JP2002189387A - Image forming method and device therefor, and transfer method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a one-pass both-side system image forming method and an image forming device capable of forming image on both sides or only on one side of a recording medium, and to provide a transfer method and a transfer device used for the image forming device. SOLUTION: A mode of forming the image (toner image) on the transfer paper P is switched by a mode switching means 200 between a both-side mode 200A of forming the images on both sides of the transfer paper P by using both the 1st image forming unit 13a and a 2nd image forming unit 13b, a front side mode 200B of forming the image only on the front side of the transfer paper P by using the 1st image forming unit 13a and a rear side mode 200C of forming the image (rear side toner image) only on the rear side of the transfer paper P by using the 2nd image forming unit 13b. Then, by using the 1-pass both-side system printer, the images can be formed on both sides of the transfer paper P, besides, only on one side of the transfer paper P, and the utilizable extent of the printer is enlarged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, and the like. First image forming means for forming;
Second image forming means for forming an image on the back surface of the recording medium conveyed by the conveying means, and without reversing the front and back of the recording medium, on the front and back surfaces of the recording medium conveyed by the conveying means. The present invention relates to a one-pass double-sided image forming method and an image forming apparatus for forming an image, and a transfer method and a transfer device used in the image forming apparatus.

[0002]

2. Description of the Related Art In general, two toner images composed of toners having the same charge polarity face each other.
It is difficult to transfer to both sides of a transfer body such as transfer paper.
For example, as shown in FIG.
Two intermediate transfer drums 8 on which a toner image composed of a negatively charged toner T is formed so as to be transferred to both surfaces of the intermediate transfer drum 8
It is assumed that the transfer paper P is sandwiched between 0 and 81. At this time, in order for one of the toner images to be transferred from the intermediate transfer drum 80 to the surface (upper surface in the drawing) of the transfer paper P, the intermediate transfer drum 80 is moved from the intermediate transfer drum 80 to the negative toner T. An electric field for applying an electrostatic force in the direction toward 81 (the direction of arrow A) must be formed between both drums. On the other hand, in order for another toner image to be transferred from the intermediate transfer drum 81 to the back surface (the lower surface in the drawing) of the transfer paper P, the direction ( An electric field for applying an electrostatic force in the direction of arrow B) must be formed between both drums. However, it is impossible to simultaneously generate electric fields in opposite directions between the two drums. Even if an attempt is made to cope with the problem by forming an alternating electric field, the direction of the electric field is reversed halfway, so that at the time of the reverse rotation, one of the toner images is reversely transferred from the transfer paper P to the drum. Also, even when the toner image is transferred only to the front surface of the transfer body, and then the transfer body is reversed and another toner image is transferred to the back surface,
At the time of the second transfer, the state shown in FIG. 15 is obtained.
The toner image transferred to the surface is reversely transferred.

Therefore, a transfer body such as transfer paper is passed through a transfer device and a fixing device to fix a toner image on only one surface thereof, and then the transfer body is inverted and then transferred to the transfer device and the fixing device again. 2. Description of the Related Art An image forming apparatus that employs a so-called switchback double-sided transfer method in which a toner image is transferred back to both sides of a transfer body is known. In this image forming apparatus, prior to the second transfer step in which a reverse electric field is applied to the toner image transferred in the first transfer step, this toner image is fixed on a transfer body. , And good double-sided transfer can be realized.

However, in this image forming apparatus, a complicated switchback mechanism for inverting the transfer member and returning it to the transfer device is required, and it is difficult to increase the speed of double-side transfer by switchback of the transfer member. There was a defect that it became.

In view of the above, an image forming apparatus has been proposed in which a pair of image carriers each individually carrying toner images composed of toners having different charging polarities are used to transfer toner images to both surfaces of a transfer body. (For example,
JP-B-51-13022, JP-A-63-6305
7, JP-A-2-259670, etc.). In this image forming apparatus, for example, as shown in FIG. 16, toner images having different polarities are opposed to each other via a transfer sheet P in a second transfer step or a double-sided simultaneous transfer step.
When an electric field that gives an electrostatic force in the direction toward the transfer paper P is applied to the negatively charged toner T on one surface of the transfer paper P in such a state that the transfer paper P is opposed to the opposite surface, The electrostatic force in the direction toward the transfer paper P can be applied to the positively charged toner T. For this reason,
It is not necessary to fix one of the toner images on the transfer sheet P in advance, and the transfer sheet P is not switched back to the first position.
By performing double-sided transfer in a pass, the above-described problem can be solved.

However, in this image forming apparatus, a pair of photosensitive drums, an optical writing unit, a developing unit, and the like for forming toner images having different polarities can use a common specification for each pair. Instead, the specifications must match the polarity of the toner. For this reason, there is a problem that the number of types of parts is much larger than that using only the toner of the same charging polarity, and the maintainability is deteriorated. Further, it is necessary to distinguish and manage toners whose appearance such as color is not substantially changed only by different charging polarities, and this has further deteriorated the maintainability.

Therefore, two toner images to be transferred to both surfaces of a transfer body using toners of the same charging polarity are formed,
An image forming apparatus has been proposed in which one of them is charged to a reverse polarity by a corona charger before being transferred to a transfer member (for example, JP-A-7-77851, JP-A-8-212664, Kaihei 10-17
1264, JP-A-10-97106, etc.).
According to this image forming apparatus, since only the toner having the same charging polarity is used, it is possible to eliminate the above-described deterioration of the maintainability. Moreover, one of the toner images is charged to the opposite polarity by a corona charger, and at the time of transfer,
The toner images having different polarities are electrostatically moved toward the transfer member interposed therebetween. Therefore, it is not necessary to fix one of the toner images on the transfer body in advance,
Two-sided transfer can be performed in one pass.

Incidentally, this type of one-pass double-sided image forming apparatus includes a dry image forming apparatus using a dry toner and a wet image forming apparatus using a liquid developer containing a toner and a liquid carrier. The present inventors have conducted various tests using a prototype of a wet image forming apparatus as shown in FIG. Referring to FIG. 1, the prototype includes an image forming apparatus 10, a paper feed tray 11, a pair of registration rollers 12, and the like.

The image forming apparatus 10 includes a photosensitive drum 1 as a latent image carrier, a corona charger 2, an optical writing unit 3, a wet developing device 50, a transfer roller 4, The photosensitive drum 1 includes a charge removing unit 5, a drum cleaning device 6, and the like, and forms an electrostatic latent image on the surface of the photosensitive drum 1 by a known electrophotographic process. On the other hand, the wet developing device 50 has a viscosity of 100% in which 15 wt% of toner is dispersed in an insulating liquid carrier such as silicon oil.
The liquid developer of [cSt] is stored and is carried on the developing roller 51. A developing bias is applied to the developing roller 51 by a power supply (not shown).
As a result, a developing electric field is formed in a developing area between the photosensitive drum 1 and the developing roller 51. In the developing area, the toner in the liquid developer on the developing roller 51 is electrophoresed toward the electrostatic latent image on the photosensitive drum 1 by the action of the developing electric field to form a toner image. As the photosensitive drum 1 rotates, the toner image is nipped by a transfer nip formed by the drum and a transfer roller 4 that comes into contact with the drum.

The paper feed tray 11 feeds out a transfer paper P as a transfer body accommodated therein by a paper feed roller 11a in accordance with the image forming timing of the image forming apparatus 10. The transferred transfer paper P is once sandwiched between the registration roller pair 12, conveyed toward the transfer nip at an appropriate timing, and is superimposed on the toner image on the photosensitive drum 1. In the transfer nip, a transfer electric field is formed by the influence of a transfer bias applied to the transfer roller 4 from a power supply (not shown), and the toner image is transferred from the photosensitive drum 1 to the transfer paper P by the action of the transfer electric field and the nip pressure. Is transferred to

The photosensitive drum 1 after passing through the transfer nip
After the surface is neutralized by the neutralization means 5, the transfer residual toner adhering to the surface is removed by the drum cleaning device 6.
Is cleaned by the cleaning blade 6a.

In a practical machine, a fixing device 30 is provided at a portion indicated by a dotted line in the figure, and the transfer paper P after passing through the transfer nip is passed through the fixing device. I was

In the prototype machine having the above-described structure, the present inventors reuse the transfer paper P in which the toner image transferred to one surface remains unfixed from the viewpoint of saving at one time. A certain test was conducted by transferring the toner image to the surface on the opposite side of the above. As a result, it was possible to transfer a new toner image to the opposite surface without substantially reversely transferring the unfixed toner image to the transfer roller 4. There was a possibility that the toner image was transferred to one surface and left for a long time, and then the toner image was transferred to the opposite surface. Similar results were obtained. That is, double-sided transfer could be performed without using two types of toners having different charging polarities or charging one toner image to a reverse polarity by a corona charger. After the two-sided transfer, a very small amount of toner adhered to the surface of the transfer roller 4, but this amount did not hinder practical use.

In the test, plain paper was used as the transfer paper P. When the same double-sided transfer was carried out instead of coated paper, the amount of residual toner on the transfer roller 4 was reduced to half that of plain paper. To a degree. From this,
The liquid carrier in the liquid developer is the toner image and the transfer roller 4
It is considered that as a result, the reverse transfer of the toner image is suppressed. Specifically, a fine toner having a much smaller diameter than a dry toner is generally used for a liquid developer. In the first transfer, the minute toner constituting the toner image is electrophoresed by the electrostatic force received from the electric field and is collected on the transfer paper P without gaps. Then, they are pressed against the transfer paper P side by the influence of the electrostatic force and the nip pressure to increase the adhesive force of each other, and form a single mass in which the liquid carrier hardly intervenes between the toners. In parallel with the formation of such a mass, the transfer paper P gradually absorbs the liquid carrier in the liquid developer. Then, by the time the first transfer is completed, most of the liquid carrier is absorbed by the transfer paper P, and only a very small amount of layer remains on the toner mass. At the time of the second transfer, a reverse electric field acts on the previously transferred toner mass, but since the liquid carrier is almost exhausted, the mass tends to move in the opposite direction rather than electrophoresis as a whole. . At this time, a small amount of the liquid carrier layer left thereon intervenes between the transfer roller 4 and functions as a release agent. In the case of coated paper having a lower liquid absorbing property than plain paper, the amount of liquid carrier remaining on the toner mass became larger than that of plain paper. Can be

[0015]

The one-pass double-sided image forming apparatus as described above is usually constructed such that the image forming means forms an image on both sides of a transfer sheet as a transfer material. Have been. However, when performing image formation using a general image forming apparatus, a user often forms an image on only one side of a transfer sheet. Therefore, it is desirable that even in this type of one-pass double-sided image forming apparatus, the user can form an image not only on both sides of the transfer paper but also on only one side of the transfer paper.

The present invention has been made in view of the above background, and an object of the present invention is to provide a one-pass double-sided image forming method capable of forming an image on only one side of a recording medium in addition to both sides of the recording medium. An object of the present invention is to provide a forming method and an image forming apparatus, and a transfer method and a transfer apparatus used for the image forming apparatus.

[0017]

In order to achieve the above-mentioned object, a first aspect of the present invention is a first image forming means for forming an image on a surface of a recording medium conveyed by a conveying means; An image forming an image on the front surface and the back surface of the recording medium conveyed by the conveyance unit without reversing the front and back of the recording medium by the second image forming unit for forming an image on the back surface of the recording medium conveyed; A method of forming
A two-sided mode for forming an image on both sides of the recording medium using the image forming unit and the second image forming unit, a surface mode for forming an image only on the surface of the recording medium using the first image forming unit, By using a mode switching unit to switch between a back mode in which an image is formed only on the back surface of the recording medium using the second image forming unit and performing image formation selectively on both sides, the front surface, or the back surface of the recording medium. It is characterized by the following.

