JP3154832B2 - Photoconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoreceptor, and more particularly, to a photoreceptor suitable for use in a high-speed recording apparatus.

[0002]

2. Description of the Related Art An electrophotographic photosensitive member generally has a structure in which a photosensitive layer containing a charge generating substance and a charge transporting substance is formed on a conductive support. Heretofore, individual researches on a charge generating substance, a charge transporting substance, and the like for improving the characteristics of a photoreceptor have been made at various places. However, the sensitivity is not sufficiently improved by any of the methods.

The process of exposing an electrophotographic photosensitive member to form an electrostatic image utilizes a potential difference between a light-irradiated portion and a non-irradiated portion of the photosensitive member. This potential difference is determined by the potential decay rate (light decay) of the light-irradiated part and the potential holding rate of the non-irradiated part. The efficiency of light decay is indicated by the quantum efficiency that indicates how much the surface charge has been canceled with respect to the number of photons in the irradiation light. To realize a higher-speed recording device, a photoconductor having a higher quantum efficiency requires a photoconductor having a higher quantum efficiency. Is desired.

[0004]

As described above, research on charge generating substances and charge transporting substances has been advanced.
A photoconductor which is practically satisfactory has not been obtained. SUMMARY OF THE INVENTION It is an object of the present invention to provide a photoconductor which solves the drawbacks of the conventional photoconductor and which can realize a high-sensitivity, high-speed recording apparatus.

[0005]

The inventor of the present invention has conducted various studies to achieve the above object. As a result, the photosensitive layer in which the relative dielectric constant of the electrostatic field changes by irradiation of light or application of an electric field. In the case where is used, a photosensitive member having higher sensitivity was obtained and the present invention was achieved.

That is, the present invention relates to a substrate and a photosensitive layer formed on the substrate and including a charge generation layer and a charge transport layer.
The charge transport layer is characterized in that the relative permittivity of the electrostatic field in the light-irradiated part is 1. due to the effect of the irradiation or the interaction between the light irradiation and other external stimuli.
A feeling characterized by being reversibly changing to 0 or more .
Provide light body .

The present invention can be applied to a laminated electrophotographic photoreceptor having a plurality of photosensitive layers, for example, a charge generating layer and a charge transporting layer. In this case, the dielectric constant of at least one of the layers may be changed by light irradiation. Further, if necessary, when a surface layer, a protective layer, and the like are formed, the dielectric constant of the irradiated portion may be changed in these layers. The electrophotographic photoreceptor of the present invention is, specifically, a type obtained by further increasing the sensitivity of a conventional electrophotographic photoreceptor,
There is a type utilizing only the phenomenon of the present invention.

In the former type, carriers are generated in a light irradiation portion, and the S / N ratio of an electrostatic image obtained by canceling surface charges is further increased. That is, the photosensitive member is configured such that the dielectric constant of the light-irradiated portion is relatively higher than the dielectric constant of the non-irradiated portion. In this type of photoreceptor, the dielectric constant of the light-irradiated portion is increased (a-
There are a 1) type and a (a-2) type in which the dielectric constant of the unirradiated portion is small.

On the other hand, the latter type is to be called a new type of electrostatic image forming body, and forms an electrostatic image by utilizing the fact that the dielectric constant is changed by an external stimulus such as light or heat. Body. This type of photoreceptor includes a (b-1) type in which the permittivity of the stimulating portion is small and a (b-2) type in which the permittivity of the stimulating portion is large.

As an example of the (a-1) type, there is a photoconductor in which a photochromic material is contained in a charge transport layer. For example, irradiation with light of wavelength A changes from X to Y and wavelength B
In the charge transport layer, a photochromic material that returns from Y to X by irradiation of light is contained. However, at this time, the permittivity is X
Assume that Y is larger than Y.

