WO2001046505A2

WO2001046505A2 - Nonwoven webs having liquid impermeability

Info

Publication number: WO2001046505A2
Application number: PCT/US2000/034633
Authority: WO
Inventors: Sharon L. Greene; Jeffrey E. Fish; Ali Yahiaoui; Rosann M. Kaylor; Jark Lau; Gene Varona
Original assignee: Kimberly-Clark Worldwide, Inc.
Priority date: 1999-12-23
Filing date: 2000-12-20
Publication date: 2001-06-28
Also published as: BR0016688A; JP2003518204A; AU2730601A; GB2375723A; AR027057A1; KR20020071901A; WO2001046505A3; MXPA02006108A; DE10085342T1; GB0216123D0

Abstract

The invention provides a fabric which acts as a barrier to liquids. The fabric may include a substrate having a coating. More particularly, this invention provides nonwoven webs having liquid impermeability; i.e., nonwoven webs having a resistance to penetration by a liquid which impinges the webs. A porous substrate comprising a fabric having pores with a diameter of less than about 12 micrometers and a surface free energy of less than about 40 dynes/cm is useful in such fabrics. The pore diameter and surface free energy values provide a fabric having (1) a water vapor transmission rate across the fabric greater than about 3000 g/m²/24 hours, and (2) a rain impact value of less than about 0.5 g at a hydrostatic head of about 91 cm.

Description

NONWOVEN WEBS HAVING LIQUID IMPERMEABILITY

The present invention relates to nonwoven webs More particularly, the present invention relates to nonwoven webs having liquid impermeability and a resistance to penetration by a liquid impinging on the web

BACKGROUND Fabrics incorporated into garments may provide protection against external elements such as ram or personal protection against liquid hazards, such as toxic chemicals Consequently, it is desirable that these fabrics, which are sometimes enhanced by chemical treatments, provide the proper repellancy

Unfortunately, garments that provide repellancy may often fail to provide breathability Breathability may be measured by the water vapor transmission rate Failure to provide a sufficient water vapor transmission rate in a fabric may result in moisture, such as sweat, being trapped within the fabπc or garment The trapped moisture may cause the garments to be uncomfortable to wear, and may result in the workers failing to wear the garments Accordingly, a fabric that provides a fluid barrier while also providing breathability would be a desirable improvement over conventional fabrics

DEFINITIONS

As used herein, the term "fabπc" refers to a material made from fibers by such methods as weaving, knitting, felting, extruding, spunbonding, and meltblowing A fabric includes nonwoven materials woven materials, laminates, coforms, and films

As used herein, the term "grafted" refers to the bonding, such as covalent bonding, of one material to another

As used herein, the term "woven" refers a network of crossed and interlaced material

As used herein, the term "nonwoven web" refers to a web that has a structure of individual fibers which are interlaid (forming a matrix), but typically not in an identifiable repeating manner Nonwoven webs have been, in the past, formed by a variety of processes known to those skilled in the art such as, for example, meltblowing, spunbonding, wet-forming and various bonded carded web processes

As used herein, the term "spunbond web" refers to a web formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries with the diameter of the extruded filaments then being rapidly reduced, for example, by fluid-drawing or other well known spunbonding mechanisms The production of spunbond nonwoven webs is illustrated in patents such as Appel, et al , U S Patent No 4,340,563

As used herein, the term "meltblown web" means a web having fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten fibers into a high-velocity gas (e g air) stream which attenuates the fibers of molten thermoplastic material to reduce their diameters Thereafter, the meltblown fibers are carried by the high- velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed fibers The meltblown process is well-known and is described in various patents and publications, including NRL Report 4364, "Manufacture of Super-Fine Organic Fibers" by V A Wendt, E L Boone, and C D Fluharty, NRL Report 5265, "An Improved Device for the Formation of Super-Fine Thermoplastic Fibers" by K D Lawrence R T Lukas, and J A Young, and U S Patent No 3,849,241 , issued November 19, 1974, to Buntin, et al , which are hereby incorporated by reference

As used herein, the term "cellulose" refers to a natural carbohydrate high polymer (polysacchaπde) having the chemical formula (C₅H₁₀O₅)_n and consisting of anhydroglucose units joined by an oxygen linkage to form long molecular chains that are essentially linear Natural sources of cellulose include deciduous and coniferous trees, cotton, flax, esparto grass, milkweed, straw, jute, hemp, and bagasse

As used herein, the term "pulp" refers to cellulose processed by such treatments as, for example, thermal, chemical and/or mechanical treatments As used herein, the term "coform" refers to a material made from nonwoven and pulp fibers

As used herein, the term "slurry" refers to a watery mixture of insoluble matter, such as pulp As used herein, the term "fiber" refers to a fundamental solid form, usually crystalline, characterized by relatively high tenacity and an extremely high ratio of length to diameter, such as several hundred to one Exemplary natural fibers are wool, silk, cotton, and asbestos Exemplary semisynthetic fibers include rayon Exemplary synthetic fibers include spinneret extruded polyamides, polyesters, acrylics, and polyolefms

