JP2599717B2 - Electrophotographic photoreceptor and electrophotographic method using the same - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoconductor for electrophotography and an electrophotographic method using the photoconductor, and more specifically, performs analog image formation with positive charge and digital image formation with negative charge. The present invention relates to a laminated electrophotographic photosensitive member suitable for a bipolar image forming method and an image forming method thereof.

[Related Art] In recent years, the performance of electrophotographic copying machines has been remarkably improved, and high-quality images have been stably obtained.

Means for forming an electrostatic latent image on a photoreceptor generally include applying a uniform charge on the photoreceptor, and then (i) copying the original using a light source such as a tungsten lamp, a halogen lamp, or a fluorescent lamp. An analog image forming method that forms an electrostatic latent image by performing image exposure using reflected light or transmitted light, and (ii) image exposure composed of dots using a light source such as a semiconductor laser or He-Ne laser Is performed to form an electrostatic latent image.

The former (i) is particularly advantageous for obtaining a continuous-tone or half-tone enhanced image, and the latter (ii) is for obtaining a negative image or reversal development to obtain a positive image (both dot-shaped images). This is a particularly advantageous method.

When considering a configuration in which one electrophotographic copying machine has both of the above functions, it is easy to provide a light source such as a tungsten lamp for analog exposure and a light source such as a semiconductor laser for digital exposure in the copying machine. However, providing two sets of photoreceptor and developing system for analog and digital use would increase the size of the machine, and would be problematic in terms of cost, which is very undesirable.

If there is an electrophotographic photoreceptor that has good sensitivity to both of the above light sources with one photoreceptor, and at the same time obtains a high-quality image by an image forming method using either light source, the photoreceptor and developing system can It is possible to design a very compact and low-cost multifunctional copier that can be completed by one set.

However, at present, there is no electrophotographic photoconductor that completely satisfies these requirements and the characteristics (cost durability and the like) required as the electrophotographic photoconductor.

For example, by stacking a CGL having sensitivity to light of 700 nm or more on a support, a charge transfer layer (CTL), and a CGL having sensitivity to light of 400 to 700 nm as one photoconductor based on the above idea, There is a photoreceptor having a sensitivity with an analog light source when positively charged and a sensitivity with a digital light source when negatively charged. (Japanese Patent Application No. 61-145948) Although this photoreceptor shows a good value in both positive and negative charging, the CG of the uppermost layer
L is composed of a thin layer of an organic substance, and the mechanical strength required for the electrophotographic photoreceptor is low, and there is a problem in terms of durability.

Then, in order to eliminate these drawbacks of the conventional photoreceptor, the present inventors placed on a conductive support (an undercoat layer if necessary) a
The first charge generation layer, the charge transfer layer, and the second charge generation layer are stacked in this order, and the second charge generation layer is a Se-based alloy, and the first charge generation layer is spectrally longer on the wavelength side than the second charge generation layer. Filed an electrophotographic photoreceptor having a charge generation layer having high sensitivity.

As a result, it was possible to obtain a photosensitive member having good sensitivity in bipolar charging. The electrophotographic photoreceptor of this configuration can withstand practical use in that the charge generation layer composed of the Se alloy layer has good mechanical strength as compared with the case where the organic charge generation layer is provided on the uppermost layer as described above. However, it is still insufficient from the viewpoint of high speed and high reliability of copying machines and printers.

Hitherto, many proposals have been made to provide a resin protective layer on a photosensitive layer in order to improve the mechanical strength of the photoreceptor surface.

For example, in JP-A-57-30843, the resistance of the protective layer resin is reduced by a specific resistance lowering agent such as a metal powder or a metal oxide to prevent an increase in the residual potential, and the low resistance protective layer has a high insulating property. Attempts have been made to provide a resin, an organometallic compound or the like on the photosensitive layer via an intermediate layer provided with functions of improving the charging ability and the adhesiveness, and have obtained good results. However, these protective layers can be relatively easily formed on the inorganic photosensitive layer having organic solvent resistance, but the organic electrophotographic photosensitive member and the photoconductive fine particles are dispersed in the binding resin. When formed on a photosensitive layer that originally has a weak mechanical strength such as a photoreceptor and requires a protective layer, the resin etc. of the photosensitive layer itself may be dissolved or deteriorated by the solvent used when coating the protective layer. At present, there is a problem that a good protective layer has not been obtained on these photoconductors.

