JPH0823722B2 - Fixing device - Google Patents

Description

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.
The present invention relates to a fixing device that fixes an unfixed image on a recording material.

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 a fixing device that performs heat fixing processing as a permanently fixed image.

(Prior Art) Conventionally, a fixing device used in this type of apparatus has an undetermined heating roller maintained at a predetermined temperature and a pressing roller having an elastic layer and pressing against the heating roller. A roller fixing method in which a recording material on which a deposited toner image is formed is heated while being nipped and conveyed is often used.

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

(Problems to be Solved by the Invention) However, the conventional thermal roll fixing method as described above,
The belt fixing method has the following problems.

Thermal roll fixing method It takes a considerable time to rise to a predetermined temperature, during which 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 high heat-resistant roller bearing 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 is wrapped around the roller due to the constant temperature and the curvature of the roller, so that a jam problem of the recording material is easily observed.

Belt fixing method This method also has the same problems as those of the above-described heat roller fixing method, such as the wait time and large power consumption.

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 a fixing and forming apparatus which has a small temperature rise in the machine and has other remarkable features.

(Means for Solving the Problems) The present invention provides a heating device including a linear or strip-shaped heating resistor that generates heat when energized, and an energizing electrode provided at an end portion in the longitudinal direction of the heating resistor. A body and a film that slides on the heating body and moves in a direction orthogonal to the longitudinal direction of the heating resistor, and an unfixed image is formed on the recording material by heat from the heating body through the film. The fixing device is characterized in that the heating resistor has a smaller resistance value per unit length on the end side where the recording material does not pass in the longitudinal direction than on the central side where the recording material passes. .

(Operation) (1) The recording material to be fixed between the fixing film and the pressing member, which is driven in the same direction at the same speed as the recording material conveyance direction, is unfixed toner on the fixing film surface. While the surface on the image carrying side is in close contact with the fixing film and receives a pressing force on the mutual press contact portion (fixing nip portion) between the heating element and the pressing member, surface displacement occurs due to a speed difference therebetween, and wrinkles occur. It passes over the body without overlapping.

Heating Process In the process of passing through the mutual pressure contact portions, 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. In this case, the heating member, the fixing film, the toner image, and the recording material are satisfactorily pressed and closely contacted by the pressing member at the mutual pressure contact portion between the heating member and the pressing member, so that the toner is sufficiently heated by heating. It is softened and melted to obtain good fixability. In the present invention, since a low-heat-capacity fixed heating element is used to heat through a thin film, it is possible to reduce standby time, power consumption, and temperature rise in the machine.

On the other hand, the temperature rise of the recording material itself is practically small, and the waste of thermal energy is small. In other words, the recording material itself is not heated substantially, and only the toner is heated and softened and melted effectively, and the heat fixing of the toner image can be satisfactorily executed with low power.

Here, note the softening and melting of the toner described in the present invention. The temperature, which is conveniently expressed as the "melting point" of the toner, means the minimum temperature required for the toner to be fixed. In some cases. Therefore, even when the term “melting” is used for the sake of convenience for fixing, the viscosity may actually decrease such as softening. The present invention also includes such a case. Similarly, when the expression that the toner is cooled and fixed is used for convenience, depending on the toner, it may be more appropriate to increase the viscosity rather than to solidify. 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. By this cooling and solidification, the cohesive force of the toner becomes very large, and the toner behaves as a group. In addition, while the adhesive / fixing force on the recording material side increases, that on the fixing film side extremely decreases. When the toner is heated and softened and melted in the heating step, the toner is pressed by the pressing member, so that at least a part of the toner image permeates into the recording material surface layer, and the permeated portion is cooled and solidified. The adhesive effect of the solidified toner on the recording material side increases due to the anchor effect of the toner.

Separation (separation) step After the toner image is cooled and solidified by the above-mentioned 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 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 to the fixing film does not occur, and the heating element with 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 device effectively, and it is possible to perform sufficiently good fixing without defective fixing with a small amount of energy, and as a result, standby when using the device. During and power consumption, and further an effect of obtaining a smaller image forming apparatus temperature rise in the apparatus.

In the above separating step, the toner does not necessarily have to be cooled and solidified at the position where the fixing film and the recording material are separated. Of the three steps of heating, cooling and separation, if the toner is sufficiently melted at high temperature, the recording material is immediately separated from the fixing film surface as soon as the toner is sufficiently melted at high temperature in the heating step. The subsequent cooling step may be abolished and is within the scope of the present invention.

