Classifications

• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
  • D04H3/08—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating
  • D04H3/12—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating with filaments or yarns secured together by chemical or thermo-activatable bonding agents, e.g. adhesives, applied or incorporated in liquid or solid form
• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/58—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by applying, incorporating or activating chemical or thermoplastic bonding agents, e.g. adhesives
  • D04H1/64—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties by applying, incorporating or activating chemical or thermoplastic bonding agents, e.g. adhesives the bonding agent being applied in wet state, e.g. chemical agents in dispersions or solutions

Definitions

• This invention relates to nonwoven fabrics having a vapor breathable film layer incorporated therein, with said fabrics being substantially impermeable to liquids.
• Nonwoven fabrics are produced by a variety of processes distinguished from weaving of yarns on a loom.
• nonwoven fabrics are made from fibers or continuous filaments, and the fibers or filaments are consolidated at points of intersection by thermal or adhesive bonding, or by fiber or filament entanglement.
• nonwovens are porous and easily transmit liquids and any agents carried by or in the liquids.
• Many existing and proposed uses for nonwovens require a fabric which is essentially liquid proof, but which can breathe by allowing transmission of water vapor.
• End uses for breathable nonwovens include clothing, such as medical apparel, components of diapers or other disposable sanitary articles, building covering materials and the like.
• a nonwoven fabric may be laminated or extrusion coated with a film, and the film may be of a non-porous or microporous type, but the lamination or extrusion coating process is expensive and requires substantial space and equipment, especially if the laminate is produced on the same line with the nonwoven.
• a nonwoven with a waterproofing agent such as a fluoro compound
• a nonwoven with a waterproofing agent such as a fluoro compound
• the average pore size of nonwoven fabrics can be decreased by providing composite fabrics, such as spunbond-meltblown-spunbond (SMS) fabrics, wherein the meltblown layer comprises very fine fibers.
• SMS spunbond-meltblown-spunbond
• a nonwoven fabric is coated with a liquid, radiation curable, film forming polymer or resin to provide a continuous and unbroken film on the fabric, and the liquid polymer film is subjected to radiation to cure the polymer and to cause a durable unbroken, flexible film to form and to adhere and bond to the fabric.
• a continuous, flexible and liquid impervious film can be formed on substrates which are porous.
• the resulting coated fabric is impervious to the transfer or passage of liquids such as water, blood and alcohol but is capable of transmitting water vapor.
• the coating and curing steps require a minimal amount of space, and the operation may be carried out on line during production of the nonwoven fabric using a small production space at normal nonwoven production line speeds.
• the coating can be selectively applied to only portions of a moving nonwoven fabric web, for example, to render only certain portions impervious to liquids, as may be desired in a component of a diaper, or in medical products.
• liquid radiation curable resins are applied to a surface of a nonwoven, followed by curing of the resin, in order to increase the hydrostatic head of the fabric by a minimum of two to three times the original hydrostatic head.
• One preferred type of radiation curable resins are ultraviolet curable resins containing a monomer having one or more functional groups, a polymer or oligomer having unsaturation sites, and a photoinitiator sensitive to UV radiation.
• the photoinitiator supplies free radicals or cations to cause polymerization of the monomer with the polymer and provide a solid film.
• nonwoven fabric means a fabric comprising man-made or polymer fibers or filaments which are bonded together at points or are entangled to provide a coherent, planar fabric.
• Various types of bonding include thermal bonding and chemical and adhesive bonding.
• the types of entanglement include needling and hydroentanglement, the latter involving impingement of jets of water on an unconsolidated web supported on a porous support. Fibers may also be consolidated by wet laying techniques.
• spunbonding refers to a method by which a large number of continuous filaments are spun or extruded, drawn and deposited on a moving conveyor as a moving web. The filaments are then thermally bonded, either by virtue of the filaments having a low softening temperature, or by incorporating some fraction of binder or lower melting point filaments into the web.
• a related process is melt blowing, in which molten filaments are extruded from small apertures, and are blown and drawn by impingement of high velocity hot air toward a conveyor to form a continuous web.
• Fabrics made from fibers usually involve the formation of a fiber web by carding or air laying, and then bonding or consolidating the web.
• the web may be pattern bonded using an engraved heated calender or an ultrasonic bonder, hot air bonded, or it may be resin bonded and heated. Entanglement procedures have been described above.
• the polymers presently used to make nonwovens include polyolefins, such as polyethylene and polypropylene, and polyester, although many others are known and can be employed, such as nylon, rayon, polyurethane, and others. It is not believed that the present invention is limited to the type of polymer or fiber employed in the nonwoven, since the film as applied mechanically interacts with the fabric and surrounds at least portions of the fibers or filaments to provide a strong mechanical bond. Continuous films are more easily applied to fabrics having a small pore size.
