JPH09258578A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To apply the optimum voltages respectively, as the primary transferring voltage at the time of transferring an image from a photoreceptor drum to an intermediate transferring drum and the secondary transferring voltage at the time of transferring from the intermediate transferring drum to a recording paper, in the case of performing an image forming on the recording paper through the intermediate transferring drum. SOLUTION: This device is provided with the drum main body 33 composed of the composition whose volume resistivity is between 10<4> to 10<8> Ωcm, and the intermediate transferring drum 16 formed by covering its outside surface by an insulator layer 34. Then, the device is made possible to apply the voltage respectively suitable for the first transferring and the second transferring, by the first transfer application roller 19 for applying the first transferring voltage, disposed on a position opposing the photoreceptor drum 21, while inscribing the intermediate transferring drum 16, and the second transferring roller 17 for applying the second transferring voltage, disposed opposite to the second grounding roller 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a so-called laser printer which forms an image by using a latent image formed on a photoconductor by a laser, through an intermediate transfer body, a paper or the like. The present invention relates to an image forming apparatus that forms an image on a recording medium.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus for forming an image using a latent image formed on a photoconductor by a light beam,
As a method of realizing a color image, there is a method of adhering the recording paper 108 to the transfer drum 101 as shown in FIG. 9 and transferring the four toner images on the photoconductor drum in sequence by directly superposing them on the transfer member.

The image forming apparatus 100 includes a corona charger 102 for adsorbing a recording paper 108 as a recording medium inside a transfer drum 101 formed of only an insulating layer.
A corona charger 104 that transfers the toner image formed on the surface of the photoconductor drum 103 to the recording paper 108 is separately provided, and the adsorption of the recording paper 108 and the transfer of the toner image to the recording paper 108 are performed separately. It is supposed to be done.

However, the image forming apparatus 10 as described above is used.
At 0, if the insulating layer of the transfer drum 101 is thick,
Since the electric power required to generate the potential difference required for transfer and adsorption increases, the conventional structure has been a single layer structure having only a thin insulator layer, and the strength is not sufficient and there is a problem in durability. In addition, even during handling during replacement work, the insulator layer is easily damaged, and there is a problem in workability. In the above structure, even if the thickness of the insulating layer is the same, the strength can be improved by reducing the outer diameter. However, in addition to the corona chargers 102 and 104 in the periphery, a corona charger for separation and static elimination is provided. Since it is necessary to dispose 105, 106, the cleaning unit 107, and the like, it is difficult to downsize the transfer drum 101.

For example, "BURIED ELEC" of US Pat. 5276490
TRODE DRUM FOR AN ELECTROPHOTOGRAPHIC PRINT ENGIN
The image forming apparatus disclosed in E "uses a transfer drum in which a plurality of electrodes extending in the axial direction are arranged in parallel between an insulating support member and a resistance layer covering the surface thereof. It is possible to simplify the charging device arranged around the drum, but the transfer drum has a problem in mass productivity because it is not easy to form electrodes formed in the axial direction.

Further, in "Intermediate transfer drum for color image forming apparatus" of Japanese Patent Laid-Open No. 4-287070, an intermediate transfer drum having a three-layer structure of a metal drum, a conductive sponge and a dielectric film is disclosed from the inside. Has been done. In the image forming apparatus using the transfer body drum, the transfer from the photosensitive drum to the intermediate transfer body drum and the transfer from the intermediate transfer body drum to the recording paper are performed by the high voltage power source connected to the metal drum of the intermediate transfer body drum. It is configured to perform transfer and
An example of the image forming apparatus having the above structure is shown in FIG.

The image forming apparatus 80 includes the photosensitive drum 8
6, a toner image is formed by the developing devices 88 to 91 arranged around the photosensitive drum 86, the toner image is once transferred onto the intermediate transfer drum 84, and then transferred to the intermediate transfer drum 84. When the recording paper 87 is passed between the roller 85 and the roller 85, a toner image is transferred to the recording paper 87 by applying a voltage having a polarity opposite to that of the toner to the transfer roller 85.

The intermediate transfer drum 84 has a three-layer structure of a metal drum 81, a conductive sponge 82, and a dielectric film 83 from the inside. A high voltage power source 92 and a high voltage power source 92 are connected to the metal drum 81. The grounding terminal 93 is switchably connected, and the transfer roller 85 is connected to a high-voltage power supply 85a having a polarity opposite to that of the toner. When a toner image is formed on the intermediate transfer body drum 84 from the photosensitive drum 86, a voltage having a polarity opposite to that of the toner is applied to the metal drum 81 from the high voltage power source 92, while the intermediate transfer body is formed. When the toner image is transferred from the drum 84 to the recording paper 87, the metal drum 81 is grounded so that the toner image is transferred to the recording paper 87 by the high voltage power supply 85a.

In the above-mentioned image forming apparatus 80, for example, by the developing device 91, one image is formed on the photosensitive drum 86.
A color toner image is formed. The photosensitive drum 86 makes one rotation, and the developing device 89 forms a second-color toner image so as to overlap the first-color image. Further, when the third color and the fourth color are formed and a color toner image is formed, the toner image is formed at the primary transfer position P between the photosensitive drum 86 and the intermediate transfer body drum 84. Transcribed onto 84. Then, the front end portion of the toner image on the intermediate transfer body drum 84 is
When the recording sheet 87 is moved to the secondary transfer position Q between the transfer roller 85 and the transfer roller 85, the recording sheet 87 is already on standby. The toner image is transferred. In the image forming apparatus described above, the primary transfer and the secondary transfer can be applied by switching between the high voltage power supply 92 connected to the metal drum 81 and the ground terminal 93.

