JP2003076073A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of excellently forming an image while avoiding such a situation that a recording medium is stressed and a transfer condition is changed by transfer pressure and transfer bias by a transfer means. SOLUTION: The distance L1 of the carrying path of transfer paper P from the secondary transfer nip N1 of a 1st image forming unit 13a to the secondary transfer nip N2 of a 2nd image forming unit 13b is made longer than the dimension (length) L2 in the carrying direction of the paper P of maximum size which can be carried. Thus, the situation that the paper P is stressed and the transfer condition is changed by the transfer pressure and the transfer bias by the 1st and the 2nd transfer means because the paper P extends over both of the nip N1 and the nip N2 is prevented and the image is made to be excellently formed.

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 machine, a printer, a printing machine, and the like, and more specifically, one of conveying means for conveying a recording medium and one of the recording media conveyed by the conveying means. First to form an image on the surface of
Image forming means and second image forming means for forming an image on the other surface of the recording medium conveyed by the conveying means, and the conveying means conveys the recording medium without inverting the front and back. Image on both sides of the recording medium to be used 1
The present invention relates to a pass double-sided image forming apparatus.

[0002]

2. Description of the Related Art Generally, two toner images composed of toners having the same charge polarity are arranged so as to face each other.
It is difficult to transfer to both sides of a recording medium such as a transfer paper or an OHP sheet. For example, as shown in FIG. 6, between two intermediate transfer drums 80 and 81 on which a toner image composed of toner T having a negative polarity is formed so as to be transferred to both sides of a transfer paper P as a recording medium. It is assumed that the transfer paper P is sandwiched between. At this time, one toner image is transferred to the intermediate transfer drum 8
0 to the one surface (upper surface in the drawing) of the transfer paper P from the top of the transfer paper P to the direction from the intermediate transfer drum 80 to the intermediate transfer drum 81 (arrow A).
An electric field that imparts a (directional) electrostatic force must be created between both drums. On the other hand, in order to transfer another toner image from the surface of the intermediate transfer drum 81 to the other surface of the transfer paper P (the lower back surface in the drawing), the negative toner T is provided on the opposite side. An electric field that imparts an electrostatic force in the direction (arrow B direction) must be formed between both drums. However, it is impossible to simultaneously form opposite electric fields between the two drums. Even if an alternating electric field is formed and the countermeasure is taken, the direction of the electric field is reversed in the middle, so that one of the toner images is reversely transferred from the transfer paper P toward the drum at the time of reverse rotation. Even when the toner image is transferred only to the front surface of the recording paper and then the recording paper is reversed and another toner image is transferred to the back surface, the second transfer is performed as shown in FIG.
As a result, the toner image transferred to the surface is reversely transferred.

Therefore, a recording medium such as transfer paper is passed through a transfer device and a fixing device to fix the toner image on only one surface of the transfer device, and then the recording medium is reversed, and then the transfer device and the fixing device are turned on again. There is known an image forming apparatus that employs a so-called switchback double-sided transfer system in which the toner image is transferred to the other surface of the recording medium. In this image forming apparatus, the toner image is fixed to the transfer body before the second transfer step in which a reverse electric field is applied to the toner image transferred in the first transfer step. It is possible to realize the good double-sided transfer by suppressing the reverse transfer of the toner.

However, in this image forming apparatus, a complicated switchback mechanism for reversing the recording medium and returning it to the transfer apparatus is required, and it is difficult to speed up double-sided transfer by switching back the recording medium. There was a problem that it became.

Therefore, an image forming apparatus has been proposed in which a pair of image carriers, which individually carry toner images composed of toners having different charging polarities, are used to transfer the toner images to both sides of the recording medium. (For example, Japanese Patent Publication No. 51-13022, Japanese Patent Laid-Open No. 63-63).
057, JP-A-2-259670, etc.). In this image forming apparatus, for example, as shown in FIG. 7, in the second transfer process or the double-sided simultaneous transfer process, toner images having different polarities are opposed to each other via the transfer paper P. In such a state of facing each other, when an electric field that gives an electrostatic force in the direction toward the transfer paper P to the toner T that is negatively charged on one surface of the transfer paper P is formed, the opposite surface is formed. Transfer paper P to toner T that is positively charged
The electrostatic force in the direction toward can be applied. As a result, it is not necessary to fix one of the toner images on the transfer paper P in advance, and double-sided transfer can be performed in one pass without switching the transfer paper P back to eliminate the above-mentioned problems. it can.

However, in this image forming apparatus, a pair of photoconductor drums for forming toner images having different polarities, an optical writing unit, a developing unit, and the like having a common specification can be used. First, the specifications must be matched to the polarity of the toner. For this reason, there is a problem that the number of types of parts is much larger than that of a toner using only toners having the same charge polarity, and maintainability is deteriorated. Further, it is necessary to distinguish and manage the toners whose appearances such as colors differ little from each other only with different charging polarities, which further deteriorates maintainability.

