JP4233067B2 - Image forming method - Google Patents

Description

【００１１】
８−ＰＮＰ−Ｏ１２のような、当方相からなるネマティック相を経ずにスメクティック相に直接転移する材料の場合、液晶層の厚みが５０μｍを超える領域では、冷却速度の変更によってドメインサイズの制御が比較的容易である。例えば、徐冷によって得られるテクスチャのドメインサイズはセルギャップと比べて十分大きいのに対して、急冷した際には明らかにセルギャップと同程度か、より細かいドメイン構造となる。偏光顕微鏡によって配向するテクスチャを焦点位置を変えながら観察すると、十分大きなドメインサイズであればその境界がセルギャップ方向に連続的に観察でき、厚み方向にはほぼモノドメイン構造であることが分かる。一方、電極表面でセルギャップと同程度以下のドメイン構造が見られる場合にはその境界を連続的に観測することは不可能で、急冷して得た配向状態ではセルギャップ方向にも細かいドメイン境界が多数存在する。
【００１２】
ドメインサイズと構造が電荷移動度に及ぼす影響をＴＯＦ（Time Of Flight）法で評価するために測定した正キャリアの過渡光電流波形を示したのが図２である。ここでは、セルギャップ１００μｍ、印加電圧１０００Ｖ、電極面積１０×１０ｍｍ² 、Ｎ₂ パルスレーザーにより励起したときの過渡光電流波形を示しており、レーザー励起により生成されたキャリアが移動するに伴って測定されるシート電流（変位電流）波形である。図中、ｒｄは形成された多数のドメインの中心的なドメインサイズの値を示し、徐冷の際はｒｄ＞１００μｍ、急冷の際はｒｄ≒２５μｍであった。
【００１３】
図２において、まず、この半導体材料が高速性を有していることが分かる。また、電荷輸送にドメイン境界が影響を及ぼすならば移動度や過渡光電流波形に顕著な差異が認められるはずであるが、実際にはいずれの場合も移動度がそれほどかわらず、ポリドメインの構造の影響が見られず、また、セルギャップ１０μｍの試料において得られている従来報告されている値とあまり変わらなかった。即ち、１０倍の輸送長においても移動度が劣化していないことが判明した。
【００１４】
また、過渡光電流の減衰の傾きは液晶層中のキャリア輸送の分散を反映するが、この傾きもドメインサイズに影響を受けておらず、液晶性有機半導体材料の欠陥準位密度が本質的に極めて低いことが分かる。光学的に観察される構造欠陥が電荷輸送に対してこのように不活性であることは、配向欠陥近傍において液晶の流動性によって隣接する分子間のホッピングサイトが分断されることが無いためと考えられる。なお、過渡光電流値に絶対値の差異が生じている原因は、ドメイン構造による光散乱の影響で、液晶層の実効的な光吸収量の違いによる電荷生成量が異なるためと考えられる。
【００１５】
このように、液晶層を厚くし、急冷処理を施し、配向処理を行わないことで意図的に微細なポリドメイン構造を導入した場合においてすら、電荷輸送特性が阻害されないことが分かる。すなわち、通常、行われる試料作成条件のもとでは、構造欠陥はさらに少なく、電荷輸送が阻害されにくいばかりでなく、電荷生成効率における構造欠陥の影響も、本来、ここに示したほど顕著には現れない。
【００１６】
次に本発明における液晶層を構成する液晶性化合物、誘電体層についてさらに詳しく説明する。
〔液晶層〕
電荷輸送性を有し、かつ強誘電性を有する液晶性化合物は、電子移動度が１×１０^-5ｃｍ² ／Ｖ・ｓｅｃ以上、正孔移動度が１×１０^-5ｃｍ² ／Ｖ・ｓｅｃ以上であり、より好ましくは、電子移動度が１×１０^-4ｃｍ² ／Ｖ・ｓｅｃ以上、正孔移動度が１×１０^-4ｃｍ² ／Ｖ・ｓｅｃ以上である。電子移動度、および正孔移動度が１×１０^-5ｃｍ² ／Ｖ・ｓｅｃ以下となると電子伝導よりもイオン伝導が支配的になり好ましくない。好ましい液晶性化合物は、（６π電子系芳香環）ｌ、（１０π電子系芳香環）ｍ及び／又は（１４π電子系芳香環）ｎ（ｌ＋ｍ＋ｎ＝１〜４、ｌ、ｍ及びｎはそれぞれ０〜４の整数を表す）をコアに有し、上記の各芳香族が、それぞれ同一または異なる組み合わせで、直接にあるいは炭素−炭素二重結合または炭素−炭素三重結合を介して連結器で連結されているものである。
【００１７】
