Breathable tear-resistant flash spinning sheet

Abstract

The present invention relates to (i) a bonded sheet of non-woven flash spun plexiform fibrils exhibiting high tear resistance, high degree of air permeability and high tensile strength; (ii) a process for preparing a bonded sheet of non-woven flash spun plexiform fibrils; and (iii) a multi-layer sheet structure and article comprising at least one bonded sheet of non-woven flash spun plexiform fibrils.

Description

TECHNICAL FIELD

[0001] The present invention relates to (i) bonded sheets of flash-spun plexifilamentary fibrils that exhibit high tear resistance, high degree of air permeability, and high tensile strength; (ii) methods for making bonded sheets of flash-spun plexifilamentary fibrils; and (iii) multi-layer sheet structures and articles comprising at least one bonded sheet of flash-spun plexifilamentary fibrils. BACKGROUND

[0002] Flash-spun nonwoven sheets having a wide range of properties suitable for use in a variety of applications, including but not limited to protective apparel, have been developed. Their production typically involves two stages, a first stage in which fibrils are produced and laid in an overlapping manner to produce an assembly of fibrils in the form of a sheet, and a second stage in which adjacent fibrils are bonded via thermal bonding to obtain a robust structure that is not easily disassembled. The properties of the final nonwoven sheet are influenced by various factors from both the first and second stages.

[0003] Flash spinning is a method for producing fibrils having a unique plexifilamentary structure. It involves preparing a solution of a polymer that forms the fibril in a spinning agent at a pressure higher than the vapor pressure of the spinning agent and at a temperature higher than the normal boiling point of the spinning agent, and releasing the solution into a region having a substantially lower temperature and pressure, so that the spinning agent flashes and the polymer solidifies in the form of plexifilamentary fibrils. Examples of flash spinning methods are disclosed in US 3,081,519 and US 3,227,794.

[0004] The properties of flash-spun fibrils depend, among other things, on the polymer or polymer blend used to form them, the spinning agent used to produce the spinning fluid, the concentration of the polymer in the spinning fluid, and the temperature of the spinning fluid during spinning. US 7,744,989 describes a flash spinning method using a hydrocarbon spinning agent in which the spinning temperature is increased to produce flash-spun fibrils having a reduced internal void volume. Thermally bonded nonwoven sheets made from these fibrils are more air permeable, but must be traded off against resistance to trapezoidal tear, which decreases in these sheets after thermal bonding.

[0005] As with other types of spinning technology, the properties of the initial assembly of fibrils are altered by subsequent thermal bonding to produce flash-spun nonwoven sheets.

[0006] Thermal bonding is a common method for bonding nonwoven sheet materials, in which heat is used to soften the polymer from which the fibers are made, typically by passing the nonwoven sheet material through an arrangement of heated rollers, either with support rollers forming a nip or without support rollers. The degree of bonding can vary based on temperature and pressure, and the time for which these temperatures and pressures are applied. The bonding of the nonwoven sheet material also varies spatially depending on the rollers used and the area over which the bonding is applied, for example, using smooth surface rollers to apply uniform heat and pressure over the entire surface, as opposed to using patterned rollers to apply heat and pressure locally over only a portion of the surface to form an embossed pattern in the final nonwoven sheet material.

[0007] US 3,442,740 and US 3,532,589 describe thermal bonding on smooth heated rollers, in which one or both sides of the nonwoven sheet material are subjected to overall uniform full-surface contact thermal bonding. In this method, a surface-bonded nonwoven sheet material product is obtained having a paper-like feel, which is suitable for uses such as packaging and printing media, but which is too stiff for use in garments, being uncomfortable and "noisy" to the wearer. Thermal bonding using hot calender bonders, such as those described in US 5,972,147, also tends to produce stiffer products, without the softness desired for most garment applications, such as protective apparel. Products having a paper-like feel also have disadvantages in other applications, such as automotive covers that need to conform to the shape of the vehicle, or roof liners that can vibrate and produce noise when the wind blows over them.

[0008] US 3,478,141 and US 4,091,137 describe thermal bonding by passing a nonwoven sheet between a heated engraved patterned roll and a rubber coated backup roll to bond one or both sides of the nonwoven sheet in defined areas only, thereby producing a softer and more drapeable material suitable for garment applications. The patterned roll can contain different patterns such as the dot pattern described in US 3,478,141, US 6,610,390 and US 2004 / 241399 Al, the rib pattern described in US 2003 / 0032355 Al and US 2003 / 00165667 Al, the flax pattern or random pattern described in US 7,744,989, or a combination of different patterns described in US 5,620,779 and US 5,964,742. The nonwoven sheet can pass through one or more pairs of heated patterned rolls and rubber coated backup rolls and can also be partially wrapped around one or more heated patterned rolls to transfer heat into the nonwoven sheet before reaching the nip between any such patterned roll and rubber coated backup roll. In addition, the nonwoven sheet can be in contact with one or more preheating or cooling rolls before and after passing through each pair of patterned roll and backup roll, configured as described in US 5,972,147. US 6,034,008 and US 2003 / 00165667 Al describe a method in which one side is embossed with a "rib" pattern of discrete bonding points and the other side is embossed with a "flax" pattern over most of the surface.

[0009] Thermal bonding affects different properties of the nonwoven sheet in different ways.

[0010] The flux properties of the nonwoven sheet, i.e. the ability of the assembly of fibrils for air or other gases (such as water vapor) to move freely through it by diffusion or by bulk flow under a pressure difference, can be changed in different ways depending on the bonding method. Heating can cause relaxation of tensions within the fibrils and shrinkage of the fibrils, resulting in an increase in the space between the fibrils and an increase in flux. Conversely, the pressure applied during bonding can compress the structure, reducing the space between the fibrils through which the gas can move, resulting in a decrease in flux. Furthermore, if the temperature and pressure are high enough to cause the fibrils to melt and extensively fuse together, this can create a film-like region that allows very little flux.

[0011] The barrier properties of the nonwoven sheet, i.e. the ability of the assembly of fibrils to prevent particles in air from passing through it, or to prevent liquids (such as water) from penetrating it under pressure, tend to change after bonding in the opposite way, for example as follows: the reduced pore size resulting from compression during bonding leads to greater resistance to the passage of particles or liquids through the structure.

[0012] Mechanical properties such as resistance to delamination, puncture and tearing, abrasion resistance, and tensile strength can increase or decrease with increasing bonding strength. However, the stronger bonds between the fibrils created by bonding and the restriction on their ability to move relative to each other increase the stiffness of the bonded sheet. Furthermore, resistance to trapezoidal tearing may be unsatisfactory.

[0013] The complex interplay of these properties means that the production of thermally bonded nonwoven sheets for specific applications typically requires a compromise between the desired properties of the final nonwoven sheet.

[0014] When the bond is applied uniformly across the entire surface, the effect of the bond on the sheet stiffness is particularly noteworthy. This results in sheets with a papery texture (often referred to as a "hard structure"), which tend to generate significant noise when bent or folded. When embossing rollers are used to create areas with varying degrees of bond, quieter and more flexible, softer fabric-like structures (often referred to as "soft structures") can be achieved. However, even soft-structure bonded sheets are stiffer and less flexible than the initial sheet before bonding.

[0015] Some of the softness of bonded nonwoven sheets can be restored by applying methods known in the textile industry, such as softening or re-lofting. In these methods, the nonwoven sheet is passed through a device that locally twists the material in a way that breaks or partially breaks some of the bonds between the fibers, thereby allowing more relative movement and increasing the flexibility of the nonwoven sheet. These changes in mechanical properties are typically accompanied by an increase in flux characteristics and a loss of barrier properties.

[0016] US 3,408,709 describes a softening method for mechanically softening nonwoven sheets using a button breaker. The button breaker employs knobbed rolls that rotate at a different speed than, or even in the opposite direction to, the movement of the nonwoven sheet as it travels over it, thereby generating a frictional effect.

[0017] US 5,966,785 and US 6,195,854 report a mechanical softening method in which a nonwoven sheet is passed through the gap of a bulging roller abutting against a soft rubber support roller. However, these documents do not provide information on how this method affects the barrier properties of the nonwoven sheet.

[0018] US 7,296,328 discloses a method for softening nonwoven sheeting, wherein the sheeting shows an increase in air permeability with an increase in softening cycles. The softening method described employs a frictional effect that utilizes the speed differential between the nonwoven sheeting and the roll or mechanical object through which it passes. However, the surface of the nonwoven sheeting is damaged as it is exposed to the frictional surface.

[0019] US 3,920,874 and US 3,811,979 describe a method employing a pair of rolls covered with square-edged cylindrical pins that interlock for softening a nonwoven sheeting passing between them, wherein the softening rolls move at the same surface speed as the nonwoven sheeting. It is necessary for the nonwoven sheeting to have an elongation of at least 10% for the method to work properly.

[0020] Desirable nonwoven sheeting for use in protective apparel should have good barrier properties to ensure protection of the wearer from external contaminants, have high flux to allow for rapid evacuation of warm air and water vapor from within the protective apparel, and maintain a comfortable environment for the wearer, while having sufficient mechanical properties, including tensile strength and tear resistance, to withstand rigorous physical work. It is also preferred that the nonwoven sheeting have low stiffness and soft texture so that it does not provide significant resistance to the wearer's movements or generate excessive noise. While flash-spun sheeting has exhibited a number of desirable properties, there is a continuing need to strike a balance between desirable comfort, air permeability, and mechanical strength. Thus, there is a need for flash-spun sheeting for use in protective apparel that provides improved mechanical strength without sacrificing air permeability and comfort for the wearer. SUMMARY

[0021] In one embodiment, the present invention relates to a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils having

[0022] (a) a basis weight of from about 32 g / m 2 to about 60 g / m 2 ,

[0023] (b) an average trapezoidal tear resistance higher than about 20 N,

[0024] (c) an average tensile strength of from about 40 N to about 90 N,

[0025] (d) a BET surface area of from about 4 m 2 / g to about 8 m 2 / g, and

[0026] (e) a Gurley porosity of from about 2 seconds to about 30 seconds.

[0027] In a further embodiment, the present invention relates to a method for preparing a nonwoven flash-spun plexifibril sheet material, the method comprising the steps of:

[0028] (i) generating a spinning fluid, the spinning fluid comprising

[0029] (a) about 8 to about 12 weight percent of a polymer, based on the total amount of the spinning fluid, and

[0030] (b) a spinning agent comprising a combination of a chlorine-containing solvent selected from the group consisting of dichloromethane, cis-1,2-dichloroethylene and trans-1,2-dichloroethylene, and a fluorine-containing solvent,

[0031] (ii) flash-spinning the spinning fluid at a temperature of 200 °C or higher and at a pressure higher than the vapor pressure of the spinning fluid into a region of substantially atmospheric pressure to form plexifibrils of the polymer,

[0032] (iii) collecting the plexifibrils of the polymer as a nonwoven flash-spun plexifibril sheet material on a collecting device and applying pressure to the sheet material to obtain a consolidated sheet material, and

[0033] (iv) heat-bonding by embossing the consolidated sheet material to obtain a bonded sheet material. DETAILED DESCRIPTION

[0034] Definitions of terms and test methods

[0035] Before presenting the details of the embodiments, some terms and test methods are defined or clarified. When an average is indicated herein, this average means the arithmetic average.

[0036] The BET surface area is measured by the BET nitrogen adsorption method of S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc, Vol. 60, pp. 309-319 (1938), based on 5 equidistant relative pressures between 0.1 and 0.25, and reported in m 2 / g. The measured samples have a total surface area higher than 2 m 2 / g. The BET surface area is measured using a Quantachrome Model NOVA 3000e from Quantachrome GmbH, Odelzhausen, Germany. The total surface area is measured by using a Porosimetr 3P supplied by 3P Instruments GmbH & Co, Odelzhausen, Germany, with a 5.86 + / - 0.23 m 2A standard alumina sample (3P-SRF586) with a BET surface area of 200 m2 / g was used to verify the performance of the equipment. Prior to the measurement, the sample was dried under vacuum at a temperature of 60 °C for at least 2 hours on a MasterPrep from the company KANTONIKA, Odelzhausen, Germany. The BET surface areas reported herein are based on 1 or 2 measurements.

[0037] The remaining tests described hereinafter were performed without pre-conditioning the samples.

