Any Docket No. 0818.01211
TEMPERATURE ADAPTABLE TEXTILE FIBERS AND METHOD OFPREPARING SAME
BACKGROUND OFTHEINVENTION
Field of the Invention
The present invention relates to a fiber composition containing a core polymer mixed with a phase change material sealed within a polymer sheath thereby allowing the fiber to store or release heat during temperature changes in the surrounding environment.
Description of the Related Art
The use of phase change materials for storing or releasing thermal energy has long been known. A phase change material may be repeatedly converted between solid and liquid phases, or thermocycled, thereby utilizing its latent heat of fusion to absorb, store and release heat during such phase conversions. The latent heat of fusion for the phase change material is greater than its sensible heat capacity. For example, in phase change materials, the amount of energy absorbed upon melting or released upon freezing is much greater than the amount of energy absorbed or released upon increasing or decreasing the temperature of the material over an increment of 10°C. Upon melting and freezing, a phase change material absorbs and releases substantially more energy per unit weight than a sensible heat storage material that is heated or cooled over the same temperature range. In contrast to a sensible heat storage material which absorbs and releases energy essentially uniformly over a broad temperature range, aphase change material absorbs and releases a large quantity of energy in the vicinity of its melting/freezing point.
Other useful materials that have high thermal storage and release properties' are commonly referred to as plastic crystalline materials. These materials have thermal energy available without undergoing a phase change, e.g. solid to liquid. Although the precise reasons why such plastic crystalline materials exhibit such thermal behavior prior to a change in state is not clear, it is believed that the thermal effect of such materials is caused by a conformational and/or rotational disorder in these substances. Regardless, plastic crystalline materials, such as polyhydric alcohols, have been found effective in providing thermal insulation to textile fibers as can be seen in U.S. Patent No. 4,781,615 (incorporated herein by reference in its entirety).
Phase change materials and plastic crystalline materials have been used in a variety of applications, including integration into textile fibers for the purpose of keeping clothing at a comfortable temperature. In such textile applications, attempts have been made to coat such materials onto fibers; however, this does not permit use of a sufficient amount of the material to provide effective thermal properties in the garment or other article formed from the fibers. Others have tried micro-encapsulating phase change materials as part of a blend within a fiber. The microcapsules, however, do not have the structural integrity required to withstand forces exerted on the encapsulated phase change material during extrusion of the fibers. One particular application of phase change materials to textile fibers is disclosed in
Salyer, U.S. Patent No. 5,885,475. That disclosure is expressly incorporated herein by reference in its entirety. In Salyer, a fiber material is disclosed that comprises, a fiber forming polymer having a phase change material integrally incorporated throughout the polymer. Silica is also incorporated into the fiber of Salyer in order to tie up the phase change material into a stable gel so as to prevent its oozing when undergoing a phase change at its melting/freezing point. However, the addition of the silica does not absolutely ensure the integrity of the fiber upon melting of the phase change material.
Accordingly, there presently exists a need to provide a textile fiber incorporating an amount of a phase change material or a plastic crystalline material that yields effective thermal insulating properties for the fiber, that can be easily manufactured by extrusion and that ensures the material will remain secured within the fiber.
SUMMARY OF THE INVENTION Therefore, in light of the above, and for other reasons that become apparent when the invention is fully described, an object of the present invention is to provide a textile fiber incorporating a sufficient amount of phase change or plastic crystalline material throughout the fiber that can be easily manufactured by extrusion.
A further object of the present invention is to provide a fiber that secures the phase change or plastic crystalline material within the fiber thereby preventing oozing of the phase change material when undergoing a melting point phase change.
A still further object of the invention is to provide a fiber that maximizes the amount of phase change or plastic crystalline material within the fiber while maintaining overall fiber strength and capability of being manufactured by extrusion.
Yet another object of the invention is to provide methods for manufacturing sheath-core and "island-in-the-sea" fibers containing one or more phase change or plastic crystalline materials so as to further enhance the thermal insulating properties of the fiber.
