Wind-tight flash-spun sheet

Abstract

The present invention relates to (i) a bonded sheet of nonwoven flash-spun plexifilamentary fibrils exhibiting high liquid barrier properties, a high level of air-tightness, a high degree of softness, and good mechanical strength, (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] .TITLE

[0002] WIND-TIGHT FLASH-SPUN SHEET

[0003] FIELD OF THE INVENTION The present invention relates to (i) a bonded sheet of nonwoven flash-spun piexifilamentary fibrils exhibiting high liquid barrier properties, a high level of air-tightness, a high degree of softness, and good mechanical strength, (ii) a process for the preparation of a bonded sheet of nonwoven flash-spun piexifilamentary fibrils, and (iii) a multilayer sheet structure and an article comprising the bonded sheet of nonwoven flash-spun piexifilamentary fibrils.

[0004] BACKGROUND

[0005] Fabrics used in the construction industry, such as in house wrap, roofing underlay , and roof lining applications are often composite fabrics wherein one or more relatively porous nonwoven sheets provide mechanical strength and one or more further barrier sheets, films, or coatings prevent transmission of liquid water through the structure:while allowing a controlled level of air permeability and moisture vapor permeability. Sheets or films used to provide the water barrier properties to the composite fabric are typically microporous films or layers made from moisture vapor permeable polymers such as thermoplastic polyurethane, and these are necessarily thin and therefore have poor mechanical properties. Nonwoven sheets used to provide mechanical strength to the composite fabric are typically spunbonded sheets, and it is common for the fragile barrier layer to be protected by sandwiching it between two nonwoven sheets. To prevent water ingress where separate sheets of composite fabric are joined in a wall or roof structure, the joints are usually taped using an adhesive tape. This taping of joints between adjacent sheets of composite fabric frequently has to be corrected during mounting, and composite fabrics of the prior art sometimes have the disadvantage that they do not remain fully intact when the adhesive tape is removed to allow the composite sheet to be re-positioned. Moreover, such composite fabrics often have an unsatisfying balance ofbreathability, strength, and liquid barrier properties for some types of construction in Certain climatic conditions.

[0006] Prior art fabrics for .protective apparel are often a composite fabric wherein a microporous film or other water vapor permeable film is laminated to a nonwoven sheet. The microporous film provides the barrier properties to the composite fabric, especially barrier to liquid penetration, and the nonwoven sheet provides the strength of the composite fabric. While the use of a film provides:a I i quid impermeable barrier, the breathability' of such films is insufficient to provide a comfortable protective garment. Composite fabrics constructed from a microporous film tn combination with a nonwoven sheet provide a balance of breathability, barrier properties to liquids, and strength, but the property balance of prior art composite fabrics for apparel is often insufficient in one or more aspects, A particular weakness of some prior art composite fabrics for protective apparel is that the microporous film laminated to the surface of the nonwoven fabric is relatively thin and mechanically weak such that the composite fabric has insufficient surface robustness for use in more severe use environments.

[0007] Flash-spun nonwoven sheets, such as Tyvek® nonwoven sheets, have been developed with wide-ranging properties suitable for use in a variety of applications, including, but not limited to, applications in construction industry and as protective apparel. 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 nonwoven 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- method for producing flbrils 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 ofthe 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

[0008] US 3,081,519 and US 3,227,794.

[0009] 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

[0010] 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 heM and pressure over the entire surface versus using paterned rolls to apply heat and pressure locally over only a portion of the surface to torm an embossed pattern in the final nonwoven sheet

[0011] 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 roof lining applications creating noise due to wind movement The obtained nonwoven sheet product also has a low to medium level of air tightness, meaning that it is too air-permeable for roof lining applications. US 5,972,147 describes thermal bonding using a thermal calendar bonder applying high compression forces; The process tends to produce a product having a medium to high level of air tightness but being too stiff and fooisy" for roof lining applications. The obtained nonwoven sheet product also has a low opacity, which is not desirable as this may compromise the printability of the nonwoven sheet.

[0012] 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 paterns, such as a point patern as described in US 3,478,141, US 6,610, 390, and US 2004 / 241399 A1 , a rib patern as described in US 2003 / 0032355 A1:and US 2003 / 00165667 A1 , a linen pattern or a random patern 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 parttally 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 toll. In addition, the norwoven sheet may be in contact with one or more pre-heat or cooling tolls before and ater passing through each pair of embossing and back-up rolls, in a configuration as desorbed in US 5,972,147. US 6,034,008 and US 2003 / 00165667 AT 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 However these prior art bonding processes with embossing roils tend to produce a nonwoven sheet having a more fragile surface

[0013] Thermal bonding impacts different properties of the nonwoven sheet in different ways.

[0014] 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-like regions which allow very little flux. 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.

[0015] ;Mechanical properties such as delamination resistance, puncture and tear resistance, nail tear resistance and tensile strength may increase or decrease, as the degree of bonding increases. However, the stronger connections between fibrils resulting from bond! ng, and the limitation of their ability to move relative to each other, increases the stiffness of the bonded sheet and tends to negatively affect the flux properties of the bonded sheet.

[0016] 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.

[0017] 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.

[0018] 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 ofthe nonwoven sheet as ittravels over them, creating a rutfoing effect.

[0019] US 5,966,785 and US 6.195.854 report a mechanical softening process where the nonwoven sheet is passed through the nip of a knobbed roil against a soft rubber backup roll However, no information is given in these documents on how this process impacts the barrier properties of the nonwoven sheet.

[0020] 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.

[0021] 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 surface speed as the nonwoven sheet. The nonwoven sheet is required to have an elongation of at least TO % tor the process to work correctly.

[0022] WO 2020 / 026062 A1 describes a process that includes a type of mechanical softening of a nonwoven sheet known as relofting. The term "relofting ' denotes a post-processing step that increases the toft (i.e. , lowers the solidity) of a bonded nonwoven sheet. The nonwoven sheets are made from melt spun or melt blown fibers and are potentially charged. According to the document, relofting reduces the pressure drop of a nonwoven sheet while having a negligible effect on its filtration efficiency when the nonwoven sheet has a solidity of below 8%, but when the nonwoven sheet has a solidity of 10 % or higher, relofting causes the filtration efficiency to decrease significantly. Therefore, the process described in this document is limited to open structures designed for filtration and cannot be used for sfructures having a high solidity that require good liquid barrier properties

[0023] An ideal nonwoven sheet for use in roof lining applications should have good mechanical properties such as high tensile strength and high nail tear resistance, and be resistant to liquid penetration while providing moisture vapor transport and high level of air tightness High levels of air tightness are also desirable for garment applications where windtightness is important)

[0024] It is also preferable that the nonwoven sheet has low stiffness and a soft texture so that it does not generate excessive noise due to wind movement or provide noticeable resistance to the wearer’s movements. While flash-spun sheets have demonstrated a good variety of desired properties, there has been a trade-off required between the desired barrier, breathability, and mechanical properties Therefore, there is a need for flash-spun sheets for use in construction applications such as roof lining or house wrap applications, or in garment applications, that provide improved air tightness and mechanical properties of the nonwoven sheet without sacrificing barrier properties and protection or creating too much noise in use.

[0025] SUMMARY OF THE INVENTION

[0026] In one embodiment, the invention is directed to a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0027] (a) a basis weight from about 38 g / m2to about 115 g / m2,

[0028] (b) a Gurley Hill porosity of about 200 seconds or more,

[0029] (c) a hydrostatic head of about 150 cmHzO or more,

[0030] (d) a handle-o-meter stiffness of about 04 N or more, and

[0031] (e) an opacity of more than about 93 %.

[0032] In a f urther 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: (i) generating a spin fluid comprising

[0033] (a) from about 12.5 to about 15 weight percent of a polymer, based on the total amount of the spin fluid, and

[0034] (b) a spin agent comprising a chlorine-containing solvent, selected from dichloromethane, cis-1 ,2-dichloroethyiene and trans-1 ,2-dichloroethylene, in combination with a fluorine-containing solvent,

[0035] (ii) flash-spinning the spin fluid at a temperature of above about 185OC 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,

[0036] (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

[0037] ( i v) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet.

[0038] DETAILED DESCRIPTION

[0039] Definitions of Terms and Test methods

[0040] Before addressing details of embodiments, some terms and test methods are defined or clarified. Unless otherwise mentioned , all tests were carried out without pre-conditioning of the samples. When average values are indicated herein, this refers to the arithmetic average.

[0041] Basis weight is determined according to EN 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.

[0042] Gurley Hill porosity (sometimes also referred to as “Gurley Porosity”) is a measure of the permeability of the sheet for gaseous materials. In particular, it is a measure of how long it takes a volume of gas to pass through an area of the sheet wherein a certain pressure gradient exists. Gurtey-Hili porosity is determined in accordance with TAPPI T-460 OM-88 (2006) using a Loreritzen & Wettre Model SB 166 or 516 from Lorentzen & Wettre, Kista, Sweden. This test method measures the time required for 100 cubic centimeters (cm3) of air to be pushed through a 28.7 mm diameter sample having an area of 6.54 cm2 (one square inch) under a pressure of approximately 1.21 kPa (4.9 inches) of water. The Gurley Hill porosity reported herein is expressed in seconds and represents an average of at least twelve individual measurements. The reported value represents an average of at least 12 individual measurements. The tower the Gurley Hill porosity, the greater the air permeability of the sheet. Particle filtration efficiency (PFE) is a measure of the relative amount, expressed in percent, of particulates which are retained by a material at given conditions and particle penetration is a measure of the relative amou nt, expressed in percent, of particulates which pass through a material at given conditions. Particle filtration efficiency (PFE) is determined by measuring the particle penetration and is calculated as 100 < minus the particle penetration. Herein particle penetration is measured on the TSI 8130 equipment form TSI Incorporated, Shoreview, MN, United States. 'The TSI 8310 is an equipment used for measurement according to US 42 GF 84 (2004), NIOSH Procedures No. RCT-APR-STP-57, 58, and 59. For determining the particle filtration efficacy of the bonded sheet described herein, the TSI 8130 equipment is used with a sodium chloride particle generation at a flow rate of 2.3 liter per minute. The sodium chloride particle distribution has a count median diameter of 0.075 pm, a mass mean diameter of 0.3 pm, and a geometrical standard deviation of 1.8 A volumetric flow rate of 2.3 L / min corresponds to a face velocity of 0.4 cm / s, which is representative of typical air flow:conditions that the bonded sheet faces when used in a protective garment. In order to achieve a flow rate of 2.3 liter per minute, the control valve is closed and the air flow results from the air through the downstream photometer only. Measurements are performed with a rise time of 25 seconds and a measurement time of 4 seconds. The particle penetration in percent is measured based on the difference in light intensity by an upstream and downstream photometer, The pressure drop over the sample is recorded in mm of water column. The maximum pressure of the TSI 8130 equipment is 110 mm of water column. The particle penetration and the particle filtration efficiency reported herein is an average of at least 12 measurements.

[0043] The particle penetration is additionally expressed as the logarithmic reduction value (LRV) based on the following formula

[0044] LRV = -logw10(penetration[%] / 100)

[0045] A higher LRV and PFE represent a higher particle barrier of the tested material.

[0046] 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. A lower Handle-o-meter stiffness value refers to a softer sheet.

[0047] The hydrostatic head is a measure of the resistance of a sheet to penetration by liquid water under a static load. Herein the hydrostatic head is determined based on AATCC 127 (2018). The hydrostatic head is reported in cm of water column. The hydrostatic head is measured on:a FX 3000 HydroTester III from TexTest AG, Schwerzenbach, Switzerland. Water in contact with one side of a 102.6 cm2section of a sample is pressurized at a rate of 60 + / - 3 cmH20 / min until three areas of the sample are penetrated by the water. The reported hydrostatic head is the average of at least 6 individual measurements. A higher hydrostatic head value refers to a sheet having a higher resistance to water penetration, that is having a lower water permeability. For a laminated product, the surface of the sheet with the barrier function is the surface in contact with the water for measurement

[0048] The moisture vapor transmission rate (MVTR) is measured according to EN ISO 12572 (2001), "Hygrothermal performance of building materials and products, Climate C”, using a Gintronic Gravitest 6400 with an ES 420A balance from MRS Seitter, Lenning-Bruck, Geimany. The following settings are applied. The measurement is performed at 23°C with a relative humidity of 100 % in the cups, and an air flow above the samples of test material of 2.5 m / s at a relative humidity of 50 and using a measurement interval of 30 minutes. A method using multiple layers of the test material is used to eliminate the impacts of the air layer above the water in each cup and of the boundary layer above each sample of test material.

