JPH10301414A - Heating element, fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heating element where fuming and ignition are prevented by surely breaking a wiring board in the case of thermorunaway though it is not broken at a normal time and to provide a fixing device and an image forming device using it. SOLUTION: Along and narrow resistance heating element is formed along the longitudinal direction of an electrically insulated long and narrow wiring board 1, and a through-hole 10 is formed at the wiring board 1 at a position where the resistance heating element is crossed by avoiding the resistance heating element, and also protective film 11 which surrounds the resistance heating element and is applied on the wiring board and also where through-hole film 11c is formed only at the inner wall of the through-hole 10 is provided. It is desirable that the through-hole film 11c is formed to be thinner than the protective film 11 of the surface of the wiring board 11 and >=20% of the inner wall of the through-hole 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heating element, a fixing device using the same, and an image forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer or a facsimile, a heating element for fixing toner is described in JP-A-6-324586.

This heating element is formed by forming an elongated resistance heating element in a thick film on an elongated wiring board made of alumina ceramics.

[0004] The heating element is a resistance heating element 12.
2 has a small heat capacity, and when a power supply voltage is applied, the working portion of the heating element that contributes to fixing of the toner instantaneously rises to a required temperature, so that there is an advantage that no preheating time is required. For this reason, it is possible to control the heating element to generate heat only when the fixing operation is performed, and it is possible to greatly reduce the power consumption.

However, due to malfunction of the temperature control circuit,
When the heating element runs out of heat, the temperature rises excessively, and cracks occur in the resistance heating element due to thermal stress. When a crack occurs, the resistance value of the cracked portion increases, so the calorific value of the portion further increases, and the cracked portion smokes or ignites before a safety device such as a thermal fuse operates. There is.

Japanese Patent Application Laid-Open No. 5-2055851 discloses that a hole or the like is provided in a longitudinal region of a resistance heating element so that a thermal stress generated in the substrate when the temperature of the heating element rises excessively increases. Is configured to be broken in a short time to cut off the current supply and stop the heat generation.

On the other hand, since the fixing heating element is operated by applying a relatively high voltage, a high pressure resistance is required.

[0008] Further, since the conveying sheet made of a polyamide resin comes into sliding contact with the surface of the heating element in a pressed state,
High wear resistance is also required.

To meet these requirements, the resistance heating element is surrounded by a vitreous protective film.

FIG. 11 is an enlarged cross-sectional view of a main part, showing a through hole portion of a conventional heating element in an enlarged manner.

In the figure, 111 is a wiring board, 112 is a through hole, 113 is a protective film, and 114 is a protective film closing member.

The through hole 112 is a fine hole formed by a fine needle and is formed at a position close to the resistance heating element. The protective film material is also filled in the inside 112, and a protective film closing body 114 is formed in the through hole 112, so that the through hole 112 is closed.

[0013]

However, in the conventional heating element shown in FIG.
It has been found that there is a problem that breakage occurs due to cracks.

As a result of the investigation by the present inventors, it was found that the protective film closing body 114 in the through hole was involved.
That is, the conventional heating element A in which the through-hole is closed by the protective film closing body 114, the heating element B in which the protective film is not formed in the vicinity of the through-hole and the book having the protective film formed only on the inner wall of the through-hole for comparison The heating element C of the invention was prepared, and these prototypes were compared.

As a result, the above problem was reproduced in the former conventional heating element A, but in the latter two heating elements B and C,
Normally, no breakage due to through holes occurred. However, the heating element B in which the protective film is not formed near the through hole
There were very few that did not break during runaway.

After all, only the heating element C of the present invention in which the protective film was formed only on the inner wall of the through-hole did not normally break, but did break during the runaway. Thus, the present invention has been completed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a heating element which does not break during normal operation but reliably breaks during thermal runaway to prevent smoke and ignition, and a fixing device and an image forming apparatus using the same. .

[0018]

According to the first aspect of the present invention, there is provided a heating element comprising: an elongated wiring board having electrical insulation; an elongated resistance heating element formed along a longitudinal direction of the wiring board; A through-hole formed in the wiring board avoiding the resistance heating element at the position; a through-hole film is formed on the wiring board so as to surround the resistance heating element and only on the inner wall of the through-hole; And a vitreous protective film.

In the present invention and the following inventions, the definitions and technical meanings of terms are as follows unless otherwise specified.

