JP4216224B2 - Electrophotographic photosensitive member and image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic photosensitive member and an image forming apparatus used in a copying machine or a printer using an electrophotographic process, and more specifically, a charge generation layer capable of obtaining a high image quality is a minute region. In particular, the present invention relates to an electrophotographic photosensitive member, a method for manufacturing the same, and an image forming apparatus.

  Conventionally, as a photoconductor used in an electrophotographic system, a photoconductive layer mainly composed of selenium or a selenium alloy is provided on a conductive support, and an inorganic photoconductive material such as zinc oxide or cadmium sulfide is used as a binder. In general, those dispersed in the material and those using an amorphous silicon-based material are known, but they are organic due to cost, productivity, high degree of freedom in designing the photoreceptor, and non-polluting. System photoreceptors are widely used.

  Organic electrophotographic photoreceptors include photoconductive resins represented by polyvinylcarbazole (PVK), charge transfer complex types represented by PVK-TNF (2,4,7-trinitrofluorenone), phthalocyanine-binders Known are pigment-dispersed types such as resin, and function-separated type photoconductors that use a combination of charge-generating materials and charge-transporting materials. However, they are conductive because of their sensitivity, durability, and freedom of design. A function-separated type photoreceptor in which a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material are laminated on a support is common.

  The mechanism of electrostatic latent image formation in this function-separated type photoreceptor is that when the photoreceptor is charged and irradiated with light, the light passes through the transparent charge transport layer and is absorbed by the charge generation material in the charge generation layer, The charge generation material that has absorbed the light generates charge carriers, which are injected into the charge transport layer, move in the charge transport layer according to an electric field, and neutralize the charge on the surface of the photoreceptor to neutralize the electrostatic latent. It forms an image. In function-separated type photoreceptors, it is known and useful to use a combination of a charge transport material having absorption mainly in the ultraviolet region and a charge generation material having absorption mainly from the visible region to the near infrared region. It is.

  However, in the case of the above-described function-separated type photoreceptor, since the distance from the charge generation layer to the surface of the charge transport layer is long, there is a problem that the carrier is diffused during transport and the resolution is lowered. In other words, the carriers are attracted to the surface of the charge transport layer and transported, but at that time, they are also diffused in the lateral direction, the carrier diameter is larger than the beam spot diameter corresponding to one dot, and the adjacent image. The dot area is entered (see FIG. 1). Furthermore, since the energy distribution of the exposure beam follows a Gaussian function (normal distribution), it will have a wide skirt, and carriers generated by the light at this skirt will easily diffuse into the adjacent image dot area, and the resolution will increase. (See FIG. 2, 600 dpi, beam diameter 68.9 μm).

Further, in the electrophotographic image forming apparatus, the beam spot diameter of the laser beam for exposing the photosensitive drum (the diameter of a circle connecting the areas where the light quantity is 1 / e ² of the peak value) is 50 μm to 80 μm. Most of the range. When the resolution is 1200 dpi, the length per pixel is 21.2 μm, which is considerably smaller than the beam diameter. Since the beam diameter is determined by the wavelength of the laser, the focal length of the optical system, and the aperture diameter, reducing the beam diameter alone involves problems such as an increase in the size of the device. There is a background that cannot be done.

  The problem that the beam spot diameter is larger than the length per pixel and the problem that occurs in the above-described function-separated type photoconductor (laminated photoconductor), that is, when the photocarrier passes through the charge transport layer. When combined with the problem that photocarriers diffuse into the surface area of the charge transport layer and enter adjacent pixel areas, conventional image forming apparatuses have a sharp electrostatic latent image (potential (charge (charge)). ) There is a problem that it is difficult to form an electrostatic latent image having a high contrast.

  When such an electrostatic latent image with a small potential contrast is formed through development, transfer, and fixing processes, the following phenomenon that leads to deterioration in image quality may occur. However, it became clear by experiments conducted by the inventors.

“First image quality degradation phenomenon: disappearance of fine lines”
When one dot line (thin line) is formed when the resolution is high (in the case of 1200 dpi), the one dot line disappears in the output image, and a phenomenon that it is not reproduced appears. In addition, even when the resolution is small (in the case of 600 dpi), when half-dot (writing with a small value at the time of multi-value writing) writing is performed, fine lines disappear in the same manner and are not reproduced. Will occur. These thin line images and images having characteristics close to those exist as low-contrast images (images such as lines and characters that appear to be very light gray) even in general images. For this reason, even in a general image, a reduction in image quality such as a decrease in reproducibility of a low contrast image is caused.

“Second image quality degradation phenomenon: abrupt density change in highlight area in gradation image”
When a gradation image such as a photographic image or a graphics image is subjected to pseudo halftone processing with a high number of lines and output as an image, a highlight portion (an area having a reflection density of about 0 to 0.2) ) Causes a sudden change in density. In such a gradation image, such a sudden density change at the highlight portion causes a phenomenon called a pseudo contour that a gradation boundary that does not exist on the original image appears. Since the pseudo contour is an abnormal image that gives a sense of incongruity in a gradation image, it is a major factor in image quality degradation.

On the other hand, the following prior art is shown.
In Patent Document 1, “in an electrophotographic photoreceptor in which at least a photosensitive layer is formed on a conductive substrate, the photosensitive layer is composed of a charge generation region and a charge transport region, and the charge generation region is formed in the charge transport region. An electrophotographic photoreceptor characterized by having a structure embedded in a provided hole ”is provided, but it is expensive because the manufacturing process is complicated, and the area of the surface layer is separated, so that foreign matter Adhesion, indentation and the like are likely to occur, and as a result, an abnormal image is likely to occur.

  Further, in Patent Document 2, “in a function separation type photoconductor in which a substrate, a carrier generation layer, and a carrier transport layer are sequentially laminated, at least the light-shielding mask pattern layer that blocks part of image exposure light is included in the carrier. An electrophotographic photoreceptor characterized in that it is provided on the surface of the generation layer ”is provided, but it is also expensive because the manufacturing process is complicated, and contamination occurs due to the material of the light-shielding mask pattern. A characteristic problem arises.

