JPH1152632A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of offset at the time of simultaneously fixing both faces by conveying plural sheets of transfer paper to a fixing device at specified intervals, and transferring a part of an offset preventing agent supplied to a surface heating means, to a back face heating means to apply the offset preventing agent to both faces of transfer paper. SOLUTION: An offset preventing agent L using silicone oil is supplied to the surface of an upper roller 17a. The supplied offset preventing agent L is applied to the upper roller 17a by a felt roller 178. The applied offset preventing agent L is transferred to a lower roller 17b rotated in contact with the offset preventing agent L, so as to form an oil layer La. After applying the offset preventing agent L, the upper and lower rollers 17a, 17b are rotated to uniform the offset preventing agent L. The offset preventing agent L on the upper roller 17a is then eliminated by a cleaning roller 186. The cleaned part of the upper roller 17a is brought into contact with the lower roller 17b in association with its rotation. The offset preventing agent L stuck to the lower roller 17b is therefore transferred to the upper roller 17a and eliminated by the cleaning roller 186.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus capable of forming an image on both sides of a transfer material. This type of image forming apparatus is used as a copying machine, a facsimile, and a printer.

[0002]

2. Description of the Related Art Double-sided image forming apparatuses are useful from the viewpoint of saving resources and reducing the amount of documents, and are widely used. By the way, in a conventional double-sided copying apparatus, a toner image is first formed on one side of a copy sheet by transferring the toner image, and the toner image is fixed through a fixing device. An image forming process of forming an image on both sides is performed. Because of this, copying speed is slow,
There was a disadvantage that the device became large. Further, there is another problem that the transfer paper is deformed due to the fixing and the transportability is reduced.

The inventor of the present invention aims at remedying such a drawback, after forming a toner image to be formed on one side on an image forming body, temporarily transferring it to an intermediate transfer body, and then transferring it on the other side. After the toner images to be formed are formed on the image forming body, these toner images are transferred to both sides of the transfer paper, and thereafter,
A double-sided image forming apparatus for simultaneously fixing toner images formed on both sides of a transfer material has been proposed. In such a two-sided image forming apparatus, the transfer path of the transfer paper is short, and a high copying speed can be realized. Therefore, there are advantages that the apparatus is downsized, and that the transfer path of the transfer paper is simple, so that the occurrence of jam is reduced. By the way, in such a double-sided image forming apparatus, the toner images formed on both sides of the transfer material must be fixed at the same time. However, the conventional fixing device is designed to fix the toner image on one side of the transfer material. Since an offset prevention technology and a fixing member cleaning technology have been developed exclusively for one-sided fixing, the conventional technology does not have a suitable double-sided fixing device.
Although it is conceivable to provide an offset preventing agent applying unit and a cleaning unit for both sides of the transfer material, however, the apparatus becomes large. Further, when an image is formed only on one side, the amount of application becomes excessive or the cleaning performance becomes excessive.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an offset prevention technique and a fixing member cleaning technique which are effective for simultaneous double-sided fixing in the above-mentioned double-sided image forming process.

Another object of the present invention is to provide an image forming method which is excellent in offset prevention performance and has a high cleaning performance for a fixing member, and which can reduce the size of the apparatus.

[0006]

According to the present invention, there is provided a double-sided image forming process as described above, that is, after transferring a toner image to both sides of a transfer material using an image forming body and an intermediate transfer body,
In an image forming process for simultaneously fixing toner images on both surfaces, when images are continuously formed on a plurality of transfer materials, the transfer materials are conveyed to a fixing device at intervals. The anti-offset agent is effectively supplied to the heating unit of the fixing device and the heating unit is cleaned. The object of the present invention is achieved by the following image forming method.

(1) Two toner images are distributed to a first toner image support and a second toner support, sequentially formed, and the toner images on the first and second toner image supports are transferred to a transfer material. An image forming method in which a toner image is formed on both sides of a transfer material and then fixed, wherein the fixing is performed by heating a surface in contact with the toner image transferred from the first toner image support to the transfer material surface. A heating unit, a back surface heating unit that contacts and heats the toner image transferred from the second toner image support to the back surface of the transfer material, and an offset preventing agent supplying unit that supplies an offset preventing agent to the front surface heating unit;
The plurality of transfer materials are transported to the fixing device at intervals equal to or longer than the length of the transfer material in the transport direction, and at the intervals, a part of the offset preventing agent supplied to the front surface heating unit is transferred to the back surface heating unit. An image forming method comprising applying an offset preventing agent to both surfaces of the transfer material and fixing the toner image.

(2) Two toner images are distributed to a first toner image support and a second toner support, sequentially formed, and the toner images on the first and second toner image supports are transferred to a transfer material. An image forming method in which a toner image is formed on both sides of a transfer material and then fixed, wherein the fixing is performed by heating a surface in contact with the toner image transferred from the first toner image support to the transfer material surface. A heating unit, a back surface heating unit that contacts and heats the toner image transferred from the second toner image support to the back surface of the transfer material, and a cleaning unit that acts on the surface of the front surface heating unit; Is transported to the fixing device at an interval equal to or longer than the length in the transport direction of the transfer material, and at the interval, the toner adhering to the back surface heating unit is transferred to the front surface heating unit. By And cleaning the front surface heating unit and the back surface heating unit.

