JP6202813B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus.

Conventionally, as an image forming apparatus such as a copying machine or a printer using an electrophotographic system, there is a system using an intermediate transfer belt. In an intermediate transfer belt type image forming apparatus, a full-color image is formed through a primary transfer process and a secondary transfer process. In the primary transfer step, the toner image formed on the surface of the electrophotographic photosensitive member is transferred onto the intermediate transfer belt. By repeating this process for a plurality of color toner images, a plurality of color toner images are formed on the surface of the intermediate transfer belt. In the secondary transfer process, the plurality of color toner images are collectively transferred onto the surface of a transfer material such as paper. The toner image transferred onto the transfer material is then fixed by fixing means. Thereby, a full color image is obtained.
As the primary transfer member of the image forming apparatus, a transfer member such as a roller shape, a blade shape, or a brush shape is used. These transfer members are in contact with the back surface of the intermediate transfer belt at positions facing the photoconductor, and are used by applying a primary transfer voltage. For example, Patent Document 1 discloses a configuration in which a brush-like conductive fiber is brought into contact with the back surface of the intermediate transfer belt. Patent Document 2 discloses a configuration in which a pressing member using an elastic body is brought into contact with a back surface portion of an intermediate transfer belt.
In particular, the brush-like transfer member is composed of a conductive fiber group, and each of the fibers can contact the back surface of the intermediate transfer belt independently. Therefore, contact unevenness that occurs when a roller-like or blade-like transfer member is used is improved, and a more uniform contact with the back surface of the intermediate transfer belt is obtained. As a result, good transferability can be obtained, and image defects such as density unevenness generated in the primary transfer process can be satisfactorily suppressed.

JP-A-5-127546 JP 2007-156455 A

  However, even with a brush-like transfer member having excellent contact properties, the contact state with the intermediate transfer belt may become unstable depending on the attached state, and good transferability may not be obtained. In particular, if the upstream side of the brush-shaped transfer member is not sufficiently pressed against the intermediate transfer belt, a region that does not contact the intermediate transfer belt is generated on the upstream side of the brush-shaped transfer member, and the contact nip width is narrowed. The upstream contact state of the brush-shaped transfer member has a great influence on the primary transfer property, and therefore needs to be contacted particularly stably.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus for transferring a toner image using a brush-like transfer member, which can stabilize the contact state of the brush-like transfer member and can improve transferability. It is to be.

In order to achieve the above object, an image forming apparatus of the present invention includes:
An image carrier for carrying a toner image;
A belt rotatable in contact with the image carrier;
A transfer unit disposed opposite to the image carrier through the belt and transferring the toner image carried on the image carrier to the belt or a transfer material conveyed on the belt;
In an image forming apparatus having
The transfer unit includes a brush-like transfer member including a plurality of conductive fibers that contact the belt and a substrate that holds the plurality of fibers, and presses the brush-like transfer member toward the belt. A pressing member,
The pressing member is made of an elastic body,
In the rotational direction of the belt, the upstream end of the brush-shaped transfer member is located upstream of the contact area between the image carrier and the belt, and is on the pressing surface that presses the substrate of the pressing member. the upstream end is characterized in that located at the end by remote upstream position of the upstream side in the brush-like transfer member positioned upstream of the contact region.

  According to the present invention, in an image forming apparatus that transfers a toner image using a brush-shaped transfer member, it is possible to stabilize the contact state of the brush-shaped transfer member and improve transferability.

1 is a schematic sectional view of an image forming apparatus according to Embodiment 1 of the present invention. Configuration diagram of a brush-like transfer member in Embodiment 1 of the present invention The perspective view of the press member in Example 1 of this invention FIG. 5 is an arrangement relation diagram of each part of the primary transfer portion in the first embodiment of the present invention. The figure of the comparative example in Example 1 of this invention Configuration diagram in Embodiment 1 of the present invention Configuration diagram of Embodiment 2 of the present invention The perspective view of the press member in Example 2 of this invention, and the figure which shows a hardness measurement position The figure of the hardness of the pressing member in Example 2 of the present invention

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

Example 1
[1. Overall configuration of image forming apparatus]
FIG. 1 is a schematic cross-sectional view illustrating a schematic configuration of an image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus 100 according to the first exemplary embodiment is an electrophotographic full color laser beam printer. The image forming apparatus 100 is of a tandem type using an intermediate transfer method. That is, the image forming apparatus 100 performs primary transfer by sequentially superimposing the toner images of the respective colors formed on the respective image carriers on the intermediate transfer body in accordance with the image information separated into a plurality of color components, and then transferring the toner image. A recorded image is obtained by performing a secondary transfer collectively.

