JPH09185283A - Heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of an offset and to obtain sufficient fixability. SOLUTION: This heating device is constituted so that a fixing film 7 is wound and extended on a heater support 2 for supporting a heating body 1, a driving roller 8 and a driven roller 9 and a pressure roller 10 is brought into press-contact with the heating body 1 with the fixing film 7, to form a fixing nip part N. At this time, a measure is adopted, for instance, a cooling system such as a cooling fan 15 is provided on the front surface of the heater base board 3 of the heating body 1 and on a side in the advancing direction of the film from the nearly center of the fixing nip part N. Thus, the temp. of the fixing nip part N is stepwise or continuously lowered in the advancing direction of the film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant film which is suspended and stretched on a film suspension tension member including a heating body to drive the film, and the surface of the film opposite to the heating body surface is heated. The present invention relates to a film heating type heating device that applies heat energy of a heating element to a material to be heated through a film by closely adhering the material and passing the heating element.

[0002]

2. Description of the Related Art Conventionally, for example, as a heating device for a recording material for heating and fixing an image, a heating roller maintained at a predetermined temperature and a pressurizing member which has an elastic layer and presses against the heating roller. A heat roller system in which a recording material is heated while being nipped and conveyed by rollers is widely used.

However, this heat roller system requires firstly a time until the temperature rises to a predetermined temperature, that is, a so-called wait time (time for prohibiting an image forming operation), and secondly, a heat capacity is required, so that the heat roller method is comparatively performed. Requires a large amount of power, third
In the rotating roller, the roller temperature is high, so a heat-resistant special bearing is required. Fourthly, since the roller is in direct contact with the hand, there is a danger or a protective member is required.
Fifthly, there has been a demand for improvement in that the recording material winds up due to the roller fixing temperature and the curvature, which causes a jam.

Therefore, recently, a film heating type heating device has been proposed and put into practical use. The heating device disclosed in, for example, Japanese Patent Application Laid-Open No. 63-313182 disclosed by the present applicant is a thin endless or endless heat-resistant film (sheet) as shown in FIG. The fixing film 7, moving driving means such as a driving roller 8 and a driven roller 9 for moving the fixing film 7, and a heater (heating body) fixedly supported on one side of the fixing film 7 with the fixing film 7 in the middle. ) 1 and a pressure roller 10 as a pressure member arranged on the other surface side so as to face the heater 1.

In this heating device, the surface of the recording material P, which is a material to be heated, is brought into close contact with the heater 1 by the pressure roller 10 via the fixing film 7, and the fixing film 7 is used as the recording material P. Run at the same speed in the forward direction,
The visible image is fixed on the recording material P by passing through a pressure contact portion (hereinafter referred to as a fixing nip portion) N between the heater 1 and the pressure roller 10 formed with the fixing film 7 sandwiched therebetween.

That is, the unfixed toner image T on the recording material P is
Heat energy from the heater 1 is applied at the fixing nip portion N to form a softened / melted toner image Tb, and thereafter, the recording material P and the fixing film 7 are separated from the fixing film 7 by the curvature at the separation point S. The toner image Tb is cooled to some extent to increase the viscosity of the toner image Tb, and is further cooled by being separated from the fixing film 7 to become the fixed image Tc.

As described above, since the heat of the heater 1 is transferred to the toner almost directly through the fixing film 7, a low heat capacity heater can be used as the heater 1, which is the heat of the conventional contact heating system. Compared with the roller system, the belt heating system, etc., it is possible to save power and shorten the wait time (quick start), and it is also effective because it has the advantage of solving the drawbacks of the conventional heating system.

[0008]

However, in the above-described conventional heating device, when the recording material P is not curved as shown in FIG. 5, the recording material P moves from the fixing nip portion N to the separation point S. By the time it reaches the fixing film 7, the toner is cooled to some extent and separated from the fixing film 7 in a state where the viscosity of the toner is sufficiently increased. Therefore, although part of the molten toner does not adhere to the fixing film 7, as shown in FIG. When the recording material P is curved downward, part of the molten toner may adhere to the fixing film 7 as the offset toner Td.

