JP3201112B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primary transfer of a transferable image (toner image) formed on a first image carrier to an intermediate transfer member as a second image carrier, and to the intermediate transfer member, 3
The present invention relates to an image forming apparatus which obtains an image-formed product (copy print) by pressing a paper sheet as an image carrier with a contact transfer member to perform secondary transfer on the paper sheet.

[0002] In the above, the first image carrier is, for example, an electrophotographic photosensitive member, an electrostatic recording dielectric, a magnetic recording magnetic material, or the like.

The process of forming a transferable image on the first image carrier is, for example, an electrophotographic process, an electrostatic recording process, a magnetic recording process, or the like.

[0004] An intermediate transfer member as a second image carrier is
Examples are a roller-shaped body (drum-shaped body) and a belt-shaped body.

The paper sheet as the third image carrier is a transfer paper, a recording paper, a printing paper, a card, an envelope, a postcard, etc., and the material is not limited to paper.

[0006]

2. Description of the Related Art An image forming apparatus using an intermediate transfer member as described above performs an intermediate transfer by repeating a process of forming a transferable image on a first image carrier and a primary transfer of the image to an intermediate transfer member. After forming a color image (or a multi-color image) composed of a plurality of color developers on the body, the image is composite-reproduced by color transfer of the color image information by collectively and secondarily transferring the image onto a paper sheet. Is effective as a device for outputting color images or an image forming device provided with a color image forming function, and an image without overlapping deviation (color deviation) of each component color image can be obtained.

As a full-color image forming apparatus using an intermediate transfer member, there is known an apparatus using a drum-shaped roller as an intermediate transfer member, as described in US Pat. No. 5,187,526.

FIG. 11 shows a schematic configuration of the image forming apparatus. That is, an electrophotographic photosensitive drum 1 as a first image carrier, which is driven to rotate clockwise as indicated by an arrow, is uniformly charged by a charger 2 according to a known electrophotographic method, and is obtained by exposure 3. The developing device 4 applies a developer (hereinafter, referred to as toner) composed of colored charged particles to visualize the electrostatic latent image. The toner image is transferred to an intermediate transfer roller 5 as a second image carrier that rotates synchronously in the forward direction at the same peripheral speed as the photosensitive drum in contact with or close to the photosensitive drum 1 and in a first transfer nip area N1. Primary transfer. That is,
The intermediate transfer roller 5 includes a core metal 51 and a surface layer 52 made of a thin layer of conductive polyurethane, and applies a bias voltage having a polarity opposite to that of the toner by a power supply 6 to electrostatically transfer the toner image on the photosensitive drum 1. .

The process of forming the toner image on the photosensitive drum 1 and the primary transfer of the toner image to the intermediate transfer roller 5 is repeatedly performed by the required number of component colors of the target full-color image information, thereby making the intermediate transfer roller A full-color image corresponding to the target color image information is synthesized and formed on the surface 5 by superimposing and transferring the toner images of the respective component colors. The developing device 4 stores the toner of the corresponding color each time a toner image of each component color is formed on the photosensitive drum 1.
At the developing position.

When the final primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer roller 5 is performed, a second transfer nip area N2 between the intermediate transfer roller 5 and the transfer roller 7 as a contact transfer member is performed. A sheet 10 such as a transfer sheet is fed at a predetermined timing from a sheet feeding unit (not shown), and the full-color image formed on the intermediate transfer roller 5 is secondarily transferred to the sheet 10.

The transfer roller 7 is constituted by a surface layer 72 made of a thin layer of conductive polyurethane on a metal core 71, and at the time of primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer roller 5, the metal core 71 is switched by the switch 9. When the secondary transfer of the full-color image from the intermediate transfer roller 5 to the paper sheet 10 is performed, the core metal 71 has the opposite polarity to the toner by the switch 9 and the power source 6 for the core metal 51 of the intermediate transfer roller 5 is connected to the ground 82.
To a bias power supply 81 having a voltage greater than the applied voltage by

The paper sheet 10 to which the full-color image has been transferred from the intermediate transfer roller 5 is introduced into a fixing device (not shown) and undergoes image fixing processing to form a full-color image formed product.

Reference numeral 12 denotes a cleaner for the photosensitive drum 1. 1
Reference numeral 1 denotes a cleaner for the intermediate transfer roller 5.
1 is moved toward and away from the intermediate transfer roller 5 by shift means (not shown), and at least after the primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer roller 5 is started, Until the secondary transfer of the full-color image to the body 10 is completed, it is moved and held at a position separated from the intermediate transfer roller 5. The transfer roller 7 is also moved toward and away from the intermediate transfer roller 5 by the shift means, so that the transfer roller 7 is pressed against the intermediate transfer roller 5 during the secondary transfer of the full-color image from the intermediate transfer roller 5 to the sheet 10. It can also be moved and held at the set position.