As used herein, the term "weight percent" refers to a percentage calculated by dividing the weight of a material of a mixture by the total weight of the mixture and multiplying this quotient by 100 As used herein, the term "percent add-on" refers to the percent of material added to a substrate after undergoing a treatment The percent addon is calculated by subtracting the pre-treatment weight from the post- treatment weight and dividing this difference by the pre-treatment weight This quotient is than multiplied by 100 to obtain the percent add-on As used herein, the term "percent reduction in bond strength" refers to the percent reduction in maximum peel load by calculating the maximum peel load difference between a treated and an untreated substrate, dividing this difference by the maximum peel load of the untreated substrate, and multiplying this quotient by 100 As used herein, the term "water vapor transmission rate" refers to the steady state water vapor flow in unit time through unit area of a body normal to specific parallel surfaces, under specific conditions of temperature and humidity at each surface and may be abbreviated "WVTR"

As used herein, the term "normalized" refers to conforming to a norm or standard In the water vapor transmission test procedure, the normalization is the correction of the "base" vapor transmission to a rate proportional to a standard of 5,000 g/m²/day for CELGARD^® 2500 microporous film This normalization corrects for variation in oven air inlet humidity

As used herein, the term "vapor pressure" refers to the pressure exerted by a vapor that is in equilibrium with its solid or liquid form

As used herein, the term "permeability" refers to the quality or state of a material that determines the amount of a flow that will pass through the material under given conditions per unit time As used herein, the term "non-hygroscopic" refers to not readily taking up and retaining moisture.

As used herein, the term "hygrometer" refers to an instrument for measuring the humidity of the air. As used herein, the term "flange" refers to a rim for attachment to another object.

As used herein, the term "sample" refers to a portion of the production which is taken for testing and is used in the laboratory as a source of test specimens. As used herein, the term "specimen" refers to a specific portion of a sample upon which a test is performed.

SUMMARY OF THE INVENTION

This present invention provides a fabric for erecting a barrier to liquids. The fabric may include a substrate having a coating. The coated fabric may have a water vapor transmission rate greater than about 3000 g/m²/24 hours, and moreover, may have a rain impact value less than about 0.3 grams at a hydrostatic head of about 91 cm. The coating may be selected from the group comprising fluorinated monomers, terpolymers (tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene and vinylidene fluoride such as

Dyneon™ THV Fluorothermoplastic material. The fluorinated monomers may be selected from the group comprising fluoroacrylate and fluoromethacrylate. Alternatively, the coating may be selected from the group comprising fluoroacrylate monomers, terpolymers and siloxanes. Furthermore, the substrate may be a nonwoven material, more particularly, a meltblown material. In addition, the substrate may be a polymer, and more particularly may be selected from the group including polyolefins, polyesters, acrylics and polyamides. Moreover, the polymer may be polypropylene. Another embodiment of the present invention is a process of making a barrier fabric. The process may include the steps of providing a substrate, applying a active agent solution to the substrate, and exposing the substrate to electromagnetic radiation, thus creating a barrier fabric. The process may include an additional step of passing the substrate applied with solution through a nip prior to radiation exposure The barrier fabric may have a water vapor transmission rate greater than about 3000 g/m /24 hours and a rain impact value less than about 0 3 grams at a hydrostatic head of about 91 cm The active agent may be a fluorinated monomer, and more particularly, a fluoroacrylate In addition, the fluorinated monomer may be dissolved in an acetone solvent forming between about 1 to about 3 weight percent fluorinated monomer in solution In addition, the substrate may be a polymer and more particularly, the polymer may be selected from the group comprising polyolefins, polyesters, and polyamides A still further embodiment of the present invention is a fabric for providing a barrier to liquids The fabric may include a polypropylene substrate The polypropylene substrate may have a fluorinated monomer coating The fabric may have a water vapor transmission rate greater than about 3000 g/m²/24 hours and a rain impact value less than about 0 3 grams at a hydrostatic head of about 91 cm

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an enlarged cross-section view of an exemplary die tip, Figure 2 is an enlarged, schematic cross-sectional view of another exemplary die tip,

Figure 3 is an enlarged, schematic cross-sectional view of still another exemplary die tip,

Figure 4 is an enlarged cross-section view of an additional exemplary die

Figure 5 is a bottom, perspective view of an exemplary die tip

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made to the embodiments of the invention, one or more examples of which are set forth below Each example is provided by way of explanation of the invention not as a limitation of the invention In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in this invention without departing from the scope or spirit of the invention For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents Other objects, features and aspects of the present invention are disclosed in or are obvious from the following detailed description It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions

It is desirable for the fabrics of the present invention to exhibit repellancy to various liquids while permitting the passage of vapor through pores in the fabric Desirably, the present invention facilitates using a fabric with a relatively large pore size for increasing breathability while still providing a liquid barrier The untreated fabrics or substrates of the present invention may be manufactured from woven materials, non-woven materials, laminates, and films These substrates may include natural fibers, such as wool, polymers, or mixtures thereof Polymers used to manufacture substrates may include polyolefins, such as polyethylene, polypropylene, and polybutylene, polyesters, polyamide polymers, such as nylon, and polyesters, such as polyethylene terephthalate, acrylics, or mixtures thereof An exemplary material is polypropylene, sold under the trade designation EXXON 3746G or EXXON 3505 by Exxon Chemical Company of Houston, Texas, or HIMONT PF-015 by Montell Polyolefins of Wilmington, Delaware Generally, the substrate used in the present invention may have several properties relating to average pore size, average fiber diameter, apparent web density, basis weight, and thickness An exemplary substrate may have an average pore size less than about 50 microns Desirably, the substrate may have an average pore size of about 1-10 microns More desirably, the substrate may have an average pore size of about 2 - 8 microns The pore size is measured by a capillary flow porometer as hereinafter described

The substrate may have an average fiber diameter from about 2 microns to about 7 microns as measured by scanning electron micrographs and image analysis Furthermore, the substrate may have an apparent web density from about 0.8 g/cm³ to about 2 g/cm³ as measured by dividing the mass by the volume (area times thickness). Moreover, the substrate may have a basis weight from about 0.5 osy (17 g/m²) to about 3 osy (102 g/m²). Desirably, the substrate may have a basis weight of about 1.5-3 osy (51-102 g/m²). The thickness of the substrate may range from about 0.015 in. (0.038 cm) to about

0.40 in. (1.02 cm).