That is, the recording material P passes through the fixing nip portion N in a state where the recording material P is likely to be bent downward after passing through the fixing nip portion N due to a difference in material, thickness, etc. of the recording material P. Since the recording material P and the toner Tb are not sufficiently cooled and the viscosity of the toner Tb has not risen since they are separated immediately after the heating, a part of the molten toner Tb remains attached to the fixing film 7. In some cases, the toner becomes offset toner Td.

The offset toner Td is used again for the recording material P.
If it adheres to the surface of the recording material P, the image may be disturbed, and the recording material P may be smeared by being transferred to the pressure roller 10.

In order to prevent this, there is a method of lowering the temperature in the fixing nip N, but in that case, sufficient fixing property could not be obtained in some cases.

Therefore, it is an object of the present invention to prevent the above-mentioned offset from occurring and to obtain a sufficient fixing property in a film heating type heating device.

[0013]

According to the first invention of the present application, the above object is to suspend a heat-resistant film on a film suspending and suspending member including a heating body so as to drive the film. ,
In a heating device that applies the heat energy of the heating element to the material to be heated through the film by bringing the material to be heated into close contact with the surface of the film opposite to the surface to be heated, and sandwiching the film. This is achieved by lowering the temperature of the fixing nip portion formed by pressure contact with the heating body in stepwise or continuously according to the traveling direction of the film.

According to a second aspect of the present invention,
The above-mentioned object is achieved in the above-mentioned first invention by having a cooling device for cooling the heating body.

Further, according to the third invention of the present application, the above object is achieved by setting the position of the heating element provided in the heating element on the upstream side in the traveling direction of the film in the first invention. To be done.

That is, according to the first aspect of the present invention, the temperature of the fixing nip portion is lowered stepwise or continuously in accordance with the traveling direction of the film, so that the unfixed toner melted in the fixing nip portion is removed. Before the toner comes out of the fixing nip part, it passes through the area lower than the melting temperature of the toner, so that the melted toner is separated from the film with a sufficiently high viscosity so that it does not offset to the film, causing an offset. Do not let

According to the second aspect of the present invention,
In the first aspect of the invention, since the cooling device for cooling the heating element is provided, the temperature of a desired region in the fixing nip portion is lowered, and the offset is prevented as described above.

Further, according to the third invention of the present application, in the first invention, the position of the heating element provided in the heating element is set to the upstream side in the traveling direction of the film.
The temperature on the downstream side becomes lower than the temperature on the upstream side in the moving direction of the film in the fixing nip portion, thus preventing the offset as described above.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS. The present embodiment is a heating device as an image heating and fixing device in an image forming apparatus.

In FIG. 1, reference numeral 1 is a low heat capacity linear heating element, and the heating element 1 has a longitudinal direction in the transverse direction of the fixing film (direction perpendicular to the running direction of the fixing film 7), a heater substrate 3 and heat generation by energization. It is provided with a body 4, a temperature detecting element 5, and a surface layer 6, and is fixedly supported by a heater support 2 having a laterally long rigidity, high heat resistance, and heat insulation.

The heater support 2 heat-insulates and supports the heating body 1 with respect to the entire machine (fixing device and copying device). For example, PPS (polyphenylene sulfide), PAI (polyidimide), 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.

The heater substrate 3 is a member having heat resistance, insulation, low heat capacity and high heat conductivity, and is, for example, an alumina substrate having a thickness of 1 mm, a width of 22 mm and a length of 30 mm.

The heating element 4 is formed along the substantially central portion of the lower surface of the heater substrate 3, for example, Ag / Pd (silver palladium) .Ta.
An electrical resistance material such as ₂ N with a thickness of about 10 μm and width of 1 to 3 mm
It is applied by screen printing or the like, and a heat-resistant glass as a surface layer 6 is provided thereon for the purpose of insulation and protection. Further, a slippery surface layer such as PFA / PTFE may be coated on the surface of the fixing film 7 in order to reduce friction with the fixing film 7.

As an example, the temperature detecting element 5 is provided with Pt by coating the upper surface of the heater substrate 3 (the surface opposite to the surface on which the heating element 4 is provided) substantially in the center by coating by screen printing or the like.
It is a side temperature resistor with a low heat capacity such as a film. As the temperature detecting element, a thermistor having a low heat capacity may be arranged in contact with the heater substrate 3 in addition to the above.

