JPH08211766A - Image heating device - Google Patents

Abstract

PURPOSE: To enable to heat an image at the moment when power is supplied and to enable to deal with the change of various conditions by heating the image on a recording material without intermediary of air layer by a heating element provided with a pulse energizing means and a pulse width switching means. CONSTITUTION: The heating element 21 is provided with a wire-like or belt-like heating surface 28 composed of, for instance, Ta2 N on the under side of a heat resistant and electrically insulating base material such as alumina and a sliding protective layer composed of, for instance, Ta2 O5 is formed on the surface. And the heating surface 28 of the heating element 21 is energized in pulselike state by the energizing means timely after the top or end of a copying paper (the recording material) P is detected by a copying paper detecting lever 25 and a copying paper detecting sensor 29. In this way, thermal energy necessary for fixing is imparted each time and the heating surface 28 having small heat capacity and fast rising time is capable of being energized periodically. Further at the time of continuously fixing, the heating surface is capable of dealing with shift to high temp. side by switching the pulse width such as decreasing stepwise the pulse width in generating heat with the switching means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating apparatus in which an image formed on a recording material is heated by a heating element without passing through an air layer to shorten the warm-up time.

[0002]

2. Description of the Related Art As a device for shortening the warm-up time, a heating device described in Japanese Patent Laid-Open No. 59-68766 has been proposed. In this heating device, a recording sheet carrying a toner image is passed through a nip between a heating head and a pressure roller, and the toner image is heated by the heat of the heating head (via a heat resistant sheet).

[0003]

However, even with such an image heating apparatus having a low heat capacity, it cannot be said that the warm-up time can be shortened sufficiently. Further, since the heat capacity is small, it is possible to change the conditions such as switching of sheet passing intervals. The temperature fluctuations at the nip tend to be large.

In view of the above problems, it is an object of the present invention to provide an image heating apparatus which is ready for image heating immediately after the start of energization and can cope with various changes in conditions.

[0005]

SUMMARY OF THE INVENTION The present invention for achieving the above object is an image heating apparatus for heating an image carried on a recording material by a heating element without passing through an air layer. And a switching means for switching the pulse width.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION First, a schematic structure of an image forming apparatus using the example of the present embodiment will be described with reference to FIG. 1. Reference numeral 1 is an original placing table made of a transparent member such as glass, and an arrow mark The document is scanned by reciprocating in the a direction. A short-focus small-diameter image-forming element array 2 is arranged immediately below the document table, and the document image G placed on the document table 1 is illuminated by an illumination lamp 7.
And the reflected light image is slit-exposed on the photosensitive drum 3 by the array 2. The photosensitive drum 3 rotates in the direction of arrow b. Reference numeral 4 is a charger, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer 3
The photosensitive drum 3 coated with a or the like is uniformly charged. The drum 3 uniformly charged by the charger 4 is
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 sheets P stored in the cassette S are
It is fed onto the drum 3 by a pair of conveying rollers 9 which are rotated in pressure contact with each other in the vertical direction at a timing synchronized with the feeding roller 6 and the image on the photosensitive drum 3. Then, the toner image formed on the photosensitive drum 3 is transferred onto the sheet P by the transfer discharger 8. afterwards,
The sheet P separated from the drum 3 by a known separating unit is guided to the fixing device 20 by the conveyance guide 10 and is 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 same. ) It has a linear or strip heating surface 28 of 216 mm and is made of, for example, Ta ₂ N, and Ta ₂ O ₅ is formed on the surface as a slide protection layer. The lower surface of the heating element 21 is smooth and the front and rear ends thereof are rounded so that they can slide on the heat resistant sheet 23. The heat-resistant sheet 23 is made of polyester as a base material and is heat-treated to have a thickness of, for example, about 9 μm. The heat-resistant sheet 23 is wound around a sheet feeding shaft 24 so as to be fed in the direction of arrow C. The heat-resistant sheet 23 comes into contact with the surface of the heating element 21 and is wound around the sheet winding shaft 27 via the separation roller 26 having a large curvature.

The heat generating surface 28 of the heat generating element has a small heat capacity, and is energized in a pulse shape by energizing means (not shown) to instantly raise the temperature to about 260 ° C. each time. By detecting the leading end and the trailing end of the transfer paper (recording material) P by the transfer paper detection lever 25 and the transfer paper detection sensor 29, the heat generating surface 28 is energized at a necessary timing. At that time, the power supply to the heating element may be controlled by using the position detection of the transfer paper by a paper feed sensor or the like 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, is driven by a drive source (not shown), and is guided by the conveyance guide 10. The transfer material P having the unfixed toner image T is brought into close contact with the heating element via the heat resistant sheet 23 that 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 heat resistant sheet 23 is set to a value corresponding to it.

