JPH1048979A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To consume appropriate energy by setting a member for fixing a toner image on the rear face of a transcription member to a roller rotation member having a heating element and setting a member for fixing a toner image on the front face of the transcription member to a film rotation member having a plate heating element. SOLUTION: A fixing device 17 is constituted of a heat fixing roller 17a as a roller rotation member for fixing a toner image on a rear image and a heat fixing film 17b as a film rotation member for fixing a toner image on the front image, and the heat fixing roller 17a is drivingly rotated by a fixing drive motor and the heat fixing film 17b is drivenly rotated. Heat and pressure are applied on a nip part formed of the heat fixing roller 17a and the heat fixing film 17b so that adhesion toner on a record paper sheet P to be fed to the nip part is fixed. A halogen lamp 177 and a ceramic heater 172 are provided inside the core bar 175 of this heat fixing roller 17a and the heat fixing film 17b respectively.

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 forming an image by transferring and fixing a toner image formed on an image carrier onto a transfer material in a copying machine, a printer, a facsimile or the like. In particular, an image is formed on both the front and back surfaces of the transfer material by transferring the toner image on the image carrier to the front surface of the transfer material or transferring the toner image once onto the toner image receiver and then to the back surface 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 two-sided reversing paper feeder, and the image bearing is again performed. 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. 4576/1994 proposes a method in which a toner image is formed on both surfaces of a transfer material and then fixed once.
JP-A-44457 and JP-A-4-214576 disclose that a plurality of sets of image forming means including an image carrier, a charging means, an image exposing means, a developing means and the like are arranged in parallel on a toner image receiving body. Has been proposed.

[0004]

However, Japanese Patent Application Laid-Open Nos. Hei 1-44457 and Hei 4-214576 mentioned above.
In the double-sided color image formation proposed in Japanese Patent Application Laid-Open Publication No. H08-27, the transferability of the transfer material is improved, but the color toner images are superimposed one by one on the toner image receiver, so that color misregistration, toner scattering and rubbing, etc. Image degradation easily occurs.

On the other hand, the present inventors once transfer the toner image formed on the image carrier (first image carrier) to a toner image receiver (second image carrier) at one time, We are studying a two-sided image forming method in which the toner image on the toner image receiving body and the toner image formed on the image carrier again are transferred to both sides of the transfer material. Heating elements are used for both the upper and lower rollers of the fixing means for fixing the image.However, since the upper and lower rollers having a large heat capacity are heated, the warm-up time becomes longer,
Since both heating elements are always in a heating state, heat is also supplied to rollers that are not required for single-sided image formation, and extra energy is required for double-sided image formation where the transfer material is intermittently fixed. This causes a problem that a large amount of energy is consumed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus provided with a fixing means for consuming appropriate energy for forming a single-sided image or for forming a double-sided image. And

[0007]

An object of the present invention is to provide a first image carrying means for carrying a toner image formed by a toner image forming means and a toner image carried by the first image carrying means. A second image carrying means for carrying the transferred toner image on the surface again, and a first transfer for transferring the toner image carried on the first image carrying means to the surface of the transfer material. Means, a second transfer means for transferring the toner image carried by the second image carrying means to the back surface of the transfer material, and a fixing means for fixing the toner images transferred to both surfaces of the transfer material. Wherein the member for fixing the toner image on the back surface of the transfer material is a roller-shaped rotating member having a heating element inside, and the member for fixing the toner image on the surface of the transfer material contacts the inner surface. Film-shaped rotating part with plate-shaped heating element It is achieved by an image forming apparatus, characterized in that it.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description of the embodiments,
When transferring the color toner image to the transfer material, the image to be transferred to the surface of the transfer material facing the image carrier in the transfer area is the front image, and the image to be transferred to the other surface of the transfer material is the back surface. It is called an 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 the image forming process described below is performed.

