Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-02-14
2003-12-16
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S100000, C524S111000, C524S126000, C524S128000, C524S136000, C524S139000, C524S147000, C524S153000, C522S075000, C522S076000, C522S078000, C522S079000, C522S150000, C522S157000, C522S161000
Reexamination Certificate
active
06664317
ABSTRACT:
The present invention relates to the stabilization of gamma irradiated polyolefin fibers, films and molded articles. Specifically, certain non-phenolic binary and ternary stabilization systems are especially effective.
Polyolefin materials are making significant inroads into areas where the item can be pre-sterilized, used for the intended purpose, and then properly disposed of. The shift from glass, metal and cloth to polyolefin based fibers and articles is driven by lower cost, greater convenience, and growing concerns related to handling of hazardous waste generated by some health science related procedures. Polyolefins are useful in a variety of end use applications where sterilization with gamma irradiation is employed, see for example U.S. Pat. Nos. 4,797,438, 5,122,593 and 5,559,167, all incorporated herein by reference. Polyolefin medical packaging, hospital garments, surgery utensils, blow-molded I.V. bottles, hypodermic syringes, needle shields, laboratory ware such as trays, funnels, Petri dishes and filters, and hygiene related articles may all require sterilization with gamma irradiation.
Sterilization can be achieved by exposure to about 0.5 to about 10 megarads of gamma irradiation. This can be done over a period of time, for example, about 1 minute to about 24 hours.
This sterilization technique is successful towards eliminating unwanted organisms and bacteria but places a significant stress on the properties of the polyolefin. Physical properties such as strength and toughness and aesthetic properties such as color, taste and odor of the polyolefin fibers and articles are affected. The sterilized fibers and articles must be able to function without cracking, bending, breaking, shredding or tearing during the intended use. Likewise, they must have low initial color and maintain low color throughout their lifetime.
U.S. Pat. No. 4,797,438 discloses polypropylene articles which are sterilized with gamma irradiation and stabilized with hindered amines of the class of polysubstituted piperazinones. U.S. Pat. No. 5,122,593 discloses polypropylene fibers stabilized against the harmful effects of gamma irradiation with the incorporation of an N-(substituted)-1-(piperazine-2-one alkyl)-&agr;-(3,5-dialkyl-4-hydroxyphenyl)-&agr;,&agr;-substituted acetamide. U.S. Pat. No. 5,559,167 teaches a method for enhancing the resistance of polymeric articles to discoloration incurred by gamma irradiation with the incorporation of one of a particular class of phosphite stabilizers.
There remains a need to supply to industry fully formulated polyolefin feedstocks that can resist the damaging effects of high energy radiation. It has now been found that certain specific binary and ternary stabilizer combinations satisfy this need. The stabilizer systems of the instant invention are essentially phenol antioxidant-free and comprise either a binary hindered amine/hydroxylamine or nitrone or amine oxide or benzofuranone system or a ternary hindered amine/hydroxylamine or nitrone or amine oxide or benzofuranone/organic phosphite or phosphonite system.
Hydroxylamine derivatives, such as N,N,-dialkylhydroxylamines and N,N-dibenzylhydroxylamine, are well known as useful stabilizers for a variety of polymeric substrates as is taught for example in U.S. Pat. Nos. 4,590,231, 4,668,721, 4,782,105 and 4,876,300, the relevant parts of which are incorporated herein by reference.
U.S. Pat. Nos. 4,649,221, 4,691,015 and 4,703,073 teach the use of polyhydroxylamine compounds, hydroxylamines derived from hindered amines and alkylated N,N-dibenzylhydroxylamine derivatives, respectively, with one or more compounds selected from the group of phenolic antioxidants, hindered amine light stabilizers, alkylated hydroxybenzoate light stabilizers, ultraviolet light absorbers, organic phosphorus compounds, alkaline metal salts of fatty acids and thiosynergists towards stabilizing polyolefins. All three patents teach that the polyolefin compositions are stabilized against degradation and/or discoloration upon exposure to heating at elevated temperatures, to the combustion products of natural gas, to gamma irradiation or to prolonged storage at ambient temperature.
U.S. Pat. No. 4,782,105 discloses the use of long chain N,N-dialkylhydroxylamines for the stabilization of poly(arylene sulfides) and unsaturated elastomers. Examples are shown where long chain N,N-dialkylhydroxylamines are used together with phosphite stabilizers in styrene/butadiene copolymer.
U.S. Pat. No. 4,876,300 discloses the use of long chain N,N-dialkylhydroxylamines as process stabilizers for polyolefin compositions. Examples are shown where long chain N,N-dialkylhydroxylamines are used together with phosphite stabilizers and also where they are used together with hindered amine stabilizers.
U.S. Pat. Nos. 4,590,231 and 4,668,721 disclose the use of N,N-dibenzylhydroxylamine or other hydroxylamine derivatives together with metal salts of fatty acids and phenolic antioxidants for the stabilization of polyolefin compositions. The compositions may also contain organic phosphorus compounds or hindered amine stabilizers. It is mentioned that the polyolefin compositions are stabilized against degradation and/or discoloration upon exposure to heating at elevated temperatures, to the combustion products of natural gas, to gamma irradiation or to prolonged storage at ambient temperature.
U.S. Pat. Nos. 5,844,029, 5,880,191 and 5,922,794 disclose the use of saturated hydrocarbon amine oxides towards the stabilization of thermoplastic resins. It is disclosed that the thermoplastic compositions may further contain a stabilizer or mixture of stabilizers selected from phenolic antioxidants, hindered amine light stabilizers, ultraviolet light absorbers, organic phosphorus compounds, alkaline metal salts of fatty acids and thiosynergists. The co-use of amine oxides with other stabilizers towards stabilizing polyolefins is not exemplified.
Benzofuranone stabilizers are known and are described for example in U.S. Pat. Nos. 5,516,920 and 5,614,572. These patents teach that benzofuranone stabilizers are suitable towards protecting organic materials including polyolefins against thermal, oxidative or light-induced degradation.
DETAILED DISCLOSURE
The present invention relates to a polyolefin article of manufacture of improved strength and/or discoloration resistance, said article being essentially phenol antioxidant-free and having incorporated therein a stabilizer system sufficient to attenuate the deleterious effects of gamma irradiation, said stabilizer system comprising
(a) one or more hindered amine stabilizers,
(b) one or more compounds selected from the group consisting of
i.) hydroxylamine stabilizers,
ii.) nitrone stabilizers,
iii.) amine oxide stabilizers and
iv.) benzofuranone stabilizers; and optionally
(c) one or more compounds selected from the group of organic phosphites and phosphonites,
said article having been subjected to one or more doses of gamma irradiation.
The present invention is also aimed at a method for imparting strength and/or discoloration resistance to gamma irradiated polyolefin articles, which articles are essentially phenol antioxidant-free,
which comprises incorporating therein a stabilizer system as described above,
in an amount sufficient to attenuate the deleterious effects of gamma irradiation.
Essentially phenol antioxidant-free in the context of this invention means that the present compositions and methods comprise either no phenolic antioxidants or only trace amounts thereof. Trace amounts are amounts that impart inconsequential effects or are inadequate to be judged as effective.
Component (a) employed in the novel process is at least one compound that contains at least one group of the formula (I)
in which R
x
is hydrogen or methyl. The compounds of component (a) are for example, of high molecular weight and may be discrete compounds or oligomeric mixtures.
For example, hindered amines of component (a) are:
The compounds of the sterically hindered amine type are known and some are commercially available.
The sterical
Ciba Specialty Chemicals Corporation
Stevenson Tyler A.
Szekely Peter
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