Dual Wall Heat Shrink Tubing

Abstract

The present disclosure provides a double-layer heat shrink tubing having an inner polymer layer having a thickness t1 and an outer diameter D1, and an expanded outer polymer layer having a thickness t2' and an outer diameter D2', obtained by expanding the polymer tubing from D2 to D2' and from t2 to t2' at a selected temperature such that D2'-2(t2')>D1, wherein when a ring is cut from a cross-section of the double-layer heat shrink tubing, slit into a rectangle, clamped at the cut ends in a tensile grip in a DMA, and subjected to a temperature sweep of 3°C / min at a frequency of 1 Hz from the onset of the melting endotherm of the inner polymer layer to the onset of the melting endotherm of the expanded outer polymer layer, the double-layer heat shrink tubing exhibits a temperature drop of more than 1°C and less than 12°C. Further, the present disclosure provides related methods of making and using such tubing, as well as products comprising such tubing.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION This application relates generally to heat shrink tubing and methods of making and using such heat shrink 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., decrease in diameter) when heated to a given temperature. Heat shrink tubing can therefore serve a variety of functions: it can provide a tight protective envelope that tightly covers and insulates various elements (e.g., protecting them from abrasion, providing thermal insulation, chemical insulation, moisture protection, and / or electrical insulation), it can be useful for bundling certain elements together (i.e., within the same heat shrink tubing), it can be useful for sealing / isolating certain elements from other elements, it can be used to join / fuse two elements, e.g., two lengths of tubing, together, and it can be useful for modifying the properties of an underlying material (e.g., by surrounding another material and causing that material to shrink as well). These properties make the tubing useful for a variety of purposes, and heat shrink tubing is used throughout a variety of fields, including the environmental, medical, chemical, electrical, optical, electronic, aerospace, automotive, and telecommunications fields. In the medical field, heat shrink tubing is particularly beneficial in the design of increasingly smaller and more complex devices (e.g., catheters, endoscopes, etc.) that are inserted into the body.

[0003] The suitability of heat shrink tubing for a given application depends, at least in part, on the physical properties of the tubing, particularly after exposure to heat. In particular, dual-layer heat shrink tubing includes an outer heat shrink tubing / layer that advantageously shrinks around a molten inner tube / layer that flows upon application of heat to properly seal the underlying component(s). Voids or irregularities in the flowed heat-shrinkable polymer material, or voids or irregularities that arise upon cooling of the heat-shrinkable material around the underlying component(s), can render the heat shrink tubing ineffective for its intended purpose. If the inner tube / layer melts earlier than the recovering tube / layer, or if the outer tube / layer has too high a recovery force, the polymer will flow when the tubing is heated, resulting in an unacceptable increase in recovered tubing length as well as overflow of the molten polymer from the tube ends. If recovery of the outer tube / layer occurs when the inner tube's polymer is not sufficiently deformable, or if the outer tube / layer's recovery force is too low, the underlying component may not be properly sealed.

[0004] It would be advantageous to provide alternative heat shrink tubing designs that ensure proper sealing of the underlying component(s) and methods for ensuring that the heat shrink tubing functions as desired, e.g., provides proper sealing of the underlying component(s). Summary of the Invention

[0005] The present disclosure provides composite heat shrink tubing, also referred to herein as "dual-layer heat shrink tubing," comprising a first inner tube / layer within a second outer tube / layer (i.e., a "tube-within-tube" configuration). For purposes of this disclosure, the inner portion is referred to as the "inner tube," "inner polymer tube," "inner layer," or "inner polymer layer." Similarly, the outer portion is referred to as the expanded or oriented "outer tube," "outer polymer tube," "outer layer," or "outer polymer layer." The first and second tubes / layers are designed and uniquely evaluated based on certain parameters to ensure that, when arranged as a dual-layer heat shrink tubing, the first inner layer melts and flows upon application of heat and the second outer layer shrinks (functioning as an effective heat shrink tubing). This design provides adequate sealing and protection of one or more underlying components upon application of heat. Furthermore, this design may allow for controllable changes in tube length, flooding of the first inner layer, and the presence of voids upon recovery. Advantageously, dual layer heat shrink tubing made as described herein and recovered under the conditions set forth can exhibit optimal sealing properties (low voids and little flooding) with the outer layer recovering to an increase in length of less than about 20% of its original length.

[0006] The present disclosure includes, but is not limited to, the following embodiments.

[0007] Embodiment 1: A double-layer heat shrink tubing comprising an inner polymer layer having a thickness t1 and an outer diameter D1, and an expanded outer polymer layer having a thickness t2' and an outer diameter D2', obtained by expanding the polymer tubing from D2 to D2' and from t2 to t2' at a selected temperature such that D2'-2(t2')>D1, wherein when a ring is cut from a cross-section of the double-layer heat shrink tubing, slits into a rectangle, and held in a DMA at the cut ends with tensile grips, the double-layer heat shrink tubing exhibits a temperature sweep of greater than 1°C and less than 12°C when subjected to a 3°C / min temperature sweep at a frequency of 1 Hz from the onset of the melting endotherm of the inner polymer layer (as determined by DSC) to the onset of the melting endotherm of the expanded outer polymer layer (as determined by DSC).

[0008] Embodiment 2: The dual-layer heat shrink tubing of embodiment 1, wherein the expanded outer polymer layer comprises a fluoropolymer.

[0009] Embodiment 3: The dual-layer heat shrink tubing of embodiment 2, wherein the expanded outer polymer layer comprises a fluoropolymer selected from the group consisting of PTFE, FEP, PFA, PEEK, PVDF, and combinations thereof.

