JP2006098728A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the potential difference between the position of a latent image detecting device and a development position even when a photoreceptor having a surface protective layer is used in an image forming apparatus having a high linear velocity, and to realize an image forming apparatus excellent in reproducibility of the gradient and halftone of an image. <P>SOLUTION: In the image forming apparatus comprising: a photoreceptor 40; a charging device 70 for charging the photoreceptor 40; a latent image forming device 76 for forming an electrostatic latent image on the charged photoreceptor 40; a potential sensor 71 for detecting the electrostatic latent image on the photoreceptor 40; and a developing device 60 for eliciting the electrostatic latent image on the photoreceptor 40 by development, the photoreceptor 40 is an organophotoreceptor having at least a charge generating layer, a charge transport layer and a surface protective layer on a conductive substrate, wherein a charge transport material is contained in the surface protective layer. The potential difference between the position of the potential sensor and a development position can be therefore reduced, and the image forming apparatus excellent in reproducibility of the gradient and halftone of an image can be realized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus having excellent durability and capable of stably obtaining a high-quality image at high speed.

  Conventionally, an image carrier such as a photosensitive member is charged by a charging unit, an electrostatic latent image is formed on the charged image carrier by a latent image forming unit, and the electrostatic latent image is developed by a developing unit to be a visible image. In the electrophotographic system, the visible image on the image carrier is transferred to a transfer material such as paper directly or via an intermediate transfer body, and the visible image transferred to the transfer material is fixed to form an image. Image forming apparatuses are well known, and are widely used as copiers, printers, plotters, facsimiles, printing machines, or a combination of these.

As a conventional technique related to such an image forming apparatus, Patent Document 1 (Japanese Patent Laid-Open No. 2000-330345) discloses an image forming apparatus provided with a potential sensor between an exposure unit and a developing unit. Of setting the target value of the photosensitive member potential in consideration of the fact that the photosensitive member potential is different between the potential sensor position and the developing position when adjusting the exposure amount of the exposure unit so that the photosensitive member potential becomes the target value. Is disclosed.
Further, in Patent Document 2 (Japanese Patent Laid-Open No. 2002-161217), metal oxide particles in which an organic pigment is supported on the surface of particles are used in a surface protective layer of an organic photoreceptor used as an image carrier. It is disclosed. Moreover, in this patent document 2, it is described as an Example that 0-50 weight% of charge transport materials are contained in a surface protective layer.
Further, in Patent Document 3 (Japanese Patent Application Laid-Open No. 2000-292959), a photocurable organic material is used as the surface protective layer of the organic photoreceptor, and 0.01 to 10% by weight of a charge transport material is contained in the surface protective layer. It is disclosed that it contains.

JP 2000-330345 A JP 2002-161217 A JP 2000-292959 A

  Conventional electrophotographic image forming apparatuses can provide an image forming apparatus with excellent image gradation and halftone reproducibility by providing a potential sensor that detects the photoreceptor potential, but the process linear velocity is high. In an image forming apparatus having a small diameter photosensitive member, since the arrival time from the exposure position to the potential sensor position is short, there is a difference between the photosensitive member potential detected at the potential sensor position and the photosensitive member potential when reaching the developing position. May occur.

  Therefore, in the above-mentioned Patent Document 1, when adjusting the exposure amount of the exposure unit so that the photosensitive member potential detected by the potential sensor becomes a target value, the installation environment of the apparatus is detected and the detection value of the potential sensor is detected. A method of correcting the above and setting a target value of the photoreceptor potential is disclosed. However, the cause of the difference in the photoreceptor potential between the potential sensor position and the development position is not only due to the installation environment, but also because the photoreceptor sensitivity is affected by the film thickness of the photoreceptor layer. The difference in the photoreceptor potential at the potential sensor position and the development position was different from the state in which the photosensitive layer was worn. Since it is difficult to accurately detect the wear amount of the photoconductor in the image forming apparatus, the conventional example cannot sufficiently correct the difference between the initial time and the time. There is also known a method for predicting the amount of wear of the photoconductor by counting the number of rotations of the photoconductor. However, the amount of wear of the photoconductor is greatly influenced not only by the number of rotations of the photoconductor but also by the image area and the like. Therefore, it is difficult to accurately predict the wear amount of the photoreceptor. Furthermore, in an image forming apparatus that forms a full-color image, in order to perform sufficient color reproduction, it is necessary to form an image of each color with good gradation and is easily affected by the wear of the photoreceptor. In particular, in a tandem-type full-color image forming apparatus provided with a photoconductor for each color, the wear amount of each photoconductor is not necessarily the same, so that it is more susceptible to changes in photoconductor sensitivity due to a decrease in the photosensitive layer thickness. .

  Patent Document 2 and Patent Document 3 described above disclose that the surface protective layer of the organic photoreceptor contains a charge transport material. However, if the charge transport material of the surface protective layer is small, the required photoconductor sensitivity cannot be obtained, and the difference between the photoconductor potential at the potential sensor position and the development position becomes large, and the charge transport material is generally a binder. Since the molecular weight is lower than that of the resin, if the surface protective layer has too much charge transport material, there is a problem that the strength of the surface protective layer is lowered. Further, in order to obtain an appropriate sensitivity as a photoreceptor, it is necessary to make the amount of the charge transport material in both the charge transport layer and the surface protective layer appropriate, but it is disclosed in Examples of Patent Document 2 and Patent Document 3. However, the contents are not fully examined.

  The present invention has been made in view of the above circumstances, and has as its object to provide a highly reliable image forming apparatus that solves the problems of the prior art and is excellent in image gradation and halftone reproducibility. To do. In addition, the present invention can improve durability without deteriorating the electrostatic characteristics and sensitivity of the image carrier (photosensitive member), and can provide a more reliable image forming apparatus, particularly a high-speed full-color image forming apparatus. The purpose is to provide.

Here, the subject matter of the present invention will be described more specifically. The present invention also relates to the position of the latent image detecting means even when an image carrier having a protective layer on the surface is used in a high linear velocity image forming apparatus. The potential difference at the development position can be reduced, the development bias etc. can be set appropriately based on the detection result of the latent image detection means, and the image has excellent gradation and halftone reproducibility. An object is to provide a forming apparatus.
Further, according to the present invention, when the time required to move from the latent image forming position to the latent image detecting means is 40 ms or less in order to form a high-speed image, the potential difference between the latent image detecting means position and the developing position is significant. However, even in such an image forming apparatus, the potential difference between the latent image detection unit position and the development position can be reduced, and the development bias and the like are appropriately set based on the detection result of the latent image detection unit. An object of the present invention is to provide an image forming apparatus that can perform image gradation and has excellent gradation and halftone reproducibility.
Furthermore, in the present invention, in addition to the above-described problems, the durability of the organic photoreceptor as an image carrier is improved, and the durability is improved without deteriorating the electrostatic characteristics of the photoreceptor. The objective is to minimize the deterioration of sensitivity and improve durability.
Another object of the present invention is to provide an image forming apparatus capable of forming a good full color image at high speed.

