JP2009265556A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device that comprises at least a charging means, an exposure means, a development means, and a transfer means around an organic photoreceptor and that forms images repeatedly, the image forming device obtaining a halftone image without a transfer memory or a ghost for a long period of time while maintaining a high transfer rate. <P>SOLUTION: In the image forming device that comprises at least the charging means 22, exposure means 30, development means 23, and transfer means 25 around the organic photoreceptor 21 and that forms an images repeatedly, the most superficial layer of the organic photoreceptor 21 contains at least N-type metal oxide particles, and a transfer current It defined below is ≥1 μA/cm and ≤10 μA/cm. The transfer current It is the current per unit length that flows to the organic photoreceptor by the transfer means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus using an electrophotographic system, a reversal developing unit that develops toner using a toner having the same polarity as a charging current applied to an organic photoreceptor is mainly used and widely used in digital image forming apparatuses. .

  The transfer current applied to the organic photoconductor by the transfer means described above is not usually applied directly to the organic photoconductor, but is applied via the transfer body or the intermediate transfer body. As the image quality increases year by year, the toner tends to have a smaller particle size, and in association with this, the transfer current flowing to the organic photoreceptor is often set higher (see, for example, Patent Document 1). .) This is because the toner having a smaller particle size has more cohesive force and is difficult to transfer.

  On the other hand, a problem when the transfer current is high is the generation of a transfer memory.

  The transfer current is uniformly applied to the toner adhering portion (toner developing portion) and the toner non-adhering portion (non-developing portion) on the organic photoreceptor. That is, an organic photoreceptor surface to which a transfer current is applied via toner and an organic photoreceptor surface to which a transfer current is directly applied can be formed, and a difference in transfer current flowing depending on a portion of the organic photoreceptor can be made.

  In the case of a negatively charged organic photoreceptor, the polarity of the current applied by the transfer means is positive, so that a positive space charge remains on the surface of the organic photoreceptor to which a positive current is applied. Generally, the positive space charge is erased in the next charging means.

  However, when the transfer current becomes higher than necessary, there is an excess of positive space charge, and even if it is negatively charged by the next charging means, a potential drop is caused by the influence of the space charge, and further, there is a sensitivity difference in the developing means. In this way, a so-called transfer memory image is generated in which the portion of the print image becomes black.

These tend to become more prominent when the transfer voltage is increased when transferring a toner having a smaller particle diameter. On the other hand, when the transfer current is lowered, transfer failure occurs and the toner cannot be transferred sufficiently.
JP 2006-220812 A

  The present invention maintains a high transfer rate in an image forming apparatus that has at least a charging unit, an exposing unit, a developing unit, and a transferring unit around an organic photoconductor (hereinafter also simply referred to as a photoconductor) and repeatedly forms an image. An object of the present invention is to provide an image forming apparatus capable of obtaining a halftone image free from transfer memory and ghost over a long period of time.

The present invention is achieved by adopting the following configuration.
1.
In an image forming apparatus that has at least a charging unit, an exposure unit, a developing unit, and a transfer unit around an organic photoreceptor, and repeatedly forms an image.
The outermost layer of the organophotoreceptor contains at least N-type metal oxide particles;
An image forming apparatus, wherein a transfer current It defined below is 1 μA / cm or more and 10 μA / cm or less.

(Transfer current It: current per unit length flowing to the organic photoreceptor by the transfer means)
2.
2. The image forming apparatus as described in 1 above, wherein the outermost layer of the organic photoreceptor contains a composition obtained by photocuring a curable compound.
3.
2. The image forming apparatus as described in 1 above, wherein the N-type metal oxide particles are titanium oxide particles.

  The image forming apparatus of the present invention has an excellent effect that an image without a transfer memory can be obtained over a long period of time while maintaining a high transfer rate.

  In image formation, in order to obtain a high-quality print image, it is important to transfer the toner image formed on the surface of the photoreceptor to a transfer material at a high transfer rate. In order to obtain a high transfer rate, measures have been taken to increase the transfer current during transfer.

  However, when the transfer current is increased with a high speed machine (for example, 50 sheets / min or more), there is a problem that a transfer memory is generated in the halftone image portion.

  In order to solve the above problem, the present inventors pay attention to the hole injection site existing on the surface of the photoconductor, and by preventing the injection of holes due to a high transfer current, it is possible to prevent the generation of a transfer memory. I guessed.

  As a result of various studies, in a photoreceptor in which a hole transport type charge transport material is contained in the outermost layer of a negatively charged photoreceptor having a laminated structure, a positive charge is generated when the location of the charge transport material transfers toner. It was inferred that transfer memory was generated as a source of injection.

  Therefore, when a photoconductor containing N-type metal oxide particles in the outermost layer is used, holes are not injected even when a high transfer current is applied, and there is no positive space charge as a source of transfer memory. I guessed and examined it.

  As a result of investigation, a photoreceptor containing N-type metal oxide particles on the outermost layer can obtain a good halftone image without generating a transfer memory even when a high transfer current is applied in order to obtain good transferability. Was confirmed.

  Further, the photoreceptor containing the N-type metal oxide particles in the outermost layer also has an unexpected effect of reducing the adhesion with the toner. As a result, the transfer rate became higher and a print image with high resolution could be obtained.

  The mechanism by which the photoreceptor containing the N-type metal oxide particles in the outermost layer lowers the adhesion with the toner is not clear, but the deformation amount of the outermost layer is reduced due to the filler effect of the N-type metal oxide particles. It is presumed that this is due to a decrease in the followability to toner deformation during transfer and a decrease in the liquid crosslinking force accompanying this.

  The transfer memory referred to in the present invention means that after printing a character image continuously (for example, 100 sheets) and then printing a halftone image, the previously printed character image appears black in the halftone image portion, or halftone. A phenomenon that appears as white spots in the image area.

  Hereinafter, the present invention will be described in detail.

First, the image forming apparatus will be described.
<Image forming apparatus>
The image forming apparatus of the present invention is an apparatus that has at least a charging unit, an exposing unit, a developing unit, a transferring unit, and a fixing unit around a photosensitive member, and can repeatedly form images.

  In the present invention, the transfer means is a means for transferring a toner image formed on the surface of the photoreceptor to a transfer material, or a toner image formed on the surface of the photoreceptor is transferred to an intermediate transfer body (primary transfer). It may be a means to do. When transferring to an intermediate transfer member, the image is transferred (secondary transfer) to a transfer material after primary transfer.

  Next, an image forming apparatus capable of performing transfer by setting the transfer current It per unit length flowing to the photosensitive member by the transfer unit to 1 μA / cm or less and 10 μA / cm or less will be described.

