JPH10112377A - Heating element, fixing device, and image forming device - Google Patents

Abstract

(57) Abstract: A heating element capable of reducing the amount of generated thermal strain to make a substrate less likely to break and, when used for fixing, to respond to high-speed fixing, a fixing device and an image using the same. A forming device is provided. An elongated first resistance heating element is attached to one surface of a base, and an elongated second resistance heating element is attached to the other surface. If necessary, the first and second resistance heating elements are thermally connected. Are arranged symmetrically. In addition, if necessary, a temperature sensor for sensing the temperature of each resistance heating element can be provided on the base to control the amount of current supplied to the resistance heating element to maintain the temperature at a predetermined temperature. Since heat is generated on both the front and back surfaces of the substrate, the amount of thermal strain caused by the difference in thermal expansion is reduced, and cracks in the substrate due to the thermal strain can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element having an elongated resistance heating element, a fixing device using the heating element, and an image forming apparatus.

[0002]

2. Description of the Related Art FIG. 8 is a sectional view showing a conventional heating element for fixing.

In the figure, 81 is an insulating substrate, 82 is a resistance heating element, 83 is a conductive path, 84 is a glass coating, 84 is a thermistor, and 85 is a conductive path.

[0004] The substrate 81 is made of alumina ceramics because of its excellent insulation and heat resistance.
A thin and narrow substrate is used so that the temperature easily rises instantaneously. Further, since it is necessary to cover the size of the body to be fixed, it is configured on an elongated substrate.

[0005] The resistance heating element 82 is provided on one surface of the substrate 81. The resistance heating element 82 is attached to the substrate 81 at a position deviated to one side from the center of the substrate. The conduction path 83 forms a conduction path to the resistance heating element 82.

The thermistor 84 is disposed at a position directly opposite the resistance heating element 82 with the substrate 81 interposed therebetween.
The temperature of the resistance heating element is controlled to be constant by sensing the temperature of the resistance heating element and controlling the amount of current supplied to the resistance heating element 82 by a control circuit (not shown).

The current path 85 constitutes a current path to the thermistor 84.

Thus, the conventional heating element is used by being incorporated in a fixing device. In the fixing device, the object to be fixed is conveyed between the heating element and the pressure roller such that the fixing object is pressed against the heating element. Then, electricity is supplied when the fixing member passes in front of the heating element. The heating element instantaneously generates heat when energized, and fuses the toner on the fixing member to the fixing member to perform fixing. When the fixing is completed, the power supply to the heating element is stopped, and the apparatus stands by for the next fixing.

[0009]

However, in the conventional heating element, when the resistance heating element 82 generates heat and rises in temperature,
As for the temperature of the substrate, a temperature difference occurs between a portion in contact with the resistance heating element and a portion separated therefrom, in particular, a surface of the substrate on which the resistance heating element is adhered and an edge in the width direction of the back surface. Thermal distortion occurs due to a difference in thermal expansion, and a warp in the thickness direction is also applied. When a complicated distortion is generated in the substrate, the rotational force of the pressure roller acts to break the substrate. In particular, due to the demand for high-speed fixing, there is a tendency that the fixing temperature is designed to be high, and the occurrence of thermal distortion when the temperature rises is becoming a problem.

The present invention provides a heating element capable of reducing the amount of thermal strain generated, making it difficult to break a substrate, and responding to a demand for high-speed fixing, a fixing device and an image forming apparatus using the same. The purpose is to:

[0011]

According to the present invention, there is provided a heating element according to the present invention, comprising: an elongate electrically insulating base; and an elongate first resistance heating element attached to one surface of the base along a longitudinal direction of the base. ;
An elongated second resistance heating element attached to the other surface of the base along the longitudinal direction of the base.

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

The substrate only needs to have electrical insulation at least on the surface where the resistance heating element is formed. Specifically, the substrate can be obtained by forming alumina ceramics into a plate shape using a doctor blade method or the like, or by forming a heat-resistant insulating layer such as glass on the surface of a metal plate such as aluminum. . Further, the planar shape of the base is not limited to a quadrangle, but may be any shape.

The resistance heating element is not particularly limited in material, but is most preferably a thick-film resistance heating element formed by printing a conductive paste containing a silver-palladium alloy as a main component by a screen method, drying and firing. It is. 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. And it is easy to set so that the calorific value can be obtained. Of course, it is possible to obtain an effective resistance heating element not only for A4 paper but also for A3 paper.

