JP2003098849A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which is an intermediate transfer type tandem color image forming device, having neither less color shift nor dropout of characters during transfer. SOLUTION: The tonner image formed on an image carrier is transferred to a recording medium through an intermediate transfer medium. Image carriers 3a-3d comprise circular rigid supporters 32a and 32b, which support the inside surfaces at both ends, with an image formation region being flexible. Elastic sections 22a and 22b constitute both ends of a cylindrical intermediate transfer medium 1, abutting on the circular rigid supporters 32a and 32b. The drive force for the image carriers 3a-3d is transferred from the cylindrical intermediate transfer medium.

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, a printer, a facsimile and a printing machine. Particularly, the present invention relates to a tandem type color image forming apparatus for sequentially transferring toner images of a plurality of colors to an intermediate transfer medium and then collectively transferring to a paper, and specifically, electrophotographic recording method, electrostatic recording method, ionography, magnetic recording method, etc. Image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a tandem type color image forming apparatus of this type is used for charging an image carrier, image exposure, development, transfer,
A single color image forming process unit that executes an image forming process for cleaning is arranged in parallel for four colors of yellow (Y), magenta (M), cyan (C), and black (Bk), and these transfer parts are arranged. Toners of respective colors are sequentially transferred onto a common transfer material passing therethrough to perform color superimposition of four colors. At this time, the image forming process units of colors not used for image formation may be separated so as not to contact the transfer material. This is to prevent unnecessary reverse transfer of the toner image to the image forming process unit. For example, when forming an image with only a black image, the image forming process units of the other three colors may be separated so as not to contact the transfer material. On the other hand, in the case of printing a color image, the image forming process unit of these three colors is also provided with a mechanism for moving from the separated position to the contact position so as to contact the transfer material.

This tandem type color image forming apparatus is classified into the following two types. The first is to use the transfer material as a final recording material, and the image is sequentially formed on the recording material such as paper, and the recording material is conveyed to the fixing portion after passing through the four-color image forming process unit. Then, the toner is fixed and the image formation is completed. Secondly, the transfer material is used as an intermediate transfer medium, and the toner image is primarily transferred to the intermediate transfer medium, secondarily collectively transferred from the intermediate transfer medium to the final recording material, and then fixed. This is an apparatus configured to convey a recording material to a section. Here, the former is called the direct type and the latter is called the indirect type.

The direct type has the advantage of simplifying the apparatus structure, but if the physical properties such as the thickness, friction coefficient and surface resistance of the recording material such as paper are different, it can be conveyed accurately at the same speed. This is difficult, and for example, there is a defect that color misregistration easily occurs on thin paper. In addition, it is common to electrostatically adsorb the recording material to the conveyor belt, but the unfixed toner on the recording material is caused by separation discharge when the recording material is separated from the conveyor belt before being conveyed to the fixing unit. The image is disturbed,
There is also a problem that the image quality deteriorates.

As a solution to this problem, there is an indirect type, and an intermediate transfer system using an endless seamless transfer belt as the intermediate transfer medium is known, and the problem of color misregistration has been improved to some extent.

[0006]

However, even in the above-mentioned conventional indirect type color image forming apparatus, since the transfer belt is used as the intermediate transfer medium, the transfer belt deteriorates or becomes dirty in the long-term use. As a result, it is inevitable that the frictional force between the driving roller and the transfer belt changes with time, and the conveyance speed may fluctuate, causing a problem of color misregistration. Further, the tension of the transfer belt may change due to environmental changes such as temperature and humidity, and the conveyance speed may change. Further, scattered toner particles or paper powder may adhere to the inside of the transfer belt to cause speed fluctuations, which may cause color misregistration. Further, in the method using the transfer belt, there is a problem that the apparatus configuration becomes complicated because a transfer belt meandering control mechanism is required.

As a method for solving these problems, for example, JP-A-7-244413 or JP-A-10-3 is used.
As disclosed in No. 01402, there is a proposal to use a cylindrical drum having an elastic layer surface instead of a transfer belt as an intermediate transfer medium. According to this method, the change in frictional force between the transfer belt and the driving roller, the change in tension of the transfer belt, and the change in speed due to the intrusion of toner particles and paper powder, which are caused in the method using the transfer belt, do not occur. The gap is significantly reduced. However,
By using a cylindrical drum as the intermediate transfer medium,
Since the contact pressure between the image carrier and the cylindrical intermediate drum is larger than that in the system using the transfer belt, when the image forming process unit for each color repeats contact and separation with this intermediate transfer medium, A new problem arises in that speed fluctuations occur and color misregistration easily occurs. Also, since the contact pressure is large, the toner in the center that forms a character or line image is compressed more strongly than the surrounding toner, and the toner in the center adheres and remains on the image carrier side and does not transfer. An image defect such as a so-called "middle-out" is likely to occur.
Furthermore, since a large contact pressure is applied, the toner layer is strongly adhered to the intermediate transfer medium even if it is viewed as a whole, and there is a drawback that the transfer efficiency onto the paper is deteriorated in the next secondary transfer step.

An image forming apparatus in which the surface of a roller-shaped image carrier is covered with an elastic material layer is disclosed in Japanese Patent Application Laid-Open No. 58-906.
No. 55 has been proposed, but similar to the above, speed fluctuations and color misregistration due to an increase in contact pressure, and "middle-out"
Is not considered at all.

[0009]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned drawbacks of the prior art, suppress the disturbance of the unfixed toner image on the recording material and the speed fluctuation of the intermediate transfer medium, and further, An object of the present invention is to provide an image forming apparatus capable of preventing a hollow image.

