Note: Descriptions are shown in the official language in which they were submitted.
l.Z~5390
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SYNERGISTIC EFFECT OF M~TAL FLAKE AND METAL OR METAL
COATED FIBER ON EMI SHIELDING EFFECTIVENESS OF
_
THERMOPLASmICS
.
1. Field of the Invention
The present invention is concerned with thermo
plastic compositions having high electromagnetic/radio
frequency interference (EMI/~FI) shielding effective-
ness as a result of the incorporation therein of asynergistic combination of conductive me~al filler~.O
More specifically, thermoplastic polymers having high
EMI/RFI shielding effectiveness may be prepared by
incorporating therein a synergis~ic combination o
10 metal flake and metal or metal coated .iber.
Electronic equipment, particularly sensitive
electronic equipment such as computers, business
machines, communications equipment a.nd the like are
all susceptible to malfunction as a result of EMI/RFI.
Furthermore, in addition to being sensitive to foreign
EMI/RFI, many of these electronic devices generate
EMI/RFI. During the early years of the electronic
age, EMI/RFI shielding of electronic equipment was
accomplished by conductive metallic housings.
How~ver, with the boom in the use of non-conductive
plastic materials in the electronic industry, particu-
: larly as sturdy, lightweight housings, EMI/RFI has
: . become a great problem~ .
Much research has.been undertaken to provide
: 25 .plastic housings ha~ing EMI/RFI shielding effective-
nes~. Until recently, EMI/~FI shielding effectiveness
in plastics was accomplished by conductive coatlngs,
metallization, and plating of mold~d plastic parts.
These methods, while effective, are ccstly and labor
intensive in that they require substantial am~unts of
material and involve secondar~ operations in preparing
the final product.
~, *
r` 1 : -
~2~5390
- 2 - 8CV-4015
Recently, attempts have been made to prepare
conductive plastics by incorporating in engineering
thermoplastics certain conductive fillers.
Specifically, these fillers include conductive
powders, flakes and fibers. Generallyr approximately
25 - 40% by wt. conductive powder, 36 - 49% by wt.
conductive 1ake or 25 - 30% by wt. (in extruded
parts, 3 - 6% in injection molded parts) c~nductive
fiber must be incorporated into plastic materials in
order to obtain EMI/RFI shielding. (Materials
Engineering, March, 1982, P. 37 - 43; Modern Plastics
International, September,-1982, P. 46 - 49).
.
More recently, attempts have been made to find
synexgistic combinations O r conductive fillers so as
to provide eYtrudable and moldable (e.g. by injection
molding, blow-molding, RIM, transfer moldinq and the
like) compounds having consistent shielding at lower
loadings which maintain properties in the finished
part and are economical to make. Such combinations
have included mixtures of flaXe and powder and
mixtures of metallized glass fiber and carbon fibers.
Canadian Patent Application, Ser-al Number
412,186, filed Septémber ~4, l9B2~ discloses the use of
aluminum flake and/or carbon fiber or a combination of
either of them with carbon black powder.
SU~RY
It has now been found that improved EMI/RFI
shielding effectiveness can be obtained in thermo-
plastic polymer compositions by incorporating therein
the synergistic combination of metal flake and metal
or metal coated fibers. Further, it has bee~ found
that the improved EMI/RFI shielding effectiveness may
be enhanced even more by the use of said synergistic
combination of mietal flake and metal or metal coated
iber in polymer blends. The compositions of this
. ., . ~
: ~
.~
` ~L2~539~
~ 3 ~ 8CV-4015
invention m~y be directly injection molded or extruded
and molded and still retain high E~iI/RFI shielding
effectiveness.
Specifically, the present invention concerns
thermoplastic compositions having high E~lI/RFI shield-
ing effectiveness comprising (a) one or more thermo-
plastic polymers; (b) from zbout 25 to about 50% by
wt., preferably from about 25 to about 40% ~y wt.,
based on the total composition, of metal flake and (c)
from about 2 to about 12% by wt., preferably from
about 4 to about 8~ by wt., based on the total compo-
sition, of metal or metal coated fibers ~herein the
weight ratio of metal flake to metal or metal coated
fiber is from about 4:1 to about 14:1, prefera~ly from
about 6:1 to about 10:1.
Preferred thermoplastic pol~mers`for which the
invention is applicable include polyesters, polycar~
bonates, copolyestercarbonates, poiyamides, polyary-
lene ether sulfones or ketones, polyamide imides,
polyetherimides, polyphenylene ethers, polystyrenes,
acrylonitrile butadiene styrene copolymers or blends
thereof. These thermoplastic polymers may further
comprise one or more addition polymers andlor one or
more rubber or rubher modified thermoplastic resins.
Suitable metal flakes may be prepared from
aluminum, copper, silver or nickel or alloys thereof.
