Thin-walled heat-shrinkable tubing

Abstract

Heat shrink tubing is provided that generally comprises at least one fluoropolymer resin and exhibits a variety of desirable properties. The tubing may exhibit desirable physical properties such as heat shrinkability, high expansion / recovery ratios, low longitudinal shrinkage, low temperature recovery, and average wall thickness of less than about 0.003 inches.

Description

[Technical Field]

[0001] This application relates to a heat-shrinkable polymer tubing that has applications in various fields, and to a method for producing such heat-shrinkable polymer tubing. [Background technology]

[0002] Heat shrink tubing generally consists of plastic material that has been extruded and expanded into a tubular shape. The extruded and expanded tube is designed to shrink (i.e., become smaller in diameter) when heated to a given temperature. For this reason, heat shrink tubing can provide a variety of functions. Heat shrink tubing can provide a tightly fitting protective sheath that closely covers various elements and insulates them (e.g., protects elements from abrasion and provides thermal, chemical, moisture, and / or electrical insulation). Heat shrink tubing can be useful for holding certain elements together (i.e., within the same heat shrink tubing). Furthermore, heat shrink tubing can act to seal / isolate certain elements from other elements and can be used to join / fuse two elements, for example, two tubes. Heat shrink tubing can also be useful for modifying the properties of an underlying material (e.g., by surrounding another material and shrinking that material as well). These properties make tubing useful for a variety of purposes, and heat-shrinkable tubing is used in a wide range of fields, such as medicine, chemistry, electrical engineering, optics, electronics, aerospace, automotive, and telecommunications.

[0003] In the field of medicine, heat-shrink tubing is particularly useful in designing increasingly small and complex devices (e.g., catheters, endoscopes, etc.) that are inserted into the body. One typical medical application of heat-shrink tubing relates to the manufacture of guide catheters having a tubular structure having an inner polymer layer, an intermediate layer of wire braid, and an outer layer of another polymer. To assemble such a catheter, expanded heat-shrink tubing is typically applied to a shaft assembled around a mandrel, and this assembly is exposed to a temperature high enough to shrink the heat-shrink tubing. Under these conditions, the outer polymer layer inside the catheter shaft melts and flows out, the heat-shrink tubing shrinks, and a compressive force is applied such that the inner and outer polymer layers of the catheter shaft bond together, enclosing the wire braid inside. The heat-shrink tubing is then removed and disposed of, and the catheter assembly is removed from the mandrel. See, for example, the disclosures in Patent Document 1 to Ross and Patent Document 2 to Lunn (which are part of this specification by reference).

[0004] It should be noted that heat-shrinkable tubing has been commercially manufactured for decades using various processes, such as vacuum expansion, gas pressure forming, and sequential heating / stretching. Known methods for expanding heat-shrinkable tubing are described, for example, in the disclosures of Edward et al. (Patent Document 3), Sullivan (Patent Document 4), Yoshida et al. (Patent Document 5), Henson (Patent Document 6), Henson (Patent Document 7), and Roof et al. (Patent Document 8, each of which is incorporated herein by reference). However, heat-shrinkable tubing is typically only commercially available in grades with a maximum recovery ratio of 4:1. For example, typical polytetrafluoroethylene ("PTFE") heat-shrinkable tubing is currently commercially available with a maximum recovery ratio of 4:1, and typical fluorinated ethylene propylene ("FEP") heat-shrinkable tubing is currently commercially available with a maximum recovery ratio of 2:1. Furthermore, these products typically involve a longitudinal length change of up to 15% during recovery.

[0005] Therefore, there is a need for tubing that can be applied to device components to enclose and compress them as needed, and that can provide a high recovery rate without increasing the corresponding longitudinal changes. Furthermore, there is a need for tubing with thin walls that can enhance heat transfer during lamination and improve 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 [Overview of the project]

[0007] This disclosure relates to an extended form of fluoropolymer heat shrink tubing that exhibits a higher recovery rate than conventional heat shrink tubing without the corresponding significant increase in the longitudinal direction (typically seen in conventional heat shrink tubing). Furthermore, certain heat shrink tubings of this disclosure have thin walls that were previously unattainable with commercially available fluoropolymer heat shrink tubing and / or are recoverable at lower temperatures than those used in conventional heat shrink processes.

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

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

[0010] Another aspect of the present disclosure provides a PTFE heat-shrinkable tubing in which the difference between the temperature corresponding to the peak fusion endothermic temperature obtained from a DSC temperature lamp 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 lamp of a heat-shrinkable tubing specimen circumferentially oriented in a tensile grip is greater than about 7.5°C. In some embodiments, the PTFE heat-shrinkable tubing may have an RR greater than about 5:1. In certain embodiments, the PTFE heat-shrinkable 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-shrinkable 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-shrinkable tubing may have an average wall thickness of about 0.0005 inches or less after expansion. In some embodiments, linear regression performed between 310°C and 330°C on a plot of diameter change versus recovery temperature yields a slope value greater than approximately 1.3% / °C for the thermal shrinkage tubing of the present disclosure.

