CA1142342A

CA1142342A - Low resistivity ptc compositions

Info

Publication number: CA1142342A
Application number: CA000340996A
Authority: CA
Inventors: Peter Van Konynenburg; Andrew Au; Chris Rauwendaal; Alan J. Gotcher
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1978-12-01
Filing date: 1979-11-30
Publication date: 1983-03-08
Also published as: FR2443123A1; JPS643322B2; FR2443123B1; GB2036754A; US4237441A; JPS5578406A; DE2948350C2; GB2036754B; DE2948350A1; HK82289A

Abstract

ABSTRACT

The invention relates to conductive polymer composition which exhibit PTC behavior. The compositions of less than 7 ohm. cm, and which comprise a crystalline polymer and a particulate filler component which comprises carbon black having a particles size, D, which is from 20 to 150 millimicrons and a surface area S in m2/gram such that S/D is not more than 10. The composition preferably has a peak resistivity of at least 1000 ohm. cm and is electrically stable when aged at elevated temperature. The quantity

Description

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This invention relates to PTC conductive polymer compositions.

It is known that crystalline polymers can be made electrically conductive by dispersing therein suitable amounts of finely divided conductive fillers. Some conductive polymers exhibit what is known as PTC (positive temperature coefficient) behavior. The term "PTC" has been used in various different ways in the past, but in this specification, the terms "composition exhibiting PTC
behavior" and "PTC composition" are used to denote a composition which has an R14 value of at least 2.5 and an Rloo value of at least 10, and preferably has an R30 value of at least 6, where Rl~ is the ratio of the resistivities at the end and the beginning of a 14~C range, R1oo is the ratio of the resistivities at the end and the beginning of a 100C
range, and R30 is the ratio of the resistivities at the end and the beginning of a 30~C range. The term "PTC element"
is used herein to denote an element composed of a PTC
composition as defined above. A plot of the log of the resistance of a PTC element (i.e. an element composed of a PTC composition) against temperature, will often show a sharp change in slope over a part of the temperature range in which the composition has an Rloo value of at least 10. The term "switching temperature'l (usually abreviated to Ts) is used ~, Z

herein to denote tha temperature at the lntersection point of extensions of the substantially straight portions o~ such a plot which lie either side of the portion showing the sharp change in slope. The term "peak resistivity" is used herein to denote the maximum resistivity which the composition exhibits above T , and the term "peak temperature" is used to denote the temperature at which the composition has its peak reslstivity.
Recent research relating to conductive polymers is described in, Eor example, United Sta-tes Patent No. 3,858,144, German Offenlegungschriften Nos.
P2,543,314.1, P2,755,077.2, P2,755,076.1, P2,821,799.4 and P2,903,442.2 and the applicati~ns correspondin~ to Canadian Patent Applications Nos. 341,384 and 341,385, filed Dece~ber 6th, 1979.
PaYticularly useful known PTC compositions comprise a thermoplastic crystalline polymer with carbon black dispersed thexein. The polymers which have been used include polyolefins, e.g. polyethylene, and copolymers of olefins and polar comonomers. Generally the composition is cross-linked, preferably by irradiation at room temperature, to imprQve its stability at temperatures above Ts. Compositions for use in self-regulating heaters must have a relatively high f~

resistivity at room temperature, usually at least 103 ohm.
cm. It has been recognised that there are important potential uses for PTC conductive polymer compositions having much lower resistivities. However, the preparation of such compositions has presented very serious problems. For example, it has been found that as the con~ent of conductive filler in a PTC conductive polymer composition has been increased, in order to reduce the resistivity of the composition, there has been a sharp reduction in the intensity of the PTC effect [see for example M. Narkis et al, Poly Eng and Sci, 18, 649 (1978)]. In addition, it has been Eound that when PTC conductive polymer compositions are exposed to elevated temperatures, their resistivity increases sharply [see for example J. Meyer, Poly Eng and Sci., 14, 706 (1974)].