~letal fibers may be selected from the group consisting
of silver, copper, nickel, aluminum or stainless
steel. The metal coated fibers comprise a base fiber
of glass, graphite and the like upon which a metal
coat of nickel, silver, copper or aluminum is applied.
The compositions may further comprise up to about
25~ of glass fibers for reinforcement and/or effective
amounts of flame retardants.
The novel compositions of the present invention
can be molded, foamed or extruded into vaxious
structures or articles, especially electronic
~ . . . .
. ~ .
lZ~539~;)
~ 4 ~ 8CV-4015
equipment components and housings, requiring EMI
shielding and such structures or articles are included
within the scope of this invention.
DESCRIPTION OF THE PREFERRED EMBOI)IMENTS
.
The present invention provides for thermoplastic
compositions comprising a thermoplastic polymer or
polymer blend and a synergistic combination of
conductive metal flake and conductive metal or metal
coated fibers to provide hish EMI/RFI shielding
effectiveness. In order to realize said synergism, it
is necessary to employ from about 25 to about 50%,
- preferably from about 25 to about 40%, by wt., basèd
on the total composition, of metal flake in
combination with from about 2 to about 12%, preferably
from about 4 to about 8%, by wt., based on the total
composition of metal or metal coated fiber.
Furthermore, the weight ratio of flake to fiber should
be from about 4:1 to 14:1, preferably from about 6:1
to about 10:1, to obtain the most cost ef~ective
materials.
Metal flalses suitable for use in the compositions
of the present invention include those prepared from
the following metals or alloys thereof: silver,
aluminum, nickel, copper and the like. Generally,
said flakes have a thickness of less than about 0.005"
and surface dimension of less than about 0.10'l each.
Preferred flakes which have been found to be highly
effective have an approY~imate size of 0.001" x 0.040"
x 0.060".
Additionally, the metal flakes may be treated
with suitable coupling agents such as, for example,
silane or titanate coupling agents, to improve
processability and/or promote compatibility or bonding
of the metal flakes to the thermoplastic resin.
Suitable metal flakes are a~ailable from a number of
sources including Transmet Corp. of Columbus~ Ohio and
Atlantic Powered Metals, Inc. of New York, New York.
~,`
:'
. ~.
~Z~539(3
- 5 - 8CV-4015
Metal and metal coated fibers useful in the
present composition are more varied and widely avail-
able. Generally, the metal fibers may be made of
aluminu~, copper, silver, nickel, stainless steel and
the like, and alloys thereof. Similarly, the metal
coated fibers are generally of a graphite or glass
core with a coating of silver, nickel, aluminum or
copper and the like and alloys thereof. Sources of
these fibers include Transmet Corp. of Columbus, Ohio;
M.B. Associates of San Ramon, Calif.; Bekaert Steel
~ire Corp. of Pittsburgh, Penn.; Brunswick Technetics
of Deland, Fla; American Cyanamide of Wayne, N.Y.;
Nichimen America Inc of N.Y., ~I.Y.; and Lundy
Electronics of Pompano Beach, Fla., among others.
Suitable fihers may be of essentially any length
an~ diameter which is practical from both a composi-
tion an~ processing standpoint, as known in the art.
For example, aluminum fibers measuring 6 mm in length
by 90 ~icrons diameter are useful and practical,
whereas stainless steel fibers of similar dimensions
may be impractical and cause unnecessary wear on
processing equipment: instead stainless steel fibers
of 3 mm length by 4 microns diameter may be more
suitable. Generally,`all suitable fibers will have a
length of about 14 mm or less, preferably about 7 mm
or less and a diameter of 0.2 mm or less, preferably
of 0.1 mm or less. Once again, the actual dimensions
of the fibers used depends in part on the composition
or the fibers and their availability.
Additionallyl the fibers used in the present
invention may be coated with any suitable sizing or
coupling agents so as to improve processability as
well as bonding and/or compatibility of the fibers and
the thermoplastic material. Preferred coupling agents
include those derived from silanes and titanates.
It is also possible, in accordance with the
present invention, to use more than one type o~ metal
~ ~ . . . .
~Z~5390
- 6 - 8~V-4015
flake and/or fiber in the compositions of ~he present
invention.
The aforementioned synergis~ic combination of
conductive metal flake and metal or metal coated fiber
S have improved EMI/RFI shielding over those employing
only one conductive filler or a combination of conduc-
tive fillers, as shown in the prior art, at the same
level of incorporation. Thus the compositions pre-
pared therefrom have reduced cost and better physical
properties since less filler is added. Furthermore,
these compositions avoid the problems associated with
coatings, metallization and the lik;e with respect to
being less labor intensive and time consuming to make
the final product, more economical and devoid of the
physical problems associated therewith including
separation of the metal layer or coat from the plastic
part.
