JPH08126580A - Cooker - Google Patents

Abstract

PURPOSE: To provide a cooker having a positive temperature characteristic by applying the constitution that a conductive film contains a binder of polyimide resin and a conductive inorganic substance having the specified grain size according to the preset ratio. CONSTITUTION: A cooker 10 has a pair of electrodes 2 at both ends of a flat insulation substrate 3, and a conductive film 1 containing a conductive material and a binder is laid between the electrodes 2. The conductive film 1 formed on the substrate 3 contains a binder at least made of polyimide resin, and metallic powder or silicide with a grain size between 1 and 20μm on the basis of a blending ratio between 1:1 and 1:6. As a result, the film 1 comes to have a positive temperature characteristic, and even if the temperature of cooking surface drops, due to the placement of a cooking ingredient thereon, power consumption becomes high and the temperature thereof quickly rises. Furthermore, power consumption becomes low, when temperature reaches the preset level. Also, when the film 1 is made to contain an insulation filler having a mean grain size equal to or less than 10μm, the resistance value of the film 1 increases, and a resistance value for a heating film can be easily established.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to household and commercial heating cookers.

[0002]

2. Description of the Related Art Conventionally, various heating resistors have been proposed. For example, a thermal head (Japanese Patent Publication No. 60-229) having a heating resistor prepared by sputtering a metal boride and a conductive silicide, a binder resin composed of a polyimide resin and a low molecular weight polymer, and a conductive powder. A film type resistor formed by dispersing the body (Japanese Patent Laid-Open No. 55-14170).
No. 5), a printed resistor (Japanese Patent Laid-Open No. 63-226901) in which a resistor made of a thermosetting polyimide resin as a binder and a conductive powder is formed on an insulating substrate has been proposed. It has been attempted to reduce the rate of resistance change during repeated use or at high temperatures.

On the other hand, as a conventional cooking device, a heating element made of a metal wire such as a nichrome wire, nickel, aluminum or a flat metal plate is supported and sandwiched by an insulating material such as a mica plate, a nichrome wire heater, and a sheath. For example, there is a heater that indirectly heats. In these heating cookers, when a cooked product is placed on the cooking plate and the surface temperature of the cooking plate decreases, the temperature sensor in contact with the cooking plate detects the decrease in the surface temperature and the temperature of the cooking plate surface is kept at a predetermined level. The applied voltage was applied to the heater until the temperature reached.

[0004]

However, in the above heating cooker in which the temperature of the surface of the cooking plate is controlled only by turning ON / OFF the heater, the temperature drop on the surface of the cooking plate when the food is placed on the cooking plate is minimized. In order to set the limit, as shown in FIG. 7, there is a problem that it is necessary to use a heater that consumes a large amount of power, or to set the set temperature in advance to be high.

The present invention has been made to solve the above-mentioned conventional problems, and when the food is placed on the cooking plate and the temperature of the surface of the cooking plate is lowered, the power consumption becomes high and the speed is promptly increased. An object of the present invention is to provide a heating cooker that consumes low power when the temperature is raised to a predetermined temperature.

[0006]

The present invention solves the above problems by the following constitutions. That is, the heating cooker of the present invention is a heating cooker provided with an insulating substrate, a conductive film formed on the substrate, and electrodes for supplying electric power to the conductive film. Is a binder composed of at least a polyimide resin and has a particle size of 1 to 2
It is characterized in that it contains 0 μm of metal powder at a compounding ratio (weight ratio) of 1: 1 to 1: 6, and that the conductive film has PTC characteristics (positive temperature characteristics).

Further, the heating cooker of the present invention is a heating cooker provided with an insulating substrate, a conductive film formed on the substrate, and an electrode for supplying electric power to the conductive film.
The conductive film contains at least a binder made of a polyimide resin and a silicide having a particle size of 1 to 20 μm in a mixing ratio (weight ratio) of 1: 1 to 1: 6, and
The conductive film has a PTC characteristic (positive temperature characteristic).