[0038] Basis weight was determined according to EN ISO 536 (1996) and EN 1849-2 (2009) using a sample size of 100 cm 2 and is reported in grams per square meter (g / m 2 ). The reported values represent the average of at least 12 individual measurements.

[0039] Trapezoidal tear strength (also referred to as trapezoid tearing strength) is a measure of the tear resistance of a fabric. Trapezoidal tear strength is measured according to EN ISO 9073-4 (1997) and is expressed in Newton (N). The average trapezoidal tear strength is reported as the average of the trapezoidal tear strength of a sheet in the machine direction (MD) and the trapezoidal tear strength of a sheet in the cross direction (XD). The reported trapezoidal tear strength in either direction is the average of at least 12 measurements. The trapezoidal tear strength of a sample tends to increase proportionally with the basis weight. Therefore, the trapezoidal tear strength can be normalized by dividing it by the actual basis weight.

[0040] In addition, the present applicants have found that the relationship between the trapezoidal tear strength of a sample and its total BET surface area depends on the flash spinning process used to produce the fibrils from which the sample was made. It is therefore appropriate to consider the ratio of the average trapezoidal tear resistance to the total surface area of the nonwoven sheet. The average trapezoidal tear strength normalized for the product of surface area and basis weight (TTNSA) is defined as:

[0041]

[0042] Tensile strength is a measure of the breaking strength of a fabric when subjected to unidirectional stress. Tensile strength is determined by EN ISO 13934-1 (1999) “Textiles - Tensile properties of fabrics - Part 1 : Determination of maximum force and elongation at maximum force using the strip method”, using a 200 mm gauge length between the jaws of a tensiometer and a test speed of 100 mm / min. Results are reported in Newtons per 50 mm of sample width. Separate measurements are made with the application of tension in the machine direction (MD) and cross direction (XD) for the material being tested, and the average of the MD and XD values are reported herein. The tensile strength reported herein is the average of at least 12 measurements in the machine direction (MD), and the average of at least 6 measurements in the cross direction (XD).

[0043] The hardness of the rubber is determined based on DIN ISO 7619-1 (2010) - Rubber, vulcanized or thermoplastic - Determination of indentation hardness - Part 1 : Durometer method (Shore hardness). Hardness is reported in Shore A.

[0044] Gurley Hill porosity (sometimes also referred to as “Gurley porosity”) is a measure of the gaseous material permeability of a sheet. In particular, it is a measure of the time taken for a certain volume of gas to pass through a region of the sheet in which there is a certain pressure gradient. Gurley Hill porosity is measured according to TAPPI T-460 OM-88 (2006), using a Lorentzen & Wettre Model SE 166 or 516 from Lorentzen & Wettre, Inc. of Kista, Sweden. This test method measures the time in seconds required to push 100 cubic centimeters (cm 3 ) of air through a 6.54 cm 2The time required for 28.7 mm diameter samples of an area of 1 square inch to pass through 1 gram of water. The Gurley porosity reported herein is expressed in seconds and represents the average of at least twelve individual measurements. The reported values represent the average of at least 12 individual measurements. The lower the Gurley porosity, the greater the air permeability of the sheet.

[0045] Hydrohead is a measure of the resistance of a sheet to liquid water penetration under static load. In this document, the hydrohead is determined based on AATCC 127 (2018). The hydrohead is reported in centimeters of water. The hydrohead is measured on a FX 3000 HydroTester III from TexTest Corporation of Schwerzenbach, Switzerland. The 102.6 cm 2 The water contacting one side of the section is pressurized at a rate of 60 + / - 3 cmH2O / min until three areas of the sample are penetrated by the water. The reported hydrohead is the average of at least 6 individual measurements. A higher hydrohead value refers to a sheet with higher resistance to water penetration (i.e., with lower water permeability). For a laminate product, the surface of the sheet with the barrier function is the surface that is contacted with the water for the measurement.

[0046] Water vapor transmission rate (MVTR) is measured according to EN ISO 12572 (2001), “Hygrothermal performance of building materials and products, Climate C [Hygrothermal performance of building materials and products, Climate C],” using a Gintronic Gravitest 6400 with an ES 420A balance from MRS Seitter GmbH of Lenning-Brück, Germany. The following settings are applied. The measurement is performed at 23 °C with a relative humidity of 100% in the cup and an air flow of 2.5 m / s over the test material sample with a relative humidity of 50% and a measurement interval of 30 minutes is used. The method with multiple layers of test material is used to eliminate the influence of the air layer above the water in each cup and the boundary layer above each test material sample.

[0047] Five test cups were each filled with water to a height of 15 mm from the top. Two of the test cups were then closed using one layer of test material, one test cup was closed using two layers of test material, and the remaining two test cups were closed with three layers of test material. The tests were then conducted simultaneously using the five test cups in the same instrument. The weight of the test cups was monitored until the rate of weight loss from each test cup stabilized within + / - 5% over 5 consecutive measurements. The rate of weight loss was then divided by the upper cross-sectional area of the test cup through which water vapor had diffused to give the water vapor transmission rate (WDD, in g / m 2 / day) for each cup, and the total resistance to water vapor diffusion (Sd, in cm of equivalent air layer thickness) for each cup was calculated using the following equation:

[0048] Sd = 2366 / WDD

[0049] The Sd value for each cup was then plotted against the number of layers of test material used for that cup, and the slope of the line through these points was determined by linear regression. This slope (SDML) represents the incremental increase in water vapor diffusion resistance that results from the addition of one layer of test material. It was then converted back to the water vapor permeability of one layer of test material by performing the inverse calculation:

[0050] MVTR = 2366 / SDML

[0051] The reported values are for one measurement, which inherently averages the properties of ten separate samples of the test material.

[0052] Ret (Resistance to evaporative heat loss through a sample) is a measure of the air permeability of a fabric, with lower values corresponding to higher air permeability. Ret is measured according to EN 31092 / ISO 11092 and is expressed in m 2 Pa / W. The Hohenstein Comfort Rating System indicates that a breathable fabric has a Ret value of less than 30 m 2 Pa / W, a very breathable fabric has a Ret value of less than 13 m 2 Pa / W, and an extremely breathable fabric has a Ret value of less than 6 m 2 Pa / W.

[0053] The thickness of the sheet was measured according to standard EN ISO 534 (2005) using a paper thickness gauge, model SE 243 from Lorentzen & Wettre, Kista, Sweden, with a 2 cm 2A circular area of 2.5 cm diameter probe measures the sheet at an applied pressure of 50 kPa. The probe is lowered for a time of 2 seconds and the hold time is 4 seconds. The reported value represents the average of at least 100 individual measurements.

[0054] The overall crystallinity index is determined as follows. A diffractometer in reflection theta-2theta Bragg-Brentano geometry (PANalytical X'Pert Pro MPD) http: / / prism.mit.edu / xray / oldsite / Basics%20of%20X-Ray%20Powder% 20Diffraction.pdf equipped with a Cu-K α x-ray tube source of wavelength 1.54 A and a one-dimensional detector. A parabolic mirror with a 1 / 16° fixed slit and a 20 mm mask was used to produce a parallel incident x-ray beam, while a 1 / 8° fixed slit, a 0.04 rad soller slit and a nickel Cu-K β filter were employed on the diffracting side before the detector. The diameter of each sample was 32 mm and mounted on a low background flat silicon wafer holder. The sample holder was mounted horizontally at the center of the diffractometer and perpendicular to the scattering vector. During the measurement, the sample was rotated in this plane.

[0055] The method used to determine the overall crystallinity index is based on the ratio of the scattered intensity of the crystalline regions to the total intensity as described in S.L. Aggarwal, G.P. Tilley, Determination of crystallinity in polyethylene by X-Ray diffractometer, Journal of Polymer Science, Volume 18, pages 17-26, 1955. The analysis reported in this publication only considers the case where the orthorhombic crystalline phase is present. Polyethylene can also crystallize in the monoclinic crystalline phase. In the current case, the crystallinity of the polyethylene samples was determined using MATLAB using the procedure described below. Due to instrument differences, sample height / texture and material properties, the scattering angle 2theta of the orthorhombic peaks and the monoclinic peaks can vary by about + / -.15°.

[0056] 1. Shift the data on the 2theta axis so that the maximum intensity of the orthorhombic 110 peak occurs at 21.55°. Sample height variations can cause this shift in 2theta.

[0057] 2. Subtract a local linear background drawn from scattering angles 2theta = 13 ± 0.5° to 28 ± 0.5°.

[0058] 3. Fit the amorphous portion of the pattern using two Gaussian peaks to give the total integrated intensity I 无定形These two Gaussian peaks require contact with data points in the [15.0° to 18.65°], [22.65° to 22.75°] and [25.2° to 28°] 2 theta range and are centered at 18.1° and 21.6° 2 theta with a peak full width at half maximum (FWHM) of 4°-5°.

[0059] 4. The total amorphous fraction is then subtracted from the complete pattern.

[0060] 5. The remaining intensity is assumed to be intrinsically crystalline, belonging to either an orthorhombic or monoclinic crystal phase, and is fitted with the following peaks with the corresponding integrated intensities:

[0061] 1) Orthorhombic 110 peak: 21.55°, Pearson VII peak shape, I 110,O .

[0062] 2) Orthorhombic 200 peak: 23.8°, Pearson VII peak shape, I 200,O .

[0063] 3) Additional peak to fit the asymmetry of the orthorhombic 110 peak: 21.0°, Pearson VII peak shape. I 110,A . Subscript "A" represents asymmetry.

[0064] 4) Monoclinic 010 peak: 19.5°, Pearson VII peak shape, I 010,M .

[0065] 5) Monoclinic 200 peak: 23.1°, Pearson VII peak shape I 200,M .

[0066] Typical peak FWHM varies between 0.5° and 1°. Pearson VII M value is allowed to vary from 1-100, but is typically around 5 for each peak. If the monoclinic peak at 19.5° is not seen, both monoclinic peaks are set to zero intensity. Peak position and width are allowed to vary slightly to obtain a good fit.

[0067] 6. The overall crystallinity index is calculated from the ratio of crystalline scattering to total scattering. Crystalline scattering is defined as the sum of the integrated intensities from the crystalline peaks (monoclinic and orthorhombic). Total scattering is defined as the sum of the integrated intensities of the crystalline and amorphous peaks:

[0068]

[0069] Thus, the partial crystallinity indices and are calculated from these expressions

[0070]

[0071]

[0072] The melting temperature is determined by differential scanning calorimetry following the guidelines provided in ASTM D3418 (Standard Test Method for Transition Temperatures and Enthalpies of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry) and ASTM Standard F2625 (Standard Test Method for Measurement of Enthalpy of Fusion, Percent Crystallinity and Melting Point of Ultra-High-Molecular weight polyethylene by means of differential scanning calorimetry). For polyethylene, heating and cooling are performed at a rate of 10 °C / minute under inert gas, first heating the sample from room temperature to 210 °C, then cooling the sample back to room temperature, and subsequently heating the sample a second time to 210 °C. The melting point reported herein is the peak temperature of the endotherm of the second heating cycle. For polypropylene, the same procedure applies - with a maximum temperature of 230 °C.

[0073] The melt flow rate is determined according to the method described in ISO 1133 (Plastics - Determination of the melt mass-flow rate (MFR) and the melt volume-flow rate (MVR) of thermoplastics). The melt flow rate of polyethylene is determined under condition "D" at a temperature of 190 °C and using a mass of 2160 grams. The melt flow rate of other polyolefins is performed at different temperatures as specified in ISO 1133.

[0074] Density was determined according to the method described in ISO 1183 (Plastics - Methods for determining the density of non-cellular plastics).

[0075] The term "polymer" is intended to encompass, but not be limited to, homopolymers, copolymers (such as, for example, block, graft, random, and alternating copolymers), terpolymers, and the like, as well as blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term "polymer" shall include all possible geometric configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and atactic symmetry.

[0076] The term "polyethylene" is intended to include not only homopolymers of ethylene, but also copolymers and terpolymers in which at least 85% of the repeating units are ethylene units. One useful polyethylene is a high density polyethylene having a melting temperature of about 123°C to about 140°C, a density in the range of 0.94 to 0.98 grams per cubic centimeter, and a melt flow rate (ISO 1133 Condition D, 190°C / 2160 grams) of between 0.1 g / 10 min and 100 g / 10 min, preferably less than 4 g / 10 min.

