JP2008129306A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents reverse transfer of toner from an intermediate transfer belt to an electrostatic latent image carrier such as a photoreceptor and reduces the degree of a central defective transfer phenomenon while achieving the reduction of cost. <P>SOLUTION: The image forming apparatus 2 is equipped with: a rotatable endless intermediate transfer belt 30; a plurality of electrostatic latent image carriers 4 arranged along the intermediate transfer belt 30; a developing device 18 forming a toner image by supplying toner to an electrostatic latent image on the surface of the electrostatic latent image carrier 4; and a transfer device 14 transferring the toner image formed on the surface of the electrostatic latent image carrier 4 to the intermediate transfer belt 30, wherein a standard electrostatic latent image carrier 4N whose surface has predetermined releasing property and a high releasable electrostatic latent image carrier 4H whose surface has higher releasing property than the surface of the standard electrostatic latent image carrier 4N are provided as the plurality of electrostatic latent image carriers 4. At least one high releasable electrostatic latent image carrier 4H is arranged on a more downstream side than at least one standard electrostatic latent image carrier 4N in the moving direction of the intermediate transfer belt 30. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly, to an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having these functions combined.

  A so-called tandem color image forming apparatus is known as an electrophotographic color image forming apparatus. The tandem image forming apparatus includes four image forming units that form single-color (yellow, magenta, cyan, and black) toner images, and a photoconductor provided for each of these image forming units is attached to the intermediate transfer belt. Are arranged along. In each image forming unit, a toner image of a corresponding color is formed on the surface of the photoconductor, and these toner images are sequentially transferred onto the intermediate transfer belt (primary transfer), thereby forming a full-color image.

  When a toner image is transferred from a photoreceptor to an intermediate transfer belt (primary transfer), a phenomenon occurs in which the central portion of a character line or the central portion of a vertical line becomes a transfer defect (hereinafter referred to as a “hollow-out phenomenon”). Depending on the degree of the void phenomenon, an image defect may occur. Occurrence of the hollowing out phenomenon occurs when the pressure at which the intermediate transfer belt is pressed against the surface of the photoconductor during the primary transfer is concentrated on the center of the vertical line of the toner image on the photoconductor. This occurs because the adhesion between the surface and the toner increases.

  Further, as a result of extensive research conducted by the inventor, the hollowing out phenomenon occurs not only when transferring from the photosensitive member to the intermediate transfer belt, but also when the toner transferred to the intermediate transfer belt is reversely transferred to the photosensitive member. It has also been found that this can occur. That is, even if the toner image on the photosensitive member can be transferred to the intermediate transfer belt satisfactorily, a part of the toner transferred to the intermediate transfer belt reaches the nip portion with the downstream photosensitive member as the belt moves. In some cases, the toner image is reversely transferred to the surface of the photoconductor, and this reverse transfer may cause a dropout phenomenon.

In view of such a problem, in the technique disclosed in Patent Document 1, the surface hardness of the intermediate transfer belt is 40 ° (JIS A) or less, and the contact angle of pure water with respect to the surface of the intermediate transfer belt is The contact angle is smaller than the contact angle of pure water with respect to the surface of the photoreceptor. With this configuration, the releasability of the surface of the photoreceptor is higher than the releasability of the surface of the intermediate transfer belt, so that the transfer performance from the photoreceptor to the intermediate transfer belt is improved, and the intermediate transfer belt to the photoreceptor It is possible to prevent reverse transcription to the. Therefore, the technique of Patent Document 1 can reduce the degree of the above-described hollowing phenomenon.
JP-A-7-152262

  However, the photoreceptor used in the technique of Patent Document 1 has a special configuration for improving the releasability (for example, a configuration in which a surface layer contains a fluorine-based resin powder). It is more expensive than a photoreceptor having a standard releasability. For this reason, if an expensive photoconductor is used in all four image forming units, the cost of the image forming apparatus increases.

  Accordingly, the present invention provides an image forming apparatus that can prevent reverse transfer of toner from an intermediate transfer belt to an electrostatic latent image carrier such as a photoconductor while reducing costs, and can reduce the degree of voiding. The purpose is to provide.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A developing device for supplying toner to the electrostatic latent image on the surface of the electrostatic latent image carrier to form a toner image;
An image forming apparatus comprising: a transfer device that transfers the toner image formed on the surface of the electrostatic latent image carrier to the intermediate transfer belt;
The plurality of electrostatic latent image carriers include a standard electrostatic latent image carrier having a predetermined releasability on the surface and a high releasability in which the surface releasability is higher than the surface of the standard electrostatic latent image carrier. Type electrostatic latent image carrier,
In the moving direction of the intermediate transfer belt, at least one high-release electrostatic latent image carrier is disposed downstream of at least one standard electrostatic latent image carrier.