[0011] A further aspect of the present disclosure includes tubing having a wall portion that includes PTFE having an inner diameter (ID), where the ID is about 0.3 inches or less after expansion and, when heated at 350 °C for 10 minutes, the ID is capable of shrinking by at least about 78%. In some embodiments, when heated to 350 °C over 10 minutes, the ID of the heat - shrink tubing is capable of shrinking by at least about 80%. 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 in a DMA temperature ramp of a circumferentially oriented heat - shrink tubing specimen in a tensile grip exceeds about 7.5 °C. In some embodiments, a linear regression performed between 310 °C and 330 °C on a plot of diameter change versus recovery temperature results in a slope value exceeding about 1.3% / °C for the 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 described briefly below. The present disclosure includes any combination of two, three, four, or more features or elements shown in the present disclosure or recited in any one or more of the claims, whether or not such features or elements are explicitly combined or otherwise recited in the specific embodiments of this specification. The present disclosure is to be read as a whole such that, unless otherwise clearly indicated by the context of the present disclosure, it is intended that any separable features or elements of the present disclosure may be combined in any of its aspects and embodiments.

[0013] To understand embodiments of the present invention, reference is made to the accompanying drawings. These are not necessarily drawn to scale, and in the drawings, reference numerals represent components of exemplary embodiments of the present invention. The drawings are merely illustrative and are not to be construed as limiting the present invention.

Brief Description of the Drawings

[0014] [Figure 1] A graph showing the storage modulus as a function of temperature for a PTFE heat - shrinkable tube made according to an exemplary embodiment of the present disclosure compared with several commercially available PTFE heat - shrinkable tubes. [Figure 2] A diagram showing an overlay of a DSC curve and a DMA curve obtained from a PTFE heat - shrinkable tube made according to an exemplary embodiment of the present disclosure. [Figure 3] A graph showing the percent change in inner diameter measured in the range of 310°C to 330°C and its linear regression for a PTFE heat - shrinkable tube made according to an exemplary embodiment of the present disclosure compared with several commercially available PTFE heat - shrinkable tubes when recovered for 10 minutes at various temperatures.

Modes for Carrying Out the Invention

[0015] Some, but not all, embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In fact, these inventions can be embodied in many different forms and are not to be construed as limited to the embodiments described herein. Rather, these embodiments are presented so that this disclosure will satisfy applicable legal requirements. Like reference numerals represent like elements throughout.

[0016] The terms used herein are intended solely to describe specific embodiments and are not intended to limit the invention. Where used herein, the singular forms "a" and "an" and "the" are intended to include the plural form unless otherwise explicitly indicated in the context. Where used herein, the terms "comprises" and / or "comprising" specify the presence of the mentioned features, integers, processes, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, processes, operations, elements, components, and / or groups thereof.

[0017] This disclosure provides heat-shrinkable tubing with specific properties and combinations of specific properties, as will be further outlined herein. Generally, “heat-shrinkable tubing” is shrinkable tubing produced by expanding a polymer (“input”) tubing (e.g., extruded tubing) to obtain heat-shrinkable tubing (also referred herein as the “expanded” form). Upon heating and / or sintering, the heat-shrinkable tubing “shrinks” to a size (generally referred to as its “recovered” size) that is equivalent to (or close to) its original / input size. The composition and overall size of the heat-shrinkable tubing according to this disclosure can be wide-ranging and are not particularly limited. The heat-shrinkable tubing can be, for example, expressed in terms of its inner diameter after expansion (“ID”) (referred herein as “expanded inner diameter” (ID)). e ) also called) or its inner diameter after recovery ("ID") (in this specification, "recovered inner diameter (ID)") r It can be defined by its length, its mean wall thickness, its expansion rate (ER), and its recovery rate (RR).

[0018] In some embodiments, the heat-shrinkable tubing disclosed comprises, essentially consists of, or comprises one or more fluorinated polymers. Exemplary fluorinated polymers according to this disclosure include, but are not limited to, fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF), perfluoroalkoxyalkanes (PFA), perfluoro(alkyl vinyl ether) (PAVE) (e.g., perfluoro(methyl vinyl) ether, PMVE, or perfluoro(propyl vinyl) ether (PPVE)), polytetrafluoroethylene (PTFE), tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride terpolymers (THV), poly(ethylene-co-tetrafluoroethylene) (ETFE), ethylene chlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene and perfluoromethyl vinyl ether copolymers (MFA), or two or more copolymers, blends, or derivatives of any of the above. In certain embodiments, the disclosed heat-shrinkable tubing contains PTFE, is essentially composed of PTFE, or is composed of PTFE, and such heat-shrinkable tubing may be referred to herein as “PTFE heat-shrinkable tubing.” In some other embodiments, the disclosed heat-shrinkable tubing contains, is essentially composed of, or may be composed of one or more non-fluorinated polymers, such as polyaryletherketones. Exemplary polyaryletherketones provided herein 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, 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 may include lubricants, such as aliphatic hydrocarbon lubricants. In certain embodiments, the lubricant may be, for example, naphthalene. Note that the 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 this disclosure. For example, in certain embodiments, the lubricant may be applied to a polymer resin (e.g., PTFE resin) before the input tubing is extruded, and the lubricant may be evaporated after the input tubing has exited the extrusion die and before the input tubing is sintered. The amount of lubricant or other additives that may be included is not particularly limited. In some embodiments, for example, an additive (e.g., a lubricant) may be included in an amount ranging from about 1% to about 30% by weight, about 16% to about 25% by weight, or about 10% to about 20% by weight relative to the total weight of the tubing. In other embodiments, the tubing may not contain any additives at all.

