CA1236246A

CA1236246A - Electrically conductive polyvinylidene fluoride compositions

Info

Publication number: CA1236246A
Application number: CA000410978A
Authority: CA
Inventors: Andrew Au; Peter Van Konynenburg
Original assignee: Raychem Corp
Current assignee: Raychem Corp
Priority date: 1981-09-09
Filing date: 1982-09-08
Publication date: 1988-05-03
Also published as: GB2106920A; GB2106920B; ATE35745T1; DE3278775D1; JPS5853939A; EP0074281A1; EP0074281B1; JPH0395248A; JPH0334498B2

Abstract

ABSTRACT
Conductive polymer compositions based on polyvinylidene fluoride have improved properties when the polyvinylidene fluoride has a very regular structure characterized by a low head-to-head content in the repeating units. The improved properties include improved electrical stability when contacted by organic fluids and/or when maintained at elevated temperatures in air. Such compositions are parti-cularly useful in the form of self-limiting heaters, e.g.
for heating diesel fuel.

Description

This invention relates to conductive polymer compositions and devices comprising them.
Conductive polymer compositions, and devices comprising them, are known or are described in cop ending patent applications. Reference may be made for example to U.S. Patents Nos. 2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,793,716, 3,823,217, 3,861,029, 4,017,715, 4,177,376, 4,188,276, 4,237,441, 4,238,812, 4,242,573, 4,246,468, 4,255,698, 4,272,471 and 4,276,466i U.S.
Patent No. 1,534,715; J. Applied Polymer Science 19, 813-815 (1975), Klason and Cubit; Polymer Engineering and Science 18, 649-653 (1978) Narkis et at;
and German OWLS Nos. 2,634,999, 2,755,077, 2,746,602, 2,755,076, 2,821,799,

2,949,173 and 3,030,799; European Published Patent Applications Nos. 0,026,571, 0,028,142, 0,030,479, 0,038,713, 0,038,714, 0,038,715, 0,038,716, 0,038,717 and 0,038,718; and U.S. Patent No. 4,334,351 granted Thea June 1982, U.S.
Patent No. 4,318,881 granted Thea March 1982, U.S. Patent No. 4,314,230 granted end February 1982, Canadian Application No. 250,491, Canadian Application No.
405,041, Canadian Application No. 405,114 and Canadian Application No. 405,113.
Electrical devices containing conductive polymers generally (though not invariably) comprise an outer jacket, usually of insulating material, to protect the conductive polymer from damage by the surrounding environment.
However, if no protective jacket is used, or if the jacket is permeable to harmful species in the environment, or if the /
Ye I

conditions of use are such that the jacket may become damaged, it is necessary or desirable to select a conductive polymer which is not damaged (or which deteriorates at an acceptably low rate) when ox-posed to the surrounding environment. Exposure of conductive polyp mews to organic fluids generally results in an increase in resist-viny; exposure to air, especially at elevated temperatures between room temperature and 35C below the melting point generally results in a decrease in resistivity both at the elevated temperature and at room temperature (a phenomenon known in the art as "resistance no-taxation").
We have discovered that conductive polymer compositions which are based on polyvinylidene fluoride exhibit substantially imp proved stability if the polyvinylidene fluoride has a very regular structure which can be characterized by a low head-to-head content in the repeating units. Polyvinylidene fluoride is made up of no-peeling units of formula -CHECKOFF-, which can be arranged head--to-tail (i.e. -CH2CF2-CH2CF2-) or head-to-head (i.e. -CH2CF2-CF2CH2-~, and we have found that the lower the head-to-head content, the greater the stability of the resistivity of the composition when exposed to organic fluids and/or when exposed to air at elevated temperature.
Previously known conductive polymer compositions based on polyvinyl-Irene fluoride have made use of polyvinylidene fluoride of relative-lye high head-to-head content, namely at least 5.2% and generally higher, which are easier to process -than the polymers used in -the present invention.
In its first aspect, the present invention provides a -pa- 27065-51 conductive polymer composition which comprises (a) polyvinylidene fluoride having a head-to-head content of less than 5.0%, preferably less than 4.5%, particularly less than 4.0%, and (b) a particulate conductive filler, especially carbon black, dispersed in the polyp vinylidene fluoride. The composition preferably exhibits PTC beta-visor. The terms "composition exhibiting PTC behavior" and "PTC
composition" are used to denote a composition which has an Rl4 value of at least 2.5 and an Loo value of at least 10, and preferably has an R30 value of at least 6, where Al is the ratio of the resistive-ties at the end and the beginning of a 14C. range, Loo is thrush 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 30C. range.

