JPH04324885A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to image forming apparatuses such as copying machines and printers using electrophotography or electrostatic recording.
In particular, images that utilize an intermediate transfer method in which a visible developed image (toner image) formed on an image carrier is transferred onto an intermediate transfer member, and the transferred image on the intermediate transfer member is then retransferred onto a transfer material. The present invention relates to a forming device.

0002

[Prior Art] Conventionally, a visible developed image (toner image) formed on an image carrier is primarily transferred onto an endlessly running intermediate transfer member, and the primary transfer toner image on this intermediate transfer member is transferred to a sheet. In image forming apparatuses that utilize an intermediate transfer method for performing secondary transfer onto a transfer material having a shape, many of them use a medium-resistance sheet member as an intermediate transfer member. In this case, if the support member that supports the intermediate transfer body is a low resistance material such as metal,
A transfer current flows along the circumferential surface of the sheet of the intermediate transfer member, forming a current loop with the intermediate transfer member supporting member being grounded. Furthermore, if metal, such as aluminum, is exposed at the end of the image carrier, the transfer current flows concentratedly at the end of the image carrier.

0003

[Problems to be Solved by the Invention] In this way, when the supporting member of the intermediate transfer member is a low resistance material, or when the metal surface at the end of the image carrier is exposed, it is necessary to When the members are in contact, the transfer current flows through the intermediate transfer body to the member with lower resistance, forming a non-uniform current loop. For this reason, there are drawbacks such as a reduction in transfer efficiency, non-uniform transfer, image blurring (image blurring during transfer), and the like.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an image forming apparatus in which a specific current loop is not formed through the intermediate transfer member even when a medium-resistance member is used as the intermediate transfer member.

[0005]

Means for Solving the Problems The above objects are achieved by an image forming apparatus according to the present invention. To summarize, the present invention primarily transfers a visible developed image formed on an image carrier onto an endlessly running intermediate transfer member, and transfers the primary transfer image on this intermediate transfer member to a sheet-like transfer material. An image forming apparatus that utilizes an intermediate transfer method for performing secondary transfer on the image forming apparatus, wherein the intermediate transfer body is supported by a support having a resistance value greater than a resistance value of the intermediate transfer body. .

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic sectional view showing a first embodiment of an image forming apparatus according to the present invention, and shows a case where the present invention is applied to an electrophotographic color laser beam printer. This color laser beam printer includes a photoreceptor drum 5 of, for example, an OPC as an image carrier, and around this photoreceptor drum 5, a pre-exposure lamp 7, a primary charger 8, and a photoreceptor drum 5 are arranged according to each color signal. An image exposure section consisting of a laser scanner 1 that irradiates laser light onto the top, first and second mirrors 2 and 3, magenta (M), cyan (C), yellow (Y) and black ( BK)
A developing unit 4 having a developing device each containing a developer, a drum cleaner 6 for removing toner remaining on the photosensitive drum 5, and the like are provided.

Although not shown in the drawings, each developing device of the developing unit 4 includes a developing cylinder and a non-magnetic blade in this embodiment, and the developer is composed of toner and carrier, which are mixed at a constant ratio. The toner and carrier are charged by friction, so that the toner is negatively charged and the carrier is charged positively. This developer is brush-like on the surface of the developing cylinder by the magnetic field of the fixed magnet, and is formed into a developer layer of uniform thickness by a blade. A developing bias is simultaneously applied to the developing cylinder. Therefore, the negative component of the developing bias is larger than the positive component. The toner is attracted to the bright area of the photoreceptor drum 5 by the surface potential of the photoreceptor drum 5 and the negative component of the developing bias, and the electrostatic latent image formed on the photoreceptor drum 5 is developed into a visible image. In this case, when the image exposure unit irradiates a color-separated light image at a predetermined timing, for example, a color image passed through a green filter, an electrostatic latent image mainly consisting of magenta components of the color image is transferred to the photoreceptor. It is formed on the drum 5. In synchronization with the feeding of this latent image, the developing unit 4 places a developing device containing magenta developer at a developing position facing the photoreceptor drum 5, so that the magenta color developer (toner) is electrostatically As a result, only a magenta toner image is formed on the photoreceptor drum 5 as a result of a developing operation being performed.