[0020] The size of the heat-shrinkable tubing described herein (e.g., length, diameter (i.e., expanded inner diameter, ID), and average wall thickness) is not particularly limited within the scope of this disclosure. For example, the length of the tubing described herein may range from individual size units (e.g., in some embodiments, approximately 0.25 inches to 120 inches in the case of catheter manufacturing) to lengths that are easily transportable and can be further cut into individual size units, or to large-scale production lengths (e.g., approximately several hundred feet). The diameter of the tubing described herein may vary in particular depending on the intended use of the tubing. Certain expanded IDs of the tubing described herein, particularly for medical applications, may range from approximately 0.01 inches to approximately 1.5 inches (e.g., approximately 0.025 inches to approximately 0.75 inches, or approximately 0.05 inches to approximately 0.5 inches), but tubing with expanded IDs outside this range is also covered by this disclosure, particularly in the context of applications in different fields. In some embodiments, for example, the expanded ID of the tubing may range from approximately 0.034 inches to approximately 4 inches.

[0021] With respect to the wall thickness of the tubing, it should be noted that the higher expansion / recovery rates demonstrated by the PTFE heat shrink tubing of this disclosure may, in some embodiments, result in thinner expanded and recovered wall sections than commercially available PTFE heat shrink tubing and / or FEP heat shrink tubing, for example, as shown in the examples below in this specification. In certain exemplary embodiments, the heat shrink tubing of this disclosure may have an average wall thickness in the range of about 0.0001 inches to about 0.005 inches, about 0.0001 inches to about 0.0025 inches, or about 0.0001 inches to about 0.0005 inches. In some embodiments, the heat shrink tubing of this 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. Such values ​​are after expansion and before recovery.

[0022] These considerably thinner wall thicknesses offer significant advantages compared to commercially available PTFE and FEP heat-shrinkable tubing currently in use. For example, the thin-walled PTFE heat-shrinkable products according to this disclosure can enhance heat transfer during reflow and improve the overall efficiency of the reflow process. With respect to FEP heat-shrinkable tubing, it should be 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 in PTFE heat-shrinkable tubing compared to FEP heat-shrinkable 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 (these are incorporated herein by reference).

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

[0024] Such characteristics can be defined using the following equations: Expansion ratio = ER = ID e / ID o Recovery ratio = RR = ID e / ID r Length change = ΔL = ((L r -L e ) / L e )(100) Diameter change = ΔD = (ID e -ID r ) / ID e [[ID=二十九]])(100)

[0025] In these equations, L e and L r are, respectively, the length of the heat - shrink tubing (expanded form) and the length of the "recovered" (i.e., heat - shrunk) tubing. ID o refers to the initial inner diameter (ID) of the input tube (i.e., the tube before expansion and subsequent "shrinkage"), ID e refers to the inner 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. When used in this specification, the above parameters were calculated as follows.

[0026] The length change (ΔL) is determined as follows: Before placing the heat-shrinkable tubing in an oven for unlimited recovery, the expanded tubing is cut to a length of 4 inches. The 4-inch length of the test specimen is carefully cut from the heat-shrinkable tubing, ensuring that there are no burrs or other deformations on the specimen and that the specimen is perpendicular to the longitudinal axis of the tubing. After the unlimited recovery process at the specified temperature, the length of the tubing is remeasured to the nearest 1 / 64 inch using a validated ruler to determine the amount of shrinkage or elongation that occurred during the process. For example, the recovered length is subtracted from the expanded length, divided by the expanded length, and then multiplied by 100 to obtain the percentage of the overall length change (ΔL). Typically, the longitudinal change is measured to be within the range of approximately ±20% (i.e., the length change is allowed to elongate or shrink by approximately 20% or less during recovery). In some embodiments, the longitudinal change is measured to be within the range of approximately ±15%, approximately ±10%, or approximately ±5%. In certain embodiments, the longitudinal change was less than 5% on average. The standard time and recovery temperature for PTFE heat shrinkage is 10 minutes at 350°C. The standard time and recovery temperature for FEP is 10 minutes at 210°C to 221°C. For catheter manufacturing, the PTFE heat shrinkage is recovered at 260°C to reflow the outer jacket.

[0027] The expansion rate (ER) is calculated by dividing the measured expanded ID by the measured input ID. The recovery rate (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 each (for example, the first specimen was heated to 310°C, the second to 320°C, the third to 330°C, the fourth to 340°C, and the fifth to 350°C). After each heat-shrink tubing specimen is exposed to the specified recovery temperature for 10 minutes, it is removed from the oven and allowed to cool to ambient temperature. This subjects the expanded heat-shrink tubing to an unlimited recovery process. After cooling to ambient temperature, the recovered tubing is cut into four sections of equal length using a sharp razor blade. This provides five different measurement locations along the length of the recovered heat-shrink tubing. Next, the ID is measured at each different location using validated measuring instruments, and the average is interpreted as the recovered ID. The recovery rate (RR) of the heat-shrinkable product at a specified temperature is obtained by dividing the ID of the expanded tubing by the ID of the recovered tubing measured after an unlimited recovery process. Subsequently, the diameter change of the heat-shrinkable tubing is calculated by subtracting the ID of the recovered tubing from the ID of the expanded tubing, dividing by the ID of the expanded tubing, and then multiplying this amount by 100 to obtain the percentage of overall diameter change (ΔD).