[0049] Five test cups are each filled with water to a height of 15 mm from the top. Two of the test cups are then closed using one layer of test material, one of the test cups is closed using two layers of test material, and the two remaining test cups are closed with three layers of test material. The test is then performed with the five test cups in the same insfrument at the same time. The weights of the test cups are monitored until the rate of weight loss from each test cup Stabilizes to Within +A5 % during 5 successive measurements. The rate of weight loss is then divided by the upper cross-sectional area of the test cup through which water vapor has diffused to give a water vapor transmission rate per cup (WDD in g / m? / day), and the total resistance to the water vapor diffusion (Sd. in cm of equivalent air layer thickness) for each cup is calculated using the formula:

[0050] Sd = 236600 / WDD

[0051] The Sd values for each cup are then plotted against the number of layers of test material used for that cup and the slope of a line through the points is determined by linear regression. This slope (SDML) represents the incremental increase in water vapor diffusion resistance created by adding one layer of test material. This is then converted back to a moisture vapor transmission rate for one layer of test material by performing the reverse calculation:

[0052] MVTR = 236600 / SDML The reported value is for one measurement, which inherently averages the property for ten individual samples of test material.

[0053] Nail tear resistance is tested according to EN12310-1 (1999), “Flexible sheets for waterproofing - Part 1 : Bitumen sheets for waterproofing - Determination of resistance to tearing (nail shank)", modifiedfor sample preparation before testing as per EN13859-1 (2010) and EN 13859-2 (2010). It measures the resistance of a material to tearing when stretched near a nail hole. The gauge length between the clamp and the hail is 11 cm and the test speed is 10 cm / min. The result is the maximum force measured. Nail tear resistance is reported as the average of the nail tear resistance in the machine direction (MD) of the sheet and of the nail tear resistance in the cross direction (XD) of the sheet. The reported nail tear is the average of at least 6 individual measurements in machine or cross direction.

[0054] BET surface area is measured by the BET nitrogen absorption method of S. Brunauer, P. H. Emmet and E. Teller, J. Am. Chem. Soc., V. 60 p 309-319 (1938) based on 5 equidistant relative pressures between 0.1 to 0.26 and is reported as mz / g. The samples measured have a total surface area above 2 m2. BET surface area is measured using a Quantachrome model NOVA 3000e from Quantachrome GmbH, Odelzhausen, Germany. Performance of the equipment is verified by using a standard aluminum oxide sample (3P-SRFS86) having a BET 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 1 or 2 measurements.

[0055] The trapezoidal tear strength (also referred to as trapezoid tearing strength) is a measure of the tear resistance of a fabric. The trapezoidal tear strength is measured according to EN ISO 9073-4 (1997) and is expressed in newton (N). The average trapezoidal tear strength is reported as the average of the trapezoidal tear strength in the machine direction (MD) of the sheet and of the trapezoidal tear strength in the cross direction (XD ) of the sheet. The reported trapezoidal tear in either direction is an average of at least 12 measurements. The trapezoidartear strength of a sample tends to increase proportionally with basis weight. Thus, the trapezoidal tear strength can be normalized by dividing it by the actual basis weight. Tensile strength is a measure of the b making strength of a fabric when subjected to unidirectional stress. Tensile strength is determined by the methods according to EN ISO 12311-1 (1999) "Flexible sheets for waterproofing - Part 1 : Bitumen sheet for roof waterproofing - Determination of tensile properties”, modified for sample preparation before testing as per EN13859-1 (2010) and EN13859-2 (2010), for folded samples with a width of 100 mm according to Annex A. Results are reported in newtons / 50 mm sample width (N / 50mm). 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 at least 6 measurements in the cross direction (XD). ; ; Opacity is tested according to ISO 2471 (1998), *Paper and board - Determination of opacity (paper backing) - Diffuse reflectance method", using a Konica Minolta CR-410 Chroma Meter from Konica Minolta Sensing Europe B.V.* Diegem, Belgium. The measurement area is 50 mm in diameter and the illuminated area is 53 mm in diameter, a Konica Minolta OF? A44 white reference plate is used as a backing for the specimen to determine its 100% reflectance intensity and a black optical cavity is used as a backing for the specimen during the measurement. The reported opacity is the average of at least 12 individual measurements.

[0056] Optical density is the logic of the ratio of the intensities of incident and transmitted light passing through a sample. It is measured in accordance with ANSI PH2.1986 using an X-Rite 361T Tabletop Transmission Densitometer, from X-Rite Europe GmbH, RegensdOrf,

[0057] Switzerland, which measures a circular field of view of approximately a 5-mm diameter. Reported values are the average of twelve measurements.

[0058] Emissivity is a dimensionless property which describes the heat absorbance and reflectance characteristics of a surface. It is measured in accordance with ASTM Standard C1371-04a (2010) using a Model AE D&S Emissometer from Devices and Services Co. ,

[0059] Dallas, Texas, USA. Reported values are the average of twelve measurements

[0060] The crystallinity index is determined as follows. A diffractometer in reflection 0-20 Bragg-Brentaho geometry fitted with a Cu-Kc, x-ray tube source with wavelength of 1.54 A and a 1-dimensional detector. A parabolic mirror with a 1 / 16° fixed 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-Kg filter are employed on the diffracted side before the detector. Each sample is 32 mm in diameter are 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.

[0061] The method used for 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 ST. 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 20 of the orthorhombic and monoclinic peaks can vary by about + / - .15° due to instrumental differences, sample height / texture and material nature.

[0062] 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.

[0063] 2. A local linear background, drawn from 20 - 13±O.5° to 28±0.5° in scattering angle, is subtracted. 3. The amorphous portion of the pattern is fited using two Gaussian peaks which are required to touch the data points in the ranges of [15.0“ to 18.65 J, [22.65;to 22.75 ], and [25.2° to 28°] 20 and which are centered around 18.1 ° and 21.6° 2o, with peak full widths at half maximum (FWHM) of 4°-5° to give a total integrated intensity lamorpna®.

[0064] 4. The total amorphous portion is then subtracted from the full pattern.

[0065] 5. The remaining intensity is assumed to be crystalline in nature, belonging to the orthorhombic or monoclinic phases, and is fitted with the following peaks having respective integrated intensities:

[0066] 1) Orthorhombic 110 peak: 21 .55°, Pearson VII peak shape, tw

[0067] 2) Orthorhombic 200 peak: 23.8t, Pearson VII peak shape, I200.es.

[0068] 3) Additional peak to fit asymmetry of die orthorhombic 1 io peak* 21 ,0°, Pearson VI I peak shape. h WA. The subscript “A” stands for asymmetric.

[0069] 4) Monoclinic 010 peak: 19.54 Pearson VII peak shape,

[0070] 5) Monoclinic 200 peak: 23.1°, Pearson VII peak shape haw.

[0071] 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.

[0072] 6 The total crystallinity 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: crystallinity

[0073] Accordingly, the partial crystallinity indices Clorthoorhombicand Clmonoclinicare calculated respectively from these expressions

[0074] Melting temperature is determined by differential scanning calorimetry, following the guidance provided in ASTM 03418 (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 sinning calorimetry). For polyethylene, heating and cooling is performed under inert gas at a rate of 10°C / 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.

[0075] 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 F262S (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°C / 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,

[0076] 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 melt flow rates of other polyolefins are performed at different temperatures as specified in ISO 1133

[0077] Density is determined according to the method described in ISO 1183 (Plastics - Methods for determining the density of non-cellular plastics).

[0078] The term “polymer* 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 a 11 possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and random symmetries.

[0079] 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 5 units. One useful polyethylene is high-density polyethylene which has a melting temperature of about 123*0 to about 140*0, 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*0 / 2160 grams) of between 0.1 g / IOmin and 100 g / IOmin, preferably less than 4 g / IOmin.

[0080] The term ‘polypropylene’’ is intended to embrace not only homopoly mers of propylene io but also copolymers and terpolymers where at least 85 % of the recurring units are propylene units. Furthermore, unless otherwise specifically limited, the term '‘polypropylene*’ shall include all possible geometrical amfigurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and random symmetries.

[0081] The term "polymer type” refers to the chemical class into which the polymer falls, for 15 example, polyethylene, polypropylene, etc.

[0082] 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 plexifilamentary structures, the fibrils are generally coextensively aligned with the longitudinal axis of the structure, and they intermitently unite and separate at irregular 20 intervals in various places throughout the length, width, and thickness of the structure to form a continuous three-dimensional network or web.

[0083] 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 25 scavengers.

[0084] 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

[0085] The term "cloud point pressure” refers to the pressure at which, at constant temperature, a clear single phase spin fluid transitions from a clear solution te a cloudy, two- 30 phase dispersion. At the cloud point pressure, a clear spin fluid becomes turbid.

[0086] Atmospheric pressure means 101.325 kPa. Essentially atmospheric pressure means 101.325 kPa ± 5 %.

[0087] The hardness of the rubber is determined based on PIN ISO 7619-1 (2010) - Rubber, vulcanized or thermoplastic - Determination of indentation hardness - Part 1: Durometer as method (Shore hardness). The hardness is reported in Shore A.

[0088] . As used herein, the singular forms "a," "an,” and “the" include the 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 tom 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. Ail ranges are inclusive and combinable.

[0089] Bonded Sheet of Nonwoven Flash-spun Plexifilamentary Fibrils

[0090] Provided herein is a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0091] (a) a basis weightfrom about 38 g / m2to about 115 g / m2,

[0092] (b) a Gurtey Hill porosity of about 2Q0 seconds or more,

[0093] (c) a hydrostatic head of about 150 cmHaO or more,

[0094] (d) a handle-o-meter stiffness of about 0.3 N or more, and

[0095] (e) an opacity of more than about 93 %.

[0096] The thermally bonded sheet described herein exhibits a desired combination of moderate to high basis weight, low air-permeability, medium to high hydrostatic head, medium to low stiffness, and high opacity.

[0097] In some embodiments, the thermally bonded sheet described herein has

[0098] (a) a basis weight from about 55 g / m2to about 115 g / m2,

[0099] (b) a Guriey Hill porosity of about 300 seconds or more,

[0100] (c) a hydrostatic head of about 195 cmHjO or more,

[0101] (d) a handle-o-meter stiffness of about 0.5 N or more, and

[0102] (e) an opacity of more than about 96 %.

[0103] Such bonded sheets are particularly suitablefor roof lining applications, without being limited thereto.

[0104] In other embodiments, the thermally bonded sheet described herein has

[0105] (a) a basis weight from about 38 ^m2to about 52 g / m2,

[0106] (b) a Gurley Hill porosity of about 200 seconds or more,

[0107] (c) a hydrostatic head of about 150 cmHjO or more,

[0108] (dj a handle-o-meter stiffness from about 0,3 N to about 0.6 N, or a handle-o-meter stiffness from about 0.3 N to about 0,45 N

[0109] (eT an opacity of more than about 93 or an opacity of more than 94 % or more or an opacity of 95 % or more, and

[0110] (f) a particle filtration efficiency of about 99 5 % or more. Such bonded sheets are particularly / suitable for protective apparel applications, without being limited thereto.

[0111] In some embodiments, the bonded sheet has a basis weight from about 55 g / m2to about 115 g / m2, and in other embodiments, the bonded sheet has a basis weight from about:75 g / m2to about 100 g / m2. In some embodiments, the bonded sheet has a basis weight from about 55 g / m2to about 65 g / m2, in other embodiments, the bonded sheet has a basis weight from about 75 g / m2to about 90 g / m2, and in other embodiments, the bonded sheet has a basis weight from about 105 g / m2to about 115 g / m2. Such bonded sheets are particularly suitable for roof lining applications, without being limited thereto.

[0112] In / some embodiments, the bonded sheet has a basis weight from about 38 g / m2to about 52 g / m2, and in other embodiments, the bonded sheet has a basis weight from about 40 g / m2to about 50 < g / m2. Such bonded sheets are particularly suitable for garment applications, witoout being limited thereto. In some embodiments, the bonded sheet has a Gurley Hill porosity from about 200 seconds to about 10,000 seconds, and in other embodiments, the bonded sheet has a Gurley Hill porosity from about 200 seconds to about 1000 seconds, in some embodiments, the bonded sheet has a Gurley Hill porosity of about 300 or more, in other embodiments, the bonded sheet has a Gurley Hill porosity from about 300 seconds to about 10,000 seconds, in other embodiments, the bonded sheet has a Gurley Hill porosity from about 400 seconds to about 8000 seconds, and in other embodiments, the bonded sheet has a Gurley Hill porosity from about 500 seconds to about 7000 seconds. In some embodiments, the bonded sheet has a Gurley Hill porosity from about 300 seconds to about 4000 seconds, in other embodiments, the bonded sheet has a Gurley Hill porosity from about 300 seconds to about 3000 seconds, and in other embodiments, the bonded sheet has a Gurley Hill porosity from about 1200 seconds to about 7000 seconds or from about 3000 seconds to about 7000 seconds.

