JP2000081805A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device capable of satisfactorily executing a fixing process while saving the power consumption, without causing irregularities in toner images on both sides, as for an image forming device for fixing transfer material holding the toner images on both sides in the lump. SOLUTION: In this image forming device, a fixing process is executed after transferring toner images formed on both sides of recording paper P as a transfer material. In this case, an upper fixing means is constituted of a fixing belt 310 as a rotary belt which is stretched and laid between a heat roller 311 as a 1st upstream roller equipped with a 1st heater 313 inside and a fixing roller 312 as a 2nd downstream roller. And, the device is provided with transfer material carrying spur members 18 under the upper fixing means, and the lower fixing means is a pressure roller 320 equipped with a 2nd heater 323 inside, and the pressure roller 320 comes into contact with the fixing roller 312 through the fixing belt 310.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transferring a toner image formed on an image forming body to a transfer material by a toner image forming means.
The present invention relates to an electrophotographic image forming apparatus such as a copier, a printer, and a facsimile, which obtains an image by fixing. More specifically, a toner image formed on an image forming body by a toner image forming unit is transferred to a surface of a transfer material. The present invention also relates to an image forming apparatus for transferring a toner image formed on an image forming body to a back surface of a transfer material via an intermediate transfer body, and then fixing the toner images on both surfaces of the transfer material collectively to obtain a double-sided image.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, an image on one surface formed on an image forming body is transferred and fixed onto a transfer material, and the transfer material is temporarily stored in a two-sided reversing feeding device. A method has been adopted in which a transfer material is fed from a two-sided reversing feeder at the same time as the image on the other surface formed on the image forming body, and the image is transferred and fixed on the other surface of the transfer material.

In this image forming apparatus, since the transfer material is transported such that the transfer material is temporarily stored in a two-sided reversing feeding device and then fed again, the transport distance of the transfer material becomes longer, and the image forming apparatus is used for both-side image formation. There has been a problem that much processing time is required. Further, since the transfer material that has easily become curled after passing through the fixing means is fed again, the reliability of transfer of the transfer material is low, which causes a jam of the transfer material and a wrinkle 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,
An image forming apparatus and an image forming method for obtaining a double-sided image by one-time fixing after transferring a toner image to both sides of a transfer material have been proposed.

The inventors of the present application dispose a plurality of sets of toner image forming means including a charging means, an image exposing means, a developing means and the like around the image forming body, and place an intermediate transfer body facing the image forming body. First, a superimposed color toner image to be a back side image is formed on the image forming body, and this is temporarily transferred to the intermediate transfer body once, and then the superimposed color toner image to be a front side image is formed on the image forming body. After forming the toner image on the image forming body on the front side of the transfer material and transferring the toner image on the intermediate transfer body to the back side of the transfer material, the toner image on the transfer material is fixed to form a two-sided color image. An image forming apparatus for forming a color image is manufactured, and a color image formation on both sides of a transfer material or a color image formation on only one side 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 two-sided image. Therefore, the transfer material transfer reliability is high and the transfer material transfer path is high. And the processing speed of copy can be increased. However, in order to collectively fix the transfer material having the toner images on both surfaces, it is necessary to have a heating unit facing both surfaces of the transfer material.

As a fixing device suitable for the above-mentioned image forming apparatus, a belt-type fixing device including a fixing belt having a heating roller and a pressure roller having a heating means therein has been recently proposed. In this fixing device, the heat capacity of the fixing belt is small, so that the warm-up time can be reduced, and the toner image on the transfer material can be preheated, so that the temperature of the nip can be kept low, and the offset margin can be improved. Oil-less fixing is also possible, and there is a feature that power consumption can be reduced.

[0008]

An image forming apparatus provided with the above-mentioned belt-type fixing device is a device capable of quickly performing double-sided fixing, but disturbs toner images carried on the front and back surfaces of a transfer material, particularly toner images on the back surface. There is no complete offer yet for the requirement to take root.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which has low power consumption and obtains an image without disturbance of a toner image when forming a two-sided image.

[0010]

In order to achieve the above object, in an image apparatus which performs fixing after forming an unfixed toner image on both sides of a transfer material, the upper fixing means includes a transfer material transporting device having a heating means therein. A rotating belt stretched between a first roller on the upstream side in the direction of transfer and a second roller on the downstream side in the direction of transfer of the transfer material. A spur member for transferring the transfer material is provided below the upper fixing means. The image forming apparatus is characterized in that the lower fixing means is a roller having a heating means therein, and the roller is in contact with the second roller via the rotating belt. You.

In the above invention, the heating means in the upper fixing means and the heating means in the lower fixing means are selectively used according to a one-sided or two-sided mode. The image forming apparatus according to the preferred embodiment is characterized in that the conveying surface of the material and the rotating belt are inclined (inclination angle = 5 to 20 °).

