JPH09329969A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a satisfactory image having no image flow and painting out by temporarily transferring a toner image on an image carrier to an intermediate transfer means, then transferring it to transfer paper, and removing residual liquid developer on the image carrier by means of the intermediate transfer means. SOLUTION: In toner-image forming units Y, M, C, and B, the photoreceptor drums 4 are discharged by their dischargers 16, made equal in potential, and uniformly charged by their chargers 8. Then, exposure is carried out by each exposure device 9 to form an electrostatic latent image, and charges in unnecessary parts are removed by an eraser 11. A liquid developer is supplied to the electrostatic latent image by a developing roller 18, so that a toner image is formed. This toner image is temporarily transferred to the intermediate transfer body 26 by applying to a transfer device 12 a voltage having the reversed polarity of the toner. Thereafter, liquid carrier 40 is brought into contact with the intermediate transfer body 26 by the rotation of the photoreceptor drum 4 to be separated as liquid carrier having a layer thickness C which remains on the photoreceptor drum 4.

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, and more particularly to a wet type image forming apparatus using a developing solution in which toner is dispersed in a liquid carrier.

[0002]

2. Description of the Related Art A toner image is formed by supplying a developing solution in which toner is dispersed in a carrier liquid by a developing roller to an electrostatic latent image formed on a photoconductor which is a latent image carrier to form a toner image. An image forming apparatus that transfers a toner image onto an image to form an image is generally well known. As a toner image transfer method, an electrostatic transfer method is used in which a transfer material is superposed on a toner image on a photoconductor, a corona charge having a polarity opposite to that of the toner is applied from the back surface of the transfer material, and the transfer is carried out by electrostatic migration in a carrier liquid. Is common. Further, there is a system in which a transfer material is brought into contact with a toner image by a transfer roller, and a transfer bias having a polarity opposite to that of the toner is applied to the transfer roller for transfer.

[0003]

SUMMARY OF THE INVENTION In the above technique,
A developing solution layer (carrier solution layer) having a thickness of 30 μm or more is formed on the photoconductor that has been developed in the developing area. Adhesion to the transfer material is poor, a sufficient toner transfer rate cannot be obtained, and image deletion and character thickening occur. On the other hand, if the carrier liquid is too small, it becomes difficult to transfer by electrophoretic migration, and the image density is lowered, or the image density is lowered only in the portion corresponding to the concave and convex portions of the surface of the transfer material, White spots may occur. If the carrier liquid is unnecessarily adhered to the photoreceptor, the transfer material will be unnecessarily wetted by the carrier liquid, which requires a large amount of heat for fixing and consumes a large amount of carrier liquid. is there.

Therefore, in order to prevent such problems from occurring, it has been practiced to squeeze the excess carrier liquid while leaving an appropriate amount of carrier liquid. As such a method, a squeeze roller provided with a cleaning mechanism is arranged at a predetermined interval with respect to the photoconductor, and the surface of the squeeze roller is opposite to the rotation direction of the photoconductor in a region facing the photoconductor. It is common to rotate it so that it moves in the direction.

However, according to this method, the gap between the squeeze roller and the photosensitive member must be maintained at several tens of μm, and the squeeze roller must be manufactured with high precision. When a bearing with a diameter larger than the diameter of the squeeze roller is provided at the end of the squeeze roller to set the gap with the photoconductor, if the squeeze roller is eccentric, the gap between the two changes with the rotation of the squeeze roller. . When the gap between the two changes, the thickness of the carrier liquid on the photosensitive member changes, which affects the transfer as described above, and causes transfer unevenness on the transferred image due to the rotation of the squeeze roller.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which is free from uneven transfer, has a good transfer rate, and can obtain a high-quality image which does not cause image drift or image collapse.

