JPH0210543Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a toner image fixing device, and particularly to a fixing device suitable for use in a double-sided copying device.

Prior Art Conventionally, in a double-sided copying machine capable of copying on both the front and back sides of copy paper, fixing processing is performed under the same conditions both during the first copy and during the second copy. However,
Copy paper that has completed the first copy has already gone through the fixing process once, so the temperature of the copy paper itself has risen, and the stress of heat and pressure is applied, causing deformation of the copy paper. There are many. If such copy paper is subjected to a fixing process for the second copy under exactly the same conditions as the first copy, both heat and pressure will be excessive. As a result, a hot offset phenomenon occurs in which the toner melts due to excessive heat and the toner image is reversely transferred to a device such as a pressure roller, and wrinkles occur in copy paper due to excessive pressure.

Purpose The present invention was devised in view of the above points, and its purpose is to provide a fixing device that can supply high-quality copies without causing hot offset or wrinkles on the copy paper even during double-sided copying. do.

Configuration First, the concept of an automatic double-sided electrophotographic copying machine to which the fixing device of the present invention is applied will be explained with reference to a block diagram based on the flow of copy paper shown in FIG. In FIG. 1, a copy sheet fed from a paper feed section I to an image forming section D is subjected to a first image forming process. The image forming section D consists of a photoreceptor drum and various processes such as uniform charging, image exposure, development, transfer, cleaning, and static electricity disposed around the photoreceptor drum, and the above-mentioned processes are carried out in approximately the same order. The first image forming process is completed as described above. The copy paper with the toner image transferred to one side in the image forming section D is then sent to the fixing section F, where heat and pressure are applied to fix the toner image on the copy paper, completing the first copying. .

Thereafter, in the one-sided copy mode, the copy sheet after one-sided copying is sent to the paper discharge section E, and the one-sided copying process is completed. On the other hand, in the double-sided copying mode, the copy sheets that have been copied on one side are sent from the fixing section F to the paper refeeding section R, where they are stacked through processes such as reversal and alignment, and are prepared for double-sided copying. and,
The image is sent to the image forming section D again with the instruction for double-sided copying.
A second image formation is performed, and a toner image is formed on the other side of the copy paper. The copy paper on which the second image formation has been completed is again sent to the fixing section F, where it is subjected to a second fixing process, and the second copy is completed. The copy paper that has been copied on both sides is then sent to the paper discharge section E, and the double-sided copying process is completed.

In order to eliminate the drawbacks of the prior art, the inventor of the present application focused on the copying paper used in the double-sided copying process configured as described above, and obtained the following knowledge. In other words, at the time when the second image is formed, the copy paper has already undergone the fixing process once, so at least the moisture content is lower than before the fixing process, and the temperature of the copy paper itself is lower. prices are also getting higher. This is thought to be because the automated system transports the copy paper without being carried out of the machine. Therefore, even if the degree of application of heat and pressure during the second fixing process is set lower than that during the first fixing process, there is no possibility that the fixing performance will fall below the allowable limit. Here, if only the prevention of the hot offset phenomenon is intended, it is sufficient to set only the heating temperature during the second fixing process to a low value. However, in order to prevent the occurrence of wrinkles on the copy paper, it is considered appropriate to set the applied pressure low. Therefore, when we experimentally performed double-sided copying by lowering the pressure during the second fixing, a correlation as shown in FIG. 2 became clear. Second
According to the figure, it can be seen that the incidence of wrinkles on the copy paper decreases in proportion to the width of the decrease in pressure during the second fixing. It was also confirmed that at this time, the degree of occurrence of the hot offset phenomenon was also reduced.

Based on the above-mentioned knowledge, the present invention aims to achieve the above-mentioned purpose of the present invention by reducing the pressure applied during the second and subsequent fixing processes by an appropriate amount within a range that ensures a predetermined fixing performance. It is something to do.

Hereinafter, the configuration of the present invention will be explained based on specific examples. FIG. 3 is a schematic diagram showing the fixing device of the present invention applied to the fixing section of the automatic double-sided electrophotographic copying machine shown in FIG. 1, and FIG. 4 is a perspective view thereof. In FIG. 3, a cylindrical fixing roller 2 serving as a support for copy paper is rotatably supported and rotated in the counterclockwise direction of the arrow. A heat generating lamp 3 as a heat source for heating the fixing roller 2 is disposed inside the fixing roller 2. Note that instead of the heating lamp 3, a heating element such as a heater may be installed approximately evenly on the inner peripheral surface of the fixing roller 2.

A pressure roller 4 is disposed so as to be in rolling contact with the fixing roller 2. The pressure roller 4 is the fixing roller 2
The toner image 1a is transferred to the rolling contact section K by the above-mentioned image forming section, and the copy paper 1 conveyed along the conveyance path T is held with appropriate pressure and conveyed to the downstream side along with its rotation. Due to the pressing force and the heating action of the fixing roller 2 at this time, the toner image 1a is transferred to the copy paper 1.
to take root.