The use of the drum-shaped intermediate transfer roller 5 as the intermediate transfer member as in the above-described apparatus does not require a mechanism for correcting the traveling accuracy as compared with the belt-shaped intermediate transfer member, and has a simple structure to reduce the color shift. There is an advantage that a full-color image can be obtained without any problem, and Japanese Patent Application No. 4-164226 according to the earlier proposal of the present applicant.
The details of which are disclosed in U.S. Pat.
According to Japanese Patent No. 87,526, the resistivity of the intermediate transfer roller 5 is less than 10 ⁹ Ω · cm, and the resistivity of the transfer roller 7 is 10 ¹⁰ Ω.
It is said that a good image can be obtained by setting the diameter to cm or more.

In the above-mentioned US Pat. No. 5,187,526, the surface layers 52 and 72 of the intermediate transfer roller 5 and the transfer roller 7 are both described as a thin layer, but polyurethane is used as a base material. No physical conditions are mentioned other than to do so.

On the other hand, according to US Pat. No. 5,084,735, which also discloses an image forming apparatus using the intermediate transfer roller 5, the Young's modulus of the intermediate transfer roller 5 is 5 × 10 ⁷ Newt.
There is a statement that it exceeds ons / m ² .

[0017]

However, in the above conventional example, it is necessary to provide a sufficient amount of transfer charge to the sheet 10 during the secondary transfer of the full-color image from the intermediate transfer roller 5 to the sheet 10. Means that the output voltage value of the power supply 81 must be increased, and the surface layer 72 made of polyurethane in which the conductivity-imparting agent is dispersed locally causes a breakdown, and particularly an image pattern in which toner is sparsely distributed, such as a halftone image. It has been found that there is a problem of causing disturbances.

That is, if the transfer current 4 μA shown in US Pat. No. 5,187,526 is to be realized in the surface layer 72 having a volume resistivity of 10 ¹⁰ Ω · cm or more, the thickness of the surface layer 72 is set to 5 mm, In the parameters of the transfer roller 7 which is usually used in a compact image forming apparatus, the nip width of the transfer nip area N2 is 2 mm and the nip longitudinal dimension is 200 mm, the transfer roller 7 is 5K without taking the paper sheet 10 into consideration.
Considering that the resistance value of V and the sheet 10 is about 10 ⁹ Ω, a voltage as high as 10 KV is required.

At such a high voltage, in a high-humidity environment in which the atmospheric humidity exceeds 60% RH, the paper sheet 10 itself has low resistance, and the transfer current leaks to the ground metal plate near the paper sheet 10. Transfer failure may occur, and in a low humidity environment where the atmospheric humidity is lower than 40% RH, partial breakdown may occur due to uneven resistance of the paper sheet 10 and transfer unevenness may occur.

Further, since the transfer roller 7 has a volume resistivity higher than that of the intermediate transfer roller 5 by 10 times or more, the paper
Is easily attracted to the intermediate transfer roller 5 side, and the paper sheet 10 that has exited the second transfer nip area N2 is
There is a problem that winds around.

That is, as shown in FIG. 12, the paper sheet 10, which is an insulator, is polarized by the transfer electric field and receives an attractive force from the intermediate transfer roller 5 and the transfer roller 7. Reference numeral 5 substantially serves as a proximity electrode, and the intermediate transfer roller 5 acts to attract the paper sheet 10.

Actually, a transfer charge (plus) is applied to the back surface (transfer roller facing surface) of the paper sheet 10, and in addition to the above-described polarization effect, the paper sheet 10 is further provided under the above-described transfer electric field arrangement. 10 is attracted to the intermediate transfer roller 5 side.

In the intermediate transfer roller 5 having a Young's modulus exceeding 5 × 10 ⁷ Newtons / m ² disclosed in US Pat. No. 5,084,735, US Pat. As described in this document, even if the transfer roller 7 is made harder than the intermediate transfer roller 5 and strongly pressed to impart curl to the paper sheet body 10 and prevent winding, it is too hard for each other. It has been found that the second transfer region N2 having an appropriate nip width cannot be obtained, and instead, a full-color image to be transferred is crushed, resulting in transfer failure.

That is, there is a problem that the paper sheet 10 is easily wound around the intermediate transfer roller 5 having high hardness and medium resistance. This is likely to occur in a low-humidity environment in which the sheet body 10 has a high resistance.

Therefore, the present invention solves the above-mentioned problems in an image forming apparatus using the above-mentioned intermediate transfer member, that is, good secondary transfer of an image from the intermediate transfer member to a paper sheet. to perform, for the purpose that you realize conveyance of the sheet member stably to prevent the winding of the intermediate transfer member Kamihatai.

[0026]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus having the following configuration.

[0027]

[0028]

[0029]

(1) An image carrier for carrying an image, an intermediate transfer body, and a transfer charging member for transferring an image on the intermediate transfer body transferred from the image carrier to a recording material, When an image on the intermediate transfer member is transferred to a recording material, the transfer charging member presses the recording material against the intermediate transfer member. In the image forming apparatus, the resistance value of the transfer charging member is the resistance of the intermediate transfer member. Value , the hardness of the intermediate transfer member is
Less than the hardness of the transfer charging member, the intermediate transfer member side
The transfer nip having a concave shape is formed between the intermediate transfer body and the transfer roller.
An image forming apparatus formed by a photo- charging member .

