CA2077631A1 - Method of increasing the tensile strength of a dilatation balloon - Google Patents
Method of increasing the tensile strength of a dilatation balloonInfo
- Publication number
- CA2077631A1 CA2077631A1 CA002077631A CA2077631A CA2077631A1 CA 2077631 A1 CA2077631 A1 CA 2077631A1 CA 002077631 A CA002077631 A CA 002077631A CA 2077631 A CA2077631 A CA 2077631A CA 2077631 A1 CA2077631 A1 CA 2077631A1
- Authority
- CA
- Canada
- Prior art keywords
- parison
- balloon
- tensile strength
- sidewall
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M25/00—Catheters; Hollow probes
- A61M25/10—Balloon catheters
- A61M25/1027—Making of balloon catheters
- A61M25/1029—Production methods of the balloon members, e.g. blow-moulding, extruding, deposition or by wrapping a plurality of layers of balloon material around a mandril
-
- 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
- B29C55/26—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of tubes biaxial
-
- 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
- B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
-
- 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
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S264/00—Plastic and nonmetallic article shaping or treating: processes
- Y10S264/90—Direct application of fluid pressure differential to shape, reshape, i.e. distort, or sustain an article or preform and heat-setting, i.e. crystallizing of stretched or molecularly oriented portion thereof
- Y10S264/904—Maintaining article in fixed shape during heat-setting
Abstract
Abstract A method of making a dilatation balloon with a high percentage of the maximum tensile strength of the balloon material from a thin wall parison of a biaxially orientable polymer, such as polyethylene terephthalate (PET). A reverse temperature gradient (decreasing going from the inner to outer diameters) in applied across the sidewall of the parison by flowing a heated fluid through the parison and then sealing one end of the parison and expanding with a heated expansion fluid. Decreases in wall thickness and/or increases in burst strength across the wall can be achieved.
Description
~, METHOD OF INCREASING THE TENSILE
STRENGTH OF A DII,ATATION BALLOON
Field of the Invention This invention relates to improvements in dilatation balloons used in medical procedures, and in particular to a method of increasing the tsnsile strength of a dilatation balloon.
Back~round of the Invention In a balloon dilatation procedure, a catheter carrying a balloon on its distal end is placed within a body cavity o~ a patient and is inflated to dilate the cavity.
The procedure is commonly employed to dilate a stenosed artery, and in particular to dilate obstructed aoronary arteries. Dilation procedure~ al~o are performed in peripheral blood ve~sels, the heart valves, and in other portions of the body.
There are several desirable features for a dilation balloon. The balloon should have a maximum ~nd controllable inflated diameter. Typically, a physician selects a balloon having an in~lated diameter which corresponds to the inner d~ameter of the unobstru~ted blood vessel adjacent the stenosis to be treated -- any expansion beyond this diameter may cause rupture of the vessel. The balloon should have a thin wall so that it can fold down closely about the catheter shaft to a low proile, thereby enabling the deflated balloon to be inserted, into and removed from narrow stenoses and pas~ageways. ~he balloon also needs to be flexible, as ~tiffness detracts ~rom the ability o~ the balloon to bend as it is advanaed through tortuous passageways, a characteristic sometimes referred to as "trackability." Low stiffness (high flexibility) also enables the balloon to be folded easily within the patient's body when the balloon 1~ deflated. In thi3 regard, it should be understood that when the balloon is deflated, it ~7tS-~ s~
v typically tends to collapse into a pair o~ wings which, if no sufficiently flexible, will not fold or wrap easily about the catheter body as the deflated balloon catheter is advanced or withdrawn against body tissue. The balloon should also have a sufficiently high burst strength to enable it to impart su~icient dilatation force to the vessel to be treated. However, the burst strength required for different procedures varies considerably because the dilating ~orce of the balloon increase~ as a funckion of the diameter of the balloon, without requiring a corresponding increase in the in~lation pressure. Thus, the larger the diameter of the balloon, the lower its bur~t ~trength may be while still developing ~ufficient dilatation ~orce. For example, a 20 mlllimeter (mm) diamater balloon used in a valvuloplasty procedure need only have a burst ~trength of about 3 to 6 atmospheres (atm), whereas a 3 mm diameter balloon used in the'dilatation of ~mall coronary arterie~
may require a burst pressure of 10 to 20 atm.
Dilatation balloons have been made from a variety of thermoplastic polymer materials, including polyesters, polyurethanes, poly~inyl chloride, thermoplastic rubber~, silicone-polycarbonate copolymer~, ethylene-vinyl acetate copolymers, ethylene-butylene-styrene block copolymers, polystyrene, acrylonitrile copolymers, polyethylenP, polypropylene, and polytetrafluoro-ethylene (PTFE). Each of these materials has di~erent intrinsic properties and may require differenk processing technique~.
U.s. Patent NO. 4,490,421 tO LQVY (nOW Reis6ue 32, 938) describes the processing of a semi-crystalline polyester homopolymer, namely, polyethylene terephthalate (PET), to produce a balloon having 8uperior toughne~s, flexibility and tensile strength. The balloon is formed by heating a tubular parl~on in an external mold to a temperature above the orientation temperature, axially drawing and circum~erentially expanding the pari~on to ~orm a balloon and then cooling below tha orientation 2 ~ 3 ~.
temperature. To heat khe parison above the orientation temperature, an external balloon mold is inserted into a heated liquid medium, or a heated liquid is passed through chambers in the mold, such that heat is applied to the exterior surface of the parison and time is allowed for the temperature across the parison sidewall to equilibrate. A
relatively thin wall and high strength balloon is produced.
One of the problems with thP known heating and expansion techniques for making PET balloons is that it produces a balloon having an optimum ~high) tensile strength on the inner surface, but a much lower degree of strength on the outer surace. This varying degree of tensile strength across the sidewall results in a lower overall or "average"
tensile strength. Ideally, it would be desirable to achieve the optimum (highest) tensile strength at both surfaces of the balloon and across the wall in order to achieve the highest average ten~ile strength.
The amount of orientation (and resulting strength) achieved at any point across the sidewall o~ a balloon made from a semi-crystalline orientable polymer (such as PET), is a function of temperature (higher temperature equals less orientation) and degrea of ~tretch (higher ~t~etch ~quals higher orientation). Thus, even if the inner and outer diameters of the parison ~tart at the same temperature a~
intended with the prior art method, the orientation achieved at the inner diameters is greater due to the greatar inherent degree o~ stretch at the inner surface. More specifically, due to the relative differences in thicknesse~
between the inner and out diameters of the parison and balloon, the inner surface stretches more, and in most cases quite significantly more, and the degree of stretch is progre~sively lec8 moving outwardly acros~ the sidewall to the outer surface. Thus, while the innar surfacQ may achieve the optimum (highest) tensila stren~th pos~ible, the outer surface achieves a much lower degree of tretch and this reduces the overall or average tensile strength. St~ll ~3d ~
further, if temperature equilibrium across the wall is not achieved and the outer sur~ace of the balloon remains at a higher temperature, then the inner surface is oriented to an even ~reater degree compared to the ouker surface and the average tensile strength is even lower.
