JPH02293776A - Thermal fixing device of image - Google Patents

Abstract

PURPOSE:To satisfactorily fix an image by providing a part supplying electric power to the heater of a fixing part with a power source voltage detecting means, a temperature detecting means, a means controlling the voltage applying time according to the voltage and temperature and a means controlling an applying cycle according to the detected voltage. CONSTITUTION:A control circuit 60 including a microcomputer controls a power source 61 according to the voltage detected by a power source voltage monitor 62 and the temperature detected by a thermistor 55, and controls power supply by altering the pulse width of electric power supplied to a heating layer 28. Where the supply power voltage V to the heating layer 28 and a pulse cycle tau are constant and where a heating part H is at a temperature T0 and a fixing operation starts at time t0, the temperature of the part H is uniquely determined from T0. The temperature T0 reaches a fixing temperature TH0 by the energization of pulse width tau0, and drops to T1 because energization is not carried out during a period(tau-tau0). At time t1, second energization is carried out with pulse width tau1<tau0 which is determined by the temperature T1. After that, the temperature of the thermistor 55 is similarly detected in the cycle tau, the heating layer 28 is energized, and the extreme temperature of the heating part is maintained at the fixing temperature TH0. Consequently, sufficient fixing performance can be obtained without consuming useless electric power.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an image heating system incorporated into an image forming apparatus such as a copying machine, a laser beam printer, a facsimile machine, a microfilm reader printer, an image display device, and a recording machine. Regarding a fixing device.

More specifically, a recording material (electrofax sheet, electrostatic recording sheet, transfer material A record in which an unfixed toner image corresponding to target image information is formed and carried on the surface of a sheet (sheet, printing paper, etc.) by a direct method or an indirect (transfer) method, and the unfixed toner image is carried on the surface of the paper. The present invention relates to a fixing device that heats and fixes a permanently fixed image on a material surface.

(Prior Art) Conventionally, a heat fixing type image fixing device uses a heating roller maintained at a predetermined temperature and a pressure roller having an elastic layer that presses against the heating roller to fix unfixed toner. A roller fixing method is often used in which a recording material on which an image is formed is heated while being supported and conveyed.

However, in this type of device, in order to prevent the so-called offset phenomenon in which toner is transferred to the heating roller,
It is necessary to maintain the heating roller at an optimum temperature, and the heat capacity of the heating roller or heating body must be increased. That is, when the heat capacity of the heating roller is small, the temperature of the heating roller tends to fluctuate greatly toward the lower or higher temperature side due to paper passing or other external factors, depending on the relationship with the amount of heat supplied by the heating element. If the temperature changes to the low temperature side,
Insufficient softening and melting of the toner causes fixing failure and low-temperature offset, and when the temperature changes to the high temperature side, the toner is completely melted and the cohesive force of the toner decreases, resulting in high-temperature offset.

In order to avoid this problem, increasing the heat capacity of the heating roller increases the time it takes to heat the heating roller to a predetermined temperature, causing another problem of increasing standby time when using the device. .

As a measure to solve this problem, US Patent No. 3,578
, 797, (1) bringing the toner image into contact with a heating web and heating it to its melting point to melt it; (2) cooling the toner image after melting to make it relatively highly viscous; (2) A method is known in which toner is fixed without causing offset by going through the process of peeling off the toner from the heating web while reducing the tendency of the toner to adhere.

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

However, as is well known, when the toner is brought into contact with a heating 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 Publication No. 51-29825 (Special Patent Application No. 47-25)
No. 896), it has been proposed that a known pressure welding technique be added to this to improve the heat transfer coefficient and to sufficiently heat and melt the toner in a short time.

(Problems to be Solved by the Invention) However, in the apparatus disclosed in this publication, in order to heat the toner sufficiently in a relatively short time, ■ Toner images and records are formed between a pair of heating elements. Since the method uses a method in which the material is held under pressure and heated, and then the heating is stopped and then forcibly cooled, the energy required for fixing increases. In other words, by heating the toner image with a pair of heating elements, the toner image is heated from above and below, which may seem efficient at first glance, but on the other hand, in order to heat the toner image from the recording material side, the recording material must first be sufficiently heated. This requires a large amount of energy. Furthermore, in the cooling process, the recording material that has been heated and humidified 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 described above, a method has been proposed in which the heated toner is cooled and then separated to fix the toner without causing high-temperature offset, but it has not been put to practical use because of the above-mentioned drawbacks.

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 through 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 It is an object of the present invention to provide an image forming apparatus that causes a small temperature rise inside the machine and has other remarkable features.

(Means for Solving the Problems) The present invention provides a fixing film, a traveling drive means for the fixing film, a heating body disposed on one side with the fixing film inside, and a heating body disposed on the other side. A pressure member is disposed opposite to the heating body and brings the image-bearing surface of the recording material to which the image is to be fixed into close contact with the heating body through the fixing film, and the fixing film is used to fix at least the image. During execution, the traveling fixing film and the introduced recording material are brought into close contact with each other by running at the same speed in the forward direction as the recording material to which the image is to be fixed, which is conveyed and introduced between the fixing film and the pressure member. By passing the recording material through a fixing nip formed by pressure contact between the heating body and the pressure member, the image bearing surface of the recording material is heated by the heating unit on the side of the heating body corresponding to the fixing nip. The heating part of the heating element raises the temperature with a heating element provided in the heating element, and the power supply part for the heating element is connected to a power source that supplies power to the heating element. a voltage detection means; a temperature detection means disposed close to the heating element; a means for controlling the application time for supplying power to the heating element according to the voltage and temperature detected by both the means; An image heat fixing device is characterized in that it has means for controlling an application period according to a voltage.