We have discovered that in order to produce a composition which exhibits PTC behavior with a switching temperature (Ts) above 0C, which has a resistivity below 7 ohm. cm and which comprises carbon black which has been dispersed in a crystalline polymer component, it is essential that the polymer component should have at least 10%
crystallinity and that the carbon black should have a particle size, D, which is from 20 to 150 millimicrons and a surface area, S, in m2/gram such that S/D is not more than f~ Z3~2 10. [Crystallinities given herein are measured by X-ray crystallography. The values of surface area, S, given herein are measured by the well-known ni.trogen adsorption method, and for details of the measurement of D and S, reference should be made to "Analysis of Carbon Black" by Schubertr Ford and Lyon, Vol. 8, Encyclopaedia of Industrial Chemical Analysis (1969), 179, published by John Wiley and Son, New York. ]

We have also discovered that the ratio by volume of the filler (i.e. the carbon black and any other particulate filler in the composition) to the polymer has an important influence on the electrical characteristics of the composition, and that this ratio should preferably be correlated with the S/D ratio referred to above so that the quantity (reerred to herein as the S/D Volume Ratio) S volume of filler component ~r X ~
VOlUme o~ polymer component is less than 1, preferably less than 0.5, particularly less than 0.4, especially less than 0.3.

We have further discovered that the power consumed in dispersing the carbon black in the polymer and in shaping the composition has an important i.nfluence on the electrical characteristics of the composition, and in particular that the power consumed in these steps is preferably 9.5 to 2900 23~2 kg. m.cc 1 (1 to 300 hp. hr. ft 3), more preferably 9.5 to 970 kg.m.cc 1, particularly 9~5 to 485 kg.m.cc 1, especially 9.5 to 240 kg.m.cc 1. If the power consumption is too great, the composition tends to have too high a resistivity at temperatures below T and/or to have unsatisfactory electrical stability on aging at elevated temperatures; on the other hand, if the power consumption is too low, this can result in a composition which exhibits unsatisfactory PTC
behavior.

The polymer component used in the present invention may be a single polymer or a mixture of two or more different polymers, and its crystallinity is preferably more than 20%, especially more than 40%. Suitable polymers include polyolefins, especially polymers of one or morec~-olefins, e.g. polyethylene, polypropylene and ethylene/propylene copolymers; copolymers of one or more ~-olefins, e.g.
ethylene, with one or more polar copolymers, e.g. vinyl acetate, acrylic acid/ ethyl acrylate and methyl acrylate;
polyarylenes, e.g. poly arylene ether ketones and sulfones and polyphenylene sulfide; polyesters, including polylactones, e.g. polybutylene terephthalate, polyethylene terephthalate and polycaprolactone; polyamides;
polycarbonates; and fluorocarbon polymers, i.e. polymers which contain at least 10~, preferably at least 20~ by weight oE fluorine, e.gO polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene/propylene copolymers, and copolymers of ethylene and a fluorine-containing comonomer, e.g. tetrafluoroethylene, and optionally a third comono~er. We have obtained excellent results with a mixture of polyethylene, preferably high density polyethylene, and a copolymer of ethylene and a polar copolymer, preferably acrylic acid. A particularly preferred polymer component comprises 25 to 75% by weight of high density polyethylene and 2 to 75% by weight of an ethylene/acrylic acid copolymer, in which the percent by weight of acrylic acid is preferably 4 to 10%.

If a polymer having relatively low crystallinity is used, then the use of a carbon black having a relatively large particle size and a relatively low value of S/D is preferred in order to obtain an intense PTC effect. However, for many polymers, carbon blacks having a particle size of 20 to 75 millimicrons give satisfactory results. A particle size greater than 30 millimicrons is preferred/ and for polymers having less than 40% crystallinity, a particle size greater than 60 millimicrons is preferred. As the particle size of the carbon black gets larger, it becomes more difficult to obtain a composition having low resistivity combined with satisfactory PTC behavior, and it is therefore preferred to use a carbon black having a particle size less than about 100 millimicrons.

