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
• • 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
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
  • A61F2/02—Prostheses implantable into the body
  • A61F2/28—Bones
• • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/001—Combinations of extrusion moulding with other shaping operations
  • B29C48/0018—Combinations of extrusion moulding with other shaping operations combined with shaping by orienting, stretching or shrinking, e.g. film blowing
• • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
  • B29C48/06—Rod-shaped
• • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
  • B29C48/07—Flat, e.g. panels
  • B29C48/08—Flat, e.g. panels flexible, e.g. films
• • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/88—Thermal treatment of the stream of extruded material, e.g. cooling
  • B29C48/911—Cooling
  • B29C48/9135—Cooling of flat articles, e.g. using specially adapted supporting means
• • 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
• • 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
  • C08J5/20—Manufacture of shaped structures of ion-exchange resins
  • C08J5/22—Films, membranes or diaphragms
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/10—Materials in mouldable or extrudable form for sealing or packing joints or covers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B5/00—Non-insulated conductors or conductive bodies characterised by their form
  • H01B5/16—Non-insulated conductors or conductive bodies characterised by their form comprising conductive material in insulating or poorly conductive material, e.g. conductive rubber
• • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/30—Extrusion nozzles or dies
  • B29C48/305—Extrusion nozzles or dies having a wide opening, e.g. for forming sheets
• • 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
  • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
  • B29C48/25—Component parts, details or accessories; Auxiliary operations
  • B29C48/88—Thermal treatment of the stream of extruded material, e.g. cooling
  • B29C48/911—Cooling
  • B29C48/9135—Cooling of flat articles, e.g. using specially adapted supporting means
  • B29C48/9175—Cooling of flat articles, e.g. using specially adapted supporting means by interposing a fluid layer between the supporting means and the flat article
• • 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. polytetrafluorethene, e.g. ePTFE, i.e. expanded polytetrafluorethene
• • 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
  • B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
  • B29K2105/04—Condition, form or state of moulded material or of the material to be shaped cellular or porous
• • 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
• • 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.]

Definitions

• the present invention relates to an expanded porous polytetrafluoroethylene film having elastic recovery property in a thickness-wise direction of the film, a production process thereof, and use of the porous film for various applications.
• the expanded porous polytetrafluoroethylene film according to the present invention can be suitably used as cushioning materials, sealing materials, semiconductor-packaging members, members for inspection of semiconductors, medical implanting material, and the like making good use of its properties such as heat resistance, chemical resistance and elastic recovery property.
• An expanded porous polytetrafluoroethylene material produced by stretching of polytetrafluoroethylene (hereinafter abbreviated as “PTFE”) has a microstructure composed of a great number of fibrils (fine fibers) and a great number of nodes connected to each other by the fibrils, and this microstructure forms a porous structure of open-cell property.
• PTFE polytetrafluoroethylene
• its porous structures such as a pore diameter and a porosity can be optionally preset by controlling stretching conditions.
• the expanded porous PTFE material has the porous structure, properties such as flexibility, fluid permeability, fine particle-collecting property, filterability, low dielectric constant and low dielectric loss tangent are imparted thereto, in addition to properties such as heat resistance and chemical resistance, and surface properties such as low frictional coefficient, water repellency and non-blocking property that PTFE itself has. Since the expanded porous PTFE material has such unique properties, its applications to general industrial field and medical field, and the like enlarge. In the medical field, the expanded porous PTFE material is a material optimum for applications that directly touch intracorporeal tissues because it has properties such as chemical stability, non-toxicity to vital bodies, non-degradability and anti-thrombus property.
• the PTFE itself forming the expanded porous PTFE film is a resin that is hard and brittle.
• the expanded porous PTFE material has good flexibility because it has the porous structure. Therefore, the expanded porous PTFE material is commonly used as cushioning materials, sealing materials and spacers. Since the expanded porous PTFE material is allowed to flexibly change its form conforming to forms of various intracorporeal tissues, or the like, it is used as medical polymeric materials such as patch materials, artificial blood vessels, catheters and artificial substitutive materials for cartilages as porous materials having a structure of a sheet or tube.
• the expanded porous PTFE material is generally produced in the form of a tube, sheet (including a film), monofilament or the like.
• a sheet-like expanded porous PTFE film is commonly used for applications such as cushioning materials and sealing materials.
• the expanded porous PTFE film is obtained by not only forming a sheet from the beginning, but also forming a tube and longitudinally cutting the tube in the form of a sheet. It is also conducted to form tubes or various kinds of structures with the expanded porous PTFE film.
• a tube can be formed by winding the expanded porous PTFE film on an outer peripheral surface of a rod-like support and fusion-bonding or adhesive-bonding its both ends.
