JPH11219065A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To save energy needed for fixing and to obtain an double-sided image having no image quality difference between a surface and a back, in the case images can be formed in a double-sided copy mode and in a one-sided copy mode. SOLUTION: An upper roller 310 facing the surface is a hard roller, and a lower roller 320 facing the back is a soft roller. Here, the inhibiting temperature of the upper roller 310 in consecutive double-sided copying which inhibits or alters an image forming operation during consecutive copying is T11 and the inhibiting temperature of the lower roller 320 is T12 , and the inhibiting temperature of the upper roller 310 in consecutive one-sided copying is T21 and the inhibiting temperature of the lower roller 320 is T22 , in the case of which the relationship between them is T22 <T21 <=T12 <T11 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic system such as a copying machine, a printer, a facsimile, etc., in which a toner image formed on an image bearing means by a toner image forming means is transferred and fixed to a transfer material to obtain an image. For more details on the image forming apparatus,
A toner image formed on the first image carrying means, having a first and a second image carrying means, and once transferring the toner image formed on the first image carrying means to the second image carrying means; The present invention relates to an image forming apparatus for transferring and fixing a toner image transferred on a transfer material to a front surface of a transfer material and a back surface of the transfer material to obtain a double-sided image.

[0002]

2. Description of the Related Art In a conventional double-sided image forming apparatus, an image on one side formed on an image bearing means is transferred and fixed on a transfer material, and the transfer material is temporarily stored in a double-sided reversing feeding device.
Next, the transfer material is fed from the double-sided inversion feeding device in synchronization with the image on the other surface formed on the image bearing means,
A method of transferring and fixing an image on the other surface of a transfer material has been adopted.

In this double-sided image forming apparatus, the transfer material is conveyed such that the transfer material is once stored in a two-sided reversal feeding device and then fed again, so that the transfer distance of the transfer material is increased, and the double-sided image forming device is formed. However, there is a problem that it takes a lot of processing time. In addition, since the transfer material which has once passed through the fixing means and is easily curled is fed again, the reliability of transfer of the transfer material is low, which causes a jam or wrinkles of the transfer material.

On the other hand, JP-B-49-37538, JP-B-54-28740, and JP-A-1-444.
No. 57 and Japanese Unexamined Patent Publication No. 4-214576,
There has been proposed an image forming apparatus and an image forming method in which a toner image is transferred to both sides of a transfer material using first and second image bearing units to obtain a double-sided image by one fixing.

The present inventors have arranged a plurality of sets of toner image forming means including a charging means, an image exposing means, a developing means, etc. around the first image bearing means, and have opposed the first image bearing means. Then, a second image carrying means is provided, and first, a superimposed color toner image serving as a back side image is formed on the first image carrying means, and this is temporarily transferred to the second image carrying means at once, Next, a superimposed color toner image serving as a surface image is formed on the first image bearing means, and the toner image on the first image bearing means is placed on the surface of the transfer material, and the toner image on the second image bearing means is placed thereon. After transferring the image onto the back side of the transfer material, an image forming apparatus is formed to fix the toner image on the transfer material to form a double-sided color image, and form a color image on both sides of the transfer material or a color image on one side only. Is being studied. For example, Japanese Patent Application Laid-Open No. 9-258518 discloses a technique relating to this.

In such an image forming apparatus, the transfer material on which the toner images have been transferred on the front and back sides only needs to be passed through the fixing device once in forming the double-sided image, so that the reliability of transfer of the transfer material is high, and the transfer path of the transfer material is reduced. It has the feature that the processing speed of copying can be shortened and shortened.

[0007]

In such an image forming apparatus, as shown in FIG. 7, paper is continuously fed during single-sided (front) image formation, and intermittently fed during double-sided image formation. Done. Therefore, the number of sheets fed per unit time is (one-sided) = (two-sided) × 2.

In order to collectively fix a transfer material having toner images on both surfaces, it is necessary to have a heating means facing both surfaces of the transfer material. When using rollers that contact the front and back surfaces of the transfer material as such fixing means, it is necessary to lengthen the nip portion where both rollers come into contact with each other.One of them is a hard roller, and the other is provided with an elastic layer on the roller peripheral surface. Must be a soft roller. The elastic layer has a lower thermal conductivity than a metal roller, and a soft roller requires more time to recover from a change in the temperature of the roller surface, and has poor thermal responsiveness. It is preferable to use a hard roller as the upper roller and a soft roller as the lower roller in contact with the back surface of the transfer material.

During one-sided (front) copying, there is no need to fix the backside image, so there is no need to control the lower roller temperature, and even if the temperature difference between the upper and lower rollers increases (even if the lower roller temperature decreases). )I do not care.

In single-sided copying, it is not preferable that the temperature of the upper roller at the time of fixing is lowered with heat due to continuous copying. However, even if the temperature gradually decreases, as long as no fixing failure occurs, the image quality difference (continuous The difference between the glossiness at the beginning and the end at the time of copying is not a problem (it is almost indistinguishable visually).

