JP3056792B2 - Transfer device for 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 a transfer device for an image forming apparatus, such as a copying machine or a printer, which performs superposition transfer on a transfer member.

[0002]

2. Description of the Related Art As an image forming apparatus for superimposing and transferring images onto a transfer member, a color-separated image is sequentially formed on a latent image carrier, for example, a photoconductor drum, and the image is brought into contact with the photoconductor drum and synchronized therewith. A color copying machine that forms a color image by superimposing and transferring, for example, yellow, magenta, cyan, and black images onto a transfer paper wound around a transfer drum that rotates at the same linear speed as the photosensitive drum. It has been known.

In such an image forming apparatus, the transfer drum is a transfer drum in which a flexible dielectric such as a polyethylene terephthalate film (trade name: Mylar) is wound around a frame, and the transfer drum is fed from a paper feed unit. It is necessary to rotate the leading end of the transfer paper to a clamp to bring the transfer paper into close contact with the peripheral surface of the latent image carrier, for example, the photosensitive drum without any gap. If there is a poor adhesion portion between the transfer paper and the peripheral surface of the photosensitive drum, transfer-missing development occurs, resulting in a blank copy, and the copy quality deteriorates. In particular, in the case of a color copying machine, in the case where the color-separated images are superimposed and transferred, if there is an incomplete transfer portion even in one color image, the quality of the obtained color image may be degraded.

As a method of bringing the transfer paper wound around the transfer film forming the outer peripheral surface of the transfer drum into close contact with the surface of the photosensitive drum at the transfer section, for example, all four circumferences of the transfer film are attached to a frame of the transfer drum. At the same time, in the vicinity of the transfer charge application area by the transfer charger, the transfer paper is pressed against the inside of the transfer film over substantially the entire width of the portion between both side ring portions of the frame inside the transfer drum to transfer the transfer paper through the transfer film to the photosensitive member. 2. Description of the Related Art There is known an apparatus provided with a presser blade that makes close contact with a drum.

However, in this apparatus, if the pressing film is used for a long time due to the deformation of the pressing member with time and the displacement of the pressing member at the place where the transfer film is stuck to the frame, the transfer film at the transfer position cannot be used. Appropriate close contact between the transfer paper and the photoconductor cannot be guaranteed, and the replacement of the pressing member and the replacement of the transfer film must be frequently performed.

When the outer surface of the transfer film is roughened (matte surface) and the transfer paper and the photoreceptor are electrostatically attracted to each other at the transfer portion, air between the transfer film and the transfer paper is released to reduce air bubbles. It is also conceivable to prevent the transfer of the transfer film, transfer paper, and photoreceptor caused by air bubbles due to defective attachment and detachment.

However, according to this method, the surface of the transfer film that is in contact with the transfer paper is made rough, so that it can be viewed microscopically.
The adhesion between the transfer film and the transfer paper is inferior to that of the transfer film having a glossy surface, and the electrostatic attraction force between the transfer paper and the transfer film is significantly deteriorated. As a result, the trailing edge of the transfer paper is likely to float from the transfer film, and during superposition transfer, it may come into contact with a peripheral member, for example, a transfer film static elimination charger casing or the like, resulting in image displacement.

In order to solve such a conventional problem, a circumscribed portion of a frame of a transfer drum is circumscribed, and is pressed against a photoreceptor drum or a rotating member integrally rotating therewith at a position facing the photoreceptor drum. An annular member made of an elastic body is provided, and the pressing force between the annular member and the photosensitive member or the rotating member is gradually increased toward the end in the axial direction in relation to the sectional shape of the photosensitive member or the rotating member. For example, the present applicant has proposed in Japanese Patent Application Laid-Open No. 2-151886 to make the shape larger. Although the transfer paper can be brought into close contact with the photoreceptor by this known means, a special member is required to ensure the close contact, and thus there is a problem that the cost is increased accordingly.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides an image forming apparatus capable of bringing a transfer member held by a flexible dielectric transfer member into close contact with a photosensitive member with a simple structure. It is an object to provide a transfer device.

[0010]

In order to solve the above-mentioned problems, the present invention provides a flexible dielectric transfer member which holds a transfer member and is arranged in contact with a latent image carrier, and the flexible dielectric transfer member. A transfer roller that contacts a surface of the transfer member opposite to the contact surface of the latent image carrier and transfers an image on the latent image carrier to a transfer member; The pressing force of the flexible dielectric transfer member pressed against the latent image carrier by the transfer roller is such that the central portion of the latent image carrier in the axial direction is larger than both ends in the axial direction. It is characterized in that it has a larger diameter as it approaches the portion corresponding to the center.

[0011]

According to the present invention, in a hollow cylindrical transfer drum formed by winding a flexible dielectric member around a frame and placed in contact with the latent image carrier, the drum is opposed to the latent image carrier. The transfer roller arranged is formed as a drum-shaped conductive elastic roller. The transfer roller presses a transfer member conveyed by the transfer drum, for example, transfer paper, against the latent image carrier, and a plurality of toner images on the latent image carrier are rotated by rotation of the latent image carrier and the transfer drum. The image is transferred to the transfer member repeatedly. When the drum-shaped transfer roller is pressed against the transfer drum, the pressing force at the central portion in the axial direction and the pressing force at both ends are increased. As a result, a larger pressing force is applied to the central portion where the adhesion between the hollow cylindrical transfer drum, the transfer member, and the latent image carrier is poor, so that good adhesion can be obtained over the entirety thereof, and Insufficient transfer is eliminated.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on an embodiment shown in the drawings.

