| Fluoropolymer composition -> Monitor Keywords |
|
|
 
Fluoropolymer compositionRelated Patent Categories: Synthetic Resins Or Natural Rubbers -- Part Of The Class 520 Series, Natural Rubber Compositions Having Nonreactive Materials (dnrm) Other Than: Carbon, Silicon Dioxide, Glass Titanium Dioxide, Water, Hydrocarbon, Halohydrocarbon, Ethylenically Unsaturated Reactant Admixed With A Preformed Reaction Product Derived From: (a) At Least One Polycarboxylic Acid, Ester, Or Anhydride; (b) At Least One Polyhydroxy Compound; And (c) At Least One Fatty Acid Glycerol Ester, Or A Fatty Acid Or Salt Derived From A Naturally Occurring Glyceride, Tall Oil, Or A Tall Oil Fatty Acid, At Least One Solid Polymer Derived From Ethylenic Reactants Only, Polymer Mixture Of Two Or More Solid Polymers Derived From Ethylenically Unsaturated Reactants Only; Or Mixtures Of Said Polymer Mixture With A Chemical Treating Agent; Or Products Or Processes Of Preparing Any Of The Above Mixtures, Solid Polymer Derived From Fluorine-containing Ethylenic ReactantFluoropolymer composition description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070117929, Fluoropolymer composition. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to fluoropolymer compositions of polytetrafluoroethylene and other perfluoropolymers. [0003] 2. Description of Related Art [0004] U.S. 2004/0242783 A1 discloses a blend of tetrafluoroethylene/hexafluoropropylene copolymer, commonly called FEP, and polytetrafluoroethylene (PTFE), the PTFE imparting the improved extrusion property of reduced cone breaks during melt draw down extrusion coating of wire. The PTFE content of the blend is disclosed to be 0.03 to 2 parts by weight based on 100 parts by weight of the copolymer. When the amount of PTFE is more than 2 parts by weight, two disadvantageous results are disclosed: the melt viscosity of the blend increases significantly and the molded article tends to become brittle [0027]. These are the same effects as adding filler to a polymer, except that in the case of adding PTFE to FEP, the disadvantageous effects arise with even small additions of the PTFE to the FEP. SUMMARY OF THE INVENTION [0005] The present invention includes the discovery of melt-fabricable perfluoropolymer compositions containing PTFE in much greater amounts than 2 parts by weight per 100 parts by weight of the perfluoropolymer that have desirable viscosities for melt fabrication and that do not become brittle. According to one embodiment, the present invention is a melt-mixed composition comprising non-melt flowable polytetrafluoroethylene (PTFE) and melt-fabricable perfluoropolymer, said PTFE constituting at least 4 wt % of the combined weight of said PTFE and said melt-fabricable perfluoropolymer, said composition exhibiting thixotropy when being subjected to increasing shear in the molten state. Thus, the compositions of the present invention exhibit reduced melt viscosity at increasing shear rate. Under shear conditions used in melt mixing involved in melt fabrication, the melt viscosity of the composition becomes low enough to enable the compositions to be melt-fabricated, notwithstanding that the PTFE is non melt flowable, i.e. the PTFE has such a high viscosity in the molten state that it does not flow and therefore is not melt-processable. Preferably this thixotropy is characterized by a reduction in melt viscosity upon increasing the shear rate applied to the molten dispersion from about 10 s.sup.-1 to 100 s.sup.-1 that is at least about 10% greater, preferably at least about 100% greater, than the reduction in melt viscosity at the same shear rates for the melt-fabricable perfluoropolymer by itself, as determined by the capillary rheometer method described later herein. The thixotropy imparted to the perfluoropolymer by non-melt flowable PTFE is a surprising result and exists for high contents for the PTFE, e.g. up to about 65 wt % thereof and even up to about 75 wt % thereof, based on the combined weight of the PTFE and the melt-fabricable perfluoropolymer. [0006] The melt-fabricable perfluoropolymer component of the composition of the present invention imparts melt-fabricability to the composition. Thus, the composition is melt-fabricable by such processes as extrusion and injection molding to form strong, tough products. Some indicia of this strength and toughness are the tensile and flexural properties of the composition disclosed herein. [0007] The fact that the composition of the present invention is not brittle is evident from the fact that it exhibits a high elongation at break. Preferably, its elongation at break is at least about 200%, more preferably at least about 250%, at up to at least about 30 wt % PTFE in the composition, based on the combined weight of the PTFE and perfluoropolymer. Most preferably, the composition exhibits an elongation at break that is at least as high as that of the melt-fabricable perfluoropolymer by itself, indicating that the presence of the PTFE is not making the composition brittle. This effect extends well above the 4 wt % PTFE content of the composition, preferably at least to up to about 15 wt % PTFE, based on the combined weight of the PTFE and melt-fabricable perfluoropolymer. The composition of the present invention also exhibits properties indicating that the PTFE in the composition is reinforcing the composition, rather than acting as a filler. For example, both the tensile strength and elongation at break can