The number of the first and second resistance heating elements is not limited to one, and one or both of them can be provided as necessary. In that case, the resistance heating element can be connected in series or parallel to the power supply.

Further, the first and second resistance heating elements include:
It is preferable that both sides of the substrate are thermally balanced, but the most problematic thermal strain that occurs in the substrate is the thermal imbalance between the front and back, so that both resistance heating elements are separated on the front and back. Significant improvements can be obtained.

Thus, in the present invention, since the resistance heating element separates into heat on the front and back surfaces of the substrate and generates heat, the effect of thermal strain on the substrate is significantly reduced, and therefore the substrate is less likely to crack. . Further, when the heating element of the present invention is used for fixing, the resistance heating element located on the back surface as viewed from the fixing object is also conducted to the front surface through the base, so that the fixing action can be promoted and no waste occurs. Therefore,
Since the amount of heat generated can be increased, the speed of fixing can be increased.

However, the heating element of the present invention can be applied not only to fixing but also to any application requiring heating for a required length.

According to a second aspect of the present invention, in the heating element according to the first aspect, the first and second resistance heating elements are arranged substantially thermally symmetric with respect to the base. And

The term “substantially thermally symmetric” means that the amount and distribution of generated heat are substantially line-symmetric or point-symmetric on both sides of the substrate. Note that “substantially” means that a slight deviation is allowed as long as the effect is not fatally affected.

Thus, in the present invention, since the heat generated by the resistance heating elements on the front and back of the base is substantially symmetric,
Thermal strain acting on the substrate is minimized, so that cracking of the substrate due to thermal strain can be significantly reduced.

According to a third aspect of the present invention, in the heating element according to the first or second aspect, each of the power receiving terminals of the first and second resistance heating elements covers the resistance heating element of the base. It is characterized by being arranged on the surface.

The power receiving terminal may be made of any material and structure as long as it has a power receiving function of receiving a current flowing through the resistance heating element from a power source. In the case of using a silver-based thick film conductor, the use of a silver-based thick-film conductor is favorable because it is well compatible with a resistance heating element and the same manufacturing method can be adopted.

Thus, in the present invention, since the power receiving terminal and the resistance heating element are on the same surface of the base, the formation of the power receiving terminal and the connection between the resistance heating element and the power receiving terminal are facilitated. In particular, the present invention is effective because it is difficult to secure a sufficient wiring space for the base in relation to the formation of the resistance heating element on the front and back of the base.

A heating element according to a fourth aspect of the present invention is the heating element according to any one of the first to third aspects, wherein the temperature of the first resistance heating element is sensed to control the temperature of the first resistance heating element. A first temperature sensor that can be used; and a second temperature sensor that can sense the temperature of the second resistance heating element and can be used for controlling the temperature of the second resistance heating element. It is characterized by.

As the temperature sensor, a thermistor can be used, but the present invention is not limited to this. If the temperature sensor has a temperature sensing function and is useful for controlling the temperature of the resistance heating element, Other elements can be used.

In the case where a plurality of resistance heating elements are provided on one surface of the base, the temperature sensor can be provided at a position where the temperature is highest by the resistance heating elements. In this case, even if there are a plurality of resistance heating elements, only one temperature sensor may be used.

For the temperature control, the current supplied to the resistance heating element or the voltage may be controlled.

Thus, according to the present invention, a temperature sensor can be provided for each resistance heating element to perform temperature control.
Accurate and quick temperature control can be performed for the entire heating element, and therefore, when the heating element is used for fixing, high-quality fixing can be performed.

A heating element according to a fifth aspect of the present invention is the heating element according to any one of the first to fourth aspects, wherein the first and second resistance heating elements are opposed to each other with the base interposed therebetween. And

Since the first and second resistance heating elements face each other, thermal symmetry can be achieved with the substrate interposed therebetween. For this reason, the thermal balance between the front and back surfaces of the base is improved, and even if the base is easily broken like ceramics, the thermal strain is extremely reduced.

