JP2022159873A - image forming device - Google Patents

Abstract

To provide an image forming device capable of reducing permanent deformation (curling) appearing on an intermediate transfer belt.SOLUTION: A part of an intermediate transfer body located at a start position of contact with a secondary transfer inner roller is moved to an end position of contact with any one of inner support rollers or with a range of ±2 mm of a start position of contact with any one of outer support rollers before stopping.SELECTED DRAWING: Figure 5

Description

The present invention relates to an apparatus for transferring a toner image formed on an image carrier to an intermediate transfer member and then transferring the toner image to a recording material in an image forming apparatus such as a copier or printer using an electrophotographic method. It is a thing.

An electrostatic latent image is formed on a photoreceptor, and the latent image is sequentially developed with yellow, magenta, cyan, and black toners to form toner images of the respective colors. These toner images are temporarily transferred onto an intermediate transfer member. 2. Description of the Related Art There is known a full-color image forming apparatus of an intermediate transfer system that obtains a recorded image by carrying out superimposed transfer (primary transfer) and then collectively transferring (secondary transfer) onto a recording material.

In such an apparatus, an endless belt-like intermediate transfer member is frequently used, in which the arrangement of the image forming unit, the recording material conveying section, and the like can be relatively freely set.

A conductive transfer roller or the like is used as the transfer means. In the primary transfer section, the primary transfer roller is brought into pressure contact with the photosensitive member with the intermediate transfer member interposed therebetween, and a primary transfer bias having a polarity opposite to that of the toner is applied to the primary transfer roller, thereby transferring the toner image onto the intermediate transfer member. transcribe. Similarly, in the secondary transfer portion, the secondary transfer roller is brought into pressure contact with a conductive opposing roller arranged inside the intermediate transfer member with the intermediate transfer member therebetween, and the recording material is conveyed to the pressure contact portion. By applying a secondary transfer bias having a polarity opposite to that of the toner, the toner image is transferred to the recording material.

An endless belt-like intermediate transfer member is wound and supported by a plurality of rollers and rotated to form an image. The intermediate transfer member is tensioned by a pressurizing means and is wound and supported in a tensioned state between rollers. However, the intermediate transfer member wound around the roller in this way is deformed so as to follow the shape of the roller at the part where it is in contact with the roller so as to wrap around the roller, so bending distortion occurs in the intermediate transfer member. do.

If the rotation of the intermediate transfer member that is supported by the winding is stopped for a long period of time, the bending strain at the winding portion with the roller will continue to occur for a long period of time. Therefore, the viscoelasticity of the intermediate transfer member causes permanent deformation (curling), which may lead to poor image quality such as poor transfer at the primary transfer portion and the secondary transfer portion.

The image forming apparatus proposed in Japanese Patent Application Laid-Open No. 2002-200003 has an intermediate transfer belt as a solution to the problem of poor transfer due to curling of the belt that occurs in the winding roller portion when the apparatus is left unused for a long time. has a reverse bending roller that bends the intermediate transfer belt in a direction opposite to the bending direction of the belt wound around the winding roller, and is for reducing curling when the intermediate transfer belt is idly rotated at a predetermined speed prior to image formation. As a sequence, drive control is performed so that the speed of the belt wound around the winding roller during non-operation is lower than the predetermined speed when passing the reverse bending roller.

JP 2007-155755 A

However, in the apparatus using the belt intermediate transfer member, a reverse bending roller that bends the belt wound around the winding roller in the opposite direction to the bending direction is required, so the apparatus becomes complicated and large. A problem arises.

The present invention has been made in view of the above points, and an object of the present invention is to prevent permanent deformation (winding) that occurs in the belt intermediate transfer member when the apparatus is left in a non-operating state for a long period of time without increasing the size of the apparatus. An object of the present invention is to provide an image forming apparatus capable of preventing image quality defects such as poor transfer by efficiently reducing peculiarities.

In order to solve the above-mentioned problems, the first aspect of the invention provides a toner image forming means for forming a toner image on an image carrier, a belt-shaped intermediate transfer member suspended by a plurality of support rollers, and an image carrier. Intermediate transfer is performed by a primary transfer means for transferring the toner image on the body onto the intermediate transfer body, a secondary transfer inner roller provided inside the intermediate transfer body, and a secondary transfer outer roller provided outside the intermediate transfer body. In an image forming apparatus equipped with secondary transfer means for transferring the toner image on the intermediate transfer body onto the recording material by pressing the intermediate transfer body and the recording material, the intermediate transfer body is rotated by a predetermined amount when the apparatus is started. The part of the intermediate transfer body that was placed at the contact start position with the roller is within ±2 mm of the contact end position with any inner support roller or the contact start position with any outer support roller. It is characterized by moving to and stopping.