  FIG. 1 is a cross-sectional configuration diagram illustrating an example of an image forming apparatus that transfers a toner image from a photosensitive member to a transfer material.

  The image forming apparatus 1 shown in FIG. 1 is capable of digital image formation, and is roughly composed of an image reading unit A, an image processing unit B, an image forming unit C, and a transfer paper transport unit D.

  In the upper part of the image reading unit A, automatic document feeding means for automatically conveying the document is provided, and the document placed on the document placing table 11 is separated and conveyed one by one by the document conveying roller 12, and the reading position 13a. Then, the image is read. The document whose image has been read is discharged onto the document discharge tray 14 by the document conveying roller 12.

  In addition to the automatic image reading described above, the image forming apparatus 1 in FIG. 1 can also read an original document placed on the platen glass 13 one by one. When reading on the platen glass 13, the original image is read by the illumination mirror constituting the scanning optical system, the first mirror unit 15 including the first mirror, and the second mirror having a structure in which two mirrors are arranged in a V shape. Each unit 16 is moved. In the image forming apparatus of FIG. 1, the document image is read with the moving speed of the first mirror unit 15 set to v and the moving speed of the second mirror unit set to v / 2.

  The image read by the image reading unit A according to the above-described procedure is converted into a digital image signal by the next image processing unit B. In the image processing unit B, first, the image read by the image reading unit A is imaged on the light receiving surface of the image sensor CCD as a line sensor through the projection lens 17. The line-shaped optical image formed on the image sensor CCD is sequentially photoelectrically converted into an electric signal (luminance signal), and further converted into an A (analog) / D (digital) signal. The image signal converted into the digital signal is subjected to processing such as density conversion and filter processing, and the formed image information is temporarily stored in the memory as an image signal.

  The image forming unit C performs toner image formation using the digital signal formed by the image processing unit B, and has a unit structure in which components used for image formation are assembled as shown in FIG. . The image forming unit constituting the image forming unit C includes a drum-shaped photoconductor 21, a charging unit (charging process) 22 for charging the photoconductor 21 on the outer periphery of the photoconductor 21, and supplying toner to the photoconductor 21. Developing means (developing step) 23 and the like are arranged. Further, on the outer periphery of the photoconductor 21, a transfer conveyance belt device 45 that is a transfer unit (transfer process) for transferring a toner image formed on the photoconductor 21 onto a sheet P or the like, and residual toner on the photoconductor 21 are removed. A cleaning device (cleaning step) 26 and a precharge lamp 27 which is a light discharging means (light slowing step) for discharging the surface of the photoreceptor 21 in preparation for the next image formation are arranged. These members from the charging unit 22 arranged on the outer periphery of the photoconductor 21 to the light neutralizing unit 27 are arranged in the order of operations performed at the time of image formation.

  Further, on the downstream side of the developing means 23, a reflection density detecting means 222 for measuring the reflection density of the patch image developed on the photosensitive member 21 is provided. The photoconductor 21 is driven and rotated in the illustrated direction, that is, clockwise when an image is formed.

  Next, a method for exposing the photosensitive member 21 will be described. The photosensitive member 21 is rotated by a driving unit (not shown), and the photosensitive member 21 is uniformly charged by the charging unit 22 during the rotation. The exposure optical system indicated by an image exposure unit (image exposure step) 30 stores the memory of the image processing unit B. The image is exposed on the basis of the image signal called from.

  An image exposure unit 30 corresponding to a writing unit that writes image information on the photosensitive member 21 uses a laser diode (not shown) as a light emission source, and an exposure sent by a polygon mirror 31, an fθ lens 34, a cylindrical lens 35, and a reflection mirror 32. Main scanning is performed with light. Image exposure is performed by irradiating the photosensitive member 21 with exposure light sent in this way at a position Ao in the drawing, and an electrostatic latent image is formed by rotation (sub-scanning) of the photosensitive member 21.

  When forming an electrostatic latent image on the photoreceptor 21, a semiconductor laser or light emitting diode with an oscillation wavelength of 350 to 500 nm is used as an exposure light source, and the dot diameter of exposure light from these exposure light sources is set to 10 to 50 μm. It is preferable to perform exposure. By exposure using so-called fine dot light in which the oscillation wavelength of the exposure light source and the exposure dot diameter are within the above ranges, it becomes possible to form a high-definition dot image compatible with digital image formation on the photosensitive member 21. . That is, when the oscillation wavelength and the exposure dot diameter are within the above ranges, it is possible to form a high-resolution image on the photosensitive member 21 of, for example, 1200 dpi (dots per inch (2.54 cm per inch)) or more. become.

The exposure dot diameter refers to the length of the exposure beam along the main scanning direction in a region where the intensity of the exposure beam is 1 / e ² or more of the peak intensity. Examples of the light source of the exposure beam include a scanning optical system using a semiconductor laser and a solid state scanner using a light emitting diode (LED). Further, the intensity of the exposure beam can be expressed by a Gaussian distribution, a Lorentz distribution, or the like. However, in the present invention, it is not necessary to specify the light intensity distribution, and the exposure beam intensity consists of a region that is 1 / e ² or more of the peak intensity. What is necessary is just to be able to form a dot diameter of 10 to 50 μm in diameter.

  Further, when a surface emitting laser array having three or more laser beam emission points in the vertical and horizontal directions is used as the exposure beam, the electrostatic latent image can be quickly written on the electrophotographic photosensitive member, so that high-speed printing can be performed. Preferred above. Then, by performing exposure with the surface emitting laser array on the electrophotographic photosensitive member according to the present invention capable of forming a stable latent image even if image formation is repeated, a printed matter having stable image quality can be quickly produced. To be able to

  The electrostatic latent image formed on the photoconductor 21 is developed by receiving toner supply from the developing unit 23, and a visible toner image is formed on the surface of the photoconductor 21. In order to realize high-definition image formation corresponding to digital, it is preferable to use polymerized toner as the developer supplied by the developing unit 23. That is, the polymerized toner can be produced while controlling the shape and particle size distribution in the production process.

  Next, the transfer paper transport unit D transports the paper P, onto which the toner image formed on the outer periphery of the photoreceptor 21 in the image forming unit C has been transferred by the transfer unit 45, toward the next fixing unit 50. The transfer paper transport section D is provided with paper feed units 41 (A), 41 (B), and 41 (C), which are transfer paper storage means for storing transfer paper P of different sizes below the image forming unit. In addition, a manual paper feeding unit 42 that performs manual paper feeding is provided on the side of the paper feeding unit. The transfer paper P is selected from any of these transfer paper storage means, and is fed along the transport path 40 by the guide roller 43.