The synergistic conductive filler combination is
useful in most any thermoplastic polymer or polymer
blend. Suitable prefe~red thermoplastic polymers
include polyesters, polycarbonates, copolyestercarb-
onates, polyamides, pol~arylene ether sulfones or
ketonesl polyphenylene ethers, polyamide imides,
polyetherimides, polystyrenes, acrylonitrile ~utadiene
styrene copolymers or blends thereof. Further, it has
been found that EMI/RFI shielding effectiveness of
blends incorporating therein the synergistic
conduc,ive filler combination often have even greater
enhancement of EMI/RFI shielding than the single
thermoplastic polymer alone.
(a) POLYESTERS
Suitable polyesters for the present invention are
derived from one or more aliphatic and/or cycloaliph
atic ~lycols and one or more aromatic dicarboxylic
acids. The glycol may be selected from the group con-
sisting essentially of ethylene ~lycol; 2 methyl-1,3
propanediol 1,4-butanediol; 1,5-pentanediol;
,
.
/r - ~
~.,'2~S39(3
~ 7 ~ 8CV-4015
1,6-hexanediol and 1,4-cyclohexanedimethanol, and the
like. ~uitable dicarboxylic acids include
terephthalic acid, phthalic acid, ~sophthalic acid and
naphthalene ~,6-dicarboxylic acid. The polyesters of
the present invention may also contain minor amounts
of other units such as aliphatic dicarboxylic acids
and/or aliphatic polyols to form copolyesters.
Generally, the polyesters of the present inven-
tion may be represented by the ~ormula
Il
10 - O ,1 C--O--
- - R--OC ~
wherein R represents the divalent radical remaining
after remova1 of the hydroxy groups from the glycol.
Preferred polyesters include poly~ethylene tere-
phthalate), poly(butylene terephthala~e~ and blends
thereof.
The polyesters described herein are either com-
mercially available or can be produced by methods well
known in the art, such as those set forth in
United States PatentsNumbers 2,465,319; 3,047,539 -
and 2,910,466. - Further, the polyesters used
herein have an intrinsic viscosity of from about 0.4
to about 2.0 dl/g as measured in 60:40 phenol/tetra-
chloroethane mixture or a similar solvent at 30C.
(b ) POLYCARBONATES
~ny of the polycarbonates known in the art may be
used in accordance with the present invention. Espec-
ially preferred polycarbonates are the aromatic poly-
carbonates. ArGmatic polycarbonates useful herein are
homopolymers, copolymers and mixtures thereof, which
have an intrinsic viscosity o~ from about 0. to about
1.0 dl/g as measured in methylene chloxide at 25C.
Generally, the aromatic polycarbonates are
~; prepared by reacting a dihydric phenol with a carbon-
atc pre~ursor su~h as phosgene, a haloformate or a
, .
1;~45390
- 8 - 8CV-4015
carbonate ester. Typical of the dihydric phenols that
may be employed are 2,2-bis(4-hydroxyphenyl)propane;
bis(4-hydroxyphenyl)methane; 2,2-bis(4~hydroxy-
3-methylphenyl)propane; (3,3'-dichloro-4,4'-dihydroxy
diphenyl)methane and the li~e. The aromatic poly-
carbonates may be formed in accordance with the
methods set forth in United States Patent Numb,ers ,
2,999,835; 3,028,365; 2,999,844; 4,018,750 and
4,123,435, as well as other processes known to those
skilled in ~he art.
The polycarbonates so produced, are typified as,
possessing recur-ing structural units of the formuia
O
_~- A _ o - C - -~-n
wherein A is a divalent aromatic radical of the
dihydric phenol employed in the polymer producing
reaction and n is ~reater than one, preferably from
about 10 to about 400.
It is of course possible to employ two or more
dif~erent dihydric phenols or a dihydric phenol in
combination with a slycol, a hydroxy or acid termin- -
ated polyester, or a dibasic acid in the event a,
carbonate copolymer or copolyester carbonate rather
than a homopolymer polycarbonate is desired for use in
the practice of th~ invention. Thus, it should be
understood that the term "polycarbonate resin"
embraces within its scope carbonate co-polymers.
Suitable copolymers also include those poly-
carbonate copolymers which comp~ise units derived from
a first dihydric phenol which is a bis(hydroxyaryl)-
sulfone and a second dihydric phenol such as2,2-bis~4-hydroxyphenyl)propane as disclosed in U.S.
Patent numbe~c 3,737,409; and 2,999,846.
