CA1206507B - Electrical devices comprising conductive polymer compositions - Google Patents
Electrical devices comprising conductive polymer compositionsInfo
- Publication number
- CA1206507B CA1206507B CA000488467A CA488467A CA1206507B CA 1206507 B CA1206507 B CA 1206507B CA 000488467 A CA000488467 A CA 000488467A CA 488467 A CA488467 A CA 488467A CA 1206507 B CA1206507 B CA 1206507B
- Authority
- CA
- Canada
- Prior art keywords
- conductive polymer
- electrodes
- process according
- polymer composition
- heating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 229920001940 conductive polymer Polymers 0.000 title claims abstract description 54
- 239000000203 mixture Substances 0.000 title claims abstract description 43
- 238000000034 method Methods 0.000 claims abstract description 48
- 238000010438 heat treatment Methods 0.000 claims abstract description 19
- 238000002844 melting Methods 0.000 claims abstract description 8
- 230000008018 melting Effects 0.000 claims abstract description 8
- 238000001816 cooling Methods 0.000 claims abstract 3
- 238000004519 manufacturing process Methods 0.000 claims abstract 3
- 229920000642 polymer Polymers 0.000 claims description 26
- 239000006229 carbon black Substances 0.000 claims description 12
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 239000010949 copper Substances 0.000 claims description 4
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 3
- 230000001681 protective effect Effects 0.000 claims description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims 2
- 238000004132 cross linking Methods 0.000 claims 2
- 239000000047 product Substances 0.000 claims 2
- 229910052709 silver Inorganic materials 0.000 claims 2
- 239000004332 silver Substances 0.000 claims 2
- 229910052759 nickel Inorganic materials 0.000 claims 1
- 229920001169 thermoplastic Polymers 0.000 claims 1
- 239000004416 thermosoftening plastic Substances 0.000 claims 1
- 238000000137 annealing Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 238000011282 treatment Methods 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 239000000155 melt Substances 0.000 description 2
- BALXUFOVQVENIU-KXNXZCPBSA-N pseudoephedrine hydrochloride Chemical compound [H+].[Cl-].CN[C@@H](C)[C@@H](O)C1=CC=CC=C1 BALXUFOVQVENIU-KXNXZCPBSA-N 0.000 description 2
- RLLPVAHGXHCWKJ-IEBWSBKVSA-N (3-phenoxyphenyl)methyl (1s,3s)-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropane-1-carboxylate Chemical compound CC1(C)[C@H](C=C(Cl)Cl)[C@@H]1C(=O)OCC1=CC=CC(OC=2C=CC=CC=2)=C1 RLLPVAHGXHCWKJ-IEBWSBKVSA-N 0.000 description 1
- 101150099190 ARR3 gene Proteins 0.000 description 1
- 241000518994 Conta Species 0.000 description 1
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- 241001481828 Glyptocephalus cynoglossus Species 0.000 description 1
- 240000007594 Oryza sativa Species 0.000 description 1
- 235000007164 Oryza sativa Nutrition 0.000 description 1
- 244000046052 Phaseolus vulgaris Species 0.000 description 1
- 235000010627 Phaseolus vulgaris Nutrition 0.000 description 1
- 241001674048 Phthiraptera Species 0.000 description 1
- 101100409194 Rattus norvegicus Ppargc1b gene Proteins 0.000 description 1
- 101150007148 THI5 gene Proteins 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000011231 conductive filler Substances 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229920001971 elastomer Polymers 0.000 description 1
- 125000001495 ethyl group Chemical group [H]C([H])([H])C([H])([H])* 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- KRTSDMXIXPKRQR-AATRIKPKSA-N monocrotophos Chemical compound CNC(=O)\C=C(/C)OP(=O)(OC)OC KRTSDMXIXPKRQR-AATRIKPKSA-N 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 150000002978 peroxides Chemical class 0.000 description 1
- 239000006187 pill Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 235000009566 rice Nutrition 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 239000005060 rubber Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
- H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
- H05B3/146—Conductive polymers, e.g. polyethylene, thermoplastics
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
- H01C7/02—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
- H01C7/027—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient consisting of conducting or semi-conducting material dispersed in a non-conductive organic material
Landscapes
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Ceramic Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Dispersion Chemistry (AREA)
- Resistance Heating (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Conductive Materials (AREA)
- Thermistors And Varistors (AREA)
- Control Of Resistance Heating (AREA)
- Apparatuses And Processes For Manufacturing Resistors (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for the manufacture of a device compris-ing at least two electrodes and a conductive polymer compos-tion in contact therewith, which process comprises (1) heat-ing a conductive polymer composition to a temperature above its melting point (Tm); (2) heating at least two electrodes, out of contact with the conductive polymer composition; (3) melt-extruding the molten conductive polymer composition from step (1) over the pre-heated electrodes from step (2), the electrodes being at a temperature Te and the conductive polymer being at a temperature Tp when the electrodes and the conductive polymer are first contacted with each other;
and (4) cooling the electrodes and the conductive polymer composition; the conditions of the process being such that the electrodes and the conductive polymer composition in contact therewith are at a temperature above Tm for a time which is sufficient to reduce the contact resistance between them and which is less than five minutes.
A process for the manufacture of a device compris-ing at least two electrodes and a conductive polymer compos-tion in contact therewith, which process comprises (1) heat-ing a conductive polymer composition to a temperature above its melting point (Tm); (2) heating at least two electrodes, out of contact with the conductive polymer composition; (3) melt-extruding the molten conductive polymer composition from step (1) over the pre-heated electrodes from step (2), the electrodes being at a temperature Te and the conductive polymer being at a temperature Tp when the electrodes and the conductive polymer are first contacted with each other;
and (4) cooling the electrodes and the conductive polymer composition; the conditions of the process being such that the electrodes and the conductive polymer composition in contact therewith are at a temperature above Tm for a time which is sufficient to reduce the contact resistance between them and which is less than five minutes.
Description
.
lZ(~507 n~ ~ ntiO . relat~ to elec~ic~l de~lc~ in whict~ an .
a~pris~ o~Anlc E~lym rs h~vir~ d~rs~ ~r~in ~ ~n~ly divid~d S ~ ill, ~ a~m blac:3c or a p4rtia~lAt ~etal.
5~ ~uch ~ ath~bit ~d P~C (Po~i~ve 5~~
C~icient) ~vior. m~ ~y ~ h~ b~ used in the p~t to de~ P~C b~vior ~ variabl- ad o~ ~r-ci~. ~n c ~ ositicn~ d-note a o~mpo~it~ ving at t~ant on t ~ ture rang- (herQina~t~r c211~d a critic~l rang~) wh~ch i~
~ithin th- llmit~ o~ -lOO-C an~-ak~ut 250-Cs at th ~ ginning of which the oo~pw ition haJ a resi~tivity.bolo~ about 105 ohQ. c~.~ and ~n which the ccnpw ltion ha~ an ~4 valu- o~ at l~t 2.S ~r an ~0O v~lu~
of at le~st 10 ~And p~ferably both), and pr~f~rably ha an ~ 0 valu of at least 6, where ~4 i3 th~ rat~o of the red~tiviti~ at the ~nd an~ the begi ~ of a 14-C rang~, ~0O is th~ rat~o of th~
re~i~tivitics at th 2nd ~nd the bQginnlng of a lOO-C r~nq-, and ~0 i~
the ratio of the r L~tlviti~ at th~ end and the beginnlng of a 30-C
range. The tcr~ ~PTC el~mentR i~ us~d herein b~ denotc an element ccmpo~d of a PrC oompo ition as definod abov-. A plot of the lcg of the r i~tance of a PTC element, meaJur-d between two electrode~ Ln oontact with tha element, against tcmptratux~, will often, t ~ h by no me~n~ invarlably, ~ho~ ~ aharp ch4ng- in ~16Qe w er a pa~t o~ th cr~tical t6np~raburo r~ng~, ~n~ In such ca~e~, th~ ter~ ~witch~ng trmperab~r~ (usually abbr-viat~d to T5) i~ u~d her~in to denot- the to~peratur- at th~ ~nO~rs ctlon point o~ exten~on~ of the sub~tantially ~traight portion~ of ~uch a plot whlch li- elther ~ide of th~ portion s~wirq th- sharp chang~ . m~ Prc c~mFo~ition in ~ a PrC de~t i~ de~crib~d h~in ~ h~ u~ful T~. me prefera~ly b~n ~ and 17S-C., ~.g. 50-C to 120-C.