[0031] (2) the hardness of the front Symbol intermediate transfer member, the image forming apparatus according to 40 degrees (JIS · A) wherein the der Turkey below (1).

(3) Image Carrier for Carrying Image and Intermediate Transfer
And the intermediate transfer member transferred from the image carrier.
And a transfer charging member for transferring an image to a recording material.
When transferring the image on the intermediary transfer member to the recording material, the transfer charge
An image forming apparatus for pressing a recording material against the intermediate transfer body
In the above, the hardness of the intermediate transfer member is the same as that of the transfer charging member.
And less than 40 degrees (JIS-A)
And the transfer nip having a shape in which the intermediate transfer body side is depressed is
The pressing force of the transfer charging member is formed by the intermediate transfer body and the transfer charging member, and when the trailing portion of the recording material passes through the transfer nip than when the leading end of the recording material passes through the transfer nip. Is characterized by being smaller
That images forming device.

(4) Image Carrier for Carrying Image and Intermediate Transfer
And the intermediate transfer member transferred from the image carrier.
And a transfer charging member for transferring an image to a recording material.
When transferring the image on the intermediary transfer member to the recording material, the transfer charge
An image forming apparatus for pressing a recording material against the intermediate transfer body
In the above, the hardness of the intermediate transfer member is the same as that of the transfer charging member.
And less than 40 degrees (JIS-A)
And the transfer nip having a shape in which the intermediate transfer body side is depressed is
A static elimination needle formed of the intermediate transfer member and the transfer charging member , provided downstream of the transfer nip in the transport direction of the recording material, and further provided with a static elimination needle housed in an insulator holder; images forming device you <br/> characterized by conveying by.

(5) The transfer charging member transfers, onto a recording material, images of a plurality of colors on the intermediate transfer body which are sequentially transferred from the image carrier in a superimposed manner. (1) to (4).
Any one of the image forming apparatuses.

(6) The image forming apparatus according to any one of (1) to (5), wherein the intermediate transfer member and the transfer charging member are formed in a roller shape.

[0036]

[Action] That is, transfer charging resistance member is minor than the resistance of the intermediate transfer member, transfer charging member and the intermediate transfer member roller type
Since the voltage applied to the transfer charging member in comparison with the prior art by being a Jo can be reduced, the recording material and the transfer charging member,
No local breakdown of the intermediate transfer member occurred,
Good secondary transfer performance can be obtained even in a low humidity environment. In other words, the resistance of the intermediate transfer member is such that approximately the same current value is applied to the potential contrast of the image portion and the non-image portion of the image carrier.
In order to prevent image disturbance during the primary transfer of an image from the image carrier to the intermediate transfer body, the resistance must be set to a medium resistance. However, in the transfer charging member , an image portion such as an image carrier such as an image carrier is not provided on the intermediate transfer body. Since there is no potential contrast in the image portion, the secondary transfer image is not disturbed even if the resistance is low.

The hardness of the intermediate transfer member depends on the transfer charging member.
Less than hardness and 40 degrees (JIS-A [= JI
SK, A type measuring device used])
The transfer nip in which the transfer body side is concave is the intermediate transfer body and
By being formed by the transfer charging member, the recording material because it is conveyed along the nip shape, the intermediate transfer against the electrostatic attraction force by utilizing stiffness of the recording material <br/> recording material It can be transported away from the body, and does not wind around the intermediate transfer body in combination with the electrostatic attraction effect of the transfer charging member .

The pressing force of the transfer charging member is applied to the tip of the recording material.
The trailing portion of the recording material than when the edge passes through the transfer nip
There is a small Kunar so towards it passes through the transfer nip, i.e. biting amount of the intermediate transfer member of the transfer charging member in response to the leading end portion of the recording material is set to be large, the subsequent recording material In the department, by making the amount of bite small, it is recorded
Tip of the timber may easily be separated from the intermediate transfer member, the pressing force to the trailing portion is reduced, never recording material curling as a whole.

[0039]

[0040]

【Example】

<First Embodiment> (FIGS. 1 and 2) FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. The same reference numerals are given to the same constituent members and portions as those in the apparatus of FIG. 11 described above, and the description will not be repeated.

The photosensitive drum 1 as an image carrier is formed by coating an organic optical semiconductor (OPC) on a cored bar, and has a process speed (peripheral speed) of 100 mm / s in a clockwise direction indicated by an arrow.
The roller 2 rotates at ec, and is uniformly charged to a surface potential of about -600 V by a charger 2, which is a contact roller in this example.

Exposure 3 is performed by turning on / off a laser beam scanned in a direction perpendicular to the paper surface by a rotating mirror (not shown) according to digital image information. , Bright part potential (where light hits)
An electrostatic latent image of about -100 V is formed.

