JPH0887156A - Image forming device - Google Patents

Abstract

PURPOSE: To improve overall transfer performance. CONSTITUTION: This image forming device is provided with an entrance auxiliary electrode 44 composed of a supporting part 46 placed in the rear side position of an intermediate transfer body 28 facing an entrance discharge circle A from a transfer roller 32 to a transferred material 43 and made of a conductive material having <=10cm<6> Ω. volume resistivity and a surface layer 45 as a middle resistance member which is supported by the supporting part 46 and has 10<8> -10<12> Ω.cm volume resistivity. The entrance auxiliary electrode 44 is separated from the intermediate transfer body 28 with a distance capable of a gap discharge and the supporting part 46 can be held at a constant potential.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of toner images which are sequentially formed on an intermediate transfer member so that the first plate to the plurality of plates are mixed in one image and the toner image is transferred onto a transfer roller. The present invention relates to an image forming apparatus that collectively transfers to a transfer target material.

[0002]

2. Description of the Related Art A full-color image forming apparatus includes an electrophotographic printer using an intermediate transfer member. This electrophotographic printer has a high output speed, good color reproducibility, and paper type. It is known because it doesn't matter. In this electrophotographic printer, the printing primary colors are cyan, magenta, yellow, and black, and toner images of these colors are sequentially formed on the photoconductor as toner images from the first plate to the fourth plate, and the intermediate images are formed. After being sequentially stacked on a transfer body, they are collectively transferred to paper by a transfer roller, and the toner images on the paper are mixed and fixed by a fixing unit to form a final color toner image. In other words, in order to accurately visualize the image in the intended color, the toner of each color formed on the photoconductor for each color distribution and sequentially transferred onto the intermediate transfer body is transferred onto the paper at a high transfer rate by the transfer roller. It is necessary to transfer.

At the portion (secondary transfer portion) where the toner on the intermediate transfer member is transferred to the paper, a counter electrode facing the transfer roller via the intermediate transfer member is essential. The role of this counter electrode is to determine the potential of one end of the transfer electric field generated by the transfer roller, and to receive the transfer current of the paper or the intermediate transfer member in the medium resistance region, for example, the intermediate transfer belt.

FIG. 3 shows a part of an example of a conventional electrophotographic printer. The photoconductor drum 1 is rotatably driven by the drive unit and uniformly charged by the charging device, and an electrostatic latent image is formed by image exposure by the exposure unit. This electrostatic latent image is formed in order from the 1st plate to the 4th plate, and each color developing device 2 to
The toner images of cyan, magenta, yellow, and black, for example, are sequentially developed with toners of various colors by 5.

The intermediate transfer belt 6 includes a belt transfer roller 7, a driven roller 8, a counter electrode 9 also serving as a belt driving roller, a tension roller 10, and a counter electrode 9 stretched around a driven roller 11 and also serving as a belt driving roller. The toner image on the photoconductor drum 1 is transferred by being rotationally driven and applying a transfer bias from a high-voltage power supply through the belt transfer roller 7. The counter electrode 9 faces the paper transfer roller 12 via the intermediate transfer belt 6 and is made of conductive rubber. The counter electrode 9 is also used as a backup roller for holding the pressure in the nip between the paper transfer roller 12 and the counter electrode 9. A transfer bias is applied from the high-voltage power supply between the paper transfer roller 12 and the counter electrode 9, and the paper 14 delivered from the registration roller 13 is transferred when passing between the intermediate transfer belt 6 and the paper transfer roller 12. The transfer roller 11 transfers the toner image on the intermediate transfer belt 6. The intermediate transfer belt 6 is cleaned by the cleaning device 15 after transferring the toner image onto the paper 14.

JP-A-2-212868 discloses a toner transfer device in which a transfer roller and a backup roller are opposed to each other through the intermediate transfer belt for the purpose of preventing the inner surface of the intermediate transfer belt from being scraped. It is described that a counter electrode roller which is slidably contacted with the inner surface of the intermediate transfer belt and is driven to rotate is provided at a position 10 to 18 mm away from the transfer position in the vicinity.

In Japanese Patent Laid-Open No. 213883/1990, in order to solve the problem that a transfer device of a transfer roller type has a poor adhesion of a paper to a photoconductor or an intermediate transfer member, the transfer performance is deteriorated. It is described that a sheet guide is provided which is brought into contact with the intermediate transfer member on the front side in the transport direction with respect to the section. JP-A-2-213884 discloses that it is difficult to transfer (secondary transfer) from an intermediate transfer body to paper with OHP paper, and pinholes and transfer defects of toner images occur when the transfer voltage is increased. In order to solve the problem, there is described one in which an electric field is applied to the toner image on the intermediate transfer member by a corotron on the entrance side near the transfer roller.

In Japanese Patent Application Laid-Open No. 4-88385, a toner image on an image carrier is transferred onto an intermediate transfer member without being disturbed to improve the transfer efficiency, and a high-quality image having high image density and no disturbance is obtained. In the transfer device for performing the primary transfer (transfer from the photosensitive member to the intermediate transfer member) of the intermediate transfer member, the photosensitive member is brought into contact with the intermediate transfer member over the entire transfer portion, and the volume of the intermediate transfer member is increased. Resistivity 10 ¹² to 10 ¹⁴ Ω · cm
The flexible endless belt is described.

Japanese Unexamined Patent Publication No. 2-50170 discloses a surface resistance of an intermediate transfer member of 10 ⁷ in order to prevent a halo phenomenon (improper coloring of edges / boundaries) in a color printer.
And to 10 ^{1 0} Omega, selectively using the engageable roller,
A transfer device is described in which an electrode is configured to apply an electrostatic field to excite transfer. In this transfer device, the thickness volume resistance or surface resistance of the intermediate transfer belt is inserted in series from the transfer position to the electrode. However, although the electrode plays a role, it may not be possible to obtain sufficient transfer performance. .

[0010]

In the transfer device such as the printer, the transfer current is delivered by the uncertain contact of the solid. However, since there are fine irregularities on the inner surface of the intermediate transfer belt and the surface of each electrode, there is always a poor contact point in the solid contact area, and there is a poor contact point with the counter electrode in the intermediate transfer belt. There will be no. Therefore, the contact portion between the intermediate transfer member and the roller facing the intermediate transfer member is not perfect in some places.

When a conductive rubber is used for the electrode / backup roller and the like, the material resistance of the conductive rubber depends on the electric field, so that the current may increase in a quadratic curve depending on the voltage. In this case, the current concentrates locally, but the current decreases in the surroundings. This means that there is a portion where the effect of the counter electrode is reduced in a plan view.

The toner image on the intermediate transfer belt is
The toner images of the respective color plates are transferred one after another from the photoreceptor, and the one-color plate toner overlapping part, the two-color plate toner overlapping part and the three-color plate toner overlapping part are mixed. As shown, the one-color plate toner overlapping portion, the two-color plate toner overlapping portion, and the three-color plate toner overlapping portion have different transfer biases for obtaining a transfer rate equal to or higher than an allowable level.

Therefore, as described above, if there is no counter electrode locally or there is a portion where the effect of the counter electrode is reduced, the transfer performance there is deteriorated and the overall transfer performance (one color on the intermediate transfer belt is reduced). The overall transfer performance of the toner image including the plate toner overlapping portion, the two-color plate toner overlapping portion, and the three-color plate toner overlapping portion) deteriorates.

An object of the present invention is to provide an image forming apparatus capable of improving the above-mentioned drawbacks and improving the overall transfer performance.