~5390
~ 9 - 8CV-4015
(c) POLYARYLE~E ~TE~ER SULF~ES OR KETONES
Polv(arylether) resin components suitable for use
herein are linear, thermoplastic polyarylene polyether
~olysulfones, wherein the arylene units are inter-
5 spersed with ether and sulfone linkages. These resinsmay be obtained by the reaction of an alkali metal
double salt of a dihydric phenol and a dihalobenzenoid
compound, either or both of which contain a sulfone or
~etone lin~age i.e., - SO2 - or -CO- between arylene
10 groupings, to provide sulfone or ketone units in the
polymer chain in addition to arylene units and ether
units. The polysulfone polymer has basic structurè
comprising recurring units of the formula:
-O-E-O-E'-
15 wherein E is the residuum of the dihydric phenol andE' is the residuum of the benzenoid compound having an
inert electron withdrawing group in at least one of
the positions ortho and para to the valence bonds;
both of said residua are valently bonded to the ether
20 oY.ygens through aromatic carbon atoms. Such polv~
sulfones are included within the class o~ polyarylene
polyether resin described in, for example, United -~-
States Patent Numbers 3,264,536 and 4,108,836.
The residuum of the dihydric phenol, E, is
derived from dinuclear phenols having the stnlcture:
(I)n (ll)m
OH-~- Ar - Rl - Ar-~-OH
wherein Ar is an aromatic group and preferably is a
phenylene group, A and Al may be the same or different
inert substituent groups, such a~ alkyl groups having
from 1 to 4 carbon atoms halogen atoms or alkoxy
radicals having from 1 to 4 carbon atoms, n and m are
integers having a value of 0 to 4, inclusive, and R
is representative of a bond between aromatic carbon
atoms as in dihydroxydiphenyl, or is a divalent
radical including, for example, CO, O, S, S-S, SO2 or
lZ45390
- 10 - ~CV-4015
a divalent or~anic hydrocarbon radicàl, such as
alkylene, alkylidene,cycloalkyene, cycloalkylidene or
the halogen, alkyl, or aryl or like substituted
alkylene, alkylidene, cycloalkylene an~
cycloalkylidene radicals.
The polyarylene ether sulfones or ketones have a
reduced viscosity of from about 0.4 to about 1.5 dl/g
as measured in an appropriate solvent at a~ appro-
priate temperature depending on the particular poly-
ether, such as in methylenechloride at 25C. Thepreferred polyarylene ether sulfones or ketones have
repeating units of the formula:
~'0 ~ SO2 ~
-+- O ~ C ~ and
lS ~ O
(d) POLYAMIDES
Polyamides suitable for the presen~ invention may
be obtained by polymerizing a monoaminomono-carboxylic
acid or a lactam thereof having at least 2 carbon
atoms between the amino and carboxylic acid group; or
by polymerizing substantially equimolar proportions of
. a diamine which contains at least 2 carbon atoms be-
tween *he amino groups and a dicarboxylic acid; or by
polymerizing a monoaminocarboxylic acid or a lactam
thereof as defined above together with substantially
equimolecular proportions of a diamine and a dicar~-
oxylic acid. The dicarboxylic acid may be used in the
form of a functional derivative thereof, far example
an ester.
, ,
, .
~S3~0
~ 8CV-4015
The term "substantially equimolecular" propor-
tions (of the diamine and of the dicarboxylic acid) is
used to cover both strict equimolecular proportions
and slight departures therefrom which are involve~ in
conventional techniques for stabilizing the viscosity
of the resultant polyamides.
Examples of the aforementioned monoaminomonocar-
boxylic acid~ or lactams thereof which are useful in
preparing the polyamides include those compounds
containing from 2 to 16 carbon atoms between the amino
and carboxylic acid groups, said carbon atoms forming
a ring with the -CO-NH- group in the case of a lactam.
As particular examples of aminocarboxylic acids and
lactams there may be mentioned ~-aminocaproic acid,
butyrolactam, pivalolactam, caprolactam, capryl-
lactam, enantholactam, undecanolactam, dodecanol~ctam
and 3- and 4- aminobenzoic acids.
Examples of diamines suitable for preparing the
polyamides include diamines of the general formula
2 ( 2)n 2
wherein n is an integer of from 2 to 16, such as
trimethylenediamine, tetramethylenediamine, penta
methylenediamine, octamethylenediamine and especially
hexamethylenediamine.
The dicarboxylic acids may be aromatic, for
example isophthalic and terephthalic acids. Preferred
dicarboxylic acids are of the formula
HOOC-Y-COOH
wherein Y represents a divalent aliphatic radical con
taining at least 2 carbon atoms, and examples of such
acids are sebacic acid, octadecanedoic acid, suberic
acid, glutaric acid, pimelic acid and adipic acid.
Preferred polyamides or nylons, as they are often
called, include nylon 6, 6/6, 11, 12, 6/3, 6/4 and
6/12. The number avera~e molecular weights of the
polyamides useful in the invention are generally a~ove
about 10,000.
