JPS62191854A - Bipolar photosensitive body - Google Patents

Abstract

PURPOSE:To obtain a photosensitive body high in sensitivity by laminating the second positive hole transfer layer, a carrier generating layer, and the first positive hole transfer layer in succession on a conductive substrate, and setting the work function of the substrate and the ionizing energy of the second hole transfer layer in a specified relationship. CONSTITUTION:The second hole transfer layer 3, the carrier generating layer 2, and the first hole transfer layer 1 are laminated in succession on the conductive substrate 4. The relationship between the work function W (eV) possessed by a substance to be used for the conductive substrate 4, and the ionization energy Ip (eV) of a substance to be used for the second hole transfer layer 3 is set to W+0.5>=Ip, thus permitting the obtained bipolar photosensitive body to be extremely enhanced in sensitivity by the presence of the single carrier generating layer, and to be reduced in image line noises in practical uses by the protection of the hole transfer layer 3, and enhanced in printing resistance.

Description

[Detailed description of the invention] Industrial applications The present invention relates to bipolar photoreceptors.

In conventional electronic photography, the surface of the photoreceptor is first given a uniform charge by corona discharge, resulting in a charging gap.

Photoreceptors are used as unipolar, depending on the polarity of the charge provided by the corona discharge. Therefore, for example, in the case of a reader printer that aims to obtain a double-sided image for both positive and negative originals, the actual situation is to use a unipolar photoreceptor and two types of developing devices. It is.

Therefore, bipolar photoreceptors have been proposed that can be used even if they are positively or negatively charged (for example, Japanese Patent Laid-Open No. 49-45737 or Japanese Patent Laid-Open No. 49-9164).
Publication No. 6).

JP-A-49-45737 and JP-A-49-91
All of the techniques disclosed in Japanese Patent No. 646 include a second charge generation layer (CG
LX5) as an inorganic photoconductive substance, such as Se, Cd
S, ZnO or C(Is.

Thereon, a charge transport layer (C'r) (6) is formed of an inorganic conductive material such as polyhinylcarbazole (PVI<) or polyvinylanthracene, and the first CGL (7) is formed of an inorganic photoconductive material. This is related to bipolar photoreceptors made by sequentially laminating polar substances.

Trying to invent or solve a problem, I tried to make 4 mushrooms per piece.

A second c c L (5) on the substrate (4) as described above,
C'rL (6) and first CGL (7) sequentially fs'
In the case of a photoreceptor having a structure in which approximately [/2] of the exposure light amount has to pass through the first CGL (7) and reach the second CGL (5), the first CGL ( 7) There is a restriction that it cannot be made thicker. To that end, the first CGI, (7
) must be very thin <f, which means that the light sensitivity is not sufficient, and because it is on the surface, for example, when a plate is used as a cleaner, it will be scraped and the drum will be scratched, causing image noise. There are problems such as it is easy to make and cannot withstand repeated use. In addition, a powder substance (Se) is formed as a result of being scraped.

There is also a problem with the pollution potential of CdS, etc.).

Among the emitted light, the light in the short wavelength range is the first CG.
In I (7), since light in the long wavelength range is absorbed by the second CGL (5), the first and second CGLs do not respond with the same photosensitivity, so the photosensitivity and image quality decrease. There are other problems, such as:

The present invention solves the problem of "two feet", has high sensitivity, and does not cause image distortion even after repeated copying! 1 mi drop,
An object of the present invention is to provide a bipolar photoreceptor that has excellent printing durability and does not cause any concern about pollution.

Means for solving the problem, that is, the present invention provides a second hole transport layer on a conductive substrate,
A charge generation layer and a first hole transport layer are sequentially laminated,
The conductivity Jl (work function W (eV) of the body and the ionization energy Ip (eV) of the second hole transport layer are expressed by the formula "I"
.

The present invention relates to a bipolar photoreceptor characterized by the following relationship: W+ 05 ≧ Ip EI].

For example, as shown in FIG. 1, the photoreceptor of the present invention includes a second hole transport layer (3) on a conductive substrate, a charge generation layer (2) on top of the second hole transport layer (3), and a first layer on top of the second hole transport layer (3). It has a structure in which the hole transport layer (+) of VI is delivered.

