JP2007114241A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve efficient and stable thermal heating, even if printing density changes. <P>SOLUTION: In the image forming apparatus using liquid developer, squeeze amount is decided from carrier amount and solid content calculated from printed image information so as to calculate the carrier amount and the solid content adhering to transfer material, and a fixing condition is controlled, based on the result of calculation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using a liquid developer.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus (wet image forming apparatus) using a liquid developer is known (Patent Document 1), and a heating device and a pressure roller are used to fix a liquid developer adhered on a print medium. Is used.

  The developer used in the wet image forming apparatus is obtained by suspending solids (toner particles) in an electrically insulating organic solvent (carrier solvent), and the particle diameter of the toner particles is 2 μm or less, usually Since it is extremely fine, about 1 μm or less, it is possible to achieve higher image quality than a dry image forming apparatus using powder toner particles of about 7 μm.

  The carrier solvent that constitutes the developer has the function of making the toner particles charged and uniformly dispersed in addition to preventing the scattering of toner particles of about 1 μm. It also serves as a bridge for easy movement.

The carrier solvent in the liquid developing printer process is a necessary component for toner storage, toner conveyance / layer formation, development, and electrostatic transfer. However, after the fixing process to a transfer material (paper, etc.) Not necessary due to image quality. For these reasons, volatile insulating liquids are currently used as carrier solvents for many liquid developers. However, liquid developers that use a non-volatile carrier solvent have also been developed due to the toner sticking in the device due to the volatilization of the carrier solvent, the influence of the volatile carrier on the human body, environmental issues, etc., one of which is HVS (High- Viscous-Silicone) toner.
JP 2000-56575 A

  In addition to the configuration as in Patent Document 1, for example, instead of a heating device and a pressure roller, a secondary transfer roller is provided to transfer a mixture of toner and carrier onto a paper medium, and then heated and pressurized with a fixing roller. There is also a method for fixing to a transfer material. In the fixing process, the amount of toner changes depending on the print density of the image, and the required amount of fixing heat also changes accordingly. Also, the amount of transfer of the carrier in the image area and the non-image area varies due to the change in the print density, so that the so-called film thickness (amount of toner and carrier) varies, and efficient fixing heating can be performed. For example, when the printing density is low, excessive heating occurs, and conversely, when the printing density is high, fixing may be caused by insufficient heating.

SUMMARY OF THE INVENTION An object of the present invention is to enable efficient and stable fixing heating against the influence of variations in the amount of toner and carrier caused by the print density as described above on the required fixing heat amount.
Therefore, in the image forming apparatus using the liquid developer, the present invention determines the squeeze amount from the carrier amount and the solid content calculated from the print image information, and calculates the carrier amount and the solid content attached on the transfer material. The fixing condition is controlled based on the calculation result.
Further, the present invention is characterized in that the squeeze amount is determined so as not to fall below a lower limit value of the carrier amount.

  The present invention is necessary for fixing by determining the squeeze amount for the liquid developer before the secondary transfer according to the print density, stabilizing the secondary transfer efficiency, and controlling the fixing conditions according to the print density. A large amount of heat can be supplied efficiently and stably.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a diagram illustrating an example of an embodiment of an image forming apparatus according to the present invention. This image forming apparatus is an example in which images of Y, M, C, and K colors are formed on an intermediate transfer member and this is collectively transferred onto a transfer material, and development and primary transfer processes are the same for each color. These steps will be described on behalf of one color.

  The liquid developer container 1 contains a liquid developer in which solid contents (toner particles) are uniformly dispersed in a non-volatile carrier liquid. The liquid developer is pumped up by the supply roller 3 and comes into contact with the supply roller 3. Then, it is supplied to the developing roller 4 whose peripheral surface rotates in the same direction. A developing roller cleaner 5 is disposed on the developing roller 4 to clean the liquid developer after development on the developing roller.

  The photosensitive member 10 whose circumferential surface rotates in the same direction in contact with the developing roller 4 is uniformly charged by a charger 11, and then an electrostatic latent image is formed by image exposure by an exposure device 12. The electrostatic latent image is developed with a liquid developer at a position facing the developing roller 4 and transferred onto the intermediate transfer belt 20 at a primary transfer position facing the primary transfer roller 14 with the intermediate transfer belt 20 interposed therebetween. The developer remaining on the photoconductor after the transfer is cleaned by the photoconductor cleaner 15.

