JPH06167894A - Image forming device - Google Patents

Abstract

PURPOSE:To maintain stable image quality by allowing all areas of a transfer form to contact with the guiding surface of a supporting base and uniformly destaticizing the transfer form. CONSTITUTION:The guiding surface 19a of the supporting base 19 disposed between a photosensitive drum 2 and a fixing device 4 is located in a region F surrounded by a tangent L1 orthogonally crossing a segment connecting the center of the drum 2 with the center of a transfer roller 17, the common tangent L2 of a pair of rollers 22 and 23 and the common tangent L3 of the bottom face sides of the surface of the drum 2 and the periphery of the fixing roller 22, so that the all areas of a form P are pressed on the guiding surface.

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 and a facsimile, and more particularly to an improvement of a transfer sheet guiding means arranged between a transfer portion and a fixing portion. Is.

[0002]

2. Description of the Related Art Generally, an image forming apparatus of this type is provided with an electrostatic latent image carrier composed of a rotary drum or the like having a photosensitive layer formed on the surface thereof, and charged along the moving direction of the carrier. Unit, an exposing unit, a developing unit and a transferring unit are provided in that order, the surface is charged by the charging unit, and then the surface of the carrier is exposed in the exposing unit to form an electrostatic latent image of image information. After that, the toner image is developed by depositing charged toner on the latent image in the developing section, and the toner image is further transferred to the transfer sheet in the transfer section, and finally, the sheet is conveyed to the fixing unit to transfer the sheet. The toner image is fixed by heating and pressurizing.

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 a toner image is applied at a position facing the electrostatic latent image carrier,
The sheet conveying 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 conveying path moves while being in contact with the surface of the carrier, and at this time, the transfer toner applied to the surface of the carrier is attracted by the transfer voltage applied to the charge supplying means, and the sheet is transferred. The transfer is performed by transferring to the top.

As the fixing means, a fixing roller which heats a sheet and a pressure roller which presses the sheet between the fixing roller are arranged above and below are generally widely used. In the case of using, the guide means whose upper surface functions as a sheet guide surface is disposed between the nip portion of the roller pair and the carrier.

By the way, since this guiding means supports the back surface of the sheet which is conveyed to the fixing means away from the transfer area on the surface of the carrier, it is necessary to carry the unfixed toner image on the sheet. It is necessary to have a volume resistance or a surface resistance enough to hold an electric charge.

From this point of view, conventionally, for example, in JP-A-1-59581, the volume resistance value of the guide means is 10 ⁶ Ω-cm or more and the surface resistance value is 10 ⁶ to 10 ⁹ Ω.
Has been proposed so that the electric charge necessary to carry the unfixed image on the sheet is left, and other excess electric charges can be gradually removed.

[0007]

However, it cannot be said that the resistance is still sufficiently high at the set value of the volume resistance value of the guide means in the above-mentioned prior art, so that the charge of the charged sheet moves on the guide surface. It will be promptly removed on the way. For this reason, when the toner reaches the fixing unit, the unfixed toner image on the sheet deviates 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, and therefore, the surface of the carrier is forcibly conveyed at the trailing edge of the sheet. There is a case where the sheet moving on the guide surface does not come into partial contact with the guide surface due to the elasticity of the sheet itself on the front end side away from the sheet, so-called waist strength, and so on. There was the inconvenience of becoming uncertain.

When such inconvenience occurs, since the sheet is not uniformly discharged, image dust is generated, and in the case where the carrier is a rotary drum, the sheet may be wound around the drum surface. . Paper is usually used as the transfer sheet, but the stiffness of the paper changes depending on the thickness and type of the paper, and changes in environmental conditions such as temperature. Was difficult to prevent.

The present invention solves the above-mentioned problems, and sets the position of the guide surface of the guide means arranged between the transfer portion and the fixing portion, and the volume resistance value of the guide means or An object of the present invention is to provide an image forming apparatus capable of uniformly removing static electricity over the entire area of a transfer sheet by appropriately setting the surface resistance value and maintaining stable image quality without image distortion. is there.

