JP4675688B2 - Heating element - Google Patents

Description

  The present invention relates to a heating element used when heating a recording sheet in order to thermally fix toner onto the recording sheet in an electrophotographic process, and more particularly to a heating element using AlN as a substrate.

  In a general electrophotographic process, after a toner image formed on the surface of a photosensitive drum is transferred onto a recording paper, the recording paper is heated by a heating body, and the toner is fixed on the recording paper by the heat of the heating body. Yes. Such a fixing process is usually performed by conveying the recording paper while sandwiching the recording paper between a heating element arranged on the back side of the recording paper and a roller arranged on the front side. In order to efficiently perform the toner fixing process while conveying the recording paper at a high speed, it is effective to increase the heating area by the heating element, that is, the heating width in the recording paper conveyance direction as much as possible.

  FIG. 2 shows an example of a heating element configured according to the above-described concept (see Patent Document 1). Note that FIG. 2 shows a cross section of the heating body, and the heating body has a substantially strip-like shape with the vertical direction in FIG. 2 as the longitudinal direction.

  A heating body A shown in FIG. 2 has an oxide film 102 covering the front and back surfaces of a ceramic substrate (hereinafter referred to as an AlN substrate) 101 containing aluminum nitride (AlN) as a main component. On the back surface, in FIG. 2, on the bottom surface is a strip-shaped heating resistor 103 printed with a thick film across the oxide film 102, and a protective film 104 mainly composed of glass, for example, printed with a thick film so as to cover it. have. Further, the surface of the AlN substrate 101, that is, the upper surface in FIG. 2, is opposed to the pressure roller R with the oxide film 102 interposed therebetween. The recording paper P onto which the toner T has been transferred is conveyed while being pressed between the pressure roller R and the heating body A, whereby the toner T is fixed to the recording paper P by the heat of the heating body A. it can.

  Since the AlN substrate 101 has very good thermal conductivity, if the heating resistor 103 is installed on the back side of the substrate as described above and the front side of the AlN substrate is a heating surface, the formation width of the heating resistor 103 is the substrate. The heat generated by the heating resistor 103 can be spread over the entire heating surface on the surface side of the AlN substrate 101. Therefore, the heating element A shown in FIG. 2 has an expanded heat generating surface area.

  On the other hand, for example, when an alumina ceramic substrate is used as the substrate of the heating body, the heating resistor is formed on the substrate surface side which becomes the heating surface, but the thermal conductivity of the substrate is not so good. The heat of the part where the recording paper is contacted and conveyed on the front side of the paper is taken away by the recording paper, and the temperature becomes lower than the other parts, and the temperature difference between the front side and the other parts causes the substrate However, in the AlN substrate 101 having good thermal conductivity, the heat is quickly supplied to the portion where the heat is taken away by the recording paper that is transported in contact. No problem of substrate cracking occurs.

However, when a thick film of glass or the like is directly formed on the AlN substrate 101, there is a disadvantage that foaming occurs in the glass in the process, and a hole defect is likely to occur. An oxide film 102 mainly composed of Al ₂ O ₃ having a thickness of 10 to 100 μm was formed. When the oxidation treatment is performed only on one surface of the substrate 101, the substrate 101 is warped during use as the heating element A, and thus the oxide film 102 is formed on both surfaces of the substrate 101.

With the oxide film 102, the AlN substrate 101 can prevent problems due to foaming when the protective film 104 is formed. However, the Al ₂ O ₃ layer which is the main component of the oxide film 102 has a thermal conductivity of about 20 W / m · K, whereas the AlN substrate 101 has a thermal conductivity of 95 to 200 W / m · K. There is a big difference. Therefore, when the oxide film 102 is thick, there is a problem that high thermal conductivity, which is the reason for using the AlN substrate 101, is lost.

For example, when the thickness of the AlN substrate 101 is about 0.6 mm, heat generated on the back surface when the Al ₂ O ₃ layer having a thickness of 0.1 mm is formed on the front and back surfaces of the substrate and when the AlN substrate is not formed. If the Al ₂ O ₃ layer is formed, it is only about 70% of the case where the Al ₂ O ₃ layer is not formed. This reduction in area means that the actual heat generation area of the heating element A becomes narrow as it is, and it is necessary to slow down the conveyance speed of the recording paper in order to obtain the same fixing effect. This increases the fixing speed, and consequently the processing speed of the electrophotographic process cannot be increased beyond a predetermined level.

JP-A-11-273736

  The present invention has been conceived under the above circumstances, and it is an object of the present invention to provide a heating element having a larger heat generation area that maximizes the heat conductivity of the AlN substrate and a method for manufacturing the same. To do.