[0009]

Embodiments of the present invention will be described below.

An image forming body, which is a typical example of the first toner image support, has a function of forming an electrostatic latent image on the surface thereof and forming a toner image by development.
A photoconductive photoreceptor such as a PC photoreceptor or an α-Si photoreceptor is typical. The one having a dielectric layer on the surface and forming an electrostatic latent image on the surface by imagewise charging can also be used. Examples of the form of the image forming body include a drum and a belt.

In FIG. 1 and FIG.
Is an example of an image forming body. For example, a cylindrical substrate formed of a transparent member of optical glass or transparent acrylic resin is provided inside, and a photosensitive layer such as a transparent conductive layer and an organic photosensitive layer (OPC) is provided. It is formed on the outer periphery of the base, and is rotated clockwise as shown by the arrow in FIG. 1 in a state where the conductive layer is grounded.

As shown in FIG. 2, the photosensitive drum 10 has flange members 10a and 10b at both ends for engaging and fixing it.
Is rotatably supported by the bearings 110a and 110b fitted to the flange members 10a and 10b at both ends on the drum shaft 110 which is erected and fixed to the apparatus main body. The apparatus is driven at a constant speed in a predetermined direction by being driven by meshing with a drive gear on the apparatus body side.

In FIG. 1, a scorotron charger 11 as a charging means is used in an image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K) and is an image forming body. A control grid mounted opposite the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10 and maintained at a predetermined potential with respect to the above-described organic photosensitive layer of the photosensitive drum 10; And a discharge electrode 11 a formed of a shape-like electrode, and performs a charging action (in this embodiment, negative charge) by corona discharge having the same polarity as the toner, thereby giving a uniform potential to the photosensitive drum 10. Other wire electrodes can be used as the discharge electrode 11a.

The exposure unit 12 as an image exposure means for each color is arranged such that the exposure position on the photosensitive drum 10 is located between the discharge electrode 11a of the scorotron charger 11 and the developing position of the developing unit 13. Be placed.

The exposure unit 12 is a linear exposure element in which a plurality of LEDs (light emitting diodes) as image exposure light emitting elements arranged in the main scanning direction in parallel with the axis 110 of the photosensitive drum 10 are arranged in an array. The exposure unit 12a and the SELFOC lens 12b as an equal-magnification imaging element are mounted on a holder (not shown). An exposure unit 12 for each color, a uniform exposure device 12
c and a transfer simultaneous exposure unit 12 d are mounted and housed inside the base body of the photosensitive drum 10. Image data of each color read by a separate image reading device and stored in the memory is sequentially read from the memory and input to the exposure unit 12 for each color as an electric signal.

As the exposure element, an element in which a plurality of light-emitting elements such as FL (phosphor emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used. The light emission wavelength of the light emitting element used in this embodiment is usually in the range of 780 to 900 nm, which is high in transmittance of the Y, M, and C toners when performing image exposure from the outside. Since the exposure method is used, a shorter wavelength of 400 to 780 nm, which does not sufficiently transmit light to the color toner, may be used.

A developing unit 13 provided in accordance with the color sequence in which an image is formed and a rotating photosensitive drum is provided in accordance with the color sequence.
In the present embodiment, the developing units 13 of Y and M are on the left side of the photosensitive drum 10 and the developing units 13 of C and K are on the right side of the photosensitive drum 10 with respect to the photosensitive drum 10 of FIG. And the developing casing 1 of the Y and M developing units 13
The scorotron chargers 11 for Y and M are disposed below 38, and the scorotron chargers 11 for C and K are disposed above the developing casing 138 of the C and K developing devices 13.

The developing device 13 as a developing means for each color includes
One-component or two-component developers of yellow (Y), magenta (M), cyan (C) and black (K) are accommodated, respectively, and a predetermined gap is maintained with respect to the peripheral surface of the photosensitive drum 10, respectively. At the developing position, for example, the thickness is 0.5 mm to 1 mm which rotates in the same direction as the rotation direction of the photosensitive drum 10,
The developing sleeve 131 is formed of a cylindrical nonmagnetic stainless steel or aluminum material having an outer diameter of 15 to 25 mm.

The developing unit 13 is set in a gap of a predetermined value from the photosensitive drum 10 by an abutting roller (not shown), for example, 100 μm.
In the developing operation of the developing device 13 for each color, the developing sleeve 131 is used.
A developing bias to which a DC voltage or an AC voltage is further applied is applied to the photosensitive drum 10 to perform a jumping development with a one-component or two-component developer contained in the developing device, and the same to the negatively charged photosensitive drum 10 in the same manner as the toner. A non-contact reversal development is performed in which a DC bias of a polarity (minus polarity in the present embodiment) is applied to attach the toner to the exposed portion.
The development interval accuracy at this time is 20 μm to prevent image unevenness.
Less than or equal to degree is required.

The developing unit 13 for each color described above converts the electrostatic latent image on the photosensitive drum 10 formed by the charging by the scorotron charger 11 and the image exposure by the exposure unit 12 into a non- In a non-contact state, the toner having the same polarity as the charged polarity (in the present embodiment, the photosensitive drum is negatively charged and the toner having a negative polarity) is reversely developed by a contact developing method.

An image read by an image sensor of an image reading apparatus separate from the apparatus or an image edited by a computer is temporarily stored as image data for each of Y, M, C, and K as an original image. And stored.

When an image recording start is started, a gear G provided on a rear flange 10b of the photosensitive drum 10 is rotated through a driving gear by a start of a photosensitive member driving motor (not shown) to move the photosensitive drum 10 to an arrow in FIG. And at the same time, yellow (Y) on the left side of the photosensitive drum 10
The application of a potential to the photosensitive drum 10 is started by the charging action of the Y scorotron charger 11 disposed below the developing casing 138 of the developing device 13 of FIG.

After the photosensitive drum 10 is applied with a potential, the first color signal, that is, Y
Exposure with an electric signal corresponding to the image data is started, and an electrostatic latent image corresponding to the Y image of the original image is formed on the photosensitive layer on the surface of the photosensitive drum 10 by rotational scanning.

The latent image is reversal-developed by the Y developing device 13 in a state where the developer on the developing sleeve is not in contact with the developer, and a yellow (Y) toner image is formed in accordance with the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 is placed on the yellow (Y) toner image, and further on the left side of the photosensitive drum 10 and above the yellow (Y), a magenta (M) developing device 1 is provided.
An electric signal corresponding to a second color signal of the M exposure unit 12, that is, an M image data, is applied by the charging action of the magenta (M) scorotron charger 11 disposed below the third developing casing 138. Is performed, and a magenta (M) toner image is formed on the yellow (Y) toner image by non-contact reversal development by the M developing device 13.

By the same process, the developing casing 13 of the developing device 13 for cyan (C) is located on the right side of the photosensitive drum 10.
The cyan (C) toner image corresponding to the third color signal is further provided by a cyan (C) scorotron charger 11, an exposure unit 12 of C, and a developing unit 13 of C, which are disposed above the photoconductor 8 A black (K) scorotron charger 11, an exposure unit 12, and a developing unit 13 are disposed on the right side of the drum 10 and below the developing casing 138 of the black (K) developing unit 13 at the lower part of the fourth unit C. A black (K) toner image corresponding to the signal is sequentially superposed, and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10 (toner image forming means).

Exposure unit 1 for Y, M, C and K
Exposure of the organic photosensitive layer of the photosensitive drum 10 by 2 is performed from the inside of the drum through the transparent substrate described above. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. It is possible to form an electrostatic latent image.

A superimposed color toner image (first toner image) serving as a backside image is formed on the photosensitive drum 10 as an image forming body by the above-described image forming process, and the backside image on the photosensitive drum 10 is overlaid. In the transfer area 14b, the transfer unit 14c (first transfer unit) to which a DC voltage having the opposite polarity (positive polarity in the present embodiment) is applied to the color toner image is stretched between the driving roller 14d and the driven roller 14e. And an intermediate transfer member 14a (second transfer member) provided near or in contact with the photosensitive drum 10.
On the toner image support). At this time, for example, uniform exposure is performed by the simultaneous transfer exposure device 12d using an LED (light emitting diode) so that good transfer is performed.

The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the image forming body AC neutralizer 16 and then enters the cleaning device 19 or the photosensitive drum 10.
Cleaning blade 19a made of rubber material in contact with
In order to eliminate the history of the photoreceptor up to the previous print, the peripheral surface of the photoreceptor is removed by exposure by a uniform exposure unit 12c before charging using, for example, an LED (light emitting diode). Then, the next surface image is formed in a color image.

After the superimposed color toner image serving as the back side image is formed on the intermediate transfer member 14a as described above, the superposed toner image (second toner image) serving as the front side image is continuously formed on the photosensitive drum 10. Is formed in the same manner as in the above color image forming process. At this time, the back side image formed on the intermediate transfer body 14a and the front side image formed on the photosensitive drum 10 are synchronized in the transfer area 14b, and the toner image is formed as shown in FIG. . It is necessary to change the image data on the photosensitive drum 10 so that the front surface image formed at this time is a mirror image of the back surface image formation.

Recording paper P, which is a transfer material, is sent out by a feed roller 15a from a paper feed cassette 15 which is a transfer material storage means, fed by a feed roller 15b, and conveyed to a timing roller 15c.