.,.~

I

In its second aspect, the invention provides an electrical device which comprises a conductive polymer element composed of a conductive polymer composition as defined above and at least one electrode in electrical contact with said element, for example, at least two electrodes which can be collected to a source of electrical power and which when so connected cause current to flow through the conductive polymer element. Preferred devices are self-limit-in heaters, e.g. flexible strip heaters, in which the conductive polymer composition exhibits PTC behavior. Such heaters are particularly useful for heating liquids in which the heater is immersed, especially diesel fuel (see Canadian Application No. 405,11~ and Canadian Application No. ~105,113.
In a third aspect, the invention provides a method of heating a liquid, particularly an organic liquid, especially diesel fuel, which comprises passing current through a self-limiting or self-regulating heater which comprise en the electrical device as defined above which is immersed in the liquid.
In a fourth aspect the invention provides a fuel feed through and heating assembly which can be positioned and connected between a fuel filter and a fuel tank of a fuel supply system to provide means for heating fuel which is being pumped through a fuel line from the fuel tank to the fuel filter, said feed through and heating assembly comprising I

I
DISC 107-~ A-5 MP0789 (A) a feed through comprising (l) a fuel conduit hulling at one end thereof a fuel line connector for connecting the feed through to a fuel fine and at the other end thereof a fuel filter connector for connecting the feed through to a fuel filter; and (it) a neck portion which protrudes from the fuel conduit between the ends thereof all which comprises a chamber;

(B) a flexible self-llmltlng strip heater as de-fined Ahab which preferably comprises a fuel-Ieslstallt insulating jacket, one end of the strip heater being within the chamber of the neck portion, and the strip heater passing through the fuel fine connector and protruding from the fuel conduit;

(C) insulated electrical leads connected to the electrodes of the heater, the connections tying within the chamber of the neck portion;

(D) a fuel-lesistant~ water-resistant and insulate lung composition which encapsulates (l) the connect lolls between the electrodes and the leads, (if) the insulation at the ends of the collected electrical leads and (ill) the lnsulatlllg jacket at the end of the collected heater; and (E) a fuel-reslstant gasket which prevents fuel Which lo being pumped through the fuel conduit from exiting through the neck portlorl.

, Polyvinylidene fluorides suitable for use in this invention are commercially available. The head-to-head content of a polyvinylidene fluoride can be measured by those skilled in the art. We have found that the measured head-to-head contents of different samples of a polymer sold under a particular trade name can differ substanti-ally. In general, the presently available po~yvinylidene fluorides made by suspension polymerization (rather than emulsion polymerization) have lower head-to-head contents.
lo The number average molecular weight of the polymer is generally at least 5,0U0, ego 7,000 to 15,UUU.

The polyvinylidene fluoride is preferably a homopolymer of vinylidene fluoride, but the presence of small quantities of comonomers, (preferably less than owe particularly less than .5~0 by weight), ego tetrafluoroethylene, hexafluoro-propylene and ethylene, is not excluded. The polyvinylidene fluoride is preferably the sole crystalline polymer in the composition, but other crystalline polymers, ego other crystalline fluoropolymers, may also be present. The composition may contain relatively small amounts (preferably less than 35,UoJ especially less than owe particularly less than Lowe by volume) of one or more elastomeric polymers, particularly solvent-resistant fluorine-containing elastomers and acrylic elastomers, which are usually added primarily to improve the flexibility and elongation of the composition.