In this image forming method, the mode for forming an image on the recording medium by the mode switching means is such that an image is formed on both sides of the recording medium using the first image forming means and the second image forming means. A two-sided mode for forming, a front-side mode for forming an image only on the front surface of the recording medium using the first image forming unit, and an image forming only on the back side of the recording medium using the second image forming unit. The mode can be switched to the back mode. This allows the user to use a one-pass double-sided image forming apparatus to form an image on only one side of the recording medium in addition to both sides of the recording medium, thereby expanding the range of use of the image forming apparatus. You.

According to a second aspect of the present invention, there is provided a conveying means for conveying a recording medium, a first image forming means for forming an image on a surface of the recording medium conveyed by the conveying means, and a recording medium conveyed by the conveying means. A second image forming means for forming an image on the back surface of the medium, wherein the image forming apparatus forms an image on the front and back surfaces of the recording medium conveyed by the conveying means without inverting the recording medium. A two-sided mode in which an image is formed on both sides of the recording medium using the first image forming means and the second image forming means, and an image is formed only on the surface of the recording medium using the first image forming means A mode switching means for switching between the front mode, a back mode in which an image is formed only on the back surface of the recording medium using the second image forming means, and a mode switching means.

In this image forming apparatus, when the mode is switched to the double-sided mode by the mode switching unit, an image is formed on both sides of the recording medium by using the first image forming unit and the second image forming unit. . When the mode is switched to the surface mode, an image is formed only on the surface of the recording medium using the first image forming means. Further, when the mode is switched to the backside mode, an image is formed only on the backside of the recording medium using the second image forming means.

According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the first image forming means includes a first image carrier and a first latent image forming a latent image on the first image carrier. Image forming means;
First developing means for forming a surface toner image on the first image carrier by forming a latent image formed on the first image carrier into a toner image with a developer, and forming the latent image on the first image carrier; A first transfer unit for transferring the formed surface toner image onto a surface of a transfer material as the recording medium, wherein the second image forming unit includes a second image carrier and a latent image on the second image carrier. Second latent image forming means for forming an image, and second developing for forming a back toner image on the second image carrier by forming the latent image formed on the second image carrier into a toner image with a developer Means, and second transfer means for transferring the back toner image formed on the second image carrier to the back surface of the transfer material.

In this image forming apparatus, the surface toner image formed on the first image carrier by the first developing means of the first image forming means is transferred to the first transfer means of the first image forming means. Is transferred to the surface of a transfer material as a recording medium. Further, the second developing means of the second image forming means transfers the back toner image formed on the second image carrier to the transfer material as a recording medium by the second transferring means of the second image forming means. Is transferred to the back side of. Here, the mode in which a toner image is formed on the transfer material by the mode switching means is changed to a front toner image and a rear toner image on both sides of the recording medium using the first image forming means and the second image forming means. A two-sided mode for forming a surface image, a front-side mode for forming a surface toner image only on the front surface of the recording medium using the first image forming unit, and a back-side mode only for the rear surface of the recording medium using the second image forming unit. The mode can be switched to the back mode in which a toner image is formed. This allows
The user can use the one-pass double-sided image forming apparatus to form an image on only one side of the recording medium in addition to both sides of the recording medium, thereby expanding the use range of the image forming apparatus.

According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, the developer comprises a liquid developer in which a toner is dispersed in a carrier liquid, and the first transfer unit applies the toner to the surface toner image. A first transfer electric field forming means for forming a transfer electric field for applying an electrostatic force in a direction toward the surface of the transfer material, wherein the second transfer means forms the transfer electric field with respect to the back toner image. A second transfer electric field forming means for forming a transfer electric field for applying an electrostatic force in a direction toward the back surface is provided.

In this image forming apparatus, the first transfer electric field forming means of the first transfer means causes an electrostatic force in a direction toward the surface of the transfer material to the surface toner image formed by the toner of the liquid developer. , A transfer electric field for providing the transfer is formed. Further, a transfer electric field for applying an electrostatic force in a direction toward the back surface of the transfer material to the back surface toner image formed by the toner of the liquid developer by the second transfer electric field forming unit of the second transfer unit is formed. It is formed.

According to a fifth aspect of the present invention, in the image forming apparatus of the second aspect, the developer comprises a liquid developer in which toner charged to the same polarity is dispersed in a carrier liquid, and the first transfer means includes: A first intermediate transfer member on which the surface toner image formed on the first image carrier is primarily transferred, and an alternating electric field for applying an alternating electric field to the surface toner image primarily transferred on the first intermediate transfer member Forming means, wherein the second transfer means has a coating layer made of an amorphous fluororesin on the surface, and the backside toner image formed on the second image carrier is primarily transferred to the coating layer. And a second intermediate transfer member.

The present inventors prototyped an electrophoresis test apparatus as shown in FIG. 1 in order to observe the state of electrophoresis of toner in a liquid developer. In FIG. 1, an electrophoresis test apparatus 100 includes a transparent glass plate 101, a T-shaped transparent second electrode 102 laminated on the surface thereof, and a migration gap G.
1 and a transparent T-shaped first electrode 103 laminated on a glass plate 101 so as to take a line-symmetrical attitude with respect to the second electrode 102. These first electrode 103 and second electrode 103
Each of the electrodes 102 is made of ITO (indium tin oxide). A conductive tape 105 is conductively connected to an end of the second electrode 102 having a thickness of 150 μm, and the conductive tape 105 is further connected to a power supply 106. Further, a grounded conductive tape 104 is connected to an end of the first electrode 103 laminated with the same thickness.

Using the electrophoresis test apparatus 100 having such a configuration, the toner charged to the positive polarity (+ polarity) is dispersed at a concentration of 15 [wt%] in the insulating liquid carrier.
A migration test of the toner was performed on the liquid developer of [cSt]. Specifically, as shown in FIG.
0 is dropped on the electrophoresis gap G1 and squeezed so as to have a thickness of about 20 [μm]. Then, a high-speed video camera 108 equipped with a 50 × objective lens and a cold light 107 as a non-heat-generating light source And the electrophoresis test apparatus 100 was disposed between them. Then, +10 from the power source 106
00 [V] is output, and the second electrode 102
From the side to the first electrode 103 side,
The above high-speed video camera 108 (Kodak high speed fil
ming camera Model 4540).

Then, immediately after the DC voltage is output from the power supply 106, electrophoresis of the toner toward the first electrode 103 starts, and after several hundred msec, most of the toner Gathered on the first electrode 103 side. At this time, the first electrode 103 where the toner collects is the first electrode 103.
The second electrode 1 which corresponds to the transfer paper in the transfer step and from which the toner is separated
02 corresponds to the photosensitive drum 1.

The output voltage value from the power supply 106 was switched from +1000 [V] to -1000 [V] in order to cause a reverse electric field to act on the toner thus collected.
Then, the reverse migration of the toner did not start immediately after the switching, and the reverse migration of the toner started after a lapse of a slight time lag. In addition, not all the toners start reverse migration at the same time, but as shown in FIG. 4, the toner is gradually separated from the surface of the aggregated toner mass and starts reverse migration. It is considered that the reason why the reverse migration is started little by little is that the adhesion between the toner mass and the first electrode 103 is superior to the adhesion between the toners. Note that FIG. 4 shows that 40 [m
[sec].

Next, the inventors of the present invention set the first electrode 103
A similar migration test was attempted by coating the surface of the sample with an amorphous fluororesin layer. Then, as shown in FIG. 5, it is the same as in the previous migration test that the toner gathers on the first electrode 103 side after several hundred msec, but immediately after the application of the reverse electric field, the toner gathered is removed. Reverse migration was started as a whole as a mass. Then, as shown in FIG.
ec], it reached the second electrode 102 side. First electrode 1
Several hundred msec for electrophoresis (transfer) of toner to 03 side
On the other hand, it took about 1/10 of the time required for reverse migration to the second electrode 102 side. When individual toners are individually electrophoresed, turbulence of a liquid carrier is generated between the toners and hinders the electrophoresis of the toner, whereas when each toner is collectively electrophoresed as a lump, this is a problem. Since no turbulence is generated, it is considered that the migration time has been shortened. In addition, the reason why the electrophoresis was started as a whole while the individual toners were agglomerated is that the adhesion between the fluororesin layer and the toner, to which substances are extremely difficult to adhere, is much weaker than the adhesion between the toners. It is considered that the lump was easily separated from the fluororesin layer.

The invention of claim 5 has been made in view of such an electrophoresis test. In this image forming apparatus, when a back toner image is formed on the second image carrier, each toner is pressed against the second image carrier by electrostatic force to increase the adhesion between the two, and the solid And form a lump of toner. This mass of toner adheres to the second image carrier with a weaker adhesive force than between the toners. Electrophoresis toward the transfer material as a whole mass, not as individual toner. Therefore, the electrophoresis of each toner is not hindered by the turbulence of the carrier generated between the toners, and the back toner image is quickly transferred onto the transfer material.
Thereby, before the front surface toner image already transferred to the front surface of the transfer material is separated from the front surface and the reverse movement is started, the back surface toner image can be transferred from the second image carrier to the back surface of the transfer material. More sure. Therefore, reverse transfer of the surface toner image previously transferred to the transfer material can be reliably suppressed. Here, the case where the front toner image is transferred to the transfer material first has been described, but the rear toner image may be transferred first.

[0032] The invention of claim 6 is the invention of claim 2, 3, or 4.
And a use frequency comparing unit that compares the use frequency of the first image forming unit with the use frequency of the second image forming unit; and a toner image on one of the front surface and the back surface of the transfer material. Forming an image based on the comparison result of the use frequency comparing means, using the image forming means of the first image forming means and the second image forming means which is less frequently used. And a mode selection control means for controlling the mode switching means so as to select the front surface mode or the back surface mode.

In the image forming apparatus according to the second to fifth aspects, an image can be formed on only one side of the recording medium in addition to both sides of the recording medium by using the image forming apparatus of the one-pass double-sided system. However, in such an image forming apparatus,
When a large amount of image formation (printing) is performed in one of the front mode using only the first image forming unit and the back mode using only the second image forming unit, the first printing is performed. The frequency of use of the image means is different from the frequency of use of the second image forming means. As a result, the total use ratio of the first image forming unit and the second image forming unit is biased. (1) The maintenance time of the first image forming unit and the second image forming unit is shifted. . (2) The service life of the transfer means for transferring the transfer material is proportional to the number of transferred transfer materials. It becomes more noticeable. (3) There is a large difference between the amount of developer consumed by the first developing unit of the first image forming unit and the amount of developer consumed by the second developing unit of the second image forming unit. Therefore, in the image forming apparatus according to the fifth aspect, the frequency of use of the first image forming unit is determined by a mode selection control unit that controls the mode switching unit.
A use frequency comparing means for comparing the use frequency of the second image forming means with a use frequency of the second image forming means; and forming a toner image on either the front surface or the back surface of the transfer material, based on a comparison result of the use frequency comparison means. The mode in which image formation is performed using the image forming means that is used less frequently among the front mode and the back mode is selected. Therefore, in this image formation, when forming an image on one side of the transfer material, the image formation is performed in the mode using the image forming means that is less frequently used, among the above-mentioned front-side mode and back-side mode. Thus, there is no large difference between the frequency of use of the first image forming means and the frequency of use of the second image forming means.
The maintenance times of the image forming means and the second image forming means are substantially the same. Further, there is no significant difference between the amount of developer consumed by the first developing unit of the first image forming unit and the amount of developer consumed by the second developing unit of the second image forming unit.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the use frequency comparing means detects a result of the first developer consumption detecting means detecting a developer consumption of the first developing means. And a detection result of the second developer consumption detecting means for detecting the developer consumption of the second developing means,
The frequency of use of the first image forming means is compared with the frequency of use of the second image forming means.

In this image forming apparatus, the detection result of the first developer consumption detecting means for detecting the developer consumption of the first developing means by the use frequency comparing means and the developing result of the second developing means by the second developing means. The frequency of use of the first image forming means and the frequency of use of the second image forming means are compared based on the detection result of the second developer consumption amount detecting means for detecting the amount of developer consumption. As a result, the difference between the amount of developer consumed by the first developing unit and the amount of developer consumed by the second developing unit is reduced.