[0007]

According to the first aspect of the present invention,
A latent image forming unit that forms an electrostatic latent image on the image carrier, a developing unit that supplies a developer to the electrostatic latent image formed on the image carrier to form a toner image, and the image carrier. And an intermediate transfer means for temporarily transferring the toner image, a voltage applying means for applying a voltage to the intermediate transfer means, and a toner image temporarily transferred to the intermediate transfer means on a transfer material. And a transfer means for transferring.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the intermediate transfer means is a belt-shaped rotating body.

According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the intermediate transfer means is a drum-shaped rotating body.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second or third aspect, cleaning means for cleaning the intermediate transfer means is provided.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect, a positioning member that is in contact with the image carrier is provided at the end of the drum of the intermediate transfer means. .

According to a sixth aspect of the invention, in the image forming apparatus according to the first aspect, a plurality of the intermediate transfer means are provided.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the interval between the intermediate transfer means is
The feature is that the number of times of transfer is gradually reduced as the number of times of transfer overlaps.

According to an eighth aspect of the invention, a developing solution is supplied to the electrostatic latent image formed on the image carrier to form a toner image, and the excess developing solution on the image carrier is removed. In the image forming method of removing and transferring the toner image to a transfer material,
An image forming method comprising: electrostatically transferring a toner image on the image carrier to an intermediate transfer member and then transferring the toner image to the transfer material.

According to a ninth aspect of the invention, in the image forming method according to the eighth aspect, the toner image on the image carrier is electrostatically transferred to the intermediate transfer member a plurality of times and then transferred to the transfer material. Is characterized by.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine which is an image forming apparatus will be described below with reference to FIG. As shown in FIG. 1, the image forming apparatus includes a yellow toner image forming unit Y, a magenta toner image forming unit M, and a cyan toner image forming unit C that form a toner image.
, A black toner image forming unit B, an intermediate transfer body 26 arranged to face each of these units and sequentially temporarily transferring toner images, and a transfer device 12 as a voltage applying means for applying a voltage to the intermediate transfer body 26. A sheet feeding device 24 for feeding a transfer sheet P as a transfer material, a transfer charger 34 for transferring a toner image to the transfer sheet P fed by the sheet feeding device 24, and a toner formed on the recording sheet P. A fixing device 28 for fixing an image is provided.

The intermediate transfer member 26 has a driving roller 30 and a driven roller 32 which are rotationally driven by a driving device (not shown).
And the toner image forming units Y, M, C, and B by the rotational force transmitted from the driving roller 30.
They move at the same speed and in the same direction as the cylindrical photosensitive drum 4 as an image carrier provided in each of the above. If the two speeds are different, the image expands and contracts in the traveling direction. The intermediate transfer member 26 is formed of a metal conductor such as aluminum or the like, a resin film dielectric such as PET, or the like into a seamless belt shape, and the surface thereof is smoothed.

As shown in FIG. 2, the intermediate transfer member 26 is arranged to face the photosensitive drum 4 with a gap X. The gap X is preferably 50 μm or less, though it depends on the amount of carrier liquid adhesion required when the toner image is transferred onto the transfer paper P. The narrower the gap X, the thinner the thickness of the carrier liquid that adheres to the toner image temporarily transferred. Therefore, the gap X is appropriately selected. When the intermediate transfer member 26 is a conductor, a bias is applied to transfer the toner image, and when the intermediate transfer member 26 is a dielectric member, the toner image is transferred by being charged with a polarity opposite to that of the toner. By thus forming the intermediate transfer member 26 into a belt shape, it is possible to avoid restrictions on the layout of the entire apparatus. Further, if the endless ring shape is adopted, the intermediate transfer member 26 having a small area can be repeatedly used, which is economical. When it is made seamless, it can be used in any part without breaking the image and without having to avoid seams, thus extending the service life of the belt.

