JPS6162037A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To form the sensitometry over the entire part of a photosensitive body into soft gradation to expand the dynamic range thereof and to obtain a reproduced image having a high grade by varying the attenuating speed of the electrostatic charge potential in each photoconductive layer, i.e., photosensitivity and interposing charge blocking layers between the photoconductive layers. CONSTITUTION:This photosensitive body is made into the construction in which the photoconductive layer laminated on a conductive substrate 1 is divided to three layers 2-4 and that charge blocking layers 5, 6 are interposed at the respective boundaries. The layers 2-4 consist of the photosensitive materials having the same quantum efficiency. The layers 3, 4 have the characteristic to allow the transmission of 30% of incident light and to absorb the remaining 70%. If the electrostatic capacities of the layers 2-4 are the same, the electrostatic charge potentials born by the layers 2-4 attenuate respectively at about 1:2:7 ratio of the speed when the photosensitive body is electrostatically charged and exposed. The part where the response is fast and the part where the response is slow are thus mixed as compared with the case in which the single layer receives 100 quantity of light. The sensimetry is thus made into the soft gradation and the dynamic range is eventually expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrophotographic photoreceptor with an expanded dynamic range in exposure characteristics.

(Prior Art) A photoreceptor used in Carlson electrophotography has a photoconductor layer provided on a conductive substrate.

Conventionally, this photoconductor layer has been made of a vapor deposited film of an inorganic photoconductor such as amorphous Se, a photoconductor crystal such as ZnO or CdS dispersed in a binder, or a coating film of various organic photoconductors. is used.

(Problems to be Solved by the Invention) However, these photoreceptors have a narrow dynamic range in exposure characteristics compared to silver halide photography, etc., and this point can be said to be the biggest obstacle in reproducing high-quality images. In order to expand the dynamic range, attempts have been made to increase the dependence of quantum efficiency on electric field strength, but this method inevitably increases the residual potential.

An object of the present invention is to provide a photoreceptor with an expanded dynamic range without causing problems such as an increase in residual potential.

(Means for Solving the Problems) The photoreceptor of the present invention has a multilayer structure of photoconductive layers provided on a conductive substrate, and each layer has a different effective photosensitivity, and The charged charge carriers are such that they do not flow across the boundaries of each layer. Here, effective photosensitivity is not the sensitivity measured by taking out each layer and irradiating it with light individually, but the sensitivity of how each layer responds to light irradiated onto the completed multilayer photoreceptor. It means something. Therefore, the photosensitivity of the lower layer is influenced by the light absorption rate of the upper layer.

(Function) In the photoreceptor constructed in this way, each photoconductive layer exhibits different photosensitivity to light irradiation from the top layer side, and the photosensitivity is not affected by the photosensitivity of other layers. , the sensitivity of the photoreceptor will be softer and its dynamic range will be expanded compared to a photoreceptor consisting of a single photoconductive layer.

(Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 shows the layer structure of the photoreceptor according to this example. As shown in the figure, in this example, the photoconductive layer laminated on the conductive substrate 1 is divided into three layers 2.3.4, and a charge blocking layer 5.6 is interposed at the boundary of each layer. It becomes. Each layer 2.3.4 is made of a photosensitive material with the same quantum efficiency, and the layer 3.4 has the property of transmitting 30% of the incident light and absorbing the remaining 70%. Therefore, when a light amount of 100 is applied from the photoconductive layer 4 side, the amount of light absorbed by each layer is as follows.

Therefore, if the electrostatic capacitance of each layer 2 to 4 is the same, when the photoreceptor is charged and exposed, the charged potential of each layer 2 to 4 attenuates at a rate of about 1=2, respectively. Therefore, compared to the case where a single layer receives a light amount of 100, the parts with fast response and parts with slow response are mixed, so
The sensitometry will be softer and the dynamic range will be expanded. Here, if the movement of charge carriers is not prevented at the boundaries of each layer 2 to 4, for example, the charge carriers photogenerated in layer 4 will also attenuate the charged potential that layers 3 and 2 have. Therefore, we cannot expect to expand the dynamic range of sensitometry.

Note that in order to prevent the movement of charges, it is not always necessary to form independent layers with a constant thickness as in the above embodiments, and an energy barrier is formed at the boundary of each photoconductive layer. Materials may be selected in the following manner. Further, each of the photoconductive layers 2 to 4 does not need to be a uniform layer, and each layer may be separated into a charge generation layer and a charge transport layer.

The conductive substrate 1 used in the photoreceptor of the present invention includes AI,
A metal support such as Ni, Cr, or Cu, a resin film coated with these metals, or a resin film coated with conductive carbon dispersed in a resin binder can be used.

As the photoconductive layer used in the present invention, any known photoconductor can be used as long as it is the bottom layer 2 in contact with the conductive substrate 1. For example, Se, 5e-Te, 5e
Chalcogenide materials such as -As, a-3i:H, etc., or various organic photoconductive materials can be used. The upper photoconductive layer 3.4 needs to have a certain degree of light transparency, so it is made of a dye-sensitized organic photoconductor,
A structure separated into a thin charge generation layer and a transparent charge transport layer is suitable.

Here, as the charge generation layer, Se, 5e-Te, 5e
-As, 5e-Te-As, CdS.

Inorganic photoconductors such as CdSeTe, amol 77 S i : H, T% Rufus Si:F, phthalocyanine,
Organic photoconductors such as merocyanine and pyrylium salts can be used. These charge generation layers can be formed not only by vapor deposition or CVD, but also by coating photoconductor particles such as dyes and pigments dispersed in a binder resin.

