Source: http://www.google.com/patents/US4859836?dq=6,959,293
Timestamp: 2014-09-16 12:26:37
Document Index: 199089121

Matched Legal Cases: ['Application No. 38', 'Application No. 38', 'Application No. 38', 'Application No. 38', 'Application No. 2', 'Application No. 63', 'Application No. 67', 'Application No. 74', 'Application No. 128', 'Application No. 119', 'Application No. 84304502', 'Application No. 84305584', 'Application No. 84306456', 'Application No. 8407984']

Patent US4859836 - Melt-shapeable fluoropolymer compositions - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsMelt-shapeable polymeric compositions comprising a first fluoropolymer of relatively low crystallinity, e.g. a copolymer of tetrafluoroethylene and a perfluorinated comonomer, and a second fluoropolymer of relatively high crystallinity, especially a fluoropolymer obtained by irradiating PTFE or another...http://www.google.com/patents/US4859836?utm_source=gb-gplus-sharePatent US4859836 - Melt-shapeable fluoropolymer compositionsAdvanced Patent SearchPublication numberUS4859836 APublication typeGrantApplication numberUS 06/896,549Publication dateAug 22, 1989Filing dateAug 14, 1986Priority dateOct 7, 1983Fee statusPaidPublication number06896549, 896549, US 4859836 A, US 4859836A, US-A-4859836, US4859836 A, US4859836AInventorsHans E. Lunk, Donald A. Reed, Marguerite E. Deep, Charles Hill, Andrew AuOriginal AssigneeRaychem CorporationExport CitationBiBTeX, EndNote, RefManPatent Citations (10), Referenced by (49), Classifications (22), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetMelt-shapeable fluoropolymer compositionsUS 4859836 AAbstract Melt-shapeable polymeric compositions comprising a first fluoropolymer of relatively low crystallinity, e.g. a copolymer of tetrafluoroethylene and a perfluorinated comonomer, and a second fluoropolymer of relatively high crystallinity, especially a fluoropolymer obtained by irradiating PTFE or another fluoropolymer which cannot be melt-shaped in the absence of other polymers. The weight ratio of the first to the second polymer is preferably 0.3:1 to 2.5:1. The compositions have a wide variety of uses, for example as insulating materials or, if they contain carbon black or another conductive filler, as PTC conductive polymers.
We claim: 1. An electrical device which comprises(1) a melt-shaped conductive polymer element which comprises a polymeric component and, dispersed therein, a particulate conductive filler, said polymeric component comprising a mixture of (A) a first fluoropolymer which has a crystallinity of less than 45% and which can be melt-shaped in the absence of other polymers, and (B) a second crystalline fluoropolymer which is polytetrafluoroethylene and which has a crystallinity of at least 50%, and (2) at least two electrodes which can be connected to a source of electrical power and which, when so connected, cause current to flow through the conductive polymer element. 2. A device according to claim 1 wherein the conductive polymer element exhibits PTC behavior.
3. A device according to claim 2 wherein the conductive polymer element has a resistivity at 23� C. of 1 to 106 ohm.cm and comprises a carbon black having a particle size D of 20 to 150 millimicrons and a surface area S in m2 /gram such that S/D is not more than 10.
4. A device according to claim 3 wherein the device is a circuit protection device having a resistance of less than 100 ohms and the conductive polymer element has a resistivity of less than 100 ohm.cm.
5. A device according to claim 2 wherein the first fluoropolymer has a melt viscosity at 380� C. of 5�103 to 1�106 poise, and the second fluoropolymer has a melt viscosity at 380� C. of less than 106 poise and the ratio by weight of the first fluoropolymer to the second fluoropolymer is from 0.3:1 to 5:1.