[0010]

An image forming apparatus according to claim 1 is an image forming apparatus having a flexible image carrier,
At least the image forming area of the image carrier is flexible, and the image carrier has a circular rigid body supporting body that supports inner surfaces of both ends thereof, and the circular rigid body is externally provided via the image carrier. The image forming apparatus includes a rotating member having an elastic body that comes into contact with the support portion.

An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the rotating member is a cylindrical intermediate transfer medium.

An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the second aspect, wherein at least the image forming area of the intermediate transfer medium is made of a rigid body and both ends thereof are made of elastic bodies.

An image forming apparatus according to a fourth aspect is the image forming apparatus according to the second or third aspect, wherein the rotational driving force of the image carrier is transmitted from the intermediate transfer medium.

An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to the second or third aspect, wherein the rotational driving force of the intermediate transfer medium is transmitted from the image carrier.

The image forming apparatus according to claim 6 is the image forming apparatus according to claim 1, wherein the rotating member is a developer carrier.

The image forming apparatus according to claim 7 is characterized in that the elastic bodies at both ends of the developer carrier have surfaces having a smaller friction coefficient than the surfaces of the other parts of the developer carrier. The image forming apparatus.

According to another aspect of the image forming apparatus of the present invention, in the developer carrier, at least the surface of the image forming region is made of a rigid body, and only the both ends of the image carrier, which are in contact with the rigid body supports, are elastic on at least the surface. The image forming apparatus according to claim 6 or 7, further comprising a layer.

[Operation]

First, the image forming process for each color will be described. The image carrier is uniformly negatively charged on the entire surface by a charging device arranged around the photosensitive body which is a flexible image carrier, and subsequently, this negatively charged portion is rotated by the image carrier. The movement reaches the exposure device of the exposure unit, and only the image portion is exposed by the image exposure based on the image signal, and a so-called electrostatic latent image in which the negative charge disappears only on the image carrier is formed.
When this electrostatic latent image reaches the developing device of the developing section, the negatively charged toner layer formed on the developer carrier is supplied to the electrostatic latent image on the image carrier to be contact-developed. Since the image carrier has flexibility, it can be flexibly deformed, and is slightly deformed by contact with the developer carrier. The distance between the center axis of the developer carrier and the center axis of the image carrier is fixed, but the contact pressure between the toner layer and the image carrier is very small due to the deformation of the image carrier. The toner layer formed by the development is not disturbed. Therefore, since the toner image developed on the image carrier is not disturbed, the resolution of the image does not decrease. Further, so-called toner scattering around the image is small.

Subsequently, the developed toner image reaches the contact portion with the cylindrical intermediate transfer medium by the rotational movement of the image carrier, and is transferred onto the cylindrical intermediate transfer medium mainly by electrostatic force. At this time as well, the image carrier has flexibility, and therefore is slightly deformed. The image forming area on the surface of the cylindrical intermediate transfer medium is made of a rigid body, and the distance between the central axis of the cylindrical intermediate transfer medium and the central axis of the image carrier is kept constant at least at the time of transfer, Since the contact pressure between the developed toner image on the image carrier and the cylindrical intermediate transfer medium is kept at a very small value due to the deformation of the image carrier, the hollow toner phenomenon does not appear in the transferred toner image. Absent. This completes the image forming process using one color toner.

In the image forming apparatus of the present invention, this monochromatic image formation is repeated to superimpose toner images of a plurality of colors on the cylindrical intermediate transfer medium. At this time, the image forming process unit of a color not used for image forming may be retracted to a position separated from the cylindrical intermediate transfer medium. In this case, the image forming process unit for the color for which the primary transfer operation is completed by contacting the cylindrical intermediate transfer medium is
The image carrier on the image forming process unit side is moved to a position away from the intermediate transfer medium.

Through the above steps, the toner layer on which the desired color superimposition is performed is formed on the cylindrical intermediate transfer medium. The toner image is secondarily transferred mainly to the electrostatic force on the recording medium conveyed to the secondary transfer position.

In the image forming apparatus of the present invention, since the flexible image carrier can be flexibly deformed and the contact pressure is minute, the toner layer is not over-compressed and is primarily transferred. Moreover, the toner layer is not pressed against the cylindrical intermediate transfer medium by excessive adhesion. Therefore, there is no phenomenon that the transfer efficiency decreases when the toner image is secondarily transferred from the cylindrical intermediate transfer medium to a recording medium such as paper.

In particular, when a primary transfer is performed from an image carrier composed of a rigid body to an intermediate transfer medium composed of an endless seamless transfer belt or a transfer drum covered with a rubber layer, which has been carried out by a conventional method, or a belt system. Image carrier to intermediate transfer medium consisting of transfer belt or transfer drum covered with rubber layer 1
In the case of the next transfer, the contact pressure at the transfer nip was very large as compared with the case of the present invention. Also, when the thickness of the toner layer in the transfer nip is thick, that is, when multiple color toners are overlaid for full-color printing,
There is a problem that the toner compression pressure in the primary transfer nip portion becomes large as compared with the case where the thickness of the toner layer is thin such as in the case of a single color, and as a result, the secondary transfer efficiency is extremely deteriorated. However, in the present invention, since a flexible image carrier that deforms more flexibly than a transfer drum covered with a rubber layer or a transfer belt under tension is used, the toner layer has a large thickness. Also, the contact pressure is kept small, and therefore, the difference between the secondary transfer efficiency in the case of a single color and the secondary transfer efficiency in the case of a full color is small and the image unevenness is small. When the secondary transfer is completed, the toner layer is fixed on the paper at the fixing unit, and the color image forming process is completed.

