JP2007232903A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily provide an image forming apparatus at a low cost, the image forming apparatus being designed so as to be compact and prevent toner from scattering in such a state that toner sticks to the leading end of a recording material. <P>SOLUTION: The image forming apparatus includes a guide part 17 that guides a recording material to a transfer area. The guide part 17 has a projection 18 formed on an upper guide member 17a and near a photosensitive drum 2. In addition, the underside of the upper guide member 17a, including the projection 18, is covered with a conductive sheet 19. This prevents toner from scattering. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a digital copying machine or a laser printer.

  The configuration of a conventional image forming apparatus is shown in FIGS. FIG. 4B is an enlarged view showing the flow of the recording material in the vicinity of the photosensitive drum 2 surrounded by a dotted line in FIG. In an image forming apparatus (for example, a printer) 1, when performing an image forming operation, a photosensitive drum 2 (image carrier) that rotates clockwise in the drawing is uniformly charged by a charging unit 3 and exposed based on document image data. An electrostatic latent image is formed on the photosensitive drum 2 by a laser beam from a unit (laser scanning unit or the like) 4, and a developer (hereinafter referred to as toner) is attached to the electrostatic latent image by the developing unit 5 to form a toner image. Is formed.

  The toner is supplied to the developing unit 5 from the toner container 6. The image data is transmitted from a personal computer (not shown) or the like. Further, a static elimination device (not shown) for removing residual charges on the surface of the photosensitive drum 2 is provided on the downstream side of the cleaning device 7.

  A recording material, which is a recording material, is guided from the paper feed cassette 8 to the guide portion 17 via the recording material supply path 9 and the registration roller 10 toward the photosensitive drum 2 on which the toner image is formed as described above. The toner image formed on the surface of the photosensitive drum 2 in the transfer area of the transfer roller 11 (transfer portion) is transferred to a recording material. The recording material onto which the toner image has been transferred is separated from the photosensitive drum 2 and conveyed to a fixing unit 12 having a fixing roller 12a to fix the toner image. The recording material that has passed through the fixing unit 12 is conveyed to the upper part of the apparatus by the recording material conveyance path 13, and is discharged from the recording material discharge port 15 onto the discharge tray 16 via the discharge roller 14.

  In such an image forming apparatus, while the recording material is being conveyed from the registration roller 10 to the transfer region of the transfer roller 11, the upper surface of the recording material may rub against the upper guide member 17a and be strongly charged. At this time, this charging causes a strong potential difference between the photosensitive drum and the recording material, and the toner on the photosensitive drum 2 is transferred to the leading end of the recording material before entering the transfer region.

  Further, when the space between the developing unit 5 and the upper guide member 17a is deleted to reduce the size and weight of the image forming apparatus and the developing unit 5 and the upper guide member 17a are brought close to each other, the photosensitive drum 2 and The above problem appears more prominently as the recording material front ends are closer.

Conventionally, as a method for solving this problem, for example, Patent Document 1 proposes that the bottom surface of the developing unit and the upper guide member are integrated to reduce the size and the guide member is made of a material having an antistatic effect. It was. Patent Document 2 proposes a method in which a conductive member is provided at a position between the guide member and the photosensitive drum, and a voltage having the same polarity as the toner is applied to the conductive member.
Japanese Patent Application Laid-Open No. 08-015936 Japanese Patent Laid-Open No. 10-171257

  However, as shown in Patent Document 1, when the developing unit and the guide member are integrated, since the photosensitive drum and the guide member are very close to each other, there is a possibility that the toner may still transfer even if charging of the recording material is prevented. . In addition, it is not realistic from the viewpoint of manufacturing cost to use a material having an antistatic effect for the guide member itself. In addition, when a device for applying a voltage is provided as in Patent Document 2, it is contrary to the downsizing of the image forming apparatus and the production cost is increased.

  Accordingly, in view of the above problems in the present invention, an object of the present invention is to provide an image forming apparatus that realizes downsizing of the image forming apparatus and prevents toner scattering from adhering to the front end of the recording material at a low cost.

