JPH08137310A - Fixing device - Google Patents

Abstract

PURPOSE: To provide a fixing device capable of preventing a recording medium from being wrinkled at a low cost. CONSTITUTION: As to this fixing device in which the recording medium having an unfixed toner image passes through between a rotating cylindrical heating roller and a fixed elastic member 12 brought into non-rotationally press-contact with the heating roller and forming a nipping part by means of the rotational force of the heating roller, so that a toner image is heated and fixed with pressure; the member 12 is formed in a state where the load distribution of a center part 22 is higher than those of both ends 25 and 25 in the length direction of the member 12 at the nipping part. Thus, frictional force between the member 12 and the recording medium is higher at the center part 22 in comparison with those at both ends 25 and 25, so that the passing speed of the recording medium at the center part becomes low; therefore, the recording medium is tensioned in both ends 25 and 25 direction so as to prevent the recording medium from being wrinkled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in a device utilizing an electrophotographic process such as an electrophotographic copying machine, a facsimile, and a printer, and more particularly to a fixing device capable of reducing cost.

[0002]

2. Description of the Related Art In a copying machine using an electrophotographic process, it is necessary to fix toner to a sheet-shaped recording medium such as paper to form a permanent image. As this fixing method, a heat fixing method in which the toner is melted by heating and fused on a recording medium is widely adopted. As shown in FIG. 6, the fixing device adopting the heat fixing method has a heater 51 arranged inside a core 50 having a cylindrical shape.
0 has a heat roller 53 having a heat resistant resin coating layer 52 formed on the outer peripheral surface thereof, and a heat resistant elastic body layer 56 has been formed on the outer peripheral surface of a cylindrical core 55, and is pressed in parallel with the heat roller 53. And a pressure roller 57 between them,
It is known that the recording paper 60 having the unfixed toner image 59 is passed therethrough and the toner image 59 is thermocompression-bonded to the recording paper 60.

In the above fixing device, an expensive heat-resistant elastic material such as silicon rubber or fluorine rubber is required for manufacturing the pressure roller, so that the cost of the device is increased and the heating roller and the pressure roller are combined. Since it is necessary to secure a contact width to some extent, miniaturization of these is difficult. Therefore, it is difficult to shorten the warm-up time for raising the heating roller to a temperature at which it can be fixed. In order to solve such a problem, the applicant has arranged a fixed elastic member, which is pressed against the heating roller in a non-rotating state, in place of the pressure roller, and presses the fixed elastic member and the heating roller against each other. Has proposed a device for fixing a toner image by passing a recording sheet through a nip part which is a part (Japanese Utility Model Application No. 61-156675).

[0004]

By the way, in the above-mentioned apparatus using the pressure roller, the outer diameter of the heating roller and the pressure roller is formed into a drum shape in which both end sides are larger than the central portion in the axial direction. The speed in the nip portion is set so that both end portions are faster than the central portion and a tensile force is exerted in the both end portions, thereby preventing wrinkles on the recording sheet. However, there is a problem that the manufacturing cost is considerably high in order to form the heating roller and the pressure roller in a drum shape. Further, even in a device using a fixed elastic member, it is necessary to form the heating roller in a drum shape for the purpose of preventing wrinkles, but in this case as well, the manufacturing cost becomes high.

Therefore, it is an object of the present invention to provide a fixing device which can realize the prevention of wrinkles on a recording sheet at a low cost as well as downsizing and simplification of the device. I am trying.

[0006]

In order to achieve the above object, the fixing device of the present invention comprises a rotatable cylindrical heating roller and a fixed roller which is pressed against the heating roller in a non-rotating state to form a nip portion. In the fixing device, wherein the recording medium having an unfixed toner image is passed between the elastic member and the elastic member by the rotating force of the heating roller, the unfixed toner image is thermocompression-bonded to the recording medium. It is characterized in that the frictional force with the recording medium at the nip portion is higher at the central portion than at both end portions in the direction orthogonal to the passing direction of the recording medium.