The contents of the present invention will be described in detail below. A conductive coating material obtained by mixing and dispersing a binder made of at least a polyimide resin, which is a heat-resistant resin, and a metal powder or a silicide having a particle size of 1 to 20 μm as a conductive material in a fixed mixing ratio is used as an insulating substrate. A heating cooker is obtained by forming a conductive film by coating the above and providing electrodes at both ends of the conductive film.

This cooking device exhibits a PTC characteristic (positive temperature characteristic) in which the resistance increases as the temperature rises due to energization, and by applying a constant voltage, high power consumption is achieved at low temperatures and the temperature rises rapidly. However, it consumes low power at high temperatures. Therefore, as shown in FIG. 7, since the heater output at low temperatures increases, it is not necessary to set the preset temperature higher than in the conventional case, and the preset temperature is quickly raised.

The insulative substrate used in the present invention may be an insulative ceramic plate or a metal surface of aluminum, iron or the like which has been subjected to an insulation treatment. Further, the electrodes provided on the insulating substrate are those obtained by spraying a metal such as nickel and aluminum, or those obtained by applying and baking a paste containing a metal such as a silver paste, and the electrodes have a conductive film with an insulating substrate. It may be provided after forming on top,
It may be provided in advance.

The binder, which is a constituent of the conductive film of the present invention, may be a polyimide resin alone, or may be prepared by mixing it with another resin. For example, epoxy resin, silicone resin, polyester resin and the like can be used in combination with the polyimide resin. However, from the viewpoint of heat resistance, it is preferable to use the polyimide resin alone or as the main component. The conductive film is formed by coating the insulating substrate with a uniform film thickness by a coating method such as screen printing, spray coating, brush coating, and then baking. The coating method is appropriately selected from the above methods depending on the resin concentration.

The metal powder used in the present invention may be any one as long as it has conductivity, such as nickel, silver,
Palladium, etc. On the other hand, the silicide used in the present invention may be any one as long as it has conductivity, and examples thereof include chromium silicide, molybdenum silicide, tungsten silicide, vanadium silicide, titanium silicide and the like. The particle size of the conductive material contained in the conductive film is preferably in the range of 1 to 20 μm. A conductive material having a particle size of less than 1 μm is difficult to physically pulverize and is manufactured, and even if it is manufactured by another method, the cost is very high and it is not practical. On the other hand, if the particle size exceeds 20 μm, it may be related to the film thickness of the conductive film, but if the film thickness is on the order of several tens of microns, the resistance may become infinite, which is not suitable for practical use.

Further, the compounding ratio (weight ratio) of the binder constituting the conductive film and the conductive material (metal powder, silicide).
Is preferably in the range of 1: 1 to 1: 6 (binder: conductive material). That is, when the ratio of the binder is larger than 1: 1 (binder: conductive material), the resistance of the film becomes unstable, and the resistance may become infinite depending on the mixed dispersion state, which is not suitable for practical use. On the other hand, 1:
When the ratio of the conductive material is increased from 6 (binder: conductive material), the ratio of the binder is decreased and the adhesion of the film is lost, which is not suitable for practical use.

The conductive film has an average particle size of 10
The inclusion of an insulating filler having a thickness of μm or less is preferable because the resistance value of the conductive film is increased and the resistance value is easily set. Examples of the insulating filler include fluororesin, mica, alumina, silica and the like. Also,
The average particle size of the insulating filler is set to 10 μm or less so that a stable dispersion state of the mixture can be obtained and the resistance value can be accurately adjusted by setting the particle size to be equal to or smaller than the particle size of the conductive material. Because you can

Further, between the insulating substrate and the conductive film,
Providing an intermediate layer containing a polyimide resin is preferable because it alleviates thermal stress on the insulating substrate and the conductive film. The intermediate layer may be a polyimide resin alone or may be prepared by mixing with another resin. For example, epoxy resin, silicone resin, polyester resin and the like can be used in combination with the polyimide resin. The resin component used for the intermediate layer is preferably the same as the resin component constituting the conductive film in terms of the coefficient of thermal expansion and the adhesiveness. Further, the intermediate layer is formed by the same method as the above-mentioned conductive film.

