JP4020648B2 - Image forming method using positively charged single layer type electrophotographic photosensitive member - Google Patents

Description

【００２２】
（ＣＧ２）オキソチタニルフタロシアニン
【化２】

【００２３】
＜ホール輸送剤＞本発明の画像形成方法に用いられる感光体のホール輸送剤は、電界強度５×１０⁵Ｖ／ｃｍにおいて１×１０^-5ｃｍ²／Ｖ／ｓｅｃ以上の移動度を有する必要がある。例えば、下記の一般式（ＨＴ１）〜（ＨＴ３）で表される化合物があげられる。
【００２４】
（ＨＴ１）移動度：１．２１×１０^-5ｃｍ²／Ｖ／ｓｅｃ
【化３】

【００２５】
（ＨＴ２）移動度：１．６９×１０^-5ｃｍ²／Ｖ／ｓｅｃ
【化４】

【００２６】
（ＨＴ３）移動度：３．３８×１０^-5ｃｍ²／Ｖ／ｓｅｃ
【化５】

【００２７】
本発明の画像形成方法に用いられる感光体においてホール輸送剤は、１種単独で用いられる他、２種以上を混合して使用することができる。またホール輸送剤の含有量は、バインダー樹脂に対して５〜５００重量％、更には２５〜２００重量％が好ましい。
【００２８】
＜電子輸送剤＞本発明の画像形成方法に用いられる単層型正帯電電子写真感光体の電子受容体としては、前記例示のホール輸送剤の移動度に対して、１／２００００以上１／１０以下の移動度を有することが必要であり、例えば、前記ホール輸送剤に対して、下記の一般式（ＥＴ１）〜（ＥＴ７）で表わされる化合物があげられる。
【００２９】
（ＥＴ１）移動度：１．７５×１０^-9ｃｍ²／Ｖ／ｓｅｃ
【化６】