[0077] The term "polypropylene" is intended to include not only homopolymers of propylene, but also copolymers and terpolymers in which at least 85% of the repeating units are propylene units. Furthermore, unless otherwise specifically limited, the term "polypropylene" shall include all possible geometric configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and atactic symmetry.

[0078] The term "polymer type" refers to the chemical class to which the polymer belongs, such as polyethylene, polypropylene, and the like.

[0079] The term "fibril" refers to a thin, ribbon-like fibril of any length and less than about 25 microns in median fibril width. The term "fibril" is intended to encompass not only individual fibrils, but also networks of fibrils, such as fibril mats, and the like.

[0080] The term "spinning agent" or "spinning agent composition" refers to a composition comprising one or more solvents and any additives for the initial dissolution of one or more polymers to form a spinning fluid. Suitable additives include stabilizers, such as antioxidants or acid scavengers.

[0081] The term "spinning fluid" refers to a solution used for spinning in a flash spinning process, which comprises a polymer and a spin agent. The solution can also comprise one or more additives.

[0082] The term "cloud point pressure" refers to the pressure at which a clear, single-phase spinning fluid transitions from a clear solution to a turbid, two-phase dispersion at a constant temperature. At the cloud point pressure, the clear spinning fluid becomes turbid.

[0083] Atmospheric pressure means 101.325 kPa. Substantially atmospheric pressure means 101.325 kPa ± 5%.

[0084] The hardness of the rubber is determined based on DIN ISO 7619-1 (2010) - Rubber, vulcanized or thermoplastic - Determination of indentation hardness - Part 1 : Durometer method (Shore hardness). The hardness is reported in Shore A.

[0085] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. References to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. When a range of values is expressed, another embodiment includes from one particular value and / or to another particular value. Similarly, when a value is expressed as an approximation, it is understood that the particular value forms another embodiment by use of the antecedent "about." All ranges are inclusive and combinable.

[0086] Bonded sheet of nonwoven flash-spun plexifilamentary fibrils

[0087] Provided herein is a bonded sheet of nonwoven flash-spun plexifilamentary fibrils having

[0088] (a) a basis weight of from about 32 g / m 2 to about 60 g / m 2 ,

[0089] (b) an average resistance to trapezoidal tear of higher than about 20 N,

[0090] (c) an average tensile strength of from about 40 N to about 90 N,

[0091] (d) a BET surface area of from about 4 m 2 / g to about 8 m 2 / g, and

[0092] (e) Gurley porosity of about 2 seconds to about 30 seconds.

[0093] The thermal bonding sheet described herein exhibits the desired combination of medium basis weight, high Tristand tear resistance, high tensile strength, and low BET surface area, in addition to the desired improved air permeability.

[0094] In some embodiments, the bonding sheet has a basis weight of about 32 g / m 2 to about 56 g / m 2 ; in other embodiments, the bonding sheet has a basis weight of about 40 g / m 2 to about 54 g / m 2 ; and in other embodiments, the bonding sheet has a basis weight of about 40 g / m 2 to about 49 g / m 2 .

[0095] In some embodiments, the bonding sheet has a BET surface area of about 4 m 2 / g to about 8 m 2 / g; in other embodiments, the bonding sheet has a BET surface area of about 5 m 2 / g to about 7 m 2 / g; and in other embodiments, the bonding sheet has a BET surface area of about 6 m 2 / g to about 7 m 2 / g.

[0096] In some embodiments, the bonding sheet has an average Tristand tear strength of about 22 N to about 50 N; and in other embodiments, the bonding sheet has an average Tristand tear strength of about 25 N to about 45 N. In some embodiments, the bonding sheet has an average Tristand tear strength higher than 30 N; in other embodiments, the bonding sheet has an average Tristand tear strength of about 30 N to about 55 N; and in other embodiments, the bonding sheet has an average Tristand tear strength of about 30 N to about 52 N. In some embodiments, the bonding sheet has an average Tristand tear strength of about 30 N to about 50 N; and in other embodiments, the bonding sheet has an average Tristand tear strength of about 35 N to about 45 N.

[0097] In some embodiments, the bonding sheet has an average Tristand tear strength normalized to basis weight of about 0.5 N / g / m 2 to about 0.8 N / g / m 2 ; in other embodiments, the bonding sheet has an average Tristand tear strength normalized to basis weight of about 0.55 N / g / m 2 to about 0.65 N / g / m 2about 0.65 N / g / m 2 about 0.8 N / g / m 2 about 0.8 N / g / m

[0098] In some embodiments, the bonding sheet has an average tensile strength of about 40 N to about 90 N; in other embodiments, the bonding sheet has an average tensile strength of about 45 N to about 80 N; in other embodiments, the bonding sheet has an average tensile strength of about 60 N to about 90 N; and in other embodiments, the bonding sheet has an average tensile strength of about 60 N to about 80 N.

[0099] In some embodiments, the bonding sheet has an average tensile strength of about 40 N to about 90 N; in other embodiments, the bonding sheet has an average tensile strength of about 45 N to about 80 N; in other embodiments, the bonding sheet has an average tensile strength of about 60 N to about 90 N; and in other embodiments, the bonding sheet has an average tensile strength of about 60 N to about 80 N.

[0100] In some embodiments, the bonding sheet has an average tensile strength of about 40 N to about 90 N; in other embodiments, the bonding sheet has an average tensile strength of about 45 N to about 80 N; in other embodiments, the bonding sheet has an average tensile strength of about 60 N to about 90 N; and in other embodiments, the bonding sheet has an average tensile strength of about 60 N to about 80 N.

[0101] In some embodiments, the bonding sheet has an average tensile strength of about 40 N to about 90 N; in other embodiments, the bonding sheet has an average tensile strength of about 45 N to about 80 N; in other embodiments, the bonding sheet has an average tensile strength of about 60 N to about 90 N; and in other embodiments, the bonding sheet has an average tensile strength of about 60 N to about 80 N.

[0102] In some embodiments, the bonding sheet has a Gurley porosity of about 2 seconds to about less than 30 seconds; in other embodiments, the bonding sheet has a Gurley porosity of about 3 seconds to about 25 seconds; in other embodiments, the bonding sheet has a Gurley porosity of about 2 seconds to about 15 seconds; and in other embodiments, the bonding sheet has a Gurley porosity of about 3 seconds to about 10 seconds.

[0103] In some embodiments, the cohesive sheet has a total crystallinity index of less than 72%; in other embodiments, the cohesive sheet has a total crystallinity index of from about 60% to about 72%; and in other embodiments, the cohesive sheet has a total crystallinity index of from about 62% to about 68%. In further embodiments, the crystallinity is based on an orthorhombic crystalline structure and a monoclinic crystalline structure.

[0104] In some embodiments, the cohesive sheet has a hydrostatic head of greater than about 105 cm H2O; in other embodiments, the cohesive sheet has a hydrostatic head of from about 105 cm H2O to greater than about 200 cm H2O, or from about 105 cm H2O to about 170 cm H2O, or from about 105 cm H2O to about 140 cm H2O, or from about 105 cm H2O to about 135 cm H2O, or from about 105 cm H2O to about 130 cm H2O, or from about 105 cm H2O to about 125 cm H2O; and in other embodiments, the cohesive sheet has a hydrostatic head of from about 115 cm H2O to about 170 cm H2O.

[0105] In some embodiments, the cohesive sheet has a hand meter stiffness of from about 0.05 N to about 0.50 N; in other embodiments, the cohesive sheet has a hand meter stiffness of from about 0.10 N to about 0.45 N; and in other embodiments, the cohesive sheet has a hand meter stiffness of from about 0.10 N to about 0.30 N.

[0106] In some embodiments, the cohesive sheet has a water vapor transmission rate (MVTR) of about 5500 g / m2 / day or greater; in other embodiments, the cohesive sheet has a MVTR of about 8000 g / m2 / day or greater; in other embodiments, the cohesive sheet has a MVTR of from about 9000 g / m2 / day to about 15000 g / m2 / day; and in other embodiments, the cohesive sheet has a MVTR of about 10000 g / m2 / day or greater. 2 2 2 2 2

[0107] In some embodiments, the cohesive sheet has a Ret of less than 13 m 2 Pa / W; in other embodiments, the cohesive sheet has a Ret of less than 6 m 2 Pa / W; in other embodiments, the Ret is between 13 m 2 Pa / W and 3 m 2 Pa / W; and in other embodiments, between 6 m 2 Pa / W and 3 m 2 Pa / W. ​​​​​

[0108] In some embodiments, the flash-spun filaments of the bonded sheet are composed of polyolefins. In some embodiments, the polyolefin is selected from polyethylene (PE), polypropylene (PP), and blends / mixtures thereof. Particularly preferred polyolefins are polyethylene (PE), particularly blends / mixtures of high-density polyethylene (HDPE), high-density polyethylene (HDPE) and low-density polyethylene (LDPE), or blends / mixtures of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). In some embodiments, the polyolefin is high-density polyethylene (HDPE).

[0109] In some embodiments, the flash-spun filaments of the bonded sheet are composed of high-density polyethylene, and the sheet has a density of approximately 32 g / m². 2 Approximately 37 g / m 2 The basis weight, the average trapezoidal tear strength from about 20 N to about 26 N, the average tensile strength from about 40 N to about 60 N, and the average tensile strength of about 4 m 2 / g to approximately 8 m 2 / g BET surface. In some embodiments, the flash-spun filaments of the bonded sheet are composed of high-density polyethylene, and the sheet has approximately 32 g / m². 2 Approximately 37 g / m 2 The basis weight, the average trapezoidal tear strength from about 20 N to about 26 N, the average tensile strength from about 40 N to about 60 N, and the average tensile strength of about 4 m 2 / g to approximately 8 m 2 / g of BET surface, and Glysh porosity from about 2 seconds to about 15 seconds.

[0110] In some embodiments, the flash-spun filaments of the bonded sheet are composed of high-density polyethylene, and the sheet has a density of approximately 39 g / m². 2 Approximately 45 g / m 2 The basis weight, the average tensile strength from about 50 N to about 80 N, and the 4 m 2 / g to approximately 8 m 2 The BET surface area is approximately 39 g / m², and the average trapezoidal tear strength is approximately 20 N to approximately 36 N, particularly approximately 20 N to approximately 32 N or approximately 24 N to approximately 36 N. In some embodiments, the flash-spun filaments of the bonded sheet are composed of high-density polyethylene, and the sheet has approximately 39 g / m². 2 Approximately 45 g / m 2 The basis weight, the average tensile strength from about 50 N to about 80 N, and the 4 m 2 / g to approximately 8 m 2 / g of BET surface, average trapezoidal tear strength of about 20 N to about 36 N, particularly about 20 N to about 32 N or about 24 N to about 36 N, and Glyhill porosity of about 2 seconds to about 15 seconds.

[0111] In some embodiments, the flash-spun filaments of the bonded sheet are composed of high-density polyethylene, and the sheet has a density of approximately 44 g / m². 2 Approximately 51 g / m 2 The basis weight, the average tensile strength from about 55 N to about 85 N, and the 4 m 2 / g to approximately 8 m 2 / g BET surface, and an average trapezoidal tear strength of about 24 N to about 38 N, particularly about 24 N to about 35 N or about 28 N to about 38 N. In some embodiments, the flash-spun filaments of the bonded sheet are composed of high-density polyethylene, and the sheet has about 44 g / m². 2 Approximately 51 g / m 2 The basis weight, the average tensile strength from about 55 N to about 85 N, and the 4 m 2 / g to approximately 8 m 2 / g of BET surface, average trapezoidal tear strength of about 24 N to about 38 N, particularly about 24 N to about 35 N or about 28 N to about 38 N, and Glyhill porosity of about 2 seconds to about 15 seconds.

[0112] The applicant has discovered that the bonded sheets described herein exhibit an unexpectedly excellent balance of breathability, tear resistance, and tensile strength, making them highly useful and comfortable for use in clothing (including, but not limited to, protective clothing such as full-body and partial protective garments (including, but not limited to, smocks, work pants, coveralls, trousers, jackets, sleeves, hoods, shoe covers, aprons, etc.)) and other applications. Unlike the bonded sheets described herein, which possess a unique balance of properties, prior art nonwoven sheets produced using hydrocarbon spinning agents in a flash spinning process often suffer a decrease in trapezoidal tear resistance as air permeability increases.

