JP2010134019A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a cleaning bias for cleaning the transfer roller deviates from a predetermined value due to discharging, to stain the rear surface, in an image forming apparatus that uses a transfer roller and a separating means for separating a recording material by use of the transfer roller and discharging. <P>SOLUTION: The separating means for separating a recording material from an intermediate transfer body is supplied with a current required for separation only during the passage of the leading end of the recording material. The DC component of a discharging current is set to 0 or below between images. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image by electrophotography.

  An electrophotographic image in which an intermediate transfer member is used to form a toner image on a photosensitive member and then transferred to the intermediate transfer member, and the toner image is transferred from the intermediate transfer member to a recording material such as paper to form an image on the recording material. The process is widely used.

  Corona charging devices and transfer rollers are widely used for transferring toner images. In transfer using a transfer roller, a transfer bias is applied between the intermediate transfer member and the transfer roller in the process of nipping and conveying the recording material between the image carrier such as an intermediate transfer member and the transfer roller, and the toner is electrostatically transferred. By moving from the intermediate transfer member to the recording material, the toner image is transferred from the intermediate transfer member to the recording material.

  In the transfer by the transfer roller, since the transfer is performed in a state where the intermediate transfer member and the recording material are in close contact with each other, there is an advantage that there is no deviation of the toner image at the time of transfer, and image quality deterioration due to the transfer is small. However, there is a problem that toner adheres to the transfer roller, and the adhered toner adheres to the back surface of the recording material in subsequent image formation, causing back surface contamination.

  When a patch for controlling image quality is formed between images, that is, between images, when a toner band for toner consumption is formed between images, a large amount of toner is transferred from the intermediate transfer member during jamming. Since it moves to and adheres to the transfer roller, significant backside contamination occurs. Therefore, a technique for removing toner from the transfer roller or preventing the toner from adhering to the transfer roller has been developed.

  As disclosed in Patent Document 1, the method of applying a cleaning bias to the transfer roller is excellent in terms of cost and the point of not reducing the productivity of image formation.

On the other hand, in order to separate the recording material that is electrostatically attracted to the intermediate transfer member, it has been proposed to provide a static eliminating device downstream of the transfer roller (Patent Document 2).
JP-A-8-328401 JP 2008-145827 A

  In order to ensure the separation of the recording material as in Patent Document 2, the recording material is discharged by supplying a static elimination current in which an alternating current (AC) is superimposed on a direct current (DC) to the static eliminator. .

  When such a static eliminator is used, there is a problem that a cleaning bias may not be properly applied when performing bias cleaning as in Patent Document 1.

That is, a. Charged toner (toner charged with polarity during development) adheres to the transfer roller due to insufficient current.
b. Due to excess current, reversely charged toner (toner charged opposite to the polarity during development) adheres to the transfer roller.
It has been found that the toner adheres to the surface and causes backside contamination.

  The present invention solves the above-described problems in an image forming apparatus that performs transfer by roller transfer, and discharges and separates a recording material by a charge removal current in which alternating current (AC) is superimposed on direct current (DC). It is an object of the present invention to provide an image forming apparatus in which the backside contamination is prevented and the recording material is easily separated.

  The object is achieved by the following invention.

1. An intermediate transfer member carrying a toner image;
A transfer roller for transferring a toner image on the intermediate transfer member to a recording material; and
A first power source for applying a transfer bias or a cleaning bias between the intermediate transfer member and the transfer roller;
The transfer bias for moving the toner image from the intermediate transfer member to the recording material during a period in which the recording material passes through the nip between the intermediate transfer member and the transfer roller;
In the image forming apparatus in which the first power supply applies the cleaning bias for attracting toner to the intermediate transfer member during a period in which the recording material does not pass through the nip between the intermediate transfer member and the transfer roller.
Separating means for neutralizing the recording material and separating it from the intermediate transfer member,
A second power source for supplying current to the separating means;
Having control means,
In the control means, at least in a period during which the leading edge of the recording material passes through the nip, the second power source supplies a static elimination current in which an alternating current is superimposed on the first direct current to the separation means,
Between the images, the second power source is controlled so that a current obtained by superimposing an alternating current on a second direct current smaller than the first direct current or an alternating current that does not include a direct current is supplied to the separation means. An image forming apparatus.

  2. The control means controls the second power supply such that the second power supply outputs the second DC current after the second power supply outputs a third DC current larger than the first DC current. The image forming apparatus according to 1.

  3. The first transfer device includes a backup roller that presses the intermediate transfer member against the transfer roller and to which a current from the first power source is applied, and the first power source is connected to the backup roller. Alternatively, the image forming apparatus described in 2 above.

