JPH01263677A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce power consumption and to form an image by conveying a transfer material which has a toner image in contact with a heating body across a fixation film by using a heat roller which is held at temperature lower than the fusion point of toner. CONSTITUTION:The toner image consisting of heat-meltable toner on the transfer paper P is heat and melted first by the heating body 21 across the fixation film 23 and, specially, its surface layer part exceeds the melting point greatly and is softened and melted completely. At this time, the heating body, fixation film, toner image, and transfer material are brought in excellent contact by a pressure roller 22 and efficient heat conduction is obtained. Then the heat generation of the heating body 21 is stopped and the transfer material is conveyed; as the material is moved away from the heating body position, the toner image radiates its heat and is cooled and solidified again and the fixation film 23 leaves the transfer paper P after passing a separation roller 26. At this time, the temperature of the pressure roller 22 is held lower than the melting point of toner to accelerate the heat radiation of the tone image. Thus, the power consumption is reduced and the image formation is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image forming apparatus that forms an image on a transfer material using heat-melting toner and heat-fixes the image.

[Prior Art] Conventionally, a fixing device used in this type of apparatus uses a heating roller maintained at a predetermined temperature and a pressure roller that breaks an elastic layer and presses against the heating roller to fix unfixed parts. A roller fixing method is often used in which a transfer material on which a toner image has been formed is heated while being nipped and conveyed. However, in this type of device, in order to prevent the so-called offset phenomenon in which toner is transferred to the heating roller, it is necessary to maintain the heating roller at an optimal temperature, and the heat capacity of the heating roller or heating element must be increased. There wasn't. That is,
When the heat capacity of the heating roller is small, the temperature of the heating roller tends to fluctuate greatly toward the lower or higher temperature side due to paper passing or other external factors, depending on 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 fixing 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 required to raise the temperature of the heating roller to a predetermined temperature, which causes another problem of increasing the waiting time when using the device. .

As a way to solve this problem, U.S. Patent Section 3,57
As disclosed in No. 8.7!17, (p) a toner image is heated to its melting point with a heating element and melted, ■ after melting, the toner is cooled to a relatively high viscosity, and ■ the toner is heated to its melting point. A method is known in which fixing is achieved without causing offset by passing through a process in which the adhesive is peeled off from the heating web in a state where the tendency to adhere is weakened.

In addition, the above-mentioned known method uses a method of heating the toner image and the transfer material without applying pressure to the heating body, so there is no need to heat the transfer material and other methods can be used. It is said that the toner can be melted with much less energy compared to the conventional method.

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

Therefore, Japanese Patent Application No. 47-25896 proposes to add a known pressure welding technique to this to improve the heat transfer efficiency and heat and melt the toner in a short time and sufficiently.

[Problem to be solved by the invention] However, in this patent application No. 47-25896, in order to heat the toner sufficiently in a relatively short time, (1) The transfer material is held under pressure and heated, and (1) the heating is stopped and then the transfer material is forcibly cooled down. This has the disadvantage that the energy required for fixing increases. In other words, the toner image is heated from above and below by heating with a pair of heating elements, which may seem efficient at first glance, but on the other hand, in order to heat the toner image from the transfer paper side, the transfer material must first be sufficiently heated. It is necessary to do something, and for that purpose, a large amount of energy is required. Furthermore, in the cooling process, the transfer material heated to a raised temperature when the toner image is heated cannot be separated unless it is cooled, and a forced cooling means is required, resulting in a large waste of energy.

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

In the above two proposed examples, the heating body is composed of a heating roller, a web fed by the heating roller, and a heat generation source built into the heating roller.Heating is performed via the web, and it functions as a web conveyance roller. have. For this reason, the method of feeding power to the heat generating source and the form of abutting support for the temperature sensing element become complicated, and the accuracy of temperature control tends to deteriorate.

Furthermore, in the structure in which the temperature sensing element slides on the heating roller, there are safety problems such as excessive temperature rise due to wire breakage.