According to an eighth aspect of the present invention, in the image forming apparatus of the sixth aspect, the use frequency comparing means includes a count value of a first counting means for counting the cumulative consumption number of the transfer material in the surface mode, and The frequency of use of the first image forming unit and the frequency of use of the second image forming unit are compared based on the count value of the second counting unit that counts the cumulative consumption number of the transfer material in the back mode. It is characterized by comprising.

As in the image forming apparatus of claim 7, the frequency of use of the first image forming means is based on the amount of developer consumed by the first developing means and the amount of developer consumed by the second developing means. When comparing the frequency of use of the second image forming means with the frequency of use of the second image forming means, there is a possibility that there is a difference between the life of the driving member of the first image forming means and the life of the driving member of the second image forming means. There is. That is, since the developer is generally replaced or replenished by the user at appropriate times, a case in which a large amount of the developer is biased and replenished to either the first developing unit or the second developing unit may be considered. In such a case, in the image forming apparatus according to the sixth aspect, the first developer is consumed until the amount of developer consumed by the second developer becomes substantially equal. The developing means of the developing means or the second developing means which has been replenished with a large amount of developer will operate more. As a result, there is a difference between the life of the driving member of the first image forming means and the life of the driving member of the second image forming means. Therefore, in this image forming apparatus, the count value of the first counting means for counting the cumulative consumption number of the transfer material in the front mode by the use frequency comparison means and the cumulative consumption number of the transfer material in the back mode are used. Based on the count value of the second counting means for counting
The frequency of use of the first image forming means is compared with the frequency of use of the second image forming means. As a result, the operating rate of the driving member of the first image forming means is substantially the same as the operating rate of the driving member of the second image forming means, and there is no significant difference.
There is no difference between the life of the driving member of the image forming means and the life of the driving member of the second image forming means.

According to a ninth aspect of the present invention, there is provided the image forming apparatus according to the sixth, seventh or eighth aspect, wherein the front mode or the back mode selected by the mode selection control means includes:
In the case where a job for continuously forming an image is executed, a mode switching function canceling means for canceling the mode switching function of the mode switching means until the job is completed is provided. is there.

In the image forming apparatus of the sixth, seventh or eighth aspect, when a job for continuously forming an image is executed, the job is selected by the mode selection control means during the execution of the job. It is conceivable that the front mode or the back mode is switched. As described above, if the mode for forming an image is switched during the execution of the job, the image forming conditions (for example, toner density, etc.) on the transfer material are changed before and after the mode is switched. And print quality may vary. Therefore, in this image forming apparatus, when a job for continuously forming an image is executed, the mode switching function of the mode switching unit is released by the mode switching function releasing unit until the job is completed. . As a result, the mode for forming an image is not switched during the execution of the job, and the print quality becomes uniform.

However, in the image forming apparatus according to the ninth aspect, a large amount of toner is consumed by the execution of the job, and the toner of the developer of the image forming means runs out during the execution of the job. In this case, the job must be stopped. For this reason, in such a case, new work such as re-executing the job or replenishing new toner is required. Therefore, a tenth aspect of the present invention is the image forming apparatus according to the sixth, seventh or eighth aspect, wherein the first toner end detecting means for notifying a state in which the toner of the developer of the first image forming means has run out; (2) Image formation is continuously performed by the second toner end detecting means for notifying a state in which the toner of the developer of the image forming means has run out, and one of the first image forming means or the second image forming means. A job for controlling the mode switching means so as to continue the job using the other image forming means when the toner of the developer of the image forming means runs out during the execution of the job to be performed. And a continuation control means.

In this image forming apparatus, the first toner end detecting means is in a state where the toner of the developer of the first image forming means has run out, or the second toner end detecting means is capable of detecting the toner of the second image forming means. The state in which the toner of the developer has run out is notified. Then, while the job of continuously forming an image is being executed by one of the first image forming unit and the second image forming unit, the developer toner of the image forming unit runs out. At this time, the job is continued using the other image forming means by the job continuation control means for controlling the mode switching means. Therefore, in this image forming apparatus, when the toner of the developer in the image forming unit runs out, the job is continuously executed using another image forming unit. As a result, even in the case described above, there is no need to re-execute the job or replenish new toner.

When a large amount of carrier is consumed by the execution of the job and the carrier of the developer of the image forming means runs out during the execution of the job, the job is similarly stopped. I have to do it. For this reason, in such a case, new work such as re-executing the job or replenishing new toner is required. Therefore, an eleventh aspect of the present invention is the image forming apparatus according to the sixth, seventh or eighth aspect, wherein the first carrier end detecting means for notifying a state in which the carrier of the developer of the first image forming means has run out; (2) Continuous image formation by the second carrier end detecting means for notifying the state in which the developer carrier of the image forming means has run out, and one of the first image forming means or the second image forming means. A job for controlling the mode switching means so as to continue the job using the other image forming means when the developer carrier of the image forming means runs out during the execution of the job to be performed. And a continuation control means.

In this image forming apparatus, the first carrier end detecting means detects that the developer carrier of the first image forming means has run out, or the second carrier end detecting means detects the developer of the second image forming means. A state in which the carrier of the developer has run out is notified. Then, while the job of continuously forming an image is being executed by one of the first image forming unit and the second image forming unit, the developer carrier of the image forming unit runs out. At this time, the job is continued using the other image forming means by the job continuation control means for controlling the mode switching means. Therefore, in this image forming apparatus, when the carrier of the developer of the image forming unit runs out, the job is continuously executed using another image forming unit. As a result, even in the case described above, there is no need to perform a new job or replenish a new carrier.

The twelfth aspect of the present invention provides the tenth or eleventh aspect.
In the image forming apparatus of (1), the developer used in the first image forming unit and the developer used in the second image forming unit are
It is characterized by being the same developer.

In this image forming apparatus, since the developer used in the first image forming means and the developer used in the second image forming means are the same, as described above, Even if the image forming means is switched during the job and the job is continued, a large difference in print quality does not occur.

According to a thirteenth aspect of the present invention,
In the image forming apparatus of 9, 10, 11 or 12, when forming a toner image on either the front surface or the back surface of the transfer material, the first image forming unit and the second image forming unit
An image forming operation control means for stopping the image forming operation on the transfer material by the image forming means which is not selected by the mode selection control means.

In this image forming apparatus, when forming a toner image on either the front surface or the back surface of the transfer material, the image forming control means controls the first image forming means and the second image forming means.
The image forming operation on the transfer material by the image forming unit that is not selected by the mode selection control unit among the image forming units is stopped. This eliminates useless image forming operation of the image forming unit not selected by the mode selection control unit, and extends the life of the image forming unit.

According to a fourteenth aspect of the present invention, in the image forming apparatus of the thirteenth aspect, the image forming operation control means stops driving of the image forming means which is not selected by the mode selection control means. It is characterized by being.

In this image forming apparatus, the drive of the image forming means which is not selected by the mode selection control means is stopped by the drive control means as the image forming operation control means. As a result, useless driving operation of the image forming unit not selected by the mode selection control unit is eliminated, and the life of the drive system of the image forming unit is extended. Also,
The power consumption of the drive power supply of the drive system is reduced, and the running cost can be reduced.

According to a fifteenth aspect of the present invention, the first transfer means for transferring the toner image formed on the first image carrier to the surface of the transfer material conveyed by the conveyance means, and the toner image formed on the second image carrier. A second transfer unit that transfers the transferred toner image to the back surface of the transfer material conveyed by the conveyance unit, and the front and back surfaces of the transfer material conveyed by the conveyance unit without reversing the front and back of the transfer material A transfer method for transferring a toner image onto the first and second image carriers on both surfaces of the transfer material using the first and second transfer units. A two-sided transfer mode for transferring an image, a surface transfer mode for transferring a toner image formed on the first image carrier to only the surface of the transfer material using the first transfer means, and a second transfer means Formed on the second image carrier only on the back surface of the transfer material using A back transfer mode for transferring the toner image, is switched by the transfer mode switching means, it is characterized in that to transfer selectively a toner image with respect to both surfaces, front or back surface of the transfer material.

In this transfer method, the mode for transferring the toner image to the transfer material by the transfer mode switching means is such that the first image is transferred to both surfaces of the transfer material using the first transfer means and the second transfer means. A two-sided transfer mode for transferring each toner image formed on the carrier and the second image carrier;
A surface transfer mode for transferring the toner image formed on the first image carrier only to the surface of the transfer material using the transfer means, and a second image carrying mode only for the surface of the transfer material using the second image forming means. The mode is switched to the backside transfer mode for transferring the toner image formed on the body.

According to a sixteenth aspect of the present invention, there is provided a first transfer means for transferring a toner image formed on a first image carrier to a surface of a transfer material conveyed by a transfer means, and a transfer conveyed by the transfer means. A second transfer means for transferring the toner image formed on the second image carrier to the back surface of the transfer material, wherein the transfer material is transferred by the transfer means without reversing the front and back of the transfer material. A transfer device for transferring a toner image to a back surface, wherein the toner image formed on the first image carrier or the second image is formed on one of a front surface and a back surface of a transfer material conveyed by the conveyance unit. When transferring the toner image formed on the carrier, a transfer function for releasing the transfer function of the first transfer unit and the second transfer unit that is not involved in the transfer of the toner image Characterized by having release means. .

In this transfer device, the toner image formed on the first image carrier or the toner image formed on either the front surface or the back surface of the transfer material conveyed by the conveyance means by the transfer function releasing means, or When transferring the toner image formed on the second image carrier, the transfer function of the transfer unit that is not involved in the transfer of the toner image is released from the first transfer unit and the second transfer unit. Is done. As a result, it is possible to eliminate unnecessary operation of the transfer unit that is not involved in the transfer of the toner image, and it is possible to reduce the running cost of the image forming apparatus equipped with this transfer device.

According to a seventeenth aspect of the present invention, in the transfer device of the sixteenth aspect, the first transfer means transports the transfer material comprising an endless belt rotatably stretched by a plurality of stretch rollers. A first transfer material transport belt as means, and a first transfer material transport belt disposed at a portion opposed to the first image carrier with the first transfer material transport belt interposed therebetween; A first transfer member for moving toward and away from the first transfer member, wherein the second transfer unit is a second transfer unit that transfers the transfer material, which is an endless belt rotatably stretched by a plurality of stretch rollers. A transfer material transport belt, and a second transfer material transport belt disposed at a portion opposed to the second image carrier with the second transfer material transport belt interposed therebetween, and moving the second transfer material transport belt toward and away from the second image carrier. A second transfer member, wherein the transfer function releasing means is provided. When forming a toner image on either the front surface or the back surface of the transfer material, the first transfer is performed such that a transfer material transport belt not involved in transfer of the toner image faces a position separated from the image carrier. And a transfer member displacing means for displacing the member or the second transfer member.

According to the transfer device of the sixteenth aspect, it is possible to eliminate useless operation of the transfer unit that is not involved in the transfer of the toner image. However, in this transfer device, for example, when a liquid developer is used as the developer, the first transfer material transport belt and the first image carrier, or the second transfer material transport belt and the second image When the carrier is kept in contact with the carrier, the toner of the liquid developer is not consumed by the transfer unit in which the transfer function is released, but the carrier of the liquid developer is absorbed by the transfer paper as the transfer material. It may be wasted. In the transfer device according to the aspect of the invention, the transfer member displacing means displaces the first transfer member or the second transfer member, so that the transfer material transport belt not involved in the transfer of the toner image is separated from the image carrier. You will be facing the position. As a result, the transfer material conveying belt that is not involved in the transfer of the toner image and the image carrier are separated from each other, and wasteful consumption of the carrier of the liquid developer is eliminated.