  According to the present invention, in an image forming apparatus in which a plurality of electrostatic latent image carriers including a standard electrostatic latent image carrier and a high-release electrostatic latent image carrier are arranged along the intermediate transfer belt, at least one Since at least one high-release electrostatic latent image carrier is disposed downstream of the two standard electrostatic latent image carriers, the toner transferred from the upstream electrostatic latent image carrier to the intermediate transfer belt Can be prevented from being reversely transferred from the belt to the high-release electrostatic latent image carrier when it reaches the nip with the high-release electrostatic latent image carrier as the belt moves. Can be reduced. Moreover, since some of the plurality of electrostatic latent image carriers are high-release electrostatic latent image carriers, all the electrostatic latent image carriers are high-release electrostatic latent image carriers. Compared to, the cost of the apparatus can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, terms indicating a specific direction and position (for example, “up”, “down”, “right”, “left” and other terms including those terms) are used as necessary. These terms are used for easy understanding of the invention with reference to the drawings, and the technical scope of the present invention is not limited by the meaning of these terms.

  FIG. 1 shows a schematic configuration of an image forming apparatus 2 according to the first embodiment of the present invention. The image forming apparatus 2 is an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having a combination of these functions. More specifically, the image forming apparatus 2 is a so-called tandem color image. Forming device.

  The image forming apparatus 2 includes an image reading unit 20 for reading a document image and a printing unit 22 for printing the read image.

  The image reading unit 20 separates and reads the original image into three colors of red (R), green (G), and blue (B) by a known mechanism, and also reads red (R), green (G), and blue ( It is configured to create the image data of B). In the figure, reference numeral 24 denotes a display unit for displaying various information relating to printing, and reference numeral 25 denotes a panel operation unit for performing a printing start operation and various setting operations relating to printing. .

  The printing unit 22 has an endless intermediate transfer belt 30. The intermediate transfer belt 30 is made of a material excellent in transfer performance. Specifically, for example, polyimide is used. Further, as the intermediate transfer belt 30, a belt having a thickness of, for example, 50 μm or more and 150 μm or less is preferably used. The contact angle of pure water with respect to the surface of the intermediate transfer belt 30 is, for example, 80 ° to 85 °, and the surface energy of the intermediate transfer belt 30 is, for example, 50 mN / m to 55 mN / m.

  In the present embodiment, the intermediate transfer belt 30 is wound around a pair of rollers 32 and 34 disposed on the right and left sides of the drawing, respectively. The roller 32 on the right side of the drawing is a driving roller that is drivingly connected to a motor (not shown). The driving roller 32 connected to the motor rotates based on the driving of the motor, and the belt 30 and the other roller 34 in contact with the belt 30. Is rotated counterclockwise in the figure.

  As the driving roller 32, one having an outer diameter of, for example, 12 mm or more and 30 mm or less is preferably used, whereby the size of the apparatus can be reduced. At least the surface of the driving roller 32 is made of a material having a large friction coefficient such as rubber or urethane, whereby the frictional force with the intermediate transfer belt 30 is increased, and the driving force is transmitted to the intermediate transfer belt 30 satisfactorily. It can be done.

  Further, in order to ensure a sufficient frictional force between the driving roller 32 and the intermediate transfer belt 30, the intermediate transfer belt 30 is given a predetermined tension by a plurality of rollers 32 and 34. The magnitude of tension applied to the intermediate transfer belt 30 is preferably 15N or more and 50N or less, for example.

  A secondary transfer roller 40 is provided outside the belt portion supported by the driving roller 32 disposed on the right side in the drawing. The secondary transfer roller 40 is in contact with the outer peripheral surface of the belt 30, and the contact portion (nip portion) forms a secondary transfer region 41.

  An intermediate transfer belt cleaning blade 42 is provided outside the belt portion supported by the roller 34 arranged on the left side in the drawing. The cleaning blade 42 is in pressure contact with the roller 34 via the belt 30, and the contact portion forms a collection region 62 for collecting untransferred toner.

  Below the belt portion moving from the roller 34 on the left side to the roller 32 on the right side in the drawing, yellow (Y), magenta (M), cyan (C), black ( Four image forming units 3 (3Y, 3M, 3C, and 3K) that respectively create toner images of corresponding colors using the developer K) are arranged along the intermediate transfer belt 30.

  Each image forming unit 3 includes a cylindrical photosensitive member 4 as an electrostatic latent image carrier. A specific configuration of the photoreceptor 4 will be described later.