It is an obje~t o~ this invention to increase the orientation at the outer surface and across the wall in order to provide a balloon having a higher averaye tensile strength.
It has been suggested in the art of making non-crystalline carbonated beverage bottles to provide a temperature gradien~ across the sidewall o~ the parison in order to prevent stre s whitening (i.e., laaX of clarity) and low impact strength which occur when the inner surface is stretched more than the out surface. However, the bottle making method is not suitable for making a much thinner dilatation balloon' and it was not known whether a temperature gradienk could even be achieved in a very thin wall parison as used to make a dilatation balloon.
Summary o~ the Invention In accordance with this invention, a dilatation balloon is formed from a tubular, thin wall parison of an orientable polymer by subjecting the parison to a radially decreasing temperature gradient going from the inner to the outer diameter of the sidewall, in order to produce a substantially uni~orm and high degree of orientation acros the sidewall and thus a higher average tensile strength.
The temperature gradient is achieved in a thin wall parison by pa~sing a heated ~luid through a pari on in a mold an then immediately drawing and expanding the parison while subject to said temperatura gradient by sealing one end of the parison and injecting a heated ~luid to expand the parison in the mold. Pre~erably, a semi~ary4talllne polymer is used such as polyethylene terephthalate. The processing parameters o~ inner and outer temperatures, and the degrees ~J ~ IJJ ~
of inner and outer stretch, are selectiYely varied ko produce a balloon dilatation catheter having an increased tensile strength and with either khinner walls or a higher burst strength.
Brief Description of the Drawinqs Fig. 1 is an illustration, in section, of a balloon-forming mold, showing a balloon within the mold, a tubular parison in phantom, and a source of heated fluid for passing through the parison.
Fig. 2 is an illustration, in section of an alternative balloon-forming mold having passages for circulating a heated fluid in the mold.
Fig. 3 i~ a diagram showing the relatlve inner and outer diameter~ of a 6tarting parison and ~ini~hed balloon for which the inner and outer stretch ratios are calculated.
Detailed Description of_~referred Embodiment A dilatatlon balloon 12 is formed in a mold as illustrated in Fig. 1. The mold includae a mold body 10 having a central internal bore 11, defining the intended outer diameter of the finished balloon 1~, and a pair of end members, including a fixed end member 14 on the le~t and a movable end member 16 on the right. Both end members include outwardly tapering bore portions 14A, 16A, respectively, which merge into smaller diamet~r central end bores 14B/ 16B respectively.
The mold receives a tubular parison, indicated in phantom at 20 in FigO 1~ The parison 20 is gripped at its Qnds which extend outwardly of ths mold, one o~ the ends being connected securely to an input fitting 22 connected to a source of heated fluid 27 under pressure Yia regulating valve 28, and the other end being aonnected ~ecurely to an output fitting 21 with a discharge valve ~r plug 29. In order to heat pari~on 20 above the orientation tamperature and form a temperature gradi~nt acros~ khe sidewall, a ~.d ~
heated fluid from source 27 (such as a gas) flows from fitting 22 through the interior of the pari~on and exits fitting 21. The parison is then axially drawn by moving (means not shown3 the end fittlngs 21 and 22 axially apart.
The parison is then circumferentially expanded by clo~ing valve 29 and injecting a heated expansion fluid (gas *rom source 27) into the parison from fitting 22; the axial drawing may also continue during expansion. Use of a hPated expansion fluid acts to preserve the temperature gradi~nt by preventing a cooliny of the inner surface of the balloon, as occurs with an unheated expansion gas. It is preferred to use a heated gas both for heating the parison and expanding the same, such as hot nitroyen gas. The temperature at the entrance and exit o~ the pari~on is monitored by sensors 30, 31 in the fittings 22, 21 re~pectively.
lS The parison is preferably formed from an orientable semi-cry~talline polymer such as polyethylene terephthalate (PET). PET is an aromatic linear polyester derived from an aromatic dicarboxylic acid or its derivative as the main acid component, and an aliphatia glycol a the main glycol component. It can be melt extruded into a variety oP formed structures~ Typical examples of other aromatic dicarboxylic acid polymar~ that meet the ~ criteria are derived from materials such as terephthalic acid, isothalic acid, naphthalene dicarboxylic acid, together with aliphatic polymethylene glycols having 2 to 10 carbon atoms~
Among these are ethylene glyaol, trimethylene glycol, tetramethylene glycol, pentamethylQne glycol, hexamethylene glycol, didecamethylene glycol and cyclohexane dimethanol, The PET parison is oriented at an elevated temperature, above the second order transition (orientation~
temperature, as controlled by khe heated Pluid which flow~
through the parison~ In an alternative ambodiment 3hown in Fig. 2, in addition to providing a heaked ~luid through the parison, and the outer mold ~acket 18 i~ provided with ~luid pa~sages 23, 24 for circulating a heated tran6~er fluid, ?4 ~
such as hot water, to heat the outer sur~ace of the parison to a lower temperature than the heated fluid which contacts the inner surface of the parison.
The orientation of the PET parison takes place at a temperature be~ween the first and second order transition temperatures of the material, preferably from about 80C to 120C, and more preferably at about 90C. The parison is axially drawn from a starting length Ll to a drawn length ~.
As shown in Fig. 3, the parison i5 circumferentially expanded from an initial internal diameter IDIand initial outer diameter ODI to a final internal diameter ID2 and final outer diameter OD2. The expanded balloon is then subjected to a heat set step in which steam is circulat~d through the outer mold at a temperature above tha or~entation or stretching temperatureO H~at setting i~ done at a temperature between about 110 and 220C, and preferably between about 130C and 170C. The heat setting temperature is maintained for a fraction of a second or more, and preferably between about 5 to 30 seconds, ~u~ficient to increase the degree of crystallinity in the balloon. The heat setting step is significant in assuring dimensional stability for the balloon, both during storage and also during inflation. After the heat set step, the balloon is then cooled to a temperature less than the second order transition temperature by flowing a cool fluid through the outer mold and/or a cool ~luid through the parison. The balloon 12 thus formed may be removed from the mold by removing the end member 16 and withdrawing the formed balloon ~rom the mold.
