Thin wall heat shrink tubing

Abstract

To provide a tubing which can be applied to a device member to encapsulate and compress it as needed and which has a high recovery rate without a corresponding increase in longitudinal change.SOLUTION: Heat shrink tubing exhibiting a variety of desirable properties is provided that generally comprises at least one fluoropolymer resin. The tubing may exhibit desirable physical properties such as heat shrink capability, high expansion / recovery rates, low longitudinal shrinkage, recovery at low temperatures, and an average wall thickness of less than about 0.003 inches.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION This application relates to heat-shrinkable polymeric tubing, which finds application in a variety of fields, and methods for making such heat-shrinkable polymeric tubing. [Background technology]

[0002] Heat shrink tubing generally comprises a plastic material that has been extruded and expanded into a tubular shape. The extruded and expanded tubing is designed to shrink (i.e., reduce in diameter) when heated to a predetermined temperature. This allows heat shrink tubing to serve a variety of functions. Heat shrink tubing can provide a tight, protective covering that closely covers and insulates various components (e.g., protecting the components from abrasion and providing thermal, chemical, moisture, and / or electrical insulation). Heat shrink tubing can also be useful for grouping certain components together (i.e., within the same heat shrink tubing). Furthermore, heat shrink tubing can act to seal / isolate certain components from other components and can be used to join / fuse two components, such as two tubes. Heat shrink tubing can also be useful for modifying the properties of an underlying material (e.g., by surrounding another material and causing it to shrink as well). These properties make the tubing useful for a variety of purposes, and heat shrink tubing is used across a variety of industries, including medical, chemical, electrical, optical, electronic, aerospace, automotive, and telecommunications.

[0003] In medical applications, heat shrink tubing is particularly useful in designing increasingly smaller and more complex devices (e.g., catheters, endoscopes, etc.) inserted into the body. One typical medical application of heat shrink tubing relates to the manufacture of guide catheters, which comprise a tubular structure having an inner layer of polymer, a middle layer of wire braid, and an outer layer of another polymer. To assemble such catheters, expanded heat shrink tubing is typically applied to a shaft assembled around a mandrel, and the assembly is subjected to a temperature high enough to shrink the heat shrink tubing. Under these conditions, the outer polymeric layer within the catheter shaft melts and flows, causing the heat shrink tubing to shrink, applying a compressive force that bonds the inner and outer polymeric layers of the catheter shaft together, encapsulating the wire braid within. The heat shrink tubing is then removed and disposed of, and the catheter assembly is removed from the mandrel. See, e.g., U.S. Patent No. 5,623,994 to Ross and U.S. Patent No. 5,623,994 to Lunn, both of which are incorporated herein by reference.

[0004] It should be noted that heat shrink tubing has been commercially manufactured for decades using a variety of processes, such as vacuum expansion, gas pressure forming, and sequential heating / stretching. Known methods for expanding heat shrink tubing are shown, for example, in U.S. Pat. No. 6,229,999 to Edward et al., U.S. Pat. No. 6,229,999 to Sullivan, U.S. Pat. No. 6,229,999 to Yoshida et al., U.S. Pat. No. 6,229,999 to Henson, U.S. Pat. No. 6,229,999 to Henson, and U.S. Pat. No. 6,229,999 to Roof et al. (each of which is incorporated herein by reference). However, heat shrink tubing is typically only commercially available in grades with a recovery ratio of up to 4:1. For example, typical polytetrafluoroethylene ("PTFE") heat shrink tubing is currently commercially available with a recovery ratio of up to 4:1, and typical fluorinated ethylene propylene ("FEP") heat shrink tubing is currently commercially available with a recovery ratio of up to 2:1. Furthermore, these products typically experience a longitudinal length change of up to 15% upon recovery.

[0005] Therefore, there is a need for tubing that can be applied to device components to encapsulate and compress them as needed, providing high recovery without a corresponding increase in longitudinal change. Additionally, there is a need for tubing with thin walls that can enhance heat transfer during stacking and increase overall efficiency. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 7,306,585 [Patent Document 2] U.S. Patent No. 5,755,704 [Patent Document 3] U.S. Patent No. 2,987,767 [Patent Document 4] U.S. Patent No. 3,412,189 [Patent Document 5] U.S. Patent No. 7,625,194 [Patent Document 6] U.S. Patent No. 9,296,165 [Patent Document 7] U.S. Patent No. 9,327,444 [Patent Document 8] U.S. Patent No. 9,440,044 Summary of the Invention

[0007] The present disclosure relates to expanded forms of fluoropolymer heat shrink tubing that exhibit higher recovery rates than conventional heat shrink tubing without a corresponding significant increase in longitudinal length (as is typically seen in conventional heat shrink tubing). Additionally, certain heat shrink tubing of the present disclosure has thin walls previously unattainable in commercially available fluoropolymer heat shrink tubing and / or is recoverable at lower temperatures than those used in conventional heat shrinking processes.

[0008] One aspect of the present disclosure provides PTFE heat shrink tubing having a recovery ratio (RR) of greater than about 5:1. In some embodiments, the PTFE heat shrink tubing of the present disclosure may have a recovery ratio of greater than about 5.5:1, greater than about 6:1, greater than about 7:1, greater than about 8:1, or greater than about 9:1. In some embodiments, the PTFE heat shrink tubing of the present disclosure may have an average wall thickness of 0.003 inches or less after expansion. In certain embodiments, the PTFE heat shrink tubing may have an average wall thickness of about 0.0005 inches or less after expansion.

[0009] Another aspect of the present disclosure provides PTFE heat shrink tubing, wherein a linear regression performed on a plot of diameter change versus recovery temperature between 310°C and 330°C produces a slope value of greater than about 1.3% / °C. In some embodiments, the PTFE heat shrink tubing has an RR greater than about 5:1. In certain embodiments, the PTFE heat shrink tubing may have an RR greater than about 5.5:1, greater than about 6:1, greater than about 7:1, greater than about 8:1, or greater than about 9:1. In some embodiments, the PTFE heat shrink tubing according to the present disclosure may have an average wall thickness of 0.003 inches or less after expansion. In certain embodiments, the PTFE heat shrink tubing may have an average wall thickness of about 0.0005 inches or less after expansion.