６π電子系芳香環としては、例えば、ベンゼン環、ピリジン環、ピリミジン環、ピリダジン環、ピラジン環、トロポロン環、１０π電子系芳香環としては、例えば、ナフタレン環、アズレン環、ベンゾフラン環、インドール環、インダゾール環、ベンゾチアゾール環、ベンゾオキサゾール環、ベンゾイミダゾール環、キノリン環、イソキノリン環、キナゾリン環、キノキサリン無、１４π電子系芳香環としては、例えば、フェナントレン環、アントラセン環等が挙げられる。中でも２−フェニルナフタレン環、ビフェニル環、ベンゾチアゾール環、ｔ−チオフェン環の何れか１種類またはそれ以上をコアに有し、かつ棒状分子構造を有する液晶化合物が好ましく、さらに２−フェニルナフタレン環をコアに有し、該ベンゼン環、およびナフタレン環の各々がアルキル基、アルコキシ基等の側鎖を有し、かつ棒状分子構造を有する液晶性化合物が好ましい。
〔誘電体層〕
本発明の電子写真感光体は電極基板上に液晶性化合物を含む液晶性電荷輸送層（光導伝層）、誘電体層を順に配置する。誘電体層は液晶性電荷輸送層の機械的強度の保持、画像形成に対するコロナ帯電保持等において重要な役割を有する。誘電体層としては、予め誘電体層として形成された可とう性フィルム、あるいはガラス等の固体層である。予め誘電体層として形成された可とう性フィルムとしては、各種のプラスチックフィルムを用いることができる。例えばポリエチレンフィルム、ポリスチレンフィルム、ポリエステルフィルム、ポリカーボネートフィルム、ポリイミドフィルム等が用いられ、機械的強度等を考慮すると、ポリエステルフィルムが好ましく用いられる。
【００１８】
誘電体層に要求される物性としては、上記液晶性電荷輸送層の保護適性の他、電気絶縁性である。これは電子写真感光体として帯電露光により両画像形成を行う上で、その帯電特性を付与する意味で重要である。帯電特性を付与するためには、該誘電体層の電気導電率が１０^-12 Ω^-1・ｃｍ^-1以下であることが必要であり、好ましくは１０^-14 Ω^-1・ｃｍ^-1である。１０^-12 Ω^-1・ｃｍ^-1以上であると、誘電体層の帯電性、並びに帯電保持性が低く、たとえ液晶性電荷輸送層が帯電露光によりその機能を発現したにしても、その機能発現を帯電電位で検出できず好ましくない。また、用いる誘電体層の厚みは液晶性電荷輸送層の厚みによって異なるが、帯電特性を考慮し、１０μｍ〜２００μｍ好ましくは１５μｍ〜１５０μｍのものを用いる。１０μｍ以下では誘電体層自体の機械的強度が低下し、また２００μｍ以上だと画像露光による帯電電位の差が検出できず好ましくない。また、画像露光に用いる波長に対し透過性であることが必要である。
【００１９】
次に、画像形成方法について説明する。
上記したように、液晶性有機半導体材料の使用により、電荷輸送層としての加工性における制約が解かれることとなり、液晶の流動性を利用したセル構造への注入により、自己組織的に大面積素子としての応用が可能である。
図３は容量像方式による画像形成を説明する図である。
記録媒体として、誘電体層１２（１２μｍ厚みのＰＥＴフィルム）／光導伝層１１／ベース層１０（ＩＴＯ電極付きガラス基板）を用い、容量像方式で画像形成した。なお、図３において、記録媒体の下側の電位を示す図は記録媒体の表面電位を示している。
【００２０】
基板の電極を接地した状態で誘電体層表面をコロナ帯電により誘電体層上に、電位Ｖまで一様な帯電を行う。このときの電荷分布は、誘電体層上の一様な正電荷に対応してベース層の電極には負電荷が一様に分布する（図３（ａ））。次いで、像露光すると、露光部の光導伝層１１の抵抗が減少し、ベース層の電極に分布していた負電荷が絶縁層と光導伝層との界面に移動し、感光体の実効的な容量が増加する。このため、露光部の電位はＶからＶ_L に低下する（図３（ｂ））。このとき、未露光部の負電荷はベース層の電極に分布している。次いで、電位Ｖまで一様に再帯電すると、露光部の実効容量が未露光部に比して大きいので、誘電体層上の電荷密度は露光部が未露光部に比して大きくなる（図３（ｃ））。次いで、全面露光を行うと、ベース層の電極に分布していた負電荷のみが誘電体層と光導伝層の界面に移動する。この結果、像露光（図３（ｂ））時の未露光部の実効容量が増加して電位はＶからＶ_L に低下し、一方、像露光時の露光部の実効容量は変化せず、電位もＶのまである（図３（ｄ））。
【００２１】
いま、絶縁層の容量をＣ_d 、光導伝層の容量をＣ_p 、未露光部の電位をＶ、露光部の電位をＶ_L 、コントラスト電位をＶ_c とすると、