At the time of double-sided copying, since the front side image and the back side image are fixed at the same time, if the temperature difference between the upper and lower rollers is greatly different, the image quality (glossiness) of the front side image and the back side image will be different. Therefore, it is necessary to control the temperature difference between the upper and lower rollers so as not to increase.

In order to save energy (fixing power consumption reduction) even during duplex copying, the upper and lower rollers need only be controlled to a temperature close to the lower limit of the feasible temperature, but the lower roller has poor thermal responsiveness. It is difficult to control just below the lower limit.

Originally, the fixing power consumption per unit time during the two-sided copy is smaller than that in the one-sided copy, and there is no need to consider energy saving. Therefore, the image quality difference (the gloss difference between the front and back surfaces and the The difference between the first and last gloss levels at the time of copying may be prioritized. That is, at the time of double-sided copying, it is necessary to control so that the temperature of both the upper and lower rollers does not drop so much (close to the set temperature) to reduce the temperature difference between the upper and lower rollers.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which eliminates a difference in image quality (glossiness difference) between a front and a back of a double-sided image and reduces fixing power consumption.

[0015]

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 transfer of the toner image carried by the first image carrying means. A second image carrying means for carrying the transferred toner image, and a first image carrying means for transferring the toner image carried on the first image carrying means onto the surface of the second image carrying means or a transfer material. Transfer means, second transfer means for transferring the toner image carried by the second image carrying means to the back surface of the transfer material,
A first image forming mode for forming an image on both sides of the transfer material, and a second image forming mode for forming an image only on the surface of the transfer material, the fixing device having a fixing unit for fixing the toner image transferred to the transfer material. And a first fixing member facing the surface of the transfer material, a first heating unit for heating the first fixing member, and a first fixing member. First temperature detecting means for detecting the surface temperature of
A second fixing member facing a back surface of the transfer material having a lower thermal conductivity in a cross-sectional direction than the first fixing member, a second heating unit for heating the second fixing member, and the second fixing member A second temperature detecting means for detecting a surface temperature of the member, wherein the first fixing member and the second fixing member sandwich and convey the transfer material to fix a toner image on the transfer material. When continuously forming images on both sides of the transfer material in the first image forming mode, the upper limit of the surface temperature of the first fixing member for inhibiting or changing the image forming operation is set to T.
₁₁ (° C.), and the upper limit of the surface temperature of the second fixing member is T ₁₂
(° C.), and when forming an image continuously only on the surface of the transfer material in the second image forming mode, the upper limit of the surface temperature of the first fixing member for inhibiting or changing the image forming operation is set to T. ₂₁ (° C.), wherein the upper limit of the surface temperature of the second fixing member is T ₂₂ (° C.), wherein T ₂₂ <T ₂₁ ≦ T ₁₂ <T ₁₁ is achieved. Is done.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the present invention, an embodiment common to an image forming apparatus in which a toner image is formed on both surfaces to which the present invention is applied and is fixed collectively will be described. The present invention is not limited to the embodiments described below. The description in this section does not limit the technical scope of the claims and the meaning of terms. Also,
In the following description of the embodiment, when transferring the toner image to the transfer material, the surface of the transfer material on the side facing the first image bearing means in the transfer area is the surface, the surface on the other side of the transfer material, The surface opposite to the second image bearing means is called a back surface, an image transferred to the front surface of the transfer material is called a front image, and an image transferred to the back surface of the transfer material is called a back image. Each of the embodiments described below is an example of an image forming apparatus for forming a color image, but the present invention is also applied to a monochrome image forming apparatus.

An image forming process and each mechanism of the embodiment of the image forming apparatus of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a color image forming apparatus according to an embodiment of the present invention, FIG. 2 is a side cross-sectional view of a first image bearing unit in FIG. 1, and FIG. 3 is a toner image according to the embodiment. FIG. 3 is a diagram illustrating a formation state and supply of a transfer material.

In FIG. 1, reference numeral 10 denotes a photosensitive drum which is a first image bearing means, 11 denotes a scorotron charger which is a charging means for each color, 12 denotes an exposure unit which is an image exposure means for each color, and 13 denotes each color. Developing device, which is a developing means for each device, 14
a is a toner image receiving body as a second image holding means, 14c is a primary transfer device as a first transfer means, 14g is a secondary transfer device as a second transfer means, and 15c is a transfer material supply means. A certain timing roller 30 is a fixing device as a fixing unit.

Photosensitive drum 10 as first image bearing means
Is obtained by forming a photosensitive layer such as a transparent conductive layer, an a-Si layer, or an organic photosensitive layer (OPC) on the outer periphery of a cylindrical substrate formed of, for example, a transparent member made of optical glass or transparent acrylic resin. Yes, it is rotated clockwise as indicated by the arrow in FIG.

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

The scorotron charger 11, which is a charging unit for each color, the exposure unit 12, which is an image exposure unit for each color, and the developing unit 13, which is a developing unit for each color, form a set of these units, Four photoconductor drums 1 are provided for image forming processes of magenta (M), cyan (C), and black (K), and are indicated by arrows in FIG.
With respect to the 0 rotation direction, they are arranged in the order of Y, M, C, and K.