Specifically, a charge transport layer containing such a photochromic material is formed on the charge generation layer,
Obtain a photoreceptor. Charges such photoconductors and generates charge
Carrier in the layer and absorbed in the charge transport layer.
When exposure is performed with light having no wavelength A, the photochromic material irradiated with light, which is present at the uppermost portion of the charge transport layer in the exposed area, changes from X to Y, and simultaneously transmits light having wavelength A. Thereafter, the same phenomenon proceeds toward the lower part of the charge transport layer in the exposed part. As a result, the dielectric constant of the charge transport layer changes significantly. At the same time, carriers are generated in the charge generation layer in the exposed portion, and the charge on the surface of the charge transport layer is canceled according to a normal process. Therefore, in a general electrophotographic photosensitive member, the surface potential is determined only by this process, whereas in the electrophotographic photosensitive member of the present invention, the electric charge is
Since the dielectric constant of the light-irradiated portion of the transport layer changes, the apparent charge potential is observed to be smaller, and high sensitivity can be obtained. Further, in this case, when the dipole moment of the light irradiation portion is reduced at the same time, the mobility of the portion is increased, which is more effective. In such a photoconductor, a photochromic material is mixed with a charge transport material.
May be used.

A non-photochromic material may be used alone (in this case, a photochromic material is used for the charge transport layer or another layer) or together with the photochromic material. Further, since the charge transport layer usually has a larger capacitance than the charge generation layer, it is more effective to use the photochromic material for the charge transport layer. The photochromic material may be used as a mixture with the charge transport material, or the charge transport material may be a photochromic material. Further, a photochromic material may be used as a binder for the charge transport layer.

In the present invention, a photochromic material can be contained in the charge generation layer instead of the charge transport layer. However, since the charge transport layer generally has a higher capacitance than the charge generation layer, it is more effective to use a photochromic material for the charge transport layer. At this time, the photochromic material may be used as a mixture with a charge generating substance, or the charge generating substance itself may be a photochromic material.

The photochromic material may be any material that changes reversibly by light or heat. That is, the above-mentioned sensitization method may be based on heat. Specifically, spiropyran, fulgide, dihydropyrene, thioindigo, viviridine, aziridine,
There are polycyclic aromatics, azobenzenes, salicyldenanilines, xanthenes and oxazines. An appropriate mixing amount of the photochromic material may be any amount as long as the change in the relative dielectric constant of the photosensitive layer exceeds 1.

Further, as a material used for the (a-1) type photoreceptor, in addition to a photochromic material, a liquid crystal material, a ferroelectric material, etc., whose dielectric constant changes reversibly upon stimulation of light irradiation or the like. What you get can be used. As the liquid crystal material, a polymer liquid crystal is particularly desirable. For example, a polymer liquid crystal having a positive dielectric anisotropy is used as a binder for the charge transport layer.
When a voltage lower than the driving voltage is applied in the case of (1), when the glass transition temperature (Tg) of the system is sufficiently higher than room temperature, the degree of orientation of the liquid crystal is small. Thereafter, when light is irradiated and the portion is instantaneously heated, the temperature rises to Tg or higher, the orientation of the liquid crystal increases, the dielectric constant of the charge transport layer in the light irradiated portion increases, and the residual potential decreases. Observed.

As an example of the (a-2) type photoreceptor, a polymer liquid crystal having negative dielectric anisotropy is used as a binder for a charge transport layer.
Some are used for In this case, after applying a voltage lower than the driving voltage to orient the entire charge transport layer to lower the dielectric constant and then performing light irradiation, the surface charges are canceled by carriers generated in the charge generation layer of the irradiated portion. Because
The electric field decreases, the molecular orientation of the liquid crystal changes, and the dielectric constant increases.

As an example of the (b-1) type and (b-2) type photoreceptors, the dielectric constant of the photosensitive layer changes due to the stimulus such as light irradiation, so that the apparent charged position of the irradiated portion is reduced. In some cases, an image is formed using this potential difference.
In any of these photoconductors, the process of canceling the surface charge with the carriers generated in the charge generation layer is not used, so that there is no need to use a charge generation material. Here, the material used for the photosensitive layer is not particularly limited as long as the dielectric constant is reversibly changed by stimulation such as light irradiation, so that the apparent potential is thereby changed. This is in accordance with the configuration of the charge transport layer containing such a material formed of the (a-1) and (a-2) type photoconductors described above.

