JPH08328398A - Electrostatic transfer method for liquid toner image and its device - Google Patents

Abstract

PURPOSE: To provide a transfer method for an excellent image adopting liquid developer and its device. CONSTITUTION: With respect to the electrostatic transfer method for transferring the liquid toner image on the transfer material 28, which is formed by developing an electrostatic image by liquid developer composed of toner particles dispersed in insulated carrier liquid, the device is at least provided with the corona discharge transfer device 14 disposed opposite to the photoreceptor 1 for impressing an electric field having a polarity opposite to the toner particle of the liquid toner image 30, and a conductive tuck down roll 13 for impressing the electric field having the same polarity with the toner particle closely arranged on the upstream side of the corona discharge transfer device 14, assuming the dynamic potential density (C/cm<2> ) of the tuck down roll 13 and the corona discharge transfer device 14 are σX, and σY respectively, next inequality is satisfied, σY=aσX+b, subject to set followingly, 0<σY>=198×10<-9> C/cm<2> , σX<0, -2.5<=a<=-1.0 5.0<=b<=15.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention visualizes an electrostatic latent image formed on a photoconductor by developing it with a liquid developer (wet developer) composed of toner particles dispersed in an insulating carrier liquid. The present invention relates to a method and apparatus for electrostatically transferring a liquid toner image that electrostatically transfers the formed liquid toner image onto a transfer body (transfer paper, etc.) or an intermediate transfer body.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic system is
A uniform charge is formed on a photoreceptor made of an inorganic or organic material, an electrostatic latent image is formed by laser light or the like modulated by an image signal, and then the electrostatic latent image is developed with charged powder toner. To visualize. As a method for electrostatically transferring the visualized developed image (toner image) to a transfer body such as a transfer sheet or a transfer paper stacked and conveyed on a transfer belt or a belt-shaped or sheet-shaped intermediate transfer body, a conductive material is added. Bias roller transfer method that transfers while applying bias voltage to the pressure roller,
A corona discharge transfer method using an electric field generated by a corona discharge wire is known.

On the other hand, an electrostatic latent image is formed by using a liquid developer (wet developer, hereinafter also referred to as liquid toner) in which toner particles are dispersed in an insulating carrier liquid, and this is formed as a transfer body or an intermediate transfer body. There is known a liquid toner transfer device that electrostatically transfers to a liquid. The toner image transferred to the intermediate transfer member is
After that, it is secondarily transferred to a transfer body such as transfer paper. However, a high image quality cannot be obtained by simply applying the above-mentioned bias transfer method or corona discharge transfer method to the transfer device for transferring the liquid development image.

The reason for this is that the toner image developed with liquid toner does not have toner particles firmly attached to the photoreceptor as in the toner image developed with powder toner, but rather softly in the carrier liquid. It is in a floating state, and even if you try to transfer it with an electric field of the opposite polarity of the charge of the toner particles, you cannot get a tight image, that is, a high-quality image with high resolution and sharpness. is there.

In order to improve the image quality in such a liquid developing toner image transfer method, JP-A-63-30537 is used.
The transfer method disclosed in Japanese Patent Laid-Open No. 5 or JP-A-1-149080 has been proposed. That is, JP-A-63-
In the invention disclosed in Japanese Patent No. 305375, the transfer process is divided into two stages, first, the toner particles are pushed to the photoconductor side by an electric field having the same polarity as the toner particles to tighten the image, and then the transfer electric field having a polarity opposite to the toner particles is applied. To transfer the toner image from the photosensitive member to the transfer member.

On the other hand, in the invention described in Japanese Patent Application Laid-Open No. 1-149080, the transfer device is composed of a tuck down roll and a transfer device (corona discharge device) equipped with a corona discharge wire and a transfer body separating device (peel off roll). , The distance between the first point on the path where the transfer body first contacts the surface of the photoconductor by the tuck down roll and the second point corresponding to the point in the path closest to the discharge wire of the corona discharge device. Within 7.6 cm (about 3 inches), preferably 3.8
cm (about 1.5 inches) or less, and the transfer member is separated from the photoconductor at the third point within the range from the second point to 15 mm along the path of the transfer member movement. Is.

It is said that it is important for high-quality transfer that the toner particles are moved quickly before turbulence occurs in the liquid layer between the transfer body and the photoconductor. In addition, it is very important that the separation device is arranged very close to the corona discharge device.

[0008]

By adopting the transfer method disclosed in each of the above publications, it is possible to transfer a liquid toner image in high definition, but there are many elements constituting the transfer device. It is difficult to determine the conditions for obtaining high-quality images and the balance of transfer parameters, etc., and it is not possible to obtain high image quality over a wide range of conditions in the transfer process. The handling of the above parameters becomes complicated during multiple transcription of
There is a problem that it is difficult to achieve both so-called retransfer and multiple transfer.

Further, the material of the transfer roll is also required to be a material which does not swell or contract with respect to the adhesion of the carrier liquid used as the developer. Further, there is a problem that the nip width between the transfer roller and the photoconductor is narrow and it is weak against a factor of changing operating conditions, which acts as various instability factors. An object of the present invention is to solve the above-mentioned problems of the prior art, clarify the specifications of various components involved in the transfer process for high image quality, and perform retransfer and multiple transfer at the time of full-color multiple transfer. In addition to setting the conditions for compatibility, a transfer roll material that does not swell or shrink is provided, and a high-quality transfer of the liquid toner image is performed with a stable transfer roll configuration with a wide nip width. An object is to provide an electrotransfer method and an apparatus therefor.

[0010]

In order to achieve the above object, the present invention has the following constitution. In addition, in order to clarify the correspondence between the basic configuration of the invention and the configuration of the embodiment, each component will be described with reference numerals. FIG. 1 is a schematic view of a main part for explaining the basic configuration of a liquid toner image electrostatic transfer method and apparatus according to the present invention, in which 1 is a photoconductor, 7 is a transfer part power supply, 13 is a tack down roll, and 14 is a corona. A discharge transfer device, 28 is a transfer body (here, a transfer sheet such as a transfer sheet or a transfer medium conveyed by a transfer body such as a belt, a sheet-shaped or belt-shaped intermediate transfer body 31), and 30 is a liquid toner image.

That is, according to the first aspect of the present invention, as shown in FIG. 1, an electrostatic charge formed on the photoconductor 1 by a liquid developer in which toner particles are dispersed in an insulating carrier liquid. Liquid toner image 30 obtained by visualizing a latent image by developing it
Is a method for electrostatically transferring a liquid toner image onto a transfer body 28, the liquid toner image 30 being in contact with the photoreceptor 1.
At least a corona discharge device 14 for applying an electric field having a polarity opposite to that of the toner particles, and a conductive tackdown roll 13 for providing an electric field having the same polarity as the toner particles by being disposed in the vicinity of the upstream side of the corona discharge device 14. And the current value flowing in the corona discharge device 14 is I (μA), the photoconductor 1
The peripheral speed of V (cm / sec), the corona discharge device 14
Is L (cm), the dynamic charge densities σ _X (C / cm ² ) and σ _Y (C / cm ² ) of the tackdown roll 13 and the corona discharge device 14 are given by σ _Y = Aσ _X + b where 0 <σ _Y ≦ I / V · L and σ _X <0 −2.5 ≦ a ≦ −1.0 5.0 ≦ b ≦ 15.0.