The scorotron charger 11, which is a charging means for each color, is mounted to face the photosensitive drum 10 in a direction perpendicular to the moving direction of the photosensitive drum 10, and the photosensitive layer of the photosensitive drum 10 described above. Has a control grid maintained at a predetermined potential and a discharge electrode 11a made of, for example, a sawtooth electrode, and performs a charging action (minus charging in the present embodiment) by corona discharge having the same polarity as the toner. A uniform potential is applied to the photosensitive drum 10. Other wire electrodes can be used as the discharge electrode 11a.

Exposure unit 1 as image exposure means for each color
2 is arranged inside the photoconductor drum 10 such that the exposure position on the photoconductor drum 10 is located on the downstream side in the rotation direction of the photoconductor drum 10 with respect to the scorotron charger 11 for each color. The exposure unit 12 includes the photosensitive drum 1
A linear light-emitting element 12a in which a plurality of LEDs (light-emitting diodes) as light-emitting elements arranged in the main scanning direction in parallel with the 0 axis are arranged; and a selfoc lens 12b as an equal-magnification imaging element. , And a holder. In addition to the exposure unit 12 for each color, a uniform exposure unit 12c and a simultaneous transfer exposure unit 12d are attached to the holding member 20, and are housed integrally inside the base body of the photosensitive drum 10.
Image data of each color read by a separate image reading device and stored in the memory is sequentially read from the memory and input to the exposure unit 12 for each color as an electric signal. As the light emitting device, a device in which a plurality of light emitting devices such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used. The emission wavelength of the light-emitting element used in this embodiment is preferably in the range of 680 to 900 nm, which has high transmittance to the Y, M, and C toners.
Since the image exposure is performed from the inside (back surface) of the photoconductor drum 10, the wavelength may be shorter than this, which does not have sufficient transparency for the color toner.

The developing device 13 as a developing means for each color includes
For example, a cylindrical non-magnetic stainless steel having a thickness of 0.5 to 1 mm and an outer diameter of 15 to 25 mm, which keeps a predetermined gap with respect to the peripheral surface of the photosensitive drum 10 and rotates in the forward direction with respect to the rotation direction of the photosensitive drum 10 or It has a developing sleeve 131 formed of an aluminum material and a developing casing 138, and contains therein a one-component or two-component developer of yellow (Y), magenta (M), cyan (C) and black (K). ing. Each of the developing devices 13 is provided with a predetermined gap, for example, 100 to 1000 μm, from the photosensitive drum 10 by an abutting roller (not shown).
m, and is kept in a non-contact state.
A non-contact reversal development is performed by applying a developing bias in which a DC voltage and an AC voltage having the same polarity as the toner (in this embodiment, a negative polarity) are superimposed, and a toner image is formed on the photosensitive drum 10. Form.

Toner image receiver 1 as second image bearing means
4a (also called an intermediate transfer member) has a volume resistivity of 10 ⁸ to 10
An endless belt of ¹⁵ Ω · cm, for example, having a thickness of 0.5 to 0.5 in which a conductive material is dispersed in silicon rubber or urethane rubber or the like.
On the outside of a 2.0 mm semiconductive rubber belt substrate, preferably as a toner filming prevention layer, having a thickness of 5 to 50 μm.
2 is a seamless belt having a two-layer structure, which is coated with fluorine. In addition to the above, a conductive material is dispersed in an engineering plastic such as a modified polyimide, a thermosetting polyimide, an ethylene tetrafluoroethylene copolymer, a polyvinylidene fluoride, or a nylon alloy. A 0 mm semiconductive film can also be used. The toner image receiver 14a is stretched in contact with a driving roller 14d and a driven roller 14e, and is rotated counterclockwise as indicated by an arrow in FIG.

A primary transfer device 14c as a first transfer means
Is provided to face the photosensitive drum 10 with the toner image receiver 14a interposed therebetween, and forms a transfer area 14b between the toner image receiver 14a and the photosensitive drum 10. Primary transfer unit 1
A DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied to 4c, and a transfer electric field is formed in the transfer area 14b, so that the toner image on the photosensitive drum 10 is transferred onto the toner image receiver 14a. Alternatively, the image is transferred onto the surface of a recording sheet P as a transfer material.

A secondary transfer unit 14g as a second transfer unit
Is provided to face a conductive roller that is grounded with the toner image receiver 14a interposed therebetween. A DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied to the toner image receiver 14a. The toner image is transferred to the back surface of the recording paper P.

Timing roller 1 as transfer material supply means
5c, the recording paper P as a transfer material is transferred to the transfer area 14 in synchronization with the color toner image of the front image on the photosensitive drum 10 or the color toner image of the back image on the toner image receiver 14a.
b.

A fixing device 30 serving as a fixing means includes a first fixing roller 310 having a heater therein and a second fixing roller 3 having a heater therein.
20 and two fixing members in the form of rollers, and heat and pressure are applied between the first fixing roller 310 and the second fixing roller 320 to fix the toner image on the recording paper P.