The pressure roller 4 is connected to a pressure means 5 having a mechanism for varying the pressing force applied to the fixing roller 3. This pressurizing means 5 is constructed as shown in FIG. In FIG. 4, the extended end of the rotating shaft 4a of the pressure roller 4 is inserted into one end of the upper pressure lever 51 of the pressure means 5. As shown in FIG. The other end of the upper pressure lever 51 is attached to a support shaft 52.
Further, one end of an L-shaped lower pressure lever 53 is rotatably fitted onto the support shaft 52. A pressure spring 54 is interposed between the opposing ends of the upper and lower pressure levers 51 and 53.
The respective ends of 53 are urged away from each other by their elastic force. In the single-sided copy mode, the pressing force in this state causes the pressure roller 4 to press the copy paper on which the toner image has been transferred on one side toward the fixing roller 2, and the first fixing process is performed.

A cam follower 55 is projectingly provided on the lower pressure lever 53, and a cam 56 is rotatably supported around a shaft 57 so as to be engageable with the cam follower 55. A clutch 58 is disposed on the cam 55 so that it can be engaged and disengaged by, for example, a spring (not shown), and this clutch 58 is connected to a driving means 5a that is operated in response to an instruction from, for example, an operation panel (not shown). .

Regarding the operation of this implementation configured as described above,
This will be explained below. In double-sided copy mode,
When single-sided copying is completed and the reversed copy sheets are aligned and stacked in the paper re-feeding section and preparation for double-sided copying is completed, a display indicating that double-sided copying can be started appears on the operation panel (not shown).

Under these conditions, when the print button (not shown) is pressed, the paper refeeding section starts the paper refeeding operation and the second copy begins, and at the same time, the clutch 58 of the fixing device operates and the cam 56 cam 5 engaged with
6 by a predetermined angle in the direction of the arrow. As a result, the cam follower 55 engages with the linear portion 56a of the periphery of the cam 56, and its position is lowered by a predetermined width. As a result, the end of the lower pressure lever 53 is further separated from the opposing upper pressure lever 51, and the elastic force of the intervening pressure spring 54 is reduced. Therefore, the pressing force of the pressure roller 4 against the fixing roller 2 is reduced to an appropriate pressure for the second fixing process.

As shown in FIG. 3, the copy paper 1 which has been subjected to the second image forming process and has the toner image 1a transferred to its other side is placed on the rolling contact portion K of both rollers 2 and 4 rotating in this state. is transported along the transport path T. Then, the toner image 1a is fixed on the copy paper 1 by being held between the rolling contact portions K, heated by the fixing roller 2, and pressed with an appropriately reduced pressure. At this time, since it is the second fixing process, the temperature of the copy paper is 1
Although it has increased compared to the previous time, since the clamping pressure has been lowered, there is less risk of hot offset occurring even if the degree of heating is not lowered. Furthermore, by lowering the pressing force of the pressure roller 4, wrinkles on the copy paper can be effectively prevented. In this way, the copy paper 1, which has been subjected to the second fixing process without any problems such as hot offset or wrinkles, is discharged to the paper discharge section E on the downstream side as both rollers 2 and 4 rotate.

In the above embodiment, the pressure varying mechanism of the pressurizing means 5 is configured in two stages, but by appropriately changing the shape of the cam 56, it is also possible to vary the pressing force in multiple stages. Furthermore, as shown in FIG. 5, the present invention can also be applied to a fixing device that uses a heat generating plate 6 with a heater embedded therein instead of the fixing roller 2, and can similarly produce high-quality double-sided copies. It becomes possible to obtain.

Effects As detailed above, according to the present invention, by reducing the pressure applied during the second fixing process in a duplex copying device by an appropriate amount, hot offsets, wrinkles, etc. can be prevented and high-quality double-sided copies can be produced. It becomes possible to obtain. It should be noted that the present invention is not limited to the specific embodiments described above, and it goes without saying that various modifications can be made within the technical scope of the present invention. For example, a configuration may be adopted in which the pressure is lowered and the temperature is lowered to some extent during the second fixing process.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the concept of an automatic double-sided electrophotographic copying machine, Fig. 2 is a graph showing the relationship between wrinkle occurrence rate and change in fixing pressure during duplex copying, and Fig. 3 is a graph showing the relationship between the occurrence rate of wrinkles and changes in fixing pressure during duplex copying. A schematic diagram showing one embodiment,
Fig. 4 is a perspective view showing one embodiment of the present invention;
The figure is a schematic diagram showing another embodiment of the present invention. Explanation of symbols, 1: Copy paper, 2: Fixing roller,
3: Heat generating lamp, 4: Pressure roller, 5: Pressure means, 6: Heat generating plate.

Claims (1)

[Scope of utility model registration request] A fixing device that fixes an image transferred to a transfer material includes: a support that supports the transfer material; a pressure roller that is rotatably supported and presses the transfer material against the support and conveys the transfer material; It has a pressure means that can variably set the pressing force of the pressure roller against the support body, and is characterized in that the pressing force when copying the second side is lower than the pressing force when copying the first side. fixing device.