  The image forming apparatus 100 includes first, second, third, and fourth stations Sa, Sb, Sc, and Sd as a plurality of image forming units. In the first embodiment, the first to fourth stations Sa to Sd are for forming toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). . There are many common parts in the configuration and operation of the stations Sa to Sd. Therefore, in the following, when it is not necessary to distinguish, subscripts a, b, c, and d for indicating an element provided for any color will be omitted.

The image forming apparatus 100 includes a photosensitive drum 1 (image carrier) in the station S. The photosensitive drum 1 is rotationally driven in a direction indicated by an arrow R1 (counterclockwise) by a driving unit (not shown). The surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, the exposure device 3 irradiates the photosensitive drum 1 with laser light L according to the image information, and an electrostatic latent image is formed. When the surface of the photosensitive drum 1 further advances in the direction of the arrow R1 shown in the figure, the latent image formed on the photosensitive drum 1 according to the image information is visualized as a toner image by the developing device 4. The developing device 4 develops the latent image on the photosensitive drum 1 by a reversal development method. That is, the developing device 4 develops a toner (negative polarity) charged with the same polarity as the charged polarity (negative polarity) of the photosensitive drum 1 on the uniformly charged image portion (exposure portion) on the photosensitive drum 1. I do.

  An intermediate transfer belt 6 (belt) as an intermediate transfer member is disposed downstream of the development position in the moving direction of the surface of the photosensitive drum 1 (in the direction of rotation of the photosensitive drum 1) indicated by an arrow R1 in the drawing. The intermediate transfer belt 6 is a cylindrical and endless belt-like film stretched around three rollers: a driving roller 61, a secondary transfer counter roller 62, and a tension roller 63. The intermediate transfer belt 6 is rotated in the direction indicated by the arrow R3 (clockwise) at substantially the same speed as the moving speed of the surface of the photosensitive drum 1 by driving the drive roller 61 in the direction indicated by the arrow R2 (clockwise). It is configured to be possible.

  A primary transfer unit is disposed at a position facing the photosensitive drum 1 with the intermediate transfer belt 6 interposed therebetween. The primary transfer means includes a brush-like transfer member, a pressing member, and an urging means, and each member will be described later. The primary transfer portion B1 is formed by the contact between the photosensitive drum 1 and the intermediate transfer belt 6. Along with the rotation of the photosensitive drum 1 and the intermediate transfer belt 6, the toner image formed on the photosensitive drum 1 is primarily transferred onto the outer peripheral surface of the intermediate transfer belt 6 by the action of the brush-like transfer member 5. At this time, a primary transfer voltage 16 is applied to the brush-like transfer member 5 by a primary transfer voltage 16 having a polarity (positive polarity) opposite to the charging polarity (negative polarity) of the toner.

  Residual toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 6 in the primary transfer process is cleaned by the photosensitive drum cleaner 7. The photosensitive drum cleaner 7 includes a cleaning blade 71 that is a plate-like elastic body that contacts the surface of the photosensitive drum 1. The photosensitive drum cleaner 7 includes a toner container 72 that collects toner removed from the surface of the photosensitive drum 1 by the cleaning blade 71.

  The charging, exposure, development, and primary transfer processes as described above are sequentially performed from the upstream side in the movement direction of the surface of the intermediate transfer belt 6 in each of the yellow, magenta, cyan, and black colors at the first to fourth stations Sa to Sd. Do about. As a result, a full-color image in which toner images of four colors of yellow, magenta, cyan, and black are superimposed on the intermediate transfer belt 6 is formed.

