JPH1010938A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent stress from being imparted to a photoconductor so as to be able to form clear images over a long period of time. SOLUTION: A semiconductive film 38 is arranged between a transfer means and a charging means, in a position spaced by the specified distance (t) (0<=t<=0.5mm, for instance) from the surface of a photoconductor 12. During image forming action, a switch 42 selects a power supply 40b, and voltage Vf of charged polarity and reversed polarity is applied to the semiconductive film 38. The semiconductive film 38 is thereby brought into electrical contact with the photoconductor 12, and image memory on the photoconductor 12 is eliminated. During non-image-forming action, voltage Vfc of charged polarity and like-polarity is applied to the semiconductive film 38 by the switch 42. Toner stuck to the semiconductive film 38 is thereby shifted to the photoconductor 12 and then recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus,
More particularly, the present invention relates to an image forming apparatus which is applied to, for example, a copying machine and a laser printer using an electrophotographic system and can remove an image memory phenomenon caused by residual toner and residual charges on a photoconductor.

[0002]

2. Description of the Related Art A system has been proposed in which a cleaning step of removing untransferred toner remaining on a photoreceptor from a photoreceptor is omitted, and in a development step, untransferred toner on the photoreceptor is collected simultaneously with toner development. (For example, Japa
n Hard Copy '89 Proceedings, p143-146). In other words, with this system, toner is attached by reverse development to the portion where the surface potential of the photoreceptor has been attenuated by the exposure means, and the untransferred toner on the photoreceptor uses the potential difference between the surface potential of the photoreceptor and the developing bias voltage Then, the toner is electrostatically attracted to the developing device (developing roller) side. By omitting the cleaning process in this way, the apparatus can be downsized, and the toner that has been conventionally discarded can be reused.

However, in a system in which the cleaning step is omitted, the untransferred toner remaining on the photoreceptor after the transfer or the residual potential on the photoreceptor after the transfer causes the photoreceptor to rotate one rotation (pre-process). This has caused a new problem that the image appears as a memory. On the other hand, the prior art disclosed in Japanese Patent Application Laid-Open No. 64-20587 (G03G 21/00), which was published on April 24, 1988, uses a conductive brush (memory removing member). It is arranged downstream of the transfer means and upstream of the charging means so as to be in slidable contact with the photoreceptor, and disturbs the toner pattern remaining on the photoreceptor, thereby suppressing the occurrence of memory. Means for disturbing the residual toner by applying a predetermined voltage having a polarity opposite to the charging potential to the brush as a memory removing member and electrically adsorbing the toner remaining on the photoreceptor to the brush is disclosed in This is disclosed in Japanese Patent Application Laid-Open No. 6-258928 filed on Sep. 16, 2016.

[0004] Further, Japanese Patent Application Laid-Open No. Hei 6-51672 (G03G 21/0) filed on Feb. 25, 1994 has been published.
0, G03G 15/00, G03G 15/08), a cleaning roller is arranged in contact with the photosensitive drum in place of the above-mentioned brush, and a predetermined bias voltage is applied to the cleaning roller. By applying the voltage, the toner remaining on the photosensitive member or the cleaning roller was collected.

[0005]

However, in the prior art using a brush, there is a problem that the surface of the photoconductor is damaged or worn, resulting in an image defect because the brush exerts a large stress on the photoconductor. Further, there is a drawback that the brush falls down with use for a long period of time, and the toner stays in the brush, thereby deteriorating the function as a memory removing member.

On the other hand, in the prior art using a conductive (cleaning) roller, there is little mechanical stress on the surface of the photoreceptor, and the function as a memory removing member can be sufficiently achieved in long-term use. However, since many components for driving the conductive roller are required, the apparatus is complicated. SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide an image forming apparatus capable of removing an image memory at low cost and maintaining the original performance of the image forming apparatus for a long period of time.

