JPH07117794B2 - Fixing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fixing device that forms an image on a transfer material using a heat-meltable toner and heat-fixes the image.

2. Description of the Related Art Conventionally, a fixing device used in an image forming apparatus includes a heating roller that is maintained at a predetermined temperature and a pressure roller that has an elastic layer and is in pressure contact with the heating roller. The roller fixing method in which the transfer material on which the toner image is formed is heated while being nipped and conveyed is often used. However, in this type of device, in order to prevent the so-called offset phenomenon in which the toner is transferred to the heating roller, it is necessary to maintain the heating roller at an optimum temperature, and the heat capacity of the heating roller or the heating body must be increased. There wasn't. That is,
When the heat capacity of the heating roller is small, the temperature of the heating roller is likely to fluctuate greatly toward the low temperature side or the 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. When it fluctuates to the low temperature side, insufficient softening and melting of the toner causes fixing failure and low temperature offset, and when it fluctuates to the high temperature side, the toner is completely melted and the cohesive force of the toner decreases. , Causing high temperature offset.

If the heat capacity of the heating roller is increased in order to avoid such a problem, another problem occurs in that the time for raising the temperature of the heating roller to a predetermined temperature becomes long and the standby time becomes long when the device is used. .

As a measure for solving such a problem, US Pat.
As disclosed in No. 7, a toner image is heated to its melting point by a heating element to be melted, and after melting, the toner is cooled to have a relatively high viscosity, and the toner adhesion tendency is weakened. A method of fixing without causing offset by a process of peeling from the heating body web is known.

In addition to this, the above-mentioned known method employs a method in which the toner image and the transfer material are heated to the heating body without press-contact, so that it is not necessary to heat the transfer material, and compared with other methods. The toner can be melted with far less energy. However, as is well known, in the case of contact with a pressure body without press-contact, the heat transfer efficiency is lowered and it takes a relatively long time to heat and melt the toner.
Therefore, in Japanese Patent Application No. 47-25896, it is proposed that a known press-contacting technique is added to this to improve the heat transfer efficiency and heat and melt the toner in a short time and sufficiently.

[Problems to be Solved by the Invention] However, in Japanese Patent Application No. 47-25896, in order to heat the toner in a relatively short time and sufficiently, a toner image and a transfer image are formed between a pair of heating members. The material is sandwiched under pressure to heat it, and then the heating is stopped and the material is forcibly cooled, so that the energy required for fixing becomes large. That is, since the toner image is heated from the top and bottom by being heated by the pair of heating elements, it is considered to be efficient at first glance, but conversely, in order to heat the toner image from the transfer paper side, the transfer material is sufficiently heated first. It is necessary to do so, and for that reason a large amount of energy is needed. Further, in the cooling step, when the toner image is heated, the transfer material that has been heated and heated cannot be separated unless it is cooled, and a forced cooling means is required, resulting in a large energy waste.

As described above, a method has been proposed in which the toner that has been heated once is cooled and then separated to fix the toner without causing high-temperature offset, but it has not been put into practical use because of the drawbacks described above.

In the above two proposals, the heating element is composed of a heating roller and a web fed by the heating roller and a heat source incorporated in the heating roller. Heating is performed through the web, and the heating roller functions as a web conveying roller. is doing. For this reason, the method of supplying power to the heat source and the form of contact and support of the temperature detecting element are complicated, and the temperature control accuracy tends to be poor. Furthermore, in the structure in which the temperature detecting element slides on the heating roller, there is a safety problem such as excessive temperature rise due to disconnection. In addition, in both of the above-mentioned two examples, since a heating body having a relatively large heat capacity is required, the heat radiation to the inside of the machine is increased, and the temperature rise inside the machine is notable.

The present invention solves the problems that the above-described conventional device has, and makes it possible to reduce the heat capacity of the heating element without causing defective fixing or offset, and as a result, standby time, power consumption, and further An object of the present invention is to provide a fixing device in which the temperature rise inside the image forming apparatus is small.