[0011]

SUMMARY OF THE INVENTION According to the present invention, an electrostatic latent image carrier is provided, and a charge supply unit, which is charged to the surface of the carrier and has a polarity opposite to that of the charged toner, faces the carrier below the carrier. And a fixing means arranged downstream of the carrier in the conveying direction of the transfer sheet and further having a guide surface of the sheet between the fixing means and the carrier. The sheet is brought into contact with the transfer area of the surface of the carrier facing the charge supplying means, and then conveyed along the conveying path passing through the fixing means via the guide surface of the guide means. The image forming apparatus configured as described above is targeted.

In order to achieve the above object, a tangent line passing through the center of the carrier transfer area and an extension line of the conveyance path in the fixing means in a vertical cross section of the conveyance path,
The guide surface of the guide means is located in an area surrounded by the carrier transfer area and a straight line connecting the sheet supporting ends of the fixing means on the upstream side in the conveying direction.

The guide means has a volume resistance value of 10 ¹⁰ to ¹⁰ 10.
It is necessary to set ¹⁴ Ω-cm and the surface resistance value to 10 ¹⁰ to 10 ¹⁴ Ω in order to perform proper charge removal of the transfer sheet.

The charge supplying means can be composed of a transfer roller, in which case the roller peripheral surface is separated from the surface of the electrostatic latent image carrier by a gap larger than the thickness of the transfer sheet. It may be arranged so as to face each other.

The fixing means may be composed of 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 tangent line passing through the center of the transfer area of the electrostatic latent image carrier is substantially coincident with the direction in which the transfer sheet is fed by the carrier. Similarly, the straight line connecting the transfer area of the carrier and the sheet supporting end of the fixing means on the upstream side in the conveying direction substantially coincides with the sheet tension position when the sheet is pulled to the maximum extent between both parts.

Therefore, by locating 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 the reaction force corresponding to the strength 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 may affect the thickness, type, and environment of the sheet. It is reliably prevented from changing under the influence of changes in conditions.

[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 body that constitutes an outer shell of a copying machine. Inside the machine body 1, a photosensitive drum 2 as an electrostatic latent image carrier, a paper feed mechanism 3, and a fixing unit are provided. A roller type fixing device 4 and the like are provided.

The photoconductor drum 2 is made of amorphous silicon (a-Si) on the surface of a metal tube made of aluminum or the like.
And a photosensitive layer formed of other photosensitive material, which is arranged substantially horizontally in the machine body 1 and is rotationally driven in the clockwise direction. The drum 2
The rotation direction of is set to be in the forward direction in the transfer portion D, which will be described later, with respect to the conveyance direction of the sheet P as a transfer sheet.

Further, around the photosensitive drum 2, a charging section A, an exposing section B, a developing section C, a transfer section D, a cleaning section E and the like are arranged in that order along the rotating direction of the drum. Further, 5 is a document table provided on the upper surface of the machine body 1.

A suitable charging device 6 such as a corona discharger is disposed in the charging section A so as to face the drum surface, and the photosensitive layer on the drum surface is charged by the charging device 6.
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 at the exposure section B, and the electrostatic latent image of the document image is formed on the drum. Formed on the surface.

A developing device 8 and a toner hopper 9 for replenishing the developing device 8 with toner are provided for the developing section C, and the developing device 8 provides a positive polarity on the electrostatic latent image on the drum surface. A so-called development is performed to attach the charged toner.

The paper feed mechanism 3 includes a paper feed cassette 10 that is removably loaded in the machine body, and a paper feed roller 1 that feeds the papers (transfer sheets) in the paper feed cassette 10 one by one.
1, a sheet reversing unit 12 for changing the conveying direction of the sheet P, a feed roller 13 provided in the sheet 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 drive-controlled at a predetermined timing associated with the drive of the drum 2 and other drive systems, so that the paper in the paper feed cassette 10 is removed. The sheets are conveyed one by one to the transfer section D.

A transfer device 15 to be described later is arranged in the transfer portion D 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 feeding mechanism 3. It is transferred onto the paper sent to D. After the transfer, the toner remaining on the surface of the drum is removed by the 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, and the toner is fixed on the sheet to complete the copying process.