• the weight of the nonwoven fabric is not critical and may range in the order of 3 to 100 grams per square meter.
• the unconsolidated web of fibers or filaments is preferably bonded prior to the application of the film coating, such that the fibers or filaments are fixed in position and the web is cohesive and shape retaining.
• the degree of bonding is not critical, as long as the web is sufficiently shape retaining to allow application of the liquid film.
• nonwoven fabric means a web of fibers or filaments which has been bonded.
• the nonwoven substrate may comprise a single layer or multiple layers, and these layers may be produced by identical or different processes.
• a composite nonwoven may include spunbond and meltblown layers.
• the film may reside as an outer bonded layer or may reside as an inner layer of a composite.
• One preferred nonwoven substrate is a fabric having at least one meltblown layer and at least one spunbond layer.
• Radiation curable polymers are available from a variety of commercial sources and are furnished in liquid form, generally free of any solvents.
• the resin is normally a mixture comprising a monomer having one or more functional groups, and a polymer or oligomer having a degree of unsaturation.
• An oligomer is selected from those capable of forming a flexible film upon curing.
• the monomer is referred to as a dilutent for the polymer, with the ratio of the two being adjustable to control viscosity.
• the uncured liquid resin must be sufficiently viscous to be applied and retained as a continuous liquid film on a nonwoven fabric for a period of several seconds up to several minutes. This parameter is usually not significant, since it is normally possible to apply and cure the liquid film within a fraction of a second and up to several seconds.
• the liquid resin may be cured directly by electron beam radiation or may be cured by ultraviolet light if a photoinitiator is incorporated into the resin.
• photoinitiators There are two principal types of photoinitiators, free radical and cationic, which are selected depending on the species of resins used. Free radical initiators are employed with acrylates, while cationic photoinitiators are employed with vinyl ethers and epoxy compounds. Formulations of a large variety of radiation curable resins are available from RadTech, Northbrook, Illinois. Radiation curable resins are described in the following United States patents, incorporated herein by references: 4,125,503; 4,649,082; 4,937,173; 5,098,982; 5,281,662; and 5,352,713.
• a radiation curable resin is selected, which when polymerized into a film, will be flexible, will be impervious to the transfer or liquids, but will have a high rate of vapor transmission, allowing the film coated fabric to breathe.
• film flexibility and breathability is determined by film thickness and film chemistry, such as, for example, the percentage of monomers, the crossline density and chemical nature of the polymer backbone.
• the cured resin should be non-toxic and non-reactive.
• the composite film and fabric will have a moisture or vapor transmission rate which exceeds 500 grams per square meter per day, and preferably exceeds 3,000 g/m 2 per day, with a hydrohead in excess of 65 cm.
• the liquid resin composition comprises (A) an unsaturated polyester component containing an unsaturated polyester polymer, an unsaturated polyester oligomer or a mixture thereof; and (B) a non-polymerized, cocurable vinyl ether component which may be separate from or structurally incorporated in the unsaturated polyester component, provided that the vinyl ether component contains an average of at least two vinyl ether groups per molecule of the vinyl either component.
• a photoinitiator is added if UV curing is desired.
• additives may be added to the liquid resin prior to application. Possible additions include antistatic agents, antimicrobial agents, fillers to control weight and viscosity, pigments and the like. The limitations on additives are that they should not interfere with the radiation curing process and should be compatible with the resin system employed. Other typical additives include defoamer, adhesion promoters, flatting agents and stabilizers.
• the liquid resin coating is applied to the nonwoven, preferably a nonwoven web carried by a conveyor, by known conventional coating processes.
• coating processes include a gravure or flexigraphic printing, roll coating, blade coating, and spray coating.
• a preferred method involves transfer coating a rubber roll with a thin layer using a gravure with a doctor blade assembly and allowing the nonwoven moving on a conveyor belt to contact the web on one side.
• the coatings will be applied zonally or uniformly to the web at a coating thickness of 3 to 500 ⁇ m, with 3 to 100 ⁇ m being preferred. Coatings may be applied to one or both sides of the fabric.
• a minimum amount of liquid resin is applied to the fabric substrate to achieve the desired properties, which also allows the coating to be cured more rapidly.
• rate of application of the liquid as a uniform coating should exceed about three grams per square meter (gsm).
• the upper limit of coating application is based on cost considerations, and generally an application rate of twenty-five gsm will not be exceeded, providing a coating thickness of 25 microns. In general, if the liquid resin does not contain solvents, the liquid application rate will be equal to the cured film rate.
