JPH0529483Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to image forming apparatuses such as copying machines, liquid crystal printers, and laser printers that apply electrophotographic technology. This invention relates to an image forming apparatus that has been improved to prevent such problems.

[Prior art]

In image forming devices such as copying machines, liquid crystal printers, and laser printers that apply electrophotographic technology, in order to prevent the so-called "thinning" of characters and lines, the area where the characters, lines, etc. are to be printed is placed on the charged photoreceptor. There is a reversal development method in which negative exposure is performed by irradiating light to form a low potential area, and toner charged to the same polarity as the photoreceptor is attached to this low potential area to create a positive image. Generally used.

The image forming apparatus often uses a one-component developer that does not require toner density control and is easy to maintain. As this one-component developer, a magnetic toner containing a magnetic material such as ferrite or magnetite is generally used.

[Problems with conventional technology]

In an image forming apparatus using a reversal development method as described above, a toner image formed on a photoreceptor is attached to a low potential portion of the photoreceptor. In this case, since the toner and the photoreceptor are charged with the same polarity, a repulsive Coulomb force acts to cause the toner to separate from the photoreceptor, but the toner is held on the photoreceptor mainly by van der Waals force. Therefore, the adhesion force of toner to the photoreceptor is weak, and since the photoreceptor rotates at a predetermined peripheral speed, centrifugal force also acts, and the adhesion force of toner tends to become even weaker.

By the way, as shown in FIG. 4, when printing an index as a type mark on B5 size paper, in order to ensure that the index portion 14 is printed on the transfer material up to the edge of the paper, it is usually photosensitive. A wide toner image is formed on the body, projecting out of the paper by a little (3 to 4 mm) than the actual width of the index portion 14 (see FIG. 1).

Coulomb force acts on the toner on the photoconductor heading toward the transfer section, in a direction that causes the toner to separate from the photoconductor between the toner and a guide plate that guides the transfer material to the transfer section.
In other words, since the guide plate is usually a conductive metal plate and is grounded, an electric field is formed between the negatively charged photoreceptor and the guide plate, and this electric field causes the negatively charged toner to be transferred to the photoreceptor. It acts in the direction of separating from the Furthermore, since magnetic toner has residual magnetization, it is more likely to be attracted to the tip of a guide plate made of a magnetic material such as an iron plate.

In particular, as mentioned above, the toner image for index printing on the photoconductor is formed protruding from the edge of the transfer material, so the transfer material of the guide plate is opposed to the protruding part where it does not intervene (pass through). Toner is more likely to adhere to the area. After this, if printing is performed using, for example, an A4 size transfer material that is wider than B5 size, toner stains will occur on the leading edge and back surface of the A4 size transfer material.

[Purpose of invention]

In view of the problems of the prior art described above, the present invention aims to prevent toner from accumulating on a guide plate that guides a transfer material in a reversal development type image forming apparatus, and to prevent toner stains on the transfer material. The purpose of the present invention is to provide an image forming apparatus that can.

[Key points of the idea]

In order to solve the above object, the present invention provides an image carrier and a toner charged to the same polarity as the predetermined polarity to a low potential portion of an electrostatic latent image of a predetermined polarity formed on the image carrier. a means for reversing and developing a toner image; a transfer section for transferring the toner image onto a transfer material; and a conductive guide that is grounded to the apparatus main body and guides the transferred transfer material toward the transfer section. In the image forming apparatus, a notch corresponding to a predetermined area including a side edge of the transferred transfer material is formed at least at a leading end of the guide member close to the surface of the image carrier. Features.

[Example of idea]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a configuration diagram showing an example of a liquid crystal printer as an example of an image forming apparatus according to the present invention.

In the figure, a photosensitive drum 1 as an image carrier is made of a conductive metal tube made of aluminum or the like, and has an organic optical semiconductor (OPC) on its outer circumferential surface.
It is formed by applying and rotates in the direction of arrow a.

Near the circumferential surface of the photoreceptor drum 1, there is a charger 2 for uniformly charging the photoreceptor drum 1;
A liquid crystal head 3 that irradiates a light image according to a recording signal onto the photoreceptor drum 1 to form an electrostatic latent image, and a developer 4 that develops the electrostatic latent image formed on the photoreceptor drum 1 with toner. A transfer device 6 that transfers the developed toner image onto a transfer material (paper) P, and a cleaner 7 that removes residual toner on the photosensitive drum 1 that has not been transferred by the transfer device 6 are provided. There is.

In the charger 2, a discharge wire 2b is stretched in a shield case 2a that is open on the circumferential side of the photosensitive drum 1, and a grid 2c is provided on the opening side of the shield case 2a. The discharge line 2b is connected to a negative high voltage power source 2d, and the shield case 2a and grid 2c are grounded via a constant voltage element 2e such as a varistor. The negative high voltage of the high voltage power supply 2d applied to the discharge line 2b charges the photosensitive drum 1 negatively by corona discharge.

