JP2000321890A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent image free from the image defect by preventing the separation discharge or the abnormal discharge from occurring in primary transfer nip parts. SOLUTION: This image forming device is, let respectively adopting elastic transfer blade in the plate shape 40, 41, 42 and 43, whose resistance is adjusted so as to become 1×101 to 1×1012 Ωcm, as a primary transfer bias applying member which abut on the rear side of an intermediate transfer belt 5 in the primary transfer nip part N so as to bring the surface side of the belt 5 into contact with photosensitive drums 1a, 2a, 3a and 4a and apply the primary transfer bias onto the belt 5. In such a manner, an area where the electric field is effected by the primary bias in the vicinity the primary transfer nip part N is narrowed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which forms an image by an electrophotographic method.

[0002]

2. Description of the Related Art As an electrophotographic multi-color or full-color image forming apparatus, a plurality of photosensitive drums are arranged for each color, and a toner image of each color formed on each photosensitive drum is transferred to a transfer material or an intermediate transfer member. 2. Description of the Related Art There has been proposed an image forming apparatus having a configuration in which a color image is formed by sequentially superimposing a color image thereon.

As this type of image forming apparatus, for example, as shown in FIG. 5, four image forming units 1, 2, 3, and
4 are photosensitive drums 1a, 2a as image carriers, respectively.
3a and 4a are arranged in a line, and each photosensitive drum 1
Black, magenta, cyan, and yellow toner images are formed on a, 2a, 3a, and 4a, respectively.

In each of the image forming units 1, 2, 3, and 4, as shown in FIG. 6 (the image forming unit 1 is shown in FIG. 6), a charger 30 is provided around the photosensitive drum 1a.
An exposure device 31, a developing device 32, and a primary transfer cleaning blade 34 are provided. Image forming unit 2,
The same applies to 3 and 4.

A primary transfer roller 9 is connected to each photosensitive drum 1a, 2a, 3a, 4a of the image forming units 1, 2, 3, 4 via an endless intermediate transfer belt 5 at a primary transfer nip N. , 10, 11, and 12 are in contact with each other.

Each of the photosensitive drums 1a, 2a, 3a, 4a
In this conventional example, the OPC photosensitive member has a negative polarity. The intermediate transfer belt 5 is extended and suspended between a driving roller 6, a secondary transfer facing roller 7, and a tension roller 8.
Is driven in the direction of the arrow. The intermediate transfer belt 5 has a thickness of 100 to 200 μm and a volume resistivity of 10
Good releasability on a resin film such as PVdF (polyvinylidene fluoride), polyamide, polyimide, PET (polyethylene terephthalate), or polycarbonate having a thickness of about ¹¹ to 10 ¹⁶ Ωcm or a rubber base layer having a thickness of about 0.5 to 2 mm. One provided with a resin layer can be used.

A neutralizer 17 and a secondary transfer cleaning blade 20 are provided outside the intermediate transfer belt 5. Primary transfer bias power supplies 13, 14, 15, and 16 are connected to the primary transfer rollers 9, 10, 11, and 12, respectively. A secondary transfer roller 18 to which a primary transfer bias power supply 19 is connected is in contact with the secondary transfer opposing roller 7 via the intermediate transfer belt 5 at the secondary transfer nip M.

[0008] The primary transfer rollers 9, 10, 11, and 12
Asker C hardness 30-60 °, volume resistivity 10 ⁵ Ω
cm or less. Secondary transfer roller 18
Is disposed so as to be able to freely contact and separate from the secondary transfer opposing roller 7 (intermediate transfer belt 5).

Next, an image forming operation by the image forming apparatus will be described.

First, the photosensitive drum 1 of the image forming unit 1
a is rotated and the surface thereof is uniformly charged to a negative polarity by the charger 30. Then, the exposure device 31 performs image exposure according to black image information to form an electrostatic latent image. Then, a toner t of negative polarity is attached to the electrostatic latent image by a reversal developing method by a developing sleeve 33 of a developing device 32, and is visualized as a black toner image.

The black toner image is primarily transferred onto the rotating intermediate transfer belt 5 by a primary transfer roller 9 to which a positive primary transfer bias is applied at a primary transfer nip N. . The primary transfer residual toner remaining on the photosensitive drum 1 a after the primary transfer is scraped off by the primary transfer cleaning blade 34 and collected in the waste toner container 35.