6. A device according to claim 2 wherein the polymeric component comprises a mixture of(1) a tetrafluoroethylene copolymer which is selected from (a) copolymers of tetrafluoroethylene and hexafluoropropylene and (b) copolymers of tetrafluoroethylene and a perfluorinated vinyl ether, and (2) polytetrafluoroethylene which has been irradiated to a dose of 5 to 30 Mrad, the ratio by weight of polymer (1) to polymer (2) being from 0.3:1 to 5:1. 7. A device according to claim 1, wherein the first and second fluoropolymers constitute at least 85% by weight of the polymeric component.
8. A device according to claim 1, wherein the polytetrafluoroethylene has been irradiated to a dose of 2.5 to 40 Mrad.
CROSS REFERENCE TO RELATED APPLICATION This application is a divisional of Application Ser. No. 720,119 filed Apr. 4, 1985, now U.S. Pat. No. 4,624,990, which is a continuation-in-part of Application Ser. No. 539,871, filed Oct. 7, 1983, now abandoned, by Lunk and Reed. The entire disclosure of those applications are incorporated herein by reference.
This invention relates to polymeric compositions comprising fluoropolyers.
Conductive polymer compositions, including such compositions exhibiting PTC behavior, and electrical devices comprising them, are well known. Reference may be made, for example, to U.S. Pat. Nos. 2,952,761; 2,978,665; 3,243,753; 3,351,882; 3,571,777; 3,757,086; 3,793,716; 3,823,217; 3,858,144; 3,861,029; 3,950,604; 4,017,715; 4,072,848; 4,085,286; 4,117,312; 4,177,376; 4,177,446; 4,188,276; 4,237,441; 4,242,573; 4,246,468; 4,250,400; 4,252,692, 4,255,698, 4,271,350, 4,272,471, 4,304,987, 4,309,596, 4,309,597, 4,314,230, 4,314,231, 4,315,237, 4,317,027, 4,318,881, 4,327,351, 4,330,704, 4,334,351, 4,352,083, 4,388,607, 4,398,084, 4,413,301, 4,425,397, 4,426,339, 4,426,633, 4,427,877, 4,435,639, 4,429,216, 4,442,139; 4,459,473, 4,481,498, 4,473,450, and 4,502,929; J. Applied Polymer Science 19, 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-653 (1978), Narkis et al; and commonly assigned U.S. Ser. Nos. 601,424 now abandoned, published as German OLS No. 1,634,999; 732,792 (Van Konynenburg et al), now abandoned, published as German OLS No. 2,746,602; 798,154 (Horsma et al), now abandoned, published as German OLS No. 2,821,799; 134,354 (Lutz); 141,984 (Gotcher et al), published as European Application No. 38,718; 141,988 (Fouts et al), published as European Application No. 38,718,141,989 (Evans), published as European Application No. 38,713, 141,991 (Fouts et al), published as European Application No. 38,714, 150,909 (Sopory), published as UK Application No. 2,076,106A, 184,647 (Lutz), 250,491 (Jacobs et al) published as European Application No. 63,440, 272,854 and 403,203 (Stewart et al), published as European Patent Application No. 67,679, 274,010 (Walty et al), 300,709 and 423,589 (Van Konynenburg et al), published as European Application No. 74,281, 369,309 (Midgley et al), 483,633 (Wasley), 493,445 (Chazan et al), published as European Application No. 128,664, 606,033 (Leary et al), published as European Application No. 119,807, 509,897, 598,048, 603,485 and 618,109 (Masia et al), published as European Application No. 84304502.2, 524,482 (Tomlinson et al), published as European Application No. 84305584.9, 534,913 (McKinley), 535,449 (Cheng et al) published as European Application No. 84306456.9, 552,649 (Jensen et al), published as European Application No. 8407984.9, 573,099 (Batliwalla et al), 904,736, published as UK Patent Nos. 1,470,502 and 1,470,503, 628,945 (Carlomagno), 650,918, 650,919, 650,920 and 663,014 (Batliwalla et al), and in the commonly assigned patent applications filed Mar. 14, 1985, by Ratell, Ser. Nos. 711,908 filed on Mar. 14, 1985, now U.S. Pat. No. 4,647,896 and 711,907 filed on Mar. 14, 1985 now U.S. Pat. No. 4,647,894 (MP1016 and MP1021), Carlomagno, Ser. No. 711,790 filed on Mar. 14, 1985, now U.S. Pat. No. 4,685,025 (MP0991), Au et al, Ser. No. 711,910 filed on Mar. 14, 1985, now U.S. Pat. No. 4,724,417 (MP1044), Deep et al, Ser. No. 711,909 filed on Mar. 14, 1985, now U.S. Pat. No. 4,774,024 (MP1022). The disclosure of each of the patents, publications and applications referred to above is incorporated herein by reference.