【００３０】
（ＥＴ２）移動度：５．３２×１０^-9ｃｍ²／Ｖ／ｓｅｃ
【化７】

【００３１】
（ＥＴ３）移動度：１．６７×１０^-8ｃｍ²／Ｖ／ｓｅｃ
【化８】

【００３２】
（ＥＴ４）移動度：６．１３×１０^-8ｃｍ²／Ｖ／ｓｅｃ
【化９】

【００３３】
（ＥＴ５）移動度：１．３７×１０^-7ｃｍ²／Ｖ／ｓｅｃ
【化１０】

【００３４】
（ＥＴ６）移動度：３．４７×１０^-7ｃｍ²／Ｖ／ｓｅｃ
【化１１】

【００３５】
（ＥＴ７）移動度：１．０４×１０^-6ｃｍ²／Ｖ／ｓｅｃ
【化１２】

【００３６】
本発明の画像形成方法に用いられる感光体において電子輸送剤は、１種単独で用いられる他、２種以上を混合して使用することができる。また電子輸送剤の含有量は、バインダー樹脂に対して５〜１００重量％、更には１０〜８０重量％が好ましい。
【００３７】
なお、上記の移動度は常温下、通常のＴＯＦ（ＴｉｍｅＯｆＦｌｉｇｈｔ）法により測定した。電界強度は５×１０⁵Ｖ／ｃｍとした。測定サンプルは、バインダー樹脂（重量平均分子量２０，０００のｂｉｓ−Ｚ型ポリカーボネート樹脂）に対して４０ｗｔ％の電荷輸送剤濃度で溶解させ、基材上に塗布し８０℃、３０分間の熱処理を行い作製した。サンプル膜厚は７μｍである。
【００３８】
＜バインダー樹脂＞前記各成分を分散させるためのバインダー樹脂は、従来から感光層に使用されている種々の樹脂を使用することができる。例えば、スチレン系重合体、スチレン−ブタジエン共重合体、スチレン−アクリロニトリル共重合体、スチレン−マレイン酸共重合体、アクリル系重合体、スチレン−アクリル系共重合体、ポリエチレン、エチレン−酢酸ビニル共重合体、塩素化ポリエチレン、ポリ塩化ビニル、ポリプロピレン、アイオノマー、塩化ビニル−酢酸ビニル共重合体、ポリエステル、アルキド樹脂、ポリアミド、ポリウレタン、ポリカーボネート、ポリアリレート、ポリスルホン、ジアリルフタレート樹脂、ケトン樹脂、ポリビニルブチラール樹脂、ポリエーテル樹脂等の熱可塑性樹脂、シリコーン樹脂、エポキシ樹脂、フェノール樹脂、尿素樹脂、メラミン樹脂、その他架橋性の熱硬化性樹脂、エポキシアクリレート、ウレタン−アクリレート等の光硬化型樹脂等の樹脂が使用可能である。これらのバインダー樹脂は単独で使用できる他、２種以上を併用することもできる。
【００３９】
感光層には、前記各成分のほかに、電子写真特性に悪影響を与えない範囲で、従来公知の種々の添加剤、例えば、酸化防止剤、ラジカル補足剤、一重項クエンチャー、紫外線吸収剤等の劣化防止剤、軟化剤、可塑剤、表面改質剤、増量剤、増粘剤、分散安定剤、ワックス、アクセプター、ドナー等を配合することができる。また、感光層の感度を向上させるために、例えば、テルフェニル、ハロナフトキノン類、アセナフチレン等の公知の増感剤を電荷発生剤と併用してもよい。
【００４０】
単層型正帯電電子写真感光体における感光層の厚さは５〜１００μｍ、好ましくは１０〜５０μｍである。
【００４１】
単層型正帯電電子写真感光体においては、導電性基体と感光層との間に、感光体の特性を阻害しない範囲でバリア層が形成されていてもよい。また、感光体の表面には、保護層が形成されていてもよい。
【００４２】
上記感光層が形成される導電性基体としては、導電性を有する種々の材料を使用することができ、例えば、鉄、アルミニウム、銅、スズ、白金、銀、バナジウム、モリブデン、クロム、カドミウム、チタン、ニッケル、パラジウム、インジウム、ステンレス鋼、真鍮等の金属単体や、上記金属が蒸着またはラミネートされたプラスチック材料、ヨウ化アルミニウム、酸化スズ、酸化インジウム等で被覆されたガラス等があげられる。
【００４３】
導電性基体の形状は、使用する画像形成装置の構造に合わせて、シート状、ドラム状等のいずれであってもよく、基体自体が導電性を有するか、あるいは基体の表面が導電性を有していればよい。また、導電性基体は、使用に際して十分な機械的強度を有するものが好ましい。
【００４４】
前記感光層を塗布の方法により形成する場合には、前記例示の正孔輸送剤、電荷発生剤、電子受容体、結着樹脂等を適当な溶剤とともに、公知の方法、例えば、ロールミル、ボールミル、アトライタ、ペイントシエーカー、超音波分散機等を用いて分散混合して分散液を調整し、これを公知の手段により塗布して乾燥させればよい。
【００４５】
上記分散液を作製するための溶剤としては、種々の有機溶剤が使用可能であり、例えば、メタノール、エタノール、イソプロパノール、ブタノール等のアルコール類、n−ヘキサン、オクタン、シクロヘキサン等の脂肪族系炭化水素、ベンゼン、トルエン、キシレン等の芳香族系炭化水素、ジクロロメタン、ジクロロエタン、クロロホルム、四塩化炭素、クロロベンゼン等のハロゲン化炭化水素、ジメチルエーテル、ジエチルエーテル、テトラヒドロフラン、エチレングリコールジメチルエーテル、ジエチレングリコールジメチルエーテル等のエーテル類、アセトン、メチルエチルケトン、シクロヘキサノン等のケトン類、酢酸エチル、酢酸メチル等のエステル類、ジメチルホルムアルデヒド、ジメチルホルムアミド、ジメチルスルホキシド等があげられる。これらの溶剤は単独で、または2種以上混合して用いられる。
【００４６】
さらに、電荷発生剤、ホール輸送剤、電子輸送剤の分散性、感光層表面の平滑性を良くするために、界面活性剤、レベリング剤等を使用してもよい。
【００４７】
【実施例】
以下、実施例、比較例をあげて本発明を説明する。なお、以下の実施形態は本発明を具体化した一例であって、本発明の技術的範囲を限定するものではない。
【００４８】
［実施例１〜１１］電荷発生剤としてＸ型無金属フタロシアニン（ＣＧＭ）４．５重量部、ホール輸送剤［前記（ＨＴ１）〜（ＨＴ３）から１種類選択］６５重量部、及び電子輸送剤［前記（ＥＴ１）〜（ＥＴ７）から１種類選択］３０重量部、バインダー樹脂として重量平均分子量３０，.０００のビスフェノールＺ型ポリカーボネート樹脂（Ｒｅｓｉｎ）１００重量部、テトラヒドロフラン７６０重量部を、ボールミル中で２７時間分散あるいは溶解させ、単層型感光層用塗布液を調合した。そして、この塗布液を、支持体としてのアルミニウム素管上にディップコート法にて塗布し、１／１０℃、４０分間の熱風乾燥を行い、膜厚２７．５μｍの単一感光層を有する単層型感光体を作製した。
【００４９】
［比較例１〜７］電子輸送剤として、（ＥＴ８）〜（ＥＴ１１）から１種類選択使用した以外は、実施例１〜１１と同様にして単層型感光体を作製した。
【００５０】
（ＥＴ８）移動度：６．００×１０^-10ｃｍ²／Ｖ／ｓｅｃ
【化１３】