[0113] In some embodiments, the bonded sheet has a hydrostatic head from about 150 cmHzO to about 450 cmHzO. In some embodiments, the bonded sheet has a hydrostatic head of about 195 cmHsO or more, in other embodiments, the bonded sheet has a hydrostatic head from about 195 cmH2O to about 400 cmH2O, in other embodiments, the bonded sheet has a hydrostatic head from about 195 cmHaO to about 350 cmH2O, in other embodiments, the bonded sheet has a hydrostatic head from about 195 cmH2O to about 300 cmH2O, and in other embodiments, the bonded sheet has a hydrostatic head from about 300 cmHaO to about 450 cmbhO. Bonded sheets sheet having a hydrostatic head of about 195 cmHzO or more are particularly suitable for roof lining applications, without being limited thereto. In some embodiments, the bonded sheet has a hydrostatic head from about 150 cmHaO to about 200 cmHaO. Such bonded sheets are particularly suitable for garment applications, without being limited thereto.

[0114] In some embodiments, the bonded sheet has a handle-o-meter stiffness from about 0.3 N to about 4.0 N, and in other embodiments, the bonded sheet has a handle-o-meter stiffness tom about 0.3 N to about 3.5 N. In some embodiments, the bonded sheet 'has . a handle-o-meter stiffness of about 0.3 N to 2.0 N, in other embodiments, the bonded sheet has a handle-o-meter stiffness from about 0.3 N to about 1.5 N, and in other embodiments, the bonded sheet has a handle-o-meter stiffness from about 1.O N to about 3.5 N. Bonded sheets having a handle-o-meter stiffness from about 0.4 N to about 4.0 N are particularly suitable for roof lining applications, without being limited thereto. In some embodiments, the bondedsheet has a handle-o-meter stiffness of about 0.3 N to about 0.6 N or about 0.4 N to about 0.6 N or about 0.3 N to about 0.45 N. Such bonded sheets are particularly suitable for garment applications, without being limited thereto.;

[0115] In some embodiments, the bonded sheet has an opacity from about 93 % to about 99.5 %, in other embodiments, the bonded sheet has an opacity from about 94 % to about 99.5 % , in other embodiments, the bonded sheet has an opacity from about 95 % to about 99.5 %, in other embodiments, the bonded sheet has an opacity from about 94 % to about 97 % and in other embodiments, the bonded sheet has an opacity from about 95 % to about 97 . In some embodiments, the bonded sheet has an opacity of more than about 96 %, in other embodiments, the bonded sheet has an opacity from about 96 % to about 99 %.

[0116] In some embodiments, the bonded sheet has a total crystallinity index of less than 73 %, and in other embodiments, the bonded sheet has a total crystallinity index from about 63 % to about 73 %. In some embodiments, the bonded sheet has a total crystallinity index from about 65 % to about 73 %, and in other embodiments, the bonded sheet has a total crystallinity index from about 67 % to about 73 % In some embodiments, the bonded sheet has a total crystallinity index of less than 72 %, in other embodiments, the bonded sheet has a total crystallinity index from about 63 % to about 72 %. and in other embodiments, the bonded sheet has a total crystallinity index from about 67 % to about 72 %. In some embodiments, the total crystallinity index may have a contribution from the orthorhombic and the monoclinic crystalline phase.

[0117] In some embodiments, the bonded sheet has a BET surface area from about 4 m2 / g to about 11 m2 / g, in other embodiments, the bonded sheet has a BET surface area from about 7 m2 / g to about 11 m2 / g, and in other embodiments, the bonded sheet has a BET surface area from about 4 m2 / g to about 7 m2 / g. In some embodiments, the bonded sheet has a moisture vapor transmission rate

[0118] (MVTR) of about 100 g / mWday or more, m other embodiments, the bonded sheet has a MVTR of about 100 g / mz / day to about 1500 g / m^ay, and in other embodiments, the bonded sheet has a MVTR of about 100 g / m2 / day to about 1000 g / m2 / day. In some embodiments, the bonded sheet has a MVTR of about 250 g / m2 / day to about 1500 g / mT / day, in other embodiments, the bonded sheet has a MVTR of about 250 g / m^day to about 1000 g / m^day, and in other embodiments, the bonded sheet has a MVTR of about 100 g / m2 / day to about 700 g / m2 / day. In other embodiments, the bonded sheet has a MVTR of about 100 g / m2 / day to about 500 g / m2 / day.

[0119] In some embodiments, the bonded sheet has a particle filtration efficiency of about 99.5 % or more, In other embodiments, the bonded sheet has a particle filtration efficiency from about 99.5 % to about 99.99 %, and in other embodiments, the bonded sheet has a particle filtration efficiency from about 99.7 % to about 99.99 %.

[0120] In some embodiments, the bonded sheet has an average trapezoidal tear strength from about 20 N to about 60 N, in other embodiments, the bonded sheet has an average trapezoidal tear strength from about 28 N to about 60 N, in other embodiments, the bonded sheet has an average trapezoidal tear strength from about 30 N to about 45 N, in other embodiments, the bonded sheet has an average trapezoidal tear strength from about 45 N to about 60 N, and in other embodiments, the bonded sheet has a trapezoidal tear strength from about 35 N to about 55 N. In some embodiments, the bonded sheet has an average trapezoidal tear strength from about 20 N to about 30 N. In some embodiments, the bonded sheet has a trapezoidal tear strength in the machine direction (MD) which is about 80 % to about 120 % of the trapezoidal tear strength in the transverse direction (XD).

[0121] In some embodiments, the bon sheet has an average nail tear resistance from about 25 N to about 140 N, in other embodiments, the bonded sheet has an average nail tear resistance from about 50 N to about 140 N, in other embodiments, the bonded sheet has an average nail tear resistance from about 50 N to about 90 N, in other embodiments, the bonded sheet has an average nail tear resistance from about 90 N to about 140 N, and in other embodiments the bonded sheet has an average nail tear resistance from about 60 N to about 100 N. In some embodiments, the bonded sheet has an average nail tear resistance from about 25 N to about 60 N. In some embodiments, the bonded sheet has an average nail tear resistance in the machine direction (MD) which is about 80 % to about 120 % of the nail tear in the transverse direction (XD). in some embodiments, the bonded sheet has an average tensile strength from about 70 N to about 500 N, in other embodiments, the thermally bonded sheet has an average tensile strength from about 100 N to about 450 N, in other embodiments, the thermally bonded sheet has an average tensile strength from about 100 N to about 280 N, in other embodiments, the thermally bonded sheet has an average tensile strength from about 280 N to about 450 N, and in other embodiments, the thermally bonded sheet has an average tensile strength from about 150 N to about 250 N. In some embodiments, the bonded sheet has an average tensile strength from about 70 N to about 100 N. In some embodiments, the bonded sheet has a tensile strength in at least one direction, selected from the machine direction (MD) and the transverse direction (XD), from about 60 N to about 550 N, in other embodiments, the bonded sheet has a tensile strength in at least one direction, selected from the machine direction (MD) and the transverse direction (XD), from about 60 N to about 500 N, in other embodiments, from about 80 N to about 500 N, and in other embodiments, from about 100 N to about 350 N. In some embodiments, the bonded sheet has a tensile strength in at least one direction, selected from the machine direction (MD) and the transverse direction (XD), from about 60 N to about 120 N. In some embodiments, the bonded sheet has a tensile strength in the machine direction (MD) which is about 60 % to about 140 % of the tensile strength in the transverse direction (XD ), in other embodiments, the bonded sheet has a tensile strength in the machine direction (MD) which is about 70 % to about 130 %, in other embodiments, the bonded sheet has a tensile strength in the machine direction (MD) which is about 80 % to about 120 % , in other embodiments, the bonded sheet has a tensile strength in the machine direction (MD) which is about 90 % to about 110 % or about 95 % to about 105 % of the tensile strength in the transverse direction (XD). in some embodiments, the bonded sheet has at least one metallized surface. In some embodiments, the surface of the sheet that is metallized has an emissivity from 0.05 to 6.26 and ah optical density above 2, 0, and in other embodiments, the surface of the bonded sheet that is metallized has an emissivity from 0.05 to 0.2 and an optical density above 2.2.

[0122] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a polyolefin. In some embodiments, the polyolefin is a polyethylene, and in particular a high-density polyethylene (HDPE). In some embodiments, the polymer is a blend / mixture of at least 80 weight percent of high-density polyethylene (HDPE), based on the total amount of the polymer, with a low-density polyethylene (LOPE) or a linear low-density polyethylene (LLDPE) or a polypropylene (PP). In other embodiments, the polymer is a blend / mixture of at least 90 weight percent of high-density polyethylene (HDPE), based on the total amount Of the polymer, with a low-density polyethylene (L.DPE) or a linear low-density polyethylene (LLDPE) or a polypropylene (PP),

[0123] In some embodimehts, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 55 g / m2to about 115 g / m2, a Gurley Hill porosity of about 300 seconds or more, a hydrostatic head of about 195 cmHzO or more, a handle-o-meter stiffness of about 0.5 N or more, and an

[0124] Opacity of more than about 96 In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene and the bonded sheet has a basis weight from about 55 g / m2to about 65 g / m2, a Gurley Hill porosity from about 300 seconds to about 4000 seconds, a hydrostatic head from about 195 cmHaO to about 300 cmHaO, a handle-o-meter stiffness from about 0.5 N to about 1.5 N, and an opacity from about 96 % to about 98%. In some embodiments, the bonded sheet has a MVTR of about 250 g / m^day to about 1000 g / m2 / day , and in .some embodiments, the bonded sheet has an average nail tear resistance from about 45 N to about 110 N.

[0125] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about

[0126] 75 g / m2to about 90 g / m2a Gurley Hill porosity from about 300 seconds to about 4000 seconds, a hydrostatic head from about 195 cmHsO to about 300 cmHsO, a handle-o- meter stiffness from about 0.5 N to about 2.0 N, and an opacity from about 96 % to about 98%. in some embodiments, the bonded sheet has a MVTR of about 200 g / m2 / day to about 700 g / m2 / day, and in some embodiments, the bonded sheet has an average nail tear resistance from about 70 N to about 130 N.

[0127] In some embodiments, the flash-spun plexifflamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the bonded sheethas a basis weight from about 105 g / m2to about 115 g / m2, a Gurley Hill porosity from about 4000 seconds to about 7000 seconds, a hydrostatic head from about 300 cmH20 to about 450 cmH2O, a handle-o- meter stiffness from about 1.5 N to about 3.5 N, and an opacity from about 97 % to about 99%. In some embodiments, the bonded sheet has a MVTR of about 100 g / m2 / day to about 500 g / m2 / day, and in some embodiments, the bonded sheet has an average nai! tear resistance from about 100 N to about 140 N. In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 55 g / m2to about 65 g / m2, a Gurley Hilf porosity from about 300 seconds to about 4000 seconds, a hydrostatic head from about 195 cmHaO to about 300 cmHzO, a handle-o- meter stiffness from about 0.5 N to about 1.5 H, and an opacity from about 96 % to about 98%. In some embodiments, the bonded sheet has a MVTR of about 250 g / m2 / day to about 1000 g / m2 / day, and in some embodiments, the bonded sheet has an average tensile strength from about 80 N to about 180 N.

[0128] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 75 g / m2to about 90 g / m2a Gurley Hill porosity from about 300 seconds to about

[0129] 4000 seconds, a hydrostatic head from about 195 cmHaO to about 300 cmHsO, a handle-o- meter stiffness from about 0.5 N to about 2.0 M, and an opacity from about 96 % to about 98%. In some embodiments, the bonded sheet has a MVTR of about 200 g / m2 / day to about 700 g / m2 / day, and in some embodiments, the bonded sheet has an average tensile strength from about 120 N to about 280 N.

[0130] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about

[0131] 105 g / m2to about 115 g / m2, a Gurley Hill porosity from about 4000 seconds to about 7000 seconds, a hydrostatic head from about 300 cmHzO to about 450 crriHzO, a handle-o- meter stiffness from about 1.5 N to about 3.5 N, and an opacity from about 97 % to about 99%. In some embodiments, the bonded sheet has a MVTR of about 100 g / m2 / day to about 500 g / m2 / day, and in some embodiments, the bonded sheethas an average tensile strength is from about 300 N to about 460 N.

