Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-07-01
2001-03-06
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S111000, C523S135000, C523S136000
Reexamination Certificate
active
06197853
ABSTRACT:
The invention is directed to transparent thermoplastic molding compositions and more particularly to a polycarbonate molding composition having improved resistance to gamma radiation-induced yellowing.
SUMMARY OF THE INVENTION
A thermoplastic polycarbonate molding composition having improved resistance to gamma radiation-induced yellowing is disclosed. Particularly suitable for the manufacture of devices geared for medical applications, the composition contains an additive amount of a stabilizing compound conforming structurally to
where R
1
denotes a C
1-30
-alkyl group and R
2
denotes an aryl radical.
BACKGROUND OF THE INVENTION
Because of their physical and mechanical properties, polycarbonate resins were found to be eminently suitable for a variety of applications in the medical field. However, those applications, which require sterilization by exposure to ionizing radiation, present a problem since polycarbonate tends to yellow and show increased haze. The relevant art is noted to include U.S. Pat. No. 4,624,972 which disclosed polycarbonate compositions resistant to gamma radiation containing an ester of aromatic polycarboxylic acid and monoalkyl or monoaryl ether of polyglycol. The properties of relevant compositions containing esters based on primary alcohols are disclosed in the '972 document.
U.S. Pat. No. 4,873,271 disclosed a gamma radiation resistant polycarbonate composition containing an ester of a poly(alkylene) oxide as a stabilizer. Also relevant are the following U.S. Patents, all of which relate to polycarbonate compositions rendered resistant to gamma radiation by the incorporation of a stabilizing agent U.S. Pat. Nos.: 5,187,211; 4,804,692; 4,963,598; 4,874,802; 5,006,572; 5,187,208; 5,274,009 and 5,214,078. Lastly, U.S. Pat. No. 5,280,050 disclosed a polycarbonate composition containing a poly(alkylene) oxide oligomer and a halogenated aromatic phthalic acid ester of a primary alcohol. U.S. Pat. No. 5,145,751 is noted for its disclosure of a magnetic recording medium which contains a non-magnetic substrate and a magnetic recording layer coated on the substrate. The magnetic recording layer contains a compound embracing the stabilizer of the present invention.
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Bolton Daniel H.
Derikart David M.
Johnson James B.
Krishnan Sivaram
Bayer Corporation
Cain Edward J.
Gil Joseph C.
Preis Aron
Wyrozebski-Lee Katarzyna
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