JPH03209702A - Ptc composition - Google Patents

Abstract

PURPOSE:To obtain a composition having the excellent PTC by dispersing conductive particles having a specified temperature coefficient of resistivity(TCR) into crystalline polymer. CONSTITUTION:The PTC characteristics as a protecting element for an electric circuit is Rpeak/R25>25 where Rpeak is the maximum resistivity of the element and R25 is the resistivity of the element at 25 deg.C. The element wherein conductive particles whose TCR is -650ppm/ deg.C are dispersed in crystalline polymer satisfies these conditions, and the element is excellent as a protecting element for an electric circuit. It is preferable that the conductive particles are of at least one kind of carbon black or porous black. Furthermore, when at least one kind of the carbon black and the porous black is made to graft with the crystalline polymer, it is effective to make the dispersion of the conductive particles uniform. It is also preferable that the crystalline polymer which is made to graft with the crystalline polymer wherein the conductive particles are dispersed or with at least one king of the carbon black and the porous black as the conductive particles is bridged.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a PTC used as an electric circuit protection element.
(Positive Temperature Coefficient of Resistance;
ture Coefficient) composition.

(Prior art) As a conventional electric circuit protection element,
As described in Publication No. 22, the above value is calculated from four elements: particle size of carbon black as conductive particles D1 specific surface area of carbon black S1 volume of filler, volume of polymer. An electric circuit protection device is known that aims to improve PTC characteristics by reducing this value to 1 or less.

(Problems to be Solved by the Invention) The physical property values described in the above-mentioned Japanese Patent Publication No. 3322/1983 are based on the physical property values of carbon black as a filler for conventional rubber, and the physical property values of this carbon black are P.T.
There is no direct relationship with C characteristics. Therefore, there is a problem in that the PTC characteristics of carbon black as conductive particles cannot be determined only from the physical property values of carbon black for rubber.

To explain this point in more detail, carbon is generally an intrinsic semiconductor, and the same number of electrons and holes are generated due to thermal excitation, which become carriers and exhibit conductivity. Therefore, carbon inherently has a large negative temperature coefficient of resistance.
of Resistwit7. It is well known that it is a substance that has a TCR (hereinafter abbreviated as TCR). In order to obtain a positive TCR by using such a substance as a conductive material, the most important issue is to develop a technology to reverse the polarity of the TCR. Although carbon inherently has a large negative TCR, it is empirically known that when carbon black is incorporated into a resistance generation mechanism as a fine particle aggregate, it exhibits a wide range of TCR. The mechanism has not yet been fully elucidated academically.

Here, P as a fine particle aggregate of carbon black
Considering that the TC properties depend on temperature changes in electrical resistance concentrated in the contact areas between particles, the TCR properties using a resin dispersion system of carbon black should become extremely important physical properties.

The purpose of the present invention is to simply measure the TCR, which is one of the physical properties of carbon black, porous black, etc. as conductive particles, and when dispersing it in a crystalline polymer to form an element, the PTC characteristics can be determined. It is possible to determine whether or not the composition is suitable as an electric circuit protection element, and provides a composition with excellent PTC characteristics.

[Structure of the invention]

(Means for Solving the Problems) The PTC composition according to claim 1 of the present invention is one in which conductive particles having a temperature coefficient of resistance (TCR) of -650 ppm/°C or more are dispersed in a crystalline polymer. It is.

The PTC composition according to claim 2 of the present invention is the PTC composition according to claim 1, in which the conductive particles are at least one of carbon black and porous black.

The PTC composition according to claim 3 of the present invention is the PTC composition according to claim 2, in which a crystalline polymer is grafted onto the surface of the conductive particles.

In the PTC composition according to claim 4 of the present invention, according to claim 2 or 3, the crystalline polymer is a polyolefin, a polymer in which a functional group is introduced into a polyolefin, or a copolymer of an olefin and a monomer having a polar group. It is at least one type of merging.

The PTC composition according to claim 5 of the present invention is the PTC composition according to claim 2 or 3, wherein the crystalline polymer is a fluoropolymer.

The PTC composition according to claim 6 of the present invention is one in which an inorganic filler is dispersed in a crystalline polymer according to any one of claims 1 to 5.

The PTC composition according to claim 7 of the present invention includes conductive particles having a temperature coefficient of resistance (TCR) of -650 ppn+/°C or higher dispersed in a crystalline polymer, and organic peroxide particles dispersed in the crystalline polymer. A crystalline polymer is crosslinked by either decomposition of a substance, irradiation with radiation, or a combination of decomposition of an organic peroxide and irradiation with radiation.

The PTC composition according to claim 8 of the present invention is the PTC composition according to claim 7, wherein the conductive particles are at least one of carbon black and porous black.

The PTC composition according to claim 9 of the present invention is the PTC composition according to claim 8, in which a crystalline polymer is grafted onto the surface of the conductive particles.

The PTC composition according to claim 10 of the present invention is characterized in that the PTC composition according to claim 8
Or in 9, the crystalline polymer is a polyolefin, a polymer obtained by introducing a functional group into a polyolefin, a copolymer of an olefin and a monomer having a polar group, or a mixture (two or more types) thereof.

The PTC composition according to claim 11 of the present invention is characterized in that the PTC composition according to claim 8
or 9, wherein the crystalline polymer is a fluoropolymer.

The PTC composition according to claim 12 of the present invention is the PTC composition according to any one of claims 5 to 11, in which an inorganic filler is dispersed in a crystalline polymer.

(Function) The PTC composition according to claim 1 of the present invention has a TCR of -650 ppm of conductive particles dispersed in a crystalline polymer.
/°C or more, when an electrical circuit protection element is formed by dispersing the conductive particles in a crystalline polymer, Rpeak/R25>25 RpeakH as shown in Japanese Patent Application No. 63-300222. Maximum resistivity R25 of the element: This is the value of the resistivity of the element at 25°C.

That is, if the PTC characteristic is explained using the resistance-temperature characteristic diagram in Figure 1 and the voltage-current characteristic diagram in Figure 2, the PTC characteristic value is as follows: PTC characteristic value = n = log (Rpeak/
Ro). The resistance value at aSb in Figures 1 and 2 is a Ro = V p / I pb R
Since l, ,,, = V t / I T and Vp x Ip = V + x Ir, n = 21og (V'/Vp).
If the voltage drop of the TC element, ①, is the circuit voltage, generally Vp must be 20% or less of Vr.

Therefore, n=21og (Vr/Vp) =21og (1/[1,2) =log25 = 1.39 Therefore, the PTC characteristic value only needs to be one digit or more.

Og Rpeak/Ro > 10g25R, and Rpeak/Ro > 25. And if it is R25Ro, then R---h/
R2, > 25.

Further, by grafting at least one of carbon black and porous black as conductive particles to a crystalline polymer, the conductive particles are uniformly dispersed.

In the PTC composition according to claim 7 of the present invention, a three-dimensional network structure is imparted to the crystalline polymer by crosslinking the crystalline polymer in which conductive particles are dispersed.

Furthermore, by grafting a crystalline polymer onto at least one of carbon black and porous black as conductive particles and crosslinking the crystalline polymer, the conductive particles are incorporated into the three-dimensional network structure of the crystalline polymer, resulting in current-limiting operation. Even if it is repeatedly expressed, the order of the conductive particles can be restored.

(Example) Carbon black as conductive particles used in carrying out the present invention is furnace black, acetylene black, Ketschen black, etc. Porous black is made by making carbon black porous by vapor phase etching method. , the specific surface area of raw carbon black is 1
．． A product that is 5 times or more higher is used.

Examples of crystalline polymers include polyethylene, polypropylene, copolymers of ethylene and propylene, copolymers of ethylene and vinyl acetate, acrylic acid, ethyl acrylate, methyl acrylate, polyvinylidene fluoride, polytetrafluoroethylene, etc. used.

Furthermore, an inorganic filler may be added to the crystalline polymer in addition to the conductive particles. As the inorganic filler, alumina, aluminum hydroxide, zinc white, calcium carbonate, magnesium carbonate, magnesium hydroxide, magnesium oxide, aluminum silicate, magnesium silicate, calcium silicate, etc. are used.

(2) Measurement of TCR of conductive particles (carbon black) Each carbon black shown in Table 1 was dehydrated and dried by heating at 200° C. for 30 minutes. Weighed 2 g of this dry sample, and weighed phenol resin (Nicanol PR15 manufactured by Mitsubishi Gas Chemical Industry ■).
40) Add 8 g (containing about 32% solvent) and knead well on a glass plate using a metal spatula. After sufficiently uniformly kneading, a screen-printable paste is prepared using ethylene glycol monobutyl ether as a solvent. At this time, the total of carbon black and resin solid components is 5Q
Adjust from wj% to 70W1%.

Transfer the sample paste to a glass fiber epoxy resin laminated board (
Using a 250-mesh stainless steel screen screen-printed on the surface (thickness: 16 μm), a putter-shaped resistance element having a width of 2 LI 1 m, a length of 3 cm, and a thickness of 20 to 25 ffm is formed. After heating and curing this resistance element at 180°C for 90 minutes, lead wires are connected to the electrodes by soldering, and the electrical resistance is measured while gradually increasing the temperature from 25°C in a furnace to create a TCR curve. . From that TCR curve 2
Determine the TCR between 5°C and 75°C.

R7,: Resistance value of the element at 75°C (Ω) R2,: Resistance value of the element at 25°C (Ω) (See next page) Table 1 *Asahi #60H was vapor phase etched at 950°C in a steam atmosphere The one that has been given.

■ Creation of electrical protection elements Each carbon black and porous black 2 shown in Table 1
A mixture of 100 g of high density polyethylene) 1i-xex1300J (manufactured by Mitsui Petrochemical Industries, Ltd.) and 0.2 g of organic peroxide (dicumyl peroxide) as a grafting agent was heated at 135°C at 60°C using a mixing roll. A primary PTC composition in which polyethylene was grafted onto carbon black and porous black was obtained by dispersing the mixture by heating and mixing for several minutes. This PTC composition is pulverized and laminated by compression molding between electrodes 1.1 (manufactured by Fukuda Metal Foil and Powder Kogyo, thickness 25I) made of electrolytic nickel foil as shown in Figure 3 to form a molded product. I got it.

Next, this molded product was crosslinked by irradiating with γ rays at 30 M+ad to obtain an element 2 made of a PTC composition of 10 W x 5 mm x 1 mm. The resistance value of the obtained element 2 was measured while heating it in a constant temperature bath, and the ratio of the resistance value at the peak to the resistance value of the element 2 at 25° C. was calculated. The results are shown in Table 1.

The PTC characteristics as an electric circuit protection element are R, esk/
It is sufficient if R2q>25. From Table 1, elements using carbon black with a TCR of -650 ppm/℃ or higher are R, eak/R2
5>25, indicating that it is excellent as an electric circuit protection element.

In the above examples, a PTC composition in which polyethylene was grafted onto carbon black was used as an electric circuit protection element, but similar results were obtained with an element using a PTC composition without grafting.

In addition, crosslinking is not caused by radiation irradiation, but a crosslinking agent such as an organic peroxide is added at the time of crosslinking, and crosslinking is performed so that the crosslinking agent remains even after crosslinking, and the same result is obtained when crosslinking is performed at a high temperature after molding. Obtained.

Furthermore, an inorganic filler may be added at the time of crosstalk. Table 2 shows the blending ratio when adding an inorganic filler.

(See next page) Table 2 [Effects of the Invention] According to the present invention, the temperature coefficient of resistance of the conductive particles is -650.
Just by knowing whether it is ppm/'C or more, it is possible to know whether the PTC properties when the conductive particles are dispersed in the crystalline polymer are excellent.

Furthermore, even if the conductive particles are a mixture of carbon black, porous black, or other materials whose physical properties are unknown or meaningless, by measuring the temperature coefficient of resistance, it is easy to find out whether a material with excellent PTC characteristics can be obtained. .

[Brief explanation of drawings]

Figure 1 is a typical resistance-temperature characteristic diagram of an electric circuit protection element using a PTC composition, Figure 2 is a typical voltage-current characteristic diagram of an electric circuit protection element using a PTC composition, and Figure 3 is a typical resistance-temperature characteristic diagram of an electric circuit protection element using a PTC composition. 1 is a perspective view of an electric circuit protection element using the PTC composition of the present invention. 1 Electrode, electric circuit protection element. January 1, 1990 ■ Inventor Noriku Kubota Naoki Yamazaki

Claims (1)

Claims: (1) A PTC composition comprising conductive particles having a temperature coefficient of resistance (TCR) of -650 ppm/°C or more dispersed in a crystalline polymer. (2) The PTC composition according to claim 1, wherein the conductive particles are at least one of carbon black and porous black. (3) The PTC composition according to claim 2, characterized in that a crystalline polymer is grafted onto the surface of the conductive particles. (4) Crystalline polymer is (1) polyolefin (2) polymer with functional groups introduced into polyolefin (3)
4. The PTC composition according to claim 2, which is at least one copolymer of an olefin and a monomer having a polar group. (5) The PTC composition according to claim 2 or 3, wherein the crystalline polymer is a fluoropolymer. (6) The PTC composition according to any one of claims 1 to 5, characterized in that an inorganic filler is dispersed in the crystalline polymer. (7) Conductive particles with a temperature coefficient of resistance (TCR) of -650 ppm/°C or higher are dispersed in a crystalline polymer, (1) decomposition of organic peroxide dispersed in the crystalline polymer, (2) radiation Irradiation (3) A PTC composition characterized in that a crystalline polymer is crosslinked by a combination of decomposition of an organic peroxide and irradiation with radiation. (8) The PTC composition according to claim 7, wherein the conductive particles are at least one of carbon black and porous black. (9) The PTC composition according to claim 8, characterized in that a crystalline polymer is grafted onto the surface of the conductive particles. (10) Crystalline polymer is (1) polyolefin (2) polymer with functional groups introduced into polyolefin (3)
The PTC composition according to claim 8 or 9, which is at least one copolymer of an olefin and a monomer having a polar group. (11) The PTC composition according to claim 8 or 9, wherein the crystalline polymer is a fluoropolymer. (12) The PTC composition according to any one of claims 7 to 11, characterized in that an inorganic filler is dispersed in the crystalline polymer.