JPH0799721B2 - Method for producing PTC composition - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an electric material, and more specifically, a property that electric resistance rapidly increases in a relatively narrow temperature range with temperature rise [PTC characteristic (Positive temperature coefficien
t)], that is, a method for producing a PTC composition.

[Conventional technology]

The PTC composition limits the overcurrent to a predetermined value or less when a circuit including a heater, a positive temperature coefficient thermistor (PTC THERMISTER), a thermal sensor, a battery, etc., which stops heat generation when the temperature rises to a certain temperature, and the short-circuiting It can be used as a circuit protection element or the like in which a circuit is restored when removed. PT
As the C composition, various substances are currently developed, for example,
There is one in which conductive particles such as carbon black are uniformly dispersed in a resin of at least one polymer such as polyethylene or ethylene-acrylic acid copolymer.

Conventionally, a method for producing a PTC composition is generally such that two or more resins used as a polymer are first mixed and uniformly dispersed, and a necessary amount of carbon black is added to the mixture and kneaded. Being manufactured.

[Problems to be solved by the invention]

The preferred properties of the PTC composition are that it has a large resistance value (peak resistance) at high temperature and a low resistance value (room temperature resistance) of 100 mΩ or less at room temperature, that is, a high peak resistance / room temperature resistance ratio. Is.

However, the conventional method for producing a PTC composition has a problem in that a high peak resistance value is not always obtained and the peak resistance varies depending on the production lot.

The present invention has been made based on the above background,
An object of the invention is to provide a method capable of producing a PTC composition having a low room temperature resistance of 100 mΩ or less and a high peak resistance with good reproducibility.

[Means for solving problems]

As a result of various tests and studies for achieving the above-mentioned object, the present inventor has found that if an appropriate amount of conductive particles is kneaded for each resin, PTC
The present inventors have completed the present invention by finding that a composition having good characteristics can be obtained.

That is, the method for producing a PTC composition of the present invention is a method for producing a PTC composition which comprises kneading at least two kinds of polymers and conductive particles to uniformly disperse the particles in the polymer. Then, the kneading of the polymer and the particles is carried out by preliminarily kneading the respective polymers and particles at a predetermined temperature higher than the melting point of the respective polymers, and then main kneading the respective preliminary kneaded products at a predetermined ratio. It is characterized by that.

As a preferred embodiment of the present invention, the preliminary kneading can be carried out in the temperature range of the melting point of the polymer and the temperature 50 ° C. higher than the melting point.

As a preferred embodiment of the present invention, the present kneading can be carried out in a temperature range of a maximum melting point in the polymer and a temperature 70 ° C. higher than the melting point.

As another aspect of the present invention, pre-kneading can be carried out by previously heating and softening the polymer in the range of the melting point of the polymer and a temperature 30 ° C. higher than the melting point, and adding the conductive particles.

In the embodiment in which the polymer is preliminarily heated and softened during the preliminary kneading, it is desirable that the preliminary kneading is performed for 60 minutes to 240 minutes and the main kneading is performed within 120 minutes.

The present invention will be described in more detail below.

The polymer used in this invention is polyethylene,
Polyethylene oxide, t-4-polybutadiene, polyethylene acrylate, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, polyester, polyamide, polyether, 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 There are oxides, polysulfones, fluororesins, and blend polymers of at least two kinds selected from these. In the present invention, the type and composition ratio of the polymer can be appropriately selected according to the desired performance, application and the like.

Further, as the conductive particles dispersed in the polymer, particles of a conductive substance such as carbon black, graphite, tin, silver, gold and copper, and silver-plated particles can be used.

When preparing the PTC composition, various additives may be mixed, if necessary, in addition to the above-mentioned polymer and conductive particles. Examples of such additives include flame retardants such as antimony compounds, phosphorus compounds, chlorine compounds and brominated compounds, antioxidants and stabilizers.

This PTC composition, its raw material, polymer, conductive particles,
It is prepared by mixing and kneading other additives in a predetermined ratio.

