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...
Reexamination Certificate
2000-09-07
2003-10-07
Szekely, Peter (Department: 1714)
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...
C524S434000, C524S486000, C524S490000, C524S491000
Reexamination Certificate
active
06630532
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to extruding of elastomeric polymer compositions, more specifically to such compositions that are extruded as films for use in disposable hygiene products such as adult, infant, and feminine hygiene products.
BACKGROUND OF THE INVENTION
Extrudable elastomeric compositions which can be easily made into elastic films having low stress relaxation, low hysteresis, and high recoverable energy are described in U.S. Pat. Nos. 4,663,220, 4,789,699, 4,970,259, or 5,093,422. Those elastomeric films are useful in making a variety of applications such as diaper waistbands and non-woven fabrics.
Polystyrene-poly(ethylene-butylene)-polystyrene elastomeric block copolymers (SEBS) and polystyrene-poly (ethylene-propylene)-polystyrene (SEPS) elastomeric block copolymers have been blended with other materials such as, for example, polyolefins, such as polypropylene and polyethylene, and oils to form extrudable elastomeric compositions which can be more easily extruded into elastic films having improved processing properties. While the additives improve the extrusion properties of the compositions and the processing properties of the elastic films, such additives have an adverse affect on the elastic properties of the resulting film, especially at temperatures above 25° C.
The currently used commercial SEBS-based compounds for elastomeric films generally have an average stress relaxation, when measured on a film in the direction that is transverse to the machine direction and tested at 100° F. (37.8° C.) at 150 percent elongation, of greater than 27 percent, and a retained tension or load of less than 105 psi. Measurement in the transverse direction is the most important because when the film is assembled into the final product, it is the direction that gets stressed. Since these films are mainly used in disposable hygiene products, they have to be able to retain their properties at body temperature when stressed. Stress relaxation refers to the percent loss of tension or load encountered after elongating an elastic material at a specified rate of extension to a predetermined length and is expressed as a percentage loss of the initial load encountered at a specified extension of the elastic material. For this application, the lower the stress relaxation the better, and higher retained tension or load, i.e. above 125 psi., will allow the use of thinner films.
SUMMARY OF THE INVENTION
The present invention is an improved block copolymer composition for extruding films having excellent stress relaxation and increased retained tension or load at elevated temperatures. The composition is comprised of:
(a) from 52 to 60 percent by weight of a block copolymer having at least two polystyrene endblocks and a midblock of hydrogenated polymerized butadiene (SEBS), having a polystyrene content of 14 to 25 percent by weight, a polystyrene block number average molecular weight of 7,000 to 11,000, a butadiene block number average molecular weight of 70,000 to 90,000, and a vinyl content of 45 percent by weight or less,
(b) from 13 to 22 percent by weight of polystyrene, and
(c) from 19 to 28 percent by weight of oil.
DETAILED DESCRIPTION OF THE INVENTION
The extrudable elastomeric composition of the present invention is an improvement of the extrudable compositions described in U.S. Pat. Nos. 4,970,259 and 5,093,422 which descriptions are incorporated by reference herein. The known compositions include one or more styrenic block copolymers, typically a polystyrene-poly(ethylene-butylene)-polystyrene (S-EB-S) or a polystyrene-poly(ethylene-propylene)-polystyrene (S-EP-S) elastomeric block copolymer which is produced by hydrogenating a polystyrene-polybutadiene-polystyrene or polystyrene-polyisoprene-polystyrene block copolymer. The extrudable compositions further comprise a polyolefin and an extending oil.
The styrenic block copolymers have at least two poly(monoalkenyl arene) blocks, preferably two polystyrene blocks, separated by a saturated block of polybutadiene (EB). The SEBS block copolymers of this invention comprise polystyrene endblocks each having a number average molecular weight of 7,000 to 11,000 and saturated polybutadiene midblocks having a number average molecular weight of 70,000 to 90,000. The saturated polybutadiene blocks must have a vinyl content of 45 percent by weight or less and a polystyrene content of 14 to 25 percent by weight.
The term “vinyl content” refers to the fact that a conjugated diene is polymerized via 1,2-addition (in the case of butadiene—it would be 3,4-addition in the case of isoprene). Although a pure “vinyl” group is formed only in the case of 1,2-addition polymerization of 1,3-butadiene, the effects of 3,4-addition polymerization of isoprene (and similar addition for other conjugated dienes) on the final properties of the block copolymer will be similar. The term “vinyl” refers to the presence of a pendant vinyl group on the polymer chain.
These polymers may be prepared using free-radical, cationic and anionic initiators or polymerization catalysts. Such polymers may be prepared using bulk, solution or emulsion techniques. In any case, the polymer containing at least ethylenic unsaturation will, generally, be recovered as a solid such as a crumb, a powder, a pellet, or the like.
In general, when solution anionic techniques are used, conjugated diolefin polymers and copolymers of conjugated diolefins and alkenyl aromatic hydrocarbons are prepared by contacting the monomer or monomers to be polymerized simultaneously or sequentially with an organoalkali metal compound in a suitable solvent at a temperature within the range from about −150° C. to about 300° C., preferably at a temperature within the range from about 0° C. to about 100° C. Particularly effective anionic polymerization initiators are organolithium compounds having the general formula:
RLi
n
wherein R is an aliphatic, cycloaliphatic, aromatic, or alkyl-substituted aromatic hydrocarbon radical having from 1 to about 20 carbon atoms; and n is an integer of 1 to 4.
In addition to sequential techniques to obtain triblocks, at least anionic initiators can be used to prepare diblocks of polystyrene-polydiene having a reactive (“live”) chain end on the diene block which can be reacted through a coupling agent to create, for example, (S-B)
x
Y structures wherein x is an integer from 2 to about 30, Y is a coupling agent, B is butadiene and greater than 65 percent of S-B diblocks are chemically attached to the coupling agent. Y usually has a molecular weight which is low compared to the polymers being prepared and can be any of a number of materials known in the art, including halogenated organic. compounds; halogenated alkyl silanes; alkoxy silanes; various esters such as alkyl and aryl benzoates, difunctional aliphatic esters such as dialkyl adipates and the like. Depending on the selected coupling agent the final polymer can be a fully or partially coupled linear triblock polymer (x=2). The coupling agent, being of low molecular weight, does not materially affect the properties of the final polymer.
It is not required in coupled polymers that the diblock units all be identical. In fact, diverse “living” diblock units can be brought together during the coupling reaction giving a variety of unsymmetrical structures, i.e., the total diblock chain lengths can be different, as well as the sequential block lengths of styrene and diene.
The styrenic block copolymers must be hydrogenated. In general, the hydrogenation or selective hydrogenation of the polymer may be accomplished using any of the several hydrogenation processes known in the prior art. For example the hydrogenation may be accomplished using methods such as those taught, for example, in U.S. Pat. Nos. 3,494,942; 3,634,594; 3,670,054; 3,700,633; and Re. 27,145, the disclosure of which patents are incorporated herein by reference. The methods known in the prior art and useful in the present invention for hydrogenating polymers containing ethylenic unsaturation and for hydrogenating or selecti
Kraton Polymer U.S. LLC
Szekely Peter
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