JP2890054B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method in which a transfer material of an image forming apparatus such as an electrophotographic copying machine is electrostatically supported and transported to transfer a toner image on an image carrier to a physical means. The present invention relates to an image forming apparatus having a transfer belt device for transferring the toner image onto the transfer material and then transferring the toner image to a fixing unit.

[Conventional technology]

FIG. 4 is a sectional view showing an embodiment of an electrophotographic copying machine which is a conventional image forming apparatus. In the figure, reference numeral 10 denotes a photosensitive drum which is a drum-shaped image carrier, reference numeral 20 denotes a charger for charging the peripheral surface of the photosensitive drum 10, reference numeral 30 denotes an exposure device, reference numeral 13 denotes an image exposure unit, reference numeral 40 denotes a developing device, and reference numeral 50 denotes a transfer. Material supply device, 53 is a paper feed roller, P is a recording paper as a transfer material, 16 is a transfer device as a charging device for transfer, 17 is a separator as a neutralizer for separation, 80 is a fixing device, and 90 is a fixing device. The cleaning device 56 is a transport belt that is a transport unit for the recording paper P.

The operation of the copying machine will be described. After the peripheral surface of the photoreceptor drum 10 is uniformly charged by the charger 20, the peripheral surface of the photoreceptor drum 10 is exposed by the image Form a latent image. Thereafter, the developing device 40 develops and visualizes the latent image to form a toner image. The toner image is transferred to the feed roller of the transfer material
The image is transferred onto the recording paper P fed by 53. This transfer is performed by applying a charge having a polarity opposite to that of the toner by the transfer device 16 from behind the recording paper P. Post-transfer separator 17
As a result, an alternating high voltage is applied to eliminate the charge, and the recording paper P is separated from the photosensitive drum 10. The separated recording paper P is conveyed to the fixing device 80 by the conveyance belt 56, and the toner image is fixed and discharged to a paper discharge tray outside the apparatus.

On the other hand, the photosensitive drum 10 to which the toner image has been transferred is cleaned by the cleaning device 90 to remove the toner remaining on the peripheral surface, and waits for the next copy.

However, in the above configuration, the transfer unit 16 and the separator 17 are required to ensure the transferability and separation of the toner image.
It is necessary to adjust the discharge efficiency during operation to find a point that works best, and this discharge efficiency is greatly affected by the environment, and has a problem that the allowable range for reliability is narrow. The transferability is influenced by the charge of the recording paper P and the mechanical properties (stiffness, surface smoothness, curl, etc.) of the recording paper P, and these are the storage state of the recording paper P and the environment at the time of transfer ( (Temperature, humidity), etc., and it is difficult to always maintain a good state.

Further, when the drum diameter of the photosensitive drum 10 is large, when the recording paper P moves to the transport belt 56, the force for returning to the original flat state is smaller than when the drum diameter is small. The recording paper P after the transfer is attached to the photoreceptor drum 10 and is liable to cause a paper jam, which has a drawback that the paper passing property as a machine is reduced and reliability is deteriorated.

As a technique for solving the above-mentioned disadvantage, a belt-shaped transfer / transport apparatus shown in FIG. 5 is disclosed in U.S. Pat. No. 3,357,325.

In FIG. 5, reference numeral 10 denotes a photosensitive drum which is a drum-shaped image carrier, 70a denotes a transfer belt device which is a belt-shaped transfer / conveyance device, 71 denotes a transfer belt which holds a charge and adsorbs a transfer material, and 72, 73 is a roller for supporting, extending and rotating the transfer belt 71, 60 is a pre-transfer paper charger for performing a corona discharge to attract the recording paper P to the transfer belt 71 by electrostatic force, and 16 is a photosensitive drum. A transfer unit 160, which is a transfer charger for transferring from 10 to the recording paper P, is a transfer unit. With this configuration, the recording paper P can be conveyed while being attached to the transfer belt 71, and excellent transfer efficiency and separation efficiency can be obtained in the transfer section.