12(~6S~7 Ca~uctive p~lymer c~T~sitions, especially PrC ç~sitions, are u~eful in elec~lc~l d~ccs ~n whi~ the o:snposition i~ in contact with an elec~cde, u~uaLly of met2Llr Device~ of this ~cind are usually manufactl~red by metldq ~pr~3~ng at~l~ or mou~d~ng the m~ltal S polymer ~ sition ~round or ag~ ~st tl~ electr~de or el ~ des. ~n the known methods, the electrode it not he~te~ prlor to oontict with the polymer w utusition or i~ heated only to a l~mitsd extent, for examçlc t~ a temperature well below the melting point of thc .~u~u~ition, for example not re than 65-C as in conventional wire-ooatinq tech~iques. ~Temperaeures ~.o in C throughout thi5 specifica ion.~ Wkll known exAmçle~ o~ such t~vices are n exl~le st-ip heater~ which ~I~Li9~ a gener~lly ribbonrsh~ped o~re of the conductive polymer compo~itlon, a pair o~ lonqitLdinally extendLng electrcdcs, gener~lly of stranded wire, mboddod in the o~re near the edges thereof, and an outer layer of a protective and msl~latlng ccmposition.
Particularly useful heater~ are those in which th~ composition e~hibits PrC behavior, and which are therefore self-regulating. In the preparation of such heaters in whlch the comFosition contains less than 15% of carbon black, the prior art has taught that it is necessary, m order to obtain a sufficiently lcw resistivity, to anneal the heater for an extended period such that ZL + 5 logl~ R< 45 where L i5 the percent hy weight of carbon and R is the resistivity in ohm.c~. at roon temperature.
A disadvantage which a~rlse~ with devices o~mprising an d ectrcde and a conductiv~ polymer oomposition in contact wnth the electrodc, and in particular with strip heater~, is that the longer they are in ser~rice, the bigh is t!~eir resistance and t~e lo~e- is their E~wer out~t, partlcularly ~hen ~hey are s~ject b~ thennal cycling.
lZ(~6S~t~
It is ~n t~at var~ au, ~n device ~ device, of the ~ntact resi~t~nce betw~ electr~e~ arr3 carb~lack-filled rub~
lt an obst~cle ~ c3~ari90n of tl e electrlcal characteristi~ of such devices ar~ e acc~at~ measureneslt of the re~i tiYity of such S rubbers, par~:ioularly at high re~ vitie~ and low voltages; ar~ it has be~ su~ted that the saDe i~ ~ue of oth~r conductive polymer amE~itions. Variou~ method~ h~ve bean su~qested for re~ucir~ the ~ntact resi tance bet~ c~bl~ck-fi1led n~ers and test ele~e~ plac~d in ccntaot therewith.. m~ preferr~ methcsd is vulcan~s~ the rubb~ while it i~ in contact with a bra~ el~ode.
Otl~ ~etlx~ds includ~ ~pcr-~lat~r~, vacw~ating ~nth ~old, ar~ the use of coLtoidal solutions of graphite betwe~ the electrcde arx3 the test plece. Ebr de~ s, r~ference s ~ ld bo made t~ ~ upter 2 of ~Conductive Rubber3 and Pla~tics~ by R ~. Nor~an, published by Applied.
15 Science P~blisher~ ~1970), from which it will be clear that the factor~
which govern the size of such 03ntact re~istance arc not well understood.
We have now disow ered ~hat the less is the initial contact resist~nce ~etween an electrode and a conductive polyme comFosition, the smaller i~ the incrc~s~ in total resistance with tLme. ~e have also disc~vered that by placiny or m~intaining an elect cde and a polymer composition in oontaot wit~ each other while both are at a temperature above the melt~nq point of the ~ vsition~ the oontact re~istance between the~ is reduc~d. The teDm ~melting po m t of the oomposition" is used hein to denote the ~rature at which the oomFo~ition begin~ t~ m d t. The time for which the electrcde and the 03mpo~ition ne~d be in oontact with each other, ~hile e~ch is at a temperature above the meltlng point of the composition, in orde- to achieve the desired r ult, i~ quite short. TLmes in exces~ of five lZ(~6S(~7 m m utes do not result in any substantial fucther ceduction of cont~ct rc~i~tance, and often times les~ than 1 m m ute are quite a~equate and are therefore preferre~. Thus the ~reatment time is of a quite diff ent order from ~hae requl~ed by the known annealing treatments bo deccease the resastlvity of the ccmçosition, as described for exæmple in ~.S. Patents No~. 3,823,217 and 3,914,363.
In one aspect, therefore, the inv~ntion prcvide~ a ~ ess ~or t~e prqparation or modification o~a device ~L~ ng an elect ode and a con~uctiv~ polymcr oomp w ition i~ oontact wi~h the clectrode, 0 whic~ xoe3~ CampriX3 contaCt~ng~ or mdintain~ng conta~t bet~een, the ~uctive p~lymcr ocmposltlon and the d ectrcde whlle the oonduc~ive polymer oomposition i3 at a te~Feraturc ~$p) ab~ve it~ melting polr.t (Tm) and the electrode is at a t~nperature ~Te~ abcve the m d ting poin~
of the conductive ccn~oo~ition, Tp and Te beinq the same or different, for a time which is sufficient to reduce the oantac~ resis nce between the electrode and the conductive polymer composition but whidh is not sufficient-substanti~lly to reduce the resistivity of the oonductive Folymer. Preferably both Tpa~d Te are at leas~ 20-C, especially at least 55-C, above Tm~ It is often preferable that both Tp and Te 2~ should be above the Ring-and-Ball softening t~mpera e of the polymer.
ocmposition.
Preferably the conductive polymer conposi~ion is subjected to pre5sure to assist m bringing it into c!ose ~onfo~ity with the electrode.
The p¢essure i~ gen ally at lea~t 14 kg/c~2, prefcrably at least 2l.
kg/c~2, for example 21 to 200 hg/cm2, especially at lea~t 35 hg/cm2, e.g. 3S-70 kg/cm2.
-. lZ~6S~7 We ~ave als~ foun~ that the contact resistance c~n be ~rrelated ~th the force ne~ded to pull the elecl.L.~le fmn the Folymer c~ltial. Acc~rd~r~ly the ~nv~elctl further prwide~ ~ deviY
ccn~rising N~ ele~e ~ contac~ ~ith a ~nd~elve polyme~
~ltion, especi~lly a ~tr~ded w~re electrode ~ dded.~n a ccx~ductive polysner ~sieio~n, the pull s~cren3th (P~ of ehe elec~ode fr~m the de,lice beir~ equal t~ at least 1.4 time~ PO, where PO i3 the p~lll stre~th of an ident~c~l elec~cde fml~ a devi~e whieh .~ises ~n idultical elec~de in clt~ct. with an identical conductive p~lymer 0 c~mposi~ and which ha~ pared b~ a pro~ess whi~:h con~ist~ of contacting the el~c~ode, while it is at a temperature not greater than 24e~, w~th the x l~en oonductive polymer oomçosition, an~ allownng t~e polymer coDposition to ~col in contact ~ith the electrode. The pull strengths P and PO are detesmined ~t 21C as describçd in detail below.
A 5.1 cm long sæmple of thc heater strip (or other device), contaLninq a-straight 5.1 cm length of the electrcd~s, i5 cut off. At one end of the samçle, 2~5 cm of the electrcde is stzipped bare of polym OE . rhe bared elect-cde is passed dcwnwardly t.~rough a hole slightly larger than the electrcde in a rigid metal plate fixed in t~e horiDontal plane. The end of the bared electrode is fi~ly clamFed in a mcvable clamp below the plate, and the other end of the sample is lightly cla~ç~d above the plate, so that the electrcde is vertic~l.
m e movable cl~mp i~ then moved vertically dcwnwards at a speed of 5.1 cm~min~, and the pe~k force needed to pull th; conductor ~ut of ~he sample is me~sured.
