JPH01263685A - Image forming device - Google Patents

Abstract

PURPOSE:To heat and melt a toner image efficiently and to save energy by arranging a linear heat generating body at right angles to the conveying direction of a transfer material and repeating specified electric heat generation pulsatively and repeatedly. CONSTITUTION:The toner image consisting of heat meltable toner on the transfer paper P is heated and melted first by the heating body 21 across a fixation film 23. At this time, the pressure roller 22 brings the heating body, fixation film, toner image, and transfer material into excellent contact. Then the transfer material is conveyed, the toner image radiates heat and is cooled and solidified, and the fixation film 23 leaves the transfer paper P after passing a separation roller 26. The linear heat generating body 18 is arranged in the heating body 21 at right angles to the conveying direction of the transfer material. The fed pulse width of the heating body 28 is set smaller than the value obtained by dividing the width of a heating part in the conveying direction by the conveying speed of the transfer material, and the pulsative electric heat generation is repeated. Thus, the toner image is heated and melted efficiently to save the energy.

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 uses heat-fixing means to form an image.

[Prior Art] Conventionally, a fixing device used in this type of apparatus uses 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. 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 transfers to the heating roller, it is necessary to maintain the heating roller at an optimal temperature, which increases the thermal capacity of the heating roller or heating element. I had to. That is,
If the heat capacity of the heating roller is small, the temperature of the heating roller tends to fluctuate greatly to the low or high temperature side due to the relationship between the heat supplied by the heating element and other external factors. If this happens, the toner will soften and melt insufficiently, resulting in poor fixing or low-temperature offset. If the temperature changes to the high temperature side, the toner will completely melt and the cohesive force of the toner will decrease, resulting in high-temperature offset. arise.

In order to avoid this problem, if the heat capacity of the heating roller is increased, the time required to raise the temperature of the heating roller to a predetermined temperature becomes longer, which causes another problem of increasing the waiting 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 heated to its melting point with a heating element to melt it;

After melting, the toner is cooled to a relatively high viscosity, and ■ the toner is peeled off from the heating web while its tendency to stick is weakened. A method of fixing without causing offset is now known. It is being

In addition, the above known method heats the toner image and transfer material without applying pressure to the heating body, so there is no need to heat the transfer 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 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 adding a known pressure welding technique to this to improve the heat transfer efficiency and heat and melt the toner in a short time and upwardly.

[Problem to be solved by the invention] However, in this Japanese Patent Application No. 47-25896, in order to heat the toner sufficiently in a relatively short time, Since the transfer material is heated by being held under pressure, then the heating is stopped and then forcibly cooled down, the energy required for fixing increases. In other words, a pair of heating elements By heating the toner image, the toner image is heated from the top F, which may seem efficient at first glance, but on the other hand, in order to heat the toner image from the transfer paper side, it is necessary to heat the transfer material sufficiently first. This requires a large amount of energy.Furthermore, in the cooling process, the transfer material heated to a raised temperature when heating the toner image cannot be separated unless it is cooled.
A forced cooling method is required, resulting in a large waste of energy.

As mentioned above, methods have been proposed in which the heated toner is cooled and then separated to fix the toner without causing high-temperature offset, but these methods have not been put to practical use due to the disadvantages described in E.

In the above two proposed examples, the heating body is composed of a heating roller, the 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. are doing. 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 a configuration in which the temperature sensing element slides on the heating roller, there are safety problems such as excessive temperature rise due to wire breakage.

Moreover, since both of the above two examples require a heating element with a relatively large heat capacity, there is also the disadvantage that heat radiation 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 includes an image forming means for forming an unfixed toner image by making a toner made of a heat-melting resin or the like coexist on a transfer material; , comprising a pressure roller that is rotationally driven while facing the heating body and brings the transfer material into close contact with the heating body via a fixing film that moves at the same speed as the conveyance speed of the transfer material;
After the unfixed toner image on the transfer material is melted by the heating element.

a heating fixing means for separating the fixing film and the transfer material after cooling and solidifying the toner image, the heating body having a linear heating element disposed with a component perpendicular to the conveyance direction of the transfer material, and It is configured by repeating energization and generating heat in a pulsed manner, and setting the pulsed energization time to be smaller than the value obtained by dividing the width of the heating section in the conveyance direction by the conveyance speed of the transfer material. .