The intermediate transfer member 26 is brought into contact with the intermediate transfer member 26.
A blade 36 is provided as a cleaning unit that scrapes off the residual toner. The blade 36 prevents the toner from adhering to the non-image portion and prevents the image transferred next time from being disturbed. In order to further ensure cleaning, a rotating sponge roller 38 that scrapes off adhered matter may be provided in front of the blade 36. The sponge roller 38 may be rotated in either direction.

The fixing device 28 heats the transfer paper P and the developing solution dispersed on the surface of the transfer paper P to melt the toner in the developing solution and fix the toner to the transfer paper P. Therefore, a liquid carrier vapor in the developer is generated at the time of fixing, so that the fixing device 28 is housed in a closed housing in order to collect the vapor. The vapor is liquefied by a liquefier (not shown). Next, the toner image forming unit will be described. Since the toner image forming units Y, M, C, and B have the same configuration, only the yellow toner image forming unit Y will be described, and the other toner image forming units M, C, and B will be described.
The same reference numerals as those of the yellow toner image forming unit Y are given and the description thereof is omitted.

The yellow toner image forming unit Y is shown in FIG.
As shown in FIG. 3, the photoconductor drum 4 is provided, and a charging charger 8, an exposure device 9, an eraser 11, a developing device 6, a transfer device 12, a cleaning device 14, and a charge eliminator 16 are provided around the photoconductor drum 4. Are provided respectively.

In the developing device 6, a developing roller 18 for supplying a developing solution having toner dispersed in a carrier solution to the photosensitive drum 4 to form a toner image, and a scraper 18a.
And a developer supply means 19 and a container 7 for accommodating each of these members.

The developing roller 18 is rotated in the direction of arrow b, which is the opposite direction of the photosensitive drum 4 rotating in the direction of arrow a, by a driving means (not shown), and the latent image of the photosensitive drum 4 is formed on the developing roller 18. A developing bias is applied so that the toner does not adhere to the background portion of. Above the developing roller 18, a developing solution supply means 19 for supplying a developer to the developing roller 18 is arranged. On the right side of the developing roller 18 in the drawing, a scraper 18a is arranged with its end portion in contact with the outer peripheral surface of the developing roller 18. Developer supply means 19
The developer supplied from the developing roller 18 and the scraper 1
8a and is accumulated in the wedge-shaped space 13 and the rotation of the developing roller 18 causes the photosensitive drum 4 and the developing roller 18 to rotate.
And are supplied to the opposing developing section. The scraper 18a not only forms the wedge-shaped space 13, but also has a function of removing the developing solution from the surface of the developing roller 18 by its pressure contact force.

The developing device 6 is provided below the photoconductor drum 4 in order to prevent the toner image on the surface of the photoconductor drum 4 from being disturbed by the leak of the developing solution from the developing device 6. . As shown in FIG. 2, the cleaning device 14 has a blade 15 as a cleaning member which is disposed in contact with the photosensitive drum 4 and removes the developer on the photosensitive drum 4.

The transfer device 12 is arranged beside the photosensitive drum 4, and the cleaning device 14 is arranged above the photosensitive drum 4. As a whole, the toner image forming units Y, M, and
C and B are arranged vertically, and the toner images are sequentially transferred to the intermediate transfer member 26.
The vertical configuration is adopted in which the transfer is performed on the transfer sheet P and the transfer charger 34 transfers the transfer sheet to the transfer sheet P at once.

The outline of the image forming process in the image forming apparatus 2 will be described. First, each toner image forming unit Y, M, C,
In B, the photoconductor drum 4 is neutralized by the static eliminator 16, averaged to the reference potential, and the charger 8 is discharged.
Are uniformly charged by. Next, an electrostatic latent image is formed by exposure by the exposure device 9, and the eraser 11 erases electric charges in unnecessary portions. The developing solution is supplied to the electrostatic latent image by the developing roller 18, and a toner image is formed. This toner image is temporarily transferred to the intermediate transfer body 26 by applying a voltage having a polarity opposite to that of the toner to the intermediate transfer body 26 to the transfer device 12.