According to a sixth aspect of the present invention, in the heating element according to any one of the first to fourth aspects, the first resistance heating element comprises two resistance heating elements separated from each other in the width direction. The second resistance heating element is disposed at a position facing the middle of the two resistance heating elements of the first resistance heating element in the width direction;

The first resistance heating element depends on the distance between the two resistance heating elements, but if the distance is not so large, the temperature is highest at an intermediate position between the resistance heating elements. Since the second resistance heating element is disposed so as to face the first maximum temperature position, a considerably balanced state can be obtained thermally. Therefore, in the present invention as well, the occurrence of thermal strain is relatively small, which is effective in preventing cracking of the substrate.

Moreover, since the first resistance heating element is composed of two resistance heating elements, the amount of heat generated can be increased. Therefore, for example, by using the heating element of the present invention for fixing, the fixing speed can be increased.

A heating element according to a seventh aspect of the present invention is the heating element according to any one of the first to fourth aspects, wherein the first resistance heating element and the second resistance heating element are substantially point-symmetric with respect to the base. It is characterized by being arranged in.

When the resistance heating element is displaced in the width direction of the surface of the substrate, the substrate may be broken by thermal strain acting on one surface of the substrate due to thermal distortion between the front and back of the substrate. . In the present invention, a portion of one surface of the substrate that is separated from the resistance heating element is heated from the opposite surface of the substrate by the heat generated by the resistance heating element disposed on the opposite surface. As a result, the thermal balance can be moderately set, so that the thermal strain acting on the substrate can be reduced, so that the crack of the substrate due to the thermal strain can be reduced.

According to the fixing device of the present invention, there is provided the fixing device of the present invention.
And a pressure roller disposed in pressure contact with the heating element.

A conveying sheet made of a plastic sheet such as a thin polyimide resin may be interposed between the heating element of the fixing device and the object to be fixed to facilitate conveyance of the object to be fixed. Further, the conveying sheet can be formed into an endless belt shape.

Also in the present invention, the function of the heating element according to claims 1 to 7 is exerted.

According to a ninth aspect of the present invention, the image forming apparatus forms a reverse image by attaching toner to the formed electrostatic latent image.
9. An image forming means for transferring an inverted image to a fixing member to form an image; and a fixing device according to claim 8, wherein the fixing device fixes the image by fusing toner attached to the fixing member. It is characterized by.

In the present invention, the image forming apparatus includes all devices having a function of forming an image using toner. The image means a character, a figure, a code, a video, and the like. Specifically, for example, there are image forming apparatuses such as a copying machine, a printer, and a facsimile.

[0042]

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

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

In the figure, 1 is a base, 2 is a first resistance heating element, 3 is a second resistance heating element, 4 is a protective film, 5a and 5b.
Is a temperature sensor such as a thermistor, and 6 is a conductive path.

The base 1 is a thin and long plate made of alumina ceramics.

The first resistance heating element 2 is disposed at substantially the center of one surface of the base 1, and is formed by screen-printing a conductive paste mainly composed of a silver-palladium alloy, drying and firing the paste. It is a film resistance heating element.

The second resistance heating element 3 is disposed directly opposite to the first resistance heating element 2 with the substrate 1 interposed therebetween, and thus is disposed substantially at the center of the other surface. The thick-film resistance heating element is made of a material and a similar manufacturing method.

The protective film 4 covers the resistance heating elements 2 and 3 to protect the resistance heating elements 2 and 3 electrically and / or mechanically, and is made of glass.

The one temperature sensor 5a is disposed on the base 1 at a position intermediate the longitudinal direction of the first resistance heating element 2 and adjacent to the resistance heating element 2.

The other temperature sensor 5 b is similarly disposed on the base 1 adjacent to the second resistance heating element 3.

The conductive path 6 forms a conductive path for the temperature sensors 5a and 5b.

FIG. 2 is a plan view showing a first embodiment of the heating element of the present invention.

In the figure, the same parts as those in FIG. 1 are denoted by the same reference numerals.

7a and 7b are power receiving terminals, and a conductive paste containing silver as a main component is applied to the base 1 by a screen printing method so that a part thereof is superimposed on one end of the resistance heating element 2.
It is obtained by drying and firing. One power receiving terminal 7a
Is directly connected to the left end of the first resistance heating element 2 in the drawing. The other power receiving terminal 7b is
Is connected to the right end of the resistance heating element 2 via a conductive path 8 (not shown in FIG. 1). The power receiving terminals 7a and 7b are arranged close to each other within a range in which a required creepage distance is secured near one end of the base 1, thereby facilitating connection of a power supply. The power receiving terminals 7a and 7b are both disposed on the surface of the base 1 on which the first resistance heating element 2 is attached.