Therefore, two toner images for transferring to both surfaces of the recording medium are formed by using toners having the same charging polarity, and are charged to opposite polarities by the corona charger before transferring either one of them to the recording medium. Image forming apparatus is proposed (for example, Japanese Patent Laid-Open No. 7-78551).
Japanese Patent Laid-Open No. 8-212664 and Japanese Patent Laid-Open No. 10-
171264, JP-A-10-97106, etc.). According to this image forming apparatus, since only the toners having the same charge polarity are used, it is possible to eliminate the above-mentioned deterioration in maintainability. Moreover, one toner image is charged to the opposite polarity by the corona charger, and at the time of transfer, the toner images having different polarities are electrostatically moved toward the recording medium interposed therebetween. Accordingly, it is not necessary to fix one toner image on the recording medium in advance, and double-sided transfer can be performed in one pass.

[0008]

By the way, this kind of 1
As a transfer method in a pass double-sided image forming apparatus, (1) on a surface of an image carrier that carries and rotates an image,
A pressure transfer method in which a recording medium is pressed by a transfer roller to transfer an image formed on the image carrier to the image forming surface of the recording medium, or (2) a surface of an image carrier that carries and rotates an image. A transfer bias between the recording medium and the image forming surface of the recording medium to transfer the image formed on the image carrier to the recording medium, (3) the pressure transfer method and the bias transfer method. A transfer method in which the above are combined is known.

In the pressure transfer method (1), the image formed on the image carrier is transferred to the recording medium by the pressing force of the transfer roller, so that the transfer rate of the image can be improved. However, when the pressure transfer method is used as the transfer method in the one-pass double-sided image forming apparatus, the first image transfer portion that transfers the first image to the one surface of the recording medium is first. High transfer pressure is applied to the recording medium by the transfer roller and the second transfer roller at the second image transfer portion that transfers the second image to the other surface of the recording medium.

Therefore, in the first image transfer portion and the second image transfer portion, variations in the nip width and the nip pressure of the transfer nip between the image carrier and the transfer roller, and in the conveyance belt for conveying the recording medium. On the other hand, wrinkles are likely to occur on the conveyed recording medium due to many factors such as the amount of water contained in the transfer paper and the grain direction. The wrinkling of the recording medium can be eliminated to some extent by forming the transfer roller into a drum shape or a drum shape. However, the transfer roller can transfer a uniform image to the entire surface of the recording medium. Since it is necessary to secure transfer performance, it is difficult to use a drum-shaped or drum-shaped transfer roller.

Particularly, the distance of the conveying path of the recording medium from the first image transfer portion to the second image transfer portion is
When the size is smaller than the size of the maximum transportable recording medium in the transport direction, a high transfer pressure is simultaneously applied to the front and back of the recording medium, and the recording medium is subjected to tensile or compressive stress. Occurrence is likely to occur.

In order to eliminate the stress of the recording medium as described above, the conveying speed of the recording medium at the first image transfer portion and the conveying speed of the recording medium at the second image transfer portion. However, it is almost impossible to eliminate the error of each transfer roller and the drive system, and it is difficult to eliminate the speed difference.

On the other hand, when the bias transfer method is used as the transfer method in the one-pass double-sided image forming apparatus, even if a transfer roller is used as the transfer means, the transfer pressure of the transfer roller with respect to the image carrier is Since it does not need to be so large, there are few problems as in the case of using the pressure transfer method.

However, even when such a bias transfer method is used, the first image transfer portion is changed to the second image transfer portion.
When the distance of the transport path of the recording medium to the image transfer portion is smaller than the dimension of the maximum transportable recording medium in the transport direction, the transfer bias from each transfer means is applied to the front and back of the recording medium. Since they are applied at the same time, the original transfer conditions may change. In particular, when the resistance value of the recording medium or the resistance value of the transfer / conveying belt that conveys the recording medium is low, the transfer current applied to one image transfer portion through the recording medium or the transfer / conveying belt is Since it easily flows to the image transfer site, the original transfer bias condition may change due to the influence of the transfer current flowing from the other side, and good image transfer may not be performed.

The present invention has been made in view of the above background. An object of the present invention is that the recording medium is stressed or the transfer condition is changed by the transfer pressure or the transfer bias by the transfer means. It is an object of the present invention to provide an image forming apparatus capable of performing excellent image formation without any trouble.

