JP2006184627A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the adhesion of staining by preventing the trailing end or the edge surface of the trailing end of recording material from coming into contact with an intermediate transfer body again. <P>SOLUTION: A bias value applied when the trailing end of the recording material in a recording material moving direction passes through a transfer nip is made larger than a bias value applied when the part other than the trailing end of the recording material passes through the transfer nip. Therefore, by increasing a destaticizing bias value only when the trailing end of the recording material passes through the transfer nip, the separability of the trailing end of the recording material is improved without causing irregularities in an image, and a situation that the recording material comes into contact with the intermediate transfer body again after it goes through the transfer nip and the trailing end or the edge surface is stained is prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and in particular, a primary transfer unit that transfers a toner image formed on an image carrier to an intermediate transfer member, and the intermediate transfer member to transfer paper onto the transfer paper. The present invention relates to a technique of an image forming apparatus having a secondary transfer unit.

As a secondary transfer means for improving the margin of moisture-controlling paper transfer, a method of applying a voltage of the same polarity as the toner from the inside of the intermediate transfer member has been adopted. The trailing edge of the paper that has passed through the nip comes into contact with the intermediate transfer member again, and the trailing edge or the edge of the recording material comes into contact with the transfer residual toner on the intermediate transfer member and becomes dirty. Referring to FIG. 4, in a system in which a transfer nip is formed between an intermediate transfer member and a transfer electric field is applied from the side of a contact transfer member (secondary transfer member) that can sandwich and convey the recording material, When the electrical resistance is low, or when the moisture content of the recording material increases in a high humidity environment and the resistance decreases, the current leaks through the recording material to the member that contacts the recording material other than the intermediate transfer member, and the reactive current As a result, the current that contributes to the formation of the transfer electric field in the gap between the recording material and the toner layer is reduced, so that the transfer electric field becomes small and the transfer rate tends to be insufficient.
Further, as shown in FIG. 5, a voltage having the same polarity as the toner (in this case, the toner is -polarity, -bias) is applied from the inside of the intermediate transfer member, and the toner image on the intermediate transfer member is applied to the recording material. There is also a transfer method. This method is advantageous when the resistance of the recording paper is low because the current that contributes to the transfer electric field in the gap between the recording material and the toner layer does not change.

As a prior art related to the present invention, Patent Document 1 discloses a primary transfer unit that transfers a toner image formed on a photosensitive drum to an intermediate transfer belt, and a secondary transfer unit that transfers the image from the intermediate transfer belt to a transfer sheet. And a paper transfer bias roller and a bias power source constituting a secondary transfer electric field forming means disposed in the secondary transfer portion, and light for detecting the rear end portion of the toner image on the intermediate transfer belt A detection device and electric field control means for lowering a transfer voltage applied to the paper transfer bias roller by a bias power source based on a signal from the light detection device are configured. For this reason, the transfer voltage of the secondary transfer electric field forming means applied to the rear end portion of the transfer paper is lowered, so that the toner image transferred onto the transfer paper does not fly to the intermediate transfer member, so that there is no print image. Can be obtained.

Japanese Unexamined Patent Publication No. 07-210003

However, in the system shown in FIG. 5, as a side effect, when the recording material passes through the transfer nip and the trailing edge of the recording material is peeled off from the intermediate transfer member, the recording material has a polarity opposite to that of the intermediate transfer member. The recording material that is separated from the recording medium is attracted to the polarity of the intermediate transfer member and comes into contact again, and cannot be transferred to the recording material. The toner remaining on the intermediate transfer member (transfer residual toner) or the scumming toner on the intermediate transfer member And the trailing edge of the paper and the edge surface become dirty (see FIG. 6).

The present invention has been made in view of the above-described problem, and eliminates the fact that the rear end or rear end edge of the recording member comes into contact with the intermediate transfer member after the rear end of the recording material passes through the transfer nip. It is an object to prevent adhesion of dirt.

