JPH11194637A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To save the energy of a fixing means by transferring a toner image on an image forming body to the front surface of transfer material or transferring it to the rear surface of the transfer material after temporarily transferring it to an intermediate transfer body. SOLUTION: In an interval between the passing of first recording paper P and that of second recording paper P, a heat storage elastic roller 17a is heated by making a thermal fixing film 17b in an on-state and setting it at higher temperature than the set value of back surface image fixing temperature. When the roller 17a is heated, the heating of the film 17b is turned off. Next, at the time of forming a one-side image on the front surface in a 2nd image forming mode, the carrying timing of the recording paper P passing through a fixing device 17 is continuously kept. At this time, the film 17b is set to the higher temperature than the set value of the rear surface image fixing temperature, and the roller 17a fixing the front surface image is heated according as it is warmed up by the film 17b. When the roller 17a is heated to the specified temperature, the heating of the film 17b is turned off.

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 for transferring and fixing a toner image formed on an image forming body onto a transfer material to form an image in a copying machine, a printer, a facsimile or the like. In particular, the toner image on the image forming body is transferred to the front surface of the transfer material, or once transferred onto the intermediate transfer body, and then transferred to the back surface of the transfer material, thereby forming an image on both the front and back surfaces of the transfer material. The present invention relates to an image forming apparatus capable of performing such operations.

[0002]

2. Description of the Related Art Conventionally, in double-sided copying, an image on one side formed on an image carrier is transferred and fixed on a transfer material, and this is temporarily stored in a double-sided reversing paper feeder and formed again. A method has been adopted in which a transfer material is fed from a double-sided reversing sheet feeder in synchronization with an image formed on the body, and an image on the other surface is transferred and fixed onto the transfer material.

In this double-sided copying apparatus, as described above, the transfer of the transfer material, such as feeding to the two-sided reversing paper feeder and passing through the fixing device twice, is performed, so that the reliability of transfer of the transfer material is low. And so on. In contrast, JP-B-49-37538 and JP-B-54-28740.
And JP-A-1-44457 and JP-A-4-21
Japanese Patent Application Laid-Open No. 1-44 proposes a method in which a toner image is formed on both surfaces of a transfer material and then fixed once.
No. 457, JP-A-4-214576, etc., a plurality of sets of image forming means including an image forming body, a charging means, an image exposing means, a developing means and the like are arranged in parallel on an intermediate transfer body, and both sides of a color image are formed. Methods have been proposed for forming copies.

[0004]

However, in the fixing means in the double-sided image forming method proposed above, both the upper and lower rollers of the fixing means for fixing the toner image of the front side image and the toner image of the back side image are heated. Although a halogen heater is used as the (heating element), since the upper and lower rollers having a large heat capacity are heated, the warming-up time becomes longer, or both the heating elements are always kept in the heating state. A problem arises in that extra energy is consumed with respect to the required energy at the time of surface image formation that does not require heat supply or at the time of double-sided image formation where the transfer material is intermittently fixed.

In addition, when a color image is fixed, if the color toner image is not sufficiently fixed, color development becomes insufficient, so that controllability of the fixing temperature is required more.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus in which the above-mentioned problems are solved and two-sided fixing is performed without providing a heating means on the front and back of the transfer material, thereby saving energy of the fixing means.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to temporarily hold a toner image formed on an image forming member on an intermediate transfer member and form a toner image on the image forming member again. The toner image held on the transfer material is transferred to the back surface of the transfer material, and the toner image formed again on the image forming body is transferred to the front surface of the transfer material. A first image forming mode in which a toner image is formed on the image forming body and then transferred to a surface of a transfer material, and the toner on the surface of the transfer material is fixed by the fixing unit. A second image forming mode for fixing an image to form a front surface image, wherein the fixing unit faces a back surface of the transfer material; a heat generating rotating member; and a heat storage elastic rotating member facing the front surface of the transfer material. In the first image forming mode. Te is the from the heat-generating rotary member between the transfer material is intermittently fed to the heat storage elastic rotation member 1
In the second image forming mode, the second heating control is performed on the continuously fed transfer material from the heat generating rotary member to the heat storage elastic rotary member. This is achieved by an image forming apparatus.

[0008]

Embodiments of the present invention will be described below. The description of the present application does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope. In the following description of the embodiment, when a color toner image is transferred to a transfer material, the color toner image is transferred to the surface of the transfer material facing the image forming body in the transfer area (referred to as the surface or upper surface of the transfer material). The image is a front image, the other side of the transfer material (called the back or bottom surface of the transfer material)
The image to be transferred to is referred to as a backside image.

An image forming process and each mechanism of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of the image forming apparatus.
FIG. 3 is a diagram illustrating a state of forming toner images on both sides related to the image forming apparatus of FIG. 1, FIG. 3 is a diagram illustrating an example of a document image reading unit, and FIG. 4 is a control circuit block diagram of the image forming apparatus It is.