The photosensitive drum 10, which is an image bearing member and serves as a first image bearing member, has a cylindrical base formed of a transparent member made of, for example, optical glass or a transparent acrylic resin, and has a transparent conductive layer. , An a-Si layer or a photosensitive layer such as 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 light-emitting wavelength of the light-emitting element used in this embodiment may be shorter than the wavelength at which the color toner does not have sufficient transparency because the image exposure is performed from the back surface.
It is used if the photoreceptor layer has sensitivity from visible light of 400 to 900 nm to infrared light.

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 that 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 drum Developing sleeve 131 made of stainless steel or aluminum material.

The developing unit 13 is provided with a gap between the photosensitive drum 10 and a predetermined value, for example, 300 to 6 by an abutting roller (not shown).
The developing unit 13 is kept in a non-contact state with an interval of
Is applied to the developing sleeve 131, a developing bias in which a DC voltage and an AC voltage are superimposed is applied, and non-contact development with a one-component or two-component developer accommodated in the developing device is performed, thereby forming a transparent conductive layer. A non-contact reversal development is performed by applying a DC bias having the same polarity as the toner (in this embodiment, a negative polarity) to the negatively-charged photosensitive drum 10 that grounds the toner. 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. Black (K) toner images corresponding to the fourth color signal are sequentially superimposed, and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10 (toner image forming means). ).

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 serving as a back surface image is formed on the photosensitive drum 10 as the first image carrying means.
0 is the transfer area 1
At 4b, the transfer device 14c to which a DC voltage having the opposite polarity (positive polarity in this embodiment) to the toner is applied is stretched between the driving roller 14d and the driven roller 14e, and comes close to or contacts the photosensitive drum 10. Is collectively transferred onto a toner image receiving member 14a as a second image carrying means provided. 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.

[0033] In an endless rubber belt toner image receiving body 14a as a second image bearing means, for example a thickness of 0.5 to 2.0 mm, 10 ⁸ ~ of silicone rubber or urethane rubber
A semiconductive substrate having a resistance value of 10 ¹² Ω · cm, and a toner filming prevention layer of 10 ¹⁰ 〜
It has a two-layer structure with a fluorine coating having a resistance value of 10 ¹⁶ Ω · cm and a thickness of 5 to 50 μm. This layer also preferably has a similar semiconductivity. Instead of the rubber belt substrate, semiconductive polyester, polystyrene, polyethylene, polyethylene terephthalate or the like having a thickness of 0.1 to 0.5 mm can 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 toner image receiver 14a is synchronized with the transfer area 14b, and the surface image of the superimposed color toner image is transferred to the photosensitive drum in the same manner as in the above-described color image forming process. 10 is formed. 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 driven by the timing roller 15b to produce a color toner image of the front surface image carried on the photosensitive drum 10 and a color toner image of the back surface image carried on the toner image receiver 14a. The paper is fed to the transfer area 14b in synchronization.

At this time, the transfer can be brought into contact with and released from the toner image receiving member 14a by using the support shaft 152 as a rotation fulcrum, and brought into contact with the recording paper P, and a DC voltage having the same polarity as the toner is applied. The recording paper P as a transfer material is charged to the same polarity as the toner by a paper charger 150 having a brush-like end as a material charging unit, is attracted to the toner image receiving body 14a, and is 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 toner image receiving member 14a or 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 toner image receiving body 14a, and the contact is released.

The paper charger 150 is released from the toner image receiver 14a immediately before or at the same time as the trailing edge 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 also possible to use a conductive roller capable of contacting and releasing contact with the toner image receiving member 14a and applying a DC voltage having the same polarity as 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 toner image receiver 14a is not transferred to the recording paper P but exists on the toner image receiver 14a.

Next, a backside image on the peripheral surface of the toner image receiving body 14a is collectively collected by a backside transfer unit 14g as a second transfer means to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. Then, the image is transferred to the lower surface side (back surface side) 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 the double-sided image formation in which the polarity of the color toner image formed on the toner image receiving body 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, Since the toner of the lower layer is not sufficiently charged to the same polarity, 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 toner image receiver 14a without changing the polarity, and then recorded without changing the polarity. Batch transfer to paper P is preferable because it contributes to improving the transferability of 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 toner image receiver 14a.
The sheet is conveyed to a fixing device 17 as a fixing unit. At this time, the paper separation AC static eliminator 14h to which the voltage is applied is arranged to face the driving roller 14d that is grounded so that good separation is performed.