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of an image forming apparatus in which a toner image is formed on both surfaces of a transfer material to which the present invention is applied and is fixed, a toner image forming means forms an image on an image forming body. After the formed toner image is transferred to the surface of the transfer material, and the toner image formed on the image forming body is transferred to the back surface of the transfer material via the intermediate transfer body, the toner images transferred to both surfaces of the transfer material are collectively transferred. An image forming apparatus that fixes by fixing will be described. The present invention is not limited to the embodiments described below. The description in this column does not limit the technical scope of the claims and the meaning of terms. Further, in the following description of the embodiment, when transferring a toner image to a transfer material, the surface of the transfer material facing the image forming body at the transfer position is referred to as the surface, and the other surface of the transfer material, that is, the intermediate transfer The surface of the transfer material on the side facing the body is called the back surface, the image transferred to the front surface of the transfer material is called the front image, and the image transferred to the back surface of the transfer material is called the 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.

The image forming process and each mechanism of the embodiment of the image forming apparatus will be described with reference to FIGS. FIG. 1 is a sectional view of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a side sectional view of the image forming body of FIG. 1, and FIG. FIG. 3 is a diagram illustrating a state of forming a toner image and supply of a transfer material.

In FIG. 1, reference numeral 10 denotes a photosensitive drum which is an image forming body, 11 denotes a scorotron charger which is a charging unit for each color, 12 denotes an exposure unit which is an image exposure unit for each color, and 13 denotes a developing unit for each color. A developing device, 14 an intermediate transfer member, 15 a primary transfer device as first and second transfer devices, 15g a secondary transfer device as a third transfer device, 16c
Denotes a timing roller as a transfer material supply unit, and 30 denotes a fixing device as a fixing unit.

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

As shown in FIG. 2, the photosensitive drum 10 has flange members 10a and 10a at both end surfaces for engaging and fixing the same.
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.

A scorotron charger 11, which is a charging unit for each color, an exposure unit 12, which is an image exposure unit for each color, and a developing unit 13, which is a developing unit for each color, form a set of these units, Four photoconductor drums 10 are provided for magenta (M), cyan (C), and black (K) image forming processes, and are indicated by arrows in FIG.
Are arranged in the order of Y, M, C, and K with respect to the rotation direction.

A scorotron charger 11, which is a charging means for each color, is mounted to face the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10, and is attached to the photosensitive layer of the photosensitive drum 10 as described above. On the other hand, it has a control grid maintained at a predetermined potential and a discharge electrode 11a formed of, for example, a sawtooth electrode, performs corona discharge (negative charging in the present embodiment) having the same polarity as the toner, and On the other hand, a uniform potential is applied. 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 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 axis of the photosensitive drum 10 are arranged in an array, It comprises a selfoc lens 12b as an 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 120, 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 exposure element, a linear element in which a plurality of light emitting elements 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 is generally high in transmittance for Y, M, and C toners. )
The wavelength may be shorter than this, since the color toner does not have sufficient transparency since the image exposure is performed from the beginning.

The developing device 13 as a developing means for each color includes
A cylindrical non-magnetic material having a thickness of, for example, 0.5 to 1 mm and an outer diameter of 15 to 25 mm, which rotates in a forward or reverse direction with respect to the rotation direction of the photosensitive drum 10 while maintaining a predetermined gap with respect to the peripheral surface of the photosensitive drum 10 A developing sleeve 131 having a magnet body inside formed of stainless steel or aluminum material;
And a developing casing 138, and contains therein one-component or two-component developers of yellow (Y), magenta (M), cyan (C) and black (K). The developing sleeves 131 of the respective developing devices 13 are kept in non-contact with the photosensitive drum 10 by a contact roller (not shown) with a predetermined gap, for example, 100 to 1000 μm. By applying a developing bias in which an AC voltage is superimposed on a DC voltage having a polarity (minus polarity in the present embodiment),
Non-contact reversal development is performed to form a toner image on the photosensitive drum 10.

The intermediate transfer member 14 has a volume resistivity of 10 ⁸ -1.
0 ¹⁵ Ω · cm endless belt, for example, preventing toner filming on the outside of a 0.5 to 2.0 mm thick semi-conductive rubber belt substrate in which a conductive material is dispersed in silicon rubber or urethane rubber or the like. 5 to 50 μm thick as a layer
2 is a seamless belt having a two-layer structure provided with a semiconductive fluorine coating. 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 0.0 mm semiconductive film can also be used. Intermediate transfer member 14
Is circulated in the counterclockwise direction indicated by the arrow in FIG. 1 by the power transmitted to the driving roller 14d in a state in which the driving roller 14d and the driven roller 14e are inscribed in the horizontal direction by the tension roller 14k.・ It is rotated.

A primary transfer device 15 as first and second transfer means is provided opposite to the photosensitive drum 10 with the intermediate transfer member 14 interposed therebetween, and is provided between the intermediate transfer member 14 and the photosensitive drum 10. Then, a transfer position 14b is formed. The primary transfer unit 15 has a polarity opposite to that of the toner (plus polarity in this embodiment).
Is applied to form a transfer electric field at the transfer position 14b, thereby transferring the toner image on the photosensitive drum 10 onto the intermediate transfer body 14 or onto the surface of the recording paper P as a transfer material.

A secondary transfer unit 15g as a third transfer unit
Is the conductive roller 1 grounded with the intermediate transfer member 14 interposed therebetween.
4p, a DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied to transfer the toner image on the intermediate transfer body 14 to the back surface of the recording paper P.