The recording paper P is driven by a timing roller 15c to form a color toner image of a front surface image carried on the photosensitive drum 10 and a color toner image of a back surface image carried on the intermediate transfer member 14a. The paper is fed to the transfer area 14b in synchronization. At this time, the recording paper P is charged to the same polarity as that of the toner by a paper charger 14f as a transfer material charging unit, is attracted to the intermediate transfer body 14a, and is transferred to the transfer area 14a.
b. By charging the paper with the same polarity as the toner, the recording paper P is prevented from attracting the toner image on the intermediate transfer body 14a or the toner image on the photosensitive drum 10 outside the transfer section, and the disturbance of the toner image is prevented. Preventing. Further, as the transfer material charging unit, a conductive roller, a brush charger, or the like, which can be brought into contact with and released from the intermediate transfer member 14a, can be used.

A surface image on the peripheral surface of the photosensitive drum 10 is collectively recorded on a recording paper by a transfer unit 14c as a second transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. It is transferred to the upper surface side (front side) of P. At this time, the back surface image on the peripheral surface of the intermediate transfer member 14a is not transferred to the recording paper P but exists on the intermediate transfer member 14a.
Next, the back side image on the peripheral surface of the intermediate transfer body 14a is collectively recorded on the recording paper P by a transfer unit 14g as a third transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. Is transferred to the lower surface side (rear surface side). At the time of transfer by the transfer unit 14c, so that good transfer is performed,
Uniform exposure is performed by a transfer simultaneous exposure device 12d using, for example, an LED (light emitting diode) provided inside the photosensitive drum 10 so as to face the transfer device 14c.

Since the toner images of the respective colors overlap with each other, it is preferable that the toner in the upper layer and the toner in the lower layer of the toner layer are charged to the same polarity with the same charge amount in order to enable batch transfer. Accordingly, in a double-sided image formation in which the polarity of the color toner image formed on the intermediate transfer member 14a is inverted by corona charging or the polarity of the color toner image formed on the photosensitive drum 10 is inverted by corona charging, the lower layer is formed. The toner is not sufficiently charged to the same polarity, so that the transfer becomes unfavorable.

The reversal development is repeated on the photoreceptor drum 10, and the color toner images of the same polarity formed by superimposition are collectively transferred to the intermediate transfer member 14a without changing the polarity, and then the recording paper is changed without changing the polarity. The batch transfer to P is preferable because it contributes to the improvement of the transferability of the backside image formation. Also for the surface image formation, reversal development is repeatedly performed on the photoreceptor drum 10, and the color toner images of the same polarity formed by superposition are collectively transferred to the recording paper P without changing the polarity. It is preferable because it contributes to the improvement of transferability.

From the above, in forming a color image, the first and second transfer means are operated to form a color toner image on the surface of the transfer material by using the above-described front and rear surface image forming method. Next, a two-sided image forming method of forming a color toner image on the back surface of the transfer material by operating the second transfer unit is preferably adopted.

The intermediate transfer member 14a is a typical example of a second toner image support. The intermediate transfer member 14a has a thickness of 0.5 to
A 2.0 mm endless belt, a semiconductive rubber having a resistance value of 10 ⁸ to 10 ¹² Ω · cm of silicon rubber or urethane rubber on a substrate, and a thickness as a toner filming prevention layer outside the rubber layer. A layer having a fluorine coating of 5 to 50 μm is formed. This layer also preferably has a similar semiconductivity. Thickness 0.1 instead of rubber belt layer
It is also possible to use semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate, polyimide or the like having a thickness of about 0.5 mm.

The recording paper P on which the color toner images are formed on both sides is neutralized by a paper separation AC neutralizer 14h for separating the transfer material, separated from the intermediate transfer body 14a, and has heaters inside both rollers. The sheet is conveyed to a fixing device 17 as a fixing unit composed of two rollers. By applying heat and pressure between the upper roller 17a and the lower roller 17b, the adhered toner on the front and back of the recording paper P is fixed, and the recording paper P on which both-side image recording has been performed is fed by the paper discharge roller 18. And discharged to a tray outside the apparatus.

The toner remaining on the peripheral surface of the intermediate transfer member 14a after the transfer is provided in an intermediate transfer member cleaning device 14i as cleaning means for the intermediate transfer member, and can be brought into contact with and released from the intermediate transfer member 14a. It is cleaned by the blade. Further, the toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the image forming body AC static eliminator 16, and then enters a cleaning device 19 or is made of a rubber material which is in contact with the photosensitive drum 10. The toner is scraped into the cleaning device 19 by the cleaning blade 19a, and is collected by a screw 19b into a waste toner container (not shown). The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is uniformly charged by the Y scorotron charger 11, and enters the next image forming cycle.

By using the above-described method, since the superimposed color toner image is transferred at a time, the color image on the intermediate transfer member (intermediate transfer member) is less likely to be misaligned and the toner is not scattered or rubbed. Good two-sided color image formation with little deterioration is performed.

The image data for each color of the document input to the color image forming apparatus is read by, for example, an image reading apparatus 50 provided separately from the apparatus main body shown in FIG.

In the case of the image reading apparatus 50 described above, the originals D are stacked in a page order from the lower side with the front surface facing downward, and the lowermost original D is directed to the transport path 53 by the operation of the discharge belt 51 and the separating roller 52. It is carried out.

The discharged original D is retracted to the position shown by the broken line without the guide plate G urged to the position shown by the solid line, and is placed on the transparent platen glass 55 via the transport belt 54. The document is fed, and is temporarily stopped at the document reading position with the back face down.

The back side image of the original D on the platen glass 55 is composed of a first mirror unit 56 composed of an illumination lamp and a first mirror constituting a scanning optical system, and a second V-shaped second mirror unit 56.
Second mirror unit 57 including a mirror and a third mirror
Of the first mirror unit 56 at the speed V and the speed V / 2 in the same direction by the second mirror unit.
Are read by the moving exposure by the camera and passed through the projection lens Lz and the dichroic prism M to the three image sensors CC.
An image is formed on D. The back side image formed on the image pickup device CCD after color separation is subjected to image processing, stored as image data for each color in the image memory (I), and sent to each of the exposure units 12 as an electric signal. The output and the latent image are formed on the photosensitive drum 10, and the toner image formed after the development is transferred by the transfer device 14c, and the back surface image is formed on the intermediate transfer member 14a described above.

When the reading of the back side image is completed in the image reading device 50, the original D is turned upside down through the reversing sheet feeding path 58 by the temporary reverse rotation of the conveying belt 54, and again passed through the conveying path 53. Through the platen glass 5
5, and is temporarily stopped at the document reading position with the front surface facing downward.

The original image on the platen glass 55 is read by the above-described scanning optical system for the front surface image, subjected to image processing, temporarily stored as image data of each color in the image memory (II), and simultaneously with each of the above-mentioned images. An electric signal is output to the exposure unit 12 to form the surface image on the photosensitive drum 10 described above.

The back side image formed on the intermediate transfer member 14a and the front side image formed on the photosensitive drum 10 are the first recording paper P fed from the paper feed cassette 15.
And the first copy cycle is completed. Recording paper P holding front side toner image and back side toner image
Is fixed by a fixing device 17, and is discharged onto a tray outside the device, with the front and back turned upside down.

When copying the second and subsequent sheets, the image of the original D is not read, and the image data from the image memory (I) is output so that the back side image and the image data from the image memory (II) are output. By outputting the image data, a front side image is formed, and the front side image and the back side image are respectively transferred to the front and back of each of the second and subsequent recording sheets P fed from the sheet feeding cassette 15. The recording paper P holding the front toner image and the rear toner image is supplied to the fixing device 1
7 and is stacked on the previously discharged recording paper with the surface facing down.

On the other hand, in the image reading device 50, the originals D whose images have been read are stacked on the tray 60 via the discharge rollers 59 by the operation of the conveyor belt 54, with the front surface facing down, in order from the bottom. Paper is discharged as follows.

The transfer of the transfer material in the above-described double-sided image forming apparatus will be described with reference to FIG.

Since the front side image and the back side image are formed at predetermined positions on the front and back surfaces of the transfer material, the image formation and the supply of the transfer material are executed in a time-controlled manner. Is formed on the photosensitive drum 10 delayed by the length of the back image. Therefore, the transfer material whose timing is adjusted to the formation of the front surface image is also supplied to the transfer position with a delay corresponding to at least one image length from the formation of the back surface image on the photosensitive drum 10. In continuous double-sided image formation, the transfer material is supplied to the transfer position for at least one image, that is, at an interval corresponding to the length of the transfer material in the transport direction. Accordingly, in the case of continuous image formation, the transfer material is similarly supplied to the fixing device 17 at an interval longer than the length of the transfer material in the transport direction.

The present invention has been made by paying attention to the intermittent conveyance of the transfer material in such continuous image formation.
As described below, in the present invention, an offset preventing agent is applied to the surface heating unit and the back surface heating unit of the fixing device by using the above-mentioned interval of the transfer material conveyed to the fixing device, and / or Cleaning of the heating means is performed.

FIG. 5 is a diagram showing details of the fixing device 17 of the image forming apparatus shown in FIG. The upper roller 17a is composed of a roller base 171 made of a metal such as aluminum and a fluororesin layer 172 formed on the outer periphery thereof. A heat source 173 such as a halogen lamp is provided inside the upper roller 17a. The lower roller 17b includes a roller base 174 made of metal such as aluminum and a heat-resistant elastic layer 175 made of silicon rubber. A heat source 176 such as a halogen lamp is provided inside the lower roller 17b. As a configuration of the fixing roller, in addition to the above-described configuration, a roller in which a silicon rubber layer and a fluororesin surface layer are provided on a metal roller base on upper and lower rollers can also be used.

The upper roller 17a is a specific example of the surface heating means in the image forming method of the present invention, and the lower roller 17b is a specific example of the back surface heating means in the present invention.

As another example of the front surface heating means and the back surface heating means, the following combinations can be used.
Examples include a combination of a roller as a surface heating unit and a belt as a back surface heating unit, a combination of a belt as a surface heating unit and a roller as a back surface heating unit, and an example using a belt as both heating units. In the case where a belt is used as the heating means, a belt having a heat source as a backup member as represented by surf fixing can be used.

An offset preventing agent L is supplied to the surface of the upper roller 17a. Silicon oil is used as the anti-offset agent, and a release-resistant and heat-resistant dimethylpolysiloxane having a viscosity of 100 to 50,000 CS is preferable. The silicone oil is contained in an oil tank 182, and is supplied from a supply port 185 by a pump 184 through a supply pipe 183 to an oil supply felt pad 180.
Supplied to The silicone oil supplied to the felt pad 180 is fed to the upper roller 1 by a felt roller 178.
7a. The silicone oil applied to the upper roller 17a is transferred to the lower roller 17b rotating in contact with the upper roller 17a, and an oil layer La indicated by a thick line in the figure is formed. As will be described later, by rotating the upper and lower fixing rollers 17a and 17b after applying the silicone oil,
The silicone oil applied to the upper and lower rollers is made uniform on the roller surface. Reference numeral 186 denotes a cleaning roller (cleaning means), which is composed of a heat-resistant fluorine rubber roller. A fluoro rubber blade can be used instead of the roller. This cleaning means removes toner, silicon oil, and the like from the upper roller 17a. The cleaned portion of the upper roller 17a contacts the lower roller 17b as it rotates. By this contact, the offset toner, silicone oil, etc. attached to the lower roller are transferred to the upper roller, and are removed from the upper roller 17a by the cleaning roller 186. That is,
Although the cleaning roller 186 is in contact with the upper roller 17a, it has a function of cleaning not only the upper roller 17a but also the lower roller 17b. A sensor 187 measures the surface temperature of the upper roller 17a to control the temperature of the fixing device, and uses a thermistor.

Next, a preferred operation of the fixing device will be described with reference to FIGS. 6 (A), 6 (B) and 6 (C). FIG. 6A shows the operation timing of the offset preventing agent applying means and the cleaning means at the time of forming a double-sided image, FIG. 6B shows the time of forming a front side image, and FIG. The relationship with the passage through the fixing device is shown.

At the time of double-side fixing shown in FIG.
The transfer material passes through the fixing device 17 during the times indicated by solid lines T ₁₁ , T ₁₂ , and T ₁₃ . The time intervals t _{1 to} t ₆ are times during which the intermediate transfer member makes one round. As described above, the transfer material passes through the fixing device passing time intervals T ₁₁ , T ₁₂ , and T ₁₃ respectively.
A time interval occurs in which the transfer material does not pass through the fixing device 17.
This time interval has a length equal to or longer than the transit time of the transfer material,
As described above, the intervals are necessarily formed in the image forming process for forming the toner images on both the front and back surfaces. It is desirable that silicon oil is applied using this interval. First, it sets the highest level V ₁₂ the coating amount of the silicone oil from the zero level V ₀ at t _1. Next, hold the V ₁₂ level, after a predetermined time coating,
Transfer material top performing coating by lowering the coated amount at a low level V ₁₁ at time t ₃ before reaching the fixing device. Time t ₄ levels of coating state of the V ₁₂ is reaching the top fixing device of the transfer material
Ends at time t _3, which is set earlier. The level of V ₁₁ continues from time t ₃ before the leading edge of the transfer material reaches the fixing device until time t ₅ the trailing edge of the transfer material passes through the fixing device. 1 imaging cycle, i.e., cycle intermediate transfer body is round ends at T _6. by rotation of the fixing roller in the time interval t ₃ ~t _4, upper and lower due to the application level is changed from V ₁₁ to V ₁₂ rollers 17a, 17
The non-uniformity of the silicon oil layer on the surface b is eliminated, and a uniform silicon oil layer is formed. At t ₆ of time t ₅ just after the trailing edge of the transfer material has passed through the fixing device, performing coating by increasing the coating weight again V ₁₂ level. Is similar to the following transfer material has been described a coating level in relation to the time T ₁₂ to pass through the fixing device on the performing coating by decreasing from V ₁₂ to V ₁₁ are the third and subsequent transfer materials , The same application operation is repeated. Oil coating weight at all time points t _n which fixing has been completed is returned to zero level V _0. Silicone oil coating level V ₁₂ is preferably set to 1.5 to 3.0 level V _11. The amount of silicone oil applied to the upper and lower rollers in this way is 3 to 15 mg for each of the upper and lower rollers.
/ A4.

As described above, it is preferable to apply the silicone oil for preventing offset at a controlled rate in synchronization with the passage of the transfer material through the fixing device. However, depending on the design of the image forming process, the properties of the toner, in particular, its offset properties, and the performance of the applied anti-offset agent, the above control varies, and
It is not necessary to control the above, instead of controlling the application amount of the offset inhibitor V ₁₁ times as described above was changed to V ₁₂ from, always a percentage, i.e., to be applied at V ₁₁ It may be. Also in this case, the amount of silicone oil applied is preferably about 3 to 15 mg / A4 for each of the upper and lower rollers.

The cleaning roller 186 is an upper roller 17
a at a predetermined pressure to clean toner, silicone oil and the like adhering to the surface of the upper roller 17a. This cleaning is also controlled in accordance with the timing at which the transfer material passes through the fixing device, as in the case of silicone oil application. That is, before the transfer material reaches the fixing device, the cleaning roller 186 is ready for the highest contact pressure P ₁₂ from the initial contact pressure P _0, show a strong cleaning action. This cleaning cleans not only the surface of the upper roller 17a but also the surface of the lower roller 17b. That is, as described above, when the cleaning roller 186 contacts the upper roller 17a and cleans the surface thereof, the upper roller 17a and the lower roller 17b keep rotating and contact with the surface of the lower roller 17b. The remaining toner, silicone oil and the like are transferred to the upper roller 17a, and the lower roller 17b is also cleaned at the same time as the upper roller 17a.

This state is maintained until the time required to clean the entire peripheral surfaces of the upper and lower rollers 17a and 17b (from t ₁ to t ₂ ). Then becomes weak contact pressure P _11, the rear end of the transfer material is continued until the time t ₅ to pass through the fixing device. Prior to the next transfer material passes through the fixing device, i.e., the upper roller 17a cleaning roller 186 with a strong contact pressure P ₁₂ again at time t ₆ just after the time t ₅ the trailing edge of the transfer material passes through the fixing device Contact This cleaning operation is repeated when forming a large number of images. As in the case of the silicone oil application described above, the cleaning may not always be performed by changing the contact pressure in synchronization with the passage of the transfer material through the fixing device, but may be always performed by a constant contact pressure.

FIG. 6B shows the timing of silicone oil application and cleaning at the time of single-sided image formation for forming an image on the surface of the transfer material. In the case of forming an image on the surface of a transfer material, in continuous image formation, unlike in the case of double-sided image formation, the transfer material is continuously sent to the fixing device without an interval. That is, as indicated by _{T 21, T 22, T 23} . The difference from the two-sided image formation is that oil application to the lower roller and cleaning of the lower roller become unnecessary, while oil application and cleaning to the upper roller are always performed. In this case, as shown in the figure, the silicon oil applying means and the cleaning roller are in their initial states V ₀ ,
The operation state shifts from P ₀ to the operation states V ₂₁ and P ₂₁ at the operation start time t ₁ , and this state is continued during the operation of the fixing device, and returns to the initial states V ₀ and P ₀ when the fixing is completed. The constant application amount V ₂₁ and contact pressure P ₂₁ in this operation are equal to or lower than the application amount (V ₁₁ ) and contact pressure (P ₁₁ ) in the case of double-sided fixing because there is no toner image on one side of the transfer material. It is good to set. The amount of oil applied to the upper roller in this way is 3
１５15 mg / A4.

One-sided image formation may also be performed in a mode in which an image is formed on the back surface of the transfer material. FIG. 6 shows the timing of silicone oil application and cleaning in this case.
It is shown in (C). The transfer material passes at a to the time interval indicated by T _31, T _32, T ₃₃ is the same timing as the case of duplex fusing.

In this case, the timing of the application and cleaning of the silicone oil is controlled in the same manner as in the case of the double-sided fixing. However, since it is fixed on one side,
The silicone oil application amounts V ₃₁ and V ₃₂ and the cleaning roller contact pressures P ₃₁ and P ₃₂ are preferably set to be equal to or lower than in the case of double-sided fixing. The amount of oil applied to the lower roller in this way is 3 to 15 mg / A4.

Forming a back surface image on the photosensitive drum 10, transferring the image to the intermediate transfer member 14a, forming a front image on the photosensitive drum 10, transferring the image to a transfer material, intermediate transfer member 14a The transfer of the upper back image to the transfer material, the operation of the fixing device, and the operation of the offset preventing agent applying means in the fixing device are performed by control means provided in the apparatus, although not shown. The control means is mainly composed of a microcomputer, and controls each process means in sequence.

FIG. 7 shows an offset preventing agent applied portion of another embodiment of the fixing device used in the present invention. In this example,
An oil regulating blade 188 is used to control the amount of application. The amount of application can be adjusted by adjusting the contact pressure of the oil regulating blade 188 with the upper roller 17a. The silicon oil removed from the surface of the upper roller 17a by the oil regulating blade 188 is returned to the oil tank 182 via the oil receiver 189.

