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  Differential basis weight nonwoven websRelated Patent Categories: Fabric (woven, Knitted, Or Nonwoven Textile Or Cloth, Etc.), Nonwoven Fabric (i.e., Nonwoven Strand Or Fiber Material)The Patent Description & Claims data below is from USPTO Patent Application 20070026753. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention is generally directed to nonwoven webs, laminates containing nonwoven webs and to a process for forming the webs. More particularly, the present invention is directed to meltspun webs having areas of lower basis weight and areas of higher basis weight. BACKGROUND OF THE INVENTION [0002] Polymeric and cellulosic articles, such as fibers and webs, are useful for a wide variety of applications. For instance, thermoplastic polymeric fibers, pulp fibers, and webs have been used in the past for making fluid absorbent wipers, towels, industrial garments, medical garments, medical drapes, and the like. Such articles are also used in recreational applications, such as for making tents and car covers. Nonwoven fabrics made from polymeric fibers have also achieved especially widespread use in the manufacture of personal care articles, such as diapers, feminine hygiene products and the like. [0003] The nonwoven fabrics identified above particularly refer to webs made via the spunbond, meltblown, coform, or carded web processes. For instance, spunbond webs are typically produced by heating a thermoplastic polymeric resin to at least its softening temperature. The polymeric resin is then extruded through a spinnerette to form continuous fibers, which can then be subsequently fed through a fiber draw unit. From the fiber draw unit, the fibers are spread onto a foraminous surface where they are formed into a web. In particular, a vacuum is created below the foraminous surface forming a suction force which draws the fibers onto the foraminous surface. The formed web is then bonded such as by chemical, thermal, or ultrasonic means. [0004] Meltblown fabrics, on the other hand, have been conventionally made by extruding a thermoplastic polymeric material through a die to form fibers. As the molten polymer filaments exit the die, a high pressure fluid, such as heated air or steam, attenuates the molten polymer filaments to form fine fibers. Surrounding cool air is induced into the hot air stream which cools and solidifies the fibers. The fibers are then randomly deposited onto a foraminous surface to form a web. The web has integrity as made but may be additionally bonded. [0005] Bonded carded webs refer to webs produced by carding a batt of fibers. Once the batt of fibers is carded into a web, the web can be folded over and needle punched in order to increase the thickness of the web. When using fibers made from synthetic polymers, in order to increase the strength and integrity of the web, the fibers can be meltbonded together. For instance, the carded web can be brought into contact with a heated roller which is at a temperature sufficient to soften the synthetic polymer. [0006] Coform webs generally refer to polymeric nonwoven webs that contain a filler. The filler incorporated into the web can be, for instance, absorbent particles, pulp fibers, or other solid materials. [0007] For most applications, nonwoven webs typically must exhibit a combination of physical properties that make the webs well suited for their intended function. For instance, for most applications, nonwoven webs should have adequate softness, strength and absorbency characteristics. For example, liners used in diapers, feminine hygiene products, and other liquid absorbable products should be relatively strong, but should also be highly liquid permeable for allowing liquids contacting the surface of the liner to be absorbed into the interior of the product. [0008] Unfortunately, when one property of a nonwoven web is improved, typically other properties of the web are adversely affected. For instance, when the liquid permeability of nonwoven webs is increased, often the strength of the web is decreased. [0009] Currently, various needs remain in methods for controlling the properties of nonwoven webs. A need further exists for nonwoven webs that exhibit an improved combination of properties, such as strength and liquid permeability characteristics. SUMMARY OF THE INVENTION [0010] The present invention is directed to further improvements in producing nonwoven webs having desired properties. [0011] Accordingly, an object of the present invention is to provide a process by which the physical properties of a nonwoven web made from polymeric fibers can be controlled. [0012] Another object of the present invention is to provide novel nonwoven webs that exhibit a desirable combination of properties. [0013] Still another object of the present invention is to provide nonwoven webs having a controlled varying basis weight made from polymeric fibers or pulp fibers. [0014] It is another object of the present invention to provide nonwoven webs that have first areas and second areas that form a predetermined pattern and wherein the basis weight of the web within the first areas is greater than the basis weight within the second areas. [0015] Still another object of the present invention is to provide laminates that contain a nonwoven web which has a varying basis weight. [0016] These and other objects of the present invention are achieved by providing a nonwoven web made from polymeric fibers, such as fibers made from a spunbond or meltblown process. The nonwoven web defines first areas having a first basis weight and second areas having a second basis weight. In particular, the first areas have a basis weight from about 1.5 to about 5 times greater than the basis weight of the second areas and particularly from about 1.5 to 3 times greater than the basis weight of the second areas. In general, the average basis weight of the web can vary from about 0.2 ounces per square yard to about 9 ounces per square yard and particularly from about 0.3 ounces per square yard to about 4 ounces per square yard. [0017] The first and second areas contained within the web can be formed according to a random pattern or according to a pattern on the forming wire which locally controls the air flow velocity. For instance, the first and second areas can form alternating columns, alternating columns and rows, or can form a checkered pattern within the web. The checkered pattern can be formed by the heavy area forming the grid or the light area forming the grid. For most applications, the first areas should comprise from about 25% to about 75% of the nonwoven web, and particularly from about 40% to about 60% of the nonwoven web. [0018] The polymeric fibers used to produce the nonwoven web can be made from various materials including elastomeric polymers, polypropylene, polyethylene, polyester, and nylon. The fibers can be monocomponent fibers or multicomponent fibers, such as bicomponent fibers. The fibers can also be continuous filaments or discontinuous fibers. In applications where high loft is desired, crimped fibers can be used. [0019] Besides the above-described nonwoven webs, the present invention is also directed to laminates incorporating the webs. For instance, in one embodiment, a laminate product can be produced in which a spunbond web as described above is laminated with a meltblown web. In a further alternative embodiment, a meltblown web can be placed in between two outer layers of spunbond webs, in which at least one of the spunbond webs has a varying basis weight. In still another embodiment, the laminate can contain a film besides other nonwoven webs. [0020] The nonwoven webs of the present invention having areas of higher basis weight and areas of lower basis weight are generally produced by extruding a thermoplastic polymer through a die to form fibers. The fibers are directed onto a foraminous surface by an airflow which is created by a vacuum under the foraminous surface. According to the present invention, the foraminous surface has a predetermined pattern of lower and higher permeability sections or regions. [0021] A nonwoven web is formed on the foraminous surface from the fibers. The formed web defines first areas having a first basis weight and second areas having a second basis weight that is lower than the first basis weight. Specifically, the second areas are formed on the foraminous surface where the lower permeability sections are located. Continue reading... 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