Further, as the organic charge transport layer, a polymer semiconductor such as PVK, or a low molecular organic semiconductor dispersed in molecular form in an insulating binder can be used. Examples of low-molecular organic semiconductors include fused polycyclic compounds such as anthracene, 2,6-dimethylanthracene, phenanthrene, pyrene, and coronene, diphenylamine, dinaphthylamine, triphenylamine, and tri-p- ) Lil Amin, N, N, N
',N'-tetraphenyl-1-3(and-1,4)-
Phenyl diamine, N, N.

N', N'-tetrabenzyl-1-3 (and -1°4)
-phenylenediamine, N, N, N', N'-tetra [
2-methylbenzyl]-1-3 (and -1,4)--7
Enylene diamine, N, N, N'.

N'-tetra[4-chlorobenzyl]-1-,3(and 1.4)-phenylenediamine, N,N.

N',N'-tetraphenyl-[1,1'-biphenyl>4',4'-diamine, N',N'-diphenyl-N
, N'-bis-[3-methylphenyl:]-[]1,1
'-biphenyl]-4,4' diamine, 4,4'-bis-CN, N', aromatic amino compounds such as diethylamino]tetraphenylmethane, 2-[: /I'-dimethylaminophenyl]-5- Oxazole derivatives such as phenyloxazole, thiazole derivatives such as 2-[4'-dimethylaminophenyl]-benzthiazole, 2
-[:4'-10-phenyl:]-]Imidazole derivative of 4.5-diphenylimidazole, 1,3°5-
) IJ phenylpyrazoline, 1-phenyl-3-[
Pyrazoline derivatives such as 4'-dithymelaminophenyl)-5-[:4''-dimethylaminophenylcupirazoline, 2,5-bis-[4'dimethylaminophenyl)-
1,3,4-oxadiazole, 2,5-bis~[4'
-diethylaminophenyl)-1,3,4-oxadiazole and other oxadiazole derivatives, carbazole and N-ethylcarbazole, N-isovylcarbazole,
Carbazole derivatives such as N-phenyl carbazole and benzcarbazole can be used. These low-molecular-weight organic semiconductors can be used by being dispersed in molecular form in an inorganic binder such as polyester or polycarbonate.

As the charge blocking layer 5.6 used in the present invention, a thin film of an insulating polymer, various semiconductor films, or an ion conductive film can be used. Furthermore, it is possible to open a film made of a dried and cured product of a solution containing at least one type of acetylacetone or alkoxide compound containing Zr5TiSAl atoms as a constituent element.

The film thickness of each photoconductor layer in the present invention is from 5μ to 60μ.
The total thickness of the photoreceptor layer (excluding the substrate) is preferably 100 tl or less. Further, the IIQ thickness of the charge blocking layer is preferably γ-less as long as the charge blocking function can be uniformly achieved, and a thickness of 2 μm or less is particularly preferable.

In the present invention, if the number of photoconductive layers constituting the photoreceptor increases, the characteristics of the sensitome (IJ-) will become smoother, but from a manufacturing point of view it is preferable to have between 2 and 5 layers.

Next, the sensitometric characteristics of the photoreceptor according to a specific example 1 of the present invention prepared as described below and a conventional example were compared. As a result, the sensitometric curve of Example 1 is as shown in FIG. 2, and the curve of the conventional example is as shown in FIG. 3, with respective dynamic ranges of approximately 2 and 0.
It became 8.

(Example 1) Approximately 4 μm of Se was formed on the substrate A1 by vacuum evaporation, and an ethyl alcohol solution of zirconium tetrabutoxide was applied thereon, followed by drying at room temperature for 8 hours. Furthermore, from above, N, N'-diphenyl-N, N'-bis-[3-methylphenyl)-[1,1'-biphenyl]
-L4'-diamine and polycarbonate at Seiyusha 1;
A retarder was added to a mixed dichloromethane solution, spray coated, and dried at 40° C. for 10 hours to form an organic charge transport layer with a thickness of 20 μm. Thereafter, as the top layer, 5e-As (5% by weight of As) was vacuum deposited with 0%
．． A photoreceptor was completed by providing a thickness of 2μ.

The surface of this photoreceptor was charged with corona charging and exposed to light reflected from originals of various densities to obtain the sensitometric curves shown in FIG.

(Conventional example) Approximately 60μ of Se was formed on the A1 substrate by vacuum evaporation,
It was used as a photoreceptor. The surface of this photoreceptor was charged with corona charging and exposed to light reflected from originals of various densities to obtain the sensitometric curves shown in FIG.

(Effects of the Invention) As explained in Section 2 below, according to the present invention, the decay rate of the charged potential in each photoconductive layer constituting the photoreceptor, that is, the photosensitivity, is different, and the Due to the interposed charge blocking portion, the decay rate of each photoconductive layer is not affected by the 'g decay rate of the other layers, so that the sensitometry of the entire photoreceptor is soft and its dynamic range is expanded. It is possible to reproduce high-quality reproduced images.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a sensitometric curve diagram of a specific embodiment of the present invention, and FIG. 3 is a sensitometric IJ curve diagram of a conventional example. 1... Conductive substrate, 2, 3.4... Photoconductive layer, 5
, 6... Charge blocking layer.

Claims (1)

[Claims] A plurality of photoconductive layers stacked on an electrically conductive support and formed at mutual boundaries of the photoconductive layers to transfer charge carriers photogenerated in each of said photoconductive layers to the other layers. and a charge blocking portion for blocking movement, wherein each of the photoconductive layers exhibits mutually different photosensitivity to light irradiation from the uppermost layer side in a laminated state. Photoreceptor.