Although the embodiment of the present invention has been described above, the present invention is not limited to such an embodiment.
Various modifications are possible within the scope of the invention described in the claims. The front surface heating means used in the present invention contacts and heats the toner image transferred from the first toner image support, and the back surface heating means contacts the toner image transferred from the second toner image support. And heat it. When an image is formed using the image reading device 50 shown in FIG. 4, a toner image corresponding to the front surface image of the document contacts the front surface heating unit, and a toner image corresponding to the back surface image of the document contacts the back surface heating unit. However, such a correspondence is not inevitable. Depending on the configuration of the image reading device, a mode in which the front surface heating unit contacts the toner image corresponding to the original back surface image and the back surface heating unit contacts the toner image corresponding to the original front surface image is also an embodiment of the present invention. Of course.

[0068]

According to the present invention, in a double-sided image forming process using an intermediate transfer member, even when images are continuously formed on a plurality of transfer materials, the transfer materials are conveyed to the fixing device at intervals. You. Focusing on this point, the offset prevention agent is applied uniformly to both upper and lower rollers using this interval to eliminate the occurrence of offset even in simultaneous double-side fixing, and the lower roller is used using the interval between transfer materials. The upper and lower rollers can be effectively cleaned only by transferring the toner adhered to the upper roller to the upper roller and causing the cleaning means to act on the upper roller.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an image forming apparatus using the present invention.

FIG. 2 is a sectional view of a photosensitive drum.

FIG. 3 is a diagram illustrating a state of forming a toner image on an image forming body and an intermediate transfer body.

FIG. 4 is a cross-sectional view of the image reading device.

FIG. 5 is a diagram illustrating an embodiment of a fixing device used in the present invention.

6 is a diagram showing operation timings of the fixing device shown in FIG.

FIG. 7 is a diagram illustrating another embodiment of the fixing device used in the present invention.

[Explanation of symbols]

Reference Signs List 10 photoconductor drum (image forming body, first toner image support) 11 scorotron charger 12 exposure unit 13 developing unit 14a intermediate transfer body (second toner image support) 14c transfer unit 14g transfer unit 17 fixing device 17a upper roller (Surface heating means) 17b Lower roller (Backside heating means) 178 Felt roller (Offset preventing agent applying means) 186 Cleaning roller L Silicon oil (Offset preventing agent)

Claims (7)

[Claims] 1. A method according to claim 1, wherein two toner images are distributed to a first toner image support and a second toner support, and are sequentially formed.
Transferring the toner image on the second toner image support to a transfer material,
In an image forming method in which a toner image is formed on both sides of a transfer material and then fixed, a surface heating means for heating the sheet in contact with the toner image transferred from the first toner image support to the surface of the transfer material in the fixing A back surface heating unit that contacts and heats the toner image transferred from the second toner image support to the back surface of the transfer material and an offset prevention agent supply unit that supplies an offset prevention agent to the front surface heating unit; The transfer material is transported to the fixing device at an interval equal to or longer than the length of the transfer material in the transport direction, and at the interval, a part of the offset preventing agent supplied to the front surface heating unit is transferred to the back surface heating unit. An image forming method, comprising applying an anti-offset agent to both sides of a transfer material and fixing a toner image. 2. The method according to claim 1, wherein two toner images are separately formed on a first toner image support and a second toner support, and are sequentially formed.
Transferring the toner image on the second toner image support to a transfer material,
In an image forming method in which a toner image is formed on both sides of a transfer material and then fixed, a surface heating means for heating the sheet in contact with the toner image transferred from the first toner image support to the surface of the transfer material in the fixing A back surface heating means for contacting and heating the toner image transferred from the second toner image support to the back surface of the transfer material and a cleaning means acting on the surface of the front surface heating means, and transferring a plurality of transfer materials. The material is transported to the fixing device at an interval equal to or longer than the length in the transport direction, and at the interval, the toner adhered on the back surface heating unit is transferred to the front surface heating unit. An image forming method comprising cleaning the front surface heating unit and the back surface heating unit. 3. The image forming apparatus according to claim 1, wherein the first toner image support is an image forming body on which a toner image is formed by charging, exposing and developing, and the second toner image supporting body is transferred from the image forming body. The image forming method according to claim 1, wherein the image forming method is an intermediate transfer member that supports the toner image. 4. The image forming method according to claim 1, wherein the surface heating unit is cleaned before supplying the offset preventing agent to the surface heating unit. 5. The method according to claim 1, wherein the cleaning unit is caused to act on the front surface heating unit, and the toner attached on the back surface heating unit is transferred onto the front surface heating unit in the space between the transfer materials. The image forming method according to claim 4, wherein the back surface heating unit is cleaned together with the front surface heating unit. 6. An apparatus according to claim 1, wherein the amount of the offset preventing agent applied to said surface heating means in said space between transfer materials is larger than when the transfer material passes.
Or the image forming method according to claim 5. 7. The image according to claim 2, wherein a contact pressure of the cleaning unit to the surface heating unit at the interval between the transfer materials is set to be larger than that when the transfer material passes. Forming method.