[0010] Another aspect of the present disclosure provides PTFE heat shrink tubing, wherein the difference between the temperature corresponding to the peak temperature of the melting endotherm obtained from a DSC temperature ramp using a heating rate of 10°C per minute and the temperature corresponding to the relative minimum in an E'-T curve obtained from a DMA temperature ramp of a circumferentially oriented heat shrink tubing specimen in tensile grips is greater than about 7.5°C. In some embodiments, the PTFE heat shrink tubing may have an RR greater than about 5:1. In certain embodiments, the PTFE heat shrink tubing may have an RR greater than about 5.5:1, greater than about 6:1, greater than about 7:1, greater than about 8:1, or greater than about 9:1. In some embodiments, the PTFE heat shrink tubing according to the present disclosure may have an average wall thickness of 0.003 inches or less after expansion. In certain embodiments, the PTFE heat shrink tubing may have an average wall thickness of about 0.0005 inches or less after expansion. In some embodiments, a linear regression performed on a plot of diameter change versus recovery temperature between 310°C and 330°C yields a slope value of greater than about 1.3% / °C for heat shrink tubing of the present disclosure.

[0011] A further aspect of the present disclosure provides heat shrink tubing comprising tubing with a wall comprising PTFE having an inner diameter (ID), the ID being about 0.3 inches or less after expansion, and capable of shrinking by at least about 78% when heated to 350°C for 10 minutes. In some embodiments, the ID of the heat shrink tubing is shrinkable by at least about 80% when heated to 350°C for 10 minutes. In some embodiments, the heat shrink tubing wall has an average wall thickness of about 0.003 inches or less after expansion. In certain embodiments, the heat shrink tubing wall has an average wall thickness of about 0.0005 inches or less after expansion. In certain embodiments, the difference between the temperature corresponding to the peak temperature of the melting endotherm obtained from a DSC temperature ramp using a heating rate of 10°C per minute and the temperature corresponding to the relative minimum in the E'-T curve obtained from a DMA temperature ramp of a heat shrink tubing specimen circumferentially oriented in tensile grips is greater than about 7.5°C. In some embodiments, a linear regression performed on a plot of diameter change versus recovery temperature between 310°C and 330°C yields a slope value of greater than about 1.3% / °C for heat shrink tubing of the present disclosure.

[0012] These and other features, aspects, and advantages of the present disclosure will become apparent from the following detailed description read in conjunction with the accompanying drawings, which are briefly described below. The present disclosure includes any combination of two, three, four, or more features or elements shown in the disclosure or recited in any one or more of the claims, regardless of whether such features or elements are explicitly combined or otherwise recited in the description of a specific embodiment or in the claims herein. The present disclosure is intended to be read holistically such that it should be considered that it is intended that any separable features or elements of the disclosure can be combined, in any of its aspects and embodiments, unless the context of the disclosure clearly dictates otherwise.

[0013] For an understanding of embodiments of the present invention, reference is made to the accompanying drawings, which are not necessarily drawn to scale and in which reference characters indicate components of exemplary embodiments of the present invention. The drawings are merely illustrative and are not to be construed as limiting the invention. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a graph showing storage modulus as a function of temperature for PTFE heat shrink tubing made according to exemplary embodiments of the present disclosure compared to several commercially available PTFE heat shrink tubings. [Figure 2] FIG. 1 shows an overlay of DSC and DMA curves obtained from PTFE heat shrink tubing made in accordance with an exemplary embodiment of the present disclosure. [Figure 3] 1 is a graph showing the percent inner diameter change and its linear regression measured in the range of 310°C to 330°C for PTFE heat shrink tubing made according to exemplary embodiments of the present disclosure compared to several commercially available PTFE heat shrink tubings when recovered at various temperatures for 10 minutes. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention is described in more detail below with reference to the accompanying drawings, some, but not all, of which embodiments are shown. Indeed, these inventions may be embodied in many different forms and are not to be construed as limited to the embodiments set forth herein. Rather, these embodiments are presented so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

[0016] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will be further understood that as used herein, the terms "comprises" and / or "comprising" specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0017] The present disclosure provides heat shrink tubing with unique properties and combinations of properties, as further outlined herein. Generally, "heat shrink tubing" is shrinkable tubing made by expanding polymeric ("input") tubing (e.g., extruded tubing) to obtain the heat shrink tubing (also referred to herein as the "expanded" form). Upon heating and / or sintering, the heat shrink tubing "shrinks" to a size equivalent to (or close to) its original / input size (commonly referred to as its "recovered" size). The composition and overall size of heat shrink tubing according to the present disclosure can vary widely and is not particularly limited. Heat shrink tubing can be measured, for example, by its inner diameter ("ID") after expansion (referred to herein as the "expanded inner diameter" (ID e )) or its inner diameter ("ID") after recovery (referred to herein as "recovered inner diameter (ID)"). r )), its length, its average wall thickness, its expansion rate (ER), and its recovery rate (RR).

[0018] In some embodiments, the disclosed heat shrink tubing comprises, consists essentially of, or consists of one or more fluorinated polymers. Exemplary fluorinated polymers according to the present disclosure include, but are not limited to, fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), perfluoroalkoxyalkanes (PFA), perfluoro(alkyl vinyl ethers) (PAVE) (e.g., perfluoro(methyl vinyl) ether, PMVE, or perfluoro(propyl vinyl) ether (PPVE)), polytetrafluoroethylene (PTFE), terpolymers of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV), poly(ethylene-co-tetrafluoroethylene) (ETFE), ethylene chlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), copolymers of tetrafluoroethylene and perfluoromethyl vinyl ether (MFA), or copolymers, blends, or derivatives of any two or more of the foregoing. In certain embodiments, the disclosed heat shrink tubing comprises, consists essentially of, or consists of PTFE, and such heat shrink tubing may be referred to herein as "PTFE heat shrink tubing." In some other embodiments, the disclosed heat shrink tubing may comprise, consist essentially of, or consist of one or more non-fluorinated polymers, such as polyaryletherketones. Exemplary polyaryletherketones according to the present disclosure include, but are not limited to, polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetheretherketoneketone (PEEKK), and polyetherketoneetherketoneketone (PEKEKK).

[0019] In some embodiments, one or more additives can be incorporated into the tubing wall. In some such embodiments, the one or more additives can be distributed (e.g., substantially uniformly) throughout the wall thickness and length of the tubing. In some embodiments, the one or more additives can include a lubricant, such as an aliphatic hydrocarbon-based lubricant. In certain embodiments, the lubricant can be, for example, naphthalene. It should be noted that one or more additives mentioned herein may or may not be present in the final product (i.e., the final heat-shrinkable tubing) according to various embodiments of the present disclosure. For example, in certain embodiments, a lubricant can be applied to a polymer resin (e.g., a PTFE resin, etc.) before extruding the input tubing, followed by evaporation of the lubricant after the input tubing exits the extrusion die and before sintering the input tubing. The amount of lubricant or other additives that can be included is not particularly limited. In some embodiments, for example, the additive (e.g., lubricant) may be included in an amount ranging from about 1% to about 30%, about 16% to about 25%, or about 10% to about 20% by weight, based on the total weight of the tubing. In other embodiments, the tubing may not include any additives therein.