  4). 4. The image forming apparatus according to any one of items 1 to 3, wherein the separating unit includes a corona charging device.

  In the present invention, when the recording material passes through the leading end, a neutralizing current having a first DC current that constitutes a direct current component sufficient to neutralize the recording material is supplied to the separating means. A current in which an alternating current is superimposed on a second direct current component smaller than the first direct current component of the current or an alternating current component that does not include a direct current component is supplied to the static elimination means.

  Therefore, the separation of the recording material is good and the toner adhesion to the transfer roller is sufficiently prevented.

  Even when a patch image for image quality control, a toner band for toner consumption, or the like is formed, or when a jam occurs, toner adhesion to the transfer roller is sufficiently prevented.

  Therefore, an image forming apparatus in which the back surface contamination is prevented and the recording material is well separated is realized.

Hereinafter, the present invention will be described based on an image forming apparatus according to an embodiment of the present invention, but the present invention is not limited to the embodiment.
[Color image forming apparatus]
FIG. 1 is a diagram showing an overall configuration of a color image forming apparatus according to an embodiment of the present invention.

  The illustrated color image forming apparatus is called a tandem type color image forming apparatus, and transports a plurality of image forming units 10Y, 10M, 10C, and 10K, an intermediate transfer body unit 7 as a transfer unit, and a recording material P. An endless belt-shaped paper feeding / conveying means 21 and a fixing device 24. A document image reading device SC is disposed on the upper part of the main body A of the color image forming apparatus.

  The image forming unit 10Y that forms a yellow image includes a drum-shaped photoreceptor 1Y, a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer roller 5Y as a primary transfer unit, and a cleaning unit 6Y. As shown in the figure, a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer roller 5Y as a primary transfer unit, and a cleaning unit 6Y are arranged around the photoreceptor 1Y.

  The image forming unit 10M that forms a magenta image includes a drum-shaped photoreceptor 1M, a charging unit 2M, an exposure unit 3M, a developing unit 4M, a primary transfer roller 5M as a primary transfer unit, and a cleaning unit 6M. As shown in the figure, a charging unit 2M, an exposure unit 3M, a developing unit 4M, a primary transfer roller 5M as a primary transfer unit, and a cleaning unit 6M are arranged around the photoreceptor 1M.

  The image forming unit 10C for forming a cyan image includes a drum-shaped photoreceptor 1C, a charging unit 2C, an exposure unit 3C, a developing unit 4C, a primary transfer roller 5C as a primary transfer unit, and a cleaning unit 6C. As shown in the figure, a charging unit 2C, an exposure unit 3C, a developing unit 4C, a primary transfer roller 5C as a primary transfer unit, and a cleaning unit 6C are arranged around the photoreceptor 1C.

  The image forming unit 10K that forms a black image includes a drum-shaped photoreceptor 1K, a charging unit 2K, an exposure unit 3K, a developing unit 4K, a primary transfer roller 5K as a primary transfer unit, and a cleaning unit 6K. As shown in the figure, a charging unit 2K, an exposure unit 3K, a developing unit 4K, a primary transfer roller 5K as a primary transfer unit, and a cleaning unit 6K are disposed around the photoreceptor 1K.

  The intermediate transfer body unit 7 includes a semiconductive endless belt-like intermediate transfer body 70 that is wound around a plurality of rollers and is rotatably supported.

  The color toner images formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred onto the rotating intermediate transfer body 70 by the primary transfer rollers 5Y, 5M, 5C, and 5K, and are combined. A toner image is formed. The recording material P such as paper stored in the paper cassette 20 is fed by the paper feeding / conveying means 21 and passes through a plurality of intermediate rollers 22A, 22B, 22C, 22D and a registration roller 23 as a secondary transfer means. Are transferred to the transfer roller 30 and the color toner images are collectively transferred onto the recording material P. The recording material P to which the color toner image has been transferred is fixed by the fixing device 24, is sandwiched between the paper discharge rollers 25, and is placed on a paper discharge tray 26 outside the apparatus.

  On the other hand, the intermediate transfer body 70 after the color toner image is transferred to the recording material P by the transfer roller 30 is cleaned by the cleaning means 6A.

  During the image forming process, the primary transfer roller 5K is always in pressure contact with the photoreceptor 1K. The other primary transfer rollers 5Y, 5M, and 5C are in pressure contact with the corresponding photoreceptors 1Y, 1M, and 1C, respectively, only during color image formation.

  Further, the housing 8 can be pulled out from the apparatus main body A through the support rails 82L and 82R.