The developing device 4 contains toners of four different colors, magenta M, cyan C, yellow Y, and black B, respectively.
The color developing units 41, 42, 43, and 44 selectively and sequentially develop the photosensitive drum 1. The toner in each developing unit is a non-magnetic one-component toner and has a weight average particle size of 5%.
１５15 μm, average area weight 0.5 to ² mg / cm ² , intrinsic charge amount is −10 μC / gr to −30 μ with negative polarity
As C / gr, the electrostatic latent image is visualized by reversal development in which toner is attached to the exposed portion of the photosensitive drum 1.

The formation of each color component toner image on the photosensitive drum 1 and the use of each color component toner image as an intermediate transfer member
The primary transfer is sequentially performed on all of the intermediate transfer rollers 5 to synthesize and form a full-color image by superimposing four color toner images on the intermediate transfer roller 5 in the same manner as the apparatus shown in FIG. The transfer residual toner on the photosensitive drum 1 is wiped by the cleaner 12, and the photosensitive drum 1 is repeatedly used for the subsequent image formation.

The intermediate transfer roller 5 is a roller having an effective length L = 250 mm having a slightly larger peripheral length than the length of the paper sheet 10 as a recording material in the transport direction, and a pipe-shaped substrate made of aluminum and having a thickness of 3 mm. 51, a conductivity imparting agent such as carbon, zinc oxide, tin oxide, and conductive whisker is dispersed in NBR rubber to obtain a volume resistivity ρ1 of about 109.
Adjusted to Ω · cm, thickness t1 = 5 mm, hardness 35 degrees
(JIS A) elastic layer 52 is formed to have a diameter of 150 mmφ.
It is driven in the counterclockwise direction of the arrow at mm / sec.

The photosensitive drum 1 and the intermediate transfer roller 5 apply a total pressure of 5
The first transfer nip area N1 has a width w1 of about 2 mm. That is, in the first transfer nip region N1, the resistance R1 of the intermediate transfer roller 5 has the following value.

R ₁ = ρ ₁ × (t ₁ / L × w ₁ ) = 10 ⁸ [Ω] The necessary transfer current in the first transfer nip area N 1 is about 5 μA, which is +500 V from the power supply 6. Core 5
1 is obtained.

A transfer roller 7 serving as a transfer charging member is provided with an EPD on a core metal 71 having a diameter of 20 mm and made of an iron pipe.
A volume resistivity ρ2 is obtained by dispersing a conductivity-imparting agent such as carbon, zinc oxide, tin oxide, and a conductive whisker in an M foam.
Was adjusted to about 106 Ω · cm, thickness t2 = 5 mm,
An elastic layer 72 having a Asker C hardness of 30 degrees is formed to have a diameter of 30 mm.
and driven in the clockwise direction indicated by the arrow at the same process speed as the intermediate transfer roller 5 at 100 mm / sec.

The intermediate transfer roller 5 and the transfer roller 7 apply a total pressure 8
Is pressed in 00gr heavy, the second transfer nip area N2 has a width w ₂ of approximately 3 mm.

That is, the resistance R ₂₁ of the intermediate transfer roller 5 and the resistance R of the transfer roller 7 in the second transfer nip area N 2
₂₂ is the following value.

R ₂₁ = ρ ₁ × (t ₁ / L × w ₁ ) = 7 × 10 ⁷ [Ω] R ₂₂ = ρ ₂ × (t ₂ / L × w ₂ ) = 7 × 10 ⁴ [Ω] Paper The plain paper used as the leaf 10 has a thickness t ₃ = 100.
μm, the volume resistivity ρ ₃ is about 10 ¹¹ Ω · cm,
Resistance R ₃ of Kamihatai 10 in the transfer nip area N2 of the are as follows.

R ₃ = ρ ₃ × (t ₃ / L × w ₂ ) = 1 × 10 ⁸ [Ω] Therefore, to obtain the transfer current value I ₂ = 5 μA required in the second transfer nip region N2, V = (R ₂₁ + R ₂₂ + R ₃ ) × I ₂ = 850 [V] may be applied to the metal core 71 of the transfer roller 7. This is a value when the core metal 51 of the intermediate transfer roller 5 is grounded. When the core metal 51 is biased to 500 V as described above, 500 + 850 = 1350
[V] may be applied.

After the secondary transfer of the full-color image from the intermediate transfer roller 5 to the sheet 10, the transfer residual toner on the intermediate transfer roller 5 is wiped off by the fur brush cleaner 11.
The intermediate transfer roller 5 is used repeatedly for subsequent image formation. The fur brush cleaner 11 and the transfer roller 7
Is kept out of contact with the intermediate transfer roller 5 by the shift means except at the time of each operation so as not to disturb the color image on the intermediate transfer roller 5.

[0054] Thus the voltage applied to the resistor R ₂₂ to the intermediate transfer roller 5 of the resistor R ₂₁ transfer roller 7 as compared with the conventional example to be smaller than the transfer roller 7 can be reduced Kamihatai 10 and transfer Local breakdown of the roller 7 and the intermediate transfer roller 5 does not occur, and good transfer performance can be obtained even in a high / low humidity environment.