According to a second aspect of the present invention, the electrostatic latent image formed on the photoconductor 1 is developed and visualized by a liquid developer in which toner particles are dispersed in an insulating carrier liquid. The liquid toner image 30 is transferred onto the transfer body 28 (transfer sheet,
A method of electrostatic transfer of a liquid toner image transferred to a transfer paper such as a belt) or an intermediate transfer member 31 (a sheet-shaped or belt-shaped intermediate transfer member), which is in contact with the photoreceptor 1. And a corona discharge device 14 for applying an electric field having a polarity opposite to that of the toner particles of the liquid toner image, and a conductive tackdown for providing an electric field having the same polarity as the toner particles by being disposed close to the corona discharge device 14 upstream of the corona discharge device 14. Roll 13
And a conductive peel-off roll 15 disposed in the vicinity of the corona discharge device 14 in the vicinity thereof, the current value flowing in the corona discharge device 14 is I (μA), and the peripheral speed of the photoconductor 1 is V (cm). / Sec), and the widthwise length of the corona discharge device 14 is L (cm), the dynamic charge density σ of the tackdown roll 13, the corona discharge device 14, and the peel-off roll 15 is
_X (C / cm ² ) and σ _Y (C / cm ² ) and σ _Z (C
/ Cm ² ), σ _Y = a σ _X + b where 0 <σ _Y ≦ I / V · L, σ _X <0 σ _Z = 0, or σ _Z ≈σ _Y −2.5 ≦ a ≦ It is characterized in that it is set to −1.0 5.0 ≦ b ≦ 15.0.

Further, the third invention according to claim 3 is
A plurality of electrostatic latent images corresponding to a plurality of colors sequentially formed on the photoconductor 1 by a plurality of liquid developers formed by dispersing toner particles of a predetermined color in an insulating carrier liquid, respectively. Liquid toner images 30 of a plurality of colors that have been sequentially developed and visualized by a transfer member 28 (transfer sheet, transfer paper conveyed by a transfer member such as a belt) or an intermediate transfer member 31 (sheet-shaped or belt-shaped intermediate transfer). And a corona discharge device for applying an electric field having a polarity opposite to that of the toner particles 30 in contact with the photoconductor 1, and a corona discharge device. A conductive tackdown roll 13 which is disposed close to the upstream of 14 and applies an electric field having the same polarity as the toner particles.
And a conductive peel-off roll 15 disposed in the vicinity of the corona discharge device 14 in the vicinity thereof, the current value flowing in the corona discharge device 14 is I (μA), and the peripheral speed of the photoconductor 1 is V (cm). / Sec), and the widthwise length of the corona discharge device 14 is L (cm), the dynamic charge density σ of the tackdown roll 13, the corona discharge device 14, and the peel-off roll 15 is
_X (C / cm ² ) and σ _Y (C / cm ² ) and σ _Z (C
/ Cm ² ), σ _Y = a σ _X + b where 0 <σ _Y ≦ I / V · L, σ _X <0 σ _Z = 0, or σ _Z ≈σ _Y −2.5 ≦ a ≦ -1.0 5.0 ≤ b ≤ 15.0 is set, and at the time of transferring the next color in the multiple transfer of the plurality of colors, σ _X : the same value as when transferring the previous color or a value σ reduced from the previous color _Y : The same value as when transferring the previous color or a value increased from the previous color σ _Z : The same value as when transferring the previous color or 0 is set.

Further, a fourth invention according to claim 4 is
In the third invention, a pre-pressing step of pressing at least the transfer member 28 or the intermediate transfer member 31 to the photoconductor 1 by the tackdown roll 13 before the photoconductor 1 enters the transfer cycle of the first color. It is characterized by having. Further, a fifth invention according to claim 5 is the same as the fourth invention, wherein the pressing force of the tackdown roll 13 to the photoconductor 1 is 50 g / cm to 200 g / cm.
It is characterized by

Further, a sixth invention according to claim 6 is
In the first, second or third invention, the I / V
-Characterized that L is 198 x 10 ^-9 cm ² .
Further, in a seventh aspect of the present invention, an electrostatic latent image formed on a photoconductor is developed and visualized by a liquid developer of at least one color in which toner particles are dispersed in an insulating carrier liquid. An electrostatic transfer device for a liquid toner image, which transfers a liquid toner image to a transfer body 28 or an intermediate transfer body 31, wherein an electric field having a polarity opposite to that of the toner particles of the liquid toner image is applied in contact with the photoconductor 1. A corona discharge device 14,
A conductive tack-down roll 13 is disposed upstream of the corona discharge device 14 to apply an electric field having the same polarity as the toner particles, and a conductive peel-off roll 15 is disposed downstream of the corona discharge device. At least prepared,
The material of at least the surface of the tack-down roll 13 and the peel-off roll 15 is at least one of a nitrile resin rubber material, a urethane resin rubber material, an epichlorohydrin resin rubber material, a fluorosilicone resin rubber material, and a fluorine resin rubber material. It is characterized in that it is a conductive roll formed by mixing a conductive substance into one.

Further, the eighth invention according to claim 8 is
In the seventh invention, the tack down roll 13
And the peel-off roll 15 has at least a two-layer structure. A ninth invention according to claim 9 is the eighth invention, wherein the tack-down roll 13 and the peel-off roll 15 are the sponge-like base layer and the sponge-like base layer described in the seventh aspect. It is characterized by being covered with a top coat layer made of a material.

The present invention is not limited to the above construction, and various modifications can be made without departing from the technical scope of the present invention.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION According to the first aspect of the present invention, a liquid toner image visualized by developing an electrostatic latent image formed on a photoconductor with a liquid developer in which toner particles are dispersed in an insulating carrier liquid is developed. A method of electrostatically transferring a liquid toner image to be transferred onto a transfer body or an intermediate transfer body, wherein the corona discharge transfer device 14 is in contact with the photoconductor 1 and applies an electric field having a polarity opposite to that of the toner particles of the liquid toner image 30. Apply.

The tack-down roll 13 is disposed in the vicinity of the upstream of the corona discharge transfer device 14 and applies an electric field having the same polarity as the toner particles. When the maximum current value flowing through the corona discharge device 14 is 70 μA, the peripheral speed of the photoconductor 1 is 16 cm / sec, and the length in the width direction of the corona discharge device 14 is 22.1 cm, the tack down roll 13 is And dynamic charge densities σ _X (C / cm ² ) and σ _Y (C / cm ² ) of the corona discharge device 14, σ _Y = aσ _X + b, where 0 <σ _Y ≦ I / V · L = 70 / 16 × 22.1 (= 198 × 10 ⁻⁹ C / cm ² ) σ _X <0 −2.5 ≦ a ≦ −1.0 5.0 ≦ b ≦ 15.0 The generation of retransfer of toner particles from the transfer body or the intermediate transfer body to the photosensitive member 1 is prevented, and a high-quality image without transfer failure or image quality deterioration can be obtained.

Under the above conditions, even when the peripheral speed of the photoconductor 1 is increased to 25 cm / sec, the I / V.multidot.
L is I / V · L = 70/25 × 22.1 (= 127 × 10 ⁻⁹ C / cm ² ), which satisfies the condition of “<198 × 10 ⁻⁹ C / cm ² ”.

The second aspect of the invention is to develop a visualized liquid toner image by developing an electrostatic latent image formed on a photoconductor with a liquid developer in which toner particles are dispersed in an insulating carrier liquid. In the electrostatic transfer method of a liquid toner image transferred to an intermediate transfer body, the corona discharge device 14 is in contact with the photoconductor 1 and applies an electric field having a polarity opposite to that of the toner particles of the liquid toner image.

The tuck down roll 13 is disposed in the vicinity of the upstream of the corona discharge device 14 and applies an electric field having the same polarity as the toner particles. The peel-off roll 15
Is composed of a conductive roll disposed in the vicinity of the downstream of the corona discharge device, and includes a photosensitive member 1 to a transfer member 28 (transfer paper).
Is peeled off to prevent winding around the photoreceptor 1.

When the maximum value of the current flowing through the corona discharge device 14 is 70 μA, the peripheral speed of the tack down roll 13 is 16 cm / sec, and the length of the corona discharge device 14 in the width direction is 22.1 cm, Dynamic charge density σ _X (C / cm of the tack-down roll 13, the corona discharge device 14, and the peel-off roll 15
² ) and σ _Y (C / cm ² ) and σ _Z (C / cm ² )
Where σ _Y = aσ _X + b, where 0 <σ _Y ≦ I / V · L = 70/16 × 22.1 (= 198 × 10 ⁻⁹ C / cm ² ) σ _X <0 σ _Z = 0, or Either of σ _Z ≈ σ _Y is set within the range of −2.5 ≦ a ≦ −1.0 5.0 ≦ b ≦ 15.0, so that the transfer body or the intermediate transfer body transfers to the photoreceptor 1. The occurrence of retransfer of toner particles is prevented, and a high-quality image without transfer failure or image quality deterioration can be obtained.