[0010] Embodiment 4: The dual-layer heat shrink tubing of any one of embodiments 1-3, wherein the expanded outer polymer layer comprises polyester.

[0011] Embodiment 5: The dual-layer heat shrink tubing of embodiment 4, wherein the expanded outer polymer layer comprises poly(ethylene terephthalate) (PET).

[0012] Embodiment 6: The dual-layer heat shrinkable tubing of any one of embodiments 1 to 5, wherein the inner polymer layer comprises a fluoropolymer.

[0013] Embodiment 7: The dual-layer heat shrink tubing of embodiment 6, wherein the inner polymer layer comprises a fluoropolymer selected from the group consisting of PFA, FEP, EFEP, PVDF, and combinations thereof.

[0014] Embodiment 8: The dual-layer heat shrinkable tubing of any one of embodiments 1 to 7, wherein the inner polymer layer comprises a polyolefin.

[0015] Embodiment 9: The dual-layer heat shrink tubing of embodiment 8, wherein the inner polymer layer comprises a polyolefin selected from the group consisting of polyethylene (PE), polypropylene (PP), and combinations thereof.

[0016] Embodiment 10: A dual-layer heat shrink tubing as described in embodiment 1, wherein the expanded outer polymer layer comprises or consists essentially of PTFE and the inner polymer layer comprises or consists essentially of PFA.

[0017] Embodiment 11: A dual-layer heat shrink tubing as described in embodiment 1, wherein the expanded outer polymer layer comprises or consists essentially of PTFE and the inner polymer layer comprises or consists essentially of FEP.

[0018] Embodiment 12: A dual-layer heat shrink tubing as described in embodiment 1, wherein the expanded outer polymer layer comprises or consists essentially of PFA and the inner polymer layer comprises or consists essentially of FEP.

[0019] Embodiment 13: A dual-layer heat shrink tubing as described in embodiment 1, wherein the expanded outer polymer layer comprises or consists essentially of PEEK and the inner polymer layer comprises or consists essentially of FEP.

[0020] Embodiment 14: A dual-layer heat shrink tubing as described in embodiment 1, wherein the expanded outer polymer layer comprises or consists essentially of FEP and the inner polymer layer comprises or consists essentially of EFEP.

[0021] Embodiment 15: A dual-layer heat shrink tubing as described in embodiment 1, wherein the expanded outer polymer layer comprises or consists essentially of FEP and the inner polymer layer comprises or consists essentially of PVDF.

[0022] Embodiment 16: A dual-layer heat shrink tubing according to any one of embodiments 1 to 15, wherein the expanded outer polymer layer is removable after heat shrinking.

[0023] Embodiment 17: A dual-layer heat shrink tubing according to any one of embodiments 1 to 16, wherein one or both of the inner polymer layer and the expanded outer polymer layer comprises a filler.

[0024] Embodiment 18: A dual-layer heat shrink tubing according to any of embodiments 1-9 and 16-17, wherein one or both of the inner polymer layer and the expanded outer polymer layer comprises a blend of polymers.

[0025] Embodiment 19: A shrunken double-layer tube produced by heating the double-layer heat shrink tube described in any of embodiments 1 to 18, wherein the inner polymer layer melts to form an inner sealing layer and the expanded outer polymer layer shrinks to form a shrunken outer polymer layer.

[0026] Embodiment 20: The shrunken double-layered tube of embodiment 19, wherein the shrunken outer polymer layer is removable.

[0027] Embodiment 21: A sealed component comprising a component within a shrunken double-layered tube according to any one of embodiments 19-20.

[0028] Embodiment 22: The sealed component of claim 21, wherein the component is completely sealed by an inner sealing layer.

[0029] Embodiment 23: A method for sealing a component, comprising applying a double-layer heat shrink tubing described in any of embodiments 1 to 18 around the component, heating the double-layer shrink tubing, and cooling the resulting sealed component.

[0030] Embodiment 24: A method for evaluating the suitability of dual layer heat shrink tubing, the method comprising: providing a dual layer heat shrink tubing comprising an inner polymer layer having a thickness t1 and an outer diameter D1, and an expanded outer polymer layer having a thickness t2' and an outer diameter D2'; cutting a ring from a cross section of the dual layer heat shrink tubing, scoring the ring into a rectangular object, placing the rectangular object and holding it at its cut end with a tensile grip in a DMA; subjecting the rectangular object to a temperature sweep of 3°C / min at a frequency of 1 Hz from the onset of the melting endotherm of the inner polymer layer (as determined by DSC) to the onset of the melting endotherm of the expanded outer polymer layer (as determined by DSC); and determining that the dual layer heat shrink tubing is suitable for good sealing of an underlying component if the difference between the melting endotherm of the inner polymer layer and the melting endotherm of the expanded outer polymer layer is more than 1°C and less than 12°C.

[0031] 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 invention also includes any combination of two, three, four, or more of the above-described embodiments, as well as any combination of two, three, four, or more features or elements described in this disclosure, regardless of whether such features or elements are specifically combined in the description of a specific embodiment herein. The present disclosure is intended to be read holistically, and therefore, in any of its various aspects and embodiments, it is considered intended that any separable features or elements of the disclosed invention may be combined, unless the context clearly dictates otherwise. Other aspects and advantages of the present invention will become apparent hereinafter.

