JP4192591B2 - Image forming apparatus - Google Patents

Description

【００３７】
上記表１から分かるように、実施例の板状グリッドを用いた場合と比較例の板状グリッドを用いた場合では、１０万枚プリント相当後の電位差はあまり変わらないものの、３０万枚プリント相当後では、実施例のものが電位差５Ｖであるのに対し、比較例のものでは電位差３０Ｖと非常に大きくなり、５０万枚プリント相当後では、実施例のものが電位差１５Ｖに抑えられているものの、比較例のものは電位差７５Ｖと非常に大きくなっている。
【００３８】
また、実際に画像の形成を行って画質を評価してみた結果、実施例のものでは、５０万枚プリント相当後でも錆や析出物などの発生がなく、画質も何ら問題なかった。これに対して、比較例のものでは、１０万枚プリント相当後までは特に問題なかったものの、３０万枚プリント相当後ではハーフトーン画質に斑が発生し始め、５０万枚プリント相当後では錆状の析出物が発生した箇所で画像の白抜けが認められた。以上の結果からも、本発明の実施形態に係る板状グリッド１２３を用いた帯電器１２を画像形成装置に搭載することにより、帯電特性を長期にわたって良好に維持できることが確認された。
【００３９】
続いて、本発明の実施形態に係る画像形成装置に適用して好適な感光体の構成について説明する。図４は本発明の実施形態に係る画像形成装置に適用される感光体の構成例を示す断面図である。図示した感光体１１の構成においては、導電性支持体１１１上に下引き層１１２を介して形成される感光層１１３が、少なくとも電荷発生層１１４と電荷輸送層１１５とを含む２層以上の層（多層）に機能分離された層構成としている。
【００４０】
導電性支持体１１１としては、アルミニウム、ニッケル、クロム、ステンレス鋼等の金属類、及びアルミニウム、チタニウム、ニッケル、クロム、ステンレス、金、バナジウム、酸化錫、酸化インジウム、ＩＴＯ等の薄膜を設けたプラスチックフィルム等、あるいは導電性付与剤を塗布又は含浸させた紙及びプラスチックフィルム等があげられる。これらの導電性支持体１１１は、ドラム状、シート状、プレート状等適宜の形状のものとして使用されるが、これらに限定されるものではない。さらに必要に応じて導電性支持体１１１の表面は、画質に影響のない範囲で各種の処理を行うことができる。例えば、表面の酸化処理や薬品処理、及び着色処理等又は、砂目立て等の乱反射処理等を行うことができる。
【００４１】
下引き層１１２は、必用に応じて導電性支持体１１１と電荷発生層１１４との間に設けられるものである。この下引き層１１２は、感光層１１３を帯電器１２で帯電させるときに、導電性支持体１１１から感光層１１３への電荷の注入を阻止すると共に、感光層１１３を導電性支持体１１１に対して一体的に接着保持させる接着層としての作用、或いは場合によっては導電性支持体１１１の光の反射光防止作用等を示す。下引き層１１２を構成する樹脂及びその他の材料としては、ポリエチレン樹脂，ポリプロピレン樹脂、アクリル樹脂、メタクリル樹脂、ポリアミド樹脂、塩化ビニル樹脂、酢酸ビニル樹脂、フェノール樹脂、ポリカーボネート樹脂、ポリウレタン樹脂、ポリイミド樹脂、塩化ビニリデン樹脂、ポリビニルアセタール樹脂、塩化ビニル−酢酸ビニル共重合体、ポリビニルアルコール樹脂、水溶性ポリエステル樹脂、ニトロセルロース、カゼイン、ゼラチン、ポリグルタミン酸、澱粉、スターチアセテート、アミノ澱粉、ポリアクリル酸、ポリアクリルアミド、ジルコニウムキレート化合物、チタニルキレート化合物、チタニルアルコキシド化合物その他の有機チタニル化合物、シランカップリング剤等の公知の材料を用いることができる。下引き層１１２の膜厚は０．０１〜１０μｍ、好ましくは０．０５〜２μｍが適当である。塗布方法としては、ブレードコーティング法、マイヤーバーコーティング法、スプレーコーティング法、浸漬コーティング法、ビードコーティイング法、エアーナイフコーティイング法、カーテンコーティング法等の通常の方法を用いることができる。
【００４２】
電荷発生層１１４は、電荷発生材料を結着樹脂中に分散して構成される。電荷発生材料としては、非晶質セレン、結晶性セレン−テルル合金、その他セレン化合物及びセレン合金、酸化亜鉛、酸化チタン等の無機系光導電性材料、フタロシアニン系、スクアリウム系、アントアントロン系、ペリレン系、アゾ系、アントラキノン系、ピレン系、ピリリウム塩、チアピリリウム塩等の有機顔料及び染料が用いられる。電荷発生層における結着樹脂としては、ポリビニルブチラール樹脂、ポリビニルホルマール樹脂、部分変性ポリビニルアセタール樹脂、ポリカーボネート樹脂、ポリエステル樹脂、アクリル樹脂、ポリ塩化ビニル樹脂、ポリスチレン樹脂、ポリビニルアセテート樹脂、塩化ビニル−酢酸ビニル共重合体、シリコン樹脂、フェノール樹脂、ポリ−Ｎ−ビニルカルバゾール樹脂等を使用できるが、これらに限定されるものではない。これらの結着樹脂は、単独あるいは２種以上混合して用いることができる。
【００４３】
電荷発生材料と結着樹脂との配合比（質量比）は、１０：１〜１：１０の範囲が好ましい。また、本発明で用いる電荷発生層の厚みは、一般的には、０．１〜５μｍ、好ましくは０．２〜２．０μｍが適当である。塗布方法としては、ブレードコーティング法、マイヤーバーコーティング法、スプレーコーティング法、浸漬コーティング法、ビードコーティング法、エアーナイフコーティング法、カーテンコティング法等の方法を用いることができる。電荷発生層を設ける際に用いる溶剤としては、メタノール、エタノール、ｎ−プロパノール、ｎ−ブタノール、ベンジルアルコール、、メチルセロソルブ、エチルセロソルブ、アセトン、メチルエチルケトン、シクロヘキサノン、酢酸メチル、酢酸ｎ−ブチル、ジオキサン、テトラヒドロフラン、塩化メチレン、クロロホルム等の有機溶剤があげられ、これらを単独又は２種以上混合して用いることができる。
【００４４】
電荷輸送層１１５は、少なくとも上記一般式（Ｉ）で示されるトリアリールアミン系化合物、上記一般式（II）で示されるベンジジン系化合物及び酸化防止剤を必須成分として結着樹脂中に含有し、必要に応じて他の膜質改良剤などを添加して構成される。
【００４５】
トリアリールアミン系化合物とベンジジン系化合物との混合割合は、質量比で１０：９０ないし９０：１０の範囲であるが、トリアリールアミン系化合物の比が３０未満の場合は、耐摩耗性、クリーニング性、クリーニング部材との摺動音が問題となることがあるので、３０：７０ないし９０：１０の範囲とすることが望ましい。トリアリールアミン系化合物とベンジジン系化合物との総和と、結着樹脂との混合割合は、質量比で３０：７０ないし６０：４０の範囲が採用できるが、電気特性、耐摩耗性、クリーニング性、クリーニング部材との摺動性等を良好に保つためには、３５：６５ないし５０：５０の範囲で使用することが好ましい。
【００４６】
酸化防止剤としては、一次酸化防止剤であるヒンダードアミン系酸化防止剤又はヒンダードフェノール系酸化防止剤が特に望ましく、それらは単体で、又は２種以上の混合物として用いられる。酸化防止剤の総添加量は、添加される層全体の１質量％以上、１５質量％以下であるが、層の機械的特性を損なわないためには、トリアリールアミン系化合物とベンジジン系化合物と酸化防止剤との総和が、それを含む層全体の６０質量％を越えないように添加することが望ましい。
【００４７】
電荷輸送層１１５に用いる結着樹脂としては、ポリカーボネート樹脂、ポリエステル樹脂、メタクリル樹脂、アクリル樹脂、ポリ塩化ビニル樹脂、ポリ塩化ビニリデン樹脂、ポリスチレン樹脂、ポリビニルアセテート樹脂、スチレン−ブタジエン共重合体、塩化ビニリデン−酢酸ビニル−無水マレイン酸共重合体、シリコン樹脂、シリコン−アルキッド樹脂、フェノール−ホルムアルデヒド樹脂、スチレン−アクリル樹脂、スチレン−アルキッド樹脂、ポリ−Ｎ−ビニルカルバゾール、ポリシランなどの公知の樹脂を用いることができる。また、電荷輸送層１１５の上には、必要に応じて保護層（不図示）を設けてもよい。保護層は、感光層１１３の帯電時における電荷輸送層１１５の化学的変質を防止すると共に、感光層１１３の機械的強度を改善するために有用である。この保護層は、導電材料を適当な結着樹脂中に含有させることにより形成される。
【００４８】
かかる構成の感光体１１を有する画像形成装置では、感光体１１の感光層１１３を電荷発生層１１４と電荷輸送層１１５の２層構成とし、さらに電荷輸送層１１５を、上記一般式（Ｉ）で示されるトリアリールアミン系化合物、上記一般式（II）で示されるベンジジン系化合物及び酸化防止剤を含有するものとしたことにより、コロナ放電によって放電生成物（オゾン、ＮＯｘ等）が発生しても、この放電生成物による感光体１１の特性劣化を有効に抑えることができる。これにより、複写操作の繰り返しによって数万枚〜数十万枚のプリントを行った後でも、画像流れやカブリなどの印刷品位の低下を防止し、優れた繰り返し安定性を実現することができる。
【００４９】
続いて、本発明の実施形態に係る画像形成装置で適用される感光体の具体的な実施例と比較例について説明する。
【００５０】
［実施例］
先ず、アルミニウムドラムからなる導電性支持体１１１上に、下記組成の塗布液を浸漬コーティング法により塗布した後、１５０℃で１０分間加熱乾燥することにより、膜厚０．１μｍの下引き層１１２を形成した。
ジルコニウム化合物 １０部
（オルガチックスＺＣ５４０、マツモト製薬社製）
シラン化合物（A1110、日本ユニカー社製） ５部
I-プロパノール ４０部
【００５１】
次に、下記組成の混合物をガラスビーズと共にサンドミルで１時間分散処理し、得られた塗布液を上記下引き層１１２上に浸漬コーティング法で塗布した後、１００℃で１０分間加熱乾燥して、膜厚２０μｍの電荷発生層１１４を形成した。
Ｘ型無金属フタロシアニン ５部
ポリビニルブチラール樹脂 ５部
（エスレックＢＭ−Ｓ、積水化学社製）
シクロヘキサノン ９０部
【００５２】
次いで、下記組成の塗布液を、上記電荷発生層１１４上に浸漬コーティング法で塗布した後、１２０℃で６０分間加熱乾燥して、膜厚２０μｍの電荷輸送層１１５を形成した。
トリアリールアミン化合物（Ｉ−１９） ４０部
ベンジジン化合物（II−５８） １０部
ヒンダードフェノール系酸化防止剤 ３部
（ＳｕｍｉｌｉｚｅｒＭＤＰ−Ｓ、住友化学社製）
下記一般式（III）で示されるポリカーボネート ４７部
（粘度平均分子量：ＭV ＝３０，０００）
ジメチルポリシロキサン ０．１部
クロロベンゼン ４００部
以上のようにして感光体ドラムを作製した。
【００５３】
【化３】