Next, the image forming process will be described.

In an image reading apparatus separate from the present apparatus, image data of a document image read by an image pickup element or image data of an image edited by a computer is Y (yellow), M (magenta), C (Cyan) and K (black) are temporarily stored and stored in the memory as image signals for respective colors.

When image recording is started, a gear G provided on the back side flange 10b of the photosensitive drum 10 is rotated through a driving gear (not shown) by starting a photosensitive member driving motor (not shown). Is rotated clockwise as indicated by the arrow in FIG. 1, and at the same time, the application of a potential to the photosensitive drum 10 is started by the charging action of the scorotron charger 11 for yellow (Y).

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

The latent image is reversal-developed by the Y developing device 13 in a non-contact state, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10.

Next, a potential is applied to the photosensitive drum 10 from above the yellow (Y) toner image by the charging action of the magenta (M) scorotron charger 11, and the second color signal of the M exposure unit 12 is applied. That is, exposure is performed by an electric signal corresponding to M image data, and the M developing device 13
Yellow (Y) by non-contact reversal development
A toner image of magenta (M) is formed on the toner image of FIG.

By the same process, a cyan (C) toner image corresponding to the third color signal is further formed by the cyan (C) scorotron charger 11, the exposure unit 12 of C and the developing unit 13 of C. Further, a black (K) toner image corresponding to the fourth color signal is sequentially superimposed and formed thereon by a black (K) scorotron charger 11, an exposure unit 12 of K, and a developing unit 13 of K. As a result, a color toner image is formed on the peripheral surface of the photosensitive drum 10 within one rotation.

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

By the above-described image forming process, a superimposed color toner image serving as a back image is formed on the photosensitive drum 10 serving as the first image bearing means, and the superimposed color toner of the back image on the photosensitive drum 10 is formed. In the transfer area 14b, the primary transfer unit 1 to which a DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied.
4c, the toner image receiving member 1 as the second image bearing means
4a. 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.

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 and then reaches the cleaning device 19 where the photosensitive drum 1
Cleaning blade 19 made of rubber material in contact with zero
In order to eliminate the history of the photoreceptor up to the previous printing, the peripheral surface of the photoreceptor is neutralized by, for example, exposure by a uniform exposure unit 12c before charging using a light emitting diode, and the previous printing is performed. After the charge is removed, the next color image is formed.

After the superimposed color toner image serving as the back side image is formed on the toner image receiving body 14a as described above, the back side image on the toner image receiving body 14a is continuously synchronized with the transfer area 14b. A superimposed color toner image serving as a surface image is formed on the photosensitive drum 10 in the same manner as in the above-described color image forming process. It is necessary to change the image data so that the front side image formed at this time is a mirror image of the back side image on the photosensitive drum 10.

A recording paper P, which is a transfer material, is fed from a paper feed cassette 15 which is a transfer material storage means to a feed roller 15a.
, And are fed by the feed roller 15b and conveyed to the timing roller 15c.

The recording paper P is driven by a timing roller 15c, which is a transfer material supply unit, to drive the timing roller 15c to form a color toner image of the front surface image formed on the photosensitive drum 10 and a back image carried on the toner image receiver 14a. Is fed to the transfer area 14b in synchronization with the color toner image. FIG. 3 shows the toner image formation state of the back side image carried on the toner image receiving body 14a and the front side image formed on the photosensitive drum 10 and the recording paper P supplied in synchronization with them.

When the recording paper P is fed to the transfer area 14b,
The recording paper P is charged to the same polarity as the toner by a paper charger 14f as a transfer material charging means capable of coming into contact with and releasing from the toner image receiver 14a. 14b. 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. In addition, as the transfer material charging unit, a conductive roller that can be brought into contact with and released from the toner image receiving body 14a, a corona discharger that does not contact the toner image receiving body 14a, or the like can be used.

In the transfer area 14b, a first voltage to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied.
The surface image on the peripheral surface of the photosensitive drum 10 is collectively transferred onto the surface (upper surface) of the recording paper P by the primary transfer device 14c as the transfer means. At this time, the toner image receiver 14a
Is not transferred to the recording paper P but exists on the toner image receiver 14a.

Next, the recording paper P on which the color toner image has been transferred onto the surface thereof is used as a second transfer means to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied.
The sheet is conveyed to the next transfer unit 14g, and the back transfer image on the peripheral surface of the toner image receiver 14a is collectively transferred to the back surface (lower surface) of the recording paper P by the secondary transfer unit 14g.

Since the toner images of the respective colors overlap with each other, it is preferable that the toner in the upper layer and the toner in the lower layer of the toner layer are charged to the same polarity with the same charge amount in order to enable batch transfer. Accordingly, in 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 photosensitive drum 10, and the color toner images of the same polarity formed by superimposing are collectively transferred to the toner image receiving member 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 and the second transfer means are separately provided, and the first transfer means is operated to form a color toner image on the surface of the transfer material. Next, a two-sided image forming method of forming a color toner image on the back surface of the transfer material by operating the second transfer unit is preferably adopted.