  To achieve the above object, the configuration of the present invention includes an image carrier that carries a toner image, a developing unit that develops an electrostatic latent image of the image carrier into a toner image, and a toner image on the image carrier. In the image forming apparatus comprising a transfer portion that transfers the recording material to the recording material, and a guide portion that guides the recording material to the transfer portion, the guide portion has an upper guide member that guides the upper surface of the recording material. A protrusion is provided in the vicinity of the end of the guide member on the image carrier side, and the lower surface of the upper guide member including the protrusion is covered with a conductive sheet member.

  According to the present invention, in the image forming apparatus configured as described above, the protruding portion is provided over the entire width direction of the upper guide member, and the conductive sheet member is covered over the entire width direction of the upper guide member. .

  According to the present invention, in the image forming apparatus configured as described above, the protrusion is provided in the vicinity of the center in the width direction of the upper guide member, and the conductive sheet member is covered in the vicinity of the center in the width direction of the upper guide member. It is characterized by.

  According to the present invention, in the image forming apparatus configured as described above, the protruding portion is provided in the vicinity of a central portion in the width direction of the upper guide member, and the conductive sheet member is covered over the entire width direction of the upper guide member. And

  According to the present invention, in the image forming apparatus configured as described above, the developing unit is a magnetic one-component developing system.

  According to the first configuration of the present invention, the recording material is guided while being rubbed with the conductive sheet member covered with the upper guide member before entering the transfer region of the transfer portion. Thereby, charging of the upper surface of the recording material can be suppressed. Accordingly, since a slight potential difference is generated between the toner on the photosensitive drum and the recording material, the toner is not transferred to the recording material before the transfer region.

  Further, by providing a protrusion in the vicinity of the end of the upper guide member on the image carrier side, the leading end of the recording material comes into contact with the protrusion immediately before entering the transfer area of the transfer portion. At this time, by providing the protrusion with a certain thickness, the leading edge of the recording material can enter the transfer area as far away from the image carrier as the thickness. Thereby, it is possible to suppress the toner on the image carrier from transferring to the leading end of the recording material before the transfer area.

  Further, during the conveyance, the central portion of the recording material may be bent in a mountain, but the deflection is eliminated by the reaction of the recording material coming into contact with the protruding portion. As a result, the crest portion does not come close to the image carrier, and toner transfer can be suppressed. Further, the recording material can be smoothly conveyed.

  Further, according to the second configuration of the present invention, by providing the protruding portion and the conductive sheet base material in the entire width direction of the upper guide member, the recording material can be transferred smoothly while maintaining the distance from the image holding member. In addition, the charging rate of the recording material can be stably suppressed.

  Further, according to the third configuration of the present invention, the conductive sheet base material is maintained while maintaining the antistatic effect and the deflection preventing effect of the recording material only by covering the conductive sheet material in the vicinity of the central portion in the width direction of the upper guide member. The production cost can be reduced by reducing the amount of use.

  Moreover, according to the 4th structure of this invention, since the protrusion part is only provided in the width direction center part of an upper side guide member, when attaching a protrusion part externally, the cost of a protrusion part can be held down. In addition, by covering the entire width of the conductive sheet member, the step formed between the upper guide member and the protruding portion can be changed to a gently inclined surface. As a result, the leading end portion of the recording material can be smoothly guided to the transfer area of the transfer portion.

  According to the fifth configuration of the present invention, in the image forming apparatus employing the magnetic one-component developing system, the developing toner and the toner that is weakly attracted to the image carrier drips and adheres to the lower part of the developing unit. In some cases, like the above effect, the leading edge of the recording material can be separated from the developing unit by the thickness of the protruding portion and enter the transfer area of the transfer portion. As a result, the front end of the recording material is warped before entering the transfer area, and the toner is not picked up.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a cross-sectional view showing the overall configuration of the image forming apparatus according to the present invention. FIG. 1B is an enlarged view showing a portion surrounded by a dotted line in FIG. In addition, the same code | symbol is attached | subjected to the part which is common in FIG. 4 of a prior art example, and description is abbreviate | omitted.