(2) Due to the following reasons (1) to (4), the heating element has a difference in heat radiation amount distribution in the longitudinal direction.

Heat is taken away by the heating film portion through which the fixing film, the pressure member surface, the recording material, etc. pass.

The heat in the vicinity of both ends of the heating body easily travels along the support bodies on both ends of the heating body and escapes.

The amount of heat dissipated in the heating element part where the temperature detection element, safety measure element, etc. are in contact with the back surface of the heater including the heating element is different from other parts.

The heat radiation amount distribution difference generated in the longitudinal direction of the heating element causes a greater distribution difference in the temperature distribution in the heating element longitudinal direction as the heating element has a lower heat capacity. Since the heat is not taken away from both end portions of the body, the temperature may be excessively raised, and the heating element may be damaged. Further, if there is a difference in temperature distribution in the longitudinal direction of the heating body due to the reasons described above, the fixing life will be non-uniform.

Regarding the low heat capacity linear heating element used in the present invention, as described above, the heating resistor has a smaller resistance value per unit length in the longitudinal direction on the end side where the recording material does not pass than on the central side where the recording material passes. Since it is configured, it is possible to prevent the damage of the heating element due to local excessive temperature rise at the heating element portion which corresponds to the both end portions of the heating element that does not contact the fixing film etc. Fixing film
The heating member portion through which the pressing member surface / recording material and the like passes can have a uniform heat generation temperature distribution along the length thereof to prevent non-uniform fixing property due to non-uniform distribution.

(Embodiment) The present embodiment is an electrophotographic copying apparatus of a reciprocating type, a rotating drum type and a transfer type on a document table.

(1) Overall Schematic Configuration of the Apparatus (FIG. 1) In FIG. 1, reference numeral 100 denotes an apparatus housing, and 1 denotes a reciprocating motion made of a transparent plate member such as a glass plate disposed on an upper plate 100a of the apparatus housing. It is a document mounting table of a mold, and is driven to reciprocate at a predetermined speed to the right side a and the left side a 'on the machine housing upper surface plate 100a in the drawing.

G is an original, which is placed on the upper surface of the original placing table 1 with the image side to be copied facing downward according to a predetermined placing reference;
The original pressure plate 1a is placed on top of it and pressed down to set it.

Reference numeral 100b denotes a slit opening serving as a document illuminating section which is opened on the surface of the machine top plate 100a with a direction perpendicular to the reciprocating direction of the document placing table 1 (direction perpendicular to the paper surface) as a longitudinal direction. The downward image surface of the document G placed and set on the document placing table 1 sequentially passes through the position of the slit opening 100b from the right side to the left side in the process of reciprocating to the right a of the document placing table 1. , Slit L the light L of the lamp in the process of passing through it
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. An original document image-exposed on the surface of the photosensitive drum 3 by being subjected to uniform charging processing of positive or negative polarity by the charger 4 and image-formed exposure (slit exposure) of the original image on the uniformly charged surface. An electrostatic latent image corresponding to the image is sequentially formed.

The electrostatic latent image is sequentially visualized by the developing device 5 with toner made of resin or the like that 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 arranged. To go.

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 transfer discharger 8 is attached to the surface of the fed sheet.
Thus, the toner images on the photosensitive drum 3 side are sequentially transferred.

The sheet to which the toner image has been transferred at the transfer portion is sequentially separated from the surface of the photosensitive drum 3 by separation means (not shown), and is guided to a fixing device 11 described later by a conveyance guide 10 to heat an unfixed toner image carried on the sheet. After undergoing the fixing process, the image is discharged onto the 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 between the four members 25, 26, 27, 20 parallel to each other of the low heating capacity linear heating body 20 as a heating body arranged below It is suspended around.

The driven roller 26 is an endless belt-shaped fixing film 24.
The fixing film that doubles as the tension roller
Reference numeral 24 denotes a transfer material sheet P having an unfixed toner image Ta, which is conveyed from the image forming portion 8 side, on the upper surface thereof at a predetermined peripheral speed in the clockwise direction as the driving roller 25 is rotated clockwise.
It is driven to rotate without wrinkling, meandering, or speed delay at the same peripheral speed as the transport speed of.

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.