[Means for Solving the Problems] In order to achieve the above object, the present invention has a heating body, a film in contact with the heating body, and a pressure roller for pressing the heating body through the film. Then, the recording material carrying the unfixed toner image is nipped and conveyed between the film and the pressure roller while the toner image is melted by the heat from the heating body, and then the toner image is cooled and solidified and then recorded with the film. In the fixing device for separating materials, the heating body is a heating body of low heat capacity in which a heat generating portion is provided on the base material, and the pressure roller has no heat source and is maintained at a temperature lower than the melting point of the toner. It consists of

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, a schematic structure of an image forming apparatus to which the apparatus of the present embodiment is applied will be described with reference to FIG. 1. Reference numeral 1 is an original placing table made of a transparent member such as glass, which reciprocates in the direction of arrow a to place an original. To scan. A short-focus small-diameter image-forming element array 2 is arranged immediately below the document table, and a document image G placed on the document table 1 is illuminated by an illumination lamp 7, and a reflected light image thereof is produced by the array 2. Slit exposure is performed on the photosensitive drum 3. The photosensitive drum 3 rotates in the direction of arrow b. Reference numeral 4 denotes a charger, which uniformly charges the photosensitive drum 3 coated with, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer 3a. On the drum 3 uniformly charged by the charger 4, the element array 2 forms an electrostatic image subjected to image exposure. This electrostatic latent image is visualized by the developing device 5 using a toner made of a resin or the like that is softened and melted by heating. On the other hand, the sheet P stored in the cassette S is drum-moved by a pair of conveyance rollers 9 which are rotated in pressure contact with each other in the vertical direction at a timing so as to be synchronized with the feeding roller 6 and the image on the photosensitive drum 3. 3 is sent. Then, the transfer discharger 8 transfers the toner image formed on the photosensitive drum 3 onto the sheet P. After that, the sheet P separated from the drum 3 by the known separation means is fixed by the conveyance guide 10 to the fixing device.
The sheet is guided to 20, heated and fixed, and then discharged onto the tray 11. After the toner image is transferred, the residual toner on the drum 3 is removed by the cleaner 12.

FIG. 2 is an enlarged view of the fixing device 20 of this embodiment. In the figure, reference numeral 21 denotes a heating element, which has a width of 160 μm and a length (length in a direction perpendicular to the paper surface) on the lower surface of a heat-resistant and electrically insulating base material such as alumina or a composite material containing the base material. is) 216 mm, for example made of Ta ₂ N or the like, the heating unit includes a heating element 28 of the linear or strip arranged with quadrature components to the conveying direction, for example, as a further sliding protective layer on the surface thereof, Ta ₂ O ₅ is formed. The lower surface of the heating element 21 is smooth and the front and rear ends are rounded, and the heating portion (heating surface)
Is formed to enable sliding with the fixing film 23. The fixing film 23 is made of PET as a base material, is heat-treated to have a thickness of, for example, about 9 μm, and is wound around a film feeding shaft 24 so as to be fed in the direction of arrow C. The fixing film 23 comes into contact with the surface of the heating body 21 and is wound around the film winding shaft 27 via the separation roller 26 having a large curvature.

The heating element 28 of the heating element has a small heat capacity, is energized in a pulse shape, and instantly raises its temperature to about 260 ° C. each time. By detecting the leading edge and the trailing edge of the transfer sheet P by the transfer sheet detection lever 25 and the transfer sheet detection sensor 29, the heating element 28 is energized at a required timing. At that time, the energization of the heating element may be controlled by detecting the position of the transfer sheet by a sheet feeding sensor of the image forming apparatus.

On the other hand, the pressure roller 22 has an elastic layer made of silicon rubber or the like on a core material made of metal or the like, and is driven by a drive source (not shown) and guided by the conveyance guide 10 to the unfixed state. The transfer material P having the toner image T is brought into close contact with the heating body via the fixing film 23 which moves at the same speed as the transfer material P. Here, the conveyance speed of the pressure roller 22 is preferably substantially the same as the conveyance speed at the time of image formation, and the movement speed of the fixing film 23 is set to a value corresponding to it.

In the present embodiment, since the heating element 28 instantly heats up, preheating is unnecessary, and heat transfer to the pressure roller during non-fixing is small. Further, even at the time of fixing, the fixing film, the toner image, and the transfer material are the heating element 28 and the pressure roller.
The temperature gradient can be made steep due to the fact that it is interposed between the pressure roller 22 and the pressure roller 22, and the pressure roller 22 is hard to heat up, and continuous images of a degree necessary for practical use are provided. Even if the toner is formed, its temperature is maintained below the melting point of the toner.

