JPH05333725A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent irregularities in a transfer image with a simple constitution by making an intermediate transfer body for transferring an image formed on a 1st image carrier to be a medium resistance elastic roller. CONSTITUTION:When the toner image on a photosensitive drum 1 is transferred-to an intermediate transfer roller 20, the potential of a non-image part is different from the potential of the toner image part, and when the potential of a core bar 21 as a reference, the potential difference between the non- image part and the core bar 21 is larger than the potential difference between the toner image part and the core bar, so that a transfer current flows to the non-image part more as compared with the toner image part. This inclination is remarkably generated when the resistance value of the intermediate transfer roller is low, on the contrary, when the resistance value is high, an electrical field generated by a bias supply 61 is too small, so that the intermediate transfer itself is damaged. Thus, the medium resistance roller whose resistance value is within 10<5>-10<11>OMEGA.cm, preferably, 10<7>-10<10> case of using an elastic body having such a volume resistance value, a proper transfer current value can be set by impressing the voltage of 2 to 5kV on the core bar 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer type image forming apparatus,
That is, a transferable image (visual image) of desired image information is formed and carried on the first image carrier by the image forming process, and the transferable image is transferred to the second image carrier to form an image-formed product. Is output, or the transferable image formed and carried on the first image carrier is once transferred onto the intermediate transfer member and then transferred to the second image carrier.
The present invention relates to an image forming apparatus such as a copying machine, a printer, or a fax machine, which further transfers the image formed product onto the image carrier.

In the above, the first image carrier is, for example, an electrophotographic photoreceptor, an electrostatic recording dielectric, a magnetic recording magnetic body or the like.

The image forming process is, for example, an electrophotographic process.
The electrostatic recording process, the magnetic recording process, and the like.

The second image carrier is, for example, a sheet material such as a transfer material, recording paper or printing paper.

[0005]

2. Description of the Related Art FIG. 21 schematically shows an example of an image forming apparatus using an intermediate transfer member. The image forming apparatus of this example is a color image forming apparatus (copier or laser beam printer) using an electrophotographic process.

[0006]. Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (hereinafter,
It is referred to as a photosensitive drum), and is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed (process speed).

The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a primary charger (corona discharger) 2 in the course of rotation, and then image exposure means (not shown) (color separation of color original image The first exposure of the target color image by receiving the image exposure 3 by the imaging exposure optical system, the scanning exposure system by the laser scanner which outputs the laser beam modulated corresponding to the time series electric digital pixel signal of the image information). An electrostatic latent image corresponding to the color component image (for example, magenta component image) is formed.

Then, the electrostatic latent image is magenta toner M of the first color by the first developing device 41 (magenta developing device).
It is developed with (colored charged particles). At this time, the second to fourth developing devices 42, 43, 44 (cyan, yellow, and black developing devices) are in the operation-off state and do not act on the photosensitive drum 1, and the first color magenta toner The image is not affected by the second to fourth developing units 42 to 44.

Reference numeral 5 denotes an endless intermediate transfer belt as an intermediate transfer member, which is suspended between three rollers 6, 71 and 72 of the conductive roller 6 and two turn rollers 71 and 72, The conductive roller 6 holds the belt 5 in pressure contact with the photosensitive drum 1 with a predetermined pressing force, and a transfer nip portion N as a transfer portion is formed between the photosensitive drum 1 and the intermediate transfer belt 5. Has been done.

The intermediate transfer belt 5 is rotationally driven in the counterclockwise direction indicated by the arrow at the same peripheral speed as the photosensitive drum 1.
A transfer bias having a polarity (plus) opposite to the toner charging polarity (negative in this example) of the formed and carried toner image on the photosensitive drum 1 is applied to the conductive roller 6 from the first bias power source 61. The intermediate transfer belt 5 is a dielectric film such as polyester / polyethylene or a composite layer type dielectric film whose back is lined with a conductor.

Thus, while the magenta toner image of the first color formed and carried on the surface of the photosensitive drum 1 passes through the transfer nip portion N, an electric field formed in the transfer nip area by the transfer bias applied to the conductive roller 6. Thus, the intermediate transfer is sequentially performed on the outer surface of the rotary intermediate transfer belt 5.

The surface of the photosensitive drum 1 which has finished transferring the magenta toner image of the first color onto the intermediate transfer belt 5 is cleaned by the cleaning device 14.

Similarly, the following: Charge on the rotating photosensitive drum 1 → image exposure 3 corresponding to a second color component image (for example, a cyan component image) → development with the cyan toner C of the second developing device 42 (cyan developing device) → the formed second color Transfer of a cyan toner image to the intermediate transfer belt 5 → cleaning of the surface of the photosensitive drum 1 by the cleaning device 14 ,. Charging of the rotating photosensitive drum 1 → image exposure 3 corresponding to a third color component image (eg, yellow component image) → third
Development with the yellow toner Y of the developing device 43 (yellow developing device) → transfer of the formed yellow toner image of the third color onto the intermediate transfer belt 5 → cleaning of the photosensitive drum 1 surface with the cleaning device 14. Charging of the rotating photosensitive drum 1 → image exposure 3 corresponding to a fourth color component image (for example, black component image)
→ Development with the black toner B of the fourth developing device 44 (black developing device) → Transfer of the formed black toner image of the fourth color onto the intermediate transfer belt 5 → Cleaning of the photosensitive drum 1 surface by the cleaning device 14 By sequentially executing the image forming and transfer cycles of No. 1 to No. 4, the above four toner images (toner images of magenta, cyan, yellow, and black) are sequentially superposed on the outer surface of the rotary intermediate transfer belt 5. A composite color toner image (mirror image) corresponding to the target color image is formed by transfer.

Next, from the paper feed cassette 9 to the paper feed roller 1
Transfer material (paper sheet) as the second image carrier by 0
24 is separated and conveyed to one sheet, and is fed to the transfer nip portion N at a predetermined timing through the register roller pair 11 and the transfer guide 12.

The bias power source for the conductive roller 6 is switched from the first power source 61 to the second bias power source 62 so that the bias of the same polarity (-) as the toner of the transferred composite color toner image on the intermediate transfer belt 5 is conductive. By being applied to the roller 6, the transfer composite color toner image on the intermediate transfer belt 5 is sequentially transferred to the surface of the transfer material 24 fed to the transfer nip portion N.

The intermediate transfer belt 5 passes through the transfer nip portion N.
The transfer material 24 on which the above toner image has been transferred is introduced into the fixing device 15 via the conveyance guide 13 and is heated and pressed by the fixing roller 16 and the pressure roller 17 which are heated and regulated in a predetermined temperature to form a toner image. And is output as a color image formed product.

Reference numeral 8 denotes a cleaning device for the intermediate transfer belt 5, which is normally held in a non-operating state with respect to the belt 5, but when the transfer of the toner image onto the transfer material 24 is completed, the cleaning device 8 is provided on the outer surface of the belt 5. On the other hand, the cleaning device 8 operates to clean the outer surface of the belt 5.

FIG. 22 shows a transferable toner image formed and carried on the surface of the rotary photosensitive drum 1 as the first image carrier by the transfer roller 23 as a transfer material 24 as the second image carrier.
1 is a schematic view of an example of an image forming apparatus of a type in which the image is transferred to a sheet. The same components, members, and parts as those of the image forming apparatus shown in FIG. 21 are designated by the same reference numerals, and the description thereof will be omitted.

Reference numeral 2A is a contact charging roller as a primary charging device for uniformly charging the surface of the photosensitive drum. 2B is a power source for applying a charging bias to the charging roller 2A.

The image forming apparatus of this embodiment is a laser beam printer, and the photosensitive drum 1 is uniformly charged with a negative polarity by a charging roller 2A, and the charged surface thereof is provided with desired image information by a laser scanner (not shown). The scanning exposure 3 of the laser beam that is modulated and output according to the time-series electric digital pixel signal of is performed. As a result, the negative charges in the portion of the surface of the photosensitive drum 1 where the laser beam scanning exposure 3 has been performed are removed, and an electrostatic latent image is formed.

Next, the surface of the photosensitive drum 1 is subjected to reversal development by a reversal developing device 4 containing a toner t of negative polarity.
As shown in FIG. 3, the toner t adheres to the exposure charge eliminating portion on the surface of the photosensitive drum 1 to form _a toner image ta.

The transfer roller 23 is comprised of a cored bar 23a and a conductive elastic layer 23b concentrically provided on the outer periphery of the cored bar 23a.
Is a roller composed of a roller, which is pressed against the photosensitive drum 1 with a predetermined pressing force, and rotates forward at the same peripheral speed as the photosensitive drum 1.

At the transfer nip portion N between the photosensitive drum 1 and the transfer roller 23, the transfer material 24 separated and conveyed from the paper feed cassette 9 by the paper feed roller 10 is transferred to the register roller 1.
1. The toner is fed at a predetermined timing through the transfer guide 12, and a transfer bias voltage having a polarity (+) opposite to that of the negative polarity toner is applied to the transfer roller 23 from the bias power source 23A to the transfer nip portion N. By the action of the electric field formed, the toner image on the surface of the photosensitive drum 1 is transferred t _b to the surface of the transfer material 24 as shown in FIG.

That is, the side of the transfer material 24 fed to the transfer nib portion N facing the transfer roller 23 is charged with positive charge, and the toner t is attracted to the transfer material 24 side between the transfer material 24 and the photosensitive drum 1. The electrostatic field in the direction
When the transfer material 24 passes through the transfer nip portion N, it is transferred t _b from the surface side of the photosensitive drum 1 to the transfer material 24 surface side.

[0025]

[Problems to be Solved by the Invention]

(I) The device using the belt 5 made of a dielectric material as the intermediate transfer member like the device shown in FIG. 21 has the following drawbacks.

A) Image disturbance at the time of transfer To transfer the toner image formed and carried on the surface of the photosensitive drum 1 as the first image carrier to the electrically insulating intermediate transfer belt 5, in order to transfer the image to the conductive roller 6. The applied voltage of the transfer bias must be increased, and a strong electric field is generated in the transfer nip portion N and the space before and after it.

Therefore, the toner image on the photosensitive drum 1 is attracted to the intermediate transfer belt 5 in front of the transfer nip portion N (on the upstream side of the transfer nip portion N in the transfer material conveying direction), and the so-called "splitting" occurs around the original image. May occur.

Further, static electricity is generated by friction between the insulating intermediate transfer belt 5 and the photosensitive drum 1, or between the insulating intermediate transfer belt 5 and the transfer material 24, and a peeling discharge mark is formed on the intermediate transfer belt 5. It may occur and disturb the image.

Furthermore, in order to obtain a strong electric field, the first or second
When the voltage applied from the bias power sources 61 and 62 to the conductive roller 6 is increased, the current leaks through minute defects such as pinholes that may exist in the intermediate transfer belt 5, and the intermediate transfer belt 5 and the photosensitive drum 1 May be damaged.