Timing roller 1 as transfer material supply means
6c supplies the recording paper P as a transfer material to the transfer position 14b in synchronization with the color toner image of the front surface image on the photosensitive drum 10 or the color toner image of the back surface image on the intermediate transfer body 14.

The fixing device 30 serving as a fixing unit is provided with a recording paper P
And a fixing belt 310 stretched between a first roller 312 provided with a heating means therein and provided with a heating means therein and a second pressure roller 312 provided downstream of the recording paper P in the conveyance direction. An upper fixing means for fixing the surface toner image on the recording paper P, a spur member 18 provided below the upper fixing means, and a heating belt inside, And a lower heating means comprising a pressure roller 320 provided opposite to the second roller 312 and in charge of fixing the back side toner image of the recording paper P. The pressure roller 320 having the following configuration is in contact with the second roller 312 via the fixing belt 310. By applying heat and pressure between the fixing belt 310 and the pressure roller 320, Fixing the toner image on Rokushi P.

Next, the image forming process will be described.

In an image reading apparatus separate from the present apparatus, image data of an original image read by an image sensor or image data of an image edited by a computer are Y (yellow), M (magenta), (cyan)
And K (black) are temporarily stored in a memory as image signals for respective colors.

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

After the photosensitive drum 10 is applied with a potential,
In the Y exposure unit 12, the 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 in a non-contact state by the Y developing unit 13 to form a yellow (Y) toner image in accordance with the rotation of the photosensitive drum 10.

Next, a potential is applied to the photosensitive drum 10 from 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 1
The magenta (M) toner image is superimposed on the yellow (Y) toner image by the non-contact reversal development by No. 3.

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

These Y, M, C and K exposure units 1
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 also performed without being affected by the previously formed toner image at all, 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 which is an image forming body, and the superimposed color toner image of the back image on the photosensitive drum 10 is transferred. Position 14b
, The toner is collectively transferred onto the intermediate transfer member 14 by a primary transfer unit 15 as a first transfer unit to which a DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. At this time, so that good transfer is performed,
For example, uniform exposure is performed by the transfer simultaneous exposure device 12d using a light emitting diode.

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

After the superimposed color toner image serving as the back surface image is formed on the intermediate transfer member 14 as described above,
Subsequently, the back surface image on the intermediate transfer body 14 and the transfer position 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 surface image formed at this time is a mirror image of the back surface image formed earlier on the photosensitive drum 10.

The recording paper P, which is a transfer material, is fed from a paper feed cassette 16 which is a transfer material storage means to a feed roller 16a.
, And are fed by the feed roller 16b and conveyed to the timing roller 16c.

The recording paper P is driven by a timing roller 16c, which is a transfer material supply means, to drive a color toner image of a front image formed on the photosensitive drum 10 and a back image of the rear image carried on the intermediate transfer member 14. The sheet is fed to the transfer position 14b in synchronization with the color toner image. At this time, the toner image formation state of the back side image carried on the intermediate transfer body 14 and the front side image formed on the photosensitive drum 10,
FIG. 3 shows the relationship between the recording sheets P fed in synchronization with these.

When the recording paper P is fed to the transfer position 14b, the recording paper P has the same polarity as the toner by a paper charger 15f serving as a transfer material charging means, which is a non-contacting corona discharger. , And is adsorbed by the intermediate transfer member 14 and fed to the transfer position 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 intermediate transfer member 14 and the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed. Further, as the transfer material charging means, a conductive brush or a conductive roller capable of contacting and releasing contact with the intermediate transfer member 14 can be used.

At the transfer position 14b, a surface image on the peripheral surface of the photosensitive drum 10 is applied by a primary transfer device 15 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. Are collectively transferred to the surface (upper surface) of the recording paper P. At this time, the back side image on the peripheral surface of the intermediate transfer body 14 is not transferred to the recording paper P, and the intermediate transfer body 1
4 above.

Next, the recording paper P on which the color toner image has been transferred onto the surface thereof is used as a third transfer means to which a voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied.
The image is conveyed to the next transfer unit 15g, and the back surface image on the peripheral surface of the intermediate transfer body 14 is collectively recorded on the recording paper P by the secondary transfer unit 15g.
Is transferred to the back surface (lower surface).

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. Therefore, in the double-sided image forming method in which the polarity of the color toner image formed on the intermediate transfer body 14 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 lower layer toner is not sufficiently charged to the same polarity, transfer failure occurs, which is not preferable.

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

As described above, in forming a color image, the first and second transfer means and the third 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. Then, a double-sided image forming method of forming a color toner image on the back surface of the transfer material by operating the third transfer unit is preferably employed.

The recording paper P on which the color toner images have been transferred on both sides is neutralized by a neutralizer 15h for transfer material separation provided opposite to a conductive drive roller 14d grounded with the intermediate transfer member 14 interposed therebetween. The fixing member has a fixing belt 310 at an upper portion and a pressing roller 320 at a lower portion, which will be described later. The sheet is conveyed to a fixing device 30 as a unit. After the recording paper P is preheated by the upper fixing belt 310, heat and pressure are applied between the fixing belt 310 and the lower pressure roller 320, so that the toner adhered to the front and back surfaces of the recording paper P is removed. The recording paper P on which the image has been fixed and on which the double-sided image has been recorded is sent by a paper discharge roller 19a and discharged to a tray 19b at the upper part of the apparatus.