A recording paper P, which is a transfer material having a color toner image formed on both sides, is used as a transfer material separating object provided on a conductive drive roller 14d grounded with a toner image receiver 14a interposed therebetween. The static electricity is removed by the paper-separating AC static eliminator 14h, separated from the toner image receiving body 14a, and fixed as a fixing unit composed of two fixing rollers having heating units (heaters) inside both upper and lower rollers to be described later. It is transported to the device 30. By applying heat and pressure to the recording paper P between the first fixing roller 310 on the upper side and the second fixing roller 320 on the lower side, the toner adhered to the front and back of the recording paper P is fixed, and the two-sided image recording is performed. The discharged recording paper P is fed by a paper discharge roller 18 and discharged to a tray outside the apparatus.

The toner remaining on the peripheral surface of the toner image receiver 14a after the transfer contacts and contacts the toner image receiver 14a provided in a toner image receiver cleaning device 14i which is a cleaning means of the toner image receiver. It is cleaned by a blade that can be released. The toner remaining on the peripheral surface of the photoconductor drum 10 after the transfer is subjected to static elimination by the photoconductor drum AC static eliminator 16 and then to a cleaning device 19.
And a cleaning blade 19a made of rubber material in contact with the photosensitive drum 10
9, and is collected by a screw 19b in a not-shown waste toner container. The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is subjected to uniform charge removal by the Y scorotron charger 11 after the peripheral surface of the photosensitive member is neutralized by exposure by the uniform exposure device 12c, and the next image is formed. Enter the formation cycle.

In the above-described image forming apparatus, it is a matter of course that one-sided copying can be performed by the first image bearing means or the second image bearing means. Copying (single-sided image formation) is often used. In this case, the photosensitive drum 10
The recording paper P passing through the fixing device 30 at the time of forming a single-sided image of only the front surface is continuously performed, but the recording paper P passing through the fixing device 30 at the time of forming a two-sided image is temporarily transferred to the toner image receiving member 14a by a reverse image. After the formation, the process of forming a surface image on the photosensitive drum 10 is repeated, so that the process is performed intermittently.

The fixing device 30 used in the image forming apparatus of the present invention includes a first fixing roller 31 facing the surface toner image.
0 (hereinafter also referred to as an upper roller) and the second fixing roller 320 (hereinafter also referred to as a lower roller) facing the back toner image need to have a heating means to heat and fix both sides of the recording paper P. Further, it is necessary to form a nip portion of several mm in the recording paper conveyance direction at the contact portion between the first fixing roller 310 and the second fixing roller 320 in order to perform fixing, and to form the nip portion It is necessary to provide one of the rollers with an elastic layer made of an elastic material such as silicon rubber.
Since the elastic layer has a lower thermal conductivity than that of the metal material, the fixing roller provided with the elastic layer is used when the recording paper P passes through the recording paper P.
The roller surface temperature, which has been lowered due to heat loss, requires a long time to recover. Therefore, the first fixing roller 310, which is responsible for forming a single-sided image on only the surface having a high printing speed, is a hard roller having a higher thermal conductivity than the second fixing roller 320, and the second fixing roller 320 is provided with an elastic layer. Rollers.

FIG. 4 is a cross-sectional configuration diagram showing an embodiment of a fixing device used in the present image forming apparatus.

The fixing device 30 includes an upper roller 310 as an upper fixing member which is in charge of fixing the front surface toner image on the recording paper P, and a lower fixing device for fixing the rear toner image on the recording paper P. Roller 320 as a second fixing member for
Presses and heats in opposition to each other and passes through the recording paper P
Is fixed.

The upper roller 310 has a first heater 311 as a first heating means comprising a halogen lamp or the like at an inner core portion.
(In the present embodiment, a halogen lamp of 800 W). The upper roller 310 wraps the outer periphery of a metal core 310a formed of a thin metal pipe having the first heater 311 therein, for example, a fluororesin such as PFA (perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) having a thickness of 30 to 200 μm. This is a hard roller having a surface layer 310b coated with a heat-resistant, high-release layer such as a silicone resin.

The lower roller 320 has a second heater 321 as a second heating means comprising a halogen lamp or the like at the inner core.
(In this embodiment, a halogen lamp of 300 W). The lower roller 320 has an elasticity such as silicone rubber having a rubber hardness of about 2 to 8 mm (5 mm in the present embodiment) Asker C having a thickness of about 55 degrees around the core bar 320 a made of a thin metal pipe having the second heater 321 built therein. An elastic layer 320b made of a body is provided, and the outer periphery thereof is covered with a surface layer 320c.
Is a soft roller having a thickness of 30 to 200 μm and coated with a heat-resistant, high-release layer such as a fluororesin such as PFA or PTFE or a silicone resin.

