JPH1097142A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent destruction of an image at the fixing time occurring because of insufficient drying of a paper sheet by satisfactorily performing the drying of the paper sheet on which the image with plenty dot numbers is transferred, in an image forming device applying the wet type developer. SOLUTION: In the case of successively performing the image formation for images of plural pages, on extending the image data of the plural pages by the image data extending part 37, and counting the image dot numbers for every page by a counter 38, performance order is decided by the image forming order deciding part 40 so as to perform the image forming in the order from the page provided with plenty image dots. The paper sheet on which the image is transferred is temporarily stacked on a stack part of a stacker, and the stacked paper sheets stacked are transported to a fixing part in the page order and fixed. Therefore, the paper sheet drying time becomes long to the paper sheet on which the image provided with plenty dot numbers becomes long, hence even the paper sheet on which the image provided with the image dot numbers can be satisfactorily dried before fixing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus using a wet developer.

[0002]

2. Description of the Related Art Conventionally, there has been known an electrophotographic image forming apparatus such as a printer or a facsimile which uses a wet developer.

A wet developer comprises a developer and a solvent that dissolves the developer. When an image developed with the wet developer is transferred to a sheet, the solvent adheres to the sheet immediately after the transfer together with the developer. A state of bulging into a meniscus shape is obtained. If the paper on which the solvent is attached in a meniscus form together with the developer is sent as it is to the fixing unit, the solvent spreads due to the pressure applied during the fixing and the image is crushed, resulting in an unclear image.

Therefore, in order to prevent the image from being collapsed during fixing, it is necessary to evaporate the solvent adhering to the sheet and dry the sheet before fixing.

As an image forming apparatus for drying a sheet on which an image is transferred before fixing, for example, Japanese Patent Application Laid-Open
No. 179,466. However, in this image forming apparatus, the moving paper and the photoreceptor are heated by the heat of the fixing device. Even if this method is applied to an image forming apparatus using a wet type developer, sufficient paper drying time is required. The paper cannot be dried sufficiently.

[0006]

The paper drying time required for evaporating the solvent of the wet developer adhering to the paper to dry the paper depends on the number of image dots of the image transferred to each paper. . That is, when the number of image dots is large, the amount of the solvent adhering to the paper increases, and the paper drying time required to dry the paper increases. When the number of image dots is small, the amount of solvent adhering to the paper is small, and the paper drying time required for drying the paper is short.

Therefore, when images are formed in the order of pages, if there is a sheet having a large number of image dots in the middle, a sufficient sheet drying time cannot be secured for the sheet, and the sheet is not sufficiently dried. Since the image is fixed, the image is crushed at the time of fixing.

If the paper drying time is set to a time sufficient to dry the paper having the maximum number of image dots, the solvent adhering to the paper is completely evaporated from all the papers, and the paper is sufficiently dried. And the image can be reliably prevented from being crushed during fixing.
However, it takes more time than necessary to dry the paper on which an image with a small number of image dots has been transferred, and the work efficiency of the image forming operation is reduced.

Therefore, according to the present invention, when forming images of a plurality of pages successively, the images are formed in order from the image having a large number of image dots in the images of the plurality of pages, and an image having a large number of image dots is transferred. For paper, take a long paper drying time to prevent image collapse during fixing due to insufficient drying of the paper, but unnecessarily for paper onto which images with a small number of image dots have been transferred. An object of the present invention is to provide an image forming apparatus capable of preventing a reduction in work efficiency of an image forming operation due to a uniform long paper drying time by preventing a long paper drying time.