SUMMARY OF THE INVENTION We have now discovered a way of utilizing many of the excellent properties of highly crystalline fluoropolymers in compositions which can be melt-shaped. In particular, we have found that it is possible to obtain melt-shapeable compositions by mixing two fluoropolymers, the first having a crystallinity of less than 45% and being melt-shapeable in the absence of other polymers (e.g. a copolymer of tetrafluoroethylene and hexafluoropropylene or a perfluorinated vinyl ether), and the second fluroropolymer having a crystallinity of at least 50% (e.g. irradiated PTFE); and that products obtained by melt-shaping such compositions have a valuable combination of properties derived from both fluoropolymers. Thus, the shaped products have tensile and elongation values which are at least adequate for many purposes, coupled with other valuable properties such as elevated melting point and low loss tangent.
In one aspect, the present invention provides a composition which can be melt-shaped and which comprises a mixture of a first fluoropolymer which has a crystallinity of less than 45% and which can be melt-shaped in the absence of other polymers, and a second cyrstalline fluoropolymer which has a crystallinity of at least 50%.
BRIEF DESCRIPTION OF THE DRAWING The invention is illustrated in the accompanying drawings in which the FIGURE shows the resistivity/temperature characteristics of various compositions of the invention and of the prior art.
The first fluoropolymer is preferably a crystalline fluoropolymer, particularly a perfluoropolymer, which can be melt-shaped in the absence of other polymers. Thus the first fluoropolymer will generally have a melt viscosity at 380� C. of less than 106 poise, preferably less than 105 poise, particularly less than 5�104 poise. The lower the melt viscosity, the easier the composition is to process, but (in general) the less desirble the properties of the final product. Accordingly, the melt viscosity of the first fluoropolymer is generally at least 103 poise, particularly at least 1�104 poise, especially at least 2�104 poise. The first fluoropolymer is generally a homopolymer or copolymer of one or more fluorine containing olefinically unsaturated monomers, or a copolymer of one or more fluorine-containing olefinically unsaturated monomers and one or more olefins. The first fluoropolymer has a melting point of at least 150� C., often at least 250� C., e.g. up to 350� C., the melting point being defined as the temperature above which no crystallinity exists in the polymer (or when a mixture of crystalline polymers is used, in the major crystalline component in the mixture). Particularly preferred first fluoropolymers are copolymers of tetrafluoroethylene with one or more perfluorinated monomers, e.g. hexafluoropropylene or a perfluorinated vinyl ether; such copolymers are preferably perfluoropolymers but can contain small proportions of units derived from monomers which are only partially substituted by fluorine or which are free from fluorine. Commercially available fluoropolymers of this type include those sold by E.I. du Pont de Nemours under the trade names FEP-100, FEP-160, and PFA, such as those sold under the trade name PFA-340 AND PFA-350. Other polymers which can be used as the first fluoropolymer include copolymers of ethylene and tetrafluoroethylene and optionally one or more other comonomers (known as ETFE polymers), e.g. a copolymer comprising 35 to 60 mole percent of ethylene, 35 to 60 mole percent of tetrafluoroethylene and up to 10 mole percent of one or more other comonomers; copolymers of ethylene and chlorotrifluoroethylene; polyvinylidene fluoride; and copolymers of vinylidene fluoride with one or both of hexafluoropropylene and tetrafluoroethylene, or with hexafluoroisobutylene.