【００５１】
（ＥＴ９）移動度：７．５６×１０^-10ｃｍ²／Ｖ／ｓｅｃ
【化１４】

【００５２】
（ＥＴ１０）移動度：２．０８×１０^-6ｃｍ²／Ｖ／ｓｅｃ
【化１５】

【００５３】
（ＥＴ１１）移動度：２．７７×１０^-6ｃｍ²／Ｖ／ｓｅｃ
【化１６】

【００５４】
［比較例８〜１４］ホール輸送剤として、（ＨＴ４）を使用した以外は、実施例１〜１１と同様にして単層型感光体を作製した。
【００５５】
（ＨＴ４）移動度：１．６０×１０^-6ｃｍ²／Ｖ／ｓｅｃ
【化１７】

【００５６】
上記各実施例、比較例の電子写真感光体について、下記の試験を行って、その特性を評価した。
【００５７】
＜初期感度評価＞ジェンテック（ＧＥＮＴＥＣ）社製のドラム感度試験機（商品名ジェンテックシンシア３０Ｍ）を用いて、各実施例、比較例の電子写真感光体に印加電圧を加えて、その表面を＋８００Ｖに帯電させた。
【００５８】
次に、上記試験機の露光光源であるハロゲンランプの白色光からバンドパスフィルターを用いて取り出した波長７８０ｎｍの単色光（半値幅２０ｎｍ，光強度１５μＷ）を、上記帯電状態の感光体の表面に露光（露光時間４０ｍｓｅｃ）した。そして、露光開始時点から５００ｍｓｅｃ経過した時点での表面電位を露光後電位Ｖ_L（Ｖ）として測定した。すなわち、露光後電位が小さいほど感光体は高感度である。
【００５９】
露光後電位については、Ａ４コピー速度が毎分５０枚以上の高速画像形成装置にて十分な画像濃度を得るためには、１７０Ｖ以下でなければならない。
【００６０】
＜初期帯電評価＞前記ドラム感度試験機を用いて、流れ込み電流値が１２μＡでの各実施例、比較例の電子写真感光体の初期表面電位Ｖ₀（Ｖ）を測定した。帯電はコロトロン方式で実施した。
【００６１】
初期表面電位については、Ａ４コピー速度が毎分５０枚以上の画像形成装置にてかぶりの無い画像を得るためには７５０Ｖ以上でなければならない。
【００６２】
＜画像評価＞各実施例、比較例で得た電子写真感光体を、Ａ４コピー速度が毎分５０枚の高速デジタル複写機［三田工業（株）社製Ｃｒｅａｇｅ７３５０］に装着し実写試験を行い、べた反射濃度を日本電色（株）社製の反射濃度測定装置を用いて測定した。
【００６３】
画像濃度（ＩＤ）はべた黒部の濃度測定値である。かぶり濃度（ＦＤ）は、複写後の非画像部の反射濃度から、複写前白紙の反射濃度を差し引いた濃度である。
【００６４】
画像濃度については、１．３以上を可、１．３未満を不可、かぶり濃度については、０．００５以下を可、０．００６以上を不可と評価した。
【００６５】
表１に評価結果を示した。比較例８〜１４に示す、電界強度５×１０⁵Ｖ／ｃｍにおけるホール輸送剤の移動度が１×１０^-5ｃｍ²／Ｖ／ｓｅｃより小さい場合は、図１に示すように該感光体の露光後電位Ｖ_Lは１７０Ｖより大きくなり、十分な画像濃度を得ることができなかった。
【００６６】
【表１】