  Around the photosensitive member 4, a charger 8, an exposure device 10, a developing device 18 (corresponding to the developing device in the claims), and a primary transfer roller in order along the rotation direction (clockwise direction in the drawing). 14 (corresponding to a transfer device in claims) and a photosensitive member cleaning member 16 are disposed.

  As shown in FIG. 2, the primary transfer roller 14 is disposed inside the endless intermediate transfer belt 30. The primary transfer roller 14K for black is always kept in pressure contact with the inner side of the intermediate transfer belt 30 by the biasing force of the spring 76, and is pressed against the photosensitive member 4 with a certain load with the intermediate transfer belt 30 interposed therebetween. The load is, for example, not less than 0.5N and not more than 10N. The black primary transfer roller 14 </ b> K is disposed at a position 2 mm away from the photoreceptor 4 in the rotation direction of the intermediate transfer belt 30.

  The yellow, magenta, and cyan primary transfer rollers 14Y, 14M, and 14C have support plates 74 that support both ends in the longitudinal direction of the primary transfer rollers 14Y, 14M, and 14C and rotate clockwise around the support shaft 77 in the figure. The position can be changed by moving. Specifically, in a color mode in which a color image is formed using four color toners, yellow, magenta, and cyan primary transfer rollers 14Y, 14M, and 14C are pressed against the intermediate transfer belt 30 as shown in FIG. In the monochrome mode in which a monochrome image is formed using one color toner (specifically, black), only the primary transfer roller 14K for black is attached to the intermediate transfer belt 30 although illustration is omitted. The primary transfer rollers 14Y, 14M, and 14C for yellow, magenta, and cyan are arranged so as to be spaced apart from the intermediate transfer belt 30.

  In the color mode, the yellow, magenta, and cyan primary transfer rollers 14Y, 14M, and 14C are pressed against the photosensitive member 4 with a certain load with the intermediate transfer belt 30 interposed therebetween, similarly to the black primary transfer roller 14K. The load is, for example, not less than 0.5N and not more than 10N. The primary transfer rollers 14Y, 14M, and 14C for yellow, magenta, and cyan are located 2 mm away from the photoreceptor 4 in the rotational direction of the intermediate transfer belt 30 in the color mode, similarly to the primary transfer roller 14K for black. It is supposed to be arranged in.

  Note that a high-voltage power supply 80 is connected to the primary transfer roller 14, and a primary transfer bias is applied by the high-voltage power supply 80 during image formation.

  Returning to FIG. 1, a paper feed cassette 44 as a paper feed device is detachably disposed below the printing unit 22. The sheets (recording media) 36 stacked and accommodated in the sheet feeding cassette 44 are sent out one by one from the uppermost one to the transport path 50 by the rotation of the sheet feeding roller 52 disposed in the vicinity of the sheet feeding cassette 44. It has become.

  A registration roller 54 for sending the paper 36 to the secondary transfer area 41 at a predetermined timing is provided near the paper feed roller 52. In the vicinity of the registration roller 54, a detection sensor 55 for detecting the leading edge of the paper 36 is provided.

  The conveyance path 50 passes from the paper feed cassette 44 through the nip portion of the registration roller pair 54, the secondary transfer region 41, the nip portion of the fixing roller pair 56, and the nip portion of the paper discharge roller pair 60, to the print unit 22. It extends to the paper discharge unit 61 provided at the top.

  An example of an image forming operation in the color mode will be briefly described.

  First, red (R), green (G), and blue (B) image data obtained in the image reading unit 20 is subjected to predetermined data processing in the control unit 70, and yellow (Y) and magenta (M). , Cyan (C), and black (K) image data.

  The yellow, magenta, cyan, and black image data are stored in the image memory 72 in the control unit 70, and after receiving a predetermined image correction for correcting the displacement, a laser diode (not shown) provided in the exposure apparatus 10 is provided. Is converted into a drive signal for emitting light.

  In the printing unit 22, first, in each image forming unit 3, the outer peripheral surface of the photosensitive member 4 that is rotationally driven at a predetermined peripheral speed is charged by the charger 8. Next, light is projected from the exposure apparatus 10 that has received the drive signal output from the control unit 70 onto the outer peripheral surface of the charged photoconductor 4 to form an electrostatic latent image. Subsequently, the electrostatic latent image is made visible by the developer toner supplied from the developing device 18. When the toner image of each color formed on the photoconductor 4 in this way reaches the primary transfer region by the rotation of the photoconductor 4, yellow, magenta, cyan, and black are sequentially transferred from the photoconductor 4 to the intermediate transfer belt 30. Transferred (primary transfer) and overlaid.

  Untransferred toner remaining on the photosensitive member 4 without being transferred to the intermediate transfer belt 30 reaches the contact portion between the photosensitive member 4 and the cleaning member 16 and is scraped off by the cleaning member 16. It is removed from the outer peripheral surface.