• a low basis weight of the liquid resin may be applied, such that when the resin is cured, the fabric will exhibit a substantial increase in hydrostatic head without any substantial impact on the softness, drape and flexibility of the fabric.
• low application rates for example three to seven gsm, it is normally possible to increase the hydrostatic head by a factor of two to three times, with the fabric remaining permeable to the transfer of liquid vapors.
• the liquid film resident on the surface is then rapidly cured, or is cured while the liquid resin still resides as a continuous and unbroken film on the nonwoven fabric.
• This is accomplished by exposing the resin coated nonwoven fabric to a source of suitable radiation.
• a source of suitable radiation For example, if the photoinitiator in the resin is activated by ultraviolet light, the coated substrate may be passed through an enclosure having a series of UV lamps, such as mercury lamps.
• ionizing radiation is employed by use of an electron beam, a one mil thick liquid film can be cured in air through its thickness upon exposure to a 0.5 to 5 megarads of ionizing radiation.
• ultraviolet radiation having a wavelength of 180-400 nanometers may be used to effect the cure.
• Typical medium pressure tubular mercury lamps have an output of 200 watts per inch along the length of the tube.
• the tubes can be in series and in parallel and are typically spaced a few inches from the uncured film.
• photosensitizers and photoinitiators are used in UV curing.
• photosensitizers include benzophenone, anthraquinone, and thioxamthone.
• photoinitiators include isobutyl benzoin ether, alpha, alpha-diethyozyacetophenone, and alpha, alpha-dimethoxy-alpha-phenylacetophenone.
• the apparatus for applying and curing the coating will be applied at the exit end of the line, that is, between the exit of the finished nonwoven web and a winding apparatus for winding the web into a roll.
• the web may be supported on a flat conveyor or a rotating roll, or may be passed unsupported through the coating apparatus.
• the web, coated with liquid resin is then passed through an enclosure containing the source of radiation.
• Line speeds are not critical, since continuous curing is possible at line speeds up to at least 300 meters per minute. The radiation capacity and amount of exposure is determined by liquid resin chemistry and thickness, fillers, if any, and line speed.
• the coating As the coating is being applied to the web and cured, it is desirable to prevent excessive penetration of the coating into the fabric. This can be accomplished, for example, by using a low pore size web or by initiating the radiation cure immediately after application. Also, a viscous coating may be used, which is heated to reduce viscosity during application, or a high shear coating method may be used.
• An important aspect of the present invention is the ability to significantly increase the hydrohead of light weight nonwoven fabrics while maintaining high vapor transmission.
• Treated fabrics having a basis weight of less than 50 gsm can easily obtain a hydrohead of greater than 90 cm while maintaining a moisture vapor transmission rate of greater than 3,000 g/m 2 per day.
• the hydrostatic head of a 20 gsm (grams per square meter) SMS nonwoven fabric can be increased from about 30 cm before coating to greater than 100 cm after coating.
• the moisture transmission rate of the fabric exceeds 5,000 g/m 2 per day. Since there are substantially no pores in the film layer, vapor transmission occurs through absorption at one surface and transmission to the other surface of the film.
• hydrohead refers to a standard test to measure the liquid barrier properties of a fabric.
• the hydrohead test determines the height of water (in centimeters) which the fabric will support before a predetermined amount of liquid will pass through, and is defined in Federal Test Standard No. 191A, Method 5514.
• the water vapor transmission rate (WVTR) of fabrics is specified in ASTM Standard Test Method E-96-80.
• Nonwoven fabrics are produced in bulk in the form of rolls and are later cut and converted into a wide variety of useful articles.
• breathable nonwoven fabrics which are fluid repellent, and which can be supplied at a low cost.
• Possible end uses include single or multiple use protective apparel, such as medical gowns and laboratory coats, industrial protective clothing and rain wear.
• the resin coating can be applied only to areas of the fabric requiring high repellency, such as the front panels and sleeves of an operating gown.
• the radiation curable resin can also be applied when the fabric is being converted to a final product.
• preselected areas of fabric may be coated, such as the inner surface of the outermost layer of fabric, in order to prevent leaking of liquids, while retaining a soft, cloth-like feel.
• a resin coating is applied to only one side of the fabric, and as thinly as possible, while still providing a good liquid barrier. This will assure that the composite will continue to have the soft feel of a fabric, and the uncoated side will have the appearance and tactile qualities of a porous fabric.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Dispersion Chemistry (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)
• Laminated Bodies (AREA)
• Manufacturing Of Multi-Layer Textile Fabrics (AREA)
• Nonwoven Fabrics (AREA)
• Synthetic Leather, Interior Materials Or Flexible Sheet Materials (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (3)

Cited By (7)

Citations (4)

• 1998
  • 1998-04-30 CA CA002236402A patent/CA2236402A1/en not_active Abandoned
  • 1998-05-07 EP EP98108294A patent/EP0893530A1/de not_active Withdrawn
  • 1998-07-23 JP JP10222477A patent/JPH11158777A/ja active Pending

Patent Citations (5)

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