[0032] 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]

[0033] [Figure 1] 1 is a generalized diagram of a portion of a dual-layer heat shrink tubing 10 according to certain embodiments of the present disclosure. [Figure 2] 1 is a schematic diagram of a method for expanding a polymer tube 11 to obtain an expanded tube 12 (shown in cross section). [Figure 3] 1 is a schematic diagram of a dual-layer heat shrink tubing 10 (shown in cross section) according to certain embodiments of the present disclosure. [Figure 4] 1 is a general diagram of a method according to certain embodiments of the present disclosure. [Figure 5] FIG. 1 shows a plot of the DMA temperature sweep of the double-walled tubing of Comparative Example 1, along with the calculation of the tan δ area. [Figure 6] FIG. 1 shows a plot of storage modulus versus temperature from a DMA sweep of the dual-layer heat shrink tubing from Example 1. [Figure 7] FIG. 1 shows a plot of the DMA temperature sweep of the double-walled tubing of Example 4, along with the calculation of the tan δ area from 235° C. to 323° C. DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention will now be described in more detail below. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As used in this specification and claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0035] The present disclosure provides dual-layer heat shrink tubing comprising a first inner layer and a second outer layer. The first inner layer of the dual-layer heat shrink tubing melts and flows at elevated temperatures, while the second outer layer shrinks, thereby sealing the underlying component or part. The inventors of the present disclosure have developed a systematic method for formulating dual-shrink tubing and evaluating the tubing prior to deployment (i.e., prior to its "recovery") in its heat shrinkability. In particular, by considering the chemical composition and physical attributes of both the inner and outer layers, dual-layer tubing exhibiting good sealing performance can be provided.

[0036] For example, various characteristics affect the ability of a dual-layer tubing to exhibit good sealing performance, including, but not limited to, inner layer polymer flow leading to an unacceptable increase in recovered tubing length (e.g., more than 20% of the original tubing length) if the inner layer recovers / melts prematurely relative to the outer layer or if the outer layer's recovery force is too high, or if the outer tubing's recovery occurs when the inner tubing's polymer is not sufficiently deformable or if the outer layer's recovery force is too low, resulting in an inadequate seal to the underlying component. Advantageously, the methods and tubing provided herein take into account the melting / flow and recovery characteristics of both layers in a non-isothermal environment, thereby providing tubing that can exhibit superior physical and functional properties in heat shrink applications.

[0037] A general schematic diagram of a dual-layer heat shrink tubing is shown in FIG. 1. As shown therein, the dual-layer heat shrink tubing 10 comprises an expanded outer layer 12 and an inner layer 14. At least a portion of the outer surface of the inner layer 14 typically contacts at least a portion of the inner surface of the expanded outer layer 12. In certain embodiments, substantially all (including all) of the outer surface of the inner layer 14 typically contacts at least a portion of the inner surface of the expanded outer layer 12. Advantageously, in some embodiments, these layers are in direct contact with each other (e.g., along the entire length of the dual-layer heat shrink tubing 10) with no space between them. The overall size of the dual-layer heat shrink tubing 10 can vary widely. The principles described herein are applicable to a wide range of tubing sizes. In certain embodiments, the overall diameter of the dual-layer heat shrink tubing provided herein (before recovery) ranges from about 2 mm to about 20 mm, e.g., from about 4 mm to about 10 mm.

[0038] The expanded outer layer 12 of the heat shrink tubing 10 is an expanded (e.g., oriented) heat-shrinkable tubing. For example, it may be an expanded extruded tubing, as outlined below. The expanded outer layer 12 generally comprises a polymer or polymer blend that can be crystallized or crosslinked and then radially expanded to a larger diameter (which is maintained by quenching the tubing). Suitable polymers include thermoplastic materials. Layer 12 may comprise, for example, a fluoropolymer, particularly a thermoplastic melt-processable fluoropolymer. Suitable fluoropolymers are known and include, but are not limited to, poly(tetrafluoroethylene) (PTFE), fluorinated ethylene propylene (FEP), polyvinylidene fluoride, perfluoroalkoxyalkanes (PFA), perfluoro(alkyl vinyl ethers) (PAVE), tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride terpolymers (THV), polyvinylidene difluoride (PVDF), poly(ethylene-co-tetrafluoroethylene) (ETFE), ethylene chlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), polytetrafluoroethylene (PTFE), ethylene, tetrafluoroethylene, and hexafluoropropylene (EFEP), copolymers of tetrafluoroethylene and perfluoromethyl vinyl ether (MFA), and copolymers and derivatives thereof. In some embodiments, the extended outer layer 12 comprises a polyester, such as poly(ethylene terephthalate) (PET), or a derivative or copolymer thereof. Additional polymers for the extended outer layer 12 are polyethylene, polypropylene, polyether block amide (PEBA), and polyaryletherketones such as PEEK. In certain embodiments, the extended outer layer 12 includes a single type of polymer, while in other embodiments, the extended outer layer 12 includes two or more of the above-referenced polymers (e.g., in a blend). In some embodiments, the extended outer layer 12 may further include one or more additives, such as pigments, dyes, fillers, etc.Certain non-limiting examples of pigments, dyes, and fillers include, for example, graphene, carbon nanotubes, clays, organoclays, silica, silicates, zeolites, and functional additives that promote slip, impart color, impart conductivity, or impart antimicrobial properties.