The conductive path 6 of the temperature sensor 5a extends near the other end of the base 1 and is connected to the terminal 9.

In FIG. 2, the protective film 4 is not shown.

FIG. 3 is a sectional view showing a heating element according to a second embodiment of the present invention.

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

In this embodiment, the first resistance heating element 2 ′
It differs from the first embodiment in that it is composed of a book. That is, the first resistance heating element 2 ′ is disposed relatively close to and parallel to one surface of the base 1.

The second resistance heating element 3 faces the middle of the first resistance heating element 2 '.

FIG. 4 is a sectional view showing a third embodiment of the heating element of the present invention.

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

This embodiment is different from the first embodiment in that the first and second resistance heating elements 2 ″ and 3 ″ are arranged symmetrically with respect to the center of the cross section of the base 1. That is, the first resistance heating element 2 ″ is shifted to the left in the drawing on one surface of the base 1, and the second resistance heating element 3 ″ is shifted to the right in the drawing on the other surface of the base 1. It is arranged.

The temperature sensor 5a is disposed at a position directly opposite to the first resistance heating element 2 "with the base 1 interposed therebetween.
b is disposed at a position directly opposite the second resistance heating element 3 ″ with the base 1 interposed therebetween.

FIG. 5 is a sectional view showing an embodiment of the fixing device of the present invention.

In the figure, 10 is a heating element, 11 is a pressure roller, 12 is a conveying sheet, 13 is a guide roller, 14 is a housing, and 15 is a fixing member.

The heating element 10 has the structure shown in FIG. 1, 3 or 4.

The pressure roller 11 is in pressure contact with the heating element 10 with the conveyance sheet 12 interposed therebetween.

The transport sheet 12 is made of, for example, a polyimide resin, and has an endless belt shape that gently makes a round around a guide 16 which also serves as a holder for the heating element 10.

The fixing member 15 is fixed to the guide roller 1.
The sheet 3 is fed between the conveying sheet 12 and the pressure roller 11. When the fixing member 15 is fed, the heating element 10 is energized by control means (not shown), and the heating element 10 instantaneously generates heat and rises to a temperature at which fixing can be performed. As a result of the heating element 10 heating the fixing member 15 via the transport sheet 12, the toner adhering to the fixing member 15 is melted and fused to the fixing member 15 by the pressure roller 11, so that fixing is performed. Will be

FIG. 6 is a conceptual diagram of a laser beam printer showing a first embodiment of the image forming apparatus of the present invention.

In the figure, reference numeral 16 denotes an image forming means, which includes a laser scanner 16a, a photosensitive drum 16b and the like. Reference numeral 17 denotes a fixing device having a structure shown in FIG. Reference numeral 18 denotes a printer main body which includes components other than the above components, for example, a paper feed tray, a power supply, a guide roller, an operation switch, a control circuit, a high voltage generation circuit, and a case.

When the laser beam printer receives the image signal, the laser beam is modulated by the image signal in the laser scanner 16a, and is scanned to partially expose the photosensitive drum 16b to form an inverted electrostatic latent image. To form Next, a reversal image is formed by attaching toner to the reversal electrostatic latent image, a fixing medium such as plain paper is fed from a tray by a guide roller, and the reversal image is transferred to the fixing medium to form an unfixed image. The obtained fixing member is obtained. Further, the fixing member is sent to the fixing device 17 by a guide roller. In the fixing device 17, fixing is performed by the above-described operation, and a fixed image is obtained.

FIG. 7 is a conceptual diagram of a copying machine showing an image forming apparatus according to a second embodiment of the present invention.

In the figure, 19 is an image reading means, 20 is an image forming means, 21 is a fixing device, and 22 is a copying machine main body.

The image reading means 19 includes a reading light source and an optical system such as a scanner.

The image forming means 20 forms an inversion electrostatic latent image on the photosensitive drum based on the image data read from the original paper by the image reading means 19, and then applies the toner to the inversion electrostatic latent image to invert the image. An image is formed, and the inverted image is transferred to a fixing medium such as plain paper to manufacture a fixing member on which the image is formed.

The fixing device 21 heats the member to be fixed and fuses the toner to perform fixing. Although the transport sheet is omitted in the figure, it is used as needed.

The copying machine body 22 is provided with the image reading means 1.
9, configurations other than the image forming unit 20 and the fixing unit 21 such as a main body case, a power supply, a control circuit, a high voltage generation circuit,
It is configured to include an operation switch, a paper feed tray, and the like.

[0080]

According to each of the first to seventh aspects of the present invention, by providing a resistance heating element on both the front and back surfaces of the substrate, the occurrence of thermal strain is reduced, the substrate is hardly broken, and the substrate is used for fixing. Can provide a heating element that can meet the demand for high-speed fixing.

According to the second aspect of the present invention, the resistance heating elements on both the front and back surfaces of the base are arranged substantially thermally symmetrically.
A heating element that minimizes thermal strain acting on the substrate can be provided.

According to the third aspect of the present invention, there is provided a heating element in which connection between the power receiving terminal and the resistance heating element is easy by forming the power receiving terminal on the same base surface as the resistance heating element. Can be.

According to the fourth aspect of the present invention, in addition, by providing a temperature sensor for each resistance heating element, it is possible to provide a heating element for accurately controlling the temperature of each resistance heating element. it can.

According to the fifth aspect of the invention, in addition, the first and second resistance heating elements can be thermally symmetrical by directly facing each other across the base, so that thermal strain acting on the base is extremely small. A heating element can be provided.

According to the sixth aspect of the present invention, by additionally providing two resistance heating elements in parallel with the first resistance heating element, it is possible to increase the amount of heat generated and to reduce the generation of the heating element in which the base is hardly broken. Can be provided.

According to the invention of claim 7, it is possible to provide a heating element in which the first and second resistance heating elements are point-symmetric with respect to the base.

According to the invention of claim 8, it is possible to provide a fixing device having the effects of claims 1 to 7.

According to the ninth aspect of the present invention, it is possible to provide an image forming apparatus having the effects of the first to seventh aspects.

[Brief description of the drawings]

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

FIG. 2 is a plan view showing a first embodiment of the heating element of the present invention.

FIG. 3 is a cross-sectional view showing a second embodiment of the heating element of the present invention.

FIG. 4 is a sectional view showing a third embodiment of the heating element of the present invention.

FIG. 5 is a sectional view showing an embodiment of the fixing device of the present invention.

FIG. 6 is a conceptual diagram of a laser beam printer showing a first embodiment of the image forming apparatus of the present invention.

FIG. 7 is a conceptual diagram of a copying machine showing a second embodiment of the image forming apparatus of the present invention.

FIG. 8 is a cross-sectional view showing a conventional heating element for fixing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Base body 2 ... 1st resistance heating element 3 ... 2nd resistance heating element 4 ... Protective film 5a ... Temperature sensor 5b ... Temperature sensor

Claims (9)

[Claims] 1. An elongated, electrically insulating substrate; an elongated first resistive heating element applied to one surface of the substrate along the longitudinal direction of the substrate; An elongated second resistance heating element attached to the heating element. 2. The heating element according to claim 1, wherein the first and second resistance heating elements are arranged substantially symmetrically with respect to the base. 3. The device according to claim 1, wherein each of the power receiving terminals of the first and second resistance heating elements is disposed on a surface of the base on which the resistance heating element is attached. Heating element. 4. A first temperature sensor which can sense the temperature of the first resistance heating element and can be used for controlling the temperature of the first resistance heating element; and sensing the temperature of the second resistance heating element. The heating element according to any one of claims 1 to 3, further comprising: a second temperature sensor that can be used for controlling the temperature of the second resistance heating element. 5. The heating element according to claim 1, wherein the first and second resistance heating elements face each other across a base. 6. The first resistance heating element comprises two resistance heating elements separated in the width direction from each other;
The heating element according to any one of claims 1 to 4, wherein the heating element is disposed at a position facing the middle of the two resistance heating elements in the width direction of the first resistance heating element. 7. The heat generation device according to claim 1, wherein the first resistance heating element and the second resistance heating element are disposed substantially point-symmetrically with respect to the base. body. 8. A fixing device comprising: the heating element according to claim 1; and a pressure roller disposed in pressure contact with the heating element. . 9. 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 member to be fixed to form an image; toner attached to the member to be fixed An image forming apparatus comprising: the fixing device according to claim 8, wherein the fixing device fixes the image by fusing.