JP2002287566A - Fixing means of image forming apparatus to enable double-sided printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize temperature rise of a photosensitive drum peculiar to a stackless system image forming apparatus to enable double-sided printing while securing fixability. SOLUTION: In this fixing means to be provided to the image forming apparatus to enable the double-sided printing and to fix a toner image transferred to paper by heat and pressure, it is characterized by having a control means to gradually transit target temperature from the first fixing temperature to the second fixing temperature with prescribed intervals whenever the prescribed number of sheets are printed and the target temperature is maintained as the second fixing temperature when it reaches the prescribed second fixing temperature while the double-sided printing is continuously performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a laser printer, a facsimile, and the like, and more particularly to a fixing unit of an image forming apparatus using an electrophotographic technique.

[0002]

2. Description of the Related Art A conventional image forming apparatus capable of duplex printing will be described with reference to FIG. In FIG. 1, sheets fed one by one from a sheet cassette 1 by a sheet feed roller 11 pass through a conveying path 21, the leading ends of which are adjusted by a registration unit 22, and stand by.
The toner image is conveyed to the image forming unit 4 at a predetermined timing, and the toner image formed by the image forming unit 4 is transferred to the first surface of the sheet by the transfer unit 45. The sheet on which the unfixed toner image has been transferred to the first surface is transported by the transport path 24 to a nip portion between the heat roller 51 and the pressure roller 52 of the fixing unit 5,
The unfixed toner image on the first surface is fixed by the two rollers nipping and heating. Next, the sheet having the image on the first surface is transferred to the switchback unit 7 via the upstream transport path 25 by the branching unit 6, the transport direction is changed in the switchback unit 7, and the downstream transport path 26
Handed over to Subsequently, the sheet having the image on the first surface is transferred to the downstream side transport path 26, the lower transport path 27, the vertical transport path 2
8, the front end is adjusted again by the registration unit 22, and the image forming unit 4 is conveyed to the image forming unit 4 at a predetermined timing. Transferred to the surface. The sheet on which the unfixed toner image has been transferred to the second surface is conveyed to the nip portion between the heat roller 51 and the pressure roller 52 of the fixing unit 5 by the conveyance path 24, and the two rollers pinch the two sheets. By heating, the unfixed toner image on the second surface is fixed. The sheet on which the image has been printed on both sides up to this point passes through the sheet discharge unit 29 by the branching unit 6 and is then discharged to the discharge tray 9.
Is discharged to

[0003]

However, according to such a conventional method, when printing on both sides continuously, the first method is required.
The sheet on which the image has been transferred to the surface is first fixed with the toner image by the fixing unit, and naturally has a high temperature. The sheet on which the image is printed on the first side is immediately conveyed again to the image forming means 4 so that the image is transferred to the second side of the sheet while maintaining the high temperature. When the heat is transferred, the temperature gradually rises. For example, if about 100 double-sided printings are performed, the surface temperature of the photosensitive drum 41 rises to about 60 ° C. The photosensitive drum 41
When the temperature rises to about 60 ° C., the surface potential of the photosensitive drum 41 in the developing area decreases. In addition, the toner used in the image forming unit 4 starts to aggregate on the surface of the photosensitive drum 41, and image defects occur. Further, due to the influence of the heat of the photosensitive drum 41, various problems such as the cleaning performance of the cleaning unit also being reduced.

Table 1 shows the sheet temperature and the temperature at each location when continuous double-sided printing is performed in the above-described conventional image forming apparatus. The conditions in this confirmation experiment 1 are as follows.・ Room temperature / humidity: 28 ° C./50% ・ Transport speed: 350 mm / sec, 40 sheets / min (A
・ Photoconductor drum diameter: φ60mm ・ Photoconductor drum heater temperature: 45 ° C (OF above 45 ° C)
F) ・ Heat roller: Heater is turned on when the temperature of the heat roller is 180 ° C
Use the one that shows a temperature drop of about 40 ° C when printing 100 sheets continuously without using.・ Heat roller temperature: 180 ± 5 ° C (ON / 175 ° C or less
(OFF at 185 ° C or higher) ・ Paper-passing method: Alternate double-sided printing of 6 sheets each, passing A4 size plain paper in the horizontal direction.

[0005]

[Table 1]

As can be seen from Table 1, when about 100 sheets are printed on both sides, the surface temperature of the photosensitive drum rises to about 60 ° C., and thereafter fluctuates at about 60 ° C. The defect of * 1 is considered to be image fogging due to a decrease in surface potential in the development area.

The problem of * 2 is that the photosensitive drum temperature is 60
It is considered that the temperature of about 0 ° C. causes the temperature of the toner on the surface to be close to the glass transition temperature, and the toner easily adheres to the surface of the photosensitive drum.

The fixability was evaluated by a two-step evaluation as to whether the fixed toner image was peeled off by rubbing with a hand. Here, there is no particular problem with the fixing property.

