CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 62/931,727, filed November 6, 2019, the content of which is hereby incorporated in its entirety.

TECHNICAL FIELD

[0002] This disclosure is generally related to fabrics for apparels, and more specifically to radiative cooling fabrics for apparels and methods for fabricating the same.

BACKGROUND

[0003] Problems associated with the energy crises and climate change are becoming more critical and needs to be addressed. According to recent research, 15% of all electricity consumed globally is used to cool homes and offices, which in turn causes an increase of greenhouse gas emissions worldwide. Therefore, development of new technologies to reduce the energy demand is needed. For example, increasing the cooling set-point temperature by 2°C can save over 20% of energy globally.

[0004] Personal cooling management would be an effective method to reduce the energy cost. In a typical indoor environment, the bodies’ radiative heat lost in the mid-infrared thermal radiation (wavelength range of 7 to 14 μm) with a skin temperature of 33.5 °C in human body accounts for more than 50% of the total heat lost. Most of the conventional textile fabrics like cotton and polyester fail as they are infrared radiation (IR) opaque materials.

SUMMARY

[0005] Described herein are radiative cooling fabrics and apparels made of the fabrics, and methods for fabricating the fabrics.

[0006] In one aspect, a fabric includes one or more yarns. Each of the one or more yarns include a plurality of filaments. Each of the filaments has an average diameter in a range of 20- 50 mih such that the fabric has an IR transmittance at a wavelength of 9.5 μm of at least 37%. In some embodiments, the fabric has a stiffness of less than 50 measured by systems from PhabrOmeter or Nu Cybertek.

[0007] In some embodiments, each of the one or more yarns has an average diameter of at most 400 μm. In some embodiments, the one or more yarns include at least one yarn having a coating on its surface. The one or more yarns may have different colors by including dyestuff. In some embodiments, the one or more yarns include an ultraviolet block agent. In some embodiments, the ultraviolet block agent includes ZnO or TiO2. In some embodiments, the one or more yarns include one or more ceramic fillers.

[0008] In some embodiments, the fabric has a porosity in a range of 0 - 12%. Porosity is defined as 1 minus cover factor in this disclosure.

[0009] In some embodiments, the filaments comprise one or more of polyethylene, polypropylene, or polyamide.

[0010] In another aspect, an apparatus includes a fabric. The fabric includes one or more yarns. Each of the one or more yarns include a plurality of filaments. Each of the filaments has an average diameter in a range of 20-50 μm such that the fabric has an IR transmittance at a wavelength of 9.5 μm of at least 37%. In some embodiments, the apparatus includes one of an apparel, a footwear, a tent, or a sleeping bag.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Certain features of various embodiments of the present technology are set forth with particularity in the appended claims. A better understanding of the features and advantages of the technology will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the disclosure are utilized, and the accompanying drawings of which:

[0012] FIG. 1 is a schematic diagram depicting yarn fabrication apparatus according to one example embodiment. [0013] FIG. 2 is a diagram showing cooling performances, fabric thicknesses, and IR transmittances of various woven fabrics.

[0014] FIG. 3 is a diagram illustrating stiffness test data and thickness data of PE fabrics formed by the disclosed techniques, according to one example embodiment.

[0015] FIG. 4 is a diagram illustrating stiffness test data and thickness data of conventional PET fabrics.

DETAILED DESCRIPTION OF EMBODIMENTS

[0016] In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the disclosure. However, one skilled in the art will understand that the disclosure may be practiced without these details. Moreover, while various embodiments of the disclosure are disclosed herein, many adaptations and modifications may be made within the scope of the disclosure in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the disclosure in order to achieve the same result in substantially the same way.

[0017] Unless the context requires otherwise, throughout the present specification and claims, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” Recitation of numeric ranges of values throughout the specification is intended to serve as a shorthand notation of referring individually to each separate value falling within the range inclusive of the values defining the range, and each separate value is incorporated in the specification as it were individually recited herein. Additionally, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0018] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may be in some instances. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0019] Various embodiments described herein are directed to IR transparent fabric for personal body cooling purposes. Prior work in the field proposed fabrics that are made with a fiber/filament having a diameter of about 1 μm or less to be effective for infrared transparency. It has been found that fibers should be made with small diameter (e.g., a few micrometers or narrower) so as to allow infrared radiation from a human body to pass through. However, fibers of small diameters are weak for normal textile manufacturing processes. Techniques disclosed herein use fibers with much larger diameters of at least 20 μm to make stronger yarns for the radiative cooling fabric, which significantly improves the production quality and rate as traditional textile materials. Further, the techniques disclosed herein provides fabrics that is infrared transparent. For example, the disclosed fabrics have an IR transmittance at a wavelength of 9.5 μm of at least 37%.

