Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D39/00—Filtering material for liquid or gaseous fluids
  • B01D39/14—Other self-supporting filtering material ; Other filtering material
  • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
  • B01D39/1692—Other shaped material, e.g. perforated or porous sheets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/30—Polyalkenyl halides
  • B01D71/32—Polyalkenyl halides containing fluorine atoms
  • B01D71/36—Polytetrafluoroethylene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/005—Shaping by stretching, e.g. drawing through a die; Apparatus therefor characterised by the choice of materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2027/00—Use of polyvinylhalogenides or derivatives thereof as moulding material
  • B29K2027/12—Use of polyvinylhalogenides or derivatives thereof as moulding material containing fluorine
  • B29K2027/18—PTFE, i.e. polytetrafluoroethylene, e.g. ePTFE, i.e. expanded polytetrafluoroethylene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
  • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
  • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08J2327/18—Homopolymers or copolymers of tetrafluoroethylene
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K1/00—Printed circuits
  • H05K1/02—Details
  • H05K1/03—Use of materials for the substrate
  • H05K1/0313—Organic insulating material
  • H05K1/032—Organic insulating material consisting of one material
  • H05K1/034—Organic insulating material consisting of one material containing halogen
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249962—Void-containing component has a continuous matrix of fibers only [e.g., porous paper, etc.]
  • Y10T428/249964—Fibers of defined composition
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/249921—Web or sheet containing structurally defined element or component
  • Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
  • Y10T428/249978—Voids specified as micro

Definitions

• This invention relates to the field of expanded i e , stretched, porous polytetrafluoroethylene (ePTFE) membranes having a microstructure of nodes interconnected by fib ⁇ ls More specifically, it is directed to novel structures of microporous ePTFE and to a novel process for prepanng the structures
• U S Patent Nos 3,953,566 and 4, 187,390 were the first U S patents to describe stretching of polytetrafluoroethylene (PTFE) to make microporous ePTFE.
• PTFE polytetrafluoroethylene
• attempts to make highly open elongated nodal structures have been unsuccessful.
• a PTFE extrudate or ePTFE article is simultaneously stretched and sintered. Simultaneous sintering and stretching of an unsintered ePTFE article leads to a highly non-uniform or inconsistent product. Further breakup of nodes and formation of fibrils continues as the unsintered article is stretched. As the article is heated to the point where it becomes amorphously locked the nature of stretching changes, once amorphously locked the nodes will no longer breakup to form new fibrils. When the sintering and stretching steps are occurring simultaneously, slight variations in the temperature and heat transfer can cause large variations in final product properties.
• PTFE can be provided with a filler material in order to modify the properties of PTFE for special applications.
• a filler material for special applications, it is known from U.S. Patent No. 4,949,284 that a ceramic filter (Si0 ) and a limited amount of microglass fibers can be incorporated in a PTFE matenal; and in EP-B-0-463106, titanium dioxide, glass fibers, carbon black, activated carbon and the like are mentioned as filler.
• the ePTFE membranes of this invention are charactenzed as having a mo ⁇ hological structure comprising a microstructure of nodes interconnected by fibrils which form a structural network of voids or pores through the spaces between the nodes and fibrils, which voids or pores extend from one side of the membrane to the other.
• the structure is formed in a novel way so that the nodes are highly elongated, having an aspect ratio of greater than 25:1 , preferably greater than 50:1 and more; preferably greater than 150:1.
• the nodes are aligned in substantially elongated parallel configurations. These aligned elongated nodes are interconnected along their length by a myriad of microfibrils. The result is a se ⁇ es of rib-like rows of nodes, with each row connected by a multitude of fibrils.
• the membranes of the invention generally have a Frazier Number between 5 and 500 and preferably above 50.
• This invention also relates to a process whereby the aforementioned articles are produced in which a polytetrafluoroethylene (PTFE) fine powder resin is blended with a lubricant, formed into a cylindrical preform and paste extruded into the desired shape.
• PTFE polytetrafluoroethylene
• a lubricant ePTFE
• This shape can be calendered between driven rolls to affect the desired thickness.
