JPH09161952A - Sheet-form heating body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain normal condition of electric connection between electrodes and resistor layers consisting of an organic composition having positive temp. characteristic and take out a desired heat quantity stably for a long time. SOLUTION: A heating element concerned is composed of an insulative base board 1, a pair of electrodes 2, 2 formed thereon, the first resistor layer 3 consisting of an organic composition having positive temp. characteristic, and the second resistor layer 7 consisting of conductive organic adhesive and installed in tight attachment between the electrodes 2, 2 and the first resistor layer 3. The resistance values of the layers should be set as conforming to Rc>=Rs and (Rc/R1 )<=(Rs/Ro), where Ro is resistance value of the first layer 3 at 20 deg.C, Rs is resistance value of the same layer at switching temp., R1 is resistance value of the second layer 7 at 20 deg.C, and Rc is resistance value of the same layer 7 at the switching temp. of first layer 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet heating element using an organic composition having a positive temperature characteristic as a resistor layer, and particularly to a normal electrical connection between an electrode and a resistor layer. The present invention relates to a device devised so that a desired heat generation amount can be taken out stably while maintaining the state.

[0002]

2. Description of the Related Art Organic compositions obtained by dispersing conductive particles such as carbon black particles and graphite particles in a crystalline resin such as polyethylene and polypropylene have a positive resistance value which increases with increasing temperature. It has temperature characteristics and is used as a resistor layer for sheet heating elements of various configurations.

As a sheet heating element using an organic composition having a positive temperature characteristic as a resistor layer, there is, for example, one having a structure as shown in FIG. First, there is an insulating substrate 11 made of a polyester film or the like, and on the insulating substrate 11, a pair of comb-shaped electrodes 12 and 12 'are provided. The electrodes 12 and 12 'are formed, for example, by punching or etching a metal foil such as copper or aluminum, or by printing a conductive paint containing a metal material such as silver, copper or aluminum. It was obtained. On the electrodes 12 and 12 ', for example, a resistor layer 13 formed of a film-shaped or sheet-shaped organic composition having a positive temperature characteristic is provided by means of thermocompression bonding (lamination molding, press molding) or the like. Has been. Sign 1
Reference numerals 6 and 16 'denote power supply portions formed continuously with the electrodes 12 and 12'. By applying a predetermined voltage to the power supply portions 16 and 16 'via terminals or lead wires (not shown), The resistor layer 13 generates heat. Reference numeral 15 is an insulating protective plate provided via an adhesive agent 14 such as a double-sided adhesive tape, and is made of a polyester film or the like like the insulating substrate 11.

[0004]

Since the sheet heating element having the above-mentioned structure has a self-temperature control function, the heating rate is high, and the amount of heat generation is self-adjusting with respect to changes in the working temperature atmosphere. There is an advantage that it is possible to suppress excessive heat generation.
However, this type of sheet heating element undergoes a cooling / heating cycle due to repeated heating over a long period of time,
Due to the difference in the coefficient of thermal expansion between the insulating substrate, the electrode, and the resistor layer, floating occurs partially between the electrode and the resistor layer, increasing the electrical contact resistance and impairing the normal electrical connection state. There were times when it ended up. When the electrical contact resistance between the electrode and the resistor layer increases, it becomes impossible to obtain a desired amount of heat generation, and the function as a heat generating element is lost.

Therefore, as a countermeasure against such a problem, for example, a material having an adhesive property with a metal is mixed in advance in a conductive coating material used as a constituent material of the electrode so that the electrode and the resistor are A method of increasing the adhesive force between the layers, or an organic composition having a positive temperature characteristic is mixed in advance with an adhesive material similar to the above, and by using this as a resistor layer, the electrode and the resistor layer A method of increasing the adhesive strength of the can be considered. However, in these methods, since the adhesive material can be added only so as not to impair the conductivity required for the electrode and the positive temperature characteristic required for the resistor layer, it is not possible to expect a great effect. Can not.

The present invention has been made on the basis of the above points, and an object of the present invention is to provide a normal electrical connection between an electrode and a resistor layer made of an organic composition having a positive temperature characteristic. An object of the present invention is to provide a planar heating element capable of maintaining a connected state and stably extracting a desired amount of heat generation for a long period of time.

