Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reissue Patent
1999-08-23
2001-05-29
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C427S384000, C427S385500, C427S407100, C428S412000, C524S083000, C524S084000, C524S099000, C524S100000, C524S111000, C524S335000, C524S338000, C524S102000
Reissue Patent
active
RE037200
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a polycarbonate composition and to articles molded therefrom; more particularly the invention relates to compositions and articles which have an improved resistance to discoloration caused by exposure to High Intensity Discharge (HID) light and heat.
SUMMARY OF THE INVENTION
A polycarbonate composition having an improved resistance to discoloration caused by exposure to High Intensity Discharge (HID) light and heat is disclosed. Accordingly, the composition which is free from hydroxyphenyl organophosphorus compounds, contains polycarbonate resin, a dimeric benzotriazole and an ester of a 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid. In a preferred embodiment, a (co)polycarbonate sheet is rendered improved resistance to discoloration by having applied to at least one of its surfaces an adherent film comprising the polycarbonate composition of the invention.
BACKGROUND OF THE INVENTION
Polycarbonate resins are characterized by their transparency, mechanical strength and dimensional stability. These properties make polycarbonate an ideal choice for the preparation of articles, especially laminates or sheets, useful in application in hostile environments. One of the drawbacks of the resin used in this application is its tendency to discolor upon prolonged exposure to the heat and/or UV. Among the relevant applications, mention may be made of lighting lenses and associated parts in conjunction with metal halide, mercury vapor, high pressure sodium and other High Intensity Discharge (HID) lamps which generate UV radiation and significant heat. The tendency of polycarbonate to discolor, limits its applicability and methods to overcome the deficiency have long been sought.
It is therefore an object of the present invention to provide polycarbonate compositions which are suitable for the preparation of articles, most especially sheets and laminates, having improved resistance to discoloration caused by exposure to heat and/or UV.
The art has long recognized the efficacy of hindered phenols as antioxidants in the context of polymeric resins. U.S. Pat. No. 4,563,516 disclosed sterically hindered phenols as stabilizers of a carbonate polymer, and a hindered phenol phosphite was disclosed in U.S. Pat. No. 4,276,233 as a thermal stabilizer of polycarbonate resins. U.S. Pat. No. 4,812,498 disclosed a polycarbonate resin composition having improved resistance to deterioration when exposed to light and containing the bisbenzotriazole stabilizer of the present invention. Importantly, the possible use of the bis-benzotriazole in combination with phenolic antioxidants is disclosed in the '498 document.
The art is noted to include Canadian Patent 1,208,873 which disclosed a polycarbonate-based panel made resistant to UV radiation. Accordingly, a panel is structured to include a core layer of polycarbonate to which there is adhesively bonded an intermediate UV absorption layer and a cover layer. The purpose of the cover layer is to prevent vaporization of the UV absorber from the intermediate layer. The intermediate, UV-absorption layer may be prepared from polycarbonate and contains derivatives of benzotriazole as UV absorbers. Also noted is German Patent Application 1,670,951 which disclosed polycarbonate molded articles, including ribbons which are rendered resistant to UV radiation by incorporating the bis-benzotriazole compound of the present invention therewith. A method for coating a polycarbonate sheet with a protective layer was disclosed in UK Patent Application 2,028,228. A layer preferably of polymethacrylate and advantageously containing a UV absorber is said to be applied to the sheet by co-extrusion. U.S. Pat. No. 3,892,889 discloses UV stabilized polycarbonate moldings, the surfaces of which have been treated with a solution containing a benzotriazole. German DE-OS 3,617,978 discloses co-extruded sheets based on a polycarbonate resin which sheets are covered by a UV absorbing layer made from a branched polycarbonate resin containing the bis-benzotriazole of the present invention. Also relevant is European Patent Application 110,221 which disclosed a panel consisting of a core layer of polycarbonate containing not more than 0.5 wt. percent of a UV absorber and having on at least one side a coating layer which has been coextruded with the core and which contains at least 3 percent of a UV absorber.