In one desired embodiment, the substrate is a meltblown web having a pore size of about 5-10 microns. This web may be formed by a meltblown process, such as disclosed in U.S. Patent No. 4,526,733 to Lau, which is hereby incorporated by reference.

Several parameters, such as melt temperature, air temperature, air pressure, forming height, and through-put affect the formation of the meltblown web. Referring to the disclosure in U.S. Patent No. 4,526,733, a desired melt temperature for the polymer in the die may range from about 400^° F (204^° C) to about 550^° F (288^° C), and more desirably from about 430^° F (221^° C) to about 500^° F (260^° C). Alternatively, the desired melt temperature for the polymer in the die may range from about 380^° F (193^° C) to about 700^° F (371^° C), and more desirably, from about 400^° F (204^° C) to about 550^° F (288^° C). Exemplary pressures and temperatures of the air entering the die through a conduit may range from about 400^° F (204^° C) to about 550^° F (288^° C) and from about 2 psig ( 13,800 Pa) to about 20 psig ( 138,000 Pa), and more desirably, from about 430^° F (221^° C) to about 500^° F (260^° C) and from about 4 psig ( 27,600 Pa) to about 12 psig ( 82,760 Pa). Alternatively, exemplary temperatures of the air entering the die through a conduit may range from about 70^° F (21 ° C) to about 550^° F (288^° C), and more desirably from about

400^° F (204^° C) to about 550^° F (288^° C). The difference in temperature between the polymer in the die and the incoming air may vary from about 0^° F (0^° C) to about 500^° F ( 278^° C), or alternatively, may vary from about 200^° F (111 ^■ C) to about 300^° F (167^° C). The forming height, which is the distance between the exit of the die and the top surface of the belt may range from about 3 in. (8 cm) to about 20 in. (51 cm), and more desirably, from about 5 in. (13 cm) to about 9 in. (23 cm). The polymer through-put may range from about 0.7 (lbs per in.)/hr (125 (g per cm)/hr) to about 5 (lbs per in.)/hr (446 (g per cm)/hr), and more desirably, about 0 7 (lbs per in )/hr (125 (ς per cm)/hr) to about 1 5 (lbs per in )/hr (268 (g per cm)/hr)

Turning now to Figure 1, an exemplary meltblown process also may include a heating element for warming the die tip One such exemplary die 10 is depicted in Figure 1 The die 10 may include a body 14, a die tip 18, and air plates 30A-B The die tip 18 may be attached to the body 14 using any suitable means, such as bolts 28A-B The air plates 30A-B may be secured proximate to the die tip 18 using any suitable means such as bolts 32A-B The body 14 and die tip 18 may form a passageway 22 terminating in a narrow cylindrical outlet 26 for ejecting polymer material Generally, this outlet 26 may have a diameter of about 0 0145 in ( 0 0368 cm) and a length of about 0 1 in (0 254 cm) Furthermore, the die tip 18 and air plates 30A-B may form channels 36A-B for allowing air past the outlet 26 for expelling polymeric fibers out the gap 38 In this exemplary die 10, the die tip 18 is in a recessed configuration

The die tip may include a tip 24, a heat insulative coating 46, a heat absorbent coating 48, and a screen filter 20 The insulative coating 46 may be a low heat conductive material, such as ceramic paint, and the absorbent coating 48 may be a high heat absorbent material, such as black stove paint The air plates 30A-B may include bolts 32A-B, spacing shims 34A-B, and heating elements 42A-B The bolts 32A-B and spacing shims 34A-B may be used to adjust the air plates 30A-B and with respect to the die tip 18 At least one heating element 42A-B may be used, but desirably, two heating elements 42A-B may be utilized The heating elements 42A-B may be resistant electric cartridge heaters or electromagnetic radiation emitters As an example, the heating elements 42A-B may be quartz glass infrared lamps or emitters, such as those available from Hereaus-Amersil of Norcross, Georgia Desirably, these lamps are as small as possible yet give sufficient heat As an example, these lamps may be 10 millimeters in diameter and extend longer than the length of the die tip 18 More desirably, these lamps emit 170 watts per inch (67 watts per cm) Moreover, these lamps may be coated with a reflective material 44A-B, such as gold, for about 270 degrees around the lamp's periphery The uncoated periphery of the heating elements 42A-B may be positioned from about 0 01 in (0 03 cm) to about 1 in (2 54 cm) from the respective flank 50A-B of the die tip 18 Desirably, the uncoated periphery of the heating elements 42A-B may be positioned about 0 25 in (0 32 cm) from the respective flank 50A-B of the die tip 18 Furthermore, the heating elements 42A-B may be recessed in the air plate 30 to minimize the creation of turbulence in the air flow through the channels 36A-B

