JPS6364783B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus in which a transfer material is superimposed on a developed image carried on an image carrier and a corona discharge is applied from the back side to perform transfer.

Conventionally, various image forming apparatuses have been proposed that use electrophotography to form a developed image on an image bearing member such as a photoreceptor and transfer it onto a transfer material. It is widely used as an excellent material that does not apply mechanical load to the body surface.

Such a corona transfer device generally has a configuration in which a corona discharge wire is stretched within a U-shaped shield case surrounded on three sides by conductive members such as metal.

The developed image to be transferred onto the transfer material by such a corona transfer device includes not only the conventional two-component developer, but also the one-component developer which has recently become popular.

When transferring such a developed image, (1) the characters in the transferred image became thicker than the original, and scattered spots appeared around the lines. Also, (2) characters on the transferred image after passing through a fixing roller such as a heating roller were crushed or had scattering marks.

Furthermore, (3) when the humidity was low, the transfer efficiency decreased and a hollow phenomenon occurred in the transferred image.

In particular, the above-mentioned problem was found to be particularly noticeable in images developed using insulating one-component developers.

The present invention has been made in view of the above points and provides a new and excellent image forming apparatus.

That is, the present invention provides an image forming apparatus in which a transfer material is brought into contact with a developed image formed on an image carrier, and a corona discharge is applied from the back side of the transfer material to transfer the developed image onto the transfer material. A transfer corona discharge means has a conductive shield case having an opening on the side opposite to the conductive shield case, an insulating member provided on the inner surface of both side walls of the conductive shield case, and a transfer corona discharge means with respect to the moving direction of the transfer material. a static eliminator disposed adjacent to the downstream side of the static eliminator, the distance between the tip of the static eliminator and the tangent to the image carrier in the transfer section on the static eliminator side of the transfer corona discharge means; The distance between the tip of the side wall of the shield case and the tangent to the image carrier in the transfer section is set to be greater than the distance between the tip of the side wall of the shield case and the tangent to the image carrier in the transfer section.

Hereinafter, details of the present invention will be explained using specific examples with reference to the drawings.

Reference numeral 1 denotes an image carrier such as a photosensitive drum, which rotates in the direction of the arrow. A developed image D is formed on the surface of the image carrier by an image forming means (not shown) and reaches the transfer position.

2 is a transfer material, and 3 is a specific example of a corona transfer device based on the present invention. The corona transfer device 3 includes a corona discharge wire 4, a shield case surrounding the corona discharge wire 4, which has a side wall 5 on the side where the transfer material enters, a bottom surface 6, and a side wall 7 on the side where the transfer material is separated, which are made of a conductive member such as metal.
Insulating members 8 and 9 are attached to the inner surfaces of the side walls 5 and 7, respectively.

In the figure, A is the close contact area where the transfer material 2 comes into close contact with the surface of the image carrier 1, B is the close contact area where the transfer material 2 is in close contact with the surface of the image carrier 1, and C is the contact area where the transfer material 2 is in close contact with the surface of the image carrier 1.
This is a separation area that separates the image carrier 1 from the surface of the image carrier 1.

Corona transfer is performed by applying a predetermined transfer voltage to the corona discharge wire 4 of the corona transfer device 3 from a power source (not shown).

Electric lines of force E ₁ and E ₂ schematically show the state of corona discharge in the above-mentioned device. As shown in the figure, the corona discharge from the corona discharge wire 4 is divided into a flow of E ₁ toward the transfer material 2 and a flow of E ₂ toward the bottom surface 6 of the shield case. The bottom surface 6 of the conductive member therefore acts as a back electrode. Moreover,
Since the insulating members 8 and 9 are provided on the inner surfaces of the side walls 5 and 7 of the shield case, corona discharge does not wastefully flow to the sides from the corona discharge wire 4, and a corona discharge current directed toward the transfer material can be obtained. . Since this corona discharge current is converged within the close contact area B of the transfer material, the transfer can be performed effectively.