(Function) (1) The recording material to which the image is to be fixed is introduced between the fixing film and the pressure member, which are running in the same direction at the same speed as the recording material conveyance direction, and the unfixed toner remains on the fixing film surface. When the image bearing side is in close contact with the fixing film and is overlapped with the fixing film, the mutual pressure contact area between the heating body and the pressure member, that is, the fixing nip area is subjected to squeezing pressure, and the surfaces may be misaligned or wrinkled due to the speed difference between them. They overlap as one and pass in close contact with each other without coming close to each other.

■Heating process During this process of passing through the fixing nip, the unfixed toner image on the recording material surface is heated and softened and melted by the heat of the heating section of the heating element through the fixing film, and in particular, the surface layer exceeds the toner melting point and is completely softens and melts. In this case, the heating body, fixing film,
The toner image/recording material is well pressed and adhered by the pressure member and heat is transferred effectively, so that the toner is sufficiently softened and melted by heating for a short period of time, and good fixing properties can be obtained. On the other hand, the temperature rise of the recording material itself is actually extremely small and there is little wastage of thermal energy.

In other words, the recording material itself is not heated substantially, only the toner is effectively heated to soften and melt, and the toner image can be successfully heat-fixed with low power.

Here, a note will be made regarding the softening and melting of the toner described in the present invention. The temperature conveniently expressed as the "melting point" of a toner means the minimum temperature necessary for the toner to fix, and there are cases where the viscosity decreases to the extent that it can be called melting at the minimum fixing temperature, In some cases, the viscosity decreases 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. The present invention also includes such cases. Similarly, even when it is conveniently expressed that the toner is cooled and fixed, depending on the toner, it may be more appropriate to say that the toner has become highly viscous rather than solidified. The present invention also includes such cases.

■Cooling process The toner image that passes through the fixing nip in close contact with the fixing film surface.The portion of the recording material that has been heated, softened and melted continues to be conveyed for a while while remaining in close contact with the fixing film surface even after passing through the fixing nip. During this period, a cooling process is performed in which the heat of the toner softened and melted in the heating process is radiated to cool and fix the toner. Due to this cooling and solidification, the cohesive force of the toner becomes extremely large, causing it to behave as a group, and while its adhesion and adhesion to the recording material side increases,
For the fixing film side, it becomes extremely low. When the toner is heated and softened and melted on the recording material, it is pressed by the pressure member, so at least a part of the toner image permeates into the surface layer of the recording material, and the permeated portion is Due to the anchor effect caused by the cooling and solidification of the toner, the adhesion and fixing power of the cooling and solidifying toner to the recording material side increases.

(2) Separation (Separation) Step After the toner image is cooled and solidified in the above cooling step, the recording material is sequentially separated from the fixing film surface. At this time of separation, the toner image is cooled and solidified and has sufficient adhesion and adhesion to the recording material, but the adhesion and adhesion to the fixing film is extremely small, so the part of the recording material where the image has been fixed causes toner offset with respect to the fixing film. They are easily separated one after another without having to do anything.

In this way, the recording material on which the image is to be fixed is made to 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 and melted by a heating body through the fixing film. In addition, since the recording material and the fixing film are separated after the toner image is cooled and fixed, toner offset with respect 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. This can be done with a simple configuration, and by maintaining the heating element at a temperature sufficiently high compared to the temperature (melting point or softening point) at which the toner should be humidified for fixing, the toner image can be improved efficiently. As a result, it is possible to achieve sufficiently good fusing with less energy and no fusing defects, resulting in an image forming device that requires less standby time during use, less power consumption, and less internal temperature rise. This effect is achieved.

Incidentally, in the above separation step O, the toner does not necessarily have to be cooled and solidified at the separation portion between the fixing film and the recording material. Also, if the toner melts sufficiently at high temperatures among the three steps of ■heating, ■cooling, and ■separation mentioned above (
Immediately after the toner is melted at a sufficiently high temperature in the heating process (if the viscosity of the toner when heated and melted is sufficiently high), the recording material is separated from the fixing film surface (when the toner temperature is above the melting point), and a cooling process is performed after the heating process. may be omitted, and this is within the scope of the present invention.

(2) Regarding the heating element, the temperature increase on the surface of the heating element is proportional to the electric power applied per surface area of the heating element. Therefore, when the voltage applied to the heating element changes, it is difficult to maintain the maximum value of the surface temperature of the heating element at a predetermined temperature, and some kind of contrivance is required.

In addition, for devices where the voltage applied to the heating element varies greatly, it is possible to make the power per area constant by having a heating element with a different surface area. Problems arise in that the amount of fixing varies because the fixable width differs, and the total power applied to the heating element varies.

