JP2000330397A - Wet image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the temperature at the time of transferring and fixing a toner image formed on an image carrier to a recording material at the same time, thereby extending the life of the image carrier and improving the structure of the apparatus. An object of the present invention is to provide a wet image forming apparatus which can be simplified and cost can be kept low. SOLUTION: In a wet image forming apparatus for transferring and fixing a wet toner image formed on a photosensitive drum 1 to recording paper 100 at the same time, the recording material is brought into contact with an intermediate transfer roller 5 and then transferred to a transfer area. And the secondary transfer power supply 8 is applied to the secondary transfer simultaneous fixing roller 8 a of the simultaneous transfer fixing device 8.
With c, the toner image on the intermediate transfer roller is transferred to the recording material. Immediately after the recording paper separates from the intermediate transfer roller, a discharge effect is generated between the recording paper and the intermediate transfer roller to increase the fixing effect, and the heater 8b in the secondary transfer simultaneous fixing roller 8a is increased. To fix the toner image on the recording paper.

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 an image forming method such as a copying machine, a facsimile, a printer and the like. The present invention relates to a wet image forming apparatus that performs simultaneous transfer and fixing by heat.

[0002]

2. Description of the Related Art As an image forming apparatus for performing simultaneous transfer and fixing, for example, a dry toner image formed on a recording drum as an image carrier is primarily transferred onto an intermediate transfer belt as an intermediate transfer body. When the toner image on the intermediate transfer belt is secondarily transferred to paper as a recording material, the toner image is heated and pressed by a heat roller facing the intermediate transfer belt via the paper, and the toner image is secondarily transferred to the paper. A method that simultaneously performs a fixing process is disclosed in "Adhesive Melt Transfer of Toner Image" (Fujitsu Laboratories) published in a preliminary collection of Japan Hard Copy. FIG. 9A is a schematic configuration diagram of a secondary transfer simultaneous fixing device for dry toner in the image forming apparatus, and FIG. 9B is an enlarged view of a secondary transfer portion of the image forming apparatus.

In this image forming apparatus, first, a dry toner image formed on the recording drum 101 is primarily transferred onto an intermediate transfer belt 102 having a surface formed of silicon rubber in a primary transfer section. You. In this primary transfer, the dry toner image on the recording drum 101 is transferred by the adhesiveness of the silicone rubber. And this one
Next, the toner image formed on the intermediate transfer belt 102 by the next transfer is heated and pressed by a secondary transfer unit facing the paper 100 and is transferred to the paper. In the secondary transfer section, the toner image on the intermediate transfer belt 102 is
It is heated by the heating roller 103 via the paper 100 and melted. Then, the dissolved dry toner image penetrates into the fibers of the paper 100 by the pressure of the heating roller 103 and, at the same time, separates from the intermediate transfer belt 102 due to the releasability of the silicone rubber forming the surface of the intermediate transfer belt 102. I do. The toner image secondary-transferred onto the paper 100 in this way is conveyed from the secondary transfer unit, and then cooled and cured to be fixed on the paper.

FIG. 10A is a graph showing the secondary transfer efficiency and the fixing rate with respect to the pressure in the secondary transfer section of the image forming apparatus. FIG. 10B is a graph showing the intermediate transfer rate in the secondary transfer section. 5 is a graph showing a secondary transfer efficiency and a fixing rate with respect to a surface temperature of a transfer belt. Considering FIG. 10A, in order to obtain sufficient secondary transfer efficiency to increase the image density, and to obtain a sufficient fixing rate and enhance the fixing effect to obtain a high-quality image, it is necessary to use about 0.2 mm. It is understood that a pressure of 4 kgf / cm or more is required. Considering FIG. 10B, it is understood that the surface temperature of the intermediate transfer belt needs to be about 150 ° C. or higher in order to obtain a high-quality image. Furthermore, in order to obtain 100% secondary transfer efficiency and fixing rate and to realize perfect simultaneous transfer fixing,
The pressure must be at least 1.0 kgf / cm and the surface temperature of the intermediate transfer belt must be 200 ° C.

A wet image forming apparatus which performs simultaneous transfer and fixing using a wet developer instead of using a dry developer as described above is disclosed in Japanese Unexamined Patent Publication No. Hei 3-154085. FIG. 11A is a schematic configuration diagram of the wet image forming apparatus. In this wet image forming apparatus,
When a normal electrophotographic process is performed, the electrostatic latent image formed on the photosensitive drum 1 as an image carrier is developed by a developing device 4 as a developing unit to form a wet toner image on the photosensitive drum. Then, the wet toner image is primarily transferred to an intermediate transfer drum 5 as an intermediate transfer body by electrostatic force.

As shown in FIG. 11B, the intermediate transfer drum 5 has a thickness of 0.5 to 2.5
mm conductive rubber layer is formed, and a thickness of 5-30
It is formed by forming a μm dielectric layer. The wet toner image primarily transferred onto the intermediate transfer drum 5 is
As a result of being pressed by the pressure roller 108 in contact with 0, secondary transfer is performed mainly on the paper by mechanical action. At this time, a voltage may be applied to the pressure roller 108 to use the electrostatic force supplementarily. Further, as shown in FIG. 11 (c), a heater 109 is provided inside the pressure roller, and the pressure is applied by the pressure roller, and at the same time, a fixing process by heat is performed to perform simultaneous transfer fixing. Will be JP-A-3-15408 discloses this wet image forming apparatus.
No. 5 does not show specific numerical values of the temperature in the secondary transfer portion, but in order to obtain a high secondary transfer efficiency and a high fixing rate, the same as in the above-described image forming apparatus using a dry developer is used. It will be obvious to those skilled in the art that very high temperatures are a necessary requirement.