[0015]

In order to achieve the above object, the invention according to claim 1 has a volume resistance of 10 ⁸ to 10 ¹² Ω.
A plurality of toner images are sequentially formed on the intermediate transfer member of cm, and the first plate to the plurality of plates are mixed in one image by the plate number,
In an image forming apparatus for collectively transferring this toner image onto a transfer material by a transfer roller, the transfer material is transferred from the transfer roller at a transfer nip that occurs when the transfer material is sandwiched between the transfer roller and the intermediate transfer member. The volume resistance is 10 ⁶ Ω at the back surface of the intermediate transfer member facing the entrance discharge zone.
The inlet auxiliary electrode has a supporting portion formed of a conductive material having a volume of 10 cm or less and a surface layer of a medium resistance member supported by the supporting portion and having a volume resistance of 10 ⁸ to 10 ¹² Ω · cm. Is separated from the intermediate transfer member by a gap dischargeable distance, and the supporting portion is held at a constant potential.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the distance between the entrance auxiliary electrode and the intermediate transfer body is gradually narrowed along the conveyance direction of the intermediate transfer body. .

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the downstream side of the entrance auxiliary electrode in the intermediate transfer body transport direction is urged to the intermediate transfer body.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus is opposed to the transfer roller via the intermediate transfer member and is made of an insulating material having a volume resistance of 10 ¹² Ω · cm or more. The backup roller and the outlet side auxiliary electrode made of the same material as the inlet auxiliary electrode and placed at the separation point between the backup roller and the intermediate transfer member are provided.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the inlet auxiliary electrode and the outlet auxiliary electrode are integrated by one support.

According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, the intermediate transfer is performed by contacting a contact surface of the entrance auxiliary electrode with the intermediate transfer body with a back surface material of the intermediate transfer body. It uses a material that wears before the back of the body.

According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, insulating spacers are installed in the non-image portion of the entrance auxiliary electrode at intervals larger than the maximum lateral width of the transferred material.

According to an eighth aspect of the present invention, in the image forming apparatus according to the third aspect, the entrance auxiliary electrode is removed from a normal position when the transfer material is not in the transfer nip, and is aligned with the entrance of the transfer material. To move it to the proper position.

According to a ninth aspect of the present invention, in the image forming apparatus according to the third aspect, the position of the entrance auxiliary electrode is shifted when the transfer material having a strong bending rigidity is passed.

[0024]

According to the first aspect of the present invention, the entrance auxiliary electrode is separated from the intermediate transfer member by a distance capable of gap discharge, and the supporting portion of the entrance auxiliary electrode is held at a constant potential.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the distance between the entrance auxiliary electrode and the intermediate transfer member is gradually narrowed along the intermediate transfer member conveyance direction.

According to a third aspect of the invention, in the image forming apparatus according to the second aspect, the downstream side of the entrance auxiliary electrode in the intermediate transfer body transport direction is urged to the intermediate transfer body.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the backup roller made of an insulating material having a volume resistance of 10 ¹² Ω · cm or more faces the transfer roller via the intermediate transfer body. Then, the outlet-side auxiliary electrode made of the same material as the inlet auxiliary electrode is placed at the separation point between the backup roller and the intermediate transfer member.

According to a fifth aspect of the invention, in the image forming apparatus according to the fourth aspect, the inlet auxiliary electrode and the outlet-side auxiliary electrode are integrated by one support.

According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, the contact surface of the entrance auxiliary electrode with the intermediate transfer member is contacted with the material of the back surface of the intermediate transfer member so that it comes from the back surface of the intermediate transfer member. Wears first.

According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, the insulating spacers are arranged in the non-image portion of the entrance auxiliary electrode at intervals larger than the maximum lateral width of the transferred material.

According to an eighth aspect of the present invention, in the image forming apparatus according to the third aspect, the entrance auxiliary electrode is deviated from the normal position when the transfer material is not in the transfer nip, and is adjusted according to the entrance of the transfer material. Move to regular position.

According to a ninth aspect of the invention, in the image forming apparatus according to the third aspect, the position of the entrance auxiliary electrode is shifted when the material to be transferred having a high bending rigidity is passed.

[0033]

FIG. 2 shows a first embodiment of the present invention. This first
The embodiment is an embodiment of the invention described in claim 1 and is an example of a color image forming apparatus, and an object thereof is to improve the overall transfer performance. The belt-shaped image bearing member 21, which is a belt-shaped image carrier, is rotationally driven by a driving unit to rotate clockwise, and is first charged to a predetermined surface potential by a charging roller 22 that constitutes a charging unit. Next, on the photoconductor 21, an electrostatic latent image, which is a high-low partial image of the surface potential, is formed by image exposure by the exposure unit 23 including a laser writing system. here,
The exposure pattern by the laser writing system 23 is an image pattern in which a desired full-color image is separated into four colors of yellow, magenta, cyan, and black. These yellow, magenta, cyan, and black image patterns are laser writing systems. 23, the photosensitive member 21 is sequentially exposed to light by yellow,
Magenta, cyan, and black electrostatic latent images are sequentially formed.

Each of the yellow, magenta, cyan, and black electrostatic latent images is developed by a rotary developing device assembly having developing devices 24 to 27 containing yellow, magenta, cyan, and black developers, respectively. At Nos. 27 to 27, yellow, magenta, cyan, and black developers are sequentially developed by a non-contact developing method or a contact developing method to develop yellow, magenta, cyan, and black toner images. In addition, the intermediate transfer member 28 including an intermediate transfer belt
Comes in contact with the photoconductor 21 and rotates counterclockwise, and the yellow, magenta, cyan, and black toner images on the photoconductor 21 are transferred in the order of development (primary transfer). The yellow toner image, the magenta toner image, the cyan toner image, and the black toner image are stacked in this order without positional deviation.

Further, the material to be transferred made of transfer paper is the paper feed table 2.
The sheet 9 is fed to the registration roller 31 by the sheet feeding roller 30, and the registration roller 31 sends the transfer sheet to the sheet transfer section in accordance with the toner image on the intermediate transfer belt 28. When this transfer paper passes between the paper transfer roller 32 and the intermediate transfer belt 28, the toner image on the intermediate transfer belt 28 is transferred (secondarily transferred) by the paper transfer roller 32, and the fixing device 3
The toner image is mixed and fixed by 3 to form a full-color image, which is discharged to the tray 34.

The untransferred toner remaining on the photoconductor 21 is cleaned and collected by the photoconductor cleaning device 35 for each color.
Furthermore, the potential unevenness due to the latent image on the photoconductor 21 is eliminated by the static eliminator 36.
Are removed by. The untransferred toner remaining on the intermediate transfer belt 28 is cleaned and collected by the intermediate transfer belt cleaning device 37 after the transfer of the toner image onto the transfer paper is completed. The intermediate transfer belt cleaning device 37 is separated from the intermediate transfer belt 28 until the transfer of the toner image onto the transfer paper is completed, but comes into contact with the intermediate transfer belt 28 after the transfer of the toner image onto the transfer paper is completed.

Next, the secondary transfer will be described in detail with reference to FIG. The intermediate transfer belt 28 has a volume resistance of 10
It is composed of a sheet-shaped belt of ⁸ to 10 ¹² Ω · cm, and the material used is fluorinated material such as PFA, PTFE, ETFE or PC. The intermediate transfer belt 28
May be a multi-layer material. Volume resistance 10 of the intermediate transfer belt 28
⁸ to 10 ¹² Ω · cm is called a medium resistance region, and conductive particles are dispersed in the intermediate transfer belt 28, or the intermediate transfer belt 28 is made of rubber or plastic having ion conductivity. It is realized by configuring 28. In the dispersion of the conductive particles, it is necessary to prevent the conductive particles from largely depositing on the surface in order to not concentrate the discharge.