Next, a portion relating to the driving of the image carrier and the cylindrical intermediate transfer medium of the present invention will be described. Circular rigid support bodies are inserted into both ends of the image carrier. A portion corresponding to an image forming area other than both ends of the cylindrical intermediate transfer medium, in which both ends of the cylindrical intermediate transfer medium, which are in contact with both ends of the image carrier in which the circular rigid support is inserted, are made of elastic bodies Is composed of a rigid body. Even with such a structure, the contact pressure between the image carrier and the image forming area of the cylindrical intermediate transfer medium can be kept low. In addition, the cylindrical intermediate transfer medium and the image carrier are pressed against each other at their ends so that they rotate at the same speed.

Here, when the rotational driving force is input to the cylindrical intermediate transfer medium, the image carrier is cylindrically intermediate due to the frictional force between the image carrier and the cylindrical intermediate transfer medium. It is rotated at the same speed as the transfer medium.

When the rotational driving force is input to the image carrier, the cylindrical intermediate transfer medium is transferred to the image carrier by the frictional force between the image carrier and the cylindrical intermediate transfer medium. Is rotated at the same speed as.

Particularly, when the rotational driving force is input to the cylindrical intermediate transfer medium, one drive input to the cylindrical intermediate transfer medium rotates a plurality of image carriers at the same speed. Since it is possible to eliminate the difference in peripheral speed between multiple image carriers, which was a problem when driving multiple image carriers with separate motors, and therefore the problem of color misregistration between colors Is also solved, and the number of drive motors can be reduced.

In either case of inputting the rotational driving force to the cylindrical intermediate transfer medium or the configuration of inputting the rotational driving force to the image carrier, the image carrier and the cylindrical intermediate transfer medium are used. Instead of transmitting driving force due to frictional force between the image carrier and the cylindrical intermediate transfer medium, the gears that are integrated with each other are provided, and the driving force is transmitted by transmitting the driving force between those gears. You may.

Next, driving of the developer carrier will be described. The length of the developer carrier is shorter than the length between the circular rigid support bodies provided at both ends of the image carrier, and the surface is formed of a rigid body or an elastic body over the entire length. Alternatively, only the portions contacting between the circular rigid body supports provided at both ends of the image carrier have rigid body surfaces, and members having elastic layer surfaces are arranged at both ends thereof, and the image carrier is an elastic body. Are abutted on the circular rigid support portions at both ends. Therefore,
The developer carrier and the flexible image carrier can be stably brought into contact with each other in a low-pressure contact force in the image forming region. And
In any case, the developer carrier is driven at different peripheral speeds by the drive transmission means separate from the image carrier, but since the image forming area has a low pressure contact force, the image carrier and the developer are Despite the difference in peripheral speed between the carrier and the carrier, the wear amount of both the image carrier and the developer carrier is kept small.

[0031]

1 is a schematic view of a main part showing an embodiment of a tandem type image forming apparatus to which the present invention is applied. In the figure, the tandem image forming apparatus has four colors (yellow, magenta, yellow, magenta, Four image carriers (photosensitive drums) 3a to 3d on which toner images of cyan and black are formed and carried are arranged, and peripheral devices for image formation are provided around the respective image carriers 3a to 3d. The charging devices 6a to 6d, the exposure devices 5a to 5d, and the developing devices 10a to 10d are provided.

The respective color toner images formed on the respective image carriers 3a to 3d are sequentially primary-transferred onto the cylindrical intermediate transfer medium 1, and the color superposed toner images on the cylindrical intermediate transfer medium 1 are recorded on the recording medium. Secondary transfer is collectively performed on a certain paper 7. The cylindrical intermediate transfer medium 1 has, for example, an aluminum sleeve and a thickness of about 20.
It is coated with a semiconductive resin layer having a thickness of μm.

The secondary transfer portion is formed on the cylindrical intermediate transfer medium 1 by two.
A secondary transfer roller 9 is arranged in pressure contact, a transfer electric field is applied between the cylindrical intermediate transfer medium 1 and the secondary transfer roller 9, and the color-superposed toner images on the cylindrical intermediate transfer medium 1 are printed on paper. Transfer to 7.

In the present embodiment, the image carriers 3a to 3d.
Is a cylindrical PET (polyethylene terephthalate) tube with a flexible aluminum vapor deposition layer as a conductive base material, and a charge injection blocking layer made of methoxymethylated nylon resin. A layered organic photoreceptor in which a layer and a charge transport layer were layered was used. PET
The thickness of the tube is preferably 30 to 200 μm.

Contact pressure between the image bearing members 3a to 3d and the developer bearing members (developing rollers) 4a to 4d, which are a kind of rotating member,
In order to set the contact pressure between the image carriers 3a to 3d and the cylindrical intermediate transfer medium 1 to a desired value, the rotation center axis of the image carriers 3a to 3d and the developer carriers 4a to 4d are set. The distance between the rotation center axis and the rotation center axis of the image carriers 3a to 3d and the rotation center axis of the cylindrical intermediate transfer medium 1, and the developer carriers 4a to 4d, Cylindrical intermediate transfer medium 1
PET constituting the image carriers 3a to 3d according to the outer diameter of the
The thickness of the tube is appropriately selected.

As the charging devices 6a to 6d, non-contact type scorotron chargers are used in this embodiment.
Instead of the scorotron charger, a contact type or non-contact type charging roller (rubber or foam roller or brush roller is possible) or a sawtooth charger may be used.

As the exposure devices 5a to 5d, LED arrays are used from the viewpoint of miniaturization. It is also possible to use a semiconductor laser type exposure device or the like instead of the LED array. Further, in FIG. 1, the exposure device 5
The image carrier 3a is an LED array that constitutes each of a to 5d.
Although the embodiment of exposing from 3 to 3d is shown,
A form in which the array is provided inside the image carriers 3a to 3d is also possible. As a result, the degree of freedom regarding the use of the peripheral space of the image carriers 3a to 3d is increased, or the overall size of the apparatus is reduced. At that time, the image carriers 3a to 3
A transparent member is used as the flexible tube constituting d, and an aluminum vapor deposition layer as a conductive base material is further used for the LED.
It is necessary to make the thickness transparent to light or to use a transparent conductive material such as ITO (indium tin oxide) as the conductive base material. Further, instead of the exposure devices 5a to 5d, the electrostatic latent image may be written only by the ion irradiation head without using the charging device.