となる。光導伝層の容量Ｃ_p は、液晶層の厚みを大きくすることにより小さくすることができるので、その分大きなコントラスト電位が得られ、像形成に寄与することができる。
【００２２】
図３に示す方法で潜像を形成し、室温（結晶相）で湿式トナーによって現像して定着し、露光パターンを反映する画像形成の例を示したのが図４である。図４においては、１２μｍのＰＥＴ誘電体層を用いていながら、光導伝層１００μｍとすることによって電位コントラストを得ることができたものである。これは高速の電荷輸送と低欠陥密度という液晶性有機半導体材料によって可能になったものである。もちろん、湿式トナーに代えて乾式トナーでもよく、また、図３において、再帯電しない図３（ｂ）の段階でトナー現像して定着するようにしてもよい。また、均一露光においては、液晶層の感光波長を含む光で露光するようにする。また、潜像を直接トナー現像する方式に代え、図３に示した電位分布を、例えば走査型の電位計を用いて読み取るようにしてもよく、その場合は、表示装置に画像出力することも可能である。
【００２３】
【発明の効果】
以上のように本発明は、光導電層に液晶性有機半導体材料を用いることを特徴としており、液晶はシリコン等の無機半導体に比べれば、光導電特性は落ちるものの有機材料としては比較的高い光導電特性を有しており、しかも形状や構造の問題は一切生じることがない。すなわち液晶の流動性のために一対の電極板がどのような形状構造のものであっても、両電極板間に充填させることが極めて容易である。このため、小ロット生産を行う場合であっても、コストを低く抑えることができ、しかも形態の自由度が高い画像記録素子を実現することができる。また、液晶の流動性に由来して均一かつ十分大きな厚みとしても、液晶の配向に基づく構造欠陥やポリドメイン構造は電気的に不活性で、電荷輸送特性はドメイン界面や配向欠陥によっては阻害されず、液晶性材料は一様に配向制御されている必要がなく、製造を容易にすることが可能である。また、液晶性材料層を十分厚くすることができるため、光吸収の効率が上がり、像形成を行うことが可能である。
【図面の簡単な説明】
【図１】 本発明の電子写真感光体の層構成の例を説明する図である。
【図２】 正キャリアの過渡光電流波形を示す図である。
【図３】 容量像方式による画像形成を説明する図である。
【図４】 容量像方式で像形成して現像した画像の例を示す図である。
【符号の説明】
１…基板、２…透明電極層、３…感光層、４…誘電体層、１０…ベース層、１１…光導伝層、１２…誘電体層。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming method using a liquid crystalline organic semiconductor material.
[0002]
[Prior art]
When an organic / inorganic charge transporting material having high mobility is used for the photosensitive layer in image formation by the capacitive image method, the photosensitive layer may be made relatively thick to several μm to several tens of μm in order to obtain a sufficiently large potential contrast. Necessary. However, the realization of such a thick organic layer has been industrially difficult due to technical limitations related to structural limitations (consideration for structural defects). Also, due to the problems associated with the fragility of the constituent layers, it has been difficult to realize a photosensitive layer with a film thickness.