  The transfer paper transport unit D is provided with a paper feed registration roller 44 configured by a pair for correcting the inclination and bias of the transfer paper P to be fed. The transfer paper P is temporarily stopped by the paper feed registration roller 44. After that, it is fed again. The re-fed transfer paper P is guided to the transport path 40, the pre-transfer roller 43a, the paper feed path 46, and the entry guide plate 47.

  The toner image formed on the photoreceptor 21 is transferred onto the transfer paper P by the transfer pole 24 and the separation pole 25 at the transfer position Bo. At this time, the transfer paper P is transferred to the transfer paper belt 454 of the transfer and transport belt device 45 while being transferred to the transfer paper belt 454. The transfer paper P on which the toner image is transferred is transferred from the surface of the photosensitive member 21. The paper is separated and conveyed toward the fixing unit 50 by the transfer conveyance belt device 45.

  The fixing unit 50 includes a fixing roller 51 and a pressure roller 52. When the transfer paper P passes between the fixing roller 51 and the pressure roller 52, the toner image on the transfer paper P is heated and pressed. To fix. When the toner image is fixed on the transfer paper P in this way, the transfer paper P is discharged onto the paper discharge tray 64.

  With the above procedure, the image forming apparatus in FIG. 1 can transfer the toner image onto one side of the transfer paper P and create a printed matter with the image formed on one side. It is also possible to create a printed matter that has been transferred.

  When toner images are formed on both sides of the transfer paper P, the paper discharge switching member 170 of the transfer paper transport unit D is actuated to open the transfer paper guide unit 177, and the transfer paper P having a toner image formed on one side is broken. It is conveyed in the direction of the arrow. The transfer paper P is transported downward by the transport mechanism 178, is switched back by the transfer paper reversing unit 179, and is transported into the duplex printing paper supply unit 130 with the side that was the rear end of the transfer paper P being the leading edge. Is done.

  The transfer paper P is moved in the paper feed direction by a conveyance guide 131 provided in the double-sided copy paper feed unit 130, and the transfer paper P is fed again by the paper feed roller 132, and the transfer paper P enters the conveyance path 40. Guided. Then, according to the above-described procedure, the transfer paper P is transported in the direction of the photoconductor 21, the toner image is transferred to the back surface of the transfer paper P, fixed by the fixing unit 50, and then discharged to the paper discharge tray 64. . By such a procedure, it is possible to create a printed matter in which toner images are formed on both sides of the transfer paper P.

  Further, in the image forming apparatus shown in FIG. 1, a so-called process cartridge having a unit structure in which the photosensitive member 21, the developing means 21, the cleaning device 26 and the like are integrally coupled is formed, and this is attached to and detached from the apparatus main body. It is also possible to adopt a method of freely configuring. Further, in addition to a unit which forms all the components as in a process cartridge, at least one of a charger, an image exposure device, a developing means 23, a transfer or separation device, and a cleaning device is integrated with the photosensitive member 21. It is also possible to form a supported cartridge and to make a unit that can be detachably set to the apparatus main body.

  As described above, the toner image formed by image formation using the photoconductor according to the present invention is finally transferred onto the transfer paper P, and fixed on the transfer paper P through a fixing process.

  FIG. 2 is a cross-sectional configuration diagram illustrating an example of a color image forming apparatus that transfers a toner image from a photosensitive member to an intermediate transfer member.

  The color image forming apparatus 1 is called a tandem type full-color copying machine, and includes an automatic document feeder 13, a document image reading device 14, a plurality of exposure means 13Y, 13M, 13C, and 13K, and a plurality of sets of images. The forming units 10 </ b> Y, 10 </ b> M, 10 </ b> C, and 10 </ b> K, the intermediate transfer body unit 17, the paper feeding unit 15, and the fixing unit 124 are included.

  An automatic document feeder 13 and a document image reading device 14 are arranged on the upper part of the main body 12 of the image forming apparatus, and an image of the document d conveyed by the automatic document feeder 13 is an optical system of the document image reading device 14. The image is reflected and imaged by the line image sensor CCD.

  An analog signal obtained by photoelectrically converting a document image read by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in an image processing unit (not shown), and then exposure means 13Y, A drum-shaped photoconductor (hereinafter also referred to as a photoconductor) 11Y as a first image carrier that is sent to 13M, 13C, and 13K as digital image data for each color and corresponding to the exposure means 13Y, 13M, 13C, and 13K. A latent image of image data of each color is formed on 11M, 11C, and 11K.

  The image forming units 10Y, 10M, 10C, and 10K are arranged in tandem in the vertical direction, and can be rotated by winding rollers 171, 172, 173, and 174 around the left side of the photoreceptors 11Y, 11M, 11C, and 11K in the drawing. An intermediate transfer member (hereinafter referred to as an intermediate transfer belt) 170, which is a semiconductive and seamless belt-like second image carrier stretched on the belt, is disposed.

  The intermediate transfer belt 170 is driven in the direction of an arrow through a roller 171 that is rotationally driven by a driving device (not shown).

  The image forming unit 10Y that forms a yellow image includes a charging unit 12Y, an exposure unit 13Y, a developing unit 14Y, a primary transfer roller 15Y as a primary transfer unit, and a cleaning unit 16Y disposed around the photoreceptor 11Y. Have.

  The image forming unit 10M that forms a magenta image includes a photoreceptor 11M, a charging unit 12M, an exposure unit 13M, a developing unit 14M, a primary transfer roller 15M as a primary transfer unit, and a cleaning unit 16M.

  The image forming unit 10C that forms a cyan image includes a photoreceptor 11C, a charging unit 12C, an exposure unit 13C, a developing unit 14C, a primary transfer roller 15C as a primary transfer unit, and a cleaning unit 16C.

  The image forming unit 10K that forms a black image includes a photoreceptor 11K, a charging unit 12K, an exposure unit 13K, a developing unit 14K, a primary transfer roller 15K as a primary transfer unit, and a cleaning unit 16K.

  The toner replenishing means 141Y, 141M, 141C, and 141K replenish new toner to the developing devices 14Y, 14M, 14C, and 14K, respectively.

  Here, the primary transfer rollers 15Y, 15M, 15C, and 15K are selectively operated according to the type of image by a control unit (not shown), and the intermediate transfer belt 170 is respectively applied to the corresponding photoreceptors 11Y, 11M, 11C, and 11K. To transfer the toner image on the photoreceptor.

  In this manner, the toner images of the respective colors formed on the photoreceptors 11Y, 11M, 11C, and 11K by the image forming units 10Y, 10M, 10C, and 10K are rotated by the primary transfer rollers 15Y, 15M, 15C, and 15K. The images are sequentially transferred onto the moving intermediate transfer belt 170 to form a combined color image.