[0016]

In order to achieve the above object, the invention of claim 1 is such that a conveying means for conveying a recording medium and one surface of the recording medium conveyed by the conveying means are opposed to each other. A first image carrier disposed on the first image carrier, first image forming means for forming a first image on the first image carrier, and the first image carrier by the first image forming means. First transfer means for transferring the first image formed on the one surface of the recording medium, and a second image arranged so as to face the other surface of the recording medium conveyed by the conveying means. A carrier, a second image forming unit for forming a second image on the second image carrier, and a second image forming unit formed on the second image carrier by the second image forming unit. A second transfer unit that transfers the image to the other surface of the recording medium, and is transported by the transport unit. An image forming apparatus for forming an image on both sides of a recording medium without reversing the front and back of the recording medium, wherein the first image is transferred to one side of the recording medium by the first transfer means. Transporting path of the recording medium transported by the transporting means from the image transfer portion to the second image transfer portion for transferring the second image to the other surface of the recording medium by the second transfer means. Is larger than the dimension of the maximum size recording medium that can be conveyed by the conveying means in the conveying direction.

In this image forming apparatus, the recording medium extends over both the first image transfer portion and the second image transfer portion by the first transfer means and the second transfer means. The recording pressure and the transfer bias prevent the recording medium from being stressed or the transfer conditions being changed. As a result, good image formation can be performed.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the conveying means sucks and conveys the recording medium onto the belt surface so as to pass through the first image transfer portion. A first belt conveying means having a transfer conveying belt, and the recording medium arranged so as to pass through the second image transfer portion, the recording medium being arranged in a position not in contact with the first transfer conveying belt. It is characterized in that it is constituted by a second belt carrying means provided with a second transfer carrying belt which is sucked and carried on the belt surface.

In this type of image forming apparatus, when the first transfer / conveyance belt and the second transfer / conveyor belt are in contact with each other, the transfer speed of one of the transfer / conveyor belts may be different from that of the other transfer / conveyor belt. The linear velocity of the conveying belt and the belt deviation direction are different from the original linear velocity and the belt deviation direction, and good image formation may be hindered. Therefore, in this image forming apparatus, the second transfer / conveying belt is arranged at a portion that is not in contact with the first transfer / conveying belt. As a result, the occurrence of defects due to the contact between the two transfer and transport belts is eliminated.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the first belt transporting means and the second belt transporting means are provided near the belt of the first transfer transporting belt and the first belt transporting means. It is characterized in that it has a belt deviation control means for independently controlling the belt deviation of the transfer / conveyance belt 2.

In this image forming apparatus, the belt deviation control means independently controls the belt deviation of the first transfer conveyance belt and the belt deviation of the second transfer conveyance belt. With this, even when the belt deviation direction of one of the transfer conveyor belts and the belt deviation direction of the other transfer conveyor belt are different, the belt deviation of each transfer conveyor belt can be individually controlled. Therefore, better image formation can be performed.

According to a fourth aspect of the present invention, in the image forming apparatus according to the second or third aspect, the first belt conveying means and the second belt conveying means are the first transfer conveying belt and the second belt. A plurality of rollers that rotatably stretch the transfer conveyance belt are provided, and at least at least one of the plurality of rollers is a discharge roller arranged at the most downstream portion of the first transfer conveyance belt in the recording medium conveyance direction, The transfer roller of No. 2 and the carry-in roller arranged at the most upstream position in the recording medium carrying direction are grounded.

In this type of image forming apparatus, when a transfer bias is applied to transfer an image to a recording medium conveyed by one transfer conveying belt, the other transfer conveying belt is stretched. The roller acting as an opposing roller at the time of transfer, the transfer current flowing through the recording medium causes peeling discharge at the transfer medium carrying-out portion and the carrying-in portion of the recording medium, and the image transferred to the recording medium is discharged. Disturbance may occur. Therefore, in this image forming apparatus, at least one of the plurality of rollers is
The carry-out roller arranged at the most downstream portion of the first transfer / conveying belt in the recording medium conveying direction and the carry-in roller arranged at the most upstream portion of the second transfer / conveying belt in the recording medium conveying direction are grounded. As a result, the transfer current flowing through the recording medium flows to the ground through the carry-out roller and the carry-in roller, and peeling discharge does not occur at the carry-out site and the carry-in site of the recording medium of the transfer / transport belt.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the conveying means adsorbs and conveys the recording medium onto the belt surface so as to pass through the first image transfer portion. And a recording medium on the surface of the belt so as to pass through the second image transfer portion, which is arranged in a non-contact position with respect to the first transfer conveying belt. And a belt transfer unit having a second transfer transfer belt that attracts and transfers the transfer unit, wherein the first belt transfer unit and the second belt transfer unit include the first transfer transfer belt and the second transfer transfer belt. A plurality of rollers for rotatably stretching the second transfer / conveying belt, and the surface of the carry-out roller arranged at the most downstream position of the first transfer / conveying belt in the recording medium conveying direction; and the second transfer / conveying belt. Recording medium carrying And the surface of the feed-in rollers arranged in the direction most upstream site, in which the belt inner peripheral surface of the other of the transfer conveyor belt, respectively, characterized in that it is configured to bite into the ring.