Under the above conditions, even when the peripheral speed of the photoconductor 1 is increased to 25 cm / sec, the I / V.multidot.
L is I / V · L = 70/25 × 22.1 (= 127 × 10 ⁻⁹ C / cm ² ), which satisfies the condition of “<198 × 10 ⁻⁹ C / cm ² ”.

Furthermore, a third aspect of the present invention is a plurality of static liquids corresponding to a plurality of colors sequentially formed on a photosensitive member by a plurality of liquid developers each of which has toner particles of a predetermined color dispersed in an insulating carrier liquid. An electrostatic transfer method of a liquid toner image in which a latent image is sequentially developed with each of the plurality of liquid developers and visualized and liquid toner images of a plurality of colors are sequentially superimposed and transferred onto either a transfer body or an intermediate transfer body. Therefore, the corona discharge device 14 contacts the photoconductor and applies an electric field having a polarity opposite to that of the toner particles.

The tuck down roll 13 is disposed in the vicinity of the upstream of the corona discharge device 14 and applies an electric field having the same polarity as the toner particles. The peel-off roll 15
Is composed of a conductive roll disposed in the vicinity of the downstream of the corona discharge device, and includes a photosensitive member 1 to a transfer member 28 (transfer paper).
Is peeled off to prevent winding around the photoreceptor 1.

When the maximum current value flowing through the corona discharge device 14 is 70 μA, the peripheral speed of the tack down roll 13 is 16 cm / sec, and the length in the width direction of the corona discharge device 14 is 22.1 cm, Dynamic charge density σ _X (C / cm of the tack-down roll 13, the corona discharge device 14, and the peel-off roll 15
² ) and σ _Y (C / cm ² ) and σ _Z (C / cm ² )
Where σ _Y = aσ _X + b, where 0 <σ _Y ≦ I / V · L = 70/16 × 22.1 (= 198 × 10 ⁻⁹ C / cm ² ) σ _X <0 σ _Z = 0, or Any one of σ _Z ≈ σ _Y is set to −2.5 ≦ a ≦ −1.0 5.0 ≦ b ≦ 15.0, and when the next color is transferred in the multiple transfer of the plurality of colors, σ _X : Same value as when transferring the previous color or a value that is reduced from the previous color σ _Y : Same value as when transferring the previous color or a value that is increased from the previous color σ _Z : Same value as when transferring the previous color or within the range set by 0 As a result, retransfer of toner particles from the transfer body or the intermediate transfer body to the photoconductor 1 is prevented, and a high-quality full-color image without transfer failure or image quality deterioration can be obtained.

Under the above conditions, even when the peripheral speed of the photoconductor 1 is increased to 25 cm / sec, the I / V.multidot.
L is I / V · L = 70/25 × 22.1 (= 127 × 10 ⁻⁹ C / cm ² ), which satisfies the condition of “<198 × 10 ⁻⁹ C / cm ² ”.

Further, in a fourth aspect based on the third aspect, before the photoconductor enters the transfer cycle of the first color, at least the transfer body or the intermediate body is applied to the photoconductor by the tack down roll. A pre-pressing step of press-contacting the transfer body is provided, which prevents the transfer material 28 and the transfer sheet 12a from being brought into close contact with the photoconductor 1 to generate bubbles or irregularities.

Further, in the fifth invention, the pressure contact force of the tack down roll with respect to the photosensitive member is 50 g / cm to
By setting it to 200 g / cm, the transfer material 28 and the transfer sheet 12a maintain the adhesiveness with the photoconductor 1 and prevent partial omission of the image. The sixth aspect of the present invention is the above first to third aspects.
The invention has been described as an embodiment. Further, a seventh invention is to transfer a liquid toner image which is visualized by developing an electrostatic latent image formed on a photoconductor with at least one color liquid developer in which toner particles are dispersed in an insulating carrier liquid. Alternatively, it is an electrostatic transfer device for a liquid toner image transferred to an intermediate transfer member, and the corona discharge device 14 is in contact with the photosensitive member and applies an electric field having a polarity opposite to that of the toner particles of the liquid toner image.

The tuck down roll 13 is disposed close to the upstream of the corona discharge device 14 and applies an electric field having the same polarity as the toner particles. The peel-off roll 15
Is composed of a conductive roll disposed in the vicinity of the downstream of the corona discharge device, and includes a photosensitive member 1 to a transfer member 28 (transfer paper).
Is peeled off to prevent winding around the photoreceptor 1.

The material of at least the surface of the tack-down roll and the peel-off roll is a nitrile resin rubber material, a urethane resin rubber material, an epichlorohydrin resin rubber material, a fluorosilicone resin rubber material, a fluorine resin rubber material. By using a conductive roll in which at least one of them is mixed with a conductive substance, the swelling and shrinkage of the liquid toner developer by the liquid carrier and the dissolution resistance are maintained.

In the eighth aspect of the invention, since the tackdown roll 13 and the peel-off roll 15 have at least a two-layer structure, it is possible to avoid swelling or shrinking of the liquid toner developer due to the liquid carrier. Further, in the ninth invention, the tuck down roll 13
By covering the peel-off roll 15 with a sponge layer and the sponge layer with a top coat layer made of the material according to the sixth aspect, it is possible to secure swelling and shrinkage of the liquid toner developer by the liquid carrier.

[0034]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a schematic diagram illustrating the configuration of an embodiment of a color copying machine as an example of an image forming apparatus using a liquid developer, in which 1 is a drum-shaped photosensitive member having a photoconductive surface, and 2 is Charger 3, exposure optical system 3a, laser beam 4Y, yellow developing device, 4M magenta developing device, 4C cyan developing device, 4K black developing device, 4a developing electrode, 4b metalling roll,
5a is a developer supply tube, 5b is a developer drain tube, 6 is a developer supply box, 9 is a surplus liquid removing roll, 10 is a vacuum tank, 10a is a surplus liquid drain tube, 11 is a vacuum pump, 12 is a transfer sheet, 1
3 is a tack down roll (pressure roll), 14 is a transfer corotron as a corona discharge device, 15 is a peel-off roll (peeling roll), 16a and 16b are peeling corotrons, 17a and 17b are static eliminating corotrons, 18 is a prewetting device, 18a Is a pre-wet roll, 18b is a pre-wet roll drive mechanism, 19 is an adsorption corotron, 20
Is a cleaning device, 20a is a sponge disturber, 20b is a cleaning blade, 21 is a discharge lamp, 22 is a carrier liquid filter, 23 is a cleaning and recovery liquid tank, 23a is a recovery tube, 24 is a recovery pump, and 25 is a transfer material unloading belt. , 26 is a fixing device, 27 is a transfer paper carry-in roll, and 28 is a transfer paper as a transfer body.

In the figure, an exposure optical system 3 is provided on a photoconductor 1 to which a predetermined uniform charging potential is given by a charger 2.
An electrostatic latent image is formed by scanning the laser beam 3a modulated by the image signal. On the other hand, the yellow developer supplied to the developing device 4Y is contained in the developer supply box 6 and flows into the developing device 4Y via the developer supply tube 5a by a supply pump (not shown). The excess developer is collected in the developer supply box 6 by the drain tube 5b.

Although the developing agents 4M, 4C, and 4K for magenta, cyan, and black are supplied with the respective developers in the same configuration, they are not shown. Hereinafter, only the yellow developer will be described, but the same applies to other developers. Now, the wet type developer supplied to the developing device 4Y slides on the upper surface of the developing electrode 4a, develops the electrostatic latent image formed on the photoconductor 1, and a visualized toner image is formed. Further, excess toner is removed from the toner image by the metalling roller 4b which rotates in the same direction as the rotation direction E of the photoconductor 1 without contact.