The liquid crystal head 3 includes a light source 3a and a liquid crystal light shutter 3.
b. Comprised of an imaging lens array 3c and a shutter drive circuit (not shown), the light emitted by the light source 3a is transmitted or blocked by a microshutter provided in the liquid crystal light shutter 3b, and the light transmitted through the microshutter is An image is formed on the surface of the photoreceptor drum 1 by an imaging lens array 3c having an imaging function.

In the developing device 4, a toner 4b is stored in a developing container 4a, and a developing roll 4c is disposed below the developing container 4a in close proximity to the circumferential surface of the photoreceptor drum 1. The toner 4b is a magnetic toner containing magnetite as a magnetic substance, and has negative charge polarity. The developing roll 4c is constructed by disposing a magnet roll 4e within a developing sleeve 4d, and the developing sleeve 4d is configured to maintain the voltage of the negative high potential portion (portion not irradiated with light) of the electrostatic latent image described above. It is connected to a bias voltage source 4f for applying a voltage equal to or slightly lower than . This results in
The developing device 4 uses a developing roll 4c to develop a low potential portion (a portion irradiated with light) of the electrostatic latent image on the photoreceptor drum 1.
Toner 4b is attached to form a toner image.

In the transfer device 6, a discharge wire 6b is stretched in a shield case 6a which is open on the circumferential side of the photoreceptor drum 1.

The discharge line 6b is connected to a positive high voltage power supply 6c,
The shield case 6a is grounded.

On the other hand, in the vicinity of the circumferential surface of the photosensitive drum 1 between the developing device 4 and the transfer device 6, there are upper and lower guide plates 8 and 9 that guide the transfer material (paper) P conveyed from a paper feeder (not shown) to the transfer position. A transfer material carrying path is formed. These upper and lower guide plates 8 and 9 are formed of conductive metal plates made of non-magnetic material such as stainless steel or aluminum, and are each grounded.

FIG. 1 is a diagram for explaining the shape of the lower guide plate 9 mentioned above. The leading end surface 9a of the lower guide plate 9 is configured to face the photosensitive drum 1 with a predetermined distance therebetween in order to guide the transfer material P to the transfer position.
A notch 9b is provided in a part of this tip surface 9a. As shown in the figure, the position of this notch 9b is at the index part P' of the B4 size transfer material P.
This is the position corresponding to the margin P'' outside the paper. In other words, when the transfer material P is conveyed on the lower guide plate 9, there is a margin between the width that the index portion P' of the transfer material P passes and that width. This is the portion in which the width of P'' is added (hereinafter, this portion will be referred to as the index area corresponding portion In).

On the other hand, on the opposite side of the transfer position, a separation claw 10 (FIG. 2) is provided to separate the transfer material P onto which the toner image has been transferred from the front surface of the photoreceptor drum 1.
A conveyance guide plate 11 is provided on the left side in FIG. A discharge roll (not shown) for discharging the material P is provided to form a transfer material discharge path. The fixing device 12 includes a heater 12a.
The heating roll 12b has a built-in heating roll 12b, and the pressure roll 12c contacts the surface of the heating roll 12b.

The operation of the image forming apparatus configured as above will be described below. First, the surface of the photoreceptor drum 1 is charged substantially uniformly by corona discharge from the charger 2. In the liquid crystal head 3, a microshutter of a liquid crystal optical shutter 3b opens and closes in response to a recording signal from a shutter drive circuit (not shown), and transmits or blocks the light emitted from the light source 3a. Here, the light passing through the microshutter is imaged on the surface of the photosensitive drum 1 by the imaging lens array 3c. Photosensitive drum 1
Negative exposure is performed on the surface of the paper, in which the characters and lines to be printed are irradiated with light, but the white background is not irradiated with light, and an electrostatic latent image is formed. This photosensitive drum 1
In the developing device 4, the electrostatic latent image formed on the surface of the electrostatic latent image is applied with a bias voltage to the developing sleeve 4e, so that the toner 4b is attached to the low potential part (the part irradiated with light) of the electrostatic latent image. The image is then developed into a toner image. This toner image is superimposed on a transfer material P conveyed from a paper feeding device (not shown), and corona discharge is performed by the transfer device 6, so that
The toner image is transferred onto the transfer material P.

The transfer material P on which the toner image has been transferred is separated by a separation claw 10.
The toner image is separated from the photosensitive drum 1 by a conveyor 12, passes through a conveying guide 11, is thermally fixed onto the transfer material P by a fixing device 12, and is discharged by a discharge roll (not shown). Furthermore, the toner image remaining on the photosensitive drum 1 without being transferred onto the transfer material P is removed from the surface of the photosensitive drum 1 by a cleaner 7.