The intermediate transfer belt 5 to which the black toner image has been transferred is rotated toward the image forming unit 2. Also on the photosensitive drum 2 a of the image forming unit 2, the magenta toner image formed in the same manner as described above is superimposed on the black toner image on the intermediate transfer belt 5 and transferred at the primary transfer nip N.

Hereinafter, the cyan and yellow toner images formed by the photosensitive drums 3a and 4a of the image forming units 3 and 4 are formed on the black and magenta toner images superimposedly transferred on the intermediate transfer belt 5 in the same manner. A full-color toner image is formed on the intermediate transfer belt 5 by superimposing sequentially.
Then, at a predetermined timing, the surface of the transfer material P conveyed to the secondary transfer nip portion M between the secondary transfer roller 18 and the intermediate transfer belt 5 is grounded or a suitable bias is applied to the back surface of the transfer material facing the secondary transfer opposing roller. A full-color toner image is secondarily transferred collectively by a secondary transfer roller 18 to which a transfer bias of a positive polarity is applied.

The secondary transfer residual toner remaining on the intermediate transfer belt 5 after the secondary transfer is scraped off by the secondary transfer cleaning blade 20 and collected in the waste toner container 21. After the secondary transfer, the intermediate transfer belt 5 is neutralized by the neutralizer 17 to prepare for the next image forming operation.

The transfer material P on which the full-color toner image has been formed is conveyed to a fixing device (not shown), is thermally fixed, and is discharged outside.

[0016]

When the primary transfer rollers 9, 10, 11, and 12 are used as the primary transfer bias applying member as in the conventional image forming apparatus described above, FIG. In this case, as shown in the image forming unit 1), the electric field E due to the primary transfer bias acts on a wide range outside the vicinity of the primary transfer nip N which contacts the photosensitive drum 1a. In addition, since the primary transfer roller 9 gradually separates from the back surface of the intermediate transfer belt 5, peeling discharge easily occurs between the primary transfer roller 9 and the back surface of the intermediate transfer belt 5. Therefore, the toner image formed on the intermediate transfer belt 5 is disturbed by the occurrence of the peeling discharge, and the toner image is partially agglomerated or lost, which appears as an image defect such as a so-called polka dot image or triassic image. .

Further, since the electric field E due to the primary transfer bias to the primary transfer roller 9 acts in a wide range outside the primary transfer nip portion N, the surface of the photosensitive drum 1a and the surface of the intermediate transfer belt 5 are changed. This electric field E also acts in the gap to be separated. For this reason, the abnormal electric discharge in the gap is promoted by the electric field E, and the transfer efficiency differs between the place where the abnormal discharge occurs and the place where the abnormal discharge does not occur, which appears as an image defect such as a so-called shark skin image. Would.

When the primary transfer rollers 9, 10, 11, and 12 are used as a primary transfer bias applying member as in the conventional image forming apparatus described above, FIG. 7 (image forming unit 1 in the figure). As shown in (1), the primary transfer roller 9 needs to be pressed against the photosensitive drum 1a with a predetermined urging force at the primary transfer nip N to obtain a nip width of a certain degree. for that reason,
The toner is agglomerated in the primary transfer nip portion N, so that a so-called hollow image is easily generated.

Accordingly, the present invention prevents the occurrence of peeling discharge and abnormal discharge near the primary transfer nip, and reduces the pressure between the primary transfer bias applying member and the photosensitive drum in the primary transfer nip. It is another object of the present invention to provide an image forming apparatus capable of obtaining a good image without image defects.

[0020]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a primary transfer unit for primary transferring a toner image formed on an image carrier to an endless intermediate transfer belt. The toner image on the transfer belt is transferred to a transfer material at a secondary transfer unit.
In the image forming apparatus for forming an image by performing the next transfer, the primary transfer unit contacts the back side of the intermediate transfer belt to bring the surface side of the intermediate transfer belt into contact with the image carrier, and A primary transfer bias applying member for applying a primary transfer bias to the transfer belt, wherein the primary transfer bias applying member has a volume resistivity of 10 ¹ to 10 ¹² Ωc;
It is characterized by being constituted by an elastic plate-like member or sheet-like member whose resistance has been adjusted to m.

Also, the surface resistance of the back side of the intermediate transfer belt which is in contact with the primary transfer bias applying member is 10 ⁸
The image forming apparatus according to claim 1, wherein the number is Ω □ or more.

