JP2001057302A - Organic ptc thermistor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic PTC(Positive Temperature Coefficient) excellent in stability and in reliability thermistor, wherein the resistance values at the standby time of thermistor elements at room temperatures are low and a deterioration of the elements due to the occurrence of the abnormal situation is not caused, and to provide the manufacturing method of the thermistor. SOLUTION: This thermistor is an organic PTC thermistor having a thermistor element of a constitution wherein conductive particles are scattered in a high-molecular polymer, and having an electrode provided on the surface of this thermistor element. Here, two kinds of thermistor elements, which are at least times different 50 in their resistance values at room temperatures, are parallel-connected to form an organic PTC thermistor, the two kinds of the thermistor elements are cut in a prescribed width, a plurality of the thermistor elements are alternately arranged, and, after the thermistors are thermocompression-bonded to each other by holding both pieces of the thermistors in one pair of electrode foils, the thermistors are cut in such a way as to comprise the two kinds of the elements to obtain the organic PTC thermistor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic PTC (Positive Temperature
cient) thermistors and methods for their manufacture.

[0002]

2. Description of the Related Art An organic PTC thermistor has a structure in which conductive particles such as carbon black and metal are dispersed in a crystalline polymer, and electrodes are provided on the surface of the thermistor body. Since the specific resistance at room temperature (non-operating specific resistance) is lower than that of the thermistor, it is suitable for applications in which a large current flows, and can be downsized.
It is known that it has an excellent characteristic that a resistance change rate (maximum resistance value / room temperature resistance value) is large. The organic PTC thermistor can be used for, for example, a self-control type heater, a temperature detector, an overcurrent protection element, and the like.

[0003] Organic PTC thermistors using carbon black as a conductive filler have already been put to practical use and are used in large quantities as overcurrent protection elements. However, there is a limit in reducing the resistance value of the element body due to the characteristics of carbon black. Currently, the area actually used is about 1cm
² , it is difficult to reduce the resistance to 0.1 Ω or less at a thickness of 1 mm. On the other hand, an organic PTC thermistor using deformed metal particles (for example, those having spike-shaped projections) as a filler can be reduced to 1 mΩ or less (Japanese Patent Laid-Open No. 5-47503, etc.). The organic PTC thermistor using the deformed metal particles as a filler has an extremely small resistance value and an operating temperature of 80 ° C.
It shows a large resistance change rate of 6 digits or more, and is suitable for applications where safety is important at low currents such as batteries. Such an organic PTC thermistor using deformed metal particles as a filler generally has a problem in stability of resistance value.

[0004] Therefore, in the case of using the deformed metal particles as a filler, a wax component that melts at about 80 ° C is added, and the matrix polymer is crosslinked to secure the operation stability and the storage stability. I have. This organic PTC thermistor has extremely low resistance. However, there is a problem that the resistance value easily increases when a large current flows or a high voltage is applied.

Further, carbon black is used as a filler,
An organic PTC thermistor using a crosslinked polyethylene as a matrix has a sufficient withstand voltage, but cannot reduce the resistance value. There is no known example in which stability against a current or voltage above a certain level is secured while maintaining an extremely low resistance value. Moreover, there is no suggestion of such a problem or suggestion of a solution.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable organic PTC thermistor having a very low resistance value at non-operation at room temperature, a high stability against a large overcurrent or a high voltage, and a manufacturing method thereof. Is to provide a way.

[0007]