[0007]

In order to achieve the above object, a sheet heating element according to the present invention comprises an insulating substrate, a pair of electrodes formed on the insulating substrate, and an organic composition having a positive temperature characteristic. A first resistor layer made of a conductive material and a second resistor layer made of a conductive organic adhesive and provided between the pair of electrodes and the first resistor layer in close contact with each other. 20.degree. C. of the first resistor layer,
Is the resistance value at the switching temperature of the first resistor layer (Rs), the resistance value of the second resistor layer at 20 ° C. is (R ₁ ), When the resistance value of the second resistor layer at the switching temperature of the body layer is (Rc), the equation (I) and the equation (I
It is characterized in that each resistance value is set so that I) holds. Rc ≧ Rs ・ ・ ・ ・ (I) (Rc / R ₁ ) ≦ (Rs / Ro) ・ ・ ・ ・ (II)

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as the insulating substrate, for example, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyphenylene sulfide, polyether ether ketone, polyether imide, polyether sulfone, polyarylate, polycarbonate, etc. Examples thereof include films and sheets made of a polymer material having a low coefficient. These materials may be used alone or in combination of a plurality of materials.

The electrode is, for example, a metal foil made of stainless steel, aluminum, copper, nickel, or an alloy thereof, and a metal obtained by surface-treating nickel, tin, silver, gold, solder, or the like. By a screen printing method or the like, a conductive paint prepared by punching or etching into a predetermined shape, or a known metallic material such as gold, silver, copper, aluminum, or nickel mixed with an appropriate binder is used. What is formed in a predetermined shape is used.

The first resistor layer is formed of a film-shaped, sheet-shaped, or paint-shaped organic composition having a positive temperature characteristic. Among these, it is particularly preferable to use a film-shaped or sheet-shaped product, because the effect of the present invention is remarkably exhibited.
As the organic composition having a positive temperature characteristic, various examples have hitherto been published. For example, various additives such as a conductivity-imparting agent to a crystalline resin and, if necessary, a release agent, an antioxidant, etc. Examples thereof include those in which additives are mixed in a predetermined ratio. Examples of the crystalline resin include polyethylene, polypropylene, ethylene vinyl acetate copolymer (E
VA), ethylene methyl methacrylate copolymer (EMM
A), ethylene-ethyl acrylate copolymer (EEA),
Ionomer resin, olefin resin such as polyethylene oxide, vinylidene fluoride, FEP, PFA, ET
Examples include simple substances such as FE and other fluorine-based resins, and blends of these resins with other resins. Examples of the conductivity-imparting agent include conductive particles such as carbon black particles and graphite particles, powdered materials such as metal powder, crushed fibers such as carbon fibers, metal oxide powder or a mixture thereof. Can be mentioned.

In the present invention, it is essential that the second resistor layer is provided in a state of being in close contact with the pair of electrodes and the first resistor layer. The second resistor layer is
It is composed of a conductive organic adhesive, and has a function as an adhesive in addition to a function as a resistor.
Therefore, due to the adhesive effect of the second resistor layer,
For example, the electrical contact resistance between the electrode and the first resistor layer does not increase due to the influence of the cooling / heating cycle, and the floating or peeling between the electrode and the first resistor layer does not occur. Therefore, it is possible to stably obtain a desired amount of heat generation for a long period of time without damaging the normal electrical connection state.

As the conductive organic adhesive forming the second resistor layer, for example, an acrylic adhesive, an epoxy adhesive, a polyester adhesive, a polyurethane adhesive,
Examples thereof include silicone-based adhesives, polyimide-based adhesives, and the like, in which conductive particles such as carbon black particles and graphite particles are blended as a conductivity-imparting agent.
Since various kinds of these are commercially available as conductive paints, conductive adhesives, etc., they may be used. Examples of means for providing the second resistor layer between the pair of electrodes and the first resistor layer include a doctor blade method, a screen printing method, and a spraying method.

In the present invention, in addition to providing the second resistor layer in a state of being in close contact between the pair of electrodes and the first resistor layer, the resistance value of the first resistor layer and the second resistor layer It is also an essential requirement that each resistance value be set so that the relationship of the following expression (I) and the following expression (II) is established with the resistance value of the resistor layer. This enables a current to be transmitted from the pair of electrodes to the first resistor layer through the second resistor layer without any problem, and further, does not impair the positive temperature characteristic of the first resistor layer. Each resistance value is set to. Therefore, the second
Even if the resistor layer of 1 is provided in a state in which it is in close contact between the pair of electrodes and the first resistor layer, if the respective resistance values do not satisfy the relations of the following equations (I) and (II), However, the positive temperature characteristic of the first resistor layer is impaired, and it becomes difficult to obtain a desired heat generation amount. Rc ≧ Rs ... (I) (Rc / R ₁ ) ≦ (Rs / Ro) ... (II) The resistance value of the first resistor layer at 20 ° C. is (Ro) the first resistor The resistance value at the switching temperature of the layer (Rs) is the resistance value of the second resistor layer at 20 ° C. (R ₁ ), and the resistance value of the second resistor layer at the switching temperature of the first resistor layer is (Rc )

The "switching temperature" is a substantially linear portion on both sides of a portion where the resistance value shows a sudden change in the resistance-temperature characteristic (positive temperature characteristic) of the first resistor layer. Means the temperature at the intersection, which is equivalent to the “Curie temperature” of an oxide semiconductor (for example, barium titanate-based ceramic element) having a positive temperature characteristic. is there. FIG. 2 shows the first
FIG. 3 is a diagram showing resistance-temperature characteristics of an organic composition having a positive temperature characteristic that constitutes the resistor layer of FIG. 1, and a portion (AB portion and CD portion) in which the rate of resistance change substantially changes linearly. ) Is provided. In the present invention, this AB section and CD
The temperature at the intersection of the respective extension lines (shown by broken lines in the figure) of the parts is defined as "switching temperature" (Ts).
In FIG. 2, the horizontal axis represents temperature (° C.), and the vertical axis represents the rate of change (R / R) from the resistance value (Ro) of the first resistor layer at 20 ° C. to the resistance value (R) at each temperature. Ro) is shown in logarithm.

Here, the reason why each resistance value is set so as to satisfy the relationship of the above formula (I) and the above formula (II) will be described in detail. When the resistance value (Rc) of the second resistor layer at the switching temperature of the first resistor layer is lower than the resistance value (Rs) of the first resistor layer at the switching temperature, a predetermined voltage is applied. As a result, the sheet heating element generates heat and the resistance value of the first resistor layer increases, but since (Rc) is lower than (Rs), the resistance value of the first resistor layer is (Rc) or more. When it is attempted to increase, the current tends to flow toward (Rc), so that the positive temperature characteristic of the first resistor layer is impaired. Therefore, by setting the above equation (I), that is, (Rc) to be equal to or greater than (Rs), a current flows in until the resistance value of the first resistor layer becomes (Rs) and heat is generated. ,
As a result, the first resistor layer exhibits a positive temperature characteristic,
It will exhibit a good self-temperature control function.

[0016] However, if greater than the rate of change in resistance _{(R 1)} from to _{(Rc) (Rc / R 1} ) is the rate of change in resistance from (Ro) to (Rs) (Rs / Ro) , (R
There is a case where c) increases and it becomes difficult to transmit a current to the first resistor layer. Therefore, it is necessary to set the equation (II), that is, (Rc / R ₁ ) to be less than (Rs / Ro). At this time, preferably, the resistance change rate (Rc / R ₁ ) of the second resistor layer is set within the range of the following formula (III). 0.5 ≦ (Rc / R ₁ ) ≦ 2.0 ... (III)

If (Rc / R ₁ ) is less than 0.5, the second
Since the resistance layer of 1 exhibits negative temperature characteristics, the resistance-temperature characteristics (positive temperature characteristics) of the first resistance layer may be impaired. On the other hand, when it exceeds 2.0, the second resistor layer exhibits a positive temperature characteristic, so that the resistance of the first resistor layer is −
It may be larger than the resistance change of the temperature characteristic (positive temperature characteristic). Therefore, in such a case, the specifications of the planar heating element must be determined after sufficiently considering the resistance-temperature characteristics of the second resistor layer, which limits the degree of freedom in design. Therefore, the above formula (III), that is, (Rc / R
_{If 1} ) is set within the range of 0.5 or more and 2.0 or less, the specifications of the planar heating element can be determined extremely easily without considering the resistance-temperature characteristic of the second resistor layer. become.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to FIGS. 1 to 3, but the present invention is not limited to these embodiments.

