Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric
Reexamination Certificate
1999-07-14
2004-07-13
Cole, Elizabeth M. (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
C442S416000, C442S408000, C162S148000
Reexamination Certificate
active
06762138
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wet-laid nonwoven webs made from unpulped long natural fiber bundles and to hydroentangled composite sheet material containing such nonwoven webs.
BACKGROUND OF THE INVENTION
In conventional wet-laid papermaking operations, pulped fibers are dispersed in an aqueous medium and deposited in sheet form on a paperforming wire or screen. The pulped fibers are the natural single elementary fiber units obtained from the pulping process. These elementary fibers, prior to the pulping process, are bundled together and held by several natural binding components such as lignin and hemicellulose. The pulping process removes these binding components, leaving behind mostly the elementary cellulosic fibers. This breakdown of the fiber bundles is desirable since the freed elementary fibers are more manageable and provide a desired sheet uniformity while contributing to the strength and brightness of the resultant sheet material.
In wet-laid nonwoven application, pulped vegetable fibers of increased length are employed as compared to the shorter wood pulp fibers. These long vegetable fibers impart improved mechanical properties and include elementary fibers such as sisal, hemp, caroa, flax, jute and abaca fibers, as mentioned in Homonoff et al U.S. Pat. No. 5,151,320 and Viazmensky et al U.S. Pat. No. 5,009,747. In this connection, the pulped vegetable fibers typically have a fiber diameter of about 5-30 &mgr;m and a fiber length of about 10 mm. In publication WO 96,12849, freed or pulped ramie fibers cut to a length of 12 mm have been used in place of 12 mm synthetic fibers to form absorbent nonwovens when appropriate dispersion agents are employed.
Wet-laid nonwovens of inorganic fibers such as glass, carbon, silica carbide and others also are known and have been used for composite applications where the anisotropic properties of the wet-laid nonwoven are desirable for reinforcement purposes. These inorganic fibers advantageously impart to the nonwovens their high modulus of elasticity, which result in improved reinforcement at a minimal weight penalty.
Interior headliners for motor vehicles heretofore have consisted of moldable multi-layer assemblies comprised of a foam core with layers of fiberglass adhered to opposite planar surfaces thereof. A plastic moisture barrier film such as a polyethylene film is applied to the backside fiberglass layer (the side closest to the vehicle roof) and paper fleeces are employed as cover layers over the film to prevent sticking during the molding operation. A cloth fabric or equivalent layer covers the front fiberglass layer closest to the interior of the vehicle. Additionally, as mentioned in the Welch et al U.S. Pat. No. 5,437,919, outside layers of woven jute fleece or flax or sisal fleece may be used. Such headliner materials exhibit not only the necessary thermoforming characteristics, but the fiberglass reinforcing fibers provide a modulus of elasticity exceeding that of the resin matrix and impart the requisite stiffness to the resultant product.
For various reasons, the industry seeks to obviate the use of fiberglass in such applications without adversely impacting on the desirable characteristics thereof, particularly the thermoforming and modulus or stiffness characteristics.
SUMMARY OF THE INVENTION
It has now been found, in accordance with the present invention, that desirable mechanical reinforcement properties can be incorporated into nonwoven web materials without using fiberglass or bulky, heavy weight materials that have evidenced nonuniform constructions hereinbefore. This is achieved by using wet-laid nonwoven webs made with long vegetable fiber bundles as the predominant fiber component. Such nonwoven webs may be used individually or as part of composite structures as the reinforcing or stiffening component of such composites.
It is an advantage of the present invention that the unpulped fiber bundles exhibit the requisite high modulus of elasticity necessary to replace the inorganic fibers employed heretofore. At the same time, the anisotropic characteristic of the wet-laid nonwoven material is maintained.
In accordance with the present invention, fiberglass mats can be replaced entirely by wet-laid sheets composed predominantly of natural long fibers having an equivalent or greater modulus of elasticity, i.e., stiffness, of about 2-5×10
6
pounds per square inch. A nonwoven web of natural long fiber bundles may be employed to replace both the fiberglass layer and the barrier film that prevents resin bleed-through. A composite thereof provides multiple layers of thermoplastic fibers, natural reinforcing fibers and woodpulp which, when combined, will withstand the thermoforming processes required where contoured reinforcement of the finished product is desired, such as in vehicle headliners or other vehicle interior trim products. The sheet material of the present invention completely replaces the inorganic reinforcing fibers and employs select unpulped natural long fiber bundles in a water-laid web. The long fiber web material may be used alone or as a composite to replace the prior three layered structure of fiberglass substrate, thermoplastic film and nonwoven backing. The resultant product combines lightweight, reduced bulk and high stiffness in molded form with good moldability and mold release as well as high elongation and barrier properties against resin flow.
Other features and advantages of the present invention will be in part obvious and in part pointed out more in detail hereinafter.
A better understanding of these advantages, features, properties and relationships of the invention will be obtained from the following detailed description which sets forth an illustrative embodiment and is indicative of the way in which the principles of the invention are employed.
DESCRIPTION OF A PREFERRED EMBODIMENT
The nonwoven fibrous web material formed in accordance with the invention is made by a wet papermaking process that involves the general steps of forming a fluid dispersion of the requisite fibers, depositing the dispersed fibers on a fiber collecting wire in the form of a continuous sheet-like web material. The fiber dispersion may incorporate up to 2% by weight, preferably about 1% by weight, of a wet strength additive and, following sheet formation, may be used as one component of a composite to provide the desired synergistic strength and modulus characteristics while facilitating use in moldable applications.
The fiber dispersion may be formed in a conventional manner using water as the dispersant or by employing other suitable liquid dispersing media. Preferably, aqueous dispersions are employed in accordance with known papermaking techniques and, accordingly, a fiber dispersion is formed as a dilute aqueous suspension or furnish of the fibers. The fiber furnish is then conveyed to the web-forming screen or wire, such as a Fourdriner wire of a papermaking machine, and the fibers are deposited on the wire to form a nonwoven fibrous web or sheet. The sheet or web is dried in a conventional manner, but is not treated with any postformation bonding agent.
The fiber furnish is a blend of natural pulp, man-made fibers and a predominant amount of unpulped natural fiber bundles. The pulp component of the fiber furnish can be selected from substantially any class of pulp and blends thereof. Preferably the pulp is characterized by being entirely natural cellulosic fibers and can include cotton as well as wood fibers, although softwood papermaking pulp, such as spruce, hemlock, cedar and pine are typically employed. Hardwood pulp and non-wood pulp, such as hemp and sisal may also be used. The natural pulp may constitute up to about 40 percent by weight of the total fiber content of the web material.
As mentioned, the nonwoven web material also may contain a significant concentration of man-made fibers blended with the wood pulp. The typical man-made fiber is a polyester such as polyethylene terepthalate. However, as will be appreciated, the synthetic fiber com
Ferreira Rui B.
Rieger Joseph A.
Ahlstrom Windsor Locks LLC
Alix Yale & Ristas, LLP
Cole Elizabeth M.
Torres Norca L.
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