[0010]

However, in the above-described image forming apparatus 80, when the optimum image forming conditions on the recording paper are to be realized, the respective primary transfer positions P are set in order to perform the respective transfer. Applies a high voltage,
Since the secondary transfer position Q is grounded, it is impossible to perform both transfers at the same time. Therefore, in the image forming apparatus 80, the maximum usable recording paper 87
It is necessary to keep the distance between the primary transfer position P and the secondary transfer position Q larger than the length of the transfer drum in the traveling direction, and the diameter of the transfer drum becomes large. Also, during continuous copying,
Since the distance between the recording sheets is wide, the copy speed becomes slow. The present invention has been made to solve the above problems, and an object thereof is to allow primary transfer and secondary transfer to be performed independently and in parallel, so that an optimum voltage value for primary transfer can be obtained. It is an object of the present invention to provide an image forming apparatus that can perform the primary transfer and the secondary transfer by the secondary transfer voltage value, does not increase in size, and does not cause a decrease in copy speed.

[0011]

In order to solve the above-mentioned problems, an image forming apparatus according to the invention of claim 1 is a primary transfer for transferring a toner image formed on a photosensitive drum to an intermediate transfer drum. In the image forming apparatus for forming an image on the recording medium by the secondary transfer of transferring the toner image from the intermediate transfer drum to the recording medium, the photosensitive drum is located at the opposite position with the intermediate transfer drum interposed therebetween. A position where the first electrode forming an electric field between the body drum and the photosensitive drum for transferring the toner image onto the intermediate transfer drum and the conductive pressing means provided outside the intermediate transfer drum are opposed to each other. And a second electrode for transferring a toner image from the intermediate transfer drum onto the recording medium by a potential difference from the pressing means, both of which are provided so as to be inscribed inside the intermediate transfer drum. Serial intermediate transfer drum, while being composed of at least the inside of the drum body and the outside of the insulating layer, the volume resistivity of the composition of the drum body is 10 ⁴ to 10 ⁸
It is characterized by being between Ωcm. With the above configuration, the influence of the applied voltage between the primary transfer performed between the photoconductor drum and the first electrode and the secondary transfer performed between the second electrode and the pressing unit is influenced by each other. It becomes smaller, and independent control of the applied voltage can be easily performed.

In order to solve the above-mentioned problems, an image forming apparatus according to a second aspect of the present invention has, in addition to the structure of the first aspect, a rubber-like elasticity between the drum body and the insulating layer. It is characterized in that an elastic layer made of a composition having a volume resistivity of 10 ⁴ to 10 ⁸ Ωcm is provided. With the above configuration, the adhesion between the surface of the intermediate transfer drum and the recording medium can be improved by the deformation of the elastic layer when the secondary transfer is performed between the intermediate transfer drum and the pressing unit.

In order to solve the above-mentioned problems, in the image forming apparatus according to the invention of claim 3, in addition to the constitution of claim 2, the pressing means has at least the surface hardness of the elastic layer. The feature is that the roller shape is higher than the hardness. With the above structure, the recording medium is bent at the time of the secondary transfer along the roller shape of the pressing means, and the separability of the recording medium after the transfer from the intermediate transfer drum can be improved.

In order to solve the above-mentioned problems, an image forming apparatus according to a fourth aspect of the present invention is, in addition to the structure of the first, second or third aspect, a potential difference required for primary transfer and secondary transfer. In order to provide the voltage, a ground electrode is provided between the first electrode and the second electrode so as to be inscribed in the intermediate transfer drum when a voltage is applied to the first electrode and the second electrode. I am trying. With the above configuration, even when different voltages are applied to the first electrode and the second electrode, the influence of the applied voltage on each electrode is further reduced by the ground electrode, and the more appropriate primary transfer voltage and secondary The transfer voltage can be easily maintained.

In order to solve the above-mentioned problems, the image forming apparatus according to the invention of claim 5 is characterized in that:
In addition to the configuration described in (1) above, at a position where a toner image is not formed on the intermediate transfer drum, a voltage having a polarity opposite to that at the time of secondary transfer is applied between the second electrode and the pressing unit. There is. With the above configuration, the toner attached to the pressing unit moves to the recording medium holding member side by the electric field formed between the second electrode and the pressing unit, so that the pressing unit can be cleaned.

In order to solve the above problems, an image forming apparatus according to a sixth aspect of the present invention has a plurality of colors around the photosensitive drum in addition to the configuration according to any one of the first to fifth aspects. A developing device is provided for each color to perform image development by developing on the photosensitive drum and transferring to the recording medium for each color, and at the transfer position between the intermediate transfer drum and the photosensitive drum. Thus, the first electrode is movable in parallel with the rotation direction of the intermediate transfer drum. According to the above configuration, without changing the applied voltage itself applied to the first electrode, according to the toner of each color,
The applied voltage at the transfer position can be adjusted.

In order to solve the above-mentioned problems, an image forming apparatus according to a seventh aspect of the present invention is, in addition to the structure according to any one of the first to fifth aspects, a photoconductor that develops different colors. It is characterized in that a plurality of drums are provided and the first electrode is provided at a position facing each of the photosensitive drums with the intermediate transfer drum interposed therebetween. With the above configuration, even when a plurality of colors are developed to form a color image, it is possible to perform the primary transfer and the secondary transfer with optimum voltage values without slowing down the image formation speed. Become.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] The following will describe one embodiment of an image forming apparatus according to the present invention with reference to FIGS. 1 to 6.

The image forming apparatus 1 according to the present embodiment, as shown in FIG. 1, stocks a recording paper 6 (recording medium) on which an image is formed with toner and supplies the paper, and a toner image. The transfer unit 3 for transferring the toner image onto the recording paper 6, the developing unit 4 for forming the toner image, and the fixing unit 5 for fusing and fixing the toner image transferred on the recording paper 6. On the recording paper 6, primary transfer is performed from the photoconductor drum 21 in No. 4 to the intermediate transfer drum 16 of the transfer unit 3, and secondary transfer is performed from the intermediate transfer drum 16 to the recording paper 6. An image is formed on.