  The housing 8 includes image forming units 10Y, 10M, 10C, and 10K, and an intermediate transfer body unit 7.

  The image forming units 10Y, 10M, 10C, and 10K are arranged in tandem in the vertical direction. An intermediate transfer body unit 7 is arranged on the left side of the photoreceptors 1Y, 1M, 1C, and 1K in the figure. The intermediate transfer body unit 7 includes an endless belt-like intermediate transfer body 70 that can be rotated by winding rollers 71, 72, 73, 74, and 76, primary transfer rollers 5Y, 5M, 5C, and 5K, and a cleaning unit 6A. Composed.

  The image forming units 10Y, 10M, 10C, and 10K and the intermediate transfer body unit 7 are integrally pulled out from the main body A by the drawer operation of the housing 8.

  A toner image is formed on the photoreceptors 1Y, 1M, 1C, and 1K by charging, exposure, and development, and a toner image of each color is superimposed on the intermediate transfer member 70 to form a color toner image. The color toner image is collectively transferred to the recording material P by the transfer roller 30, and the color toner image on the recording material P is pressed and heated by the fixing device 24 and fixed.

In the color image forming apparatus, an elastic blade is used as a cleaning member of the cleaning unit 6A for cleaning the intermediate transfer member 07.
(Transfer separation part)
FIG. 2 is a schematic diagram of a transfer separation unit that transfers a color toner image from the intermediate transfer body 70 to the recording material P and separates the transferred recording material P from the intermediate transfer body 70.

  A transfer roller 30 is a roller in which a semiconductive rubber layer is formed on a metal shaft.

  The intermediate transfer body 70 is made of a resin such as PI (polyimide) imparted with semiconductivity by a conductive treatment.

  A backup roller 74 supports the intermediate transfer body 70, and is a roller having a semiconductive rubber layer formed on a metal shaft.

  By pressing the backup roller 74 from the back side of the intermediate transfer member 70, a nip N is formed between the transfer roller 30 and the intermediate transfer member 70, and the nip N transfers the toner image from the intermediate transfer member 70 to the recording material P. A transfer region is formed.

  A power source 31 as a first power source is connected to the shaft of the backup roller 74, and a bias is applied to the backup roller 74 and the intermediate transfer member 70 by the power source 41. In the present embodiment in which negatively charged toner is used, the power supply 31 applies a negative transfer bias to the intermediate transfer member 70 to transfer the color toner image from the intermediate transfer member 70 to the recording material P.

  The power source 31 also supplies toner to the intermediate portion during continuous image formation, that is, between the images, that is, between the images and in a period in which the recording material P is not interposed between the intermediate transfer member 70 and the transfer roller 30. A cleaning bias attracting the transfer body 70 is applied to the intermediate transfer body 70. In an embodiment using negatively charged toner, the cleaning bias is positive.

  Reference numeral 32 denotes a corona charging device as a separating means for separating the recording material P from the intermediate transfer member 70, and discharges from the tip of the discharge needle 31 </ b> A to neutralize the recording material P.

  As the corona charging device 32, a corona charging device having a discharge wire or a corona charging device having a sawtooth discharge electrode can be used.

  Reference numeral 33 denotes a power source as a second power source that supplies current to the corona charging device 32, and supplies to the corona charging device 32 a static elimination current in which alternating current (AC) is superimposed on direct current (DC).

  The corona charging device 32 neutralizes the recording material P, whereby the recording material P that is electrostatically attracted is separated from the intermediate transfer body 70.

  In the continuous image formation, the color toner image transfer step and the separation step of separating the transferred recording material P from the intermediate transfer body 70 are repeatedly performed every time the recording material P passes through the nip N.

  In this step, cleaning of the transfer roller 30 is repeatedly performed between the preceding recording material P and the subsequent recording material P, that is, between images.

  However, it has been found that there is a problem that a desired cleaning bias may not be applied in the cleaning of the transfer roller 30 performed between images.

  FIG. 3 is a diagram showing the relationship between the discharging current for discharging the recording material P and the cleaning bias.

  In FIG. 3, the horizontal axis indicates the DC component of the static elimination current, and the vertical axis indicates the output voltage of the power supply 31.

  The power source 31 is a constant current power source.

  When the output voltage of the power supply 31 is plus (+), a cleaning bias that attracts negatively charged toner to the intermediate transfer member 70 is applied between the intermediate transfer member 70 and the transfer roller 30, and the toner on the transfer roller 30 is transferred to the intermediate transfer member. The toner on the intermediate transfer body 70 is held as it is.

  When the output of the power supply 31 is negative (−), a transfer bias for moving the negatively charged toner to the transfer roller 30 is applied, and the toner moves from the intermediate transfer body 70 to the transfer roller 30 side.