When the heating elements 42A-B are activated, they typically provide heat proximate to the die tip apex 24 The heating elements 42A-B may either radiate heat to the tip 18 near the die tip apex 24 where the heat may travel to the apex 24 by conduction, or desirably, the heating elements 42A-B may directly radiate heat to the apex 24 The radiated heat is absorbed by the absorbent coating 48 to aid heating the apex 24, and the insulative coating 46 helps maintain the heat within the tip 18

Referring to Figure 2, a lower portion of another exemplary V-shaped die 100 is depicted The die 100 may include a die tip 118 and a die tip apex 124 The die tip 118 may have at least one embedded electric cartridge heater, although desirably four embedded electric cartridge heaters 142A-D are used These cartridge heaters 142A-D provide heat to the polymer within the apex 124, and desirably, are positioned as close to the apex 124 as possible

Referring to Figure 3, another exemplary die 200 is depicted The die 200 may include a die tip 218 and a die tip apex 224 Desirably, the die tip 218 has at least one passage extending the length of the die 200, although desirably four passages 242A-D extend the length of the die 200 These passages 242A-D may be filled with a heated fluid, such as steam, oil, polymer, wax, air, or water, that is pumped the length of the die 200 to heat a polymer within a die tip apex 224 Desirably, these passages 242A-D are positioned as close to the die tip apex 224 as possible

Referring to Figures 4 and 5, a still further exemplary die 300 is depicted The die 300 may include a die tip 318, which in turn, may include a positive electrode 342, a negative electrode 344, an electrical insulating layer 352, and a die tip apex 324 Current may flow from the electrode 342 over the apex 324 of the die 300 between orifices 350 to the electrode 344, thereby using resistance to heat the die tip 318, and more desirably, the die tip apex 324 Alternatively, referring to Figure 5, the electrodes 362 and 364 may be placed at either end of the die 300 for causing current to flow lengthwise across the die 300 For either of the sets of electrodes 342 and 344, or 362 and 364, alternating current may be used In some cases, the alternating current may be at a high frequency

The present invention may form meltblown webs from materials such as polymers Exemplary polymers include polyesters, polyolefins, such as polyethylene and polypropylene, polyamides, such as nylon, elastomeπc polymers, and block copolymers These materials may have melt flow rates varying from about 12 to about 1200 decigrams per minute Exemplary polypropylenes are sold underthe trade designation EXXON 3746G or EXXON 3505 by Exxon Chemical Company of Houston, Texas, or HIMONT PF-015 by

Montell Polyolefins of Wilmington, Delaware Furthermore, these materials may have additives to reduce their viscosity, such as peroxide, or additional materials may be placed in the die to impart properties to the extruded polymers, such as fluoroacrylate monomers The DuPont Corporation of Wilmington, Delaware sells a group of fluoroacrylate monomers underthe trade name ZONYL-T ®

The fabrics formed by these meltblown processes may have an average pore size of approximately 50 microns or less Desirably, these fabrics may have an average pore size of about 1 to about 10 microns More desirably, these fabrics may have an average pore size of about 2 to about 8 microns

Fabrics having these pore sizes may be made into garments for providing a liquid barrier

In one desired embodiment, the substrates may be treated first by applying a solution and then exposing the substrate to electron beam induced grafting The solution may include an active agent and solvent Active agents may include fluorinated monomers, fluorinated polymers, such as terpolymers of tetrafluoroethylene vinyhdene fluoride and polytetrafluoropropylene, perfluoπnated polymers, and polyalkyl siloxanes, such as organomodified siloxane emulsions An exemplary terpolymer is a fluorothermoplastic sold under the trade designation THV-330R by Dyneon LLC of St Paul, MN. An exemplary siloxane emulsion is sold under the trade designation NUDRY TM 30 by the Witco Corporation, OSi Specialties Group, of Sistersville, WV

Exemplary fluorinated monomers include 2-Propenoιc acid, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl ester, 2-Propenoιc acid, 2- methyl-2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl ester, 2-Propenoιc acid, pentafluoroethyl ester, 2-Propenoιc acid, 2-methyl-, pentafluorophenyl ester, Benzene, ethenylpentafluoro-, 2-Propenoιc acid, 2,2,2-tπfluoroethyl ester, and 2-Propenoιc acid, 2-methyl-, 2,2,2-trιfluoroethyl ester Other fluoroacrylate monomers that may be used in the solution have the general structure of

CH₂=CROCO(CH₂)_x(C_nF_2n+1)

wherein n is an integer ranging from 1 to 8, x is an integer ranging from 1 to 8, and R is H or CH₃ In many instances, the fluoroacrylate monomer may be comprised of a mixture of homologues corresponding to different values of n

Monomers of this type may be readily synthesized by one of skill in the chemical arts by applying well-known techniques Additionally, many of these materials are commercially available The DuPont Corporation of Wilmington,

Delaware sells a group of fluoroacrylate monomers under the trade name ZONYL® These agents are available with different distributions of homologues More desirably, ZONYL® agents sold underthe designation "TA- N" and "TM" may be used in the practice of the present invention Solvents used in the present invention may include halogens, ketones, esters, such as ethyl acetate, and ethers, such as diethyl ether, and water Halogens may include chloroform, methylene chloride, perchloroethylene, and halogens sold under the trade designation FREON® by the DuPont Corporation Ketones may include acetone and methyl ethyl ketone The weight percent of active agent in solution may range from about 0 5 to about 50 Desirably, the weight percent of active agent in solution may range from about 0 5_ to about 30 More desirably, the weight percent of active agent in solution may range from about 1 to about 10

After impregnating or saturating the nonwoven substrates with the solution, the substrates are exposed to electron beam radiation, which results in the grafting of the active agent to the substrate, thereby forming a coat One exemplary electron beam apparatus is manufactured under the trade designation CB 150 ELECTROCURTAIN® by Energy Sciences Inc of Wilmington, Massachusetts This equipment is disclosed in U S Patent Nos 3,702,412; 3,769,600; and 3,780,308; each of which are hereby incorporated by reference.