According to the present invention, when the apparatus is started, the intermediate transfer member is rotated by a predetermined amount, and the portion of the intermediate transfer member arranged at the contact start position with the secondary transfer inner roller is moved to one of the inner support rollers. By moving the intermediary transfer member to within ±2 mm of the contact end position or the contact start position with one of the external supporting rollers and stopping, the state in which the rotation of the intermediate transfer member is stopped can be continued for a long period of time. As a result, permanent deformation (curling) occurring in the intermediate transfer body in excess of the permissible value can be efficiently reduced.

More specifically, it is possible to shorten the time required to reduce the curl to an allowable value. Therefore, it is possible to provide an image forming apparatus that prevents image quality defects such as transfer defects.

1 is an overall explanatory diagram of an image forming apparatus; FIG. FIG. 4 is an explanatory diagram of a stretched construction of an intermediate transfer belt; FIG. 4 is an explanatory diagram of deformation that occurs in an intermediate transfer belt; 4 is a flowchart of a curl reduction sequence; FIG. 10 is an operation explanatory diagram of a curl reduction sequence; It is an effect explanatory drawing of a curl reduction sequence.

An embodiment of an image forming apparatus according to the present invention will be described below.

<Image forming apparatus>
As shown in FIG. 1, the image forming apparatus 100 includes a tandem type intermediate transfer belt 100a in which image forming units 1Y, 1M, 1C, and 1Bk are arranged along a straight section below the intermediate transfer belt 8. It is a transfer type full color printer.

In the image forming section 1Y on the most upstream side in the image forming process, a yellow toner image is formed on the photosensitive drum 2a and is primarily transferred onto the intermediate transfer belt 8 at the primary transfer section Ta. In the image forming section 1M, a magenta toner image is formed on the photosensitive drum 2b, and is primarily transferred on the yellow toner image on the intermediate transfer belt 8 in the primary transfer section Tb. Similarly, in the image forming sections 1C and 1Bk, a cyan toner image and a black toner image are formed on the photosensitive drums 2c and 2d, respectively, and similarly primary transferred onto the intermediate transfer belt 8 in the primary transfer sections Tc and Td. .

The four-color toner images sequentially primarily transferred to the intermediate transfer belt 8 are conveyed to a secondary transfer section 30 as a transfer section, and are secondary transferred onto a sheet of paper (hereinafter referred to as a sheet) P collectively. Transfer residual toner remaining on the intermediate transfer belt 8 after passing through the secondary transfer portion 30 is removed by the belt cleaning device 9 .

The belt cleaning device 9 causes a cleaning blade (not shown) to rub against the intermediate transfer belt 8 to remove transfer residual toner adhering to the surface of the intermediate transfer belt 8 that has passed through the secondary transfer portion 30 . The residual toner removed by the cleaning blade is conveyed by the toner conveying screw 9a of the belt cleaning device 9 through the toner conveying section on the inner side of the main body to the collected toner container.

The sheet P onto which the four-color toner images have been transferred is heated and pressed by the fixing device 16 to fix the toner images on the surface, and then discharged from the discharge roller pair 15 to the discharge tray 17 . The fixing device 16 forms a fixing nip by pressing a pressure roller 16b against a fixing roller 16a provided with a heater. The sheet P is heated and pressurized in the process of being nipped and conveyed by the heating nip, and the toner image is melted and fixed on the surface as a full-color image.

A paper feed cassette 18 is accommodated and arranged in the lower portion of the apparatus main body 100a. The separation roller 19 separates the sheets P pulled out from the paper feed cassette 18 one by one and sends them out to the registration roller pair 14 . The registration roller pair 14 receives and waits the sheet P in a stopped state, and feeds the sheet P to the secondary transfer portion 30 in timing with the toner image on the intermediate transfer belt (image carrier belt) 8 .

