Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1995-07-07
1997-09-09
Marquis, Melvyn I.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524269, 524493, 428323, 428327, 19299, C08K 554
Patent
active
056658036
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATION
Nonwoven webs having improved tensile strength characteristics are described and claimed in copending and commonly assigned application Ser. No. 07/783,438, entitled THERMOPLASTIC COMPOSITIONS AND NON-WOVEN WEBS PREPARED THEREFROM and filed Oct. 25, 1991, U.S. Pat. No. 5,344,862, in the names of Ronald S. Nohr and J. Gavin MacDonald.
BACKGROUND OF THE INVENTION
The present invention relates to a melt-extrudable thermoplastic composition which contains an additive system, and to shaped articles made therefrom.
Thermoplastic compositions are described in U.S. Pat. No. 4,923,914 to Ronald S. Nohr and J. Gavin MacDonald, incorporated herein by reference, which include at least one thermoplastic polymer and at least one defined additive. The additive particularly is a siloxane-containing compound. The compositions are especially useful for the formation of nonwoven webs by such melt-extrusion processes as meltblowing, coforming, and spunbonding. Upon being melt-extruded, such compositions result in a fiber having a differential, increasing concentration of the additive from the center to the surface thereof, such that the concentration of additive toward the surface of the fiber is greater than the average concentration of additive in the more central region of the fiber and imparts to the surface of the fiber at least one desired characteristic which otherwise would not be present. The additive is miscible with the polymer at melt extrusion temperatures, under which conditions the additive and the polymer form a metastable solution. As the temperature of the newly formed fiber drops below melt extrusion temperatures, the additive becomes significantly less compatible with the polymer. Concurrent with this marked change in compatibility, the polymer begins to solidify. Both factors contribute to the rapid migration or segregation of the additive toward the surface which takes place in a controllable manner.
It subsequently was discovered that the use of an additive system comprising certain polysiloxane polyether additive s of U.S. Pat. No. 4,923,914 and a modified fumed silica having a hydrophobic surface unexpectedly gave a nonwoven web which was not wettable, but exhibited improved tensile strength characteristics as compared with a nonwoven web prepared from a thermoplastic composition lacking the hydrophobic fumed silica. This discovery is part of the disclosure of cross-referenced application Ser. No. 07/783,438 filed Oct, 25, 1991, U.S. Pat. No. 5,344,862. However, a further improvement of tensile strength characteristics, exceeding the improvements taught by application Ser. No. 07/783,438, filed Oct 25,1991, U.S. Pat. No. 5,344,862 now has been discovered.
Silica and other materials have been incorporated into thermoplastic polymers, including polypropylene. For example, the inclusion of an organic peroxide and a nucleating agent in polypropylene is described in Japanese Patent Publication No. 60-217207. The nucleating agent can be an organic salt, an organic compound, or an inorganic material such as silica, alum, titanium dioxide, carbon black, and various clay minerals.
References which describe the inclusion in polypropylene or other thermoplastic polymer of an organic material include U.S. Pat. Nos. 3,207,735 to Wijga (benzoic acid, substituted benzoic acids, hexahydro analogs thereof, and related compounds), 3,207,737 to Wales (aluminum salts of benzoic acid and related compounds), 3,207,739 to Wales (Group I and II metal salts of certain mono- and polycarboxylic acids), 3,299,029 to Binsbergen et at. (aluminum salts of benzoic acid and related compounds), 4,611, 024 to Wolfe (an acetal of an alditol and a hydrotalcite), and 4,808,650 to Titus et al. (fluorinated dibenzylidene sorbitol additives); and Japanese Patent Publication No. 51-22740 (benzylidene sorbitol).
Finally, studies relating to the heterogeneous nucleation of polymers have been reported. Examples of such studies include Chatterjee and Price, "Heterogeneous Nucleation of Crystallization of
REFERENCES:
patent: 5336707 (1994-08-01), Nohr et al.
patent: 5344862 (1994-09-01), Nohr et al.
patent: 5413655 (1995-05-01), Nohr et al.
Gillberg-LaForce Gunilla Elsa
Kobylivker Peter Michlovich
MacDonald John Gavin
Nohr Ronald Sinclair
Kimberly-Clark Corporation
Marquis Melvyn I.
Maycock William E.
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