JPH07176364A - Heater - Google Patents

Abstract

PURPOSE:To make a heater operable at high temperatures by making the surface temperature of the heater almost equal to the heating temperature of a heating element. CONSTITUTION:A heater includes a plurality of heating elements 1... and two heat conducting plates 2, 2 sandwiching the heating elements 1... from the upper and lower sides, each of the heating elements 1 comprising a positive temperature coefficient thermistor having electrodes 1b, 1b on its upper and lower sides. Each heat conducting plate 2, 2 comprises an electrically insulating base 2a made from an inorganic material of high heat conductivity and a conductive layer 2b formed over the base 2a by the flame-spraying or baking of metal on one side of the base 2a. The conductive later 2b is disposed on the heating- element 1 side of the heat conducting plate 2 so that the electrodes 1b... on the upper sides of the heating elements are electrically connected to one another and that the electrodes 1b... on the lower sides of the heating elements are electrically connected to one another.

Description

Detailed Description of the Invention

[0001]

The present invention has a positive temperature coefficient (Positiv
e Temperature Coefficient) A heater using a thermistor as a heating element.

[0002]

2. Description of the Related Art Heretofore, a planar heater using a plate-shaped heating element made of barium titanate-based porcelain semiconductor, which is a positive temperature coefficient thermistor having a self-temperature control function, has been considered. This planar heater does not require a temperature control circuit for maintaining a constant heat generation temperature or an overheat prevention circuit for preventing overheating, and has extremely high safety.

In the above-mentioned sheet heater, electrodes are provided on the front surface and the back surface of the heating element, and lead wires are soldered to these electrodes to connect to an external power source, so that the heat generated by the heating element is heated. In order to transfer the heat evenly to the case, a case made of a molded article of ceramics such as alumina having excellent electrical insulation, heat resistance, mechanical strength and thermal conductivity, or an insulating sheet made of a thermoplastic resin, etc. The body is covered.

Since the lead wire is directly soldered to the electrodes provided on the front surface and the back surface of the heating element, there is a convex portion at that portion. If a space (gap) is formed between the case or the insulating sheet and the heating element, the thermal conductivity between the heating element and the object to be heated is reduced. Therefore, when covering the above heating element with a case, The case is provided with a concave portion in conformity with the soldering convex portion, and attention is paid to the adhesion between the case and the heating element.

[0005]

However, in the above conventional structure, when the heating element is covered with the insulating sheet, it is necessary to fix the heating element to the insulating sheet so that the heating element does not move in the insulating sheet. Therefore, there is a problem that an adhesive or the like must be used.

Further, when the heating element is covered with a case made of a ceramics molded article, it is necessary to separately prepare this case, the thickness of the planar heater becomes thicker, and the number of parts and steps for manufacturing the planar heater are increased. There is a problem that the number increases and the cost increases.

Further, since the above case is made of a ceramic molded product, it is poor in workability. Since it takes time to form unevenness in its shape, the case where the heating element has a low operating temperature and has heat resistance is not required. In this case, the above problem becomes more serious.

In view of this, there has been considered a planar heater in which a heating element is sandwiched between metal plates which also serve as a heat dissipation plate and an electrode plate and which are sealed with a resin package. In order to improve heat conduction, the resin package is formed integrally with the metal plate by compression molding.

However, since this sheet heater uses the resin package, it is difficult to efficiently conduct the heat from the heating element to the object to be heated. For this reason,
It has a problem that it cannot be used for high temperature heating.

[0010]

In order to solve the above-mentioned problems, a heater according to the present invention comprises a plurality of heating elements composed of a positive temperature coefficient thermistor having electrodes on the upper and lower surfaces, and a plurality of these heating elements. It is equipped with two heat conduction plates sandwiched between the above, and the above heat conduction plates are a base made of an inorganic material having high electrical conductivity and high heat conductivity, and a metal is sprayed or burned on one side of the base. And a conductive layer formed on the base by means of which the conductive layer is arranged on the heating element side of the heat conduction plate so as to electrically connect the electrodes on the upper surface and the electrodes on the lower surface of the heating element. It is characterized by being.

[0011]

According to the above construction, since the heating element composed of the positive temperature coefficient thermistor is provided, the heating temperature of the heater can be kept constant without providing the temperature control circuit.
Moreover, since the conductive layer is formed on the base by spraying or baking a metal on one surface of the base made of an inorganic material, the base and the conductive layer firmly adhere to each other. Therefore, the heat from the heating element is easily transmitted to the outside through the heat conducting plate. Therefore, the surface temperature of the heater is substantially equal to the heat generation temperature of the heating element. That is, the heat generated by the heating element can be efficiently extracted to the outside. Therefore, the heater can be operated at a high temperature.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS. 1 and 2.