In FIG. 1, after a latent image carrier 1, for example, a photosensitive drum 1 is charged by a charger (not shown), image light from a document 3 is separated by a filter 2 and exposed. As the filter 2, for example, a blue filter 2
B, green filter 2G, red filter 2R, yellow filter 2
The one having Y and formed to be switchable is used. A developing device having a developer of a color corresponding to the color of each filter by a developing device 4 by sequentially exposing and exposing the image light of the document through blue, green, red, and yellow filters to form a latent image;
For example, the four color toner images obtained by developing with a yellow developing unit 4Y, a magenta developing unit 4M, a cyan developing unit 4C, and a black developing unit 4BK are arranged in contact with the photosensitive drum 1, and at the same linear speed. One color is transferred to the transfer paper S wound around the transfer drum 5 rotated in synchronization with 1 for each rotation, and the toner images of four colors are superimposed and transferred by four rotations. At the time of transfer, a transfer roller 6 serving as a transfer unit disposed inside the photosensitive drum 1 so as to face the photosensitive drum 1 acts.

As shown in FIGS. 2 and 3, the transfer drum 5 has a metal frame 9 made of aluminum or the like including annular portions 7 at both ends and one connecting beam portion 8 connecting the annular portions 7 to each other. , The front edge in the rotation direction of the frame 9 is held by the connecting beam portion 8,
A flexible dielectric member which is wound around the outer peripheral surface of the frame 9 by making the side edge contact along the outer peripheral surface of the ring portion 7 and the rear edge abuts on the connecting beam portion 8 can be used. The flexible transfer film 10 forms a hollow cylindrical body. As the transfer film 10, for example, a polyethylene terephthalate film (trade name: Mylar) of about 75 to 150 μm is generally used.

The leading end of the transfer paper S fed from the paper supply unit 12 is gripped by a clamper 11 provided on the connecting beam 8 of the transfer drum 5 and electrostatically attracted to the transfer film 10 as the transfer drum 5 rotates. The toner image is wound around the transfer drum 5 in a fixed state without any deviation. When the transfer paper S wound around the transfer drum 5 passes through the contact position between the transfer drum 5 and the photosensitive drum 1, a toner image is transferred from the photosensitive drum 1 under the action of the transfer roller 6.

When the necessary rotation, for example, four rotations, and the transfer of the toner images of all colors is completed, the clamper 11 is moved to the position B.
Is released and the separation claw 13 acts to transfer the transfer paper to the transfer drum 5.
And is fixed by the fixing device 14 and discharged.

The transfer roller 6 is arranged inside the transfer drum 5, is arranged to be in pressure contact with the photosensitive drum 1 via the transfer film 12, and is rotated according to the rotation of the transfer roller 6 or the photosensitive drum 1.

The transfer roller 6 is formed of a conductive material, and is formed in a center convex drum shape as an elastic body having a larger diameter as it approaches a portion corresponding to the center of the photosensitive drum 1 in the axial direction.

Since the transfer roller 6 is made of a conductive material, it can apply a bias voltage, and can have a transfer function of transferring the toner image on the photosensitive drum 1 to transfer paper. Since the transfer film 12 is an elastic body, the transfer film 12 can be satisfactorily adhered to the photosensitive drum 1 in the entire area where the transfer film 12 is pressed in the axial direction.

The annular portions 7 on both sides of the transfer drum 5 are pressed against the outer peripheral surface of the photosensitive drum 1, and the transfer roller 6 formed shorter than the length between the annular portions 7 as shown in FIG. It is pressed into contact with the photosensitive drum 1 via the transfer film 10. As a result, the transfer roller 6 is closer to the central portion where poor adhesion is likely to occur.
And the transfer paper S can be securely brought into close contact with the photosensitive drum 1 without any looseness.

Since the transfer roller 6 can directly press the transfer film toward the photosensitive drum 1 without contacting the annular portion 7 of the transfer drum 5, the transfer paper can be surely pressed.

A high voltage is applied to the transfer roller 6 so that the transfer roller 6 can be used as an alternative to a normal transfer charger, and can also be used as a means for adhering the transfer device and the transfer paper.

[0023]

According to the present invention, by using a transfer roller made of a drum-shaped conductive elastic material, the transfer paper can be simultaneously brought into close contact with the photosensitive drum and the transfer operation can be performed simultaneously. It was possible to satisfactorily adhere at any position in the above.

According to the present invention, the transfer means is provided as usual, and both the function as the means for bringing the transfer paper into close contact and the transfer function as the normal transfer means can be achieved without requiring any additional means. Thus, the number of parts was reduced and the cost was reduced.

[Brief description of the drawings]

FIG. 1 is an overall explanatory diagram of an image forming apparatus.

FIG. 2 is a cross-sectional view illustrating a relationship between a photosensitive drum, a transfer drum, and a transfer roller.

FIG. 3 is a perspective view of a transfer drum.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Latent image carrier 5 Transfer drum 6 Transfer roller 7 Annular part 8 Connecting beam 9 Frame 10 Transfer film

Claims (1)

(57) [Claims] 1. A flexible dielectric transfer member that holds a transfer member and is arranged in contact with a latent image carrier, and a flexible dielectric transfer member that is opposite to a contact surface of the latent image carrier of the flexible dielectric transfer member. A transfer roller that contacts a surface and transfers an image on the latent image carrier to a transfer member, wherein the transfer roller is pressed against the latent image carrier by the transfer roller. As the pressing force of the flexible dielectric transfer member is larger at the center than at both ends in the axial direction,
A transfer device characterized in that the transfer device has a larger diameter as it approaches a portion corresponding to the center of the latent image carrier in the axial direction.