This and other objects are achieved by the present invention described below. (1) An organic PTC thermistor having a thermistor element having a structure in which conductive particles are dispersed in a polymer and an electrode provided on the surface of the thermistor element, and having a resistance value of at least 50 at room temperature. Organic PT characterized by connecting two kinds of thermistor bodies twice different in parallel
C thermistor. (2) The organic PTC thermistor according to the above (1), wherein at least the low-resistance-side thermistor element has a configuration in which conductive deformed metal particles are dispersed in a high-molecular polymer. (3) The resistance at room temperature differs at least 50 times2
The organic PTC thermistor according to the above (1) or (2), wherein different kinds of thermistor bodies are bonded in parallel by a pair of electrode foils. (4) Resistance values at room temperature differ at least 50 times2
The organic PTC according to any one of the above (1) to (3), wherein, when connecting the kinds of thermistor elements in parallel, the operating temperature of the high-resistance thermistor element is higher than that of the low-resistance thermistor element. Thermistor. (5) The resistance at room temperature differs at least 50 times2
When the types of thermistor bodies are connected in parallel, the slope of the temperature-resistance curve of the high-resistance thermistor body is smaller than the slope of the temperature-resistance curve of the low-resistance thermistor body. The organic PTC thermistor according to any one of the above. (6) Resistance values at room temperature differ at least 50 times2
The organic PTC according to any one of the above (1) to (5), wherein when the kinds of thermistor bodies are connected in parallel, the resistance values of the two at at the same temperature ranging from room temperature to 120 ° C. are different by at least 50 times. Thermistor. (7) The resistance at room temperature differs at least 50 times2
A method of manufacturing an organic thermistor in which two types of thermistor bodies are connected in parallel, in which two types of thermistor bodies are cut into a predetermined width, a plurality of thermistor bodies are alternately arranged, and both pieces are sandwiched between a pair of electrode foils and heated and pressed. And then cutting to include two types of element bodies to obtain an organic PTC thermistor.

In Japanese Utility Model Application Laid-Open No. 60-38038, a rush current protection device capable of rapidly bringing a circuit into a steady state regardless of the ambient temperature conditions is electrically connected in parallel and mutually connected. It shows a thermally coupled positive temperature coefficient thermistor and negative temperature coefficient thermistor, wherein the initial resistance value of the positive temperature coefficient thermistor is lower than the initial resistance value of the negative temperature coefficient thermistor on the low temperature side. However, this device is completely different from the organic PTC thermistor of the present invention in which two kinds of thermistors having resistance values at room temperature differing by at least 50 times are connected in parallel.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The organic PTC thermistor of the present invention is a thermistor element formed by connecting two types of thermistor element bodies having different element resistance values at non-operation at room temperature at least 50 times in parallel. As a result, a thermistor element having an extremely low resistance value at the time of non-operation at room temperature and stable against an abnormal situation caused by a large current or a high voltage can be obtained. On the other hand, if the element resistance value is less than 50 times, a large current flows through the low-resistance element even in an abnormal situation, causing element deterioration. Further, the element having only one of the element resistance values cannot achieve both a low resistance value at the time of non-operation at room temperature and prevention of element deterioration due to occurrence of an abnormal situation.

FIG. 1 shows a structural example of the organic PTC thermistor of the present invention. The organic PTC thermistor 1 shown in FIG.
High molecular polymer, preferably crystalline high molecular polymer (hereinafter, referred to as
A thermistor element (first element) 2 in which conductive particles are dispersed in a polymer) and a thermistor element having a resistance value at least 50 times higher than that of the element 2 at room temperature. Body (second prime field) 3 and these prime fields 2 and 3
Are arranged in parallel, and a pair of electrodes 4 and 5 are provided so as to sandwich the two types of element bodies.

Assuming that the resistance of the first body 2 at room temperature is R ₁ and the resistance of the second body 3 at room temperature is R ₂ , R ₂ / R ₁ is
It is 50 or more, and its upper limit is not particularly limited, but its value is usually about 70 to 300.

Further, the relationship of R ₂ / R ₁ ≧ 50 at the same temperature ranging from room temperature to the temperature immediately before the operating temperature of the first element 2 on the low resistance side (normally, about 120 ° C.). Is preferably maintained.

The room temperature refers to a temperature of about 10 to 30 ° C.

Further, in the event of an abnormal situation, the current mainly flows through the second element on the high resistance side at room temperature, and the current flowing through the first element on the low resistance side at room temperature is minimized. In order to prevent deterioration, it is preferable that the operating temperature of the second element body 3 on the high resistance side is higher than that of the first element body 2 on the low resistance side, and the temperature difference is unique due to other factors. Although it cannot be determined, it is usually about 40 to 150 ° C. The temperature of the second element 3 having a high-resistance at room temperature - preferably smaller than the slope a ₁ of the resistance curve - a first temperature of the element body 2 of the gradient a ₂ of the low-resistance at room temperature of the resistance curve , for example, a ₁ / a ₂ indicates a value of about 1.5 to 3.5.