  The intermediate transfer belt 20 is stretched between a driving roller 21 and a driven roller 22 and is rotationally driven counterclockwise by the driving roller 21. The driving roller 21 and the secondary transfer roller 24 are transfer materials such as paper. A position opposite to each other is a secondary transfer position. A belt cleaner 23 is disposed with the driven roller 22 as a backup roller, and the developer remaining on the intermediate transfer belt 20 after being collectively transferred to the transfer material at the secondary transfer position is cleaned. Further, a squeeze roller 30 is disposed between the photosensitive members of the respective colors and between the photosensitive member at the right end in the drawing and the secondary transfer position, and the excess on the intermediate transfer belt 20 after being transferred at the primary transfer position of each color. The carrier liquid is removed.

  A transfer material such as paper is sequentially fed from a cassette 40 by a roller 41, conveyed through a path 42, transferred at a secondary transfer position, and then fixed by a fixing device 50 including a heating roller 50a and a pressure roller 50b. Sent out.

FIG. 2 is a diagram for explaining a squeeze mechanism and a squeeze roller that is provided in the subsequent stage of each color of the intermediate transfer belt and removes the carrier liquid.
In FIG. 2A, the squeeze roller 30 is for removing the carrier liquid contained in the liquid developer on the intermediate transfer belt. The squeeze roller is configured by winding a PFA tube 20 μm around a surface layer of urethane rubber (hardness JIS-A30 °) having a thickness of 2 mm (outside diameter φ14 mm) on a φ10 mm metal shaft, and has a roller width of 307 mm. A squeeze backup roller 31 (φ10 mm metal shaft) is disposed opposite to the intermediate transfer belt 20 and is in contact with the intermediate transfer belt at a linear pressure of about 50 gf / cm. The resistance value of the roller is an actual resistance value of about Log 4Ω, and a bias voltage is applied from the power source 32 between the squeeze roller 30 and the squeeze backup roller 31 so that the solid content in the developer is not removed. The squeeze roller 30 is cleaned by contact with a cleaning blade 33 made of urethane rubber (hardness JIS-A 70 °). With these configurations, the carrier liquid of the liquid developer is squeezed out and stored in the container on the intermediate transfer belt.

FIG. 2B shows how the film thickness (solid content and carrier amount) of the liquid developer on the intermediate transfer member is changed by the squeeze roller.
When the liquid developer on the intermediate transfer member 20 having a predetermined film thickness comes into contact with the squeeze roller 30, the speed difference between the squeeze roller and the intermediate transfer member, the surface tension of the liquid developer, the wettability with the squeeze roller, and the viscosity. , A part adheres to the squeeze roller surface and separates, and the film thickness changes. At this time, since a bias voltage is applied to the squeeze roller, the charged solid content is attracted to the intermediate transfer member side so as not to move to the squeeze roller side. Therefore, the solid content also changes. By changing the squeeze bias voltage value, the amount of solid content transferred to the squeeze roller side also changes, so that the film thickness after squeezing can be controlled.

FIG. 3 is a diagram showing the relationship between the squeeze bias and the film thickness.
As shown in the figure, the squeeze bias voltage and the film thickness after squeezing are inversely proportional, and the squeeze amount increases when the speed difference between the intermediate transfer member and the squeeze roller increases. Thus, when the speed difference is small, the film thickness increases.

  By the way, in the liquid developer, the solid content moves by electrophoresis in the carrier due to the transfer bias voltage. However, if the amount of the carrier is small at this time, the electrophoresis is inhibited and the solid content is not sufficiently moved. The transfer efficiency is lowered and the printed image becomes light.

  On the other hand, as shown in FIG. 4, the film thickness and the amount of fixing heat required in the fixing device increase in proportion to the film thickness. For this reason, the thinner the film thickness, the smaller the amount of heat required for fixing.However, as described above, if the amount of carrier is too small, the transfer efficiency decreases, so that the lower limit of the amount of carrier that does not hinder the transfer efficiency is not reduced. It is necessary to determine the film thickness, that is, the squeeze amount.