Here, as shown in FIG. 2, a large amount of carrier liquid 40 is also attached to the toner image, and the film thickness A immediately after development is 30 μm or more. After that, the carrier liquid 40 comes into contact with the intermediate transfer member 26 by the rotation of the photosensitive drum 4, so that the carrier liquid having the film thickness B remaining on the photosensitive drum 4 and the carrier liquid having the film thickness C moving to the intermediate transfer member 26. Divided into By temporarily transferring to the intermediate transfer member 26 in this manner, the excess carrier liquid is removed.

On the intermediate transfer member 26, the yellow toner image forming unit Y forms a yellow toner image, the magenta toner image forming unit M forms a magenta toner image, and the cyan toner image forming unit C forms a cyan toner image. In the toner image forming unit B, the black toner images are sequentially superposed and transferred by the transfer device 12, and are collectively transferred by the transfer charger 34 onto the transfer paper P conveyed by the paper feeding device 24. The transfer paper P on which the toner image has been transferred is separated from the intermediate transfer member 26, a toner image is formed by the fixing device 28, and the paper is discharged to the paper discharge tray 50.

On the other hand, the residual toner remaining on the photosensitive drum 4 is scraped off by the cleaning blade 15. After that, the residual charges on the photosensitive drum 4 are eliminated by the elimination light, and the toner-free initial state is obtained, and the process proceeds to the next image forming step again.

According to this embodiment, the toner image formed on the photosensitive drum 4 is temporarily transferred to the intermediate transfer member 26 to remove excess carrier liquid, and then transferred to the transfer paper P, so that good transfer is achieved. An image is obtained. Transfer of the toner image to the intermediate transfer body 26 as described above generally causes almost no deterioration due to transfer, as compared with the case of transferring the toner image to the transfer paper P. This is the transfer paper P
This is because the surface of the intermediate transfer member 26 can be processed more smoothly and the carrier liquid does not infiltrate into the inside of the intermediate transfer member 26. When the carrier liquid soaks, the carrier liquid in the transfer area becomes insufficient,
It may prevent the toner from electrophoresing in the carrier liquid. Since there is a gap X between the photoconductor drum 4 and the intermediate transfer member 26, unlike the method of transferring the transfer paper by pressing it onto the photoconductor drum, the image is not crushed. Since a surplus carrier liquid is not removed using a squeeze roller as in the conventional case, squeeze unevenness does not occur.

FIG. 3 shows another embodiment. This embodiment differs from the embodiments shown in FIGS. 1 and 2 only in that a drum-shaped intermediate transfer member 46 is arranged in place of the intermediate transfer member 26, and the transfer paper P conveyance direction is reversed. To do. Intermediate transfer member 46
Also, a blade 36 for scraping off the residual toner and a sponge roller 38 are provided in front of the blade 36. To the intermediate transfer member 46, a power supply 44 that applies a voltage for temporarily transferring the toner image formed on the photosensitive drum 4 to the intermediate transfer member 46 is connected. The intermediate transfer member 46 is formed of, for example, a metal in a drum shape, and is rotated at the same speed as the photosensitive drum 4 in the direction of arrow c by an appropriate driving unit. When the intermediate transfer member 46 is formed of a metal in a drum shape in this manner, the gap X with the photosensitive drum 4 can be maintained with high accuracy, which is also advantageous for downsizing of the apparatus. In addition, the peripheral length of the intermediate transfer member 46 is set to the transfer paper P applied to the image forming apparatus.
When the length is longer than the maximum length, a good image in which unevenness of carrier liquid adhesion is not noticeable can be obtained.

Further, as shown in FIG. 4, bearings 48 as positioning members which are in contact with the photosensitive drum 4 may be provided at both ends of the intermediate transfer member 46. The bearings 48 are fixed to both ends of the intermediate transfer member 46, and
Together with 6, rotates in the direction of arrow c. The difference between the outer diameter of the bearing 48 and the outer diameter of the intermediate transfer member 46 is set to be twice the gap X. In this way, the intermediate transfer member 46
If the bearings 48 are provided at both ends of the gap, the gap X can be kept stable.