~2~53~30
- 12 - 8CV-4015
(e) ~OLYAMIDE-I~5IDES
The polyamide-imide copolymers useful for the
present invention generally ha~re a crystalline struc-
ture and a melting point of over about 340C. They
5 are prepared by the reaction of dianhydrides with
- diamines containing preformed amide groups resulting
in an amide-imide structure as follows:
O O
\ ~ C C - NH N \ ~ N-
~ ~ ~C~ .
Other copolymers can be prepared by the reaction
of trimelletic anhydride acid chloride with aromatic
diamines. These copolymers can be prepared by ths
methods disclosed in Supplement Volume, Kirk - Othmer
Encyclopedia of Chemical Technology, pages 746 ~ 773
(1971).
~f) POLYPHENYLE~E ETHER
The polyphenylene ether resins useful for the
present invention comprise ho~opolymers and copolymers
of structural units of the formula:
1~~
Q " Q' n
wherein Q, Q', Q'' and Q' " are independently selected
from the group consisting of hyflrogen, hydrocarbon
radicals, halohydrocarbon radicals having at least 2
carbon atoms between the halogen atom and the phenyl
nucleus, hydrocaxbonoxy radicals and halohydrocar-
bonoxy radicals having at least 2 carbon atoms betweenthe halogen atom and phenyl nucleus, and Q', Q'' and
Q''' in addition may be halogen with the provi~o that
Q and Q' are both free of a tertiary carbon atom; and
lZ45390
- 13 - 8CV-4015
n represents the total number of monomer residues and
is an interger of at least 50.
The preferred polyphenylene ether resin is a
poly~2,6-dimethyl-1,4-phenylene)ether resin having an
intrinsic viscosity of from about 0.3 dlJg to about
0.60 dl/g in chloroform. The polyphenylene ether
resins useful herein are well known in the art and may
be prepared from a number of catalytic and non-cata
lytic processes from correspondiny phenols or reactive
derivates thereof. Examples of polyphenylene ethers
and methods for their production are disclosed in U.S.
Patent numbers 3,306,874; 3,306,875; 3,257,357 and
3,257,358.
(c? POLYETHERIMIDES
Polyetherimides useful for the present invention
may be prepared from the reaction between sub-
stantially equimolar amounts o' aromatic bis(ether
anhydride)s of the formula,
O - O
I O /\ ~ O-P~-O - ~ /O
ll ll
O O
and organic diamine of the formula,
I T
the reaction may take place in the prsence or absence
of a solvent and/or catalytic agent or compound, as
known in the art.
~s shown in formula I, R is a member selected
from the class consisting of (a) the following
divalent organic radicals:
'
--- lZ4S39~
-14 - 8CV-4015
CH3 Cl'13 3 CH3
c~3 c~3
CH ~ Br Br ~ CH3
and
3 Br Br 3
Br Br
C(CH3)
Br Br
and (b) divalent organic radicals of the general
formula
( )m ~
where X is a member selected from the class consisting
of divalent radicals of the formula
O O
CyR2~ C-, -S-, -O-, -C(CH )
o
and - S-, m is 0 or l, and y is a whole number from 1
to 5. R' as shown in formula II is a divalent organic
rad.ical selected from the class consisting of (a)
aromatic hydrocarbon radicals having from 6 - 20
carbon atoms and halogenated derivates thereof, ~b)
15 alkylene radicals, C(2 8) alkylene terminated
polvdiorganosiloxan~, cvcloalkylene radicals having
from 2 - 20 carbon atoms and (c) di~alent radicals
included by the formula,
'
~2453~0
- 15 - 8CV-4015
~ (Q)m ~
where Q is a member selected from the class consisting
~f
O O
~l , CXH2x- and -C(C~ )
and x is a whole number from 1 to 5 inclusive, and m
is as previously defined. These polyetherimides are
prepared by methods well known in the art such as
those described in, for example~ U.S. Patent numbers
3,917,643; 3,~52,242; 3,855,176; 3,~33,546; 3,875,116;
3,83~,097; 3,905,942 and 3,933,719.
-,,~; .
(h) ACR'LONITRILE BUTADIENE STYRENE COPOLYMERS
In general, ABS type polymers contain two or more
polymeric parts of different compositions which are
15 bonded chemically. The polymer is preferably prepared
by polymerizing a conjugated diene, such as butadiene
or a conjugated diene with a monomer copolymerizable
therewith, ~uch as styrene, to provide a polymeric
backbone. After formation of the backbone, at least
20 one grafting monomer, and preferably two, are pol~er-
ized in the presence of the prepolymerized backbone to
obtain the graft polymer. These resins are prepared
by methods well known in the art. -
The backbone polymer, as mentioned, is preferably
25 a conju~ated diene polymer such as polybutadiene,
-polyisoprene, or a copolymer, such as butadiene-
styrene, butadiene-acrylonitrile, ox the like.