The magenta toner image formed on the photoreceptor drum 5 is transferred to an intermediate transfer member, in this embodiment, which runs endlessly in contact with or slightly apart from the photoreceptor drum 5 in the primary transfer section. The image is transferred onto the intermediate transfer belt 18. This intermediate transfer belt 18 is stretched between a fixed roller 15 and a tension roller 12 so as to run between a pair of opposing secondary transfer rollers 13A and 13B, and a photosensitive drum is provided at the primary transfer section. A primary transfer roller 9 is arranged on the back side of the intermediate belt 18, facing the intermediate belt 5. The intermediate transfer belt 18 is driven by the motor 16 through the motor control drive circuit 17, and the fixed roller 15 coupled to the motor output shaft rotates, so that the intermediate transfer belt 18 travels in the direction of the arrow in the figure. Note that the pair of secondary transfer rollers 1
3A and 13B are the toner image holding surfaces of the intermediate transfer belt 18 (
One of the rollers 13A disposed on the front surface side is a bias roller configured to be able to come into contact with and separate from the belt 18, and is biased during the transfer operation and positioned in contact with or slightly separated from the belt 18. be done. Note that the primary transfer roller 9 and the secondary transfer roller 13A on the surface side of the intermediate transfer belt
A corona charger may be used instead.

The magenta toner image formed on the photoreceptor drum 5 is formed by applying a predetermined positive voltage as shown in the figure to the primary transfer roller 9 serving as the opposing electrode of the photoreceptor drum 5. Intermediate transfer belt 1
electrostatically transferred onto 8. During this primary transfer, a paper feed roller (not shown) for feeding the transfer material 19 from the paper feed cassette 30 is not operated. Also, at this time, the secondary transfer rollers 13A and 13B are open (that is, the bias roller 13A on the belt surface side is separated).
Therefore, the magenta toner image transferred onto the intermediate transfer belt 18 is not transferred even if the transfer material 19 is fed.
Further, as the belt 18 moves, the image is conveyed to the primary transfer section again while being held on the intermediate transfer belt 18 without contacting the secondary transfer rollers 13A, 13B.

After the magenta toner image is thus transferred onto the intermediate transfer belt 18, the remaining toner on the photosensitive drum 5 is completely cleaned by a drum cleaner 6. Furthermore, before forming a latent image of the next color, the pre-exposure lamp 7 is operated to irradiate the surface of the photoreceptor drum 5 with light to erase any residual charge on the drum surface.

[0011] The above-mentioned pre-exposure, primary charging, laser exposure,
A series of image forming processes including development, primary transfer, and drum cleaning are repeated in the same way when forming cyan toner images, yellow toner images, and black toner images, and thus the above magenta toner image,
Four color toner images, a cyan toner image, a yellow toner image, and a black toner image, are transferred in an overlapping state.

The above four color toner images are transferred to the intermediate transfer belt 18.
When the multiple color toner images are transferred onto the intermediate transfer belt 18, the paper feed roller is driven and the transfer material 19 passes through the pair of registration rollers 10 and 11 and is transferred to the secondary transfer roller 13A in synchronization with the position of the four color toner images on the intermediate transfer belt 18. , 13B are provided. When the transfer material 19 approaches the secondary transfer section, the secondary transfer roller 13A on the belt surface side of the secondary transfer rollers 13A and 13B is urged, and the intermediate transfer belt 18
The intermediate transfer belt 18 and the transfer material 19 are sandwiched between the secondary transfer rollers 13A and 13B. At this time, a predetermined positive voltage is applied to the secondary transfer roller 13A on the front side as shown in the figure, and as a result, the bonding force between the transfer material 19 and the toner is stronger than the bonding force between the intermediate transfer belt 18 and the toner. becomes stronger, the toner on the transfer belt 18 adheres to the transfer material 19, and the four-color toner image is retransferred to the transfer material 19.

When the secondary transfer is performed, a transfer material separating means (not shown) is operated, and the transfer material 19 to which the toner image has been transferred is separated from the intermediate transfer belt 18 by this separating means, and then transferred to a pair of fixing members by a conveying means (not shown). The image is sent to a fixing section composed of rollers 14, 14. In this embodiment, each fixing roller 14 has a built-in heater lamp, and when the transfer material 19 passes between the fixing rollers, the four color toner images are fixed all at once by heat and pressure, and a permanent image is created. Convert to When the secondary transfer is completed, a belt cleaner (not shown) that has been separated until now comes into contact with the intermediate transfer belt 18 to clean the toner remaining on the transfer belt 18 without being transferred. In addition, toner stains on the surface of the front roller 13A, which functions as a bias roller of the secondary transfer roller, are removed by a scraper (not shown), causing stains on the back of the transfer material and deterioration of the function of the roller 13A as an electrode. is prevented.