Further, it is preferable to provide a surface protective layer containing a polyimide resin on the conductive film, because the conductive material is prevented from being oxidized by oxygen or moisture in the air. The surface protective layer is formed by coating the conductive film with a binder containing a polyimide resin or by adhering a film containing the polyimide resin on the conductive film. The surface protective layer may be a polyimide resin alone, or may be prepared by mixing with another resin. For example, epoxy resin, silicone resin, polyester resin and the like can be used in combination with the polyimide resin. The resin component used for the surface protective layer is preferably the same as the resin component constituting the conductive film in terms of the coefficient of thermal expansion and the adhesiveness. The surface protective layer is formed by the same method as the above-mentioned conductive film.

[0017]

According to the cooking device of the present invention, the conductive film formed on the insulating substrate comprises a binder made of at least a polyimide resin and a metal powder or a silicide having a particle size of 1 to 20 μm. : Mixing ratio (weight ratio) of 1 to 1: 6
Since the above-mentioned conductive film contains PTC characteristics (positive temperature characteristics), even if food is placed on the surface of the cooking surface and the surface temperature drops, the power consumption will be high and the temperature will rise rapidly. When the temperature rises to the set temperature, the power consumption becomes low (see FIG. 7).

When the conductive film contains an insulating filler having an average particle size of 10 μm or less, the resistance value of the conductive film is increased and the resistance value of the heat generating film is easily set.
Furthermore, by setting the particle size of the insulating filler to be substantially equal to or smaller than the particle size of the conductive material, the dispersed state of the mixture is stabilized.

By providing an intermediate layer containing a polyimide resin between the insulating substrate and the conductive film, the polyimide resin has flexibility to some extent, so that the intermediate layer generates heat. It has a function of alleviating thermal strain caused by the difference in thermal expansion coefficient between the coating and the substrate.

Further, by providing a surface protective layer containing a polyimide resin on the conductive film, oxidation of the conductive material due to moisture and oxygen in the air can be prevented.

[0021]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Example 1 Polyimide resin (heat resistant insulating varnish “Trenis # 3000” manufactured by Toray Industries, Inc.), nickel powder having a particle size of 1 to 20 μm, and solvent n-methyl-2-pyrrolidone 4: 2: 1.
The mixture was mixed at a ratio of (weight ratio), and the obtained mixture was coated on an insulating substrate by a screen printing method so as to have a uniform film thickness. Next, this coating film is coated with 100
° C x 30 min. , 150 ° C. × 30 min. , 250 ℃
× 30 min. And 350 ° C. × 30 min. Was heat-treated to form a conductive film.

A heating cooker to which the conductive film thus obtained is applied is shown in FIGS. 1 and 2. FIG. 1 is a schematic sectional view showing an embodiment of the heating cooker of the present invention, and FIG. 2 is an external perspective view of the heating cooker of FIG. As shown in FIGS. 1 and 2, the heating cooker 10 of the present invention is
A pair of electrodes 2 are formed on both ends of a planar insulating substrate 3, and a conductive film 1 containing a conductive material and a binder is formed between the electrodes 2.

The sheet resistance of the conductive film formed under the above conditions is 0.13 Ω / □ at room temperature and 1.3 W / cm ^2.
0.31Ω / when heated up to 225 ℃ under
It was □. That is, the sheet resistance at the time of temperature increase was about 2.4 times that at room temperature, and the PTC characteristic showed that the resistance value increased as the temperature increased (see FIG. 6). Therefore,
A heating cooker having a characteristic that the power consumption increases largely when the rising rate of heat generation is high and the film surface temperature is lowered was obtained. The surface resistance of the conductive film prepared by using nickel as the conductive material is relatively small, but without applying a heating element to the entire surface and providing electrodes at both ends as shown in FIG. Change the electrode structure,
The above problem is solved by forming the heating film in a pattern.