[0020] The size (e.g., length, diameter (i.e., expanded inner diameter, ID), and average wall thickness) of heat shrink tubing within the scope of the present disclosure is not particularly limited. For example, the lengths of the tubing described herein can vary from discretely sized units (e.g., in some embodiments, on the order of 0.25 inches to 120 inches for catheter manufacturing) to lengths that can be easily transported and further cut into discretely sized units to large-scale production lengths (e.g., on the order of several hundred feet). The diameters of the tubing described herein can vary, among other things, depending on the intended use of the tubing. Certain expanded IDs of tubing described herein, particularly for medical applications, can range from about 0.01 inches to about 1.5 inches (e.g., about 0.025 inches to about 0.75 inches, or about 0.05 inches to about 0.5 inches), although tubing having expanded IDs outside this range are also encompassed by the present disclosure, particularly in the context of different fields of application. In some embodiments, for example, the expanded ID of the tubing can range from about 0.034 inches to about 4 inches.

[0021] With respect to tubing wall thickness, it should be noted that the higher expansion / recovery ratios exhibited by the PTFE heat shrink tubing of the present disclosure may, in some embodiments, result in thinner expanded and recovered walls than commercially available PTFE and / or FEP heat shrink tubing, for example, as shown in the examples provided herein below. In certain exemplary embodiments, the heat shrink tubing of the present disclosure may have an average wall thickness ranging from about 0.0001 inches to about 0.005 inches, from about 0.0001 inches to about 0.0025 inches, or from about 0.0001 inches to about 0.0005 inches. In some embodiments, the heat shrink tubing of the present disclosure may have an average wall thickness of about 0.005 inches or less, about 0.003 inches or less, about 0.001 inches or less, about 0.00075 inches or less, or about 0.0005 inches or less. These values ​​are after expansion and before recovery.

[0022] These significantly thinner wall thicknesses can provide significant advantages over commercially available PTFE and FEP heat shrink tubing currently used in the market. For example, thin-walled PTFE heat shrink products according to the present disclosure can enhance heat transfer during reflow, increasing the overall efficiency of the reflow process. With respect to FEP heat shrink tubing, it is noted that the thermal conductivity of FEP (0.180 W / m·K at reflow temperatures above 200°C) is much lower than that of PTFE (0.280 W / m·K at reflow temperatures above 200°C), thus demonstrating improved heat transfer for PTFE heat shrink tubing compared to FEP heat shrink tubing. See, for example, DM Price, M. Jarratt, Thermochimica Acta, 392, 231, 2002, and LK Olifirov, AA Stepashkin, G. Sherif, VV Tcherdyntsev, Polymers, 13, 781, 2021, which are incorporated herein by reference.

[0023] The heat shrink tubing described herein may exhibit advantageous properties and combinations of properties such as two or more thereof: high expansion rate, high recovery rate, recovery at lower temperatures, small length change upon recovery, and / or thin wall after expansion and / or recovery. In some embodiments, heat shrink tubing is provided that exhibits two of these properties (e.g., high expansion rate and high recovery rate, high expansion rate and recovery at lower temperatures, high recovery rate and recovery at lower temperatures, high expansion rate and low length change during recovery, high recovery rate and low length change during recovery, low temperature recovery and low length change during recovery, high recovery rate and thin wall, high expansion rate and thin wall, low temperature recovery and thin wall, low length change and thin wall), three or more of these properties (e.g., high recovery rate, high expansion rate and thin wall, high recovery rate, high expansion rate and recovery at lower temperatures, high recovery rate, high expansion rate and low length change during recovery, etc.), four or more of these properties (e.g., high recovery rate, high expansion rate, thin wall and recovery at lower temperatures, high recovery rate, high expansion rate, thin wall and low length change after recovery, etc.), or all five of these properties.

[0024] Such a property may be defined using the following equation: Expansion rate = ER = ID e / ID o Recovery rate=RR=ID e / ID r Change in length = ΔL = ((L r -L e ) / L e )(100) Diameter change = ΔD = (ID e -ID r ) / ID e )(100)

[0025] In these equations, L e and L r are the length of the heat-shrink tubing (in the expanded form) and the length of the "recovered" (i.e., heat-shrunk) tubing, respectively. o refers to the original inside diameter (ID) of the delivery tube (i.e., the tube before expansion and subsequent "deflation"), and ID e refers to the inside diameter (ID) of the expanded heat shrink tubing, and ID r refers to the inner diameter (ID) of the recovered (heat-shrunk) tubing. ER, RR, ΔL, and ΔD can be evaluated at any recovery temperature. As used herein, the above parameters were calculated as follows:

[0026] The change in length (ΔL) is determined as follows: Before placing the heat-shrink tubing in an oven for indefinite recovery, cut the expanded tubing to a 4-inch length. Carefully cut 4-inch test specimens from the heat-shrink tubing, ensuring that the specimen is free of burrs or other deformations and perpendicular to the longitudinal axis of the tubing. After the indefinite recovery process at the specified temperature, re-measure the length of the tubing to the nearest 1 / 64 inch using a verified ruler to determine the amount of shrinkage or elongation that occurred during the process. For example, subtract the expanded length from the recovered length, divide by the expanded length, and then multiply this amount by 100 to obtain the overall length change percentage (ΔL). Typically, the longitudinal change is measured within a range of about ±20% (i.e., the length change is allowed to elongate or shrink by no more than about 20% during recovery). In some embodiments, the longitudinal change is measured within a range of about ±15%, about ±10%, or about ±5%. In certain embodiments, longitudinal changes averaged 5% or less. The standard time and recovery temperature for PTFE heat shrink is 350°C for 10 minutes. The standard time and recovery temperature for FEP is 210°C-221°C for 10 minutes. For catheter manufacturing, PTFE heat shrink is recovered at 260°C to reflow the outer jacket.