The area where the primary transfer is performed between the photosensitive drum 21 and the intermediate transfer drum 16 is the primary transfer position X, and the secondary transfer is performed on the recording paper 6 between the intermediate transfer drum 16 and the transfer roller 17. The area where the transfer is performed will be referred to as the secondary transfer position Y.

The configuration of the image forming apparatus will be described in detail below with reference to FIG. The paper feed unit 2 is detachably disposed at the lowest stage of the image forming apparatus 1, and the paper feed cassette 10 that stocks the recording paper 6 and supplies the recording paper 6 to the transfer unit 3 and the front surface of the image forming apparatus 1 ( A manual sheet feeding unit 11 that manually feeds the sheets one by one is provided on the side surface in the arrow L direction). A pickup roller 12 for feeding the recording papers 6 one by one from the top of the paper feed cassette 10, a pre-feed roller (PF roller) 13 for conveying the recording papers 6 fed by the pickup roller 12, and a manual feed Provided are a manual feed roller 14 that conveys the recording paper 6 from the paper unit 11, and a registration roller 15 that temporarily stops the recording paper 6 conveyed by the PF roller 13 and the manual feed roller 14 before the transfer unit 3 for timing. Has been.

The paper feed cassette 10 is provided with a delivery member (not shown) biased upward by a spring or the like.
The recording paper 6 is designed to be placed on this delivery member. Then, the uppermost recording paper 6 in the paper feed cassette 10 contacts the pickup roller 12 by the urging force of the delivery member, and the pickup roller 12 is fed to the PF roller 13 one by one by rotation in the arrow direction, It is conveyed to the registration roller 15. On the other hand, the manual paper feed unit 11
When the recording paper 6 is supplied from the recording paper 6, the recording paper 6 is conveyed to the registration rollers 15 by the manual feed roller 14.

The transfer section 3 includes the intermediate transfer drum 1
6 and the transfer roller 1 around the intermediate transfer drum 16.
7 and the separation claw 18 that is separable so as to come into contact with the intermediate transfer drum 16 after the secondary transfer to forcibly separate the recording paper 6 and otherwise separate from the intermediate transfer drum 16. Is provided.

A high voltage power source 19a is connected to the inner surface of the intermediate transfer drum 16 at the primary transfer position X,
A primary transfer applying roller 19 for applying a primary transfer voltage, and 2
Secondary transfer ground roller 2 grounded at the next transfer position Y
0 is inscribed. Since the surfaces of the primary transfer applying roller 19 and the secondary transfer grounding roller 20 that are inscribed in the inner surface of the intermediate transfer drum 16 are covered with an elastic member such as urethane rubber or silicon, the intermediate transfer drum 16 does not rotate. On the other hand, the rotation of the intermediate transfer drum 16 can be stabilized without transmitting unnecessary vibration.

Further, since a toner image is formed on the surface of the intermediate transfer drum 16 by static electricity, a charge charged on the surface of the intermediate transfer drum 16 is further formed around the intermediate transfer drum 16. While a static eliminator for removing the toner, a cleaning device for removing toner and the like adhering to the surface of the intermediate transfer drum 16 and the like are also provided, flanges made of an insulating member are provided at both axial ends of the intermediate transfer drum 16. By being attached to the main body frame via the bearing attached to this flange, the main body frame is rotatably fixed while being insulated from the main body frame, and electrical influences from other devices are eliminated. It maintains the electrical stability of the surface.

Then, in the developing section 4, the intermediate transfer drum 1
The photoconductor drum 21 is rotatably provided in pressure contact with the primary transfer position X with respect to the photosensitive drum 6. The photoconductor drum 21 has an OPC (Organic Photoconductive Condenser) on its outer surface.
ductor) An aluminum tube on which a film is formed, and this aluminum tube is grounded. Around the photosensitive drum 21, a developing device 2 that stores yellow, magenta, cyan, and black toners, respectively.
2, 23, 24, 25 are provided, and the charger 26 and the photoconductor drum 21 for charging the surface of the photoconductor drum 21.
A cleaning device 27 for removing the residual toner on the surface is provided, and a toner image is formed on the photosensitive drum 21 for each toner of each color. That is, charging, exposure, development and transfer are repeated for each color on the photosensitive drum 21. Therefore, when a color toner image is transferred, a toner image for each color is transferred onto the intermediate transfer drum 16 every time the intermediate transfer drum 16 makes one rotation, and a color toner image is normally obtained by four rotations. Although not shown, the light beam that exposes the surface of the photosensitive drum 21 is applied between the charger 26 and the developing unit 4.

In the fixing section 5, a fixing roller 28 that fuses the toner image at a predetermined temperature and pressure to fix the toner image on the recording paper 6, and after the secondary transfer, is separated from the intermediate transfer drum 16 by a separation claw 18. The recording paper 6 to the fixing roller 2
A conveyance guide 29 and a fixing guide 30 that guide up to 8 are provided. Further, a discharge roller 31 and a discharge tray 32 for receiving the recording paper 6 discharged after fixing are provided on the downstream side of the fixing unit 5 from the conveyance of the recording paper 6.

Next, the structure of the intermediate transfer drum 16 will be described with reference to FIG. The intermediate transfer drum 16
As shown in FIG. 2, a resin having a volume resistivity between a so-called conductor and an insulator by filling a conductive additive as a base material (this resin is called semi-conductive, (Hereinafter referred to as semi-conductive resin) is used, and an elastic layer 35 made of semi-conductive urethane foam or silicon is provided on the outer surface of the drum main body 33. Further, an insulating layer 34 made of polyvinylidene fluoride is provided on the outer surface of the elastic layer 35.

However, regarding the drum body 33,
When the required applied voltage is different between the primary transfer position X and the secondary transfer position Y, the applied voltages may interfere with each other. Therefore, in order to prevent this interference, the semiconductive resin The volume resistivity is preferably in the range of 10 ⁴ to 10 ⁸ Ωcm. In addition, the thickness is 1 to 1 in terms of ensuring rigidity and functionally.
It should be in the range of 30 mm. For the same reason as above, the elastic layer 35 also needs to have a volume resistivity in the range of 10 ⁴ to 10 ⁸ Ωcm, and at the same time, in order to obtain a sufficient nip width, the layer thickness is It is preferably in the range of 1 to 10 mm.