（ｎ′は上記分子量の範囲の重合度を意味する。）
【００５４】
［比較例１］
上記実施例において、電荷輸送層１１５の形成時に酸化防止剤であるヒンダードフェノール系酸化防止剤：ＳｕｍｉｌｉｚｅｒＭＤＰ−Ｓを添加しない以外は、全く同様にして感光体ドラムを作製した。
【００５５】
［比較例２］
上記実施例において、酸化防止剤として、ＳｕｍｉｌｉｚｅｒＭＤＰ−Ｓの代わりに、有機硫黄系酸化防止剤であるＳｕｍｉｌｉｚｅｒＴＰＭ（住友化学社製）を用いた以外は、全く同様にして感光体ドラムを作製した。
【００５６】
［比較例３］
上記実施例において、電荷輸送材料であるトリアリールアミン化合物及びベンジジン化合物の代わりに、下記一般式（IV）で示されるヒドラゾン系化合物を用いた以外は、全く同様にして電子写真感光体ドラムを作製した。なお、ヒドラゾン化合物の添加量は、トリアリールアミン化合物とベンジジン化合物を合計した量と等しい量にした。
【００５７】
【化４】

【００５８】
上記実施例及び比較例１〜３で作製した感光体ドラムを、本発明の実施形態に係る導電層付き（導電材料にカーボン、グラファイト等を採用）の板状グリッド１２３を用いた帯電器１２を備えるデジタル複合機（DCC500、富士ゼロックス社製）にそれぞれ搭載し、初期においてレーザー非露光時の表面電位ＶH が−７００Ｖ、レーザー露光時の表面電位ＶL が−３００Ｖになるように、スコロトロン及びレーザー露光条件を設定し、除電後の表面電位ＶR を記録した。その条件で、複写操作を繰り返し行って、それぞれ３０万枚、５０万枚プリントした後、非露光時の表面電位ＶH 、露光時の表面電位ＶL 、及び除電後の表面電位ＶR を測定し、プリント前後における変化量を調べた。また、ハーフトーンプリントにより、１０万枚、３０万枚、５０万枚プリント後の画像流れを評価した。画像流れの評価結果を下記表２に示すとともに、プリント前後の電位変化量の測定結果を下記表３に示す。画像流れの評価は、「○；未発生」、「×；発生し１００枚以上プリントしても消えない」、「△；発生し１００枚程度のプリントで消える」の３段階で行った。また、この評価実験は、感光体の劣化が激しいとされる高温高湿（２８℃、８５％ＲＨ）の環境条件で行った。
【００５９】
【表２】