In order to solve the above-described problems, the present invention adopts the following means.
The first means of the present invention includes an image carrier, charging means for charging the image carrier, latent image forming means for forming an electrostatic latent image on the charged image carrier, and the image carrier. In an image forming apparatus comprising a latent image detecting means for detecting an electrostatic latent image and a developing means for developing and developing the electrostatic latent image on the image carrier, the image carrier is electrically conductive. An organic photoreceptor having at least a charge generation layer, a charge transport layer, and a surface protective layer on a substrate, wherein the surface protective layer contains a charge transport material (claim 1).

According to a second means of the present invention, in the image forming apparatus of the first means, the time required for the image carrier during the image forming operation to move from the latent image forming position to the latent image detecting means is t1, from the latent image forming position. When the time to move to the development position is t2,
20ms <t1 <40ms
And,
(T1 × 2.5) <t2 <(t1 × 3.5)
(Claim 2).

According to a third means of the present invention, in the image forming apparatus of the first or second means, the surface protective layer of the image carrier is an organic photoreceptor in which metal oxide particles are dispersed in a base resin. It is characterized (Claim 3).
According to a fourth means of the present invention, in the image forming apparatus of the first or second means, the surface protective layer of the image carrier is an organic photoreceptor containing a heat or photocurable resin. (Claim 4).

According to a fifth means of the present invention, in the image forming apparatus according to any one of the first to fourth means, a ratio of the charge transport material to the base resin contained in the surface protective layer is included in the charge transport layer. The ratio is lower than the ratio of the charge transport material to the base resin to be printed (claim 5).
According to a sixth means of the present invention, in the image forming apparatus according to any one of the first to fifth means, the charge transport material of the charge transport layer is 30 to 50 wt% by weight, and the surface protective layer The charge transport material is 15 to 30 wt% by weight (claim 6).
Further, according to a seventh means of the present invention, in the image forming apparatus of any one of the first to sixth means, the thickness of the surface protective layer is 1/10 or more and 1/4 of the thickness of the charge transport layer. And the thickness of the surface protective layer is 3 to 8 μm (Claim 7).

  According to an eighth means of the present invention, in the image forming apparatus according to any one of the first to seventh means, the image forming apparatus includes a plurality of image carriers, and after images having different colors are formed on the image carriers, the image Is transferred onto a transfer material directly or via an intermediate transfer member to form a full-color image, and each image carrier is provided with a latent image detection means. ).

  In the image forming apparatus of the first means, the image carrier is an organic photoreceptor having at least a charge generation layer, a charge transport layer, and a surface protective layer on a conductive substrate, and a charge transport material is applied to the surface protective layer. By including the potential difference between the latent image detecting means position and the developing position, the development bias can be appropriately set based on the detection result of the latent image detecting means. An image forming apparatus excellent in reproducibility and halftone reproducibility is obtained.

In the image forming apparatus of the second means, the time for the image carrier during the image forming operation to move from the latent image forming position to the latent image detecting means is t1, and the time for the image carrier to move from the latent image forming position to the developing position is t2. When
20ms <t1 <40ms
And,
(T1 × 2.5) <t2 <(t1 × 3.5)
Therefore, even when the time required to move from the latent image forming position to the latent image detecting means for forming a high-speed image is 40 ms or less, the potential difference between the latent image detecting means position and the developing position is reduced. Therefore, it is possible to appropriately set the developing bias and the like based on the detection result of the latent image detecting means, and an image forming apparatus having excellent image gradation and halftone reproducibility can be obtained.

In the image forming apparatus of the third means, in addition to the effects of the first or second means, the durability of the organic photoreceptor can be greatly improved by dispersing the metal oxide in the surface protective layer.
In the image forming apparatus of the fourth means, in addition to the effects of the first or second means, the surface protective layer of the image carrier is a heat or photocurable resin layer, so that the durability of the organic photoconductor is improved. Can be greatly improved.

In the image forming apparatus of the fifth means, in addition to the effects of any one of the first to fourth means, the charge transport layer contains the ratio of the charge transport material to the base resin contained in the surface protective layer. By being lower than the ratio of the charge transport material to the base resin, it is possible to prevent the response time of the photoreceptor from being lowered.
In addition, in the image forming apparatus of the sixth means, in addition to the effect of any one of the first to fifth means, the charge transport material of the charge transport layer is 30 to 50 wt% by weight, and the surface protective layer When the charge transport material is 15 to 30 wt% in weight ratio, it is possible to minimize the decrease in the response time of the photoreceptor without decreasing the wear resistance of the protective layer.
Further, in the image forming apparatus of the seventh means, in addition to the effect of any one of the first to sixth means, the thickness of the surface protective layer is 1/10 or more, 1/4 of the thickness of the charge transport layer. The thickness of the surface protective layer is 3 to 8 μm, and by setting the thickness of the surface protective layer in this range, there is little deterioration in sensitivity of the photoreceptor even if a protective layer is provided, The durability of the photoreceptor can be greatly improved.

  In the image forming apparatus of the eighth means, in addition to the effects of any one of the first to seventh means, a plurality of image carriers are provided, and after images having different colors are formed on each image carrier, The image is transferred onto the transfer material either directly or via an intermediate transfer member to form a full-color image, and each image carrier is equipped with a latent image detection means, making it possible to produce gradation in each color. Therefore, it is possible to form a high-quality full-color image at high speed.

Hereinafter, the configuration, operation and action of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic overall configuration diagram of an image forming apparatus showing an embodiment of the present invention, and shows an example in which the present invention is applied to a tandem intermediate transfer type full-color copying machine.
The full-color copying machine includes an apparatus main body 100, a paper feed table 200 on which the main body is placed, a scanner 300 mounted on the copying machine main body, an automatic document feeder (ADF) 400 mounted on the scanner, and the like.

  In the center of the apparatus main body 100, a tandem in which four image forming units 18Y, 18C, 18M, and 18Bk corresponding to each color of yellow (Y), cyan (C), magenta (M), and black (Bk) are arranged side by side. A mold image forming apparatus 20 is configured. Each of the image forming units 18Y, 18C, 18M, and 18Bk of the tandem type image forming apparatus 20 forms toner images of respective colors of yellow (Y), cyan (C), magenta (M), and black (Bk). It has drum-shaped photoreceptors 40Y, 40C, 40M, and 40Bk as image carriers.