[0007]

SUMMARY OF THE INVENTION The present invention provides an image carrier,
Charging means for uniformly charging the surface of the image carrier with the first polarity;
Electrostatic latent image forming means for forming an electrostatic latent image on a charged image carrier, developing means for developing the electrostatic latent image into a toner image, transfer means for transferring the toner image to a transfer material, transfer means A semiconductive film member arranged in a non-contact state with the surface of the image carrier between the charging means and the charging means, and a semiconductive film member having a first polarity opposite to the first polarity on the semiconductive film member during the first period of the image forming operation. A first voltage applying means for applying a first predetermined voltage having two polarities, wherein the first predetermined voltage is applied to the semiconductive film member so that the semiconductive film member comes into surface contact with the image carrier to form an image; An image forming apparatus for reducing a residual charge of a carrier.

[0008]

The toner remaining on the image carrier after the transfer is positively charged together with the image carrier by the charging means. Then, when a first predetermined voltage having a polarity opposite to the charging (first) polarity (second polarity) is applied to the semiconductive film member by the first voltage applying means, the semiconductive film member becomes an image carrier. The semiconductive film member is drawn toward the carrier, and makes electrical surface contact with the surface of the image carrier. Therefore, the residual potential on the image carrier is neutralized by the first predetermined voltage. At this time, a part of the residual toner is adsorbed on the semiconductive film.

The toner adhering to the semiconductive film member is transferred to the surface of the image carrier by applying a second predetermined voltage having the same polarity as the charging polarity to the semiconductive film member, and then developing. Collected by a roller (developing device). Further, by providing a plurality of slits in the semiconductive film member, the semiconductive film member can be uniformly contacted over the entire surface of the image carrier.

[0010]

According to the present invention, the semiconductive film is disposed on the image carrier in a non-contact state, so that no mechanical stress is applied to the image carrier and the film is formed on the image carrier. Image memory can be effectively suppressed. Therefore, a stable image can be formed over a long period of time. The above object of the present invention,
Other objects, features and advantages will become more apparent from the following detailed description of embodiments, which proceeds with reference to the accompanying drawings.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus 10 according to an embodiment shown in FIG. 1 includes a photosensitive member 12 which is an image carrier and rotates in the direction of an arrow. The photoconductor 12 is obtained by applying a positively charged OPC photoconductor to a conductive substrate made of aluminum, for example. On the left side of the photoconductor 12, a charger 14 is disposed.
4, the photoconductor 12 is uniformly positively charged.

An exposure unit 16 is disposed below and to the right of the photoreceptor 12, and the original light image formed by the exposure unit 16 is transferred to the mirror 1
8, the light is incident on the photoconductor 12. As a result, an electrostatic latent image is formed on the photoconductor 12 exposed by the light image of the document. A developing roller 2 is provided below the photoconductor 12.
0 is arranged so as to contact the photoconductor 12. The developing roller 20 supplies a developer (toner) to the photoconductor 12, and therefore, the developing roller 20 constitutes a developer supply unit.

The toner supplied to the photoreceptor 12 is stored or stored in a storage chamber 22, and the toner is supplied to a developing roller 20 as a developer carrier by an agitator 24 and a supply roller 26 provided in the storage chamber 22. Supplied.
Further, in this embodiment, the blade 28 is arranged so as to elastically contact the surface of the developing roller 20, and the blade 28 and the supply roller 26 cause the developing roller 2
0, a thin toner layer having a regulated thickness is formed.
Note that toner is replenished into the storage chamber 22 by, for example, a cartridge 30 that is detachably attached. The developing roller 20 and the supply roller 26 are supplied with a developing bias voltage from a high-voltage power supply (not shown).

A transfer unit 32 is disposed above the photoconductor 12. The transfer device 32 electrostatically attracts a toner image to a transfer material such as paper conveyed by a paper supply device 34. Then, the toner on the transfer material is fixed to the transfer material by the fixing device 36. In such an image forming apparatus 10,
The electrophotographic process is repeated around photoreceptor 12. That is, the photoreceptor 12 is charged by, for example, 10
It is uniformly charged to about 00V and positively charged. Then, the exposure device 16 exposes the document image to form an electrostatic latent image on the photoconductor 12. This electrostatic latent image is developed with toner by a developing roller 20 that receives a developing bias voltage (for example, +400 V) from a high-voltage power supply (not shown). As described above, a thin toner layer having a thickness of, for example, 10 μm to 30 μm is formed on the developing roller 20 by the blade 28 and the supply roller 26. The thinned toner is charged to a positive polarity by friction between the blade 28 and the supply roller 26, as shown in the characteristic diagram of FIG.