  That is, the intermediate transfer belt primarily transfers the toner image carried on the surface of the photosensitive member to the surface, and holds the transferred toner image.

  Further, the transfer material P as a recording medium accommodated in the paper feeding cassette 151 is fed by the paper feeding means 15 and then passed through a plurality of intermediate rollers 122A, 122B, 122C, 122D, and a registration roller 123, and the secondary material P. The toner image is conveyed to a secondary transfer roller 117 serving as a transfer unit, and the combined toner image on the intermediate transfer member is collectively transferred onto the transfer material P by the secondary transfer roller 117.

  That is, the toner image held on the intermediate transfer member is secondarily transferred to the surface of the transfer object.

  Here, the secondary transfer unit 6 presses the transfer material P against the intermediate transfer belt 170 only when the transfer material P passes through the secondary transfer unit 6 and performs the secondary transfer.

  The transfer material P onto which the color image has been transferred is fixed by the fixing device 124, sandwiched by the paper discharge roller 125, and placed on the paper discharge tray 126 outside the apparatus.

  On the other hand, after the color image is transferred to the transfer material P by the secondary transfer roller 117, the residual toner is removed by the cleaning unit 8 from the intermediate transfer belt 170 from which the transfer material P is separated by curvature.

  Here, the intermediate transfer member may be replaced with a rotating drum-like member as described above.

  Next, the configuration of the primary transfer rollers 15Y, 15M, 15C, and 15K as the primary transfer means in contact with the intermediate transfer belt 170 and the secondary transfer roller 117 will be described.

The primary transfer rollers 15Y, 15M, 15C, and 15K disperse a conductive material such as carbon in a rubber material such as polyurethane, EPDM, or silicone on a peripheral surface of a conductive core metal such as stainless steel having an outer diameter of 8 mm. Or containing an ionic conductive material, in a solid state or foamed sponge state with a volume resistance of about 10 ⁵ to 10 ⁹ Ω · cm, a thickness of 5 mm, and a rubber hardness of about 20 to 70 ° (asker It is formed by coating a semiconductive elastic rubber having a hardness C).

For example, the secondary transfer roller 117 disperses a conductive material such as carbon in a rubber material such as polyurethane, EPDM, or silicone on a peripheral surface of a conductive metal core such as stainless steel having an outer diameter of 8 mm, or an ionic conductive material. Semi-conducting material containing a material and having a volume resistance of about 10 ⁵ to 10 ⁹ Ω · cm in a solid state or foamed sponge state with a thickness of 5 mm and a rubber hardness of about 20 to 70 ° (Asker hardness C) It is formed by covering an elastic rubber.

(Transfer material)
The transfer material used in the present invention is a support for holding a toner image, and is usually called an image support, a transfer material, or transfer paper. Specific examples include various kinds of transfer materials such as plain paper from thin paper to thick paper, coated printing paper such as art paper and coated paper, commercially available Japanese paper and postcard paper, plastic films for OHP, and cloth. However, it is not limited to these.
<Transfer current>
When the toner image on the photosensitive member is transferred to the transfer material or the intermediate transfer member by the transfer means in the present invention, the current per unit length flowing to the photosensitive member (this is defined as “transfer current It” in this application) is 1 μA / cm or more and 10 μA / cm or less, preferably 2 μA / cm or more and 8 μA / cm or less.

  By setting the transfer current It to 1 μA / cm or more, a high transfer rate can be secured, and by setting the transfer current It to 10 μA / cm or less, generation of a transfer memory can be prevented.

  FIG. 3 is a schematic diagram of a measuring apparatus for measuring the transfer current It flowing to the photosensitive member.

  The transfer current It can be measured using the measuring apparatus of FIG. A value obtained by dividing the current value (μA) flowing through the photoconductor obtained by the measuring apparatus of FIG. 3 by the length (cm) in the longitudinal direction of the transfer means is the transfer current It (μA / cm) of the present application.

  The transfer current It is measured in a measurement environment of 20 ° C. and 50% RH.

Next, the photoconductor used in the present invention will be described.
<Photoconductor>
The photoreceptor used in the present invention has a multilayer structure and is characterized by containing at least N-type metal oxide particles in the outermost layer.

  As a layer structure of the photoreceptor, a layer structure as shown in FIG. 4 can be exemplified.

  FIG. 4 is a schematic diagram showing an example of the layer structure of the photoreceptor.

  In the figure, 11 is a conductive support, 12 is an intermediate layer, 13 is a photosensitive layer, 14 is a charge generation layer, 15 is a charge transport layer, 16 is a protective layer, and 19 is N-type metal oxide particles.

  The photoreceptor shown in FIG. 4A has a photosensitive layer having a charge generating substance and a charge transporting substance on a conductive support, and a layer containing N-type metal oxide particles in the photosensitive layer. It is a thing of composition.

  The photoreceptor shown in FIG. 4B has a multilayer structure having an intermediate layer, a charge generation layer, and a charge transport layer on a conductive support, and N-type metal oxide particles are contained in the charge transport layer. It has a layer structure.

  The photoconductor shown in FIG. 4C has a multilayer structure having an intermediate layer, a charge generation layer, a charge transport layer, and a protective layer on a conductive support, and an N-type metal oxide in the protective layer. It has a layer structure containing particles.

In FIG. 4, the outermost layer is a photosensitive layer in FIG. 4A, a charge transport layer in FIG. 4B, and a protective layer in FIG.
<< N-type metal oxide particles >>
The N-type metal oxide particles referred to in the present invention mean particles whose main charge carriers are electrons. If a photoconductor containing N-type metal oxide particles in the outermost layer is used, it is assumed that holes are not injected even when a high transfer current is applied, and there is no positive space charge that is the source of transfer memory. ing.

  A method for discriminating N-type semiconductive particles according to the present invention will be described.

  An outermost layer having a thickness of 5 μm is formed on a substrate (on a conductive support) using a dispersion liquid in which particles of about 50% by mass are dispersed in a binder resin. The outermost surface layer is charged to a negative polarity, and the light attenuation characteristic is evaluated. In addition, the light attenuation characteristics are similarly evaluated by charging to positive polarity.

  N-type semiconductive particles are particles that are dispersed in the outermost layer when the light attenuation when charged negatively is larger than the light attenuation when charged positively. It is called semiconductive particle.

Examples of the N-type metal oxide particles used in the present invention include metal oxide particles such as titanium oxide (TiO ₂ ), zinc oxide (ZnO), and tin oxide (SnO ₂ ). Titanium is preferred.

  Examples of the crystalline form of titanium oxide include an anata form, a rutile form, a brookite form, and an amorphous form. Among these, anatase-type titanium oxide is preferable because it has high electron mobility and can prevent generation of a transfer memory.