  The superimposed four color toner images are conveyed to the secondary transfer region 41 by the intermediate transfer belt 30. On the other hand, the paper 36 accommodated in the paper feed cassette 44 is conveyed to the secondary transfer area 41 in accordance with the timing. The four color toner images are secondarily transferred from the intermediate transfer belt 30 to the paper 36 in the secondary transfer region 41. The paper 36 to which the four color toner images have been transferred is transported further downstream in the transport path 50, and the toner image is fixed on the paper 36 by the fixing roller 56, and then sent to the paper discharge unit 61 by the paper discharge roller 60. It is.

  The intermediate transfer belt 30 that has passed through the secondary transfer region 41 is cleaned by the cleaning blade 42. The toner removed from the intermediate transfer belt 30 by the cleaning blade 42 is taken into the cleaner housing 61 and is sent to the toner collection box 68 through the joint pipe 66 by the rotation of the screw 64 provided in the cleaner housing 63. . Thereafter, the rotational drive of each photoreceptor 4 and the intermediate transfer belt 30 is stopped.

  Next, the configuration of the photoreceptor 4 will be described.

  As shown in FIG. 2, the four photoconductors 4 have, for example, two standard photoconductors 4N whose surfaces have predetermined releasability (corresponding to high-release electrostatic latent image carriers in claims). For example, two high-release photoconductors 4H (corresponding to the standard electrostatic latent image carrier in the claims) having higher surface releasability than the surface of the standard photoconductor 4N are configured.

  In the embodiment, in the moving direction of the intermediate transfer belt 30, a black toner image forming photoconductor disposed at the most downstream portion and a cyan toner image forming device disposed at the downstream side next to the most downstream portion. The photoconductor is a high-release photoconductor 4H, and a yellow and magenta toner image forming photoconductor disposed upstream of these photoconductors is a standard photoconductor 4N.

  As described above, since the high-releasing photoconductor 4H is disposed on the downstream side, the toner transferred from the upstream photoconductor 4 to the intermediate transfer belt 30 is moved along with the movement of the intermediate transfer belt 30. Can be prevented from being reversely transferred from the belt 30 to the photoconductor 4H when reaching the nip portion between the belt 30 and the high-release photoconductor 4H on the downstream side.

  Further, since the relatively inexpensive standard photoconductor 4N is used as the upstream photoconductor, the cost can be reduced as compared with the case where all the photoconductors are the high release photoconductor 4H.

  In the embodiment, two high release photoconductors 4H are used, but the number of high release photoconductors 4H may be one or three.

  In addition to the arrangement of the present embodiment, various arrangements of the high-release photoconductor 4H and the standard photoconductor 4N are conceivable, but at least one standard photoconductor is used regardless of the number of the high-release photoconductors 4H. It is assumed that at least one high-release photoconductor 4H is disposed on the downstream side of the body 4N. Further, regardless of the number of the high-release photoconductors 4H, it is preferable to dispose the high-release photoconductor 4H in the most downstream portion, and all the high-release photoconductors 4H are arranged downstream of the remaining photoconductors 4N. It is desirable to arrange on the side.

  The releasability of the surface of the photoconductor 4 is represented by the contact angle of pure water with respect to the surface of the photoconductor 4, the surface energy of the photoconductor 4, the friction coefficient of the surface of the photoconductor 4, or the like. That is, the higher the releasability of the surface of the photoconductor 4, the larger the contact angle of pure water with the surface of the photoconductor 4, the lower the surface energy of the photoconductor 4, and the lower the friction coefficient of the surface of the photoconductor 4.

(Standard photoconductor)
When the intermediate transfer belt 30 made of polyimide is used, the contact angle of pure water with respect to the surface of the standard photoconductor 4N is, for example, 90 ° to 95 °, and the surface energy of the standard photoconductor 4N is 40 mN / m to 45 mN / m. The friction coefficient of the surface of the standard photoconductor 4N is 0.4 or more and 0.6 or less.

  Thus, the standard photoconductor 4N has a larger contact angle of pure water with respect to the surface and lower surface energy than the above-described intermediate transfer belt 30. That is, the standard photoconductor 4N is higher in releasability than the intermediate transfer belt 30 and has a low adhesion to toner, so that the toner image formed on the surface of the standard photoconductor 4N can be transferred to the intermediate transfer belt 30 satisfactorily. it can.