The particulate conductive filler preferably comprises carbon black, and often consists essentially of carbon black. Choice of the carbon black will influence the resistivity/temperature characteristics of the composition.
Compositions exhibiting PTC behavior are preferred for many I) I S C 1 0 7 - Jo A - 7 ~236~ MPC7~9 Jo ^'~

devices of the invention, especially self-limiting heaters, and for these a carbon black having a ratio of surface area mug to particle size (mu) of 0.0~ to 6.0 is preferred.
For otter uses, compositions exhibiting ZTC or NTC behavior may be preferred. The amount of conductive filler used will depend upon the desired resistivity of the composition. For flexible strip heaters which are to be used for heating diesel fuel and powered by a 12 volt battery, we prefer a PTC composition whose resistivity at 25C is less than 200 10 ohm.cm ego about 10 to about 100 ohm.cm. In such compost-lions the amount of carbon black may for example be 16 to 25C~ by weight.

In addition to one or more conductive fillers, the compositions may also comprise other conventional additives, such as non-conductive fillers (including flame retardants), antioxidant and cross linking agents (or residues thereof if the composition has been cross-linked).

The compositions of the invention are preferably cross-linked (particularly by irradiation), since this has been found to enhance their resistance to organic solvents.

Preparation of the compositions of the invention can be carried out in conventional fashion Often it will be convenient to melt-extrude the composition directly into a water bath (which may be heated), and using this technique subsequent annealing is often not required.

The invention is illustrated by the following Examples, in which Examples 1, 2, 3, 7, 12 and 13 are Comparative Examples not in accordance with the invention.

DISC 107-2 Aye ? I MP0789 Jo <. .

The ingredients listed for Composition A in Table 1 below were mixed in a Danbury mixer. The mixture was dumped, placed on a steam-heated mill and extruded into a water bath through a 3.5 inch (8.9 cm) extrude fitted with a poulticing die. The extradite was chopped into pellets which were dried for 16 hours at 80C.

The ingredients listed for Composition B in Table 1 were mixed and poulticed in the same way as for Composition A.

owe by weight of the Composition A pellets and 17Uo by weight of the Composition B pellets were tumble blended and dried at 110C. The composition of the resulting Final Blend is shown in Table 1. Using a 1.5 inch (3.8 cm) diameter extrude fitted with a crosshead die having an orifice 0.4 inch (1.0 cm) x 0.1 inch (0.3 cm), the blend was melt-extruded over a pair of preheated 14 AWN (1. 85 mm diameter) 19/27 nickel-coated copper wires with a center-to-center separation of 0.25 inch (U.64 cam The extradite was passed immediately through a bath of water at room temperature air-dried7 and then irradiated to a dosage of 10 Mad. The conductive polymer had a resistivity of about 50 ohm.cm at 25 C.

_,~

Composition B Composition A Final Blend Wt(g)Wt~oVolO Wt(g)WtoYolO White Volvo Conner 460~16,798 72 72.616,33970 70.6 71.7 72.3 Furnex N765~ 4,433 19 18.74,9U1 21 20.7 19.3 19.0 Jo Vito AH 1,400 6 5.9 1,400 6 5.9 600 5.9 Omya-BSH 467 2 1.3 467 2 1.3 it 1.3 TIC 233 1 1.5 233 1 1.5 1.0 1.5 Conner 460 is polyvinylidene fluoride available from Penlight and having a head-to-head content of about OWE.

Furnex N765 is a carbon black available from Columbia Chemical having a particle size of about 60 millimicrons, a surface area of about 32 mug and a DIP value of about 112 cm3/100 9.

Vito AH is a copolymer of hexafluoropropylene and polyp vinylidene fluoride manufactured by duo Pont.

Omya-BSH is calcium carbonate available from Omya Inc.

TIC is triallyl isocyanurate, a radiation cross-linking agent.
I k DISC 107-2 A-10 ~23~ MP0789 ;^, I` EXAMPLES

The ingredients listed for Examples 2 to 6 in fable 2 below were mixed in a Danbury mixer. The mixture was dumped, granulated and dried for 72 hours at 75C under vacuum. Using a 0.75 inch (1.9 cm) single screw extrude fitted with a cross-head die having an orifice 0.3 inch (0.76 cm) x û.1 inch (0.3 cut the blend was melt-extruded over a pair of preheated 18 AWN (1.2 mm diameter) 19/27 nickel-coated copper wires with a center-to-center separation of lo 0.25 inch (0.64cm). The extradite was passed immediately through a bath of water at room temperature, air-dried, and then irradiated to a dosage of 10 Mad.

