JP2008139668A - Fixing device for image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an offset due to high temperature and damage to a part such as fixing film, pressurizing roller and a film guide by reducing the generation of heat in a non paper passing region. <P>SOLUTION: The fixing device is configured so that a heat generating body provided with a positive resistance temperature coefficient characteristic is divided into branches from a pair of electrodes installed for energizing. When an unnecessary temperature rise starts to occur in the non paper passing region, since a heating body pattern going through a part in which the temperature is raised has the positive resistance temperature coefficient, a resistance value is raised and the heat generating amount is reduced compared to the heating body pattern only going through the paper passing part region. Therefore, effects are provided preventing occurrence of high temperature offset due to rising of the temperature in the non paper passing part, driving instability in the film, occurrence of wrinkling in the film. Furthermore, by making a resistance value higher for a heat generating pattern only passing through the paper passing region than the heat generating pattern going through the non paper passing region, heat generating amount in a ceramic substrate end part is made great. Therefore, no fixing failure occurs in a paper end part even in image formation carried out to a maximum size transfer material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device that heats and fixes a toner image formed on a recording material, and an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus having an external fixing device.

  Conventionally, in an electrophotographic system, which is an example of an image forming system, fixing of a toner image visualized on a recording material is performed by pressing a heating roller controlled to a predetermined temperature and an elastic layer. A method (pressure roller method) is generally used in which a recording material is nipped and conveyed while being heated and pressed by a pressure roller.

  However, recently, in order to realize power saving and shortening the time from power-on to image output, as described in JP-A-63-313182 and JP-A-2-157878, at least fixed. A heater unit comprising a heated body (heater) and a heat-resistant film (fixing film) conveyed while being in pressure contact with the heater, and a pressure member for bringing a recording material into close contact with the heater unit. There has been proposed a fixing device (film heating fixing method) having a configuration and a configuration in which heat is applied to a recording material through a film to heat and fix a toner image formed on the surface of the recording material.

  FIGS. 5A, 5B, and 5C are views in which the conventional heating body is viewed from below, above, and from the front, that is, a bottom view, a top view, and a front view, respectively.

  Reference numeral 1 in these drawings denotes a ceramic base material using alumina or aluminum nitride, and the heating element 2F is obtained by mixing silver with palladium to form an alloy, mixing these with glass paste and screen printing. In addition, as the shape of the heating element, a linear or narrow strip shape is used on the film contact surface side along the length of the surface. In order to supply power to the heating element, a conductor pattern 8 is formed by screen-printing silver or silver / platinum mixed with glass paste. A glass coat 10 is applied to the surface of the heating body in order to improve slidability and obtain a withstand voltage.

An electrode 5 is formed at the end of the conductor pattern 8. A thermistor 2 and a conductor pattern 12 for detecting its resistance are formed on the back surface of the ceramic substrate. The conductor pattern 12 is connected to the electrode by a through hole.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878

  In the fixing device using the heating body as described above, when the transfer material P having a small size such as an envelope or a postcard is passed, heat is not consumed by the transfer material P in the non-sheet passing region at both longitudinal ends of the heating body D. Therefore, heat is accumulated and the temperature becomes high. As a result, the silicone rubber used in the fixing device or the surface of the fluororesin coat layer is peeled off and the compression set becomes large. When the coat layer is peeled off, toner accumulates on the surface of the pressure roller to contaminate the image, and the paper transfer material P sticks to the paper transfer material P to cause a winding jam. Further, when the compression set becomes large, the elasticity of the pressure roller is lost and the pressure is not periodically applied, so that the fixing property becomes uneven.

  The present invention has been made in view of the above-described circumstances, and prevents a non-sheet passing region at both ends of the heating body from being unnecessarily heated even when a small-sized transfer material is continuously fed. It is an object of the present invention to provide a heating body and a fixing device including the heating body.

In order to achieve the above object, the first invention according to the present application is to heat a material to be heated in close contact with a surface opposite to the heating side of the heat resistant film that moves in close contact with the heating body, together with the heat resistant film. In the heating device that applies the heat energy of the heating body to the non-heating material through the heat-resistant film by passing the body position,
The heating element is an energization heating element having a positive resistance temperature coefficient, and a plurality of electrodes having different lengths in the longitudinal direction of the heating element from a pair of electrodes arranged for energization of the heating element The heating element is configured in a branch shape.

  According to a second aspect of the present invention, in the heating apparatus according to the first aspect, the heating element branches off from the center in the longitudinal direction of the heating element, and the longer the heating element is, the more outwardly configured. It is characterized by.