【００６０】
【表３】

【００６１】
これらの表から明らかなように、実施例の感光体を用いた場合は、高温高湿の環境下で３０万枚、５０万枚とプリントしたときでも、カブリや黒点の発生、画像流れの発生などの感光体の劣化に起因する大きな印刷欠陥はなく、さらに帯電器に起因する斑もなく、感光体表面についた機械的傷による若干の筋が発生する程度であった。これらの評価結果は、本発明の画像形成装置で採用する感光体が優れた繰り返し安定性を有していることを示している。
【００６２】
一方、酸化防止剤を添加しなかった比較例１の感光体を使用した場合は、３０万枚のプリント後において、ＶL 及びＶR が大幅に上昇しており、印刷にも全面カブリが大量に発生し、画像流れも発生したため、３０万枚プリントした時点で評価実験を中止した。比較例２の感光体を使用した場合は、比較例１の場合に比較して酸化防止剤の効果が認められるものの、ヒンダーフェノール系酸化防止剤を用いた実施例のものに比較すると、その効果は小さく、５０万枚プリント時で印刷にも全面カブリと画像流れが発生した。ヒドラゾン系化合物を電荷輸送材料に用いた比較例３の感光体を使用した場合は、ＶH が低下し、ＶL 及びＶR が大幅に上昇し、３０万枚プリント後は、印刷にかなりのカブリと画像流れが発生したため、その時点で評価実験を中止した。
【００６３】
【発明の効果】
以上説明したように本発明の画像形成装置によれば、感光体を帯電させる帯電手段に板状グリッドを設けるとともに、この板状グリッドのグリッド基材の表面に導電材料としてグラファイトを含む導電層を形成したので、グリッド表面での錆の発生やこれに伴う絶縁化を有効に防止することができる。これにより、長期にわたって帯電ムラのない安定した帯電特性を維持し、画像斑の発生を抑えることができる。また、グリッド基材の表面に高価な金メッキを施す必要がないため、画像形成装置を安価に提供することができる。
【００６４】
さらに、上記帯電手段によって帯電される感光体の構成として、電荷発生層と電荷輸送層を含む少なくとも２層の感光層を有し、かつ、電荷輸送層は、少なくとも上記一般式（Ｉ）で示されるトリアリールアミン系化合物、上記一般式（II）で示されるベンジジン系化合物及び酸化防止剤を含有するものとすることにより、コロナ放電によって発生する放電生成物によって感光体の特性が劣化することを有効に抑えることができる。これにより、画像流れやカブリなどの印刷品位の低下を防止し、優れた繰り返し安定性を実現することができる。
【図面の簡単な説明】
【図１】 本発明が適用される画像形成装置の構成例を示す概略図である。
【図２】 本発明の実施形態に係る画像形成装置に適用される帯電器の構成例を示す組立斜視図である。
【図３】 本発明の実施形態に係る画像形成装置に適用される帯電器の構成例を示す分解斜視図である。
【図４】 本発明の実施形態に係る画像形成装置に適用される感光体の構成例を示す断面図である。
【符号の説明】
１０…画像形成装置、１１…感光体、１２…帯電器、１３…レーザー書き込み装置、１４…現像器、１５…転写電極、１６…分離電極、１７…搬送機構、１８…定着器、１９…クリーナー、１１１…導電性支持体、１１２…下引き層、１１３…感光層、１１４…電荷発生層、１１５…電荷輸送層、１２１…支持筐体、１２２…帯電ワイヤ、１２３…板状グリッド、１２４…バネ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a printer or a copying machine that forms an image based on an electrophotographic system.
[0002]
[Prior art]
In an image forming apparatus employing an electrophotographic system, a corona discharger (charger) is widely used for charging the surface of a photoconductor as an image carrier. In this type of image forming apparatus, the open surface of the shield case that serves as a support housing for the corona discharger is opposed to a charged member such as a photosensitive drum as an image carrier in a close state, and is stretched in the shield case. By supplying a discharge current to the charging wire provided to generate corona discharge, a charge is imparted to the surface to be charged of the member to be charged.
[0003]
Such a corona discharger uses a control grid that controls the charged potential on the surface of the photoreceptor by regulating the amount of charge applied by the charging wire. As a control grid of a corona discharger, a grid using a plate grid in which a large number of holes (pores) are formed by etching or the like on a sheet metal such as SUS (suspension) is known (for example, Patent Document 1). 2).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-40316
[Patent Document 2]
JP 2001-166669 A
[0005]
On the other hand, with respect to a photoreceptor as an image carrier, research on an electrophotographic photoreceptor using an organic photoconductive material having advantages that are inexpensive and has excellent advantages in terms of manufacturability and discardability has been actively conducted. In particular, a function-separated organic laminated photoconductor formed by laminating a charge generation layer that generates a charge upon exposure and a charge transport layer that transports the charge generated in the charge generation layer has a sensitivity, chargeability, and the like. It is excellent in terms of electrophotographic characteristics such as repetitive stability, and various proposals have been made and put into practical use. In particular, with respect to the charge transport material contained in the charge transport layer, for example, it has been proposed to use a mixture of a benzidine compound and a triarylamine compound (see, for example, Patent Documents 3 and 4).
[0006]
[Patent Document 3]
JP-A-6-75408
[Patent Document 4]
JP-A-6-95405
[0007]
[Problems to be solved by the invention]
However, the conventional image forming apparatus has the following drawbacks. In other words, when a corona discharger (charger) using a plate-like grid is used for a long time in a low humidity environment, uneven charging occurs in the longitudinal direction of the charger, which may cause image defects such as density unevenness. there were. When these causes were investigated, an insulating metal oxide (hereinafter referred to as rust) such as Fe2 O3 was partially generated on the surface of the plate-like grid due to a chemical reaction with a discharge product generated by corona discharge. Insulation of the plate-like grid due to this rust reduces the amount of charge flowing into the plate-like grid, which increases the charge in the direction of the photoreceptor serving as the image carrier, resulting in uneven charging potential. It has been found that
[0008]
Although SUS is generally highly corrosive, it is presumed that when active oxygen such as ozone is generated by corona discharge, iron (Fe) contained in SUS reacts with ozone and leads to rust. . When a specific experiment was conducted regarding the occurrence of such rust, when the corona discharge current was -700 μA and the grid voltage was -720 V, the photoconductor was charged to about -700 V when a new plate grid was used. On the other hand, in the portion where rust is generated, the charged potential of the photosensitive member becomes −730 to −740 V, and as a result, image spots (image density unevenness) occur in the image quality obtained by printing, particularly in the halftone. did.
[0009]
Conventionally, as a countermeasure against this, it has been proposed that the surface of the grid base material of the plate-shaped grid (base surface) is gold-plated mainly for the purpose of rust prevention. This leads to other problems such as a significant increase in the unit price of the grid and the possibility of pinholes.
[0010]
Accordingly, the first object of the present invention is to effectively prevent the occurrence of rust on the grid surface and to generate image spots due to uneven charging when a corona discharger (charger) using a plate grid is mounted. An object of the present invention is to provide an image forming apparatus capable of suppressing the above problem at low cost.
[0011]
On the other hand, those containing a benzidine compound, a triarylamine compound, or a mixture thereof in the charge transport layer of the photoreceptor exhibit sufficient characteristics in terms of photosensitivity, printing characteristics, durability, etc. Although there is no problem in the range of printing about several thousand sheets using ordinary copiers and laser printers, if the number of printed sheets exceeds tens of thousands, image deterioration or fogging may occur due to deterioration of the photoreceptor. However, there was a problem that the image quality of printing deteriorated. Further, the deterioration of the image quality due to the deterioration of the photoconductor tends to be remarkable particularly in a high temperature and high humidity environment.