~he relative amounts of stretch achleved at the inner and outer diameters is illustrated in Fig. 3. During the circumferential expansion from parison 20 to balloon 12, the inner diameter ~tret~h ratio ID2/ID~, is greater than the outer diameter stretch ratio OD2/OD~, because o~ the relative thicknesses of the parison and balloon -- pari~on 20 being much thicker relative to balloon 12. In this lnvention, the 3~
temperature across the sidewall is varled to compensate for the higher stretch ratio at the inner diameter, namely by providing a linearly decreasing temperature gradient across the sidewall going from the inner to outer surfaces. The lower temperature at the outer surface thus produces more orientation from a given amount of stretch.
The use of a temperature gradient according to this invention enables one to produce a halloon having an average tensile strength of greater than 60% of the maximum potential tensile strength of the polymer. For PET, this would be a tensile strength of at least about 70 kpsi (thousand pounds per square inch). In ~urther prePerred embodiments the tensile strength is increased to at lea~t about 90%, and more preferably 95% of the ultimate tensile strength~
The thin wall parison ~hould have a wall thickne~s of no greater than'about 25 mils. In further preferred embodiments the wall thickness would be no greater than about 20 mils, and more preferably no greater than about 15 mils.
The use of a temperature gradlent iB not beneficial where there is a substantial differenae be$ween the inner and outer diameter stretch ratios. Thus, for differences in stretch ratios of at least about 25%, and more preferably greater than 50%, the temperature gradient compensates ~or the difference and produces a substantially uniform amount of orientation across the sidewall. It has been observed that with the prior known methods o~ making balloons, the tensile strength at the outer dlameter is at least 50% less than that at the inner diameter.
Preferably, in accordance with this invention, the difference in orientation across the sidewall of the balloon is no greater than about 50~, more preferably no greatQr than about 25~, and ~till further no greater, than about 10%.
The amount of average orientation across the sidewall can be Qstimated ba~ed on the increa~e in mea~ured ten~ile strength ~74~
_ g O or may be determinable directly by measuring the optical activity across the sidewall.
Although semi crystalline polymers such as PET are described herein as the preferred embodiment, other polymeric materials may be utilized with the temperature gradient method of thi~ invention in order to increase the tensile strength of the balloon to a relatively high percentage of the maximum tensile strength of the given balloon material. Other suitable balloon materials may include polyurethane, nylon, polybutylene terephthalate (PBT), polyester and/or polyether block copolymers, ionomer resins, and combinations thereof. For example, a suitable polyester/polyether block copolymer may be tha~ sold by E.I.
Dupont de Nemaur~ and Co., Wilmington, Del~warQ, under the trade name "Hytrel." Likewise, "Surlyn" i~ an ionomer resin sold by the same company.
In additi~n to increasing the average tensile strength, either the wall thickness can be decreased or burst strength may be increased, or a partial combination thereof (greater wall thickness corresponding to greater burst strength). In a preferred embodiment, the balloon ha~
a wall thickness o~ no greater than about 4 mils (thousands of an inah), and more preferably no greater than about 1 mil. Alternatively, the bur3t ~trength ¢an ba increa~ed to greater than 20 atm, and more preferably greater than 25 atm, without increasing the wall thickness.
The following theoretical examples illustrate the properties which may be achievable with the present f invention as compared to a prior art ~alloon.
As a basis of comparison, a method of making a known balloon i8 described in the first column of Table 1.
In this known proaess, a tubular parison is ~xtruded ~rom a high molecular weight PET homopolyester r~sin having an initial intrinsic vlscosity in the range o~ 1.01 and 1.02~
before extrusion. The intrinsic viscosity ls slightly lowered during extrusion. The parison is heated in an c~ ~-~ 10 external mold at a temperature o~ 90.6C for a period of about 1.13 minutes, on the assumption that the temperature across the entire sidewall of the parison will stabili~e at 91C. The parison is then stretched axially at the ratio of 3.3X, circumferentially at the inner diameter at 7.0X, and circumferentially at the outer diameter at 4.5X. The average circumferential stretch ratio is 5.5X, calculated by dividing the balloon outer diameter by the average diameter of the parison. The balloon is heat set at 150~C for about ten seconds. The final balloon has an outer diameter of 4.omm and a wall thickness o~ 0.00889mm.
The balloon has a calculated measured burst strength of 18.2 atm. Burst pressure is determined by a simple laboratory procedure whereby one end of the polymeric balloon is sealed off and a pressurized gas is introduced incrementally into the other end. The in~lation pr~ssure at which the balloon bu~sts at about 37C ~body temperature) is referred to herein as the burst pre~ure.
The average circum~erential design tensile strength is calculated from the well known thin-walled pressure vessel equation:
Sc = PD/2t where Sc is the circumferential tensile strength, P is the burst pressure, D is the original (as molded) outer diameter of the balloon, and t is the wall thickness of the balloon (as molded). The calculated average ciraumferential tensile strength is 63.9 kpsi.
Example 1 In a first theoretical example of the present invention, the goal is to optimize the average tansile strength of utilizing the known mold temperature (91C) and substituting the known ID stretch ratio (about 7.0X) for the OD stretch ration. Thi~ will orient/streng~hen the outside of the balloon to the strength o~ the strongest part of the known balloon. The lnside of the balloon would be ~tretchQd -- 11 ~
much further, to about 14.1X, and the inside temperature would be raised about 91C to allow this hlgher stretch.
The temperature o the ID would be ranged to find the temperature which produced the highest tensile strength. If the temperature is too low, the balloon will not ~orm or the inner sur~ace may be damaged. If the temperature is too high, the orientation would be less than optimum~ This is an extreme process aimed at producing the ultimate tensile strength~
As shown in Table 1, it is estimated khat a 56.5%
increase in tensile strength can be achieved along with a 50.7% reduction in wall thickness. The burst strength is reduced 15.9%.
Example 2 In a second example, a balloon is produced having the same wall thick~eRs as the known product, but a higher average tensile strength. In this proaess, the ID stretch and temperature ara kept the Rame as in the known process and the outer diameter (mold) temperature is lowered to increase the orientation/strength of the outer layers of the wall. The OD temperature would be ranged in ord~r to equalize the orientation. The amount the OD temperatur may be reduced is limited by the second order transmission temperature which may prevent achieving the optimum tensile strength.
As shown in Table 1, it i~ anticlpated that a 56.5% inCrQase in tensile strength ma~ be achiQved for the same wall thickness as the known example. In addition, a 70% increase in the burst strength may be achieved.