  An exposure device 21 is provided above the tandem image forming apparatus 20. Although not shown, the exposure apparatus 21 includes four laser diode (LD) light sources prepared for each color, an optical system that collimates a laser beam emitted from the light source, and a six-sided polygon mirror. And a polygon scanner composed of a polygon motor, an fθ lens arranged in the optical path of each light source, a lens such as a long WTL, a mirror, and the like. The laser light emitted from the laser diode in accordance with the image information of each color is deflected and scanned by the polygon scanner, and is irradiated onto the photoconductor of each color.

  Below the tandem type image forming apparatus 20, an endless belt-shaped intermediate transfer belt 10 is installed. In the illustrated example, the intermediate transfer belt is wound around three support rollers 14, 15, 16 and can be rotated and conveyed in the clockwise direction in the figure. The first support roller 14 is a driving roller that drives the intermediate transfer belt 10 to rotate. It is. A primary transfer roller 65Y is provided between the first support roller 14 and the second support roller 15 as a primary transfer unit that transfers the toner image from the photoconductors 40Y, 40C, 40M, and 40Bk of the respective colors to the intermediate transfer belt 10. , 65C, 65M, and 65Bk are provided so as to face the photoreceptors 40Y, 40C, 40M, and 40Bk with the intermediate transfer belt 10 interposed therebetween. Further, an intermediate transfer belt cleaning device 17 that removes residual toner remaining on the intermediate transfer belt 10 after image transfer is provided on the downstream side of the third support roller 16 in the belt conveyance direction.

  As the material of the intermediate transfer belt 10, resin materials such as polyvinylidene fluoride, polyimide, polycarbonate, and polyethylene terephthalate can be used by molding these resin materials into a seamless belt. These materials can be used as they are, or the resistance can be adjusted with a conductive material such as carbon black. Further, using these resins as a base layer, a surface layer may be formed by a method such as spraying or dipping to form a laminated structure.

  A secondary transfer device 22 is provided below the intermediate transfer belt 10. In the illustrated example, the secondary transfer device 22 is configured by spanning a secondary transfer belt 24, which is an endless belt, between two rollers 23, and is connected to the third support roller 16 via the intermediate transfer belt 10. The image on the intermediate transfer belt 10 is transferred to a transfer material by being pressed. As the secondary transfer belt 24, the same material as that of the intermediate transfer belt 10 can be used.

Next to the secondary transfer device 22, a fixing device 25 for fixing an image on the transfer material is provided. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt, and has a heating source for a roller or the like that supports the fixing belt 26.
The secondary transfer device 22 described above is also provided with a sheet transport function for transporting the transfer material after image transfer to the fixing device 25. Of course, a transfer roller or a transfer charger may be disposed as the secondary transfer device. In such a case, it is necessary to separately provide this transfer material conveying function.
In the illustrated example, the transfer material is reversed and discharged under the secondary transfer device 22 and the fixing device 25 in parallel with the tandem image forming device 20 described above, or an image is formed on both surfaces of the transfer material. And a reversing device 28 for reversing and transferring the transfer material.

When copying using this full-color copying machine, a document is set on the document table 30 of the ADF 400. Alternatively, the ADF 400 is opened and an original is set on the contact glass 32 of the scanner 300, and the ADF 400 is closed and the original is pressed.
When a start switch of an operation unit (not shown) is pressed, when a document is set on the ADF 400, the scanner 300 is driven after the document is transported and moved onto the contact glass 32. When the document is set, the scanner 300 is immediately driven to travel on the first traveling body 33 that holds the light source and the first mirror, and the second traveling body 34 that holds the second mirror and the third mirror. Then, the first traveling body 33 emits light from the light source and the reflected light from the document surface is reflected by the first mirror toward the second traveling body 34, and the second and third mirrors of the second traveling body 34. Then, the light is reflected into the reading sensor 36 such as a CCD through the imaging lens 35, and the reading sensor 36 reads the content of the original. Thereafter, when the mode setting is set in the operation unit or the automatic mode selection is set in the operation unit, the image forming operation is started in the full color mode or the monochrome mode according to the reading result of the original.

  Here, when the full color mode is selected, the photoconductors 40Y, 40C, 40M, and 40Bk of the image forming units 18Y, 18C, 18M, and 18Bk of the tandem type image forming apparatus 20 are counterclockwise in FIG. Rotate respectively. The surfaces of the photoreceptors 40Y, 40C, 40M, and 40Bk are uniformly charged by a charging device (for example, a charging roller 70 as shown in FIG. 2). The photoconductors 40Y, 40C, 40M, and 40Bk of the respective colors are respectively irradiated with laser beams corresponding to the images of the respective colors from the exposure device 21, so that latent images corresponding to the image data of the respective colors are formed. Each latent image is developed and visualized with toner of each color by the developing devices 60Y, 60C, 60M, and 60Bk for each color as the photoreceptors 40Y, 40C, 40M, and 40Bk rotate. The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 10 by the primary transfer rollers 65Y, 65C, 65M, and 65Bk along with the conveyance of the intermediate transfer belt 10 to form a full color image on the intermediate transfer belt 10.

  On the other hand, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated to feed a transfer material such as paper from one of the paper feed cassettes 44 provided in multiple stages into the paper feed table 43, and one sheet is separated by the separation roller 45. The paper is separated and put into a paper feed path 46, transported by a transport roller 47, guided to a paper feed path 48 in the main body, and abutted against a registration roller 49 and stopped. Alternatively, the transfer roller 50 is rotated to feed the transfer material on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped. Then, the registration roller 49 is rotated in synchronization with the full-color image on the intermediate transfer belt 10, the transfer material is fed between the intermediate transfer belt 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. The toner image is transferred onto the transfer material.

  The transfer material onto which the toner image has been transferred is conveyed by the secondary transfer belt 24 of the secondary transfer device 22 and sent to the fixing device 25. The fixing device 25 applies heat and pressure to form the toner image on the transfer material. After fixing, the sheet is switched by the switching claw 55, discharged by the discharge roller 56, and stacked on the discharge tray 57. Alternatively, the sheet is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and fed again to the secondary transfer position 22. To be discharged. Thereafter, when the formation of two or more images is instructed, the above-described image forming process is repeated.

  Next, when the monochrome mode is selected, the support roller 15 moves downward to separate the intermediate transfer belt 10 from the photoreceptors 40Y, 40C, and 40M. Only the black (Bk) photoconductor 40Bk rotates counterclockwise in FIG. 1, and the surface of the black (Bk) photoconductor 40Bk is uniformly charged by the charging roller 70. A latent image is formed by irradiating a laser beam corresponding to the image, and is developed with Bk toner of the developing device 60Bk to form a toner image. This toner image is transferred onto the intermediate transfer belt 10. At this time, the three color photoconductors 40Y, 40C, and 40M other than Bk and the developing devices 60Y, 60C, and 60M are stopped, and unnecessary wear of the photoconductor and the developer is prevented.