[0007]

According to the present invention, since the frictional force between the fixed elastic member and the recording medium is higher in the central portion than in the both end portions, the passing speed of the recording medium in the central portion is higher than that in the both end portions. Become slow. Therefore, the recording medium is pulled toward both ends, and wrinkles are prevented from occurring.

[0008]

【Example】

A. First Embodiment (1) Configuration of Embodiment A first embodiment of the present invention will be described below with reference to FIGS. 1 to 3. In FIG. 1, reference numeral 11 is a cylindrical heating roller, reference numeral 12 is a non-rotating fixed elastic member arranged in parallel with the heating roller 11 and in pressure contact, reference numeral 1
Reference numeral 3 denotes a sheet of paper as a recording medium having the unfixed toner image 14 on the upper surface. Then, the sheet (recording medium) 13 has a pressure contact portion between the heating roller 11 and the fixed elastic member 12, that is, a nip portion 15 at the heating roller 11.
The toner image 14 is heated and pressure-bonded by being passed by the rotational force of.

The heating roller 11 has a cylindrical shape with a uniform outer diameter, and has a cylindrical core 17, a release layer 18 uniformly coated on the outer peripheral surface of the core 17, and an inner side of the core 17. And a heating source 19 such as an infrared lamp, which is driven by a driving source (not shown) to rotate about its central axis. Further, it has a temperature controller for controlling the amount of heat generated by the heating source 19 based on a signal from the temperature sensor 20 provided on the fixed elastic member 12 and thereby keeping the temperature of the nip portion 15 constant.

In this embodiment, the core 17 has a diameter of 15
mm, wall thickness 0.3 mm, and axial length 225 mm, which is made of iron, and the release layer 18 has a thickness of 30 μm and high heat resistance RTV (Room Temperature Vulcanizatio).
n) Silicone rubber is dip coated. An infrared lamp of 100 V and 300 W is used as the heating source 19, and the temperature controller controls the temperature of the nip portion 15 to be 150 ° C. at all times. As the release layer 18, in addition to the above, HTV (High Temperature
Vulcanization) It is also possible to adopt other heat resistant elastic bodies such as silicone rubber and fluororubber.

The fixed elastic member 12 is fixedly arranged with its longitudinal direction parallel to the axis of the heating roller 11. The fixed elastic member 12 has a substantially rectangular parallelepiped shape,
The portion on the pressure contact side with respect to the heating roller 11 has an arc shape so that the central portion in the passage direction of the paper 13 (the left-right direction in FIG. 1) projects toward the heating roller 11.

In this embodiment, as the fixed elastic member 12, a thin sponge sheet 24 made of Teflon having a low friction coefficient is formed on the surface of the silicone sponge 23 having excellent heat resistance on the pressure contact side. The silicone sponge 23 employed here has a rubber hardness of 35 ± 3 ° (measurement result by a rubber hardness meter for sponge of Asker C type manufactured by Kobunshi Kagaku Co., Ltd. at a load of 300 g). Further, the fixed elastic member 12 has a radius of curvature of 60 mm and a thickness of 20 m at a pressure contact portion with the heating roller 11, that is, a nip portion 15.
m, the width is about 6 mm. As the thin film sheet 24, other low friction coefficient materials such as fluororesin can be adopted in addition to the above.

Here, in order to convey the sheet 13 by the rotational force of the heating roller 11, the release layer 18 of the heating roller 11 is used.
The coefficient of friction of the fixed elastic member 12 with respect to the sheet 13 is set higher than the coefficient of friction of the thin film sheet 24 of the fixed elastic member 12 with respect to the sheet 13.

Further, the fixed elastic member 12 has a load distribution in the nip portion 15 at the time of pressure contact with the heating roller 11 such that both ends 25 in the longitudinal direction of the fixed elastic member 12 are
The central portion 22 is higher than 25. That is, in the state where the pressure contact with the heating roller 11 is released, the portion (upper part in FIG. 2) of the fixed elastic member 12 on the pressure contact side with the heating roller 11 is the central portion in the length direction of the fixed elastic member 12. It has a substantially arc shape so that 22 is convex. Here, the protrusion amount of the central portion 22 is about 1 m with respect to both end portions 25, 25 in the length direction.
It is about m. As shown in FIG. 3, the load distribution in the nip portion 15 when the fixed elastic member 12 is pressed against the heating roller 11 is higher in the central portion 22 than in the both end portions 25, 25 in the length direction. Has become.

