JP2001066911A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the carrying stability of a transfer material by a secondary transfer belt after the transfer material is passed through a secondary transfer part and to prevent an image from being scattered when the transfer material is separated by surely discharging the transfer material extending over the trailing edge thereof by a discharge means at a transfer belt separation part. SOLUTION: By applying secondary transfer bias being V1=+2.0 kV to a transfer roller 31 supporting the secondary transfer belt 3 constituting a secondary transfer means, a toner image formed on an intermediate transfer drum 2 is secondarily transferred on the transfer material P. Even after the material P is passed through a secondary transfer position, secondary transfer bias V2=±1.5 kV is supplied. Then, the secondary transfer bias is cut after the trailing edge of the material P is passed through a separation point (position of a driving roller 32). When the leading edge part of the material P arrives at the separation point, AC voltage being 11 kV is applied to a separation discharger 14 as the discharge bias. When a discharge current being equal to over -18 μA flows, a separation discharge effect is obtained. While the transfer material is passed through a secondary transfer nip, -22 μA is obtained. After it is passed through the secondary transfer nip, -20 μA is obtained.

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 such as a copying machine, a printer, a facsimile and the like using an electrophotographic system. The present invention relates to an image forming apparatus in which a color image is obtained on a transfer material by superimposing and transferring the image on an intermediate transfer member as a second image carrier, and then transferring the image from the intermediate transfer member to a transfer material at a time.

[0002]

2. Description of the Related Art An electrophotographic full-color image forming apparatus using an intermediate transfer member is known. When a primary transfer process from a photoreceptor is repeated for each color, a transfer material such as paper is used. There is almost no effect, stable formation of multicolor images is possible, and there is no need to wind the transfer material around the transfer drum, so the transfer material transport path can be configured linearly, and thin paper, thick paper, envelopes, etc. It is advantageous in that various kinds of transfer materials can be used.

An image forming apparatus using the intermediate transfer member includes a photosensitive member as a first image carrier, an intermediate transfer member as a second image carrier, a primary charging unit, an exposure unit, a developing unit, It is composed of a secondary transfer unit, a separation / elimination unit, a fixing unit, and the like.

[0004] The surface of the photoreceptor is uniformly charged by primary charging means, and an image pattern is exposed by exposure means such as a laser. An electrostatic latent image is formed. When this latent image is developed by a developing device using toner, the toner adheres to the exposed portion and the latent image is visualized as a toner image.

In the toner image formed on the photoreceptor, the photoreceptor is brought into contact with the intermediate transfer member by applying a voltage (primary transfer bias) having a polarity opposite to that of the toner at a constant value to the intermediate transfer member. In the primary transfer section, the image is transferred onto the surface of the intermediate transfer member (primary transfer). In full-color image formation, by repeating this process for a plurality of colors, a color image in which a plurality of color toner images are superimposed on the intermediate transfer member is formed.

The toner images of a plurality of colors superimposedly transferred on the intermediate transfer body are transferred by applying a voltage (secondary transfer bias) having a polarity opposite to that of the toner to a transfer belt, for example, a transfer belt. At the secondary transfer portion where the belt and the intermediate transfer member are in contact, the image is collectively transferred to the transfer material conveyed thereto (secondary transfer). The transfer material onto which the four color toner images have been transferred is attracted to a transfer belt and conveyed to a fixing device, where the toner images are fixed to the transfer material and formed into a full-color print image.

FIG. 5 shows an intermediate transfer member, a secondary transfer portion, and a separation portion of the image forming apparatus.

The transfer belt 3 as a secondary transfer means is wound around a transfer roller 31 and a drive roller 32 and rotated in the direction of the arrow. The transfer material P is supplied to a secondary transfer nip where the intermediate transfer drum 2 and the transfer belt 3 are in contact with each other.
While being conveyed while being attracted to the transfer belt 3, it is separated by a separation unit spanning the drive roller 32, but if this separation is not performed correctly, the transfer material P remains attached to the transfer belt 3. If the diameter of the driving roller 32 is small,
Although it is possible to separate the curvature of the transfer material P, in this case, a peeling discharge occurs, and unfixed toner scatters, which may result in an image defect.

In order to separate the transfer material P from the transfer belt 3 by installing a separation neutralizer 14 at the separation portion of the secondary transfer belt 3, a high-voltage power supply 141 applies a neutralization bias to the separation neutralizer 14. By removing the charge of the transfer material P, the attraction force between the transfer material P and the transfer belt 3 is reduced to improve the separability, and peeling discharge is suppressed to prevent image defects such as toner scattering.