2 ~
o .C r` 1~ N 117 r' Il- N
1 ~ N O O t` O
C: O O O O ~ O
.. 1 . . . . .1 ~i O
O
V ~ ~ O~ O ~,~
~ ,~ r OD ~ D
N ~ O~ ) ') a ~ ~ O
.... ~ ..
s ~ u~
N r~) N O t.) r o lU~ O O O O d u~ o .. ~ . . . . ~ ., ~ O
~ O ~c~ o 15 X ~ ~ ~ . ~ o o N
_I N ~` Ir~ .. C r~
~ 3 0 0 Q 0 3 ,,, o 2 0 IYI A Ul ~I U L~
o ~
2 5 d o o o o c:
..1 ~1 o a o ~ O U~ Ln ~ '~r d~
a ~ 1 a O O
3û
. . ~ â ~~ ~ ~
3 5 o H 1i4 ~ ~ H O ~ ~ -- ~ ~
U~ ~ E-1 E l 1-l Q Q Q E l ~ Q t,) H ~ ~ m ~ æ z P~ ~ 1~ i- tl C~ ~. H H
~ a o ~i @ o H U~ ~ ~ 8 3 1~ ~ dP dP o'P
Example 3 In a third embodiment, a "middle ground" approach is used in which the "average" diameter is stretched the same as the known ID stretch ratio with the ID at a temperature higher than the known process and the OD at a temperature lower than the known process. ~hus, a higher average tensile strength would be achieved with a lower wall thickness.
As shown in Table 1, a 56~5% increase ~n tensile strength is estimated, along with a 40% reduction in wall thickness. The burst strength remains unchanged.
Balloons made at the various conditions set forth above can burst a body temperaturQ, and the t~nsilQ strength then calculated from the measured burst prsssure. By plotting the variou tensil~ ~trengths it i~ po~ible to locate the parameters necessary to achieve the maximum average tensile stre'ngth.
Having thus described the invention, what I desire to claim and secure by letters patent is:
STRENGTH OF A DII,ATATION BALLOON
Field of the Invention This invention relates to improvements in dilatation balloons used in medical procedures, and in particular to a method of increasing the tsnsile strength of a dilatation balloon.
Back~round of the Invention In a balloon dilatation procedure, a catheter carrying a balloon on its distal end is placed within a body cavity o~ a patient and is inflated to dilate the cavity.
The procedure is commonly employed to dilate a stenosed artery, and in particular to dilate obstructed aoronary arteries. Dilation procedure~ al~o are performed in peripheral blood ve~sels, the heart valves, and in other portions of the body.
There are several desirable features for a dilation balloon. The balloon should have a maximum ~nd controllable inflated diameter. Typically, a physician selects a balloon having an in~lated diameter which corresponds to the inner d~ameter of the unobstru~ted blood vessel adjacent the stenosis to be treated -- any expansion beyond this diameter may cause rupture of the vessel. The balloon should have a thin wall so that it can fold down closely about the catheter shaft to a low proile, thereby enabling the deflated balloon to be inserted, into and removed from narrow stenoses and pas~ageways. ~he balloon also needs to be flexible, as ~tiffness detracts ~rom the ability o~ the balloon to bend as it is advanaed through tortuous passageways, a characteristic sometimes referred to as "trackability." Low stiffness (high flexibility) also enables the balloon to be folded easily within the patient's body when the balloon 1~ deflated. In thi3 regard, it should be understood that when the balloon is deflated, it ~7tS-~ s~
v typically tends to collapse into a pair o~ wings which, if no sufficiently flexible, will not fold or wrap easily about the catheter body as the deflated balloon catheter is advanced or withdrawn against body tissue. The balloon should also have a sufficiently high burst strength to enable it to impart su~icient dilatation force to the vessel to be treated. However, the burst strength required for different procedures varies considerably because the dilating ~orce of the balloon increase~ as a funckion of the diameter of the balloon, without requiring a corresponding increase in the in~lation pressure. Thus, the larger the diameter of the balloon, the lower its bur~t ~trength may be while still developing ~ufficient dilatation ~orce. For example, a 20 mlllimeter (mm) diamater balloon used in a valvuloplasty procedure need only have a burst ~trength of about 3 to 6 atmospheres (atm), whereas a 3 mm diameter balloon used in the'dilatation of ~mall coronary arterie~
may require a burst pressure of 10 to 20 atm.
Dilatation balloons have been made from a variety of thermoplastic polymer materials, including polyesters, polyurethanes, poly~inyl chloride, thermoplastic rubber~, silicone-polycarbonate copolymer~, ethylene-vinyl acetate copolymers, ethylene-butylene-styrene block copolymers, polystyrene, acrylonitrile copolymers, polyethylenP, polypropylene, and polytetrafluoro-ethylene (PTFE). Each of these materials has di~erent intrinsic properties and may require differenk processing technique~.
U.s. Patent NO. 4,490,421 tO LQVY (nOW Reis6ue 32, 938) describes the processing of a semi-crystalline polyester homopolymer, namely, polyethylene terephthalate (PET), to produce a balloon having 8uperior toughne~s, flexibility and tensile strength. The balloon is formed by heating a tubular parl~on in an external mold to a temperature above the orientation temperature, axially drawing and circum~erentially expanding the pari~on to ~orm a balloon and then cooling below tha orientation 2 ~ 3 ~.
temperature. To heat khe parison above the orientation temperature, an external balloon mold is inserted into a heated liquid medium, or a heated liquid is passed through chambers in the mold, such that heat is applied to the exterior surface of the parison and time is allowed for the temperature across the parison sidewall to equilibrate. A
relatively thin wall and high strength balloon is produced.
One of the problems with thP known heating and expansion techniques for making PET balloons is that it produces a balloon having an optimum ~high) tensile strength on the inner surface, but a much lower degree of strength on the outer surace. This varying degree of tensile strength across the sidewall results in a lower overall or "average"
tensile strength. Ideally, it would be desirable to achieve the optimum (highest) tensile strength at both surfaces of the balloon and across the wall in order to achieve the highest average ten~ile strength.
The amount of orientation (and resulting strength) achieved at any point across the sidewall o~ a balloon made from a semi-crystalline orientable polymer (such as PET), is a function of temperature (higher temperature equals less orientation) and degrea of ~tretch (higher ~t~etch ~quals higher orientation). Thus, even if the inner and outer diameters of the parison ~tart at the same temperature a~
intended with the prior art method, the orientation achieved at the inner diameters is greater due to the greatar inherent degree o~ stretch at the inner surface. More specifically, due to the relative differences in thicknesse~
between the inner and out diameters of the parison and balloon, the inner surface stretches more, and in most cases quite significantly more, and the degree of stretch is progre~sively lec8 moving outwardly acros~ the sidewall to the outer surface. Thus, while the innar surfacQ may achieve the optimum (highest) tensila stren~th pos~ible, the outer surface achieves a much lower degree of tretch and this reduces the overall or average tensile strength. St~ll ~3d ~
further, if temperature equilibrium across the wall is not achieved and the outer sur~ace of the balloon remains at a higher temperature, then the inner surface is oriented to an even ~reater degree compared to the ouker surface and the average tensile strength is even lower.