  Further, in Patent Document 3, “a multilayer electrophotographic photosensitive member including a charge generation layer and a charge transport layer contains a photocurable resin and other resin components in the charge transport layer to form a charge transport layer. By irradiating light in a wavelength range capable of curing the photocurable resin in a lattice shape, a portion where the content of the photocurable resin is larger than the unexposed portion is formed in a lattice shape, and the lattice-shaped exposed portion Is provided in a region where the surface resistance or the volume resistance is larger than that of the unexposed portion. However, it is expensive because the manufacturing process is complicated, and is a photocurable resin. In general, the mobility of carriers is lowered, and the photoresponsiveness as a photoreceptor is greatly lowered. Further, since the pattern is formed in a lattice pattern, it cannot be said that the effect on the resolution reduction is great.

  Further, in Patent Document 4, “in an image forming apparatus that forms a visible image by charging, image exposure and development on the surface of an image carrier on which a photoconductive photosensitive layer is formed, the image exposure is performed. In contrast, an image forming apparatus characterized in that minute regions in which the potential does not decay is dispersed and formed in the photosensitive layer ”is provided, but it is effective for improving solid and graphic image density uniformity. However, it is thought that there is no effect in improving the resolution. The production method is also formed by laser beam irradiation, and the process is complicated and the influence on the electrostatic properties of carbides generated by laser beam irradiation cannot be ignored.

  In the above-mentioned Patent Documents 1 to 4, which are conventional techniques, problems such as those already described, such as an increase in cost due to the complexity of the production method, a decrease in durability on electrostatic characteristics due to non-uniformity of the light shielding pattern and the charge transport layer, Although a problem occurs, there is a further problem that it is not sufficiently efficient in forming an electrostatic latent image having a large potential contrast.

  In the prior art described above, the generation ratio (so-called sensitivity) of photocarriers generated in CGL is constant in any part of CGL (any part of the unmasked part). In such a configuration, when combined with the current situation that the beam spot diameter cannot be actively reduced, the generation ratio of the photocarriers generated in the unmasked portion is the region where this mask is not applied. It becomes almost constant within. In this case, the photocarrier generation region is slightly concentrated by the mask region. However, since the effect is limited to the size of the mask region, an electrostatic latent image having a sufficiently large contrast ( There has been a problem that an electrostatic latent image having a contrast that is so large that the above-described problems such as disappearance of fine lines and abrupt density change in a highlight portion in a gradation image do not occur.

  For the above-mentioned problem that an electrostatic latent image having a sufficiently high contrast cannot be formed, the mask area is further increased (the charge generation area is reduced), and the photocarrier generation location is set within one pixel. Improvement is also possible by limiting to the central part. However, in this case, there is a new problem that a so-called solid image (an image in which toner is uniformly attached to the entire region) cannot be obtained. This is because if the masked area is made large, the charge in this part cannot be canceled by writing, and toner cannot adhere to this part.

JP 2000-231203 A JP 2001-75301 A JP-A-11-258837 JP 11-338170 A

  An object of the present invention is to provide an image forming apparatus capable of uniformly adhering toner to the entire surface of a solid image while forming an electrostatic latent image having a sufficiently large contrast.

The above-mentioned problem is that (1) “a charge generation region having at least a charge generation material on a conductive support and a charge transport layer containing at least a charge transport material on a conductive support, The electrophotographic photosensitive member is characterized in that each dot-shaped charge generation region has a shape in which the thickness increases from the peripheral part toward the central part. ;
(2) "The electrophotographic photosensitive member according to (1) above, wherein an average particle diameter of the charge generation material contained in the charge generation material is 0.2 µm or less";
(3) The item (1) or (2) , wherein the charge generation layer comprises a solidified array of droplets of the charge generation layer coating solution supplied on the electrophotographic substrate. The electrophotographic photosensitive member according to claim 1;
(4) "The electrophotographic photosensitive member according to (3) above, wherein the charge generation layer is formed by ejecting a charge generation layer coating solution using an inkjet method";
(5) “The electrophotographic photosensitive member according to item (4), wherein the inkjet method is a piezo method”;
(6) “Process cartridge having at least the electrophotographic photosensitive member according to any one of (1) to (5) ”;
(7) “Image forming apparatus characterized by having at least the electrophotographic photosensitive member according to any one of (1) to (5) and outputting an image”;
(8) “Image forming apparatus according to item (7), wherein the pitch of the dots formed in the charge generation region of the electrophotographic photosensitive member is equal to the resolution of the image forming apparatus” ;
(9) “When the electrophotographic photosensitive member represents the thickness distribution of the charge generation region on the vertical axis and the thickness distribution of the charge generation region on the horizontal axis. , Half width W (the size of the horizontal axis where the thickness is h / 2, where h is the thickness of the charge generation region at the center), and the length L corresponding to one pixel (the charge The image formation according to (7) above , wherein the relationship with the bottom diameter of the generation region, for example, L = 21.2 μm at 1200 dpi, satisfies the relational expression of W ≦ 0.75 × L. Solved by " device ".

  In the present invention, the charge generation layer is formed as a minute region dispersed in dots, and each dot-like charge generation region has a shape in which the thickness increases from the peripheral portion toward the central portion. Thus, at the time of exposure, more photocarriers can be generated in the central portion than in the peripheral portion of the pixels constituting the image. As a result, the problem pointed out in the section of the prior art, that is, when photocarriers pass through the charge transport layer in the function-separated type photoconductor, the photocarrier spreads in the surface direction (lateral direction), resulting in resolution. It becomes possible to solve the problem that the performance is lowered. Since the structure of the charge transport layer generates more photocarriers in the central part than in the peripheral part of the pixel, almost the same amount of photocarriers are present in any part of the charge generation region as in the prior art. Compared to photoconductors that generate (the amount of photocarriers generated in the peripheral and central portions of the pixel is almost the same), this greatly contributes to the solution of the above-described problem that the resolution is deteriorated. To do. As a result, even when a grayscale image such as a photographic image or a graphics image is subjected to pseudo halftone processing with a high number of lines and an image is output, the highlight portion (reflection density is 0 to 0). (Region of about .2), there is no rapid density change and an image with good reproducibility can be obtained.

