JPH0690577B2 - Image forming device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, a facsimile, a microfilm reader printer, an image display (display) device, and a recording machine.

More specifically, a recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, transfer material sheet, etc.) is formed by using a toner made of a heat-meltable resin by an appropriate image forming process means such as electrophotography, electrostatic recording, magnetic recording, etc. An unfixed toner image corresponding to desired image information is formed and carried on a surface of a printing paper or the like by a direct method or an indirect (transfer) method, and the unfixed toner image is carried on a recording material surface carrying the image. The present invention relates to an image forming apparatus of a type in which heat fixing processing is performed as a permanently fixed image.

(Prior Art) Conventionally, a fixing device used in this type of device is unfixed by 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 recording material on which an attached toner image is formed is heated while being nipped and conveyed.

A belt fixing system as disclosed in US Pat. No. 3,578,797 is also known. This is because the toner image is brought into contact with the heating element web and is heated to its melting point to be melted, and after the melting, the toner is cooled to have a relatively high viscosity, and the toner adhesion tendency is weakened from the heating element web. It is a method of fixing without causing offset by going through the process of peeling.

(Problems to be Solved by the Invention) However, the above-described conventional thermal roll fixing method and belt fixing method have the following problems.

Heat roll fixing method It takes a considerable amount of time for the temperature to rise to a predetermined temperature, and during that time the image forming operation is prohibited. That is, there is a so-called wait time.

A large amount of electric power is required because a heat capacity is required.

A rotating roller with a high roller temperature requires a heat resistant special bearing.

The roller comes into direct contact with the hands, which is dangerous and requires a protective member.

The recording material wraps around the roller due to the constant temperature and curvature of the roller, making it easy to see jams on the recording material.

Belt fixing method This method also has the same problems as the above heat roller fixing method and the same wait time and large power consumption as those mentioned above.

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 fixing failure or offset, and as a result, standby time or power consumption, and further It is an object of the present invention to provide an image forming apparatus having a small temperature rise in the machine and having other remarkable features.

(Means for Solving Problems) The present invention is an image forming means for forming a non-fixed toner image corresponding to target image information by carrying a toner made of a heat-meltable resin or the like on a recording material surface, A fixing film, a running drive means for the fixing film, a heating body fixedly supported on one surface side of the fixing film, and a heating body arranged on the other surface side of the fixing film. A conveying member is provided with a pressure member for closely contacting the surface of the recording material on which the unfixed toner image is carried with a fixing film, and the same speed as that of the recording material carrying the unfixed toner image conveyed from the image forming means side. A toner image heat fixing means for introducing the recording material between the fixing film and the pressure member driven in the same direction to heat and fix the unfixed toner image on the surface of the recording material. Image heating fixing hand The heating element of the step has at least an insulating property. A low heat capacity line having a substrate having good thermal conductivity, a heating element provided on one surface side of the substrate, and a temperature detecting element provided on a surface portion position opposite to the heating element on the other surface side of the substrate. An image forming apparatus characterized in that the image forming apparatus is a heating element.

Further, the present invention is the above-mentioned apparatus, wherein the substrate of the heating element has a thickness of 3 mm or less.

Furthermore, the present invention is the above-mentioned apparatus, wherein the temperature detecting element of the heating element is a temperature measuring resistor printed on the surface of the substrate.

(Operation) (1) The recording material to be image-fixed, which is introduced between the fixing film and the pressing member, which is driven to run at the same speed and in the same direction as the conveying direction of the recording material, is the unfixed toner on the surface of the fixing film. While the image-bearing surface is in close contact with the fixing film and the overlapping state with the fixing film, the pressure difference between the heating member and the pressing member (fixing nip portion) is applied while the surface pressure difference occurs between the heating member and the pressing member, and wrinkles occur. They do not get close to each other, and they pass over each other in close contact with each other.

In the heating step, the unfixed toner image on the surface of the recording material is heated and softened and melted by the heating body through the fixing film, and in particular, the surface layer portion thereof is much higher than the melting point of the toner and completely softened and melted. In this case, the heating element, the fixing film, the toner image, and the recording material are satisfactorily pressed and brought into close contact with each other at the mutual pressure contact portion between the heating element and the pressing member, and the heat is effectively transferred. The toner is sufficiently softened and melted to obtain good fixing property.
On the other hand, the temperature rise of the recording material itself is practically small, and the waste of thermal energy is small. That is, the recording material itself is not substantially heated, and only the toner is effectively heated and softened / melted, and the toner image can be satisfactorily heat-fixed with low power.