As will be described in detail later, the fixing device 17 includes a heat fixing roller 17a as a roller-shaped rotating member for fixing the toner image of the front image, and a film-shaped rotating member for fixing the toner image of the back image. The heat and pressure are controlled by a nip formed by a heat fixing roller 17a disposed on the upper side and a heat fixing film 17b disposed on the lower side in FIG. As a result, the attached toner on the front and back sides of the recording paper P is fixed, and the recording paper P on which double-sided image recording has been performed is discharged by the discharge rollers 1.
8 and is discharged to a tray outside the apparatus with the toner image of the front surface image as the upper surface. 1, a switching member (not shown) is provided at the exit of the fixing device 17 so that the recording paper P is inverted and conveyed, and the toner image of the front surface image is discharged to the upper portion of the device as a lower surface. You may.

A toner image receiver cleaning device 140 as cleaning means for the toner image receiver 14a is provided opposite to the driven roller 14e, and the toner remaining on the peripheral surface of the toner image receiver 14a after the transfer is removed. The cleaning device 140 is provided in the image receiving member cleaning device 140 and is cleaned by a toner image receiving member cleaning blade 141 that can be brought into and out of contact with the toner image receiving member 14 a with the support shaft 142 as a rotation fulcrum.

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 original PS on one side is read by the original image reading unit shown in FIG. 3, and the first image holding unit stored in the ROM shown in FIG. A single-sided image forming program P2 by the photosensitive drum 10 is read into the RAM through the control unit, and the single-sided image forming program P2 on the front side is executed by the control unit. The forming process is performed continuously.

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 the fixing device, and FIG. 6 is a detailed explanatory diagram of the 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, the fixing device 17 includes a heat fixing roller 17a as a roller-shaped rotating member for fixing the toner image of the front surface image, and a film-shaped rotating member for fixing the toner image of the rear surface image. Fixing film 1
7b, the heat fixing roller 17a is driven and rotated by a fixing drive motor (not shown),
7b is driven and rotated. By applying heat and pressure to the nip formed by the heat fixing roller 17a and the heat fixing film 17b, the toner adhered on the recording paper P fed to the nip is fixed.

The heat fixing roller 17a for fixing the toner image of the front surface image includes a metal core 175 and a metal core 1 around the metal core 175.
A rubber roller 176 having a thickness of, for example, 3 mm, and a rubber rubber coated on its surface with a fluorine rubber latex, and a halogen lamp 177 as a heating element provided inside a metal core 175. You. 178 is an oil supply roller, 179 is a cleaning roller, and TS2 is a temperature sensor provided in contact with the rubber roller 176. The rubber roller 176 is made soft so that the nip portion is made large.

The surface of the heat fixing roller 17a is coated with a fluoro rubber latex, so that the heat fixing film 17
In addition to providing a sufficient driving force to the fixing film 171 and the recording paper P of (b), a frictional force and a high releasability that does not contaminate with toner can be obtained to prevent offset.

The heat fixing film 17b for fixing the toner image of the back side image is, for example, a thin fixing film 171 having a thickness of 40 to 100 μm, a ceramic heater 172 as a plate-like heating element, and a ceramic heater 172 for holding the ceramic heater 172. And a heater holder 173. TS1 is a thermistor mounted on the back surface of the ceramic heater 172 for performing temperature control.

The heat capacity of the fixing film 171 is about 1/100 of that of the heat fixing roller 17a, and a quick start with almost zero warm-up is possible. The heater holder 173 holds the rotating fixing film 17.
1, while being pressed against the thermal fixing roller 17a via a ceramic heater 172 to be held. The fixing film 171 loosely fits into the heater holder 173, and is driven to rotate by the surface frictional force of the heat fixing roller 17a that rotates while fitting. Heat fixing film 17b
Has a small heat capacity, so the heat of the heat fixing roller 17a is hardly removed.