.. _ _ .. _ _ .. . . _ . . _ . _ . _ ~ . .
lZ-~S~7 Wk h~ve also found that ~or strip heaters, curren ~y the most widely ~lCAd d~vic~s m which current is passed through conductive polymer oompo~it~on~, e~e oontact resi-~tance can be o~rrelated with the linearity ratio, a qu~nt$ty which can re~dily be ~easured as described bel~w. Accordingly th~ 1nventlon ~ur~her provides a strip heatcr oomprising:
(1) an elongatc core o a conductive poly~er comçosition which exhibits ~TC beh~lor, whlch comprise-~ car~on blac*, and in which, if the oontent (L) of carboQ black Ln percent by weight is less.
~han lS, L and the resi~t$vity R o~ the oompo3ition in oh~. om are such that 2~ ~ 5 log10 ~ > 45 ~2) at least tw~ longit~dinally extending electrcoes embedded Ln said composition par~llel to e~ch other: and IS `(3) an out~r layer o~ a protectlve and msulatmg comFo~ition;
the average line~rity ratio (and prefcrably the linearity ratio at 211 points~ betwe~n ~ny pair o~ elect mde~ being at ~ost 1.2, pre~erably at most 1.15, especially at mcst 1.10. m e l m e~rity ratio of a strip heater is defined as Resistance at 30 MV.
Resistance at 100 V.
the resiQtances be mg m~swr~d at 21C between tw~ electrodes which are contacted by prcbe~ push~d thro~yh the outer jacket and the oonductive polymeric sore oS the strip heater. The o~ntact re-~istance i~
neql~gible at 100 V., ~o that the closcr the l~n ity ratio i3 bo 1, the lower the contact re~istance.
The LnVention i~ useful with any txpe of electIode, for exaTçle~plates, strip~ or wires, but particularly so with electrcdes haYiny Dn irregular surfac~, e.g. str nded wire electrcdes as conventionally used ln ~trip hcaters, br~ided wire electrode~ (for examçle a descr~bed ~n Ger~an Offenl q ungschrift No. 2,635,000.5) ~2~6S07 and expar~able elect~de5 as describ~ in Gerrran Off~legungs*~ift No.
2,655,543.1. Preferred ~tranded wire~ are silver-)at~d and nic~
~ated copper w~res, wh1~h are 1e~Q su~tible to difficultie5, such as melt~ or oxidatiotn, than t~coats~ or unc~ted copper wire~, S t~uqh the latter can ~e usad wit~ut difficulty pr~vid~ng the t~at~es ~r~l~d are not too high.
The c~uctive polyn~ c~psitioru ~sed in thi~ ~nves~tion gener~lly c:on~n car~on black a~ the conductive filler~ e.g. in zn~t gre~ter or le53 than 15% by weight, f~r example greater t~an 17% or 20%
by wcight. In many caxs, lt ~ prderr~d that the ca~sitionJ s~ld exhibit ~C behavior. The resistivity of the c~osition i5 generally le~s than 50,000 oh~ at 21-C, for ex ~ le 100 to 50,000 ohm.~n. Fbr strip h~ters designed bo b~ powered by A.C. of 115 ~olts or more, the composition generally ha~ a resis~vity o~ 2,000 to 50,000 ohm.c~, e.g.
2,000 to 40,000 ohm.cm. 5he oomposition 1~ pr~ferably thesmoplastic.
~owever, it may be ligh~ly cro59-linked, or be in the process of being cross,linked, provided that it is sufficiently fluid under the contacting condition to conform closely to the electrode surface.
The polymer is preferably a cry-st lline polymer.
The strip heater~ with which the invention is concerned generally have two electrcde~ separat~d by a distance of O.lS to 1 c~, :-: but gre~ter separations, e.g. up to 2.5 cm. or even more, can be used.
m e o3re of oonductive polymer can be of c~nventional shape, but preferably it has a cros~-sectl~n which is not re than 3 times, especi lly nct re than 1.5 times, e.g. not more than 1.1 times, its smallest dimension, especially a round cross-sect~on.
_7_ lZ~65~7 In one pre~erred embcdiment of the ~nveneion, the electrcde and the polymer composition are hea~ed ~epara~ely ~efore be mg contacted. In this ol~Jlment, it i~ p~eferred that the coTposition should be melt-e~truded cver the electrcde, e.g~ by ~xtrusion around a S pa~r of spaced-apart wire electrodes using a cross-head die. m e el ~ e i3 pre-heated to a t2mperature (Te) which may be greater or les~ than the melt temperab~re of the polymer .~4usition (Tp) bu~ i~
gen ally more than ~Tp-55) and prefer~bly more than (Tp-30). Tp will norm~lly be substanti~lly ab w e the meltlng point of the oomposi~on, tO ~or examçle 30 to 80C abcv~. Of o~urse, nelther the elec ~ ~de nor the ocmp~ition sh2uld b~ he~tod to a t3mp~rature at which ~t undergocs substanti 1 ox~dation or oth degradation.
In another embodiment of the m vention, the coTposition is shaped in contact w~th the elec W e (wnthout pre-heating the electrode) and the elec~rode and the composition are then heated, while in oontac~ wnth each other, to a t~mperature ab~ve the melting ~OLnt of the composition. Care is needed to ensure a useful reduction in the contact resistance by this method. The optimum conditions wlll depend upon the electrode and the ~usitiGn~ but inc~eased ti~e, t~mperablre and pressure help to ac~ieve the desired result. me pressure may be applled for examç~e in a press or by means of nip roller~ is embodiment o~ tbe ~nvention is particularly use~ul when tbc need for, or deeir~bility of, an anneAling treatment does not arise at all, for exam~le, w~hen the ocmposition ha~ a c~rbon blac~ oontent gre~ter than 1~% by weight, e.g. greater than 17% or 20% by weight, or when only a limlted anne ling treatment is carried out, such that at the end of the annealing tbe o~ntent of c~rbon black tL) and the resis~ivity (R) are sucb that 2L + 5 log10 > 45.
one w~y of heatlng the eleotrcde and the ccmposition surr~unding it is to pas~ a high current ~hrough the electrcde and thus produce tbe desired he~t by res~stance heating of thc electrcde.
:12(~65~7 ~n another ~mbodlment Of the invention, the conductive polymer 03mposition is initialiy in the fonm of a shaped article, e.g.
one or xre pill~ or pellet~, whlch ha~ not been 5hyped in contac~ with the electrode, and the electrode an~ the c~l~us~tion are heated bogether under pretsurc, for e ~ o ln a compresslon mould.
. 2~rticularly when the oonductive poly~er oompo d tion exhibits PTC behavior, it ~ often des~rahl~ that Ln the final prcduct the ccmposition sh~uld be crc~-linkod. Cr~3s-linking c~n be carried out as a separate strp after thQ troat~ent b~ reduce oaQtact resistance; in 10- this c~se, cro3s-linking with aid of radla~ion ls preferr~d.
Alternatively crc~rl~nkinq c m be c~rriod out simultan~eously with the said treat~ent, ~n which case che~ical cross-l~nking with the aid of cross-linXing lnitiators such as peroxides is preferred.
me invention is illustrated by th~ foll~ ExamFles, scre of which are canparative E~mple~.
In ea~ of the Example3 a strip heat ~QS prepared as describff~ below The cor~uctive p~lymer ccrnFosition wa5 obtained by blend$ng a ~edi~ den~ity poly~thyl~ne containing ~ antiox$dant wit~
carbon black ma~ter batch ~npr$s$nq an ethsylene,/ethyl aylate c~lymer to giv~ ~ ~5it$0n containing the indicated perc&nt bv weight of ca~on black ¦ ~Ihe m~t~ng po~nt o~ th~ ~os~t~on waa ~out f ~115-6~ me ccmp~$tian wa~ melt-extn~ed at a mclt temperatl~re of aba~t 180-C through a cro~ he~ d$e h~v$ng a circular or~ice 0 36 a~ in diameter over a pair of ~randed ilvcr-coated oopper wires, each w$re having a di m et r of 0.08 cm and o~mpr~inq 19 st:ands, and the a~es of the wires being on a di3meter of the ori ice and 0.2 cm aFart.