• a conventional expanded porous PTFE film is flexible, but has involved a problem that when the film is deformed by applying a load in a thickness-wise direction thereof, it is hard to recover its form to the original form even when the load is removed because the film is left great residual strain by deformation.
• the conventional expanded porous PTFE film is insufficient in elastic recovery property in the thickness-wise direction. Therefore, the film cannot be used repeatedly because of difficulty of recovering its form when the film is pressed in the thickness-wise direction to deform it once or at most several times. Under the circumstances, thus the expanded porous PTFE film cannot but use it only once and then discard it according to its applications.
• the expanded porous PTFE film is used in a field of, for example, intracorporeally implanting materials such as artificial substitutive materials for cartilages.
• the expanded porous PTFE film may not exhibit its sufficient function in some cases due to insufficient cushioning property because it is hard to recover its form to the original form when it is pressed and deformed in vivo.
• Patent Art. 1 Japanese Patent No. 2547243 (hereinafter referred to as “Patent Art. 1) corresponds to U.S. Pat. Nos. 4,877,661 and 5,308,664.
• Patent Art. 1 shows that when a mixture of a PTFE aggregate and a liquid lubricant is extruded in the form of a tube or sheet, and the extrudate is then stretched in its longitudinal direction, an expanded PTFE tube or sheet, which has a microstructure of nodes connected by fibrils, and in which the fibrils are stretched in the longitudinal direction, is obtained.
• Patent Art. 1 describes a process comprising compressing such an expanded porous PTFE material in the longitudinal direction to reduce its size, fixing the compressed state, heating the compressed expanded porous PTFE material and re-stretching it in the first stretched direction.
• a formed product of the expanded porous PTFE material which can be stretched in the longitudinal direction and rapidly recover its length to the original length.
• stretchability in a stretched direction plane direction
• elastic recovery property cannot be imparted in its thickness-wise direction.
• a high-density region can be formed by selectively compressing the expanded porous PTFE material to partially enhance its rigidity, thereby retaining its shape, but elastic recovery property cannot be imparted in its thickness-wise direction.
• the present inventors have carried out an investigation as to production conditions in detail to optimize the conditions with a view toward obtaining an expanded porous PTFE films having elastic recovery property in its thickness-wise direction. As a result, it has been found that a new step of compressing a sintered expanded porous PTFE film is added, whereby the above-described objects can be achieved.
• an expanded porous PTFE film is produced through an extrusion step of extruding a mixture of unsintered PTFE powder and a lubricant to prepare an extrudate in the form of a sheet or rod, a rolling step of rolling the extrudate to prepare a rolled sheet, a stretching step of stretching the rolled sheet to prepare an unsintered expanded porous PTFE film and a sintering step of heating the unsintered expanded porous PTFE film to sinter it.
• an expanded porous PTFE film As a sealing material, cushioning material or the like, the film has heretofore required a relatively great thickness, so that it has been general to produce such a film under production conditions that a rolling ratio and/or a draw ratio is made low.
• an expanded porous PTFE film obtained under such production conditions has been poor in elastic recovery property in its thickness-wise direction.
• the present inventors have carried out an extensive investigation. As a result, it has been surprisingly found that a draw ratio in the stretching step is made high, and a compression step is added after sintering, thereby obtaining an expanded porous PTFE film improved in elastic recovery property in its thickness-wise direction. It is desirable that the rolling ratio be also made high in the rolling step from the viewpoint of improving the elastic recovery property.
• the expanded porous PTFE film according to the present invention is small in residual strain even when it is deformed by applying a load in its thickness-wise direction, it is excellent in shape-recovering ability.
• the present invention has been led to completion on the basis of these findings.
• an expanded porous polytetrafluoroethylene film having a microstructure composed of fine fibrils and nodes connected by the fibrils and elastic recovery property in its thickness-wise direction, wherein the film has residual strain of at most 11.0% as measured after a load required to indent a rod, which is in a columnar form that its outer diameter is at least 2 mm and at least 1.9 times as much as the thickness of the film, and has a smooth plane perpendicular to its axis at a free end surface thereof and a modulus of longitudinal elasticity of at least 1.0 ⁇ 10 4 kgf/mm 2 , up to 20% of the film thickness at a strain rate of 100%/min from the free end surface is applied repeatedly 20 times.
• the expanded porous PTFE films according to the present invention are excellent in elastic recovery property against deformation by compression in the thickness-wise direction, they can be used repeatedly when they are used in applications such as sealing materials and cushioning materials, are convenient for use and can contribute to reductions in cost to a great extent and in discharge of waste matter.