[0113] Preparation of bonded sheets of polymer nonwoven flash-spun filaments

[0114] In another embodiment, a method for preparing nonwoven flash-spun filament sheets is provided, the method comprising the following steps:

[0115] (i) Generating a spinning fluid, the spinning fluid comprising

[0116] (a) Based on approximately 8 to approximately 12% by weight of the polymer in the total amount of the spinning fluid, and

[0117] (b) a spinning agent comprising a combination of a chlorinated solvent selected from the group consisting of dichloromethane, cis-1,2-dichloroethylene and trans-1,2-dichloroethylene, and a fluorinated solvent,

[0118] (ii) flash spinning the spinning fluid at a temperature of 200 °C or higher and at a pressure higher than the vapor pressure of the spinning fluid into a region of substantially atmospheric pressure to form polymeric plexifibril fibers,

[0119] (iii) collecting the polymeric plexifibril fibers as a nonwoven flash-spun plexifibril sheet on a collection device and applying pressure to the sheet to obtain a consolidated sheet, and

[0120] (iv) obtaining a bonded sheet by thermal bonding of the consolidated sheet by embossing.

[0121] Flash spinning, collection and consolidation

[0122] Flash spinning is a process for producing fibrils having a unique plexifibril structure. It involves preparing a solution of a polymer forming a fibril in a spinning agent (spinning fluid) at a pressure higher than the vapor pressure of the spinning agent and at a temperature higher than the normal boiling point of the spinning agent, and releasing the spinning fluid into a region having a substantially lower temperature and pressure, so that the spinning agent flashes and the polymer solidifies in the form of plexifibril fibers. Suitable flash spinning processes and apparatus that can be used herein are described in US 3,081,519, US 3,227,794, US 3,860,369 and US 7,744,989.

[0123] The formed polymeric plexifibril fibers exit each spinning orifice, and the shape of these polymeric plexifibril fibers can be altered by any method known in the art. In some embodiments, the polymeric plexifibril fibers exiting each spinning orifice can be altered by passing into a shroud as described in US 3,387,326, in other embodiments into a slot-type outlet as described in US 3,467,744 or US 5,788,993, and in other embodiments into a slot-fan nozzle as described in US 8,114,325. In some embodiments, the fibril stream from multiple orifices can exit via a common slot, as described in US 3,564,088.

[0124] Sheets comprising polymeric plexifilamentary fibrils can be formed by any method known in the art. In some embodiments, the stream of fibrils exiting each spin orifice is directed toward a deflector device that alternately directs the stream of fibrils to the left and to the right onto a moving collection device, such that the fibrils accumulate in the form of a sheet formed of fibrils oriented in an overlapping multidirectional configuration. Deflection of the stream of fibrils can be achieved by any suitable means known in the art, including but not limited to those described in US 3,277,526 and US 3,387,326, US 3,169,899, US 3,497,918, US 3,593,074, US 3,851,023, and US 3,860,369, US 4,148,595, US 5,045,258, US 5,643,524, US 5,731,011, US 5,750,152, and WO 92 / 20511 Al. The stream of fibrils can also be laid down without deflection to form a sheet, as described in US 5,788,993 and US 8,114,325. The method of forming the sheet can further utilize structures in the spin cell, such as those described in US 5,123,983, US 5,296,172, and WO 92 / 20511 Al.

[0125] In some embodiments, the stream of fibrils exits the spin orifice from a spin orifice located on a rotating support, and the fibrils are collected on a collection belt circumferentially surrounding the rotating arrangement, as described in US 7,118,698, US 7,621,731, US 7,786,034, and US 7,998,388.

[0126] Sheets formed by flash spinning as described herein can be consolidated by applying a small amount of pressure to the sheet. In some embodiments, the sheet can be passed under a roller that applies pressure to the sheet to form a lightly consolidated sheet.

[0127] A wide range of different polymers and blends thereof can be used in the processes described herein. In some embodiments, the polymer is selected from polyolefins. In some embodiments, the polyolefin is polyethylene (PE), polypropylene (PP), and blends thereof. A particularly preferred polyolefin is polyethylene (PE), particularly high density polyethylene (HDPE), blends of high density polyethylene (HDPE) and low density polyethylene (LDPE), or blends of high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). In some embodiments, the polyolefin comprises at least 80 weight percent high density polyethylene (HDPE) based on the total amount of polymer. In other embodiments, the polyolefin comprises at least 90 weight percent high density polyethylene (HDPE) based on the total amount of polymer; and in other embodiments, the polyolefin comprises at least 95 weight percent high density polyethylene (HDPE) based on the total amount of polymer.

[0128] The spin agent comprises a combination of a chlorine-containing solvent selected from dichloromethane, cis-1,2-dichloroethylene, and trans-1,2-dichloroethylene and a fluorine-containing solvent. The spin fluid comprises the polymer in an amount of about 8 to about 12 weight percent based on the total amount of the spin fluid; in other embodiments, the spin fluid comprises the polymer in an amount of about 8.5 to about 11.5 weight percent based on the total amount of the spin fluid; in other embodiments, the spin fluid comprises the polymer in an amount of about 9 to about 11.5 weight percent based on the total amount of the spin fluid.

[0129] In some embodiments, the spin fluid comprises the spin agent in an amount of about 88 to about 92 weight percent based on the total amount of the spin fluid; in other embodiments, the spin fluid comprises the spin agent in an amount of about 88.5 to about 91.5 weight percent based on the total amount of the spin fluid; and in other embodiments, the spin fluid comprises the spin agent in an amount of about 88.5 to about 91 weight percent based on the total amount of the spin fluid.

[0130] In some embodiments, the flash spinning is conducted at a temperature of about 200 °C to about 230 °C, in other embodiments about 205 °C to about 225 °C, and in other embodiments about 210 °C to about 220 °C.

[0131] In some embodiments, the spin fluid comprises the polymer in an amount of about 8 to about 12 weight percent based on the total amount of the spin fluid, and the flash spinning is conducted at a temperature of about 205 °C to about 230 °C; and in other embodiments, the spin fluid comprises the polymer in an amount of about 9 to about 11.5 weight percent based on the total amount of the spin fluid, and the flash spinning is conducted at a temperature of about 205 °C to about 220 °C, particularly about 210 °C to about 220 °C.

[0132] In some embodiments, the spin agent comprises a combination of a chlorine-containing solvent selected from dichloromethane, cis-1,2-dichloroethylene, and trans-1,2- dichloroethylene and a fluorine-containing solvent that is a hydrofluorocarbon compound having three to six carbon atoms, a perfluorocarbon compound having three to six carbon atoms, or a hydrofluoroether. In some embodiments, the perfluorocarbon compound or hydrofluorocarbon compound having three to six carbon atoms of the spin agent is perfluoropentane, perfluorohexane, 1,1,1,3,3-pentafluorobutane, 1H,4H-perfluorobutane, 2H,3H-decafluoropentane, 1H,6H-perfluorohexane, or 1H-perfluorohexane.

[0133] In some embodiments, the spin agent consists essentially of dichloromethane and a mixture of 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, and 1,1,1,3,3-pentafluorobutane; in other embodiments, the spin agent consists essentially of about 70 to about 85 weight percent dichloromethane and about 15 to about 30 weight percent of 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane, and in other embodiments consists of about 75 to about 85 weight percent dichloromethane and about 15 to about 25 weight percent of 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane.

[0134] In some embodiments, the spin agent consists essentially of dichloromethane and a mixture of 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, and 1,1,1,3,3-pentafluorobutane; in other embodiments, the spin agent consists essentially of about 70 to about 85 weight percent dichloromethane and about 15 to about 30 weight percent of 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane, and in other embodiments consists of about 75 to about 85 weight percent dichloromethane and about 15 to about 25 weight percent of 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane.

[0135] In some embodiments, the plexifilamentary fibrils are spun using a spin fluid at a spin temperature of about 205 °C to about 230 °C, the spin fluid comprising about 8 to about 12 weight percent of the polymer, and comprising a spin agent comprising, consisting essentially of, or consisting of dichloromethane and 2H,3H-decafluoropentane, 1H,4H- perfluorobutane, 1H,6H-perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane. In other embodiments, the plexifilamentary fibrils are spun using a spin fluid at a spin temperature of about 210 °C to about 230 °C, the spin fluid comprising about 9 to about 11.5 weight percent of the polymer, and comprising a spin agent comprising, consisting essentially of, or consisting of dichloromethane and 2H,3H-decafluoropentane, 1H,4H- perfluorobutane, 1H,6H-perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane.

[0136] The spin fluid can comprise an additive, such as a small amount of antioxidant or acid scavenger. In some embodiments, the spin fluid comprises an additive in an amount of about 1.5 weight percent or less, based on the total amount of the spin fluid, and in other embodiments about 0.1 weight percent or less, based on the total amount of the spin fluid.

[0137] Thermal bonding by embossing

[0138] After the sheet is formed into a consolidated sheet as described herein, the consolidated sheet is then subjected to thermal bonding via embossing, which includes but is not limited to bonding one or both sides of the consolidated sheet using one or more heated embossing rollers and one or more rubber coated backup rollers to form a thermally bonded sheet.

[0139] In some embodiments, at least one side of the consolidated sheet is embossed; in other embodiments, only one side of the consolidated sheet is embossed; and in other embodiments, both sides of the consolidated sheet are embossed.

[0140] The one or more embossing rollers locally apply heat and pressure to a portion of the surface of the consolidated sheet to bond the consolidated sheet and form an embossed pattern. The degree of bonding can be varied by adjusting the nip pressure, temperature, and length of time these are applied.

[0141] In some embodiments, each embossing roller has a temperature of about 135 °C to about 210 °C during bonding; and in other embodiments, each embossing roller has a temperature of about 140 °C to about 155 °C during bonding.

[0142] In some embodiments, the static pressure in the nip of the embosser (nip pressure) is between about 150 kPa and about 750 kPa. As used herein, "embosser" means a pair of two rollers forming a nip, one of which is a heated embossing roller and the other is a rubber coated backup roller. In other embodiments, the static pressure in the nip of the embosser is between about 150 kPa and about 500 kPa, and in other embodiments about 150 kPa to about 400 kPa.

[0143] In some embodiments, the consolidated sheet is wrapped around the heated embossing roller such that the angle between the entry direction and the exit direction (wrap angle) is about 10° to about 140°; in other embodiments, the wrap angle is about 10° to about 100°; and in other embodiments, the wrap angle is about 10° to about 60°.

[0144] In some embodiments, the consolidated sheet can be in contact with a pre-heat roller before thermal bonding and / or can be in contact with a cooling roller after thermal bonding, configured as described in US 5,972,147. In some embodiments, the temperature of the pre-heat roller can vary from 50°C to 20°C below the polymer's melting peak temperature.

[0145] Each side of the consolidated sheet can be embossed using the same pattern or different patterns. In some embodiments, the consolidated sheet is embossed on both sides using the same pattern; and in other embodiments, the consolidated sheet is embossed on both sides using different patterns. In some embodiments, the consolidated sheet is embossed on one side using a dot pattern and on the other side using a herringbone pattern; and in other embodiments, the consolidated sheet is embossed on one side using a rib pattern and on the other side using a herringbone pattern.

[0146] In some embodiments, the one or more rubber coated backup rollers have a Shore A hardness of 50 to 70. If two or more embossing steps are performed, the hardness of the rubber coated backup rollers can be the same or different.

[0147] The pattern on one or more embossing rollers can be any suitable depth known in the art. Each embossing roller can have the same or different depth patterns. In some embodiments, the consolidated sheet is embossed using embossing rollers having patterns at different depths such that certain portions of the consolidated sheet are subjected to more bonding than other portions.

[0148] The percentage of the area of each side of the consolidated sheet that is embossed can vary. In some embodiments, from about 12% to about 85% of the area of at least one side of the consolidated sheet, in other embodiments from about 20% to about 50%, in other embodiments from about 26% to about 45%, and in other embodiments from about 20% to about 40% is embossed. In some embodiments, from about 12% to about 50% of the area of both sides of the consolidated sheet, in other embodiments from about 20% to about 50%, in other embodiments from 26% to about 45%, and in other embodiments from about 20% to about 40% is embossed.

[0149] In some embodiments, from about 50% to about 85% of the area of one side of the consolidated sheet is embossed using a herringbone pattern, and from about 20% to about 40% or from about 26% to about 45% of the area of the other side of the consolidated sheet is embossed using a ribbed pattern. In some embodiments, from about 50% to about 85% of the area of one side of the consolidated sheet is embossed using a herringbone pattern, and from about 20% to about 40% or from about 26% to about 45% of the area of the other side of the consolidated sheet is embossed using a dotted pattern.