On the other hand, it is necessary for the insulating layer 34 to have an appropriate charge holding force between the intermediate transfer drum 16 and the transfer roller 17 or the photosensitive drum 21.
The charge retention, that is, the capacitance c is generally c = ε, where ε is the relative permittivity, s is the area of the insulator layer, and d is the layer thickness.
It is represented by xs / d. From the above equation, it can be said that the thinner the thickness, the larger the electrostatic capacitance c can be.
The layer thickness d is preferably about 50 μm to 300 μm in view of obtaining a uniform layer thickness and considering mass productivity and durability.

In the above equation, if the relative permittivity ε is small, the electrostatic capacitance c is small, so that the transfer efficiency is improved, while if the attraction force is reduced and the relative dielectric constant ε is large, the electrostatic capacitance c is reduced. , The transfer efficiency will deteriorate, while
The adsorption power increases. The magnitude of the layer thickness d is opposite to that of the magnitude of the relative permittivity ε. Therefore, there is an appropriate range of relative permittivity with respect to the above range of the layer thickness d.

At this time, if the resistance of the insulating layer 34 is too low, the toner on the photosensitive drum 21 will be transferred to the intermediate transfer drum 1.
The secondary transfer because the current component flowing due to the circuit contact satisfying Ohm's law flows between the photosensitive drum 21 and the intermediate transfer drum 16 with priority over the current component flowing when moving to the 6 side. The toner transferred to the recording paper 6 at the position Y returns to the intermediate transfer drum 16 and retransfer occurs. On the contrary, when the resistance is too high, the toner on the photosensitive drum 21 moves to the intermediate transfer drum 16. Both the current component flowing at that time and the current component flowing between the photoconductor drum 21 and the intermediate transfer drum 16 due to the circuit contact satisfying Ohm's law are less likely to flow, so that they move to the recording paper 6 at the secondary transfer position. Since the amount of non-printable toner increases and transfer failure occurs, there is an appropriate volume resistivity for the layer thickness d.

As a composition of the insulator layer 34, it has been experimentally found that it is preferable that the relative dielectric constant is in the range of 8 to 12 and the volume resistivity is 10 ¹² to 10 ¹⁷ Ωcm. For example, the relative permittivity and volume resistivity of the above-mentioned polyvinylidene fluoride satisfy the above conditions. Also,
If it satisfies the above range, it can be used as the insulator layer 34, and other examples include polyethylene terephthalate.

In the above, the drum body 33, the elastic layer 35 and the insulating layer 34 are used as the intermediate transfer drum 16.
The elastic layer 35 has a three-layer structure
Is not always necessary. For example, the outer surface of the drum main body 33 may be directly covered with the insulating layer 34. However, the intermediate transfer drum 1 according to the present embodiment is not limited thereto.
If the elastic layer 35 is provided as in 6, the separability between the recording paper 6 and the intermediate transfer drum 16 after the transfer of the toner image can be improved as described later.

In the above, the primary transfer voltage is supplied from the high voltage power source 19a to the primary transfer position X inside the intermediate transfer drum 16, and the secondary transfer position Y is at the ground roller 20.
However, since the intermediate transfer drum 16 uses the drum main body 33 made of a semiconductive resin inside as described above, the intermediate transfer drum 16 has a primary transfer position X and a secondary transfer position. The potential difference at the position Y can be maintained, and the primary transfer and the secondary transfer can be performed in parallel with different voltage values.

Next, the structure of the transfer roller 17 will be described. In the following, the discussion will be made on the assumption that a negative polarity toner is used, but the same idea can be applied to a positive polarity toner.

To the transfer roller 17 provided below the intermediate transfer drum 16, a high voltage power supply 17a shown in FIG. 3 applies a reverse polarity to the toner, that is, a positive voltage. As a result, when the recording paper 6 passes the secondary transfer position Y between the transfer roller 17 and the intermediate transfer drum 16, the toner moves in the direction of the transfer roller 17 and the photosensitive drum 2
The toner image formed on the recording sheet 1 is transferred onto the recording sheet 6.

Since the hardness of the surface of the transfer roller 17 is higher than the hardness of the elastic layer 35 of the intermediate transfer drum 16, when the recording paper 6 passes the secondary transfer position Y, the intermediate transfer is performed. The recording paper 6 is deformed on the drum 16 side.
Is given a curl along the transfer roller 17,
After passing the next transfer position Y, the separability of the recording paper 6 from the intermediate transfer drum 16 becomes good.

Further, in the image forming process, in order to prevent the toner image formed on the intermediate transfer drum 16 from being disturbed by being pressed against the transfer roller 17,
The transfer roller 17 is in a state of being separated from the intermediate transfer drum 16 at times other than the secondary transfer. Since it is configured to be mechanically performed by disposing a solenoid, etc., the transfer roller 17 always obtains a stable nip width and a predetermined separation amount at the secondary transfer position Y. It is like this.

Here, 1 by the intermediate transfer drum 16 is used.
The next transfer / secondary transfer operation will be described below. First, in the primary transfer process, a toner image having a negative charge is formed on the surface of the photosensitive drum 21. The toner image formed on the photosensitive drum 21 is the photosensitive drum 2
With the rotation of 1, the sheet is sent to the primary transfer position X between the photoconductor drum 21 and the intermediate transfer drum 16.