• the expanded porous PTFE films according to the present invention are also suitable for use as intracorporeally implanting materials having cushioning property.
• the expanded porous PTFE films according to the present invention are further suitable for use as base films of anisotropically conductive films for inspection of electronic parts required to be used repeatedly.
• the expanded porous PTFE film according to the present invention can be produced in accordance with the following process.
• the first production process according to the present invention comprises the following steps 1 to 6:
• the extrusion step 1 can be carried out in accordance with a method well known in this technical field.
• a mixture of unsintered PTFE powder (fine powder for paste extrusion) and a lubricant (for example, solvent naphtha, petroleum or the like) is compressed in a cylinder to preform it into a columnar form, and the resultant preform (billet) is then charged into an extrusion cylinder and pressurized by a ram to extrude it through a die, thereby preparing an extrudate in the form of a sheet or rod.
• a T-die is connected to the tip of the extrusion cylinder, and a die opened in a circular form is used to obtain the rod-like extrudate.
• the rolling step 2 can also be carried out in accordance with a conventional method.
• the sheet-like or rod-like extrudate obtained in the extrusion step is rolled by means of a rolling mill such as a roll or press before the lubricant is vaporized out to prepare a rolled sheet having a predetermined thickness.
• a rolling ratio is preferably as high as possible.
• the extrudate is in the form of a sheet, the extrudate is rolled in such a manner that the rolling ratio (T1/T2) represented by a value obtained by dividing a film thickness T1 before the rolling by a film thickness T2 after the rolling is generally at least 1.3 times, preferably at least 1.5 times, more preferably at least 1.8 times, particularly preferably at least 2.0 times.
• the rolling ratio is controlled to at least 2.0 times in particular, a variation of tangent modulus (which will be described subsequently) can be made markedly narrow. As a result, the elastic recovery property in the thickness-wise direction can be more improved.
• the upper limit of the rolling ratio is of the order of generally 10 times, preferably 8 times, more preferably 5 times.
• the rolling ratio is controlled in view of the thickness of a sheet formed from the rod.
• the thickness of the rolled sheet may be suitably preset as needed. However, it is within a range of generally 0.3 to 2.0 mm, preferably 0.4 to 1.5 mm, particularly preferably 0.5 to 1.3 mm. If the thickness of the rolled sheet is too small, difficulty is encountered upon stretching at a high draw ratio, or the thickness of the resulting expanded porous PTFE film becomes too small. If the thickness of the rolled sheet is too great, difficulty is encountered upon even stretching, or it may be difficult in some cases to sufficiently enhance the draw ratio.
• the rolled sheet is stretched after the lubricant is removed from the rolled sheet or without removing the lubricant.
• the lubricant is removed in a subsequent step such as the stretching step.
• a method that the rolled sheet is passed through, for example, a drying oven of 100 to 300° C. to volatilize off the lubricant can be adopted.
• the rolled sheet is biaxially stretched in lengthwise and crosswise directions to prepare an expanded porous PTFE film (A) in an unsintered state.
• a biaxially stretching method for the rolled sheet can be adopted a simultaneous biaxially stretching method or sequential biaxially stretching method. It is however preferable to adopt the sequential stretching method that the rolled sheet is first stretched in a lengthwise direction (longitudinal direction or machine direction) and then stretched in a crosswise direction (width direction).
• the sequential stretching method may be adopted, for example, a method that the rolled sheet is stretched in the lengthwise direction between a low-speed roll and a high-speed roll, and then stretched in the crosswise direction by means of a tenter.
• the draw ratio in the lengthwise direction is generally 1.2 to 10.0 times, preferably 1.5 to 8.0 times, more preferably 2.0 to 5.0 times.
• the draw ratio in the crosswise direction is generally 3.0 to 20.0 times, preferably 4.0 to 15.0 times, more preferably 5.0 to 13.0 times.
• the biaxial stretching is conducted in such a manner that the total draw ratio (E1 ⁇ E2) represented by a product of the draw ratio El in the lengthwise direction and the draw ratio E2 in the crosswise direction exceeds 12 times.
• the total draw ratio (E1 ⁇ E2) represented by a product of the draw ratio El in the lengthwise direction and the draw ratio E2 in the crosswise direction exceeds 12 times.
• the total draw ratio is preferably at least 15 times, more preferably at least 20 times.
• the upper limit of the total draw ratio is of the order of generally 40 times, preferably 30 times.
• the total draw ratio can be controlled within a desired range by controlling the draw ratio in the lengthwise direction and the draw ratio in the crosswise direction.
