JPH0519652A - Heating device - Google Patents

Abstract

PURPOSE:To solve problems, such as generation of the high-temp. offset occurring in the heating up of a non-paper passage part, unstable driving of a film, and wrinkling of the film, by preventing the heating up of the non-paper passage part of the heating device of a film heating system. CONSTITUTION:This heating device imparts the heat energy of a heating element 4 to a material P to be heated via a heat resistant film 1 moving in tight contact with the heating element 4 by bringing the material P to be heated into tight contact with the surface of the heat resistant film 1 on the side opposite from the heating element 4 side and passing this material in the position of the heating element 4 together with the heat resistant film 1. The heating element 4 of the above-mentioned device is an electric heating element of a self- temp. control type having a positive resistance temp. characteristic and is provided with a pair of electrodes 6a, 6b for energization to the heating element 4 along the longitudinal direction of the heating element 4 respectively in both longitudinal side parts of the heating element 4, the longitudinal direction of which is in the direction orthogonal with the moving direction of the heat resistant film 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device of the type which applies heat energy to a material to be heated such as a recording material through a heat resistant film.

This device is an electrophotographic copying machine, printer,
An image heating and fixing device in an image forming apparatus such as a fax, that is, a recording material (electrofax sheet. A recording material carrying an unfixed toner image corresponding to the target image information formed on the surface of an electrostatic recording sheet, a transfer material sheet, a printing paper, etc. by a direct method or an indirect (transfer) method. It can be used as an image fixing device that performs heat fixing processing as a permanently fixed image on the surface.

In addition, it can be used, for example, as a device for heating a recording material carrying an image to modify the surface properties of gloss and the like, and a device for post-fixing.

[0004]

2. Description of the Related Art Conventionally, a heating device for a recording material, for example, for heating and fixing an image, includes a heating roller which is maintained at a predetermined temperature, and a pressure roller which has an elastic layer and is in pressure contact with the heating roller. Therefore, a heat roller method is widely used in which a recording material is nipped and conveyed and heated.

Various methods and configurations such as a flash heating method, an oven heating method and a hot plate heating method are known and put into practical use.

Recently, a fixedly supported heating element, a heat-resistant film (fixing film) which is conveyed while being pressed against the heating element, and a pressing member for bringing a recording material into close contact with the heating element via the film. An apparatus having a system and configuration that has the heat-fixing property of an unfixed image formed and carried on the surface of the recording material by applying the heat of the heating body to the recording material through the film (film heating method). Has been devised.

According to the applicant's earlier proposal, for example, Japanese Patent Laid-Open No.
The system, device, etc. disclosed in Japanese Patent Laid-Open No. 3-313182 belong to this, and a thin heat-resistant film (sheet), a moving driving means for the film, and a fixed support of one side of the film with the film inside. Pressurizing the heating element (heater) arranged on the other surface side and the developing material image-bearing surface of the recording material, which is arranged facing the heating element on the other surface side and through which the image is fixed, to the heating element. The member has a member, and at least when performing image fixing, the film is moved at a same speed in the forward direction as the recording material to be image-fixed which is conveyed and introduced between the film and the pressure member to move the moving film. The recording medium is passed through a fixing nip portion as a fixing portion formed by pressure contact between a heating body and a pressing member, and the developed image bearing surface of the recording material is heated by the heating body through the film to produce a developed image. Thermal energy to (unfixed toner image) Chromatography granted to allowed softened and melted, and then a heating means or apparatus which is based on that are spaced from each other by a separation point of the recording material and the film after fixing portion passes.

In such a film heating type apparatus, since a low heat capacity heating element can be used as a heating element, power consumption is reduced as compared with the conventional contact type heating roller type or belt heating type apparatus. This is an effective one because it has advantages such as reduction of operating time and reduction of wait time (quick start), and resolution of various drawbacks of other conventional heating type devices.