[Purpose] Therefore, an object of the present invention is to provide a better sensitivity in both positive and negative charging, and to selectively perform analog copying using a tungsten lamp or the like as a light source and digital copying using a semiconductor laser or the like as a light source. Another object of the present invention is to provide an electrophotographic photosensitive member having dramatically improved durability and an ambipolar electrophotographic method using the photosensitive member.

[Construction] The photoreceptor of the present invention comprises an undercoat layer, a first charge generation layer, a charge transfer layer, a second charge generation layer, and, if necessary, an intermediate layer and a protective layer on a conductive support. In the electrophotographic photoreceptor having a configuration in which the charge transfer layers are sequentially stacked, the first charge generation layer is a charge generation layer having sensitivity to light of a longer wavelength side than the second charge generation layer, and the charge transfer layer and the protective layer or the charge transfer layer Containing 20 to 40% by weight of arsenic having solvent resistance in the middle between
The second charge generation layer is made of a base alloy.

Further, the electrophotographic method of the present invention applies a positive charge when performing image exposure using light of a wavelength in a visible region (mainly 450 to 700 nm) using this photoreceptor, and applies an infrared region (mainly 700 n
m) is applied by applying a negative charge.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. 1 (a), 1 (b), 1 (c) and 1 (d) are cross-sectional views of a photoreceptor according to the present invention. Attraction layer, 3 is a first charge generation layer, 4 is a charge transfer layer, 5 is a second charge generation layer 6 is an intermediate layer,
7 represents a protective layer.

In this photoreceptor, a positive charge is present on the surface of the photoreceptor when positively charged, and a negative charge is present on the interface between the support and the first charge generation layer or the undercoat layer. When this is irradiated with light in the visible wavelength range (mainly 400 to 700 nm) such as a tungsten lamp, charge carriers (positive and negative pairs) are generated by the second charge generation layer in that region, and negative carriers are generated. Neutralizes the positive charge on the photoreceptor surface, the positive carrier is injected into the charge transfer layer, and is attracted by the negative charge on the interface side of the support. And neutralizes with the negative electrode at the interface. On the other hand, in the non-exposed area, a positive charge remains on the surface of the photoconductor, and an electrostatic latent image is formed.

Next, at the time of negative charging, the surface of the photosensitive member has a negative charge,
Positive charges exist at the interface with the charge generation layer or the undercoat layer. This is reflected in light in the infrared region such as a semiconductor laser (mainly
(700 nm or longer), this light passes through the second charge generation layer and the charge transfer layer and reaches the first charge generation layer, where the charge carriers (positive and negative polarity pairs) are generated by the first charge generation layer. ) Occurs, the negative carrier is neutralized with the positive charge at the support side interface, and the positive carrier is injected into the charge transfer layer and is attracted and moved by the negative charge on the surface of the photoreceptor. And neutralize. On the other hand, in the non-exposed area, a negative charge remains on the surface of the photoconductor, and an electrostatic latent image is formed.

A feature of the present invention resides in that a Se-based alloy is used for the second charge generation layer. Due to its high charge generation ability and high infrared light transmittance for visible light, good sensitivity in ambipolar charging can be obtained. The lamination of the protective layer, the intermediate layer, and the protective layer, which has been difficult, can be facilitated, and the mechanical strength can be dramatically improved.

To actually prepare the photoreceptor of the present invention, an undercoat layer is formed on a conductive support as necessary, a first charge generation layer is formed thereon by vacuum deposition or coating, and then charge transfer is performed. The layer is formed by applying and drying a resin solution containing a charge transfer material, and a second charge generation layer of a Se-based alloy is provided thereon by a method such as vacuum evaporation, and a protective layer or an intermediate layer is further provided thereon. The protective layer may be provided by coating and drying by dipping or spraying.

Here, as the conductive support, a conductor or an insulator subjected to a conductive treatment is used.