For the developing devices 10a to 10d, the contact or non-contact type one-component non-magnetic developing system is preferable from the viewpoint of miniaturization. In this embodiment, the contact type non-magnetic one-component developing method is used.

In FIG. 1, developing devices 10a-10a are shown.
d has a rigid developer carrier 4a to 4d, and a toner layer having a predetermined thickness and a predetermined charge amount is formed on the developer carrier 4a to 4d by a toner layer restriction member (not shown). After that, this toner layer comes into contact with the image carriers 3a to 3d.

As the developer carriers 4a to 4d, an aluminum sleeve whose surface is sandblasted only in the image forming area, a resin roller made of a semiconductive polymer, or the like can be used. The distance between the rotation center axis of the image carriers 3a to 3d and the rotation center axis of the developer carriers 4a to 4d is fixed. The distance between the axes can be determined in consideration of the outer diameter tolerance of the image carriers 3a to 3d, the outer diameter tolerance of the developer carriers 4a to 4d, and the shape and dimensional tolerances of the fixing members for mounting these shafts. A range in which the flexible image carriers 3a to 3d are slightly deformed to absorb the stacking of the tolerances, the developing nip width in a predetermined range is always secured, and the pressing force is not excessive (0 to 0). 200 g / cm ² ) is selected and used.

When a conventional developer carrier made of an elastic body is brought into contact with a rigid image carrier for development, the contact pressure is about 250 to 600 g / cm ² , but in comparison to this, In the embodiment, the contact pressure is set to be smaller and
Since it can be set to about 200 g / cm ² , the toner image on the image carrier immediately after development in the so-called developing nip is much less disturbed, resulting in deterioration of image resolution and toner scattering. Can be prevented. Further, even if a difference in peripheral speed is provided between the developer bearing members 4a to 4d and the image bearing members 3a to 3d, the degree of wear between them is also small and the life of the members is extended.

Further, the toner left on the image carriers 3a to 3d without being transferred is collected in the contact developing section. In order to extend the life of the developing device, a two-component developing device may be used.

Image forming process unit 2a arranged around the cylindrical intermediate transfer medium 1 and using toner of each color.
The image carriers 3a to 3d of 2d are separated from the cylindrical intermediate transfer medium 1 when the apparatus is stopped, and their rotations are stopped. Cylindrical intermediate transfer medium 1 only when image formation is required
The image carrier 3a to 3d corresponding to the required color and the charging devices 6a to 6d, the exposure devices 5a to 5d, and the developing devices 10a to 10d around the image carrier 3a to 3d corresponding to the required color are contacted by the known cam mechanism or the like. As a unit, they can be moved for each color. Alternatively, the image carriers 3a to 3d may be in constant contact with the cylindrical intermediate transfer medium 1.

In the conventional apparatus using an image carrier composed of a rigid body, the impact force at the time of contact and separation causes the intermediate transfer medium (an endless seamless transfer belt or a cylindrical drum, etc.) and the image carrier to rotate. The speed fluctuated, causing a color shift. Even if the surface of the intermediate transfer medium is formed of a rubber layer in order to alleviate the impact force, it has been a difficult problem to solve this speed fluctuation problem. Even if a foam is used as a material that is more flexible than rubber, the outer diameter tolerance of the intermediate transfer medium that uses the foam as the outermost layer is significantly deteriorated, and the variation in the contact pressure with the image carrier is significantly large. However, the transfer efficiency was uneven, and a void occurred, which was not practical.

However, according to the invention, for example PET
Since the flexible image carriers 3a to 3d made of (polyethylene terephthalate) tube and capable of being deformed flexibly contact and separate from the cylindrical intermediate transfer medium 1, the impact force generated at the time of contact and separation can be almost ignored. It was reduced to the level. Therefore, the fluctuations in the rotational speed of the cylindrical intermediate transfer medium 1 and the image carriers 3a to 3d are eliminated, and the image color misregistration problem is remarkably improved.

Next, FIG. 2 shows a schematic view of the contact state of the image carriers 3a to 3d, the developer carriers 4a to 4d, and the cylindrical intermediate transfer medium 1. The width (length) of the developer carriers 4a to 4d is A, the width (length) of the cylindrical intermediate transfer medium of the image carriers 3a to 3d is B, and the width (length) of the cylindrical intermediate transfer medium 1 is ), Where C is, C is formed so that A <C ≦ B.

Each of the image carriers 3a to 3d comprises a flexible image carrier tube 31 which forms an image forming area and circular rigid body supports 32a and 32b, and an image carrier tube made of PET. Rigid circular rigid body supports 32 a and 32 b are fitted and adhered to the inside of both ends of 31. Since the circular rigid body supports 32a and 32b on both ends are fixedly connected by the shaft 33, the image carrier 31 rotates without being twisted. In the X portion, which is the image forming area, the image bearing members 3a to 3d are deformed extremely slightly due to the contact with the cylindrical intermediate transfer medium 1.