(2) Operation / Effects of Embodiment According to the fixing device having the above-described structure, the central portion 2 in the lengthwise direction of the fixed elastic member 12 on the side in pressure contact with the heating roller 11.
By making 2 convex, the load distribution in the nip portion 15 becomes higher at the central portion 22 than at both end portions 25, 25 in the longitudinal direction of the fixed elastic member 12. Therefore, the frictional force between the fixed elastic member 12 and the paper 13 is higher in the central portion 22 than in the both end portions 25, 25, and the passing speed of the paper 13 at the central portion 22 is at the both end portions 25, 25. It will be slower than that. Therefore, the sheet 13 is pulled toward both ends 25, 25, and wrinkles are prevented from occurring.

Here, when the height of the central portion 22 with respect to the both end portions 25, 25 is set to 0 mm, 0.3 mm, and 0.5 mm, the wrinkles occurring on the respective sheets 13 are 0 mm as shown in Table 1. In case of 0.3m, 0.3m
Experimental results have been obtained that the probability of occurrence is rare when m is set and does not occur when 0.5 mm is set.
From the results of this experiment, the central portion 2 with respect to both end portions 25, 25
It was found that the height of 2 must be 0.3 mm or more.

[0017]

[Table 1]

Further, in the above embodiment, since the central portion 22 of the fixed elastic member 12 on the side in pressure contact with the heating roller 11 is formed to be convex, for example, the fixed elastic member 12 is injection molded. It can be mass-produced, for example, and the manufacturing cost can be significantly reduced as compared with the conventional one in which the heating roller has an hourglass shape.

(3) Modified Example The above first embodiment can also be applied to a fixing device as shown in FIG. In this fixing device, the upstream side portion of the heating roller 11 in the sheet passing direction, that is, the area 15a on the inlet side of the nip portion 15 is brought into pressure contact with only the thin film sheet 24 made of Teflon (that is, there is no silicone sponge), and the downstream side thereof. The portion, that is, the area 15b on the outlet side of the nip portion 15 is pressed against the fixed elastic member 12 (the portion composed of the silicone sponge 23 and the thin film sheet 24) biased by the leaf spring 27. Even in this case, if the one in which the central portion 22 has a convex shape is applied as the fixed elastic member 12, the same effect as the above can be obtained.

B. Second Embodiment Next, FIG. 5 is a diagram showing a second embodiment of the present invention. The fixed elastic member 12 of this embodiment has a constant height along the direction of pressure contact with the heating roller 11 in the state where pressure contact with the heating roller 11 is released, and the pressure contact side with respect to the heating roller 11 (upper part in FIG. 6). The width of the central portion 22 (width along the passage direction of the sheet 13) in the length direction of the fixed elastic member 12 is set wider than the end portions 25, 25. Specifically, both side portions in the width direction are arcuate in plan view so that the central portion 22 is convex outward in the width direction.

Here, the width of the central portion 22 is set to be about 1 to 2 mm wider than the width of the both end portions 25, 25 in the length direction. The load distribution in the nip portion 15 when such a fixed elastic member 12 is pressed against the heating roller 11 is also
Similar to the first embodiment, both end portions 25, 2 in the length direction thereof
The center portion 22 is higher than the center portion 5. Therefore, as in the first embodiment, it is possible to prevent the occurrence of wrinkles. In addition, since wrinkles can be prevented by a simple process of widening the central portion 22 of the portion that comes into pressure contact with the heating roller 11, the manufacturing cost can be significantly increased as compared with the case where the heating roller 11 is formed in an hourglass shape. It can be reduced.

