JPH0455447B2 - - 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 (patent application 1983).
−188356). As a result of further studies, the present inventors surprisingly found that by kneading the raw material polyethylene and the conductive filler at a higher temperature and for a shorter time than the usual method, the specific resistance at room temperature could be further improved. They have found that it is possible to lower the amount of heat and have completed the present invention based on this knowledge. That is, the present invention is characterized in that polyethylene and a conductive filler are kneaded for less than 10 minutes at a temperature 50°C or more higher than the melting point of the polyethylene, and then crosslinked so that the gel fraction is 20 to 55% of the polyethylene. The present invention provides a method for producing a heat-sensitive resistive conductive composition. The polyethylene used in the present invention may have different densities. These polyethylenes have the same temperature dependence during kneading and crosslinking as a composition containing a conductive filler such as carbon black. 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. Also, the average particle size of this conductive filler is 10mμ to 1μ, preferably 15mμ
~100 mμ. 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, for 100 parts by weight of polyethylene,
15 to 150 parts by weight of the above conductive filler, preferably
Add 40 to 120 parts by weight. 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. In the present invention, the above-mentioned polyethylene and conductive filler are kneaded at a temperature that is 50°C or more higher than the melting point of the polyethylene used, preferably at a temperature that is 50 to 150°C higher than the melting point. If the kneading temperature is outside the above range, the specific resistance at room temperature will increase, which is not preferable. Further, the kneading time is set to within 10 minutes, preferably within 5 minutes, after reaching the above-mentioned kneading temperature, that is, a temperature 50° C. or more higher than the melting point of the polyethylene used. If the kneading time after reaching this temperature exceeds 10 minutes, the specific resistance at room temperature will increase, which is not preferable. In addition,
This kneading may be carried out using a kneading machine such as a Banbury mixer or a mixing roll. 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. Examples of the organic peroxide include benzoyl peroxide, t-butylperoxybenzoate, dicumyl peroxide, t-butylcumyl peroxide, t-butyl peroxide, 2,5-dimethyl-2,5-di( Examples include t-butylperoxy)hexyne-3. The degree of crosslinking mentioned above is such that the gel fraction is 20 to 55% by weight, preferably 30 to 50% by weight based on the polyethylene used.
It should be adjusted within a range such that the percentage by weight. 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 decreases, which is undesirable. In this way, the degree of crosslinking of polyethylene can be adjusted within the above-mentioned range by adjusting the temperature and time during the crosslinking reaction. For example, when using organic peroxide as a crosslinking agent in high-density polyethylene, the amount of organic peroxide used is 0.05 to 0.30% by weight based on the high-density polyethylene.
By kneading the mixture at a temperature of 160 to 180°C for about 0.5 to 5 minutes, and heating it at around 190°C for about 5 to 15 minutes during molding, crosslinking will proceed to the desired range. In addition, when crosslinking using organic peroxide in this way, the temperature difference between the ignition point of the organic peroxide and the kneading temperature of the resin composition containing the conductive filler is small, so it is difficult to ignite the organic peroxide. Easy to invite. For this reason, the organic peroxide is added to the resin composition at room temperature in advance, and the organic peroxide is added to the resin composition at room temperature in advance. It is preferable to carry out this by supplying a mixture of oxide and a portion of polyethylene to a kneader.
In addition, inert gases such as nitrogen gas, argon gas, and carbon dioxide gas are introduced into the kneading machine to maintain the _O2 temperature.
It is preferable to write it as 10% or less. When using a crosslinking material such as organic peroxide,
It is preferable to use a mixture of a crosslinking agent and a portion of polyethylene in advance, and more preferably in the presence of an inert gas. In addition, when crosslinking is performed using ozone, after being exposed to a gas containing 0.5 to 20% by volume of ozone for 0.5 to 8 hours, a crosslinking agent such as divinylbenzene is added to 100 parts by weight of high density polyethylene, and 0.5 to 8 hours are added. Crosslinking progresses by adding 10 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 is as low as about 2 to 3 Ω·cm. Moreover, the heat-sensitive resistive conductive composition of the present invention has a large resistance increase ratio when the temperature is increased, and exhibits extremely advantageous characteristics as a heat-sensitive resistive material. Therefore, the present invention can be effectively utilized for manufacturing heat-sensitive resistive conductive materials used in heat-sensitive resistance elements, self-temperature-controlled heating elements, and the like. Next, examples of the present invention will be shown. Example 1 100 parts by weight of high-density polyethylene with a melting point of 132°C,
60 parts by weight of carbon black (manufactured by Mitsubishi Chemical Industries, Ltd.; Diamond Black E) having an average particle diameter of 43 mm was kneaded using a Banbury mixer at a kneading temperature of 185°C and a kneading time of 5 minutes after reaching this kneading temperature. The kneading chamber of the Banbury mixer was then flushed with _N2
2,5-dimethyl-di(t-butylperoxy)hexyne-3 as a crosslinking agent after purging with gas.
0.5 parts by weight of was added and kneaded at 170° C. for 2 minutes to crosslink, thereby obtaining a heat-sensitive resistive conductive composition. The obtained composition is molded using a heat press machine at
Heat press molded at 190℃ and molding pressure 100Kg/ ^cm2G for 10 minutes to form a sheet, and one piece was heated to 125℃.
After immersing the polymer in paraxylene at a temperature of 8 hours, the carbon black was removed from the remaining gel content, and the gel fraction was calculated by the gravimetric method, and the gel fraction was 33% by weight. Furthermore, a wall thickness of 35 μm was added on both the front and back sides of the obtained sheet.
A square test piece of 1.5 cm on a side was cut out from the copper foil, and the resistivity at 25°C and 130
The resistance increase ratio (multiplier relative to the resistance value at 25°C) when the temperature was raised to ℃ was measured. The results are shown in Table 1. Example 2 A composition was obtained and measured in the same manner as in Example 1, except that the kneading time in the Banbury mixer was changed to 10 minutes. Results first
Shown in the table. Comparative Examples 1 to 3 Compositions were obtained and measured in the same manner as in Example 1, except that the kneading temperature and kneading time in the Banbury mixer were set to the predetermined values shown in Table 1. Ta. The results are shown in Table 1. 【table】

Claims (1)

[Claims] 1. Kneading polyethylene and a conductive filler at a temperature 50°C or more higher than the melting point of the polyethylene for less than 10 minutes, and then crosslinking so that the gel fraction is 20 to 50% of the polyethylene. A method for producing a heat-sensitive resistive conductive composition. 2. The method according to claim 1, wherein the crosslinking is carried out using a mixture of a crosslinking agent and a portion of polyethylene in advance. 3. The method according to claim 1, wherein the crosslinking is carried out in the presence of an inert gas.