Elastomeric meltblown webs have been proposed for use in a variety of products including composite fabrics including hydroentangled fabrics; in diapers, training pants and other personal hygiene products in which stretch and conformability to body shapes are considered important. Fully hydrogenated (saturated) diblock and/or triblock copolymers and mixtures thereof based on polystyrene blocks and poly(ethylene-butylene) blocks have been the subject of considerable attention for producing meltblown elastomeric webs because of their high temperature stability and their ability to produce meltblown webs with desirable properties.
Commercially available polystyrene-(ethylene-butylene) diblock and triblock copolymers include the KRATON-G resins commercially available from Shell Chemical Company. Because of the high viscosities associated with these resins, the manufacturer's literature suggests blending of the resins with certain relatively low molecular weight materials. The blending of such materials with the KRATON resins can reduce the processing temperatures, thereby minimizing the degradation of the materials, or can reduce melt processing viscosities, thereby enabling throughputs to be increased at lowered pressures in extrusion processes, such as meltblowing processes. The Shell literature teaches that the lower molecular weight materials which are useful in blends include those which are compatible with the polystyrene (PS) segments of the copolymer, and materials which are compatible with the ethylene-butylene (EB) segments. Materials which are compatible with the (PS) segments include polystyrene and poly(methylacrylate) while polyolefins are compatible with the (EB) segments.
U.S. Pat. No. 4,663,220 to Wisneski and U.S. Pat. No. 4,692,371 to Morman disclose the preparation of meltblown webs from blends of saturated (PS)-(EB) diblock and triblock elastomers together with polyolefin resins. However, the preparation of meltblown webs at high throughput rates using these blends can result in processing difficulties rendering the high throughput meltblowing process uneconomical.
U.S. Pat. No. 4,323,534 to Des Marais discloses the use of fatty acids or fatty alcohols as plasticizers useful in the meltblowing of KRATON G, fully saturated elastomers. More recently, U.S. Pat. No. 4,892,203 to Himes discloses blends of the fully saturated KRATON G-type resins plasticized with anionically polymerized styrene or alpha-methyl styrene or their copolymers, or hydrogenated polystyrene. Optionally, a microcrystalline wax may also be added.
U.S. Pat. No. 4,874,447 to Hazelton discloses a method for preparing a nonwoven web from a blend comprising (i) an elastomeric copolymer of an isoolefin and a conjugated diolefin, and (ii) a thermoplastic olefin polymer resin. The elastomers (i) disclosed include copolymers of styrene and butadiene, but none of the fully hydrogenated block copolymers of the KRATON G-type are disclosed. A wide range of thermoplastic resins are disclosed as component (ii), including polyolefins, such as polyethylene, polypropylene, polybutylene, polypentene, copolymers of ethylene and propylene, copolymers of ethylene with unsaturated esters of lower carboxylic acids including copolymers of ethylene with vinylacetate or alkyl acrylates, and the like. However, the unsaturated block copolymers lack the high temperature stability of the saturated block copolymers, and thus elastomeric webs from these materials or blends of these materials can be more difficult to process.
U.S. Pat. No. 4,769,279 to Graham discloses meltblown webs formed from blends of ethylene-acrylic copolymer or ethylene-vinylacetate blended with a second fiber-forming polymer such as a polyolefin. However, the elastomeric webs formed from blends based on ethylene-acrylic copolymers and/or ethylene vinylacetate copolymers, as the elastomeric material, have only limited stretch and recovery properties.
Despite substantial effort and experimentation in the art, only a limited number of elastomeric materials have been used with any substantial commercial success to produce elastomeric webs. Moreover, various processing difficulties are still encountered when attempts are made to produce meltblown elastomeric webs at relatively high throughput rates.