2 and 3 schematically show the structures of the transfer device 15 provided for the transfer portion D and the fixing device 4 provided on the downstream side in the paper transport direction. As shown in FIG. 2, the transfer device 15 includes a transfer roller 17, a paper guide member 18 arranged on the upstream side of the transfer roller in the paper conveying direction, and a support base 1 as guide means arranged on the downstream side.
9 and a power source 20 for supplying a bias voltage to the transfer roller 17 and the like.

Below the drum 1, the transfer roller 17 has its peripheral surfaces facing each other with a gap t larger than the surface of the drum 1 and the thickness of the paper P, specifically, a constant width of about 0.2 to 0.5 mm. Can be produced as a molded product made of a conductive resin material or a conductive resin material in which carbon or an alkali metal is mixed in a urethane resin, a silicon resin, or the like. 10 ⁷
It has a volume resistance value on the order of Ω-cm.

Further, at the time of transfer, the transfer roller 17 is applied with a voltage having a polarity opposite to that of the charged toner adhered to the drum surface, that is, a negative polarity voltage, so that the charged toner adhered to the drum surface in the developing section C is transferred. As shown in FIG. 3, the toner image forming area on the surface of the drum is formed to have the axial length of the toner image forming area or longer than that.

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 its upper surface functions as a guide surface that defines the lower limit of the paper transport path. Thus, the end portion facing the registration roller pair 14 is set to substantially the same height as the nip portion of the roller pair 14, and the end portion on the transfer roller 17 side is directed upward toward the drum surface. It is formed on an inclined surface.

Reference numeral 21 is a cover member which is arranged so as to face the upper surface of the upstream side paper guide member 18 and which restricts the upward movement of the paper P passing over the guide member 18 and allows toner from the developing device 8 to be removed. When it falls, it serves to prevent the toner from adhering to the paper.

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

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

That is, in the present embodiment, the guide surface 19a of the support 19 is located at the center of the transfer area on the drum surface (area where the paper P contacts the drum surface) in the vertical section of the paper transport path, that is, on 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 conveyance path in the fixing device, that is, a common tangent line L2 of the roller pair 22 and 23.
And an area F surrounded by a straight line connecting the drum transfer area and the sheet supporting end of the fixing device 4 on the upstream side in the conveying direction, that is, a common tangent line L3 between the lower surface side of the drum 2 and the lower surface side of the peripheral surface of the fixing roller 22. Is configured to be located within.

The tangent line L1 and the common tangent line L2 of the roller pairs 22 and 23 are substantially coincident with the direction in which the paper 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 drum 2 and the roller pair 22,
It is almost the same as the paper tension position when the maximum tension is applied between the nip portions 23.

More specifically, the guide surface 19a of the support base 19 is formed in the area F such that most of its downstream side is an inclined surface that is gently inclined toward the downstream side. Sliding of the paper P, which has descended apart, to the downstream side is performed smoothly.

When the guide surface 19a of the support base 19 is positioned in the area F in this manner, the entire area of the paper P separated from the drum 2 is pressed against the guide surface 19a as the paper P moves away. A reaction force corresponding to the strength of the waist is applied to the paper P on the sheet 19a, and as a result, the paper P
The sheet P is kept in close contact with the sheet P in the transfer state of the sheet and the transfer area of the drum 2.

In addition, in the upstream end of the support base 19,
A static elimination lamp 24 is built in, and after the transfer, the static elimination lamp 24 is turned on so that the light beam passes through the upper surface of the guide member and the paper P and reaches the drum surface. The surface of the drum is transferred by the light of D
The charge is removed when it rotates to the downstream side.

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 is used.
It is necessary to gradually remove the electric charge of the paper P moving on the guide surface 19a during the movement. Due to 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. Therefore, the support base 19 has such a volume. It is formed of a material having a resistance value and a surface resistance value, for example, antistatic ABS resin.