[0007]

As described above, in a conventional image forming apparatus which performs simultaneous transfer and fixing, when a dry developer is used, the secondary transfer section is required to have a high secondary transfer efficiency and a high fixing rate. It had to operate at a high temperature of about 200 ° C. Therefore, there is a problem that the life of the intermediate transfer belt is shortened. Further, in order to secure the necessary adhesiveness in the primary transfer section and prevent the recording drum from deteriorating, the surface of the intermediate transfer belt heated to around 200 ° C. reaches the primary transfer section. It is necessary to cool to near room temperature before doing so.
For this reason, it is necessary to provide a large-scale cooling mechanism, which complicates the structure of the image forming apparatus and increases the cost.

In a wet image forming apparatus which performs simultaneous transfer and fixing using the above-mentioned wet type developer, Japanese Patent Application Laid-Open No. 3-154085 discloses the wet type image forming apparatus. Although specific numerical values are not shown, those skilled in the art are aware that in order to obtain high secondary transfer efficiency and fixing rate, a considerably high temperature is indispensable similarly to the image forming apparatus using the dry developer described above. Is self-evident. Therefore, in this wet image forming apparatus, it is considered that the problem that the life of the intermediate transfer drum is shortened and the problem that the structure becomes complicated and the cost becomes high due to cooling of the intermediate transfer drum arise.

By the way, when fixing the toner image transferred to the paper as the recording material on the paper, the present applicant drastically lowers the fixing temperature and the fixing pressure by applying a corona discharge current to the toner image. We have proposed a fixing device that can do this. Here, in this fixing device, an experiment is performed to measure the fixing rate of the toner to the corona discharge current flowing through the heating roller when a voltage is applied to the pressure roller, and the fixing effect is confirmed.

FIG. 12 is a schematic configuration diagram of a fixing device used in this experiment. This fixing device comprises a pressure roller 110 formed of an aluminum tube and a heating roller 111 having a high-resistance aluminum oxide thin layer on the surface. FIG. 13 is a graph showing the results of this experiment. In this experiment, while the surface temperature of the heating roller 111 was maintained at 70 ° C., the voltage applied to the pressure roller 110 was changed to change the current value of the corona discharge current, and the toner fixing rate Dn was measured. did. In this experiment, yellow toner (hereinafter, referred to as “Y toner”), magenta toner (hereinafter, referred to as “M toner”), cyan toner (hereinafter, referred to as “C toner”), and black toner (hereinafter, referred to as “C toner”). The measurement was performed on a full-color toner image formed by sequentially superimposing the respective toner images developed with the four color liquid developers of “Bk toner”.
The toner used in these liquid developers has an average particle diameter of about 2.0 μm and is positively charged.

[0011] Toner fixing rate D as a criterion for determining the fixing effect
n means that the light reflection density of the toner image on the paper 100 is first measured before fixing, the toner image fixed on the paper is fixed with a predetermined adhesive tape after fixing, and the toner remaining on the paper after the separation is removed. The light reflection density of the image is measured, and this value is calculated by dividing the measured value by the measured value before fixing. That is, when the toner fixing rate Dn is 1, it indicates that the toner is completely fixed. Also,
When the toner image formed on the paper 100 is in a completely unfixed state, there is a limit to the amount of the toner image that can be peeled off with the adhesive tape, so that the toner fixing rate Dn is reduced only to about 0.4.

Considering the graph shown in FIG.
When no corona discharge current flows, the toner image hardly fixes, and it can be seen that the toner fixing rate Dn increases as the amount of corona discharge current increases. Then, among the color toners forming the toner image, C
It was found that the toner was about 1.5 mA, and the Y and M toners were about 2.0 mA.
Further, when no corona discharge current is passed at 70 ° C. as in this experiment, the toner image hardly fixes, but conversely, even when a 2.0 mA corona discharge current is passed. Did not set at room temperature.
In this experiment, the measurement was performed on the discharge current using corona discharge. However, the same effect can be obtained with other discharges such as glow discharge as long as the discharge is not limited to corona discharge. .

An experiment was also conducted to determine whether the same effect as the above-described corona discharge current can be obtained with a normal current. In this experiment, the other conditions were the same as the above-mentioned experiment except that a heating roller having no aluminum oxide thin layer on the surface was used.

FIG. 14 is a graph showing the results of this experiment. Considering this figure, it can be seen that even if the current value of the normal current increases, the toner fixing rate Dn remains at about 0.4 or less, and the toner image is hardly fixed. That is, in the case of corona discharge current, complete fixing was realized at 2 mA, but at normal current, no fixing was performed even at 2 mA. The reason that the ordinary current has almost no effect is that the ions generated by the discharge are uniformly supplied to the entire toner image in the case of the current caused by the discharge, whereas in the case of the normal current the ions generated by the discharge are uniformly supplied. This is considered to be because the current that should flow into the toner image flows into the path with the smallest resistance without passing through the toner image. As a result, in order to improve the fixing effect at low temperature and low pressure,
It has been found that the discharge current must be a current instead of a normal current.

Although it has been found that fixing can be performed at a low temperature and a low pressure when a discharge current flows as described above, its mechanism has not been elucidated yet. However, the present inventors believe that this is based on the following two hypotheses.

The first hypothesis is that at the time of fixing, the toner forming the toner image is more positively charged due to a discharge current flowing through the toner image on the paper, and a very strong toner is formed between the toner and the paper surface. The effect of the mirror image is to improve the fixing efficiency. Each of the toners forming the toner image is deformed and agglomerated under the influence of the mirror image force, thereby discharging silicone oil which is a solvent interposed between the toners. As a result, it is presumed that the adhesion between the respective toners was enhanced, and a high aggregation effect was obtained, so that the toner could be fixed even at a low fixing temperature. In this case,
The toner to be used must be crushed by its electrostatic force when a strong image force is applied, and its outer shape must be deformed, not a hard toner like a dry developer,
It is assumed that the toner must be relatively soft like a liquid developer.