  As shown in FIG. 1B, an upper guide member 17a and a lower guide member 17b are provided vertically so that the recording material fed from the registration roller 10 is reliably guided to the transfer roller 11. At this time, since the upper surface of the recording material is conveyed toward the transfer roller while rubbing against the lower surface of the upper guide member 17a, the recording material arriving near the transfer roller is strongly charged.

  Thereafter, the recording material is carried into a transfer region sandwiched between the photosensitive drum 2 and the transfer roller 11, where a voltage of reverse polarity is applied to the toner image formed on the photosensitive drum 2 to transfer the toner image.

  However, when the strongly charged recording material front end is conveyed to a position close to the photosensitive drum 2, a strong potential difference is generated between the recording material front end and the photosensitive drum 2. Due to this potential difference, a part of the toner image on the photosensitive drum 2 may be electrostatically attracted and transferred to the recording material front end before the recording material front end enters the transfer region and is transferred.

  The problem is that as the distance between the front end of the recording material and the photosensitive drum 2 becomes closer, the electric field becomes larger and the toner is more easily attracted to the recording material side.

  In an image forming apparatus that employs a one-component development system, the attracting force of toner carried on a development pull-back recording material liner or development drum is weakened, and the toner may hang down and adhere to the lower part of the development jaw or the development unit 5. is there. At this time, the tip of the conveyed recording material may bend upward and pick up the adhered toner.

  This problem becomes more prominent as the distance between the developing unit 5 and the guide portion 17 becomes closer, and the leading edge of the recording material and the toner adhesion portion approach each other.

  However, in order to reduce the size of the image forming apparatus, it is necessary to arrange the guide unit 17 and the photosensitive drum 2 and the developing unit 5 close to each other. Therefore, in order to solve the above problem, the guide portion 17 is disposed close to the photosensitive drum 2 and the developing unit 5 to prevent charging of the recording material in the conveyance process and to transfer the recording material being conveyed to the photosensitive drum 2. In addition, it is necessary not to be close to the developing unit 5.

  Next, a method for solving the above problem will be specifically described. FIG. 2A is a cross-sectional view showing the structure of the upper guide member 17a among the guide portions 17 provided vertically. 2B, 2C, and 2D are cross-sectional views of the upper guide member 17a viewed from the direction of the arrow x in FIG.

  As shown in FIG. 2A, the lower surface of the upper guide member 17 a is provided with a protrusion 18 that protrudes downward from the front end of the photosensitive drum 2, and the lower surface including the protrusion 18 is covered with a conductive sheet 19. ing.

  As a result, the recording material is conveyed and charged while being rubbed against the upper guide member 17a up to the vicinity of the photosensitive drum 2 (see FIG. 1B). However, when the lower surface of the upper guide member 17 a is covered with the conductive sheet 19, the recording material rubs against the conductive sheet 19, so that charging is greatly reduced. Therefore, even when the front end of the recording material comes close to the photosensitive drum 2 immediately before entering the transfer area, a potential difference hardly occurs between the front end of the recording material and the photosensitive drum 2. This eliminates the problem of toner adhesion at the front end of the recording material before the transfer area.

  Further, by providing a protrusion on the lower surface of the upper guide member 17a, the leading end of the recording material is guided by the upper guide member 17a and comes into contact with the protrusion 18 immediately before entering the transfer area. At this time, the leading end of the recording material is guided to a position separated from the photosensitive drum 2 by the thickness of the protrusion 18. As a result, even when a potential difference is generated between the recording material leading edge and the photosensitive drum 2, the toner on the photosensitive drum 2 is difficult to transfer to the recording material leading edge. Therefore, the problem of toner adhesion is further solved.

  In addition, in order to reduce the size and simplify the image forming apparatus, when the recording material is laterally conveyed by a single registration roller 10, the registration roller 10 sends out the recording material while supporting one point at the central portion of the recording material. At this time, the central portion of the recording material is bent in a mountain shape during the conveyance process, and the recording material may be strongly charged by being pressed against the lower surface of the upper guide member 17a.