The invention is of particular value when the second fluoropolymer has been obtained by irradiating (e.g. with an electron beam) a fluoropolymer which, prior to irradiation, had a melt viscosity at least 3 times, preferably at least 10 times, particularly at least 100 times, that of the first fluoropolymer (the difference can be very much larger, e.g. by a factor of the order to 105 or more). The second fluoropolymer can be (prior to irradiation) a melt-shapeable polymer, but the invention is particularly useful when the second polymer is one which, prior to irradiation, could not be melt-processed under practical conditions, because the invention makes it possible to utilize at least some of the valuable properties of such polymers while yet retaining the enormous advantages of melt-processing. Preferred second fluoropolymers are polymers of tetrafluoroethylene, in particular polytetrafluoroethylene (PTFE), for example that commercially available under the trade name Teflon from E.I. du Pont de Nemours. Surprisingly, the presence of the irradiated polymer does not have a substantial adverse effect on the processing characteristics of the first polymer, and can indeed substantially improve those characteristics. Thus the novel compositions have a melt viscosity which is preferably less than 1 time, especially less than 0.5 time, the melt viscosity of the first fluoropolymer. The irradiation will generally be carried out in the substantial absence of any radiation cross-linking agent, so that the predominant effect of the radiation is to degrade the fluoropolymer to a lower molecular weight, more brittle material. The radiation dose is preferably 2.5 to 40 Mrad, particularly 5 to 30 Mrad. The second fluoropolymer can be in the form of granules or any other form when it is irradiated.
The relative amounts of the first and second fluoropolymers can vary widely, depending primarily on the desired final product. Thus te ratio by weight of the first to the second fluoropolymer can be from 0.05:1 to 20:1. For many end uses, the preferred ratio is 0.3:1 to 2.5:1, particularly 0.3:1 to 1:1, e.g. 0.4:1 to 0.6:1. For many other end uses, particularly where the fluoropolymer composition comprises a conductive filler, the preferred ratio is 0.3:1 to 5:1, particularly 1:1 to 4:1, e.g. 2.5 to 1 to 3.5 to 1. The polymers can be blended in any convenient way, for example by physical blending of the polymers in the form of granules.
Particularly useful compositions are electrically conductive compositions which comprise a dispersion of one or more particulate conductive fillers, especially carbon black, in the mixture of first and second fluoropolymers. The electrical characteristics of such compositions depend upon the amount and type of the filler, and by following the teaching of the documents incorporated herein, by reference, a wide range of useful compositions can be obtained. Preferred compositions exhibit PTC behavior, and in such compositions the conductive filler preferably comprises a carbon black having a particle size D of 20 to 150 millimicrons and a surface area S in m2 /gram such that S/D is not more than 10. The carbon black is preferably the sole conductive filler, but it can be mixed with another carbon black or other conductive filler, which preferably constitutes not more than 30%, particularly not more than 10%, by weight of the total conductive filler. Preferably the quantity ##EQU1## is less than 1, where the filler component is the total of conductive and (if present) non-conductive fillers. The resistivity of the preferred PTC compositions at 23� C. depends upon the devices in which they are to be used, but is generally from 1 to 106 ohm.cm, e.g. 1 to 100 ohm.cm for circuit protection devices and 100 to 105 ohm.cm for self-limiting heaters, depending on the supply voltage. For further details of conductive fillers for use in the novel compositions and of devices in which such compositions can be employed, reference should be made to the documents incorporated herein by reference. The PTC compositions of the invention are particularly useful because they exhibit a very useful combination of good physical properties at high temperatures and good PTC behavior with a high switching temperature. This combination is useful for example in heaters and protection devices to be used in vehicles, e.g. in electrical harnessing systems for automobiles. For example in mixtures of PFA and irradiated PTFE, the PTFE greatly enhances the crystallinity (e.g. from about 26% to about 36 %) and increases the height of the PTC anomaly (e.g. from about 5 decades to greated than 7 decades).