The toner remaining on the intermediate transfer body 14 after the transfer is provided by an intermediate transfer body cleaning device 140 which is a cleaning means for the intermediate transfer body 14, using a blade capable of coming into contact with and releasing the intermediate transfer body 14. Will be cleaned. Further, the toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the static eliminator 17, reaches the cleaning device 19, and is cleaned by the cleaning blade 19 a made of a rubber material in contact with the photosensitive drum 10. The toner is scraped off into the cleaning device 19 and collected by a screw 19b into a waste toner container (not shown). The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is 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, the color toner images superimposed as described above are collectively transferred to form a color image on both sides of the recording paper P. It is possible to form a favorable double-sided color image with less occurrence of misalignment, toner scattering and rubbing, and little image deterioration.

Next, the state of the toner image formed on the photosensitive drum 10 until it is transferred to both sides or one side of the recording paper P and enters the fixing device will be described with reference to FIGS. 4 and 5. explain. Here, the photosensitive drum 10 serving as an image forming body is negatively charged, and the latent image on the photosensitive drum 10 is subjected to reversal development by a toner having a negative charge, so that a toner image having a negative charge is exposed. The case in which it is formed on the body drum 10 will be described.

FIG. 4 shows the state in which the toner image of the surface image formed on the photosensitive drum 10 is directly transferred onto the recording paper P, and the toner image is adhered only to the surface of the recording paper P. FIG. 4 is an explanatory diagram when the vehicle enters the fixing device 30. The toner image of the negative polarity surface image formed on the photoreceptor drum 10 is applied with a positive polarity voltage by the primary transfer unit 15 through the recording paper P and the intermediate transfer body 14 behind the recording paper P, and the recording paper P is applied. Transfer is performed on P (FIG. 4A). The recording paper P holding the toner image of the negative polarity surface image on the upper surface is charged on the static eliminator 1 to which the AC voltage is applied.
After 5h, the charge is removed, separated from the intermediate transfer member 14, and enters the fixing device 30 (FIG. 4B).

FIG. 5 shows a first example in which the toner image of the surface image formed on the photosensitive drum 10 is directly transferred onto the recording paper P.
And a second image forming step of transferring the toner image of the back side image formed on the photosensitive drum 10 onto the recording paper P via the intermediate transfer member, thereby forming the toner image on both sides of the recording paper P. FIG. 6 is an explanatory diagram when the fixing device 30 enters the fixing device 30 while being carried. The toner image of the negative polarity rear surface image formed on the photosensitive drum 10 is applied with a positive polarity voltage from behind the intermediate transfer body 14 by a primary transfer unit 15 as a first transfer unit, and the intermediate transfer is performed. The image is transferred onto the body 14 (FIG. 5A).

Subsequently, a toner image having a negative polarity surface image is formed on the photosensitive drum 10. A positive transfer voltage is applied to the toner image of the front surface image by the primary transfer device 15 as a second transfer via the recording paper P and the intermediate transfer member 14 carrying the toner image of the back surface image behind the recording paper P, The image is transferred onto the upper surface of the recording paper P (FIG. 5B).
Next, the toner image of the back surface image adhered on the intermediate transfer body 14 is applied to the lower surface of the recording paper P by applying a positive polarity voltage from the upper side of the recording paper P by a secondary transfer device 15g as a third transfer unit. The transfer is made. At this time, the potential of the toner image of the surface image on the upper surface of the recording paper P is changed from negative polarity to positive polarity by applying a positive polarity voltage from directly above by the secondary transfer unit 15g (FIG. 5).
(C)). The recording paper P is neutralized by the static eliminator 15h in a state in which the toner image of the front surface image of the positive polarity is carried on the upper surface of the recording paper P, and the toner image of the rear surface image of the negative polarity is carried on the lower surface thereof. And enters the fixing device 30 (FIG. 5D).

FIG. 6 is a sectional view of an image forming apparatus showing another embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, have the same functions, and detailed description is omitted.

In the image forming apparatus of the present embodiment, the first and second process units 2A and 2B are horizontally arranged on the upper surface of the rotating intermediate transfer member 14. The first and second
Each of the process units 2A and 2B is composed of photosensitive drums 20A and 20B, which are image forming members that carry toner images, and toner image forming units 26A and 26B that form toner images on the photosensitive drums 20A and 20B. This is a process unit that forms a toner image on the photosensitive drums 20A and 20B by a well-known electrophotographic process, and has the same configuration except for control, as described in detail later. Since the first and second process units 2A and 2B have the same configuration, reference numerals other than the suffixes A and B may be used. The process unit 2 is mounted in a position-restricted manner from above the apparatus main body via a guide member (not shown) so that the peripheral surface of each photosensitive drum 20 comes into contact with the intermediate transfer body 14 with a predetermined contact pressure. The toner image forming unit 26 includes a scorotron charger 21 as a charging unit, an exposure unit 25 as an exposure unit, and a developing unit 2 as a developing unit.
3 and a cleaning device 24 as cleaning means.