In this embodiment, the intermediate transfer belt 18
As shown in FIG. 2, the tension roller 12 and fixed roller 15 that support the The tension roller 12 and fixed roller 15 have a two-layer structure, and the resistance value of the portions of the tension roller 12 and fixed roller 15 that contact the intermediate transfer belt 18 is made higher than the resistance value of the intermediate transfer belt 18. In this case, the resistance value of the insulating material is preferably 1015 Ω·cm or more. Further, it is preferable that the primary transfer roller 9 and the secondary transfer rollers 13A and 13B also be dielectric rollers with relatively high resistance values, rather than metal rollers.

Note that the tension roller 12 and fixed roller 15 that support the intermediate transfer belt 18 are not limited to the configuration shown in FIG. It is sufficient if the resistance value of the intermediate transfer belt 18 is higher than the resistance value of the intermediate transfer belt 18. For example, as shown in FIG. 3, a metal roller shaft 31
An insulating tube 33 such as a resin tube or a rubber tube is placed over the outer periphery of the metal roller with a metal roller outer layer 32 laminated around it to insulate the outer peripheral surface of the metal roller, and the intermediate transfer belt of the tension roller 12 and fixed roller 15 is 18
The resistance value of the portion in contact with the intermediate transfer belt 18 may be higher than the resistance value of the intermediate transfer belt 18. In this case as well, the insulation tube 33
The resistance value is preferably 1015 Ω·cm or more.

FIG. 4 shows the intermediate transfer belt 1 in this embodiment.
8. FIG. Intermediate transfer belt 18 of this embodiment
has a structure in which a high-resistance seal 42 having a volume resistivity of 1015 Ω·cm or more is attached along both ends in the belt movement direction excluding the image area 41 on the surface thereof. In this embodiment, the intermediate transfer belt 18 has a diameter of 108 to 1012.
It was formed from a material having a volume resistivity of Ω·cm. Furthermore, PET (polyethylene terephthalate) was used as the high-resistance seal 42.

In this way, at least the contact surfaces of the tension roller 12 and fixed roller 15 that support the intermediate transfer belt 18 are made of a material having a resistance value greater than that of the intermediate transfer belt 18, and the intermediate transfer belt 1
By coating the surfaces of both ends of the photosensitive drum 8 that come into contact with the photoreceptor drum with a material having a higher resistance than the image area 41 to increase the resistance, problems such as a decrease in transfer efficiency, uneven transfer, and image deletion can be avoided. I was able to solve it.

The volume resistivity of the intermediate transfer belt 18 was selected to be 108 to 1012 Ω·cm.
This is because when a sheet with a resistance of Ω·cm or less is used, the transfer efficiency is significantly reduced, and when a sheet with a resistance of 10 13 Ω·cm or more is used, the phenomenon of toner scattering becomes noticeable. The reason why the transfer efficiency significantly decreases when a sheet with a resistance of 10 8 Ω·cm or less is used is considered to be that it is no longer possible to maintain the potential required to bring the sheet into close contact with the photoreceptor drum 5 for good transfer. Also, 1013Ω・
The reason why the toner scattering phenomenon becomes noticeable when using a sheet with a size of 1 cm or more is that if the resistance value of the intermediate transfer belt is high, when the intermediate transfer belt separates from the photoreceptor drum at the end of transfer, the difference between the two It is thought that as the distance increases, the capacitance decreases, and the potential between them increases rapidly, causing local discharge, which disrupts the image and causes the toner to scatter. Therefore, it is preferable to use an intermediate transfer member having a volume resistivity in the range of 10 8 to 10 12 Ω·cm.

In the above embodiment, a belt-shaped intermediate transfer member (intermediate transfer belt) is used as the intermediate transfer member that runs endlessly.
Although the present invention has been described in the case where the present invention is applied to an image forming apparatus using The present invention can also be easily applied to forming apparatuses. Next, a second embodiment of the present invention will be described with reference to FIGS. 5 and 6.

FIG. 5 is a schematic sectional view showing a second embodiment of the image forming apparatus according to the present invention, which is an electrophotographic color laser using a drum-shaped intermediate transfer member (intermediate transfer drum) as described above. A case where the present invention is applied to a beam printer is shown. This color laser beam printer includes a photosensitive drum 53 as an image carrier.
Image forming means is arranged around 3. This image forming means may be any means, but in this embodiment, a primary charger 54 uniformly charges the photoreceptor drum 53, a color-separated light image or a light image E corresponding thereto is irradiated, and the photosensitive drum 53 is An exposure means 58 formed of, for example, a laser beam exposure device, which forms an electrostatic latent image on the body drum 53, and a photosensitive drum 5.
A rotary developing device 51 that develops the electrostatic latent image formed on the photoreceptor drum 53 into a visible image, a drum cleaner 52 that removes toner remaining on the photoreceptor drum 53, and the like are provided.