  Furthermore, the charge generation layer also exists in the peripheral portion of the pixel (which is naturally configured so that the thickness of the charge transport layer is smaller than that in the central portion of the pixel). For this reason, a small amount of photocarriers are also generated in the peripheral portion, which is important when a solid image (high density image) is formed. In the prior art, in order to solve the resolution problem described in the previous paragraph, a method for limiting the photocarrier generation region has been proposed. However, in the case of a solid image, it is necessary to attach toner to the entire surface. It is necessary to cancel the charge on the surface of the photosensitive member by a photo carrier even in a region where no occurrence of the phenomenon occurs. For this reason, it has been difficult for the conventional method to achieve both resolution and solid image. On the other hand, in the present invention, in order to achieve compatibility with this black solid, a photo carrier is generated (a central portion of the pixel) so that a solid image can be reproduced (a gap is filled). A small amount). This makes it possible to achieve both resolution and solid image (high density).

  Furthermore, the conventional method (1) is expensive because the manufacturing process is complicated, (2) there is adhesion of foreign matter (described in Patent Document 1) due to the region being divided in the surface layer, and (3) light shielding. Contamination occurs depending on the material of the mask pattern (described in Patent Document 2), (4) mobility when using a photo-curing resin is decreased (described in Patent Document 3), and (5) carbonization generated by a laser beam. It is possible to eliminate all the problems such as adverse effects on the electrostatic properties of hydrogen (described in Patent Document 4).

In addition, by making the pitch of the charge generation region equal to the resolution of the image forming apparatus, the above effect becomes more remarkable.
Further, as shown in FIG. 6, when the thickness distribution of the charge generation region is expressed by a graph in which the vertical axis represents the thickness (height) of the charge generation region and the horizontal axis represents the spread of the charge generation region, Half-value width W (the size of the horizontal axis where the thickness is h / 2, where h is the thickness of the charge generation region at the center), and the length L corresponding to one pixel (the charge generation When the relationship with the bottom diameter of the region, for example, L = 21.2 μm at 1200 dpi, satisfies the relational expression of W ≦ 0.75 × L, both resolution and solid image can be realized. It becomes like this. Further, if the half width (W) is less than 0.6 × L, a desired solid ID cannot be secured.
According to the experiment conducted by the inventor, with the above-described configuration, from the viewpoint of resolution, the reproduction and highlight portion of the 400-line line image described in detail in the section of Example 1 is used. Satisfying more specific conditions such as the autocorrelation coefficient (R ^ 2) value of 0.95 or higher when linear approximation is performed on the γ characteristics of It became clear that there was. Further, it has been clarified from experiments that the reflection density of a solid image is 1.4 or more even with a solid image by the above-described photoconductor configuration.

  Furthermore, when the average particle size of the charge generation material contained in the charge generation material is 0.2 μm or less, dot reproducibility is improved, and unevenness of the entire image is reduced, and a good image can be obtained. It becomes possible. In addition, by applying the charge generation layer using the ink jet method, it is possible to form dots with an extremely simple manufacturing apparatus and at a low cost as compared with the conventional case. By using the piezo method as an ink jet method, it is possible to prevent alteration of the charge generation layer coating solution, which is easily altered by heat, and an image-like black that is a concern when applied using the bubble jet (foaming jet) method. It is possible to prevent a spot and to obtain a manufacturing method that can bring out the effects of the present invention very well. Furthermore, a process cartridge having such an effect can be obtained, and an image forming apparatus can be obtained.

That is, as a result of intensive studies, the present inventors can solve the above-mentioned problems by forming the charge generation layer as a minute region dispersed in dots as compared to the conventional electrophotographic photosensitive member and manufacturing method. I found out.
Further, since the material itself constituting the present invention does not use a light-shielding material, a curable material, or the like, it can be used without changing from a conventional photoconductor, and uses a simple and accumulated photoconductor technology. As a result, it is possible to easily design a photoreceptor corresponding to high sensitivity and high image quality.
That is, the present invention has a photosensitive layer comprising a charge generation layer having at least a charge generation material and a charge transport layer containing at least a charge transport material on a conductive support, and the charge generation layer has a dot shape as a minute region. Further, the individual dot-shaped charge generation regions are related to the electrophotographic photosensitive member having a structure in which the thickness increases from the peripheral portion toward the central portion, thereby sufficiently It is possible to provide an electrophotographic photosensitive member capable of uniformly depositing toner on the entire surface of a solid image while forming an electrostatic latent image having a high contrast.

Next, a method for manufacturing the charge generation region formed by dispersing the dots of the photosensitive member used in the present invention will be described.
The shape of the dot-like charge generation region whose thickness increases as it goes from the peripheral part to the central part is, for example, that the charge generation layer coating liquid with an appropriate viscosity and charge generation substance content ratio is formed on an electrophotographic substrate. The droplets are supplied by, for example, intaglio gravure printing, silk screen printing, ink-jet method, etc., and this is solidified as it is under appropriate drying conditions (dry conditions that do not cause deformation such as sagging or bleeding). This makes it easy and reliable to manufacture.
Here, the ink jet method used in the present invention will be described as an example.
The ink jet method is a method used in an ink jet printer. Recently, an ink jet recording method using this ink jet method has begun to spread widely. This ink jet recording method is a printing method in which printing is performed by causing small droplets of an ink composition to fly and adhere to a recording medium such as paper. An ink jet recording apparatus using this method has a feature that a high-resolution and high-quality image can be printed at a high speed with a relatively inexpensive apparatus. For this reason, ink jet recording apparatuses have come to be used as digital printing machines, plotters, CAD output devices, and the like. In particular, since the ink jet recording apparatus can print a digitally processed sentence or image, it can store a document or an image original semipermanently and can print the contents. The ink jet recording apparatus can realize high analysis and high pixel printing by discharging ink composition droplets from a recording head under appropriate system processing.