.:

The amount of carbon black in the composition should be such that the composition has a resistivity less than 7 ohm. cm, preferably less than 5 ohm. cm, especially less than 2 ohm. cm, particularly less than 1 ohm. cm, at a temperature between -40C and Ts, and preferably at 20C.
The amount needed to achieve such resistivity, in combination with the desired PTC behavior, will depend on the polymer component, the carbon black and any other particulate flller present, and the method used to prepare and shape the composition. The ratio by volume of the carbon black to the polymer component is generally at least O.lS and preferably at least 0.25, and can be substantially greater, e.g. at least 0.~0 or 0.50.

The composition may contain other particulate fillers in addition to the carbon black, for example non-conductive inorganic or organic fillers, e.g. zinc oxide, antimony trioxide or clay. The term "filler componentl' is used herein to denote all the particulate fillers in the composition. The composition preferably comprises an antioxidant or other additive which ~ill stabilise the composition against degradation, e.g. thermo-oxidative degradation, the amount of such additive generally being 0.005 to 10%, preferably 0.5 to 4~! by weight, based on the weight of the polymer. Preferably the additive is an organic ~23~;~

antioxidant, for example a hindered phenol such as those disclosed in U.S. Patent No. 3,986,981 (Lyons) and those manufactured by Ciba Geigy under the trade mark Irganox. The choice of antioxidant wil] of course be dependent on the polymer, and it is important to note also that some materials which are generally useful as antioxidants ~or polymers can ca~se the electrical properties oE the composition to become less stable on exposure to elevated temperatures.

When the composition is to be cross-linked it may also contain a compound which can be decomposed by heat to initiate cross-linking, or a compound which promotes cross-linking when the composition is irradiated.

It is preferred that the compositions of the invention should have a peak resistivity of at least 1,000 ohm. cm, more preferably at least 5,000 ohm. cm, particularly at least 10,000 ohm. cm, especially at least 50,000 ohm. cm.

It is also preferred that the composition, a~ter having been subjected to a thermal aging treatment which consists of maintaining the composition, by ; external heating thereof, for 25 hours at a temperature at which the resistivity of the composition is between 100 ohm. cm and the peak resistivity, !~

ta) exhibit5 PTC behavior, and (b) has a resistivity at at least one temperature between Ts and -40C, and preferably at all temperatures between Ts and -40C, which is between 0.5 times and 2 times the resistivity of the composition at the same temperature before said thermal aying.
Preferably the composition has these properties after thermal aging as defined for 40 hours, and especially after thermal aging as defined for 50 hours. It is also preferred that the composition, after such thermal aging, has a peak resistivity of at least 1,000 ohm. cm, more preferably at least 5,000 ohm. cm, particularly at least 10,000 ohm. cm, especially at least 50,000 ohm. cm.

~he thermal aging treatment referred to above is a passive treatment, and some compositions which show satisfactory resistance stability, when subjected to such aging, deteriorate relatively quickly when aged under active conditions, i.e~ at elevated temperature caused by I R
heating~ It is, therefore, preferred that that the composition, after having been subjected to a voltage aging treatment which consists of passing current through the composition for 25 hours so that I2R heating thereof maintains the composition at a temperature between Ts and (Ts+ 50)C

;' :

(a) exhibits PTC behavior; and (b) has a resistivity at at least one temperature between Ts and -40~C, and preferahly at all temperatures between Ts and -40C, which is between 0.5 times and 2 times the resistivity o~ the composition at the same temperature before said voltage aging.
Preferably the composition has these properties after voltage aging as defined for 40 hours, and especially after voltage aging as defined for 50 hours. It is also preferred that the composition, after such voltage aging, has a peak resistivity o at least 1,000 ohm cm, more preferably at least 5,000 ohm. cm, particularly at least 10,000 ohm. cm, especiaLly at least 50,000 ohm. cm.

