Softened flash-spun sheet

Abstract

The present invention relates to (i) a bonded sheet of nonwoven flash-spun plexifilamentary fibrils exhibiting good barrier properties and a high degree of breathability and softness, (ii) a process for the preparation of a bonded sheet of nonwoven flash-spun plexifilamentary fibrils, and (iii) multilayer sheet structures and articles comprising at least one bonded sheet of nonwoven flash-spun plexifilamentary fibrils.

Description

[0001] .TITLE

[0002] SOFTENED FLASH-SPUN SHEET

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to (i) a bonded sheet of nonwoven flash-spun plexifilamentary fibrils exhibiting good barrier properties and a high degree of breathability and softness, (it) 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.

[0005] BACKGROUND

[0006] Flash-spun nonwoven materials have been developed with wide-ranging properties suitable for use in a variety of applications, including, but not limited to, protective apparel. Their production usually involves two stages, a first stage in which fibrils are produced and laid down in an overlapping manner to produce a fibril assembly in the form of a sheet, and a second stage in which adjacent fibrils are bonded via thermal bonding to obtain a robust structure which cannot be easily disassembled. / The properties of the final nonwoven sheet are impacted by various fectors from the first and second stages.

[0007] 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 at a pressure above the vapor pressure of the spin agent and at a temperature above the normal boiling point of the spin agent, and releasing that solution into a zone of substantially lower temperature and pressure such that the spin agent flash evaporates and the polymer solidifies in the form of plexifilamentary fibrils. Examples of flash spinning processes are disclosed in US 3,081 ,519 and US 3.227,794

[0008] 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 ofthe 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.

[0009] Thermal bonding is a common process for bonding nonwoven sheets in which heat is used to soften the polymer from which the fibrils are made, typically, by passing the nonwoven sheet through an arrangement of heated rolls, with a back-up roll which forms a nip or without a back-up roll. The degree of bonding can vary based on the temperature and pressure, and time -during which these are applied. : Bonding of the nonwoven sheet also- varies spatially depending on the rolls used and area to which the bonding is applied, e,g., using smooth surfaced rolls to apply uniform heat and pressure over the entire surface versus using patterhed rolls to apply heat and pressure locally over only a portion of the surface toform an embossed pattern in the final nonwoven sheet .

[0010] US 3,442,740 and US 3,532,589 describe thermal bonding on a smooth heated roll > where one or both sides of the nonwoven sheet are subjected to generally uniform, full surface contact thermal bonding. In this process, a surface bonded nonwoven sheet product is obtained having a paper-like feel which is suitable for uses such as packaging and print media but too stiff for use in garments, being uncomfortable and "noisy” for the wearer. Thermal bonding using a thermal calendar bonder, such as that described in US 5,972,147, also tends to produce a stiffer nonwoven sheet product without the softness desired for most garment applications, such as protective apparel. Products having a paper-like feel also have disadvantages in other applications such as car covers which need to conform to the shape of the vehicle, or roof linings which can vibrate and create noise when wind blows over them.

[0011] 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 roil can contain different:paterns, such as a point pattern as described.;in US 3,478,141 , US 6,610,390, and US 2004 / 241399 Al . a rib patern as described in US 2003 / 0032355 A1 and US 2003 / 00165667 AT, a linen pattern or a random pattern as described in US 7,744,989, or a combination of different patterns as described in US 5,620,779 and US 5,964,742. The nonwoven sheet may pass through one or multiple pairs of a heated embossing roll and a rubber-coated back-up roll and may also wrap partially around one or more heated embossing rolls to transfer heat into the nonwoven sheet prior to reaching the nip between any such embossing roll and a rubber-coated back-up roll. In addition, the nonwoven sheet may be in contact with one or more pre-heat or cooling rolls before and after passing through each pair of embossing and back-up roils, in a configuration as described in US 5.972,147 US 6,034,008 and US 2003 / 00165667 Al describe a process in which one side is embossed with a W pattern of discrete bond points and the other side is embossed over a substantial portion of the surface with a Tinen’’ patern.

[0012] Thermal bonding impacts different properties of the nonwoven sheet in different ways. 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 leadto 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- flbrils through which gases can move, resulting in a decrease in flux. Moreover, if temperatures and pressures are high enough to causes fibrils to melt and fuse together extensively, this can create film-like regions which allow very little flux.

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

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

[0015] The effect of bonding on sheet stiffness is especially notable when bonding is applied uniformly over the whole surface This results in sheets having a paper-life texture often referred to as “hard-structures” which tend to produce a lot of noise when flexed or bent When embossed rolls are used to create areas having greater and lesser degrees of bonding, quieter and more flexible, softer, fabric-like structures can be achieved, often referred to as “soft- structures " However, even soft-structure bonded sheets are stiffer and less flexible than the starting sheet before bonding.

[0016] It is possible to recover some softness m a bonded, nonwoven sheet, by applying processes known in the textile industry such as softening Or re-lofting. In these processes, the 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 sheet. These changes in mechanical properties are typically accompanied by an increase in flux properties and a loss in barrier properties. US 3,408,709 describes a softening process using a button breaker to mechanically soften a nonwoven sheet. The button breaker employs knobbed rolls which turn at a different speed to, or even in the opposite direction to the movement of the nonwoven sheet as it travels over them, creating a -rubbing effect. :

[0017] 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 roll against a soft rubber backup roll. However, no information is given in these documents on how -this process impacts the barrier properties of the nonwoven sheet. 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 rubbirig surface, its surface is damaged.

[0018] US 3,920.874 and US 3,81 1 ,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 10 % for the process to work correctly,

[0019] WO 2020 / 026062 Al 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 loft (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° / o, 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 structures having a high solidity that require good liquid barrier properties

[0020] While the above processes might provide the possibility to make sheets that are more comfortable to touch, e g., less stiff or softer, the barrier properties of such materials are usually significantly reduced as a consequence of the softening.

[0021] An ideal nonwoven sheet for use in protective apparel should have high barrier properties to ensure the protection of the wearer against external contaminants, have high flux to allow rapid exhaust of warm air and water vapor from within the protective apparel, and maintain a comfortable environment for the wearer, while having adequate mechanical properties to withstand the rigors of physical work

[0022] It is also preferable that the nonwoven sheet has low stiffness and a soft texture so that it does not provide noticeable resistance to the wearer’s movements or generate excessive noise. While flash-spun sheets have demonstrated a good variety of desired properties, there has been a trade-off required between the desired comfort and protection properties. Therefore, there is a need for a flash-spun sheet for use in protective apparel which provide improved comfort for the wearer without sacrificing barrier properties and protection. SUMMARY OF THE INVENTION

[0023] In one embodiment, the invention is directed to a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0024] (a J a basis weight from about 32 g / m2to about 56 g / m2,

[0025] (b) a Gurley Hill porosity from about 1 seconds to about 30 seconds.

[0026] (c) a particle filtration efficiency of about 90 % or more, and

[0027] (d> a handle-o-meter stiffness from about 0.05 N to about 0.70 N.

[0028] In a further embodiment, the invention is directed to a process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps of:

[0029] (i) generating a spin fluid comprising :

[0030] (a) from about 8.0 to about 11.5 weight percent of a polymer, based on the total amount of the spin fluid, and

[0031] (b) a spin agent: comprising a chlorine-containing solvent, selected from dichloromethane, cis-1,2-dichloroethylene, andtrans-‘l,2*dichloroethyfene, in combination with a fluorine-contaihing solvent,

[0032] (ii) flash spinning the spin fluid at a temperature at or above about 205“C and at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of the polymer, (iii) collecting the plexifilamentary fibrils of the polymer on a collecting means as a sheet of nonwoven flash-spun plexifilamentary fibrils and applying: pressure: to the sheet to obtain a consolidated sheet,

[0033] (iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet, and (v) mechanically softening the bonded sheet by passing it through one or more nips between rotating rolls driven at substantially the same speed as the speed of the bonded sheet to obtain a softened sheet of nonwoven flash-spun plexifilamentary fibrils. In a still further embodiment, the invention is directed to a process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps of:

[0034] (I) generating a spin fluid comprising;

[0035] (a) from about 12.0 to about 19.0 weight percent of a polymer, based on the total amountof the spin fluid, and (b) a spin agent comprising one or more hydrocarbons. (fl) flash spinning the spin fluid at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmosphericpressure 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

[0037] (iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet, and

[0038] (v) mechanically softening the bonded sheet to obtain a softened sheet of nonwoven flash-spun plexifilamentary fibrils by passing it through one or more nips between rolls driven < at substantially ; the same speed as the speed of the bonded sheet, wherein each roll has interpenetrating pins and rotates in the opposite direction as the other roll, and wherein each interpenetrating pin is a blunt pin. BRIEF DESCRIPTION OF THE FIGURES

[0039] FIGS. 1A to 1C show exemplary illustrations of "point" patterns which can be used in embossing a sheet.

[0040] FIG. 2 shows an exemplary illustration of a rib" pattern which can be used in embossing a sheet.:FIG. 3 shows an exemplary illustration of a “linen” pattern which can be used in embossing a sheet.

[0041] FIG. 4A shows a side view of an exemplary illustration of a blunt pin with a hexagonal cross-section which can be used in softening a bonded sheet. FIG 4B shows a 3D view of that pin, and FIG. 4C shows a top view of that pin. , FIG. 5A Shows a side view of an exemplary illustration of another blunt pin with a shaft having a square cross-section which can be used in softening a bonded sheet, FIG. 5B shows a 3D view of that pin, and FIG 5C shows a top view of that pin.

[0042] FIG. 6A shows a side view of an exemplary illustration of a cylindrical blunt pin which can be used in softening a bonded sheet, FIG. 6B shows a top view of that pin, and FIGS. 6G to 6E show 3D views of differentalternatives of that pin.

[0043] FIG. 7A shows a side view of an exemplary illustration of another cylindrical blunt pin which can be used in softening a bonded sheet, FIG. 7B shows a top view of that pin, and FIGS. 70 to 7E show 3D views of different alternatives of that pin. It will be appreciated that the embossing patern shown in Figures 1 to 3 and the pin configurations shown in Figures 4 to 7 described herein are given by way of example only, and are not meant to limit the scope of the invention in any way. DETAILED DESCRIPTION

[0044] Definitions of Terms and Test methods

[0045] Before addressing details of embodiments, some terms and test methods are defined or clarified Unless otherwise mentioned, all tests were carried out without preconditioning of the samples. When average values are indicated herein, this refers to the arithmetic average.

[0046] Basis weight is determined according to EN ISO 636 (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.;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. Gurley-Hill porosity is determined in accordance with TAPPI T-460 OM-88 (2006) using a Lorentzen & Wettre Model SE 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 lower the Gurley Hill porosity, the greater the air permeability of the sheet.

[0047] 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 amount, 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 OF 84 (2004), NIOSH Procedures No. RCT-APR-STP-67, 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.

[0048] The particle penetration is additionally expressed as the logarithmic reduction value (LRV) based on the following formula -

[0049] LRV - -logio(penetration[%y 100)

[0050] A higher LRV and PFE represent a higher particle barrier of the tested material.

[0051] 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. Jt?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.

[0052] The hydrostatic head is a measure of the resistance of asheet 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 ill 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 cmHaO / 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. the moisture vapor transmission rate (MVTR) is measured according to EM IS0 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, Germany. 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. Five test cups are each filled with water te a height of 15 mm tom 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 instrument 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 + / -5 ° / o 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 (WDP 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:

[0053] Sd - 236600 / WDD

[0054] 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 materia! by perform ing the reverse calculation:

[0055] MVTR = 236600 / SDML

[0056] The reported value is for one measurement, which inherently averages the property for ten individual samples of test material. Elongation to break (herein also referred to as elongation ") of a sheet is a measure of the amount a sheet stretches prior to failure (breaking) in strip tensile test Herein the elongation is determined based on standard EN ISO 13934-1 (99) The gauge length is 200 mm and the speed of the clamps is 100 mm / min. The reported elongation corresponds to the elongation at the point of maximum force on the stress-strain curve. The elongation is reported in the machine direction (MD) of the sheet, in the cross direction (XD) of the sheet, and as average of the elongation in MD and the elongation in XD.