In the apparatus of the present embodiment having such a configuration, the toner image formed of the heat-meltable toner on the transfer paper P is first heated by the heating element 21 via the heat resistant sheet 23, and at least the surface layer thereof. The part is completely softened and melted. After that, while the toner image is separated from the heating element 21 and reaches the separation roller 26, the toner image naturally radiates heat and is cooled and solidified again.
After passing through the pair of separation rollers 26 having a large curvature, the heat-resistant sheet 23 separates from the transfer paper P. As described above, the toner T
Since the toner is completely softened and melted and then solidified again, the cohesive force of the toner is very large and the toner behaves as a group. Further, when the toner image T is heated and softened and melted, it is pressed by the pressure roller 22.
Of the transfer material P penetrates into the surface layer of the transfer material and is cooled and solidified as it is.
Fixed on top.

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

Further, in this embodiment, the heat-resistant sheet 23 may be heat-treated on the basis of a thin and inexpensive polyester sheet, so that the heat-resistant sheet 23 is used in a winding method as shown in FIG. It can be replaced later. That is, a roll wound with a sheet of a predetermined length is set on the sheet feeding shaft 24, and the leading end of the sheet is fixed to the winding shaft 27 through a space between the heating element, the pressure roller and the separation roller pair. When such a method is adopted, the heat-resistant sheet sensor arm 30 and a sensor (not shown) detect the remaining amount of the heat-resistant sheet, and when the sheet is near the end, a warning display or a warning sound is given to the user to notify It is good to encourage exchange. When the heat resistant sheet 23 is replaced, it is desired that the heat generating element, 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 heat-resistant sheet 23 can be thinned by the winding exchange method as described above regardless of the durability of the heat-resistant sheet, and the power consumption can be reduced. Further, in the present embodiment, since the offset to the heat resistant sheet does not occur as described above, if the heat deformation or deterioration of the heat resistant sheet is small,
It is possible to reuse the wound heat resistant sheet,
Rewind automatically. Alternatively, it may be used a plurality of times by exchanging the winding side and the sending side.

Further, in this embodiment, by providing the separation roller 26, it is possible to sufficiently secure the cooling time of the toner image T in the pressurized state up to the separation roller, and to increase the curvature of the separation roller 26. By heat-resistant sheet 23
The separation of the transfer material P and the transfer material P can be facilitated, and the offset in the separation portion can be prevented in synergy with the above-mentioned effect. However, when the heat capacities of the heat generating layer 28 and the heat-resistant sheet are sufficiently small and the fixing processing speed is low, the transfer material P can be obtained without providing special means such as the separation roller 26.
Since the toner image T is cooled in a short range after passing through the heat generating layer, even if the separation roller 26 shown in this embodiment is omitted,
Fixing processing without offset is possible. That is, it is sufficient that the heat-resistant sheet and the transfer material can be separated after the toner image is once heated and softened and melted, and then radiated and solidified again.

Next, the results of implementation by the apparatus of this embodiment will be shown with specific numerical values. Canon PPC
Using a wax type toner for PC-30 (trade name),
A toner image T was formed, and a fixing test was carried out by heating in pulses at a rate of 2 ms every 10 ms so that the heat generation amount was about 2000 W · S per A4 size paper at a fixing processing speed of about 15 mm / s. However, an image having no problem in practical use was obtained. Due to this energization, the heat generating layer is about 260 ° C.
The temperature is raised to the front and back, and since the heat capacity is small, the temperature is lowered by stopping the energization for 8 ms. Therefore, the waiting time for heating the heating element is not necessary. Further, in this embodiment, since the heat energy necessary for fixing is given by pulse heating in each case, the heat generating layer having a small heat capacity and a very fast rise is periodically and substantially the same in temperature. This can be done relatively easily. Further, when the fixing process is continuously performed, the pulse width of heat generation is gradually reduced by a switching means (not shown), and the pulse width is switched to prevent the heat generating layer from shifting to an abnormally high temperature side. Can handle. Further, even if the temperature of the toner layer T momentarily exceeds the temperature which is conventionally said to cause a high temperature offset, as described above, the heat resistant sheet 23 and the transfer material P are cooled and fixed again sufficiently and then the heat resistant sheet 23 and the transfer material P are fixed. If separated, the offset can be reliably prevented. When heated, the wax, which is the main component of the toner used in this exemplary embodiment, has a melting point of about 80 ° C., and when it is heated by a heating element at about 260 ° C. because it has a low viscosity when melted, In the heating roller type 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 the embodiment, since the heat capacity of the heat generating layer 28 is small and the heating time is short, 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 heat fixing device 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 belt is used instead of the heat resistant sheet 23, and the heat resistant belt 40 is heated many times and is repeatedly contacted with the toner layer T. Therefore, P, which has excellent releasability and high heat resistance,
A belt having a thickness of 30 μm is formed of FA resin. The heat-resistant belt 40 is driven by a belt drive shaft 41 so as to have the same peripheral speed as the transfer material conveying speed, and is urged to apply tension to the heat-resistant belt 40.
It is driven to rotate while being strained by.