One of the features of the present invention is to knead the polymer and the conductive particles, for each polymer, preknead the polymer and the conductive particles, and then main knead each prekneaded product in a predetermined ratio. It consists of doing. In this invention, the preliminary kneading is
For each polymer, the polymer and the conductive particles are kneaded. The blending ratio of the polymer and the particles can be appropriately selected depending on the particle content of the target composition, the type of the polymer, the type of the mixer and the kneader, and the like. In the present invention, pretreatment such as crushing, heating, and mixing may be performed before the preliminary kneading. The temperature for the pre-kneading is in the temperature range from the melting point of the polymer to be pre-kneaded to 60 ° C, preferably 50 ° C higher than the melting point. This is because the kneaded polymer can be gelated and the conductive particles can be uniformly dispersed in the range.

When the polymer is pretreated by heating before the pre-kneading, it is preferable to pre-knead the polymer by heating it to a temperature within the range of + 30 ° C. from its melting point to soften it, and then adding conductive particles. In this embodiment, the pre-kneading is desirably performed for a long time of 60 to 240 minutes.

After pre-kneading, each of the resulting pre-kneaded products, at a predetermined ratio,
The book is kneaded. The proportion of each pre-kneaded product is preferably appropriately selected according to the polymer and the conductive particle composition in the target composition. As in the case of pre-kneading, pre-treatment such as pre-mixing, heating, and mixing of additives can be performed before the main kneading. The apparatus used for the preliminary kneading and the main kneading may be a kneading machine which is usually used. The temperature at the time of kneading in the present invention is a temperature range from the highest melting point of the polymers used to 80 ° C., preferably 70 ° C. higher than the melting point. Therefore, the temperature range varies depending on the type of polymer used. In the case of heating and softening in advance during pre-kneading, the melting point of the polymer used is higher than the highest melting point.
It is preferable to perform the main kneading at a temperature from 20 ° C. higher to 50 ° C. higher than the melting point.

When the additive is mixed in the PTC composition, the additive may be added either before or after the preliminary kneading, before or after the main kneading, or simultaneously with the preliminary kneading or the main kneading.

The PTC composition obtained according to the present invention can be used in various applications. For example, when used for PTC elements,
This PTC composition is formed into a film, and the electrodes of the metal foil are thermocompression-bonded to the top and bottom of the film to form a laminate, which is cut to a predetermined size, and lead wires are soldered to the electrode surface. The PTC element can be manufactured by welding.

[Work]

Since the present invention is configured as described above, it operates as follows.

The uniform dispersion of the polymer and the conductive particles is preferably carried out by mixing and kneading under conditions depending on the type of the polymer, for example, temperature and shearing force. In the conventional production method, conductive particles are mixed and kneaded into several kinds of polymers having different melting points, so that it is impossible to knead all the polymers under the optimum conditions. Therefore, it is considered that the conductive particles are not uniformly dispersed in the polymer, and a part of the conductive particles remains in the continuous layer to have high electric conductivity. On the other hand, in the present invention, since each polymer is kneaded under each optimum condition, the conductive particles are sufficiently uniformly dispersed in the polymer. Therefore, since the conductive particles are discontinuously present in the insulating polymer, the PTC composition according to the present invention is provided with high resistance.

In the embodiment of preheating and softening the polymer during the pre-kneading according to the present invention, the polymer is softened, so that the structure of the conductive particles such as carbon black added is not destroyed by the shearing force and uniformly. Distributed. Furthermore, since this kneading is carried out at a melting point of the polymer of + 20 ° C to + 50 ° C, the structure of the conductive particles such as carbon black is not destroyed by the shearing force, and since the temperature is not high, the polymer is deteriorated and fluidized. Can be prevented.

〔Example〕

 The present invention will be specifically described by way of example.

Example 1 53 parts of an ethylene-acrylic acid copolymer (abbreviated as EAA, Dow Chemical, Primacol 3460, melting point 97 ° C.) was heated to 127 ° C., which is 30 ° C. higher than the melting point, and gelled. 47 parts (47% by weight with respect to the polymer) of black (Stirling V, manufactured by Cabot Corporation) was added and kneaded with a kneader. Separately, 53 parts of high-density polyethylene (abbreviated as HDPE, manufactured by Toyo Soda Co., Ltd., Nippon Hard 5100, melting point 127 ° C.) was heated to 167 ° C., which is 40 ° C. higher than the melting point, and carbon black was added and kneaded as in EAA.

The respective pre-kneaded products were compounded so that the weight ratio of EAA / HDPE was 6/4, and the main kneading was carried out at a temperature 45 ° C. higher than the melting point of HDPE.