Therefore, in the present invention, as described above, the power supply unit for the heating element includes a detection means for detecting the power supply voltage that supplies power to the heating element, a temperature detection means arranged close to the heating element, and a power supply unit that responds to the voltage and temperature detected by both means. By providing a means for controlling the application time for supplying power to the heating element using the voltage detection means, it is possible to control the local maximum value of the surface temperature of the heating element to a predetermined temperature regardless of changes in the applied voltage. By providing a means for determining the difference between the heat generating parts according to the voltage detected by the means and controlling the period of energization, it is possible to stabilize the power supply to the heat generating parts. As a result, more accurate temperature management control can be performed, and significant effects can be achieved in energy saving, prevention of temperature rise inside the machine, and prevention of damage (heat loss) to the heating element and fixing film. In addition, the control device can be visualized without depending on the manual voltage.

(Embodiment) FIG. 3 shows a schematic configuration of an example of an image forming apparatus incorporating an image heat fixing device 20 according to the present invention. The image forming apparatus of this example is an electrophotographic copying apparatus of a reciprocating document table type, a rotating drum type, and a transfer type.

(1) Overall schematic structure of the copying apparatus In FIG. 3, 100 is a machine housing of the machine, and 1 is a reciprocating original document holder made of a transparent plate member such as a glass plate disposed on the top plate 100a of the machine housing. It is a mounting stand, and is driven to reciprocate at a predetermined speed on the top plate 100a of the machine casing in the right direction a and the left direction a in the drawing, respectively.

G is a document, which is placed by placing the image side to be copied facing down on the top surface of the document table 1 according to a predetermined placement standard, and placing the document pressure bonding plate 1a on top of it and pressing it down. .

Reference numeral 100b denotes a slit opening, which serves as a document illumination section, and is opened on the surface of the top plate 1008 of the machine casing, with its length extending in a direction perpendicular to the direction of reciprocating movement of the document table 1 (direction perpendicular to the plane of the paper). The downward image surface of the document G set on the document platform 1 passes through the position of the slit opening 100b sequentially from the right side to the left side during the forward movement of the document platform 1 to the right side a. During the passing process, the light L from the lamp 7 is received through the slit opening 100b and the transparent original table 1, and the document is illuminated and scanned. The illumination scanning light reflected from the document surface is imaged and exposed on the surface of the photosensitive drum 3 by the short focus and small diameter imaging 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 clockwise as indicated by an arrow b around a central support shaft 3a at a predetermined circumferential speed. The surface of the photosensitive drum 3 is uniformly charged with positive or negative polarity by the charger 4, and the uniformly charged surface is exposed to image formation (slit exposure) of the original image. Electrostatic latent images corresponding to the original image are sequentially formed.

This electrostatic latent image is sequentially visualized by a developing device 5 using toner made of a resin or the like that softens and melts when heated, and the developed toner image is transferred to a location where a transfer discharger 8 is provided as a transfer section. I will do it.

S is a cassette loaded with transfer material sheets P as recording materials, and the sheets in the cassette are fed and fed one by one by the rotation of the feeding roller 6, and are then fed onto the drum 3 by the registration roller 9. The timing is set so that when the leading edge of the toner image forming section reaches the position of the transfer discharger 8, the leading edge of the transfer material sheet P also reaches a position between the transfer discharger 8 and the photosensitive drum 3, and the two coincide. The data is taken and fed synchronously. Then, the toner image on the photosensitive drum 3 side is sequentially transferred onto the surface of the fed sheet by the transfer discharger 8.

The sheet to which the toner image has been transferred in the transfer section is sequentially separated from the three surfaces of the photosensitive drum by a separating means (not shown), and guided by a conveyance guide 10 to a fixing device 20, which will be described later, to heat the unfixed toner image carried thereon. After undergoing a fixing process, the image is discharged onto a paper discharge tray 11 outside the machine as an image formed product (copy).

On the other hand, after the toner image has been transferred, the surface of the photosensitive drum 3 is subjected to removal of adhered contaminants such as residual toner by a cleaning device 12, exposed to light over the entire surface, and subjected to static electricity removal by the cleaning device 12 to erase electrical residual memory and erase the electrical residual memory. It is then used for image formation.

PH1 is a paper feed detection sensor (for example, a photo sensor) disposed in the sheet path section between the feed roller 6 and the registration roller 9, and PH2 is a paper discharge detection sensor (for example, a photo sensor) disposed next to the fixing device 20. It is.

(2) Fixing device 20 FIG. 1 is an enlarged view of a portion of the fixing device 20 in an image fixing state.

24 is a fixing film feeding shaft, on which the fixing film 23 of a desired set length is wound into a roll, and the leading end of the fixing film 23 is connected to the fixing film winding shaft 2.
It is locked at 7. The fixing film 23 in this embodiment is a thin plastic long film having a heat-resistant treatment and having a thickness of, for example, PET (polyester) as a base material.

Reference numerals 21 and 22 denote a heating body and a pressure roller, which are disposed facing each other on the upper and lower sides of the fixing film portion between the shafts 24 and 27, respectively. The heating body 21 and the pressure roller 22 are constantly pressed and urged with the fixing film 23 in between by an unillustrated urging means to apply a desired contact pressure (for example, a total pressure of 4 to 6 kg for A4 width). Reference numerals 26 and 33 indicate separation upper rollers having a large curvature (strong curvature, small radius) and disposed next to the heating body 21 and the pressure roller 22 so as to face the upper and lower surfaces of the fixing film, respectively. This is the lower separation roller. Reference numeral 32 denotes a guide plate disposed between the pressure roller 22 and the lower separation roller 33. They face each other substantially parallel to each other with a gap between them or in slight contact with each other. 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. The upper separation roller 26 and the lower separation roller 33 are rollers that are free to rotate.