Example 2 A conductive film was formed under the same conditions as in Example 1 except that chromium silicide was used as the conductive material. The sheet resistance of the obtained conductive film is 43 Ω / □ at room temperature, 1.3 W / cm
51 Ω / □ when the temperature is raised to 245 ° C under the energization condition of ²
Met. That is, the sheet resistance at the time of temperature rise was about 1.2 times that at room temperature, and the PTC characteristic showed that the resistance value increased as the temperature rose (see FIG. 6). Since the initial resistance of the film obtained in this example is relatively high and the tendency of PTC characteristics (resistance at energization / resistance at room temperature) is small, the rush current is small and the power consumption increases when the temperature drops. A cooker was obtained with the property of being low. However, compared to the conventional nickel and chromium heater wires, the power consumption is high at low temperatures and low at high temperatures.

Example 3 The same as Example 1 except that a fluororesin (made of polytetrafluoroethylene, having an average particle size of 5 μm) containing 30% of the amount of the conductive material was added to the conductive film as an insulating filler. A conductive film was formed under the conditions. A schematic sectional view of the obtained conductive film is shown in FIG. In FIG. 3, 4 is a conductive material, 5 is an insulating filler, and 6 is a binder. The sheet resistance of the conductive film prepared by combining nickel and fluororesin at room temperature was 0.22 Ω / □, which was about 1.7 times that of Example 1. From the above results, it was found that the initial resistance value of the film is increased by mixing the insulating filler into the conductive film.

Example 4 The same as Example 2 except that a fluororesin (made of polytetrafluoroethylene, having an average particle size of 5 μm) in an amount of 30% of the conductive material was added as an insulating filler in the conductive film. A conductive film was formed under the conditions. The surface resistance of the conductive film prepared by combining chromium silicide and fluororesin at room temperature was 72 Ω / □, which was about 1.7 times that of Example 2. From the above results, it was found that the initial resistance value of the film is increased by mixing the insulating filler into the conductive film.

Example 5 Mica was used except that 10% or 30% of the amount of the conductive material (mica "Dymo Leaf F" manufactured by Topy Industries, average particle size 10 μm) was added to the conductive film as an insulating filler. A conductive film was formed under the same conditions as in Example 1. The sheet resistance of the conductive film prepared by the combination of nickel and mica at room temperature is 0.2Ω / □, 30 when it is 10%.
In the case of%, the value was 5.2Ω / □, which was 1.5 times and 40 times that of Example 1, respectively. From the above results, it was found that the initial resistance value of the film is increased by mixing the insulating filler into the conductive film.

Example 6 As shown in FIG. 4, the heating cooker of this example has an intermediate layer 7 made of a binder interposed between an insulating substrate 3 and a conductive film 1. The intermediate layer was formed as follows. Polyimide resin (Toray, heat-resistant insulating varnish "Treney # 3000") and solvent n-methyl-2
-Pyrrolidone was mixed in a ratio of 1: 1.5 (weight ratio),
The obtained mixture was coated on an insulating substrate by a spray coating method so as to have a uniform film thickness. Next, this coating film was formed at 100 ° C. for 30 min. 1
50 ° C. × 30 min. , 250 ° C. × 30 min. And 3
50 ° C. × 30 min. Was heat-treated to form an intermediate layer. The conductive film provided on this intermediate layer was prepared under the same conditions as in Example 1.

As a result of conducting an energization test (30 minutes, ON-OFF cycle test 20 times) of the one with the intermediate layer and the one without the intermediate layer, the resistance value of the one with the intermediate layer was the initial resistance. Although it was 1.01 times that of the initial resistance, the resistance value was 1.
It has increased 11 times. From this result, it became clear that the resistance of the conductive film is stabilized by forming the intermediate layer.

Example 7 In the heating cooker of this example, as shown in FIG. 5, a surface protective layer 8 made of a binder was provided on the surface of the conductive film 1 formed on the insulating substrate 3. It is a thing. The surface protective layer was formed as follows. Polyimide resin (Toray, heat-resistant insulating varnish "Treney # 300"
0 ″) and the solvent n-methyl-2-pyrrolidone at a ratio of 2: 1 (weight ratio), and the resulting mixture was coated on the conductive film by a screen printing method so as to have a uniform film thickness. Then, apply this coating film at 100 ℃
30 min. , 150 ° C. × 30 min. , 250 ° C x 3
0 min. And 350 ° C. × 30 min. Was heat-treated to form a surface protective layer. The conductive film provided under the surface protective layer was prepared under the same conditions as in Example 1.

