Field of the disclosure

[0001] The present invention relates generally to fibers, more particularly to thermally insulating fibers and the method of making same.

Background of the disclosure

[0002] Fibers enclosing cavities, also called hollow fibers, are known for being suitable for the production of various types of textiles and materials.

[0003] Hollow fibers are sometimes used in the production of textile surfaces to obtain garments which are lighter and more thermally insulating. Typical hollow fibers include hollow cross-sections, with a generally open configuration, such that air is contained within the fiber. Although such fibers provide some thermal insulation, the air provides a substantial degree of convective heat transfer, which generally impedes the thermal insulating properties of the textile. The open cross-sections of the fibers also typically allow the air to circulate, thus increasing heat exchanges within the textile.

[0004] Therefore, it is desirable to have a fiber or filament providing a more efficient thermal insulation.

Summary

[0005] In one aspect of the disclosure, there is provided a fiber having an elongated body defining a longitudinal axis and at least one cavity defined therein, the at least one cavity being defined symmetrically with respect to a plane containing the longitudinal axis, and an insulating gas trapped in the at least one cavity, the insulating gas being less thermally conductive than air.

[0006] In a further aspect of the disclosure, there is provided a method of manufacturing a fiber, said method comprising: a) extruding an extrudable material to form a fiber having an elongated body with at least one cavity defined in the body; b) introducing an insulating gas in the at least one cavity, the insulating gas being less thermally conductive than air; and c) closing the at least one cavity to trap the insulating gas therein. Brief description of the drawings

[0007] Figs.1A-C are side cross-sectional views illustrating different possible configurations for a fiber or filament according to the present disclosure; and

[0008] Figs.2A-l are front cross-sectional views illustrating possible configurations for the fiber or filament of Figs. 1 A-C.

Description of embodiments

[0009] The present disclosure provides a fiber or filament having thermal insulation properties. The fiber or filament may be used in various fields of the textile industry, including, but not limited to, technical garments that need a high level of thermal insulation such as military, aerospace, or sports and leisure garments, as well as insulation in construction, automotive or aeronautics, etc. This fiber may be spun or used as a filament in a multifilament and/or monofilament structure. As used in the following description and claims, the term "fiber" is intended to encompass "fiber or filament".

[0010] As shown in Figures 1A to 1C, the fiber 10, 110, 210, 310 has an elongated body 12, 1 12, 212, 312 which defines a longitudinal axis L. The body 12, 1 12, 212, 312 can be of any length or occupy any area within the fiber 10, 1 10, 210, 310. The body 12, 1 12, 212, 312 can be produced by an extrusion process depending of the desired application. The body 12, 1 12, 212, 312 can vary with respect to the type of application. For example, the body can be relatively short, if it is a staple fiber with a length of 5 mm to 20 mm. In another example, for a staple fiber with a length of 20 mm to 200 mm, the body is usually of medium size. Alternatively, the body is very long ("endless"). The diameter of the body 12, 1 12, 212, 312 can generally be from about 5 μπι to about 3 mm. The diameter may vary depending on the application.

[0011] The cross-sectional shape of the body 12, 1 12, 212, 312 may vary depending on the application; in a particular embodiment, the body 12, 1 12, 212, 312 has a cross-sectional shape obtainable by extrusion process. As shown in Figures 2A, 2B, 2C, 2D, 2E and 2F, the body 12, 112, 212, 312 has a circular cross-sectional shape F1. In an alternate embodiment, the body 12, 112, 212, 312 has a rectangular or square cross-sectional shape F2, as illustrated in Figs. 2H and 2I. In another alternate embodiment, the body 12, 1 12, 212,312 has a triangular cross- sectional shape F3, as shown in Fig. 2G Alternate cross-sectional shapes are also possible.

[0012] The body 12, 1 12, 212, 312 has at least one elongated cavity defined therein, with the cavity(ies) being symmetrically arranged with respect to at least one plane P (see Figs. 2A-2F) containing the longitudinal axis L of the fiber. In other words, and as will be described further below, the cavity(ies) extend along the longitudinal axis L and/or are distributed about the longitudinal axis L in a symmetrical manner with respect to the plane P.

[0013] In particular, in one embodiment shown in Fig. 1A, the body 12 has a single elongated cavity 14 centered along the longitudinal axis L and extending along a major portion of the length of the fiber 0. The single cavity 14 has a constant cross-section and closed ends such as to define an enclosure.

[0014] In another embodiment, the body 112 has a plurality of spaced apart elongated cavities 1 14 extending along the longitudinal axis L, as illustrated in Fig.l B. In the embodiment shown, the cavities 114 have similar or equal lengths and are regularly spaced apart. Each cavity 1 14 further has a constant cross-section and closed ends such as to define separate enclosures. Although not shown, it is understood that cavities with different lengths, irregularly spaced apart and/or having different cross-sections may also be possible. These embodiments provide fibers having cavities defined therein with smaller volume. The smaller and separated cavities may increase mechanical, thermal, electrical and chemical properties of the fiber. A ratio of insulation by technical performance of the fiber may be defined depending on the application.

[0015] As shown in Fig. 1 C, in a further embodiment, the body 212 has a single elongated cavity 214 defined along the longitudinal axis L and extending along a major portion of the length of the fiber 210, with the cavity 214 having longitudinally spaced apart reduced diameter portions 215. The single cavity 214 has closed ends such as to define a series of chambers 216 interconnected by the reduced diameter portions 215 and together defining a single enclosure. This shape provides a good compromise towards the technical performance and the insulation of the fiber.

[0016] In another embodiment, the body 312 has a plurality of cavities 314 defined therein which are circumferentially spaced apart, as shown in Figs. 1 D and 2B to 2D. Each cavity 314 extends along a major portion of the length of the fiber 310, and the cavities 314 are also symmetrically distributed about the longitudinal axis L. As shown in Fig. 2D, the body may include a cavity extending along the longitudinal axis L in addition to a plurality of cavities extending spaced apart from the longitudinal axis L.

[0017] Although not shown, alternate configurations for the cavities are also possible, for example the replacement of each cavity 314 of Fig. 1 D with a series of longitudinally spaced apart cavities such as illustrated in Fig. 1 B, or with a variable cross-section cavity such as illustrated in Fig. 1 C.

[0018] The cavity(ies) 14, 114, 214, 314 may have any cross-sectional shape that can be produced by an extrusion process. Possible shapes of the cavity(ies) 14, 114, 214, 314 include, but are not limited to, a cross-section (i.e. defined perpendicularly to the longitudinal axis L) having a circular shape C1 as shown in Figs. 2A to 2D, a rectangular or square shape C2 as shown in Figs. 2H and 2E, a triangular shape C3 as shown in Figs.2F and 2G, and a multi- lobed shape C4 as shown in Fig. 21. It is understood that any of the cross-sectional shapes C1 , C2, C3, C4 can apply to any of the cavity configurations shown in Figs. 1A-1 D; alternate cross- sectional shapes for the cavities are also possible.

[0019] The ratio of the cross-sectional area of the cavities 14, 114, 214, 314 to that of the fiber 10, 110, 210, 310 is selected according to the application, to obtain the best insulating properties while maintaining adequate material properties: e.g. mechanical properties (elongation and breaking strength for example), physical properties, electrical properties, chemical properties, but also for durability and costs.

[0020] The fiber 10, 110, 210, 310 can be composed of any type of material that can be used in an extrusion process. Suitable extrudable materials include, but are not limited to, organic polymers and inorganic materials. In a particular embodiment, the extrudable material provides some impermeability to limit gas diffusion, as will be further detailed below. Examples of suitable organic polymers includes, but are not limited to, poly(ether sulfones) (PES), polyamide (PA), polyethylene terephthalate (PET), poly(p-phenylene sulfide) (PPS), polypropylene (PP), polyvinyl alcohol (PVA), polyether ether ketone (PEEK), polyacrilonitrile (PAN) or mixtures thereof. An example of a suitable inorganic material is glass.