The transfer belt device 70a is a preferable device in a color image forming apparatus in which toner images are formed on the photosensitive drum 10 in a superimposed manner and are transferred onto the recording paper P at one time. In the color image forming apparatus, a plurality of developing devices are provided on the peripheral edge of the photoconductor drum 10 to superimpose the toner image on the photoconductor drum 10, and the drum diameter becomes large. High separation performance is required because a high separation performance cannot be obtained, and a large transfer charge amount is required because the toner adhering amount is large in the method of superimposing toner images. This is because the transfer belt device is excellent in two points that the transfer belt device is required.

[Problems to be solved by the invention]

In the transfer belt device shown in FIG.
The pre-transfer charging of the recording paper P is performed by the corona discharge. However, the charging due to corona discharge often becomes uneven due to discharge unevenness caused by contamination of the discharge electrode and the like, so that the adsorption of the recording paper P to the transfer belt 71 becomes uneven, and the transfer property also becomes uneven. There was a problem.

Further, the techniques disclosed in Japanese Patent Application Laid-Open Nos. 1-11878 and 1-121879 have not solved the above-mentioned problem because the recording paper is charged by corona discharge.

In the case of reversal development, which has recently come into wide use, the above problem is often caused by charging to (-), and in the case of (-) charging by corona discharge, charging becomes uneven particularly easily. I have.

2. Description of the Related Art There is known a charger which uses an elastic brush made of a conductive elastic fiber member as a charging means and applies a voltage thereto. However, during operation of the elastic brush, it is necessary to keep the bristle tip pressed against the member to be charged with a constant pressure. For this reason, there has been a problem that if the dirt on the belt is collected or used for a long period of time, the belt loses its elasticity or has a bending habit and comes into pressure contact unevenly, resulting in a short life.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which is provided with a transfer belt device having a long life of an elastic brush by solving the above-mentioned problems, and which has excellent transferability of a toner image and excellent separability to a photosensitive drum. .

[Means for solving the problem]

The object is to provide an image forming apparatus that uses a transfer belt that is stretched and rotated between holding rollers, forms a toner image on an image carrier, and transfers and conveys the toner image on a transfer material that moves in a transfer unit. The transfer belt is configured to allow contact and separation between the image carrier at the time of image formation and non-image formation at the transfer unit, and a holding roller positioned upstream of the transfer unit of the transfer belt, A conductive member opposed to the transfer belt is provided, and at the time of image formation, the transfer belt is also in contact with the conductive member, and applies a predetermined bias voltage to the conductive member to cause a transfer between the transfer belt and the transfer member. The transfer material to be pinched and conveyed is charged, and then the transfer unit transfers the toner image. In the non-image formation, the transfer belt is retracted and the image carrier and the conductive member are moved. Away from And configured for placement position is accomplished by an image forming apparatus, characterized in that.

〔Example〕

FIG. 1 is a sectional view showing the configuration of an embodiment of the image forming apparatus of the present invention, and FIG. 2 is a sectional view showing the operation state of the transfer belt device of FIG.

In the figure, the same portions as those of the conventional image forming apparatus and the transfer belt device 70a shown in FIGS. 4 and 5 are denoted by the same reference numerals, and their operations are almost the same, so that detailed description of the overlapping portions will be omitted.

54 is a guide plate provided between the paper feed roller 53 and the holding roller 72, 70 is a transfer belt device, and 65 is a transfer unit 16 of the apparatus main body.
An elastic brush 66, which is a conductive member fixed on the upstream side of 0 and made of a conductive fiber material and performs a function of charging the paper before transfer, is a power supply for applying a bias voltage to the elastic brush 65.
A protection resistor may be inserted between the elastic brush 65 and the power supply 66 in series in order to prevent a large current from flowing when the elastic brush 65 comes into contact with a ground portion or the like.