The composition can be melt-shaped in any convenient way, including molding and melt-extrusion, which is generally preferred. The composition can be electrically conductive, as discussed above, or it can be electrically insulating, in which case it can provide the sole insulation over an electrical component, or it can provide one of two or more insulating jackets. The composition can be formed as part of the shaping operation, and this is particularly desirable when it is to provide insulation having low loss at high frequencies, for example the insulation in a coaxial cable transmitting high frequency electro-magnetic energy.
EXAMPLES 1-10 Examples 1-10, in which Examples 1-5 are comparative Examples, are summarized in Table 1 below, the tensile strengths and elongations reported in the Table were measured by pulling a cylindrical rod in an Instron Tensile Testing Machine using an elongation rate of 2 inches/minute. The irradiated PTFE's were too brittle for their tensile strengths and elongations to be measured.
The crystallinities reported in the Table are calculated from measured heates of fusion, using a value of 22.2 calories/gram for 100% crystalline polymer.
The blends were prepared by dry-mixing the components, followed by melt-blending in a counter-rotating twin-screw extruder. Cylindrical rods for tensile testing were melt-shaped from the blends (or from the individual polymers) by extrusion through a cylindrical die at 380� C..
TABLE 1__________________________________________________________________________        Viscosity             Loss Tangent                    Tensile                        Elongation                              Tm (�C.)                                   CrystallinityExample No.  (poise)             (� 104)                    (psi)                        %     �C.                                   %__________________________________________________________________________  FEP-160    3.7 � 104             6.5    3000                        300   268  11  PFA-350    5.0 � 104             11.0   4000                        300   310  20  PTFE (10 MR)        2.3 � 104             --     0   0     338  65  PTFE (20 MR)        3.1 � 103             --     0   0     339  67  PTFE (30 MR)        1.4 � 103             --     0   0     333  67  50% PTFE (10 MR)        3.6 � 104             6.2    1990                        45    330  29  50% FEP-160  50% PTFE (20 MR)        2.6 � 104             6.2    2250                        125   329  27  50% FEP-160  50% PTFE (30 MR)        2.3 � 104             7.5    2098                        225   329  27  50% FEP-160  66% PTFE (30 MR)        8.7 � 103             5.9    1994                        92    325  45  34% FEP-16010.  40% PTFE (30 MR)        2.5 � 104             --     3100                        370   322  30  60% PFA-350__________________________________________________________________________
EXAMPLES 11-14 Examples 11-14, in which Examples 11 and 12 are comparative Examples, are summarized in Table 2 below. The ingredients (and amounts thereof) listed in Table 2 were dried and mixed by adding the fillers to the molten polymer in a Brabender mixer. The mixture was cooled, granualted and compression molded into plaques, from which 1 by 1.5 inch samples were cut. Silver electrodes were painted onto the ends of the samples, and the resistance/temperature characteristics were determined by measuring the resistance of the samples as they were externally heated from 0� to 400� C. at a rate of 3.9� C./minute. The resistivities of the compositions were then calculated, and the results are presented graphically in the Figure, in which the flat portion at the top of one of the curves is produced by the maximum resistance which could be measured by the test apparatus.
TABLE 2__________________________________________________________________________                   Volume %Example         Manufacturer                   11 12 13  14__________________________________________________________________________PFA Teflon PFA 340J           Du Pont 68.0  51.0FEP Teflon FEP 100           Du Pont    66.0   49.5PTFE (40 MR) Teflon PTFE 7A           Du Pont       17.0                             16.5Carbon Black Statex G           Columbian                   27.0                      29.0                         27.0                             29.0           ChemicalsZnO Kadox 15    Gulf &amp; Western                   4.0                      4.0                         4.0 4.0Triallyl Isocyanurate   1.0                      1.0                         1.0 1.0Resistivity at 23� C. (ohm � cm)                   3.72                      3.38                         3.12                             2.64PTC anomaly height (decades)                   4.99                      3.50                         &gt;7.48                             4.63% Crystallinity         26.6                      11.2                         35.8                             24.3__________________________________________________________________________
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