[0039] Expanded outer layer 12 has a wall thickness of t2' and an outer diameter of D2'. As shown in FIG. 3, expanded outer layer 12 can be made, for example, by providing tube 11 and expanding it to decrease its wall thickness t2 and increase its outer diameter D2. The method for providing tube 11 is not particularly limited, and in some embodiments, tube 11 is an extruded tube. Methods for expanding tubes are known in the art, and the present disclosure is not limited to any particular method for providing expanded outer layer 12. Typically, tube 11 is radially expanded (e.g., by mechanical means) to provide an expanded tubing material that can function as a heat shrink material (i.e., a material that returns to its unexpanded form when heated above a certain temperature, thereby "shrinking"). The expansion can be either in-line with the manufacturing (e.g., extrusion) of tube 11 or offline (i.e., performed independently of the manufacturing of tube 11). The expansion can be carried out at a variety of temperatures (typically elevated temperatures), including, but not limited to, temperatures greater than about 250°C, or greater than about 300°C (e.g., in certain embodiments, about 330°C-350°C).

[0040] Any means of radially expanding a tube is intended to be encompassed by the present invention. In certain embodiments, the tube is radially expanded by pressurizing the tube from the inside out, transferring stress to the tube wall. This pressurization can be achieved by any means capable of creating a pressure differential between the inside and outside of the tube. Such a pressure differential can be caused 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 the two. The stress induced in the tube wall causes the tube to expand outward. The rate of expansion can be controlled so that the tube remains expanded and does not recover until subjected to further thermal cycling.

[0041] The extent to which tube 11 is expanded depends on the intended use of the tube and, at least in part, on the diameter (D1) of the inner layer to be combined with it. Tube 11 is generally expanded such that D2' - 2 × t2' > D1 at a selected temperature. For example, in some embodiments, the tube is expanded to an outer diameter D2' between about 1.05 times its original (unexpanded) diameter D2 and about 10 times its original (unexpanded) diameter D2, e.g., between about 1.5 times its original (unexpanded) diameter D2 and about 4 times its original (unexpanded) diameter D2, or between about 2 times its original (unexpanded) diameter D2 and about 4 times its original (unexpanded) diameter D2. This expansion not only results in an increase in outer diameter D2 to D2', but also in a decrease in wall thickness (from t2 to t2'). The values ​​of D2 and t2 are not particularly limited, and the principles outlined herein are applicable to tubes having a wide range of sizes. In some embodiments, D2 is about 1 mm to about 30 mm. In some embodiments, D2' is about 2 mm to about 50 mm. In some embodiments, t2' is about 100 μm to about 500 μm, although the expanded outer layer of the disclosed double-walled tube is by no means limited to such diameters and wall thicknesses.

[0042] In some embodiments, the extended outer layer 12 is formulated to be easily removed, torn, or peeled away after recovery on the sealed article, leaving only the inner layer 14 sealing the article. Such removability can include, for example, ease of peeling the outer layer off after recovery. Certain suitable materials and methods for making such removable extended outer layers are described, for example, in U.S. Pat. No. 9,440,044 to Roof et al., which is incorporated herein by reference. To facilitate ease of removal, in some embodiments, the material of the extended outer layer 12 is selected to be largely incompatible with the material of the inner layer 14, for example, to avoid significant adhesion between the two layers (which is likely to occur, for example, when both layers are fluoropolymer layers). One non-limiting example of such incompatibility that may provide a removable outer layer is a PEEK outer layer and an FEP inner layer. In some embodiments, the material is selected so that the outer layer cannot be easily removed after recovery (e.g., it is intended to remain with the sealed component).

[0043] The inner layer 14 of the dual-layer heat shrink tubing 10 is a tube, including, but not limited to, extruded tubing. In some embodiments, the layer 14 is not expanded or oriented (although during the manufacture of the dual-layer heat shrink tubing, in some embodiments, the layer may be expanded to some extent to provide the dual-layer heat shrink tubing). The inner layer 14 typically comprises a melt-processable polymer, particularly selected from a polymer or blend of polymers that softens and begins to flow before or in the temperature range at which the outer layer material recovers. The inner polymer layer 14 may comprise, for example, a fluoropolymer, particularly a thermoplastic melt-processable fluoropolymer. Suitable fluoropolymers are known and include, but are not limited to, fluorinated ethylene propylene (FEP), polyvinylidene fluoride, perfluoroalkoxyalkanes (PFA), perfluoro(alkyl vinyl ethers) (PAVE), tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride terpolymers (THV), polyvinylidene difluoride (PVDF), poly(ethylene-co-tetrafluoroethylene) (ETFE), ethylene chlorotrifluoroethylene (ECTFE), polychlorotrifluoroethylene (PCTFE), ethylene, tetrafluoroethylene, and hexafluoropropylene (EFEP), copolymers of tetrafluoroethylene and perfluoromethyl vinyl ether (MFA), and copolymers and derivatives thereof. In some embodiments, the inner layer 12 may comprise polyamide, polyether block amide (PEBA), or polyethylene terephthalate (PET). In some embodiments, the inner layer 12 of the dual-layer heat shrink tubing 10 may comprise a polyolefin, particularly a thermoplastic, melt-processable polyolefin, including, but not limited to, polyethylene or polypropylene. In certain embodiments, the inner polymer layer 14 comprises a single type of polymer, while in other embodiments, the inner polymer layer 14 comprises two or more polymers (e.g., in a blend).

[0044] In some embodiments, the inner polymeric layer 14 can further include one or more additives, such as pigments, dyes, fillers, etc. Some specific, non-limiting examples of pigments, dyes, and fillers include, for example, graphene, carbon nanotubes, clays, organoclays, silica, silicates, zeolites, and functional additives that promote slip, impart color, impart conductivity, or impart antimicrobial properties. For example, in one embodiment, the inner layer 14 includes carbon black (e.g., in a relatively small amount, such as about 1% to about 10% by weight).