  A secondary transfer roller 8 as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 62 with the intermediate transfer belt 6 interposed therebetween. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6 to form a secondary transfer portion B2 (nip portion) where the intermediate transfer belt 6 and the secondary transfer roller 8 are in contact with each other. The toner image on the intermediate transfer belt 6 is secondarily transferred onto the transfer material P by the action of the secondary transfer roller 8. That is, in the transfer material supply unit 20, the transfer material P accommodated in the cassette 21 is sent out by the supply roller 22, and then the secondary transfer in which the intermediate transfer belt 6 and the secondary transfer roller 8 come into contact with each other by the registration roller 23. It is supplied to the part B2 at a predetermined timing. At substantially the same time, a secondary transfer voltage having a polarity (positive polarity) opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 8 by the secondary transfer power supply 80.

  A cleaning blade 64 is disposed at a position facing the driving roller 61 with the intermediate transfer belt 6 interposed therebetween. The cleaning blade 64 comes into contact with the intermediate transfer belt 6 and collects transfer residual toner remaining on the intermediate transfer belt 6 without being transferred to the transfer material P in the secondary transfer process.

The transfer material P onto which the toner image has been transferred is conveyed to a fixing device 9 as a fixing unit, where the toner image on the transfer material P is melted, mixed, and fixed, and then a full-color image formed product (print, copy). Are discharged to the outside of the image forming apparatus 100.

  The image forming apparatus 100 can form a single-color or multi-color image by forming an image only in a desired single or plural (not all) image forming units S.

  The image forming apparatus according to the present exemplary embodiment is a printer compatible with A4 size paper with a process speed of 100 mm / sec.

[2. Brush-like transfer member]
FIG. 2 is a schematic view (perspective view) of the configuration of the brush-like transfer member 5 in the present embodiment. As the brush-like transfer member 5, a brush in which conductive fibers are densely arranged can be used. Specifically, it has a raised portion made of the conductive fiber 5α and a substrate 5β on which the root of the conductive fiber 5α is fixed (held). The dimension W of the brush-like transfer member 5 in the short direction (direction parallel to the movement (rotation) direction of the intermediate transfer belt) is W = 4 mm. The dimension L in the longitudinal direction of the brush-like transfer member 5 (the direction perpendicular to the movement (rotation) direction of the intermediate transfer belt) is L = 250 mm. Among them, the conductive fiber 5α is provided in the substrate 5β in the region of K = 230 mm (raised portion), and the portions where the fibers are not provided at both longitudinal ends (non-raised portion K0) Are uniformly provided with a width of 10 mm. By setting W = 4 mm, a nip having a sufficient width (described later) can be formed between the intermediate transfer belt and by setting K = 230 mm, an image having a sufficient width with respect to the width of A4 paper can be obtained. Formation can be performed.

  Here, the upstream end shape of the raised portion (K = 230) will be described. The upstream end portion of the brush-like transfer member 5 is formed in a substantially linear shape over the longitudinal direction. As the method, for example, a blade member made of metal or the like is heated to at least a temperature at which conductive fibers, which will be described later, can be welded, and then contacted and pressed to the raised portion (to partially melt the raised portion). There is. In this embodiment, the device is created using the above-described device. However, a device using another method may be used as long as the device can form a similar shape. For example, the roll member may be heated to at least a temperature at which the conductive fibers can be welded, and contacted and pressed to the raised portions to be welded, or the blade member or roll member may be vibrated at a high frequency to A method of welding by contact and pressing may be used. Further, the raised portions may be formed in a substantially linear shape by, for example, a cutting process instead of the welding process.

  In addition, as the brush-shaped transfer member 5, a pile fabric type or an electrostatic flocking type can be used. Pile fabric is made by weaving pile yarn that becomes brush fibers into the gap between the base fabric consisting of warp and weft, and bonding this onto the substrate with a conductive adhesive or the like makes the brush-like transfer member can get. Electrostatic flocking is a method in which short fibers are cast almost vertically onto a substrate on which an adhesive has been applied in advance, using electrostatic attraction in a high-voltage electrostatic field. This also provides a brush-like transfer member. It is done. When manufacturing with electrostatic flocking, masking is performed and fibers are planted at the necessary site. At the upstream end, the upstream portion is made substantially linear by making the masking shape substantially linear. Can be formed.