An important point in the present invention is that the work function a of the substance used for the conductive substrate (4) is W (eV), and the second hole transport! If the strike ionization energy of the substance used for rJ (3) is Ip (eV), then Kawane is expressed by the formula [I]
The relationship W + 0.5 ≧ 1p exists. When a photoreceptor is formed of a material that satisfies the relationship W+ 05 ≦ Ip, it becomes difficult to inject positive charges from the conductive 7Iri body (4) to the hole transport layer (3), resulting in a decrease in photosensitivity. At the same time, it no longer functions as a bipolar photoreceptor.

Regarding the present invention, the work function refers to a photoelectronic work function actually measured using an external photoelectric effect method, and is expressed in eV small units.

The ionization energy referred to in the present invention is the value measured by the external photoelectric effect method for the hole transport layer, which refers to the energy difference between the valence band of the hole transport layer and the vacuum degree, and is expressed in eV small units. means.

Metals that can be used for the conductive substrate (4) include Group I elements, such as gold, silver, copper, or Group I elements, such as aluminum, or Group V elements, such as iron, cobalt, nickel, etc. However, the selection depends on the material used for the hole transport layer (3), which will be described later.
1, so as to satisfy the relationship of formula [I].

The metal used for the conductive substrate (4) may be used as the gold layer itself, or may be applied to the surface of a flexible film, such as a polyester film or a polyethylene telefoil film, by sputtering or vapor deposition. It may be used by covering it using some means. The degree of coverage is not particularly limited. The substance used for the second hole transport layer (3) is a hole-transporting substance. Examples of the hole-transporting substance include hydrazones, such as eddylaminobenzaldehyde diphenyl. Hydrazone (
DEH), pyrazolines such as 1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)-pyrazoline (ASPP), and oxadiazoles, such as 112.3- Oxadiazole, 1.2.4-oxadiazole, oxazoles, triphenylamines, anones,!・You can list examples such as liphenylmethanes.

The substance used for the second hole transport layer (3) has an ionization energy of 1111 ((4V)) as described above for the conductive layer (3).
Work function W (eV) of the metal used in the body (・1)
Select and use so that the relationship between and the expression [+] is satisfied.

A preferred combination of substances used for the conductive substrate (4) and the second hole transport layer (3) is gold and DE'l-
1. Nickel and DErl, copper and DEl(, silver and AS
I) P, etc. can be mentioned, but B is not limited to this combination, and it is sufficient if both substances satisfy the relationship of formula [r].

The second hole transport layer (3) is composed of an organic material having surface hole transport properties, a transparent resin such as polycarbonate, acrylic resin, etc., and a suitable solvent such as tetrahydrofuran (
A conductive substrate (4
) by dipping, spinner coating, etc., and drying the solvent.

The hole-transporting organic material has an IO heavy claw shape to the resin.
The content is 0% by weight, preferably 20% to 60% by weight. If it is more than 60% by weight, it will not be possible to form a film as a layer, and if it is less than 20% by weight, it will not function as a hole transport layer.

The second hole transport layer (3) is laminated to a thickness of 3 μm to 30 μm, preferably 5 μm to 25 μm. If it is thinner than 3 μm, the charging ability will be poor, and if it is thicker than 30 μm, the electrophotographic sensitivity will be poor.

The charge generating layer (2) is made of an inorganic photoconductive material such as selenium (Se), cadmium sulfide (CdS), zinc oxide (Z
(nO) is laminated using a method such as vacuum evaporation or sputtering in step 11 A to a film thickness having a white light transmittance of about 10% or less.

The charge generation layer (2) may use an azo pigment, a phthalocyanine pigment, a perylene pigment, a triphenylmethane pigment, a cyanine pigment, or the like as an organic photoconductive substance.

The present invention is characterized by the fact that the charge generation layer (2) can be stacked with +y<y to the extent that sufficient photosensitivity is obtained because the charge generation layer (2) only needs to be one layer, and furthermore, the charge generation layer (2) can be stacked to the extent that sufficient photosensitivity is obtained. Since it is located below the hole transport layer, its surface will not suffer wear damage even after repeated copying.

The first hole transport layer (1) may be formed in the same manner as the second hole transport layer (3) using the hole transporting organic substance described above. The organic materials used in the first and second hole transport layers may be the same or different, but are preferably the same.

The first hole transport layer (1) is laminated to a thickness of 3 μm to 30 μm, preferably 5 μm to 25 μm. If it is thinner than 3 μm, the charging ability will be poor, and if it is thicker than 30 μm, the electrophotographic sensitivity will be poor.