• the unsintered expanded porous polytetrafluoroethylene film is heated to a temperature not lower than the melting point (327° C.) of PTFE in a state fixed so as not to shrink the film to sinter the film.
• the sintering step can be conducted by passing the expanded porous PTFE film through an oven the atmosphere in which is generally 330 to 500° C., preferably 340 to 400° C.
• the stretched state is sintered and fixed by the sintering, whereby an expanded porous PTFE film improved in strength can be obtained.
• an expanded porous PTFE film having a porosity of generally at least 66%, preferably at least 68%, more preferably at least 70% is prepared.
• the upper limit of the porosity in the sintered expanded porous PTFE film is of the order of generally 80%, preferably 76%.
• the thickness of the sintered expanded porous PTFE film (A) is generally 0.02 to 1.0 mm, preferably 0.03 to 0.8 mm, more preferably 0.04 to 0.5 mm, particularly preferably 0.05 to 0.3 mm.
• the expanded porous PTFE film (A) that is in a state heated to a high temperature upon the sintering is cooled.
• the sintered expanded porous PTFE film is air-cooled at ambient temperature or quenched by blowing a cooling medium against the film.
• the film may be air-cooled at ambient temperature. It is however preferable to blow a cooling medium such as air against the expanded porous PTFE film (A) to quench it when the thickness is great. By quenching the film, the elastic recovery property in the thickness-wise direction of the film can be more improved.
• the sintered expanded porous PTFE film (A) is generally cooled to room temperature (ordinary temperature of 10 to 30° C.).
• the cooled expanded porous PTFE film (A) is compressed in the thickness-wise direction of the film to make the thickness of the film small.
• the expanded porous PTFE film (A) is compressed by means of a pressure roll or press.
• a rolling treatment has been already conducted once in the rolling step 2, so that the compression in the compression step 6 may be referred to as “re-rolling”, and the compression step may be referred to as “re-rolling step”.
• the expanded porous PTFE film (A) is compressed in such a manner that the compression ratio (t1/t2) represented by a value obtained by dividing a film thickness tl before the compression (re-rolling) by a film thickness t2 after the compression is generally 1.1 to 4.0, preferably 1.2 to 3.0, particularly preferably 1.5 to 2.5.
• an expanded porous PTFE film (B) having good elastic recovery property in the thickness-wise direction of the film is provided.
• the porosity of the expanded porous PTFE film (B) is generally 40 to 75%, preferably 45 to 70%. If the porosity of the expanded porous PTFE film (B) is too low, such a film shows a tendency to lower the elastic recovery property in the thickness-wise direction of the film.
• the upper limit of the porosity in the expanded porous PTFE film (B) is limited to about 75% or lower by compression.
• an expanded porous PTFE film (B) having excellent elastic recovery property in the thickness-wise direction of the film can be provided.
• This elastic recovery property can be quantitatively evaluated by measuring a value of “residual strain” in a film sample after a load required to indent a rod, which is in a columnar form that its outer diameter is at least 2 mm and at least 1.9 times as much as the thickness of the film, and has a smooth plane perpendicular to its axis at a free end surface thereof and a modulus of longitudinal elasticity of at least 1.0 ⁇ 10 4 kgf/mm 2 , up to 20% of the film thickness at a strain rate of 100%/min from the free end surface is applied repeatedly 20 times.
• An indenter used in the measurement of the residual strain is a rod, which is in a columnar form that its outer diameter is at least 2 mm and at least 1.9 times as much as the thickness of the film.
• the free end surface of this rod is a smooth plane perpendicular to its axis (major axis).
• This rod is a cemented carbide rod having a modulus of longitudinal elasticity of at least 1.0 ⁇ 10 4 kgf/mm 2 .
• a material of the rod is, for example, hardened steel. This rod is sufficiently harder than the expanded porous PTFE film.
• This rod and the expanded porous PTFE film are arranged in such a manner that the axis of the rod and the plane of the film cross at right angles, and the rod is indented into the porous film at a strain rate of 100%/min from the free end surface of the rod. A load required to indent the rod up to 20% of the film thickness is applied to the rod.
• the method for measuring the residual strain making use of this rod is applied to not only the above expanded porous PTFE film (B), but also an expanded porous PTFE film (B1), which will be described subsequently.
• the outer diameter of the columnar rod is determined to be at least 2 mm and at least 1.9 times as much as the film thickness.
• the thickness of the expanded porous PTFE film is not greater than 1 mm, the value of residual strain can be measured with good precision by using a rod having an outer diameter of 2 mm.
• a rod having an outer diameter greater than 2 mm and 1.9 times as much as the film thickness is used.