Any method can be used to disperse the filler component in the polymer component and to shape the resulting dispersion. The methods which are currently of most practical interest comprise subjecting a mixture of the solid polymer and the ~iller component to mechanical shear working (and optionally also to external heating) which causes the polymer to melt and disperses the filler in the molten polymer. The dispersion can be carried out in, for example, a Banbury mixer, a roll mill or a single screw or twin screw extruder. The dispersion may be extruded directly into the final shaped form desired or may be removed from the mixer in any convenient way, chopped into small pieces, and subsequently melt shaped, e.g. by extrusion, molding or sintering. The total power consumption in the dispersing and shaping steps is preferably within the limits set out above.
The carbon black should be dispersed sufficiently to give a composition which has substantially uniform electrical properties, and up to a certain point an increase in the power consumed often results in a composition which shows a more intense PTC effect~ On the other hand~ if the power consumed is too great, this can cause the composition to be electrically unstable when aged at elevated temperatures and/or can cause the composition to have too high a resistivity at temperatures below Ts.

lS The invention includes electrical devices, particularly circuit control devices, which comprise a PTC
element obtained by shaping a composition of the invention.

The invention is illustrated by the following Examples~ which are summarised in Tables I, II, III and IV
below. Table I shows the ingredients and methods used in preparing the various samples. In Table I, the polymers are identified by type, trade name, crystalline melting point ~TM) and percent crystallinity (cryst ~) and the amount thereof in weight percent of the composition. The 3~2 abbreviations used in the TYPE column are further identified below:

HDPE high density polyethylene LnpE how density polyethylene MDPE medium density polyethylene EAA copolymer oE ethylene and acrylic acid PP polypropylene PVF2 polyvinylidene fluoride PB poly-1-butene FEP fluorinated ethylene/propylene copolymer In examples 16~ 51-61, 72, 73 and 78, the polymer component comprised, in addition to the polymer spec-ified in Table 1, the following additional polymer component.

15 Example No. ~y~ Name T~C Cryst~ Amt. Wt%
16 EAA EAA 449 106 10-30 30.0 51 PP PROFAX8523 16530-60 36.9 53 and 54 EAASURLYN 1652 102 10-30 28.23 55 and 56 EAAEAA 455 106 10 30 30.0 57 PP PROFAX8623 16530-60 31~4 58 and 59 PBNITRON 100 124 30-55 30.4 60 and 61 FEPFEP 100 275 40 30.6 72 and 73 RULBER VITO~ A-HV - - 6.0 78 EAA EAA 449 106 10-30 30,.0 The word "PLUS" has been put in the Type Column by each of these Examples to indicate the above-identified additional ingredient.
*

Trademarks.

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Table I also identifies the carbon blacks used by trade name, particle size in millimicrons (D), surface area in m /gram (S) and the amount thereof in weight percent of the composition; the ratio S/D is also given for each black.
The ratio by volume of carbon black to polymer (RATIO
CB/POLY) is also given in Table I~

Table I also shows any materials present in the composition in addition to the polymer(s) and carbon black.
These additives are identified by type and name and the amount thereof in weight percent o the composition. The abbreviations used in the TYPE column are further identified below:

AO antioxidant, the antioxidant used being, except where otherwise noted in the NAME column, an oligomer of 4,4l-thiobis (3-methyl-6-t-butyl phenol) with an average degree of polymerisation of 3-4, as described in U.S.
Patent No. 3,986,981 CXA cross-linking agent Acid acid scavenger XLA cross-linking agent FR ire retardant The abbreviations used in the NAME column are further identified below.