Endless belt-shaped fixing film 24 driven to rotate
Since the toner is repeatedly used for heat fixing of the toner image, it has excellent heat resistance, releasability and durability, and is generally 100 μm or less, preferably 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, is provided on at least the image contact surface side with PTFE. For example, a release coating layer having a conductive material added to (tetrafluoroethylene resin) is applied to a thickness of 10 μm.

For the low heat capacity linear heating element as a heating element, see 20 (4) below.
As will be described in detail later, in the present embodiment, a linear or band-shaped heating element 22 is formed by coating an electrical resistance material such as silver palladium along the length on the substantially central portion of the lower surface of the alumina substrate 21. It is something that can be done. In the case of this example, the linear or belt-shaped heating element 22 is energized from both longitudinal ends thereof to generate heat over the entire length. Power supply is DC100V
With a pulse-shaped waveform having a cycle of 20 msec, the temperature is controlled by the temperature measuring 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 The heating element 22 is controlled within a range of 4 msec, and the heating element 22 is 200 to 300 instantly each time a pulse is input.
Raise the temperature to around ℃. In this embodiment, a sensor for detecting the leading and trailing edges of the sheet (not shown) is provided closer to the fixing device on the upstream side of the fixing device 11 in the transfer material sheet conveyance direction, and the sensor supplies a current to the heating element 22 according to a sheet detection signal. The period is controlled only for the necessary period during which the sheet P passes through the fixing device 11.

The fixing film 24 is not limited to the endless belt shape,
As shown in the example, the end-fixed film 24 wound in a roll around the feed shaft 30 is locked to the take-up shaft 31 between the heating body 20 and the pressure roller 28, under the separation roller 27, and the like. The transfer material sheet P may travel from the delivery shaft 30 to the take-up shaft 31 at the same speed as the transfer speed of the transfer material sheet P.

(3) Fixing operation The leading end of the transfer material sheet P carrying the unfixed toner image Ta on the upper surface, which has been conveyed from the transfer unit 8 to the fixing device 11 by the image forming operation of the apparatus in response to the image forming start signal, is fixed to the fixing device. The rotation (or running) of the fixing film 24 is started when it is detected by the above-mentioned sensor (not shown) disposed closer to it,
The transfer material sheet P is guided by the guide 29 and enters between the fixing sheet 24 and the pressure roller 22 at the pressure contact portion N between the heating body 20 and the pressure roller 28, and the unfixed toner image surface is the sheet P. Fixing film 24 that moves in the same direction as the transport speed in the same direction
Of the heating member 20 and the pressure roller 28 in a state of overlapping with the fixing film 24 without causing a surface shift or a wrinkle while passing a pressing force between them.

The toner image is heated and softened and melted as described in the item (1)-of the above-mentioned (action) as a heating step in the process of passing through the mutual pressing portion. As described above, in the heating step in this embodiment, a linear heating element 22 is provided on the heating element 20, and the heating element 22 having a low heat capacity formed integrally with the heating element 21 is energized in a pulse shape to repeat heat generation. This is performed by the heating body 21 configured as described above. In other words, the toner image Ta on the sheet P conveyed at the predetermined conveying speed, together with the fixing film 24 on which the sheet P is conveyed, is a linear heating unit which is sequentially determined according to the width of the heating element 22 of the heating element 20. After being fed into the effective width W and receiving heat, it becomes 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 the cooling process in (1) of (Operation) above.
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 traveling direction of the fixing film 24 is turned in a direction away from the sheet P along the surface of the separation roller 27 having a large curvature, and the fixing film 24 and the sheet P are separated from each other ( Then, the sheet P is discharged to the discharge tray 11. By the time of the separation, the toner is sufficiently cooled and solidified, and the above (action) (1)-
As described in the section, the adhesion and fixing force of the toner to the sheet P is sufficiently large, and the adhesion to the fixing film 24 is extremely small. Therefore, the separation between the fixing film 24 and the sheet P substantially causes the toner offset to the fixing film 24. It can be easily and sequentially performed without accidentally occurring.

