JPH04125674A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a spalling discharge due to the accumulation of a charge at the end edge part of a transfer material, and enable an uniform electrostatic charge on an image carrying body by providing a pressurizing member which pressurizes a transfer material carrying member, forming a conductive part on the pressurizing member, and making the potential of the conductive part variable. CONSTITUTION:A pressurizing member 18 which pressurizes a transfer carrying member 93 is provided in the discharging width of a discharging means, a conductive part 19 is formed on the pressurizing member 18, and the potential of the conductive part 19 is made variable. That is, the terminatory part of the transfer paper is turned into a state in which the conductive part 19 is directly grounded, and the electrostatic charge generated by the discharge of a corona discharger 10 for transfer is flowed to the conductive part 19 whose impedance is low. Therefore, the flow and accumulation of a plus electrostatic charge to the terminatory part of the transfer paper can be prevented. Thus, a satisfactory image without any image defect can be obtained even under a high wet circumstance.

Description

[Detailed Description of the Invention] No. 1 The present invention generally relates to an image forming apparatus,
In particular, an image obtained by transferring a toner image formed on an image carrier by an electrophotographic method or an electrostatic recording method to a transfer material supported on a transfer carrier member by applying a transfer electric field. The present invention relates to a forming device. Such image forming apparatuses include black-and-white, monochrome, or full-color electrophotographic copying machines, printers, and various other recording devices.

1. J and l1 Various multicolor (full color) image forming apparatuses have been proposed in the past, but a multicolor electronic image forming apparatus equipped with a developing device called a so-called rotary developing device is shown in FIG. A photocopying device (or printer) is illustrated.

To briefly explain with reference to FIG. 5, the multicolor electrophotographic copying apparatus includes an image bearing member, that is, a photosensitive drum 3, which is rotatably supported on a shaft and rotates in the direction of the arrow, and an image forming means is provided on the outer periphery of the image bearing member, that is, a photosensitive drum 3. is placed. The image forming means may be any means, but in this example, a primary charger 4 that uniformly charges the photosensitive drum 3 and a color-separated light image or a light image equivalent thereto are irradiated to form an image on the photosensitive drum 3. The photosensitive drum 3 includes an exposure means 8 formed of, for example, a laser beam exposure device, which forms an electrostatic latent image on the photosensitive drum 3, and a rotary developing device 1, which converts the electrostatic latent image on the photosensitive drum 3 into a visible image.

The rotary developing device 1 includes four developing devices lY, IM, and IC1I that separately store four color developers: yellow developer, magenta developer, cyan developer, and black developer.
BK and these four developing devices IY, IM, IC1IBK
It consists of a substantially cylindrical casing that holds and is rotatably supported. The rotary developing device 1 transports a desired developing device to a position facing the outer circumferential surface of the photosensitive drum 3 by rotating the housing, and develops an electrostatic latent image on the photosensitive drum, thereby producing full-color development for four colors. is configured to allow.

The visible image, that is, the toner image, on the photosensitive drum 3 is transferred onto a transfer material P carried by a transfer device 9 and conveyed. In this example, the transfer device 9 is a rotatably supported transfer drum, and the transfer drum 9 has cylinders 9a and 9 disposed at both ends, as will be understood with reference to FIG.
b, and a connecting portion 9c that connects both the cylinders 9a, 9b, and a transfer material carrying member 93 is stretched over the opening area of the outer peripheral surface of the cylinders 9a, 9b. The transfer material carrying member 93 is usually a film-like dielectric sheet such as polyethylene terephthalate or polyvinylidene fluoride resin film.

Further, the connecting portion 9c includes a transfer material gripper 7 that grips the transfer material P fed from the paper feeding device. Further, transfer dischargers 10 are arranged inside and outside the transfer drum 5.

A brief explanation of the process of forming a full-color image using the multicolor electrophotographic copying apparatus configured as described above is as follows.

The photosensitive drum 3 is uniformly charged by the primary charger 4, and the exposing means 8 irradiates the photosensitive drum 3 with a light image E according to image information, thereby forming an electrostatic latent image on the photosensitive drum 3. The electrostatic latent image is visualized as a toner image on the photosensitive drum 3 by the rotary developing device 1 using resin-based toner.

On the other hand, the transfer material P is sent to the transfer drum 9 by the registration roller 6 in synchronization with the image, its tip is gripped by the gripper 7, etc., and then conveyed by the transfer drum 9 in the direction of the arrow in the figure. .