  However, when the protrusion 18 is provided on the lower surface of the upper guide member 17a, the crest portion at the center of the recording material contacts the protrusion 18 during the conveyance of the recording material. This reaction eliminates the deflection of the recording material. As a result, it is possible to suppress the charging of the recording material and to prevent the paper jam and smoothly guide the recording material to the transfer area. Further, it is possible to prevent the peak portion at the center of the recording material from approaching the photosensitive drum 2.

  Next, the arrangement of the protrusions 18 and the covering range of the conductive sheet 19 on the lower surface of the upper guide member 17a will be described. In the traveling direction of the upper guide member 17a, the protrusion 18 may be disposed in the vicinity of the front end of the photosensitive drum, and is not limited to the front end of the photosensitive drum 2 as shown in FIG. Absent. This is because, due to the structure of the upper guide member 17a, when the protruding portion 18 cannot be provided at the tip position or when the recording material is warped upward, the tip portion of the upper guide member becomes an umbrella to prevent toner adhesion. It is.

  In order to prevent electrification, it is optimal to cover the conductive sheet 19 to the vicinity of the registration roller in the traveling direction of the upper guide member 17a. However, in order to reduce the manufacturing cost, it is sufficient to cover a portion where the recording material being conveyed contacts frequently.

  Further, the step formed between the protrusion 18 and the upper guide member 17 a can be changed to a gentle inclination by covering the protrusion 18 with the conductive sheet 19. Accordingly, the recording material front end can be smoothly conveyed without being caught by the step.

  Various arrangements of the projecting portions 18 and the arrangement ranges of the conductive sheets 19 in the width direction of the upper guide member 17a are conceivable as shown in FIGS. 2B, 2C, and 2D.

  In FIG. 2B, the protrusion 18 is provided in the entire width direction of the upper guide member 17a, and the conductive sheet 19 is covered in the entire width direction. Thereby, charging of the recording material is prevented, and the leading end portion of the recording material can be guided to a position away from the photosensitive drum 2 by the protrusion 18. Further, since the protrusions 18 are provided in the entire width direction, the flow of the recording material becomes smooth.

  Moreover, in FIG.2 (c), the protrusion part 18 and the electrically conductive sheet 19 are provided in the width direction center part vicinity of the upper side guide member 17a. In this case, the usage amount of the conductive sheet 19 can be reduced, and the manufacturing cost can be reduced. Further, since the protruding portion 18 is provided in the central portion, even when the central portion of the recording material is bent in a mountain shape, the protruding portion 18 comes into contact with the protruding portion 18 to suppress the deflection and the mountain portion is rubbed with the conductive sheet. It is possible to reduce the charging of the recording material. Moreover, when attaching the protrusion part 18 externally, the usage-amount of the protrusion part 18 can also be reduced.

  The widths of the conductive sheet and the protruding portion 18 do not need to be the same, and it is considered that the longer the conductive sheet 19 is than the width of the protruding portion 18, the better the recording material flow and adhesiveness.

  In FIG. 2D, a protrusion 18 is provided near the center in the width direction of the guide portion 17, and the conductive sheet 19 is covered over the entire width direction of the guide portion 17. In this case, the peak portion at the center of the recording material and the protruding portion 18 come into contact with each other, so that the deflection of the recording material tip can be suppressed and charging of the entire recording material can be reduced. Moreover, it is thought that the adhesiveness of the electrically conductive sheet 19 and the protrusion part 18 also increases.

  Next, the conductive sheet 19 will be described. The conductive sheet preferably has a low surface resistance in order to reduce charging of the recording material. Further, since the conductive sheet repeatedly rubs with the recording material being conveyed, the conductive sheet is preferably made of a material having excellent wear resistance and impact strength. In the present invention, an ultra high molecular weight polyethylene sheet (manufactured by Nitto Denko, 0.3 mm thickness) was used. Moreover, it is thought that the same effect is exhibited even if it uses a fluorine-type sheet | seat other than high molecular polyethylene for a conductive sheet.