On the peripheral surfaces of the upper and lower rollers 310 and 320,
Cleaning rollers 312 and 322 for adsorbing and removing toner, paper powder and the like adhering to the peripheral surface, and oil applying rollers 313 and 323 for applying silicone oil as a release agent for preventing offset are provided. I have.
For the surfaces of the cleaning rollers 312 and 322, a material that does not absorb oil, such as foamed silicone rubber, is used. If an absorbent material is used, the collected absorbed oil will be discharged, resulting in uneven oil. Therefore, a non-absorbable material is used for the cleaning rollers 312 and 322, and the variation in the amount of applied oil is suppressed. Further, in order to improve the performance of removing foreign matter such as toner, a material having a low releasability and a material having a small heat capacity so as not to absorb heat from the upper and lower rollers 310 and 320 are selectively used. Oil application roller 3
13 and 323 are pressed against the upper and lower rollers 310 and 320, respectively, and are driven to rotate.

The first temperature sensor 31 which is a first and second temperature detecting means comprising a thermistor or the like at a position in contact with or very close to each of the upper roller 310 and the lower roller 320.
4. A second temperature sensor 324 is provided to detect the surface temperature of the roller, and based on this detection signal, energization control of the first heater 311 and the second heater 321 is performed as described later, and a predetermined temperature is determined. Is kept within the range.

Between the upper roller 310 and the lower roller 320, a linear pressure of 0.8 to 1..
The nip is pressed at 8 kg / cm. At this time, the length of the nip varies depending on the linear pressure and the hardness of the roller, but is approximately 2 to 7 mm. The upper roller 310 and the lower roller 320 are driven by the same drive source so as not to cause a slip at the nip, rotate at the same linear speed (160 mm / sec in this embodiment), and perform double-sided fixing at the nip.

In the image forming apparatus 100, the fixing device 30 as a fixing means forms an electric field between each of the upper and lower rollers 310 and 320 and the recording paper P sandwiched and conveyed therebetween, which is not shown. An electric field forming means such as a corona charger or a roller charger which is conductive and capable of driven sponge-like rotation is provided, or the surface layers 310b and 320c and the elastic layer 320b of the upper and lower rollers 310 and 320 are provided. For example, it is made of a conductive material having conductivity by adding carbon black or titanium oxide, and a bias power source (not shown) and cores 310a and 320a of the rollers are connected to each other via a safety resistor, thereby increasing Roller 310
The upper roller 310 is charged with the same polarity as the toner charge of the front toner image, and the lower roller 320 is charged with the back toner by an electric field forming means such as applying a bias voltage of +200 V to the lower roller 320. By increasing the electrical repulsion between the toner and the roller by performing charging with the same polarity as the toner charge of the image, an image forming apparatus that collectively fixes a double-sided toner image can reduce the electrical electrostatic offset. I try to eliminate it completely.

The image forming apparatus 100 includes a single-side (front) copy mode in which a toner image is formed on only one side (front) of the transfer material and fixing is performed as a second image forming mode, and a transfer as a first image forming mode. It has a double-sided copy mode in which toner images are formed on both sides of the material and the image is fixed at once. When the mode is set with the copy mode setting button, excellent control of image formation and fixing according to the mode is performed. And good image recording.

FIG. 5 is a block diagram of an image forming apparatus provided with such a fixing device 30. The main body operation panel is provided with a double-sided / single-sided copy mode selecting means 51. Make a selection. In addition, there is an automatic copy mode for automatic selection,
When reading an image of a document with a document reading device (not shown),
The presence or absence of an image on the back side of the document is detected, and if no back side image is detected, the one-sided copy mode is automatically selected. If the back side image is detected, the two-sided copy mode is automatically selected to perform image formation and fixing.

When the one-sided copy mode is selected, the control unit 50 calls up the one-sided print program from the ROM (1) 53, calls up the image information on the front side from the memory or from the document reading apparatus, and outputs the toner image of the front side image. Is formed on the photosensitive drum 10, and the toner image of the surface image on the photosensitive drum 10 is transferred onto the recording paper P fed synchronously by the primary transfer unit 14c (first image forming step). . The fixing device 30 holds the toner image on the upper surface, and the fixing device 30 fixes the surface image on the recording paper P conveyed to the fixing device 30. The fixed recording paper P is sent by the paper discharge roller 18. It is discharged to a tray outside the device.

When the two-sided copy mode is selected, the control unit 50 calls up the two-sided print program from the ROM (1) 53, first calls up the image information of the back side from the memory or from the document reading apparatus, and outputs the toner image of the back side image. Is formed on the photoreceptor drum 10, and the back side toner image is transferred onto the toner image receiver 14a by the primary transfer device 14c. Next, a toner image of a surface image is formed on the photosensitive drum 10 after the transfer and cleaning. Then, the toner image of the front surface image is transferred to the front surface (upper surface) of the recording paper P fed synchronously by the primary transfer device 14c (first image forming step), and is transferred to the back surface (lower surface) of the recording paper P. The toner image of the back surface image on the toner image receiver 14a is transferred by the secondary transfer device 14g (second image forming step). The fixing device 30 fixes the double-sided image on the recording paper P, which holds the toner image on both sides and is conveyed to the fixing device 30, and the fixed recording paper P is discharged to the outside of the device by a discharge roller 18. It is discharged to a tray.