[0012]
Although the details of the cause of such printing defects are unknown, it is considered that discharge products such as ozone, nitrogen oxides (NOx), etc. generated by corona discharge and nitrates based on the nitrogen oxides are affected. ing.
[0013]
As a countermeasure, for example, Japanese Patent Laid-Open No. 61-144670 discloses a conductive paint containing reactive metal particles (Ni, Ag, Cu, Zn, Pb) that adsorbs nitrogen oxides as a plate shape of a corona discharger. A technology is proposed to form a conductive layer by coating on the surface of the grid so that nitrogen oxides generated by corona discharge are adsorbed by the plate-like grid, thereby preventing deterioration of the photoreceptor due to nitrogen oxides. Has been. However, in this technique, when the number of printed sheets exceeds tens of thousands, the reactive metal adsorption function is used up and disappears, and further, the accumulation of nitrate as an insulator causes the rust on the grid surface. Similarly, there is a problem that image spots are generated in the halftone in an image quality, particularly in a low humidity environment.
[0014]
Therefore, the second object of the present invention is to stabilize the image flow and fog due to deterioration of the photoreceptor, and image spots due to uneven charging even when printing is performed on the order of several hundred thousand sheets. An object of the present invention is to provide an image forming apparatus capable of maintaining image quality.
[0015]
[Means for Solving the Problems]
An image forming apparatus according to the present invention forms a toner image by developing a photosensitive member on which an electrostatic charge image is formed, a charging unit for charging the photosensitive member, and developing the electrostatic charge image formed on the photosensitive member. An image forming apparatus comprising: a developing unit that transfers the toner image onto a transfer material; and a fixing unit that fixes the toner image on the transfer material. It has a plate-like grid in which holes are formed, and the plate-like grid is a conductive material on the surface of the grid base material. Including graphite A conductive layer is formed.
[0016]
In the image forming apparatus having the above-described configuration, the surface of the plate-like grid of the charging unit is covered with the conductive layer, so that generation of rust of the grid base material in a low-humidity environment is prevented, and the conductive material in the conductive layer However, it is not chemically reactive (chemically inert) to NOx, which is a type of discharge product. Graphite Therefore, even if it is exposed to NOx generated by corona discharge for a long time, the plate-like grid is not insulated by a chemical reaction with NOx.
[0017]
In addition, the photoreceptor applied to the image forming apparatus having the above structure includes at least two photosensitive layers including a charge generation layer and a charge transport layer, and the charge transport layer includes at least the general formula (I). It preferably contains a triarylamine compound represented by the formula (II), a benzidine compound represented by the general formula (II) and an antioxidant.
[0018]
In the image forming apparatus to which the photoreceptor is applied, the photosensitive layer of the photoreceptor has at least two layers including a charge generation layer and a charge transport layer, and the charge transport layer further includes a tria represented by the general formula (I). Even if discharge products (ozone, NOx, etc.) are generated by corona discharge, this discharge is caused by the inclusion of the reelamine compound, the benzidine compound represented by the general formula (II) and the antioxidant. Deterioration of the characteristics of the photoreceptor due to the product (deterioration of various characteristics such as printing characteristics, photosensitivity, chargeability, and repetitive stability) can be effectively suppressed.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
FIG. 1 is a schematic diagram showing a configuration example of an image forming apparatus to which the present invention is applied. The illustrated image forming apparatus 10 includes a photosensitive member 11, a charger 12, a laser writing device (laser ROS; Laser Raster Output Scanner) 13, a developing device 14, a transfer electrode 15, a separation electrode 16, and a transport mechanism. 17, a fixing device 18, and a cleaner 19.
[0021]
The photoreceptor 11 is formed in a drum shape as a whole, and is driven to rotate at a predetermined speed during image formation. The charger 12 charges the photoreceptor 11 during image formation, and is configured using a corona discharger. The laser writing device 13 forms an electrostatic charge image on the surface of the photoconductor 11 by exposing and scanning the surface of the photoconductor 11 charged by the charger 12 with a laser beam (laser beam).
[0022]
The developing unit 14 visualizes the electrostatic charge image formed on the photoconductor 11 by the laser writing device 13 and forms a toner image (visible image). The transfer electrode 15 is for transferring the toner image formed on the photoconductor 11 by the developing unit 14 to a transfer material such as paper. The separation electrode 16 separates a transfer material that is in close contact with the photoconductor 11 from the photoconductor 11.
[0023]
The transport mechanism 17 transports the transfer material separated from the photoconductor 11 by the separation electrode 16. The fixing device 18 fixes the toner image transferred to the transfer material by the transfer electrode 15 by heating and pressurizing the transfer material conveyed by the conveyance mechanism 17. The cleaner 19 removes residual toner remaining on the photoconductor 11 after transfer.
[0024]
FIG. 2 is an assembled perspective view showing a configuration example of the charger 12 applied to the image forming apparatus 10, and FIG. 3 is an exploded perspective view showing a configuration example of the charger 12. The illustrated charger 12 includes a support housing 121, a charging wire 122, a plate-like grid 123, and a spring 124.
[0025]