In this image forming apparatus, the surface of the carry-out roller and the surface of the carry-in roller are configured such that the belt inner peripheral surfaces of the other transfer and transport belts bite into the crocodile. The transfer direction of the leading end of the recording medium at the most downstream portion of the transfer transport belt in the recording medium transport direction suddenly changes at the most upstream portion of the second transfer transport belt in the recording medium transport direction. As a result, the recording medium attracted and conveyed by the first transfer and conveyance belt is
The curvature is smoothly separated at the most downstream portion of the first transfer / conveyance belt in the recording medium conveyance direction.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, at least one of the carry-out roller and the carry-in roller has the second transfer of a portion stretched by the carry-in roller. When the recording medium is not present between the belt surface of the transport belt and the belt surface of the first transfer transport belt, the belt surface of the first transfer transport belt and the second transfer transport belt It is characterized in that it is configured to come into contact with and separate from the other belt surface so as to be retracted to a position where it is separated from the belt surface.

In the image forming apparatus according to the fifth aspect of the present invention, the recording medium can be smoothly separated from the first transfer / conveyance belt by the curvature, while the first transfer / conveyor belt and the second transfer / conveyor belt are separated. However, the contact is made at the curvature separation site. As a result, a problem occurs due to the contact between the transfer and transfer belts as described in claim 3. Therefore,
In this image forming apparatus, at least one of the carry-out roller and the carry-in roller is configured to be contactable with and separable from the surface of the other belt. Then, in a state where the recording medium does not exist between the belt surface of the second transfer / transport belt and the belt surface of the first transfer / transport belt in the portion stretched by the carry-in roller, The roller is retracted to a position where the belt surface of the first transfer / transport belt and the belt surface of the second transfer / transport belt are separated from each other. As a result, the problem caused by the contact between the transfer transfer belts is eliminated.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to a printer (hereinafter simply referred to as a printer) using an electrophotographic liquid developer which is an image forming apparatus using a liquid developer will be described below. FIG. 1 is a schematic configuration diagram of a printer according to this embodiment. In FIG. 1, the printer includes a first image forming unit 13a that forms an image to be transferred on the upper surface (front surface) of the transfer paper P and a second image forming unit 13a that forms an image to be transferred on the lower surface (back surface) of the transfer paper P. And a 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 devices 14a, 15a,
An optical writing unit 3a, an intermediate transfer belt 16a which is 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] and a urethane rubber layer having a thickness of 0.3 [mm] and a thickness of 0.1 to 0.1 mm.
It is a laminate of an amorphous fluororesin layer of 1.0 [μm] and has a volume specific resistance value of about 10 ⁸ [Ωc.
m] has been adjusted. The material of this fluororesin layer is
CYTOP (trade name) manufactured by Asahi Glass Co., Ltd. and a silicon-containing organic fluoropolymer manufactured by Daikin Industries, Ltd. (Patent Publication No. 28).
74715) is used. 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 fluororesin, and in many cases it was coated with a mixed resin of fluororesin and other binder resin. The liquid repellency and releasability of the belt were worse than in 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 remarkably poor and it was immediately peeled off.

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

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

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

In the developing device 50 of the image forming device 14a, 15 [wt%] of toner and an appropriate amount of the charge imparting agent C are contained in a liquid carrier made of an insulating liquid such as silicon oil.
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
Holds the liquid developer on its surface while being rotationally driven by a driving means (not shown). A developing bias is applied to the developing roller 51 by a power source (not shown), whereby a developing electric field is formed in the developing area between the developing roller 51 and the photosensitive drum 1. The electrostatic latent image moved to the developing area is reversely developed by this developing 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 side, and is electrostatically charged. Electrophores toward the latent image. Then, it 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 directed 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 while sandwiching the intermediate transfer belt 16a therebetween to form a primary transfer nip. The toner image that has undergone reversal development in the development area is sandwiched by this primary transfer nip as the photosensitive drum 1 rotates. A transfer electric field is formed in the primary transfer nip due to the effect of a transfer bias applied to the transfer roller 4 from a power source (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 contains a binder resin as a main component, and at the time of this primary transfer, the toner is pressed against the surface of the intermediate transfer belt 16a and compressed due to the influence of the transfer electric field, thereby increasing the mutual adhesive force. , Becomes a solid toner mass.

