JPH03194879A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent overwarming due to unnecessary heating of no sheet passing part of a heating element by providing a branched electric way to be selectively charging controlled while being branched from at least one prescribed position of a halfway part along the longitude of a charge heating layer. CONSTITUTION:A heating element 12 has charge heating layers 14, 14' having the direction crossing the traveling passage direction of a recording material 16 as the longitude and being charged from both end parts while having branched electric circuit 18b, 18e and 18c, which are branched from at least one prescribed position of a halfway part along the longitude of those charge heating layers 14 and 14' for being charge controlled. Further, resistance value of the part of the charge heating layer 14' near the conductive connection part of the charge heating layer 14 and the branched electric circuit 18b, 18e and 18c is relatively heightened than that of the part of the other charge heating layer 14. Thereby, required heating relating to the longitude of the heating element 12 can be limited to the range of no sheet passing part corresponding to the width of the size of a used recording material 16 so as to suppress needless heating relating to the range of no sheet passing part, thus to prevent overwarming of no sheet passing part of the heating element 12.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fixing device that applies thermal energy to a recording material through a film.

More specifically, a film is brought into contact with a heating body and moved, a recording material is brought into close contact with the surface of the film opposite to the heating body, and the recording material is moved together with the film through the heating body position to be transferred from the heating body 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 in image forming devices such as copying machines, laser beam printers, facsimile machines, microfilm reader printers, image display devices, and recording machines to perform appropriate image forming processes such as electrophotography, electrostatic recording, magnetic recording, etc. A target image formed directly or indirectly (transfer) on the surface of a recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, printing paper, etc.) using a toner made of heat-meltable resin, etc. It can be utilized as an image fixing device that heats and fixes a visible image (unfixed toner image) corresponding to image information on the surface of a recording material carrying the image as a permanently fixed image.

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

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

However, this heat roller fixing method requires a relatively long wait time, which is the time during which image forming is prohibited until the temperature reaches a predetermined temperature, and secondly, it requires a relatively large amount of electric power because it requires heat capacity. It is necessary, and thirdly,
A heat-resistant special bearing is required because the roller temperature is high for rotating rollers.Fourthly, the child comes into direct contact with the roller, which is dangerous and requires a protective member.Fifthly, due to the roller fusing temperature and curvature, There were drawbacks such as the recording material wrapping around the roller and causing jams.

The film heating type fixing device that is the object of the present invention has the following characteristics: Since a heat capacity linear heating element can be used, it saves power and shortens wait time (quick start); ■Fixing point and separation point can be set separately, preventing offset;
It is effective and has the advantage of being able to overcome various drawbacks of other systems.

For example, Japanese Patent Application Laid-Open No. 63-3131 related to the applicant's previous proposal
The method, device, etc. disclosed in Publication No. 82 belongs to this category, and includes a thin heat-resistant film (sheet), a means for moving the film, and a device fixedly supported on one side of the film with the film inside. a heating member, and a pressure member disposed on the other side facing the heating member to bring the image-bearing surface of the recording material to which the image is to be fixed into close contact with the heating member via the film; At least when performing image fixing, the film is moved at the same speed in the same direction as the recording material on which the image is to be fixed, which is conveyed and introduced between the film and the pressure member, and is heated with the heating body with the moving film in between. By passing through a fixing nip formed by pressure contact with a pressure member, the image-bearing surface of the recording material is heated by the heating body through the film, and thermal energy is applied to the image to soften and melt it. This is a heating device that is basically used to separate the film and recording material after the toner has cooled and solidified, or to separate the film and the recording material after the toner has cooled and solidified.

The linear heating body conventionally used in such a film heating type fixing device has an energized heat generating layer whose length is in a direction intersecting the direction in which the recording material moves, and the energized heat generating layer is energized at both longitudinal ends of the energized heat generating layer. By applying a voltage between the electrodes, each part of the effective full length region of the heat generating layer generates heat with a predetermined amount of heat generated per unit length. The effective full length region of this heat generating layer has a length dimension corresponding to the width (maximum width, maximum size width) of a maximum size recording material that can be supplied and used in an image forming apparatus incorporating the fixing device.

Therefore, when fixing is executed, regardless of the size width of the recording material used, the heating layer is energized to generate heat with a predetermined amount of heat per unit length over the entire effective length of the heating layer, so that the recording material used is the one with the largest width. However, even for various sizes smaller than this, image fixing processing is performed on the surface of the supplied recording material.

(Problem to be solved by the invention) However, in the heating body configuration as described above, if the size width of the used recording material supplied to the apparatus is smaller than the maximum width, the size width of the used recording material and the heat generating layer Even in the recording material non-communicating area of the heating body (hereinafter referred to as a non-paper passing area), which is a difference area from the effective full length area, the heating layer portion corresponding to the non-paper passing area is
Like the heat generating layer portion corresponding to the paper passing section, it generates heat with a predetermined amount of heat per unit length. The heat generated energy in the heat generating layer corresponding to the paper passing section is consumed for image fixing, but
The heat generated energy in the heat generating layer portion corresponding to the non-sheet passing portion is not consumed for fixing the image and is therefore stored as heat.

As a result, the temperature of the heating element in the non-paper passing area rises abnormally (excessive temperature rise).
This causes a decrease in the durability life due to heat loss of the heating element or heat generating layer, a decrease in the durability of the fixing film and pressure member, etc., and instability of the running properties of the fixing film (occurrence of unevenness of the film, wrinkles, etc.) etc. may occur.

The present invention prevents the above-mentioned situation from occurring in such a film heating type fixing device, that is, prevents unnecessary heating of the non-sheet passing portion of the heating body and causing an excessive temperature rise. It is an object of the present invention to provide an improved fixing device of this type, which also has advantages.

(Means for Solving the Problems) The present invention involves moving a film in contact with a heating body, bringing a recording material into close contact with the surface of the film opposite to the heating body, and moving the film along with the film to the heating body position. The fixing device is a fixing device that applies heat energy to a recording material from a heating body through a film by moving the recording material through the film, and the heating body has a current-carrying heat generating layer whose length is in a direction intersecting the moving and passing direction of the recording material and which is energized from both ends. and has a branch electrical path that branches from at least one predetermined position along the length of the current-carrying heat-generating layer and is selectively energized, in the vicinity of a conductive connection between the current-carrying heat-generating layer and the branch electrical path. The fixing device is characterized in that the resistance value of the energized heat generating layer portion is relatively higher than that of the other energized heat generating layer portions.

In the above, the means for making the resistance value of the current-carrying heat-generating layer portion near the conductive connection portion between the current-carrying heat-generating layer and the branch circuit relatively higher than that of other current-carrying heat-generating layer portions is specifically: For example, making the current-carrying heat-generating layer near the conductive connection part of the branch circuit a material with a different resistance value from the other parts, making the width and thickness of the current-carrying heat-generating layer part narrower or thinner than those of other current-carrying layer parts, etc. Examples include treatment.

(Function) (A) The effective full length region between one end and the other end of the energizing heat generating layer in the longitudinal direction 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 a midway position of the effective full length region of the energized heat generating layer, corresponding to the boundary line position between the sheet passing portion and the non-sheet passing portion of the heating body when a small size recording material is supplied.

■When performing image fixing processing by supplying the maximum size recording material, the sunrise end side of the branch electrical circuit is controlled to be in an open state, and a predetermined Q voltage is applied between one end and the other end of the energized heat generating layer. By energizing the energized heat generating layer, each part of the energized heat generating layer generates heat with a predetermined amount of heat per unit length in its effective entire length area, and image fixing processing for the largest size recording material is performed without any trouble.

■When performing image fixing processing by supplying small-sized recording material,
When a voltage is applied to one end of the current-carrying heat-generating layer and the free end of the branch circuit and the current-carrying heat-generating layer is energized, the part of the current-carrying heat-generating layer corresponding to the paper passing section (from one end of the current-carrying heat-generating layer to the branch of the branch circuit) The section up to the point) generates heat with a predetermined amount of heat per unit length, and image fixing processing for the small-sized recording material is executed.

In this case, the portion of the energized heat generating layer corresponding to the non-paper passing portion (the section from the branch point of the branch circuit to the other end of the energized heat generating layer) is not energized and does not generate heat, and therefore the non-paper passing portion of the heating body Excessive temperature rise is suppressed, and the above-mentioned problems caused by 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 energized heating layer, and the corresponding branches are connected according to the size width of the supplied recording material. By selectively controlling the energization of the electric circuits, it is possible to suppress excessive temperature rise in the heating body non-paper-passing area for recording materials of various sizes.

(B) The temperature of the current-carrying heat-generating layer near the conductive connection between the current-carrying heat-generating layer and the branch circuit tends to decrease slightly due to heat dissipation from the branch circuit, compared to other current-carrying heat-generating layer parts along the length of the current-carrying heat-generating layer. Therefore, there is no problem when heating the smallest size recording material, but it is necessary to heat the recording material larger than the minimum size, such as the largest size that can be passed through the device. At this time, due to the above-mentioned slight temperature drop in the part of the current-carrying heat-generating layer near the conductive connection between the current-carrying heat-generating layer and the branched electrical path, which is present in the middle of the paper passing width, the image fixing property of the recording material portion corresponding to the part decreases. Sometimes I do.

In the present invention, the part of the current-carrying heat-generating layer near the conductive connection part of the current-carrying heat-generating layer and the branch circuit is made of a material with a different resistance value from that of the other part of the current-carrying heat-generating layer, or by making the width and thickness narrower or thinner. As a result of the treatment, the resistance value of this part is made relatively higher than that of other parts, so the heat generation in this part increases more than that of other parts, and the heat dissipation by the branch electric circuit is compensated for (cancelled). This prevents a local temperature drop in the area.

Therefore, even when a recording material of a size larger than the minimum size is passed through the device, such as the largest size recording material that can be passed through the device, and the recording material is heated, there is continuity between the current-carrying heat generating layer and the branch electrical path that exist in the middle of the paper passing width. The occurrence of fixing unevenness caused by a local temperature drop in the energized heat generating layer near the connecting part is prevented, and uniform fixing performance is ensured in each part.

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

The image forming apparatus of this example is a transfer type electrophotographic copying apparatus that uses a fixed document table and moving optical system, uses a rotating drum type photoreceptor, and is capable of double-sided and multiple copying. Image forming principle of the copying device in this example
Since the process/mechanical configuration itself is publicly known, the explanation thereof will be kept brief.

Reference numeral 2 denotes a fixed document table glass, on which the image surface of the document 0 to be copied faces downward, and a predetermined! ! Place the gantry cover 3 on top of the gantry cover 3 to set it. In response to the copy start signal, the rotating drum type photoreceptor 6 is rotated clockwise as indicated by the arrow at a predetermined peripheral speed (process speed), and the peripheral surface of the photoreceptor is uniformly charged to a predetermined potential by the charger 30. Ru. In addition, the movable illumination lamp of the imaging optical system moves at a predetermined speed V, and the movable second mirror 1b and third mirror 1c move from the left side of the document table glass 2 at a speed of V/2. The downward image surface of set document 0 is sequentially optically scanned from the left side to the right side by being driven forward to the right side, and the scanned R8I image is captured by the imaging lens 1d, the fixed fourth mirror 1e, the fixed fifth mirror 1f, and the like.
Through the sixth mirror 1g, the surface of the rotating photoreceptor 6, which has been charged by the charger 3o, is imaged and exposed, so that an electrostatic latent image corresponding to the original image is formed on the circumferential surface of the photoreceptor 6. They are formed sequentially.

The latent image is then sequentially developed by a developing device 4 using toner (developer) made of resin or the like that softens and melts when heated. Then, the developed toner image is fed into the apparatus one by one from the first paper feeding cassette $531 or the second paper feeding cassette section 32, or by using the manual paper feeding means 33, and is fed into the apparatus by a pair of registration rollers 34. As a result, the images are sequentially transferred onto the surface of a transfer material sheet serving as a recording material that is fed to a transfer section between the photoreceptor 6 and the transfer/separation charger 5 at a predetermined timing.

The transfer material sheet that has undergone the image transfer is introduced into the fixing device 7 by the conveying device 36, where it undergoes image fixing processing and becomes an image-formed product (
The paper is ejected out of the machine by the paper ejection roller 37 as a copy (in the case of one-sided copy mode).

In the case of double-sided or multiple copying mode, the transfer material sheet that has been copied on one side or that has been copied for the first time from the fixing device 7 is introduced into the re-transport sheet bus mechanism section 38, and is transferred to the transfer section 5 where it is reversed or reversed. Duplex or multiple copying is performed by refeeding without being reversed.

After the image has been transferred, the photoreceptor 6 is cleaned by a cleaning device 35 to have a clean surface, turned over, and used for image formation.

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

Reference numeral 9 denotes an endless belt-shaped fixing film, which includes a driving roller 8 on the left side, a driven roller 11 on the right side, and a low heat capacity linear film as a heating element fixedly supported below between both rollers 8 and 11. The heating body 12 and a guide roller 8a disposed below the drive roller 8 are suspended between the four members 8, 11, 12, and 8a that are parallel to each other.

The driven roller 11 also serves as a tension roller for the fixing film 9, and the fixing film 9 rotates clockwise at a predetermined circumferential speed as the drive roller 8 rotates clockwise without wrinkling, meandering, or speed delay. Driven.

Reference numeral 17 designates a pressure roller having a rubber elastic layer made of silicone rubber or the like having good releasability, which serves as a pressure member and holds the downward film portion of the endless belt-shaped fixing film 9 between it and the heating member 12. The heating member 12 is pressed against the lower surface of the heating member 12 by a biasing means with a total contact pressure of, for example, 4 to 7 kg, and is rotated forward and counterclockwise in the conveyance direction of the transfer material sheet 16.

The rotatably driven endless belt-shaped fixing film 9 is repeatedly used to heat and fix toner images, so it has excellent heat resistance, releasability, and durability, and has a diameter of 100 μm or less, preferably 50 μm or less. Use thin-walled ones. For example, polyimide, polyetherimide, PES-PF
A single layer film of heat-resistant resin such as A (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin), or a composite layer film such as a 20 μm thick film, with PTFE (tetrafluoroethylene resin) on at least the image contact side. This includes a releasable coating layer made of a fluororesin such as PAF to which a conductive material is added to a thickness of 10 μm.

The low heat capacity linear heating body 12 as a heating body in this example has rigidity, high heat resistance, and heat insulation properties, and is horizontally long with the length extending in the transverse direction of the fixing film (direction perpendicular to the running direction of the fixing film 9). The heater support 12a has a heater support 12a, and a heater substrate 13 is integrally attached and held on the lower surface side of the support along the longitudinal direction of the lower surface.

As will be described later, this heater board 13 includes an energizing heat generating layer 14, a branch electrical path for limiting the heat generation (heating) range with respect to the length of the energizing heat generating layer 14 (heating body 12) as required,
It is equipped with a current-carrying electrode, a temperature sensor (temperature detection element) 10, and the like.

The heater support 12a is a heat insulating member that ensures the overall strength of the heating body 12, and is made of, for example, pps (polyphenylene sulfide), PAf (polyamideimide), PI (polyimide), or PEEK (polyetheretherketone).
, high heat-resistant resins such as liquid crystal polymers, and composite materials of these resins and ceramics, metals, glass, etc.

The heater board 13 is heat resistant and electrically insulating, and has, for example, a thickness of 1.0 mm, a width of 10 mm, and a length of 24 mm.
It is a 0mm alumina substrate. Or a composite material substrate containing this.

The heat generating layer 14 is, for example, coated with an electrically resistive material such as Ta2N, silver palladium, etc. to a width of 1.0 mm along the length approximately at the center of the lower surface of the substrate 13 on the film sliding side (screen printing, etc.). This is a linear or strip-shaped current-carrying heat generating layer with low heat capacity.

The temperature sensor 10 has an energizing heat generating layer 14 disposed on the surface of the substrate 13 on the opposite side to the side where the number is placed.

In this example, the temperature of the substrate 13 is detected as the temperature of the heating element 12 by the temperature sensor 10.

In this example, electricity is applied to the linear or band-shaped heat generating layer 14 from both longitudinal ends thereof to generate heat over the entire length of the heat generating layer. For example, electricity is supplied with a pulsed waveform of a DC power supply, and the temperature sensor 10 and the microcomputer-MPU
19 (IT diagram) Pulse (driving pulse) according to the desired temperature and energy release amount controlled by
The energization control circuit is configured to vary the pulse width.

In addition, in this example, a sheet leading/trailing edge detection sensor (
(not shown), and the period of energization of the heating element 14 is controlled to only the necessary period during which the sheet 16 passes through the fixing device 7 based on the sheet detection signal of the sensor.

The fixing film 9 is not limited to an endless belt shape, and as shown in the example in FIG.
It may be configured such that it passes under the guide roller 8a and is locked to the take-up shaft 41, and is caused to travel from the feed-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 an image forming start signal, and the transfer material sheet 16 carrying an unfixed toner image 15 on its upper surface is conveyed from the transfer section (5) side to the fixing device 7.
When the leading edge of the fixing film 9 is detected by the aforementioned sensor (not shown) disposed near the fixing device, rotation (or running) of the fixing film 9 is started, and the transfer material sheet 16 is guided by the guide 42 to the heating body 12. The toner enters between the fixing film 9 and the pressure roller 17 at the pressure contact portion N (fixing nip) between the toner and the pressure roller 17, and the unfixed toner image surface is brought into close contact with the lower surface of the fixing film 9 in the state of surface movement. The heating element 1 is placed in an overlapping state with the movable fixing film 9 without causing surface misalignment or wrinkles.
2 and the pressure roller 17 while being subjected to a pinching force.

W is the width of the heating element 14 provided on the lower surface of the heating element, and the heating element 14 is within the area where the lower surface of the heating element 12 and the upper surface of the pressure roller 17 are in mutual pressure contact, that is, the width of the fixing nip N. Exists within the area.

The toner image bearing surface of the sheet 16 receives heat from the heating element 14 via the fixing film 9 while passing through the fixing nip N while being in close contact with the fixing film surface, and the toner image is melted at a high temperature and the sheet 16 Soft adhesive 15a is applied to the surface.

In the case of the apparatus of this embodiment, the sheet 16, which is a recording material, and the fixing film 9 are separated from each other when the sheet 16 passes through the fixing nip N and comes out.

At this time of separation, the temperature of the molten toner 15a is still higher than the glass transition point of the toner, and therefore the bonding force between the sheet 16 and the fixing film 9 at this time of separation (
Since the sheet 16 has a small adhesion force, there is almost no toner offset to the fixing film 9 surface, and due to poor separation, the sheet 16 remains stuck to the fixing film 9 surface and gets wrapped around and jammed. It always separates smoothly.

The toner 15a is in a state where the temperature is higher than the glass transition point.
has appropriate rubber properties, so the toner image surface upon separation does not follow the surface of the fixing film and has an appropriate unevenness, and this surface property is maintained and the toner is cooled and individualized. Excessive image gloss does not occur on the fixed toner image surface, resulting in high quality images.

While the sheet 16 separated from the fixing film 9 is guided by a guide 43 and reaches the paper ejection roller pair (37), the temperature of the toner 15a, which is higher than the glass transition point, naturally cools down (naturally cools) to below the glass transition point. When the temperature reaches , individualization 15b is achieved, and a sheet 16 on which the image has been fixed is output.

(4) Heating range control of heating element FIG. 1 is a block diagram of a heating control circuit for the heating element 12. As shown in FIG.

In the figure, 14-18b and 18s-18c are heating elements 1
A current-carrying heat generating layer (14) formed on the lower surface of the substrate 13 on which the film moves, and three branches, first, second, and third, branching from predetermined positions in the middle of this heat generating layer. These are electric circuits (18b, 18e, 18C). Electric heating layer 14
is formed in a straight line along the length of the substrate approximately at the center of the lower surface of the substrate 13. 18a and 18d are this current heating layer 1
These are current-carrying electrodes (input terminals) made of a highly conductive material such as silver, which are provided at the left and right ends of 4. Each of the first to third branch electric circuits 18
b, 18e, and 18c are also made of a conductive material such as silver.

k is the effective full length range of the energizing heat generating layer 14 between the electrodes 18a and 18a, and 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 is set to correspond to the sheet width. It is.

In addition, in the case of this example, transfer material sheets of various sizes are supplied on a so-called one-sided basis, which is a baseline on the left end side of the energizing heat generating layer 14, and the first branch electric line 18b, the second branch electric line 18e and the third branch electric circuit 18c are branched from the energizing heat generating layer 14 at a distance h-1-j from the base line A, and each free end is located at a position corresponding to the right end of the energizing heat generating layer 14, or It is formed by extending to the outer position.

In this example, each distance 11h-1-j is 85th edition,
The length dimension is set to correspond to the width of the A4 size and 84 size sheets.

Since the lower surface of the heater substrate on which the energizing heat generating layer 18, the branch electric circuit 1B (b-e-c), etc. are formed is the sliding surface with the film 9, a sliding protection layer such as Ta205 is formed to protect the surface. It is preferable to do so.

The temperature sensor 10 is disposed on the upper surface side of the substrate 13, that is, on the side opposite to the side where the energizing heat generating layer 14 and the like are provided, and within an area that is the minimum paper passing area.

Reference numeral 22 denotes an operation panel of the image forming apparatus, which, as shown in the example in FIG. 9, includes a power switch 22a, a copy number setting key 22b,
A number display 22c, a transfer material size designating operation key (size selection key) 22d, a copy start key button 22e, and the like are arranged.

The size information selected and designated by the size selection key 22d is taken into the microcomputer MPU 19. M.P.
U19 sends a decoding signal corresponding to the specified size width to the decoder 20, and the decoded signal selectively drives the heating element driving circuits ~2 in accordance with the specified size width.

Each of the circuit engineers ~■ connects one of the terminals to the above-mentioned first to third terminals.
Branch electric circuits 18b, 18e, 18c and energizing heat generating layer 14
The other terminal of each circuit is shared and connected to the other current-carrying electrode 18a (common electrode) of the current-carrying heat generating layer 14 via the power source E. 21 is a memory circuit.

■When an A3 size sheet, which has the maximum size width, is selected as the transfer material sheet to be used, only the heating element drive circuit ■ is driven, and the electrodes 18a and
Voltage E is applied only between 18a, each of the first to third branch circuits ISB, 18e, and 18c is kept open, and the effective full length region k of the current-carrying heat generating layer 14 has a predetermined amount of heat generated per unit length. This generates heat and fixes the image on the A3 size sheet supplied to the apparatus without any problem.

■When the 85th plate sheet is selected as the transfer material sheet to be used, the heating element drive circuit is driven and the electrode 18
A voltage E is applied between the terminal a and the first branch circuit 18b.

As a result, the heat generating layer portion in the area corresponding to the paper passing portion of the 85-size sheet, that is, the heat generating layer portion from the electrode 18a on one end side of the energized heat generating layer 14 to the branching point of the first branch electric circuit 18b is per unit length. It generates heat with a predetermined amount of heat, and the image fixing of the 85-size sheet supplied to the apparatus is carried out without any problem.

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

■When an A4 size sheet is selected as the transfer material sheet to be used, the heating element drive circuit ■ is driven, and voltage E is applied between the electrode 18a and the second branch electric path 18e. The heat generating layer portion of area i corresponding to the paper passing section of the A4 size sheet generates heat with a predetermined amount of heat per unit length, and image fixation of the A4 size sheet supplied to the device is performed without any trouble, and the image is fixed without any problem. The heat generating layer portion corresponding to the paper passing portion (ki) does not generate heat, and excessive temperature rise of the heating body portion corresponding to the non-paper passing portion (ki) is suppressed.

■When the 84-size sheet is selected as the transfer material sheet to be used, the heating element drive circuit ■ is driven, and voltage E is applied between the electrode 18a and the third branch electric path 18c, The heating layer portion of the region j corresponding to the paper passing portion of the plate sheet generates heat with a predetermined amount of heat per unit length,
The image fixing of the 84-size sheet supplied to the apparatus was performed without any problem, and the heating layer portion corresponding to the non-sheet passing area (k-j) did not generate heat, and the heating layer corresponding to the non-sheet passing area (k-j) did not generate heat. Excessive temperature rise in body parts is suppressed.

(5) Structure of electric circuit branch part (Figs. 2 and 3) Current-carrying heat generating layer 1
In this example, as shown in the partially enlarged view of FIG. ' and the other part 14, the resistance value per unit area is the former part 14
2 so that ′ is higher than the latter part 14.
The entire length of the current-carrying heat generating layer 14 is constructed by applying different types of resistance materials.

Specifically, the portion 14 is coated with silver/palladium, and the portion 14' is coated with ruthenium oxide to constitute the entire length of the energizing heat generating 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 energized heat generating layer 14, the amount of heat generated in the portion 14' increases compared to that in the portion 14.

In other words, the temperature of the current-carrying heat-generating layer portion 14' near the conductive connection between the current-carrying heat-generating layer 14 and the branch circuits 18 (b-c, e) is compensated for by the presence of the branch circuit, and the temperature decreases with respect to other portions 14. Prevented.

Therefore, as explained in section (B) of the above (effects), the large size recording material (A4/B4) is larger than the small size recording material (B5).
・A3) Even when the paper is passed through, the first
- The problem of deterioration of fixing performance at the branch portions of the third branch electric circuits 18b, 18e, and 18c does not occur.

Although silver palladium and honey oxide have been described above as examples of two types of materials, the invention is not limited to this, and combinations of various materials are possible.

It is also possible to increase the resistance value per unit area of the portion 14' relative to the portion 14 by changing the mixing ratio of silver and palladium.

As a means of making the resistance value of the portion 14' higher than that of the portion 14, as shown in FIG.
It is also good to make it gradually narrower than 4. This results in part 14
' has a higher resistance than the portion 14, making it possible to gradually increase the amount of heat generated by the portion 14'.

In this case, there is no need to separately apply two different types of resistance materials as in the case of FIG. 2, so that the manufacturing process can be simplified.

Another method is to change the thickness of the heat generating layer. That is, in FIG. 2, by making the thickness of the heat generating layer 14' thinner than that of the heat generating layer 14, the resistance value of the heat generating layer 14' near the branch of the branch circuit can be made smaller than that of the other heat generating layer parts 1.
It is also possible to increase the amount of heat generated by making the temperature relatively higher than 4.

In any of the above cases, the resistance value of the portion 14' is
By compensating for the heat dissipation due to the presence of the branch circuit from the section 14
The amount of heat generated is set so that there is no substantial temperature difference between the

(6) Others ■Each branch electric circuit 18b, 18e, 18c has a current heating layer 14
The conductive connection may be made at an inclined angle with respect to ' as shown in FIGS. 1 to 3, or the conductive connection may be made at a substantially right angle as shown in FIG.

■Electricity heating layer 14 of each branch circuit 18b, 18e, 18c
The branch side end portion relative to ' may be superimposed on the upper side of the energizing heat generating layer 14' for electrical connection, or may be interposed between the energizing heat generating layer 14' and the substrate 13 for electrical connection.

(2) FIG. 5 shows an example of the structure of the branch electric circuit in the case of sheet feeding based on the so-called central reference. The mouth is the central baseline.

(Effects of the Invention) As explained above, according to the present invention, the required heating (heat generation) in the longitudinal direction of the heating body is limited to the paper passing section range corresponding to the size width of the recording material used by providing the branch electric circuit. , it is possible to suppress unnecessary heating in the non-paper passing area, and prevent excessive temperature rise in the non-sheet passing area of the heating body. It becomes possible to maintain a substantially uniform temperature over the entire effective length of the heating element.

As a result, the durability life of the linear heating element, fixing film, pressure member, etc. may be reduced due to temperature non-uniformity, and their damage may occur.
Contamination, etc. can be prevented. In addition, it is possible to suppress runnability defects such as offset and wrinkles of the fixing film.

In addition, by making the resistance value of the current-carrying heat-generating layer near the conductive connection between the current-carrying heat-generating layer and the branch current path relatively higher than that of other current-carrying heat-generating layer parts, the conductive connection between the current-carrying heat-generating layer and the branch current path is made relatively higher. This eliminates local temperature drops in the area, and uniformizes the heat generation (temperature distribution) along the length of the current-carrying heat generating layer, allowing for good fixing processing for each size of recording material without causing localized defective fixing areas. can be executed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the heating control circuit. FIG. 2 is an enlarged view of the conductive connection between the current-carrying heat generating layer and the branch circuit. Figures 3 and 4 are the same diagrams of other examples. FIG. 5 is an example of another configuration of the branch circuit. FIG. 6 is a schematic diagram of the configuration of an example of a fixing device. FIG. 7 is the same diagram as above of another example. FIG. 8 is a schematic diagram of the configuration 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 document table glass, 3 is a yX document gantry bar, 4 is a developer, 5 is a transfer/separation charger, 6 is a rotating drum type photoreceptor, 7 is a fixing device, 8 is a drive roller, 9 is a film, 10 is a temperature sensor, 11 is a driven roller, 1
2 is a heating element, 13 is an alumina substrate, 14 and 14' are energizing heating resistors, 18b-18e-18c are branch electrical circuits, 15
1 is a toner image, 16 is a transfer material sheet, and 19 is an MPU.

Claims (4)

[Claims] (1) A film is brought into contact with the heating element and moved, a recording material is brought into close contact with the surface of the film opposite to the heating element side, and the recording material is moved and passed through the heating element position together with the film to record from the heating element through the film. The heating body is a fixing device that applies thermal energy to a recording material, and the heating body has a current-carrying heat-generating layer whose length is in a direction intersecting the moving direction of the recording material and is energized from both ends, and the heating body has a current-carrying heat-generating layer that extends along the length of the current-carrying heat-generating layer. It has a branch electric path which branches from at least one predetermined position in the middle and is selectively controlled to be energized, and the resistance value of the energized heat generating layer portion near the conductive connection portion between the energized heat generating layer and the branched electric path is determined by another energization. A fixing device characterized by being relatively higher than a heat generating layer portion. (2) The current-carrying heat-generating layer portion near the conductive connection between the current-carrying heat-generating layer and the branch circuit is made of a material with a different resistance value from that of the other parts, so that the resistance value of the current-carrying heat-generating layer portion is made to be relatively higher than that of other current-carrying heat-generating layer portions. 2. The fixing device according to claim 1, wherein the fixing device has a high height. (3) By narrowing the width of the current-carrying heat-generating layer near the conductive connection between the current-carrying heat-generating layer and the branch circuit, the resistance value of the current-carrying heat-generating layer can be made relative to that of other current-carrying heat-generating layer parts. The fixing device according to claim 1, wherein the fixing device is raised. (4) By making the thickness of the current-carrying heat-generating layer portion near the conductive connection between the current-carrying heat-generating layer and the branch current line thinner than the other parts, the resistance value of the current-carrying heat-generating layer portion is made relative to that of other current-carrying heat-generating layer portions. 2. The fixing device according to claim 1, wherein the fixing device has a high height.