【００６７】
図２に、電界強度５×１０⁵Ｖ／ｃｍにおけるホール輸送剤の移動度が１×１０^-5ｃｍ²／Ｖ／ｓｅｃ以上の場合、露光後電位Ｖ_L（Ｖ）と移動度比［電子輸送剤（ＥＴＭ）／ホール輸送剤（ＨＴＭ））］との関係を、図３に初期表面電位Ｖ₀と移動度比との関係を示した（実施例１〜１１、比較例１〜７について）。
【００６８】
図２、３より、移動度比が１／２００００以上１／１０以下の場合に、感光体の露光後電位Ｖ_Lが１７０Ｖ以下、初期表面電位Ｖ₀が７５０Ｖ以上となり、表１より、Ａ４コピー速度が毎分５０枚の高速画像形成装置での実写試験でも、画像かぶりが無く、ＩＤが１．３以上の十分な画像濃度が得られた。
【００６９】
一方、移動度比が１／２００００より小さい場合、該感光体の露光後電位Ｖ_Lは１７０Ｖより大きくなり、十分な画像濃度を得ることができなかった。移動度比が１／１０より大きい場合、該感光体の初期表面電位Ｖ₀が７５０Ｖより小さく、画像かぶりが発生した。
【００７０】
【発明の効果】
本発明によれば、像担持体として、導電性基体上に少なくとも電荷発生剤、ホール輸送剤、電子輸送剤及びバインダー樹脂から構成される感光層を備え、電界強度が５×１０⁵Ｖ／ｃｍにおける前記ホール輸送剤の移動度が１×１０^-5ｃｍ²／Ｖ／ｓｅｃ以上であり、且つ前記ホール輸送剤の移動度に対して、前記電子輸送剤の移動度が１／２００００以上１／１０以下である正帯電単層型電子写真感光体ドラムを備え、波長７８０ｎｍの単色光（半値幅２０ｎｍ，光強度１５μＷ）を、＋８００Ｖに帯電させた前記感光体ドラム表面に露光（露光時間４０ｍｓｅｃ）し、露光開始時点から５００ｍｓｅｃ経過した時点で測定した露光後電位が１７０Ｖ以下であることを特徴とする画像形成方法が、高速及び省エネルギー画像形成装置の提供を可能とする。
【００７１】
【図面の簡単な説明】
【図１】感光体の露光後電位とホール輸送剤（ＨＴＭ）の移動度との関係
【図２】電界強度５×１０⁵Ｖ／ｃｍにおけるホール輸送剤の移動度が１×１０^-5ｃｍ²／Ｖ／ｓｅｃ以上の場合、感光体の露光後電位と移動度比［電子輸送剤（ＥＴＭ）／ホール輸送剤（ＨＴＭ））］との関係
【図３】電界強度５×１０⁵Ｖ／ｃｍにおけるホール輸送剤の移動度が１×１０^-5ｃｍ²／Ｖ／ｓｅｃ以上の場合、感光体の初期表面電位と移動度比［電子輸送剤（ＥＴＭ）／ホール輸送剤（ＨＴＭ））］との関係[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming method used in an image forming apparatus such as an electrostatic copying machine, a facsimile machine, or a laser beam printer using a positively charged single layer type electrophotographic photosensitive drum as an image carrier.
[0002]
[Prior art]
In the image forming apparatus, various organic photoreceptors having sensitivity in the wavelength region of the light source used in the image forming apparatus can be used. This organic photoconductor is easier to manufacture than conventional inorganic photoconductors, and there are various options for photoconductor materials such as a charge transport agent, a charge generator, and a binder resin, and the degree of freedom in functional design is high. In recent years, it has been widely used because of its advantages.
[0003]
The organic photoreceptor includes a single layer type photoreceptor in which a charge transport agent is dispersed in the same photosensitive layer together with a charge generator, a charge generation layer containing a charge generator, and a charge transport layer containing a charge transport agent. There is a laminated type photoreceptor in which is laminated.
[0004]
In particular, single-layer photoreceptors have become very popular in recent years because of their simple structure and ease of manufacture, suppression of film defects when forming layers, reduced interface between layers, and improved optical characteristics. In the spotlight. The single-layer type photoreceptor can be used for both positive and negative charge types, but the positive charge type is generally the mainstream at present due to the characteristics of the photoconductor constituent materials.
[0005]
The image forming apparatus using the single-layer type photoreceptor has the following advantages and is expanding its market.
1) High image quality since there is no disturbance of charge transfer at the interface between the charge generation layer and the charge transport layer as in the stacked type.
2) When used with a positive charge, ozone that is harmful to the human body is hardly generated.
[0006]
[Problems to be solved by the invention]
In order to satisfy the demand for higher speed and energy saving of an image forming apparatus that has been increasing in recent years, the conventional single layer type photoreceptor is already insufficient in sensitivity. .
[0007]
That is, in the conventional positively charged single-layer type electrophotographic photosensitive member, for example, in an image forming apparatus with a high process speed of A4 copy speed of 50 sheets per minute or less, the exposure light amount is small, and the photosensitive drum is moved from the exposure position to the development position. Since the time required to reach is short, the phenomenon that the development process is reached during the potential decay due to exposure occurs.
[0008]
As a result, an excessive amount of light is required to reduce the light potential of the photoconductor, the change in the light potential due to environmental fluctuations increases during the potential decay, and photoconductor fatigue due to repeated exposure and development. A large image occurs, and it is difficult to obtain a good image.
[0009]
An object of the present invention is to provide an image forming method that uses a high-sensitivity positively charged single-layer type electrophotographic photosensitive member as an image carrier and sufficiently meets the demands for high speed and energy saving.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors, as a result of diligent research, have developed a photosensitive layer composed of at least a charge generator, a hole transport agent, an electron transport agent and a binder resin on an electroconductive substrate as an image carrier. When the electric field strength is 5 × 10 ⁵ V / cm and the mobility of the hole transport agent measured using the TOF method is HTM, and similarly the mobility of the electron transport agent is ETM, the hole The mobility (HTM) of the transport agent is set to a value of 1 × 10 ⁻⁵ cm ² / V / sec or more, and the mobility ratio represented by ETM / HTM is within a range of 1/20000 to 1/10. Image forming method using a positively charged single layer type electrophotographic photosensitive drum having a value, monochromatic light having a wavelength of 780 nm, a half width of 20 nm and a light intensity of 15 μW was charged to +800 V by applying an applied voltage. The photosensitive drum An image forming method characterized in that the surface is exposed at an exposure time of 40 msec and the post-exposure potential measured when 500 msec has elapsed from the start of exposure is 170 V or less. Made it possible.
