Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-04-03
2004-04-27
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...
C524S166000, C524S268000, C525S474000
Reexamination Certificate
active
06727302
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to fire resistant polycarbonate compositions and more particularly transparent, fire resistant polycarbonate compositions.
Plastics are increasingly being used to replace metals in a wide variety of applications, from car exteriors to aircraft interiors. Flame retardant plastics have been especially useful, particularly in applications such as housings for electronic devices. The use of plastic instead of metal decreases weight, improves sound dampening and makes assembly of the device easier. Flame resistance has been predominantly provided by halogenated flame retardants, especially bromine- and chlorine-based flame retardants. However, plastics employing halogenated flame retardants may release toxic gas when heated to elevated temperatures. As a result, bromine- and chlorine-free fire resistant materials are in demand for a wide range of applications.
Transparent, fire resistant polycarbonate products are widely used in various applications such as household appliances, computers, electronic devices and glazing material for the building and construction industry. Acceptable flame resistance in combination with transparency in a polycarbonate composition is presently achieved using halogenated polycarbonate building blocks together with one or more sulphonate salt based fire retardants such as potassium diphenylsulfon-3-sulphonate (KSS) or potassium-perfluorobutane-sulphonate (Rimar salt). The combination of the halogenated building blocks and the sulphonate salt based fire retardants results in a synergistic effect. While these materials do not burn, they could release toxic gas when heated to elevated temperatures.
Polysiloxanes are known to impart fire resistance to many plastics, including polycarbonate materials. The resulting materials are not likely to release toxic gas when exposed to high temperatures. Unfortunately, the commonly known polysiloxanes cause haziness in polycarbonate materials thus diminishing the desired transparency.
Accordingly there remains a need in the art for transparent, fire resistant polycarbonate compositions which are essentially free of halogens.
BRIEF SUMMARY OF THE INVENTION
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a transparent, fire resistant polycarbonate composition comprising polycarbonate, poly(methylphenylsiloxane) and a salt based flame retardant, wherein the polycarbonate composition has a UL94 V0 rating for the fire resistance at thickness greater than or equal to about 1.6 millimeters.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
The transparent, fire resistant polycarbonate composition comprises polycarbonate, poly(methylphenylsiloxane) and a salt based flame retardant wherein the polycarbonate composition has a UL94 V0 rating for the fire resistance at thickness greater than or equal to about 1.6 millimeters.
Unexpectedly, poly(methylphenylsiloxane), unlike most polysiloxanes, does not affect the optical properties of polycarbonate compositions. Thus, when poly(methylphenylsiloxane) is used in a polycarbonate composition in combination with a salt based flame retardant, such as KSS or Rimar salt, the resulting transparent polycarbonate composition is fire resistant. Transparent is herein defined as having a percent transmission of about 85 and a haze value of about 5 when measured according to ASTM D1003, which is incorporated herein by reference, at a thickness of 3.2 mm. Preferably the transparent polycarbonate composition has a percent transmission of about 90 and a haze value of about 2.
Such transparent polycarbonate compositions can obtain UL94 V0 ratings at 1.6 mm thickness, something previously achievable only with a bromine or chlorine based fire retardant.
In an important feature of the present composition, the polycarbonate is essentially free of halogens. Essentially free of halogen is herein defined as amounts insufficient to produce toxic fumes when burned. In general, therefore, the polycarbonate will comprise less than about 1.0, preferably less than about 0.5, and most preferably less than about 0.2 percent by weight of a halogen. As used herein, the terms “polycarbonate” and “polycarbonate composition” includes compositions having structural units of the formula (I):
in which at least about 60 percent of the total number of R
1
groups are aromatic radicals and the balance thereof are aliphatic, alicyclic, or aromatic radicals. Preferably, R
1
is an aromatic radical and, more preferably, a radical of the formula (II):
wherein each of A
1
and A
2
is a monocyclic divalent aryl radical and Y
1
is a bridging radical having one or two atoms which separate A
1
from A
2
. In an exemplary embodiment, one atom separates A
1
from A
2
. Illustrative non-limiting examples of radicals of this type are —O—, —S—, —S(O)—, —S(O
2
)—, —C(O)—, methylene, cyclohexyl-methylene, 2-[2.2.1]-bicycloheptylidene, ethylidene, isopropylidene, neopentylidene, cyclohexylidene, cyclopentadecylidene, cyclododecylidene, and adamantylidene. The bridging radical Y
1
can be an unsaturated hydrocarbon group or a saturated hydrocarbon group such as methylene, cyclohexylidene or isopropylidene.
Polycarbonates may be prepared by reacting a dihydroxy compound 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. Useful polymerization methods include interfacial polymerization, melt polymerization, and redistribution. Dihydroxy compounds in which only one atom separates A
1
and A
2
are the most widely used. As used herein, the term “dihydroxy compound” includes, for example, bisphenol compounds having general formula (III) as follows:
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 (IV):
wherein R
c
and R
d
each independently represent a hydrogen atom or a monovalent linear or cyclic hydrocarbon group and R′ 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 (III) includes the following:
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-hydroxy-phenyl) 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. Branched polycarbonates are also useful, as well as blends of linear polycarbonate and a branched polycarbonate. The branched polycarbonates may be prepared by adding a branching agent during polymerization.
These branching agents are well known and may comprise polyfunctional organic compounds containing at least three functional groups which may be hydroxyl, carboxyl, carboxylic anhydride, and mixtures
Goossens Johannes M. D.
Hendrix Bart P. G.
Maas Christianus J. J.
van der Heijden Walter
Verhoogt Hendrik
General Electric Company
Oppedahl & Larson LLP
Szekely Peter
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