[0028] Regarding thermal shrinkage capability, in certain embodiments, the tubing disclosed herein is capable of shrinking (reducing in diameter) when exposed to heat (e.g., being in an expanded state). The thermal shrinkage material is generally applied to a substrate material (e.g., a catheter structure, a medical device component, etc.) and heated. When subjected to a thermal cycle, the inner and outer diameters of the tubing decrease (resulting in an inner diameter (ID) and outer diameter (OD) smaller than those indicated by the expanded tubing, referred to as "recovered" ID and OD). Preferably, only the diameter of the tubing shrinks substantially, and the length does not shrink substantially (i.e., the tubing shrinks on only one side). As described above, the ratio between the expanded ID and the original input ID is called the expansion ratio. The expansion ratio is the expanded ID divided by the original input ID. It has been found that by using die temperatures higher than those typically used, expansion ratios far exceeding 4:1 can be obtained. For example, typical expansion ratios for the types of tubing described herein may 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] While high expansion ratios can be achieved using commercially available heat shrinkage methods, it should be noted that the heat shrinkage tubing of this disclosure can surprisingly exhibit higher recovery ratios compared to conventional heat shrinkage tubing known in the art (for example, conventional heat shrinkage tubing known in the art typically has a recovery ratio of 4:1 or less). As stated above, the recovery ratio is defined as, for example, the ratio between the expanded ID and the recovered ID. The recovery ratio is the expanded ID divided by the recovered ID. Although not intended to be theoretically binding, it has been found that rapid cooling of the expanded tubing is effective in fixing the tubing in an entropically undesirable expanded state before it clearly begins to recover, thus producing final products with recovery ratios exceeding the maximum commercially available 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-shrinkable tubing of the present disclosure may exhibit recovery ratios 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 rate of the heat-shrinkable tubing of this disclosure can also be characterized in terms of the possibility of reduction in their inner diameter (ID) (e.g., the percentage of their overall diameter change (ΔD) calculated using the equation above). For example, a recovery rate of 4.55:1 corresponds to an ID that can be reduced by about 78%, and a recovery rate of 5:1 corresponds to an ID that can be reduced by about 80%. As shown in Figure 3, both Example 1 and Example 2, prepared according to the method of this disclosure, showed a percentage of diameter change of about 80% or more after recovery, whereas each of the comparative examples showed a significantly lower percentage of diameter change after recovery.

[0031] In some embodiments, if the recovery rate is within the ranges described herein, the heat-shrinkable tubing will exhibit a small change in the longitudinal direction when it shrinks, for example, less than about 20%. In certain embodiments, such heat-shrinkable tubing may exhibit an even smaller change in the longitudinal direction, for example, 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-shrinkable tubing described herein offer certain distinct advantages compared to commercially available heat-shrinkable tubing. In particular, such higher recovery rates can enable the encapsulation of complex mandrel shapes (including, but not limited to, tapered mandrels or mandrels with steep transitions). Furthermore, by achieving such high recovery rates at low temperatures, as described herein, an advantageous increase in the variety of polymer materials that can be encapsulated without decomposition is achieved. For example, in some embodiments, a double heat-shrinkable structure with an outer layer having a higher recovery rate (e.g., a PTFE heat-shrinkable outer layer) can enable complete encapsulation of the molten inner layer around complex parts and shapes. Examples of double heat-shrinkable structures and applications are shown, for example, in the disclosure of Hunter et al., U.S. Patent Application Publication No. 2021 / 0370581, which is, by reference, entirely part of this specification. Furthermore, as described herein, such a high recovery rate may result in heat-shrinkable tubing capable of recovering over the entire contour of complex mandrels, such as those with varying diameters or taper angles and taper lengths, thus providing thin-walled catheter liners that are not currently available on the market.

[0033] In certain embodiments, the heat-shrinkable tubing described herein may be described as “peeling” and can be easily peeled or torn longitudinally (e.g., removed from the underlying material). This peeling property may, advantageously, allow the tubing to be installed, used, and removed in some embodiments without any cuts, breaks, indentations, or perforations along the length of the tubing. It should be noted that PTFE is inherently peeling in the flow direction (e.g., longitudinal direction), which may result in easy removal of the heat-shrinkable tubing after reflowing the inner polymer material (e.g., catheter jacket, medical device, or double heat-shrinkable structure). Examples of peeling heat-shrinkable tubing are shown, for example, in Roof et al. Patent Document 8 (which, by reference, is in whole part herein).

[0034] Certain properties of the tubing disclosed herein can be evaluated by differential scanning calorimetry (DSC). DSC is an analytical technique that provides information on the thermal properties of a material and is well known to those skilled in the art. A typical DSC experiment (generally called a single heat temperature ramp) can be performed to determine the peak temperature of the endothermic melt transition for semicrystalline polymer materials (e.g., PTFE). The peak temperature of the melt endothermic transition may vary depending on the specific composition of the tubing (i.e., the type of fluorinated polymer resin) and the previous thermal history of the tubing (i.e., the thermomechanical history given to the material during processing). The peak temperature of the melt endothermic transition observed in the DSC thermogram is generally T m This is abbreviated as follows. The thermomechanical history given to the heat shrink tubing of this disclosure using the method described herein is observed in the DSC thermogram for virgin PTFE resin from T m It changes.

