JPH0746231B2 - Positively charged photoconductor for electrophotography - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrophotographic photoreceptor used in a copying machine, a laser printer, etc., and more specifically,
The present invention relates to a positive charging type electrophotographic photosensitive member which is prevented from being deteriorated by ultraviolet rays.

(Prior Art) In the field of electrophotographic photoreceptors, so-called function-separated type organic photoreceptors in which a charge generation layer (CGL) and a charge transport layer (CTL) are laminated, and charge generation in a medium of a charge transport substance A single-layer dispersion type organic photoconductor in which a substance is dispersed is known.

As a charge-transporting substance for this type of organic photoreceptor, one having a high carrier mobility is required, and a polymer dispersion material such as polyvinylcarbazole (PVK) used in the early days is now used as a resin dispersion system. It is shifting to low molecular compound materials used in. However, the charge transport material is preferably a film-forming material that can be used alone. Mentioned above
Although PVK can be formed into a film, it has a problem that a dimer site formed by two adjacent carbazole rings acts as a structural hole carrier trap and causes deterioration of electrophotographic characteristics of the photoconductor.

Recently, Japanese Unexamined Patent Publication (Kokai) No. 61-170747 proposes a photoreceptor containing organic polysilane as a hole transport material. It is also known that this organic polysilane can be formed into a film from a solution and has a high hole drift mobility (up to 10 ⁻⁴ cm ² / V · sec) among amorphous polymer materials.

(Problems to be Solved by the Invention) As a photoreceptor to be mounted on a copying machine or the like, not only initial characteristics but also stability under an environment normally used are required. The inventors of the present invention have conducted a study to apply the organic polysilane to a commercial electrophotographic photoreceptor, and when the photoreceptor is irradiated with a fluorescent lamp, a xenon lamp, or sunlight, these light The surface potential and residual potential of the photoconductor rises due to the ultraviolet rays contained in it, which causes density changes and fog in the copy image. It was found to be significant when organopolysilane was applied to the body.

Therefore, an object of the present invention is to suppress an increase in surface potential and residual potential during irradiation of ultraviolet light in a positively charged type photoreceptor of a monodispersed layer using an organic polysilane as a charge transporting material (hole transporting material), for a long period of time. It is an object of the present invention to provide a positive charging type electrophotographic photosensitive member capable of obtaining stable electrophotographic characteristics.

(Means for Solving Problems) According to the present invention, in a positive charging type electrophotographic photosensitive member including a monodisperse type photosensitive layer containing a charge generating substance and a charge transporting substance, the charge transporting substance is , 2,6-dichloro-p-benzoquinone or an organic polysilane composition containing p-benzoquinone is provided.

In the organic polysilane composition used in the present invention, 2,6
The dichloro-p-benzoquinone or p-benzoquinone is preferably used in an amount of 0.1 to 30 parts by weight per 100 parts by weight of organic polysilane.

(Function) In the present invention, when the organic polysilane is blended with 2,6-dichloro-p-benzoquinone or p-benzoquinone as an electron-accepting substance, the light resistance of the photoreceptor when irradiated with ultraviolet light is improved. It is based on the finding that the rise in surface potential and residual potential can be significantly suppressed.

As described above, when the photoreceptor using the organic polysilane as the charge transport material is irradiated with ultraviolet light, both the surface potential and the residual potential are significantly increased, and when applied to the positive charging type photoreceptor, the surface potential The upward trend is particularly remarkable. For example, with respect to a negative charging type laminated organic photoreceptor and a positive charging type monodisperse organic photoreceptor using organic polysilane, the surface potential V _1sp when the voltage of ± 6 kV is applied to positively or negatively charge,
The results of comparison of the surface potential V _1rp (residual potential) after second exposure and the surface potential V _2sp and residual potential V _2rp after irradiation with ultraviolet rays for 2 minutes are shown in Comparative Examples 1 and 2 described later. The results are summarized in Table 1 below.