The photosensitive drums 20A and 20B as the first and second image forming bodies are formed on an outer periphery of a grounded cylindrical aluminum substrate having an outer diameter of 30 to 80 mm, and an organic photosensitive layer (OPC) is provided.
The intermediate transfer body 14 is driven and rotated clockwise by the power of the apparatus main body at the same speed as the peripheral speed of the intermediate transfer body 14.

The scorotron charger 21 is composed of a corona discharge electrode composed of a saw-tooth electrode or a wire electrode, and a control grid maintained at a predetermined potential with respect to the above-mentioned organic photosensitive layer of the photosensitive drum 20. The photoconductor drum 20 is attached to face the photoconductor drum 20 in a direction perpendicular to the moving direction of the drum 20. Scorotron charger 21
Performs corona discharge (minus charge in the present embodiment) having the same polarity as the toner, and uniformly charges the photosensitive drum 20.

The exposure unit 25 includes a linear exposure element in which a plurality of LEDs (light emitting diodes) as image exposure light emitting elements arranged in the main scanning direction in parallel with the axis of the photosensitive drum 20 are arranged in an array. , And a selfoc lens as an equal magnification imaging element. As the exposure element, a linear 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 exposure unit performs image exposure on the photosensitive drum 20 based on image data read by a separate image reading device and stored in the memory, and forms a latent image on the photosensitive drum 20.

The developing device 23 has a thickness of, for example, 0.5 to 1 m.
m, cylindrical developing sleeve 2 made of non-magnetic stainless steel or aluminum material having an outer diameter of 10 to 30 mm
30 and contains therein a one-component or two-component developer. The developing sleeve 230 is provided on the photosensitive drum 20.
Is rotated in the forward direction with respect to the rotation direction of the developing sleeve 23.
By applying a DC bias of the same polarity as the toner (negative polarity in the present embodiment) or a developing bias to which an AC voltage is further applied to 0, a contact or non-contact state with the exposed portion of the photosensitive drum 20 is achieved. Reversal development is performed.

The primary transfer unit 15B as the first transfer unit and the primary transfer unit 15A as the second transfer unit apply a charge of the opposite polarity to the toner on the back surface of the intermediate transfer body 14 to expose the photosensitive member. A transfer electric field of the toner image is formed between the photosensitive drum 20 and the primary transfer device 15A.
On the upper surface (front surface) of the recording paper P as a transfer material to which the toner image is supplied, the primary transfer device 15B
The B toner images are respectively transferred onto the intermediate transfer member 14.

The paper charger 15f, which is a transfer material charging means,
A charging device comprising a corona discharger, which is located between the first process unit 2A and the second process unit 2B, is disposed opposite the grounded driven roller 14m, and is in non-contact with the intermediate transfer member 14; The recording paper P supplied when the recording paper P is conveyed to the intermediate transfer member 14 is charged to the same polarity as the toner, and the charged recording paper P is transferred onto the intermediate transfer member 14 by the primary transfer device 15B. The photosensitive drum 20A is conveyed to the transfer position on the photosensitive drum 20A via an image or directly adsorbed.

A secondary transfer unit 15g as a third transfer unit
Is to transfer the toner image on the intermediate transfer member 14 to the lower surface (rear surface) of the recording paper P by applying a charge of the opposite polarity to the toner to the upper surface (front surface) of the recording paper P on the intermediate transfer member 14. , And are arranged to face the grounded roller 14p.

The static eliminator 15h, which serves as a separating unit, neutralizes the recording paper P on which the toner image has been transferred on the upper and lower sides, that is, on the front and back surfaces, and separates the recording paper P from the peripheral surface of the intermediate transfer member 14. Adjacent and grounded drive roller 1
4d.

The fixing device 30 as a fixing means is provided with a recording paper P
The fixing belt 3 stretched between a first roller provided on the upstream side in the conveying direction and having a heating means therein and a second roller 312 for pressing provided on the downstream side in the conveying direction of the recording paper P
10, an upper fixing means for fixing the surface toner image on the recording paper P, a spur member 18 provided below the upper fixing means, and a spur member 18 provided opposite to the second roller 312. A belt-type fixing device including a pressure roller 320 having a heating means therein and a lower fixing means for fixing the back surface toner image of the recording paper P; Then, the recording paper P conveyed through the spur member 18 is nipped and conveyed, so that the toner images transferred to the front and back surfaces are simultaneously pressed and heated to be fixed.

Next, the process of the image forming apparatus will be described. When image data is input from an image reading device or a personal computer (not shown), image processing is performed, and the image data is temporarily stored in a memory, and the image data of the front surface and the back surface is processed in a mirror image relationship in accordance with an image forming process. ,
Exposure units 25A, 25 sequentially (respectively selected)
B.

First, the image data on the back side is input to the exposure unit 25B of the second process unit 2B. In the second toner image forming means 26B of the second process unit 2B, the scorotron charger 21B, the exposure unit 25B, and the developing unit 23B By operation, a toner image on the back surface is formed on the peripheral surface of the photosensitive drum 20B as the second image forming body based on the image data on the back surface, and this toner image is transferred to the primary transfer device 15B as the first transfer means. As a result, the back surface of the intermediate transfer member 14 is charged, and is temporarily transferred onto the peripheral surface of the intermediate transfer member 14.