  The N-type metal oxide particles according to the present invention may be treated with a surface treatment agent, and the dispersibility becomes better by the surface treatment.

  The N-type metal oxide particles preferably have a number average primary particle size of 5 to 300 nm, more preferably 10 to 200 nm.

  Here, the number average primary particle size is a value obtained by observing 100 particles as primary particles at random by magnifying the particles 100000 times by observation with a transmission electron microscope and performing image analysis.

  Examples of the transmission electron microscope (TEM) include “H-9000NAR” (manufactured by Hitachi, Ltd.), “JEM-200FX” (manufactured by JEOL Ltd.), and the like.

  The observation method using a transmission electron microscope is performed by a normal method performed when measuring the particle size of the particles. For example, the procedure is as follows. First, materials for observation are prepared. The inorganic oxide particles are sufficiently dispersed in a room temperature curable epoxy resin, and then embedded and cured to produce a block. The prepared block is cut into a thin piece having a thickness of 80 to 200 nm using a microtome equipped with diamond teeth to produce a measurement sample.

  Next, it magnifies 100000 times using a transmission electron microscope (TEM), and photographs the N-type metal oxide particles. Next, the image information of 100 N-type metal oxide particles photographed by an image processing apparatus “Luzex F” (manufactured by Nicole) is arithmetically processed to determine the number average primary particle size.

  The N-type metal oxide particles having a number average primary particle size in the above range can be uniformly dispersed in the binder forming the coating film, thereby preventing formation of aggregated particles and generation of large irregularities on the surface. It is possible to form a good toner image in which particles become charge traps and black spots and transfer memory are not generated, and black spots due to the large unevenness are not generated. Further, the N-type metal oxide particles are difficult to settle in the coating solution, and the dispersion stability of the solution is also excellent.

  Next, the photoconductor used in the present invention will be described in detail.

  In the present invention, the organic photoconductor means an electrophotographic photoconductor constituted by providing an organic compound with at least one of a charge generation function and a charge transport function essential to the configuration of the electrophotographic photoconductor. All known photoconductors such as a photoconductor composed of an organic charge generating material or an organic charge transport material, a photoconductor composed of a polymer complex with a charge generating function and a charge transport function are contained.

  The photoreceptor according to the present invention contains N-type metal oxide particles in the outermost layer. The amount of the N-type metal oxide particles contained in the outermost layer is preferably 20 to 70 parts by mass with respect to the total mass of the outermost layer.

  By setting the amount of the N-type metal oxide particles to 20 to 70 parts by mass of the total mass of the outermost layer, the generation of a transfer memory can be prevented even when the transfer current flowing to the photoreceptor is increased, and a high transfer rate can be secured. Further, by setting the amount of the N-type metal oxide particles to 20 parts by mass or more of the total mass of the outermost layer, wear of the outermost layer is reduced, it is possible to prevent the halftone image from being rough without causing scratches and the like, and 70 mass By setting it to less than or equal to the part, the outermost layer becomes a strong film, and the generation of cracks can be prevented.

  The outermost layer is preferably a layer composed of N-type metal oxide particles, a charge transport material, and a binder resin. As the charge transport material (CTM), a known hole transport property (P-type) charge transport material (CTM) is preferably used. For example, a triphenylamine derivative, a hydrazone compound, a styryl compound, a benzidine compound, a butadiene compound, or the like can be used. These charge transport materials are usually dissolved in a suitable binder resin to form a layer.

  A known resin can be used as the binder resin in the outermost layer. Specifically, a thermoplastic resin or a thermosetting resin can be used.

  The mass ratio of the binder resin and the charge transport material in the outermost layer is preferably 30 to 200 parts by mass, and more preferably 50 to 150 parts by mass with respect to 100 parts by mass of the binder.

  The outermost layer preferably contains an antioxidant. By containing the antioxidant and the N-type metal oxide particles according to the present invention in the outermost layer, it prevents fluctuations in the characteristics of the outermost layer during repeated use, and the occurrence of fogging and a decrease in tip concentration in the counter development method. And a good electrophotographic image can be provided. Typical examples of the antioxidant include a property that prevents or suppresses an oxidizing action under conditions such as light, heat, and discharge with respect to an auto-oxidizing substance present in the photoreceptor or on the surface of the photoreceptor. It is a substance having

  The antioxidant according to the present invention has the property of preventing or suppressing the action of oxygen on auto-oxidizing substances existing in the photoreceptor or on the surface of the photoreceptor under conditions such as light, heat and discharge. It is a substance.

  Further, as the antioxidants that have been commercialized, the following compounds, for example, “Irganox 1076”, “Irganox 1010”, “Irganox 1098”, “Irganox 245”, “Irganox” as hindered phenols, are used. Knox 1330 "," Irganox 3114 "," Irganox 1076 "," 3,5-di-t-butyl-4-hydroxybiphenyl ", hindered amine series" Sanol LS2626 "," Sanol LS765 "," Sanol LS770 " , “Sanol LS744”, “Tinuvin 144”, “Tinuvin 622LD”, “Mark LA57”, “Mark LA67”, “Mark LA62”, “Mark LA68”, “Mark LA63”, and “Sumilyzer TPS” "," Sumi Iser TP-D ", and the phosphite system is" Mark 2112 "," Mark PEP-8 "," Mark PEP-24G "," Mark PEP-36 "," Mark 329K "," Mark HP-10 " Is mentioned.

  Examples of the layer structure of the photoreceptor according to the present invention include the structure shown in FIG.

  Hereinafter, description will be made with a focus on the layer structure of FIGS. 4B and 4C.

  First, the photoconductor having the layer structure of FIG. 4B will be described.

  The photoreceptor shown in FIG. 4B has a multilayer structure having an intermediate layer, a charge generation layer, and a charge transport layer on a conductive support, and N-type metal oxide particles are contained in the charge transport layer. contains.

The photoconductor shown in FIG. 4C has a multilayer structure having an intermediate layer, a charge generation layer, a charge transport layer, and a protective layer on a conductive support, and an N-type metal oxide in the protective layer. Contains particles.
(Conductive support)
As the conductive support, either a sheet shape or a cylindrical shape may be used, but in order to design the image forming apparatus compactly, the cylindrical conductive support is preferable.

  Cylindrical conductive support means a cylindrical support necessary for forming an endless image by rotating. Conductivity is within a range of 0.1 mm or less in straightness and 0.1 mm or less in deflection. A support is preferred. Exceeding the range of straightness and shake makes it difficult to form a good image.

As the conductive material, a metal drum such as aluminum or nickel, a plastic drum deposited with aluminum, tin oxide, indium oxide or the like, or a paper / plastic drum coated with a conductive substance can be used. The conductive support preferably has a specific resistance of 10 ³ Ωcm or less at room temperature. The conductive support according to the present invention is most preferably an aluminum support. As the aluminum support, one in which components such as manganese, zinc, magnesium and the like are mixed in addition to the main component aluminum is also used.