Before reaching th~ crosJ-head die, th~ wires were pre-heated by passing th~m through an oven 60 c~ long at 800-C. m e temperature of the wires entering the die w~s 82-C in the comparative EXa~ples 1, 4 and 6, in which the speed of the wires thr3ugh the cven and the die _g_ was 21m/m~, 165-C in Ex~e~ 2 ~ 7 and 193C in E~amples 3 ar~ 5.
me extr~ate wQ.~ then given an insl?lating j~cket by melt-ex~ud~ng aro~d lt ~ layer 0.051 ~n thick of ~lorinat~ F~lyethylene or an ethylene~te~ r~etl~lene copolymer. me coats~ ~xtru~at~ was t~ irr~iated in order to os9-link the c~ ctive polyner cc~sition.
EX~ES 1-3 5hese E~ople~, in which Exa:nE~e 1 is a c~nparative Ex2~21e, domonstrate the inQ uence of ~inearity R~tio (LR) on Pcwer ~utput wh~n the heater is subjected to te~perature changes~ In eadh Ex~mple, tbe Linearity Ratio of the he~t ~as me~sured and the heater wQ~ then oonnected to a 120 volt AC supply and the ambient temperature was changed continuously over a 3 minute cycle, being raised frJR -37-C bo 65C over a pericd of 90 seconds and then reduced to -37C 3gain cver the next 90 seconds.
m e peak power out2ut of the heater du- m~ each cycle ~as measured initi~lly and at interval and expressed as a ~roportion ( ~ ) of the initial peak power output.
m e polymer ccm~vsition used in EXample 1 oontained a~out 25 carb~n black. T~he polymer compwitlon used in E~amçles 2 and 3 contained about 22~ carbon black.
12~651~7 ~he results obt~ined are ~ in Table 1 below.
. of C~cles ~Ec2mple 1 Example 2 Eurr~le 3 PN ~R PN ~R N
None 1 1.3 1 1.1 500 0.5 1.6 1.3 - 1 1 1100 0.3 2~1 1.2 - 1 1 ltOO - - 1.1 1.1 1 1 ~a~arative E~nple E~MP~ 4-7 These E~c~mple~, which are Sumnarised in Table 2 below, da~ns~ate thc effect of pre-heating the ~ec~odes on t!le Linearity Ratio arYI Pull Strength of the produ::t.
~.BLE 2 .
l; E:xample No. ~ Carbon_31ac!c Lirle ~ ~tio ~4 22 1.6 ~2 1.0 *6 23 1.3S
7 23 1.1 20~Ca~arative E~t~nple The r2tio of the pull ~trengt~s of the heater strlps of B~eq 7 and 6 (P/PO) was 1.45.
lZ(~507 n~ ~ ntiO . relat~ to elec~ic~l de~lc~ in whict~ an .
a~pris~ o~Anlc E~lym rs h~vir~ d~rs~ ~r~in ~ ~n~ly divid~d S ~ ill, ~ a~m blac:3c or a p4rtia~lAt ~etal.
5~ ~uch ~ ath~bit ~d P~C (Po~i~ve 5~~
C~icient) ~vior. m~ ~y ~ h~ b~ used in the p~t to de~ P~C b~vior ~ variabl- ad o~ ~r-ci~. ~n c ~ ositicn~ d-note a o~mpo~it~ ving at t~ant on t ~ ture rang- (herQina~t~r c211~d a critic~l rang~) wh~ch i~
~ithin th- llmit~ o~ -lOO-C an~-ak~ut 250-Cs at th ~ ginning of which the oo~pw ition haJ a resi~tivity.bolo~ about 105 ohQ. c~.~ and ~n which the ccnpw ltion ha~ an ~4 valu- o~ at l~t 2.S ~r an ~0O v~lu~
of at le~st 10 ~And p~ferably both), and pr~f~rably ha an ~ 0 valu of at least 6, where ~4 i3 th~ rat~o of the red~tiviti~ at the ~nd an~ the begi ~ of a 14-C rang~, ~0O is th~ rat~o of th~
re~i~tivitics at th 2nd ~nd the bQginnlng of a lOO-C r~nq-, and ~0 i~
the ratio of the r L~tlviti~ at th~ end and the beginnlng of a 30-C
range. The tcr~ ~PTC el~mentR i~ us~d herein b~ denotc an element ccmpo~d of a PrC oompo ition as definod abov-. A plot of the lcg of the r i~tance of a PTC element, meaJur-d between two electrode~ Ln oontact with tha element, against tcmptratux~, will often, t ~ h by no me~n~ invarlably, ~ho~ ~ aharp ch4ng- in ~16Qe w er a pa~t o~ th cr~tical t6np~raburo r~ng~, ~n~ In such ca~e~, th~ ter~ ~witch~ng trmperab~r~ (usually abbr-viat~d to T5) i~ u~d her~in to denot- the to~peratur- at th~ ~nO~rs ctlon point o~ exten~on~ of the sub~tantially ~traight portion~ of ~uch a plot whlch li- elther ~ide of th~ portion s~wirq th- sharp chang~ . m~ Prc c~mFo~ition in ~ a PrC de~t i~ de~crib~d h~in ~ h~ u~ful T~. me prefera~ly b~n ~ and 17S-C., ~.g. 50-C to 120-C.
12(~6S~7 Ca~uctive p~lymer c~T~sitions, especially PrC ç~sitions, are u~eful in elec~lc~l d~ccs ~n whi~ the o:snposition i~ in contact with an elec~cde, u~uaLly of met2Llr Device~ of this ~cind are usually manufactl~red by metldq ~pr~3~ng at~l~ or mou~d~ng the m~ltal S polymer ~ sition ~round or ag~ ~st tl~ electr~de or el ~ des. ~n the known methods, the electrode it not he~te~ prlor to oontict with the polymer w utusition or i~ heated only to a l~mitsd extent, for examçlc t~ a temperature well below the melting point of thc .~u~u~ition, for example not re than 65-C as in conventional wire-ooatinq tech~iques. ~Temperaeures ~.o in C throughout thi5 specifica ion.~ Wkll known exAmçle~ o~ such t~vices are n exl~le st-ip heater~ which ~I~Li9~ a gener~lly ribbonrsh~ped o~re of the conductive polymer compo~itlon, a pair o~ lonqitLdinally extendLng electrcdcs, gener~lly of stranded wire, mboddod in the o~re near the edges thereof, and an outer layer of a protective and msl~latlng ccmposition.
Particularly useful heater~ are those in which th~ composition e~hibits PrC behavior, and which are therefore self-regulating. In the preparation of such heaters in whlch the comFosition contains less than 15% of carbon black, the prior art has taught that it is necessary, m order to obtain a sufficiently lcw resistivity, to anneal the heater for an extended period such that ZL + 5 logl~ R< 45 where L i5 the percent hy weight of carbon and R is the resistivity in ohm.c~. at roon temperature.
A disadvantage which a~rlse~ with devices o~mprising an d ectrcde and a conductiv~ polymer oomposition in contact wnth the electrodc, and in particular with strip heater~, is that the longer they are in ser~rice, the bigh is t!~eir resistance and t~e lo~e- is their E~wer out~t, partlcularly ~hen ~hey are s~ject b~ thennal cycling.
lZ(~6S~t~
It is ~n t~at var~ au, ~n device ~ device, of the ~ntact resi~t~nce betw~ electr~e~ arr3 carb~lack-filled rub~
lt an obst~cle ~ c3~ari90n of tl e electrlcal characteristi~ of such devices ar~ e acc~at~ measureneslt of the re~i tiYity of such S rubbers, par~:ioularly at high re~ vitie~ and low voltages; ar~ it has be~ su~ted that the saDe i~ ~ue of oth~r conductive polymer amE~itions. Variou~ method~ h~ve bean su~qested for re~ucir~ the ~ntact resi tance bet~ c~bl~ck-fi1led n~ers and test ele~e~ plac~d in ccntaot therewith.. m~ preferr~ methcsd is vulcan~s~ the rubb~ while it i~ in contact with a bra~ el~ode.