[0003]
[Problems to be solved by the invention]
In an electrophotographic photoreceptor in which a photosensitive layer is formed on an electrode plate, no problem occurs in image formation regardless of the shape and configuration of the electrode plate. If attention is paid only to the photoconductivity in the photosensitive layer, an element using a semiconductor such as silicon is more efficient. However, when a solid element is used as the charge transport material, its shape and structure are greatly limited. In particular, in the case of an element using a silicon single crystal substrate, its vulnerability is a problem, and it is difficult to use a substrate that is thicker than a certain degree.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems, and an object of the present invention is to sufficiently increase the thickness of a photosensitive layer regardless of the structural limitations and increase the light absorption efficiency so as to obtain a large potential contrast.
[0005]
[Means for Solving the Problems]
The present invention, on the electrode substrate, the liquid crystal compound organic semiconductor material, a liquid crystal compound is a dye-sensitized organic semiconductor material or a photoconductive layer comprising a liquid crystalline compound organic semiconductor material sensitized by fullerene C _70,, Using an electrophotographic photosensitive member in which a dielectric layer is arranged in order, a first uniform corona charging step, an image exposure step, a second uniform corona charging step having the same polarity as the first, and a uniform by light including the photosensitive wavelength of the photosensitive member Image forming corresponding to image exposure is performed by sequentially performing exposure, dry or wet toner development process, toner transfer process to a transfer medium, and toner fixing process.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 1 is a diagram for explaining an example of the layer structure of the electrophotographic photosensitive member of the present invention. A transparent electrode (ITO) layer 2, a photoconductive layer (photosensitive layer) 3, and a dielectric layer 4 are sequentially laminated on a substrate 1. The substrate 1 is made of, for example, a glass substrate (non-alkali glass, alkali glass, quartz glass, etc.), an ITO electrode layer 2 is formed thereon, and a photoconductive layer (photosensitive layer) made of a liquid crystalline organic semiconductor material described later. About 100 μm is formed, and a dielectric layer 4 made of PET film is formed to a thickness of 10 μm or more. As a specific forming method, the PET film 4 is temporarily fixed to a supporting substrate in advance, and the supporting substrate and the glass substrate 1 with an ITO electrode are disposed on the inner surface of the PET film 4 to inject liquid crystal in a conventional sad-itch cell configuration. After sealing, a uniform liquid crystal layer is obtained by removing the support substrate of the PET film. The cell gap is ensured by dispersing insulating inorganic or organic fine particles in the liquid crystalline organic semiconductor material, or by providing a spacer layer at a non-image forming site. If the electrophotographic photosensitive member is formed in a cylindrical drum shape, an image can be formed by arranging components in a conventional copying machine or printer.
[0008]
The liquid crystalline organic semiconductor material is derived from the fluidity of the liquid crystal material, and structural defects based on the orientation of the liquid crystal and the polydomain structure are electrically inactive, and the transport properties of the carriers generated by exposure depend on the domain interface and alignment defects. Is essentially unhindered, and the liquid crystalline material in the photosensitive layer does not necessarily need to be uniformly controlled, and can be easily manufactured. As the wavelength used for exposure, ultraviolet light (near 337 nm) is used when a liquid crystalline organic semiconductor material not dye-sensitized is used. In this case, the image forming process can be performed consistently in a bright room environment. In addition, when sensitization is performed by adding a dye to the liquid crystal layer, image formation in the visible light region is facilitated. When performing sensitized with fullerene C ₇₀ as a dye, although in principle there is sensitization effect, the solubility of the dye can not be raised enough to not be able to ensure a sufficient thickness in a conventional sensitizing Although no effect was obtained, in the present invention, since the liquid crystal layer can be made sufficiently thick, the efficiency of light absorption is increased and a sufficient sensitizing effect is obtained.
[0009]
Next, the fact that the charge transport property is not affected by the polydomain structure will be described in more detail.