It is an obje~t o~ this invention to increase the orientation at the outer surface and across the wall in order to provide a balloon having a higher averaye tensile strength.
It has been suggested in the art of making non-crystalline carbonated beverage bottles to provide a temperature gradien~ across the sidewall o~ the parison in order to prevent stre s whitening (i.e., laaX of clarity) and low impact strength which occur when the inner surface is stretched more than the out surface. However, the bottle making method is not suitable for making a much thinner dilatation balloon' and it was not known whether a temperature gradienk could even be achieved in a very thin wall parison as used to make a dilatation balloon.
Summary o~ the Invention In accordance with this invention, a dilatation balloon is formed from a tubular, thin wall parison of an orientable polymer by subjecting the parison to a radially decreasing temperature gradient going from the inner to the outer diameter of the sidewall, in order to produce a substantially uni~orm and high degree of orientation acros the sidewall and thus a higher average tensile strength.
The temperature gradient is achieved in a thin wall parison by pa~sing a heated ~luid through a pari on in a mold an then immediately drawing and expanding the parison while subject to said temperatura gradient by sealing one end of the parison and injecting a heated ~luid to expand the parison in the mold. Pre~erably, a semi~ary4talllne polymer is used such as polyethylene terephthalate. The processing parameters o~ inner and outer temperatures, and the degrees ~J ~ IJJ ~
of inner and outer stretch, are selectiYely varied ko produce a balloon dilatation catheter having an increased tensile strength and with either khinner walls or a higher burst strength.
Brief Description of the Drawinqs Fig. 1 is an illustration, in section, of a balloon-forming mold, showing a balloon within the mold, a tubular parison in phantom, and a source of heated fluid for passing through the parison.
Fig. 2 is an illustration, in section of an alternative balloon-forming mold having passages for circulating a heated fluid in the mold.
Fig. 3 i~ a diagram showing the relatlve inner and outer diameter~ of a 6tarting parison and ~ini~hed balloon for which the inner and outer stretch ratios are calculated.
Detailed Description of_~referred Embodiment A dilatatlon balloon 12 is formed in a mold as illustrated in Fig. 1. The mold includae a mold body 10 having a central internal bore 11, defining the intended outer diameter of the finished balloon 1~, and a pair of end members, including a fixed end member 14 on the le~t and a movable end member 16 on the right. Both end members include outwardly tapering bore portions 14A, 16A, respectively, which merge into smaller diamet~r central end bores 14B/ 16B respectively.
The mold receives a tubular parison, indicated in phantom at 20 in FigO 1~ The parison 20 is gripped at its Qnds which extend outwardly of ths mold, one o~ the ends being connected securely to an input fitting 22 connected to a source of heated fluid 27 under pressure Yia regulating valve 28, and the other end being aonnected ~ecurely to an output fitting 21 with a discharge valve ~r plug 29. In order to heat pari~on 20 above the orientation tamperature and form a temperature gradi~nt acros~ khe sidewall, a ~.d ~
heated fluid from source 27 (such as a gas) flows from fitting 22 through the interior of the pari~on and exits fitting 21. The parison is then axially drawn by moving (means not shown3 the end fittlngs 21 and 22 axially apart.
The parison is then circumferentially expanded by clo~ing valve 29 and injecting a heated expansion fluid (gas *rom source 27) into the parison from fitting 22; the axial drawing may also continue during expansion. Use of a hPated expansion fluid acts to preserve the temperature gradi~nt by preventing a cooliny of the inner surface of the balloon, as occurs with an unheated expansion gas. It is preferred to use a heated gas both for heating the parison and expanding the same, such as hot nitroyen gas. The temperature at the entrance and exit o~ the pari~on is monitored by sensors 30, 31 in the fittings 22, 21 re~pectively.
lS The parison is preferably formed from an orientable semi-cry~talline polymer such as polyethylene terephthalate (PET). PET is an aromatic linear polyester derived from an aromatic dicarboxylic acid or its derivative as the main acid component, and an aliphatia glycol a the main glycol component. It can be melt extruded into a variety oP formed structures~ Typical examples of other aromatic dicarboxylic acid polymar~ that meet the ~ criteria are derived from materials such as terephthalic acid, isothalic acid, naphthalene dicarboxylic acid, together with aliphatic polymethylene glycols having 2 to 10 carbon atoms~
Among these are ethylene glyaol, trimethylene glycol, tetramethylene glycol, pentamethylQne glycol, hexamethylene glycol, didecamethylene glycol and cyclohexane dimethanol, The PET parison is oriented at an elevated temperature, above the second order transition (orientation~
temperature, as controlled by khe heated Pluid which flow~
through the parison~ In an alternative ambodiment 3hown in Fig. 2, in addition to providing a heaked ~luid through the parison, and the outer mold ~acket 18 i~ provided with ~luid pa~sages 23, 24 for circulating a heated tran6~er fluid, ?4 ~
such as hot water, to heat the outer sur~ace of the parison to a lower temperature than the heated fluid which contacts the inner surface of the parison.
The orientation of the PET parison takes place at a temperature be~ween the first and second order transition temperatures of the material, preferably from about 80C to 120C, and more preferably at about 90C. The parison is axially drawn from a starting length Ll to a drawn length ~.
As shown in Fig. 3, the parison i5 circumferentially expanded from an initial internal diameter IDIand initial outer diameter ODI to a final internal diameter ID2 and final outer diameter OD2. The expanded balloon is then subjected to a heat set step in which steam is circulat~d through the outer mold at a temperature above tha or~entation or stretching temperatureO H~at setting i~ done at a temperature between about 110 and 220C, and preferably between about 130C and 170C. The heat setting temperature is maintained for a fraction of a second or more, and preferably between about 5 to 30 seconds, ~u~ficient to increase the degree of crystallinity in the balloon. The heat setting step is significant in assuring dimensional stability for the balloon, both during storage and also during inflation. After the heat set step, the balloon is then cooled to a temperature less than the second order transition temperature by flowing a cool fluid through the outer mold and/or a cool ~luid through the parison. The balloon 12 thus formed may be removed from the mold by removing the end member 16 and withdrawing the formed balloon ~rom the mold.
~he relative amounts of stretch achleved at the inner and outer diameters is illustrated in Fig. 3. During the circumferential expansion from parison 20 to balloon 12, the inner diameter ~tret~h ratio ID2/ID~, is greater than the outer diameter stretch ratio OD2/OD~, because o~ the relative thicknesses of the parison and balloon -- pari~on 20 being much thicker relative to balloon 12. In this lnvention, the 3~
temperature across the sidewall is varled to compensate for the higher stretch ratio at the inner diameter, namely by providing a linearly decreasing temperature gradient across the sidewall going from the inner to outer surfaces. The lower temperature at the outer surface thus produces more orientation from a given amount of stretch.
The use of a temperature gradient according to this invention enables one to produce a halloon having an average tensile strength of greater than 60% of the maximum potential tensile strength of the polymer. For PET, this would be a tensile strength of at least about 70 kpsi (thousand pounds per square inch). In ~urther prePerred embodiments the tensile strength is increased to at lea~t about 90%, and more preferably 95% of the ultimate tensile strength~
The thin wall parison ~hould have a wall thickne~s of no greater than'about 25 mils. In further preferred embodiments the wall thickness would be no greater than about 20 mils, and more preferably no greater than about 15 mils.
The use of a temperature gradlent iB not beneficial where there is a substantial differenae be$ween the inner and outer diameter stretch ratios. Thus, for differences in stretch ratios of at least about 25%, and more preferably greater than 50%, the temperature gradient compensates ~or the difference and produces a substantially uniform amount of orientation across the sidewall. It has been observed that with the prior known methods o~ making balloons, the tensile strength at the outer dlameter is at least 50% less than that at the inner diameter.
Preferably, in accordance with this invention, the difference in orientation across the sidewall of the balloon is no greater than about 50~, more preferably no greatQr than about 25~, and ~till further no greater, than about 10%.
The amount of average orientation across the sidewall can be Qstimated ba~ed on the increa~e in mea~ured ten~ile strength ~74~
_ g O or may be determinable directly by measuring the optical activity across the sidewall.
Although semi crystalline polymers such as PET are described herein as the preferred embodiment, other polymeric materials may be utilized with the temperature gradient method of thi~ invention in order to increase the tensile strength of the balloon to a relatively high percentage of the maximum tensile strength of the given balloon material. Other suitable balloon materials may include polyurethane, nylon, polybutylene terephthalate (PBT), polyester and/or polyether block copolymers, ionomer resins, and combinations thereof. For example, a suitable polyester/polyether block copolymer may be tha~ sold by E.I.
Dupont de Nemaur~ and Co., Wilmington, Del~warQ, under the trade name "Hytrel." Likewise, "Surlyn" i~ an ionomer resin sold by the same company.
In additi~n to increasing the average tensile strength, either the wall thickness can be decreased or burst strength may be increased, or a partial combination thereof (greater wall thickness corresponding to greater burst strength). In a preferred embodiment, the balloon ha~
a wall thickness o~ no greater than about 4 mils (thousands of an inah), and more preferably no greater than about 1 mil. Alternatively, the bur3t ~trength ¢an ba increa~ed to greater than 20 atm, and more preferably greater than 25 atm, without increasing the wall thickness.
The following theoretical examples illustrate the properties which may be achievable with the present f invention as compared to a prior art ~alloon.
As a basis of comparison, a method of making a known balloon i8 described in the first column of Table 1.
In this known proaess, a tubular parison is ~xtruded ~rom a high molecular weight PET homopolyester r~sin having an initial intrinsic vlscosity in the range o~ 1.01 and 1.02~
before extrusion. The intrinsic viscosity ls slightly lowered during extrusion. The parison is heated in an c~ ~-~ 10 external mold at a temperature o~ 90.6C for a period of about 1.13 minutes, on the assumption that the temperature across the entire sidewall of the parison will stabili~e at 91C. The parison is then stretched axially at the ratio of 3.3X, circumferentially at the inner diameter at 7.0X, and circumferentially at the outer diameter at 4.5X. The average circumferential stretch ratio is 5.5X, calculated by dividing the balloon outer diameter by the average diameter of the parison. The balloon is heat set at 150~C for about ten seconds. The final balloon has an outer diameter of 4.omm and a wall thickness o~ 0.00889mm.
The balloon has a calculated measured burst strength of 18.2 atm. Burst pressure is determined by a simple laboratory procedure whereby one end of the polymeric balloon is sealed off and a pressurized gas is introduced incrementally into the other end. The in~lation pr~ssure at which the balloon bu~sts at about 37C ~body temperature) is referred to herein as the burst pre~ure.
The average circum~erential design tensile strength is calculated from the well known thin-walled pressure vessel equation:
Sc = PD/2t where Sc is the circumferential tensile strength, P is the burst pressure, D is the original (as molded) outer diameter of the balloon, and t is the wall thickness of the balloon (as molded). The calculated average ciraumferential tensile strength is 63.9 kpsi.
Example 1 In a first theoretical example of the present invention, the goal is to optimize the average tansile strength of utilizing the known mold temperature (91C) and substituting the known ID stretch ratio (about 7.0X) for the OD stretch ration. Thi~ will orient/streng~hen the outside of the balloon to the strength o~ the strongest part of the known balloon. The lnside of the balloon would be ~tretchQd -- 11 ~
much further, to about 14.1X, and the inside temperature would be raised about 91C to allow this hlgher stretch.
The temperature o the ID would be ranged to find the temperature which produced the highest tensile strength. If the temperature is too low, the balloon will not ~orm or the inner sur~ace may be damaged. If the temperature is too high, the orientation would be less than optimum~ This is an extreme process aimed at producing the ultimate tensile strength~
As shown in Table 1, it is estimated khat a 56.5%
increase in tensile strength can be achieved along with a 50.7% reduction in wall thickness. The burst strength is reduced 15.9%.
Example 2 In a second example, a balloon is produced having the same wall thick~eRs as the known product, but a higher average tensile strength. In this proaess, the ID stretch and temperature ara kept the Rame as in the known process and the outer diameter (mold) temperature is lowered to increase the orientation/strength of the outer layers of the wall. The OD temperature would be ranged in ord~r to equalize the orientation. The amount the OD temperatur may be reduced is limited by the second order transmission temperature which may prevent achieving the optimum tensile strength.
As shown in Table 1, it i~ anticlpated that a 56.5% inCrQase in tensile strength ma~ be achiQved for the same wall thickness as the known example. In addition, a 70% increase in the burst strength may be achieved.
2 ~
o .C r` 1~ N 117 r' Il- N
1 ~ N O O t` O
C: O O O O ~ O
.. 1 . . . . .1 ~i O
O
V ~ ~ O~ O ~,~
~ ,~ r OD ~ D
N ~ O~ ) ') a ~ ~ O
.... ~ ..
s ~ u~
N r~) N O t.) r o lU~ O O O O d u~ o .. ~ . . . . ~ ., ~ O
~ O ~c~ o 15 X ~ ~ ~ . ~ o o N
_I N ~` Ir~ .. C r~
~ 3 0 0 Q 0 3 ,,, o 2 0 IYI A Ul ~I U L~
o ~
2 5 d o o o o c:
..1 ~1 o a o ~ O U~ Ln ~ '~r d~
a ~ 1 a O O
3û
. . ~ â ~~ ~ ~
3 5 o H 1i4 ~ ~ H O ~ ~ -- ~ ~
U~ ~ E-1 E l 1-l Q Q Q E l ~ Q t,) H ~ ~ m ~ æ z P~ ~ 1~ i- tl C~ ~. H H
~ a o ~i @ o H U~ ~ ~ 8 3 1~ ~ dP dP o'P
Example 3 In a third embodiment, a "middle ground" approach is used in which the "average" diameter is stretched the same as the known ID stretch ratio with the ID at a temperature higher than the known process and the OD at a temperature lower than the known process. ~hus, a higher average tensile strength would be achieved with a lower wall thickness.
As shown in Table 1, a 56~5% increase ~n tensile strength is estimated, along with a 40% reduction in wall thickness. The burst strength remains unchanged.
Balloons made at the various conditions set forth above can burst a body temperaturQ, and the t~nsilQ strength then calculated from the measured burst prsssure. By plotting the variou tensil~ ~trengths it i~ po~ible to locate the parameters necessary to achieve the maximum average tensile stre'ngth.
Having thus described the invention, what I desire to claim and secure by letters patent is:
Claims (31)
1. A method of making a thin wall dilatation balloon having a high percentage of the maximum tensile strength of the balloon material, the method comprising the steps of:
heating a thin wall, tubular parison of a biaxially orientable polymer by flowing a heated fluid through the interior of the parison to achieve a radially decreasing temperature gradient across the sidewall of the parison going from the inner to the outer surface of the parison, the outer surface being heated to a temperature no less than the orientation temperature of the polymer and the parison having a wall thick-ness of no greater than about 25 mils;
axially drawing and circumferentially expanding the parison while subject to said temperature gradient, said circumferential expansion being achieved by sealing one end of the parison and injecting a heated fluid to expand the parison; and wherein the temperature gradient is selected to compensate for differing degrees of stretch across the sidewall and produce a thin wall dilatation balloon having a sub-stantially uniform and relatively high degree of orientation across the sidewall and thus a high average tensile strength.
heating a thin wall, tubular parison of a biaxially orientable polymer by flowing a heated fluid through the interior of the parison to achieve a radially decreasing temperature gradient across the sidewall of the parison going from the inner to the outer surface of the parison, the outer surface being heated to a temperature no less than the orientation temperature of the polymer and the parison having a wall thick-ness of no greater than about 25 mils;
axially drawing and circumferentially expanding the parison while subject to said temperature gradient, said circumferential expansion being achieved by sealing one end of the parison and injecting a heated fluid to expand the parison; and wherein the temperature gradient is selected to compensate for differing degrees of stretch across the sidewall and produce a thin wall dilatation balloon having a sub-stantially uniform and relatively high degree of orientation across the sidewall and thus a high average tensile strength.
2. The method of claim 1, wherein the tempera-ture gradient is selected to produce a balloon having an average tensile strength greater than 60% of the maximum potential tensile strength of the polymer.
3. The method of claim 1, wherein the tempera-ture gradient is selected to produce a balloon having a difference in orientation across the sidewall of less than 50%.
4. The method of claim 1, wherein the parison is axially drawn and circumferentially expanded to produce a balloon having a wall thickness of no greater than about 4 mils.
5. The method of claim 1, wherein the parison has a wall thickness of no greater than about 25 mils.
6. The method of claim 1, wherein the polymer is selected from the group consisting of polyester, polyurethane, nylon, polyester and/or polyether block copolymers, ionomer resins, and combinations thereof.
7. The method of claim 1, wherein the polymer is semi-crystalline.
8. The method of claim 7, wherein the polymer is polyethylene terephthalate.
9. The method of claim 8, wherein the tempera-ture gradient is selected to form a balloon having an average tensile strength of at least 70 kpsi.
10. A dilatation balloon made according to the method of claim 1.
11. A method of making a thin wall dilatation balloon having a high percentage of the maximum tensile strength of the balloon material, the method comprising the steps of:
heating a thin wall, tubular parison of a biaxially orientable semi-crystalline polymer to achieve a radially decreasing temperature gradient across the sidewall of the parison going from the inner to the outer surfaces of the parison, the outer surface being heated to a temperature no less than the orientation temperature of the polymer, and the parison having a wall thickness of no greater than about 25 mils;
axially drawing and circumferentially expanding the parison while subject to said temperature gradient, said circumferential expansion being achieved by sealing one end of the parison and injecting a heated fluid to expand the parison; and wherein the temperature gradient is selected to compensate for differing degrees of stretch across the sidewall and produce a thin wall dilatation balloon having a sub-stantially uniform and relatively high degree of orientation across the sidewall and thus a high average tensile strength.
heating a thin wall, tubular parison of a biaxially orientable semi-crystalline polymer to achieve a radially decreasing temperature gradient across the sidewall of the parison going from the inner to the outer surfaces of the parison, the outer surface being heated to a temperature no less than the orientation temperature of the polymer, and the parison having a wall thickness of no greater than about 25 mils;
axially drawing and circumferentially expanding the parison while subject to said temperature gradient, said circumferential expansion being achieved by sealing one end of the parison and injecting a heated fluid to expand the parison; and wherein the temperature gradient is selected to compensate for differing degrees of stretch across the sidewall and produce a thin wall dilatation balloon having a sub-stantially uniform and relatively high degree of orientation across the sidewall and thus a high average tensile strength.
12. The method of claim 11, wherein the tempera-ture gradient is selected to produce a balloon having an average tensile strength greater than 60% of the maximum potential tensile strength of the polymer.
13. The method of claim 11, wherein the tempera-ture gradient is selected to produce a balloon having a difference in orientation across the sidewall of less than 50%.
14. The method of claim 11, wherein the parison is axially drawn and circumferentially expanded to produce a balloon having a wall thickness of no greater than about 4 mils.
15. The method of claim 11, wherein the polymer is polyethylene terephthalate.
16. A dilatation balloon made according to the method of claim 1.1.
17. A method of making a thin wall expanded article from a tubular parison, wherein although the parison is expanded at substantially different inner and outer diameter stretch ratios, the resulting expanded article has a high percentage of the maximum tensile strength of the parison material, the method comprising the steps of:
heating a thin wall, tubular parison of a biaxially orientable polymer of flowing a heated fluid through the interior of the parison to achieve a radially decreasing temperature gradient across the sidewall of the parison going from the inner to the outer surfaces of the parison, the outer surface being heated to a temperature no less than the orientation temperature of the polymer and the parison having a wall thick-ness of no greater than about 25 mils;
axially drawing and circumferentially expanding the parison while subject to said temperature gradient, said circumferential expansion being achieved by sealing one end of the parison and injecting a heated fluid to expand the parison, and wherein the inner and outer diameter stretch ratios differ by at least about 25%; and wherein the temperature gradient across the sidewall is selected to compensate for the differing degrees of stretch across the sidewall and produce an article having a substantially uniform and relatively high degree of orientation across the sidewall and thus a high average tensile strength.
heating a thin wall, tubular parison of a biaxially orientable polymer of flowing a heated fluid through the interior of the parison to achieve a radially decreasing temperature gradient across the sidewall of the parison going from the inner to the outer surfaces of the parison, the outer surface being heated to a temperature no less than the orientation temperature of the polymer and the parison having a wall thick-ness of no greater than about 25 mils;
axially drawing and circumferentially expanding the parison while subject to said temperature gradient, said circumferential expansion being achieved by sealing one end of the parison and injecting a heated fluid to expand the parison, and wherein the inner and outer diameter stretch ratios differ by at least about 25%; and wherein the temperature gradient across the sidewall is selected to compensate for the differing degrees of stretch across the sidewall and produce an article having a substantially uniform and relatively high degree of orientation across the sidewall and thus a high average tensile strength.
18. The method of claim 17, wherein the tempera-ture gradient is selected to produce an article having an average tensile strength of greater than 60% of the maximum potential tensile strength of the polymer.
19. The method of claim 17, wherein the tempera-ture gradient is selected to produce an article having a difference in orientation across the sidewall of less than 50%.
20. The method of claim 17, wherein the parison has a wall thickness of no greater than about 25 mils.
21. The method of claim 17, wherein the parison is axially drawn and circumferentially expanded to produce an article having a wall thickness of no greater than about 4 mils.
22. The method of claim 16, wherein the polymer is selected from the group consisting of polyester, polyurethane, nylon, polyester and/or polyether block copolymers, ionomer resins, and combinations thereof.
23. The method of claim 21, wherein the polymer is polyethylene terephthalate.
24. An article made according to the method of claim 17.
25. A method of making a thin wall dilatation balloon having a high percentage of the maximum tensile strength of the balloon material, the method comprising the steps of:
heating a thin wall, tubular parison of a biaxially orientable, semi-crystalline polymer to achieve a radially decreasing temperature gradient across the sidewall of the parison going from the inner to the outer surfaces of the parison, the outer surface being heated to a temperature no less than the orientation temperature of the polymer, and the parison having a wall thickness of no greater than about 25 mils;
axially drawing and circumferentially expanding the parison while subject to said temperature gradient, said circumferential expansion being achieved by sealing one end of the parison and injecting a heated fluid to expand the parison; and wherein the temperature gradient is selected to compensate for differing degrees of stretch across the sidewall to produce a thin wall dilatation balloon having a sub-stantially uniform and relatively high degree of orientation across the sidewall and thus a high average tensile strength, and heat setting the drawn and circumferen-tially expanded parison by elevating the temperature of the formed balloon and main-taining the temperature for a period of time sufficient for heat setting the balloon and ensuring the dimensional stability of the balloon.
heating a thin wall, tubular parison of a biaxially orientable, semi-crystalline polymer to achieve a radially decreasing temperature gradient across the sidewall of the parison going from the inner to the outer surfaces of the parison, the outer surface being heated to a temperature no less than the orientation temperature of the polymer, and the parison having a wall thickness of no greater than about 25 mils;
axially drawing and circumferentially expanding the parison while subject to said temperature gradient, said circumferential expansion being achieved by sealing one end of the parison and injecting a heated fluid to expand the parison; and wherein the temperature gradient is selected to compensate for differing degrees of stretch across the sidewall to produce a thin wall dilatation balloon having a sub-stantially uniform and relatively high degree of orientation across the sidewall and thus a high average tensile strength, and heat setting the drawn and circumferen-tially expanded parison by elevating the temperature of the formed balloon and main-taining the temperature for a period of time sufficient for heat setting the balloon and ensuring the dimensional stability of the balloon.
26. The method of claim 25, wherein the semi-crystalline polymer is polyethylene terephthalate.
27. The method of claim 26, wherein the heat setting temperature is between about 110°C. and 220°C.
28. The method of claim 25, wherein the tempera-ture gradient is selected to produce a balloon having an average tensile strength greater than 60% of the maximum potential tensile strength of the polymer.
29. The method of claim 25, wherein the tempera-ture gradient is selected to produce a balloon having a difference in orientation across the sidewall of less than 50%.
30. The method of claim 25, wherein the parison is axially drawn and circumferentially expanded to produce a balloon having a wall thickness of no greater than about 4 mils.
31. A dilatation balloon made according to the method of claim 25.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US75569691A | 1991-09-06 | 1991-09-06 | |
US07/755,696 | 1991-09-06 |
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CA2077631A1 true CA2077631A1 (en) | 1993-03-07 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA002077631A Abandoned CA2077631A1 (en) | 1991-09-06 | 1992-09-04 | Method of increasing the tensile strength of a dilatation balloon |
Country Status (6)
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US (1) | US5304340A (en) |
EP (1) | EP0531117B1 (en) |
JP (1) | JPH05192408A (en) |
CA (1) | CA2077631A1 (en) |
DE (1) | DE69216513T2 (en) |
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-
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- 1992-08-26 JP JP4227550A patent/JPH05192408A/en active Pending
- 1992-09-03 ES ES92307979T patent/ES2097285T3/en not_active Expired - Lifetime
- 1992-09-03 EP EP92307979A patent/EP0531117B1/en not_active Expired - Lifetime
- 1992-09-03 DE DE69216513T patent/DE69216513T2/en not_active Expired - Fee Related
- 1992-09-04 CA CA002077631A patent/CA2077631A1/en not_active Abandoned
-
1993
- 1993-04-06 US US08/043,409 patent/US5304340A/en not_active Expired - Lifetime
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ES2097285T3 (en) | 1997-04-01 |
EP0531117B1 (en) | 1997-01-08 |
JPH05192408A (en) | 1993-08-03 |
EP0531117A2 (en) | 1993-03-10 |
EP0531117A3 (en) | 1993-04-14 |
US5304340A (en) | 1994-04-19 |
DE69216513D1 (en) | 1997-02-20 |
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