In addition, the first charge transport layer (1) and the second charge transport layer (3
) preferably have substantially the same thickness. Charge transport layer (
If there is a large difference in the thickness of the charge transport layer (1) and the charge transport layer (3), there will be a difference in the electrostatic properties in both polarities, so by using the same developer and changing the development bias, you can produce positive, positive, and negative images. In reader printers and the like whose purpose is to obtain the same, problems arise such as differences in image characteristics due to bipolar polarity.

The image forming principle of the photoreceptor according to the present invention is illustrated in Figures 2-a-f and 3.
-a-e.

When the surface of the photoreceptor is charged (+) in the charging process, electrons are induced on the base metal side, resulting in the charge distribution shown in Figure 2-a. When exposure is performed in this state, the electrons generated in the charge generation layer, Among the hole pairs, the holes travel through the second hole transport layer (3) and neutralize the base electrons (Fig. 2-b), while the electrons remain in the charge generation layer and pass through the second hole transport layer (3). The charge distribution becomes as shown in the figure. First hole transport layer (1) and second hole transport layer (3)
When they are made of the same material and have the same thickness, the potential of the exposed part becomes approximately 1/2 of the potential of the unexposed part, and one quadrant is formed.

Next, in the photo-erase process, the charge distribution inside the photoreceptor is
When (-) charging is performed after making the state shown in the figure (Figure 2-e), holes are induced in the base, but the work function of the base is lower than the ionization energy of the second hole transport layer (3). If the size is large, the injection of holes from the base to the second hole transport layer (3) is very smooth, and the induced holes directly flow into the second hole transport layer (3). At the same time as it is injected, it travels through the hole transport layer and neutralizes the electrons in the charge-generating region. At this time, since the (+) charge on the surface has already been neutralized by the (-) charge at the time of (-) charging, the photoreceptor returns to its initial state (Fig. 2-f).

When the surface of the photoreceptor is charged to (-) (Fig. 3-a), the holes induced in the base will be generated if the work function of the base metal is approximately equal to the ionization energy of the second hole transport layer (3) or Since it is large and does not have an injection barrier, it is smoothly injected into the second hole transporting stone (3), simultaneously travels through the hole transporting layer, and flows into the second hole transporting layer (3) and charge generation layer (2).
) (Figure 3-b). I wanted to do it, (
-) The charge distribution after charging is exactly the same as when using a normal laminated photoreceptor with (-) band 7u as shown in Figure 3-b. The normal process shown in Figures ce) will still be applied.

As is clear from the above image forming principle, the photoreceptor of the present invention can be charged to either positive or negative polarity. Then, a method for obtaining a positive image from a negative or positive original will be explained. To obtain a positive blurred image when positively charged, the photoreceptor is charged, exposed, developed, and erased through the steps shown in Figures 2-a to 2-r. In the process, an electrostatic latent image is formed on the photoreceptor with the unexposed area serving as an image area, and is regularly developed with negative polarity toner to obtain a positive image from a positive original. On the other hand, if the charge polarity is changed to negative to obtain a negative/outlined image, an electrostatic latent image is formed with the light irradiation area as the image area as shown in Figure 3-d, and the negative polarity toner forms a reflective ring ('ρ). You can get blurry images from unfinished manuscripts.

As described above, the photoreceptor according to the present invention can be charged to either polarity, and a single blank image can be created from a blank original or a negative original using a single developing device. In other words, conventional photoreceptors cannot be charged with one polarity, and the developing device is
, 9 is necessary, and the disadvantage of increasing the size of the entire device is therefore avoided.The photoreceptor of the present invention overcomes the disadvantages listed in item 111j.

The present invention will be explained below using examples.

Example 1 - Au-deposited polyethylene terephthalate film (1
25 μm) on top of polycarbonate with the following composition...60 parts by weight D E
H...40 parts by weight TIIF
・・・・・・・・・ After applying and drying the solution of 400 layers to form a second hole transport FJC3) with a thickness of 12 μm, amorphous selenium with a thickness of about 1 μm was deposited using a vacuum evaporation method. A charge generation layer was formed.

Next, a solution having the above composition was further applied and dried on this amorphous selenium layer to form a first hole transport layer (1) with a thickness of 12 μm, and a photosensitive plate with a total thickness of 1'; The evaluation was made using a photoreceptor tester (not shown).

