JP3256000B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electronic copying machine, a printer, a facsimile, and the like, and more particularly, to an improvement in a transfer sheet guiding means provided between a transfer section and a fixing section. It is.

[0002]

2. Description of the Related Art Generally, an image forming apparatus of this type includes an electrostatic latent image carrier constituted by a rotating drum or the like having a photosensitive layer formed on a surface thereof, and is charged along a moving direction of the carrier. Section, an exposure section, a development section and a transfer section in that order, and after charging the surface in the charging section, in the exposure section, the surface of the carrier was exposed to form an electrostatic latent image of image information. Thereafter, in the developing section, the toner image is developed by attaching the charged toner on the latent image, and further in the transfer section, the toner image is transferred to a transfer sheet. The toner image is fixed by heating and pressing.

The transfer section is provided with a charge supply means to which a transfer voltage having a polarity opposite to that of the charged toner forming the toner image is applied at a position facing the electrostatic latent image carrier,
A sheet transport path is set so that the transfer sheet moves between the charge supply unit and the carrier in the moving direction of the carrier. Then, the transfer sheet passing through the sheet conveyance path moves while contacting the surface of the carrier, and at this time, the charged toner attached to the surface of the carrier is suctioned by the transfer voltage applied to the charge supply means, and the sheet is transferred. The transfer is performed by transferring to the upper side.

As the fixing means, a fixing roller which heats a sheet and a pressure roller which presses the sheet between the fixing roller and the fixing roller are disposed vertically, and the fixing means is widely used. In the above-described apparatus, a guide means whose upper surface functions as a sheet guide surface is disposed between the nip portion of the roller pair and the carrier.

Since the guide means supports the back surface of the sheet conveyed to the fixing means away from the transfer area on the surface of the carrier, it is necessary to carry an unfixed toner image on the sheet. It is necessary to have a volume resistance or a surface resistance enough to hold electric charges.

From this point of view, conventionally, for example, Japanese Patent Laid-Open No. 1-59581 discloses that the volume resistance of the guide means is 10 ⁶ Ω-cm or more and the surface resistance is 10 ⁶ to 10 ⁹ Ω.
Is set so that the electric charge necessary to carry the unfixed image on the sheet is left, and other unnecessary electric charges can be gradually removed.

[0007]

However, when the volume resistance of the guide means in the above-mentioned prior art is about the set value, it cannot be said that the resistance is still high enough, so that the charge of the charged sheet moves on the guide surface. It is quickly removed on the way. For this reason, there is a problem in that when the toner reaches the fixing unit, the unfixed toner image on the sheet is perturbed on the sheet, and the image after fixing is disturbed.

Further, in the conventional guide means, the position of the guide surface is not set corresponding to the positions of the carrier and the fixing means, so that the surface of the carrier is forcibly conveyed when the rear end of the sheet is forcibly conveyed. In some cases, the sheet moving on the guide surface may not partially contact the guide surface, such as the elasticity of the sheet itself, the so-called stiffness of the sheet, so that the sheet moving away from the guide surface may partially contact the guide surface. There was the inconvenience of becoming uncertain.

[0009] If such a problem occurs, the sheet is not uniformly discharged, so that image dust is generated, and when the carrier is a rotating drum, the sheet is wrapped around the surface of the drum. . Paper is usually used for the transfer sheet. However, the strength of the paper varies depending on the thickness and type of the paper and environmental conditions such as temperature. Was difficult to prevent.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and it is intended to set the position of a guide surface of a guide means provided between a transfer section and a fixing section, and to set a volume resistance value or a volume resistance value of the guide means. An object of the present invention is to provide an image forming apparatus capable of uniformly discharging electricity over the entire area of a transfer sheet by appropriately setting a surface resistance value and maintaining stable image quality without image disturbance. is there.