As can be understood from these results, in any type of photoconductor, the residual potential is remarkably increased by the irradiation of ultraviolet rays, but especially when the surface potential is observed, the negative charge laminated photoconductor has an increase of about 60 V. On the other hand, the surface potential of the positively charged single-layer photoconductor has risen by about 120V, while it has stopped. Thus, when the organic polysilane is applied to the positively charged single-layer photoconductor, the increase in the surface potential due to the ultraviolet light irradiation is remarkable as compared with the other types of photoconductors, as well as the residual potential.

Such an increase in surface potential or residual potential is caused by the deterioration of the surface of the organic polysilane layer due to ultraviolet light, the main chain of Si-Si is cut, and the insulating film such as siloxane is formed, so that the carrier transport ability of the surface part is increased. However, it is not clear why the surface potential of the positive-charged single-layer photoconductor is remarkable. Probably, in the positively charged single-layer photoconductor, the organic polysilane layer is exposed on the surface, so that it is exposed to ultraviolet light directly and is affected by the charge generating agent blended in the organic polysilane layer.
This is probably because the degradation of the main chain is promoted to form a deteriorated product, and the formed deteriorated product acts to further inhibit the positive charge as compared with the negative charge.

However, according to the present invention, 2,6-dichloro-p-benzoquinone and p-benzoquinone are selected from a large number of electron-accepting substances, and these are compounded in an organic polysilane to prepare the above-mentioned positively charged monolayer. It is possible to effectively suppress a remarkable increase in the surface potential and an increase in the residual potential due to the irradiation of ultraviolet light on the photoconductor. It has been found as a result of many experiments that the stability to ultraviolet light is improved by blending such an electron-accepting substance, and the reason thereof has not been fully clarified. However, the electron affinity of 2,6-dichloro-p-benzoquinone is 2.3 and that of p-benzoquinone is 1.98, but the fluorescence of the organic polysilane is effectively quenched by the electron accepting substance having an electron affinity of about 2.0 or more. Based on this experimental fact, it can be seen that the compounding of the above-mentioned specific electron-accepting substance deactivates the excited state of the organic polysilane due to the irradiation of ultraviolet rays and suppresses the deterioration of the surface and the generation of radical species. Therefore, it is considered that the stability against ultraviolet light is improved.

(Preferred Embodiment) The organic polysilane used in the present invention may be any known per se, but generally, the main chain is composed of a chain of silicon, and the side chain has an organic group, particularly a monovalent hydrocarbon. Those having a group, for example, the following formula (1): In the formula, each of R ₁ and R ₂ is a monovalent hydrocarbon group, particularly an alkyl group having 4 or less carbon atoms, an aryl group or aralkyl group having 6 or more carbon atoms, and a repeating unit represented by It is suitable. Specific examples include methylphenyl polysilane, methylpropyl polysilane, methyl t-butyl polysilane, diphenyl polysilane, methyl tripolysilane, and copolymers thereof.

The organopolysilane used should have a molecular weight sufficient to form a so-called film, generally 5,000 to 50,00.
It is preferred to have a weight average molecular weight (M _w ) of 0, especially 5,000 to 20,000. Also, the end of the organic polysilane is
It may be a silanol group, an alkoxy group or the like.

In the present invention, as the electron accepting substance,
2,6-dichloro-p-benzoquinone or p-benzoquinone, alone or in combination, is used in combination with the above-mentioned organic polysilane, and the amount thereof is 0.1 to 30 parts by weight, particularly 1 to 15 parts by weight per 100 parts by weight of organic polysilane. It is recommended that the amount be part by weight. If the amount is less than this range, the effect of suppressing the increase of the surface potential and the residual potential upon irradiation with ultraviolet light becomes low, and if the amount is more than the above range, the sensitivity tends to decrease.

Used as an electron-accepting substance in the present invention 2,6-
Dichloro-p-benzoquinone and p-benzoquinone are
Since the organic polysilane is soluble in a solvent such as tetrahydrofuran (THF), both can be mixed uniformly.

The photoconductor of the present invention comprises a single-layered photosensitive layer in which a charge generating substance is further dispersed in a charge transport medium composed of an organic polysilane in which the above-mentioned specific electron accepting substance is dispersed. It is a dispersion type photoconductor, and is particularly used as a positive charging type photoconductor.