[0035] PTFE is known to have a high melting temperature and melt viscosity; the melting temperature of virgin PTFE resin is approximately 342°C to 345°C, and the melt viscosity is in the range of approximately 1 GPa·s to 10 GPa·s. This high melt viscosity suppresses flow, thereby allowing other thermoplastics to be processed by conventional melt extrusion techniques (e.g., using a screw extruder). Due to the high melt viscosity of PTFE, 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 tubes can be sintered at temperatures above the melting point of virgin PTFE resin (i.e., 342°C to 345°C), for example, in the range of approximately 360°C to approximately 380°C. Typically, PTFE tubes are sintered for a period of time sufficient to allow fusion, bonding, and void removal to proceed and maximize certain properties of the PTFE tube.

[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 in response to time, temperature, and frequency. The storage modulus (E') is a measure of the elastic behavior of a material (i.e., the material's ability to elastically store energy). A typical DMA temperature ramp experiment involves increasing the temperature at a constant (i.e., linear) rate while simultaneously applying sinusoidal deformation at a specified frequency and monitoring the material's response (i.e., stress).

[0037] As described above in DMA, the storage modulus of the specimen obtained from the heat shrink tubing in the circumferential direction receiving the temperature lamp decreases with temperature until it approaches the expansion temperature. At this point, a significant minimum is reached in the E'-T (storage modulus vs. temperature) curve, and thereafter E' increases as the heat shrink tubing recovers in the direction of the dynamic mechanical test. From there, the minimum value in the E'-T curve is E' min Let's call it that. minThe presence of this material is thought to be unrelated to the crystallization process and is due to entropic elasticity, as seen in the recovery of pre-expanded specimens. See, for example, L. Andena el al., Polym. Eng. Sci, 44, 2004, 1368-1378 (which, by reference, constitutes part of this specification).

[0038] E' min It should be noted that this has proven to be an important parameter in describing the heat shrink tubing of the present invention. Typically, the combination of processing parameters and material properties determines the crystalline / amorphous morphology of the expanded heat shrink tubing, which is fixed in an entropically unfavorable state after the expansion process. This morphology determines not only the entropic elasticity available to the tubing to recover from its expanded shape, but also the degree to which the tubing recovers when exposed to various recovery temperatures. While not intended to be theoretical, the T of the heat shrink tubing m In relation to E', at the lowest possible temperature min It was found that adjusting the processing parameters to produce this result is important. For example, heat shrink tubing that recovers to a greater extent at lower temperatures performs better in many applications. Therefore, it is desirable to manufacture PTFE heat shrink tubing that exhibits a large temperature difference between the molten endothermic peak obtained from a DSC temperature lamp and the minimum value in the E'-T curve obtained from a DMA temperature lamp.

[0039] The heat-shrinkable tubing provided herein can be used in a variety of applications. In specific applications, these heat-shrinkable tubings can be applied to a substrate material (e.g., a device, device component, joint, mounting part, wire, etc.) and heated to form a coating on the substrate material. Therefore, this disclosure encompasses materials or objects to which the tubing disclosed herein has been applied. For example, in some embodiments, coated devices (e.g., medical devices) including the tubing disclosed herein are provided. Exemplary coated devices include, but are not limited to, medical devices (e.g., catheters) to which any of the tubing disclosed herein has been applied.

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

[0041] Any fluorinated polymer resin can be used in accordance with this disclosure. Fluoropolymer resins are of particular interest to this disclosure. 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 tubing commercially available today, but this disclosure is not limited to these. Exemplary fluorinated polymer resins useful in this disclosure include, but are not limited to, resins in which the polymer comprises, consists of, or is essentially composed of, two or more copolymers, blends, or derivatives thereof, 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)), tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride terpolymers (THV), poly(ethylene-co-tetrafluoroethylene) (ETFE), ethylene chlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoromethyl vinyl ether (MFA), or two or more copolymers, blends, or derivatives thereof.

[0042] In certain embodiments, the heat-shrinkable tubing of this disclosure is made using PTFE resin, and therefore in some embodiments, it may consist of PTFE, may essentially consist of PTFE, or may contain PTFE. Typically, PTFE resin can be provided in a variety of different forms, such as solids, powders, granules, dispersions, solutions, gels, etc. In certain embodiments, PTFE heat-shrinkable tubing may be made using PTFE powder in particular. The type of PTFE powder incorporated in such embodiments may vary and may include not only conventional PTFE extruded grade powders, but also PTFE granules, particles, etc., of various particle sizes. Extruded 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-shrinkable tubing provided herein is not limited to PTFE resin and may be made using one or more fluorinated polymer resins described herein in addition to or instead of PTFE.

[0043] In general, there can be a variety of methods for producing such heat-shrinkable tubing. Generally, the desired resin(s) (e.g., PTFE resin) is formed into a tube shape, for example by extrusion molding, and then mechanically expanded. The means for carrying out these steps can vary as described herein.