For example, Al, Ni, Fe, Cu, Au, etc. metal or alloy, polyester, polycarbonate, polyimide, glass or other insulating support Al, Ag, Au or other metal or
Examples thereof include those in which a thin film of a conductive material such as In ₂ O ₃ and SnO ₂ is formed, paper subjected to a conductive treatment, and the like. The shape of the conductive support is not particularly limited, and may be a plate, a cylinder,
A belt-shaped thing is used.

The undercoat layer is effective for improving the chargeability and fatigue properties, and has a volume resistance of 10 ⁵ to 10 ¹⁴ Ωcm, preferably 10 ⁸ to 10 Ωcm.
¹⁴ Ωcm. The thickness of the intermediate layer is suitably from 0.1 to 10 μm.

Examples of the material of the intermediate layer having such a function include resin layers such as polyamide resin, polyvinyl alcohol, polyvinyl acetal, and polyacrylic acid; or TiO ₂ , SnO ₂ , SiO ₂ , MgO, ZnO, etc. White pigment dispersed; trimethylmonomethoxysilane, γ
Silane coupling agents such as glycidoxypropyltrimethoxysilane; metal acetylacetone complexes such as titanium acetylacetonate and zirconium acetylacetonate; and metal alkoxides such as titanium tetrabutoxide and zirconium tetrabutoxide.

The first charge generation layer is a layer having a charge generation ability in a light wavelength region (mainly 700 nm or more) or longer than the second charge generation layer. Examples of such a material include metal-free phthalocyanine and metal phthalocyanine. , Squaric dye, azurenium dye, trisazo pigment or
An Se-based alloy or the like can be used.

These materials may be used alone, for example, by vacuum evaporation or casting of a solution dissolved in a solvent, or may be pulverized and finely divided into polyester, polystyrene,
It is used by being dispersed in a resin such as polycarbonate, polyacrylate, polyvinyl butyral, polyvinyl acetate, and ethyl cellulose.

The thickness of the first charge generation layer is preferably about 0.05 to 3 μm. When used in a state of being dispersed in a resin, the amount of the charge generation substance in the first charge generation layer is 1 to 95% by weight.
Is appropriate.

The charge transfer layer formed on the first charge generation layer comprises polyvinyl carbazole, an α-phenylstilbene compound (JP-A-58-198043), and a hydrazone compound (JP-A-55-46).
No. 760) is dissolved in a film-forming resin.

This is because the charge transporting substance is generally low in molecular weight and poor in film forming properties by itself. As such a film-forming resin, a condensation resin such as polyamide, polyurethane, polyester, epoxy resin, polyketone, and polycarbonate, and a vinyl polymer such as polyvinyl ketone, polystyrene, and polyacrylamide are used. Any resin having an infrared light transmitting property can be used. If necessary, a plasticizer may be added to these resins. Examples of such a plasticizer include halogenated paraffin, polychlorinated biphenyl, dimethylnaphthalene, dibutylphthalate, and the like.

The thickness of the charge transfer layer is 3 to 100 μm, preferably 5 to 50 μm.
μm is appropriate. The amount of the charge transport material in the charge transfer layer is 10 to 95% by weight, preferably 30 to 90% by weight.

The second charge generation layer to be formed next is made of a Se alloy (Se, Se-T
e, Se-As, Se-As-Te, etc.) are used.
Se-As based Se alloys are preferred from the viewpoint of thermal stability. in this case
The As content of the Se-As alloy is 0.5 to 50% by weight, preferably 2 to 50% by weight.
0 to 40% by weight. Further, halogen (I or Cl or the like) may be contained as needed. Halogen abundance is 10 ~
10,000 ppm is appropriate. As described above, the second charge generation layer is very thin, so that the material cost is lower than that of the electrophotographic photoreceptor (film thickness: 50 to 60 μm) made of a Se-based alloy, which is advantageous in terms of cost.

Further, in laminating the intermediate layer and the protective layer, a conventionally known technique can be used for the material and the film forming method.