[0045] The size of the inner polymeric layer 14 can vary widely, but generally has an outer diameter D1 small enough to fit within the inner diameter of the expanded tube / layer 14. Similarly, the wall thickness t1 of the inner polymeric layer 14 is not particularly limited. In some embodiments, t1 is from about 25 μm to about 900 μm, although the double-layered tubes provided herein are not limited to such thicknesses. In some embodiments, t1 is greater than t2′ (i.e., the thickness of the expanded outer layer 12), while in other embodiments, t1 is less than t2′.

[0046] In accordance with the present disclosure, the expanded outer and inner layers 12, 14 are selected and combined in a specific manner designed to provide a suitable dual-layer heat shrink tubing. The properties of the individual resins selected for each layer, as well as the manner of expansion of the outer polymer layer 12 (e.g., rate, degree, and temperature of expansion), affect the overall performance of the resulting composite heat shrink tubing 10.

[0047] The inventors have evaluated certain interactions, taking into account, for example, the melting properties of the inner layer 14, which are designed to advantageously melt / flow, and the heat shrinking properties of the expanded outer layer 12, which are designed to advantageously seal to any underlying component(s). A mismatch between the melting / flowing properties of the inner layer and the recovery temperature and recovery force of the expanded outer layer can cause problems during sealing of the components, including, for example, but not limited to, the presence of voids within the recovered / heat-shrunk tubing, unacceptable tubing elongation, and flooding of the inner layer polymer outside the recovered tubing ends. The principles of the present disclosure address certain such difficulties in balancing the various properties of dual-layer heat-shrink tubing to help obtain a good seal.

[0048] For example, but not limited to, such difficulties include the fact that the melting range of the inner layer polymer can be very large (e.g., as high as 40°C to 50°C for some polymers), making it difficult to determine the point at which a normal force is applied during heating at which a significant portion of the molten polymer mass will flow and effectively seal the part. Furthermore, the melt viscosity, as well as the force applied by the shrink tubing, are themselves functions of temperature. The situation can be further complicated if the method of heating the double shrink tubing is not performed at a stable temperature in field applications (i.e., by using a heat gun). Furthermore, the viscosity of the inner layer polymer will vary widely depending on the temperature and the type and grade of polymer, and the recovery force of the outer layer is also a function of temperature and the process parameters of wall thickness and expansion. Furthermore, the recovery process itself may be non-isothermal.

[0049] According to the present disclosure, dual-layer heat shrink tubing can be provided that results from an evaluation process that considers the complex interaction of both layers in a non-isothermal environment and takes into account the above-referenced considerations. More specifically, the disclosed method simultaneously considers melting / flowing and recovery characteristics by evaluating the dynamic mechanical response of the entire composite structure over a wide temperature range. In this manner, dual-layer heat shrink tubing can be designed based on the net effect of temperature-dependent deformation and flowing of the composite structure. The inventors have identified a method that can understand the interplay of complex phenomena within dual-layer heat shrink tubing so that the melting inner layer can be effectively deformed around the component by the recovering outer layer (during heat shrink deployment). Dual-layer heat shrink tubing manufactured using the disclosed method can therefore be optimized for recovery sealing quality. This method enables the efficient design of dual-layer heat shrink tubing by combining an outer recoverable tube with an inner melting tube in rapid DMA tests to determine the appropriate / optimal combination.

[0050] A method for making dual-layer heat shrink tubing is shown in Figure 4. As referenced above, this method generally involves combining an inner layer tube with an expanded outer tube to obtain an assembled dual-layer tube. Steps 21 (creating a tube, e.g., extruding a resin into a tube), 22 (expanding the tube), and 23 (creating a tube, e.g., extruding a resin into a tube) are optional in the context of the disclosed method (i.e., one or both of the inner layer tube and the expanded outer layer tube can be created via steps 21, 22, and / or 23), or these tubes can be provided and subjected to assembly step 24.

[0051] The assembly step 24 involves combining both the inner and outer layers in tubular form. These layers may be combined in a conventional manner. For example, in some embodiments, the inner layer 14 is inserted into the expanded outer layer 12 to form a double-layer heat shrink tube. In some embodiments, the inner layer 14 is partially expanded within and into the expanded outer layer 12, e.g., by applying heat and / or pressure. In some embodiments, the expanded outer layer 12 is partially restored onto the inner layer 14, e.g., by heating the outer layer.

[0052] Advantageously, upon assembly, a given dual-layer heat shrink tubing is subjected to evaluation 26 to determine whether it functions as an effective heat shrink tubing (as defined for purposes herein, e.g., effective heat shrink tubing as a heat-shrinking material exhibits low voids, little to no overflow, and a change in recovered length of less than about 20% of its original length). The unique evaluation performed at this stage is based, at least in part, on evaluation of the area under the tan δ curve of the dual-layer heat shrink tubing in a DMA machine subjected to a heat ramp. For composite tubing, tan δ has been found to be affected by both the softening and melting of the inner polymer layer 14 and the recovery of the outer layer 12. With increasing temperature ramps, tan δ increases rapidly as the inner layer softens and melts. Thus, the greater the integral of tan δ with temperature, the greater the tendency for the inner tubing polymer to flow freely when heated. Finally, upon reaching the expansion temperature, the restoring force exerted by the outer layer 12 increases the constraint on polymer flow, causing a decrease in tan δ of the composite structure. The storage modulus E' of the outer tube decreases with temperature until the expansion temperature is reached. At this point, a noticeable kink in E' is observed, followed by an increase as the outer layer recovers. The kink in the E'-T curve is due to entropic elasticity, as observed in the recovery of a pre-extended sheet. See L. Andena et al., Polym. Eng. Sci, 44, 2004, 1368-1378 (incorporated herein by reference). After all stresses are released, the E' curve again decreases with temperature. We have now found that these competing phenomena can be explained using the area under the tan δ curve, calculated from the onset of melting of the inner tube to the onset of melting of the outer tube. We have found that when the area under the tan δ curve is below about 1°C, the mobility of the polymer within the inner tube is insufficient to adequately seal the underlying components. We have found that when this area is above about 12°C, the polymer within the inner tube freely flows outside the confines of the outer tube and does not adequately seal the underlying components.Therefore, the value targeted by the present disclosure is 1°C to 12°C, for example, 2°C to 12°C, 3°C to 12°C, 4°C to 12°C, or 5°C to 12°C.