As shown in FIG. 2, the intermediate transfer belt 28 is stretched around a backup roller 38, a driven roller 39 and a belt transfer roller 40, and is rotationally driven by the backup roller 38 which also functions as a belt drive roller. A transfer bias is applied via the roller 40 to transfer the toner image on the photoconductor 21 as described above. The backup roller 38 also serves as a counter electrode, and is installed so as to face the paper transfer roller 32 via the intermediate transfer belt 28.

The backup roller 38 has a volume resistance of 1
A roller having a conductive rubber is 0 ⁸ Ω · cm or less, is grounded. The backup roller 38 has a volume resistance of 1
In some cases, the insulating property is 0 ¹² Ω · cm or more. As shown in FIG. 1, the toner 41 transferred from the photoconductor 21 to the intermediate transfer belt 28 has a negative charging polarity, and is individually colored yellow, magenta, cyan, or black with a pigment or the like. The toner 41 on the intermediate transfer belt 28 is
1 to 1st to 4th color plate toners (yellow, magenta, cyan and black toners, and 1st color toner in the case of monochromatic recording) are sequentially transferred and stacked. One image color to a maximum of four image colors are mixed in one image. This mixed manner is irregular, and the mixed toners are adjacent to each other. Toner M / A indicates the toner accumulation state by weight per area. If the number of plate colors increases,
The toner accumulation amount also increases, and the toner M / A also increases.

The paper transfer roller 32 is connected to the transfer roller bias power supply 42 and is connected to the transfer roller bias power supply 42.
Transfer bias is applied from the intermediate transfer belt 2 to the intermediate transfer belt 28 while the transfer paper 43 is sandwiched between the intermediate transfer belt 2 and the intermediate transfer belt 2.
The toner 41 on the sheet 8 is transferred onto the transfer paper 43. The paper transfer roller 32 is a single-layer rubber roller having a volume resistance of 10 ⁸ to 10 ¹² Ω · cm. The paper transfer roller 32 may be multilayered or foamed (as a sponge).

The transfer paper 43 is a general purpose paper here. The transfer paper 43 has a volume resistance in a medium resistance region and no initial residual charge. The entrance auxiliary electrode 44 is composed of a medium resistance surface layer 45 made of rubber or plastic and a conductive support portion 46 provided integrally with the middle resistance surface layer 45. Here, the medium resistance surface layer 45 is
For example, it is applied to the support portion 46, or a separately formed material is provided on the support portion 46 with a conductive adhesive or a conductive double-sided tape, so that the support portion 46 is supported and conducted. Medium resistance surface layer 45 is the volume resistivity is ^{10 8 ~10 1 2 Ω · cm} , the conductive support 46 and a volume resistivity is 10 ⁶ Ω · cm. Note that the entrance auxiliary electrode 44 needs to have a medium resistance in the surface layer 45 even when it has a multilayer structure.

The conductive support 46 of the entrance auxiliary electrode 44 is
It is connected to the auxiliary electrode bias power source 47, and a constant bias potential is applied from the auxiliary electrode bias power source 47.
The auxiliary electrode bias power supply 47 is for setting the potential of the inlet auxiliary electrode 44, and may be grounded. In this embodiment, the auxiliary electrode bias power supply 47 applies a potential of about −400 V to the conductive support portion 46 of the entrance auxiliary electrode 44.

The transfer roller bias power supply 42 is the same as a normal high voltage power supply in terms of specifications. As will be described later, it is desirable that the transfer roller bias power source 42 perform constant current control. In this embodiment, the transfer roller bias power supply 42 is a +30 μA constant current power supply, and the output voltage is +1 to +7 kV. The paper entrance guide 48 is
It is made of float metal or insulating plastic and is installed in front of the secondary transfer nip, and the transfer paper 43 is pressed against the intermediate transfer belt 28.

The transfer discharge area A is an entrance discharge area from the transfer roller 32 to the transfer paper 43 at the transfer nip, which is generated when the transfer paper 43 is sandwiched between the transfer roller 32 and the intermediate transfer belt 28. It is between the secondary transfer nip. The transfer discharge area entrance back surface position B is the back surface (inner surface) position of the intermediate transfer belt 28 facing the transfer discharge area A via the transfer paper 43, and the contact start position C between the transfer paper 43 and the intermediate transfer belt 28 is the transfer position. This is the position where the paper 43 enters the intermediate transfer belt 28. The entrance auxiliary electrode 44 is installed at a back surface position B of the intermediate transfer belt 28 facing the entrance discharge area A and separated from the intermediate transfer belt 28 by a distance capable of gap discharge.

Next, it will be explained that the discharge stability between dielectrics is affected by the dielectric resistance. Here, the discharge stability means that the electric charge is diffused and supplied in a wide range to continue in macro time. 5 to 7 show dielectric discharge models. As shown in FIG. 5, object 49 to object 5
In order to generate a discharge to 0, as shown in FIG. 8, a gap voltage equal to or higher than the discharge start voltage Vh determined by the atmospheric pressure P and the gap length δ between the objects 49 and 50 is supplied from the power source 51 to the object 4.
It is necessary to apply between 9 and 50 (Paschen's law). However, it should be noted that the Paschen's law indicates the spark voltage transfer voltage between conductors and explains the discharge start condition, but in the dielectric, the air space charge generated by the discharge is The duration is suppressed, and as shown in FIG. 9, a minute short-duration pulse of several μs is transmitted / received.

Therefore, in order to continuously supply the electric charge from the surface of the object 49 to the surface of the object 50 by the discharge, it is necessary to send the pulse current with high efficiency, which is necessary for impedance matching in the high frequency electric circuit. It will be the same as what is needed. In the model (AC equivalent circuit) shown in FIG. 7, considering that AC power is sent from the power source side (object 49) to the load side (object 50 side) via the transmission path, in order to continue stable discharge. Needs to drive the AC equivalent circuit including the capacitance with high efficiency. In order to apply the maximum AC power to the load, the resistance R _Z of the transmission line during energization and the resistance R ₂ on the load side may be of the same order.

Further, in order to continue the aerial discharge between the dielectrics for a long period of time, it is necessary to replenish the generated opposite polarity charge on the receiving side of the discharge. Therefore, it is necessary that the opposite-polarity charges be stably discharged from the receiving side, and that R ₂ is the same as R _Z , which is the same as the resistance R ₁ on the power supply side. R ₁ ≈R _Z ≈ Must be R ₂ . This applies to electric discharges between objects that are at rest. The power source side capacitance C ₁ , the transmission line capacitance C _Z, and the load side capacitance C ₂ are
Assume that C ₁ ≈C _d ≈C ₂ . The resistance Zd of the transmission line in the model (DC equivalent circuit) shown in FIG. 6 is a current-carrying resistance at the time of dielectric breakdown in air, and is about Zd≈10 ⁸ Ω · cm.

Now, the present embodiment will be considered. As shown in FIG. 1, in the transfer discharge area A on the inlet side of the transfer roller 32, the gap δ _{11 at} which the transfer roller 32 having the surface potential Vs starts discharging to the transfer paper 43 and the transfer roller 32 due to the charge accumulation of the transfer paper 43. The gap δ ₁₂ at which the discharge is stopped when the voltage between the gap with the transfer paper 43 becomes small or when the gap is too close to the Paschen's law is applied to the relative positions of the curved surface of the transfer roller 32 and the back surface of the transfer paper 43. Transfer paper 4
It is a section projected on three planes.

The transfer roller 3 in the transfer discharge area A
The average of the gap between 2 and the transfer paper 43 is δ ₁ . The electric charge is supplied in the nip for the secondary transfer by the transfer roller 32 and the transfer paper 4 due to the fine unevenness of the transfer roller 32 and the transfer paper 43.
Since the contact with 3 is uncertain, it can be ignored compared to the air breakdown at the inlet side of the transfer nip. Note that charge injection is basically not suitable for performing a transfer action because charges cannot be diffused and supplied.

Since the transfer discharge area A is located downstream of the contact start position C between the transfer paper 43 and the intermediate transfer belt 28 in the transport direction of the transfer paper 43, the transfer paper 43 is in close contact with the intermediate transfer belt 28 in the transfer discharge area A. . Actually, the front side of the transfer paper 43 (lower surface)
And the intermediary transfer belt 28 has a microscopic gap δ ₂
There is. In the region where the transfer paper 43 and the intermediate transfer belt 28 are in close contact with each other, the discharge start voltage is rather high because the transfer paper 43 and the intermediate transfer belt 28 are too close to each other.
Gap discharge does not occur. In the gap between the transfer paper 43 and the intermediate transfer belt 28, a transfer electric field having a sufficient height is formed, so that a transfer action occurs and the toner 41 on the intermediate transfer belt 28 is transferred to the transfer paper 43.

The transfer electric field is transferred from the transfer roller 32 to the transfer paper 43.
Is formed by the electric charge discharged on the back of the. Since the Coulomb force has a large influence on the toner-sized particles, the transfer of the toner 41 is instantaneous. However, when the toner 41 is transferred to the transfer paper 43, a pseudo current corresponding to dq / dt = i flows between the intermediate transfer belt 28 at the bottom of the toner image portion and the toner receiving portion on the surface of the transfer paper 43. This current indicates that charge replenishment and neutralization have occurred on the toner sending side and the toner receiving side, respectively.

Although the absolute charge amount of the toner is small, it is sufficiently larger than the surface charge density of the intermediate transfer belt 28 and the transfer paper 43. The charge amount of the intermediate transfer belt 28 (which should be considered as the surface charge density) is biased toward the (+) side. On the other hand, the charge of the transfer paper 43 is neutralized by the transfer of the (-) toner (the surface charge density is neutralized). In the transfer discharge area A, the charge of the transfer paper 43 is replenished, but the situation in which the transfer electric field is weaker than the surroundings remains unchanged.
Further, such a current is not generated in a portion where there is no toner image, but since the volume resistance of the transfer paper 43 and the intermediate transfer belt 28 is medium resistance, the current at the center of the toner image diffuses to the surroundings. Therefore, the charges on the margins on the transfer paper 43 are neutralized.

These charge transfer operations vary depending on the amount of charges supplied to the back surface of the transfer paper 43 (per area), the amount of charges held by the toner, and the overall charge transfer speed in the gap. The current flowing through the transfer roller 32 is the sum of the current due to this charge replenishment action, the charge stored and conveyed in the transfer paper 43, and the current leaking out of the transfer unit including the transfer roller 32 and the auxiliary electrode 44. is there.

In summary, when the toner is actually transferred, (+) charges are accumulated on the inner surface (back surface) of the intermediate transfer belt 28. This amount is the toner Q (charge amount)
Correlates with the size of. This indicates that, in correlation with the transferred toner Q, the surface charge density on the surface side of the transfer paper 43 and the surface side of the intermediate transfer belt 28 vary, and the transfer electric field also varies.

Now, consider the portion below the transfer discharge area A where transfer actually occurs as shown in FIG. In this part,
The stage in which the transfer has already progressed to some extent and the toner has transferred to the transfer paper 43 side is shown. In this case, the (+) polarity induced charges remain on the surface of the intermediate transfer belt 28. The (+) charge is continuously replenished on the back side of the transfer paper 43.

As shown in FIG. 11, when the electrode is not provided at the transfer discharge area entrance back surface position B, the (+) charge on the surface of the intermediate transfer belt 28 is not consumed, so that the intermediate transfer belt 28 is not consumed.
An electric field (named a suppression electric field) is formed in a direction of pushing up the surface charge density of the above and canceling the transfer electric field. The transfer rate varies depending on the toner M / A.

As shown in FIG. 12, when the conductive electrode 52 is placed in contact with the back side of the intermediate transfer belt 28 so as to be separated from the transfer discharge area entrance back surface position B, and the conductive electrode 52 is grounded, (- ) A small amount of electric charge is supplied by the resistance component R of the intermediate transfer belt 28, and (+) on the back side of the transfer paper 43.
The charge is neutralized, and the increase in the surface charge density of the intermediate transfer belt 28 is slightly suppressed. Therefore, the formation of the suppression electric field is small, and the transfer rate is slightly changed according to the toner M / A.

As shown in FIG. 13, when the conductive electrode 52 is installed at the transfer discharge area entrance back surface position B on the back side of the intermediate transfer belt 28, there is a microscopic gap between the inner surface of the intermediate transfer belt 28 and the electrode 52. , Gap discharge is generated at the distance δ ₃ . The (-) charges from the electrode 52 are concentratedly discharged to a place where the (+) electric field is the largest (for example, a place where the potential is the highest or a convex portion). There is no charge supply in other parts. That is, the suppression electric field is formed in relation to the image pattern and the unevenness of the inner surface of the intermediate transfer belt 28, and the transfer rate varies.

When a conductive electrode is placed in contact with the inner surface of the intermediate transfer belt 28 at the back surface position B of the transfer discharge area inlet (see the above-mentioned conventional apparatus), the (-) charge from the electrode is a convex portion on the inner surface of the intermediate transfer belt 28. Concentrate on. There is no charge supply in other parts. That is, the suppression electric field is formed in relation to the unevenness of the inner surface of the intermediate transfer belt 28, and the transfer rate fluctuates.

In the present embodiment in which the auxiliary electrode 44 is installed at the back surface position B of the transfer discharge area entrance as shown in FIG. 14, the (−) charge from the auxiliary electrode 44 is diffused and supplied onto the intermediate transfer belt 28. To be done. Therefore, the (+) charges excited on the intermediate transfer belt 28 according to the toner Q are neutralized by the continuous diffusion discharge without local variations. Therefore, the suppression electric field is uniformly formed in the transfer region, and the transfer of the untransferred toner (subsequent toner) on the intermediate transfer belt 28 is improved.

As a result, in the same manner as (+) charges are diffused and supplied to the back of the transfer paper 43 in the transfer discharge area A, (-) charges are diffused and supplied from the auxiliary electrode 44 to the intermediate transfer belt 28. The charge imbalance in the transfer area is eliminated. As a result, as long as the transfer bias is the optimum transfer current in the single-layer toner transfer, the multi-layer toner is continuously transferred in succession, and the transfer action less affected by the toner holding charge (= mass) is achieved. Can be performed, and the overall transfer performance can be improved.

In the description of the conventional transfer mechanism, it is 1
In many cases, the discharge from the direction is considered, but in the present embodiment, the discharge from the two opposite directions is limited to the local area of the transfer discharge area A at the entrance of the transfer nip. Also,
When such a charge flow is formed by diffusion, when the material resistance of the transfer paper 43 or the intermediate transfer belt 28 is medium resistance, static elimination is actively performed in the toner-free portion (the portion where the (+) charge remains on the transfer paper 43). become. As a result, when this portion is separated via the transfer nip, the charge neutralization is almost completed, and there is an effect that diffusion scattering at the time of separation and toner charge polarity change are prevented and the image quality is improved.

In realizing the present embodiment, the voltage between the intermediate transfer belt 28 and the auxiliary electrode 44 must be about the discharge start voltage. This can be done by increasing the bias voltage of the transfer roller bias power supply 42 or by setting the voltage V ₀ of the auxiliary electrode 44 to the opposite polarity. This embodiment relies on the latter.

Now, the conventional example shown in FIG. 3 will be described for comparison with the present embodiment. In the conventional example, the transfer roller 12
The backup roller 9 made of conductive rubber is opposed to this. In the transfer discharge area at the entrance of the transfer nip, the charge transfer to and from the intermediate transfer belt 6 varies due to the unevenness of the inner surface of the intermediate transfer belt 6, the unevenness of the backup roller 9, and the variation in rubber resistance as described above. When the intermediate transfer belt 6 is made of a medium resistance material, some internal diffusion occurs, so that the transfer performance does not deteriorate completely. Further, since the transfer pressure is applied in the transfer nip, the untransferred toner receives the cohesive force on the intermediate transfer belt 6,
It becomes difficult to transfer. However, the transferred toner is mainly subjected to the cohesive force with respect to the surface of the transfer paper 14 due to the pressure of the transfer nip, so that it is not a serious problem in transfer performance.

In this embodiment, as described above, the volume resistance 10
^A plurality of toner images are sequentially formed on the intermediate transfer belt 28 of ⁸ to 10 ¹² Ω · cm, the first plate to the plurality of plates are mixed in one image by the number of plates, and this toner image is transferred by the transfer roller 32. In the image forming apparatus that transfers the transfer material 41 to the transfer paper 41 at a time, the transfer roller 32 is transferred from the transfer roller 32 to the transfer material 41 at a transfer nip that occurs when the transfer material 41 is sandwiched between the transfer roller 32 and the intermediate transfer belt 28. At the back surface position B of the intermediate transfer belt 28 facing the entrance discharge area A of
Support part 46 made of a conductive material of 0 ⁶ Ω · cm or less
And the volume resistance 10 ⁸ to 1 supported by the support portion 46.
There is an entrance auxiliary electrode 44 consisting of a surface layer 45 of a medium resistance member of 0 ¹² Ω · cm, and the entrance auxiliary electrode 44 is separated from the intermediate transfer belt 28 by a distance capable of gap discharge,
Moreover, since the supporting portion 46 is held at a constant potential by the auxiliary electrode bias power source 47, it is possible to uniformly transfer the current between the inner surface of the intermediate transfer belt 28 and the transfer counter electrode by using the gap discharge. Therefore, it is possible to prevent the transfer current from being excessive or insufficient in the image. As a result, the same transfer bias can be used for transferring the single-layer toner and the multi-layer toner on the intermediate transfer belt 28, and the overall transfer performance can be improved.

The first embodiment is also an embodiment of the invention described in claim 2, and an object of the invention in claim 2 is to reliably generate a charge flow path. In the first embodiment, if the resistance of the auxiliary electrode 44 is small, the current can flow even if the contact state of the transfer roller 32, the transfer paper 43, and the intermediate transfer belt 28 is a little bad. However, under this condition, the above-mentioned stabilization condition of the gap discharge is not satisfied, and therefore the discharge is locally concentrated and is not diffused.

Managing the gap by using a medium resistance material for the auxiliary electrode 44 is a condition for diffusing and stabilizing the discharge. Therefore, in order to stably pass a minute current in the entrance discharge area A in which the transfer roller 32 is rotating, it is assumed that the air insulation breakdown is surely caused, and the gap between the transfer roller 32 and the transfer paper 43 is as shown in FIG. Can be gradually narrowed gradually, so that gap discharge can be surely caused. In addition, if such a shape is adopted, even if fine powder such as toner or paper dust is mixed in the contact portion between the transfer roller 32 and the transfer paper 43, there is a place where the electric discharge is always generated, so that it is resistant to dirt and the like. From the intermediate transfer belt 28 to the auxiliary electrode 4
It is possible to reliably and reliably generate a gap discharge to 4 and obtain high transfer performance.

FIG. 15 shows a partially exploded perspective view of the second embodiment of the present invention. The second embodiment is an embodiment of the invention described in claim 3, and aims to surely secure the discharge gap. In the above-described first embodiment, the distance between the intermediate transfer belt 28 and the auxiliary electrode 44 requires a very high accuracy, but the intermediate transfer belt 28 is unstable and difficult to stabilize. Therefore, in the second embodiment, the shaft 54 of the auxiliary electrode 44 in the first embodiment is rotatably supported by a supporting member, and the auxiliary electrode 44 is pressed against the intermediate transfer belt 28 by the spiral spring 53 with a predetermined pressure. I will. By doing so, even if the intermediate transfer belt 28 slightly fluctuates,
The gap between the intermediate transfer belt 28 and the auxiliary electrode 44 can be properly secured.

With such a shape, the space can be reduced when the intermediate transfer belt 28 and the auxiliary electrode 44 are incorporated in the machine. If the surface properties of the end portions of the intermediate transfer belt 28 and the auxiliary electrode 44 that are in contact with each other are not smooth, friction may cause frictional self-excited vibration. This is called a stick-slip phenomenon because it occurs with a combination of a belt and a rubber blade. This phenomenon occurs due to the balance between the rigidity of the blade material and the frictional force, and it is less likely to appear when the downstream side of the blade in the belt conveying direction contacts the belt than when the upstream side of the blade in the belt conveying direction contacts the belt. .

Therefore, in the second embodiment, in the first embodiment, the spiral spring 53 is inserted into the left and right convex portions (shafts) 54 of the support portion 46 and hooked on the edge 56 of the support portion 46, and a predetermined pressure is applied. The auxiliary electrode 44 is pressed against the inner surface of the intermediate transfer belt 28. It is also possible not to apply the pressure when the machine is not operating. Of course, the spring 53 may take another form such as a tension spring. Further, the insulating material 57 is installed or applied so that the portion of the auxiliary electrode 44 that contacts the intermediate transfer belt 28 does not directly contact the intermediate transfer belt 28. The left and right convex portions 54 of the support portion 46 are inserted into the holes 58 (one of which is not shown) on the main body side in this embodiment.

As described above, in the second embodiment, the auxiliary electrode 44
Since the downstream side of the intermediate transfer belt 28 in the conveying direction is urged to the intermediate transfer belt 28, a gap discharge from the intermediate transfer belt 28 to the auxiliary electrode 44 can be stably and reliably generated, and as a result, high transfer performance can be obtained. To be

Next, an embodiment of the invention described in claim 4 will be described. The third embodiment of the present invention is an embodiment of the invention as set forth in claim 4, and an object thereof is to make it possible to use inexpensive rubber for the backup roller. Rubber molding in the medium resistance region is generally expensive because the material is special (for example, the molding yield is poor). It is common to mold the backup roller with normal insulating rubber (10 ¹² Ω · cm or more). In this case, the charge on the transfer paper or the intermediate transfer belt is carried to the transfer nip or later if the charge removal is incomplete, and the charge on the back of the transfer paper raises the potential of the entire intermediate transfer belt and is not good for other processes. There is. Therefore, it is desirable that the intermediate transfer belt be discharged as much as possible when the transfer is discharged. In this case, it is necessary to secure not only the transfer discharge area A but also the discharge path of the charge flow at the time of separating the transfer paper in consideration of winding discharge and separation discharge with the backup roller of the intermediate transfer belt.