[0057] The hardness of the rubber is determined based on DIN ISO 7619-1 (2010) - Rubber, vulcanized or thermoplastic - Determination of indentation hardness - Part 1 : Durometer method (Shore hardness). The hardness is reported in Shore A. Thickness of the sheet is measured according to standard EN ISO 534 (2005) using a

[0058] Model SE 243 Paper Thickness Gauge from Lorentzen & Wettre, Kista, Sweden. The sheet is a measured using a probe having a circular area of 2 cm2with an applied pressure of 50 kPa. The time to lower the probe is 2 seconds and the hold time is 4 seconds. The reported value represents an average of at least 100 individual measurements.

[0059] 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 The samples measured have a total surface area above 2 m?. BET surfece area is measured using a Quantachrome model NOVA 3000e from Quantachrome GmbH, Odelzhausen, Germany. Performance Of foe equipment is verified by using a standard aluminium oxide sample (3P-SRF586) having a BET surface area of 5.86 * / - 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.

[0060] Melting temperature is determined by differential scanning calorimetry, following the guidance provided in ASTM D3418 (Standard Test Method for Transition Temperatures and Enthalpies Of Fusion and Crystallization of Polymers by Differential Scanning Calorimetry ) and ASTM Standard F2625 (Standard:Test Method for Measurement of Enthalpy of Fusion , Percent Crystallinity and Melting Point of Ultra-High-Molecular weight polyethylene by means of differential scanning calorimetry). For polyethylene, heating and cooling is performed under inert gas at a rate of 10°C / minute, heating the sample first from room temperature to 21 O^C, then cooling the sample back to room temperature and subsequently heating the sample a second time to 2108C. 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.

[0061] 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.

[0062] Density is determined according to the method described in ISO 1183 (Plastics - Methods for determining the density of non-cellular plastics).

[0063] 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 all possible geometrical configurations of foe material These configurations include, but are not limited to, isotactic, syndiotactic, and random symmetries. The term “polyethylene” is intended to embrace not only homopolymers of ethylene, but also copolymers and terpolymers wherein at least 85 % of the recurring units are ethylene units One useful polyethylene is high-density polyethylene which has a melting temperature of about 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, 19Q°C / 2160 grams) of between 0.1 g / IOmin and 100 g / IOmin, preferably less than 4 g / IOmin.

[0064] The term "polypropylene” is intended to embrace not only homopolymers of propylene but also copolymers and terpolymers where at least 85 % of the recurring units are propylene units. Furthermore, unless otherwise specifically limited, the term '‘polypropylene” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and random symmetries.

[0065] The term “polymer type” refers to the chemical class into which the polymer falls, for example, polyethylene, polypropylene, etc. ,

[0066] 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 intervals in various places throughout the length; width, and thickness of the structure to form a continuous three-dimensional network or web. 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 pofymer(s) to form the spin fluid. Suitable additives include stabilizers, such as antioxidants or acid scavengers.

[0067] 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.

[0068] The term cloud point pressure refers to the pressure at which, at constanttemperature; a clear single phase spin fluid tansitions from a clear solution to a cloudy, two- phase dispersion. At the cloud point pressure, a clear spin fluid becomes turbid.

[0069] Atmospheric pressure means 101.325 kPa. Essentially atmospheric pressure means 101.325 kPa ± 5 %.

[0070] As used herein, the singular forms "a," "an," and "the" include the plural, and reference to a particular numerical value incdudes at least that particular value, unless the context clearly dictates otherwise. When a range of values is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent ’’about," it will be understood that the particular value forms another embodiment. All ranges are inclusive and combinable. Bonded Sheet of Nonwoven Flash-spun Plexifilamentary Fibrils

[0071] Provided herein is a thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0072] ; (a) a basis weight from about 32 g / m2to about 56 g / m2,

[0073] (b) a Gurley Hill porosity from about 1 seconds to about 30 seconds,

[0074] (c) a particle filtration efficiency of about 90 % or more, and

[0075] (d) a handle-o-meter stiffness from about 0.05 N to about 0 70 N.

[0076] The thermally bonded sheet described herein exhibits a; desired com bination of moderate basis weight, low Gurley Hill porosity, high particle filtration efficiency, and < low handle-o-meter stiffness.

[0077] In some embodiments, the bonded sheet has a Gurley Hill porosity from about 3 seconds to about 25 seconds, in other embodiments, the bonded sheet has a Gurley Hill porosity from about 5 seconds to about 22 seconds, in other embodiments, the bonded sheet has a Gurley Hill porosity from about 5 seconds to about 20 seconds, and in other embodiments, the bonded sheet has a Gurley Hill porosity from about 3 seconds to about 15 seconds.

[0078] In some embodiments, the bonded sheet has a basis weight from about 32 g / m2to about 56 g / m2, in other embodiments, the bonded sheet has a basis weight from about 38 g / m2to about 52 g / m2, in other embodiments, the bonded sheet has a basis weight from about 40 g / m2to about 50 g / m2, and in other embodiments, the bonded sheet has a basis weight from about 41 g / m2to about 49 g / m2. in some embodiments, the bonded sheet has a handle-o-meter stiffness from about 0.10 N to about 0 40 N. in other embodiments, the bonded sheet has a handle-o-meter stiffness from about 0.12 N to about 0 35 N, and in other embodiments, the bonded sheet has a handle-o-meter stiffness from about 0.15 N to about 0.30 N.

[0079] In some embodiments, the bonded sheet has a particle filtration efficiency from about 90.0 % to about 99.9 %, in other embodiments, the bonded sheet has a particle filtration efficiency from about 95.0 % to about 99.9 %. in other embodiments, the bonded sheet has a particle filtration efficiency from about 97.0 % to about 99.9 %, and in other embodiments, the bonded sheet has a particle filtration efficiency from about 99.0 % to about 99.9 %.

[0080] In some embodiments, the bonded sheet has an elongation in at least one direction, selected from the machine direction (MD) and the transverse direction (XD), of less than about 12 %, and in other embodiments, the bonded sheet has an elongation in at least one direction, selected from the machine direction (MD) and the transverse direction (XD), of more than about 5 %. In some embodiments, the bonded sheet has an elongation in at least one direction, selected from the machine direction (MD) and the transverse direction (XD), from more than about 5 % to less than about 10 %, and in other embodiments, from more than about 6 % to less than about 8 %

[0081] In some embodiments the bonded sheet has an average elongation of less than about 25 %, in other embodiments, the bonded sheet has an average elongation of more than about 5 %. In some embodiments, the bonded sheet has an average elongation from more than about 5 % to less than about 14 %, and in other embodiments, from more than about 6 % to less than about 12 %. The average elongation is calculated as (elongation in MD + elongation in XD) divided by two.

[0082] In some embodiments, the bonded sheet has a hydrostatic head from about 50 cmHjO to about 170 cmHzO, in other embodiments, the bonded sheet has a hydrostatic head from about 100 cmHjO to about 150 cmH?O, and in other embodiments, the bonded sheet has a hydrostatic head from about 120 cmHjO to about 140 cmHzO.

[0083] In some embodiments, the bonded sheet has a BET surface area from about 4 m2 / g to about 12 m2 / g, in other embodiments, the bonded sheet has a BET surface area from about 4 m*7g to about 8 m2 / g, and in other embodiments, the bonded sheet has a BET surface area from about 8 m2 / g to about 12 m2 / g.

[0084] In some embodiments, the bonded sheet has a MVTR from about 5000 g / m2 / day to about 16,000 g / m2 / day, in other embodiments, the bonded sheet has a MVTR from about 6000 g / m2 / day to about 16,000 g / m2 / day, and in other embodiments, the bonded sheet has a MVTR from about 8000 g / m2 / day to about 14,000 g / mVday.

[0085] In some embodiments, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a polyolefin. In some embodiments, the polyolefin is selected from polyethylene (PE), polypropylene (PP). and blends / mixtures thereof. Particularly preferred polyolefins are polyethylene (PE), in particular high-density polyethylene (HDPE), and blends / mixtures of high-density polyethylene (HDPE) and low-density polyethylene (LDPE), in particular linear low-density polyethylene (LLDPE). In some embodiments the polyolefin is a high-density polyethylene (HDPE).

[0086] 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 32 g / nr:to about 38 g / m2. a Gurley Hill porosity from about 3 seconds to 15 seconds, a particle filtration efficiency from about 90.0 % to about 95.0 %, and a handle-o-meter stiffness from about 0.1 N to about 0.3 N. In another embodiment, 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 40 g / m2to about 45 g / m2, a Gurley Hill porosity from about 3 seconds to 15 seconds, a particle filtration efficiency from about 91 .0 % to about 99.5 %, and a handle-o-meter stiffness from about 0.15 N to about 0.45 N. In another embodiment, the flash-spun plexifilamentary fibrils of the bonded sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 43 g / m2to about 50 g / m2a Gurley Hill porosity from about 3 seconds to 15 seconds, a particle filtration efficiency from about 95.0 % to about 99.0 %, and a handle- o-meter stiffness from about 0.2 N to about 0.5 N.

[0087] Applicant has found that the bonded sheets according to the invention surprisingly have a very good balance of barrier properties, breathability and softness, which makes them very useful and comfortable for use in garments, including, but not limited to, protective apparel such as full body protective clothing and partial body protective clothing (including, but not limited to, gowns, overalls, coveralls, trousers, coats, sleeves, hoods, shoe protectors, aprons, etc ), and further applications.

[0088] Preparation of Bonded Sheet of Nonwoven Flash-spun Plexifilamentary Fibrils of Polymer?

[0089] In a further embodiment, there is provided a process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps of:

[0090] (i) generating a spin fluid comprising

[0091] (a) from about 8.0 to about 11 5 weight percent of a polymer, based on the total amount of the spin fluid, and

[0092] (b) a spin agent comprising a chlorine-containing solvent, selected from dichloromethane, cis-l,2-dichloroethylene and trans-1 ,2-dichloroethylene, in combination with a fiuorine-containing Solvent,

[0093] (ii) flash spinning the spin fluid at a temperature at or above about 205°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 fitxiis of the polymer, (iii) collecting the plexifilamentary fibrils of the polymer on a collecting means as a sheet of nonwoven flash-spun plexifilamentary fibrils and applying pressure to the sheet to obtain a consolidated sheet,

[0094] (iv) thennally bonding by embossing the consolidated sheet to obtain a bonded sheet, and (v) mechanically softening the bonded sheet by passing it through one or more nips between rotating rolls driven at substantially the same speed as the speed of the bonded sheet to obtain a softened sheet of nonwoven flash-spun plexifilamentary fibrils. In a still further embodiment, the invention is directed to a process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps of.

[0095] (i) generating a spin fluid comprising

[0096] (a) from about 12.6 to about 19.0 weight percent of a polymer, based on the total amount of the spin fluid, and

[0097] (b) a spin agent comprising one or more hydrocarbons,

[0098] (ii) flash spinning the spin fluid 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,

[0099] (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,

[0100] (iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet, and

[0101] (v) mechanically softening the bonded sheet to obtain a softened sheet of nonwoven flash-spun plexifilamentary fibrils by passing it through one or more nips between rolls driven at substantially the same speed as the speed of the bonded sheet, wherein each roll has interpenetrating pins and rotates in the opposite direction as the other roll, and wherein each interpenetrating pin is a blunt pin.

[0102] Flash-Spinning, Collecting, and Consolidating

[0103] Flash-spinning is a method tor 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 tempemture 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,

[0104] The formed plexifilamentary fibrils of polymer are discharged from each spin orifice, and the shape of these plexifilamentary fibrils of polymer may be modified by any methods known in the art. In some embodiments, the plexifilamentary fibrils of polymer discharged from each spin orifice may be modified by passing into a shroud such as described on US 3,387,326, in other embodiments by passing into a sloted outlet such .as described in US 3,467,744 or US 5,788,993, and in other embodiments by passing into a slot fan jet as described in US 8,114,325. In some embodiments, streams of fibrils from multiple orifices may exit via a common slot as described in US 3,564,088.

[0105] Sheets comprising plexifilamentary fibrils of polymer can be formed by any method known in the art. In some embodiments, the stream of fibrils discharged from each spin orifice is directed towards a deflector device which alternately directs the stream of fibrils to the left and right onto a moving collecting device such that the fibrils accumulate in the form of a sheet, formed from fibrils oriented in an overlapping, multi^directional configuration. Deflection of the stream of fibrils may be achieved by any suitable means known in the art, including, but not limited to, those described in US 3,277,526 and US 3,387,326, US 3,169,899, US 3,497,918, US 3,593,074, US 3,851 ,023 and US 3,860,369, US 4,148,595, US 5,045,258, US 5,643,524, US 5,731 ,011 , US 5,750, 152 and WO 92 / 20511 Al. The stream of fibrils may also be laid down to form a sheet without deflection as described in US 5,788,993 and US 8,114,325. The method of forming a sheet may further utilize structures in the spin cell such as those described in US 5,123,983, US 5, 296,172, and WO 92 / 20511 A1. In some embodiments, the streams of fibrils are discharged from spin orifices located on a rotating support, and the fibrils are collected on a collecting belt which surrounds the rotating arrangement circumferentially as described in US 7,118,698, US 7,621,731, US 7,786,034, and US 7,998,388

[0106] 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.

[0107] A broad range of different polymers and blends / mixtures thereof can be used in the process described herein. In some embodiments, the polymer is selected from polyolefins. In some embodiments, polyolefins are polyethylene (PE), polypropylene (PP), and blends / mixtures thereof Particularly preferred polyolefins are polyethylene (PE), in particular high-density polyethylene (HDPE). and blends / mixtures of high-density polyethylene (HDPE) and low-density polyethylene (LDPE), in particular linear low-density polyethylene (LLDPE). In some embodiments, the polyolefin comprises at least 80 weight percent of high-density polyethylene (HDPE), based on the total amount of polymer. In other embodiments, the polyolefin comprises at least 90 weight percent of high-density polyethylene (HDPE), based on the total amount of polymer, and in other embodiments, the polyolefin comprises at least 95 weight percent of high-density polyethylene (HDPE), based on the total amount of polymer.

[0108] Process with one or more hydrocarbons as spin agent The spin agent may include one or more hydrocarbons. In some embodiments, the spin fluid comprises the polymer in an amount of from about 12.0 to about 19.0 weight percent, based on the total amount of toe spin fluid, in other embodiments, the spin fluid comprises toe polymer in an amount from about 13.0 to about 18.0 weight percent, based on the total amount of the spin fluid, and in other embodiments, the spin fluid comprises the polymer in an amount from about 14.0 to about 17.0 weight percent, based on the total amount Of the spin fluid;

[0109] In some embodiments, the spin fluid comprises the spin agent in an amount of from about 81 .0 to about 88 0 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 82.0 to about 87.0 weight percent, based on the total amount of the spin fluid, and in other embodiments,, tie spin fluid comprises the spin agent in an amount from about 83.0 to about 86.0 weight percent, based on the total amount of the spin fluid. In some embodiments, the flash-spinning is performed at a temperature from about 185°Gto about 205°G, and in other embodiments, from about 195°C to about 205°C.

[0110] In some embodiments, the spin; agent comprises one or more hydrocarbons. In some embodiments, toe one or more hydrocarbons of the spin agent are selected from n-pentene, cyclopentane,;hexane, cyclohexane, 2,2-dimethylbutene, n-butane or mixtures thereof. In some embodiments, the spin agent comprises n-pentane or cyclopentane or a mixture thereof.

[0111] In some embodiments, the spin agent consists essentially of n-pentane. in some embodiments, the spin agentconsists essentially of a mixture of n-pentane and cyclopentane, in other embodiments, the spin agent consists essentially of from about 60 to about 85 weight percent n-pentane and from about 15 to about 40 weight percent cyclopentane, in other embodiments from about 65 to aboutSO weight percent n-pentane and from about 20 to about

[0112] 35 weight percent cyclopentane, and in other embodiments from about 70 to about 80 weight percent n-pentane and from about 20 to about 30 weight percent cyclopentane. In some embodiments, the spin agent comprises or consists essentially of a mixture of n-pentane, cyclopentane, and 2,2-dimethylbutane. In other embodiments, the spin agent consists essentialiy of from about 60 to about 85 weight percent n-pehtane, from about 13 to about 33 weight percent cyclopentane, and from about 2 to about 7 weight percent 2,2- dimethylbutane.

[0113] In some embodiments, the spin agent consists of n-pentane In some embodiments, the spin agent consists of a mixture of n-pentane and cyclopentane, in other embodiments, the spin agent consists of from about 60 to about 85 weight percent n-pentane and from about

[0114] 15 to about 40 weight percent cyclopentane, in other embodiments from about 65 to about 80 weight percent n-pentane and from about 20 to about 35 weight percent cyclopentane, and in other embodiments from about 70 to : about 80 weight percent n-pentane and from; about 20 to about 30 weight percent cyclopentane. In some embodiments, the spin agent consists of a mixture of n-pentane, cyclopentene and 2,2-dimethylbutane In other embodiments, the spin agent consists of from about 60 to about 85 weight percent n-pentane, from about 13 to about 33 weight percent cyclopentane, and from about 2 to about 7 weight percent 2,2- dimethylbutane.

[0115] 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, based on the total amount of the spin fluid, and in other embodiments in an amount of about 0.1 weight percent or less, based on the total amount of the spin fluid

[0116] In some embodiments, the plexifilamentary fibrils are spun at a spin temperature from about 185°C to about 205°C using a spin fluid comprising about 12.0 to about 19.0 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 n-pentane. In other embodiments, the plexifilamentary fibrils are spun at a spin temperature from about 195<’C to about 205° G using a -spin: fluid comprising about 14.0 to about 19.0 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 n-pentane.

[0117] In some embodiments, the plexifilamentary fibrils are spun at a spin temperature from about 190°C to about 205°C using a spin fluid comprising about 12.0 to about 19.0 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 a mixture of n-pentane and cyclopentane. In other embodiments, the plexifilamentary fibrils are Spun at a spin temperature from about 195°C to about 205°C using a spin fluid comprising about 14.0 to about 19.0 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 n-pentane and cyclopentane. Process with the mixture of chlorine- and fluorine-containing solvents

[0118] The - spin agent may include -a- chlorine-containing solvent, selected from dichloromethane, cis- 1 ,2-dichloroethylene and trans-1 ,2-dichloroethylene, in combination with a fluorine-containing solvent. In some embodiments, the spin fluid comprises the polymer in an amount from about 8.5 to about 11.5 weight percent, based on the total amount of the spin fluid, in other embodiments, the spin fluid comprises the polymer in an amount from about 9.0 to about 11.0 weight percent, based on the total amount of the spin -fluid, and in other embodiments, the spin fluid comprises the polymer in an amount from about 9.5 to about 11.0 weight percent, based on the total amount of the spin fluid.

[0119] In some embodiments, the spin fluid comprises the spin agent in an amount from about 88.5 to about 91.5 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 89.0 to about 91.0 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 from about 89.0 to about 90.5 weight percent, based on the total amount of the spin fluid

[0120] In some embodiments, the flash-spinning is performed at a temperature from about 205 C to about 230 'C. and tn other embodiments from about 205 ’C to about 220' C

[0121] 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. 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, a perfluorocarbon 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, 1 H,6H-perfluorohexane, or 1 H-perfluorohexane.

[0122] In some embodiments, the spin agent consists essentially of a mixture of dichloromethane and 2H,3H-decafluoropentane, 1 H,4H-perfluorobutane, 1H,6H- perfluorohexane, 1 H-perfluorohexane, perfluoropentane, perfluorohexane and 1 ,1,1 ,3,3- pentafluorobutane, in other 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, 1 H,4H-perfluorobutane, 1H,6H-perfluorohexane, 1H- perfluorohexane. perfluoropentane, perfluorohexane, or 1 ,1 ,1 ,3,3-pentafluorobutane, and in other embodiments, from about 75 to about 85 weight percent dichioromethane and from about 15 to about 25 weight percent 2H.3H-decafluoropentane. 1H,4H-perfluorobutane, 1H.6H-perfluorohexane. 1 H-perfluorohexane. perfluoropentane, perfluorohexane, or 1 ,1 ,1 ,3,3-pentafluorobutane.

[0123] In some embodiments, the spin agent consists of a mixture of dichioromethane and 2H,3H-decafluoropentane, 1 H,4H-perfluorobutane, 1H,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 dichioromethane and from about 15 to about 30 weight percent 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H-perfluorohexane, 1 H-perfluorohexane, perfluoropentane, perfluorohexane or 1,1 ,1,3,3-pentafluorobutane, and in other embodiments, from about 75 to about 85 weight percent dichioromethane and from about 15 to about 25 weight percent of 2H,3H-decafluoropentane, 1H,4H-perfluorobutane, 1H,6H-perfluorohexane, 1H- perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane. 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

[0124] 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. In some embodiments, the plexifilamentary fibrils are spun ata spin temperature from about 205°C to about 230°C using a spin fluid comprising about 8.0 to about 11.5 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^,3, 3- pentafluorobutane. In other embodiments, the plexifilamentary fibrils are spun at a spin temperature from about 205°C to about230°C using a spin fluid comprising about 8.5 to about

[0125] 11.5 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, 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 205°C to about 220°C using a spin fluid comprising about 9.0 to about 11.0 weight percent polymer and comprising a spin agent which comprises, consists essentially of, or ojnsists of dichloromethane and 2H,3H- decafluoropentane, 1 H,4H-perfluorobutane, 1 H,6H-perfluorohexane, 1 H-perfluorohexane, perfluoropentane, perfluorohexane, or 1 ,1, 1,3, 3-pentafluorobutane.

[0126] Thermal Bonding By Embossing

[0127] After the sheet is formed into a consolidated sheet as described herein, the consolidated sheet is then subjected to thermal bonding via embossing by any methods known in the art, including, but not limited to, using heated embossing roll(s) and rubber coated backup roll(s) to bond one or two sides of the consolidated sheet, to form a thermally bonded sheet. In some embodiments, only one side of the consolidated sheet is embossed. In other embodiments, one side of the consolidated sheet is embossed and the other side of the consolidated sheet is calendared by passing the sheet through a nip formed between a flat smooth roll and ^a rubber coated back-up roll. In other embodiments, one side of the consolidated sheet is embossed and;the other side of the consolidated sheet is toll surface bonded.

[0128] 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 temperature and pressure, and length of time during Which these are applied. In some embodiments, each embossing roll(s) have a temperature of about 135“C to about 21 O’C during bonding, and in other embodiments each embossing roll(s) have a temperature of about 14O°C to about 155OC during bonding. The nip pressure can be varied with embossing roll configuration and engraving paftems, backup roll diameter, rubber hardness and thickness.

[0129] In some embodiments, the consolidated sheet wraps the heated embosser roll such that the angle between the direction of entry and the direction of exit (the wrap angle) is from about 10° to about 140°, in other embodiments, the wrap angle is from about 10° to about 100°, and in other embodiments, the wrap angle is from about 10° to about 60°. In some embodiments, the static pressure in the nip of the embosser is between about 150 kPa and about 750 kPa. An “embosser" as used herein means a pair of two rolls forming a nip, one being a heated embossing roll and the other being a rubber coated back-up roll. In some embodiments, when using a consolidated sheet originally formed tom the spinning process as described herein using a spin agent comprising one or more hydrocarbons as spin agent, the static pressure in the nip of the embosser is between about 150 kPa to about 750kPa, and in other embodiments from about 250 kPa to about 600 kPa. In some embodiments, when using a consolidated sheet originally formed from the spinning process as described herein using a spin agent comprising a mixture of chlorine- and fluorine- containing solvents as spin agent, the static pressure in the nip of the embosser is between about 150 kPa to about 600 kPa, and in other embodiments from about 150 kPa to about 500 kPa.

[0130] In some embodiments, the consolidated sheet may be in contad with pre-heat rolls before thermally bonding and / or may be in contact with cooling rolls after thermally bonding, as described in US 5,972,147. The embossing roll(s) may be any suitable material known in the art. In some embodiments the embossing roll(s) are metal.

[0131] The embossing roll( s) are engraved witi a pattern The embossing roli(s) may include any pattern known in the art, including, but not limited to, a point pattern as described in US 3,478,141, US 6,610,390, and US 2004 / 241399 Al, a rib pattern as described in US 2003 / 0032355 Al and US 2003 / 0165667 Al, a linen pattern as described in US 2008 / 0220681 A1, a random pattern as described in US 7,744,989, and other variations of patterns as described in US 5,620,779 and US 5,964,742, The degree of bonding can vary depending on the embossing pattern chosen. Exemplary illustrations of suitable embossing patterns are shown in Figures 1 to 3; exemplary point patterns are illustrated in FIGS. 1A to 1C, an exemplary rib pattern is illustrated in FIG.2, and an exemplary linen pattern is illustrated in FIG, 3 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 patern, and in other embodiments, the consolidated sheet is embossed oh both sides using different paterns. In some embodiments, the consolidated sheet is embossed on both sides using a point patern, in other embodiments, the consolidated sheet is embossed on both sides using a rib pattern, and in other embodiments, the consolidated sheet is embossed on both sides using a linen patern. In some embodiments, the consolidated sheet is embossed on one side using a point pattern and, on another side, using a rib pattern, in other embodiments, the consolidated sheet is embossed on one side using a point patern 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 patern.

[0132] The patterns on the embossing roll(s) 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 paterns at different depths such that certain portions of the consolidated sheet are subjected to more bonding than others.

[0133] 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 % ofthe area of at least one side of the consolidated sheet is embossed, in other embodiments, from about 10 % to about 60 %, in other embodiments, from about 15 % to about 60 %, in other embodiments, from about 20 % to about 60 %, in other embodiments, from about 26 % to about 60 %. in other embodiments, from about 30 % to about 60 %, and in other embodiments, from about 50 % to about 85 %. In some embodiments, abbut 6 % to about 85 % of the area of both sides of the consolidated sheet is embossed, in other embodiments, from about 10 % to about 60 %, in other embodiments, from about 15 % to about 60 %, in other embodiments, from about 20 % to about 60 %, in other embodiments, from about 26 % to about 60 %, in other embodiments, from about 30 % to about 60 %, and in other embodiments, from about 50 % to about 85 %. In some embodiments, about 50 % to about 85 % of the area of one side of the consolidated sheet is embossed using a linen pattern, and about 15 % to about 60 % or about 20 % to about 60 % or about 26 % to about 60 % of the area of other side of the consolidated sheet is embossed using a rib pattern. Mechanical Softening

[0134] 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 rolls which are driven at substantially the same surface 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 rol Is that are dri ven at a different speed than the speed of the thermally bonded sheet. This difference in speed creates a rubbing effect that may create loose fibrils, which can jeopardize the barrier properties ofthe softened sheet.

[0135] In some embodiments, when using a thermally bonded sheet originally formed from the spinning process as described herein using a spin agent comprising one or more hydrocarbons or using a spin agent comprising a mixture of chlorine- and fluorine-containing solvents, the thermally bonded sheet is mechanically softened by passing it through one or more nips between rolls driven at substantially the same speed as the speed of the bonded sheet, wherein each roll has interpenetrating pins and rotates in the opposite direction to the other roll, and wherein each interpenetrating pin is a blunt pin. By “blunt pin" is meant a pin that includes at least a distal end that has a blunt surface (i.e. , a surface not having a sharp edge or point) and a shaft that has a surface.;

[0136] As shown in Figure 4A, the blunt pin 10 has a proximal end 11 , a distal end 12, and a shaft 14< The shaft 14 may comprise one or more tapered portions. The shaft 14 of the blunt pin 10 may be any shape known in the art. The shaft 14 may be sfraight (i.e., having basically the same cross-section along the longitudinal axis ofthe shaft 14), or tapered toward the distal end 12 (i.e.,: having a decreasing cross-section along the longitudinal axis of the shaft 14 from the proximal end 11 toward the distal end 12), or a combination thereof (as exemplarily illustrated in Figure 4A). In some embodiments, the shaft 14 has edges 47 that are parallel, in other embodiments, the shaft 14 has edges 17 that are tapered toward the distal end 12,: and in other embodiments, the shaft 14 has edges 17 that begin parallel at the proximal end 11 of the shaft 14 but then taper toward the distal end 12 of the shaft 14 such that the shaft 14 comprises a tapered end portion 13. The tapered end portion 13 may have more than one taper portion, each with an increasing angle of taper toward the distal end 12 of the shaft 14 (not shown). In some embodiments, the cross-section of the shaft 14 is a regular or irregular polygon, including, without being limited thereto, a rectangle, a pentagon, a hexagon, or an octagon. In some embodiments, the Cross-section 14 ofthe shaft is a hexagon (as exemplarily illustrated in Figures 4A to 4C). In some embodiments, the cross-section of the shaft 14 is a square (as exemplarily illustrated in Figures 5A to 50). In some embodiments, the crosssection of the shaft 14 is round, including a circle (see Figures 6A to 6D and Figures 7A to 7D ) or an oval (not shown). The distal end 12 has a blunt surface 15 that is flat. In some embodiments, the blunt surface 15 may have the shape of a regular or irregular polygon, including, without being limited thereto, a rectangle, a pentagon, a hexagon, or an octagon, when viewed from above. In some embodiments, the blunt surface hasthe shape of a hexagon (as exemplarily illustrated in Figures 4B and 4G). In some embodiments, the blunt surface 15 has the shape of a quadrilateral, for example a rectangle or a square (not shown). In some embodiments, the blunt surface 15 has the same or a different shape as the cross-section of the shaft 14. In some embodiments, both die blunt surface 15 and the cross-section of the shaft have the same shape, for example, the shape of a hexagon (as exemplarily illustrated in Figures 4A to 4G). In some embodiments, both the blunt surface 15 and the cross-section of the shaft have the shape of a square (not shown). In some embodiments, the blunt surface 15 may have a different shape than the cross-section of the shaft 14 (as exemplarily illustrated in Figures 5A to 50). In some embodiments, the blunt surface 15 has the shape of an octagon and the cross- section of the shaft 14 is a square (as exemplarily illustrated in Figures 5B and 5C). In some embodiments, the shaft 14 has the cross-section of an octagon and the blunt surface 15 has the shape of a square (not shown). In some embodiments, the blunt surface 15 has a circular shape (as exemplarily illustrated in Figures 6A to 60 and Figures 7A to 70). in some embodiments, the blunt surface 15 has an oval shape (not shown). In some embodiments, the blunt surface 15 has a circular shape and the cross-section of the shaft 14 is circular as well (see Figures 6A to 60 and Figures 7Ato 7D). ; However, the distal end 12 may have any type of blunt surface (i e., surface not having a sharp edge or point) known in the art, including, but not limited to, a blunt surface 15 that is rounded, forming a smooth curving surface In some embodiments, the distal end 12 has a blunt surface 15 that is flat, and in other embodiments, the distal end 12 has a blunt surface 15 that is rounded. A blunt surface 15 that is rounded can be seen in Figures 6E and 7E.: The distal end 12 and shaft 14 meet to form an edge 16. The edge 16 between the distal end 12 and shaft 14 may be any type of edge known in the art, including, but not limited to, a corner edge, a rounded edge, or a chamfer edge; provided, however, that all corner edges must form an angle 18 greater than 90 degrees. In some embodiments, the edge 16 between the distal end 12 and the shaft 14 is a corner edge at an angle greater than 90 degrees, in other embodiments, the edge 16 between the distal end 12 and the shaft 14 is a corner edge at an angle greater than 100 degrees, and in other embodiments, the edge 16between the distal end 12 and the shaft 14 is a corner edge at an angle greater than

[0137] 2,4 135 degrees. In some embodiments, the edge 16 is a rounded edge, and in other embodiments, the edge 16 is a chamfer edge.

[0138] In some embodiments, the edge 16 between the distal end 12 and shaft 14 is a rounded edge having a radius of curvature of from about 0.1 mm to about 0.5 mm, and in other embodiments, having a radius of curvature of from about 0.25 mm to about 0.4 mm.

[0139] In some embodiments, the shaft 14 has a cylindrical shape (see Figures 6A to 7E). In some embodiments, the cylindrical shaft 14 may comprise a tapered end portion 13 (see Figures 6A to 6E), in other embodiments the cylindrical shaft 14 may be fully tapered from the proximal end 11 toward the distal end 12 (not shown), te„ the shape of the blunt pin 10 has the shape of a truncated cone, and in some other embodiments the cylindrical shaft 14 does not comprise a tapered portion (see Figures 7A to 7E).

[0140] I n som e embodiments, the shaft 14 has a cylindrical shape with a circular cross-section at the proximal end 11 , the cross section at the proximal end 11 having a diameter of from about 0.6 mm to about 2 mm, in other embodiments, having a diameter of from about 0.8 mm to about 1 .8 mm, and in other embodiments, having a diameter of from about 1 .0 mm to about 1 6 mm.

[0141] In some embodiments, the distal end 12 of the blunt pins 10 has a blunt surface having a diameter of from about 0.4 mm to about 1 .8 mm, in other embodiments, having a diameter of from about 0.6 mm to about 1 .6 mm, and in other embodiments, having a diameter of from about 1.0 mm to about 1.4 mm.

[0142] In some embodiments, the blunt pins 10 have a length of about 0.5 mm to about 6mm, in other embodiments, of about 1 mm to about 4 mm, and in other embodiments, of about 2 to 3 mm.

[0143] In some embodiments, the diameter of the distal end 12 of the blunt pins 10 is less than 100 % of the diameter of the base of the shaft 14. in other embodiments the diameter of the distal end 12 of the blunt pins 10 is less then 90 % of the diameter of the base of the shaft 14, in other embodiments, the diameter of the distal end 12 of the blunt pins 10 is less than 80 % of the diameter of the base of the shaft 14, in other embodiments, the diameter of the distal end 12 of the blunt pins 10 is less than 70 % of the diameter of the base of the shaft 14, in other embodiments, the diameter of the distal end 12 of the blunt pins 10 is less than 60 % of the diameter of the base of the shaft 14, in other embodiments, the diameter of the distal end 12 of the blunt pins 10 is less than 50 % of the diameter of the base of the shaft 14, in other embodiments, the diameter of the distal end 12 of the blunt pins 10 is less than 40 % of the diameter of the base of the shaft 14, in other embodiments, the diameter of the distal end 12 of the blunt pins 10 is less than 30 % of the diameter of the base of the shaft 14, in other embodiments, the diameter of the distal end 12 of the blunt pins 10 is less than 20 % of the diameter Of the base of the shaft 14, and in other embodiments, the diameter of the distal end 12 of the blunt pins 10 is less than 10 % of the diameter of the base of the shaft 14.

[0144] Figures 6A to 6E and Figures 7A to 7E show diferent cylindrical blunt pins 10 with blunt surfaces 15 with varying diameters. The blunt surface 15 can have a slightly smaller diameter than the smallest diameter of the tapered end portion 13 of the shaft 14 (see Figure

[0145] 6C), can have a significantly smaller diameter than the smallest diameter of the tapered end portion 13 of the shaft 14 (see Figure 6D), can be a rounded distal end 12 (see Figure 6E), or can have the same diameter as the smallest diameter of the tapered end portion 13 of the shaft 14 (not shown). The blunt surface 15 can have a slightly smaller diameter than the diameter of the shaft 14 (see Figure 7C). can have a significantly smaller diameter than the diameter of the shaft 14 (see Figure 70), or can be a rounded distal end 12 (see Figure 7E).

[0146] The blunt pin 10 may include one or more intermediate surfaces 20 between the distal end 12 and the proximal end 11. I n some embodiments the one or more intermediate surfaces 20 are comprised in one or more tapered portions of the shaft 14, including, but not limited to the tapered end portion 13, as exemplarily shown in Figures 4A and 5A. Each of the one or more intermediate surfaces 20 meet with an adjacent surface within the tapered portion to form an edge 17. The edge 17 between each of the one or more intermediate surfaces 20 and the adjacent surfaces within the tapered portion 13 may be any type of edge known in the art, including, but not limited to, a corner edge, a rounded edge, or a chamfer edge The blunt pin 10 may include one or more intermediate surfaces 22 between the distal end 12 and the proximal end 11 . In some embodiments the one or more intermediate surfaces 22 meet with one or more adjacent intermediate surfaces 20 to form an edge 19. the one or more intermediate surfaces 20 and 22 being adjacent along the longitudinal axis of the shaft 14. The edge 19 may be any type of edge known in the art including, but not limited to, a corner edge, a rounded edge, ora chamfer edge provided, however, that all corner edges 19 must form an angle between adjacent intermediate surfaces 20 and 22 greater than 90 degrees In some embodiments, the edge 19 between adjacent intermediate surfaces 20 and 22 is a corner edge at an angle greater than 90 degrees, in other embodiments, the edge 19 between adjacent intermediate surfeces 20 and 22 is a corner edge at an angle greater than 100 degrees, and in other embodiments, the edge 19 between adjacent intermediate surfaces 20 and 22 is a corner edge at an angle greater than 135 degrees.

[0147] The blunt pins 10 of each roll are arranged in an array and have distal ends 12 that are equidistant from the roll’s axis,; The array of blunt pins 10 on one roll interpenetrates the array of blunt pins 10 on the opposite roil by a depth that is at least equal to the thickness of the sheet, In some embodiments, the blunt pins 10 are separated by about 1.5 mm to about 5.0 mm center-to-center in the machine direction (MD) and by about 1.5 mm to about 5.0 mm center-to-center in the transverse direction (XD) direction. In some embodiments, the blunt pins 10 are separated by about 2.5 mm to about 4.0 mm center-to-center:in the machine direction, and in other embodiments, the blunt pins 10 are separated by about 3.0 mm to about 3.5 mm center-to-center in the machine direction. In some embodiments, the blunt pins 10 are separated by about 2.5 mm to about 4.0 mm center-to-center in the transverse direction, and in other embodiments, the blunt pins 10 are separated by about 3.0 mm to about 3.5 mm center-to-center in the transverse direction. The blunt pins 10 in the machine direction may be separated by the same or a different distance as the distance separating the blunt pins 10 in the transverse direction. The blunt pins 10 may be arranged in various arrays, including, but not limited to, square, rectangular, and triangular arrays. In some embodiments, the blunt pins 10 are arranged in an array wherein the ratio of center-to-center distance •between adjacent blunt pins 10 to the diameter of the adjacent blunt pins 10 is from about 2:1 to about 10:1, and in other embodiments, from about 3:1 to about 5’1. ft has been discovered that the absence of sharp points and / or sharp edges on the distal end 12 of the blunt pins 10 allows the mechanical softening process to operate with an increased degree of interpenetration of the array of blunt pins 10 on one roll Into the array of blunt pins 10 on the other roll without wmpromising the barrier properOes of the sheet. In contrast thereto, the use of other pin configurations, such as the square edged pins of US 3,920,874 and US 3,811,979, may lead to excessive localized deformation or fracture at higher degrees of interpenetration, resulting in compromised barrier properties in the softened sheet. The use of a blunt pin 10 allows a softer product to be achieved in a single step, whereas multiple pin softening steps may be needed with other pin configurations to reach the desired level ot softness for a garment application. Mechanically softening the bonded sheet using interpenetrating blunt pins 10 as described above can be applied, irrespective of whether the sheet of nonwoven flash-spun plexifilamentary fibrils is originally formed from the spinning process as described herein using a spin agent comprising one or more hydrocarbons or formed from the spinning process as described herein using a spin agent comprising a mixture of chlorine- and fluorine-containing solvents.

[0148] Mechanically softening the bonded sheet using interpenetrating blunt pins 10 as described above can be applied to a sheet of nonwoven flash-spun plexifilamentary fibrils originally formed from the spinning process as described herein using a spin agent comprising one or more hydrocarbons, as well as to a sheet of nonwoven flash-spun plexifilamentary fibrils originally formed tom the spinning process as described herein using a spin agent comprising a mixture of chlorine- and fluorine-containing solvents. Contrary to the mechanically softening described in US 3,920,874, the mechanically softening using interpenetrating blunt pins 10 as described herein can also be used to soften a bonded sheet wherein the average elongation is below 10 %.

[0149] For the process using a thermally bonded sheet originally formed from the spinning process as described herein using a spin agent comprising a mixture of chlorine- and fluorine- containing solvents, various additional softening procedures can be applied

[0150] In some embodiments, when using a thermally bonded sheet originally formed from the spinning process as described herein using a spin agent comprising a mixture of chlorine* and fluorine-containing solvents, the thermally bonded sheet is mechanically softened by passing it through one or more nips between rolls, each rotating in the opposite direction as the other roll and each bearing a multiplicity of interpenetrating square-ended pins By "square-ended pin" is meant that the distal end of the pin and the shaft of the pin form an edge at an angle 18 of 90 degrees or less providing a relatively sharp edge around the periphery of each pin end. In some embodiments, the square-ended pins have a square edged cylindrical Shape as disclosed in US 3,920,874 and US 3,811 ,979. in some embodiments, when using a thermally bonded sheet originally formed from the spinning process as described herein using a spin agent comprising a mixture of chlorine- and fluorine-containing solvents, the thermally bonded sheet is mechanically softened (as described in US 5,966,785 or US 6,195,854) by passing it through a nip of two rolls, each rotating in the opposite direction as the other roll, wherein one of the rolls bears a multiplicity of knobs and the other roll is a soft rubber back-up roll

[0151] In some embodiments, the sheet of nonwoven flash-spun plexifilamentary fibrils (originally formed from the spinning processes as described herein using a spin agent comprising either one or more hydrocarbons or a mixture of chlorine- and fluorine-containing solvents) is passed once through the median cal softening step as described herein, and in other embodiments, the sheet of nonwoven flash-spun plexifilamentary fibrils is passed multiple times through the mechanical softening step as described herein The depth of interpenetration of the pins may be adjusted as desired for each pass through the mechanical softening step as described herein. In some embodiments, the depth of interpenetration of the pins is the same for each pass through the mechanical softening step as described herein, and in other embodiments, the depth of interpenetration of the pins is different in at least one pass through the mechanical softening step as described herein than the depth of interpenetration of the pins used in any other passes. In some embodiments, the configuration of the pins is different in at least one pass through the mechanical softening step as described herein than the configuration of the pins used in any other passes.

[0152] In some embodiments, an antistatic treatment is applied to the thermally bonded or bonded and softened sheet. Antistatic treatment improves electrostatic properties of a textile, in particular surface resistivity. In some embodiments, the antistatic treatment is applied by applying a coating composition comprising an antistatic compound In some embodiments, the antistatic compound is a phosphate ester, in particular a phosphate ester defined by the formula: MnRs nPO.:, 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 com binations thereof.

[0153] In some embodiments,: there is provided a sheet of nonwoven flash-spun plexifilamentary fibrils obtained or obtainable by the process described herein.

[0154] In some embodiments, the obtained sheet has

[0155] (a) a basis weight from about 32 g / m2to about 56g / m2,

[0156] (b) a Gurley Hill porosity from about 1 seconds to about 30 seconds,

[0157] (c) a particle filtration efficiency of about 90 % ormore, and

[0158] (d) a handie-o-meter stiffness from about 0.05 N to about 0.70 N.

[0159] Uses, Multilayer Structures, and Articles

[0160] The sheet of nonwoven flash-spun plexifilamentary fibrils as described herein has many uses and may be used in a variety of applications, including, but not limited to, multilayer structures, garments (including, but not limited to, protective apparel), house wrap, roof lining, car covers, medical packaging, and filtration media.

[0161] Further embodiments relate to a multilayer structure comprising at feast one sheet of nonwoven flash-spun plexifilamentary fibrils as described herein, and at least one further sheet or a film.

[0162] In some embodiments, the multilayer structure comprises a film that is a microporous film . I n one embodiment, the microporous film is a film that is filled and stretched as described in US 9,809,00482. Microporous films from highly fifed 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.

[0163] In some embodiments, the multilayer structure is a laminated Structure comprising a microporous film laminated with at least one sheet of nonwoven flash-spun plexifilamentary fibrils as described herein. In some embodiments, a micropordus 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 t»th the microporous film and the sheet of nonwoven flash-spun plexifilamentary fibrils, as described in US 9,809,004 B2.

[0164] Further embodiments relate to use of the sheet of nonwoven flash-spun plexifilamentary fibrils as described herein for preparing a multilayer structure.

[0165] Further embodiments relate to use of the sheet of nonwoven flash-spun plexifilamentary fibrils as described herein for the production of garments.

[0166] Further embodiments relate to use of the multilayer structure as described herein for the production of garments. 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 tom garment, protective apparel, house wrap, roof lining, car cover, medical package, and filtration media. Protective apparel includes foil 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 garmente 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. In some embodiments, the article is medical packaging, including, but not limited to. medical wrap for the packaging of medical items such as surgical instruments during sterilization.

[0167] EXAMPLES

[0168] 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

[0169] Trichlorofluoromethane (Freon 11), CAS Nr. 75-69-4 has an atmospheric boiling point of 23.8°C, e -molecular weight of 248 g / mol and a critical point of 198X. The trichlorofluoromethane used had a purity level above 99.5 percent by weight.

[0170] N-pentane, CAS Nr 109-66-0, has an atmospheric boiling point of 36.1 °C, a molecular weight of 72.151 g / mol and a critical temperature of 196 7°C. The n-pentane used had a purity level above 95 percent by weight

[0171] Cyclopentane, 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.

[0172] 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' C The dichloromethane used had a purity level above 99.5 percent by weight. 2H,3H-decafluoropentane (HFC-4310-mee), CAS Nn 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.

[0173] The polyethylene used had a density of 0.957 g / cm3(ISO 1183) and melt flow rates of 0.3 g / 10min (ISO 1133 condition D, 19O°C / 2.16 kg) and 22 g / IOmin (IS0 1133 condition G, 190°C / 21 6 kg).

[0174] The polyethylene blend used was a blend of a high-density polyethylene with a density >0.95 g / cm3and a melt flow rate of 0.7 g / 1 Omin (ASTM 1238 190°C / 2.16 kg) and a linear low- density polyethylene (LLDPE, an ethylene-hexene copolymer) with a density of 0918 g / cm3and a melt flow rate of 1.0 g / 10min (ASTM 1238 190°C / 2.16kg) in a 90:10 ratio by weight.

[0175] 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.

[0176] Results Comparative examples 1 and 2

[0177] A flash-spun sheet was produced using the flash spinning process described by US 3,227,794 and US 3,851,023 using a spin fluid of 12 wt% polyethylene having a density >0.95 g / cm3and a melt flow rate of 0.74 g / 10min (ASTM 1238 190°C / 2.16 kg), in a spin agent of F11 (trichlorofluoromethane) at a spin temperature of 180°C. The flash-spun sheet was subsequently thermally bonded and embossed. For comparative example 1, one side was calendared by passing the sheet through a nip formed between a smooth heated roil and a rubber roll and the opposite side was embossed through a nip formed between a heated embosser roll having a rib pattern and a rubber roll. For comparative example 2, one side was embossed by passing the sheet through a nip formed between a heated roll with a linen pattern and a rubber roll and the opposite side was embossed through a nip formed between a heated embosser roll having a rib pattern and a rubber roll.

[0178] The thermally bonded sheets of both comparative examples (CE1a and CE2a) were subsequently passed between two rolls with interpenetrating blunt pins having a diameter of 1 mm, with an upper edge radius of curvature of 0.25 mm. The blunt pins were separated by

[0179] 3.3 mm center-to-center in MD direction and 3.2 mm center-to-center m XD direction at the point of interacting with the flash-spun sheets. The softened sheets are represented below as CElb and CE2b.

[0180] The spinning, bonding, and softening conditions and sheet properties are reported in Table 1 , below.

[0181] Table 1: Summary of the sheet preparation of Comparative Examples 1 and 2.

[0182] * not applicable

[0183] Comparative example 1 (CE1a and CElb) shows that for a full surface area bonded sheet, the sheet was not significantly softened by mechanical pin softening. Additionally, there were no significant changes in the air permeability, hydrostatic head , and particle -filtration -efficiency upon softening.

[0184] Comparative example 2 (CE2a and CE2b) shows that with an embossed surface area on both sides, with mechanical pin softening, the softness increases and -the Gurley Hili porosity decreases (better air permeability), but the particle filtration efficiency decreases as does the hydrostatic head. Comparative example 2 demonstrates that with mechanical pin softening, there is a trade-off between the air permeability and the barrier properties when using F11 (trichlorofluoromethane) as the spin agent.

[0185] Examples l and 2 Flash-spun sheets were produced using the flash spinning process described by US 3,227,794 and US 3.851.023 at a spin temperature of 190 C. using a spin fluid of 17 wt% polymer in a hydrocarbon-based spin agent that was a mixture of n-pentane and cyclopentane (herein also referred to as “H”). the 17 wt% polymer was a blend of a high-density polyethylene with a density >0.95 g / cm3and a melt flow rate of 0.74 g / 10min (ASTM 1238 190 C / 2.16 kg) an ethylene-hexene copolyme' with a density of 0 918 g / cm ' and a melt flow rate of 1.0 g / lOmin (ASTM 1238 190 W 16kg) in a 90:10 ratio by weight. The flash spin sheets were subsequently thermally bonded.

[0186] For Example 1, one side was calendared by passing the sheet through a nip formed between a flat smooth roll and a rubber roll and the opposite side was embossed through a nip fbnned between an embosser roll having a rib pattern and a rubber rcrfl.

[0187] For Example 2, one side was embossed by passing the sheet through a nip formed between a heated roll with a linen pattern and a rubber roll and the opposite side was embossed through a nip formed between an embosser roll having a rib patern and a rubber roll.

[0188] The thermally bonded sheets of both examples were subsequently transferred through a nip of two rolls with interpenetrating blunt pins having a diameter of 1 mm, with an upper edge radius of curvature of 0.25 mm. The blunt pins were separated by 3.3 mm center-to- center in MD direction and 3.2 mm center-to-center in XD direction at the point of interacting with the flash-spun sheets.

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

[0190] Table 2* Summary of the sheet preparation of Examples 1 and 2.

[0191] * not applicable

[0192] Example 1 (El a and E1b) and Example 2 (E2a and E2b) show a mechanical pin softening process with blunt pins for a sheet having an elongation in the machine direction (MD) below 10%. Additionally, Example 1 shows a mechanical pin softening process with blunt pins for a flash-spun sheet with a 100% full surface area bonded. Example 1 (Eta and Elb) shows that for a sheet that was full surface area thermally bonded on one side, with mechanical pin softening, the softness increases (reduced Handle- O-Meter stiffness) and the Gurley Hill porosity decreases (better air permeability), while the particle filtration efficiency unexpectedly increases. Additionally, there is no clear indication of a change in the hydrostatic head These observations differ from the findings of ComparativeExample 1 (where Fl 1 was used as spin agent). Surprisingly, it has been found that when using a hydrocarbon-based spin agent, with mechanical pin softening, the air permeability of the softened sheet improves, while the dry particulate barrier improves and the liquid barrier is maintained. i

[0193] Example 2 (E2a and E2b) illustrates that for a thermally bonded sheet with linen / rib embossing, with mechanical pin softening, the softness increases and the Gurley Hill porosity decreases (better air permeability), while the particle filtration efficiency increases. The increase in the particle filtration efficiency with mechanical pin softening is opposite to the trend seen in comparative Example 2.

[0194] Examples 3 and 4 Flash-spun sheets were produced using the flash spinning process described by US 3,227,794 and US 3,851,023 at different spin temperatures using a;spin fluid of a polyethylene with a density >0.95 g / cm3and a melt flow rate of 0.74 g / 10mtn (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 sheets of Examples 3 and 4 were subsequently thermally bonded. One side of each flash-spun Sheet was embossed by passing the sheet through a nip formed between a heated embosser roll with a linen pattern and a rubber roll and the opposite side was embossed through a hip formed between a heated embosser roll having a rib pattern and a rubber roil.

[0195] The thermally bonded sheets of both examples were subsequently transferred through a nip of two rolls with interpenetrating blunt p ns having a diameter of 1 mm. with an upper edge radius 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 XP direction at the point of interacting with the flash- spun sheets.

[0196] The spinning, bonding, and softening conditions and sheet properties are reported in Table 3, below. Table 3: Summary of the sheet preparation of Examples 3 and 4.

[0197] : Example 3 (E3a and E3b) and Example 4 (E4a and E4b) show that for a flash-spun sheet prepared using a chlorine-containing solvent in combination with a hydrofluorocarbon, mechanical pin softening with increased interpenetration of the blunt pins results in a reduction in the Gurley Hill porosity (better air permeability) and an increase in the particle filtration efficiency.

[0198] Examples 5 to 7 Flash-spun sheets were produced using the flash spinning process described by

[0199] US 3,227,794 and US 3,851,023 at different spin temperatures and polymer concentrations, using a spin fluid of a 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 mixture of n-pentane and cyclopentane (herein also referred to as "H ). The flash-spun sheets of Examples 5 to 7 were subsequently thermally bonded. One side of each flash-spun sheet was embossed by passing the sheet through a nip formed between a heated embosser roll with a linen pattern and a rubber roll, and the opposite side was embossed by passing the sheet through a nip formed between a heated embosser roll having a rib pattern and a rubber roll. The thermally bonded sheets of the examples were subsequently transferred through a nip of two rolls with interpenetrating blunt p ns 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 fiash-spun sheets.

[0200] The spinning, bonding, and softening conditions and sheet properties are reported in Table 4Sbelow.

[0201] Table 4; Summary of the sheet preparation of Bcamples 5, 6 and 7. * not applicable

[0202] Examples 5 (E5a and E5b) / 6 (E6a and E6b), and 7 (E7a and E7b) show that for a flash-spun sheet with a basis weight of about 42 and 52 g / m2, mechanical pin softening with increased interpenetration of the blunt pins results in a reduction in the Gurley Hill porosity while also leading to an increase in the particle filtration efficiency. Example 8

[0203] A flash-spun sheet was produced using the flash spinning process described by US 3,227.794 and US 3,851 ,023 at a spin temperature of 210 C and a polymer concentration of 10.5 wt%, using a spin fluid of a polyethylene having a density >0.95 g / cm3and a melt flow rate of 0.74 g / IOmin (ISO 1133 190°C / 2.16 kg), in a spin agent mixture of dichloromethane and 2H,3H-decafluoropentane (herein also referred to as “D”). The ratio of the spin agent mixture was adjusted to change the cloud point pressure of the spin fluid as illustrated in Figure 2 of US 6,004.672 The flash-spun sheet of Example 8 was subsequently thermally bonded using a process as described in US 2003 / 0165667. The consolidated sheet was first in alternating contact with two pre-heat rolls set at a temperature of 60°C before being embossed on both sides with rib patterns. The thermally bonded sheet of example 8 was subsequently transferred through a nip of two rolls with interpenetrating blunt pins having a diameter of 1 mm, with an upper edge radius of curvature of 0.25 mm. The blunt pins were separated by 3.3 mm center-to-center in MD direction and 3.2 mm center-to-center in XD direction at the point of interacting with the flash-spun sheet.

[0204] The spinning, bonding, and softening conditions and sheet properties are reported in

[0205] Table 5, below.

[0206] Table 5: Summary of the sheet preparation of Example 8. In Example 8 (E8a and E8b), with mechanical pin softening with increased interpenetration of the blunt pins, the air permeability of the sheet improves, as reflected by a decrease in the Gurley Hill porosity, while the particle filtration efficiency improves. Examples 9 and 10

[0207] Flash-spun sheets were produced using the flash spinning process described by US 3,227,794 and US 3.851,023 at a spin temperature of 200' C using a spin fluid of a polyethylene having a density >0.95 g / cm3and melt flow rate of 0,74 g / IOmin (ISO 1133 190°C / 2.16 kg), at different polymer concentrations in a hydrocarbon-based spin ragent mixture of n-pentane and cyclopentane (herein also referred to as’H”). The flash-spun sheets of Examples 9 and 10 were subsequently thermally bonded using a process as described in US 2003 / 0165667. The consolidated sheets were first in alternating contact with two pre-heat rolls set at a temperature of 60°C before being embossed on both sides with rib patterns. The thermally bonded sheets of examples 9 and 10 were subsequently transferred 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 rand 3.2 mm center-to-center in XO direction at the point of interacting With the flash-spun sheets.

[0208] The spinning, bonding, and softening conditions and sheet properties are reported in Table 6, below.

[0209] Table 6: Summary of the sheet preparation of Examples 9 and 10.

[0210] In Examples 9 (E9a and E9b) and 10 (ElOa and El Ob), with mechanical pin softening with increased interpenetration of the blunt pins, the sheet becomes softer and the air permeability of the sheet improves, as reflected by a decrease in the Gurley Hill porosity. In addition, the particle filtration efficiency improves with increasing interpenetration of the blunt pins.

[0211] Examples 11 and 12

[0212] Flash-spun sheets were produced using the:flash spinning process described by US 3,227,794 and US 3,851 ,023 US 3,851 ,023 at a spin temperature of 200°C and a polymer concentration of 16 wt%, using a spin fluid of a polyethylene with a density >0.95 g / cm3and melt flow rate of 0.75 g / 10min (ISO 1133 190X / 2.16 kg) in a hydrocarbon-based spin agent mixture of n-pentane and cyclopentane (herein also referred to as “H*). The flash-spun sheets of Examples 11 and 12 were subsequently thermally bonded. For each Example, one side of the flash-spun sheet was embossed by passing the sheet through a nip formed between a heated embosser roll with a linen pattern and a rubber roll. For Example 11 , the opposite side was embossed by passing the sheet through a nip formed between a heated embosser roll having a point bonded patern A (as shown in FIG. TO) and a rubber roll. For Example 12, the opposite side was embossed by passing the sheet through a nip formed between a heated embosser roll having a point bonded pattern B (as shown in FIG. 1B) and a rubber roll.

[0213] The thermally bonded sheets of both examples were subsequently transferred through a nip of two rolls with interpenetrating blunt p ns having a diameter of 1 mm. with an upper edge radius of curvature 0,25 mm. The blunt pins were separated by 3.3 mm in MD direction and 3.2 mm center-to-center in XD direction at the point of interacting with the flash-spun sheets.

[0214] The spinning, bonding, and softening conditions and sheet properties are reported in Table 7, below. Table 7: Summary of the sheet preparation of Examples 11 and 12.

[0215] Tn Example 11 (El la and El 1b) and Example 12 (El2a and El 2b), with mechanical pin softening with increased interpenetration of the blunt pins, the sheet becomes softer and the air permeability of the sheet improves, as reflected by a decrease in the Gurley Hill porosity. In addition, the particle filtration efficiency unexpectedly improves with increasing interpenetration of the blunt pins.

[0216] OTHER EMBODIMENTS

[0217] 1. In some embodiments, the present application provides a thermally bonded sheet of nonwoven flash^spun plexifilamentary fibrils, the sheet having

[0218] (a) a basis weight from about 32 g / m2to about 56 g / m2,

[0219] (b) a Gurley Hill porosity from about 1 seconds to about 30 seconds,

[0220] (c) a particle filtration efficiency of about 90 % or more, and

[0221] (d) a handle-o-meter stiffness from about 0.05 N to about 0 70 N.

[0222] 2. The sheet of embodiment 1 having a basis weight from about 38 g / m2to about 52 g / m2.

[0223] 3 The sheet of any one of the preceding embodiments having a basis weight from about

[0224] 40 g / m2to about 50 g / m2.

[0225] 4. The sheet of any one of the preceding embodiments having a basis weight from about

[0226] 41 g / m2to about 49 g / m2. 5. The sheet of any one of embodiments having a Gurley Hill porosity from about 3 seconds to about 25 seconds.

[0227] 6. The sheet of any one of embodiments having a Gurley Hili porosity from about 5 seconds to about 22 seconds. 7. The sheet of any one of embodiments having a Gurley Hl porosity from about 5 seconds to about 20 seconds.

[0228] 8. The sheet of any one of embodiments having a Gurley Hill porosity from about 3 seconds to about 15 seconds.

[0229] 9. The sheet of any one of the preceding embodiments having a handle«o-meter stiftoess from about 0.10 N to about 0.40 N.

[0230] 10. The sheet of any one of the preceding embodiments having a handle^o-meter stiffness from about 0.12 N to about 0,35 W

[0231] 11. The sheet of any one of the preceding embodiments having a handle*o-meter stiffness from about 0.15 N to about 0.30 N. 12. The sheet of any one of the preceding embodiments having a particle filtration efficiency from about 90.0 % to about 99.9 %.

[0232] 13. The sheet of any one of the preceding embodiments having a particle filtration efficiency from about 95.0 % to about 99.9 %.

[0233] 14.;The sheet ^ any one of the preceding embodiments having a particle flitration efficiency from about 97.0 % to about 99,9 %.

[0234] 15. The sheet of any one of the preceding embodiments having a particle filtration efficiency from about 99.0 % to about 99.9 %.

[0235] 16. The Sheet of any one of the preceding embodiments having a hydrostatic head tom about 50 cmHzO to about 170 cmH?O. 17. The sheet of any one of the preceding embodiments having a hydrostatic head from about 100 cmHjO to about 150 cmHzO.

[0236] 18. The sheet of any one of the preceding embodiments having a hydrostatic head from about 120 cmHzO to about 140 cmHzO.

[0237] 19. The sheet of any one of the preceding embodiments having an elongation in at least one direction, selected from the machine direction (MB) and the transverse direction

[0238] (XD), of less than about 12 %.

[0239] 20. The sheet of any one of the preceding embodiments having an elongation in at least one direction, selected from the machine direction (MD) and the transverse direction (XD), of more than about 5 %. 21. The sheet of any one of the preceding embodiments having an elongation in at least one direction, selected from the machine direction (MD) and the transverse direction (XO), from more than about 5 % to less than about 10 %. 22. The sheet of any one of the preceding embodiments having an elongation in at least one direction,:selected from the machine direction (MP) and the transverse direction (XP), from more than about 6 % to less than about 8 %.

[0240] 23. The sheet of any one Of the preceding embodiments having a BET surface .area from about 4 m2 / g to about 12 m2 / g.

[0241] 24. The sheet of any one of the preceding embodiments having a BET surface area from about 4 m2 / g to about 8 rh2^.

[0242] 25. The sheet of any one of the preceding embodiments having a BET surface area from about 8 m2 / g to about 12 m2 / g. 26, The sheet of any one of the prececing embodiments having a Moisture vapor transmission rate (MVTR) from about 5000 g / mlday to about 16,000 g / m2 / day.:

[0243] 27. The sheet of any one of the preceding embodiments having a MVTR from about 6000 g / miday to about 16,000 g / m2 / day

[0244] 28. The sheet of any one of the preceding embodiments having a MVTR from about 8000 g / m^day to about 14,000 g / m2 / day

[0245] 29. The sheet of any one of the preceding embodiments, wherein the flash-spun plexifilamentary fibrils are comprised of a polyolefin, selected from the group of polyethylene (PE), polypropylene (PP), and blends / mixtures thereof.

[0246] 30. The sheet of embodiment 29, wherein said polyolefin is a high-density polyethylene, a blend of a high-density polyethylene (HOPE) with a linear low-density polyethylene

[0247] ^LLPPE), or a blend of a high-density polyethylene (HOPE) with a lbw-density polyethylene (LDPE).

[0248] 31. The sheet of any of the preceding embodiments, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 32 g / m- to about 38 g / m- . a Guriev Hill porosity from about 3 seconds to 15 seconds, a particle filtration efficiency from about 90 0 % to about 95.0 %. and a handle-o-meter stiffness from about 0 1 N to about 0.3 N

[0249] 32. The sheet of any of the preceding embodiments, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 40 g / m2to about 45 g / m2, a Gurley Hill porosity from about 3 seconds to 15 seconds, a particle filtration efficiency from about 91 .0 % to about 99.5 %, and a handle-o-meter stiffness from about 0.15 N to about 0.45 N.

[0250] 33. The sheet of any of the preceding embodiments, wherein the flash-spun plexifilamentary fibrils of the sheet are comprised of a high-density polyethylene, and the sheet has a basis weight from about 43 g / m2to about 50 g / m2, a Gurley Hill porosity from about 3 seconds to 15 < seconds, a particle ■ filtration efficiency from about 95.0 % to about 99.0 %, and a handle-o-meter stiffness from about 0.2 N to about 0.5 N. 34. A process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps oft

[0251] (i) generating a spin fluid comprising

[0252] (a) from about 8.0 to about 11 .5 weight percent of a polymer, based on the total amount of the spin fluid and

[0253] (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,

[0254] (ii) flash spinning the spin fluid at a temperature at or above about 205°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,

[0255] (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*

[0256] ( i v) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet* and

[0257] (v) mechanically softening the bonded sheet by passing it through one or more hips between rotating rolls driven at substantially the same speed as the speed of the bonded sheet to obtain a softened sheet of nonwoven flash-spun plexifilamentary fibrils.

[0258] 35. The process of embodiment 34, wherein the spin fluid comprises the polymer in an amount of from about 8.5 to about 1 1 .5 weight percent, based on the total amount of the spin fluid.

[0259] 36. The process of any one of embodiments 34 to 35, wherein the spin fluid comprises the polymer in an amount of from about 9.0 to about 11 .0 weight percent, based on the total amount of the spin fluid.

[0260] 37. The process of any one of embodiments 34 to 36* wherein the spin fluid comprises the polymer in an amount of from about 9.5 to about 11 .0 weight percent, based on the total amount of the spin fluid.

[0261] 38. The process of any one of embodiments 34 to 37, wherein the spin fluid comprises the spin agent in an amount of from about 88 5 to about 92 0 weight percent, based on the total amount of the spin fluid.

[0262] 39. The process of any one of embodiments 34 to 38, Wherein the spin fluid comprises the spin agent in an amount of from about 89.0 to about 91.0 weight percent, based on the total amount of the spin fluid. , 40. The process of any one of embodiments 34 to 39, wherein the spin fluid comprises the spin agent in an amount of from about 89.0 to about 90.5 weight percent, based on the total amount of the spin fluid.

[0263] 41. The process of any one of embodiments 34 to 40, wherein the flash-spinning is performed at a temperature from about 205:C to about 230' C

[0264] 42. The process of any one of embodiments 34 to 41, wherein the flash-spinning is performed at a temperature from about 205°C to about 220ilC.

[0265] 43. The -process of any one of embodiments 34 to - 42, wherein the fluorine-containing solvent is a hydrofluorocarbon having three to six carbon -atoms, perfluorocarbons having three to six carbon atoms or a hydrofluoroether.

[0266] 44. The process of embodiment 43, wherein 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, 1 H,6H-perfluorohexane, or 1 H-perfluorohexane. 45. The process of any one of embodiments 34 to44, wherein the plexifllamentary fibrils are spun at a spin temperature from about 205°C to about 230’C using a spin fluid comprising about 8.0 to about 11 .5 weight percent polymer, and comprising a spin agent which comprises, consists essentially of, or consists of dichloromethane and 2H.3H- decafluoropentane, IHAH-perfiuorobutane, 1H,6H-perfluorohexane, 1H- perfluorohexane, perfluoropentane, perfluorohexane, or 1,1,1,3,3-pentafluorobutane.

[0267] 46. The process of any one of embodiments 34 to 45, wherein the plexifllamentary fibrils are spun at a spin temperature from about 205"C to about 220°C using a spin fluid comprising about 9 0 to about 11.0 weight percent polymer and comprising a spin agent which comprises, consists essentially of, or consists of dichioromethane and 2H.3H- decafluoropentane, l H,4H-perfluorobutane. 1H,6H-perfluorohexane, 1H- perfluorohexane, perfluoropentane, perfluorohexane. or 1 . 1 ,1.3.3-pentafluorobutane

[0268] 47. The process of any one of embodiments 34 to 46. wherein in step (v), the bonded sheet is softened by passing it through one or more nips between rolls driven at substantially the same speed as the speed of the bonded sheet, wherein each roll has interpenetrating pins and rotates in the opposite direction as the other, and wherein each interpenetrating pin is a blunt pin,

[0269] 48. A process tor the preparation of a sheet of nonwoven flash-spun plexifilameritary fibrils which comprises the stops ofi

[0270] (I) generating a spin fluid comprising (a) from about 12,0 to about 19.0 weight percent of a polymer, based on the total amount of the spin fluid, and

[0271] (b) a spin agent comprising one or more hydrocarbons, (fl) flash spinning the spin fluid 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,

[0272] (iii) collecting the plexifilamentary fibrils of the polymer on a collecting means as. a sheet of nonwoven flash-spun plexifilamentary fibrils and apply ing pressure to the sheet to obtain a consolidated sheet,

[0273] (iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet, and

[0274] (v) mechanically softening the bonded sheet to obtain a softened sheet of nonwoven flash-spun plexifilamentary fibrils by passing : it through one or more nips between rolls driven at substantially the same speed as the speed of the bonded sheet, wherein each roil has interpenetrating pins and rotates in the opposite direction as the other roll, and wherein each interpenetrating pin is a blunt pin.

[0275] 49. The process of any one of embodiments 34 to 48, wherein the polymer is a polyolefin, selected from the group of polyethylene (PE), polypropylene (PP), and blends / mixtures thereof.

[0276] 50. The process of any one of embodiments 34 to 49 , wherein the polyolefin is a high- density polyethylene (HOPE), a blend Of a high-density polyethylene (HOPE) with a linear low-density polyethylene (LLDPE), or a blend of a high-density polyethylene (HDPE) with a low-density polyethylene (LOPE).

[0277] 51. The process of any one of embodiments 48 to 50, wherein the spin fluid comprises the polymer in an amount of from about 13.0 to about 18.0 weight percent, based on the total amount of the spin fluid.

[0278] 52. The process of any one of embodiments 48 to 51 , wherein the spin fluid comprises the polymer in an amount of from about 14.0 to about 17.0 weight percent, based on the total amount of the spin fluid

[0279] 53. The process of any one of embodiments 48 to 52, wherein the spin fluid comprises the spin agent in an amount of from about 82 0 to about 87.0 weight percent, based on the total amount of the spin fluid.

[0280] 54. The process of any one of embodiments 48 to 53, wherein the spin fluid comprises the spin agent in an amount of from about 83.0 to about 86.0 weight percent, based on the total amount of the spin fluid.

[0281] 55. The:: process of any one of embodiments 48 to 54, wherein the flash-spinning is performed at a temperature from about 185°C to about 205°C.

[0282] 56. The precess of any one of embodiments 48 to :55, wherein the flash-spinning is perfermed at a temperature from about 195°C to about 205°C. 57. The process of any one of embodiments 48 to 56, wherein the one or more hydrocarbons of the spin agent are selected from n-pentane, cyclopentane, hexane, cyclohexane, 2,2- dimethyibutane, n-butane, or mixtures thereof.

[0283] 58. The process of any one Of embodiments 48 to 57, wherein the spin agent comprises n-pentane, cyclopentane, or a mixture thereof

[0284] 59. The process of any one of embodiments 48 to 58, wherein the spin agent consists essentially of or consists of n-pentane.

[0285] 60. The process of embodiment 59, wherein the flash-spinning is performed at a temperature from about 185°C to about 205°C. 61. The process of any one of embodiments 48 to 58, wherein the spin agent consists essentially of or consists of a mixture of n-pentane and cyclopentane.

[0286] 62. The process of any one of embodiments 48 to 58, wherein the spin agent consists essentially of or consists of from about 60 to about 85 weight percent n-pentane and from about 15 to about 40 weight percent cyclopentane. 63. The process of any one of embodiments 48 to 58, wherein the spin agent consists essentially of or consists of from about 65 to about 80 weight percent n-pentane and from about 20 to about 35 weight percent cyclopentane.