  According to a third aspect of the present invention, in the heating apparatus according to the first aspect, the heating element branches off from an end portion in the longitudinal direction of the heating element, and the longer the heating element is configured to be outward. It is characterized by that.

  According to a fourth aspect of the present invention, in the heating device according to the first to third aspects, the heating element configured to the outside has a lower resistance value than the heating element configured to the inside. And

  As described above, according to the present invention, when the temperature of the non-sheet passing region is unnecessarily increased, the heating element pattern passing through the portion where the temperature has increased has a positive resistance temperature coefficient, and thus the resistance value is increased. The amount of heat generation is smaller than that of the heating element pattern passing only through the sheet passing area. Therefore, it has the effect of preventing the occurrence of high temperature offset, film driving instability, film wrinkling and the like due to non-sheet passing portion temperature rise.

  In addition, by increasing the resistance value of the heating element pattern that passes only through the paper passing area rather than the heating element pattern that passes through the non-sheet passing area, the amount of heat generated at the end of the ceramic substrate is increased and the transfer material of the maximum size can be obtained. Even when an image is formed, it is configured so as not to cause a fixing failure at the end of the sheet.

(Example 1)
FIG. 1 shows an example of a fixing device according to this embodiment. This figure is a longitudinal sectional view of a fixing device using the fixing film 4.

  The fixing device shown in FIG. 1 includes a heating body (heater) A, a film guide 3, a fixing film 4, and a pressure roller 5.

  The heating element A is a plate-like member that is formed long in the width direction of the transfer material P. On the surface (1) of the ceramic substrate 1, the heating element pattern 2A is provided on the lower surface, and the surface of the heating element pattern 2A is glass coated. It is formed by covering with 10. The purpose of the glass coat 10 is to improve slidability and to ensure withstand voltage. The heating element A will be described in detail later.

  The fixing film 4 is formed by endlessly forming a 4 μm primer and a 10 μm surface layer (Teflon (registered trademark) layer) on a polyimide having a diameter of 24 mm and a thickness of 50 μm, and is stretched over the film guide 3. It is. The fixing film 4 is driven to rotate in the direction of the arrow R6 in accordance with the rotation direction of the arrow R5 of the pressure roller 5 described later.

  The pressure roller 5 is formed by coating a 3.5 mm thick silicone rubber 5 b around an aluminum core 5 a having a diameter of 13 mm and covering the surface layer with a PFA tube, or by applying a fluororesin or fluorotelax. . The pressure roller 5 presses the fixing film 4 against the pressure body A from below. As a result, a belt-like fixing nip portion N having a nip width a is formed between the fixing film 4 and the pressure roller 5. The pressure roller 5 is rotationally driven in the direction of arrow R5 by a driving means (not shown), thereby conveying the transfer material P in the direction of arrow K at the fixing nip portion.

  The thermistor 2 which is a temperature detection means is attached to the back surface (upper surface in FIG. 1) of the heating body A described above, and the CPU 7 turns on / off the triac 6 according to the output of the thermistor 2 in the heating body A. The temperature is adjusted accordingly.

  2A, 2B, and 2C show the configuration of the heating element A. FIG. In addition, it is a bottom view, a top view, and a front view in this order. In the following description, the vertical dimension in (a), (b), (c) is the “length L” of the heating element A (or ceramic substrate 1), and the horizontal dimension in (a), (b). Is the “width W” of the heating element A (or ceramic substrate 1), and the horizontal dimension in (c) is the “thickness t” of the heating element A (or ceramic substrate 1). Further, the lower surface shown in (a) is called “front surface”, and the upper surface shown in (b) is called “back surface”.

  The heating element A has a long plate-shaped ceramic substrate 1, a heating element pattern 2 </ b> A, a conductor pattern 8, and an electrode 9.

  The ceramic substrate 1 (heat-resistant member) is made of alumina in the form of a long plate having a length of L270 mm, a width of W7.78 mm, and a thickness of t0.635 mm.

  The heating element pattern 2A (resistance heating element) is formed on the surface side of the ceramic substrate 1 along the inner side of the resistance pattern 2B that goes around the end from the center in the length L direction and the pattern 2B that goes around the end. It has a structure divided into two hands of a resistance pattern formed so as to surround the central portion of the ceramic substrate 1. The resistance pattern 2B that goes around the end is 215 mm long, and the length of the resistance pattern 2C that goes around the center is 100 mm.