For example, the intermediate layer is a layer for increasing the adhesiveness between the protective layer and the photosensitive layer and for stopping the charged charge at the interface between the protective layer and the photosensitive layer to prevent a decrease in the charged potential due to charge injection from the protective layer. As the material of the intermediate layer having such a function, for example, epoxy resin, polyester resin, polyamide resin, polystyrene resin, polyvinylidene chloride resin,
Various organic polymer compounds such as polyvinyl acetate, polyvinyl chloride, acrylic resin, silicone resin, and fluororesin; trimethylmonomethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, etc. Silane coupling agent: titanium tetrabutoxide, aluminum tripropoxide,
Metal alkoxides such as zirconium tetrabutoxide; and high molecular compounds formed from metal acetylacetone complexes such as titanium acetylacetonate, zirconium, and acetylacetonate can be used. The thickness of the intermediate layer is usually 10 μm or less, preferably 1 μm or less.

As the protective layer, a layer obtained by adding a conductivity controlling agent such as an organic compound or an inorganic compound to an organic polymer compound as a binder is used. Specific examples of the conductivity control agent include metallocene compounds as organic compounds and inorganic compounds as
Metal powders such as Au, Ag, Ni, Al, zinc oxide, titanium oxide,
Metal oxide powders such as tin oxide, indium oxide, tin oxide containing antimony oxide, and indium oxide containing tin oxide are exemplified.

The particle size of these powders is preferably 0.05 to 0.3 μm, and the amount used is preferably 20 to 80 parts by weight based on 100 parts by weight of the binder resin. On the other hand, as the binder resin used in combination with these conductivity control agents, silicone resin, polyurethane resin, acrylic resin, polyester resin, polycarbonate resin,
Typical commercial resins such as styrene resin and epoxy resin can be exemplified. The thickness of this protective layer is usually 0.1 to 10 μm, preferably 2 to 7 μm. When the thickness is 0.1 μm or less, the mechanical strength of the protective layer is weak, and the abrasion resistance is small.
As described above, charges are accumulated in the protective layer, and the residual potential increases during repeated use.

Multilayer type electrophotographic photoreceptor according to the present invention but is intended to take such a structure described above, an In ₂ O in glass or resin as the support
_{3. When} light irradiation is performed from the support side using a transparent conductive support formed with a thin film of a conductive material such as SnO ₂ , the support (undercoat layer), the second charge generation layer, the charge transfer layer,
The first charge generation layer (in this case, composed of a solvent-resistant Se alloy layer), an (intermediate layer), and a protective layer are laminated in this order to form a bipolar photoconductor similar to the present invention. It goes without saying that it fulfills the function of

If the charge transfer layer has a high mobility of the negative charge carrier and has the same configuration as the present invention, a photoreceptor having the functions of negative charge-analog copying and positive charge-digital copying can be obtained. However, there is a problem that it is difficult to form a charge transfer layer having a large negative charge carrier mobility.

Next, an image forming method using this photoconductor will be described.

As described above, when the photosensitive member is positively charged and the image is exposed to visible light, an electrostatic latent image is formed on the surface of the photosensitive member by the positive charge.

If this is developed with a toner of negative polarity (electric detection fine particles), a positive image can be obtained (analog copying with positive charge).

On the other hand, when the photosensitive member is negatively charged and image exposure is performed with infrared light from a semiconductor laser or the like, an electrostatic latent image due to the negative charge is formed on the surface of the photosensitive member that has not been exposed. If this is developed with a positive polarity toner, a negative image can be obtained. Alternatively, if reversal development is performed using negatively charged toner, a positive image can be obtained. (Digital copying with negative charge).

As is clear from the above, when designing a copying machine having both functions of analog copying with positive charging and digital copying with negative charging by reversal development, if this photoconductor is used,
The development system can be a single set using negatively charged toner, and a very compact and low-cost copying machine can be designed.

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

Example 1 Aluminum cylindrical support (outer diameter 80 mmφ, length 340 m)
m) 1 part by weight of a mixture having the following composition ratio TiO ₂ (Taipec manufactured by Ishihara Sangyo Co., Ltd.) 1 part by weight of polyamide resin (CM-8000 manufactured by Toray Industries, Inc.) 1 part by weight Methanol 25 parts by weight was dispersed in a ball mill for 12 hours to prepare an intermediate layer forming liquid. Was applied by an immersion method so that the film thickness after drying was about 2 μm to form an intermediate layer.

A mixture containing the following trisazo pigment was dispersed on the intermediate layer by a ball mill for 48 hours, Polyester resin (Toyobo's Byron 200) 12 parts by weight Cyclohexanone 360 parts by weight Cyclohexanone: methyl ethyl ketone (ME
A dispersion prepared by diluting with 500 parts by weight of a mixed solvent (K) = 1: 1 (weight ratio) was applied by a dipping method to form a first charge generation layer having a thickness of about 0.15 μm.

Next, a coating liquid having the following composition was dried on the first charge generation layer to a thickness of about 20 μm. Polycarbonate resin (Panelite C-1400 manufactured by Teijin Limited)
150 parts by weight Tetrahydrofuran 910 parts by weight Silicon oil (KF50 manufactured by Shin-Etsu Chemical Co., Ltd.) was applied by an immersion method to 0.03 parts by weight to form a charge transfer layer.

Further, the support on which the above layers were formed was set on the mandrel portion 13 of the vacuum evaporation apparatus shown in FIG. 2, and the inside of the vacuum layer 11 was evacuated to 10 ⁻⁵ torr or less, and the temperature of the support 12 was reduced to 80 ° C. The heating source 15 was heated while keeping the temperature at ℃, and a Se—As alloy 16 containing 35.5% by weight of As was deposited to a thickness of 1 μm to form a second charge generation layer.

Further, 10 parts by weight of methylsilyl isocyanate, 10 parts by weight of tetrasilyl isocyanate,
A mixed solution consisting of 80 parts by weight of butyl acetate is applied by a dipping method, and dried at 25 ° C. and 60% RH for 2 hours.
Was provided.

Finally, 15 parts by weight of an acrylic polyol (copolymer of styrene-methacrylic acid-dihydroxyethyl methacrylate), 20 parts by weight of tin oxide powder containing 10% by weight of antimony oxide, and an appropriate amount of a solvent are dispersed on the ball mill for 72 hours. After mixing, a solution containing 5 parts by weight of a polyisocyanate-based curing agent is applied by dipping and dried (80 ° C. for 2 hours).
Then, a protective layer having a thickness of about 5 μm was formed.

In the photoreceptor thus prepared, the charge transfer layer was not dissolved or deteriorated by a solvent or the like at the time of forming the intermediate layer and the protective layer.

FIG. 4 shows the spectral sensitivities of the photoreceptor obtained in this manner during positive and negative polarity charging. It can be seen that good sensitivity is exhibited in visible light and infrared light.

Comparative Example 1 On the same support as in Example 1, an intermediate layer, a first charge generation layer and a charge transfer layer were formed exactly as in Example 1.

On this After 300 parts by weight of cyclohexanone is pulverized and dispersed by a ball mill for 48 hours, 30 parts by weight of polystyrene (HRM manufactured by Denki Kagaku Co., Ltd.) is added, and the dispersion is diluted with 400 parts by weight of a mixed solvent of cyclohexanone: MEK = 1: 1 (weight ratio). Was applied by a spray method to form a second charge generation layer having a thickness of about 1 μm.

When an intermediate layer and a protective layer were to be laminated on the second charge generation layer in the same manner as in Example 1, the photosensitive layer was dissolved when immersed in an intermediate layer forming solution, and the film was formed successfully. I couldn't do that.

Comparative Example 2 A photoconductor was produced in exactly the same manner as in Example 1 except that the intermediate layer and the protective layer were not laminated.

These photoconductors were set in a copying machine shown in FIG. 3 and a test was conducted.

In order to obtain a positively charged analog image using the photoconductor of the first embodiment, first, a voltage of 6 kv is applied to the positive charger 22 to charge the surface of the photoconductor 21 with 800 V, and analog light (visible light) is applied.
After image exposure using the optical system 23 (halogen lamp light), development (negative toner), transfer, and fixation, a very clear image was obtained.