Photoreceptor drum 1 that has passed through the primary transfer nip
After the charge is removed by the charge removing unit 5, the transfer residual toner adhering to the surface is removed by the drum cleaning device 6.
It 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 15 a forms the electrostatic latent image on the photosensitive drum 1 in the image forming device 14 a.
The developing device 50a for a develops a different color. The color of the toner in the liquid developer is different. In addition, the toner images of different colors are primarily transferred by being superimposed on the toner images transferred onto the intermediate transfer belt 16a by the image forming device 14a. By this primary transfer, the toner particles of other colors are pressed against the toner particles previously formed on the intermediate transfer belt 16a to be integrated, and the toner particles of two colors are formed on the intermediate transfer belt 16a. A two-color toner image is formed. The two-color toner image enters the secondary transfer nip facing the transport path of the transfer paper P as the intermediate transfer belt 16a rotates. The above-mentioned tension drum 18
An AC secondary transfer bias is applied to a by the AC power supply 19.

Next, the second image forming unit 13b will be described. Like the first image forming unit 13a, the second image forming unit 13b also includes two image forming devices 14b and 15b, an optical writing unit 3b, an intermediate transfer belt 16b which is a second image carrier, a driving drum 17b, and The suspension drum 18b is provided. However, an AC secondary transfer bias is applied to the tension drum 18b by the AC power source 19 as in the tension drum 18a of the first image forming unit 13a. The intermediate transfer belt 16b has the same structure as the intermediate transfer belt 16a of the first image forming unit 13a.

The second image forming unit 13b has a transfer paper conveying path at a portion separated by a distance L1 downstream of the secondary transfer nip of the stretching drum 18a of the first image forming unit 13a in the transfer paper conveying direction. The secondary transfer nip is formed by abutting the tension drum 18b. Also in the second image forming unit 13b, the intermediate transfer belt 16 is processed by the same process as the first image forming unit 13a.
2 color toner image is formed on the intermediate transfer belt 16b.
And enters the secondary transfer nip. The entry of the two-color toner image on the intermediate transfer belt 16b is synchronized with the timing when the transfer paper P having the two-color toner image transferred to the surface by the first image forming unit 13a enters the secondary transfer nip. Has become.

On the other hand, the present printer is equipped with a paper feeding device (not shown), which allows the timing when the two-color toner images on the intermediate transfer belt 16a of the first image forming unit 13a enter the secondary transfer nip. Then, the transfer paper P is sent out toward the secondary transfer nip. Then, in the secondary transfer nip of the first image forming unit 13a, an alternating electric field is formed by the alternating secondary transfer bias applied to the stretching drum 18a. As a result, the toner image formed by the first image forming unit 13a is secondarily transferred to the surface of the transfer paper P. Next, in the secondary transfer nip of the second image forming unit 13b, an alternating electric field is formed by the alternating secondary transfer bias applied to the stretching drum 18b. As a result, the toner image formed by the second image forming unit 13b is secondarily transferred to the back surface of the transfer paper P.

In this way, the transfer paper P on which the two-color toner images have been transferred to both the front and back sides is printed by the second image forming unit 13b.
After passing through the next transfer nip, it is discharged to the outside of the machine through a fixing device (not shown).

FIG. 2 is a schematic block diagram showing the developing device 50 of the printer according to this embodiment. This developing device 50
It is composed of a pump unit 57, a tank unit 59, and a developing unit 60. The pump portion 57 is the tank portion 59.
And the developing section 60 are provided so as to communicate with each other, and an impeller 58 made of an elastic material such as rubber is provided in the communication path. The impeller 58, which can be rotated by a driving means (not shown), is in close contact with the inner wall of the communication passage to block the communication passage when not rotating. Further, at the time of normal rotation or reverse rotation, the propeller imparts a propulsive force to the liquid developer 150 to convey the liquid developer 150 between the tank portion 59 and the developing portion 60. Specifically, the impeller 60 is
Immediately before the main body of the developing device enters the standby state, the reverse rotation is performed to
All the liquid developer 150 in 0 is carried into the tank portion 59. Immediately before starting the developing operation or during the developing operation, the normal rotation is appropriately performed to replenish the developing unit 60 with an appropriate amount of the liquid developer 150. This replenishment is controlled based on the detection result of a liquid level detection means (not shown) that detects the liquid level in the developing unit 60.

The tank portion 59 is provided with an agitating blade 55 which is rotationally driven in the horizontal direction by a motor 56, whereby the liquid developer 150 stored in the tank is provided.
Is stirred. The developing unit 60 includes a developing roller 51a as a developer bearing member, a coating roller 52, a cleaning blade 53, a metering blade 54, and the like. The developing roller 51a and the coating roller 52 contact each other while rotating in the counter direction to form a coating nip. The coating roller 52 scoops up the liquid developer 150 in the developing section 60 as it rotates. The film of the liquid developer 150 drawn up is regulated in film thickness by the metering blade 54 that abuts on the application roller 52, and then part of the film is applied to the developing roller 51a by being sandwiched by the application nip and developed. It becomes a thin liquid layer. Then, with the rotation of the developing roller 51a, the developing roller 51a 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 thin layer of the developer remaining on the surface is the cleaning blade 5
3 and is returned to the tank portion 59.