In other words, the resistance R ₁ of the intermediate transfer roller 5 is such that the potential of the dark portion on the photosensitive drum 1 is −600 V and the potential of the bright portion is −100 V.
Although it is necessary to prevent image disturbance at the time of transfer of a visible image obtained by reversal development by flowing substantially the same current value for the contrast of the transfer roller 7, the transfer roller 7 must have a medium resistance of 10 ⁷ to 10 ¹⁰ Ω. image disturbance does not occur even on the intermediate transfer roller 5 with a low resistance of the resistance R ₂₂ potential contrast no 10 ³ to 10 ⁶ Omega-mentioned image portions and non-image portion on the photosensitive drum 1.

The power supply 81 has a constant current characteristic as the paper sheet 1.
0 of the resistor R ₃ is is desirable so as to impart a constant current value is also different.

[0057] or more and the resistivity [rho ₁ of the intermediate transfer roller 5 in the examples the results of testing the transfer performance resistivity [rho ₂ of the transfer roller 7 as a different value shown in Table 1.

[0058]

[Table 1] In Table 1, the NG ₁ in which the image is distorted during the primary transfer, and NG ₂ in which the image is distorted during the secondary transfer.
Δ is OK under normal use conditions, but when the resistance R ₃ of the paper sheet 10 is high, that is, on the back side of paper that has been left in a low-humidity environment for a long time or paper that has once passed through a heat fixing device. This means that when performing double-sided color printing for forming a color image, image disturbance occurs.

As described in the description of the conventional example, the image disturbance at the time of the secondary transfer is caused by poor transfer due to local breakdown and winding of the paper sheet 10 around the intermediate transfer roller 5. In the "" or "な か っ" area, the paper sheet 10 did not wind.

By combining these, the resistance R _{22 of the} transfer roller 7 is
There smaller than the resistance R ₂₁ of the intermediate transfer roller 5, and the resistance R ₂₁ of the intermediate transfer roller 5 can be obtained excellent transfer performance when in resistance region in the 10 ⁶ ~10 ⁹ Ω.

In the above embodiment, the elastic layer 7 of the transfer roller 7 is used.
2 was a foam, but this was used as a solid elastic layer 72 of urethane rubber, silicon rubber, fluorine rubber, etc., and the surface was made to be a uniform surface with little unevenness, and was constantly brought into contact with the intermediate transfer roller 5. A configuration may be adopted in which a bias voltage having the same polarity as that of the toner is applied to the gold 71 to prevent transfer of the toner from the intermediate transfer roller 5 to the transfer roller 7.

FIG. 2 is a diagram showing a charge arrangement model in the second transfer nip region N2 in this embodiment. 11 and 1
Unlike the second conventional example, it can be seen that the transfer roller 7 becomes an electrode closer to the paper sheet 10 and the dielectrically polarized paper sheet 10 is attracted to the transfer roller 7 side. In order to prevent the paper sheet 10 from being wound around the intermediate transfer roller 5, the intermediate transfer roller 5 is moved upward and the transfer roller 7 is moved downward so that the direction of gravity acting on the paper sheet 10 is directed toward the transfer roller 7. Is preferably arranged.

<Second Embodiment> (FIG. 3) FIG. 3 is a schematic diagram of a main part of an image forming apparatus according to a second embodiment of the present invention. The device configuration and image forming operation other than those described below are the same as in the first embodiment.

The intermediate transfer roller 5 is a medium-resistance roller as in the first embodiment. The transfer roller 7 is a roller having a diameter of 30 mm obtained by mirror-finishing an aluminum pipe, and does not have the elastic layer 72 in which the conductivity-imparting material is dispersed in the surface layer like the transfer roller 7 of the first embodiment. It is configured to directly contact the back surface of the paper sheet 10. Resistance R ₂₂ of the metal roller is 10 ⁰ to 10 ² Omega, than the intermediate transfer roller 5 of a medium resistivity with a low resistance, further resistance is uniform, breakdown by conductive material dispersed heterogeneous Therefore, good transfer performance and an effect of preventing the paper sheet 10 from winding around the intermediate transfer roller 5 can be obtained.

Further, the hardness of the intermediate transfer roller 5 is JIS A
At 35 degrees, the transfer roller 7 is made of aluminum, is a rigid body having a Young's modulus of 1.0 × 10 ¹¹ N · m ⁻² , and the Young's modulus converted value of the intermediate transfer roller 5 is 1.6 × 10 ^4.
Is sufficiently harder than N · m ^-2 , and the transfer roller 7 has a total pressure of 80
By pressing the intermediate transfer roller 5 with 0 gr weight, the surface layer 52 of the intermediate transfer roller 5 is deformed into a concave shape as shown in FIG.
Is formed, and the sheet body 10 is conveyed along this nip shape, so that the sheet body 10 is not wound around the intermediate transfer roller 5 in combination with the electrostatic attraction effect of the transfer roller 7.