[0011]
The positively charged single layer type electrophotographic photosensitive member used in the image forming method of the present invention exhibits very high sensitivity. The reason why a highly sensitive positively charged single layer type electrophotographic photosensitive member was obtained is presumed as follows.
[0012]
Among the photogenerated carriers, electrons reach the surface of the photosensitive layer and holes reach the conductive substrate side, causing light attenuation. In addition, since the charge generation distribution is unevenly distributed near the surface of the photosensitive layer, the moving distance of holes is inevitably longer than the moving distance of electrons.
First, when the mobility of an electron transport agent is less than 1/20000 with respect to a hole transport agent having a mobility of 1 × 10 ⁻⁵ cm ² / V / sec or more at an electric field strength of 5 × 10 ⁵ V / cm, Due to the difference in mobility between the transport agent and the electron transport agent, electrons that could not reach the surface of the photosensitive layer remain in the photosensitive layer. For this reason, the charge generation efficiency does not increase, leading to a decrease in sensitivity of the photoreceptor, and it is difficult to obtain a sufficient image density in a high-speed image forming apparatus.
[0014]
On the contrary, when the mobility of the electron transport agent is larger than 1/10 with respect to the hole transport agent, the positive charge on the surface of the photosensitive layer is canceled faster than the holes reach the conductive substrate, and the electric field strength of the photosensitive layer is reduced. Decreases. For this reason, the movement of holes becomes increasingly rate-limiting, leading to a reduction in sensitivity. Further, since the positive charge on the surface of the photosensitive layer is canceled out, the surface potential of the photosensitive member tends to decrease, and image fog is likely to occur.
[0015]
Next, the photosensitive layer of the positively charged single layer type electrophotographic photosensitive drum used in the image forming method of the present invention is composed of at least a charge generator, a hole transport agent, an electron transport agent and a binder resin, as will be described later. Any conventionally known additive can be added. A barrier layer may be formed between the conductive substrate and the photosensitive layer.
[0016]
However, the addition of the above-mentioned additives to the photosensitive layer and the provision of a barrier layer adversely affect the electrophotographic characteristics (sensitivity, charging ability, etc.) of the photosensitive drum. The kind of additive and the material used for the barrier layer must be selected so that it becomes 170 V or less.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
A single layer type electrophotographic photosensitive member is obtained by providing a single photosensitive layer on a conductive substrate. This photosensitive layer is formed by dissolving or dispersing a charge generator, a hole transport agent, an electron transport agent, a binder resin, etc. in an appropriate solvent, coating the resulting coating solution on a conductive substrate, and drying. The
[0018]
Next, various constituent materials of the positively charged single layer type electrophotographic photosensitive member used in the image forming method of the present invention will be described.
[0019]
<Charge generating agent> Examples of the charge generating material of the electrophotographic photosensitive member used in the image forming method of the present invention include various phthalocyanine pigments, polycyclic quinone pigments, azo pigments, perylene pigments, indigo pigments, quinacridone pigments, and azureniums. Salt pigments, squarylium pigments, cyanine pigments, pyrylium dyes, thiopyrylium dyes, xanthene dyes, quinone immuno dyes, triphenylmethane dyes, styryl dyes, selenium, tellurium, amorphous silicon, cadmium sulfide, etc. Can be used. These charge generating agents are preferably contained in an amount of 0.1 to 30% by weight, more preferably 0.5 to 10% by weight, based on the binder resin.
[0020]
Among the charge generating agents exemplified above, in particular, image forming apparatuses of digital optical systems such as laser beam printers and facsimiles using a light source such as a semiconductor laser require a photosensitive member having sensitivity in a wavelength region of 700 nm or more. Therefore, for example, a metal-free phthalocyanine represented by the general formula (CG1) and a phthalocyanine-based pigment such as oxotitanyl phthalocyanine represented by the general formula (CG2) are preferably used. The crystal form of the phthalocyanine pigment is not particularly limited, and various types can be used.
[0021]
(CG1) Metal-free phthalocyanine

