Image forming machine

Details Image forming machine Image forming machine

2001-06-18

2002-04-16

Grimley, Arthur T. (Department: 2852)

Electrophotography

Image formation

Transfer

C399S169000, C399S176000, C399S303000, C399S313000, C399S314000

Reexamination Certificate

active

06374073

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an electrostatic process image forming machine, such as an electrostatic copier, printer or facsimile. More particularly, the invention relates to an image forming machine comprising image bearing means which may be a rotating drum or an endless belt, charging means for charging the image bearing means to a predetermined polarity, exposure means for selectively static-eliminating the charged image bearing means to form an electrostatic latent image, reversal development means for developing the electrostatic latent image on the image bearing means into a toner image, transfer means for transferring the toner image on the image bearing means onto an image receiving member which may be a plain paper, and cleaning means for removing a toner remaining on the image bearing means after transfer.
DESCRIPTION OF THE PRIOR ART
In the foregoing image forming machine, the charging means, which can be composed of a corona discharger, charges the image bearing means to a specific polarity over a predetermined effective charging width. The width of the image bearing means is larger than the effective charging width. On both sides of the effective charging width, the surface of the image bearing means is not stably charged to a predetermined potential, and can be of a potential considerably lower than the predetermined potential, or of substantially zero potential, or even of the opposite polarity. Development by the reversal development means does not apply a toner to a site where the charge potential remains, but applies the toner to a static elimination site where the charge potential has disappeared. In the image forming machine employing the reversal development means, therefore, the toner tends to adhere to both sides of the effective charging width on the surface of the image bearing means, thereby causing staining there. Even if an effective development width by the development means is rendered substantially the same as, or somewhat smaller than, the effective charging width, a floating toner, such as toner repelled by the charge potential on the image bearing means, can adhere onto the image bearing means on both sides of the effective charging width.
As transfer means in the image forming machine in the above-described configuration, a form composed of a transfer roller to receive a transfer voltage, or a form including an endless transfer belt to be rotationally driven, and transfer voltage applicator means for applying a transfer voltage to the back side of the transfer belt has recently been proposed and put to practical use, instead of a transfer corona discharger. The transfer roller or transfer belt is brought into contact with the image bearing means via the image receiving member and directly over the entire width of the transfer roller or transfer belt. The transfer voltage applicator means is usually composed of a voltage applicator roller formed from an electrically conductive material and receiving a transfer voltage. The width of the voltage applicator roller is substantially the same as the width of the transfer belt, so that the transfer belt is contacted with the image bearing means over the entire width of the transfer belt, and given a transfer voltage over its entire width.
If the width of the transfer roller or transfer belt is larger than the aforementioned effective charging width, however, the transfer roller or transfer belt is brought into contact with the image bearing means not via the image receiving member, but directly on both sides of the effective charging width, because a maximum image receiving member is normally somewhat smaller than the effective charging width. As a result, the toner adhering to the image bearing means is transferred onto the transfer roller or transfer belt. Consequently, the surface of the transfer roller or transfer belt is stained with the toner. When both side portions of the face side of the transfer roller or transfer belt are stained with the toner, the state of contact between the image bearing means and the transfer roller or transfer belt is deteriorated, posing problems, such as poor transfer or damage to the surface of the image bearing means. To solve such problems, Japanese Patent No. 2597540 proposes that the width of the transfer roller (or transfer belt) be made smaller than the effective charging width.
If the width of the transfer roller or transfer belt is made smaller than the effective charging width, the toner adhering to the image bearing means on both sides of the effective charging width is prevented from being transferred to the transfer roller or transfer belt, but other problems occur. First, when the width of the transfer roller or transfer belt is made smaller than the effective charging width, the width of the transfer roller or transfer belt becomes nearly equal to or smaller than the width of the maximum image receiving member. As a result, the transportability of the image receiving member by the transfer roller or transfer belt lowers, causing a tendency toward a skew motion or a jam of the image receiving member. Secondly, particularly when the effective cleaning width of the cleaning means is substantially the same as or smaller than the effective charging width, the toner adhering to areas on both sides of the effective charging width on the surface of the image bearing means is not removed, but accumulated, thereby arousing the following phenomena: The accumulated toner accidentally floats, often contaminating the interior or surroundings of the image forming machine. Particularly, the floating toner adheres to the bearing mechanism of the transfer roller, or the bearing mechanism of a support roller for the transfer belt, the transfer voltage applicator means for the transfer roller or transfer belt, and so on, thereby not only staining these members, but also impeding their functions. Furthermore, the charging means, the reversal development means, and the cleaning means are provided with constituent elements extending or located widthwise outwardly of the effective charging width, the effective development width, and the effective cleaning width, respectively, for example, spacing setting rollers for setting spacing from the image bearing means sufficiently precisely, and various sealing members for preventing scatter of toner. The toner adhering to the areas on both sides of the effective charging width on the surface of the image bearing means stagnates and builds up between these constituent elements and the surface of the image bearing means. This is highly likely to destroy the spacing setting function of the spacing setting rollers, spoil the sealing function of the various sealing members, and damage the image bearing means, the spacing setting rollers, or the various sealing members.
SUMMARY OF THE INVENTION
The object of the present invention is to solve the above-described various problems, which are concerned with the toner adhering to both sides of the effective charging width on the surface of the image bearing means, by employing a unique configuration for the transfer means.
In an aspect of the present invention, transfer means is composed of a transfer belt to be rotationally driven, and transfer voltage applicator means for applying a transfer voltage to the back side of the transfer belt, the transfer voltage applicator means applies the transfer voltage to the transfer belt over a predetermined effective transfer width, the face side of the transfer belt is brought into contact with image bearing means via an image receiving member and directly over a predetermined effective contact width, and the effective contact width is set to be larger than the effective charging width of charging means and larger than the effective transfer width.
That is, according to an aspect of the present invention, there is provided, as an image forming machine which attains the above main object, an image forming machine comprising image bearing means moved sequentially through a charging zone, an exposure zone, a development zone, a tra

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