Reference numeral 25 denotes a guide table provided on the fixing device side, and the upper surface of the guide table 25 has the roller pair 22,
It is provided so as to substantially follow the common tangent line L2 of 23.

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 paper P is sent out at the conveying speed equal to the peripheral speed of the drum surface, and the upstream paper guide. It is guided by the upper surface of the member 18 and passes through the gap t between the transfer roller 17 and the drum 2. When the paper P passes through this gap, the paper P is
The peripheral surface of No. 7 is in contact with the drum surface over a certain range while maintaining a 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 from the power source 20 to the transfer roller 17, and the Coulomb force generated by the transfer voltage causes the charged toner adhering to the surface of the paper P. Transfer to the surface of. Note that the reason why sufficiently good transfer can be realized even if the paper P is not in contact with the transfer roller 17 is that 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 sheet P separated from the drum surface is conveyed to the fixing device 4 while being pressed against the guide surface 19a of the support table 19. In this case, as described above, the reaction force due to the stiffness of the paper P is applied to the paper P, and the support table 19 has a volume resistance value or a surface enough to gradually remove the electric charge from the paper P that has received the charge at the transfer portion. Since the resistance value is set, the conveyance state and the adhesion of the drum surface to the transfer area hardly change due to changes in the paper thickness, type, temperature and other environmental conditions.

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

[0045]

As described above, in the image forming apparatus of the present invention, in the vertical cross section of the transfer sheet conveying path,
It is surrounded by a tangent line passing through the center of the transfer area of the electrostatic latent image carrier, an extension line of the conveying path in the fixing means, and a straight line connecting the transfer area of the carrier and the sheet supporting end of the fixing means on the upstream side in the conveying direction. By configuring the guide surface of the guide means to be located in the area to be covered, the entire area of the sheet is pressed against the guide surface, so that the static elimination of the sheet is made uniform and image dust and the surface of the carrier are removed. The sheet is prevented from being wrapped around or the rear end of the sheet from jumping up.

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

[Brief description of 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 the configurations of a transfer device and a fixing device.

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

[Explanation of symbols]

 2 electrostatic latent image carrier (photosensitive drum) 4 fixing means (fixing device) 17 charge supplying means (transfer roller) 19 guiding means (supporting base) 19a guiding surface 22 fixing roller 23 pressure roller F area L1 tangent line L2 extension Line L3 Straight line P Transfer sheet t Gap

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Tanaka 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Engineering Co., Ltd. No. 11

Claims (5)

[Claims] 1. An electrostatic latent image carrier is provided, and a charge supplying unit that is charged with a polarity opposite to that of the charged toner adhering to the surface of the carrier is disposed below the carrier and at a position facing each other. The fixing means is disposed on the downstream side of the carrier in the conveying direction of the transfer sheet, and the guide means having the guide surface of the sheet is disposed between the fixing means and the carrier. An image forming apparatus in which a sheet comes into contact with a transfer area of the surface of the carrier facing the charge supplying means, and then is conveyed along a conveying path passing through the fixing means via the guide surface of the guide means. In the vertical cross section of the transport path, a tangent line passing through the center of the carrier transfer area, an extension line of the transport path in the fixing unit, an upstream side of the carrier transfer area and the fixing unit in the transport direction. Surrounded by a straight line connecting the seat support edges An image forming apparatus, characterized in that the guide surface of the guide means is located in a region to be covered. 2. The volume resistance value of the guide means is 10 ¹⁰ to 10 ¹⁴
The image forming apparatus according to claim 1, wherein Ω-cm and a surface resistance value are set to 10 ¹⁰ to 10 ¹⁴ Ω. 3. The image forming apparatus according to claim 1, wherein the charge supply unit is composed of a transfer roller. 4. The transfer roller according to claim 3, wherein the peripheral surface is arranged so as to face the surface of the electrostatic latent image carrier and the surface of the carrier with a gap larger than the thickness of the transfer sheet. The image forming apparatus according to claim 1. 5. The image forming apparatus according to claim 1, wherein the fixing unit includes a fixing roller that heats the transfer sheet and a pressure roller that presses the sheet between the fixing roller and the fixing roller.