Next, a printer of another embodiment will be described. In this printer, as shown in FIG. 3, as transfer means for the transfer paper P, transfer rollers 400a and 500a as a plurality of stretching rollers and a deviation correction roller 400 are provided.
b, 500b, and tension transfer rollers 400c, 500c, the transfer and transport belts 400, 500 are composed of endless belts rotatably stretched.

When a liquid developer composed of toner and carrier is used as the developer, the secondary transfer rollers 20a and 20b and the transfer / conveying belts 400 and 500 are kept in contact with each other. In this state, the toner of the developer of the image forming unit on the side where the image formation is stopped is not consumed, but the carrier of the developer is absorbed by the transfer paper P and consumed.

Therefore, in this printer, the transfer paper P conveyed by the transfer conveyor belts 400, 500 is pressed by pressing the inner peripheral surfaces of the transfer conveyor belts 400, 500 with the transfer rollers 20a, 20b. Intermediate transfer belts 16a and 16b to which the toner image is secondarily transferred
The front surface toner image and the rear surface toner image are selectively secondary-transferred to the front surface and the back surface of the transfer paper P by contacting and separating with each other.

As a result, when the toner image is formed on either the front surface or the back surface of the transfer paper P, the one of the first image forming unit 13a and the second image forming unit 13b which is not operated is operated. The transfer material conveying belt can be separated from the intermediate transfer belt of the image forming unit. In this way, by separating the intermediate transfer belts 16a and 16b from the transfer conveyance belts 400 and 500,
The carrier of the liquid developer is not absorbed by the transfer paper P and consumed.

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

Here, when a toner image is formed on either the front surface or the back surface of the transfer paper P, the fixing device 3 is used.
It is preferable to stop the fixing operation of the heating roller of No. 00 in which the toner image is not transferred to the transfer paper P.
As a result, the wasteful fixing operation of the heating roller on which the toner image is not transferred onto the transfer paper P is eliminated. Also,
The power consumption of the heating roller on which the toner image is not transferred onto the transfer paper P is reduced, and the running cost can be reduced.

Further, in this printer, the constituent members of the first image forming unit 13a and the second image forming unit 13b and the constituent members of the conveying means are composed of members having substantially the same mechanical life. deep. This makes it possible to match the maintenance timing of the constituent members of each image forming unit and the constituent members of the transporting unit, and reduce the labor of maintenance and the cost for maintenance.

In the one-pass double-sided printer as described above, the transfer paper P from the secondary transfer nip N1 of the first image forming unit 13a to the secondary transfer nip N2 of the second image forming unit 13b is transferred. When the distance L1 of the transport path is smaller than the dimension (length) L2 in the transport direction of the maximum transportable transfer sheet P, a transfer bias is simultaneously applied to the front and back of the transfer sheet P from each transfer unit. Therefore, the original transfer conditions may change.
In particular, the resistance value of the transfer paper P and the transfer / transport belts 400, 5
When the resistance value of 00 is low, the transfer current applied to one image transfer portion easily flows through the transfer paper P and the transfer / conveying belts 400 and 500 to the other image transfer portion, so that it flows from the other. The original transfer bias condition may change due to the influence of the transfer current, and good image transfer may not be performed.

Therefore, in the printer according to this embodiment, as shown in FIGS. 1 and 3, the first image forming unit 1
From the secondary transfer nip N1 of 3a, the second image forming unit 13
The distance L1 of the transfer path of the transfer sheet P to the secondary transfer nip N2 of b is set to be larger than the dimension (length) L2 of the maximum transferable size transfer sheet P in the transfer direction. As a result, the transfer paper P straddles both the secondary transfer nip N1 of the first image forming unit 13a and the secondary transfer nip N2 of the second image forming unit 13b, and the first transfer unit and the second transfer unit are provided.
The transfer pressure and the transfer bias by the transfer means prevent the transfer paper P from being stressed and the transfer conditions not to be changed, and a good image can be formed.

Here, the first image forming means and the second image forming means
Among these image forming means, at least the image forming means for forming an image to be transferred first onto the transfer paper P preferably has an image forming means for forming the image using a liquid developer. . That is, in this type of 1-pass double-sided printer, basically, each unfixed image transferred onto both surfaces of the transfer paper P is fixed in one fixing step. Therefore, the image previously transferred to the one surface of the transfer paper P remains unfixed when the second image transfer is performed to the other surface of the transfer paper P. Will be subject to transfer bias and transfer pressure during image transfer. Therefore, when an image to be transferred first on one surface of the transfer paper P is formed by using a solid developer (dry toner), the transfer bias and the transfer pressure at the time of transferring the second image may cause an influence. In some cases, the previously transferred image may be disturbed due to transfer dust, or the image may be attached to a transfer roller for performing the second image transfer to reduce the transfer rate of the image.