~ he specific conjugated diene monomers normally
utilized in preparing the backbone of the graft
30 polymer are generically descrihed by the follo~ing
formula:
.
. .
'~.
~2~5~390
- 16 - 8CV-4015
X X ~;
\C=C--C=C~
X/ X
wherein X is selected from the group consisting of
hydrogen, alkyl groups containing from one to five
carbon atoms, chlorine or bromine. Examples of dienes
that may be used are butadiene, isoprene, 1,3-hepta-
diene, methyl-1,3-pentadiene, 2,3-dimethyl-1,3-buta-
diene, 2-ethyl-1,3-pentadiene; 1,3- and 2,4-hexa-
dienes, chloro and bromo substituted butadienes such
as dichlorobutadiene, bromobutadiene, dibromobuta-
diene, mi~tures thereof, and the like. A preferredconjugated diene~is butadiene.
One monomer or group of monomers that may be
polymerized in the presence of the prepolymerized
backbone are monovinylaromatic hydrocarbons. The
monovinylaromatic monomers utilized are generically
described by the following formula:
X X X
X~ I=C\
v,~, X X
., X
wherein .~ is as previously defined. Examples of the
monovinylaromatic compounds and alkyl-, cycloalkyl-,
aryl-, alkaryl-, aralkyl-, alkoxy-, aryloxy-, and
other substituted vinylaromatic compounds include
styrene, 3-methylstyrene; 3,5-diethylstyrene, 4-n-
propylstyrene, ~-methylstyrene, ~-methyl vinyltoluene,
~-chlorostyrene, ~-bromostyrene, dichlorostyrene,
dibromostyrene, tetera-chlorostyrene, mixtures
thereof, and the like. ~he preferred monovinylaro-
matic hydrocarbons used are styrene and/or
~-methylstyreneO
A second sroup of monomers that may be polymer-
iæed in the presence of the prepolymeri~ed backbone
;.
~2~S390
- 17 - 8CV-4015
are acrylic monomers such as acrylonitrile, substi-
tuted acrylonitrile and/or acrylic acid esters/ exem-
plified bv acrylonitrile, and alkyl acrylates such as
methyl methacrylate.
The acrylonitrile, substituted acrylonitrile, or
acrylic acid esters are described generically by the
following formula:
X\ X
, /C=C Y
X
wherein Y~ is as previously defined and Y is selected
from the group consisting of cyano and carbalkoxy
wherein the alkoxy group of the carbalkoxy contains
from one to about twelve carbon atoms. Examples of
such monomers include acrylonitrile, ethacrylonitrile,
methacrylonitrile, ~-chloroacrylonitrile, ~-chloro-
acrylonitrile, ~-bromoacrylonitrile, and ~-bromo-
acrylonitrile, methyl acrylate, methyl methacrylate,
ethyl acrvlate, butyl acrylate, propyl acrylate,
isopropyl acrylate, and mixtures thereof. The
preferred acrylic monomer is acrylonitrile and the
preferred acrylic acid esters are ethyl acrylate and
methyl methacrylate.
In the preparation of the graft polymer, the
conjugated diolefin polymer or copolymèr exempli~ied
by a 1,3-butadiene polymer or copolymer comprises
about 50% by weight of the total graft polymer compo-
sition. The monomers polymerized in the presence of
the backbone, exemplified by styrene and acrylo-
nitrile, comprise from about 40 to about 95~ by weight
of the total graft polym~er composition.
The second ~roup of grafting monomers, exempli-
fied by acrylonitrile, ethyl acrylate or methyl meth-
acrylate, of the graft polymer composition, preferably
comprise from about 10% to about 40~ by weight of the
total graft copolymer composition. The mono~inylaro-
matlc hydrocarbon exemplified by styrene comprise from
.
.
~53~
- 18 - 8CV-4015
about 30 ~o about 70% by ~eight of the total graft
polymer composition.
In preparing the polymer, it is normal to have a
certain percentage of the polymerizing monomers that
are grafted on the backhor.e co~bine with each other
and occur as free copolymer. If styrene is utilized
as one of the grafting monomers and acrylonitrile as
the second grafting monomer, a certain portion of the
composition will copolymerize as free styrene-acrylo-
nitrile copolymer. In the case where ~methylstyrene(or other monomer) is substituted ~or the styrene in
the composition used in preparing the graft polymer, a
certain percentage of the composition may be an
~-methylstyrene-acrylonitrile copolymer. Also, there
are occasions where a copol~ner, such as ~-methyl-
styrene-acrylonitrile, is added to the graft polymer
copolymer blend. When the graft as polymer-copolymer
blend is referred tc herein, it is meant optionally to
include at least one copolvmer blended with the graft
polymer composition and which may contain up to 90% of
free copolymer.