[0150] In other embodiments, from about 20% to about 40% or from about 26% to about 45% of the area of one side of the consolidated sheet is embossed using a ribbed pattern, and from about 20% to about 40% or from about 26% to about 45% of the area of the other side of the consolidated sheet is embossed using a ribbed pattern. In other embodiments, from about 20% to about 40% or from about 26% to about 45% of the area of one side of the consolidated sheet is embossed using a dotted pattern, and from about 20% to about 40% or from about 26% to about 45% of the area of the other side of the consolidated sheet is embossed using a dotted pattern.

[0151] The methods described herein provide a bonded sheet of nonwoven flash-spun plexifibrils that has sufficient strength while still having high air permeability.

[0152] In some embodiments, after the consolidated sheet is heat-bonded as described herein, the heat-bonded sheet is then subjected to a mechanical softening process to obtain a softened sheet of nonwoven flash-spun plexifibrils. During the mechanical softening process described herein, the heat-bonded sheet is passed through one or more nip(s) between rotating rollers that are driven at substantially the same speed as the speed of the heat-bonded sheet as it passes through the rollers. This is in contrast to some prior art softening methods in which the heat-bonded sheet passes through a series of rollers that are driven at different speeds than the speed of the heat-bonded sheet. This speed differential creates a frictional effect that causes the loose fibrils, which can compromise the barrier properties of the softened sheet.

[0153] In some embodiments, the thermal bonding sheet is mechanically softened by passing it through one or more roll gaps between rotating rolls, where each roll has interpenetrating pins and rotates in the opposite direction of the other roll. The pins of each roll can be arranged in an array and have ends equidistant from the axis of the roll. The array of pins on one roll interpenetrates the array of pins on the opposite roll by an amount at least equal to the thickness of the sheet. Various geometries can be used for the interpenetrating pins, including but not limited to blunt pins, which means at least pins having a blunt end and a shaft with a surface. Blunt surfaces (i.e., surfaces that do not have a point) include but are not limited to: blunt surfaces that are rounded so as to form a smooth curved surface; or flat blunt surfaces.

[0154] In some embodiments, the thermal bonding sheet is subjected to a mechanical softening process as described in US 3,408,709. In some embodiments, the thermal bonding sheet is subjected to a mechanical softening process as described in US 5,966,785 and US 6,195,854. In some embodiments, the thermal bonding sheet is subjected to a mechanical softening process as described in US 3,920,874 and US 3,811,979.

[0155] In some embodiments, the thermally bonded or bonded and softened sheet is subjected to an antistatic treatment. The antistatic treatment improves the electrostatic properties, in particular the surface resistivity, of the textile. In some embodiments, the antistatic treatment is applied by applying a coating composition comprising an antistatic compound. In some embodiments, the antistatic compound is a phosphate ester, in particular a phosphate ester defined by the formula: M n R 3-n PO4, wherein M is selected from the group consisting of lithium, sodium, potassium, and ammonium ions, R represents an alkyl group containing 3 to 5 carbon atoms, and n is selected from the integers 1 and 2. In some embodiments, the antistatic compound is selected from the group consisting of potassium di-n-propyl phosphate, di-potassium n-propyl phosphate, potassium diisopropyl phosphate, di-potassium isopropyl phosphate, potassium di-n-butyl phosphate, di-potassium n-butyl phosphate, potassium diisobutyl phosphate, di-potassium isobutyl phosphate, and combinations thereof.

[0156] In some embodiments, a nonwoven flash-spun plexifilamentary sheet is provided, obtained or obtainable by the methods described herein.

[0157] In some embodiments, the obtained sheet has

[0158] (a) a basis weight of from about 32 g / m 2 to about 60 g / m 2 ,

[0159] (b) an average trapezoidal tear of higher than about 20 N,

[0160] (c) an average tensile strength of from about 40 N to about 90 N,

[0161] (d) about 4 to about 8 m 2 / g BET surface area, and

[0162] (e) a Gurley Stak porosity of about 2 seconds to about 30 seconds.

[0163] Uses, Multilayer Structures, and Articles

[0164] The nonwoven flash-spun plexifilamentary fibrous sheet as described herein has many uses and can be used in a variety of applications, including but not limited to multilayer structures, garments (including but not limited to protective apparel and gowns), and medical drapes.

[0165] Further embodiments are directed to a multilayer structure comprising at least one nonwoven flash-spun plexifilamentary fibrous sheet as described herein, and at least one additional sheet or film.

[0166] In some embodiments, the multilayer structure comprises a film that is a microporous film. In one embodiment, the microporous film is a filled and stretched film as described in US 9,809,004 B2. Microporous films from highly filled polymers, typically polyolefins, can be made by any method known in the art. Typically, a combination of a polyolefin, typically polyethylene, is compounded with a filler, typically calcium carbonate, and extruded and stretched into a film to form a microporous film. Suitable examples of microporous films include those described in US 4,472,328, US 4,350,655, and US 4,777,073. Multilayer structures comprising a microporous film and at least one nonwoven flash-spun plexifilamentary fibrous sheet as described herein can be used in a variety of applications, including but not limited to protective apparel.

[0167] In some embodiments, the multilayer structure is a laminate structure comprising a microporous film laminated to at least one nonwoven flash-spun plexifilamentary fibrous sheet as described herein. In some embodiments, the microporous film and the nonwoven flash-spun plexifilamentary fibrous sheet can be laminated using an adhesive layer that is in contact with at least a portion of both the microporous film and the nonwoven flash-spun plexifilamentary fibrous sheet, as described in US 9,809,004 B2, US 5,750,444, or US 5,294,258.

[0168] Further embodiments are directed to the use of a nonwoven flash-spun plexifilamentary fibrous sheet as described herein for the manufacture of a multilayer structure.

[0169] Further embodiments are directed to the use of a nonwoven flash-spun plexifilamentary fibrous sheet as described herein for the production of a garment.

[0170] Further embodiments are directed to the use of a multilayer structure as described herein for the production of a garment.

[0171] Additional embodiments are directed to an article comprising at least one nonwoven flash-spun plexifilamentary sheet as described herein or comprising at least one multi-layer structure as described herein. In some embodiments, the article is selected from the group consisting of garments, protective apparel, and medical wraps. Protective apparel includes full-body protective apparel and partial-body protective apparel (including but not limited to coveralls, overalls, jumpsuits, pants, coveralls, coats, sleeves, head coverings, shoe coverings, aprons, and the like) and other garments whose purpose is to protect the wearer from exposure to harmful substances in the environment, or to protect the environment from contamination by the wearer. In some embodiments, the article is a medical wrap for packaging medical items (such as surgical instruments) during sterilization. Examples

[0172] Different bonded sheets of nonwoven flash-spun plexifilamentary have been prepared. The experimental procedures and results are provided below. These examples are given to illustrate exemplary embodiments of the application and should not be construed as limiting in any way.

[0173] Materials Used

[0174] n-Pentane (CAS number 109-66-0) has an atmospheric boiling point of 36.1 °C, a molecular weight of 72.151 g / mol, and a critical temperature of 196.7 °C. The n-pentane used had a purity level higher than 95 weight percent.

[0175] Cyclopentane (CAS number 287-92-3) has an atmospheric boiling point of 49.2 °C, a molecular weight of 70.13 g / mol, and a critical temperature of 238.6 °C. The cyclopentane used had a purity level higher than 95 weight percent.

[0176] Methylene chloride (CAS number 75-09-2) has an atmospheric boiling point of 39.6 °C, a molecular weight of 84.93 g / mol, and a critical temperature of 236.68 °C. The methylene chloride used had a purity level higher than 99.5 weight percent.

[0177] 2H,3H-decafluoropentane (HFC-4310-mee) (CAS number 138495-42-8) has an atmospheric boiling point of 55 °C, a molecular weight of 252.05 g / mol, and a critical temperature of 181 °C. The 2H,3H-decafluoropentane used had a purity level higher than 99.5 weight percent.

[0178] The polyethylene used had a density of 0.957 g / cm 3density of 0.95 g / cm3(ISO 1183) and a melt flow rate of 0.74 g / 10 min (ISO 1133 Condition D, 190°C / 2.16 kg) and 22 g / 10 min (ISO 1133 Condition G, 190°C / 21.6 kg).

[0179] The flash-spun sheets in the examples were produced using the flash-spun process described by US 3,227,794 and US 3,851,023. US 3,227,794 describes a flash-spun process in which the pressure is reduced below the cloud point of the spinning fluid before the spinning fluid is released into a region of significantly lower temperature and pressure, such that the spinning agent flashes and the polymer solidifies in the form of plexifibril. The cloud point pressure of hydrocarbon spinning agents is reported in, but not limited to, US 5,147,586, US 6,004,672, and US 6,638,470, and for mixtures of trans-1,2-DCE and DCM with fluorinated compounds, in, but not limited to, US 6,004,672, US 7,300,968, and US 7,179,413.

[0180] Results

[0181] Comparative Examples 1 to 6

[0182] Using the flash-spun process described by US 3,227,794 and US 3,851,023, a flash-spun sheet was produced at a spinning temperature of 190°C using a spinning fluid of 17 wt% polyethylene in a spinning agent of a hydrocarbon-based spinning agent that was a mixture of n-pentane and cyclopentane (also referred to herein as “H”), using a spinning fluid of 17 wt% polymer. 3 and a melt flow rate of 0.74 g / 10 min (ASTM 1238 190°C / 2.16 kg), at a spinning temperature of 190°C, using a spinning fluid of 17 wt% polymer in a hydrocarbon-based spinning agent that was a mixture of n-pentane and cyclopentane (also referred to herein as “H”).

[0183] The flash-spun sheets were subsequently heat-bonded and embossed. For all Comparative Examples 1 to 6, one side was embossed by passing the sheet through a nip formed between a heated roll having a flax pattern and a rubber roll having a Shore A hardness of 70, and the opposite side was embossed by passing through a nip formed between an embossing roll having a ribbed pattern and a rubber roll having a Shore A hardness of 70. The fabrics were subsequently mechanically softened by passing them through a nip of two rolls of interpenetrating blunt pins having a diameter of 1 mm and an upper edge radius of curvature of 0.25 mm. The blunt pins were 3.3 mm center-to-center in the MD direction and 3.2 mm center-to-center in the XD direction at the point of interaction with the flash-spun sheet.

[0184] The spinning, bonding, and softening conditions and sheet properties are reported in Table 1 below.

[0185] Table 1 : Overview of sheet preparation for Comparative Examples 1 to 6.

[0186]

[0187] Comparative Examples 7 to 8

[0188] Spunlaced sheets were produced using the spunlacing process described in US 3,227,794 and US 3,851,023 at different spinning temperatures using a polyethylene having a density > 0.95 g / cm 3 and a melt flow rate of 0.74 g / 10 min (ISO 1133 190°C / 2.16 kg) at different polymer concentrations in a spinning fluid which was a mixture of dichloromethane and 2H,3H-decafluoropentane (herein also referred to as "D"). The spunlaced sheets were subsequently thermally bonded and embossed. For Comparative Examples 7 to 8, one side was embossed by passing the sheet through a nip formed between a heated roller having a flax pattern and a rubber roller having a hardness of 70 Shore A, and the opposite side was embossed by passing the sheet through a nip formed between an embossing roller having a ribbed pattern and a rubber roller having a hardness of 70 Shore A. The fabrics were subsequently mechanically softened by passing them through a nip of two rollers having interpenetrating blunt pins with a diameter of 1 mm and an upper edge radius of curvature of 0.25 mm. At the point of interaction with the spunlaced sheet, the blunt pins were 3.3 mm centre to centre in the MD direction and 3.2 mm centre to centre in the XD direction.

[0189] The spinning, bonding and softening conditions and sheet properties are reported in Table 2 below.

[0190] Table 2: Overview of sheet preparation for Comparative Examples 7 and 8.