When such a current leak occurs, the toner image cannot be transferred onto the belt 5 as an intermediate transfer member, and the toner image transferred onto the intermediate transfer belt 5 is partially missing.

B) Cleaning of the surface of the intermediate transfer belt 5 Since the intermediate transfer belt 5 is insulating, toner is transferred from the belt 5 to the transfer material 24 side when the toner image is transferred from the intermediate transfer belt 5 side to the transfer material 24 side. Even if a bias voltage repulsive to is applied to the conductive roller 6 from the second bias power source 62, 100% of the toner does not move from the intermediate transfer belt 5 side to the transfer material 24 side, and transfer residual toner occurs.

A cleaning device 8 is required to remove and clean the transfer residual toner from the surface of the belt 5. Further, the cleaning device 8 must be controlled to contact and separate from the surface of the belt 5 at a predetermined timing. However, it requires a complicated mechanism.

C) Belt drive mechanism The intermediate transfer belt 5 is stretched between the rollers 6, 71 and 72 and is rotatably driven by the turn rollers 71 and 72. -It is usual that one side of 72 is displaced in one axial direction. Therefore, for example, it is necessary to provide a mechanism for correcting the one side movement of the belt 5 by controlling the roller 71 to be inclined in the axial direction. The mechanism becomes complicated.

Therefore, it is a first object of the present invention to provide an image forming apparatus of the type using an intermediate transfer member, which does not have the above problems a) to c).

(II) Further, when the toner image on the photosensitive drum 1 is transferred onto the belt 5 which is an intermediate transfer member, a so-called "blank area" is formed on the toner image T transferred onto the belt 5 as shown in FIG. "A" is apt to occur. This is because the surface of the photosensitive drum 1 has an adhesive force to the toner, and tends to occur as the toner adhesive force of the belt 5 is poor.

On the other hand, the same can be said when the toner images are transferred from the intermediate transfer belt 5 side to the transfer material 24 side after the sequential superimposing transfer process of all the toner images of the first to fourth colors. Contrary to the above, the poorer the toner adhesion force of the belt 5, the less likely it is that voids will occur.

Therefore, in the image forming apparatus using the intermediate transfer member 5 as described above, there is no intermediate transfer member having a surface layer suitable for toner adhesion, and an image having no hollow portion a is formed on the transfer material 24. It was difficult to form.

Therefore, a second object of the present invention is to provide an image forming apparatus of the type using an intermediate transfer member, which is capable of obtaining an image without the hollow portion a as described above.

[0039] (III) the formation carrying toner images t _a of the photosensitive drum 1 surface of the first image bearing member as the device described above Figure 22, Figure 23, has a conductive elastic body 23b, a transfer bias The following problems occur in the case of transferring the toner image carried on the intermediate transfer body to the transfer material by the transfer roller 23 to which the toner is applied by the transfer roller 23 to which the toner is applied, or transferring the toner image carried on the intermediate transfer body to the transfer material. There is.

That is, to explain with reference to FIG. 23 as an example, the transfer material 24 as the second image carrier has a resistivity of 10 ⁷ to 10 ¹⁴ Ω · cm depending on its material, It behaves in a manner that can be considered, and the transfer roller 23 to the transfer material 24
23 (positive charge in FIG. 23) is not easily attenuated, and is induced on the surface of the transfer material 24 facing the photosensitive drum (hereinafter referred to as the surface) and the surface facing the transfer roller (hereinafter referred to as the back surface). Charges are difficult to neutralize.

Further, when the transfer material 24 is discharged from the transfer nip portion N, the transfer material 24 as a whole is positively or negatively charged by peeling charging, but due to the charges induced on the front surface and the back surface of the transfer material 24. When the transfer material 24 is discharged from the transfer nip portion N, the mirroring force also acts, and the transfer material 24 receives a suction force from both the photosensitive drum 1 and the transfer roller 23.

Conventionally, it has been known that the radius r _T of the transfer roller 23 is smaller than the radius r _D of the photosensitive drum 1, r _T <r _D, but the curvature of the transfer roller 23 in the transfer nip portion N is as described above. When 1 / r _T is larger than the curvature 1 / r _{D of the} photosensitive drum 1, when 1 / r _D <1 / r _T, the above-mentioned suction force and the rigidity of the transfer material 24 themselves are combined, and the transfer material 24 is exposed to light. It is discharged from the transfer nip portion N while being sucked to the drum 1 side.

Therefore, the transfer path drawn by the transfer material 24 is biased toward the photosensitive drum 1 side with respect to the tangent line 0 of the transfer nip portion N.

In particular, the front end portion and the rear end portion of the transfer material 24, which are the free ends, tend to be attracted to the photosensitive drum 1, and when the transfer material 24 has a basis weight of 60 to 80 gr / m ^{2 and} is relatively light, The front end or the rear end of the cleaning device 14 (FIG. 22) is rubbed against an object near the transport path, for example, the edge of a tree is contaminated, or the image in the image area is disturbed. In some cases, the tip may not be sufficiently separated from the photosensitive drum 1 and may rush into the cleaning device 14 to cause a jam or the like. In particular, when the diameter of the photosensitive drum 1 exceeds 60 mm and the curvature 1 / r _D is small, such a transfer material separation failure phenomenon is likely to occur in a low humidity environment.

A third object of the present invention is to provide a transfer type image forming apparatus which solves the above problems.

[0046]

The present invention is an image forming apparatus having the following configuration.

(1) In an image forming apparatus in which an image formed on a first image carrier is transferred onto an intermediate transfer member and then further transferred onto a second image carrier, the intermediate transfer member is An image forming apparatus, which is an elastic roller having resistance.

(2) Image formation according to (1), characterized in that image transfer from the intermediate transfer member to the second image carrier is performed at a contact portion between the first image carrier and the intermediate transfer member. apparatus.

(3) In an image forming apparatus in which an image formed on a first image carrier is transferred onto an intermediate transfer member and then further transferred onto a second image carrier, the intermediate transfer member is intermediate. An elastic roller of resistance, which transfers an image formed on a first image carrier to an elastic roller of medium resistance as an intermediate transfer member a plurality of times and then collectively transfers it to a second image carrier. Mode and a second mode in which an image formed on the first image carrier is directly transferred to the second image carrier can be selectively executed, and an intermediate transfer member in the first mode can be selectively used. An image forming apparatus, wherein an elastic roller of resistance acts as a transfer roller in the second mode.

(4) In an image forming apparatus for transferring an image formed on a first image carrier to an intermediate transfer member and then further transferring it to a second image carrier, the intermediate transfer member is An elastic roller having a resistance, which is formed by first transferring the first image formed on the first image carrier to the elastic roller having a medium resistance as an intermediate transfer member, and then transferring the second image on the first image carrier. An image is formed and the second image carrier is introduced into the contact portion formed by the first image carrier and the intermediate transfer member, so that the first image and the second image are formed on both sides of the second image carrier. An image forming apparatus characterized in that they are simultaneously transferred.

(5) In the image forming apparatus for transferring the image formed on the first image bearing member onto the intermediate transferring member, and further transferring it onto the second image bearing member, the surface of the intermediate transferring member. An image forming apparatus, wherein a moving speed is different from a surface moving speed of the first image carrier.

(6) The surface moving speed of the intermediate transfer member is different from the surface moving speed of the second image carrier (5).
The image forming apparatus according to item 1.

(7) In an image forming apparatus in which an image formed on a first image carrier is transferred onto an intermediate transfer member and then further transferred onto a second image carrier, the intermediate transfer member is It is an elastic roller of resistance, and the image transfer from the intermediate transfer member to the second image carrier is performed at the contact portion between the first image carrier and the intermediate transfer member and is formed on the first image carrier. When the image is transferred onto the intermediate transfer member composed of a medium resistance roller, the transfer bias applied from the intermediate transfer member to the first image carrier is controlled to be a constant current I. An image formation characterized in that the bias voltage value V applied to the intermediate transfer member at the time of retransfer of the image on the intermediate transfer member to the second image carrier is determined based on the voltage value V _T at that time. apparatus.

(8) The bias voltage applied to the intermediate transfer member when the image transferred on the intermediate transfer member composed of a medium resistance roller is retransferred onto the second image bearing member is the voltage value. Using V _T , the following transfer voltage calculation formula (A) | V | = a · | V _T | + b (A) a and b are voltage values calculated by constants (including zero) V
The image forming apparatus according to (7), wherein the constant voltage control is performed.

(9) The bias voltage applied to the intermediate transfer member when the image transferred on the intermediate transfer member composed of a medium resistance roller is retransferred onto the second image bearing member is the voltage value. Using V _T , the following transfer voltage calculation formula (A) | V | = a · | V _T | + b (A) a and b are voltage values calculated by constants (including zero) V
Constant voltage control, and the value of the voltage value | V _T | in the equation (A) is compared with a predetermined reference voltage value, and the constants a and b are controlled to be changed to optimum values according to the result. The image forming apparatus according to (7).

(10) When the image forming apparatus has a double-sided image forming function or a multiple image forming function, the constants a and b in the transfer voltage calculation formula (A) are the first surface or the first image forming execution. The image forming apparatus according to (8) or (9), wherein the image forming apparatus is controlled to be changed to an appropriate value based on the difference between the mode and the mode such as the second surface or the second image forming execution mode.

(11) In an image forming apparatus for transferring an image formed on a first image carrier to another image carrier by a transfer means, the transfer means has a transfer roller having a conductive elastic body to which a bias voltage is applied. The transfer roller is pressed by the first image carrier to form a transfer nip portion between the transfer roller and the first image carrier, and the curvature of the transfer roller (1 /
The image forming apparatus is characterized in that r; r is a radius) is smaller than the curvature of the first image carrier.

(12) Another image carrier is a paper sheet,
The image forming apparatus according to (11), wherein the bias voltage corresponding to the front end and the rear end of the paper sheet is smaller in absolute value than the bias voltage corresponding to the image area of the paper sheet. ..

(13) The peripheral length of the transfer roller is larger than the length of the paper sheet, and the tip of the paper sheet is brought into contact with a fixed position on the surface of the transfer roller, and the transfer roller surface at and near the fixed position. The image forming apparatus described in (11) is characterized in that is made of an insulating material.

(14) The transfer roller is used as an intermediate transfer member, images of different colors are formed on the first image carrier, and the images are repeatedly transferred onto the transfer roller to form an intermediate image. The image forming apparatus according to any one of (11) to (13), characterized in that the multiple images are collectively transferred to a sheet later.

[0061]

[Action]

a) By setting the intermediate transfer member to a medium resistance, the transfer bias voltage applied to the intermediate transfer member does not generate a strong voltage in the transfer nip portion with the first image carrier and the space before and after the transfer nip portion, and Even if there is a minute defect such as a pinhole on the intermediate transfer body, it can be set to an appropriate voltage that does not cause current leakage, so that the intermediate transfer can be performed well without causing image distortion such as skipping. it can.