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 plate-shaped 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 having excellent 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, and the heat conduction becomes large, so that it becomes difficult to heat up instantaneously and the electric power used increases.

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 rear end 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
In this case, the rubber thickness of the rubber roller 176 is reduced to 3 mm as described above, and a material having good heat conductivity, such as an aluminum material, is used for the cored bar 175. A level that does not cause any problems.

As shown in FIG. 7, during the double-sided image formation, the conveyance timing of 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 is intermittently different from the continuous one-sided printing. Although performed every other sheet, the heat fixing roller 17a for fixing the toner image of the surface image is
During copying by double-sided image formation, the heating temperature of the heat fixing roller 17a is controlled so that the halogen lamp 177 is turned on before the recording paper P passes and the fixing temperature set value T1 during image formation is maintained at an appropriate value. Will be

On the other hand, the heat fixing film 17b for fixing the toner image of the back side image is heated with the ceramic heater 172 turned on in synchronization with the passage timing of the recording paper P, and the fixing temperature during the image forming pause is stopped. The temperature control of the heat fixing film 17b is performed at an alternate level between the set value T and the proper fixing temperature set value T2 during image formation. At this time, since the double-sided image formation is performed intermittently every other sheet, the non-passing time of the recording paper P is long, so that the temperature can be controlled and the temperature can be made uniform and the heat fixing film 17b having a small heat capacity can be used. Fixing of the back side image is possible.

The temperature control is performed by fixing temperature setting values T, T1, T2 stored in advance in the ROM and temperature sensors TS1, T2.
This is performed through the control unit via the comparison circuit by the detection in S2.

In FIG. 7, the temperature control on the side of the heat fixing film 17b is performed in a region sandwiching the front and rear ends 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, the conveyance timing of the recording paper P passing through the fixing device 17 is continuously adjusted in accordance with the continuous image formation on the front surface by the photosensitive drum 10. However, the heat fixing roller 17a for fixing the toner image of the front surface image is supplied with the halogen lamp 17a before the recording paper P passes during the copying by the double-sided image formation.
7 is turned on, and the heating temperature of the heat fixing roller 17a is controlled so as to maintain an appropriate fixing temperature set value T1 during image formation.

On the other hand, the heat fixing film 17b
During copying by forming a single-sided image on the front surface, the heating control is not performed, or the temperature of the heat fixing film 17b is controlled so as to maintain the fixing temperature set value T during the suspension of image formation.

The temperature control is performed through a control unit via a comparison circuit based on fixing temperature set values T and T1 stored in a ROM in advance and detection by temperature sensors TS1 and TS2.

According to FIGS. 7 and 8, when the surface is changed from single-sided image formation to double-sided image formation or when double-sided image formation is changed to single-sided image formation, the toner image of the front surface image is fixed. Is performed by the heat fixing roller 17a which is always in a fixable state, and the fixing of the toner image of the back side image is performed by the heat fixing film 17b having a small heat capacity and capable of quick start. Fixing is performed accordingly. Similarly, a warm-up time is not required at the time of backside image formation.

At the start of single-sided image formation or double-sided image formation on the front surface, the heat fixing roller 1 having a large heat capacity is used.
Since it is necessary to fix the front surface image by 7a, a warm-up time of the heat fixing roller 17a is required.

This warming-up time becomes longer when the heat fixing roller 17a having a high linear velocity and a large heat capacity is required. In the case of the heat fixing roller 17a having a small heat capacity at a low speed, a warm-up time may not be required in some cases.

In particular, since the double-sided image formation is intermittently performed every other sheet, the heat fixing film 17 having a small heat capacity is used.
b, the heat capacity is sufficient, and the heat-fixing film 17b can fix the rear surface image. Also, when forming a single-sided image on only the back side, no warm-up time is required.

