JPH0519654A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent curl from occurring and to improve carrying quality by providing a means for cooling a transfer material on the side of the heated surface of the transfer material near a transfer material passing path from a press-contact part to a carrying means. CONSTITUTION:A toner image visualized on a recording paper 8 passes through the press-contact part where a pressuring roller 23 is allowed to press-contact with a fixing roller 21 in which a heater 22 is incorporated, and heated and fixed while passing. Continuously, the recording paper 8 is separated from the roller 21 by a separation pawl 25, and guided by a carrying guide 14 to be ejected by a carrying roller 12. In such a case, the heat absorbing part 26 and the heat radiating part 27 of a heat pipe are provided on a downstream side and an upstream side in a paper feeding and carrying direction. Therefore, the recording paper 8 passing through the press-contact part 24 is cooled in a free state by the heat absorbing part 26, and then abuts on the guide 14 or the roller 12. The heat absorbing part 26 of the heat pipe is provided on the roller 21 side near the passing path for the recording paper 8.

Description

Detailed Description of the Invention

[0001]

2. Description of the Related Art In a fixing device used in an image forming apparatus such as a copying machine, when the transfer paper is sandwiched between pressure contact portions and heated and pressed, curling occurs in the transfer paper inside the fixing device and on the downstream side. There is a case. As a technique for preventing this, for example, one in which a specific relationship is given to the speed of the fixing rotator and a plurality of conveying means located downstream thereof (see Japanese Patent Application Laid-Open No. 61-228482), a fixing device is used. There has been proposed one in which a cooling means is provided between the roller pair on the downstream side (see Japanese Utility Model Laid-Open No. 61-28755).

On the other hand, regarding the relationship between the fixing roller and the pressure roller in the fixing device, conventionally, as shown in FIG. 6, the materials of the fixing roller 21 'and the pressure roller 23' are aluminum, Teflon, and silicon, respectively. The fixing roller 21 'is formed in a drum shape and the pressure roller 23' is formed in a cylindrical shape so that wrinkles do not occur when the paper is conveyed. That is, a difference is provided between the diameter of the end portion and the diameter of the central portion of the fixing roller in the lengthwise direction, and due to this difference, a peripheral speed difference of the fixing roller is generated for the paper passing through the central portion, and wrinkles of the paper are generated. It was preventing the occurrence.

[0003]

However, in the conventional fixing device as described above, in the one disclosed in Japanese Patent Laid-Open No. Sho 61-228482, the transfer paper hits the conveyance guide at a high temperature before reaching the conveyance means. It is not possible to completely prevent the transfer paper from waviness. If the conveyance guide is not provided in order to solve this problem, the transfer paper cannot be regulated, jams frequently occur, and it is necessary to separately provide a conveyance belt or the like, so that the apparatus cannot be downsized.

Further, in Japanese Utility Model Laid-Open No. 61-28755, a long conveyance path is required after the fixing device, and the device cannot be downsized.

On the other hand, regarding the material and shape of the fixing roller and the pressure roller, since low hardness rubber has been used as the material of the pressure roller, the conventional roller pair as shown in FIG. There was a problem that wrinkles could not be prevented.

Particularly in laser printers, their widespread use and generalization of their uses are remarkable, and they are also used as output devices for LOW END personal computer users. Along with this, the paper used for printing is not only plain paper, but also postcards,
It has a wide range of envelopes. The rubber hardness of the pressure roller is lower than that of the conventional one so as to be able to handle such various types of paper.

When the pressure roller 23 'made of such low hardness rubber is brought into pressure contact with the fixing roller 21', when the fixing roller has a drum shape and the pressure roller has a cylindrical shape, as shown in FIG. The end portion of the pressure roller 23 'is largely deformed (also shown in FIG. 7B), and the deformation of the center portion (also shown in FIG. 7C) is small.