The operation curves of the element body 2 on the low resistance side at the first room temperature and the element body 3 on the high resistance side at the second room temperature are, for example, as shown in FIG. That is, the relationship of R ₂ / R ₁ ≧ 50 is maintained up to a temperature around the operating temperature of the first element body of 80 ° C.,
At the boundary of 80 ° C. where the resistance value R ₁ of the _first element and the resistance value R ₂ of the second element become the same, this time the resistance value R ₂ of the second element
Is higher. Then, the resistance value of the second element body rises around its operating temperature of around 120 ° C., and eventually R ₁ ≧ R ₂ , and reaches an equilibrium again.

From room temperature to R₁= R_TwoUp to a temperature around 80 ° C
Then R₁<R_TwoAnd the current mainly flows through the first element
Is R₁= R_TwoFrom 80 ° C until equilibrium is reached.
Then R ₁> R_TwoAnd the current mainly flows through the second element
(See the thick line in the figure).

Referring to FIG. 3, the operation mechanism of the thermistor element according to the present invention is as follows. Since the element bodies with different resistance values at least 50 times (the first element body 2 on the low resistance side at room temperature and the second element body 3 on the high resistance side at room temperature) are connected in parallel, the normal current is Resistance value ratio of 50:
It flows overwhelmingly to the first body 2 on the low resistance side at a ratio of 1 or more (see FIG. 3A).

As shown in FIG. 3B, when an abnormal current flows,
At this time, the current mainly flows through the first element on the low resistance side as in the normal state, but the resistance of the element 2 rapidly increases. The rise rate is extremely fast, in less than 0.1 seconds to reach a resistance value of more than 50 times. After this time, the resistance of the second element body 3 on the high resistance side becomes lower, and the current mainly switches on this side. Thereafter, the operating temperature is reached and the resistance value increases. The resistance value at this time also increases, for example, to a value exceeding 10 ⁴ Ω (see (1) to (4) in FIG. 3B).

As described above, by distributing the abnormal current, it is possible to prevent an excessive load from being applied to the first body 2 on the low resistance side. In particular, if the slope of the resistance-temperature curve of the second element 3 on the high resistance side is small or the operating temperature is high,
For a considerable time until the equilibrium is reached, the resistance value at the operating temperature of the second element 3 on the high resistance side becomes small, and most of the current is taken over by the element 3 on the high resistance side,
The burden on the first body 2 on the low resistance side is reduced. As a result, the thermistor element of the present invention hardly deteriorates even when a large current flows, despite its extremely low resistance at room temperature. In other words, this is a result of separating functions by connecting different elements in parallel between the normal current range and the overcurrent operation. As described above, the present invention protects a circuit from an abnormal current with a small peak and an abnormal current that gradually increases, rather than a so-called rush current in which a large current flows in a short time of 0.1 second or less. It will be very effective to do.

The polymer used in the present invention is not particularly limited.
Any material can be used without limitation as long as it can exhibit PTC characteristics when the conductive particles are dispersed into a body.

The polymers usable in the present invention include, for example, polyethylene, polyethylene oxide, t-4-polybutadiene, polyethylene acrylate, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, polyester, polyamide, poly Ether, polycaprolactam, fluorinated ethylene-propylene copolymer, chlorinated polyethylene, chlorosulfonated ethylene,
Ethylene-vinyl acetate copolymer, polypropylene, polystyrene, styrene-acrylonitrile copolymer, polyvinyl chloride, polycarbonate, polyacetal, polyalkylene oxide, polyphenylene oxide, polysulfone, fluorine-based resin and the like, and at least one of these. It may be used. Specifically, it may be appropriately selected according to the method of forming the electrodes, the required PTC thermistor characteristics, and the like.

Preferred examples of the polymer include polyethylene, nylon 12 and polyethylene oxide (PE).
O). Of these, polyethylene oxide, or a mixture of high-density polyethylene and low-density polyethylene with wax is preferred when operation at a relatively low temperature of about 60 to 70 ° C. is targeted, and in particular, for the purpose of lowering the operating temperature. Preferred are waxes mixed with mixed polyethylene or polyethylene oxide.

Polyethylene oxide has a weight average molecular weight
Mw is preferably 2 million or more, more preferably 3 million to 600
It is ten thousand. If the Mw is too small, the viscosity at the time of melting becomes too low, and the dispersibility of the conductive particles deteriorates, making it difficult to lower the resistance at room temperature. Polyethylene oxide with Mw of 2 million or more has a melting point of about 65 to 70 ° C and a density of 1.15
It is about 1.22 g / cm ³ .

The polyethylene may be any of low density polyethylene, medium density polyethylene and high density polyethylene.

The low density polyethylene has a density of 0.91
0 to 0.929 g / cm ³ . 0.93 density
Those having 0 to 0.941 g / cm ³ are called medium density polyethylene, and those having 0.942 g / cm ³ or more are called high density polyethylene. The low-density polyethylene is produced by a high-pressure method, that is, a high-pressure radical polymerization method of 1000 atm or more, and contains a long-chain branch in addition to a short-chain branch such as an ethylene group. High-density polyethylene is produced by coordination anion polymerization using a transition metal catalyst under medium or low pressure of several tens of atmospheres or less, and is linear. However, even when the α-olefin is copolymerized in the medium / low pressure method, short-chain molecules are introduced and the medium / low density polyethylene is obtained. Of these, those with low density are referred to as linear low density polyethylene.

Nylon 12 is a lactam polymer of 12-aminododecanoic acid, having a melting point of 177 ° C., a density of 1.03 g / cm ³ and a Mw of 20,000 to 50,000.

As the fluororesin, polyvinylidene fluoride is preferred. Polyvinylidene fluoride exhibits self-extinguishing properties. The self-extinguishing property is a property that, even after ignition, the fire extinguishes naturally when the flame is kept away. For this reason, polyvinylidene fluoride is suitable for applications in which ignition is possible.

Both the first element on the low resistance side and the second element on the high resistance side may be appropriately selected from the above polymers. As the polymer used for the second element on the high resistance side, a polymer having a high operating temperature may be used, so that the resistance value is maintained at least 50 times from room temperature to, for example, 120 ° C. Can be. The polymer of the second element which has high resistance and operates on the high-temperature side may be selected from the above-mentioned polymers, and includes the above-mentioned fluorine-based resins such as polyvinylidene fluoride.

The conductive particles used in the present invention are not particularly limited, such as metal and carbon black. Any conductive particles can be used without limitation as long as they can provide the required conductivity and at least a 50-fold difference in resistance value.

Examples of the conductive particles can be used in the present invention, metal particles: Ni, Ti, Cu, Ag , Pd, Au, Pt or the like; metal-coated particles: carbon black, A1 ₂ 0 _3, Ti0
Those forming the Ag plated layer on the particles of ₂ or the like, BaTi0 _3, such as metal fibers as to form a Pd plating layer into particles of: length less than 1mm aspect ratio of 10 or more (usually more than 0.001 mm) (generally 100 or less) Ni, Ti, Cu, Ag, Pd, A
u, Pt, etc. Conductive ceramics: tungsten carbide, etc. Carbon black: acetylene black, furnace black, etc. At least one of these conductive particles or fibers may be selected. Specifically, it is sufficient that a difference in resistance value of at least 50 times is obtained, and it may be appropriately selected.However, in order to make the low resistance value at room temperature as low as possible, it is preferable to use metal particles for one element. preferable. Therefore, it is preferable to use metal particles for the first element on the low resistance side, and to use carbon black for the second element on the high resistance side, and to use carbon black.
Even if the same polymer is used, at least a 50-fold resistance value can be easily obtained.

The shape of the conductive metal particles is not particularly limited.
Flaky, spherical, amorphous, etc. may be any, preferably, for example, JP-A-5-47503 and Japanese Patent Application No.
A deformed metal particle having spike-shaped protrusions as described in US Pat.

The preferred average particle size of the conductive metal particles varies depending on the type, shape, method of measuring the diameter, and the like.
Usually, it is about 0.8 to 10 μm, preferably about 1 to 5 μm.

The conductive metal particles having spike-shaped projections are formed from primary particles each having one sharp projection, and have a height of 1/3 to 1/50 of the particle diameter. Spike-like projections are formed on a single particle (usually 10 to 500
) Exist. The material is particularly preferably Ni or the like.