For example, characterization of 2-phenylnaphthalene derivative 8-PNP-O12 having the following structural formula is performed at 90 ° C., SmB layer, 100 μm gap (glass / ITO / liquid crystal / ITO / glass) cell (no alignment treatment) ) Was used to examine the tolerance of the polydomain structure.
[0010]
[Chemical 1]

[0011]
In the case of a material such as 8-PNP-O12 that directly transitions to a smectic phase without passing through a nematic phase composed of a weotropic phase, the domain size can be controlled by changing the cooling rate in the region where the thickness of the liquid crystal layer exceeds 50 μm. It is relatively easy. For example, the domain size of the texture obtained by slow cooling is sufficiently larger than the cell gap, but when rapidly cooled, the domain structure is clearly the same as or finer than the cell gap. When observing the texture oriented with a polarizing microscope while changing the focal position, it can be seen that if the domain size is sufficiently large, the boundary can be continuously observed in the cell gap direction and has a substantially monodomain structure in the thickness direction. On the other hand, when a domain structure that is less than or equal to the cell gap is observed on the electrode surface, it is impossible to observe the boundary continuously. In the alignment state obtained by quenching, a fine domain boundary is also observed in the cell gap direction. There are many.
[0012]
FIG. 2 shows a transient photocurrent waveform of a positive carrier measured in order to evaluate the influence of the domain size and structure on the charge mobility by the TOF (Time Of Flight) method. Here, a transient photocurrent waveform is shown when the cell gap is 100 μm, the applied voltage is 1000 V, the electrode area is 10 × 10 mm ² , and the N ₂ pulse laser is excited, and the measurement is performed as the carriers generated by the laser excitation move. It is a sheet current (displacement current) waveform. In the figure, rd represents the value of the central domain size of a large number of formed domains, rd> 100 μm during slow cooling, and rd≈25 μm during rapid cooling.
[0013]
In FIG. 2, first, it can be seen that this semiconductor material has high speed. In addition, if domain boundaries affect charge transport, there should be significant differences in mobility and transient photocurrent waveforms. However, in all cases, the mobility is not so much, and the structure of the polydomain And the value reported in the sample having a cell gap of 10 μm was not much different from the conventionally reported value. That is, it was found that the mobility was not deteriorated even at a transport length of 10 times.
[0014]
In addition, the slope of transient photocurrent decay reflects the dispersion of carrier transport in the liquid crystal layer, but this slope is also not affected by the domain size, and the defect level density of the liquid crystalline organic semiconductor material is essentially It can be seen that it is extremely low. The optically observed structural defects are inactive to charge transport in this way because the hopping sites between adjacent molecules are not divided by the fluidity of the liquid crystal in the vicinity of the alignment defects. It is done. In addition, it is considered that the reason why the absolute value difference is generated in the transient photocurrent value is due to the effect of light scattering due to the domain structure, and the charge generation amount due to the difference in effective light absorption amount of the liquid crystal layer is different.
[0015]
Thus, it can be seen that even when a fine polydomain structure is intentionally introduced by increasing the thickness of the liquid crystal layer, applying a rapid cooling process, and not performing an alignment process, the charge transport characteristics are not hindered. That is, under the sample preparation conditions that are usually performed, there are fewer structural defects and not only charge transport is hardly inhibited, but also the influence of structural defects on the charge generation efficiency is inherently as remarkable as shown here. It does not appear.
[0016]
Next, the liquid crystal compound and dielectric layer constituting the liquid crystal layer in the present invention will be described in more detail.
[Liquid crystal layer]
A charge-transporting property and a liquid crystalline compound having ferroelectricity, electron mobility is ^{1 × 10 -5 cm 2 / V} · sec or more, the hole mobility of ^{1 × 10 -5 cm 2 / V} · More preferably, the electron mobility is 1 × 10 ⁻⁴ cm ² / V · sec or more, and the hole mobility is 1 × 10 ⁻⁴ cm ² / V · sec or more. When the electron mobility and the hole mobility are 1 × 10 ⁻⁵ cm ² / V · sec or less, ion conduction is more dominant than electron conduction, which is not preferable. Preferred liquid crystalline compounds are (6π electron aromatic ring) 1, (10π electron aromatic ring) m and / or (14π electron aromatic ring) n (l + m + n = 1 to 4, l, m and n are each 0 to Each having the same or different combination, either directly or via a carbon-carbon double bond or a carbon-carbon triple bond, via a coupler. It is what.