[0027] The expansion ratio (ER) is calculated by dividing the measured expanded ID by the measured input ID. The recovery ratio (RR) is determined as follows: Five 4-inch long specimens are cut from the expanded tubing, and the expanded ID of each is measured. The specimens are then individually placed in an oven set to a specified temperature for approximately 10 minutes (e.g., the first specimen is heated at 310°C, the second at 320°C, the third at 330°C, the fourth at 340°C, and the fifth at 350°C). After exposing each heat shrink tubing specimen to the specified recovery temperature for 10 minutes, it is removed from the oven and allowed to cool to ambient temperature. This allows the expanded heat shrink tubing to undergo an unlimited recovery process. After cooling to ambient temperature, the recovered tubing is cut into four equal-length pieces with a sharp razor blade. This provides five distinct measurement locations along the length of the recovered heat shrink tubing. The ID is then measured at each different location using a validated measuring device, and the average is taken as the recovered ID. Dividing the expanded tubing ID by the recovered tubing ID measured after the unlimited recovery process gives the recovery rate (RR) of the heat shrink product at the specified temperature. Subsequently, the diameter change of the heat shrink tubing is calculated by subtracting the recovered tubing ID from the expanded tubing ID, dividing by the expanded tubing ID, and then multiplying this amount by 100 to get the overall diameter change percentage (ΔD).

[0028] Regarding heat shrinkability, in certain embodiments, the tubing disclosed herein is capable of shrinking (reducing in diameter) when exposed to heat (e.g., due to being in an expanded state). Heat shrink material is typically applied to a substrate material (e.g., a catheter structure, a medical device member, etc.) and heated. When subjected to a thermal cycle, the inner and outer diameters of the tubing are reduced (resulting in a smaller inner diameter (ID) and smaller outer diameter (OD) than those exhibited by the expanded tubing, referred to as the "recovered" ID and OD). Preferably, only the diameter of the tubing substantially shrinks, and not its length (i.e., the tubing shrinks only in one plane). As noted above, the ratio between the expanded ID and the original input ID is referred to as the expansion ratio. The expansion ratio is the expanded ID divided by the original input ID. It has been discovered that expansion ratios of much greater than 4:1 can be obtained by using die temperatures higher than those typically used. For example, typical expansion ratios for the types of tubing described herein can be at least about 4:1, at least about 5:1, at least about 6:1, at least about 7:1, at least about 8:1, at least about 9:1, or at least about 10:1.

[0029] It should be noted that while high expansion ratios can be achieved using commercially available heat shrinking methods, the heat shrink tubing of the present disclosure can surprisingly exhibit higher recovery ratios compared to conventional heat shrink tubing known in the art (e.g., conventional heat shrink tubing known in the art typically has recovery ratios of 4:1 or less). As noted above, for example, the ratio between the expanded ID and the recovered ID is referred to as the recovery ratio. The recovery ratio is the expanded ID divided by the recovered ID. While not intending to be bound by theory, it has been found that rapid cooling of the expanded tubing is effective in locking the tubing into an entropically unfavorable expanded state before it begins to appreciably recover, thereby producing a final product with recovery ratios that exceed the commercially available maximum of 4:1 recovery ratio. In some embodiments, this rapid cooling can be achieved by a water-cooled annular fixture attached to the end of a heated die. For example, in some embodiments, the PTFE heat shrink tubing of the present disclosure may exhibit a recovery ratio of at least about 4:1, at least about 5:1, at least about 6:1, at least about 7:1, at least about 8:1, at least about 9:1, or at least about 10:1.

[0030] The recovery rates of the heat shrink tubings of the present disclosure can also be characterized in terms of their inner diameter (ID) reducibility (e.g., their overall percent diameter change (ΔD) calculated using the equation above). For example, a recovery rate of 4.55:1 equates to an ID that is reducible by about 78%, and a recovery rate of 5:1 equates to an ID that is reducible by about 80%. As shown in Figure 3, both Example 1 and Example 2, made according to the methods of the present disclosure, exhibited a percent diameter change of about 80% or more after recovery, while each of the comparative examples exhibited a significantly lower percent diameter change after recovery.

[0031] In some embodiments, when the recovery percentage is within the ranges described above, the heat shrink tubing exhibits a small change in the longitudinal direction upon shrinking, such as less than about 20%. In certain embodiments, such heat shrink tubing may exhibit even smaller changes in the longitudinal direction, such as less than about 20%, less than about 15%, less than about 10%, less than about 9%, less than about 8%, less than about 7%, less than about 6%, less than about 5%, less than about 4%, less than about 3%, less than about 2%, less than about 1%, less than about 0.5%, or less than about 0.1%.

[0032] It should be noted that the higher recovery rates of the heat shrink tubing described herein provide certain distinct advantages over commercially available heat shrink tubing. In particular, such higher recovery rates may enable the encapsulation of complex mandrel shapes (e.g., including, but not limited to, tapered mandrels or mandrels with abrupt transitions). Furthermore, providing such high recovery rates at low temperatures as described herein advantageously increases the variety of polymeric materials that can be encapsulated without degradation. For example, in some embodiments, a dual heat shrink structure with an outer layer (e.g., a PTFE heat shrink outer layer) having a higher recovery rate may enable complete encapsulation of a meltable inner layer around complex parts and shapes. Examples of dual heat shrink structures and applications are shown, for example, in the disclosure of U.S. Patent Application Publication No. 2021 / 0370581 to Hunter et al., which is incorporated herein by reference in its entirety. Furthermore, as described herein, such high recovery rates can result in heat shrink tubing with the ability to recover over complex mandrel contours, such as those with varying diameters or taper angles and lengths, resulting in thin-walled catheter liners not currently available on the market.

[0033] In certain embodiments, the heat shrink tubing described herein can be described as "peelable," meaning that it can be easily peeled or torn longitudinally (e.g., to remove the heat shrink tubing from the underlying material). This peelability can advantageously allow the tubing to be provided, used, and, in some embodiments, removed without any nicks, break lines, indentations, or perforations along the length of the tubing. It is noted that PTFE is inherently peelable in the direction of flow (e.g., longitudinally), which can result in easy removal of the heat shrink tubing after reflowing the inner polymeric material (e.g., catheter jacket, medical device, or dual heat shrink structure). Examples of peelable heat shrink tubing are shown, for example, in U.S. Patent No. 6,249,999 to Roof et al., which is incorporated herein by reference in its entirety.

[0034] Certain properties of the tubing disclosed herein can be evaluated by differential scanning calorimetry (DSC). DSC is an analytical technique that provides information about the thermal properties of a material and is well known to those skilled in the art. A typical DSC experiment (commonly referred to as a single heat temperature ramp) can be performed to determine the peak temperature of the endothermic melting transition for a semi-crystalline polymer material (e.g., PTFE). The peak temperature of the melting endotherm can vary depending on the specific configuration of the tubing (i.e., the type of fluoropolymer resin) and the previous thermal history of the tubing (i.e., the thermo-mechanical history imparted to the material during processing). The peak temperature of the melting endotherm observed in a DSC thermogram is generally referred to as T m The thermo-mechanical history imparted to the heat shrink tubing of the present disclosure using the methods described herein results in a T m changes.