As shown in FIG. 1, the heater of this embodiment has a plurality of heating elements 1, ..., Two heat conduction plates 2 and 2 for sandwiching the heating elements 1 ... It is provided with a screw 3 and a nut 4 for fixing the 2 and 2 to each other.

The heating element 1 comprises a disc-shaped heating member 1a made of a material having a PTC (positive temperature coefficient) characteristic, and electrodes 1b and 1b formed on the upper and lower surfaces of the heating member 1a. The heating element 1 is formed with a hole 1c vertically passing therethrough for passing the screw 3. As the material of the heat generating member 1a, for example, a semiconductor material containing barium titanate as a main component is used.

The heat conducting plate 2 includes a base 2a and a base 2a.
And the conductive layer 2b formed on the conductive layer 2b.
b is arranged on the heating element 1 side. The heat conduction plates 2 and 2 are provided with through holes 6 for allowing the screws 3 to pass therethrough. If necessary, the heads of the screws 3 should not be projected on the surface of the upper heat conduction plate 2. In order to achieve the above, the entrance portion of the through hole 6 is widened.

Any material can be used for the base 2a as long as it is an inorganic material having excellent electric insulation and high thermal conductivity. Specifically, for example, alumina, aluminum nitride, magnesia, porcelain, ceramics and the like can be used. In addition,
Higher density is preferable because it has higher thermal conductivity.

The conductive layer 2b is formed by spraying a metal having a high electric conductivity such as aluminum on the base 2a and fusing the same. Alternatively, it is formed by applying a paste containing metal fine particles such as a silver paste on the base 2a and baking at a high temperature.

The lead wire 5 for connecting to the power supply is fixed to the conductive layer 2b by a conductive adhesive.

An electrically insulating material such as polycarbonate or ceramics is used for the screws 3 and the nut 4 so that the upper and lower conductive layers 2b and 2b are not short-circuited.
The surfaces of the metal screws 3, ..., Nuts 4 ... Can be used by coating them with an insulator.

In the above structure, when the lead wires 5 and 5 are connected to a power source, a current flows through each heat generating element 1 through the conductive layers 2b and 2b of the heat conducting plate 2.2. Since the heating element 1 has the PTC characteristic, the heating temperature can be kept constant without providing a temperature control circuit.

That is, the heating elements 1 ... Have low resistance from room temperature to the Curie temperature Tc (rapid change temperature), but when the Curie temperature Tc is exceeded, the resistance value sharply increases. Characteristic thermistor.
Due to this characteristic, when a voltage is applied from the power source, the heating elements 1 ... Initially have a low resistance value and a large current flows because of a low temperature. As a result, the temperature rises rapidly while the temperature rises. When the temperature exceeds the Curie temperature Tc, the resistance value sharply increases, so that the temperature does not rise above a certain temperature and the certain temperature is kept stable.

That is, the heating elements 1 ... Have a self-temperature control function. Therefore, the planar heater consumes less power,
The temperature control circuit and the overheat prevention circuit can be omitted, and the size can be reduced. Further, there is no fear of ignition due to local overheating.

Moreover, the base 2 is made of a metal having high electric conductivity.
Since the conductive layer 2b is formed on the base 2a of the heat conduction plate 2 by spraying or baking on the surface a, the base 2a and the conductive layer 2b are firmly adhered to each other. Therefore, the heat from the heating element 1 is easily transmitted to the outside through the heat conduction plate 2. Therefore, the surface temperature of the heater is substantially equal to the heat generation temperature of the heating element 1. That is, the heat generated in the heating element 1 can be efficiently extracted to the outside. Therefore, the heater can be operated at a high temperature.

Furthermore, since the conductive layer 2b can be thinned, the heater can be made lighter and thinner than when a metal plate is used. Moreover, since the number of parts is small, the manufacturing cost can be kept low.

Since the Curie temperature Tc of this heating element 1 can be arbitrarily set within the range of about 30 to 250 ° C. depending on the material composition, the heating element 1 in this embodiment is effective for heating the object to be heated. The Curie temperature Tc may be set in consideration of safety and power saving while achieving a high surface temperature of the heat conductive plate 2.

Specific examples of the heater will be shown below.

As the heating element 1, a heating member 1a containing barium titanate as a main component, a Curie temperature Tc of 62 ° C. and a resistance value of 150Ω was used. The heating element 1 was obtained by applying and baking silver as the electrodes 1b and 1b on the upper and lower surfaces of the heating member 1a. The size of the heating element 1 is the outer diameter 1
The thickness is 5 mm, the inner diameter is 5 mm, and the thickness is 2.5 mm.

