JP2540036B2 - Electrophotographic photoreceptor - Google Patents

Description

TECHNICAL FIELD The present invention relates to improvement of an electrophotographic photoreceptor having a layer in which a charge generating substance is dispersed.

[Prior art]

2. Description of the Related Art Electrophotographic photoreceptors provided with a charge generation layer in which various resins are blended with a charge generation substance have been conventionally known. Examples thereof include polyvinyl butyral (JP-A-58-105154), fatty acid cellulose ester (JP-A-58-166353), acrylic resin having a Tg of 70 ° C. or less and an acid value of 10 to 40 (JP-A-58-106353). 58-192040), a mixture of a resin having a Tg of 70 ° C. or lower and a resin having a Tg of 75 ° C. or higher (JP-A-58-193).
No. 549), a resin-solvent system having a lower compatibility with the charge-generating material-resin-solvent system is added and redispersed (Japanese Patent Application Laid-Open No.
-12646), polyvinylpyrrolidone (JP-A-56-11314)
No. 0), polyvinyl formal resin (JP-A-61-235844)
No.) and the like.

However, conventionally known photoconductors have a problem that the sensitivity and the chargeability against pre-exposure fatigue vary depending on the mixing ratio of the charge generating substance and the binder resin.

That is, the conventional photoreceptor can increase the sensitivity by reducing the amount of the binder resin used for the charge generating substance, but the chargeability with respect to the pre-exposure fatigue becomes remarkable,
On the other hand, if the amount of the binder resin used with respect to the charge generating substance is increased, it is possible to suppress the deterioration of the chargeability due to pre-exposure fatigue, but this involves the problem of a marked decrease in sensitivity.

Further, the conventional photoreceptor also has a drawback that the charging potential is significantly reduced when charging and exposure are repeated.

〔Purpose〕

The present invention provides an electrophotographic photosensitive member which has excellent charging characteristics, high sensitivity, and a significantly small decrease in charging property due to pre-exposure fatigue, and in which the charging potential does not decrease even after repeated charging and exposure. To aim.

〔Constitution〕

According to the present invention, in an electrophotographic photoreceptor having at least a layer in which a charge generating substance is dispersed on a conductive support, one or two selected from a fluorenone type disazo pigment, a styrylstilbene type disazo pigment, and a trisazo pigment. Provided is an electrophotographic photoreceptor, wherein a layer in which at least one kind of charge generating substance is dispersed contains polypropylene glycol.

Since the electrophotographic photoreceptor of the present invention contains polypropylene glycol in the layer in which the charge generating substance consisting of a specific azo pigment is dispersed, it has excellent charging characteristics, high sensitivity and chargeability due to pre-exposure fatigue. Is remarkably small and the charging potential does not decrease even when charging and exposure are repeated.

Generally, the chargeability of a highly sensitive photoreceptor is reduced due to pre-exposure fatigue. In the pre-exposure fatigue, as the time during which charges generated by light absorption remain in the photosensitive member in a movable state and the number of the charges are increased, the chargeability due to the pre-exposure fatigue is remarkably reduced. That is, even if the charging operation is performed in the state where the electric charges generated by the light absorption remain, the surface charges are neutralized by the movement of the remaining carriers, so that the surface potential does not rise until the residual potential is consumed. Therefore, the rise of the surface potential is delayed by the amount of the pre-exposure fatigue, and the apparent charging potential is lowered.

As a result of intensive studies to improve this point, the present inventors have found that the above-mentioned drawbacks can be solved by including polypropylene glycol in a layer in which a charge generating substance composed of a specific azo pigment is dispersed, and the present invention It came to completion.

The reason why the present invention has such remarkable effects is not always clear at the local point of view, but since polypropylene glycol is chemically adsorbed on the charge generating substance and becomes a recombination center of the charges generated by light absorption, pre-exposure fatigue It is considered that this is due to the fact that the electric charges generated in (1) are recombined promptly and the electric charges are eliminated to suppress the decrease in the charging potential of the photoconductor.