Furthermore, since both of the above two examples require a heating element with a relatively large heat capacity, there is an inconvenience that the amount of heat radiated into the machine increases and the temperature inside the machine increases significantly.

The present invention solves the problems of the conventional apparatus described above, and makes it possible to reduce the heat capacity of the heating element without causing fixing failure or offset. As a result, standby time, power consumption, and An object of the present invention is to provide an image forming apparatus with a small internal temperature rise.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an image forming means for forming an unfixed toner image by supporting a toner made of heat-melting resin or the like on a transfer material. The above-mentioned transfer is performed via a fixing film that moves at the same speed as the conveyance speed of the upper transfer material, using a pressure roller that is rotationally driven while being in pressure contact with a heating body and maintained at a temperature lower than the melting point of the toner. A heating fixing means that melts the unfixed toner image on the transfer material by bringing the material into close contact with the heating body, cools and solidifies the toner image, and then separates the fixing film from the transfer material. and consists of.

[Example] Hereinafter, an example of the unreleased January will be described based on the attached drawings.

First, the general structure of the image forming apparatus of this embodiment will be described with reference to FIG. 1. 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. Immediately below the document table is a short-focus, small-diameter imaging element array.
2 is arranged, and the original image G placed on the original storage table 1
is irradiated by the illumination lamp 7, and its reflected light image is slit-exposed onto the photosensitive tram 3 by the array 2. Note that this photosensitive drum 3 rotates in the direction of the arrow.

A charger 4 uniformly charges the photosensitive drum 3 coated with, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer 38. The drum 3, which is uniformly charged by the charger 4, is subjected to image exposure by the element array 2 to form an electrostatic image. This electrostatic latent image is visualized by a developing device 5 using toner made of a resin or the like that softens and melts when heated. On the other hand, the sheet P stored in the cassette S is transported by a pair of conveyance rollers 9 that are rotated while being pressed vertically in synchronization with the images of the feed roller 6 and the photosensitive tram 3''. It is fed onto the drum 3. Then, the toner image formed on the photosensitive tram 3 is transferred onto the sheet P by the transfer discharger 8. Thereafter, the sheet P separated from the tram 3 by a known separating means is guided to a fixing device 20 by a conveying guide 10, subjected to heat fixing processing, and then discharged onto a tray 11. Incidentally, after the toner image is transferred, the residual toner on the tram 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 g ra and a length of length) 21δll11 and is made of, for example, Ta2N, and has a linear or band-shaped heating element 28 disposed with a component perpendicular to the conveying direction in the heating section, and further has a sliding protective layer on its surface, such as Ta2O, or is formed. The lower surface of the heating body 21 is smooth, and the front and rear ends are rounded to form a heating section (heating surface), allowing sliding movement with the fixing film 23. The fixing film 23 is made of PET as a base material, heat-resistant treated, and has a thickness of, for example, about 9 tiles, and is wound around a film delivery shaft 24 so as to be delivered in the direction of arrow C. The fixing film 23 comes into contact with the surface of the heating body 21 and is wound onto a film winding shaft 27 via a separation roller 26 having a large curvature.

The heating element 28 of the heating element has a small heat capacity, and is energized in a pulsed manner, and the temperature is instantaneously raised to around 260°C each time. By detecting the leading and trailing ends of the transfer paper P by the transfer paper detection lever 25 and the transfer paper detection sensor 29, the heating element 28 is energized at a timely manner when necessary. At that time, the image forming device's paper feed sensor detects the position of the transfer paper.

The power supply to the heating element may be controlled.

On the other hand, the pressure roller 22 has an elastic layer made of silicone rubber or the like on a core material made of metal or the like, and is driven by a drive source (not shown) and is guided by a conveyance guide A transfer material P having a toner image T is closely viewed by a heating body via a fixing film 23 that moves at the same speed as the transfer material P. Here, the pressure roller 22
It is preferable that the conveying speed is approximately the same as the conveying speed during image formation, and the moving speed of the fixing film 23 is set at a value corresponding to this.

