Transparent, fire-resistant polycarbonate compositions

Details Transparent, fire-resistant polycarbonate compositions Transparent, fire-resistant polycarbonate compositions

2001-07-18

2003-12-09

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...

C524S162000, C524S394000, C524S400000, C524S505000, C524S588000

Reexamination Certificate

active

06660787

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to fire resistant polycarbonate compositions and more particularly transparent, fire resistant polycarbonate compositions.
BACKGROUND OF THE INVENTION
Polycarbonate is widely used in the manufacture of molded parts because of its excellent impact resistance, high heat distortion temperature, and transparency. Flame-retardant grades of polycarbonate have been developed for applications such as housings for electronic devices, where safety considerations require certain levels of flame-resistance. These flame-retardant polycarbonates are typically prepared using bromine- or chlorine-containing flame-retardants. Recently, concerns about environmental contamination from the bromine- or chlorine-containing flame-retardants has created a need for transparent polycarbonates that contain little or no bromine or chlorine. Moreover, as molded parts become larger and contain more plastic, there is a need for flame-retardant grades that can pass more stringent flame-retardant testing, such as that set out in the Underwriter's Laboratory 5V A test protocol.
Siloxane additives have been used to improve the flame retardancy of polycarbonate as taught by U.S. Pat. Nos. 5,449,710 and 6,184,312, but may create certain performance issues in certain applications. Siloxane additives may migrate to the surface of molded parts and affect their performance. They may volatize from the parts and affect the performance of nearby electrical components. In a different embodiment, U.S. Pat. Nos. 3,189,662; 3,419,635; 4,732,949 and 5,068,302 disclose a variety of polycarbonate/siloxane copolymer structures that overcome the problems associated with siloxane additives. In yet another teaching, U.S. Pat. No. 6,072,011 discloses a polycarbonate/siloxane copolymer based on 4-8 wt. % of a eugenol-capped linear siloxane with block lengths of 45-55 dimethylsiloxane units. This material provides excellent hydrolytic stability, low temperature ductility, and 5V flame-retardant performance at 3 mm thickness, but the material is not transparent.
Applicants have surprisingly found that by dramatically lowering the amount of short-chained eugenol-capped siloxanes, one obtains a transparent branched polysiloxane-polycarbonate block copolymer that meets the more stringent UL 5V ratings, and which is essentially free of volatile siloxanes and bromine or chlorine-containing flame retardants.
BRIEF SUMMARY OF THE INVENTION
The invention relates to a transparent branched polysiloxane-polycarbonate block copolymer composition comprising less than 1 wt. % of an eugenol-capped siloxane having block lengths of 5-15 dimethyl siloxane units, wherein the polycarbonate composition has a UL94 5V rating at thickness greater than or equal to about 4 millimeters.
The invention also relates to a process for preparing a branched polysiloxane-polycarbonate block copolymer composition comprising less than 1 wt. % of an eugenol-capped siloxane having block lengths of 5-15 dimethyl siloxane units.
DETAILED DESCRIPTION OF THE INVENTION
Transparent is herein defined as having a percent transmission of about 85 or greater and a haze value of about 5 or less when measured according to ASTM D1003, which is incorporated herein by reference, at a thickness of 3.2 mm.
Polydiorganosiloxane/polycarbonate block copolymers are well-known in the art, see for example U.S. Pat. Nos. 3,189,662; 3,419,634; 4,732,949; and 5,068,302 which are incorporated here by reference disclosing resins comprising polycarbonate and polysiloxane blocks and processes for preparing polycarbonate-polysiloxane block copolymers.
Polycarbonate Block.
The polycarbonate blocks in the composition of the present invention comprise recurring units of formula I:
wherein R
a
and R
b
each represent a monovalent hydrocarbon group and may be the same or different; p and q are each independently integers from 0 to 4; and X