be greater than for the melt-fabricable perfluoropolymer by itself. Another indicia of the composition of the present invention not being brittle arises from its exhibiting an MIT Flex Life of at least 500 cycles, preferably at least 1000 cycles, i.e. film made from the composition by the MIT Flex Life test procedure is flexed over upon itself repeatedly without breaking. Preferably the MIT flex life of the composition is at least as great as for the perfluoropolymer by itself. The melt-mixed composition of this embodiment of the present invention can be considered as a melt blend of the PTFE and perfluoropolymer components. [0008] According to another embodiment, the present invention is a melt-mixed composition comprising a dispersion of submicrometer-size particles comprising non-melt flowable polytetrafluoroethylene (PTFE) in a continuous phase comprising melt-fabricable perfluoropolymer, said dispersion exhibiting thixotropy when subjected to increasing shear in the molten state. The continuous phase being the melt flowable perfluoropolymer is confirmed by the melt fabricability of the melt mixed composition. Articles molded from the composition are transparent to translucent, rather than opaque as are articles molded from PTFE. [0009] Both the non-brittle and thixotropic attributes described above are believed to arise from this novel dispersion/continuous phase structure, wherein the PTFE is present in such small particle size within the perfluoropolymer continuous phase. This novel structure exists at compositions containing less than 4 wt % PTFE although this is a preferred minimum amount. For example, the melt-mixed dispersion composition can contain as little as about 0.1 wt % PTFE based on the combined weight of the PTFE and perfluoropolymer, and the dispersion structure can exist for amounts of PTFE greater than about 50 wt %, e.g. up to about 65 wt % PTFE and even up to about 75 wt %, based on the combined weight of the PTFE and perfluoropolymer, because of the small size of the PTFE particle. All of the thixotropy, elongation at break, tensile strength, and MIT Flex Life parameters applied to the first mentioned embodiment of the present invention also apply to this embodiment. [0010] The melt-mixed nature of the compositions of the present invention means that it has been preferably heated to the state at which both the PTFE and the perfluoropolymer are molten and then the molten mass is subjected to mixing of the two polymers together, such as may occur in the typical melt fabrication processes of extrusion or injection molding. In the case of extrusion, the extruded, melt-mixed product can be molding pellets for further melt fabrication into final product or final product. Thus, the compositions of the present invention can be in any form such as the molding pellet or final product form formed by melt fabrication process. [0011] It is surprising that compositions of the present invention can contain much more PTFE than 2/100 parts by weight and exhibit the properties described above, denoting melt-fabricability and absence of brittleness. U.S. 2004/0242783 A1 discloses the uses of a multi-screw kneader in an attempt to homogeneously disperse the small amount of PTFE in the FEP [0029] and the use of pre-mixing to improve the degree of dispersion of the PTFE [0042], indicating that the dispersion achieved by the multi-screw kneader by itself is deficient. In Example 1 of '783, powders of the PTFE and copolymer are mixed together, followed by kneading in a twin-screw extruder to produce molding pellets, which are then melt-draw down extruded, using a single screw extruder, as a coating onto wire. The PTFE powder used in the premixing has an average particle size of 450 micrometers. The particle size of the FEP is not disclosed in Example 1, but the aqueous emulsion polymerization to obtain this copolymer is disclosed. This copolymer is recovered from emulsion polymerization by coagulation, which provides a dry powder particles that are agglomerates of the FEP particles of the emulsion. The FEP particles of the emulsion are the primary particles, which are submicrometer-size in average particle size so as to be in the emulsion state. The agglomerates of the primary particles are the secondary particles, which are typically hundreds of time larger in diameter than the primary particles. The 450 micrometer PTFE fine powder particles used in the Example are secondary particles. Thus, in Example 1, secondary particles of the FEP and of the PTFE are pre-mixed before kneading in a twin screw extruder. [0012] The novel structure of the melt-mixed compositions of the present invention, wherein the PTFE is dispersed in a continuous phase of the melt-fabricable perfluoropolymer, is obtained by carrying out the melt mixing on a mixture of submicrometer-size particles of the PTFE and of the melt-fabricable perfluoropolymer. Thus, these polymers are present as a mixture of primary particles, rather than secondary particles. This mixture can be achieved by providing the PTFE primary particle inside the perfluoropolymer particle, i.e. in the form of a core/shell polymer. Alternatively, each of the polymers can be provided in the form of aqueous dispersions, e.g. from the aqueous dispersion polymerization process for making each of them, followed by mixing these dispersions together to form the mixture of primary particles of each polymer. Core/shell polymer is preferred, because of the greater intimacy of the two polymers and the ability of the molten perfluoropolymer to integrate the particles together without needing to overcome the incompatibility between the melt-fabricable perfluoropolymer and the PTFE. Thus, the melt mixing converts the mixture of primary particles that already exists into the composition of the present invention, whether considered as a melt blend or as a dispersion as described above. DETAILED DESCRIPTION OF THE INVENTION [0013] The PTFE and melt-fabricable perfluoropolymer components of the melt-mixed compositions of the present invention will be described individually hereinafter, sometimes with reference to their being supplied to the melt-mixed composition as a core/shell polymer. This description of polymer components, however, also applies to the supply of these polymers to the melt-mixed composition from separate sources, e.g. from the combination of core/shell polymer (PTFE core/perfluoropolymer shell) and separately supplied perfluoropolymer or from separately supplied PTFE and perfluoropolymer. [0014] With respect to the PTFE component, the non-melt flowability of the PTFE can also be characterized by high melt creep viscosity, sometimes called specific melt viscosity, which involves the measurement of the rate of elongation of a molten sliver of PTFE under a known tensile stress for 30 min., as further described in and determined in accordance with U.S. Pat. No. 6,841,594, referring to the specific melt viscosity measurement procedure of U.S. Pat. No. 3,819,594. In this test, the molten sliver made in accordance with the test procedure is maintained under load for 30 min, before the measurement of melt creep viscosity is begun, and this measurement is then made during the next 30 minutes of applied load. The PTFE preferably has a melt creep viscosity of at least about 1.times.10.sup.6 Pas, more preferably at least about 1.times.10.sup.7 Pas, and most preferably at least about 1.times.10.sup.8 Pas, all at 380.degree. C. This temperature is well above the first and second melt temperatures of PTFE of about 343.degree. C. and 327.degree. C., respectively. The difference between non-melt flowability of the PTFE core and the melt flowability of the melt-fabricable perfluoropolymer shell is apparent from the melt flow rate (MFR) test procedure of ASTM D 1238-94a. In this procedure, the MFR is determined by the rate in g/10 min that perfluoropolymer that flows through a defined orifice under a specified load at a specified temperature, usually 372.degree. C. The PTFE used in the present invention has no melt flow (zero MFR). The high melt creep viscosity of the PTFE present in the core of the core/shell polymer also means that the PTFE is sinterable, i.e. a molded article, unsupported by the mold (free-standing), of the PTFE can be heated above the melting point of the PTFE to coalesce the PTFE particles without the molded article flowing to lose its shape. The PTFE used in the present invention is also often characterized by standard specific gravity (SSG), which is the ratio of weight in air of a PTFE specimen prepared in a specified manner to an equal volume of water at 23.degree. C. as further described in U.S. Pat. No. 4,036,802 and ASTM D 4894-94. The lower the SSG, the higher the molecular weight of the PTFE. The specimen preparation procedure as disclosed in ASTM D-4894-94 includes compression molding the test specimen, removing the compression molded test specimen from the mold, and sintering the specimen in air, i.e. free standing, at 380.degree. C. The non-melt flowability of the PTFE enables this sintering to be carried out without the test specimen losing its compression molded shape and dimensions. [0015] The PTFE can be the granular type or the fine powder type, made by suspension or aqueous dispersion polymerization, respectively. The PTFE can be homopolymer of tetrafluoroethylene or a copolymer thereof with a small amount of comonomer, such as hexafluoropropylene or perfluoro(alkyl vinyl ether), preferably wherein the alkyl group contains 1 to 5 carbon atoms, that improves the sinterability of the TFE, to obtain such improvement as reduced permeability and greater flex life, as compared to the TFE homopolymer. This type of PTFE is sometimes referred to as modified PTFE. Examples of modified PTFE are disclosed in U.S. Pat. Nos. 3,142,665, 3,819,594, and 6,870,020. For simplicity and because the modified PTFE exhibits the same non-melt flow, high melt creep viscosity of PTFE homopolymer, this type of PTFE is included in the term polytetrafluoroethylene or PTFE used herein. [0016] The non-melt flowable PTFE used in the present invention is to be distinguished from low molecular weight PTFE, which because of its low molecular weight has melt flowability but not melt-fabricability. This melt flowable PTFE, which has an MFR that is measurable by ASTM D 1238-94a, is obtained by direct polymerization under conditions that prevent very long polymer chains from forming, or by irradiation degradation of non-melt flowable PTFE. Such melt flowable PTFE is commonly called PTFE micropowder. It is not considered as being melt fabricable because the article molded from the melt is useless, by virtue of extreme brittleness. Because of its low molecular weight (relative to non-melt-flowable PTFE), it has no strength. An extruded filament of the PTFE micropowder is so brittle that it breaks upon flexing. [0017] With respect to the melt-fabricable perfluoropolymer component of the melt-mixed composition of the present invention, as indicated by the prefix "per" in perfluoropolymer, the monovalent atoms bonded to the carbon atoms making up the polymer are all fluorine atoms. Other atoms may be present in the polymer end groups, i.e. the groups that terminate the polymer chain. The perfluoropolymer is a perfluoroplastic, not a perfluoroelastomer. [0018] If the non-melt flowable PTFE and melt-fabricable perfluoropolymer is supplied to the melt-mixed composition of the present invention as core/shell polymer, the PTFE forms the core and the perfluoropolymer forms the shell. [0019] The melt flow rate (MFR) of the perfluoropolymers used in the present invention can vary widely, depending on the proportion of PTFE, the melt-fabrication technique desired for the core/shell polymer or melt-mixed composition, as the case may be, and the properties desired in the melt-fabricated article. Thus, MFRs for the melt-fabricable perfluoropolymer can be in the range of about 0.1 to 500 g/10 min, but will usually be preferred as about 0.5 to 100 g/10 min, and more preferably 0.5 to 50 g/10 min., as measured according to ASTM D-1238-94a and following the detailed conditions disclosed in U.S. Pat. No. 4,952,630, at the temperature which is standard for the resin (see for example ASTM D 2116-91a and ASTM D 3307-93 that are applicable to the most common melt-fabricable perfluoropolymers, both specifying 372.degree. C. as the resin melt temperature in the Plastometer.RTM.). The amount of polymer extruded from the Plastometer.RTM. in a measured amount of time is reported in units of g/10 min in accordance with Table 2 of ASTM D 1238-94a. If the perfluoropolymer is present as the shell of core/shell polymer, the MFR of the perfluoropolymer in the shell is determined by carrying out the polymerization of the perfluoromonomers used to form the perfluoropolymer by themselves, i.e. no core, using the same recipe and polymerization conditions used to form the shell, to obtain perfluoropolymer that can be used in the MFR determination. The higher the MFR of the perfluoropolymer, the greater is the tendency to generate smoke when the polymer is subjected to the NFPA-255 burn test, thus failing such test. The shell can have high MFR, e.g. greater than 20 g/10 min without the article melt-fabricated from the core/shell polymer or separately-supplied PTFE and perfluoropolymer components failing the NFPA-255 burn test, because in the presence of the PTFE, the article molded from the melt-mixed composition, notably as dispersed submicrometer-size particles in a perfluoropolymer continuous phase does not flow, and thus, does not drip to cause smoke generation. [0020] Even when the core/shell polymer exhibits an MFR of 0 g/10 min, i.e. there is no flow of the polymer when measured by ASTM D 1238-94a at the temperature that is standard for the melt-fabricable perfluoropolymer, the core/shell polymer can still be melt-fabricable. The thixotropy exhibited by the core/shell polymer and by the mixture of separately supplied PTFE and perfluoropolymer components, as submicrometer-size particles when subjected to the higher shear associated with melt fabrication enables the melt mixing and melt fabrication to occur. [0021] The melt-fabricability of the melt-mixed compositions of the present invention can also be characterized by their melt flowability, which enables the melt fabrication to be carried out. In this regard, these compositions preferably have a melt viscosity of no more than about 5.times.10.sup.5 Pas, more preferably, no more than about 1.times.10.sup.5 Pas, and most preferably, no more than about 5.times.10.sup.4 Pas, all at a shear rate of 100 s.sup.-1 and melt temperature in the range of about 350.degree. C. to 400.degree. C. The determination of melt viscosities disclosed herein, unless otherwise indicated, is by dividing shear stress applied to the polymer melt by shear rate applied to the polymer melt as disclosed on p. 31 of F. N. Cogswell, Polymer Melt Rheology, A Guide for Industrial Practice, published by Woodhead Publishing (1996). As a practical matter, the equivalent melt viscosities are obtained simply by readout from the computer accompanying the rheometer used to determine shear rate and shear stress. The melt viscosity of the melt-fabricable perfluoropolymer by itself is such that the above mentioned melt viscosities for the polymer mixture are obtained. The melt viscosity of the perfluoropolymer component by itself can also be characterized by the above mentioned melt viscosities. Continue reading about Fluoropolymer composition... Full patent description for Fluoropolymer composition Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Fluoropolymer composition patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Fluoropolymer composition or other areas of interest. ### Previous Patent Application: Fluoropolymer blending process Next Patent Application: Rubber-like articles and rubber-like material-containing articles Industry Class: Synthetic resins or natural rubbers -- part of the class 520 series ### FreshPatents.com Support Thank you for viewing the Fluoropolymer composition patent info. IP-related news and info Results in 0.28175 seconds Other interesting Feshpatents.com categories: Computers: Graphics , I/O , Processors , Dyn. Storage , Static Storage , Printers 174 |
 * Protect your Inventions * US Patent Office filing 
PATENT INFO |
|