An additional object of the invention is to provide fabrics manufactured by fibers of the invention containing one or more phase change or plastic crystalline materials.
The aforesaid objects are achieved in the present invention by providing a fiber composition comprising a blend or mixture of core polymer and phase change or plastic crystalline material enclosed within a polymer sheath. The core and sheath polymers of the invention can be any number of polymers including, but not limited to, polyolefins, polyamides, polyesters and the like, as well as copolymers, terpolymers and blends thereof. The core and sheath polymers may also be elastomeric polymers, such as polyurethane. The preferable materials for both the core and sheath are polyethylene, polypropylene or a combination thereof. Any phase change or plastic crystalline material can be utilized that has a melting point or a thermal storage/release point at a desired temperature, preferably in a range from about -5 °C to about 121 ° C, and that maintains such melting or thermal storage/release point upon mixing with the core polymer. Typical phase change materials that are useful and that blend easily with a core polymer of the invention are long chain paraffinic hydrocarbons, polyethylene oxides and . . . polyethylene glycols. Plastic crystalline matenals useful in the invention are polyhydric alcohols.
The fiber composition of the invention is capable of being manufactured by a melt spinning process, wherein the fiber is formed by extruding melted polymer material such that the core polymer and phase change material are encased in the outer sheath polymer upon exiting the extruder. The fiber composition can also be manufactured utilizing a solution spinning process. Fibers formed in the invention can be of the sheath-core or "island-of-the-sea" type and can be incorporated into various forms of textile fabrics. Each fiber may contain a blend of phase change materials or plastic crystalline materials to enhance the thermal properties of the fiber. Alternatively, a fabric maybe manufactured containing fibers of the invention having different phase change materials or plastic crystalline materials. The fiber compositions of the invention can be repeatedly thermocycled, storing and releasing heat in sufficient quantity, thereby providing a fabric formed from such fibers with enhanced thermal properties for a significant period of time. Fibers formed according to the invention also maintain complete enclosure of the internal material such that oozing or leakage of phase change or plastic crystalline material is prevented when it is thermocycled.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic side view of a typical spunbound web forming apparatus utilized in forming the fiber of the invention.
Figure 2 is a perspective view, including a view in cross-section, of a sheath-core fiber of the invention. Figure 3 is a perspective view, including a view in cross-section, of an island-in-the-sea fiber of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a polymer fiber having an internal polymer component that comprises a first polymer fiber composition mixed with a thermal stabilizing material, and a second polymer fiber composition that surrounds such mixture and forms the exterior or sheath of the fiber. The term "thermal stabilizing material" is defined herein to encompass both phase change materials as well as plastic crystalline materials utilized in the invention. The fiber may be of a sheath-core configuration, wherein the first polymer mixed with the thermal stabilizing material forms the core and the second polymer forms the sheath of the fiber. Alternatively, the fiber may be of an "island-in-the-sea" configuration, wherein a number of mixtures of first polymer with thermal stabilizing material extend substantially the length of the fiber and are separated from each other and surrounded by a second polymer thereby forming "islands" within the second polymer "sea". The first and second polymers may each be any conventional material utilized in making textile fibers. Examples of such fiber materials are polyolefms, such as polyethylene or polypropylene, polyamides, such as nylon, polyesters, and the like, as well as copolymers, terpolymers and blends thereof. The first and second polymers may also be elastomeric polymers, such as polyurethane. Preferably, the first and second polymers are either polyethylene, polypropylene or a mixture thereof.
Phase change materials useful in the invention include any material that undergoes a phase change in a desirable temperature range and has a latent heat of fusion that is greater than its sensible heat capacity. Any plastic crystalline material that exhibits heat storage or release properties in a desired temperature range is also useful in the invention. Preferably, the thermal stabilizing material is compatible or non-reactive with the second or sheath polymer. The thermal stabilizing material may or may not react with the first polymer. In either case, such material preferably maintains its phase change or heat storage/release properties at the desired temperature after mixing with the first polymer. Phase change materials used in the invention will have phase change temperatures in the range of about -5°C to about 125 °C. Similarly, plastic crystalline materials of the invention will store or release heat in the same temperature range. In many clothing applications, preferable phase change or plastic crystalline materials will undergo a phase change or exhibit thermal storage/release properties between about 22 °C and about 28 °C.