By setting the intermediate transfer member to have a medium resistance, it becomes possible to sufficiently separate the transfer residual image portion on the intermediate transfer member by applying the cleaning bias, and to make the intermediate transfer member after the transfer into a cleaning state. It is not necessary to provide a special cleaning device for the intermediate transfer member, and the device configuration can be simplified.

By making the intermediate transfer member a roller member,
It is not necessary to provide a complicated belt deviation preventing mechanism as in the case of a belt body, and the device configuration can be simplified.

B) Differentiating the surface moving speed of the intermediate transfer member from the surface moving speed of the first image bearing member, and making the surface moving speed of the intermediate transfer member different from the surface moving speed of the second image bearing member. Then, due to the speed difference, shearing force acts to wipe the image from the first image carrier surface to the intermediate transfer member side, and from the intermediate transfer member side to the second image carrier side, thereby improving the transfer efficiency. It is possible to perform image transfer without "blank".

C) When the image on the first image carrier is transferred to the intermediate transfer medium of medium resistance, only the image is transferred without passing through the second image carrier, so that the second image at the time of transfer is transferred. Since it is not necessary to consider the size of the image carrier and the like, constant current bias control is possible. Further, according to the constant current bias control, a voltage that causes a constant current to flow is applied to the first image bearing member, so that the first image bearing member is not affected by resistance fluctuation due to the environment of the intermediate transferring member. A good image can be transferred to.

Further, when the image on the intermediate transfer member is transferred to the second image carrier, the transfer voltage calculation formula (A) is used.
Basically, the intermediate transfer member is controlled at a constant voltage during transfer with the voltage value V calculated by
By comparing the value of V _T | with a predetermined reference voltage value and changing and controlling the constants a and b to correct V, and by performing constant voltage control with the corrected voltage value V, the calculated voltage value V is an intermediate value. Even if the resistance values of the transfer body and the second image carrier fluctuate significantly due to environmental changes, optimum transferability can always be obtained, and a wide margin for transferability can be secured.

Further, in the image forming apparatus having the double-sided image forming function and the multiple image forming function, the constant changing condition of the calculation formula (A) includes the image forming execution mode of the first side (or the first time) and the image forming execution mode of the first side. By changing and controlling the constants a and b in consideration of the mode difference from the two-side (or second) image forming execution mode, there is no difference in transferability between the above two modes, It is possible to always obtain stable transferability in the mode.

D) By making the curvature of the transfer roller smaller than that of the first image carrier, the other image carrier (second image carrier) emerging from the transfer nip portion has a smaller curvature. The toner is fed out on a separation locus biased toward the roller side, and is rubbed with other objects on the surface of the second image carrier due to being sucked by the first image carrier, and jam due to poor separation. Is prevented from occurring.

The transfer bias of the transfer roller is sequence-controlled to weaken the bias value at the front end or rear end of the second image carrier, and an insulating part is provided on a part of the surface of the transfer roller. With the configuration in which the tip portion of the second image carrier is brought into contact with the second image carrier, separation at the time of discharging the second image carrier from the transfer nip portion can be facilitated, and the second image due to poor separation can be obtained. Dirt on the edge of the carrier at the front and rear ends,
It is possible to prevent image distortion and jamming.

[0070]

【Example】

A. The following first to fourth embodiments are embodiments relating to the invention described in claims 1 to 4 of the claims, and the first object (prevention of image disturbance at transfer, device configuration) (Simplification, etc.) has been achieved.

<First Embodiment> (FIG. 1) In FIG. 1, an intermediate transfer elastic roller (intermediate transfer roller) 20 is used in place of the intermediate transfer belt 5 in the image forming apparatus of FIG. 21 as an intermediate transfer member. FIG. 3 is a schematic configuration diagram of an example of an image forming apparatus. The same components, members, and parts as those of the image forming apparatus shown in FIG. 21 are designated by the same reference numerals, and the description thereof will be omitted.

The intermediate transfer roller 20 of this embodiment comprises a pipe-shaped core metal 21 and a medium resistance elastic layer 2 formed on the outer peripheral surface thereof.
It consists of two.

The elastic layer 22 of medium resistance is made of silicone rubber.
Teflon rubber, chloroprene rubber, urethane rubber, EP
An electric resistance value (volume resistivity) of 10 is obtained by blending and dispersing an elastic material such as DM with a metal oxide such as carbon or zinc oxide.
^{It is} a solid or foamed meat layer adjusted to a medium resistance of ⁵ to 10 ¹¹ Ω · cm.

In the image forming apparatus of this embodiment, an A4 size transfer material (paper sheet) 24 is vertically fed and used, and the peripheral length of the intermediate transfer roller 20 is slightly larger than the length of the A4 size transfer material 24. It is set to 314 mm (roller outer diameter 100 mm). The elastic layer 22 has a wall thickness of 8 mm and Asker C
The hardness was set in the range of 20 ° to 40 °.

The intermediate transfer roller 20 is disposed in contact with the lower surface of the photosensitive drum 1 by bearing in parallel with the photosensitive drum 1, and at the same peripheral speed as the photosensitive drum 1, the counterclockwise direction indicated by the arrow. Rotate to.

Reference numeral 25 denotes a transfer roller which is arranged so as to bear in parallel with the intermediate transfer roller 20 and is brought into contact with the lower surface of the intermediate transfer roller 20. The transfer roller 25 has the same peripheral speed as the intermediate transfer roller 20 and the clockwise direction indicated by the arrow. Rotate to.

The transfer roller 25 includes a core metal roller 26,
The release layer 27 is a thin layer formed on the outer periphery of the release layer 27. In this example, the release layer 27 is made of a fluororesin such as PFA / PTFE and has a thickness of 20 to 100 μm.

The process for sequentially forming the toner images of the first to fourth colors on the photosensitive drum 1 is the same as that of the apparatus shown in FIG. The toner is a non-magnetic one-component toner having a volume average particle diameter of 5 to 8 μ and an intrinsic charge amount of −8 to −18 μc / g.
The negative polarity toner of r was used.

In order to sequentially superpose and transfer the toner images of the first to fourth colors from the photosensitive drum 1 to the outer peripheral surface of the intermediate transfer roller 20, the core metal 21 of the intermediate transfer roller 20 is subjected to the first bias power supply 61 for the intermediate transfer roller. To opposite polarity to toner (+)
The transfer bias is applied in the state of being applied. The applied voltage is +2 KV to +5 KV in this example.

In the process of sequentially transferring the toner images of the first to fourth colors from the photosensitive drum 1 to the intermediate transfer roller 20, the core metal 26 of the transfer roller 25 receives toner from the second bias power source 29 for the transfer roller. A bias voltage of the same polarity (-) is applied. This bias voltage generates an electric field that repels the toner image from the transfer roller 25 to the intermediate transfer roller 20, and prevents the transfer of the toner image on the intermediate transfer roller 20 side to the transfer roller 25.

When the toner image on the photosensitive drum 1 is transferred to the intermediate transfer roller 20, the electric potential of the non-image portion is different from the electric potential of the toner image portion. Since the potential difference between the toner image area and the toner image area is larger than the potential difference between the toner image area and the toner image area, the transfer current flows more in the non-image area.

This tendency remarkably occurs when the resistance value of the intermediate transfer roller 20 is low. For example, when the current value to the non-image portion is more than twice the current value to the toner image portion, the non-image portion is The electric field of influences the toner image, and the toner image causes “splitting” in the periphery. That is, the low resistance roller 20 is not suitable for an intermediate transfer member.

On the other hand, in the case of a high resistance roller, the electric field that can be formed by the bias power source 61 becomes too small, and the intermediate transfer itself is damaged.

Therefore, a roller having a medium resistance in the range of 10 ⁵ to 10 ¹¹ Ω · cm, preferably 10 ⁷ to 10 ¹⁰ Ω · cm is suitable for the intermediate transfer member. If the elastic volume 22 having the volume resistance value in this range is used, by applying +2 to +5 KV to the core metal 21, the above-mentioned appropriate transfer current value can be set.

Transfer of the toner images of the first to fourth colors, which have been sequentially superposed and transferred from the photosensitive drum 1 side to the intermediate transfer roller 20 side, to the transfer material 24 is performed from the paper feeding cassette 9 side to the intermediate transfer roller 20. The transfer material 24 is fed to the pressure contact nip portion n with the roller 25 at a predetermined timing, and the bias power source for the core metal 26 of the transfer roller 25 is switched from the second bias power source 29 to the first bias power source 28. Accordingly, a transfer bias having a polarity (+) opposite to that of the toner is applied to the core metal 26. This transfer bias has an absolute value larger than that of the bias applied to the core metal 21 of the intermediate transfer roller 20 from the bias power source 61 and having a polarity (+) opposite to that of the toner. The toner image on the roller 20 side is fed to the pressure contact nip portion n between the intermediate transfer roller 20 and the transfer roller 25.
It is transferred to the side. Transfer material 2 that received the toner image transfer
4 is introduced into the fixing device 15.

When the transfer material 24 passes through the pressure contact nip portion n, the core metal 21 and the transfer roller 25 of the intermediate transfer roller 20.
The second bias power source 6 applies the bias of the same polarity (-) as that of the toner to the core metal 26 of
2, 29.

By this bias switching, the transfer residual toner on the surface of the intermediate transfer roller 20 is returned to the surface of the photosensitive drum 1 and is collected by the cleaning device 14, so that the surface of the intermediate transfer roller 20 is cleaned.

The toner adhering to the surface of the transfer roller 25 is also returned to the surface of the intermediate transfer roller 20, and further returned to the surface of the photosensitive drum 1 and collected by the cleaning device 14, so that the transfer roller 25 is also cleaned.

As described above, the intermediate transfer roller 20 includes the elastic layer 2
Since 2 is a medium resistance, by applying a bias (cleaning bias) having the same polarity as the toner, the transfer residual toner can be sufficiently returned and transferred to the surface of the photosensitive drum 1 to be in a cleaning state, and a special cleaning device can be provided. It is not necessary and the device configuration can be simplified.

The intermediate transfer roller 20 is driven by a cored bar 21.
The structure of the apparatus depends on a gear (not shown) provided integrally with the device, and does not require a complicated structure such as a belt deviation preventing mechanism as in the case where the intermediate transfer member is the belt 5 (FIG. 21). Can be simplified.

<Second Embodiment> (FIGS. 2 to 4) In the apparatus of the first embodiment (FIG. 1), the intermediate transfer roller 2 is used.
The transfer of the toner image from 0 to the transfer material 24 was carried out by feeding the transfer material 24 to the pressure contact nip portion n between the intermediate transfer roller 20 and the transfer roller 25 provided in pressure contact with the intermediate transfer roller 20. Then, as shown in FIG. 2, the photosensitive drum 1 and the intermediate transfer roller 2
The transfer material 24 is fed to the transfer nip portion N with respect to 0, and the transfer roller 25 is not required.

The sequential bias transfer of the toner images of the first to fourth colors from the photosensitive drum 1 side to the intermediate transfer roller 20 side is performed by the first bias power source 6 with respect to the core metal 21 of the intermediate transfer roller 20.
This is executed by applying a transfer bias having a polarity (+) opposite to that of the toner from 1.

The transfer material 24 is fed from the side of the intermediate transfer roller 20.
To transfer the toner image to the side, the bias power source for the core 21 of the intermediate transfer roller 20 is switched from the first bias power source 61 to the second bias power source 62 as shown in the model diagram of FIG. This is executed by applying a bias voltage having the same polarity (-) as the above.

[0094] As in FIG. 4 in the case of monochrome printing, without transferring the photosensitive drum 1 side of the toner image (single-color toner image) t _a to the intermediate transfer roller 20, the photosensitive drum 1 and the intermediate transfer roller 20 The transfer material 24 is fed to the transfer nip portion N at a predetermined timing, and a transfer bias having a polarity (+) opposite to that of the toner is applied to the cored bar 21 of the intermediate transfer roller 20 from the first bias power source 61. transfer t _b to the transfer sheet 24 side of the toner image t _a of the drum 1 side directly
The printing process can be shortened in this case.

Even when the transfer material 24 is present between the photosensitive drum 1 and the intermediate transfer roller 20, there is an unbalanced relationship between the transfer currents of the toner image portion and the non-image portion as described in the first embodiment. Since the elastic layer 22 of the roller 20 has a medium resistance, good transfer is achieved.

In both cases of FIGS. 3 and 4, the removal of the toner adhering to the intermediate transfer roller 20 after the transfer of the toner image onto the transfer material 24 is carried out by the second bias power source 62 with respect to the core metal 21 of the roller 20. By applying a bias voltage having the same polarity (-) as that of the toner, the toner remaining on the roller 20 is transferred back to the photosensitive drum 1 side and transferred, and is collected by the cleaning device 14 of the photosensitive drum 1 to clean the roller 20. ..

<Third Embodiment> (FIG. 5) FIG. 5 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. The apparatus of this example has three bias power sources, first to third, for the intermediate transfer roller 20. The other structure is the same as that of the second embodiment device (FIG. 2). The first and second bias power sources 61 and 62 are respectively applied to the core metal 21 of the intermediate transfer roller 20 at the time of transferring the toner image from the photosensitive drum 1 to the intermediate transfer drum 20, as in the case of the apparatus of the second embodiment. A power supply that applies a transfer bias having a polarity (+) opposite to that of the toner, and a core metal 21 of the intermediate transfer roller 20 having the same polarity (-) as the toner when the toner image is transferred from the intermediate transfer roller 20 to the transfer material 24.
Is a power source for applying the transfer bias of.

The third bias power supply 63 is a cleaning bias application power supply, and after the transfer of the toner image from the intermediate transfer roller 20 to the transfer material 24 is completed, the bias power supply to the cored bar 21 of the intermediate transfer roller 20 is the second power supply 62.
Is switched to the third bias power source 63 and a cleaning bias voltage having the same polarity (-) as the toner is applied to the intermediate transfer roller 20.
Transfer residual toner remaining on the outer peripheral surface of the intermediate transfer roller 2 is returned to the surface of the photosensitive drum 1 at the transfer nip portion N.
0 cleaning is performed. The toner returned to the surface of the photosensitive drum 1 is collected by the cleaning device 14 and the surface of the photosensitive drum 1 is also cleaned.

<Fourth Embodiment> (FIGS. 6 and 7) This embodiment is a double-sided print image forming apparatus capable of printing on both surfaces of the transfer material 24.

In FIG. 6, reference numerals 45 and 46 denote a negative developing device containing negative polarity toner and a positive developing device containing positive polarity toner, respectively.

On the surface of the photosensitive drum 1, first, a latent image of the image information on the first surface is formed, and the latent image is developed by the negative developing device 45 (the positive developing device 46 is kept inoperative), and the minus The polar toner image is temporarily transferred onto the outer peripheral surface of the intermediate transfer roller 20. The intermediate transfer is executed by applying a positive bias voltage to the cored bar 21 of the roller 20 from the first bias power source 61.

Then, the latent image of the image information on the second surface is formed on the surface of the photosensitive drum 1 and the latent image is developed by the positive developing device 46 (the negative developing device 45 is kept inoperative).

Synchronized with the formation of this toner image, the photosensitive drum 1 and the intermediate transfer roller 20 are transferred from the paper feed cassette 9 side.
The transfer material 24 is fed to the transfer nip portion N.

Immediately before the feeding transfer material 24 enters the transfer nip portion N, the bias power source for the core metal 21 of the intermediate transfer roller 20 is switched from the first bias power source 61 side to the second bias power source 62 side, and the core metal is provided. A negative polarity bias voltage is applied to 21. As shown in FIG. 7, as a result, the negative polarity toner image t _c transferred and carried on the side of the intermediate transfer roller 20 with respect to the first surface (downward surface) of the feeding transfer material 24 is also fed. The positive polarity toner image t _d on the surface of the photosensitive drum 1 is transferred to the second surface (upward surface) of the above.

The transfer material 24 exiting the transfer nip portion N has a toner image on both sides, and the conveying guide 13 is directed upward by the fan 13a so that the toner image is guided to the fixing device 15 so as not to rub against other objects. It is configured to generate an air flow. In this way, the toner images on both sides of the transfer material 24 guided to the fixing device 15 are fixed.

As described above, by using the roller 20 as the intermediate transfer member, double-sided printing can be realized with a simple paper conveyance path.

Negative developing unit 4 in the one-sided print mode
5 or the positive developing device 46 is used to form a toner image on the surface of the photosensitive drum 1, and the transfer material 24 is transferred to the transfer nip portion N.
To the core metal 21 of the intermediate transfer roller 20 and a bias voltage having a polarity opposite to that of the toner is supplied to the first or second bias power source 61.
Alternatively, the voltage may be applied at 62.

Even when the toners having different polarities are transferred in this way, the medium resistance roller 20 as an intermediate transfer member exhibits a stable transfer performance and a good image can be obtained.
In the above description, the intermediate transfer roller 20 provided with one elastic layer 22 is exemplified, but a plurality of elastic layers 22 or a configuration in which a smooth surface layer is formed on the elastic layer 22 is used. You can also

As described in the first to fourth embodiments above, by using the medium resistance elastic roller 20 as an intermediate transfer body or a transfer roller, the disturbance of the transferred image can be prevented and a simple mechanism can be used. An image forming apparatus using the intermediate transfer member can be realized. B. The following fifth to eighth embodiments are embodiments of the invention described in claims 5 and 6 of the claims, and achieve the second object (prevention of missing of toner image). is there.

<Fifth Embodiment> (FIGS. 8 and 9) FIG. 8 is a schematic diagram of an image forming apparatus according to this embodiment, which is substantially the same as the apparatus according to the first embodiment (FIG. 1). ..

In the present embodiment, the intermediate transfer roller 20 has a low volume efficiency of 10 by uniformly dispersing fine carbon or metal powder in aramid resin, polycarbonate or fluororesin on the outer periphery of the pipe-shaped core metal 21. ^{7 ~10 10 Ω}
-The thing covered with the resistance layer 22 adjusted to cm was used.

The peripheral length of the intermediate transfer roller 20 is set to be slightly larger than the length of the transfer material sheet 24. In the present embodiment, the transfer material sheet 24 is used by vertically feeding an A4 size. Has an outer diameter of 100 mm and a perimeter of 31
The resistance layer 22 has a thickness of 100 μm.

The transfer roller 25 has a carbon-dispersed EPDM foam material (volume resistivity of about 10 ⁹ Ω · cm) on the outer periphery of the core metal 26.
Is provided as the elastic layer 27 and has an Asker C hardness of 4
The thing of 0 degrees or less was used.

The sequential superposition transfer of the toner images of the first to fourth colors from the photosensitive drum 1 side to the intermediate transfer roller 20 side is the same as in the case of the apparatus shown in FIG. Applies a transfer bias voltage +2 to +5 KV having a polarity (+) opposite to that of the toner from the bias power source 61.

In this embodiment, the transfer roller 25 is held in contact with and separated from the intermediate transfer roller 20 during this transfer process so that the toner image on the intermediate transfer roller 20 is not disturbed.

Reference numeral 8 denotes a cleaning device for the intermediate transfer roller 20, which is normally kept in a non-contact non-operating state with respect to the intermediate transfer roller 20.

Further, the intermediate transfer roller 20 is constituted so as to rotate by 0.5% faster than the peripheral speed of the photosensitive drum 1.
As a result, the toner image on the photosensitive drum 1 is efficiently transferred onto the intermediate transfer roller 20 and "middle-out" is prevented.

The transfer of the toner images of the first to fourth colors, which have been sequentially transferred from the photosensitive drum 1 side to the intermediate transfer roller 20 side, onto the transfer material 24 precedes the leading edge of the toner image on the intermediate transfer roller 20. The transfer roller 25 is the intermediate transfer roller 20.
Then, a bias power source 28 applies a transfer bias voltage having a polarity (+) opposite to that of the toner to the core metal 26 of the transfer roller 25.

Next, the intermediate transfer roller 20 and the transfer roller 2
5, the transfer material 24 enters the pressure contact nip portion n and the transfer material 2
The toner image on the side of the intermediate transfer roller 20 is transferred to the surface of No. 4.

The appropriate voltage value of the transfer bias applied to the core metal 26 of the transfer roller 25 varies depending on the transfer voltage value applied to the core metal 21 of the intermediate transfer roller 20.

Specifically, good transfer was obtained when the transfer bias of the transfer roller 25 to the cored bar 26 was made larger by 2 to 4 KV in absolute value than the transfer bias applied to the cored bar 21 of the intermediate transfer roller 20. ..

In this embodiment, when the toner image is transferred from the intermediate transfer roller 20 to the transfer material 24, the intermediate transfer roller 20
The voltage applied to the core metal 21 of the transfer roller 25 is 3 KV because the voltage applied to the core metal 21 is + 500V.
Set to.

Further, in this embodiment, the peripheral speed of the transfer roller 25 is 0.5% more than that of the intermediate transfer roller 20.
By rotating the transfer material 24 at a high speed, the transfer speed of the transfer material 24 is made higher than the peripheral speed of the intermediate transfer roller 20. As a result, the transfer of the toner image from the side of the intermediate transfer roller 20 to the side of the transfer material 24 is also efficiently transferred to prevent the hollow image.

Therefore, from the photosensitive drum 1 to the intermediate transfer member 20.
After that, the toner image can be transferred to the transfer material 24 while preventing the hollow image.

In this embodiment, the toner image on the photosensitive drum 1 is about 1.5% extended on the transfer material 24 in the sheet conveying direction, but the latent image formed on the photosensitive drum 1 is preliminarily set to 1%. The print magnification is adjusted by reducing the shape by 0.5%.

Here, the effect of preventing a hollow defect due to the difference in peripheral speeds performed in this embodiment will be described. FIG. 9 shows the peripheral speed of the intermediate transfer roller 20 and the level of voids when the peripheral speed of the photosensitive drum 1 is 100. As is clear from the figure, the level of the hollow area is improved by providing the peripheral speed difference. It is considered that the transfer efficiency is improved by applying a shearing force such as wiping the toner image. Such a tendency is caused by the transfer roller 25.
And the transfer material 24 have the same tendency. In this embodiment, the peripheral speed of the intermediate transfer roller 20 with respect to the photosensitive drum 1 and the peripheral speed of the transfer roller 25 with respect to the intermediate transfer roller 20 are determined based on this result. Image formation was carried out at 0.5% faster, respectively, and good results were obtained.

<Sixth Embodiment> In this embodiment, in the image forming apparatus of the fifth embodiment (FIG. 8), the peripheral speed of the intermediate transfer roller 20 is made 1% slower than that of the photosensitive drum 1, and the transfer is performed. The peripheral speed of the roller 25 is 1.5 than that of the intermediate transfer roller 20.
% Faster. The effect of this is to prevent the hollowing out during the intermediate transfer and the transfer and to correct the shrinkage or expansion of the toner image.

That is, when the toner image formed on the photosensitive drum 1 is transferred to the intermediate transfer roller 20, it is contracted by 1% due to the difference in peripheral speed to form a transferred image. When the transfer roller 25 is rotated 1.5% faster when transferring this image to the transfer material 24, the transfer material 24 is actually intermediate between the intermediate transfer roller 20 and the transfer roller 25 having a larger frictional force. Since the image is conveyed at a speed that is approximately 1% faster than the transfer roller 20, the image finally formed on the transfer material 24 can be the same size as that formed on the photosensitive drum 1. Due to this action, it is possible to provide a relatively large peripheral speed difference, and the effect of preventing the hollow portion is correspondingly strong.

<Seventh Embodiment> (FIG. 10) FIG. 10 is a schematic configuration diagram of an image forming apparatus according to the present embodiment, in which a toner image is transferred onto a transfer material 24 by transfer between a photosensitive drum 1 and an intermediate transfer roller 20. This is done at the nip N,
This is almost the same as the device of the second embodiment (FIG. 2).

As shown in the model diagrams of FIGS. 3 and 4, the transfer mode of the four-color toner image from the intermediate transfer roller 20 to the transfer material 24 and the direct transfer of the single-color toner image from the photosensitive drum 1 to the transfer material 24 are performed. Any of the modes can be executed.

The elastic layer 22 of the intermediate transfer roller 20 is 10 ⁷
It has a volume resistivity of -10 ¹⁰ Ω · cm.

In this embodiment, by using the elastic roller 20 as the intermediate transfer member, the transfer material 24 at the transfer nip portion N is
However, the peripheral speed of the roller 20, which is an intermediate transfer member, is 0.5% slower than that of the photosensitive drum 1, so that the transfer with the intermediate transfer roller 20 is performed. A difference in speed is also generated between the material 24 and intermediate loss during transfer and during transfer can be prevented. This is also effective in the case of single-color transfer, but there is also an advantage that the expansion of the image formed on the transfer material 24 can be reduced particularly during the operation of four-color transfer.

As a further development example of this embodiment, 4
Changing the peripheral speed of the intermediate transfer member during the intermediate transfer and during the transfer in the color transfer is also effective in preventing the voids and ensuring the printing accuracy.

For example, the peripheral speed of the intermediate transfer roller 20 is made 0.5% faster than that of the photosensitive drum 1 at the time of intermediate transfer, and 1% faster at the time of transfer. Thus, the image on the transfer material 24 can be made substantially equal to that on the photosensitive drum 1 for the same reason as described in the sixth embodiment. Further, since the peripheral speed difference between the transfer speed of the transfer material 24 at the time of transfer is also sufficiently given, the effect of preventing the voids becomes large.

<Eighth Embodiment> (FIG. 11) FIG. 11 is a schematic view of the configuration of the image forming apparatus of this embodiment, which is an intermediate transfer roller 20 in comparison with the apparatus of the seventh embodiment (FIG. 10). The feature is that the diameter of is small.

That is, this embodiment utilizes the expansion and contraction of the image that occurs when a speed difference is applied between the photosensitive drum 1 and the intermediate transfer body 20, and between the intermediate transfer body 20 and the transfer material 24 during the intermediate transfer and transfer. It is characterized in that the roller 20 as an intermediate transfer member has a circumferential length shorter than that of the transfer material 24.

That is, at the time of four-color intermediate transfer, the peripheral speed of the intermediate transfer roller 20 is set to 50% faster than that of the photosensitive drum 1 so as to prevent voids, and the image on the intermediate transfer roller 20 is enlarged by 50%. It is possible to compress.

When transferring to the transfer material 24, the transfer material 24 is fed to the transfer nip portion N by the register roller 11 at the same speed as the photosensitive drum 1, and the toner image is developed to the original size. At this time, since there is a difference in speed at the time of intermediate transfer between the transfer material 24 and the intermediate transfer roller 20, the void is prevented.

Generally, when the roller 20 is used as the intermediate transfer member, the peripheral length of the roller 20 is required to be equal to or longer than the length of the transfer material 24. However, according to the present embodiment, the peripheral length of the intermediate transfer roller 20 is half, In other words, the diameter can be halved, and there is an advantage that the device can be downsized.

In the case of A4 size vertical feed, the diameter of the intermediate transfer roller 20 is usually required to be 100 mm, which is difficult in terms of separation, but if the means of this embodiment is used, the diameter of the intermediate transfer roller 20 can be increased. The diameter can be reduced to 50 mm, the curvature facilitates separation, and it is also possible to reduce conveyance defects such as jams.

As described above, in the image forming apparatus in which the image formed on the first image carrier is transferred to the intermediate transfer member and then further transferred to the second image carrier, the surface of the intermediate transfer member is transferred. By making the moving speed different from the surface moving speed of the first image carrier, it becomes possible to perform the intermediate transfer without a hollow portion, and further, the surface moving speed of the intermediate transfer member and the surface move of the second image carrier. By making the speed different from that of the image, it was possible to form an image without a hollow image on the second image carrier. In this case, the intermediate transfer member may be of the belt type as shown in FIG.

C. The following ninth to eleventh embodiments are the embodiments of the invention described in claims 7 to 10 of the above-mentioned claims, and are the same as those of the above-mentioned first to eighth embodiments. It is an example of a further improved invention of an apparatus using a roller body of medium resistance as the above.

(1) Medium resistance elastic layer 22 of the intermediate transfer member 20
As described above, the resistance is adjusted by adding and dispersing carbon, metal oxide or the like to the elastic material. The resistance value of such a medium resistance elastic layer 22 fluctuates during manufacturing, or the resistance value fluctuates depending on the environment. Even if such a change in the resistance value of the medium resistance elastic layer 22 occurs, stable intermediate transfer must be performed.

In the conventional constant voltage control, when the resistance value of the intermediate transfer body 20 is high, a sufficient current cannot be passed to the photosensitive drum 1, so the toner image on the photosensitive drum 1 is sufficiently transferred to the intermediate transfer body 20. It becomes impossible and a transfer failure occurs. On the contrary, when the resistance value of the intermediate transfer member 20 decreases in a high humidity environment, a current larger than the appropriate current value flows to the photosensitive drum 1, and the drum memory and the transferred toner return to the photosensitive drum 1 again. Re-transfer phenomenon etc. will occur.

Further, since the proper transfer voltages when transferring the toner images of the first to fourth colors are different, it is difficult to control.

(2) Under a high humidity environment, the intermediate transfer member 20
The resistance value of the transfer material 24 is significantly reduced, and the appropriate transfer voltage when the image on the intermediate transfer body 20 is transferred onto the transfer material 24 is changed.

Therefore, even if the transfer voltage is appropriate in the normal humidity environment, the transfer voltage is too strong in the high humidity environment where the resistance of the transfer material 24 is extremely reduced, and the transfer material punch-through phenomenon of the transfer current occurs. The transfer current is less likely to flow in the portion of the intermediate transfer body 20 where the toner is present, and the transfer current is concentrated in the portion where the toner is not present, and as a result, the "drip" phenomenon of the image may occur. ..

Further, these problems are caused by the fact that when the resistance of the intermediate transfer body 20 is relatively high, the resistance value of the entire system including the photosensitive drum 1, the intermediate transfer body 20, and the transfer material 24 is the transfer material 24.
However, when the resistance of the intermediate transfer body 20 is low, the resistance of the entire system is greatly affected by the resistance fluctuation of the transfer material 24, and the resistance is likely to occur.
Especially in a high-humidity environment, the resistance of the intermediate transfer member 20 tends to be greatly reduced to 1/2 to 1/3 by leaving it for a long time, which is also a main cause for making the above phenomenon easy to occur. There is.

(3) Further, when the image forming apparatus has an automatic double-sided image forming function, a multiple image forming function, etc., the image transfer on the first surface (or the first time) of the transfer material 24 is not possible. By being executed and fixing processing of the transferred image is performed, the transfer material 24 is in a state in which moisture is evaporated and the resistance is increased.

Therefore, when the transfer material 24 is again inserted into the transfer portion for the second surface (or second time) image transfer, the transfer material 24 at this time has a high resistance as described above. In order to perform good transfer at the time of image transfer on the second surface (or second time), a higher transfer voltage is required than at the transfer voltage at which good transfer is performed at the time of image transfer on the first surface (or first time). If it is not applied, a transfer failure will occur.

The item C is an embodiment of an invention in which the above-mentioned problems are further resolved in an apparatus using a roller body of medium resistance as an intermediate transfer body.

<Ninth Embodiment> (FIG. 12) FIG. 12 is a schematic diagram of an image forming apparatus according to the present embodiment, which has substantially the same configuration as the apparatus of the second embodiment (FIG. 2).

The intermediate transfer roller 20 which is an intermediate transfer member has a volume resistivity of 10 ⁵ to 10 ¹¹ on a pipe-shaped cored bar 21 in which fine carbon or metal powder is uniformly dispersed in an elastic body made of EPDM or the like. What is covered with the elastic layer 22 adjusted to Ω · cm is used. The peripheral length of the intermediate transfer roller 20 is set to be slightly larger than the length of the transfer material 24. In the present embodiment, the transfer material 24 is used by longitudinally feeding an A4 size. Therefore, the intermediate transfer roller 20 has an outer diameter of 100 mm and a peripheral length. Three
The elastic layer 22 has a thickness of 8 mm and an Asker C hardness of 30 to 50 degrees.

Specifically, the process speed is 90 mm / s.
ec, the diameter of the photosensitive drum 1 was 30 mm.

Reference numeral 50 is a bias power source for the intermediate transfer roller 20, and the bias power source 50 is a constant current power source.
It can be used as a constant voltage power supply, and the polarity can be changed.

Reference numeral 51 is a bias voltage detecting means for the intermediate transfer roller 20, 52 is a CPU, 53 is an I / O port, 54
Is a memory and 56 is a ground.

The control of this embodiment will be described below.