[0035] PTFE is known to have a high melting temperature and melt viscosity; virgin PTFE resin has a melting temperature of approximately 342°C to 345°C and a melt viscosity in the range of about 1 GPa·s to 10 GPa·s. This high melt viscosity limits flow, thereby enabling other thermoplastics to be processed by conventional melt extrusion techniques (e.g., using a screw extruder). Due to PTFE's high melt viscosity, it is typically extruded as a paste through a ram extruder and sintered using equipment and procedures well known in the art. For example, PTFE tubing can be sintered at temperatures above the melting point of virgin PTFE resin (i.e., 342°C to 345°C), e.g., at temperatures in the range of about 360°C to about 380°C. Typically, the PTFE tubing is sintered for a period sufficient to promote fusion, coalescence, and void removal, thereby maximizing certain properties of the PTFE tubing.

[0036] Certain properties of the tubing disclosed herein can be evaluated by dynamic mechanical analysis (DMA). DMA is an analytical technique used to study and characterize the viscoelastic behavior of polymers as a function of time, temperature, and frequency. The storage modulus (E') is a measure of a material's elastic behavior (i.e., its ability to store energy elastically). A typical DMA temperature ramp experiment involves applying a sinusoidal deformation at a specified frequency while increasing the temperature at a constant (i.e., linear) rate and simultaneously monitoring the material's response (i.e., stress).

[0037] As noted above in DMA, the storage modulus of a specimen obtained from heat shrink tubing in the circumferential direction subjected to a temperature ramp decreases with temperature until the expansion temperature is approached. At this point, a significant minimum is reached in the E'-T (storage modulus vs. temperature) curve, after which E' increases as the heat shrink tubing recovers in the direction of dynamic mechanical testing. The minimum in the E'-T curve is then referred to as E' min Let's call it E'. minThe presence of is believed to be independent of the crystallization process and is due to entropic elasticity as seen in the recovery of pre-stretched specimens. See, e.g., L. Andena et al., Polym. Eng. Sci, 44, 2004, 1368-1378, which is incorporated herein by reference.

[0038] E' min It should be noted that T has been found to be an important parameter in describing the heat shrink tubing of the present invention. Typically, a combination of processing parameters and material properties determines the crystalline / amorphous morphology of the expanded heat shrink tubing, which becomes locked in an entropically unfavorable state after the expansion process. This morphology determines not only the entropic resilience available for the tubing to recover from its expanded shape, but also the extent to which the tubing recovers when exposed to various recovery temperatures. Without intending to be bound by theory, it is believed that the T of the heat shrink tubing m at the lowest possible temperature relative to E' min It has been found that it is important to adjust the processing parameters so that a heat shrink tubing that recovers to a greater extent at lower temperatures will perform better in many applications. Therefore, it is desirable to produce PTFE heat shrink tubing that exhibits a large temperature difference between the melting endothermic peak obtained from the DSC temperature ramp and the minimum in the E'-T curve obtained from the DMA temperature ramp.

[0039] The heat shrink tubing provided herein can be used in a variety of applications. In certain applications, these heat shrink tubings can be applied to an underlying material (e.g., a device, device component, joint, fitting, wire, etc.) and heated to form a coating on the underlying material. Accordingly, the present disclosure encompasses materials or objects to which the tubing disclosed herein is applied. For example, in some embodiments, coated devices (e.g., medical devices) are provided that include the tubing disclosed herein. Exemplary coated devices include, but are not limited to, medical devices (e.g., catheters) to which any of the tubing disclosed herein is applied.

[0040] In various embodiments, the heat-shrinkable tubing disclosed herein is made from one or more fluoropolymer resins. As used herein, "resin" refers to a material consisting essentially of a given type of polymer (e.g., copolymer) or two or more polymers / copolymers. Resins are typically provided in solid form (e.g., as solid pellets), but are not limited thereto (they have other forms, including, but not limited to, powders, pastes, granules, dispersions, solutions, gels, etc.). In some embodiments, the heat-shrinkable tubing disclosed herein can comprise, consist of, or consist essentially of one or more forms of the fluoropolymer resins described herein. In some cases, the term "resin" as used herein may include one or more additional components and / or one or more additives (e.g., lubricants, colorants, etc.) can be added thereto. In other embodiments, one or more additives (in granular, powder, or pellet form, or in gel or liquid form) can be included with and extruded together with the fluoropolymer resin.

[0041] Any fluorinated polymer resin can be used in accordance with the present disclosure. Of particular relevance to the present disclosure are fluoropolymer resins. Fluoropolymer resins are often used as heat-shrinkable tubing for many applications requiring lubricity, chemical inertness, or high-temperature stability. FEP, PFA, and PTFE are among the more common fluoropolymer heat-shrinkable tubings commercially available today, but the present disclosure is not limited thereto. Exemplary fluorinated polymer resins useful according to the present disclosure include, but are not limited to, resins wherein the polymer comprises, consists of, or consists essentially of fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), perfluoroalkoxyalkanes (PFA), perfluoro(alkyl vinyl ethers) (PAVE) (e.g., perfluoro(methyl vinyl) ether, PMVE, or perfluoro(propyl vinyl) ether (PPVE)), terpolymers of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV), poly(ethylene-co-tetrafluoroethylene) (ETFE), ethylene chlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoromethyl vinyl ether (MFA), or copolymers, blends, or derivatives of any two or more thereof.

[0042] In certain embodiments, the heat shrink tubing of the present disclosure is made using PTFE resin and, therefore, in some embodiments, can consist of, consist essentially of, or include PTFE. Typically, PTFE resin can be provided in a variety of different forms, such as, for example, a solid, powder, granules, dispersion, solution, gel, etc. In certain embodiments, the PTFE heat shrink tubing can be made using, among other things, PTFE powder. The type of PTFE powder incorporated in such embodiments can vary and can include not only traditional PTFE extrusion-grade powder, but also PTFE granules, particles, etc., of various particle sizes. Extrusion-grade PTFE resins are commercially available as POLYFLON™ PTFE F-205 from Daikin Industries, Ltd. and DYNEON™ PTFE TF 2053Z from 3M™. However, it should be understood that the heat shrink tubing provided herein is not limited to PTFE resin and can be made using one or more of the fluorinated polymer resins described herein in addition to or in place of PTFE.