At the primary transfer position X, the high voltage power supply 19a
By applying a voltage having a polarity opposite to that of the toner, that is, a positive voltage, to the secondary transfer applying roller 19, the primary transfer applying roller 19
From the above, an electric field is generated in the direction of the photoconductor drum 21, and the negative toner moves to the surface of the intermediate transfer drum 16 and the toner image is transferred. The intermediate transfer drum 16 and the photosensitive drum 21 are pressed against each other at the primary transfer position X so as to have a predetermined nip width. By repeating the same process as above four times for each color, a color toner image composed of four color toner images is formed on the intermediate transfer drum 16, and this color toner image is rotated in the direction of the arrow of the intermediate transfer drum 16. Along with this, the sheet is conveyed to the secondary transfer position Y between the intermediate transfer drum 16 and the transfer roller 17.

In the secondary transfer process, when the recording paper 6 passes the secondary transfer position Y, the transfer roller 1 is transferred from the high voltage power source 17a.
By applying a voltage having a polarity opposite to that of the toner, that is, a positive voltage, the toner having a negative polarity moves toward the recording paper 6 and a toner image is transferred onto the recording paper 6.

In the above, generally, when the transfer roller 17 is used for a long time, unnecessary toner adheres to the surface of the transfer roller 17 and stains the back of the recording paper 6, so that the voltage applied to the transfer roller 17 is increased. The polarity can be switched, and when the recording paper 6 does not pass the secondary transfer position Y, the transfer roller 17 is brought into close contact with the intermediate transfer drum 16,
A voltage having the same polarity as that of the toner is applied to move the unnecessary toner adhering to the transfer roller 17 onto the intermediate transfer drum 16. The unnecessary toner that has moved onto the intermediate transfer drum 16 is collected by the cleaning device.

As described above, since transfer is performed by contact instead of transfer by conventional charge injection by air discharge, the voltage can be low and the voltage can be easily controlled.
It requires less energy for driving. Further, the surface of the intermediate transfer drum 16 can be charged more stably than in the conventional case where the surface of the intermediate transfer drum 16 is charged by inducing electric charge to be charged, so that the transfer can be performed stably. it can.

Furthermore, since the charging of the intermediate transfer drum 16 is performed by contact charging, even if the surface of the intermediate transfer drum 16 is flawed, the electric field area does not change. Therefore, the electric field balance is achieved at the flawed portion of the surface of the intermediate transfer drum 16. Will never go mad. As a result, transfer failure such as white spots does not occur at that portion, so that transfer efficiency can be improved.

An image forming process in the image forming apparatus 1 will be described below based on the above configuration. First, FIG.
As shown in, the toner image of the first color is formed on the photosensitive drum 21, and the toner image is sent to the primary transfer position X as the photosensitive drum 21 rotates. At that time, a voltage having a polarity opposite to that of the toner is applied to the primary transfer applying roller 19,
The toner image of the first color is transferred onto the intermediate transfer drum 16 at the primary transfer position X. The photoconductor drum 21 is charged, exposed, developed, and transferred for each color. Therefore,
By rotating the intermediate transfer drum 16 four times, one full-color image is obtained. However, in the case of obtaining a monotone image using the prepared toners of each color alone, for example, a monochrome image, the intermediate transfer drum 16 may be rotated once.

The primary transfer applying roller 19 is inscribed in the intermediate transfer drum 16 by a driving means (not shown),
It is movable in an arc shape with respect to the center of the intermediate transfer drum 16 (in the direction of the arrow in the figure), and the position is changed according to the electrical characteristics of each color toner to perform primary transfer. At this time, the moving amount of the primary transfer applying roller 19 is such that the electric field formed between the intermediate transfer drum 16 and the photosensitive drum 21 at the primary transfer position X has a transfer characteristic with respect to the applied voltage of the toner of each color. It is set according to the appropriate value. This makes it possible to transfer the toner of each color with uniform transfer efficiency without changing the transfer voltage. After all the toner images have been transferred onto the intermediate transfer drum 16, they are sent to the secondary transfer position Y as the intermediate transfer drum 16 rotates.

On the other hand, in parallel with the above-mentioned image formation, in the case of automatic sheet feeding, the recording sheet 6 is picked up one by one by the pickup roller 12 from the top by the sheet feeding cassette 10 provided at the bottom of the main body. This is sent to the PF roller 13 and this PF
The recording paper 6 that has passed the roller 13 is registered by the registration roller 15
The secondary transfer position Y depending on the image forming timing
Transported to Further, in the case of manual paper feeding, the recording papers 6 are sent out one by one from the manual paper feeding section 11 provided on the front surface of the main body, and are conveyed to the registration rollers 15 by the manual paper feeding roller 14. Then, the recording paper 6 is transferred to the registration roller 15
The sheet is conveyed to the secondary transfer position Y according to the image forming timing.

The recording paper 6 conveyed from the registration roller 15 is conveyed to the secondary transfer position Y between the intermediate transfer drum 16 and the transfer roller 17, and is applied with a voltage having a polarity opposite to that of the toner applied to the transfer roller 17. The toner image formed on the intermediate transfer drum 16 is transferred to the recording paper 6. Then, the recording paper 6 on which the secondary transfer has been performed is separated from the surface of the intermediate transfer drum 16 by the separation claw 18 and then guided to the conveyance guide 29 and the fixing guide 30. Further, the fixing guide 30 guides the fixing roller 28,
The toner image is fused on the recording paper 6 by the temperature and pressure of the fixing roller 28. Recording paper 6 with the image fixed
Are discharged onto the discharge tray 32 by the discharge roller 31. On the other hand, the intermediate transfer drum 16 from which the recording paper 6 is separated
Is cleaned, and when the image formation is continued again, the above-mentioned primary transfer and secondary transfer are repeated.

When the above cleaning is performed, the timing at which the transfer roller 17 is brought into close contact with the intermediate transfer drum 16 is set so that the trailing end of the toner image on the intermediate transfer drum 16 onto which the toner images of the third color are superposed and transferred is the secondary transfer position. Immediately after passing Y, the cleaning time can be extended. As a result, the transfer roller 1 for performing the secondary transfer
Since the contacting operation of 7 can be continued, the separating operation of the transfer roller 17 can be reduced.