Examples of the conductive fiber 5α include a material made of nylon or polyester in which carbon powder is dispersed, and a material in which a conductive material such as carbon is encapsulated in nylon or polyester. Moreover, what has arrange | positioned or covered electrically conductive materials, such as carbon, on outer peripheral surfaces, such as nylon and polyester, is mentioned. Moreover, it is preferable to use one having a single yarn fineness of 2 to 15 dtex [dtex: indicates mass (unit of gram) per 10000 meters of short fibers], a diameter of 10 to 40 μm, and a dry strength of 1 to 3 cN / dtex. it can. The fiber resistivity ρfiber is preferably in the range of 10 to 10 ⁸ Ωcm. The resistivity ρfiber is measured by the following method. That is, 50 fibers are made into one bundle, and a metal probe is brought into contact with the surface of the bundle at an interval of about 1 cm. Then, using a high resistance meter Advantest R8340A or the like, the resistance value Rfiber is measured under an applied voltage of 100 V, and the resistivity ρfiber is calculated by the following equation.
ρfiber = Rfiber × (fiber diameter / 2) ² × 3.14 × 50 ÷ 1.0

The conductive fiber 5α is fixed to the stainless steel substrate 5β and is raised in a direction perpendicular to the substrate (normal direction). In the brush-like transfer member in a non-contact state, the direction in which the fibers extend from the substrate surface is referred to as a raised direction. The fiber length starting from the substrate of each fiber can be 1 to 5 mm, and the arrangement density on the substrate can be 5000 to 50000 pieces / cm ² . In this embodiment, the fiber length is 2 mm, which is half of 4 mm of the dimension W of the base 5β. When the fiber length is short with respect to the dimension W as in the present embodiment, the amount of falling down of the conductive fibers 5α following the belt is reduced, and the conductive fibers 5α are stably brought into contact with the intermediate transfer belt. It is possible.

In addition, as a brush-shaped transfer member in a present Example, the brush of the following specification is used as what has a typical characteristic.
<Specifications of brush-like transfer member>
-Material type: Pile fabric-Material: Nylon fiber with carbon powder dispersed-Single yarn fineness: 7 dtex
・ Fiber diameter: 28μm
Dry strength: 1.6 cN / dtex
・ Resistivity: 10 ⁶ Ωcm
・ Fiber length: 2mm
Array density: 10850 / cm ²

  The brush-like transfer member 5 is brought into contact with the back surface of the intermediate transfer belt 6 at a position facing the photosensitive drum 1 on the intermediate transfer belt. The diameter of the photosensitive drum 1 is 20 mm. Further, a primary transfer voltage of 0 to 1.0 kV can be applied to the brush-like transfer member 5 from the primary transfer power supply 16.

[3. Intermediate transfer belt]
As the intermediate transfer belt 6, a polyimide resin film having a thickness of 60 μm and a volume resistivity adjusted to 10 ⁹ Ωcm by mixing a conductive agent can be used. The intermediate transfer belt 6 is stretched around three axes of a drive roller 61, a secondary transfer counter roller 62, and a tension roller 63, and a tension of about 20 N is applied to the intermediate transfer belt 6 by the tension roller 63.

  Further, an intermediate transfer belt cleaner 65 having a cleaning blade 64 which is a plate-like elastic body is provided on the surface of the intermediate transfer belt 6 as a cleaning member for removing attached toner. The toner removed from the surface of the intermediate transfer belt by the cleaning blade 64 is collected in the toner container 66.

[4. Secondary transfer roller]
As the secondary transfer roller 8, an elastic roller having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm and a hardness of 30 ° to 40 ° can be used. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6 with a total pressure of about 39.2N. Further, the secondary transfer roller 8 is driven to rotate as the intermediate transfer belt 6 rotates. Further, a secondary transfer voltage of 0 to 4.0 kV can be applied to the secondary transfer roller 8 from a secondary transfer power supply 80.

[5. Pressing member]
A pressing member for pressing the brush-like transfer member 5 against the intermediate transfer belt 6 will be described with reference to FIG. FIG. 3 is a perspective view of the pressing member 50 and its size.

