JPH06100873B2 - 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 heated to its melting point to melt, and after melting, the toner is cooled to have a relatively high viscosity and the heating element web is weakened in a state in which the toner adhesion tendency is weakened. It is a method of fixing without causing an offset by going through the process of peeling from.

(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 traveling drive means for the fixing film, a heating body disposed on one side of the fixing film, and a heating body disposed on the other side of the fixing film with the fixing film interposed therebetween. A pressure member for closely contacting the surface of the recording material on which the unfixed toner image is carried, and 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 heating and fixing means for introducing the recording material between the running-dried fixing film and the pressure member to heat and fix the unfixed toner image on the surface of the recording material. The heating body of A low-heat-capacity linear heating element having a linear or band-shaped energization heating element which has a longitudinal direction in the transverse direction of the fixing film and is energized in the longitudinal direction to generate heat, and an effective length corresponding to the recording material passage width portion of the energization heating element. The heating element surplus portion outside the range has a heating element portion within the effective length range and a series of energization bottleneck portions having a cross-sectional area smaller than the cross-sectional area of the heating element portion in series. An image forming apparatus.

(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 be fixed. There is a case where the viscosity is reduced to such an extent. Therefore, even if it is expressed as melting when 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.

In this way, 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 surface of the running fixing film, and the toner image is heated and melted by the heating body through the fixing film. At the very least, since the recording material and the fixing film are separated from each other after the toner image is cooled and fixed, the toner offset does not occur on the fixing film and the heating element having a small heat capacity is used, and the power is supplied to the heating element. It becomes possible to carry out with a simple structure, and by maintaining a heating body of a sufficiently high temperature with respect to the temperature (melting point or softening point) at which the toner should be heated for fixing, toner image efficiency can be improved. It is possible to heat the unit effectively, and it is possible to perform good 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 used in the present invention is a low heat capacity linear heating element having the linear or strip-shaped energization heating element as described above, the heating rate of the heating element is extremely high. Although it has the advantages described in the item 1), on the other hand, in the case where the heating element overheats due to the control microcomputer going out of control, the conventional heating roll type or the like is used. In the case of the heat fixing device, it is possible to take a measure to cut off the energization by adding the temperature fuse means and the thermoswitch means, but the low heat capacity linear heating element used in the present invention has a high temperature rising rate. Even if temperature fuse means and thermoswitch means are added, overheating occurs before the power is cut off due to their operation, reaching the ignition temperature, causing heat loss to the fixing film, recording material, pressure member, etc. Occurs It is envisioned that or.

Therefore, according to the present invention, as described above, the heating element surplus portion outside the effective length range corresponding to the recording material passage width portion of the energization heating element is connected to the heating element portion within the effective length range in series. The configuration is such that a current carrying bottleneck portion having a cross-sectional area smaller than the cross-sectional area is provided.

That is, when the energization heating element becomes over-energized due to power supply abnormality or temperature control abnormality, the energization bottleneck portion provided in the extra length portion is overheated before the effective length range part of the energization heating element reaches the overheating state and the fusing temperature is exceeded. Then, the energization bottleneck portion is melted and the electricity to the heating element is cut off. Therefore, it is possible to strictly prevent overheating of the entire length of the energization heating element to reach the ignition temperature, which causes heat loss to the fixing film, recording material, pressure member, and the like, and smoking.

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

(1) Overall schematic configuration of device (FIG. 1) In FIG. 1, 100 is a device casing, 1 is a top plate 1 of the casing.
This is a reciprocating type document placing table made of a transparent plate member such as a glass plate disposed on 00a, and reciprocates at a predetermined speed on the machine casing 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 housing upper surface 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 process of reciprocating to the right a of the document placing table 1. , Slit L opening the light L of the lamp 7 in the course of its 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 a clockwise direction indicated by an arrow b at a predetermined peripheral speed around the central support shaft 3a. A uniform charging process of positive or negative polarity is performed by the charger 4, and the uniformly charged surface is subjected to imagewise exposure (slit exposure) of the original image, so that the surface of the photosensitive drum 3 is imagewise exposed. 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 portion 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 counter-pressure contact with an urging means (not shown) with a total pressure of 4 to 7 kg, and rotates counterclockwise in the forward direction of the transfer material sheet P conveyance direction.

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 capacity linear heating element 20 as a heating element has, for example, a thickness of 1.
Along the length, an electrical resistance material such as Ta ₂ N is formed along the length of the lower surface of the alumina substrate 21 having a width of 0 mm, a width of 10 mm, and a length of 240 mm.
It is provided with a linear or band-shaped heating element 22 coated on 1.0 mm. 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 DC100V cycle
With a pulsed waveform of 20 msec, the temperature is controlled by the temperature sensing element 23, and a pulse corresponding to the amount of energy released is provided in the energization control circuit configuration, and the pulse width is approximately 0.5 to 5 msec. The heating element 22 is controlled within a range, and the temperature of the heating element 22 instantly rises to around 200 to 300 ° C. each time 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. The period is controlled only to the required period in which the sheet P is passing through the fixing device 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 between the fixing sheet 24 and the pressure roller 22 at the pressure contact portion N with the sheet P, the lower surface of the fixing film 24 is surface-moved in the same direction at the same speed as the conveyance speed of the sheet P. The heating body 20 and the pressure roller in an overlapping state with the fixing film 24 without causing a surface shift or wrinkling due to close contact.
It passes between the mutual pressure contact portion N with 28 while receiving a clamping pressure.