After that, the toner image is further absorbed by the liquid absorbing roll 9 for removing the excess liquid before the transfer,
The developer amount of the toner image adhered on the photoconductor 1 is adjusted to an appropriate amount. The excess liquid absorbed by the liquid supply roll 9 is stored in the vacuum tank 10 by the vacuum pump 11. On the other hand, a transfer sheet (hereinafter, the transfer sheet is used as the transfer sheet in this embodiment) that is a transfer body 28 on which a final image is placed is carried in by a transfer sheet carry-in roll 27, and a transfer drum (described later).
It is electrostatically attached to the transfer sheet 12 carried by the adsorption corotron 19. And the pre-wetting device 18
The pre-wet roll 18a is wetted with an appropriate amount of the carrier liquid that is the same as the developer carrier liquid, and is guided to the transfer region where the transfer corotron 14 is arranged.

In the transfer area, a tack down roll (pressure roll) 13 to which a bias is applied and a transfer corotron 1
4, the toner image of the first color (yellow: Y) is transferred onto the transfer paper 28. After this, the second color (magenta: M),
When the third color (cyan: C) and the fourth color (black: B) latent image formation, development, and transfer are performed in the same manner, peeling corotron 1
The copying paper 28 is peeled from the transfer sheet 12 by 6a and 16b, conveyed to the fixing device 26 through the transfer material discharge belt 25 in the direction of arrow B, and fixed to form a permanent image in the direction of arrow C. .

In this way, a full-color image is formed on the transfer paper 28 with high image quality. It should be noted that the toner and the developing solution remaining on the photoconductor 1 are removed by the sponge disturber 20a of the cleaning device 20 and the cleaning blade 20.
In step (b), it is removed by cleaning, directly or through the carrier liquid filter 22 and recovered by the pump 24 in the cleaning recovery liquid tank 23 for reuse.

FIG. 3 is a schematic view of the main part for explaining the structure of the transfer part of the color copying machine shown in FIG.
Photoconductive layer, 12 is a transfer sheet, 12a is a transfer drum,
12b is a frame structure of the transfer drum 12a, 29 is a gap maintaining roller, and the same reference numerals as those in FIG. 1 correspond to the same portions. In the figure, the transfer sheet 12 circulated and carried on the frame body structure 12 b of the transfer drum 12 a faces the photoconductor 1 via the gap maintaining roller 29. The transfer unit is composed of a tack down roll 13, a transfer corotron 14, a peel-off roll 15 and a transfer unit power supply 7 as a unit.

The tack-down roll 13 and the peel-off roll 15 constituting this transfer unit are normally retracted inside the transfer drum 12a, and a stepping motor means (not shown) approaches when the developed toner image approaches. Also, the photosensitive member 1 is tacked by the spring means or the like. The gap maintaining roller 29 maintains the gap between the transfer drum 12a and the photosensitive drum 1 at a predetermined value.

FIG. 4 is a schematic perspective view for explaining an example of the structure of the transfer drum, and the same reference numerals as those in FIG. 3 correspond to the same parts. This figure shows a state during the transfer process in which the tack down roll 13 is moved from the retracted position to the position where it is pressed against the photoconductor 1. The transfer drum 12a has a frame body structure 2b,
A transfer sheet (also referred to as a screen sheet) 12 is mechanically attached to a front end and a rear end of the frame body structure 12b, and a main portion thereof has a degree of freedom in a radial direction of the transfer drum 12a.

The transfer sheet 12 preferably has a volume resistance in the high resistance region from semi-conductivity to 10 ⁸ to 10 ¹⁶ Ω.
cm, preferably 10 ¹⁰ to 10 ¹² Ω · cm. Further, its surface resistance is also preferably 10 ⁸ to 10 ¹⁶ Ω · cm, preferably 10 ⁹ to 10 ¹¹ Ω · cm. As a material for this purpose, a coated paper, a resin film such as PVdF, and a conductive PET (polyethylene terephthalate) film can be used.

One rotation before entering the transfer process, as shown in FIG.
As shown in FIG. 3, the transfer unit presses the transfer sheet 28 and the transfer sheet 12 which are wetted with a liquid, which is preferably the same liquid as the carrier liquid constituting the developer, by the pre-wet roll 9 on the photoconductor 1. By doing so, the transfer paper 28 and the transfer sheet 12 are brought into close contact with each other with the carrier liquid, and bubbles and unevenness are removed.

In the transfer process, the tack-down roll 13 moves toward the photoconductor 1 with the transfer paper (not shown) in close contact with the transfer sheet 12 to move the transfer paper to the photoconductor 1.
The toner image carried on the photoconductor 1 is transferred onto the transfer paper by the transfer electric field generated by the transfer corotron 14 while being pressed against the surface of the transfer paper. The transfer sheet on which the toner image is transferred is peeled off from the photoconductor 1 by the peel-off roll 15.

FIG. 5 is a flow chart for explaining an example of the transfer cycle of the color copying machine shown in FIG. In the figure, when the transfer cycle starts, in the first color transfer cycle S-1, the first color latent image formation (S-1a)
A transfer drum for performing transfer material pressure contact in which the transfer sheet 28 is sandwiched between the transfer sheet 12 and the photoconductor 1 before the transfer of the toner image developed and visualized by the development (S-1b). The idle rotation of 12a is executed (S-1c).
Then, the toner image is transferred and the first color transfer cycle is completed.

After the first color transfer cycle is completed, the next color (second color) transfer cycle, the third color transfer cycle (third color), and the fourth color transfer cycle (fourth color) are executed. (Next color transfer cycle, S-2, S-
3) After the transfer of all colors is completed (Yes in S-3), the transfer paper 28 is peeled from the transfer sheet 12, conveyed to the store arrival device 26, and fixed (S-4).

As described above, in the pre-pressurizing cycle before one rotation of the transfer cycle by the transfer unit, the tack down rolls 13 to which the bias is not applied are pressed. At this time, the peel-off roll 15 and the transfer corotron 14 do not contribute anything to the pre-press contact. It is also possible to provide a separate roll means for this pre-press contact to execute dummy idle rotation.

After the pre-press contact rotation by the tack down roll, the original transfer process is started. In the transfer cycle, a voltage having the same polarity as the polarity (eg, −) of the developed toner image is applied to the tackdown roll 13. At the same time, the pressure for pressing the photoconductor 1 is 50 g / cm to 200 g.
A force of / cm is applied. If the pressing force is out of this pressure range and the pressing force is weak, the transfer sheet 12 and the transfer paper 28 do not come into close contact with the photoconductor 1 and a defect (image quality defect) in which the toner image is partially removed occurs. When the value is high, a defect that the transferred toner image is disturbed or flows may occur. Therefore, it is necessary to maintain the pressure within the above range.

As described above, the voltage of the same polarity as the toner particles (toner image) is applied to the tack down roll 13 and then the transfer is performed by the transfer corotron 14, so that the sharpness of the obtained image quality can be improved. Dramatically better. Figure 6
FIG. 4 is an explanatory diagram of measurement results of evaluation of respective dynamic charge densities flowing by a voltage applied to a transfer corotron and a tuck down roll and image quality of a transferred image.

In the figure, the absolute values of the dynamic charge densities (C / cm ² ) of the transfer corotron, the tack-down roll, and the peel-off roll are σ _X , σ _Y , and σ, respectively.
_{When Z} , σ _Y = a σ _X + b, where 0 <σ _Y ≦ 198 × 10 ⁻⁹ C / cm ² , σ _X <0 −2.5 ≦ a ≦ −1.0 5.0 ≦ b ≦ 15.0 Furthermore, by setting the respective charge densities so that σ _Z = 0, it is possible to obtain a transferred image having a high image quality with excellent sharpness.

That is, in the figure, "normal" is placed on the boundary between the ◯ point indicating "good" and the x point indicating "bad" in the image quality evaluation.
The line connecting the upper limit Δ points indicating Y is − = 2.5 × + 15, and the line connecting the lower limit is Y = −X + 5. Here, the dynamic charge density σ _Y of the transfer corotron is indicated by Y, and the dynamic charge density σ _X of the tackdown roll is indicated by X.

The lower limit of the dynamic charge density of the transfer corotron can be expressed as a limit value at which a bias having the same polarity as the toner depending on the polarity of the tack down roll can push the toner once toward the photoconductor to pull the image. On the other hand, the upper limit of the dynamic charge density of the transfer corotron is the allowable charge density just before the leak occurs.