  In this embodiment, the pressing member 50 is formed of urethane foamed sponge-like elastic body (foamed sponge body), and has a thickness (t1) of 2 mm, a width (w1) of 6 mm, and a longitudinal length (l1) of 230 mm. An approximately rectangular parallelepiped shape was used. The width (w1) is the length in the direction along the movement (rotation) direction of the intermediate transfer belt 6, and the longitudinal length (l1) intersects the movement (rotation) direction of the intermediate transfer belt 6 (in this embodiment). It is the length along the direction of (substantially orthogonal). Accordingly, the pressing member 50 is formed as a substantially rectangular parallelepiped pad having a substantially rectangular cross section. By forming such a pressing member 50 with an elastic body and pressing the brush-like transfer member 5 against the intermediate transfer belt 6, the surface of the brush-like transfer member 5 can follow the back surface of the intermediate transfer belt 6. As a result, uniform contact between the brush-like transfer member 5 and the intermediate transfer belt 6 is ensured, and transfer defects due to contact unevenness in the longitudinal direction between the brush-like transfer member 5 and the intermediate transfer belt 6 are prevented. Can be prevented.

In this example, the resistance value of the pressing member 50 was 4 × 10 ⁷ Ω when 500 V was applied. In this example, the hardness of the pressing member 50 was 30 ° in Asker C (500 gf). In addition, it is preferable that the hardness of the pressing member 50 is 40 degrees or less in Asker C (500 gf).

[6. Positional relationship between pressing member and brush-like transfer member]
With reference to FIG. 4, the positional relationship between the brush-like transfer member 5 and the pressing member 50 for pressing it against the intermediate transfer belt 6 will be described. FIG. 4 is a schematic cross-sectional view showing a schematic configuration of the primary transfer portion. Among them, a region formed by the brush-like transfer member 5 and the pressing member 50, and further, the brush-like transfer member 5, the photosensitive drum 1, and the intermediate transfer belt 6 are formed. The positional relationship is shown. The upper surface (pressing surface) of the pressing member 50 is configured to support (press) the lower surface of the substrate β of the brush-like transfer member 5. The pressing surface is a surface that is substantially parallel to the intermediate transfer belt 6 in the primary transfer, that is, a substantially parallel surface.

  In FIG. 4, A indicates a contact area between the intermediate transfer belt 6 and the photosensitive drum 1 in the moving (rotating) direction of the intermediate transfer belt 6. B is the upstream end (contact start end) of the contact area between the intermediate transfer belt 6 and the brush-like transfer member 5 in the moving (rotating) direction of the intermediate transfer belt 6, and C is the intermediate transfer belt 6 and the brush. The downstream end (contact end) of the contact area with the shape transfer member 5 is shown.

  In this embodiment, on the upstream side in the moving direction of the intermediate transfer belt 6, the upstream end Bj of the brush-like transfer member 5 is located at a position B 0 that is out of the contact area A between the intermediate transfer belt 6 and the photosensitive drum 1. . Also on the downstream side, the downstream end Bk of the brush-like transfer member 5 is located at a position outside the contact area A between the intermediate transfer belt 6 and the photosensitive drum 1. Then, in order to press the brush-like transfer member 5 against the intermediate transfer belt 6, it is pressed with a force F using a pressure spring 51.

  On the upstream side of the brush-shaped transfer member 5, the end position Pj (of the pressing surface) of the pressing member 50 is disposed at the same position as the upstream end Bj of the brush-shaped transfer member 5. On the other hand, on the downstream side of the brush-shaped transfer member 5, the end position Pk (of the pressing surface) of the pressing member 50 is disposed at the same position as the downstream end Bk of the brush-shaped transfer member 5.

In the moving direction of the intermediate transfer belt 6, the contact start end B between the intermediate transfer belt 6 and the brush-like transfer member 5 is located outside the contact area A between the photosensitive drum 1 and the intermediate transfer belt 6. Yes. The contact end C between the intermediate transfer belt 6 and the brush-like transfer member 5 is located outside the downstream side of the contact area A between the photosensitive drum 1 and the intermediate transfer belt 6. The pressing member 50 is also arranged so as to have the same positional relationship as the brush-like transfer member 5.