The image forming units 1Y, 1M, 1C, and 1Bk have the same configuration except that the toner colors used in the attached developing devices 4a, 4b, 4c, and 4d are different from yellow, magenta, cyan, and black. there is In the following description, the image forming section 1Y, which is the most upstream in the image forming process, will be mainly described, and the other image forming sections 1M, 1C, and 1Bk will be described by replacing the a at the end of the reference numeral with b, c, and d. shall be

The image forming section 1Y includes a charging device 3a, a developing device 4a, a primary transfer roller 5a, and a cleaning device 6a provided around the photosensitive drum 2a. The image forming section 1Y having the photosensitive drum 2a, the developing device 4a, and the like is made into a process cartridge for maintenance purposes.

The photosensitive drum 2a is composed of a metal cylinder on which a photosensitive layer having a negative charging polarity is formed on the surface thereof. Driving force is transmitted from a driving motor (not shown), and the photosensitive drum 2a rotates clockwise in FIG. 1 at a predetermined process speed. do. In the charging device 3a, a charging roller is rotated while being pressed against the photosensitive drum 2a, and a voltage obtained by superimposing a DC voltage and an AC voltage is applied to the charging roller to uniformly charge the surface of the photosensitive drum.

The photosensitive drum 2a is irradiated with a laser 7a from an exposure device 7. As shown in FIG. The exposure device 7 scans a laser beam obtained by ON-OFF-modulating scanning line image data, which is a yellow separation color image, with a polygonal mirror, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 2a. The exposure device 7 has laser emitting means for emitting light corresponding to time-series electrical digital pixel signals of supplied image information, a polygon lens, a reflecting mirror, and the like.

The developing device 4a reversely develops the electrostatic image by depositing negatively charged toner on the exposed portion of the electrostatic image on the photosensitive drum 2a. The developing device 4a is rotated in the counter direction with respect to the photosensitive drum 2a around the fixed magnetic pole of the developing sleeve 21a carrying toner, and a negative DC voltage and an AC voltage are superimposed on the developing sleeve 21a from a power source (not shown). Apply the development voltage.

The primary transfer roller 5a is pressed against the photosensitive drum 2a via the intermediate transfer belt 8 to form a primary transfer portion Ta between the photosensitive drum 2a and the intermediate transfer belt 8. As shown in FIG. While the intermediate transfer belt 8 passes through the primary transfer portion Ta while being superimposed on the negatively charged toner image, a positive DC voltage is applied to the primary transfer roller 5a from a power source (not shown) to transfer the toner. The image is primarily transferred.

Toner bottles 70 a , 70 b , 70 c and 70 d are arranged above the exposure device 7 . The toners consumed by the developing devices 4a, 4b, 4c, and 4d by forming images on the sheet P are replenished from toner bottles 70a, 70b, 70c, and 70d, respectively.

The cleaning device 6a rubs a cleaning blade against the photosensitive drum 2a to remove transfer residual toner remaining on the surface of the photosensitive drum 2a after passing through the primary transfer portion Ta. The removed toner is transported by the toner transport screw 60a to a toner discharge port (not shown).

<Intermediate transfer belt>
The intermediate transfer belt 8 is stretched over a tension roller 11, a secondary transfer inner roller (driving roller) 10, and a tension roller 13, and is driven by the secondary transfer inner roller 10 in the direction of arrow R2. Rotate.

The secondary transfer portion 30 that transfers the toner image onto the sheet P is formed by the secondary transfer outer roller 12 coming into contact with the intermediate transfer belt 8 whose inner surface is stretched by the secondary transfer inner roller 10 .

The secondary transfer portion 30 includes an intermediate transfer belt 8 that carries a toner image, and a secondary transfer outer roller 12 that forms a transfer nip T2 that sandwiches the sheet P between the intermediate transfer belt 8 and the intermediate transfer belt 8 and to which a transfer bias is applied. and have That is, the secondary transfer outer roller 12 contacts the intermediate transfer belt 8 wound around the drive roller 10 to form a transfer nip T2 and applies a transfer bias to the drive roller 10 through the intermediate transfer belt 8 .

Further, the secondary transfer outer roller 12 has an elastic layer made of rubber, sponge or the like to form a transfer nip T2. A positive DC voltage is applied to the secondary transfer outer roller 12 from a power source (not shown), so that the secondary transfer portion 30 and the driving roller 10 connected to the ground potential generate a transfer electric field of the toner image. is formed.