[0053] Evaluation 26 includes providing an assembled double-layer tubing to be evaluated, cutting the assembled double-layer tubing into rings, scoring it into rectangles, gripping it with tensile grips, and holding the cut ends of the rectangles in a DMA to evaluate the area under the tan δ curve when subjected to a temperature sweep of 3°C / min at a frequency of 1 Hz from the onset of the melting endotherm of the inner layer (as determined by DSC) to the onset of the melting endotherm of the outer layer (as determined by DSC). A combination of inner and outer layers is determined to provide a suitable combination of inner and outer layers if: a) the area under the tan δ curve is less than about 12°C and greater than about 1°C. By confirming that a given combination of inner and outer layers exhibits such properties, the inventors have found that it is reasonably predictable that a double-layer heat shrink tubing has been produced that will exhibit acceptable heat shrink / sealing properties upon recovery, such as few voids, little overflow, and a change in recovered length of less than about 20% of the original length. The new procedure allows for the rapid design of dual-layer heat shrink tubing by combining an outer recoverable layer with an inner meltable layer in a DMA and evaluating the results, eliminating the need to produce and test production quantities of such tubing.

[0054] The dual-layer heat shrink tubing provided herein can be used in a variety of fields. For example, they can be used in environmental, medical, chemical, electrical, optical, electronic, aerospace, automotive, and telecommunications fields, as well as various medical applications. Accordingly, the present disclosure includes, for example, components (e.g., environmental, medical, chemical, or electrical, optical, electronic, aerospace, automotive, or telecommunications components) sealed within the tubing, created by healing the dual-layer heat shrink tubing around the component. Similarly, methods for effectively sealing components (e.g., methods that meet the criteria set forth herein) are encompassed by the present disclosure. These methods can result in components sealed with two layers (a healed outer layer and a fused inner layer) provided herein, where, in some embodiments, the healed outer layer can be removed and the final sealed component can include only a coating of the inner layer material. [Example]

[0055] Aspects of the present invention will be more fully described by the following examples, which are presented to illustrate certain aspects of the invention and should not be construed as limiting the invention.

[0056] A TA Instruments DSC Q2000 was used to study the thermal behavior of both the inner and outer tubes of the composite samples and to determine the onset of the melting zone for both the inner and outer tubes. The samples were first equilibrated at -60°C and heated to 400°C at a constant rate of 10°C / min. The onset of the melting zone was then determined using TA Instruments Universal Analysis 2000 (version 4.5A) software.

[0057] The thermomechanical properties of the composite tubes were determined using a TA Instruments Q800 DMA equipped with a film tension fixture operated in tension mode. Here, the primary property of interest was tan delta (δ). The composite tubes were cut perpendicular to their length to form rings, which were subsequently cut open into rectangular specimens. Both layers of the rectangular specimens were placed in tensile grips so that the cut edges of the tube were parallel to the plane of the grips. A constant temperature ramp rate of 3°C / min was performed, and the test frequency was 1 Hz. Once the temperature scan was complete, the DMA data was imported into TA Instruments TRIOS software (version 4.3). The raw data files were exported to Microsoft Excel 2016. The Excel data files were then imported into OriginLab's OriginPro 2020 (version 9.7) data analysis and graphing software to plot tan delta versus temperature. The OriginLab integration gadget was used to calculate the area under tan delta versus temperature. where the lowest temperature limit is the onset temperature of the melting endotherm of the inner tube as determined by DSC, the highest temperature limit is the onset temperature of the melting endotherm of the outer tube as determined by DSC, and the region of interest (ROI) is between these two limits. For all calculations, the baseline was set at y = 0 (i.e., tan δ = 0).

[0058] The seal quality was evaluated as follows: A composite tube having a length of approximately 15 cm was placed on a mandrel equal to 60% ± 10% of the inner diameter of the composite tube. A forced air oven was used to perform recovery at a temperature higher than the initial expansion temperature. At 10 minutes, the sealed mandrel was removed from the oven and allowed to cool to ambient temperature. Once cooled, the outer layer of the recovered composite tube was measured to determine the percent longitudinal change. A length increase of more than 15% of the initial length or a length decrease of more than 2% of the initial length was indicative of a poor seal. A visual inspection was then performed to ensure the absence of large voids, i.e., voids greater than 2 mm in diameter. A seal was considered poor if the width of the molten polymer spill from each end of the recovered outer tube exceeded 5 mm.