The ingredients shown for Examples 7-15 in Table 2 were mixed in a Danbury mixer, dumped and then granulated.
The granulated materials were molded into slabs of thick-messes of 0.030" (U.076 cm) to 0.036" (.091 cm) by come press ion molding at 200C for three minutes.

L23~

Lo Lo J

I CO

Lo Lo`\
I o O
I

to I

J
CC)I X
ED
a D I
ill to O
r- X

I

3 ED Jo X Us . Jo C
. Jo 3 I_, X
O C I O I

.

I

Conner 45U is polyvinylidene fluoride available from Penlight and having a head-to-head content in the range 5.5 to 6.3.

Sole 1û1û is a polyvinylidene fluoride available from Sylvia et ate of Belgium, and having a head-to head content of owe.

KF1000 and KF1100 are polyvinylidene fluorides available from Query Chemical Industry Co. of Japan? and having a head-to-head content of 3.5 to owe.

lo State G is a carbon black available from Cities Services Co., Columbia Division having a particle size of about 60 millimicrons, a surface area of about 32 mug and a DIP
value of about 90 cm3/100 9.

Deflower 2000 M is a polyvinylidene fluoride available from Kay-Fries, Inc. 9 member of Dynamite Nobel Chemikalien of Federal Republic of Germany and having a head-to-head content of about 4.4-4.9.

Vulcan XC-72 is a carbon black available from Cabot Co., having a particle size of about 30 millimicrons, a surface area of about 224 mug and a DIP value of about 178 cm3/100 9.

~23~2~6 Jo TESTS FOR STABILITY IN ORGANIC SOLVENTS

Tile extradites obtained in Examples 1 and 4 were compared by the following tests. Samples 2 inch (5.1 cm) long were cut from the extradites. The samples were immersed in various solvents at 25C and the resistance of the samples was measured at intervals. The solvents used, and their volubility parameters, were Solvent Volubility Parameter 3 n 5 (colloquium ) lo Tulane 8.9 Methylethylketone (ME) 9.3 Acetone 9.9 o - dichlorobenzene 10.0 Acetic Android 10.3 Pardon 10.7 Dimethylacetamide (DMAC) 10.8 Dimethylsulphoxide(DMSO) 12.0 ~imethylformamide (DMF) 12.1 Ethanol 12.7 The results For Examples 1 and 4 are shown in Figures 1 and 2 respectively of the accompanying drawings, where the ratio of the resistance at a given time (Of) to the initial resistance (Rip) is plotted against lime. The greater stability of the composition of the invention (Example 4, shown in Figure 2) is apparent.
The extradites obtained in Examples 1 to 6 were compared in the following way. Samples 2 inch (5.1 am) long were cut from the extradites and were immersed in various test liquids maintained at 160 F (71C). The test liquids are Jo I I 1 DISC 1U7-2 A-14 - MP07~9 listed below and include diesel fuel and various commercially available additives for diesel fuel alone and mixed with diesel fuel. At intervals, the samples were removed, cooled to 25DC and dried, and their resistance measured. Table 3 shows the value of the ratio Rf/Ri for the different samples at various times. The additives tested, and their main ingredients, were as follows:

I Tulane, methanol acetone, naphthalenic mineral oil and ethylene glycol monobutylether.
0 Fire Prep 100 Naphthalenic oil and partly oxidized aliphatic hydrocarbon Sta-Lube Naphthalenic mineral oil Redline Naphthalenic mineral oil, barium carbonate and Catalyst other inorganic carbonates, and sulfur-containing material Wins Naphthalenic mineral oil/and isopropanol Conditioner umout Naphthalenic mineral oil, non-aromatic ester and aliphatic acid.

