JPH02281283A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent toner from being offset onto a heat resistant sheet by providing a press-contact member pressing transfer material against the heat resistant sheet downstream of its moving direction while the transfer material is separated from a heating element. CONSTITUTION:The transfer material 12 having an unfixed toner image transferred onto its front surface is carried in the direction shown by the arrow B by a means such as a conveying belt, and smoothly enters the heating element 16 and the nip part of a pressure roller 13. Consequently, the toner image is heated by the heating element 16 via the heat resistant sheet 1, and its front surface is softened and fused. Then, the transfer material is separate from the heating element, enters the press-contact surface of the tape 25 of a pressure plate 24 with the heat resistant sheet 1, is again cooled and solidified without separating from the heat resistant sheet 1, after which it separates from the heat resistant sheet 1. Thus, toner can be fixed without being offset on the heat resistant sheet 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing device used in an image forming apparatus such as a copying machine or a printer.

[Prior Art] Conventionally, a fixing device using a heat-resistant sheet, for example,
It consists of the configuration shown in the figure.

In FIG. 5, 41 is a heat-resistant sheet, 42 is a metal roller (driven roller), and 43 is a metal roller (drive roller).

That is, the metal rollers 42 and 43 are supported by the side plates via sliding bearings (not shown), and both rollers 42 and 43 are
, 43, a heat-resistant sheet 41 having a thickness of approximately 25 μm is placed under a certain amount of tension. Also, metal roller 4
3 is driven in the direction of arrow A by a gear train and motor (not shown). Then, the heat-resistant sheet 41 is rotated by a driving force determined by the friction coefficient between the metal roller 43 and the heat-resistant sheet 41 and the tension of the heat-resistant sheet 41, and then the driving force between the metal roller 42 and the heat-resistant sheet 41 is similarly driven. force is transmitted.

A pressure roller 45 has a metal core and a rubber surface layer, and is driven by the frictional force between it and the heat-resistant sheet 41 in the same way as the metal roller 42 .

48 is a heating element, and a linear or band-shaped heating surface 49 is provided on the bottom surface.
have.

In addition, 44 is a transfer material such as transfer paper, 46 is a fixing entrance guide, and 47 is a paper discharge guide.

In the heat fixing device configured as shown in FIG. 5, the transfer material 44 on which the unfixed toner image has been transferred by the image transfer means is conveyed in the direction of arrow B by means such as a conveyor belt. It smoothly enters the nip portion between the heating element 48 and the pressure roller 48 along the fixing entrance guide 46.

The toner image made of heat-meltable toner on the transfer material 44 is first heated by the heating element 48 via the heat-resistant sheet 41, and at least its surface layer portion is softened and melted.

Thereafter, the toner image is separated from the heating element 48, cools and solidifies again by natural heat dissipation, and the transfer material 44 is sent along the paper discharge guide 47 and discharged from the fixing device.

[Problems to be Solved by the Invention] However, in the heat fixing device shown in FIG. 48
When the transfer material 44 separates from the heat-resistant sheet 41 before the toner image cools and solidifies due to the weight of the transfer material 44 after being separated from the toner image, a part of the near surface layer of the toner image is offset onto the heat-resistant sheet 41. There was a problem.

As a result, firstly, the glossiness of the image becomes uneven between offset and non-offset portions of the toner image;
Then, during the subsequent fixing operation of the transfer material 44, the toner offset onto the heat-resistant sheet 41 is heated and melted again by the heating element 48 and fixed onto the transfer material 44, or is offset onto the surface of the pressure roller 45, A problem arises in that the toner is fixed on the back side of the transfer material 44.

The present invention aims to solve the above-mentioned problems. That is, an object of the present invention is to provide a fixing device that can prevent offset of toner onto a heat-resistant sheet.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a heat-resistant material that is in contact with a transfer material on a surface having an unfixed toner image and that moves at approximately the same speed as the transfer material speed. In a heat fixing device in which the toner image is heated and melted by a heating element that generates heat by being energized in a pulsed manner through the sheet, the toner image is cooled and solidified, and then the heat-resistant sheet is separated from the transfer material. , a pressure contacting member for pressing the transfer material against the heat-resistant sheet is provided immediately downstream from the heating element in the moving direction of the transfer material.