  The resistance value of the resistance pattern 2B surrounding the end portion was 48Ω, and the resistance value of the resistance pattern 2C surrounding the center portion was 52Ω. By forming the resistance value of the pattern 2B around the end portion smaller than the resistance value of the pattern 2C around the center portion, the amount of heat generated at the end portion of the ceramic substrate 1 is increased, and the image is formed on the transfer material P of the maximum size. In this case, it is configured so as not to cause a fixing failure at the end of the sheet. The total resistance of the heating element pattern 2A (resistance value between the electrodes 9) is 48Ω as the resistance value of the resistance pattern 2B around the end portion, and the combined resistance value of 52Ω as the resistance value of the resistance pattern 2C around the center portion. It is 24.96Ω.

  The heating element pattern 2A is formed by applying a paste material, and this paste material has a positive temperature resistance characteristic (PTC characteristic). Examples of the material having PTC characteristics include barium titanate, and FIG. 4 shows an example of its temperature-resistance characteristics. It can be seen from FIG. 4 that the resistance value rapidly increases at a predetermined temperature (switching temperature).

  The conductor pattern 8 is formed so as to be connected to the heating element pattern 2A at the center in the length L direction of the ceramic substrate 1. The conductor pattern 8 is connected to the electrode 9 at the end from the heating element pattern 2A.

  An electrode 10 is also provided at the lower part of the surface of the ceramic substrate 1 in FIG. These electrodes 10 are connected to the conductor pattern 8 on the back surface side through through-holes, and the thermistor 2 arranged on the back surface side of the ceramic substrate 1 and substantially at the center of the length L is connected to these electrodes. Yes.

  Each of the above patterns is formed on the front surface or the back surface of the ceramic substrate 1 by, for example, screen printing.

  Note that a portion of the surface of the ceramic substrate 1 that contacts the fixing film 4 is coated with glass (not shown) in order to ensure slidability and withstand voltage.

  The heating element A having the above configuration was incorporated into the fixing device 20 as the heating element shown in FIG. When a small-size transfer material P is passed through such a fixing device 20, the temperature of the end portion of the ceramic substrate 1 rises because the amount of heat released from the non-sheet passing area is small. However, if the ceramic substrate 1 exceeds the switching temperature, the resistance value of the resistance pattern 2B that surrounds the end portion rapidly increases, so that the amount of power supplied to the end portion decreases, and as a result, the temperature of the non-sheet passing portion increases. Will be suppressed.

  That is, in the region where the small-size transfer material P passes, a sufficient power supply state that does not cause a fixing failure is maintained by the resistance pattern 2C around the center. In the non-sheet-passing region, when the non-sheet-passing region reaches a predetermined temperature or more, the resistance value of the pattern 2B that goes around the end portion rapidly increases, thereby limiting the current and relaxing the temperature rise.

  Specifically, when a conventional heating element D (see FIG. 5) is used to continuously feed an envelope having a width of 100 mm and a length of 240 mm at a speed of 8 sheets per minute, the non-passage of the envelope is not passed. It reached 270 ° C in the area. On the other hand, when the heating element A shown in the above-described embodiment is used, if the non-sheet passing region exceeds 230 ° C., the resistance in this region becomes about 10 times higher, and the resistance pattern around the center portion. Compared with 2C, the amount of heat generated by the resistance pattern 2B around the end is about 1/10. As a result, excessive heat is not supplied in the non-sheet passing portion area, and the temperature is not raised to 230 ° C. or more in order to balance natural heat dissipation. Therefore, it is possible to prevent the occurrence of high temperature offset, film driving instability, film wrinkling due to non-sheet passing portion temperature rise.

(Example 2)
FIG. 3 shows another configuration example of the heating element. The heating element described in Example 1 is formed so as to be included in an image forming apparatus having a conveyance reference in the center in a direction orthogonal to the conveyance direction. However, in this embodiment, the image forming apparatus is formed so as to be provided on the left and right sides in the direction orthogonal to the transport direction. Since the fixing device according to the present embodiment is realized by the same configuration as that of the first embodiment, detailed description thereof is omitted.

  FIGS. 3A, 3B, and 3C show the configuration of the heating element A according to this embodiment. In addition, it is a bottom view, a top view, and a front view in this order. In the following description, the vertical dimension in (a), (b), (c) is the “length L” of the heating element A (or ceramic substrate 1), and the horizontal dimension in (a), (b). Is the “width W” of the heating element A (or ceramic substrate 1), and the horizontal dimension in (c) is the “thickness t” of the heating element A (or ceramic substrate 1). Further, the lower surface shown in (a) is called “front surface”, and the upper surface shown in (b) is called “back surface”.