[0059] Comparative Example 1 Dual-layer heat shrink tubing with an initial outer diameter of 3.59 mm was fabricated using an outer layer of PTFE (104 μm wall thickness) and an inner layer of PFA (315 μm wall thickness) expanded at a 2:1 ratio between 330°C and 350°C. The onset of melting from the DSC endotherm was determined to be 265°C for PFA. The onset of melting from the DSC endotherm was determined to be 323°C for PTFE. Recovery was performed in a 350°C hot air circulating oven for 5 minutes. A DMA temperature sweep was performed at 1 Hz on a rectangular sample cut open from the periphery of the original composite tubing. The area under the tan δ curve from 265°C to 323°C was determined to be 19.48°C. The E' curve showed a positive slope near the recovery temperature. When recovered / heat shrunk at 350°C on a 1.74mm diameter mandrel, the mandrel seal was found to have a void and a length change of -4.6%, but with significant flooding of the PFA layer. Figure 5 shows the DMA temperature sweep of the dual-layer heat shrink tubing and the calculation of the tan δ area from 265°C to 323°C.

[0060] Example 1 Dual-layer heat shrink tubing with an initial outer diameter of 3.52 mm was fabricated using an outer layer of PTFE (with a wall thickness of 107 μm) and an inner layer of PFA (with a wall thickness of 219 μm) expanded at a 2:1 ratio between 330°C and 350°C. The onset of melting from the DSC endotherm was determined to be 265°C for PFA. The onset of melting from the DSC endotherm was determined to be 323°C for PTFE. The tubing was recovered / shrunk on a 1.48 mm mandrel at 350°C for 10 minutes. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1. Figure 6 shows the change in modulus as a function of temperature for the dual-layer heat shrink tubing.

[0061] Example 2 Dual-layer heat-shrink tubing with an initial outer diameter of 8.37 mm was fabricated using an outer layer of PTFE (with a wall thickness of 162 μm) and an inner layer of PFA (with a wall thickness of 315 μm) expanded at a 2:1 ratio between 330°C and 350°C. The onset of melting from the DSC endotherm was determined to be 265°C for PFA. The onset of melting from the DSC endotherm was determined to be 323°C for PTFE. The tubing was recovered / heat-shrunk on a 3.83 mm mandrel at 350°C for 10 minutes. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1.

[0062] Comparative Example 2 Dual-layer heat shrink tubing with an initial outer diameter of 5.85 mm was fabricated using an outer tube of unexpanded PTFE (365 μm wall thickness) and an inner tube of PVDF (445 μm wall thickness). The onset of melting from the DSC endotherm was determined to be 160°C for PVDF. The onset of melting from the DSC endotherm was determined to be 323°C for PTFE. The dual-layer heat shrink tubing was allowed to recover on a 4.37 mm mandrel at 350°C for 10 minutes. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1.

[0063] Example 3 Dual-layer heat-shrink tubing with an initial outer diameter of 4.22 mm was fabricated using an outer layer of PTFE (with a wall thickness of 260 μm) and an inner layer of PFA (with a wall thickness of 315 μm) expanded at a 2:1 ratio between 330°C and 350°C. The onset of melting from the DSC endotherm was determined to be 265°C for PFA. The onset of melting from the DSC endotherm was determined to be 323°C for PTFE. The tubing was recovered / heat-shrunk on a 1.91 mm mandrel at 350°C for 10 minutes. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1.

[0064] Comparative Example 3 Dual-layer heat-shrink tubing with an initial outer diameter of 14.06 mm was fabricated using an outer layer of PTFE (with a wall thickness of 251 μm) and an inner layer of FEP (with a wall thickness of 750 μm) expanded at a 2:1 ratio between 330°C and 350°C. The onset of melting from the DSC endotherm was determined to be 235°C for FEP. The onset of melting from the DSC endotherm was determined to be 330°C for PTFE. The tubing was recovered / heat-shrunk on a 6.53 mm mandrel at 350°C for 10 minutes. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1.

[0065] Example 4 Dual-layer heat-shrink tubing with an initial outer diameter of 4.22 mm was fabricated using an outer layer of PTFE (with a wall thickness of 260 μm) and an inner layer of FEP (with a wall thickness of 200 μm) expanded at a 2:1 ratio between 330°C and 350°C. The onset of melting from the DSC endotherm was determined to be 235°C for FEP. The onset of melting from the DSC endotherm was determined to be 323°C for PTFE. The tubing was recovered / heat-shrunk on a 1.90 mm mandrel at 350°C for 10 minutes. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Tables 1 and 7.

[0066] Comparative Example 4 Dual-layer heat shrink tubing with an initial outer diameter of 7.88 mm was fabricated using an outer tube of PTFE (200 μm wall thickness) expanded at a 2:1 ratio between 330°C and 350°C and an inner layer of 4% (wt / wt) carbon black-filled PFA (51 μm wall thickness). The onset of melting from the DSC endotherm was determined to be 290°C for the filled PFA. The onset of melting from the DSC endotherm was determined to be 323°C for the PTFE. The dual-layer heat shrink tubing was recovered / heat shrunk on a 4.17 mm mandrel at 350°C for 10 minutes. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1.

[0067] Example 5 Dual-layer heat-shrink tubing with an initial outer diameter of 7.88 mm was fabricated using an outer tube of PTFE (200 μm wall thickness) expanded at a 2:1 ratio between 330°C and 350°C and an inner layer of FEP (358 μm wall thickness) filled with 15% (wt / wt) carbon black. The onset of melting from the DSC endotherm was determined to be 265°C for the FEP blend. The onset of melting from the DSC endotherm was determined to be 330°C for the PTFE. The tubing was recovered / heat-shrunk on a 2.28 mm mandrel at 350°C for 10 minutes. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1.