As shown in FIGS. 3 and 4, a document image reading device 500 as a document image reading means includes a reading device main body 501, a document storage plate 505 for storing a document PS, a document sending roller 502, a transparent plate 503. , Document feed roller 504, document discharge tray 506, and transparent plate 503
And a control unit configured by a signal line incorporated in an external device or the color image forming apparatus described above. Connected to.

When the original PS sent by the original sending roller 502 passes through the transparent plate 503, the original PS is converted into a single-sided original by original image reading sensors PS1 and PS2 provided above and below the transparent plate 503. Determination of whether the document is a double-sided document (single-sided or double-sided) and reading of image data of the document PS are performed.

In the present embodiment, one-sided and two-sided discrimination and image data reading are performed by one set of upper and lower sensors. However, a plurality of sensors respectively corresponding to image data reading and one-sided and two-sided discrimination may be provided. For example, image data may be read after a single-sided or double-sided discrimination has been performed using a plurality of sensors respectively corresponding to each other. Original image reading sensor PS1
Alternatively, the image data of one bundle of originals PS is read by PS2 and stored in the RAM through the control unit.

According to the above, when it is determined that the image is a double-sided image,
The image data of the document PS is read by the document image reading means shown in FIG. 3, and the double-sided image forming program P1 stored in the ROM shown in FIG. P1 is executed, and an image forming process in a double-sided image forming mode, which is a first image forming mode described below, is performed.

The photosensitive drum 10, which is an image forming member, has a cylindrical base formed of a transparent member of, for example, optical glass or transparent acrylic resin provided inside, and a transparent conductive layer,
A photosensitive layer such as an a-Si layer or an organic photosensitive layer (OPC) is formed on the outer periphery of the substrate, and is rotated clockwise as indicated by an arrow in FIG. 1 in a grounded state.

Scorotron charger 11 as charging means
Are used in image forming processes of yellow (Y), magenta (M), cyan (C), and black (K), and face the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10. Attached to the photosensitive drum 1
A control grid maintained at a predetermined potential with respect to the photosensitive layer 0, and a saw-tooth electrode as the discharge electrode 11a,
The charging action (minus charging in the present embodiment) is performed by corona discharge having the same polarity as the toner, and a uniform potential is applied to the photosensitive drum 10. Other wire electrodes can be used as the discharge electrode 11a.

The exposure unit 12 as an image exposure unit for each color moves an exposure position on the photosensitive drum 10 between a discharge electrode 11a of the scorotron charger 11 and a development position of the development unit 13 by a developing sleeve 131. Is provided on the upstream side in the rotation direction of the photosensitive drum 10 with respect to the photosensitive drum 10.

The exposure unit 12 is a linear exposure element 12a 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 of the photosensitive drum 10 are arranged in an array. And a SELFOC lens 12b as an equal-magnification imaging element are configured as an exposure unit attached to a holder (not shown). The exposure unit 12 for each color is attached to the holding member 20. In addition to the exposure unit 12 for each color, the uniform exposure unit 12c and the simultaneous transfer exposure unit 12d are attached to the holding member 20 to form the base of the photosensitive drum 10. Housed inside.

Uniform exposure unit 12c and simultaneous transfer exposure unit 12
d may be only the exposure element 12a such as an LED. However, it is preferable to use the exposure unit 12 for image exposure because it is possible to expose a narrow area without diffusing the exposure light and to remove electricity from the photoconductor layer.

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 emission wavelength of the light emitting element for image exposure light is usually 780 to 90, which is highly transparent to Y, M, and C toners.
In the present embodiment, since a method of performing image exposure from the back side is used, the transparency of the color toner is not sufficiently high.
A wavelength of 780 nm may be used.

Developing device 1 provided in accordance with the color order in which an image is formed and the rotating photosensitive drum 10
3, in the present embodiment, the Y and M developing units 13 are on the left side of the photosensitive drum 10 and the C and K developing units 13 are photosensitive on the photosensitive drum 10 indicated by arrows in FIG. The Y and M scorotron chargers 11 are disposed below the developing casing 138 of the Y and M developing units 13, and the developing casing 1 of the C and K developing units 13 is disposed on the right side of the body drum 10.
The C and K scorotron chargers 11 are arranged above 38.

A developing device 13 as a developing means for each color contains a one-component or two-component developer of yellow (Y), magenta (M), cyan (C) and black (K), respectively. A non-magnetic cylindrical member having a thickness of, for example, 0.5 to 1 mm and an outer diameter of 15 to 25 mm, which rotates in the same direction as the rotation direction of the photosensitive drum 10 at the developing position while maintaining a predetermined gap with respect to the peripheral surface of the body drum 10 Developing sleeve 131 made of stainless steel or aluminum material.