[0287] 64. The process of any one of embodiments48 to 58, wherein the spin agent comprises or consists essentially of a mixture of n-pentane, cyclopentane, and 2, 2-dimethylbutane. 65. The process of any one of embodiments 48 to 58, wherein the spin agent consists essentially of or consists of a mixture of 60 to about 85 weight percent n-pentane, from about 13 to about 33 weight percent cyclopentane and from about 2 to about 7 weight percent 2.2-dimethylbutane

[0288] 66. The process of any one of embodiments 61 to 65, wherein the flash-spinning is performed at a temperature from about 195°C to about 205*0.

[0289] 67. The process of any one of embodiments 34 to 66, wherein at least one side of the consolidated sheet is embossed,

[0290] 68. The process of any one of embodiments 34 to 67. wherein the embossing roll(s) apply a pressure during bonding from about 150 kPa to about 750 kPa. 69. The process of any one of embodiments 34 to 68, wherein the consolidated sheet is embossed on both sides using the same patern.

[0291] 70. The process of embodiment 69, wherein the consolidated sheet is embossed on both sides using a point pattern, or the consolidated sheet is embossed on both sides using a rib patern, or the consolidated sheet is embossed on both sides using a linen pattern. 71. The process of any one of embodiments 34 to 68, wherein the consolidated sheet is embossed on both sides using different patterns. 72. The process of embodiment 71, wherein the consolidated sheet is embossed on one side using a point pattern and on another side using a rib pattern, or the consolidated sheet is embossed on one side using a point pattern and on another side using a linen pattern, or the consolidated sheet is embossed on one side using a rib pattern and on another side using a linen pattern.;

[0292] 73. The process of any one of embodiments 34 to 72, wherein in the mechanical softening step, each interpenetrating pin is a blunt pin 10 that includes at least a distal end 12 that has a blunt surface 15 and a shaft that has a surface 14.

[0293] 74. The process of embodiment 73, wherein the edges 17 of the shaft 14 are parallel, tapered toward the distal end 12, or a combination thereof.

[0294] 75. The process of any one of embodiments 73 to 74, wherein the cross-section of the shaft 14 is a regular or irregular polygon.

[0295] 76. The process of embodiments 75, wherein the xyoss^section of the shaft 14 is a rectangle, a pentagon, a hexagon, or an octagon. 77. The process of any one of embodiments 73 to 74, wherein the cross-section of the shaft 14 is round, including a cirde or an oval.

[0296] 78. The process of any one of embodiments 73 to 77, wherein the blunt surface 15 is flat and has the shape of a regular or irregular polygon, including a rectangle, a pentagon, a hexagon, or an octagon. 79. The process of any one of embodiments 73 to 77, wherein the blunt surface 15 is round or oval.

[0297] 80. The process of any one of embodiments 73 to 79, wherein the blunt pins 10 have a cylindrical shape with a circular cross-section at the proximal end I t, wherein the cross- section at the proximal end 11 has a diameter tom about O.8 mm to about 1.8 mm, and wherein the distal end 12 of the blunt pins 10 has a blunt surface having a diameter of from about 0.6 mm to about 1 .6 mm.

[0298] 81. The process of any one of embodiments 73 to 80 wherein the blunt pins 10 are separated by about 1.5 mm to about 5.C mm center-to center in the machine direction (MD) and by about 1.5 mm to about 5.0 mm center-to center in the transverse direction (XD) direction.

[0299] 82. The process of any one of embodiments 34 to 81, wherein the obtained sheet has

[0300] (a) a basis weight from about 32 g / m2to about 56 g / m2,

[0301] (b) a Gurley Hill porosity from about 1 seconds to about 30 seconds,

[0302] (c) a particle filtration efficiency of about 90 % or more, and

[0303] (d) a handle-o-meter stiffness from about 0.05 N to about 0.70 N.

[0304] 83. A sheet of nonwoven flash-spun plexifilamentary fibrils obtainable by the process of any one of embodiments 34 to 82. 84. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils, the sheet having

[0305] (a) a basis weight from about 32 g / m2to about 56 g / m2,

[0306] (b) a Gurley Hill porosity from about 1 seconds to about 30 seconds, (c) a particle filtration efficiency of about 90 % or more, and

[0307] (d) a handle-o-meter stiffness from about 0.05 N to about 0.70 N, wherein the sheet is obtained by the process of any one of embodiments 34 to 82.

[0308] 85. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils comprised of a high-density polyethylene, wherein the sheet has a basis weight from about 32 g / m2to about 38 g / m2, a Gurley Hill porosity from about 3 seconds to 15 seconds, a particle filtration efficiency from about 90.6 % to about 95.0 %, and a handle-o-meter stiffness from about 0.1 N to about 0.3 N, and wherein the sheet is obtained by the process of any one of embodiments 34 to 82;

[0309] 86. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils comprised of a high-density polyethylene, wherein the sheet has a basis weight from about 40 g / m2to about 45 g / m2, a Gurley Hill porosity from about 3 seconds to 15 seconds, a particle filtration efficiency from about 91.0 % to about 995 %, and a handle-o-meter stiffness from about 0.15 N to about 0.45 N, and wherein the sheet is obtained by the process of any one of embodiments 34 to 82. 87. A thermally bonded sheet of nonwoven flash-spun plexifilamentary fibrils comprised of a high-density polyethylene, wherein the sheet has a basis weight from about 43 g / m2to about 50 g / m2, a Gurley Hili porosity from about 3 seconds to 15 seconds, a particle filtration efficiency from about 95.0 % to about 99.0 %, and a handle-o-meter stiffness from about 0.2 N to about 0.5 N, and wherein the sheet is obtained by the process of any one of embodiments 34 to 82.

[0310] 88. A multilayer structure comprising at least one sheet according to any one of embodiments 1 to 33 or 83 to 87 and at least one further sheet or film

[0311] 89. The multilayer structure of embodiment 88 comprising a film that is a microporous film.

[0312] 90. The multilayer structure of embodiment 88 to 89, wheran the microporous film is prepared from filled polyolefins.

[0313] 91. The multilayer structure of any one of embodiments 88 to 90, wherein the multilayer structure is a laminated structure comprising a microporous film bonded with at least one sheet according to any one of embodiments 1 to 33 or 83 to 87.

[0314] 92. Use of the sheet of any one of embodiments 1 to 33 or 83 to 87 for preparing a multilayer structure.

[0315] 93. Use of a sheet of any one of embodiments 1 to 33 or 83 to 87 or of the multilayer Structure of any of embodiments 88 to 91 for the production of garments. 94. An article comprising a sheet of any one of embodiments 1 to 33 or 83 to 87 or a multilayer structure of any of embodiments 88 to 91 ,

[0316] 95. The article of embodiment 94, wherein the article is selected from garment, protective apparel, medical packaging, and house wrap.

[0317] 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 invention.

[0318] 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 form 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.

[0319] 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 plexifilamentary fibrils, the sheet having;(a) a basis weight from about 32 g / m2to about 56 g / m2,(b) a Gurley Hill porosity from about 1 seconds to about 30 seconds,(c) a particle filtration efficiency of about 90 % or more, and(d) a handle-o-meter stiffness from about 005 N to about 0.70 N.

2. The sheet of claim 1 having an elongation in at least one direction, selected from the machine direction (MD) and the transverse direction (XD), of less than about 12 % and / or having a BET surface area from about 4 m;' / 'g to about 12 m / g.

3. The sheet of any one of claims 1 to 2 having a hydrostatic head from about SO cmHzO to about 160 cmH>O, or having a Gurley Hill porosity from about 3 seconds to about25 seconds.

4. The sheet of any one of claims 1 to 3 having a handle-o-meter stiffness from about 0.1 N to about 0.4 N, or having a particle filtration efficiency from about 90 0 % to about 99.9 %.

5. The sheet of any one of claims 1 to 4, wherein the flash-spun plexifilamentary fibrils are comprised Of a polyolefin, selected from the group of polyethylene (PE), polypropylene (PP), and blends / mixtures thereof, or wherein the flash-spun plexifilamentary fibrils are comprised of a polyolefim wherein said polyolefin is a high-density polyethylene, a blend of a high-density polyethylene (HDPE) with a linear low-density polyethylene (LLDPE), or a blend of a high-density polyethylene (HDPE) with a low-density polyethylene (LDPE).6: A process for the preparation of a sheet of nonwoven flash-spun plexifilamentary fibrils which comprises the steps of:(i) generating a spin fluid comprising(a) from about 8.0 to about 11.5 weight percent of a polymer, based on the total amount of the spin fluid, and(b) a spin agent comprising a chlorine-containing solvent, selected from dichloromethane, cis- 1 ,2-dichloroethylene, and trans- 1 ,2-dichloroethylene, in combination with a fluorine-containing solvent,(ii) flash spinning the spin fluid at a temperature at or above about 205°C and at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of the polymer,(iii) collecting the plexifilamentary fibrils of the polymer on a collecting means as;a sheet of nonwoven flash-spun plexifilamentary fibrils and applying pressure to the sheet to obtain a Consolidated sheet,(iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet, and(v) mechanically softening the bonded sheet by passing ft through one or more nips between rotating rolls driven at substantially the same speed as the speed of the bonded sheet to obtain a softened sheet of nonwoven flash-spun plexifilamentary fibrils.

7. The process of claim 6, wherein in step (v), the bonded sheet is softened by passing it through one or more nips between rolls driven at substantially the same speed as the speed of the bonded sheet, wherein each roll has interpenetrating pins and rotates in the Opposite direction as the other, and wherein each interpenetrating pin is a blunt pin.

8. The process of any one of claims 6 to 7, wherein the spin agent comprises dichloromethane in combination with perfluoropentane, perfluorohexane, 1,1, 1,3, 3- pentafluorobutane, 1H,4H-perfluorobutane, 2H,3H-decafluoropentane, 1H.6H- perfluorohexane, or 1H-perfluorohexane.

9. 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) ftom about 12.0 to about 19.0 weight percent of a polymer, based on the total amount of the spin fluid, and(b) a spin agent comprising one or more hydrocarbons,(ii) flash spinning the spin fluid at a pressure that is above the vapor pressure of the spin fluid into a region of essentially atmospheric pressure to form plexifilamentary fibrils of the polymer,(iii) collecting the plexifilamentary fibrils of the polymer on a collecting means as a sheet of nonwoven flash-spun plexifilamentary fibrils and applying pressure to the sheet to obtain a consolidated sheet, :(iv) thermally bonding by embossing the consolidated sheet to obtain a bonded sheet, and(v) mechanically softening the bonded sheet to obtain a softened sheet of nonwoven flash-spun plexifilamentary fibrils by passing it through one or more nips between rolls driven at substantially the same speed as the speed of the bonded sheet, wherein each roll has interpenetrating pins and rotates in the opposite direction as the other roll, and wherein each interpenetrating pin is a blunt pin.

10. The process of claim 9, wherein the spin agent comprises n-pentane, cyclopentane, or a mixture thereof.

11. The process of any one of claims 6 to 10, wherein the polymer is a polyolefin, selected from the group of polyethylene (PE), polypropylene (PP), and blends / mixtures thereof, or wherein the polymer is a polyolefin, wherein said polyolefin is a high-density polyethylene (HDPE), a blend of a high-density polyethylene (HOPE) with a linear low-density polyethylene (LLDPE), or a blend of a high-density polyethylene (HDPE) with a low-density polyethylene (LOPE).

12. The process of any one of claims 6 to 11 , wherein the obtained Sheet has(a) a basis weight from about 32 g / m2to about 56 g / m2,(b) a Gurtey Hill porosity from about 1 seconds to about 30 seconds,(c) a particle filtration efficiency of about 90 % or more, and(d) a handle-o-meter stiffness from about 0.05 N to about 0.70 N.

13. A sheet of nonwoven flash-spun plexifilamentary fibrils obtainable by the process of any one of claims 6 to 12.

14. A multilayer structure comprising at least one sheet according to any one of claims 1 to 5 or 13 and at least one further sheet or film15. Use of the sheet of any one of claims 1 to 5 or 13 for preparing a multilayerstructure.

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

17. An article comprising a sheet of any one of claims 1 to 5 or 13 or a multilayer structure of claim 14.;18 The article of claim 17, wherein the article is selected from garment, protective apparel, medical packaging, and house wrap.

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