In the apparatus of this embodiment having such a configuration, the toner image made of the heat-fusible toner on the transfer paper P is first heated and melted by the heating body 21 through the fixing film 23, and especially the surface layer portion has a melting point. Is greatly exceeded and completely softened and melted.
At that time, the heating roller, the fixing film, the toner image, and the transfer material are in good contact with each other by the pressure roller 22, and the heat is efficiently transferred.

Then, as the heating of the heating element 21 stops, and as the transfer material is conveyed and moves away from the position of the heating element, the toner image radiates heat and cools and solidifies again, and passes through the separation roller pair 26 having a large curvature. After that, the fixing film 23 is separated from the transfer paper P. At that time, in this embodiment, the pressure roller
Since the temperature of 22 is kept lower than the melting point of the toner, it is possible to accelerate the heat dissipation of the toner image. Therefore, the time required for cooling is short, and the device can be downsized.

As described above, after the toner T is completely softened and melted,
Since the toner solidifies again, the cohesive force of the toner becomes very large, and the toner behaves as a group. Further, since it is pressed by the pressure roller 22 when it is heated and softened and melted, at least a part of the toner image T permeates the transfer material surface layer and is cooled and solidified as it is.
It is fixed on the transfer material P without being offset to 23.

As is apparent from the present embodiment, the heating body (heating unit) of the present invention may be small in size, so that the heat capacity becomes small and it is not necessary to raise the temperature of the heating unit in advance. Can be reduced, and the temperature rise inside the machine can be prevented.

Further, in this embodiment, the fixing film 23 may be heat-treated on the basis of a thin and inexpensive PET film. Therefore, as shown in FIG.
Can be replaced by a winding method after use. That is, a roll wound with a film of a predetermined length is set on the film feeding shaft 24, and the leading end of the film is fixed to the winding shaft 27 through a space between the heating body, the pressure roller and the separation roller pair. When such a method is adopted, the fixing film sensor arm 30 and a sensor (not shown) detect the remaining amount of the fixing film, and when the film is near the end, a warning display or a warning sound is given to the user to notify the fixing film of the fixing film. It is good to encourage exchange. When the fixing film 23 is replaced, it is desirable that the heating body, the pressure roller, and the separation roller pair can be opened and closed about the rotation shaft 31 as shown in FIG. In this embodiment,
The fixing film 23 can be thinned by the winding exchange method as described above regardless of the durability of the fixing film, and the power consumption can be reduced.

Further, in this embodiment, as described above, the offset to the fixing film does not occur, so if the thermal deformation or deterioration of the fixing film is small, the wound fixing film can be reused and automatically rewound. Alternatively, the winding side and the sending side may be exchanged with each other and used a plurality of times.

Further, in this embodiment, by providing the separation roller 26,
A sufficient time for cooling the toner image T in the pressurized state up to the separation roller is ensured, and the curvature of the separation roller 26 is increased to facilitate the separation of the fixing film 23 and the transfer material P. It is possible to prevent the offset in the separation part in synergy with the above effect. However, in this embodiment, since the pressure roller 22 promotes cooling of the toner image, when the heat capacity of the heating unit 28 and the fixing film is sufficiently small and the fixing processing speed is low, a special roller such as the separating roller 26 is used. Since the toner image T is cooled in a short range after the transfer material P passes through the heating portion without providing any means, the separation roller 26 shown in this embodiment can be omitted to perform the fixing process without offset. Becomes That is, it suffices that the fixing film and the transfer material can be separated after the toner image is once heated, softened and melted, and then thermally solidified again.

Next, the results of implementation by the apparatus of this embodiment will be shown with specific numerical values. A toner image T is formed using a wax-based toner for Canon PPC PC-30 (trade name), and the fixing processing speed is about 15 mm / s, and about 2000 W per A4 size paper.
When a fixing test was conducted by heating in pulses at a rate of 2 ms every 10 ms so that the heat generation amount of S was obtained, an image having no problem in practical use was obtained. This energization causes the heating layer to
The temperature rises to around 260 ° C, and since the heat capacity is small, the temperature is lowered by stopping the energization for 8ms. Therefore, the waiting time for heating the heating element is not necessary. In addition, in this embodiment, since the heat energy necessary for fixing is given each time by the pulse-shaped heating, the heating unit has a small heat capacity and a heating element having a very fast rise has a substantially equal cycle. It is relatively easy to indicate the temperature. Furthermore, when the fixing process is continuously performed, it is easy to prevent the heating unit from abnormally shifting to the high temperature side by gradually reducing the pulse width for heat generation. In the above case, the temperature of the toner layer T momentarily exceeds the temperature that is conventionally said to cause high temperature offset, but as described above, the fixing film 23 is sufficiently cooled and fixed again.
Since the transfer material P and the transfer material P are separated from each other, no offset occurs. When heated, the wax, which is the main component of the toner used in this example, has a melting point of about 80 ° C., and since the viscosity at the time of melting is low, it is heated by a heating body at about 260 ° C.,
In the conventional heating and fixing device, the melted toner penetrates too much into the transfer material, which causes problems such as image bleeding or show-through, which is an obstacle to lowering the melting point of the toner. In this case, since the heat capacity of the heating element 28 is small and the heating time is short, the temperature gradient is large, so that only the surface layer of the transfer paper is heated for a short time, so that the above-mentioned adverse effects caused by the excessive permeation of the toner do not occur.

FIG. 4 is a sectional view of a heating and fixing device applied to an image forming apparatus according to another embodiment of the present invention. The same parts as those in the previous embodiment are designated by the same reference numerals, and the description thereof will be omitted.

In this embodiment, a heat resistant endless film is used instead of the endless fixing film 23.
40 is heated many times, and contact with the toner layer T is repeated. For this reason, a 30 μm-thick endless sheet is formed using a PFA resin, which has excellent mold release properties and high heat resistance, as a base material. The endless fixing film 40 is driven by a drive shaft 41 so as to have the same peripheral speed as the transfer material conveying speed, and is urged to give tension to the endless fixing film 40.
It is driven to rotate while being strained by 42.

The heating body 21 is provided with a temperature detecting element 43 for detecting the temperature of its base material, and further, a temperature fuse or a thermostat is provided as a safety device 44,
Excessive temperature rise is prevented. Further, the timing of energizing the heating element 21 in this embodiment is controlled based on the signal generated in the image forming means. Since the fixing processing speed of this embodiment (same during image formation) is 50 mm / s, which is faster than that of the previous embodiment, the width (heating width) of the heating element 28 is increased to 300 μm and the heating element is The heat generation was about 2400 W · S per A4 size paper at a rate of 1.25 ms every 5 ms by changing the energization time to. Here, the maximum temperature of the heating element is about 300 ° C. or more, the power density of the heating element 28 is higher than that in the previous embodiment, and further, the above-mentioned amount of heat is given in a short time. , Heating element
Since the temperature rise (heat storage) of 21 itself becomes large as compared with the case of the previous embodiment, in this embodiment, the energization pulse is generated according to the detection value of the above-mentioned temperature detection element 43 provided on the support material of the heating body 21. The width of is adjusted. That is, when the base material temperature of the heating element 21 is high, the width of the energizing pulse is reduced to prevent abnormal heating of the heating element itself. Furthermore, when the safety device 44 has reached a predetermined temperature or higher, the heating element 28 is de-energized.

Here, the temperature drop of the transfer material and the toner image T is also disadvantageous as compared with the previous embodiment. That is, in order to eliminate the disadvantages such as increasing the fixing processing speed, the temperature of the heating element is increased, the amount of heat generated per sheet is increased, and the time until separation after heating is reduced. A cooling means for cooling and solidifying is required until the films are separated. For example, it is a heat radiating plate 45 made of aluminum which is brought into contact with the endless fixing film 40, and is provided between the heating element 21 and the separation roller 26. In addition to this, a blower or the like may be used as the cooling means. Since the pressure roller of the present invention also has the effect of cooling as described above, when the speed is increased as in this embodiment, it is necessary to cool the pressure roller 22. In this embodiment, a pressure roller cooling fan 49 is provided to blow air to the pressure roller to maintain the temperature lower than the melting point of the toner. Further, a separation claw 46 is arranged in the separation portion, a transfer pad is prevented from being wrapped around, and a cleaning pad 47 made of felt is brought into contact with the endless fixing film 40 in order to remove foreign matters such as paper dust and the like. ing. Further, the felt pad may be impregnated with a slight release agent such as silicone oil to improve the release property of the endless fixing film 40. Further, since the insulating PFA resin is used in this embodiment, static electricity that disturbs the toner image is likely to be generated in the fixing film. Therefore, in order to deal with this, the static elimination brush 48 grounded is used to eliminate static electricity. Here, the endless fixing film may be charged within a range that does not disturb the toner image by applying a bias voltage to the brush without grounding. Furthermore, it is also a measure to prevent the image distortion due to the static electricity described above by adding a conductive powder fiber such as carbon black to the PFA resin. Also,
Depressurization and conductivity of the pressure roller can be performed by the same means. Further, an antistatic agent or the like may be applied or added. In addition, the front and back of the fixing film may be discharged.

Here, the pressure contact portion between the pressure roller 22 and the heating element 28 is the heating element 21.
The pressure contact width between the pressure roller 22 and the pressure roller 22 is closer to the inlet side in the transport direction, and prevents the endless fixing film 40 and the transfer material P from being separated immediately after heating.

In the present embodiment, the maximum power consumption increases to about 1600 W due to the increased speed. Therefore, the maximum power consumption may be reduced to 400 W by dividing the heating element into four in the longitudinal direction and sequentially supplying electricity.

In the present embodiment shown above, by adding the cooling means and the separating means, it is possible to obtain a stable image without offset at a relatively high speed, and by using a heat-resistant endless fixing film, it is economical. It has become possible to improve.

Further, as the above-described embodiments of the present invention, two examples of the copying machine using the electrophotographic method have been described, but the present invention is not limited to this, and a toner that is softened and melted by heating of a laser beam printer or the like is used. The image forming apparatus can be applied to a conventional image forming apparatus, and the heating and fixing process can be performed without requiring a waiting time.

EFFECTS OF THE INVENTION As described above, according to the present invention, the transfer material having the toner image is brought into close contact with the heating body through the fixing film by using the pressure roller which is maintained at a temperature lower than the melting point of the toner. By transporting the toner, efficient heat transfer can be achieved, and cooling of the toner image can be promoted. Therefore, it is possible to reduce the heat capacity of the heating element without causing defective fixing or offset. As a result, it is possible to obtain the effect of obtaining an image forming apparatus that has a small standby time when the apparatus is used, power consumption, and further, the temperature rise inside the apparatus.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus of an embodiment of the present invention, FIG. 2 is an enlarged sectional view of a fixing device of FIG. 1, and FIG. 3 is a fixing film exchange of the device of FIG. 4 is a sectional view of a fixing device of another embodiment of the present invention. 3 ... Image forming means (photosensitive drum) 20 ... Heat fixing means 21 ... Heating body 22 ... Pressure roller 23, 40 ... Fixing film P ... Transfer material T ... Toner image

Continuation of front page (56) Reference JP 61-122665 (JP, A) JP 59-68766 (JP, A) JP 59-157678 (JP, A) JP 50-134436 (JP , A) Actually open 49-136238 (JP, U) Actually open 59-25549 (JP, U) Actually open 49-7938 (JP, U) Special public Sho 50-16936 (JP, B1) Special public Sho 51-29825 (JP, B2) JP-B-56-28263 (JP, B2) JP-B-56-19638 (JP, B2) JP-A-58-105178 (JP, A) JP-A-63-313182 (JP, A) JP-A-1-187582 (JP, A) JP-A-54-158935 (JP, A) JP-A-50-39553 (JP, A) JP-A-51-69633 (JP, A) JP-A-55 -39303 (JP, A) JP-A-56-123579 (JP, A)

Claims (1)

[Claims] 1. A heating body, and a film in contact with the heating body,
A pressure roller for pressing the heating body through the film, and a recording material carrying an unfixed toner image is nipped and conveyed between the film and the pressure roller while being heated by the heating body. In a fixing device that melts a toner image and then separates the film and the recording material after the toner image is cooled and solidified, the heating body is a heating body of a low heat capacity in which a heating portion is provided on a base material, and the pressure roller Is a fixing device characterized by having no heat source and being maintained at a temperature lower than the melting point of the toner.