Optionally, the elastomeric backbone may be an
acrylate rubber, such as one based on n-butyl acryl-
ate, ethylacrylate, 2-ethylhexylacrylate, and the
li~ie. Additionally, minor amounts of a diene may be
copolymerized in the acrylate rubber backbone to yield
impro~ed grafting Wit]l the matrix polymer.
These resins are well known in the art and many
are commercially available.
It is also pos ible to use blends of the forego-
ing thermoplastic polymers in 'he present invention.
These blends often result in composition having en-
hanced ~MI/RFI shielding effectiveness as compared to
the single thermoplastic polymer. Exemplary of useful
blends are poly(ethylene terephthalate~/poly(1,4-
butylene terephthalate), polycarbonate/poly(ethylene
-- lZ~5390
- 19 - 8CV-4015
terephthalate) and polycarbonate/poly(~,4-butylene
terephthalate).
The ~MI/RFI shielding compositions of the present
invention may further comprise thermoplastic addition
polymers, rubbers or rubber modified resins.
Preferred addition polymers include those selected
from the group consisting of styrene resins, alkyl
acrylate resins, or combinations thereof. h~hen used
herein and in the appended claims, the terms "styrene
resins" and alkyl "acrylate resins" are meant to be
defined as set forth below.
Suitable styrene resins include homopolymers~
copolymers and graft copolymers thereof. Especially
preferred styrene resins include homopolymer poly-
styrene, ABS type graft copolymers, and core-shell
type graft copolymers as discIosed in U.S. Patent
numbers 4,180,494, 3,808,180; 4,096,20 ; 4,260,693,
4,034,013 and 4,292,233. Also preferred are rubber
modified poly~tyrene such as a butadiene rubber modi-
fied polystyrene also referred to as high l~act poly-
styrene or HIPS; styrene-butadiene-styrene block co-
~ ~ ~r ~
polymer such as the Kraton or Kraton-G polymers that
are described in U.S. Patent numbers 3,646,162 and
3,595,942; the modified alpha and para substituted
styrenes or any of the styrene resins disclosed
in United States Patent number 3,383,435.
.
Alkyl acrylate resins which may be used herein
include homopolymers and copolymers of alkyl acrylates
and alkyl methacrylates in which the alkyl group
contains from 1 to 8 carbon atoms, such as methyl
acrylate, ethyl acrylate, butyl acrylate, methyl
methacrylate, ethyl methacrylate and butyl methacryl-
ate. Suitable copolymers include the copolymers of the
foregoing ~lith vinyl or allyl monomers (e.g. acrylo-
nitrile, N-allymaleimide or N-vinyl maleimide~ or with
olefins (e.g. ethylene). Especially preferred alkyl
... . .
~'~45390
- 20 - 8CV-4015
acrylate resins are the homopolymers and copolymers of
methyl methacrylate ~e.g. polymethyl methacrylate)~
~ dditional acrylic resins useful in the present
invention include the core-shell type graft
S copolymers, wherein the alkyl acrylate resin, alone or
copolymerized wlth a vinvl monomer, may be gxafted
onto an elastomeric polyolefin backbone, such as
polybutadiene, polybutadiene-styrene, polyisoprene,
znd/or butadiene or isoprene copolymers or a rubbery
crosslinked acrylate or alkyl acrylate backbone such
as n-butylacrylate. These resins are well known in
the art (~I.S. 4~o3atol3; U.S. 4,096,202, U.S.
3,808,180, among others) and are commercially
available (for e~ample, Rohm & Haas Acryloid XM 653,
~l1 330 and K~ 611).
Also suitable for the present invention are
rubbers including ethylene-propylene-diene monomer
type rubbers and ethylene-propylene rubbers. Many of
these are described in IJ.S. Patent numbers 2,933,480;
3,000,866; 3,407,158; 3,093,621 and 3,379,701.
Especially preferred compositions incorporating
therein one or more of the aforementioned addition
polymers and the like include polycarbonate/ABS compo-
sitions, polyphenylene ether/high impact polystyrene
compositions, and poly(butylene terephthalate)/-
ethylene ethylacrylate~EEA)-acrylic core-shell gra~t
copolymers (Rohm & Haas KM-330).
Optionally, the compositions of this invention
may further contain one or more reinforcing agents.
Typical reinorcing agents useful for the invention
include but are not limited to, glass fiber, mica or
both. The filAmentous glass that may be used in the
embodiments of this invention is well known to those
skilled in the art and is widely available from a
number of manufacturers. The glass may be untreated
or, preferably, treated with suitable coupling agents,
especially preferred are the silane and titanate
,;
~245390
- 21 - 8CV-4015
coupling agents. The glass filaments are made by
standard processes, e.g., by steam or air blowing,
flame blo~ing and mechanical pulling.