[0044] For example, a resin (e.g., PTFE resin) can be molded into a tube by extrusion molding. Extrusion molding generally involves placing the desired resin(s) into an extruder (e.g., a ram extruder). Inside the extruder, the resin(s) are heated, compressed, and pushed through an annular die set to produce a tube. Tubes of various diameters and lengths can be manufactured. The dimensions of the tube can be determined by the tool size on the extrusion molding line, and other parameters of the extrusion molding 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 mounted on the end of the extrusion molding cylinder and generally includes a rod, mandrel, master die, tube die, and end cap heater.

[0045] The appropriate tool to be used is determined by the required size of the finished product and the drawing ratio. The drawing ratio controls the extrusion pressure, fibrillation, and mechanical properties of the PTFE resin or PTFE powder. The drawing ratio is a dimensionless number calculated from the ratio of the cross-sectional area of ​​the mandrel rod to the cross-sectional area of ​​the extrusion cylinder minus the cross-sectional area of ​​the mandrel tip to the cross-sectional area of ​​the extrusion die minus the cross-sectional area of ​​the mandrel tip.

[0046] During the extrusion process, as resin particles enter the zone of the tube die, they are subjected to high pressure. Due to the reduction in cross-sectional area in the flow direction, the particles deform and rub against each other under the applied high pressure. The PTFE initiates secondary particle shearing, and the microcrystals begin to mechanically entangle, resulting in the interconnection of adjacent particles. As the particles flow toward the die exit, they accelerate and stretch, during which the mechanically entangled microcrystals unravel, generating fibrils. Typically, the more fibrils generated, the more elastic and stretchable the paste becomes, leading to higher extrusion pressures.

[0047] In some embodiments, upon exiting the extruder, the newly formed extruded tube can be transferred to an evaporating oven having a temperature in the range of about 232°C to about 260°C to remove all lubricants used during the pre-forming and extrusion processes. In certain embodiments, the extruded tube can then be sintered at a desired temperature for a certain period of time to obtain 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, in the range of about 360°C to about 380°C. Typically, the extruded tube is sintered for a period of time sufficient to allow fusion, bonding, and void removal to proceed and maximize certain properties of the PTFE tube.

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

[0049] Next, the extruded tube form is typically expanded radially (e.g., by mechanical means) to obtain expanded tubing material, i.e., heat-shrinkable tubing (i.e., tubing whose diameter decreases when heated). The expansion of the input tubing (i.e., the initial extruded tube form) can be performed in-line together with the extrusion or offline (i.e., independently of and / or following the extrusion process). It is intended that all means of expanding the tubing radially are encompassed by the present invention. Generally, during the expansion process, the tubing is expanded radially by pressurizing the inside of the tubing and applying stress to the tube wall. This pressurization can be done by any means that can create a differential pressure between the inside and outside of the tubing. Such a differential pressure can be created by applying a pressure above atmospheric pressure to the center of the tube, a pressure below atmospheric pressure to the outside of the tube, or a combination of both. The stress induced in the tube wall causes the tube to expand radially, i.e., its diameter increases. The expansion rate can be controlled so that the tube remains expanded and does not recover until it undergoes further thermal cycling. The degree 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 approximately 1.05 times its original (unexpanded) diameter to approximately 10 times its original (unexpanded) diameter.

[0050] In certain embodiments, a PTFE heat-shrinkable tube manufactured according to this disclosure can be radially expanded using, for example, a process described in Henson's Patent Document 6 (which, by reference, forms an entirety of this specification). For example, the Patent Document 6 describes a process for producing a fluoropolymer heat-shrinkable tubing by expanding the tube using a first fluid inside the tube and suppressing expansion within the expansion chamber using a second fluid outside the tube. In other embodiments, the tubing can be expanded by, for example, adjusting the flow rate of air outside the tube, the chamber temperature, the air pressure inside the tube, and the speed at which the tube passes through the expansion chamber. In certain embodiments, the heat-shrinkable tube of this disclosure is expanded at a high temperature through a die using any number of methods known in the art, and subsequently cooled at the die outlet. Cooling can be achieved using a fluid such as water, oil, or air. Adjustable machining parameters include die type, die diameter and length, die temperature, fluid pressure inside the tube, fluid pressure outside the tube, cooling method, type and temperature of refrigerant, expansion ratio, tube material, tube ID, tube OD, and tube wall thickness.

[0051] The heat-shrinkable tubing provided herein can be used in a variety of applications. In specific applications, the heat-shrinkable tubing provided herein can be applied to a substrate material (e.g., a device, device component, joint, mounting part, wire, etc.) and then heated / recovered to form a coating on the substrate material. Therefore, this disclosure encompasses materials or objects to which the tubing disclosed herein has been applied. For example, in some embodiments, coated devices (e.g., medical devices) including the heat-shrinkable tubing disclosed herein (e.g., in a recovered form) are provided. Exemplary coated devices include, but are not limited to, medical devices (e.g., catheters) to which any of the tubing disclosed herein has been applied.

[0052] Furthermore, while this application focuses on tubing, it should be noted that other products exhibiting the remarkable advantageous properties described herein can also be manufactured. For example, a wide range of PTFE heat-shrinkable products can be formed according to this disclosure, and in some embodiments, they may exhibit the heat-shrinkability, higher expansion / recovery rates, lower longitudinal shrinkage, lower temperature recovery, and / or thin-walled structures disclosed herein.