Therefore, as described above, the image previously transferred to the transfer paper P is formed using the liquid developer. The image formed by this liquid developer is less likely to cause a decrease in the transfer rate of the image and the occurrence of transfer dust as described above. Further, a higher transfer pressure is required to transfer an image onto a paper having a rough surface, but an image formed using a liquid developer is unlikely to affect the image quality even under high pressure.

Further, in this type of printer, when the transfer / conveying belt 400 and the transfer / conveying belt 500 are in contact with each other, the linear speed of one of the transferring / conveying belts or the deviation of the belt causes the linear speed of the other transferring / conveying belt. The belt deviation direction is different from the original linear velocity or the belt deviation direction, and good image formation may be hindered. Therefore, in the printer according to the present embodiment, as shown in FIG. 4, the transfer / conveyance belt 400 and the transfer / conveyance belt 500 are arranged in non-contact portions. As a result, the occurrence of defects due to the contact between the two transfer and transport belts is eliminated.

The transfer-conveying belt 400 and the transfer-conveying belt 500 are arranged to be controlled independently of each other. With this, even when the belt deviation direction of one of the transfer conveyor belts and the belt deviation direction of the other transfer conveyor belt are different, the belt deviation of each transfer conveyor belt can be individually controlled. Therefore, better image formation can be performed.

In this type of printer, for example, in FIG. 3, when the transfer bias is applied and the image is transferred to the transfer paper P which is being conveyed by the one transfer conveying belt 400, the other transfer is performed. The roller 500a, which stretches the conveyor belt 500, acts as a counter roller at the time of transfer, and the transfer current flowing through the transfer paper P causes peeling discharge at the carry-out and carry-in sites of the transfer paper P of the transfer conveyor belts 400 and 500. Occurrence may occur and the image transferred to the transfer paper P may be disturbed.

Therefore, in this printer, at least the transfer / transport belt 500 among the plurality of rollers is used.
Roller (delivery roller) 500a arranged at the most downstream portion of the transfer paper conveyance direction, and roller (intake roller) 400 arranged at the most upstream portion of the transfer conveyance belt 400 in the transfer paper conveyance direction.
a and ground. As a result, the transfer current flowing through the transfer paper P flows to the ground through the carry-out roller 500a and the carry-in roller 400a, and peeling discharge may occur at the carry-out site and the carry-in site of the recording medium of the transfer / transport belts 400 and 500. Disappear.

Further, as shown in FIG. 5, this printer has the surface of the carry-out roller 500a and the carry-in roller 4a.
00a and the surface of
The belt inner peripheral surface of 0,500 is configured to bite into the crocodile. Therefore, the transport direction of the leading edge of the transfer paper in the most downstream portion of the transfer transport belt 500 in the transfer paper transport direction suddenly changes at the most upstream portion of the transfer transport belt 400 in the transfer paper transport direction. As a result, the transfer sheet P attracted and transported by the transfer and transport belt 500 is transferred to the transfer and transport belt 50.
Curvature is smoothly separated at the most downstream position of 0 in the transport direction.

Here, it is preferable that at least one of the carry-out roller 500a and the carry-in roller 400a is configured so that it can come into contact with and separate from the surface of the other belt. Then, the belt surface of the transfer / transport belt 400 and the transfer / transport belt 5 at the portion stretched by the carry-in roller 400a.
No transfer paper is present between the transfer transport belt 500 and the transfer transport belt 500, when at least one of the carry-out roller 500a and the carry-in roller 400a is used.
And the belt surface of the transfer / conveying belt 400 are moved back to a position (a position indicated by a chain double-dashed line in FIG. 5) where they are separated from each other. As a result, the problem caused by the contact between the transfer transfer belts is eliminated.

[0061]

According to the inventions of claims 1 to 6, the recording medium extends over both the first image transfer portion and the second image transfer portion, and the first transfer means and the second transfer means are provided. By the transfer pressure and transfer bias due to, the recording medium is not stressed or the transfer conditions are changed,
There is an excellent effect that good image formation can be performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a printer according to an embodiment of the invention.

FIG. 2 is a schematic configuration diagram showing a developing device of the printer.

FIG. 3 is a schematic configuration diagram of a printer according to another embodiment of the invention.

FIG. 4 is an enlarged view of a transfer paper transport unit of a printer according to another embodiment.