Then, a charge eliminating means 10 such as a charge eliminating needle for removing excess charge on the transfer material is disposed in the transfer material separation region or a region subsequent to the transfer material separation region. By arranging this charge eliminating means, it is possible to eliminate the possibility that corona charges on the transfer material may be discharged to nearby metal parts during conveyance and disturb the transferred image.

By the way, in the conventional corona transfer device, as shown in the second diagram, the corona discharge current e ₁ directed toward the transfer material of the corona transfer device 11 is not limited to the transfer material contact area B;
This extends to the close contact area A of the transfer material and/or the separation area C of the transfer material.

In particular, the corona discharge current that reaches the close contact area A acts to attract the developed image D on the image carrier onto the transfer material 2 that is not yet in close contact. At this time, the developed image D is transferred onto the transfer material at a position shifted from the position where it should be originally transferred, which causes thickening of characters in the transferred image and scattering marks around the line image.

On the other hand, the corona discharge current reaching the separation area C is in a state where the transfer material is separated, contrary to the area A.
Since the image bearing member and the transfer material are separated and misaligned, this also promotes misaligned transfer of the developer. The influence of the corona discharge current in this region C also contributed to the thickening of the characters in the transferred image T and the scattering marks around the line image. In addition, in the conventional device, the corona discharge current is e ₁ in the direction of the image carrier, outside the back direction e ₂ , and in the side e ₃
Since the beam was also directed towards the shield case, there was a large difference in charge that was absorbed by the shield case.

Moreover, the charge eliminating means 10' is connected to the corona transfer device 1.
1, a part of the corona discharge current that should be directed to the transfer material flows to the static eliminating means 10', increasing current consumption.

On the other hand, in the configuration of the present invention, as described above, the corona discharge current converges on the contact area B of the transfer material, and the corona discharge current is not substantially directed to the areas A and/or C where the above-mentioned disadvantages occur. This will solve the inconvenience. Moreover, the attachment of charges to the back surface of the transfer material by the corona discharge current directed toward the image carrier surface is more effective than otherwise.

FIG. 3 is a side view illustrating a different embodiment of the corona transfer device according to the present invention. Components common to the device shown in FIG. 1 described above are indicated by the same numbers.

In the illustrated example, in the corona transfer device 3', the upper edge of the insulating member 8' on the inner surface of the side wall 5 on the side where the transfer material transfer position enters is protruded so as to partially cover the opening of the shield case. A protrusion 8 ₁ ' is formed therein. The front edge of this protruding portion 8 ₁ ' is positioned at an appropriate space between directly above the corona discharge wire 4 and the side wall 5 of the shield case.

By providing the eaves of the insulating member in this manner, the weak corona discharge current emitted from the shield case side wall 5 is cut off, and a stronger corona discharge current acts at the initial stage of transfer. For this reason, the transfer of the developed image is strongly initiated. In this way, reliable transfer is efficiently performed. At this time, similar transfer can be achieved even if the opening width of the shield case is narrow. Moreover, since corona discharge is performed through the narrow opening width of the shield case,
The amount of corona discharge acting on the image carrier can be reduced.
When a large amount of corona discharge is applied to an image carrier during transfer, traces of transfer material may appear during subsequent image formation due to the difference in the amount of residual charge between areas with and without transfer material. In this case, such inconvenience does not occur at all.

Of course, the member forming the eave-like protrusion is the side wall 5.
It may be molded integrally with the insulating member along the line, or it may be fixed as a separate piece.

FIG. 4 is a side view showing a further modification of the device shown in third figure.

In the illustrated example corona transfer device 3'', a conductive portion 51' extending from the upper edge of the side wall 5' of the shield case is provided on the upper surface of the protruding eave-like insulating member 8'', similar to the device ₃ '. It is something that

Due to the presence of the conductive portion ₅₁ ', charges that tend to accumulate on the upper surface of the eave-like insulating member are released, and when charges are accumulated on the upper surface of the eave-like insulating member, floating developer is adsorbed, and this developer is transferred. Inconveniences such as the developer adhering to the back surface of the material and causing backside stains, or the adverse effects of the adhering developer on transfer can be effectively prevented.