To prevent the paper sheet 10 from being wound around the intermediate transfer roller 5, the transfer roller 7 is displaced upstream from the lowermost point of the intermediate transfer roller 5, and the paper sheet 10 is placed on the intermediate transfer roller 5. 5, the leading end of the paper sheet 10 after the second transfer nip area is discharged is made farther from the intermediate transfer roller 5 by using the stiffness of the paper sheet body 10 so as to be inserted into the second transfer nip. Is preferred.

Third Embodiment (FIG. 4) FIG. 4 shows a schematic configuration of an image forming apparatus according to a third embodiment of the present invention. The same reference numerals are given to the same constituent members and portions as those in the apparatus of FIG. 1 described above, and the description will not be repeated.

Reference numeral 13 denotes the photosensitive drum 1 to the intermediate transfer drum 5
A pre-charger for reducing the difference between the dark and light portions of the surface potential of the photosensitive drum 1 prior to the primary transfer of the toner image to the
For example, a potential difference of 500 V between light and dark portions is converged within 200 V.

When the potential on the photosensitive drum 1 is equalized as described above, the difference between the light and dark portions of the transfer current at the time of the primary transfer is reduced, so that the resistance R ₂₁ of the surface layer 52 of the intermediate transfer roller 5 is reduced to 10 ^3.
Even when the resistance is set to 10 ⁵ Ω, image disturbance during transfer does not occur.

The pre-charger 13 may be appropriately configured such as a device that performs a negative charge by using a negative corona discharge so as to make the bright portion potential close to the dark portion potential, and a device that removes the charge by using an AC corona discharge.

It is also possible to arbitrarily select exposure instead of the pre-charger 13 to reduce the contrast in the bright and dark areas by exposing.

The transfer roller 7 has a thickness of 50 μm obtained by dispersing carbon and imparting conductivity to an aluminum core 71.
The PFA tube 72 is bonded to the outside diameter of 30 mm and the resistance R
₂₂ = 10 ³ [Ω].

The PFA tube 72 has excellent releasability, and easily peels off even if toner adheres to the surface thereof. By switching the polarity to minus, there is an advantage that the toner can be returned to the intermediate transfer roller 5 and collected by the cleaner 11.

In this embodiment, since the transfer is performed under extremely low resistance during the primary transfer, the output voltage of the power source 6 is 100
Is sufficient V or less, the power source 81 of the transfer roller 7 may be considered only to provide transfer current to the resistance R ₃ of Kamihatai 10, suffice about 500V～1000V.

Table 2 shows test results obtained by changing the resistivity ρ and the resistance R of the intermediate transfer roller 5 and the transfer roller 7 with respect to the winding of the paper sheet 10.

[0076]

[Table 2] The symbol Δ indicates that there is no problem under the normal environment, but the paper sheet 10 left for a long period of time in a low humidity environment or winding occurs during double-sided printing.

[0077] it is possible to transport the stable Kamihatai 10 to be smaller than the resistance R ₂₁ of resistor R ₂₂ of the transfer roller 7 thus intermediate transfer roller 5. Further, by using the intermediate transfer roller 5 and the transfer roller 7 having low resistance, the resistance fluctuation due to the environment occurring in the medium resistance region does not occur, and the power supply voltage control (ATVC method or the like) according to the resistance value becomes unnecessary. Further, the low-resistance roller has a merit that stable production can be performed as compared with the medium-resistance roller, and lower cost can be realized.

<Fourth Embodiment> (FIG. 5) FIG. 5 is a schematic diagram of a main part of an image forming apparatus according to a fourth embodiment of the present invention. The device configuration and image forming operation other than those described below are the same as in the first embodiment.

This embodiment is characterized in that the intermediate transfer roller 5 is
A thick elastic layer 52 of 3 mm to 10 mm made of a foam such as EPDM / chloroprene / urethane in which a conductivity-imparting material such as carbon / zinc oxide / tin oxide / conductive whisker is dispersed is formed on a cored bar 51. 5-3 such as urethane, PFA, PVdF or the like in which a conductivity imparting material is dispersed in the upper layer 53
JIS A hardness of 4 having a thin surface layer 53 of 0 μm
A low-hardness roller having 0 degree or less or Asker C hardness of 60 degrees or less is used.

Compared with the Young's modulus of the intermediate transfer roller 5 of 5 × 10 ⁷ N · m ⁻² shown in the conventional example, the converted value of the intermediate transfer roller 5 of this embodiment is 2.3 × 10 ³ N · m. ^-2 or less, the transfer roller 7 having a relatively high hardness, that is, a solid elastic body 72 such as urethane, silicon rubber, or fluoro rubber in which a conductivity-imparting material is dispersed is formed on a core metal 71 as shown in the conventional example. In combination with the transfer roller described above, the shape of the second transfer nip area N2 can be concave toward the intermediate transfer roller 5, and the paper sheet 10 can resist the electrostatic attraction force.
Can be transported away from the

Table 3 shows the intermediate transfer roller 5 and the transfer roller 7.
The results of testing the transportability of the paper sheet body 10 with different hardnesses are shown. In this test, the resistance R ₂₁ of the intermediate transfer roller 5 is set to 10 ⁷ to 10 ⁸ [Ω], and the resistance R _{22 of the} transfer roller 7 is
Is 10 ⁷ to 10 ⁸ [Ω], and the transfer voltage is 500 to 1
Transfer was performed at 500 [V].

[0082]

[Table 3] △ indicates that the paper sheet 10 having a normal basis weight of 75 to 135 gr / m ² is OK, but the thin paper sheet 10 having a basis weight of 50 to 64 gr / m ² may be wound. .

As described above, the hardness of the intermediate transfer roller 5 is set to 40
Degree (JIS A) or less, and the hardness of the transfer roller 7 is made larger than the hardness of the intermediate transfer roller 5, so that the shape of the second transfer nip region N2 can be concave toward the intermediate transfer roller 5 side. Winding can be prevented by using the body of the body 10.

The hardness of the intermediate transfer roller 5 is J40 degrees (J
In the region exceeding IS A), the pressing force of the transfer roller 7 needs to be 5000 gr weight or more in order to make the shape of the second transfer nip region N2 concave toward the intermediate transfer roller 5, and the rotation torque becomes large. In addition to the difficulty in smooth conveyance, the pressing force acting on the toner is also large, and good transfer performance cannot be obtained.

Also in this embodiment, as described in the second embodiment, the transfer roller 7 is disposed so as to be shifted upstream from the lowermost point of the intermediate transfer roller 5, and the sheet 10 is Is inserted in the second transfer nip area N2 along the direction, and the effect of realizing the stable conveyance of the paper sheet 10 is recognized.

<Fifth Embodiment> (FIGS. 6 and 7) FIG. 6 is a schematic diagram of a main part of an image forming apparatus according to a fifth embodiment of the present invention. The device configuration and image forming operation other than those described below are the same as in the first embodiment.

The transfer roller 7 is configured such that the shape of the second transfer nip region N2 is concave toward the intermediate transfer roller 5 according to the combination with the hardness of the intermediate transfer roller 5, as in the fourth embodiment. The feature of the present embodiment is that the amount of bite of the transfer roller 7 into the intermediate transfer roller 5 is increased corresponding to the leading end of the sheet 10, and the amount of bite is small in the subsequent portion of the sheet 10. That is to say.

The bite amount of the transfer roller 7 is controlled by switching the position of the transfer roller positioning lever 14.
By doing so, the leading end of the paper sheet 10 can be easily peeled off from the intermediate transfer roller 5 and the pressing force to the subsequent portion is reduced, so that the paper sheet 10 does not curl as a whole.

The broken line in FIG. 6 shows the positional relationship between the paper sheet 10 and the transfer roller 7 in the succeeding portion. Further, the output voltage of the transfer power supply 81 is reduced by the amount corresponding to the increase in the nip width at the leading end portion, and the output voltage is controlled to increase as the nip width decreases in the subsequent portion, so that the transfer current is controlled. Is set to be a constant value over the entire area of the paper sheet 10, and the transfer performance can be further stabilized.

FIG. 7 shows how the nip width w ₂ and the transfer voltage change with time at this time.

<Sixth Embodiment> (FIGS. 8 to 10) FIG. 8 is a schematic diagram of a main part of an image forming apparatus according to a sixth embodiment of the present invention. The device configuration and image forming operation other than those described below are the same as in the first embodiment.

The transfer roller 7 is configured such that the shape of the second transfer nip area N2 is concave toward the intermediate transfer roller side in combination with the intermediate transfer roller 5 as in the fourth embodiment. The feature of this example is that a static elimination needle 17 made of a thin sheet metal as shown in FIG.
The static eliminator 15 housed in a holder 16 made of an insulating resin such as Noryl is disposed downstream of the transfer roller 7 in the paper sheet transport direction, and the insertion direction of the paper sheet 10 into the second transfer nip region N2 and The paper sheet 10 discharged from the nip oriented according to the shape of the nip is conveyed while being supported by the holder 16, so that more stable conveyance of the paper sheet 10 is realized.

When the process speed is as low as about 50 mm / sec, the discharging needle 17 is grounded so that the
0 is sufficiently neutralized, but at medium to high speeds exceeding 100 mm / sec, the neutralization needle 17 is more effectively neutralized by applying a reverse polarity or alternating current bias to the transfer power supply 81 from a power supply (not shown). Yes, holder 16 and paper leaf 10
Of the toner image due to the charging due to the contact of the toner.

In order to stably transport the paper sheet 10, the opening of the holder 16 is set to 3 to 7 mm, the height of the upstream wall is made higher than the height of the downstream wall, and paper is inserted into the opening. Leaf 10
It is good not to let the tip of the rush.

As shown in FIG. 10, a rotatable roller 18 may be provided at the opening to reduce the transport resistance of the paper sheet 10.

