JP3210093B2 - 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 electrophotographic apparatus such as a copying machine and a printer, and an image forming apparatus such as an electrostatic recording apparatus.

2. Description of the Related Art Conventionally, a transfer process of electrostatically transferring a toner image on an image carrier such as a photoconductor to a transfer sheet as a transfer material has been used.

In an image forming apparatus using an electrostatic transfer process, when the transfer paper is dry or when the apparatus is used in a dry environment, the resistance of the transfer paper increases, so that the transfer paper is transported before image transfer. The inside is charged by friction with a paper feed roller, a registration roller, and the like. In a triboelectrically charged transfer paper, the toner on the image carrier scatters on the transfer paper at a position upstream of the transfer position at which the image carrier and the transfer paper come into contact with each other, disturbing the image (hereinafter referred to as "blur"). There is.

Further, when thick transfer paper such as a postcard absorbs moisture, charges flow into the transfer paper from the transfer charger, and the charges are accumulated on the surface of the transfer paper. There is a problem that scattering occurs.

A transfer means is provided for abutting the transfer paper on the transferable toner image formed on the surface of the image carrier and for applying a transfer charge from the back surface of the transfer paper. An image forming apparatus configured to transfer a toner image to a transfer material is known.

In such an image forming apparatus, a contact-type transfer unit has been proposed which is configured to be used in a state in which it is in contact with a transfer material such as a transfer roller transfer belt as a transfer unit.

The transfer roller does not require a high-voltage power supply, does not generate ozone, and is transported and fixed after the transfer position, as compared with transfer means using a corona discharger having a wire electrode and a shield electrode. There are many advantages such as a small possibility of transfer misalignment due to the relationship with the mechanism, and a compact and compact structure as a whole.

However, at the transfer position, the transfer material is pressed against the image carrier by the transfer means, so that there is a case where the inside of the transferred image, that is, in the case of the character image, the inside of the character becomes missing during the transfer. . This hollowing occurred remarkably when a thicker paper than a plain paper such as a postcard or a business card was used as a transfer material. This is thicker than plain paper,
This is because the contact pressure against the image carrier increases.

(Object of the Invention) It is an object of the present invention to provide an image forming apparatus in which omission during transfer is prevented.

Another object of the present invention is to provide an image forming apparatus in which scattering of toner is prevented.

Another object of the present invention is to provide an image forming apparatus in which, when thick paper is used as the transfer material, the contact pressure of the thick paper against the image carrier is reduced.

(Constitution of the Invention) In order to achieve the above object, the present invention provides an image bearing member and an image bearing member which is opposite to the image bearing member side of the transfer material for transferring a toner image formed on the image bearing member to the transfer material. In the image forming apparatus having a transfer unit that contacts the side and a grounded guide member that guides the transfer material to the transfer position, the guide member has a small size smaller than the maximum width of the transfer material usable in the apparatus. It has a cutout portion corresponding to the transfer material, and the apparatus has a charge removing member provided corresponding to the cutout portion for discharging the transfer material before transfer.

[0013]

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

FIG. 1 is a schematic side view of a main part of an image forming apparatus showing an embodiment of the present invention.

A transfer roller 4 having an axis parallel to the axis of the photoconductor 1 is provided on the photoconductor 1 as a cylindrical image carrier that has an axis perpendicular to the paper surface and rotates in the direction of arrow A. It is pressed against the photoreceptor 1 by the urging means and rotates in the direction of arrow B.

The transfer material P guided to the transfer position by the transfer guides 2 and 3 is fed to the left side in the figure in synchronization with the toner image formed on the surface of the photosensitive member 1 in advance.
During the transfer, a DC voltage having a polarity opposite to that of the toner image is applied to the transfer roller 4 by a transfer power supply 4a.

After the photoconductor 1 contacts the photoconductor 1 and is uniformly negatively charged by the charging roller 1 which is a charging member to which a voltage is applied, the toner image is transferred to the photoconductor 1 in accordance with image information of an original or the like. Is subjected to image exposure L, and the electrostatic latent image formed thereby is visualized by toner powder (positively charged) by the developing device 23.
After the transfer, the residual toner is removed from the photosensitive drum 1 by the cleaner 24, and then the charge is uniformly removed by the pre-exposure lamp, and the next image is formed again.

On the other hand, the transfer material P after the transfer is neutralized by the needle electrode 7b supported by the insulating member 7. At this time, a voltage having a polarity opposite to the transfer voltage is applied to the needle electrodes by the power supply 7a. The toner image is fixed on the transfer material P from which the charge has been removed by the fixing device 25.

It is a matter of course that a cleaner for removing residual toner remaining on the surface of the photoreceptor after transfer and other members necessary for image formation are provided.

Reference numeral 6 denotes a charge removing member made of a conductive material such as iron or aluminum, which is located between the transfer guides 2 and 3 and the transfer roller 4, and is connected to the ground so that the potential is maintained at 0V. I have. The volume resistance of the static elimination member is 10
^It is preferably ⁹ Ωcm or less.