In this state, the rotation of the fixing roller 21 ', which is rotated by the transmission of the driving force by the gear device 30, is transmitted to the pressure roller 23' from the end pressure contact portion of the paper 8'outside the paper passing area, and is applied. The pressure roller 23 'is driven to rotate. On the other hand, assuming that the friction coefficients between the fixing roller 21 'and the pressure roller 23' with the paper are μ _A and μ _B , respectively, the relationship of μ _B >> μ _A is satisfied, so that the paper 8'is on the pressure roller side. It is given a carrying force.

As a result, the sheet conveyed on the pressure roller side at the pressure contact portion is subjected to a force in a direction causing wrinkles as indicated by an arrow in the figure due to the restoring force after the deformation of the pressure roller. And the printing speed of the LOW END printer is low for cost reduction (4-6 minutes for printing one sheet of A4)
Therefore, while being fed at a low speed, the heated sheet discharges the retained moisture as water vapor, thereby generating wrinkles as shown in FIG.

Therefore, the present invention solves the above problems in the prior art, prevents curling from occurring without increasing the size of the apparatus, or causes wrinkles even when a pressure roller made of a material having low hardness is used. First, it is an object of the present invention to provide a fixing device having good conveyance quality.

[0011]

In order to solve the above problems, the present invention provides a transfer material carrying an unfixed toner image through a pressure contact portion between a fixing roller and a pressure roller. In the fixing device of the image forming apparatus, the transfer device sends the transfer material to the downstream side in the transfer material passing direction of the fixing device that heats and fixes the toner image by the transfer from the pressure contact portion to the transfer means. The invention according to claim 2 is characterized in that a cooling means for cooling the transfer material that has passed through the pressure contact portion is provided on the heated surface side of the transfer material in the vicinity of the passage path of the material. The cooling means is a heat absorbing portion of a heat pipe, and the heat radiating portion of the heat pipe is arranged on the upstream side of the pressure contact portion in the passing direction, and the invention of claim 3 is the invention of claim 1 or 2. In addition to the features of the invention, The invention according to claim 4 is characterized in that a heat insulating member is provided between the fixing means and the cooling means, and the transfer material carrying the unfixed toner image is passed through a pressure contact portion between the fixing roller and the pressure roller. In the fixing device for heating and fixing the toner image, the fixing roller has a cylindrical shape, and the pressure roller has a drum shape made of a material having low hardness rubber as a main component.

[0012]

According to the first aspect of the invention, the transfer material passing through the pressure contact portion on the heated surface side of the transfer material is cooled in the vicinity of the passage path of the transfer material between the pressure contact portion and the conveying means. Since the cooling means is provided, the transfer material is cooled before it comes into contact with the conveying means, and thus the occurrence of curling of the transfer material is prevented. Since the cooling means is provided up to the conveying means, the device can be downsized.

According to the second aspect of the invention, the cooling means is the heat absorbing portion of the heat pipe, and the heat radiating portion of the heat pipe is arranged upstream of the pressure contact portion. Therefore, in addition to the above, cooling of the transfer material is possible. The thermal efficiency in the fixing system is improved while being performed uniformly.

According to the third aspect of the invention, since the heat insulating member is provided between the pressure contact portion and the cooling means, heat transfer from the fixing roller side to the cooling means is reduced, and the cooling efficiency is further improved.

According to the fourth aspect of the present invention, the fixing roller has a cylindrical shape and the pressure roller has an hourglass shape whose main component is low hardness rubber. Therefore, the pressure roller is pressed against the fixing roller. In doing so, the pressure roller applies a force in the direction in which the wrinkles are stretched to the transfer material when restoring after the deformation.

[0016]

1 shows a schematic structure of a laser printer which is an example of an image forming apparatus equipped with a fixing device of the present invention. Around the periphery of the drum-shaped photosensitive member 1, a charger 2 for uniformly charging the photosensitive member and a laser beam L emitted by the laser optical system 3 based on the original image data are arranged in the order of the rotation direction indicated by the arrow. An exposure unit 4 that forms an image, a developing device 5 that visualizes an electrostatic latent image formed on the photosensitive member 1 by exposure with toner, and a paper feeding device 6 that is fed in the direction of arrow A from a registration roller 7. A transfer charger 9 that transfers a toner image to the recording paper 8 that is sent at the same timing, a separation charger 10 that electrostatically separates the recording paper, and a toner that remains on the photoconductor 1 after transfer is removed and collected. A cleaning device 11 and the like are provided.

The recording paper on which the toner image is transferred is heated and fixed on the unfixed toner image thereon by the fixing device 20, and then is discharged from the direction of arrow B to the discharge tray 13 by the conveying roller 12 as a conveying means. Then, the image is completed. In this printer, the recording paper is passed above the photoconductor 1, but the fixing device of the present invention can be applied to the image forming device of the lower conveyance. Further, the recording paper may be conveyed from the conveying roller 12 to the reversing mechanism.

Reference numerals 26 and 27 respectively denote a heat absorbing portion and a heat radiating portion of a heat pipe as a cooling means.

FIG. 2 shows a schematic structure of the fixing device 20.
The toner image visualized on the recording paper 8 passes through a pressure contact portion 24 in which a pressure roller 23 is pressed against a fixing roller 21 having a heater 22 built therein, and the toner image thereon is heat-fixed. Subsequently, the recording paper 8 is separated from the fixing roller 21 by the separation claw 25, guided by the conveyance guide 14, and ejected by the conveyance roller 12.

In such a fixing device, the heat absorbing portion 26 and the heat radiating portion 27 of the heat pipe are provided on the downstream side and the upstream side in the sheet feeding and conveying direction as described above. Therefore, the recording paper 8 that has passed through the pressure contact portion 24 is cooled by the heat absorbing portion 26 in a free state, and then comes into contact with the transport guide 14 or the transport roller 12. As a result, the occurrence of waviness and curl of the recording paper 8 can be reduced, and the degree of freedom of the position of the conveyance roller is increased, so that the overall size of the image forming apparatus can be reduced.

It is desirable that the heat absorbing portion 26 of the heat pipe is provided on the fixing roller 21 side in the vicinity of the passage of the recording paper 8 and at a position where it does not come into contact with the recording paper 8 passing therethrough. This is because waviness may occur when they come into contact with each other.

As the cooling means, it is also possible to consider a suction fan with a narrow opening. However, some measures must be taken to make the cooling of the recording paper uniform. On the other hand, when a heat pipe is used, it is possible to easily cope with it by changing the gap in the fixing roller direction (depth direction in the drawing) according to the cooling capacity.

Next, in the heat radiating portion 27 of the heat pipe provided on the upstream side, the heat absorbed in the heat absorbing portion 26 is radiated,
The recording paper 8 is preliminarily heated. As a result, the thermal efficiency of the fixing system can be improved.

FIG. 3 shows another embodiment, in which two pairs of pressure rollers 23a and 23b are provided. In this device, heat insulating sheets 28a and 28b as heat insulating members are provided on the downstream side of the press contact portion 24, and cover 29a and
It is attached to 29b. As a result, the inside of the fixing device and the heat absorbing portion 26 of the heat pipe are separated from each other to improve the fixing efficiency and the cooling efficiency.

FIG. 4 shows an embodiment of the invention of claim 4. The fixing roller 21 and the pressure roller 23 have a cylindrical shape and a drum shape, respectively, and are made of aluminum and Teflon, and low hardness rubber and Teflon.

The fixing roller 21 is rotationally driven by a driving force transmitted from the printer body side via the gear device 30. On the other hand, the pressure roller 23, as shown in FIG.
When the recording paper 8 is pressed against the fixing roller 21, the recording paper 8 is driven and rotated by the pressure contact portions outside the passage area of the recording paper 8.

With such a structure, when the pressure roller 23 is brought into pressure contact with the fixing roller 21, the rubber stamp of the pressure roller 23 is compressed, as shown in FIG. Although it deforms largely as shown in FIG. 5, it deforms slightly in the central part as shown in FIG. 9A, and the contact cross section becomes linear along the cylindrical surface of the fixing roller 21 which is not deformed due to the solid core of aluminum. .