The developing unit 13 is moved to a predetermined distance from the photosensitive drum 10 by an abutting roller (not shown).
Developing device 1 for each color which is kept in
In the developing operation of the developing device 3, a developing bias in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 131, and non-contact development is performed by a one-component or two-component developer accommodated in the developing device, thereby forming a transparent conductive material. A non-contact reversal development is performed in which a DC bias of the same polarity as the toner (in this embodiment, a negative polarity) is applied to the negatively charged photosensitive drum 10 that grounds the layer, and the toner adheres to the exposed portion. . At this time, the accuracy of the development interval needs to be about 20 μm or less in order to prevent image unevenness.

The developing device 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 writing by the exposure unit 12 into a DC voltage and an AC voltage. In a non-contact state by a non-contact developing method by applying a developing bias in which the developing roller is superimposed, reverse development is performed with a toner having the same polarity as the charged polarity (in the present embodiment, the photosensitive drum is negatively charged and has a negative polarity).

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

When the image recording starts, the photosensitive drum driving motor (not shown) is started to rotate the photosensitive drum 10 clockwise as indicated by the arrow in FIG. 1, and at the same time, yellow (Y) development is performed on the left side of the photosensitive drum 10. Developing casing 1 of container 13
The application of a potential to the photoconductor drum 10 is started by the charging action of the Y scorotron charger 11 arranged below 38.

After the photosensitive drum 10 is applied with a potential, the Y exposure unit 12 starts exposure scanning with an electric signal corresponding to the first color signal, that is, the Y image data. An electrostatic latent image corresponding to the Y image of the original image is formed on the photosensitive layer on the surface.

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 according to the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 has a magenta (M) developing device 1 on the yellow (Y) toner image and further on the left of the photosensitive drum 10 and above the yellow (Y).
An electric signal corresponding to the second color signal of the M exposure unit 12, that is, the 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 sequentially superimposed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 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 obtained by the cyan (C) scorotron charger 11, the exposure unit 12 of C, and the developing unit 13 of C, which are arranged above the photoconductor 8 A black (K) scorotron charger 11, a K exposure unit 12, and a K 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 below the C. A black (K) toner image corresponding to the fourth color signal is sequentially superposed, and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10.

These Y, M, C and K exposure units 1
2 is performed on the photosensitive layer of the photosensitive drum 10 through the above-described transparent substrate from inside the drum. Therefore, the writing 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. Can be formed.

By the above-described image forming process, a superimposed color toner image as a backside image is formed on the photosensitive drum 10 as an image forming body, and the superimposed color toner image of the backside image on the photosensitive drum 10 is transferred to the transfer area. At 14b, the transfer device 14c to which a DC voltage having the opposite polarity (positive polarity in the present embodiment) to the toner is applied is stretched between the driving roller 14d, the driven roller 14e, and the tension roller 14i. The images are collectively transferred onto an intermediate transfer belt 14a which is an intermediate transfer member provided close to or in contact with the intermediate transfer belt. At this time, for example, uniform exposure is performed by the simultaneous transfer exposure device 12d using a light emitting diode so that good transfer is performed.

Intermediate transfer belt 14a as an intermediate transfer member
Is an endless belt that is stretched between the driving roller 14d, the driven roller 14e, and the tension roller 14i, and is provided in contact with the photosensitive drum 10;
5 to 50 μm thick semiconducting layer having a thickness of 5 μm to 50 μm as a toner filming prevention layer on the outside of a semiconductive rubber belt base made of silicon rubber or urethane rubber having a volume resistivity of 5 to 2.0 mm and a volume resistivity of 10 ⁸ to 10 ¹⁴ Ω · cm. And a two-layer structure with fluorine coating. Instead of a rubber belt substrate, a thickness of 0.1 to 0.5 mm and a volume resistivity of 10 ⁸ to 10
¹⁴ Ωcm semi-conductive polyester, polystyrene,
Polyethylene, polyethylene terephthalate, polyimide, modified polyimide, ETFE (ethylene-tetrafluoroethylene copolymer), and the like can also be used.

After the toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the photosensitive drum AC static eliminator 16, the toner is transferred to a cleaning device 19 as cleaning means for the photosensitive drum 10, The photosensitive drum is cleaned by a cleaning blade 19a made of a rubber material in contact with the drum 10. Further, in order to eliminate the history of the photoconductor in the previous image formation, for example, the light is exposed by a uniform exposure device 12c before charging using a light emitting diode. The peripheral surface of the photoconductor is neutralized, and the next image is formed.

The back side image formed on the intermediate transfer belt 14a is synchronized with the transfer area 14b, and the surface image of the superimposed color toner image is transferred to the photosensitive drum 10 in the same manner as in the above-described color image forming process. Formed on top. The surface image formed at this time is the photosensitive drum 1
On 0, it is necessary to change the image data so that the back side image formation is a mirror image of each other.