  When the recording material P is present in the nip N between the intermediate transfer body 70 and the transfer roller 30, the toner image is transferred from the intermediate transfer body 70 to the recording material P by the transfer bias.

  As shown in the straight line SL in the figure, when the static elimination direct current that is the direct current component of the static elimination current increases, the output of the power supply 31 increases to the negative side, and a strong transfer bias is applied to the intermediate transfer member 70.

  Therefore, when the static elimination current is large, a predetermined cleaning bias is not applied between images.

  As a result, the transfer roller 30 is not sufficiently cleaned, and the back surface is stained.

  In the present invention, in order to solve such a problem of back surface contamination, the static elimination direct current, which is the direct current component of the static elimination current, is kept low between images.

  As shown in FIG. 3, the output voltage of the power supply 31 changes from the negative side to the positive side by lowering the current value of the static elimination direct current. In the illustrated example, the output of the power supply 31 is positive when the static elimination direct current is 20 μA or less.

  That is, when the static elimination direct current is 20 μA or less, a cleaning voltage is applied between the intermediate transfer body 70 and the transfer roller 30.

  As a result, the toner on the transfer roller 30 moves onto the intermediate transfer member 70 and the toner on the intermediate transfer member is held as it is.

  During the period when the recording material P passes through the nip N and the recording material P needs to be separated, the static elimination direct current necessary for the separation is supplied to the corona discharge device 32, and the static elimination direct current is kept low between the images. The separation of the recording material P and the cleaning of the transfer roller 30 are compatible, and each is sufficiently performed.

  The neutralizing DC current J2 during the cleaning bias between images is preferably 15% or less of J1 with respect to the neutralizing DC current J1 required for separation.

  Note that the neutralizing DC current J2 between images may be zero.

  The transfer separation process will be described with reference to FIG. The control of the transfer bias, the cleaning bias, and the charge removal current shown in FIG. 4 is performed by the control of the control unit 35 in FIG.

  The recording material P passes through the transfer region, that is, the nip N in FIG. 2 during the period from t1 to t3.

  t1 is the time when the leading edge of the recording material P reaches the nip, and t2 is the time when the leading edge of the recording material P reaches a straight line connecting the tip of the discharge needle 32A of the corona charging device 32 and the center of the backup roller 74. t2 is the time when the recording material P reaches a position where it is charged by the corona charging device 32.

  t3 is the time when the trailing edge of the recording material P passes through the nip N, and t5 is the time when the leading edge of the next recording material P reaches the nip N. A period from t3 to t5 is an interval between the images in which the recording material P is not interposed between the transfer rollers 30 of the intermediate transfer member 70.

  Between the images, a patch image for image quality control and a toner band for toner consumption pass through the nip N. These patch images and toner bands pass through the nip N while being transferred onto the intermediate transfer body 70 without being transferred.

  When the front end of the recording material P passes through the nip N and reaches the charging position by the corona charging device 32, that is, from t1 to t2 and from t5 to t6, the DC component of the discharging current (hereinafter referred to as discharging DC current) is The high value L1a is maintained.

  The AC component takes a constant value as shown.

  The value L1a of the static elimination direct current in the periods t1 to t2 and the periods t5 to t6 is set as an optimum condition for eliminating and separating the recording material P that is electrostatically adsorbed to the intermediate transfer member 70. .

  When the leading edge of the recording material P passes through the nip N, it is neutralized by the neutralizing current including the neutralizing DC current of the value L1a and reliably separated from the intermediate transfer member.

  At the time t2 when the leading edge of the recording material P passes through the charging position by the corona charging device 32, the static elimination direct current is switched to a low value L1b close to zero.

  The value L1b of the static elimination direct current is maintained until a time point t5a immediately before the front end of the next recording material P reaches the nip N.

  The time point t5a is a time point immediately before the leading edge of the succeeding recording material P reaches the nip N.

  At time t5a, the static elimination direct current rises to the maximum value L1c.

  The static elimination direct current increases to the maximum value L1c and then decreases to L1a at time t5b.

  The static elimination direct current decreases from L1a to L1b at time t6.

  By forming the pulse having the maximum value L1c at the head of the pulse having the value L1a, the static elimination direct current can reach L1a within a short time.

  In the periods t1 to t3 and t5 to t7 in which the recording material P passes through the nip N, a transfer current L2 for moving the toner image from the intermediate transfer body 70 to the recording material P is set.

  Further, a patch image for image quality control and a toner band for toner consumption are formed in the image interval t3 to t5. In the image interval t3 to t5, the toner is held by the intermediate transfer member 70, and the transfer roller. An inter-image current L3 is set so as not to move to 30.

  A cleaning bias is applied between the intermediate transfer member 70 and the transfer roller 30 by the inter-image current L3, the toner is attracted to the intermediate transfer member 70, and the transfer roller 30 is cleaned. As shown in the figure, during the period in which the inter-image current L3 is supplied, the static elimination direct current is set to a value L1b that is close to 0. Therefore, a predetermined cleaning bias is applied to perform good cleaning of the transfer roller 30. Is called.

  As shown in the figure, the neutralizing direct current is set to a low value L1b in the interval between images t3 to t5. Therefore, the cleaning bias between the intermediate transfer member 70 and the transfer roller 30 between the images is set to an optimum value without being affected by the charge removal current.

  As a result, the toner on the transfer roller 30 is prevented from adhering between the images, and the back surface contamination is sufficiently prevented.

(1) Configuration of image forming apparatus Linear velocity of intermediate transfer member: 320 / s
Development: Two-component reversal developing photoconductor using negatively charged toner: Drum-like OPC photoconductor of φ 60 mm (photosensitive layer having a film pressure of 25 μm in which a phthalocyanine pigment is dispersed in polygarbonate)
Primary transfer roller: φ22mm, resistance 10 ⁶ Ω
Material: Foaming roller As the primary transfer current, a transfer current according to a matrix created using temperature and the number of images formed as variables was used.
Intermediate transfer member: surface resistance 19 ¹¹ Ω / □, volume resistance 10 ⁸ Ω · cm
Seam Resin Belt
Tension 6kgf
Secondary transfer roller: φ24mm, resistance 10 ⁷ Ω
Backup roller: φ24mm, resistance 10 ⁷ Ω
As the secondary transfer current, the transfer current was set from a table in which a matrix created by using the temperature and the number of formed images as variables was assembled.
Separation means: Corona charging device provided with discharge needles arranged at a pitch of 4 mm (2) Example Neutralization current: Neutralization DC current La1: 40 μA during separation
Maximum value of static elimination direct current Lc1: 60 μA
Neutralizing direct current between images Lb1: 5 μA
Cleaning bias (voltage): As a result of setting the static elimination current as described above, the cleaning bias was 0.8 kV (see the straight line SL in FIG. 3).
In image formation, patch images were formed between images and image quality control was performed, but there was no backside contamination.
Comparative example 1
Through the image area and between the images, a discharging current including a discharging current of 40 μA was supplied to the corona charging device to form an image.

  As a result, the cleaning bias became −0.7 kV, a large amount of negatively charged toner adhered to the transfer roller during patch image formation, and backside contamination occurred.

1 is a diagram illustrating an overall configuration of a color image forming apparatus according to an embodiment of the present invention. It is a schematic diagram of a transfer separation unit. It is a graph which shows the relationship between a static elimination current and a cleaning bias. It is a timing chart of a transfer separation process.

Explanation of symbols

Reference Signs List 30 Transfer roller 31, 33 Power supply 32 Corona charging device 35 Control means 70 Intermediate transfer member 74 Backup roller

Claims (4)

An intermediate transfer member carrying a toner image;
A transfer roller for transferring a toner image on the intermediate transfer member to a recording material; and
A first power source for applying a transfer bias or a cleaning bias between the intermediate transfer member and the transfer roller;
The transfer bias for moving the toner image from the intermediate transfer member to the recording material during a period in which the recording material passes through the nip between the intermediate transfer member and the transfer roller;
In the image forming apparatus in which the first power supply applies the cleaning bias for attracting toner to the intermediate transfer member during a period in which the recording material does not pass through the nip between the intermediate transfer member and the transfer roller.
Separating means for neutralizing the recording material and separating it from the intermediate transfer member,
A second power source for supplying current to the separating means;
Having control means,
In the control means, at least in a period during which the leading edge of the recording material passes through the nip, the second power source supplies a static elimination current in which an alternating current is superimposed on the first direct current to the separation means,
Between the images, the second power source is controlled so that a current obtained by superimposing an alternating current on a second direct current smaller than the first direct current or an alternating current that does not include a direct current is supplied to the separation means. An image forming apparatus. The control means controls the second power supply such that the second power supply outputs the second DC current after the second power supply outputs a third DC current larger than the first DC current. Item 2. The image forming apparatus according to Item 1. 2. The apparatus according to claim 1, further comprising a backup roller that presses the intermediate transfer member against the transfer roller and to which a current from the first power source is applied, and the first power source is connected to the backup roller. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the separating unit includes a corona charging device.

Images