A note will now be given regarding the softening / melting of the toner described in the present invention. The temperature that is conveniently expressed as the "melting point" of the toner means the minimum temperature required for the toner to fix, and at the fixing lower limit temperature, when the viscosity decreases to the melting point or when the softening occurs. There is a case where the viscosity is reduced to such an extent. Therefore, even if the melting is conveniently expressed at the time of fixing, it may actually show a decrease in viscosity such as softening. The present invention also includes such a case. Similarly, even when it is expressed for convenience that the toner has been cooled and fixed, it may be more appropriate for some toners not to be solidified but to have higher viscosity. The present invention also includes such a case.

Cooling process Sequentially passes through the mutual pressure contact area between the heating element and the pressure member in close contact with the fixing film surface.The recording material part that has been softened / melted by the toner image remains in close contact with the fixing film surface after passing through the pressure contact area. Is continuously continued for a while, and a cooling step is performed during this period to radiate heat of the toner softened and melted in the heating step to cool and fix the toner. Due to this cooling and solidification, the cohesive force of the toner becomes very large, and the toner behaves as a group, and the adhesiveness / fixing force to the recording material side increases, while that to the fixing film side extremely decreases. When the recording material is heated and softened and melted in the heating step, the toner is pressed by the pressure member, so at least a part of the toner image penetrates into the surface layer of the recording material, and the solidified portion is cooled and solidified. Due to the anchor effect, the adhesion and fixing force of the cooled and solidified toner to the recording material side increases.

Separation (Separation) Step After the toner image is cooled and solidified by the cooling step, the recording material is sequentially separated from the fixing film surface. At the time of this separation, the toner image is cooled and solidified to have a sufficiently large adhesion / adhesion force to the recording material and an extremely small amount to the fixing film, so that the recording material portion on which the image is fixed causes toner offset to the fixing film. It can be easily and sequentially separated.

The recording material to be image-fixed is run in close contact with the fixing film at the same speed so that the unfixed toner image bearing surface faces the running fixing film surface, and the toner image is heated by the heating body through the fixing film. Since the recording material and the fixing film are separated from each other after being melted and the toner image has been cooled and fixed, a toner offset to the fixing film does not occur, and a heating element with a small heat capacity is used, and power is supplied to the heating element. Can be performed with a simple structure, and the toner image can be formed by maintaining the heating body at a temperature sufficiently higher than the temperature (melting point or softening point) at which the toner should be heated for fixing. It is possible to heat efficiently, and it is possible to perform satisfactory fixing without defective fixing with a small amount of energy, and as a result, during standby while using the device. And, power consumption, and further an effect of obtaining a smaller image forming apparatus temperature rise in the apparatus.

If the toner is sufficiently melted at a high temperature among the three steps of heating, cooling, and separation, the recording material is immediately separated from the fixing film surface and heated immediately after the toner is sufficiently melted at a high temperature in the heating step. The cooling process after the process may be eliminated and is within the scope of the present invention.

(2) Since the heating element is fixed and supported, the fixing nip portion, that is, the portion between the running fixing film and the heating element at the pressure contact portion between the heating element and the pressing member that sandwich the fixing film and press each other. It is easy to detect the temperature of the fixing nip portion in real time accurately because a temperature gradient is easily generated in the heating body due to the thermal energy taken into the recording material and the running fixing film that are introduced into and passing through the image fixing material. It is difficult, and the temperature of the fixing nip, that is, the appropriate fixing temperature to be controlled in a predetermined temperature is likely to largely change due to a delay in temperature detection.

In the present invention, as described above, a heating element is provided on at least an insulating / heat-conductive substrate (heater substrate), a heating element provided on one surface side of the substrate, and the other surface side of the substrate. Since the low-heat-capacity linear heating element having the temperature sensing element provided at the surface portion position facing the heating element is used, the temperature gradient between the heating element and the temperature sensing element can be reduced,
More accurate temperature detection becomes possible. In other words, it is possible to detect the temperature in the fixing nip portion of the heating body, that is, the fluctuation of the fixing temperature, more accurately in real time, thereby properly controlling the temperature of the surface of the heating body to keep the fixing temperature substantially constant. It becomes easy to stably maintain the value, and it becomes possible to always output a good fixed image without uneven fixing.

By setting the substrate to a thin thickness of 3 mm or less, the temperature gradient between the heating element and the temperature detecting element can be made smaller, so that the fixing nip temperature can be measured more accurately in real time.

Since the temperature sensing element is equipped with a resistance temperature detector on the surface of the board by a printing technique such as screen printing, the placement position accuracy with respect to the board is easy to obtain, and the adhesion to the board is good and the adhesion resistance can be made small and accurate. Can secure temperature measurement,
It is also effective in making the heating element thin and compact.