The selection of a specific phase change material will be dependent upon the desired phase change temperature and the specific application of the fiber. For instance, a phase change material having a melting point near room temperature would be desirable for applications in which the associated fiber is incorporated into fabrics such as clothing designed to maintain a comfortable temperature for the user during slight changes in climate. Particularly useful phase change materials that are well known in the art are long, straight chain paraffinic hydrocarbons, typically in the range of C,0 - C44 carbon atoms. The length of the carbon chain correlates to the melting point of the material. For example, an n-Octacosane, which contains twenty eight straight chain carbon atoms per molecule, has a melting point of 61.4°C. Comparatively, an n- Tridecane, which contains thirteen straight chain carbon atoms per molecule, has a melting point of -5.5°C. An n-Octadecane, containing eighteen straight chain carbon atoms per molecule, is particularly desirable in most clothing applications as it has a melting point of 28.2°C. Other useful phase change materials are polyethylene glycols, wherein the melting point can be varied by varying the molecular weight of the glycol. A polyethylene glycol having a molecular weight range of 570 - 630 (Carbowax 600) will have a melting point of 20-25 °C, making it is useful in most clothing applications. Other polyethylene glycols that may be useful at other temperature ranges are Carbowax 400 (melting point of 4-8 °C), Carbowax 1500 (melting point of 44-48°C) and Carbowax 6000 (melting point of 56-63 °C). Further phase change materials that may be utilized in the present invention are polylethylene oxides (melting point in the range of 60-65 °C).
Effective plastic crystalline materials for use in the invention are polyhydric alcohols. Preferable polyhydric alcohols are pentaerythritol, 2,2-dimethyI-l,3-propanediol, 2- hydroxymethyl-2-methyl-l,3-propanediol, or a ino alcohols such as 2-amino-2-methyl-l,3- propanediol.
Thermal stabilizing materials may be used individually or in combination in single or multiple fibers of the invention. The selection of one or more thermal stabilizing materials will depend upon the intended use of the fabric formed by fibers including such materials as well as the ability of the selected materials to maintain their thermal storage and release properties after repeated thermocycling. A whole range of sheath-core and "island-in-the-sea" fibers are possible under the invention. For example, one sheath-core fiber embodiment may consist of a core mixture of a single thermal stabilizing material and a core polymer cqntained within a polymer sheath. In another embodiment, the core polymer may contain two or more different thermal stabilizing materials mixed with the core material. Depending on the thermal stabilizing materials selected and their reactivity with one another, a combination of two or more thermal stabilizing materials within the fiber core will result in enhanced thermal energy storage and release properties for the fiber and resultant fabric formed from such fibers. A mixture of two different phase change materials, for example, within a fiber core could result in the fiber exhibiting two distinct phase change temperature points if the phase change materials are non- reactive with each other. Alternatively, the phase change materials could react, resulting in a modified phase change that may be useful in certain applications.
Fibers containing a blend of different thermal stabilizing materials would be useful in a variety of applications where it may be desirable for a fabric to exhibit enhanced thermal insulating properties at two or more distinct temperature ranges. For instance, a fabric for use in manufacturing a glove might be composed of fibers of the invention containing phase change materials A and B, wherein phase change material A has a melting point of about 5 °C and phase change material B has a melting point of about 75 °C. The combination of those phase change materials into the core of sheath-core fibers which form the glove would provide the glove with enhanced thermal insulating properties in cold environments (e.g. in outdoor use during winter conditions) as well as warm environments (e.g. when handling heated objects such as oven trays). Alternatively, a fabric could be manufactured from a plurality of sheath-core fibers, wherein two or more fibers contain a different thermal stabilizing material in their cores. The fabric could, for example, be composed a certain percentage of sheath-core fibers containing a first thermal stabilizing material and the remaining percentage of sheath-core fibers containing a second thermal stabilizing material. Additionally, "island-in-the-sea" fibers of the invention may include one or more "islands" that contain one or more different thermal stabilizing materials in comparison to other "islands" within the same fiber. A vast number of different fiber combinations utilizing one or more thermal stabilizing materials is possible under the invention to provide a fabric with a wide range of enhanced thermal insulating properties.
Providing the "island" or core polymer in the fibers of the invention is essential in that such polymer serves as a carrier for the thermal stabilizing material as the fiber is formed. Without the addition of the "island" or core polymer, the thermal stabilizing material may not be capable of maintaining core integrity by itself during the fiber processing steps in a typical fiber extrusion apparatus. Additionally, a resultant fiber would be much weaker and less effective for use in manufacturing fabrics without the addition of an internal polymer to provide support.
Conversely, it is desirable to provide a sufficient amount of thermal stabilizing material to a fiber of the invention in order to maximize the thermal energy storing and releasing properties of such fiber and thus the enhanced insulating effect of a fabric formed from a plurality of such fibers. Depending on the specific materials used to form the fiber, the amount of the core or "island" polymer may be increased with respect to the sheath polymer, thereby increasing the amount of thermal stabilizing material that can be carried within the fiber, while maintaining a threshold level of strength for the fiber. The inventor has determined that utilizing a weight ratio of thermal stabilizing material in the core or "island" mixture of up to about 50%, with a weight ratio of core or "island" mixture in the entire fiber also being up to about 50%, will provide effective thermal insulating and strength properties for the resultant fiber. Utilizing such weight ratios provides the fiber with up to about 25% by weight of the thermal stabilizing material.
The fibers of the invention may be manufactured utilizing a melt spinning process or a solution spinning process (wet or dry). In each process, the fibers are formed by extruding the material forming the fiber through a plurality of tiny orifices in a spinneret to form filaments emerging from the orifices. The term "spinneret" refers to a portion of the extrusion device that delivers polymer and phase change and/or plastic crystalline material through the orifices for extrusion into the environment. A typical spinneret may contain from 1000 to 5000 orifices per meter of length of the spinneret. The spinneret can be implemented with holes drilled or etched through a plate or any other structure capable of issuing the required fiber streams. In a melt spinning process, the polymeric material delivered to the orifices is in a viscous, molten state. The thermal stabilizing material is typically a liquid at the polymer melt temperature. Prior to passing through the spinneret orifices, the thermal stabilizing material is mixed with the first polymer to form either the core of a sheath-core fiber or an "island" for an "island-in-the-sea" fiber. The mixing will result in a dispersion and microencapsulation of portions of the thermal stabilizing material throughout the first polymer. Portions of the thermal stabilizing material that are not completely encapsulated within the first polymer will still be contained by the second polymer upon emerging from the spinneret and therefore effectively sealed within the resultant fiber.
In a solution spinning process, the polymeric material of the fiber is dissolved in a solvent prior to passing through the spinneret orifices. In a wet spinning process, the spinneret is submerged in a chemical bath such that, upon exiting the spinneret, the polymeric material precipitates from solution and forms a solid fiber. In dry spinning, the polymeric material emerges from the spinneret in air and solidifies due to the solvent (e.g. acetone) dissolving in air. Since solution spinning processes are well-known in the art and are capable of producing sheath- core and "island-in-the-sea" fibers, such process can also be utilized in forming fibers of the invention.
