JPH0381774A - Photosensitive material and electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To allow the storage of an electrostatic image and to eliminate the need for repeating image projection at every one time of copying by using a material which changes from a high resistance state to a low resistance state by a light irradiation and can be forcibly released in the low resistance state. CONSTITUTION:The thin film consisting of this material changes from the high resistanced R1 state to the low resistance R3 state and maintains this state for a specified period of time when the voltage above the threshold voltage Vth is impressed thereto while the thin film is not irradiated with the light. The thin film is reset to the R1 state from the R3 state when a reverse voltage is impressed thereto. The threshold voltage Vth' drops while the thin film is irradiated with light. The thin film changes from the high resistance R2 state to the low resistance R4 state and maintains this state for a specified period of time when the voltage above the voltage Vth' is impressed thereto. The thin film is reset to the R2 state when the reverse voltage is impressed thereto. The thin film, therefore, exhibits an optical switching function and a memory function when irradiated with light after the voltage above the voltage Vth' and below the voltage Vth is impressed thereto. Lead phthalocyanine having a crystal structure contg. much monoclinic crystal system is preferably used for this material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a photosensitive material having an optical memory function suitable for the information industry or a photoreceptor for electrophotography.

2. Description of the Related Art Conventionally, organic photoreceptors such as polyvinylcarbazole/trinitrofluorenone and phthalocyanine are known as electrophotographic photoreceptors. These photoreceptors take advantage of the fact that the area exposed to light is in a low resistance state only during light irradiation (image projection). However, if the light irradiation is stopped, the low resistance state is released, so the latent image is not stored in memory. If the latent image can be stored in memory, there is no need to project an image every time one copy is made, and it becomes possible to copy the image many times with one image projection.

Problems to be Solved by the Invention Recently, in the above electrophotographic photoreceptor, Cu/TCN
A method has also been proposed in which the memory function of Q is combined to memorize latent images so that multiple copies can be made with one image projection (Journal of the Electrophotographic Society Vol. 24, p. 86, 1986) ).

However, this proposed electrophotographic photoreceptor has a complicated structure, is difficult to manufacture, and is expensive, so it is impractical.

In view of the above circumstances, the present invention provides a photosensitive material and an electrophotographic photosensitive material that have an optical memory function, have a simple material composition, a simple structure, are easy to manufacture, and have a low manufacturing cost. The challenge is to provide one's body.

Means for Solving the Problems In order to solve the problems, the photosensitive material according to claim 1 and the electrophotographic photoreceptor according to claim 3 are organic thin films,
A characteristic that changes to a low resistance state when a voltage equal to or higher than a certain threshold voltage is applied, a characteristic that the threshold voltage decreases in a light irradiation state, a characteristic that the low resistance state can be maintained for at least a certain period of time, and the low resistance Each has the characteristic that the state is released by applying a reverse voltage.

As seen in the photosensitive material of claim 2, the organic thin film is formed of lead phthalocyanine on the surface of the electrode base material, has a crystal structure containing a large amount of monoclinic system, and has a C-axis of the crystal. Those oriented parallel to the substrate surface are used.

The organic thin film basically has photoconductivity, and
The crystal axes are aligned (orientated) in a specific direction, and the electrical conduction has anisotropy. Usually, a thin film is formed on an electrode serving as a substrate, and the highly conductive crystal axis is oriented mainly parallel to the surface of the substrate. Of course, the voltage (electric field) is applied in a direction perpendicular to the highly conductive crystal axis.

In this invention, although the mechanism is not fully understood, a change from a high resistance state to a low resistance state is observed by light irradiation, and it is possible to forcibly release the memory state of the low resistance state. A photoreceptor can store electrostatic images.

EXAMPLES Below, examples of the present invention will be described in detail, taking the case of a lead phthalocyanine thin film as an example, with regard to applied voltage, changes in resistance state of the thin film, and memory function.

In the state without light irradiation (dark state), as shown by the solid line in FIG. 1, if the applied voltage V<threshold voltage vth, the thin film maintains the high resistance R1 state, but if the applied voltage V≧threshold voltage v th When , the thin film changes from the high resistance R state to the low resistance R3 state. In other words, the switching function is demonstrated.

