JPH08241003A - Image heating device - Google Patents

Abstract

PURPOSE: To prevent the irregularities of an unfixed toner image from occurring by water vapor and to enhance the image quality by setting the center position of a heating element on a more downstream side than the center position of a nip with respect to the moving direction of a film. CONSTITUTION: The heat resistant film 25 is an endless belt-like film and hung and spread among three mutually parallel members of a driving roller, a driven roller and a heating body 20 disposed so as to be fixed and supported by being held by a heater supporting body 21 at the lower part between both rollers. In this case, a position between a heater unit and a pressure roller 28 is decided by the nip formed by the heater unit and the roller 28 through the film 25 after a heater is stuck to the supporting body 21 so that the center position Wc of the heating element 23 in the heater is positioned on a more paper ejection side (the downstream side in the moving direction of the film 25) than the center position Nc of the nip. Then, the stacked toner is crushed and fixed to a recording material mainly by pressing force on the entrance side of the nip when the quantity of the water vapor is compratively small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating apparatus applied to a copying machine, a laser beam printer and the like, and more particularly to an apparatus for heating an unfixed toner image by heat from a heating body via a film.

[0002]

2. Description of the Related Art Conventionally, a film heating type heating device is
For example, JP-A-62-313182 and JP-A-2-1.
No. 57878 and the like, an example of which is shown in FIG.
Shown in

FIG. 5 shows an enlarged cross-sectional model view of a main part of a film heating type heating device (image heating and fixing device).

Reference numeral 200 denotes a heating body (ceramic heater). A heat-resistant film (fixing film) 250 is brought into close contact with the heating body 200 by a pressure roller 280 as a pressure member to be slid and conveyed. A recording to be image-fixed as a material to be heated between the pressure roller 280 and the heat resistant film 250 in the pressure contact nip portion (fixing nip portion) N formed by the heating body 200 and the pressure roller 280 with the 250 sandwiched therebetween. The heat of the heating element 200 is applied to the recording material P through the heat-resistant film by introducing the material P and nip-conveying the pressure contact nip portion N together with the heat-resistant film 250, and the unfixed image on the recording material P is exposed. An image (toner image) is heated and fixed on the surface of the recording material P. The recording material P passing through the pressure nip portion N is separated from the surface of the film 250 and conveyed.

The heating element 200 comprises a heat-resistant film 250 or an elongated heat-resistant / heat-conductive substrate 220 having a lengthwise direction perpendicular to the conveying direction a of the recording material P as a material to be heated, and the substrate 220. A resistance heating element 230 formed along the length of the substrate at the center in the lateral direction on the surface side, a heat resistant overcoat layer 240 for protecting the surface of the heating element on which the resistance heating element is formed, and a length of the resistance heating element 230. It is a linear heating element having a low heat capacity as a whole, which is composed of a power feeding electrode (not shown) at both ends and a temperature detecting element such as a thermistor for detecting the temperature of the heating element provided on the back surface side of the substrate.

This heating element 200 is fixedly arranged by holding it on a heater support 210 having rigidity and heat insulation by exposing the surface side on which the resistance heating element 230 is formed and provided downward.

The heater support 210 is provided on the heater substrate 2
For the purpose of protecting the heat resistant film from the edges of 20 and ensuring slidability, convex portions are provided on both sides thereof.

The heating element 200 is heated by heating the resistance heating element 230 over the entire length of the resistance heating element 230 by supplying power to the electrodes at both ends thereof, and the temperature rise is detected by a temperature detecting element. The current is fed back to the control circuit (not shown) and the energization of the resistance heating element 230 is controlled so that the temperature of the heating element is maintained at a predetermined temperature.

The heat-resistant film 250 may have a structure in which it is formed into an endless belt shape and is rotationally driven and conveyed, or there is a structure in which it is a roll-wound long film and is fed out and conveyed.

In the conventional apparatus, the center of the width of the heating element substrate 220 in the widthwise direction and the center of the width W of the resistance heating element 230 in the widthwise direction Wc are substantially aligned with the center Nc of the pressure contact nip portion N. It was

The width W of the resistance heating element 230 in the widthwise direction is almost equal to or less than the width of the pressure contact nip portion N, and the pressure contact nip portion N is heated intensively. It was

[0012]

However, in the above-mentioned conventional example, since the heating element is located substantially in the center of the nip portion N in the pressure contact nip portion N, that portion has the highest temperature in the nip portion. At this time, when the process speed is low, it does not appear so much, but as the process speed increases, the following problems occur.

At the same time when the recording material P carrying the unfixed toner image T plunges into the pressure contact nip portion N, the water contained in the recording material P explosively becomes a large amount of water vapor at one time, which is recorded in the nip portion. Since it blows out in the material carrying-in direction, there is a problem that the unfixed toner image T is scattered.

This phenomenon occurs especially when the water vapor b generated in the pressure contact nip portion N blows out in a line image perpendicular to the recording material conveying direction a when the water vapor escape path of the line image is blocked. Cheap.

[0015]

In order to solve the above problems, the present invention provides a heating element having a heating element, a film sliding on the heating element, and a nip with the heating element via the film. An image heating device for heating the unfixed toner image by sandwiching and transporting a recording material carrying an unfixed toner image in the nip, the central position of the heating element in the moving direction of the film. Is on the downstream side of the central position of the nip.

[0016]

【Example】

(Embodiment 1) FIG. 1 is a schematic configuration diagram of an example of a film heating type image heating apparatus as a heating apparatus of the present embodiment, and FIG. 2 is an enlarged cross-sectional model view of a main portion.

In FIG. 1, the heat-resistant film 25 is an endless belt-shaped film, and is fixedly supported by a driving roller 26, a driven roller 27, and a heater support 21 below the rollers 26 and 27. And the three members 26, 27, 20 parallel to each other
It is suspended between them.

The driven roller 27 also serves as a tension roller for the film 25, and the film 25 is conveyed in a clockwise direction at a predetermined peripheral speed as the drive roller 26 is driven to rotate in the clockwise direction, that is, from the image forming portion side (not shown). The unfixed toner image T is rotatively driven without wrinkles, meandering, or speed delay at the same peripheral speed as the conveying speed of the recording material P as a material to be heated having the unfixed toner image T carried on the upper surface.

The pressure roller 28, which is a pressure member, is a roller having a rubber elastic layer having a good releasability such as a silicone gome, and is placed on the lower surface of the heating body 20 with the lower film portion of the film 25 sandwiched therebetween. On the other hand, by the biasing means, for example, abutting pressure of a total pressure of 4 to 10 kg is applied to face each other.
The recording material P is rotated counterclockwise in the forward direction in the conveying direction.

Since the endless belt-shaped film 25 that is rotationally driven is repeatedly subjected to heat fixing of a toner image, it has excellent heat resistance, releasability and durability, and generally has a total thickness of 100 μm or less, preferably Is a thin wall of 40 μm or less.

For example, polyimide / polyetherimide /
A single layer film of a heat-resistant resin such as PES / PFA (tetrafluoroethylene-barfluoroalkyl vinyl ether copolymer resin) or a composite layer film, for example, a 20 μm thick film, is provided with PTFE (tetrafluoroethylene) at least on the image contact surface side. (Resin) -PAF or the like, and a release coating layer having a thickness of 10 μm in which a conductive material is added to a fluororesin.

In the present embodiment, the substrate 22 of the heating body 20
Is, for example, alumina or aluminum nitride, and is both heat conductors having a thickness of 1 mm, a width of 7 mm, and a length of 240 mm. Further, on the surface of the substrate 22, a current-carrying heating element 2 is provided in the longitudinal direction.
3 which is, for example, Aa / Pd, PuO ₂ , Ta ₂
An electrical resistance material such as N is applied in a band shape by screen printing or the like.

At both ends of the electric heating element 23, there are power supply electrodes formed on both end surfaces of the substrate surface for conduction.
It is formed by coating Ag or the like by screen printing or the like. The energization heating element 23 generates heat over the entire length by energizing an energization circuit (not shown) between the electrodes. The heater support 21 is, for example, PPS (polyphenylene sulfide), PAI.
(Polyamide imide), PI (polyimide), PEEK
(Polyether ether ketone) A high heat resistant resin such as a liquid crystal polymer or a composite material of these resins and ceramics, metal, glass or the like can be used. At this time, after the heater is attached to the heater support, the nip formed with the pressure roller via the heater unit and the film is such that the center position Wc of the heating element in the heater is as shown in FIG. The positions of the heater unit and the pressure roller are determined so that they are located on the paper discharge side (downstream in the moving direction of the film) with respect to the central position Nc.

Further, the heater support is configured to have a wider front side (θ ₁ ≧ θ ₂ ) than the discharge side.

That is, the shape of the heater support has an inflection point on both the upstream and downstream sides of the material to be heated, and the nip horizontal line (tangent at the nip) and the slope (that is, the support) from this inflection point. If the angle formed by the film surface guided by the body is θ ₁ on the upstream side in the transport direction and θ ₂ on the downstream side, then θ ₁
It has a relation of ≧ θ ₂ .

Reference numeral 29 denotes a temperature detecting element, which is arranged in contact with the position on the back surface side of the substrate corresponding to the position of the resistance heating layer.
The resistance heating element 23 is temperature-controlled to a predetermined temperature according to the output of the temperature detecting element 29 provided on the back surface of the substrate.

With the above-mentioned structure, conventionally, a heater heating element is located substantially in the center of the nip, which is a remarkable phenomenon due to rapid heating, especially in a high temperature environment. However, the moisture contained in the recording material explodes. However, a large amount of water vapor was generated at one time, and this was blown out in the recording material intrusion direction of the nip portion and the unfixed toner image was scattered, but by adopting the present invention, the most heat is generated in this embodiment. By moving such a part from the central part of the nip to the paper discharging side, it is possible to crush the mountain of the toner mainly by the pressing force and fix it to the recording material when the generation of water vapor is relatively small on the nip entering side. Although a large amount of water vapor is generated in the latter half of the nip, scattering of the toner image can be suppressed.

Further, the heater support for supporting the heater is asymmetric between the recording material entrance side and the paper discharge side, and the shape at that time is θ ₁ when the angle with the recording material is the entrance side θ ₁ and the paper discharge side θ _{2. 1} ≧
By setting θ ₂ and widening the front side of the sheet passing side, it is possible to reduce the momentum of the generation of water vapor, which cannot be completely eliminated, and suppress the toner image from scattering backward.

(Embodiment 2) In Embodiment 1, the present invention is explained with respect to a film fixing system in which a tension is applied to a film, a drive roller is provided on the inner surface of the film, and the film is rotated by driving the drive roller. However, in the present embodiment, the present invention is applied to a film tension free type film fixing device as shown in FIG.
FIG. 4 is an enlarged cross-sectional model view of a main part. Reference numeral 25 denotes an endless heat-resistant film, which is externally attached to the heating body support 30 which is also a guide member for the film including the heating body 20. The guide member 30 of the film has an inner peripheral length of the endless heat-resistant film 25 and an outer peripheral length of the heating body support 2 including a heating body of the film 1 of, for example, about 3 mm so as not to hinder the film running. It's big. The pressure roller (driving roller) is in pressure contact with the heater 3 with the film sandwiched therebetween, and by being rotationally driven in the direction of the arrow, the endless film 1 rotates following the direction of the arrow B.

At this time, the shape of the film guide member is
The recording material P is asymmetric on the entrance side and the paper discharge side, and when the shape of the recording material P at that time is the entrance side θ ₁ and the paper discharge side θ ₂ , θ ₁ ≧ θ ₂ The difference between the inner peripheral length of the film and the outer peripheral length of the guide member is about 3 mm.

The center position Wc of the heating element 23 of the heating element 20 in the moving direction of the film is the central position Nc of the nip formed in the nip formed by pressing the pressure roller.
It is arranged so as to be located on the paper discharge side (downstream side).

By doing so, even in the tension-free type film fixing method, it is possible to eliminate the scattering of the toner image to the rear, which is particularly noticeable in a high humidity environment.

Further, in the present embodiment, the film running property can be stabilized by making the heater support asymmetrical, widening the front side of the entrance side, and correcting the amount by which the peripheral length is shortened on the paper discharge side.

[0034]

As described above, according to the present invention, it is possible to prevent the unfixed toner image from being disturbed by the water vapor from the recording material and improve the image quality.

[Brief description of drawings]

FIG. 1 is a sectional view of an image heating apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged view of the vicinity of the nip portion of FIG.

FIG. 3 is a sectional view of an image heating apparatus that is another embodiment of the present invention.

FIG. 4 is an enlarged view of the vicinity of the nip portion of FIG.

FIG. 5 is a diagram showing a conventional image heating apparatus.

[Explanation of symbols]

 20 heating element 21 heater support 23 heating element 25 film 28 pressure roller Nc nip center position Wc heating element center position

Claims (2)

[Claims] 1. A heating element having a heating element, a film that slides on the heating element, and a pressure member that forms a nip with the heating element through the film, and the undetermined value at the nip. In an image heating device for nip-conveying a recording material carrying a deposited toner image and heating an unfixed toner image, the center position of the heating element is downstream from the center position of the nip with respect to the moving direction of the film. Image heating device. 2. An angle formed by the film guided by the guide member with respect to a tangent line at the nip, the guide member guiding the movement of the film before and after the heating body with respect to the moving direction of the film. The image heating apparatus according to claim 1, wherein the inlet side is larger than the outlet side.