The 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, and is conveyed to a timing roller 15b as a transfer material feeding means.

The recording paper P is synchronized with the color toner image of the front surface image carried on the photosensitive drum 10 and the color toner image of the rear surface image carried on the intermediate transfer belt 14a by driving the timing roller 15b. And is fed to the transfer area 14b.

At this time, the transfer material can be brought into contact with and released from the intermediate transfer belt 14a by using the support shaft 152 as a rotation fulcrum, brought into contact with the recording paper P, and applied with a DC voltage having the same polarity as the toner. The recording paper P as the transfer material is charged to the same polarity as the toner by the paper charger 150 having a brush-like end as a charging unit, and is attracted to the intermediate transfer belt 14a and fed to the transfer area 14b. The paper charger 150 is provided to oppose the grounded driven roller 14e.

By charging the paper with the same polarity as the toner, the toner is prevented from being attracted to the toner image on the intermediate transfer belt 14a and the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed. Simultaneously with the passage of the recording paper P, the paper charger 150 is separated from the intermediate transfer belt 14a, and the contact is released.

The paper charger 150 is released from the intermediate transfer belt 14a immediately before or simultaneously with the passage of the rear end of the recording paper P, and is separated from the recording paper P. Further, the voltage is applied to the paper charger 150 only when the recording paper P is being fed, and the voltage applied to the paper charger 150 is cut off simultaneously with the separation from the recording paper P.

Further, as the transfer material charging means, it is possible to use a conductive roller capable of contacting and releasing contact with the intermediate transfer belt 14a and applying a DC voltage having the same polarity as that of the toner.

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 first transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in this 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 belt 14a is not transferred to the recording paper P but exists on the intermediate transfer belt 14a.

Next, a backside image on the peripheral surface of the intermediate transfer belt 14a is collectively collected by a backside transfer unit 14g as a second transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied. Then, the image is transferred to the lower surface (back surface) of the recording paper P. At this time, the backside transfer unit 14g to which the voltage is applied is arranged so as to face the grounded drive roller 14d so that the backside image can be favorably transferred. In addition, at the time of transfer by the transfer unit 14c, one transfer unit 12d using a light emitting diode, for example, provided inside the photosensitive drum 10 facing the transfer unit 14c so that good transfer is performed. Exposure may be performed.

Since the toner images of the respective colors overlap 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 belt 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 photosensitive drum 10, and the color toner images of the same polarity formed by superimposition are collectively transferred to the intermediate transfer belt 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 photosensitive drum 10 to collectively transfer color toner images of the same polarity formed by superimposition onto the recording paper P without changing the polarity.
It is preferable because it contributes to improvement of the transferability of surface image formation.

As described above, in the color image formation, the first transfer means is operated to form a color toner image on the surface of the transfer material by using the above-described image forming method for the front surface and the back surface. 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 means is preferably employed.

The recording paper P having the color toner images formed on both sides is transferred to a paper separation AC neutralizer 14h as a transfer material separating means.
, And is separated from the intermediate transfer belt 14a.
The recording sheet P is conveyed to a fixing device 17 as a fixing unit by a spur 162 that conveys the recording sheet P while preventing the toner image of the back side image from being disturbed. At this time, to achieve good separation,
The paper separating AC neutralizer 14h to which the voltage is applied is arranged to face the driving roller 14d that is grounded.

As will be described later in detail, a fixing device 17 as a fixing means includes a heat storage elastic roller 17a which is a heat storage elastic rotating member for fixing a toner image of a front image, and a fixing device 17 for fixing a toner image of a back image. A heat-fixing film 17b, which is a heat-generating rotary member, is used to generate heat at a nip formed by a heat-storage elastic roller 17a disposed on the upper side and a heat-fixing film 17b disposed on the lower side in FIG. By applying pressure, the toner adhered to the front and back surfaces of the recording paper P is fixed. The recording paper P on which double-sided image recording has been performed is sent upside down, and is discharged by a discharge roller 18 to a tray outside the apparatus.

An intermediate transfer member cleaning device 140, which is a cleaning means for the intermediate transfer belt 14a, is provided so as to face the driven roller 14e.
The toner remaining on the peripheral surface of the intermediate transfer member 4a is provided on the intermediate transfer member cleaning device 140, and is cleaned by the intermediate transfer member cleaning blade 141 which can be brought into contact with and released from the intermediate transfer belt 14a using the support shaft 142 as a rotation fulcrum. Is done.

The toner remaining on the peripheral surface of the photoconductive drum 10 after the transfer is subjected to static elimination by the photoconductive drum AC static eliminator 16 in the same manner as when the back side image is formed, and then enters the cleaning device 19 or the photoconductor. The toner is scraped off into the cleaning device 19 by a cleaning blade 19a made of a rubber material, which is in contact with the drum 10, and is collected by a screw 19b in a waste toner container (not shown). Photoconductor drum 10 from which residual toner has been removed by cleaning device 19
Is uniformly charged by the Y scorotron charger 11 and enters the next image forming cycle.