According to an eighteenth aspect of the present invention, in the transfer device according to the seventeenth aspect, the transfer member is constituted by a transfer roller disposed so as to be able to freely contact and separate from the back surface of the transfer material conveying belt. It is assumed that.

In this transfer device, since the transfer member is constituted by a transfer roller which is disposed so as to be capable of coming and going with respect to the back surface of the transfer material conveying belt, the transfer roller is brought into contact with / separated from the transfer member. The toner image and the transfer material can be easily brought into contact with and separated from each other. Further, the transfer roller can have a function as a stretching roller for the transfer material transport belt.

The invention according to claim 19 is the invention according to claims 6, 7, 8,
In the image forming apparatus according to any one of 9, 10, 11, 12, 13 and 14, a first fixing unit for fixing the toner image transferred to the front surface of the transfer material, and a toner image transferred to the back surface of the transfer material are fixed. And forming a toner image on one of the front surface and the back surface of the transfer material. When the toner image is formed on the transfer material of the first fixing device and the second fixing device, The image forming apparatus has a fixing control unit for stopping the fixing operation of the fixing unit on which the image is not transferred.

In this image forming apparatus, when a toner image is formed on either the front surface or the back surface of the transfer material, the toner image is formed on the transfer material of the first fixing means and the second fixing means. The fixing operation of the non-transferred fixing unit is stopped by the fixing control unit. This eliminates useless fixing operation of the fixing unit on which the toner image has not been transferred to the transfer material.

According to the twentieth aspect of the present invention,
In the image forming apparatus according to any one of 9, 10, 11, 12, 13, 14 and 19, the constituent members of the first image forming unit and the second image forming unit and the constituent member of the transport unit are substantially the same mechanical members. It has a life span.

In this image forming apparatus, since the constituent members of the first image forming means and the second image forming means and the constituent member of the conveying means have substantially the same mechanical life, The components of the first image forming unit and the second image forming unit and the component of the transporting unit can be maintained at the same time of maintenance, so that the time and effort for maintenance and the cost for maintenance can be reduced. Become like

According to the twenty-first aspect of the present invention,
In one of the image forming apparatuses 1, 12, 13, 14, 19, and 20, a job for continuously forming an image is executed by one of the first image forming unit and the second image forming unit. On the way, when the job is continued by using the other image forming means by the job continuation control means for controlling the mode switching means, the transfer material on which the toner image is transferred by using the other image forming means. Characterized in that it has a transfer material reversing means for reversing the front and back and discharging it outside the apparatus.

As described above, during the execution of the job for continuously forming an image, the job continuation control means controls, for example, the first toner image forming means for forming the front toner image and the rear toner image. It is assumed that the job has been continued using the second image forming means for forming. In this case, a front toner image is formed on the transfer material on which the job has been executed by the first image forming means, and a back toner image is formed on the transfer material on which the job has been executed by the second image forming means. Will be. For this reason, when the image forming means for executing the job is switched, the image forming surface of the transfer material discharged to the outside of the machine is inverted before and after the switching of the image forming means, so that the print surface is inconsistent. It will be aligned. In this image forming apparatus,
The transfer material reversing means reverses the front and back of the transfer material on which the toner image has been transferred using the other image forming means and discharges the transfer material outside the apparatus. As a result, it is possible to prevent the image forming surface of the transfer material from being inverted before and after the switching of the image forming means and the printed surface from becoming uneven.

According to a twenty-second aspect of the present invention, in the image forming apparatus of the twenty-first aspect, the transfer material reversing means fixes the toner image on the transfer material by the first fixing means or the second fixing means of the nineteenth aspect. Thereafter, the transfer material is disposed at a portion where the front and back of the transfer material are reversed.

In this image forming apparatus, after the toner image is fixed on the transfer material by the first fixing means or the second fixing means, the transfer material reversing means reverses the front and back of the transfer material. . Thus, the transfer material is not inverted before the toner image is fixed, and the unfixed toner image is not disturbed by the inversion.

[0066]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment in which the present invention is applied to an electrophotographic wet printer (hereinafter simply referred to as a printer) which is a wet image forming apparatus will be described.
FIG. 7 is a schematic configuration diagram of the printer according to the present embodiment.
In the figure, the printer includes a first image forming unit 13a.
And a second image forming unit 13b.

First, of these two action units,
The first image forming unit 13a will be described. The first image forming unit 13a includes two image forming apparatuses 14a, 15a,
An optical writing unit 3a, an intermediate transfer belt 16a as a first image carrier, a driving drum 17a, a stretching drum 18a, an AC power supply 19, and the like are provided.

The intermediate transfer belt 16a has a thickness of 0.3
An endless belt-shaped urethane resin film of [mm], a urethane rubber layer of 0.3 [mm] thickness, and a thickness of 0.1 to 0.1 mm
A 1.0 [μm] amorphous fluororesin layer is laminated, and the volume specific resistance value of the entire belt is about 10 ⁸ [Ωc].
m]. The material of this fluororesin layer includes
CYTOP (trade name) manufactured by Asahi Glass Co., Ltd. and silicon-containing organic fluorine-containing polymer manufactured by Daikin Industries, Ltd.
74715). These can be coated with a pure fluororesin on the urethane rubber layer. Before these were developed, it was extremely difficult to coat the surface of urethane rubber with pure fluorocarbon resin, and in many cases, it was coated with a mixed resin of fluorocarbon resin and other binder resin. The liquid repellency and the releasability of the belt were deteriorated as compared with the case of coating with a resin. Further, even if the surface of the urethane rubber could be coated with a pure fluororesin, the durability of the coating layer was extremely poor, and the urethane rubber was immediately peeled off.

The driving drum 17a and the tension drum 18a
This means that the intermediate transfer belt 18a is stretched, and the intermediate transfer belt 18a is moved endlessly in the direction of the arrow in the figure with the rotation of the driving drum 17a which is driven to rotate by a driving unit (not shown).

Each of the two image forming devices 14a and 15a includes a photosensitive drum 1, a corona charger 2, a transfer roller 4, a charge removing unit 5, a drum cleaning device 6, a developing device 50, and the like. In addition, these image forming apparatuses 1
4a and 15a share one optical writing unit 3a.

In the image forming apparatus 14a, the following image forming process is performed. That is, a part of the surface of the photosensitive drum 1 charged uniformly to a predetermined potential by the corona charger 2 while rotating in the direction of the arrow in the drawing is exposed to laser light by the optical writing unit 3a driven based on image information. Is done. The exposed portion moves to a developing area, which is a position facing the developing device 50, after the charged potential is attenuated to form an electrostatic latent image.

In the developing device 50 of the image forming device 14a, a liquid carrier made of an insulating liquid such as silicon oil contains 15 wt% of toner and an appropriate amount of the charge imparting agent C.
A liquid developer having a viscosity of 100 [cSt] in which CA is dispersed is stored. This toner is positively charged in the liquid carrier. Developing roller 51 in developing device 50
Carries a liquid developer on the surface thereof while being rotationally driven by driving means (not shown). A developing bias is applied to the developing roller 51 by a power supply (not shown), and thereby a developing electric field is formed in a developing region between the developing roller 51 and the photosensitive drum 1. The electrostatic latent image moved to the development area is reversely developed by this development electric field to become a toner image. Specifically, in the developing area, the toner located between the developing roller 51 and the electrostatic latent image on the photosensitive drum 1 receives an electrostatic force from the developing roller 51 side toward the photosensitive drum 1 and receives the electrostatic force. Perform electrophoresis toward the latent image. Then, the toner adheres to the electrostatic latent image to form a toner image. On the other hand, the toner located between the developing roller 51 and the background portion of the photosensitive drum 1 receives an electrostatic force in the opposite direction and electrophoreses toward the surface of the developing roller 51. By this electrophoresis, the background portion of the photosensitive drum 1 becomes a non-image portion without toner adhesion.

The photosensitive drum 1 and the transfer roller 4 rotate in the forward direction with the intermediate transfer belt 16a interposed therebetween to form a primary transfer nip. The toner image reversal-developed in the developing area is sandwiched between the primary transfer nips as the photosensitive drum 1 rotates. In the primary transfer nip, a transfer electric field is formed under the influence of a transfer bias applied to the transfer roller 4 from a power supply (not shown), and the toner image is transferred from the photosensitive drum 1 to the intermediate position by the action of the transfer electric field and the nip pressure. The primary transfer is performed on the transfer belt 16a. The toner in the toner image has a binder resin as a main component. During the primary transfer, the toner is pressed against the surface of the intermediate transfer belt 16a under the influence of the transfer electric field and is compressed, thereby increasing the mutual adhesion. , Resulting in a solid toner mass.

The photosensitive drum 1 having passed through the primary transfer nip
After the surface is neutralized by the neutralization means 5, the transfer residual toner adhering to the surface is removed by the drum cleaning device 6.
Is cleaned by the cleaning blade.

Also in the image forming device 15a, a toner image is formed on the photosensitive drum 1 by the same image forming process as that of the image forming device 14a. However, the developing device 50 of the image forming device 15a converts the electrostatic latent image on the photosensitive drum 1 to the image forming device 14a.
The developing device 50a develops a color different from that of the developing device 50a. The color of the toner in the liquid developer is different. Further, the toner images of different colors are primarily transferred by being superimposed on the toner image transferred onto the intermediate transfer belt 16a by the image forming device 14a. Due to this primary transfer, the lump of toner of another color is pressed and integrated with the lump of toner previously formed on the intermediate transfer belt 16a, and the lump of toner of two colors is formed on the intermediate transfer belt 16a. A two-color toner image is formed. The two-color toner image enters a later-described secondary transfer nip as the intermediate transfer belt 16a rotates.

An AC power supply 19 is connected to the tension drum 18a.
This applies an AC secondary transfer bias.

Next, the second image forming unit 13b will be described. Similarly to the first image forming unit 13a, the second image forming unit 13b includes two image forming apparatuses 14b and 15b, an optical writing unit 3b, an intermediate transfer belt 16b as a second image carrier, a driving drum 17b, A tension drum 18b and the like are provided. However, unlike the stretching drum 18a of the first image forming unit 13a, the stretching drum 18b is grounded.

The intermediate transfer belt 16b has the same configuration as the intermediate transfer belt 16a of the first image forming unit 13a.

The second image forming unit 13b includes the tension drum 1
The second transfer nip is formed by bringing the second transfer nip 8b into contact with the stretching drum 18a of the first image forming unit 13a. Also in the second image forming unit 13b, a two-color toner image is formed on the intermediate transfer belt 16b by the same process as that of the first image forming unit 13a.
With the rotation of 6b, it enters the secondary transfer nip. This approach is performed by the intermediate transfer belt 16a of the first image forming unit 13a.
The timing is synchronized with the timing at which the upper two-color toner image enters the secondary transfer nip.

On the other hand, the present printer is provided with a paper feeding device (not shown), so that when the two two-color toner images enter the secondary transfer nip, the transfer paper is moved toward the secondary transfer nip. Send out P. Due to such feeding, in the secondary transfer nip, between the two intermediate transfer belts 16a and 16b, the two-color toner image formed by the first image forming unit, the transfer paper P, and the second image forming unit The formed two-color toner image is sandwiched.

In the secondary transfer nip, the first image forming unit 1
An alternating electric field is formed by the influence of the secondary transfer bias of the alternating current applied to the stretching drum 18a of 3a.

In the secondary transfer nip, as shown in FIG. 8A, between the two intermediate transfer belts 16a and 16b, a two-color toner image or a transfer paper P is formed by a two-color toner. , A liquid carrier layer Ce1, a transfer paper P, a liquid carrier layer Ce2, and a toner mass Ts2 composed of two color toners. In this sandwich state, if the direction of the alternating electric field is such that, for example, the toner T charged positively is electrostatically moved from the upper side to the lower side in the figure, the intermediate transfer belt 16a The lump Ts1 of the toner adhered to the fluororesin layer is quickly separated from the fluororesin layer having excellent liquid repellency, electrophoreses in the liquid carrier layer Ce1, and reaches the transfer paper P. And FIG.
As shown in (b), the sheet is electrostatically pressed against the transfer paper P and adheres to it.

