JPH02271376A - Fixing device - Google Patents

Abstract

PURPOSE:To obtain a fixing device which does not cause curl of a heat-fixed recording material by forming the film contact surface of a heating body so that it is warped in the prescribed direction to the downstream of a nip from its center. CONSTITUTION:A protecting layer is formed into a radiused shape on its surface so that the surface where the fixing film 16 comes into contact with the heating body 12, that is, the surface forming the nip together with a pressure roller 19, is formed to protrude toward the pressure roller 19. Owing to this shape, the recording material is heated in condition where it forms a parabola opening upward in the nip, and is ejected thereafter by the roller. Thereby, the recording material is formed into a radiused shape of a projecting, that is, comes to curl upward. Therefore, though the recording material P curls downward when the surface of the heating body 12 is flat, the straight and uncurled recording material P can be obtained after fixing by setting off various factors through the formation of the R shape.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing device for an image forming apparatus that heats and fixes a toner image onto a recording material.

[Prior Art] Conventionally, in an image forming apparatus such as a copying machine, a pressure roller is brought into pressure contact with a heat roller having a built-in heater, and a recording material carrying an unfixed image is passed through a nip between these rollers. A hot roll method for fixing is known. In this heat roll type fixing device, the heat roll must always be heated above a certain temperature, so when not copying, it is a waste of electricity, and even after the main switch of the copier is turned on, Also, the ohm-up time required to perform the first copy was approximately one minute.

Therefore, the present applicant has proposed a fixing method that causes less heat loss and has an extremely short warm-up time. This fixing method consists of a heat-resistant fixing film that vibrates at the conveyance speed of the recording material while in contact with the visible image formed on the recording material, and a fixed heating element that heats and melts the visible image by applying electricity in a pulsed manner. , a pressure mechanism that presses the heating element and a pressure roller with the fixing film sandwiched therebetween, and a mechanism that separates the fixing film from the recording material after the heated and melted image is cooled and solidified. It is something.

[Problems to be Solved by the Invention] However, the above fixing device has low heat loss;
Moreover, it has the advantage that the warm-up time is extremely short, but when the recording material is sandwiched between the fixed heating body and the pressure roller together with the fixing film, the upper side of the recording material is the plane of the heating body, In addition, since the lower side is a curved surface of the pressure roller having a relatively large curvature, there is a problem in that the heated recording material curls as it moves along the pressure roller on the lower side. In addition to this, the recording material is subjected to downward force due to gravity, and especially if the recording material is paper that contains a lot of moisture, the moisture in the paper white evaporates due to heating and the paper shrinks, so curling is prevented. , more likely to occur.

That is, when the recording material passes through the fixing device and is heat-fixed, there is a problem in that it curls in the opposite direction to the planar heating body, that is, toward the pressure roller.

The present invention attempts to solve these problems. That is, an object of the present invention is to provide a fixing device that prevents a heat-fixed recording material from curling.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an image forming means for forming a visible image on a recording material, and an image forming means for forming a visible image on a recording material, and an image forming means for forming a visible image on a recording material, and an image forming means for forming a visible image on a recording material, and an image forming means for forming a visible image on a recording material. In a fixing device that heats and fixes the visible image using a pressure member that brings a recording material into close contact with the heating body, the film contacting surface of the heating body is opposite to the pressure rotating body from at least the center of the nip toward the downstream side of the nip. It shall be substantially curved to the side.

[Function] According to the present invention, the shape of the contact surface of the heating body with the fixing film is opposite to the curvature R of the pressure roller, that is,
Since it has a convex shape in the direction of the pressure roller, curling of the recording material can be suppressed.

[Embodiment] FIGS. 1 to 3 show a first embodiment of the present invention.

Since FIG. 2 shows a schematic structure of the image forming apparatus, FIG. 2 will be explained first.

In FIG. 2, reference numeral 1 denotes a document mounting table made of a transparent member such as glass, which scans the document by reciprocating in the direction of arrow a.