Actually, it is considered that sufficient effects can be obtained if the residual potential is reduced by 10% in the (a-1) type and (a-2) type photoconductors. FIG. 1 shows the relationship between the relative dielectric constant of the entire photosensitive layer and the surface potential at the same surface charge amount. As shown in FIG. 1, when the relative dielectric constant changes from 3 to 4, the surface potential decreases from 100 (V) to 75 (V). From this result, it can be seen that when the relative dielectric constant changes by 1 or more, a sufficient decrease in potential is observed, and high sensitivity is achieved.

As described above, the added amount of the material for changing the relative dielectric constant of the photosensitive layer is an amount sufficient to change the relative dielectric constant of the photosensitive layer by one or more due to an external stimulus such as light irradiation or application of an electric field. It is.

The photosensitive layer of the electrophotographic photosensitive member of the present invention is not limited to a layer whose relative dielectric constant changes by irradiation of light or application of an electric field. Good. In the case of a photosensitive layer whose relative dielectric constant changes by light irradiation, the light is usually data writing light, but in some cases, the relative dielectric constant changes by irradiation with light other than data writing light. It may be something. However, in this case, it is necessary to separately provide a light source. In addition, the photosensitive layer whose relative dielectric constant has changed once needs to return to the original relative dielectric constant at the end of the image recording process. Return. Of course, it may return naturally after a predetermined time.

The charge generating substance used in the photoreceptor of the present invention may be any substance capable of absorbing light and generating charges with high efficiency, such as selenium and selenium alloys, CdS and CdSe. Inorganic photoconductors such as AsSe, ZnO, amorphous silicon, phthalocyanine pigments such as metal phthalocyanine and non-metal phthalocyanine, azo dyes and pigments such as monoazo and disazo, perylene pigments, indigo dye pigments, quinacridone pigments, anthraquinone , A polycyclic quinone pigment such as anthrone, a cyanine dye, a charge transfer complex composed of an electron accepting substance and an electron donating substance, a eutectic complex composed of a pyrylium dye and a polycarbonate resin, an azulhenium salt, etc. Can be mentioned. When forming the charge generating layer, it may be mixed with a polymer.

The method for forming the charge generating layer varies depending on the type of the charge generating substance used, and includes, for example, a spin coating method, a dip coating method, a roller coating method, and a spray coating method.
Various coating methods such as a coating method, a vacuum evaporation method, a sputtering method, and a plasma CVD method using a glow discharge can be appropriately selected and used. In the case of a single-layer type photoreceptor, a photosensitive layer can be formed by appropriately selecting and using the above method. The thickness of the charge generation layer to be formed is appropriately determined depending on the electrostatic characteristics required for the electrophotographic photoreceptor, but is usually preferably about 0.1 to 5 μm.

The charge transport layer usually provided on the charge generation layer is composed of a charge transport material and a polymer, and if necessary, other additives. Charge transport substances are those that transport charge, for example, anthracene in the main chain or side chain,
Polycyclic aromatic compound structure such as pyrene, phenanthrene, coronene or indole, carbazole, oxazo-
Compounds having a nitrogen-containing cyclic compound structure such as oxazole, oxazole, thiazole, imidazole, pyrazol, oxadiazol, pyrazoline, thithiazole, triazole, hydrazone compound, styryl compound, Amine compounds and the like can be mentioned.

As the polymer used for the charge transport layer, various known polymers can be used. For example, polyethylene resin, nylon resin, polyester resin,
Polycarbonate resin, polyarylate resin, butyrate
Resin, polystyrene resin, styrene-butadiene copolymer resin, polyvinyl acetal resin, diallyl phthalate resin, silicone resin, polysulfone resin, acrylic resin, vinyl acetate, polyphenylene oxide resin, alkyd resin, styrene-anhydride Maleic acid copolymer resin,
Phenol resin, paraffin wax and the like can be mentioned. These may be used alone or as a mixture of two or more.