a
represents one of the groups of formula:
wherein R
c
and R
d
each independently represent a hydrogen atom or a monovalent linear or cyclic hydrocarbon group and R
e
is a divalent hydrocarbon group.
The polycarbonate blocks may be prepared by reacting a dihydroxy compound such as bisphenol with a carbonate precursor such as phosgene, a haloformate, a carbonate or a carbonate ester, generally in the presence of an acid acceptor and a molecular weight regulator. It is also possible that the block copolymer may be made by other methods known in the art for making polycarbonates such as transesterification as disclosed in U.S. Pat. No. 3,154,008.
Useful polymerization methods include interfacial polymerization, melt polymerization, and redistribution.
As used herein, the term “dihydroxy compound” includes, for example, bisphenol compounds of formula II:
wherein R
a
and R
b
each represent a monovalent hydrocarbon group and may be the same or different; p and q are each independently integers from 0 to 4; and X
a
represents one of the groups of formula:
wherein R
c
and R
d
each independently represent a hydrogen atom or a monovalent linear or cyclic hydrocarbon group and R
e
is a divalent hydrocarbon group.
Some illustrative, non-limiting examples of suitable dihydroxy compounds include the dihydroxy-substituted aromatic hydrocarbons disclosed by name or formula (generic or specific) in U.S. Pat. No. 4,217,438, which is incorporated herein by reference. A nonexclusive list of specific examples of the types of bisphenol compounds that may be represented by formula (II) includes: 1,1-bis(4-hydroxyphenyl) methane; 1,1-bis(4-hydroxyphenyl) ethane; 2,2-bis(4-hydroxyphenyl) propane (hereinafter “bisphenol A” or “BPA”); 2,2-bis(4-hydroxyphenyl) butane; 2,2-bis(4-hydroxyphenyl) octane; 1,1-bis(4-hydroxyphenyl) propane; 1,1-bis(4-hydroxyphenyl) n-butane; bis(4-hydroxyphenyl) phenylmethane; 2,2-bis(4-hydroxy-1-methylphenyl) propane; 1,1-bis(4-hydroxy-t-butylphenyl) propane; bis(hydroxyaryl) alkanes such as 2,2-bis(4-hydroxyphenyl) propane; 1,1-bis(4-hydroxyphenyl) cyclopentane; and bis(hydroxyaryl) cycloalkanes such as 1,1-bis(4-hydroxyphenyl) cyclohexane.
It is also possible to employ two or more different dihydroxy compounds or copolymers of a dihydroxy compound with a glycol or with a hydroxy- or acid-terminated polyester or with a dibasic acid or hydroxy acid in the event a carbonate copolymer rather than a homopolymer is desired for use. Polyarylates and polyester-carbonate resins or their blends can also be employed.
Siloxane Block.
The siloxane blocks for use in preparing the branched copolymer of the invention may be characterized as bisphenolsiloxanes. The preparation of these bisphenolsiloxanes is accomplished by the addition of a polydiorganosiloxane to a phenol containing an alkenyl substituent, according to the schematic formula:
wherein R1 and R2 are each independently hydrocarbyl and where D is an integer of from about 5 to about 20. In one embodiment, R1 is methyl and R2 is methyl or phenyl, and D is about 5-15.
The essential features of the process to prepare the bisphenolsiloxanes are described by Vaughn, U.S. Pat. No. 3,419,635 (December 1968). For instance, the process is exemplified in example 8 of this Vaughn patent which describes the addition of a hydrogen-terminated polydimethylsiloxane to an allylphenol in the presence of a catalytic amount of chloroplatinic acid-alcohol complex at 90-115.degree. C.
In one embodiment, the polysiloxane blocks are made from bisphenolpolysiloxanes where R1 and R2 are methyl, and where Y is methoxy located ortho to the phenolic substituent. These are readily prepared by addition of a hydrogen-terminated polysiloxane to two molar equivalents of eugenol (4-allyl-2-methoxyphenol) in a reaction advantageously catalyzed by platinum or its compounds.
The allylphenols in the schematic formula above are also well known compounds, described along with methods for their preparation, by Tarbell, Chemical Reviews 27, 495ff (1940). In one embodiment, the allylphenol is eugenol, 4-allyl-2-methoxyphenol, since it is readily available as a synthetic or as a natural product and affo

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