[0043] Generally, methods for making such heat-shrinkable tubing can vary. Generally, the desired resin(s) (e.g., PTFE resin, etc.) are formed into a tubular form, for example, via extrusion, and then mechanically expanded. The means for carrying out these steps can vary, as described herein.

[0044] For example, resins (such as PTFE resins) can be formed into tubing by subjecting the resin to extrusion. Extrusion generally involves placing the desired resin(s) into an extruder (e.g., a ram extruder). Within the extruder, the resin(s) are heated, compressed, and forced through an annular die set to produce tubing. Tubes of various diameters and lengths can be produced. The dimensions of the tube can be determined by the tooling size on the extrusion line, and other parameters of the extrusion process can be adjusted and optimized to produce the desired tubing. In some embodiments, tubing with a relatively uniform wall thickness is provided. The tube-forming tool is attached to the end of the extrusion cylinder and generally includes a rod, a mandrel, a master die, a tube die, and end cap heaters.

[0045] The required size of the finished product and the reduction ratio determine the appropriate tooling to be used. The reduction ratio controls the extrusion pressure, fibrillation, and mechanical properties of the PTFE resin or PTFE powder. The reduction ratio is an absolute number calculated from the ratio of the cross-sectional area of ​​the extrusion cylinder minus the cross-sectional area of ​​the mandrel rod to the cross-sectional area of ​​the extrusion die minus the cross-sectional area of ​​the mandrel tip.

[0046] During the extrusion process, resin particles are highly pressurized as they enter the tube die zone. Because their cross-sectional area in the flow direction decreases, the particles deform and rub against each other under the applied pressure. The PTFE begins to shear the secondary particles, causing the crystallites to mechanically interlock, resulting in interconnections between adjacent particles. As the particles flow toward the die exit, they accelerate and elongate, loosening the mechanically interlocked crystallites and creating fibrils. Typically, the more fibrils formed, the more elastic the elongational properties of the paste, leading to higher extrusion pressures.

[0047] In some embodiments, upon exiting the extruder, the newly formed extruded tube can be transferred to an evaporation oven having a temperature ranging from about 232°C to about 260°C to remove any lubricants used during the preforming and extrusion processes. In certain embodiments, the extruded tube can then be sintered at a desired temperature for a period of time to achieve the desired final properties of the PTFE tube. In some embodiments, the extruded tube is sintered at a temperature above the melting point of virgin PTFE resin (i.e., 342°C to 345°C), for example, at a temperature in the range of about 360°C to about 380°C. Typically, the extruded tube is sintered for a period of time sufficient to promote fusion, coalescence, and void removal to maximize certain properties of the PTFE tube.

[0048] In certain embodiments, the extruded tubing can be air-cooled following a sintering process to achieve a desired level of crystallinity in the final tubing. The level of crystallinity in the final tubing can vary as known in the art. For example, in some embodiments, the degree of crystallinity in the final PTFE tubing can range from about 32% to about 48%.

[0049] The extruded tubular form is then typically radially expanded (e.g., by mechanical means) to provide expanded tubing material, i.e., heat-shrink tubing (i.e., tubing that reduces in diameter upon heating). The expansion of the input tubing (i.e., the initial extruded tubular form) can occur in-line with the extrusion or can occur offline (i.e., independent of and / or subsequent to the extrusion process). All means of radially expanding tubing are intended to be encompassed by the present invention. Generally, during the expansion process, the tubing is radially expanded by pressurizing the inside of the tubing and applying stress to the tube walls. This pressurization can be achieved by any means capable of creating a pressure differential between the inside and outside of the tubing. Such a pressure differential can be created by applying a pressure above atmospheric pressure to the center of the tubing, a pressure below atmospheric pressure to the outside of the tubing, or a combination of the two. The stress induced in the tubing walls causes the tubing to radially expand, i.e., increase in diameter. The rate of expansion can be controlled so that the tubing remains in its expanded state and does not recover until subjected to further thermal cycling. The extent to which the tube is expanded depends on the intended use of the tubing, in some embodiments, the tubing is expanded to an inner diameter of about 1.05 times its original (unexpanded) diameter to about 10 times its original (unexpanded) diameter.

[0050] In certain embodiments, PTFE heat shrink tubing made according to the present disclosure can be radially expanded using, for example, the process described in U.S. Patent No. 6,299,949 to Henson, which is incorporated herein by reference in its entirety. For example, the U.S. Patent No. 6,299,949 patent describes a process for producing fluoropolymer heat shrink tubing using a first fluid inside the tube to expand the tube and a second fluid outside the tube to constrain expansion in an expansion chamber. In other embodiments, the tubing can be expanded by, for example, adjusting the air flow rate outside the tube, the chamber temperature, the air pressure within the tube, and the speed at which the tube passes through the expansion chamber. In certain embodiments, the heat shrink tubing of the present disclosure is expanded at an elevated temperature through a die using any number of methods known in the art and subsequently cooled at the die exit. Cooling can be achieved using a fluid such as water, oil, or air. Processing parameters that can be adjusted include die type, die diameter and length, die temperature, fluid pressure inside the tube, fluid pressure outside the tube, cooling method, refrigerant type and temperature, expansion rate, tube material, tube ID, tube OD, and tube wall thickness.

[0051] The heat shrink tubing provided herein can be used in a variety of applications. In certain applications, the heat shrink tubing provided herein can be applied to an underlying material (e.g., a device, device component, joint, fitting, wire, etc.) and heated / cured to form a coating on the underlying material. Accordingly, the present disclosure encompasses materials or objects to which the tubing disclosed herein is applied. For example, in some embodiments, a coated device (e.g., a medical device) is provided that includes the heat shrink tubing disclosed herein (e.g., in a cured form). Exemplary coated devices include, but are not limited to, medical devices (e.g., catheters) to which any of the tubing disclosed herein is applied.

[0052] Furthermore, while this application focuses on tubing, it is noted that other products can be produced that exhibit the surprising and advantageous properties described herein. For example, a wide range of PTFE heat shrink products can be formed in accordance with the present disclosure and, in some embodiments, can exhibit the heat shrink capabilities, higher expansion / recovery, low longitudinal shrinkage, lower temperature recovery, and / or thin wall construction disclosed herein.

[0053] experiment Aspects of the present invention will be more fully described by the following examples, which are provided to illustrate certain aspects of the invention and should not be construed as limiting the invention. While the examples given relate specifically to PTFE heat shrink tubing, it will be understood that fluoropolymer heat shrink tubing generally will benefit from the present invention.