• Lubricant is removed from the shaped article and then the article is expanded to form microporous expanded PTFE (ePTFE) uniaxially or biaxially at a temperature below the crystalline melt temperature of the PTFE resin, or if a blend or mixture of PTFE resins is used below the crystalline melt temperature of the lowest melting resin.
• ePTFE microporous expanded PTFE
• the expanded article is then heated to a temperature above the crystalline melt temperature of the highest melting PTFE present to amorphously lock the structure.
• the expanded amorphously locked article is then heated to a temperature above the crystalline melting temperature of the highest melting PTFE present and stretched in at least the direction orthogonal to the direction of the first stretch that took place below the melt temperature of the PTFE present.
• Articles of this invention are highly uniform, strong, have low resistance to fluid flow. Articles of this invention are particularly well suited for use in the filtration, electronic product and medical fields.
• Number and Ball Burst is at least 100. Further, the membranes of the present invention possess improved uniformity, optical clarity and handleability.
• the membrane can contain filler material.
• filler material By appropriate choice of filler it is possible to increase various properties, for example, abrasion resistance.
• FIGS 1a and 1b depict the product of the invention produced in Example 1.
• Figure 2 depicts the product of the invention produced in Example 2.
• Figure 3 depicts the product of the invention produced in Example 3.
• Figure 4 depicts the product of the invention produced in Example 4.
• Figure 5 depicts the product of the invention produced in Example 5.
• Figure 6 depicts the product of the invention produced in Example 6.
• Figure 7 depicts the product of the invention produced in Example 7.
• Figure 8 depicts the product of the invention produced in Example 8.
• Figures 9a and 9b depict a product of the invention with 5 percent Al 2 0 3 nanoparticles present as filler taken at 2000 and 3500 fold magnification
• Figures 10a and 10b depict a product of the invention with 5 percent T ⁇ 0 2 nanoparticles present as filler taken at 2000 and 3500 fold magnification
• the compounded resin is formed into a cylind ⁇ cal pellet and paste extruded by known procedure into a desired extrudable shape, preferably a tape or membrane.
• the article can be calendered to the desired thickness between rolls and then thermally dned to remove the lubncant.
• the dned article is expanded in a first stretch in the machine and/or transverse direction according to the teachings of U S Patent 3,953,566 to produce an expanded PTFE structure characte ⁇ zed by a series of nodes which are interconnected by fib ⁇ ls
• the ePTFE article is then amo ⁇ hously locked by heating the article above the crystalline melt point of PTFE (343°C), for example, 343-375°C
• the amo ⁇ hously locked article is then further stretched at a temperature above the crystalline melt point in at least the direction orthogonal to the direction of greatest expansion in the first stretch.
• one paste extruded tape or membrane can be layered with another paste extruded tape or membrane to produce an asymetric composite form of the invention in which the node-fibril microstructure is different on one side as opposed to the other Lamination is achieved by preparing an extrudate of each membrane and rolling down as described further above, and then combining the two membranes into layers, followed by calendering, drying, and the stretching, sintering, and stretching again, all as described further above
• the resulting ePTFE articles are extremely uniform and possess a unique microstructure characterized as having highly elongated nodes interconnected by fibnls
• the resulting articles also have a unique set of physical properties including high strength and low resistance to fluid flow
• the present invention can be used to produce membranes or tapes with a wide range of physical properties It is quite surprising that this novel type of process would produce a highly uniform continuous film, especially with the large node, i e , coarse, microstructures which are possible.
• the present invention allows the creation of open pore membranes and tapes, with low resistance to fluid flow by combining two types of stretching techniques, one before and one after amorphous locking
• Initial expansion in the longitudinal direction is carried out pnor to amorphous locking to set the scale of the microstructure (i e. fib ⁇ l and node dimensions)
• the uniformity of this expanded tape is extremely high.
• This highly uniform microstructure is then amo ⁇ hously locked by heating above the crystalline melting point of the highest melting PTFE present This coalesces the nodes into sections of solid polymer This locking step helps to preserve the uniformity of that initial expansion step.
• the nodes In the final transverse stretching step, when the expanded tape is heated to a temperature above the crystalline melt point of the PTFE resins present, the nodes elongate while the fib ⁇ ls separate. The nodes do not continue to fracture and flb ⁇ llate upon further stretching as occurs in expansions with non-amorphously locked PTFE tapes. Because no additional fib ⁇ llation takes place in this stretch step, very open, high flow, high strength membranes can be produced.