[0068] Example 6 Dual-layer heat-shrink tubing with an initial outer diameter of 4.19 mm was fabricated using an outer tube of FEP (435 μm wall thickness) and an inner layer of EFEP (254 μm wall thickness) expanded at a 1.6:1 ratio between 180°C and 220°C. The onset of melting from the DSC endotherm was determined to be 175°C for EFEP. The onset of melting from the DSC endotherm was determined to be 245°C for FEP. The tubing was recovered / heat-shrunk at 350°C for 10 minutes on a 1.42 mm mandrel. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1.

[0069] Example 7 Dual-layer heat-shrink tubing with an initial outer diameter of 5.95 mm was fabricated using a PTFE outer tube (284 μm wall thickness) and a PVDF inner layer (445 μm wall thickness) expanded at a 2:1 ratio between 330°C and 350°C. The onset of melting from the DSC endotherm was determined to be 160°C for PVDF. The onset of melting from the DSC endotherm was determined to be 323°C for PTFE. The tubing was recovered / heat-shrunk on a 2.22 mm mandrel at 350°C for 10 minutes. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1.

[0070] Example 8 Dual-layer heat-shrink tubing with an initial outer diameter of 6.29 mm was fabricated using an outer tube of FEP (262 μm wall thickness) and an inner layer of PVDF (445 μm wall thickness) expanded at a 1.3:1 ratio between 180°C and 220°C. The onset of melting from the DSC endotherm was determined to be 160°C for PVDF. The onset of melting from the DSC endotherm was determined to be 240°C for FEP. The tubing was recovered / heat-shrunk on a 2.51 mm mandrel at 220°C for 10 minutes. Upon removal from the oven, it was found that the outer FEP tubing could be easily removed from the inner PVDF tubing. DMA temperature sweeps were performed at 1 Hz on rectangular samples cut open from the periphery of the original composite tubing. The results are shown in Table 1.

[0071] [Table 1]

[0072] Many variations and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing description. It is to be understood, therefore, that the invention is not to be limited to the specific 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. Thickness t １ and outer diameter D １ an inner polymer layer having Thickness t ２ ' and outer diameter D ２ ', and an extended outer polymer layer having a wherein the expanded outer polymer layer is obtained by expanding a polymer tube having an outer diameter D and a thickness t at a selected temperature such that D '-2(t ') is greater than D ; The double-layer heat shrinkable tube has an area under the tan δ curve of 1° C. to 12° C.; The area under the tan delta curve is determined using a dynamic mechanical analyzer (DMA) by testing a ring cut from a cross section of the dual layer heat shrink tubing, slit into a rectangle, and gripped in a DMA with tensile grips at the cut ends, the DMA being used at a frequency of 1 Hz and a rate of 3°C / min from the onset of melting of the inner polymer layer to the onset of melting of the expanded outer polymer layer.

2. 10. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymer layer comprises a fluoropolymer.

3. 10. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymer layer comprises a fluoropolymer selected from the group consisting of PTFE, FEP, PFA, PEEK, PVDF, and combinations thereof.

4. 10. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymeric layer comprises polyester.

5. 10. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymer layer comprises poly(ethylene terephthalate) (PET).

6. The dual layer heat shrink tubing of claim 1 , wherein the inner polymer layer comprises a fluoropolymer.

7. 10. The dual layer heat shrink tubing of claim 1, wherein the inner polymeric layer comprises a fluoropolymer selected from the group consisting of PFA, FEP, EFEP, PVDF, and combinations thereof.

8. The dual layer heat shrink tubing of claim 1 , wherein the inner polymeric layer comprises a polyolefin.

9. 10. The dual layer heat shrink tubing of claim 1, wherein the inner polymer layer comprises a polyolefin selected from the group consisting of polyethylene (PE), polypropylene (PP), and combinations thereof.

10. 2. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymeric layer is made of PTFE and the inner polymeric layer is made of PFA.

11. 2. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymeric layer is made of PTFE and the inner polymeric layer is made of FEP.

12. 2. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymer layer is made of PFA and the inner polymer layer is made of FEP.

13. 2. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymeric layer is made of PEEK and the inner polymeric layer is made of FEP.

14. 2. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymeric layer is comprised of FEP and the inner polymeric layer is comprised of EFEP.

15. 2. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymeric layer is made of FEP and the inner polymeric layer is made of PVDF.

16. 10. The dual layer heat shrink tubing of claim 1, wherein the expanded outer polymeric layer is removable after heat shrinking.

17. The dual layer heat shrink tubing of any one of claims 1 to 9, wherein one or both of the inner polymer layer and the expanded outer polymer layer include a filler.

18. The dual layer heat shrink tubing of any one of claims 1 to 9, wherein one or both of the inner polymeric layer and the expanded outer polymeric layer comprise a blend of polymers.

19. A shrunken dual-layer tube made by heating the dual-layer heat shrink tube of any one of claims 1 to 16, wherein the inner polymer layer melts to form an inner sealing layer and the expanded outer polymer layer shrinks to form a shrunken outer polymer layer.

20. 20. The shrunken dual layer tube of claim 19, wherein the shrunken outer polymeric layer is removable.

21. 20. An assembled article comprising a component within the shrunken dual-wall tube of claim 19.

22. 22. The assembly of claim 21, wherein the component is completely encapsulated by the inner polymeric layer.

23. The dual layer heat shrink tubing of claim 1, wherein the onset of melting of the inner polymer layer and the onset of melting of the expanded outer polymer are determined by differential scanning calorimetry (DSC).

Images