The toner image formed on the photosensitive member 12 is transferred to a transfer material by a transfer device 32. At this time, a transfer bias voltage having a polarity opposite to that of the developing bias voltage (negative pole in this embodiment) is applied to the transfer device 32. And
The transfer material is separated from the photoconductor 12 by a separator (not shown), and is conveyed to the fixing device 36. The untransferred toner remaining on the photoconductor 12 without being transferred to the transfer material is guided to the charger 14 while adhering to the photoconductor 12, and is uniformly charged (positively charged) together with the photoconductor 12. Is given.

The untransferred toner remaining on the photoreceptor 12 is
The background electric field formed between the photoconductor 12 and the developing roller 20 attracts the toner in a direction opposite to the developing electric field.
That is, the photoconductor 12 and the developing roller 20 are both charged to the same polarity, and the absolute value of each potential has a relationship of charging potential> developing bias potential> exposure potential as shown in FIG. Therefore, the positively charged toner always receives a downward electrostatic force in FIG. Thereby, the electrostatic latent image formed on the photoconductor 12 is visualized, and the untransferred toner on the photoconductor 12 moves from the photoconductor 12 to the developing roller 20 in the opposite direction to the development toner. .

However, in a system in which the untransferred toner is collected simultaneously with the toner development, there is a problem that the image of the previous process appears as a memory due to the untransferred toner and the latent image potential remaining on the photoreceptor 12. That is, as shown in FIG. 4A, when the toner image on the photoreceptor 12 is transferred to the transfer material and the latent image potential is charged on the photoreceptor 12 as shown in FIG. As shown in ()), in the previous process, the charged potential of the portion where the image exposure has been performed is slightly lower than the charged potential of the portion where the image exposure has not been performed. When the non-uniformly charged photoreceptor 12 is image-exposed by the exposure unit 16, an image memory is generated in a portion where the charged potential is reduced, as shown in FIG.

The image memory can be classified into a positive memory in which an image of a previous process appears as an afterimage, and a negative memory in which an image of a previous process appears in an image portion (a portion other than a white background) of the next process in which black and white are inverted. Generally, positive memory is
When the untransferred toner generated in the previous process is not collected in the developing process of the next process and remains in the developed toner image, or an electrostatic latent image (latent image potential) remaining on the photoconductor 12
This occurs when the charging potential on the photoconductor 12 becomes non-uniform. On the other hand, the negative memory occurs when an unsatisfactory amount of exposure occurs due to untransferred toner on the photoreceptor 12 and the developing potential becomes insufficient.

It is also known that the image memory generated due to the untransferred toner depends on the residual amount of the untransferred toner, and does not occur as the transfer efficiency increases. FIG. 5 shows the rate of occurrence of image memory when the transfer efficiency is used as a parameter. In FIG. 5, the strong effect area is an area where the image pattern of the previous process appears so strongly that characters can be recognized on the image, and the weak effect area is an area where the image pattern of the previous process slightly appears. Say. As can be seen from FIG. 5, when the transfer efficiency is reduced (30% or less for the positive memory and 50% or less for the negative memory), the image pattern of the pre-process clearly appears on the image (reaches the strong effect area).

The image memory using the untransferred toner can be suppressed to some extent by optimizing the transfer device 32. However, the image memory generated by the non-uniform charging potential cannot be eliminated, and the spread of dots and Problems such as fogging between dots have occurred. On the other hand, in the embodiment shown in FIG.
Upstream of 4 and downstream of the transfer device 32, a semiconductive film 38 is disposed in relation to the photoconductor 12. In this embodiment, the semiconductive film 38 is made of urethane rubber mixed with a conductive material such as carbon, and has a thickness of about 0.1 to 0.2 mm so as to have flexibility. It is formed.