130XL Peroxide cross-linking agent (Luperco* 130XL) ARD Agerite* Resin Ca CO3 calcium carbonate Irganox tetrakis [methylene (3,5-di-tert.butyl 4-1010 hydroxy-hydrocinnamate)] methane TAIC triallyl isocyanurate Santovar*A 2t5-di-tert.amyl hydroquinone Dechlorane decachlorobiphenyl Sb23 antimony trioxide Table I also identifies the particular fabrication technique used to mix and shape the ingredients to-gether (FAB TECH)/ the process temperature in C (PROCTEMP~, the process time in minutes (PROC TIME) and the total amount of energy in kg. m.cc 1 used in the fabrication ~SHEAR HISTORY). The abbreviations used in the FAB TECH column are further identified below.
.
0 BAN Suitable amounts of the specified ingredients (e.g.
in Examples IA and IB, 1504.8 g of the high density polyethylene, 1208.4 g of the carbon black and 22.8 g of the antioxidant) were mixed at flux temperature for 5 minutes in a steam-heated Banbury mixer having *

Trademark 3~2 a water-cooled rotor. The mixture was dumped from the mixer, cooled and chopped into small pieces. Part of the chopped mixture was compression molded at 180C and a pressure of 70 kg/cm2 for 5 minutes into a slab about 0.1 cm. thick. Rectangular samples 2.5 x 3.75 cm. were cut from the slab. In those Examples in which the sample was irradiated, as indicated in Table I and further discussed below, the sample was irradiated to the specified dosage to cross-link the composi-tion.
Silver electrodes were provided on the samples by painting 0.6 x 2.5 cm. strips of a silver-epoxy com-position (Electrodag* 504) on each end of the sample.
The samples were thermally conditioned by maintaining them at 160C or 15 minutes by external heating and then cooling to room -temperature at a rate of 1C/minute.

MIL~ Suitable amounts of the specififed ingredients were mixed at flux temperature in a 7.6 cm. electrically heated roll mill. The mixture was sheeted from the mill, cooled and chopped into small pieces. Part of the chopped mixture was compression molded at a suitable temperature and 70 kg/cm2 pressure for 3 minutes into a slab about 0.06 cm. thick.
Rectangular samples 2.5 x 3.75 cm. were cut from *
Trademark Z3~2 the slab. ~fter irradiation where specified, silver electrodes were provided on the samples as described in BAN. The samples were then thermally conditioned by maintaining them at a temperature of (TM + 30)C for 15 minutes by external heating and then cooling to room temperature at a rate of 1C/minute.

BRA Suitable amounts of the specified ingredients were mixed in a counter-rotating twin screw mixer ~a Brabender Plastograph) and the mixture dumped, cooled and chopped into small pieces. Samples were prepared from the chopped mixture as described in MILL above.

' ZSK Suitable amounts of the specified ingredients were ; mixed in a co~rotating twin screw extruder (a ZSK
extruder) and the mixture extruded as a strand.
The strand was cooled and chopped into small pieces. Samples were prepared from the chopped mixture as described in MILL above.

Table I also shows the radiation dosage in megar-ads ~RAD DOSE) for those samples which were cross-linked by irradiation. Where the radiation dose was 20 megarads, the sample was irradiated first on one side to a dose of 10 megarads and then on the other side to a dose of 10 megarads.
*

Trademark ~r . . ~

In Example 76 the samples were cross-linked by heating at 200C for 12 minutes.

~able II below shows the value of the quantity S volume of filler component D volume of polymer component and the resistivity/temperature characteristics of the various samples. The resistivities given in Table II
were calculated from resistance measurements taken on . the thermally conditioned samples as they were extern-: ally heated from room temperature at a rate of 1C/minute, and the various abbreviations in Table II
are further identified below @20 resistivity at 20C in ohm~ cm Q p peak resistivity in ohm. cm ~ T2X the temperature in C at which the : 15 resistivity is twice the resistivity at 20C
Ts the switching temperature in C
Tp the peak temperature in C

Table III below shows, for a number of the samples~
the effect on resistivity of thermal aging at elevated temperature. Table III shows, in the columns headed ORIGINAL
PERFORMANCE, the resistivity at 20 C (e20) of the samples which had been externally heated at a rate oE 1C/min to .. ,. ~

-.