[0011]

According to the present invention, there is provided an electrostatic latent image carrier, and a charge supply unit, which is charged in a polarity opposite to that of the charged toner adhered to the surface of the carrier, is provided below the carrier. And a fixing unit disposed downstream of the carrier in the transfer direction of the transfer sheet, and a guide unit having a guide surface of the sheet between the fixing unit and the carrier. The guide means is provided with a static elimination rail.
After the sheet comes into contact with a transfer area on the surface of the carrier facing the charge supply unit, the sheet passes through the fixing unit via the guide surface of the guide unit. together to be conveyed along the path
Static elimination of the surface of the carrier after transfer by the static elimination lamp
The present invention is directed to an image forming apparatus that performs the above .

In order to achieve the above object, in a vertical cross section of the transport path, a tangent passing through the center of the transfer region of the carrier, an extension of the transport path in the fixing unit,
The guide surface of the guide unit is configured to be located in a region surrounded by a straight line connecting the transfer region of the carrier and the sheet support end on the upstream side in the conveyance direction of the fixing unit.

The guiding means has a volume resistance of 10 ¹⁰ to 10.
It is necessary to set the resistance to ¹⁴ Ω-cm and the surface resistance to 10 ¹⁰ to 10 ¹⁴ Ω in order to properly remove electricity from the transfer sheet.

The charge supply means can be constituted by a transfer roller. In this case, the peripheral surface of the roller is separated from the surface of the electrostatic latent image carrier by a gap larger than the thickness of the transfer sheet. They may be arranged to face each other.

The fixing means may include a fixing roller for heating the transfer sheet and a pressure roller for pressing the sheet between the fixing roller and the fixing roller.

[0016]

The tangential line passing through the center of the transfer area of the electrostatic latent image carrier substantially coincides with the direction in which the transfer sheet is fed by the carrier. Similarly, a straight line connecting between the transfer area of the carrier and the sheet support end on the upstream side in the conveyance direction of the fixing unit substantially coincides with the sheet extending position when the sheet is pulled to the maximum extent between both parts.

Therefore, by arranging the guide surface of the guide means in the area surrounded by these straight lines, the sheet separated from the carrier is supported by the guide surface and is prevented from hanging down by its own weight. The entire area of the sheet is pressed against the guide surface. Therefore, since a reaction force corresponding to the stiffness of the sheet is applied to the sheet on the guide surface, the sheet conveyance state and the adhesion of the sheet in the transfer area of the carrier are affected by the thickness, type, and environment of the sheet. It is surely prevented from being affected by the change of the condition.

[0018]

1 to 3 show an embodiment in which the present invention is applied to an electronic copying machine. FIG. 1 shows the copying machine partially cut away. In FIG. 1, reference numeral 1 denotes a machine main body constituting an outer shell of a copying machine. Inside the machine main body 1, a photosensitive drum 2 as an electrostatic latent image carrier, a paper feeding mechanism 3, and a fixing unit as fixing means are provided. A roller-type fixing device 4 and the like are provided.

The photosensitive drum 2 is made of amorphous silicon (a-Si) on the surface of a metal tube made of metal such as aluminum.
A photosensitive layer made of a photosensitive material or other photosensitive material is formed. The photosensitive layer is disposed substantially horizontally in the machine main body 1 and is driven to rotate clockwise. The drum 2
Is set so as to be in the forward direction with respect to the transport direction of the sheet P as a transfer sheet in a transfer section D described later.

A charging unit A, an exposing unit B, a developing unit C, a transfer unit D, a cleaning unit E, and the like are arranged around the photosensitive drum 2 in the rotation direction of the drum. Reference numeral 5 denotes a document table provided on the upper surface of the machine body 1.

In the charging section A, an appropriate charging device 6 such as a corona discharger is provided so as to face the drum surface, and the charging device 6 charges the photosensitive layer on the drum surface.
On the other hand, the image of the document set on the document table 5 is read by the exposure optical system 7 and the reflected light is irradiated on the surface of the drum 2 in the exposure section B, so that the electrostatic latent image of the document image is Formed on the surface.