The charge transport layer is formed by dissolving the charge transport substance in an organic solvent together with a suitable polymer compound in a predetermined ratio to form a uniform solution, and then applying the solution by a general method, for example, dip coating. After drying, preferably 15 to 25 μm
Is generally used. If a substance having a charge transporting ability for the polymer compound itself is selected, the amount of the charge transporting substance can be further reduced, and in some cases, it is not necessary to add the charge transporting substance at all. In addition, if the charge transport material has a sufficient film-forming property, the amount of the polymer compound can be minimized.

The electrophotographic photoreceptor of the present invention may be irradiated with light from either the substrate side or the opposite side. Therefore, the substrate may be transparent. When irradiating from the side opposite to the substrate, the substrate does not need to be transparent, and any substrate may be used as long as it is generally used as a conductive support of an electrophotographic photosensitive member. Examples of such a conductive support include metal materials such as brass, aluminum, gold, and silver; those obtained by coating the surface of the metal with a thin plastic film; metal-coated paper, metal-coated plastic sheets, chromium oxide and oxidized metal. Examples include tin and the like, glass and plastic sheets coated with a conductive polymer. They are,
Used as a thin cylindrical sheet with appropriate thickness, hardness and flexibility, the support itself is conductive or its surface is conductive and has sufficient strength for handling. Preferably, it is

In the case of a backside exposure system in which exposure is performed from the substrate side,
The substrate to be used only needs to be transparent in the wavelength range of the light source to be used. For example, the substrate may be transparent to a wavelength of 780 nm for a semiconductor laser, 630 nm for an LED, and 580 nm for an EL. 400 to 6 which is the visible range for ordinary resin
It is transparent in the range of 00 nm and has a long wavelength range of 800
Many maintain transparency up to around nm. Therefore, a film of polyvinyl chloride, polyvinylidene chloride, polyethylene, polycarbonate, polyester, polyamide, acrylic resin, polyimide, or the like having sufficient mechanical strength may be used as the substrate of the photoreceptor. It is good to select a material that can be easily made seamless when the belt is formed. Of course, sheets may be joined together by a method such as fusion.

In the photoreceptor used in the back exposure method, the conductive layer formed under the photosensitive layer and the conductive layer formed on the exposed surface are usually formed of the same wavelength as that of the resin as described above. Any material may be used as long as it is transparent, and in general, metal or metal oxide is deposited or baked after being applied by some means, and fine powder having conductivity is dispersed in a binder, and then dried or cured after being applied. And the like. These conductive layers may be electrically conductive and may be grounded, or may be separately grounded. The conductive layer on which the photosensitive layer is formed must be grounded, but the conductive layer serving as the exposed surface is not necessarily grounded.

When the surface of the photoreceptor is charged, there are various methods such as corona discharge by corotron or scorotron, contact charging, frictional charging and the like, but the photoreceptor of the present invention is not limited to any of them.

In the photoreceptor of the present invention, if necessary, at least one of the intermediate layer and the protective layer may be formed. As the substance used for the intermediate layer, casein, nylon, polyvinyl alcohol, gelatin, cellulose and derivatives thereof are generally used. Its thickness is 0.1-10μ
m, preferably about 0.2 to 2 μm. Further, as the material used for the protective layer, known acrylic resins, fluororesins, thermoplastic resins such as silicone resins, phenol resins, thermosetting resins such as melamine resins, photocuring,
EB, X-ray, UV curable resin, and the like.

A small amount of an additive such as an antioxidant, an ultraviolet absorber or an antioxidant may be added to at least one of the formed photosensitive layers. For example, hindered phenols,
Aromatic amines, organic sulfur compounds, phosphites,
There are chelating agents, benzophenones, benzotriazoles, nickel complexes and the like.