In parallel with the formation and transfer of the toner image on the back surface, the recording paper P is started to be fed from the paper feed cassette 16 by the operation of the carry-out roller 16a, and the recording paper P is fed via the paper feed path 16d to the timing roller. 16c.

On the other hand, there is a predetermined time difference between the input of the back side image data (the front end position of the back side toner image transferred onto the intermediate transfer body 14 and the front end position of the front side toner image formed therefrom is the first position). Transfer position 14 of process unit 2A
b), the image data on the front surface is input to the exposure unit 25A of the first process unit 2A with a time difference determined to be the same in the first process unit 2A, and the scorotron charger 21A in the first toner image forming unit 26A of the first process unit 2A. By the operation of the exposure unit 25A and the developing unit 23A, a toner image on the surface is formed on the peripheral surface of the photosensitive drum 20A as the first image forming body.

The timing roller 16 c is synchronized with both the formation of the toner image on the front surface on the peripheral surface of the photosensitive drum 20 A in the first process unit 2 A and the position of the toner image on the back surface transferred onto the intermediate transfer member 14. The operation is started, and the sheet is fed onto the intermediate transfer body 14 such that the front end position of the toner image on the front and back sides matches the front end position of the recording paper P.

At this time, the recording paper P is attracted onto the intermediate transfer member 14 via the toner image on the intermediate transfer member 14 by the charging of the paper charger 15f, and is transported integrally with the intermediate transfer member 14.
Then, the back surface of the intermediate transfer body 14 is charged by a primary transfer unit 15A as a second transfer unit, and the toner image on the surface of the photosensitive drum 20A of the first process unit 2A is conveyed. The image is transferred onto the upper surface of the paper P. Next, the surface of the recording paper P is charged by a secondary transfer unit 15g as a third transfer unit, and the toner image on the back surface of the intermediate transfer body 14 transferred from the photosensitive drum 20B of the second process unit 2B is transferred. Is transferred to the lower surface of the recording paper P.

The recording paper P on which the toner images have been transferred to the front and back surfaces is discharged by the discharger 15h and is separated from the peripheral surface of the intermediate transfer member 14, and passes through the spur member 18 which guides the lower surface of the recording paper P. After being conveyed to the fixing device 30 and the toner image is fused and fixed in the fixing device 30, the toner image is discharged to a tray 19b via a paper discharge roller 19a. When the curvature separation is used, the static eliminator 15h can be omitted. On the other hand, each of the photosensitive drums 20A and 20B and the intermediate transfer body 14 after the transfer of the toner image is cleaned by removing the residual toner by a cleaning device 24A, 24B or 140 provided respectively, and is then cleaned to form and transfer the subsequent toner image. Prepare.

As described above, in the image forming apparatus of the present embodiment, the toner images are formed on the photosensitive drums 20A and 20B by the respective toner image forming means 26A and 26B.
The toner image formed on the photoconductor drum 20B is temporarily transferred onto the intermediate transfer body 14, and thereafter, the photoconductor drum 20A,
Since the toner image on the intermediate transfer member 14 is transferred to both sides of the recording paper P and fixed at the same time, the image forming speed can be remarkably increased. In particular, since the front and back toner images are formed at short time intervals, and the transfer of the recording paper P to the front and back is performed during one rotation of the intermediate transfer member 14, the time required for recording the two-sided image is remarkably large. Will be shortened.

When images are formed on both sides of the recording paper P, the transfer conditions of the primary transfer units 15A and 15B and the secondary transfer unit 15g are different. This is because when the toner images are transferred by the transfer units 15A, 15B, and 15g, the conditions and conditions of the recording paper and the toner image interposed between the transferred toner image and the transfer units are different. Therefore, in the present embodiment, each transfer device 15A, 15B, 15
The optimum transfer condition for g is stored in the storage unit, and the control unit reads out and sets the optimum transfer condition from the storage unit according to the image forming condition selected on the operation panel of the main body.

(Embodiment Related to Fixing) The fixing device 30 which is a fixing unit used in the above-described two image forming apparatuses has an upper fixing unit facing the surface toner image.
It is necessary that both the lower fixing means facing the backside toner image have a heating means and heat and fix the recording paper P from both sides. Further, a nip portion of several mm is formed in the conveying direction of the recording paper P at the contact portion between the fixing roller 312 as the second roller and the pressing roller 320 as the lower fixing means. In order to form the nip, it is necessary to provide an elastic layer made of an elastic material such as silicon rubber on any of the rollers. Since the elastic layer has a lower thermal conductivity than the metal material, the fixing roller provided with the elastic layer is deprived of heat by the recording paper P when the recording paper P passes, and the lowered roller surface temperature is restored. It will take a lot of time. However, in the present embodiment, the fixing belt 310 is heated by the heating roller 311 which is the first roller,
Since the surface toner image on the recording paper P is fixed by the heated fixing belt 310, the fixing roller 312 as the second roller does not need to be a hard roller having a high thermal conductivity. The soft roller provided with the pressure roller 320 is a hard roller capable of quickly heating and returning the temperature.

FIG. 7 is a sectional view showing an example of an embodiment of a fixing device used in the image forming apparatus of the present invention.