[0020] Embodiments will now be explained with accompanying figures. Reference is first made to FIG. 1. FIG. 1 is a schematic diagram depicting yarn fabrication apparatus 100 according to one example embodiment. The yarn fabrication apparatus 100 includes a food hopper 102 configured to receive polymer granules 104. The polymer granules 104 includes one or more materials that are selected to form thin filaments for the yarn. For example, the materials may include selected polymers and other additives. In some embodiments, the selected polymers may include one or more of polyethylene, polypropylene, or polyamide. In some embodiments, the selected additives may include a coloring agent, an ultraviolet (UV) block agent or other functional agents.

[0021] The yarn fabrication apparatus 100 further includes a heating unit 106 that melts the polymer granules 104 at a predetermined elevated temperature to generate a polymer melt 108. The polymers used in making polymer yarn may include, for example, linear low-density PE (LLDPE) or high-density PE (HDPE) with a viscosity in the range of 17-30 g/10min (based on ASTM D1238), which provides moderate mobility in following melt extrusion process. A pump 110 is employed to move the polymer melt 108 to a spinneret apparatus 112 that includes a plurality of spinnerets 112-1. Each of the spinneret 112-1 extmdes/produces a filament/fiber 114 that is collected by a yarn driving roller 116. Depending on a number of spinnerets 112-1 in the spinneret apparatus and a material flow rate, different filament sizes with various filament numbers may be obtained. In some embodiments, an average diameter of the filaments 114 is controlled to be in a range of 20-50 μm. In some embodiments, to form a cooling fabric that has a nice skin touch, the average diameter of the filaments 114 is controlled in a range of 25-50 μm, 30-50 μm, 35-50 μm, 40-50 μm, 20-45 μm, 25-45 μm, 30-45 μm, 35-45 μm, 20-40 μm, 25-40 μm, 30-40 μm, 20-35 μm, 25-35 μm, or 20-30 μm.

[0022] While the filaments 114 are pulled by the yarn driving roller 116, the filaments 114 are cooled by air 118. In some embodiments, alternatively or additionally, after the filaments 114 are cooled, they may be subject to steam treatment 120 to modify its property. In some embodiments, the as-spun multi-filament yarn is drawn from the spinnerets 112-1 with a draw ratio of at least 2.2:1 and twisted at least 155/m to form a strong yam. The drawing process increases mechanical strength, e.g., tenacity and elongation, of a polymer yarn 122. For example, a drawn PE yam may have a tenacity of at least 1.61 g/d and elongation of at most 111.26%. The filaments 114 are collected by the yam driving roller 116 to form the yarn 122, which is fed to feed roller 124. Then the yarn 122 is rolled on a bobbin 126 and ready for making a fibric.

[0023] One or more yams 122 are made into a fabric for personal cooling garment by weaving and knitting techniques. In some embodiments, reduction of the fabric thickness and control of the fiber/filament and yam size may have significant effects on the cooling performance of garment as both of the fiber and yarn sizes affect IR transmittance. Particularly, it has been discovered that the fiber size of a yam should have a diameter of about 1 μm to be effective for acceptable IR transmittance. However, using the techniques disclosed herein, the fiber size of the yarn 122 is controlled to be in the range of 20-50 μm, about 20 to 50 times larger than the fiber size in the prior work of the field for cooling garment. The disclosed techniques include selection of polymer materials, the size of the fiber, and the size of the yam for forming a fabric that is strong and IR transparent. For example, one or more polyethylene, polypropylene, or polyamide are employed for the material that can achieve acceptable IR transmittance for the fibers having a diameter in the range of 20-50 μm, 25-50 μm, 30-50 μm, 35-50 μm, 40-50 μm, 20-45 μm, 25-45 μm, 30-45 μm, 35-45 μm, 20-40 μm, 25-40 μm, 30-40 μm, 20-35 μm, 25-35 μm, or 20-30 μm. [0024] To be effective for IR transmission, a diameter of the yarn 122 is controlled to be at most 400 μm. In some embodiments, a diameter of the yarn 122 is at most 350 μm, 300 μm, 250 μm, or 200 μm. In some embodiments, a diameter of the yarn 122 is in the range of 200-400 μm, 200-350 μm, 200-300 μm, 200-250 μm, 250-400 μm, 250-350 μm, 250-300 μm, 300-400 μm, 300-350 μm, or 350-400 μm.

[0025] These discoveries allow a fabric to have IR transmittance at a wavelength of 9.5 μιη of at least 37%. In some embodiments, a fabric formed by the techniques disclosed herein may have IR transmittance at a wavelength of 9.5 μιη of at least 38%, 40%, 42%, 45%, or 50%. In some embodiments, a fabric formed by the techniques disclosed herein may have IR transmittance at a wavelength of 9.5 μιη in the range of 37-50%, 37-45%, 37-40%, 38-50%, 38- 45%, 40-50%, 40-45%, or 45-50%.