(Middle layer)
An intermediate | middle layer is a layer which has binder resin as a main component and disperse | distributed the inorganic particle as needed, and is provided on a conductive support body.

  The intermediate layer can be formed by applying and drying a coating solution in which inorganic particles are dispersed in a binder resin solution as necessary on a conductive support. As the binder resin forming the layer structure of the intermediate layer, a polyamide resin is preferable in order to obtain good dispersibility of particles, and the polyamide resin shown below is particularly preferable. Examples of the inorganic particles include metal oxides such as magnesium oxide, silica, titanium oxide, zinc oxide, alumina, and iron oxide.

(Charge generation layer)
The charge generation layer is a layer containing a charge generation material and, if necessary, a binder resin, and is provided on the intermediate layer.

  As the charge generation material (CGM), titanyl phthalocyanine adduct pigments, phthalocyanine pigments, azo pigments, perylene pigments, azulenium pigments, and the like can be used.

  When a binder is used as the CGM dispersion medium in the charge generation layer, a known resin can be used as the binder, but the most preferred resins include formal resin, butyral resin, silicone resin, silicone-modified butyral resin, phenoxy resin, and the like. Can be mentioned. The ratio of the binder resin to the charge generating material is preferably 20 to 600 parts by mass with respect to 100 parts by mass of the binder resin. By using these resins, the increase in residual potential associated with repeated use can be minimized. The thickness of the charge generation layer is preferably from 0.3 to 2 μm.

(Charge transport layer)
The charge transport layer is a layer containing N-type metal oxide particles, a charge transport material (CTM) and a binder resin, and is provided on the charge generation layer.

  Specifically, a coating liquid in which N-type metal oxide particles are dispersed in a solution in which a charge transport material (CTM) and a binder resin are dissolved in a solvent is prepared using a known dispersing device. The charge transport layer can be formed by coating and drying on the generation layer.

  As the charge transport material (CTM), a known hole transport property (P-type) charge transport material (CTM) is preferably used. For example, a triphenylamine derivative, a hydrazone compound, a styryl compound, a benzidine compound, a butadiene compound, or the like can be used. These charge transport materials are usually dissolved in a suitable binder resin to form a layer.

  As the binder resin, a known thermoplastic resin or thermosetting resin can be used. Specifically, polystyrene, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, polyvinyl butyral resin, epoxy resin, polyurethane resin, phenol resin, polyester resin, alkyd resin, polycarbonate resin, silicone resin, melamine resin, and Examples thereof include copolymer resins containing two or more of the repeating unit structures of these resins. Among these, a polycarbonate resin having a low water absorption rate and excellent in electrophotographic characteristics and abrasion resistance is preferable.

  The ratio of the binder resin to the charge transport material is preferably 50 to 200 parts by mass with respect to 100 parts by mass of the binder resin.

  The thickness of the charge transport layer is preferably 10 to 40 μm. By setting the film thickness to 10 μm or more, a highly sharp printed image can be obtained, and by setting the film thickness to 40 μm or less, an increase in residual potential can be suppressed.

  The film thickness can be measured with an optical film thickness meter, for example, “USB Simple Film Thickness Measurement Device (Handy Lambda II Thickness)” manufactured by Spectra Corp.

  Solvents or dispersion media used to form layers such as intermediate layers, charge generation layers, and charge transport layers include n-butylamine, diethylamine, ethylenediamine, isopropanolamine, triethanolamine, triethylenediamine, N, N-dimethylformamide, acetone , Methyl ethyl ketone, methyl isopropyl ketone, cyclohexanone, benzene, toluene, xylene, chloroform, dichloromethane, 1,2-dichloroethane, 1,2-dichloropropane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, trichloroethylene, Tetrachloroethane, tetrahydrofuran, dioxolane, dioxane, methanol, ethanol, butanol, isopropanol, ethyl acetate, butyl acetate, dimethyl sulfoxide, methyl cello Lube, and the like. Although this invention is not limited to these, Dichloromethane, 1, 2- dichloroethane, methyl ethyl ketone, etc. are used preferably. These solvents may be used alone or as a mixed solvent of two or more.

  Further, the coating solution for each layer is preferably filtered with a metal filter, a membrane filter or the like in order to remove foreign matters and aggregates in the coating solution before entering the coating step. For example, it is preferable to select a pleat type (HDC), a depth type (profile), a semi-depth type (profile star), etc., manufactured by Nippon Pole Co., Ltd. according to the characteristics of the coating solution and perform filtration.

  Next, the photoconductor having the layer structure shown in FIG. 4C will be described.

  The photoreceptor shown in FIG. 4C has a multilayer structure having an intermediate layer, a charge generation layer, a charge transport layer, and a protective layer on a conductive support.

  It is preferable that a protective layer having N-type metal oxide particles is provided on the charge transport layer, so that a photoconductor excellent in high transfer rate and transfer memory and excellent in durability can be obtained.

(Conductive support)
The conductive support described in FIG. 4B can be used.

(Middle layer)
The intermediate layer described in FIG. 4B can be used.

(Charge generation layer)
The charge generation layer described in FIG. 4B can be used.

(Charge transport layer)
When a protective layer is provided on the charge transport layer, the charge transport layer is a layer containing a charge transport material (CTM) and a binder resin or N-type metal oxide particles, a charge transport material (CTM) and a binder resin. , Provided on the charge generation layer.

  The charge transport layer containing the charge transport material (CTM) and the binder resin is formed by applying and drying mainly a paint in which the charge transport material and the binder resin are dissolved in a solvent. Examples of the charge transport material used include triarylamine compounds, hydrazone compounds, stilbene compounds, pyrazoline compounds, oxazole compounds, triallylmethane compounds, and thiazole compounds.

  These are combined with 0.5 to 2 times the amount of binder resin, applied and dried to form a charge transport layer. Examples of the binder resin include polystyrene, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, polyvinyl butyral resin, epoxy resin, polyurethane resin, phenol resin, polyester resin, alkyd resin, polycarbonate resin, silicone resin, melamine resin. And a copolymer resin containing two or more of the repeating unit structures of these resins. In addition to these insulating resins, high molecular organic semiconductors such as poly-N-vinylcarbazole can be used.

  The charge transport layer preferably contains an antioxidant. The antioxidants are typically representative of preventing or suppressing the action of oxygen on auto-oxidizing substances present in the photoreceptor or on the photoreceptor surface under conditions such as light, heat, and discharge. It is a substance with the property to do.