(High release photoconductor)
The contact angle of pure water on the surface of the high release photoreceptor 4H is preferably 5 ° or more and 25 ° or less, and preferably 10 ° or more and 20 ° or less larger than that of the standard photoreceptor 4N. Even if the contact angle of pure water with respect to the surface of the high release photoconductor 4H is larger than the contact angle of pure water with respect to the surface of the standard photoconductor 4N, the difference between the contact angles is less than 5 °. , The adhesion force with the toner cannot be sufficiently reduced. Even if the contact angle of pure water with respect to the surface of the high release photoreceptor 4H is larger than the contact angle of pure water with respect to the surface of the standard photoreceptor 4N, the difference between the contact angles is more than 25 °. If it is larger, the frictional force between the high-releasing photoconductor 4H and the cleaning member 16 becomes smaller, and toner passes between the photoconductor 4H and the cleaning member 16, and filming is likely to occur on the surface of the photoconductor 4H. turn into.

  The surface energy of the surface of the high release photoconductor 4H is preferably 5 mN / m or more and 25 mN / m or less, preferably 10 mN / m or more and 20 mN / m or less, compared with the surface energy of the standard photoconductor 4N. Is desirable. Even when the surface energy of the surface of the high release photoconductor 4H is smaller than the surface energy of the surface of the standard photoconductor 4N, if the difference between the surface energies is less than 5 mN / m, The wearing force cannot be reduced sufficiently. Even if the surface energy of the surface of the high release photoconductor 4H is smaller than the surface energy of the standard photoconductor 4N, if the difference between the surface energies is greater than 25 mN / m, the The frictional force between the photosensitive drum 4H and the cleaning member 16 is reduced, so that toner passes between the photosensitive member 4H and the cleaning member 16, and filming is likely to occur on the surface of the photosensitive member 4H.

  The friction coefficient of the surface of the high release photoreceptor 4H is preferably 0.1 or more and 0.3 or less smaller than the friction coefficient of the surface of the standard photoreceptor 4N. Even when the friction coefficient of the surface of the high-release photoconductor 4H is smaller than the friction coefficient of the surface of the standard photoconductor 4N, if the difference in the friction coefficient is less than 0.1, the toner is attached to the toner. The wearing force cannot be reduced sufficiently. Even if the friction coefficient of the surface of the high-releasing photoconductor 4H is smaller than the friction coefficient of the surface of the standard photoconductor 4N, if the difference between the friction coefficients is larger than 0.3, the high The frictional force between the photosensitive drum 4H and the cleaning member 16 is reduced, so that toner passes between the photosensitive member 4H and the cleaning member 16, and filming is likely to occur on the surface of the photosensitive member 4H.

  As with the standard photoconductor 4N, the high release photoconductor 4H has a higher releasability than the intermediate transfer belt 30, and as described above, it has a higher releasability than the standard photoconductor 4N. Therefore, the toner image formed on the surface of the high release photosensitive member 4H can be satisfactorily transferred to the intermediate transfer belt 30, and the toner on the intermediate transfer belt 30 is prevented from being reversely transferred to the high release photosensitive member 4H. it can.

(Photoreceptor structure)
Next, the structure of the photoreceptor 4 will be described with reference to FIG. Since the structure of the photoconductor 4 is common to the standard photoconductor 4N and the high release photoconductor 4H, both will be described together.

  As shown in FIG. 3, the photosensitive member 4 includes a conductive support 82, a photosensitive layer 88 formed outside the conductive support 82, and the conductive support 82 and the photosensitive layer 88. Intermediate layer 86. Further, the photosensitive member 4 includes a sealing treatment layer 84 interposed between the conductive support 82 and the intermediate layer 86.

(Conductive support)
As the conductive support 82, for example, a cylindrical conductive member is used. As a material for the conductive support 82, for example, aluminum is used, but a metal other than aluminum (for example, nickel) can also be used. Further, as the conductive support 82, a material other than metal may be used. For example, a material in which a conductive member such as aluminum is vapor-deposited on a plastic surface, or a conductive material is applied on a paper or plastic surface. Can also be used.

(Sealing treatment layer)
The sealing treatment layer 84 is an anodized film formed by anodizing the surface of the conductive support 82, and the sealing treatment is performed by a known method. For example, when the conductive support 82 is made of aluminum, the sealing treatment layer 84 is a sealed anodized film. The thickness of the sealing treatment layer 84 is preferably 10 μm or less.

(Middle layer)
The intermediate layer 86 is a layer provided for the purpose of improving the adhesion between the conductive support 82 and the photosensitive layer 88 and preventing charge injection from the conductive support 82. As the intermediate layer 86, a material in which titanium oxide is dispersed in a binder resin is used. As the binder resin, for example, a polyamide resin is used. As the titanium oxide, for example, silica / alumina treatment and surface treatment with a silane compound are used. The thickness of the intermediate layer 86 is, for example, 1 μm.