Next, the transfer material carrying member of the transfer drum 9, i.e., the dielectric sheet 93, is subjected to a corona discharge of opposite polarity to the toner by the transfer discharger 10 from the back side of the transfer material carrying member of the transfer drum 9 in the area in contact with the photosensitive drum 3. The toner image is transferred to the transfer material P.

After the transfer material P has been subjected to the necessary number of transfer steps, it is separated by the separation claw 1.
5, it is peeled off from the transfer drum 9 and the conveyor belt 1
6 to the fixing device 17. After being fixed by heat in the fixing device 17, it is discharged outside the machine.

On the other hand, after the residual toner on the surface of the photosensitive drum 3 is cleaned by a cleaning device 12, the photosensitive drum 3 is subjected to the image forming process again.

Similarly, the surface of the dielectric sheet of the transfer drum 9 is cleaned by a cleaning device 13 such as a fur brush and a cleaning auxiliary means 14, and then subjected to the image forming process again.

Although the multicolor electrophotographic copying apparatus with the above configuration operates extremely well, research experiments conducted by the present inventors have shown that during the transfer process,
In particular, it has been found that when a polyvinylidene fluoride resin film or the like is used as the dielectric sheet 93, which is a transfer material carrying member, and a transfer paper is used as the transfer material P, a problem occurs particularly when the humidity is high. This point will be explained next.

FIG. 7 shows that a toner image of one color is transferred to a transfer material P on a transfer drum 9, and then this transfer material P is not separated (it is wound around the transfer drum 9 and transferred to the next transfer material P). 2 shows the state of charge at the trailing end of the transfer material P when it is rotated together with the transfer drum 9 to transfer a toner image corresponding to a color image.

In this state, the transfer discharger 10 is still in operation with respect to the end portion of the transfer material. The polarity of the transfer voltage supplied to the transfer discharger IO is, for example, when a latent image is formed with a negative charge and the toner of each developer is negatively charged to reversely develop the latent image. It is set to positive.

According to research experiments conducted by the present inventors, when a polyvinylidene fluoride resin film is used as the dielectric sheet 93 and a transfer paper is used as the transfer material P, the volume resistivity of the polyvinylidene fluoride resin film is 1QI8Ω・cm. , the volume resistance of the transfer paper is 109 (at high humidity) to 10111 (
(at low humidity) Ω・cm, the positive charge from the transfer discharger 10 of the transfer paper is injected into the transfer paper via the dielectric sheet 93, and the positive charge is applied to the terminal end of the transfer paper. It has been found that the particles are accumulated in the surface area Pa.

In addition, the present inventors have discovered that the positive charge accumulated in the surface area Pa of the trailing edge of the transfer paper generates a high electric field between the surface of the photosensitive drum and the trailing edge of the transfer paper as shown in FIG. Pa
When it leaves the photosensitive drum 3, a peeling discharge occurs, and the negative charge in the air is attracted by the positive charge on the transfer paper P and moves onto the transfer paper, but the positive charge in the air becomes negatively charged. Move onto the photosensitive drum 3 and press the photosensitive drum 3.
It has been found that damage, or memory effect, occurs over a width of several millimeters along the axial direction.

Further, since the photosensitive drum 3 is made to be negatively charged, if a positive charge adheres to the photosensitive drum, the positive charge does not attenuate easily.

This memory effect is caused by the -order charger 4 on the photosensitive drum 3.
The amount of primary charge on the photosensitive drum decreases in a striped manner along the axial width direction of the photosensitive drum, making it impossible to charge the photosensitive drum uniformly and causing image defects.

According to the results of experimental research conducted by the present inventors, the higher the humidity, the more severe the image defects are, and the longer the size of the transfer material P, for example, when an A3 size sheet is fed vertically, the more severe the image defects are. That's what I found out.

Therefore, an object of the present invention is to prevent peel-off discharge caused by accumulation of charge at the end of a transfer material, enable negative charging on an image carrier, and obtain high-quality images without image defects. The objective is to provide an image forming apparatus that can.

of The above object is achieved by an image forming apparatus according to the present invention.

In summary, it includes an image carrier on which a toner image is formed and a transfer material carrier that supports and conveys a transfer material, and the toner image on the image carrier is transferred to the image carrier of the transfer material carrier. and a transfer device that transfers onto a transfer material supported on the transfer material carrying member by an electric field generated by a discharge means disposed on the opposite side, the transfer device is configured to transfer images to a transfer material supported on the transfer material carrying member by an electric field generated by a discharge means disposed on the opposite side. a pressing member extending downstream from the introduction side in the moving direction of the transfer material carrying member and pressing the transfer material carrying member; further, a conductive portion is formed on the pressing member; The image forming apparatus is characterized in that the potential of the conductive portion is variable.

