JPH05204261A - Image forming device - Google Patents

Abstract

PURPOSE:To improve tight contact between a transfer material and an image carrier and to attain excellent transfer by setting the pressing position of a transfer material holding sheet in an area where the transfer material holding sheet is pressed to a photosensitive drum through the transfer material. CONSTITUTION:A pressing sheet 40 consisting of dielectric and elastic synthetic resin film such as polyethylene, which elongates from the introducing side of a dielectric screen 38 being the transfer material holding sheet to a downstream side in the moving direction thereof in the discharge width of a corona discharger 25, is disposed all over the area of a transfer part. The sheet 40 presses the screen 38 by the elasticity of its own, and the leading edge thereof on the screen side is set at a position corresponding to a position where a transfer paper 20 finishes coming in contact with a photosensitive drum 1 or where it starts coming in contact with it. Namely, the pressing position of the sheet 40 pressing the screen 38 to the photosensitive drum 1 is set in an area where the screen 38 is pressed to the photosensitive drum 1 through the transfer paper 20.

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 for transferring an image on an image carrier such as a photoconductor or a dielectric to a transfer material held on a transfer material holding sheet.

BACKGROUND ART As an example of the image forming apparatus, there is a color copying machine to which an electrophotographic method is applied. The main part of the structure of this color copying machine will be described with reference to the sectional view of the apparatus shown in FIG.

FIG. 1 shows an example of a transfer type color electrophotographic copying machine to which the present invention is applicable. Although this figure shows the case where a dielectric mesh screen is used as a means for carrying the transfer material, it is also possible to use a dielectric sheet having no holes other than the screen.

In FIG. 1, reference numeral 1 is an electrophotographic photosensitive drum having a surface insulating layer, a photoconductive layer and a conductive substrate, and a shaft 2
It is rotatably supported by and is started to rotate in the direction of arrow 3 by a copy command. When the drum 1 is rotated to a fixed position, the document 0 placed on the platen glass 4 is illuminated by an illumination lamp 6 which is integrated with the first scanning mirror 5, and the reflected light is reflected by the second scanning mirror 5. Scanned at 7. The reflected light image passes through the lens 8 and the third mirror 9, and then the color separation filter 1
Color separation is performed by 0, and the image is formed on the drum 1 at the exposure unit 13 through the fourth mirror 11 and the dustproof closed glass 12.

The drum 1 is neutralized by the static eliminator 14 and then charged by the primary charger 15, and then the exposure unit 13 slit-exposes the image irradiated by the illumination lamp 6.
At the same time, the static eliminator 16 is used to remove static electricity of AC or primary and reverse polarity.
Then, the entire surface is exposed by the entire surface exposure lamp 17 to form an electrostatic latent image on the drum 1.

The electrostatic latent image on the photosensitive drum 1 is then developed by the developing device 1.
By 8, the toner image is visualized. The developing device 18 is composed of four developing devices of yellow 18a, magenta 18b, cyan 18c, and black 18d, and the developing device designated corresponding to the color separation filter used for exposure works,
The toner image of the required color is obtained.

Transfer paper 2 using plain paper in cassette 19
0 is fed into the machine by the paper feed roller 21, is roughly timed by the first register roller 22, then is accurately timed by the second register roller 23, and the tip thereof is the gripper 24 of the transfer drum 33. Is gripped by. Then, as the transfer drum 33 rotates, the transfer drum 33 is conveyed while being wound around the screen stretched on the transfer drum, and transferred to the transfer charger 2.
While the transfer paper 20 passes between the photosensitive drum 1 and the photosensitive drum 1, the toner image on the photosensitive drum 1 is transferred onto the transfer paper, and at the same time, the transfer paper 20 is held on the screen surface by electrostatic attraction.

In the first transfer, the transfer paper 20 is electrostatically attracted to the screen after the transfer charger 25, and the binding force until then is weak, so that the transfer paper 20 is pulled by the photosensitive drum 1 and a color shift occurs. Since it becomes a cause, it is prevented by the pressing roller 35. The pressing roller 35 and the paper feed guide plate 34 move away from the transfer drum 33 after the first paper passes. The transfer drum 33 uses the gripper 24 to transfer the transfer paper 2
The image of the required number of colors is transferred by rotating the required number of times while holding the tip of 0 and electrostatically adhering to the screen.