The winding shaft 27 is rotationally driven in the clockwise direction as indicated by the arrow by a drive system (not shown), whereby the fixing film 23 is moved from the feeding shaft 24 side to the winding shaft 27 side to the image forming section (transfer section 8).
The sheet P is wound up and run in the same direction at the same speed as the conveyance speed of the sheet P, which is conveyed from the sheet P to the fixing device 20 via the guide 10. The pressure roller 22 is rotationally driven in the counterclockwise direction of the arrow by a drive system (not shown) at a circumferential speed that is approximately the same as the conveyance speed of the sheet P.

Reference numeral 30 denotes a fixing film remaining amount sensor arm that is brought into contact with the outer surface of the rolled fixing film 23 on the feed-out shaft 24 side, and is used as the fixing film is sequentially transferred to the winding shaft 27 side by executing the fixing process. The remaining amount is detected from the gradual decrease in the roll diameter, and when the film is near the end, a warning display or sound is displayed to prompt the user to replace the fixing film.

Reference numerals 29 and 25 are the same levers as the sheet detection sensors disposed on the lower surface side of the transfer material conveyance guide 10 from the toner image transfer section 8 to the fixing device 20 near the fixing device 20. The tip end of the lever 25 projects upward into the guide 10 from a through hole 10a provided in the guide 10 in the free state. In this state, sensor 29 is off. Guide 1
The transfer material sheet P is conveyed from the transfer unit 8 side to the fixing device 20 side along the top surface of the sheet P, and the protruding tip of the lever 25 is cut by the tip of the sheet P, so that the back side of the sheet P is conveyed along the top surface of the sheet P. It goes to the side, sinks into the through hole 10a, and rotates. This lever 25
The sensor 29 is turned on by the downward rotation of the seat P, and the arrival of the seat P at the sensor position is detected by a control circuit (not shown). The lever 25 is pressed against the back surface of the seat P until the seat P finishes passing through the lever position, so that the lever 25 is kept in a sunken and rotating state during that time, and therefore the sensor 29 is kept in the on state. be done. Thereafter, when the rear end of the seat P passes the position of the lever 25 and is separated from the lever 25, the lever 25 becomes free and returns to the position in which the tip protrudes from the through hole 10a again and rotates. . This return rotation turns off the sensor 29, and the control circuit detects that the seat P has passed the sensor position.

FIG. 2 is a schematic enlarged cross-sectional view showing the configuration of the heating body 21. FIG. The heating element 2.1 in this example is heated in the transverse direction of the fixing film (
It is a horizontally elongated low heat capacity linear heating body whose longitudinal direction is a direction perpendicular to the running direction of the fixing film 24.

52 is a heat-resistant and electrically insulating thin heater substrate made of alumina or the like.

Reference numeral 28 denotes a linear or narrow strip-shaped thin film of silver palladium, Ta2N, Rub2, nichrome, etc., formed by a printing method or the like along the length of the lower surface of the substrate 52 (the surface facing the fixing film 23). It is a heating layer (resistance heating element).

Reference numerals 50 and 50 are electrically conductive electrodes (for example, gold electrodes) for the heat generating layer 28, which are also formed on the lower surface of the substrate 52. The heat generating layer 28 receives pulsed current through the electrodes 50, and generates heat by being energized in a pulsed manner.

Reference numeral 51 denotes a thin sliding protective layer made of Ta205, heat-resistant glass, etc., which is formed to completely cover the lower surface of the substrate 52 on which the heat generating layer 28 and electrodes 50 are provided. The outer surface of this protective layer 51 is smooth, and the leading and trailing edges in the direction of travel of the fixing film are rounded (chamfered) to enable smooth sliding movement with the fixing film.

Reference numeral 55 designates a temperature sensing element such as a thermistor having a small heat capacity or a temperature measuring resistor such as a PT film, which is provided on the upper surface side of the substrate 52.

This temperature sensing element 55 is disposed close to the heat generating layer 28 on the lower surface side of the substrate.

The above substrate structure (52, 28, 50, 55) is then used as a heater assembly through a heat insulating layer 53 made of a material with low thermal conductivity, heat resistance, and electrical insulation, such as Bakelite. The heating element 21 is attached to a rigid support 54. A surface area on the lower surface of the heating body 21 that substantially corresponds to the width of the heat generating layer 28 is a heating portion H.

(3) Operation After setting the original N4G on the original platen 1, setting the number of images to be formed, specifying the size of the sheet P to be used, and specifying the magnification, the image forming start switch is pressed. The feeding of the sheet P in the cassette S is started by the feed roller 6, and the feeding of the sheet P is detected by the sensor PH1. Also, image formation on the three surfaces of the photosensitive drum is started.