The base 2a of the heat conducting plate 2 has a purity of 9
9.5% alumina is used and its size is 150m
It is m × 150 mm × 5 mm. Alumina base 2a
A conductive layer 2b was obtained by applying an electrode paste (silver-electric paste SR5080 manufactured by Hokuriku Paint Co., Ltd.) by screen printing on one surface of the above, drying with an infrared lamp, and baking at 560 ° C. for 5 minutes.

The lead wire 5 was fixed to the conductive layer 2b of the heat conductive plate 2 by soldering. Polycarbonate was used as the material for the screws 3 ... and the nuts 4 ...

Five heating elements 1 ... Are arranged substantially evenly on the conductive layer 2b of the lower heat conductive plate 2 as shown in FIG. Next, the upper heat conduction plate 2 is stacked, each screw 3 is passed from the through hole 6 of the upper heat conduction plate 2 to the hole 1c of the heating element 1 and the through hole 6 of the lower heat conduction plate 2, and the nut 4 is inserted. A planar heater was obtained by screwing with.

The conductive layer 2b is the alumina base 2
It could also be obtained by melting and spraying iron powder on one surface of a with a combustion flame of oxygen-acetylene.

The conductive layer 2b does not necessarily have to be provided on the entire surface of the base 2a, but may be provided only on a portion necessary for connecting the heating elements 1 ... In parallel.

The heater corresponding to the present invention comprises a plurality of heating elements 1 ... Composed of positive temperature coefficient thermistors having electrodes 1b and 1b on the upper and lower surfaces, and two heating elements for sandwiching these heating elements 1 ... The heat conduction plates 2 and 2 are provided with a base 2a made of an inorganic material having electrical insulation and high heat conductivity, and a metal is sprayed on one surface of the base 2a or It is composed of a conductive layer 2b formed on the base 2a by baking, and the conductive layer 2b conducts heat so as to electrically connect the electrodes 1b ... On the upper surface and the electrodes 1b ... On the lower surface of the heating element. This is a configuration in which the plate 2 is arranged on the heating element 1 side.

According to this, since the heating elements 1 made of the positive temperature coefficient thermistor are provided, the heating temperature of the heater can be made constant without providing the temperature control circuit. In addition, since the conductive layer 2b is formed on the base by spraying or baking a metal on one surface of the base 2a made of an inorganic material, the base 2a and the conductive layer 2b are firmly adhered to each other. Therefore, the heat from the heating elements 1 ... Is easily transmitted to the outside through the heat conducting plate 2. Therefore, the surface temperature of the heater is substantially equal to the heat generation temperature of the heating elements 1. That is, the heat generated by the heating elements 1 ... Can be efficiently extracted to the outside. Therefore, the heater can be operated at a high temperature.

[0035]

As described above, the heater according to the present invention has a plurality of heating elements each composed of a positive temperature coefficient thermistor having electrodes on the upper and lower surfaces, and two heat conducting members sandwiching these heating elements from above and below. The heat conducting plate is formed on the base by spraying or baking a metal on one side of the base and a base made of an inorganic material having electrical insulation and high heat conductivity. And a conductive layer
Since the conductive layer is arranged on the heating element side of the heat conduction plate so as to electrically connect the electrodes on the upper surface and the electrodes on the lower surface of the heating element, the heat generated by the heater can be generated without providing a temperature control circuit. The temperature can be constant. Moreover, since the conductive layer is formed on the base by spraying or baking a metal on one surface of the base made of an inorganic material, the base and the conductive layer firmly adhere to each other. Therefore, the heat from the heating element is easily transmitted to the outside through the heat conducting plate. Therefore, the surface temperature of the heater is substantially equal to the heat generation temperature of the heating element. That is, the heat generated by the heating element can be efficiently extracted to the outside. Therefore, there is an effect that the heater can be operated at a high temperature.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a heater according to the present invention.

FIG. 2 is a plan view showing a specific example of the heater of FIG. 1 and showing a schematic configuration of the heater.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating element 1a Heating member 1b Electrode 2 Heat conduction plate 2a Base 2b Conductive layer 3 Screw 4 Nut 5 Lead wire

Claims (1)

[Claims] 1. A plurality of heating elements composed of positive temperature coefficient thermistors having electrodes on the upper and lower surfaces, and two heat conduction plates for sandwiching these heating elements from above and below are provided. The plate is composed of a base made of an inorganic material having electrical insulation and high thermal conductivity, and a conductive layer formed on the base by spraying or baking a metal on one surface of the base. A heater characterized in that it is arranged on the heating element side of a heat conduction plate so as to electrically connect electrodes on the upper surface of the body and electrodes on the lower surface.