By using the above-mentioned method, since the superimposed color toner images are transferred at a time, color misregistration of the color image on the toner image receiving body, scattering or rubbing of the toner, and the like are less likely to occur, and image deterioration is small. A double-sided color image is formed.

In the original image reading apparatus 500,
When it is determined that the image is a single-sided image of only the front side, the image data of the single-sided original PS is read by the original image reading means shown in FIG. 3, and the image forming body stored in the ROM shown in FIG. The single-sided image forming program P2 by the body drum 10 is read into the RAM through the control unit, and the single-sided image forming program P2 of the front side is executed by the control unit.
The image forming process of only the front surface by the photosensitive drum 10 described in (1) is performed.

FIG. 5 shows the structure of the fixing means and the temperature control.
This will be described with reference to FIG. FIG. 5 is a cross-sectional configuration diagram of a fixing unit, and FIG. 6 is a detailed explanatory diagram of a fixing film.
FIG. 7 is a temperature control timing chart during double-sided image formation, and FIG. 8 is a temperature control timing chart during single-sided image formation.

As shown in FIG. 5, a fixing device 17 as a fixing means includes a heat storage elastic roller 17a as a heat storage elastic rotating member for fixing a toner image of a front image, and a fixing device 17 for fixing a toner image of a back image. The heat storage elastic roller 17a is driven and rotated by a fixing drive motor (not shown), and the heat fixing film 17b is driven to rotate. Heat storage elastic roller 1
7a and nip portion N formed by heat fixing film 17b
By applying heat and pressure, the toner adhered on the recording paper P fed to the nip N is fixed.

The heat storage elastic roller 17a for fixing the toner image of the surface image includes a core 175, a silicon rubber having a thickness of, for example, 20 mm, which is formed integrally with the core 175 on the outer periphery of the core 175, and the like. An elastic rubber roller 176 having a surface coated with a fluoro rubber latex is used. By increasing the thickness of the elastic rubber roller 176, the heat storage elastic roller 17a having a large heat storage amount can be obtained. The elastic rubber roller 176 is made soft to make the nip portion N large. By coating the surface of the heat storage elastic roller 17a with a fluoro rubber latex, a sufficient driving force is given to the fixing film 171 of the heat fixing film 17b and the recording paper P, and a large frictional force and high releasability without contamination with toner. And the offset is prevented. Further, the thermal conductivity from the heat fixing film 17b to the heat storage elastic roller 17a is improved. 178 is an oil supply roller.
Is a cleaning roller, and TS2 is a temperature sensor provided in contact with the elastic rubber roller 176. The temperature of the heat storage elastic roller 17a, which is heated by receiving heat from the heat fixing film 17b, is controlled by the temperature sensor TS2 of the heat storage elastic roller 17a to control the temperature of the heat fixing film 17b for fixing the back (lower) image. The temperature value of the heat fixing film 17b is controlled by a temperature sensor TS1 for turning on and off the heat fixing film 17b).

The heat fixing film 17b for fixing the toner image of the back side image holds, for example, a thin fixing film 171 having a thickness of 40 to 100 μm, a ceramic heater 172 as a fixed heating element (heating means), and a ceramic heater 172. And a heater holder 173.
TS1 is a thermistor (temperature sensor) attached to the back surface of the ceramic heater 172 for performing temperature control.

The heat storage amount of the fixing film 171 is about 1/100 of that of the heat storage elastic roller 17a, and a quick start with almost zero warm-up is possible. The heater holder 173 holds the rotating fixing film 1.
While serving as a traveling guide for the roller 71, the roller 71 comes into pressure contact with the heat storage elastic roller 17 a via a ceramic heater 172 which is held. The fixing film 171 is a heater holder 17.
3. Thermal storage elastic roller 1 loosely fitted to 3 and fitted and rotated
The rotation is driven by the surface frictional force 7a. The heat storage elastic roller 17a which rotates from the heat-fixing film 17b which rotates by the rotation
Is supplied with heat.

As the ceramic heater 172, an alumina substrate provided with a resistor and overcoat glass by thick film printing is used, and the thermal resistance between the fixing film 171 is lower than that of the fixed heating element.

Further, as shown in FIG.
1 includes a base material 171a, a conductive layer 171b, and a release layer 171c.

As the base material 171a, a polyimide resin excellent in strength and dimensional stability at high temperatures is preferable, and the thickness is preferably as thick as about 40 to 100 μm. By increasing the thickness to about 40 μm, the strength and rigidity are increased, and the end of the fixing film 171 during rotation can be regulated without buckling. On the other hand, if the thickness is more than 100 μm, the heat conduction becomes poor,
a, the heat transfer to the heat-fixing film 17b and the heat storage elastic roller 17a become difficult to heat instantaneously, and the electric power used also increases. Would.

