JPH07111606B2 - Fixing device - Google Patents

Description

The present invention relates to a fixing device of a system that applies thermal energy to a recording material via a film.

More specifically, the film is brought into contact with the heating body and moved, the recording material is brought into close contact with the surface of the film opposite to the heating body side, and the film is moved through the heating body position together with the film to pass through the film. The present invention relates to a fixing device that applies heat energy to a recording material (film heating method).

This device is used for image forming devices such as copiers, laser beam printers, facsimiles, micro film reader printers, image display (display) devices, recorders, etc., and suitable image forming processes for electrophotography, electrostatic recording, magnetic recording, etc. By means of a toner made of a heat-meltable resin or the like by means of a means, it is formed on the surface of a recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, printing paper, etc.) by a direct method or an indirect (transfer) method. It can be utilized as an image fixing device that heats and fixes a visible image (unfixed toner image) corresponding to image information as a permanently fixed image on the surface of a recording material carrying the image.

Further, the invention is not limited to the image fixing device, and can be widely used as a means and a device for heat-treating an image carrier, such as a device for heating a recording material carrying an image to modify the surface property.

(Prior Art) Conventionally, an image heating and fixing device has a heating roller that is maintained at a predetermined temperature and a pressure roller that has an elastic layer and is brought into pressure contact with the heating roller. A heat 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.

However, in this heat roller fixing method, firstly, a time for inhibiting the image forming operation, that is, a so-called wait time, is required until the temperature is raised to a predetermined temperature, that is, a considerably long time is required. Secondly, since a heat capacity is required, a relatively large electric power is required. Necessary, and third,
Since the roller temperature of the rotating roller is high, a heat-resistant special bearing is required. Fourthly, there is a danger that the roller will be directly touched by the hand and a protective member is required. Fifth, due to the roller fixing temperature and curvature. There is a drawback that the recording material may wind around the roller and cause a jam.

The film heating type fixing device targeted by the present invention has a low heat capacity line in comparison with the above heat roller fixing system and other known heat fixing devices such as belt fixing system, flash fixing system and oven fixing system. -Shaped heater can be used, which saves power and shortens the wait time (quick start property), and the fixing point and separation point can be set separately to prevent offset. In addition, various other types of devices It is effective because it has the advantage of being able to solve the drawbacks of.

The method / apparatus disclosed in, for example, JP-A-63-313182 according to the applicant's earlier proposal belongs to this, and includes a thin heat-resistant film (sheet), a moving driving means for the film, and the film. A heating member fixedly supported on one side of the heating member, and a recording material to be fixed on the other side of the heating member to face the heating member via the film. The film has a pressing member for closely contacting the visible image-carrying surface, and the film is conveyed at the same speed in the forward direction as the recording material to be image-fixed which is conveyed and introduced between the film and the pressing member at least during image fixing. The recording medium is moved in a traveling manner and passed through a fixing nip portion formed by pressing a heating member and a pressing member with the traveling moving film sandwiched therebetween, so that the visible image bearing surface of the recording material is passed through the film by the heating member. Softens by applying heat energy to the visible image by heating Melt allowed, then separating the film and the recording material. Alternatively, the heating device is based on separating the film and the recording material after the toner is cooled and solidified.

A linear heating element conventionally used in such a film heating type fixing device has an energization heat generating layer having a longitudinal direction in a direction intersecting a moving passage direction of a recording material, and energization of both longitudinal end portions of the energization heating layer. When a voltage is applied between the working electrodes, each part of the effective length region of the heat generating layer generates heat with a predetermined heat generation amount per unit length. The effective total length area of the heat generating layer has a length dimension corresponding to the width (maximum width, maximum size width) of the maximum size recording material that can be supplied and used in an image forming apparatus incorporating the fixing device.

Thus, when fixing is performed, the recording material used has a maximum width because the effective total length of the heating layer generates a predetermined amount of heat generation per unit length to generate heat regardless of the size width of the recording material used. The image fixing process is performed on the surface of the supplied recording material regardless of whether the size of the recording material is smaller than that of the recording material.