After the transfer is completed, the transfer paper is released from the gripper 24 and the separation nails 26 are assisted by the separation static eliminators 36 and 37.
The sheet is separated by the guide belt 27, guided to the fixing belt pair 28, 29, fixed by pressing and heating, and then discharged to the tray 30. The surface of the photosensitive drum 1 after transfer is cleaned by a cleaning device 31 composed of an elastic blade, and the process proceeds to the next cycle.

FIG. 2 is a perspective view showing the transfer drum 33 and the transfer charger 25 of the copying machine. Transfer drum 3 in the figure
Reference numeral 3 denotes a frame body composed of a cylindrical portion 33a at both ends and a connecting band 33b integrally connecting the both cylindrical portions, and a porous dielectric screen 3 stretched over an opening formed in a circumferential portion of the frame body.
8 and a gripper 24 for gripping the leading end portion of the transfer paper provided on the connecting belt portion. Further, the spacer 39 provided on the peripheral surface of the cylindrical portion sets the distance between the two drums by pressing the transfer drum 33 against the photosensitive drum.

In the transfer section of the copying machine, the corona charger 25 has a discharge distribution as shown by the curve A in FIG.
Is acting on. In this transfer section, the photosensitive drum and the transfer paper are in contact with each other with a width a due to the pressing force of the dielectric screen and the electrostatic attraction force of the charging voltage of the transfer corona discharge band. Then, the toner image on the photosensitive drum is transferred to the transfer paper by the strong electric field generated by the transfer corona charger.

However, when the above-mentioned dielectric screen or a dielectric sheet having no holes is used as the transfer material holding sheet, the adhesion between the transfer paper held on the transfer material holding sheet and the photosensitive drum is unsatisfactory. Since it is sufficient, transfer failure may occur.

(Object of the Invention) It is an object of the present invention to provide an image forming apparatus capable of enhancing the adhesion between the transfer material held by the transfer material holding sheet and the image carrier to perform good transfer.

(Constitution of the Invention) In order to achieve the above object, the present invention provides an image carrier, a transfer material holding means for holding a transfer material and a transfer material holding means for conveying the transfer material, and the image carrying means. In an image forming apparatus having a transfer unit that transfers an image of a body to a transfer material held by the transfer material holding unit at a transfer position, the image forming apparatus is provided on a side opposite to the image carrier with respect to the transfer material holding unit. A pressing member that presses the transfer material holding sheet toward the image carrier, and the pressing position is within a region where the transfer material holding sheet presses the image carrier through the transfer material. It is characterized by.

[0015]

EXAMPLES The present invention will be described below based on examples and experimental results.
This will be described in more detail.

Similar to FIG. 3, FIG. 4 is an enlarged cross-sectional view of the transfer portion, showing the relationship of forces acting during transfer.

As shown in the figure, even if the dielectric screen 38 is in close proximity to or in line contact with the photosensitive drum before transfer, an electrostatic attraction force is generated between the dielectric screen 38 and the photosensitive drum 1 due to the charges charged on the discharger 25 side during transfer. It acts and is pulled toward the photosensitive drum 1 by force f. On the other hand, since the transfer paper 20 is sandwiched between the screen 38 and the drum 1, the distorted screen 38 exerts a restoring force to press the transfer paper 20 against the drum 1, and the screen 38 transfers the transfer paper 20. The strain force f ″ is generated by being pushed back by 20. The forces f and f ″ have substantially the same relationship although the directions are different.

In the transfer section, if the total force F of the above-mentioned forces, which is the suction force of the transfer paper to the photosensitive drum, is small, a gap is apt to be formed between the drum and the transfer paper. When the gap becomes several tens of μm or more, the image quality of the transferred image is extremely deteriorated.

By the way, regarding the screen 38, if the thickness of the screen 38 is increased to allow the transfer sheet to move, the transfer paper can be pressed against the photosensitive member with a sufficient force, thus improving the transfer efficiency. Seen. However, the distance between the charge on the transfer discharger side on the screen, which contributes to the suction support, and the transfer paper becomes large, and it becomes impossible to perform sufficient suction conveyance, and uneven transfer or color misregistration easily occurs.

On the contrary, if the screen is made thin, the frame supporting the screen is easily wavy or distorted, and uniform suction conveyance is not possible, and uneven transfer is likely to occur during transfer. ..

Next, one embodiment of the constitution of the present invention made in consideration of these phenomena will be described.