FIG. 2 is a perspective view showing the positional relationship between the charge removing member 6, the lower transfer guide 3, and the transfer roller 4.

The transfer lower guide 3 is made of a conductive material such as aluminum, iron, etc.
Has the function of releasing the electric charge of

Here, a notch corresponding to the passage area of the small-size paper is provided in the lower transfer guide 3 in order to prevent the transfer omission which is likely to occur when a small-size thick paper such as a postcard or a business card is used as the transfer material P. Part is provided. This notch is the maximum size of the transfer material that can be used for this device, A4
The postcard and the business card are provided such that the approach contact angle of the transfer material to the photoconductor 1 is smaller for the postcard than for the plain paper and for the business card than for the postcard. That is, the smaller the size of the transfer material, the greater the distance between the most downstream portion guided by the guide 3 and the transfer position, and the approach of the leading end of the transfer material to the transfer position approaches the tangent of the photoconductor 1. Become. Therefore, the smaller the size of the transfer material, the smaller the contact pressure with the photoreceptor.

However, while the maximum sheet passing width is A4 size in a direction substantially perpendicular to the transfer material moving direction, notches corresponding to postcards and business card sizes are provided, so that A4 size paper is used as the transfer material. Is used, the A4 size paper and the transfer lower guide 3 do not come into contact with each other at the cutout portion. For this reason, if the transfer material P is guided to the transfer position without removing the triboelectric charge or the like in the area corresponding to the cutout portion of the A4 size paper, the toner may be scattered in this area.

Since the charge removing member 6 has the same width as the postcard and is in contact with the transfer material P, the charge removal which was insufficient with the transfer lower guide 3 is completed. That is, the charge removing member 6 removes the charge of at least the area of the transfer material P corresponding to the notch of the lower guide 3 in a direction substantially perpendicular to the transfer material moving direction. The charge removing member 6 may be provided so as to correspond to the maximum size width of the transfer material.

As shown in FIG. 3, since the electric field generated by the transfer roller 4 is shielded by the conductive charge eliminating member 6, the transfer material can be prevented from being charged by the electric field of the transfer roller. That is, the charge-up of the transfer material does not occur, and the toner image is transferred before the photoconductor and the transfer material come into contact with each other, thereby preventing the image from being disturbed (scattered) due to the scattering of the toner.

In this embodiment, an OPC photosensitive member having a diameter of 24 mm and a process speed of 50 mm / sec, and an OPC photosensitive member having a diameter of 12 mm
A transfer roller having a volume resistance of 10 ⁶ Ωcm was used. In addition, stainless steel was used for the static elimination member, and 10 mm from the transfer roller.
In a low temperature and low humidity environment at a temperature of 15 ° C. and a humidity of 10%, a good transfer image was obtained without scattering images.

FIG. 4 is a schematic view of a main part of an image forming apparatus showing a second embodiment of the charge removing member.

Reference numeral 3 'denotes a transfer guide, which has the same shape as the transfer guide 3 of FIG. 2, and is made of a material such as resin which is easy to process.

The static elimination member 6 is formed by bonding two members of a conductive metal portion 8 and a conductive sheet portion 9 with an adhesive layer 10 such as a conductive double-sided tape or a conductive adhesive to establish electrical continuity. . There is no problem even if it is firmly fixed with metal screws or the like instead of bonding.

The sheet portion 9 is formed by coating a thin layer film (thickness: 10 to 200 μm) of polyimide, PET (polyethylene terephthalate), polypropylene or the like with carbon, carbon dispersed PTFE or the like, or by depositing aluminum, and has a resistance value. Those having a value of 10 ⁹ Ωcm or less are preferable. The sheet portion 9 is provided so as to be in contact with the transfer material P in a direction substantially perpendicular to the transfer material moving direction, corresponding to at least a portion of the guide 3 ′ with a notch. In the present embodiment, the sheet portion 9 of the charge removing member 6 has the same width as a postcard, uses carbon-added silicon rubber having a film thickness of about 50 μm, and sets the length of the free end portion from the sheet metal portion to 2.
When the distance was set to 5 mm, the resistance value became 10 ² Ωcm, and a good result against image scattering was obtained. In addition, the smaller the resistance value of the sheet portion, the greater the effect obtained on the stiffness.

In this embodiment, since the sheet portion has elasticity, the charge removing member comes into contact with the transfer paper sufficiently effectively.
The static elimination effect further increases. Further, since the sheet portion is softly contacted with a light pressure, the transfer path of the transfer material does not change, and the contact pressure of the transfer material against the photosensitive member does not change. For this reason,
Even if a small-sized cardboard is used as the transfer material, no hollowing occurs.

FIG. 5 is a schematic view of a main part of an image forming apparatus showing a third embodiment of the charge removing member.

The fiber elimination member 11 has a brush-like fiber member at the tip end. The brush fiber comes into contact with the transfer material P at least in a portion where the guide 3 ′ has a notch (a paper passing area of a postcard) in a substantial direction of the transfer material movement direction.