The means for varying the potential of the conductive part may be at least two resistors with different values provided between the conductive part and the ground, or at least two or more resistors with different values applied to the conductive part. can have different bias values. Furthermore, the potential of the conductive portion can be switched based on a signal from a means for detecting the position of the transfer material, and can also be switched using a signal obtained by a temperature and humidity detection member that detects the temperature and humidity inside the image forming apparatus. It is also possible to switch by

Next, one embodiment of the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

The present invention may be preferably practiced in a multicolor electrophotographic reproduction machine having a rotary development device as previously described in connection with FIG.

Therefore, in this embodiment, the image forming apparatus is embodied in the multicolor electrophotographic copying apparatus shown in FIG. 5, and is also equipped with the transfer device 9 shown in FIG. 6, whose structure and operation are as described above. Therefore, a description of the overall structure and operation of the multicolor electrophotographic copying device and transfer device 9 will be omitted.

FIG. 1 is a drawing that best represents the features of the present invention, and shows a part of the transfer device shown in FIG. 6, that is, a transfer drum 9. As shown in FIG. As described above, the transfer drum 9 has a dielectric constant of 3.0 to 13.0 and a volume resistivity of 10'' to IQ1 between the two cylinders 9 a s 9 b made of a conductive member such as metal.
A transfer material supporting member that satisfies at least two of the conditions of 4 Ω·cm and a thickness of 70 to 200 μm, that is, a dielectric sheet 93, such as a polyvinylidene fluoride resin (PV
dF) It is constructed by stretching a film.

The front and rear ends of the dielectric sheet 93 are fixed onto a connecting portion 9c that connects two cylinders 9a and 9b that constitute the transfer drum 9.

In this embodiment, the diameter of the transfer drum 9 is 160 mm,
The moving speed was set at 160 mm/sec. At the same time, the process speed, which is the moving speed of the photosensitive drum 3, etc., was also set to 160 mm/sec. Also, a transfer charger, that is,
The corona waste electric device 10 has an opening width of 19 mm, a distance between the discharge wire 101 and the outer peripheral surface of the photosensitive drum 3 which is an image bearing member is 10.5 mm, and a shield plate of the discharge wire 101 and the transfer corona discharge device 10. The distance between it and the bottom is 16m.
m, respectively.

In addition, the transfer corona discharger 10 has, for example, +4KV to +
A voltage of 10 KV is applied, and the transfer current is +25 μA ~ +
It is assumed to be 500μA.

On the other hand, an elastic suppressing member 18 was provided within the discharge width of the transfer corona discharger IO, extending from the introduction side of the dielectric sheet 93 toward the downstream side in the direction of movement thereof. The pressing member 18 is made of a synthetic resin film made of polyethylene, polypropylene, polyester, polyethylene terephthalate, etc., preferably having a volume resistivity of 10"Ω·cm or more, and is disposed over the entire area of the transfer section. In this embodiment, a polyethylene terephthalate resin film was used. Note that it is also possible to use a synthetic resin film having a volume resistivity of 1010 Ω·cm or more as the pressing member 18.

Further, the pressing member 18 presses the dielectric sheet 93 with its own elastic force, and its tip on the dielectric sheet side is located at the position where the transfer material P has finished contacting the photosensitive drum 3 or has started contacting it. It is preferable to set the position to a position corresponding to a position that is located at the same time as possible, or a position that is as close as possible.

As mentioned above, the pressing member 18 applies an appropriate pressing force to the dielectric sheet and has a thickness of 10 μm to 2 mm, preferably 75 μm for reasons such as not affecting the transfer electric field. Very good results were obtained when the thickness was set to 200 μm.

By the way, if the dielectric sheet 93 of the transfer drum 9 is simply pressed, the pressing member 18 may be provided from the side opposite to the introduction side of the dielectric sheet 93 toward the upstream side in the moving direction. With this configuration, transfer starts before the photosensitive drum and the transfer material come into contact with each other, and the effect of suppressing image scattering caused by this cannot be obtained. Therefore, as shown in this example, the pressing member is a dielectric sheet. It is preferable to provide it from the introduction side of 93 toward the downstream side in the moving direction.

According to the present invention, as shown in FIG. 1, a conductive portion 19 is formed on the pressing member 18. The conductive portion 19 is connected to the transfer corona discharger lO of the pressing member 18, as shown in the figure.
Although it is preferable to arrange it on the side, it is also possible to arrange it on the photosensitive drum 3 side, as shown by the dashed line.