The timing of performing the above cleaning will be described below with reference to FIGS. 4 and 5. The distance from the primary transfer position X to the secondary transfer position Y is Ls, and the recording paper 6
Let be the length of Lp. A in the figure shows the timing of the toner image passing through the primary transfer position X, B is the timing of the toner image passing through the secondary transfer position Y, and C is the application of the voltage applied to the primary transfer applying roller 19. Timing, D
Is the timing of separating / contacting the transfer roller 17 from the intermediate transfer drum 16, and E is the timing of applying the voltage applied to the transfer roller 17.

In the above, the following two timing charts can be considered depending on the relationship between the distance Ls and the length Lp. First, when Ls <Lp, as shown in FIG. 4, during the primary transfer of the final toner image to the intermediate transfer drum 16, the secondary transfer to the recording paper 6 starts, and the primary transfer position X,
When a simultaneous application section in which a voltage is applied simultaneously at the secondary transfer position Y occurs and Ls> Lp, as shown in FIG. 5, the recording paper 6 is always transferred after the primary transfer of the recording paper 6 is completed.
There is no interval for the initiation of secondary transcription of. Also,
If the distance between the recording papers 6 is shortened in order not to reduce the copy speed during continuous copying, the primary transfer of the next image formation starts during the secondary transfer regardless of the distance Ls and the length Lp. Simultaneous application sections of primary transfer and secondary transfer occur.

In the image forming apparatus of the present embodiment, even if the simultaneous application section in which the primary transfer and the secondary transfer are simultaneously performed as described above, the primary transfer and the secondary transfer are performed. Since it is possible to apply an appropriate voltage to each of the above, the recording paper 6 can be smoothly transported, an efficient image forming operation can be performed, and a high-quality image can be obtained. it can. 4 and 5
In the above, the contact timing of the transfer roller 17 with the transfer drum 16 is set to immediately after the trailing edge of the recording paper 6 on which the three color toner images have been transferred as described above has passed the suction position Y. It is possible to take the cleaning time, that is, the cleaning period as long as possible.

Further, the image forming apparatus 1 is provided with a secondary transfer applying roller 40 to which a high voltage power source 40a is connected, as shown in FIG. 6, in place of the secondary transfer ground roller 20 shown in FIG. Therefore, a secondary transfer voltage may be applied to the secondary transfer applying roller 40 and the transfer roller 17 side may be grounded. In this case, both of the voltages of the primary transfer and the secondary transfer are applied from the inside,
A ground roller 41 is provided between the primary transfer applying roller 19 and the secondary transfer applying roller 40 in order to eliminate mutual interference between the primary transfer and the secondary transfer. The secondary transfer applying roller 40 and the ground roller 41 are the primary transfer applying roller 19,
Like the secondary transfer grounding roller 20, it is covered with an elastic body so as not to affect the rotation of the intermediate transfer drum 16. At the time of the secondary transfer, a voltage having the same polarity as that of the toner is applied to the secondary transfer applying roller 40 to transfer the toner image formed on the intermediate transfer drum 16 onto the recording paper 6.

By applying the secondary transfer voltage from the inside of the intermediate transfer drum 16 as described above, the supply mechanism of the voltage supply means can be easily shared, and the structure of the power supply can be simplified. Further, since the secondary transfer applying roller 40 for applying a high voltage does not need to be separated / contacted, it is possible to stably apply a high voltage. Further, since the secondary transfer voltage is applied from the inner surface, it is possible to improve the transfer efficiency of the toner image formed inside the intermediate transfer drum 16, that is, the first formed toner image.

[Second Embodiment] The following will describe another embodiment of the present invention in reference to FIGS. 7 and 8. For convenience of explanation, members having the same functions as those shown in the drawings of the first embodiment will be designated by the same reference numerals, and the description thereof will be omitted.

In the image forming apparatus of the present embodiment, as shown in FIG. 7, four photoconductor drums 21 for forming toner images of respective colors are arranged around the intermediate transfer drum 16, and each photoconductor drum 21 is also exposed. Around the body drums 21 ... For charging an image, a charger 26, an exposing means (not shown), and a developing device 22 to
A cleaning device 27 is provided along with any one of 25. Further, on the inner surface of the intermediate transfer drum 16, primary transfer applying rollers 19 are provided so as to be in contact with each photosensitive member 21 at each primary transfer position X. A grounding roller (not shown) is provided between the primary transfer applying rollers 19 to eliminate the mutual influence caused by the difference in applied voltage between the primary transfer applying rollers 19.

An image forming process in the image forming apparatus having the above structure will be described below. First, each developing device 22
25 to 25, latent images corresponding to the signals of the respective colors are formed on the respective photosensitive drums 21. The latent image is formed by uniformly charging it by a charger 26 provided on the surface of the photosensitive drum 21 and exposing it by the exposing means.

These latent images are developed by the developing devices 22 to 22, respectively.
25 is developed into a toner image of each color. The developed toner images are sequentially transferred onto the intermediate transfer drum 16 in an overlapping manner by applying an appropriate transfer voltage for each color to the primary transfer applying rollers 19. After the transfer of the final toner image is completed, as the intermediate transfer drum 16 rotates,
The toner image formed on the intermediate transfer drum 16 is sent to the secondary transfer position Y between the intermediate transfer drum 16 and the transfer roller 17.

On the other hand, in parallel with the above image formation, the recording paper 6
The secondary transfer ground roller 20 is used as a counter electrode before the high voltage power supply 17 supplies a negative voltage having a polarity opposite to that at the time of secondary transfer, that is, the same negative voltage as the toner polarity.
By applying the toner from a to the transfer roller 17, unnecessary toner adhering to the transfer roller 17 is removed.
Move up and remove.