[0017]
Examples of the 6π electron aromatic ring include a benzene ring, a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a tropolone ring, and a 10π electron aromatic ring, for example, a naphthalene ring, an azulene ring, a benzofuran ring, an indole ring, Examples of the indazole ring, benzothiazole ring, benzoxazole ring, benzimidazole ring, quinoline ring, isoquinoline ring, quinazoline ring, no quinoxaline, and 14π electron aromatic ring include a phenanthrene ring and an anthracene ring. Among them, a liquid crystal compound having one or more of 2-phenylnaphthalene ring, biphenyl ring, benzothiazole ring and t-thiophene ring in the core and having a rod-like molecular structure is preferable. A liquid crystal compound having a rod-like molecular structure in which the benzene ring and the naphthalene ring each have a side chain such as an alkyl group or an alkoxy group is preferable.
(Dielectric layer)
In the electrophotographic photoreceptor of the present invention, a liquid crystalline charge transport layer (photoconductive layer) containing a liquid crystalline compound and a dielectric layer are arranged in this order on an electrode substrate. The dielectric layer has an important role in maintaining the mechanical strength of the liquid crystalline charge transport layer, maintaining corona charge for image formation, and the like. The dielectric layer is a flexible film previously formed as a dielectric layer, or a solid layer such as glass. Various plastic films can be used as the flexible film previously formed as a dielectric layer. For example, a polyethylene film, a polystyrene film, a polyester film, a polycarbonate film, a polyimide film, and the like are used. In consideration of mechanical strength and the like, a polyester film is preferably used.
[0018]
The physical properties required for the dielectric layer are electrical insulating properties in addition to the protective suitability of the liquid crystalline charge transport layer. This is important in terms of imparting charging characteristics when both images are formed by charging exposure as an electrophotographic photosensitive member. In order to impart charging characteristics, the electric conductivity of the dielectric layer needs to be 10 ⁻¹² Ω ⁻¹ · cm ⁻¹ or less, preferably 10 ⁻¹⁴ Ω ⁻¹ · cm ⁻¹ . is there. When it is 10 ⁻¹² Ω ⁻¹ · cm ⁻¹ or more, the chargeability and charge retention of the dielectric layer are low, and even if the liquid crystalline charge transport layer exhibits its function by charge exposure, its function The expression cannot be detected by the charged potential, which is not preferable. The thickness of the dielectric layer to be used varies depending on the thickness of the liquid crystalline charge transport layer, but in consideration of charging characteristics, a thickness of 10 μm to 200 μm, preferably 15 μm to 150 μm is used. If it is 10 μm or less, the mechanical strength of the dielectric layer itself is lowered, and if it is 200 μm or more, a difference in charging potential due to image exposure cannot be detected. Further, it is necessary to be transparent to the wavelength used for image exposure.
[0019]
Next, an image forming method will be described.
As described above, the use of the liquid crystalline organic semiconductor material will release restrictions on processability as a charge transport layer, and self-organized large-area devices by injection into the cell structure utilizing the fluidity of liquid crystals. Application as is possible.
FIG. 3 is a diagram for explaining image formation by the capacitive image method.
Dielectric layer 12 (12 μm thick PET film) / photoconductive layer 11 / base layer 10 (glass substrate with ITO electrode) was used as a recording medium, and an image was formed by a capacitive image method. In FIG. 3, the diagram showing the lower potential of the recording medium shows the surface potential of the recording medium.