As for the dynamic charge density of the peel-off roll, as a result of various tests, the electrically floating state (σ _Z = 0) is the best. However, the current value of the transfer corotron is not limited to this (σ
_Z = σ _Y ). This peel-off roll does not electrically contribute to the transfer of an image, and rather its function is that the position of the peeling point between the photoconductor 1 and the transfer sheet formed by the height of the peel-off roll is greater than the position of the corotron wire of the transfer corotron. It is more important not to go ahead and not too far (within 15 mm).

Next, the full color transfer will be described. At the time of full-color transfer, since toner images of a plurality of colors are sequentially superposed on the transfer paper 28, the tack down roll 13 also having a function as a bias roll has a negative (-) polarity, and the transfer corotron 14 has a positive (+) polarity. In such a transfer method, the negative component of the tack-down roll 13 inevitably acts in the direction of stripping the toner particles transferred to the copy paper at the time of the next toner image transfer. So-called retransfer occurs in which the toner particles move to.

The conditions for transferring the toner image of the next color while suppressing the retransfer are as follows:
In full-color multiple transfer, the dynamic charge density flowing in each element (tuck down roll 13, transfer corotron 14, or peel-off roll 15) that constitutes the transfer part is the same as that in the previous color transfer, σ _X : Value or a value reduced from the previous color σ _Y : The same value as when transferring the previous color or a value increased from the previous color σ _Z : The same value as when transferring the previous color or set to 0 (electrically floating state) Prevent retransfer,
High-quality full-color images can be transferred by multiple transfer.

This will be described in more detail with reference to FIG. The following numerical values are charge densities, and each numerical value is in units of C / c multiplied by (2.8 × 10 ⁻⁹ ).
m ² . First, set the parameters for the transfer of the first color (Y) to -15 for the tack down roll, 30 for the transfer corotron, and float for the peel off roll.

Next, the parameters for the transfer of the second color (M) were set to -12 for the tack down roll, 35 for the transfer corotron and float for the peel off roll. further,
The transfer parameters for the third color (C) were set to -9 for the tackdown roll, 40 for the transfer corotron, and float for the peel-off roll. Then, the parameter at the time of transfer of the fourth color (K) is set to -6 for the tack down roll, 45 for the transfer corotron, and float for the peel off roll.

This makes it possible to suppress the occurrence of retransfer described above. Next, the materials constituting the tack down roll and the peel off roll will be described. These rolls must be made of a material that is inert to the carrier liquid that constitutes the liquid developer, and that does not swell or shrink, and have electrical conductivity and appropriate hardness It is important to be able to form a stable nip width under pressure.

As the material, a solvent resistant material selected from nitrile rubber, urethane rubber, epichlorohydrin rubber, fluorosilicone rubber, fluorine rubber, fluororesin rubber and the like is suitable. The rubber material here means a material having elasticity. In order to secure conductivity, the resistivity is 10 ⁴ to 10 ¹² Ω · c.
m, preferably 10 ⁶ to 10 ⁹ Ω · cm is suitable as the resistance value for arbitrarily controlling the charge density.

The hardness is 25 ° to 70 in terms of rubber hardness.
The angle is preferably 30 °, preferably 30 ° to 50 °. Figure 7
And FIG. 8 are explanatory views of a structural example of a tackdown roll, (a) of each drawing is a side view, (b) is a sectional view taken along the line AA of (a), and 13 is a tackdown roll. Roll, 13a
Is a shaft, 13b is a roll layer, 13c is a top coat layer, 1
3d is a base layer.

FIG. 7 shows a tackdown roll 1 in which only one roll layer 13b made of the above material is formed on the shaft 13a.
3 is set. Further, FIG. 8 shows a two-layer structure in which an underlayer 13d made of an appropriate sponge material is wound around the shaft 13a, and the surface thereof is covered with a topcoat layer 13c made of any of the above materials.

When the sponge material is used as the underlayer 13d, the sponge hardness is 10 ° to 60 °, preferably 2 °.
It is preferably 0 ° to 40 °. In any case, it is necessary to have the above-mentioned conductivity in the thickness direction of the roll. The peel-off roll 15 may have the same structure. By using the tack-down roll 13 and the peel-off roll 15 as described above, it is inactive to the carrier liquid constituting the liquid developer, does not swell or shrink, has conductivity, and has an appropriate hardness. It is possible to obtain a high-quality transferred image by forming a stable nip width under a predetermined pressing force.

9A and 9B are explanatory views of concrete size examples of the tackdown roll, the transfer corotron and the peel-off roll which constitute the transfer part. FIG. 9A is a side view of the tackdown roll, and FIG. 9B is a view of the transfer corotron. A top view, (c) is a sectional view of the transfer corotron cut along the line C-C in (b), and (d) is a side view of the peel-off roll. The tack-down roll 13 has a widthwise length of 222 mm and a diameter of 16 mm, and the corotron wire 14a of the transfer corotron 14 has a length of 221 mm. The peel-off roll 15 has a widthwise length of 222 mm, which is the same as that of the tack-down roll 13, and a diameter of 16 mm. Other dimensions are as shown.

As shown in the section (c), the transfer corotron 14 has a structure in which the corotron wire 14a is surrounded by a shield 14b except for the side facing the photoconductor, and the opening direction of the shield 14b is the same. A transfer electric field is formed on the. It should be noted that the above size example is merely an example, and the size is not limited to this.

The copying machine of the above-described embodiment is of a type in which the toner image formed on the drum-shaped photosensitive member 1 is directly transferred to a transfer member such as transfer paper. However, the toner image formed on the photosensitive member is temporarily transferred to the intermediate transfer member. The present invention can be similarly applied to a copying machine of the type in which after the primary transfer to the transfer material, the secondary transfer is performed on the transfer material. FIG. 10 is a schematic diagram illustrating the configuration of an embodiment of a color copying machine using an intermediate transfer body as another example of an image forming apparatus using a liquid developer, and 31 is an intermediate transfer body as a transfer body. The intermediate transfer belts 31a, 31b, and 31c are belt conveying rollers, 32 is a bias roll that constitutes a secondary transfer unit, 33 is a backup roll, and 34 is a secondary transfer power source.

In the figure, the first formed on the photoconductor 1
The electrostatic latent image of color (Y) is toner-developed by the developing device 4Y for the first color, and is primarily transferred to the intermediate transfer belt 31 at the primary transfer portion where the transfer corotron 14 is installed. At this time, the tack-down roll 13 and the peel-off roll 15 are respectively arranged upstream and downstream of the transfer corotron 14 as in the above-described embodiment. The peel-off roll 15 is not always necessary.

After the transfer of the toner image of the first color, a toner image of the second color (M) is formed on the photoconductor 1. At this time, the intermediate transfer belt 31 has the belt conveying rollers 31a, 31b, 3
1c and the backup roll 33, and is circulated and conveyed in the direction of the arrow.
When the color toner image reaches the position of the transfer corotron 14 of the primary transfer portion, the intermediate transfer belt 31 arrives at the position of the transfer corotron 14 at the same timing as the toner image of the first color that has been primarily transferred first.

Thereafter, similarly, the toner image of the third color (M) and the toner image of the fourth color (K) are transferred onto the intermediate transfer belt 31 in an overlapping manner. In this primary transfer cycle, the bias roll 32 is retracted to a position away from the intermediate transfer belt 31. Synchronized with the timing when the intermediate transfer belt 31 carrying the full-color toner images is rotated and reaches the secondary transfer portion where the bias roll 32 is arranged after the superposed transfer of all the required color toner images is completed. The transfer paper is fed from a transfer material carry-in roll (not shown) and enters the nip between the bias roll 32 and the intermediate transfer belt 31.

The intermediate transfer belt 31 and the transfer paper 28 are conveyed in the arrow direction while receiving a predetermined pressing force by the bias roll 32 and the backup roll 33 arranged on the back surface of the intermediate transfer belt 31. At this time, a transfer voltage is applied to the bias roll from the secondary transfer power source 34, and the multicolor toner image carried on the intermediate transfer belt 31 is secondarily transferred onto the transfer paper 28.

The transfer paper 28 to which the toner image from the intermediate transfer belt 31 is secondarily transferred is conveyed to a fixing device (not shown) and subjected to a fixing process. Also in this embodiment, the toner image developed on the surface of the photoconductor 1 using the liquid developer is applied to the primary transfer portion of the tack-down roll 1 as in the above-described embodiment.
3, or by installing the tack-down roll 13 and the peel-off roll 15, it is possible to obtain a high-quality color image.

Next, the present invention is applied to an image forming apparatus in which a photoconductor is separately prepared for each color and the toner images formed on the photoconductors are sequentially superposed on one transfer material to form a full-color image. The embodiment will be described. FIG. 11 is a schematic diagram for explaining the configuration of still another embodiment of a color copying machine as an example of an image forming apparatus using a liquid developer, in which each toner formed on a plurality of photoconductors corresponding to each color. The present invention is applied to a so-called tandem-type full-color copying machine using an intermediate transfer body, which is configured such that images are sequentially superimposed and transferred onto an intermediate transfer belt, and then simultaneously transferred onto a transfer sheet and fixed.

In the figure, 1Y, 1M, 1C and 1K are yellow, magenta, cyan and black photoconductors,
2Y, 2M, 2C, 2K are chargers, 3Y, 3M, 3C,
3K is an exposure optical system, 3Ya, 3Ma, 3Ca and 3Ka are laser beams, 4Y, 4M, 4C and 4K are developing devices using a liquid developer, 9Y, 9M, 9C and 9K are excess liquid removing rollers, 13Y, 13M, 13C and 13K are tack down rolls, 14Y, 14M, 14C and 14K are transfer corotrons, 20Y, 20M, 20C and 20K are cleaning devices, 21Y, 21M, 21C and 21K are static elimination lamps, 28 is transfer paper, and 35 is a transfer member. Intermediate transfer belt, 36 is a belt conveying roller, 37 is a heating roller, 3
8 is a pressure roller, 39 is a belt cleaning device, and 40
Is a belt static charge corotron.

In the same figure, this copying machine has a charger 2Y,
2M, 2C, 2K uniformly charged photoconductors 1Y, 1M,
1C, 1K laser beams 3Ya, 3Ma, which are modulated according to image signals by exposure optical systems 3Y, 3M, 3C, 3K,
The electrostatic latent image formed by the scanning of 3Ca and 3Ka is developed and visualized by the developing devices 4Y, 4M, 4C and 4K using the liquid developer.

The visualized liquid toner images of the respective colors are primarily transferred onto the intermediate transfer belt 35 which is stretched around the belt conveying roller 36 and the heating roller 37. This primary transfer is performed by the tack down rolls 13Y, 13M, 13 described in the above embodiment.
C, 13K and transfer corotron 14Y, 14M, 14C,
14K. The excess liquid carrier image is removed by the excess liquid removing rollers 9Y, 9M, 9C and 9K.

The liquid toner images formed on the photoconductors 1Y, 1M, 1C and 1K are sequentially superposed in accordance with the movement of the intermediate transfer belt 35 in the direction of arrow G, and the toner images of all colors are superposed. After being heated, the heating roller 37 and the pressure roller 3
At the same time as being transferred onto the transfer paper 28 conveyed during 8, the toner is heated and pressurized and fixed. The intermediate transfer belt 35 is formed by coating a heat-resistant film of conductive polyimide or the like with a thin layer of silicone rubber, fluororubber or the like, and is a heating roller 37 that is a drive and transfer simultaneous fixing roll with a built-in heater.
Driven by.

At each transfer station composed of the photoconductors 1Y, 1M, 1C and 1K, the tack down rolls 13Y, 13M, 13C and 13K and the transfer corotrons 14Y, 14M, 14C and 14K, the excess liquid removing roller 9Y,
The toner images after the excess carrier liquid is absorbed by 9M, 9C, and 9K are tack down rolls 13Y, 13M,
Corotron 14 negatively transferred at 13C and 13K
In Y, 14M, 14C, and 14K, transfer is performed with a plus (+) dynamic current value under the parameters set in the condition shown in FIG. 6 and the multicolor condition.

In this case, since the peeling point is regulated by the moving line of the intermediate belt 35, the peel-off roll is not necessary. In addition, the wet transfer paper 28 and the photoconductors 1Y, 1
Since it is not necessary to apply a pressure between M, 1C and 1K, the pressure roller shown in FIG. 2 is also unnecessary. The photosensitive members 1Y, 1M, 1C and 1K after the toner image is primarily transferred onto the intermediate transfer belt 35 are cleaned by the cleaning device 20Y,
The residual toner is removed by 20M, 20C and 20K, and the residual charge is removed by the static elimination lamps 21Y, 21M, 21C and 21K.

On the intermediate transfer belt 35 after the secondary transfer of the full-color toner image onto the transfer paper 28, the residual charge is removed by the belt discharging corotron 40, and the residual toner is removed by the belt cleaning device 39. Also in this embodiment, a high quality transferred image can be obtained using the liquid developer.

In the tandem type similar to the above,
A tuck-down roll is used in which a transfer belt for placing and transporting a transfer sheet is used instead of the intermediate transfer belt 35, and the toner images formed on the photoconductors 1Y, 1M, 1C, and 1K are sequentially superimposed and transferred onto the transfer sheet. Alternatively, tuck down rolls and peel off rolls can be provided. Next, a more detailed specific example of the embodiment of the present invention will be described.

[Specific Example 1] In the configuration shown in FIG.
A selenium-based photoconductor is used as the photoconductor 1, Isopar L (manufactured by Exxon) is used as a carrier liquid for the liquid developer, and a developer in which negative (-) chargeable toner particles are dispersed is used. A picture output (transfer) test was conducted using the copying machine described.

The developer of each color has a charging potential in the dark,
+650 V, +50 V as the background potential, -50 V for the fixed electrode (developing electrode) 4a, ... Of the developing device, and a metering roll 4b, ... Rotating in the same direction as the photoconductor.
A bias of + 250V is applied to. The rotation speed of the metering rolls 4b, ... Was set to twice the surface speed of the photoconductor 1. After that, while applying -2 KV as a bias voltage by the liquid absorbing roller 9 of the conductive sponge, the liquid was absorbed by the sponge layer, and the pre-transfer condition was adjusted.

One cycle before this cycle, the transfer paper 28 is fed to the transfer sheet 12 constituting the transfer drum by the carry-in roller 27, and electrically stuck to the transfer sheet 12 by the suction corotron 19. A transfer sheet (screen sheet) 12 (see FIG. 3) that constitutes the transfer drum.
As reference), coated paper was used. Next, the transfer paper 28 was wetted by rotating the pre-wet roll 18a from the transfer surface side of the transfer paper 28 at 1000 rpm in the direction opposite to the rotation direction of the transfer drum 12.

Further, the tuck down roll 13 is also used as a roll means for pressing the transfer sheet 28 and the transfer sheet 12 constituting the transfer unit to the photoconductor 1 at 150 g /
The transfer sheet (screen sheet) 12 and the transfer paper 28 were pre-press-contacted to the photoconductor 1 by press contacting with a pressure (line load) of cm. The order of colors to be developed and transferred is Y, M, C, and K, and the condition of the transfer unit is set to the dynamic charge density, as shown in Table 1, and when multiple transfer is performed, retransfer and hollow defects occur. A high-quality transferred image free of transfer defects and other image quality defects was obtained.

After that, the transfer material 28 was peeled from the transfer drum 12 and passed through the fixing device 26. As a result, a copy image having gloss and sharpness and excellent copy quality was obtained.

[0086]

[Table 1]

[Concrete Example 2] As a condition for producing a single color without the pre-pressing step, the transfer condition for the first color (Y color) in Table 1 was used, and the pressure of the tack down roll 13 was 30 g / cm.
To 50 g / cm, 80 g / cm, 120 g / cm, 1
A single color test was conducted by changing the values to 50 g / cm, 200 g / cm and 230 g / cm. Other conditions are the same as in [Specific Example 1].