The heating element 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 to prevent excessive temperature rise. Has been done. In addition, the timing of energizing the heating element 21 in the present embodiment is
It is controlled based on a signal generated in the image forming means. The fixing processing speed of this example (same during image formation) is set to 5
Since the speed is set to 0 mm / s as compared with the previous embodiment, the width (heating width) of the heat generating layer 28 is increased to 300 μm, and the time for energizing the heat generating layer is changed to 1.
Approximately 2400 per A4 size paper at a rate of 25 ms
Heat generation of WS was performed. Here, the maximum temperature of the heat generating layer exceeds about 300 ° C., the power density of the heat generating layer 28 is higher than that in the previous embodiment, and further, the above-mentioned amount of heat is given in a short time. From the above, since the temperature rise (heat storage) of the heating element 21 itself is larger than that in the case of the previous embodiment, in the present embodiment, the detected value of the temperature detection element 43 provided on the support material of the heating element 21 is The width of the energizing pulse is adjusted accordingly. 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 reaches a predetermined temperature or higher, the heat generation layer 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 heat generating layer 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 belts are separated. For example, it is a heat radiating plate 45 made of aluminum that is in contact with the heat resistant belt 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. Further, a separating claw 46 is arranged in the separating portion, and a cleaning pad 47 made of felt is brought into contact with the transfer material to prevent the transfer material from winding and remove foreign matter such as paper dust or the like adhering to the heat-resistant belt 40. There is. Further, the felt pad may be impregnated with a slight release agent such as silicone oil to improve the release property of the heat resistant belt 40. Further, in this embodiment, the insulating P
Since the FA resin is used, static electricity that disturbs the toner image is likely to be generated on the heat-resistant sheet. Therefore, in order to cope with this, the static elimination brush 48 grounded is used to eliminate static electricity. Here, the heat-resistant belt may be charged within a range in which the bias voltage is applied to the brush without grounding and the toner image is not disturbed. Further, 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. In addition, 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.

Here, the pressure contact portion between the pressure roller 22 and the heat generating layer 28 is closer to the inlet side in the transport direction within the pressure contact width between the heat generating element 21 and the pressure roller 22, and the heat resistant belt 40 immediately after heating. The transfer material P is prevented from being separated from the transfer material P.

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

In the present embodiment described 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 belt, It has become possible to improve economic efficiency.

Further, as the above-described embodiments of the present invention, two cases have been described in which it is used in a copying machine using an electrophotographic system, but the present invention is not limited to this, and heating of a laser beam printer or the like is not limited to this. Therefore, it is applicable to an image forming apparatus using a toner that softens and melts, and it is possible to perform heat fixing processing without requiring a waiting time.
It is also suitably used as a facsimile output device.

[0023]

The image heating device for heating the image carried on the recording material without passing through the air layer by the heating element is provided with the pulse energizing means and the pulse width switching means, so that the image can be heated instantly after the energization is started. It can be put into a state and can cope with various changes in conditions.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus using an image heating apparatus of the present invention.

FIG. 2 is an enlarged cross-sectional view of the fixing device in FIG.

FIG. 3 is a cross-sectional view of the apparatus of FIG. 2 when a heat resistant sheet is replaced.

FIG. 4 is a cross-sectional view of another embodiment of the present invention.

[Explanation of symbols]

 3 Image Forming Means (Photosensitive Drum) 20 Heat Fixing Means 21 Heating Element 23,40 Heat Resistant Sheet D Transfer Material T Toner Image

Claims (1)

[Claims] 1. An image heating apparatus for heating an image carried on a recording material by a heating element without interposing an air layer, comprising an energizing means for energizing the heating element with a pulse and a switching means for switching a pulse width. Image heating device characterized by.