In order to solve the above-mentioned problem, a technique for performing double-sided printing at a set temperature lower than the set temperature for fixing only single-sided printing is generally adopted. In many image forming apparatuses, the above problem can be solved by applying this. However, when the conditions used in this experiment, such as stackless, the photoreceptor drum temperature characteristics were severe, the glass transition temperature of the toner was low, and the number of prints were large, the conventional technology described above also failed. Was found to occur. In the image forming apparatus according to the related art described above, the sheet temperature when performing continuous double-sided printing,
Table 2 shows the temperature at each location. The conditions in this confirmation experiment 2 are as follows.・ Room temperature / humidity: 28 ° C./50% ・ Transport speed: 350 mm / sec, 40 sheets / min (A
・ Photoconductor drum diameter: φ60mm ・ Photoconductor drum heater temperature: 45 ° C (OF above 45 ° C)
F) ・ Heat roller: Heater is turned on when the temperature of the heat roller is 180 ° C
Use the one that shows a temperature drop of about 40 ° C when printing 100 sheets continuously without using.・ Heat roller temperature: 160 ± 5 ° C (ON / 155 ° C or less
OFF at 175 ° C or higher) ・ Paper passing method: Alternate double-sided printing every 6 sheets, passing A4 size plain paper in the horizontal direction

[0010]

[Table 2]

As can be seen from Table 2, when about 50 sheets are printed on both sides, the surface temperature of the photosensitive drum rises to about 50 ° C., and thereafter fluctuates at about 50 ° C. It can be seen that the rise in the temperature of the photoreceptor drum is also considerably suppressed, and defects such as image fogging and poor cleaning which have occurred in Confirmation Experiment 1 have been eliminated.

However, it was confirmed that the fixability of the initial few sheets was poor. This seems to be due to the fact that if the fixing temperature is set low in a state where the photosensitive drum and the transport path of the image forming apparatus are cooled, the fixing property is deteriorated.

In order to solve the second problem, it may be possible to solve the problem by setting the temperature setting for double-sided printing a little higher. However, the temperature of the photosensitive drum is already raised to a temperature higher than the temperature change. That is dangerous.

[0014]

In order to solve the above-mentioned problems, a first invention of the present application is provided in an image forming apparatus capable of printing on both sides, and fixes a toner image transferred to a sheet by heat and pressure. In the fixing unit, when performing continuous double-sided printing, the target temperature is changed stepwise from the first fixing temperature to the second fixing temperature by a predetermined temperature every time a predetermined number of sheets are printed, and the second fixing is performed. When a temperature is reached, a fixing means having a control means for maintaining the temperature at this temperature is used.

In a second aspect of the present invention, the first fixing temperature is the same as a set temperature for one-sided printing, and the second fixing temperature is lower than the first fixing temperature. The fixing means described in the invention is used.

According to a third aspect of the present invention, there is provided the fixing means according to the first or second aspect, wherein the control means performs control for decreasing the temperature stepwise by the same predetermined temperature for each same predetermined number of sheets. Used.

[0017]

According to the first to third aspects of the present invention, during double-sided printing, the fixing temperature is set to the same temperature as that for single-sided printing during a predetermined number of printings from the beginning. By bringing the temperature closer to the set temperature for duplex printing,
The temperature rise of the photosensitive drum can be solved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of an image forming apparatus capable of double-sided printing to which one embodiment of the present invention is applied to print images on both sides will be described with reference to FIG. In the drawing, sheets fed one by one from a sheet feed cassette 1 by a sheet feed roller 11 pass through a conveying path 21, where the leading ends thereof are adjusted by a registration unit 22, and stand by, and are sent to the image forming unit 4 at a predetermined timing. The toner image formed by the image forming unit 4 is conveyed, and is transferred to the first surface of the sheet by the transfer unit 45. The sheet on which the unfixed toner image has been transferred to the first surface is conveyed to the nip portion between the heat roller 51 and the pressure roller 52 of the fixing unit 5 by the conveyance path 24, and the two rollers pinch and heat the sheet. The unfixed toner image on the first surface is fixed. Next, the sheet having the image on the first surface is transferred to the switchback unit 7 via the upstream transport path 25 by the branching unit 6, the transport direction is changed in the switchback unit 7, and the downstream transport path 26 Handed over to At this time, the sheet in the switchback means 7 is guided to a predetermined position in the width direction by the guide means 8. Subsequently, the sheet having an image on the first surface is transported from the downstream transport path 26 to a lower transport path 27, and is guided in the width direction while being transported by the guide means 8 in the lower transport path 27. 28, the front end is adjusted again by the registration unit 22 and the apparatus waits. The toner image formed by the image forming unit 4 is conveyed to the image forming unit 4 at a predetermined timing.
5 is transferred to the second side of the sheet. The sheet on which the unfixed toner image has been transferred to the second surface is conveyed to the nip portion between the heat roller 51 and the pressure roller 52 of the fixing unit 5 by the conveyance path 24, and the two rollers pinch the two sheets. By heating, the unfixed toner image on the second surface is fixed.
The sheet on which the image has been printed on both sides so far is discharged to the discharge tray 9 via the discharge unit 29 by the branching unit 6.

