Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1996-04-30
2001-11-27
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
active
06323291
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to a thermoplastic molding composition and more particularly to a composition containing polycarbonate and a copolyester of cyclohexane dimethanol.
SUMMARY OF THE INVENTION
A thermoplastic molding composition suitable for the preparation of articles having low birefringence is disclosed. Accordingly, the composition contains polycarbonate and a polyester copolymer based on cyclohexane-dimethanol, ethylene glycol and phthalic acid. The invention resides in the findings that the incorporation of a polycarbonate resin having a melt flow index greater than 18g/10 minutes impart to the composition low birefringence values. The composition is suitable for the preparation of optical storage media, including compact discs.
BACKGROUND OF THE INVENTION
Thermoplastic compositions containing polycarbonate and polyester resins are known. Thermoplastic molding compositions containing a mixture of polycarbonate and a polyester copolymer derived from cyclohexane dimethanol and phthalic acid are also known and such compositions have been disclosed in U.S. Pat. No. 4,786,692. Characterized by their low heat distortion temperatures, high tensile and flexural strength, the compositions are said to be compatible with impact modifiers and flame retardants.
Polycarbonate resins and compositions based thereon have been extensively used in the preparation of optical storage media, such as compact discs. A critical parameter relative to such media and the molding materials therefor is their low birefringence.
DETAILED DESCRIPTION OF THE INVENTION
The composition of the invention contains
(i) about 60 to 99, preferably 70 to 90 percent by weight of a polycarbonate resin having a high melt flow index, and
(ii) about 1 to 40, preferably 10 to 30 percent by weight of a polyester copolymer of phthalic acid and cyclohexanedimethanol (CHDM)-/ethylene glycol (EG).
The invention resides in the finding that compositions of the invention are characterized by their low birefringence, a characteristic which makes these compositions suitable in the manufacture of compact discs. The suitability for such disc manufacture has been determined by first extruding the composition and then forming a disc having a diameter of about 120 mm, by injection molding. The optical path difference at a disc radius of 30 mm to 60 mm was then measured using a birefringence meter with a 780 nm red laser. The discs made of the inventive compositions have lower optical path difference and therefore lower birefringence values than corresponding discs made of polycarbonate resin alone.
Aromatic polycarbonates suitable in the context of the present invention are homopolycarbonates and copolycarbonates and mixtures thereof. These polycarbonates generally have a weight average molecular weight of about 16,000 to 21,000, most preferably 18,000 to 19,000 and their high melt flow index (determined in accordance with the procedure of ASTM D-1238 at 300° C./under 1.2 kg load) is at least about 18, preferably 50 to 80, most preferably 65 to 75 g/10 minutes. These resins are known and are readily available in commerce. Suitable polycarbonate resins are prepared, for example, by the known diphasic interface process from a carbonic acid derivative such as phosgene and dihydroxy compounds by polycondensation (see German Offenlegungsschriften 2,063,050; 2,063,052; 1,570,703; 2,211,956; 2,211,957 and 2,248,817; French Pat. No. 1,561,518; and the monograph H. Schnell, “Chemistry and Physics of Polycarbonates”, Interscience Publishers, New York, N.Y., 1964, all incorporated herein by reference).
In the present context, dihydroxy compounds suitable for the preparation of the 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, —SO— or —SO
2
— or a radical conforming to
e and g both denote the number 0 to 1; Z denotes F, Cl, Br or C
1
-C
4
-alkyl and if several Z radicals are substituents in one aryl radical, they may be identical or different from one another; d denotes an integer of from 0 to 4; and f denotes an integer of from 0 to 3.
Among the dihydroxy compounds useful in the practice of the invention are hydroquinone, resorcinol, bis-(hydroxyphenyl)-alkanes, bis-(hydroxyphenyl)ethers, bis-(hydroxyphenyl)-ketones, bis-(hydroxyphenyl)-sulfoxides, bis-(hydroxyphenyl)-sulfides, bis-(hydroxyphenyl)-sulfones, and &agr;,&agr;-bis-(hydroxyphenyl)diisopropylbenzenes, as well as their nuclear-alkylated compounds. These and further suitable aromatic dihydroxy compounds are described, for example, in U.S. Pat. Nos. 3,028,356; 4,982,014; 5,010,162; 2,999,835; 3,148,172; 2,991,273; 3,271,367; and 2,999,846, all incorporated herein by reference.