The second hypothesis is that the positive ions generated by the discharge adhere to the toner, and any of the base resin, the dye / pigment, the polarity controlling agent, and the dispersant constituting the toner is heated to 70 ° C.
By causing a chemical change in the vicinity, the toner is fixed on the paper. This is because the fixing rate Dn is changed only by changing the dye and pigment constituting the toner as shown in FIG.
It is presumed that the aggregation and curing of the toner and the binding of the toner to the paper fibers were promoted by the dyes and pigments and the positive ions.

In these hypotheses, it is considered that the discharge current is not limited to the corona discharge current used in the above experiment, but may be the same for glow discharge and other discharge currents.

Here, the configuration of the fixing device and the configuration of the transfer unit of the conventional image forming apparatus will be compared. FIG. 15 is a schematic configuration diagram of a secondary transfer unit that transfers a toner image to paper as a recording material in a conventional wet image forming apparatus. In this secondary transfer section, the toner image on the intermediate transfer roller 5 as an intermediate transfer member is secondarily transferred to the paper 100. In this image forming apparatus, in the primary transfer section, not only toner but also silicone oil as a solvent adheres to the intermediate transfer roller 5 together. Then, in the primary transfer section, the toner is electrophoresed in a solvent by a predetermined primary transfer electric field and is primarily transferred onto the intermediate transfer roller 5. Also, 2
In the next transfer, the toner image on the intermediate transfer roller 5 is secondarily transferred onto paper by electrophoresis of the toner in a solvent by a predetermined secondary transfer electric field. In the secondary transfer unit, the secondary transfer roller 12
By applying a predetermined voltage to the intermediate transfer roller 5 and applying a predetermined voltage to the intermediate transfer roller 5, a secondary image is formed in the developer layer, which is a toner image on the paper 100 sandwiched between the rollers. A transfer electric field is formed. At this time, for example, when −1500 V is applied to the secondary transfer roller 120 and −500 V is applied to the conductive support of the intermediate transfer roller 5, a part of the 1000 V potential difference generated during this time is applied to the paper 100. To a very thin developer layer having a thickness of several μm, and a high secondary transfer electric field is formed.

The configuration of the secondary transfer portion in such a conventional wet image forming apparatus is such that the corona discharge current described above is applied in that a high voltage is applied to one of the rollers with the paper interposed between the two rollers. It is similar to a fixing device that performs fixing by utilizing. Accordingly, it has been found that simultaneous transfer and fixing can be performed at a low temperature and a low pressure if simultaneous transfer and fixing can be performed in the secondary transfer section of the conventional image forming apparatus by using the fixing method of the fixing device.

The present invention has been made in view of the above background, and an object of the present invention is to suppress the temperature when transferring and fixing a toner image formed on an image carrier to a recording material at the same time. Accordingly, an object of the present invention is to provide a wet image forming apparatus capable of extending the life of the image carrier, simplifying the structure of the apparatus, and suppressing the cost.

[0022]

In order to achieve the above object, the invention according to claims 1 to 7 is directed to a liquid developer formed on the image carrier by the action of a transfer electric field formed in a transfer area. Image forming apparatus having a transfer simultaneous fixing means for transferring a toner image developed by the method to a recording material entering the transfer area, and fixing the toner image transferred to the recording material by heating the recording material. Wherein the simultaneous transfer fixing means has discharge generating means for generating a discharge between the recording material and the image carrier immediately after the recording material separates from the image carrier; After the recording material is brought into contact, the recording material is caused to enter the transfer area, and the toner image on the image carrier is transferred to the recording material and fixed.

In this wet image forming apparatus, when performing simultaneous transfer and fixing, the discharge generating means generates a discharge between the recording material and the image carrier after the recording material separates from the image carrier. Accordingly, the fixing effect can be enhanced even at low temperature and low pressure for the same reason as the conventional fixing device described above.

Further, simply employing a fixing method in which fixing is performed by using a discharge current in a transfer portion of a conventional image forming apparatus simply results in a corona discharge (hereinafter, referred to as “corona discharge”) generated when a recording material enters a transfer area. The transfer efficiency may be reduced due to “entrance discharge”). For example, when transferring a toner image formed of positively charged toner to a recording material, when this entrance discharge occurs, a problem occurs that negative corona ions adhere to the paper surface side and transfer efficiency is reduced. However, the problem caused by the discharge at the entrance is that when the recording material comes into contact with a member having a lower potential first,
The negative corona ions enter the liquid developing material layer, which is a toner image on the recording material, and cancel the charge of the positively charged toner. Therefore, if the recording material is brought into the transfer area after the recording material is brought into contact with the image carrier as in the wet image forming apparatus according to claim 1, the negative corona ions are transferred and fixed simultaneously. Since a normal transfer electric field is formed with the counter charge generated on the device side, the above-described problem does not occur.

According to a second aspect of the present invention, in the wet image forming apparatus of the first aspect, the simultaneous transfer and fixing means heats the recording material for a predetermined time after the discharge is generated by the discharge generating means. It is a feature. According to the study of the present inventors, when a discharge current is applied to the toner image after heating the toner image on the recording material, fixing is performed as compared with the case where heating is performed after applying a discharge current to the toner image. It has been found that the effect is low. Therefore, claim 2
Improving the fixing effect by making it possible to continue heating the toner image even after a discharge current is applied to the toner image on the recording material by the discharge generating means as in the wet image forming apparatus of (1). Can be achieved.