FIG. 5 shows still another embodiment. This embodiment differs from the embodiment shown in FIG. 3 only in that first, second, and third intermediate transfer bodies 46A, 46B, and 46C are provided. The first, second, and third intermediate transfer bodies 46A, 46B,
46C are configured to be able to come into contact with and separate from each other.
The second and third intermediate transfer members 46A, 46B and 46C have
Blade cleaning 36A, 36B, 36C respectively
Also, sponge rollers 38A, 38B and 38C are provided.

When a plurality of intermediate transfer members are used, the amount of carrier liquid that adheres to the toner image gradually decreases as the number of times of transfer increases, so that the photosensitive drum 4 and the first intermediate transfer member 4
The first intermediate transfer member 46A is larger than the gap X1 with 6A.
The gap X2 between the second intermediate transfer body 46B and the second intermediate transfer body 46B is narrowed, and the gap X3 between the second intermediate transfer body 46B and the third intermediate transfer body 46C is set narrower than that.

As described above, the toner image is formed on the photosensitive member 4, and the first intermediate transfer member 46A and the second intermediate transfer member 46 are formed.
B and B are placed in contact with each other. The toner image formed on the photosensitive member 4 has a voltage of 300 V applied to the first intermediate transfer member 46A (when the charging polarity of the toner is negative in this embodiment).
Is applied, it moves to the first intermediate transfer member 46A and is temporarily transferred. Next, the photosensitive drum 4 and the first intermediate transfer body 46A, and the second intermediate transfer body 46B and the third intermediate transfer body 46C are placed in contact with each other, respectively.
300V to the intermediate transfer member 46A of the first intermediate transfer member 46A
By applying a voltage of 0V to A, the toner image temporarily transferred to the first intermediate transfer member 46A is transferred to the second intermediate transfer member 46B.
When transcribed. The toner images thus formed on the photosensitive member 4 are sequentially transferred to the first, second, and third intermediate transfer members 46A and 4A.
The transfer is repeated to 6B and 46C, and finally transferred to the transfer paper P. When a plurality of intermediate transfer bodies are used, the latent image formed on the photosensitive drum 4 is a mirror image when the intermediate transfer body is an odd number, and a normal image when the intermediate transfer body is an even number.

As described above, by transferring the toner image a plurality of times, the carrier liquid 40 having the thickness A of the carrier liquid 40 immediately after development remains on the photosensitive drum 4 and the first intermediate transfer member 46A. Into a carrier liquid of film thickness C that moves to
Similarly, the carrier liquid having the film thickness C is divided into the film thickness D and the film thickness E, the film thickness E is further divided into the film thickness F and the film thickness G, and the carrier liquid around the toner image is gradually reduced. , An appropriate amount of carrier liquid is obtained and transferred to the transfer paper P.

Further, the transfer paper P is attached to the first intermediate transfer member 46.
A and the second intermediate transfer member 46B, the second intermediate transfer member 4
6B and the third intermediate transfer member 46C can be conveyed, and when a large amount of carrier liquid is required at the time of transfer due to the liquid supply property of the transfer paper P, the first intermediate transfer member 46A transfers to the transfer paper P. When a small amount of carrier liquid is transferred, it is possible to transfer from the third intermediate transfer member 46C to the transfer paper P.

[0038]

According to the first and eighth aspects of the invention, the toner image on the image carrier is temporarily transferred to the intermediate transfer means and then transferred to a transfer paper to remove the excess developer on the image carrier. Since it is removed by, a high-quality image free from image flow and crushing can be obtained. In addition, squeeze unevenness due to pitch unevenness when using a conventional squeeze roller becomes inconspicuous.