C. Modification Example The fixed elastic member may have a shape that combines the first embodiment and the second embodiment. That is, it is also possible to form the fixed elastic member so that the central portion in the lengthwise direction is convex and wide. Further, in the above-described embodiment, the fixed elastic member is configured so that it gradually becomes convex (first embodiment) or gradually widens (second embodiment) from both ends toward the central portion. However, it may be configured so as to be gradually convex or wide.

Furthermore, in the first embodiment described above, the upper surface of the fixed elastic member 12 is formed so that the central portion has a convex shape. However, the fixed elastic member 12 has a uniform cross section so that the central portion has a convex shape. It can also be bent and used. For example, a fixed elastic member having a rectangular cross section and having a uniform cross section is attached to a pedestal having a convex central portion, whereby the same configuration as described above can be obtained.

Further, the friction coefficient of the upper surface of the fixed elastic member can be set so that the central portion is higher than both end portions by the following constitution. The value of the surface roughness of the fixed elastic member is set so that the central portion is high and both end portions are low. The central portion and both end portions of the fixed elastic member are made of different materials. With this configuration, the shape of the fixed elastic member can be made uniform in cross section. Of course, it is also possible to combine such a configuration with the configuration of the above-mentioned cabinet embodiment.

[0025]

As described above in detail, according to the fixing device of the present invention, the frictional force between the fixed elastic member and the recording medium is higher in the central portion than in the both end portions. The passing speed of the recording medium becomes slower than that at the both ends, so that the recording medium is pulled toward both ends and wrinkles can be prevented from occurring. Moreover, the wrinkle prevention is achieved with a fixed elastic member that is easy to mold, rather than a heating roller.
The manufacturing cost can be reduced.

Further, by a simple structure in which the central portion of the fixed elastic member is made convex, the load at the nip portion which is in pressure contact with the heating roller is higher at the central portion than at both end portions in the length direction. Since the fixed elastic member can be formed more easily, the manufacturing cost can be further reduced (claim 2).

Further, by a simple structure in which the central portion of the fixed elastic member is widened, the load at the nip portion that is in pressure contact with the heating roller is higher at the central portion than at the both end portions in the length direction. Therefore, the fixed elastic member can be formed more easily, and the manufacturing cost can be further reduced (claim 3).

[Brief description of drawings]

FIG. 1 is a sectional view showing a fixing device according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a fixed elastic member of the fixing device according to the first exemplary embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a load distribution (vertical axis) with respect to a longitudinal position (horizontal axis) of the fixed elastic member of the fixing device according to the first exemplary embodiment of the present invention.

FIG. 4 is a sectional view showing another example of the fixing device according to the first exemplary embodiment of the present invention.

FIG. 5 is a perspective view showing a fixed elastic member of a fixing device according to a second exemplary embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a conventional fixing device.

[Explanation of symbols]

11 ... Heating roller, 12 ... Fixed elastic member, 13 ... Paper (recording medium), 14 ... Unfixed toner image, 15 ... Nip portion, 22 ... Central portion, 25 ... Both end portions.

Claims (3)

[Claims] 1. A recording medium having an unfixed toner image is heated between a rotatable cylindrical heating roller and a fixed elastic member which is pressed against the heating roller in a non-rotating state to form a nip portion. In a fixing device for passing the unfixed toner image onto the recording medium by heating and pressing it by the rotational force of a roller, the fixed elastic member has a frictional force with the recording medium at the nip portion in a passing direction of the recording medium. 2. A fixing device, characterized in that the central portion is higher than both end portions in the direction orthogonal to the above. 2. The surface of the fixed elastic member facing the heating roller side has a convex shape in which the central portion projects toward the heating roller side from both ends in the direction orthogonal to the passing direction of the recording medium. The fixing device according to claim 1, wherein 3. The surface of the fixed elastic member facing the heating roller is wider in the central portion in the passage direction of the recording medium than at both ends in the direction orthogonal to the conveying direction of the recording medium. It has a shape, and it is characterized by the above-mentioned.
Or the fixing device described in 2.