After emerging from the spinneret, extruded fibers are typically drawn or stretched utilizing a godet and/or an aspirator. For example, extruded fibers emerging from the spinneret in a melt spinning process form a vertically oriented curtain of downwardly moving strands that are at least partially quenched before entering a long, slot-shaped air aspirator positioned below the spinneret. The aspirator introduces a rapid downwardly moving air stream produced by compressed air from one or more air aspirating jets. The air stream creates a drawing force on the fibers, causing them to be drawn between the spinneret and the air jet, thereby attenuating the fibers. During this portion of the spinning process for fibers of the invention, the sheath and core or "island" polymers are solidifying. Although the thermal stabilizing material may be liquid or only partially solidified at such time due to the temperature of the emerging fiber, such material is substantially prevented from oozing or leaking from the fiber because it is effectively sealed within the polymer sheath as well as the microencapsulations formed within the first polymer. The fibers of the invention may be utilized in any fiber application known in the art to form various types of woven or non-woven fabrics. For example, the drawn fibers may be wound on a bobbin or other winding mechanism for forming a woven fabric utilizing any conventional knitting or weaving technique. Alternatively, the fibers may be randomly laid on a forming surface, such as a moving conveyor screen belt (e.g., a Fourdrinier wire), to form a continuous non-woven web of fibers. The web may then be bonded using one of several known techniques to form a stable, non-woven fabric for use in manufacturing a variety of textile products. A common bonding method involves lifting the web from the moving screen belt and passing the web through two heated calender rolls. Often, one of the rolls is embossed, causing the web to be bonded in numerous spots. Air carded or spun-laid webs can also be formed from such polymeric fibers. Staple fibers can also be manufactured in practicing the invention, wherein the fibers are cut into short fibers prior to forming a web therefrom. One potential advantage of employing staple fibers is that a more isotropic fabric can be formed, since the staple fibers potentially can be oriented in the web more randomly than continuous fibers.
Figure 1 diagrammatically depicts an apparatus 10 for producing sheath-core or "island- in-the-sea" fibers incorporating one or more thermal stabilizing materials in accordance with an exemplary embodiment of the invention. The apparatus further subjects the fibers to a spunbond process thereby producing a nonwoven fabric having selected thermal insulating properties. The term "spunbond" refers to a process of forming a non-woven fabric or web from an array of thin, melt-spun polymeric fibers or filaments produced by extruding molten polymer from orifices of the spinneret.
The apparatus of Figure 1 includes spin pack 28 for extruding and forming the fibers. The term "spin pack" as used herein refers to the assembly for processing molten polymer to produce extruded polymer streams, including final polymer filtration, distribution systems and the spinneret. Spin packs suitable for forming sheath-core, "island-in-the-sea" and other plural component fiber configurations are well known in the art. For example, one such spin pack is disclosed in U.S. Patent No. 5,162,074, the disclosure of which is incorporated herein by reference in its entirety. Essentially, such a spin pack provides a flow path for two or more polymers that results in filaments emerging from spinneret orifices which include core or "island" polymers surrounded by a polymer sheath.
Apparatus 10 includes hoppers 12 and 14 which receive pellets of two different polymers, sheath polymer A and core or "island" polymer B. Those two polymers are respectively fed from hoppers 12 and 14 into screw extruders 16 and 18 and are melted as they are conveyed toward heated pipes 20 and 22. Thermal stabilizing material C can be added and mixed with polymer B at any point along apparatus 10 prior to encountering polymer A at the spinneret 30. Some examples showing different points of addition of material C to polymer B in apparatus 10 are provided in Figure 1. For example, material C may be added in solid or liquid form at location 13 to the hopper 14 or at location 19 in screw extruder 18. Alternatively, material C may be added at location 27 in spin pack 28.
The mixing of thermal stabilizing material with core polymer material can also be accomplished in either a static or dynamic fashion. Dynamic mixing can occur by any mechanical means that effectively mixes the components, such as the screw extruder 18. For example, when phase change material is added to hopper 14 or screw extruder 18, dynamic mixing occurs as the stream is moved within extruder 18 toward heated pipe 22. Upon heating of polymer B and material C to the melting temperature of polymer B, the two components can be effectively mixed.
In contrast to dynamic mixers, static mixers do not utilize any mechanical agitating or mixing means. Rather, mixing is effected by crossing the pathways of at least two traveling streams of different materials, in molten or liquid state, a sufficient number of times resulting in a desired dispersion of each material in at least one stream. Static mixers utilized in forming extruded fibers containing two or more mixed polymers are well known in the art. An example of one such static mixer, disclosed in U.S. Patent No. 5,851,562, is incorporated herein by reference in its entirety. Static mixing may occur within spin pack 28 or at any other point within the apparatus prior to combining with the sheath polymer at the spinneret. For example, in apparatus 10, thermal stabilizing material C may be added at location 21 and statically mixed with polymer B during travel within heated pipe 22.
Depending on the selected thermal stabilizing material and its corresponding melting temperature during mixing, the thermal stabilizing material may have a viscosity that varies considerably with the core or "island" polymer. For example, at the polymer melting temperature, the core or "island" polymer may be in a very viscous, molten state whereas the thermal stabilizing material is in a less viscous, liquid state. The thermal stabilizing material may or may not be evenly dispersed within the core or "island" polymer after mixing. Regardless of the level of dispersion, the resultant fiber will still have effective heat storing and releasing properties provided a sufficient amount of thermal stabilizing material is sealed within the fiber. The molten polymers respectively flow through heated pipes 20 and 22 to metering pumps 24 and 26. The pumps feed the two polymer streams to spin pack 28 having suitable internal components capable of forming a sheath-core or "island-in-the-sea" fiber configuration. In the apparatus of Figure 1, spin pack 28 includes a spinneret 30 with orifices 32 which shape the sheath-core fibers extruded therethrough. An array of sheath-core fibers 34 exit the spinneret 30 and are pulled downward and attenuated by an aspirator 36 which is fed by compressed air or steam from pipe 38. Aspirator can be, for example, of the gun type or of the slot type, extending across the full width of the fiber array, i.e., in the direction cprresponding to the width of the web to be formed by the fibers.
Aspirator 36 delivers attenuated fibers 40 onto a web-forming screen belt 42 which is supported and driven by rolls 44, 46 and 50. A suction box 48 is connected to a fan (not shown) to pull ambient air through screen belt 42 and cause fibers 40 to form a nonwoven web on screen 42. The nonwoven web that forms can then be further processed to form desired fabrics, clothing or other textile products that are endowed with the thermal properties of the combined fibers of the invention. Figure 2 depicts a cross-sectional view of a typical sheath-core fiber 100 of the invention that is capable of being produced by the apparatus of Figure 1. Fiber 100 contains phase change material that is dispersed throughout the core polymer 120 of fiber 1. Sheath 110 surrounds the circumference of fiber 100, thereby preventing phase change material portions from escaping from the fiber when thermocycling between liquid and solid phases. Portion 130 represents one such phase material portion that lies between core polymer 120 and sheath polymer 110. Core polymer 120 surrounds or encapsulates some phase change material portions, such as portion 140, that are internal to the core of fiber 100, thereby preventing those portions from escaping the fiber.
Figure 3 depicts a cross-sectional view of a typical "island-in-the-sea" fiber 200 of the invention also capable of being manufactured by the apparatus of Figure 1. The sheath or "sea" 210 of fiber 200 surrounds "islands" 220, 230, 240 and 250. Four "islands" are depicted for illustrative purposes only, and an "island-in-the-sea" fiber of the invention may contain more or less "islands" depending on the specific application of the fiber. "Islands" 220, 230, 240 and 250 contain "island" polymers 222, 232, 242 and 252, respectively. Thermal stabilizing material portions, such as those are either incorporated within their respective "islands" or between the "islands" and the "sea". Fiber 200 contains two different types of thermal stabilizing materials. "Islands" 220 and 250 contain the same thermal stabilizing material, as depicted by portions 260, and "islands" 230 and 240 contain the same thermal stabilizing material, as depicted by portions 270. Thermal stabilizing material enclosed within portions 270 differs from thermal stabilizing material enclosed within portions 260. Having described preferred embodiments of new and improved fibers of the invention as well as their methods of manufacture, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope of the present invention as defined by 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.