In the heating element 1 of this embodiment, the heating element 4 is energized from both end portions in the longitudinal direction thereof to cause the heating element 4 to generate heat over substantially the entire length. The energization is AC 100V, and the energization power is controlled by controlling the phase angle of the energization to the heating element 4 by the energization control circuit (not shown) including the triac according to the detected temperature of the temperature detection element 5.

A driving roller 8 and a driven roller 9 are disposed above the heating body 1 substantially in parallel with the heating body 1, and the heater support 2 and the driving roller for supporting the heating body 1 are provided. An endless belt-shaped fixing film 7, which is a heat-resistant film, is stretched and stretched by a film suspension tension member 8 and a driven roller 9.

The driving roller 8 is rotated clockwise by a driving source (not shown), and the driven roller 9 is fixed to the fixing film 7.
Since the fixing film 7 also serves as a tension roller, the fixing film 7 is unfixed as a heated material conveyed from the image forming section (A) side in a clockwise direction at a predetermined peripheral speed as the driving roller 8 is rotationally driven. It is rotationally driven at the same peripheral speed as the conveying speed of the recording material P carrying the toner image Ta on the upper surface.

Since the endless belt-shaped fixing film 7 which is rotationally driven in this manner is repeatedly used for heat fixing of the toner image, it has excellent heat resistance, releasability and durability, and is generally used. Is 100 μm or less, preferably 40 μm
Use a thin wall with a thickness of m or less. For example, polyimide, polyether imide, PES, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin)
Single layer film of heat resistant resin such as, or composite layer film,
For example, it is a film having a thickness of 20 μm and a release coating layer having a thickness of 10 μm formed by adding a conductive material to a fluororesin such as PTFE (tetrafluoroethylene resin) / PAF on at least the image contact surface side.

A pressure roller 10 serving as a pressure member is disposed below the heating body 1, and the pressure roller 10 is made of a rubber elastic layer 1 such as silicone rubber having a good releasability.
2, the endless belt-shaped fixing film 7 is sandwiched by the descending film portion, and a total pressure of 4 to 12 k is applied to the lower surface of the heating body 1 by urging means (not shown).
The core metal 11 is rotated in the counterclockwise direction, which is the forward direction in the transport direction of the recording material P, with the pressure contact force of g.

The drive roller 8 is provided with a cleaning brush 13 having excellent heat resistance and durability, which is made of a highly heat-resistant resin such as liquid crystal polymer, so as to come into contact with the driving roller 8.
The surface of the drive roller 8 is cleaned.

In the above heating device, the image forming section (A) is operated by the image forming start signal and the unfixed toner image T conveyed from the image forming section to the fixing device.
The recording material P carrying a on the upper surface is guided by the guide 14 and enters between the fixing film 7 and the pressure roller 10 in the pressure contact portion (fixing nip portion) N between the heating body 1 and the pressure roller 10. , The unfixed toner image surface is in close contact with the lower surface of the fixing film 7 which is rotated in the same direction at the same speed as the conveyance speed of the recording material P in the overlapping state with the fixing film 7 and the heating body 1 and the pressure roller 10. The fixed image Tc is formed and the fixing is performed by passing through between the mutual pressure contact portions N with and while receiving the sandwiching pressure.

However, as described in the conventional example, when the recording material P is easily bent downward, the recording material P is separated from the fixing film 7 immediately after passing through the fixing nip portion N, so that the recording material P is melted. Since the toner Tb and the recording material P are not sufficiently cooled and the viscosity of the molten toner Tb is not sufficiently increased, offset may occur.

Therefore, in the present embodiment, only the fixing film advancing direction side of the upper surface of the heater substrate 3 is cooled by a cooling device, for example, a cooling fan 15, so that the fixing nip portion N is fixed from substantially the center. The temperature on the film advancing direction side was lowered so that the offset was not generated even when the recording material P was easily bent downward.

FIG. 2 shows the temperature distribution of the fixing nip portion N in the moving direction of the fixing film. As shown in FIG. 2, the temperature of the fixing nip N is lower on the fixing film advancing direction side than the substantial center of the fixing nip N. When the recording material P passes through the fixing nip N, first, The toner image Ta is sufficiently heated in the high temperature portion to become the softened / melted image Tb, and then the toner is cooled in the low temperature portion until the offset phenomenon does not occur and passes through the fixing nip portion N. Even when P is separated from the fixing film 7, the toner is sufficiently cooled and solidified by the time it is separated and completely fixed on the recording material P (toner image Tc).