As a result, a restoring force is generated in the rubber portion of the pressure roller brought into pressure contact, and as shown in the figure, the direction in which the wrinkle is extended with respect to the recording paper 8 contrary to the conventional one shown in FIGS. Force of. Therefore, even when the recording paper 8 is conveyed at a low speed, wrinkles do not occur on the recording paper.

[0029]

As described above, according to the present invention, in the first aspect of the invention, the transfer material is cooled before it comes into contact with the conveying means, so that the curling of the transfer material can be prevented. Further, the size of the device can be reduced.

In the invention of claim 2, since the cooling means is the heat absorbing portion of the heat pipe and the heat radiating portion of the heat pipe is arranged on the upstream side of the pressure contact portion, in addition to the above, the cooling of the transfer material is uniform. In addition, the thermal efficiency of the fixing system can be improved.

According to the third aspect of the present invention, since the heat insulating member is provided between the pressure contact portion and the cooling means, heat transfer from the fixing roller side to the cooling means is reduced, and the curl of the transfer material is effectively reduced. Rippling can be prevented.

In the invention of claim 4, when the pressure roller is brought into pressure contact with the fixing roller, the pressure roller applies a force in the direction of extending the wrinkle to the transfer material when the pressure roller is restored after being deformed. Can be prevented. Further, since the fixing roller has a straight cylindrical shape, a constant linear velocity can be given to the transfer material in the width direction thereof.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a laser printer that is an example of an image forming apparatus to which a fixing device according to an embodiment is mounted.

FIG. 2 is an explanatory diagram of a fixing device according to an embodiment.

FIG. 3 is an explanatory diagram of a fixing device according to another embodiment.

FIG. 4 is an explanatory diagram showing shapes of a fixing roller and a pressure roller of a fixing device according to an embodiment of the invention of claim 4;

5A and 5B are explanatory views showing a pressure contact state of the pressure roller to the fixing roller, FIG. 5A is a side view, FIG.
And (C) is a central part sectional view.

FIG. 6 is an explanatory diagram showing shapes of a fixing roller and a pressure roller of a conventional fixing device.

7A and 7B are explanatory views showing a state in which a conventional pressure roller is pressed against a fixing roller, FIG. 7A is a side view, and FIG. 7B is an end sectional view.
And (C) is a central part sectional view.

FIG. 8 is an explanatory diagram showing a state of wrinkles occurring on a recording sheet.

[Explanation of symbols]

8 Recording paper (transfer material) 21 fixing roller 23 Pressure roller 24 Pressure contact part 26 Heat absorption part of heat pipe 27 Heat pipe heat dissipation part 28 Heat insulating sheet (heat insulating member)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G03G 15/20 103 6830-2H 107 6830-2H

Claims (4)

[Claims] 1. A transfer material on the downstream side in the transfer material passing direction of a fixing device for heating and fixing the toner image by passing the transfer material carrying an unfixed toner image through a pressure contact portion between a fixing roller and a pressure roller. In the fixing device of the image forming apparatus provided with a conveying unit that sends out the transfer member, the pressing unit is provided on the heated surface side of the transfer member in the vicinity of the transfer material passage between the pressing unit and the conveying unit. A fixing device comprising a cooling means for cooling the passed transfer material. 2. The fixing device according to claim 1, wherein the cooling means is a heat absorbing portion of a heat pipe, and the heat radiating portion of the heat pipe is arranged upstream of the pressure contact portion in the passing direction. . 3. The fixing device according to claim 1, further comprising a heat insulating member provided between the pressure contact portion and the cooling unit. 4. A fixing device for heating and fixing the toner image by passing a transfer material carrying an unfixed toner image through a pressure contact portion between a fixing roller and a pressure roller, wherein the fixing roller has a cylindrical shape, The fixing device, wherein the pressure roller is made of a material having low hardness rubber as a main component and has a drum shape.