  The film thickness of the charge transport layer is preferably 5 to 40 μm, more preferably 15 to 30 μm.

As a coating method for each of these layers, a dip coating method, a spray coating method, a spinner coating method, a bead coating method, a blade coating method, a slide hopper method, or the like can be used.
(Protective layer)
The protective layer is provided on the charge transport layer.

  In the present invention, the protective layer only needs to contain N-type metal oxide particles, but more preferably contains a composition obtained by photocuring a curable compound in addition to the N-type metal oxide particles. Moreover, after apply | coating the coating liquid containing a polymerization initiator and a sclerosing | hardenable compound and forming a coating film, the layer formed by irradiating this coating film with active light and photocuring is still more preferable.

  The polymerization initiator and curable compound used to form the protective layer resin will be described.

(Polymerization initiator)
The polymerization initiator is used to form a resin by polymerizing a curable compound by irradiation with active light.

  The polymerization initiator contains 0.0025 to 0.5000 parts by mass, preferably 0.0080 to 0.2000 parts by mass per 100 parts by mass of the protective layer after forming the protective layer.

  When the protective layer contains 0.0025 parts by mass or more of a polymerization initiator per 100 parts by mass of the protective layer, image blurring in a high temperature and high humidity environment can be prevented. Can be reduced.

  As the polymerization initiator, either a photopolymerization initiator or a thermal polymerization initiator can be used.

  Further, both polymerization initiators for light and heat can be used in combination. In this invention, the photoinitiator which is easy to control the amount of polymerization initiators in a protective layer to a specific range is preferable.

  Specific compounds include acetophenone, benzyl ketal, benzoin and the like. Among these, acetophenone and benzyl ketal are preferable from the viewpoint of reaction efficiency upon irradiation with active energy rays.

(Curable compound)
The curable compound is polymerized and cured by irradiation with actinic light in the presence of a polymerization initiator.

  As the curable compound, a compound having a trifunctional or higher functional group is preferable. Specific compounds include those having three or more acrolyl groups or metalloyl groups in one molecule, and specifically include curable acrylic monomers or oligomers.

  Although the curable compound used by this invention is suitably selected by the reaction form, a photocurable acrylic compound is preferable.

  Next, the coating liquid used for forming the protective layer, the formation of the coating film, and the curing of the coating film will be described.

(Coating solution)
The coating liquid used for forming the protective layer contains at least N-type metal oxide particles, a polymerization initiator, and a curable compound.

  The coating solution is prepared so that the amount of the polymerization initiator is 5 to 20 parts by mass per 100 parts by mass of the solid content in the coating solution. By containing the said amount, it is easy to control the amount of polymerization initiator in a protective layer to the target amount, and it is preferable.

  In addition, solid content in a coating liquid turns into solid content when a coating liquid is dried, and is the total mass of a N-type metal oxide particle, a polymerization initiator, and a curable compound.

(Formation of coating film)
The coating film is formed by applying and drying the coating solution on the charge transport layer. As a coating method for forming a coating film, a dip coating method, a spray coating method, a spinner coating method, a bead coating method, a blade coating method, a beam coating method, a slide hopper method, or the like can be used.

(Curing the coating)
The coating film is a protective layer having a uniform hardness over the entire circumference by polymerization of the polymerization initiator and the curable compound by irradiation with active light.

  The active light may be any electromagnetic wave having sufficient energy for initiating the polymerization reaction, and examples thereof include visible light, ultraviolet light, X-rays, and electron beams. In particular, ultraviolet rays are preferable from the viewpoint of ease of handling. In order to emit ultraviolet rays, a lamp is used as an ultraviolet ray generation source. The type of the lamp may be any of a low-pressure mercury lamp such as a xenon lamp and a fluorescent chemical lamp, a high-pressure discharge lamp such as a high-pressure mercury lamp and a metal halide lamp, and a xenon lamp emitting short arc discharge pulses.

  In the present invention, the wavelength of the active light is preferably 200 to 500 nm, and more preferably 250 to 450 nm. When the wavelength is from 250 nm to 450 nm, deterioration of the photosensitive layer can be suppressed, and both curing and deterioration of the photosensitive layer can be achieved.

  The thickness of the protective layer is preferably from 0.1 to 10.0 μm, more preferably from 0.5 to 7.0 μm. By setting it as this range, durability and electrical characteristics can be satisfied.

  As a coating method for manufacturing the protective layer, a coating method such as dip coating or spray coating is used. For forming the outermost layer according to the present invention, it is most preferable to use a circular slide hopper type coating apparatus.

  The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited to these examples.

<< Production of photoconductor >>
A photoreceptor was prepared as follows.
<Preparation of N-type metal oxide particles>
N-type metal oxide particles 1: titanium oxide particles, number average primary particle size 35 nm
N-type metal oxide particles 2: titanium oxide particles, number average primary particle size 10 nm
N-type metal oxide particles 3: tin oxide particles, number average primary particle size 140 nm
N-type metal oxide particles 4: zinc oxide particles, number average primary particle size 60 nm
N-type metal oxide particles 5: titanium oxide particles, number average primary particle size 80 nm
<Preparation of Photoreceptor 1>
(Preparation of conductive support)
A cylindrical aluminum substrate was prepared by cleaning the substrate processed to a 10-point surface roughness Rz: 0.81 μm defined by JISB-0601 by cutting. This is referred to as “support 1”.

(Formation of intermediate layer)
Binder resin (N-1) 1 part by mass Ethanol / n-propyl alcohol / tetrahydrofuran
(45:20:35 volume ratio) 20 parts by mass After mixing the above, stirring and dissolving,
Rutile-type titanium oxide particles (mass ratio 5% methyl hydrogen polysiloxane surface-treated) 4.2 parts by mass were mixed, and the mixture was dispersed by a bead mill. At this time, an average particle diameter of 0.1 to 0.5 mm of beads was used and dispersed at a filling rate of 80%, a peripheral speed setting of 4 m / sec, and a mill residence time of 3 hours to prepare an intermediate layer coating solution. After the same solution was filtered through a 5 μm filter, the intermediate layer coating solution was applied to the outer periphery of the “support 1” prepared above by a dip coating method to form “intermediate layer 1” having a dry film thickness of 2 μm.

(Formation of charge generation layer)
The following components were mixed and dispersed using a sand mill disperser to prepare a charge generation layer coating solution.

Y-type titanyl phthalocyanine (a titanyl phthalosine pigment having a maximum diffraction peak at a Bragg angle (2θ ± 0.2 °) of 27.3 ° in the spectrum of X-ray diffraction by Cu-Kα characteristic X-ray) 20 parts by mass of polyvinyl butyral ( BX-1, manufactured by Sekisui Chemical Co., Ltd.) 10 parts by weight Methyl ethyl ketone 700 parts by weight Cyclohexanone 300 parts by weight This coating solution was applied by a dip coating method, and a “charge generation layer having a dry film thickness of 0.3 μm was formed on the intermediate layer. 1 "was formed.