Examples of the charge generating substance include selenium and selenium-
Examples include tellurium, amorphous silicon, pyrylium salts, azo pigments, disazo pigments, ansanthuron pigments, phthalocyanine pigments, indigo pigments, slene pigments, toluidine pigments, pyrazoline pigments, perylene pigments, and quinacdrine pigments. One kind or a mixture of two or more kinds is used so as to have an absorption wavelength region in a desired region. These charge generating substances are preferably present in the photosensitive layer in an amount of 1 to 15 parts by weight, especially 5 to 10 parts by weight, per 100 parts by weight of the organic polysilane.

In the positively charged photoreceptor of the present invention, the above-mentioned organic polysilane has a function as a hole transport material,
At the same time, it also has a function as a binder resin for forming layers. Therefore, in forming the photosensitive layer, it is not necessary to use a special binder resin, but a known binder resin may be used as the layer forming resin as long as the characteristics of the organic polysilane as a hole transporting material are not impaired. Can also be used as Examples of such a binder resin include styrene polymers, acrylic polymers, styrene-acrylic copolymers, ethylene-vinyl acetate copolymers, polypropylene, olefin polymers such as ionomers, and polyvinyl chloride. , Vinyl chloride-vinyl acetate copolymer, polyester, alkyd resin, polyamide, polyurethane, epoxy resin, polycarbonate, polyarylate, polysulfone, diallyl phthalate resin, silicone resin, ketone resin, polyvinyl butyral resin, polyether resin, phenol resin, And photo-curable resin such as epoxy acrylate,
Various polymers can be mentioned.

As the conductive substrate, various conductive materials can be used, such as aluminum, copper, tin, platinum, gold,
Metals such as silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, indium, stainless steel, and brass, and plastic materials in which these metals are vapor-deposited or laminated, aluminum iodide, tin oxide, indium oxide, etc. Illustrated are, for example, the formed glass.

The photosensitive layer is formed, for example, by using a roll mill, a ball mill, an attritor, or a paint shaker by adding an organic polysilane, 2,6-dichloro-p-benzoquinone or p-benzoquinone, a charge generating substance, and a binder resin component used if necessary. It can be easily carried out by dissolving or dispersing in an organic solvent soluble in organic polysilane using an ultrasonic disperser to prepare a coating solution, coating the solution on a conductive substrate, and drying. The thickness of the photosensitive layer is usually 10 to 40
It is preferable that the thickness is μm, particularly 15 to 30 μm.

According to the present invention, 2,6-dichloro-p-benzoquinone or p-benzoquinone as an electron transporting substance is dispersed in an organic polysilane as a hole transporting material together with a charge generating substance to form a photosensitive layer. By suppressing the increase of the surface potential and the residual potential due to the irradiation of ultraviolet rays and effectively preventing the remarkable increase of the surface potential at the time of positive charging, the positive charge type photosensitive member is stable for a long period of time. It has become possible to maintain the electrophotographic characteristics. In addition, since it retains the high hole drift mobility inherent in organic polysilanes, it can be used as a high-sensitivity photoconductor for copiers and laser printers.

(Example) <Synthesis of phenylmethylpolysilane> 100 g of methylphenyldichlorosilane, 26 sodium metal
g was added to 400 ml of dry toluene, heated to 130 ° C., stirred for 11 hours, and then cooled.

After adding ethanol to the obtained reaction solution (solution containing a dark purple precipitate) to convert unreacted sodium into ethoxide,
The precipitate was separated by filtration, dried, and then dissolved in toluene and further dropped into ethanol to reprecipitate to obtain white phenylmethylpolysilane (yield 22.0 g: yield 34
%).

Comparative Example 1 α-type oxotitanyl phthalocyanine (charge generation material) 10
0 parts by weight and 4000 parts by weight of tetrahydrofuran (solvent) were charged into a ball mill, stirred for 24 hours, and then 100 parts by weight of polyvinyl butyral (binder resin: Sekisui Chemical Co., Ltd., trade name Eslec BM-3) was added. The mixture was stirred and mixed for 1 hour to prepare a charge generation layer coating solution. After applying this coating solution on aluminum foil with a wire bar (No. 5),
It was dried with hot air at 100 ° C. for 30 minutes to form a charge generation layer having a thickness of 5 μm.