[0009]

In the heat roller system, when the heat fixing operation is continuously performed by using a recording material having a small size, the heat roller portion where the recording material comes into contact and the heat roller portion where the recording material does not come into contact with each other. There is a difference in heat dissipation. That is, the surface temperature of the heat roller is higher in the heat roller area where the recording material does not pass than in the area where the recording material passes. This is a phenomenon conventionally called "temperature rise in non-sheet passing portion".

In the case of the heat roller method, the temperature of the heat roller surface at the position where all usable recording materials always pass is detected to control the temperature, but the temperature rise in the non-sheet passing portion occurs. At that time, if the size of the recording material used is changed to a larger size, the surface temperature of the heat roller part outside the smaller size processed up to that point becomes too high due to the temperature rise in the non-sheet passing part. High temperature offset may occur.

Even in the film heating method, when a small-sized recording material is continuously heat-treated, the same mechanism as the heat roller method causes a temperature rise in the non-sheet passing portion on the heating body and the film, which causes a high temperature offset. It may occur.

Further, when an endless belt-shaped film is used in the film heating system, the temperature of the drive shaft for driving the film also rises due to heat conduction from the film. Therefore, when a small-sized recording material is continuously processed, the temperature of the drive shaft is not uniform in the axial direction due to the temperature rise in the non-sheet passing portion of the heating body and the belt. Then, the diameter of the drive shaft becomes non-uniform in the axial direction.

It has been conventionally known that when the shaft for driving the endless belt has a taper difference in diameter, the belt is displaced in the large diameter direction. Therefore, if the outer shape of the drive shaft in the axial direction changes over time by continuously heating the small-sized recording material as described above, the film difference due to the difference in the outer shape of the drive shaft will occur. The displacement direction also changes with time, and the film drive tends to become unstable.

Further, as a film, 100 μm or less,
In particular, when a thin material having a thickness of about 40 μm or less and a high elastic modulus such as polyimide is used, wrinkles may occur if the displacement direction of the film on the drive shaft is not uniform.

In particular, in the case of a film heating system in which a heating body having a low heat capacity can be used as the heating body, since the heating body has a smaller heat capacity than the heating roller system, the temperature rise in the non-sheet passing portion of the heating body is large and the heating temperature is high. Offset is likely to occur, and problems such as instability of film drive and wrinkles of the film are likely to occur.

In the case of the film heating method, the heating element and the film slide, and in this case, it is known that the friction coefficient has temperature dependency. Experiments by the present inventors have revealed that when the friction coefficient between the heating body and the film changes, the displacement speed of the film in the direction of the drive axis changes. Then, the temperature of the heating element in the direction of the drive shaft axis becomes non-uniform, the driving stability of the film is further impaired, and the risk of wrinkling of the film becomes even greater.

The problems with the above film are:
This can occur not only when a small-sized continuous sheet is passed, but also when the running width of the film is wider than the maximum width of the recording material.

Therefore, the present invention prevents the above-described temperature rise in the non-sheet passing portion in the heating device of the film heating type, thereby generating a high temperature offset due to the temperature rise in the non-sheet passing portion and unstable driving of the film. The purpose is to eliminate problems such as wrinkling of the film.

[0019]

The present invention is a heating device characterized by the following constitutions.

(1) A material to be heated is brought into close contact with the surface of the heat-resistant film that moves in close contact with the heating body on the side opposite to the side of the heating body, and is passed through the position of the heating body together with the heat-resistant film. In a heating device for applying heat energy to a material to be heated through a heat resistant film, the heating body is
A self-temperature control type energization heating element having a positive resistance temperature characteristic, wherein a pair of electrodes for energizing the heating element has a longitudinal direction in a direction intersecting the moving direction of the heat resistant film. A heating device, wherein the heating device is provided along both sides of the heating element on both sides of the heating element.

(2) The heating device according to (1), wherein the width of the film, which is a direction intersecting the moving direction of the heat-resistant film, is wider than the maximum width of the heated material that can be passed through.

[0022]

The self-temperature control type heating element having a positive resistance temperature characteristic (PTC characteristic) (hereinafter referred to as PTC heating element) is, for example, a fired molded body of barium titanate or the like. -As shown in an example of the resistance value characteristic, the resistance value has a property of rapidly increasing at a predetermined temperature (switching temperature). By using this characteristic, if the temperature of the heating element in the paper passing portion of the material to be heated (recording material) is set to be almost the same as the switching temperature, the amount of heat radiated in the non-paper passing portion area of the heating element is small Even if the temperature rises, the resistance of the heating element sharply increases, so that the calorific value only sharply decreases only in the non-sheet passing area of the heating element, and as a result, the temperature rise of the non-sheet passing portion is suppressed.

In this case, when a current is applied to the PTC heating element in the longitudinal direction from both ends of the PTC heating element, electric power is not supplied at the sheet passing portion in the longitudinal direction, and fixing failure occurs. Because the temperature is higher than the specified temperature in the non-sheet passing area, the resistance in this area is rapidly increasing.
This is because the current does not flow.

Therefore, according to the present invention, a pair of electrodes for energizing the PTC heating element are provided on both longitudinal sides of the PTC heating element along the longitudinal direction, respectively, and the PT is provided between the pair of electrodes.
The PTC heating element is configured to generate heat by passing an electric current through the C heating element. With this, in the longitudinal direction of the PTC heating element, fixing failure does not occur in the heating element portion corresponding to the sheet passing portion. The electric power supply state is maintained, and the heating element portion corresponding to the non-sheet passing portion becomes a predetermined temperature or higher, so that the resistance value suddenly rises and the current decreases and the temperature rise is moderated. The temperature distribution in the longitudinal direction of is uniformized.

Therefore, the occurrence of temperature rise in the non-sheet passing portion is suppressed,
It is possible to prevent the occurrence of high-temperature offset, the unstable driving of the film, the wrinkling of the film, and the like due to the temperature rise in the non-sheet passing portion.

Since the PTC heating element has a self-temperature control characteristic, it is possible to eliminate a special temperature control means.

[0027]

【Example】

<Example 1> (Figs. 1 and 2) Fig. 1 is a schematic configuration diagram of a heating device according to an example, and Fig. 2 is a vertical plan view in which a middle portion of a heating element is omitted. The heating device of this example is an image heating and fixing device of an image forming apparatus. (1) The device structure 1 is an endless belt-shaped fixing film (heat-resistant film), and includes a left driving roller 2, a right driven roller 3, and a heating element disposed below the driving roller 2 and the driven roller 3. 4 are suspended between the three members 2, 3, and 4 which are parallel to each other.

This endless belt-shaped fixing film 1
Is rotated and repeatedly used for heating and fixing a toner image, and therefore, it has excellent heat resistance, releasability, and durability, and generally has a thickness of 100 μm or less, preferably less than 40 μm. . For example, a single layer film of a heat-resistant resin such as polyimide, polyether imide, PES, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin) or a composite layer film, for example, a 20 μm thick film at least on the image contact surface side. In addition, a releasable coating layer obtained by adding a conductive material to a fluororesin such as PTFE (tetrafluoroethylene resin) / PAF and having a thickness of 10 μm is used.

The driven roller 3 also serves as a tension roller for the endless belt-shaped fixing film 1, and the fixing film 1 is rotated at a predetermined peripheral speed in the clockwise direction with the clockwise rotation of the driving roller 2, that is, image formation. Department side (20)
The unfixed toner image Ta conveyed from the recording medium is rotatably driven at a peripheral speed substantially the same as the conveying speed of the recording material P as a material to be heated, which is carried on the upper surface.

The drive roller 2 is a metal roller coated with a heat resistant material having a high friction coefficient with respect to the film 1, for example, silicon rubber, and the driven roller 3 has a friction coefficient lower than that of the drive roller 2, for example, a solid metal. For example, Laura.

Numeral 8 is a pressure roller having a rubber elastic layer such as silicon rubber having a good releasability as a pressure member, and the lower side film portion of the endless belt-shaped fixing film 1 is sandwiched between the heating rollers. The lower surface of the body 4 is pressed against the lower surface of the body 4 by an urging means (not shown) with a total pressure of 4 to 7 kg, and rotates counterclockwise in the forward direction of the conveyance direction of the recording material P.

As shown in FIG. 2, the heating element 4 is a horizontally long thin plate-like PTC heating element having a length in a direction intersecting the moving direction of the film 1 (film width direction). A pair of energizing electrodes 6 along the length
It is equipped with a.6b. The pair of electrodes 6a
By energizing the PTC heating element 4 between 6b, the PTC
The heating element 4 generates heat over the entire length. This heating element 4
6a and 6b are fixedly supported by attaching and holding them to the support 5.

The support 5 has a heat insulating property, a high heat resistance, and a rigidity for adiabatically supporting the heating body 4 to the fixing device and the image forming apparatus. For example, PPS (polyphenylene sulfide), PAI (polyamideimide), PI ( It can be made of high heat resistant resin such as polyimide), PEEK (polyether ether ketone), liquid crystal polymer, or a composite material of these resins and ceramics, metal, glass, or the like.

(2) Fixing Execution Operation The image forming start signal causes the apparatus to perform an image forming operation and is conveyed from the image forming unit side (20) to the fixing apparatus. The recording material P is guided by the guide and enters between the fixing film 1 and the pressure roller 8 at the pressure contact portion (fixing nip portion) N between the heating body 4 and the pressure roller 8 to form an unfixed toner image. The surface is in close contact with the lower surface of the fixing film 1 which is rotated in the same direction as the recording material P at the same speed as the conveyance speed of the recording material P, and in the overlapping state with the fixing film 1, the mutual pressure contact portion between the heating body 4 and the pressure roller 8 is pressed. It passes through N while receiving a clamping pressure. Since the heating element 4 is electrically heated by the image forming start signal at a predetermined timing, the toner image Ta is heated at the press contact portion N and becomes the softened / melted image Tb.

The running direction of the fixing film 1 is turned at a steep angle (the bending angle θ is about 45 °) at the edge portion S (having a radius of curvature of about 2 mm) of the support 5 having a large curvature. Therefore, the recording material P conveyed through the pressure contact portion N while being overlapped with the fixing film 1 is separated from the fixing film 1 at the edge portion S by curvature and is discharged. By the time the paper is discharged, the toner is sufficiently cooled and solidified and is in a state of being completely fixed on the sheet P (toner image Tc).

In FIG. 2, the length dimension of the pressure roller 8 is A, the length dimension of the heating element (PCT heating element) 4 is B, the width dimension of the film is C, and the maximum width dimension of the recording material that can be passed. D,
Then, the relational structure of A>B>C> D is set.

Further, E is a paper passing area when a small-sized recording material is passed, and F is a non-paper passing area. PT which is a heating element
If the temperature of the heating element portion of the recording material sheet passing area E of the C heating element 4 is set to be substantially the same as the switching temperature, the temperature rises because the heat radiation amount of the heating element non-sheet passing area F is small. Also, since the resistance of the heating element portion corresponding to the non-sheet passing area F sharply rises, only the non-sheet passing area F of the heating element rapidly lowers the calorific value, and as a result, the temperature rise of the non-sheet passing portion is suppressed. It will be.

That is, with respect to the longitudinal direction of the PTC heating element 4, the heating element portion corresponding to the sheet passing area E is kept in a sufficient power supply state that does not cause fixing failure, and the heating element corresponding to the non-sheet passing area F. A portion of the PTC heating element 4 has a temperature rise above a predetermined temperature, so that the resistance value suddenly increases to reduce the current, and the temperature rise is moderated.

Therefore, the occurrence of temperature rise in the non-sheet passing portion is suppressed,
It is possible to prevent the occurrence of high-temperature offset, the unstable driving of the film, the wrinkling of the film, and the like due to the temperature rise in the non-sheet passing portion. Further, since the PTC heating element 4 has a self-temperature control characteristic, it is possible to eliminate a special temperature control means.

Example 2 (FIG. 4) FIG. 4 shows another structural example of the heating body. In the heating element of this example, the PTC heating element 4 is integrally formed on the heat transfer plate 9 having good heat conduction, and the surface of the heat transfer plate 9 opposite to the PTC heating element 4 side is made of a heat-resistant material such as fluororesin. The protective layer 10 made of a material having excellent properties and slidability is formed, and the surface of the protective layer 10 is covered with the film 1
The film 1 is brought into close contact as a contact surface with and run.

A pair of energizing electrodes 6a and 6b for the PTC heating element 4 are provided on both sides of the PTC heating element 4 in the longitudinal direction (direction intersecting with the moving direction of the film 1) in the same manner as in the first embodiment. It is equipped with.

The support 5 for the heating element is a heat insulating material such as bakelite, and heat-insulates and supports the heating elements 4, 6a and 6b with respect to the entire fixing device and image forming apparatus.

The heat generated by the PTC heating element 4 is applied to the recording material P through the heat transfer plate 9 having good thermal conductivity, the protective layer 10 and the film 1.

<Embodiment 3> (FIG. 5) FIG. 5 shows a structural example of still another heating body. A heat transfer plate 9 having good heat conduction is integrally formed so as to surround the PTC heating element 4, and a pair of energizing electrodes 6a and 6b are provided on the upper and lower portions of the heating element 4 along the length of the heating element. By energizing, the heating element 4 is caused to generate heat and the heat transfer plate 9 is maintained at a predetermined temperature.

The heat insulating support 5 such as bakelite is the heating body 4.
6a and 6b are thermally insulated, and heat is efficiently applied to the recording material P side through the electrode 6b, the heat transfer plate 9 and the film 1.

A protective layer (10) may be provided on the surface of the heat transfer plate 9 in contact with the film 1 as in the second embodiment.

The film 1 is not limited to the endless belt-shaped one, and a roll-wound long end film can be fed and run.

[0048]

As described above, according to the present invention, in the film heating type heating device, it is possible to suppress the occurrence of the temperature rise in the non-sheet passing portion, the occurrence of the high temperature offset due to the temperature rise in the non-sheet passing portion, Driving instability and film wrinkles are prevented. Further, since the PTC heating element as a heating element has a self-temperature control characteristic, it is possible to eliminate a special temperature control means, and the power supply configuration to the heating element (heating element) becomes very simple. Further, it is possible to realize an image forming apparatus or the like that has a small standby time, power consumption, and low temperature rise inside the machine.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a heating device (image heating and fixing device) according to an embodiment.

FIG. 2 is a vertical cross-sectional plan view of a heating element using a PTC heating element.

FIG. 3 is a graph showing an example of temperature-resistance value characteristics of a PTC heating element.

FIG. 4 is a main part diagram of a second embodiment device.

FIG. 5 is a main part diagram of a third embodiment device.

[Explanation of symbols]

1 Heat resistant film (fixing film) 2 drive roller 3 Driven roller 4 Heating element (PTC heating element) 5 support 6a ・ 6b Current-carrying electrodes 8 pressure roller P Recording material (heated material)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryo Hayakawa             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Shunji Nakamura             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation

Claims (2)

[Claims] 1. The heat of the heating body is obtained by bringing a material to be heated into close contact with the surface of the heat-resistant film that moves in close contact with the heating body on the side opposite to the side of the heating body, and passing the material together with the heat-resistant film through the position of the heating body. In a heating device for applying energy to a material to be heated through a heat resistant film, the heating element is a self-temperature control type energization heating element having positive resistance temperature characteristics, and for energizing the heating element. A heating device, characterized in that a pair of electrodes are provided along both sides of the heating element on both longitudinal sides of the heating element having a length in a direction intersecting the moving direction of the heat resistant film. 2. The heating device according to claim 1, wherein the width of the film, which is a direction intersecting with the moving direction of the heat resistant film, is wider than the maximum width of the heated material that can be fed.