Generally, the substrates may be exposed to an electron beam operating at an accelerating voltage from about 80 kilovolts to about 350 kilovolts. Desirably, the accelerating voltage may be from about 80 kilovolts to about 250 kilovolts. More desirably, the accelerating voltage is about 175 kilovolts. The substrate may be irradiated from about 0.1 million rads (Mrad) to about 20 million rads (Mrad). Desirably, the substrates may be irradiated from about 0.5 Mrad to about 10 Mrad. More desirably, the substrates may be irradiated from about 1 Mrad to about 5 Mrad.

TESTS

Several tests were conducted on the samples made in accordance with the present invention. These tests included basis weight, pore size, thickness, and water vapor transmission rate (WVTR). The pore size was determined in accordance with ASTM procedure F-316-86, which is a published test procedure incorporated herein by reference. The pore diameter was measured using a capillary flow porometer and adapted for the test which is available from Porous Materials, Inc. of Ithaca, New York.

THICKNESS TESTING The thickness of samples was determined by the Starrett bulk test which measures the thickness or bulk of a nonwoven or wipe material under a controlled loading pressure of 0.05 lbs/inch psi. The specified specimen size is at least 3 inches by 4 inches The thickness of a textile material is usually determined as the distance between an anvil, or base, and a pressure foot used to apply the specified pressure. Thickness is one of the basic physical properties of textile materials and is a useful measure of performance characteristics. Thickness varies considerably depending on the pressure applied to the specimen when the thickness is measured, and therefore, it is essential to specify the pressure under which the thickness is measured.

This procedure measures thickness of the designated area under a controlled loading pressure of 0.05lbs/square inch. The data is recorded to the nearest 0.001 inch for nonwoven material and to 0.001mm for wipe material. Tests are conducted in a standard laboratory atmosphere of about 23^°C (about 73^°F) and the material typically is measured after ambient conditions have been met For a nonwoven product, a minimum 5 inch X 5 inch specimen is cut from the roll to be tested For a nonwoven product, the test indicator is zeroed, and platen is gently raised by depressing the foot pedal The specimen is placed and centered on a circle over a base, and the platen is gently lowered onto the specimen by releasing the foot pedal After 3 seconds, the display value is read, and for a nonwoven product it is recorded to the nearest 0 001 inch After reading, the display is re-zeroed for further test specimens

WATER RESISTANCE TESTING

The resistance of fabrics to penetration of water by impact using a standard rain tester is accomplished The test is a useful indicator of the probable rain penetration resistance of the fabric The rain penetration is applicable to any fabric woven or nonwoven, whether or not it has been treated for water resistance or water repellency The test can be used to determine or predict the probable resistance to rain penetration of the fabric, and is especially suitable for measuring the penetration resistance of garment fabrics such as those used for raincoats and the like The water resistance of fabπc depends on the repellant properties of individual fibers as well as on the construction of the fabric as a whole The fabric can be tested at different intensities of water impact by changing the pressure on the fabric In this procedure, an 8 inch x 8 inch specimen is used as a protective barrier covering a sheet of pre-weighed absorbent blotting paper A horizontal water spray with a pre-determined hydro-static head is directed against the specimen for exactly 5 minutes and the blotter is then weighed again The difference between the initial and final weights of the blotting paper is the weight of the water that has penetrated and passed through the specimen The greater the difference, the more water that has passed through the fabric, i e the less water repellant is the fabric Thus, higher numbers indicate a lower water resistance The test used in this instance conforms to specifications of Federal test methods standard 191 A, the AATCC standard 35-1980 and the ASTN standard D583 Five specimens are tested from each sample, and water is sprayed onto the sample for 5 minutes A standard AATCC standard rain tester is used, which is available from MICO Instrument Company, in

Cambridge, Massachusetts The impact rain tester includes two standard spray nozzles, a specimen holder, a rigid frame to support the specimen holder and a shield to shut off spray between tests The blotting paper is available from James River Paper Company, in Richmond, Virginia, and is specified as "white AATCC textile blotting paper " The testing equipment is located in and the samples are conditioned to the testing atmosphere Standard atmosphere for testing is air maintained at a relative humidity of about 50± 2% and a temperature of about 73°F Conditioning time is 2 hours, however this time may be shortened if equilibrium is reached Equilibrium is considered to have been reached when the increase in the weight of the specimen, in successive weighings taken at least 30 minutes apart, is less than 0 1 % of the weight of the specimen The specimen size is 8 inches x 8 inches

WATER VAPOR TRANSMISSION RATE TESTING

The water vapor transmission rate (WVTR) was determined using test methods described below The fabric to be evaluated was sealed to the top of a cup of water and placed in a temperature controlled environment Evaporation of water in the cup resulted in a relatively higher vapor pressure inside the cup than the vapor pressure of the environment surrounding the outside of the cup This difference in vapor pressure caused the vapor inside the cup to flow through the test material to the outside of the cup The rate of this flow was dependent upon the permeability of the test material sealed to the top of the cup The difference between the beginning and ending cup weights was used to calculate the water vapor transmission rate

Apparatus and materials used included a cutting die, a mallet, a cutting board, blotter paper, vapometer cups, a balance, a tray, an oven, a graduated cylinder, microporous film, hygrometer, and stopcock grease The cutting die typically is 2 875 in (7 303 cm) or 3 000 in (7 620 cm) in diameter The die may be of the hand held type used with a mallet and cutting board or of the type used in a mechanical die press It is recommended that blotter paper (or any suitably stiff, heavy-weight paper) be used underneath the sample as this allows the sample to be removed from the die more easily The blotter paper may be chosen from any type and thickness that can be easily cut using the chosen method of die cutting

The mallet may be approximately 5 pounds (2 kilograms) with a soft face, which may not be required if using a mechanical die press The cutting board may be of any appropriate size and material The vapometer cups may be cast aluminum of a flange type The cups may be 2 in (5 cm) deep with a mechanical seal and neoprene gasket Exemplary cups are sold under part number 681 from the Thwing-Albert Instrument Co , of Philadelphia, PA The balance should be capable of holding the vapometer cups and accurate to ± 0 01 gram The tray should be suitable for use in transporting the cups to and from the oven, desirably a tray that will allow the maximum number of cups to be placed in the oven at one time The tray should be non-hygroscopic and of a material capable of withstanding about 100^°F (37 7^°C) for prolonged periods of time The tray should have an appropriate lip around its perimeter to contain water in case of spillage The oven should be a convection type, capable of maintaining about 100 ± 1 ^°F (37 7 ± 0 6^°C)

The graduated cylinder should have a 100 mL capacity An exemplary microporous film used as a control standard is sold under the trade designation CELGARD^®2500 from the Separations Products Division of Hoechst Celanese Corporation from Charlotte, NC The hygrometer should range from 0 to 100 ± 3% relative humidity or equivalent The stopcock grease sold under the trade designation THOMAS LUBRISEAL^® or DOW CORNING HIGH-VACUUM GREASE^® may be used The hygrometer and grease may be obtained from Fisher Scientific of Pittsburgh, PA 15219

The samples were prepared by selecting samples from material that is clean and dry The test specimens were taken from areas of the sample that were free of folds and wrinkles and any distortions rendering these specimens abnormal from the rest of the test material The number of specimens per sample was chosen for providing the desired level of confidence Several devices e-e verified or calibrated. The balance and oven used in this procedure were calibrated regularly to insure accurate and repeatable readings. Generally, a calibration system was established and maintained, in part, by consulting equipment manufacturers or their literature. The apparatus and materials were prepared in the following manner.

The oven was turned on and set for about 100^°F (37.7^°C). The oven temperature was verified that it was holding at a constant temperature. The vapometer cups were checked to ensure that they were clean, dry, and contained no foreign matter. Each test specimen along with the two specimens per tray of CELGARD^® 2500 control standard were cut using either the 2.875 in. (7.3 cm) or 3 in. (7.6 cm) diameter die. The specimens were handled carefully to prevent excessive moisture, oils, or other contaminants from accumulating on the specimens, which may cause erroneous results. The samples were tested without any specific preconditioning, however, the samples were checked to ensure that they were free of any surface contamination.

The testing procedure included labeling each vapometer cup with appropriate identifying information. Next, the graduated cylinder was filled with about a 100 ml of room temperature 72 ± 5^°F or (22.2 ± 3.1^°C) distilled water and poured into the vapometer cup body. This 100 ml of water in the vapometer cup resulted in a water level of 0.75 in. (19 mm) from the top of the cup body. This 0.75 in. (19 mm) distance from the water level to the top of the vapometer cup body was critical in maintaining reproducible results from test to test. The sealing surface of the vapometer cup gasket was coated with grease. The top flange on the vapometer cup body was placed aligning the screw holes in the top flange with the cup body flange. The neoprene gasket was positioned contacting the sample to provide a vapor tight seal around the edge. The screws were placed in the screw holes and finger tightened evenly. Each loaded vapometer cup was weighed and recorded as the "before" weight. At least two specimens of CELGARD^® 2500 control standard microporous film were prepared for every tested specimen tray. The loaded vapometer cups were carefully transferred to the tray facing up. Care was taken to avoid "sloshing" that would bring the water in the cups into contact with the specimen. If water contacted the specimen due to "sloshing", the results obtained from that specimen were regarded as invalid. When testing multiple specimens of the same material, the specimens were randomly positioned in the tray to avoid grouping together specimens of the same material. At least two vapometer cups containing the CELGARD^® 2500 control standard were placed in each tray of specimens. After placing the tray containing the specimens in the oven and the time and relative humidity at the oven air inlet was recorded as the "before" relative humidity reading. The samples remained in the oven for 24 hours. The samples were removed from the oven and the time and the relative humidity at the oven air inlet was recorded as the "after" relative humidity reading. The loaded vapometer cups were immediately weighed and recorded as the "after" weight.