The cylindrical intermediate transfer medium 1 is composed of a rigid body portion 21 and elastic body portions 22a and 22b at both ends. And
Circular rigid body supports 32a at both ends of the image carriers 3a to 3d,
The elastic bodies 22a and 22b at both ends of the cylindrical intermediate transfer medium 1 are elastically deformed following the shape of 32b, and the fixed distance L1 between both members is maintained. Due to the presence of the elastic body portions 22a and 22b of the cylindrical intermediate transfer medium 1,
Since the force of pressing the image carrier tube 31 against the circular rigid body supports 32a and 32b is large as compared with the case without them, both ends of the image carrier tube 31 are circular rigid body supports 3.
The trouble of peeling from 2a, 32b is reduced. In addition, the elastic body portions 2 at both ends of the cylindrical intermediate transfer medium 1
When there is no abrupt bending deformation or permanent deformation of the image carrier tube 31 at the positions corresponding to both ends of the rigid body portion 21 which is the image forming area of the cylindrical intermediate transfer medium 1 due to the presence of 2a and 22b. Since it can be relaxed compared to the above, it is possible to prevent the occurrence of cracks in the photoconductor layer due to the image carrier tube 31 being deformed extremely slightly as described above.
This is effective in extending the life of the image carrier tube 31. Preferably, for this purpose, it is desirable that the outer peripheral portions of the inner end surfaces of the circular rigid body supports 32a and 32b of the image carriers 3a to 3d have a smooth shape.

In the embodiment shown in FIG. 2, the rotational driving force from the motor M2 of the image forming apparatus is the cylindrical intermediate transfer medium 1.
Is input to a gear 23 integrated with the image carrier, the cylindrical intermediate transfer medium 1 is rotated at a constant speed, and the image carrier is pressed by the elastic body portions 22a and 22b at both ends of the cylindrical intermediate transfer medium 1. The rotational driving force is also transmitted to the 3a to 3d by frictional force, and the image carriers 3a to 3d are rotated at substantially the same peripheral speed as the cylindrical intermediate transfer medium 1. On the other hand, the developer carrying members 4a to 4d are transmitted with a rotational driving force from another motor M1 and rotate at a peripheral speed higher than that of the image carrying members 3a to 3d. All surfaces of the developer carriers 4a to 4d are made of a rigid body, and the image carriers 3a to 3d are flexibly deformed at contact portions between the developer carriers 4a to 4d and the image carriers 3a to 3d.

Modifications of the driving force transmission path different from those in FIG. 2 are shown in FIGS. In the modification shown in FIG. 3, the rotational driving force from the motor M2 is input to the gear 23 integrated with the cylindrical intermediate transfer medium 1 to rotate the cylindrical intermediate transfer medium 1 at a constant speed, and Cylindrical intermediate transfer medium 1 coaxially and integrally provided with the gear 23
Gear 24 and image carriers 3a to 3 meshing with the gear 24
The driving force is transmitted to the image carriers 3a to 3d via the gear 34 on the d side, and the image carriers 3a to 3d are rotated at substantially the same speed as the cylindrical intermediate transfer medium 1 at the peripheral speed.
At this time, the elastic body portions 22 at both ends of the cylindrical intermediate transfer medium 1
A and 22b are elastically deformed so as to form a stable transfer nip in the image forming area. On the other hand, the developer carrier 4a
Rotational driving force is transmitted from another motor M1 to 4d, and they rotate at a peripheral speed higher than that of the image carriers 3a to 3d.
All surfaces of the developer carriers 4a to 4d are made of a rigid body, and at the contact portions between this and the image carriers 3a to 3d,
The image carriers 3a to 3d are flexibly deformed. In this embodiment, in order to stabilize the meshing of the gears 24 and 34, it is desirable that the image carriers 3a to 3d and the cylindrical intermediate transfer medium 1 are always in contact with each other without repeating contact and separation.

In the modification of FIG. 4, the rotational driving force from the motor M2 is input to the gear 34 integrally provided on the image carriers 3a to 3d. Each of the four image carriers 3a to 3d is a separate motor M2 provided for each image carrier 3a to 3d.
To rotate at the same speed, or gear 3
4 sprocket wheel and image carrier 3a-
It is rotated at the same speed by a single motor M2 via a driving force transmission means (may be a gear train) such as a timing belt wound around each sprocket wheel for every 3d. Then, the cylindrical intermediate transfer medium 1 is pressed by the elastic body portions 22a and 22b at both ends of the cylindrical intermediate transfer medium 1.
The rotational driving force is also transmitted to the cylindrical intermediate transfer medium 1 and the cylindrical intermediate transfer medium 1 is rotated at a peripheral speed at substantially the same speed as the image carriers 3a to 3d. On the other hand, the developer carrying members 4a to 4d are transmitted with the rotational driving force by another motor M1 and a gear, and rotate at a peripheral speed higher than that of the image carrying members 3a to 3d. The entire surface of each of the developer carriers 4a to 4d is made of a rigid body, and at the contact portion between the developer carrier 4a to 4d and the image carrier 3a to 3d, the image carrier 3 is formed.
a to 3d are flexibly deformed.

In the modification shown in FIG. 5, the rotational driving force from the motor M2 of the image forming apparatus is input to the gear 34 of the image carriers 3a to 3d, and the image carriers 3a to 3d rotate at a constant speed. Then, the driving force is transmitted to the cylindrical intermediate transfer medium 1 via the gear 34 and the gear 24 integrally provided on one side of the cylindrical intermediate transfer medium 1. The cylindrical intermediate transfer medium 1 is rotated at substantially the same peripheral speed as the image carriers 3a to 3d. At this time, the elastic body portions 22a and 22b at both ends of the cylindrical intermediate transfer medium 1 are elastically deformed so as to form a stable transfer nip in the image forming area. On the other hand, the developer carrying members 4a to 4d are transmitted with a rotational driving force from another motor M1 and rotate at a peripheral speed higher than that of the image carrying members 3a to 3d. All the surfaces of the developer carriers 4a to 4d are made of a rigid body, and this and the image carriers 3a to 4d.
At the contact portion with 3d, the image carriers 3a to 3d are flexibly deformed. In this modification, the gears 24, 3
In order to stabilize the meshing of No. 4, it is desirable that the image carriers 3a to 3d and the cylindrical intermediate transfer medium 1 are always in contact with each other without repeating contact and separation.