Otl~ ~etlx~ds includ~ ~pcr-~lat~r~, vacw~ating ~nth ~old, ar~ the use of coLtoidal solutions of graphite betwe~ the electrcde arx3 the test plece. Ebr de~ s, r~ference s ~ ld bo made t~ ~ upter 2 of ~Conductive Rubber3 and Pla~tics~ by R ~. Nor~an, published by Applied.
15 Science P~blisher~ ~1970), from which it will be clear that the factor~
which govern the size of such 03ntact re~istance arc not well understood.
We have now disow ered ~hat the less is the initial contact resist~nce ~etween an electrode and a conductive polyme comFosition, the smaller i~ the incrc~s~ in total resistance with tLme. ~e have also disc~vered that by placiny or m~intaining an elect cde and a polymer composition in oontaot wit~ each other while both are at a temperature above the melt~nq point of the ~ vsition~ the oontact re~istance between the~ is reduc~d. The teDm ~melting po m t of the oomposition" is used hein to denote the ~rature at which the oomFo~ition begin~ t~ m d t. The time for which the electrcde and the 03mpo~ition ne~d be in oontact with each other, ~hile e~ch is at a temperature above the meltlng point of the composition, in orde- to achieve the desired r ult, i~ quite short. TLmes in exces~ of five lZ(~6S(~7 m m utes do not result in any substantial fucther ceduction of cont~ct rc~i~tance, and often times les~ than 1 m m ute are quite a~equate and are therefore preferre~. Thus the ~reatment time is of a quite diff ent order from ~hae requl~ed by the known annealing treatments bo deccease the resastlvity of the ccmçosition, as described for exæmple in ~.S. Patents No~. 3,823,217 and 3,914,363.
In one aspect, therefore, the inv~ntion prcvide~ a ~ ess ~or t~e prqparation or modification o~a device ~L~ ng an elect ode and a con~uctiv~ polymcr oomp w ition i~ oontact wi~h the clectrode, 0 whic~ xoe3~ CampriX3 contaCt~ng~ or mdintain~ng conta~t bet~een, the ~uctive p~lymcr ocmposltlon and the d ectrcde whlle the oonduc~ive polymer oomposition i3 at a te~Feraturc ~$p) ab~ve it~ melting polr.t (Tm) and the electrode is at a t~nperature ~Te~ abcve the m d ting poin~
of the conductive ccn~oo~ition, Tp and Te beinq the same or different, for a time which is sufficient to reduce the oantac~ resis nce between the electrode and the conductive polymer composition but whidh is not sufficient-substanti~lly to reduce the resistivity of the oonductive Folymer. Preferably both Tpa~d Te are at leas~ 20-C, especially at least 55-C, above Tm~ It is often preferable that both Tp and Te 2~ should be above the Ring-and-Ball softening t~mpera e of the polymer.
ocmposition.
Preferably the conductive polymer conposi~ion is subjected to pre5sure to assist m bringing it into c!ose ~onfo~ity with the electrode.
The p¢essure i~ gen ally at lea~t 14 kg/c~2, prefcrably at least 2l.
kg/c~2, for example 21 to 200 hg/cm2, especially at lea~t 35 hg/cm2, e.g. 3S-70 kg/cm2.
-. lZ~6S~7 We ~ave als~ foun~ that the contact resistance c~n be ~rrelated ~th the force ne~ded to pull the elecl.L.~le fmn the Folymer c~ltial. Acc~rd~r~ly the ~nv~elctl further prwide~ ~ deviY
ccn~rising N~ ele~e ~ contac~ ~ith a ~nd~elve polyme~
~ltion, especi~lly a ~tr~ded w~re electrode ~ dded.~n a ccx~ductive polysner ~sieio~n, the pull s~cren3th (P~ of ehe elec~ode fr~m the de,lice beir~ equal t~ at least 1.4 time~ PO, where PO i3 the p~lll stre~th of an ident~c~l elec~cde fml~ a devi~e whieh .~ises ~n idultical elec~de in clt~ct. with an identical conductive p~lymer 0 c~mposi~ and which ha~ pared b~ a pro~ess whi~:h con~ist~ of contacting the el~c~ode, while it is at a temperature not greater than 24e~, w~th the x l~en oonductive polymer oomçosition, an~ allownng t~e polymer coDposition to ~col in contact ~ith the electrode. The pull strengths P and PO are detesmined ~t 21C as describçd in detail below.
A 5.1 cm long sæmple of thc heater strip (or other device), contaLninq a-straight 5.1 cm length of the electrcd~s, i5 cut off. At one end of the samçle, 2~5 cm of the electrcde is stzipped bare of polym OE . rhe bared elect-cde is passed dcwnwardly t.~rough a hole slightly larger than the electrcde in a rigid metal plate fixed in t~e horiDontal plane. The end of the bared electrode is fi~ly clamFed in a mcvable clamp below the plate, and the other end of the sample is lightly cla~ç~d above the plate, so that the electrcde is vertic~l.
m e movable cl~mp i~ then moved vertically dcwnwards at a speed of 5.1 cm~min~, and the pe~k force needed to pull th; conductor ~ut of ~he sample is me~sured.
.. _ _ .. _ _ .. . . _ . . _ . _ . _ ~ . .
lZ-~S~7 Wk h~ve also found that ~or strip heaters, curren ~y the most widely ~lCAd d~vic~s m which current is passed through conductive polymer oompo~it~on~, e~e oontact resi-~tance can be o~rrelated with the linearity ratio, a qu~nt$ty which can re~dily be ~easured as described bel~w. Accordingly th~ 1nventlon ~ur~her provides a strip heatcr oomprising:
(1) an elongatc core o a conductive poly~er comçosition which exhibits ~TC beh~lor, whlch comprise-~ car~on blac*, and in which, if the oontent (L) of carboQ black Ln percent by weight is less.
~han lS, L and the resi~t$vity R o~ the oompo3ition in oh~. om are such that 2~ ~ 5 log10 ~ > 45 ~2) at least tw~ longit~dinally extending electrcoes embedded Ln said composition par~llel to e~ch other: and IS `(3) an out~r layer o~ a protectlve and msulatmg comFo~ition;
the average line~rity ratio (and prefcrably the linearity ratio at 211 points~ betwe~n ~ny pair o~ elect mde~ being at ~ost 1.2, pre~erably at most 1.15, especially at mcst 1.10. m e l m e~rity ratio of a strip heater is defined as Resistance at 30 MV.
Resistance at 100 V.
the resiQtances be mg m~swr~d at 21C between tw~ electrodes which are contacted by prcbe~ push~d thro~yh the outer jacket and the oonductive polymeric sore oS the strip heater. The o~ntact re-~istance i~
neql~gible at 100 V., ~o that the closcr the l~n ity ratio i3 bo 1, the lower the contact re~istance.
The LnVention i~ useful with any txpe of electIode, for exaTçle~plates, strip~ or wires, but particularly so with electrcdes haYiny Dn irregular surfac~, e.g. str nded wire electrcdes as conventionally used ln ~trip hcaters, br~ided wire electrode~ (for examçle a descr~bed ~n Ger~an Offenl q ungschrift No. 2,635,000.5) ~2~6S07 and expar~able elect~de5 as describ~ in Gerrran Off~legungs*~ift No.
2,655,543.1. Preferred ~tranded wire~ are silver-)at~d and nic~
~ated copper w~res, wh1~h are 1e~Q su~tible to difficultie5, such as melt~ or oxidatiotn, than t~coats~ or unc~ted copper wire~, S t~uqh the latter can ~e usad wit~ut difficulty pr~vid~ng the t~at~es ~r~l~d are not too high.
The c~uctive polyn~ c~psitioru ~sed in thi~ ~nves~tion gener~lly c:on~n car~on black a~ the conductive filler~ e.g. in zn~t gre~ter or le53 than 15% by weight, f~r example greater t~an 17% or 20%
by wcight. In many caxs, lt ~ prderr~d that the ca~sitionJ s~ld exhibit ~C behavior. The resistivity of the c~osition i5 generally le~s than 50,000 oh~ at 21-C, for ex ~ le 100 to 50,000 ohm.~n. Fbr strip h~ters designed bo b~ powered by A.C. of 115 ~olts or more, the composition generally ha~ a resis~vity o~ 2,000 to 50,000 ohm.c~, e.g.
2,000 to 40,000 ohm.cm. 5he oomposition 1~ pr~ferably thesmoplastic.
~owever, it may be ligh~ly cro59-linked, or be in the process of being cross,linked, provided that it is sufficiently fluid under the contacting condition to conform closely to the electrode surface.
The polymer is preferably a cry-st lline polymer.
The strip heater~ with which the invention is concerned generally have two electrcde~ separat~d by a distance of O.lS to 1 c~, :-: but gre~ter separations, e.g. up to 2.5 cm. or even more, can be used.
m e o3re of oonductive polymer can be of c~nventional shape, but preferably it has a cros~-sectl~n which is not re than 3 times, especi lly nct re than 1.5 times, e.g. not more than 1.1 times, its smallest dimension, especially a round cross-sect~on.
_7_ lZ~65~7 In one pre~erred embcdiment of the ~nveneion, the electrcde and the polymer composition are hea~ed ~epara~ely ~efore be mg contacted. In this ol~Jlment, it i~ p~eferred that the coTposition should be melt-e~truded cver the electrcde, e.g~ by ~xtrusion around a S pa~r of spaced-apart wire electrodes using a cross-head die. m e el ~ e i3 pre-heated to a t2mperature (Te) which may be greater or les~ than the melt temperab~re of the polymer .~4usition (Tp) bu~ i~
gen ally more than ~Tp-55) and prefer~bly more than (Tp-30). Tp will norm~lly be substanti~lly ab w e the meltlng point of the oomposi~on, tO ~or examçle 30 to 80C abcv~. Of o~urse, nelther the elec ~ ~de nor the ocmp~ition sh2uld b~ he~tod to a t3mp~rature at which ~t undergocs substanti 1 ox~dation or oth degradation.
In another embodiment of the m vention, the coTposition is shaped in contact w~th the elec W e (wnthout pre-heating the electrode) and the elec~rode and the composition are then heated, while in oontac~ wnth each other, to a t~mperature ab~ve the melting ~OLnt of the composition. Care is needed to ensure a useful reduction in the contact resistance by this method. The optimum conditions wlll depend upon the electrode and the ~usitiGn~ but inc~eased ti~e, t~mperablre and pressure help to ac~ieve the desired result. me pressure may be applled for examç~e in a press or by means of nip roller~ is embodiment o~ tbe ~nvention is particularly use~ul when tbc need for, or deeir~bility of, an anneAling treatment does not arise at all, for exam~le, w~hen the ocmposition ha~ a c~rbon blac~ oontent gre~ter than 1~% by weight, e.g. greater than 17% or 20% by weight, or when only a limlted anne ling treatment is carried out, such that at the end of the annealing tbe o~ntent of c~rbon black tL) and the resis~ivity (R) are sucb that 2L + 5 log10 > 45.
one w~y of heatlng the eleotrcde and the ccmposition surr~unding it is to pas~ a high current ~hrough the electrcde and thus produce tbe desired he~t by res~stance heating of thc electrcde.
:12(~65~7 ~n another ~mbodlment Of the invention, the conductive polymer 03mposition is initialiy in the fonm of a shaped article, e.g.
one or xre pill~ or pellet~, whlch ha~ not been 5hyped in contac~ with the electrode, and the electrode an~ the c~l~us~tion are heated bogether under pretsurc, for e ~ o ln a compresslon mould.
. 2~rticularly when the oonductive poly~er oompo d tion exhibits PTC behavior, it ~ often des~rahl~ that Ln the final prcduct the ccmposition sh~uld be crc~-linkod. Cr~3s-linking c~n be carried out as a separate strp after thQ troat~ent b~ reduce oaQtact resistance; in 10- this c~se, cro3s-linking with aid of radla~ion ls preferr~d.
Alternatively crc~rl~nkinq c m be c~rriod out simultan~eously with the said treat~ent, ~n which case che~ical cross-l~nking with the aid of cross-linXing lnitiators such as peroxides is preferred.
me invention is illustrated by th~ foll~ ExamFles, scre of which are canparative E~mple~.
In ea~ of the Example3 a strip heat ~QS prepared as describff~ below The cor~uctive p~lymer ccrnFosition wa5 obtained by blend$ng a ~edi~ den~ity poly~thyl~ne containing ~ antiox$dant wit~
carbon black ma~ter batch ~npr$s$nq an ethsylene,/ethyl aylate c~lymer to giv~ ~ ~5it$0n containing the indicated perc&nt bv weight of ca~on black ¦ ~Ihe m~t~ng po~nt o~ th~ ~os~t~on waa ~out f ~115-6~ me ccmp~$tian wa~ melt-extn~ed at a mclt temperatl~re of aba~t 180-C through a cro~ he~ d$e h~v$ng a circular or~ice 0 36 a~ in diameter over a pair of ~randed ilvcr-coated oopper wires, each w$re having a di m et r of 0.08 cm and o~mpr~inq 19 st:ands, and the a~es of the wires being on a di3meter of the ori ice and 0.2 cm aFart.
Before reaching th~ crosJ-head die, th~ wires were pre-heated by passing th~m through an oven 60 c~ long at 800-C. m e temperature of the wires entering the die w~s 82-C in the comparative EXa~ples 1, 4 and 6, in which the speed of the wires thr3ugh the cven and the die _g_ was 21m/m~, 165-C in Ex~e~ 2 ~ 7 and 193C in E~amples 3 ar~ 5.
me extr~ate wQ.~ then given an insl?lating j~cket by melt-ex~ud~ng aro~d lt ~ layer 0.051 ~n thick of ~lorinat~ F~lyethylene or an ethylene~te~ r~etl~lene copolymer. me coats~ ~xtru~at~ was t~ irr~iated in order to os9-link the c~ ctive polyner cc~sition.
EX~ES 1-3 5hese E~ople~, in which Exa:nE~e 1 is a c~nparative Ex2~21e, domonstrate the inQ uence of ~inearity R~tio (LR) on Pcwer ~utput wh~n the heater is subjected to te~perature changes~ In eadh Ex~mple, tbe Linearity Ratio of the he~t ~as me~sured and the heater wQ~ then oonnected to a 120 volt AC supply and the ambient temperature was changed continuously over a 3 minute cycle, being raised frJR -37-C bo 65C over a pericd of 90 seconds and then reduced to -37C 3gain cver the next 90 seconds.
m e peak power out2ut of the heater du- m~ each cycle ~as measured initi~lly and at interval and expressed as a ~roportion ( ~ ) of the initial peak power output.
m e polymer ccm~vsition used in EXample 1 oontained a~out 25 carb~n black. T~he polymer compwitlon used in E~amçles 2 and 3 contained about 22~ carbon black.
12~651~7 ~he results obt~ined are ~ in Table 1 below.
. of C~cles ~Ec2mple 1 Example 2 Eurr~le 3 PN ~R PN ~R N
None 1 1.3 1 1.1 500 0.5 1.6 1.3 - 1 1 1100 0.3 2~1 1.2 - 1 1 ltOO - - 1.1 1.1 1 1 ~a~arative E~nple E~MP~ 4-7 These E~c~mple~, which are Sumnarised in Table 2 below, da~ns~ate thc effect of pre-heating the ~ec~odes on t!le Linearity Ratio arYI Pull Strength of the produ::t.
~.BLE 2 .
l; E:xample No. ~ Carbon_31ac!c Lirle ~ ~tio ~4 22 1.6 ~2 1.0 *6 23 1.3S
7 23 1.1 20~Ca~arative E~t~nple The r2tio of the pull ~trengt~s of the heater strlps of B~eq 7 and 6 (P/PO) was 1.45.