• the upper limit of the outer diameter of the rod may vary according to the thickness of the expanded porous PTFE film. However, it is of the order of generally 20 mm, preferably 10 mm.
• the residual strain of the expanded porous PTFE film (B) according to the present invention is generally controlled within a range of 11.0% or lower so as to give a proper value according to its application.
• the residual strain is desirably controlled to 11.0% or lower, preferably 10.5% or lower.
• the residual strain is desirably controlled to preferably 10.0% or lower, more preferably 9.0% or lower, particularly preferably 6.5% or lower.
• the lower limit of the residual strain is generally 2.0, often 3.0.
• the tangent modulus means a ratio of a compression pressure to shrinkage strain, which is represented as a slope of the tangent at an optional point on a compression pressure-shrink curve in the thickness-wise direction of the film.
• the tangent modulus is measured in accordance with a method described below.
• a variation of tangent modulus in the expanded porous PTFE film (B) according to the present invention is generally 10.0% or lower, preferably 7.0% or lower, more preferably 5.0% or lower.
• the expanded porous PTFE film (B) according to the present invention is low in the variation of tangent modulus. This fact also indicates that the film is even and excellent in elastic recovery property in the thickness-wise direction of the film.
• the expanded porous PTFE film (B) according to the present invention is preferably such that the residual strain is at most 10.5%, and the variation of tangent modulus is at most 7.0%, and more preferably such that the residual strain is at most 6.5%, and the variation of tangent modulus is at most 7.0%.
• the thickness of the expanded porous PTFE film (B) according to the present invention may be suitably determined. However, it is generally 0.01 to 0.8 mm, preferably 0.02 to 0.5 mm, more preferably 0.03 to 0.4 mm, particularly preferably 0.04 to 0.3 mm. If the thickness of the expanded porous PTFE film (B) is too small, the flexibility of such a film as a sealing material, cushioning material or the like by itself becomes insufficient. On the other hand, since the expanded porous PTFE film (B) is composed of a single layer, it is difficult to make its rolling ratio and draw ratio high in the production process if the thickness thereof is made great in excess.
• a multi-layer film-forming step may be provided to obtain an expanded porous PTFE film (B1).
• This expanded porous PTFE film (B1) can be produced in accordance with the following process. Namely, the second production process according to the present invention comprises the following steps I to VII:
• the extrusion step I, rolling step II and stretching step III correspond to the extrusion step 1, rolling step 2 and stretching step 3 in the first production process, respectively.
• the features of the second production process according to the present invention reside in that the multi-layer film-forming step IV is provided and that the sintering step V of integrally fusion-bonding the respective layers to each other at the same time as the sintering.
• the multi-layer film-forming step IV at least two unsintered expanded porous polytetrafluoroethylene films (A) obtained in the stretching step are laminated to prepare the multi-layer film (A1).
• the respective films are in a state separate from each other and not integrally bonded.
• the number of the unsintered expanded porous polytetrafluoroethylene films (A) used in the preparation of the multi-layer film (A1) may be suitably determined in view of the thickness of the individual films, the finally required thickness of the expanded porous PTFE film (B1) and the like.
• the number of the films is of the order of generally 2 to 30, preferably 2 to 20, more preferably 3 to 15. However, the number of films is not limited thereto.
• the multi-layer film (A1) is heated to a temperature not lower than the melting point of PTFE in a state fixed so as not to shrink all the layers to sinter the film, and at the same time the respective layers are integrally fusion-bonded to each other to prepare the expanded porous polytetrafluoroethylene film (A2).
• Sintering conditions such as a sintering temperature are the same as those in the stretching step 3 of the first production process.
• the heat for the sintering in the sintering step is utilized to fusion-bond the respective layers to each other.
• an expanded porous PTFE film (A2) having a porosity of generally at least 66%, preferably at least 68%, more preferably at least 70% is prepared.
• the upper limit of the porosity in the sintered expanded porous PTFE film (A2) is of the order of generally 80%, preferably 76%.
• the thickness of the expanded porous PTFE film (A2) obtained after the sintering step is designed as necessary for the end application intended.
• the film thickness is generally 0.04 to 2.0 mm, preferably 0.06 to 1.6 mm, more preferably 0.08 to 1.3 mm, particularly preferably 0.1 to 1.1 mm.
• the product thickness of about 2.0 mm or greater, more preferably about 3.0 to 10.0 mm may be required in some cases.
• the thickness of the expanded porous PTFE film (A2) is desirably controlled so as to be greater than 2.0 mm, more preferably 5.0 to 30.0 mm.
• the expanded porous PTFE film (A2) that is in a state heated to a high temperature upon the sintering is cooled.