The wiring board only needs to have electrical insulation at a portion where a resistance heating element and a conductor pattern and a terminal pattern attached to the resistance heating element are formed. Alumina ceramics formed in a plate shape using a doctor blade method or the like can be used.

The wiring board is preferably made of a heat-resistant material such as ceramics, but the heat resistance is not an essential requirement. Of course, the shape of the base may be elongated, and other shapes are free. Therefore, not limited to flat plates,
If necessary, it may be a three-dimensional shape.

The resistance heating element is not particularly limited in material, shape, size, manufacturing method and the like, but is most preferably formed by printing and firing a conductive paste mainly containing a silver-palladium alloy by a screen printing method. It is a thick-film resistance heating element. According to this thick-film resistance heating element, the resistance value of the resistance heating element is increased to a required value in a long heating element capable of fixing toner satisfactorily on paper of mainly A4 size which is frequently used. It is easy to set so that is obtained.

The number of resistance heating elements is not limited to one, and a plurality of resistance heating elements may be arranged in parallel. Further, a single resistance heating element may be bent to form a plurality of action portions.

One or a plurality of through holes are formed at a position crossing the resistance heating element of the wiring board, that is, at a side of the resistance heating element. In addition, in order to connect the resistance heating element to the power supply terminal, a conductive film having a conductor film formed on the inner surface is provided between the conductor pattern connected to one end of the resistance heating element and the terminal pattern formed on the opposite surface of the wiring board. It is permissible to connect via a hole, but by forming the through hole of the present invention on the side of the conductive through hole, the conductive through hole and the through hole cooperate, so that they are easily broken during thermal runaway .

The protective film surrounds the resistance heating element and is applied only to the inner wall of the through hole without closing the through hole. A through hole film may be formed on the entire inner wall of the through hole, or a part of the inner wall may be formed.

Although the protective film is glassy, it may be a single layer or a plurality of layers. When using multiple layers, first form a protective film with good moisture resistance on the resistance heating element,
Further, a protective film having good wear resistance can be formed thereon.

To form a through-hole film only on the inner wall of the through-hole, any method may be used. For example, after screen-printing the paste for the protective film on the wiring board, if the vacuum is used to suck the paste for the protective film filled in the through-hole, the paste for the protective film filled in the through-hole is removed. At the same time, the paste for the protective film is applied on the inner wall of the through hole in a film form and remains. By firing after drying, the through-hole film can be formed only on the inner wall of the through-hole together with the protective film surrounding the resistance heating element.

In order to keep the temperature of the resistance heating element constant, a heat sensor, for example, a thermistor can be provided at a position where the resistance heating element receives heat. If necessary, an over-temperature prevention means such as a thermal fuse may be provided.

The heating element of the present invention is suitable for fixing, but is not limited thereto, and is applicable to all uses.

Thus, in the present invention, since the through-hole film is formed only on the inner wall of the through-hole and the through-hole is not closed, the breakage due to the through-hole does not occur in a normal state. To break.

According to a second aspect of the present invention, there is provided a heating element, comprising: an elongated wiring board having electrical insulation; and an elongated resistance heating mainly composed of a silver / palladium alloy formed by thick film printing along the longitudinal direction of the wiring board. A through hole formed in the wiring board so as to avoid the resistance heating element at a position crossing the resistance heating element; and a through-hole formed on the wiring board so as to surround the resistance heating element and being covered only on the inner wall of the through-hole. And a vitreous protective film that is attached to form a through-hole film.

The present invention differs from the first aspect in that the resistance heating element is formed by thick-film printing mainly composed of a silver-palladium alloy.

Therefore, the resistance heating element, which is a main component, can be formed by thick-film printing, and if necessary, almost all of the resistive element including the conductor pattern and the terminal pattern can be formed by thick-film printing. Can be reduced.

According to a third aspect of the present invention, in the heating element according to the first or second aspect, the through-hole film attached to the inner wall of the through-hole is thinner than the protective film on the surface of the wiring board. And

In order to reliably break the wiring board only during thermal runaway, it is desirable to reduce the diameter of the through hole as much as possible. Therefore, a through hole film is formed only on the inner wall without closing the small diameter through hole. In order to achieve this, the through-hole film on the inner wall of the through-hole is preferably as thin as possible.

Therefore, the present invention shows a preferable configuration.