Further, the conductive portion 19 is formed, for example, by coating on the pressing member 18 or by providing a sheet-like member on the pressing member 18.

As can be understood by referring to FIG. 2, it is preferable that the conductive portion 19 be formed in a region where discharge for transfer is actually performed. It was provided over a width of 7 mm from a position approximately 1 mm away from the tip of the pressing member 18, that is, the portion that contacts the dielectric sheet 93 of the transfer drum 9. At this time, the thickness of the conductive portion 19 was approximately 30 μm.

If the conductive part 19 is provided near the leading edge of the pressing member 18, it will be violently rubbed by the dielectric sheet 93 and further by the connecting part 9C of the transfer drum 9, which is undesirable as it may be damaged or worn out. . Conversely, the conductive part 19 is pressed by the pressing member 18
If it is formed at a distance of, for example, 5 mm or more from the tip, the effects brought about by the present invention will be reduced, which is also not preferable.

In FIG. 2, the part below the black line is a part for fixing the pressing member 18 to its support member, and the suppressing member 18
exerts its elastic force above the dotted line.

Furthermore, as will be better understood with reference to FIGS. 1 and 2, the conductive portion 19 provided on the pressing member 18 has a portion thereof, for example, an end portion extended, and a connecting portion 191 with the main body side. be done. The conductive portion 19 is grounded through this connecting portion 191, via a resistor R provided on the main body side, or directly.

The connection operation by the switching means such as directly grounding the conductive part 19 or grounding it through the resistor R1 provided on the main body side is performed by the paper guide 21 (the first 5) and the transfer section in which the transfer corona discharger IO is disposed downstream from the paper guide 21 in the transfer drum rotational direction. Refer to the figure. That is, in the transfer section, when the rear end of the transfer material passes, the conductive section 19 is directly grounded, and in other conditions, the resistor R1
It will be grounded via. Also, this resistance R5 is
It is good to set it to approximately 104Ω or more, preferably 10' to IQIOΩ. Furthermore, it is also possible to set it in a floating state without grounding it through a resistor.

The present inventors formed a latent image on the negatively charged photosensitive drum 3 in the image forming apparatus of this embodiment, and obtained a toner image by reversal development using toner having an average particle size of approximately 12 μm. Ta. At this time, the toner is composed of a resin containing a coloring material and a small amount of additives to improve charge control and lubricity, and is triboelectrically charged with carrier particles in a developing device to become negatively charged. Ta.

The toner image was then transferred to a transfer material by the transfer device having the above-mentioned structure.Then, the transfer material was separated from the transfer drum 9 and fixed by a fixing device.

When image formation was performed in a high temperature environment using a transfer device having such a configuration, it became possible to obtain a good image without image defects. This is considered to be due to the reasons described below.

In other words, as pointed out in Item 1 above, in a high temperature environment, the dielectric sheet 93
The resistance value of both the transfer paper and the transfer paper as the transfer material P decreases, and a positive charge is injected into the transfer paper due to the electric field created by the transfer discharger 10.

However, as can be better understood with reference to FIG. 3, at the end of the transfer paper, the conductive part 19 is directly grounded, so that the electric charge generated by the discharge of the transfer corona discharger 10 is reduced. A large portion, or a large portion, flows toward the conductive portion 19, which has a lower impedance. Therefore,
The inflow and accumulation of positive charges to the end of the transfer paper is reduced or prevented, and a high electric field is not generated between the photosensitive drum 3 and the surface of the photosensitive drum 3, causing damage on the photosensitive drum 3, that is, a memory effect. As a result, good images without image defects can now be obtained even in high-temperature environments.

Further, by providing the conductive portion 19, it is possible to prevent unevenness in the surface potential of the pressing member 18, and it is also possible to prevent uneven transfer from occurring at the same time.

Furthermore, in this embodiment, the transfer material position detection member 20 is provided outside the transfer drum 9;
Needless to say, the sensor may be provided inside the transfer drum 9, or furthermore, a light transmission type sensor or the like may be provided inside the transfer drum 9 on the outside image side.

Further, in this embodiment, the resistor R1 is used as a means for varying the potential, but a bias may be applied instead of connecting the resistor. In this case, for example, usually +50
It is preferable to apply a voltage of about 0 to +2000 V and ground the trailing edge of the paper. The bias to be applied is not limited to those mentioned above,
Direct current, alternating current, and direct current with alternating current superimposed are also suitably used.