(Embodiment) The apparatus of this embodiment is a reciprocating type / rotating drum type / transfer type electrophotographic copying apparatus.

(1) Overall schematic configuration of the apparatus (Fig. 1) In Fig. 1, 100 is an apparatus box, 1 is an upper plate 1 of the apparatus box.
This is a reciprocating type document placing table composed of a transparent plate member such as a glass plate disposed on 00a, and reciprocates at a predetermined speed on the machine top plate 100a to the right a and the left a'in the drawing. Driven.

Reference numeral G denotes a document, which is placed by placing the document surface of the document table 1 on the upper surface of the document table 1 according to a predetermined mounting standard with the image surface side to be copied facing downward, and by pressing the document pressure plate 1a onto the document platen 1a. .

Reference numeral 100b denotes a slit opening serving as a document illuminating section which is opened on the surface of the machine top plate 100a with a direction perpendicular to the reciprocating direction of the document placing table 1 (direction perpendicular to the paper surface) as a longitudinal direction. The downward image surface of the document G placed and set on the document placing table 1 sequentially passes through the position of the slit opening 100b from the right side to the left side in the forward movement process of the document placing table 1 to the right a. The light L of the lamp 7 is passed through the slit opening portion during the passage.
100b is received through the transparent document placing table 1 and is illuminated and scanned. The light reflected from the document surface of the illumination scanning light is image-wise exposed on the surface of the photosensitive drum 3 by the short-focus small-diameter image-forming element array 2.

The photosensitive drum 3 is coated with a photosensitive layer such as a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer, and is rotated in the clockwise direction indicated by the arrow b at a predetermined peripheral speed around the central support shaft 3a. The surface of the photosensitive drum 3 is imagewise exposed by subjecting the container 4 to uniform positive charging or negative charging, and the imagewise exposure (slit exposure) of the original image on the uniformly charged surface. An electrostatic latent image corresponding to the original image is sequentially formed.

The electrostatic latent image is sequentially visualized by the developing device 5 with toner made of resin or the like which is softened and melted by heating, and the toner image as the visualized image is transferred to a portion where the transfer discharger 8 as a transfer portion is provided. I will do it.

Reference numeral S denotes a cassette in which transfer material sheets P as recording materials are stacked and housed, the sheets in the cassette are fed out and fed one by one by the rotation of the feeding roller 6, and then the toner on the drum 3 is fed by the registration roller 9. When the leading edge of the image forming portion reaches the portion of the transfer discharger 8, the leading edge of the transfer material sheet P also reaches the position between the transfer discharger 8 and the photosensitive drum 3 and is timed and synchronized so as to coincide with each other. Be delivered. Then, the toner images on the photosensitive drum 3 side are sequentially transferred to the surface of the fed sheet by the transfer discharger 8.

The sheet that has received the toner image transfer at the transfer portion is sequentially separated from the surface of the photosensitive drum 3 by separation means (not shown), and is conveyed as a guide.
The unfixed toner image guided and carried by a fixing device 11 to be described later by 10 undergoes heat fixing processing, and is discharged onto a paper discharge tray 12 outside the machine as an image formed product (copy).

On the other hand, the surface of the photosensitive drum 3 after the transfer of the toner image is repeatedly used for image formation after the adhering contaminants such as the transfer residual toner are removed by the cleaning device 13.

(2) Fixing device (FIGS. 1 and 2) 24 is an endless belt-shaped fixing film, and includes a left driving roller 25, a right driven roller 26, and a driving roller 25.
Between the separating roller 27 arranged below the driving roller 25 and the driven roller 26, and the low heat capacity linear heating body 20 as a heating body disposed below the driving roller 25 and the driven roller 26 in parallel with each other. It is suspended.

The driven roller 26 also serves as a tension roller for the endless belt-shaped fixing film 24.
Is a predetermined peripheral speed in the clockwise direction with the clockwise rotation of the drive roller 25, that is, the same as the conveying speed of the transfer material sheet P having the unfixed toner image Ta conveyed from the image forming unit 8 side on its upper surface. It is driven to rotate with peripheral speed without wrinkles, meandering, or speed delay.

Reference numeral 28 denotes a pressure roller having a rubber elastic layer having a good releasability such as silicon rubber as a pressure member, and sandwiching the film portion on the descending side of the endless belt-shaped fixing film 24 of the heating body 20. The lower surface is brought into contact with the lower surface of the transfer material sheet P in a counter pressure direction with a contact pressure of, for example, a total pressure of 4 to 7 kg, and is rotated counterclockwise in the transport direction of the transfer material sheet P.