The transfer drum used in this embodiment is as shown in FIG.
The polyester resin was used as the dielectric screen for the frame body described in 1 above, and one having a mesh size of about 100 mesh and a thickness of 0.4 mm was used, and the screen was bonded to the frame body to complete the process. The transfer device of the present embodiment, as shown in FIG.
A dielectric and elastic pressing sheet 40 extending from the introduction side of the screen toward the downstream side in the moving direction was provided within the discharge width of the corona discharger 25. The pressing sheet 40 is made of a synthetic resin film of polyethylene, polypropylene, polyester or the like, and is arranged over the entire transfer portion. Then, the pressing sheet 40 presses the screen 38 by its own elastic force, and the front end portion of the screen side corresponds to the position where the transfer paper 20 has finished contacting the photosensitive drum or the position where the contact starts. Position.

With the above structure, the distribution of the discharge current by the corona discharger 25 is as shown by the curve B in FIG. Therefore, the phenomenon that the transferred image is blurred due to the transfer of the toner in the state where the photosensitive drum and the transfer paper are not in contact with each other (curve A in FIG. 3) is solved. That is, the discharge width b of the corona discharger 25 is the contact width a
To solve the phenomenon that the toner flies from the photosensitive drum to the transfer paper before the photosensitive drum and the transfer paper come into contact with each other over the distance, which hinders the transfer of a clear toner image. Further, the transfer start position can be accurately determined because the pressing sheet 40 is in contact with the screen 20.

Further, the above-mentioned structure also makes it possible to prevent the toner from scattering due to the transfer paper 20 on the screen being pressed against the photosensitive drum. The details will be described with reference to FIG.

FIG. 6 shows the amount of toner scattered at the transfer portion when the pressing sheet is not provided in the transfer device using the 100-mesh screen as 1, and the amount of scattering when the pressing sheet is provided. It is a comparison. The vertical axis of the graph represents the amount of toner scattered, and the horizontal axis represents the pressing force of the transfer sheet on the photosensitive drum by the pressing sheet.
The scattering amount of the toner was obtained by using a line original and calculating the ratio of the area of the toner portion scattered between the lines to the total measured area.

As is clear from the graph, it is understood that the toner scattering at the time of transfer can be minimized under certain conditions. Further, since the amount of scattering is improved compared to the conventional case even when no pressing force is applied, there is a problem of toner scattering only when the pressing sheet is in contact with the screen on the transfer start side within the transfer width. You can see that is improving. Such an effect cannot be obtained even if the discharge is reduced by the opening of the shield plate of the transfer corona discharger. Further, even if a sheet such as the pressing sheet 40 is used, if the tip is away from the screen, the transfer corona also wraps around to the back side of the sheet, and the same effect cannot be obtained.

From the above graph, the pressing force by the pressing sheet when using the 100-mesh screen is
It can be understood that the range of about 10 to 50 g / cm is most preferable. The pressing force is set in consideration of the elastic force of the pressing sheet, the mounting angle, and the waist strength of the screen. For example, if the stiffness of the screen is strong, the pressing force will be large, and conversely, if it is weak, it will be small. It should be noted here that when a pressing force of more than about 50 g / cm is applied, it is easy to cause development in which the central portion of the transferred image in the developed image is not transferred, particularly in the developed image. I need it.

Further, the pressing position of the pressing sheet on the screen is within the area where the transfer sheet and the photosensitive drum are in electrostatic surface contact with the screen, which causes abnormal deformation of the screen. It is preferable in terms of prevention.
For example, when a pressing sheet made of a polyester film having a thickness of 120 μ is used, it is necessary to set the contact angle θ (FIG. 5) to an angle smaller than 90 ° in order to prevent an abnormal force from acting on the screen. The contact angle θ is an angle formed by the pressing sheet and the holding sheet on the upstream side in the holding sheet moving direction from the pressing position where the pressing sheet presses the transfer material holding sheet. Further, by setting the contact angle θ to an acute angle, it is possible to suppress the vibration given to the transfer drum by the pressing sheet when the transfer drum rotates and the connecting portion 33b which is the supporting member of the holding sheet passes the pressing position. Therefore, with this configuration, image blur due to vibration of the transfer drum can be prevented.

Further, since the presence of the pressing sheet compensates for the deformation of the screen at the transfer position toward the photosensitive drum, it is not necessary to make the screen itself excessively flexible.
Therefore, even if the screen is brought into sufficient contact with the photosensitive drum, the screen is not made too flexible and the screen surface is not distorted, and the screen having an appropriate waist can be used. This makes it possible to prevent the occurrence of problems due to the use of the screen having too strong stiffness or the screen having too weak stiffness.