Further examples of suitable bisphenols are 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A), 3,3,5-trimethyl-1,1-bis(4-hydroxyphenyl)-cyclohexane, 2,4-bis-(4-hydroxyphenyl)-2-methyl-butane, 1,1-bis-(4-hydroxyphenyl)-cyclohexane, &agr;,&agr;′-bis-(4-hydroxyphenyl)-p-diisopropylbenzene, 2,2-bis-(3-methyl4-hydroxyphenyl)-propane, 2,2-bis-(3-chloro-4-hydroxyphenyl)propane, bis-(3,5-dimethyl4-hydroxyphenyl)-methane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane, bis-(3,5-dimethyl-4-hydroxyphenyl)-sulfide, bis-(3,5dimethyl-4-hydroxyphenyl)-sulfoxide, bis-(3,5-dimethyl-4-hydroxyphenyl)-sulfone, dihydroxy-benzophenone, 2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-cyclohexane, &agr;,&agr;′-bis-(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropylbenzene and 4,4′-sulfonyl diphenol.
Examples of particularly preferred aromatic bisphenols are 2,2,-bis-(4-hydroxyphenyl)-propane, 3,3,5-trimethyl-1,1-bis(4-hydroxyphenyl)-cyclohexane, 2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane and 1,1-bis-(4-hydroxyphenyl)-cyclohexane.
The most preferred bisphenol is 2,2-bis-(4-hydroxyphenyl)-propane (bisphenol A).
The polycarbonates of the invention may entail in their structure units derived from one or more of the suitable bisphenols.
Among the resins suitable in the practice of the invention are included phenolphthalein-based polycarbonates, copolycarbonates and terpolycarbonates such as are described in U.S. Pat. Nos. 3,036,036 and 4,210,741, both incorporated by reference herein.
The polycarbonates of the invention may also be branched by condensing therein small quantities, e.g., 0.05 to 2.0 mol % (relative to the bisphenols) of polyhydroxyl compounds.
Polycarbonates of this type have been described, for example, in German Offenlegungsschriften 1,570,533; 2,116,974 and 2,113,374; British Patents 885,442 and 1,079,821 and U.S. Pat. No. 3,544,514. The following are some examples of polyhydroxyl compounds which may be used for this purpose: phloroglucinol; 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane; 1,3,5-tri-(4-hydroxyphenyl)-benzene; 1,1,1-tri-(4-hydroxyphenyl)-ethane; tri-(4-hydroxyphenyl)-phenylmethane; 2,2-bis-[4,4-(4,4′-dihydroxydiphenyl)]-cyclohexylpropane; 2,4-bis-(4-hydroxy-1-isopropylidene-)-phenol; 2,6bis-(2′-dihydroxy-5′-methylbenzyl)-4-methylphenol; 2,4-dihydroxybenzoic acid; 2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane and 1,4-bis-(4,4′-dihydroxytriphenylmethyl)-benzene. Some of the other polyfunctional compounds are 2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and 3,3-bis-(4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.
In addition to the polycondensation process mentioned above, other processes for the preparation of the polycarbonates of the invention are polycondensation in a homogeneous phase and transesterification. The suitable processes are disclosed in the incorporated herein by reference, U.S. Pat. Nos. 3,028,365; 2,999,846; 3,153,008; and 2,991,273.
The preferred process for the preparation of polycarbonates is the interfacial polycondensation process.
Other methods of synthesis in forming the polycarbonates of the invention such as d
Mason James P.
Newcome Jon M.
Tennant Jeff M.
Bayer Corporation
Buttner David J.
Gil Joseph C.
Preis Aron
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