JPH03180881A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent transfer belt where the production of ozone is reduced by permitting a recording paper to abut on a transfer belt when the leading edge of the recording paper passes through the fixed length of a transferring part and securing a non-transfer area having a sharp boundary. CONSTITUTION:A roller supporting member 74 whose one end has the shaft center of a roller 73 as a fixed shaft and whose other end is connected to the movable shaft of the roller 72 supports a transfer bias roller 75 so as to abut on the transfer belt 70 via an insulating material. The supporting member 74 is turned by a solenoid or a motor which is operated by the control of a device main body control part when a transfer is performed, and the belt 71 is abutted on a photosensitive body 10. At this time, the prescribed length of the tailing edge of the transfer material is secured as the non-transfer area, then a transfer bias is applied on the roller 75, and a toner image is transferred on the transfer material. Therefore, the fixed length of non-transfer area having the sharp boundary is secured in the leading edge part of the transfer material, and a non-image area is not enlarged. Thus, an efficient separation from an image carrier is obtained, the production of ozone influencing the service life of the belt 70 is reduced, and an image part is enlarged.

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. 5 is a sectional view showing an embodiment of a conventional electrophotographic copying machine. In the figure, IO is a photoreceptor drum which is a drum-shaped image bearing member, 201 is a charging W device that charges the circumferential surface of the photoreceptor drum 10, 30 is an exposure device, 13 is an image exposure section, 40
50 is a transfer material supply device, 53 is a paper feed roller, P is a recording paper which is a transfer material, 16 is a transfer device which is a transfer band tS, and 17 is a separator which is a static eliminator for separation. , 80 is a fixing device, 90 is a cleaning device, and 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 turned into a toner image by the developing device 40. This toner image is transferred onto the recording paper P fed by the paper feeding roller 53 of the paper feeding device 50 at the same timing.

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 is applied by the post-transfer separator 17 to eliminate static electricity, and the recording paper P is separated from the photoreceptor drum 10.

The separated recording paper P is transferred to the fixing device 8 by the conveyor belt 56.
0, the toner image is fixed and discharged onto 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 discharge efficiency between the transfer device 16 and the separator 17 must be adjusted to find the point that functions best. , and this discharge efficiency is greatly influenced by the environment, and the tolerance range for reliability is narrow. The transferability is influenced by the electric charge of the recording paper P and the mechanical properties of the recording paper P (stiffness 1 surface smoothness, curl, etc.),
These vary greatly depending on the storage condition of the recording paper P, the environment at the time of transfer (temperature, humidity), etc., and it is difficult to always maintain them in a good condition.

Furthermore, when the drum diameter of the photoreceptor drum 10 is large, when the recording paper P is wrapped around the photoreceptor drum 10, the force of trying to return to the original flat state is smaller than when the drum diameter is small, so the toner After the image has been transferred, the recording paper P remains attached to the photoreceptor drum 1O, easily causing a paper jam.
This method has disadvantages such as a decrease in paper passing performance as a machine and a deterioration in reliability.

As a technique for improving the above-mentioned drawbacks, a belt-shaped transfer/transport device shown in FIG. 6 is disclosed in US Pat. No. 3,357,325 and the like.

In FIG. 6, 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 L-172 consisting of a dielectric single layer belt, 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; 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 fed by the paper feed roller 53 is transferred to the transfer belt 71.
It is possible to firmly adhere to the surface and transport it reliably, and it is possible to obtain excellent transfer efficiency and separation efficiency.

The transfer belt device 70a is a preferred device in a color image forming apparatus in which toner images are formed on the photoreceptor drum 10 in a superimposed manner 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 needs to have a large amount of transfer charge because the toner image stacking method requires a large amount of toner adhesion, so it needs to have a large transfer charge retention ability. This is because it is excellent.

[Problem to be solved by the invention]

In the transfer belt device shown in FIG. 6, a pre-transfer paper charger 60
As the recording paper P is charged, the transfer belts 71 are charged with opposite polarities and attract each other, and the transfer belts 1-7
1, the recording paper P is conveyed. However, when transfer charging for toner image transfer is performed, the suction force becomes weaker and separation from the photoreceptor drum 10 becomes worse. In order to obtain good separability, a non-transfer area is formed at the leading edge of the recording paper P (length approximately 5+wm), and even after this area passes through the transfer section 160, it is firmly attached to the transfer belt 7.
It is necessary that it be attached to 1. For this reason, recording paper P
The timing of image exposure is controlled so as to form a non-image area at the leading edge, and after a portion of the leading edge of this non-image area passes through the transfer unit 160, corona discharge of the transfer ``516'' is started to form a non-transfer area. need to be formed.

FIG. 4 is a diagram showing the transfer electric field intensity distribution formed by the conventional transfer devices 16a and 16b. In the figure,
161 is a shield member made of an aluminum plate, stainless steel plate, surface-treated steel plate, etc.; 162 is a discharge electrode made of a thin tungsten wire; 16a is a shield member 161
16b is a transfer device with a narrow opening of the shield member 161, E is a transfer device 16a,
16b.

As shown in FIG. 4, in the conventional transfer devices 16a and 16b, the transfer electric field strength distribution has a wide spread, so that the transfer electric field rises slowly at the boundary between the non-transfer area and the transfer area, and the transferability is affected. Insufficient areas of the area. Therefore, since the non-image area must be widened, there is a problem that the image area becomes narrow.

Furthermore, since the conventional transfer device 16 is accompanied by corona discharge, it deteriorates the transfer belt 71 and has a short lifespan, which has a negative effect on the human body.

The present invention solves the above problems, secures a non-transfer area with sharp boundaries and a constant length, does not unnecessarily enlarge the non-image area, has excellent conveyance and separation properties, and transfer belt An object of the present invention is to provide an image forming apparatus that has a transfer belt device that has a long service life, generates little ozone, and has good paper passing properties.

[Means to solve the problem]

The purpose of MO is to use an image forming apparatus that uses a rotating transfer belt stretched between rollers to transfer and convey a toner image on an image carrier onto a moving transfer material in a transfer section. A transfer bias roller to which a transfer bias can be applied is brought into contact with the back surface of the transfer belt, a predetermined length of the leading edge of the transfer material is set as a non-transfer area, and after that, the transfer bias is applied to transfer the transfer material. It is distantly related to image forming apparatuses that are characterized by performing the entire transfer of a toner image onto an image forming apparatus.

〔Example〕

FIG. 1 is a sectional view showing the structure of an embodiment of an image forming apparatus according to the present invention.

In the figure, parts that are the same as those of the conventional image forming apparatus and transfer belt device 70a shown in FIGS. 5 and 6 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 roller 72, 70 is a transfer belt device, 75 is a transfer bias roller made of a conductive metal material, and 76 is a toner attached to the transfer bias roller 75. This is a transfer power supply that supplies a high voltage of opposite polarity. The rollers 72 and 73 are rollers made of conductive metal material, and the roller 72 on the upstream side is grounded or at a predetermined potential close to the grounded state. 74 indicated by a two-dot chain line is a roller support member, one end of which has the axis of the roller 73 as a fixed shaft, and the other end connected to the movable shaft of the roller 72, and transfers the transfer bias roller 75 through an insulating material. It is supported so as to be in contact with the belt 71. The roller 72 is normally urged downward by an elastic member (not shown). Therefore, except during transfer, the transfer belt 71 is separated from the circumferential surface of the photoreceptor drum 10, as shown by the dashed line, and during transfer, the roller support member 74 is moved by, for example, a renoid or a motor operated under the control of the control section of the main body of the apparatus. The transfer belt 71 is rotated counterclockwise.
is brought into contact with the photoreceptor drum 10. The guide plate 54 can also be removed by moving the paper feed roller 53 closer to the roller 72.

The structure of the transfer belt 71 is, for example, composed of two layers, and the main body is made of endless volume resistance 1 made of silicone rubber, polyurethane rubber, butyl rubber, etc. with a thickness of about 0.5 to 1 mm.
It is a high resistance sheet of around 0.010 Ω·cm, and the frictional resistance is lowered by spraying fluorocarbon resin on the upper layer of the sheet.

FIG. 2 is a diagram showing the distribution of the transfer electric field strength E when the transfer bias roller 75 of FIG. 1 is brought into contact with the transfer belt 71 and a bias voltage is applied. The transfer electric field strength distribution has a sharper shape than in the case of No. 16, and charging can be limited to an extremely narrow range. Further, since no corona discharge is involved, ozone is not generated, and the life of the transfer belt 71 is not deteriorated, thereby reducing the adverse effects on the human body.

I: It is desirable that the diameter of the transfer bias roller 75 is as small as its strength allows, and that the transfer electric field strength distribution range is made as narrow and sharp as possible.

Next, the operation of the transfer belt device 7o will be explained.

At the same time as the paper feed roller 53 starts rotating, the transfer belt 71, which has already been rotated at the same time as the start of the copying operation, comes into contact with the photosensitive drum IO and a high voltage is applied to the discharge electrode 62 of the pre-transfer paper charger 60. The leading edge of the recording paper P is connected to the discharge electrode 6 of the pre-transfer paper charger 60 by the paper feed roller 53.
2 and the transfer belt 71 into the effective discharge area. Here, the recording paper P is electrostatically attracted to the transfer belt 71 and conveyed to the transfer section 160. When the leading edge of the recording paper P passes the transfer section 160 by a certain length (for example, 5 to 7 mm), the transfer power source 76 of the transfer bias roller 75 is turned on to start transferring the toner image. In this way, the recording paper P
It is possible to form a non-transfer area of a certain length at the tip and then use a very small distance as a transfer area.

Note that the transfer bias roller 75 is configured to be movable and switchable so as to come into contact with or release from the transfer belt 71, and transfer charging and non-charging can be switched by bringing the transfer bias roller 75 into contact with or releasing contact from the transfer belt 71. It is also possible to do this. That is, even when a transfer bias is applied, the transfer bias roller 75 is normally separated from the transfer belt 71, and when the leading edge of the recording paper P passes through the transfer section 160 for a certain length, it is brought into contact with the transfer belt 71. It is also possible to perform transfer charging and make the area after this a transfer area, and to form a non-transfer area at the leading edge of the recording paper P.

Note that since the transfer charging is not by corona discharge but by charge injection, a low power supply voltage is sufficient, and there is an advantage that the cost of the transfer power supply 76 can be reduced.

FIG. 3 shows a conventional transfer device 16 (16a
, 16b). According to the present invention, it is possible to form a non-transfer area d with a sharp boundary at the leading edge of the recording paper P, and since the transferability rises sharply at the boundary transitioning to the transfer area, a non-transfer area d at the leading edge of the recording paper P can be formed. There is no need to make the area unnecessarily long.

The non-transfer area d continues to be charged by the pre-transfer paper charger 60, and even after the toner image is transferred, the non-transfer area d at the leading edge of the recording paper P is firmly attracted to the transfer belt 71. , the separation of the recording paper P from the photoreceptor drum 10 is improved.

The pre-transfer paper charger 60 of this embodiment is provided at a position facing the roller 72 that is grounded or close to the ground, and causes corona discharge toward the recording paper P fed from the transfer material supply device 50. The roller 72, which is close to the grounded state, is used as a counter electrode to perform charging efficiently and reliably. In addition, since the distance to the transfer unit 160 is very short, there is less reduction in charge due to leakage during transfer. The belt 71 can firmly adsorb and hold the recording paper P and convey it.

Further, a high voltage having the same polarity as the charging of the toner of the developer is applied to the discharge electrode 62 of the pre-transfer paper charger 60.

Therefore, the toner on the photosensitive drum 10 is not attracted to the recording paper P until the recording paper P reaches the transfer section 160, so that a clear copy image quality can be obtained.

The application of the high voltage is carried out at a linear velocity of movement of the circumferential surface of the photoreceptor drum 10 of 140 mm/5ee1 image width of 300 to 350 mm,
When the paper thickness is 65 g/m", the charging current is controlled to be 20 to 50/jA, and at this time, the current component flowing in the direction of the recording paper P is 10 to 20 μA when the humidity is high, and 5 μA when the humidity is low.
~lOμA.

Further, a high voltage having a polarity opposite to that of the toner charging is applied to the transfer bias roller 75 under constant voltage control to transfer the toner image. If such constant voltage control is performed, the voltage between the roller and the drum will be constant regardless of environmental changes, and stable transfer will be possible.

〔Effect of the invention〕

According to the present invention, with the configuration and operation control as described above, a non-transfer area of a constant length with sharp boundaries is secured at the leading edge of the transfer material, and the non-image area is not unnecessarily enlarged. The image forming device is equipped with a transfer belt device that has excellent separation properties from the image carrier, has excellent paper passing properties, reduces the life of the transfer belt and reduces ozone generation, which has a negative impact on the human body, and has a wide image area. Now we can provide it.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the structure of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the structure near the transfer bias roller of FIG. 1 and its transfer electric field strength distribution, and FIG. Diagrams showing non-transfer areas and non-image areas on recording paper, Fig. 4(a), (
b) is a diagram showing the cross-sectional shape of a conventional transfer device and its transfer electric field strength distribution, FIG. 5 is a cross-sectional configuration diagram showing the configuration of a conventional electrophotographic copying machine, and FIG. 6 is an implementation of a conventional transfer belt device. FIG. 2 is a schematic configuration diagram showing an example. DESCRIPTION OF SYMBOLS 10... Photosensitive drum 50... Transfer material supply device 53... Paper feed roller 60... Pre-transfer paper charger 70... Transfer belt device 7i...
・Transfer belt 72.73...Roller 74
...Roller support member 75...Transfer bias roller
76...Transfer power supply 160...Transfer section
d...Non-transfer area E...Transfer electric field strength h
...Non-image area P...Recording paper

Claims (1)

[Claims] In an image forming apparatus that uses a rotating transfer belt stretched between rollers to transfer and convey a toner image on an image carrier onto a moving transfer material in a transfer section, the transfer section transfers the toner image to a conductive roller. A transfer bias roller to which a bias can be applied is brought into contact with the back surface of the transfer belt, a predetermined length at the leading edge of the transfer material is set as a non-transfer area, and the transfer bias is applied after that to form a toner image on the transfer material. An image forming apparatus characterized by performing transfer.