According to a fourth aspect of the present invention, in the heating element according to any one of the first to third aspects, the through-hole film is formed on a portion having an area of 20% or more of the inner surface of the through-hole. It is characterized by.

The present invention shows the limitation of the preferable area range of the through-hole film formed on the inner wall of the through-hole. That is, if a through-hole film is formed on 20% or more of the inner surface of the through-hole, the wiring board can be more reliably broken at the time of thermal runaway.

According to a fifth aspect of the present invention, there is provided the heating element according to any one of the first to fourth aspects, wherein the protective film comprises a plurality of layers of different materials, and the innermost protective film is formed on the inner wall of the through hole. Only the formation of a through-hole film is characterized.

The present invention shows a structure suitable for a case where a protective film is formed into multiple layers and functions are assigned to each layer.
That is, for example, the innermost layer can be a protective film having good pressure resistance, and the outermost layer can be a protective film having good wear resistance.

Since the through-hole film is formed on the inner wall of the through-hole only by the innermost protective film, the through-hole film on the inner wall of the through-hole can be formed thinner than the protective film on the wiring board surface. To form a protective film other than the innermost layer, for example, a region near the through hole may be masked and screen printed.

According to a sixth aspect of the present invention, there is provided a fixing device comprising: the heating element according to any one of the first to fifth aspects; and a pressure roller disposed in pressure contact with the heating element. It is characterized by having.

According to the present invention, by using the heating element according to claims 1 to 5, the wiring board is not broken at normal times.
In the event of a thermal runaway of the heating element, the fixing device can be reliably broken to prevent smoke and ignition.

According to a seventh aspect of the present invention, the image forming apparatus forms a reverse image by attaching toner to the formed electrostatic latent image.
Image forming means for forming a predetermined image by transferring an inverted image to a fixing member; and a fixing device according to claim 6, which fixes the image by melting toner adhered to the fixing member. It is characterized by:

According to the present invention, there is provided an image forming apparatus including a heating element having the structure of any one of the first to fifth aspects, wherein the wiring board is reliably broken at the time of thermal runaway of the heating element to prevent smoking and ignition.

[0046]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view showing a first embodiment of the heating element of the present invention.

FIG. 2 is a rear view of the same.

In the drawing, 1 is a wiring board, 2 is a resistance heating element, 3a and 3b are first terminal patterns, 4 is a first conductor pattern, 5 is a first conductive through hole, 6 is a thermal sensor, 7 Is a pair of second conductor patterns, 8 is a second terminal pattern, 9 is a pair of second conductive through holes, and 10 is a through hole.

The wiring substrate 1 is an elongated thin plate made of alumina ceramics.

The resistance heating element 2 contains 55% by weight of palladium.
This is a thick-film resistance heating element formed by screen-printing a conductive material containing a silver-palladium-based alloy as a main component on the surface of the wiring substrate 1, drying and firing.

The first terminal pattern 3a is provided on the back surface of the wiring board 1 and has a first conductive through hole 5 and a first conductive pattern.
Is connected to one end of the resistance heating element 2 through the conductor pattern 4. The other terminal pattern 3 b is provided on the surface of the wiring board 1 and is directly connected to the other end of the resistance heating element 2.

In the present invention, the conductive through-hole means a small through-hole in the wiring board 1 including the first and second conductive through-holes, and a conductive pattern formed on the inner surface of the through-hole. This is for electrically connecting both surfaces of the wiring board 1.

The first conductor pattern 4 is provided on the surface of the wiring board 1, and one end thereof is connected to the other end of the resistance heating element 2.

The thermal sensor 6 is formed of a thermistor, and is formed on the back surface of the wiring board 1 at a position facing the resistance heating element 2 by thick film printing or by conductive bonding of a chip-shaped thermistor.

The other end of the second conductor pattern 7 is connected to a second conductive through hole 8.

The second conductive through hole 8 is
Are connected to a pair of second terminal patterns 9 disposed on the surface of the second terminal pattern 9.

Next, the through hole 10 will be described with reference to FIG.

FIG. 3 is an enlarged front view of a main part of the heating element according to the first embodiment of the present invention.

The same parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

The through holes 10 are formed so that two of them cross the width direction of the wiring board 1 on the side of the resistance heating element 2. More specifically, the through hole 1
0 is formed on both sides of the conductive through hole 5 at the position where the first conductive through hole 5 is formed.

Further, details of the through hole 10 will be described with reference to FIG.

FIG. 4 is an enlarged sectional view showing the through-hole portion of the heat generating element according to the first embodiment of the present invention in a further enlarged manner.

In the figure, the same parts as those in FIG.

Reference numeral 11 is a protective film. This protective film 11
Although not shown in FIGS. 1 to 3 because it is transparent, it is covered almost all over the surface of the wiring board 1 surrounding the resistance heating element, and has a two-layer structure. That is, it is composed of the first protective film 11a in the innermost layer and the second protective film 11b in the outermost layer.

The first protective film 11a is formed in direct contact with the wiring board 1, and is made of a material having excellent pressure resistance.

The second protective film 11b is formed of the first protective film 11
a formed of a material having excellent wear resistance.

The first protective layer 11a forms a through-hole film 11c which is relatively thin and has a substantially uniform thickness on the entire inner wall of the through-hole 10. The portion protruding downward from the through hole 10 is attached to the back surface of the wiring board 1.

On the other hand, the second protective layer 11b is formed so as to avoid the vicinity of the through hole 10.

FIG. 5 is an enlarged cross-sectional view showing a main part of a heating element according to a second embodiment of the present invention in an enlarged manner.

In the figure, the same parts as those of FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, the through-hole film 11 c ′ is formed on the entire inner wall of the through-hole 10, although there is no protruding portion on the back side of the wiring board 1. However, the deposition layer 1
1c 'has a gently reduced thickness on the back side.

FIG. 6 is an enlarged cross-sectional view showing a main part of a heating element according to a third embodiment of the present invention.

In the figure, the same parts as those in FIG.

In this embodiment, a through-hole film 11c ″ is formed on about 20% of the inner wall of the through-hole 10.
This embodiment shows the limit of achieving the preferable effects of the present invention.

FIG. 7 is an enlarged sectional view showing a main part of a fourth embodiment of the present invention.

In the figure, the same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, the protective film 11 'has a single-layer structure. The through-hole film 11d is formed on about 70% of the inner wall of the through-hole 10.

FIG. 8 is a sectional view showing an embodiment of the fixing device of the present invention.

In the figure, reference numeral 12 denotes a heating element having the structure shown in FIGS. Reference numeral 13 denotes a pressure roller which has a pressure-contact relationship with the heating element 12, and conveys the fixing member 14 between the two while narrowing the pressure, thereby fixing the fixing member 14.
The toner 14a adhering to the heating element 12 is melted by the heat of the heating element 12, and fixing is performed. It should be noted that a conveyance sheet (not shown) made of polyimide resin or the like, which can be endless, may be interposed between the fixing member 14 and the pressure roller 13. Reference numeral 15 denotes a support for the heating element 12. Reference numeral 16 denotes a fixing device main body, which accommodates each of the above components.

FIG. 9 is a conceptual diagram of a copying machine which is a first embodiment of the image forming apparatus of the present invention.

In the figure, 17 is a reading device, 18 is an image forming means, 19 is a fixing device, and 20 is an image forming device main body.

The reading device 17 optically reads the base paper to form an image signal.

The image forming means 18 forms an electrostatic latent image on the photosensitive drum 18a on the basis of the image signal, attaches toner to the electrostatic latent image to form an inverted visible image, and forms this image on paper or the like. The image is formed by transferring the image to the fixing member.

The fixing device 19 has the structure shown in FIG. 8, and fixes the toner adhered to the fixing object by heating and melting the toner.

The main body 20 of the image forming apparatus accommodates the above-mentioned respective devices and means 17, 18 and 19, and includes a transport device, a power supply device, a control device and the like.

FIG. 10 is a conceptual diagram of a printer which is a second embodiment of the image forming apparatus of the present invention.

In the figure, 21 is an image forming means, 22 is a fixing device, and 23 is a printer main body.

The image forming means 21 includes a laser scanner 21
a and the photosensitive drum 21b, and forms an image based on an image signal input from the outside.

The fixing device 22 has the structure shown in FIG.

The printer body 23 houses the image forming means 21 and the fixing device 22, and includes a transport device, a power supply device, a control device, and the like.

[0092]

According to each of the first to fifth aspects of the present invention, the through-hole film is formed only on the inner wall of the through-hole. Thus, it is possible to provide a heating element that prevents smoke and ignition.