The brush portion is made of stainless steel, carbon fiber, and the like, and has a bundle of 20 to 200 fine wires of stainless steel and 5 to 40 μm in thickness and 200 to 1 carbon fiber.
It is a bundle of 000 pieces, and is coated with a resin or the like except for the cut surface to give a film to the brush.

A bundle of 100 stainless steel brushes having a diameter of 5 μm was installed at a pitch of 1.6 mm, and the hair length was set to 2.5 mm.
As a result, good results were obtained with respect to both voids and scattering.

FIG. 6 is a schematic view of a main part of an image forming apparatus showing a fourth embodiment of the charge removing member.

The charge removing member 6 is a varistor 2 as a constant voltage element.
0 is grounded. In the case where the charge removing member 6 is directly grounded as in the above-described embodiment, in a high-temperature and high-humidity environment, the transfer material has a low resistance, and the transfer current flows out through the transfer material and the charge removing member. And the transfer may be lost. A varistor 20 is provided to prevent this transfer omission. By providing the varistor 20, when a transfer current flows, a predetermined voltage is applied to the neutralization member with respect to the ground. If the value of this voltage is small, there is no effect on transfer omission, and if it is too large, scattering occurs. The effect is reduced.

In an experiment, when the transfer bias voltage applied to the transfer roller is -3.0 kV, good results can be obtained with respect to transfer omission by setting the varistor threshold voltage to 600 V to 1.2 kV.

FIG. 7 is a schematic view of a main part of an image forming apparatus showing a fifth embodiment of the charge removing member. In the present embodiment, a power supply 21 is used instead of the constant voltage element 20 in FIG. 6, and a DC voltage having the same polarity as the toner and a polarity opposite to the transfer bias voltage is applied to the charge removing member 6 by the power supply 21.

In the experiment, the transfer bias voltage was -2.5 kV
At this time, when a voltage of +1 kV to 2 kV was applied to the charge removing member, the effect on scattering was further increased.

Further, in this case, even if the charge removing member 6 and the transfer material P were not in contact with each other, the effect of scattering was observed.

FIG. 8 is a schematic view of a main part of an image forming apparatus showing a sixth embodiment of the charge removing member.

The discharging member 6 is inclined at an acute angle θ in the direction in which the transfer material P is transported. The width of the charge removing member is the same as in the above embodiment. For this reason, even if the transferred transfer material is lower curl paper, the transfer material easily comes into contact with the charge removing member 6 and is transferred, so that the occurrence of jams is reduced.

Further, the contact pressure against the photosensitive drum due to the elasticity of the sheet portion is reduced, which is also effective against dropout.

Further, since the discharging member wraps around the transfer roller, the effect of shielding the electric field is increased, and the effect of reducing the electric field is obtained.

[0047]

As described above, the transfer material guide member has a region which does not come into contact with the transfer material having the maximum width, and the charge removing member provided at least in correspondence with the region to remove the charge of the transfer material before transfer. Is provided, it is possible to prevent the toner on the image bearing member from scattering on the transfer material without causing a dropout during the transfer.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an image forming apparatus embodying the present invention.

FIG. 2 is a perspective view illustrating a positional relationship among a transfer roller, a transfer guide, and a charge removing member.

FIG. 3 is an explanatory diagram illustrating a difference in a charge state of a transfer material depending on the presence or absence of a charge removing member.

FIG. 4 is a schematic view of an image forming apparatus showing a second embodiment of the charge removing member.

FIG. 5 is a schematic view of an image forming apparatus showing a third embodiment of a charge removing member.

FIG. 6 is a schematic diagram of an image forming apparatus showing a fourth embodiment of a charge removing member.

FIG. 7 is a schematic view of an image forming apparatus showing a fifth embodiment of the charge removing member.

FIG. 8 is a schematic view of an image forming apparatus showing a sixth embodiment of a charge removing member.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum 2 upper transfer guide 3 lower transfer guide 4 transfer roller 6 neutralizing member (before transfer) 7 neutralizing member (after transfer) 8, 12 sheet metal member 9, 13 sheet member 11 brush-like neutralizing member 4a power supply 20 varistor 21 power supply

Claims (4)

(57) [Claims] An image carrier; a transfer unit that contacts a side of the transfer material opposite to the image carrier side to transfer a toner image formed on the image carrier to a transfer material; A grounded guide member for guiding the material, wherein the guide member has a cutout portion corresponding to a small-sized transfer material smaller than the maximum width of the transfer material usable in the device,
The image forming apparatus according to claim 1, wherein the apparatus includes a charge removing member provided corresponding to the cutout portion for removing charge from a transfer material before transfer. 2. The image forming apparatus according to claim 1, wherein the charge removing member has a conductive sheet member. 3. The image forming apparatus according to claim 1, wherein the charge removing member has a brush-like fiber. Wherein said guide member is an image forming apparatus according to any one of claims 1 to 3, characterized in that for guiding the transfer material lower surface.