[Example] υ Below, the present invention will be described in detail based on the accompanying drawings.

First, the mechanical structure of the image forming apparatus of this embodiment will be explained based on FIG. 1. L is 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 located directly below the document table.
A document image G placed on a document table L is irradiated by an illumination lamp 7, and the reflected light image is slit-exposed onto the photosensitive drums 3-H by the array 2. Note that this photosensitive tram 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 conductor photosensitive layer 3a. 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 transferred to the drum by a pair of conveyance rollers 9 which are rotated while being pressed vertically in synchronization with the image on the feed roller 6 and the photosensitive drum 3. 3 is sent above. Then, the toner image formed on the photosensitive drum 3F- is transferred onto the sheet PJ2 by the transfer discharger 8. Thereafter, the tram 3 is separated by known separation means.
The sheet P separated from the sheet P is guided to the fixing device 20 by the conveyance guide 1O, heated and fixed, and then transferred to the tray 11.
is discharged. Note that after the toner image is transferred, residual toner on the drum 3 is removed by a 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 and a length (the length in the direction perpendicular to the plane of the paper) on the bottom surface of a base material made of a heat-resistant and electrically insulating base material such as alumina or a composite material containing the same. 216+u+ 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,... It 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, is formed to have a thickness of about 9 mm, for example, and is heated by heating means, and is wound around the film delivery shaft 24 so as to be able to be sent out 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 25 having a large curvature.

The heating element 28 of the heating element has a small heat capacity, and is energized in pulses to instantaneously raise the temperature to around 260°C each time. By detecting the leading edge and trailing edge 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 the appropriate timing when necessary. At this time, energization to the heating element may be controlled by detecting the position of the transfer paper using a paper feed sensor of the image forming apparatus or the like.

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. A transfer material P having a toner image T is brought into close contact with 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 similar to that.

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-fusible toner on the transfer paper P is first processed through a fixing step.
It is heated and melted by the heating body 21 through the ilm 23, and in particular, its 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.

Thereafter, the heating element 28 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.

Here, a note will be made regarding the expression of the state of the toner described in the present invention.

The temperature conveniently expressed as the melting point of the toner means the minimum temperature necessary for the toner to be fixed, and there are cases where the viscosity is low enough to be called melting at the minimum fixing temperature,
There may be a decrease in viscosity to the extent of softening. Therefore, even if it is conveniently expressed as melting during fixing, the viscosity may actually decrease to the extent of softening.

Similarly, even when it is conveniently expressed that the toner is cooled and solidified, depending on the toner, it may be more appropriate to say that the toner has become highly viscous rather than solidified.

As described above, in the heating step in the present invention, a linear heating element is provided on the heating element, and electricity is applied in a pulsed manner to the heating element with a low heat capacity that is integrally formed with the heating element.

This is done using a heating element configured to repeatedly generate heat. As shown in Fig. 4, the conveyance speed Vp (+us/
The toner image T on the transfer material P transported in step s) is transferred to the fixing film 2, which is transported without deviation according to the transport speed of the transfer material.
Together with this, it is sequentially fed into the heating section (heating element 28) of the heating element 21.

FIG. 5 shows that in the configuration of this embodiment, a polyimide film with a thickness of 6 pm is used as the fixing film, and a toner with a thickness of 20 mm and a minimum fixing temperature of 125° C.
It shows the temperature change over time when fixing on a thick transfer paper, and shows the surface layer part of the heating section, the middle layer part of the toner, and the middle layer part of the transfer material, respectively. Figure 5 above shows an example where the pulse width of the current applied to the heating element is 2 ms, and even though the middle layer of toner has been sufficiently heated to exceed the minimum fixing temperature and is ready for fixing. On the other hand, it can be seen that the temperature of the middle layer of the transfer material hardly increases. This shows that the shorter the energization pulse width, the more energy can be saved.