(Photosensitive layer)
The photosensitive layer 88 includes a charge generation layer 90 and a charge transport layer 92 formed outside the charge generation layer 90.

(Charge generation layer)
The charge generation layer 90 includes a charge generation material. The charge generation layer 90 is formed, for example, by dissolving a charge generation material in a dispersion together with a binder resin, and applying the liquid obtained thereby to the surface of the intermediate layer 86. When the charge generation material and the binder resin are dispersed in the dispersion, specifically, for example, 4.5 parts by weight of X-type phthalocyanine as the charge generation material, 2.5 parts by weight of butyral resin as the binder resin, and phenoxy resin 2.5 parts by weight are dispersed in 500 parts by weight of dichloroethane as a dispersion. The thickness of the charge generation layer 90 is, for example, 0.3 μm.

(Charge transport layer)
The charge transport layer 92 includes a charge transport material. The charge transport layer 92 is formed, for example, by dissolving a charge transport material together with a binder resin and an ultraviolet absorber in a dispersion, and coating the resulting liquid on the surface of the charge generation layer 90. When dispersing the charge transport material or the like in the dispersion, specifically, for example, 40 parts by weight of a styryl compound as a charge transport material, 60 parts by weight of a polycarbonate resin as a binder resin, and a phenol compound butyl as an ultraviolet absorber. 2 parts by weight of hydroxytoluene are dispersed in 400 parts by weight of tetrahydrofuran as a dispersion. The thickness of the charge transport layer 92 is, for example, 20 μm.

  The configuration of the photoconductor 4 described above is common to the standard photoconductor 4N and the high release photoconductor 4H, but the charge transport layer 92 of the high release photoconductor 4H includes the above-described materials such as a charge transport material. In addition to fluorine resin. As described above, in the high release photoconductor 4H, the surface layer includes the fluororesin, so that the surface releasability is remarkably enhanced as compared with the standard photoconductor 4N.

  Specifically, the charge transport layer 92 of the high release photoreceptor 4H is obtained by dissolving a powder of fluororesin in a dispersion together with the above-described materials such as a charge transport material, and the resulting liquid is charged into the charge generation layer. It is formed by applying to the surface of 90. As the fluororesin powder, for example, polytetrafluoroethylene having a particle diameter of 0.12 μm is used, and for example, 40 parts by weight is dissolved in the above-described dispersion.

  While the present invention has been described with reference to the above-described embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiment, a case has been described in which the high-release photoconductor 4H is configured by containing a fluorine-based resin powder in the charge transport layer 92 that is the outermost layer of the photoconductor. A mechanism for applying a release agent (for example, calcium stearate) to the surface of 4 is provided inside the apparatus 2, and a release agent is applied to the surface of the photoreceptor 4 by such a mechanism to constitute a high release photoreceptor 4H. May be.

  When a plurality of high-release photoconductors 4H are used, high-release photoconductors 4H having different releasability may be used. In that case, these high-release photoconductors 4H are used as the intermediate transfer belt 30. It is preferable to arrange so that the part provided on the downstream side in the moving direction has higher releasability.

(Test 1)
Using 16 types of image forming apparatuses (apparatus 1 to apparatus 16) having different arrangements of the standard photoconductor and the high release photoconductor, images having vertical lines (width: 300 μm) of each color of yellow, magenta, cyan, and black are used. One sheet was printed and a test was conducted to confirm the occurrence of the void phenomenon.

  As the apparatus main body of the image forming apparatus, an apparatus main body common to all of the apparatuses 1 to 16 is used. As the yellow, magenta, cyan, and black photoconductors mounted on the respective apparatuses, standard photoconductors (FIG. 4) are used. Or “×” shown in FIG. 4 or a high release type photoconductor (“◯” shown in FIG. 4).

  As shown in FIG. 4, in the apparatus 1, standard photoconductors were used as all four photoconductors. In the devices 2 to 5, three standard photoconductors and one high release photoconductor were used. In the apparatuses 6 to 11, two standard photoreceptors and two high release photoreceptors were used. In the devices 12 to 15, one standard photoconductor and three high release photoconductors were used. In the apparatus 16, high release type photoconductors were used as the four photoconductors.

  As the standard photoconductor, a photoconductor having a contact angle of pure water to the surface of 90 °, a surface energy of 45 mN / m, and a surface friction coefficient of 0.6 was used. As the high-release photoconductor, a photoconductor having a contact angle of pure water with respect to the surface of 100 °, a surface energy of 35 mN / m, and a surface friction coefficient of 0.3 was used.