According to a third aspect of the present invention, in the wet image forming apparatus of the second aspect, a temperature adjusting means for adjusting a temperature of the toner image in the transfer area is provided. . In this wet image forming apparatus,
By maintaining the temperature of the toner image in the transfer area at an appropriate temperature by the temperature adjusting means, the toner image can be heated substantially after discharging. As the temperature adjusting unit, a unit for adjusting the heating temperature of the simultaneous transfer fixing unit, a unit for adjusting the contact pressure or the nip width with respect to the image carrier in the transfer area, and the like can be considered.

According to a fourth aspect of the present invention, in the wet image forming apparatus of the first, second or third aspect, an image carrier cooling means for cooling the temperature of the surface of the image carrier passing through the transfer area is provided. It is characterized by the following. In this wet image forming apparatus, the temperature of the surface of the image carrier that has passed through the transfer area is reduced to an appropriate temperature by the image carrier cooling unit, so that the temperature of the image carrier increases. It is possible to prevent the life of the peripheral members of the image carrier from being shortened. Further, when the image carrier is an intermediate transfer body, the temperature of the surface of the intermediate transfer body that has passed through the secondary transfer area by the image carrier cooling means is reduced to an appropriate temperature by the primary transfer area. It is possible to prevent a decrease in transfer efficiency of the primary transfer portion due to a rise in surface temperature of the intermediate transfer member. Further, since the image carrier is cooled before passing through the transfer area and returning to the transfer area again, it is possible to suppress a rise in temperature of the toner image in the transfer area. Therefore, it is possible to substantially heat the toner image after discharging. As the image carrier cooling means, there can be conceived one which forms the image carrier with an endless belt so as to be easily cooled naturally, or one which forcibly cools the surface of the image carrier.

Also, the invention of claim 5 is based on claims 1, 2,
In the wet image forming apparatus of (3) or (4), the simultaneous transfer and fixing unit includes a recording material transport belt formed of an endless belt that contacts and transports the recording material that has entered the transfer area, and the recording material transport belt. A transfer member that stretches upstream of the transfer area in the recording material transport direction and forms a transfer electric field in the transfer area; and a recording material transport belt that stretches the transfer area downstream of the transfer area in the recording material transport direction. A transfer simultaneous fixing member for forming a transfer electric field in the area and heating the recording material via the recording material conveying belt.

In this wet image forming apparatus, a recording material conveying belt formed by an endless belt that is brought into contact with and conveys the recording material that has entered the transfer area is employed. The temperature can be cooled before the surface of the conveyor belt returns to the transfer area next time. As a result, it is possible to prevent the temperature of the surface of the image bearing member disposed opposite to the transfer region from rising, and to prevent the life of the image bearing member and the peripheral members of the image bearing member from being shortened due to the temperature rise of the image bearing member. be able to. Further, when the image carrier is an intermediate transfer member, the temperature of the surface of the intermediate transfer member that has passed through the secondary transfer area can be prevented from rising, and the primary transfer portion caused by the surface temperature increase of the intermediate transfer member can be prevented. A decrease in transfer efficiency can be prevented. Further, it is possible to suppress a rise in temperature of the toner image in the transfer area, and it is possible to substantially heat the toner image after discharging.

In this wet image forming apparatus, the recording material that has entered the transfer area is first transferred by the transfer electric field formed by the transfer member, and then the transfer and fixing is performed by the transfer and fixing member. Thus, the transfer efficiency can be improved.

According to a sixth aspect of the present invention, in the wet image forming apparatus of the fifth aspect, there is provided a pressurizing means which opposes the transfer member and presses the recording material toward the recording material transport belt at a predetermined pressure. It is characterized by having been provided. In this wet image forming apparatus, a recording material located in the transfer area is pressed against the image carrier with a predetermined pressure by a pressing unit, so that a fixing effect by a mechanical action can be enhanced. However, if pressure is applied to a portion of the transfer area where heating is performed, the temperature of the toner image increases at that portion, and the fixing effect is reduced. In view of this, in the sixth aspect, the recording material is pressurized at a portion different from the portion for heating the toner image and at a position upstream of the portion to be heated in the recording material conveyance direction. Thereby, the fixing effect can be enhanced without increasing the temperature of the toner image in the transfer area.

The invention of claim 7 is the invention of claim 5 or 6
In the wet image forming apparatus, the recording material transport belt is formed of a medium-resistance material, and an earth member is provided to abut the back surface of the recording material transport belt so that the transfer member has a predetermined potential without using a power supply. It is characterized by the following.
In this wet image forming apparatus, the transfer member can be set to a predetermined potential without providing a power supply necessary for applying a voltage to the transfer member.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a full-color electrophotographic copying machine (hereinafter, referred to as a copying machine) which is a wet image forming apparatus will be described below. First,
A schematic configuration of the entire copying machine according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram of the entire copying machine according to the present embodiment. In this copying machine, a charger 2 serving as charging means, an optical writing unit 3 serving as exposure means, a developing unit 4 serving as developing means, and an intermediate transfer member serving as an image carrier are provided around a photosensitive drum 1. , A photosensitive member cleaning unit 6 as a cleaning unit, and a discharge lamp 7 as a discharge unit. Around the intermediate transfer roller 5, a simultaneous transfer fixing device 8 as a simultaneous transfer fixing unit for transferring and fixing the wet toner image formed on the intermediate transfer belt onto a recording paper 100 as a recording material. And a cleaning unit 9 as a cleaning means.