The results were calculated using several formulas. The correction factor for each tray was calculated with the following formulas. The weight lost for each cup containing the test standard was calculated by:

"before" mass of test standard cup (g) -"after" mass of test standard cup (q) mass lost test standard cup (g)

The test standard base rate was calculated by:

mass loss standard cup (q) x 7571 = standard base rate test hours (g/m²/day)

The average of the standard base rates (BR) for each tray was calculated as follows:

Standard BR cup 1 + Standard BR cup ^#2 = avg. Celgard^® BR 2 The correction factor (CF) was calculated as follows

5000 = CF avg Celgard^® BR

The standardized WVTR for the specimens was calculated with the following formulas The weight lost for each cup containing sample material was calculated as follows

"before" mass of specimen cup (g)

-"after" mass of specimen cup (q) mass lost specimen cup (g)

The specimen base rate was calculated as follows

mass lost specimen cup (q) X 7571 = specimen base rate test hours (g/m²/day)

The specimen WVTR was calculated as follows

(specimen base rate) X (CF) = WVTR (standardized)

The rain impact test was conducted in substantial accordance with Method 5524 of the Federal Test Methods Standard No 191 A, and reported hydrostatic head values reported herein are for cm or inches of water

However, the following changes were made from this method Changes included using five specimens for each sample instead of three, spraying water onto the specimen for 5 minutes at one of the following hydrostatic pressure heads as required at 24 inches (61 centimeters), 36 inches (91 centimeters), or 48 inches (122 centimeters)

EXAMPLES

A substrate was made according to the meltblown process described above from polypropylene sold under the trade designation HIMONT PF-015 from Montell Polyolefins of Wilmington, Delaware. This substrate was divided into three samples. One sample was used as a control and the other two samples were treated. The aminosiloxane dipped samples were passed through nip rolls two times before drying at room temperature. The fluoroacrylate was dipped then hung in a hood to dip dry with some samples and passed through nip rolls with others.

The two substrates were saturated with an active agent dissolved in a solvent. The substrates were saturated with this solution and allowed to dry for about 12 hours. The nip rolls were operating under a pressure of about 2.5 pounds per linear inch, which is equivalent to about 0.45 kg/lineal cm. Then, the substrates were passed through the electron beam apparatus and irradiated. Afterwards, the samples were dried to a constant weight. The following Table 1 lists samples and the conditions under which the samples were prepared:

TABLE 1

Sample Active Aqent Weiqht Solvent Irradiation

N u m ber Percent Mrad

1 aminosiloxane ^"10 ^~ water 18 min tot

90-132 deg. C

2 fluoroacrylate 2 acetone 5 Mrads

The above tests were run on the two samples as well as the control The results, which are the mean of three specimens, are depicted in Table 2 below:

TABLE 2

S a m p e Basis Weiqht Thickness Averaqe Pore WVTR Rain Impact

Number osy (gsm) Diameter

(microns) (microns) (grams/m²/ ( g r a m a t

24 hours) about 91 cm)

Control 2 (70) 67043 ^~€A 5128 8.2

1 _2 (70 _. _.. _.0JJ43 _. 8_;0 4935 _._ 0.2 2 (70) 0.043 9.2 4213 0.8

It is desirable to have a fabric with a WVTR greater than 3000 g/m²/24 hours and a rain impact value less than about 0.5 gram at a hydrostatic head of about 91 cm. As depicted in Table 2, Sample 1 exceeds a WVTR value of

3000 g/m²/24 hours as well as having a rain impact value less than 0.3 gram at about 91 cm. Sample 2 also exceeds the WVTR value while having a rain impact value approaching 0.3 gram at about 91 cm. Although the control has the highest WVTR value, it has a rain impact value a magnitude greater than either of the Samples 1 and 2.

In addition, another fabric was made according to the meltblown process described above from polypropylene sold underthe trade designation EXXON 3746G by Exxon Chemical Company of Houston, Texas. This fabric was subdivided into samples, which were treated by the processes of the present invention except one sample was kept as a control. The samples had a basis weight of about 2 osy (70 gsm).

The treated samples were saturated with an active agent dissolved in a solvent. The fabrics were saturated with this solution and allowed to dry for about 12 hours. In addition, some fabrics were also passed between two rubber nip rolls on a lab wringer prior to drying. The nip rolls were operating under a pressure of about 2.5 pounds per lineal inch 0.45 kg/lineal cm.

Afterwards, the samples were dried to a constant weight. Afterwards, the substrates were passed through the electron beam apparatus and irradiated.

The following Table 3 lists the samples and the conditions under which they were prepared:

TABLE 3

Sample Active Aqent Weiqht Solvent Irradiation

N u m be r Percent Mrad

1 Fluoroacrylate 1.0% acetone 3 2 Fluoroacrylate 1.0 acetone 5 3 Fluoroacrylate 3.0 acetone 5 4 Fluoroacrylate 3.0 acetone 3 5 Fluoroacrylate 3.0 acetone 5 ^"6 Fluoro meth aery late 3.0 ^" acetone 3^'

7 Fluoromethacrylate 3.0 acetone ^' 3

8 THV-200P 5.0 water 5

9 THV-330R 5.0 water 5

10 Siloxane water 5

11 THV-200P 5.0 water 5

12 THV-200P water

13 Siloxane 5.0 acetone 5

14 Fluoromethacrylate 5.0 acetone 5

15 Fluoroacrylate

acetone A^" ].^".^".