  To confirm the hollowing out phenomenon, the vertical line of each color printed with each device is used to observe the portion where the hollowing out phenomenon appears most prominently with a 10-fold magnifier, and to determine the rank of the hollowing out phenomenon. went. In the rank determination of the hollow out phenomenon, the optimum rank (0.5 unit) was determined in the range of rank 1 to rank 5 based on the determination criteria shown in FIG.

  Consider the results of Test 1.

  As shown in FIG. 4, in the device 16, since all four photoconductors are high-release photoconductors, the rank of the hollowing out phenomenon is 5 for any color, and no hollowing out phenomenon occurred. . This is because the apparatus 16 uses high-release photoconductors in all of the image forming units, and therefore, in each image forming unit, the transfer from the photoconductor to the intermediate transfer belt is performed well and the intermediate transfer belt performs photosensitivity. This is probably because reverse transcription to the body did not occur. However, since the device 16 uses four expensive high-release photoconductors, the cost of the image forming apparatus increases.

  On the other hand, in the apparatus 1 in which all four photoconductors are standard photoconductors, the rank of any color is lower than that of the high-release photoconductor, and when the ranks of the respective colors are compared, yellow (rank 2), magenta ( Rank 2.5), cyan (rank 3), black (rank 3.5) in this order. That is, the rank of the color where the photosensitive member is arranged on the upstream side is lower, and in particular, the rank of yellow and magenta is less than 3. This is because the standard photoconductor is used in all the image forming units in the apparatus 1, and reverse transfer from the intermediate transfer belt to the photoconductor occurs in each image forming unit except the yellow image forming unit at the most upstream portion. This is probably because the reverse transfer is more likely to occur in the color where the photoconductor is arranged on the upstream side.

  Next, apparatus 2 to apparatus 5 using one high release type photoconductor will be examined.

  Device 5 has a higher yellow rank than device 1 only, device 4 has a higher yellow and magenta rank than device 1, device 3 has a higher yellow, magenta, and cyan rank than device 1, and device 2 has all ranks. The color rank was higher than device 1. Thus, when the devices 2 to 5 were compared, good results were obtained in the order of the device 2, the device 3, the device 4, and the device 5. From this result, it was confirmed that when one high-release photoconductor is provided, the hollow-out phenomenon can be better prevented as the high-release photoconductor is disposed on the downstream side.

  As in the apparatus 1, the rank of yellow and magenta was low in the apparatus 5. This is probably because reverse transfer occurred in a plurality of downstream image forming units for the yellow toner image and the magenta toner image, as in the apparatus 1.

  As with the device 5, the devices 2 to 4 had a low yellow rank. In the devices 2 to 4, since the high-release photoconductor is used in any one of the image forming portions of magenta, cyan, and black, the yellow toner image is not reversely transferred to the high-release photoconductor. It is thought that there is nothing. However, since the yellow toner image is reversely transferred to the remaining two photoconductors excluding the yellow photoconductor and the high release type photoconductor, it is considered that the yellow rank is lowered.

  In the device 2, the rank of black was 5. This is presumably because the transfer performance of the black toner image was improved because the high-releasable photoconductor is used in the black image forming unit in the apparatus 2.

  Next, the devices 6 to 11 using two high release photoconductors will be examined.

  When the devices 6 to 11 are compared, the best result was obtained with the device 6 in which the two high-release photoconductors are arranged on the downstream side of the remaining two photoconductors. From this result, when two high release photoconductors are used, it can be confirmed that the degree of the hollowing out phenomenon can be reduced most by disposing the two high release photoconductors on the downstream side of the remaining two photoconductors. It was.

  Device 6 was one rank higher in yellow and magenta than device 1. This is because the apparatus 6 is provided with a high release type photoconductor in the cyan image forming portion and the black image forming portion, so that the yellow toner image and the magenta toner image transferred to the intermediate transfer belt are cyan. This is probably because reverse transfer does not occur when passing through the black image forming portion and the black image forming portion, and there are few opportunities for reverse transfer to occur.

  In the device 6, the rank of cyan and black is 5, which is significantly higher than that of the device 1. This is because the cyan toner image and the black toner image are satisfactorily transferred from the high-release photoconductor to the intermediate transfer belt, and after being transferred to the intermediate transfer belt, do not pass through the nip portion with the standard photoconductor. This is probably because reverse transcription does not occur.