The rotationally driven endless belt-shaped fixing film 24 is repeatedly subjected to heat fixing of the toner image, and therefore has excellent heat resistance, releasability and durability, and generally 100 μm or less,
It is preferable to use a thin film having a thickness of 50 μm or less. For example, a single layer film of a heat-resistant resin such as polyimide / polyetherimide / PEA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin) or a composite layer film, for example, a 20 μm thick film, at least on the image contact surface side.
For example, a releasable coating layer obtained by adding a conductive material to PTFE (tetrafluoroethylene resin) is applied to a thickness of 10 μm.

The low heat melting linear heating element 20 as a heating element has, for example, a thickness of 1.
An electric resistance material such as Ta ₂ N is applied to the width of 1.0 mm along the length of the bottom surface of the alumina substrate (heater substrate) 21 of 0 mm, width 10 mm, length 240 mm, which has good insulating properties and good heat conductivity. It is provided with a linear or band-shaped heating element 22 by working. In the case of this example, the linear or strip heating element 22 is energized from both longitudinal ends thereof to cause the heating element 22 to generate heat over its entire length. Energization is a pulse waveform with a cycle of 20 msec of DC 100 V, a desired temperature controlled by a temperature detecting element 23 provided at a surface portion position facing the heat generating element 22 on the upper surface of the substrate 21, and a pulse according to the amount of energy emission. It has an energization control circuit configuration that changes and gives the pulse width,
The pulse width is controlled within a range of about 0.5 to 5 msec, and the heating element 22 is heated to about 200 to 300 ° C. at every instant when a pulse is input. Further, in this example, a sheet front and rear end detection sensor (not shown) is provided on the upstream side of the fixing device 11 in the transfer material sheet conveying direction, and the sheet detection signal of the sensor is used to energize the heating element 22. Sheet P is the fixing device during the period
It controls only for the necessary period of passing 11.

The fixing film 24 is not limited to the endless belt shape, but the endless fixing film 24 wound around the delivery shaft 30 as shown in FIG. 3 is wound between the heating body 20 and the pressure roller 28 and the separation roller 27. It may be configured such that it is engaged with the take-up shaft 31 via the lower side and travels from the delivery shaft 30 side to the take-up shaft 31 side at the same speed as the conveyance speed of the transfer material sheet P.

(3) Fixing Execution Operation The image forming start signal causes the apparatus to perform an image forming operation, and the leading end of the transfer material sheet P having the unfixed toner image Ta carried on the upper surface and conveyed to the fixing apparatus 11 from the transfer unit 8 is the fixing apparatus. When it is detected by the above-mentioned sensor (not shown) arranged nearer, rotation (or running) of the fixing film 24 is started, and the transfer material sheet P is guided by the guide 29 and the heating body 20 and the pressure roller 28. When the unfixed toner image surface enters the space (fixing nip portion) between the fixing sheet 24 and the pressure roller 22 at the pressure contact portion N with the sheet P, the surface of the unfixed toner image surface moves in the same direction in the same direction. It passes through the mutual pressure contact portion N between the heating body 20 and the pressure roller 28 while receiving a sandwiching pressure in a state of overlapping with the fixing film 24 without coming into close contact with the lower surface of the film 24 and causing a surface shift or wrinkling. Go.

The above-mentioned (action)
The toner image is heated and softened / melted as described in the item (1)-. As described above, the heating step in the present embodiment provides the heating element 20 with the linear heating element 22, and the heating element 22 integrally formed with the heating element 21 is energized in a pulsed manner to repeat heat generation. This is performed by the heating body 21 configured as described above. That is, the toner image Ta on the sheet P, which is conveyed at a predetermined conveying speed, is transferred to the fixing film 24 on which the sheet P is conveyed, and the toner image Ta of the linear heating portion is sequentially determined according to the width of the heating element 22 of the heating element 20. It is fed into the effective width W and is heated to become a softened / melted image Tb.

The sheet portion that has passed through the mutual pressure contact portion N between the heating body 20 and the pressure roller 28 is stretched between the heating body 20 and the separation roller 27 until it reaches the position of the separation roller 27. The film is continuously conveyed while being in close contact with it.

This transportation process is referred to as a cooling process, and (1)-
As described in the section, the heat of the softened / melted toner Tb is radiated to cool and solidify the toner Tc.