The one with a surface protective layer and the one without a surface protective layer were subjected to a thermoshock test in water at 300 ° C. After the test, the resistance change was 1% when the surface protective layer was provided, but the resistance change was 5.3% when the surface protective layer was not provided. From this result, it was found that the oxidation protection of the conductive material can be prevented by providing the surface protective layer.

[0032]

According to the cooking device of the present invention, the conductive film formed on the insulating substrate is composed of at least a binder made of a polyimide resin and a metal powder or a silicide having a particle size of 1 to 20 μm. Since the conductive film contains PTC in a mixing ratio (weight ratio) of 1: 1-1: 6, the conductive film exhibits PTC characteristics (positive temperature characteristics), and the heater output increases at low temperatures. It is not necessary to make the temperature higher than the desired temperature in advance, and the temperature can be quickly raised to the set temperature.

By including an insulating filler having an average particle size of 10 μm or less in the above-mentioned conductive film, the resistance value of the conductive film is increased and the resistance value of the heat-generating film is easily set, so that the power consumption is reduced. Since the amount can be adjusted and the film shape can be designed arbitrarily, a heating cooker of any capacity and shape can be provided. Further, by setting the particle size of the insulating filler to be substantially equal to or smaller than the particle size of the conductive material, a stable dispersed mixture can be obtained, and the resistance value can be adjusted accurately.

By providing an intermediate layer containing a polyimide resin between the insulating substrate and the conductive film, the polyimide resin has flexibility to some extent, so that the intermediate layer generates heat. It has a function of alleviating thermal strain caused by the difference in the coefficient of thermal expansion between the coating and the substrate, and as a result, the generation of cracks is suppressed and the stability of the heating coating is improved.

Further, by providing a surface protective layer containing a polyimide resin on the conductive film, oxidation of the conductive material due to moisture and oxygen in the air is prevented, and the resistance value of the heat generating film is stabilized. It is possible to provide a durable heating element.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of a heating cooker according to the present invention.

2 is a schematic bottom view of the heating cooker of FIG. 1. FIG.

FIG. 3 is a cross-sectional view of an essential part of a conductive film containing an insulating filler.

FIG. 4 is a schematic cross-sectional view showing one embodiment of the heating cooker of the present invention provided with an intermediate layer.

FIG. 5 is a schematic cross-sectional view showing an embodiment of the heating cooker of the present invention provided with a surface protective layer.

FIG. 6 is a diagram showing resistance-temperature characteristics of the heating film of the present invention.

FIG. 7 is a diagram showing a comparison of temperature characteristics and the like between the product of the present invention and the conventional product.

[Explanation of symbols]

 1 Conductive Film 2 Electrode 3 Insulating Substrate 4 Conductive Material 5 Insulating Filler 6 Binder 7 Intermediate Layer 8 Surface Protective Layer 10 Heating Cooker

Claims (5)

[Claims] 1. A heating cooker comprising an insulating substrate, a conductive film formed on the substrate, and electrodes for supplying electric power to the conductive film, wherein the conductive film is at least a polyimide resin. And a particle size of 1-2
A cooker characterized by containing 0 μm of metal powder in a compounding ratio (weight ratio) of 1: 1 to 1: 6, and the conductive film has PTC characteristics (positive temperature characteristics). . 2. A heating cooker comprising an insulating substrate, a conductive film formed on the substrate, and electrodes for supplying electric power to the conductive film, wherein the conductive film is at least a polyimide resin. And a particle size of 1-2
A cooker characterized by containing a silicide of 0 μm in a compounding ratio (weight ratio) of 1: 1 to 1: 6, and the conductive film has PTC characteristics (positive temperature characteristics). . 3. The conductive film has an average particle size of 1
The heating cooker according to claim 1 or 2, further comprising an insulating filler having a size of 0 µm or less. 4. The heating cooker according to claim 1, wherein an intermediate layer containing a polyimide resin is provided between the insulating substrate and the conductive film. 5. The heating cooker according to claim 1, wherein a surface protective layer containing a polyimide resin is provided on the conductive film.