A developing unit 8 and a toner hopper 9 for replenishing toner to the developing unit 8 are provided for the developing unit C. The developing unit 8 puts a positive polarity on the electrostatic latent image on the drum surface. So-called development is performed in which charged toner is attached.

The paper feed mechanism 3 includes a paper feed cassette 10 that is removably mounted on the main body of the machine, and a paper feed roller 1 that feeds out sheets (transfer sheets) in the paper feed cassette 10 one by one.
1, a paper reversing unit 12 for changing the transport direction of the paper P, a feed roller 13 provided in the paper reversing unit 12, and a registration roller pair 14.

At the time of copying, the paper feed roller 11, the feed roller 13, and the registration roller pair 14 are driven and controlled at a predetermined timing related to the driving of the drum 2 and other driving systems, and the paper in the paper feed cassette 10 is removed. The sheets are transported one by one to the transfer section D.

In the transfer section D, a transfer device 15 to be described later is disposed at a position facing the drum surface, and the toner image formed on the drum surface is transferred by the transfer device 15 by the paper feed mechanism 3 to the transfer section. D is transferred onto the sheet sent to D. After the transfer, the toner remaining on the drum surface is removed by a cleaning device 16 provided for the cleaning unit E, and thereafter, the charge is removed by a charge removing unit (not shown) to prepare for the next charging.

The sheet on which the toner image of the original image has been transferred in this manner is pressed and heated by the fixing device 4 so that the toner is fixed on the sheet and the copying process is completed.

FIGS. 2 and 3 schematically show the structure of the transfer device 15 provided for the transfer section D and the fixing device 4 provided downstream of the transfer device 15 in the sheet conveyance direction. As shown in FIG. 2, the transfer device 15 includes a transfer roller 17, a sheet guide member 18 disposed on the upstream side of the transfer roller in the sheet conveying direction, and a support table 1 disposed on the downstream side as guide means.
9 and a power supply 20 for supplying a bias voltage to the transfer roller 17.

The transfer roller 17 has a roller peripheral surface facing a lower side of the drum 1 with a gap t having a certain width larger than the surface of the drum 1 and the thickness of the sheet P, specifically, about 0.2 to 0.5 mm. It is arranged so that, for example, a urethane resin, a conductive resin material obtained by mixing carbon or an alkali metal in a silicon resin, or the like, or can be manufactured as a molded product made of a conductive rubber or the like. 10 ⁷
It has a volume resistivity on the order of Ω-cm.

The transfer roller 17 applies a voltage having a polarity opposite to that of the charged toner adhering to the drum surface during transfer, that is, a negative voltage, so that the charged toner adhering to the drum surface in the developing section C is transferred. The toner image is transferred onto the sheet P, and as shown in FIG. 3, is formed to have a length in the axial direction of the toner image forming area on the drum surface or more.

The upstream paper guide member 18 is disposed between the transfer roller 17 and the registration roller pair 14 of the paper feed mechanism 3, and the upper surface thereof functions as a guide surface for defining the lower limit of the paper transport path. The opposite end of the pair of registration rollers 14 is set to be substantially the same height as the nip portion of the pair of rollers 14, and the end of the transfer roller 17 side is directed upward so as to face the drum surface. It is formed on an inclined surface that is inclined.

Numeral 21 denotes a cover member arranged opposite to the upper surface of the upstream paper guide member 18, which regulates the upward movement of the paper P passing over the guide member 18, and which removes toner from the developing device 8. If it falls, it functions to prevent the toner from adhering to the paper.

The fixing device 4 includes a fixing roller 22 for heating the sheet P and a pressure roller 23 for pressing the sheet P between the fixing roller 22 and both rotating in the same direction as the sheet conveying direction. It is configured to be driven.

The support table 19 is provided between the drum 2 and the fixing device 4, and the upper surface thereof is configured to define a lower limit of a sheet transport path as a sheet guide surface.