When the fixing film 24 reaches the position of the separation roller pair 27, the fixing film 24 is moved along the surface of the separation roller 27 having a large curvature.
Fixing film with the traveling direction turned away from the surface
24 and the sheet P are separated from each other (separated), and the sheet P is discharged to the discharge tray 11. By the time of this separation, the toner is sufficiently cooled and solidified, and as described in (1)-(1)-(action), the toner has a sufficiently large adhesion / adhesion force to the sheet P and an extremely small amount to the fixing film 24. In this state, the fixing film 24 and the sheet P are easily separated from each other without causing toner offset to the fixing film 24.

In this embodiment, since the linear heating element 22 of the heating element 20 is instantly heated to a sufficiently high temperature with respect to the melting point (or fixing temperature) of the toner when energized, preheating of the heating element is unnecessary. The heat transfer to the pressure roller 28 during non-fixing is small. Also during fixing, since a fixing film, a toner image, and a sheet are present between the heating body 20 and the pressure roller 28 and the heat generation time is short, a sharp temperature gradient occurs,
The pressure roller 28 does not easily heat up, and its temperature is maintained below the melting point of the toner even when continuous image formation is carried out to the extent practically required. In the apparatus of this embodiment having such a configuration, the toner image formed of the heat-fusible toner on the sheet P is first heated and melted by the heating body 20 via the fixing film 24, and in particular, its surface layer portion is completely melted. It softens and melts. At this time, the heating roller, the fixing film, the toner image, and the sheet are in good contact with each other by the pressure roller 28, and the heat is efficiently transferred. As a result, the heating of the sheet P itself can be suppressed as much as possible, and the toner image can be efficiently heated and melted. In particular, energy saving can be achieved by limiting the heating time for energization.

Since a small heating element is sufficient and therefore the heat capacity is small and it is not necessary to raise the heating element in advance, it is possible to reduce the power consumption during non-image formation and also to prevent the temperature rise inside the machine. .

In this embodiment, since the temperature of the pressure roller 28 is maintained lower than the melting point of the toner as described above, it is possible to promote the heat dissipation of the toner image in the subsequent cooling step following the toner image heating step. . Therefore, the time required for cooling is short and the device can be downsized.

(4) Heated body 20 FIG. 4 shows a configuration example of the heated body 20.
Is a plan view of the lower surface of the heating element, that is, the side that is rubbed against the fixing film 24, FIG. 6B is a vertical side view, and FIG.

The substrate (heater substrate) 21 is a horizontally long thin plate member having a longitudinal direction in the transverse direction of the fixing film (direction perpendicular to the running direction of the fixing film). The material should be an electrically insulating material with good thermal conductivity such as alumina.

The heating element 22 is provided linearly or in a strip shape along the length in the substantially central portion of the surface of the substrate on which the fixing film 24 is rubbed, and in addition to Ta ₂ N in the above example, Nichrome / RuO ₂ -A resistor such as Ag / Pd or a surface heating element such as a ceramic heater can be used.

Reference numerals 22a and 22a denote electrodes for energizing the heating element 22, which are provided on both end sides of the substrate, and are made of a metal such as Ag / Au / Cu or a conductive material such as a resistor such as RuO ₂ / Ag / Pd. Both ends of the heating element 22 are electrically connected to the electrodes 22a, 22a and are energized in the longitudinal direction so that the entire length of the heating element 22 generates heat.

The temperature detection element 23 uses a bead type thermistor in this example, and this element 23 is a surface opposite to the surface of the substrate 21 on the side where the heating element is arranged, and the surface of the surface facing the heating element is It is provided in contact with the longitudinal central position. The temperature detecting element 23 detects the temperature of the fixing nip portion (fixing temperature), and the detection output thereof turns on / off the pulsed energization to the heating element 22 by an energization control circuit (not shown). The pulse width is controlled to control the fixing temperature to a predetermined value.

As described above, the heating body 20 and the pressure roller as the pressure member that are in pressure contact with each other with the running fixing film 24 interposed therebetween.
Heat is generated from the heating element 22 in the process of introducing and energizing the transfer material sheet P, which is a recording material to be image-fixed, into the fixing nip portion between the fixing film 24 and the pressure roller 28 in the pressure contact portion N with the pressure roller 28. Energy is applied to the sheet P via the film 24 to heat and fix the toner image.

At this time, the surface temperature of the heating element 20 (fixing film 24 of substrate 21
The temperature of the surface that rubs against) is important. That is, when the surface temperature of the heating element is lower than the predetermined temperature, the heat energy applied to the toner is insufficient, and problems such as poor fixing and low temperature offset occur. On the contrary, when the surface temperature of the heating body is higher than the predetermined temperature, the thermal energy applied to the toner becomes excessive and a high temperature offset occurs, and also excessive thermal energy is applied to the fixing film, which causes thermal deformation of the fixing film. Absent. Therefore, the surface of the heating element is required to be in a predetermined temperature range. For this purpose, it is necessary to adjust the temperature of the surface of the heating body, and it is necessary to accurately detect the surface temperature of the heating body.