[0010]

However, the above-mentioned conventional image forming apparatus has the following problems.

The secondary transfer bias applied to the secondary transfer belt 3 from the bias power supply 33
This is for transferring the upper toner image onto the transfer material P. When the rear end of the transfer material P passes through the secondary transfer nip and the secondary transfer bias from the power source 33 to the transfer roller 31 is turned off. When a medium-resistance belt is used as the transfer belt 3, no charge is held on the surface of the transfer belt 3,
The surface potential decreases.

As a result, the charge elimination current from the separation charge eliminator 14 to the transfer belt 3 decreases, and the charge elimination effect on the transfer material P decreases. For this reason, at the rear end of the transfer material P, peeling discharge from the transfer belt 3 is likely to occur, and there is a possibility that an image defect such as toner scattering may occur. In addition, when the surface potential of the transfer belt is reduced, the attraction force between the transfer material and the belt is reduced, and there is a possibility that the transfer of the transfer material may be defective.

It is an object of the present invention to ensure the stability of the transfer of the transfer material by the transfer belt after passing through the secondary transfer portion, and to reliably remove the charge of the transfer material to the rear end by the charge removing means in the separation portion of the transfer belt. It is another object of the present invention to provide an image forming apparatus capable of preventing scattering of an image when a transfer material is separated.

[0014]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A first image carrier, a second image carrier, and a toner image formed on the first image carrier is primarily transferred onto the second image carrier at a first transfer position. A primary transfer means to which a primary transfer bias is supplied, a secondary transfer of a toner image on the second image carrier onto a transfer material at a second transfer position, and a suction and transfer of the transfer material A belt-shaped secondary transfer unit to which a secondary transfer bias is supplied, and a separation to which a discharge bias is supplied, wherein the transfer material is discharged when the transfer material is separated from the secondary transfer unit after the secondary transfer. A belt-like secondary transfer unit, wherein the belt-like secondary transfer unit is opposed to the endless belt, a first roller around which the endless belt is looped, the second roller being arranged to face the second transfer position, and the separation and neutralization unit. An image forming apparatus comprising: a second roller disposed on the second roller; The bias is supplied until the rear end of the transfer material is separated from the timing at which the transfer material separates from the belt-shaped secondary transfer means, and the bias value V1 during which the transfer material passes through the second transfer position, An image forming apparatus having two set values of a bias value V2 after passing a second transfer position of a material.

According to the present invention, the endless belt is disposed in contact with the second image carrier at the second transfer position, and supplies a secondary transfer bias to the first roller. Is connected to the second roller. Alternatively, the endless belt is disposed so as to be able to freely contact and separate from the second image carrier at the second transfer position. The endless belt is 1
It has a resistance value of 0 ⁵ to 10 ¹³ Ω, and furthermore has a resistance value of 10 ⁵ to 10 ⁹
It has a resistance of Ω. Further, a plurality of toner images are sequentially formed on the first image carrier for a plurality of colors, and the toner images are sequentially superimposed on the second image carrier at the first transfer position and primary-transferred, and the second transfer is performed. A plurality of color toner images on the image carrier can be collectively and secondarily transferred onto the transfer material at the second transfer position.

[0016]

Embodiments of the present invention will be described below in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention.

In this embodiment, a full-color laser beam printer using a negative process will be described.

In this embodiment, the printer has a photosensitive drum 1 as a first image bearing member.
Is driven to rotate in the direction of the arrow. Around the photosensitive drum 1, a primary charger 7 for uniformly charging the surface of the photosensitive drum 1 to a negative polarity in the direction of rotation thereof, and exposing the surface of the photosensitive drum 1 based on an image signal to form an electrostatic latent image. , A fixed developing device 8 for developing an electrostatic latent image using toner and three rotating developing devices 9, an intermediate transfer drum 2 as a second image carrier, and A drum cleaner 6 is provided. Intermediate transfer drum 2
, A secondary transfer belt 3 is disposed on the side opposite to the photosensitive drum 1, a separation static eliminator 14 is disposed at a downstream end of the secondary transfer belt 3, and a fixing device 20 is disposed on an extension thereof. Have been.

A full-color image signal is sent to the printer in a state where it is separated into four colors of yellow, magenta, cyan, and black. The surface of the photosensitive drum 1 is uniformly charged to, for example, −550 V by the primary charger 7,
Next, a pattern corresponding to the yellow image signal is exposed by the laser exposure device 3. Photosensitive drum 1 after exposure
Has a potential VD of -550 V at the unexposed portion and a potential VL of -180 V at the exposed portion, thereby forming a yellow electrostatic latent image.

The yellow developing unit 9Y of the rotary developing unit 9 is located at a developing position facing the photosensitive drum 1. When a developing bias in which an AC voltage and a -350V DC voltage are superimposed is applied to the developing sleeve, the photosensitive developing unit 9Y is exposed. The VL portion on the surface of the drum 1 is developed with a negatively charged yellow toner,
The latent image is visualized as a yellow toner image.

The intermediate transfer drum 2 also serves as a first transfer means, contacts the photosensitive drum 1 to form a primary transfer nip, and is driven to rotate at substantially the same speed as the photosensitive drum 1. The primary transfer bias power supply 21 supplies +200 V to the core of the intermediate transfer drum 2 as the primary transfer bias T1.
Is applied, the yellow toner image on the photosensitive drum 1 becomes 1
In the next transfer nip portion, primary transfer is performed on the surface of the intermediate transfer drum 2 by a potential difference of 380 V between the VL portion of the photosensitive drum 1 and the intermediate transfer drum 2.

After the photosensitive drum 1 is cleaned by the cleaning blade 5 of the drum cleaner 6, the steps of charging, exposure and development are repeated again to form a magenta toner image. Then, the primary transfer bias T1 is applied at +300 V higher than that at the time of transfer of yellow, and the magenta toner image is primary-transferred onto the intermediate transfer drum 2 from the yellow toner image. Thereafter, a series of steps of charging, exposure, development and primary transfer are repeated for cyan and black, and a color image in which four toner images of yellow, magenta, cyan and black are superimposed on the intermediate transfer drum 2 is formed. .

Secondary transfer belt 3 constituting secondary transfer means
Means that the resistance value is 1 × 10¹³Ω resin belt
Transfer roller 31 and drive roller 32
In the hooked state, it is rotated in the direction of the arrow in the figure. Secondary transfer
The resistance value of 10 is 10 ^Five-10¹³Ω is preferred.
The measurement environment of the resistance value was 23 ° C. and 60% RH.
The pressure is 100V.

A secondary transfer bias power supply 33 is connected to the core of the transfer roller 31. In the present embodiment, a secondary transfer bias power supply 33 is also connected to the core of the drive roller 32. The transfer material separating portion of the transfer belt 3
The position 2 is a separation point, and the potential of the separation portion is a potential corresponding to the bias applied to the drive roller 32. In this embodiment, the distance between the transfer roller 31 and the drive roller 32 is set to 100
mm.

The secondary transfer belt 3 is pressed against the intermediate transfer drum 2 on which the four color toner images are superimposed and transferred to form a secondary transfer nip, and the leading end of the image on the intermediate transfer drum 2 and the transfer material P The transfer material P is sent to the secondary transfer section with the leading ends synchronized. For example, about 2 kV as the secondary transfer bias (T2)
, The four color toner images on the intermediate transfer drum 2 are secondarily transferred onto the transfer material P at once.

The transfer material P to which the four color toner images have been transferred is
While being adsorbed on the transfer belt 3, the sheet is conveyed to the separation static eliminator 14. The separation static eliminator 14 has the same configuration as a general corona charger, and has a U-shaped metal shield electrode having a width of 15 mm covered with a tungsten charging wire having a diameter of 60 μm. Power supply 141
Is connected.

The separation static eliminator 14 is disposed slightly above the separation portion of the secondary transfer belt 3. The closer to the separation point, the higher the static elimination effect of the separation static eliminator 14. However, if the distance to the transfer belt 3 is too small, the transfer property of the transfer material P is reduced. The obtained position was 15 mm.

When an AC voltage of 11 kV (peak-to-peak voltage) is applied to the separation / eliminator 14 when the leading end of the transfer material P reaches the separation point of the transfer belt 3, the transfer material P is discharged. Separate from the transfer belt. Subsequently, the transfer material P is sent to the fixing device 20, and when the transfer material P passes through the fixing device 20, the toner image is fixed on the transfer material P at the same time as the color mixture by heat and pressure.
A full-color print image is obtained.