.. Sequence control is performed by the CPU 52, and the core metal 21 of the intermediate transfer roller 20 is set to I in this embodiment.
A voltage V _T0 for applying a constant current of 4 μA is applied to control the intermediate transfer roller 20 at a constant current, and the toner image is transferred from the ram 1 to the intermediate transfer roller 20 by photosensitization.

Of course, the amount of toner on the intermediate transfer roller 20 increases and the voltage V _T0 also increases each time the first to fourth colors are transferred. In addition, the voltage V _T0 changes according to the amount of toner even within a single color image. The voltage V _T0 at this time has a polarity opposite to that of the toner.

.. Therefore, it is considered that the time point at which the toner image of the fourth color is transferred reflects the resistance value of the entire color image. The transfer voltage V _T0 at the constant current bias control at this time was measured, and the average value [V
Let _T0 ] be the voltage V _T used for control.

.. The measured voltage V _T according to the transfer voltage calculation formula (A) in which the constants a and b are preset predetermined values a1 and b1.
The appropriate transfer voltage value V corresponding to is calculated.

| V | = a · | V _T | + b (A) Then, the toner image on the intermediate transfer roller 20 is transferred to the transfer material 2
When the toner image is transferred to No. 4, the intermediate transfer roller 20 is subjected to constant voltage control with the calculated transfer voltage value V to transfer the toner image onto the transfer material 24. Further, the transfer voltage V at this time is applied so as to have the same polarity as the toner.

Specifically, when the constants a and b were set to a1 = 1.0 and b1 = 1.2, a good transferred image could be obtained.

Further, the constant term b of the calculation formula (A) is a term set by assuming a voltage drop due to the resistance of the transfer material at the time of transfer (at the time of sheet passing).

<Tenth Embodiment> The image forming apparatus of this embodiment is the same as that of the ninth embodiment, but the control is performed in the following procedure.

.. Sequence control is performed by the CPU 52, and the core metal 21 of the intermediate transfer roller 20 is set to I in this embodiment.
A voltage V _T0 for applying a constant current of 4 μA is applied to control the intermediate transfer roller 20 at a constant current to transfer the toner image from the photosensitive drum 1 to the intermediate transfer roller 20.

Of course, the amount of toner on the intermediate transfer roller 20 increases and the voltage V _T0 also increases each time the first to fourth colors are transferred. In addition, the voltage V _T0 changes depending on the amount of toner even within a single color image. The voltage V _T0 at this time is
It has the opposite polarity to the toner.

.. Therefore, it is considered that the time point at which the toner image of the fourth color is transferred reflects the resistance value of the entire color image. The transfer voltage V _T0 at the constant current bias control at this time was measured, and the average value [V
Let _T0 ] be the voltage V _T used for control.

.. The measured voltage V _T is compared with the reference voltage (judgment voltage) V1.

.. In this comparison, when | V _T | ≧ V1, normal control is performed, that is, constants a and b are the same as in the ninth embodiment.
The appropriate transfer voltage value V corresponding to the measured voltage V _T is calculated according to the transfer voltage calculation formula (A) with the predetermined values a1 and b1 set in advance.

When the toner image on the intermediate transfer roller 20 is transferred to the transfer material 24, the intermediate transfer roller 20 is controlled at a constant voltage by the calculated transfer voltage value V to transfer the toner image to the transfer material 24. Let Also, the transfer voltage V at this time
Has the same polarity as the toner.

.. However, when | V _T | <V1, the resistance value of the intermediate transfer member 20 decreases in a high humidity environment, and at the same time, the resistance value of the transfer material 24 also decreases. Judging that it is in a state in which the "drip" phenomenon due to excessive transfer current is likely to occur,
The transfer voltage calculation formula in which the constants a and b are changed and controlled to appropriate a2 and b2 so that the voltage V calculated by the transfer voltage calculation formula (A) becomes small, and the constants a and b are changed to a2 and b2 An appropriate transfer voltage value V corresponding to the measured voltage V _T is calculated according to (A).

When the toner image on the intermediate transfer roller 20 is transferred to the transfer material 24, the intermediate transfer roller 20 is controlled at a constant voltage by the calculated transfer voltage value V to transfer the toner image to the transfer material 24. Let Also, the transfer voltage V at this time
Has the same polarity as the toner.

Specifically, in the above, the reference voltage V1 = 1
KV, constants a and b of the calculation formula (A) were set to a1 = 1.0, b1 = 1.2, a2 = 2.2, b2 = 0.

By doing so, when the absolute value of the measured voltage V _T is 1 KV (= V1) or more, the appropriate transfer voltage value V is calculated as described above, and the intermediate transfer member 20 is calculated according to the calculated voltage value V. During transfer from the transfer medium to the transfer material 24, constant voltage control of the intermediate transfer roller 20 is executed.

When the measured voltage V _T becomes 1 KV or less, the proper transfer voltage value V for weakly outputting the transfer voltage is calculated as described above, and the constant voltage of the intermediate transfer roller 20 at the time of transfer is calculated by the calculated voltage value V. Control is executed.

At the measured voltage V _T = 1 KV, the control voltage is kept continuous because a1 · | V _T | + b1 = a2 · | V _T | = b2, but it is always required to be continuous. There is no.

Further, the voltage serving as a judgment reference for determining the constants a and b is not limited to one voltage V1, but a plurality of voltages may be used.

Further, the constant term b of the transfer voltage calculation formula (A)
Is a term set on the assumption of a voltage drop due to transfer material resistance during transfer (paper passing).

Therefore, when the transfer material 24 absorbs moisture in a high temperature and high humidity environment and the resistance of the transfer material decreases, the transfer voltage V is optimized by reducing the constant term b.

<Eleventh Embodiment> (FIG. 13) FIG. 13 is a schematic diagram of the image forming apparatus according to the present embodiment, which has substantially the same configuration as the apparatus according to the ninth embodiment (FIG. 12).

After the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer roller 20, the toner image is inserted into the transfer nip portion N between the photosensitive drum 1 and the intermediate transfer roller 20 to receive the image transfer on the first surface. The transfer material 24 is the first in the fixing device 15.
After the surface transfer image is fixed, the transfer material 24 is conveyed to the reversing device 81 along the path of the arrow c by the re-feeding device 80 attached to the lower portion of the main body of the image forming apparatus, and the reversing device 81.
And the transfer guide 12 is reintroduced by the path indicated by the arrow d.
The image is transferred to the second surface of the transfer material 24 by being inserted into the transfer nip portion N between the photosensitive drum 1 and the intermediate transfer roller 20. When the operation of the reversing device 81 is turned off, the transfer material 24 is not reversed and the multiple transfer is executed.

In such an apparatus, as described above, the transfer material 24 after the image transfer on the first surface, which is re-fed to the transfer nip portion N for image transfer on the second surface, fixes the image on the first surface. As a result, the resistance value of the transfer material 24 becomes higher than that at the time of image transfer on the first surface due to the dehumidification due to the heat.

Therefore, under high humidity, the resistance of the transfer material 24 at the time of image transfer to the first surface is low, and at the time of image transfer to the first surface of the transfer material 24, it is the same as in the tenth embodiment. As described above, unless the transfer voltage is lowered, an image defect occurs due to excessive transfer voltage. That is, there is no condition that is satisfied when the image is transferred on the first surface and when the image is transferred on the second surface of the transfer material 24.

In such a case, the constants a and b of the transfer voltage calculation formula (A) may be determined in each case in consideration of the conditions of the first surface transfer and the second surface transfer of the transfer material 24.

Therefore, in the tenth embodiment,
After the image is formed on the first side by the procedure of 1., when the image is formed on the second side by the re-feeding device 80 ,. According to the transfer voltage calculation formula (A) in which the constants a and b of the transfer voltage calculation formula (A) in the second-side image formation mode in the double-sided image formation are set to predetermined values a3 and b3, the measured voltage V _T is obtained. A corresponding appropriate transfer voltage V is calculated.

Then, when the toner image on the intermediate transfer roller 20 is transferred onto the transfer material 24, the intermediate transfer roller 20 is subjected to constant voltage control by the calculated transfer voltage value V, and the second transfer image is transferred to the transfer material 24.
Transfer the surface image. Also, the transfer voltage V at this time
Has the same polarity as the toner.

By the control described above, the transfer in the case of double-sided printing and multiplex printing can be executed well.

Specifically, (a) a reference voltage for comparison V1 = 1.0 KV (b) | V _T | ≧ V1 and the constant a of the transfer voltage calculation formula (A) in the first surface image forming mode , B are a1 = 1.0, b1 = 1.2 (c) | V _T | <V1, the constants a and b of the transfer voltage calculation formula (A) in the first surface image forming mode are a2 = 2 ., 2, b2 = 0 (d) In the double-sided image formation, the constants a and b of the transfer voltage calculation formula (A) in the second-side image formation mode are set to a3 = 1.0 and b3 = 1.7, and the control is performed. I did.

As a result, the transfer material 2 is transferred under the above-mentioned high humidity environment.
Even when the resistance value of No. 4 is low, the constants a = a2 and b = b2 are obtained at the time of image transfer to the first surface of the transfer material 24, and due to the excessive transfer voltage, as in the tenth embodiment described above. It was possible to prevent the transfer current from penetrating the transfer material and scattering.

Further, when an image is transferred to the second surface of the transfer material that has been dehumidified and has a high resistance by the fixing process of the transferred image on the first surface, a transfer failure due to insufficient transfer current due to the high resistance of the transfer material 24 is caused. , By setting the constants a = a3 and b = b3,
The transfer voltage was set so that no transfer failure occurred.

The constant term b of the calculation formula (A) is a term set by assuming the voltage drop due to the resistance of the transfer material at the time of transfer (at the time of sheet passing). Therefore, when the transfer material 24 is dehumidified by the fixing device 15 and the transfer material resistance increases,
It is considered that the transfer voltage V is optimized by increasing the constant term b.

The present invention described in claims 7 to 10 of the claims represented by the ninth to eleventh embodiments is limited to the improvement of the transfer performance under the high humidity environment. It goes without saying that the present invention can also be applied to optimize transfer performance in an environment of normal humidity or low humidity.

In the present invention according to claims 7 to 10, the image formed on the first image carrier is transferred onto an intermediate transfer member composed of a medium resistance roller, and then the second image is transferred. In the image forming apparatus for further transferring onto the image carrier, even if the resistance value of the intermediate resistance intermediate transfer member or the resistance value of the transfer material fluctuates significantly due to environmental changes, etc. When transferring the image on the intermediate transfer body, it is possible to obtain optimum transferability by applying a constant current bias to the intermediate transfer body. Also, the image on the intermediate transfer body is transferred onto the transfer material. In doing so, an optimum voltage is applied to the intermediate transfer member to obtain optimum transferability. Further, even in the transfer process when performing double-sided or multiple image formation, there is no difference between the first surface (or the first time) and the second surface (or the second time), and stable transferability is always obtained. D. The following twelfth to fifteenth embodiments are examples of the invention described in claims 11 to 14 of the claims, and the third object (when the transfer material is discharged from the transfer nip portion) Is facilitated and the image disturbance at the time of transfer is prevented).