[0010]

According to the first aspect of the present invention,
An optical writing unit that writes an electrostatic latent image according to image data on a photoconductor, a developing unit that develops the written electrostatic latent image with a wet developer, and a transfer device that transfers the developed image to paper And an image forming apparatus having a fixing unit for fixing an image transferred to a sheet, an image data developing unit on which a plurality of pages of image data are developed, and the number of image dots for each page from the developed image data. A counter for counting, an image forming order determining unit for determining an image forming order so that images are formed in order from a page having a large number of counted image dots, and a multi-stage stack for stacking sheets onto which images are transferred one by one A stacker provided with a fixing unit, and a fixing conveyance unit that conveys the sheets stacked in the stack unit to the fixing unit in the order of pages. Therefore, when image data of a plurality of pages is developed by the image developing unit, the number of image dots of each page is counted by a counter, and image formation is performed in order from a page having a large number of image dots. The sheets are stacked one by one on the stacking section of the stacker. The sheets stacked in the stacking section are conveyed to the fixing section by the fixing conveyance section in the order of pages and fixed.
As a result, the time from the transfer of the image to the paper to the fixing, that is, the paper drying time of the paper on which the image has been transferred becomes longer on the paper on which the page with a large number of image dots has been transferred, and the paper is sufficiently dried, This prevents image collapse at the time of fixing due to insufficient drying of the sheet onto which the image has been transferred. In addition, a long paper drying time is not uniformly applied to all the papers, and the work efficiency of the image forming operation does not decrease.

According to a second aspect of the present invention, in the first aspect of the present invention, a judging means for judging whether or not the number of image dots counted by the counter is equal to or more than a set value; Paper drying time extending means for extending the paper drying time of each sheet, and fixing timing adjusting means for adjusting the timing of starting conveyance from the stack section to the fixing section according to the paper drying time extended by the paper drying time extending means. Was provided. Therefore, when the number of image dots of pages to be continuously formed is equal to or larger than the set value, the paper drying time of each sheet is extended, and the number of image dots of the transferred image increases. However, a sufficient paper drying time can be secured for each paper.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic structure of a color laser printer which is an image forming apparatus of the present embodiment. This color laser printer uses a wet toner as a wet developer, and is broadly divided into an image forming section 1, a paper drying section 2, and a fixing section 3.

The image forming section 1 processes image data transmitted from an external storage device and outputs a signal corresponding to the processing, and forms an image based on an output signal from the image processing section 4. Four recording stations 5Y, 5
M, 5C, 5BK (Y, M, C, BK are each yellow,
A transport control unit 9 that picks up the paper 7 on the paper feed tray 6 according to an output signal from the image processing unit 4 and transports the paper 7 in a paper transport path 8;
A transfer belt 10 for electrostatically attracting and transporting the sheet 7 is provided. The recording stations 5Y, 5M, 5C,
5BK have the same structure, and for simplicity of description, here, the configuration and operation of the recording station 5C for cyan will be described as an example, and the same configuration among the other recording stations 5Y, 5M, and 5BK will be described. Portions are denoted by the same reference numerals and are distinguished by subscripts Y, M, and BK.

The recording station 5C includes a drum-shaped photosensitive member 11C on which an electrostatic latent image corresponding to image data is written.
A charger 12C for uniformly charging the surface of the photoconductor 11C,
An optical writing section 13C for writing an electrostatic latent image on the photoreceptor 11C by irradiating a laser beam, and a wet toner 14 which is a wet developer composed of a toner and a solvent in which the toner is dissolved, is accommodated. Developing unit 15C for developing an electrostatic latent image by using the transfer belt 1
A transfer unit 16C for transferring the sheet 7 onto the sheet 7 electrostatically attracted to
It is constituted by a cleaning unit 17C for removing residual toner on the photoconductor 11C and the like.

The paper drying unit 2 is configured to stack a stacker 19 having a plurality of stacks 18 and an image-transferred paper 7 separated from the transfer belt 10 into each stack 18.
And a fixing conveying unit 21 for conveying the sheets 7 stacked on each stack unit 18 to the fixing unit 3. A heater 22 is arranged below the stacker 19. Between the heater 22 and the stacker 19, a shielding plate 23 for preventing the heat of the heater 22 from being directly transmitted to the stacker 19 and uniformly heating the entire periphery of the stacker 19 is arranged. Above the stacker 19,
A solvent recovery unit 24 that recovers the solvent evaporated from the paper 7 is provided.

The stack section 18 includes a driving roller 25, a driven roller 26, and a transport belt 27. The transport belts 27 are arranged substantially horizontally, and a sensor 28 for detecting that the paper 7 has been fed onto the transport belts 27 to a predetermined position is disposed above each of the transport belts 27.