For the lower limit of the carrier amount, the weight before removal of the carrier on the intermediate transfer body after squeezing and on the paper (carrier + solid weight) is determined by the tape transfer method (unit: mg / cm ² ). The liquid toner on the body and paper is collected with a spatula, the carrier is blown off by heating or the like, and the solid content is measured to determine the solid content / (carrier + solid content) (solid content ratio). The secondary transfer efficiency is obtained from the solid content ratio on the intermediate transfer member and paper thus obtained, and the secondary transfer efficiency is drastically lowered when the carrier amount is changed variously. For example, the secondary transfer efficiency is 90% to 70%. The lower limit value of the carrier amount can be obtained from the solid content ratio when it rapidly decreases to%. When the lower limit value of the carrier amount is obtained, the squeeze bias is determined so that the solid content ratio giving a carrier amount slightly larger than the lower limit value is set as the target value.

The squeeze bias needs to be changed depending on the print density. This is because the solid content ratio after squeezing changes depending on the print density.
Therefore, various squeeze biases are applied, and the change in the solid content ratio before and after squeezing is measured for each printing density. For example, when a printing density of 20% and a squeeze bias of 500 V are applied and the solid content ratio before squeezing is 15%, the solid content ratio after squeezing is 25%. Further, it is assumed that a printing density of 30% and a squeeze bias of 600 V are applied, and the solid content ratio before squeezing is 15%, but becomes 20% after squeezing. Assuming that the solid content ratio of 25% after squeezing is a target value that slightly exceeds the lower limit of the carrier amount that does not decrease the secondary transfer efficiency, the solid density ratio is 25% of the target with a printing density of 30% and a squeeze bias of 700V. It can be.

  By the way, the fixing condition (necessary heat amount condition) in the fixing device varies depending on the print density of the image to be printed when the film thickness of the liquid developer is made constant. explain.

FIG. 5 is a block diagram illustrating a configuration for controlling the fixing conditions in accordance with the print density, FIG. 6 is a diagram illustrating the print density, and FIG. 7 is a diagram illustrating a control flow of the fixing conditions.
The control device 100 and the image memory 101 are built in the image forming apparatus. The control device 100 reads the paper size from the image memory and acquires the number of pixels in the main scanning direction and the sub scanning direction as shown in FIG. The total number of pixels per page is acquired (steps S1 to S3). Next, print image data per page is acquired from the image data in the image memory 101 (step S4), and the ratio of the print image data to the total number of pixels (print density in one page) is calculated (step S5). . When the print density is obtained in this way, the squeeze bias corresponding to the print density can be determined as described above (step S6). When the squeeze bias is determined, the necessary amount of fixing heat can be calculated, and the electric power is controlled accordingly. Perform (step S7).

  In step S7, when the carrier is vegetable oil, an oxidative polymerization reaction occurs and tends to be accelerated as the temperature rises. The solidified carrier is wrapped around by oxidative polymerization, and as a result, is fixed on paper. It is necessary to correct the temperature to be controlled.

  According to the present invention, the secondary transfer efficiency can be stabilized, and the amount of heat necessary for fixing can be supplied efficiently and stably. Therefore, the industrial utility value is great.

It is a figure explaining an example of an embodiment of an image forming device of the present invention. It is a figure explaining the mechanism of a squeeze roller and a squeeze. It is a figure explaining the relationship between a squeeze bias and a film thickness. It is a figure explaining the relationship between a film thickness and fixing calorie | heat amount. It is a figure explaining the control apparatus of the fixing conditions of this invention. It is a figure explaining printing density. It is a figure explaining the control flow of fixing conditions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid developer container, 3 ... Supply roller, 4 ... Developing roller, 5 ... Developing roller cleaner, 10 ... Photoconductor, 15 ... Photoconductor cleaner, 20 ... Intermediate transfer belt, 21 ... Drive roller, 22 ... Driven roller, 23 ... belt cleaner, 30 ... squeeze roller.

Claims (2)

In an image forming apparatus using a liquid developer, the carrier amount and solid content adhering to the transfer material are calculated by determining the squeeze amount from the carrier amount and solid content calculated from the print image information, and fixing based on the calculation result An image forming apparatus characterized by controlling conditions. The image forming apparatus according to claim 1, wherein the squeeze amount is determined so as not to fall below a lower limit value of the carrier amount.

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