  The inventor of the present application pays attention to the fact that the oxide film substantially reduces the heat generation area in the heating body using the conventional AlN substrate, which reduces the thermal efficiency of the heating body, and forms the oxide film as much as possible. As a result of various studies on methods for compensating for the problems caused by foaming during the formation of the protective film, the present invention has been achieved.

That is, the heating element provided by the first aspect of the present invention includes an AlN substrate having a first surface and a second surface opposite to the first surface, and a lengthwise direction of the AlN substrate directly on the first surface. A porous heating resistor formed to extend in a strip shape along the first surface, a region of the first surface not covered with the heating resistor, and an oxide film formed on the second surface, and the first a heating member and a protective film formed so as to cover over the heating resistor and the oxide film in the surface, the protective film, porous first the upper Symbol heating resistor and in contact with the oxide film a protective film, has a non-porous second protective film covering the first protective film, both the thickness of the region and the second surface to form respectively the above oxide film in the first surface The thickness of the AlN substrate It is within 2% of the, and, the first protective film is characterized in that the glass softening point is formed by a 700 ° C. or more of the crystallized glass or semi-crystallized glass.

In a preferred embodiment, the second surface of the upper Symbol AlN substrate is caused to function as a heating surface.

In a preferred embodiment, a Ag · Pd resistor weight ratio of 15% or more of Pd, or, preferably the thickness of the AlN substrate 0.5-0.7 mm, above the AlN substrate The thickness of the oxide film is within 1.0 to 10 μm.

In the heating body according to the first aspect of the present invention, the oxide film covering the AlN substrate is significantly thinner than the conventional one. This oxide film is not consciously formed on the AlN substrate, but is inevitably formed due to the influence of heat when forming a thick heating resistor on the AlN substrate. By setting the value within the predetermined range, even the oxide film inevitably formed as described above can be made to have a thickness equal to or less than the predetermined value. In addition, in this heating body, basically no oxide film is interposed between the AlN substrate and the heating resistor formed on the AlN substrate. Therefore, when the heating resistor is formed on the first surface side of the AlN substrate and the second surface of the AlN substrate functions as a heating surface, heat transfer from the heating resistor to the AlN substrate is extremely good. In addition, heat transfer from the heat generating surface to the recording paper is also excellent. For this reason, the high thermal conductivity inherent in the AlN substrate that was not sufficiently exhibited by the oxide film in the conventional heating body is exhibited in the heating body according to the present invention.

According to a second aspect of the present invention, there is provided a method for manufacturing a heating element, wherein the first surface of an AlN substrate having a first surface and a second surface opposite to the first surface is directly applied to the longitudinal direction of the AlN substrate. Forming a heating resistor extending in a strip shape along the surface, forming a first protective film on the first surface so as to cover the heating resistor, and second protection so as to cover the first protective film Forming the heating resistor, wherein the step of forming the heating resistor is a step of printing an Ag / Pd resistor paste in which the weight ratio of Pd to the resistor component is 15% or more. And baking the printed paste at 700 to 850 ° C., and simultaneously forming an oxide film on the second surface and a region of the first surface not covered with the heating resistor during the baking. Including , The step of forming the first protective film, the step of printing a glass paste of the crystallized glass or semi-crystallized glass glass softening point of 700 ° C. or higher so as to cover the heating resistor, and is the printed And baking the paste at 800 to 850 ° C.

Method for manufacturing a heating element according to the second aspect of the present invention is a method of producing a heating element without Do what form the pre-oxide film on the AlN substrate. Conventionally, an oxide film is required for an AlN substrate in order to prevent foaming due to a reaction between the AlN substrate and a glass component or the like when a heating resistor and a glass protective film are printed on the AlN substrate in a thick film. It was. In the method of manufacturing a heating body according to the second aspect of the present invention, this problem is solved by forming a thin oxide film during the formation of the heating resistor and suppressing the reaction between the glass component and the AlN substrate as much as possible. The problem is solved by quickly removing the generated gas by forming the heating resistor and the first protective film in a porous film. Therefore, it is not necessary to form an oxide film in advance .

  However, since the thick film is formed in the air, the surface of the AlN substrate is somewhat oxidized. For example, if firing at 700 to 850 ° C., an oxide film of 1 to 8 μm is formed. However, this thickness is about one-tenth of the thickness of a conventional oxide film, and does not significantly reduce the thermal conductivity of the AlN substrate.

  In the heating resistor, the state of the film surface changes depending on the weight ratio of Ag and Pd. When Ag is 90% or more and Pd is 10% or less, Ag film sintering proceeds. In this state, sintering proceeds before the gas generated by the reaction between the glass component in the AlN substrate and the heating resistor is released, leading to blistering and foaming of the film. For this reason, the weight ratio of Ag and Pd is at least 15% or more, preferably 30% or more of Pd.