The material of the intermediate transfer belt 8 is a sheet obtained by adjusting the resistance by dispersing a conductive material such as carbon black in a dielectric resin such as polyethylene terephthalate, polyvinylidene fluoride, polyurethane, or polyimide. A belt that is joined into an endless shape or a seamless belt that has no joints is used. In this embodiment, a seamless belt made of polyimide resin having a thickness of 100 μm is used.

As shown in FIG. 2, the intermediate transfer belt 8 is wound around three tension rollers, ie, a drive roller 10, a tension roller 11, and a support roller 13, which support the inside of the belt.

The tension roller 11 is pressurized from the inside to the outside of the belt by a pressurizing means (spring) (not shown) to apply tension to the intermediate transfer belt 8 between the tension rollers.

The tension applied to the intermediate transfer belt 8 depends on the material of the intermediate transfer belt 8, but is set so that the elongation rate is within 1% so that the intermediate transfer belt 8 does not break or become permanently deformed. It is desirable to In this embodiment, a load of 15 kgf is applied to the intermediate transfer belt 8 made of polyimide resin.

The secondary transfer outer roller 12 is pressed from the outside of the intermediate transfer belt 8 toward the secondary transfer inner roller (driving roller) 10 so as to sandwich the intermediate transfer belt 8 .

The position of the secondary transfer outer roller 12 is shifted to the upstream side in the belt rotation direction R2, and the contact area between the intermediate transfer belt 8 and the secondary transfer inner roller 10 is shifted by pressing the secondary transfer outer roller 12. They are arranged in a positional relationship such that they increase.

Therefore, at the contact start position between the inner secondary transfer roller 10 and the intermediate transfer belt 8 , the intermediate transfer belt 8 is pressed by the inner secondary transfer roller 10 by the outer secondary transfer roller 12 . This is because the secondary transfer outer roller 12 is already in contact with the intermediate transfer belt 8 on the upstream side of the intermediate transfer belt 8 .

FIG. 3 shows deformation of the intermediate transfer belt 8 at the contact start position between the inner secondary transfer roller 10 and the intermediate transfer belt 8 . A positive strain indicates a tensile strain, and a negative strain indicates a compressive strain.

The intermediate transfer belt 8 is sandwiched between a secondary transfer inner roller 10 and a secondary transfer outer roller 12 which are shifted upstream in the belt rotation direction R2, and is deformed into a so-called S-shape. Therefore, when viewed along the belt rotation direction R2, the + and - of the strain generated in the belt has a distribution that switches from - to + on the belt outer surface side with the contact start position A with the secondary transfer inner roller 10 as a boundary. On the inner side of the belt, the distribution switches from + to -.

Further, it is known that the S-shaped permanent deformation that occurs in the belt is most likely to cause image defects due to poor transfer. If the countermeasure is taken to eliminate the problem, the image defect due to permanent deformation (curling) occurring in the entire belt can be eliminated.

<Belt curl reduction operation>
The inner secondary transfer roller 10 is also a drive roller. As described above, the intermediate transfer belt 8 is driven by the drive roller 10 to rotate in the direction of the arrow R2.

By controlling the motor that drives the driving roller 10, the intermediate transfer belt 8 can be rotated by a predetermined amount and then stopped.

The rotation angle of the drive roller 10 is calculated from the rotation angular velocity and rotation time of the drive roller 10 , and the rotation distance of the drive roller 10 is calculated from the rotation angle and the circumference of the drive roller 10 . The rotational distance of the driving roller 10 is multiplied by a predetermined correction factor determined in consideration of the slippage between the driving roller 10 and the intermediate transfer belt 8, and the correction determined in consideration of the elongation of the intermediate transfer belt 8 is performed. By doing so, the conveying distance of the intermediate transfer belt 8 is estimated.

Permanent deformation (curling) occurs in the intermediate transfer belt 8 when the image forming apparatus 100 is left in a non-operating state (for example, at night when the power is not turned on, during standby time, etc.) and left for a long time.

Therefore, in the present embodiment, a curl reduction sequence is performed prior to image formation to reduce the curl of the intermediate transfer belt 8 . This curl reduction sequence is executed when the non-operating state is canceled, such as when the apparatus is turned on or after standby, to reduce the curl of the intermediate transfer belt 8 .