Then, by switching the voltage polarity of the transfer roller 17 to the toner image formed on the intermediate transfer drum 16 and applying a voltage having a polarity opposite to that of the toner,
The toner image is transferred to the recording paper 6 sent to the secondary transfer position Y. After that, the separation claw 1 is removed from the intermediate transfer drum 16.
The recording paper 6 separated by 8 is conveyed to the fixing unit 5 and the toner image is fused to the recording paper 6.

Here, the timing of the primary transfer, the secondary transfer and the cleaning of the transfer roller 17 will be described below with reference to FIG. In FIG. 8, F indicates the timing when the recording paper 6 passes the primary transfer position X of the developing device 22, and hereinafter, G, H, and I indicate the recording paper 6 of the developing devices 23, 24, and 25, respectively. The timing when the primary transfer position X is passed is shown, and J and K are the timing when the color toner image passes the secondary transfer position Y and 2 respectively.
The timing for applying the next transfer voltage and the voltage for cleaning the transfer roller 17 is shown.

In the case of the above construction, the primary transfer position X is set for each color.
However, it is unrealistic to set the interval between the primary transfer positions X to the maximum length of the recording paper 6 even if the size of the image forming apparatus is taken into consideration. There is a simultaneous application section between subsequent transfers. Further, since the secondary transfer can be started from the position where the primary transfer of the fourth color is completed, there is a simultaneous application section of the primary transfer and the secondary transfer. Since it is not necessary to bring the transfer roller 17 into and out of contact with the transfer roller 17, except when the secondary transfer is performed as shown by K in FIG.
If a voltage having a polarity opposite to that of the secondary transfer is applied, the transfer roller 1
7 can be cleaned.

In the image forming apparatus of this embodiment,
Even if the simultaneous application section in which a plurality of primary transfers are simultaneously performed and the simultaneous application section in which the primary transfer and the secondary transfer are simultaneously performed as described above, an appropriate transfer voltage is individually applied. Therefore, as in the first embodiment, the recording paper 6 can be smoothly transported, color copy can be performed at a copy speed equivalent to that of monocopy, and efficient image forming operation can be performed. A high quality image can be obtained. In addition, in the image forming apparatus according to each of the above-described embodiments, inside and outside the intermediate transfer drum 16,
Although a conductive roller is used for applying an applied voltage or grounding, a conductive roller such as a conductive brush may be used.

[0065]

According to the first aspect of the present invention, there is provided an image forming apparatus comprising:
As described above, by the primary transfer for transferring the toner image formed on the photosensitive drum to the intermediate transfer drum and the secondary transfer for transferring the toner image from the intermediate transfer drum to the recording medium, the transfer to the recording medium is performed. In an image forming apparatus that forms an image, it is located at a position opposite to each other with the intermediate transfer drum of the photoconductor drum interposed therebetween, and an electric field is formed between the photoconductor drum and the photoconductor drum to transfer the toner image onto the intermediate transfer drum. Is provided at a position opposite to the first electrode that forms the third electrode and the third electrode provided outside the intermediate transfer drum, and the toner image is transferred from the intermediate transfer drum onto the recording medium by the potential difference between the third electrode and the third electrode. Two electrodes are provided so as to be inscribed inside the intermediate transfer drum, while the intermediate transfer drum is composed of at least an inner drum body and an outer insulating layer. In a configuration in which the volume resistivity of the composition of the drum body is between 10 ⁴ ~10 ⁸ Ωcm.

Therefore, the influence of the applied voltage between the primary transfer performed between the photosensitive drum and the first electrode and the secondary transfer performed between the second electrode and the pressing means is influenced. Since it is possible to easily control the applied voltage independently, it is possible to apply an appropriate applied voltage to each of the primary transfer and the secondary transfer, and improve the efficiency of the image forming process. There is an effect that can be done.

As described above, in the image forming apparatus according to the second aspect of the present invention, in addition to the structure of the first aspect, a rubber-like elasticity is exhibited between the drum body and the insulating layer, and the volume resistance is increased. The elastic layer is made of a composition having a ratio of 10 ⁴ to 10 ⁸ Ωcm. Therefore, Claim 1
In addition to the effect of the configuration described above, the elastic layer is deformed when the secondary transfer is performed between the intermediate transfer drum and the pressing unit, thereby improving the adhesion between the surface of the intermediate transfer drum and the recording medium. Therefore, there is an effect that it is possible to prevent the transfer failure from occurring easily.

As described above, in the image forming apparatus according to the invention of claim 3, in addition to the configuration of claim 2,
The outer surface of the electrode is covered with at least an elastic body exhibiting rubber-like elasticity, and the hardness of the elastic body is smaller than that of the elastic layer. Therefore, in addition to the effect of the configuration of claim 2, the intermediate transfer drum side is always deformed by the pressure on the recording medium at the time of the secondary transfer, and the bending along the roller shape of the pressing means is given. The recording medium after the transfer is easily separated from the intermediate transfer drum, and the paper jam is less likely to occur.

As described above, the image forming apparatus according to the fourth aspect of the present invention, in addition to the structure of the first, second or third aspect, provides a potential difference required for the primary transfer and the secondary transfer. A ground electrode is provided between the first electrode and the second electrode so as to be inscribed in the intermediate transfer drum when a voltage is applied to the first electrode and the second electrode.
Therefore, in addition to the effect of the configuration of claim 1, 2 or 3, even when different voltages are applied to the first electrode and the second electrode, each electrode is influenced by the change in the applied voltage due to the ground electrode. Is further reduced, it is possible to stably supply the primary transfer voltage and the secondary transfer voltage, and it is possible to stably maintain a high-quality image.

As described above, in the image forming apparatus according to the invention of claim 5, in addition to the structure of claim 1, 2, 3 or 4, the position where the toner image is not formed on the intermediate transfer drum. In this configuration, a voltage having a polarity opposite to that at the time of secondary transfer is applied between the second electrode and the third electrode. Therefore, in addition to the effect of the first, second, third, or fourth aspect, the toner adhered on the pressing unit is transferred to the recording medium holding member side by the electric field formed between the second electrode and the pressing unit. Since the pressing means is moved to be cleaned, it is not necessary to provide a cleaning means for the pressing means, and the structure can be simplified.

As described above, in the image forming apparatus according to the invention of claim 6, in addition to the structure of any one of claims 1 to 5, a developing device for a plurality of colors is provided around the photosensitive drum. An image is formed by performing development on the photosensitive drum and transfer to the recording medium for each color, and at the same time with respect to the transfer position between the intermediate transfer drum and the photosensitive drum. In this structure, one electrode is movable in parallel with the rotation direction of the intermediate transfer drum. That is, even if the same applied voltage is applied by the resistance of the intermediate transfer drum, the electric field formed between the intermediate transfer drum and the photosensitive drum changes depending on the position of the first electrode. In addition, the transfer characteristics with respect to the applied voltage of each toner are also different. therefore,
In addition to the effects of the configurations of claims 1 to 5, if the electric field is adjusted by making the first electrode movable, an electric field suitable for each toner can be obtained without changing the voltage applied to the first electrode. It is possible to perform the transfer to the intermediate transfer drum by forming the.

As described above, in the image forming apparatus according to the invention of claim 7, a plurality of photosensitive drums for developing different colors are provided in addition to the structure of any one of claims 1 to 5. In addition, the first electrodes are provided at opposing positions of the respective photosensitive drums with the intermediate transfer drum interposed therebetween. Therefore, in addition to the effects according to the first to fifth aspects, even when a plurality of colors are developed to form a color image, the voltage applied to the first electrode of each color can be individually controlled, and therefore, for each color. Highly reproducible images can be easily obtained even when the appropriate primary transfer voltage is different.
Further, there is an effect that a color image can be formed without slowing down the image forming speed.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic perspective view of the intermediate transfer drum shown in FIG.

FIG. 3 is a schematic diagram of an image forming apparatus according to another embodiment of the present invention.

FIG. 4 is a timing chart showing the application timing of the primary transfer voltage and the secondary transfer voltage when Ls <Lp in the image forming apparatus of FIG.

5 is a timing chart showing the application timing of the primary transfer voltage and the secondary transfer voltage when Ls ≧ Lp in the image forming apparatus of FIG.

FIG. 6 is a schematic diagram of an image forming apparatus according to another embodiment of the present invention.

FIG. 7 is a schematic diagram of an image forming apparatus according to still another embodiment of the present invention.

8 is a primary transfer voltage in the image forming apparatus of FIG.
6 is a timing chart showing the timing of application of a next transfer voltage.

FIG. 9 is a schematic sectional view of a main part of a conventional image forming apparatus.

FIG. 10 is a schematic sectional view showing another conventional image forming apparatus.

[Explanation of symbols]

 1 Image Forming Apparatus 6 Recording Paper (Recording Medium) 16 Intermediate Transfer Drum 17 Transfer Roller (Pressing Means) 19 Primary Transfer Applying Roller (First Electrode) 20 Secondary Transfer Grounding Roller (Second Electrode) 21 Photosensitive Drum 33 Drum Main body 34 Insulator layer 35 Elastic layer 40 Secondary transfer applying roller (second electrode) 41 Grounding roller (grounding electrode) X Primary transfer position Y Secondary transfer position

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Atsushi Ide 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Kazuyuki Onishi 22-22, Nagaike-cho, Abeno-ku, Osaka, Osaka Within the corporation

Claims (7)

[Claims] 1. A primary transfer for transferring a toner image formed on a photosensitive drum to an intermediate transfer drum, and a secondary transfer for transferring the toner image from the intermediate transfer drum to a recording medium.
In an image forming apparatus that forms an image on a recording medium, it is located at a position opposite to each other with the intermediate transfer drum of the photosensitive drum interposed therebetween, and the photosensitive drum is used to transfer the toner image from the photosensitive drum onto the intermediate transfer drum. Is provided at a position opposite to the first electrode that forms an electric field between the first transfer electrode and a conductive pressing unit provided outside the intermediate transfer drum. Due to a potential difference between the first electrode and the conductive pressing unit, a toner image is formed on the recording medium from the intermediate transfer drum. A second electrode for transferring is provided so as to be inscribed inside the intermediate transfer drum, while the intermediate transfer drum is composed of at least an inner drum body and an outer insulating layer. An image forming apparatus characterized in that the volume resistivity of the composition of the drum body is between 10 ^{4 and} 10 ⁸ Ωcm. 2. An elastic layer having a rubber-like elasticity and a composition having a volume resistivity of 10 ⁴ to 10 ⁸ Ωcm is provided between the drum body and the insulating layer. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. 3. The image forming apparatus according to claim 2, wherein the pressing means has a roller shape whose surface has a hardness at least higher than that of the elastic layer. 4. In order to give a potential difference required for the primary transfer and the secondary transfer, when a voltage is applied to the first electrode and the second electrode, the first electrode is inscribed in the intermediate transfer drum.
The image forming apparatus according to claim 1, wherein a ground electrode is provided between the electrode and the second electrode. 5. At a position where a toner image is not formed on the intermediate transfer drum, 2 is provided between the second electrode and the pressing means.
The image forming apparatus according to claim 1, 2, 3 or 4, wherein a voltage having a polarity opposite to that at the time of the next transfer is applied. 6. A developing device for a plurality of colors is provided around the photosensitive drum, and image formation is performed by developing on the photosensitive drum and transferring to a recording medium for each color, and at the same time, the intermediate transfer is performed. 6. The first electrode is movable in parallel with the rotation direction of the intermediate transfer drum with respect to the transfer position between the drum and the photoconductor drum. The image forming apparatus according to item 1. 7. A plurality of photoconductor drums for developing different colors are provided, and a first electrode is provided at each opposing position of the photoconductor drums sandwiching the intermediate transfer drum. The image forming apparatus according to any one of 1 to 5.