Further, since the pressing sheet 40 is arranged in a state of being pressed in the same direction as the moving direction of the screen 38 which supports the transfer paper, the deformation of the screen due to this pressing can be minimized. For example, in the case where the 120 μ pressing sheet generates a pressing force of 50 g / cm against the 100-mesh screen and the pressing position is within the area where the screen is attracted to the photosensitive drum by electrostatic force, P in the circumferential direction of the screen
The elongation was only within 0.1%. Of course, even if the pressing position is set on the upstream side of the suction area, the expansion in the circumferential direction of the screen can be ignored depending on the pressing force or the position.

In the above description, the case where a screen having a dielectric fine opening is used as the supporting member of the transfer paper has been exemplified, but for a dielectric sheet made of the same material as the above screen having no such opening, However, the present invention can be applied and the effect is as good as in the case of the screen. FIG. 7 illustrates a case where the present invention is applied to such a dielectric sheet 41.

Another embodiment of the present invention will be described below with reference to the drawings.

In FIG. 8, a conductive layer is provided on the corona discharger 25 side of the pressing sheet 40 so as not to contact the screen. The pressing sheet in this case is the dielectric sheet 42.
And a conductive layer 43. A bias voltage having the same polarity as the corona discharge from the transfer discharger is applied to the conductive layer 43 from the power supply 44. With the above configuration, the screen 38
It becomes possible to maintain a uniform predetermined potential on the corona discharger 25 side. The reason is that the corona applied to the screen 38 and the electric potential on the corona discharger side of the pressing sheet have the same polarity, so that the corona from this discharger is drawn to the screen side. As a result, the screen is charged to a high density, which enables more uniform transfer of toner without transfer unevenness.

In the embodiment shown in FIG. 8, the conductive layer 43 of the pressing sheet has a thickness of 1 to 3 under the conditions already described.
Good results were obtained when a voltage of KV was applied. Here, if this bias voltage is set to 1 KV or less, the discharger 25
The amount of corona flow into the transfer paper or the screen 38 decreases, the transfer effect and the holding power of the transfer paper decrease, which is not preferable. Also,
If it exceeds 3 KV, the effect of the electric field from the conductive layer toward the screen or the photosensitive drum becomes large, and the toner flies from the photosensitive drum 1 before the transfer, which deteriorates the image quality of the transferred image, which is not preferable.

In the embodiment shown in FIG. 9, instead of applying a bias voltage to the conductive layer 43, this conductive layer is electrically floated and further grounded via a varistor or a Zener diode 45 and a protective resistor 46. is there. With this configuration, the conductive layer is
Automatically set to ~ 3KV. The effect at this time is that, in addition to the effect of FIG. 7, no special power source is required.

When the transfer paper is held on the transfer drum 33, the gripper 24 may be used as shown in FIG. In this case, even if the gripper has a structure projecting to the transfer discharger 25 side, the pressing sheet does not hinder the passage of the gripper, so that no problem occurs. That is, since the disposing direction of the pressing sheet is along the moving direction of the screen, at the same time as the above effect, it also effectively acts on the passage of the gripper.

Here, when the pressing sheet vibrates when passing the gripper and hits the screen, the pressing sheet may be moved in the direction away from the screen only when the gripper passes. FIG. 10 is a cross-sectional view of the transfer drum showing a structure for separating the pressing sheet from the screen, and FIG. 11 is a partial perspective view of a frame body of the transfer drum used for setting a timing for separating the pressing sheet.

In FIG. 10, reference numeral 47 denotes a roller which is rotatably attached to one end of an L-shaped arm 49 which rotates about a shaft 48. At the other end of this arm 49, there is an arm rotatably attached to the shaft, and at the other end of this arm,
The pressing sheet 52 is adhered. And the arm 4
A rotational force of 9 is always applied in the clockwise direction by a spring 52, and the rotation range is restricted by a stopper 53. On the other hand, a stopper 54 is provided for the arm 51 so as to sandwich the arm, and the movement range thereof is regulated by this. The link mechanism is used for the transfer drum frame 55.
Can be attached to both sides of. Specifically, the rotation shaft 48 and the stopper 5 are provided on the side plates of the main body device side corresponding to both sides of the frame body 55.
3. Support members for 54 and spring 52 are fixed.