FIG. 4 is a flow chart in this embodiment. According to this chart, in addition to the normal wait time sequence, a sequence for reducing the curling tendency is carried out.

FIG. 5 is a diagram showing the operation of the intermediate transfer belt 8 in the curl reduction sequence.

In the sequence for reducing curling, the intermediate transfer belt 8 is rotated by a predetermined amount S, and the portion of the intermediate transfer belt 8 that has been disposed at the contact start position A with the secondary transfer inner roller 10 is shifted to one of the inner rollers. It is moved within ±2 mm of the contact end position B with the hanging support rollers (the inner secondary transfer roller 10, the tension roller 11, and the tension roller 13) and stopped. That is, the belt distance AB is the predetermined amount S to rotate.

Alternatively, in a stretched structure having outer support rollers, the belt may be moved within ±2 mm of the contact start position with any of the outer support rollers and then stopped.

By setting the predetermined amount S within a range of ±2 mm of the contact end position B with the secondary transfer inner roller 10, that is, by setting the winding amount of the intermediate transfer belt 8 around the secondary transfer inner roller 10 within a range of ±2 mm. , the predetermined amount S can be minimized. As a result, it is possible to effectively reduce the curl while minimizing the amount of rotation of the intermediate transfer belt 8 .

<Effect of reducing belt curl>
In this embodiment, the amount of winding of the intermediate transfer belt 8 around the inner secondary transfer roller 10 is 18 mm, so the amount of rotation of the intermediate transfer belt 8 is also set to 18 mm accordingly.

FIG. 6A shows the relationship between the amount of rotation of the intermediate transfer belt 8 and the amount of curl in this embodiment. The stop time for reducing the curl is set to 0.5 hours, and the amount of curl is set to 100% when the sequence for reducing the curl is not performed. It can be seen that when the amount of rotation of the intermediate transfer belt 8 is 18 mm, the curl amount is reduced to 42%, which is the minimum. Moreover, within the range of ±2 mm, it is possible to exhibit the effect of reducing curl.

FIG. 6B shows the relationship between the stop time of the intermediate transfer belt 8 and the curl amount in this embodiment. The amount of rotation of the intermediate transfer belt 8 is set to 18 mm, and the curl amount before stopping is set to 100%. It can be seen that the speed of reduction of the curl is greatest immediately after stopping, and the amount of curl is reduced to about 50% when the intermediary transfer belt 8 is stopped for 0.5 hours.

As described above, when the image forming apparatus left for a long time is started, the intermediate transfer belt 8 is rotated by a predetermined amount S, and the intermediate transfer belt 8 arranged at the contact start position A with the secondary transfer inner roller 10 is rotated. The part is moved within ±2 mm of the contact end position B with any of the inner support rollers (secondary transfer inner roller 10, tension roller 11, tension roller 13) and stopped, furthermore, a predetermined amount By setting S within the range of the amount of winding of the intermediate transfer belt 8 around the inner secondary transfer roller 10 ±2 mm, it is possible to efficiently reduce the curl.

3 Charging Device 4 Developing Device 5 Primary Transfer Roller 6 Cleaning Device 8 Intermediate Transfer Belt 14 Registration Roller Pair 15 Discharge Roller Pair 16 Fixing Device 18 Paper Feed Cassette 30 Secondary Transfer Section 100 Image Forming Device 100a Apparatus Main Body

Claims (2)

A toner image forming means for forming a toner image on an image carrier, a belt-shaped intermediate transfer member suspended by a plurality of supporting rollers, and a primary transfer means for transferring the toner image on the image carrier onto the intermediate transfer member. A secondary transfer inner roller provided inside the intermediate transfer member and a secondary transfer outer roller provided outside the intermediate transfer member press the intermediate transfer member and the recording material to record a toner image on the intermediate transfer member. In an image forming apparatus equipped with a secondary transfer means for transferring onto a material,
When the apparatus is started, the intermediate transfer member is rotated by a predetermined amount,
The portion of the intermediate transfer body that was placed at the contact start position with the secondary transfer inner roller is changed to the contact end position with any inner support roller or the contact start position with any outer support roller. An image forming apparatus characterized by moving within a range of ±2 mm and then stopping. 2. The image forming apparatus according to claim 1, wherein the predetermined amount is within a range of ±2 mm of the winding amount of the intermediate transfer body around the inner secondary transfer roller.

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