As a result, the pressure contact force of the tack-down roll 13 was preferably 50 to 200 g / cm, and at 30 g / cm, the tack-down roll was found to be floating and poorly following. Also, 2
Even at 30 g / cm or more, the disturbance of the toner was observed as the occurrence of flow, especially at the trailing edge of the transferred image. Here, in order to further understand [Specific Examples 1 and 2] of the present invention, comparative examples will be shown.

[Comparative Example] A drawing test was conducted under exactly the same conditions as in [Specific Example 1] except that the pre-pressing process was not carried out. As a result, transfer defects of the second and third colors, particularly 40 in the low coverage area, were observed. % Transfer dropout occurs in the area below the halftone dot,
Also, a dropout due to retransfer was observed in the overlapping portion of the solid images of the third color.

It is considered that the above-mentioned difference from the specific example in which the pre-pressing process is performed is the adhesion between the transfer sheet and the transfer sheet. [Specific Example 3] The pressure contact force of the tack-down roll 13 in the pre-pressing process is 30 g / g as in [Specific Example 2].
When tested under exactly the same conditions as [Specific Example 1] except that the content was changed from cm to 230 g / cm, [Specific Example 2]
The result shows the latitudinal force of the contact pressure force. From this, it was found that the condition of the pre-pressing process may be the condition setting of the tack down roll 13.

[Specific Example 4] With the pre-pressing process provided, a single-color drawing condition, particularly, the peel-off roll 15 remains electrically floating, and only two dynamic charge densities of the tack-down roll 13 and the transfer corotron 14 are used. When the drawing test was conducted under different conditions, a graph showing a latitude region similar to that shown in FIG. 6 was obtained.

A nearly linear relationship was found in the charge density maps of the tackdown roll 13 and the transfer corotron 14.
Also, in other areas, a significant image quality defect was observed. [Specific Example 5] As an experiment of multiple transfer, the first color is Y color, and 2 is
As a parameter of the transfer process, a two-color drawing of M color is provided as a color, and as a parameter of the transfer process, the first color (Y color) is as shown in [Table 1] and only the condition of the second color (M color) is shown in [Table 2]. As described above, it was changed into a matrix. The peel-off roll 15 was left electrically floating (σ _Z = 0).

[0093]

[Table 2]

In Table 2, "flat" means that the dynamic charge density is the same as that of the first color, "UP" means that the absolute value of the dynamic charge density is large, and "Do"
“Wn” means that the absolute value of the dynamic charge density becomes small. Further, the numbers shown in the result column relatively indicate the sensory evaluation results, and "5" of 5 grades is good and "1" is not so good.

Summarizing these results, from the viewpoint of preventing retransfer of the first color, the tack down roll charge density: σ _X = Down is good. The transfer corotron charge density: σ _Y = any, and the transferability of the second color is good. From the viewpoint of tack down roll charge density: σ _X = flat transfer Corotron charge density: σ _Y = Up, or flat, and from the viewpoint of total image quality defect prevention, tack down roll charge density: σ _X = Down transfer Corotron charge density: σ _Y = Up, or flat, and the conditions that satisfy these conditions are that the tack down roll charge density is lower than that at the time of previous color transfer, or the same transfer corotron charge density as at the time of previous color transfer is used. It has been found that it is better to use the increased value or the same value.

[Embodiment 6] Using the tandem type full color copying machine shown in FIG.
0 mm / sec, pre-pressing process, and other conditions except the condition of peel-off roll which is not used in this copying machine are the same as those in [Specific Example 1], and a semi-conductive intermediate transfer belt made of polyimide and fluorosilicone rubber. Three
5 was transferred. When this was further transferred onto the transfer paper 28 and fixed, a glossy and sharp image was obtained.

Specific Example 7 As materials for the tack-down roll 13 and the pick-off roll 15, urethane rubber, nitrile rubber, epichlorohydrin rubber, fluorosilicone rubber, fluororubber, fluororesin, silicone rubber, and natural rubber are used. Cut into 1 cm and 1 cm wide chips, soak in Isopar L for 1 week at room temperature,
When the dimensional change was measured, the silicone rubber and the natural rubber showed swelling at a size of + 30%, but other rubbers had a swelling shrinkage of about -3% or 0%. In particular, the fluororubber did not show any change.

From this fact, the tack down roll 13,
It was found that the swelling resistance and shrinkage resistance with respect to the liquid developer can be secured by using the above-mentioned materials other than silicone rubber and natural rubber as the material of the pickoff roll 15. [Specific Example 8] From the measurement in the above [Specific Example 7], a tack-down roll and a peel-off roll each having a size of 16φ were prepared from a material that did not swell or shrink.

For the level of conductivity, the material is adjusted so that the resistance value calculated from the current flowing through the metal drum is 10 ⁸ Ω · cm, and the rubber hardness is 30 ° so that the nip width is stable. It was selected in the range of -40 °. Since rubber materials other than fluororesin (urethane rubber, epichlorohydrin rubber, nitrile rubber, fluorosilicone rubber, fluororubber) can be rolled as they are, one-layer rolls made of these materials can be prepared. As a top coat layer, the surface of nitrile rubber was coated with a thin and conductive material to form a two-layer structure.

These rolls were tack-down rolls 13
The peel-off roll 15 was placed in the transfer section and tested under the same conditions as in [Specific Example 1]. [Specific Example 9] As a structure of the tack-down roll 13 and the peel-off roll 15, a shaft 13a (Figs. 7, 8, and 9)
Silicon sponge or urethane sponge was formed around the core metal to be the reference), and the material described in [Specific Example 8] was thinly coated on the sponge.

This coat layer had an average thickness of about 100 μ so that the lower sponge layer could not be seen from the surface.
Although a roll having such a two-layer structure was made, it is easy to make a urethane sponge, but it is difficult to make a silicone sponge. However, silicone sponges are somewhat easier to make if they are electrically conductive. Since this silicone sponge swells significantly, the entire roll was sealed with the top coat layer when applying the top coat.

Among the fluororesins, there are heat-shrinkable tube-like ones, which were used to form the top coat layer. These rolls were tested under the same conditions as in [Specific Example 1], but no matter which roll was used, high quality copies were similarly obtained.

[0103]

As described above, according to the present invention,
By setting the range of the dynamic charge density of the transfer portion in the image transfer by the electrostatic transfer method of the wet liquid toner image, it is possible to obtain high-quality images of single color and full color under a wide range of conditions. In addition, in both single-color and full-color cases, the liquid developer has high sharpness, and it is possible to obtain a high-quality transfer image without retransfer, transfer failure, or other image quality failure.

Furthermore, by using the material of the present invention, it is possible to form a stable transfer nip-width tack-down roll or peel-off roll having no swelling or shrinking property, and a stable and high-quality transfer is possible. A liquid toner image electrostatic transfer method and apparatus for obtaining an image can be provided.

[Brief description of drawings]

FIG. 1 is a schematic view of a principal part for explaining a basic configuration of a liquid toner image electrostatic transfer method and apparatus according to the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of an embodiment of a color copying machine as an example of an image forming apparatus that uses a liquid developer.

FIG. 3 is a schematic view of a main part for explaining a configuration of a transfer section of the color copying machine shown in FIG.

FIG. 4 is a schematic perspective view illustrating a structural example of a transfer drum.

5 is a flow chart illustrating an example of a transfer cycle of the color copying machine shown in FIG.

FIG. 6 is an explanatory diagram of measurement results in which respective dynamic current values flowing by a voltage applied to a transfer corotron and a tuck down roller and image quality of a transferred image are evaluated.

FIG. 7 is an explanatory diagram of a structural example of a tuck down roll.

FIG. 8 is an explanatory diagram of another structural example of a tuck down roll.

FIG. 9 is an explanatory diagram of specific dimensional examples of a tack-down roll, a transfer corotron, and a peel-off roll that form a transfer unit.

FIG. 10 is a schematic diagram illustrating a configuration of an embodiment of a color copying machine using an intermediate transfer body as another example of an image forming apparatus using a liquid developer.

FIG. 11 is a schematic diagram illustrating the configuration of another embodiment of a color copying machine as an example of an image forming apparatus using a liquid developer.