As means for solving the above problems, the present invention has the following features.
The image forming apparatus according to claim 1, wherein a primary transfer unit that transfers a toner image having a positive or negative polarity formed on a photosensitive member to an intermediate transfer member, and a surface having the toner image of the intermediate transfer member. And a secondary transfer member that forms a transfer nip between the intermediate transfer member and can transfer the recording material. The intermediate transfer member and the secondary transfer member are disposed inside the intermediate transfer member. A bias that can apply a voltage having the same polarity as the toner image is applied to the recording material that is nipped and conveyed between the recording medium and an inner roller that further transfers the toner image on the intermediate transfer material to the recording material, and the transfer In an image forming apparatus having a neutralizing unit for neutralizing the recording material in the vicinity of the downstream side of the unit and a neutralizing bias applying unit for applying a neutralizing bias to the neutralizing unit, the trailing end of the recording material in the recording material moving direction forms a transfer nip. Apply when passing Bias value, characterized in that the non trailing end of the recording material to a value greater than the bias value to be applied as it passes through the transfer nip.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, an AC voltage is applied as the static elimination bias.
In the image forming apparatus according to claim 3, a primary transfer unit that transfers a toner image having a positive or negative polarity formed on the photosensitive member to an intermediate transfer member;
A secondary transfer member that faces the surface of the intermediate transfer member having a toner image, forms a transfer nip with the intermediate transfer member, and can sandwich and convey the recording material;
A bias that can apply a voltage having the same polarity as the toner image is applied to the inside of the intermediate transfer member so that a voltage having the same polarity as the toner image is applied to the recording material that is nipped and conveyed between the intermediate transfer member and the secondary transfer member. In the image forming apparatus provided with an inner roller that further transfers the toner image on the recording material,
When the trailing edge of the recording material in the recording material moving direction passes through the transfer nip, the transfer bias value applied to the inner roller is made smaller than when the trailing edge of the recording material passes through the transfer nip. It is characterized by.

As described above, according to the means for solving the above problems, the image forming apparatus of the present invention has the following effects.
According to the first aspect of the present invention, only when the trailing edge of the recording material passes through the transfer nip, by increasing the static elimination bias value, the separation property of the trailing edge of the recording material is improved without disturbing the image. It is possible to prevent the recording material from coming into contact with the intermediate transfer member again after passing through the transfer nip, and the rear end or the edge surface from becoming dirty.
According to the second aspect of the present invention, in addition to the effect of the first aspect, positive and negative discharges are excited, and the rear end of the recording material can be discharged more effectively. Further, it is possible to prevent the rear end portion of the recording material from coming into contact with the intermediate transfer member again.
According to the third aspect of the invention, after the trailing edge of the recording material has passed through the transfer nip, the trailing edge or trailing edge edge surface of the recording material is prevented from recontacting with the intermediate transfer member, and dirt is attached. To prevent.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus showing an embodiment of the present invention. This embodiment shows a tandem indirect transfer type image forming apparatus having a configuration in which a plurality of image forming units 101Y to 101Bk are arranged side by side along an intermediate transfer body 201. In the center of the image forming apparatus, a transfer device including an endless belt-like intermediate transfer member (intermediate transfer belt) 201 is provided. The intermediate transfer member 201 is looped around a plurality of support rollers and can be rotated and conveyed clockwise in the figure.

In the present embodiment, an intermediate transfer body cleaning device 210 that removes residual toner remaining on the intermediate transfer body 201 after image transfer is provided on the left side of the first support roller 202 in the drawing among the plurality of support rollers. ing. Further, on the intermediate transfer member 201 stretched between the first support roller 202 and the second support roller 203, yellow (Y), magenta (M), cyan ( C) Four image forming units (image forming units) 101Y, 101M, 101C, 101Bk for each color of black (Bk) are arranged side by side, and these image forming units (image forming units) 101Y, 101M are arranged side by side. , 101C, 101Bk constitute a tandem image forming unit. The image forming units (image forming units) 101Y, 101M, 101C, and 101Bk of the tandem image forming unit have the same configuration, for example, as shown in FIG.