In the present invention, the energization pulse width τ of the heating element is determined so as to maintain the relationship τ<Vp/Vp. this is,
Time for the transfer material to pass through the effective width of the heating section <1/Vp)
It is shown that it is essential for the present invention that the energizing pulse width τ is smaller than . That is, in the present invention, the heating element is integrally formed in a linear shape, and the toner image within the effective width of the linear heating part, which becomes high temperature distant from the temperature rise of the heating element, can be efficiently and quickly heated. While ensuring sufficient heat to heat and melt the toner image, pulsed current heating suppresses the temperature rise of the transfer material, prevents unnecessary heating of the toner image, and reduces the energy due to heating. The width is set based on the above relationship. If the energization pulse width is larger than u 2 /Vp and the toner image is sufficiently heated, the portion of the toner image that is heated overlappingly becomes large and requires excessive energy. Furthermore, in this case, the temperature of the transfer material also increases, resulting in an increase in unnecessary energy. On the other hand, as in the present invention, the energizing pulse width τ
By making l/Vp smaller than l/Vp, it is possible to avoid unnecessary and redundant heating of the toner image, and furthermore, the smaller the energization pulse width τ is, the smaller the heating temperature of the transfer material becomes, which can save energy. becomes.

The minimum value here is determined depending on the heat resistance temperature and thermal shock resistance of the heating element, the fixing component such as the fixing film, and the thermal shock resistance.

As is clear from this example, the heating element (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, so the power consumption during non-image formation is This also means that the temperature inside the machine can be prevented from rising.

In addition, in this embodiment, the fixing film 23 is made of a thin and inexpensive PET film that has been subjected to heat treatment, so the fixing film 23 is wound up as shown in FIG. In other words, a roll with a predetermined length of film wound thereon is set on the film feed shaft 24, and the film is passed between the heating element, the pressure roller, and the pair of separation rollers and then placed on the winding shaft 27. If such a method is adopted, the remaining amount of the fixing film is detected by the fixing film sensor arm 30 and a sensor (not shown), and a warning message is displayed or displayed to the user when the film is near the end. It would be better to use a warning sound to prompt the replacement of the fixing film.Then, when replacing the fixing film 23, the heating body, pressure roller,
The rotating shaft 3 is rotated so as to separate the pair of separation rollers from each other.
It is desirable that the fixing film 23 be opened and closed as shown in FIG. This makes it possible to reduce power consumption.

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 use the wound fixing film again, and the fixing film can be automatically wound. It may be used multiple times by returning it or replacing 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 in the pressurized state up to the separation roller, and by increasing the curvature of the separation roller 26, the toner image T is fixed. Filno 423 and transfer material P
In addition to facilitating the separation from the wafer, it is possible to combine the above-mentioned effects and prevent offset at the separation portion. However, in this embodiment, since cooling of the toner image is accelerated by the pressure roller 22, if the heating element 28 and the fixing film heating stage ψ are sufficiently small and the speed of the fixing means is small, the separation roller Even without special measures such as 26,
Since the toner image T is cooled in a short range after the transfer material P passes through the heating section, even if the zero roller 26 shown in this embodiment is omitted, the fixing means without off-pits can be used. In other words, it is sufficient that the fixing film and the transfer material can be separated from each other after the toner image is softened and melted by -Q heating 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 wax-based toner manufactured by Canon Co., Ltd., PPCP (Nie 30 (trade name)), with a heating value of approximately 2000 W-3 per sheet of A4 size paper at a fixing means speed of 15 mm/s. so that τ<
A fixing test was conducted by pulse heating at a rate of 2ss every 10m5 so as to satisfy the relationship of l/Vp.
Practical use 1 An image with no 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 ss. This makes the waiting time for heating the heating element a concern. In addition, in this embodiment, the thermal energy necessary for fixing is stored each time by heating in a pulsed manner, so that the heating layer, which has a small heat capacity and rises very quickly, is periodically heated to approximately the same temperature. It is relatively easy to do as shown. Furthermore, when the fixing means is used continuously, it is easy to prevent the heating section from shifting to an abnormally high temperature side by gradually decreasing the pulse width for generating heat. In the above case, the temperature of the toner layer T exceeds, even momentarily, the temperature that is conventionally said to cause high temperature offset;
As described above, the fixing film 23 and the transfer material P are separated after being sufficiently cooled and fixed again, so that no offset occurs. The wax, which is the main component of the toner used in this example, has a melting point of about 80°C when heated, and also has a low viscosity when melted, so when heated with a heating element of about 260°C, In conventional heat fixing devices, the molten toner penetrates into the transfer material too much, causing problems such as blurring or show-through of the image, which hinders lowering the melting point of the toner, but this example 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, and 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 toner penetration.