  The first protective film needs to suppress the fluidity as much as possible in order to suppress the reaction with the AlN substrate as much as possible. Therefore, a glass having a glass softening point close to a firing temperature of 800 to 850 ° C., specifically, 700 ° C. or higher is used. Furthermore, it is more effective to use crystallized glass or semi-crystallized glass that tends to be a porous film.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIG.

As shown in FIG. 1, the heating element A includes a heating resistor 3 formed on the back side of the AlN substrate 1, a first protective film 4 a formed so as to cover the heating resistor 3, And a second protective film 4b formed to further cover the first protective film 4a. As shown in FIG. 1, on the back surface (first surface) of the AlN substrate 1, the region other than the region where the heating resistor 3 is formed and the surface (second surface) of the AlN substrate 1. The oxide film (Al ₂ O ₃ ) 2 having a predetermined thickness is formed. However, as will be described later, this oxide film 2 is not intentionally formed, and is inevitably formed when the heating resistor 3 is formed. Is formed.

  The AlN substrate 1 is a substrate made of aluminum nitride / ceramic, and has a thickness of 0.5 to 0.7 mm, for example, and has a strip plate shape having a desired length in a direction orthogonal to the plane of FIG. 1 having a width of 7 to 14 mm. It has an outer shape. The AlN substrate 1 has a very good heat conduction performance of, for example, 95 to 200 W / m · K.

  The heating resistor 3 is formed in a strip shape along the longitudinal direction of the AlN substrate 1 by a thick film printing method, and since it needs to generate large Joule heat by flowing a relatively large current, Ag / Pd is the main component. The heating resistor 3 is used. The Ag / Pd resistor has a Pd weight ratio of 15% or more. The reason for this will be described later in the description of the manufacturing method, but the gas generated by the reaction between the glass component of the resistor paste and the component of the AlN substrate 1 at the time of firing the heating resistor 3 is preferably released to the outside. This is to form the heating resistor 3 having properties. The thickness of the heating resistor 3 may be determined according to the required amount of generated heat, and is, for example, 7 to 23 μm.

  The oxide film 2 is inevitably formed by heat when forming the heating resistor 3 as described above, but the thickness thereof is controlled so that the firing temperature of the heating resistor 3 is lower than the normal firing temperature. By doing so, it can be made extremely thin, such as 1.0 to 10 μm. Note that the thickness of the oxide film 2 should be within 2% of the thickness of the AlN substrate.

  The first protective film 4a is formed by using a glass paste mainly composed of crystallized glass or semi-crystallized glass, has a porous property, and has a thickness of, for example, 20 to 40 μm. It is formed.

  The second protective film 4b is formed with a thick film using a glass paste containing amorphous glass as a main component, and has a smooth surface. This 2nd protective film 4b is formed in the thickness of 30-50 micrometers, for example.

  Next, an example of the manufacturing method of the heating body A will be described.

  As a first step, the heating resistor 3 is formed on the back side of the AlN substrate 1. This step includes printing using a resistor paste containing a resistor component made of Ag · Pd and having a Pd weight ratio of 15% or more in the resistor component, and firing the paste at 700 to 850 ° C. . By setting the weight ratio of Pd as described above, the firing proceeds while suppressing the film sintering of Ag during firing. Therefore, the gas generated by the reaction between the glass component of the resistor paste and the component of the AlN substrate 1 is reduced. It can escape suitably and it can prevent that the hole defect resulting from foaming arises in the heat-generating resistor 3 baked. At the same time, the heating resistor 3 after firing can have a porous property. Moreover, since the firing temperature (700 to 850 ° C.) of the heating resistor 3 is lower than the normal firing temperature (eg, 1200 ° C.), it is inevitable in the region where the heating resistor 3 is not formed in the AlN substrate 1. Thus, the thickness of the oxide film 2 formed can be suppressed to a very thin thickness of 1.0 to 10 μm.

  As a second step, a first protective film 4 a is formed so as to cover the heating resistor 3. The first protective film 4a is formed by printing using a glass paste and baking the first protective film 4a. The glass used has a glass softening point relatively close to the baking temperature. Specifically, the glass to be used is one having a glass softening point close to 800 to 850 ° C., which is a normal firing temperature, and 700 ° C. or higher. Thus, more preferably, crystallized glass or semi-crystallized glass can be selected as the glass to be used. By doing in this way, the fluidity of the glass at the time of baking is suppressed, the reaction between the glass component and the component of the AlN substrate 1 can be suppressed as much as possible, the occurrence of hole defects due to gas foaming can be suppressed, In addition, porous properties can be imparted to the first protective film 4a.