In the secondary transfer step, the CPU shown in FIG. 2 sends a secondary transfer bias ON signal to the bias power supply 33 in synchronization with the leading edge of the transfer material P entering the secondary transfer nip. Then, the transfer material P on which the four color toner images are secondarily transferred
When the leading end of the power supply starts passing through the separation section, an ON signal of the separation / discharge high-voltage is sent from the CPU to the separation high-voltage power supply 141. According to the present embodiment, as shown in FIG.
Even after passing through the next transfer nip, the secondary transfer bias is continuously supplied to the transfer roller 31, and after the rear end of the transfer material P passes the separation point, an OFF signal of the secondary transfer bias is sent, and the secondary transfer bias is turned off. Be cut off.

For example, process speed Vp = 100 m
Considering the case where A4 paper is passed as the transfer material P at m / sec, the length G of the A4 paper is L = 210 mm, and the distance G from the secondary transfer nip to the separation point of the transfer belt is G = 10.
In the case of 0 mm, the high voltage output time = (L + G) ÷ Vp = 3.1 That is, the secondary transfer bias is set to O in synchronization with the leading edge of the transfer material.
N, and after 3.1 seconds, the secondary transfer bias is turned off.
F.

In this embodiment, at this time, the secondary transfer bias V1 applied while the transfer material P is passing through the secondary transfer nip is used.
With respect to (T2), the secondary transfer bias applied after passing the transfer material P was V2. V1 is a bias necessary for transferring the toner to the transfer material in the secondary transfer step, and V1 = +
2.0 kV (a voltage having a polarity opposite to the normal charge polarity of the toner). V2 is determined by an experiment as a voltage at which an excessive current does not flow through the intermediate transfer drum 2 when the secondary transfer nip is in a non-sheet passing state, and V2 = + 1.5 kV (a polarity opposite to the normal charging polarity of the toner) Voltage).

As described above, by making the polarity of V2 positive, separation and charge elimination can be performed satisfactorily without changing the direction of the charge elimination current by the separation charge eliminator 14.

The effect of separating and discharging the transfer material P by the separating and discharging device 14 was obtained when the discharging current was -18 μA or more. As described above, while the transfer material P is passing through the secondary transfer nip, the secondary transfer bias V1 = + 2.0 kV is output, and the current flowing to the separation neutralizer 14 at this time is −22 μm.
A. After the transfer material P passed through the secondary transfer nip, a secondary transfer bias V2 = 1.5 kV was output, and the current flowing through the separation neutralizer 14 at this time was −20 μA.

The image fixed and output by the fixing device 14 is
There were no image defects such as scattering at the rear end of the transfer material. Further, it was visually confirmed that the transfer material adhered to the transfer belt up to the rear end of the transfer material and was stably conveyed.

Embodiment 2 In this embodiment, as shown in FIG. 3, the secondary transfer belt 3 is swingable about a driving roller 32 as a rotation center.
When the transfer material P passes through the next transfer nip, the transfer belt 3 and the intermediate transfer drum 2 come into contact with each other via the transfer material P.

If the secondary transfer belt 3 and the intermediate transfer drum 2 come into contact with each other in the non-sheet passing area, the surface of the secondary transfer belt 3 may be stained if the non-sheet passing area of the intermediate transfer drum 2 is dirty. Therefore, after the transfer material P has passed, the secondary transfer belt 3 and the intermediate transfer drum 2 are separated from each other as shown in FIG.

In the present embodiment, the secondary transfer belt 3 has 10 ⁹
A low resistance rubber belt of Ω was used. The resistance value is 10
^{5 ~10 13 Ω} is preferable. The resistance measurement environment is 23 ° C,
60% RH and the applied voltage is 100V.

Since a low-resistance belt is used as the secondary transfer belt 3, the potential of the separation portion of the transfer belt 3 is a potential corresponding to the bias applied to the secondary transfer roller 31. The secondary transfer roller 31 is supplied with a secondary transfer bias from a bias power supply 33.

In the present embodiment, the secondary transfer bias V1 = + 2.0 k applied while the transfer material P passes through the secondary transfer nip
V, secondary transfer bias V2 applied after passing through transfer material P
= + 1.7 kV.

In the secondary transfer step, a secondary transfer bias ON signal is sent from the CPU in synchronization with the leading end of the transfer material P entering the secondary transfer nip, and the secondary transfer bias V1 is output. When the leading end of the transfer material starts to pass through the separation section, a separation charge eliminating high voltage ON signal is sent. At this time, the separation static elimination current is-
20 μA. When the rear end of the transfer material passes through the secondary transfer nip, the secondary transfer belt 3 is separated from the intermediate transfer drum 2, but the secondary transfer bias is continuously output at V2,
A bias of +1.7 kV is applied.