[0034] Such conductive metal particles may be a powder in which one particle is present individually, but the primary particles may be one particle.
It is preferred that about 0 to 1000 chains are continuous to form secondary particles. Some primary particles may be present in the chain. An example of the former is a spherical nickel powder having spike-like projections, and the product name is INCOTy.
It is commercially available as pe 123 nickel powder (manufactured by Inco Corporation), has an average particle size of about ³ to 7 μm, an apparent density of about 1.8 to 2.7 g / cm ³ , and a specific surface area of about 0.3 to 0.3 g / cm ^3.
It is about 4 to 0.44 m ² / g.

An example of the latter, which is preferably used, is filamentous nickel powder, trade name IN
It is commercially available as CO Type 210, 255, 270, 287 nickel powder (manufactured by INCO), of which INCO Type 255, 287 is preferable.
The average particle size of the primary particles is particularly 0.5 to 4 μm.
m is preferred. Further, the apparent density is 0.3-1.
The specific surface area is about 0 g / cm ^{3 and} about 0.4 to ^2.5 m ² / g.

The average particle size in this case is measured by the fish-sub-sieve method.

On the other hand, carbon black having an average particle size of 20 to 150 nm and a specific surface area of 200 to 2000 m ² / g is preferred. Specifically, known commercial products can be used.

The ratio (volume ratio) of the conductive particles in the body is
What is necessary is just to determine appropriately so that the required PTC thermistor characteristics are obtained and the resistance value is sufficiently low during non-operation.
The preferred ratio of the conductive particles {conductive particles / (polymer + conductive particles)} varies depending on various conditions such as the type and shape of the conductive particles, but is preferably 15 to 65% by volume, more preferably 20 to 50% by volume. If the ratio of the conductive particles is too low, the resistance of the element increases, and the resistance becomes unstable, which is not preferable. If the ratio of the conductive particles is too high, uniform dispersion becomes difficult when kneading the conductive particles with the polymer, and characteristics such as withstand voltage tend to deteriorate.
In addition, PTC characteristics may not be exhibited.

The thermistor body is usually manufactured by the following procedure. First, first conductive particles and the like are added to the first crystalline polymer, and the mixture is kept at a temperature equal to or higher than the softening point of the polymer and sufficiently kneaded until the conductive particles are uniformly dispersed. Next, it is formed into a sheet or the like using an extrusion molding machine or a roll molding machine, and subjected to a crosslinking treatment as necessary,
Obtain the first thermistor body. Similarly, a second thermistor body is obtained in the same manner as described above by adding second conductive particles and the like to the second crystalline polymer.

A thermistor is obtained from these element bodies, for example, in the process shown in FIG.

The strips 21 and 31 are formed by cutting the two types of the first plate-shaped element 20 and the second plate-shaped element 30 into necessary widths (FIG. 4 (a)). Then, two kinds of strips 21
And 31 are alternately arranged (FIG. 4 (b)), sandwiched between a pair of electrode foils 40 and 50 from above and below (FIG. 4 (c)), and heat-pressed. The crimped body 60 thus obtained is cut at a position including two types of thermistors (FIG. 4D) to obtain a thermistor element 1 as shown in FIG. 1 (FIG. 4E). The width of each strip may be determined in consideration of the ratio of distribution to the thermistor elements from the resistance value and the current value in the normal state, the current value in the abnormal state, and the like. Normally the final area ratio in the thermistor element is 1: 1
What should be done is.

In particular, as described above, the thermistor of the present invention preferably has a structure in which two types of thermistor bodies are bonded in parallel by a pair of electrode foils.

In the present invention, after the thermistor body is manufactured, the crystalline polymer is selectively removed from the surface of the thermistor body to expose conductive particles to the thermistor body surface. Is preferably provided.

Thus, the polymer film covering the conductive particles existing near the surface of the element can be removed, and the contact resistance between the electrode and the element can be reduced.

The search for removal of the polymer may be appropriately determined according to the combination of the conductive particles and the polymer so that the conductive particles are sufficiently exposed, but is preferably 0.1 to 20 μm.
And more preferably 0.5 to 10 μm. If the depth of the selective removal is too shallow, the effect of the selective removal becomes insufficient. On the other hand, if the depth for selective removal is too deep, the conductive particles completely float from the polymer, which causes a decrease in electrode adhesion strength and an increase in electrode resistance.