The fixing device 30 serving as a fixing unit is provided between a heating roller 311 serving as a first roller having a first heater 313 serving as a first heating unit and a fixing roller 312 serving as a second pressing roller. And a plurality of spurs provided below the upper fixing means, the upper fixing means being composed of a fixing belt 310 which is a rotating belt stretched on the recording paper P and responsible for fixing the surface toner image on the recording paper P. A member 18, a pressure roller 320 below the fixing roller 312, and a lower fixing unit that is in charge of fixing the back surface toner image of the recording paper P;
The fixing roller 312 and the pressure roller 320 are opposed to each other via the fixing belt 310 to press and heat, and pass between the fixing belt 310 and the pressure roller 320. The toner image carried on the recording paper P is fixed.

The heating roller 311 has a first heater 313 (7 in this embodiment) composed of a halogen lamp or the like at the inner core.
The fixing belt 310 is heated with a (00 W halogen lamp).

The fixing belt 310 is formed, for example, by using a metal belt made of nickel electrocasting and having a thickness of 40 μm as a base, and the surface thereof is coated with 150 μm high-release silicone rubber.

After being heated by the heating roller 311, the fixing belt 310 passes through the inclined portion while emitting a small amount of heat, and releases the heat held in the nip by heat conduction to heat the recording paper P. Since the fixing of the toner image is performed, the required heat capacity per area of the fixing belt 310 is determined in consideration of the heating temperature of the heating roller 311 and the thermal conductivity of the belt. The thickness is selected.

The fixing roller 312 has a concave nip portion on the lower side, and is a soft roller for bringing the fixing belt 310 into contact with the recording paper P carrying an unfixed toner image.
It has an elastic layer made of silicon sponge or the like having a certain rubber hardness. The fixing roller 312 is a fixing belt 310.
Is also driven.

The pressure roller 320 is a roller that forms a nip by abutting below the fixing roller 312 by a biasing member such as a spring (not shown), and has a rubber hardness of about 40 degrees, which is harder than the elastic layer of the fixing roller 312. This is a fast-heating hard roller made of a thin metal cylinder with or without an elastic layer of silicon rubber or the like. In the case of exclusive use for color image formation, a soft roller is preferable. Pressure roller 32
Reference numeral 0 denotes a second heater 323 (500 W in the present embodiment) which is a second heating means comprising a halogen lamp or the like on the inner core.
Halogen lamp).

A plurality of spur members 18 are provided below the fixing belt 310, and convey the unfixed recording paper P separated from the intermediate transfer member 14 to the fixing device 30. Conveying surface of recording paper P by spur member 18 and fixing belt 3 for recording paper P
10, the distance between the recording sheet P and the fixing belt 310 decreases as the recording sheet P approaches the fixing device 30. As a result, the recording paper P is preheated by the fixing belt 310 which is close to and in a high temperature state, and the temperature gradually increases. Accordingly, since the toner image on the recording paper P is preheated before reaching the nip, the fixing temperature of the nip can be kept low. Conveying surface of recording paper P by spur member 18 and fixing belt 3 for recording paper P
It is preferable that the inclination angle α with respect to the plane No. 10 is 5 to 20 °. If the angle is less than 5 °, the recording paper P may contact the fixing belt 310 before reaching the nip portion and damage the toner image. If the angle exceeds 20 °, the effect of the preheating is hardly recognized.

Below the plurality of spur members 18, a heat reflecting plate 33 made of copper, aluminum or the like having good heat reflectivity is provided to prevent heat diffusion. Thereby, thermal efficiency can be improved and power consumption can be reduced.

Cleaning rollers 314 and 324 are provided on the peripheral surfaces of the fixing belt 310 and the pressure roller 320 in order to adsorb and remove toner, paper powder and the like adhering to the peripheral surfaces.
And oil application rollers 315 and 325 that apply silicone oil as a release agent to prevent offset. For the surfaces of the cleaning rollers 314 and 324, a material that is non-absorbable with respect to 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 314 and 324, and the variation in the amount of applied oil is suppressed. 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 fixing belt 310 and the pressure roller 320 are selectively used. Cleaning rollers 314, 32
4 and the oil application rollers 315 and 325 are pressed against the fixing belt 310 and the pressure roller 320, respectively, and are driven to rotate.

A first temperature sensor 316 and a second temperature sensor 326 as temperature detecting means, such as a thermistor, are provided at a position in contact with or very close to the heating roller 311 and the pressure roller 320. And the surface temperature of the pressure roller 320 is detected. Based on the detection signal, the energization control of the first heater 313 and the second heater 323 is performed, and the surface temperatures of the fixing belt 310 and the pressure roller 320 are set within a predetermined temperature range. Hold within. The first temperature sensor 316 is connected to the fixing belt 310 on the heating roller 311.
May be provided at a position abutting on or very close to the device.

The fixing roller 312 and the pressing roller 320 are pressed against each other by an appropriate linear pressure by a biasing member such as a spring (not shown). 2 to 8 mm depending on the hardness of the roller
It has become. The fixing roller 312 and the pressure 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, and perform double-sided fixing at the nip.