In order to prevent offset, the release layer 1
71c is preferably provided with a layer of, for example, a fluororesin (PFA or PTFE).
A conductive layer 171b is provided and grounded to eliminate the influence of frictional charges generated by sliding between the inner surface of the base member 171a and the surface of the ceramic heater 172.

Further, a conductive filler is inserted in the release layer 171c to reduce the resistance so as to release the charged charges separated from the trailing edge of the recording paper P in a low humidity environment, thereby preventing the offset.
However, if the resistance value is too low, the transfer charge leaks and an offset occurs, so that 2 × 10 ^{10 to} 5 × 10 ¹¹ Ω / cm.
A resistance value of ² is preferred.

Further, when small size paper is continuously passed, the temperature becomes excessively high in the non-paper passing portion. Due to the temperature non-uniformity in the direction perpendicular to the conveying direction of the recording paper P, the fixing film 1
71 may be twisted or the heater holder 173 may be thermally degraded.
6 is coated with a fluoro rubber latex, or a core material 175 made of a material having good heat conductivity, for example, an aluminum material is used to improve the heat conductivity from the heat fixing film 17b to the heat storage elastic roller 17a to prevent this.

As shown in FIG. 7, during the double-sided image formation in the first image formation mode, the recording sheet P passing through the fixing device 17 in response to the image formation on the front and back sides by the photosensitive drum 10 has a continuous one-sided timing. Intermittently unlike print
The heat fixing film 17b for fixing the toner image of the back side image is turned on from room temperature T while image formation is suspended, although performed every other sheet.
As the state, the temperature T higher than the backside image fixing temperature set value T1
As 11 (preliminary heating temperature), the heat storage elastic roller 17a for fixing the toner image of the surface image is heated by warming up the heat storage elastic roller 17a by the heat fixing film 17b, and the heat storage elastic roller 17a is stored and gradually heated. When the heat fixing film 17b is heated to a temperature T21 slightly higher than the front image fixing temperature set value T2 necessary for fixing the front image, the heating of the heat fixing film 17b is turned off. Due to the temperature of the heat storage elastic roller 17a having a large heat capacity, the temperature of the heat fixing film 17b is maintained at a temperature T12 slightly lower than the back image fixing temperature set value T1. Preheating temperature T11
May be the backside image fixing temperature set value T1, but if it is higher than this, the heat storage elastic roller 17a may take the temperature to reach the backside image fixing temperature set value T1 during fixing.

The heat fixing film 17b is turned on in synchronization with the passage timing of the first recording sheet P, and the proper back image fixing temperature set value T1 during image formation necessary for fixing the toner image of the back image is set. Is set to
The heat storage elastic roller 17a fixes the surface image while gently lowering the temperature from the temperature T21 to a proper surface image fixing temperature set value T2 during image formation by the heat stored for fixing the toner image of the surface image. The two-sided toner image on the first recording sheet P is fixed. While the recording paper P does not pass, heat is transferred from the lower heat fixing film 17b to the upper (front surface) heat storage elastic roller 17a, and the toner image of the surface image is fixed by the heat storage elastic roller 17a. Heat storage elastic roller 1
7a has a heat capacity that can withstand the temperature drop caused by the passage of the recording paper P.

Between the passage of the first recording paper P and the second recording paper P, the heat fixing film 17b is turned on,
The heat storage elastic roller 17a is heated at a temperature T13 higher than the back side image fixing temperature set value T1, and the heat storage elastic roller 17a is heated.
Is heated to a temperature T21 slightly higher than the surface image fixing temperature set value T2 necessary for fixing the surface image, the heating of the heat fixing film 17b is turned off. Due to the temperature of the heat storage elastic roller 17a having a large heat capacity, the temperature of the heat fixing film 17b is maintained at a temperature T12 slightly lower than the back image fixing temperature set value T1.

The heat fixing film 17b is turned on in synchronization with the passage timing of the second recording paper P, and the proper back image fixing temperature set value T1 during image formation necessary for fixing the toner image of the back image is set. And the heat storage elastic roller 17a is gently moved from the temperature T21 to the proper back image fixing temperature set value T2 during image formation due to the heat stored necessary to fix the toner image of the front image. The lower surface image is fixed while lowering the temperature, and the double-sided toner image on the second recording sheet P is fixed. The fixing control of the double-sided toner images on the third and subsequent sheets of recording paper P is similarly performed. (Figure 7 above)
1st heating control shown in FIG.

In the first image forming mode, since the heat storage amount of the heat storage elastic roller 17a is large and the double-sided image formation is performed intermittently every other sheet, the recording paper P
Since the non-passing time is long, it is possible to control the temperature and make the temperature uniform, and it is possible to fix the two-sided image even with the heat fixing film 17b having a small heat capacity.