[0191]

[0192] Examples 1 to 6

[0193] Spunlaced sheets were produced using the spunlacing process described in US 3,227,794 and US 3,851,023 at different spinning temperatures using a polyethylene having a density > 0.95 g / cm 3and a polyethylene having a melt flow rate of 0.74 g / 10 min (ISO 1133 190°C / 2.16 kg) were produced into flashspun sheet in a spinning fluid that was a mixture of dichloromethane and 2H,3H-decafluoropentane (also referred to herein as "D") at different polymer concentrations. The flashspun sheet was subsequently heat-bonded and embossed. For Examples 1 to 4, one side was embossed by passing the sheet through a nip formed between a heated roll having a herringbone pattern and a rubber roll having a hardness of 70 Shore A, and the opposite side was embossed by passing through a nip formed between an embossing roll having a ribbed pattern and a rubber roll having a hardness of 70 Shore A. For Example 5, one side was embossed by passing the sheet through a nip formed between a heated roll having a herringbone pattern and a rubber roll having a hardness of 60 Shore A, and the opposite side was embossed by passing through a nip formed between an embossing roll having a ribbed pattern and a rubber roll having a hardness of 70 Shore A. For Example 6, one side was embossed by passing the sheet through a nip formed between a heated roll having a herringbone pattern and a rubber roll having a hardness of 50 Shore A, and the opposite side was embossed by passing through a nip formed between an embossing roll having a ribbed pattern and a rubber roll having a hardness of 70 Shore A. The fabrics were subsequently mechanically softened by passing them through a nip of two rolls with interpenetrating blunt pins having a diameter of 1 mm and an upper edge radius of curvature of 0.25 mm. The blunt pins were 3.3 mm center-to-center in the MD direction and 3.2 mm center-to-center in the XD direction at the point of interaction with the flashspun sheet.

[0194] The spinning, bonding, and softening conditions, as well as the sheet properties, are reported in Table 3 below.

[0195] Table 3: Summary of sheet production for Examples 1 to 6.

[0196]

[0197] Examples 1 to 6 demonstrate that when using a chlorine-containing solvent as the spinning agent, a beneficial combination of properties can be obtained compared to the hydrocarbon-based spinning agents used in Comparative Examples 1 to 6. Comparative Examples 1 to 6, which used a hydrocarbon-based spinning agent, show a correlation between resistance to ladder tear and BET surface area, but this trend is not seen in the examples that used a chlorine-containing solvent as the spinning agent, where a decrease in the BET surface area of the bonded sheet did not result in a decrease in tear properties. Furthermore, the examples with low BET surface area that used a chlorine-containing solvent as the spinning agent had improved air permeability properties (low Gurley porosity).

[0198] Examples 7 to 13

[0199] Example 7 to 13 were produced from a polyethylene having a density of > 0.95 g / cm3 3 Example 7 to 13 were produced from a polyethylene having a density of > 0.95 g / cm3

[0200] The spinning, bonding and softening conditions as well as the sheet properties are reported in Table 4 below.

[0201] Table 4: Overview of sheet production for Examples 7 to 13.

[0202]

[0203] Examples 7 to 13 show that when using a chlorine-containing solvent as a spin agent, a beneficial combination of properties, in particular a lower BET surface area, can be obtained for a variety of different production conditions compared to the hydrocarbon-based spin agents used in Comparative Examples 1 to 6. In addition, it has been surprisingly observed that the sheets of the examples combine good flux properties (as reflected by low Gurley porosity and good MVTR) while maintaining high resistance to trapezoidal tear. In addition, comparing Examples 3 to 6 with Examples 7 to 10, it is observed that a reduction of the compression force in the linter press results in improved air permeability of the fabric. The improved air permeability is reflected by a significant reduction of the Gurley porosity and an improvement of the water vapor transmission rate.

[0204] Examples 14 to 17

[0205] Spunlaced sheets were produced using the spunlacing process described by US 3,227,794 and US 3,851,023 at a spinning temperature of 210 °C using a polyethylene having a density > 0.95 g / cm 3 and a melt flow rate of 0.74 g / 10 min (ISO 1133 190 °C / 2.16 kg) in a spinning fluid which is a mixture of dichloromethane and 2H,3H-decafluoropentane (also referred to herein as "D") at different polymer concentrations. For all examples, one side was embossed by passing the sheet through a nip formed between a heated roller having a linter pattern and a rubber roller having a hardness of 70 Shore A, and the opposite side was embossed by passing the sheet through a nip formed between an embossing roller having a rib pattern and a rubber roller having a hardness of 70 Shore A. The fabric was not mechanically softened.

[0206] Spinning, bonding and softening conditions and sheet properties are reported in Table 5 below.

[0207] Table 5: Overview of sheet production for Examples 14 to 17.

[0208]

[0209] Examples 14 to 17, which were performed without a mechanical softening step, show that when using a chlorine-containing solvent as a spin agent, a beneficial combination of properties can be obtained compared to the hydrocarbon-based spin agents as used in Comparative Examples 1 to 6. In addition, comparing Examples E14 and E15 and E16 and E17 shows that a reduction of the compression force in the linter press has a significant improvement of the air permeability of the fabric, as seen by a reduction of the Gurley porosity and an increase of the water vapor transmission rate.

[0210] Comparative Examples 9 and 10

[0211] Example 18 to 20 3 Example 18 to 20

[0212] The flash-spun sheets of Comparative Examples 9 and 10 were subsequently heat-bonded using a process as described in US 2003 / 0165667. The consolidated sheets were first brought into alternating contact with two preheated rolls set at a temperature of 65 °C, and then embossed on both sides with a ribbed pattern. The heat-bonded sheets of Comparative Examples 9 and 10 were subsequently transferred through a nip of two rolls having interpenetrating blunt pins with a diameter of 1 mm and an upper edge radius of curvature of 0.25 mm. At the point of interaction with the flash-spun sheet, the blunt pins were 3.3 mm center-to-center in the MD direction and 3.2 mm center-to-center in the XD direction.

[0213] The spinning, bonding and softening conditions as well as the sheet properties are reported in Table 6 below.

[0214] Table 6: Overview of sheet production of Comparative Examples 9 and 10.

[0215]

[0216] Example 18 to 20

[0217] Example 18 to 20 3and a polyethylene having a melt flow rate of 0.74 g / 10 min (ISO 1133 190°C / 2.16 kg) was produced into flashspun sheet in a spinning fluid which was a mixture of dichloromethane and 2H,3H-decafluoropentane (herein also referred to as "D") at different polymer concentrations. Subsequently, the flashspun sheet was first brought into alternating contact with two preheated rolls set at a temperature of 60°C to 65°C, and then heat-bonded and embossed using a method as described in US 2003 / 0165667 Al. For Examples 18 to 20, the temperature of the preheated rolls was set to 60°C. Examples 18 to 20 were then softened by passing through a nip of two rolls with interpenetrating blunt pins having a diameter of 1 mm and an upper edge radius of curvature of 0.25 mm. At the point of interaction with the flashspun sheet, the blunt pins were centered 3.3 mm center-to-center in the MD direction and 3.2 mm center-to-center in the XD direction.

[0218] The spinning, bonding and softening conditions as well as the sheet properties are reported in Table 7 below.

[0219] Table 7: Overview of sheet production for Examples 18 to 20.

[0220]

[0221] The above shows that the sheet produced by using a hydrocarbon-based mixture as spinning fluid has a lower average trapezoidal tear strength (normalized against the product of BET surface area and basis weight) compared to the sheet produced by using a spinning fluid comprising a chlorine-containing solvent.

[0222] Examples 18 to 20 show that when using a chlorine-containing solvent as spinning fluid, a beneficial combination of properties can be obtained, in particular a lower BET surface area, compared to the hydrocarbon-based spinning fluids as used in Comparative Examples 9 and 10. In addition, it has been surprisingly observed that the sheet of the Examples combines good throughput properties (as reflected by low Gurley porosity and good MVTR) while maintaining high resistance to trapezoidal tear. In addition, when comparing E13 to E18 to E20, it has been observed that the rib x rib configuration gives an improved balance of physical properties compared to the flax x rib embossing pattern, in particular a higher tear resistance and tensile strength compared to the flax x rib embossed samples. This is different from US 2003 / 0165667, where the use of rib x rib embossed fabrics resulted in a decrease in tear resistance. Further embodiments

[0223] 1. In some embodiments, the present application provides a heat-bonded sheet of nonwoven flashspun plexifilamentary fibrils having

[0224] (a) about 32 g / m 2Approximately 60 g / m 2 The base weight,

[0225] (b) Average resistance to trapezoidal tearing above approximately 20 N.

[0226] (c) Average tensile strength from about 40 N to about 90 N, and

[0227] (d) Approximately 4 m 2 / g to approximately 8 m 2 / g BET surface area.

[0228] 2. The sheet as described in Example 1 has a density of approximately 32 g / m². 2 Approximately 56 g / m 2 The base weight.

[0229] 3. The sheet as described in any of the foregoing embodiments, having a density of approximately 40 g / m². 2 Approximately 54 g / m 2 The base weight.

[0230] 4. The sheet as described in any of the foregoing embodiments, having a density of approximately 40 g / m². 2 Approximately 49 g / m 2 The base weight.

[0231] 5. The sheet as described in any of the foregoing embodiments has an average trapezoidal tear strength of about 22 N to about 50 N.

[0232] 6. The sheet as described in any of the foregoing embodiments has an average trapezoidal tear strength of about 25 N to about 45 N.

[0233] 7. The sheet as described in any of the foregoing embodiments has an average trapezoidal tear strength of about 30 N to about 55 N.

[0234] 8. The sheet as described in any of the foregoing embodiments has an average trapezoidal tear strength of about 30 N to about 50 N.

[0235] 9. The sheet as described in any of the foregoing embodiments, having a thickness of approximately 4 μm 2 / g to approximately 8 m 2 / g BET surface area.

[0236] 10. The sheet as described in any of the foregoing embodiments, having a thickness of approximately 5 μm 2 / g to approximately 7 m 2 / g BET surface area.

[0237] 11. The sheet as described in any of the foregoing embodiments, having a thickness of approximately 6 μm 2from about 0.1 g to about 7 m 2 a BET surface area of from about 0.1 g to about 7 m

[0238] 12. The sheet of any of the preceding embodiments having an average tensile strength of from about 40 N to about 80 N.

[0239] 13. The sheet of any of the preceding embodiments having an average tensile strength of from about 45 N to about 80 N.

[0240] 14. The sheet of any of the preceding embodiments having an average tensile strength of from about 60 N to about 90 N.

[0241] 15. The sheet of any of the preceding embodiments having an average tensile strength of from about 60 N to about 80 N.

[0242] 16. The sheet of any of the preceding embodiments having a tensile strength of from about 35 N to about 90 N in at least one direction selected from the machine direction (MD) and the cross direction (XD).

[0243] 17. The sheet of any of the preceding embodiments having a tensile strength of from about 45 N to about 90 N in at least one direction selected from the machine direction (MD) and the cross direction (XD).

[0244] 18. The sheet of any of the preceding embodiments having a tensile strength of from about 60 N to about 90 N in at least one direction selected from the machine direction (MD) and the cross direction (XD).

[0245] 19. The sheet of any of the preceding embodiments having a tensile strength in the machine direction (MD) that is from about 80% to about 120% of the tensile strength in the cross direction (XD).

[0246] 20. The sheet of any of the preceding embodiments having a tensile strength in the machine direction (MD) that is from about 95% to about 105% of the tensile strength in the cross direction (XD).

[0247] 21. The sheet of any of the preceding embodiments having a Gurley Hill porosity of from about 2 seconds to about 30 seconds.

[0248] 22. The sheet of any of the preceding embodiments having a Gurley Hill porosity of from about 3 seconds to about 25 seconds.

[0249] 23. The sheet of any of the preceding embodiments having a Gurley Hill porosity of from about 3 seconds to about 15 seconds.

[0250] 24. The sheet of any of the preceding embodiments having a Gurley Hill porosity of from about 3 seconds to about 10 seconds.

[0251] 25. The sheet of any of the preceding embodiments having a total crystallinity index of less than about 72%.

[0252] 26. The sheet of any of the preceding embodiments having a total crystallinity index of from 60% to about 72%.

[0253] 27. The sheet of any of the preceding embodiments having a total crystallinity index of from about 62% to about 68%.

[0254] 28. The sheet of any of the preceding embodiments having a hydrohead of greater than about 105 cm H20.

[0255] 29. The sheet of any of the preceding embodiments having a hydrohead of from about 105 cm H20 to greater than about 200 cm H20.

[0256] 30. The sheet of any of the preceding embodiments having a hydrohead of from about 105 cm H20 to about 170 cm H20, or from about 105 cm H20 to about 140 cm H20, or from about 105 cm H20 to about 135 cm H20, or from about 105 cm H20 to about 130 cm H20, or from about 105 cm H20 to about 125 cm H20.