The hardness of the conductive film 38 in this embodiment is 70 to 93 degrees (JIS A), the surface resistivity is 7 × 10 ³ Ω (JIS K6723), and the tensile strength is 370 kg /. cm ² , elongation is 540% and tear strength is 110 kg / cm. As shown in FIG. 6A, the semiconductive film 38 is disposed in a non-contact state at a position separated from the surface of the photoconductor 12 by a predetermined distance (t) (for example, 0 ≦ t ≦ 0.5 mm). . The semi-conductive film 38 has power supplies 40a and 40a having different polarities.
b is selectively connected. That is, a switch 42 is provided between the semiconductive film 38 and the power supplies 40a and 40b, and the switch 42 selects the power supply 40b during the image forming operation. On the other hand, the period from the start of rotation of the photoconductor 12 to the lighting of the exposure unit 16 and the period from the transfer of the toner image to the transfer material by the transfer unit 32 until the rotation of the photoconductor 12 is stopped, that is, the image forming operation is stopped. During the non-image forming operation period (second period) in which the switch 42 is not performed, the switch 42
Selects the power supply 40a.

Accordingly, during the image forming operation in which the switch 42 selects the power supply 40b, the bias voltage (V) of the polarity (second polarity) opposite to the charging polarity is applied to the semiconductive film 38.
f) is given. Thereby, the semiconductive film 3
As shown in FIG. 6B, 8 is electrically attracted to and contacts the photoconductor 12. Therefore, the latent image potential remaining on the photoconductor 12 is neutralized by the bias voltage (Vf) from the power supply 40b, and the unevenness of the charged potential shown in FIG. 4A is smoothed.

On the other hand, during the period when the switch 42 selects the power supply 40a, a bias voltage (Vfc) having the same polarity (first polarity) as the charging polarity is applied to the semiconductive film 38. As a result, the toner adhered to the surface of the semiconductive film 38 is transferred to the photoconductor 12 and
The toner adsorbed on the photoreceptor 12 simultaneously with the development process
The toner is collected by the developing roller 20 due to a potential difference (cleaning potential) between the developing roller 20 and the developing roller 20. The bias voltages (Vf, Vfc) applied to the semiconductive film 38
Is set in consideration of damage to the photoconductor 12 and stress on the toner.

Further, in this embodiment, FIGS. 7 and 8
As shown in FIG. 5, the semiconductive film 38 has a semiconductive film 3 at least in a contact area with the photoconductor 12.
A plurality of slits 44 for dividing 8 in the width direction are formed at a predetermined pitch. The inclination angle α and the slit width W of the slit 44 with respect to the direction of displacement of the photoconductor 12 are represented by Lc> W.
If it is set so as to satisfy tan α (Lc: the length in the displacement direction of the photoconductor 12 in contact with the photoconductor 12), the semiconductive film 38 can be in contact with the entire surface of the photoconductor 12. preferable. Further, the pitch width (Ps) of the slits 44 is preferably set to Ps> W (1 + Lc · cos α). Thus, by providing the slit 44 in the semiconductive film 38, the semiconductive film 38 can be effectively brought into contact with the entire surface of the photoconductor 12.

FIG. 9 shows the charged potential difference between a portion where image exposure is performed and a portion where image exposure is not performed, using the bias voltage (Vf) applied to the semiconductive film 38 as a parameter. From this figure, by applying a bias voltage (Vf) having a polarity opposite to the charging polarity to the semiconductive film 38, the potential of the latent image on the photoconductor 12 can be removed, and the bias voltage (Vf) is represented by an absolute value. If the voltage is 200 V or more, it can be predicted that the image memory can be effectively removed. The image area ratio (the ratio of the black image area to the transfer material area) was set to about 4%, and a print durability test was performed on about 40,000 A4 sheets. Was not done.

As described above, since the semiconductive film 38 is arranged in a non-contact state with the photoconductor 12 and is brought into electrical contact with the photoconductor 12 as necessary, the photoconductor 12 is not stressed. In addition, the latent image potential and untransferred toner that cause the image memory can be removed. Therefore, the image memory on the photoconductor 12 can be suppressed for a long time,
The original performance of the image forming apparatus 10 can be maintained. In addition, manufacturing costs can be reduced, and running costs can be minimized.