In this embodiment, the primary transfer power supply 16 is connected to the brush-like transfer member 5 and a voltage of 500 V is applied as a representative value during the image forming operation. Further, in this embodiment, the pressing member 50 is pressed against the brush-like transfer member 5 toward the photosensitive drum 1 (that is, toward the intermediate transfer belt 6) by a pressurizing spring 51 as an urging means (ie, toward the intermediate transfer belt 6). Pressed).
As described above, the pressing member 50 presses the brush-like transfer member 5 in order to cause the brush-like transfer member 5 to follow the intermediate transfer belt 6. Further, since the pressing member 51 needs to follow the pressing member itself to some extent, the pressing member 51 is formed of an elastic body in this embodiment, but it is necessary to uniformly transmit the pressing force of the pressing spring 51 to the brush-like transfer member 5. Therefore, a certain degree of hardness is required with respect to the applied pressure. As shown in FIG. 4, the pressing member 51 is longer than the pressing spring 51 in the direction parallel to the belt rotation direction, and can appropriately apply pressure to the brush-like transfer member 5.

[7. Action]
With reference to FIGS. 5a and 5b, the difference in the contact state with the intermediate transfer belt 6 on the upstream side of the brush-like transfer member 5 due to the difference in configuration will be described, and the operation due to these differences will be described.

  FIG. 5 a shows a configuration of a comparative example of this embodiment. As a difference from FIG. 4, there is a region D where the brush-like transfer member 5 is not in contact with the intermediate transfer belt 6. The amount of protrusion Bh that is not in contact is 1.0 mm upstream. In this embodiment, the pressing member 50 has a substantially rectangular parallelepiped shape, and the brush-like transfer member 5 is also substantially linear in the longitudinal direction. Therefore, the brush-like transfer member 5 is an area where the upstream side is not in contact with the longitudinal direction uniformly. D is present.

  FIG. 5 b shows an important configuration of the present embodiment. In order to eliminate the region D in which the brush-like transfer member 5 is not in contact with the intermediate transfer belt 6, the upstream end portion and the position of the brush-like transfer member 5 are positioned. It is a figure which shows the structure which extended the upstream edge part of the press member 50 so that may be arranged. Specifically, it is a diagram of a configuration extended by 1.0 mm.

  The upstream transfer electric field formed with the bias applied at the primary transfer portion varies depending on whether or not the upstream transfer region of the brush-like transfer member 5 is in contact with the intermediate transfer belt 6 or the contact state. As a result, the reproducibility of the toner image when the toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 6 is different. That is, by controlling the contact state of the upstream portion of the brush-shaped transfer member 5, the transfer electric field formed between the photosensitive drum 1 and the intermediate transfer belt 6 and the brush-shaped transfer member 5 can be controlled.

  When the non-contact region D exists on the upstream side as shown in the cross-sectional view of the primary transfer portion in FIG. 5 a, the brush-like transfer member 5 is caused by a minute undulation or the like of the upstream end portion of the brush-like transfer member 5. There may be a region that does not contact the intermediate transfer belt 6. In this non-contact area D, the distance between the intermediate transfer belt 6 and the brush-like transfer member 5 cannot be controlled, so that the amount of the non-contact area D in the non-contact area D is different (intermediate transfer belt 6 and Non-contact distance with the tip of the brush-like transfer member 5). In such a case, the transfer electric field due to the primary transfer bias formed by the difference in the amount of the non-contact area D (non-contact distance between the intermediate transfer belt 6 and the tip of the brush-like transfer member 5) becomes non-uniform in the longitudinal direction. End up. The non-uniformity of the transfer electric field appears on the intermediate transfer belt 6 in the form of potential unevenness (about several tens [V]), and as a result, the toner image on the photosensitive drum is disturbed and the toner image is blurred. So-called scattering) and density unevenness occur.

On the contrary, as shown in FIG. 5b, when the non-contact area D does not exist, the abnormal transfer electric field as described above can be suppressed or eliminated, so that the toner image is blurred (so-called scattering or density unevenness). Can be suppressed. That is, as shown in FIG. 5 b, the upstream end Bjt of the brush-like transfer member 5 is aligned with the upstream end Pjt of the pressing member 50, so that the upstream side of the brush-like transfer member 5 is securely attached to the intermediate transfer belt 6. And the occurrence of image defects can be suppressed.