In the present embodiment, since the linear heating element 22 of the heating element 20 is instantaneously heated to a sufficiently high temperature relative to the melting point (or fixable temperature) of the toner by energization, it is not necessary to preheat the heating element. The heat transfer to the pressure roller 28 during non-fixing is small. Also during fixing, the fixing film, toner image,
Since the sheet is interposed between the heating body 20 and the pressure roller 28 and a short heat generation time causes a rapid temperature gradient, the pressure roller 28 is unlikely to rise in temperature and is continuous as much as practically required. The temperature is maintained below the melting point of the toner even when the image formation is performed. 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 particularly, the surface portion thereof is completely removed. Softens and melts. At this time, the heating member, the fixing film, the toner image, and the sheet are satisfactorily adhered 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 effectively heated and melted, and in particular, energy saving can be achieved by limiting the heat generation time by energization.

Since the heating body is small enough, the heat capacity is small, and it is not necessary to raise the temperature of the heating body in advance. Therefore, the power consumption during non-image formation can be reduced, and the temperature rise in the apparatus can be prevented. .

In the present 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 radiation of the toner image in the 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 The low heat capacity linear heater 20 as a heater has a structure as shown in the cross-sectional model view of FIG.

Reference numeral 20a denotes a heater fixing support member, which is a laterally long rectangular member made of high rigidity and low thermal conductivity, such as PPS / polyimide / bakelite, having a longitudinal direction in the transverse direction of the fixing film (the direction perpendicular to the running direction of the fixing film 24). The member 20a can be a composite member in which at least the contact portion with the heater body 21a described below is made of the above-mentioned material having heat resistance and low thermal conductivity, and the other materials can be any desired material.

Reference numeral 21a is a horizontally long heater body integrally attached and fixed to the lower surface of the support member 20a. This heater body 21a has a length of 240 mm, a width of 10 mm, and a thickness of 1.0 mm, which is an alumina substrate (electrically insulating / heat-conductive member) 21 and a thickness of 100 μm formed on the surface (lower surface) of the substrate 21. Of the glaze layer 21b, and silver formed in a linear or strip-like shape with a thickness of 10 μm along the longitudinal direction at approximately the center of the surface of the glaze layer-
A heating resistance layer made of palladium (Ag / Pd) as the heating element 22 and a thickness of 10 on the glaze layer 21b surface including the heating element 22.
The heater surface protection image 21c and the like are made of a wear-resistant material such as glass, etc. Reference numeral 23 is a low-heat-capacity temperature detecting element (temperature detecting body) such as a bead thermistor which is embedded in or in contact with the central portion of the back surface (upper surface) of the heater substrate 21 in the longitudinal direction.

With respect to the lower surface of the heater body 21a of the heating body 20, the upper surface portion of the pressure roller 28 as a pressure member sandwiches the fixing film 24 or the fixing film 24 and the transfer material sheet P as a recording material with a predetermined pressing force. Pressure contact. Figure 5 shows fixing film 24
9 is a front view of the heating body 20 and the pressure roller 28 that are in pressure contact with the transfer material sheet P sandwiched therebetween.

FIG. 6 is a view showing a plane pattern of an Ag / Pd heat generating resistance layer as a heat generating element 22 formed in the longitudinal direction on the glaze layer 21b surface of the heater substrate 21. This heating resistance layer has a width of 1 mm and heat of 1
0 μm ・ L ₁ = 230 mm linear or strip-shaped effective heat generating part 22a (resistance value per unit length 1 Ω / cm) and effective heat generating part 22a on each end side, a width of 5 mm Thickness 10
Low heat generation part 22b / 22b with wide width of μm (resistance value part, resistance value
0.2 Ω / cm), and power supply electrodes 22c and 22c are crimped to the two wide and low heat generating portions 22b and 22b on both ends.

The heating element (Ag / Pd) 22 generates heat when electricity is applied between the electrodes 22c and 22c. However, the two wide and low heat generating parts 22b and 22b on both ends are the same in thickness and 10 μm in the heat generating resistance layer as compared with the effective heat generating part 22a, but the width is 5 times wider and the resistance per unit length is larger. Since the value is 1/5, the value for heat generation per unit length is also as small as 1/5.

Then, the heater substrate 21 is heated mainly by the heat generated by the effective heating element portion 22a, and the temperature is detected by the temperature detecting element 23 and fed back to an energization control circuit (not shown) to control the energization of the heating element 22 to effectively generate heat. The temperature of the fixing nip portion corresponding to the portion 22a is maintained and controlled at a predetermined fixing temperature. In FIGS. 5 and 6, l ₂ is the length of the pressure roller 28, g ₁ is the width of the fixing film 24, g ₂ is the maximum width of the transfer material that can be passed through the apparatus, and l ₂ > g ₁ The relationship of> l ₁ > g ₂ is satisfied, and at least the end portions of the heating element where the fixing film 24 is not pressed by the pressure roller 28 correspond to the wide heating portions 22b and 22b having a small heating value. ing.