(Formation of charge transport layer)
The following components were mixed and dissolved to prepare a charge transport layer coating solution.

Charge transport material (structure shown below) 75 parts by weight Polycarbonate resin “Iupilon-Z300” (Mitsubishi Gas Chemical Co., Ltd.) 100 parts by weight Antioxidant 2,6-di-tert-butyl-4-methylphenol 8 parts by weight Tetrahydrofuran / Toluene (Volume ratio 8/2) 750 parts by mass

  This coating solution was applied onto the charge generation layer by a dip coating method and dried at 120 ° C. for 70 minutes to form “charge transport layer 1” having a dry film thickness of 20 μm.

(Protective layer)
<Preparation of protective layer coating solution>
The following components were mixed and dispersed with an ultrasonic homogenizer to prepare a dispersion containing N-type metal oxide particles 1, a curable compound, and a polymerization initiator. This is designated as “protective layer coating solution 1”.

Curable compound (Exemplary compound 1) 1.0 part by mass 1-propanol 5.1 part by mass Methyl isobutyl ketone 2.4 part by mass N-type metal oxide particle 1 0.1 part by mass Polymerization initiator (compound D) 0. 05 parts by mass

<Application and curing of protective layer>
The protective layer coating solution 1 was applied by dip coating on the “charge transport layer 1” and dried at room temperature for 10 minutes to form a coating film.

  Then, using a 2 kW high-pressure mercury lamp at a position 10 cm from the light source while rotating the support, it was irradiated with light (precured) for 10 minutes at an illuminance of 0.1 mW and then irradiated for 30 seconds (postcured) at an illuminance of 1000 mW. The film was photocured.

  After photocuring, heat drying was performed at 120 ° C. for 30 minutes to prepare “Photoreceptor 1” having a “protective layer”.

<Preparation of photoconductors 2-6>
“Photoconductors 2 to 6” were prepared in the same manner except that the protective layer N-type metal oxide particles and the amount thereof used in the production of the photoconductor 1 were changed as shown in Table 1.

<Preparation of photoconductor 7>
In the same manner as the production of the photoreceptor 1, the layers up to “charge transport layer 1” were formed.

(Formation of protective layer)
The following components were mixed and dissolved to prepare a protective layer coating solution 7. This coating solution was applied on the “charge transport layer 1” by a circular slide hopper type coating method and dried at 120 ° C. for 70 minutes to form a “protective layer 7” having a dry film thickness of 5 μm.

Charge transport material (same structure as charge transport layer 1) 75 parts by weight Polycarbonate resin “Iupilon-Z300” (manufactured by Mitsubishi Gas Chemical) 100 parts by weight N-type metal oxide particles 1 10 parts by weight Antioxidant 2,6-di -T-Butyl-4-methylphenol 8 parts by mass Tetrahydrofuran / toluene (volume ratio 8/2) 750 parts by mass Table 1 shows the N-type metal oxide and the amount of the protective layer formed of the photoreceptors 1 to 7.

<Evaluation>
<Evaluation image forming apparatus>
As an image forming apparatus for evaluation, a commercially available image forming apparatus “bizhub PROC6500” (printing speed 65 sheets / min) (made by Konica Minolta Business Technologies, Inc.) having the structure shown in FIG. Was used so that the transfer current could be changed. The evaluation was performed for the following items by sequentially loading the photoconductors prepared above into the image forming apparatus and changing the transfer current flowing to the photoconductor.
(Transfer rate)
The transfer rate was evaluated based on the primary transfer rate (transfer rate from the photosensitive member to the intermediate transfer member).

  The transfer rate was evaluated in a low temperature and low humidity (10 ° C., 20% RH) environment with a primary transfer rate after 1000 sheets were printed. When a solid image (20 mm × 50 mm) with a pixel density of 1.30 is formed on the photoconductor, the transfer rate is determined after the toner mass of the toner image formed on the photoconductor and the toner image are transferred onto the intermediate transfer body. Then, the toner mass of the transfer residue remaining on the photoconductor was obtained, and the transfer rate was obtained from the following formula.

Transfer rate (%) = ((toner mass before transfer on photoconductor−mass of residual toner on photoconductor) / toner mass before transfer on photoconductor) × 100
The primary transfer rate was evaluated as good when 95% or more.

(Transfer memory)
The transfer memory was evaluated by printing a continuous chart of 2 cm square with a halftone image with a density of 0.4 on cyan toner, and printing a 2 cm square image on the 1st and 5000th prints. Was visually observed in the cyan halftone image (transfer memory was generated) or not (transfer memory was not generated).

○: No transfer memory is generated ×: Transfer memory is generated

  Table 2 shows the evaluation results.

  From Table 2, it can be seen that Examples 1 to 8 are excellent in evaluation of transfer rate and transfer memory. On the other hand, it can be seen that Comparative Examples 1 to 3 are not excellent in all evaluation items and the object of the present invention is not achieved.

1 is a cross-sectional configuration diagram illustrating an example of an image forming apparatus that transfers a toner image from a photoreceptor to a transfer material. FIG. 2 is a cross-sectional configuration diagram illustrating an example of a color image forming apparatus that transfers a toner image from a photoreceptor to an intermediate transfer member. It is a schematic diagram of a measuring device for measuring a transfer current flowing to a photoconductor. It is a schematic diagram which shows an example of the layer structure of a photoreceptor.

Explanation of symbols

1 Image forming apparatus 21 Photoconductor (electrophotographic photoconductor)
DESCRIPTION OF SYMBOLS 22 Charging means 23 Development means 26 Cleaning apparatus 27 Photostatic discharge means 30 Image exposure means 45 Transfer means 50 Fixing means A Image reading part B Image processing part C Image formation part D Transfer paper conveyance part P Transfer paper

Claims (3)

In an image forming apparatus that has at least a charging unit, an exposure unit, a developing unit, and a transfer unit around an organic photoreceptor, and repeatedly forms an image.
The outermost layer of the organophotoreceptor contains at least N-type metal oxide particles;
An image forming apparatus, wherein a transfer current It defined below is 1 μA / cm or more and 10 μA / cm or less.
(Transfer current It: current per unit length flowing to the organic photoreceptor by the transfer means) The image forming apparatus according to claim 1, wherein the outermost layer of the organic photoreceptor contains a composition obtained by photocuring a curable compound. The image forming apparatus according to claim 1, wherein the N-type metal oxide particles are titanium oxide particles.

Images