z obtain the data in Table II and then cooled to 20C, and the peak resistivity of these samples when again externally heated at 1C/min t ep). The samples were then cooled to room temperature and reheated to the temperature T shown in Table III, and the resistivity at this temperature is given in the column headed eT. The samples were maintained at this temperature for 52 or 73 hours, with intervals after 2 hours, 9 hours and 27 hours, and for the samples aged for 73 hours after 46 hours, in which intervals the samples were cooled to 20C and their resistivity measured before being reheated to te~perature T. The resistivities of the samples at 20C after aging at temperature T for the indicated time are given in the columns headed , together with the percent change in resistivity at 20C, namely the value of e- e 20 x 100 e20 Table IV below shows, for a number of samples, the effect on resistivity of voltage aging at elevated temperature. These samples were prepared by taking a part of the chopped mixture of the indicated example and compression molding it at 180C and a pressure of 70 kg/cm2 for S minutes into a slab 0.2 cm. thick; a round disc, 1.9 cm. in diameter, was punched out of the slab; an electrode was formed on the face of each disk by molding into it a disc 1.9 cm. in 23~2 diameter cut from an expanded metal mesh composed of nic~el-plated copper; the sample was irradiated to 20 megarads; and 20 AWG leads were attached to the elec-trodes. The samples were thermally conditioned by maintaining them at (TM -~ 30)C for 15 minutes by external heating and then cooling to room temperature at a rate of 1C per minute. The leads of the device were then attached to a variable voltage AC power supply. The voltage of the supply was maintained at 120 volts except when the device was first connected or reconnected to the power supply, when the voltage was 30-35 volts for the first 30 seconds and was then increased to 120 volts over a period of 2 minutes. The samples were aged under these conditions for 30 to 50 hours, with intervals after 5, lO, 20 or 30 hours, in which intervals the samples were cooled to 20C and their resistivity measured before re-applying the voltage. The resistivities of the samples at 20C
after aging under these conditions for the indicated time are given in the columns headed ~ , together with the percent change in resistivity.

Similar voltage aging tests carried out on the compositions of Examples 54, 56, 63, 65, 85, 91 and 93 showed that the compositions of Examples 54, 56 and 65 were stable under voltage aging, their resistivity increasing less than twice after 30 hours of aging, whereas the comp-ositions of Examples 63 85, 91 and 93 were not stable, their resistivity increasing more than 10 times after 30 hours of aging.

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TABLE II

ELECTRICAL n ( ) ~20 ~P T2x Ts T~ p D polymer -1A 0.12 6.5x10 1 4.2x10125 139 144 1B 0.12 1.3x10>1.7x106120132 >145 2 1.32 3.6x105.1x102 105127 137

3 1.32 5.9x105.3x105 87124 137

4 0.15 8.0x10 1 2.4x103 113 130 142 0.15 9.0x10 1 2.2x105 97 130 138 6 1.08 5.8x10>2.0x106110130 >137 7 1.08 5.1x10>1.5x10~100125 >137 8 0.31 9.0x10 1 1.7x106 97 123 >150 9 0.31 1.1x102.1x103 123136 145 0.88 1.9x101.1x106 118131 >160 11 0.28 5.9x101.4x106 105125 >130 12 0.33 5.6x101.6x106 110131 >140 14 0.17 4.5x10 1 8.9x102 130 134 140 0.17 6.9x10 1 1.7x104 123 136 >160 16 0.33 2.9x109.5x105 8185 >175 17 0.43 2.2x101.3x103 126130 140 18 0.43 3.4x102.6x102 118126 >175 3~

TABLE II (Cont. ) Example ~Vol ~ P 20 ~ p 2x s T ~ pNo. S ~ filler D ~ po l yme r __ 23 0.17 4.4x10 >1.8x106115 132 >140 24 0 17 8.4x10 >1.5x10695 127 >135 .

