JPH0374002B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a heat-sensitive resistive conductive composition having a low specific resistance at room temperature.

Various methods have been known for producing materials that have a positive temperature coefficient (PTC), particularly materials that have a property in which the positive temperature coefficient increases rapidly when the electrical resistance value reaches a certain temperature range. (Japanese Patent Publication No. 36-16338, Japanese Patent Publication No. 50-33707, Japanese Patent Publication No. 56-10352).

However, the materials obtained by these conventional methods have a problem in that they have a large specific resistance at room temperature, and the rate of increase in resistance value when reaching a specific temperature range is not sufficiently high.

The inventors of the present invention have investigated ways to solve these conventional problems. By adjusting the gel fraction during crosslinking, the inventors have developed a thermosensitive material with low resistivity at room temperature and excellent positive temperature coefficient characteristics. We have proposed a method for manufacturing resistive conductive materials (Japanese Unexamined Patent Publication No. 1983
−80201).

As a result of further studies, the present inventors found that by preheating the raw material crystalline resin and conductive filler at a specific temperature and then kneading and crosslinking, a composition with even lower resistivity at room temperature was created. Based on this knowledge, we have completed the present invention.

That is, the present invention prepares a kneaded product of a crystalline resin and a conductive filler with a gel fraction of 20 to 55 of the crystalline resin.
% by weight to produce a heat-sensitive resistive conductive composition, the crystalline resin and conductive filler are preheated at a temperature of 100°C or higher and below the melting point of the crystalline resin. The present invention provides a method for producing a heat-sensitive, resistive, conductive composition, which is then subjected to kneading and crosslinking.

Various crystalline resins can be used in the present invention, but usually high-density polyethylene,
polyolefins such as low-density polyethylene, polypropylene, and ethylene-propylene copolymers;
These include olefin copolymers, various polyamides, polyesters, fluorine-based polymers, and modified products thereof.

Next, various conductive fillers can be used. Specifically, carbon black such as oil furnace black, thermal black, acetylene black; graphite;
Examples include metal particles or mixtures thereof, with carbon black, graphite, and mixtures thereof being particularly preferred. In addition, the average particle size of this conductive filler is 10 mμ to 1μ, preferably 15 μm.
mμ to 100mμ.

The blending ratio of each component is not particularly limited and varies depending on the desired physical properties, etc., and cannot be determined unambiguously, but usually 15 to 150 parts by weight of the above conductive filler is added to 100 parts by weight of the crystalline resin. , preferably 40
~120 parts by weight is blended. If the amount of the conductive filler is less than the above ratio, the specific resistance at room temperature, that is, the initial resistance value of the resulting heat-sensitive resistive conductive composition will become large, whereas if it is too much than the above ratio, the specific temperature range The rate of increase in resistance value decreases.

The present invention is characterized in that the crystalline resin and conductive filler are preheated and then kneaded and crosslinked.

Here, the preheating temperature is 100℃ or higher,
And the temperature is below the melting point of the crystalline resin used.

If the preheating temperature is less than 100°C, the specific resistance of the resulting conductive composition will increase, which is not preferable.

Further, the preheating method is not particularly limited, but heating with hot air using a hot air dryer, heating under reduced pressure, etc. are suitable. This preheating time is usually 1 to 5
time, preferably 2 to 3 hours. Here, if the preheating time is longer than this range, the crystalline polymer will be thermally degraded, and if it is shorter, the specific resistance of the resulting conductive composition will increase, which is not preferable. In addition,
The crystalline resin and conductive filler may be preheated before kneading and crosslinking, and it goes without saying that each of the above components may be preheated separately before being mixed, kneaded and crosslinked. Both components are mixed in advance, preheated, then kneaded,
Crosslinking may also be performed.

After the above preheating, the crystalline resin and the conductive filler are kneaded. This kneading is done using a Banbury mixer.
This may be carried out by a conventional method using a mixing roll or the like. Usually, it is sufficient to carry out the reaction at 150 to 200°C for 3 to 30 minutes.

After this kneading, crosslinking is performed. Crosslinking can be carried out by various means, including a method of adding a crosslinking agent such as an organic peroxide, a method of using ozone, a method of irradiating with active energy rays such as electron beams, and the like. Here, the organic peroxides include benzoyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, t-butylcumyl peroxide, t-butyl peroxide, 2,5-dimethyl-2,5-di(t -butylperoxy)hexyne-3 and the like.

The degree of crosslinking mentioned above should be adjusted to a range such that the gel fraction is 20 to 55% by weight, preferably 30 to 50% by weight, based on the crystalline resin used. If the gel fraction is less than 20% by weight, the resulting conductive composition will not have sufficient positive temperature coefficient characteristics, and if it exceeds 55% by weight, the rate of increase in resistance value in a specific temperature range will decrease, which is undesirable.

In this way, the degree of crosslinking of the crystalline resin can be adjusted within the above-mentioned range by appropriately determining the temperature, time, amount of crosslinking agent, etc. used during the crosslinking reaction. For example, when organic peroxide is used as a crosslinking agent in high-density polyethylene, the amount of organic peroxide used is 0.05-0.30% by weight based on the high-density polyethylene, and the temperature is 145-165°C for about 0.5-5 minutes. Knead,
If you heat it for about 5 to 15 minutes at around 190℃ during molding,
Crosslinking progresses to the desired range.

In addition, when crosslinking is performed using ozone, after exposure to a gas containing 0.5 to 20% by volume of ozone for 0.5 to 8 hours, a crosslinking aid such as divinylbenzene is added at a concentration of 0.5 to 10% by volume per 100 parts by weight of high density polyethylene. Crosslinking progresses by adding parts by weight, preferably 1 to 5 parts by weight, and kneading.

Further, when crosslinking is performed using an electron beam, high density polyethylene may be irradiated with a dose of about 2 to 15 megarads.

The heat-sensitive resistive conductive composition of the present invention obtained by the above-described operation has an extremely low electrical resistance value at room temperature. In other words, the electrical resistance value of conventional conductive materials at room temperature is 5 to 5, even if the value is low.
On the other hand, the electrical resistance value of the heat-sensitive resistive conductive composition of the present invention at room temperature was about 6Ω・cm.
It has an extremely low resistance of less than 2Ω・cm, and exhibits extremely advantageous properties as a heat-sensitive resistance material.

Therefore, the present invention can be effectively utilized in the production of heat-sensitive resistive conductive materials used in heat-sensitive resistance elements, self-temperature control heating elements, and the like.

Next, examples of the present invention will be shown.

Example 1 100 parts by weight of high-density polyethylene (manufactured by Idemitsu Petrochemical Co., Ltd.; Idemitsu Polyethylene 520B) as a crystalline resin and carbon black (manufactured by Mitsubishi Chemical Industries, Ltd.; Dia Black) with an average particle diameter of 43 mμ as a conductive filler. E) 75 parts by weight were placed separately in a shallow container and preheated at 110°C for 2 hours in a hot air dryer, and then fed to a Banbury mixer to produce 170 parts by weight.
The mixture was melt-kneaded at ℃ for 15 minutes. Next, 0.5 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 was added as a crosslinking agent, and the mixture was kneaded at 170°C for 5 minutes to crosslink and form a heat-sensitive resistive conductive composition. I got something. The gel fraction of this composition was 33% by weight.

Next, this composition is molded using a heat press machine at a temperature of
A sheet was formed by hot press molding at 190℃ and a molding pressure of 100Kg/cm ² G for 10 minutes. Copper foil with a thickness of 35μ was bonded to both the front and back sides of the sheet, and a square test piece with a side of 1.5cm was cut out. Ta.

The specific resistance of this test piece at 25°C was measured and found to be 1.96Ω·cm. Also, this test piece
The resistance increase factor (multiplying factor relative to the resistance value at 25°C) when the temperature was raised to 130°C was 10 ^4.5 .

Comparative Example 1 A composition was obtained in the same manner as in Example 1, except that the raw materials were not preheated, and further test pieces were prepared.

The gel fraction of this composition was 33% by weight. In addition, the specific resistance of the obtained test piece at 25℃ is
It was 2.4Ω·cm, and the resistance increase factor when the temperature was raised to 130°C was 10 ^4.5 .

Claims (1)

[Claims] 1. When producing a heat-sensitive conductive composition by crosslinking a kneaded material of a crystalline resin and a conductive filler until the gel fraction becomes 20 to 55% by weight of the crystalline resin, the crystalline 1. A method for producing a heat-sensitive conductive composition, which comprises preheating a conductive resin and a conductive filler at a temperature of 100° C. or higher and below the melting point of the crystalline resin, followed by kneading and crosslinking.