Further, a toner image of a plurality of colors is sequentially formed on one image carrier, and a primary transfer bias is applied to the primary transfer bias applying member in a primary transfer section to thereby form the intermediate transfer belt. The toner images of the plurality of colors are sequentially primary-transferred and superimposed thereon, and the superimposed toner images of the plurality of colors are collectively secondary-transferred to a transfer material by a secondary transfer unit.

Further, an image forming unit having at least the image carrier for carrying an electrostatic latent image of an arbitrary color corresponding to image information on a surface thereof, and developing means for developing the electrostatic latent image as a toner image. And a plurality of the image carriers of each of the image forming units are arranged in a line, and the respective image carriers are brought into contact with the surface side of the intermediate transfer belt at a primary transfer unit, respectively. A primary transfer bias is applied to the primary transfer bias applying member at the primary transfer unit of each image carrier by applying a primary transfer bias to the toner images of different colors formed on the image carriers, respectively, on the intermediate transfer belt. The method is characterized in that primary transfer is performed by sequentially superimposing, and a plurality of color toner images superimposed in the secondary transfer unit are collectively and secondarily transferred to a transfer material.

[0024]

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

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. The same members as those of the conventional image forming apparatus shown in FIG. 5 are denoted by the same reference numerals, and overlapping description will be omitted.

The configuration and image forming operation of the image forming apparatus of this embodiment are the same as those of the conventional image forming apparatus shown in FIG. 5 except for the primary transfer member. Only the application member will be described.

In the present embodiment, the image forming unit 1
Plate-like transfer blades 40, 41, 42, and 43 having elasticity were used as the primary transfer bias applying members 2, 3, and 4, respectively.

The transfer blades 40, 41, 42, 43
It is composed of a hydrin rubber blade having a thickness of about 2 mm and a volume resistivity adjusted to about 10 ⁸ Ωcm. As shown in FIG. 2 (the transfer blade 40 of the image forming unit 1 in the figure), each of the transfer blades 40, 41, 42, and 43 is fixed to an L-shaped sheet metal 44 by an electrically conductive adhesive. A primary transfer bias power supply 1 is
3 are connected. The primary transfer bias power supply 13 applies a positive transfer bias to the L-shaped sheet metal 44 in the present embodiment.

In this embodiment, the intermediate transfer belt 5 has a circumference of 400 mm, a thickness of 100 μm, a volume resistivity of about 10 ¹³ Ωcm, and a surface resistance on the back surface (on the side of the primary transfer bias application) of 10 ¹¹ Ω. A polyimide resin film adjusted to about □ is used. That is, the intermediate transfer belt 5 having a high resistance was used in order to form a surface potential that holds the toner on the intermediate transfer belt 5 in order to suppress toner scattering during the primary transfer.

Therefore, in order to obtain a sufficient primary transfer current, it is necessary to apply a higher primary transfer bias.
In this embodiment, each primary transfer bias power supply 1
3, 14, 15, 16 from each transfer blade 40, 41,
A voltage of 1 KV was applied to 42 and 43 (at this time, the potentials of the respective photosensitive drums 1a, 2a, 3a and 4a were -600V for the non-exposed portion and -200V for the exposed portion). Therefore, discharge is easily generated in the gap near the primary transfer nip portion N.

However, in the present embodiment, plate-like transfer blades 40, 4 are used as primary transfer bias applying members.
As shown in FIG. 3 (the transfer blade 40 of the image forming unit 1 in the figure), the transfer blade 40 is rotated at the primary transfer nip N during the primary transfer of the toner image by using 1, 42, and 43. As a result, the range in which the electric field E due to the primary transfer bias acts is narrower than in the case of the above-described conventional transfer roller (see FIG. 7). Become.

For this reason, the promotion of abnormal discharge in the gap between the photosensitive drum 1a and the intermediate transfer belt 5 near the primary transfer nip N can be suppressed, and the occurrence of image defects such as so-called shark skin images can be prevented. did it.

As shown in FIG. 3, the transfer blade 40 rapidly approaches and separates from the rotating intermediate transfer belt 5 at the primary transfer nip portion N during the primary transfer of the toner image. As compared with the case of the conventional transfer roller (see FIG. 7), the range in which peeling discharge occurs between the transfer blade 40 and the intermediate transfer belt 5 is narrowed.

For this reason, it was possible to prevent the occurrence of image defects such as a so-called polka dot image and a triassic image in which the toner image is partially aggregated or lost.

