JPH03194578A - Image forming device - Google Patents

Abstract

PURPOSE:To keep the elasticity of an elastic brush to be constant for a long period by holding a transfer material between a transfer belt and a conductive member to carry it when the transfer material passes and separating the conductive member from the belt when the transfer material does not pass. CONSTITUTION:Holding rollers 72 and 73 consist of a metallic material and the roller 72 is grounded or set at prescribed potential in a state approximate to a state that it is grounded. The shaft core of the roller 73 is used as the fixing shaft of a roller supporting member 74. Besides, the member 74 is energized by the elastic member so that the roller 72 is positioned downward and separated from the circumferential surface of a photosensitive drum 10 at ordinary time. At this time, the bristle tip of the elastic brush 65 is separated from the transfer belt 71. Therefore, the sticking of dirt is little and the elasticity of the brush 65 is not lost for long period. Besides, a bending does not occur to the brush 65. At the time of transfer, the member 74 is turned counter clockwise against the force of the elastic member and the belt 71 abuts on the drum 10 and the bristle tip of the brush 65.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a transfer material for an image forming apparatus such as an electrophotographic copying machine,
The present invention relates to an image forming apparatus having a transfer belt device that electrostatically supports and transports a toner image on an image carrier, transfers it onto the transfer material by physical means, and then transports the toner image to a fixing means.

[Conventional technology]

FIG. 4 is a cross-sectional configuration diagram showing an embodiment of an electrophotographic copying machine which is a conventional image forming apparatus. In the figure, 10 is a photoreceptor drum that is a drum-shaped image carrier, 20 is a charger that charges the circumferential surface of the photoreceptor drum 10, 30 is an exposure device, and 13
5 is an image exposure unit, 40 is a developing device, 50 is a transfer material supply device, and 5
3 is a paper feed roller, P is a recording paper that is a transfer material, 16 is a transfer device that is a charger for transfer, 17 is a separator that is a static eliminator for separation, 80 is a fixing device, 90 is a cleaning device, 56
is a conveyor belt which is a means for conveying the recording paper P.

To explain the operation of the copying machine, after the charger 20 uniformly charges the circumferential surface of the photoreceptor drum 10, the photoreceptor drum 1
The exposure device 30 performs exposure in the image exposure section 13 on the zero peripheral surface to form an electrostatic latent image. Thereafter, the latent image is developed and visualized by the developing device 40 to become a toner image. This toner image is transferred to the transfer material supply device 50 at the same time.
The image is transferred onto the recording paper P fed by the paper feed roller 53 . This transfer is performed by charging the recording paper P with a polarity opposite to that of the toner by a transfer device 16 from behind. After the transfer, a high AC voltage IIFE is applied by the post-transfer separator I7 to eliminate the charge, and the recording paper P is separated from the photosensitive drum IO. The separated recording paper P is conveyed to a fixing device 80 by a conveyor belt 56, the toner image thereof is fixed, and is 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 of residual toner on the circumferential surface by a cleaning device 90, and is ready for the next copy.

However, in the above configuration, in order to ensure the transferability and separation of the toner image, the transfer device 16 and the separator 1 are
However, the discharge efficiency must be adjusted to find the point that works best, and this discharge efficiency is greatly affected by the environment, and there is a problem that the tolerance range for reliability is narrow. The transferability is influenced by the electric charge of the recording paper P, the mechanical properties of the recording paper P (stiffness 9 surface smoothness,
curl, etc.), and these vary greatly depending on the storage condition of the recording paper P and the environment at the time of transfer (temperature, humidity), etc.
It is difficult to maintain it in good condition all the time.

Furthermore, when the drum diameter of the photosensitive drum 10 is large, when the recording paper P is transferred to the conveyor belt 56, the force to return to the original flat state is smaller than when the drum diameter is small, so that the toner image is After the transfer, the recording paper P adheres to the photoreceptor drum 10 and tends to cause paper jams, which leads to a decrease in the paper passing performance of the machine, resulting in deterioration of reliability.

As a technique for improving the above-mentioned drawbacks, a belt-shaped transfer/conveying device shown in FIG. 5 is disclosed in US Pat. No. 3,357,325 and the like.

In FIG. 5, IO is a photosensitive drum which is a drum-shaped image carrier, 70a is a transfer belt device which is a belt-shaped transfer/conveyance device, 71 is a transfer belt which holds charge and attracts a transfer material, 72. 73 is a roller for supporting, stretching and rotating the transfer belt 71; 60 is a pre-transfer paper charger that performs corona discharge to attract the recording paper P to the transfer belt 71 by electrostatic force; 16 is a charger for transferring the toner image to a photoreceptor; A transfer unit 160, which is a transfer charger for transferring the image from the drum 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,
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 in a superimposed manner on the photoreceptor drum IO and transferred to the recording paper P at one time.

In the color image forming apparatus, the photosensitive drum lO
In order to superimpose toner images on top of each other, multiple developing units are provided at the peripheral edge of the photoreceptor drum 10, which increases the diameter of the drum.Since the conventional electrostatic transfer separation method cannot obtain sufficient separation performance, more reliable separation performance is required. The transfer belt device has two points: 1. The transfer belt device needs to have a large transfer charge retention capacity because the toner image stacking method requires a large amount of toner adhesion and a large amount of transfer charge. This is because it is excellent.