In the image forming apparatus of the present invention, when the double-side copy mode, which is the first image forming mode, is selected, the first fixing member, the upper roller 310,
A heater 311 and a lower roller 320 as a second fixing member
Of the roller surface by the first temperature sensor 314 and the second temperature sensor 324 are compared with the set fixing temperature Ts.
The N / OFF control is performed, and the recording paper holding the toner images on both sides is fixed. Note that the set fixing temperature Ts does not need to be set to the same temperature for the upper roller 310 and the lower roller 320.
The temperature is set to 190 ° C. for the lower roller 320.

When the one-sided copy mode, which is the second image forming mode, is selected, since the fixing of the back side of the recording paper is not required, the first heater of the upper roller 310 is also used to save power consumption. ON / OF by setting only the operation temperature of the roller 311 to the operating state and comparing the detected temperature of the roller surface by the first temperature sensor 314 with the set fixing temperature Ts.
The F control is performed to fix the recording paper holding the toner image on the surface.

In the fixing device 30 of the present embodiment, the maximum power consumption is reduced, and the internal second heater 321 for the lower roller 320 of the soft roller having poor thermal response is supplied with a low power consumption of 300 W. The surface temperature of the lower roller 320 is caused by internal heating, while the upper roller 3 that rotates in contact with the sheet feeding interval of the recording paper on which fixing is performed.
The fixing temperature is maintained by heat conduction from the first heater 10, and an 800 W halogen lamp is used as the first heater 311.

Since most of the fixing power at the time of continuous copying is the amount of heat carried away by the recording paper, the first heater 311 that performs continuous fixing in the one-sided copy mode has 800 W of power for the first heater 311 in this embodiment. Is appropriate.

In the fixing device 30 in which the maximum power consumption is limited and is limited to 1100 W (800 W + 300 W) in this embodiment, the amount of recording paper passing per unit time when performing continuous fixing increases. Then, the amount of heat carried away by the recording paper is larger than the amount of heat supplied to both the upper roller and the lower roller, and the roller surface temperature falls below the initial set fixing temperature Ts. For example, A3 size continuous copy with respect to A4 size continuous copy corresponds to this. If the temperature of the roller surface drops significantly, fixing failure occurs. In the duplex mode, if the temperature difference between the upper roller 310 and the lower roller 320 is large, the image quality (glossiness) of the front and rear images after fixing is high. Will be different. In the one-side (front) copy mode, the second heater 321 is not operated because the lower roller 320 does not need to be fixed on the back surface. , A lot of waiting time is required. The present invention is characterized in that the following control is performed in view of such a situation, and a good image can be obtained in the continuous copy state in both the double-sided copy mode and the single-sided copy mode.

(1) The surface temperature of the upper roller 310 is equal to or lower than T ₁₁ (° C.) and the surface temperature of the lower roller 320 is equal to T ₁₂ (° C.) when images are continuously formed on both sides of the recording paper in the double-sided copy mode. When the following occurs, the control unit 50 performs control to prohibit or change the image forming operation (for example, change the copy interval to be wider than the normal image interval).

The image forming operation in the prohibited state is restarted when the roller surface temperature rises to the set fixing temperature Ts. In the image forming operation in the changed state, the roller surface temperature is reduced to the set fixing temperature Ts. When it rises, it returns to the normal image forming operation.

Here, there is a relationship of T ₁₂ <T ₁₁ between the prohibited temperature T ₁₁ (° C.) and T ₁₂ (° C.), and 5 ° C. ≦ T ₁₁ −T ₁₂
Preferably it is between ≦ 20 ° C.

In this embodiment, the inhibition temperature T ₁₁ = 18
5 ° C. and T ₁₂ = 170 ° C. are set. This set temperature satisfies the above conditions.

(2) The surface temperature of the upper roller 310 is equal to or lower than T ₂₁ (° C.) and the surface temperature of the lower roller 320 is equal to T ₂₂ (° C.) when images are continuously formed on the surface of the recording paper in the single-sided copy mode. In the following cases, the control unit 50 controls to inhibit or change the image forming operation (for example, change the copy interval to be wider than the normal image interval).
The image forming operation in the prohibited state is restarted when the roller surface temperature returns to the set fixing temperature Ts.
In the image forming operation in the changed state, the operation returns to the normal image forming operation.

Here, there is a relationship of T ₂₂ <T ₂₁ between the prohibited temperatures T ₂₁ (° C.) and T ₂₂ (° C.), and 20 ° C. ≦ T ₂₁ −T
It is preferably between ₂₂ ≦ 80 ° C.

In this embodiment, the prohibited temperature is set to T ₂₁ = 1.
The temperature is set to 65 ° C. and T ₂₂ = 95 ° C. This set temperature satisfies the above conditions. Note The T ₂₂ is less than the offset threshold temperature Tc (150 ℃).