[Function] According to the present invention, the pressure contact member that presses the transfer material against the heat-resistant sheet is provided immediately downstream from the heating element in the moving direction of the transfer material, so that the toner image on the transfer material is transferred through the heat-resistant sheet. Immediately after the transfer material is heated by the heating element, softened and melted and separated from the heating element, the transfer material is pressed against the heat-resistant sheet by the pressure contact member, and the transfer material does not separate from the heat-resistant sheet until the toner is solidified. This prevents the near surface layer of the image from being offset onto the heat-resistant sheet.

[Example] Figures 1 and 2 show a first example of the present invention, and a third example
FIG. 4 shows a second embodiment of the invention.

In FIGS. 1 and 2, 1 is a heat-resistant sheet, 3 is a metal roller (driven roller), and 4 is a metal roller (driving roller).

That is, the metal roller 3.4 is supported by the side plate 6.9 via a sliding bearing (not shown), and both rollers 3.4
, 4, a heat-resistant sheet 1 having a thickness of approximately 25 μm is placed under a certain amount of tension. The metal roller 4 is driven in the direction of arrow A in FIG. 1 by a gear train and a motor (not shown). Then, the metal roller 4 and the heat-resistant sheet 1
The heat-resistant sheet 1 is rotated by a driving force determined by the friction coefficient between 0 and the tension of the heat-resistant sheet 1, and then the driving force is similarly transmitted between the metal roller 3 and the heat-resistant sheet 1.

A pressure roller 13 has a metal core and a rubber surface layer, and is driven by the frictional force between it and the heat-resistant sheet 1, similar to the metal roller 3.

Reference numeral 16 denotes a heating element, which has a heat-resistant and electrically insulating base material such as alumina and has a linear or band-shaped heating surface 17 made of, for example, Ta2N on the lower surface thereof.

24 is a pressure plate made of a metal plate, and a heat-resistant tape 2 with a small coefficient of friction is attached to the surface in contact with the heat-resistant sheet 1.
5 is attached to improve sliding properties when the transfer material 12 such as transfer paper passes through, and the pressure contact plate 24 is pressed against the heat resistant sheet 1 via this tape 25.

Further, the tape 25 is located immediately behind the heating element 16 on the downstream side, as shown in FIG.

In the fixing device configured as shown in FIGS. 1 and 2, the transfer material 12 on which the unfixed toner image has been transferred by the image transfer means is transferred as shown in FIG. The heating element 16 and the pressure roller 13 are conveyed in the direction shown by the arrow B, and the heating element 16 and pressure roller 13 are smoothly moved along the fixing entrance guide.
enters the nip section.

The toner image made of heat-meltable toner on the transfer material 12 is first heated by the heating element 16 via the heat-resistant sheet 1, and at least its surface layer portion is completely softened and melted.

Thereafter, it moves away from the heating element and immediately enters the pressure contact surface between the tape 25 of the pressure contact plate 24 and the heat resistant sheet 1, and the heat resistant sheet 1
It cools and solidifies again without separating from it.

Thereafter, the paper passes through the pressure contact surface and is discharged from the fixing device along the paper discharge guide.

In this way, the toner image is separated from the heat-resistant sheet 1 after being cooled and solidified, so that it can be fixed on the heat-resistant sheet 1 without being offset.

Next, a method of releasing the pressure contact between the pressure contact plate 24 and the pressure roller 13 will be described.

The side plate portion 28 of the pressure contact plate 24 holds a bearing 29 of the pressure roller 13, and is supported by the main body of the image forming apparatus at the rotation center 27.

Further, the pressure contact plate 24 is supported by a cam 26, and the cam 26
is coaxially connected to a motor (not shown), and the rotation of the motor causes the pressure plate 24 and the pressure roller 13 to move up and down.