- Once changed to the low resistance R3 state, this state persists for at least a certain period of time. In other words, the memory function is demonstrated. However, as shown in FIG. 1, by applying a reverse voltage, the low resistance R3 state can be forcibly returned to the original high resistance 'fL1 state.

The memory state is released.

In the light irradiation state, as shown by the broken line in FIG. 1, when the applied voltage is <threshold voltage v th', the thin film has a high resistance
in a state. However, this high resistance R2 state is similar to the previous high resistance R2 state.
, the resistance value is lower compared to the state. This is because conductivity increases as carriers are generated depending on the amount of light irradiation. Then, while keeping the light irradiation state, the applied voltage V
When ≧threshold voltage V th', the thin film (the area on which the light hits) changes from the high resistance R2 state to the low resistance R4 state.

- Once the resistance changes to the low resistance R4 state, this state continues for a certain period of time. However, as shown in FIG. 1, by applying a reverse voltage, the low resistance state R4 can be forcibly returned to the high resistance state.

As can be seen from the above, in the photosensitive material of the present invention, the threshold voltage is V' th −+v th' upon irradiation with light.
This results in a decline to Therefore, the threshold voltage V
If a voltage greater than or equal to th' and less than the threshold voltage vth is applied and light is irradiated, the optical switching function and memory function will be exhibited. The resistance value in the low resistance R4 state is the same or lower than that in the low resistance R3 state.

Organic thin films with such characteristics are found, for example, in thin films formed of metal complexes, charge transfer complexes, etc. that have low-dimensional conductive anisotropy, but it goes without saying that they are not limited to these. do not have. More specifically, the organic thin film is
It is formed by, but not limited to, a metal complex of a polymer compound such as a metal complex of phthalocyanine or a metal complex of porphyrin, or a combination of various donors and acceptors.

The thickness of the organic thin film is in the range of about 0.01 to 10 μm, preferably about 0.1 to 5 μm, but is not limited thereto.

The organic thin film in this invention can be made by ordinary thin film formation methods such as vacuum evaporation and sputtering.
Film formation is controlled so that the crystals are oriented so that the low-dimensional (preferably one-dimensional) conductive direction is parallel to the electrode.

For example, in electrophotographic photoreceptors, etc., an organic thin film is usually formed on an electrode that also serves as a base material. Examples of electrode materials include Au, Ags AA! ,C! Examples include, but are not limited to, metals and alloys such as u, and semiconductors such as silicon. Further, a protective insulating thin film may be laminated on the surface of the organic thin film.

In this invention, although the mechanism of changing from a high resistance state to a low resistance state as described above is not sufficiently detailed, for example,
We speculate that the mechanism is as follows. Of course, the present invention is not limited in any way by this explanation of the mechanism.

As shown in FIG. 2(a), the low-dimensional conductive organic thin film 1 has highly conductive columns 7 parallel to the surface of the substrate 2. For example, if a person is an acceptor and B is a donor, these columns Although this is an alternately laminated charge transfer complex, A may be a metal complex and B may be an axial ligand, or both A and B may be metal complexes. Of course, the direction perpendicular to column 7 is sufficiently electrically insulated (high resistance).

However, if there is a defect in the column 7 or if there is an interaction between the column 7 and the column 7, if a voltage is applied in the direction perpendicular to the column 7, the electric field exists in the region E. As shown in FIG. 2(b), the interaction of the columns 7 is induced, and the resistance value in this region becomes low. The interaction is thought to be based on the formation of new charge transfer complexes due to charge transfer due to the electric field, or the formation of new low-dimensional columns between columns due to molecular rotation due to the electric field. .

These conditions are maintained for a certain relaxation time (eg, several hours to a day or more) and the low resistance state is memorized. If the relaxation time passes or a reverse electric field (reverse voltage) is applied, it returns to its original high resistance state.

When light irradiation is performed, it is presumed that the presence of carriers generated by the light lowers the resistance value in the insulation direction, resulting in a decrease in the threshold voltage.

Next, the image memory function of the electrophotographic photoreceptor according to the third aspect of the present invention will be explained.

As shown in FIG. 3(a), the surface of the photoreceptor 1 is charged by corona charging. In this case, charging occurs when the voltage applied to the photoreceptor is equal to or higher than the threshold voltage Vth'.
Adjusted to the ungrooved range.