Example A planar heating element having the structure shown in FIG. 1 was manufactured. First,
There is an insulating substrate 1 made of a PET film having a length of 30 mm, a width of 20 mm, and a thickness of 25 μm. On the insulating substrate 1,
A pair of comb-teeth-shaped electrodes 2 and 2'obtained by etching a copper foil having a thickness of 18 μm is formed.
Reference numeral 3 is a first resistor layer, which is composed of a sheet-shaped organic composition having a volume resistivity of 1.7 Ω · cm in which conductive particles such as carbon black particles are mixed in a crystalline resin such as polyethylene. As shown in FIG. 2, the resistance-temperature characteristic of the first resistor layer 3 has a positive temperature characteristic that the resistance value increases as the temperature rises. In FIG. 2, (T
s) indicates the switching temperature of the first resistor layer 3. In this embodiment, the resistance value (Ro) of the first resistor layer 3 at 20 ° C. is 3.8Ω, the switching temperature (Ts) of the first resistor layer 3 is 110 ° C., and the first resistor layer is The resistance value (R _S ) at the switching temperature was set to 20Ω.

Reference numeral 7 is a second resistor layer provided in a state in which the electrodes 2 and 2'and the first resistor layer 3 are in close contact with each other. Volume resistivity 1.0 Ω · cm in which the conductive particles are dispersed
It is composed of an organic conductive adhesive. The second resistor layer 7 has resistance-temperature characteristics as shown in FIG. In this embodiment, the resistance value (R ₁ ) of the second resistor layer 7 at 20 ° C. is 30Ω, and the resistance value (Rc) of the second resistor layer 7 at the switching temperature of the first resistor layer 3 is It was set to 46Ω.

Reference numeral 5 is an insulating protection plate formed on the first resistor layer 3 with a double-sided adhesive tape 4 interposed therebetween, and a vertical 3
It is made of a PET film having a thickness of 0 mm, a width of 20 mm, and a thickness of 80 μm. Reference numerals 6 and 6 ′ represent the pair of electrodes 2,
2'is a power supply unit formed continuously, and a first voltage is applied by applying a predetermined voltage to the power supply units 6 and 6 '.
The resistor layer 3 and the second resistor layer 7 of 1 generate heat.

As described above, in this embodiment, the resistance value (Ro) of the first resistor layer 3 at 20 ° C. is 3.8Ω,
The resistance value (Rs) at the switching temperature of the first resistor layer 3 is 20Ω, the resistance value (R ₁ ) at 20 ° C. of the second resistor layer 7 is 30Ω, and the resistance value at the switching temperature of the first resistor layer 3 is 30Ω. The resistance value (Rc) of the second resistor layer 7 was set to 46Ω. That is, (Rc) and (Rs) satisfy the relationship of the following expression (I). Further, since the value of (Rc / R ₁ ) is 1.53 and the value of (Rs / Ro) is 5.26, (Rc / R ₁ ) and (Rs / Ro) are related by the following equation (II). Are satisfied. Further, the value of (Rc / R ₁ ) is 1.
53, which is a preferred setting range of the present invention (II
I'm satisfied. Rc ≧ Rs ... (I) (Rc / R ₁ ) ≦ (Rs / Ro) ... (II) 0.5 ≦ (Rc / R ₁ ) ≦ 2.0 ... (III)

20 of the sheet heating element thus obtained
Initial resistance in a ℃ atmosphere is 2.9Ω, initial heat generation temperature is 110 ° C, electrodes and resistor layers (sheet-shaped organic composition)
The initial peel strength between them was 5.3N. The peel strength was measured at a pulling speed of 5 mm / min based on the T-type peel test defined in JIS K 6854 (1977).

Comparative Example A planar heating element was manufactured by using the same material and the same construction method as in the above-mentioned example except that the second resistor layer made of an organic conductive adhesive was not formed. The initial resistance value of this planar heating element in an atmosphere of 20 ° C. is 2.6Ω, and the initial heating temperature is 110.
The initial peel strength between the electrode and the resistor layer (sheet-shaped organic composition) was 2.1 N. The peel strength is JIS K
It was measured at a pulling speed of 5 mm / min based on a T-type peel test defined in 6854 (1977).

Here, the following two types of comparative tests were conducted using the above two kinds of sheet heating elements as samples. First, each sample was left in an atmosphere of 20 ° C. for continuous energization heat generation and intermittent energization heat generation (3 minutes of energization and 3 minutes of rest for 1 cycle), and the exothermic temperature was measured every predetermined time and every predetermined cycle. Then, the rate of change from the initial exothermic temperature was calculated by the following equation. Exothermic temperature change rate (%) = ((Exothermic temperature-Initial exothermic temperature) / Initial exothermic temperature) × 100 After the continuous energization and the intermittent energization are finished, the resistance value in the atmosphere of 20 ° C. and the electrode The peel strength between the resistor layers (sheet-shaped organic composition) was measured. These measurement results are shown in Table 1 and Table 2.
Respectively. Table 1 shows heat generation by continuous energization, and Table 2 shows heat generation by intermittent energization.