Claims (36)
1. A process for the manufacture of a device comprising an electrode and a conductive polymer composition in contact therewith, which process comprises (1) heating a conductive polymer composition to a temperature (Tp) above its melting point (Tm);
(2) heating an electrode, out of contact with the conductive polymer composition, to a temperature (Te) above the melting point of the conductive polymer composition, (3) contacting the electrode, while it is at a temperature above Tm, with the molten polymer composition; and (4) cooling the electrode and conductive polymer composition in contact therewith.
(2) heating an electrode, out of contact with the conductive polymer composition, to a temperature (Te) above the melting point of the conductive polymer composition, (3) contacting the electrode, while it is at a temperature above Tm, with the molten polymer composition; and (4) cooling the electrode and conductive polymer composition in contact therewith.
2. A process according to Claim 1 wherein the conductive polymer composition exhibits PTC behavior.
3. A process according to Claim 1 or Claim 2 wherein the polymeric composition is thermoplastic.
4. A process according to Claim 1 wherein T? is at least (Tp-55)°C.
5. A process according to Claim 1 wherein both Tp and Te are at least 20°C above Tm.
6. A process according to Claim 5 wherein both Tp and Te are at least 55°C above Tm.
7. A process according to Claim 1 wherein both Tp and Te are above the Ring-and-Ball softening point of the conductive polymer composition.
8. A process according to Claim 1 wherein the conductive polymer composition is melt-extruded over at least two spaced-apart electrodes.
9. A process according to Claim 8 wherein the conductive polymer composition is extruded over a pair of stranded wire electrodes.
10. A process according to Claim 9 wherein the electrodes are separated by a distance of 0.15 to 1 cm.
11. A process according to any one of Claim 8 to 10 wherein the electrodes are silver-coated copper wires or nickel-coated copper wires.
12. A process according to any one of Claims 8 to 10 wherein the conductive polymer composition is extruded as an extrudate having a cross-section which the largest dimension is not more than 3 times the smallest dimension.
13 13. A process according to Claim 1 wherein the conductive polymer composition exhibits PTC behaviour and has a resistivity at 21°C of 100 to 50,000 ohm. cm.
14. A process according to Claim 1 wherein the conductive polymer composition contains at least 15% by weight of carbon black.
15. A process according to Claim 1 wherein the conductive polymer composition contains carbon black dispersed in a crystalline polymer and exhibits PTC behaviour.
16. A process according to Claim 1 which also comprises the further step of cross-linking the conductive composition.
17. A process according to Claim 16 wherein the cross-linking is effected by irradiation.
18. A strip heater comprising (1) an elongate core of a conductive polymer composition which exhibits PTC behaviour, which comprises carbon black, and in which, if the content (L) of carbon black in percent by weight is less than 15, L and the resistivity (R) of the composition in ohm. cm at room temperature are such that 2L + S log10 R > 45;
(2) at least two longitudinally extending electrodes embedded in said composition parallel to each other; and (3) an outer layer of a protective and insulating composition;
the average linearity ratio between any pair of electrodes being at most 1.2.
(2) at least two longitudinally extending electrodes embedded in said composition parallel to each other; and (3) an outer layer of a protective and insulating composition;
the average linearity ratio between any pair of electrodes being at most 1.2.
19. A strip heater according to Claim 18 wherein the average linearity ratio between any pair of electrodes is at most 1.10.
20. A strip heater according to Claim 18 or 19 wherein the electrodes are silver-coated wires or nickel-costed copper wires.
21. A process for the manufacture of a device comprising at least two electrodes and a conductive polymer composition in contact therewith, which process comprises (1) heating a conductive polymer composition to a tem-perature above its melting point (Tm);
(2) heating at least two electrodes, out of contact with the conductive polymer composition;
(3) melt-extruding the molten conductive polymer com-position from step(1) over the pre-heated electro-des from step(2), the electrodes being at a temperature Te and the conductive polymer being at a temperature Tp when the electrodes and the con-ductive polymer are first contacted with each other; and (4) cooling the electrodes and the conductive polymer composition;
the conditions of the process being such that the electrodes and the conductive polymer composition in contact therewith are at a temperature above Tm for a time which is sufficient to reduce the contact resistance between them and which is less than five minutes.
(2) heating at least two electrodes, out of contact with the conductive polymer composition;
(3) melt-extruding the molten conductive polymer com-position from step(1) over the pre-heated electro-des from step(2), the electrodes being at a temperature Te and the conductive polymer being at a temperature Tp when the electrodes and the con-ductive polymer are first contacted with each other; and (4) cooling the electrodes and the conductive polymer composition;
the conditions of the process being such that the electrodes and the conductive polymer composition in contact therewith are at a temperature above Tm for a time which is sufficient to reduce the contact resistance between them and which is less than five minutes.
22. A process according to Claim 21 wherein Te is at least (Tp-55)°C.
23. A process according to Claim 21 wherein Te is at least (Tp-30)°C.
24. A process according to Claim 21 wherein Te is at least (Tm-25)°C.
25. A process according to Claim 21 wherein Te is greater than 65°C.
26. A process according to Claim 21 wherein Te is greater than 82°C.
27. A process according to Claim 21 wherein Te is at least about 165°C.
28. A process according to Claim 21, 22 or 26 which comprises heating the electrodes and the conductive polymer in contact therewith.
29. A process according to Claim 21, 22 or 26 which comprises heating the electrodes and the conductive polymer in contact therewith by resistance heating of the electrodes.
30. A process according to Claim 21, 22 or 26 which comprises, after step(3), heating the electrodes and the con-ductive polymer in contact therewith, said heating of the electrodes after step(3) being insufficient substantially to reduce the resistivity of at least part of the conductive polymer extrudate.
31. A process according to Claim 21, 22 or 26 which comprises, after step(3), heating the electrodes and the con-ductive polymer in contact therewith, said heating of the electrodes after step(3) being such that, if the same process is carried out without said heating the electrodes after step(3), the resistivity at 21°C of the conductive polymer in the pro-duct is less than 50,000 ohm.cm.
32. A process according to Claim 21, 22 or 26 wherein (a) the conductive polymer comprises carbon black dispersed in a crystalline polymer, and exhibits PTC behavior;
(b) the conductive polymer is melt-extruded over two parallel electrodes; and (c) the process conditions are such that the device which is manufactured is a self-regulating strip heater having an average linearity ratio of at most 1.2.
(b) the conductive polymer is melt-extruded over two parallel electrodes; and (c) the process conditions are such that the device which is manufactured is a self-regulating strip heater having an average linearity ratio of at most 1.2.
33. A process according to Claim 21, 22 or 26 wherein (a) the conductive polymer comprises carbon black dispersed in a crystalline polymer, and exhibits PTC behavior;
(b) the conductive polymer is melt-extruded over two parallel stranded wire electrodes; and (c) the process conditions are such that the device which is manufactured is a self-regulating strip heater having an average linearity ratio of at most 1.1.
(b) the conductive polymer is melt-extruded over two parallel stranded wire electrodes; and (c) the process conditions are such that the device which is manufactured is a self-regulating strip heater having an average linearity ratio of at most 1.1.
34. A process according to Claim 21, 22 or 26 wherein (a) the conductive polymer comprises carbon black dispersed in a crystalline polymer, and exhibits PTC behavior;
(b) the conductive polymer is melt-extruded over two parallel electrodes; and (c) after step(3), the electrodes and the conductive polymer in contact therewith are heated under con-ditions such that the resistivity of at least part of the conductive polymer extrudate is not substantially reduced by said heating of the electrodes after step(3).
(b) the conductive polymer is melt-extruded over two parallel electrodes; and (c) after step(3), the electrodes and the conductive polymer in contact therewith are heated under con-ditions such that the resistivity of at least part of the conductive polymer extrudate is not substantially reduced by said heating of the electrodes after step(3).
35. A process according to Claim 21, 22 or 26 wherein (a) the conductive polymer comprises carbon black dispersed in a crystalline polymer, and exhibits PTC behavior;
(b) the conductive polymer is melt-extruded over two parallel electrodes; and (c) after step(3), the electrodes and the conductive polymer composition in contact therewith are heated under conditions such that, if the same process is carried out without said heating of the electrodes after step(3), the resistivity at 21°C of the conduc-tive polymer in the product is less than 50,000 ohm.cm.