  The heating element A has a long plate-shaped ceramic substrate 1, a heating element pattern 2 </ b> A, a conductor pattern 3, and an electrode 9.

  The ceramic substrate 1 (heat-resistant member) is made of alumina in the form of a long plate having a length of L270 mm, a width of W7.78 mm, and a thickness of t0.635 mm.

  A heating element pattern 2A (resistance heating element) is divided into two hands from the electrode 9 on the surface side of the ceramic substrate 1, and a resistance pattern 2D that goes around the end of the substrate along the length of the substrate, along the length of the substrate. The resistor pattern 2E extends to the vicinity of the center and returns to the electrode. The resistance pattern 2D surrounding the end is 215 mm in length, and the resistance pattern 2E extending to the vicinity of the center and returning to the electrode 9 is 100 mm.

  Similar to Example 1, the resistance value of the resistance pattern 2D surrounding the end portion was 48Ω, and the resistance value of the resistance pattern 2E surrounding the center portion was 52Ω. The amount of heat generated at the end of the ceramic substrate 1 is increased by making the resistance value of the pattern 2D surrounding the end smaller than the resistance value of the resistance pattern 2E extending near the center and returning to the electrode 9. Even when an image is formed on the material P, it is configured so as not to cause a fixing failure at the end of the sheet. The total resistance of the heating element pattern 2A (resistance value between the electrodes 9) is 48Ω. The resistance value of the resistance pattern 2D that goes around the end is 48Ω, and the resistance value of the resistance pattern 2E that returns to the electrode is 52Ω. The combined resistance value is 24.96Ω.

  The heating element A having the above configuration was incorporated into the fixing device 20 as the heating element shown in FIG. When a small-size transfer material P is passed through such a fixing device 20, the temperature of the end portion of the ceramic substrate 1 rises because the amount of heat released from the non-sheet passing area is small. However, when the ceramic substrate 1 exceeds the switching temperature, the resistance value of the resistance pattern that surrounds the end portion rapidly increases, so that the amount of power supplied to the end portion decreases, and as a result, the temperature rise of the non-sheet passing portion increases. It will be suppressed.

  That is, in the region through which the small-size transfer material P passes, a sufficient power supply state that does not cause fixing failure is maintained by the resistance pattern 2E that extends to the vicinity of the center and returns to the electrode 9. Further, in the non-sheet-passing area, when the non-sheet-passing area reaches a predetermined temperature or more, the resistance value of the pattern 2D that surrounds the end portion rapidly increases, thereby limiting the current and reducing the temperature rise.

Longitudinal sectional view of the fixing device of Example 1 (A) is the bottom view of the heating body of Example 1. FIG. (B) is a top view of the heating body of Example 1. FIG. (C) is a front view of the heating body of Example 1 (A) is the bottom view of the heating body of Example 2. FIG. (B) is a top view of the heating body of Example 2. FIG. (C) is the front view of the heating body of Example 2. Graph of an example of temperature-resistance characteristics of a heating element having a positive resistance temperature coefficient (A) is a bottom view of a conventional heating element. (B) is a top view of a conventional heating element. (C) is a front view of a conventional heating element

Explanation of symbols

1 Heat-resistant member (ceramic substrate)
2 Thermistor 2A, 2B, 2C, 2D, 2E, 2F Heating element pattern 5 Pressure roller 8 Conductor pattern 9 Electrode 20 Fixing device A, B, C Heating element (heater)
P transfer material

Claims (4)

The material to be heated is brought into close contact with the surface opposite to the heating side of the heat-resistant film that moves in close contact with the heating body, and the heat energy of the heating body is passed through the position of the heating body together with the heat-resistant film. In the heating device that is applied to the non-heating material via
The heating element is an energization heating element having a positive resistance temperature coefficient, and a plurality of electrodes having different lengths in the longitudinal direction of the heating element from a pair of electrodes arranged for energization of the heating element The heating device, wherein the heating element is configured in a branch shape.   2. The heating device according to claim 1, wherein the heating element branches off from the center in the longitudinal direction of the heating element, and the longer the heating element is configured, the outward.   2. The heating device according to claim 1, wherein the heating element branches off from an end portion in the longitudinal direction of the heating element, and the longer the heating element is configured to be outward.   4. The heating apparatus according to claim 1, wherein the heating element configured to the outside has a lower resistance value than the heating element configured to the inside.

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