FIG. 2 shows an example of a black (Bk) image forming unit 101Bk. In this image forming unit 101Bk, a drum-shaped photoconductor 102Bk as an image carrier and a toner image on the photoconductor. A charging device 103Bk, an exposure device 110Bk, and a developing device 104Bk constituting an image forming unit for forming are provided.
Here, the charging device 103Bk uniformly charges the photoconductor 102Bk using, for example, a charging brush to which a DC voltage is applied. In addition to the charging brush, a charging roller, a charging charger, or the like can be used.

In the illustrated example, the exposure device 110Bk is an LED writing type exposure device comprising a light emitting diode (LED) array and a lens array arranged in the axial direction (main scanning direction) of the photoconductor 102Bk. In addition to this, an electrostatic latent image is formed on the photosensitive member. In addition, a laser scanning type exposure apparatus comprising a laser light source, an optical deflector (rotating polygon mirror, etc.) and an imaging scanning optical system is provided. Can be used.
The developing device 104Bk includes a developing roller (or developing sleeve) that carries and rotates the developer, and a stirring / conveying member that stirs and conveys the developer and supplies the developer to the developing roller (or developing sleeve). The electrostatic latent image formed on the body 102Bk is developed with a developer toner to form a visible image. As the developer, a one-component developer composed only of toner or a two-component developer composed of toner and a magnetic carrier is used. 2 is an example of the image forming unit 101Bk for black (Bk), black toner is used as the toner, but the image forming units 101Y, 101M, and 101C of other colors shown in FIG. In this case, yellow (Y), magenta (M), and cyan (C) toners are used.

The toner image formed on the photosensitive member 102Bk by the above charging, exposure, and development is transferred to the intermediate transfer member 201 at the primary transfer portion, but faces the photosensitive member 102Bk with the intermediate transfer member 201 of the primary transfer portion interposed therebetween. A transfer brush 105Bk, which is a primary transfer means, is disposed at the position where the transfer is performed, and a transfer bias is applied to the transfer brush 105Bk by a DC power source. Further, a photoreceptor cleaning device 106Bk for removing residual toner remaining on the photoreceptor 102Bk after image transfer is provided on the downstream side of the primary transfer portion in the rotation direction of the photoreceptor 102Bk.
The black (Bk) image forming unit 101Bk has been described above as an example, but the configurations of the other yellow (Y), magenta (M), and cyan (C) image forming units 101Y, 101M, and 101C. Is the same. In FIG. 1, the same number is assigned to the same component, and the symbols Y, M, C, and Bk are added after each number to distinguish the colors.

In the tandem type image forming unit described above, during color image formation, image forming units (image forming units) 101Y, 101M, and yellow (Y), magenta (M), cyan (C), and black (Bk) are provided. 101C and 101Bk respectively form yellow (Y), magenta (M), cyan (C), and black (Bk) toner images on the photoreceptors 102Y, 102M, 102C, and 102Bk, respectively, on the intermediate transfer member 201. To form a color image. Further, when forming a black and white image, the image is formed only by the black image forming unit 101Bk and transferred onto the intermediate transfer member 201.

On the other hand, a secondary transfer unit 309 is provided on the opposite side of the intermediate transfer member 201 from the tandem image forming apparatus. The secondary transfer unit 309 includes a secondary transfer roller 308 that is an external roller, a cleaning blade 305, and a static elimination needle 307. The secondary transfer roller 308, which is an external roller, is disposed so as to be pressed against the third support roller 304, which is an internal roller, via the intermediate transfer member 201, and the toner image on the intermediate transfer member 201 is transferred to a sheet or the like. Transfer to recording medium.
Further, on the upstream side of the secondary transfer unit in the recording medium conveyance direction, a sheet feeding unit including a sheet feeding cassette 151 and a sheet feeding roller 152, a sheet feeding path 155 having a sheet feeding roller 153, and a registration roller 154 are provided. Is provided. Further, on the downstream side of the secondary transfer unit, a transport unit 156 that transports the recording medium onto which the image has been transferred, a fixing device 107 that fixes the transferred image on the recording medium, and a recording medium after fixing the paper discharge unit A paper discharge roller 108 for discharging the paper is provided.