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 (separated) from each other, 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. Since it is in the state, the fixing film 24 and the sheet P
The separation of the toners is easily and sequentially performed without substantially causing toner offset to the fixing film 24.

In the present embodiment, 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 by energization, so that preheating of the heating element is unnecessary, There is little heat transfer to the pressure roller 28 during non-fixing. 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) Heater 20 FIG. 4 (a) is a bottom view of the heater 20, that is, the fixing film 24.
FIG. 7 is a plan view of the sliding surface side with respect to FIG.

Reference numeral 21 denotes a heat-resistant substrate, which is a horizontally long member having a longitudinal direction in the transverse direction of the fixing film (direction perpendicular to the running direction of the fixing film). In addition to ceramics such as alumina described above, heat-resistant glass, heat-resistant resin such as PI / PPS, or the like can be used as the material. L is a maximum passage width area of the recording material which can be passed through the apparatus, and the length dimension of the substrate 21 is longer than this width area L, and both end portions thereof are outside the width area L respectively. It is projected as a long part l·l.

Reference numeral 22 is a heating element provided in a linear or strip shape along the length in a substantially central portion of the outer surface of the substrate 21. W is the width dimension of this heating element. In addition to Ta ₂ N etc. in the above example, Nichrome Ru
It is also possible to use a resistor such as O ₂ · Ag / Pd.

22a and 22a are electrodes for energizing the heating element 22, which are provided on the outer surfaces of the extra length portions 1 and 1 on both ends of the substrate 21, respectively.
It is a conductive material such as a metal such as Au / Cu or 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. In this example, one end side of the heat generating element 22 is electrically connected to the electrode 22a on that side through an energization bottleneck portion 22b. The energization bottleneck portion 22b is made to exist in the extra length portion 1 area of the substrate 21, and the length portion of the heating element 22 corresponding to the maximum passage width area L of the recording material is set as the effective length range of the heating element. At this time, the cross-sectional area (FIG. 4 (C)) is smaller than the cross-sectional area (FIG. 4 (b)) of the heating element in this range. In this example, the energization bottleneck portion 22b and the heating element of the effective length range portion L are formed in series, and the thickness d is the same as that of the heating element of the effective length range portion, and the width is the effective length. By setting the width W ₁ smaller than the width W of the heating element in the range portion, a small cross-sectional area portion functioning as a fusing portion is formed.

In general, when the same electric power is applied to the resistor, the smaller the cross-sectional area, the higher the temperature rising rate at the time of energization, and the temperature rising rate can be controlled by defining the cross-sectional area.

When fixing is performed, the electrodes 22a ・ 2 on both ends of the heating element 22
2a and the current bottleneck portion 22b are energized to heat the heating element 22 over the entire length, and the current bottleneck portion 22 is also heated.
Increase b. In this case, the conduction bottleneck portion 22b is
The temperature rises more. During normal operation, the heating element 22 is finely turned on and off in order to adjust the heating element to a predetermined temperature. Therefore, the heating element 22 and energization bottleneck part
22b is kept below a certain constant temperature (which is lower than the melting temperature of the resistor), and the fixing operation is performed without delay.

If abnormal power supply such as continuous power supply is performed due to power supply abnormality or temperature control abnormality, the temperature of the heating element 22 and the energization bottleneck portion 22b rises at once. At this time, the temperature of the effective length range portion of the heating element 22 reaches the ignition and smoke temperatures of the fixing film 24, the pressure roller 27, the transfer material P, etc. by setting the line width ratio of the heating element 22 and the conduction bottleneck portion 22b. Before that, it is possible to make the energization bottleneck portion 22b reach the fusing temperature and fuse it. Energization bottleneck part 22b
If fusing occurs, the power supply to the heating element 22 is cut off, so there is no danger of smoking or ignition.

Further, since the energization bottleneck portion 22b serving as the fusing unit at the time of abnormality is provided outside the paper passing region L, the temperature distribution in the paper passing region is kept constant, a good fixed image without unevenness can be obtained, and at the same time as the fusing unit. Since the vicinity of the energization bottleneck part can be composed only of flame-retardant / heat-resistant material, there is an effect that it is possible to prevent smoking / ignition even at the time of temperature rise and melting due to continuous energization.