When the direction of the alternating electric field is reversed, the toner mass Ts2 adhering to the fluororesin layer of the intermediate transfer belt 16b is quickly separated from the fluororesin layer having excellent liquid repellency, and the liquid carrier Ce2 is removed. Inside and transfer paper P
Move up to. At this time, the toner mass Ts1 electrophoresed to the transfer paper P first receives an electrostatic force on the reverse movement side toward the intermediate transfer belt 16a, but is not a fluororesin layer having excellent liquid repellency but a liquid carrier. Is strongly attached to the transfer paper P, which takes in a part of the toner into the fiber while absorbing the toner, so that the reverse movement does not immediately start. Further, although the same thickness is shown in the drawing for convenience, many liquid carriers have been absorbed by the transfer paper P, and only the liquid carrier layer Ce1 having a small thickness remains on the moving side. The liquid carrier layer Ce1 functions not as an electrophoretic medium for the toner mass Ts1 but rather as a release agent for promoting the separation of the toner mass Ts1 from the intermediate transfer belt 16a. On the other hand, on the opposite side of the transfer sheet P, the liquid carrier layer Ce2 in contact with the transfer sheet P continues to be absorbed by the liquid carrier layer P, and thus functions not as a release agent but rather as an electrophoretic medium for the toner mass Ts2. Therefore, as shown in FIG. 8C, the toner masses Ts1 and Ts2 are adhered and transferred to both surfaces of the transfer paper P, and only a very small amount of the toner T remains on the surfaces of the intermediate transfer belts 16a and 16b.

As described above, the liquid developer has a viscosity of 10
A high-viscosity and high-concentration toner having a toner concentration of 0 [cSt] and a toner concentration of 15 [wt%] is used. A wet image forming technique using such a liquid developer has recently been devised by the present inventors. is there. Before that, the viscosity was 1-5 [cS
t] and a toner having a low viscosity and a low density of 1 to 3 [wt%]. In such a low-viscosity, low-concentration liquid developer, a large amount of liquid carrier remains even if it is absorbed by the transfer paper P at the transfer nip, and the toner is easily electrophoresed. Surface transfer is extremely difficult. It is considered that it is desirable to adjust the toner concentration to 10 [wt%] or more.

Note that, depending on the timing at which the transfer paper P enters the secondary transfer nip, the direction of the alternating electric field at the beginning of the transfer differs, so that the transfer of the toner mass Ts2 precedes the transfer of the toner mass Ts1. May begin.

The transfer paper P on which the two-color toner image has been transferred on both sides passes through a secondary transfer nip, and is then discharged outside the apparatus via a fixing device (not shown).

FIG. 9 is a schematic structural view showing the developing device 50 of the printer according to the present embodiment. This developing device 50
It comprises a pump section 57, a tank section 59, and a developing section 60.

The pump section 57 is disposed so as to communicate the tank section 59 with the developing section 60, and has an impeller 58 made of an elastic material such as rubber in the middle of the communication path. The impeller 58, which is rotatable by a driving means (not shown), is in close contact with the inner wall of the communication passage and shuts off the communication passage when not rotating. Further, at the time of forward rotation or reverse rotation, the propeller gives a propulsive force to the liquid developer 150 to convey the liquid developer 150 between the tank unit 59 and the developing unit 60. More specifically, the impeller 60 rotates backward just before the developing device main body enters the standby state, and
The entire liquid developer 150 is conveyed into the tank 59. In addition, just before the developing operation is started or during the developing operation, the rotation is properly performed to replenish the developing unit 60 with an appropriate amount of the liquid developer 150. This replenishment is controlled based on a detection result of a liquid level detecting unit (not shown) for detecting the liquid level in the developing unit 60.

The tank section 59 is provided with a stirring blade 55 which is driven to rotate in the horizontal direction by a motor 56, whereby the liquid developer 150 stored in the tank is provided.
Is agitated.

The developing section 60 includes a developing roller 51a as a developer carrier, a coating roller 52, a cleaning blade 53, a metering blade 54, and the like. The developing roller 51a and the application roller 52 come into contact with each other while rotating in the counter direction to form an application nip. The application roller 52 draws up the liquid developer 150 in the developing unit 60 as it rotates. The film thickness of the pumped-up liquid developer 150 is regulated by the metering blade 54 in contact with the application roller 52, and a part of the film is applied to the development roller 51 a by being sandwiched between the application nips. It becomes a liquid thin layer. Then, with the rotation of the developing roller 51a, the developer is conveyed to a developing area which is a position facing a photosensitive drum (not shown), and contributes to the development here. Developing roller 51a that has passed the developing area
The developer thin layer remaining on the surface is
3 and is returned to the tank 59.

[Double-sided transfer test 1] A printer having the above-described configuration was prototyped, and double-sided transfer was tested under the following conditions. In addition, the process linear velocity refers to the intermediate transfer belt 16a,
16b and the linear velocity of each photosensitive drum 1 and the like. Also,
The secondary transfer nip width is defined as 2 in the transport direction of the transfer paper P.
This is the length of the next transfer nip. -Process linear velocity = 300 [mm / sec]-Secondary transfer nip width = 45 [mm]-Transfer paper P passage time through the secondary transfer nip = 150 [mm / sec]
sec] • Transfer paper P = Type6000 manufactured by Ricoh Co., Ltd. • Vp-p of secondary transfer bias = 2 [kV] • Period of secondary transfer bias T = 100 [msec] • Waveform of secondary transfer bias = square wave

As a result, a two-color toner image having a high image density and excellent sharpness could be transferred to both sides of the transfer paper P.

[Double-sided transfer test 2] Next, the same double-sided transfer test was performed by changing the secondary transfer nip width and the secondary transfer nip passage time as follows.・ Secondary transfer nip width = 30 [mm] ・ Secondary transfer nip passage time of transfer paper P = 100 [mm /
sec]

Then, a transfer failure of the two-color toner image occurred on one of the surfaces of the transfer paper P. The cause of such transfer failure is considered as follows. That is, in the double-sided transfer test 2, the passing time of the secondary transfer nip is equal to the period T of the alternating electric field formed in the secondary transfer nip. From 100 msec for one cycle. Therefore, in FIG. 7, when the direction from the upper side to the lower side in the figure is considered as the forward direction, 2
The two two-color toner images facing each other across the transfer paper P at the next transfer nip have an electrostatic force in the forward direction and an electrostatic force in the reverse direction of 50 [each] while passing through the secondary transfer nip. msec]. However, the time of 50 [msec] is a total time, and it is not always the case that each electrostatic force is continuously received for this time. For example, suppose that the transfer paper P enters the secondary transfer nip after 25 [msec] has elapsed after the alternating electric field has switched its direction to the forward direction. Then, the leading end of the two-color toner image (hereinafter, referred to as the front toner image) adhered to the intermediate transfer belt 16a of the first image forming unit causes the transfer paper P to be moved by the influence of the electrostatic force in the forward direction. Start electrophoresis toward the front surface (upper surface in the figure). Since this forward electrostatic force lasts only the remaining 25 [msec],
After 25 [msec], it starts receiving the electrostatic force in the reverse direction.
At this time, it is considered that the leading end portion of the front toner image has not reached the transfer paper P, and the absorption of the liquid carrier by the transfer paper P has not progressed so much. For this reason, the front toner image is not restrained by the adhesive force to the transfer paper P, and starts reverse migration immediately in the abundant liquid carrier, and the intermediate transfer belt 16
It is probable that a U-turn was made to a.

From this, it is needless to say that half of the period T needs to be longer than the time required for the migration of the toner image. In addition to this, at what timing the secondary transfer of the transfer paper P is performed. Even when entering the nip, it is necessary to set the process linear velocity, the cycle T, and the secondary transfer nip width so that the forward and reverse electrostatic forces can be applied continuously for the required migration time. Specifically, these are set so that the nip passing time of the transfer paper P is 1.5 times or more the cycle of the secondary transfer bias. With this setting, even when the transfer body P enters the secondary transfer nip at any timing, the electrostatic force in the direction toward the transfer paper P with respect to the front side toner image and the back side toner image is reliably migrated. It works continuously for the length of time required. Previous double-sided transfer test 1
In such a case, the transfer failure did not occur because of such a setting.

Next, a printer according to another embodiment will be described. In the printer of the embodiment, the double-sided transfer test 1
Even when the two-sided transfer is performed under the same conditions as described above, small two-color toner images transferred on both sides of the transfer paper P may cause small transfer unevenness. The present inventors have investigated the cause of the transfer unevenness and found that there is a problem in how to peel off the transfer paper P from the intermediate transfer belt at the moment when the transfer paper P comes out of the secondary transfer nip. Specifically, as the transfer paper P closely adhered to the intermediate transfer belts 16a and 16b at the secondary transfer nip is vigorously peeled off from the transfer paper P, reverse transfer is more likely to occur. Therefore,
It is desirable that the transfer paper P be peeled off from the intermediate transfer belts 16a and 16b with as little force as possible. However, in the printer shown in FIG. 7, when the transfer paper P is moved closer to one of the intermediate transfer belts to lower the peeling force therefrom downstream of the secondary transfer nip, the transfer paper P is moved to the other intermediate transfer belt. There is a trade-off in which the distance from the transfer belt is increased to increase the peeling force in the future.

Therefore, the present inventors prototyped a printer as shown in FIG. 10, the printer of the first embodiment is different from the printer (FIG. 7) of the embodiment in which the first image forming unit 13a and the second image forming unit 13b face each other in a straight line. Position. The first image forming unit 13a and the second image forming unit respectively include secondary transfer rollers 20a and 20b that form a secondary transfer nip while sandwiching the intermediate transfer belts 16a and 16b between the tension drums 18a and 18b. Have. A DC secondary transfer bias is applied to the secondary transfer rollers 20a and 20b by a power source (not shown).

A guide plate 83 for guiding the moving direction of the transfer paper P is provided downstream of the secondary transfer nip N1 of the first image forming unit 13a.

The transfer paper P is placed in the second image forming unit 13a.
Among the next transfer nip N1 and the secondary transfer nip N2 of the second image forming unit 13b, first, it enters the secondary transfer nip N2. Then, the leading end of the transfer paper P coming out of the secondary transfer nip N2 immediately hits the intermediate transfer belt 16b of the first image forming unit 13a, moves together with the intermediate transfer belt 16b, and is sandwiched between the two stretching rollers 18a, 18b. It is. The transfer paper P sandwiched in this manner is, as shown in FIG.
The position downstream of the second transfer nip N2 is closer to the intermediate transfer belt 16b than the tangent L2 to the tension drum 18b at the outlet of the secondary transfer nip N2. In such a posture,
The peeling force of the transfer paper P from the intermediate transfer belt 16b can be weaker than the posture along the tangent to the tension drum 18b downstream of the secondary transfer nip as in the printer of FIG. Note that, in the present printer, the transfer paper portion downstream of the secondary transfer nip N2 is 45 ° away from the tangent L2.
The arrangement positions of the first image forming unit 13a and the second image forming unit 13b are adjusted so as to take a posture approaching the stretching drum 18b by about [°].

When the leading end of the transfer paper P sandwiched between the two stretching rollers 18a and 18b comes out, it hits the secondary transfer roller 20a of the first image forming unit 13a, and moves with it to perform secondary transfer. It is sandwiched between nips N1. And
After exiting from the secondary transfer nip N1, the guide plate 8
The movement direction is regulated by 3. Due to this regulation, the transfer paper P is moved downstream from the secondary transfer nip N1 by 2
The posture is such that the tangent line L3 to the tension drum 18a at the exit of the next transfer nip N1 is closer to the intermediate transfer belt 16a. In such a posture, as shown in FIG.
The peeling force of the transfer paper P from the intermediate transfer belt 16a can be weaker than the posture along the tangent to the tension drum 18a downstream of the next transfer nip. Note that, in the present printer, the transfer paper portion downstream of the secondary transfer nip N1 is also set to take an attitude such that it is closer to the stretching drum 18a by about 45 [°] than the tangent line L3. .

