 Single-sided colored sphere
151a coloring
152 Insulating liquid
153 Insulating holding medium
154 Transparent conductive layer
155 Insulation layer
156 Support substrate

Claims (3)

Two sheets facing each other with a predetermined gap, at least one of which is light transmissive,
One or more developer containing cells formed between the two sheets and surrounded by a partition wall;
A dry developer contained in each cell;
Have
The dry developer contains at least two types of dry developing particles having triboelectric charging properties having different charging polarities and different optical reflection densities.
A reversible image display medium,
Preparing a reversible image display medium in which at least two types of dry developer particles constituting the dry developer in the developer containing cell are frictionally charged to different charging polarities;
A charging step of uniformly charging the sheet surface of the reversible image display medium to a predetermined potential;
An electrostatic latent image corresponding to the image to be displayed is formed on the surface of the sheet charged in the charging step, and an image to be displayed on the developer particles in the developer containing cell is formed based on the electrostatic latent image. A step of displaying the image by moving the developing particles by forming a predetermined electrostatic field for each corresponding pixel;
A reversible image display method comprising:   The reversible image display method according to claim 1, wherein the electrostatic latent image on the sheet is directly formed on the surface of the sheet charged in the charging step.   The electrostatic latent image on the sheet is a sheet obtained by charging the electrostatic latent image formed in correspondence with the image to be displayed on the electrostatic latent image carrier outside the reversible image display medium in the charging step. The reversible image display method according to claim 1, wherein the reversible image is transferred and formed on the surface.

Images