The stack transport section 20 is composed of a driving roller 29, a driven roller 30, and a transport belt 31. The position where the driven roller 30 side faces the entrance side of each stack section 18 with the driving roller 29 side as a fulcrum. It is provided to be rotatable. The stack conveyance unit 20 rotates around a rotation fulcrum in conjunction with the image forming operation, and
Are stacked in order from the top stacking section 18.

The fixing conveyance section 21 includes a driving roller 32
, A driven roller 33, and a transport belt 34, and the driven roller 33 side is rotatably provided at a position facing the outlet side of each stack 18 with the drive roller 32 side as a fulcrum. The fixing conveyance section 21 rotates around the rotation fulcrum so as to convey the sheets 7 stacked in each stack section 18 to the fixing section 3 in the order of pages.

FIG. 2 is a block diagram showing the structure of the image processing unit 4. The image processing unit 4 includes a data receiving unit 3 that receives image data transmitted from an external storage device.
5. A hard disk 36 for temporarily storing received image data, and a bitmap as an image data developing unit for developing, as image data, image data of a plurality of pages for which image formation is continuously performed among image data stored in the hard disk 36. A deployment section 37 is provided. The bitmap developing unit 37 is connected to a plurality of memories 38 for storing the developed image data for each page.
The memory 38 stores the image data in each color (Y, M, C, B).
K) and stored separately.

Each memory 38 is connected to a counter 39 having an adder circuit configuration for counting the number of image dots of the image data stored in the memory 38.
Are connected to a ranking circuit 40, which is an image formation ranking determination unit. In this ranking circuit 40, the counter 39
The image forming order is determined so that the images are formed in order from the page with the largest count value, and a drive signal is output to the transport control unit 9. The ranking circuit 40 and each memory 38 are connected to a selector 41, and the selector 41 is connected to a modulation circuit 42, and the modulation circuit 42
3 is connected. In the selector 41, the output to the modulation circuit 42 is switched so that the image is formed in the page order determined by the ranking circuit 40, and the laser light is emitted from the optical writing unit 13 by the output from the modulation circuit 42. .

The color laser printer according to the present embodiment includes a microcomputer-based control unit (not shown) mainly including a CPU and a memory, and the control unit controls the image processing unit 4 and the stack. The operation of each unit such as the transport unit 20 for fixing and the transport unit 21 for fixing is controlled. The structure and basic processing of such a control unit are the same as those of the well-known structure and processing, and a description thereof will be omitted.

Further, the color laser printer according to the present embodiment is provided with a judging unit, a paper drying time extending unit, and a fixing timing adjusting unit as processes executed by the control unit having the above-described microcomputer configuration.

The judging means fetches the data of the number of image dots of each page counted by each counter 39, temporarily stores the fetched data in the RAM, and averages the number of image dots per page based on the stored data. The average value is calculated as a predetermined value (for example, when the number of image dots is 3).
10 million) or more.

The paper drying time extending means, when the determining means determines that the average value is equal to or more than a predetermined value, a predetermined time (for example, 10
Second).

The fixing timing adjusting means starts the conveyance of the fixing conveyance section 21 for conveying the sheet 7 from the stack section 18 to the fixing section 3 so as to secure the sheet drying time extended by the sheet drying time extension section. This is a process for delaying the timing.

In such a configuration, an outline of an image forming operation by the color laser printer will be described. The paper 7 fed from the paper feed tray 6 is transported in the paper transport path 8, and the paper 7 is transported by being electrostatically attracted to the transfer belt 10. Then, the images formed at the respective recording stations 5 are sequentially transferred to the paper 7 that is electrostatically attracted and conveyed, and a color image is formed on the paper 7. In addition,
When only one recording station 5 is driven,
A monochromatic image is formed on the paper 7.

The sheet 7 on which the image has been transferred is peeled off from the transfer belt 10 and sent one by one to each stack unit 18 by the stack transport unit 20, and stopped when the leading end of the sheet 7 is detected by the sensor 28. Is done. Each sheet 7 sent to the stacking section 18 is
After a predetermined period of stop on the stack 8, the transport belt 27 of each stack section 18 is rotated and the fixing transport section 21 is driven to be fed into the fixing section 3, where the transferred image is fixed.