With the above structure, the rollers 47 rotate the frame 5
When it rides on the connecting band 55a of No. 5, it is displaced to the chain line position, and otherwise returns to the solid line position, that is, the position close to the screen 38.

The corona discharger 25 for transfer and the roller 47
In the configuration of the frame body 33 in FIG. 2 described above, the operation timings of the pressing sheet 52 accompanying the passage of the connecting band 55a to the discharger 25 do not match. Therefore, as shown in FIG. 11, a part of the coupling band 55a is displaced by the distance C toward the upstream side in the rotational direction, thereby solving the above-mentioned timing problem. Instead of the cam as described above, the displacement mechanism of the pressing sheet may use a means such as an electromagnetic solenoid that operates by an electric signal to pull the pressing sheet away from the connecting band 35a. Reference numeral 56 in FIG. 11 indicates a gripper that holds the leading end of the transfer paper.

With the above structure, the discharge width at the transfer portion can be regulated well, which could not be achieved by the conventional method using the shield plate of the corona discharger, and as a result, toner scattering and flying can be prevented as much as possible. , It became possible to obtain a high-definition transferred image. Further, since the pressing sheet presses and contacts the screen supporting the transfer paper or the sheet-shaped dielectric, the transfer paper should be pressed sufficiently against the image carrier such as the photoconductor or the insulating drum. It was possible to improve the transfer efficiency. Furthermore, by compensating the strength of the above-mentioned dielectric with the pressing sheet by the pressing force of the pressing sheet, it becomes possible to widen the selection range of the material and conditions of the dielectric. Of course, since the pressing sheet presses the transfer paper against the image carrier via the dielectric, the pressing force is made sufficiently uniform by this dielectric, and the transfer paper is pressed uniformly against the image carrier. Therefore, even if the surface of the dielectric is slightly distorted, this distortion can be corrected and a high quality transferred image can be obtained. INDUSTRIAL APPLICABILITY The present invention is effective not only for single transfer of a single-color toner image but also for multiple transfer of a plurality of color toners or multiple transfer of the same toner, and it is possible to transfer an electrostatic latent image to a transfer paper whose surface is insulated. It also acts effectively on transcription. Further, the dielectric may be a belt-shaped one that moves endlessly outside the drum-shaped one.

[0042]

As described above, according to the present invention, it is possible to provide an image forming apparatus which enhances the adhesion between the transfer material held on the transfer material holding sheet and the image bearing member and does not cause transfer failure. it can.

Further, according to the present invention, since the pressing position of the pressing member for pressing the transfer material holding sheet is set within the area where the transfer material holding sheet presses the image carrier via the transfer material, the transfer material holding sheet The deformation of can be suppressed.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an electrophotographic color copying machine to which the present invention can be applied.

FIG. 2 is a perspective view of a transfer drum of the copying machine.

FIG. 3 is an explanatory diagram showing a discharge distribution by a transfer discharger at a transfer position.

FIG. 4 is an explanatory diagram showing directions of forces received by respective members at a transfer position.

FIG. 5 is a cross-sectional view of a transfer portion showing an embodiment of the present invention.

FIG. 6 is a graph showing the effect of the present invention.

FIG. 7 is a sectional view of a transfer portion according to another embodiment of the present invention.

FIG. 8 is a sectional view of a transfer portion according to another embodiment of the present invention.

FIG. 9 is a sectional view of a transfer portion according to another embodiment of the present invention.

FIG. 10 is a sectional view of a transfer portion showing a moving mechanism of a pressing sheet.

FIG. 11 is a partial perspective view of the frame body of the transfer drum for the moving mechanism of the pressing sheet.

[Explanation of symbols]

 1 Photosensitive Drum 20 Transfer Material 25 Transfer Discharger 33 Transfer Drum 38 Dielectric Screen 40 Pressing Sheet

Claims (1)

[Claims] 1. An image carrier, a transfer material holding unit that has a transfer material holding sheet that holds the transfer material, and that conveys the transfer material, and an image of the image carrier is held by the transfer material holding unit at a transfer position. An image forming apparatus having a transfer means for transferring the transfer material to the transferred transfer material, and the transfer material holding sheet is provided on the opposite side of the transfer material holding means to the image carrier. An image forming apparatus, comprising: a pressing member that presses the transfer material, the pressing position being within a region where the transfer material holding sheet presses the image carrier via the transfer material.