[0132] Such bonded sheets are particularly suitable for roof lining applications, without being limited thereto.;tn 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 38 g / m2to about 52 g / m2, a Gurley Hill porosity of about 200 seconds or more, a hydrostatic head of about 150 omHjO or more, a handle-o-meter stiffness from about 0.3 N to about 0.6 N or from about 0.3 N to about 045 N, an opacity of more than about 93 %, or of about 94 % or more, orof about 95 % or more, and a particle filtration efficiency of about 99 5 % or more.

[0133] 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 38 g / m-’ to about 52 g / m2, a Gurley Hill porosity from about 300 seconds to about 1000 seconds, a hydrostatic head from about 160 cmHzO to about 230 cmHzO , a handle-o-meter stiffness from about 0 5 N to about 0.6 N. an opacity from about 94 % to about 97 %, and a particle filtration efficiency from about 99.6 % to about 99.9 %.

[0134] 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 38 g / m?to about 52 g / m2, a Gurley Hill porosity from about 300 seconds to about 1000 seconds, a hydrostatic head from about 160 cmHaO to about 230 cmHaO, a handle-o-meter stiffness from about 0.5 14 to about 0.6 N, an opacity from about 94 % to about 97 %, a particle filtration efficiency from about 99.6 % to about 99.9 %, and an average tensile strength from 75 to 100 N.

[0135] 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 38 g / m2to about 52 g / m2, a Gurley - Hill porosity ; from about 300 seconds to about 1000 seconds, a hydrostatic head from about 160 cmH2O to about 230 cmHzO, a handle-o-meter stiffness from about 0.5 N to about 0.6 N, an opacity from about 94 % to about 97 %, a particle filtration efficiency from about 99.6 % to about 99.9 %, and an average nail tear from 45 to 60 N.?

[0136] 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 38 g / rrfi to about 52 g / m2, a Gurley Hill porosity from about 300 seconds to about 1000 seconds, a hydrostatic head from about 160 cmH?O to about 230 cmH2O, a handle-o-meter stiffness from about 0.5 N to about 0.6 N, an opacity from about 94 % to about 97 a particle filtration efficiency from about 99.6 % to about 99.9 %, and an average trapezoidal tear from 20 to 30 N.

[0137] Such bonded sheets are particularly suitable for protective apparel applications, without being limited thereto.

[0138] Applicant has found that the bonded sheets according to the invention surprisingly have a very good balance of liquid barrier properties, air tightness, stiffness, and opacity, which mates them very usefol in construction applications, including, but not limited to, roof lining and house wrap applications, 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 ), as well as in further applications.

[0139] Moreover, the bonded sheets described herein have a good hail tear resistance and strength, which makes them very useful in construction applications such as house wrap and roof lining applications, in particular in a multilayer structure with a further sheet.

[0140] The bonded sheets described herein are robust, breathable, and wind-tight, which makes them very suitable for garment applications, as a monolayer or in a multilayer structure with a further sheet or film.

[0141] Preparation of Bonded Sheet of Nonwoven Flash-spun Plexifilamentary Fibrils of Polymer

[0142] 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:

[0143] (i) generating a spin fluid comprising

[0144] (a) from about 12.5 to about 15 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 tom dichloromethane, cis-1 ,2-dichloroethylene and trans-1 ,2-dichloroethylene, in combination with a fluorine-contalning solvent,

[0145] (ii) flash-spinning the spin fluid at a temperature of above about 185‘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,

[0146] (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.

[0147] Flash-Spinning, Collecting, and Consolidating

[0148] Flash-spinning is a 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.

[0149] 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, tfie 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 tom multiple orifices may exit via a common slot as described in US 3,564,088. : Sheets comprising plexifilamentary fibrils of polymer can be formed by any method known in the art. In some embodiments, the stream of fibrife 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 fromfibrils 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, US 3,387,326, US 3,169,899, US 3,497,918, US 3,593,074, US 3,851,023, US 3,860,369, US 4,148,595, US 5,045,258, US 5.643,524, US 5,731, Oi l, US 5,750,152, and WO 92 / 20511 A1. 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 A1. in some embodiments, file sfreams 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.

[0150] 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.

[0151] In some embodiments, the polymer is selected from polyolefins. In some embodiments, the polymer is a polyethylene and in particular a high-density polyethlene (HDPE). In some embodiments, the polymer is a blend / mixture of at least 80 weight percent of high-density polyethylene (HDPE), based on the total amount of the polymer, with a low- density polyethylene (LDPE) or linear low-density polyethylene (LLDPE) or polypropylene (PP), and in other embodiments, the polymer is a blend / mixture of at least 90 weight percent of high-density polyethylene (HDPE), based on the total amount of the polymer, with a low- density polyethylene (LDPE) or linear low-density polyethylene (LLDPE) or polypropylene (PP).

[0152] 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. The spin fluid comprises the polymer in an amount from about 12.5 to about 15 0 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 13.0 to about 15.0 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 14.0 to about 15.0 weight percent, based on the total amount of the spin fluid. In some embodiments, the spinfluid comprises the spin agent in an amount from about 85.0 to about 88.5 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 86,0 to about 87.0 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 tom about 85.0 to about 860 weight percent, based on the total amount of the spin fluid.

[0153] In some embodiments, the flash-spinning is performed at a temperature of about 185°c or above, in other embodiments,- from about from about 185°C to about 210°C, in -other embodiments, from about from about 185°C to about 200°C, and in other embodiments, from about 190°C to about 200°C.

[0154] 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 hydrofluorocarbons 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 1Hiperfluorohexane.

[0155] In some embodiments, the spin agent consists essentially of a mixture of dichloromethane and 2H,3H-decafluoropentane, lH,4H-perfluorobutane, 1H,6H- perfluorohexane, IH-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3- pentafluorobutane, in oher 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-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 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H-perfluorohexane. 1H -perfluorohexane. perfluoropentane, perfluorohexane or 1.1 , 1 .3.3- pentafluorobutane.

[0156] In some embodiments, the spin agent consists of a mixture of dichloromethane and 2H,3H-decafluoropentane, iH,4H-perfluorobutane, lH,6H-perfluorohexane, 1H- 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. 1H,4H-perfluorobutane, 1H,5H-perfluorohexane, IH-perfluorohexane, perflubropehtane, perfluorohexane, or 1.1.1,3,3-pentafluorobutare, 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, 1H,4H-perfluorobutane, 1H,6H-perfluorohexane, IH- perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane.

[0157] In some embodiments, the plexifilamentary fibrils are spun at a spin temperature from about 185°C to about 21O°C using a spin fluid comprising about 12,5 to about 15.0 weight percent polymer, 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- pentafluorobutane. In other embodiments, the plexifilamentary fibrils are spun at e spin temperature from about 185°C to about 200oC using a spin fluid comprising about 12,5 to about 15.0 weight percent polymer, and comprising a spin agent which comprises, consists essentially of, or consists of dichloromethane and 2H,3H-decafluoropentane, 1H,4H- perfluorobutane, 1H.6H-perfiuorohexane. 1H-perfluorohexane, perfluoropentane. perfluorohexane, or 1,1,1, 3,3-pentafluorobutane.

[0158] , In some embodiments, the plexifilamentary fibrils are spun at a spin temperature from about 185°C to about JlQ-C using a spin fluid comprising about 12;5 to about 15.0 weight percent high density polyethylene, and comprising a spin agent which comprises, consists essentially of, or consists of dichloromethane and 2H,3H-decafluoropentane, 1H,4H- perfluorobutane, 1H,6H-perfluorohexane, 1H-perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1 , 3,3-pentafluorobutane. In other embodiments, the plexifilamentary fibrils are spun at a spin temperature from about 185°C to about 200°C using a spin fluid comprising about 12.5 to about 15.0 weight percent polymer, and comprising a spin agent which comprises, consists essentially of, or consists of dichloromethane and 2H.3H- decafluoropentane, 1H,4H-perfluorobutane, lH,6H-perfluorohexane, IH-perfluorohexane, perfluoropentane, perfluorohexane, or 1 ,1 ,1 , 3,3-pentafluorobutane

[0159] 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.

[0160] Thermal Bonding By Embossing After the sheet is formed into a consolidated sheet as described herein, the consolidated sheet is then subjected to thermal bonding via embossing including, but not limited to. using embossing rollisj and rubber coated back-up rolfisj to bond one or two sides of the consolidated sheet, to form a thermally bonded sheet In some embodiments, at least one side of the consolidated sheet Is embossed, in other embodiments, only one side of the consolidated sheet is embossed, and In other embodiments, both sides of the consolidated sheet are embossed.

[0161] 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 pattern. The degree of bonding can vary by adjusting the nip pressure, temperature, and length of time during which these are applied. In some embodiments, each embossing roll has a temperature from about 135°C to about 210oC during bonding, and in other embodiments, each embossing roll has a temperature from about 140°C to about 155°C during bonding.

[0162] In some embodiments, the consolidated sheet may be in contact with pre-heat rolls before thermal bonding and / or may be in contact with cooling rolls after thermally bonding, in a configuration as desaibed 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 of the plexifilamentary fibrils.

[0163] In some embodiments, the static pressure in the nip of the embosser (nip pressure) is between about 450 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. i n other embodiments, the static pressure in the nip of the embosser is between about 450 kPa and about 1000 kPa, in other embodiments from about 450 kPa to about 750 kPa, and in other embodiments from about 750 kPa to about 1000 kPa. In some embodiments, the static pressure in the nip of the embosser with a linen pattern is between about 450 kPa and about 1000 kPa. In other embodiments, the static pressure in the nip of the embosser is from about 450 kPa to about 750 kPa, and in other embodiments, from about 750 kPa to about 1000 kPa .

[0164] 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 TO5to 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"

[0165] The nip pressure can be varied with embossing roll configuration and engraving patterns backup roll diameter, rubber hardness and thickness. The embossing roll(s) may be any suitable material known in the art. In some embodiments, the embossing roll(s) are metal. The embossing roll(s) are engraved with a pattern including, but not limited to. a linen pattern as described in US 7.744,989. Further patterns which may be used on one side of the sheet in case both sides of the sheet are bonded, are 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. Each side of the consolidated sheet may be embossed using the same pattern or a different pattern. 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 linen pattern. In some embodiments, the consolidated sheet is embossed on one side using a point pattern and on another side using a linen pattern, and in:other embodiments, the consolidated sheet is embossed on one side using a rib patern and on another side using a linen pattern.

[0166] In some embodiments, the one or more rubber coated back-up rollfs) have a Shore A hardness of 50 to 70. If two or more embossers are used, the hardness of the rubber coated back-up rolls of the embossers may be the same or different If two or more embossing steps are performed.

[0167] The patterns on the embossing rollfs) may be any suitable depth known in the art. Each embossing roll may have paterns 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.

[0168] 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 % of the area of at least one side of the consolidated sheet is embossed. In some embodiments, from about 10 % to about 60 % of the area of one side of the consolidated sheet is embossed, or from about

[0169] 15 % to about 60 % or from about 20 % to about 60 % or from about 26 % to about 60 % from about 30 % to about 60 %. In other embodiments, from about 50 % to about 85 % of the area Of one side of the consolidated sheet is embossed. In some embodiments, from about 6 % to about 85 % of the area of both sides of the consolidated sheet is embossed. In some embodiments, from about 10 % to about 60 % of the area of both sides of the consolidated sheet is embossed, or from about 15 % to about 60 % or from about 20 % to about 60 % or from about 26 % to about 60 % from about 30 % to about 60 %. In other embodiments, from about 50 % to about 85 % of the area of both sides of the consolidated sheet is embossed.

[0170] In some embodiments, about 50 % to about 85 % of the area of one side of the consolidated sheet is embossed using a linen oattern. 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.

[0171] The process described herein provides a bonded sheet of nonwoven flash-spun plexifilamentary fibrils having sufficient strength and resistance to liquid penetration, while still, having high breathability.

[0172] In some embodiments, after the consolidated sheet is thermally bonded as described herein, the thermally bonded sheet is then subjected to a mechanical softening process to obtain a 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 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 rolls 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 jeopardize the barrier properties of the softened sheet.

[0173] ;In some embodiments, 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. 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.

[0174] In some embodiments the thermally bonded sheet is subjected to a mechanical softening process as described in US 3;408,709. 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;

[0175] In some embodiments, an antistatic treatment is applied to the thermally bonded sheet or the bonded and softened sheet Antistatic treatment improves electrostatic properties of a textile, in particular surface resistivity. In some embodiments, theantistatic 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„ R-., ,, 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 di-n-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.

[0176] In some embodiments, there is provided a sheet of nonwoven flash-spun plexifilamentary fibrils obtained or obtainable by the process described herein.

