JPH0711704B2 - Multilayer type photoconductor for electrophotography - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laminated electrophotographic photoreceptor, and more specifically, it is composed of a charge transport layer containing an organic material and a charge generation layer, and is an electrophotographic copying machine or printer. The present invention relates to a positive charging type laminated electrophotographic photoconductor used for such purposes.

[Conventional technology]

Conventionally, a photoconductor for electrophotography (hereinafter also referred to as a photoconductor).
Examples of the photosensitive material include an inorganic photoconductive substance such as selenium or a selenium alloy, an inorganic photoconductive substance such as zinc oxide or cadmium sulfide dispersed in a resin binder, poly-N-vinylcarbazole or polyvinylanthracene. And the like, organic photoconductive substances such as phthalocyanine compounds or bisazo compounds, and those obtained by dispersing these organic photoconductive substances in a resin binder are used. In addition, the photoconductor must have the function of retaining surface charge in the dark and the function of receiving light and transporting charge, but a so-called single-layer type photoconductor having both of these functions in one layer There is a so-called multi-layer type photoreceptor in which functionally separated layers are laminated mainly in a layer that contributes to charge generation and a layer that contributes to retaining surface charges in a dark place and transporting charges during light reception. For example, the Carlson method is applied to the image formation by the electrophotographic method using these photoconductors.
Image formation by this method is performed by charging the photoconductor in the dark by corona discharge, forming an electrostatic latent image such as characters and pictures on the document by exposing the surface of the charged photoconductor, and forming the electrostatic latent image. It is performed by developing the latent image with toner, transferring the developed toner image to a support such as paper, and fixing it. After the toner image is transferred, the photoconductor is neutralized, residual toner is removed, and light is neutralized. Used for reuse.

In recent years, laminated type photoreceptors using an organic material have been put into practical use due to advantages such as flexibility, thermal stability, and film formability. As shown in the schematic cross-sectional view of FIG. 2, this type of multi-layered photosensitive member generally includes a charge generation layer 3 containing an organic charge generating substance and a charge transport layer 2 containing an organic charge transporting substance on a conductive substrate 1. The layers are sequentially laminated, and the negative corona charging method is used for the above-mentioned image formation. However, since a large amount of ozone is generated in negative corona discharge, the surface of the photoreceptor is strongly oxidized by ozone during charging, which is not preferable. on the other hand,
The positive corona charging method is superior to the negative corona charging method in that the corona discharge is more stable, less ozone is generated, and a suitable developer can be easily manufactured. However, an organic charge generating substance and an organic charge transporting substance suitable for forming a photoconductor to which the positive corona charging method can be applied in the layer structure shown in FIG. In order to apply the corona charging method, the layer structure of the photoconductor has to be changed.

FIG. 3 shows an example of a typical layer structure of a layered type photoconductor that can be used in the positive corona charging system. In order to manufacture the photoreceptor shown in FIG. 3, the charge transport layer 2 is first formed on the conductive substrate 1 made of aluminum, copper, stainless steel or the like. Charge transport layer 2
Is a material obtained by uniformly dissolving an organic charge-transporting substance such as a pyrazoline compound, a hydrazone compound or a styryl compound and a resin binder such as polymethylmethacrylate polymer, polycarbonate or polyurethane in an organic solvent by a dipping method or an ironing method. It is applied and formed by a spray method or the like. Next, the charge generation layer 3 is composed of a phthalocyanine compound having an absorption peak in the infrared light region for a printer, an azo compound having an absorption peak in the visible light region for a copying machine, polyester, polymethacryl It is formed by similarly applying a material obtained by dissolving a resin binder such as acid methyl polymer in an organic solvent. Finally, the coating layer 4 can be manufactured by using an organic insulating material such as polyester or polyamide for the purpose of protecting the charge generation layer 3.

As the charge generation layer constituent material and the charge transport layer constituent material in the case of the negative corona charging method shown in FIG. 2, substantially the same materials as those in the case of the positive corona charging method are used.

[Problems to be solved by the invention]

However, in the laminated type photoreceptor using the organic material as described above, the electrophotographic characteristics of the photoreceptor are largely changed by the resin binder forming the charge transport layer 2. Table 1 shows that a charge generation layer made by dispersing X-type phthalocyanine in polyester (Vylon 200 manufactured by Toyobo) is coated on an aluminum substrate, and p-diethylaminobenzaldehyde-diphenylhydrazone (ABPH) is applied as a hydrazone compound. Half-exposure when the resin binder for the charge transport layer in the negative corona charging type photoreceptor having the charge transport layer is polycarbonate having a molecular weight of 50,000 and polymethyl methacrylate polymer (PMMA) having a molecular weight of 700,000. It is a comparison of the amounts E _1/2 (μJ / cm ² ). The half-dose exposure amount was measured by performing a −6 kV corona discharge in the dark for 10 seconds to charge the surface of the photoconductor, and irradiating 1 μm of monochromatic light with a wavelength of 780 nW.