A short-focus, small-diameter imaging element array 2 is arranged directly below the original table 1, and the original image placed on the original table 1 is illuminated by an illumination lamp 3, and the reflected light image is reflected from the array 2. slit exposure is performed on the photosensitive drum 4. Note that this photosensitive drum 4 rotates in the direction of the arrow. A charger 5 uniformly charges the photosensitive drum 4 coated with, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer. , an electrostatic image is formed by image exposure by the array 2. This electrostatic image (electrostatic latent image) is visualized by a developing device 6 using toner made of a resin or the like that softens and melts when heated. On the other hand, the recording material P, such as recording paper, stored in the cassette S is conveyed by a pair of rollers that are pressed against each other in the vertical direction and rotated in synchronization with the image on the feeding roller and the photosensitive drum 4. It is sent onto the photosensitive drum 4 by the roller 8 . Then, the toner image formed on the photosensitive drum 4 is transferred onto the recording material P by the transfer discharger 9. Thereafter, the recording material P separated from the photosensitive drum 4 by a known separation means is guided to a fixing device 11 by a conveyance guide 10, subjected to heat fixing processing, and then discharged onto a tray 22. Note that after the toner image is transferred, residual toner on the photosensitive drum 4 is removed by a cleaner 23.

FIG. 3(a) shows the fixing device 11 of FIG. 2 in an enlarged manner.

In the figure, reference numeral 12 denotes a linear heating element with a low heat capacity fixed to the device, and has a thickness of, for example, 1.0 m11. Width 1
0ia+, an alumina substrate 13 with a longitudinal length of 240 mm is coated with a resistive material 14 to a width of 1.0 m + w, and one energization from both ends in the longitudinal direction is a DC 100 V cycle of 20
With a pulse waveform of m5ec, a pulse corresponding to the desired temperature and energy release amount controlled by the temperature measuring element 15 is given by changing the pulse width. The pulse width is 0.5 to 51 Bsec.

In this way, the heating element 12 whose temperature and energy are controlled
The fixing film 16 moves in the direction of the arrow in the figure. As an example of this fixing film 16, the thickness is 20 μm.
It is an endless film in which a heat-resistant film of, for example, polyimide, polyetherimide, PES, or PFA is coated with 10 μm of a release layer made of a fluororesin such as PTFE%PFA and a conductive material added to at least the image contacting side. −
Numerically, the total thickness is 100μ, more preferably less than 40μ. The fixing film 16 is driven by the driving roller 17 and the driven roller 18 and tension, so that the fixing film 16 moves in the direction of the arrow without wrinkles.

Reference numeral 19 denotes a pressure roller having a rubber elastic layer having good releasability such as silicone rubber, which presses the heating body 12 through the fixing film 16 with a total pressure of 4 to 7 kg, and rotates in pressure contact with the film 16.

The unfixed toner 20 on the recording material P is guided to the fixing section by the entrance guide 21, and a fixed image is obtained by the above-mentioned heating.

In FIG. 3(a), the fixing film 16 is an endless belt, but as shown in FIG. 3(b), the fixing film 16 may be a film with ends. Further, as an image forming apparatus, the present invention is applicable to a fixing device of any apparatus that forms an image using toner, such as a copying machine, a printer, and a facsimile.

FIG. 1 is a partially enlarged view of the heating body 12 of the fixing device shown in FIG. 3(a).

As mentioned above, 13 is an alumina substrate, on which is coated a resistive material 14 which is a heating element. Furthermore, a protective layer 51 of glass material is covered thereon.

The alumina substrate 13, resistance material 14, and protective layer 5I described above are integrally attached to the heat insulator 53 with a heat-resistant double-sided tape or a heat-resistant adhesive. This heat insulating body 53 is attached to a stay 52 that supports the heating body portion. This stay 52 needs to be made of a material and have a structure that will not cause large deflection in the center even when it is pressed by the pressure roller 19.