In the above embodiment, the motors M1 and M2 are
May be the same motor. In that case, the rotational driving force is transmitted to the gear for transmitting the rotational driving force to the gear 23 of the cylindrical intermediate transfer medium 1 or the gear 34 of the image bearing members 3a to 3d and the gear of the developer bearing members 4a to 4d. A power transmission mechanism provided with a gear for transmission is provided, and the power transmission mechanism is connected to the gear 23 or the gear 34 and the developer carrier 4a.
It is arranged to be interposed between the gear of 4d and the motor.

Next, a concrete example of material selection of each component will be briefly described.

[Example 1]

First, regarding the image carrier tube 31 which constitutes the main part of the image carriers 3a to 3d, the thickness 70 μm, the outer diameter 26 mm, and the length 3 formed by the inflation method are used.
An aluminum vapor-deposited layer was formed on the outer surface of a 60 mm PET tube, and a methoxymethylated nylon resin was applied thereon by a dip coating method to a thickness of about 0.1 μm and dried to form a charge injection blocking layer. Further, a charge generation layer composed of titanyl phthalocyanine and polyvinyl butyral resin is applied and dried to a thickness of about 0.3 μm, and a triphenylamine charge transport material is dispersed in a polycarbonate resin at a weight ratio of 1: 0.8. The charge transport material was applied and dried to obtain an image carrier tube 31 made of a flexible tube of an organic photoreceptor. This tube can maintain a cylindrical shape by itself. Then, circular rigid support bodies 32a and 32b having a width of 10 mm were fitted and fixed at both ends thereof to obtain image bearing bodies 3a to 3d.

The developer carrier 4a-4d has a length of 3
A 20 mm aluminum cylinder with a width (3
The surface roughness Rz was set to 20 μm ± 15 μm only by applying a sand blast treatment to the surface of only (00 mm). The distance L2 (see FIG. 2) between the rotation center axis of the developer carriers 4a to 4d and the rotation center axis of the image carrier tube 31 is set in consideration of the component tolerance. Is the image carrier tube 31
The amount of bite into was set to 0 to about 100 μm.

An aluminum cylinder having a length of 320 mm was used as the rigid body of the cylindrical intermediate transfer medium 1, and the surface was covered with a carbon black dispersed semiconductive urethane resin to a thickness of about 20 μm. The surface resistance value was set to 1 to 5 × 10 ⁷ Ω. This surface coating layer also has the purpose of preventing accidental discharge accidents and may be used as an insulating protective layer. The insulating protective layer may consist of any inorganic layer and / or organic polymer layer as long as it is a continuous film. For example, when the rigid body is aluminum, the protective layer is a sealed anodized aluminum (alumite) layer, especially a thickness of 5 to 50 μm.
An alumite layer of m may be used. Further, this protective layer may be made of alumina, titania, zirconia, silica, borosilicate glass, dielectric ceramics such as barium titanate, or organic polymer derivatives such as polyethylene terephthalate and acrylic resin. On the other hand, in order to prevent the charge amount of the toner, which is sequentially primary-transferred and held on the cylindrical intermediate transfer medium 1, from being attenuated due to the influence of the bias voltage applied to the cylindrical intermediate transfer medium 1, etc. It is desirable that the resistance value of the protective layer on the surface of the intermediate transfer medium 1 is sufficiently high.

The distance L1 between the central axis of rotation of the cylindrical intermediate transfer medium 1 and the central axis of rotation of the image carrier tube 31 (see FIG. 2).
(See reference), the amount of biting of the surface of the rigid body portion of the cylindrical intermediate transfer medium 1 into the image carrier tube 31 is 0 in consideration of the component tolerance.
.About.100 .mu.m. Cylindrical intermediate transfer medium 1
A cylindrical member having a width of 20 mm and made of urethane rubber having a JIS-A hardness of 25 degrees is provided at both ends of the elastic body portion 22a,
22b. The secondary transfer roller 9 has a resistance value of 1 × 10 ⁷ Ω (when 500 V is applied) between the roller surface and the shaft center when a load of 500 g is applied to both ends of the shaft.
The semi-conductive foam roller of the above was used.

As the toner, the volume center particle diameter is 7.0 μm.
A negatively charged toner was used in which pigment particles were dispersed in a binder composed mainly of a polyester resin consisting of m, wax was added internally, and silica fine particles were added externally. As the toner layer restricting member, a thin plate made of stainless steel whose tip portion was bent into an L-shape was pressed at a linear pressure of 2 g / cm.

In the embodiment to which the modification of FIG. 4 is applied, the rotational driving force is input to one end of the image carrier tube 31, and the peripheral speed of the image carrier tube 31 is 120 mm / sec.
The developer carriers 4a to 4d were rotated at a peripheral speed 1.8 times that of the developer carriers 4a to 4d. An image carrier tube 3 is provided on the cylindrical intermediate transfer medium 1.
The driving force was transmitted by frictional force from the pressure contact portion with No. 1 and rotated at almost the same speed as the image carrier tube 31 at the peripheral speed. Image carrier tube 31 and cylindrical intermediate transfer medium 1
The difference in surface speed between the two did not cause the image to be misaligned.