0.17 7.1x10>1.4x106111 131>139 ; 26 0.17 9.4x10>1.6x10685 125>135 27 0.28 1.5x101.3x105115 131140 28 0.28 3.1x101.5x105IOB 129140 29 .27 1.1x108.5x104112 133145 .27 3.5x10>1.4x106100 127137 31 .15 4.6x10>1.8x10694 134>145 32 .15 1.4x101 >1.8x106 100126 >139 33 .17 2.4x10>1.9x106118 138>146 34 .17 7.9x10>1 ~ 9x106 112130 >138 .20 1.6x102.1x104120 l3~150 36 .20 4.0x101.9x105115 131>175 41 .18 5.1x10>1.6x106112 130>138 42 .18 3.8x10~1.5x106117 128>140 :
~:

TABLE II (Cont. ) )( ) ~20 ~P 2x sT ~p (D po l yme r 53 .24 1.9x105.8x103 75 87 121 54 .24 5.0xlO0 >1.7x106 78 99 >175 .22 2.2x103.4x103 65 85 115 56 .22 3.6x102.2x104 67 83>175 57 .28 4.3x10>1.4x106 104 129>140 58 .28 2.3x103.6x102 101 120140 59 .28 3.6x107.7x102 103 125>175 .10 1.3x10~ 2.2x104 117 138 145 61 .10 1.9x10>2.2x106 117 129>175 62 .23 1.7x101.7x104 100 114130 63 .23 2.6x~04.3x105 100 114>180 64 .29 2.4x101.7x104 59 85 108 3~2 ~A8L I I (Cont . ) Exanple ~1 T T ~_ ~. (SD)(~ f~20 ~C7p 2x s ,c,p .29 2.~x10 5.6x103 87 82 ' 180 6~ .22 1.5x1~ 3.1x104 126 132 144 67 ~.2~ 1.6x10 4~2x104 116 -" 131 11~9 68 ., 23 1 . 6xl 0 2 . Sxl 03 75 100 120 69 .23 2.1xlo 4.8xl04 75 93 ~ 18 .23 2.4x10 3.2x103 120 142 183 3 3.8x10 3.3x103 115 136 166 72 ~30 3.4xlO 9.3x103 llS 1~5 166 73 .30 2.~xlO1 1.8x106 105 138 :' 161 74 . 23 2, 6xl 0~ 4, Oxl 03 50 5 ,23 2.6x10 5,7~103 50 - 55 6~
7~ .33 7.1x10 1 .7xl~5 lQ5 128 ~ 16û
77 .33 ~. 6xl t . ~xl o6 1 ~5 1 27 > 1 ~5 73 .33 2.9xl ~5xlo5 81 85 ' 175 79 .33 5.8x1~ l.7xlo6 120 129 140 1.50 9.1x10 3.6x103 110 12g ~ 160 f~3~

TA8LE I I (Cont . ) ~x~le /Vol ( D)~pO~r) ~ 2û ~p T2x 5 .;~7P

81 l.S0 1 . 5xl O13 . 6x1 04 1 1 0 1 30 ~t 60 82 .33 1.1x10 ~1.8x106 108 125 ~135 83 .33 7.1xlQ >1.7x106 110 1~5 >137 84 .2S 8.6xlO-1 8.6x102 112 132 1~0 .. 25 1 .4x10 4.3x103 110 125 >16n 8~ 1.02 7.4xlO-~ 6.gxlol 1~0 130 ~40 8? 1.~2 g.4xlO 15.2x102 105 125 140 8a 1.92 l.9x10 l.9xlO1 125 12? 140 89 1.92 2.0~10 12.~x1~5 125 125 ~160 .
.14 6.0xlO-1 1.S~103 122 131 140 91 . 14 1 . 4xl 0~1 . 5xl o6 1 1 ~ 1 27 >1 ~
92 .17 4.5xlO 18.9x102 130 ~34 14~, 93 .17 6.9xlO-1 1.7x104 123 126 ~160 94 .49 3.0xlOl l.OxlOS 90 l~ 1 40 9S .49 4.4xlO 1 .6A10 80 116 ~135 3~

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A conductive polymer composition which exhibits PTC behavior with a switching temperature Ts above 0°C, which has a resistivity of less than 7 ohm. cm at at least one temperature between Ts and -40°C; and which comprises (1) a polymer component having at least 10%
crystallinity and (2) a particulate filler component which has been dispersed in said polymer component and which comprises carbon black having a particle size, D, which is from 20 to 150 millimicrons and a surface area, S, in m2/gram such that S/D is not more than 10.