The support housing 121 has an electrical shielding effect, and is formed in an elongated box shape with one surface open. The support housing 121 is disposed in a state where the open surface is opposed to the outer peripheral surface of the photoconductor 11. The charging wire 122 performs corona discharge, and is stretched inside the support housing 121 substantially parallel to the longitudinal direction of the support housing 121. As the charging wire 122, it is preferable to use, for example, a tungsten wire having a wire diameter of 0.03 mm (30 μm) subjected to gold plating to improve durability.
[0026]
The plate-like grid 123 controls the charging potential on the surface of the photoconductor 11 and is attached to the open surface of the support housing 121. The plate-like grid 123 is disposed close to the outer peripheral surface of the photoconductor 11. A grid voltage is applied to the plate-like grid 123 by a voltage applying means (not shown). The grid voltage applied to the plate-like grid 123 is controlled (feedback control or the like) based on a detection signal of a potential detector (such as a potential sensor) that detects the potential of the surface of the photoconductor 11.
[0027]
The spring 124 is formed of a tension coil spring and is used to stretch the plate-like grid 123 on the open surface of the support housing 121. That is, on the open surface of the support housing 121, one end side in the longitudinal direction of the plate-like grid 123 is locked to one end portion of the support housing 121, and the other end side in the longitudinal direction of the plate-like grid 123 is two springs 124. The other end of the support housing 121 is locked via the.
[0028]
Here, the plate-like grid 123 has a grid base material in which a large number of through holes are formed by etching or the like on a thin plate-like metal plate made of stainless steel or the like, and a conductive layer containing a conductive material on the surface of the grid base material. Is used. In addition, the conductive material for forming the conductive layer includes at least one of materials that are chemically inert to discharge products generated by corona discharge from the charging wire 122, that is, carbon and graphite. Yes.
[0029]
The conductive layer that covers the plate-like grid 123 is obtained, for example, by applying a conductive paint containing the conductive material to the surface (entire surface) of the grid substrate. At that time, the conductive paint is obtained by mixing a resin serving as a binder (binder) with the conductive material previously granulated or powdered. Moreover, an epoxy resin, a phenol resin, a urethane resin, an acrylic resin, etc. are used for the resin material used as a binder.
[0030]
Thus, as a configuration of the plate-like grid 123 provided in the charger 12, the surface of the grid base material is formed by forming a conductive layer containing at least one of carbon and graphite as a conductive material on the surface (base) of the grid base material. Since (entire surface) is covered with the conductive layer, generation of rust (metal oxide) of the grid base material in a low-humidity environment can be prevented. Further, since carbon, graphite, or the like that is chemically reactive with NOx (chemically inert) is used as the conductive material contained in the conductive layer, even if it is exposed to NOx generated by corona discharge. , Deterioration of conductivity (insulation) due to the chemical reaction with NOx can be prevented. Therefore, it is possible to maintain a stable charging characteristic without charging unevenness over a long period of time.
[0031]
Next, specific examples and comparative examples of the plate grid 123 used in the charger 12 will be described.
[0032]
[Example]
First, a plate-like grid to which the present invention was applied was manufactured by the following method. That is, a conductive coating is applied to a grid base material such as stainless steel in which a large number of holes are formed in advance by etching or the like. As the conductive paint used at this time, Dag 213 (manufactured by Nippon Atchison Co., Ltd.) containing graphite as a conductive material was used, and this Dag 213 was uniformly applied to the surface (entire surface) of the grid base material by a spray method. At that time, for the purpose of improving the adhesion between the grid base material and the conductive paint, the grid base material was previously degreased, and the conductive paint was applied to the grid base material after the degreasing treatment. In this case, as a pretreatment for coating, in addition to the degreasing treatment, for example, a Parker treatment (zinc phosphate coating treatment) may be performed to further improve the adhesion.
[0033]
After applying the conductive paint to the surface of the grid substrate, the conductive layer formed by this application may be dried at room temperature, but in this embodiment, in order to realize a stronger conductive layer, The conductive layer was dried by applying a heat treatment recommended by Dag 213 (baked at 180 ° C. for 60 minutes). As a result, a plate-like grid in which a conductive layer having a thickness of 25 μm and a surface resistivity (sheet resistance) of 700Ω / □ was formed on the surface of the grid base material was obtained.
[0034]
[Comparative example]
In the above embodiment, the conductive material contained in the conductive paint used for forming the conductive layer is replaced with the above graphite and nickel is used, and the conductive paint containing nickel as a conductive material is used in the same manner as in the above embodiment. A plate shape in which a conductive layer having a thickness of 25 μm and a surface resistivity (sheet resistance) of 700Ω / □ is formed on the surface of the grid base material by applying to the grid base material by (spray method) and drying. Got the grid.
[0035]
The plate grid of the embodiment and the plate grid of the comparative example created in this way are each mounted on the charger 12, and the charger 12 is mounted on a digital multifunction machine (DCC500, manufactured by Fuji Xerox Co., Ltd.) In a low-temperature and low-humidity environment (10 ° C, 15% RH) where rust and other precipitates are likely to occur, a discharge experiment corresponding to 100,000 prints, 300,000 prints, and 500,000 prints was conducted. The difference between the initial charging potential and the charging potential after printing a predetermined number of sheets was examined. As a result, the results shown in Table 1 below were obtained.
[0036]
[Table 1]