As described above, since the apparatus of the present invention effectively directs the corona discharge current toward the transfer material, it is possible to obtain the same or higher transfer efficiency with lower power consumption than the conventional apparatus.

By the way, as the diameter of the image bearing drum becomes smaller with the downsizing of image forming apparatuses, the corona transfer device and the above-mentioned static eliminator may also be placed close to each other. Particularly when the two are disposed close to each other, as shown in the first diagram, if the side wall 7 of the corona transfer device is low, a portion of the corona discharge current directed toward the transfer material may leak to the static eliminator 10.

FIG. 5 shows the arrangement of both devices to enable effective transfer even in such a case. The corona transfer device 3 has its side wall 7' on the transfer material separation side slightly higher than the tip of the static eliminating means. It is composed of That is, the distance between the tip of the static eliminating means 10 and the tangent to the image carrier in the transfer section is the distance between the tip of the shield case side wall 7' of the corona transfer device 3 and the tangent to the image carrier in the transfer section. It is larger than. The same applies to the insulating member 9' on the inner surface of the side wall 7'. This height difference G is usually 1~
Approximately 4 mm is good. Of course, in addition to providing a step on both side walls of the shield case as shown in the figure, both walls may be made higher.

FIG. 6 is a side view illustrating the arrangement of the embodiment device which is a modified version of the device shown _in the fourth figure.
mm, l ₂ is 20mm, l ₃ and l ₄ are 9.5mm, l ₅ is 10mm, l ₆ is 8
mm and l ₇ were set to 6 mm, and polyethylene terephthalate (100 μm thick) was used for the insulating members 8″ and 9.
Corona discharge wire 4 with developer and opposite polarity DC 8.0KV
was applied to perform the transfer.

Not only was a good transferred image obtained in a normal atmosphere, but also a sufficiently good transferred image was obtained in an environment with a room temperature of 35° C. and a humidity of 20% RH.

As described above in detail in the specific examples, the apparatus of the present invention enables efficient and reliable transfer by effectively directing the corona discharge current. Furthermore, efficient operation is possible without wasting device drive current.

Moreover, the apparatus of the present invention is excellent in that the characters in the transferred image are faithfully transferred, and a good transferred image is obtained without scattering marks around line images or the like.

Furthermore, since the transferred image is sufficiently electrostatically attracted to the transfer material, there is no problem in that the transferred image is disturbed during fixation or transportation. Moreover, there is no fear that the transferred image will be disturbed before it is fixed, and a good final image can be obtained.

[Brief explanation of drawings]

FIG. 1 is a side view illustrating a specific example of a corona transfer device based on the present invention. FIG. 2 is a side view illustrating a conventional device. FIG. 3 and FIG. 4 are side views each illustrating a modified corona transfer device. FIG. 5 is a side view illustrating a further configuration of the present invention. FIG. 6 is a side view illustrating the configuration of a further embodiment of the present invention. In the figure, 1: image carrier, 2: transfer material, 3: corona transfer device, 4: corona discharge wire.

Claims (1)

[Scope of Claims] 1. An image forming apparatus that brings a transfer material into contact with a developed image formed on an image carrier and applies corona discharge from the back side of the transfer material to transfer the developed image onto the transfer material, comprising: A transfer corona discharge means having a conductive shield case having an opening on the side facing the carrier, and an insulating member provided on the inner surface of both side walls of the conductive shield case; a static eliminator disposed adjacent to the downstream side of the corona discharge means; An image forming apparatus characterized in that the distance is greater than the distance between the tip of the side wall of the shield case on the means side and the tangent to the image carrier in the transfer section.