Further, since the effect on the pre-exposure fatigue as described above also appears during actual use in which charging and exposure are repeated, the electrophotographic photoreceptor according to the present invention is more electrically charged than the conventional one. Even when the exposure is repeated, the decrease in the charged potential is remarkably small.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

FIGS. 1 to 4 are drawings for explaining a typical layer structure of the electrophotographic photoreceptor of the present invention.

FIG. 1 shows a structure in which a charge generation layer 1 and a charge transfer layer 2 are sequentially laminated on a conductive support 3, and FIG. 2 shows a structure in which the charge generation layer 1 and the charge transfer layer 2 are laminated in FIG. The charge generation layer 1 is formed by a coating method that does not disturb the charge transfer layer 2, such as a spray coating method.

FIG. 3 is different from the laminated photosensitive layer of FIGS.
1 shows a photoconductor composed of a single-layer type photosensitive layer having a charge generation function and a charge transfer function in one layer.

FIG. 4 shows a structure in which an undercoat layer 5 is provided between the conductive support 3 and the charge generation layer 1 in FIG. Such an undercoat layer 5 can be similarly applied to the structure shown in FIGS. 2 and 3.

When the undercoat layer is intended to prevent light interference in a photoreceptor for a laser printer, a light-scattering undercoat layer or a light-absorbing undercoat layer is used. A resin undercoat layer such as polyamide, polyester, vinyl chloride-vinyl acetate copolymer, or polyvinyl butyral having good properties is used.

Next, each constituent material used in the present invention will be described.

The conductive support is intended to supply a charge having a polarity opposite to that of the charged charge to the substrate side, and has an electric resistance of
A material having a resistance of 10 ⁸ Ωcm or less and capable of withstanding the film formation conditions of the charge generation layer, the charge transfer layer and the undercoat layer can be used. Examples of these include electrically conductive metals and alloys such as Al, Ni, Cr, Zn, and stainless steel, and inorganic insulating substances such as glass and ceramics and organic insulating properties such as polyester, polyimide, phenol resin, nylon resin, and paper. The surface of the material, by vacuum evaporation, sputtering, spray coating, etc., Al, Ni, Cr, Zn, stainless steel, carbon,
Examples thereof include those obtained by coating an electrically conductive substance such as SnO ₂ or In ₂ O ₃ and performing a conductive treatment.

The layer in which the charge generating substance is dispersed is constituted as a charge generating layer in the laminated photosensitive layer as shown in FIGS. 1, 2 and 4, and a single layer type as shown in FIG. In the photosensitive layer, it is formed in the photosensitive layer.

In the multilayer photosensitive layer, the charge generation layer is composed of a charge generation substance and a resin binder.

In the present invention, at least polypropylene glycol is used as the resin binder. Although various commercially available polypropylene glycols are used, those having a molecular weight of 130 to 500,000, preferably 500 to 10,000 are suitably used.

Further, the layer in which the charge-generating substance of the present invention is dispersed contains polypropylene glycol as a resin binder, but other resin binders used in this type of charge-generating layer can be used in combination if necessary.

Such resin binders include polystyrene,
Styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer,
Polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyacrylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly- Thermoplastic or thermosetting resins such as N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin, phenol resin, and alkyd resin.

The total amount of the binder resin is 100
It is suitably used in an amount of 0.01 to 200 parts by weight, preferably 1 to 50 parts by weight based on parts by weight. In addition, it is necessary that polypropylene glycol be contained in an amount of at least 0.01 parts by weight, preferably 1 part by weight or more in 100 parts by weight.

As the charge generating substance, a fluorenone type compound and a styrylstilbene type compound among disazo pigments and a trisazo pigment are used.

Fluorenone-based disazo pigment compounds have the general formula It is an azo pigment compound having a structure shown by.

The trisazo pigment compound has the general formula It is an azo pigment compound having a structure shown by.

The styrylstilbene-based disazo pigment compound has the general formula It is an azo pigment compound having a structure shown by.

 Specific examples of the azo pigment are shown below.