The fixing device 20 operates when a predetermined timer period elapses from the time when the sensor PH1 detects paper feeding, that is, when the sheet P fed from the cassette S is transferred to the registration roller pair 9, the transfer section 8, and the guide 1.
0 and the tip reaches a position near the pressure contact portion between the heating body 21 and the pressure roller 22. At the point in time when the time required has elapsed, the drive system of the fixing device starts rotating the winding shaft 27 and the pressure roller 22. A winding drive state is entered in which the fixing film 23 travels from the delivery shaft 24 side to the winding shaft 27 side at the same speed as the conveyance speed of the sheet P. Further, the heating body 21 is energized at necessary timings when the leading and trailing ends of the conveyance sheet P are detected by the sensor 29 and the lever 25. At this time, the supply of electricity to the heating body may be controlled by detecting the position of the sheet using a paper feed sensor of the image forming apparatus or the like.

Unfixed toner image Ta transported to fixing device 20
The upper surface of the sheet supporting the fixing film 23 is in close contact with the lower surface of the running fixing film 23, and the heating body 21 and the pressure roller 22 are mutually overlapped together with the fixing film 23 without causing surface misalignment or wrinkles. It passes through the pressure contact part (fixing nip part) while being subjected to a squeezing force.

This process of passing through the mutual pressure bonding part is a heating process, and the heat of the heating part H is transmitted to the sheet P side via the fixing film 23, so that the toner image is heated and softened and melted as described in (1)-70 of the above (effect). or is done.

As mentioned above, the heating process in this embodiment is as follows:
A linear heat generating layer 28 with low heat capacity is provided in the heat generating layer 28.
This is done by a heating element 21 configured to apply electricity in a pulsed manner to generate heat. That is, the toner image Ta on the sheet P conveyed between the fixing film 23 and the pressure roller 22 in the fixing nip portion of the fixing device is transferred along with the fixing film 23, which is conveyed without deviation according to the conveyance speed of the sheet P. , is sequentially heated in the heating section H determined according to the width of the heat generating layer 28 of the heating body 21, and becomes a softened/fused image Tb.

The sheet portion that has passed through the mutual pressure contact between the heating body 21 and the pressure roller 22 is spread between the heating body 21 and the upper separation roller 26 and travels forward until it reaches the position of the separation rollers 26 and 33. The fixing film continues to be conveyed while remaining in close contact with the fixing film portion. The guide plate 32 functions to support the back surface of the sheet P and maintain close contact with the fixing film 22.

Instead of this guide plate 32, a rotary guide belt is hung around the pressure roller 22 and the lower separation roller 33, and this belt supports the back side of the sheet P to maintain close contact with the fixing film 23. It is also possible to do so.

This conveyance process is referred to as a cooling process, and as described in item (1) (1) of (Operation) above, the heat of the softened and melted toner Tb is radiated, and the toner is cooled and solidified Tc.

When the fixing film 23 reaches the position of the upper separation roller pair 26, the traveling direction of the fixing film 23 is turned in a direction away from the surface of the sheet P along the surface of the upper separation roller 26 having a large curvature, and the fixing film 23 and the sheet P are separated from each other. are separated from each other (minute M) and are discharged to the paper discharge tray 11. By the time of separation, the toner has sufficiently cooled and solidified, and as described in (1) item 10 of the above (effect), the adhesion and adhesion of the toner to the sheet P is sufficiently large, and the toner has a sufficiently strong adhesion and adhesion force to the fixing film 23. Since it is in an extremely small state, the fixing film 23 and the sheet P can be separated easily and sequentially without substantially generating toner offset with respect to the fixing film 23.

The winding drive of the fixing film 23 of the fixing device 20 is stopped when the sheet P finishes passing through the fixing device 20 and its trailing edge is detected by the sheet discharge detection sensor PH2.

In the present embodiment, the fixing film 23 is sequentially wound from the feed shaft 24 side to the winding shaft 27 side at the same speed as the transport speed of the sheet P every time the sheet P is fixed as described above. and used.

The fixing film winding forward drive control starts driving when a predetermined first timer time elapses from the time when paper feed is detected by the paper feed detection sensor PH1, and stops the drive when a predetermined second timer time elapses. During this time, the fixing process for the sheet P is executed, and the discharge detection sensor PH
It is also possible to have a configuration that does not use 2.

Further, it is also possible to adopt a configuration in which the drive is controlled by the leading and trailing end detection signals of the seat P from the sensor 29 and the lever 25.

In this embodiment, the linear heat generating layer 28 of the heating element 21 is instantaneously heated to a high enough temperature relative to the melting point (or fixable temperature) of the toner by pulsed energization. Heat transfer to the pressure roller 22 is small. Also, during fixing, the fixing film, toner image, and sheet are interposed between the heating element 21 and the pressure roller 22, and the heat generation time is short, resulting in a rapid temperature gradient, so the pressure roller 22 does not rise in temperature. Even if continuous image formation is carried out to the extent necessary for practical purposes, the temperature is maintained below the melting point of the toner. In the device of this embodiment having such a configuration,
The toner image made of heat-fusible toner on the sheet P is first heated and melted by the heating body 21 via the fixing film 23, and in particular, its surface layer portion is completely softened and melted. At this time, the heating body, the fixing film,
The toner image and sheet are well adhered and heat is transferred efficiently. As a result, 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 time for energization and heat generation.

A small heating element is sufficient, so its heat capacity is small, and there is no need to heat up the heating element in advance, so power consumption during non-image formation can be reduced, and temperature rise inside the machine can also be prevented. .

In this embodiment, since the temperature of the pressure roller 22 is maintained lower than the melting point of the toner as described above, it is possible to promote heat dissipation of the toner image in the cooling process following the toner image heating process. . Therefore, the time required for cooling can be shortened, and the device can be downsized.

(4) Power supply to the heating element 21 FIG. 4 shows the temperature of the heating part H when the heat generating layer 28 is energized in a pulsed manner in the fixing device of this embodiment, and the temperature of the thermistor 55.
It is a graph showing the detected temperature. The temperature of the heating section H is based on a value measured without contact with an infrared radiation thermometer, and the temperature detected by the thermistor is based on a value obtained by converting the output power of the thermistor into temperature. The pulse period when this graph was obtained was approximately 10 msec, and the energization time was approximately 2 m.
sec. The temperature of the heating section H rises rapidly when energized, and then rapidly falls when it is stopped. In this embodiment, the non-energized time is sufficiently longer than the energized time, and the presence of the heat insulating layer 53 makes it difficult to maintain the minimum value of the pulse waveform. At the time when the heat generating layer 28, the insulating substrate 52, and the thermistor 55 are taken, the temperature becomes approximately the same. The thermistor used in this example cannot follow a pulse-like temperature change with a short cycle of 10 msec, and indicates a substantially minimum value of the pulse waveform. Therefore, the envelope of the minimum value of the surface temperature of the heating section H substantially matches the temperature curve detected by the thermistor 55.

FIG. 5 is an explanatory diagram showing a mechanism for supplying power to the heat generating layer 28 in the heating body 21 of this embodiment. 6o is a control circuit including a microcomputer, and a power supply voltage monitor circuit 6
The power supply 61 is controlled according to the detected voltage of 2 and the temperature detected by the thermistor 55, and the power supplied to the heat generating layer 28 is controlled by changing the pulse width of the power supply to the heat generating layer 28.

The reason why the above power control is performed in this embodiment is as follows. In this embodiment, a heat insulating layer 53 is provided to prevent heat radiation from the heat generating layer 28 to the support body 54. Its purpose is
There are two points: (1) saving energy by eliminating wasteful heat radiation and increasing energy efficiency; and (2) reducing temperature rise inside the machine due to heat radiation from the support body 54.

However, if the heat generation layer 28 is simply insulated without controlling the power supplied to the heat generation layer 28, the amount of heat generated will significantly exceed the amount of heat radiation, and the temperature of the heat generation layer 28 and the heating section H will rise abnormally. The fixing film may be damaged by heat. Therefore, in order to prevent abnormal temperature rise of the heating section H when the heat insulating layer 53 is provided, it is effective to control the power supplied to the heat generating layer.

Next, a method of power control in this embodiment will be described.

■When the power supply voltage is not monitored In the pulse heating fixing method of this embodiment, as mentioned above, the toner is heated only for a short time on the order of msec, so the temperature of the heating section H rather than the toner heating time is related to the fixing performance. The temperature of the toner layer increases according to the maximum temperature reached by the heating section H. Then, the temperature of the heating section H when the toner is softened to a state sufficient for fixing is THo.
In this case, if the power supply to the heat generating layer 28 is controlled so that the maximum temperature of the heating section H is maintained at approximately THo during the fixing process, sufficient fixing performance can be obtained without wasting power. can.

The temperature of the heating section H is the reference temperature T. Assume that when power is supplied to the heating layer at a constant voltage V for a time to, the temperature of the heating section H reaches the fixing temperature THo (see FIG. 6). At this time THO. "Between ro.to, -BtO THO= To + A (1 e)..."
There is a relationship called equation (1). Here, A and B are heat generating layers 2
This is a constant determined by the power supply conditions to 8 and the heat radiation path from heating section H.

From this formula we get: Therefore T. o, A, and B are determined in advance through experiments, and T. By measuring , τ8 can be found.

In this embodiment, as described above, when the heating layer 28 is energized in a pulsed manner at a sufficiently small duty ratio, when the heating part H that generates heat in a pulsed manner shows the minimum temperature, that is, when the next pulsed energization Just before the start, the temperature of the heating section H becomes approximately equal to the temperature detected by the thermistor 55. Therefore, using the temperature detected by the thermistor 55 at this time, the control circuit 60 in FIG. 5 calculates the next energization time according to equation (2), and the power supply 61 supplies power to the heat generating layer 28 for the calculated time.

FIG. 7 is a graph showing temporal changes in the temperature of the heating section H during the fixing operation in this embodiment, together with a timing diagram of power supply to the heat generating layer 28.

In this embodiment, the power supply voltage V to the heat generating layer 28 is constant,
The period τ of the energization pulse is also constant. The temperature of heating part H is T
. At time t. If the fixing operation is started at , the temperature of the heating section H is temperature T. It is uniquely determined from. Pulse width τ0
After the fixing temperature THo is reached by energization, τ. T during a non-powering time (τ - τ.) that is sufficiently longer than T. higher temperature T
, decreases to . Next, time t. The second energization is performed at time t1, which is a pulse period τ after τ. By applying a pulse width τ1, which is shorter than the temperature T1, to the heating layer, the temperature of the heating section H rises again to THo, and then decreases when the power supply is stopped.