Inside this fixing device, the transfer material 12 stays and becomes clogged, and a paper jam signal is generated from a transfer paper detection sensor (not shown), and the pressure of the pressure plate 24 and the pressure roller 13 is applied to the motor. A release command is given, rotation is performed, the paper jam is removed, and the paper is rotated until pressure is applied again.

In FIGS. 3 and 4 showing the second embodiment of the present invention,
The same members as in FIGS. 1 and 2 described above are given the same reference numerals.

In FIGS. 3 and 4, reference numeral 31 denotes a metal pressure roller, and both ends thereof are held by a side plate 30 made of sheet metal via bearings 32. As shown in FIG. Further, the side plate 30 holds the pressure roller 13 via a bearing 29, and is rotatable about a point 27. In addition, the pressure roller 31
is located immediately behind the heating element 16 on the downstream side.

In the fixing device configured as shown in FIGS. 3 and 4, the toner image of the transfer material 12, on which the unfixed toner image has been transferred by the image transfer means, is
The image is fixed in exactly the same manner as in the first embodiment described above. However, in this second embodiment, as soon as the transfer material 12 separates from the heating element 16, it enters the pressure contact surface between the pressure roller 31 and the heat-resistant sheet 1, and the toner image is transferred without separating from the heat-resistant sheet 1. It solidifies again.

Therefore, also in this second embodiment, since the toner image is separated from the heat-resistant sheet 1 after being cooled and solidified, it can be fixed on the heat-resistant sheet 1 without being offset.

The side plate 30 is supported by a cam 26, and the cam 26 is coaxially connected to a motor (not shown), and the rotation of the motor causes the pressure roller 31 and the pressure roller 13 to move up and down.

Inside the fixing device of this second embodiment, the transfer material 12
When the paper jams due to accumulation, a paper jam signal is issued from a transfer paper detection sensor (not shown), and a command to release the pressure of the pressure roller 31 and the pressure roller 13 is issued to the motor, and the rotation is performed. Once the paper jam is removed, it is rotated until it is pressed again.

[Effects of the Invention] As explained above, according to the present invention, the pressure member that presses the transfer material against the heat-resistant sheet is provided immediately downstream from the heating element in the moving direction of the transfer paper. The toner image is heated by a heating element through a heat-resistant sheet,
Immediately after the transfer material softens and melts and separates from the heating element, the transfer material is pressed against the heat-resistant sheet by the pressure contact member, and the transfer material does not separate from the heat-resistant sheet until the toner cools and solidifies.
This prevents the vicinity of the surface layer of the toner image from being offset onto the heat-resistant sheet.

[Brief explanation of drawings]

FIG. 1 is a side view showing a first embodiment of the present invention, FIG. 2 is a plan view of FIG. 1, FIG. 3 is a side view showing a second embodiment of the present invention, and FIG. 3 is a plan view, and FIG. 5 is a side view showing an example of the conventional technology. 1...Heat-resistant sheet 3.4...Metal roller 12
...Transfer material 13...Pressure roller 16...
Heating element 24...Press plate 26...Cam 31...Press roller 29...Bearing 32...Bearing. 4 other people

Claims (1)

[Scope of Claims] 1. The toner image is fixed by a heating element that generates heat by being energized in a pulsed manner through a heat-resistant sheet that is in contact with the transfer material on the surface having the unfixed toner image and moves at approximately the same speed as the transfer material speed. After heating and melting, the toner image is cooled and solidified, and then, in a heat fixing device in which the heat-resistant sheet is separated from the transfer material, the toner image is transferred immediately downstream from the heating element in the moving direction of the transfer material. A fixing device comprising a pressure member that presses a material against the heat-resistant sheet. 2. The fixing device according to claim 1, further comprising means for simultaneously pressing and releasing a pressure member that presses the transfer material against the heating element when heating and melting the toner, and a pressing member provided immediately downstream of the heating element.