In the above-described embodiment, the electrophotographic process using the positively charged photosensitive member 12 is performed. However, an image forming apparatus using the negatively charged photosensitive member 12 with the toner of the same polarity as the photosensitive member 12 may be used. The same effect can be obtained.
It goes without saying that the optimum value of the absolute value of each bias potential differs depending on the electrical resistance value of the components used and the like.

[Brief description of the drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention;

FIG. 2 is a graph showing charging characteristics of a thin toner layer formed on a developing roller.

FIG. 3 is an illustrative view showing a relationship between a charging potential, a developing bias potential, and an exposure potential in a reversal developing method;

FIG. 4 is a graph showing the occurrence of an image memory;
Indicates the surface potential of the photoconductor after transfer, (B) indicates the surface potential of the photoconductor after being charged by the charger,
(C) shows the surface potential of the photoreceptor after image exposure using an exposure device.

FIG. 5 is a graph showing a relationship between an image memory and transfer efficiency.

FIG. 6 is an illustrative view explaining a semiconductive film in the embodiment of FIG. 1; FIG. 6 (A) shows a case where a bias voltage (Vfc) having the same polarity as the charging polarity is applied to the semiconductive film; 3B is an illustrative view showing a state in which a bias voltage (Vf) having a polarity opposite to the charging polarity is applied to the semiconductive film 38 and the semiconductive film 38 is in electrical contact with the photoconductor 12.

FIG. 7 is an enlarged view showing a semiconductive film in the embodiment of FIG.

FIG. 8 is an enlarged view showing a semiconductive film in the embodiment of FIG.

FIG. 9 is a graph showing a relationship between a bias voltage (Vf) controlled according to the embodiment of FIG. 1 and a memory potential.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 12 ... Photoconductor 14 ... Charging device 16 ... Exposure device 20 ... Developing roller 32 ... Transfer device 38 ... Semiconductive film 40a, 40b ... Power supply 42 ... Switch 44 ... Slit

Claims (5)

[Claims] 1. An image carrier, charging means for uniformly charging the surface of the image carrier with a first polarity, and forming an electrostatic latent image on the charged image carrier. Means, developing means for developing the electrostatic latent image into a toner image, transfer means for transferring the toner image to a transfer material, and the surface of the image carrier between the transfer means and the charging means A semiconductive film member arranged in a non-contact state, and a first applying a first predetermined voltage having a second polarity opposite to the first polarity to the semiconductive film member during a first period of an image forming operation. A voltage application unit, wherein the first predetermined voltage is applied to the semiconductive film member, whereby the semiconductive film member comes into surface contact with the image carrier and reduces residual charges of the image carrier. Decrease,
Image forming device. 2. The image according to claim 1, further comprising a plurality of slits formed in said semiconductive film member at a predetermined pitch and dividing said semiconductive film member in a width direction thereof in a region of said surface contact. Forming equipment. 3. Each of the slits has a length Lc in a displacement direction of the image carrier where the semiconductive film member contacts the image carrier, a width W of the slit, and a width of the slit. The image forming apparatus according to claim 2, wherein when an angle of the image carrier with respect to a displacement direction of the image carrier is α, Lc> W · tan α is satisfied. 4. A second voltage applying means for applying a second predetermined voltage having the same polarity as the first polarity to the semiconductive film member during a second period different from the first period of the image forming operation, 2. The toner applied to the semiconductive film member transitions to the surface of the image carrier by applying the second predetermined voltage to the semiconductive film member. 3.
4. The image forming apparatus according to any one of claims 1 to 3. 5. The image bearing member is a rotator, and the second period is a period from the start of rotation of the image carrier to activation of the electrostatic latent image forming unit, and the transfer unit. 5. The image forming apparatus according to claim 4, wherein the period is from when the toner image is transferred to the transfer material by the time the rotation of the image carrier stops.