In the printer of the first embodiment having the above configuration, the secondary transfer bias is used as the secondary transfer bias.
Double-side transfer was performed while applying a DC bias of +1000 [V] to each of 0a and 20b. As a result, double-sided transfer could be performed without causing transfer unevenness on the front side toner image and the back side toner image.

In the printer shown in FIG. 10, the image density of the back side toner image (the two-color toner image transferred to the lower side of the transfer paper P in FIG. 10) is reduced depending on the type of liquid developer used. A situation occurred. Then, when the secondary transfer bias for the secondary transfer roller 20b of the two secondary transfer rollers 20a and 20b was increased beyond +1000 [V], a decrease in image density was suppressed. Therefore, if the toner image to be transferred earlier is more strongly compressed toward the transfer paper P among the toner image to be transferred earlier and the toner image to be transferred later to the transfer paper P, this toner image It was found that the decrease in image density can be suppressed.

However, increasing only one of the secondary transfer biases may cause a problem that two secondary transfer bias power sources are required or discharge is easily caused.

As a method for suppressing the lowering of the image density of the back toner image without causing such a problem, the second method is used.
A method of making the diameter of the stretching drum 18b and the secondary transfer roller 20b of the image forming unit 13b larger than that of the first image forming unit 13a to make the secondary transfer nip N2 longer than the secondary transfer nip N1. Conceivable. However, in this method, the sizes of the tension drum, the secondary transfer roller, and the intermediate transfer belt are made different between the two image forming units 13a and 13b. It causes troubles such as worsening.

Therefore, the present inventors prototyped a printer as shown in FIG. In FIG. 11, the printer according to the second embodiment includes a transfer auxiliary roller pair 21 as a toner image compressing unit in a transport path between the secondary transfer nips N1 and N2.
It has. Transfer paper P that has passed through secondary transfer nip N2
Is a transfer auxiliary roller pair 2 made of an elastic member such as rubber.
1 after passing through the auxiliary transfer nip formed by
It enters the secondary transfer nip N1.

Of the two rollers 21a and 21b in the transfer assist roller pair 21, the roller 21b that contacts the back surface of the transfer sheet P is grounded. The roller 21a is connected to a common power supply so that a transfer assist bias having the same value as that of the two secondary transfer rollers 20a and 20b is applied. The back side toner image secondarily transferred to the back side of the transfer paper P by the secondary transfer nip N2 of the second image forming unit 13b passes through the auxiliary transfer nip formed by the transfer auxiliary roller pair 21 when the transfer auxiliary bias is applied. Is electrostatically compressed toward the back surface of the transfer paper P.

In the printer according to the second embodiment having the above configuration, the roller 21a of the transfer auxiliary roller pair 21 and the two secondary transfer rollers 20a and 20b are respectively +1000.
Double-sided transfer was performed while applying a DC bias of [V]. Then, the two-color toner image could be transferred to both sides of the transfer paper P without lowering the image density of the back side toner image. Therefore, in the printer according to the second embodiment, two secondary transfer bias power supplies are provided, one secondary transfer bias is excessively increased to cause discharge, the number of types of components of the image forming unit is increased, and maintenance is easy. It is possible to suppress a decrease in the image density of the back side toner image without causing a problem such as deterioration.

The one-pass double-sided printer as described above is generally configured such that the image forming means forms an image on both sides of a transfer sheet as a transfer material. When performing image formation, a user often forms an image on only one side of transfer paper. Accordingly, it is desirable that the printer of this type also be configured so that the user can form an image not only on both sides of the transfer paper but also on only one side of the transfer paper.

Therefore, in the printer according to the present embodiment, as shown in FIG. 12, the mode for forming an image (toner image) on the transfer paper P by the mode switching means 200 is set to the first image forming unit 13a. And a two-sided mode 200A in which images are formed on both sides of the transfer sheet P using both the second image forming unit 13b, and an image (surface toner image) only on the surface of the transfer sheet P using the first image forming unit 13a. The mode is switched between a front surface mode 200B to be formed and a back surface mode 200C for forming an image (backside toner image) only on the back surface of the transfer paper P using the second image forming unit 13b.

Thus, the user can use the one-pass double-sided printer to print the transfer paper P on both sides,
An image can be formed on only one side of the transfer paper P,
The range of use of the printer is expanded.

By the way, either one of the front mode 200B using only the first image forming unit 13a or the back mode 200b using only the second image forming unit 13b forms a large amount of images (printing). It is assumed that In this case, the frequency of use of the first image forming unit 13a differs from the frequency of use of the second image forming unit 13b.

As a result, the total use ratio of the first image forming unit 13a and the second image forming unit 13b is biased. Therefore, (1) the maintenance time of the first image forming unit 13a and the maintenance time of the second image forming unit 13b are shifted. (2) Since the life of the transporting means for transporting the transfer paper P is proportional to the number of transported transfer papers P, maintenance of the transporting means and the first image forming unit 13a or the second image forming unit 13b which is used less frequently is performed. The timing shift becomes more pronounced. (3) A large difference occurs between the developer consumption of the developing device of the first image forming unit 13a and the developer consumption of the developing device of the second image forming unit 13b.

In the printer according to the present embodiment, the frequency of use of the first image forming unit 13a is compared with the frequency of use of the second image forming unit 13b. When forming a toner image on either the front surface or the back surface of the transfer paper P, the first image forming unit 13a and the second image forming unit 13b are used based on the comparison result of the frequency of use. The mode switching means 2 to select the front mode 200B or the back mode 200C so as to form an image using an image forming unit which is used less frequently.
00 is controlled.

In this printer, when forming an image on one side of the transfer sheet P, the image is formed in the mode using the image forming unit which is used less frequently, of the front mode 200B or the back mode 200C. Will be Thus, there is no large difference between the frequency of use of the first image forming unit 13a and the frequency of use of the second image forming unit 13b, and the first image forming unit 13a and the second image forming unit 13b Maintenance time is almost the same.

Here, as a method of comparing the frequency of use of the first image forming unit 13a with the frequency of use of the second image forming unit 13b, the developer consumption of the developing device of the first image forming unit 13a is described. And a method of comparing the amount of developer consumed by the developing device of the second image forming unit 13b with the amount of developer consumed. As a result, there is no significant difference between the amount of developer consumed by the developing device of the first image forming unit 13a and the amount of developer consumed by the second developing device of the second image forming unit 13b.

Another method of comparing the frequency of use of the first image forming unit 13a with the frequency of use of the second image forming unit 13b is as follows: And the count value
It is also possible to use a count value obtained by counting the cumulative number of sheets of the transfer sheet P in the back mode 200C.

When the frequency of use of the first image forming unit 13a and the frequency of use of the second image forming unit 13b are compared based on the amount of developer consumed by the developing device, the respective image forming units There is a possibility that the life of the driving member may differ. That is, since the developer is generally replaced or replenished by the user at appropriate times, a case in which a large amount of the developer is biased and replenished to either the first developing unit or the second developing unit may be considered. In such a case, the developing device in which a large amount of the developer is replenished operates until the developer consumption of each developing device becomes substantially equal. As a result, the life of the driving member of the first image forming unit 13a and the second image forming unit 1
3b, the life of the driving member will be different.

On the other hand, the frequency of use of the first image forming unit 13a is compared with the frequency of use of the second image forming unit 13b by using the count value of the cumulative consumption number of the transfer sheets P. The operating rate of the driving member of the first image forming unit 13a is substantially the same as the operating rate of the driving member of the second image forming unit 13b. Thus, there is no difference between the life of the driving member of the first image forming means and the life of the driving member of the second image forming means.

When a job for continuously forming an image is executed in the printer, the mode switching means 200 is executed during the execution of the job.
The front mode 200B or the back mode 2
00C may be switched. As described above, if the mode for forming an image is switched during the execution of the job, the image forming conditions (for example, toner density, etc.) on the transfer sheet P are changed before and after the mode is switched. ) Is different, and the print quality may vary.

Therefore, in the printer according to the present embodiment, when a job for continuously forming an image is executed, the mode switching means 20 until the job is completed.
Release the mode switching function of 0. As a result, the mode for forming an image is not switched during the execution of the job, and the print quality becomes uniform.

However, as described above, if the mode switching function of the mode switching means 200 is canceled until the job is completed, a large amount of toner is consumed by the execution of the job, and the job is executed. If the developer of the image forming unit runs out of toner during the operation, the job must be stopped. For this reason, in such a case, new work such as re-executing the job or replenishing new toner is required.

Therefore, in the printer of this embodiment, the state in which the toner of the developer of the first image forming unit 13a has run out and the state of the developer of the second image forming unit 13b are A state in which the toner has run out can be detected. While one of the first image forming unit 13a and the second image forming unit 13b is executing a job for continuously forming an image, the toner end detecting unit develops the image forming unit. When the state in which the toner of the agent is exhausted is detected, the mode switching means 200 is used to continuously execute the job using the other image forming unit. As a result, even in the case described above, there is no need to re-execute the job or replenish new toner.

By the way, if a large amount of carrier is consumed by the execution of the job and the carrier of the developer of the image forming means runs out during the execution of the job, the job is similarly stopped. I have to do it. For this reason, in such a case, new work such as re-executing the job or replenishing new toner is required.

In such a case, the state in which the carrier of the developer in the first image forming unit 13a and the second image forming unit 13b has run out is detected by the carrier end detecting means. Then, while a job of continuously forming an image is being executed by one of the first image forming unit 13a and the second image forming unit 13b,
When the carrier end detecting means detects that the developer carrier of the image forming unit has run out,
By the mode switching means 200, the job is continuously executed using the other image forming unit. As a result, even in the case described above, there is no need to re-execute the job or replenish new toner.

Here, it is preferable that the developer used in the first image forming unit 13a and the developer used in the second image forming unit 13b are the same.

As described above, the first image forming unit 13a
When the same developer is used in the second image forming unit 13b and the second image forming unit 13b, even if the image forming unit is switched and the job is continued in the middle of the job, a large difference occurs in print quality. Disappears.

When forming a toner image on either the front surface or the back surface of the transfer sheet P, the image forming operation on the transfer sheet P by the unused image forming unit is stopped. Is preferred. This eliminates useless image forming operation of the image forming unit that is not used, and extends the life of the image forming unit.

In particular, by stopping the driving of the image forming unit that is not being used, useless driving operation of the image forming unit that is not used is eliminated, and the life of the drive system of the image forming unit is extended. Become. In addition, the power consumption of the driving power supply of the driving system is reduced, and the running cost can be reduced.

As the means for conveying the transfer paper P, for example, as shown in FIG. 13, conveying rollers 400a and 500a as a plurality of stretching rollers, shift correction rollers 400b and 500b, and tension rollers 400c and 50c.
The transfer material transport belts 400 and 500 may be endless belts that are rotatably stretched by Oc.

However, when a liquid developer comprising a toner and a carrier is used as the developer, the secondary transfer rollers 20a and 20b and the transfer material transport belts 400 and 500 are kept in contact with each other. In the state of
Although the toner of the developer of the image forming unit on which the image formation is stopped is not consumed, the carrier of the developer is absorbed by the transfer paper P and consumed.

Therefore, in the printer according to the present embodiment, the inner peripheral surfaces of the transfer material conveying belts 400 and 500 are pressed by the transfer rollers 20a and 20b to be conveyed by the transfer material conveying belts 400 and 500. The transfer paper P to be transferred is brought into contact with and separated from the intermediate transfer belts 16a and 16b on which the toner images are secondarily transferred, and the front toner image and the back toner image are selectively secondarily transferred to the front and back surfaces of the transfer paper P. The configuration is as follows.