[0021] The fiber 10, 1 10, 210, 310 further comprises an insulating gas layer 16 which is trapped within each cavity 14, 1 14, 214, 314. The insulating gas layer includes a gas having a lower thermal conductivity than air such as to decrease the rate of heat transfer through the fiber and as such increase the thermal insulation property of the fiber. In a particular embodiment, the insulating gas layer 16 includes an appropriate gas or a mixture of gases selected from group 18 of the periodic table: noble gases. For example, the insulating gas layer 16 can be one or more of argon, krypton, xenon and radon. These are noble gases having a high density (for example atomic weights of Ar=40 and Kr=84) much more than air with 29 g/mol, and having lower thermal conductivity than air. In a preferred embodiment, the insulating gas layer 16 is krypton or argon or a mixture of both. Since the insulating gas layer 16 includes a gas having a lower thermal conductivity than air, noble gases having a higher thermal conductivity than air (e.g. helium and neon) are not suitable therefor.

[0022] In a particular embodiment, the material of the fiber 10, 110, 210, 310 itself has adequate impermeability properties such that the interior surface 18, 1 18, 218, 318 of the fiber which defines each cavity 14, 1 14, 214, 314 provides by itself very limited or no diffusion of the insulating gas layer 16 therethrough, such that the insulating gas layer 16 is trapped within at least one of the cavity, multiple cavities or all cavities defined in the fiber. It is understood that depending on the shape of each cavity 14, 1 14, 214, 314, the interior surface 18, 1 18, 218, 318 enclosing the cavity may have more than one side. For example, in Fig. 2H, the interior surface enclosing the cavity has 4 sides.

[0023] In another embodiment illustrated in Fig. 2A, the interior surface 18, 118, 218, 318 defining each cavity 14, 114, 214, 314 is covered with a coating 20 having a substantially equal or lower permeability to the insulating gas than that of the material of the body. The coating 20 thus further decreases the diffusion of the insulating gas therethrough. The surface 18, 118, 218, 318 can be partially or fully coated. It is understood that the coating may be omitted if the material of the fiber 10, 1 10, 210, 310 provides a sufficient barrier against the diffusion of the insulating gas layer out of the cavities, and that although not shown, the coating may be applied to any of the above described embodiments.

[0024] In another embodiment, the material of the coating 20 has a lower emissivity than that of the material of the fiber 10, 1 10, 210, 310, to reduce heat transfer by radiation through the fiber. This may be in addition to or as an alternative to the lower permeability to the insulating gas discussed above.

[0025] In a particular embodiment, the coating 20 is a metallic or a metallic oxide composition or a mixture thereof. For example, the metallic composition may be at least partly made of silver, aluminum, copper, gold, tin or a mixture thereof; the metallic oxide composition may be least partly made of tin oxide, indium oxide, zinc oxide or a mixture thereof. In a particular embodiment, the thickness of the metallic coating varies from about 10 to about 15 nm.

[0026] In a particular embodiment, the fibers of the present disclosure are made by an extrusion process such as extrusion through a spinneret. The spinneret creates the outside cross-sectional shape of the fiber as well as the cross-sectional shape of the interior surface 18, 1 18, 218, 318 defining each cavity. The cross-sectional shape of each cavity 14, 1 14, 214, 314 is stabilized using a stream of air.

[0027] The deposit of the coating 20 on the surface 18, 118, 218, 318 defining each cavity can be achieved by evaporation, spraying or by pyrolysis. The technique used is relative to the material of the fiber. For example, the pyrolysis technique may be used when the fiber is at least partially made of glass. Examples of spraying techniques include, but are not limited to, vacuum and magnetron.

[0028] In an embodiment, the introduction of the insulation gas within each cavity is performed during the extrusion of the fiber material. The air injected in each cavity to stabilize it during the extrusion is replaced by the insulating gas by any adequate process, for example a vacuum process. Alternately, the insulating gas may be used directly during the extrusion process to stabilize the cavity. Each cavity is closed once it is filled with the insulating gas. [0029] The embodiments of the present disclosure described above are intended to be examples only. Those of skill in the art may effect alterations, modifications and variations to the particular exemplary embodiments without departing from the intended scope of the present disclosure. In particular, selected features from one or more of the above-described exemplary embodiments may be combined to create alternative exemplary embodiments not explicitly described, features suitable for such combinations being readily apparent to persons skilled in the art. The subject matter described herein in the recited claims intends to cover and embrace all suitable changes in technology.