  On the other hand, the transfer material is fed from the paper feed cassette 44 in the paper feed table 43 and is conveyed to the secondary transfer device 22 by the registration roller 49 at the same timing as the toner image formed on the intermediate transfer belt 10. The The transfer material onto which the toner image has been transferred by the secondary transfer device 22 is fixed by the fixing device 25 as in the case of a full-color image, and processed through a paper discharge system corresponding to the designated mode. Thereafter, when the formation of two or more images is instructed, the above-described image forming process is repeated.

  Next, a specific configuration example of the image forming units 18Y, 18C, 18M, and 18Bk for each color is shown in FIG. Since the configurations of the image forming units 18 (Y to Bk) of the respective colors are common, the suffixes of Y to Bk of the respective symbols are omitted. Around the photosensitive member 40 as an image carrier, a charging roller 70 for uniformly charging the photosensitive member 40, a potential sensor (latent image detecting means) 71 for detecting the potential of the photosensitive member 40, and the photosensitive member 40 are formed. A developing device (developing unit) 60 that develops the electrostatic latent image with toner to make it visible, a static elimination lamp 72 that neutralizes the surface of the photoreceptor 40 after the toner image is transferred, and a cleaning residual toner. A photoreceptor cleaning device 80 (for example, two brush rollers 73 and 74 and a cleaning blade 75) is disposed. The case of the image forming unit 18 is provided with an opening for allowing the exposure light 76 from the exposure apparatus to pass through.

  Here, in the image forming unit 18 shown in FIG. 2, if the potential sensor 71 which is a latent image detecting means is installed outside the developing area of the developing position 60, the photosensitive member potential at the developing position can be accurately detected. Therefore, it is necessary to significantly increase the length of the photoconductor 40 and the charging roller 70, which leads to an increase in the size of the apparatus. For this reason, the potential sensor 71 is disposed between the exposure position and the development position. However, in order to achieve both a reduction in the size of the apparatus and a high output speed, the movement time of the photosensitive member 40 from the exposure position to the potential sensor position is reduced. It is necessary to detect at a position that is 40 ms or less. However, when the potential sensor 71 is too close to the exposure position so that the movement time of the photoreceptor 40 from the exposure position to the potential sensor position is 20 ms or less, the potential of the photoreceptor 40 is not sufficiently attenuated and an accurate potential is obtained. It cannot be detected.

In addition, the closer the distance from the potential sensor position to the developing position, the more accurately the photosensitive member potential can be detected. However, the potential sensor 71 cannot be arranged so close to the shape of the developing unit 60 that If it is too close to 60, the toner scattered from the developing unit 60 may adhere to the potential sensor 71 and the detection accuracy may deteriorate, or the potential sensor 71 may break down. For this reason, in consideration of the above points, the photosensitive member 40 (more specifically, the electrostatic latent image on the photosensitive member) during the image forming operation moves from the latent image forming position to the latent image detecting means (the potential sensor 71). When the moving time is t1, and the moving time from the latent image forming position to the developing position is t2,
20ms <t1 <40ms
And,
(T1 × 2.5) <t2 <(t1 × 3.5)
It is desirable to arrange the potential sensor 71 at such a position.

  Next, the configuration of each part of the image forming unit 18 will be described in more detail. A solid lubricant 78 is in contact with the brush roller 74 of the cleaning device 80 and also has a function as a lubricant supply member to the photoreceptor 40. Examples of solid lubricants include zinc stearate, barium stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, magnesium stearate, zinc oleate, oleic acid Fatty acid metal salts such as cobalt, magnesium oleate, and zinc palmitate, natural waxes such as carnauba wax, and fluorine-based resins such as polytetrafluoroethylene can be used.

  The toner scraped from the photoreceptor 40 by the brush rollers 73 and 74 of the cleaning device 80 and the cleaning blade 75 made of polyurethane rubber is recovered by the toner transport coil 79 provided at the lower portion of the cleaning device 80, and the recovered waste. The toner is configured to be conveyed by a toner conveying coil 79 to a waste toner storage unit (not shown). Instead of the above configuration, the toner collected by the toner transport coil 79 may be transported to the toner replenishing unit of the developing device 60 and reused.

FIG. 3 shows a cross-sectional view of the charging roller 70 used in the image forming unit 18 according to the present invention. The charging roller 70 includes a cored bar 101 as a conductive support, a resin layer 102 as a charging member, and a gap holding member 103.
A metal such as stainless steel is used for the core metal 101. If the core metal 101 is too thin, the influence of the deflection when the charging member is cut or when the photosensitive member 40 is pressed cannot be ignored, and the required gap accuracy is difficult to obtain. Further, when the core metal 101 is too thick, there is a problem that the charging roller 70 becomes large or the mass becomes heavy. Therefore, the diameter of the core metal 101 is preferably about 6 to 10 mm.

The resin layer 102 of the charging roller 70 is preferably made of a material having a volume resistance of 10 ⁴ to 10 ⁹ Ωcm. If the resistance is too low, charging bias leaks easily when there is a defect such as a pinhole in the photoconductor 40. If the resistance is too high, the discharge is not sufficiently generated and a uniform charging potential cannot be obtained. Therefore, as a method for adjusting the resistance of the resin layer 102, a desired volume resistance can be obtained by blending a conductive material with the resin serving as the base material. As the base resin, resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, and polycarbonate can be used. Since these base resins have good moldability, they can be easily molded.

  As the conductive material, an ion conductive material such as a polymer compound having a quaternary ammonium base is preferable. Examples of polyolefins having a quaternary ammonium base include polyethylene, polypropylene, polybutene, polyisoprene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-san vinyl acetate copolymer, ethylene-propylene having a quaternary ammonium base. Polyolefins such as copolymerization and ethylene-hexene copolymerization. In the present embodiment, the polyolefin having a quaternary ammonium base is exemplified, but a polymer compound other than the polyolefin having a quaternary ammonium base may be used.

  The ion conductive material is uniformly blended with the base resin by using means such as a biaxial kneader or a kneader. The compounded material can be easily molded into a roller shape by injection molding or extrusion molding on a core metal. The blending amount of the ion conductive material and the base resin is desirably 30 to 80 parts by weight of the ion conductive material with respect to 100 parts by weight of the base resin. The thickness of the resin layer 102 of the charging roller 70 is desirably 0.5 to 3 mm. If the resin layer 102 is too thin, it is difficult to mold and there is a problem in terms of strength. On the other hand, if the resin layer 102 is too thick, the charging roller 70 is increased in size and the actual resistance of the resin layer 102 is increased, so that the charging efficiency is lowered.

  After the resin layer 102 is molded, the gap holding member 103 molded in advance on both ends of the resin layer 102 is fixed to the cored bar 101 by press-fitting, bonding, or both. In this way, the charging member (resin layer) 102 and the gap holding member 103 are integrated with the cored bar 101, and then the outer diameter of the charging roller 70 is adjusted by performing processing such as cutting and grinding. Layer) 102 and the gap holding member 103 can be made to have the same phase of fluctuation, and fluctuations in the charging gap can be reduced.

  As the material of the gap holding member 103, a resin such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polycarbonate, etc. can be used in the same manner as the base material of the charging member (resin layer) 102. . However, since the gap holding member 103 is brought into contact with the photosensitive layer of the photoreceptor 40, it is desirable to use a grade having a lower hardness than the charging member in order to prevent the photosensitive layer from being damaged. In addition, as a resin material having excellent slidability and hardly damaging the photosensitive layer, polyacetal, ethylene-ethyl acrylate copolymer, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoro A resin such as a propylene copolymer can also be used. Further, a surface layer on which the toner or the like hardly adheres can be formed on the resin layer 102 or the gap holding member 103 with a thickness of about several tens of μm by coating or the like.

  A gap is formed between the resin layer 102 of the charging roller 70 and the photoreceptor 40 by applying the gap holding member 103 to the outside of the image area of the photoreceptor 40. The charging roller 70 has a gear (not shown) attached to the end of the core metal 101 meshed with a gear (not shown) formed on the photosensitive member flange, and is photosensitive by a photosensitive member driving motor (not shown). When the body 40 rotates, the charging roller 70 also rotates in the follower direction at a linear speed almost equal to that of the photoreceptor 40. At this time, since the resin layer 102 and the photosensitive member 40 do not come into contact with each other, even when a hard resin material is used as the charging roller 70 and an organic photosensitive member is used as the photosensitive member 40, the photosensitive layer in the image area may be damaged. Never do. In addition, if the gap is too wide, abnormal discharge occurs and charging cannot be performed uniformly. Therefore, the maximum gap needs to be suppressed to 100 μm or less. When the charging roller 70 having a gap between the photosensitive member and the charging roller is used, it is desirable to superimpose an alternating current (AC) voltage on a direct current (DC) voltage as a charging bias.

  The charging roller 70 is in contact with a cleaning roller 77 for cleaning the roller surface. The cleaning roller 77 is a brush roller in which conductive fibers are electrostatically flocked on a metal core, and is in contact with the charging roller 70 by its own weight. The surface of the charging roller rotates while the charging roller 70 rotates. Removes dirt such as toner adhering to the surface.

  The charging means that can be used in the present invention is not limited to the non-contact roller charging method as described above, and may be roller charging in which the charging roller is in contact with the photoreceptor 40, or a charging brush is used. Brush charging may be used. Alternatively, a non-contact charging method other than a roller such as a charger may be used.

  The developing devices 60 (Y to Bk) of the image forming units 18 (Y to Bk) of the respective colors have the same configuration, and they are two-component developing type developing devices that differ only in the color of the toner used. A two-component developer composed of toner and a magnetic carrier is accommodated in the unit of the developing device 60 for each color.

  The developing device 60 includes a developing roller 61 facing the photoreceptor 40, screws 62 and 63 for conveying and stirring the developer, a toner concentration sensor 64, and the like. The developing roller 61 includes an outer rotatable sleeve and a plurality of magnets (or a magnet roller magnetized with a plurality of magnetic poles) fixed inside the sleeve. Then, according to the output of the toner density sensor 64, a necessary amount of toner is supplied from a toner supply device (not shown).

The toner includes a binder resin, a colorant, and a charge control agent as main components, and other additives are added as necessary. Specific examples of the binder resin include polystyrene, styrene-acrylic acid ester copolymer, polyester resin, and the like. As the colorant (for example, yellow, magenta, cyan and black) used for the toner, those known for toner can be used. The amount of the coloring material is suitably 0.1 to 15 parts by weight with respect to 100 parts by weight of the binder resin.
Specific examples of the charge control agent include nigrosine dyes, chromium-containing complexes, quaternary ammonium salts, and the like, which are properly used depending on the polarity of the toner particles. The amount of the charge control agent is 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  It is advantageous to add a fluidity imparting agent to the toner particles. Examples of the fluidity-imparting agent include fine particles of metal oxides such as silica, titania and alumina, and those obtained by surface-treating these fine particles with a silane coupling agent, titanate coupling agent, etc., polystyrene, polymethyl methacrylate, polyvinylidene fluoride. Polymer fine particles such as are used. These fluidity imparting agents have a particle size in the range of 0.01 to 3 μm. The addition amount of these fluidity-imparting agents is preferably in the range of 0.1 to 7.0 parts by weight with respect to 100 parts by weight of the toner particles.

  The toner for the two-component developer according to the present invention can be manufactured by various known methods or a combination of them. For example, in the kneading and pulverization method, a binder resin, a colorant such as carbon black, and necessary additives are dry-mixed, heated and melt-kneaded with an extruder or two-roll, three-roll, etc., and after cooling and solidification Then, the toner is pulverized by a pulverizer such as a jet mill and classified by an airflow classifier. In addition, a toner can be directly produced from a monomer, a colorant, and an additive by suspension polymerization or non-aqueous dispersion polymerization.

The carrier is generally composed of the core material itself, or a carrier provided with a coating layer on the core material. The core material of the resin-coated carrier that can be used in the present invention is a ferromagnetic material such as ferrite or magnetite. An appropriate particle size of the core material is about 20 to 60 μm.
Materials used for forming the carrier coating layer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinyl ether substituted with fluorine atoms, and vinyl ketone substituted with fluorine atoms. . As a method for forming the coating layer, a resin may be applied to the surface of the carrier core material particles by a spraying method, a dipping method, or the like, as in the conventional case.

  Next, FIG. 4 shows a cross-sectional configuration of the photoreceptor 40 used in the present invention. As shown in FIG. 4, the photosensitive member 40 used in the present invention includes a conductive support (conductive substrate) 201 and a charge generation layer 203 formed on the conductive support (conductive substrate) 201. And a layered organic photoreceptor comprising a photosensitive layer 202 comprising a charge transport layer 204 and a surface protective layer 205 provided on the outermost layer.

The conductive support (conductive substrate) 201 has a volume resistance of 10 ¹⁰ Ωcm or less, for example, a metal such as aluminum, nickel, chromium, nichrome, copper, silver, gold, platinum, tin oxide, oxidation Cutting, superfinishing, polishing, etc. of metal oxide such as indium by vapor deposition or sputtering, film or cylindrical plastic, or paper coated with aluminum, or aluminum, aluminum alloy, nickel, stainless steel, etc. Consists of surface-treated materials.

  The charge generation layer 203 constituting the photosensitive layer 202 is a layer mainly composed of a charge generation material. As the charge generation material, an inorganic or organic material is used, and typical examples include monoazo pigments, disazo pigments, trisazo pigments, perylene pigments, perinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squaric. Examples include acid dyes, phthalocyanine pigments, naphthalocyanine pigments, azulenium salt dyes, selenium, selenium-tellurium alloys, selenium-arsenic alloys, and amorphous silicon. These charge generation materials may be used alone or in combination of two or more.

  The charge generation layer 203 is obtained by dispersing the above charge generation material together with a binder resin, using a solvent such as tetrahydrofuran, cyclohexanone, dioxane, 2-butanone, dichloroethane or the like by a ball mill, an attritor, a sand mill, or the like, and applying a dispersion. Can be formed. The charge generation layer 203 can be applied by dip coating, spray coating, bead coating, or the like.

Examples of the binder resin used as appropriate include resins such as polyamide, polyurethane, polyester, epoxy, polyketone, polycarbonate, silicone, acrylic, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polyacryl, and polyamide. The amount of the binder resin is suitably 0 to 2 parts with respect to 1 part of the charge generating material on a weight basis.
The charge generation layer 203 can also be formed by a known vacuum thin film manufacturing method. The film thickness of the charge generation layer 203 is usually 0.01 to 5 μm, preferably 0.1 to 2 μm.

  The charge transport layer can be formed by dissolving or dispersing the charge transport material and the binder resin in an appropriate solvent, and applying and drying the solution. Moreover, a plasticizer, a leveling agent, etc. can also be added as needed. Among charge transport materials, low molecular charge transport materials include electron transport materials and hole transport materials.

  Examples of the electron transport material include chloroanil, bromanyl, 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] thiophene-4-one, 1,3,7-tri Examples thereof include electron accepting substances such as nitrodibenzothiophene-5,5-dioxide. These electron transport materials may be used alone or as a mixture of two or more.

  Examples of the hole transport material include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-diethylaminostyrylanthracene), 1,1-bis- (4-dibenzylaminophenyl) propane. , Styrylanthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, thiophene derivatives, and the like. These hole transport materials may be used alone or as a mixture of two or more.

Examples of the binder resin used in the charge transport layer together with the charge transport material include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, and vinyl chloride. Vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate, phenoxy, polycarbonate, cellulose acetate, ethyl cellulose, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, acrylic, silicone, epoxy, melamine, urethane, phenol, alkyd, etc. A thermoplastic or thermosetting resin is mentioned.
Examples of the solvent include tetrahydrofuran, dioxane, toluene, 2-butanone, monochlorobenzene, dichloroethane, methylene chloride and the like.

The thickness of the charge transport layer 204 may be appropriately selected in the range of 15 to 35 μm according to desired photoreceptor characteristics.
Examples of the plasticizer that is optionally added to the charge transport layer 204 include general-purpose plasticizers such as dibutyl phthalate and dioctyl phthalate. The amount of the plasticizer is 0 to 30 based on the weight of the binder resin. % Is appropriate.
Examples of the leveling agent that is optionally added to the charge transport layer 204 include silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, and polymers or oligomers having a perfluoroalkyl group in the side chain. Is about 0 to 1% based on the weight of the binder resin.

  In the present invention, the content of the charge transport material contained in the photosensitive layer 202 is preferably 30% by weight or more of the charge transport layer 204. If it is less than 30% by weight, a sufficient light decay time in a high-speed electrophotographic process cannot be obtained in pulsed light exposure in laser writing on the photoreceptor 40, which is not preferable.

In the photoreceptor 40 of the present invention, an undercoat layer (not shown) may be formed between the conductive support (conductive substrate) 201 and the photosensitive layer 202. The undercoat layer generally contains a resin as a main component. However, considering that the photosensitive layer 202 is applied on the resin layer using a solvent, these resins are resins having high solubility resistance to general organic solvents. It is desirable. Such resins include water-soluble resins such as polyvinyl alcohol, casein, sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine, alkyd-melamine, epoxy, etc., three-dimensional Examples thereof include a curable resin that forms a network structure.
Further, fine powder of metal oxide such as titanium oxide, silica, alumina, zirconium oxide, tin oxide, and indium oxide may be added to the undercoat layer in order to prevent moire and reduce residual potential.
This undercoat layer can be formed by using an appropriate solvent and coating method as in the case of the photosensitive layer.

Furthermore, it is also useful to use a metal oxide layer formed by, for example, a sol-gel method using a silane coupling agent, a titanium coupling agent, a chromium coupling agent or the like as the undercoat layer. In addition, the undercoat layer is formed by anodizing Al ₂ O ₃ , organic matter such as polyparaxylylene (parylene), inorganic matter such as SiO, SnO ₂ , TiO ₂ , ITO, CeO ₂ It is also effective to form the film by a vacuum thin film manufacturing method. The thickness of the undercoat layer is suitably from 0 to 5 μm.

In the photoreceptor 40 of the present invention, as a surface layer, a surface protective layer 205 is formed on the photosensitive layer 202 for the purpose of protecting the photosensitive layer 202 and improving durability.
As the structure of the surface protective layer 205, metal oxide fine particles such as alumina, silica, titanium oxide, tin oxide, zirconium oxide, and indium oxide are dispersed in a binder resin for the purpose of improving wear resistance. Binder resins include styrene-acrylonitrile copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, olefin-vinyl monomer copolymer, chlorinated polyether, allyl, phenol, polyacetal, polyamide, polyamide Imide, polyacrylate, polyallylsulfone, polybutylene, polybutylene terephthalate, polycarbonate, polyethersulfone, polyethine, polyethylene terephthalate, polyimide, acrylic, polymethylpentene, polypropylene, polyphenylene oxide, polysulfone, polyurethane, polyvinyl chloride, polyvinylidene chloride And resins such as epoxy.

  The amount of metal oxide fine particles added to the surface protective layer 205 is 5 to 30% on a weight basis. If the amount of the metal oxide fine particles is less than 5%, the effect of improving the wear resistance is small and the durability is inferior. If it exceeds 30%, the bright portion potential is significantly increased at the time of exposure, and the sensitivity reduction cannot be ignored. So undesirable. As a method for forming the surface protective layer 205, a normal coating method such as a spray method is employed. The thickness of the surface protective layer 205 is 1 to 10 μm, preferably about 3 to 8 μm. If the thickness of the surface protective layer 205 is too thin, the durability is inferior. If the thickness of the surface protective layer 205 is too thick, not only the productivity at the time of producing the photoreceptor is lowered, but also the residual potential increases with time. It gets bigger. The particle size of the metal oxide particles added to the surface protective layer 205 is suitably 0.1 to 0.8 μm. When the particle size of the metal oxide fine particles is too large, the unevenness on the surface of the protective layer becomes large and the cleaning property is deteriorated, and the exposure light is easily scattered by the protective layer, so that the resolution is lowered and the image quality is inferior. If the particle size of the metal oxide fine particles is too small, the wear resistance is poor.

  Furthermore, a dispersion aid can be added to the surface protective layer 205 in order to improve the dispersibility of the metal oxide fine particles in the base resin. As the added dispersion aid, those used in paints and the like can be used as appropriate, and the amount is usually 0.5 to 4%, preferably 1 to 2 with respect to the amount of metal oxide fine particles contained on a weight basis. %.

As shown in FIG. 2, in an image forming apparatus provided with a potential sensor 71 as a latent image detecting means between a latent image forming position and a developing position, a charge transport material is added to the surface protective layer 205 of the photoreceptor 40. As a result, the movement of charges in the protective layer can be promoted, and the difference between the photoreceptor potential detected by the potential sensor 71 and the photoreceptor potential at the development position can be reduced. Accordingly, an image forming apparatus that can appropriately set the developing bias and the like based on the photosensitive member potential (latent image potential) detected by the potential sensor 71 and has excellent image gradation and halftone reproducibility. Can be realized.
As the charge transport material added to the surface protective layer 205 of the photoreceptor 40, the same material as the charge transport layer 204 can be used, or another material can be used.

  In order to reduce the difference in the photoreceptor potential between the potential sensor position and the development position, it is better to increase the ratio of the base resin and the charge transport material of the surface protective layer 205 of the photoreceptor 40. However, since the charge transport material generally has a molecular weight smaller than that of the binder resin, if the amount of the charge transport material in the protective layer is too large, the strength of the surface protective layer 205 is lowered and the wear resistance is lowered. There is. Even if the surface protective layer 205 contains more charge transport material than the charge transport layer 204, not only does the speed of movement of the charge transport layer 204 become dominant, but the sensitivity as a photoreceptor is not improved, The strength of the protective layer is reduced. Therefore, it is desirable to make the ratio of the base resin and the charge transport material in the protective layer smaller than the ratio of the base resin and the charge transport material in the charge transport layer.

Note that the photoreceptor 40 used in the present invention has an antioxidant, a plasticizer, an ultraviolet absorber, and a leveling agent in each layer for the purpose of preventing the decrease in sensitivity and the increase in residual potential, in order to improve the environmental resistance. An agent or the like can be added.
Further, the configuration of the surface protective layer 205 that can be used in the present invention is not limited to the type in which metal oxide particles are dispersed, and surface protection can be achieved by using a photo-curing or thermosetting resin material. Layer 205 can also be formed.

  In the present invention, the wear resistance of the photoreceptor 40 is improved by using the photoreceptor 40 having the surface protective layer 205 as described above. Therefore, since the wear of the photoconductor 40 is reduced, the change in the photoconductor sensitivity due to the decrease in the photoconductor film thickness is small even when used for a long time, and a stable image can be output for a long time.

Hereinafter, the present invention will be described in more detail with reference to more detailed examples, but the present invention is not limited to these examples.
The configuration of the image forming apparatus used is the full-color copying machine shown in FIG. 1, and the configuration of each image forming unit 18 (Y, C, M, Bk) is as shown in FIG. Each photoconductor 40 (Y, C, M, Bk) has a diameter of 60 mm and a process linear velocity of 280 mm / s. In this image forming apparatus, the time required for each photoconductor 40 (Y, C, M, Bk) to rotate from the exposure position (latent image forming position) to the potential sensor position is 35 ms, and from the exposure position (latent image forming position). The rotation time to the development position is 110 ms. A potential sensor 71 mounted on the apparatus is used for measuring the photosensitive member potential at the potential sensor position, and the developing roller 61 is removed for measuring the photosensitive member potential at the developing position, and a surface potential meter (model 344 manufactured by Trek) is installed at that position. ) Was placed in the measurement. The exposure means is a laser diode (LD) having a wavelength of 655 nm, and an LED having a wavelength of 680 nm is used as the charge eliminating lamp 72.

  The photoreceptor 40 includes an undercoat layer having a thickness of 3.5 μm, a charge generation layer 203 having a thickness of 0.15 μm, a charge transport layer 204 having a thickness of 22 μm, and a surface protective layer 205 having a thickness of 5 μm on an aluminum substrate 201. This is an organic photoreceptor having a laminated structure. At this time, the surface protective layer 205 was applied by a spray method, and the other layers were applied by a dip coating method. Polycarbonate was used as the base resin for both the charge transport layer 204 and the surface protective layer 205. The charge transport material of the charge transport layer 204 was 40 wt% in weight ratio, and alumina particles having an average particle size of 0.3 μm were added to the surface protective layer 205 at 10 wt% with respect to the total solid content of the protective layer.

Here, the amount of the charge transport material contained in the surface protective layer 205 was changed, and the photoreceptor potential was measured at the potential sensor position and the developing roller position. At this time, in order to increase or decrease the ratio of the amount of the charge transport material, the amount of the base resin was changed and adjusted.
The relationship between the amount of charge transport material in the protective layer and the photoreceptor potential at the potential sensor position is shown in Table 1 below, and the relationship between the amount of charge transport material in the protective layer and the photoreceptor potential at the development position is shown in Table 2 below. . At this time, the measurement is performed by setting the charging potential of the photosensitive member 40 to −700 V and changing the exposure energy. Table 3 below shows the difference between the photosensitive member potential at the potential sensor position and the development position from Tables 1 and 2 below. From this result, it can be seen that increasing the amount of the charge transport material of the protective layer 205 of the photoreceptor 40 can reduce the photoreceptor potential difference between the potential sensor position and the developing roller position.

  As described above, in the image forming apparatus according to the present invention, the photosensitive member 40 as the image carrier is an organic material including at least the charge generation layer 203, the charge transport layer 204, and the surface protective layer 205 on the conductive substrate 201. By including a charge transport material in the surface protective layer 205, the photoconductor can reduce the potential difference between the latent image detecting means (potential sensor 71) position and the developing position, and the photoconductor potential detected by the potential sensor 71 can be reduced. Based on (latent image potential), it is possible to appropriately set the developing bias and the like, and it is possible to realize an image forming apparatus having excellent image gradation and halftone reproducibility.

