Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-12-27
2004-05-04
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...
Reexamination Certificate
active
06730720
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to methods of producing transparent, fire resistant polycarbonate compositions and more particularly transparent, fire resistant polycarbonate compositions comprising flame retardant salts.
Plastics, and in particular polycarbonates, are increasingly being used to replace metals in a wide variety of applications, from car exteriors to aircraft interiors. The use of polycarbonate instead of metal decreases weight, improves sound dampening, and makes assembly of the device easier. Unfortunately, polycarbonates are inherently flammable, and thus require the addition of flame retardants. A variety of different materials have been used, some of which are set forth in U.S. Pat. Nos. 3,971, 4,028,297, 4,110,299, 4,130,530, 4,303,575, 4,335,038, 4,552,911, 4,916,194, 5,218,027, and 5,508,323. The challenge is to identify economical, environmentally friendly flame retardant additives that provide the requisite flame resistance, but without compromising desirable polycarbonate properties such as strength and clarity.
Flame resistance in polycarbonate compositions may be achieved using a sulfonic acid salt such as potassium perfluorobutane sulfonate (also known as “Rimar salt”, or “KPFBS”) as disclosed, for example, in U.S. Pat. No. 3,775,367. While flame resistant, transparent polycarbonate compositions may be produced using KPFBS, optimum flame resistance is found for levels of salt that can result in haze, especially for thicker samples. The amount of flame retardant that can be added when an optically clear product is desired is thus limited. Addition of synergistic additives such as tetrabromobisphenol A to improve flame retardancy is not possible where “ECO-friendly” standard that prohibit the inclusion of bromine or chlorine are in place. Accordingly, there remains a need in the art for methods of producing polycarbonates that are not only highly flame resistant, but also transparent.
BRIEF SUMMARY OF THE INVENTION
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a method for reducing haze in fire resistant polycarbonate compositions, comprising
blending a flame retardant salt with a first polycarbonate to produce a concentrate; and,
blending the concentrate with a second polycarbonate to form a transparent, fire resistant polycarbonate composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has surprisingly been found that highly flame resistant and transparent polycarbonate compositions may be obtained by blending a flame retardant salt with a first polycarbonate to produce a concentrate, then blending the concentrate with a second polycarbonate to form a transparent, fire resistant polycarbonate composition. The concentrate is preferably a pelletized blend of KPFBS and polycarbonate. In another preferred embodiment, the first polycarbonate and the second polycarbonate are the same.
Not wishing to be bound by any theory, it is believed that the present method of using the flame retardant salt-polycarbonate concentrate aids in completely dissolving the salt into the final polycarbonate composition by giving the salt crystals an additional heat history. The additional heat history may allow for effectively solubilizing greater amounts of salt into the matrix. The present method allows for the use of higher levels of flame retardant salt, thereby providing robust flame performance while at the same time maintaining polymer transparency.
Non-limiting examples of suitable sulfonic acid salts are perfluoroalkane sulfonate alkali metal, C
1
-C
6
alkylammonium, or ammonium salts. Such salts are described in the above-mentioned U.S. Pat. No. 3,775,367, and include, for example, salts such as sodium, potassium, or tetraethyl ammonium perfluoromethylbutane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoromethane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoroethane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoropropane sulphonate; sodium, potassium, or tetraethyl ammonium perfluorohexane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoroheptane sulphonate; sodium, potassium, or tetraethyl ammonium perfluoroctanesulphonate; sodium, potassium, or tetraethyl ammonium perfluorobutane sulfonate; and sodium, potassium, or tetraethyl ammonium diphenylsulfon-3-sulphonate; and mixtures comprising at least one of the foregoing salts. Potassium perfluorobutane sulfonate (KPFBS) and potassium diphenylsulfon-3-sulphonate (KSS) are particularly preferred.
The salt, and KPFBS in particular, is present in the final composition in quantities effective to achieve a flame resistance rating of UL94-V0 at 3.2 millimeters. Generally, effective amounts of flame retardant salt present in the final composition is about 0.01 to about 1.0, preferably about 0.05 to about 0.20, and most preferably about 0.06 to about 0.12, and even more preferably 0.08-0.10% by weight based upon the total weight of the resin in the final composition. To achieve these final concentrations, it is convenient to produce a concentrate wherein the amount of flame retardant salt in the concentrate is about 0.1 to about 5.0, preferably about 0.5 to about 2.0, and most preferably about 0.8 to about 1.2% by weight of the total amount of the concentrate.
The polycarbonate component may be made by interfacial processes or by catalytic transesterification, may be either branched or linear in structure, and may include functional substituents. 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 organic radicals and the balance thereof are aliphatic, alicyclic, or aromatic radicals. Preferably, R
1
is an aromatic organic radical and, more preferably, a radical of the formula (II):
—A
1
—Y
1
—A
2
— (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 a hydrocarbon group or a saturated hydrocarbon group such as methylene, cyclohexylidene or isopropylidene.
Polycarbonates can be produced by the interfacial reaction of dihydroxy compounds in which only one or two atoms separate A
1
and A
2
. 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 Re 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;
2,2-bis(4-hydroxy-phenyl) propane;
1,1-bis(4-hydroxyphen
Gohr Eric Thomas
Goossens Johannes Martinus Dina
Rosenquist Niles Richard
Singh Rajendra Kashinath
Stoddard Gregory James
General Electric Company
Szekely Peter
LandOfFree
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