  Next, the protrusion 18 will be described. FIG. 3 shows an embodiment of the present invention. A lumira (polyethylene terephthalate sheet) 21 having a certain thickness is used as a protruding portion, and is fixed to the lower surface of the upper guide member 17a via a double-sided tape 22b. In addition, a high-molecular polyethylene sheet 20 is used as a conductive sheet, and the upper guide member 17a is covered from above the Lumila 21 via a double-sided tape 22a. Reference numerals 23a and 23b are release papers for the respective double-sided tapes. By adhering the Lumira 21 by this method, it is not necessary to newly design the upper guide member 17a, and the protruding portion 18 can be easily provided later. Moreover, the protrusion part 18 does not need to be limited to Lumira, and the protrusion part 18 and the guide part 17 may be integrally formed.

  In the present embodiment, the conductive sheet covers only the lower surface of the upper guide member, but may cover the upper surface of the lower guide member. As a result, charging of both sides of the recording material can be prevented and toner scattering can be further suppressed. Further, the leading end of the recording material is not warped downward, and can be smoothly conveyed to the transfer area.

  Note that the configuration of the image forming apparatus of the present invention is not limited to the above-described embodiment, and the shape of the protruding portion, the position, the type of the conductive sheet, and the covering range do not depart from the spirit of the present invention. The range can be appropriately changed as necessary. Further, the transfer portion is not limited to the transfer roller method, and a transfer charger method, a transfer belt method, or the like can be adopted.

  The present invention can be used in an image forming apparatus such as a digital copying machine or a laser printer.

1 is a schematic cross-sectional view showing an overall configuration of an embodiment of the present invention and a schematic cross-sectional view showing a flow of a recording material in the vicinity of a transfer region of an image forming apparatus. It is a schematic sectional drawing which shows the upper side guide member in the image forming apparatus of embodiment of this invention. It is a schematic sectional drawing which shows the protrusion part in the image forming apparatus of embodiment of this invention. FIG. 6 is a schematic cross-sectional view showing an overall configuration of a conventional image forming apparatus and a schematic cross-sectional view showing a flow of a recording material in the vicinity of a transfer area of the conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 3 Charging unit 4 Exposure unit 5 Development unit 6 Toner container 7 Cleaning device 8 Paper feed cassette 9 Recording material supply path 10 Registration roller 11 Transfer roller (transfer part)
DESCRIPTION OF SYMBOLS 12 Fixing part 13 Recording material conveyance path 14 Discharge roller 15 Recording material discharge port 16 Discharge tray 17 Guide part 17a Upper guide member 17b Lower guide member 18 Projection part 19 Conductive sheet 20 Polymer polyethylene sheet 21 Lumira 22 Double-sided tape 22a Polymer Double sided tape for polyethylene recording material 22b Double sided tape for lumira 23 Release paper 23a Double sided tape release paper for high molecular polyethylene recording material 23b Double sided tape release paper for lumira

Claims (5)

An image carrier for carrying a toner image;
A developing unit for developing an electrostatic latent image on the image carrier into a toner image;
A transfer portion for transferring a toner image on the image carrier to a recording material;
In the image forming apparatus provided with a guide unit for guiding the recording material to the transfer unit,
The guide part has an upper guide member for guiding the upper surface of the recording material;
Protruding part is provided in the vicinity of the image carrier side end of the upper guide member,
An image forming apparatus, wherein the lower surface of the upper guide member including the protruding portion is covered with a conductive sheet member.   The image forming apparatus according to claim 1, wherein the protruding portion is provided over the entire width direction of the upper guide member, and the conductive sheet member is covered over the entire width direction of the upper guide member.   2. The image forming apparatus according to claim 1, wherein the protruding portion is provided in the vicinity of the center portion in the width direction of the upper guide member, and the conductive sheet member is covered in the vicinity of the center portion in the width direction of the upper guide member. .   The image forming apparatus according to claim 1, wherein the protruding portion is provided in the vicinity of a central portion in the width direction of the upper guide member, and the conductive sheet member is covered over the entire width direction of the upper guide member.   The image forming apparatus according to claim 1, wherein the developing unit is a magnetic one-component developing system.

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