FIG. 5 is an enlarged view showing another configuration of the transfer paper transport unit.

FIG. 6 is a schematic configuration diagram of a transfer portion of a conventional printer.

FIG. 7 is a schematic diagram showing two toner images facing each other on both sides of a transfer paper P.

[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 Tension drum 19 AC power supply 20a, 20b Secondary transfer roller 21 Transfer auxiliary roller pair 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 Backside mode 300 Fixing device 400, 500 Transfer conveyor belt 600 Transfer material reversing unit L1 Distance L2 between the secondary transfer nip of the first image forming unit and the secondary transfer nip of the second image forming unit L2 Length in conveyance direction N1 Secondary transfer nip N2 of first image forming unit Secondary transfer nip T toner P transfer paper 2 the image forming unit

Continued front page    (72) Inventor Shunichi Abe             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F-term (reference) 2H028 BA06 BA16 BC01                 2H072 CA07 CB02 JA02 JA03                 2H200 FA17 GA12 JA02 JA18 JB06                       JB15

Claims (6)

[Claims] 1. A transport means for transporting a recording medium, a first image carrier arranged so as to face one surface of a recording medium transported by the transport means, and a first image carrier on the first image carrier. First image forming means for forming a first image on the first surface, and the first image formed on the first image carrier by the first image forming means is transferred to one surface of the recording medium. A first transfer means, a second image carrier arranged so as to face the other surface of the recording medium conveyed by the conveying means, and the second image carrier.
Second image forming means for forming a second image on the image carrier, and the second image formed on the second image carrier by the second image forming means on the other side of the recording medium. An image forming apparatus for forming an image on both sides of a recording medium conveyed by the conveying means without reversing the front and back sides of the recording medium. The second image is transferred to the other surface of the recording medium from the first image transfer portion where the first image is transferred to the one surface by the first transfer means, and the second image is transferred to the other surface of the recording medium. The distance of the transport path of the recording medium transported by the transport unit to the second image transfer portion is
An image forming apparatus, wherein a size of a maximum size recording medium that can be conveyed by the conveying unit is larger than a dimension in a conveying direction. 2. The image forming apparatus according to claim 1, wherein said conveying means adsorbs said recording medium on a belt surface so as to pass through said first image transfer portion and conveys said recording medium.
A first belt conveying means having a transfer conveying belt, and the recording medium arranged so as to pass through the second image transfer portion, the recording medium being arranged in a position not in contact with the first transfer conveying belt. An image forming apparatus comprising: a second transfer conveying belt that is sucked onto a belt surface and conveyed; and a second belt conveying unit. 3. The image forming apparatus according to claim 2, wherein the first belt transporting means and the second belt transporting means are disposed near the belt of the first transfer transporting belt and the second transfer transporting belt. An image forming apparatus having a belt deviation control means for independently controlling the belt deviation. 4. The image forming apparatus according to claim 2, wherein the first belt conveying means and the second belt conveying means rotate the first transfer conveying belt and the second transfer conveying belt. A plurality of rollers that are freely stretched are provided, and among the plurality of rollers, at least an unloading roller disposed at the most downstream position of the first transfer / transport belt in the recording medium transport direction, and the second transfer / transport belt. The image forming apparatus is characterized in that the carry-in roller arranged at the most upstream position in the recording medium conveying direction is grounded. 5. The image forming apparatus according to claim 1, wherein the conveying means adsorbs the recording medium on a belt surface so as to pass through the first image transfer portion and conveys the recording medium.
And a belt conveying means provided with the transfer conveying belt, and a portion which is not in contact with the first transfer conveying belt,
And a belt transfer means including a second transfer transfer belt for adsorbing and transferring the recording medium on the belt surface so as to pass through the second image transfer portion. The second belt conveying means includes a plurality of rollers that rotatably stretch the first transfer conveying belt and the second transfer conveying belt, respectively. The recording medium conveying direction of the first transfer conveying belt The surface of the carry-out roller arranged at the most downstream part and the surface of the carry-in roller arranged at the most upstream part of the second transfer / conveying belt in the recording medium conveying direction are the inner peripheral surfaces of the other transfer / conveying belt. An image forming apparatus configured to bite into an image forming apparatus. 6. The image forming apparatus according to claim 5, wherein at least one of the carry-out roller and the carry-in roller is a belt surface of the second transfer / conveying belt at a portion stretched by the carry-in roller. And the belt surface of the first transfer / conveyor belt, the belt surface of the first transfer / conveyor belt and the belt surface of the second transfer / conveyor belt are separated from each other in a state where the recording medium is not present. An image forming apparatus characterized in that the image forming apparatus is configured so as to be able to come into contact with and separate from the surface of the other belt so as to retract to a position where the belt is moved.