Next, the image forming operation of the copying machine will be described. In this copying machine, the surface of the photosensitive drum 1 is uniformly charged by the charger 2, and then the laser is irradiated by the optical writing unit 3 based on the image information of the original read by image reading means such as a scanner. Then, the photosensitive drum is exposed to light. As a result, an electrostatic latent image is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 includes yellow (hereinafter, referred to as “Y”), magenta (hereinafter, referred to as “M”), cyan (hereinafter, referred to as “C”), and black. (Hereinafter, "B
k ”. ) Is formed by monochrome image information decomposed into color information. Here, when the present invention is applied to a printer, an electrostatic latent image is formed based on image information from image information output means for outputting image information, for example, a personal computer.

The electrostatic latent image is developed with predetermined Y, M, C and Bk toners when the respective color developing units of the developing unit 4 come into contact with the photosensitive drum 1, and the photosensitive drum is A toner image of each color is formed thereon.
The toner images of the respective colors formed on the photosensitive drum 1 are sequentially superimposed on the intermediate transfer roller 5 driven at a constant speed with the photosensitive drum for each of the colors Y, M, C and Bk. Next is transferred. The formed toner image superimposed on the intermediate transfer roller 5 in this manner is conveyed from a paper cassette (not shown) to a secondary transfer section including the intermediate transfer roller and the simultaneous transfer fixing device 8. At the same time, the toner image is transferred onto the recording paper 100 at the same time and is fixed on the recording paper.

After the simultaneous transfer and fixing in the secondary transfer section is completed, the recording paper 100 is discharged to a discharge tray (not shown). The liquid developer remaining on the intermediate transfer roller 5 is removed by the cleaning unit 9. The liquid developer remaining on the photoconductor drum 1 without being transferred onto the intermediate transfer roller 5 is removed from the photoconductor drum by the photoconductor cleaning unit 6. Then, the residual potential is removed from the cleaned surface of the photosensitive drum 1 by the charge removing lamp 7 to prepare for the next image forming step.

[Structural Example 1] Next, a structural example of a secondary transfer unit which is a characteristic part of the present invention (hereinafter, this structural example is referred to as "Structure Example 1")
That. ) Will be described. FIG. 2 is a schematic configuration diagram of a secondary transfer unit in the copying machine. The secondary transfer section includes the intermediate transfer roller 5 and the simultaneous transfer fixing device 8.
It is composed of The intermediate transfer roller 5 is formed by coating a medium resistance rubber layer 5b on a hollow aluminum tube 5a, and performs a primary transfer for applying a voltage for forming a primary transfer electric field to the hollow aluminum tube. A power supply 5c is provided. A voltage of -500 V is applied to the intermediate transfer roller of this configuration example by the primary transfer power supply 5c. Medium resistance rubber layer 5b forming the surface of the intermediate transfer roller 5
It is preferable to use a material which is very smooth, has excellent releasability, and has high heat resistance. Specifically, the intermediate transfer roller 5 of this configuration example uses a hollow aluminum roller having a diameter of 60 mm as the hollow aluminum tube 5a, contains carbon black as the medium resistance rubber layer 5b, and has a volume resistivity of 10 mm. ^A 3 mm thick silicone rubber layer made of silicone rubber adjusted to ⁸ Ωcm was used. The material used for the surface of the intermediate transfer roller may be polyurethane, polyurea, EPDM, or the like, in addition to the silicone rubber.

The simultaneous-transfer fixing device 8 comprises a secondary-transfer simultaneous fixing roller 8a made of a hollow aluminum tube having an aluminum oxide layer on the surface, and a heat source disposed inside the secondary-transfer simultaneous fixing roller. It comprises a heater 8b and a secondary transfer power source 8c for applying a voltage for forming a secondary transfer electric field to the hollow aluminum tube. In this configuration example,
The secondary transfer power supply 8c is connected to the secondary transfer simultaneous fixing roller 8a.
, A voltage of -2000V is applied. Further, the transfer and fixing device 8 is provided with a spring (not shown) as a pressing unit for pressing the secondary transfer and fixing roller 8 a toward the intermediate transfer roller 5. The surface temperature of the secondary transfer simultaneous fixing roller 8a is maintained at about 70 ° C. by a sensor (not shown) and a control system for controlling the heater 8b.

Next, the operation in the secondary transfer section will be described. In the present configuration example, the secondary transfer from the intermediate transfer roller 5 to the recording paper 100 is mainly performed by applying the secondary transfer power supply 8c to the secondary transfer simultaneous fixing roller 8a. It is performed by electrostatic force due to an electric field. Specifically, when a voltage is applied to the secondary transfer simultaneous fixing roller 8a, the toner in the liquid developer on the intermediate transfer roller 5 moves in the carrier liquid against the viscous resistance of the carrier liquid. This causes a so-called electrophoresis phenomenon.
The time required for the toner to reach the recording paper 100 due to the electrophoresis phenomenon is determined by the secondary transfer electric field, the charge amount of the toner, and the kinematic viscosity of the carrier liquid. Therefore, in the secondary transfer section, the moving time of the toner moving in the carrier liquid by a fixed distance is equal to the charge amount of the toner, and when a liquid developer having the same kinematic viscosity of the carrier liquid is used, It is determined only by the secondary transfer electric field.

Therefore, in order to confirm the electrophoretic characteristics of the liquid developer used in the present embodiment, an experiment for measuring the electrophoretic characteristics of the liquid developer was performed. Since this electrophoretic property is used at the time of development rather than at the time of secondary transfer,
Here, the electrophoretic characteristics at the time of development are measured.

The liquid developer used in the present embodiment is obtained by dispersing a positively charged toner in an insulating solvent that is a carrier liquid, and is the same as a commonly used liquid developer. The toner in the liquid developer has a structure in which a dye or pigment for representing a color and a polarity control agent for giving a charge are embedded in the base resin or on the surface thereof. As the insulating solvent, a petroleum-based solvent is usually used in many cases, but in this embodiment, a non-volatile silicon oil is used. Further, a low melting point resin is used as a base resin constituting the toner, and the fixing temperature is lowered to reduce energy consumption. The liquid developer used in the exemplary embodiment has an average particle size of the toner of 2.0.
μm, the average charge amount is +62 μC / g, the kinematic viscosity of the silicone oil as the solvent is 500 cSt, and the toner concentration is 15
What is wt% is used.