All samples were soaked in solution, but only Samples 4, 5, and 7 were pressed through the nip rolls as well. These samples were subjected to the basis weight, WVTR, and rain impact tests. The data depicted below in Table 4 represents the mean of three specimens except for a few of the rain impact samples. Samples 11 , 12, and 15 are represented by data from one specimen for rain impact; samples 3 and 7 are represented by data from the mean of two specimens for rain impact; and sample 5 is represented by data from the mean of four specimens for rain impact. No rain impact tests were conducted for Sample 14, which was marked with "N/A". TABLE 4

Sample Basis Weiqht WVTR Rain mpact

N u m b e r osv (osm) (grams/m ²/24 hours) (gran- i at about 91 cm)

C o n t r o l ^~ 2(70) 4705 0.49

1 2168) _. 4243 0.22

₂

2 (68) 4265 0.47

3 _^ 168) 4423 0.28

- 4 2 (68) 4274 1.3 5 2 (68) 4316 0.23

6 2 (68) 3842 12

7 2 (68) 4274 0 46

8 2 (68) 4158 13

9 2 (68) 4065 0.24

10 2 (68) 4224 0 20

11 2 (68) 4227 5.8

12 2 (68) 4501 12

13 2 (68) 4224 0.23

14 2 (68) 4414 N/A

15 2 (68) 4266 0.28

As depicted in Table 4, Samples , 3, 5, 9, 10, 13, and 15 have a WVTR that exceeds 3000 g/m²/24 hours and a rain impact less than 0.3 grams.

Comparatively, the control sample has a rain impact value greater than 0.5 grams. Consequently, the treated fabric of the present invention provides a material that has acceptable breathability and barrier protection.

While the present invention has been described in connection with certain described embodiments, it is to be understood that the subject matter encompassed by way of the present invention is not to be limited to those specific embodiments. On the contrary, it is intended for the subject matter of the invention to include all alternatives, modifications and equivalents as can be included within the spirit and scope of the following claims

Claims

WHAT IS CLAIMED IS

1 A substrate having a surface free energy of less than about 40 dynes/cm, the substrate defining at least one pore having a smallest dimension of less than about 12 micrometers, and

(a) wherein the substrate has a water vapor transmission rate through it which is greater than about 3000 g/m²/24 hours, and

(2) a ram impact value of less than about 0 5 g at a hydrostatic head of about 91 cm

2 The porous substrate of claim 1 wherein the fabric is a fibrous nonwoven web

3 The nonwoven web of claim 2 in which the fibers of the nonwoven web are coated with a surface free energy lowering material

4 The nonwoven web of claim 3, in which the coating is a fluorinated monomer, a fluorinated terpolymer, a siloxane, or a polysiloxane.

5 The web of claim 4, in which the fluorinated monomer is a fluoroacrylate or a fluoromethacrylate

6 The web of claim 4, in which the coating is a fluoroacrylate monomer, a fluoroacrylate terpolymer, a siloxane or a polysiloxane.

7 The liquid-impermeable nonwoven web of claim 2, in which the fibrous nonwoven web is comprised of a thermoplastic polymer

8 The nonwoven web of claim 7, in which the thermoplastic polymer is selected from the group comprising polyolefins, polyesters, polyurethanes, and polyamides

9 The nonwoven web of claim 8, in which the thermoplastic polymer is a polyolefin

10. The nonwoven web of claim 9, in which the thermoplastic polymer is polypropylene or polyethylene.

1 1. A liquid-impermeable nonwoven web comprising: a polyolefin nonwoven web material having fibers, the web further having pores, wherein the diameter of the pores is between about 3 and about 12 micrometers, wherein the fibers have been

(a) coated with a fluorinated monomer which is effective to impart to the web material a surface free energy of less than about 40 dynes/cm , and

(b) exposed to heat or ionizing radiation, in which the pore diameter and surface free energy values are adapted to facilitate: i) a water vapor transmission rate greater than about 3000 g/m²/24 hours and ii) a rain impact value of less than about 0.5 g at a hydrostatic head of about 91 cm.

12. A method of making a liquid-impermeable nonwoven web comprising:

(a) providing a nonwoven web of fibers having pore diameters which are between about 3 and about 12 micrometers; and

(b) coating the fibers with a surface free energy lowering material;

(c) wherein the pore diameter value and surface free energy lowering material values are chosen to facilitate a water vapor transmission rate in the nonwoven web of: i) greater than about 3000 g/m²/24 hours and ii) a rain impact value of less than about 0.5 g at a hydrostatic head of about 91 cm.

13. The method of claim 12 further comprising exposing the coated fibers to heat or ionizing radiation.

14. The method of claim 12 further comprising passing the coated nonwoven web through a nip prior to heat or radiation exposure. 15 The method of claim 12, in which the surface free energy lowering material is a fluorinated monomer

16 The method of claim 15, in which the fluorinated monomer is a fluoroacrylate

17 The method of claim 15, in which the fluorinated monomer is dissolved in acetone prior to the coating step to provide a solution containing from about 1 to about 3 percent by weight of the fluorinated monomer

18 The method of claim 12, in which the nonwoven web fibers are comprised of a thermoplastic polymer

19 The method of claim 18, in which the thermoplastic polymer is selected from the group comprising polyolefins, polyesters, polyurethanes and polyamides

20 The method of claim 19, in which the thermoplastic polymer is a polyolefin

21 The method of claim 20, in which the thermoplastic polymer is polypropylene