The rotary developing device 51 includes four developing units 51Y, 51M, which respectively store four color developers: yellow developer, magenta developer, cyan developer, and black developer. 51C, 51BK, and these 4
It holds the developing devices 51Y, 51M, 51C, and 51BK and is composed of a rotatably supported substantially cylindrical casing.By rotating this casing, a desired developing device can be placed on the photosensitive drum 53. The electrostatic latent image formed on the photoreceptor drum 53 is transported to a development position facing the outer circumferential surface and developed. Therefore, this developing device 51 is configured to be capable of full-color development for four colors.

In this embodiment, each developing device of the developing device 51 includes a developing cylinder and a non-magnetic blade (not shown), and the developer is composed of toner and carrier, which are mixed at a constant ratio. . The toner and carrier are charged by friction, so that the toner is negatively charged and the carrier is charged positively. This developer is brush-like on the surface of the developing cylinder by the magnetic field of the fixed magnet, and is formed into a developer layer of uniform thickness by a blade. A developing bias is simultaneously applied to the developing cylinder. Therefore, the negative component of the developing bias is larger than the positive component. The toner is attracted to the bright area of the photoreceptor drum 53 by the surface potential of the photoreceptor drum 53 and the negative component of the developing bias, and the electrostatic latent image formed on the photoreceptor drum 53 is developed into a visible image. For example, when a color image passing through a green filter is irradiated, an electrostatic latent image mainly consisting of magenta components of the color image is formed on the photoreceptor drum 53. The developing device 51 rotates in synchronization with the feeding of the latent image, and the developing device 51M containing the magenta color developer is placed at the developing position facing the photoreceptor drum 53.
The magenta developer (toner) electrostatically flies and adheres to the electrostatic latent image on the photoreceptor drum 53, so that only a magenta toner image is formed on the photoreceptor drum 53.

The magenta toner image formed on the photoreceptor drum 53 is transferred to the photoreceptor drum 5 in the primary transfer section.
The image is transferred onto an intermediate transfer member, in this embodiment, an intermediate transfer drum 59, which rotates in the direction of the arrow shown in the drawing while being in contact with or slightly separated from the image forming apparatus 3. This intermediate transfer drum 59 has a configuration in which an intermediate transfer sheet 59A is wound in a drum shape between a pair of ring-shaped members, as will be described in detail later.
Further, in the primary transfer section, a primary transfer roller 55 (
A corona charger may be used instead of the roller). By applying a positive voltage to the primary transfer roller 55, the magenta toner image formed on the photoreceptor drum 53 is transferred to the intermediate transfer drum 59 (specifically, the intermediate transfer sheet 59A) as described above. electrostatically transferred onto the top. During this primary transfer, the paper feed roller (not shown) for feeding the transfer material 19 from the paper feed cassette is not operated, so the magenta toner image transferred onto the intermediate transfer drum 59 is not transferred to the transfer material. While being held on the intermediate transfer drum 59, as the intermediate transfer drum 59 rotates, it is conveyed again to the primary transfer section.

After the magenta toner image is thus transferred onto the intermediate transfer drum 59, the remaining toner on the photosensitive drum 53 is completely cleaned by the drum cleaner 52. Also, before forming a latent image of the next color, a pre-exposure lamp (not shown) is operated to protect the photoreceptor drum 53.
The surface of the drum is irradiated with light to erase any residual charge on the drum surface.

[0025] The above-mentioned pre-exposure, primary charging, laser exposure,
The series of image forming processes of development, primary transfer, and drum cleaning are repeated in the same way when forming cyan toner images, yellow toner images, and black toner images, and thus the above magenta toner image,
Four color toner images, a cyan toner image, a yellow toner image, and a black toner image, are transferred in an overlapping state.

The above four color toner images are transferred to the intermediate transfer drum 59.
When the multiple color toner images are transferred onto the intermediate transfer drum 59, the paper feed roller is driven and the transfer material 19 passes through the pair of registration rollers 10 and 11 and is transferred to the secondary transfer roller 56 in synchronization with the position of the four color toner images on the intermediate transfer drum 59. (A corona charger may be used in place of the roller). When the transfer material 19 approaches the secondary transfer section, the secondary transfer roller 56 is urged and comes into contact with the intermediate transfer drum 59, and the transfer material 19 is sandwiched between the secondary transfer roller 56 and the intermediate transfer drum 59. . At this time, a predetermined positive voltage is applied to the secondary transfer roller 56, and as a result, the bonding force between the transfer material 19 and the toner becomes stronger than the bonding force between the intermediate transfer drum 59 and the toner. The toner on the toner 59 adheres to the transfer material 19, and the four color toner images are simultaneously retransferred onto the transfer material 19.