As described above, according to the present invention, the offset can be prevented without increasing the temperature of the fixing nip portion N, and the fixing property is not impaired.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 3 shows the configuration around the heating element 1 in this embodiment. In the present embodiment, a heat absorbing member 16 made of a metal such as Al having a large heat capacity is brought into contact with the film advancing side of the upper surface of the heater substrate 3 as a cooling device. Therefore, the temperature distribution in the advancing direction in the fixing nip portion N is almost the same as that in the first embodiment. This configuration is simpler than that of the first embodiment using a cooling fan, has an effect of preventing offset, and can reduce cost.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 4 shows the configuration of the heating element 1 in this embodiment. In this embodiment, the heating element 4 is arranged in the fixing nip N on the side opposite to the fixing film advancing direction.
The temperature of the portion without the heating element 4 is lower than that of the portion with the heating element 4, so that the temperature distribution in the advancing direction in the fixing nip portion N is substantially the same as that in the first and second embodiments. With this configuration, since the position of the heating element 4 is simply shifted, the cost can be reduced more easily than the configuration of the second embodiment, and the offset prevention effect is sufficient.

The heating device of the present invention is an image heating and fixing device in an image forming apparatus such as an electrophotographic copying machine, a printer and a fax, that is, an appropriate image forming process means such as electrophotography, electrostatic recording and magnetic recording. The target image formed on the surface of the recording material (electrofax sheet, electrostatic recording sheet, transfer material sheet, printing paper, etc.) using toner made of heat-meltable resin, etc., either directly or indirectly (transfer) It can be utilized as an apparatus for heating and fixing an unfixed toner image corresponding to information as a permanently fixed image on the surface of a recording material carrying the image. Further, for example, it can be widely used as a means / apparatus for heat-treating a material to be heated, such as an apparatus that heats a recording material carrying an image to modify the surface property (gloss or the like), an apparatus that performs hypothetical adhesion processing, and the like.

[0042]

As described above, the first embodiment according to the present application is described.
According to the invention, in the heating method of the film heating method,
By lowering the temperature of the fixing nip stepwise or continuously in the film advancing direction, the lower curl is large depending on the material of the recording material. Even when the recording material is separated from the fixing film, the occurrence of offset can be prevented and the stable image can be provided without impairing the fixing property.

According to the second aspect of the present invention,
In the first invention, since the cooling device for cooling the heating body is provided, the temperature of a desired region in the fixing nip portion can be lowered, and the occurrence of offset can be prevented without impairing the fixing property. it can.

Further, according to the third invention of the present application, in the first invention, the position of the heating element provided in the heating element is set to the upstream side in the film advancing direction.
In the fixing nip portion, the temperature on the downstream side can be made lower than the temperature on the upstream side in the traveling direction of the film, and the occurrence of offset can be prevented without impairing the fixability with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a heating device according to a first embodiment of the present invention.

FIG. 2 is a temperature distribution diagram in the fixing nip according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram around a heating body of a heating device according to a second embodiment of the present invention.

FIG. 4 is a schematic view around a heating body of a heating device according to a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a conventional heating device.

FIG. 6 is an explanatory diagram of an offset in a conventional heating device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heater 2 Heater support (film suspension tension member) 4 Heating element 7 Fixing film (heat resistant film) 8 Driving roller (Film suspension tension member) 9 Driven roller (Film suspension tension member) 10 Pressure roller (pressurizing member) 15 Cooling fan (cooling device) 16 Endothermic member (cooling device) N Fixing nip portion P Recording material (heated material) Ta, Tb Toner (heated material)

Claims (3)

[Claims] 1. A heat-resistant film is suspended and stretched on a film suspension tension member including a heating body to drive the film, and a material to be heated is brought into close contact with the surface of the film opposite to the heating body surface to heat the film. By passing the body position, in the heating device for applying the heat energy of the heating body to the material to be heated through the film,
A heating device characterized in that the temperature of a fixing nip portion formed by pressure contact with a heating body sandwiching a film is lowered stepwise or continuously according to the traveling direction of the film. 2. The heating device according to claim 1, further comprising a cooling device for cooling the heating body. 3. The heating device according to claim 1, wherein the position of the heating element provided in the heating element is set on the upstream side in the traveling direction of the film.