<Twelfth Embodiment> (FIG. 14) FIG. 14 is an enlarged cross-sectional view of an essential part of the apparatus of this embodiment, in which the photosensitive drum 1 and the transfer roller 23 of the image forming apparatus of FIG.
Of the transfer nip portion N.

The curvature 1 / r ' _T of the transfer roller 23' is smaller than the curvature 1 / r ' _D of the photosensitive drum 1 (1 / r'
_T <1 / r ′ _D ), and when the transfer material 24 is discharged from the transfer nip portion N, the transfer material 24 has a mirror image force attracted to the photosensitive drum 1 side by electric charges on the surface and In addition to receiving a mirroring force that is attracted to the transfer roller 23 ′ side by the electric charge, and the balance of the force that tries to separate from each surface due to the rigidity of the transfer material 24 itself, as a result, it is biased toward the transfer roller 23 ′ side having a small curvature. The separation is done.

In other words, the locus of the transfer material 24 is biased toward the transfer roller 23 'side with respect to the tangent line 0 of the transfer nip portion N, and it rubs against the bottom of the cleaning device 14 (FIG. 23) or has a plunge jam. Will never occur.

The transfer material 24 is sucked by the transfer roller 23 'and discharged from the transfer nip portion N. In the transfer nip portion N, the elastic transfer roller 23' is pressed against the rigid photosensitive drum 1. When the tip of the transfer material 24 is discharged from the transfer nip portion N, a concave nip shape is formed on the upper side. Due to the rigidity of the transfer material 24 in the subsequent transfer nip portion N, the tip end of the transfer roller 23 ′ is reached. The transfer material 24 does not wind around the transfer roller 23 because a force that separates the transfer material 24 acts.

(Experimental Example 1) A photosensitive drum 1 having an outer diameter of 25 mm in which an organic optical semiconductor (OPC) is coated on an aluminum cored bar is used, and the peripheral speed (process speed) is 50.
It was driven at mm / sec. Primary charging roller 2A (Fig. 2
After being uniformly charged to −700 V by 2), exposure 3 for scanning with a laser beam is performed, and the light portion potential −100.
I got V. A one-component toner t having a charge amount of −12 μc / gr and a volume average particle size of 7 μm was applied from the developing device 4 to the photosensitive drum 1 by reversal development to obtain a visible image.

The transfer roller 23 '(FIG. 14) is an elastic layer 23b made of expanded EPDM in which zinc oxide and carbon are dispersed as conductive materials on a cored bar 23a made of stainless steel and having an outer diameter of 20 mm.
Is formed to have an outer diameter of 40 mm, a roller having a hardness of 30 ° (Asker C) and a resistance of 10 ⁹ Ω · cm is used to press the photosensitive drum 1 at a total pressure of 800 gr to form the transfer nip portion N. did.

+30 is applied to the core metal 23a of the transfer roller 23 '.
Basis weight 6 applied from 00V and sent from the paper feed cassette 9
When the A4 size transfer material 24 at 4 gr / m ² is controlled by the registration roller 11 and is inserted into the transfer nip portion N, 1
At a low humidity of 5 ° C. and 10%, both the leading end and the trailing end of the transfer material 24 are separated without being adsorbed by the photosensitive drum 1, and there is no dirt on the leading end or the trailing end of the transfer material or image disturbance. No rush jam into the cleaning device 14 occurred.

<Thirteenth Embodiment> (FIGS. 15 and 16) FIGS. 15 and 16 are explanatory diagrams of a control result of the transfer bias voltage to the transfer material 24 and a control sequence diagram in the image forming apparatus of the present embodiment. Is.

In this embodiment, when a transfer roller 23 'having a curvature 1 / r' _T smaller than the curvature 1 / r ' _D of the photosensitive drum 1 is used as shown in FIG. By reducing the absolute value of the transfer bias voltage at the end portion to reduce the mirroring force on the photosensitive drum 1 side and the transfer roller 23 ′ side when the transfer material 24 is discharged from the transfer nip portion N, the transfer material is reduced. It is intended to make the separation of 24 more smoothly.

As shown in FIG. 16, when the print signal is transmitted from the host computer, the photosensitive drum 1 starts rotating and the charging of the primary charging roller 2 (FIG. 22) also starts at the same time.

[0205] Time τ when the surface potential of the photosensitive drum 1 becomes stable
_{At 0} , laser scanning exposure 3 starts.
Of the time Δτ ₁ corresponding to the length of the transfer material 24, the exposure is not performed during the time Δτ ₂ corresponding to the front end portion and the time Δτ ₃ corresponding to the rear end portion, and the front end portion and the rear end portion of the transfer material 24 are not exposed. No latent image is formed, but a blank area is formed. A developing bias acts on the developing device 4 to perform development. The developing bias is turned on from a time point (τ ₀ + τ ₄ ) where the image area of the photosensitive drum 1 faces the developing device 4, and the time Δτ corresponding to the image area is reached. ₁ Development bias is activated and turned off.

The register roller 11 starts rotating at a time point τ ₅ , and the transfer material 24 passes through the transfer guide 12 and reaches the transfer nip portion N with the leading end of the image area and the leading end of the transfer material 24 aligned. A bias starts to be applied to the transfer roller 23 ′ at time τ ₆ when the leading end of the transfer material 24 reaches the transfer nip portion N.

The transfer bias is applied for a time Δτ ₁ corresponding to the length of the transfer material 24, but the value of the applied voltage is applied during the time Δτ ₇ and Δτ ₈ corresponding to the leading end and the trailing end. Is weakened. That the transfer voltage of the image area and V _Tr, 'if _Tr | V' transfer voltage V of the front end portion and the rear end portion _Tr | <
| V _Tr |

The value of _V'Tr depends on the material and shape (curvature 1 / r _T ) of the transfer roller 23 ', and the leading end and the trailing end of the transfer material 24 are sucked by the transfer roller 23', resulting in poor separation. The value may be within a range that does not _exist, and an appropriate value including V ′ _Tr = 0 [V] may be selected.

Further, the transfer voltage V'which is different between the front end portion and the rear end portion
_Tr may be used. Since the margins corresponding to Δτ ₂ and Δτ ₃ are formed at the leading end portion and the trailing end portion of the transfer material 24, even if the transfer bias is weakened, the transfer failure of the image does not occur, and the good separation performance is achieved. FIG. 15 is an explanatory diagram showing how the strength of the transfer bias changes according to the transport length of the transfer material 24.

<Fourteenth Embodiment> (FIG. 17) In this embodiment, as shown in the cross-sectional model view of the main part of FIG. 17, the radius r ′ _D of the photosensitive drum 1 and the radius r of the transfer roller 23 ′ are shown. ′ _T is large, and the curvature is 1 / r ′ _T <1 / r ′ _D , and is arranged so that the transfer material 24 is attracted to the transfer roller 23 ′ more strongly than the transfer material 24 is attracted to the photosensitive drum 1.

The feature of this embodiment is that the insulating region 18 is provided on at least a part of the surface of the transfer roller 23 '. The insulating region 18 has a P on the surface of the conductive elastic layer 23b.
It can be obtained by forming an insulating material having good releasability such as TFE / PFA / PET / PVDF into a film and embedding it in the elastic layer 23b so as to cover the entire area of the transfer roller 23 'in the longitudinal direction.

When the length of the transfer material 24 in the transport direction is L, the radius r ′ _T of the transfer roller 23 ′ is set to L ≦ 2πr ′ _T , and the circumferential length of the area 18 is set to l. Then, 2πr ′ _T −l <L is set, and the sequence control is performed so that the front end of the transfer material 24 matches the area 18.

In the area 18, the transfer material 2 is formed by the action of the insulator.
Since the application of the transfer charge to the recording medium 4 is weakened, the mirroring power is also reduced, and the tip of the transfer material 24 is not attracted to the transfer roller 23 '. It is separated smoothly.

[0214] Also now coincides with the rear end portion even area 18 with the transfer material 24 choose _T 'radius r' of the transfer roller 23 in the above range, the rear end is also well separated.

<Fifteenth Embodiment> (FIGS. 18 to 20) FIG. 18 is a model view of a main portion of the image forming apparatus of this embodiment.

In the apparatus of this embodiment, the transfer roller 23 'also functions as an intermediate transfer member.

The transfer roller 23 'has 10 ³ on the whole core 23a.
A conductive elastic layer 23b of -10 ⁶ Ω · cm is formed on top of which a thin layer 23c of medium resistance of 10 ⁷ -10 ¹¹ Ω · cm is formed to form an elastic roller of medium resistance as a whole. r ′ _T is L <2π, where L is the length of the transfer material 24.
r ′ _T.

[0218] The photosensitive drum 1 is' in _D, curvature 1 / r 'radius r is set such that _T <1 / r' _D, similarly to the apparatus of the aforementioned first embodiment (FIG. 1) The sequential formation of toner images of the first to fourth colors on the photosensitive drum 1 and the sequential superimposition transfer of the toner images of the first to fourth colors onto the outer peripheral surface of the transfer roller 23 'as an intermediate transfer member are performed. A composite color toner image is formed on the outer peripheral surface of the transfer roller 23 '.

The transfer of the toner image intermediately transferred onto the outer peripheral surface of the transfer roller 23 'to the transfer material 24 is performed from the paper feed cassette 9 side to the photosensitive drum 1 in the same manner as in the apparatus of the second embodiment (FIG. 2). The transfer material 24 is fed to the transfer nip portion N of the transfer roller 23 'at a predetermined timing, and a bias voltage having the same polarity (-) as the toner is applied to the core metal 23a of the transfer roller 23' by the second bias. It is done by being applied from the power supply 62. FIG. 19 shows a model diagram of the transfer process.

Transfer material 24 discharged from transfer nip portion N
Is attracted to the transfer roller 23 'rather than being attracted to the photosensitive drum 1, and the habit of the transfer material 24 in the transfer nip portion N is convex upward. The transfer material 24 can be easily separated by promoting the peeling of the tip portion from 23 '.

[0221] The transfer roller 23 'at the time of monochromatic image formation may be used to transfer t _b the toner image t _a on the photosensitive drum 1 onto the direct transfer material 24 as shown in FIG. 20. Even in this case, the separation of the transfer material 24 from the transfer nip portion N is easily performed, as described above.

(Experimental Example 2) As the photosensitive drum 1, the one having a radius of 35 mm in which an organic optical semiconductor (OPC) is coated on an aluminum cored bar is used and driven at a peripheral speed of 100 mm, in the same manner as in the above (Experimental Example 1) A latent image was formed and a color toner image was sequentially formed.

The black, magenta, cyan, and yellow toners are non-magnetic one-component toners having a volume average particle size of 5 to 8 μ, and are negative polarity toners having a specific charge amount of −8 to −18 μc / gr. By reversal development, a toner image was obtained.