The method used for selective removal of the polymer is such that the combination of the two can be selectively removed from the thermistor body composed of the polymer and the conductive particles so as not to damage the thermistor body. The method may be appropriately selected in consideration of the method, and is not particularly limited. However, in the present invention, for example, a method described below is preferably used.

In this method, a discharge gas is introduced into a vacuum chamber in which a thermistor element is placed to generate a gas plasma, which is generated by ion bombardment of the plasma or generated in the plasma. The polymer is selectively removed by the active oxidizing gas. As the discharge gas, an inert gas such as Ar, an oxidizing gas such as oxygen, or a mixed gas thereof may be used, but a gas containing at least an oxidizing gas is preferably used. Specifically, a plasma treatment method, a reactive ion etching method, a reverse spak method, or the like may be used. An oxidizing gas such as oxygen is used as a discharge gas in the reactive ion etching method, and an inert gas such as Ar is used as a discharge gas in the reverse spacking method. In both methods, an object to be etched is used as an electrode. On the other hand, the plasma processing method is different from the reactive ion etching method and the reverse spak method in that the object to be etched is not used as an electrode but is simply exposed to a plasma atmosphere.

The processing apparatus used for the plasma processing method is not particularly limited, but it is usually preferable to use a barrel-type plasma processing apparatus. In a barrel-type plasma processing apparatus, unlike a reactive ion etching apparatus or a sputter etching apparatus used for a reverse sputtering method, a sample to be etched is not disposed on an electrode, but is exposed to plasma while being electrically insulated from the surroundings. You. Specifically, for example, the counter electrode is arranged in a quartz chamber. In this apparatus, first, after inserting a sample to be etched into the chamber, the inside of the chamber is evacuated to, for example, 10 Pa or less. Next, a discharge gas containing an oxidizing gas such as oxygen is introduced into the chamber, and the pressure inside the chamber is maintained at about 100 Pa by adjusting the evacuation speed of the vacuum pump. In this state, plasma is generated by applying high frequency power to the electrodes. By heating the sample to about 100 ° C. during the etching, the etching time can be reduced to 1 or less. The high frequency power used for plasma excitation is 13.56 M
The same etching effect can be obtained as long as the frequency is such that the plasma can be generated from a relatively low frequency of about 100 kHz to a microwave of about 2.45 GHz.

In the method utilizing gas discharge plasma, it is possible to selectively remove the polymer on the surface of the elementary body from tens of seconds to tens of minutes to a depth of about 20 μm at maximum depending on the composition of the polymer. It is possible.

Selective removal method using at least one of ultraviolet irradiation and exposure to an ozone-containing atmosphere By irradiating the thermistor element with ultraviolet light, bonds between atoms in the polymer can be broken. If the ultraviolet irradiation is performed in an oxidizing atmosphere, the decomposed product can be oxidized and removed by a surrounding oxidizing gas. On the other hand, the polymer can also be removed by performing ultraviolet irradiation in an inert gas, followed by washing with water or etching. In addition,
The etching of the molten metal may be performed using an organic solvent or the like.

Further, the polymer can be selectively removed by exposing the thermistor body to an atmosphere containing ozone having a strong oxidizing power to directly react the ozone with the polymer.

It is also possible to use both ultraviolet irradiation and exposure to an ozone-containing atmosphere. In the combined method, bonds between atoms in the polymer are cut by irradiation with ultraviolet rays, and the bonds are strongly oxidized and removed by ozone.

The oxidizing atmosphere used in the ultraviolet irradiation method is not particularly limited, and may be, for example, air. Also,
The ozone concentration in the ozone-containing atmosphere used in each of the above methods is not particularly limited, and may be appropriately determined so as to obtain a necessary removal rate.

In the method using ultraviolet irradiation and the method of exposing to an ozone-containing atmosphere, the etching rate is slower than the method using gas discharge plasma, but the cost is reduced because no vacuum device is used. It is also excellent in that a large area etching process can be performed. In addition, in the method using both the ultraviolet irradiation and the exposure to the ozone-containing atmosphere, an etching rate comparable to the method using gas plasma can be obtained. Specifically, for example, if a commercially available UV ozone cleaner is used, it is possible to selectively remove up to a search of about 20 μm in about 10 minutes. The UV ozone cleaner is a device that oxidizes oxygen in the air with ultraviolet rays at the same time as irradiating a sample with ultraviolet rays by an ultraviolet lamp, and reacts the generated ozone with the sample.