Therefore, it is possible to eliminate the risk that the end portions of the heating element that are not in contact with the fixing film or the pressure roller 28 will overheat due to insufficient heat radiation and the heating element portion corresponding to that portion will be damaged (burned out).

According to the experiment, in the above, the heating element portions 22b, 22b on both sides of the heating element which are not in contact with the fixing film are also effective heating elements 22b.
In the case of a heating element having the same width and thickness and the same resistance value (1 Ω / cm) as a, the heating element portion 22b which is not in contact with the fixing film is damaged due to excessive temperature rise by heating for several minutes. On the other hand, as in the example of FIG. 6 described above, the effective heating element portion 22a of the heating element is provided with wide low-heating portions (low resistance value portions) 22b and 22b on both ends thereof in the longitudinal direction 22a portion-high resistance, Part 22b-The heating element having a low resistance distribution did not cause any problem even after the electric heating for several hundred hours.

As a means for imparting a required resistance distribution in the longitudinal direction of the heating element 22, in addition to making the thickness along the length of the heating element constant and widening the width along the length as in the above example, the heating element For example, the width along the length is made constant, the thickness along the length is changed to be thin or thin, and the resistance value distribution is provided along the length.

FIG. 7 shows that the heating element portions 22b and 22b on both end portions of the heating element which are not in contact with the fixing film have the thickness t ₂ of the effective heating element portion 22a.
The thickness is smaller than the thickness t ₁ (the width is the same for both portions 22a and 22b) and the resistance is reduced to form a low heat generating portion. It is also effective to form, for example, silver layers 22b 'and 22b' having lower resistance than silver-palladium on the surfaces of the portions 22b and 22b as shown in FIG.

The heating element portion (effective heating element portion 22a of the heating element 22) corresponding to the width region g ₂ in which the transfer material sheet P is energized during the fixing process prevents uneven fixing due to uniform temperature distribution in each longitudinal direction. Is important for.

However, in reality, as shown by the arrow in FIG.
The heat in the vicinity of both ends of the heater is easily dissipated by being transmitted through the support members 50, 50 on both ends of the heating body, and since the temperature detecting element 23 and the thermal fuse 23a are provided in the central part on the back of the heater, the heat dissipation characteristics in that part Therefore, a difference in temperature distribution due to a difference in heat radiation distribution is generated in the longitudinal direction of the heating element as shown by a broken line graph B in FIG.

Therefore, in the example of FIG. 11, the transfer material sheet P is set by widely changing the width dimension along the longitudinal direction of the heating element 22 in accordance with the temperature distribution difference, that is, the heat radiation distribution difference (the thickness is made constant at each part).
The temperature distribution along the longitudinal direction of the heating element portion corresponding to the passage portion of is made uniform as shown by the solid line graph A in FIG. As a result, during the fixing process, the temperature of the heating element in the transfer material sheet passing portion was substantially constant in each portion in the longitudinal direction, and uniform fixing property was obtained.

In the heating element 20 of the illustrated example, as the heating element 22, in addition to silver-palladium, nichrome / tungsten / ruthenium oxide (RuO ₂ ) / Ta ₂ N or the like, or a resistance material mainly containing them, or a ceramic heater It is also possible to use a surface heating element or the like. As the temperature detecting element 23, a resistance temperature detector such as a Pt film is provided on the back surface of the heater substrate 21 or on the same glaze layer surface side as the heating element 22 in parallel with the heating element 22 or laminated (screen printing etc.). You can also let it. Heating element 22
It is also possible to adopt a form provided on the back side of the substrate 21.

(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, an inexpensive base material such as a PET (polyester) film or the like may be used as the fixing film, and a heat-treated thin film having a thickness of about 12.5 μm or less may be used.

Or, since the toner offset to the fixing film surface does not substantially occur as described above, if the thermal deformation or deterioration accompanying the use of the fixing film is small, the used sheet wound on the take-up shaft side can be removed in a timely manner. And rewinding control to the shaft side,
Alternatively, it can be used a plurality of times by reversing the winding shaft side and the sending shaft side, etc. (rewinding repetitive use type).