The transfer roller 23 'has a resistivity of 10 in which carbon is dispersed on an aluminum core metal 23a having a radius of 40 mm.
PVdF having a resistivity of 10 ⁹ Ω · cm formed on a layer 23b of foamed EPDM having a resistance of ³ Ω · cm and containing tin oxide thereon.
A layer 23c having a medium resistance with a radius of 50 mm was used. The hardness of the transfer roller 23 'was 35 ° (Asker C), and the transfer nip portion N was captured by pressing the photosensitive drum 1 with a total pressure of 1000 gr including the self-weight of the transfer roller 23'. As the transfer material 24, A4 size (L = 297 mm) plain paper of 90 gr / m ² was used.

At the time of intermediate transfer of toner of each color, the core metal of the photosensitive drum 1 is grounded, and +1000 V is applied to the core metal 23a of the transfer roller 23 '. Further, when the color toner image is transferred to the transfer material 24 from the transfer roller 23 ', -3000V is applied to the core metal 23a of the transfer roller 23'.

In this way, when the transfer material 24 is separated from the transfer nip portion N, the transfer material 24 is not deflected to the photosensitive drum 1 side, and a good transferred image without image dirt or disorder is obtained. Was given.

As described above, the curvature 1 / r ' _T of the transfer roller 23' having the conductive elastic layer is made smaller than the curvature 1 / r ' _D of the photosensitive drum 1 (1 / r' _T <1 / r. ′
_D ) makes it possible to easily separate the transfer material 24 from the transfer nip portion N.

The twelfth to fifteenth embodiments have been described using the combination of the photosensitive drum 1 and the transfer roller 23 '.
Since each curvature in the transfer nip portion N becomes a problem, the photosensitive member as the first image bearing member 1 does not necessarily have to be a drum shape, and for example, a belt-shaped photosensitive member is backed up as a rigid body in the transfer nip portion. It is obvious that the present invention also includes the case where a roller is used to impart a certain curvature, and the like.

[0229]

By using the elastic roller of medium resistance as the intermediate transfer body or the transfer roller, it is possible to realize the image forming apparatus using the intermediate transfer body with a simple mechanism while preventing the disorder of the transferred image.

In an image forming apparatus in which the image formed on the first image carrier is transferred to the intermediate transfer member and then further transferred to the second image carrier, the surface moving speed of the intermediate transfer member is set to the first value. By making the surface moving speed of the image carrier different from that of the image carrier, it becomes possible to perform the intermediate transfer without a hollow portion, and to make the surface moving speed of the intermediate transfer member different from the surface moving speed of the second image carrier. As a result, an image with no voids could be formed on the second image carrier.

The image formed on the first image carrier is
In an image forming apparatus that transfers onto an intermediate transfer member composed of a medium resistance roller and then further transfers onto a second image carrier, the resistance value of the intermediate resistance intermediate transfer member and the resistance value of the transfer material are Optimum transfer performance by applying a constant current bias to the intermediate transfer body when transferring the image on the first image carrier to the intermediate transfer body, even if it fluctuates significantly due to environmental changes. In addition, when the image on the intermediate transfer member is transferred onto the transfer material, the optimum voltage is applied to the intermediate transfer member to obtain the optimum transfer property. Further, even in the transfer process when performing double-sided or multiple image formation, there is no difference between the first surface (or the first time) and the second surface (or the second time), and stable transferability is always obtained. By making the curvature 1 / r ′ _T of the transfer roller having the conductive elastic layer smaller than the curvature 1 / r ′ _D of the photosensitive drum 1 (1 / r ′ _T <1 / r ′ _D ),
It is possible to easily separate the second image carrier from the transfer nip portion.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram of an image forming apparatus according to a second embodiment.

FIG. 3 is a model diagram of a transfer process of a synthetic color toner image from an intermediate transfer roller to a transfer material.

FIG. 4 is a model diagram of a transfer process in the case of monochrome printing

FIG. 5 is a schematic diagram of an image forming apparatus according to a third embodiment.

FIG. 6 is a schematic diagram of an image forming apparatus according to a fourth embodiment.

FIG. 7: Model diagram of the transfer process of double-sided printing

FIG. 8 is a schematic diagram of an image forming apparatus according to a fifth embodiment.

FIG. 9 is a correlation diagram of the peripheral speed of the intermediate transfer roller and the level of image dropout.

FIG. 10 is a schematic diagram of an image forming apparatus according to a seventh embodiment.

FIG. 11 is a schematic diagram of an image forming apparatus according to an eighth embodiment.

FIG. 12 is a schematic diagram of an image forming apparatus according to a ninth embodiment.

FIG. 13 is a schematic diagram of an image forming apparatus according to an eleventh embodiment.

FIG. 14 is a model diagram of a main part of an image forming apparatus according to a twelfth embodiment.

FIG. 15 is an explanatory diagram of the control result of the transfer bias voltage to the transfer material in the image forming apparatus according to the thirteenth embodiment.

FIG. 16 is a control sequence diagram.

FIG. 17 is a model diagram of a main part of an image forming apparatus according to a fourteenth embodiment.

FIG. 18 is a schematic diagram of an image forming apparatus according to a fifteenth embodiment.

FIG. 19 is a model diagram of a transfer process of a synthetic color toner image from an intermediate transfer roller to a transfer material.

FIG. 20 is a model diagram of a transfer process in the case of monochrome printing

FIG. 21 is a schematic view of an example of a conventional image forming apparatus.

FIG. 22 is a schematic view of another example of a conventional image forming apparatus.

FIG. 23 is an enlarged model diagram of a transfer roller portion.

FIG. 24 is a diagram of an example of a hollow image portion.

[Explanation of symbols]

 1 Photosensitive Drum as First Image Carrier 20 Intermediate Transfer Roller 24 Transfer Material as Second Image Carrier 23 '· 25 Transfer Roller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Nanaki Taki, 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Akihiko Takeuchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya Non non corporation

Claims (14)

[Claims] 1. An image forming apparatus in which an image formed on a first image carrier is transferred onto an intermediate transfer member and then further transferred onto a second image carrier, wherein the intermediate transfer member has a medium resistance. Image forming apparatus, which is an elastic roller of. 2. The image forming apparatus according to claim 1, wherein the image transfer from the intermediate transfer member to the second image carrier is performed at a contact portion between the first image carrier and the intermediate transfer member. .. 3. An image forming apparatus in which an image formed on a first image carrier is transferred onto an intermediate transfer member and then further transferred onto a second image carrier, wherein the intermediate transfer member has a medium resistance. The first mode in which the image formed on the first image bearing member is transferred to the second image bearing member at a time after transferring the image formed on the first image bearing member to the medium resistance elastic roller as the intermediate transfer member a plurality of times. And a second mode in which the image formed on the first image carrier is directly transferred to the second image carrier can be selectively executed, and a medium resistance as an intermediate transfer member in the first mode can be achieved. 2. The image forming apparatus according to claim 1, wherein the elastic roller acts as a transfer roller in the second mode. 4. An image forming apparatus in which an image formed on a first image carrier is transferred onto an intermediate transfer member and then further transferred onto a second image carrier, wherein the intermediate transfer member has a medium resistance. Elastic roller, the first image formed on the first image carrier is once transferred to the medium resistance elastic roller as an intermediate transfer member, and then the second image is formed on the first image carrier. And the second image bearing member is introduced into the contact portion formed by the first image bearing member and the intermediate transfer member, and the first image and the second image are formed on both surfaces of the second image bearing member, respectively. An image forming apparatus characterized by simultaneous transfer. 5. An image forming apparatus for transferring an image formed on a first image bearing member onto an intermediate transferring member and then further transferring it onto a second image bearing member, wherein a surface movement of the intermediate transferring member. An image forming apparatus, wherein a speed is different from a surface moving speed of the first image carrier. 6. The image forming apparatus according to claim 5, wherein the surface moving speed of the intermediate transfer member is different from the surface moving speed of the second image carrier. 7. An image forming apparatus in which an image formed on a first image carrier is transferred onto an intermediate transfer member and then further transferred onto a second image carrier, wherein the intermediate transfer member has a medium resistance. Image forming device formed on the first image bearing member by performing image transfer from the intermediate transferring member to the second image bearing member at a contact portion between the first image bearing member and the intermediate transferring member. Is transferred onto the intermediate transfer member composed of a medium resistance roller, the transfer bias applied from the intermediate transfer member to the first image carrier is controlled to be a constant current I. At this time, Voltage value V _T
An image forming apparatus, which determines a bias voltage value V applied to the intermediate transfer member when re-transferring the image on the intermediate transfer member onto the second image carrier based on the above. 8. A bias voltage applied to the intermediate transfer member when the image transferred on the intermediate transfer member composed of a medium resistance roller is retransferred onto the second image carrier, and the voltage value V _{Using T} , the following transfer voltage calculation formula (A) | V | = a · | V _T | + b (A) a and b are voltage values V calculated by constants (including zero)
8. The image forming apparatus according to claim 7, wherein the constant voltage control is performed. 9. A bias voltage applied to the intermediate transfer member when the image transferred onto the intermediate transfer member composed of a medium resistance roller is retransferred onto the second image bearing member. _{Using T} , the following transfer voltage calculation formula (A) | V | = a · | V _T | + b (A) a and b are voltage values V calculated by constants (including zero)
Constant voltage control, and the value of the voltage value | V _T | in the equation (A) is compared with a predetermined reference voltage value, and the constants a and b are controlled to be changed to optimum values according to the result. The image forming apparatus according to claim 7. 10. When the image forming apparatus has a double-sided image forming function or a multiple image forming function, the constants a and b in the transfer voltage calculation formula (A) are the first surface or the first image forming execution mode. 10. The image forming apparatus according to claim 8, wherein the image forming apparatus is controlled to be changed to an appropriate value based on a mode difference such as a second surface or a second image forming execution mode. 11. An image forming apparatus for transferring an image formed on a first image carrier to another image carrier by a transfer means, wherein the transfer means is a transfer roller having a conductive elastic body to which a bias voltage is applied. The transfer roller is pressed by the first image carrier to form a transfer nip portion with the first image carrier, and the curvature (1 / r; r is a radius) of the transfer roller is An image forming apparatus having a curvature smaller than that of the first image carrier. 12. The other image carrier is a paper sheet, and a bias voltage corresponding to a front end and a rear end of the paper sheet is smaller in absolute value than a bias voltage corresponding to an image area of the paper sheet. The image forming apparatus according to claim 11, wherein the image forming apparatus comprises: 13. The peripheral length of the transfer roller is larger than the length of the paper sheet, and the tip of the paper sheet is brought into contact with a fixed position on the surface of the transfer roller. The image forming apparatus according to claim 11, wherein the image forming apparatus is made of an insulating material. 14. A transfer roller is used as an intermediate transfer member, an image of a different color is formed on the first image carrier, and the image is repeatedly transferred onto the transfer roller to form an intermediate image. The image forming apparatus according to any one of claims 11 to 13, wherein the multiple images are collectively transferred onto a paper sheet.