At this time, the current for separation and elimination was -18 μA. During the time when the transfer material P passes through the separation unit, a necessary neutralization current flows, so that the intermediate transfer drum 2 and the secondary transfer belt 3
, The static elimination of the transfer material in the separation section was performed normally.

The output image was free from image defects such as scattering at the rear end of the transfer material. Further, it was visually confirmed that the transfer material adhered to the transfer belt up to the rear end of the transfer material and was stably conveyed.

In this embodiment, an endless belt is used as a secondary transfer means, and a secondary transfer bias is applied to a roller at a secondary transfer position around which the belt is looped to perform secondary transfer of a toner image. However, the secondary transfer may be performed by using an endless belt, using a conductive blade or a corona charger instead of the transfer roller, and applying a secondary transfer bias. Good.

[0045]

As described above, according to the present invention,
The toner image on the intermediate transfer body of the second image carrier primarily transferred from the photosensitive drum of the first image carrier is secondary-transferred onto a transfer material by a belt-shaped secondary transfer means, and the secondary transfer is performed. When the transfer material is conveyed by the means and the transfer material is discharged by the separation / discharge means in the transfer material separating section of the secondary transfer means, and the transfer material is separated from the secondary transfer means,
The supply of the next transfer bias is performed until the rear end of the transfer material is separated from the timing at which the rear end of the transfer material is separated from the secondary transfer means. , And the separation / discharge current flows from the separation / discharge means to the transfer material without fail. As a result, image defects such as scattering due to peeling discharge at the rear end of the transfer material are prevented,
A good image can be obtained. Also belt-shaped 2
Since the adsorbing force of the transfer material to the next transfer means is also ensured, the transportability to the transfer material is also stabilized. Further, by setting the secondary transfer bias to a different value between when the transfer material passes through the secondary transfer position and after the transfer material passes, when the transfer material is in a non-sheet passing state in the secondary transfer nip portion, An excessive current does not flow through the intermediate transfer member, and the potential of the separation portion can be maintained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram illustrating a secondary transfer unit and a separation unit in the image forming apparatus of FIG. 1;

FIG. 3 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 4 is an explanatory view showing a state where a detachable secondary transfer belt installed in the image forming apparatus of FIG. 3 is separated from an intermediate transfer drum.

FIG. 5 is an explanatory diagram showing an intermediate transfer member, a secondary transfer portion, and a separation portion in a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Intermediate transfer drum 3 Secondary transfer belt 14 Separation neutralizer 31 Secondary transfer roller 32 Drive roller 33 Secondary transfer high voltage power supply 141 Separation high voltage power supply P Transfer material

Claims (6)

[Claims] A first image carrier; a second image carrier;
A primary transfer unit supplied with a primary transfer bias for primary transferring a toner image formed on the first image carrier onto the second image carrier at a first transfer position; Belt-shaped secondary transfer means to which a secondary transfer bias is supplied, which secondary-transfers the toner image on the second image carrier onto a transfer material at a second transfer position and adsorbs and transports the transfer material And a charge-eliminating means to which a charge-eliminating bias is supplied, the charge-eliminating bias being supplied to the transfer material when the transfer material is separated from the secondary transfer means after the secondary transfer of the transfer material. An image forming apparatus comprising: a belt; a first roller around which the endless belt is looped; a first roller opposed to the second transfer position; and a second roller opposed to the separation / discharge unit. The secondary transfer bias is such that the rear end of the transfer material is The transfer material is supplied until later than the timing of separation from the belt-shaped secondary transfer means, and the bias value V1 when the transfer material is passing through the second transfer position, and after the transfer material passes through the second transfer position of the transfer material. An image forming apparatus having two set values of the bias value V2. 2. The endless belt is disposed in contact with the second image carrier at the second transfer position, and is supplied to a second power supply for supplying a secondary transfer bias to the first roller. The image forming apparatus according to claim 1, wherein the rollers are connected. 3. The image forming apparatus according to claim 1, wherein the endless belt is disposed so as to be able to freely contact and separate from the second image carrier at the second transfer position.
Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the endless belt has a resistance of 10 ⁵ to 10 ¹³ Ω. 5. The image forming apparatus according to claim 4, wherein the endless belt has a resistance value of 10 ⁵ to 10 ⁹ Ω. 6. A plurality of toner images are sequentially formed on the first image carrier for a plurality of colors, and are sequentially superimposed on the second image carrier at the first transfer position and primary-transferred. The image forming apparatus according to claim 1, wherein a plurality of color toner images on a second image carrier are secondarily transferred collectively onto the transfer material at the second transfer position.