  In the first to fourth image forming portions Sa to Sd, the upstream end portion of the pressing member 50 and the upstream end portion of the brush-like transfer member 5 are combined in the first to fourth image forming portions Sa to Sd, respectively. Can be obtained at

[8. Evaluation]
In order to investigate the effect of this embodiment (FIG. 5b), using the image forming apparatus 100 with a process speed of 100 mm / sec, together with the comparative example shown below, after the initial and 100k sheets have passed, uneven density in the longitudinal direction, scattering, The peel discharge trace was evaluated. In the comparative image forming apparatus shown below, the upstream end of the pressing member 50 and the upstream end of the brush-like transfer member 5 in the first to fourth image forming portions Sa to Sd have the same configuration. Have.

(Comparative example)
In the comparative example, as shown in FIG. 5 a, the upstream end of the pressing member 50 is located downstream of the upstream end of the brush-like transfer member 5 (that is, the upstream side of the brush-like transfer member 5 protrudes from the pressing member 50. ) Is in the state.
(Evaluation results)
The evaluation results are shown in Table 1. Here, the evaluation was performed by paying attention to scattering on the intermediate transfer belt 6 in the longitudinal direction and density unevenness in an 80% printed halftone image. Further, the paper passing durability test was performed with a 4024 basis weight of 75 g / m ² manufactured by Xerox, and an image after passing 100 k sheets was evaluated. Here, k represents 1000 sheets.
(Table 1)

  In this example, both scattering and density unevenness were good from the initial stage until 100 k sheets were passed. In the comparative example, the upstream end portion of the pressing member 50 is arranged on the downstream side of the upstream end portion of the brush-like transfer member 5. For this reason, since the non-contact area described above exists, an abnormal transfer electric field formed between the brush-like transfer member 5 and the photosensitive drum 1 causes a region on the photosensitive drum 1 from the contact area B to the brush upstream end Bjt. The toner image was scattered on the intermediate transfer belt 6. Further, density unevenness having a low density occurred in an 80% printed image. Further, in the latter half of the endurance, the tip of the hair of the brush-like transfer member 5 slightly fell to the downstream side, so that a space in the upstream portion was increased and the image was slightly deteriorated.

  As described above, according to the present embodiment, the brush-shaped transfer member 5 is placed on the back surface of the intermediate transfer belt 6 by aligning the upstream end position of the pressing member 50 with the upstream end of the brush-shaped transfer member 5. Can be contacted steadily. As a result, an abnormal transfer electric field that occurs in a non-contact area can be suppressed, image defects such as scattering can be prevented, and more stable and better transfer performance can be obtained.

(Example 2)
An image forming apparatus according to a second embodiment of the present invention will be described with reference to FIGS. The image forming apparatus according to the present embodiment is the same as the image forming apparatus according to the first embodiment (FIG. 1) in terms of the overall configuration of the apparatus. However, there is a new feature in the contact position configuration of the pressing member 50 and the brush-like transfer member 5. Note that matters not specifically described here are the same as those in the first embodiment. The same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof is omitted.

  FIG. 6 is a diagram showing a positional relationship with each member in the primary transfer portion in the present embodiment. The upstream end position Pjt of the pressing member 50 of the image forming apparatus according to the present embodiment is configured to protrude further upstream than the upstream end Bjt of the brush-like transfer member 5. As described in the first embodiment, the pressing member 50 is formed of a urethane foamed sponge-like elastic body (foamed sponge body), and has a thickness (t1) of 2 mm, a width (w1) of 6 mm, and a longitudinal length ( l1) A substantially rectangular parallelepiped shape of 230 mm is used. Since such a pressing member 50 is an elastic body, the hardness of the end portion tends to be lower than that of the central portion. This tendency shows that the same elastic body exists in the vicinity of the central part, and even if the central part is deformed, the elastic body in all directions in the periphery is in a state of supporting, so the hardness decreases. There is almost no. On the other hand, when the end portion is deformed, since the elastic body has only an elastic body in a predetermined direction, the hardness tends to be apparently lower because the elastic body is not supported in all directions like the central portion. There is.