Then, as shown in FIG. 3(b), when an image is projected, the area hit by the light changes to a low resistance state as described above, and this state is stored in memory. Then, as shown in FIG. 3(C), when it is charged again, the charges are immediately neutralized in the memorized low resistance state region, and an electrostatic image corresponding to the projected image is obtained.

This will be explained in more detail below.

First, an example of the photosensitive material according to claim 1.2 will be described.

A photosensitive material made of a thin lead phthalocyanine film having a thickness of 3 μm was provided on an Al substrate. The thin film was formed in a vacuum atmosphere of 1σ5 Torr at a deposition rate of 1e/SEC. The effective area of this photosensitive material is 1-.

A voltage of 300V is applied to this photosensitive material, and a halogen tungsten lamp (with a white tip of about 20V) is applied to the photosensitive material.
mW/cri), the surface voltage was approximately 10
It decreased to 0-150v. Even when the light irradiation was stopped, there was no change in the voltage drop state on the surface.

From this, it can be seen that in this photosensitive material, the threshold value for changing from a high resistance state to a low resistance state is lowered by light irradiation, and it is also understood that the low resistance state is maintained.

In addition, when we measured the high resistance value of the photosensitive material before light irradiation and compared it with the low resistance value in the memory state after light irradiation, we found that the resistance value significantly decreased after light irradiation was completed. A decrease was observed. When a reverse voltage was applied to the photosensitive material and the resistance was examined, it was found that the resistance had returned to its original value.

Next, an example of the electrophotographic photoreceptor according to claim 3 will be described.

An electrophotographic photoreceptor using a lead phthalocyanine thin film was produced in the same manner as in the previous example except that the effective area was 6C71LX5crIL.

This electrophotographic photoreceptor was mounted on the alumite drum of an existing copying machine, and after image projection was performed only once using halogen tungsten as a light source, 80 copies were made in succession. No image changes were observed. It can be seen that the electrophotographic photoreceptor of this example has a sufficient image memory function.

Incidentally, when the lead phthalocyanine thin films of both of the above Examples were analyzed by X-ray diffraction, it was confirmed that the C axis of the crystal was oriented parallel to the surface of the hl substrate.

Effects of the Invention The photosensitive material and the electrophotographic photoreceptor of the present invention are highly functional materials that can be changed from a high resistance state to a low resistance state by light irradiation, and can also be used as a memory in a low resistance state and forcibly release the memory state. In the electrophotographic photoreceptor,
Since electrostatic images can be stored, there is no need to repeat image projection each time a copy is made, and the copying system can be simplified.

Moreover, the photosensitive material and electrophotographic photoreceptor of the present invention actually only require a film made of lead phthalocyanine formed by vapor deposition, so the material composition and film structure are simple. Since it is easy to manufacture and the manufacturing cost is low, it is highly practical.

[Brief explanation of drawings]

FIG. 1 is a graph showing the applied voltage-current characteristics of the organic thin film in the invention according to claims 1 to 3, and FIG. 2(a)
, (b) are schematic cross-sectional views for explaining the conductive mechanism of this organic thin film, and FIGS. 3(a) to (c) are schematic diagrams of the image memory function in the electrophotographic photoreceptor according to claim 3. It is an explanatory diagram. 1... Organic thin film, 2... Electrode base material, R1, R2
...High resistance, R3, R4...Low resistance.

Claims (3)

[Claims] (1) A characteristic of an organic thin film that changes to a low resistance state when a voltage higher than a threshold voltage is applied, and a characteristic that the threshold voltage is lower in a light irradiation state than in a non-light irradiation state;
A photosensitive material having a characteristic that the low resistance state continues for at least a certain period of time, and a characteristic that the low resistance state is returned to the original high resistance state by application of a reverse voltage. (2) An organic thin film is formed on the surface of the electrode substrate using lead phthalocyanine, and has a crystal structure containing a large amount of monoclinic crystal, and the c-axis of the crystal is oriented parallel to the substrate surface. The photosensitive material according to claim 1, which is oriented. (3) An electrophotographic photoreceptor comprising the photosensitive material according to claim 1 or 2.