According to the second aspect of the invention, since the intermediate transfer means is belt-shaped, it is possible to avoid restrictions on the layout of the entire apparatus.

According to the third aspect of the invention, since the intermediate transfer means is formed in a drum shape, the gap between the intermediate transfer means and the image carrier can be maintained with high accuracy, which is also advantageous for downsizing the apparatus.

According to the fourth aspect of the invention, since the cleaning means cleans the intermediate transfer means, the same surface of the intermediate transfer means can be used to prevent the toner from adhering to the non-image area, and It is possible to prevent the image transferred to the image from being disturbed.

According to the fifth aspect of the invention, the positioning member can keep the gap between the intermediate transfer means and the image carrier stable.

According to the sixth and ninth aspects of the present invention, since a plurality of intermediate transfer means are provided, the excess developing solution is removed by the intermediate transfer means a plurality of times to ensure the amount of the developing solution when transferring to the transfer paper. It is possible to obtain a high-quality image with no image flow or crushing.

According to the invention of claim 7, the interval between the intermediate transfer means is made narrower successively as the number of times of transfer overlaps.
The developing solution can be surely attached to the next intermediate transfer means, and at the same time, the developing solution can be reduced, and a high-quality image with no image flow or crushing can be obtained.

[Brief description of drawings]

FIG. 1 is a front view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a front view showing a schematic configuration of a yellow toner image forming unit of FIG.

FIG. 3 is a front view showing a schematic configuration of an image forming apparatus of another embodiment.

FIG. 4 is a front view showing a schematic configuration of an image forming apparatus showing a modified example of the embodiment shown in FIG.

FIG. 5 is a front view showing a schematic configuration of an image forming apparatus of still another embodiment.

[Explanation of symbols]

 4 Photoreceptor Drum as Image Carrier 6 Developing Device 8 Charging Charger 9 Exposure Device 12 Transfer Device 14 Cleaning Device 16 Electrifier 18 Developing Roller 24 Feeding Device 26, 46 Intermediate Transfer Body 34 Transfer Charger 36 Blade as Cleaning Means P Transfer paper as transfer material

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeo Tsukamoto 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd.

Claims (9)

[Claims] 1. A latent image forming means for forming an electrostatic latent image on an image carrier, and a developing means for supplying a developing solution to the electrostatic latent image formed on the image carrier to form a toner image. An intermediate transfer unit that is arranged to face the image carrier at a predetermined interval and that temporarily transfers the toner image; a voltage applying unit that applies a voltage to the intermediate transfer unit; and a toner that is temporarily transferred to the intermediate transfer unit. An image forming apparatus comprising: a transfer unit that transfers an image to a transfer material. 2. The image forming apparatus according to claim 1, wherein the intermediate transfer means is a belt-shaped rotating body. 3. The image forming apparatus according to claim 1, wherein the intermediate transfer means is a drum-shaped rotating body. 4. An image forming apparatus according to claim 1, 2 or 3, further comprising cleaning means for cleaning the intermediate transfer means. 5. The image forming apparatus according to claim 3, wherein a positioning member that is in contact with the image carrier is provided at an end of the drum of the intermediate transfer means. 6. The image forming apparatus according to claim 1, wherein a plurality of the intermediate transfer means are provided. 7. The image forming apparatus according to claim 6, wherein the interval between the intermediate transfer means is gradually reduced as the number of times of transfer overlaps. 8. A toner image is formed by supplying a developing solution to the electrostatic latent image formed on the image carrier by a developing means, and the excess developing solution on the image carrier is removed to form a transfer material. In the image forming method for transferring the toner image, the toner image on the image carrier is electrostatically transferred to an intermediate transfer member and then transferred to the transfer material. 9. The image forming method according to claim 8, wherein the toner image on the image carrier is electrostatically transferred to the intermediate transfer member a plurality of times and then transferred to the transfer material.