Since the heating element 20 used in the present invention is fixedly supported and has a constant film contact surface, a temperature distribution is likely to be generated in the heating element due to the thermal energy taken by the transfer material sheet P by the fixing operation, so that the heating element 22 and The temperature difference increases as the distance increases. Therefore, in the heating element 20, the temperature detecting element 23 is preferably close to the heating element 22. It is also preferable to make a material having a high thermal conductivity between the heating element 22 and the heating element 22 because the temperature difference can be reduced.

When the temperature detecting element 23 is brought into contact with the substrate 21 to detect the temperature of the substrate, as shown in FIG. 4 and FIG. 7 (a), the rear surface of the substrate 21, that is, the surface of the substrate opposite to the side where the heating element is disposed. It is considered that the element 23 is brought into contact with the substrate 23 and the side surface of the substrate is brought into contact with the device 23 as shown in FIG. 7 (b).

In the case of being arranged in contact with the back surface of the substrate, if it is arranged at a position displaced from the surface facing the heating element as shown in FIG. 7 (a), the distance from the heating element 22 which is the main heating source to the temperature detecting element 23 is The temperature difference becomes long and accurate temperature detection is difficult.

Further, in the case of the contacting arrangement on the side surface of the substrate 21 as shown in FIG. 7 (b), a certain nip width is required at the pressure contact portion N between the heating body 20, the fixing film 24 and the pressure roller 28. Board 21
Since a certain width is required, the distance between the temperature detecting element 23 and the heating element 22 becomes long, and accurate temperature detection is difficult in this case as well.

Therefore, in order to accurately detect the temperature of the heating element 22 which is the main heating source through the substrate 21, the temperature detecting element 23 is opposed to the heating element 22 through the substrate 21 as shown in FIG. It is most preferable and effective to place them at the shortest distance.

Also, the thermal conductivity of the substrate 21 is important. That is, when a material having poor thermal conductivity such as glass is used as the substrate 21, the temperature gradient in the substrate becomes large and the temperature detection becomes inaccurate. In the case of an insulating material having good thermal conductivity such as alumina or diamond, the temperature gradient can be made small and the surface temperature of the heating body can be accurately detected even through the substrate 21.

Specifically, an alumina substrate with a thickness of 1.0 mm and a width of 10 mm is used as the substrate 21, and Ag / Pd is screen-printed with a thickness of 20 μm and a width of 2.0 mm as the heating element 22 along the central length of one side thereof. And a bead type thermistor as a temperature detecting element 23 is arranged in contact with the position of the surface opposite to the heating element on the other surface side of the substrate to form the heating element 20, and the heating element forming portion of the heating element 20. The pressure roller 28 and the pressure roller 28 are brought into pressure contact with each other with a nip width of 4 mm through the fixing film 24 to form a fixing device.

Thus, the origin is set at the origin (0 mm) at the center of the width of the heat generating element facing surface on the side opposite to the heat generating element side of the board, and 1 mm, 2 mm, 3 mm, 4 mm from the origin in the width direction of the board. The bead type thermistor as a temperature sensing element is placed in contact with each other by sequentially shifting the position, and experimentally a thermocouple is attached to the surface of the heating element to directly measure the temperature of the heating element and execute the fixing operation to determine the surface temperature. The maximum temperature difference of the bead type thermistor detection temperature was measured. The results are shown in the table below.

When the heating element 22 and the temperature detecting element 23 are arranged on the one surface side and the other surface side of the substrate 21 in a facing relationship with each other, the maximum temperature difference that occurs during paper passing is minimized, and the surface temperature is most accurately measured. Can be measured.

When the substrate 21 was changed to glass and the maximum temperature difference at the facing position was measured, it was ΔT = 32 ° C.

That is, when an insulator having good thermal conductivity such as alumina is used as the substrate 21 and the heat generating element 22 and the temperature detecting element 23 are arranged in a facing relationship, the temperature difference between the two is minimized and the most accurate temperature detection is possible. Become.

In the example shown in FIG. 5, the heat generating element 2 is provided on one surface side of the insulating / good heat conducting substrate 21 through a heat insulating layer 21a in order to enhance thermal efficiency.
2, the surface of the heat insulating layer 21a including the heating element 22 is further covered with a protective layer 21b in order to enhance the sliding wear resistance of the surface,
A bead type thermistor 23 as a temperature detecting element is arranged in contact with the other side of the substrate 21 as in the case of FIG.