Thus, when forming a toner image on one of the front surface and the back surface of the transfer paper P, one of the first image forming unit 13a and the second image forming unit 13b which is not operated is used. The transfer material transport belt can be separated from the intermediate transfer belt of the image forming unit. From the transfer member displacing mechanism to face a position separated from the inner peripheral surface of the transfer material transport belt. Thus, the intermediate transfer belts 16a and 16b and the transfer material transport belt 40
By separating from 0,500, the carrier of the liquid developer is not absorbed by the transfer paper P and consumed.

On the other hand, as a fixing device 300 for fixing the front toner image transferred to the front surface of the transfer paper P and the back toner image transferred to the rear surface of the transfer paper P, for example, as shown in FIG. And a pair of heating rollers 300a and 300b that rotate in contact with each other to heat and fix the toner image on the transfer material by a built-in heater.

Here, when forming a toner image on either the front surface or the back surface of the transfer paper P, the fixing device 3
00, it is preferable to stop the fixing operation of the heating roller on which the toner image is not transferred onto the transfer paper P.
As a result, useless fixing operation of the heating roller on which the toner image is not transferred onto the transfer sheet P is eliminated. Also,
The power consumption of the heating roller on which the toner image is not transferred to the transfer paper P is reduced, and the running cost can be reduced.

Further, in the printer of the present embodiment, the components of the first image forming unit 13a and the second image forming unit 13b and the component of the transporting means are members having substantially the same mechanical life. Configure it. This makes it possible to match the maintenance time of the constituent members of each image forming unit with the constituent members of the transporting means, thereby reducing maintenance labor and costs for maintenance.

During the execution of the job for continuously forming images, for example, the first image forming unit 13a for forming a front toner image is changed to the second image forming unit 13b for forming a back toner image. Assume that the job has been continued using. In this case, a front toner image is formed on the transfer paper P on which the job has been executed by the first image forming unit, and a back toner image has been formed on the transfer paper P on which the job has been executed by the second image forming unit. Will be formed. For this reason, when the image forming unit that executes the job is switched, the image forming surface of the transfer paper P discharged outside the machine is reversed before and after the image forming unit is switched, and the print surface is changed. Become irregular.

Therefore, the printer according to the present embodiment includes the first image forming unit 13a or the second image forming unit 13a.
b, while the job for continuously forming an image is being executed by one of the image forming units b.
00, when the job is continued using the other image forming unit, the transfer sheet P on which the toner image has been transferred using the other image forming unit is turned over and discharged outside the machine. A material reversing unit 600 is provided.

Accordingly, in this printer, when the image forming unit is switched by the transfer material reversing unit 600, the transfer paper P on which the toner image has been transferred is inverted and discharged outside the apparatus. This prevents the image forming surface of the transfer paper P from being inverted before and after the switching of the image forming units, and the printing surface from becoming uneven.

The transfer material reversing unit 600 is disposed at a portion where the transfer paper P is turned over after the toner image is fixed on the transfer paper P by the fixing device 300. This prevents the transfer paper P from being inverted before the toner image is fixed, and prevents the unfixed toner image from being disturbed by the inversion.

Although a printer provided with an intermediate transfer belt as an intermediate transfer member has been described above, the present invention can be applied to an image forming apparatus provided with another intermediate transfer member such as an intermediate transfer drum. .

Although the printer which performs double-side transfer in the secondary transfer step has been described, double-side transfer is performed in the primary transfer step from the photosensitive drum 1 to the transfer paper P as shown in FIG. You can also. In such a configuration, 2
Since the next transfer step is omitted, the image forming speed can be increased as compared with the case where the secondary transfer is performed.

Further, the printer adopting the electrophotographic method of developing an electrostatic latent image formed on a latent image carrier such as a photosensitive drum has been described. However, a liquid developer is applied to a recording medium by a piezoelectric element or an electrode. The present invention is also applicable to an image forming apparatus that forms an image by flying.

[0143]

According to the first aspect of the present invention, the mode for forming an image on the recording medium is set by the mode switching means using the first image forming means and the second image forming means. A two-sided mode for forming an image on both sides, a front-side mode for forming an image only on the front side of the recording medium using the first image forming unit, and a front-side mode for forming an image only on the front side of the recording medium using the second image forming unit. The mode can be switched to a back mode in which an image is formed. As a result, the user can form an image on only one side of the recording medium in addition to both sides of the recording medium using the one-pass double-sided image forming apparatus, thereby expanding the range of use of the image forming apparatus. Has an excellent effect.

Claims 2, 3, 4, 5, 6, 7, 8, 9,
10, 11, 12, 13, 14, 15, 16, 17, 1
According to the invention of 8, 19 or 20, images can be formed on both sides of the recording medium by switching to the duplex mode by the mode switching means, and images can be formed only on the surface of the recording medium by switching to the surface mode. Further, there is an excellent effect that an image can be formed only on the back surface of the recording medium by switching to the back surface mode.

In particular, according to the invention of claim 6, when forming an image on one side of the transfer material, the image is formed in the mode using the less frequently used image forming means in the front mode or the back mode. The formation takes place. Thus, there is no large difference between the frequency of use of the first image forming means and the frequency of use of the second image forming means, and the maintenance of the first image forming means and the second image forming means is not performed. The timing is almost the same. Also, there is an excellent effect that the difference between the amount of developer consumed by the first developing unit of the first image forming unit and the amount of developer consumed by the second developing unit of the second image forming unit is not so large. .

According to the seventh aspect of the present invention, the first
There is an excellent effect that the difference between the developer consumption of the developing means and the developer consumption of the second developing means is reduced.

According to the eighth aspect of the present invention, the first type
The operating rate of the driving member of the image forming means and the operating rate of the driving member of the second image forming means are substantially the same, so that there is no significant difference, and the life of the driving member of the first image forming means is reduced. There is an excellent effect that there is no difference in the life of the driving member of the second image forming means.

According to the ninth aspect of the present invention, the mode for forming an image is not switched during the execution of the job, and there is an excellent effect that the print quality becomes uniform.

According to the tenth aspect, when the toner of the developer in the image forming means runs out, the job is continuously executed using another image forming means. Accordingly, even in the case described above, there is an excellent effect that new labor such as re-executing the job and replenishing new toner does not occur.

According to the eleventh aspect of the present invention, when the developer carrier in the image forming means runs out, the job is continuously executed using another image forming means. Thus, even in the case described above, there is an excellent effect that new labor such as re-executing the job or replenishing a new carrier does not occur.

According to the twelfth aspect of the present invention, the developer used in the first image forming means and the developer used in the second image forming means are the same developer. As described above, even when the image forming means is switched and the job is continued during the job, there is an excellent effect that a large difference in print quality does not occur.

According to the thirteenth aspect of the present invention, there is no wasteful image forming operation of the image forming means not selected by the mode selection control means, and the life of the image forming means is prolonged. effective.

According to the fourteenth aspect of the present invention, there is no needless driving operation of the image forming means that is not selected by the mode selection control means, and the life of the drive system of the image forming means is extended. Further, there is an excellent effect that the power consumption of the drive power supply of the drive system is reduced, and the running cost can be reduced.

According to the fifteenth aspect, the mode for transferring the toner image onto the transfer material is set by the transfer mode switching means.
A two-sided transfer mode for transferring each toner image formed on the first image carrier and the second image carrier to both surfaces of the transfer material using the first transfer unit and the second transfer unit; A surface transfer mode for transferring the toner image formed on the first image carrier only to the surface of the transfer material by using the second image forming means; The mode can be switched to a backside transfer mode for transferring the formed toner image. As a result, there is an excellent effect that it is possible to use the one-pass double-sided image forming apparatus to transfer not only both sides of the transfer material but also only one surface of the transfer material.

According to the sixteenth to eighteenth aspects of the present invention, it is possible to eliminate the useless operation of the transfer means which is not involved in the transfer of the toner image, and to reduce the running cost of the image forming apparatus equipped with this transfer device. There is an excellent effect that reduction can be achieved.

In particular, according to the seventeenth aspect of the present invention, the first transfer member or the second transfer member is displaced by the transfer member displacing means, so that the transfer material conveying belt not involved in the transfer of the toner image carries the image. You will be facing a position away from your body. As a result, the transfer material transport belt not involved in the transfer of the toner image and the image carrier are separated from each other. For example, when a liquid developer is used as a developer, wasteful consumption of the carrier of the liquid developer is reduced. There is an excellent effect that it can be eliminated.

According to the eighteenth aspect of the present invention, since the transfer member is constituted by a transfer roller disposed so as to be capable of coming and going with respect to the back surface of the transfer material conveying belt, the transfer roller is in contact with the transfer roller. By the separating operation, the toner image and the transfer material can be easily brought into contact with and separated from each other. Also,
There is an excellent effect that the transfer roller can have a function as a stretching roller for the transfer material conveying belt.

Further, according to the nineteenth aspect of the invention, there is an excellent effect that the useless fixing operation of the fixing means on which the toner image is not transferred to the transfer material is eliminated.

According to the twentieth aspect, the constituent members of the first image forming means and the second image forming means and the constituent member of the transfer means have substantially the same mechanical life. And the constituent members of the first image forming means and the second image forming means,
This makes it possible to match the timing of the maintenance with the components of the transporting means, and has an excellent effect that it is possible to reduce the labor for maintenance and the cost for maintenance.

According to the twenty-first aspect of the present invention, the transfer material reversing means reverses the front and back of the transfer material on which the toner image has been transferred by using the other image forming means and discharges the transfer material outside the machine. You. As a result, there is an excellent effect that the image forming surface of the transfer material is not reversed before and after the switching of the image forming means and the printed surface is not aligned.

According to the twenty-second aspect of the present invention, after the toner image is fixed on the transfer material by the first fixing means or the second fixing means, the transfer material reversing means sets the front and back of the transfer material. Is inverted. Thus, there is an excellent effect that the transfer material is not inverted before the toner image is fixed, and the unfixed toner image is not disturbed by the inversion.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an electrophoresis test device prototyped by the present inventors.

FIG. 2 is an explanatory view illustrating a migration test method using the same migration test apparatus.

FIG. 3 is a schematic diagram showing a state of electrophoresis of toner observed in a migration test using the same migration test apparatus.

FIG. 4 shows a case where a reverse electric field is formed from the state of FIG.
c] A schematic diagram showing a state of electrophoresis of the toner when a lapse has elapsed.

FIG. 5 is a schematic diagram showing the state of toner electrophoresis observed in an improved apparatus in which the first electrode of the electrophoresis test apparatus is coated with an amorphous fluororesin layer.

FIG. 6 shows a case where a reverse electric field is formed from the state of FIG.
c] A schematic diagram showing a state of electrophoresis of the toner when a lapse has elapsed.

FIG. 7 is a schematic configuration diagram of a printer according to the embodiment.

FIGS. 8A to 8C are enlarged schematic diagrams each showing a state of a toner image in a secondary transfer nip.

FIG. 9 is a schematic configuration diagram showing a developing device of the printer.

FIG. 10 is a schematic configuration diagram illustrating a printer according to the first embodiment.

FIG. 11 is a schematic configuration diagram illustrating a printer according to a second embodiment.

FIG. 12 is a block diagram for explaining a mode switching unit of the printer according to the embodiment of the present invention.

FIG. 13 is a schematic configuration diagram of a printer according to the embodiment of the invention.

FIG. 14 is a schematic configuration diagram of a transfer portion of a conventional printer.

FIG. 15 is a diagram illustrating a state in which two sides of the transfer paper P face each other via the transfer paper P;
FIG. 2 is a schematic diagram illustrating two toner images.

FIG. 16 is a schematic configuration diagram showing a conventional image forming apparatus.