Selective Removal Method Using Laser Light Irradiation When a laser light is irradiated to the thermistor body, the intermolecular bonds of the polymer are broken by strong photochemical excitation of the laser light, and the polymer is separated, decomposed, and scattered. By utilizing this, the polymer can be selectively removed from the element body surface. This method is generally called a laser ablation method, and is a type of photolytic removal processing. The etching rate is high for resins having relatively weak intermolecular bonds, and generally low for inorganic materials such as metals. It is excellent in selectivity when the polymer is selectively removed from the element body. Further, since there is almost no rise in the temperature of the element body during processing, high-quality processing is possible. Further, deep etching can be performed in a short time. In addition, a large area can be processed by scanning with a laser beam.

As a laser processing apparatus used in this method, an excimer laser processing apparatus is preferable. The excimer laser may be any of KrF, ArF, NeF, XeF, and the like, and all have the same effect. The power of the excimer laser is not particularly limited, and may be appropriately determined according to the combination of the polymer and the conductive particles.
The energy density is about 0.1 to 6 J / cm ² , preferably
It is about 0.5 to ⁴ J / cm ² .

Note that the etching principle is different from that of the excimer laser, and the etching selectivity is inferior to the case of using the excimer laser. However, the etching can also be performed with a carbon dioxide gas laser or a YAG laser.

In addition, the selectivity at the time of selective removal of the polymer is inferior, and physical damage of the thermistor body and contamination of impurities are apt to occur. There is a selective removal method that utilizes sandblasting to remove nearby polymers.

The electrode used in the present invention may be any known one, but a metal foil such as Ni is preferable. The thickness of the metal foil is about 0.05 to 0.15 mm.

The electrodes are formed by selectively removing the polymer,
This is performed on the surface of the thermistor body, but by a known method.
Preferably, the electrode is formed by heating and joining a metal foil of roughened Ni or the like.

[0061]

The present invention will be specifically described below with reference to examples. Example 1 An organic PTC thermistor element sample was manufactured according to the following procedure.

Preparation of First Thermistor Element High-density polyethylene (Idemitsu Petrochemical Co., Ltd.)
Manufactured by Idemitsu Polyethylene 520B), and filamentous nickel powder (INCO Type 255 nickel powder, manufactured by Inco Corporation) as conductive particles. The filament-like powder is composed of particles formed by connecting particles having spike-like projections.
The particles having this spike-like projection have an average particle size of 2.2 to
2.8μm, apparent density 0.5 ~ 0.65g / cm ³ , specific surface area
0.68 m ² / g.

Next, conductive particles were added to the polymer, and the mixture was kneaded in a mill at 130 ° C. for 5 minutes. Next, 2,5-dimethyl-2,5-di (t-butylperoxy) hexine-3 was added as a crosslinking agent to obtain a crosslinked composition. The obtained kneaded material was molded by a press molding machine to obtain a sheet-shaped first thermistor body having a thickness of 1 mm.

The thermistor body was irradiated with ultraviolet rays in an ozone-containing atmosphere using a UV ozone cleaner (UVM-3073-13-00, manufactured by Oak Manufacturing Co., Ltd.) to perform a selective removal step. This UV ozone cleaner is equipped with four 40 W low-pressure mercury lamps, and the effective irradiation area is 20 cm x 2
0 cm. UV irradiation for 5 minutes and exposure to an ozone-containing atmosphere selectively removed the polymer from the thermistor body surface to a depth of about 10 μm.

Preparation of Second Thermistor Element The conductive particles were carbon black (Diablack (registered trademark) E, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.) having an average particle size of 43 nm.
A second thermistor body was prepared in the same manner as the first thermistor body except that the compounding ratio was 75 parts by weight with respect to 100 parts by weight of the resin.

The resistance (initial resistance) of each of the above-mentioned element bodies was measured at 25 ° C. Next, the two types of element bodies were arranged in parallel, and a pair of roughened Ni foils were heat-pressed from above and below, and the two were cut into equal areas to obtain a thermistor element (see FIG. 1). The thickness of the Ni foil was 0.1 mm. This is designated as Sample No. 1.