20 Wins Naphthalenic mineral oil, non-aromatic ester, Anti- aliphatic aside, and aliphatic acid.
Knock ;

FPPF Ethyl cellulose, ethylene glycol monobutylether, and oxidized hydrocarbons.
i, rice rr7~ rJc I.

36Z~6 Jo Table 3 Example No. 1C(C) I I 4 5 6 _ .
Rip (ohms) 9-3 8.8 2.3 14.1 19.7 10.4 Rf/Ri after 19 hours in B12 23X104 28X104 43X104 3.3X104 133 33g Fire Prep 100U 1.02 1.U4 0.96 0.91 0.94 0.92 Sta-Lube 1.09 1.04 1.11 0.94 0.95 0.91 Red-line Catalyst 1.22 1.06 1.33 1.00 0.97 1.05 lo Wins Conditioner 1.39 1.18 1.19 1.13 1.08 1.15 ~umout 1.14 1.10 1.22 1.01 1.01 1.0 Wins Anti 1.12 1.04 1.18 0.99 1.0U 1.09 Rf/Ri after 110 hours in 15 Diesel Fuel 1.û3 0.97 1.07 0.93 1.00 0.92 Rf/Ri after 69 hours in Diesel Fuel +
duo B12 1.26 1.10 1.67 1.15 1.05 1~12 20 Diesel Fuel +
owe FPPF 1.32 1.12 1.2u 1.08 1.05 1.12 Diesel Fuel +
owe gasoline 1.17 1.05 1.15 1.01 0.99 1.07 fry after 25 275 hours in Diesel Fuel 1.U9 1.01 1.12 0.950.93 1.04 Rf/Ri after 157 hours in Diesel fuel +
duo B12 1. 66 1.17 2. 97 1.37 1.08 1 O 35 Diesel Fuel +
owe FPPF- 1.7~ 1.30 1.47 1.171.14 1.27 Diesel Fuel +
10,Uo gasoline 1.33 1.10 1.28 1.0~ 1.U1 1.16 RESISTANCE RELAXATION TESTS

The compositions of Examples 7-15 were tested by the following tests. Samples 1 inch (2.54cm) by 1.5 inch (3.8 cm) were cut From the molded slabs. Electrodes were formed on each sample by painting a strip 0.25 inch (0.62 cm) wide at each end with a suspension of silver particles (Electrodag 504 available from Atchison Collolds). The samples were annealed for 5 minutes at 2U0C, and then cooled. The samples were then placed in an oven at 100C
lo and their resistances measured at intervals. It was found at the lower the head-to-head content of the polymer, the less lots change in resistance.

ok Roy my, k

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 comprises a particulate conductive filler dispersed in polyvinylidene fluoride which has a head-to-head content of less than 5.0%.

2. A composition according to Claim 1 wherein the polyvinylidene fluoride has a head-to-head content of less than 4.5%.

3. A composition according to Claim 2 wherein the polyvinylidene fluoride has a head-to-head content of less than 4.0%.

4. A composition according to Claim 1, 2 or 3 wherein the conductive filler is carbon black.

5. A composition according to Claim 1, 2 or 3 wherein the conductive filler is carbon black and which exhibits PTC behavior.

6. An electrical device which comprises (i) a conductive polymer element comprising a particulate conductive filler dispersed in polyvinylidene fluoride which has a head-to-head content of less than 5%; and (ii) at least one electrode which is in electrical contact with the conductive polymer element.

7. A device according to Claim 6 wherein the polyvinylidene fluoride has a head-to-head content of less than 4.5%.

8. A device according to Claim 7 wherein the polyvinylidene flouride has a head-to-head content of less than 4.0%.

9. A device according to Claim 6 which is a self-regulating heater in which the conductive polymer composition comprises carbon black and exhibits PTC behavior.

10. A method of heating diesel fuel which comprises passing current through a self-regulating heater which is immersed in the diesel fuel, wherein the heater is a self-regulating heater which comprises (1) a conductive polymer element comprising a part-iculate conductive filler dispersed in polyvinyl-idene fluroide which has a head-to-head content of less than 5%; and (2) at least two electrodes which can be connected to a power source to cause current to pass through the conductive polymer element.