It should be noted that the image forming apparatus is set so that the temperature control is automatically performed in the double-sided image forming state at the time of the 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 the heating control of the heat fixing roller 17a so that the heating control is turned off when the unused time elapses a predetermined time.

FIG. 9 shows another example of the fixing device, in which a fixing belt 17d bridged between a heat fixing roller 17a and an auxiliary roller 17c arranged on the upstream side in the conveying direction of the recording paper P.
Are provided so as to face the heat fixing film 17b disposed below the fixing belt 17d, and a nip portion between the fixing belt 17d and the heat fixing film 17b is widened. By widening the nip portion, it is possible to improve the fixing efficiency at the time of single-sided image formation or double-sided image formation.

In the case of forming a single-sided image on only the back side, FIG.
In this case, the heating control of the heat fixing film 17b may be performed without performing the control of the heat fixing roller 17a.

[0079]

According to the first to third aspects of the present invention, different energy consumptions are performed during the single-sided image formation and the double-sided image formation on the front surface, respectively, as compared with the conventional fixing means using a heating element for the upper and lower rollers. In addition, proper energy consumption is performed during single-sided image formation and double-sided image formation, and both require less energy consumption. In particular, a fixing means suitable for a medium-to-high-speed machine requiring a large heat capacity in one-sided continuous copying is provided.

According to the fourth aspect, when the front surface is changed from single-sided image formation to double-sided image formation, the film-shaped rotating member for fixing the toner image on the back surface image is quick-started to be in a fixable state. Therefore, the warm-up time is substantially zero. Further, when changing from the double-sided image formation to the single-sided image formation, the warm-up time is set to substantially zero because the roller-shaped rotating member for fixing the toner image of the single-sided surface image is always in a fixable state. You. As a result, it can be used for a copying machine in which a waiting time cannot be provided at the time of change.

According to the fifth aspect, the present invention can be further applied to a copying machine in which a waiting time can be provided at the start.

[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 device.

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 the fixing device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum 11 scorotron charger 12 exposure unit 13 developing device 14 a toner image receiver 14 c transfer device 14 g backside transfer device 17 fixing device 17 a heat fixing roller 17 b heat fixing film 171 fixing film 172 ceramic heater 176 rubber roller 177 halogen lamp P recording paper

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Matsubara Konica Corporation, 2970 Ishikawacho, Hachioji-shi, Tokyo (72) Inventor Tadayoshi Ikeda 2970, Ishikawacho, Hachioji-shi, Tokyo Konica Corporation (72) Invention Person Masakazu Fukuchi 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation

Claims (5)

[Claims] A first image carrying means for carrying the toner image formed by the toner image forming means; and a toner image carried by the first image carrying means, which is collectively transferred and transferred. A second image holding unit for holding the toner image on the surface again; a first transfer unit for transferring the toner image held on the first image holding unit to a surface of a transfer material; and the second image An image forming apparatus comprising: a second transfer unit configured to transfer a toner image carried by a support unit to a back surface of the transfer material; and a fixing unit configured to fix the toner image transferred to both surfaces of the transfer material. A film for fixing a toner image on the back surface of the transfer material is a roller-shaped rotating member having a heating element therein, and a film for fixing the toner image on the surface of the transfer material having a plate-shaped heating element in contact with the inner surface Characterized by being a rotating member Image forming device. 2. The image forming apparatus according to claim 1, wherein, when forming a single-sided image on the front surface, the roller-shaped rotating member is subjected to heating control, and the film-shaped rotating member is not subjected to heating control. . 3. The double-sided image forming apparatus according to claim 1, wherein the heating of the film-shaped rotating member is controlled when the transfer material passes, and the heating of the roller-shaped rotating member is controlled before the transfer material passes. Item 2. The image forming apparatus according to Item 1. 4. A warming-up time is not provided when changing from single-sided image formation to double-sided image formation or from double-sided image formation to single-sided image formation. The image forming apparatus according to claim 1. 5. The image forming apparatus according to claim 1, wherein a warming-up time is provided at the time of starting single-sided image formation or double-sided image formation on the front surface.