[0022]
(CG2) Oxo titanyl phthalocyanine

[0023]
<Hole Transfer Agent> The hole transfer agent for the photoreceptor used in the image forming method of the present invention must have a mobility of 1 × 10 ⁻⁵ cm ² / V / sec or more at an electric field strength of 5 × 10 ⁵ V / cm. There is. Examples thereof include compounds represented by the following general formulas (HT1) to (HT3).
[0024]
(HT1) Mobility: 1.21 × 10 ⁻⁵ cm ² / V / sec
[Chemical 3]

[0025]
(HT2) Mobility: 1.69 × 10 ⁻⁵ cm ² / V / sec
[Formula 4]

[0026]
(HT3) Mobility: 3.38 × 10 ⁻⁵ cm ² / V / sec
[Chemical formula 5]

[0027]
In the photoreceptor used in the image forming method of the present invention, the hole transport agent can be used alone or in combination of two or more. The content of the hole transport agent is preferably 5 to 500% by weight, more preferably 25 to 200% by weight, based on the binder resin.
[0028]
<Electron Transfer Agent> The electron acceptor of the single-layer type positively charged electrophotographic photosensitive member used in the image forming method of the present invention is 1/20000 or more and 1/10 with respect to the mobility of the exemplified hole transfer agent. For example, compounds represented by the following general formulas (ET1) to (ET7) with respect to the hole transporting agent are included.
[0029]
(ET1) Mobility: 1.75 × 10 ⁻⁹ cm ² / V / sec
[Chemical 6]

[0030]
(ET2) Mobility: 5.32 × 10 ⁻⁹ cm ² / V / sec
[Chemical 7]

[0031]
(ET3) Mobility: 1.67 × 10 ⁻⁸ cm ² / V / sec
[Chemical 8]

[0032]
(ET4) Mobility: 6.13 × 10 ⁻⁸ cm ² / V / sec
[Chemical 9]

[0033]
(ET5) Mobility: 1.37 × 10 ⁻⁷ cm ² / V / sec
Embedded image

[0034]
(ET6) Mobility: 3.47 × 10 ⁻⁷ cm ² / V / sec
Embedded image

[0035]
(ET7) Mobility: 1.04 × 10 ⁻⁶ cm ² / V / sec
Embedded image

[0036]
In the photoreceptor used in the image forming method of the present invention, the electron transport agent can be used alone or in combination of two or more. The content of the electron transfer agent is preferably 5 to 100% by weight, more preferably 10 to 80% by weight, based on the binder resin.
[0037]
The mobility was measured by a normal TOF (TimeOfFlight) method at room temperature. The electric field strength was 5 × 10 ⁵ V / cm. The measurement sample was dissolved in a binder resin (bis-Z type polycarbonate resin having a weight average molecular weight of 20,000) at a concentration of 40 wt%, applied onto a substrate, and heat-treated at 80 ° C. for 30 minutes. Produced. The sample film thickness is 7 μm.
[0038]
<Binder Resin> Various resins conventionally used in photosensitive layers can be used as the binder resin for dispersing each component. For example, styrene polymer, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, acrylic polymer, styrene-acrylic copolymer, polyethylene, ethylene-vinyl acetate copolymer Polymer, chlorinated polyethylene, polyvinyl chloride, polypropylene, ionomer, vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, Thermosetting resins such as polyether resins, silicone resins, epoxy resins, phenol resins, urea resins, melamine resins, other cross-linkable thermosetting resins, epoxy acrylate, urethane acrylate, etc. Resins and the like can be used. These binder resins can be used alone or in combination of two or more.
[0039]
In the photosensitive layer, in addition to the above-described components, various conventionally known additives such as an antioxidant, a radical scavenger, a singlet quencher, an ultraviolet absorber, etc., as long as the electrophotographic characteristics are not adversely affected. An anti-degradation agent, softener, plasticizer, surface modifier, extender, thickener, dispersion stabilizer, wax, acceptor, donor, and the like can be blended. In order to improve the sensitivity of the photosensitive layer, for example, a known sensitizer such as terphenyl, halonaphthoquinones, acenaphthylene and the like may be used in combination with the charge generator.
[0040]
The thickness of the photosensitive layer in the single-layer type positively charged electrophotographic photosensitive member is 5 to 100 μm, preferably 10 to 50 μm.
[0041]
In the single-layer type positively charged electrophotographic photosensitive member, a barrier layer may be formed between the conductive substrate and the photosensitive layer as long as the characteristics of the photosensitive member are not impaired. Further, a protective layer may be formed on the surface of the photoreceptor.
[0042]
As the conductive substrate on which the photosensitive layer is formed, various materials having conductivity can be used. For example, iron, aluminum, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium Examples thereof include simple metals such as nickel, palladium, indium, stainless steel, and brass, plastic materials on which the above metals are vapor-deposited or laminated, glass coated with aluminum iodide, tin oxide, indium oxide, and the like.
[0043]
The shape of the conductive substrate may be any of a sheet shape and a drum shape according to the structure of the image forming apparatus to be used. The substrate itself has conductivity or the surface of the substrate has conductivity. If you do. The conductive substrate preferably has sufficient mechanical strength when used.
[0044]
When the photosensitive layer is formed by a coating method, the above-exemplified hole transport agent, charge generator, electron acceptor, binder resin and the like together with a suitable solvent, a known method such as a roll mill, a ball mill, What is necessary is just to disperse and mix using an attritor, a paint shaker, an ultrasonic disperser, etc., adjust a dispersion liquid, apply | coat this by a well-known means, and dry it.
[0045]
As the solvent for preparing the dispersion, various organic solvents can be used, for example, alcohols such as methanol, ethanol, isopropanol and butanol, and aliphatic hydrocarbons such as n-hexane, octane and cyclohexane. , Aromatic hydrocarbons such as benzene, toluene, xylene, halogenated hydrocarbons such as dichloromethane, dichloroethane, chloroform, carbon tetrachloride, chlorobenzene, ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, Ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and methyl acetate, dimethylformaldehyde, dimethylformamide, dimethyl sulfoxide, etc. Can be given. These solvents are used alone or in combination of two or more.
[0046]
Further, a surfactant, a leveling agent and the like may be used in order to improve the dispersibility of the charge generating agent, hole transporting agent and electron transporting agent and the smoothness of the photosensitive layer surface.
[0047]
【Example】
Hereinafter, the present invention will be described with reference to examples and comparative examples. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
[0048]
[Examples 1 to 11] 4.5 parts by weight of an X-type metal-free phthalocyanine (CGM) as a charge generating agent, 65 parts by weight of a hole transporting agent [selected from the above (HT1) to (HT3)], and an electron transporting agent [Select one from the above (ET1) to (ET7)] 30 parts by weight, 100 parts by weight of bisphenol Z-type polycarbonate resin (Resin) having a weight average molecular weight of 30,000 as binder resin, and 760 parts by weight of tetrahydrofuran in a ball mill A coating solution for a single-layer type photosensitive layer was prepared by dispersing or dissolving for 27 hours. Then, this coating solution is applied on an aluminum base tube as a support by a dip coating method, followed by hot air drying at 1/10 ° C. for 40 minutes, and a single photosensitive layer having a thickness of 27.5 μm. A layer type photoreceptor was prepared.
[0049]
[Comparative Examples 1 to 7] Single layer type photoreceptors were produced in the same manner as in Examples 1 to 11 except that one type of electron transfer agent selected from (ET8) to (ET11) was used.
[0050]
(ET8) Mobility: 6.00 × 10 ⁻¹⁰ cm ² / V / sec
Embedded image