[Explanation of symbols]

1 ... Drum-shaped photoreceptor having photoconductive surface, 2
.... Charger, 3 ... Exposure optical system, 3a ...
Laser beam, 4Y ... Yellow developing device, 4M
··· Magenta developing device, 4C ···, cyan developing device, 4K ···, black developing device, 4a ··· developing electrode, 4b ··· metalling roll, 5a ··· developer Supply tube, 5b ... ・ Developer drain tube, 6 ・ ・ ・ ・ Developer supply box, 9 ・ ・ ・ ・ Excess liquid removal roll, 10 ・ ・ ・ ・ ・ ・ Vacuum tank, 10
a ... excess liquid drain tube, 11 ... vacuum pump, 12 ... transfer sheet, 12a ... transfer drum, 12b ... frame structure of transfer drum,
13 ··· Tuck down roll (press roll), 14
.... Transfer corotron, 15 ... Peel off rolls (peeling rolls), 16a, 16b ...
... Prewetting device, 18a ... Prewetting roll, 18b ... Prewetting roll drive mechanism,
19 ... Adsorption corotron, 20 ... Cleaning device, 20a ... Sponge disturber, 20
b ... cleaning blade, 21 ... static elimination lamp, 22 ... carrier liquid filter, 23 ...
Cleaning recovery liquid tank, 23a ... Recovery tube, 24 ... Recovery pump, 25 ... Transfer material unloading belt, 26 ... Fixing device, 27 ... Transfer material loading roll, 28 .... Transfer bodies (transfer paper, etc.), 30 ...
... Toner image, 31 ... Intermediate transfer belt, 32.
... Bias roll, 33 ... Backup roll, 34 ... Secondary transfer power supply, 35 ... Intermediate transfer belt, 36 ... Belt transport roller, 37 ...
Heating roller, 38 ... Pressure roller, 39 ... Belt cleaning device, 40 ... Belt destaticizing corotron.

Front page continuation (72) Inventor Shinichi Utsumi 430 Sakai, Nakai-cho, Ashigarakami-gun, Kanagawa Green Tech Nakai Fuji Xerox Co., Ltd.

Claims (9)

[Claims] 1. A liquid toner image visualized by developing an electrostatic latent image formed on a photoconductor with a liquid developer in which toner particles are dispersed in an insulating carrier liquid and transferring the visualized liquid toner image to a transfer body or an intermediate transfer body. A method of electrostatically transferring a liquid toner image, comprising: a corona discharge device that is in contact with the photoconductor and applies an electric field having a polarity opposite to that of the toner particles of the liquid toner image; At least a conductive tackdown roll for applying an electric field of the same polarity as the toner particles is provided, a current value flowing in the corona discharge device is I (μA), a peripheral speed of the photoconductor is V (cm / sec), When the length in the width direction of the corona discharge device is L (cm), dynamic charge densities σ _X (C / cm ² ) and σ _Y (C / c) of the tack down roll and the corona discharge device are set.
m ² ) is set to σ _Y = aσ _X + b, where 0 <σ _Y ≦ I / V · L, σ _X <0 −2.5 ≦ a ≦ −1.0 5.0 ≦ b ≦ 15.0 An electrostatic transfer method for a liquid toner image, characterized in that 2. A liquid toner image visualized by developing an electrostatic latent image formed on a photoconductor with a liquid developer in which toner particles are dispersed in an insulating carrier liquid and transferring the visualized liquid toner image to a transfer body or an intermediate transfer body. A method of electrostatically transferring a liquid toner image, comprising: a corona discharge device that is in contact with the photoconductor and applies an electric field having a polarity opposite to that of the toner particles of the liquid toner image; At least a conductive tack-down roll for applying an electric field having the same polarity as the toner particles, and a conductive peel-off roll arranged in the vicinity of the downstream of the corona discharge device are provided, and a current value flowing in the corona discharge device is I ( μA), the peripheral speed of the photoreceptor is V (cm / sec), and the length of the corona discharge device in the width direction is L (cm), the tack down roll and the corona discharge device are Dynamic charge density of the fine the peel-off roll sigma _X (C /
cm ² ) and σ _Y (C / cm ² ) and σ _Z (C / c
m ² ), σ _Y = a σ _X + b where 0 <σ _Y ≦ I / V · L, σ _X <0 σ _Z = 0, or σ _Z ≈σ _Y −2.5 ≦ a ≦ − An electrostatic transfer method for a liquid toner image, wherein 1.0 5.0 ≦ b ≦ 15.0 is set. 3. A plurality of electrostatic latent images corresponding to a plurality of colors sequentially formed on a photoconductor by a plurality of liquid developers in which toner particles of a predetermined color are dispersed in an insulating carrier liquid. Is a method of electrostatically transferring a liquid toner image in which the liquid toner images of a plurality of colors visualized by sequentially developing with each of the liquid developers are sequentially transferred onto either a transfer body or an intermediate transfer body. A corona discharge device that applies an electric field having a polarity opposite to that of the toner particles in contact with, and a conductive tack-down roll that is arranged close to and upstream of the corona discharge device and applies an electric field having the same polarity as the toner particles. At least a conductive peel-off roll disposed near the downstream of the corona discharge device, the current value flowing in the corona discharge device is I (μA), the peripheral speed of the photoconductor is V (cm / sec), When the length in the width direction of the corona discharge device is L (cm), the dynamic charge density σ _X (C / C) of the tackdown roll, the corona discharge device and the peel-off roll.
cm ² ) and σ _Y (C / cm ² ) and σ _Z (C / c
m ² ), σ _Y = a σ _X + b where 0 <σ _Y ≦ I / V · L, σ _X <0 σ _Z = 0, or σ _Z ≈σ _Y −2.5 ≦ a ≦ − 1.0 5.0 ≤ b ≤ 15.0, and at the time of transferring the next color in the multiple transfer of the plurality of colors, σ _X : the same value as when transferring the previous color or a value reduced from the previous color σ _Y : Same value as when transferring the previous color or a value increased from the previous color σ _Z : Same value as when transferring the previous color or 0, which is an electrostatic transfer method of a liquid toner image. 4. The pre-pressing step of pressing at least the transfer member or the intermediate transfer member to the photoconductor by the tack down roll before the photoconductor enters the transfer cycle of the first color. An electrostatic transfer method for a liquid toner image, comprising: 5. The pressure contact force of the tackdown roll with respect to the photoconductor according to claim 4, which is 50 g / cm to 20.
An electrostatic transfer method for a liquid toner image, characterized in that it is 0 g / cm. 6. The I according to claim 1, 2 or 3.
/ V · L is 198 × 10 ⁻⁹ C / cm ² and an electrostatic transfer method for a liquid toner image. 7. A liquid toner image visualized by developing an electrostatic latent image formed on a photoconductor by a liquid developer of at least one color in which toner particles are dispersed in an insulating carrier liquid, and a liquid toner image or a transfer medium or an intermediate transfer. An electrostatic transfer device for transferring a liquid toner image to a body, which comprises a corona discharge transfer device which is in contact with the photoconductor and applies an electric field having a polarity opposite to that of the toner particles of the liquid toner image, and an upstream of the corona discharge device. And a conductive tack-down roll for applying an electric field having the same polarity as the toner particles by being disposed in proximity to the toner particle, and a conductive peel-off roll disposed in proximity to the downstream of the corona discharge device, wherein the tack-down roll and the At least the surface material of the peel-off roll is a nitrile resin rubber material, urethane resin rubber material, epichlorohydrin resin rubber material, fluoro Recone resin rubber material, electrostatic transfer system for a liquid toner image, which is a conductive roller formed by mixing a conductive material into at least one fluorine-based resin rubber material. 8. The electrostatic transfer device for a liquid toner image according to claim 7, wherein the tack-down roll and the peel-off roll have at least a two-layer structure. 9. The tack down roll and the peel-off roll according to claim 8, wherein the tack-down roll and the peel-off roll are formed by coating a sponge-like base layer and the sponge-like base layer with a top coat layer made of the material according to claim 7. Electrostatic transfer device for liquid toner image.