As the solvent used for forming the photosensitive layer, various organic solvents can be used. Specific examples of the organic solvent include alcohols, ketones, amides, sulfoxides, ethers, esters, aromatic halogenated hydrocarbons, and aromatics.

When a photosensitive layer is provided on a substrate by a dip coating method, the photosensitive layer may adhere particularly to the lower end. This adhesion can be removed by wiping with a solvent in which the layer dissolves or dipping in the solvent. In the present invention, when the substrate used is in the form of an endless belt, the substrate has a substantially hollow structure. Will be formed. In such a case,
A sponge, foamed polyethylene, foamed polyurethane, or the like conforming to the shape of the lower end portion may be impregnated with a solvent capable of dissolving the attached matter, and may be wiped while pressing and performing a motion such as rotation. There is also a method of directly immersing them in a solvent capable of dissolving them, and performing vertical movement, rotational movement, and the like to elute the deposits. When these movements are performed, they may be taken in and out of the solvent tank. In this case, it is more effective to provide two or more solvent tanks instead of one solvent tank. It is also effective to apply ultrasonic waves to the solvent tank and perform ultrasonic cleaning. It should be noted that a seamed film having a seam may be used for such an endless belt-shaped substrate. Gives favorable results. Hereinafter, specific examples of the present invention will be described. However, it goes without saying that the present invention is not limited by these specific examples.

[0034]

EXAMPLES Examples of the present invention will be described below by taking an organic electrophotographic photosensitive member as an example, but the present invention is not limited by these examples. Example 1

The surface resistance of the polyester film (240 mm × 200 mm) having a thickness of 100 μm is 50
A coating of indium oxide was formed without tin oxide so as to have a resistance of 0Ω. This film was rounded into a cylindrical shape, and the butted long sides were fused to form a substrate of 240 mm × 60 mmφ. An alcohol-soluble nylon (k-80, manufactured by Toray Co., Ltd.) dissolved in methanol as an intermediate layer was dip-coated on the outer surface of the substrate so that the film thickness after drying was 0.6 μm, and dried.

Next, a solution prepared by mixing thioindigo and polyvinyl butyral (SLEC BM-1 manufactured by Sekisui Chemical) in cyclohexanone at a weight ratio of 10: 1 as shown in the following Chemical Formula 1 (1) as a charge generating substance was used. A coating solution obtained by mixing the resulting vehicle with a ball mill for 24 hours was applied so that the film thickness after drying was 2 μm, and then dried to form a charge generation layer. Here, the thioindigo itself, which is a charge generating substance, is used as a photochromic material. Next, a compound shown in Table 1 as a charge transporting material was used as a binder polycarbonate (K-1300 manufactured by Teijin Chemicals Limited).
w) was dissolved in 1,1,2-trichloroethane at a weight ratio of 1: 1 to form a uniform solution, and the film thickness after drying was 20 μm.
And then dried to form a charge transport layer.

The photoreceptor having a three-layer structure thus produced was incorporated in a back-exposure type electrophotographic printer. This is one in which an LED is incorporated as a light source inside a cylindrical photoreceptor, and each unit of charging, development, transfer, and static elimination is conventionally disposed outside the photoreceptor. Light having a wavelength of about 580 nm is used as the irradiation light, and a wavelength of 720 nm is used as the charge removing light.
Nearby light was used. Run this printer continuously,
The change in the relative dielectric constant and the change in the surface potential of the photosensitive layer were measured, and the potential difference (ΔV) of the electrostatic image was obtained. Example 2

A charge generating layer using dibromoanthanthrone as a charge generating substance is formed on a substrate, and further, a compound shown in Table 1 is used thereon as a charge transporting substance. A photoconductor was prepared in the same manner as in Example 1 except that the charge transporting layer was formed by adding 2) at a weight ratio of 1: 0.2. The change in the dielectric constant and the change in the surface potential are measured, and the potential difference (Δ
V) was determined. Example 3