[0051]
(ET9) Mobility: 7.56 × 10 ⁻¹⁰ cm ² / V / sec
Embedded image

[0052]
(ET10) Mobility: 2.08 × 10 ⁻⁶ cm ² / V / sec
Embedded image

[0053]
(ET11) Mobility: 2.77 × 10 ⁻⁶ cm ² / V / sec
Embedded image

[0054]
[Comparative Examples 8 to 14] Single layer type photoreceptors were produced in the same manner as in Examples 1 to 11 except that (HT4) was used as the hole transport agent.
[0055]
(HT4) Mobility: 1.60 × 10 ⁻⁶ cm ² / V / sec
Embedded image

[0056]
The electrophotographic photosensitive member of each of the above examples and comparative examples was subjected to the following tests to evaluate the characteristics.
[0057]
<Initial Sensitivity Evaluation> Using a drum sensitivity tester (trade name Gentec Cynthia 30M) manufactured by GENTEC, an applied voltage is applied to the electrophotographic photosensitive member of each example and comparative example, and the surface is applied. Charged to + 800V.
[0058]
Next, monochromatic light having a wavelength of 780 nm (half-value width 20 nm, light intensity 15 μW) extracted from the white light of a halogen lamp, which is an exposure light source of the test machine, using a bandpass filter is applied to the surface of the charged photoreceptor. Exposure (exposure time 40 msec) was performed. Then, the surface potential after 500 msec from the exposure start time was measured as a post-exposure potential V _L (V). That is, the smaller the post-exposure potential, the higher the sensitivity of the photoreceptor.
[0059]
The post-exposure potential must be 170 V or less in order to obtain a sufficient image density in a high-speed image forming apparatus with an A4 copy speed of 50 sheets per minute or more.
[0060]
<Evaluation of Initial Charging> Using the drum sensitivity tester, the initial surface potential V ₀ (V) of each of the electrophotographic photosensitive members of Examples and Comparative Examples at an inflow current value of 12 μA was measured. Charging was performed by the corotron method.
[0061]
The initial surface potential must be 750 V or higher in order to obtain an image without fogging in an image forming apparatus having an A4 copy speed of 50 or more per minute.
[0062]
<Image evaluation> The electrophotographic photosensitive member obtained in each example and comparative example was mounted on a high-speed digital copying machine [Creage7350 manufactured by Mita Kogyo Co., Ltd.] having an A4 copy speed of 50 sheets per minute, and a live-action test was performed. The solid reflection density was measured using a reflection density measuring device manufactured by Nippon Denshoku Co., Ltd.
[0063]
The image density (ID) is a density measurement value of the solid black part. The fog density (FD) is a density obtained by subtracting the reflection density of the blank paper before copying from the reflection density of the non-image area after copying.
[0064]
The image density was evaluated as 1.3 or more, less than 1.3 was not possible, and the fog density was evaluated as 0.005 or less and 0.006 or more as improper.
[0065]
Table 1 shows the evaluation results. When the mobility of the hole transport agent at the electric field strength of 5 × 10 ⁵ V / cm shown in Comparative Examples 8 to 14 is smaller than 1 × 10 ⁻⁵ cm ² / V / sec, the photoconductor as shown in FIG. The post-exposure potential V _L was greater than 170 V, and sufficient image density could not be obtained.
[0066]
[Table 1]