The temperature control is performed through a control unit via a comparison circuit based on the front-side image fixing temperature set value T1 and the back-side image fixing temperature set value T2 stored in advance in the ROM and detection by the temperature sensors TS1 and TS2. Heating control is performed.

In FIG. 7, the temperature control on the side of the heat fixing film 17b is performed in a region sandwiching the leading and trailing edges of the recording paper P. However, if the linear velocity is high, it is necessary to set the temperature control timing earlier. .

As shown in FIG. 8, when forming a single-sided image on the front surface in the second image forming mode, the photosensitive drum 10
The transfer timing of the recording paper P passing through the fixing device 17 is continuously performed in response to the continuous image formation on the front surface by the above-described process, but the heat fixing film 17b is set to an on state from the room temperature T during which the image formation is suspended, and the back image fixing is performed. As the temperature T11 (preheating temperature) higher than the temperature set value T1, the heat fixing film 1
Heat storage elastic roller 1 for fixing a toner image of a surface image by warming up heat storage elastic roller 17a by 7b
7a, the heat storage elastic roller 17a is stored, and the temperature is gradually increased. When the heat storage elastic roller 17a is heated to a temperature T21 slightly higher than the surface image fixing temperature set value T2 required for fixing the surface image, the heat fixing film is heated. Turn off the heating of 17b.
The temperature of the heat fixing film 17b is reduced by the temperature of the heat storage elastic roller 17a having a large heat capacity to the rear image fixing temperature set value T1.
It is maintained at a slightly lower temperature T12. The preheating temperature T11 may be the backside image fixing temperature set value T1, but even if the preheating temperature T11 is higher than this, if the temperature is taken by the heat storage elastic roller 17a and the heat storage elastic roller 17a becomes the front image fixing temperature set value T2 during fixing. Good.

The heat-fixing film 17b is turned on at the same timing as the recording paper P passes, the temperature T14 is set to a temperature T14 higher than the set value T1 of the back-side image fixing temperature, and the heat-storage elastic roller 17a is heated from the back of the recording paper P, and the heat-storage elasticity is increased. Roller 17a
Each of the recordings that fix the surface image while gradually lowering the temperature from the temperature T21 to an appropriate surface image fixing temperature set value T2 during image formation from the temperature T21 by the heat stored for fixing the toner image of the surface image, The toner image on the surface of the paper P is fixed. The heat storage elastic roller 17a has a heat capacity enough to withstand the temperature drop caused by the passage of the recording paper P. During the time when the recording paper P is passed, the recording paper P is heated by the high temperature T14 of the heat fixing film 17b which is maintained for a time longer than the width of the recording paper P, and the heat storage elastic roller 17a is required to fix the toner image of the surface image. Temperature T2 due to the stored heat
When the temperature is raised to 1, the heat fixing film 17b is turned off, but the temperature of the heat fixing film 17b is set at a temperature T12 slightly lower than the backside image fixing temperature set value T1 due to the temperature of the heat storage elastic roller 17a having a large heat capacity. Will be maintained. The high temperature T14 of the heat fixing film 17b, which is maintained for a time longer than the width of the recording paper P, prevents the temperature of the upper heat storage elastic roller 17a from lowering. (The above is the second heating control shown in FIG. 8).

As compared with the first image forming mode in which double-sided image formation is performed, the single-sided image formation in the second image forming mode has a shorter sheet passing interval. By setting the temperature of the heat fixing film 17b to be higher, the temperature of the upper heat storage elastic roller 17a is prevented from lowering. That is, T14> T13 is set. Preferably, T14 is 150-200 ° C., T14-T13
Is 10 to 30 ° C.

The temperature control is performed by setting the front-side image fixing temperature set value T2 stored in advance in the ROM and the temperature sensors TS1 and TS1.
2, the second heating setting is performed through the control unit via the comparison circuit.

According to FIGS. 7 and 8, when the single-sided image formation on the front surface is changed from the single-sided image formation in the second image formation mode to the double-sided image formation in the first image formation mode, or when both sides are changed in the first image formation mode. At the time of changing from the image formation to the one-sided image formation of the front side in the second image formation mode, the fixing of the toner image of the front side image is performed by the heat storage elastic roller 17a which is always in a fixable state, and the toner image of the back side image is formed. Is performed by the heat fixing film 17b having a small heat capacity and capable of quick start, so that the fixing is performed according to the change without providing a warm-up time. Similarly, a warm-up time is not required at the time of backside image formation.

At the start of single-sided image formation on the front surface in the second image formation mode or double-sided image formation in the first image formation mode, the surface image must be fixed by the heat fixing roller 17a having a large heat capacity. A warm-up time for the heat fixing roller 17a is required.
The warming-up time becomes long when the heat storage elastic roller 17a having a high linear velocity and a large heat capacity is required.