(Problems to be solved by the invention) However, when the size width of the recording material used supplied to the apparatus is smaller than the maximum width in the above heating element configuration, the size width of the recording material used and the effective total length of the heat generating layer are In the recording material non-passing area (hereinafter referred to as the non-paper passing portion) of the heating body, which is the area different from the area, the heat generating layer portion corresponding to the non-paper passing portion is the heat generating layer corresponding to the paper passing portion. Like the part, it generates heat with a predetermined amount of heat generation per unit length. The heat generation energy of the heat generation layer portion corresponding to the paper passing portion is consumed for image fixing, but the heat generation energy of the heat generation layer portion corresponding to the non-paper passage portion is not consumed for image fixing, so that heat is accumulated.

Therefore, the temperature of the heating element in the non-sheet passing area rises abnormally (overheating)
The durability of the fixing film and the pressing member is reduced due to the heat loss of the heating element or the heat generating layer, the durability of the fixing film is reduced, and the running property of the fixing film becomes unstable (deviation of the film or wrinkles). It may cause

The present invention prevents such a situation as described above with respect to such a film heating type fixing device, that is, it does not unnecessarily heat the non-sheet passing portion of the heating body to raise the temperature. Another object of the present invention is to provide an improved device of this type, which also has advantages.

(Means for Solving Problems) In the present invention, a film is brought into contact with a heating body and moved, and a recording material is brought into close contact with the surface of the film opposite to the heating body side to move the heating body position together with the film. It is a fixing device which gives heat energy to a recording material from a heating body through a film by passing the heating body, and the heating body has an energization heat generation layer having a length in a direction intersecting with a moving passage direction of the recording material and energized from both ends. And a branch electric path branched from at least one predetermined position in the middle of the energization heat generating layer along the length thereof and selectively energized and controlled, in the vicinity of the conduction connecting portion of the energization heat generating layer and the branch electric path. The fixing device is characterized in that the resistance value of the energization heating layer portion is relatively higher than that of the other energization heating layer portions.

In the above, as a means for making the resistance value of the energizing heat generating layer portion near the conduction connecting portion of the energizing heat generating layer and the branch electric path relatively higher than that of the other energizing heat generating layer portion, specifically, A treatment such that the current generating layer portion near the conduction connecting portion of the electric path is made of a material having a resistance value different from that of other materials, and the width and thickness of the current generating layer portion are sandwiched or thinner than those of other current generating layer portions. Is mentioned.

(Operation) (A) The effective total length region between one end and the other end in the longitudinal direction of the energization heat generating layer is set to a length dimension corresponding to the width of the maximum size recording material that can be supplied to the apparatus and used. Further, a branch electric path is provided at an intermediate position in the effective full-length area of the electric heating layer, which corresponds to the position of the boundary between the paper passing portion and the non-paper passing portion of the heating element when a certain small-sized recording material is supplied.

During the image fixing process by supplying the maximum size recording material, the free end side of the branch electric circuit is controlled to be in an open state, and a predetermined voltage is applied between one end and the other end of the energization heat generating layer to energize it. By energizing the heat generating layer, each part of the effective heat generating layer generates heat with a predetermined heat generation amount per unit length, and the image fixing process for the maximum size recording material is executed without any trouble.

During the image fixing process by supplying a small-sized recording material, when a voltage is applied to one end of the energizing heat generating layer and the free end of the branch electric path to energize the energizing heat generating layer, it corresponds to the paper passing portion. The energizing heat generating layer portion (the section from one end of the energizing heat generating layer to the branch point of the branch electric path) generates heat with a predetermined amount of heat generation per unit length, and the image fixing process is executed on the small-sized recording material. .

In this case, the energizing heat generating layer portion (the section from the branch point of the branch electric path to the other end of the energizing heat generating layer) corresponding to the non-sheet passing portion is non-energized and does not generate heat, and thus the non-sheet passing portion of the heating element. Is suppressed, and the above-mentioned problems caused by the excessive temperature rise are eliminated. A plurality of branch electric circuits corresponding to the widths of recording materials of various sizes smaller than the maximum size recording material are provided at required positions in the middle of the energization heat generating layer, and the recording material is supplied depending on the size width of the recording material. By selectively controlling the energization of the branch circuit, it is possible to cope with the recording materials of various sizes so as to suppress the excessive temperature rise of the heating member non-sheet passing portion.

