JP2829659B2 - 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. 5 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 transfer charger, 17 is a separator as a divider 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. 6 is disclosed in U.S. Pat. No. 3,357,325.

In FIG. 6, 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 charger for performing corona discharge to attract the recording paper P to the transfer belt 71 by electrostatic force, and 16 is a device for recording a toner image from the photosensitive drum 10. A transfer unit 160, which is a transfer charger for transferring to the paper P, is a transfer unit. With this configuration, the recording paper P can be conveyed with the recording paper P adhered to the transfer belt 71, and excellent transfer efficiency can be obtained at the transfer section.
Separation efficiency can be obtained.

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. 6, the recording paper P is charged for adsorption by corona discharge of the charger 60 for adsorbing the transfer material. 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 particular, when the polarity of the toner is negative, the charge to the transfer material is negative, and in the case of (-) charging by corona discharge, there is a problem that the discharge is likely to be uneven and the charge is uneven.

In order to solve the above problem, there is known a charger in which an elastic brush made of a conductive elastic fiber member is used as a transfer material charging unit, and a voltage is applied to the elastic brush, which performs uniform charging. Very effective on the above. However, it is necessary to keep the tip of the elastic brush in contact with the recording paper P, which is a member to be charged, for charging. In addition, if the environment is humid, turn off the DC power supply for charging the transfer material.
Even if F, the resistance value between the ground and the ground does not become infinite, so that the transfer charge easily leaks through the transfer belt 71, the recording paper P and the elastic brush, so that sufficient transfer charge cannot be obtained and the transfer efficiency decreases. However, there is a problem that normal transfer is not performed.

The present invention solves the above problems with a simple configuration,
It is an object of the present invention to provide an image forming apparatus that performs uniform transfer charging and has uniform and good transferability and separability.

[Means for solving the problem]

The object is to provide 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 that transfers and conveys the toner image on a transfer material that moves in a transfer unit. A conductive member to which a predetermined voltage is applied to the holding roller located on the upstream side of a transfer portion of the transfer belt, the voltage being applied across the belt; Is achieved by an image forming apparatus in which a predetermined bias voltage is applied to charge the transfer material, and a zener diode is inserted in series between the conductive member and a power supply for charging the transfer material. Is done.

〔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.

5, the same parts as those of the conventional image forming apparatus and the transfer belt apparatus 70a shown in FIGS. 5 and 6 are denoted by the same reference numerals, and their operations are almost the same.

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 made of a conductive fibrous material fixed on the upstream side through an insulating material and serving as a conductive member for charging the transfer material, and 66 is a transfer material charging device for applying a bias voltage to the elastic brush 65. A DC power source 67 is a Zener diode inserted between the elastic brush 65 and the DC power source 66 to prevent a leakage current described later. The holding rollers 72 and 73 are rollers made of a conductive metal material, and the holding rollers 72 on the upstream side
Is set to a grounded state or a predetermined potential close to the grounded state. A roller supporting member 74 indicated by a two-dot chain line has one end having the fixed shaft as the axis of the holding roller 73 and the other end having the holding roller 72.
The holding roller 72 is normally urged by an elastic member (not shown) so as to be located at a lower position as shown in FIG. 1 and is separated from the peripheral surface of the photosensitive drum 10. I have. At this time, the elastic brush 65 is separated such that the bristle tip is completely separated from the transfer belt 71 or slightly touched. Therefore, since there is little adhesion of dirt, the elastic brush 65 does not lose its elasticity or bend over a long period of time because it is always separated, complete charging is performed, and its life is extended. be able to.

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 is brought into contact with the photosensitive drum 10 and the bristle tip 65a of the elastic brush 65 with a predetermined pressure.

Note that the elastic brush 65 is not fixed to the main body of the apparatus, but its base.
The roller tip is provided rotatably around the roller holding member 74 via a mounting portion.
The transfer member is urged by an elastic member so as to be separated from the first member, and during transfer, for example, a solenoid, a motor, or the like is operated under the control of the control unit, and the bristle tip 65a of the elastic brush 65 is rotated so as to contact the transfer belt 71 with a predetermined pressure. It is good also as a structure to make it.