(b) the conductive polymer is melt-extruded over two parallel electrodes; and (c) after step(3), the electrodes and the conductive polymer composition in contact therewith are heated under conditions such that, if the same process is carried out without said heating of the electrodes after step(3), the resistivity at 21°C of the conduc-tive polymer in the product is less than 50,000 ohm.cm.
36. A process according to Claim 21, 22 or 26 wherein (a) the conductive polymer comprises carbon black dispersed in a crystalline polymer, and exhibits PTC behavior;
(b) the conductive polymer is melt-extruded over two parallel electrodes which are at a temperature Te which is greater than Tm when the electrodes and the conductive polymer are first contacted with each other; and (c) the process conditions are such that the device which is manufactured is a self-regulating strip heater having an average linearity ratio of at most 1.2.
(b) the conductive polymer is melt-extruded over two parallel electrodes which are at a temperature Te which is greater than Tm when the electrodes and the conductive polymer are first contacted with each other; and (c) the process conditions are such that the device which is manufactured is a self-regulating strip heater having an average linearity ratio of at most 1.2.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US75014976A | 1976-12-13 | 1976-12-13 | |
| US750,149 | 1976-12-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1206507B true CA1206507B (en) | 1986-06-24 |
Family
ID=25016715
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA292,832A Expired CA1106890A (en) | 1976-12-13 | 1977-12-12 | Electrical devices comprising conductive polymer compositions |
| CA000488467A Expired CA1206507B (en) | 1976-12-13 | 1985-08-09 | Electrical devices comprising conductive polymer compositions |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA292,832A Expired CA1106890A (en) | 1976-12-13 | 1977-12-12 | Electrical devices comprising conductive polymer compositions |
Country Status (10)
| Country | Link |
|---|---|
| JP (4) | JPS6057192B2 (en) |
| AU (1) | AU515034B2 (en) |
| BE (1) | BE861776A (en) |
| CA (2) | CA1106890A (en) |
| DE (1) | DE2755077A1 (en) |
| FR (1) | FR2392572A1 (en) |
| GB (2) | GB1600256A (en) |
| NL (1) | NL185545C (en) |
| NO (1) | NO147735C (en) |
| SE (3) | SE434587B (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4238812A (en) * | 1978-12-01 | 1980-12-09 | Raychem Corporation | Circuit protection devices comprising PTC elements |
| CA1150754A (en) * | 1979-05-10 | 1983-07-26 | George M. Gale | Flexible heating elements and processes for the production thereof |
| CA1156300A (en) * | 1980-04-01 | 1983-11-01 | Gordon S. Carlson | Electric blanket safety circuit |
| US4591700A (en) * | 1980-05-19 | 1986-05-27 | Raychem Corporation | PTC compositions |
| CA1168433A (en) * | 1980-05-19 | 1984-06-05 | Umesh K. Sopory | Ptc conductive polymers and devices comprising them |
| US4309596A (en) * | 1980-06-24 | 1982-01-05 | Sunbeam Corporation | Flexible self-limiting heating cable |
| EP0250776B1 (en) | 1983-06-30 | 1992-06-10 | RAYCHEM CORPORATION (a Delaware corporation) | Method for detecting and obtaining information about changes in variables |
| GB8623082D0 (en) * | 1986-09-25 | 1986-10-29 | Raychem Gmbh | Heated conduit |
| DE4024268A1 (en) * | 1990-07-31 | 1992-02-06 | Lehmann & Voss & Co | Electroconductive plastics element for heater or electronic device - contains synergistic mixt. of carbon or graphite powder and fibres and opt. metal fibres |
| DE4307371A1 (en) * | 1993-03-09 | 1994-09-15 | Hit Hillesheim Innovations Und | Heatable line for a flow medium |
| DE4426188A1 (en) * | 1994-07-23 | 1996-01-25 | Mekra Rangau Plastics | Outside mirrors for motor vehicles |
| CN113635534A (en) * | 2021-08-10 | 2021-11-12 | 芜湖佳宏新材料股份有限公司 | Process method for reducing contact resistance of conductive polymer and metal conductor |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB828334A (en) * | 1956-10-30 | 1960-02-17 | British Insulated Callenders | Improvements in or relating to electrically conductive non-metallic materials |
| US3861029A (en) * | 1972-09-08 | 1975-01-21 | Raychem Corp | Method of making heater cable |
| US3858144A (en) | 1972-12-29 | 1974-12-31 | Raychem Corp | Voltage stress-resistant conductive articles |
| JPS5432173B2 (en) * | 1974-03-29 | 1979-10-12 | ||
| JPS5530669B2 (en) * | 1974-03-29 | 1980-08-12 | ||
| US4177376A (en) * | 1974-09-27 | 1979-12-04 | Raychem Corporation | Layered self-regulating heating article |
| CA1100561A (en) * | 1975-12-08 | 1981-05-05 | Stephen H. Diaz | Apertured deformable laminar heating elements |
-
1977
- 1977-12-07 GB GB50916/77A patent/GB1600256A/en not_active Expired
- 1977-12-07 GB GB26479/80A patent/GB1600257A/en not_active Expired
- 1977-12-09 FR FR7737164A patent/FR2392572A1/en active Granted
- 1977-12-09 AU AU31394/77A patent/AU515034B2/en not_active Expired
- 1977-12-10 DE DE19772755077 patent/DE2755077A1/en active Granted
- 1977-12-12 BE BE183389A patent/BE861776A/en not_active IP Right Cessation
- 1977-12-12 NO NO774258A patent/NO147735C/en unknown
- 1977-12-12 CA CA292,832A patent/CA1106890A/en not_active Expired
- 1977-12-13 SE SE7714126A patent/SE434587B/en not_active IP Right Cessation
- 1977-12-13 NL NL7713800A patent/NL185545C/en not_active IP Right Cessation
- 1977-12-13 JP JP52149792A patent/JPS6057192B2/en not_active Expired
-
1983
- 1983-07-19 SE SE8304042A patent/SE447781B/en not_active IP Right Cessation
-
1985
- 1985-08-09 CA CA000488467A patent/CA1206507B/en not_active Expired
- 1985-10-28 SE SE8505088A patent/SE8505088D0/en not_active Application Discontinuation
-
1989
- 1989-05-22 JP JP1128617A patent/JPH0256887A/en active Granted
- 1989-05-22 JP JP1128616A patent/JPH0256886A/en active Granted
-
1990
- 1990-10-23 JP JP2286933A patent/JPH03257783A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPH03257783A (en) | 1991-11-18 |
| JPH0562439B2 (en) | 1993-09-08 |
| JPS6057192B2 (en) | 1985-12-13 |
| SE8304042D0 (en) | 1983-07-19 |
| AU515034B2 (en) | 1981-03-12 |
| SE7714126L (en) | 1978-06-14 |
| JPH0256886A (en) | 1990-02-26 |
| NO147735C (en) | 1983-06-01 |
| DE2755077A1 (en) | 1978-06-29 |
| GB1600257A (en) | 1981-10-14 |
| AU3139477A (en) | 1979-06-14 |
| SE8505088L (en) | 1985-10-28 |
| NL185545B (en) | 1989-12-01 |
| BE861776A (en) | 1978-06-12 |
| FR2392572A1 (en) | 1978-12-22 |
| SE8505088D0 (en) | 1985-10-28 |
| NO774258L (en) | 1978-06-14 |
| CA1106890A (en) | 1981-08-11 |
| SE434587B (en) | 1984-07-30 |
| GB1600256A (en) | 1981-10-14 |
| NL7713800A (en) | 1978-06-15 |
| JPH053120B2 (en) | 1993-01-14 |
| JPH0559557B2 (en) | 1993-08-31 |
| FR2392572B1 (en) | 1984-03-30 |
| SE447781B (en) | 1986-12-08 |
| DE2755077C2 (en) | 1987-06-11 |
| SE8304042L (en) | 1983-07-19 |
| JPS5395298A (en) | 1978-08-21 |
| NO147735B (en) | 1983-02-21 |
| JPH0256887A (en) | 1990-02-26 |
| NL185545C (en) | 1995-01-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| NARE | Reissued | ||
| MKEX | Expiry |