The holding rollers 72 and 73 are rollers made of a conductive metal material, and the upstream holding roller 72 is grounded or set to a predetermined potential close to the grounded state. Reference numeral 74 shown by a two-dot chain line is a roller supporting member, one end of which is a fixed axis with the axis of the holding roller 73 as a fixed axis,
The other end is connected to the movable shaft of the holding roller 72, and is always urged by an elastic member (not shown) so that the holding roller 72 is positioned below as shown in FIG. , Are spaced apart from the peripheral surface of the photosensitive drum 10. At this time, the elastic brush 65 is separated such that the bristle tips 65a are completely separated from the transfer belt 71 or slightly touched. Therefore, since the adhesion of dirt is small and they are always separated, the elasticity of the elastic brush 65 is lost for a long time,
There is no bending tendency, and complete charging is performed at the time of charging, so that the life can be extended.

At the time of transfer, the roller support member 74 is rotated counterclockwise against the force of the elastic member by, for example, a solenoid or a motor that operates under the control of the apparatus main body control unit.
As shown in the figure, the transfer belt 71 comes into contact with the photosensitive drum 10 and the bristle tips 65a of the elastic brush 65.

A stainless steel wire may be used as the conductive fiber of the elastic brush 65, but in this embodiment, the volume resistivity is 10 ^4.
Good results have been obtained using rayon mixed with up to 10 ⁶ Ω · cm.

The transfer belt 71 is composed of, for example, two layers, and the main body has an endless volume resistivity of about 0.5 to 1 mm, such as silicon rubber, polyurethane rubber, or butyl rubber.
This is a high resistance sheet of about ¹⁰ Ω · cm. For example, a fluorine resin is spray-coated on the upper layer of the sheet to reduce the frictional resistance and prevent the adhesion of dirt.

Next, the operation of the transfer belt device 70 will be described. At the same time as the rotation of the paper feed roller 53 starts, the transfer belt 71 that is already rotationally driven at the same time as the start of the copy operation is brought into contact with the photosensitive drum 10, and the elastic brush 65 is brought into contact with the transfer belt 71 by the mechanism described above. Further, a bias voltage for paper charging before transfer is applied from a power source 66. The leading end of the recording paper P is fed between the elastic brush 65 and the transfer belt 71 by the paper feed roller 53. Here, the recording paper P is charged uniformly by the charge from the elastic brush 65, is adsorbed on the transfer belt 71, and is conveyed to the transfer unit 160. The leading edge of the recording paper P is the transfer unit 160
When a predetermined length (for example, 5 mm) has passed through, the transfer power supply of the transfer unit 16 (not shown) is turned on to start the transfer of the toner image. When the transfer is completed, the transfer belt 71 is separated from the photosensitive drum 10 and the elastic brush 65 by the elastic member described above.

By the operation control, as shown in FIG.
A non-transfer area d and a non-image area h are formed at the tip. The start of the scanner reading of the image reading or the start of the printer writing is slightly delayed so that the leading end of the image coincides with the leading end of the transfer region k (image region) slightly shifted behind by the formation of the non-image region h. Is performed.

As a result, a non-transfer area d having a length of several mm, for example, 5 mm is formed at the front end of the recording paper P, and the second half of the non-image section k following the non-transfer area d is sufficiently transferred while passing through the transfer section 160. A transfer voltage is applied so that the raw material rises.

Since the non-transfer area d of the recording paper P continues to be charged by the elastic brush 65, the recording paper P is firmly attracted to the transfer belt 71 even after the transfer of the toner image. The transfer area k is uniformly charged with the pre-transfer paper by the elastic brush 65, so that the transfer charging is uniformly performed without unevenness, and extremely good transfer without unevenness is achieved. Will be performed.

As the bias voltage applied to the elastic brush 65, a voltage lower than that of corona discharge is sufficient, and the cost of the power supply 66 can be reduced. In addition, since the charge is directly injected into the recording paper P without corona discharge and charged, no ozone is generated, and there is an advantage that the life of the transfer belt 71 can be reduced and adverse effects on the human body can be reduced. .