This measurement was performed using the liquid developer described above.
The amount of toner transferred from the developing roller, which is the developer carrying member of the developing unit 4, onto the photosensitive drum is measured. Specifically, using a photosensitive drum having a different thickness of the photosensitive drum, a dielectric constant of the photosensitive drum, and a surface potential of the photosensitive drum, changing a developing bias applied to the developing roller. Measurement. The amount of the toner transferred onto the photosensitive drum is determined by peeling off the toner on the photosensitive drum using an adhesive tape, and measuring the light reflection density when the toner is attached to a white paper. It was measured.

FIG. 3 is a graph showing the results of the above measurement. In this figure, the measurement results obtained by using different photosensitive drums are represented by different symbols.
Considering this figure, the amount of toner in the liquid developer that has moved onto the photosensitive drum due to the electrophoretic phenomenon depends on the thickness, dielectric constant, and surface potential of the photosensitive drum. It can be seen that it is determined only from the electric field due to the developing bias applied to the liquid developer layer formed in FIG. Therefore, it can be confirmed that the electrophoretic characteristics of the liquid developer are determined only by the electric field applied to the liquid developer.

Now, the operation of the secondary transfer section in this configuration example will be described. First, the toner image primarily transferred from the photosensitive drum 1 by the rotation of the intermediate transfer roller 5 is secondarily transferred together with the insulating solvent. It is transported to the transfer area. The recording paper 100 also enters the secondary transfer area at the timing when the toner image enters the secondary transfer area. At this time, the recording paper 100 first contacts the intermediate transfer roller 5 having the toner image, is superimposed on the toner image, and wound around the intermediate transfer roller. The toner enters a secondary transfer area formed by a narrow gap with the simultaneous transfer fixing roller 8a. At this time, due to the voltage applied to the secondary transfer simultaneous fixing roller 8a, an entrance discharge occurs with the recording paper 100, and negative corona ions are generated on the surface of the recording paper. The negative corona ions form an electric field with the secondary transfer simultaneous fixing roller 8a, and are applied to the liquid developer layer for forming a toner image on the intermediate transfer roller 5 to contribute to secondary transfer. .

On the exit side of the secondary transfer area, when the recording paper 100 is separated from the secondary transfer simultaneous fixing roller 8a, a corona discharge (corona discharge) occurs between the recording paper and the intermediate transfer roller 5. Hereinafter, this will be referred to as “exit discharge”). The positive corona ions generated by the outlet discharge promote the effect of fixing the toner image on the recording paper for the above-described reason.

[Structural Example 2] Next, another structural example of the secondary transfer portion in the image forming apparatus of the present embodiment (hereinafter, this structural example is referred to as "Structure Example 2") will be described. In the above configuration example 1, the toner image to be secondarily transferred onto the recording paper 100 is subjected to corona discharge after being heated, but in this case, the fixing effect was not so much improved. Therefore, the present inventors have found that, as a result of the research, the recording paper 100
It has been concluded that a higher fixing effect can be obtained by applying a corona discharge to the toner image secondary-transferred above and then heating the toner image.

FIG. 4 is a schematic configuration diagram of a secondary transfer section according to this configuration example. The secondary transfer section includes the intermediate transfer roller 5 and the secondary transfer simultaneous fixing roller 8 as temperature control means.
The contact pressure between the toner image and the toner image is set to be relatively low so that the temperature of the toner image in the secondary transfer area does not increase.
Further, the leading end of the recording paper 100 which has passed through the secondary transfer area is clamped, and the recording paper is fixed to the secondary transfer simultaneous fixing roller 8a.
The roller is configured to rotate half a rotation together with the secondary transfer simultaneous fixing roller in a state of being in close contact with the roller. Therefore, in the secondary transfer area, the temperature rise of the toner image secondary-transferred onto the recording paper 100 is suppressed, and an outlet discharge is applied to the toner image when the recording paper passes through the secondary transfer area. Thereafter, heating can be performed in a state of being in close contact with the secondary transfer simultaneous fixing roller.

[Structural Example 3] Next, another structural example of the secondary transfer section in the image forming apparatus of the present embodiment (hereinafter, this structural example is referred to as "Structure Example 3") will be described. Although a high fixing effect can be obtained by the configuration example 2, when the copying machine to which the configuration example 2 is applied performs continuous copying, the fixing effect may gradually decrease. This is because the surface temperature of the intermediate transfer roller gradually increased due to continuous copying, and the primary transfer efficiency when the surface reached the primary transfer area facing the photosensitive drum was reduced. It turns out that.

FIG. 5 is a schematic configuration diagram of the secondary transfer section according to this configuration example. In this configuration example, an intermediate transfer belt 50 composed of an endless belt is used instead of the intermediate transfer roller 5. By changing from the roller shape to the belt shape in this way, the time required for the surface passing through the secondary transfer area to return to the secondary transfer area is longer, and the belt shape is smaller than the roller shape. Since it is easy to cool, the fixing effect at the time of performing continuous copying can be maintained. In the present configuration example, the intermediate transfer belt 50
Surface temperature can be suppressed up to about 70 ° C,
Since the difference from the room temperature is about 45 ° C., it is possible to sufficiently cool the surface until it reaches the primary transfer area only by air cooling with one small fan 51.

[Structural Example 4] Next, another structural example of the secondary transfer portion in the image forming apparatus of the present embodiment (hereinafter, this structural example is referred to as "Structure Example 4") will be described. In the above configuration example 3, a high fixing effect could be obtained even in continuous copying, but the transfer efficiency to plain paper was not so good. It has been found that the cause is that almost no pressure is applied during the secondary transfer.

FIG. 6 is a schematic configuration diagram of the secondary transfer section according to this configuration example. In this configuration example, instead of the secondary transfer simultaneous fixing roller 8a, a recording material transport belt 81 formed by an endless belt that contacts and transports the recording paper that has entered the secondary transfer area, and the recording material transport belt A heating roller 82 as a simultaneous transfer fixing member for forming a secondary transfer electric field in the secondary transfer area and heating the recording paper via the recording material transport belt; and a recording paper of the heating roller. A simultaneous transfer and fixing device 80, which is located on the upstream side in the transport direction and has a transfer roller 83 as a transfer member for stretching the recording material transport belt and forming a secondary transfer electric field in the secondary transfer area, is used. ing.

The recording material conveying belt 81 is formed of an insulating material.
A voltage of 2000 V is applied, and a voltage of -1000 V is applied to the transfer roller 83 by a transfer power supply 83a. In the present configuration example, a pressure roller 10 is provided at a position facing the transfer roller 83 as a pressure unit that contacts the back surface of the intermediate transfer belt 50 and presses the transfer roller at 10 N. I have. This pressure roller 1
By applying a pressure to the recording paper that has entered the secondary transfer area with 0, high transfer efficiency can be obtained even for plain paper. Also, as described above, the heating roller 82
Instead, by applying pressure in the secondary transfer area corresponding to the transfer roller 83, it is possible to prevent the temperature of the toner image in the secondary transfer area from rising, and enhance the fixing effect.

[Structural Example 5] Next, another structural example of the secondary transfer unit in the image forming apparatus of the present embodiment (hereinafter, this structural example is referred to as "Structure Example 5") will be described. In the above configuration example 4, high transfer efficiency could be obtained even for plain paper. However, when continuous image copying was performed using this copying machine,
There is a possibility that the surface temperature of the recording material conveying belt increases, and the fixing effect decreases. Therefore, in the present configuration example, as shown in FIG. 7, a cooling fan 84 as cooling means for cooling the recording material transport belt is provided downstream of the heating roller 82 in the recording paper transport direction. As a result, a high fixing effect can be obtained even in continuous copying.

[Structural Example 6] Next, another structural example of the secondary transfer unit in the image forming apparatus of the present embodiment (hereinafter, this structural example is referred to as "Structure Example 6") will be described. FIG.
FIG. 3 is a schematic configuration diagram of a secondary transfer unit according to the present configuration example. In this configuration example, the recording material transport belt 81 in the configuration example 5 is used.
Containing carbon black and having a volume resistivity of 10 ⁸ Ωc
It is made of urethane rubber adjusted to m. Further, the secondary transfer portion of this configuration example includes a metal as a ground member that contacts the back surface of the recording material transport belt 81 that is located downstream of the heating roller 82 in the belt rotation direction and upstream of the transfer roller 83 in the belt rotation direction. A roller 85 is provided. Further, a power supply for applying a voltage to the transfer roller 83 is not connected, and the transfer roller 83 is in a floating state.

Since the metal roller 85 is grounded, -2000 V applied to the heating roller 82
Becomes zero potential at the metal roller portion. Further, since the recording material conveying belt 81 is formed of a medium resistance material,
The potential of the transfer roller 83 becomes -10 due to the potential gradient.
It can be set to about 00V. In this way, the transfer roller 83 is connected to a power source without connecting the power source to the transfer roller 83.
Since a potential of 00 V can be obtained, an expensive power supply can be omitted, and the same effect as in the above configuration example 5 can be obtained.

[Structural Example 7] Next, another structural example of the secondary transfer section in the image forming apparatus of the present embodiment (hereinafter, this structural example is referred to as "Structure Example 7") will be described. In the above configuration example 6, there is a possibility that the discharge at the entrance may have some adverse effect on transfer or fixing. Therefore, in the present configuration example, a voltage of −500 V, which is the same voltage as that of the intermediate transfer belt 50, is applied to the transfer roller 83. This allows
At the entrance of the secondary transfer area, there is no potential difference between the transfer roller 83 and the intermediate transfer belt 50, so that corona discharge does not occur. In the secondary transfer area, after the recording paper 100 completely contacts and adheres to the recording material transport belt 81, the potential of the recording material transport belt gradually increases toward the exit. As the potential rises, transfer proceeds in the secondary transfer area, and fixing is performed by an outlet discharge generated at the outlet of the secondary transfer area.

In the present embodiment, the secondary transfer from the intermediate transfer member to the recording material has been described. However, the present invention directly transfers the image from the photosensitive drum or the like as the image bearing member without the intermediate transfer member. The present invention can also be applied to an image forming apparatus that performs the processing. Further, in the present embodiment, the corona discharge has been described as an example of the discharge, but the present invention can obtain the same effect by a glow discharge or another discharge.

[0058]

According to the first to seventh aspects of the present invention, the temperature at the time of simultaneously transferring and fixing the toner image formed on the image carrier to the recording material is kept low, so that the life of the image carrier is reduced. , The structure of the device can be simplified, and the cost can be kept low.

In particular, according to the second aspect of the present invention, a higher fixing effect can be obtained by continuing to heat the toner image even after a corona discharge current is applied to the toner image on the recording material. Has an effect.

According to the third aspect of the present invention, by suppressing the rise in the temperature of the toner image in the transfer area, the toner image can be heated substantially after corona discharge, and a higher fixing effect can be obtained. There is an excellent effect that can be obtained.

According to the fourth aspect of the present invention, since the surface of the image carrier is cooled before passing through the transfer area and returning to the transfer area again, the temperature of the toner image in the transfer area rises. And an excellent effect that a higher fixing effect can be obtained. Further, when the image carrier is an intermediate transfer member, there is an excellent effect that it is possible to prevent a decrease in transfer efficiency of the primary transfer portion due to a rise in surface temperature of the intermediate transfer member.

According to the fifth aspect of the present invention, the surface of the recording material conveying belt in contact with the recording material is cooled before passing through the transfer area and returning to the transfer area again. Also, there is an excellent effect that a rise in the temperature of the toner image inside can be suppressed, and a higher fixing effect can be obtained.

In particular, according to the invention of claim 6, since the pressure required for transfer can be applied, there is an excellent effect that transfer efficiency can be improved.

In particular, according to the invention of claim 7, there is an excellent effect that an expensive high-voltage power supply can be omitted.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an entire copying machine according to an embodiment.

FIG. 2 is a schematic configuration diagram showing a secondary transfer unit of Configuration Example 1 in the copying machine.

FIG. 3 is a graph showing electrophoretic characteristics of a liquid developer used in the embodiment.

FIG. 4 is a schematic configuration diagram showing a secondary transfer unit of Configuration Example 2 in the copying machine.

FIG. 5 is a schematic configuration diagram showing a secondary transfer unit of Configuration Example 3 in the copying machine.

FIG. 6 is a schematic configuration diagram showing a secondary transfer unit of Configuration Example 4 in the copying machine.

FIG. 7 is a schematic configuration diagram showing a secondary transfer unit of Configuration Example 4 in the copying machine.

FIG. 8 is a schematic configuration diagram showing a secondary transfer unit of Configuration Example 4 in the copying machine.

FIG. 9A is a schematic configuration diagram of a secondary transfer simultaneous fixing device of a conventional dry image forming apparatus. (B) is an enlarged view of a secondary transfer portion of the secondary transfer simultaneous fixing device.

FIG. 10A is a graph illustrating a secondary transfer efficiency and a fixing rate with respect to a pressure in a secondary transfer unit of the secondary transfer simultaneous fixing device. 3B is a graph illustrating the secondary transfer efficiency and the fixing rate with respect to the surface temperature of the intermediate transfer belt in the secondary transfer unit.

FIG. 11A is a schematic configuration diagram of an entire wet image forming apparatus that performs conventional simultaneous transfer and fixing. FIG. 2B is an explanatory diagram illustrating a schematic configuration of an intermediate transfer drum of the wet image forming apparatus.
FIG. 3C is an explanatory diagram illustrating a schematic configuration of a pressure roller of the wet image forming apparatus. .

FIG. 12 is a schematic configuration diagram of a conventional fixing device.

FIG. 13 is a graph showing a fixing effect by a corona discharge current of the identification attaching device.

FIG. 14 is a graph showing a fixing effect by a normal current.

FIG. 15 is a schematic configuration diagram showing a secondary transfer unit of a conventional wet image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charger 3 Optical writing unit 4 Developing unit 5 Intermediate transfer roller 6 Photoconductor cleaning unit 7 Static elimination lamp 8 80 Simultaneous transfer fixing device 9 Cleaning unit 10 Pressure roller 50 Intermediate transfer belt 51 Small fan 81 Recording material Conveying belt 82 Heating roller 83 Transfer roller 84 Cooling fan 85 Metal roller 100 Recording paper

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Sadayuki Iwai 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H032 BA04 BA09 BA19 BA21 2H033 AA02 AA21 AA31 BA09 BA13 BA29 BA32 BA58 BE00 BE09 2H074 CC00 CC33

Claims (7)

[Claims] A transfer device that transfers a toner image developed by a liquid developer formed on the image bearing member to a recording material entering the transfer region by an action of a transfer electric field formed in the transfer region; In a wet image forming apparatus including a simultaneous transfer fixing unit that heats a recording material and fixes a toner image transferred to the recording material, the simultaneous transfer fixing unit is configured to operate immediately after the recording material is separated from the image carrier. And a discharge generating means for generating a discharge between the recording material and the image carrier. After the recording material is brought into contact with the image carrier, the recording material enters the transfer area, and A wet image forming apparatus, wherein a toner image on a carrier is transferred and fixed to the recording material. 2. A wet image forming apparatus according to claim 1, wherein said transfer and fixing means heats said recording material for a predetermined time after a discharge is generated by said discharge generating means. . 3. A wet image forming apparatus according to claim 2, further comprising a temperature adjusting means for adjusting the temperature of the toner image in said transfer area. 4. A wet image forming apparatus according to claim 1, further comprising an image carrier cooling means for cooling the temperature of the surface of the image carrier passing through said transfer area. apparatus. 5. A recording material according to claim 1, wherein said simultaneous transfer and fixing means is formed by an endless belt which is conveyed in contact with said recording material entering said transfer area. A transport belt, a transfer member that stretches the recording material transport belt upstream of the transfer area in a recording material transport direction, and forms a transfer electric field in the transfer area; and a recording material that transports the recording material transport belt to the transfer area. A transfer simultaneous fixing member that stretches downstream in the transport direction to form a transfer electric field in the transfer area and heats the recording material via the recording material transport belt. 6. A wet image forming apparatus according to claim 5, further comprising a pressurizing means facing said transfer member and pressurizing said recording material at a predetermined pressure toward said recording material transport belt. Wet image forming apparatus. 7. The recording material conveying belt according to claim 5, wherein said recording material conveying belt is formed of a medium-resistance material, and said recording material conveying belt is set at a predetermined potential without using a power source. A wet image forming apparatus, wherein an earth member is provided in contact with the back surface of the belt.