Thereafter, in the same manner, the temperature of the thermistor 55 is read at every pulse period after the start of energization, and based on the detected temperature, power is supplied to the heat generating layer 28 with a pulse width determined by equation (2), so that the maximum temperature of the heating section H is set to the fixing temperature. It can be maintained at THo.

■When monitoring the power supply voltage According to experiments by the inventors, if V is the power supply voltage to the heating layer in general at the constant A shown in equation (1), then A=kV2...・・・・・・
...There was a relationship called equation (3). Here, k is a constant related to the configuration of the heating body 21 that is not dependent on voltage. From this fact, it is not necessary to find the constant A experimentally for all power supply voltages, and using the constant A1 when the power supply voltage is 1, v2 A=A,,2 ..・・・・・・・・・
...obtained from equation (4). In the present inventor, the power supply is turned on without giving the value of the constant A for all power supply voltages.
It is determined using equation (4) from the detected voltage of the power supply voltage monitor circuit 62 at the time. Further, since the constant A is given by equation (3), the constant A is greatly influenced by voltage fluctuations. For example, if the power supply voltage changes by 10%, the value of constant A changes by about 20%. Therefore, if the power supply voltage fluctuates by 10%, the control temperature value TIIo
This will result in an error of 20%.

According to the present invention, when calculating the next energization time in the control circuit 60 of FIG. 5 using the temperature detected by the thermistor 55,
Using the detected voltage of the power supply voltage monitor circuit 62, A is determined according to equation (4), the energization time is calculated according to equation (2), and highly accurate control is achieved by supplying power to the heat generating layer 28 by the power source 61 for the calculated time. It can be carried out.

Further, even in the case where the heating element is selected according to the power supply voltage, the control circuit 60 converts the period of pulse energization in accordance with the detected voltage of the power supply voltage monitor 62.
It can be done with.

FIG. 8 shows a flowchart in the control circuit 60.

Turn on the power in step ■. After that, first, the input voltage is detected, and it is determined whether the cycle is changed by changing the surface area of the heat generating layer (step 2). The cycle is determined in steps ■ and ■ according to the determination in step ■. For example 100
When the voltage is V, the time is 20 msec in step ■, and when the voltage is 200V, the time is 40 msec in step ■. Next, in step (2), it is determined whether fixing has started.

When entering the fixing control, first detect the human voltage in step ■,
Using that value, determine the value of constant A using equation (4): A=A, (V2/V, 2). Here, V,,A, are the values of the reference human power voltage V and constant A (step 2). Next, in step (2), the temperature is detected by the temperature detection element, and in step (2), the energization time is calculated using A determined in step (2) and the temperature detected in step (2). Same as step ■ A pulse corresponding to the results of ■ and ■ is output in step [phase]. Then, in step (2), it is determined whether the fixing has been completed, and if it continues, the process returns to step (2) at the cycle determined in steps (2) and (2).

(5) In addition, the fixing film 23 is sequentially wound and run from the delivery shaft 24 side to the take-up shaft 27 side every time the fixing process is performed, as in the embodiment device, and when the entire length has been wound and used, a new fixing film is created. In addition to using a rewinding system that replaces the film 23, since toner offset to the surface of the fixing film 23 does not substantially occur, if the thermal deformation or deterioration of the film is small, it can be wound onto the winding shaft 27 side. It is also possible to use the fixed film 23 repeatedly several times by controlling the fixed film 23 to be rewound to the delivery shaft 24 side in a timely manner, or by reversing and exchanging the winding side and the delivery side. formula).

Further, it is also possible to adopt a configuration in which the belt is of an endless belt type and rotated to perform the fixing process.

In the roll-up and replaceable type, the fixing film 23 can be made of, for example, a thin and inexpensive polyester base material that has been subjected to heat-resistant treatment, and it can be made thin regardless of durability, and power consumption can be reduced. can. When such a method is adopted, the fixing film remaining amount detection arm 30 and sensor 30a detect the remaining amount of fixing film on the feed shaft 24 side, and when the film is near the end, a warning is displayed or a warning is given to the user. It is better to use a sound to prompt the replacement of the fixing film. When replacing the fixing film 23, the heating body 21, pressure roller 22, separation roller pair 26 and 3
It is desirable to be able to open and close the fixing device 20 around the rotating shaft 31, as shown in the example in FIG.

In the unwinding and reversing type, the fixing film is, for example, a 25 μm thick polyimide resin film as a base material with excellent heat resistance and mechanical strength, and a release layer made of a fluororesin or the like with high mold release properties is applied to the surface of the film. It is possible to use a composite layer film provided with the following, and it is preferable that the contact pressure between the heating body 21 and the pressure roller 22 is released during rewinding and reverse running.