FIG. 3A shows the sheet 7 immediately after the image is transferred. The wet toner 14 is a toner 14a.
And a solvent 14b in which the toner 14a is dissolved.
On the sheet 7 immediately after the image is transferred, the solvent 14b adheres together with the toner 14a and swells in a meniscus shape.
For this reason, if the paper 7 immediately after transferring the image is directly sent to the fixing unit 3, the solvent 1
4b spreads and the image collapses. FIG. 3 (b)
Indicates a sheet 7 sent to the fixing unit 3 after being stopped in the stack unit 18 for a predetermined time. The sheet 7 on which the image is transferred is stopped on the stack unit 18 for a predetermined time, and
Since the area around the stacker 19 is heated to about 35 ° C. by the heat of the heater 22, the solvent 14b evaporates from the sheet 7 during fixing. Accordingly, as shown in FIG. 3B, fixing is performed on the sheet 7 in a state where the solvent 14b evaporates and the toner 14a is aggregated, and the image is prevented from being crushed at the time of fixing.

Next, the first main operation of the present invention at the time of image formation will be described. At the time of image formation, of the image data transmitted from the external storage device and stored on the hard disk 36, image data of a plurality of pages for which image formation is continuously performed is developed by the bitmap developing unit 37 as image data. The developed image data is stored in the memory 38 for each page, and the number of image dots of the image data stored in each memory 38 is counted by the counter 39. The count values from the respective counters 39 are input to the ranking circuit 40, and the respective count values are compared to determine the image formation order so that images are formed in order from the page having the largest count value. Then, laser light corresponding to the image data of the page is emitted from the optical writing unit 13 in the determined page order, and the image is formed.

FIG. 4 shows the state after the image is transferred to the sheet 7.
After being stacked on the stack unit 18 and temporarily stopped,
This indicates the time required for the paper 14 to be conveyed to the fixing unit 3 and fixed, in other words, the paper drying time allocated to the evaporation of the solvent 14b attached to the paper 7 during transfer. FIG.
(A) is a case where image formation is performed in page order. The paper drying time “t1,
t2, t3, t4 "are the same regardless of the amount of image data of the image transferred to each sheet 7.

FIG. 4B shows a state in which the image formation of the second page is performed first because the number of image dots of the image data of the second page is larger than that of the other pages. Fixing conveyance section 21
Is carried from the stack unit 18 to the fixing unit 3 in the order of pages. As a result, the paper drying time “T2” of the paper 7 on which the image of the second page having a large number of image dots is transferred is
It is longer than when image formation is performed in page order. Therefore, on the sheet 7 on which the image of the second page has been transferred,
Even if the amount of the solvent 14b attached to the sheet 7 increases due to the large number of image dots, the solvent 14b can be reliably evaporated because the sheet drying time “T2” is long, and the sheet 7 is fixed at the time of fixing. It is sufficiently dried to prevent image collapse at the time of fixing.

The sheets 7 are stacked on the stacking section 18 in order from the uppermost stacking section 18 in the order of image formation. It is remembered. When the sheet is transported from the stack unit 18 to the fixing unit 3, the RAM
The fixing conveyance unit 21 is sequentially rotated to a position facing the predetermined stack unit 18 based on the data of the number of stacks 18 on the stack unit 18 stored in the stack unit. 7 are conveyed to the fixing unit 3 in page order.

According to the present embodiment, the paper 7 on which an image having a small number of image dots has been transferred does not require an unnecessarily long paper drying time. It is possible to prevent the work efficiency of the image forming work from decreasing due to the time taken to dry the paper.

Next, the process of extending the paper drying time, which is the second main operation of the present invention during image formation, is shown in FIG.
A description will be given based on the flowchart of FIG. During image formation,
Data of the number of image dots of each page counted by each counter 39 is temporarily stored in the RAM. Then, the CPU calls the data stored in the RAM to calculate the average value of the number of image dots per page, and determines whether or not the average number of image dots is equal to or more than the predetermined value of 30 million. Is done.

If the average number of image dots is less than 30,000,000, the paper drying time is not extended, and the standard paper drying time "To" is used as it is as the paper drying time "Ts".
To form an image. On the other hand, if the average number of image dots is 30,000,000 or more, image formation is performed with the value obtained by adding 10 seconds to the standard paper drying time “To” as the paper drying time “Ts”.

When the paper drying time is extended, the transport start timing of the fixing transport unit 21 that transports the paper 7 from the stack unit 18 to the fixing unit 3 is delayed. For this reason,
If the average value of the number of image dots of a plurality of pages for which images are to be formed continuously is high, the paper drying time is extended for all pages, so that sufficient paper drying time is obtained for each paper 7 on which an image has been transferred. Can be secured, and it is possible to prevent the image from being crushed at the time of fixing due to insufficient drying of the paper 7.

[0037]

According to the first aspect of the present invention, when a plurality of pages of images are continuously formed by an image forming apparatus using a wet developer, the image data of the plurality of pages is developed by an image developing unit. Then, the number of image dots of each page is counted by a counter, images are formed in order from the page having the largest number of image dots, and the sheets on which the images are transferred are stacked one by one on a stacker of the stacker. Since the sheets stacked in the unit are conveyed to the fixing unit in the page order by the fixing and conveying unit and fixed, the time from image transfer to fixing on the sheet, that is, the paper drying time of the sheet on which the image is transferred, is an image dot. It is possible to lengthen the paper on which a large number of pages have been transferred, and to sufficiently evaporate the solvent adhered during transfer and dry the paper sufficiently. Transcribed drying of the paper is insufficient can be prevented collapse during fixation of an image that causes.

According to the second aspect of the present invention, when the number of image dots of a page on which images are to be continuously formed is equal to or larger than the set value, the paper drying time of each paper is extended. Even when the number of image dots of an image to be printed increases, a sufficient paper drying time can be secured for each sheet, and it is possible to prevent image collapse during fixing due to insufficient drying of the sheet onto which the image has been transferred.

[Brief description of the drawings]

FIG. 1 is a front view showing a schematic structure of an entire color laser printer according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a structure of an image processing unit.

FIG. 3 shows the state of adhesion of wet toner to paper,
(A) is a state immediately after the image is transferred and the solvent is not dried, and (b) is a state where the solvent is dried and fixing is performed.

4A and 4B show paper drying times allocated to each paper, where FIG. 4A shows a case where images are formed in page order, and FIG.
Is a case where the image of the second page is formed first.

FIG. 5 is a flowchart illustrating a process of extending a paper drying time.

[Explanation of symbols]

 Reference Signs List 3 fixing unit 7 paper 11 photoreceptor 13 optical writing unit 14 wet developer 15 developing unit 16 transfer unit 18 stack unit 19 stacker 21 fixing transport unit 37 image data developing unit 39 counter 40 image forming order determining unit

Claims (2)

[Claims] An optical writing unit for writing an electrostatic latent image corresponding to image data on a photoreceptor; a developing unit for developing the written electrostatic latent image with a wet developer; An image forming apparatus having a transfer unit for transferring an image transferred to a sheet and a fixing unit for fixing an image transferred to a sheet, an image data developing unit that develops image data of a plurality of pages, A counter that counts the number of image dots, an image formation order determination unit that determines the order of image formation so that images are formed in order from the page with the largest number of image dots, and a stack of sheets onto which images have been transferred. An image forming apparatus comprising: a stacker having a plurality of stacking sections to be stacked; and a fixing transport section for transporting the sheets stacked in the stack section to the fixing section in page order. Apparatus. A determining means for determining whether or not the number of image dots counted by the counter is equal to or greater than a set value; and a paper drying time extending means for extending a paper drying time for each sheet when the image dot number is equal to or greater than the set value. 2. The image according to claim 1, further comprising: a fixing timing adjusting unit that adjusts a timing of starting conveyance from the stack unit to the fixing unit according to the sheet drying time extended by the sheet drying time extending unit. Forming equipment.