(4-) Regarding charging: 100OV as initial surface potential
was applied, irradiated with white light from a halogen lamp, and further photoerased to raise the surface potential to 530V1.
．． : Attenuated. Furthermore, (), ji; electric erase was performed. The residual potential is 30V and the surface potential is 100OV.
Half-reduction exposure that attenuates from to 750V! 11E1/2 had 7 Jlux-sec.

The above cycle of (+) charging - exposure - photo erasing - (-) charging erase was repeated 100 times, but no change in characteristics was observed.

()4: Regarding the lip d, the initial surface potential is -500V
, apply white light from a halogen lamp, and
Optical erase was performed.

The half-exposure Hk Et 72 in which the surface potential attenuates from 1500V to 1250V was 7 lux-sec, and the residual potential was 20V.

10 or more (-) charging-exposure-photo-erase cycles
No change in characteristics was observed, probably because it was repeated 0 times.

At this time, the work function of the Au evaporated surface was measured using the external photoelectric effect method, and it was 5.2 eV, and when the ionization energy rp of C T L was measured using the external photoelectric effect method, it was 5.2 eV.
It was IeV.

Example 2 The photoreceptor shown in Example I was formed on a temporary Ni layer, and as in Example I, it was charged with a 3.V value using a reciprocating photoreceptor testing machine for both +) and (-) charging. Similar to (1), good results were obtained.

In addition, when the N1 provisional work function at this time is measured using the external photoelectric effect method, 4. There was BeV.

Example 3 Cu-deposited polyethylene terephthalate film (1
The photoreceptor shown in Example I was formed on a surface of 25 μm) and evaluated using a reciprocating photoreceptor tester, and the same good results as in Example 1 were obtained for both +) and (-) charging.

Example 4 Ag-deposited polyethylene terephthalate film (1
25μm) on top of the following composition ASI) l')...
-1300 to 100 parts by weight polycarbonate tinone
)...... 10 parts by weight, 4 parts 'I''IIF... 80 parts by weight of the solution was applied and dried to form a hole transport layer with a thickness of 12 μm, and then a layer with a thickness of approximately A charge generating layer of 1 μm of amorphous selenium was formed.

Next, a solution having the above composition was further applied and dried on this amorphous selenium layer to form a hole transport layer with a thickness of 12 μm.
A 25 μm photosensitive plate was prepared and evaluated using a reciprocating photoreceptor tester, and as in Example 1, good results were obtained with (10X-) bipolarity.

Note that the work function of the Ag-deposited surface at this time was 4.4 eV when measured using an external photoelectric effect method. CT at this time again
The ionization energy of L was 4.8 eV.

Example 5 Au-deposited polyethylene terephthalate film (1
A solution having the composition used in Example 1 was applied and dried to form a hole transport layer with a thickness of 12 μm.
)... 10 heavy! i part polyester (V-200) IO overlapping part cyclohexanone 200 parts by weight of the dispersion was applied using a spin cord to form a charge generation layer of 0.05 μm.

Next, a solution having the composition used in Example 1 was again coated on the charge generation layer and dried to form a hole transport layer with a thickness of 12 μm to prepare a photosensitive plate with a total thickness of 25 μm, and the same evaluation as in Example 1 was carried out. and (+), (), l+F electrics both E (12”
Good results were obtained for 5 LuX'' SeC.

Example 6 The bipolar photoreceptor (13) prepared as shown in Example 1 on the Au-deposited Ai woodwind was mounted on the electrophotographic apparatus shown in FIG. 5, and image evaluation was performed.

For (+) charging, after charging to +000V with a bipolar charger (14), a positive image was exposed to white light (15) from a halogen lamp to form an electrostatic image.

Next, development was carried out on this photoreceptor using a developing device (IG) at a developing bias potential of 650 V, and then transferred onto paper (17
). The photoreceptor was cleaned by a cleaning unit (18), and a good blurred image was obtained by removing static electricity using an optical eraser (9) and a (-) polar charger (20). The behavior of the charging potential at that time is shown in Figure 4-a. In the figure, the solid line indicates the change in surface potential of the exposed area, and the dotted line indicates the change at position 11 on the surface of the non-exposed area. In FIG. 4-a, the photoreceptor is first charged to 1000V, and there is no change at the point indicated by the arrow (8).