Further, in the image forming apparatus according to the present invention, the time during which the photoconductor 40 during the image forming operation moves from the latent image forming position to the potential sensor 71 is t1, and the time when the photosensitive body 40 is moved from the latent image forming position to the developing position is t2. When
20ms <t1 <40ms
And,
(T1 × 2.5) <t2 <(t1 × 3.5)
As a result, even when the time required to move from the latent image forming position to the potential sensor 71 in order to form a high-speed image is 40 ms or less, the potential difference between the potential sensor position and the developing position can be reduced. In addition, it is possible to provide an image forming apparatus excellent in image gradation and halftone reproducibility.

Furthermore, in the image forming apparatus according to the present invention, the durability of the organic photoreceptor 40 can be greatly improved by dispersing the metal oxide in the surface protective layer 205.
Further, the durability of the organic photoreceptor can be greatly improved by making the surface protective layer 205 of the photoreceptor 40 a thermosetting or photocurable resin layer.
In the image forming apparatus according to the present invention, the ratio of the charge transport material to the base resin contained in the surface protective layer 205 is lower than the ratio of the charge transport material to the base resin contained in the charge transport layer 204. It is possible to prevent the response time of the photoreceptor 40 from being lowered.

Furthermore, in the image forming apparatus according to the present invention, the charge transport material of the charge transport layer 204 is 30 to 50 wt% by weight, and the charge transport material of the surface protective layer 205 is 15 to 30 wt% by weight, Without lowering the wear resistance of the protective layer 205, the reduction in the response time of the photoreceptor 40 can be minimized.
In the image forming apparatus according to the present invention, the thickness of the surface protective layer 205 is not less than 1/10 and not more than 1/4 of the thickness of the charge transport layer 204, and the thickness of the surface protective layer 205 is 3 By setting the thickness of the surface protective layer 205 within this range, the sensitivity of the photoconductor 40 is hardly deteriorated even when the protective layer 205 is provided, and the durability of the photoconductor 40 is greatly improved. Can do.

  Further, as shown in FIG. 1, the image forming apparatus according to the present invention includes a plurality of photoconductors 40Y, 40C, 40M, and 40Bk, and images having different colors are provided on the photoconductors 40Y, 40C, 40M, and 40Bk. After the formation, the image is superimposed and transferred onto the intermediate transfer belt 10 and further transferred from the intermediate transfer belt 10 to a transfer material to form a full-color image. As shown in FIG. By providing the latent image detecting means (potential sensor 71), an image with excellent gradation can be formed for each color, so that a high-quality full-color image can be formed at high speed.

  Although FIG. 1 illustrates an image forming apparatus of a tandem type and an intermediate transfer method, in addition to this, instead of the intermediate transfer belt, a transfer conveyance belt that carries and conveys a transfer material is used, and an image on each color photoconductor is displayed. The present invention can be similarly applied to a tandem type direct transfer type image forming apparatus which directly superimposes and transfers to a transfer material.

  As described above, according to the present invention, it is possible to realize a highly reliable image forming apparatus with excellent image gradation and halftone reproducibility, and further, electrostatic characteristics and sensitivity of the photoreceptor. The durability can be improved without deteriorating the image quality, and a more reliable image forming apparatus, particularly a high-speed full-color image forming apparatus can be realized. Therefore, the image forming apparatus according to the present invention can be suitably used as a copying machine, a printer, a plotter, a facsimile, a printing machine, or a complex machine of these.

1 is a schematic overall configuration diagram of an image forming apparatus showing an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a configuration example of an image forming unit of the image forming apparatus illustrated in FIG. 1. FIG. 3 is a schematic cross-sectional view illustrating a configuration example of a charging roller used in the image forming unit illustrated in FIG. 2. FIG. 3 is a schematic cross-sectional view of an essential part showing a configuration example of a photoreceptor used in the image forming unit shown in FIG. 2.

Explanation of symbols

10: Intermediate transfer belt (intermediate transfer member)
17: Intermediate transfer belt cleaning device 18 (18Y, 18C, 18M, 18Bk): Image forming unit 20: Tandem type image forming device 21: Exposure device 22: Secondary transfer device 24: Secondary transfer belt 25: Fixing device 40 ( 40Y, 40C, 40M, 40Bk): photoconductor (image carrier)
44: paper feed cassette 49: registration roller 57: paper discharge tray 60 (60Y, 60C, 60M, 60Bk): developing device (developing unit)
61: Development roller 62, 63: Screw 64: Toner density sensor 65 (65Y, 65C, 65M, 65Bk): Primary transfer roller 70: Charging roller 71: Potential sensor (latent image detection means)
72: Static elimination lamp 73, 74: Brush roller 75: Cleaning blade 76: Exposure light 78: Lubricant 80: Photoconductor cleaning device 100: Device main body 101: Core metal 102: Resin layer (charging member)
103: Gap holding member 200: Paper feed table 201: Conductive support (conductive base)
202: Photosensitive layer 203: Charge generation layer 204: Charge transport layer 205: Surface protective layer 300: Scanner 400: Automatic document feeder (ADF)

Claims (8)

An image carrier, a charging unit for charging the image carrier, a latent image forming unit for forming an electrostatic latent image on the charged image carrier, and a latent image for detecting the electrostatic latent image on the image carrier. In an image forming apparatus comprising an image detecting means and a developing means for developing and developing an electrostatic latent image on the image carrier,
The image carrier is an organic photoreceptor having at least a charge generation layer, a charge transport layer, and a surface protective layer on a conductive substrate, and the surface protective layer contains a charge transport material. Image forming apparatus. The image forming apparatus according to claim 1.
When the time for the image carrier during the image forming operation to move from the latent image forming position to the latent image detecting means is t1, and the time for the image carrier to move from the latent image forming position to the developing position is t2,
20ms <t1 <40ms
And,
(T1 × 2.5) <t2 <(t1 × 3.5)
An image forming apparatus. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein the surface protective layer of the image carrier is an organic photoreceptor in which metal oxide particles are dispersed in a base resin. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein the surface protective layer of the image carrier is an organic photoreceptor containing heat or a photocurable resin. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the ratio of the charge transport material to the base resin contained in the surface protective layer is lower than the ratio of the charge transport material to the base resin contained in the charge transport layer. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the charge transport material of the charge transport layer is 30 to 50 wt% by weight, and the charge transport material of the surface protective layer is 15 to 30 wt% by weight. The image forming apparatus according to any one of claims 1 to 6,
The thickness of the surface protective layer is 1/10 or more and 1/4 or less of the thickness of the charge transport layer, and the thickness of the surface protective layer is 3 to 8 μm. . The image forming apparatus according to any one of claims 1 to 7,
It has a configuration that includes a plurality of image carriers, and after forming images of different colors on each image carrier, the images are transferred to a transfer material by superimposing them directly or via an intermediate transfer member to form a full-color image. An image forming apparatus comprising a latent image detecting means for each image carrier.

Images