[0067]
In FIG. 2, when the mobility of the hole transport agent at an electric field strength of 5 × 10 ⁵ V / cm is 1 × 10 ⁻⁵ cm ² / V / sec or more, the post-exposure potential V _L (V) and the mobility ratio [electron Transport Agent (ETM) / Hole Transport Agent (HTM))], and FIG. 3 shows the relationship between the initial surface potential V ₀ and the mobility ratio (Examples 1 to 11 and Comparative Examples 1 to 7). ).
[0068]
2 and 3, when the mobility ratio is 1/20000 or more and 1/10 or less, the post-exposure potential V _L of the photoreceptor is 170 V or less and the initial surface potential V ₀ is 750 V or more. Even in a shooting test using a high-speed image forming apparatus at a speed of 50 sheets per minute, there was no image fogging and a sufficient image density with an ID of 1.3 or more was obtained.
[0069]
On the other hand, when the mobility ratio is smaller than 1/20000, the post-exposure potential V _L of the photoconductor is higher than 170 V, and a sufficient image density cannot be obtained. When the mobility ratio was larger than 1/10, the initial surface potential V ₀ of the photoconductor was smaller than 750 V, and image fogging occurred.
[0070]
【The invention's effect】
According to the present invention, the image carrier is provided with a photosensitive layer composed of at least a charge generator, a hole transport agent, an electron transport agent and a binder resin on a conductive substrate, and the electric field strength is 5 × 10 ⁵ V / cm. The mobility of the hole transport agent is 1 × 10 ⁻⁵ cm ² / V / sec or more, and the mobility of the electron transport agent is 1/20000 or more of the mobility of the hole transport agent. It is equipped with a positively charged single layer type electrophotographic photosensitive drum of 10 or less, and monochromatic light having a wavelength of 780 nm (half width 20 nm, light intensity 15 μW) is exposed on the surface of the photosensitive drum charged to +800 V (exposure time 40 msec) An image forming method characterized in that the post-exposure potential measured after 500 msec from the exposure start time is 170 V or less provides a high-speed and energy-saving image forming apparatus. Make it possible.
[0071]
[Brief description of the drawings]
FIG. 1 shows the relationship between the post-exposure potential of a photoreceptor and the mobility of a hole transport agent (HTM). FIG. 2 shows that the mobility of a hole transport agent is 1 × 10 ⁻⁵ cm at an electric field strength of 5 × 10 ⁵ V / cm. ^{In the case of 2} / V / sec or more, the relationship between the post-exposure potential of the photoreceptor and the mobility ratio [electron transport agent (ETM) / hole transport agent (HTM))] [FIG. 3] electric field strength 5 × 10 ⁵ V / When the mobility of the hole transport agent in cm is 1 × 10 ⁻⁵ cm ² / V / sec or more, the initial surface potential of the photoreceptor and the mobility ratio [electron transport agent (ETM) / hole transport agent (HTM))] Relationship with

Claims (2)

As an image carrier, a photosensitive layer comprising at least a charge generator, a hole transport agent, an electron transport agent and a binder resin on a conductive substrate,
When the electric field strength is 5 × 10 ⁵ V / cm, the mobility of the hole transport agent measured using the TOF method is HTM, and similarly, the mobility of the electron transport agent is ETM.
The mobility (HTM) of the hole transport agent is set to a value of 1 × 10 ⁻⁵ cm ² / V / sec or more, and the mobility ratio represented by ETM / HTM is in the range of 1/20000 to 1/10. An image forming method using a positively charged single-layer type electrophotographic photosensitive drum having a value within the range,
Monochromatic light having a wavelength of 780 nm, a half width of 20 nm, and a light intensity of 15 μW was exposed to the surface of the photosensitive drum charged to +800 V by applying an applied voltage at an exposure time of 40 msec, and 500 msec had elapsed from the start of exposure. An image forming method, wherein the post-exposure potential measured at the time is 170 V or less.   2. The image forming method according to claim 1, wherein the A4 copy speed is 50 sheets or more per minute.

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