[0026]

[Table 1]

[0027]

[Table 2]

According to Tables 1 and 2, the sheet heating element of this example provided with the second resistor layer made of an organic conductive adhesive had an initial peel strength of 5.3 N before the test. The adhesive strength is 2.5 times or more the initial peel strength (2.1 N) of the sheet heating element of the comparative example. Further, the peel strength after the test is 5.0 N to 5.1 N, which maintains the initial peel strength, and the peel strength (0.6 N to 0.1. 7 to 8 times compared to 7N)
It has double the adhesive strength. Furthermore, regarding the resistance value,
Almost no difference is seen from the initial resistance value.

On the other hand, the planar heating element of the comparative example which does not include the second resistor layer made of the organic conductive adhesive is
The initial peel strength (2.1 N) before the test was performed was 0.6 N to 0.7 N after the test was completed, and decreased to about 1/3 or less, and the resistance value also increased significantly. In particular, the resistance value after completion of the intermittent energization heat generation test is 22.8Ω, which is increased to about 9 times the initial resistance value (2.6Ω).

The increase of the resistance value due to the decrease of the peeling strength is remarkably shown in the change of the heat generation temperature. That is, the planar heating element of the comparative example has a value of 1 in continuous energization heat generation.
In the intermittent energization heat generation after 600 hours, the rate of change in heat generation temperature shows a negative value after 600 cycles, which is lower than the initial heat generation temperature. On the other hand, in the planar heating element of the present example, the rate of change in heat generation temperature hardly changed in both cases of continuous heat generation and intermittent heat generation, and no decrease in heat generation temperature was observed.

According to these results, the sheet-like heat generation according to this embodiment provided with the second resistor layer made of the organic conductive adhesive between the electrode and the first resistor layer (sheet-shaped organic composition). It can be seen that the body can stably take out a desired calorific value for a long period of time.

[0032]

As described in detail above, according to the present invention, an organic conductive adhesive is used between the pair of electrodes and the first resistor layer made of the organic composition having a positive temperature characteristic. The second resistor layer is formed in close contact with the first resistor layer.
By setting the respective resistance values such that the relationship of the formula (I) and the formula (II) is established between the resistance value of the resistance layer and the resistance value of the second resistance layer, It is possible to obtain a planar heating element capable of maintaining a normal electrical connection with the body layer and stably extracting a desired heating value for a long period of time.

[Brief description of the drawings]

1A and 1B are views showing an embodiment of the present invention, in which FIG. 1A is a plan view of a planar heating element, and FIG. 1B is a sectional view of FIG.

FIG. 2 is a resistance-temperature characteristic diagram of a first resistor layer that constitutes the planar heating element of the present invention.

FIG. 3 is a resistance-temperature characteristic diagram of a second resistor layer that constitutes the planar heating element of the present invention.

FIG. 4 is a diagram showing a conventional example (comparative example), (a) is a plan view of a planar heating element, and (b) is a sectional view of (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Electrode 2'electrode 3 First resistor layer 4 Double-sided adhesive tape 5 Insulation protection plate 6 Power supply section 6'Power supply section 7 Second resistor layer

Claims (1)

[Claims] 1. An insulating substrate, a pair of electrodes formed on the insulating substrate, a first resistor layer made of an organic composition having a positive temperature characteristic, and a conductive organic adhesive. And a second resistance layer provided in a state of being in close contact between the first resistance layer and the electrode of 20.degree. C. of the first resistance layer. (Ro), the resistance value at the switching temperature of the first resistor layer (Rs), and the resistance value of the second resistor layer at 20 ° C.
Where (R ₁ ) is the resistance value of the second resistor layer and (Rc) is the resistance value of the second resistor layer at the switching temperature of the first resistor layer, equations (I) and (II) are established. A sheet heating element characterized in that each resistance value is set as described above. Rc ≧ Rs ・ ・ ・ ・ (I) (Rc / R ₁ ) ≦ (Rs / Ro) ・ ・ ・ ・ (II)