[0177] In some embodiments, the obtained sheet has

[0178] (a) a basis weight from about 38 g / m2to about 115 g / m2, (b) a Gurley Hill porosity of about 200 seconds or more,

[0179] (c) a hydrostatic head of about 150 cmH2O or more,

[0180] (d) a hahdle-o-meter stiffness of about 0.3 N or more, and

[0181] (e) an opacity of more than about 93 %.

[0182] Uses, Multilayer Structures and Articles

[0183] The sheet of nonwoven flash-spun plexifilamentary flbrils as described herein has many uses and may be used in a variety of applications, including, but not limited to, multilayer structures, roof lining, house wrap, garments (including, but not limited to, protective apparel), car covers, and medical packaging.

[0184] Further embodiments relate to a multilayer; structure comprising at least one sheet of nonwoven flash-spun plexifilamentary fibrils as described herein, and at leastone further sheet orafilnr

[0185] 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 82. Microporous fBms 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 include 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.

[0186] 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. 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 material, and / 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.

[0187] In some embodiments, the at least one bonded sheet of nonwoven flash-spun plexifilamentary fibrils and the one further Sheet at least are held together by thermal lamination, in some embodiments, the at least one bonded sheet of nonwoven flash-spun plexifilamentary fibrils and the one further sheet are held together by thermal welding, and in some embodiments, the at least one bonded sheet of nonwoven flash-spun plexifilamentary fibrils and the one further sheet are held together by using an adhesive, such as a hot melt adhesive, applied to at least a portion of the surface of the at least one bonded sheet of nonwoven flash-spun plexifilamentary fibrils. Suitable lamination or bonding techniques are described in US 5,750,444, US 5,294,258, and US 9,816,264. The same or different bonding techniques may be applied within one composite structure.

[0188] In some embodiments, the thermoptastic reinforcing material is a thermoplastic reinforcing grid material having a structure formed of relatively thick, strong fibres regularly spaced in one layer to form an open mesh with regularly shaped openings.

[0189] In other embodiments, the thermoplastic reinforcing material Is a spunbonded sheet having a structure with randomly laid continuous fibres in multiple, overlapping layers and thermally or adhesively bonded. In some embodiments, the spunbonded material is made of polyethylene, in other embodiments, the spunbonded material is made of polypropylene, and in other embodiments, the spunbonded material is made of polyester. In some embodiments, the thermoplastic reinforcing material is a spunbonded nonwoven having a basis weight from about 45 g / m2to about 120 g / m2. In some embodiments, the spunbonded nonwoven is made of polypropylene (SBPP). Useful commercially available spunbonded nonwovens are Typar® 3267-P or Typar® SF32.

[0190] In some embodiments the multilayer structure comprises one or more water absorbing sheets, in some embodiments, the one or more water absorbing sheets are needle felts. In some embodiments, the needle felts comprise synthetic fibres, natural fibres, or combinations thereof. In some embodiments, the synthetic fibres comprising the needle felts are polyester fibres, polypropylene fibres, polyethylene fibres, acrylic fibres, or combinations thereof.

[0191] In some embodiments, the multilayer structure is an at least three-layered composite structure comprising at least one bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein, a thermoplastic reinforcing grid material and a spunbonded material. In some embodiments, the bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein is an outer layer, the sheet of thermoplastic reinforcing grid material forms the middle layer and the sheet of spunbonded material is another outer layer. In other embodiments, the bonded sheet of nonwoven flash-spun plexifiiamentary fibrils as described herein is an outer layer, the sheet of spunbonded material forms the middle layer and the sheet of thermoplastic reinforcing grid materia! is another outer layer. In other embodiments, the bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein is arranged between the at least two further layers of the multilayer.

[0192] In some embodiments, the multilayer structure is at least a three-layered composite structure comprising at least one bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein, a sheet of thermoplastic reinforcing grid material and a needle felt sheet. In some embodiments, the bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein is a first outer layer, the sheet of thermoplastic reinforcing grid material is a middle layer, and the needle felt sheet is a second outer layer. In other embodiments, the bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein is a first outer layer, the needle felt sheet is a middle layer, and the sheet of thermoplastic reinforcing grid material is a second outer layer. In other embodiments, the bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein is arranged between the at least two further layers of the multilayer In some embodiments, the multilayer structure is at least a three-layered composite structure comprising at least One bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein, a sheet of spunbonded material and a needle felt sheet, in some embodiments, the bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein is a first outer layer, the sheet of spunbonded material is a middle layer, and the needle felt sheet is a second outer layer. In other embodiments, the bonded sheet of nonwoven flash- spun plexifilamentary fibrils as described herein is a first outer layer, the needle felt sheet is a middle layer, and the sheet of spunbonded material is a second outer layer. In other embodiments, the;bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein is arranged between the at least two further layers of the multilayer.

[0193] In some embodiments, the multilayer structure is at least a four-layered composite structure comprising at least one bonded sheet of nonwoven flash-spun plexifilamentary fibrils as described herein, a sheet of spunbonded material, a sheet of thermoplastic reinforcing grid material, and a needle felt sheet.

[0194] In some embodiments, the multilayer structure has

[0195] (a j an average tensile strength from about 200 N to about 600 N,

[0196] (b) an average nail tear strength from about 130 N to about 600 N,

[0197] (c) a Moisture Vapor Transmission Rate from about 100 g / m2 / day to about 800 g / m2 / day, and

[0198] (d) a hydrostatic head of about 250 cmHsO or more. Further embodiments relate to use of the sheet of nonwoven flash-spun plexifilamentary fibrils as described herein for preparing a multilayer structure In some embodiments, the prepared 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 material, and / or a water absorbing sheet, such asa needle felt.

[0199] Further embodiments relate to use of the sheet of nonwoven flash-spun plexifilamentary fibrils as described herein for the production of garments or construction applications including roof linings and house wraps.

[0200] Further embodiments relate to use of the multilayer structure as described herein for the production of garments or construction applications including roof linings and house wraps.

[0201] :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 roof linings, house wraps, garments, protective apparel, and car covers. Protective apparel includes full 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.

[0202] :EXAMPLES ^ 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

[0203] N-pentane, CAS Nr 109-66-0, has an atmospheric boiling point of 36.1 °C, a molecular weight of 72.l 5l g / mol and a critical temperature of 196.FC. The n-pentane used had a purity level above 95 percent by weight. Cycfopentane, CAS Nr 287-92-3, has an atmospheric boiling point of 49.2°C, a molecular weight of 70.13 g / mol and a critical temperature of 238.6<’C. The cyclopentane used had purity level above 95 percent by weight.

[0204] Dichloromethane, CAS Nr. 75-09-2, has an atmospheric boiling of 39.6°C, a molecular weight of 84.93 g / mol and a critical temperature of 236.68’d The dichloromethane used had a purity level above 99.5 percent by weight

[0205] 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

[0206] The polyethylene used had a density of 0.957 g / cm3(IS0 1183), and melt flow rate of 0.3 / 1 Omin (ISO 1133 condition D, 190*0 / 2.16 kg) and 22 / 1 Omin (ISO 1133 condition G, 190*0 / 21.6 kg).

[0207] The flash-spun sheets in the examples are produced using the flash spinning process described by US 3.227,794 and US 3.851 023. 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 lower 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 hydrocarbon spin agents is reported in but not limited to, US 5,147.586, US 6,004.672, and US 6,638.470. and for mixtures of trans-1 ,2-DCE and DCM with fluorinated compounds in, but not limited to, US 6,004,672, US 7,300,968, and US 7,179,413.

[0208] Results

[0209] Comparative examples CE1 to CE3

[0210] Rash-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 185°C, using a spin fluid of 17 wt% polyethylene having a density >0.95 g / cm3and a melt flow rate of 0.74 g / 10min (ISO 1133 190*02.16 kg) in a hydrocarbon-based spin agent that was a mixture of n-pentane and cyclopentane (herein also referred to as "H").

[0211] The flash-spun sheet was subsequently thermally bonded using a process as described in US 2003 / 0165667 The consolidated sheets were embossed on one side with a linen pattern and on the other side with a rib pattern With decreasing pressure of the nip on the linen embosser. The sheets were subsequently mechanically softened by passing them through a nip of two rolls with interpenetrating blunt pins having a diameter of t mto, witi 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

[0212] The spinning, bonding, and softening conditions and sheet properties are reported in Table 1, below.

[0213] Table 1: Summary of the sheet preparation of Comparative Examples CE1 to CE3.

[0214] :Comparative examples CEi to CE3 show that when using a hydrocarbon-based spin agent, increasing the pressure in the nip on the linen embosser results in a lower permeability to gas as reflected by an increase in Gurley Hill porosity. However, the sheets still have a tow Gurley Hill porosity making them unsuitable for applications where wind-tightness is important. Examples GE1 to GE3

[0215] A flash-spun sheet was produced using the flash-spinning precess described by US 3,227,794 and US 3,851 ,023 at different spin temperatures, using ® spin fluid of 14 wt% polyethylene having a density >0.95 g / cm3and a melt flow rate of 0.74 g / lOmin (ISO 1133 190®C / 2.16 kg) in a spin agent that was a mixture of dichloromethane and 2HGH- decafluoropentane (herein also referred to as^ “D”) . The flash-spun sheet was subsequently thermally bonded using a process as described in US 2003 / 0165667. The consolidated sheets were embossed on one side with a linen patern and on the other side with a rib patern. The sheets were subsequently mechanically softened by passing them through a nip of two rolls witi 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.

[0216] The spinning bonding, and softening conditions and sheet properties are reported in Table 2, below

[0217] Table 2: Summary of the sheet preparation of examples GE1 to GE3

[0218] Examples GE1 to GE3 illustrate that, for similar basis weights, a beneficial combination of properties can be obtained when using a chlorine-containing solvent as spin-agent compared to a hydrocarbon-based spin agent as used in Comparative examples CE1 bis CE3 The sheets of examples GE1 to GE3 show a higher level of air tightness (high Gurley Hill porosity) combined with a higher liquid barrier (i.e„ a hydrostatic head of above 200 cmHaO) and good mechanical properties in terms of tensile strength and nail tear resistance.

[0219] Comparative Examples RCE1 and RCE2 and Examples RE1 to RE3 and RE5 to RE7

[0220] A flash-spun sheet was 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 with different concentrations of polyethylene having a density >0.95 g / cm3and a melt flow rate of 0.74 g / 10min (ISO 1133 190°C / 2.16 kg) in a spin agent that was a mixture of dichloromethane and 2H,3H-decafluoropentane (herein also referred to as "D*). The flash-spun sheet was subsequently thermally bonded using a process as described in US 2003 / 0165667. All flash- spun sheets were additionally first in alternating contact with two pre-heat rolls set at a temperature of 105°C before being thermally bonded and embossed. The consolidated and pre-heated sheets were then embossed on one side with a linen pattern and on the other side with a nb pattern. The sheets were subsequently mechanically softened by passing them through a nip of twb 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.

[0221] The spinning, bonding, and softening conditions and sheet properties are reported in Tables 3 and 4, below.

[0222] Table 3: Summary of the sheet preparation of Comparative Example RCE1 and examples RE1 to RE3

[0223] Table 4; Summary of the sheet preparation of Comparative Example RCE2 and examples RE5 to RE7

[0224] Examples RE1 to RE3 and Comparative Example RCE1 illustrate for basis weights around 60 g / m2that increasing the polymer concentration results in a beneficial combination of properties in terms of air tightness (Gurley Hill porosity), liquid barrier (i.e.. a hydrostatic head of above 200 cmHzO) and good mechanical properties. Tn particular, the sheets of examples RE1 to RE3 show a much higher level of air tightness (high Gurley Hill porosity) than the sheet of comparative example RCE1 The same trend can be observed for Examples RE5 to RE7 and Comparative Example RCE2 having basis weights around 80 g / m;Moreover, an increase in polymer concentration results in an increase in Gurley Hill porosity, as illustrated by a comparison between comparative example RCE2 and examples RE5 to RE7,

[0225] Examples RE8 to RE12

[0226] A flash-spun sheet was 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 14 wt% of polyethylene having a density >0.95 g / cm3and a melt flow rate of 0.74 g / 10min (ISO 1133 19O°C / 2.16 kg) in a spin agent that was a mixture of dichloromethane and 2H,3H- decafluoropentane (herein also referred to as "O’). The flash-spun sheet was subsequently thermally bonded using a process as described in US 2003 / 0165667 All flash-spun sheets were additionally first in alternating contact with two pre-heat rolls set at a temperature of 105°C before being thermally bonded and embossed. The consolidated and pre-heated sheets were then embossed on one side with a linen pattern and on the other side with a rib pattern. The sheets 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 MO direction and 3.2 mm center-to-center in XD direction at the point of interacting with the flash-spun sheet.