  In the apparatus 11 in which two high-release photoconductors are arranged on the upstream side of the remaining two photoconductors, since the standard photoconductors are used in the cyan and black image forming units, the rank of cyan and black is the same as that of the apparatus 1. It was the same. Further, in the apparatus 11, the rank of magenta was not significantly higher than that of the apparatus 1. This is because when the magenta toner image transferred to the intermediate transfer belt passes through the nip portion of the cyan image forming portion with the photosensitive member and the nip portion of the black image forming portion with the photosensitive member, reverse transfer is performed. This is thought to be due to the occurrence. In device 11, the rank of yellow was one rank higher than that of device 1. This is because the yellow image forming portion is provided with a high-release photoconductor, which improves the transfer performance of the yellow toner image, and the magenta image forming portion is provided with a high-release photoconductor. When the yellow toner image transferred to the intermediate transfer belt passes through the nip portion with the photoconductor of the magenta image forming portion, reverse transfer does not occur, and there is less chance of reverse transfer compared with the apparatus 1. This is probably because of this.

  The device 9 in which the high release type photoconductors are arranged in the magenta and cyan image forming sections has a higher magenta and cyan rank than the device 11. The reason why the magenta rank is higher than that of the apparatus 11 is considered to be that the magenta toner image transferred to the intermediate transfer belt has less chance of reverse transfer than the apparatus 11, and the cyan rank is higher than that of the apparatus 11. The reason is considered to be that the cyan image forming portion was transferred well from the high-release photoconductor to the intermediate transfer belt.

  The device 7 in which the high release type photoconductors are arranged in the magenta and black image forming portions has a higher rank of magenta, cyan, and black than the device 11. The reason why the magenta and cyan ranks of the device 7 are higher than that of the device 11 is considered to be the same reason as that of the device 9 described above, and the reason why the black rank is higher than that of the device 11 is that the black image forming portion has a high separation. This is thought to be due to the good transfer from the mold photoconductor to the intermediate transfer belt.

  Finally, apparatus 12 to apparatus 15 using three high release photoconductors will be examined. When the devices 12 to 15 were compared, good results were obtained in the order of the device 12, the device 13, the device 14, and the device 15. From this result, it was confirmed that when three high-release photoconductors were used, the more the number of high-release photoconductors arranged on the downstream side than the standard photoconductor, the more the degree of hollowing out phenomenon could be reduced.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention. FIG. 4 is a cross-sectional view illustrating a circulation path of an intermediate transfer belt in a color mode. It is sectional drawing which shows the structure of a photoreceptor. 6 is a table showing the results of Test 1. It is a figure and table | surface which show the rank criteria of the hollow out phenomenon in Test 1.

Explanation of symbols

2: Image forming apparatus,
4: Electrostatic latent image carrier (photoconductor),
4N: Standard electrostatic latent image carrier (standard photoreceptor),
4H: high release electrostatic latent image carrier (high release photoconductor),
14: Transfer device (primary transfer roller),
18: Developing device (developing device),
30: Intermediate transfer belt.

Claims (8)

A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A developing device for supplying toner to the electrostatic latent image on the surface of the electrostatic latent image carrier to form a toner image;
An image forming apparatus comprising: a transfer device that transfers the toner image formed on the surface of the electrostatic latent image carrier to the intermediate transfer belt;
The plurality of electrostatic latent image carriers include a standard electrostatic latent image carrier having a predetermined releasability on the surface and a high releasability in which the surface releasability is higher than the surface of the standard electrostatic latent image carrier. Type electrostatic latent image carrier,
An image in which at least one high-release electrostatic latent image carrier is disposed downstream of at least one standard electrostatic latent image carrier in the moving direction of the intermediate transfer belt. Forming equipment.   2. The image forming apparatus according to claim 1, wherein the electrostatic latent image carrier disposed at the most downstream portion in the moving direction of the intermediate transfer belt is the high-release electrostatic latent image carrier. .   3. The high-separation type electrostatic latent image carrier in the moving direction of the intermediate transfer belt is disposed on the downstream side of the remaining electrostatic latent image carrier. The image forming apparatus described.   4. The surface releasability of the standard electrostatic latent image carrier and the high release electrostatic latent image carrier is higher than the surface releasability of the intermediate transfer belt. The image forming apparatus according to any one of the above.   The high release electrostatic latent image carrier has a contact angle of pure water to the surface of the electrostatic latent image carrier that is 5 ° to 25 ° larger than that of the standard electrostatic latent image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The high release electrostatic latent image carrier has a surface energy of 5 mN / m or less and 25 mN / m or less smaller than that of the standard electrostatic latent image carrier. The image forming apparatus according to claim 1.   The high-release electrostatic latent image carrier has a friction coefficient on the surface of the electrostatic latent image carrier that is smaller by 0.1 or more and 0.3 or less than that of the standard electrostatic latent image carrier. The image forming apparatus according to claim 1.   8. The electrostatic latent image carrier is a cylindrical photoconductor, and the surface layer of the high-release electrostatic latent image carrier contains a fluororesin. Image forming apparatus.

Images