The image forming operation of the liquid crystal printer is performed as described above. During this time, the toner image formed on the circumferential surface of the photoreceptor drum 1 by the developing device 4 is transferred to the transfer device 6 as described in the conventional example. centrifugal force, Coulomb force,
A portion of the photoreceptor drum 1 detaches from the circumferential surface of the photoreceptor drum 1 due to the force such as magnetic force. In particular, a large amount of toner adheres to the circumferential surface of the photoreceptor drum 1 corresponding to the index printing area, and since there is no transfer material P in the margin area P'', the amount of toner released in this area is small. The amount of separated toner is incomparably greater than that of other parts.This separated toner scatters onto the tip surface 9a of the lower guide plate 9 provided near the circumferential surface of the photosensitive drum 1.

However, in the lower guide plate 9, the index area corresponding portion In is cut out as described above. Therefore, most of the scattered toner passes through the notch 9b and falls downward without adhering to the lower guide plate 9. Therefore, staining of the tip end surface 9a due to toner is suppressed.

Therefore, for example, in the case of a liquid crystal printer that can use transfer materials of A4 and B5 sizes, it is necessary to cut out the index area corresponding portion In of the tip end surface 9a of the lower guide plate 9 in advance, as shown in FIG. Therefore, even if A4 size printing is performed after performing index printing on B5 size paper, the leading end surface 9a is not stained with toner, so the A4 size paper will not be stained.

FIG. 3 is a diagram showing the configuration of another embodiment of the image forming apparatus of the present invention, and is a diagram showing the configuration of the lower guide plate 13. As shown in FIG. The configuration other than the lower guide plate 13 is the same as that shown in FIG. 2 described above, and a description thereof will be omitted. As shown in the figure, the lower guide plate 13 has a distal end surface 13a formed in a comb-like shape having a plurality of notches in the index area corresponding portion In and other locations.

With this configuration, it is possible to suppress the detached toner from adhering and accumulating in areas other than the index area corresponding portion In of the lower guide plate tip end surface 13a. As the printing operation is repeated over a long period of time, the detached toner gradually adheres to areas other than the index area corresponding portion In, but by forming the tip surface 13a in a comb-like shape, the degree of adhesion can be reduced. In this case, it is more effective to form a large number of narrow comb blades that do not interfere with paper conveyance in order to prevent the paper from becoming stained.

The case of magnetic toner has been explained above, but
In the case of non-magnetic toner, a similar configuration can prevent toner staining on the transfer material. However, in this case, it goes without saying that the upper and lower guide plates may be magnetic or non-magnetic.

In addition, as mentioned above, if the upper and lower guide plates are grounded, there is a concern that the transfer efficiency will decrease in high humidity.
As a result of the experiment, no decrease in transfer efficiency was observed even under high humidity. This is because the photoreceptor drum 1 and the toner image are not attracted to each other by electrostatic force.
This seems to be because negative polarity toner is easily transferred due to positive polarity corona discharge.

Furthermore, the present invention is widely applicable not only to liquid crystal printers but also to image forming apparatuses using a reversal development method.

[Effect of the invention]

As explained above, according to the present invention, in a reversal development type image forming apparatus, the part of the guide member for the transfer material that is likely to be contaminated in a concentrated manner is cut out in advance, so that toner does not accumulate on the guide member. This prevents the transfer material being conveyed in contact with the guide member from becoming dirty.

Further, by forming the tip end surface of the guide member into a comb-like shape having a plurality of notches, it is possible to economically prevent staining due to toner accumulation.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an index area as an embodiment of the present invention and a notch corresponding to the index area of the lower guide plate, and FIG. 2 is a configuration diagram of a liquid crystal printer to which the above embodiment is applied. Figure, 3rd
This figure is a configuration diagram of a lower guide plate as another embodiment of the present invention, and FIG. 4 is an explanatory diagram showing an index of transfer material. 1... Photosensitive drum, 8... Upper guide plate, 9,
13... lower guide plate, 9a, 13a... tip surface,
9b...notch part, 11...guide plate, P...transfer material, P'...index part, P''...margin part, In...
...Index area corresponding part.

Claims (1)

[Claims for Utility Model Registration] A toner image is produced by applying toner charged to the same polarity as the predetermined polarity to an image carrier and a low potential portion of an electrostatic latent image of a predetermined polarity formed on the image carrier. a transfer section that transfers the toner image onto a transfer material; and a conductive guide member that is grounded to the apparatus main body and guides the transferred transfer material toward the transfer section. In the image forming apparatus, a notch corresponding to a predetermined area including a side edge of the transferred transfer material is formed at least at a leading end of the guide member close to the surface of the image carrier. Forming device.