[0227] The spinning, bonding, and softening conditions and sheet properties are reported in Table 5, below. Table 5: Summary of the sheet preparation of examples

[0228] Examples RE8 to RE 12 show a beneficial combina tton of properties in terms of air tightness (Guriey Hill porosity), liquid barrier (i.e., a hydrostatic head of above 200 cmHjO), and good mechanical properties. In addition, Examples RE12 and RE 10 illustrate that increasing the nip pressure results in an increase of the Gurley Hill porosity, an increase in the hydrostatic head, and a reduction of the MVTR. Further, Examples RE 12 and RE11 illustrate that increasing the nip pressure also results in a decrease in opacity. All examples and comparative examples show that an increase in basis weight is generically associated with a higher Gurley Hill porosity, a higher hydrostatic head, and a higher softness (as reflected by a lower handle-o-meter stiffness). Comparative example RCE3

[0229] The sheet of comparative example RCE3 is a commercially available sheet which had been subjected to a thermal bonding on a smooth heated roll where one or both sides of the sheet are subjected to generally uniform, full surface contact thermal bonding as described in US 3,442,740.

[0230] The sheet properties of comparative example RCE3 are reported in Table 6. below

[0231] Table 6: Summary of the sheet properties of Comparative Example RCE3.

[0232] For a comparable basis weight, the full surface area bonded sheet of comparative example RCE3 has a notable higher stiffness (higher handle-o-meter value) compared to the sheets of examples RE1 to RE3. In addition, the sheet of comparative example RCE3 has a lower Gurley Hill porosity and a lower opacity compared to the Sheets of examples RE1 to RE3.

[0233] Laminate Examples L1 to L2

[0234] Flash-spun sheets of Example RE9 were laminated to different spunbonded nonwoven sheets having different basis weights, see Table 7 below.

[0235] Table 7- Laminates L1 to 12 made of inventive bonded flash-spun sheets and spunbonded nonwoven sheets.

[0236] The laminates have a good combination of mechanical properties such as tensile strength and nail tear resistance while having good breathability (MVTR, Gurley Hill porosity) and high hydrostatic head, making them suitable for use in roof lining and house wrap applications. Metallization Examples ME1

[0237] Flash-spun sheets of Example RE9 have been metallized with aluminum on the side that was embossed with the linen pattern using the process described in EP 1789622 B 1 The resulting optical density and emissivity measured on the metallized side are provided in Table 8, below. Table 8i Metallized flash-spun sheets.

[0238] OTHER EMBODIMENTS 1. In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash-spun plexifllamentary fibrils, the sheet having

[0239] (a) a basis weight from about 38 g / m2to about 115 g / m2,

[0240] (b) a Gurley Hill porosity of about 200 seconds or more,

[0241] (c) a hydrostatic head of about 150 cmHaO or more, (d) a handle-o-meter stiffness of about 0.3 N or more, and

[0242] (e) an opacity of more than about 93 %. 2. The sheet of embodiment 1 having

[0243] (a) a basis weight from about 55 g / m2to about 115 g / m2,

[0244] (b^a Gurley Hill porosity of about 300 seconds or more,

[0245] (c) a hydrostatic head of about 195 cmHaO or more,

[0246] (d> a handie-o-meter stffness of about 0.5 N or more, and

[0247] (e) an opacity of more than about 96 %.

[0248] 3. The sheet of embodiment 1 having

[0249] (a) a basis weight from about 38 g / m2to about 52 g / m2,

[0250] (b) a Gurley Hill porosity of about 200 seconds or more,

[0251] (c) a hydrostatic head of about 150 cmHaO or more,

[0252] (d) a handle-o-meter stiffness from about 0.3 N to about 0.6 N, or from about 0.3 N to about 0.45 N,

[0253] (e) an opacity of more than about 93 %, or of about 94 % or more, or of about 95 % or more, and

[0254] (f) a particle filtration efficiency of about 99.5 % or more.

[0255] 4. The sheet of embodiment 1 Or 2 having a basis weight from about 55 g / m2to about 115 g / m2.

[0256] 5. The sheet of embodiment 1 or 2 having a basis weight from about 75 gm,2to about 100 g / m2.

[0257] 6.;The sheet of embodiment 1 or 2 having a basis weight from about 75 g / m2to about

[0258] 90 g / m2.

[0259] 7 The sheet of embodiment 1 or 2 having a basis weight from about 55 g / m2to about 65 g / m2.

[0260] 8. The sheet of embodiment 1 or 3 having a basis weight from about 38 g / m2to about 52 g / m?

[0261] 9. The sheet of embodiment 8 having a basis weight from about 40 g / m2to about 50 g / m2.

[0262] 10. The sheet of any one of the preceding embodiments having a Gurley Hill porosity from about 200 seconds to about 10,000 seconds.

[0263] 11. The sheet of any one ofthe preceding embodiments having a Gurley Hill porosity from about 200 seconds to about 1000 seconds.

[0264] 12. The sheet of any one of the preceding embodiments having a Gurley Hill porosity of about 300 seconds or more.

[0265] 13. The sheet of sheet of any one of the preceding embodiments having a Gurley Hill porosity from about 300 seconds to about 10,000 seconds.

[0266] 14. The sheet of any one ofthepreceding embodiments having a Gurley Hill porosity from about 400 seconds to about 8000 seconds, or about 500 seconds to about 7000 seconds. 15. The sheet of any one of the preceding embodiments having a Gurley Hill porosity from about 1200 seconds to about 7000 seconds or from about 3000 seconds to about 7000 seconds.

[0267] 16. The sheet of any one of embodiments 10 to 13 having a Gurley Hill porosity from about 300 seconds to about 4000 seconds.

[0268] 17. The sheet of any one of embodiments 10 to 13 having a Gurley Hill porosity from about 300 seconds to about 3000 seconds.

[0269] 18. The sheet of any one of the preceding embodiments having a hydrostatic head from about 150 cmHaO to about 450 cmHzOi 19. The sheet of any one of the preceding embodiments having a hydrostatic head of about

[0270] 195 cmH2O or more.

[0271] 20. The sheet of any one of the preceding embodiments having a hydrostatic head from about 195 cmHzO to about 400 cmHaO.

[0272] 21. The sheet of any one of the preceding embodiments having a hydrostatic head from about 195 crnHzO to about 350 cmH^O.

[0273] 22 The sheet of any one of the preceding embodiments having a hydrostatic head from about 195 cmHjO to about 300 cmHjO.

[0274] 23 The sheet of embodiment 18 having a hydrostatic head from about 300 cmHzO to about 450 cmH2O. 24. The sheet of embodiment 18 having a hydrostatic head from about ISOcmHjO to about 200 cmH2O.

[0275] 25. The sheet of any one of the preceding embodiments having a handle-o-meter stiffness from about 0.3 N to about 4.0 N.

[0276] 26. The sheet of any one of the preceding embodiments having a handle-o-meter stiffness from about 0 3 N to about 3.5 N

[0277] 27 The sheet of any one of the preceding embodiments having a handle-o-meter stiffness from about 0.3 N to about 2*0 N.

[0278] 28. The sheet of any one of the preceding embodiments having a handle-o-meter stiffness from about 0.3 N to about 1 .5 N. 29. The sheet ofany one of the preceding embodiments having a handle-o-meter stiffness from about 0.3 N to about 0.6 Or from about 0,3 N to about 0.45 N.

[0279] 30. The sheet of embodiment 25 having a handle-o-meter stiffness from about 1 .0 N to about 3.5 N.

[0280] 31. The sheet of embodiment 25 having a handle-o-meter stiffness from about 0.4 N to about 4.0 N*

[0281] 32. The sheet of any one of the preceding embodiments having an opacity from about 93.0 % to about 99.5 %, 33. The sheet of any one of the preceding embodiments having an opacity from about 94.0 % to about 99.5 %, or from about 95.0 % to about 99.5 %.

[0282] 34. The sheet of any one of the preceding embodiments having an opacity from about 94.0 % to about 97.0 %, or from about 95.0 % to about 97.0 %.

[0283] 35. The sheet of any one of the preceding embodiments having an opacity of more than

[0284] 96.0 %; :

[0285] 36. The sheet of embodiment 35 having an opacity from about .96.0 % to about 99.0 %.

[0286] 37. The sheet of any one of the preceding embodiments having a total crystallinity index of less than about 73 %.

[0287] 38. The sheet of any one of the preceding embodiments having a total crystallinity index of from 63 % to about 73 %.

[0288] 39. The sheet of any one of the preceding embodiments having a total crystallinity index from about 65 % to about 73 %.

[0289] 40;:The sheet of any one of the preceding embodiments having a total crystallinity index from about 67 % to about 73 %.

[0290] 41. The sheet of any one of the preceding embodiments having a total crystallinity index of less than about 72 %.

[0291] 42. The sheet of any one of the preceding embodiments having a total crystallinity index from about 63 % to about 72 %.

[0292] 43. The sheet of any one of the preceding embodiments having a total crystallinity index from about 67 % to about 72 %.

[0293] 44. The sheet of any one of the preceding embodiments having a BET surface area from about 4 nWg to about 11 mWg.

[0294] 45. The sheet of any one of the preceding embodiments having a BET surface area from about 7 m^g to about 11 m2 / g.

[0295] 46. The sheet of embodiment 44 having a BET surface area from about 4 rrr7g to about 7 m2 / g.

[0296] 47. The Sheet of any one of the preceding embodiments having a MVTR of about 100 g / m2 / dayor more.

[0297] 48. The sheet, of any One of the preceding embodiments having a MVTR from about 100 g / m2 / day to about 1500 g / m2 / day.

[0298] 49. The sheet of any one of the preceding embodiments having a MVTR from about 100 g / m2 / day to about 1000 g / m^day.

[0299] 50. The sheet of any one of the preceding embodiments having a MVTR from about 250 g / m^day to about 1500 g / m2 / day.

[0300] 51. The sheet of any one of the preceding embodiments having a MVTR from about 250 g / m2 / day to about 1000 g / mWay. 52. The sheet of any one of the preceding embodiments having a MVTR from about 100 g / m2 / day to about TOO g / m^day.

[0301] 53. The sheet of any one of the preceding embodiments having a MVTR from about

[0302] 100 g / m2 / day to about 500 g / m^day. : > 54. The sheet of any one of the preceding embodiments having a particle filtration efficiency of about 99.50 % or more.

[0303] 55. The sheet of any one of the preceding embodiments having a particle filtration efficiency from about 99.50 % to about 99.99 %.

[0304] 56. The sheet of any one of the preceding embodiments having a particle filtration efficiency from about 99.70 % to about 99.99 %.

[0305] 57. The sheet of any one of the preceding embodiments having an average trapezoidal tear strength from about 20 N to about 60 N

[0306] 58. The sheet of any one of the preceding embodiments having an average trapezoidal tear strength from about 28 N to about SO N 59. The sheet of any one of the preceding embodiments having an average trapezoidal tear strength from about 30 N to about 45 N.

[0307] 60. The sheet of embodiment 57 or 58 having an average trapezoidal tear strength from about 45 N to about 60 N.

[0308] 6T The sheet of embodiment 57 or 58 having an average trapezoidal tear strength from about 35 N to about 55 N.

[0309] 62. The sheet of embodiment 57 or 58 having an average trapezoidal tear strength from about 20 N to about 30 N.

[0310] 63. The sheet of any one of the preceding embodiments having an average nail tear from about 25 N to about 140 N.::64. The sheet of any one of the preceding embodiments having an average nail tear from about 50 N to about 140 N.

[0311] 65. The sheet of any one of the preceding embodiments an average nail tear from about 50 N to about 90 N.

[0312] 66. The sheet of embodiment 63 or 64 having an average trapezoidal tear strength from about 90 N to about 140 N

[0313] 67. The sheet of embodiment 63 or 64 having an average trapezoidal tear strength from about 60 N to about 100 N.

[0314] 68. The sheet of embodiment 63 or 64 having an average trapezoidal tear strength from about 25 N to about 60 N. 69. The sheet of any one of the preceding embodiments having an average tensile strength from about 70 N to about SOO N. 70. The sheet of anyone of the preceding embodiments having an average tensile strength from about 100 N to about 450 N.

[0315] 71. The sheet of any one of the preceding embodiments having an average tensile strength from about 100 N to about 280 N.

[0316] 72. The sheet of embodiment 69 or 70 having an average tensile strength from about 280 N to about 450 N.

[0317] 73. The sheet of embodiment 69 or 70 having an average tensile strength from about 150 N to about 250 N.

[0318] 74. The sheet of embodiment 69 having an average tensile strength from about 70 N to about 100 N.

[0319] 75. The sheet of any one of the preceding embodiments having at least one metallized surface.

[0320] 76. The sheet of embodiment 75, wherein the surface of the sheet that is metallized has an emissivity from 0.05 to 0 25 and an optical density above 2.0, or an emissivity from 0.05 to 0.2 and an optical density above 2.2.

[0321] 77. The sheet of any one of the preceding embodiments, wherein the flash-spun plexifilamentary fibrils ate comprised of a polyolefin.

[0322] 78. The sheet of embodiment 77, wtierein the polyolefin is a polyethylene.

[0323] 79 The sheet of embodiment 77, wherein the polyolefin is a high-density polyethylene

[0324] (HDPE), a bfend / mixture of at least 80 weight percent of high-density polyethylene (HOPE), based on the total amount of the polymer, with a low-density polyethylene (LDPE) or a linear low-density polyethylene (LLDPE).

[0325] 80. The sheet of any one of embodiments T to 79, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 55 g / m* to about 115 g / nr. a Gurley Hill porosity of about 300 seconds or more, a hydrostatic head of about 195 cmH?O or more, a handle- o-meter stiffness of about 0 5 N or more, and an opacity of more than about 96 %

[0326] 81. The sheet of any one of embodiments ' to 79, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 55 g / m2to about 65 g / m2, a Gurley Hiir porosity tom about 300 seconds to about 4000 seconds, a hydrostatic head from about 195 cmH?O to about 300 cmH20, a handle-o-meter stiffness from about 0.5 N to about 1 5 N, and an opacity from about 96 % to about 98%.

[0327] 82. The sheet of embodiment 81 having a MVTR tom about 250 g / m^day to about 1000 g / mlday.

[0328] 83. The sheet of any one of embodiments 81 to 82, having an average nail tear resistance from about 45 N to about 110 N. 84. The sheet of any one of embodiments 81 to 82, having an average tensile strength from about 80 N to about 180 N

[0329] 85. The sheet of any One of embodiments 1 to 79, wherein the flash-spun plexifiiamentary fibrils of the sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 75 g / m® to about 90 g / m2, a Gurley Hill porosity from about 300 seconds to about 4000 seconds, a hydrostatic head from about 195 cmH_O to about 300 crnHsO, a handle-o-meter stiffness from about 0.5 N to about 2.0 N, and an opacity from about 96 % to about 98%.

[0330] 86. The sheet of embodiment 85, having a MVTR from about 200 g / m2 / day to about 700 g / m2 / day.

[0331] 87. The sheet of any one of embodiments 85 to 86, having an average nail tear resistance from about 70 N to about 130 hi.

[0332] 88. The sheet of any one of embodiments 85 to 86, having an average tensile strength from about 120 N to about 280 N.

[0333] 89. The sheet of any one of embodiments 1 to 79, wherein the flash-spun plexifiiamentary fibrils of the sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 105 g / m2to about 115 g / m2, a Gurley Hill porosity from about 4000 seconds to about 7000 seconds, a hydrostatic head from about 300 cmHjO to about 450 cmKaO, a handle-o-meter stiffness from about 1.5 N to about 3 5 N, and an opacity from about 97 % to about 99%.

[0334] 90. The sheet of embodiment 89, having a M VTR from about 100 g / m2 / day to about 500 g / m2 / day.

[0335] 91. The sheet of any one of embodiments 89 to 90, having an average nail fear resistance from about 100 N to about 140 N.

[0336] 92. The sheet of any one of embodiments 89 to 90. having an average tensile strength from about 300 N to about 460 N

[0337] 93. The sheet of any one of embodiments 1 to 79, wherein the flash-spun plexifiiamentary fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from .about 38 g / m® to about 52 g / m®, a Gurley Hill porosity of about 200 seconds or more, a hydrostatic head of about 150 cmHaO or more, a handle-o- meter stiffness from about 0.3 N to about 0.6 N, an opacity of more than about 93 %, and a particle filtration efficiency of about 99.5 % or more.

[0338] 94. The sheet of any one of embodiments ' to 79, wherein the flash-spun plexifiiamentary fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 38 g / m® to about 52 g / m®, a Gurley Hill porosity from about 300 seconds to about 1000 seconds, a hydrostatic head from about 160 cmHaO to about 230 cmHzO, a handle-o-meter stiffness from about 0.5 N to about 0,6 N, an opacity from about 94 % to about 97 % and a particle filtration efficiency from about 99.6 % t0 about 99.9 %.

[0339] 95. The sheet of embodiment 94 having an average tensile strength from 75 to 100 K.

[0340] 96. The sheet of embodiment 94 having an average nail tear from 45 to 60 N.

[0341] 97. The sheet of embodiment 95 having an average trapezoidal tear from 20 to 30 N.

[0342] 98. A process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps oft.

[0343] (i) generating a spin fluid comprising

[0344] (a) from about 12.5 to about 15.0 weight percent of a polymer, based on the total amount of the spin fluid, and

[0345] (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-containing solvent,

[0346] (ii) flash-spinning the spin fluid at a temperature of above about 185’C and at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure toform plexifilamentary flbrils of the polymer,

[0347] (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

[0348] (iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet.

[0349] 99. The process of embodiment 98, wherein the spin fluid comprises the polymer in an amount from about 13.0 to about 15.0 weight percent, based on the total amount of the spin fluid.

[0350] 100 The process of any one of embodiments 98 or 99 wherein the spin fluid comprises the polymer in an amount from about 14.0 to about 15.0 weight percent, based on the total amount of the spin fluid.

[0351] 101. The process of any one of embodiments 98 to 100, wherein the spin fluid comprises the spin agent in an amount from about 85.0 to about 88.5 weight percent, based on the total amount of the spin fluid.

[0352] 102. The process of any one of embodiments 98 to 100, wherein the spin fluid comprises .the spin agent in an amount from about 85.0 to about 87.0 weight percent, based on the total amount of the spin fluid.

[0353] 103. The process of any of embodiments 98 tolOO, wherein the spin fluid comprises the spin agent in an amountfrom about 85.0 to about 86 weight percent, based on the total amount of the spin fluid. 104. The process Of any one of embodiments 98 to 103, wherein flash spinning of the spin fluid is carried but at a temperature from about 185°C to about 210°C.

[0354] 105. The process of any one of embodiments 98 to 103, wherein flash spinning Of the spin fluid is carried out at a temperature from about 185 ’C to about 200nC. 106. The process of any one of embodiments 98 to 103, wherein flash spinning of the spin fluid is carried out at a temperature from about 190°C to about 200°C.

[0355] 107. The process of any of embodiments 98 to104, wherein the fluorine-containing solvent is a hydrofluorocarbon having three to s ix carbon atoms, perfluorocarbons having three to six carbon atoms or a hydrofluoroether. 108. The process of embodiment 108, 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-perfluorobutane, 2H,3H- decafluoropentane, 1H, ©H-perfluorohexane, or 1H-perfluorohexane.

[0356] 109. The process of any one of embodiments 98 to 108, wherein the spin agent consists or consists essentially of dichloromethane in combination with perfluoropentane, perfluorohexane, 1 ,1 ,1 ,3,3-pentafluorobutane, IHMH-perfluorobutane, 2H,3H- decafluoropentane, 1H,6H-perfluorohexane or 1H-perfluorohexane.

[0357] 110. The process of any one of embodiments 98 to 109, 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, 1H-perfluorohexane, perfluoropentane, perfluorohexane or 1 , 1 ,1 ,3,3-pentafluorobutane.

[0358] 111. The process of any one of embodiments 98 to 110, wherein 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, 1H.4H-perfluorobutane. 1H.6H- perfluorohexane. 1H-perfluorohexane, perfluoropentane, perfluorohexane or 1 ,1 ,1,3,3-pentafluorobutane.

[0359] 112. The process of any one of embodiments 98 to 111 , wherein the plexifilamentary fibrils are spun at a spin temperature from about 185°C to about 210’C using a spin fluid comprising about 12.5 to about 15.0 weight percent 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, 1H-perfluorohexane, perfluoropentane, perfluorohexane or 1,1 ,1 ,3,3-pentafluorobutane. 113. The process of any one of embodiments 98 to 112, wherein the plexifilamentary fibrils are spun at a spin temperature from about 185°C to about 200°C using a spin fluid comprising about 14.0 to about 15.0 weight percent -polymer and comprising a spin agent which comprises, consists essentially of, or consists of dichloromethane and 2H,3H-decafluoropentane, 1H,4H-perfluor0butane, 1H,6H-perfluorohexane, 1H- perfluorohexahe, perfluoropentane, perfluorohexane or 1,1, 1 ,3,3-pentafluorobutane.

[0360] 114. The process of any one of embodiments 98 to 113, wherein the consolidated sheet is thermally bonded by passing through a nip of two rolls of an embosser, wherein the static pressure in the nip of the embosser is between about 450 kPa and about 1000 kPa or from 450 kPa to about 750 kPa, or from about 750 kPa to about 1000 kPa.

[0361] 115. The process of embodiment 114, wherein one roll is engraved with a linen patern.

[0362] 116. The process of any of embodiments 98 to 115, wherein the consolidated sheet is thermally bonded by passing through a nip of two rolls of an embosser, wherein the consolidated sheet wraps a heated embosser roll at a wrap angle from about 10° to about 140*.

[0363] 117; The process of any one of embodiment 98 to 116, wherein the process further comprises mechanically softening the bonded sheet. 118. The process of embodiment 117, wherein the thermally bonded sheet is mech^ 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.

[0364] 119. The process of embodiment 118, wherein the pins are blunt pins.

[0365] 120. The process of any one of embodiments 98 to 119, wherein the process further comprises applying an antistatic treatment to the bonded sheet.

[0366] 121: The process of any one of embodiments 98 to 120, wherein the sheet is bonded over between about 6 % to about 85 % of at least one surface of the sheet.

[0367] 122. Theprocess erf any one of embodiments 98 to 121, wherein from about 6 % to about 85 % of the area of at least one side of the consolidated sheet is embossed. 123. The process Of any one of embodiments 98 to 121, Wherein from about 10 % to about

[0368] 60 % of the area of at least one side of the consolidated sheet is embossed

[0369] 124 The process of any one of embodiments 98 to 121 . wherein from about 20 % to about 60 % of the area of at least one side of the consolidated sheet is embossed.

[0370] 125. Theprocess of any one of embodiments 98 to 121, wherein from about 30 % to about 60 % of the area of at least one side of the consolidated sheet is embossed.

[0371] 126. The process of any one of embodiments 98 to 121 . wherein from about 50 % to about 85 % of the area of at least one side of the consolidated sheet is embossed.

[0372] 127. The process of any one of embodiments 98 to 121, wherein from about 6 % to about 85 % of the area of both sides of the consolidated sheet is embossed. 128. The process of any one of embodiments 98 to 121, wherein from about 10 % to about

[0373] 60 % of the area of both sides of the consolidated sheet is embossed, 129. The process of any one Of embodiments 98 to 121, wherein from about 20 ° / o to about 60 % of the area of both sides of the consolidated sheet is embossed.

[0374] 130. The process of any one of embodiments 98 to 121, wherein from about 26 % to about 60 % of the area of both sides of the consolidated sheet is embossed 131. The process of any one of embodiments 98 to 121, wherein from about 50% to about

[0375] 85 % of the area of both sides of the consolidated sheet is embossed.

[0376] 132. The process of any one of embodiments 98 to 121, wherein about 50 % to about 85 % of the area of one side of the consolidated sheet is embossed using a linen pattern and wherein about 15 % to about 60 % of the area of other side of the consolidated sheet is embossed using a rib pattern.

[0377] 133. The process of any one of embodiments 98 to 132, wherein the sheet is embossed by passing through a nip of two rolls, one being an embossing roll engraved with a linen patern and the other a back-up roll with a Shore A hardness of 50 to 70,

[0378] 134. The process of any one of embodiments 98 to 133, wherein the polymer is a polyolefin. 135. The process of embodiment 134, wherein the polyolefin is a high-density polyethylene (HDPE), a blend / mixture of at least 80 weight percent of high-density polyethylene (HOPE), based on the total amount of the polymer, with a low-density polyethylene (LOPE) or a linear low-density polyethylene (LLDPE)

[0379] 136. A sheet of nonwoven flash-spun plexifilamentary fibrils obtainable by the process of any one of embodiments 98 to 135.

[0380] 137. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0381] (a) a basis weight from about 38 g / m2to about 115 g / m2,

[0382] (b) a Gurley Hill porosity of about 200 seconds or more. (c) a hydrostatic head of about 150 cmHzO or more,

[0383] (d) a handle-o-meter stiffness of about 0.3 N or more, and

[0384] (e) an opacity of more than about 93 %. and wherein the sheet is obtained by the process of any one of embodiments 98 to 135. /

[0385] 138. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0386] (a) a basis weight from about 55 g / m2to about 115 g / m2,

[0387] (b) a Gurley Hill porosity of about 300 seconds or more,

[0388] (c) a hydrostatic head of about 195 cmHaO or more,

[0389] (d) a handle-o-meter stiffness:of about 0.5 N or more, and (e) an opacity of more than about 96 %, and wherein the sheet is obtained by the process of any one of embodiments 98 to 135. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0390] (a) a basis weight from about 38 g / m2to about 52 g / m2,

[0391] (b) a Gurley Hill porosity of about 200 seconds or more,

[0392] (c) a hydrostatic head of about 150 cmHzO or more,

[0393] (d) a handle-o-meter stiffness tom about 0.3 R to about 0.6 N, or tom about 0.3 N to about 0.45 N,

[0394] (e) an opacity of more than about 93 %, or of about 94 % or more, or of about 95 % or more, and

[0395] (f ) a particle filtration efficiency of about 99.5 % or more, and wherein the sheet is obtained by the process of any one of embodiments 98 to 135. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 55 g / m2to about 115 g / m2, a Gurley Hill porosity of about 300 seconds or more, a hydrostatic head of about 195 cmH2O or more, a handle-o-meter stiffness of about 0.5 N or more, and an opacity of more than about 96 %, and wherein the sheet is obtained by the process of any one of embodiments 98 to 135. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, wherein the flash-spun plexifilamentary fibrils of the sheet are / comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 55 g / m2to about 65 g.rw a Gurley Hili porosity tom about 300 seconds to about 4000 seconds, a hydrostatic head tom about 195 cmHzO to about 300 cmHzO, a handle-o-meter stiffness tom about 0.5 N to about 1.5 N, and an opacity tom about 96 % to about 98 %, and wherein the sheet is obtained by the process of any one of embodiments 98 to 135.. The sheet of embodiment 141 having a MVTR from about 250 g / m-' / day to about 1000 g / mtoay. The sheet of any one of embodiments 141 to 142, having an average nail tear resistance tom about 45 N to about 110 N. The sheet of any one of embodiments 141 to 142, having an average tensile strength tom about 80 N to about 180 N A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight tom about 75 g / m2to about 90 g / m2, a Gurley Hill porosity tom about 300 seconds to about 4000 seconds, a hydrostatic head tom about 195 cmHzO to about 300 cmHzO, a handle-o-meter stiffness from about 0.5 N to about 2.0 N, and an opacity from about 96 % to about 98 %, and wherein the sheet is obtained by the process Of any one of embodiments 98 to 135.

[0396] 146. The sheet of embodiment 145, having a MVTR from about 200 g / m^day to about 700 g / m^day.

[0397] 147. The sheet of any one of embodiments 145 to 146, having an average nail tear resistance from about 70 N to about 130 N.:

[0398] 148. The sheet of any one of embodiments 145 to 146, having an average tensile strength from about 120 N to about 280 N.

[0399] 149. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the bonded sheet has a basis weight from about 105 g / m2to about 115 g / m2, a Gurley Hill porosity from about 4000 seconds to about 7000 seconds, a hydrostatic head from about 300 crnHsO to about 450 cmHjO, ra handle-o-meter stiffness from about 1 5 N to about 3.5 N, and an opacfly from about 97 % to about 99 % , and wherein the sheet is obtained by the process of any one of embodiments 98 to 135.

[0400] 150. The sheet of embodiment 149, having a MVTR from about 100 g / m2 / day to about 500 g / m2 / day.

[0401] 151. The sheet of any one of embodiments 149 to 150, having an average nail tear resistance from about 100 N to about 140 N.

[0402] 152. The sheet of any one of embodiments 149 to 150, having an average tensile strength from about 300 N to about 460 N.

[0403] 153. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, 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 38 g / m2to about 52 g / m2, a Gurley Hill porosity of about 200 seconds or more, a hydrostatic head of about 150 cmHaQ or more, a handle-o-meter stiffness from about 0.3 N to about 0.6 N, an opacity of more than about 93 % and a particle filtration efficiency Of about 99.5 % or more, and wherein the sheet is obtained by the process of any one of embodiments 98 to 135.

[0404] 154. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, 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 38 g / m2to about 52 g / m2, a Gurley Hi porosity from about 300 seconds to about 1000 seconds, a hydrostatic head from about 160 onHaO to about 230 cmHzO, a handle-o-meter stiffness from about 0.5 N to about 0.6 N, an opacity from about 94 % to about 97 % and a particle filtration efficiency from about 99.6 % to about 99.9 %tand wherein the sheet is obtained by the process of any one of embodiments 98 to 135.

[0405] 155. A multilayer structure comprising at least one sheet according to any one of embodiments I to 97 or 136 to 154 and at least one further sheet or film.

[0406] 156. The multilayer structure Of embodiment 155i comprising at least one further film, wherein the at least one further film is a microporous film.

[0407] 157. The multilayer structure of embodiment 155 which is a composite structure comprising at least one further sheet, wherein The at least one further sheet is a sheet of a thermoplastic reinforcing material having reinforcing properties.

[0408] 158. The multilayer structure of embodiment 157 wherein the sheet of thermoplastic reinforcing material is thermoplastic reinforcing grid;material or a spunbonded material .

[0409] 159. The multilayer structure according to any one of 157 to 158 which is a composite structure comprising at least one further sheet, wherein the at least one further sheet is a water absorbing sheet.

[0410] 160. The multilayer structure of embodiment 159 wherein the water absorbing sheet is a needle felt.

[0411] 161; The multilayer structure according to arty one of embodiments 155 to 160, wherein the at least one further sheet is a spunbonded nonwoven having a basis weight from about 45 gfrn2to about 120 g / m2.

[0412] 162. The multilayer structure according to any one of embodiments 155 to 161 , wherein the multilayer structure is a composite structure comprising three or more sheets.

[0413] 163. The multilayer structure according to ary one of embodiments 155 to 162. wherein the multilayer structure is a composite structure comprising four or more sheets,

[0414] 164. The multilayer structure according to any one of embodiments 155 to 163, wherein a sheet of thermoplastic reinforcing grid material and a sheet of spunbonded material are used as the further sheets.

[0415] 165. The multilayer structure according to any one of embodiments 155 to 163, wherein a sheet of thermoplastic reinforcing grid material and a needle felt sheet are used as the further sheets.

[0416] 166. The multilayer structure according to any one of embodiments 155 to 163, wherein a sheet of spunbonded material and a needle felt sheet are used as the further sheets.

[0417] 167. The multilayer structure of any one of embodiments 155 or 161 , having

[0418] (a) an average tensile strength from about 200 N to about 600 fit,

[0419] (b) an average nail tear resistance from about 130 N to about 600 N,

[0420] (c) a moisture vapor transmission rate from about 100 g / m^day to about 800 g / m2 / day, and

[0421] (d) a hydrostatic head of about 250 cml-feO or more. 168. Use of the sheet of any one of embodiments 1 to 97 or 136 to 154 for preparing a multilayer structure.

[0422] 169. Use of a sheet Of any one of embodiments 1 to 97 or 136 to 154 or of the multilayer structure of any one of embodiments 155 to 167 for the production of garments or roof linings. ’

[0423] 170. An article comprising a sheet of any one of embodiments 1 to 97 or 136 to 154 or a multilayer structure of any one of embodiments 155 to 167.

[0424] 171. The article of embodiment 170. wherein the article is selected from house wraps, roof linings, garments, protective apparel, or car covers.

[0425] While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein without departing from the spirit and scope of the present i nvention. Thus, it should be appreciated that, while the invention has been described with reference to the above exemplary embodiments, other embodiments are within the scope of the claims. Moreover, it should be understood that the exemplary embodiments described herein may be combined to fbrm other embodiments. After reading the above description, it will be apparent to one skilled in the relevant art(s) how to implement the invention in alternative embodiments. Thus, the present invention should not be limited by any of the above-described exemplary embodiments

Claims

CLAIMS1. A thermally bonded sheet of nonwoven flash-spun plexifllamentary fibrils, the sheet having;(a) a basis weight from about 38 g / m2to about 115g / m2,(b) a Gurley Hill porosity of about 200 seconds or more*(c) a hydrostatic head of about 150 cmHaO or more,(d> a handie-o-meter stiffness of about 0,3 N or more, and (e) an opacity of more than about 93 %.

2. The sheet of claim 1 having(a) a basis weight from about 55 g / m2to about 115 g / m2,(b) a Gurley Hill porosity of about 300 seconds dr more,(cj a hydrostatic head of about 195 cmH2O or more, (d> a handle-o-meter stiffness of about 0,5 N or more, and(e) an opacity of more than about 96 %.

3. The sheet of claim 1 having(a) a basis weight from about 38 g / m2to about 52 g / m2. (b) a Gurley Hill porosity of about 200 seconds or more,(c) a hydrostatic head of about 150 cmH2O or more,(d) a handle-o-meter stiffness from about 0.3 N to about 0.6 N, (ey an opacity of more than about 93 %, and(f) a particle filtration efficiency of about 99.5 % or more.

4. The sheet of any one of claims 1 to 3 having a BET surface area of about 4 m2 / g to about 11 m2 / g, or having a total crystallinity incex of less than about 73 %.

5. The sheet of any one of claims 1 to 4 having a Moisture Vapor Transmission Rate of about 100 g / m2 / day or mwe, or having an average nail tear resistance from about 45 N to about 140 N.6 The sheet of any one of claims 1 to 5 wherein the flash-spun plexifllamentary fibrils are comprised of a polyolefin which is a polyethylene.

7. The sheet of claim 6, wherein the polyolefin is a high-density polyethylene (HOPE), a blend / mixture of at least 80 weight percent of high-density polyethylene (HOPE), based on the total amount of the polymer, with a low-density polyethylene (LDPE) or a linear low-density polyethylene (LLDPE).:

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 12.5 to about 15 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-dichloroethyiene and trans-1 ,2-dichloroethyiene, in combination with a fluorine-containing solvent,(ii) flash-spinning the spin fluid at a temperature of above about 185’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 fibrilsand applying: pressure to the sheet to obtain a consolidated sheet, and (iv) thermally bonding by embossingthe consolidated sheetto obtain a bonded sheet.

9. The process of claim 8, wherein the consolidated sheet is thermally bonded by passing through :a: nip of two rolls of an embosser, wherein the static pressure in the nip of the embosser is between about 450 kPa and about 1000 kPa:10 The process of claim 9, wherein one roll is an embossing roll engraved with a linen pattern.11, The process of any one of claims 8 to 10, wherein the process further comprises mechanically softening the bonded sheet.12, The process of any one of claims 8 to 11, wherein the polymer is polyethylene.13, The process of claim 12, wherein the polyolefln is a high-density polyethylene (HOPE), a blend / mixture of at least 80 weight percent of high-density polyethylene (HDPE), based on the total amount of the polymer, with a low-density polyethylene (LDPE) or a linear low-density polyethylene (LLDPE).

14. A Sheet of nonwoven flash-spun plexifllamentary fibrils obtainable by the process of any one of Claims 8 to 13.

15. A multilayer structure comprising at least one sheet according to any one of claims 1 to 7 or 14 and at least one fiirther sheet or film.

16. The multilayer structure of claim 15 comprising at least one further sheet, wherein the at least one further sheet is a spunbonded nonwoven having a basis weight from about 45 g / m2to about 120 g / m2.

17. The multilayer structure of claim 15 or 16, having(a) an average tensile strength from about 200 N to about 600 N,(b) an average nail tear strength from about 130 N to about 600 N, (c) a Moisture Vapor Transmission Rate from about 100 g / m2 / day to about 800 g / m2 / day, and(d) a hydrostatic head of about 250 cmHjO or more.18 Use of the sheet of any one of claims 1 to 7 or 14 for preparing a multilayer structure .

19. Use of a sheet of any one of claims 1 to 7 or 14 or of the multilayer structure of any one of claims 15 to 16 for the production of roof linings or garments20 An article comprising a sheet of any one of claims 1 to 7 or 14 or a multilayer structure of any one of claims 15 to 1721. The article of claim 20, wherein the article is selected from house wraps, roof linings, garments, protective apparel, or car covers.

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