[0037]
As can be seen from Table 1 above, when the plate-like grid of the example is used and when the plate-like grid of the comparative example is used, the potential difference after equivalent to 100,000 prints does not change much, but equivalent to 300,000 prints. Later, the potential difference in the example is 5 V, whereas the potential difference in the comparative example is as large as 30 V, and after the equivalent of 500,000 prints, the example is suppressed to a potential difference of 15 V. The comparative example has a very large potential difference of 75V.
[0038]
In addition, as a result of actually forming an image and evaluating the image quality, in the example, there was no generation of rust and precipitates even after printing of 500,000 sheets, and there was no problem with the image quality. On the other hand, in the comparative example, there was no particular problem until after the equivalent of 100,000 prints, but halftone image quality started to appear after the equivalent of 300,000 prints, and rust after the equivalent of 500,000 prints. The white spots of the image were observed at the places where the precipitates were generated. From the above results, it was confirmed that the charging characteristics can be satisfactorily maintained for a long time by mounting the charger 12 using the plate-like grid 123 according to the embodiment of the present invention in the image forming apparatus.
[0039]
Next, a configuration of a photoreceptor that is suitable for application to the image forming apparatus according to the embodiment of the present invention will be described. FIG. 4 is a cross-sectional view showing a configuration example of a photoreceptor applied to the image forming apparatus according to the embodiment of the present invention. In the configuration of the illustrated photoreceptor 11, the photosensitive layer 113 formed on the conductive support 111 via the undercoat layer 112 includes at least two layers including the charge generation layer 114 and the charge transport layer 115. The layer structure is functionally separated into (multilayer).
[0040]
As the conductive support 111, a plastic provided with a metal such as aluminum, nickel, chromium, stainless steel, and a thin film such as aluminum, titanium, nickel, chromium, stainless steel, gold, vanadium, tin oxide, indium oxide, ITO, etc. Examples thereof include films and the like, and paper and plastic films coated or impregnated with a conductivity-imparting agent. These conductive supports 111 are used in an appropriate shape such as a drum shape, a sheet shape, or a plate shape, but are not limited thereto. Further, the surface of the conductive support 111 can be subjected to various treatments as long as the image quality is not affected. For example, surface oxidation treatment, chemical treatment, coloring treatment, or irregular reflection treatment such as graining can be performed.
[0041]
The undercoat layer 112 is provided between the conductive support 111 and the charge generation layer 114 as necessary. The undercoat layer 112 prevents injection of charges from the conductive support 111 to the photosensitive layer 113 when the photosensitive layer 113 is charged by the charger 12, and causes the photosensitive layer 113 to move away from the conductive support 111. In other words, it exhibits an action as an adhesive layer that is integrally bonded and held, or an action of preventing reflection of light from the conductive support 111 depending on circumstances. As the resin and other materials constituting the undercoat layer 112, polyethylene resin, polypropylene resin, acrylic resin, methacrylic resin, polyamide resin, vinyl chloride resin, vinyl acetate resin, phenol resin, polycarbonate resin, polyurethane resin, polyimide resin, Vinylidene chloride resin, polyvinyl acetal resin, vinyl chloride-vinyl acetate copolymer, polyvinyl alcohol resin, water-soluble polyester resin, nitrocellulose, casein, gelatin, polyglutamic acid, starch, starch acetate, amino starch, polyacrylic acid, polyacrylamide Well-known materials such as zirconium chelate compounds, titanyl chelate compounds, titanyl alkoxide compounds, other organic titanyl compounds, and silane coupling agents can be used. The thickness of the undercoat layer 112 is 0.01 to 10 μm, preferably 0.05 to 2 μm. As a coating method, a usual method such as a blade coating method, a Meyer bar coating method, a spray coating method, a dip coating method, a bead coating method, an air knife coating method, or a curtain coating method can be used.
[0042]
The charge generation layer 114 is configured by dispersing a charge generation material in a binder resin. Examples of charge generation materials include amorphous selenium, crystalline selenium-tellurium alloy, other selenium compounds and selenium alloys, inorganic photoconductive materials such as zinc oxide and titanium oxide, phthalocyanine-based, squalium-based, anthrone-based, perylene. Organic pigments and dyes such as azo-type, azo-type, anthraquinone-type, pyrene-type, pyrylium salt and thiapyrylium salt are used. As the binder resin in the charge generation layer, polyvinyl butyral resin, polyvinyl formal resin, partially modified polyvinyl acetal resin, polycarbonate resin, polyester resin, acrylic resin, polyvinyl chloride resin, polystyrene resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate A copolymer, silicon resin, phenol resin, poly-N-vinylcarbazole resin, or the like can be used, but is not limited thereto. These binder resins can be used alone or in combination of two or more.
[0043]
The blending ratio (mass ratio) between the charge generating material and the binder resin is preferably in the range of 10: 1 to 1:10. The thickness of the charge generation layer used in the present invention is generally 0.1 to 5 μm, preferably 0.2 to 2.0 μm. As a coating method, a blade coating method, a Meyer bar coating method, a spray coating method, a dip coating method, a bead coating method, an air knife coating method, a curtain coating method, or the like can be used. Solvents used for providing the charge generation layer include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, Examples thereof include organic solvents such as tetrahydrofuran, methylene chloride, and chloroform, and these can be used alone or in admixture of two or more.
[0044]
The charge transport layer 115 contains at least a triarylamine compound represented by the general formula (I), a benzidine compound represented by the general formula (II) and an antioxidant as essential components in the binder resin, It is constituted by adding other film quality improving agents as required.
[0045]
The mixing ratio of the triarylamine compound and the benzidine compound is in the range of 10:90 to 90:10 by mass ratio, but when the ratio of the triarylamine compound is less than 30, the wear resistance, cleaning And sliding noise with the cleaning member may be a problem, so it is desirable to set the ratio in the range of 30:70 to 90:10. The mixing ratio of the sum of the triarylamine-based compound and the benzidine-based compound and the binder resin can be in the range of 30:70 to 60:40 by mass ratio, but the electrical characteristics, wear resistance, cleaning properties, In order to maintain good slidability and the like with the cleaning member, it is preferably used in the range of 35:65 to 50:50.
[0046]
As the antioxidant, a hindered amine antioxidant or a hindered phenol antioxidant which is a primary antioxidant is particularly desirable, and they are used alone or as a mixture of two or more. The total addition amount of the antioxidant is 1% by mass or more and 15% by mass or less of the whole layer to be added. In order not to impair the mechanical properties of the layer, the triarylamine compound and the benzidine compound It is desirable to add so that the total amount with the antioxidant does not exceed 60 mass% of the entire layer containing the antioxidant.
[0047]
Examples of the binder resin used for the charge transport layer 115 include polycarbonate resin, polyester resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, styrene-butadiene copolymer, and vinylidene chloride. -Use a known resin such as vinyl acetate-maleic anhydride copolymer, silicone resin, silicone-alkyd resin, phenol-formaldehyde resin, styrene-acrylic resin, styrene-alkyd resin, poly-N-vinylcarbazole, polysilane, etc. Can do. Further, a protective layer (not shown) may be provided on the charge transport layer 115 as necessary. The protective layer is useful for preventing chemical alteration of the charge transport layer 115 during charging of the photosensitive layer 113 and improving the mechanical strength of the photosensitive layer 113. This protective layer is formed by including a conductive material in a suitable binder resin.
[0048]
In the image forming apparatus having the photoconductor 11 having such a configuration, the photoconductive layer 113 of the photoconductor 11 has a two-layer configuration of a charge generation layer 114 and a charge transport layer 115, and the charge transport layer 115 is further represented by the general formula (I). Even if discharge products (ozone, NOx, etc.) are generated by corona discharge, the triarylamine compound shown, the benzidine compound shown by the general formula (II) and the antioxidant are included. Therefore, it is possible to effectively suppress the characteristic deterioration of the photoconductor 11 due to the discharge product. Thereby, even after tens of thousands to hundreds of thousands of prints are made by repeating the copying operation, it is possible to prevent deterioration in print quality such as image flow and fog, and to realize excellent repeat stability.
[0049]
Next, specific examples and comparative examples of the photoreceptor applied in the image forming apparatus according to the embodiment of the present invention will be described.
[0050]
[Example]
First, after applying a coating liquid having the following composition on a conductive support 111 made of an aluminum drum by a dip coating method, the undercoat layer 112 having a thickness of 0.1 μm is formed by heating and drying at 150 ° C. for 10 minutes. Formed.
Zirconium compound 10 parts
(Orgachicks ZC540, manufactured by Matsumoto Pharmaceutical Co., Ltd.)
Silane compound (A1110, manufactured by Nihon Unicar) 5 parts
40 parts of I-propanol
[0051]
Next, a mixture of the following composition is dispersed with a glass bead for 1 hour in a sand mill, and the resulting coating solution is applied onto the undercoat layer 112 by a dip coating method, and then heated and dried at 100 ° C. for 10 minutes, A charge generation layer 114 having a thickness of 20 μm was formed.
X-type metal-free phthalocyanine 5 parts
Polyvinyl butyral resin 5 parts
(ESREC BM-S, manufactured by Sekisui Chemical Co., Ltd.)
90 parts of cyclohexanone
[0052]
Next, a coating solution having the following composition was applied onto the charge generation layer 114 by a dip coating method, and then heated and dried at 120 ° C. for 60 minutes to form a charge transport layer 115 having a thickness of 20 μm.
Triarylamine compound (I-19) 40 parts
Benzidine Compound (II-58) 10 parts
3 parts of hindered phenolic antioxidant
(Sumilizer MDP-S, manufactured by Sumitomo Chemical Co., Ltd.)
47 parts of polycarbonate represented by the following general formula (III)
(Viscosity average molecular weight: MV = 30,000)
Dimethylpolysiloxane 0.1 part
400 parts of chlorobenzene
A photoreceptor drum was produced as described above.
[0053]
[Chemical 3]