A tetrachlorothioindigo was used as the charge generating substance, and the charge generating layer and the charge transporting layer obtained using the compounds shown in Table 1 as the charge transporting substance further contained (3) of the formula 1 as a photochromic material. A photoconductor was prepared in the same manner as in Example 1, except that a protective layer was provided.
For this photoreceptor, the change in relative dielectric constant and the change in surface potential in the photosensitive layer were measured in the same manner as in Example 1, and the potential difference (ΔV) of the electrostatic image was determined. Example 4

Tetrachlorothioindigo was used as a charge generating substance, compound 4 shown in Table 1 was used as a charge transporting substance, and (3) of formula 1 was used as a photochromic material in a weight ratio of 1: 1: 0.5. A single-layer type photoreceptor was prepared by dispersing in a polycarbonate resin as a binder to form a photosensitive layer having a thickness of 20 (μm). The change in rate and the change in surface potential were measured to determine the potential difference (ΔV) of the electrostatic image. Examples 5, 6, 7

Tetrachlorothioindigo is used as a charge generating substance, and a high-molecular liquid crystal compound (4), (5) or (6) is used as a binder for forming a charge transport layer.
A photosensitive member was prepared in the same manner as in Example 1 except that the photosensitive material was used, and a change in the relative dielectric constant and a change in the surface potential of the photosensitive layer were measured in the same manner as in Example 1, and the electrostatic charge was measured. The potential difference (ΔV) of the image was determined. Example 8

Using the cylindrical polyester film used in Example 1 as a substrate, a photosensitive layer having a thickness of 20 [μm] made of high-molecular liquid crystal (1) was formed on the surface of the substrate. I got a body. A voltage equal to or lower than the driving voltage is applied to the photosensitive layer by corona discharge, and then thermal writing is performed by flash light, a change in relative dielectric constant in the photosensitive layer is measured, and a potential difference (ΔV) of the formed electrostatic image is measured. I asked. Comparative Example 1

A photoreceptor was prepared in the same manner as in Example 1 except that metal-free phthalocyanine was used instead of thioindigo as the charge generating substance. Was measured, and the potential difference (ΔV) of the electrostatic image was obtained. Comparative Examples 2 to 4

A photoconductor was prepared in the same manner as in Examples 2 to 4, except that no photochromic material was used.
The change in surface potential of this photoreceptor was measured in the same manner as in Example 1, and the potential difference (ΔV) of the electrostatic image was obtained. Table 1
The measurement results of the change in the relative dielectric constant and the change in the surface potential in the photosensitive layer of the photoconductors of the examples and comparative examples of the present invention described above are summarized below.

As is clear from the results shown in Table 1, the photosensitive member according to the embodiment of the present invention has a potential difference (ΔV) of an electrostatic image,
In other words, the difference in surface potential between the light-irradiated part and the non-irradiated part in the photosensitive layer increases. After completion of the image recording process, the photosensitive members of Examples 1 to 4 and 7 are subjected to a charge elimination step, and the photosensitive members of Examples 5, 6 and 8 are irradiated with flash light, so that the relative dielectric constant of the photosensitive layer is reduced. The ratio returned to the value before charging, and according to the photoconductor of this example, an electrostatic image having a high SN ratio was always obtained, and it was confirmed that the photoconductor had excellent sensitivity.

[0046]

Embedded image

[0047]

[Table 1]

[0048]

As described above, according to the present invention,
It is possible to obtain a photosensitive member having high sensitivity and realizing a high-speed recording device.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between a relative dielectric constant and a surface potential in a photosensitive layer when an amount of surface charge is made equal in an electrophotographic photosensitive member.

Claims (1)

(57) [Claims] 1. A light-emitting device comprising: a substrate; and a photosensitive layer formed on the substrate and including a charge generation layer and a charge transport layer, wherein the charge transport layer has a relative dielectric constant of an electrostatic field in a portion irradiated with light. A photoreceptor wherein the ratio reversibly changes by 1.0 or more.