• the sintered expanded porous PTFE film is air-cooled at ambient temperature or quenched by blowing a cooling medium against the film.
• the sintered expanded porous PTFE film (A2) may be air-cooled at ambient temperature. It is however preferable to blow a cooling medium such as air against the film to quench. By quenching the film, the elastic recovery property in the thickness-wise direction of the film can be more improved.
• the sintered expanded porous PTFE film (A2) is generally cooled to room temperature (ordinary temperature of 10 to 30° C.).
• the cooled expanded porous PTFE film (A2) is compressed in the thickness-wise direction of the film to make the thickness of the film small.
• the expanded porous PTFE film (A2) is compressed in such a manner that the compression ratio is generally 1.1 to 4.0, preferably 1.2 to 3.0, particularly preferably 1.5 to 2.5.
• an expanded porous PTFE film (B1) having good elastic recovery property in the thickness-wise direction of the film is provided.
• the porosity of the expanded porous PTFE film (B1) is generally 40 to 75%, preferably 45 to 70%.
• an expanded porous PTFE film (B1) having good elastic recovery property in the thickness-wise direction of the film can be provided.
• the residual strain of the expanded porous PTFE film (B1) according to the present invention is generally controlled within a range of 11.0% or lower so as to give a proper value according to its application.
• the residual strain is desirably controlled to 11.0% or lower, preferably 10.5% or lower.
• the residual strain is desirably controlled to preferably 10.0% or lower, more preferably 9.0% or lower, particularly preferably 6.5% or lower.
• the lower limit of the residual strain is generally 2.0, often 3.0.
• a variation of tangent modulus in the expanded porous PTFE film (B1) according to the present invention is generally 10.0% or lower, preferably 7.0% or lower, more preferably 5.0% or lower.
• the expanded porous PTFE film (B1) according to the present invention is low in the variation of tangent modulus. This fact also indicates that the film is even and excellent in elastic recovery property in the thickness-wise direction of the film.
• the expanded porous PTFE film (B1) according to the present invention is preferably such that the residual strain is at most 10.5%, and the variation of tangent modulus is at most 7.0%, and more preferably such that the residual strain is at most 6.5%, and the variation of tangent modulus is at most 7.0%.
• the thickness of the expanded porous PTFE film (B1) after the compression step may be suitably designed as necessary for the end application intended. However, it is generally 0.02 to 1.6 mm, preferably 0.04 to 1.2 mm, more preferably 0.06 to 1.0 mm.
• the film can be provided so as to give a thickness of greater than 2.0 mm, preferably about 3.0 to 10.0 mm.
• the expanded porous PTFE films having elastic recovery property in the thickness-wise direction of the film according to the present invention can be produced in accordance with the first production process and second production process.
• the residual strain of the expanded porous PTFE films according to the present invention is 11.0% or lower, preferably 10.5% or lower, more preferably 10.0% or lower, still more preferably 9.0% or lower, particularly preferably 6.5% or lower.
• the expanded porous PTFE films according to the present invention are such that the tangent modulus is generally at least 800 gf/mm 2 , preferably at least 1,000 gf/mm 2 on the average, and the variation of tangent modulus is generally at most 10.0%, preferably at most 7.0%, more preferably at most 5.0%.
• the porosity of the expanded porous PTFE films according to the present invention is generally 40 to 75%, preferably 45 to 70%.
• the expanded porous PTFE films having elastic recovery property in the thickness-wise direction of the film according to the present invention can be used as sealing materials and cushioning materials by cutting them in proper shapes and sizes.
• the expanded porous PTFE films according to the present invention can also be used as intracorporeally implanting materials, anisotropically conductive films and the like as they are, or by forming them into structures of proper shapes or secondarily forming them.
• the expanded porous PTFE films according to the present invention are suitable for use as base films of anisotropically conductive films.
• the anisotropically conductive film can be produced in accordance with, for example, a process comprising forming through-holes in the expanded porous PTFE film and selectively applying a conductive metal only to wall surfaces of the respective through-holes.
• a process comprising arranging a masking material for plating on both surfaces of the expanded porous PTFE film, applying a plating catalyst only to the respective through-holes, conducting electroless plating after separating the masks and further conducting electroplating as needed. Since such an anisotropically conductive film is excellent in elastic recovery property in the thickness-wise direction of the film, it can be preferably used in electrical connection between circuit devices in semiconductor devices or inspection of electrical reliability in circuit boards or the like.
• the expanded porous PTFE film according to the present invention When used in a field of intracorporeally implanting materials such as artificial substitutive materials for cartilages, the expanded porous PTFE film can exhibit its sufficient function without lacking cushioning property because its form is easily recovered to the original form when it is pressed and deformed in vivo.
• a value obtained by dividing a film thickness T1 before rolling by a film thickness T2 after rolling was regarded as a rolling ratio (T1/T2).
• a value obtained by dividing a film thickness t1 before compression (re-rolling) by a film thickness t2 after compression (re-rolling) was regarded as a re-rolling ratio (t1/t2).
• Draw ratio in a lengthwise direction Finishing speed (take-up speed) of a stretched product/Feeding speed of a material before stretching
• Draw ratio in a crosswise direction was calculated out in accordance with the following equation (ii).
• Draw ratio in lengthwise direction Distance between tenter chucks before stretching/Distance between tenter chucks after stretching (ii)
• a volume was determined on the basis of a difference between a dry weight of an expanded porous PTFE material and its weight in water. Regarding a true specific gravity of PTFE as 2.25 g/cc, a volume of the resin was calculated out from this true specific gravity and the dry weight of the expanded porous PTFE material. A void volume was determined by subtracting the volume of the resin from the volume of the expanded porous PTFE material. A porosity (%) was calculated out in accordance with the following equation (iv). (Void volume/Volume of the material) ⁇ 100 (iv) (4) Tangent Modulus and Variation Thereof:
• a cemented carbide rod having an outer diameter of 2 mm and a smooth plane at its free end surface was indented into an expanded porous PTFE film at a strain rate of 100%/min in the thickness-wise direction of the film from the free end surface thereof to measure a “stress (gf/mm 2 )-strain curve” at 4 points.
• a cemented carbide rod having an outer diameter of 2 mm and a smooth plane at its free end surface was indented into an expanded porous PTFE film at a strain rate of 100%/min in the thickness-wise direction of the film from the free end surface thereof to measure a load required to indent the rod up to 20% of the thickness of the film at 4 points to determine a “20% average load”. After the average load was then applied repeatedly 20 times at a strain rate of 100%/min by means of the same device, residual strain was measured at a point.
• the rolled sheet obtained above was stretched at a draw ratio of 2.25 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 11.0 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 24.75 times.
• the resultant expanded sheet was passed through an oven, the atmosphere in which was 350° C., to sinter it.
• the porosity of the expanded sheet as measured at this point of time was about 72%, and the thickness of the film was 0.08 mm.
• this expanded sheet was compressed (compression ratio: 2.0) by means of a rolling mill so as to give a film thickness of about 0.04 mm.
• the porosity of the thus-obtained expanded porous PTFE film was about 50%.
• Table 1 The results are shown in Table 1.
• the rolled sheet obtained above was stretched at a draw ratio of 2.25 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 11.0 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 24.75 times.
• the resultant expanded sheet was passed through an oven, the atmosphere in which was 350° C., to sinter it.
• the porosity of the expanded sheet as measured at this point of time was about 72%, and the thickness of the film was 0.12 mm.
• this expanded sheet was compressed (compression ratio: 1.7) by means of a rolling mill so as to give a film thickness of about 0.07 mm.
• the porosity of the thus-obtained expanded porous PTFE film was about 50%.
• Table 1 The results are shown in Table 1.
• the rolled sheet obtained above was stretched at a draw ratio of 2.25 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 11.0 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 24.75 times.
• the resultant expanded sheet was then passed through an oven, the atmosphere in which was 350° C., to sinter it.
• the porosity of the expanded sheet as measured at this point of time was about 72%, and the thickness of the film was 0.18 mm.
• the expanded sheet was compressed (compression ratio: 1.2) by means of a rolling mill so as to give a film thickness of about 0.15 mm.
• the porosity of the thus-obtained expanded porous PTFE film was about 65%.
• Table 1 The results are shown in Table 1.
• the rolled sheet obtained above was stretched at a draw ratio of 2.25 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 11.0 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 24.75 times.
• the resultant expanded sheet was then passed through an oven, the atmosphere in which was 350° C., to sinter it.
• the porosity of the expanded sheet as measured at this point of time was about 72%, and the thickness of the film was 0.18 mm.
• this expanded sheet was compressed (compression ratio: 1.8) by means of a rolling mill so as to give a film thickness of about 0.10 mm.
• the porosity of the thus-obtained expanded porous PTFE film was about 50%.
• Table 1 The results are shown in Table 1.
• the resultant rolled sheet was stretched at a draw ratio of 2.25 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 11.0 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 24.75 times.
• Six expanded sheets obtained in such a manner were superimposed on one another and fixed by holding them between aluminum-made frames having an inner diameter of 300 mm. This laminate was left to stand for 2 hours in a thermostat, the atmosphere in which was 350° C., thereby conducting sintering and fusion bonding between the respective layers at the same time. After the sintering, the expanded sheet obtained by integrally bonding the layers was taken out of the thermostat and air-dried.
• the porosity of the expanded sheet as measured at this point of time was about 72%, and the thickness of the film was 1.05 mm.
• the expanded sheet was then compressed (compression ratio: 1.8) by means of a rolling mill so as to give a film thickness of about 0.60 mm.
• the porosity of the thus-obtained expanded porous PTFE film was about 50%. The results are shown in Table 1.
• the resultant rolled sheet was stretched at a draw ratio of 2.25 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 11.0 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 24.75 times.
• Six expanded sheets obtained in such a manner were superimposed on one another and fixed by holding them between aluminum-made frames having an inner diameter of 300 mm. This laminate was left to stand for 2 hours in a thermostat, the atmosphere in which was 350° C., thereby conducting sintering and fusion bonding between the respective layers at the same time.
• the rolled sheet obtained above was stretched at a draw ratio of 2.25 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 11.0 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 24.75 times.
• the resultant expanded sheet was passed through an oven, the atmosphere in which was 350° C., to sinter it.
• the porosity of the expanded sheet as measured at this point of time was about 72%, and the thickness of the film was 0.26 mm.
• the expanded sheet was compressed (compression ratio: 1.7) by means of a rolling mill so as to give a film thickness of about 0.15 mm.
• the porosity of the thus-obtained expanded porous PTFE film was about 50%.
• Table 2 The results are shown in Table 2.
• the rolled sheet obtained above was stretched at a draw ratio of 2.25 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 11.0 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 24.75 times.
• the resultant expanded sheet was passed through an oven, the atmosphere in which was 350° C., to sinter it.
• the porosity of the expanded sheet as measured at this point of time was about 72%, and the thickness of the film was 0.28 mm.
• the expanded sheet was compressed (compression ratio: 1.8) by means of a rolling mill so as to give a film thickness of about 0.16 mm.
• the porosity of the thus-obtained expanded porous PTFE film was about 50%.
• Table 2 The results are shown in Table 2.
• the rolled sheet obtained above was stretched at a draw ratio of 3.00 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 4.00 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 12.00 times.
• the resultant expanded sheet was passed through an oven, the atmosphere in which was 350° C., to sinter it.
• the porosity of the expanded sheet as measured at this point of time was about 66%, and the thickness of the film was 0.85 mm.
• Table 2 The results are shown in Table 2.
• the rolled sheet obtained above was stretched at a draw ratio of 3.00 times at 200° C. in a lengthwise direction thereof and then at a draw ratio of 4.00 times at 200° C. in a crosswise direction thereof.
• the total draw ratio was 12.00 times.
• the resultant expanded sheet was passed through an oven, the atmosphere in which was 350° C., to sinter it.
• the porosity of the expanded sheet as measured at this point of time was about 66%, and the thickness of the film was 0.85 mm.
• the expanded sheet was compressed (compression ratio: 1.5) by means of a rolling mill so as to give a film thickness of about 0.58 mm.
• the porosity of the thus-obtained expanded porous PTFE film was about 50%.
• Table 2 The results are shown in Table 2.
• Example 5 and Example 6 were compared with each other, the expanded porous PTFE film of Example 6 obtained by forcedly quenching the expanded film was smaller in residual strain, and thus had better elastic recovery property.
• the residual strain was as small as at most 10.0%, and so the elastic recovery property in the thickness-wise direction of the film was good.
• the variation of the tangent modulus exceeded 5.0%, further 7.0%, and so the films were somewhat poor in even elastic recovery property compared with those of Examples 1 to 6. This is considered to be attributable to the fact that the rolling ratio is lower than 2.0.
• the expanded porous PTFE film of Comparative Example 1 was great in residual strain and poor in elastic recovery property in the thickness-wise direction of the film because the total draw ratio was 12.00 times, and no compression step was provided.
• the expanded porous PTFE film of Comparative Example 2 was that obtained by adding the compression step after the stretching step. However, residual strain could not be made sufficiently small, and the variation of tangent modulus was also great because the total draw ratio was 12.00 times.
• the expanded porous PTFE film of Comparative Example 3 was that obtained by raising the total draw ratio to 24.75 times. However, residual strain was great, and elastic recovery property in the thickness-wise direction of the film was also poor because no compression step was provided.
• the expanded porous PTFE films according to the present invention can be suitably used as cushioning materials, sealing materials, semiconductor-packaging members, members for inspection of semiconductors, medical implanting material, and the like making good use of their properties such as heat resistance, chemical resistance and elastic recovery property.

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