[0020]
With the electrode of the substrate grounded, the surface of the dielectric layer is uniformly charged to the potential V on the dielectric layer by corona charging. The charge distribution at this time corresponds to uniform positive charges on the dielectric layer, and negative charges are uniformly distributed on the electrodes of the base layer (FIG. 3A). Next, when the image is exposed, the resistance of the photoconductive layer 11 in the exposed portion decreases, and the negative charges distributed on the electrodes of the base layer move to the interface between the insulating layer and the photoconductive layer. Capacity increases. For this reason, the potential of the exposed portion decreases from V to V _L (FIG. 3B). At this time, the negative charge in the unexposed portion is distributed to the electrodes of the base layer. Next, when the surface is uniformly recharged to the potential V, the effective capacity of the exposed portion is larger than that of the unexposed portion, so that the charge density on the dielectric layer becomes larger than that of the unexposed portion in the exposed portion (see FIG. 3 (c)). Next, when the whole surface exposure is performed, only the negative charges distributed on the electrodes of the base layer move to the interface between the dielectric layer and the photoconductive layer. As a result, the effective capacity of the unexposed area during image exposure (FIG. 3B) increases and the potential decreases from V to V _L , while the effective capacity of the exposed area during image exposure does not change, The potential is also up to V (FIG. 3D).
[0021]
Now, _let C _{d be} the capacitance of the insulating layer, C _{p be} the capacitance of the photoconductive layer, V be the potential of the unexposed area, V _{L be} the potential of the exposed area, and V _c be the contrast potential.

It becomes. Since the capacitance C _p of the photoconductive layer can be reduced by increasing the thickness of the liquid crystal layer, a larger contrast potential can be obtained and contribute to image formation.
[0022]
FIG. 4 shows an example of image formation in which a latent image is formed by the method shown in FIG. 3, developed and fixed with wet toner at room temperature (crystalline phase), and an exposure pattern is reflected. In FIG. 4, while using a 12 μm PET dielectric layer, a potential contrast can be obtained by setting the photoconductive layer to 100 μm. This is made possible by a liquid crystalline organic semiconductor material with high-speed charge transport and low defect density. Of course, a dry toner may be used in place of the wet toner, and the toner may be developed and fixed at the stage of FIG. 3B where recharging is not performed in FIG. In uniform exposure, exposure is performed with light including the photosensitive wavelength of the liquid crystal layer. Further, instead of the method in which the latent image is directly developed with toner, the potential distribution shown in FIG. 3 may be read using, for example, a scanning electrometer, and in that case, the image may be output to a display device. Is possible.
[0023]
【The invention's effect】
As described above, the present invention is characterized in that a liquid crystalline organic semiconductor material is used for the photoconductive layer. Although the liquid crystal has a lower photoconductive property than an inorganic semiconductor such as silicon, the organic material is relatively light. It has conductive properties and does not cause any problems in shape and structure. In other words, because of the fluidity of the liquid crystal, it is very easy to fill between the two electrode plates regardless of the shape of the pair of electrode plates. For this reason, even when small-lot production is performed, the cost can be kept low, and an image recording element having a high degree of freedom can be realized. Even if the thickness is uniform and sufficiently large due to the fluidity of the liquid crystal, structural defects and polydomain structures based on the alignment of the liquid crystals are electrically inactive, and the charge transport properties are hindered by domain interfaces and alignment defects. In addition, the liquid crystal material does not need to be uniformly controlled and can be easily manufactured. In addition, since the liquid crystalline material layer can be made sufficiently thick, light absorption efficiency can be improved and image formation can be performed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a layer structure of an electrophotographic photosensitive member of the present invention.
FIG. 2 is a diagram showing a transient photocurrent waveform of a positive carrier.
FIG. 3 is a diagram illustrating image formation by a capacitive image method.
FIG. 4 is a diagram illustrating an example of an image formed and developed by a capacitive image method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Transparent electrode layer, 3 ... Photosensitive layer, 4 ... Dielectric layer, 10 ... Base layer, 11 ... Photoconductive layer, 12 ... Dielectric layer.

Claims (1)

On the electrode substrate, the liquid crystal compound organic semiconductor material, a dye sensitized liquid crystal compound organic semiconductor material or a fullerene C ₇₀ photoconductive layer comprising a liquid crystalline compound organic semiconductor material sensitized by, the dielectric layer Using the electrophotographic photoreceptors arranged in order , the first uniform corona charging step, the image exposure step, the second uniform corona charging step having the same polarity as the first, the uniform exposure by light including the photosensitive wavelength of the photoreceptor, the dry type or An image forming method comprising: sequentially performing any one of a wet toner developing step, a toner transferring step onto a transfer medium, and a toner fixing step to form an image corresponding to image exposure.

Images