That is, in this embodiment, the guide surface 19a of the support base 19 is located at the center of the transfer area on the drum surface (the area on the drum surface where the paper P contacts) in the vertical section of the paper transport path, that is, the drum 2 A tangent line L1 orthogonal to a line segment connecting the center and the center of the transfer roller 17, and an extension line of the transport path in the fixing device, that is, a common tangent line L2 of the roller pairs 22 and 23
And an area F surrounded by a straight line connecting the drum transfer area and the sheet support end on the upstream side in the conveyance direction of the fixing device 4, that is, a common tangent L3 between the lower surface side of the drum 2 and the lower surface side of the fixing roller 22. It is configured to be located within.

The tangent line L1 and the common tangent line L2 of the roller pairs 22 and 23 substantially coincide with the direction in which the sheet P is fed by the carrier. A common tangent line L3 between the drum surface and the peripheral surface of the fixing roller indicates that the paper P is
The position is almost the same as the position where the sheet is stretched when the nip portion 23 is pulled to the maximum extent.

More specifically, the guide surface 19a of the support base 19 is formed in the region F as an inclined surface in which the majority of the downstream side is gradually inclined toward the downstream side, whereby the guide surface 19a is formed from the drum surface. The paper P, which has descended away, is smoothly slid to the downstream side.

When the guide surface 19a of the support base 19 is positioned in the area F, the entire area of the sheet P separated from the drum 2 is pressed against the guide surface 19a as the paper P moves. A reaction force corresponding to the strength of the waist is applied to the sheet P on the sheet 19a, and as a result, the sheet P
And the adhesion of the sheet P in the transfer area of the drum 2 is maintained.

In the upstream end of the support 19,
After the transfer, the lamp 24 is turned on, and the light beam passes through the upper surface of the guide member and the paper P to reach the drum surface. The drum surface is transferred by the light of
The charge is removed when it is rotated to the downstream side of the.

Further, since the unfixed toner image on the sheet is conveyed to the fixing device 4 while holding the transfer position, the support table 19
It is necessary to gradually remove the electric charge of the paper P moving on the guide surface 19a during the movement. From the necessity, the support base 19 is set to have a volume resistance value of 10 ¹⁰ to 10 ¹⁴ Ω-cm or a surface resistance value of 10 ¹⁰ to 10 ¹⁴ Ω. It is formed of a material having a resistance value and a surface resistance value, for example, an antistatic ABS resin or the like.

Reference numeral 25 denotes a guide table provided on the fixing device side.
23 are provided substantially along the common tangent line L2.

In the transfer device 15 having the above-described structure, the registration roller pair 14 is driven in synchronization with the rotation of the drum 2, whereby the sheet P is sent out at a transport speed equal to the peripheral speed of the drum surface. It is guided on the upper surface of the member 18 and passes through the gap t between the transfer roller 17 and the drum 2. The paper P is transferred to the transfer roller 1 when passing through the gap.
7 is in close contact with the peripheral surface of the drum over a certain range of the drum surface while maintaining the non-contact state.

At this time, a transfer voltage having a polarity opposite to that of the charged toner adhering to the drum surface is applied to the transfer roller 17 from the power supply 20, and the charged toner adhering to the drum surface is caused by the Coulomb force generated by this. Transfer to the surface. It should be noted that sufficiently good transfer can be realized even when the paper P is not in contact with the transfer roller 17 because a minute corona discharge is generated from the transfer roller 17 toward the back surface of the paper P in the transfer range C. It is estimated to be.

Next, the paper P separated from the drum surface is conveyed to the fixing device 4 while being pressed against the guide surface 19a of the support base 19. In this case, as described above, a reaction force due to the stiffness of the paper P is applied to the paper P, and the support base 19 has a volume resistance value or a surface resistance such that the charge is gradually removed from the paper P having received the electric charge in the transfer portion. Since the resistance value is set, a change in environmental conditions such as the thickness, type, and temperature of the paper hardly changes the transport state or the adhesion of the drum surface to the transfer area.

In the above-described embodiment, the transfer roller 17 provided as a charge supply means is disposed slightly apart from the drum surface.
However, the present invention is also applicable to an image forming apparatus using a mode in which the peripheral surface of a transfer roller is in contact with the drum surface as in a well-known roller transfer method, or an image forming apparatus using a corona transfer method. The fixing means is not necessarily limited to the roller type.

[0045]

As described above, according to the image forming apparatus of the present invention, in the vertical cross section of the transfer path of the transfer sheet,
Surrounded by a tangent passing through the center of the transfer area of the electrostatic latent image carrier, an extension of the transport path in the fixing unit, and a straight line connecting the carrier transfer area and the upstream sheet support end in the transport direction of the fixing unit. Since the guide surface of the guide means is configured to be located in the area to be pressed, the entire area of the sheet is pressed against the guide surface, so that the charge of the sheet is made uniform, and image dust and the surface of the carrier are removed. Winding of the sheet or jumping of the rear end of the sheet is prevented.

Further, since the sheet pressed against the guide surface of the guide means is restricted from being deflected, a stable and good image quality is always obtained without being affected by changes in the thickness, type, and environmental conditions of the sheet. be able to.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view showing an embodiment of a copying machine to which the present invention is applied.

FIG. 2 is a front view of a main part schematically showing a configuration of a transfer device and a fixing device.

FIG. 3 is a perspective view of the main part.

[Explanation of symbols]

 Reference Signs List 2 electrostatic latent image carrier (photosensitive drum) 4 fixing means (fixing device) 17 charge supply means (transfer roller) 19 guide means (support table) 19a guide surface 22 fixing roller 23 pressure roller F area L1 tangent L2 extension Line L3 Straight line P Transfer sheet t Gap

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinichi Tanaka 1-2-28 Tamazo, Chuo-ku, Osaka-shi Inside Mita Industries Co., Ltd. (72) Inventor Yasuo Hatate 4--20-11 Hoshigamine, Kagoshima City, Kagoshima Prefecture (56) References JP-A-1-200277 (JP, A) JP-A-4-42654 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/16

Claims (4)

(57) [Claims] 1. An image forming apparatus comprising: an electrostatic latent image carrier; and a charge supply unit having a polarity opposite to that of the charged toner adhered to the surface of the carrier. than said carrier is disposed a fixing unit in the conveying direction downstream side of the transfer sheet, it is further provided a guide means having a guide surface of the sheet between the fixing means and the bearing member, the Inside the guide is a discharge lamp inside the upstream end
After the sheet comes into contact with a transfer area on the surface of the carrier facing the charge supply unit, the sheet is conveyed along a conveyance path passing through the fixing unit via a guide surface of the guide unit. With the lamp for static elimination
An image forming apparatus configured to perform charge elimination on a surface of a carrier after photographing, wherein in a vertical cross section of the transport path, a tangent passing through a center of the carrier transfer area and an extension of a transport path in the fixing unit. So that the guide surface of the guide means is located in an area surrounded by a line and a straight line connecting the transfer direction of the carrier and the sheet support end on the upstream side in the conveyance direction of the fixing means.
The volume resistance value of the guide means is 10 ¹⁰ -1
0 ¹⁴ Ω-cm, surface resistance is set to ¹⁰ 10 Ω to 10 ¹⁴ Ω
An image forming apparatus characterized by being configured as described above. 2. The image forming apparatus according to claim 1, wherein said charge supply means comprises a transfer roller. 3. The transfer roller according to claim 1, wherein a peripheral surface of the transfer roller is opposed to the surface of the electrostatic latent image carrier with a gap larger than a thickness of the transfer sheet. 2 image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the fixing unit includes a fixing roller for heating the transfer sheet, and a pressure roller for pressing the sheet between the fixing roller and the fixing roller.