The thickness of the charge generation layer 1 is suitably about 0.05 to 2 μm, and preferably 0.1 to 1 μm.

The charge generation layer 1 can be formed by dissolving or dispersing a resin binder and a charge generation substance in an appropriate solvent, and applying and drying this. As the solvent, benzene, toluene, xylene, methylene chloride, dichloroethane, monochlorobenzene, dichlorobenzene, ethyl acetate, butyl acetate, methyl ethyl ketone, dioxane, tetrahydrofuran, cyclohexanone, methyl cellosolve, ethyl cellosolve or the like may be used alone or in combination. it can.

The charge transfer layer 2 is prepared by dissolving or dispersing a charge transfer substance and a resin binder in an appropriate solvent, and then dissolving the dispersion in a suitable solvent.
It can be formed by coating and drying on the top. If necessary, a plasticizer or a leveling agent can be added.

Examples of charge transfer materials include poly-N-vinylcarbazole and its derivatives, poly-γ-carbazolylethylglutamate and its derivatives, pyrene-formaldehyde condensate and its derivatives, polyvinylpyrene, polyvinylphenanthrene, oxazole derivatives, oxadiazole Derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-diethylaminostyryl) anthracene, 1,1-bis- (4-dibenzylaminophenyl) propane, styrylanthracene, styrylpyrazolin, phenylhydrazones, α-phenyl Electron donating substances such as stilbene derivatives;

Examples of the resin binder include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, and vinyl chloride-vinyl acetate copolymer used in the charge generation layer. Coalescence, polyvinyl acetate, polyvinylidene chloride, polyacrylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin And a thermoplastic or thermosetting resin such as melamine resin, urethane resin, phenol resin and alkyd resin.

As the solvent at this time, tetrahydrofuran, dioxane, toluene, monochlorobenzene, dichloroethane, methylene chloride or the like can be used.

The thickness of the charge transfer layer 2 is suitably about 5 to 100 μm.

In addition, when the layer in which the charge generating substance is dispersed is a single layer type photosensitive layer as shown in FIG. 3, the charge generating substance used in the charge generating layer, polypropylene glycol, resin binder and, if necessary, charge It can be formed by mixing the charge transfer substance used in the transfer layer and dry-coating these coating solutions on a conductive support or the like.

Further, in the present invention, as described above, an undercoat layer can be provided between the conductive support and the photosensitive layer, if necessary.

The light-scattering subbing layer and the light-absorbing subbing layer are layers for preventing light interference in the photoreceptor for a printer as described above. The light-scattering undercoat layer is formed by dispersing a conductive powder such as tin oxide and antimony oxide and a white pigment such as zinc oxide, zinc sulfide and titanium oxide in the following thermosetting resin. The light-absorbing undercoat layer is formed by dispersing a conductive light-absorbing pigment such as carbon and various metals and / or a light-absorbing organic pigment in a similar thermosetting resin. The thermosetting resin used here is, for example, active hydrogen (-OH group,-
It is obtained by thermally polymerizing a compound containing a plurality of hydrogens such as NH ₂ groups and —NH groups) with a compound containing a plurality of isocyanate groups and / or a compound containing a plurality of epoxy groups. As the compound containing a plurality of active hydrogen, for example, polyvinyl butyral, phenoxy resin, phenol resin, polyamide, polyester, polyethylene glycol, polypropylene glycol, polypolypropylene glycol, acrylic resin containing active hydrogen such as hydroxyethyl methacrylate group. Etc. Examples of the compound having a plurality of isocyanate groups include tolylene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, and prepolymers thereof, and examples of the compound having a plurality of epoxy groups include bisphenol A type epoxy resin. can give.

In any case, the light-scattering or light-absorbing undercoat layer is applied on a substrate with a solution obtained by dissolving or dispersing the above components on a substrate.
It is formed by thermal polymerization at 200 ° C. The thickness of the undercoat layer is preferably 1 to 10 μm. The weight ratio of the conductive powder, the white pigment, and the thermosetting resin is suitably 2 to 6/1 to 5/2 to 6, and the weight ratio of the light-absorbing pigment to the thermosetting resin is 4 to 9/1 to 6 are suitable.