In the present invention, the surface of the heating body 12 that is in contact with the fixing film 16, that is, the surface that forms a nip with the pressure roller 19, has a convex shape relative to the pressure roller 19. With this shape, the recording material P is heated in a downwardly convex shape within the nip and is then discharged by the roller, so that the recording material P such as paper has a convex shape R of the heating body 12.
It will follow the shape, that is, it will curl upwards.

By the way, if the surface of the heating body 12 is flat, as described above, it will have a shape that follows the pressure roller 19, that is, it will curl downward. If the surface of 12 is properly rounded to have a convex R shape, each factor will be canceled out, and a straight, curl-free recording material P can be obtained after fixing.

As mentioned above, the film contacting surface of the heating element 12 is shaped like a convex R.
In order to form the shape, as shown in Figure 1, a protective layer 5 on the surface is applied.
1 should be cut into an R shape.

FIG. 4 shows a second embodiment of the invention.

In this second embodiment, an alumina substrate 13 is shaved in advance into a convex R shape, a resistive material 14 is applied thereon, and a protective layer 51 is evenly covered.

FIG. 5 shows a third embodiment of the invention.

In this third embodiment, a substrate 55, a resistive material 14, a protective F
This is a case where I51 is flexible, and the heat insulating body 53 has a convex R shape. The heat insulator 53 is preferably made of numerically heat-resistant resin, such as pps (bolyphrylene sulfide) or PEEK (polyetherketone).

FIG. 6 shows a fourth embodiment of the invention.

In this fourth embodiment, instead of the heat insulator 53 having a convex R shape in the third embodiment, the stay 52 has a convex R shape.

FIG. 7 shows a fifth embodiment of the invention.

In this fifth embodiment, an alumina substrate 13, a resistive material 14
, instead of making the surface of the heater formed into a convex R-shape consisting of the protective layer 51, as shown in FIG. There is. In this case, the surface of the protective layer 51 of the heater may be flat, so it is inexpensive. On the other hand, as described above, if the heat insulator 53 is made of PPS or PEEK, injection molding or the like can be performed, so that the convex round shape can be easily and inexpensively realized, which is advantageous.

In any of the above embodiments, only the portion downstream from the center of the nip (the side of the paper discharge guide 54) within the nip may be formed into a convex R shape.

[Effects of the Invention] As explained above, according to the present invention, the shape of the heating body in the nip is made into a convex R shape with respect to the pressure roller in the direction of movement of the recording material, so that Curling in the direction of the pressure roller, that is, downward curling can be prevented.

[Brief explanation of drawings]

341 is an elevational sectional view showing the heating body of the first embodiment of the present invention, FIG. 2 is an elevational sectional view of an image forming apparatus using the fixing device having the heating body of FIG. Figure 3 (a), (
b) is an explanatory diagram of the fixing film of the fixing device shown in FIG. 2, FIG. 4 is an elevational cross-sectional view showing the heating body of the second embodiment of the present invention, and FIG. 5 is a heating element of the third embodiment. FIG. 6 is an elevational sectional view showing the heating element of the fourth embodiment, and FIG. 7 is an elevational sectional view of the heating element of the fifth embodiment. . 11... Fixing device 12... Heating body 13...
Alumina substrate 14... Resistance material 15... Temperature measuring element 16... Fixing film 17... Drive roller
18...Followed roller 19...Pressure roller 20
...Unfixed toner 21...Entrance guide 51...
・Protective layer 52... Stay 53... Heat insulator 5
4... Paper discharge guide 55... Board. Figure 1

Claims (1)

[Scope of Claims] 1. An image forming means that forms a visible image on a recording material, and a pressure member that presses against a fixed heating body and brings the recording material into close contact with the heating body through a fixing film. In the fixing device that heats and fixes the visualized image, the film contacting surface of the heating body is substantially curved from at least the center of the nip toward the downstream side of the nip to the side opposite to the pressure rotating body. Fusing device. 2. The fixing device according to claim 1, wherein the heating body has a crown shape in the conveyance direction of the recording material in the nip portion.