Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-09-21
2002-06-04
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S176000, C528S198000, C528S271000, C528S272000, C528S322000, C528S332000, C428S411100
Reexamination Certificate
active
06399737
ABSTRACT:
BACKGROUND OF INVENTION
Electronic devices require protection from electromagnetic interferences in order to function properly. As a result, these devices are often made of materials exhibiting a high electromagnetic/radio frequency interference (EMI/RFI) shielding effectiveness (SE). Introduction of conductive material to thermoplastic resins increases the electromagnetic shielding effectiveness of the resulting thermoplastic compositions. Unfortunately, obtaining a high level of shielding effectiveness is limited by the amount of conductive filler that can be added to the composition. Often, low loading of conductive fillers does not provide adequate shielding. Consequently, there is a need for thermoplastic compositions with low loadings of conductive fillers while at the same time providing good electromagnetic shielding properties.
SUMMARY OF INVENTION
The above-described and other drawbacks and disadvantages of the prior art are alleviated by a composition comprising a thermoplastic resin and about 1 to about 30 weight percent of an electromagnetic shielding agent, wherein the electromagnetic shielding agent comprises a metal-coated fiber and a metal fiber, and wherein the composition after molding has a shielding effectiveness of at least about 10 decibels measured according to ASTM D4935.
Other embodiments, including a method of preparing the compositions and articles comprising the compositions, are described below.
DETAILED DESCRIPTION
One embodiment is a composition comprising a thermoplastic resin and about 1 to about 30 weight percent of an electromagnetic shielding agent, wherein the electromagnetic shielding agent comprises a metal-coated fiber and a metal fiber, and wherein the composition after molding has a shielding effectiveness of at least about 10 decibels measured according to ASTM D4935.
Suitable thermoplastic resins include polycarbonates, polyesters, polyamides, polyetheresters, polyestercarbonates, poly(arylene ether)s, polyamideimides, polyetherimides, polystyrenes, acrylonitrile-butadiene-styrene copolymers, blends comprising at least one of the foregoing resins, and the like.
Suitable polycarbonates include compositions having structural units of the formula (I):
wherein R
1
is selected from the group consisting of C
1
-C
12
aliphatic radicals, C
5
-C
7
alicyclic radicals, C
6
-C
20
aromatic radicals, and C
6
-C
20
aromatic organic radicals having the structural formula (II):
—A
1
—Y
1
—A
2
— (II)
wherein A
1
and A
2
are each independently a monocyclic divalent C
6
-C
20
aryl radical and Y
1
is a bridging radical having one or two atoms that separate A
1
from A
2
. In a preferred embodiment, one atom separates A
1
from A
2
. Illustrative non-limiting examples of Y
1
bridging 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.
Polycarbonates may be produced by the interfacial reaction of dihydroxy compounds in which only one atom separates A
1
and A
2
. As used herein, the term “dihydroxy compound” includes, for example, bisphenol compounds having the formula (III):
wherein R
a
and R
b
each independently represent a halogen atom or a C
1
-C
6
monovalent hydrocarbon group; 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 C—C monovalent linear or cyclic hydrocarbon group, and R
e
is a C—C 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. 4,217,438, which is incorporated herein by reference. Specific bisphenol compounds that may be represented by formula (III) include 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-3-bromophenyl)propane; 1,1-bis(4-hydroxyphenyl)cyclopentane; and 1,1-bis(4-hydroxyphenyl)cyclohexane; and the like.
It is also possible to employ two or more different dihydric phenols or a copolymer of a dihydric phenol 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. Polyestercarbonate resins may 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, haloformyl and mixtures thereof. Specific examples include trimellitic acid, trimellitic anhydride, trimellitic trichloride, tris-p-hydroxy phenyl ethane, isatin-bis-phenol, tris-phenol TC (1,3,5-tris((p-hydroxyphenyl)isopropyl)benzene), tris-phenol PA (4(4(1,1-bis(p-hydroxyphenyl)-ethyl) alpha,alpha-dimethyl benzyl)phenol), 4-chloroformyl phthalic anhydride, trimesic acid and benzophenone tetracarboxylic acid. The branching agents may be added at a level of about 0.05 to about 2 weight percent. Branching agents and procedures for making branched polycarbonates are described in U.S. Pat. Nos. 3,635,895 and 4,001,184, which are incorporated by reference. All types of polycarbonate end groups are contemplated as being within the scope of the polycarbonate compositions.
Preferred polycarbonates are based on bisphenol A, in which each of A
1
and A
2
is p-phenylene and Y
1
is isopropylidene. Preferably, the weight average molecular weight of the polycarbonate is about 5,000 to about 100,000 AMU. Within this range, the polycarbonate molecular weight is preferably at least about 10,000 AMU, more preferably at least about 35,000 AMU. Also within this range, the polycarbonate molecular weight is preferably up to about 65,000 AMU, more preferably up to about 35,000 AMU.
Suitable thermoplastic resins also include polyestercarbonates, which contain, in addition to recurring polycarbonate chain units of the formula (V):
wherein D is a C
6
-C
20
divalent aromatic radical of the dihydroxy compound employed in the polymerization reaction, recurring carboxylate units, for example of the formula (VI):
wherein D is a defined above and T is a C
6
-C
20
divalent aromatic radical such as phenylene, naphthylene, biphenylene, substituted phenylene and the like; a C
6
-C
20
divalent aliphatic-aromatic hydrocarbon radical such as an alkaryl or alkaryl radical; or two or more aromatic groups connected through such aromatic linkages.
The polyestercarbonate resins may be prepared by interfacial polymerization techniques as described in, for example, U.S. Pat. Nos. 3,169,121 and 4,487,896.
In general, any dicarboxylic acid conventionally used in the preparation of linear polyesters may be utilized in the preparation of the polyestercarbonate resins described herein. Generally, suitable dicarboxylic acids include C
2
-C
20
aliphatic dicarboxylic acids, C
6
-C
20
aromatic dicarboxylic acids, and C
6
-C
30
aliphaticaromatic dicarboxylic acids. These acids are well known and are disclosed, for example, in U.S. Pat. No. 3,169,121. Mixtures of dicarboxylic acids may be employed. Most preferred as aromatic dicarboxylic acids are isophthalic acid, terephthalic acid, and mixtures thereof.
Rather than utilizing the dicarboxylic acid per se, it is possible, and sometimes even preferred, to employ the reactive derivatives of said acid. Illustrative of these rea
Boykin Terressa M.
General Electric Company
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