According to the second aspect of the present invention, in addition to the fact that the resistance heating element mainly composed of a silver / palladium alloy is formed as a thick film, it is possible to provide a heating element having a suitable length for fixing. it can.

According to the third aspect of the present invention, the diameter of the through hole is made smaller by making the through hole film attached to the inner wall of the through hole thinner than the protective film on the wiring board surface. Even so, it is possible to provide a heating element in which only the through-hole film is formed on the inner wall, and the wiring board is surely broken only at the time of thermal runaway.

According to the fourth aspect of the present invention, in addition, since the through-hole film is formed in a portion having an area of 20% or more of the inner wall of the through-hole, the wiring board can be more reliably broken only during thermal runaway. A heating element capable of being provided can be provided.

According to the fifth aspect of the present invention, in addition, only the innermost protective film is applied to the inner wall of the through hole, so that the through hole film on the inner wall of the through hole is formed thinner than the surface of the wiring board. Can be provided.

According to the sixth aspect of the invention, it is possible to provide a fixing device having the effects of the first to fifth aspects.

According to the invention of claim 7, an image forming apparatus having the effects of claims 1 to 5 can be provided.

[Brief description of the drawings]

FIG. 1 is a front view showing a first embodiment of a heating element of the present invention.

FIG. 2 is a rear view of the same.

FIG. 3 is an enlarged front view of a main part of the heating element according to the first embodiment of the present invention.

FIG. 4 is an enlarged cross-sectional view of a main part, showing a through-hole portion in the first embodiment of the heating element of the present invention in a further enlarged manner.

FIG. 5 is an enlarged cross-sectional view of a main part, further showing a through-hole portion in a second embodiment of the heating element of the present invention.

FIG. 6 is an enlarged cross-sectional view showing a main part of a heating element according to a third embodiment of the present invention;

FIG. 7 is an enlarged cross-sectional view of a main part of a fourth embodiment of a heating element according to the present invention, showing a through-hole portion further enlarged.

FIG. 8 is a conceptual diagram showing an embodiment of the fixing device of the present invention.

FIG. 9 is a conceptual diagram of a copying machine which is a first embodiment of the image forming apparatus of the present invention.

FIG. 10 is a conceptual diagram of a printer which is a second embodiment of the image forming apparatus of the present invention.

FIG. 11 is an enlarged cross-sectional view of a main part, showing a through hole portion of a conventional heating element in an enlarged manner.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Wiring board 10 ... Through-hole 11 ... Protective film 11a ... First protective film 11b ... Second protective film 11c ... Through-hole film

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masahiko Honbo Toshiba Litec Co., Ltd. 4-3-1 Higashishinagawa, Shinagawa-ku, Tokyo

Claims (7)

[Claims] An elongated wiring board having electrical insulation; an elongated resistance heating element formed along a longitudinal direction of the wiring board; and a wiring board formed at a position crossing the resistance heating element so as to avoid the resistance heating element. A through-hole; and a vitreous protective film that is attached to the wiring board so as to surround the resistance heating element and that is attached only to the inner wall of the through-hole to form a through-hole film. A heating element characterized in that: 2. An elongated wiring board having electrical insulation; an elongated resistance heating element mainly composed of a silver-palladium alloy formed by thick-film printing along the longitudinal direction of the wiring board; A through-hole formed in the wiring board avoiding the resistance heating element at the position; and a through-hole film formed on the wiring board so as to surround the resistance heating element and only on the inner wall of the through-hole. And a vitreous protective film. 3. The heating element according to claim 1, wherein the through-hole film attached to the inner wall of the through-hole is thinner than a protective film on the surface of the wiring board. 4. The heating element according to claim 1, wherein the through-hole film on the inner wall of the through-hole is formed in a portion having an area of 20% or more of the inner surface of the through-hole. 5. The protective film comprises a plurality of layers made of different materials,
5. The through hole film according to claim 1, wherein only the innermost protective film is formed on the inner wall of the through hole.
A heating element according to any one of the above. 6. A fixing device comprising: the heating element according to claim 1; and a pressure roller disposed in pressure contact with the heating element. . 7. An image forming means for forming a reversal image by adhering toner to the formed electrostatic latent image and transferring the reversal image to a fixing member to form a predetermined image; and adhering to the fixing member. An image forming apparatus, comprising: the fixing device according to claim 6, wherein the fixing unit fixes the image by melting the toner.