That is, the ink jet method can attach small droplets to a specific place so that photographic image quality can be output, and there is almost no loss as a liquid. Therefore, it is possible to form a high-quality coating film at low cost as a liquid. In addition, as used in digital equipment, the ON / OFF of droplet flight can be digitally controlled, so that liquid can be output and applied only where needed, and unnecessary parts can be easily removed. It can be uncoated. In addition, because of the widespread use of inkjet printers, equipment that is used in the inkjet method, such as nozzle heads, is easily available at low cost, high quality, and high stability, and is compact. Does not require large-scale equipment. Further, as can be seen from the recent trend of inkjet printers, productivity can be dealt with by increasing the number of nozzles, and productivity can be easily improved.
The ink in the present invention for such an ink jet system preferably has a solid content of 1.5 to 5 wt% and a viscosity of 1.5 to 10 cP. If it is lower than this, the shape of the desired dot-like charge generation region in the present invention cannot be formed and spreads or spreads. If it is high, the liquid discharge becomes unstable, and the shape shown in this patent cannot be formed stably.

  As an ink jet method used in the manufacturing method by the ink jet method of the present invention, a bubble jet (foaming jet) type using an electrothermal transducer as an energy generating element or a piezo jet type using a piezoelectric element can be used. It is. However, the piezo-type ink jet method only applies pressure to the ink and basically has no degradation effect on the ink, whereas the bubble-type ink-jet method instantaneously moves the micro heater embedded in the nozzle. In any case, since the ink is ejected by heating to 200 to 300 ° C. and generating bubbles, it has a deteriorating effect such as ink kogation. Due to the influence of this kogation, the background stain of the image may occur, and the piezo jet type is preferably used in consideration of the influence of heat or the like on the ink, that is, the coating liquid. Also, by changing the ink jet nozzle and pressurizing / heating time, the amount of ink per ink drop and the amount of ink applied per colored part can be set arbitrarily, so that charge generation is important in the present invention. It becomes possible to control the dot shape (diameter) of the layer.

Next, the electrophotographic photosensitive member used in the present invention will be described with reference to the drawings.
FIG. 3 shows a structure in which a charge generation layer (35) mainly composed of a charge generation material and a charge transport layer (37) containing a charge transport material are laminated on a conductive support (31). ing.
FIG. 4 shows a configuration in which an intermediate layer (33) is provided between the conductive support (31) and the charge generation layer (35) in FIG.
Although these illustrated charge generation layers are depicted as uniform layers, it is needless to say that they are actually formed by being dispersed in the form of dots as minute regions.

FIG. 5 is an image pattern of 400 lines used in the present invention to evaluate the reproducibility of thin lines.
FIG. 6 is a schematic diagram illustrating the relationship between W (half-value width), which is an index representing the cross-sectional shape of the charge generation region (35), and the length L corresponding to one pixel in the present invention. When the height (thickness) of the generation region is h, the half width (W) of the region where the height (thickness) of the half is h / 2 (the thickness of the charge generation region at the center is h) In this case, the relationship (W ≦ 0.75 × L) between the length L corresponding to one pixel and the length L corresponding to one pixel will be described.

As the conductive support (31), a material having a volume resistance of 10 ¹⁰ Ω · cm or less, for example, a metal such as aluminum, nickel, chromium, nichrome, copper, gold, silver, platinum, tin oxide, oxidation Metal oxide such as indium by vapor deposition or sputtering, film or cylindrical plastic, paper coated, or aluminum, aluminum alloy, nickel, stainless steel plates, etc. and methods such as extrusion and drawing After forming the tube, it is possible to use a tube subjected to surface treatment such as cutting, superfinishing or polishing. Further, an endless nickel belt and an endless stainless steel belt disclosed in Japanese Patent Application Laid-Open No. 52-36016 can be used as the conductive support (31).

In addition, the conductive support dispersed in a suitable binder resin and coated on the support can also be used as the conductive support (31) of the present invention. Examples of the conductive powder include carbon black, acetylene black, metal powder such as aluminum, nickel, iron, nichrome, copper, zinc, and silver, or metal oxide powder such as conductive tin oxide and ITO. It is done. The binder resin used at the same time is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer. , Polyvinyl acetate, polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinylcarbazole, acrylic resin, silicone resin, epoxy resin, Examples thereof include thermoplastic, thermosetting resins, and photocurable resins such as melamine resin, urethane resin, phenol resin, and alkyd resin. Such a conductive layer can be provided by dispersing and coating these conductive powder and binder resin in a suitable solvent such as tetrahydrofuran, dichloromethane, methyl ethyl ketone, and toluene.
Furthermore, it is electrically conductive by a heat-shrinkable tube in which the conductive powder is contained in a material such as polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber, Teflon (registered trademark) on a suitable cylindrical substrate. Those provided with a conductive layer can also be used favorably as the conductive support (31) of the present invention.

Next, the charge generation layer (35) is a layer mainly composed of a charge generation material, in which the charge generation material, binder resin or the like is dispersed or dissolved in an appropriate solvent, and this is formed on the conductive support or the intermediate layer. It can be formed by coating and drying on top.
As the charge generation layer (35), a known charge generation material can be used, and representative examples thereof include phthalocyanine pigments such as titanyl phthalocyanine, vanadyl phthalocyanine, copper phthalocyanine, hydroxygallium phthalocyanine, and metal-free phthalocyanine, monoazo pigments, Known azo pigments such as disazo pigments, asymmetric disazo pigments, trisazo pigments, perylene pigments, perinone pigments, indigo pigments, pyrrolopyrrole pigments, anthraquinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squalium pigments, etc. Materials are mentioned and these are usefully used. These charge generation materials may be used alone or in combination of two or more.

  In the charge generation layer (35), the charge generation material is dispersed in a suitable solvent together with a binder resin if necessary using a ball mill, attritor, sand mill, ultrasonic wave, etc., and this is applied onto the conductive support. And formed by drying. The particle size of the charge generation material is preferably 0.2 μm or less. If it is larger than 0.2 μm, the dots are not formed cleanly and uniformly, so that the resolution of isolated dots decreases. In particular, the influence becomes significant when a high resolution of 1200 dpi or more and a writing system of a small diameter beam are used.