〔effect〕

Since the electrophotographic photoreceptor of the present invention contains polypropylene glycol in the layer in which the charge generating substance consisting of the specific azo pigment is dispersed, it has excellent charging characteristics, high sensitivity, and chargeability due to pre-exposure fatigue. Is remarkably small and the charging potential does not decrease even when charging and exposure are repeated.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 [Coating liquid for charge generation layer] 5 parts by weight of azo pigment (Pigment No. 1) shown in Table 1 and 0.39% by weight solution of polypropylene glycol in cyclohexanone
160 parts by weight of the mixture was mixed with a ball mill for 72 hours to obtain a pigment dispersion, and then 90 parts by weight of methyl ethyl ketone was additionally mixed with 100 parts by weight of this pigment dispersion to prepare a charge generation layer coating solution.

(Coating liquid for charge transfer layer)

α-Phenylstilbene type charge transfer material (the following compounds) 100 parts by weight Polycarbonate (trade name, Panlite C1400: Teijin Ltd.) 100 parts by weight Silicone oil (trade name, KF50: Shin-Etsu Silicone Co., Ltd.)
0.1 parts by weight Tetrahydrofuran 800 parts by weight Next, the above charge generation layer coating solution was blade coated onto a 75 μm polyester film substrate on which Al was vacuum-deposited, and dried by heating at 120 ° C. for 10 minutes to a thickness of about 0.2 μm. A charge generation layer was formed. Next, a charge transfer layer coating solution having the following composition was blade coated on the charge generation layer, and dried by heating at 120 ° C. for 20 minutes to form a charge transfer layer of about 20 μm to prepare a photoreceptor.

Example 2 A photoconductor was prepared in the same manner as in Example 1, except that the azo pigment of the coating solution for the charge generation layer was changed to Pigment No. 39.

Example 3 A coating solution for a charge transfer layer used in Example 1 was coated on a 75 μm polyester film substrate on which Al was vacuum-deposited with a blade in the same manner as in Example 1, and then dried to transfer a charge of about 20 μm. A layer was formed. Then, the coating liquid for a charge generation layer used in Example 1 was spray-coated on the charge transfer layer, and dried by heating at 120 ° C. for 30 minutes to form a charge generation layer of about 0.2 μm. Created.

Example 4 A photoconductor was prepared by the same way as that of Example 1 except that the α-phenylstilbene compound in the coating solution for the charge transfer layer was changed to a compound having the following structure.

Examples 5 and 6 90 parts by weight of methyl ethyl ketone used in the preparation of the coating liquid for the charge generation layer was polyvinyl butyral (trade name: XYHL,
Photoconductors were prepared in the same manner as in Examples 1 and 2, except that 90 parts by weight of 0.43% by weight methyl ethyl ketone solution (made by Union Carbide Plastic Co., Ltd.) was used.

Example 7 Fine powder of tin oxide containing 10% by weight of antimony oxide 8
Parts by weight, 5 parts by weight of titanium oxide white pigment powder, and 68 parts by weight of a 12% by weight solution of polyvinyl butyral (trade name: BL-1, manufactured by Sekisui Chemical Co., Ltd.) in methyl ethyl ketone are treated with a ball mill for 72 hours, and then 47 parts by weight of methyl ethyl ketone. Additional parts were added and treated again on the ball mill for 48 hours. Next, while stirring 80 parts by weight of this pigment dispersion, 8 parts by weight of 20% by weight of tolylene diisocyanate and a methyl ethyl ketone solution were additionally mixed to obtain a coating liquid for the undercoat layer for light scattering.

Next, the above-mentioned undercoat layer coating solution for light scattering was coated on a 75 μm polyester film substrate on which Al was vacuum-deposited with a blade, and heated and cured at 120 ° C. for 30 minutes to form an undercoat layer for light scattering of about 2.5 μm. Was formed.

Next, a photoreceptor having a charge generation layer and a charge transfer layer formed on the light scattering subbing layer in the same manner as in Example 2 was prepared.