In the two image forming apparatuses, the fixing device 30 is provided with a corona charging device (not shown) for forming an electric field between each of the fixing belt 310 and the pressure roller 320 and the recording paper P sandwiched and conveyed therebetween. Electric field forming means such as a charger or a roller charger which is conductive and capable of driven sponge-like rotation, or is provided on the surface layer of the fixing belt 310, the fixing roller 312, and the pressure roller 320 by, for example, carbon black or titanium oxide. The fixing belt 310 has +200 V and a pressure roller by connecting a bias power supply (not shown) and a core of the roller via a safety resistor to each other via a safety resistor. 32
The fixing belt 310 is charged with the same polarity as the toner charge of the front toner image, and the pressing roller 320 is charged with the toner charge of the back toner image by an electric field forming means such as applying a bias voltage of -200 V to 0. In an image forming apparatus in which two-sided toner images are fixed at a time by increasing the electric repulsion between the toner and the belt or between the toner and the roller by performing charging of the same polarity, the electric electrostatic offset is completely reduced. To be resolved.

The image forming apparatus includes a double-sided copy mode in which toner images are formed on both sides of a transfer material and fixed at a time as a first image forming mode, and a double-sided copy mode in which only a surface of the transfer material is fixed as a second image forming mode. A front side copy mode in which a toner image is formed and fixing is performed, and a back side copy mode in which a toner image is formed only on the back side of the transfer material and fixing is performed as a third image forming mode. When one of the modes is set, excellent control of image formation and fixing according to the mode is performed, and excellent image recording is performed.

In the two-sided copy mode, control for turning on / off the first and second heaters 313 and 323 is performed, and the surface temperatures of the fixing belt 310 and the pressure roller 320 are set to a predetermined temperature suitable for the two-sided copy mode. To hold.

In the front copy mode, the second heater 323
Of the first heater 313 is turned off, or the power of only the first heater 313 is turned off.
N / OFF control is performed to maintain the surface temperature of the fixing belt 310 at a predetermined temperature suitable for the front copy mode.

In the back side copy mode, the first heater 313
Of the second heater 323 is turned off, or the power of only the second heater 323 is turned off.
N / OFF control is performed to maintain the surface temperature of the pressure roller 320 at a predetermined temperature suitable for the backside copy mode.

[0090]

According to the first and third aspects of the present invention, as described above, the fixing belt and the spur member which are small heat capacity rotating belts are used, so that the unfixed toner image on the back surface is not disturbed. It is possible to fix both sides of the image, and the toner is heated in the preheating step, so that the temperature of the nip can be kept low, and it is possible to fix the toner image without drastically reducing the viscosity of the toner image, thereby providing a margin for offset. Thus, an image forming apparatus capable of improving the degree of fixing, enabling oilless fixing, reducing fixing power consumption, and obtaining good image quality is provided.

According to the first and second aspects, the power supply to the first or second heating means is turned off in the single-sided copy mode for the front side or the back side, so that the power consumption for fixing is further reduced and the image quality is improved. And an image forming apparatus capable of obtaining the same.

[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 the image forming body of FIG. 1;

FIG. 3 is an explanatory diagram illustrating a state of forming a toner image and supply of a transfer material during double-sided image formation.

FIG. 4 is an explanatory diagram illustrating a state of a toner image and a transfer material when forming a single-sided (front) image.

FIG. 5 is an explanatory diagram illustrating a state of a toner image and a transfer material during double-sided image formation.

FIG. 6 is a cross-sectional configuration diagram illustrating another example of the embodiment of the image forming apparatus of the present invention.

FIG. 7 is a sectional configuration diagram of a fixing device used in the present invention.

[Explanation of symbols]

10, 20A, 20B Photoconductor drum (image forming body) 11, 21A, 21B Scorotron charger 12, 25A, 25B Exposure unit 13, 23A, 23B Developing device 14 Intermediate transfer member 15, 15A, 15B Primary transfer device (No. 1, 2nd transfer means) 15g Secondary transfer device (third transfer means) 15h Static eliminator 16 Paper feed cassette 18 Spur member 30 Fixing device 33 Heat reflection plate 310 Fixing belt (rotating belt) 311 Heating roller (No. 1 roller 312 fixing roller (second roller) 313 first heater (first heating unit) 320 pressure roller (lower fixing unit) 323 second heater (second heating unit) 316 first temperature sensor 326 Second temperature sensor P Recording paper (transfer material)

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kuki Nagase 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation F-term (reference) 2H027 DA50 EA16 ED25 EF09 FA11 2H028 BB02 BC00 2H033 AA10 AA32 AA46 BA01 BA08 BA11 BB21 CA01 CA48

Claims (3)

[Claims] In an image apparatus for performing fixing after forming an unfixed toner image on both surfaces of a transfer material, an upper fixing means includes a first roller having a heating means therein and a first roller on an upstream side in a transfer material transport direction and a transfer material. Second on the downstream side in the transport direction
A roller having a spur member for transferring a transfer material at a lower portion of the upper fixing unit, and a lower fixing unit is a roller having a heating unit therein,
The image forming apparatus, wherein the roller is in contact with the second roller via the rotating belt. 2. The image according to claim 1, wherein a heating unit in the upper fixing unit and a heating unit in the lower fixing unit are selectively used according to a single-sided or double-sided mode. Forming equipment. 3. The image forming apparatus according to claim 1, wherein a transfer surface of the transfer material by the spur member and the rotating belt are inclined (inclination angle = 5 to 20 °).