When the secondary transfer is performed, a transfer material separating means (not shown) is operated, and the transfer material 19 to which the toner image has been transferred is separated from the intermediate transfer drum 59 by the separating means, and then transferred to a pair of fixing rollers by the conveying means 60. 61
, 61 is sent to a fixing section. In this embodiment, each fixing roller 61 has a built-in heater lamp, and when the transfer material 19 passes between the fixing rollers by heat and pressure, the four color toner images are fixed all at once, and a permanent image is created. Convert to

As described above, in this embodiment, the endlessly running intermediate transfer member is configured as a rotatably supported intermediate transfer drum 59, and as shown in FIG. A pair of ring-shaped members 59a arranged at
, 59b and a connecting member 59c that connects both ring-shaped members 59a and 59b form a drum frame, and an intermediate transfer sheet 59A is attached to the pair of ring-shaped members so as to cover the opening of this drum frame. It has a configuration in which it is wound in a drum shape between 59a and 59b. In this example, a film-like dielectric sheet was used as the intermediate transfer sheet 59A. As explained in the first embodiment, this intermediate transfer sheet 59A has a resistance of 108 to 1012 Ω.
Preferably, it is made of a material having a volume resistivity of cm. Further, the intermediate transfer sheet 59A and the ring-shaped member 5
9a, 59b, the contact surface between intermediate transfer sheet 59A and connecting member 59c, and ring-shaped members 59a, 59.
A seal made of resin such as polyethylene terephthalate or polyvinylidene fluoride is stuck on the circumferential surface of b (the surface that comes into contact with the photoreceptor drum). As mentioned above, the seal preferably has a volume resistivity of 1015 Ω·cm or more.

As described above, in this embodiment, the contact surface between the intermediate transfer sheet 59A and the ring-shaped members 59a, 59b, the contact surface between the intermediate transfer sheet 59A and the connecting member 59c, and the periphery of the ring-shaped members 59a, 59b. Since a seal with higher resistance than the intermediate transfer sheet 59A is pasted on the surface,
This intermediate transfer sheet 59A is substantially in a floating state, reliably preventing the formation of specific current loops. In this way, problems such as decreased transfer efficiency, uneven transfer, and blurred images can be solved.

In each of the above embodiments, the present invention is applied to an electrophotographic color image forming apparatus, but the present invention can be applied to various electrophotographic copying machines, electrostatic recording copying machines, etc. other than the embodiments. It is equally applicable to image forming apparatuses such as printers. Furthermore, it goes without saying that various modifications and changes can be made to the members, elements, etc. constituting the image forming apparatus as necessary.

[0031]

As explained above, in the image forming apparatus according to the present invention, since the resistance value of the support supporting the intermediate transfer member is made larger than the resistance value of the intermediate transfer member, specific It has the remarkable effect of reliably preventing the formation of current loops and preventing problems such as reduced transfer efficiency, uneven transfer, and image blurring even when using a medium-resistance member that is easy to use as an intermediate transfer member. .

[Brief explanation of the drawing]

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

FIG. 2 is a sectional view showing the structure of a tension roller and a fixed roller, which are intermediate transfer body supports used in the image forming apparatus of FIG. 1;

3 is a sectional view showing another configuration of a tension roller and a fixed roller, which are intermediate transfer body supports used in the image forming apparatus of FIG. 1. FIG.

4 is a perspective view showing the structure of an intermediate transfer belt, which is an intermediate transfer member used in the image forming apparatus of FIG. 1. FIG.

FIG. 5 is a schematic cross-sectional view showing a second embodiment of the image forming apparatus according to the present invention.

6 is a partially cutaway perspective view showing the structure of an intermediate transfer drum, which is an intermediate transfer member used in the image forming apparatus of FIG. 2. FIG.

[Explanation of symbols]

Claims (3)

[Claims] Claim 1: A visible developed image formed on an image carrier is primarily transferred onto an endlessly running intermediate transfer member, and the primary transfer image on this intermediate transfer member is secondarily transferred onto a sheet-like transfer material. An image forming apparatus that uses an intermediate transfer method for transferring, characterized in that the intermediate transfer member is supported by a support having a resistance value greater than a resistance value of the intermediate transfer member. 2. At least a surface of an end portion of the intermediate transfer member that comes into contact with the image carrier has a higher resistance than an image portion of the intermediate transfer member to which the developed image is transferred. Item 1. Image forming apparatus. 3. The volume resistivity of the intermediate transfer member is 108.
Claim 1 characterized in that it is ~1012 Ω·cm.
image forming device.