It should be noted that the image forming apparatus is set so that temperature control is automatically performed in the state of double-sided image formation at the time of initial operation when the power switch is turned on, or when the mode is changed from the pause mode to the print operation mode. Further, it is also possible to control so that the heating control of the heat fixing film 17b is turned off when the unused time passes a predetermined time.

FIG. 9 shows another example of the fixing means. As a heat-generating rotating member for fixing the toner image of the back side image, a heat fixing roller 17c is provided opposite to the heat storage elastic roller 17a instead of the heat fixing film 17b. And a fixing device 17 as fixing means.

Heat fixing roller 17c, which is a heat generating rotating member
Is formed integrally with the metal pipe 275 on the outer periphery of the metal pipe 275, for example, with a thickness of 3 mm.
And a rubber roller 276 whose surface is coated with a fluoro rubber latex, and a halogen heater 277 as a heating element (heating means) provided inside the metal pipe 275. TS1 is rubber roller 1
This is a temperature sensor provided in contact with 76. The rubber roller 276 is made soft so that the nip portion N is made large.

By using the heat fixing roller 17c having the above structure, it is possible to drive the roller pair by the lower heat fixing roller 17c. In this case, a sufficient driving force is applied to the recording paper P by the heat fixing roller 17c, which is a hard roller, and a high releasability that does not stain with toner and frictional force is obtained by the fluorine rubber latex coating on the surface of the heat fixing roller 17c. Offset is prevented. A large nip N formed by the upper soft roller (heat storage elastic roller 17a) and the lower hard roller (heat fixing roller 17c) causes recording to be wound around the upper hard roller by the toner image on the surface. The paper P is easily separated from the hard rollers. In particular, this effect works effectively in the case of single-sided image formation only on the front surface.

At the time of starting double-sided image formation in the first image formation mode or starting single-sided image formation in the second image formation mode, the heat storage elastic roller 17 having a large heat capacity is used.
Since it is necessary to fix the surface image by a, immediate startup is difficult, and a warm-up time of the heat fixing roller 17c is required. Also, a warm-up time is required when forming a single-sided image on only the back side.

[0082]

According to the present invention, double-sided fixing is performed without providing heating means on the front and back of the transfer material, and energy saving of the fixing means can be achieved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus.

FIG. 2 is a diagram illustrating a state where toner images are formed on both sides of the image forming apparatus of FIG. 1;

FIG. 3 is a diagram illustrating an example of a document image reading unit.

FIG. 4 is a block diagram of a control circuit of the image forming apparatus.

FIG. 5 is a sectional configuration diagram of a fixing unit.

FIG. 6 is a detailed explanatory view of a fixing film.

FIG. 7 is a temperature control timing chart during double-sided image formation.

FIG. 8 is a temperature control timing chart during one-sided image formation.

FIG. 9 is a diagram illustrating another example of a fixing unit.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum 11 scorotron charger 12 exposure unit 13 developing unit 14a intermediate transfer belt 17 fixing device 17a heat storage elastic roller 17b heat fixing film 17c heat fixing roller 171 fixing film 172 ceramic heater 176 elastic rubber roller 275 metal pipe 276 rubber roller 277 halogen heater P Recording paper

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Haneda Konica Corporation 2970 Ishikawacho, Hachioji-shi, Tokyo

Claims (4)

[Claims] 1. A toner image formed on an image forming body is temporarily held on an intermediate transfer body, and after a toner image is formed on the image forming body again, the toner image held on the intermediate transfer body is A toner image formed again on the back surface of the transfer material and on the image forming body is transferred to the front surface of the transfer material, and the toner images on the front and back surfaces of the transfer material are fixed by a fixing unit to form a double-sided image. Forming a toner image on the image forming body, transferring the toner image to the surface of a transfer material, and fixing the toner image on the surface of the transfer material by the fixing unit to form a surface image. A second image forming mode to be formed, wherein the fixing means comprises a heat generating rotating member facing the back surface of the transfer material, and a heat storage elastic rotating member facing the surface of the transfer material; In the image forming mode, the sheet is intermittently fed. A first heating control from the heat generating rotary member to the heat storage elastic rotary member is performed between the transfer materials. In the second image forming mode, the heat transfer rotary member is continuously fed from the heat generating rotary member to the transfer material. An image forming apparatus for performing a second heating control on a heat storage elastic rotating member. 2. The image forming apparatus according to claim 1, wherein the temperature of the heat generating rotary member when passing through the transfer material is higher in the second image forming mode than in the first image forming mode. apparatus. 3. The image forming apparatus according to claim 1, wherein said heat generating rotating member comprises a fixing film and a fixed heat generating element. 4. The image forming apparatus according to claim 1, wherein said heat generating rotary member comprises a heat generating element and a metal pipe.