2. A composition according to Claim 1 which has a peak resistivity of at least 1000 ohm. cm.

3. A composition according to Claim 1 in which the amount of said filler component is such that the quantity is less than 1.

4. A composition according to Claim 3 wherein said quantity is less than 0.5.

5. A composition according to Claim 1 which, after having been subjected to a thermal aging treatment which consists of maintaining the composition by external heating thereof, for 25 hours at a temperature at which the resistivity of the composition is between 100 ohm. cm and the peak resistivity, (a) exhibits PTC behavior, (b) has a resistivity at at least one temperature between Ts and -40°C
which is between 0.5 times and 2 times the resistivity at the same temperature before said thermal aging treatment, and (c) has a peak resistivity of at least 1000 ohm. cm.

6. A composition according to Claim 5 which, after said thermal aging treatment, has, at all temperatures between Ts and -40°C, a resistivity which is between 0.5 and 2 times the resistivity at the same temperature before said thermal aging treatment.

7. A composition according to Claim 5 which, after having been subjected to a voltage aging treatment which consists of passing current through the composition for 25 hours so that I2R heating thereof maintains the composition at a temperature between Ts and (Ts + 50)°C, (a) exhibits PTC
behavior, (b) has a resistivity at at least one temperature between Ts and -40°C which is between 0.5 times and 2 times the resistivity at the same temperature before said voltage aging treatment and (c) has a peak resistivity of at least 1000 ohm. cm.

8. A composition according to Claim 7 which, after said voltage aging treatment, has, at all temperatures between Ts and -40°C, a resistivity which is between 0.5 and 2 times the resistivity at the same temperature before said voltage aging treatment.

9. A composition according to Claim 2, 3 or 5 wherein said polymeric component has at least 40%
crystallinity and comprises at least one polymer selected from polyolefins, copolymers of at least one olefin and at least one polar comonomer, polyarylenes, polyesters, polyamides, polycarbonates and fluorine-containing polymers, said carbon black has a particle size of 20 to 75 millimicrons, and the ratio by volume of the carbon black to the polymer component is at least 0.25.

10. A composition according to Claim 2, 3 or 5 which has a resistivity of less than 2 ohm. cm at at least one temperature between Ts and -40°C.

11. An electrical device which comprises a PTC
element and at least two electrodes which can be connected to a source of electrical power and which, when so connected, cause current to flow through said PTC element, wherein said PTC element has been obtained by shaping a PTC conductive polymer composition as claimed in Claim 1.

12. An electrical device which comprises a PTC
element and at least two electrodes which can be connected to a source of electrical power and which, when so connected, cause current to flow through said PTC element, wherein said PTC element has been obtained by shaping a PTC conductive polymer composition as claimed in Claim 2, 3 or 5.

13. A process for the preparation of a shaped article of a conductive polymer composition as claimed in Claim 1 which comprises dispersing said filler component in said polymer component and shaping the resulting dispersion, the total energy used in preparing and shaping said dispersion being from 9.5 to 2900 kg.m.cc 1.

14. A process according to Claim 13 wherein the total energy used in preparing and shaping said dispersion is from 9.5 to 970 kg.m.cc

15. A process according to Claim 14 wherein the total energy used is from 9.5 to 485 kg.m.cc

16. A process according to Claim 15 wherein the total energy used is from 9.5 to 240 kg.m.cc 1.

17. A process according to Claim 13, 14 or 15 wherein the dispersion is melt-shaped.

18. A process for the preparation of a shaped article of a conductive polymer composition as claimed in Claim 2, 3 or 5 which comprises dispersing said filler component in said polymer component and melt-shaping the resulting dispersion, the total energy used in preparing and melt-shaping the dispersion being from 9.5 to 970 kg.m.cc 1.