Next, development is performed under the application of a development bias potential indicated by an arrow (11). At the point of arrow (9), the optical erase shift and the surface potential of the exposed area change by 4'', and the potential of only the non-exposed area decreases to be the same as the potential of the exposed area, and at the point of arrow (10) it becomes negative.
Power up once to return vJ to its initial state. The potential represented by (12) is the residual potential.

(-) When charging, charge to -500V with the bipolar charger (14), then expose to negative image to form a latent image, and develop the latent image at a development bias potential of -350■ to create a good positive image. Got the image. The behavior of the surface potential at that time is shown in Figure 4-b. In the figure, the solid line represents the change in surface potential of the exposed area, and the dotted line represents the change in surface potential of the non-exposed area. In Fig. 4-b, first the photoreceptor is turned on at -500V.
image exposure is performed at the point of arrow (8), the surface potential of only the exposed area is reduced, and then development is carried out under application of a bias potential, a phenomenon represented by arrow (11). Further, at the point of arrow (9), photo-erasing is performed, and both the exposed and non-exposed areas have the same surface potential, returning to the initial state. The potential represented by (12) is the residual potential.

Comparative Example I Ag-deposited polyethylene terephthalate film (1
The photoreceptor shown in Example 1 was formed on the photoreceptor (25 μm) and evaluated using a reciprocating photoreceptor tester.

Regarding (+) charging, the sensitivity was a only in the first charging and exposure process, and there was no sensitivity at all in the second and subsequent processes.

Regarding (-) charging, it was found that the residual potential was large and increased to a large +j level with repeated charging and exposure, so that it could not withstand repeated use.

The work function of the Ag-deposited surface at this time was measured using the external light 7u effect method and was 4.4 (!V).

Comparative Example 2 A4 vapor-deposited polyethylene terephthalate film (1
The photoreceptor shown in Example 1 was formed on 25 μl (1 liter) of the photoreceptor, and evaluated using a photoreceptor tester of the iJ: Retrospective type. As in Comparative Example 1, it was found that the photoreceptor did not withstand repeated use.

In addition, to this time! The work function of the vapor-deposited surface was measured by external photoelectric effect method and was found to be 4.3 eV.

From the above Examples and Comparative Examples, it can be seen that not only the case of Example (1) where the work function of the base is larger than the ionization energy of the hole transport layer, but also the case where the work function of the base is smaller than the ionization energy of the hole transport layer. The difference between them is 0.5eV
It has been found that if the photoreceptor is below, holes can be easily injected from the base into the hole transport layer with the help of an electric field, and the photoreceptor can function satisfactorily as the bipolar photoreceptor which is the gist of the present invention.

According to the present invention, a second hole transport layer, a charge generation layer, and a first hole transport layer are sequentially laminated on a conductive outer body.
．． An ambipolar sensor constructed of a material in which the work function W (eV) of the nuclear conductive 11r) body and the ionization energy +p (eV) of the second hole transport layer satisfy the following relationship: The light body has extremely high sensitivity due to the charge generation layer, and is protected by the hole transport layer, so it produces less image noise and is highly durable during actual use. ing.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of the bipolar photoreceptor of the present invention, and Figure 2-a-
FIG. , FIG. 6 is a cross-sectional view of a conventional bipolar photoreceptor. The symbols in the figure are as follows. 1... First hole transport layer, 2... Charge generation layer,
3. Second hole transport layer, 4. Conductive substrate, 5.
...Second charge generation layer, 6...Charge transport layer, 7
1st Tri charge generation layer, 8... Time of exposure, 9... Time of photo erasure, 10... Time of (-) charging, 11
-Development bias potential, I2...Residual potential, 13.Bipolar photoreceptor, 14.Bipolar charger, 15.Light, 1G...Developer, 17.Transfer device, 18.Cleaning unit, 19.. Optical eraser, 20...(-) polar charger. Figure 1 Figure 2-d Figure 2-e Figure 2-f Procedural amendment April 1, 1986

Claims (1)

[Claims] 1. A second hole transport layer, a charge generation layer, and a first hole transport layer are sequentially laminated on a conductive substrate, and the work function W (eV) of the conductive substrate is and the ionization energy Ip (eV) of the second hole transport layer have the following relationship: W+0.5≧Ip[I].