  The binder resin used for the charge generation layer (35) as necessary may be polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polysulfone, poly -N-vinyl carbazole, polyacrylamide, polyvinyl benzal, polyester, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyphenylene oxide, polyamide, polyvinyl pyridine, cellulosic resin, casein, polyvinyl alcohol, polyvinyl pyrrolidone Etc. The amount of the binder resin is suitably 0 to 500 parts by weight, preferably 10 to 300 parts by weight with respect to 100 parts by weight of the charge generating material. The binder resin may be added before or after dispersion.

  Examples of the solvent used here include isopropanol, acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethyl cellosolve, ethyl acetate, methyl acetate, dichloromethane, dichloroethane, monochlorobenzene, cyclohexane, toluene, xylene, and ligroin. In particular, ketone solvents, ester solvents, and ether solvents are preferably used. These may be used alone or in combination of two or more.

The charge generation layer (35) is mainly composed of a charge generation substance, a solvent and a binder resin, and includes known additives such as a sensitizer, a dispersant, a surfactant, and silicone oil. It may be.
As a coating method of the coating solution, an inkjet method is preferable as shown in the present invention.
The film thickness of the charge generation layer (35) is suitably about 0.01 to 5 μm, preferably 0.1 to 2 μm.

The charge transport layer (37) can be formed by dissolving or dispersing a charge transport material and a binder resin in a suitable solvent, and applying and drying the solution on the charge generation layer. Moreover, it is possible and useful to add one or two or more kinds of plasticizers, leveling agents, antioxidants, lubricants and the like as necessary.
As the solvent used here, tetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene, dichloroethane, cyclohexanone, methyl ethyl ketone, acetone and the like are used. These may be used alone or in combination of two or more.
As a coating method of the coating solution, methods such as dip coating, spray coating, beat coating, nozzle coating, spinner coating, ring coating, and the like can be used.

The charge transport material is classified into a hole transport material and an electron transport material. Examples of the electron transporting material include chloroanil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4 , 5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophen-4-one, 1,3,7-tri Examples thereof include electron-accepting substances such as nitrodibenzothiophene-5,5-dioxide and benzoquinone derivatives.
Examples of hole transport materials include poly-N-vinylcarbazole and derivatives thereof, poly-γ-carbazolylethyl glutamate and derivatives thereof, pyrene-formaldehyde condensates and derivatives thereof, polyvinylpyrene, polyvinylphenanthrene, polysilane, oxazole derivatives, Oxadiazole derivatives, imidazole derivatives, monoarylamine derivatives, diarylamine derivatives, triarylamine derivatives, stilbene derivatives, α-phenylstilbene derivatives, benzidine derivatives, diarylmethane derivatives, triarylmethane derivatives, 9-styrylanthracene derivatives, pyrazolines Derivatives, divinylbenzene derivatives, hydrazone derivatives, indene derivatives, butadiene derivatives, pyrene derivatives, bisstilbene derivatives, enamine derivatives, etc. Other known materials may be used. These charge transport materials may be used alone or in combination of two or more.

  As the binder resin, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, Polyvinylidene chloride, polyarylate, 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, melamine resin, urethane resin, Examples thereof include thermoplastic or thermosetting resins such as phenol resins and alkyd resins.

  Moreover, it is preferable that the film thickness of a charge transport layer shall be 5-40 micrometers or less. The lower limit varies depending on the system to be used (particularly charging potential), but is preferably 5 μm or more.

A protective layer (not shown) may be formed on the charge transport layer (37) for the purpose of improving durability.
As the protective layer, for example, a layer containing a hole transporting hydroxyarylamine having a hydroxy functional group and a polyamide film forming binder capable of forming a hydrogen bond with the hydroxy functional group (Japanese Patent Laid-Open No. 7-253683) ), A hydroxyarylamine compound having a hydroxy functional group in a thermosetting polyamide resin, and a film (described in US Pat. No. 5,670,291) which is heated and cured after adding a curing catalyst, A layer cured with an alkoxysilyl group-containing charge transport compound and an alkoxysilane compound (described in JP-A-3-191358), organopolysiloxane and colloidal silica, and conductive metal oxide and acrylic resin are used. Hardened layer (described in JP-A-8-95280), conductive metal oxidation A layer obtained by crosslinking together with an acrylic ester having a silicon functional group (described in JP-A-8-160651), and a layer obtained by crosslinking a conductive metal oxide together with a photocurable acrylic monomer or oligomer (JP-A-8-184980). A layer cured with a charge transporting compound containing an epoxy group (described in JP-A-8-278645), diamond-like carbon having hydrogen, or crystalline carbon having amorphous carbon or fluorine. Layer (described in JP-A-9-101625, JP-A-9-160268, JP-A-10-73945, etc.), layer mainly composed of cyanoethyl pullulan (described in JP-A-9-90650) A layer obtained by crosslinking a silyl acrylate compound and colloidal silica (described in JP-A-9-319130), poly A layer using a sulfonate graft copolymer (described in JP-A-10-63026), a layer obtained by curing colloidal silica particles and a siloxane resin (described in JP-A-10-83094), a charge containing a hydroxy group Examples thereof include a layer cured with a transport compound and an isocyanate group-containing compound (described in JP-A-10-177268).

  The film thickness of the entire protective layer is 1 μm to 10 μm, preferably 2 to 6 μm. If the protective layer thickness is extremely thin, the uniformity of the film may be reduced or sufficient wear resistance may not be obtained.If the thickness is extremely thick, there is an effect of an increase in residual potential. In some cases, the resolution or dot reproducibility may decrease due to an increase in light transmittance.