In the rewinding repeated use type, as the fixing film, for example, a 25 μm thick polyimide resin film is used as a base material having excellent heat resistance, mechanical strength, etc., and a release layer made of a highly releasable fluororesin or the like on its surface. It is preferable to automatically control the pressure release mechanism during reverse rewinding to keep the contact between the heating element and the pressure roller in the released state.

In the case of multiple use such as a rewinding repetitive use type or an endless belt type, a felt pad is provided for cleaning the film surface, and a slight release agent, for example, silicon oil is impregnated to contact the pad 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 surface image. Further, it is one measure to add conductive powder fibers, for example, carbon black or the like, to the fluororesin to prevent the above-mentioned image disturbance due to static electricity. 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.

The fixing film is endless belt type, winding exchange type,
Regardless of the rewinding and reusing type, the fixing film can be easily replaced at a predetermined portion of the fixing device 11 so that the fixing film can be easily replaced.

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 normal AC energization.

The cooling and solidification of the toner heated and melted in the heating step may be performed by natural heat radiation, or may be performed by forced cooling by arranging a blowing means, a heat radiation fin, or the like.

In the apparatus shown in FIGS. 2 and 3, the toner does not necessarily have to be cooled and solidified at the position of the separation roller 27. Also, if the toner melts sufficiently at high temperature, if the toner is melted at a sufficiently high temperature in the heating step (fixing nip part) as shown in Fig. 12, the recording material (transferring The material sheet P may be separated from the surface of the fixing film 24.

The apparatus of the above embodiment is a transfer type electronic copying apparatus,
The image forming process and means are electrofax paper,
An image is formed on the recording material by a heat-meltable toner by a direct method in which a toner image is directly formed and carried on an electrostatic recording paper or the like, a magnetic recording image forming method, or other appropriate image forming process / means, and the image is heated. The fixing device of the present invention can be effectively applied to various image forming apparatuses such as a copying type copying machine, a laser beam printer, a facsimile, a microfilm reader printer, a display device, and a recording machine.

(Effect of the Invention) As described above, in the present invention, in the toner image heating and fixing device, 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 it is possible to further reduce the standby time and the power consumption. 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 a small temperature rise in the machine. Further, the fixing film can be repeatedly used for a long period of time without any problem without generation of wrinkles without any problem.

Regarding the low heat capacity linear heating element used in the present invention, as described above, the heating resistor has a smaller resistance value per unit length in the longitudinal direction on the end side where the recording material does not pass than on the central side where the recording material passes. Since it is configured, it is possible to prevent the damage of the heating element due to local excessive temperature rise at the heating element portion which corresponds to the both end portions of the heating element that does not contact the fixing film etc. Fixing film
The heating member portion through which the pressing member surface / recording material and the like passes can have a uniform heat generation temperature distribution along the length thereof to prevent non-uniform fixing property due to non-uniform distribution.

[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. Cross section model diagram, No. 5
FIG. 6 is a front view of a heating element and a pressure roller, FIG. 6 is a plan view of a heating element pattern, FIGS. 7 and 8 are other structural examples of the heating element, FIG. FIG. 10 is a temperature distribution graph along the length of the heating element, FIG. 11 is a plan view of a heating element pattern in which the temperature distribution difference is eliminated, and FIG. 12 is a schematic view of another configuration example of the fixing device. Reference numeral 3 denotes a drum-type rotating photoconductor, 11 denotes a fixing device, 24 denotes a fixing film, 20 denotes a heating member, 28 denotes a pressure roller, and P denotes a transfer material sheet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kensaku Soka Kensou Soka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Hiroyuki Adachi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (56) Reference JP-A-2-131271 (JP, A) Actually opened 62-74777 (JP, U) Actually opened 63-91194 (JP, U) Actually opened 2-81552 (JP, U)

Claims (1)

[Claims] 1. A heating body provided with a linear or strip-shaped heating resistor that generates heat when energized, and an energizing electrode provided at an end portion in the longitudinal direction of the heating resistor, and a sliding body with the heating body. And a film moving in a direction orthogonal to the longitudinal direction of the heating resistor, wherein the heat from the heating member through the film fixes an unfixed image on a recording material. The fixing device is characterized in that the resistor has a resistance value per unit length smaller on the end side where the recording material does not pass in the longitudinal direction than on the center side where the recording material passes.