The heat insulating layer 21a is a layer of a heat insulating material such as glass having a thickness of 5 to 20 μm. If such a heat insulating layer 21a is interposed, the thermal efficiency will be 10
% Or more and the fixing power is reduced, which is preferable. However, on the other hand, the heat conduction of the substrate 21 deteriorates and the temperature sensing element on the back side
There is a problem that it becomes easy to create a large temperature gradient between the two. In this case, as described above, the heating element 22 and the temperature sensing element
It is of course important that the 23 be opposed to each other, but the thickness t of the substrate 21 is also an important factor. That is, a temperature gradient is likely to occur as the thickness t increases. The present inventors derived from another experiment that when the MAX value of the temperature difference between the heating body surface temperature and the temperature detection means is less than 20 ° C., it is possible to perform temperature control without poor fixing at low temperature and without high temperature offset. It was More preferably, if it is 10 ° C. or less, temperature control becomes easy. When the relationship between the thickness t of the substrate 21 and the temperature difference was investigated, the temperature difference was below 20 ° C. when the substrate thickness t was 3 mm or less, and below 10 ° C. when it was 1.5 mm or less. Therefore, the thickness t of the substrate can be adjusted to 3 mm or less, more preferably 1.5 mm or less.

The temperature detecting element 23 is not limited to the bead type thermistor of the above-mentioned example, and other known temperature detecting elements may be used. Fig. 6 (a)
(B) shows an example using a resistance temperature detector 23 such as Pt.
That is, on the surface of the substrate 21 on the side opposite to the side where the heat generating element is arranged, along the length of the surface of the surface facing the heat generating element, the resistance temperature detector 23 as a temperature detecting element is line-printed by printing such as screen printing. It is formed in the shape of a strip or a strip.

As described above, the one in which the temperature measuring resistor 23 as the temperature detecting element is formed and provided by the printing technique is easy to obtain the arrangement position accuracy of the element with respect to the substrate surface, and the contact resistance with the substrate can be made small so that the temperature can be accurately measured. It can be secured and the heating element can be made thin.
It is effective in making it compact.

(5) Others When the end film is used as the fixing film 24 as shown in FIG. 3, if the fixing film on the delivery shaft side is almost completely wound on the winding shaft side and used, a new roll winding film is used. It is also possible to use a method of exchanging (winding exchange type).

In the case of such a take-up exchange type, it is possible to make the fixing film thin regardless of the durability of the fixing film and to reduce the power consumption. For example, PET (polyester) as a fixing film
It is possible to use an inexpensive base material such as a film, which is heat-treated and has a thin wall thickness of, for example, about 12.5 μm or less.

Alternatively, since toner offset to the surface of the fixing film does not substantially occur as described above, if the thermal deformation or deterioration associated with the use of the fixing film is small, the used sheet wound on the winding shaft side can be timely It is also possible to use it repeatedly for a plurality of times by controlling the rewinding to the feeding shaft side or reversing the winding shaft side and the feeding shaft side (rewinding repetitive use type).

As the fixing film in the rewinding and reusing type, for example,
It is possible to use a composite layer film in which a 25 μm-thick polyimide resin film is used as a base material having excellent heat resistance and mechanical strength, and a release layer made of fluorine resin or the like having a high release property is provided on the surface of the polyimide resin film. At the time of rewinding and reverse running, it is preferable to automatically control the pressure release mechanism to keep the pressure contact between the heating body and the pressure roller in the released state.

When it is used multiple times such as rewinding repetitive use type or endless belt type, a felt pad is provided for cleaning the film surface, and a slight release agent such as silicone oil is impregnated to bring the pad into contact with the film surface. For example, the film surface may be cleaned and the releasability may be further improved. When the fixing film is an insulative fluororesin-treated product, static electricity that disturbs the toner image is easily generated in the film. Therefore, in order to deal with the static electricity, a grounding brush may be used. A bias voltage may be applied to the brush without grounding to charge the film within a range that does not disturb the toner image. 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 fluororesin. 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.

Regardless of whether the fixing film is of the endless belt type, the rewinding exchange type, or the rewinding repetitive use type, the fixing film can be detachably attached to the fixing portion of the fixing device 11 to facilitate the exchange of the fixing film. it can.

The structure of the heating element 20 and the control of energization to the heating element 22 are not limited to those of the embodiment, the heating element 20 may be a non-rotating heat roller type, and the heating element 22 may be a thick film resistor or PTC. It may be a ceramic chip array or the like having characteristics,
The energization control is not limited to the pulsed application, and the normal energization may be performed.

The toner solidified by heating and melting in the heating step may be cooled and solidified by natural heat dissipation, or may be forcedly cooled by arranging an air blowing means, heat dissipation fins or the like.