  Next, image formation by the image forming apparatus having the above configuration will be described in more detail. When a start switch of an operation unit (not shown) is pressed, one of the support rollers 202, 203, and 304 is driven to rotate by a drive motor (not shown), and the other two support rollers are driven to rotate, and an intermediate transfer member ( Intermediate transfer belt 201 is rotated and conveyed. At the same time, the image forming units (image forming units) 101Y, 101M, 101C, and 101Bk of the respective colors rotate the photoconductors 102Y, 102M, 102C, and 102Bk that are image carriers, and the photoconductors 102Y, 102M, and 102B, respectively. Monochromatic images of yellow, magenta, cyan, and black are formed on 102C and 102Bk, respectively. Then, along with the conveyance of the intermediate transfer member 201, these single color images are sequentially superimposed and transferred onto the intermediate transfer member 201 at the primary transfer unit, and a composite color image is formed on the intermediate transfer member 201.

When the start switch is pressed as described above, the sheet feeding roller 152 is rotated, and a sheet-like recording medium such as a sheet is fed out from the sheet feeding cassette 151 and guided to the sheet feeding path 155, and then the registration roller. It stops at 154.
Thereafter, the registration roller 154 is rotated in synchronization with the composite color image on the intermediate transfer member 201, and a recording medium is interposed between the intermediate transfer member 201 and the secondary transfer roller (secondary transfer member) 308 of the secondary transfer unit. Is sent. Then, the color image is transferred onto the recording medium by the transfer by the secondary transfer roller 308.

  Here, in the present embodiment, as shown in FIG. 3, a third support roller 304 which is an internal roller disposed inside the intermediate transfer member 201 so as to face the secondary transfer roller (secondary transfer member) 308. In addition, a bias having the same polarity as that of the toner is applied by a DC power source (in this embodiment, since the toner is negative (−) charged, a negative (−) bias voltage is applied), and the toner is ejected from the intermediate transfer body 201. As a result, the toner is transferred to the recording medium, and the transfer margin of the low-resistance recording medium is increased. The secondary transfer roller (secondary transfer member) 308 is grounded.

The recording medium after the image transfer is transported by the transport unit 156 and sent to the fixing device 107, and heat and pressure are applied by the fixing device 107 to fix the transferred image. Stacked on a paper tray. On the other hand, the intermediate transfer member 201 after the image transfer is subjected to removal of residual toner remaining on the intermediate transfer member 201 after the image transfer by the intermediate transfer member cleaning device 210, and the next tandem image forming units 101Y to 101Bk re-image. Prepare for formation.

  The resistance of the intermediate transfer member 201 is set to a logarithm of volume resistivity (LogR) of 10.0 or less so that there is no afterimage problem due to residual potential and a stable transfer image is obtained. In addition, since the secondary transfer roller 308 of the secondary transfer unit 309 is in contact with the intermediate transfer body 201, the background dirt toner on the intermediate transfer body or the portion between the recording medium such as transfer paper or between the sheets is not present. Since the pattern for process control is transferred and the secondary transfer roller 308 is soiled, the secondary transfer roller 308 has a two-layer structure (for example, the surface layer 308b is coated on the rubber layer 308a, and the surface layer 308b The cleaning blade 305 removes the toner and the like on the secondary transfer roller 308.

  Further, in this embodiment, a static elimination needle 307 is provided on the downstream side of the secondary transfer unit 309 so that a recording medium (transfer paper or the like) after image transfer is not wound around the intermediate transfer body 201 (secondary transfer). The subsequent recording medium is in close contact with the intermediate transfer member 201 and is difficult to peel off.) From the back surface of the recording medium, the neutralization needle 307 is supplied with a high voltage power source (not shown) to a peak-to-peak voltage of 10 kV and a 1 kHz sinusoidal AC. A voltage is applied to neutralize (eliminate) the accumulated charge on the recording paper.