  FIG. 7 a is a perspective view of the pressing member 50, and shows a cross-sectional position S that is cut to measure the hardness. FIG. 7 b shows the state of hardness in the cut section S from position A to position B. In this embodiment, a product having a hardness of Asker C (500 gf) and 30 ° is used as the elastic body. As can be seen in FIG. 7b, the hardness of the central portion C is the target 30 °, but as described above, the hardness of the end portions A and B is 27 °. The hardness is 29 ° between the central portion C and the end portion A, that is, at a position 1.5 mm from the end portion, and between the central portion C and the end portion B, that is, at a position 1.5 mm from the end portion. Although slightly lower than the central portion, the brush-like transfer member 5 can be firmly pressed even if this position is set as the end portion position of the pressing member 50, and the upstream portion between the intermediate transfer belt 6 and the pressing member 50 There is no gap. Therefore, in the present embodiment, the upstream end portion of the pressing member 50 protrudes more than the upstream end portion of the brush-like transfer member 5 (1.5 mm in this embodiment) so that the hardness is higher than that in the first embodiment. It becomes possible to produce. As a result, the brush-like transfer member 5 and the upstream portion of the intermediate transfer belt 6 can be brought into a more stable contact state. As a result, the generation of an abnormal electric field on the upstream side of the brush-like transfer member 5 can be further prevented, and better primary transferability than that of Example 1 can be obtained.

  As described above, in this embodiment, the configuration of the primary transfer unit in the tandem type full-color image forming apparatus using the intermediate transfer method using the intermediate transfer belt 6 has been described. However, even with a rotary type full-color image forming apparatus using one photosensitive drum, good transferability can be obtained by the configuration of the present invention.

  Further, as an image forming apparatus of a type in which the brush-like transfer member 5 is brought into contact with the image carrier via the intermediate transfer belt 6, an image forming apparatus having another configuration can be considered. For example, there is a full color image forming apparatus that sequentially transfers toner images on a plurality of photosensitive drums onto a transfer material conveyed on a transfer material conveyance belt. Also in this case, it is possible to obtain good transferability by the configuration of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (image carrier), 5 ... Brush-like transfer member, 6 ... Intermediate transfer belt (belt), 50 ... Pressing member, 16 ... Primary transfer power supply

Claims (10)

An image carrier for carrying a toner image;
A belt rotatable in contact with the image carrier;
A transfer unit disposed opposite to the image carrier through the belt and transferring the toner image carried on the image carrier to the belt or a transfer material conveyed on the belt;
In an image forming apparatus having
The transfer unit includes a brush-like transfer member including a plurality of conductive fibers that contact the belt and a substrate that holds the plurality of fibers, and presses the brush-like transfer member toward the belt. A pressing member,
The pressing member is made of an elastic body,
In the rotational direction of the belt, the upstream end of the brush-shaped transfer member is located upstream of the contact area between the image carrier and the belt, and is on the pressing surface that presses the substrate of the pressing member. end of the upstream side, an image forming apparatus, characterized in that located at the end portion by remote upstream position of the upstream side in the brush-like transfer member positioned upstream of the contact region.   The image forming apparatus according to claim 1, wherein the pressing surface is a surface substantially parallel to the belt.   3. The image forming apparatus according to claim 1, wherein the substrate of the brush-shaped transfer member has a length in a rotation direction of the belt longer than a length of the fiber in a raising direction. 4.   The brush-like transfer member is a weave-shaped brush-like transfer member formed by weaving in a gap between a base fabric made of warp and weft. Image forming apparatus.   The image forming apparatus according to claim 4, wherein the brush-shaped transfer member is configured so that an upstream side in the rotation direction of the belt is substantially linear by welding or cutting the plurality of fibers.   The brush-like transfer member is an electrostatic flocking-type brush-like transfer member formed by using an electrostatic attraction force in an electric field and casting the fibers substantially vertically on a substrate to which an adhesive has been applied in advance. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 6, wherein the brush-shaped transfer member is configured to be substantially linear on the upstream side in the rotation direction of the belt by masking the substrate. The image forming apparatus according to any one of claims 1 to 7, characterized in that it has a biasing means for biasing towards the pressing member in the brush-like transfer member. The image forming apparatus according to any one of claims 1 to 8, characterized in that it comprises a transfer power source for applying a voltage to the brush-like transfer member. The elastic body, an image forming apparatus according to any one of claims 1 9, characterized in that a foamed sponge body.

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