In the image forming apparatus of the present embodiment, the elastic brush 65 is provided at a position opposite to the holding roller 72 that is in contact with the ground or in a state close to the ground, so that the recording paper P fed from the transfer material supply device 50 is more efficiently and reliably. Since the charging is performed and the distance to the transfer unit 160 is configured to be short, the transfer belt 71 can strongly transport the recording paper P while adsorbing and holding the recording paper P. Become.

Further, since a bias voltage having the same polarity as the charging of the developer toner is applied to the elastic brush 65, the recording paper P is transferred to the transfer unit.
Until 160, the toner on the photosensitive drum 10 is not attracted to the recording paper P. Therefore, clear copy image quality can be obtained. This bias voltage is applied when the moving linear velocity of the peripheral surface of the photosensitive drum 10 is 140 mm / sec, and the image width is 300 to 300 mm.
When the paper thickness is 350 mm and the paper thickness is 65 g / m ^2, the constant voltage control is performed so as to be 0.5 to 2.0 KV (the same polarity as the toner).

The transfer device 16 transfers a toner image by applying a high voltage having a polarity opposite to that of toner charging under constant current control. In the constant current control, for example, switching control is performed so as to be 300 μA in the case of high humidity and 200 μA in the case of low humidity, and charging is performed. Therefore, the charging current is changed in accordance with the change in humidity which is most susceptible to
In addition to the uniform charging of the pre-transfer paper, it is possible to obtain a constant and secure suction / transport force and a high transfer efficiency which are always independent of the environment.

〔The invention's effect〕

According to the invention, the elasticity of the transfer belt and the elastic brush, which is a conductive member, is kept constant over a long period of time by the above-described configuration and operation control, and the adhesion of dirt from the transfer belt by toner or the like is prevented. Prevents uniform charging of the paper before transfer, and conveys the recording paper with good transferability of the toner image and good separability from the photosensitive drum, and generates less ozone, which has a bad influence on the transfer belt and the human body. An image forming apparatus including an excellent transfer belt device can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the configuration of an embodiment of the image forming apparatus of the present invention, FIG. 2 is a sectional view showing the operation state of the transfer belt of FIG. 1, and FIG. FIG. 4 is a side view showing the leading end of the obtained recording paper P, FIG. 4 is a sectional view showing the structure of a conventional electrophotographic copying machine, and FIG. 5 is a schematic view showing one embodiment of a conventional transfer belt device. is there. 10 photoreceptor drum, 50 transfer material supply device 53 feeding roller, 65 elastic brush 66 power supply 70 transfer belt device 71 transfer belt 72, 73 holding roller 74: Roller support member, 160: Transfer section d: Non-transfer area, h: Non-image area k: Transfer area, P: Recording paper

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-209471 (JP, A) JP-A-62-151877 (JP, A) JP-A-59-204857 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G03G 15/16

Claims (1)

(57) [Claims] An image forming apparatus that forms a toner image on an image carrier using a transfer belt that is stretched and rotated between holding rollers, and transfers and conveys the toner image on a transfer material that moves in a transfer unit. The transfer belt is configured to be able to contact and separate from the image carrier at the time of image formation and at the time of non-image formation at the transfer portion, and a holding roller positioned upstream of a transfer portion of the transfer belt is provided. A conductive member that is opposed to the transfer belt with the transfer belt interposed therebetween. During image formation, the transfer belt also contacts the conductive member, and applies a predetermined bias voltage to the conductive member to cause a gap between the transfer belt and the transfer member. The transfer unit is configured to charge the transfer material to be pinched and conveyed, and then transfer the toner image in the transfer unit. When a non-image is formed, the transfer belt is retracted and the image carrier and the conductive member are transferred. Away from It was configured so as to be located in the position, the image forming apparatus characterized by.