When using multiple times, such as a rewinding type or an endless belt type, provide a felt pad for cleaning the film surface, impregnate it with a slight release agent, such as silicone oil, and bring the pad into contact with the film surface. The film surface may be cleaned and the mold releasability may be further improved by cleaning the film surface. When the fixing film is treated with an insulating fluororesin, static electricity that disturbs the toner image is likely to be generated on the film, so it is a good idea to remove the static electricity using a grounded static eliminator brush. The film may be charged within a range that does not disturb the toner image by applying a bias voltage to the brush without being grounded. Furthermore, conductive powder is added to the fluororesin. One measure is to add non-fibers, such as carbon black, to prevent the above-mentioned image disturbance caused by static electricity. Furthermore, the charge removal and conductivity of the pressure roller can be carried out by the same means. Also,
An antistatic agent or the like may be applied or added.

In either method, the fixing film 23 is configured as a cartridge that can be freely attached to and removed from a predetermined portion of the fixing device 20, thereby facilitating the work of replacing the fixing film.

As long as the viscosity of the toner when it is heated and melted is sufficiently high, the toner temperature when separating the toner from the fixing film may be equal to or higher than the toner melting point. In that case, in the apparatus shown in FIG.
The fixing film and the toner image may be separated from each other when the transfer paper P passes through the pressure contact portion, as shown in FIG. 10. At this time, the temperature of the pressure roller 22 does not need to be kept below the toner melting point. FIG. 11 shows an example in which the fixing film is an endless belt.

The above-described embodiments are transfer-type electronic copying devices, but the image forming process and means include a direct type in which a toner image is directly formed and carried on electrofax paper, electrostatic recording paper, etc., and a magnetic recording image forming type. Copying machines, laser beam printers, facsimile machines, microfilm readers, display devices, and recording systems that form an image using heat-fusible toner on a recording material using other appropriate image-forming processes and means and fix it by heating. The invention can be effectively applied as an image heat fixing device in various image forming apparatuses such as machines.

(Effects of the Invention) As described above, the invention of the tree makes it possible to reduce the heat capacity of the heating body, which is the heating means, without causing fixing failure or offset in a toner image heat fixing type image forming apparatus. As a result, it is possible to realize an image forming apparatus with low standby time, low power consumption, and low internal temperature rise. Furthermore, the thin fixing film can be used repeatedly over a long period of time without any problem of wrinkles.

Further, the present invention relates to a heating element, and a power supply section for the heating element includes a detection means for detecting a power supply voltage for supplying power to the heating element, a temperature detection means arranged close to the heating element, and generates heat according to the voltage and temperature detected by both means. By providing means for controlling the application time for supplying electric power to the body, it is possible to control the maximum value of the surface temperature of the heating element to a predetermined temperature regardless of changes in the applied voltage, and the voltage detecting means By providing means for determining the difference between the heat generating parts according to the voltage detected by the controller and controlling the period of energization, it is possible to stabilize the power supply to the heat generating parts. As a result, more accurate temperature management control can be performed, and significant effects can be achieved in energy saving, prevention of temperature rise inside the machine, and prevention of damage (heat loss) to the heating element and fixing film. In addition, the control device can be standardized regardless of the manual voltage.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of the fixing device, FIG. 2 is a schematic enlarged cross-sectional view showing the configuration of a heating body, and FIG. 3 is a schematic configuration diagram of an image forming apparatus incorporating the fixing device. Figure 4 is a diagram of changes over time in the surface temperature of the heating section and the temperature detected by the temperature detection element, Figure 5 is a block diagram of the energization system, and Figure 6 is a graph of
Figure 7 is a diagram of the temperature change over time in the heating part during pulsed power supply, Figure 7 is a diagram of the temperature change in the heating part when the pulse width is changed, Figure 8 is a control flow diagram of the control circuit, and Figure 9 is a diagram of the fixing device being opened. FIG. 10 is a schematic diagram of a fixing device in which the fixing film and recording material are separated immediately after the heating process, and FIG.
The figure is a schematic diagram of a fixing device in which the fixing film is of an endless belt type. 3 is a photosensitive drum, 8 is a transfer discharger, P is a transfer material sheet (
(recording material), 20 is the overall code of the fixing device, 21 is the heating element,
22 is a pressure roller, 23 is a fixing film, 23 is a take-up shaft (or drive roller), and 24 is a delivery shaft (or driven roller). 8811

Claims (1)

[Claims] (1) A fixing film, a traveling drive means for the fixing film, a heating body disposed on one side of the fixing film with the fixing film inside, and a heating body disposed opposite to the heating body on the other side of the fixing film. The fixing film has a pressure member that brings the image-bearing surface of the recording material on which the image is to be fixed into close contact with the body through the fixing film, and the fixing film has a pressure member that presses the fixing film and the pressure member at least when fixing the image. The traveling fixing film and the introduced recording material are formed in close contact with each other by pressure contact between the heating body and the pressure member by traveling in the forward direction at the same speed as the recording material to be image-fixed, which is conveyed and introduced between them. The image carrying surface of the recording material is heated through the fixing film by the heat of the heating section on the heating body side corresponding to the fixing nip, and the image is thermally fixed. The heating part of the heating element is heated by a heating element provided in the heating element, and a power supply part for the heating element is arranged close to the heating element and a detection means for a power supply voltage that supplies power to the heating element. It has a temperature detection means, a means for controlling the application time for supplying power to the heating element according to the voltage and temperature detected by the voltage detection means, and a means for controlling the application period according to the voltage detected by the voltage detection means. An image heat fixing device characterized by: