JP2851938B2 - Fixing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for heating and fixing a visible image on a recording material via a film.

[Background Art] Conventionally, as a fixing device used in an image forming apparatus,
It has a heating roller maintained at a predetermined temperature, and a pressure roller having an elastic layer and pressed against the heating roller, and the two rollers sandwich and convey a recording material on which an unfixed toner image is formed. A heat roller fixing method of heating while heating is often used.

However, this heat roller fixing method has a problem that a warm-up time until the surface of the heat roller is raised to a predetermined fixing temperature becomes long.

In view of this, the applicant has previously disclosed in Japanese Patent Application Laid-Open No. 63-313182 a fixing device which is power-saving and has greatly reduced or eliminated warm-up time.

This fixing device uses a fixed heating element having a linear current-carrying heating layer and a film that moves in close contact with a recording material, and instantaneously reaches a fixing temperature.

However, if the size width of the used recording material supplied to the apparatus is smaller than the maximum width in the above-described heating element configuration, the heating element is a difference area between the size width of the used recording material and the effective full length area of the heating layer. In the recording material non-passing area (hereinafter, referred to as a non-paper passing portion), the heat generating layer portion corresponding to the non-paper passing portion has a predetermined length per unit length similarly to the heat generating layer portion corresponding to the paper passing portion. It generates heat with the calorific value of. The heat generation energy of the heat generation layer corresponding to the paper passing portion is consumed for fixing the image, but the heat generation energy of the heat generation layer corresponding to the non-paper passing portion is not consumed for fixing the image, so the heat is stored. .

As a result, the temperature of the heating member in the non-sheet passing portion tends to rise abnormally (excessive temperature), shortening the durable life due to heat loss of the heating member or the heat generating layer, lowering the durability of the fixing film and the pressing member, and fixing. There is a possibility that the running property of the film becomes unstable (the film is shifted or wrinkles are generated).

In view of this, the present applicant has disclosed a fixing device in Japanese Patent Application No. 1-282574 in which a heating layer is branched at a non-paper passing portion, a conduction current is shunted, and a calorific value of the non-paper passing portion is reduced to prevent the non-paper passing portion from heating up. Offered.

[Problems to be Solved by the Invention] However, when a heating element having a structure in which the heat generating layer is branched is used, when a large-sized recording material is fixed, the fixability near the branch portion is deteriorated.

This is because a partial temperature drop occurs near the branch.

It is considered that the reason for this is that the heat generation layer has an extension in the branch portion, and the apparent resistance decreases by that much, and the heat generation amount decreases.

[Means for Solving the Problems] The present invention for solving the above problems includes a heating element, a film which moves by contacting one surface with the heating element and the other surface with the recording material, and a moving direction of the film provided on the heating element. A fixing device provided with a heat generating layer which is energized from both ends and which is energized from both ends, and heat-fixes a visible image on a recording material via a film, at least one of the heat generating layers branches off in the middle of the fixing area The heat generating layer is characterized in that it has an energizing path through which current flows, and has a higher resistance in the vicinity of the branch portion of the heat generating layer than in other portions.

Examples of the Invention Hereinafter, examples of the present invention will be described.

 FIG. 1 is a sectional view of a fixing device according to an embodiment of the present invention.

Reference numeral 2 denotes an endless belt-shaped fixing film, which is a left driving roller 3, a right driven roller 4, and a low heat capacity linear member as a heating member fixed and supported below the rollers 3, 4. It is suspended between the heating element 1 and the heating element 1.

The driven roller 4 also serves as a tension roller for the fixing film 2, and the fixing film 2 rotates clockwise at a predetermined peripheral speed with the clockwise rotation of the driving roller 3 without wrinkling, meandering, and speed delay. It is driven dynamically.

Reference numeral 5 denotes a pressing roller having a rubber elastic layer having good releasability such as silicon rubber as a pressing member, and the downward film portion of the endless belt-shaped fixing film 2 is sandwiched between the heating member 1 and the heating roller 1. On the other hand, the lower surface of the heater 1 is pressed against the lower surface of the heater 1 by an urging means with a contact pressure of, for example, 4 to 7 kg, and rotates in the counterclockwise direction in the transport direction of the transfer material sheet 10.

Endless belt-shaped fixing film 2 driven to rotate
Is repeatedly used for heating and fixing a toner image, and therefore, a thin film having excellent heat resistance, releasability and durability, generally 100 μm or less, preferably 50 μm or less is used. For example, a single-layer film of a heat-resistant resin such as polyimide / polyetherimide / PES / PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer resin) or a composite layer film such as a 20 μm thick film at least on the image contacting surface side. A releasable coating layer consisting of fluororesin such as PTFE (tetrafluoroethylene resin) and PFA with a conductive material added has a thickness of several μm
For example, those applied to a thickness of several tens μm.

The low-heat-capacity linear heating element 1 as a heating element according to the present embodiment has a transversely long rigidity, a high heat resistance, and a heat insulating property whose longitudinal direction is the transverse direction of the fixing film (the direction perpendicular to the running direction of the fixing film 2). And a heater substrate 12 integrally mounted and held on the lower surface side of the support along the length of the lower surface.

As will be described later, the heater substrate 12 has an energizing heating layer.
13. A branch electric circuit, a current-carrying electrode, a temperature sensor (temperature detecting element), and the like (not shown) for limiting a heat-generating (heating) range with respect to the length of the current-carrying heat-generating layer 13 (heating body 12) as required is there.

The heater support 11 serves to ensure the overall strength of the heating element 1, and includes, for example, PPS (polyphenylene sulfide), PAI (polyamide imide), PI (polyimide), PEEK (polyether ether ketone), High heat-resistant resins such as liquid crystal polymers, these resins and ceramics
It can be composed of a composite material such as metal and glass.

The heater substrate 12 has heat resistance and electrical insulation, and is, for example, an alumina substrate having a thickness of 1.0 mm, a width of 10 mm, and a length of 240 mm.

As an example, the heat generating layer 13 is formed by coating an electric resistance material such as Ta ₂ N / silver palladium to a width of 1.0 mm along a length substantially at a central portion of a lower surface of the substrate 12 on a film sliding side (screen printing or the like). This is a linear or belt-like conductive heating layer having a low heat capacity.

The transfer material 10 on which the toner image is loaded in the above-described configuration passes under the heating body 1 while moving synchronously with the film 2 and the roller 5. The image is softened and fixed on the transfer material 10.

Thereafter, the transfer material leaves the film 2 roller 5 and is discharged out of the apparatus by a pair of discharge rollers 7 and 8.

 Next, the heating element will be described in more detail.

The heating element used in this example has a heating layer branched, and this example is located at positions B4, A4R, and B5 on the opposite side to the one-sided paper passing reference line A as shown in FIG. Each of the heat generating layers has a branch portion, and electrodes 15a to 15e are provided at the end of each heat generating layer, so that electric current is selectively supplied.

When fixing an A3-size recording material, a voltage is applied between the electrodes 15a and 15b.

When fixing B4 size recording material, electrodes 15a and 15b, 15e
A voltage is applied between the two heating layers 13 and 13 in the non-sheet passing portion.
The current shunts to d.

When fixing A4R size recording material, electrodes 15a and 15b, 15
A voltage is applied between d.

When fixing B5R size recording material, electrodes 15a and 15b, 15
A voltage is applied between c.

As described above, when the recording material is smaller than the maximum size, the amount of heat generated in the non-sheet passing portion is reduced because current is diverted to the plurality of heat generating layers.

In addition, since the non-sheet passing portion generates an appropriate amount of heat, the temperature difference between the non-sheet passing portion and the sheet passing portion is small, and there is no effect on the film conveyance.

 Next, the shape of the branch portion of the heat generating layer will be described.

FIG. 3 is an enlarged view of a branch portion. In all the branch portions, the heat generating layers have concave portions 16 as can be seen from the drawing. (The hatched portion is a heat generating layer.) The heat generating layer is wide at the branch portion and the heat generation amount is small due to the small resistance. However, in the present embodiment, the heat generating layer is formed narrow by providing the concave portion 16 at the branch portion and making the heat generating layer narrow. Since the spread of the layer is canceled out, the resistance of this portion is almost equal to other portions, and the calorific value is also equal. Therefore, the temperature distribution of the heating element in A3 paper passing and the like is uniform including the branch portion, and the fixing property is also uniform. Even when a small size paper is passed, the branch portion is narrowed, so that the temperature is not excessively reduced. Even if the end of the B5R passes this boundary, no fixing failure occurs.

 Next, an experimental example of this embodiment will be described.

A heating layer pattern shown in FIG. 2 having a line width of 1.5 mm was formed on an alumina substrate having a width of 20 mm and a length of 340 mm as a heating element.
The branch portion had a dent (recess) of 0.1 mm as shown in FIG.

In such a pattern, the temperature distribution was observed while controlling the heater surface to 220 ° C. As shown in FIG. 4, the temperature difference between the branch portion and its periphery was at most 5 ° C. or less. There was no problem with the fixing property. (When the concave portion is not provided at the branch portion, as shown by the dotted line in FIG. 4, a temperature drop of 15 ° C. or more was observed.) The shape of the branch portion where the width of the heating element is narrowed is nothing. It is not limited to FIG. 3 of the present example, and there are countless others.

FIG. 5 shows an example of another means for preventing the temperature drop at the branch portion, in which the resistor may be thinned instead of slightly reducing the resistor width at the branch portion. This figure is an enlarged vertical cross section of the heater centering on one portion of the branch portion. A heating layer 13 is provided on a heater substrate 12, and this heating layer is covered with a protective film 16 such as glass. The heating layer 13
It has a uniform thickness in the width direction and a uniform thickness in the thickness direction except for the branches. The branching part is a dent 17 as shown in the figure.
And the film thickness is thinner than other portions. In such a configuration, in the case of full-size paper passing, as in the above-described example, since the resistance layer is uniform except for the branch portion, the temperature distribution is also uniform, and in the branch portion, the resistance layer extends in the width direction. Although it has a spread, it is formed into a thin film, and therefore has substantially the same resistance as other parts. Therefore, the temperature distribution at the branch portion does not cause a problem in terms of temperature distribution. Therefore, similarly to the above example, the fixing property is substantially uniform in the longitudinal direction of the heating element.

Further, although an example in which the width and the thickness of the heat generating layer in the branch portion are changed as means for preventing the temperature drop of the branch portion has been disclosed, in the present invention, the substantial resistance value of the branch portion is made different from that of other portions. It is the gist of what is equivalent, and the method of realizing this is not limited to dimensions and shapes such as width and thickness. For example, the material of the heating element may be changed only in the vicinity of the branch portion. Specifically, the heat generating layer is formed by mixing several kinds of electric resistance materials such as silver palladium, and the resistance value can be easily changed by changing the composition ratio. Therefore, according to the study of the present inventors, the branch portion has a composition different in composition from the other portions and has a higher resistance value. According to the study of the present inventors, a uniform temperature distribution can be obtained by making the branch portion higher in resistance by several percent than the other portions. A uniform change in the fixing property was realized.

[Effects of the Invention] As described above, according to the present invention, it is possible to secure sufficient fixing property by making the temperature distribution substantially uniform in the paper passing area.

[Brief description of the drawings]

FIG. 1 is a sectional view of a fixing device according to an embodiment of the present invention. FIG. 2 is a front view of a fixing heating element used in the embodiment of FIG. 1. FIG. 3 is a branch of the heating element shown in FIG. FIG. 4 is a temperature distribution diagram in the longitudinal direction of the heating element, FIG. 5 is a sectional view showing another embodiment of the present invention, 1... Heating element 2... Thin film belt 3. … Driving roller 5… Pressure roller 6… Inlet guide 7,8… Discharge roller pair 10… Transfer material 11… Heater support 12… Heater base 13… Heat generation layers 15a to e… electrode

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-121985 (JP, A) JP-A-3-297087 (JP, A) JP-A-3-144777 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G03G 13/20 G03G 15/20 H05B 3/00-3/20

Claims (2)

(57) [Claims] 1. A heating member, a film having one surface moving in contact with the heating member and the other surface contacting a recording material, and a film provided on the heating member in a direction intersecting with the moving direction of the film and being energized from both ends to generate heat. And a heating device for heating and fixing a visible image on a recording material via a film. A fixing device characterized in that the vicinity of a branch portion of the heat generating layer has higher resistance than other portions. 2. The fixing device according to claim 1, wherein said apparatus further comprises a selection means for selecting an energizing path according to the size of the recording material.