• the stretch above the crystalline melt point of the present invention is much less sensitive to changes in temperature or rate
• the membranes produced by the present invention are much more uniform than traditional expanded PTFE products
• the nodes of this structure are necessarily highly elongated and oriented Aspect ratios on these nodes are greater than about 25 or 50 1 and preferably greater than 150 1
• the present invention provides extremely coarse microstructures where a large percentage of the total mass is retained in the nodes This results in a much higher mass article for a given openness or air flow thus yielding higher strength and durability Mat ⁇ x tensile strength can also be increased by increasing stretch ratio By balancing the first and second stretch steps, a balance in strength in the x and y direction can be obtained
• the PTFE starting material can be any type of coagulated dispersion
• PTFE which lends itself to the formation of fibrils and nodes upon expansion This is generally a polymer of high molecular weight.
• the preferred starting material is a blend of high molecular weight fine powder PTFE homopolymer and a Iower molecular weight modified PTFE polymer This matenal is readily processed to form uniform expanded products with large nodes and long fib ⁇ ls.
• a family of high flow, strong, uniform, handleable membranes can be produced. This family of membranes has in common a combination of physical properties which are not possible by any of the traditional techniques
• the PTFE starting matenal used in the process of the invention can be homopolymer PTFE or a blend of PTFE homopolymers It can also be a blend of homopolymer and a PTFE copolymer in which the comonomer units are not present in amounts which cause the polymer to lose the non-melt- processible charactenstics of pure homopolymer PTFE
• fine powder PTFE is meant that PTFE prepared by the “aqueous dispersion "polyme ⁇ zation technique Both terms are well-known terms in the PTFE art
• the copolymers are called "modified PTFE homopolymers" in the art
• modified PTFE is used here to describe a non-melt-processible polymer which is not a PTFE homopolymer but is a copolymer in which the homopolymer has been modified by copolyme ⁇ sation with a copolyme ⁇ sable ethylenically unsaturated comonomer in a small amount of less than 2% preferably less than 1%, by weight of copolymer
• These copolymers have been called “modified” PTFE by those skilled in the art because presence of comonomer units does not change the basic nonmelt processable character of homopolymer PTFE
• the term 'modified is used to connote that the good toughness, heat resistance and high temperature stability of the homopolymer is not altered when the homopolymer chain is interrupted by smaller trace units of the comonomer
• comonomers include olefins such as ethylene and propylene; halogenated olefins such as hexa
• the homopolymer can also be blended with low molecular weight PTFE known as micropowders, which are made by irradiation of high molecular weight PTFE, or are made by special TFE polymerization
• the homopolymer can also be blended with melt-processible TFE copolymers such as FEP or PFA (hexafluoropropylene/tetrafluoroethylene copolymers or perfluoroalkyl vinyl ether/tetrafluoroethylene copolymer).
• FEP or PFA hexafluoropropylene/tetrafluoroethylene copolymers or perfluoroalkyl vinyl ether/tetrafluoroethylene copolymer.
• Blends of two or more PTFE polymers can be used, as can blends of PTFE with other fluoropolymers No particular preference is made over the ratios of ingredients of these blends.
• One ingredient can be 5% or 95%, by either weight or volume
• even greater openness of structure can be achieved without sac ⁇ ficing uniformity or handleabi ty by carrying out an additional longitudinal stretch after amo ⁇ hous locking but prior to the final transverse stretch.
• the first post amo ⁇ hous locking stretch in the longitudinal direction does little to further break up nodes but does elongate existing fib ⁇ ls and separate existing nodes.
• nodes are separated and fib ⁇ ls lengthened.
• the structure thus created has a significantly larger average effective pore size. This added step does not reduce the overall uniformity of the final article Adding this step greatly increases the total post amorphous locking stretch ratio possible with a given precursor.
• Typical constructions can be stretched to ratios between 9:1 and 12.1 in the transverse direction above 327°C
• total stretch ratios after amo ⁇ hous locking of 24.1 and greater can be achieved.