[0026] In some embodiments, the weaving and knitting process to form the fabrics may result in pores in the fabric structure. For example, the fabrics may have a porosity in a range of 0 - 12%. The pores may be used to modify the characteristics of the fabric, including IR transmittance and air permeability.

[0027] In some embodiments, the yarn may be formed with various coloring agents to provide colors to the yams for creating patterns or colors on a fabric. In some embodiments, the yarns may be formed with other functional agents. For example, one or more UV-block agents may be added to the yam to give the yarn the ability to provide a better UV-block function. In some embodiments, the UV-block agent may include ZnO and T1O2. In some embodiments, the functions agents may be added to the yarn in the form of ceramic fillers. In some embodiments, the added functional agents is added at most to the point that the IR transmittance (at a wavelength of 9.5 μm) drop of the fabric does not exceed beyond 15%.

[0028] FIG. 2 is a diagram showing cooling performances, fabric thicknesses, and IR transmittances of various fabrics. First, FIG. 2 indicates the cooling performance of two woven PE fabric samples formed with the techniques disclosed herein compared with traditional polyester and cotton woven fabric samples. The results indicated that the PE fabric (150D (denier)/24F (filament count per yam), yam diameter of 285 μm, filament diameter of 37μm) with a thickness of 0.28 mm is 2.1 and 1.9 °C cooler than conventional PET woven fabric (0.29 mm in thickness) and cotton broadcloth fabric (0.27mm in thickness), respectively in skin temperatures; while the PE fabric (150D/50F yarn diameter of 285 μm, filament diameter of 22 μm) with a thickness of 0.36 mm was 1.8 and 1.6°C cooler than the PET woven fabric and the cotton broadcloth fabric, respectively in skin temperatures. Further, The IR transmittance is 50%, 37%, 0%, and 0% for the 150D/24F PE fabric, the 150D/50F PE fabric, the PET woven fabric, and cotton broadcloth fabric, respectively. These results demonstrate the advantages of the disclosed PE fabrics in thermal regulation.

[0029] In some embodiments, the fabrics formed by the techniques disclosed herein may have stiffness less than 50. FIG. 3 is a diagram illustrating stiffness test and thickness data of PE fabrics formed by the disclosed techniques, according to one example embodiment. FIG. 4 is a diagram illustrating stiffness test and thickness data of conventional PET fabrics. The stiffness test is conducted based on American Association of Textile Chemists and Colorists (AATCC) TM202 standard.

[0030] As shown in FIG. 3, the woven fabric made of 150D/24F PE yarn (yarn diameter of 285 μm; filament diameter of 37 μm) having 0.26 mm in thickness has a stiffness of 42.55 while the woven fabric made from 500D/72F PE yarn (yarn size of 376 μm; filament diameter of 37 μm) having 0.53 mm in thickness has a stiffness of 49. The woven fabric made of 150D/24F PE yarn has a softer touch than that of the woven fabric made from 500D/72F PE yarn. The results indicate the additional benefits of controlling the yarn diameter to be at most 400 μm in apparel applications as smaller yarn size contributes to thinner fabrics with better drapability.

[0031] As shown in FIG. 4, woven PET fabric sample 1 (0.38 mm in thickness) with a filament diameter of 36 μm has a stiffness of 56.64 while woven PET fabric sample 2 (0.41 mm in thickness) with 15 μm filament diameter has a stiffness of 44.24. For the conventional fabric, the filament diameter needs to be below 20 μm (15 μm in this example) to obtain the acceptable skin touch (less than 50 in stiffness). Referring back to FIG. 3, the fabrics made from the techniques disclosed herein can achieve the acceptable stiffness even with a filament diameter of 37 μm.

[0032] In summary, the fabrics consistent with this disclosure achieve good infrared- transmittance, good cooling performance, and good drapeability which makes them appropriate for apparel applications. The fabrics can also be employed in other fields that need cooling fabrics.

[0033] In one aspect, a disclosed radiative cooling fabric has an IR transmittance at a wavelength of 9.5 μm of at least 37%, e.g., from transmittance data collected from a thermal camera.

[0034] In another aspect, the fabrics may be made from material which has a transmittance of infrared radiation at a wavelength of 9.5 μm of at least 38%. The materials may include, but not limited to, polyethylene, polypropylene, and polyamide.

[0035] In yet another aspect, the fabrics are made from a yarn with filaments having an average diameter in the range of 20-50 μm. The yarn has an average diameter of at most 400 μm.

[0036] In yet another aspect, a radiative cooling fabric made by drawn PE yarns has thickness of at most 400 μm with porosity range of 0 - 12%.

[0037] In yet another aspect, the yarn may be coated with sizing material before weaving or knitting to avoid the statics, enhance strength, and improve bonding of the filaments.

[0038] The foregoing description of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Many modifications and variations will be apparent to the practitioner skilled in the art. The modifications and variations include any relevant combination of the disclosed features. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical application, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalence.