Soft, flash-spun sheet

Abstract

The present invention relates to (i) a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils exhibiting high tensile strength and a high degree of softness, (ii) a process for the preparation of a bonded sheet of nonwoven flash-spun plexifilamentary fibrils, and (iii) a multilayer sheet structure and an article comprising the bonded sheet of nonwoven flash-spun plexifilamentary fibrils.

Description

[0001] SOFT, FLASH-SPUN SHEET FIELD OF THE INVENTION

[0002] The present invention relates to (i) a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils exhibiting high tensile strength and a high degree of softness, « a process for the preparation of a bonded sheet of nonwoven flash-spun plexifilamentary fibrils, and (iii) a multilayer sheet structure and an article comprising the bonded sheet of nonwoven flash-spun plexifilamentary fibrils.

[0003] BACKGROUND

[0004] Flash-spun nonwoven materials have been developed with wide-ranging properties suitable for use in a variety of applications, including, but not limited to. protective apparel, car covers, and roof lining. Their production usually involves two stages, a first stage in which fibrils are produced and laid down in an overlapping manner to produce a fibril assembly in the form of a sheet, and a second stage in which adjacent fibrils are bonded via thermal bonding to obtain a robust structure which cannot be easily disassembled. The properties of the final nonwoven sheet are impacted by various factors from the first and second stages. Flash-spinning is a i method for producing fibrils having a unique plexifilamentary structure. It involves preparing a solution of a fibril-forming polymer in a spin agent at a pressure above the vapor pressure of the spin agent and at a temperature above the normal boiling point of the spin agent, and releasing that solution into a zone of substantially lower temperature and pressure such that the spin agent flash evaporates and the polymer solidifies in the form of plexifilamentary fibrils. Examples of flash-spinning processes are disclosed in

[0005] US 3,081 ,51 S and US 3,227,794.

[0006] The properties of flash-spun fibrils depend on, among other factors, the polymer or blend of polymers used to form them, the spin-agent used to produce the spin-fluid, the concentration of polymer in the spin-fluid, and the temperature of the spin-fluid during spinning, As with other types of spinning technology, the properties of an initial fibril assembly are modified by subsequent thermal bonding to produce a flash-spun nonwoven sheet

[0007] Thermal bonding is a common process for bonding nonwoven sheets in which heat is used to soften the polymer from which the fibrils are made, typically, by passing the nonwoven sheet through an arrangement of heated rolls, with a back-up roll which forms a nip or without a back-up roll. The degree of bonding can vary based on the temperature and pressure, and time during which these are applied Bonding of the nonwoven sheet also varies spatially depending on the rolls used and area to which the bonding is applied, e.g., using smooth surfaced rolls to apply uniform heat and pressure over the entire surface versus using patterned rolls to apply heat and pressure locally over only a portion of the surface to form an embossed pattern in the final nonwoven sheet.

[0008] US 3,442,740 and US 3,532,589 describe thermal bonding on a smooth heated roll where one or both sides of the nonwoven sheet are subjected to generally uniform, full surface contact thermal bonding. In this process, a surface bonded nonwoven sheet product is obtained having a paper-like feel which is suitable for uses such as packaging and print media but too stiff for use in garments, being uncomfortable and “noisy" for the wearer. Thermal bonding using a thermal calendar bonder, such as that described in US 5,972,147, also tends to produce a stiffer product 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 car covers which need to conform to the shape of the vehicle, or roof linings which can vibrate and create noise when wind blows over them.

[0009] US 3,478,141 and US 4,091 ,137 describe thermal bonding carried out by passing nonwoven sheets between heated engraved embossing rolls and rubber-coated back-up rolls to bond one or both sides of the nonwoven sheet only in defined areas, producing softer and more drapable materials suitable for use in garment applications. The embossing roll can contain different patterns, such as a point pattern as described in US 3,478,141 , US 6,610,390, and US 2004 / 241399 A1 , a rib pattern as described in US 2003 / 0032355 A1 and US 2003 / 00165667 A1 , a linen pattern or a random pattern as described in US 7,744,989, or a combination of different patterns as described in US 5,620.779 and US 5.964.742. The nonwoven sheet may pass through one or multiple pairs of a heated embossing roll and a rubber-coated back-up roll and may also wrap partially around one or more heated embossing rolls to transfer heat into the nonwoven sheet prior to reaching the nip between any such embossing roll and a rubber-coated back-up roll. In addition, the nonwoven sheet may be in contact with one or more pre-heat or cooling rolls before and after passing through each pair of embossing and back-up rolls in a configuration as described in US 5.972, 147 US 6,034,008 and US 2003 / 00165667 A1 describe a process in which one side is embossed with a “rib” pattern of discrete bond points and the other side is embossed over a substantial portion of the surface with a “linen" pattern.

[0010] Thermal bonding impacts different properties of the nonwoven sheet in different ways.

[0011] The flux properties of nonwoven sheets, i.e., the ability of the fibril assembly to allow free movement of air or other gases such as water vapor through it, either by diffusion or by bulk flow under a pressure difference, may be altered in different ways depending on the bonding process. Heating can lead to relaxation of tension within the fibrils and fibril shrinkage, resulting in an increase in the space between the fibrils and an increase in flux. Conversely, pressure applied during bonding can compress the structure, reducing the space between the fibrils through which gases can move, resulting in a decrease in flux. Moreover, if temperatures and pressures are high enough to cause fibrils to melt and fuse together extensively, this can create film-lite regions which allow very little flux.

[0012] The barrier properties of nonwoven sheets, i,e., the ability of the fibril assembly to prevent particles in the air from passing through it, or liquids such as water to penetrate it under pressure, tend to change in the converse manner after bonding as, for instance, reduced pore sizes created by compression during bonding result in greater resistance to the passage of particles or liquids through the structure.

[0013] Mechanical properties such as delamination resistance, puncture and tear resistance, abrasion resistance, and tensile strength may increase or decrease, as the degree of bonding increases. However, the stronger connections between / fibrils resulting from bonding, and the limitation of their ability to move relative to each other, increases the stiffness of the bonded sheet.

[0014] These complex interactions of behaviors mean that thermally bonding a nonwoven sheet to produce a product for a particular application typically requires a compromise in the desired properties of the final nonwoven sheet

[0015] The effect of bonding on sheet stiffness is especially notable when bonding is applied uniformly over the whole surface. This results in sheets having a paper-like texture often referred to as “hard-structures” which tend to produce a iot of noise when flexed or bent. When embossed roils are used to create areas having greater and iesser degrees of bonding, quieter and more flexible, softer, fabric-rite structures can be achieved, often referred to as ‘’soft- structures.” However, even soft-structure bonded sheets are stiffer and less flexible than the starting sheet before bonding. it is possible to recover some softness in a bonded, nonwoven sheet, by applying processes known in the textile industry such as softening or re-lofting. In these processes the nonwoven sheet is passed through equipment which locally distorts the material in a way that breaks or partially breaks some of the bonding between fibrils, allowing more relative motion and increasing the flexibility of the nonwoven sheet. These changes in mechanical properties are typically accompanied by an increase in flux properties and a loss in barrier properties.

[0016] . US 3,408,709 describes a softening process using a button breaker to mechanically soften a nonwoven sheet. The button breaker employs knobbed rolls which turn at a different speed to, or even in the opposite direction to the movement of the nonwoven sheet as it travels over them, creating a rubbing effect US 5,966,785 and US 6,195,854 report a mechanical softening process where the sheet is passed through the nip of a knobbed roll against a soft rubber backup roll. However, no information is given in these documents on how this process impacts the barrier properties of the sheet. US 6,117,801 describes a process of flash-spinning specific ethylene copolymers comprising copolymerized units of alpha olefins such as butene, hexene and octene, to provide softness and quietness to nonwoven sheet structures formed of plexifiiamentary film- fibril material. The softness and quietness are rated based on subjective qualitative tests. In the examples in US 6,117,801, a flammable hydrocarbon-based spin agent was used which requires special precautions for safe operation. Further, US 6,117,801 teaches applying bonding uniformly over the whole surface rather than using patterned rolls to apply heat and pressure locally over only a portion of the surface.

[0017] US 7,296,328 discloses a process for the softening of a nonwoven sheet in which with increasing softening cycles, the sheet shows an increase in breathability. The described softening process employs a rubbing effect using a speed difference between the nonwoven sheet and the roller or mechanical object over which it passes. However, since the nonwoven sheet is exposed to a rubbing surface, its surface is damaged,

[0018] US 3,920,874 and US 3,811 ,979 describe a process employing pairs of rolls covered with square edged cylindrical pins which interlock for the softening of a nonwoven sheet passed between them, with the softening rollers moving at the same surfece speed as ftie nonwoven sheet. The nonwoven sheet is required to have an elongation of at least 10 % for the process to work correctly

[0019] An ideal nonwoven sheet for use in protective apparel, car cover, or roof lining applications should have good mechanical properties to ensure that the sheet does not tear when used as a garment, placed over a car, or installed at the roof of a house. It is also preferable that the nonwoven sheet has low stiffness and a soft texture so that it does not provide noticeable resistance to the wearer s movements or generate excessive noise in use. While flash-spun sheets have demonstrated a good variety of desired properties, there has been a trade-off required between the desired strength and stiffness properties. Therefore, there is a need for a flash-spun nonwoven sheet for use in protective apparel, car covers, or roof lining that provide high strength without sacrificing the wearer’s comfort and / or generating excessive noise.: SUMMARY OF THE INVENTION

[0020] In one embodiment, the invention is directed te a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0021] (a) a basis weight from about 50 g / m2to about 85 g / m2, (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and:

[0022] (c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, is below about 2.30.

[0023] In a further embodiment, the invention is directed to a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having (a) a basis weight from about 43 g / m2to about 85 g / m2,

[0024] (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and

[0025] (c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the handle-o-meter stiffness, normalized to (basis weight)3, is below about 5.0μNm6 / g3.

[0026] In a further embodiment, the invention is directed to a process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps of:

[0027] (i) generating a spin fluid comprising

[0028] (a) from about 8 to about 14 weight percent of a polymer, based on the total amount of the spin fluid, and

[0029] (b) a spin agent comprising a chlorine-containing solvent, selected from dichloromethane. cis-1.2-dichloroethylene and trans-1 2-dichloroethylene, in combination with a fluorine-rmntaining solvent,

[0030] (ii) flash spinning the spin fluid at a temperature at or above about 190 C and at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of the polymer, (iii) collecting / the plexifilamentary fibrils of the polymer on a collecting means as a sheet of nonwoven flash-spun plexifilamentary fibrils and applying pressure to the sheet to obtain a consolidated sheet, and

[0031] (iv> thermally bonding by embossing the consolidated sheet to obtain a bonded sheet.

[0032] DETAILED DESCRIPTION

[0033] Definitions of Terms and Test methods

[0034] Before addressing details of embodiments, some terms are-defined or clarified. Unless otherwise mentioned, all tests were carried out without preconditioning of the samples. When average values are indicated herein, this refers to the arithmetic average.

[0035] Basis weight is determined according to BN ISO 536 (1996) & EN 1849-2 (2009) using a sample size of 100 cm2and is reported in gram per square meter (g / m2). The reported value represents an average of at least 12 Individual measurements, 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 the tensilometer and a test speed of 100 mm / min. Results are reported in newtons (per 50 mm sample width). Separate measurements are carried out with tension applied in the machine direction (MD) and in the cross direction (XD) for the material being tested, and the average of the MD and XD values is reported herein The tensile strength reported herein is an average of at least 12 measurements in the machine direction (MD), and an average of at least 6 measurements in the cross direction (XD). Handle-o-meter stiffness is a measure of the resistance of a sample to being pressed into a 10mm slot by a blade attached to a 100g penetrator beam that is motor driven. It is measured by ASTM 6828 (2002) - Stiffness of Fabric by Blade / Slot Procedure and is expressed in gram-force (gf), convertible to N by multiplying gf by 9.8067 and dividing by 1000. In accordance with ASTM 6828 (2002), separate measurements are carried out in the machine direction (MD) and in the cross direction (XD) for the material being tested, and the average of the MD and XD values is reported -herein.- A lower Handle-o-meter stiffness value refers to a softer sheet.

[0036] The tensile strength Of a uniform sheet is proportional to the thickness of the sheet, whereas the flexural stiffness of a uniform sheet is proportional to the third power of the thickness- of the sheet As sheet- thickness- generally correlates with basis -weight, when comparing different samples, tensile strength can be normalized to the basis weight, and Handle-o-meter stiffness can be normalized to the third power of the basis weight.

[0037] Thickness of the sheet is measured according to standard EN ISO 534 (2005) using a Model SE 243 Paper Thickness Gauge from Lorentzen & Wettre. Kista. Sweden. The sheet is a measured using a probe having a circular area of 2 cm2with an applied pressure of 50 kPa. The time to lower the probe is 2 seconds and the hold time ts 4 seconds. The reported value represents an average of at least 100 individual measurements.

[0038] BET surface area is measured by the BET nitrogen absorption method of S Brunauer, P. H. Emmet and E. Teller, J. Am. Ghem, Soc., V. 60 p 309-319 (1938) based on 5 equidistant relative pressures between 0.1 to 0.25 and is reported as m2 / g. The samples measured have a total surf ace area above 2 m2. B ET surface area is measured using a Quantachrome modelNOVA 3000e from Quantachrome GmbH, Odelzhausen, Germany. Performance of the equipment is verified by using a standard aluminum oxide sample (3P-SRF586) having a SET surface area of 5.86 +A 0.23 m2 / gram supplied by 3P Instruments GmbH & Co, Odelzhausen, Germany. Before measurement, the samples are dried for at least 2 hours at a temperature of 60°C under vacuum on equipment Degasser MasterPrep from Quantachrome GmbH, Odelzhausen, Germany. The BET surface area reported herein is based on T or 2 measurements.

[0039] The total crystallinity index is determined as follows. A diffractometer in reflection o-2(> Bragg-Brentano geometry is fitted with a Cu-Kax-ray tube source with wavelength of 1.54 A and a 1-dimensional detector A parabolic mirror with a 1 / 161fixed slit and 20mm mask is used to create a parallel incident x-ray beam while a fixed slit of 1 / 8°, Seller slits of 0 04 rad and a nickel Cu-Ks filter are employed on the diffracted side before the detector. Each sample is 32 mm in diameter and is mounted onto low background, flat silicon wafer holders. The sample holder is mounted horizontally at the center of the diffractometer and normal to the scattering vector. During the measurement, the sample rotates in this plane.

[0040] The method used tor the determination of the total crystallinity index is based on the ratio of the scattering 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, Vol. 18, pp. 17-26, 1955. The analysis reported in this publication only considers the case in which the orthorhombic phase is present. Polyethylene can also crystallize in the monoclinic phase. In the current case, the procedure as described below is used to determine the crystallinity of the polyethylene samples using MATLAB. The scattering angle 2u of the orthorhombic and monoclinic peaks can vary by about + / - . 15?due to instrumental differences, sample height / texture and material nature 1, Data are shifted on the 20 axis such that the maximum intensity of the orthorhombic 110 peak occurs at 21.55°. Sample height variations can cause this shift in 20. 2. A local linear background, drawn from 20 - 13±0.5° to 28±0.5° in scattering angle, is subtracted 3. The amorphous portion of the pattern is fitted using two Gaussian peaks which are required to touch the data points in the ranges of (15.0° to 18.65°], (22.65° to 22 75°], and [25.2° to 28°] 20 and which are centered around 18.1° and 21.6° 2 o. with peak full widths at half maximum (FWHM) of 4 -5 to give a total integrated intensity

[0041] 4. The total amorphous portion is then subtracted from the full pattern. 5. The remaining intensity is assumed to be crystalline in nature, belonging to the orthorhombic or monoclinic phases, and is fited with the following : peaks having respective integrated intensities:

[0042] 1 ) Orthorhombic 110 peak: 21.55°, Pearson VII peak shape, Imo.

[0043] 2) Orthorhombic 200 peak: 23 8°, Pearson VII peak shape, I2000. 3) Additional peak to fit asymmetry of me orthorhombic 110 peak: 21,0°, Pearson VII peak shape, IHO, A. The subscript W stands for asymmetric.

[0044] Typical Peak FWHMs vary between 0.5° and 1°. Pearson VII M-values are allowed to vary from 1-100, but typically fall around 5 for each peak, If no monoclinic peak is visible at 19.5°, then both monoclinic peaks are set to zero intensity Peak positions and widths are allowed to vary slightly to obtain a good fit.

[0045] 6. The total aystallinity index is calculated from the ratio of crystalline scattering to total scattering. The crystalline scattering is defined as the sum of the integrated intensities from the crystalline peaks (monoclinic and orthorhombic). The total scattering is defined as the sum of the integrated intensity of crystalline and amorphous peaks: respectively from these expressions Melting temperature is determined by differential scanning calorimetry, following the guidance 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 is performed under inert gas at a rate of 10°G / minute, heating the sample first 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 - where the maximum temperature is 230°C.

[0046] 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 for polyethylene is determined under condition “D” at a temperature of 190’C and using a mass of 2160 grams. The rnelt flow rates of other polyolefins are performed at different temperatures as specified in IS0 1133.

[0047] Densify is determined according to the method described in ISO 1183 (Plastics - Methods for determining the densify of non-cellular plastics).:

[0048] The term "poiymert is intended to embrace, without limitation, homopolymers, copolymers (such as for example, block graft, random, and alternating copolymers), terpolymers, etc , and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term • polymer'' shall include all possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and random symmetries. '

[0049] The term "polyethylene ' is intended to embrace not only homopolymers of ethylene but also copolymers and terpolymers wherein at least 85 % of the recurring units are ethylene units One useful polyethylene is high-density polyethylene which has a melting temperature of about 123nC 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 / 10min and 100 g / 10min, preferably less than 4 g / 10min.

[0050] The term “polypropylene" is intended to embrace not only homopolymers of propylene but also copolymers and terpolymers where at least 85 % of the recurring units are propylene units. Furthermore, unless otterwise specifically limited, the term '‘polypropylene" shall include all possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and random symmetries.

[0051] ) The term "polymer type” refers to the chemical class into which the polymer falls, for example, polyethylene, polypropylene, etc. The term “plexifilamentary” refers to a three-dimensional integral network or web of a multitude of thin, ribbon-like, fibrils of random length and a median fibril width of less than about 25 microns. In plexifilameritary structures, the fibrils are generally coextensively aligned with the longitudinal axis of the structure, and they intermittently unite and separate at irregular intervals in various places throughout the length, width, and thickness of the structure to form a continuous three-dimensional network orweb.

[0052] The terms “spin agent” or “spin agent composition" refers to a composition comprising one or more solvents and any additives that are used to initially dissolve the polymer(s) to form the spin fluid. Suitable additives include stabilizers, such as antioxidants or acid scavengers.

[0053] The term “spin fluid” refers to a solution for spinning in a flash spinning process comprising a polymer and a spin agent. The solution may also include one or more additives.

[0054] The term “cloud point pressure’' refers to the pressure at which, at constanttemperature, a clear single phase spin fluid transitions from a clear solution to a cloudy, two* phase dispersion. At the cloud point pressure, a clear spin fluid becomes turbid.

[0055] Atmospheric pressure means 101.325 'kPa. Essentially atmospheric pressure means 101.325 kPa 15%.

[0056] As used herein, the singular forms "a,* ‘'an," and ”the" includethe plural, and reference 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 the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about,” it will be understood that the particular value forms another embodiment. All ranges are inclusive and combinable. Bonded Sheet of Nonwoven Flash-spun Plexifilamentary Fibrils Provided herein is a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0057] (a) a basis weight from about 50 g / m2to about 85 g / m2,

[0058] (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XO>, and .

[0059] (c) a handie-o-meter stiffness from about 150 mN to about 1500 mN, wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in p.NnT / g3. to the tensile strength, normalized to basis weight, in Nm; / g. is below about 2 30 In a still further embodiment, the invention is directed to a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0060] (a) a basis weight from about 43 g / m2to about 85 g / m2,

[0061] (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD),

[0062] (c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the handle-o-meter stiffness, normalized to (basis weight)3, is below about 5.0 frNm6 / g3.

[0063] The thermally bonded sheet described herein exhibits a desired combination of moderate to high basis weight, high tensile strength, and low to moderate handle-o-meter stiffness.

[0064] In some embodiments, the thermally bonded sheet has a basis weight from about

[0065] 43 g / m- to about 85 g / m2in other embodiments, the thermally bonded sheet has a basis weight from about 50 g / m2to about 85 g / m2, in other embodiments, the thermally bonded sheet has a basis weight from about 55 g / m2to about 85 g / m2, in other embodiments, the thermally bonded sheet has a basis weight from about 44 g / m2to about 65 g / m2, in other embodiments, the thermally bonded sheet has a basis weight from about 44 g / m2to about 55 g / m2, and in other embodiments, the thermally bonded sheet has a basis weight from about

[0066] 44 g / m2to about 50 g / m2.

[0067] In some embodiments, the thermally bonded sheet has an average tensile strength from about 50 N to about 250 N, in other embodiments, the thermally bonded sheet has an average tensile strength from about 60 N to about 85 N, in other embodiments, the thermally bonded sheet has an average tensile strength from about 90 N to about 120 N, and in other embodiments, the thermally bonded sheet has an average tensile strength from about 120 N to about 170 N.

[0068] In some embodiments, the thermally bonded sheet has a handle-o-meter stiffness from about 150 mN to about 1400 mN (this value represents the average of the handle-o-meter stiffness value measured in the machine direction and in the cross direction), in other embodiments, the thermally bonded sheet has a handle-o-meter stiffness from about 150 mN to about 450 mN, in other embodiments, the thermally bonded sheet has a handle-o-meter Stiffness from about 400 mN to about 1000 mN, and in other embodiments, the thermally bonded sheet has a handle-o-meter stiffness from about 500 mN to about 1500 mN. In some embodiments, the handle-o-meter stiffness of the thermally bonded sheet is isotropic. In some embodiments, the ratio of the handle-o-meter stiffness measured in the machine direction (MD) to the handle-o-meter stiffness measured in the cross direction (XD) is from about 0.2 to about 5. In some embodiments, the ratio of the handle-o-meter stiffness measured in the machine direction (MD) to the handle-o-meter stiffness measured in the cross direction (XD) is from about 0.25 to about 4, and in some embodiments, the ratio of the handle-o-meter stiffness measured in the machine direction (MD) to the handle-o-meter stiffness measured in the cross direction (XD) is from about 0.33 to about 3. In some embodiments, the ratio of the handle-o-meter stiffness measured in the machine direction (MD) to the handle-o-meter stiffness measured in the cross direction (XD) is from about 0.5 to about 2, and in some embodiments, the ratio of the handle-o-meter stiffness measured in the machine direction (MD) to the handle-o-meter stiffness measured in the cross direction (XD) is from about 0.7 to about 1.3.

[0069] In some embodiments, the thermally bonded sheet has a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, of below about 2:2 and in other embodiments, a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, of more than about 0.1. In some embodiments, the thermallybonded sheet has a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, from about 0.2 to about 2.2, and in other embodiments, from about 0.2 to about 2.0 In some embodiments, the thermally bonded sheet has a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, tn μNm6 / g3, to the;tensile strength, normalized to basis weight, in Nm2 / g, from about 0.2 to about 1.7, and in other embodiments, from about 0.2 to about 1.0. In some embodiments, the thermally bonded sheet has a handle-o-meter stiffness , normalized to (basis weight)3, of below about 4 μNm6 / g3and in other embodiments, has a handle-o-meter stiffness, normalized to (basis weight)3, of more than about 0.1 μNm6 / g3. In some embodiments, the thermally bonded sheet has a hahdle-o-meter stiffness, normalized to (basis weight)3, of more than about 0.2 tiNm / g ’ to less than about 3 5 uNml7g;. In other embodiments, the thermally bonded sheet has a handle-o-meter stiffness, normalized to (basis weight)3, of more than about 0.5 μNm6 / g3to less than about 3.0 μNm6 / g3.

[0070] In some embodiments, the bonded sheet has a total crystallinity index from about 60 % to about 72 %, in other embodiments, the bonded sheet has a total crystallinity index from about 62 % to about 72 %, and in other embodiments, the bonded sheet has a total crystallinity index from about 62 % to about 68 %. In some embodiments, the thermally bonded sheet has a BET surface area from about 4 m2 / g to about 10 m^g, and in other embodiments, the bonded sheet has a BET surface area from about 5 m2 / g to about 9 m2 / g.

[0071] In some embodiments, the thermally bonded sheet has a thickness from about 140 pm to about 200 pm, in other embodiments, the bonded sheet has a thickness from about 140 pm to about 185 pm. In some embodiments, the thermally bonded sheet has a thickness from about 185 pm to about 220 pm, and in other embodiments, the bonded sheet has a thickness from about 190 pm to about 220 pm. in some embodiments, the thermally bonded sheet has a thickness from about 220 pm to about 290 pm, and in other embodiments, the bonded sheet has a thickness from about 230 pm to about 280 pm.

[0072] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a polyolefin, in some embodiments, the polyolefin is selected from polyethylene (PE), polypropylene (PP), and blends / mixtures thereof. Particularly preferred polyolefins are polyethylene (PE), in particular high-density polyethylene (HOPE), blends / mixtures of 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 comprises at least 80 weight percent of high-density polyethylene (HDPE), based oh the total amount Of polymer. In other embodiments, the polyolefin comprises at least 90 weight percent of high-density polyethylene (HDPE), based on the total amount of polymer, and in other embodiments, the polyolefin comprises at least 95 weight percent of high-density polyethylene (HDPE), based on the total amount of polymer.

[0073] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 45 g / nfr to about 85 g / m2. an average tensile strength from about 50 N to about 250 N, a handie-o- meter stiffness from about 400 mN to about 1400 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in pNms / g3, to the tensile strength, normalized to basis weight, in Nm^ / g, from about 0.2 to less than about 2.0. in some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 43 g / m2to about 49 g / m2, an average tensile strength from about 50 N to about 85 N, a handle-o-meter stiffness from about 150 mN to about 450 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile sfrength, normalized to basis weight, in Nm2 / g, from about 0.2 to less than about 2.0.

[0074] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene and the sheet has a basis weight from about 55 g / m:' to about 65 g / m2, an average tensile strength from about 85 N to about 135 N, a handle-o- meter stiffness from about 300 mN to about 1000 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in j.tNm6 / g3, to the tensile strength, normalized to basis weight, in Nm^g, from about 0.2 to less than about 2.0. In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 55 g / m2to about 65 g / m2, an average tensile , strength from about 85 N to about 110 N , a handle-o- meter stiffness from about 300 mN to about 1000 mN, and a ratio of the handle-o-meter -stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, from about 0.2 to less than about 2.0.

[0075] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 75 g / m2to about 85 g / m2, an average tensile strength from about 120 N to about 170 N, a handle-o- meter stiffness from about 500 mN to about 1400 mN, and a ratio of the haridle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2g, from about 0.2 to less than about 2.0.

[0076] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 75 g / m to about 85 g / m2, an average tensile strength from about 120 N to about 230 N, a handle-o- meter stiffness from about 500 mN to about 1400 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in |.iNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, from about 0.2 to less than about 2.0.

[0077] Applicant has found that the thermally bonded sheets of the invention - surprisingly have a very good balance of mechanical properties, in - particular tensile strength and softness, which makes them very useful and comfortable for use in garments, including, but not limited to, protective apparel such as full body protective clothing and partial body protective clothing (including, but not limited to, gowns, overalls, coveralls, trousers, coats, sleeves, hoods, shoe protectors, aprons, etc ), and further applications, including, but not limited to, car -covers and roof linings.

[0078] Preparation of Bonded Sheet of Nonwoven Flash-spun Plexifilamentary Fibrils of Polymer

[0079] In a further embodiment of the invention, there is provided a process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps of:

[0080] (i) generating a spin fluid comprising (a) from about 8 to about 14 weight percent of a polymer, based on the total amount of the spin fluid , and

[0081] (b) a spin agent comprising a chlorine-containing solvent, selected from dichlbromethane, cis-1,2-dichloroethylene and trans-1 ,2-dichloroethylehe, in combination with a fluorine-containing solvent,

[0082] (ii) flash spinning the spin fluid at a temperature at or above about 190°C and at a pressure that is above the vapor pressure of the spin fluid into a< region of essentially atmospheric pressure to form plexifilamentary fibrils of the polymer,

[0083] (iii| collecting the plexifilamentary fibrils of the polymer on a collecting means as a sheet of nonwoven flash-spun plexifilamentary fibrils and applying pressure to the sheet to obtain a consolidated sheets and

[0084] (iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet.

[0085] Flash-Spinning, Collecting, Consolidating and Bonding

[0086] Flash-spinning is » method for producing fibrils having a unique plexifilamentary structure. It involves preparing a solution of a fibril-forming polymer in a spin agent (the spin fluid) at a pressure above the vapor pressure of the spin agent and at a temperature above the normal boiling point of the spin agent, and releasing that spin fluid into a zone of substantially lower temperature and pressure such that the spin agent flash evaporates and the polymer solidifies in the form of plexifilamentary fibrils. Suitable flash spinning processes and equipment which can be used herein are described in US 3,081 ,519, US 3,227,794, US 3,860,369, and US 7,744,989.

[0087] The formed plexifilamentary fibrils of polymer are discharged from each spin orifice, and the shape of these plexifilamentary fibrils of polymer may be modified by any methods known in the art. In some embodiments, the plexifilamentary fibrils of polymer discharged from each spin orifice may be modified by passing into a shroud such as described on US 3,387,326, in other embodiments by passing into a slotted outlet such as described in US 3,467,744 or US 5 788.993. and in other embodiments by passing into a slot fan jet as described in US 8, 114.325. in some embodiments, streams of fibrils from multiple orifices may exit via a rfommon slot as described in US 3,564,088.

[0088] Sheets comprising plexifilamentary fibrils of polymer can be formed by any method known in the art. In some embodiments, the stream of fibrils discharged from each spin orifice is directed towards a deflector device which alternately directs the stream of fibrils to the left and right onto a moving collecting device such that the fibrils accumulate in the form of a sheet, formed from fibrils oriented in an overlapping, multi-directional configuration. Deflection of the stream of fibrils may 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, 152and WO 92 / 20511 Al. The stream of fibrils may also be laid down to form a sheet without deflection as described in US 5,788,993 and US 8,114,325. The method of forming a sheet may further utilize structures in the spincell such as those described in US 5,123,983, US 5,296,172, and WO 92 / 20511 At.

[0089] In some embodiments, the streams of fibrils are discharged from spin orifices located on a rotating support, and the fibrils are collected on a collecting belt which surrounds the rotating arrangement circumferentially as described in US 7,118,698, US 7,621,731, US 7,786,034, and US 7,998,388. The sheet formed by flash-spinning as described herein may be consolidated by applying a small amount of pressure to the sheet. In some embodiments, the sheet may be passed under a roller which applies pressure to the sheet to form a lightly consolidated sheet.

[0090] A broad range of different polymers and blends / mixtures thereof can be used in the process described herein. In some embodiments, the polymer is selected from polyolefins. In some embodiments, polyolefins are polyethylene (PE), polypropylene (PP), and blends / mixtures thereof. Particularly preferred polyolefins are polyethylene (PE), in particular in particular high-density polyethylene (HDPE), blends / mixtures of high-density polyethylene (HOPE) and low-density polyethylene (LOPE), or blends / mixtures of high-dehsity polyethylene (HOPE) and linear low-density polyethylene (LLDPE). In some embodiments, the polyolefin comprises at least 80 weight percent of high-density polyethylene (HDPE), based on the total amount of polymer. In other embodiments, the polyolefin comprises at least 90 weight percent of high-density polyethylene (HDPE), based on the total amount of polymer, and in other embodiments, the polyolefin comprises at least 95 weight percent of high-density polyethylene (HDPE ), based oh the total amount of polymer.

[0091] The spin agent may include » chlorine-containing solvent, selected from dichloromethane, cis-1 ,2-dichloroethylene and trans-i ,2-dichloroethylene, in combination with a fluorine-containing solvent, in some embodiments, the spin fluid comprises the polymer in an amount from about 8 to about 14 weight percent, based on the total amount of the spin fluid, in other embodiments, the spin fluid comprises the polymer in an amount from about 9 to about 13 weight percent, based on the total amount of the spin fluid, in other embodiments, the spin fluid comprises the polymer in an amount from about 9 to about 12 weight percent, based on the total amount of the spin fluid, and in other embodiments, the spin fluid comprises the polymer in an amount from about 9 to about 11 weight percent, based on the total amount of the spin fluid.

[0092] I n some embodiments, the spin fluid comprises the spin agent in an amount from about 86 to about 92 weight percent, based on the total amount of the spin fluid, in other embodiments, the spin fluid comprises the sp in agent in an amount from about 87 to about 91 weight percent, based on the total amount of the spin fluid, in other embodiments, the spin fluid comprises the spin agent in an amount from about 88 to about 91 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 from about 89 to about 91 weight percent, based on the total amount of the spin fluid.

[0093] In some embodiments, the flash-spinning is performed at a temperature in the range of about 190°C to about 230ºC, in other embodiments, in the range of about 20ºC to about 220ºC, and in other embodiments, in the range of about 205°C to about 220°C, In some embodiments, the spin agent comprises a chlorine-containing solvent, selected from dichloromethane, cis-1 ,2-dichloroethylene and trans- 1 ,2-dichloroethylene, in combination with a fluorihe-containing solvent. .In some embodiments, the spin agent comprises a chlorine-containing solvent, selected from dichloromethane, cis- 1,2- dichloroethylene and trans-1 ,2-dichloroethylene, in combination with a fluorine-containing solvent which is a hydrofluorocarbon having three to six carbon atoms, perfluorocarbons having three to six carbon atoms or a hydrofluoroether. In some embodiments, the perfluorocarbons or hydrofluorocarbbns having three to six carbon atoms of the spin agent are perfluoropentane, perfluorohexane, 1,1,1,3,3-pentafluorobutane, 1H,4H-perfluorobutane, 2H,3H-decafluoropentane, 1H,6H-perfluorohexane, or IH-perfluorohexane,

[0094] In some embodiments, the spin agent consists essentially of a mixture of dichloromethane and 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1 H-perfluorohexane, perfluoropentane, perfluorohexane and 1 ,1 ,1 ,3.3- pentafluorobutane, inother embodiments, the spin agent consists essentially of from about 70 to about 85 weight percent dichloromethane and from about 15 to about 30 weight percent 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H-perflu0rohexane, IH- perfluorohexane, perfluoropentane, perfluorohexane or 1 ,1,1 ,3,3-pentafluorobutane, and in other embodiments, from about 75 to about 85 weight percent dichloromethane and from about 15 to about 25 weight percent 2H,3H-decafluoropentane, 1 H,4H-perfluorobutane, TH,6H-perfluorohexane, IH-perfluorohexane, perfluofopentane, perfluorohexane, or 1 ,1 ,1 ,3,3-pentafluorobutane.

[0095] In some embodiments, the spin agent consists of a mixture of dichloromethane and 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H-perfluorohexane, IH- perfluorohexane, perfluoropentane, perfluorohexane or 1 , 1 , 1 ,3,3-pentafluorobutane. in other embodiments, the spin agent consists of from about 70 to about 85 weight percent dichloromethane and from about 15 to about 30 weight percent 2H,3H-decafluoropentane, 1 H.4H-perfluorobutane. 1H.6H-perfluorohexane. IH-perfluorohexane, perfluoropentane, perfluorohexane or 1 ,1 ,1,3,3-pentafluorobutane, and in other embodiments, from about 75 to about 85 weight percent dichloromethane and from about 15 to about 25 weight percent of 2H)3H-decafluoropentane, 1 H,4H-perfluorobutane, 1Ht6H-perfIuorohexane, IH- perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane.

[0096] The spin fluid may include additives, such as antioxidants or acid scavengers in minor amounts. In some embodiments, the spin fluid comprises additives in an amount of about 1 .5 weight percent or less of the total amount of the spin fluid, and in other embodiments in an amount of about 0 1 weight percent or less of the total amount of the spin fluid.

[0097] In some embodiments, the plexifilamentary fibrils are spun at a spin temperature in the range of about 190°C to about 230°C using a spin fluid comprising about 8 to about 14 weight percent polymer, and comprising a spin agent which comprises, consists essentially Of, or consists of dichloromethane and 2H,3H-decafluoropentane, 1 H,4H-perfluorobutane, 1H,6H- perfluorohexane, IH-perfluorohexane, perfluoropentane, perfluordhexane or 1,1,1 ,3,3- pentafluorobutane. In other embodiments, the plexifilamentary fibrils are spun at a spin temperature in the range of about 200 C to about 220’C using a spin fluid comprising about 9 to about 13 weight percent polymer and comprising a spin agent which comprises, consists essentially of, or consists of dichloromethane and 2H,3H-decafluoropentane, 1H,4H- perfluorobutane, 1 H,6H-perfluorohexane, IH-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane. In other embodiments, the plexifilamentary fibrils are spun at a spin temperature in the range of about 205°C to about 220° C using a spin fluid comprising about 9 to about 11 weight percent polymer and comprising a spin agent which comprises, consists essentially of,:or consists of dichloromethane and 2H.3H- decafluoropentane, lH,4H-perfluorobutane, 1H,6H-perfluorohexane, lH*perfluorohexane, perfluoropentane, perfluorohexane, or 1 , 1 , 1 ,3,3-pentafluorobutane.

[0098] After the sheet is formed into a consolidated sheet as described herein, the consolidated sheet Is then subjected to thermal bonding via embossing by any methods known in the art, including, but not limited to, using heated embossing roil(s) and rubber coated backup roll(s) to bond one ortwo sides ofthe consolidated sheet, to form a thermally bonded sheet, In some embodiments, only one side erf the consolidated sheet is embossed. In other embodiments, one side of the consolidated sheet is embossed and the other side of the consolidated sheet is calendared by passing the sheet through a nip formed between a flat smooth roll and a rubber coated back-up roll. In other embodiments, one side of the consolidated sheet is embossed and the other side of the consolidated sheet is full surface bonded.

[0099] The embossing roll(s) apply heat and pressure locally over a portion of the surface of the consolidated sheet to bond the consolidated sheet and form an embossed patern. The degree of bonding can vary by adjusting the temperature and pressure, and length of time during which these are applied.:

[0100] In some embodiments, each embossing roll has a temperature of about 135' C to about 200°C during bonding, and in other embodiments, each embossing roll has a temperature of about 140“C to about 155°C during bonding.

[0101] The nip pressure can be varied with embossing roll configuration and engraving paterns, backup roll diameter, rubber hardness and thickness. In some embodiments, the static pressure in the nip of the embosser (nip pressure) is between about 150 kPa and about 1000 kPa . An “embosser" as used herein means a pair of two rolls forming a nip, one being a heated embossing roll and the other being a rubber coated back-up roll. In other embodiments, the static pressure in the nip of the embosser is between about 150 kPa and about 750 kPa, and in other embodiments, from about 150 kPa to about 500 kPa

[0102] In some embodiments, the consolidated sheet wraps the heated embosser roll such that the angle between the direction of entry and the direction of exit (the wrap angle) is from about 10" to about 140°, in other embodiments, the wrap angle is from about 10" to about 100”, and in other embodiments, the wrap angle is from about 10” to about 60°.

[0103] In some embodiments, the consolidated sheet may be in contact with pre-heat rolls before thermally bonding and / or may be in contact with cooling rolls after thermally bonding, in a configuration as described in US 5,972,147, In some embodiments, the temperature of the pre-heat roll may be varied from 50°C to 20°C below the melting peak temperature of the polymer.

[0104] The embossing roll(s) may be any suitable material known in the art. In some embodiments, the embossing roll(s) are metal.

[0105] The embossing roll(s) are engraved with a pattern. The embossing roll(s) may include any patern known in the art, including, but not limited to, a point pattern as described in US 3,478,141 , US 6,610,390, and US 2004 / 241399 A1 , a rib pattern as described in US 2003 / 0032355 A1 and US 2003 / 0165667 A1 , a linen pattern or a random pattern as described in US 7,744,989, and other variations of patterns as described in US 5,620,779 and US 5,964,742. The degree of bonding can vary depending on the embossing pattern chosen.

[0106] Each side of the consolidated sheet may be embossed using the same pattern or a different patern. 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 both sides using a point pattern, in other embodiments, the consolidated sheet is embossed on both sides using a rib pattern, and in other embodiments, the consolidated sheet is embossed on both sides using a linen pattern. In some embodiments, the consolidated sheet is embossed on one side using a point pattern and on another side using a rib pattern, in other embodiments, the consolidated sheet is embossed on one side using a point pattern and on another side using a hnen pattern, and in other embodiments, the consolidated sheet is embossed on one side using a rib pattern and on another side using a linen pattern.

[0107] The patterns on the embossing roll(s) may be any suitable depth known in the art. Each embossing roll may have patterns at the same depth or at different depths. In some embodiments, the consolidated sheet is embossed using embossing rolls having patterns at different depths such that certain portions of the consolidated sheet are subjected to more bonding than others. The percentage of surface area on each side of the consolidated sheet that is embossed may vary. In some embodiments, from about 6 % to about 85 ft of the area of at least one side of the consolidated sheet is embossed, in other embodiments, tom about 10 % to about 60 ft, in other embodiments, from about 15 % to about 60 ft, in other embodiments, from about 20 ft to about 60 ft, in other embodiments, from about 26 ft to about 60 %, in other embodiments, from about 30 ft to about 60 ft, and in other embodiments, from about 50 % to about 85 ft. In some embodiments, from about 6 % to about 85 % of the area of both sides of the consolidated sheet is embossed, in other embodiments, from about 10 ft to about 60 ft, in other embodiments, from about 15 ft to about 60 ft, in other embodiments, from about 20 ft to about 60 ft, in other embodiments, from about 26 ft to about 60 ft, in other embodiments, from about 30 % to about 60 ft, and in other embodiments, from about 50 % to about 85 ft, in some embodiments, about 50 ft to about 85 ft of the area of one side of the consolidated sheet is embossed using a linen pattern, and about 15 ft to about 60 ft or from about 20 ft to about 60 ft or from about 26 ft to about 60 % of the area of other side of the consolidated sheet is embossed using a rib pattern. in some embodiments, after the consolidated sheet is thermally bonded as descrtbed herein, the thermally bonded sheet is then subjected to a mechanical softening process to obtain s softened sheet of nonwoven flash-spun plexifilamentary fibrils. During the mechanical softening process described herein, the thermally bonded sheet is passed through one or more nips between rotating rolls which are driven at substantially the same speed as the speed of the thermally bonded sheet as it passes through the rolls. This is in contrast to some prior art softening processes where the thermally bonded sheet is passed over a sequence of roils that are driven at a different speed than the speed of the thermally bonded sheet This difference in speed creates a rubbing effect that leads to loose fibrils, which can jeopardizes the barrier properties of the softened sheet.

[0108] In some embodiments, the thermally bonded sheet is mechanically softened by passing it through one or more nips between rotating rolls, wherein each roil has interpenetrating pins and rotates in the opposite direction aS the Other roll. The pins of each roll may be arranged in an array and have ends that are equidistant from the roll’s axis. The array of pins on one roll interpenetrates the array of pins on the opposite roll by an amount that is at least equal to the thickness of the sheet. Various geometric configurations may be used for the interpenetrating pins, including, but not limited to, blunt pins, meaning a pin that includes at least a distal end that has a blunt surface and a shaft that has a surface. A blunt surface, i.e , a surface not having a sharp point, includes, but is not limited to, a blunt surface that is rounded, forming a smooth curving surface, or a blunt surface that is flat. In some embodiments, the thermally bonded sheet is subjected to a mechanical softening process as described in US 3408.709 In some embodiments, the thermally bonded sheet is subjected to a mechanical softening process as described in US 5,966,785 and US 6, 195,854, In some embodiments, the thermally bonded sheet is subjected to a mechanical softening process as described in US 3,920, 874 and US 3,811, 979.

[0109] In some embodiments, an antistatic treatment is applied to the thermally bonded or bonded and softened sheet. Antistatic treatment improves electrostatic properties of a textile, in particular surface resistivity. 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<, Rj.„ PO4, where 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 potassium dim-propyl phosphate, dipotassium n-propyl phosphate, potassium di-i-propyl phosphate, dipotassium i-propyl phosphate, potassium di-n-butyl phosphate, dipotassium n-butyl phosphate, potassium di-i-butyl phosphate, dipotassium i-butyl phosphate, and combinations thereof. In some embodiments, 'there:is provided a sheet of nonwoven flash-spun piexifilamentary fibrils obtained or obtainable by the process described herein.

[0110] In some embodiments, the obtained sheet has

[0111] (a) a basis weight from about 43 g / mzto about 85 g / m2,

[0112] (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and

[0113] (c) , a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, is below about

[0114] 2.30.

[0115] In some further embodiments, the obtained sheet has

[0116] (a) a basis weight from about 43 g / m2to about 85 g / m2, (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and (c) a handle-o-meter stiffness tom about 150 mN to about 1500 mN, wherein the handle-o-meter stiffness, normalized to (basis weight)3, is below about

[0117] 5.0 μNm6 / g3;

[0118] Uses, Multilayer Structures, and Articles

[0119] The sheet of nonwoven flash-spun plexifilamentary fibrils as described herein has many uses and may be used in a variety of applications, including, but hot limited to, multilayer structures, garments (including, but not limited to. protective apparel), house wrap, roof lining, car covers, and filtration media.

[0120] Further embodiments relate to a multilayer structure comprising at least one sheet of nonwoven flash-spun plexifilamentary fibrils as described herein, and at least one further sheet or a film.

[0121] In some embodiments, the multilayer structure comprises a film that is a microporous film In one embodiment, the microporous film is a film that is filled and stretched as described in US 9,809,004 B2. Microporous films from highly filled polymers, usually polyolefins, may be prepared by any methods known in the art. Typically, a combination of a polyolefin, usually a polyethylene, is compounded with a filler, usually calcium carbonate, and extruded and stretched into a film to form a microporous film. Suitable examples of microporous films indude those described in US 4,472,328, US 4,350,655, and US 4,777,073. A multilayer structure comprising a microporous film and at least one sheet of nonwoven flash-spun plexifilamentary fibrils as described herein can be used in a variety of applications, including, but not limited to, protective apparel.

[0122] In some embodiments, the multilayer structure is a laminated structure comprising a microporous film laminated to at least one sheet of nonwoven flash-spun plexifilamentary fibrils as described herein. In some embodiments, a microporous film and a sheet of nonwoven flash-spun plexifilamentary fibrils may be laminated using an adhesive layer Situated in contact with a least a portion of both the microporous film and the sheet of nonwoven flash-spun plexifilamentary fibrils, as described in US 9,809,004 B2, US 5,750,444 or US 5,294,258. Such multilayer structures may be particularly suitable for, without being limited to, garment applications.

[0123] In some embodiments, the multilayer structure is a composite structure comprising at least one bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein and at least one further sheet, which is a sheet of a thermoplastic reinforcing material having reinforcing properties, such as a thermoplastic reinforcing grid material and / or a spunbonded non woven material, or a water absorbing sheet such as a needle felt. In some embodiments, the multilayer;structure Is a composite structure comprising two or more sheets, in other embodiments, the multilayer structure is a composite structure comprising three or more sheets, and in other embodiments, the multilayer structure is a composite structure comprising four or more sheets, In some embodiments, the sheet of a thermoplastic reinforcing material having reinforcing properties and the at least one sheet of nonwoven flash-spun plexifilamentary fibrils are held together by thermal lamination, in some embodiments, the Sheet of a thermoplastic reinforcing material having reinforcing properties and the at least one sheet of nonwoven flash-spun plexifilamentary fibrils are held together by using an adhesive applied to at least a portion of the surface of the at least one sheet of nonwoven flash-spun plexifilamentary fibrils. In some embodiments, such multilayer structure further comprises a water absorbing sheet, such as a needle felt. Such multilayer structures may be particularly suitable for, without being limited to, roof lining applications.

[0124] Further embodiments relate to use of the sheet of nonwoven flash-spun plexifilamentary fibrils as described herein for preparing a multilayer structure. Further embodiments relate to use of the sheet of nonwoven flash-spun plexifilamentary fibrils as described herein for the production of garments.

[0125] Further embodiments relate to use of the multilayer structure as described herein for the production of garments .

[0126] Further embodiments relate to an article comprising at least one sheet of nonwoven flash-spun plexifilamentary fibrils as described herein or comprising at least one multilayer structure as described herein. In some embodiments, the article is selected from garments, protective apparel, house wraps, roof linings car covers, medical package, and filtration media. Protective apparel includes Ml body protective clothing and partial body protective clothing (including, but not limited to. gowns, overalls, coveralls, trousers, smocks, coats, sleeves, hoods, shoe protectors, aprons, etc ) and other garments whose purpose is to protect the wearer against exposure to hazardous materials in the environment, or to protect the wearer’s environment against being contaminated by the wearer. EXAMPLES

[0127] Different bonded and softened sheets of nonwoven flash-spun plexifilamentary fibrils have been prepared. The experimental procedure and results are provided below. These examples are given to illustrate exemplary embodiments of the invention and should not be interpreted as limiting in any way. Materials Used

[0128] Trichlorofluoromethane (Freon 11) GAS Nr. 75-69-4 has an atmospheric boiling point of 23.8°C, a molecular weight of 248 g / mol and a critical point of 198’0, The trichlorofluoromethane used had a purity level above 99.5 percent by weight.

[0129] Dichloromethane, CAS Nr. 75-09-2, has an atmospheric boiling of 39.6’G, a molecular weight of 84.93 g / mol and a Critical temperature of 236.68’C The dichloromethane used had a purity level above 99.5 percent by weight.

[0130] 2H,3H-decafluoropentane (HFC-4310-mee), CAS Nr. 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 above 99.5 percent by weight.

[0131] The polyethylene used had a density of 0.957 g / cm3(IS0 1183), and melt flow rate of 0.3 g / IOmin (ISO 1133 condition D, 190’0 / 2.16 kg) and 22 g / 10min (ISO 1133 condition G, 190’0 / 21.6 kg).

[0132] The polyethylene blend used was a blend of a high-density polyethylene with a density >0;95 g / cm3and a melt flow rate of 0;7 g / 10min (ASTM 1238 190’0 / 2.16 kg) and a linear low- density polyethylene (LLDPE, an ethylene-hexene copolymer) with a density of 0.918 g / cm3and a melt flow rate of 1.0 g / 10min (ASTM 1238 l90oC / 2.16kg) in a 90:10 ratio by weight.

[0133] The flash-spun sheets in the examples are produced using the flash spinning process described by US 3,227,794 and US 3,850023. US 3,227,794 describes a flash spinning process where the pressure is reduced below the cloud point of the spin fluid before it is released into a zone of substantially tower temperature and pressure such that the spin agent flash evaporates and the polymer solidifies in the form of plexifilamentary fibrils. The cloud point pressure for mixtures of trans-1,2-DGE and DGM with fluorinated compounds is reported in, but not limited to, US 6,004,672, US 7,300.968, and US 7,179,413. Results

[0134] Comparative examples 1 to 3

[0135] A flash-spun sheet was produced using the flash spinning process described by US 3 ,227,794 and US 3,851,023 at a spin temperature of 1800C using a spin fluid of 12 wt% polyethylene with a density >0.95 g / cm3and a melt flow rate of 0;74 g / 1 Omin (ASTM 1238 190°C / 2.16 kg) In a spin agent of Fl 1 (trichlorofluoromethane).

[0136] The flash-spun sheet was subsequently thermally bonded and embossed. < For comparative example 1, one side was embossed by passing the sheet through a nip formed between a heated roll with a linen pattern and a rubber roll and the opposite side was embossed through a nip formed between a heated embosser roll having a rib pattern and a rubber roll.

[0137] For comparative example 2 and 3, thermally bonded sheets prepared in accordance with comparative example 1 were subsequently passed between two rolls with interpenetrating blunt pins having a diameter of 1 mm, with an upper edge radius of curvature of 0.25 mm. The blunt pins were separated by 3.3 mm center-to-center in MD direction and 3.2 mm center-to-center in XD direction at the point of interacting with the flash-spun sheet. For comparative example 2 the pin interpenetration was 0.4 mm and for comparative example 3 the pin interpenetration was 1.4 mm. The spinning, bonding, and softening conditions and sheet properties are reported in

[0138] Table 1, below.

[0139] Table 1: Summary of the sheet preparation of Comparative Examples 1 to 3.

[0140] Comparative examples 1 to 3 show that there is a trade-off between average strength and softness when using Fl 1 (trichlorofluoromethane) as the spin agent.

[0141] Examples 1 to 6

[0142] Flash-spun sheets were produced using the flash spinning process described by US 3,227,794 and US 3,851 ,023 at a spin temperature of 210°C using a spin fluid of a : polyethylene with a density >0.95 g / cm3and a melt flow rate of 0,74 g / IOmin (ISO 1133 19O°C / 2.16 kg) at a polymer concentration of 11 wt% in a spin agent that was a mixture of dichloromethane and 2H,3H-decafluoropentane (herein also referred to as “0”). The flash- spun sheets of Examples 1 to 6 were subsequently thermally bonded. One side of each flash- spun sheet was embossed by passing the sheet through a nip formed between a heated roll with a linen pattern and a rubber roll and the opposite side was embossed through a nip formed between a heated embosser roll having a rib pattern and a rubber roll.

[0143] The thermally bonded sheets of examples 2, 3, 4 and 6 were subsequently mechanically softened by passing them through a nip of two rolls with interpenetrating blunt pins having a diameter of 1 mm, with an upper edge radius of curvature of p, 25 mm. The blunt pins were separated by 3.3 mm center-to-center in MD direction and 3.2 mm center-to-center in XD direction at the point of interacting with the flash-spun sheet.

[0144] The spinning, bonding, and softening conditions and sheet properties are reported in Table 2, below.

[0145] Table 2: Summary of the sheet preparation of Examples 1 to 6.

[0146] Table 2 shows that the sheets of examples 1 to 6, prepared using a dichloromethane- based spin agent, are, for similar basis weight and strength and similar softening, significantly less stiff compared to the sheets of comparative examples 1 to 3 prepared using F11 as spin agent. Additionally, the stiffness of the sheets of examples 1 to 6 is even comparable to the stiffness of the sheet of comparative example C£3 which was subjected to a high level of softening. Moreover, the ratio of the handle-omieter stiffness, normalized to (basis weight)3, to the tensile strength, normalized to basis weight, is lower for the sheets of examples 1 to 6, which is indicative of a favorable balance of softness to tensile strength. Examples 7 to 16

[0147] J Rash-spun sheets were produced using the flash spinning process described by US 3,227,794 and US 3,851 ,023 at different spin temperatures using a spin fluid of a polyethylene with a density >0.95 g / cm3and a melt flow rate of 0.74 g / 10min (ISO 1133 190°C / 2.16 kg) and at different polymer concentrations in a spin agent that was a mixture of dichloromethahe and 2H(3H-decafluoropentahe (herein also referred to asWD‘). The flash- spun sheets of Examples 7 to 16 were first heated by two chrome plate pre-heat roils set at different temperatures and subsequently thermally bonded.:For Examples 7 to 14, one side of each flash-spun sheet was embossed by passing the sheet through a nip termed between a heated roll with a linen pattern and a rubber roll and the opposite side was embossed through a nip formed between a heated embosser roll having a rib pattern and a rubber roll. For Examples 15 and 16, both sides are embossed with a rib pattern.

[0148] The thermally bonded sheets of examples 7, 9, 11, 12, 14, 15 and 16 were subsequently mechanically softened by passing them through a nip of two rolls with interpenetrating blunt pins having a diameter of 1 mm, with an upper edge radius of curvature of 0.25 mm. The blunt pins were separated by 3.3 mm center-to-center in MD direction and 3.2 mm center-to-center in XD direction at the point of interacting with the flash-spun sheet.

[0149] The spinning, bonding, and softening conditions and sheet properties of Examples 7 to 12 are reported in Table 3, below.

[0150] Table 3: Summary of the sheet preparation of Examples 7 to 12.

[0151]

[0152] The spinning, bonding, and softening conditions and sheet properties of Examples 13 to 16 are reported in Table 4, below.

[0153] Table 4: Summary of the sheet preparation of Examples 13 to 16. Tables 3 and 4 show that the sheets; of examples 7 to 16, prepared using a dichloromethane-based spin agent, are, for similar basis weight and strength and similar softening, significantly less stiff compared to the sheets of comparative examples 1 to 3 prepared using F11 as spin agent. Additionally, the stiffness of the sheets of examples 13 to 15 is even lower to the stiffness of the sheet of comparative example CE3 which was subjected to a high level of softening. Moreover, the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, to the tensile strength, normalized to basis weight, is lower for the sheets of examples 7 to 16, prepared using a diGhloromethane-based spin agent.

[0154] Hence, the thermally bonded sheets according to the invention surprisingiy have a very good balance of mechanical properties, in particular tensile strength and softness.

[0155] OTHER EMBODIMENTS

[0156] 1 In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash-spun plexifilamentary flbrils, the sheet having::(a) a basis weight from about 43 g / m2to about 85 g / m2,

[0157] (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD). and (c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nmlg, is below about 2.30.

[0158] 2. In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0159] (a) a basis weight from about 50 g / m2to about 85 g / m2,

[0160] (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and (c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm^g, is below about 2.30. 3. In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0161] (a) a basis weight from about 43 g / m2to about 85 gfrn2,

[0162] (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MO) and the tensile strength in the transverse direction (XD), and

[0163] (c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the handle-o-meter stiffness, normalized to (basis weight)3, is below about 5,0 μNm6 / g3.

[0164] 4. The sheet of any one of the preceding embodiments having a basis weight from about 50 g / m2to about 85 g / m2or having a basis weight from about 55 g / m2to about 85 g / m2or having a basis weight from about 44 g / m2to about 65 g / m2.

[0165] 5. The sheet of any one of the preceding embodiments having a basis weight from about 44 g m to about 55 g / m2or having a basis weight from about 44 g / m2to about 50 g / m2.

[0166] 6. The sheet of any one of the preceding embodiments having a BET surface area of about 4 m^g to io m2 / g,

[0167] 7. The sheet of any one of the preceding embodiments having a BET surface area of about 5 m2 / g to about 9 m2 / g.

[0168] 8. The sheet of any one of the preceding embodiments having a total crystallinity index of about 60 % to about 72 %. 9. The sheet of any one of the preceding embodiments having a total crystallinity index Of about 62 % to about 72 %.

[0169] 10. The sheet of any one of the preceding embodiments having a total crystallinity index of about 62 % to about 68 %.

[0170] 11. The sheet of any one of the preceding embodiments having a tensile strength from about 50 N to about 250 N.

[0171] 12. The sheet of any one of the preceding embodiments having a tensile strength from about 60 N to about 250 N.

[0172] 13. The sheet of any one of me preceding embodiments having a tensile strength from about 60 N to about 85 N. 14. The sheet of any one any one Of embodiments 1 to 12 having a tensile strength from about 90 N to about 120 N. 15. The sheet of any one of embodiments 1 to 12 having a tensile strength from about 120 N to about 170 N.

[0173] 16. The sheet of any one of the preceding embodiments having a thickness from about

[0174] 140 pm to about 300 pm. 17. The sheet of any one of the preceding embodiments having a thickness from about

[0175] 140 pm to about 200 pm.

[0176] 18 The sheet cff any one of the preceding embodiments having a thickness from about 140 pm to about 185 pm.

[0177] 19. The sheet of any one any one of embodiments 1 to 16 having a thickness from about 185 pm to about 220 pm.

[0178] 20. The sheet of embodiment 19 having a thickness from about 190 pm to about 220 pm.

[0179] 21. The sheet of any one any one of embodiments 1 to 16 having a thickness from about 220 pm to about 290 pm.

[0180] 22 The sheet of embodiment 21 having a thickness from about 230 pm to about 280 pm. 23 The sheet of any one of the preceding embodiments having a handle-o-meter stiffness from about 150 mN to about 1400 mN.

[0181] 24. The sheet of any one of the preceding embodiments having a handle-o-meter stiffness from about 150 mN to about 450 mN .

[0182] 25. The sheet of any one any one of embodiments 1 to 23 having a handle-o-meter stiffness from about 400 mN to about 1000 mN or having a:handle-o-meter stiffness from about 500 mN to about 1500 mN.

[0183] 26. The sheet of any one any one of embodiments 1 to 25 wherein the ratio of the handle- o-meter stiffness measured in the machine direction (MD) to the handle-o-meter stiffness measured in the cross direction ( XD) is from about 0.2 to about 5. or the ratio of the handle-o-meter stiffness measured in the machine direction (MD) to the handle- o-meter stiffness measured in the cross direction (XD) is from about 0.25 to about 4.

[0184] 27. The sheet of any one any one of embodiments 1 to 26 wherein the ratio of the handle- o-meter stiffness measured in the machine direction (MD) to the handle-o-meter stiffness measured in the cross direction (XD) is from about 0.33 to about 3, or the ratio of the handle-o-meter stiffness measured in the machine direction (MD) to the handle- o-meter stiffness measured in the cross direction (XD) is from about 0.5 to about 2, or the ratio of the handle-o-meter stiffness measured in the machine direction (MD) tothe handle-o-meter stiffness measured in the cross direction (XD) is from about:0.7 to about 1.3. 28. The sheet of any one of the preceding embodiments, wherein the ratio of the handle* o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, is of below about 2.2.

[0185] 29. The sheet of any one of the preceding embodiments, wherein the ratio of the handle* o-meter stiffness, normalized to (basis weight)3, in pNm6 / g\ to the tensile strength, normalized to basis weight, in Nm2 / g, is of more than about 0.1.

[0186] 30. The sheet of any one of the preceding embodiments, wherein the ratio of the handle- o-meter stiffiiess, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, is from about 0.2 to less than about 2.2, or of from more than about 02 to less than about 2.0.

[0187] 31 . The sheet of any one of the preceding embodiments, wherein the ratio of the handle- o-meter stiffness, normalized to (basis weight)3, in uNnTVg3, to the tensile strength, normalized to basis weight, in Nm2 / g, is of from more than about 0.2 to less than about 1.7, 32. The sheet of any one of the preceding embodiments, wherein the ratio of the handle- o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, is of torn more than about 0.2 to less than about 1.0.

[0188] 33. The sheet of any one of the preceding embodiments having a handle-o-meter stiffness, normalized to (basis weight)3, of below about 4 μNm6 / g3.

[0189] 34. The sheet of any one of me preceding embodiments having a handle-o-meter stiffness, normalized to (basis weight)3, of more than about 0.1 μNm6 / g3.

[0190] 35. The sheet of any one of the preceding embodiments having a handle-o-meter stiffness, normalized to (basis weight)3. of more than about 0.2 uNmf / g;to less than about 3.5 μNm6 / g3.

[0191] 36. The sheet of any one of the preceding embodiments having a handle-o-meter stiffness, normalized to (basis weight)3, of more than about 0.5 μNm6 / g3to less than about 3.0 μNm6 / g3.

[0192] 37 The sheet of any one of the preceding embodiments, wherein the flash-spun plexifilamentary fibrils are comprised of a polyolefin, selected from the group of polyethylene (PE), polypropylene (PP), and blends / mixtures thereof.

[0193] 38. The sheet. of embodiments 37, wherein said polyolefin is a high-density polyethylene (HDPE), a blend of a high-density polyethylene (HDPE) and a low-density polyethylene (1_DPE), and blend of a high-density polyethylene (HOPE) and linear low-density polyethylene (LtOPE). 39. The sheet of any one of the preceding embodiments, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 45g / m2to about 85g / m2, an average tensile strength from about 50 N to about 250 N, a handle-o-meter stiffness from about 400 mN to about 1400 mN, and a ratio of the handle-o-meter stiffness, normalized to

[0194] (basis weight)3, in pNmSg3, to the tensile strength,, normalized to basis weight, in Nm2 / g, from about 0.2 to less than about 2.0.

[0195] 40. The sheet of any one of embodiments 1 to 38, wherein the flash-spun plexifilamentary : fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 43 g / m2to about 49 g / m2, an average tensile strength from about 50 N to about 85 N, a handle-o-meter stiffness from about 150 mN to about 450 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in pNnWg3, to the tensile strength, normalized to basis weight, in Nm2 / g, from about 0 2 to less than about 2.0. 41. The sheet of any one of embodiments I to 38, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 55 g / m2to about 65 g / m2, an average tensile strength from about 85 N to about 135 N, a handle-o-meter stiffness from about 300 mN to about 1000 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength* normalized to basis weight, in Nm^g, from about 0.2 to less than about 2.0,

[0196] 42. The sheet of any one of embodiments 1 to 38, wherein the flash-spun. plexifilamentary fibrils ofthe sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 55 g / m2to about 65 g / m2, an average tensile strength from about 85 N to about 110 N, a handle-o-meter stiffness from about 300 mN to about

[0197] 1000 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm^g, from about 0.2 to less than about 2.0.

[0198] 43, The sheet of any one of embodiments t to 38, wherein the ® sh-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 75 g / m2to about 85 g / m2, an average tensile strength from about 120 N to about 170 N, a handle-o-meter stiffness from about 500 mN to about 1400 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm^g, from about 0.2 to less than about 2,0. 44. The sheet of any one of embodiments 1 to 38, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 75 g / m2to about 85 g / m2an average tensile strength from about 120 N to about 230 N, a handle-o-meter stiffness from about 500 mN to about 1400 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight}3, in uNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, from about 0.2 to less than about 2.0,

[0199] 45. A process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps of:;(i) generating a spin fluid comprising

[0200] (a) from about 8 to about 14 weight percent of a polymer, based on the total amount of the spin fluid, and

[0201] (b) a spin agent comprising a chlorine-containing solvent, selected from dichloromethane, cis-1 ,2-dichloroethylene and traris-l,2-dichloroethylene, in combination with a fluorine-containing solvent;

[0202] (ii} flash spinning the spin fluid at a temperature at or above about 190°C and at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of the polymer, (iii) collecting the plexifilamentary fibrils of the polymer:on a collecting means as a sheet of nonwoven flash-spun plexifilamentaryfibrils and applying pressure to the sheet to obtain a consolidated sheet, and

[0203] (iv} thermally bonding by embossing the consolidated sheet to obtain a bonded sheet,

[0204] 46. The process of embodiment 45, wherein the spin fluid (tomprises from about 9 to about 13 weight percent of a polymer, based on the total amount of the spin fluid. 47. The process of embodiment 45, wherein the spin fluid comprises from about 9 to about

[0205] 12 weight percent of a polymer, based on the total amount of the spin fluid.

[0206] 48. The process of embodiment 45, wherein the spin fluid comprises from about 9 to about 11 weight percent of a polymer, based on the total amount of the spin fluid.

[0207] 49. The process of any one of embodiments 45 to 48, wherein flash spinning of the spin fluid is carried out at a temperature of about 190°C to about 230°G.

[0208] 50. The process of any one of embodiments 45 to 48, wherein flash spinning of the spin fluid is carried outat a temperature of about 200*0 to about 22G°C.

[0209] 51. The process of any one of embodiments 45 to 48, wherein flash spinning of the spin fluid is carried out at a temperature of about 205*0 to about 220’0. 52, The process of any one of embodiments 45 to 51, wherein the fluorine-containing solvent is a : hydrofluorocarbon having three to six carbon atoms, perfluorocarbons having three to six carbon atoms or a hydrofluoroether. 53. The process of embodiment 52, wherein the perfluorocarbons or hydrofluorocarbons having three to six carbon atoms Of the spin agent are perfluoropentane, perfluorohexane, 1,1, 1,3, 3-pentafluorobutane, lH,4H.perfluorobutarie, 2H,3H- decafluoropentane, 1H,6H-perfluorohexane, or 1 H-perfluorohexane. 54. The process of any one of embodiments 45 to 53, wherein the spin agent consists or consists essentially of dichloromethane in combination with perfluoropentane, perfluorohexahe, 1,1^1, 3, 3-pentafluorobutane, 1H,4H*perfluorobutane, 2H,3H- decafluoropentane, 1H,6H-perfluorohexane, or 1 H-perfluorohexane,

[0210] 55. The process of any one of embodiments 45 to 54, wherein the spin agent consists essentially of from about 70 to about 85 weight percent dichloromethane and from about 15 to about 30 weight percent 2H,3H-decafluoropentane. 1H,4H- perfluorobutane, 1H,6H-perfluorohexane, 1 H-perfluorohexane, perfluoropentane, perfluorohexane, or l, 1,1, 3, 3-pentafluorobutane.

[0211] 56. The process of any one of embodiments 45 to 54, wherein the spin agent consists of from about 70 to;about 85 weight percent dichloromethane and from about 15 to about

[0212] 30 weight percent 2H,3H-decafluoropentane, 1H,4H-perflu0robutane,:1H.6H- perfiuorohexane, 1 H-perfluorohexane, perfluoropentane, perfluorohexane, or 1 ,1,1, 3, 3-pentafluorobutane.

[0213] 57. The process of any one of embodiments 45 to 56, wherein the plexifilamentary flbrils are spun at a spin temperature in the range of about 190°C to about 230°C using a spin fluid comprising about 8 to about 14 weight percent of a polymer, based on the total amount of the spin fluid, and comprising a spin agent which comprises, consists essentially of. or consists of dichloromethane and 2H.3H-decafluoropentane. 1H.4H- perfluorobutane, 1H,6H-perfluorohexane, 1 H-perfluorohexane, perfluoropentane, perfluorohexane, or 1.1 , 1.3.3-pentafluorobutane.

[0214] 58 The process of any one of embodiments 45 to 56. wherein the plexifilamentary fibrils are spun at a spin temperature in the range of about 200°C to about 220°C using a spin fluid comprising about 9 to about 13 weight percent of a polymer based on the total amount of the spin fluid, and comprising a spin agent which comprises, consists essentially of, or consists of dichloromethane and 2H,3H-decafluoropentane, 1H,4H- perfluorobutane, 1H,6H-perfluorohexane, 1 H-perfluorohexane, perfluoropentane, peBuorohexane, or 1,1,1,3,3-pentafluorobutane.

[0215] 59. The process of any one of embodiments 45 to 56, wherein the plexifilamentary fibrils are spun at a spin temperature in the range of about 205°C to about 220°C using a spin fluid comprising about 9 to about 11 weight percent of a polymer, based on the total amount of the spin fluid, and comprising a spin agent which comprises, consists essentially of, or consists of dichloromethane and 2H,3H-decafluoropentane, 1H.4H- perfluorobutane, 1H,6H-perfluorohexane, IH-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1, 1,3, 3-pentafluorobutahe,

[0216] 60. The process of any one of embodiments 45 to 59, wherein the spin fluid further includes additives. 61 . The process of embodiment 60, wherein the spin fluid comprises the additives in an amount of about 1 .5 weight percent or less of the total amount of the spin fluid.

[0217] 62. The process of any one of embodiments 45 to 61 , wherein heated embossing roll(s) and rubber coated back-up roll<s) are used to bond one or two sides of the consolidated sheet, to form a thermally bonded sheet. 63. The process of any one of embodiments 45 to 62, wherein the sheet wraps the heated embosser roll by a wrap angle of about 10° to about 140°.

[0218] 64. The process of any one of embodiments 45 to 62, wherein the sheet wraps the heated embosser roll by a wrap angle of about 10° to about 60°.

[0219] 65. The process of any one of -embodiments 62 to 64, wherein the embossing roll(s) have a temperature of about 135°C to about 210°C during bonding.

[0220] 66. The process of any one of embodiments 62 to 64, wherein the embossing roll(s) have a temperature of about 140°G to about 155°C during bonding.

[0221] 67. The process of any one of embodiments 62 to 66, wherein the static pressure in the nip of the embosser is between about 150 kPa and about 1000 kPa. 68 The process of any one of embodiments 62 to 66, wherein the static pressure in the nip of the embosser is between about 150 kPa and about 750 kPa.

[0222] 69 The process of any one of embodiments 62 to 66, wherein the static pressure in the nip of the embosser is between about 150 kPa and about 500 kPa.

[0223] 70. The process of any one of embodiments 45 to 69, wherein the consolidated sheet is embossed on both sides.

[0224] 71 The process of any one of embodiments 45 to 69 wherein the consolidated sheet is embossed on only one side,

[0225] 72. The process of any one of embodiments 45 to 69, wherein one side of the consolidated sheet is embossed and the other side of the consolidated sheet is calendared by passing the sheet through a nip formed between a flat smooth roll and a rubber coated back-up roll.

[0226] 73. The process of any one of embodiments 45 to 69, wherein one side of the consolidated sheet is embossed and the other side cf the consolidated sheet is full surface bonded.

[0227] 74. The process of any one of embodiments 45 to 73, wherein from about 6 % to about 85 % of the area of at least one side of the consolidated sheet is embossed.

[0228] 75. The process of any one of embodiments 45 to 73, wherein from about 15 % to about 60 % of the area of at least one side of the consolidated sheet is embossed. 76. The process of any one of embodiments 45 to 73, wherein from about 26 % to about 60 % of the area of at least one side of the consolidated sheet is embossed,

[0229] 77. The process of any one of embodiments 45 to 73, wherein from about 50 % to about 85 % of the area of at least one side of the consolidated sheet is embossed, 78. The process of any one of embodiments 45 to 73, wherein from about 6 % to about 85 % of the area of both sides of the consolidated sheet is embossed.

[0230] 79. The process of any one of embodiments 45 to 73, wherein from about 15 % to about 60 % of the area of both sides of the consolidated sheet is embossed.

[0231] 80. The process of any one of embodiments 45 to 73, wherein from about 6 % to about 85 % of the area of both sides of the consolidated sheet is embossed.

[0232] 81. The process of any one of embodiments 45 to 73, wherein from about 26 % to about 60 % of the area of both sides of the consolidated sheet is embossed.

[0233] 82. The process of any one of embodiments 45 to 73, wherein from about 50 % to about 85 % of the area of both sides of the consolidated sheet is embcssed.;83. The process of any one of embodiments 45 to 73, wherein about 50 % to about 85 % of the area of one side of the Consolidated sheet is embossed using a linen pattern, and about 15 % to about 60 % or from about 20 % to about 60 % or from about 26 % to about 60 % of the area of other side of the consolidated sheet is embossed using a rib pattern. 84. The process of any one of embodiments 45 to 83, wherein the process further comprises mechanically softening the bonded sheet,

[0234] 85, The process of embodiment 84, wherein the thermally bonded sheet is mechanically softened by passing it through one or more nips between rotating rolls, wherein each roll has interpenetrating pins and rotates in the opposite direction as the other roll 86. The process of embodiment 84 or 85, wherein the pins are blunt pins.