  In the photoreceptor of the present invention, an intermediate layer (33) can be provided between the conductive support (31) and the charge generation layer (35). The intermediate layer (33) generally has a resin as a main component, but these resins are resins having a high solvent resistance with respect to a general organic solvent in consideration of applying a photosensitive layer thereon with a solvent. It is desirable. Examples of such resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine resin, phenol resin, alkyd-melamine resin, and epoxy. Examples thereof include a curable resin that forms a three-dimensional network structure such as a resin. However, when the charge generation layer is dispersed in the form of dots as shown in the present invention, the intermediate layer contains a filler and is porous in order to improve the uniformity of size of the charge generation dots to be formed and to prevent bleeding. It preferably has a quality structure.

Further, fine powder pigments of metal oxides exemplified by titanium oxide, silica, alumina, zirconium oxide, tin oxide, indium oxide and the like may be added to the intermediate layer in order to prevent moire and reduce residual potential. These intermediate layers can be formed using an appropriate solvent and a coating method like the above-mentioned photosensitive layer. Furthermore, a silane coupling agent, a titanium coupling agent, a chromium coupling agent, or the like can be used as the intermediate layer of the present invention. Furthermore, various dispersing agents can be added. In addition, in the intermediate layer of the present invention, Al ₂ O ₃ is provided by anodic oxidation, organic substances such as polyparaxylylene (parylene), SiO ₂ , SnO ₂ , TiO ₂ , ITO, CeO _2, etc. Those provided with an inorganic material by a vacuum thin film forming method can also be used favorably. However, the unevenness of the charge generation layer is likely to cause unevenness in the image, particularly non-uniformity of the halftone density. For this reason, the intermediate layer is porous in the micron order so that the coating solution does not bleed when the substrate adheres. Such an intermediate layer is desirable. The thickness of the intermediate layer is suitably from 0 to 5 μm.

  In the photoreceptor of the present invention, another intermediate layer can be provided between the photosensitive layer and the protective layer. In the intermediate layer, a binder resin is generally used as a main component. Examples of these resins include polyamide, alcohol-soluble nylon, water-soluble polyvinyl butyral, polyvinyl butyral, and polyvinyl alcohol. As a method for forming the intermediate layer, a generally used coating method as described above is employed. In addition, about 0.05-2 micrometers is suitable for the thickness of an intermediate | middle layer.

EXAMPLES Next, although this invention is demonstrated based on an Example, this invention is not limited by these Examples.
<Photoreceptor configuration>
・ Intermediate layer An intermediate layer coating solution having the following formulation was prepared.
(Intermediate layer coating solution)
Polyamide resin (CM8000, manufactured by Toray Industries, Inc.) 2 parts Methanol 58 parts n-Butanol 40 parts This coating solution is dip-coated on an aluminum drum having a diameter of 30 mm and a length of 340 mm, and dried at 120 ° C. for 20 minutes to obtain a film thickness. A 0.3 μm intermediate layer was created.
-Charge generation layer Next, the coating liquid for charge generation layers of the following prescription was created.
10 parts by weight of a trisazo pigment represented by the following structural formula (A) is added to a resin solution obtained by dissolving 4 parts by weight of polyvinyl butyral (BM-2: manufactured by Sekisui Chemical Co., Ltd.) in 150 parts by weight of cyclohexanone, and 72 hours by a ball mill. Dispersion was performed. After the completion of dispersion, 250 parts by weight of cyclohexanone and 200 parts by weight of 2-butanone were added and dispersed for 3 hours to prepare a charge generation layer coating solution, and a viscosity of 3.3 with a mixed solvent of cyclohexanone: butanone = 2: 1. Adjusted to 0 cP. This coating solution was applied onto the intermediate layer in the form of dots under the following conditions and dried at 120 ° C. for 20 minutes to form a charge generation layer (both ends 10 mm uncoated portion).

Although some unevenness was observed due to bleeding and spreading of the coating liquid, the coating liquid could be satisfactorily coated without roughening and non-uniformity of the coating film. Moreover, since the coating width was controlled, the uncoated part was not wiped off, and the defect due to wiping (thickening of the coating film thickness at the end, splashing at the time of wiping) was good. The amount of coating solution used was about 0.5 ml.
The particle diameter of the charge generation material after dispersion was 0.07 μm. The particle size was measured by centrifugal sedimentation using CAPA-700 manufactured by Horiba.
In the present invention, the coating was performed by modifying a commercially available IP-4000 A0 printer (compatible with oil-based pigment ink) manufactured by Seiko Denshi Kogyo. A piezo type recording head was used. The ink in the ink cartridge can be replaced. In addition, the aluminum drum was remodeled so that it could be rotated at the ink adhering part and paper position. In addition, coating by the ink jet method can be controlled from a personal computer, and the liquid discharge amount (which changes the dot size) and the dot interval are controlled from the personal computer as well as the coating width.
-Charge transport layer Next, the coating liquid for charge transport layers of the following prescription was created.
7 parts by weight of the charge transport material represented by the following structural formula (B) and 10 parts by weight of polycarbonate (Z type: viscosity average molecular weight 50,000) were dissolved in 100 parts by weight of tetrahydrofuran to prepare a charge transport layer coating solution. This coating solution was dip-coated on the charge generation layer, dried at 130 ° C. for 20 minutes, and a charge transport layer having a thickness of 20 μm was applied to produce the photoreceptor of the example.

<Image output, image quality evaluation>
An image was output using the photosensitive drum that was prototyped by the above manufacturing method, and the image quality was evaluated.
As for image output, paying attention to two items of “good reproduction of fine lines” and “stable density change in highlight portion”, the following image output experiments were performed respectively.
First, “good reproduction of fine lines” was evaluated visually using an image pattern with 400 lines shown in FIG. 5 using an image output experimental machine with a resolution of 1200 dpi described below. The case where a 400-line line image was reproduced was marked as ◯, and the case where a 400-line line image was not reproduced was marked as x. Whether or not the 400-line line image is set as a criterion for determination is based on the outline of the character part (not to become a rattling outline) and the color of the character when a low-contrast character / color character is printed with a printer. This is set as a substitute characteristic for reproducing both the reproducibility (the target color can be reproduced) and the like.