[0096]

As described above, according to the present invention,
The resistance of the transfer charging member is smaller than the resistance of the intermediate transfer member.
The effect of drawing the recording material to the transfer charging member side
As a result, the hardness of the intermediate transfer member is higher than the hardness of the transfer charging member.
The transfer nip, which is small and has a concave
Recording by a structure formed by a transfer body and a transfer charging member
Intermediate transfer material of recording material
It is possible to effectively prevent winding around. Also,
Furthermore, the hardness of the intermediate transfer member is 40 degrees (JIS-A) or less.
According to one configuration, low pressure is applied when making the nip shape concave
As a result, it can be transported smoothly due to large rotating torque.
When it becomes difficult to feed or when a large force acts on the toner
Prevent problems such as transfer failure due to toner image collapse
Can do things.

[0097]

[Brief description of the drawings]

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

FIG. 2 is a charge distribution model diagram in a second transfer nip region.

FIG. 3 is a schematic diagram of a main part of an image forming apparatus according to a second embodiment.

FIG. 4 is a schematic configuration diagram of an image forming apparatus according to a third embodiment.

FIG. 5 is a schematic diagram of a main part of an image forming apparatus according to a fourth embodiment.

FIG. 6 is a schematic diagram of a main part of an image forming apparatus according to a fifth embodiment.

FIG. 7 is a graph showing a change with time of a nip width and a transfer voltage in a second transfer nip region.

FIG. 8 is a schematic diagram of a main part of an image forming apparatus according to a sixth embodiment.

FIG. 9 is a plan view of a static elimination needle.

FIG. 10 is a side view of a modified example of the static elimination needle holder.

FIG. 11 is a schematic configuration diagram of a conventional device.

FIG. 12 is a model diagram of charge distribution in a second transfer nip region.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (first image carrier) 2 primary charger 3 exposure 4 developing device 5 intermediate transfer roller (second image carrier) 6 bias power supply for intermediate transfer roller 7 transfer roller (contact transfer member) 81 transfer Roller bias power supply 9 switch 10 paper sheet (third image carrier) 11 cleaner for intermediate transfer roller 12 cleaner for photosensitive drum 13 pre-transfer charger 14 transfer roller positioning lever 15 static eliminator 16 holder 17 static elimination needle 18 roller

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yozo Hotta 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yuko Ogama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside (72) Inventor Masahiro Goto 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Satoru Sawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. ( 56) References JP-A-4-281485 (JP, A) JP-A-4-335381 (JP, A) JP-A-50-156941 (JP, A) JP-A 1-269967 (JP, A) JP JP-A-5-134562 (JP, A) JP-A-3-243973 (JP, A) JP-A-6-289729 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15 / 16 G03G 15/01 114

Claims (6)

(57) [Claims] An image bearing member for carrying an image, an intermediate transfer member, and a transfer charging member for transferring an image on the intermediate transfer member transferred from the image carrier to a recording material; In an image forming apparatus in which the transfer charging member presses a recording material against the intermediate transfer member when transferring an image on the intermediate transfer member to a recording material, a resistance value of the transfer charging member is a resistance value of the intermediate transfer member. Less than the hardness of the intermediate transfer member, the transfer charge
A shape that is smaller than the hardness of the member and the side of the intermediate transfer member is concave
The transfer nip of the intermediate transfer body and the transfer charging member
Image forming apparatus characterized by being formed by. Hardness of 2. A front Symbol intermediate transfer member, 40 degrees (JI
The image forming apparatus according to claim 1, S · A) wherein the der Turkey below. 3. An image bearing member for bearing an image, and an intermediate transfer member.
And an image on the intermediate transfer body transferred from the image carrier
And a transfer charging member for transferring the image to a recording material.
When transferring the image on the transfer body to the recording material, the transfer charging unit
The material is used in an image forming apparatus that presses the recording material against the intermediate transfer body.
Oite, hardness of the intermediate transfer member, than the hardness of said transfer charging member
Smaller than 40 degrees (JIS-A)
The transfer nip in which the intermediate transfer body side is depressed is the intermediate transfer.
Formed by the body and the transfer charging member, the pressing force of the transfer charging member is greater when the trailing portion of the recording material passes through the transfer nip than when the leading end of the recording material passes through the transfer nip. images forming device you <br/> being smaller. 4. An image bearing member for bearing an image, and an intermediate transfer member
And an image on the intermediate transfer body transferred from the image carrier
And a transfer charging member for transferring the image to a recording material.
When transferring the image on the transfer body to the recording material, the transfer charging unit
The material is used in an image forming apparatus that presses the recording material against the intermediate transfer body.
Oite, hardness of the intermediate transfer member, than the hardness of said transfer charging member
Smaller than 40 degrees (JIS-A)
The transfer nip in which the intermediate transfer body side is depressed is the intermediate transfer.
Further comprising a static elimination needle formed of a body and the transfer charging member , provided downstream of the transfer nip in the transport direction of the recording material, and housed in an insulator holder, and transporting the recording material in contact with the holder. images forming device you <br/> characterized by. 5. any of claims 1 to 4 wherein the transfer charging member is characterized by transferring a plurality of color images of on the intermediate transfer member is transferred sequentially superimposed from the image bearing member onto a recording material Image forming apparatus. 6. The image forming apparatus according to claim 1, wherein the intermediate transfer member and the transfer charging member are formed in a roller shape.