[0257] 31. The sheet of any of the preceding embodiments having a hydrohead of from about 115 cm H20 to about 170 cm H20.

[0258] 32. The sheet of any of the preceding embodiments having a hand meter stiffness of from about 0.05 N to about 0.50 N.

[0259] 33. The sheet of any of the preceding embodiments having a hand meter stiffness of from about 0.10 N to about 0.45 N.

[0260] 34. The sheet of any of the preceding embodiments having a hand meter stiffness of from about 0.10 N to about 0.30 N.

[0261] 35. The sheet of any of the preceding embodiments having a water vapor transmission rate of about 5500 g / m2 / day or greater. 2

[0262] 36. The sheet of any of the preceding embodiments having a water vapor transmission rate of about 8000 g / m2 / day or greater. 2

[0263] ​​37. The sheet as described in any of the foregoing embodiments, having a density of approximately 9000 g / m². 2 / day to approximately 15000 g / m 2 / day or higher water vapor transmission rate.

[0264] 38. The sheet as described in any of the foregoing embodiments, having a density of approximately 10,000 g / m². 2 / day or higher water vapor transmission rate.

[0265] 39. The sheet as described in any of the foregoing embodiments, having a thickness of 13 m 2 Pa / W and 3 m 2 Ret between Pa / W.

[0266] 40. The sheet as described in any of the foregoing embodiments, having a thickness of 6 to 3 μm 2 Ret between Pa / W.

[0267] 41. The sheet as described in any of the foregoing embodiments, having a density of approximately 0.5 N / g / m 2 Up to 0.8 N / g / m 2 The average trapezoidal tear strength is normalized to the basis weight.

[0268] 42. The sheet as described in any of the foregoing embodiments has a density of approximately 0.55 N / g / m³. 2 Approximately 0.65 N / g / m 2 The average trapezoidal tear strength is normalized to the basis weight.

[0269] 43. The sheet as described in any of the foregoing embodiments has a density of approximately 0.65 N / g / m³. 2 Approximately 0.8 N / g / m 2 The average trapezoidal tear strength is normalized to the basis weight.

[0270] 44. The sheet as described in any of the preceding embodiments has an average trapezoidal tear strength normalized to the product of BET surface area and basis weight of about 0.082 N to 0.125 N.

[0271] 45. The sheet as described in any of the preceding embodiments has an average trapezoidal tear strength normalized to the product of BET surface area and basis weight of about 0.085 N to about 0.110 N.

[0272] 46. ​​The sheet as described in any of the preceding embodiments has an average trapezoidal tear strength normalized to the product of BET surface area and basis weight of about 0.110 N to about 0.125 N.

[0273] 47. The sheet of any of the preceding embodiments having an average tensile strength of about 40 N to about 80 N.

[0274] 48. The sheet of any of the preceding embodiments having an average tensile strength of about 45 N to about 80 N.

[0275] 49. The sheet of any of the preceding embodiments having an average tensile strength of about 60 N to about 90 N.

[0276] 50. The sheet of any of the preceding embodiments having an average tensile strength of about 60 N to about 80 N.

[0277] 51. The sheet of any of the preceding embodiments having a tensile strength in at least one direction selected from the machine direction (MD) and the cross direction (XD) of about 35 N to about 90 N.

[0278] 52. The sheet of any of the preceding embodiments having a tensile strength in at least one direction selected from the machine direction (MD) and the cross direction (XD) of about 45 N to about 90 N.

[0279] 53. The sheet of any of the preceding embodiments having a tensile strength in at least one direction selected from the machine direction (MD) and the cross direction (XD) of about 60 N to about 90 N.

[0280] 54. The sheet of any of the preceding embodiments having a tensile strength in at least one direction selected from the machine direction (MD) and the cross direction (XD) of about 60 N to about 80 N.

[0281] 55. The sheet of any of the preceding embodiments having a tensile strength in the machine direction (MD) that is about 80% to about 120% of the tensile strength in the cross direction (XD).

[0282] 56. The sheet of any of the preceding embodiments having a tensile strength in the machine direction (MD) that is about 90% to about 110% of the tensile strength in the cross direction (XD).

[0283] 57. The sheet of any of the preceding embodiments having a tensile strength in the machine direction (MD) that is about 95% to about 105% of the tensile strength in the cross direction (XD).

[0284] 58. The sheet of any of the preceding embodiments wherein the flash-spun plexifibril fibers are comprised of a polyolefin selected from the group of polyethylene (PE), polypropylene (PP), and blends and mixtures thereof.

[0285] 59. The sheet of any of embodiments 58, wherein the polyolefin is high density polyethylene (HDPE), a blend of high density polyethylene (HDPE) and linear low density polyethylene (LLDPE), or a blend of high density polyethylene (HDPE) and low density polyethylene (LDPE).

[0286] 60. The sheet of any of the preceding embodiments, wherein the flash-spun plexifiber fibrils of the bonding sheet are comprised of high density polyethylene, and the sheet has a basis weight of about 32 g / m 2 to about 37 g / m 2 , an average Tristand tear strength of about 20 N to about 26 N, an average tensile strength of about 40 N to about 60 N, and a BET surface of about 4 m 2 / g to about 8 m 2 / g.

[0287] 61. The sheet of embodiment 60, wherein the sheet has a Gurley porosity of about 2 seconds to about 15 seconds.

[0288] 62. The sheet of any of embodiments 1 to 59, wherein the flash-spun plexifiber fibrils of the bonding sheet are comprised of high density polyethylene, and the sheet has a basis weight of about 39 g / m 2 to about 45 g / m 2 , an average tensile strength of about 50 N to about 80 N, a BET surface of about 4 m 2 / g to about 8 m 2 / g, and an average Tristand tear strength of about 20 N to about 32 N.

[0289] 63. The sheet of any of embodiments 1 to 59, wherein the flash-spun plexifiber fibrils of the bonding sheet are comprised of high density polyethylene, and the sheet has a basis weight of about 39 g / m 2 to about 45 g / m 2 , an average tensile strength of about 50 N to about 80 N, a BET surface of about 4 m 2 / g to about 8 m 2 / g, and an average Tristand tear strength of about 24 N to about 36 N.

[0290] 64. The sheet of embodiment 62 or 63, wherein the sheet has a Gurley porosity of about 2 seconds to about 15 seconds.

[0291] 65. The sheet of any of embodiments 1 to 59, wherein the flash-spun plexifiber fibrils of the bonding sheet are comprised of high density polyethylene, and the sheet has a basis weight of about 44 g / m 2 to about 51 g / m 2about 55 N to about 85 N average tensile strength, about 4 m 2 / g to about 8 m 2 / g BET surface, and about 24 N to about 35 N average

[0292] 66. The sheet of any one of embodiments 1 to 59, wherein the flash-spun plexifibril sheet is comprised of high density polyethylene, and the sheet has a basis weight of about 44 g / m 2 to about 51 g / m 2 , about 55 N to about 85 N average tensile strength, about 4 m 2 / g to about 8 m 2 / g BET surface, and about 28 N to about 38 N average

[0293] 67. The sheet of embodiment 65 or 66, wherein the sheet has a Gurley porosity of about 2 seconds to about 15 seconds.

[0294] 68. A method for making a nonwoven flash-spun plexifibril sheet, the method comprising the steps of:

[0295] (i) producing a spinning fluid, the spinning fluid comprising

[0296] (a) about 8 to about 12 weight percent of a polymer based on the total amount of the spinning fluid, and

[0297] (b) a spinning agent comprising a combination of a chlorinated solvent selected from the group consisting of dichloromethane, cis-1,2-dichloroethylene, and trans-1,2-dichloroethylene, and a fluorinated solvent;

[0298] (ii) flash-spinning the spinning fluid at a temperature of at or above about 200 °C and a pressure above the vapor pressure of the spinning fluid into a region of substantially atmospheric pressure to form plexifibrils of the polymer,

[0299] (iii) collecting the plexifibrils of the polymer as a nonwoven flash-spun plexifibril sheet on a collection device, and applying pressure to the sheet to obtain a consolidated sheet, and

[0300] (iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet.

[0301] 69. The method of embodiment 68, wherein the spinning fluid comprises about 8.5 to about 11.5 weight percent of a polymer based on the total amount of the spinning fluid.

[0302] 70. The method of either of embodiments 68 or 69, wherein the spin fluid comprises about 9 to about 11.5 weight based on the total amount of the spin fluid.

[0303] 71. The method of any of embodiments 68 to 70, wherein the flash spinning of the spin fluid is conducted at a temperature of about 205 °C to about 225 °C.

[0304] 72. The method of any of embodiments 68 to 71, wherein the flash spinning of the spin fluid is conducted at a temperature of about 210 °C to about 220 °C.

[0305] 73. The method of any of embodiments 68 to 72, wherein the fluorosolvent is a hydrofluorocarbon having three to six carbon atoms, a perfluorocarbon having three to six carbon atoms, or a hydrofluoroether.

[0306] 74. The method of embodiment 73, wherein the perfluorocarbon or hydrofluorocarbon having three to six carbon atoms of the spin agent is perfluoropentane, perfluorohexane, 1,1,1,3,3- pentafluorobutane, 1H,4H-perfluorobutane, 2H,3H-decafluoropentane, 1H,6H- perfluorohexane, or 1H-perfluorohexane.

[0307] 75. The method of any of embodiments 68 to 74, wherein the spin agent consists of or consists essentially of a combination of dichloromethane and perfluoropentane, perfluorohexane, 1,1,1,3,3- pentafluorobutane, 1H,4H-perfluorobutane, 2H,3H-decafluoropentane, 1H,6H- perfluorohexane, or 1H-perfluorohexane.

[0308] 76. The method of any of embodiments 68 to 75, wherein the spin agent consists essentially of about 70 to about 85 weight percent dichloromethane and about 15 to about 30 weight percent of 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3- pentafluorobutane.

[0309] 77. The method of any of embodiments 68 to 76, wherein the spin agent consists of about 70 to about 85 weight percent dichloromethane and about 15 to about 30 weight percent of 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3- pentafluorobutane.

[0310] 78. The method of any one of embodiments 68-77, wherein the plexifibril fibers are spun using a spin fluid at a spin temperature of about 205 °C to about 230 °C, the spin fluid comprising about 8 to about 12 weight percent polymer and comprising a spin agent, the spin agent comprising, consisting essentially of, or consisting of dichloromethane and 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H-perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane.

[0311] 79. The method of any one of embodiments 68-78, wherein the plexifibril fibers are spun using a spin fluid at a spin temperature of about 210 °C to about 230 °C, the spin fluid comprising about 9 to about 11.5 weight percent polymer and comprising a spin agent, the spin agent comprising, consisting essentially of, or consisting of dichloromethane and 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H-perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane.

[0312] 80. The method of any one of embodiments 68-79, wherein the spin fluid further comprises an additive.

[0313] 81. The method of embodiment 80, wherein the spin fluid comprises an additive in an amount of about 1.5 weight percent or less of the total amount of the spin fluid.

[0314] 82. The method of any one of embodiments 68-81, wherein one or more heated embossing rollers and one or more rubber-coated backup rollers are used to bond one or both sides of the consolidated sheet.

[0315] 83. The method of any one of embodiments 68-82, wherein the consolidated sheet wraps the heated embossing roller at a wrap angle of about 10° to about 140°.

[0316] 84. The method of any one of embodiments 68-83, wherein the static pressure in the nip of the embosser is between about 150 and about 750 kPa.

[0317] 85. The method of any one of embodiments 68-84, wherein the static pressure in the nip of the embosser is between about 150 kPa and about 500 kPa or between about 150 kPa and about 400 kPa.

[0318] 86. The method of any one of embodiments 68-85, wherein the one or more rubber-coated backup rollers have a Shore A hardness of 50 to 70.

[0319] 87. The method of any of embodiments 68-86, wherein the consolidated sheet is embossed on both sides using the same pattern.

[0320] 88. The method of embodiment 87, wherein the consolidated sheet is embossed on both sides using a dot pattern; or the consolidated sheet is embossed on both sides using a rib pattern.

[0321] 89. The method of embodiment 87 or 88, wherein about 20% to about 40% or about 26% to about 45% of the area of one side of the consolidated sheet is embossed using a rib pattern, and about 20% to about 40% or about 26% to about 45% of the area of the other side of the consolidated sheet is embossed using a rib pattern.