Therefore, in the third embodiment of the present invention, the outlet side auxiliary electrode 59 is installed at the separation point between the backup roller 38 and the intermediate transfer belt 28 as shown in FIG. 16 in the first embodiment. The outlet side auxiliary electrode 59 is composed of a supporting portion and a surface layer made of the same material as the inlet auxiliary electrode 44.
The charge flow flows at the position E shown in the figure when the transfer paper is separated, and subsequently flows at the position F shown in the figure when the backup roller 38 and the intermediate transfer belt 28 separate. When the discharge side auxiliary electrode 59 secures the discharge path in this way, the discharge path is expanded, which is advantageous for stabilizing the transfer performance. In addition, a cheap insulating rubber material can be used for the backup roller 38, and the cost can be reduced as a whole.

Next, an embodiment of the invention described in claim 5 will be described. The fourth embodiment of the present invention is the same as the third embodiment except that the auxiliary electrodes 44 and 59 are provided for the purpose of cost reduction.
Are integrated. As shown in FIGS. 17 and 18, the supporting portions of the auxiliary electrodes 44 and 59 are one supporting portion 6.
1 and the surface layers 45 and 60 of the auxiliary electrodes 44 and 59.
Is attached by, for example, a conductive double-sided tape. The support portion 61 is rotatably supported about the shaft 55, and the surface layers 56 and 60 of the auxiliary electrodes 44 and 59 are pressed against the intermediate transfer belt 28 with a predetermined pressure by a spiral spring. The fifth embodiment of the present invention is the same as the fourth embodiment except that the auxiliary electrode 4 is used.
As shown in FIG. 19, the surface layers 45 and 60 of 4, 59 are
One surface layer 62 covers one surface of the support portion 61.
The fourth and fifth embodiments are embodiments of the invention described in claim 5, and the cost can be reduced by integrating the auxiliary electrodes 44 and 59.

Next, an embodiment of the invention described in claim 6 will be described. A sixth embodiment of the present invention is an embodiment of the invention described in claim 6, and it is an object of the present invention to attain long-term stabilization of discharge and to enable long-term use even in an environment where toner is often scattered. . The sixth embodiment is different from the first embodiment in that the surface of the auxiliary electrode 44 on the side of the intermediate transfer belt 28 is made of a material that wears before contacting with the material of the back surface of the intermediate transfer belt 28. Configure. Specifically, as shown in FIG. 20, this material is formed by forming an insulating rubber 63 such as urethane or EPDM with a foam having low strength, and appropriately dispersing conductive particles 64 such as carbon black or ZnO therein. I will let you.

By abrasion of the surface of the auxiliary electrode 44 on the side of the intermediate transfer belt 28, the contact surface between the auxiliary electrode 44 and the intermediate transfer belt 28 can be cleaned and the gap can be maintained. Therefore, the discharge can be expected to be stabilized for a long period of time, and it can be used for a long period of time even in an environment in which toner is scattered. However, if the auxiliary electrode 44 is excessively worn, a problem occurs, so that the surface of the auxiliary electrode 44 on the intermediate transfer belt 28 side must be easily scraped. Here, the surface layer 45 of the auxiliary electrode 44 is preferably made of a material having a high porosity so as to be easily scraped and the inside is made dense. In this sixth embodiment, the auxiliary electrode 4
The surface layer 45 of No. 4 is self-lubricated by the wear caused by the contact with the intermediate transfer belt 28, and the mixture of the insulating material can be prevented.
The discharge can be stabilized in the long term.

The seventh embodiment of the present invention is an embodiment of the invention described in claim 7, and an object thereof is to prevent the medium resistance material from being worn. In the seventh embodiment, in order to maintain the gap as shown in FIGS. 21 and 22, in the first embodiment, the insulating spacer 65 made of a wear-resistant material having a thickness higher than that of the surface layer 45 is formed on the support portion 46. , 66 are provided at intervals larger than the maximum width of the transfer paper 41.
Is brought into contact with the intermediate transfer belt 28. Spacers 65 and 6
6 is made of plastic such as polyacetal or high-molecular polyethylene. Instead of providing the spacers 65 and 66, hair may be planted at both ends of the support portion 46. Support part 4
Since the normal discharge cannot be performed in the image area, the places where the spacers 65 and 66 of 6 are attached are in the non-image area, for example, both ends.

In the seventh embodiment, since the insulating spacers 65 and 66 are provided in the non-image portion of the auxiliary electrode 44 at intervals larger than the maximum width of the transfer paper 41, the surface layer 45 of medium resistance in the auxiliary electrode 44 is formed. It is not scraped off due to wear, and resistance fluctuation can be prevented for a long period of time.

FIG. 23 shows a part of the eighth embodiment of the present invention. The eighth embodiment is an embodiment of the invention described in claim 8 and is intended to prevent the surface layer 45 of medium resistance from being worn. The medium resistance surface layer 45 of the auxiliary electrode 44 is the most important part of the auxiliary electrode 44. Surface layer 45
If the wear is too easy, uneven wear may occur locally. Originally, the abrasion of the surface layer 45 was caused by the intermediate transfer belt 28.
This occurs because the surface of the surface layer 45 constantly contacts the unevenly distributed unevenness and the high hardness portion. It is necessary to avoid uneven wear of the surface layer 45.

The surface layer 45 may be brought to the regular position only when necessary. Therefore, in the eighth embodiment, the second
In the embodiment, when the transfer paper 41 enters the paper entrance position C, the auxiliary electrode 44 is moved to the regular position shown by the solid line in FIG. 23, and at other times, the auxiliary electrode 44 is moved to the non-use position shown by the dotted line in FIG. To move. A stepping motor 67 is used to move the auxiliary electrode 44, and the stepping motor 67 drives the auxiliary electrode 44 via a reduction gear. An input / output unit (I / O) 68 and a CPU 69 are used as control means for controlling the stepping motor 67.

The CPU 69 controls the transfer paper 4 as shown in FIG.
When 1 enters the paper entry position C, the stepping motor 67 is instructed via the I / O 68 to move the auxiliary electrode 44 to the regular position, and this instruction causes the stepping motor 67 to move the auxiliary electrode 44 to the regular position. Also,
When the discharge of the transfer paper 41 between the auxiliary electrode 44 and the intermediate transfer belt 28 is completed, the CPU 69 instructs the stepping motor 67 via the I / O 68 to move the auxiliary electrode 44 to the non-use position. The stepping motor 67 moves the auxiliary electrode 44 to the non-use position.

In the ninth embodiment of the present invention, in the above eighth embodiment, when the transfer paper 41 is not in the secondary transfer nip, the urging pressure of the spiral spring 53 is reduced and the auxiliary electrode 44 is moved from the normal position. As shown in FIGS. 25 to 27, the spiral spring 53 is inserted into the left and right convex portions (shafts) 54 of the supporting portion 46 and hooked by the edge 56 of the supporting portion 46 and the cam 70. The cam 70 is driven by the stepping motor 67. When the transfer paper 41 enters the paper entrance position C, the stepping motor 67 rotates the cam 70 to the left to make the pressure of the spiral spring 53 a normal pressure and transfer between the auxiliary electrode 44 and the intermediate transfer belt 28. When the discharge of the paper 41 is completed, the cam 70 is rotated to the right to make the pressure of the spiral spring 53 smaller than the normal pressure.