[0053] experiment The embodiments of the present invention will be further illustrated by the following examples, which are provided to illustrate certain specific embodiments of the invention and should not be construed as limiting the invention. The examples shown relate particularly to PTFE heat shrink tubing, but it will be understood that fluoropolymer heat shrink tubing will generally benefit from the present invention.

[0054] Comparative Example 1 First, unexpanded control PTFE tube samples were prepared with a nominal recovery ratio of 1:1 according to the method described below herein. First, PTFE fine powder was mixed with 16%–25% aliphatic hydrocarbon lubricant, rolled for 10 minutes, and then aged for 24 hours in a temperature-controlled environment of 26°C. The lubricant was then impregnated into the aggregated PTFE particles over 24 hours, forming a coating. After aging, the PTFE powder / lubricant mixture was formed into a preform or billet by pressurization in a preform press. Here, the PTFE powder / lubricant mixture was compacted into a cylindrical preform or billet. The preform press has a rod in the center, allowing PTFE to flow around a mandrel to form a tube shape.

[0055] Next, the cylindrical / tubular preform or billet was loaded into the barrel or cylinder of a ram extruder equipped with a rod matching 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 transferred to an evaporation oven with a temperature in the range of approximately 232°C to 260°C. The evaporation oven was used to remove the lubricants used during the pre-forming and extrusion processes.

[0056] Next, the PTFE tubes were sintered at a desired temperature for a set period of time to obtain the final properties of the PTFE tubes. The PTFE tubes were sintered at a temperature exceeding the melting point of virgin PTFE resin (342°C to 345°C), for example, in the range of 360°C to 380°C. The PTFE tubes were sintered for a period of time that allowed melting, bonding, and void removal to proceed, maximizing the properties of the PTFE tubes. Subsequently, the PTFE tubes were air-cooled to achieve the specified level of crystallinity of the final product. Typically, PTFE has a degree of crystallinity in the range of approximately 32% to approximately 48%. The final product of Comparative Example 1 (e.g., a PTFE tube) was manufactured as described above to have an inner diameter of 0.359 inches and an average wall thickness of approximately 0.033 inches.

[0057] Comparative Example 2 PTFE tubes were fabricated using the same method and conditions as shown in Comparative Example 1. The resulting PTFE tubes had an inner diameter of 0.487 inches and an average wall thickness of approximately 0.025 inches.

[0058] After fabrication, the PTFE tubes were expanded by pressurizing them with air when they entered a heated die, increasing their inner diameter to the required expansion ratio. Subsequently, the expanded PTFE tubes were cooled and fixed at their expanded diameter so that the RR value was approximately 2 when the tubes were reheated to 350°C. The inner diameter and average wall thickness of the expanded PTFE tubes were measured. These results are summarized in Table 1.

[0059] Comparative Example 3 PTFE tubes were fabricated using the same method and conditions as shown in Comparative Example 1. The resulting PTFE tubes had an inner diameter of 0.159 inches and an average wall thickness of approximately 0.015 inches.

[0060] After fabrication, the PTFE tubes were expanded by pressurizing them with air when they entered a heated die, increasing their inner diameter to the required expansion ratio. Subsequently, the expanded PTFE tubes were cooled and fixed at their expanded diameter so that the RR value was approximately 4 when the tubes were reheated to 350°C. The inner diameter and average wall thickness of the expanded PTFE tubes were measured. These results are summarized in Table 1.

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

[0062] Next, the PTFE tube was heated and expanded using compressed air when it entered the die. The die had an opening along its ID, which allowed compressed air to circulate between the OD of the PTFE tube and the ID of the die, maintaining the desired expanded diameter. Subsequently, the thus expanded PTFE tube was cooled when it exited the die, fixing it to an 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. These are summarized in Table 1.

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

[0064] Example 1 PTFE tubes were fabricated using the same method and conditions as shown in Comparative Example 1. The resulting PTFE tubes had an inner diameter of 0.042 inches and an average wall thickness of approximately 0.013 inches.

[0065] After fabrication, the PTFE tubes were then expanded using the process of Comparative Example 4. However, in this example, all processing parameters, including expansion air pressure, expansion air temperature, die air pressure, die air temperature, die air flow rate, tube processing volume, cooling air temperature, and flow rate, were adjusted to obtain the PTFE heat-shrinkable tubes according to the present disclosure. In particular, the PTFE tubes were 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 inner diameter and average wall thickness of the expanded PTFE tubes were measured. These are summarized in Table 1.

[0066] Example 2 PTFE tubes were fabricated using the same method and conditions as shown in Comparative Example 1. The resulting PTFE tubes had an inner diameter of 0.042 inches and an average wall thickness of approximately 0.013 inches.

[0067] The PTFE tube was then expanded using the process of Comparative Example 4. However, in this example, all processing parameters, including expansion air pressure, expansion air temperature, die air pressure, die air temperature, die air flow rate, tube processing volume, cooling air temperature, and cooling air flow rate, were adjusted to obtain the PTFE heat-shrinkable tube according to the present disclosure. In particular, the PTFE tube 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 inner diameter and average wall thickness of the expanded PTFE tube were measured. These are summarized in Table 1.

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

[0069] [Table 1]

[0070] Table 2 below summarizes the DMA and DSC temperature lamp data for the final PTFE tubes produced in Comparative Examples 1 to 5 and Examples 1 to 2. Figure 2 shows the DMA and DSC data for exemplary embodiments of the present invention. Specific parameters recorded in Table 2 include the temperature at which the minimum storage modulus occurs (E'). min ), peak temperature of fusion endothermic reaction (T m ), and the difference between the temperature at which the minimum storage modulus occurs and the peak temperature of melt endothermation (ΔT(T m -E' min )) are examples. To obtain a DSC thermogram, a test specimen of approximately 10 mg is cut from a PTFE tube, crimped in an unsealed aluminum pan, and heated from ambient temperature to 400°C at a heating rate of 10°C / min using a single temperature lamp in a TA Instruments DSC2500 (Newcastle, Delaware). mThe following was determined. To obtain DMA temperature ramp data, specimens were prepared by cutting a 5 mm length from heat shrink tubing and then cutting the annular piece lengthwise into strips to obtain rectangular specimens oriented circumferentially. Temperature scans of E' were collected in tensile mode on a TA Instruments Q800 DMA (Newcastle, Delaware) at a heating rate of 3°C per minute, 1 Hz, and a deformation amplitude of 15 μm from ambient temperature up 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. While not intended to be theoretically binding, this is because some specimens recovered to some extent before reaching 340°C, causing the tensile grips to physically contact and the instrument to forcibly terminate the experiment.

[0071] [Table 2]

[0072] Figure 1 shows the separation at the temperature of the minimum E' for Comparative Examples 1 to 5 and Examples 1 to 2. As shown in Figure 1, the control sample (Comparative Example 1) does not show a clearly defined relative minimum in the E'-T curve as shown by Comparative Examples 2 to 5 and Examples 1 to 2. Thus, the E' defined and disclosed herein min However, it is demonstrated that this is directly influenced by the amount of entropic elasticity available when the PTFE heat-shrinkable tubing is heated, as it is moved by an entropically unfavorable state fixed within the tubing during expansion and recovery is initiated by heating of the PTFE heat-shrinkable tubing.

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

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

[0075] [Table 3]

[0076] Table 4 below summarizes the diameter changes of the PTFE heat-shrinkable tubing samples from Comparative Examples 2 to 5 and Examples 1 to 2 after recovery for 10 minutes at various temperatures. As shown in Table 4, Examples 1 and 2 showed significantly higher percentages of 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 linear regression of diameter change for each example in 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 the diameter change was plotted against the recovery temperature. Linear regression was performed on the diameter change versus recovery temperature plot for each example in the range of 310°C to 330°C (well below 350°C, where the maximum achievable RR for PTFE heat shrinkage occurs) to assess the tendency for each example's heat shrink tubing to recover more significantly at lower temperatures. Figure 3 shows the diameter change versus recovery temperature plot for each example, including the respective regression lines.

[0079] [Table 5]

[0080] Table 6 below summarizes the average diameter change for each example in the 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 / diameter change explains that the heat shrink tubing recovers to a greater extent at lower temperatures. On the other hand, a smaller slope / diameter change explains that the heat shrink tubing recovers to a lesser extent at lower temperatures. As shown in Table 6, Examples 1 and 2 showed significantly larger diameter changes over the measured temperature range compared to the comparative example, demonstrating that the heat shrink tubing recovers to a greater extent at lower temperatures.

[0081] [Table 6]

[0082] Many variations and other embodiments of the present disclosure will be conceivable to those skilled in the art in which the present disclosure relates, who are interested in the teachings presented in the above description. Therefore, it should be understood that the present disclosure is not limited to the specific embodiments disclosed, and that variations and other embodiments are intended to be included within the scope of the appended claims. Certain terms are used herein, but these terms are used only in a general and descriptive sense, and not for restrictive purposes.

Claims

1. PTFE heat-shrinkable tubing in which the difference between the temperature corresponding to the peak temperature of melt endothermic heat obtained from a DSC temperature lamp using a heating rate of 10°C per minute and the temperature corresponding to the relative minimum value in the E'-T curve obtained from a DMA temperature lamp of a heat-shrinkable tubing test specimen circumferentially oriented in a tensile grip exceeds approximately 7.5°C.

2. The PTFE heat shrink tubing according to claim 1, wherein the PTFE heat shrink tubing has an RR greater than about 5:

1.

3. The PTFE heat shrink tubing according to claim 1, wherein the PTFE heat shrink tubing has an RR greater than about 5.5:

1.

4. The PTFE heat shrink tubing according to claim 1, wherein the PTFE heat shrink tubing has an RR greater than about 6:

1.

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

6. The PTFE heat-shrinkable tubing according to claim 1, wherein a linear regression performed between 310°C and 330°C on a plot of diameter change versus recovery temperature yields a slope value greater than approximately 1.3% / °C.

7. A tubing comprising a wall portion containing PTFE having an inner diameter (ID), wherein the inner diameter (ID) is about 0.3 inches or less after expansion, and the inner diameter (ID) can be reduced by at least about 78% when heated at 350°C for 10 minutes. A heat-shrinkable tubing in which the difference between the temperature corresponding to the peak temperature of melt endothermic heat obtained from a DSC temperature lamp using a heating rate of 10°C per minute and the temperature corresponding to the relative minimum value in the E'-T curve obtained from a DMA temperature lamp of a heat-shrinkable tubing specimen circumferentially oriented in a tensile grip exceeds approximately 7.5°C.

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