On the other hand, in order to obtain a digital image by negative charging, a voltage of -6 KV is applied to the negative charger 24 to charge the surface of the photoreceptor with -800 V, and the digital light (infrared light) optical system 25 (semiconductor laser light (780 mm )), Image exposure was performed, and the exposed portion was developed, transferred and fixed by reversal development (negative toner). As a result, a clear digital image was obtained as in the case of positive charging.

As a result of repeatedly collecting images in this manner, clear images were obtained in both polarities even after 300,000 cycles.

In comparison with this, a similar test was performed using the photoreceptor of Comparative Example 2. As a result, a clear image similar to that of Example 1 was obtained up to 20,000 cycles. The two charge generation layers were scratched, and black streak-like abnormalities occurred at the time of analog images, making it practically unbearable.

As is clear from this, it can be seen that the durability is significantly improved by providing the protective layer on the second charge generation layer.

Comparative Example 3 As in the Se—As alloy in the second charge generation layer of Example 1
The photoreceptor of Comparative Example 3 was prepared in the same manner except that the content was changed to 5 wt%.

The photoreceptor is heated when forming the protective layer,
The second charge generation layer was crystallized, causing problems such as peeling of the protective layer and unevenness of the image.

[Effects] As is clear from the above description, the photoreceptor according to the configuration of the present invention has two functions, analog copying and digital copying, and thus one photoconductor has both functions. The realization of the holding makes it possible to design a compact and low-cost multifunctional copying machine. Further, the photoreceptor of the present invention has improved mechanical strength and excellent durability, and has a remarkable effect that a clear image can be stably obtained.

[Brief description of the drawings]

1 (a), (b), (c) and (d) are views for explaining the cross section of the photoreceptor of the present invention, FIG. 2 is a vacuum deposition apparatus, and FIG. 3 is an electrophotograph of the present invention. FIG. 4 is a diagram for explaining the method, and FIG. 4 is a diagram showing the spectral sensitivity (800 V → 400 V) of the photoconductor obtained in Example 1 when charging both positive and negative polarities. DESCRIPTION OF SYMBOLS 1 ... Conductive support, 2 ... Undercoat layer, 3 ... First charge generation layer, 4 ... Charge transfer layer, 5 ... Second charge generation layer, 6 ... Intermediate layer, 7 ... Protection Layer 21 Photoconductor 22 Positive charger 24 Negative charger 23 Analog light (visible light) optical system 25 Digital optical (infrared light) optical system

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Oshima 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company Limited (72) Inventor Rokutanen Section 1-3-3 Nakamagome, Ota-ku, Tokyo No. 6 Inside Ricoh Company, Ltd. (72) Inventor Shinji Narisho 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company Limited (56) References JP-A-58-203446 (JP, A) JP-A Sho 60-263946 (JP, A) JP-A-60-250348 (JP, A)

Claims (2)

(57) [Claims] 1. A structure in which an undercoat layer, a first charge generation layer, a charge transfer layer, a second charge generation layer, an intermediate layer, and a protective layer, if necessary, are laminated on a conductive support in this order. In the electrophotographic photoreceptor, the second charge generation layer is a Se alloy layer containing 20 to 40 wt% of arsenic, and the first charge generation layer is a photocharge which is spectrally longer than the second charge generation layer. A laminated bipolar electrophotographic photoreceptor comprising a charge generating layer having a generating ability. 2. A structure in which an undercoat layer, a first charge generation layer, a charge transfer layer, a second charge generation layer, an intermediate layer, and a protective layer as necessary are laminated on a conductive support in this order. In the electrophotographic photoreceptor, the second charge generation layer is a Se alloy layer containing 20 to 40 wt% of arsenic, and the first charge generation layer is a photocharge which is spectrally longer than the second charge generation layer. In the method of forming an image using an ambipolar electrophotographic photoreceptor having a charge generating layer having a generating ability, a visible region (mainly 400 to 700 nm) is used.
An electrophotographic method characterized in that a positive charge is applied when performing image exposure with light having a wavelength of, and a negative charge is applied when performing image exposure with light having a wavelength in the infrared region (mainly 700 nm or more).