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-based resin is spray-coated on the upper layer of this sheet to lower 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 charging the transfer material is applied to the elastic brush 65 from the DC power supply 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 elastic brush 65 and is uniformly charged.
And is conveyed to the transfer unit 160. When the leading end of the recording paper P has passed the transfer section 160 for a predetermined length (for example, 5 mm), the transfer power supply of the transfer device 16 (not shown) is turned on, and the transfer of the toner image is started. After that, when the recording paper P is charged to 40 to 50 mm from the leading end, the DC power supply 66 for charging the transfer material is turned off, but the zener diode 67 removes a small leakage current (1 μA or less to about 5 μA). Since the transfer charge is prevented from leaking through the recording paper P and the elastic brush 65, a normal transfer potential is maintained. 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 writing to the printer is slightly delayed so that the leading end of the transfer area k (image area) slightly behind by the formation of the non-image area h coincides with the leading end of the image. 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 area h following the non-transfer area d is sufficiently transferred while passing through the transfer unit 160. The transfer power supply is turned on and the transfer bias voltage is applied so that the transfer characteristic rises.

Since the non-transfer area d of the recording paper P continues to be charged by the elastic brush 65, the transfer 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 to the recording paper P by the elastic brush 65, and the transfer charge is less leaked by the action of the Zener diode 67, so that the transfer charge is reduced. Is performed uniformly without unevenness, and extremely excellent transfer without unevenness is performed.

FIG. 4 is a graph showing the characteristics of the Zener diode 67. The vertical axis indicates the current I flowing through the Zener diode 67, and the horizontal axis indicates the voltage V applied to the Zener diode 67. Zener voltage Vz is equal to voltage Vb between elastic brush 65 and ground.
If a sufficiently large zener diode 67 is used, the leakage of the transfer charge can be reduced.

The application of the bias voltage for charging the transfer material is performed such that the moving linear velocity of the peripheral surface of the photosensitive drum 10 is 140 mm / sec, and the image width is 300 to 350 m.
m and a paper thickness of 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).

Now, when the applied voltage for charging the recording paper P requires -1.5 KV, the zener voltage Vz uses a zener diode 67 having a voltage of -0.4 KV, and the output voltage Vp of the DC power source 66 for charging the transfer material is-.
If 1.9 KV is applied, the applied voltage to the recording paper P becomes (−1.9) KV − (− 0.4) KV = 1.5 KV, and the required applied voltage can be obtained. When the DC power source 66 is turned off, the voltage Vb between the elastic brush 65 and the ground due to the transfer charge is −0.1 to −0.2 KV due to a voltage drop due to the resistance value of the recording paper P, and the Zener leakage current (leakage current) ) Is 5 μA or less, so that the influence of the leakage current on the normal discharge current of the transfer unit 16 of 30 μA is extremely small.

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 DC 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 facing the holding roller 72 which 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 can be efficiently processed. The transfer unit 160
Since the distance to the transfer belt 71 is short, the decrease due to the leakage of the charged charges during the conveyance is small, and the transfer belt 71 can strongly convey and convey the recording paper P while holding it.

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, and a clear copy image quality can be obtained.

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 a toner image. In this constant current control, for example, switching control is performed so as to be 300 μA for high humidity and 200 μA for low humidity,
It is charged.

Therefore, the charging current is changed in accordance with the change in humidity, which is most susceptible to the influence, and the uniform charging of the recording paper P by the elastic brush 65 and the action of the zener diode 67 are combined to ensure a constant and secure adsorption regardless of the environment. -A transfer force and high transfer efficiency can be obtained.

〔The invention's effect〕

According to the present invention, with the configuration and operation control described above, uniform transfer material charging and transfer charging can be performed without complicating the configuration, and the transfer charge can be performed even under high humidity conditions. This makes it possible to provide an excellent image forming apparatus having excellent transferability and separability with extremely low leakage of the toner.

[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 characteristic view of the Zener diode of FIG. 1, FIG. 5 is a sectional view showing the configuration of a conventional electrophotographic copying machine, and FIG. FIG. 1 is a schematic configuration diagram illustrating an example of a transfer belt device according to an embodiment. 10 photoconductor drum, 50 transfer material supply device 53 paper feed roller 65 elastic brush 66 DC power supply 67 zener diode 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 Continued on the front page (72) Inventor Masayoshi Kanno 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation (72) Inventor Yoshio Yamazaki 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation Inspector Fumio Komiyama (56) reference Patent flat 2-106775 (JP, a) JP flat 2-24683 (JP, a) JitsuHiraku Akira 62-127561 (JP, U) (58 ) investigated the 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 at a transfer unit. A conductive member to which a predetermined voltage is applied opposite to the transfer belt on a holding roller positioned upstream of a transfer portion of the transfer belt, and the conductive member passes a predetermined length from the leading end of the transfer material. An image forming apparatus, wherein a predetermined bias voltage is applied to the transfer material to charge the transfer material, and a zener diode is inserted in series between the conductive member and a power supply for charging the transfer material. .