JPH04195077A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent the generation of offsetting and to obtain a copied image with gloss and a translucent copy with good transmittance by constituting heating belt by providing an elastic layer and a mold released layer on a belt base body. CONSTITUTION:The heating belt 3 is constituted from the belt base body 31, the elastic layer 32, and the mold released layer 33. Then, toner image is heated from its surrounding by the effect of the elastic layer 32 of the heating belt 3, and heating is carried out efficiently and evenly. Thus, the copied image with gloss and the translucent copied image with good transmittance can be obtained, and fixing at a high speed can be carried out without necessitating a heating source of a great heating capacity necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fixing device for an electrophotographic image forming apparatus.

[Conventional technology]

Conventionally, a fixing device used in an electrophotographic image forming apparatus uses a heating roller maintained at a predetermined temperature and a pressure roller that has an elastic layer and presses against the heating roller to fix unfixed toner. A heat roller fixing method is often used in which a recording material on which an image is formed is held and conveyed while being heated and fixed.

However, in this type of device, in order to prevent the so-called offset phenomenon in which particles are transferred to the heating roller,
In order to maintain the heating roller at an optimum temperature, it is necessary to increase the heat capacity of the heating roller or the heating body. That is, when the heat capacity of the heating roller is small, the temperature of the heating roller tends to fluctuate greatly toward a low temperature side or a high temperature side due to paper passing or other external factors due to the relationship with the amount of heat supplied by the heating element. If the temperature changes to the low temperature side, the toner softens and melts insufficiently, resulting in poor fixation or low temperature offset. If the temperature changes to the high temperature side, the toner completely melts and the cohesive force of the toner decreases. , resulting in a high temperature offset.

In order to avoid this problem, increasing the heat capacity of the heating roller increases the time it takes to heat the heating roller to a predetermined temperature, causing another problem of increasing standby time when using the device. .

As a measure to solve this problem, U.S. Patent No. 3.57
As disclosed in No. 8.797, (1) the toner image is brought into contact with a heating body web and heated to its melting point to melt it, and (2) after melting, the toner is cooled to a relatively high viscosity. (3) Peel it off from the heating element web while weakening the tendency of the toner to adhere.

There is a known method of fixing without causing offset by going through this process.

In addition, in the known method, the toner image and the recording material are heated without pressurizing the heating body, so there is no need to heat the recording material, compared to other methods. The company says it can melt toner using much less energy.

However, as is well known, when the toner is brought into contact with a heating body without being pressurized, the heat transfer efficiency decreases and it takes a relatively long time to heat and melt the toner.

Therefore, it has been proposed in Japanese Patent Publication No. 51-29825 to improve the heat transfer efficiency by adding a known pressure welding technique to this method, thereby sufficiently heating and melting the toner in a short time.

Further, the uses of electrophotographic image forming apparatuses are rapidly expanding as modern information becomes more complex and diversified.

Accordingly, the image forming technology is required to be compatible with various uses such as digitization and colorization. Among these required technologies, copies (hereinafter referred to as translucent copies) in which characters and images are formed using black or chromatic toner on a transparent film are produced on a screen using an overhead projector (OHP), etc. Projection is already widely practiced. However, when a translucent copy is created using such an electrophotographic image forming device, even if the toner image is a chromatic color other than black, the projected image obtained is not a chromatic color but a black-gray color. There is a problem.

As described above, the reason why a clear color projected image could not be obtained in a transparent copy using a toner image is that the transparency of the toner is low, the unevenness of the surface of the toner image, and furthermore,
Bubbles and cracks exist inside the toner layer due to incomplete melting and pressurization, and light is scattered or reflected diffusely, so the light from the toner image area cannot reach the projected surface, and the image area appears as a shadow. It's for a reason.

Therefore, in order to improve the compatibility between the binder, dye, and pigment contained in the toner, and to remove the unevenness on the surface of the toner image, the translucent copy is conveyed while being held between rollers equipped with a heating source, and the toner image is A method of heating and pressurizing was tried.

[Problem to be solved by the invention]

The proposal disclosed in the above-mentioned Japanese Patent Publication No. 51-29825 is to heat the toner in a relatively short time and sufficiently. (1) Press the toner image and recording material between a pair of heating bodies. - (2) After stopping the heating, it is forcibly cooled.

method. When using such means, there arises a disadvantage that the energy required for fixing increases. That is, by heating the toner image with a pair of heating elements, the toner image is heated from above and below, which may seem efficient at first glance, but on the other hand, in order to heat the toner image from the recording material side, the recording material must first be sufficiently heated. It is necessary to do so, and for that purpose, a large amount of energy is required. Furthermore, in the cooling process, when heating the toner image, the recording material that has been heated to an elevated temperature cannot be separated unless it is cooled, which requires forced cooling means, which has the disadvantage of a large waste of energy. Not put into practical use.

Further, in the two examples described above, the heating body is constituted by a heating roller and a heat generation source built therein, and furthermore, the heating roller has a function as a web conveyance roller. For this reason, the method of feeding power to the heat generating source and the contact support of the temperature sensing element become complicated, and the accuracy of temperature control tends to deteriorate.

Further, in the above two cases, since both require a heating element with a relatively large heat capacity, there is also the disadvantage that heat dissipation into the apparatus increases, causing unnecessary temperature rise inside the apparatus.

Furthermore, conventionally, when a toner image and a recording material are held under pressure between a heating body and a pressure body using a heating roller and fixed by heating, the width of the pressure contact portion between the heating body and the pressure body is the heating width. , fixation is performed during this time. However, in order to obtain a sufficient heating width, the pressure between the heating body and the pressing body is usually applied at both ends in the longitudinal direction, but in this case, the heating body and the pressing body become deflected. The pressure contact width between the heating body and the pressure body becomes uneven in the longitudinal direction. This causes problems in that the heating time for the toner image becomes non-uniform in the longitudinal direction, resulting in large fixation irregularities on the same recording material and offset easily occurring.

Furthermore, in the conventional method for translucent copying, the toner image on the transparent film is not only peeled off by being pulled by the surface of a roller having a heating source or retransferred, staining the image surface, but also the toner image surface The unevenness was not removed and the projected image did not become chromatic.

In order to improve these shortcomings, if silicone oil, etc., which has good mold release properties, is applied, the oil will remain on the resulting film, resulting in drawbacks such as staining hands and the OHP stand glass. there were.

Therefore, even with a fixing device that has achieved offset prevention, it cannot meet the recent demand for obtaining glossy color images, and conventional fixing devices are not used to make transparent color copies for OHP. There has been a problem in that electrophotographic image forming apparatuses are not fully utilized.

The present invention solves these problems, prevents the occurrence of offset, makes it possible to obtain glossy copy images and transparent copies with good transparency, and provides high-speed fixing that does not require a heating source with a large heat capacity. The purpose is to provide a possible fixing device.

[Means to solve the problem]

The above object is a fixing device that performs fixing by bringing a recording paper having a toner image into contact with a heating belt, wherein the heating belt is characterized in that an elastic layer and a release layer are provided on an endless belt base. This is accomplished by a fixing device.

〔Example〕

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG.
FIG. 3 is an enlarged cross-sectional view of the heating belt 3 shown in the figure.

In Fig. 1, 1 is a heating pressure bonding section, 3 is a heating belt, and 4 is a heating belt.
5 is a heater, 5 is a conveyor belt, 11 is a heating roller, 12 is a pressure roller, 21 is a 20th roller, 22 is a 30th roller, 6
Reference numeral 1 denotes a spring, and a heater 4 made of a halogen lamp or the like is provided inside the heating roller 11. The conveyor belt 5 is an elastic belt made of, for example, cloth-filled rubber with a hardness of 50° or more, and is stretched between the pressure roller 12 and the 30th roller 22.

The heating roller 11 is forcibly driven and rotated in a clockwise direction indicated by an arrow at a fixed position by a power device of the main body of the image forming apparatus. As the heating roller 11 rotates, the heating belt 3 and the 20th roller 21 are rotated clockwise, and the conveyor belt 5, the pressure roller 12, and the 30th roller 22 are driven to rotate counterclockwise.

A predetermined load is applied toward the heating roller 11 by a spring 61 on the axis 123 at both ends of the pressure roller 12, so that a constant pressure is applied to the heating and pressing portion l.

As shown in FIG. 2 in cross section, the heating belt 3 consists of three layers: a belt base 31, an elastic layer 32, and a release layer 33, and is made of phosphor bronze or stainless steel with a thickness of about 10 to 100 μm. An elastic layer 32 made of, for example, elastic rubber and having a thickness of about 3 mm is provided on the outer periphery of a belt base body 31 made of a flexible endless metal band, and further thereon, an elastic layer 32 made of, for example, polytetrafluoroethylene (PTFE) is provided. A mold release layer 33 with a thickness of approximately 30 μm and a smooth surface with excellent heat resistance and mold release properties.
is provided.

In addition to metal, a resin belt having excellent heat resistance, such as polyimide resin, can be used for the belt base 31.

The surface temperature of the heating belt 3, which is heated by the heater 4 via the heating roller 11, is 190° C. during the heating and pressing sl.
℃, and the load applied by the pressure roller 12 in the heating and pressing section l is controlled at a linear velocity of 150°C.
mm/sec, the spring 6 should be adjusted so that the weight per unit length in the direction parallel to the axis of the pressure roller 12 is about 4 Kg/cm.
1 adjustment is made.

As the toner used in the developing device of an image forming apparatus equipped with this fixing device, it is preferable to use a toner having a viscoelastic region over as wide a temperature range as possible. A toner mainly composed of a high molecular weight polymer exhibits a temperature and an elastic modulus corresponding to the temperature as shown in FIG. 3, and at low temperatures, the molecules, also called glass regions, are arranged in an amorphous state.

When the toner temperature rises and passes the glass transition point Tg, molecules move freely and the elastic modulus becomes a viscoelastic region with a decrease. High molecular weight polymers with a weight average molecular weight of approximately 10,000 or more have a freely movable molecular arrangement that takes a spiral or other form, and has a rubber-like region with stable viscoelasticity. . When the temperature is further increased, the temperature exceeds the melting temperature TH and becomes a liquid flow region with fluidity.

When fixing is carried out by heat-pressing using a heating roller or a heating belt, the temperature conditions for fixing without causing offset need to be within the temperature range of the rubber-like region. In addition, in order to obtain a glossy toner image, it is desirable to heat the toner above the melting temperature TH to the fluid region. , the glass transition point T when sufficiently pressed by a smooth surface such as a roller or belt.
g, and the fixing device of the present invention satisfies this condition.

Next, the operation of this fixing device will be explained.

The recording paper on which the toner image has been transferred is conveyed from six directions in FIG. 1 to the heat-pressing unit l of the fixing device, and is heated and pressurized while being held and conveyed by the heating belt 3 and the conveying belt 5.

As a result, the toner image, which is a layered state of toner particles T as shown in FIG. will be held.

As a result, the temperature of the toner particles T rises to the rubber-like region or flow region, and the toner particles T are pressurized by the load.

At the initial stage of fixation, the toner image contains minute air bubbles 8 and cracks 9 and reflects transmitted light diffusely, as shown in FIG. It is cooled and pressurized while passing through the glass transition point Tg, and the internal bubbles and cracks disappear and become homogeneous.
The toner layer becomes a translucent and glossy toner layer as shown in Figure (C), and fixing is completed. The recording paper that has been fixed is conveyed by the heating belt 3 and the conveyor belt 5, and is discharged from the fixing device.

When the heating belt 3 was made inflexible except for the elastic layer 32, and a fixing experiment was conducted under the same conditions as above.
Uneven fixing occurred because the pressing force against the recording paper could not be obtained uniformly, and only copy images with uneven gloss and unstable fixing properties were obtained. Further, when an experiment was conducted under the same conditions except for the configuration in which the release layer 33 of the heating belt 3 was removed, the toner T adhered to the elastic layer 32 due to offset, and good fixing was not achieved.

〔Effect of the invention〕

According to the present invention, the configuration and control as described above are provided.

By applying pressure in an appropriate temperature range, it was possible to prevent the occurrence of offset and obtain glossy copy images and translucent copies with good transparency. Moreover, due to the effect of the elastic layer, efficient heating is performed, making it possible to provide a fixing device capable of high-speed fixing without requiring a heat source with a particularly large heat capacity compared to conventional fixing devices.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing the relationship between the elastic modulus of toner and temperature, and FIG. 4 is a diagram showing how toner is fixed.

Claims (1)

[Claims] A fixing device that performs fixing by bringing a recording paper bearing a toner image into contact with a heating belt, characterized in that the heating belt is provided with an elastic layer and a release layer on an endless belt base. Fixing device.