• Frazier number values have been increased by a factor of 25 while ball burst values decreased by a factor of only 3 when a 4.1 longitudinal stretch after amo ⁇ hous locking was added.
• membranes with unique properties or combinations of properties can be produced.
• Membranes of this invention have a microstructure which can be characterized as having highly elongated nodes with aspect ratios greater than 25 or 50, preferably greater than 150.
• Node shape and orientation can be designed to prevent notch propagation.
• Membranes of this invention are extremely uniform in mass per area, thickness and resistance to fluid flow. Finished membrane properties are insensitive to small changes in temperature during the final stretching operation.
• Uniformity as determined by the coefficient of va ⁇ abiiity of mass per area is less than 11% and preferably less than 8%.
• Membranes with extremely high air flow values can be made which are easily handled and further processed
• Membranes of this invention are characterized as having a unique combination of high air flow and high burst strength. This relationship is shown by the fact that membranes of this invention can have Frazier number air flow values and Ball Burst strength values such that the product of these two values is greater than 60, and preferably greater than 100.
• the membranes of the invention are useful as filters in filtration devices, as scaffolding for holding reactive or conductive fillers, or as support layers in composite constructions.
• the membrane can contain filler matenal, such as carbon black or other conductive filler, catalytic particulate, thermal stability type particulate, and the like.
• the ePTFE structures of the present invention comp ⁇ ses the stretched polytetrafluoroethylene (ePTFE) with a filler of particles in the nanometer size range. These filler particles have a size from 5 to 500 nm, preferably from 10 to 300 nm. They will be referred to for short as
• nanoparticles A number of properties can be enhanced depending on the filler material used. For example, a significant increase in water flow rate can be achieved by incorporating hydrophilic nanoparticles in the structure This enhances use of the membranes of the invention in aqueous filtration. In addition, nanosize ceramic particulate in the filled membranes makes them useful in dialysis cells
• Inorganic filters especially oxides and mixed oxides can be used, e g , oxides of Group 2A, Group 4, as fillers, including those oxides and mixed oxides whose surface is chemically modified
• ferromagnetic properties can be achieved with fillers of this type.
• Materials of this type can be used to shield electrical cables or in circuit boards.
• Preferred examples of ceramic fillers include Al 2 0 3 and Ti0 2
• Other types of useful fillers include, for example, of carbon (graphite) or of metals.
• the mixing of nanosize particles of filler in the PTFE resins occurs prior to addition of lubricant.
• the mixing can occur in general in three different ways, namely by dispersion mixing, dry mixing, or co-coagulation.
• a filler dispersion can be first produced by slowly introducing an oxide, e.g., Ti0 2 , into a lubncant, e.g., Shellsol® product, to which a limited amount of launc acid is added.
• PTFE powder is next introduced to a mixer and the lubricated Ti0 2 slowly metered in.
• a PTFE powder can be mixed with powdered oxide of nanoparticle size in a mixer. The lubncant is then metered into this mixture with launc acid dissolved in it.
• an aqueous dispersion of nanoparticles can be mixed with an aqueous dispersion of PTFE, and the mixture made to coagulate by addition of an electrolyte.
• the water can be separated and the matenal dried. The aforementioned stretching steps of the invention are then employed to obtain filled ePTFE structures.
• Samples were 15 mm wide. Gauge length (distance between clamps) was 50 mm. Samples were pulled at a crosshead speed of 100 mm/min. At 20°C and 65% humidity. Elongation at break and maximum load were recorded.
• SSG the standard specific gravity of the PTFE. SSG may be calculated in accordance with ASTM standards D1457 - 62 T and D727 -
• the data for the particle size of commercially available materials were taken from data sheets of the manufacturer.
• a sample membrane having a 25 mm diameter was obtained and wetted with perfluoropolyether.
• the wetted membrane were placed in a Coulter Porometer wherein the average pore diameter of the final product was determined.
• Air permeability was measured by clamping a test sample in a circular gasketed flanged fixture 5.5 inches in diameter (23.76 square inches in area).
• the upstream side of the sample fixture was connected to a flow meter in line with a source of dry compressed air
• the downstream side of the sample fixture was open to the atmosphere.
• Testing was accomplished by applying an air pressure of 0.5 inches of water to the upstream side of the sample and recording the flow rate of air passing through the in-line fiow meter (a ball-float rotameter).
• Results are reported in terms of Frazier Number which has units of cubic feet/minute/square foot of sample at 0.5 inches of water pressure.
• Air permeability for very high air flow membranes was measured by clamping a test sample in a gasketed flanged 30 cm x 50 cm rectangular fixture. Air flow was adjusted to 480 liters per minute which equates to a face air velocity of 3.2 meters per minute. An electronic manometer was used to measure the pressure drop value across the test sample. This pressure drop value was corrected for slight vanations in air flow by normalizing to exactly 3.2 meters per minute face velocity. The corrected value was recorded as resistance in units of inches of water per 3.2 meters per minute face velocity.
• Node Aspect Ratio A representative sample of membrane is chosen and scanning electron micrographs are prepared of the surface of the specimen. Measurements of node length and corresponding node width are made directly from an appropriate micrograph. No fewer than five such measurements are taken of representative nodes. Aspect ratio is calculated and the values are averaged and reported as Node-Aspect Ratio. Mass per Area
• a high molecular weight PTFE homopolymer, in dispersion form was obtained from E I DuPont de Nemours Co , Inc and combined with the dispersion form of CD090 (a modified PTFE produced by ICI) in amounts such that the resins were combined in a 50/50 ratio based on solids.
• the modified polymer was made mostly of recurring units of tetrafluoroethylene with a very small amount of units of fluo ⁇ nated comonomers A total of 30 pounds of polymer was prepared at a solids concentration of 15% The mixture was coagulated by agitation using a motor dnven impeller After coagulation, the blended resin was separated from the bulk water by filtration and dned in an air oven to remove any remaining water.
• This resin (about 30 pounds) was compounded with 23.37% aliphatic hydrocarbon (boiling range 170 °c - 210 °c) by weight.
• a cylind ⁇ cal pellet was formed and extruded through a rectangular orifice die to form a tape approximately 6 inches wide and 0 028 inch thick This tape was calendered between rolls to give a final thickness of 0 0105 inch
• the extruded, calendered tape was thermally dned to remove lubncant and then expanded in the longitudinal direction 9.1 at 300°C.
• This expanded tape was amo ⁇ hously locked by contacting 365°C heated rolls.
• the amorphously locked tape was stretched in the transverse direction to a ratio of 9 1 1 in an air heated chamber at 375°C running at a line speed of 32.8 ft/mm.
• the finished membrane was continuous, had no breaks or holes, and was extremely uniform Membrane bulk properties are given in Table 1
• the SEM of Figures 1a and 1b depict the final product, shown at different magnifications (50x and 500x).
• Example 2 An extruded calendered down tape prepared as in Example 1 was expanded in the longitudinal direction a total of 5 06 1 at 300°C This tape was amorphously locked by contacting heated rolls at a temperature of 365°C The tape was then stretched in the transverse direction a total of 4 15 1 in an air heated ' chamber at 375°C running at a line speed of 32 8 ft/mm The resulting membrane was continuous with no breaks or holes and was extremely uniform Membrane physical properties are given in Table 1 The SEM of Figure 2 depicts the product
• the blended resin formulation used in Example 1 was compounded with 23.37% aliphatic hydrocarbon and formed into a cylindrical pellet.
• the pellet was extruded through a rectangular orifice die to give a continuous tape 12" wide and 0.030 inch thick.
• This tape was calendered between rollers to give a final thickness of 0.006 inch
• the tape was thermally dried to remove the aliphatic hydrocarbon and then was expanded in the longitudinal direction in a heated chamber at 300°C to a ratio of 8: 1.
• the expanded tape was amorphously locked by heating in 360°C air.
• the amorphously locked tape was further stretched in the longitudinal direction in a heated chamber at 360°C to an a additional ratio of 4:1.
• the tape was then stretched in a 375°C heated chamber in the transverse direction at a line speed of 32.8 ft. per minute to a ratio of 5.6:1.
• the resulting membrane was uniform, free of holes or breaks and was visually translucent.
• Membrane physical properties are listed in Table 1.
• the SEM of Figure 3 depicts the product.
• Example 4 The blended resin used in Example 1 was compounded with 23.37% aliphatic hydrocarbon and formed into a cylindrical pellet.