Next, with respect to “stable density change in the highlight portion”, an 8-bit Tiff image data including patches of 0 to 256 gradations (15 mm square) is used by using an image output experimental machine with a resolution of 1200 dpi described below. Output image data (post-pseudo halftone processed data) that has been subjected to dither processing (screen line number of about 170 lines, screen angle of 45 degrees, line screen type, quantization number of 2 bits, resolution of 1200 dpi) is prepared in advance. The image output is performed using the output image data. The evaluation of the output image was performed using the result of measuring the reflection density (ID value) of the highlight portion (data 0 to 32) with a spectral reflection densitometer (X-Rite model 938). A linear equation is approximated with respect to the relationship between the reflection density value and the input data value. The case was marked with x. The condition that the value of R ^ 2 of the linear expression approximation in the highlight portion (data 0 to 32) set as the determination criterion here is 0.95 or more is an abnormal image called a pseudo contour in a gradation image This is set as a substitute characteristic to reproduce well without occurrence.
An example of “approximate a linear expression for the relationship between the reflection density value and the input data value” will be specifically described. For example, as a result of the experiment, the reflection density value (vertical axis) and the input data (horizontal axis: The relationship of 0 to 255) is obtained as shown in FIG.
Such a relationship can be obtained by measuring the output image with a reflection densitometer. If the highlighted part of this relationship (the circled part in Fig. 7) is fitted with a linear expression (can be easily done with least squares, Excel, etc.), how close this relationship is to the linear expression (linear Can be determined). If R ^ 2 (square of autocorrelation coefficient) is close to 1.0, it indicates that the relationship is almost linear, and the smaller the value is, the more the value deviates from the linear relationship. It expresses that
Dither processing is one of the following forms of pseudo halftone processing. That is, the image data input to the image forming apparatus has multi-value data of 8 to 12 bits per pixel in a gradation image such as a photograph. In contrast, in an image forming apparatus (including an electrophotographic system) that forms an image (so-called hard copy) on paper, the number of gradations that can be expressed per pixel is substantially very small. In order to solve such a problem, in a hard copy device, the resolution is improved to 600 dpi, 1200 dpi, etc., and a plurality of pixels are used to modulate the image density in an area to produce a pseudo halftone image. Express.
When dither processing is performed and pseudo halftone processing is performed, when an intermediate density (gray) image is enlarged, the toner adhering portion and the white background portion have a halftone dot shape as shown in FIG. The number of screen lines and the screen angle in the dither processing can be derived from a relational expression as shown in FIG.

  Next, the experimental machine used for image output will be explained. This experimental machine is an experimental machine modified on the basis of Ricoh's Imagio Color 5100, which is mainly a modified writing unit. In this experimental machine, a 4-channel LD array in which four light emitting points (laser diodes) are formed in a line on one chip is used as an LD element. Thereby, a resolution of 1200 dpi was realized. In this experimental machine, the optical element and the aperture are adjusted so that the beam diameter is 40 (main scanning direction) × 40 (sub-scanning direction) μm on the photosensitive member position. Further, the amount of the stationary beam of the laser beam is adjusted and set by measurement using an optical power meter.

Next, an image output experiment and its results will be described.
The prototype photoconductor used in the experiment was prepared by the method described in the section <Photoreceptor configuration> (CGM is trisazo pigment: structural formula (A)).
At this time, it was prepared so that the constitution of the charge generation layer was different at a resolution of 1200 dpi while adjusting various preparation conditions including the coating liquid preparation conditions of the ink jet printer. In the prototype photoconductor drum, the sample in which the charge generation region was formed was used exclusively for charge generation region measurement without providing a charge transport layer. The charge generation region is measured using a Keyence laser microscope (model number: VK-8550) capable of measuring height information, the distance from the center of the charge generation region to the ridge, and the charge generation region. The height distribution was measured. In addition, since the height cannot be measured accurately when using the above-mentioned laser microscope (this is because the reflectance of the laser beam is low due to the charge generation region), after the gold plating is applied to the surface, the height of the charge generation region is high. Measuring. From the height distribution of the charge generation region thus obtained, W (half-value width) that is an index representing the cross-sectional shape of the charge generation region is derived by calculation. FIG. 6 is a schematic diagram showing W (half-value width) which is an index representing the cross-sectional shape of the charge generation region. When the height (thickness) of the charge generation region at the center is h, half of that is shown. The width (W) of the region where height (thickness) = h / 2 is derived from the measurement result of the height distribution as shown in FIG.
Using the photosensitive drum thus produced, an image is output, and the above two items (“400 line image reproduction” and “highlight portion are approximated by a linear expression, and the value of R ^ 2 is The following table shows the results of evaluation of “0.95 or more”). Since the full width at half maximum (W) was less than 0.6 × L, a solid ID could not be secured, so it is not listed in the table.

  From the results of the table, when W (half-value width), which is an index representing the shape of the charge generation region, is 0.75 or less, it is possible to improve the problems described in the section of the prior art. , Solid ID = 1.4 or more can be secured, and good image quality can be realized.

  That is, in the present invention, the charge generation layer is formed as a minute region dispersed in a dot shape, and each dot-like charge generation region has a shape in which the thickness increases from the peripheral portion toward the central portion. Thus, at the time of exposure, more photocarriers can be generated in the central portion than in the peripheral portion of the pixels constituting the image. As a result, the problem pointed out in the section of the prior art, that is, when photocarriers pass through the charge transport layer in the function-separated type photoconductor, the photocarrier spreads in the surface direction (lateral direction), resulting in resolution. It becomes possible to solve the problem that the performance is lowered. Since the structure of the charge transport layer generates more photocarriers in the central part than in the peripheral part of the pixel, almost the same amount of photocarriers are present in any part of the charge generation region as in the prior art. Compared to photoconductors that generate (the amount of photocarriers generated in the peripheral and central portions of the pixel is almost the same), this greatly contributes to the solution of the above-described problem that the resolution is deteriorated. To do. As a result, even when a grayscale image such as a photographic image or a graphics image is subjected to pseudo halftone processing with a high number of lines and an image is output, the highlight portion (reflection density is 0 to 0). (Region of about .2), there is no rapid density change and an image with good reproducibility can be obtained.

  Furthermore, the charge generation layer also exists in the peripheral portion of the pixel (which is naturally configured so that the thickness of the charge transport layer is smaller than that in the central portion of the pixel). For this reason, a small amount of photocarriers are also generated in the peripheral portion, which is important when a solid image (high density image) is formed. In the prior art, in order to solve the resolution problem described in the previous paragraph, a method for limiting the photocarrier generation region has been proposed. However, in the case of a solid image, it is necessary to attach toner to the entire surface. It is necessary to cancel the charge on the surface of the photosensitive member by a photo carrier even in a region where no occurrence of the phenomenon occurs. For this reason, it has been difficult for the conventional method to achieve both resolution and solid image. On the other hand, in the present invention, in order to achieve compatibility with this black solid, a photo carrier is generated (a central portion of the pixel) so that a solid image can be reproduced (a gap is filled). A small amount). This makes it possible to achieve both resolution and solid image (high density).

Furthermore, the conventional method (1) is expensive because the manufacturing process is complicated, (2) there is adhesion of foreign matter (described in Patent Document 1) due to the region being divided in the surface layer, and (3) light shielding. Contamination occurs depending on the material of the mask pattern (described in Patent Document 2), (4) mobility when using a photo-curing resin is decreased (described in Patent Document 3), and (5) carbonization generated by a laser beam. It is possible to eliminate all the problems such as adverse effects on the electrostatic properties of hydrogen (described in Patent Document 4).
In addition, by making the pitch of the charge generation region equal to the resolution of the image forming apparatus, the above effect becomes more remarkable.
Further, as shown in FIG. 6, when the thickness distribution of the charge generation region is expressed by a graph in which the vertical axis represents the thickness (height) of the charge generation region and the horizontal axis represents the spread of the charge generation region, Half-value width W (the size of the diameter where the thickness is h / 2, where h is the thickness of the charge generation region at the center), and the length L corresponding to one pixel (the charge generation region If the relationship with the bottom diameter of L, for example 1200 dpi, L = 21.2 μm) satisfies the relational expression of W ≦ 0.75 × L, it is possible to achieve both resolution and solid image. become.
According to the experiment conducted by the inventor, with the above-described configuration, from the viewpoint of resolution, the reproduction and highlight portion of the 400-line line image described in detail in the section of Example 1 is used. Satisfying more specific conditions such as the autocorrelation coefficient (R ^ 2) value of 0.95 or higher when linear approximation is performed on the γ characteristics of It became clear that there was. Further, it has been clarified from experiments that the reflection density of a solid image is 1.4 or more even with a solid image by the above-described photoconductor configuration.

  Furthermore, when the average particle size of the charge generation material contained in the charge generation material is 0.2 μm or less, dot reproducibility is improved, and unevenness of the entire image is reduced, and a good image can be obtained. It becomes possible. In addition, by applying the charge generation layer using the ink jet method, it is possible to form dots with an extremely simple manufacturing apparatus and at a low cost as compared with the conventional case. By using the piezo method as an ink jet method, it is possible to prevent alteration of the charge generation layer coating solution, which is easily altered by heat, and an image-like black that is a concern when applied using the bubble jet (foaming jet) method. It is possible to prevent a spot and to obtain a manufacturing method that can bring out the effects of the present invention very well. Furthermore, a process cartridge having such an effect can be obtained, and an image forming apparatus can be obtained.

FIG. 3 is a diagram illustrating a mechanism for forming an electrostatic latent image on a function-separated type photoreceptor. It is a figure which shows that the carrier generate | occur | produced with the light of the tail part of the energy distribution of an exposure beam spread | diffuses to the area | region of an adjacent image dot, and is causing the resolution to fall. It is a figure which shows an example of the electrophotographic photoreceptor of this invention. It is a figure which shows the other example of the electrophotographic photoreceptor of this invention. It is explanatory drawing (at the time of resolution 1200 dpi) of the 400 line image pattern used by evaluation of an Example. It is a schematic diagram which shows the parameter | index W (half value width) showing the cross-sectional shape of an electric charge generation region. It is a figure which shows the example of 1 relationship between a reflection density value and an input data value. It is a figure explaining the screen line and screen angle in the pseudo halftone part by a dither process.

Explanation of symbols

31 Conductive Support 33 Intermediate Layer 35 Charge Generation Layer 37 Charge Transport Layer

Claims (9)

The conductive support has a charge generation region having at least a charge generation material and a charge transport layer containing at least a charge transport material, and the charge generation region is formed by being dispersed in the form of dots as micro regions, The electrophotographic photosensitive member is characterized in that each dot-like charge generation region has a shape in which the thickness increases from the peripheral part toward the central part. 2. The electrophotographic photosensitive member according to claim 1 , wherein an average particle size of the charge generation material contained in the charge generation material is 0.2 [mu] m or less. The charge generating layer, an electrophotographic photosensitive member according to claim 1 or 2, characterized in that it consists of solidified product array of droplets of the charge generation layer coating liquid supplied to the electrophotographic substrate. The electrophotographic photosensitive member according to claim 3 , wherein the charge generation layer is formed by spraying a charge generation layer coating solution using an ink jet method. The electrophotographic photosensitive member according to claim 4 , wherein the inkjet method is a piezo method. Process cartridge and having at least an electrophotographic photosensitive member according to any one of claims 1 to 5. Wherein in any of claims 1 to 5 having at least an electrophotographic photosensitive member according, the image forming apparatus characterized by performing the output image. The image forming apparatus according to claim 7 , wherein a pitch of the dots formed in the charge generation region of the electrophotographic photosensitive member is equal to a resolution of the image forming apparatus. When the electrophotographic photosensitive member represents a thickness distribution of the charge generation region in a graph in which the vertical axis represents the thickness (height) of the charge generation region and the horizontal axis represents the spread of the charge generation region, the half-value width W ( When the thickness of the charge generation region at the center is h, the horizontal axis at the location where the thickness is h / 2) and the length L corresponding to one pixel (the bottom diameter of the charge generation region) The image forming apparatus according to claim 7 , wherein a relational expression with a relation of W ≦ 0.75 × L is satisfied.

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