Classifications

• • 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
  • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
  • B29C55/04—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique
  • B29C55/06—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique parallel with the direction of feed
  • B29C55/065—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets uniaxial, e.g. oblique parallel with the direction of feed in several stretching steps
• • 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
  • 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
  • B29C55/22—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of tubes
• • 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

Definitions

• This invention relates to methods of expanding fluoropolymer products and, more particularly, to methods of expanding polytetrafluoroethylene products.
• PTFE polytetrafluoroethylene
• PTFE polytetrafluoroethylene
• a lubricant may be volatilized, and the "green" PTFE may be expanded into a fibrillated state (referred to as expanded PTFE or ePTFE) and, thereafter, heated above sintering temperature to coalesce the material into a stable state.
• Figure 1 is a micrograph showing a typical fibrillated microstructure of uniaxially expanded PTFE.
• the elongated dark portions which generally extend in a top-to-bottom direction in the plane of Figure 1 are nodes.
• Fibrils are thin hair-like structures which extend left- to-right in the plane of Figure 1 and interconnect the nodes. As is typical with uniaxially expanded PTFE, the fibrils are disposed generally along the expansion direction.
• U.S. Patent No. 5,749,880 which issued on May 12, 1998 to Banas et al. discloses longitudinally expanding PTFE tubes; encasing a stent within the tubes; sintering the tubes; and causing radial expansion of the assembly, which results in nodal deformation in the tubes.
• the previous multiple expansion techniques have never dealt with obtaining ultra-high uniaxially expanded fluoropolymer, more particularly, ultra-high uniaxially expanded PTFE.
• This invention relates to a method of uniaxially expanding a fluoropolymer product including the steps of expanding a green fluoropolymer product in a first direction to create a first-expanded fluoropolymer product, and expanding the first-expanded fluoropolymer product in the same first direction.
• a method of uniaxially expanding a fluoropolymer product including the steps of expanding a green fluoropolymer product in a first direction to create a first-expanded fluoropolymer product, and expanding the first-expanded fluoropolymer product in the same first direction.
• a "green” product is an unexpanded or essentially unexpanded product.
• a “green” product may include minimal expansion that occurs unintentionally such as, for example, during take-up from extrusion which may generate a tensive force in the product. In any regard, no intentional expansion has occurred to a "green” product.
• Figure 1 is a micrograph of a typical uniaxially expanded PTFE structure
• Figure 2 is a flow chart of a process related to the subject invention.
• Figures 3(a)-8(b) are micrographs of various expanded PTFE structures formed in accordance with the subject invention. Each figure labeled as “a” is shown under a magnification of lOOx, while the corresponding figure labeled “b” is the same structure as the "a” figure, but shown under a magnification of 500x.
• the invention provides a process of uniaxially expanding a fluoropolymer product from a green state which includes subsequent steps of uniaxially expanding the fluoropolymer product.
• a flow chart is provided setting forth process steps relating to the subject invention, including optional steps. The discussion herein will be with reference to PTFE for illustrative purposes. It is to be understood that the process can be used with other fluoropolymers.
• Box A of Figure 2 represents an initial forming process. Any method of preparing green PTFE may be utilized. By way of non-limiting example, steps 10-16 are described to provide an exemplary process of preparing green PTFE.
• raw PTFE resin may be blended with a lubricant to aid in extrusion (step 10); the blended PTFE may then be preformed into a billet (step 12); and, the billet ram extruded into a desired shape, such as a tube or sheet (step 14).
• the lubricant may then be volatilized to remove the lubricant (step 16), thus providing "dry" green PTFE.
• the green PTFE now is prepared for a first expansion step as represented by box B. More specifically, as represented by step 18, the green PTFE undergoes a first uniaxial expansion. It is preferred that the direction of expansion be coincident with the direction in which the PTFE product was formed or extruded. Although not required, it is further preferred that the green PTFE be heated prior to the first expansion as represented by step 20. Heating may be performed during other steps of the process, such as during the expansion of step 18. Expansion can be performed using any known technique, preferably using any known expansion oven.
• the first-expanded PTFE product is then subjected to a second expansion step as represented by box C.
• the first-expanded PTFE product is expanded a second time uniaxially, in the same direction as the first expansion was performed in step 18.
• preheating be performed prior to the second expansion (step 24). Heating may be continued during the expansion of step 22, or, alternatively the first-expanded PTFE product may only be heated during expansion. If heating during steps 18 and or 20 cause to heat the PTFE first-expanded product to a greater temperature than that desired in steps 22 and/or 24, it is preferred that a sufficient cooling interval be provided before steps 22 and/or 24 to allow for effective preheating.
• steps 22 and/or 24 calling for heating to a greater temperature than that used with any of the steps in box B, a time interval between the steps of box B and the steps of box C is optional.
• the PTFE product may be cut in between expansion steps as represented by step 26.
• a cut segment of the first-expanded PTFE product resulting from step 18 may be utilized and subsequently expanded in step 22.
• step 28 the product is sintered (step 28) and unloaded (step 30) from the expansion equipment, e.g. an expansion oven.
• additional steps may be performed in the process.
• the acted- upon PTFE may be internally pressurized during, before or between expansion steps 18 and/or 22 to promote radial expansion.
• the PTFE product may be rotated during expansion (steps 18 and/or 22).
• the PTFE product may be heated at various stages of the process or heating may be continuous during all steps of the process (at the same or different temperatures).
• the PTFE product may be optionally subjected to various post-forming operations (step 32).
• the PTFE product may be formed as a tube and slitted to form a sheet.
• the sheet may then be later acted upon, e.g., be uni-axially or multi-axially expanded.
• Sintering may be performed before or after the post- forming operations.
• Figures 4(a) and (b) The structure of Figures 4(a) and (b) is similar to that of Figures 3(a) and (b), but with smaller nodes.
• Figures 5(a) and (b) show a structure with small nodes and large LND, however, the fibrils are generally axially aligned and not branched.
• Figures 6(a) and (b) show a structure with axially aligned fibrils and large IND; here, however, the nodes are larger in size.
• Figures 7(a)-(b) and 8(a)-(b) depict the densest structures with relatively small LND, small nodes and axially aligned fibrils.
• Figures 8(a) and (b) is the densest with the Figure 7(a)-(b) structure having more porosity due to slightly longer fibril lengths (i.e., slightly larger END).
• slightly longer fibril lengths i.e., slightly larger END.
• various parameters in the process of the subject invention can be varied to obtain desired structural qualities, such as smaller or larger nodes, LND, fibril branching, and so forth.
• the following table includes a listing of parameters that may be manipulated in the process of the subject invention to affect physical characteristics of the resulting structure: Table 1
• Table 1 does not provide an exhaustive list of parameters that can be altered to affect the process of the subject invention.
• the composition e.g., the resin grade; manufacturer
• the raw PTFE resin itself may have an affect on obtainable PTFE structures.
• Example 1 PTFE green tube was subjected to two expansion stages, the first expansion stage percentage being 300% and the second expansion stage percentage being 1500% for a collective expansion of 6300%.
• the first expansion stage included a preheating at 580°F for 4 minutes and was conducted at a rate of 35 cm/s, while the second expansion stage included a preheating at 350°F for 4 minutes and was conducted at a rate of 1 cm/s.
• Figures 3(a) and (b) are micrographs taken from the outer surface of the resulting structure.
• the resulting structure has an LND of 80-100 ⁇ m and nodal lengths of approximately 40 ⁇ ,m.
• Example 2 PTFE green tube was subjected to two expansion stages, the first expansion stage percentage being 620% and the second expansion stage percentage being 620% for a collective expansion of 5084%.
• the first expansion stage included a preheating at 350°F for 20 minutes and was conducted at a rate of 35 cm/s, while the second expansion stage included a preheating at 580°F for 4 minutes and was conducted at a rate of 1 cm/s.
• Figures 4(a) and (b) are micrographs taken from the outer surface of the resulting structure.
• the resulting structure has an LND of 80-100 ⁇ m and nodal lengths of less than 40 ⁇ m.
• Example 3 PTFE green tube was subjected to two expansion stages, the first expansion stage percentage being 300% and the second expansion stage percentage being 1500% for a collective expansion of 6300%.
• the first expansion stage included a preheating at 350°F for 4 minutes and was conducted at a rate of 35 cm s, while the second expansion stage included a preheating at 580°F for 20 minutes and was conducted at a rate of 1 cm/s.
• Figures 5(a) and (b) are micrographs taken from the outer surface of the resulting structure.
• the resulting structure has an LND of approximately 230 ⁇ m and nodal lengths of approximately 7.9 ⁇ m.
• Example 4 PTFE green tube was subjected to two expansion stages, the first expansion stage percentage being 620% and the second expansion stage percentage being 620% for a collective expansion of 5084%.
• the first expansion stage included a preheating at 350°F for 4 minutes and was conducted at a rate of 1 cm/s, while the second expansion stage included a preheating at 350°F for 4 minutes and was conducted at a rate of 1 cm s.
• Figures 6(a) and (b) are micrographs taken from the outer surface of the resulting structure.
• the resulting structure has an LND of approximately 60 ⁇ m and nodal lengths of approximately 80 ⁇ m.
• Example 5 PTFE tube was subjected to two expansion stages, the first expansion stage percentage being 300% and the second expansion stage percentage being 1500% for a collective expansion of 6300%.
• the first expansion stage included a preheating at 350°F for 20 minutes and was conducted at a rate of 35 cm/s, while the second expansion stage included a preheating at 350°F for 4 minutes and was conducted at a rate of 35 cm/s.
• Figures 7(a) and (b) are micrographs taken from the outer surface of the resulting structure.
• the resulting structure has an LND of approximately 40 ⁇ m and nodal lengths of approximately 10 ⁇ m.
• Example 6 PTFE green tube was subjected to two expansion stages, the first expansion stage percentage being 300% and the second expansion stage percentage being 1500% for a collective expansion of 6300%.
• the first expansion stage included a preheating at 350°F for 4 minutes and was conducted at a rate of 1 cm/s, while the second expansion stage included a preheating at 580°F for 4 minutes and was conducted at a rate of 35 cm/s.
• Figures 8(a) and (b) are micrographs taken from the outer surface of the resulting structure.
• the resulting structure has an LND of approximately 15 ⁇ m and nodal lengths of approximately 3.9 ⁇ m.
• the second expansion pull rate has the strongest correlative effect on the physical properties of the final expanded PTFE product.
• the radial strength and toughness of the final product is positively correlated to the second expansion pull rate, wherein the radial strength and axial toughness of a final PTFE product are greater where a higher second expansion pull rate is used with the inventive process.
• Example 1 For example, with reference to Example 1, a second expansion pull rate of 1 cm/s was used, resulting in an average radial load at peak of 65.90 g and an average axial toughness of .86 kg/mm 2 , while in Example 5, a second expansion pull rate of 35 cm s was used, resulting in an average radial load at peak of 83.7 lg and an average axial toughness of 1.19 kg/mm 2 .
• the LND of the final product correlatively decreases with (i.e., has a negative correlation to) an increase in second expansion pull rate.
• Example 1 the LND is 80-100 ⁇ m with a second expansion pull rate of 1 cm/s, while in Example 5, the LND is -40 ⁇ m with a second expansion pull rate of 35 cm/s.
• Table 4 The following is a table of identified process parameters along with product characteristics to which the identified parameters are positively or negatively correlated: Table 4
• each expansion step can expand a product an expansion percentage of 1% - 800%.
• the collective expansion resulting from the various individual expansion steps can be significantly larger than the expansion provided by each of the individual stages. As will be appreciated by those skilled in the art, various combinations of expansions can be utilized.
• the pull rates of expansions are critical factors in practicing the subject invention.
• the pull rates of expansion of any of the expansion steps (steps 18 and 22) falls in the range of about 50 cm s or less.
• the different expansion steps (steps 18 and 22) may be conducted at different rates, more preferably with the expansion rate of the first expansion step (step 18) being greater than the expansion rate of the second expansion step (step 22).
• the lower expansion rate of the second expansion step (step 22) allows for more uniform expansion than if the rate was not lowered from the first expansion step (step 18).
• the expansion rate of the first expansion step (step 18) can be about 35 cm s with the expansion rate of the second expansion step (step 22) being about 1 cm/s.
• the pull rates of expansion need not remain constant during an expansion step, but may be varied during an expansion step (e.g., from faster to slower, or vice versa).
• heating may occur at various points in the subject process, but is most preferred as preheating before expansion. Heating may occur for any duration, but it is preferred that the preheat steps (steps 20 and 24) each be conducted for between about 4 and 20 minutes prior to the corresponding expansion step.
• the most critical factor in determining duration of heating lies in the time needed to achieve a desired temperature. The longer a heating operation is conducted, the more likely it is that a desired temperature is achieved which can evenly affect the PTFE product.
• the preheat temperatures be maintained below the sintering temperature of the relevant material (e.g., 660° F for PTFE) and, more preferably, that the preheat temperature of the first preheat step (step 20) be higher than the preheat temperature of the second preheat step (step 24).
• the first preheat step may have a temperature of about 580° F
• the second preheat step (step 24) may have a temperature of about 350° F.
• Preheating can be conducted at any temperature, although using a temperature in the range of 350° F to 580° F generally avoids sintering effects. Some sintering may be desired to achieve a desired node and fibril structure and higher temperatures can be accordingly utilized.
• heating outside of the preheating steps (steps 20 and 24) the same criteria discussed above apply.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Shaping By String And By Release Of Stress In Plastics And The Like (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=34748853

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (1)

Citations (2)

Family Cites Families (40)

• 2004
  • 2004-12-30 JP JP2006547588A patent/JP5132153B2/ja not_active Expired - Fee Related
  • 2004-12-30 US US11/026,158 patent/US8298462B2/en not_active Expired - Fee Related
  • 2004-12-30 EP EP04816004.8A patent/EP1713634B1/en not_active Expired - Lifetime
  • 2004-12-30 WO PCT/US2004/044020 patent/WO2005065918A1/en not_active Ceased
  • 2004-12-30 CA CA002564964A patent/CA2564964A1/en not_active Abandoned
• 2010
  • 2010-09-07 JP JP2010200395A patent/JP2011025703A/ja not_active Withdrawn

Patent Citations (2)

Also Published As

Similar Documents

Legal Events