Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coated or impregnated synthetic organic fiber fabric
Reexamination Certificate
1999-10-04
2002-04-16
Cole, Elizabeth M. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Coated or impregnated synthetic organic fiber fabric
C442S170000, C442S173000, C442S180000, C427S421100, C427S430100, C524S813000, C524S820000, C524S827000, C524S828000, C524S829000, C524S831000
Reexamination Certificate
active
06372675
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a nonwoven fabric of chemically bonded non-cellulose fibers having improved water tensile properties. More particularly, the present invention relates to a nonwoven fabric of non-cellulose fibers including an essentially formaldehyde free latex binder capable of providing improved water tensile properties.
BACKGROUND OF THE INVENTION
A nonwoven fabric is a web or continuous sheet of fibers laid down mechanically. The fibers may be deposited in a random manner or oriented in one direction. Most widely used fibers include cellulosics, polyamides, polyesters, polypropylene and polyethylene. The spun fibers, which may be drawn, are laid down directly onto a porous belt by carding, airlaying or wet-laying, often with the aid of an electrostatic charge. The sheet is then bonded together with a binder subsequently treated in an oven or a calendar to complete the bonding process.
A number of methods have been developed for applying a binder to randomly-dispersed fibers. Typically, a water based emulsion binder system is used in which a thermoplastic or thermoset synthetic polymer latex is prepared and a loose web of fibers to be treated is immersed therein, saturated or sprayed using special equipment in view of the structural weakness of the web; the thus treated web is dried and cured to effect proper bonding. Alternatively, an aqueous or solvent solution binder system of a thermoplastic or thermoset resin may be used to impregnate the fibrous web.
Still other methods include the application of thermoplastic or thermoset resin powders to the fibers, before or after making a web of the same, and passing the web through hot rolls or a hot press to bind the fibers together. Alternatively, thermoplastic fibers having a-softening point below that of the base fibers may be interdispersed in a web of the latter and sufficient heat and pressure applied, such as by the use of heated rolls, to soften the thermoplastic fibers and bind the fiber network together.
Commonly used lattices for non-woven fabrics are those prepared from polymers of butadiene-styrene, butadiene-acrylonitrile, vinyl acetate, acrylic monomers such as methyl acrylate, ethyl acrylate, methyl methacrylate and the like. While the emulsion binder system is the most popular method of forming non-woven fabrics, the homopolymers, copolymers and terpolymers heretofore used therein have suffered from one or more disadvantages. To be useful as a textile material, the synthetic polymer must possess several physical properties. The desired properties include adequate tensile strength over a fairly wide temperature range, a high modulus or stiffness under certain conditions, and good textile qualities such as tenacity, handle and drape.
It will be appreciated that it has been an accepted practice to use self crosslinking or melamine formaldehyde resin posted lattices to give improved water tensiles to a nonwoven non-cellulose product. These systems, however, contain and liberate formaldehyde during the dry/cure cycle. In addition, essentially all commercial self crosslinking and melamine posted lattices require a temperature of at least 280° F. and preferably 300° F. for proper crosslinking. However, it will be appreciated that because the melting point of many non-cellulose fibers is below the temperature required for proper crosslinking, e.g., polypropylene is around 250° F., conventional lattices cannot be used. Accordingly, polypropylene fiber in the nonwoven industry has never enjoyed large success. The problem has been in the specific development of a suitable latex binder to give acceptable tensile properties.
It is an object of the present invention to provide a nonwoven fabric of chemically bonded non-cellulose fibers. Another object of the present invention is to provide a nonwoven fabric including a random arrangement of non-cellulose fibers and an essentially formaldehyde free latex binder capable of developing maximum tensile properties at temperatures less than the melt bonding temperature of the non-cellulose fibers. Yet another object of the present invention is to provide a nonwoven fabric including a random arrangement of non-callulose fibers and an essentially formaldehyde free latex binder capable of providing improved water tensile properties. It is another object of the present invention to provide a nonwoven fabric of chemically bonded non-cellulose fibers that is simple and economical to manufacture.
SUMMARY OF THE INVENTION
Briefly, according to this invention there is provided a nonwoven fabric including a random arrangement of non-cellulose fibers and an essentially formaldehyde free latex binder. The latex binder includes a polymer latex prepared by emulsion polymerization of a monomeric mixture in the presence of a polymeric surfactant. The monomeric mixture consists of a conjugated diene monomer, a vinyl substituted aromatic monomer and a vinyl cyanide monomer. The conjugated diene monomer may be selected from piperylene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-butadiene. The vinyl substituted aromatic monomer may be selected from &agr;-methyl styrene, p-tertiary butyl styrene, m-vinyl toluene, p-vinyl toluene, 3-ethyl styrene and styrene. The vinyl cyanide monomer may be selected from acrylonitrile, methacrylonitrile, ethacrylonitrile and phenylacrylonitrile.
The polymeric surfactant is about 15-35 wt % on a dry latex basis. The polymeric surfactant contains about 25-27 wt % styrene/acrylic acid/&agr;-methyl styrene copolymer in water neutralized with about 6-7 wt % ammonium hydroxide.
The essentially formaldehyde free latex binder contains at least about 6.7 wt % vinyl cyanide monomer to bond said non-cellulose fibers and form a nonwoven fabric capable of retaining at least about 78% wet tensile strength measured in the cross direction. Alternatively, the nonwoven fabric of chemically bonded non-cellulose fibers has at least a 10% improvement in wet tensile strength over a comparable, the same type, nonwoven fabric having substantially the same monomeric formulation of essentially formaldehyde free latex binder but free of vinyl cyanide monomer.
Suitable non-cellulose fibers include glass fibers or fibers made from high polymers. The high polymers include polyolefins, polyesters, and acrylics, polyamides and the like. The polyolefin fibers include polypropylene, polyethylene, polybutene and their copolymers. The polyester fibers include any long chain synthetic polymer composed of at least 85% by weight of an ester of a dihydric alcohol and terephthalic acid such as polyethylene terephthalate, and, in addition liquid crystal polyesters, thermotropic polyesters and the like. The acrylic fibers include any fiber forming substance containing a long chain synthetic polymer composed of at least 85% by weight acrylonitrile units —CH
2
CH(CN)—. It will be appreciated that other types of non-cellulose fibers may also be employed in accordance with the teachings of the present invention. For example, high modulus fibers more commonly known as graphite fibers made from rayon, polyacrylonitrile or petroleum pitch may also be used.
The nonwoven fabric of non-cellulose fibers is formed by providing a random arrangement of non-cellulose fibers. Next, an essentially formaldehyde free latex binder is applied to the fibers. Then the latex binder is heat treated to chemically bond the non-cellulose fibers to form a dimensionally stable nonwoven fabric.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a nonwoven fabric of chemically bonded non-cellulose fibers. The fabric may be used for soft and drapable fabrics such as diaper cover stock, feminine hygiene cover stock, medical gowns, masks, caps and drapes, and for stiff and resilient fabrics such as apparel interliners, furniture skirting, quilts, water bed baffles and clothing insulation and padding.
The fabric of the present invention is made by forming a mat of randomly arranged non-cellulose fibers which are chemically bonded by an essentially formaldehyde free latex bi
Cole Elizabeth M.
Meenan Larry R.
Omnova Solutins Inc.
Rywalski Robert F.
LandOfFree
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