U.S. Pat. No. 4,948,666 is noted to disclose a polycarbonate composition containing the bis-benzotriazole of the present invention useful in the preparation of a stain-protective layer for polycarbonate sheets. Also relevant in the present context is U.S. patent application Ser. No. 07/732,262 filed Jul. 18, 1991 which disclosed relevant technology.
The present invention resides in the finding of a particularly efficient combination of stabilizers.
DETAILED DESCRIPTION OF THE INVENTION
The (co)polycarbonate resins useful in the practice of the invention are homopolycarbonate, copolycarbonate and terpolycarbonate resins or mixtures thereof. Preferably, the (co)polycarbonate resins have molecular weights of 18,000-200,000 (weight average molecular weight), more preferably 20,000-80,000, and may alternatively be characterized by their melt flow of 1-65 gm/10 min. at 300° C. per ASTM D-1238. These (co)polycarbonates may be prepared, for example, by the known diphasic interface process from phosgene and dihydroxy compounds by polycondensation (see German DOS 2,063,050; 2,063,052; 1,570,703; 2,211,956; 2,211,957 and 2,248,817 and French Patent 1,561,518 and the monograph, H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York 1964, all incorporated herein by reference).
In the present context, dihydroxy compounds suitable for the preparation of the (co)polycarbonates of the invention conform to the structural formulae (1) or (2)
wherein
A denotes an alkylene group with 1 to 8 carbon atoms, an alkylidene group with 2 to 8 carbon atoms, a cycloalkylene group with 5 to 15 carbon atoms, a cycloalkylidene group with 5 to 15 carbon atoms, a carbonyl group, an oxygen atom, a sulfur atom, an —SO— or —SO
2
-radical; or a radical of the general formula
g denotes the number 0 or 1;
e denotes the number 0 or 1;
Z denotes F, Cl, Br or a C
1
-C
2
alkyl and if several Z radicals are substituents in one aryl radical, they may be identical or different;
d denotes 0 or an integer of from 1 to 4; and
f denotes 0 or an integer of from 1 to 3.
Among the useful dihydroxy compounds in the practice of the invention are hydroquinone, resorcinol, bis-(hydroxyphenyl)-alkanes, bis(hydroxyphenyl)-cycloalkanes, bis-(hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones, bis-(hydroxyphenyl)-sulfoxides, bis-(hydroxyphenyl)-sulfones and &agr;,&agr;-bis-(hydroxyphenyl)-diisopropylbenzenes. These and further suitable aromatic dihydroxy compounds are described, for example, in U.S. Pat. Nos. 3,028,365; 2,999,835; 3,148,172; 3,271,368; 2,991,273; 3,271,367; 3,280,078; 3,014,891 and 2,999,846 (all incorporated herein by reference), in German Offenlegungsschriften (German Published Specifications) 1,570,703; 2,063,050; 2,063,052; 2,211,956 and 2,211,957, in French Patent Specification 1,561,418 and in the monograph, H. Schnell, Chemistry and Physics of Polycarbonates, Interscience Publishers, New York, 1964. Further examples of suitable dihydroxy compounds are 2,2-bis-(4 -hydroxyphenyl)-propane(bisphenol A), 2,4-bis-(4-hydroxyphenyl)-2-methyl-butane, 1,1-bis-(4-hydroxyphenyl)-cyclohexane, 2,2,4-trimethylcyclohexyl 1,1-diphenol, &agr;,&agr;-bis-(4-hydroxyphenyl)-p-diisopropylbenzene, 2,2-bis-(3-chloro-4-hydroxyphenyl)-propane, hydroxybenzo-phenone and 4,4′-sulfonyl diphenol; the most preferred one is 2,2-bis-(4 -hydroxyphenyl)-propane(bisphenol A).
The (co)polycarbonates of the invention may entail in their structure, units derived from one or more of the suitable dihydroxy compounds.
The preparation of (co)polycarbonate resins may be carried out in accordance with any of the processes known in the art, for example, by the interfacial polyconde
Dunay Kevin F.
Krishnan Sivaram
Paul Winfried G.
Bayer Corporation
Boykin Terressa M.
Gil Joseph C.
Preis Aron
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