As can be seen in Table 1, the half-exposure amount of the photoreceptor using the low molecular weight polycarbonate as the resin binder for the charge transport layer is obviously smaller than that of the photoreceptor using the high molecular weight PMMA, It can be seen that the sensitivity is high.
A similar phenomenon was observed in photoconductors for copiers that used the azo pigment chlorodian blue as the charge generation substance, and the half-exposure amount (lux · s
ec) is smaller for photoreceptors in which the charge transport layer resin binder is polycarbonate.

However, when a polycarbonate having a small molecular weight is used as the resin binder for the charge transport layer of the layered type photoreceptor of the positive corona charging type as shown in FIG. 3, it is attempted to improve the sensitivity. Since the charge transport layer is melted, it cannot be applied well and the appearance is extremely deteriorated, resulting in a defect. That is, since a resin having a small molecular weight is easily dissolved in a solvent, when a charge generating layer is formed by coating on a charge transporting layer formed of a resin having a low molecular weight, the solvent of the charge generating layer coating solution is It melts the resin and deteriorates the appearance. This drawback cannot be completely removed even if various solvents are used for the charge generation layer coating liquid. Therefore, in the case of a positive corona charging type laminated photoreceptor, there is a problem that a low molecular weight resin binder such as polycarbonate cannot be used in the charge transport layer.

The present invention has been made in view of the above points, and includes a charge transport layer made of an organic material, a charge generation layer, excellent electrophotographic characteristics, particularly high sensitivity, and a good appearance,
It is an object of the present invention to provide a laminate type electrophotographic photoreceptor for a positive corona charging type copying machine or printer.

[Means for solving problems]

In order to achieve the above object, according to the present invention, a charge transport layer formed by applying a liquid in which an organic charge transporting substance is dispersed in a resin binder onto a conductive substrate, and an organic charge generating substance as a resin binder. In a laminated electrophotographic photoreceptor used in the positive corona charging system, which is formed by sequentially laminating a charge generation layer and a coating layer formed by applying a liquid dispersed therein, the charge transport layer has a molecular weight of a resin binder. It is a laminate of two different layers, of which the layer in contact with the conductive substrate is made of a low molecular weight resin binder, and the layer in contact with the charge generation layer is made of a higher molecular weight resin binder. The laminated-type electrophotographic photoreceptor is

[Action]

As described above, since the charge transport layer has a two-layer structure and a resin binder having a large molecular weight is used for the layer in contact with the charge generation layer, this layer serving as the base during the formation of the charge generation layer coating does not melt. The charge generation layer having a good appearance can be formed by coating. Further, since the resin binder having a small molecular weight is used for the layer in contact with the conductive substrate, the sensitivity can be improved as compared with the case where the charge transport layer has a single layer structure of the resin binder having a large molecular weight.

〔Example〕

FIG. 1 shows a schematic sectional view of an embodiment of the photoconductor of the present invention. A charge transport layer (A) 21 and a charge transport layer (B) 22 are provided on a conductive substrate 1 such as aluminum, and a charge generation layer 3 and a coating layer 4 are sequentially laminated. It is a thing. Polycarbonate having a low molecular weight is used as the resin binder for the charge transport layer (A) 21, and PMMA having a large molecular weight is used for the charge transport layer (B) 22. Therefore, when the charge generation layer is applied, PMMA having a large molecular weight is present as an intermediate layer in the base, so that the charge generation layer 3 can be applied neatly without melting this layer. Moreover, since the charge transport layer (A) 21 uses polycarbonate as the resin binder, the sensitivity can be improved as compared with the case where the charge transport layer has a single layer structure using PMMA as the resin binder.

When various polymer resins having different average molecular weights were used as the resin binder used in the charge transport layer (B) 22, the appearance after coating the charge generation layer was observed in detail, and as a result, the average molecular weight of the charge transport layer (B) 22 was 10 It has been found that a photoreceptor having a good appearance can be obtained when the amount exceeds 10,000, preferably around 200,000.

Example 1 In Table 2, a positive corona charging system for a printer having a charge generation layer formed of X-type phthalocyanine and Byron using p-diethylaminobenzaldehyde-diphenylhydrazone (ABPH) as a hydrazone compound as a charge transporting substance. In the laminated photoconductor of, the case where the resin binder of the charge transport layer has a single layer structure of PMMA having an average molecular weight of 700,000, and a two-layer structure of a layer made of polycarbonate having an average molecular weight of 50,000 and the layer made of PMMA described above. If you do, +
The difference in half-exposure amount when the surface of the photoconductor is charged by performing corona discharge of 6 kV for 10 seconds and the monochromatic light of 1 μW is irradiated at a wavelength of 780 nm is shown. Compared to the single-layer structure, the photoreceptor having a two-layer charge transport layer was excellent not only in sensitivity but also in appearance as well as the single-layer structure.

In addition, 1-phenyl-3- (p-diethylaminostyryl) -as a charge transporting substance as a pyrazoline compound
A positive corona charging type laminated photoreceptor for a printer in which a charge transport layer was formed by using 5- (paradiethylaminophenyl) -2-pyrazoline was similarly tested, and as a result, two charge transport layers were similarly formed. The structured photoreceptor showed higher sensitivity and exhibited a good appearance.

Example 2 Next, as a second example of the present invention, the results of a photoconductor for a copying machine using chlorodian blue for the charge generation layer will be described. Table 3 shows a positive corona charging type laminated photoreceptor in which a charge transport layer was formed using p-diethylaminobenzaldehyde-diphenylhydrazone (ABPH) and a charge generation layer composed of chlorodian blue and byron was provided thereon. Regarding the charge transport layer, a single layer structure using PMMA having an average molecular weight of 700,000 as a resin binder and an average molecular weight of 4
The difference in half-exposure between a double layer structure consisting of 10,000 polycarbonate layers and 700,000 PMMA layers is shown.
The half-exposure amount was measured under irradiation with 2 lux of white light.

In this case as well, similarly to the one for a printer, the two-layer structure photoreceptor had higher sensitivity and a good appearance.

In addition, 1-phenyl-3- (p-diethylaminostyryl) -as a charge transporting substance as a pyrazoline compound
A positive corona charging type laminated type photoreceptor for a copying machine, in which a charge transport layer was formed by using 5- (paradiethylaminophenyl) -2-pyrazoline, was similarly tested. The photoreceptor having a layered structure showed higher sensitivity and exhibited a good appearance.

Example 3 Furthermore, as a third example of the present invention, the results when using two types of PMMA having the same structure but different average molecular weights of 100,000 and 700,000 as low molecular weight resin binders other than the polycarbonate, respectively. Indicates. In addition, these two types
As a result of trial manufacture of negative corona charging type laminated type photoreceptors using PMMA, low molecular weight PMMA showed higher sensitivity, but when only this low molecular weight PMMA is applied to the positive corona charging type resin binder, As in the case of the low molecular weight polycarbonate in the prior art, the appearance was extremely deteriorated. Table 4 shows a normal corona for a printer in which p-diethylaminobenzaldehylo-diphenylhydrazone (ABPH) is used as a hydrazone compound as a charge transporting material, and a charge generating layer composed of X-type phthalocyanine and byron is provided thereon. In the charging type laminated type photoreceptor, the resin binder of the charge transport layer is polymer PMMA (average molecular weight 70
Half-exposure amount of the two-layer structure in which the low molecular weight PMMA (average molecular weight 100,000) is used on the substrate side and the high molecular weight PMMA (average molecular weight is 700,000) is used on the charge generation layer side. Is shown. In this case as well, the two-layer structure photoreceptor has higher sensitivity and a good appearance.

EFFECTS OF THE INVENTION According to the present invention, a positive corona charging type laminated electron in which a charge transport layer and a charge generation layer made of an organic material are sequentially formed on a conductive substrate, and a coating layer is further provided thereon In the photographic photoreceptor, the charge transport layer has a two-layer structure in which the molecular weight of the resin binder is different, a low molecular weight resin binder is used for the layer in contact with the conductive substrate, and a high molecular weight layer is used for the layer in contact with the charge generation layer. A resin binder is used.

With such a configuration, the charge transport layer is not dissolved by the solvent of the coating liquid when the charge generation layer is formed by coating on the charge transport layer, and the charge generation layer having a good appearance can be formed. Further, it has higher sensitivity than the photoreceptor in which the charge transport layer is formed of a single layer of a high molecular weight resin binder.

In the present invention, the charge-generating substance can be freely selected according to the type of exposure light source used, and thus has a charge-transporting layer and a charge-generating layer made of an organic material and has excellent electrophotographic characteristics, particularly high sensitivity. It is possible to obtain a laminated-type electrophotographic photoconductor for a copying machine or a printer of the positive corona charging type, which has a good appearance and has a good appearance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the structure of an example of the photosensitive member of the present invention, FIG. 2 is a schematic diagram of an example of a negative corona charging type photosensitive member, and FIG. 3 is a schematic diagram showing the structure of a conventional example of a positive corona charging type photosensitive member. FIG. 1 ... Conductive substrate, 2 ... Charge transport layer, 3 ... Charge generation layer, 4 ... Covering layer, 21 ... Charge transport layer (A), 22 ... Charge transport layer (B).

Claims (2)

[Claims] 1. A charge transport layer formed by coating a liquid in which an organic charge transporting substance is dispersed in a resin binder on a conductive substrate, and a liquid in which an organic charge generating substance is dispersed in a resin binder. In the laminated electrophotographic photoreceptor used in the positive corona charging system, which is formed by sequentially laminating the charge generation layer and the coating layer formed as described above, the charge transport layer is a laminate of two layers having different molecular weights of resin binders, Of the two layers, the layer in contact with the conductive substrate comprises a low molecular weight resin binder, and the layer in contact with the charge generation layer comprises a higher molecular weight resin binder. Photoconductor. 2. The photosensitive member according to claim 1, wherein among the two layers constituting the charge transport layer, the layer in contact with the conductive substrate is made of a resin binder having an average molecular weight of 100,000 or less, A laminated electrophotographic photoreceptor characterized in that the layer in contact with the generating layer is composed of a resin binder having an average molecular weight of more than 100,000.