Next, 100 parts by weight of the phenylmethylpolysilane synthesized above and 1000 parts by weight of tetrahydrodolofuran were mixed by stirring with a homomixer to prepare a charge transport layer coating liquid.
This coating solution is applied on the above charge generation layer with a wire bar (No. 60), and then dried with hot air at 100 ° C for 30 minutes,
A laminated electrophotographic photosensitive member was prepared by forming a charge transport layer having a thickness of 5 μm.

Comparative Example 2 100 parts by weight of phenylmethylpolysilane (charge-transporting substance) synthesized above, 4 parts by weight of α-type oxotitanyl phthalocyanine (charge-generating material), and 1000 parts by weight of tetrahydrofuran (solvent) were stirred and mixed in a ball mill for 24 hours. To prepare a single layer type photosensitive layer coating liquid. This coating solution is applied on an aluminum foil with a wire bar (No.60) and then dried with hot air at 100 ° C for 30 minutes to form a photosensitive layer having a thickness of about 10 µm, thereby forming a single layer type electrophotographic photosensitive material. Created the body.

Example 1 About 10 μm in exactly the same manner as in Comparative Example 2 except that 10 parts by weight of 2,6-dichloro-p-benzoquinone was further added to prepare a coating solution for a single-layer type photosensitive layer. A single-layer type electrophotographic photoreceptor having a thick photosensitive layer was prepared.

<Experimental Example> The photoconductors prepared in the above Examples and Comparative Examples were charged positively or negatively at an applied voltage of ± 6.0 kV using an electrostatic copying tester (Model-8100, manufactured by Kawaguchi Electric Co., Ltd.), and Conditions: Exposure time: 10 seconds Irradiation light: Wavelength 780 nm Exposure intensity: 10 μW / cm ² Dark decay after charging: 2 seconds initial surface potential V _1sp (V), half exposure E ₁ 1/2
(ΜJ / cm ² ), residual potential V _1rp (V) and attenuation rate (%) were measured.

The initial surface potential V _1sp is the initial surface potential of the photoconductor when the photoconductor is charged by applying the above voltage, and the half-exposure amount E ₁ 1/2 is the surface potential of the initial surface potential V _1sp . The amount of exposure was calculated from the exposure time required to halve, and the attenuation rate was the value calculated by the following formula.

In addition, ultraviolet rays (300-400nm, 60nW / c
m ^-2 ) for 2 minutes and then the surface potential V of the photoconductor
_2sp (V), half exposure E ₂ 1/2 (μJ / cm ² ), residual potential V
_2rp (V) and decay rate were measured. The results are shown in Table 2.

From the above results, comparing Comparative Examples 1 and 2, in particular, when the organic polysilane was used, the residual potential of the single-layer positively charged photoreceptor and the laminated negatively charged photoreceptor was reduced by the irradiation of ultraviolet rays. However, it is understood that the surface potential is remarkably increased particularly in the single-layer type positively charged photoreceptor (Comparative Example 2). On the other hand, in the single-layer positively charged photoreceptor (Example 1) in which 2,6-dichloro-p-benzoquinone was used in combination with the organic polysilane according to the present invention, the surface potential and the residual potential were increased by ultraviolet irradiation. It is understood that all of the above are eliminated, the sensitivity is good, and the light resistance is excellent.

Claims (2)

[Claims] 1. A positively chargeable electrophotographic photoreceptor comprising a monodisperse type photosensitive layer containing a charge generating substance and a charge transporting substance, wherein the charge transporting substance is 2,6-dichloro-p-benzoquinone or A positive charging type electrophotographic photoreceptor comprising an organic polysilane composition containing p-benzoquinone. 2. 2,6-Dichloro-p-benzoquinone or p
A photoreceptor according to claim 1, wherein the benzoquinone is used in an amount of 0.1 to 30 parts by weight per 100 parts by weight of the organopolysilane.