[0322] 90. The method of embodiment 87, wherein about 20% to about 40% or about 26% to about 45% of the area of one side of the consolidated sheet is embossed using a dot pattern, and about 20% to about 40% or about 26% to about 45% of the area of the other side of the consolidated sheet is embossed using a dot pattern.

[0323] 91. The method of any of embodiments 68-86, wherein the consolidated sheet is embossed on both sides using different patterns.

[0324] 92. The method of embodiment 91, wherein the consolidated sheet is embossed on one side using a dot pattern and on the other side using a flax pattern; or the consolidated sheet is embossed on one side using a rib pattern and on the other side using a flax pattern.

[0325] 93. The method of embodiment 91 or 92, wherein about 50% to about 85% of the area of one side of the consolidated sheet is embossed using a flax pattern, and about 20% to about 40% or about 26% to about 45% of the area of the other side of the consolidated sheet is embossed using a rib pattern.

[0326] 94. The method of embodiment 91 or 92, wherein about 50% to about 85% of the area of one side of the consolidated sheet is embossed using a flax pattern, and about 20% to about 40% or about 26% to about 45% of the area of the other side of the consolidated sheet is embossed using a dot pattern.

[0327] 95. The method of any of embodiments 68-94, wherein the method further comprises mechanically softening the cohesive sheet.

[0328] 96. The method as described in Example 95, wherein the thermally bonded sheet is mechanically softened by passing it through one or more gaps between rotating rollers, wherein each roller has interpenetrating pins and rotates in the opposite direction to the other roller.

[0329] 97. The method as described in Example 95 or 96, wherein the pins are blunt pins.

[0330] 98. The method of any one of Examples 68 to 97, wherein the polymer is a polyolefin selected from the group consisting of polyethylene (PE), polypropylene (PP), and blends and mixtures thereof.

[0331] 99. The method as described in Example 98, wherein the polyolefin is high-density polyethylene (HDPE), a blend of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE), or a blend of high-density polyethylene (HDPE) and low-density polyethylene (LDPE).

[0332] 100. The method of any one of Examples 98 to 99, wherein the polyolefin comprises at least 80 weight percent of high-density polyethylene (HDPE) based on the total amount of the polymer.

[0333] 101. The method of any one of Examples 98 to 100, wherein the polyolefin comprises at least 95% by weight high-density polyethylene (HDPE) based on the total amount of the polymer.

[0334] 102. The method as described in any one of Examples 68 to 101, wherein the obtained sheet has

[0335] (a) Approximately 32 g / m 2 Approximately 60 g / m 2 The base weight,

[0336] (b) Average trapezoidal tear strength above approximately 20 N,

[0337] (c) Average tensile strength from about 40 N to about 90 N, and

[0338] (d) Approximately 4 m 2 / g to approximately 8 m 2 / g BET surface area.

[0339] 103. A nonwoven flash-spun filament sheet, which can be obtained by any one of Examples 68 to 102.

[0340] 104. A thermally bonded sheet of nonwoven flash-spun filament fiber, said sheet having

[0341] (a) Approximately 32 g / m2 from about 60 g / m 2 to about 65 g / m

[0342] (b) an average resistance to trapezoidal tear greater than about 20 N,

[0343] (c) an average tensile strength from about 40 N to about 90 N, and

[0344] (d) a BET surface area from about 4 m 2 / g to about 8 m 2 / g,

[0345] and wherein the sheet is obtained by the method of any one of embodiments 68 to 102.

[0346] 105. A nonwoven flash-spun plexifibril thermally bonded sheet of nonwoven flash-spun plexifibrils composed of high density polyethylene, wherein the sheet has a basis weight from about 32 g / m 2 to about 37 g / m 2 , an average tensile strength from about 40 N to about 60 N, a BET surface from about 4 m 2 / g to about 8 m 2 / g, and an average trapezoidal tear strength from about 20 N to about 26 N, and wherein the sheet is obtained by the method of any one of embodiments 68 to 102.

[0347] 106. A nonwoven flash-spun plexifibril thermally bonded sheet of nonwoven flash-spun plexifibrils composed of high density polyethylene, wherein the sheet has a basis weight from about 39 g / m 2 to about 45 g / m 2 , an average tensile strength from about 50 N to about 80 N, a BET surface from about 4 m 2 / g to about 8 m 2 / g, and an average trapezoidal tear strength from about 20 N to about 32 N, and wherein the sheet is obtained by the method of any one of embodiments 68 to 102.

[0348] 107. A nonwoven flash-spun plexifibril thermally bonded sheet of nonwoven flash-spun plexifibrils composed of high density polyethylene, wherein the sheet has a basis weight from about 39 g / m 2 to about 45 g / m 2 , an average tensile strength from about 50 N to about 80 N, a BET surface from about 4 m 2 / g to about 8 m 2 / g, and an average trapezoidal tear strength from about 24 N to about 36 N, and wherein the sheet is obtained by the method of any one of embodiments 68 to 102.

[0349] 108. A thermobonded sheet of nonwoven flash-spun plexifibril fibers, the nonwoven flash-spun plexifibril fibers consisting of high-density polyethylene, wherein the sheet has a basis weight of about 44 g / m2to about 51 g / m2, an average tensile strength of about 55 N to about 85 N, a BET surface of about 4 m2 / g to about 8 m2 / g, and an average trapezoidal tear strength of about 24 N to about 35 N, and wherein the sheet is obtained by the method of any one of Examples 68 to 102. 2 2 2 2 2 2 2 2

[0350] 109. A thermobonded sheet of nonwoven flash-spun plexifibril fibers, the nonwoven flash-spun plexifibril fibers consisting of high-density polyethylene, wherein the sheet has a basis weight of about 44 g / m2to about 51 g / m2, an average tensile strength of about 55 N to about 85 N, a BET surface of about 4 m2 / g to about 8 m2 / g, and an average trapezoidal tear strength of about 28 N to about 38 N, and wherein the sheet is obtained by the method of any one of Examples 68 to 102.

[0351] 110. The thermobonded sheet of nonwoven flash-spun plexifibril fibers of any one of Examples 104 to 109, wherein the sheet has a Gurley porosity of about 2 seconds to about 15 seconds, and wherein the sheet is obtained by the method of any one of Examples 68 to 102.

[0352] 111. A multi-layer structure comprising at least one sheet of any one of Examples 1 to 67 or 103 to 110 and at least one additional sheet or film.

[0353] 112. The multi-layer structure of Example 111, comprising a film that is a microporous film.

[0354] 113. The multi-layer structure of any one of Examples 111 to 112, wherein the structure is a laminate structure comprising a microporous film laminated to at least one sheet of any one of Examples 1 to 67 or 103 to 110.

[0355] 114. Use of a sheet of any one of Examples 1 to 67 or 103 to 110 for making a multi-layer structure.

[0356] ​​​​​​​​115. Use of the sheet as described in any of embodiments 1 to 67 or 103 to 110 or the multilayer structure as described in any of embodiments 111 to 113 to produce a garment or a medical wrap.

[0357] 116. An article comprising the sheet as described in any of embodiments 1 to 67 or 103 to 110 or the multilayer structure as described in any of embodiments 111 to 113.

[0358] 117. The article of embodiment 116, wherein the article is selected from a garment, a protective apparel, a gown, or a medical wrap.

[0359] While various embodiments of the application have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the application. Thus, the present application should not be limited by any of the above-described exemplary embodiments.

Claims

1. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having (a) a basis weight of about 32 g / m 2 to about 60 g / m 2 of about 32 g / m (b) an average resistance to trapezoidal tear higher than about 20 N, (c) an average tensile strength of about 40 N to about 90 N, (d) about 4 m 2 / g to about 8 m 2 / g, and (e) a Gurley porosity of about 2 seconds to about 30 seconds.

2. The sheet of claim 1 having a total crystallinity index of less than about 72%.

3. The sheet of any one of claims 1 to 2 having a hydrohead higher than about 105 cmH20, or having a hand meter stiffness of about 0.05 N to about 0.50 N.

4. The sheet as described in any one of claims 1 to 3, having a density of about 5500 g / m². 2 / day or higher water vapor transmission rate, or with approximately 0.5 N / g / m 2 Up to 0.8 N / g / m 2 The average trapezoidal tear strength normalized to the basis weight, or the average trapezoidal tear strength normalized to the product of the BET surface area and basis weight, having a range of approximately 0.082 N to 0.125 N.

5. The sheet of any one of claims 1 to 4, wherein, the flash-spun plexifilamentary fibrils are composed of a polyolefin selected from the group of polyethylene (PE), polypropylene (PP), and blends and mixtures thereof, or wherein the flash-spun plexifilamentary fibrils are composed of a polyolefin that is high density polyethylene (HDPE), a blend of high density polyethylene (HDPE) with linear low density polyethylene (LLDPE), or a blend of high density polyethylene (HDPE) with low density polyethylene (LDPE).

6. A method for making a nonwoven flash-spun plexifilamentary fibril sheet, the method comprising the steps of: (i) producing a spinning fluid, the spinning fluid comprising (a) about 8 to about 12 weight percent of a polymer based on the total amount of the spinning fluid, and (b) a spinning agent comprising a combination of a chlorine-containing solvent selected from the group of dichloromethane, cis-1,2-dichloroethylene, and trans-1,2-dichloroethylene, and a fluorine-containing solvent, (ii) flash-spinning the spinning fluid at a temperature of at or above about 200 °C and at a pressure above the vapor pressure of the spinning fluid into a region of substantially atmospheric pressure to form plexifilamentary fibrils of the polymer, (iii) collecting the plexifilamentary fibrils of the polymer as a nonwoven flash-spun plexifilamentary fibril sheet on a collection device and applying pressure to the sheet to obtain a consolidated sheet, and (iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet.

7. The method of claim 6, wherein, the spinning fluid comprises about 9 to about 11.5 weight percent of a polymer based on the total amount of the spinning fluid, and wherein the flash-spinning of the spinning fluid is carried out at a temperature of at or above about 205 °C.

8. The method of claim 6 or 7, wherein, the method further comprises mechanically softening the bonded sheet.

9. The method of any one of claims 6 to 8, wherein, the sheet is embossed by passing through a nip of two rollers of an embosser, one of the rollers being an embossing roller and the other of the rollers being a rubber coated backup roller having a Shore A hardness of 50 to 70, and wherein the static pressure in the nip of the embosser is between about 150 kPa and about 750 kPa, or wherein about 12% to about 85% of the area of at least one surface of the sheet is bonded.

10. The method of any one of claims 6 to 9, wherein, The polymer is a polyolefin selected from the group of polyethylene (PE), polypropylene (PP), and blends and mixtures thereof, or wherein the flash-spun plexifibril fibers are composed of a polyolefin which is high density polyethylene (HDPE), a blend of high density polyethylene (HDPE) with linear low density polyethylene (LLDPE), or a blend of high density polyethylene (HDPE) with low density polyethylene (LDPE).

11. The method of any one of claims 6 to 10, wherein, The spinning agent consists essentially of dichloromethane in combination with perfluoropentane, perfluorohexane, 1,1,1,3,3-pentafluorobutane, 1 H,4H- perfluorobutane, 2H,3H-decafluoropentane, 1 H,6H-perfluorohexane, or 1 H- perfluorohexane.

12. The method of any one of claims 6 to 11, wherein, The obtained sheet has (a) a basis weight of about 32 g / m 2 to about 60 g / m 2 . (b) an average trapezoidal tear of higher than about 20 N, (c) an average tensile strength of from about 40 N to about 90 N, (d) about 4 m 2 / g to about 8 m 2 BET surface area, and (e) a Gurley porosity of from about 2 seconds to about 30 seconds.

13. A nonwoven flash-spun plexifibril sheet obtainable by the method of any one of claims 6 to 12.

14. A multilayer structure comprising at least one sheet of any one of claims 1 to 5 or 13 and at least one further sheet or film.

15. Use of a sheet of any one of claims 1 to 5 or 13 for the preparation of a multilayer structure.

16. Use of a sheet of any one of claims 1 to 5 or 13 or a multilayer structure of claim 14 for the production of a garment or a medical wrap.

17. An article comprising a sheet of any one of claims 1 to 5 or 13 or a multilayer structure of claim 14.

18. The article of claim 17, wherein, The article is selected from the group of a garment, a protective apparel, a gown, or a medical wrap. The article is selected from the group of a garment, a protective apparel, a gown, or a medical wrap.

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