Specifically, substrate 21: length 270 mm, width 10 mm, thickness 1 mm alumina heating element 22: length 220 mm, width 1.5 mm, thickness 20 μm Ag / Pd resistor energization bottleneck 22b: length 5 mm, width 300 μm Then, a heating body 20 is manufactured with a specification of Ag / Pd having a thickness of 20 μm (the heating body 22 and the conduction bottleneck portion 22b are simultaneously formed by screen printing) and incorporated as a heating body of the fixing device 11 of the image forming apparatus. , A4 (width 210mm) under temperature control control by energization control so that the surface of the heating body becomes 200 ° C
After passing 30,000 sheets of the transfer material sheet P, the image fixing process was executed without any problem.

On the other hand, when the temperature of the heating element 20 is cut off and the heating element 22 is continuously energized, the energization bottleneck portion 22b melts down when the temperature of the sheet passing portion rises to about 320 ° C. before the ignition temperature reaches 430 ° C. 22 was cut off without heating.

In order to help disconnection due to melting of the energization bottleneck portion 22b, the energization bottleneck portion 22b is formed on a substrate of a heat insulating material such as heat resistant glass,
It is also possible to cause a crack in the substrate due to thermal strain due to an abnormal temperature rise of the energization bottleneck portion 22b, and to reliably disconnect the energization bottleneck portion 22b melted by the cracking due to the abnormal temperature rise.

5 (a), (b), and (c), the current-carrying bottleneck portion 22b is formed in series with the same material as the heating element of the effective length range portion L,
The width W is set to be the same as that of the heating element in the effective length range, and the thickness d ₁ is set to be smaller than the thickness d of the heating element in the effective length range to form a small cross-sectional area portion functioning as a fusing part. is there.

(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 winding exchange type, the thickness can be reduced regardless of the durability of the fixing film, and the power consumption can be reduced. 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 polyimide resin film having a thickness of 25 μm is used as a base material having excellent heat resistance and mechanical strength, and a release layer made of fluororesin or the like having high release properties is provided on the surface of the polyimide resin film. At the time of rewinding and reverse traveling, 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, it is also possible to remove the static electricity with a grounded static elimination brush. A bias voltage may be applied to the brush without being grounded 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 an endless belt type, a rewinding exchange type, or a rewinding repetitive use type, the fixing film can be detachably attached to a predetermined 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 heat roller type, and the heating element 22 has a thick film resistor or a PTC characteristic. It may be a ceramic chip array or the like, and the energization control may not be given in a pulsed manner, but may be a normal energization.

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 melted at a sufficiently high temperature in the heating step (fixing nip portion) as shown in FIG. 6, 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.

In addition, if an abnormal energization situation occurs such that the heating element of the heating element overheats due to power supply abnormality or temperature control abnormality and causes ignition or smoke, the energization provided as described above before the heating element overheats Since the bottleneck part quickly melts and the power is cut off instantly, it is strictly prevented that the heating element actually overheats and causes a heat loss trouble such as ignition or smoke generation. It has a simple structure without any additional means, is much more reliable than the case using them, and is extremely effective in terms of safety measures.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view showing a schematic configuration of an apparatus of one embodiment, FIG. 2 is an enlarged view of a fixing device portion, FIG. 3 is a schematic view of another configuration example of the fixing device, and FIG. The bottom view of the heating element, FIG. 2B and FIG. 2C are respectively bb line and c- in FIG.
c line sectional view, FIG. 5 (a) is a bottom view of a heating element having another configuration, and FIGS. 5 (b) and (c) are respectively bb lines in FIG. 5 (a).
FIG. 6 is a schematic view of another configuration example of the fixing device, taken along the line cc. 3 is a drum type rotary photosensitive member, 11 is a fixing device, 24 is a fixing film, 20 is a heating member, 28 is a pressure roller, and P is a transfer material sheet.

Front page continuation (72) Inventor Masahide Kinoshita 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroyuki Adachi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP 59-157678 (JP, A) JP 59-68766 (JP, A) JP 61-109083 (JP, A) JP 61-122666 (JP, A) Kaihei 2-134667 (JP, A) JP-A-1-187582 (JP, A) JP-A-1-263677 (JP, A) JP-A-2-143279 (JP, A) Actual Kai Sho-54-30846 ( JP, U) Actual Open Sho 58-190659 (JP, U) Actual Open Sho 63-120267 (JP, U)

Claims (1)

[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 disposed on one side of the fixing film with the fixing film in the middle, and an unfixed toner image bearing of a recording material on the other side of the heating body via the fixing film. And a fixing film that is driven to run in the same direction at the same speed as the conveying speed of the recording material carrying the unfixed toner image conveyed from the image forming means side. A toner image heating and fixing means for introducing the recording material between the pressure member and the toner image to heat and fix the unfixed toner image on the surface of the recording material. With the longitudinal A low-heat-capacity linear heating element having a linear or strip-shaped energization heating element that is energized in the longitudinal direction to generate heat, and a heating element outside the effective length range corresponding to the recording material passage width portion of the energization heating element. The image forming apparatus characterized in that the long portion has a heating element portion within the effective length range and a series of energization bottleneck portions having a cross-sectional area smaller than the cross-sectional area of the heating element portion in series.