If the toner is sufficiently melted at a high temperature, if the toner is sufficiently melted at a high temperature in the heating step (fixing nip portion) as shown in FIG. 8, the recording material (transfer material) is immediately transferred without a cooling step after the heating step. The sheet P may be separated from the surface of the fixing film 24.

The above-described apparatus is a transfer type electronic copying apparatus, but the image forming process / means is a direct type in which a toner image is directly formed and carried on electrofax paper, electrostatic recording paper, or a magnetic recording image forming type. , A copier, a laser beam printer, a facsimile, a microfilm reader printer, a display device, and a recording device in which an image is formed on a recording material by a heat-fusible toner by an appropriate image forming process / means and the image is heated and fixed. The present invention can be effectively applied to various image forming apparatuses such as.

(Effects of the Invention) As described above, according to the present invention, in the toner image heat fixing type image forming apparatus, it is possible to reduce the heat capacity of the heating member which is the heating means without causing the fixing failure or the offset, and the waiting time or It is possible to realize an image forming apparatus capable of always stably outputting an image-formed product having a good fixed image quality with low power consumption and further temperature rise inside the apparatus. Further, the fixing film can be repeatedly used for a long period of time without any problem of wrinkling and without any problem.

Further, with respect to the heating element, the heating element surface and the temperature detecting element 3 are provided with a simple structure in which the heating element and the temperature detecting element are arranged so as to face each other with the substrate inside on one side and the other side of the substrate.
Since the temperature difference between the heating element and the heating element can be minimized, it is possible to detect the temperature in the fixing nip portion of the heating element, that is, the variation of the fixing temperature, more accurately in real time, and thereby to properly control the temperature of the heating element surface. It is easy to stably maintain the fixing temperature at a predetermined substantially constant value, and it becomes possible to always output a good fixed image without unevenness in fixing.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional front view showing a schematic configuration of an apparatus of one embodiment, FIG. 2 is an enlarged view of a fixing apparatus portion, FIG. 3 is a schematic view of another example of the configuration of the fixing apparatus, and FIG. 4 (a). (B) and (c) are a plan view of the lower surface of the heating body, a longitudinal side view, a cross-sectional view, and a fifth view.
The figure is a cross-sectional view of another example of a heating body, FIGS. 6 (a) and 6 (b) are vertical cross-sectional views and cross-sectional views of a heating body of still another example, and FIGS. 7 (a) and 7 (b) are temperatures. FIG. 8 is a diagram showing an example of arrangement of sensing elements, FIG.
The figure is a schematic view of another configuration example of the fixing device. Reference numeral 3 is a drum type rotary photoreceptor, 11 is a fixing device, 24 is a fixing film, 20 is a heating body, 21 is a substrate, 22 is a heating element, 23 is a temperature detecting element, 28 is a pressure roller, and P is a transfer material sheet.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Masahide Kinoshita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroyuki Adachi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (56) Reference JP 59-157678 (JP, A) JP 55-75625 (JP, A) JP 59-68766 (JP, A) JP 55-39303 (JP, A) JP-A-56-19889 (JP, A) JP-A-1-263683 (JP, A) JP-A-2-134667 (JP, A) Actually open 54-30846 (JP, U) Actual-open Sho 58 -190659 (JP, U)

Claims (3)

[Claims] 1. An image forming means for forming an unfixed toner image corresponding to desired image information by carrying a toner made of a heat-meltable resin or the like on a recording material surface, a fixing film, and running of the fixing film. A driving unit, a heating body fixedly supported on one side of the fixing film, and a heating body disposed on the other side of the fixing film, and the recording material is unfixed with respect to the heating body via the fixing film. A fixing member provided with a pressure member for closely contacting the surface on which the deposited toner image is carried, and fixed by running in the same direction at the same speed as the carrying speed of the recording material carrying the unfixed toner image carried from the image forming means side. A toner image heat fixing means for introducing the recording material between the film and the pressure member to heat and fix the unfixed toner image on the surface of the recording material, and the heating body of the toner image heat fixing means is At least Sex. A low heat capacity line having a substrate having good thermal conductivity, a heating element provided on one surface side of the substrate, and a temperature detecting element provided on a surface portion position opposite to the heating element on the other surface side of the substrate. An image forming apparatus, wherein the image forming apparatus is a heating element. 2. The image forming apparatus according to claim 1, wherein the substrate of the heating body has a thickness of 3 mm or less. 3. The temperature detecting element of the heating element is a temperature measuring resistor printed on a substrate surface.
Alternatively, the image forming apparatus according to claim 2.