[Problem to be solved by the invention]

In the transfer belt device shown in FIG. 5, a pre-transfer paper charger 60
The recording paper P is charged before transfer by the corona discharge. However, charging due to corona discharge often becomes non-uniform due to discharge unevenness caused by dirt on the discharge electrode, etc. Therefore, the adsorption of the recording paper P to the transfer belt 71 becomes non-uniform, resulting in non-uniform transferability. There was a problem.

Also, JP-A-1-121878 and JP-A-1-121879
Even in the technique disclosed in the above publication, the above problem has not been solved because the recording paper is charged by corona discharge.

The problem mentioned above is that in the case of reversal development, which has recently become popular, the material is often (-) charged, and in the case of (-) charging due to corona discharge, it tends to become non-uniformly charged, which is a problem. There is.

2. Description of the Related Art A charger is known in which a voltage is applied to an elastic brush made of a conductive elastic fiber member as a charging means. However, when the elastic brush is operated, it is necessary to keep the tips of the bristles in contact with the object to be charged with a constant pressure. For this reason, when the belt collects dirt or is used for a long period of time, it loses its elasticity and tends to bend, resulting in uneven pressure contact, resulting in a short service life.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an image forming apparatus equipped with a transfer belt device having a long life of elastic brushes and with excellent toner image transferability and separation onto a photoreceptor drum. .

[Means to solve the problem]

The purpose is to provide an image forming apparatus that uses a rotating transfer belt stretched between holding rollers to form a toner image on an image carrier, and in a transfer section transfers and conveys the toner image onto a moving transfer material. A holding roller located upstream of the transfer portion of the transfer belt is provided with a conductive member to which a predetermined voltage is applied, which faces the belt across the holding roller, and a bias voltage is applied to the conductive member when the transfer material passes. The transfer material is charged by sandwiching and conveying the transfer material between the belt and the conductive member, and the conductive member is separated from the belt when the transfer material does not pass. This is achieved by an image forming apparatus that uses

〔Example〕

FIG. 1 is a cross-sectional view of the construction of an embodiment of the image forming apparatus of the present invention, and FIG. 2 is a cross-sectional view of the construction of the transfer belt device of FIG. 1, showing the operating state thereof.

In this case, the same parts as those of the conventional image forming apparatus and 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 a detailed explanation of the overlapping parts 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 conductive fiber material fixedly installed on the upstream side of the transfer section 160 of the main body of the device. An elastic brush 66, which is a conductive member that acts to charge the paper, is a power source for applying a bias voltage to the elastic brush 65. A protective resistor may be inserted in series between the elastic brush 65 and the power source 66 in order to prevent a large current from flowing in the event that the elastic brush 65 comes into contact with a grounded portion or the like.

The holding rollers 72 and 73 are rollers made of a conductive metal material, and the holding roller 72 on the upstream side is grounded or at a predetermined potential close to the grounded state. Reference numeral 74 indicated by a two-dot chain line is a roller support member, one end of which has the axis of the holding roller 73 as a fixed shaft, and the other end connected to the movable shaft of the holding roller 72.
At all times (when not transferring), the holding roller 72 is urged by an elastic member (not shown) to be positioned downward, as shown in FIG. 1, and is spaced apart from the circumferential surface of the photosensitive drum 10. At this time, the elastic brush 65 is spaced so that its bristle tips 65a are either completely separated from the transfer belt 71 or just barely touch it. Therefore, since the elastic brushes 65 are always separated from each other with little dirt attached to them, the elastic brushes 65 do not lose their elasticity or become bent over a long period of time, and when they are charged, they are completely charged, extending their lifespan. be able to.

During transfer, the roller support member 74 is rotated counterclockwise against the force of the elastic member by, for example, a solenoid or a motor operated under the control of the apparatus main body control section, and the second
As shown in the figure, the transfer belt 71 comes into contact with the photoreceptor drum IO and the bristles 65a of the elastic brush 65.

Note that the elastic blank 65 is not fixed to the main body of the apparatus, but is attached to the roller holding member 74 via a member so as to be rotatable about its base 65b, and its bristles 65a are separated from the transfer belt 71 when not transferring. At the time of transfer, a solenoid or the like is actuated under the control of a control section so that the bristles 65a of the elastic brush 65 touch the transfer belt 7.
1 may be rotated so as to come into contact with a predetermined pressure.

Stainless steel wire can also be used as the conductive fiber of the elastic brush 65, but in this embodiment, the conductive fiber has a volume resistivity of 10.
Good results have been obtained using carbon-containing rayon of 4 to 10'' Ω·cm.

The structure of the transfer bell 1-71 is, for example, composed of two layers, and the main body is made of endless material such as silicone rubber, polyurethane rubber, butyl rubber, etc. with a thickness of about 0.5 to 1 mm, and has a volume resistivity of about 10'Ω·Cm. This is a high-resistance sheet, and the upper layer of this sheet is spray-coated with, for example, fluorine thread resin to lower frictional resistance and prevent dirt from adhering to it.

Next, the operation of the transfer belt device 70 will be explained.

At the same time as the paper feed roller 53 starts to rotate, the transfer belt 71, which has already been rotationally driven at the same time as the start of the copying 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, Furthermore, a bias voltage is applied from a power source 66 for charging the paper before transfer. The leading end of the recording paper P is moved by an elastic brush 6 by a paper feed roller 53.
5 and the transfer belt 71. Here, the recording paper P is injected with charge from the elastic brush 65 and charged in a negative manner, and is attracted to the transfer belt 71 and conveyed to the transfer section 160. When the leading edge of the recording paper P has passed through the transfer section 160 by a certain length (for example, 5 mm), the transfer power of the transfer device 16 (not shown) is turned on to start transferring the toner image. When the transfer is completed, the transfer belt 71 is separated from the photosensitive drum IO and the elastic brush 65 by the aforementioned elastic member.

As shown in FIG. 3, the operation control causes a non-transfer area d and a non-image area to be formed at the leading edge of the recording paper P. Process control in which the start of scanner reading for image reading or the start of printer writing is slightly delayed so that the leading edge of the image coincides with the leading edge of transfer area k (image area), which is slightly shifted backward due to the formation of the non-image area. will be held.

As a result, a few mm, for example 5 mm, can be added to the front edge of the recording paper P.
A non-transfer area d having a length d is formed, and a transfer voltage is applied so that transferability is sufficiently increased while the latter half of the non-image area following this non-transfer area d passes through the transfer unit 160.

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 toner image is transferred, and the photosensitive drum 10 In addition to improving the separation property from
Since the transfer area is uniformly charged with the pre-transfer paper by the elastic brush 65, the transfer is evenly and uniformly charged.
Very good transfer without unevenness is achieved.

It is sufficient that the bias voltage applied to the elastic brush 65 is lower than that for corona discharge, and the cost of the power source 66 can be reduced. In addition, since the recording paper P is charged by directly injecting electric charge without performing corona discharge, no ozone is generated, which has the advantage of reducing the deterioration of the life of the transfer belt 71 and the negative effects on the human body. .

In the image forming apparatus of the present embodiment, the elastic brush 65 is provided at a position facing the holding roller 72 that is on the ground or in a near-ground state, and the
In addition to charging more efficiently and reliably, the transfer section 1
Since the distance to the transfer belt 60 is short, the transfer bell 1-71 is able to firmly adsorb and hold the recording paper P while transporting the recording paper P, with less loss due to leakage of charged charges during transport.

Furthermore, since a bias voltage having the same polarity as the charge of the toner in the developer is applied to the elastic brush 65, the toner on the photoreceptor drum IO is attracted to the recording paper P until the recording paper P reaches the transfer section +60. never be done.

Therefore, clear copy image quality can be obtained.

The bias voltage is applied at a moving linear velocity of the circumferential surface of the photoreceptor drum 140 mm/see, and an image width of 300-350 mm.
mm, in the case of paper thickness 65 g/m2, 0.5-2. OKV
Constant voltage control is performed so that the polarity is the same as that of the C toner.

Further, a high voltage having a polarity opposite to that of toner charging is applied to the transfer device 16 under constant current control to transfer the toner image. This constant current control is performed by switching control such that, for example, the current is 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 according to changes in humidity, which is the most susceptible, and combined with the pre-transfer paper charging by the elastic brush 65, it is possible to achieve constant and reliable adsorption/conveying force and high transfer regardless of the environment. You can gain efficiency.

[Effects of the Invention] According to the present invention, with the configuration and operation control as described above, the elasticity of the elastic brush, which is a conductive member, is maintained constant over a long period of time, and dirt is prevented from adhering to the elastic brush, thereby uniformly cleaning the elastic brush. An excellent transfer belt device that charges the paper before transfer, transports the recording paper with good toner image transfer performance and separation from the photoreceptor drum, and generates little ozone that is harmful to the transfer belt and the human body. It is now possible to provide an image forming apparatus equipped with the following.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the image forming apparatus of the present invention, FIG. 2 is a cross-sectional view showing the operating state of the transfer belt in FIG. 1, and FIG. FIG. 4 is a side view showing the leading end of the resulting recording paper P, FIG. 4 is a cross-sectional configuration diagram showing the configuration of a conventional electrophotographic copying machine, and FIG. 5 is a schematic configuration diagram showing an example of a conventional transfer belt device. be.

Claims (1)

[Claims] In an image forming apparatus that uses a rotating transfer belt stretched between holding rollers to form a toner image on an image carrier and then transfers and conveys the toner image onto a moving transfer material in a transfer section, the transfer belt is On the holding roller located upstream of the transfer section,
A conductive member to which a predetermined voltage is applied is provided opposite to the belt, and when the transfer material passes, a bias voltage is applied to the conductive member to sandwich the transfer material between the belt and the conductive member. An image forming apparatus characterized in that the conductive member is configured to charge the transfer material by conveying the belt, and to separate the conductive member from the belt when the transfer material does not pass.