(B) Regarding the portion of the energized heat generating layer and the portion of the energized heat generating layer in the vicinity of the conduction connecting portion between the energized heat generating layer and the branch electric path, heat is radiated from the branch electric path, and the temperature tends to be slightly lower than that of the other energized heat generating layer portions along the length of the energized heat generating layer. Therefore, there is no problem when heat-treating the smallest size recording material, but heat treatment is performed by passing a recording material that is larger than the minimum size such as the largest size recording material that can be passed through the device. At that time, due to the slight decrease in temperature in the portion of the energizing heat generating layer existing in the middle of the sheet passing width and the portion of the energizing heat generating layer in the vicinity of the conductive connection portion of the branch electric path, the image fixing property of the recording material portion corresponding to the portion is deteriorated. There are also things to do.

In the present invention, the energizing heat generating layer and the energizing heat generating layer portion in the vicinity of the conduction connection portion of the branch electric path are made of a material having a resistance value different from those of the other energizing heat generating layer portions, and the width and thickness are sandwiched or thinned. By the treatment, the resistance value of the portion was made relatively higher than that of the other portion, so that the heat generation in the portion increased more than that in the other portion, and the heat dissipation by the branch circuit was compensated (cancelled out). Therefore, it is possible to prevent a local temperature drop in this portion.

Therefore, even when a recording material of a size larger than the minimum size such as the largest recording material that can be passed through the device is passed through and heat treated, conduction between the energization heat generation layer and the branch circuit that exists in the middle of the paper passing width It is possible to prevent the occurrence of fixing unevenness and the like due to a local temperature drop in the energization heat generating layer portion near the communication portion, and to secure uniform fixing property in each portion.

(Example) (1) Example of image forming apparatus (FIG. 8) FIG. 8 shows a schematic configuration of an example of an image forming apparatus provided with a fixing device 7 according to the present invention.

The image forming apparatus of this embodiment is a transfer type electrophotographic copying apparatus in which a document table is fixed and the optical system is moved, a rotary drum type photoconductor is used, and double-sided / multiple copying is possible. Imaging principle of the copying machine of this example
Since the process / mechanical structure itself is publicly known, its explanation will be briefly described.

Reference numeral 2 denotes a fixed platen glass, on which an original O is placed with the image surface to be copied facing downward according to a predetermined placement standard, and the original plate cover 3 is placed on the original O to set it. Rotating drum type photoconductor 6 by a copy start signal
Is the prescribed peripheral speed (process speed) in the clockwise direction indicated by the arrow
The peripheral surface of the photoconductor is uniformly charged to a predetermined potential by the charger 30. Further, the moving illumination lamp 1 and the moving first mirror 1a of the imaging optical system are at a predetermined speed V,
Further, the moving second mirror 1b and the third mirror 1c are driven forward from the left side to the right side of the platen glass 2 at a speed of V / 2, and the downward image surface of the set document O moves from the left side to the right side. Optical scanning is sequentially performed, and the scanned original image is formed by the imaging lens 1d.
An image forming exposure L is performed on the surface of the rotating photoconductor 6 charged by the charger 30 through the fixed fourth mirror 1e, the fifth mirror 1f, and the sixth mirror 1g, so that the circumference of the photoconductor 6 is reduced. An electrostatic latent image corresponding to the original image is sequentially formed on the surface.

The latent image is then visualized by the developing device 4 in order by toner (developer) made of resin or the like that is softened and melted by heating. Then, the visualized toner image is fed one sheet into the apparatus from the first paper feeding cassette unit 31 or the second paper feeding cassette unit 32 or by using the manual paper feeding unit 33, and the registration roller pair 34 The toner is sequentially transferred onto the surface of the transfer material sheet as a recording material fed to the transfer portion between the photoconductor 6 and the transfer / separation charger 5 at a predetermined timing.

The transfer material sheet that has received the image transfer is conveyed to the fixing device 7 by the conveying device 36.
The image is subjected to an image fixing process by being introduced into the apparatus and is ejected outside the apparatus as an image formed product (copy) by the sheet ejection roller 37 (in the case of the single-sided copy mode).

In the case of the double-sided or multi-copy mode, the transfer material sheet that has exited the fixing device 7 and has been copied on one side or has been copied for the first time is introduced into the re-conveying sheet bus mechanism section 38 and turned upside down or transferred to the transfer section 5. Duplexing or multiple copying is executed by re-feeding without inverting.

After the image transfer, the photoconductor 6 is subjected to cleaning by the cleaning device 35 to have a clean surface, and is repeatedly used for image formation.

(2) Fixing Device FIG. 6 is an enlarged structural diagram of the fixing device 7.

Reference numeral 9 denotes an endless belt-shaped fixing film, which has a driving roller 8 on the left side, a driven roller 11 on the right side, and a linear low heat capacity as a heating body fixedly supported below both rollers 8 and 11. The heating member 12 and the guide roller 8a arranged below the drive roller 8 are arranged in parallel with each other by the four members 8/11.
・ Suspended between 12 and 8a.

The driven roller 11 also serves as a tension roller of the fixing film 9, and the fixing film 9 rotates with a predetermined peripheral speed in the clockwise direction with the clockwise rotation of the driving roller 8 without wrinkling, meandering, or speed delay. Driven.

Reference numeral 17 is a pressure roller as a pressure member having a rubber elastic layer having a good releasability such as silicon rubber, and sandwiching the descending film portion of the endless belt-shaped fixing film 9 with the heating body 12. However, the lower surface of the heating element 12 is pressed against the lower surface of the heating element 12 with a contact pressure of, for example, a total pressure of 4 to 7 kg, and rotates in the forward counterclockwise direction in the transport direction of the transfer material sheet 16.

Since the endless belt-shaped fixing film 9 that is rotationally driven is repeatedly used for heat fixing of the toner image, it is excellent in 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, PES, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin), or a composite layer film, for example, a 20 μm thick film on at least the image contact surface side. For example, a release coating layer made by adding a conductive material to a fluororesin such as PTFE (tetrafluoroethylene resin) / PAF is applied to a thickness of 10 μm.

The low-heat-capacity linear heating element 12 as a heating element of this example has laterally long rigidity, high heat resistance, and heat insulating property with the longitudinal direction in the transverse direction of the fixing film (direction perpendicular to the running direction of the fixing film 9). A heater support 12a having the heater substrate and a heater substrate integrally attached and held on the lower surface side of the support along the length of the lower surface.
Comprises 13.

As will be described later, the heater substrate 13 is provided with an electric heating layer 1
4. A branch electric circuit, a current-carrying electrode, a temperature sensor (temperature detecting element) 10 and the like are provided to limit the heat generation (heating) range with respect to the longitudinal direction of the current-generating heat generating layer 14 (heating body 12).

The heater support 12a is a heat insulating member that secures the overall strength of the heating body 12, and for example, PPS (polyphenylene sulfide), PAI (polyamide imide), PI (polyimide), P
High heat resistant resins such as EEK (polyether ether ketone) and liquid crystal polymers, these resins and ceramics / metals /
It can be composed of a composite material such as glass.

The heater substrate 13 has heat resistance and electrical insulation,
As an example, it is an alumina substrate having a thickness of 1.0 mm, a width of 10 mm, and a length of 240 mm. Alternatively, it is a composite material substrate containing the same.

As an example, the heat generating layer 14 is formed by coating an electric resistance material such as Ta ² N and silver palladium with a width of 1.0 mm along the length on the substantially central portion of the lower surface of the substrate 13 on the film sliding side (screen printing, etc.). This is a linear or strip-shaped low-heat-capacity energizing heat generating layer.

The temperature sensor 10 is. It is arranged on the surface of the substrate 13 opposite to the side on which the electric heating layer 14 is provided. In this example, the temperature of the substrate 13 is detected by the temperature sensor 10 as the temperature of the heating body 12.

In the case of this example, the linear or strip-shaped heat generating layer 14 is energized from both longitudinal ends thereof to generate heat over the entire length of the heat generating layer. Energization is, for example, a pulsed waveform of a DC power supply,
Temperature sensor 10 and microcomputer MPU19 (first
The energization control circuit is configured to give a pulse (driving pulse) according to a desired temperature and energy release amount controlled by the drawing) by changing its pulse width.

Further, in this embodiment, a sheet front end / rear end detection sensor (not shown) is provided on the upstream side of the fixing device 7 in the transfer material sheet conveying direction, and the sheet detection signal of the sensor is used to energize the heating element 14. The period is controlled only for the required period in which the sheet 16 is passing through the fixing device 7.

The fixing film 9 is not limited to the endless belt shape, and the endless fixing film 9 wound around the delivery wheel 40 in a roll winding as shown in FIG. 7 is provided between the heating body 12 and the pressure roller 17, and the guide roller 8a. It may be configured such that it is engaged with the take-up shaft 41 via the bottom of the lower part and travels from the sending-out shaft 40 side to the take-up shaft 41 side at a predetermined speed.

(3) Fixing Execution Operation The image forming apparatus performs an image forming operation in response to the image formation start signal and is conveyed from the transfer section (5) side to the fixing apparatus 7. The above-mentioned sensor (not shown) in which the front end of the transfer material sheet 16 carrying the unfixed toner image 15 on the upper surface is arranged near the fixing device.
The rotation (or running) of the fixing film 9 when detected by
Then, the transfer material sheet 16 is guided by the guide 42 and enters between the fixing film 9 and the pressure roller 17 in the pressure contact portion N (fixing nip portion) between the heating body 12 and the pressure roller 17, The unfixed toner image surface is in close contact with the lower surface of the fixing film 9 in the surface moving state, and the heating body 12 and the pressure roller 17 are overlapped with the moving fixing film 9 without causing surface deviation or wrinkling.
And passes through the fixing nip portion N while receiving a pinching pressure.

w is the width dimension of the heating element 14 provided on the lower surface of the heating element, and the heating element 14 is within the mutual pressure contact width area between the lower surface of the heating element 12 and the upper surface of the pressure roller 17, that is, the width of the fixing nip portion N. It exists in the area.

The toner image bearing surface of the sheet 16 is heated against the surface of the fixing film while passing through the fixing nip portion N in a pressing contact state.
Is received through the fixing film 9 and the toner image is melted at a high temperature to be softened and adhered 15a to the surface of the sheet 16.

In the case of the apparatus of this example, the recording material sheet 16 and the fixing film 9 are used.
The sheet 16 is separated when the sheet 16 passes through the fixing nip portion N and exits.

At the time of this separation, the temperature of the molten toner 15a is still higher than the glass transition point of the toner. Therefore, the bonding force (adhesive force) between the sheet 16 and the fixing film 9 at this time of separation is small, so that the sheet 16 is fixed. The toner is hardly separated on the surface of the film 9, and the separation is always performed smoothly without causing the sheet 16 to be wound around the fixing film 9 while being adhered to the fixing film 9 due to poor separation and jamming.

Further, since the toner 15a at a temperature higher than the glass transition point has appropriate rubber characteristics, the toner image surface at the time of separation has an appropriate uneven surface property without following the fixing film surface. As a result, the toner image surface on which the toner image has been fixed does not generate excessive image gloss, resulting in a high quality image.

The sheet 16 separated from the fixing film 9 is guided by the guide 43, and the temperature of the toner 15a higher than the glass transition point is naturally lowered (natural cooling) while reaching the paper discharge roller pair (37). At the following temperature, it reached to individualization 15b,
The image-fixed sheet 16 is output.

(4) Heating Range Control of Heating Body FIG. 1 is a block diagram of a heating control circuit for the heating body 12.

In the figure, reference numerals 14, 18b, 18e, and 18c denote current-generating layers (1) formed on the lower surface of the substrate 13 of the heating body 12, which is the film sliding surface side.
4) and the first, second, and third branch electrical circuits (18b, 18e
18c). The energization heat generating layer 14 is formed in a straight line along the length of the substrate in the substantially central portion of the lower surface of the substrate 13. 18a and 18d
Is an energizing electrode (input terminal) made of a material having good conductivity such as silver provided at the left end and the right end of the energization heat generating layer 14. First to third
Each of the branch electric paths 18b, 18e, and 18c is also formed of a conductive member such as silver.

k is the effective total length area of the electric heating layer 14 between the electrodes 18a and 18d. In this example, the maximum size transfer material sheet that can be supplied to the device and used is A3 size, and the length dimension corresponding to the sheet width is set. I am doing it.

Further, in the case of this example, the transfer material sheets of various sizes are supplied on the basis of the so-called one side reference with respect to the base line a on the left end side of the energization heat generating layer 14, and the first branch electric path 18b and the second branch electric path are provided. 1
8e and the third branch electric circuit 18c are respectively from the base line a to h.i.
At the distance position of j, branch from the portion of the electric heating layer 14
Each free end is formed to extend to a position corresponding to the right end of the electric heating layer 14 or to a position outside thereof.

Here, in the case of this example, the distances h, i, and j are B5 version and A4 version, respectively.
The length dimension is set to correspond to the width of the plate and B4 plate.

Since the lower surface of the heater substrate provided with the energization heat generating layer 18, the branched electric circuit 18 (b · ec), etc. is a sliding surface with the film 9, a sliding protection layer such as Ta ₂ O ₅ is formed on the surface. It is preferable to protect.

The temperature sensor 10 is arranged on the upper surface side of the substrate 13, that is, on the side opposite to the side on which the electric heating layer 14 and the like are provided, and in the area h which is the minimum sheet passing area.

Reference numeral 22 denotes an operation panel of the image forming apparatus. As shown in FIG. 9, a power switch 22a, a copy number setting key 22b, a number display 22c, a transfer material size designation operation key (size selection key) 22d, and a copy start. Key buttons 22e and the like are arranged.

The size information selected and specified by the size selection key 22d is taken into the microcomputer MPU19. The MPU 19 sends a decode signal corresponding to the designated size width to the decoder 20, and the decoded signal selectively drives the heating element drive circuits I to IV corresponding to the designated size width. Each of the circuits I to IV
Are respectively connected to one of the terminals at the first to third branch electric circuits 18b.
18e, 18c and one terminal 18d of the current-generating layer 14 are connected, and the other terminal of each circuit is shared and connected to the other electrode 18a (common electrode) of the current-generating layer 14 via the power source E. I am doing it. 21 is a memory circuit.

When the A3 size sheet having the maximum size width is selected and designated as the transfer material sheet to be used, only the heating element drive circuit IV is driven and the voltage E is applied only between the electrodes 18a and 18d at both ends of the energization heat generation layer 14. Is applied to each of the first to third branch electric lines 18b.
・ Eyes 18e and 18c are kept open, and the effective length k of the energization heat generation layer 14 generates heat with a predetermined amount of heat generation per unit length, so that image fixing of the A3 size sheet supplied to the device can be performed without problems. To be done.

When the B5 size sheet is selected and designated as the transfer material sheet to be used, the heating element drive circuit I is driven to drive the electrode 18a.
And the voltage E is applied between the first branch circuit 18b and the first branch circuit 18b.

As a result, the heat-generating layer portion in the area h corresponding to the sheet passing portion of the B5 plate, that is, the electrode 18a on one end side of the electric heat-generating layer 14
The heat generating layer portion up to the branch point of the branch electric circuit 18b generated heat with a predetermined heat generation amount per unit length and was supplied to the device.
Image fixing of B5 sheet is executed without any problem.

On the other hand, the heat generating layer portion corresponding to the non-sheet passing portion (kh), that is, the heat generating layer portion from the branch point of the first branch electric circuit 18b to the electrode 18d on the other end side of the electric heat generating layer 14 does not generate heat. Therefore, the excessive temperature rise of the heating body portion corresponding to the non-sheet passing portion (kh) can be suppressed.

When the A4 size sheet is selected and designated as the transfer material sheet to be used, the heater E driving circuit II is driven to apply the voltage E between the electrode 18a and the second branch electric path 18e, The heat generating layer portion of the area i corresponding to the sheet passing portion of the plate sheet generates heat with a predetermined heat generation amount per unit length, and the image fixing of the A4 size sheet supplied to the apparatus is executed without any trouble, and the sheet does not pass through. The heat generating layer portion corresponding to the paper portion (ki) does not generate heat, and the excessive temperature rise of the heating body portion corresponding to the non-sheet passing portion (ki) is suppressed.

When the B4 plate is selected and designated as the transfer material sheet to be used, the voltage E is applied between the electrode 18a and the third branch electric circuit 18c by driving the heating body drive circuit III, and the B4 plate is selected. The heat generating layer portion of the area j corresponding to the sheet passing portion of the sheet generates heat with a predetermined heat generation amount per unit length, and the image fixing of the B4 plate sheet supplied to the apparatus is executed without any trouble, and the non-sheet passing portion. The heating layer portion corresponding to (k-j) does not generate heat, and the excessive temperature rise of the heating element portion corresponding to the non-sheet passing portion (k-j) is suppressed.

(5) Constitution of electric circuit branching portion (Figs. 2 and 3) Electric heating layer 14 and first to third branch electric circuits 18b, 18e, 18C
In the case of this example, the current-generating layer portion 14 'in the vicinity of each conduction connecting portion has a resistance value per unit area of the former portion 14' and other portions 14 as shown in the partially enlarged view of FIG. Two types of resistance materials are separately applied so that the portion 14 ′ is higher than the latter portion 14 to form the full-length portion of the electric heating layer 14.

Specifically, part 14 is coated with silver / palladium, and part 1
4'constitutes ruthenium oxide to form the entire length of the electric heating layer 14. Here, the ruthenium oxide in the portion 14 'has a higher resistance value per unit area than the silver / palladium in the portion 14'. Therefore, when electricity is applied to the electricity-generating layer 14, the amount of heat generated in the portion 14 ′ is larger than that in the portion 14.

That is, the heat generation layer portion 14 'near the conduction connecting portion between the electricity generation layer 14 and the branch electric path 18 (b, c, e) is supplemented with the heat radiation due to the existence of the branch electricity path, and the temperature drop with the other portion 14 occurs. To be prevented.

Therefore, as described in the section (B) of the above (action), the recording material (A4 / B4 / A3) of a larger size than the recording material (B5) of a small size is used.
Even when the paper is passed, the problem of deterioration of the fixing property at the branch portions of the first to third branch electric lines 18b, 18e, 18c with respect to the electric heating layer 14 does not occur.

In the above description, silver palladium and hathenium oxide were described as examples of the two types of materials, but the present invention is not limited to this, and various materials can be combined. It is also possible to increase the resistance value per unit area of the portion 14 'with respect to the portion 14 by changing the mixing ratio of silver palladium.

As a means for making the resistance value of the portion 14 'higher than that of the portion 14, the width of the portion 14' may be made narrower than that of the portion 14 as shown in FIG. This causes part 14 'to become part 14
The resistance becomes higher than that of the above, and it becomes possible to gradually increase the heat generation amount of the portion 14 '.

In this case, it is not necessary to separately coat two different types of resistance materials as in the case of FIG. 2 described above, so that the manufacturing process can be simplified.

As another method, it is possible to change the film thickness of the heat generation amount. That is, in FIG.
By thinning the 14 'portion, it is possible to increase the amount of heat generation by making the resistance value of the heating layer portion 14' near the branch portion of the branch electric path relatively higher than that of the other heating layer portion 14.

In any of the above cases ,. The resistance value of the portion 14 'is set so as to compensate for the heat radiation due to the existence of the branch electric path from the portion 14', and to generate a heat value that does not substantially cause a temperature difference with the portion 14.

(6) Others Each of the branch electric lines 18b, 18e, and 18c may be electrically connected to the electric heating layer 14 'with an inclination angle as shown in FIGS. 1 to 3, or as shown in FIG. You may make a right angle and carry out continuity connection.

The branch side ends of the respective branch electric lines 18b.18e and 18c with respect to the current-generating layer 14 'may be superposed on the upper side of the current-generating layer 14' so as to conduct electrical connection, or between the current-generating layer 14 'and the substrate 13. May be intervened to establish continuity communication.

FIG. 5 shows an example of the configuration of the branch electrical circuit in the case of so-called center reference sheet feeding. B is the central baseline.

(Effect of the Invention) As described above, according to the present invention, by disposing the branch electric path, the required heating (heating) with respect to the length of the heating body is limited to the range of the sheet passing portion corresponding to the size width of the recording material used. Unnecessary heating in the non-sheet passing area can be suppressed, and overheating of the non-sheet passing portion of the heating element can be prevented. It becomes possible to maintain a substantially uniform temperature over the entire effective length of the heating element.

As a result, the durability of the linear heating element, the fixing film, the pressure member, etc. is shortened due to temperature non-uniformity, and their damage,
It is possible to prevent stains and the like. In addition, it is possible to prevent uneven running of the fixing film such as wrinkles and wrinkles.

Further, by setting the resistance value of the energization heat generation layer portion near the conduction connection part of the conduction heat generation layer and the branch electric path to be relatively higher than that of the other conduction heat generation layer part, the conduction connection between the conduction heat generation layer and the branch electric path is established. There is no local temperature drop in the area, the heat generation (temperature distribution) along the length of the energization heat generation layer is made uniform, and good fixing processing is performed on recording materials of each size without causing local fixing failure areas. Can be executed.

[Brief description of drawings]

FIG. 1 is a block diagram of a heating control circuit. FIG. 2 is an enlarged view of a conduction connecting portion between the electric heating layer and the branch electric path. Figures 3 and 4 are the same as above for other examples. FIG. 5 shows another example of the configuration of the branch circuit. FIG. 6 is a schematic diagram of an example of a fixing device. FIG. 7 is the same as above for another example. FIG. 8 is a schematic diagram of an example of an image forming apparatus. FIG. 9 is a plan view of the operation panel section. 1 is a document illumination lamp, 2 is a platen glass, 3 is a platen cover, 4 is a developing device, 5 is a transfer / separation charger, 6 is a rotary drum type photoconductor, 7 is a fixing device, 8 is a drive roller, and 9 is a roller. Is a film, 10 is a temperature sensor, 11 is a driven roller, 12 is a heating element, 13 is an alumina substrate, 14 and 14 'are energization heating resistors, 18
b, 18e, and 18c are branch circuits, 15 is a toner image, 16 is a transfer material sheet, and 19 is an MPU.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-3-144477 (JP, A) JP-A-3-33783 (JP, A) JP-A-2-143278 (JP, A)

Claims (4)

[Claims] 1. A film is brought into contact with a heating body to move the film,
A fixing device for closely adhering a recording material to the surface of the film opposite to the heating body side, moving the recording material together with the film through a position of the heating body, and applying heat energy to the recording material from the heating body through the film. Has an energization heat generation layer having a length in a direction intersecting the moving passage direction of the recording material and energized from both ends, and branches from at least one predetermined position in the middle part along the length of the electricity generation heat generation layer to selectively And a resistance value of the energization heat generation layer portion near the conduction connection portion of the energization heat generation layer and the branch conduction path is made relatively higher than that of the other conduction heat generation layer parts. A fixing device characterized by the above. 2. A conductive heating layer and a conductive heating layer portion in the vicinity of a conductive connecting portion of a branch circuit are made of a material having a resistance value different from that of the other, and the resistance value of the conductive heating layer portion is set to be greater than that of another conductive heating layer portion. 2. The fixing device according to claim 1, wherein the fixing device is also relatively high. 3. The resistance value of the energizing heat generating layer portion relative to that of the other energizing heat generating layer portion is made smaller by sandwiching the width of the energizing heat generating layer portion near the conduction connecting portion of the branch electric circuit than the other. The fixing device according to claim 1, wherein the fixing device is made higher. 4. The resistance value of the energizing heat generating layer portion is made smaller than that of the other energizing heat generating layer portion by making the thickness of the energizing heat generating layer portion near the conduction connecting portion of the energizing heat generating layer and the branch electric circuit smaller than that of the other energizing heat generating layer portion. The fixing device according to claim 1, wherein the fixing device is relatively high.