Example 8 A photoconductor was prepared in the same manner as in Example 4 except that the No. 57 compound shown as a specific example of the pigment was used instead of the azo pigment of the charge generation layer coating solution.

Comparative Examples 1 to 2 Photoreceptors were prepared in the same manner as in Examples 1 and 2 except that polyvinyl butyral (trade name: XYHL, manufactured by Union Carbide Plastics Co., Ltd.) was used as the polypropylene glycol of the charge generation layer coating liquid.

Comparative Example 3 A photoconductor was prepared in the same manner as in Example 3 except that polyvinyl butyral (trade name: XYHL, manufactured by Union Carbide Plastics Co., Ltd.) was used as the polypropylene glycol of the charge generation layer coating liquid.

Comparative Example 4 A photoconductor was prepared in the same manner as in Example 4 except that polyvinyl butyral (trade name: XYHL, manufactured by Union Carbide Plastics Co., Ltd.) was used as the polypropylene glycol of the charge generation layer coating liquid.

Comparative Example 5 A photoconductor was prepared in the same manner as in Example 2 except that polyester (trade name: Byron 200, manufactured by Toyobo Co., Ltd.) was used as the polypropylene glycol of the charge generation layer coating liquid.

Comparative Example 6 As Example 1 except that the 0.39 wt% cyclohexanone solution of polypropylene glycol at the time of preparing the coating liquid for the charge generation layer was changed to the 5.88 wt% cyclohexanone solution of polyvinyl butyral (trade name: XYHL, manufactured by Union Carbide Plastics Co., Ltd.). A photoconductor was prepared in the same manner.

Comparative Example 7 A photoconductor was prepared in the same manner as in Example 4 except that the azo pigment of the charge generation layer coating liquid was changed to Chlordiane blue (a known diazo type as an electrophotographic photoconductor).

The electrophotographic photosensitive member prepared as described above was evaluated for electrophotographic characteristics as follows using an electrostatic copying paper test apparatus (Kawaguchi Electric Mfg. Co., Ltd., Model SP428). First, a -6 KV corona discharge was applied to each photoconductor for 20 seconds, during which a charge potential V ₂ (volt) 2 seconds after the start of corona discharge was measured.
Then, when light was discharged in a dark place and the surface potential became −800 V, tungsten light was irradiated to determine the exposure amount S (lux sec) necessary for the surface potential to be optically attenuated to −400 V. After that, the tungsten light with a color temperature of 2856 ° K is exposed to 100000 lux sec
After the irradiation, the charged potential V ₂ ′ after the light fatigue is again applied as described above.
(Volt) and exposure amount S ′ (lux sec) were determined. The above results are shown in Table-1.

In addition, the type photoreceptor shown in FIG.
It is performed for 0 seconds, and during that time, the charged potential V ₂ is measured 2 seconds after the start of corona discharge, and then it is left in the dark and the surface potential is +80.
When the voltage reached 0 V, the substrate was irradiated with tungsten light, and an exposure amount S required for the surface potential to attenuate to +400 V was obtained. After that, after irradiation with 100000 lux · sec in the same manner as described above, the charged potential V ₂ ′ and the exposure amount S ′ after light fatigue were determined.

[Brief description of drawings]

1 to 4 are schematic cross-sectional views of various electrophotographic photoconductors according to the present invention. 1; charge generation layer 2; charge transfer layer 3; conductive support 4; single-layer photosensitive layer 5; undercoat layer

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shoichi Ota 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Kayoko Yokoyama 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (56) Reference JP-A-54-4137 (JP, A) JP-A-58-72152 (JP, A)

Claims (1)

(57) [Claims] 1. An electrophotographic photoreceptor having at least a layer in which a charge generating substance is dispersed on a conductive support, and one or more selected from fluorenone-based disazo pigments, styrylstilbene-based disazo pigments, and trisazo pigments. An electrophotographic photoreceptor, wherein the layer in which the charge generating substance is dispersed contains polypropylene glycol.