Charging device 6a of the image carrier tube 31
As 6d, a scorotron charger was used, the grid voltage was adjusted, and the surface potential was set to about -850V. A bias of -150V was applied to the conductive base materials of the image carriers 3a to 3d, and the developing bias was set to -430V. The transfer voltage applied to the aluminum cylinder of the cylindrical intermediate transfer medium 1 is +2000.
The secondary transfer roller 9 was applied with + 3500V. LED arrays having a resolution of 600 dpi were used as the exposure devices 5a to 5d.

[Example 2]

As the image carrier tube 31, a tube obtained by centrifugally molding polyetherimide was used instead of the PET tube of [Example 1]. According to the embodiment to which the modification example of FIG. 2 is applied, the rotation driving force is input from the motor M2 to the gear 23 provided at one end of the cylindrical intermediate transfer medium 1. The image carrier tube 31 corresponding to the four colors was driven at a peripheral pressure with a driving force transmitted from the pressure contact portion with the cylindrical intermediate transfer medium 1 by frictional force, and was rotated at substantially the same speed as the cylindrical intermediate transfer medium 1. The difference between the peripheral speeds of the image carriers 3a to 3d and the cylindrical intermediate transfer medium 1 did not cause an image shift. In addition, by simply rotating one cylindrical intermediate transfer medium 1 at a constant speed, a plurality of image carrier tubes 31
Was able to rotate at the same peripheral speed. There was no color shift. This was considered to be due to the fact that there was no variation in the rotation speed among the plurality of image carriers 3a to 3d. Other conditions were the same as those in [Example 1].

[Example 3]

As the conductive base material of the image carrier tube 31, a nickel tube having a thickness of about 30 μm prepared by electroforming was used. Image carrier bias to conductive substrate-150
V was applied. The grid voltage of the charging devices 6a to 6d composed of scorotron chargers was adjusted so that the surface potential of the image carrier tube 31 was −850 V, respectively.
The developing bias was -430V. The transfer voltage applied to the aluminum cylinder of the cylindrical intermediate transfer medium 1 is + 1500V,
+ 3000V was applied to the secondary transfer roller 9. Others were the same as in [Example 2].

Next, another embodiment will be described. As shown in FIG. 6, as the developer carrying members 4a to 4d, elastic body layers 42a and 42b having elastic body surfaces are provided at both ends of the rigid body surface 41 corresponding to the image forming area. As a result, the elastic body layers 42a and 42b of the developer carriers 4a to 4d are pressed against the portions of the image carriers 3a to 3d facing the circular rigid body supports 32a and 32b.

Elastic layer 42 of developer carrier 4a-4d
Since a and 42b are present, the force for pressing the image carrier tubes 31 of the image carriers 3a to 3d against the circular rigid body supports 32a and 32b is large compared to the case where they are not present. The trouble that both ends of the body tube 31 are separated from the circular rigid support bodies 32a and 32b is reduced. Further, the elastic body layers 42a, 4a of the developer carrier 4a-4d
Due to the presence of 2b, the image carrier tube 3 at positions corresponding to both ends of the image forming areas of the developer carriers 4a to 4d.
Since the sharp bending deformation and permanent deformation of No. 1 can be relaxed as compared with the case where they are not present, it is possible to prevent the image carrier tube 31 from being deformed extremely slightly and to prevent the occurrence of cracks in the photoreceptor layer. This is effective in extending the life of the carrier tube 31. For this purpose, the outer peripheral portion Y of the inner end faces of the circular rigid support members 32a and 32b at both ends of the image bearing members 3a to 3d.
Preferably has a smooth shape. This makes it possible to prevent sudden bending deformation and permanent deformation of the image carrier tube 31. As described above, it is effective in extending the life of the image carrier tube 31.

As the developer carriers 4a to 4d, the entire surface may be composed of an elastic surface layer. At this time, the elastic layers 42a and 42b at both ends and the elastic layers in the image forming area can be made of materials having different surface roughness and surface energy. Preferably, the developer carrier 4a-
It is desired that the elastic layers 42a and 42b at both ends of 4d have surfaces having a smaller friction coefficient than the other surface portions (image forming areas) of the developer carriers 4a to 4d. Since the surfaces of the developer carriers 4a to 4d move at a peripheral speed different from that of the surfaces of the image carriers 3a to 3d, both ends of the developer carriers 4a to 4d and both ends of the image carriers 3a to 3d. The surface of the part is always worn due to frictional force. Therefore, in order to reduce the amount of wear and prolong the service life of the members, it is preferable that the friction coefficients of the surfaces of the elastic body layers 42a and 42b at both ends of the developer carriers 4a to 4d are small. As the material of the elastic layers 42a and 42b at both ends of the developer carriers 4a to 4d, various rubbers coated with a resin having excellent releasability such as fluororubber, PFA, and PTFE can be used. . Other conditions were the same as those in [Example 2].

In the above embodiment and its modifications,
Although the example in which the cylindrical intermediate transfer medium 1 has a rigid surface in the image forming area has been described, the cylindrical intermediate transfer medium having the elastic layer also in that portion and formed in the entire axial direction with the elastic layer is described. Is used, it does not mean that the purpose of the present invention is satisfied. Further, although only the example of developing by bringing the developer carriers 4a to 4d into contact with the image carriers 3a to 3d has been described, even if a conventionally known non-contact developing method is used, the gist of the present invention is satisfied. There is no change in being there.

[0071]

In the image forming apparatus of the present invention, the elastic body exists at both ends of the circular rigid support or the developer carrier, so that the image carrier is formed as compared with the case where there is no elastic body. Since the force of pressing the tube against the circular rigid support is large, it is less likely that both ends of the tube forming the image carrier will be separated from the circular rigid support. In addition, since it is possible to mitigate the sudden bending deformation and permanent deformation of the tube that forms the image bearing member, it is possible to prevent the occurrence of cracks in the photoconductor layer due to the tube that forms the image bearing member being deformed extremely slightly. , Is effective in extending the life of the tube forming the image carrier.