Next, regarding the apparatus of this embodiment, a test similar to that shown in FIG. 5 was conducted with different conditions from those shown in FIG. 5, and this is shown in FIG.

Heating conditions: Energy density: 2ms heating at 12W/am2, toner fixing temperature = 80°C, film: polyimide (thickness: 25mm), toner thickness: 201L, transfer paper thickness: 1001Lm, room temperature: In this test, the temperature of the heating section was raised to approximately 380°C, which is much higher than the toner's fixing temperature of 80°C, so the toner was sufficiently heated to exceed the fixing temperature by heating for an extremely short time of 2ms, resulting in a good result. Provides good fixing properties. On the other hand, the temperature rise of the transfer paper is extremely small, and compared to conventional heat roller fixing, there is less energy wasted.

Furthermore, in this test, even when excessive energy is applied due to variations in heating time and heating energy density, no high temperature offset occurs, and it is clear that the tolerance range for heating control is wide.

[Effects of the Invention] As shown in L below, the present invention provides a heating element with a linear heating section formed integrally with the heating element, and is configured to repeat energization and heat generation in a pulsed manner. We decided to maintain the following relationship: τ/Vp when the transfer material conveying speed Vp and the heating section are effective at an energization time of , so by heating the toner image in a short time, By creating a sharp temperature gradient in the thickness direction of the image and transfer material, it is possible to suppress the heating of the transfer material as much as possible and efficiently heat and melt the toner image.In particular, it saves energy by limiting the time when electricity is applied and heat is generated. This has the effect of making it possible to achieve this goal.

In addition, it is possible to reduce the heat capacity of the heating element without causing fixing failure or offset, and as a result,
It is also possible to obtain an image forming apparatus that requires less standby time before 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. 4 is an enlarged sectional view showing the heating element and its vicinity in the device shown in FIG. 2, and FIG. 5 is a diagram showing temperature changes in each part during the heating process under certain conditions in the device shown in FIG. 2. , and FIG. 6 are diagrams showing temperature changes in various parts during a test using the apparatus shown in FIG. 2 under conditions different from those shown in FIG. 5. 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

Claims (1)

[Scope of Claims] An image forming means for forming an unfixed toner image by carrying toner made of heat-melting resin or the like on a transfer material; A pressure roller is provided that brings the transfer material into close contact with the heating body via a fixing film that moves at the same speed as the conveyance speed of the transfer material, and after the unfixed toner image on the transfer material is melted by the heating body, The toner image has a heat fixing unit that separates the fixing film and the transfer material after the toner image is cooled and solidified, and the heating body includes:
It has a linear heating element arranged with a component perpendicular to the conveyance direction of the transfer material, and it repeats energization and heat generation in a pulsed manner. An image forming device that is set to be less than the value divided by the speed.