In this embodiment, the intermediate transfer belt 5 has a surface resistance of about 10 ¹¹ Ω □ on the back side (primary transfer bias application side) as described above. ^If it is less than ⁸ Ω □, the potential becomes the same as the primary transfer bias over a certain wide range on the back side of the intermediate transfer belt 5 on the primary transfer bias application side (transfer blades 40, 41, 42, 43 side). As a result, the transfer blade 4
Since the electric field formed by the primary transfer bias applied to 0, 41, 42 and 43 acts on a wide range, the effect of the present invention described above is weakened.

Therefore, the effect of the present invention is enhanced by setting the surface resistance of the back surface of the intermediate transfer belt 5 on the primary transfer bias application side to 10 ⁸ Ω □ or more as in this embodiment. The surface resistance of the back surface of the intermediate transfer belt 5 on the primary transfer bias application side is measured using a high resistance meter (ADVANTE) using a measurement probe conforming to JIS K6911.
The value measured by applying 100 V with ST Corporation; R8340) was normalized and used.

In this embodiment, the transfer blade 4
As described above, those having a volume resistivity of about 10 ⁸ Ωcm were used as 0, 41, 42, and 43. However, when the volume resistivity of the transfer blades 40, 41, 42, and 43 became 10 ¹² Ωcm or more, it was sufficient. The primary transfer voltage required to secure a proper primary transfer current becomes a very high value. As a result, expensive transformers and leakage countermeasures are required,
This leads to an increase in the cost of the device.

Therefore, as in the present embodiment, the volume resistivity of the transfer blades 40, 41, 42, 43 is 10 ¹ to 10 ⁵ .
By using the one with 10 ¹² Ωcm, expensive transformers and leak countermeasures are not required, and an increase in the cost of the apparatus can be suppressed.

As described above, in this embodiment, the volume resistivity of the primary transfer bias applying member is 10 ¹ to 10 ¹² Ωc.
By using the plate-shaped transfer blades 40, 41, 42, and 43 of m, abnormal discharge and peeling discharge in the vicinity of the primary transfer nip portion N are suppressed, and image defects (such as shark skin image, polka dot image, and triassic image) Etc.) can be prevented, and a high-quality image can be obtained.

<Embodiment 2> In this embodiment, as shown in FIG. 4, the primary transfer bias applying members of the image forming units 1, 2, 3, and 4 have a thickness of about 0.5 mm or less and a rigidity. This is a configuration using a conductive transfer sheet 45 having no configuration, and other configurations and image forming operations are the same as those of the conventional example shown in FIG.
And the same as the image forming apparatus of the first embodiment shown in FIG. Note that the same members as those of the image forming apparatus according to the first embodiment shown in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description will be omitted.

As the transfer sheet 45, for example, PBT
(Polybutylene terephthalate) elastomer or styrene elastomer, or PVdF or P with adjusted resistance
ES (polyether sulfone) can be used. Further, also in the present embodiment, the transfer sheet 45
Has a volume resistivity of 10 ¹ to 10 ¹² as in the first embodiment.
The resistance is adjusted to Ωcm.

As shown in FIG. 4 (the transfer sheet 45 of the image forming unit 1 in the figure), each of the transfer sheets 45 is fixed to the L-shaped sheet metal 44 with an electrically conductive adhesive.
The primary transfer bias power supply 13 is connected to the L-shaped sheet metal 44. The primary transfer bias power supply 13 applies a positive transfer bias to the L-shaped sheet metal 44 in the present embodiment.

In the present embodiment, the surface resistance of the intermediate transfer belt 5 is 10 ⁸ Ω as in the first embodiment.
□ The above was used.

In this embodiment, the leading end of the non-rigid transfer sheet 45 contacts the photosensitive drum at the primary transfer nip, and the contact pressure at this time is about 5 g / cm.

On the other hand, the transfer roller of the conventional example described above (FIG. 7)
In the case of (1), the transfer roller is urged by a spring or the like from both ends thereof to uniformly contact the transfer roller with the photosensitive drum, so that the contact pressure against the photosensitive drum increases. As a result, toner collection at the primary transfer nip is promoted,
Although the hollow image is likely to occur, as described above, in the present embodiment, the transfer sheet 45 is used, so that the contact pressure against the photosensitive drum can be reduced. Can be prevented.

As described above, in the present embodiment, in addition to the effects obtained in the first embodiment, a high quality image can be obtained by preventing the toner image from missing at the primary transfer nip. .

In each of the above embodiments, the toner image is formed in the order of black, magenta, cyan, and yellow by the image forming units 1, 2, 3, and 4. The arrangement order of 3 and 4 may be switched so that the toner images of the respective colors are sequentially superimposed.