In the image forming apparatus of the present invention,
Since the image carrier can be flexibly deformed, the developed toner image is not disturbed in the developing nip, and it is possible to prevent the resolution of the image from being deteriorated and the toner from scattering. In addition, since the developing contact pressure is set to be extremely small compared to the developing contact pressure when a conventional developer carrier having elasticity is brought into contact with a rigid image carrier to develop, Even if a peripheral speed difference is provided between the agent carrier and the image carrier, the wear is less likely to proceed, and therefore the life of the image carrier and the developer carrier is extended.

Further, since the image carrier which can be deformed flexibly comes in contact with and separates from the cylindrical intermediate transfer medium, the impact force at the time of separation and contact is reduced to a level which can be almost ignored, and accordingly, the rotation of the cylindrical intermediate transfer medium. The speed fluctuation is eliminated and the image color misregistration problem is remarkably improved.

In the case where a configuration in which a plurality of image carriers are rotated at the same speed by one drive input to the cylindrical intermediate transfer medium is applied, the plurality of image carriers are driven by separate motors. The effect of eliminating the peripheral speed difference between multiple image carriers, which has been a problem when driving, and thus the problem of color misregistration between colors, and the effect of reducing the number of drive motors There is also.

Next, since the contact pressure between the developed toner image on the image carrier and the cylindrical intermediate transfer medium is kept at a very small value by the deformation of the image carrier, the transferred toner image is transferred. The hollow phenomenon does not appear. Further, since the transfer toner layer is not excessively compressed, the toner layer is not pressed against the cylindrical intermediate transfer medium with an excessive adhesive force. Therefore, there is also an effect that it is possible to prevent a phenomenon that the transfer efficiency is lowered when the toner image is secondarily transferred from the cylindrical intermediate transfer medium to a recording medium such as paper. In particular, since the difference in the force for compressing the toner between the thick toner layer in full color and the thin toner layer in single color is small, the transfer efficiency is uniform and the image uniformity is improved.

Finally, with the configuration of the present invention, the flexible image carrier is deformed by a very small amount, and the tolerance stackup is absorbed without particularly tightening the manufacturing tolerance of parts such as the roller outer diameter. However, a predetermined small pressure contact force can be secured. Since the outer diameter tolerance and the axial distance tolerance of the image carrier and the developer carrier can be made larger than when using an image carrier consisting of a rigid body, it is possible to design the device. In addition, there is another effect that the cost of parts can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main configuration of an image forming apparatus according to an embodiment to which the present invention is applied.

FIG. 2 is a schematic diagram schematically showing a contact state of a developer carrier, an image carrier, and an intermediate transfer medium in the image forming apparatus of the embodiment.

FIG. 3 is a schematic diagram schematically showing a modified example of a contact state of a developer carrier, an image carrier, and an intermediate transfer medium in the image forming apparatus.

FIG. 4 is a schematic view schematically showing another modified example of the contact state of the developer carrier, the image carrier, and the intermediate transfer medium in the image forming apparatus.

FIG. 5 is a schematic view schematically showing still another modified example of the contact state of the developer carrier, the image carrier, and the intermediate transfer medium in the image forming apparatus.

FIG. 6 is a schematic view schematically showing a contact state of a developer carrier, an image carrier, and an intermediate transfer medium in an image forming apparatus of another embodiment.

[Explanation of symbols]

1 Cylindrical intermediate transfer medium (rotating member) 2a-2d image forming process unit 3a to 3d image carrier 4a to 4d Developer carrier (rotating member) 5a-5d exposure device 6a to 6d charging device 7 Recording medium (paper) 8 paper cassettes 9 Secondary transfer roller 10a to 10d developing device 11 Cleaning unit 21 Rigid part 22a, 22b Elastic body part 23 gears 24 gears 31 Image carrier tube 32a, 32b circular rigid support 33 axes 34 gears 42a, 42b elastic layer

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H035 CB02 CB03 CB04 CD14 CG03                 2H071 BA03 BA20 BA27 CA05 DA08                       DA09 DA15 EA04 EA18                 2H077 AD02 AD06 AD17 AD35 BA07                       EA03 FA22 GA13                 2H200 FA17 GA15 GA23 GA44 GA47                       GA52 GB12 HA12 HB03 JB10                       JB15 JC02 JC13 JC15 MA02

Claims (8)

[Claims] 1. An image forming apparatus having a flexible image bearing member, wherein the image bearing member is flexible in at least an image forming area, and a circular rigid body supporting member supporting inner surfaces of both end portions thereof. An image forming apparatus comprising: a rotating member that has an elastic body that has and that contacts the circular rigid support from the outside through the image bearing body. 2. The image forming apparatus according to claim 1, wherein the rotating member is a cylindrical intermediate transfer medium. 3. The image forming apparatus according to claim 2, wherein at least the image forming area of the intermediate transfer medium is made of a rigid body and both ends thereof are made of elastic bodies. 4. The image forming apparatus according to claim 2, wherein the rotational driving force of the image carrier is transmitted from the intermediate transfer medium. 5. The image forming apparatus according to claim 2, wherein the rotational driving force of the intermediate transfer medium is transmitted from the image carrier. 6. The image forming apparatus according to claim 1, wherein the rotating member is a developer carrier. 7. The image according to claim 6, wherein the elastic bodies at both ends of the developer carrier have surfaces having a friction coefficient smaller than that of the surface of the other part of the developer carrier. Forming equipment. 8. The developer carrier comprises a rigid body at least in a surface of an image forming region, and has an elastic layer on at least both surfaces of both ends of the image carrier which come into contact with a rigid body support. The image forming apparatus according to claim 6 or 7, which is characterized in that.