A PTC element was prepared from the kneaded PTC composition by an ordinary method. The characteristics of this PTC element were tested and the results are shown in FIG.

Comparative Example A PTC composition was prepared by a conventional method. That is, E
AA and HDPE were prepared by the same procedure as in Example 1 except that AA and HDPE were kneaded at the same time, and then carbon black was added and kneaded, and their properties were tested. The results are shown in FIG.

As is clear from the comparison between FIG. 1 and FIG. 2, the peak resistance is 3 digits in the comparative example, while the peak resistance is 5 digits in Example 1, and the PTC composition according to the present invention is excellent. It can be seen that it has the following characteristics.

Example 2 A substance having PTC characteristics having the following composition was prepared.

% By weight Polymer ... High-density polyethylene ... 26 (Showa Denko, Showlex S6002) Ethylene-acrylic acid copolymer ... 26 (Mitsubishi Yuka, Yucaron EAA) Conductive particles ... Carbon black ... 47 Antioxidant ... 1 (Irganox 1010) EAA and HDPE were softened in a kneader at 120 to 140 ° C and 150 to 170 ° C, respectively, and then carbon black was added to each of them and pre-kneaded at a time shown in Table 1 to homogenize them. Dispersed. Each preliminary kneaded product was subjected to main kneading at a ratio of 1: 1 with a two-roll machine at 180 ° C. for 30 minutes to obtain a PTC composition. Further, a film having a thickness of 250 μ was formed by an extrusion molding machine or a roll forming machine, and a nickel foil having a thickness of 60 μ was thermocompression bonded to the upper and lower sides of the film to prepare a laminate. The obtained laminated body is given a predetermined size (10.5 ×
10.5 × 0.37 mm) was cut to obtain a PTC element. The room temperature resistance and the peak resistance of this PTC element were measured. The results are shown in Table 1.

From this result, by preheating in the pre-kneading to soften the polymer, the room temperature resistance can be 40 milliohms or less, this resistance is a loss of electrical energy at room temperature when using a PTC element as a circuit protection element. Reduce. Further, it can be seen that when the pre-kneading time is set to 60 minutes or longer, the peak resistance becomes 1 kiloohm or more.

〔The invention's effect〕

 According to the present invention, the following effects can be obtained.

As demonstrated in the examples, a large peak resistance can be obtained with good reproducibility as compared with the PTC composition according to the conventional method.

Further, since the kneading is performed under the optimum conditions, the time required for uniform dispersion can be shortened.

Furthermore, by heating and softening the polymer in advance during the preliminary kneading, it is possible to produce a PTC element having a room temperature resistance of 40 milliohms or less and a peak resistance of 1 kiloohm or more which is particularly preferable.

[Brief description of drawings]

FIG. 1 is a diagram showing the resistance-temperature characteristic of the PTC composition obtained by the production method according to the present invention, and FIG. 2 is a diagram showing the resistance-temperature characteristic of the PTC composition obtained by the conventional method. .

Claims (6)

[Claims] 1. A method for producing a PTC composition, which comprises kneading at least two kinds of polymers and conductive particles to uniformly disperse the particles in the polymer. Kneading with particles is characterized in that each polymer is pre-kneaded with the polymer and the particles in a predetermined ratio, and then each of the obtained pre-kneaded products is main-kneaded in a predetermined ratio. And a method for producing a PTC composition. 2. Pre-kneading is carried out by the melting point of the polymer and 50 from the melting point.
The manufacturing method according to claim 1, which is carried out in a temperature range of a temperature higher by ° C. 3. The production method according to claim 1, wherein the main kneading is carried out in a temperature range of a maximum melting point in the polymer and a temperature 70 ° C. higher than the melting point. 4. Pre-kneading is carried out by the melting point of the polymer and 30
The production method according to claim 1, which comprises adding conductive particles to a polymer which has been preheated to a temperature range of a temperature higher by 0 ° C. and softened, and kneading the polymer for a long time. 5. The production method according to claim 4, wherein the preliminary kneading is performed for 60 to 240 minutes. 6. The production according to claim 4 or 5, wherein the main kneading is carried out in a temperature range of 20 ° C. higher than the highest melting point in the polymer and 50 ° C. higher than the melting point. Law.