In the eighth and ninth embodiments, the auxiliary electrode 44 is removed from the normal position when the transfer paper 41 of the transfer material is not in the transfer nip, and the auxiliary electrode 44 is moved in accordance with the entry of the transfer material. Since the intermediate transfer belt 2 is moved to the position, the intermediate transfer surface layer 45 of the auxiliary electrode 44 is not necessary when the intermediate resistance surface layer 45 is not needed.
It is possible to reduce the abrasion of the surface layer 45 without contacting the surface layer 8.

A rotary solenoid or the like may be used instead of the stepping motor 67. Further, the I / O 68 and the CPU 69 used to control the stepping motor 67
It is desirable that the I / O and the CPU used for other control be used in common. This is because the CPU and I / O that can detect the input / output timing of the transfer paper 41 can be used, and it is not necessary to bother to have a sensor or the like.

By the way, in the above embodiment, since the actual intermediate transfer belt 28 has a certain degree of bending stiffness, when wound around the backup roller 38, there is a winding correction angle α as shown in FIG. . Due to this winding correction angle α, the transfer discharge area A is usually slightly displaced from the layout to the upstream side in the rotation direction of the intermediate transfer belt 28.

When a transfer paper having a high bending stiffness (for example, 135 kg paper manufactured by Nippon Business Supply Co., Ltd.) is passed, the result shown in FIG.
The intermediate transfer belt 28 bends at the paper entrance position C as shown in FIG. As a result, the transfer discharge area A shifts downward. This makes precise gap adjustment completely meaningless. Therefore, when the transfer paper is stiff, the auxiliary electrode 44
Needs to be moved to the optimum position. Note that, as described above, the position setting of the auxiliary electrode 44 by the spring is not very effective. This is because the transfer paper has the greatest difference in stiffness at the paper entry position C, and when the transfer paper comes near the transfer nip, the pressure of the transfer paper on the intermediate transfer belt 28 is weakened.

When the trailing edge of the transfer paper moves downstream of the paper entrance position C, the position of the intermediate transfer belt 28 jumps up (is reciprocated). In order to deal with this, it is necessary to sufficiently press the auxiliary electrode 44 against the intermediate transfer belt 28, but it is not preferable to increase this pressing too much. Therefore, the tenth embodiment of the present invention aims to move the auxiliary electrode 44 to an optimum position in accordance with the waist of the transfer paper. In the second embodiment, when the transfer paper having strong bending stiffness is passed through, The auxiliary electrode 44 was displaced, and the control system was computerized in order to obtain a sufficient response speed.

The tenth embodiment is an embodiment of the invention described in claim 9, and a displacement amount sensor 71 is arranged on the inner surface side of the intermediate transfer belt 28 at the paper entry position C as shown in FIG. This displacement amount sensor 71 detects the amount of deflection of the intermediate transfer belt 28 at the paper entry position C, and the displacement amount sensor 7
The detection signal from 1 is input to the CPU 73 via the I / O 72. Similar to the eighth embodiment, the stepping motor 67
Drives the auxiliary electrode 44 via the reduction gear and controls the stepping motor 67 by the I / O 72 and the CP.
U73 is used. Here, note that
Not only the paper entrance position C but also the transfer nip passage time of the transfer paper is set as the control target period. The auxiliary electrode 44 needs to remain in the same position until the trailing edge of the transfer paper is completely discharged from the transfer nip. This is to prevent the occurrence of uncontrollable transfer blur at the trailing edge of the image.

As shown in FIGS. 31 and 32, the CPU 73 takes in the detection signal from the displacement amount sensor 71 when the transfer sheet 41 is not in the entry position C to the intermediate transfer belt 28 or the secondary transfer nip, and the intermediate value is obtained. The amount of deflection of the transfer belt 28 at the paper entry position C is detected, and this amount of deflection is stored as a variable T ₀ . Further, the CPU 73 takes in a detection signal from the displacement amount sensor 71 when the transfer paper 41 enters the approach position C to the intermediate transfer belt 28, and reads the deflection amount of the intermediate transfer belt 28 at the paper entrance position C, The auxiliary electrode 44 is moved to the optimum position by driving the stepping motor 67 to drive the auxiliary electrode 44 in the vertical direction according to the amount of deflection.

Further, the CPU 73 assumes that the amount of deflection of the intermediate transfer belt 28 is T ₀ when the trailing edge of the transfer paper 41 passes through the entry position C with respect to the intermediate transfer belt 28, and the stepping motor 67 is operated according to this T _0. By driving the auxiliary electrode 44 in the vertical direction, the auxiliary electrode 44 is moved to the optimum position. Further, when the rear end of the transfer paper 41 exits the transfer nip, it is determined that the image output for one sheet is completed, and the stepping motor 67 is driven to drive the auxiliary electrode 44.
To the unused position.

In the tenth embodiment, the position of the auxiliary electrode 44 is shifted when the transfer paper having a strong bending stiffness is passed through.
Since the transfer paper is stiff, the gap distance important for discharge can be accurately adjusted when pressure is applied to the intermediate transfer belt 28 when it enters the intermediate transfer belt 28. The present invention is not limited to the above-described embodiments, and can be similarly applied to image forming apparatuses other than the above-mentioned embodiments, for example.

[0092]

As described above, according to the first aspect of the present invention, a plurality of toner images are sequentially formed on the intermediate transfer member having a volume resistance of 10 ⁸ to 10 ¹² Ω · cm, and the first image is printed. In an image forming apparatus in which a plurality of plates are mixed in one image and the toner images are collectively transferred to a transfer material by a transfer roller, the transfer material is interposed between the transfer roller and the intermediate transfer member. A support portion formed of a conductive material having a volume resistance of 10 ⁶ Ω · cm or less at a position on the back surface of the intermediate transfer body facing the entrance discharge zone from the transfer roller to the transfer material of the transfer nip that occurs when the sheet is nipped; It has an entrance auxiliary electrode composed of a surface layer of a medium resistance member having a volume resistance of 10 ⁸ to 10 ¹² Ω · cm supported by the supporting portion, and the entrance auxiliary electrode has a gap discharge distance with respect to the intermediate transfer member. And separate the support part Since the potential is maintained, it is possible to uniformly transfer the current between the inner surface of the intermediate transfer member and the end-facing counter electrode by using the gap discharge, and prevent the transfer current from being excessive or insufficient within the image. You can As a result, the same transfer bias can be used for transferring the single-layer toner and the multi-layer toner on the intermediate transfer member, and the overall transfer performance can be improved.

According to a second aspect of the invention, in the image forming apparatus according to the first aspect, the gap between the entrance auxiliary electrode and the intermediate transfer body is gradually narrowed along the intermediate transfer body transport direction. The gap discharge from the intermediate transfer member to the entrance auxiliary electrode can be reliably generated, and as a result, high transfer performance can be obtained.

According to the third aspect of the invention, in the image forming apparatus according to the second aspect, the downstream side of the entrance auxiliary electrode in the intermediate transfer body transport direction is urged toward the intermediate transfer body, so that the intermediate transfer body is urged. The discharge can be stably generated by ensuring a gap from the electrode to the auxiliary auxiliary electrode, and as a result, high transfer performance can be obtained.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus is opposed to the transfer roller via the intermediate transfer member and is made of an insulating material having a volume resistance of 10 ¹² Ω · cm or more. Backup roller and an outlet side auxiliary electrode that is placed at a separation point between the backup roller and the intermediate transfer member and is made of the same material as the inlet auxiliary electrode. Insulating rubber can be used, and the discharge path is expanded, which is advantageous for stabilizing the transfer performance.

According to the fifth aspect of the invention, in the image forming apparatus according to the fourth aspect, the inlet auxiliary electrode and the outlet side auxiliary electrode are integrated by one support, so that the cost can be reduced. You can

According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, the contact surface of the entrance auxiliary electrode with respect to the intermediate transfer member is brought into contact with the back surface material of the intermediate transfer member. Since a material that wears before the back surface of the intermediate transfer body is used, the surface layer of the entrance auxiliary electrode can be self-lubricated by the wear caused by contact with the intermediate transfer body and prevent the mixture of insulators, and discharge over a long period of time. Can be stabilized.

According to the seventh aspect of the invention, in the image forming apparatus according to the first aspect, the insulating spacers are provided in the non-image portion of the entrance auxiliary electrode at intervals larger than the maximum lateral width of the transferred material. The surface layer of medium resistance in the auxiliary inlet electrode is not scraped off by abrasion, and resistance fluctuation can be prevented for a long period of time.

According to the eighth aspect of the invention, in the image forming apparatus according to the third aspect, the inlet auxiliary electrode is removed from the normal position when the transfer material is not in the transfer nip.
Since the material to be transferred is moved to the proper position in accordance with the entry of the material to be transferred, it is possible to reduce the abrasion of the surface layer of the entrance auxiliary electrode without contacting the intermediate transfer member when it is not necessary.

According to the ninth aspect of the invention, in the image forming apparatus according to the third aspect, the position of the inlet auxiliary electrode is shifted when the material to be transferred having a strong bending rigidity is passed, so that the material to be transferred is strong. Therefore, when a pressure is applied to the intermediate transfer member when the intermediate transfer member enters, the gap distance important for discharge can be accurately adjusted.

[Brief description of drawings]

FIG. 1 is a schematic view showing a part of a first embodiment of the present invention in an enlarged manner.

FIG. 2 is a sectional view showing the first embodiment.

FIG. 3 is an enlarged sectional view showing a part of the first embodiment.

FIG. 4 is a characteristic diagram showing a relationship between a paper transfer bias of each layer toner and a transfer rate in the image forming apparatus.

FIG. 5 is a diagram for explaining discharge stability between dielectrics.

6 is a circuit diagram showing a DC equivalent circuit of FIG.

7 is a circuit diagram showing an AC equivalent circuit of FIG.

FIG. 8 is a characteristic diagram showing the relationship between the atmospheric pressure and the gap length and the discharge start voltage.

FIG. 9 is a diagram for explaining discharge stability between dielectrics.

FIG. 10 is a perspective view showing a part of the first embodiment.

FIG. 11 is a diagram for explaining the first embodiment.

FIG. 12 is a diagram for explaining a transfer action.

FIG. 13 is a diagram for explaining a transfer action.

FIG. 14 is a diagram for explaining the transfer action of the first embodiment.

FIG. 15 is an exploded perspective view showing a part of a second embodiment of the present invention.

FIG. 16 is a side view showing a part of the third embodiment of the present invention.

FIG. 17 is a side view showing a part of the fourth embodiment of the present invention.

FIG. 18 is an exploded perspective view showing a part of the fourth embodiment.

FIG. 19 is a perspective view showing an auxiliary electrode according to a fifth embodiment of the present invention.

FIG. 20 is a perspective view showing a part of an auxiliary electrode according to a sixth embodiment of the present invention.

FIG. 21 is an exploded perspective view showing a part of the seventh embodiment of the present invention.

FIG. 22 is a partially cutaway side view showing an auxiliary electrode according to the seventh embodiment.

FIG. 23 is a schematic view showing a part of an eighth embodiment of the present invention.

FIG. 24 is a flow chart showing an auxiliary electrode position control flow of the eighth embodiment.

FIG. 25 is a side view showing a part of the ninth embodiment of the present invention.

FIG. 26 is a perspective view showing a part of the ninth embodiment.

FIG. 27 is a perspective view showing a part of the ninth embodiment.

FIG. 28 is a side view for explaining the tenth embodiment of the present invention.

FIG. 29 is a side view for explaining the tenth embodiment.

FIG. 30 is a schematic view showing a part of the tenth embodiment.

FIG. 31 is a flowchart showing a part of an auxiliary electrode position control flow of the tenth embodiment.

FIG. 32 is a flowchart showing another portion of the auxiliary electrode position control flow of the tenth embodiment.

[Explanation of symbols]

 28 Intermediate Transfer Belt 32 Paper Transfer Roller 38 Backup Roller 41 Toner 42 Bias Power Supply for Transfer Roller 43 Transfer Paper 44 Inlet Auxiliary Electrode 45 Surface Layer 46 Support Part 47 Bias Power Supply for Auxiliary Electrode 48 Paper Inlet Guide 53 Spiral Spring 59 Outlet Auxiliary Electrode 62,66 Insulating spacer 67 Stepping motor 69,73 CPU 71 Displacement amount sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Motohashi 1-3-3 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd.

Claims (9)

[Claims] 1. A plurality of toner images are sequentially formed on an intermediate transfer member having a volume resistance of 10 ⁸ to 10 ¹² Ω · cm, and the first plate to the plurality of plates are mixed in one image in terms of plate number. In an image forming apparatus for collectively transferring a toner image onto a transfer material by a transfer roller, the transfer nip from the transfer roller to the transfer material occurs when the transfer material is sandwiched between the transfer roller and the intermediate transfer member. At the back surface of the intermediate transfer member facing the entrance discharge zone, and made of a conductive material having a volume resistance of 10 ⁶ Ω · cm or less, and a volume resistance of 10 ⁸ to 10 ¹² Ω supported by the support portion. Cm having a surface layer of a medium resistance member, the auxiliary auxiliary electrode is separated from the intermediate transfer member by a gap dischargeable distance, and the supporting portion is held at a constant potential. Image forming apparatus characterized by . 2. The image forming apparatus according to claim 1, wherein the entrance auxiliary electrode has a gap between the intermediate transfer body and the inlet auxiliary electrode that gradually narrows along the conveyance direction of the intermediate transfer body. 3. The image forming apparatus according to claim 2, wherein a downstream side of the entrance auxiliary electrode in the conveying direction of the intermediate transfer body is urged to the intermediate transfer body. 4. The image forming apparatus according to claim 1, wherein the backup roller is opposed to the transfer roller via the intermediate transfer body and is made of an insulating material having a volume resistance of 10 ¹² Ω · cm or more, and the backup roller. An image forming apparatus comprising: an outlet side auxiliary electrode that is placed at a separation point between a roller and the intermediate transfer member and is made of the same material as the inlet auxiliary electrode. 5. The image forming apparatus according to claim 4, wherein the inlet auxiliary electrode and the outlet side auxiliary electrode are integrated by one support. 6. The image forming apparatus according to claim 1, wherein a contact surface of the entrance auxiliary electrode with respect to the intermediate transfer body is contacted with a material of the back surface of the intermediate transfer body, so as to come before the back surface of the intermediate transfer body. An image forming apparatus using a material that wears. 7. The image forming apparatus according to claim 1, wherein an insulating spacer is provided in a non-image portion of the entrance auxiliary electrode at an interval larger than the maximum lateral width of the transfer material. 8. The image forming apparatus according to claim 3, wherein the entrance auxiliary electrode is removed from a normal position when the transfer material is not in the transfer nip, and is moved to a normal position in accordance with the entrance of the transfer material. An image forming apparatus characterized by: 9. The image forming apparatus according to claim 3, wherein the position of the entrance auxiliary electrode is shifted when the material to be transferred having a high bending stiffness is passed.