  As a third step, the second protective film 4b is formed so as to cover the first protective film 4a. The second protective film 4b is preferably formed by printing using a glass paste containing amorphous glass as a main component and firing the glass paste. By using amorphous glass, the second protective film 4b does not have a porous property, and the surface becomes relatively smooth. Further, since the first protective film 4a is a porous film, the adhesion between the first protective film 4a and the second protective film 4b is enhanced, and the second protective film 4b is caused by an external impact. The peeling is avoided.

  The effect of the heating body A manufactured by said method is demonstrated.

  Since the components of the heating resistor 3 and the firing temperature are selected as described above, the gas generated by the reaction with the AlN substrate component during firing can be escaped well. Accordingly, it is not necessary to consciously form an oxide film on the surface of the AlN substrate before the formation of the heating resistor as in the prior art, and the heating resistor 3 is formed directly on the surface of the AlN substrate 1. Moreover, the thickness of the oxide film 2 inevitably formed at the time of firing is very thin as described above. As a result, the heat generated by the heating resistor 3 is first transmitted directly to the AlN substrate 1, and there is no problem that the entire surface of the AlN substrate 1 functions as a heating surface. Since the thickness of the oxide film 2 formed on the surface side of the AlN substrate 1 is very thin, the heat from the heat generating surface to the recording paper can be obtained even when this heating element 3 is used as a heat source for fixing toner in an electrophotographic process. Transmission is very good.

  The heating resistor 3 formed on the back side of the AlN substrate 1 and the first protective film 4a covering the heating resistor 3 are both porous films. Therefore, the first protective film 4a functions as a good heat insulating material, and it is also suitably avoided that the heat generated by the heating resistor 3 escapes from the back side of the AlN substrate 1 and the thermal efficiency deteriorates.

  Thus, the problem that a hole defect due to foaming occurs in the heating resistor 3 and the first protective film 4a is solved at the same time.

  Furthermore, since the surface property of the second protective film 4b is smooth, it is possible to ensure smooth slidability with the heating target even when the heating body A is used as the heating surface.

  Of course, the scope of the present invention is not limited to the above-described embodiments, and all modifications within the scope of the matters described in the claims are all included in the scope of the present invention.

It is sectional drawing showing one Example of the heating body which concerns on this invention. It is sectional drawing showing one Example of the conventional heating body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AlN substrate 2 Oxide film 3 Heating resistor 4 Protective film 4a 1st protective film A Heating body P Recording paper T Toner R Pressure roller

Claims (5)

An AlN substrate having a first surface and a second surface opposite to the first surface; and a porous heating resistor formed so as to extend in a strip shape along the longitudinal direction of the AlN substrate directly on the first surface ; A region of the first surface that is not covered with the heating resistor and an oxide film formed on the second surface, and the heating resistor and the oxide film on the first surface are formed so as to cover them. A heating body having a protective film formed,
The protective layer has a first protective layer of porous contacting the upper Symbol heating resistor and the oxide film, and a non-porous second protective layer which covers the first protective layer,
Also the thickness of the region and the above oxide films formed on the second surface is one of the first surface is within 2% of the thickness of the AlN substrate, and,
The heating body, wherein the first protective film is formed of crystallized glass or semi-crystallized glass having a glass softening point of 700 ° C or higher . The second surface of the upper Symbol AlN substrate is caused to function as a heating surface, heating body according to claim 1.   The heating element according to claim 1, wherein the heating resistor is an Ag · Pd resistor having a Pd weight ratio of 15% or more. The thickness of the AlN substrate is 0.5-0.7 mm, the thickness of the oxide film is Ru 1.0~10μm der heating body according to any one of claims 1 to 3. Forming a heating resistor extending in a strip shape along the longitudinal direction of the AlN substrate directly on the first surface of the AlN substrate having a first surface and a second surface opposite to the first surface; A method of manufacturing a heating body, comprising: forming a first protective film on the first surface so as to cover a body; and forming a second protective film so as to cover the first protective film,
The step of forming the heating resistor includes:
A step of printing an Ag · Pd resistor paste having a Pd weight ratio of 15% or more to the resistor component, and firing the printed paste at 700 to 850 ° C. Forming an oxide film on the region not covered with the heating resistor and the second surface;
The step of forming the first protective film includes:
A step of printing a glass paste of crystallized glass or semi-crystallized glass having a glass softening point of 700 ° C. or higher so as to cover the heating resistor, and a step of firing the printed paste at 800 to 850 ° C. A manufacturing method of a heating element characterized by including .

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