Further, in this embodiment, the transfer material trailing edge position detection member 20
However, when using a transfer drum that grips the leading edge of the transfer material with a gripper 7 or the like and carries and conveys the transfer material onto the transfer drum as shown in this embodiment, For example, the distance from the gripper position to the trailing edge position of the paper may be calculated in advance based on the size detection signal of the paper cassette, and the resistance and grounding may be switched based on the data.

Furthermore, it goes without saying that the same effect can be obtained even if the transfer drum described above does not have the gripper 7 on the transfer drum and the transfer material is supported on the transfer drum by electrostatic adsorption means.

As a result of further research, the present inventors installed a temperature/humidity detecting member (not shown) inside the main body of the image forming apparatus, and based on the signal from the temperature/humidity detecting member, the The conductive portion 19 is grounded based on a signal indicating the rear end position of the transfer material obtained by the transfer material position detection member 20. Even better results were obtained with the refusal configuration.

Furthermore, it is also possible to change the time during which the conductive portion 19 is grounded by the switching means based on the signal from the temperature/humidity detection member. It has been found that a good effect can be obtained by keeping the conductive part grounded for a long time in a high-temperature environment, for example. Furthermore, at the same time, it has been found that the same effect can be obtained by reducing the resistance value connected to the conductive part in a high temperature environment.

The present invention can also be embodied in a multicolor electrophotographic copying apparatus having four image forming units I to TV as shown in FIG.

In this embodiment, each image forming unit I-IV has photosensitive drums 38-3d, and primary chargers 4a-4d are arranged around the photosensitive drums 38-3d.
, exposure means 8a to 8d, developing devices 1a to 1d, transfer chargers 10a to 10d, static eliminators 11a to lid
and 13a to 13ds cleaners 12a to 12d
Further, an endless belt-shaped conveying means 22, which is a transfer material carrying member, is arranged below the photosensitive drums so as to pass through each image forming unit.

On the other hand, a pressing member 18 (18a to 18d) is provided to press the endless belt-like conveying means 22 toward each photosensitive drum within the discharge width of each of the transfer dischargers 10a=10d, and the suppressing member The conductive part 19 (19a-1
9d) is formed. A part of the conductive part 19 is provided with a connecting part 191 (191a-191d) to the main body side, and is configured to be grounded to the main body side via a resistor R (Ra=Rd) or directly. ing.

Furthermore, a transfer material position detection member 20a is provided between the paper feed guide 21 and the first transfer section. Based on the signal indicating the rear end of the transfer material obtained by the transfer material position detection member 20a, when the rear end of the transfer material passes through the transfer position in each image forming unit 1-IV, the conductive portion 19a=19
d is directly grounded, and in other states it is grounded through a resistor.

According to the present invention, in this example as well, it was possible to form a good image without image defects, as in the above-mentioned example.

The image forming apparatus according to the present invention, which has the configuration described in detail above, prevents peeling discharge caused by accumulation of charge at the end of the transfer material, and prevents -like charge on the image carrier. It has the advantage of being able to obtain high-quality images without image defects.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the vicinity of a transfer means of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged front view of the pressing member and the conductive part in the embodiment of FIG. 1. FIG. 3 is a principle explanatory diagram for explaining the effects of the present invention. FIG. 4 is a sectional view of another embodiment of an image forming apparatus that can embody the present invention. FIG. 5 is a sectional view of a conventional image forming apparatus. FIG. 6 is a sectional view of a main part of a conventional transfer device. FIGS. 7 and 8 are principle explanatory diagrams showing the vicinity of a transfer means of a conventional image forming apparatus and explaining the problems thereof. 3.3a to 3d: Photosensitive drum 9: Transfer drum 93.22: Transfer material carrying member (dielectric sheet, conveyor belt) 10, lOa to lOd: Transfer discharger 18.18a to 18d: Pressing member 19.19a to 19d: Conductive part 191: Connection part 20: Transfer material position detection member Fig. 2 Fig. 3 Fig. 4 Fig. 5

Claims (1)

[Claims] 1) An image carrier on which a toner image is formed, and a transfer material carrier that supports and conveys a transfer material, the toner image on the image carrier being opposite to the image carrier of the transfer material carrier. In the image forming apparatus, the image forming apparatus includes a transfer device that performs transfer onto a transfer material supported on the transfer material carrying member by an electric field generated by a discharge means disposed on the side, and the transfer device transfers the image within the discharge width of the discharge means. It has a pressing member that extends downstream from the introduction side in the moving direction of the transfer material carrying member and presses the transfer material carrying member, further, a conductive part is formed on the pressing member, and the conductive part An image forming apparatus characterized in that the potential of is variable.