In this embodiment, the temperature of the heating element 28 rises instantaneously, so there is no need for preheating, and there is little heat transfer to the pressure roller during non-fixing. Furthermore, during fixing, the fixing film, toner image, and transfer material are interposed between the heating element 28 and the pressure roller 22, and the heating time is short, so that the temperature gradient can be made steep. The temperature of the pressure roller 22 is difficult to rise, and its temperature is maintained below the melting point of the toner even if continuous image formation is performed to the extent required for practical use.

In the apparatus of this embodiment having such a configuration, the toner image made of heat-meltable toner on the transfer paper P is first heated and melted by the heating body 21 via the fixing film 23.
In particular, the surface layer exceeds the melting point and completely softens and melts. At this time, the heating body, the fixing film, the toner image, and the transfer material are brought into close contact with each other by the pressure roller 22, and heat is efficiently transferred.

After that, the heating element 21 stops generating heat, and as the transfer material is transported and moved away from the heating element position, the toner image radiates heat, cools and solidifies again, and passes through the separating roller pair 26 with a large curvature. After that, the fixing film 23 is separated from the transfer paper P. At this time, in this embodiment, the temperature of the pressure roller 22 is maintained lower than the melting point of the toner, so it is possible to promote heat dissipation from the toner image. Therefore, the time required for cooling can be shortened, and the device can be downsized.

As mentioned above, once the toner T is completely softened and melted,
As the toner solidifies again, the cohesive force of the toner becomes very large, causing it to behave in clumps. In addition, since it is pressed by the pressure roller 22 when it is heated, softened and melted, at least a part of the toner image T penetrates the surface layer of the transfer material and is cooled and solidified as it is, so that it is offset to the fixing film 23. The image is fixed on the transfer material P without any process.

As is clear from this example, the heating body (heating section) of the present invention can be small enough to have a small heat capacity, and there is no need to raise the temperature of the heating section in advance. This also means that the temperature inside the machine can be prevented from rising.

Further, in this embodiment, it is possible to use a heat-resistant film based on a thin and inexpensive PET film as the fixing film 23, so as shown in FIG. 2, the fixing film 23 is wound up and replaced after use. It is possible to take the form of That is, a roll wound with a predetermined length of film is set on the film feed shaft 24, and the leading end of the film is fixed to the winding shaft 27 through between the heating body, the pressure roller, and the pair of separation rollers. If such a method is adopted,
The fixing film sensor arm 30 and a sensor (not shown) may be used to detect the remaining amount of the fixing film, and when the film is near the end, a warning display or sound may be displayed to prompt the user to replace the fixing film. . When replacing the fixing film 23, the rotating shaft 31 is moved so that the heating body, the pressure roller, and the separation roller pair are separated from each other.
It is desirable to be able to open and close the door as shown in Figure 3. In this embodiment, by winding and replacing the fixing film 23 as described above, it is possible to make the fixing film thinner, regardless of the durability of the fixing film, and the power consumption can be reduced.

In addition, in this embodiment, as mentioned above, no offset occurs to the fixing film, so if the fixing film has little thermal deformation or deterioration, it is possible to reuse the fixing film that was taken once, and it is automatically rewound. It may be used multiple times, or by exchanging the take-up side and the delivery side.

Further, in this embodiment, by providing the separation roller 26, sufficient cooling time is ensured for the toner image T even if the pressure is not good up to the separation roller, and furthermore, by increasing the curvature of the separation roller 26, the toner image T is fixed. This facilitates the separation of the film 23 and the transfer material P, and in combination with the above-mentioned effects, it is possible to prevent offset at the separation portion. However, in this embodiment, since the cooling of the toner image is promoted by the pressure roller 22, if the heat capacity of the heating unit 28 and the fixing film is sufficiently small and the fixing processing speed is low, the special pressure roller 26, etc. Since the toner image T is cooled within a short range after the transfer material P passes through the heating section without providing any other means, offset-free fixing processing is possible even if the separation roller 26 shown in this embodiment is omitted. becomes. That is, it is sufficient if the fixing film and the transfer material can be separated after the toner image is once heated to soften and melt and then solidified again by heat radiation.

Next, the results obtained using the apparatus of this embodiment will be shown with specific numerical values. A toner image T is formed using PPCPC-30 (trade name) Kawa's wax-based toner manufactured by Canon Inc., and the heat generation amount is approximately 2000W-3 per sheet of A4 size paper at a fixing processing speed of 15III/S. like,
When a fixing test was conducted by applying pulsed heating for 2 ms every 10 m5, an image with no practical problems was obtained. This energization raises the temperature of the heat generating layer to around 260° C., and since the heat capacity is small, the temperature decreases when the energization is stopped for 8 ms. This eliminates the need for waiting time for heating the heating element. In addition, in this embodiment, since the thermal energy necessary for fixing is applied each time by heating in a pulsed manner, the heating section is periodically heated to a heating element that has a small heat capacity and is very quick to stand up or burn out. It is relatively easy to make them exhibit the same temperature. Furthermore, when the fixing process is performed continuously, it is easy to prevent the heating section from shifting to an abnormally high temperature side by sequentially decreasing the pulse width for heat generation. In the above case, toner layer T
The temperature of

Although the temperature exceeds even momentarily the temperature that is conventionally said to cause high-temperature offset, as mentioned above, the fixing film 23 and the transfer material P separate after being sufficiently cooled and fixed again, so no offset occurs. . The wax, which is a product of the toner used in this example when heated, is about 8
It has a melting point of 0°C and also has a low viscosity when melted, so when heated by a heating element at around 260°C, in conventional heat fixing devices, the molten toner penetrates into the transfer material too much and the image is damaged. However, in this embodiment, the heat capacity of the heating element 28 is small and the heating time is short, so that the temperature is low. Since the slope is large, only the surface layer of the transfer paper is heated for a short period of time, so there is no problem described above caused by excessive penetration of the 1-ner.

FIG. 4 is a sectional view of a heat fixing device applied to an image forming apparatus according to another embodiment of the present invention. Note that the same parts as in the previous embodiment are denoted by the same reference numerals, and the explanation thereof will be omitted.

In this embodiment, a heat-resistant endless film is used in place of the fixed end film 23, and this endless fixing film 40 is heated many times and is repeatedly brought into contact with the toner layer T. Therefore, PF with excellent mold releasability and high heat resistance
An endless sheet having a thickness of 1 OJLJ was formed using resin A as a base material. The endless fixing film 40 is driven by a drive shaft 41 at a circumferential speed that is the same as the conveying speed of the transfer material, and rotates while being tensioned by an idler 42 that is biased to give tension to the endless fixing film 40. Driven.

The heating body 21 is provided with a temperature detection element 43 for detecting the temperature of its base material, and is further provided with a temperature fuse or thermostat as a safety device 44 to prevent excessive temperature rise.

Furthermore, the timing of energizing the heating body 21 in this embodiment is controlled based on a signal generated in the image forming means. The fixing processing speed in this example (same during image formation) is 50 mm/s, which is faster than in the previous example, so the width of the heating element 28 (heating width) is 300 J.
5 by increasing Lm and changing the time of energization to the heating element.
Approximately 2400'#-3 of heat was generated per sheet of A4 size paper at a rate of 1.25 m5 per ms. Here, the maximum temperature of the heating element is approximately over 300°C, the power density of the heating element 28 is higher than that of the previous embodiment, and the above-mentioned amount of heat can be given in a short time. Therefore, the temperature rise (heat storage) of the heating element 21 itself is greater than that in the previous embodiment, so in this embodiment, the temperature increase (heat storage) of the heating element 21 itself is increased in accordance with the detected value of the temperature detection element 43 provided on the support material of the heating element 21. The width of the energizing pulse is adjusted accordingly. That is, heating body 2
When the temperature of the base material No. 1 is high, the width of the energizing pulse is made small to prevent abnormal temperature rise of the heating element itself. Furthermore, when the temperature of the safety device 44 mentioned above falls below a predetermined temperature, the power supply to the heating element 28 is cut off.

Here, the temperature drop of the transfer material and toner image T is also disadvantageous compared to the previous embodiment. In other words, by increasing the fixing processing speed, the temperature of the heating element is increased, the amount of heat generated per sheet is also increased, and the time required for separation after heating is also shortened. In addition, a cooling means is required to cool and solidify the film before it is separated. For example, it is a heat dissipation plate 45 made of aluminum that 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 a or the like may be used as the cooling means. Since the pressure roller of the present invention also has a cooling effect as described above, when the speed is increased as in this embodiment, the pressure roller 22 needs to be cooled. In this embodiment, a pressure roller cooling fan 19 is provided to blow air to the pressure roller to maintain the temperature lower than the melting point of the toner. In addition, a separation claw 46 is arranged in the separation section to prevent the transfer material from being rolled up, and a cleaning pad 47 made of felt is applied to remove foreign matter such as paper dust attached to the endless fixing film 40. I'm letting you touch me. Furthermore, the felt pad may be impregnated with some release agent, for example, silicone oil, to improve the release properties of the endless fixing film 40. Furthermore, since an insulating PFA resin is used in this embodiment, static electricity that disturbs the toner image is likely to be generated in the fixing film. To deal with this, static electricity is removed using a grounded static electricity removal brush 48. Here, the endless fixing film may be charged without being grounded by applying a bias voltage to the brush to the extent that the toner image is not disturbed. Furthermore, one measure is to add conductive powder fibers, such as carbon black, to the PFA resin to prevent the above-mentioned image blur due to static electricity. Furthermore, the charge removal and conductivity of the pressure roller can be carried out by similar means.

Further, an antistatic agent or the like may be applied or added.

Further, static electricity may be removed from both the front and back sides of the fixing film.

Here, the pressure contact portion between the pressure roller 22 and the heating element 28 is closer to the entrance side in the conveying direction within the pressure contact width between the heating member 21 and the pressure roller 22, and the endless fixing film 4 immediately after heating
0 and the transfer material P are prevented from separating.

In this example, the maximum power consumption is approximately 1,600 yen due to high speed.
Since the power consumption is large (W), the maximum power consumption may be reduced to 400W by dividing the heating element into four parts in the longitudinal direction and sequentially energizing them.

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

In addition, as the above embodiments of the present invention, two copying apparatuses using an electrophotographic method have been described, but the present invention is not limited thereto; The present invention can be applied to image forming apparatuses such as those used in conventional image forming apparatuses, and heat-fixing processing can be performed without particularly requiring waiting time, so that it is also suitably used as an output device for facsimile.

[Effects of the Invention] As described above, the present invention uses a pressure roller maintained at a temperature lower than the melting point of the toner to bring a transfer material having a toner image into close contact with a heating body via a fixing film. By conveying the toner image, efficient heat transfer becomes possible and the cooling of the toner image is promoted. Therefore, it is possible to reduce the heat capacity of the heating element without causing fixing failure or offset. As a result, it is possible to obtain an image forming apparatus that requires less standby time during use, less power consumption, and less internal temperature rise.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the general configuration of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of the fixing device shown in FIG. 1, and FIG. 3 is a fixing film replacement of the device shown in FIG. 2. 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 rollers 23, 40.
...Fixing film P...Transfer material T...Toner image

Claims (1)

[Scope of Claims] An image forming means for forming an unfixed toner image by carrying toner made of a heat-melting resin or the like on a transfer material; By using a pressure roller maintained at a temperature lower than the melting point and bringing the transfer material into close contact with the heating body through a fixing film that moves at the same speed as the conveyance speed of the upper transfer material, the undefined state on the transfer material is An image forming apparatus comprising: a heat fixing means for separating a fixing film and a transfer material after the toner image is cooled and solidified after being melted by the heating body.