[Explanation of symbols]

 13a First image forming unit 13b Second image forming unit 14, 15 Image forming device 16a, b Intermediate transfer belt 17a, b Drive drum 18a, b Stretch drum 19 AC power supply 20a, 20b Secondary transfer roller 21 Transfer assist roller pair Reference Signs List 30 fixing device 50 developing device 80, 81 intermediate transfer drum 83 guide plate 100 migration test device 101 glass plate 102 second electrode 103 first electrode 104, 105 conductive tape 150 liquid developer 200 mode switching means 200A double-sided mode 200B surface mode 200C Back mode 300 Fixing device 400,500 Transfer material transport belt 600 Transfer material reversing unit T Toner P Transfer paper

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B65H 5/02 G03G 15/00 106 2H072 G03G 15/00 106 518 3F049 518 15/16 5C072 15/16 B41J 3 / 00 S 21/14 G03G 21/00 372 H04N 1/04 H04N 1/12 Z (72) Inventor: Katsuo Sakai 1-36 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. 2C061 AP03 AP04 AQ06 AR01 AR03 AS02 HK15 HN20 HV14 HV44 HV49 2C062 RA06 2H027 DA44 DA45 DC02 DE07 DE09 EC06 ED24 EE02 EE07 EE08 EF09 FA13 FA35 FA37 FB18 2H028 BA06 BA09 BA14 BB02 BB04 2H03 A03A23A23A23A23A23A23A23A23A23A23A23A23A23A3 BA14 DA03 LA02 LA05 LA07 5C072 AA03 NA01 WA02 XA01 XA04

Claims (22)

[Claims] A first image forming unit that forms an image on a front surface of a recording medium conveyed by the conveying unit; and a second image forming unit that forms an image on the back surface of the recording medium conveyed by the conveying unit. An image forming method for forming an image on a front surface and a back surface of a recording medium conveyed by the conveying unit without reversing the front and back of the recording medium, wherein the first image forming unit and the second image forming unit A two-sided mode for forming an image on both sides of the recording medium using the first image forming means; a surface mode for forming an image only on the surface of the recording medium using the first image forming means; An image forming method, wherein a mode switching unit switches between a back mode and an image forming mode only on the back surface of a recording medium to selectively form an image on both sides, the front surface, or the back surface of the recording medium. 2. A conveying means for conveying a recording medium, a first image forming means for forming an image on a front surface of the recording medium conveyed by the conveying means, and an image on a back surface of the recording medium conveyed by the conveying means. An image forming apparatus for forming an image on a front surface and a back surface of a recording medium conveyed by the conveying unit without reversing the front and back of the recording medium. A two-sided mode in which an image is formed on both sides of the recording medium using the image forming unit and the second image forming unit, a surface mode in which an image is formed only on the surface of the recording medium using the first image forming unit, An image forming apparatus comprising: a back surface mode for forming an image only on the back surface of the recording medium using a second image forming unit; and a mode switching unit for switching each mode. 3. An image forming apparatus according to claim 2, wherein said first image forming means comprises: a first image carrier; a first latent image forming means for forming a latent image on said first image carrier; First developing means for forming a surface toner image on the first image carrier by forming a latent image formed on the first image carrier into a toner image with a developer, and forming the latent image on the first image carrier; A first transfer unit for transferring the formed surface toner image onto a surface of a transfer material as the recording medium, wherein the second image forming unit includes a second image carrier and a latent image on the second image carrier. Second latent image forming means for forming an image, and second developing for forming a back toner image on the second image carrier by forming the latent image formed on the second image carrier into a toner image with a developer Means, and second transfer means for transferring the back toner image formed on the second image carrier to the back surface of the transfer material. Image forming device. 4. The image forming apparatus according to claim 3, wherein said developer comprises a liquid developer in which a toner is dispersed in a carrier liquid, and said first transfer means is configured to transfer said transfer material to said surface toner image. A first transfer electric field forming means for forming a transfer electric field for applying an electrostatic force in a direction toward the front surface of the transfer material; An image forming apparatus comprising: a second transfer electric field forming unit that forms a transfer electric field for applying an electrostatic force. 5. An image forming apparatus according to claim 3, wherein said developer is a liquid developer in which toner charged to the same polarity is dispersed in a carrier liquid, and said first transfer means is said first image carrier. A first intermediate transfer body on which a surface toner image formed on the body is primarily transferred; and an alternating electric field forming means for applying an alternating electric field to the surface toner image primarily transferred on the first intermediate transfer body. The second transfer means has a coat layer made of an amorphous fluororesin on the surface, and the second transfer means on which the back toner image formed on the second image carrier is primarily transferred to the coat layer. An image forming apparatus comprising an intermediate transfer member. 6. The image forming apparatus according to claim 3, wherein the use frequency comparing means compares the use frequency of the first image forming means with the use frequency of the second image forming means. When forming a toner image on either the front or back surface of the material,
The front mode or the back mode in which an image is formed by using an image forming unit of the first image forming unit and the second image forming unit that is less frequently used based on a comparison result of the use frequency comparing unit. And a mode selection control means for controlling the mode switching means so as to select the image forming apparatus. 7. The image forming apparatus according to claim 6, wherein the use frequency comparing unit detects a detection result of the first developer consumption amount detecting unit for detecting a developer consumption amount of the first developing unit and the second use frequency comparison unit. The frequency of use of the first image forming means and the frequency of use of the second image forming means are compared based on the detection result of the second developer consumption detecting means for detecting the amount of developer consumed by the developing means. An image forming apparatus characterized in that: 8. The image forming apparatus according to claim 6, wherein the use frequency comparing means includes a count value of a first counting means for counting a cumulative consumption number of the transfer material in the front mode, and a transfer value in the back mode. Based on the count value of the second counting means for counting the cumulative consumption number of materials,
An image forming apparatus configured to compare the frequency of use of the first image forming means with the frequency of use of the second image forming means. 9. The image forming apparatus according to claim 6, wherein the job for continuously forming an image is executed by the front mode or the back mode selected by the mode selection control means. Until the job is finished
An image forming apparatus comprising a mode switching function canceling unit for canceling a mode switching function of the mode switching unit. 10. An image forming apparatus according to claim 6, wherein said first image forming means includes a first toner end detecting means for notifying a state in which toner of a developer has run out, and said second image forming means. The second toner end detecting means for notifying the state in which the toner of the developer has run out and the job for continuously forming an image by one of the first image forming means and the second image forming means are executed. A job continuation control unit that controls the mode switching unit so as to continue the job by using the other image forming unit when the developer of the image forming unit runs out of toner during the operation. An image forming apparatus comprising: 11. An image forming apparatus according to claim 6, 7 or 8, wherein said first image forming means has a first carrier end detecting means for informing that the carrier of the developer has run out, and said second image forming means. The second carrier end detecting means for notifying the state in which the carrier of the developer has run out, and a job for continuously forming an image by one of the first image forming means and the second image forming means is executed. A job continuation control unit that controls the mode switching unit so that when the developer carrier of the image forming unit runs out during the process, the job is continued using the other image forming unit. An image forming apparatus comprising: 12. The image forming apparatus according to claim 10, wherein a developer used in said first image forming means and a developer used in said second image forming means are the same developer. Characteristic image forming apparatus. 13. The image forming apparatus according to claim 6, 7, 8, 9, 10, 11, or 12, wherein when forming a toner image on one of a front surface and a back surface of the transfer material, the first operation is performed. Image forming operation control means for stopping the image forming operation on the transfer material by the image forming means which is not selected by the mode selection control means among the image forming means and the second image forming means; An image forming apparatus comprising: 14. An image forming apparatus according to claim 13, wherein said image forming operation control means is a drive control means for stopping the driving of the image forming means which is not selected by said mode selection control means. Image forming apparatus. 15. A first transfer device for transferring a toner image formed on a first image carrier to a surface of a transfer material conveyed by a conveying means.
A transfer unit, and a second unit that transfers the toner image formed on the second image carrier to the back surface of the transfer material conveyed by the conveyance unit.
A transfer means for transferring a toner image to a front surface and a back surface of the transfer material conveyed by the transfer means without reversing the front and back of the transfer material by the transfer means, wherein the first transfer means and the second transfer means A two-sided transfer mode for transferring each toner image formed on the first image carrier and the second image carrier to both surfaces of the transfer material using a means, and a transfer mode of the transfer material using the first transfer means. A surface transfer mode for transferring the toner image formed on the first image carrier only on the front surface, and a toner image formed on the second image carrier only on the back surface of the transfer material using the second transfer means. A transfer method, wherein a transfer mode switching unit switches a toner image to a back side transfer mode to transfer a toner image selectively to both sides, a front side, or a back side of the transfer material. 16. A first image transfer apparatus for transferring a toner image formed on a first image carrier onto a surface of a transfer material conveyed by a conveyance unit.
A transfer unit, and a second unit that transfers the toner image formed on the second image carrier to the back surface of the transfer material conveyed by the conveyance unit.
A transfer device for transferring a toner image to a front surface and a back surface of the transfer material conveyed by the conveyance device without reversing the front and back of the transfer material, the transfer device comprising: When transferring the toner image formed on the first image carrier or the toner image formed on the second image carrier to either one of the front surface and the back surface of the material, the first transfer means Of the second transfer means,
A transfer device comprising a transfer function canceling unit for canceling a transfer function of a transfer unit that is not involved in the transfer of the toner image. 17. The transfer device according to claim 16, wherein the first transfer means is a first transfer means for transferring the transfer material, which is an endless belt rotatably stretched by a plurality of stretch rollers. A transfer material transport belt, and a first transfer material transport belt disposed at a position opposed to the first image carrier with the first transfer material transport belt interposed therebetween, and moving the first transfer material transport belt toward and away from the first image carrier. A first transfer member, wherein the second transfer means is a second transfer material transport belt as a transport means for transporting the transfer material comprising an endless belt rotatably stretched by a plurality of stretch rollers. A second transfer member disposed at a position facing the second image carrier with the second transfer material transport belt interposed therebetween, and configured to move the second transfer material transport belt toward and away from the second image carrier; The transfer function releasing means is provided with The first transfer member or the second transfer member such that a transfer material transport belt not involved in transfer of the toner image faces a position separated from the image carrier when forming a toner image on one of the surface and the back surface. A transfer device comprising a transfer member displacing means for displacing a member. 18. The transfer device according to claim 17, wherein the transfer member is constituted by a transfer roller disposed so as to be able to freely contact and separate from a back surface of the transfer material conveying belt. 19. The method of claim 6, 7, 8, 9, 10, 11, 1.
The image forming apparatus according to any one of 2, 13 and 14, wherein a first image fixing the toner image transferred to the surface of the transfer material
A fixing unit for fixing the toner image transferred to the back surface of the transfer material; and a first fixing unit for forming the toner image on one of the front surface and the back surface of the transfer material. An image forming apparatus comprising: a fixing control unit that stops a fixing operation of a fixing unit that is not involved in fixing the toner image, of the fixing unit and the second fixing unit. 20. The method according to claim 6, 7, 8, 9, 10, 11, 1.
2. The image forming apparatus according to 2, 13, 14 or 19, wherein: constituent members of the first image forming unit and the second image forming unit;
The image forming apparatus according to claim 1, wherein the component of the conveying unit has substantially the same mechanical life. 21. The method of claim 9, 10, 11, 12, 13, 1.
In the image forming apparatus of (4), (19) or (20), the mode switching is performed while a job for continuously forming an image is being executed by one of the first image forming unit and the second image forming unit. When the job is continued using the other image forming means by the job continuation control means for controlling the means, the transfer material on which the toner image has been transferred using the other image forming means is inverted. An image forming apparatus comprising a transfer material reversing means for discharging the transfer material outside the apparatus. 22. The image forming apparatus according to claim 21, wherein the transfer material reversing means is configured to fix the toner image on the transfer material by the first fixing means or the second fixing means. An image forming apparatus, wherein the image forming apparatus is disposed at a part where the material is turned upside down.