[0235] 87. The process of any one of embodiments 45 to 86, wherein the polyolefin is a high- density polyethylene (HDPE), a blend of a high-density polyethylene (HDPE) with a linear low-density polyethylene (LLDPE), or a blend of a high-density polyethylene (HDPE) with a low-density polyethylene (LDPE). 88. The process of embodiment 87, wherein said polyolefin is a high-density polyethylene

[0236] (HDPE), a blend of a high-density polyethylene (HDPE) with a linear low-density polyethylene (LLDPE), or a blend of a high-density polyethylene (HDPE) with a low- density polyethylene (LDPE).

[0237] 89. The process of any of embodiments 87 to 88, wherein the polyolefin comprises at least 80 weight percent of high*density polyethylene (HDPE), based on the total amount of polymer. 90. The process of any of embodiments 87 to 89, wherein the polyolefin comprises at least 95 weight percent of high-density polyethylene (HOPE), based on the total amount of polymer.

[0238] 91. The process erf any one of embodiments 45 to 90, wherein the obtained sheet has

[0239] (a) a basis weight from about 43 g / m2to about 85g / m2,

[0240] (b) a tensile strength from about 40 to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XO), and

[0241] (c) a handle-o-meter stiffness from about 150 mN to about 1500 mN,:wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm^g, is below about

[0242] 2.30.

[0243] 92. The process of any one of embodiments 45 to 90, wherein the obtained sheet has

[0244] (a) a basis weight from about 43 g / m2to about 85 g / m2,

[0245] (b) a tensile strength from about 40 to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction <MD) and the tensile strength in the transverse direction (XD), and

[0246] (c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the handle-o-meter stiffness, normalized to (basis weight)3, is below about 5.0 pNme / g3.

[0247] 93. In some embodiments the present application provides a thermally bonded sheet of nonwoven flash-spun plexifliamentary fibrils obtainable by the process of any one of embodiments 45 to 92.;

[0248] 94. In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash-spun plexifliamentary fibrils, the sheet having

[0249] (a) a basis weight from about 43 g / m2to about 85 g / m2,

[0250] (b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and

[0251] (c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, : wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm^g, is below about

[0252] 2.30, and wherein the sheet is obtained by the process of any one of embodiments 45 to 92.

[0253] 95. In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash^spun plexifilamentary fibrils, the sheet having (a) a basis weight from about43 g / m2to about 85 g / m2,

[0254] (b) / a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensiie strength in the transverse direction (XD). and (c) < a hahdle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the handle-o-meter stiffness, normalized to (basis weight)3, is below about 5.0 μNm6 / g3, and wherein the sheet is obtained by the process of any one of embodiments 45 to 92.

[0255] 96, Io some embodiments, the present application provides a thermally bonded sheet of nonwoven flash-spun plexifllamentary fibrils comprised of a high-density polyethylene, wherein the sheet has a basis weight from about 45 g / m2to about 85 g / m2, an average tensile strength from about 50 N to about 250 N, a handle-o-meter stiffness from about 400 mN to about 1400 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, from about 0.2 to less than about 2.0, and wherein the sheet is obtained by the process of any one of embodiments 45 to 92.

[0256] 97. In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash-spun plexifllamehtary fibrils comprised ofa high-density polyethylene, wherein the sheet has a basis weight from about 43 g / m2to about 49 g / m2, an average tensile strength from about 50 N to about 85 N, a handle-o-meter stiffness from about 150 mN to about 450 mN, and a ratio of the handle-o-meter stiffriess, normalized to (basis weight)3, in pNm^ / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, from about 0,2 to less than about 2.0, and wherein the sheet is obtained by the process of any one of embodiments 45 to 92. 98. In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash-spun plexifllamentary fibrils comprised of a high-density polyethylene, the sheet has a basis weight from about 55 g / m2to about 65 g / m2, an average tensile strength from about 85 N to about 135 N, a handle-o-meter stiffness from about 300 mN to about 1000 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in

[0257] Nm2 / g, from about 0.2 to less than about 2.0, and wherein the sheet is obtained by the process of any one of embodiments 45 to 92.

[0258] 99. In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash-spun plexifllamentary fibrils comprised of a high-density polyethylene, wherein the sheet has a basis weight from about 55 g / m- to about 65 g / m2, an average tensile strength from about 85 N to about 110 N, a handle-o-meter stiffness from about 300 mN to about 1000 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight) ', in jNm' .g . to the tensile strength, normalized to basis weight, in Nm2 / g, from about 0.2 to less than about 2.0, and wherein the sheet is obtained by the process of any one of embodiments 45 to 92. 100. in some embodiments the present application provides a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils comprised of a high-density polyethylene, wherein the sheet has a basis weight from about 75 g / m2to about 85 g / m2, an average tensile strength from about 120 N to about 170 N, a handle-o-meter stiffness from about 500 mN to about 1400 mN, and a ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2 / g, from about 0.2 to less than about 2.0, and wherein the sheet is obtained by the process of any one of embodiments 45 to 92.

[0259] 101. A multilayer structure comprising at least one sheet according to any one of embodiments 1 to 44 or any one of embodiments 93 to 100 and at least one further sheet or film

[0260] 102. The multilayer structure of embodiment 101 wherein the at least one further sheet is a spunbonded nonwoven sheet or a sheet of thermoplastic reinforcing grid material.

[0261] 103. Use of the sheet of any one of embodiments 1 to 44 or any one of embodiments 93 to WO for preparing a multilayer structure 104. Use of a sheet of any one of embodiments 1 to 44 orany one of embodiments 93 to

[0262] 100 or of the multilayer structure of any one of embodiments 101 to 102 for the production of garment or protective apparel.

[0263] 105. , Use of a sheet of any one of embodiments I to 44 or any one of embodiments 93 to

[0264] 100 or of the multilayer structure of any one of embodiments 101 to 102 for the production for the production of roof lining.

[0265] 106. An article comprising a sheet of any one of embodiments 1 to 44 or any one of embodiments 93 to 100 or of the multilayer structure of any one of embodiments 101 to 102.

[0266] 107. The article of embodiment 106, wherein the article is selected from garment, protective apparel, medical wrap, house wrap, roof lining, or car cover.

Claims

CLAIMS1. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having ; (a) a basis weight from about 50 g / m2to about 85 g / m2,(b) a tensile strength from about 40 N to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and(c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in itNm' 7g\ to the tensile strength normalized to basis weight in Nm / g, is below about 2.30* 2. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having(a) a basis weight tom about 43 g / m2to about 85 g / m2,(b) a tensile strength from about 40 N to about 250 M wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and(c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the handle-o-meter stiffness, normalized to (basis weight)3, is below about 5.0 μNm6 / g3.:

3. The sheet of any one of claims 1 to 2 having a BET surface area of about 4 m2 / g to 10 m2 / g, or having a total crystallinity index of about 62 % to about 72 %.

4. The sheet of any one of claims 1 to 3 having a tensile strength from about 60 N to about 250 N, or having a thickness from about 140 pm to about 300 pm5. The sheet of any one of claims 1 to 4 having a handle-o-meter stiffness from about 150 mN to about 1400 mN.

6. The sheet of any one of claims 1 to 5, wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm3 / g, is between about 0.2 about 2.

0.

7. The sheet of any one of claims 1. to 6, wherein the flash-spun plexifilamentary fibrils are comprised of a polyolefin, selected from the group of polyethylene (PE), polypropylene (PP), and blends / mixtures thereof, or wherein the flash-spun plexifilamentary fibrils are comprised of a polyolefin which is a high-density polyethylene (HDPE), a blend of a high- density polyethylene (HDPE) with a linear low-density polyethylene (LUDPE), or a blend of a high-density polyethylene (HOPE) with a low-density polyethylene (tDPE).8 A process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps of:(I) generating a spin fluid comprising (a) from about 8 to about 14 weight percent of a polymer, based on the total amount of the spin fluid, and(b) a spin agent comprising a chlorine-containing solvent, selected from dichloromethane, cis-1 ,2-dichloroethylene and trans-1 ,2-dichloroethylehe, in combination with a fluorine-containing solvent, (ii) flash spinning the spin fluid at a temperature at or above about 190°C and at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form piexifilamentary fibrils of the polymer,(iii) collecting the plexifilamentary fibrils of the polymer on a collecting means as a sheet of nonwoven flash-spun plexifilamentary fibrils 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, wherein the sheet is bonded over about 6 % to about 85 % of at least one surface of the sheet.

9. The process of claim 8, wherein the process further comprises mechanically softening the bonded sheet,10. The process of any one of claims 8 to 9, wherein the polymer is a polyolefin, selected from the group of polyethylene (PE), polypropylene (PP), and blends / mixtures thereof, or wherein the polyolefin is a high-density polyethylene (HDPE), a blend of a high-density polyethylene (HDPE) with a linear low-density polyethylene (LLDPE), or a blend of a high- ; density polyethylene (HDPE ) with a low-density polyethylene (LDPE).

11. The process of any one of claims 8 to 10, wherein the spin agent consists essentially of dichloromethane in combination with perfluoropentane, perfluorohexane, 1. 1 , 1 3.3- pentafluorobutane, 1H,4H-perfluorobutane, 2H.3H-decafluoropentane. 1H.6H- perfluorohexane, or 1 H-perfluorohexane.

12. The process of any one of claims 8 to 11, wherein the obtained sheet has(a) a basis weight from about 50 g / m2to about 85 g / m2,(b) a tensile strength from about 40 to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and(c) a handle-o-meter stiffness from about 150 mN to about 1500 mN, wherein the ratio of the handle-o-meter stiffness, normalized to (basis weight)3, in μNm6 / g3, to the tensile strength, normalized to basis weight, in Nm2^, is below about2.30, or wherein the obtained sheet has(a) a basis weight from about 43 g / m2to about 85 g / m2, (b) a tensile strength from about 40 to about 250 N, wherein the tensile strength is the average of the tensile strength in the machine direction (MD) and the tensile strength in the transverse direction (XD), and;(C) a handle-o-meter stiffness from about 150 mN to about 1500 mN. wherein the handle-o-meter stiffness, normalized to (basis weight)3, is below about 5.0 μNm6 / g3.

13. A sheet of nonwoven flash-spun plexifllamentary fibrils obtainable by the process of any one of claims 8 to 12. 14.;A multilayer structure comprising at least one sheet according to any one of claims 1 to 7 or 13 and at least one further sheet or film.

15. The multilayer structure of claim 14, wherein the at least one further sheet is a spunbonded nonwoven sheet or a sheet of thermoplastic reinforcing grid material16. Use of the sheet of any one of claims 1 to 7 or 13 for preparing a multilayer structure.

17. Use of a sheet of any one of claims 1 to 7 or 13 or of the multilayer structure of claim 14 or 15 for the production of garments or protective apparel.

18. Use of a sheet of any one of claims 1 to 7 dr 13 or of the multilayer structure of claim14 or 15 for the production of roof linings.

19. An article comprising a sheet of any one of claims I to 7 or 13 or a multilayer structure of claim 14 or 15.

20. The article of claim 19, wherein the article is selected from garments, protective apparel, medical wraps, house wraps, roof linings, or car covers.

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