Then, as shown in FIG. 7, the rear end of the recording medium passes through the transfer nip, and at the same time, a sine wave AC voltage of 1 kHz with a peak-to-peak voltage 12 kV larger than usual is applied to the neutralizing needle 307. After the toner has passed through the transfer nip, it comes into contact with the intermediate transfer member 201 again, and the trailing edge and the edge surface of the recording medium are prevented from becoming dirty due to secondary transfer residue on the intermediate transfer member 201 and the like.

Further, as shown in FIG. 8, in this embodiment, the current (secondary transfer current) applied from the third support roller 304 inside the intermediate transfer body 201 at the same time that the rear end of the recording medium passes through the transfer nip. By setting it to 0, the potential of the intermediate transfer member 201 can be brought close to 0, and the rear end of the recording medium is prevented from coming into contact with the intermediate transfer member again.

1 is a schematic configuration diagram of a color image forming apparatus according to an embodiment. FIG. 2 is a schematic configuration diagram of an image forming unit for black (Bk) in the present embodiment. FIG. 2 is a schematic diagram illustrating a relationship between an intermediate transfer member and a recording medium in the present embodiment. Schematic explaining the prior art. Schematic explaining the prior art. Schematic explaining the prior art. FIG. 3 is a schematic diagram illustrating a state when a recording medium rear end in contact with an intermediate transfer member in the present embodiment. FIG. 3 is a schematic diagram illustrating a state when a recording medium rear end in contact with an intermediate transfer member in the present embodiment.

Explanation of symbols

101Y to 101Bk Image forming unit 102Bk Photoconductor 103Bk Charging device 110Bk Exposure device 104Bk Development device 105Bk Transfer brush 106Bk Photoconductor cleaning device 107 Fixing device 108 Paper discharge roller 151 Paper feed cassette 152 Paper feed roller 153 Paper feed roller 154 Registration roller 155 Feed Paper path 156 Conveying unit 201 Intermediate transfer member 202 First support roller 203 Second support roller 210 Intermediate transfer member cleaning device 304 Third support roller 305 Cleaning blade 307 Static elimination needle 308 Secondary transfer roller 308a Rubber layer 308b Surface layer 309 Secondary transfer section

Claims (3)

A primary transfer means for transferring a toner image having a positive or negative polarity formed on a photoconductor to an intermediate transfer body;
A secondary transfer member that faces the surface of the intermediate transfer member having a toner image, forms a transfer nip with the intermediate transfer member, and can sandwich and convey the recording material;
A bias that can apply a voltage having the same polarity as the toner image is applied to the inside of the intermediate transfer member so that a voltage having the same polarity as the toner image is applied to the recording material that is nipped and conveyed between the intermediate transfer member and the secondary transfer member. An inner roller for further transferring the toner image on the recording material;
Neutralizing means for neutralizing the recording material in the vicinity of the downstream side of the transfer means;
In an image forming apparatus having a static elimination bias applying means for applying a static elimination bias to the static elimination means,
The bias value applied when the trailing edge of the recording material in the recording material moving direction passes through the transfer nip is set to a value larger than the bias value applied when the recording material other than the trailing edge of the recording material passes through the transfer nip. A featured image forming apparatus. The image forming apparatus according to claim 1, wherein an AC voltage is applied as the static elimination bias. A primary transfer means for transferring a toner image having a positive or negative polarity formed on a photoconductor to an intermediate transfer body;
A secondary transfer member that faces the surface of the intermediate transfer member having a toner image, forms a transfer nip with the intermediate transfer member, and can sandwich and convey the recording material;
A bias that can apply a voltage having the same polarity as the toner image is applied to the inside of the intermediate transfer member so that a voltage having the same polarity as the toner image is applied to the recording material that is nipped and conveyed between the intermediate transfer member and the secondary transfer member. In the image forming apparatus provided with an inner roller that further transfers the toner image on the recording material,
When the trailing edge of the recording material in the recording material moving direction passes through the transfer nip, the transfer bias value applied to the inner roller is made smaller than when the trailing edge of the recording material passes through the transfer nip. An image forming apparatus.

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