(N ′ means the degree of polymerization within the above molecular weight range.)
[0054]
[Comparative Example 1]
In the above example, a photosensitive drum was prepared in exactly the same manner except that the hindered phenol antioxidant: Sumilizer MDP-S, which is an antioxidant, was not added when the charge transport layer 115 was formed.
[0055]
[Comparative Example 2]
In the above examples, photoconductor drums were produced in exactly the same manner except that Sumilizer TPM (manufactured by Sumitomo Chemical Co., Ltd.), which is an organic sulfur-based antioxidant, was used as the antioxidant in place of Sumilizer MDP-S.
[0056]
[Comparative Example 3]
In the above examples, an electrophotographic photosensitive drum was prepared in the same manner except that a hydrazone compound represented by the following general formula (IV) was used instead of the triarylamine compound and the benzidine compound which are charge transport materials. did. The amount of hydrazone compound added was equal to the total amount of triarylamine compound and benzidine compound.
[0057]
[Formula 4]

[0058]
The charger 12 using the plate-like grid 123 with the conductive layer (using carbon, graphite or the like as the conductive material) according to the embodiment of the present invention is used for the photosensitive drum manufactured in the above-mentioned Examples and Comparative Examples 1-3. Equipped in each digital multifunction device (DCC500, manufactured by Fuji Xerox Co., Ltd.), scorotron and laser exposure so that the initial surface potential VH at non-laser exposure is -700V and the surface potential VL at laser exposure is -300V. Conditions were set and the surface potential VR after static elimination was recorded. Under these conditions, the copying operation was repeated to print 300,000 sheets and 500,000 sheets, respectively, and the surface potential VH at the time of non-exposure, the surface potential VL at the time of exposure, and the surface potential VR after static elimination were measured and printed. The amount of change before and after was examined. In addition, the image flow after 100,000, 300,000 and 500,000 prints was evaluated by halftone printing. The evaluation results of image flow are shown in Table 2 below, and the measurement results of the amount of potential change before and after printing are shown in Table 3 below. The evaluation of the image flow was performed in three stages: “◯: not generated”, “×: generated and not erased even after printing 100 sheets”, “Δ; generated and disappeared after printing about 100 sheets”. Further, this evaluation experiment was performed under environmental conditions of high temperature and high humidity (28 ° C., 85% RH), which are considered to cause severe deterioration of the photoreceptor.
[0059]
[Table 2]