The control of the temperature setting of the fixing means 5, which is a feature of the present invention, will be described with reference to FIG. The fixing unit 5 includes a heat roller 51 having a heater 511 such as a halogen lamp therein and made of a base material 512 having excellent heat conductivity such as aluminum, and a roller 521 made of aluminum having good heat conductivity having heat resistance. A pressure roller covered with an elastic layer 522 made of conductive urethane rubber and further having a release layer of a fluororesin such as PTFE, a temperature detecting means 53 for detecting the surface temperature of the heat roller, and a heater A power supply 511, a switching unit 55 for turning on / off the heater 511, and a fixing temperature control unit for controlling these units are provided. The temperature control of the fixing unit of the image forming apparatus according to the present embodiment changes at a set temperature of 180 ± 5 ° C. during printing on only one side of a sheet and in a normal stable standby state. In this case, the temperature detecting means 5
When the surface temperature of the heat roller 51 converted from the value detected in Step 3 falls below a first fixing threshold value (175 ° C. in this case) determined from the temperature to be controlled, the switching means is turned on to turn on the switching means. The temperature of the heat roller 51 is increased, and when the temperature exceeds a second fixing threshold value (185 ° C. in this case) determined from the temperature to be controlled, the switching unit is turned off, and the temperature of the heat roller 51 is heated to paper or air. Threshold control is performed.

At the time of double-sided printing of this embodiment, the following Table 3
Temperature control based on the fixing temperature control table of FIG. In Table 3, the predetermined number of sheets is 10 sheets each,
Is used for control to lower the fixing temperature by 180 °, the second fixing temperature by 160 °, and the temperature at predetermined intervals by 2 °.

[0021]

[Table 3]

Table 4 shows the sheet temperature and the temperature at each place when continuous double-sided printing is performed in the image forming apparatus according to the present invention described above. The conditions in this confirmation experiment 3 are as follows.・ Room temperature / humidity: 28 ° C./50% ・ Transport speed: 350 mm / sec, 40 sheets / min (A
・ Photoconductor drum diameter: φ60mm ・ Photoconductor drum heater temperature: 45 ° C (OF above 45 ° C)
F) ・ Heat roller: Heater is turned on when the temperature of the heat roller is 180 ° C
Use the one that shows a temperature drop of about 40 ° C when printing 100 sheets continuously without using.・ Heat roller temperature: threshold control based on Table 3 ・ Paper passing method: Alternate double-sided printing of 6 sheets, passing A4 size plain paper in the horizontal direction

[0023]

[Table 4]

As is evident from the results shown in Table 4, it was found that the fixing property could be cleared while suppressing the rise in the temperature of the photosensitive drum.

[0025]

According to the present invention, the temperature rise of the photosensitive drum, which is peculiar to the image forming apparatus capable of performing the stackless double-sided printing, can be realized while securing the fixing property.

[Brief description of the drawings]

FIG. 1 is a schematic view of a stackless type double-sided printable image forming apparatus according to the related art and the present invention.

FIG. 2 is a schematic diagram of a fixing unit of the present invention.

[Explanation of symbols]

 4; image forming means 5; fixing means 51; heat roller 52; pressure roller 7;

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Eiichiro Morisaki 1-2-28 Tamazuki, Chuo-ku, Osaka, Osaka Inside Mita Kogyo Co., Ltd. (72) Inventor Masamitsu Yamane 1-2-2 Tamazuki, Chuo-ku, Osaka, Osaka No. 28 Mita Industries Co., Ltd. F term (reference) 2H028 BA16 BB02 2H033 AA02 AA46 BA30 BB01 CA07 CA19 CA30 CA48 3K058 AA64 BA18 CA12 CA22 CC06 GA06

Claims (3)

[Claims] An image forming apparatus capable of performing double-sided printing;
In a fixing unit for fixing a toner image transferred to a sheet by heat and pressure, when continuous double-sided printing is performed, the target temperature is increased from a first fixing temperature to a second fixing temperature every time a predetermined number of sheets are printed. The fixing means has a control means for changing the temperature stepwise at intervals of the following and maintaining the temperature at the second fixing temperature. 2. A fixing means according to claim 1, wherein said first fixing temperature is the same as a set temperature for one-sided printing, and said second fixing temperature is lower than said first fixing temperature. . 3. The fixing means according to claim 1, wherein said control means performs control to lower the temperature by the same predetermined temperature step by step for each same predetermined number of sheets.