Further, in each of the above-described embodiments, the image forming apparatus is provided with the plurality of image forming units 1, 2, 3, and 4. However, other than this, for example, the image forming apparatuses are sequentially formed on one photosensitive drum. Primary transfer of an image forming apparatus in which toner images of a plurality of colors are superimposed and primary-transferred at a primary transfer nip and collectively secondary-transferred at a secondary transfer nip to obtain a color image The present invention can be applied to a bias applying member.

[0049]

As described above, according to the present invention, 1
When the secondary transfer bias applying member has a volume resistivity of 10 ¹ to 10
^The range in which the electric field due to the primary transfer bias in the primary transfer unit acts is narrower than that of the conventional transfer roller by using an elastic plate-like member or sheet-like member having a resistance adjusted to ¹² Ωcm. It is possible to do
The occurrence of peeling discharge or abnormal discharge in the vicinity of the primary transfer portion can be prevented, and a high-quality image free from image defects can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a side view showing a transfer blade of the image forming apparatus according to the first embodiment.

FIG. 3 is a diagram showing the vicinity of a primary transfer nip at the time of primary transfer of the image forming apparatus according to the first embodiment.

FIG. 4 is a side view showing a transfer sheet of the image forming apparatus according to the second embodiment.

FIG. 5 is a schematic configuration diagram showing an image forming apparatus in a conventional example.

FIG. 6 is a schematic configuration diagram showing an image forming unit of an image forming apparatus in a conventional example.

FIG. 7 illustrates a first example of a conventional image forming apparatus during primary transfer.
FIG. 7 is a diagram illustrating the vicinity of a next transfer nip portion.

[Explanation of symbols]

1, 2, 3, 4 Image forming unit 1a, 2a, 3a, 4a Photosensitive drum (image carrier) 5 Transfer belt 13, 14, 15, 16 Primary transfer bias power supply 18 Secondary transfer roller 40, 41, 42, 43 transfer blade (primary transfer bias applying member) 44 L-shaped sheet metal 45 transfer sheet (primary transfer bias applying member)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Karashima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akihiko Uchiyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon F term in reference (reference) 2H030 AD01 AD04 BB02 BB23 BB42 BB54 2H032 AA05 AA15 BA05 BA09 BA19 BA23 CA02

Claims (4)

[Claims] 1. A toner image formed on an image carrier is primarily transferred to an endless intermediate transfer belt at a primary transfer section, and the toner image on the intermediate transfer belt is transferred at a secondary transfer section. In the image forming apparatus, which forms an image by secondary transfer to a material, the primary transfer unit contacts the back side of the intermediate transfer belt to contact the front side of the intermediate transfer belt with the image carrier. A primary transfer bias applying member for applying a primary transfer bias to the intermediate transfer belt, wherein the primary transfer bias applying member has a volume resistivity of 10 ^1.
An image forming apparatus comprising: an elastic plate-shaped member or sheet-shaped member having a resistance adjusted to 10 to ^{12 12} Ωcm. 2. A surface resistance of a back side of the intermediate transfer belt which is in contact with the primary transfer bias applying member has a surface resistance of 10 ⁸ Ω □.
The image forming apparatus according to claim 1, wherein: 3. The intermediate transfer belt, wherein a plurality of color toner images are sequentially formed on one image carrier, and a primary transfer bias is applied to a primary transfer bias applying member in a primary transfer unit. The plurality of color toner images are sequentially primary-transferred and superimposed thereon, and the superposed plurality of color toner images are collectively secondary-transferred to a transfer material by a secondary transfer unit. The image forming apparatus according to claim 1. 4. An image forming unit including at least the image carrier that carries an electrostatic latent image of an arbitrary color corresponding to image information on a surface thereof, and a developing unit that develops the electrostatic latent image as a toner image. The image forming units of the image forming units are arranged in a line, and the image transferring units are brought into contact with the surface side of the intermediate transfer belt at a primary transfer unit, respectively. A primary transfer bias is applied to the primary transfer bias applying member at the primary transfer unit of each image carrier by applying a primary transfer bias to the toner images of different colors formed on the image carriers, respectively, on the intermediate transfer belt. 3. The image forming apparatus according to claim 1, wherein the toner images of a plurality of colors superimposed in a secondary transfer unit are collectively and secondarily transferred to a transfer material by sequentially superimposing the primary images. .