[0060]
[Table 3]

[0061]
As is clear from these tables, when the photoconductors of the examples are used, fogging, black spots, and image blur are generated even when printing 300,000 sheets and 500,000 sheets in a high temperature and high humidity environment. There was no large print defect due to deterioration of the photoconductor, and there were no spots due to the charger, and some streaks due to mechanical scratches on the surface of the photoconductor were generated. These evaluation results indicate that the photoreceptor used in the image forming apparatus of the present invention has excellent repeated stability.
[0062]
On the other hand, when the photoconductor of Comparative Example 1 to which no antioxidant was added was used, VL and VR increased significantly after printing 300,000 sheets, and a large amount of fogging occurred on the entire surface. However, since an image flow also occurred, the evaluation experiment was stopped when 300,000 sheets were printed. When the photoconductor of Comparative Example 2 is used, the effect of the antioxidant is recognized as compared with the case of Comparative Example 1, but the effect is compared with that of the example using the hindered phenolic antioxidant. The image was small, and the entire surface was fogged and the image flow occurred when printing 500,000 sheets. When the photoconductor of Comparative Example 3 using a hydrazone compound as a charge transport material was used, VH decreased, VL and VR increased significantly, and after 300,000 prints, considerable fog and images were printed. Because of the flow, the evaluation experiment was stopped at that time.
[0063]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, the charging means for charging the photosensitive member is provided with a plate-like grid, and the surface of the grid base material of the plate-like grid is used as a conductive material. Including graphite Since the conductive layer is formed, it is possible to effectively prevent the generation of rust on the grid surface and the accompanying insulation. As a result, stable charging characteristics without uneven charging can be maintained over a long period of time, and occurrence of image spots can be suppressed. Further, since it is not necessary to perform expensive gold plating on the surface of the grid base material, the image forming apparatus can be provided at a low cost.
[0064]
Further, the photosensitive member charged by the charging means has at least two photosensitive layers including a charge generation layer and a charge transport layer, and the charge transport layer is represented by at least the general formula (I). By containing a triarylamine compound, a benzidine compound represented by the above general formula (II), and an antioxidant, the characteristics of the photoconductor are deteriorated by discharge products generated by corona discharge. It can be effectively suppressed. As a result, it is possible to prevent deterioration in print quality such as image flow and fog, and to realize excellent repeated stability.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration example of an image forming apparatus to which the present invention is applied.
FIG. 2 is an assembled perspective view illustrating a configuration example of a charger applied to the image forming apparatus according to the embodiment of the invention.
FIG. 3 is an exploded perspective view showing a configuration example of a charger applied to the image forming apparatus according to the embodiment of the invention.
FIG. 4 is a cross-sectional view illustrating a configuration example of a photoreceptor applied to an image forming apparatus according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 11 ... Photoconductor, 12 ... Charger, 13 ... Laser writing apparatus, 14 ... Developing device, 15 ... Transfer electrode, 16 ... Separation electrode, 17 ... Conveyance mechanism, 18 ... Fixing device, 19 ... Cleaner , 111 ... conductive support, 112 ... undercoat layer, 113 ... photosensitive layer, 114 ... charge generation layer, 115 ... charge transport layer, 121 ... support housing, 122 ... charging wire, 123 ... plate-like grid, 124 ... Spring

Claims (3)

A photosensitive member on which an electrostatic charge image is formed, a charging means for charging the photosensitive member, a developing means for visualizing the electrostatic charge image formed on the photosensitive member to form a toner image, and the toner image An image forming apparatus comprising: transfer means for transferring to a transfer material; and fixing means for fixing the toner image to the transfer material,
The charging means has a plate-like grid in which a large number of holes are formed, and the plate-like grid is formed by forming a conductive layer containing graphite as a conductive material on a surface of a grid base material. Image forming apparatus. The photoreceptor has at least two photosensitive layers including a charge generation layer and a charge transport layer, and the charge transport layer includes at least a triarylamine compound represented by the following general formula (I), The image forming apparatus according to claim 1, comprising a benzidine-based compound represented by the formula (II) and an antioxidant.

(In the formula, R1 represents a halogen atom, an alkyl group, an alkoxy group, a substituted or unsubstituted aryl group or an aralkyl group, and R2 and R3 represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, substituted or unsubstituted, respectively. (Represents a substituted aryl group or aralkyl group, and k represents 1 or 2.)

(Wherein R4 represents a hydrogen atom, a halogen atom, an alkyl group or an alkoxy group, R5 and R6 each represents a halogen atom, an alkyl group, an alkoxy group or a substituted amino group, and m and n are each 0, 1 or 2 is shown.) The image forming apparatus according to claim 2, wherein the antioxidant is at least one selected from a hindered amine compound and a hindered phenol compound.

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