[0054] Comparative Example 1 First, unexpanded control PTFE tubing samples were prepared with a nominal recovery ratio of 1:1 according to the method described herein below. First, PTFE fine powder was mixed with 16% to 25% aliphatic hydrocarbon-based lubricant, rolled for 10 minutes, and then aged for 24 hours in a temperature-controlled environment at 26°C. The lubricant penetrated and coated the agglomerated PTFE particles over the 24 hours. After aging, the PTFE powder / lubricant mixture was pressed into a preform or billet by compression in a preform press, where the PTFE powder / lubricant mixture was consolidated into a cylindrical preform or billet. The preform press had a central rod that allowed the PTFE to flow around a mandrel to form the tubular shape.

[0055] The cylindrical / tubular preform or billet was then loaded into the barrel or cylinder of a ram extruder equipped with a rod that matched the inner diameter of the cylindrical preform. During the extrusion process, the PTFE preform was highly pressurized and extruded to form a pressurized PTFE tube. Upon exiting the extruder, the newly formed PTFE tube was transported to an evaporation oven having a temperature ranging from about 232°C to about 260°C. The evaporation oven was used to remove the lubricant used during the preforming and extrusion processes.

[0056] The PTFE tube was then sintered at a desired temperature for a period of time to achieve the final properties of the PTFE tube. The PTFE tube was sintered at a temperature above the melting point of virgin PTFE resin (342°C to 345°C), for example, at a temperature in the range of 360°C to 380°C. The PTFE tube was sintered for a period of time to allow melting, coalescence, and void removal to proceed, maximizing the properties of the PTFE tube. The PTFE tube was then air-cooled to achieve the specified crystallinity level of the final product. Typically, PTFE has a crystallinity level ranging from about 32% to about 48%. The final product (e.g., PTFE tube) of Comparative Example 1 was produced as described above to have an inner diameter of 0.359 inches and an average wall thickness of about 0.033 inches.

[0057] Comparative Example 2 A PTFE tube was fabricated using the same method and conditions as set forth in Comparative Example 1. The resulting PTFE tube had an inner diameter of 0.487 inches and an average wall thickness of about 0.025 inches.

[0058] After fabrication, the PTFE tube was expanded by pressurizing it with air as it entered a heated die to increase the inner diameter to the required expansion ratio. The expanded PTFE tube was subsequently cooled and set at the expanded diameter such that the RR value was approximately 2 when the tube was reheated to 350°C. The inner diameter and average wall thickness of the expanded PTFE tube were measured and are summarized in Table 1.

[0059] Comparative Example 3 A PTFE tube was fabricated using the same method and conditions as set forth in Comparative Example 1. The resulting PTFE tube had an inner diameter of 0.159 inches and an average wall thickness of about 0.015 inches.

[0060] After fabrication, the PTFE tube was expanded by pressurizing it with air as it entered a heated die to increase the inner diameter to the required expansion ratio. The expanded PTFE tube was subsequently cooled and set at the expanded diameter such that the RR value was approximately 4 when the tube was reheated to 350°C. The inner diameter and average wall thickness of the expanded PTFE tube were measured and are summarized in Table 1.

[0061] Comparative Example 4 PTFE tubes were fabricated using the same method and conditions as those shown in Comparative Example 1. The inner diameter and average wall thickness of the PTFE tubes were measured and are summarized in Table 1.

[0062] The PTFE tube was then expanded by heating it and inflating it with compressed air as it entered the die. The die had an opening along its ID that allowed compressed air to circulate between the OD of the PTFE tube and the ID of the die to maintain the desired expanded diameter. The expanded PTFE tube was subsequently cooled as it exited the die, and the expanded diameter was set such that the RR value was approximately 4 when the tube was reheated to 350°C. The inside diameter and average wall thickness of the expanded PTFE tube were measured and are summarized in Table 1.

[0063] Comparative Example 5 Commercially available PTFE heat shrink tubing was purchased from the market. The inner diameter and average wall thickness of the PTFE tubing were measured and are summarized in Table 1. After preparation, the PTFE tubing was then heated in an oven to 350°C for 10 minutes. The RR was calculated to be approximately 4.

[0064] Example 1 PTFE tubing was fabricated using the same method and conditions as set forth in Comparative Example 1. The resulting PTFE tubing had an inner diameter of 0.042 inches and an average wall thickness of about 0.013 inches.

[0065] After fabrication, the PTFE tubing was then expanded using the process of Comparative Example 4. However, in this example, the processing parameters of expansion air pressure, expansion air temperature, die air pressure, die air temperature, die air flow rate, tube throughput, cooling air temperature, and flow rate were all adjusted to obtain PTFE heat shrink tubing according to the present disclosure. Specifically, the PTFE tubing was expanded using an expansion temperature of 443°C, an internal air pressure of 40 psi, and a die air flow rate of 2 cubic feet per minute (cfm). The inside diameter and average wall thickness of the expanded PTFE tubing were measured, and are summarized in Table 1.

[0066] Example 2 PTFE tubing was fabricated using the same method and conditions as set forth in Comparative Example 1. The resulting PTFE tubing had an inner diameter of 0.042 inches and an average wall thickness of about 0.013 inches.

[0067] The PTFE tubing was then expanded using the process of Comparative Example 4. However, in this example, the processing parameters of expansion air pressure, expansion air temperature, die air pressure, die air temperature, die air flow rate, tube throughput, cooling air temperature, and cooling air flow rate were all adjusted to obtain PTFE heat shrink tubing according to the present disclosure. Specifically, the PTFE tubing was expanded using an expansion temperature of 443°C, an internal air pressure of 45 psi, and a die air flow rate of 2 cubic feet per minute (cfm). The inside diameter and average wall thickness of the expanded PTFE tubing were measured, and are summarized in Table 1.

[0068] Cumulative results Table 1 below shows the nominal tube dimensions of the final PTFE tubes made in Comparative Examples 1-5 and Examples 1-2. Dimensions measured include the inside diameter after expansion, the average wall thickness after expansion, and the nominal recovery rate. Both the inside diameter and the wall thickness were measured in inches. As shown in Table 1 below, the PTFE tubes made according to Examples 1 and 2 exhibited significantly smaller inside diameters than most of the comparative examples, significantly smaller wall thicknesses than Comparative Examples 1 and 2, and the highest recovery rates.

[0069] [Table 1]

[0070] Table 2 below summarizes the DMA and DSC temperature ramp data for the final PTFE tubing produced in Comparative Examples 1-5 and Examples 1-2. DMA and DSC data for an exemplary embodiment of the invention is shown in Figure 2. Specific parameters recorded in Table 2 include the temperature at which minimum storage modulus occurs (E' min ), the peak temperature of the melting endotherm (T m ), and the difference between the temperature at which the minimum storage modulus occurs and the peak temperature of the melting endotherm (ΔT(T m -E' min To obtain DSC thermograms, approximately 10 mg specimens were cut from the PTFE tubing, crimped in non-hermetically sealed aluminum pans, and heated in a TA Instruments DSC2500 (New Castle, Delaware) using a single temperature ramp from ambient to 400°C at a heating rate of 10°C / min to obtain T mwas determined. To acquire the DMA temperature ramp data, specimens were prepared by cutting 5 mm lengths from shrink tubing and slicing the annulus longitudinally to obtain circumferentially oriented rectangular specimens. Temperature scans of E' were collected on a TA Instruments Q800 DMA (New Castle, Delaware) in tensile mode at a heating rate of 3 °C per minute and a deformation amplitude of 15 μm at 1 Hz from ambient temperature to approximately 340 °C. Note that, as shown in Figure 1, some of the collected temperature scans were automatically stopped by the instrument before reaching the final temperature of 340 °C. Without intending to be bound by theory, this may be because some specimens recovered to some degree before reaching 340 °C, causing physical contact with the tensile grips and forcing the instrument to terminate the experiment.

[0071] [Table 2]

[0072] Figure 1 shows the separation in temperature of the E' minimum for Comparative Examples 1-5 and Examples 1-2. As shown in Figure 1, the control sample (Comparative Example 1) does not exhibit a clearly defined relative minimum in the E'-T curve as exhibited by Comparative Examples 2-5 and Examples 1-2. This allows for the separation of E' as defined and disclosed herein. min It is demonstrated that is driven by the entropically unfavorable state locked within the PTFE heat shrink tubing during expansion and is directly influenced by the amount of entropic elasticity available when heating of the PTFE heat shrink tubing initiates recovery.

[0073] 2 shows the separation in temperature of the E' minimum and the peak of the melting endotherm for Example 1, which is representative of an exemplary embodiment of the present disclosure. As shown in FIG. 2, the heat shrink tubing of Example 1 exhibits a large temperature difference between the melting endotherm peak observed in the DSC thermogram and the minimum in the E'-T curve obtained during the DMA temperature ramp.

[0074] Table 3 below summarizes the percent recovery (RR) and change in length (ΔL) for the PTFE heat shrink tubing samples of Comparative Examples 2-5 and Examples 1-2 when recovered for 10 minutes at various temperatures as described above herein. As shown in Table 3, Examples 1 and 2 exhibited significantly higher percent recovery compared to the Comparative Examples without significantly adversely affecting the length change of the final product upon recovery.

[0075] [Table 3]

[0076] Table 4 below summarizes the diameter change for the PTFE heat shrink tubing samples of Comparative Examples 2-5 and Examples 1-2 upon 10 minute recovery at various temperatures. As shown in Table 4, Examples 1 and 2 exhibited a significantly higher percentage in diameter change compared to the Comparative Examples across the entire temperature range.

[0077] [Table 4]

[0078] Table 5 below shows the linear regression data obtained from the linear regression of diameter change for each example over the range of 310°C to 330°C. Diameter change was calculated at various recovery temperatures to which the PTFE tubing was exposed for 10 minutes. This data was imported into OriginLab's OriginPro 2019 v.9.6 data analysis and graphing software, and diameter change was plotted against recovery temperature. To assess the tendency of the example heat shrink tubing to recover more at lower temperatures, a linear regression was performed on the plot of diameter change versus recovery temperature for each example over the range of 310°C to 330°C (well below 350°C, where the maximum achievable RR for PTFE heat shrink occurs). The plot of diameter change versus recovery temperature for each example, including the respective regression lines, is shown in Figure 3.

[0079] [Table 5]

[0080] Table 6 below summarizes the average diameter change for each example over the temperature range of 310°C to 330°C. The average diameter change values ​​correspond to the slope values ​​obtained from the linear regression data in Table 5. From this analysis, it can be concluded that a larger slope value / diameter change explains a greater degree of recovery of the heat shrink tubing at lower temperatures, while a smaller slope value / diameter change explains a lesser degree of recovery of the heat shrink tubing at lower temperatures. As shown in Table 6, Examples 1 and 2 exhibited significantly greater diameter change over the measured temperature range compared to the Comparative Example, demonstrating a greater degree of recovery of the heat shrink tubing at lower temperatures.

[0081] [Table 6]

[0082] Many variations and other embodiments of the present disclosure will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing description. It is to be understood, therefore, that the present disclosure is not limited to the particular embodiments disclosed, and that variations and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. PTFE heat shrink tubing having a recovery ratio (RR) of greater than about 5:

1.

2. 10. The PTFE heat shrink tubing of claim 1, wherein the recovery ratio (RR) is greater than about 5.5:

1.

3. 10. The PTFE heat shrink tubing of claim 1, wherein the recovery ratio (RR) is greater than about 6:

1.

4. 10. The PTFE heat shrink tubing of claim 1, wherein the PTFE heat shrink tubing has an average wall thickness of 0.003 inches or less after expansion.

5. PTFE heat shrink tubing, where a linear regression performed on a plot of diameter change versus recovery temperature between 310°C and 330°C yields a slope value greater than about 1.3% / °C.

6. 6. The PTFE heat shrink tubing of claim 5, wherein the PTFE heat shrink tubing has a RR greater than about 5:

1.

7. 6. The PTFE heat shrink tubing of claim 5, wherein the PTFE heat shrink tubing has an RR greater than about 5.5:

1.

8. 6. The PTFE heat shrink tubing of claim 5, wherein the PTFE heat shrink tubing has an RR greater than about 6:

1.

9. 6. The PTFE heat shrink tubing of claim 5, wherein the PTFE heat shrink tubing has an average wall thickness of 0.003 inches or less after expansion.

10. 1. A heat shrinkable tubing comprising: tubing having a wall comprising PTFE having an inner diameter (ID), the inner diameter (ID) being about 0.3 inches or less after expansion, and capable of shrinking by at least about 78% when heated at 350°C for 10 minutes.

11. 11. The heat shrink tubing of claim 10, wherein the inside diameter (ID) is reducible by at least about 80% when heated at 350°C for 10 minutes.

12. 11. The heat shrink tubing of claim 10, wherein the walls of the heat shrink tubing have an average wall thickness of about 0.003 inches or less after expansion.

13. 11. The heat shrink tubing of claim 10, wherein a linear regression performed on a plot of diameter change versus recovery temperature between 310°C and 330°C produces a slope value of greater than about 1.3% / °C.

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