• the pellet was extruded through a rectangular orifice die to give a continuous tape 6 inches wide and 0.027 inch thick.
• the extruded tape was calendered between rollers to give a final thickness of 0.006 inch.
• the tape was thermally dned to remove the aliphatic hydrocarbon and then was expanded in the longitudinal direction a ratio of 6.25.1 at 300°C.
• the expanded tape was amo ⁇ hously locked by contacting heated rolls at 370°C.
• the locked tape was stretched an additional ratio of 4 1 in the longitudinal direction at 375°C at a line speed of 20 ft/mm.
• the pellet was extruded through a rectangular orifice die to form a tape 6 inches wide and 0 027 inch thick
• the tape was calendered between rolls to give a final thickness of 0 006 inch
• the tape was thermally dried to remove lubricant and then was expanded in the longitudinal direction at 300°C and a line speed of 10 ft/mm to a total ratio of 5.06 1 the expanded tape was amorphously locked by contacting heated rolls at 370°C
• the amorphously locked tape was stretched in the transverse direction to a ratio of 6 56 1 in a 375°C heated chamber at a line speed of 32.8 ft/min.
• the resulting membrane was extremely uniform, very strong and free of holes or breaks Membrane physical properties are listed in Table 1
• the SEM of the product is shown in Figure
• the tape was calendered between rolls to give a final thickness of 0.0105 inch.
• the tape was thermally dried to remove lubncant and then was expanded in the longitudinal direction at 300°C and a line speed of 10 ft./min. to a total ratio of 9:1.
• the expanded tape was amorphously locked by contacting heated rolls at 370°C
• the amorphously locked tape was stretched in the transverse direction a total ratio of 7 13 1 in a 375°C heated chamber at a line speed of 32 8 ft /mm
• the resulting membrane was extremely uniform, very strong and free of holes or breaks Five sections of this membrane were taken along its length at roughly 15 ft intervals.
• Standard Deviation X 100 % Coefficient of Variability (%CV)
• % coefficient of variability is used here as a measure of overall uniformity of the membrane with respect to the specific property measured. Average, standard deviation and % coefficient of variability for each of the three properties measured are listed below:
• Example 7 A high molecular weight PTFE emulsion polyme ⁇ sate (molecular weight >
• the extruded, rolled down tape was thermally dried to remove lubricant and then expanded in the longitudinal direction 4 1 at 235°C
• This expanded tape was amorphously locked by contacting 361 °C heated rolls
• the tape was running at a line speed of 43 m/min
• the amorphously locked tape was stretched in the transverse direction at a total ratio of 10 0 1 in a 355°C heated chamber at a line speed of 20 m/min
• Membrane bulk properties are given in Table 2
• the SEM of Figure 6 depicts the final product shown at magnifications of 2000x
• Example 8 A high molecular weight PTFE emulsion polyme ⁇ sate (molecular weight >
• the amorphously locked tape was stretched in the transverse direction at a total ratio of 10.0:1 in a 355°C heated chamber at a line speed of 20 m/min.
• Membrane bulk properties are given in Table 2.
• the SEM of Figure 8 depicts the final product, shown at magnifications of 2000.
• Example 11 The lubricant was removed thermally. For this pu ⁇ ose the film was passed over heated rolls (240 ⁇ C - 250 ⁇ C) after the calendering step. The film was then stretched in the machine direction, and then in the transverse direction, at 240°C (200%/s) and sintered at temperatures greater than 330 ⁇ C. This film was then stretched pe ⁇ endicular to the machine direction (transverse) at a temperature above the crystalline melt point. The draw ratio was 10:1.
• Example 10 The same procedure for Example 10 was followed to produce a filled tape that contained titanium oxide (R-320 from Hombitan) instead of 600 g aluminum oxide. This film was then stretched two-fold perpendicularly to the machine (transverse) direction at a temperature above the crystalline melt point The draw ratio was 10 1 and for Example 11 2 4 (see Table 3), the draw ratio was 5 1
• Figures 9A and 9B show ePTFE membranes of the invention at different magnification (200x and 3500x), but with a nanoparticle filler, namely 5% Al 2 0 3 , produced according to Example 10.

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• 1996
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