As a comparative example, a single thermistor element was prepared by heating and pressing a pair of Ni foil electrodes.
The sample using the first elementary body is referred to as Sample No. 2, and the one using the second elementary body is referred to as Sample No. 3. Further, by controlling the amount of carbon black in the second body, the ratio R2 of the room temperature resistance R2 of the _second body to the room temperature resistance R1 of the _first body is obtained.
_A product having a ratio of ₂ / R ₁ of 30 was prepared. This is sample N
o.4.

A current of 6 V, 10 A, 20 A, 30 A, and 40 A was applied to these elements to operate them 200 times, and the room temperature resistance after the operation was measured. Table 1 shows the results.

[0069]

[Table 1]

Table 1 clearly shows the effect of the present invention.
Comparing the initial resistance value at 25 ° C. and the resistance value after the current test, the thermistor element according to the present invention has a very low resistance value at room temperature and maintains a sufficiently low resistance value even after a large current flows. On the other hand, in the element made of the first element having a low resistance, the resistance at room temperature is sufficiently low, but the resistance is increased after the operation by the large current. Further, in the element made of the second element having a relatively high resistance, a change in resistance value is small even after the operation by the large current. However, the resistance value itself at room temperature is quite high, and cannot be said to be sufficient characteristics. Also, R ₂ / R ₁ is 5
If it is less than 0, deterioration of the element cannot be sufficiently prevented.

[0071]

According to the present invention, it is possible to obtain an organic PTC thermistor having a very low resistance value at the time of non-operation at room temperature and having high stability and high reliability without element deterioration due to occurrence of an abnormal situation.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration example of a thermistor of the present invention.

FIG. 2 is a graph showing a temperature-resistance curve of the thermistor of the present invention and a body forming the thermistor.

FIG. 3 is a conceptual diagram showing the behavior of the thermistor of the present invention.

FIG. 4 is a process chart showing a method for manufacturing a thermistor of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermistor 2 1st element (low-resistance side at room temperature) 3 2nd element (high-resistance side at room temperature) 4,5 Electrode

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukie Yoshinari F-term (reference) in TDK Corporation, 1-13-1, Nihonbashi, Chuo-ku, Tokyo 5E034 AA07 AA08 AA09 AB01 AC10 DA02 DC03 DC05 DD07 DE05 DE17

Claims (7)

[Claims] An organic PTC thermistor having a thermistor element having a configuration in which conductive particles are dispersed in a polymer and an electrode provided on the surface of the thermistor element, and having a resistance value at room temperature. An organic PTC thermistor characterized by connecting two types of thermistors at least 50 times different in parallel. 2. The at least low-resistance thermistor body,
2. The organic PTC thermistor according to claim 1, wherein the conductive PTC thermistor has a structure in which conductive deformed metal particles are dispersed in a polymer. 3. The organic PTC thermistor according to claim 1, wherein two types of thermistors having resistance values different at least 50 times at room temperature are bonded in parallel by a pair of electrode foils. 4. When two kinds of thermistor bodies having different resistance values at room temperature at least 50 times are connected in parallel,
The organic PTC thermistor according to any one of claims 1 to 3, wherein the high resistance side thermistor body has a higher operating temperature than the low resistance side thermistor body. 5. When connecting two kinds of thermistor bodies having resistance values different at least 50 times at room temperature in parallel,
The organic PTC thermistor according to any one of claims 1 to 4, wherein the slope of the temperature-resistance curve of the high-resistance thermistor body is smaller than the slope of the temperature-resistance curve of the low-resistance thermistor body. 6. A method for connecting two types of thermistor bodies having resistance values different from each other by at least 50 times at room temperature in parallel.
The organic PTC thermistor according to any one of claims 1 to 5, wherein the resistance values of the two at the same temperature in the range from room temperature to a maximum of 120 ° C differ by at least 50 times. 7. A method for producing an organic thermistor in which two types of thermistors having resistance values different from each other by at least 50 times at room temperature are connected in parallel, wherein the two types of thermistors are cut into a predetermined width and alternately cut in plural numbers. A method for producing an organic PTC thermistor, comprising: arranging two pieces, sandwiching both pieces with a pair of electrode foils, and pressing them under pressure to obtain an organic PTC thermistor by cutting to include two types of element bodies.