(3) Between the prohibited temperatures T ₁₁ (° C.) and T ₁₂ (° C.) in the two-sided copy mode and the prohibited temperatures T ₂₁ (° C.) and T ₂₂ (° C.) in the one-sided copy mode, T ₂₂ <T. It is required that the relationship of ₂₁ ≦ T ₁₂ <T _{11 be} satisfied. In the present embodiment, the forbidden temperatures T ₂₂ = 95 ° C., T ₂₁ = 165 ° C., T ₁₂ = 170 ° C.
T ₁₁ = 185 ° C. satisfies the above condition.

FIG. 6 shows the relationship between the roller surface temperature of the upper roller 310 and the lower roller 320 and the forbidden temperature in the double-sided and single-sided copy modes. By providing such a prohibition mode and managing and controlling the roller surface temperature in each copy mode, a good fixed image can be obtained during continuous copying in both of the two-sided and one-sided copy modes.

[0079]

According to the present invention, in an image forming apparatus for forming an image in the double-sided or single-sided mode, the maximum power consumption in the fixing device is greatly restricted, and a good fixed image can be obtained. . Further, even in continuous copying in which the fixing conditions are deteriorated, the image forming operation is prohibited or the image forming operation is changed before the fixed image is visually deteriorated, and the image is discharged after finishing the image processing. As for the recording paper, good image quality is guaranteed, and a power saving type image forming apparatus is provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram illustrating an example of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a side sectional view of a first image bearing unit in FIG. 1;

FIG. 3 is an explanatory diagram illustrating a toner image forming state and supply of a transfer material.

FIG. 4 is a sectional configuration diagram of a fixing device used in the present invention.

FIG. 5 is a block diagram of a control system of the image forming apparatus of the present invention.

FIG. 6 is an explanatory diagram showing a relationship between a roller surface temperature and a forbidden temperature.

FIG. 7 is an explanatory diagram illustrating a sheet feeding state during double-sided and single-sided image formation.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum (first image holding unit) 11 scorotron charger 12 exposure unit 13 developing unit 14a toner image receiver (second image holding unit) 14c primary transfer unit 14g secondary transfer unit 14h paper separation AC removal Electric device 30 Fixing device (fixing unit) 310 Upper roller (first fixing roller) 320 Lower roller (second fixing roller) 311 First heater 321 Second heater 314 First temperature sensor 324 Second temperature sensor

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

Claims (4)

[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 being transferred, and transferring the transferred toner image. A second image carrying means for carrying, a first transfer means for transferring a toner image carried on the first image carrying means to a surface of the second image carrying means or a transfer material,
A second transfer unit for transferring the toner image carried by the image carrying unit to the back surface of the transfer material; and a fixing unit for fixing the toner image transferred to the transfer material. An image forming apparatus having a first image forming mode for forming an image and a second image forming mode for forming an image only on the surface of the transfer material, wherein the fixing unit comprises: a first fixing unit facing the surface of the transfer material. A member, a first heating unit for heating the first fixing member, a first temperature detecting unit for detecting a surface temperature of the first fixing member, and a cross-sectional direction more than the first fixing member. A second fixing member facing a back surface of the transfer material having low heat conduction, a second heating unit for heating the second fixing member, and a second temperature for detecting a surface temperature of the second fixing member Detecting means, wherein the first fixing member and the second fixing member And fixing the toner image on the transfer material by sandwiching and transferring the transfer material. When forming images continuously on both surfaces of the transfer material in the first image forming mode, the image forming operation is prohibited. Alternatively, the upper limit of the surface temperature of the first fixing member to be changed is T ₁₁ (° C.),
The upper limit of the surface temperature of the second fixing member is T ₁₂ (° C.), and when forming an image continuously only on the surface of the transfer material in the second image forming mode, the image forming operation is prohibited or changed. The upper limit of the surface temperature of the first fixing member is set to T.
₂₁ (° C.), and the upper limit of the surface temperature of the second fixing member is T ₂₂
(℃) when the image forming apparatus characterized by a _{T 22 <T 21 ≦ T 12} <T 11. When wherein images are formed continuously on both sides of the transfer material by said first image forming mode, the upper limit T ₁₁ of the surface temperature of the first fixing member to prohibit or modify an image forming operation The image forming apparatus according to claim 1, wherein a difference between a surface temperature of the second fixing member and an upper limit T ₁₂ is 5 ° C. ≦ T ₁₁ −T ₁₂ ≦ 20 ° C. 5. 3. An upper limit T _{21 of} a surface temperature of the first fixing member for inhibiting or changing an image forming operation when continuously forming an image only on the surface of a transfer material in the second image forming mode. And the upper limit T ₂₂ of the surface temperature of the second fixing member.
2. The image forming apparatus according to claim 1, wherein the difference is set to 20 ° C. ≦ T ₂₁ −T ₂₂ ≦ 80 ° C. 3. 4. When an image is formed on both sides of a transfer material in the first image forming mode, the image forming apparatus according to the first embodiment detects the first temperature detecting unit and the second temperature detecting unit. When the first heating unit and the second heating unit are controlled and an image is formed only on the surface of the transfer material in the second image forming mode, the detection result by the first temperature detection unit is Controlling the first heating means accordingly,
Wherein the heating means is not operated.
4. The image forming apparatus according to any one of 3.