The thermoplastic compositions of the present
invention may also be rendered flame retardant with an
effective amount of a conventional flame retardant
agent. As is well known, flame retardants can be
based on elementary red phosphorus, phosphorus com-
pounds, halogen and nitrogen compounds alone or pre-
ferably in further combination with synergists such asantimony compounds. Especially useful are polymeric
and oligomeric flame retardant agents comprising
tetrabromohisphenol-A carbonate units, e.g., U.S.
~atent number 3,833,685, alone or in combination with
an antimony compound.
The compositions of the present invention may be
prepared by known methods. For example, the ingre-
dients may be placed into an extrusion compounder with
the thermoplastic resin to produce molding pellets
wherein the additive ingredients are dispersed in a
matrix of the thermoplastic resin. Alternatively, the
ingredients may be mixed with a thermoplastic resin by
dry blending, then either fluxed on a mill and
comminuted, or eXtruded and chopped. Further, the
ingredients may also be mixed with powder or granuIar
thermoplastic resin and directly molded, e.g., by
injection or transferred molding techniques.
Finally, the conductive thermoplastic composi-
tions of the present invention may be prepared by
first forming a concentrate of any one or more con-
ductive fillers in the base thermoplastic resin or any
compatible thermoplastic resin (i.e. one which will
not cause delamination in the blended composition) and
thereafter incorporate the concentrate into the compo-
sition hy any of the foregoing methods or methodsknown in the art.
' '
,
5390
- 22 - 8CV-4015
The novel compositions or composites of the
present invention may be molded, ~oamed or e:struded
into various structures or articles, especially into
electronic equipment, components or housings, requir-
ing EMT/RF shielding, and such structures or articlesare included within the scope of the present inven-
tion. Examples include, but are not limited to~ panel
boards for printed circuits, radio and television
panels and housings, and housings for computers and
large calculators, audio and high fidelity equipment,
~ensitive test instruments and the like.
In order that those s~illed in the art may better
understand how to practice the present invention, the
followin~ e~amples are given by way of illustration
and not by way of limitation.
E~lI Shielding effectiveness data was determined
based on a coaxial transmission method developed by
Battelle Laboratorv of Columbus, Ohio. Shielding
effectiveness is a measure of the attenuation of
EMItRFI expressed in decibels wherein attenuation is a
functi~n of the electrical conductivity andjor
magnetic susceptability of the shield. ~he decibel
unit is a logarithmic measure of the degree of the
shielding. A 10 decibel reading indicates that q0% of
the EMI/RFI energy is effectively dissipated. Twenty
decibels means that 99g of the EMI/RFI is dissipated,
and so on. The shielding effectiveness is measured at
various radio frequencies (in MHz). In each o~ the
following examples, shielding effectiveness was
determined over a frequency range of 0.5MHz to
1000MHz, however, only the results for shielding
effectiveness at 0.5MHz and 1000MHz are shown.
Unless other~ise specified, all compositions were
prepared by extrusion compounding.
FXAMPLES El-E2, Comparative EXAMPLES CEl-CE3
Conductive glass filled and unfilled poly~l,4-
butylene terephthalate) compositions were prepared
' ~:
Z~5390
- 23 - 8CV-4015
incorporating therein conductive fillers of the prior
art as well as the synergistic combination of conduc-
tive fillers taught by the present inventio~ All
conductive fillers were incorporated by ~te~iknr
molding. The compositions and their shielding effec-
tiveness are shown in Table 1. The improved shielding
effectiveness of the present invention demonstrated by
eY.amples E1 + E2 clearly is shown over the prior art
formulation of comparative examples CE1 - CE3
(Table 1).
TABLE 1
CEl CE2 El E2 CE3
- Poly(1,4-butylene60 55 60 55 55
terephthalate)a
Glass Fiber - 10 5 - 5 5
Aluminum Flake - 40 36 ~6 36
Aluminum.Fiber 30 - -4 4-
Carbon Fiber - - - - 4
Shielding effec-13-20 25-23 45-31 51-4514-38
tiveness
(dB) @ 0.5-lOOOMHz
includes 0.2% by wt. stabilizer
F..XAMPLES E3-E6, Comparative EXA~IPLES CE3-CE4
A series of glass filied poly(l,4-butylene
: ~erephthalate) composition were prepared with various
metal and metal coated fiber in combination with the
aluminum flake. The specific compositions and their
.Shielding effectiveness are shown in Table 2.
.
24539~)
-- 24
8CV-401 5
~c ~;r
In
n Ln u~ ~ I I ~ I I
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er
,~ I
C
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- o
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,:
~LZ~53~0
- 25 - 8CV-4015
~ x2mples F,3 - ~6 demonstrate the usefulness of
various me.al and metal coated fibers for the present
invention. A comparison of CE2 and CE4 with E3
clearly demonstrates the enhancement in shielding
5 effectiveness by the use of the synergistic combin-
ation of conductive fillers.
EX~PLrS E7-E12, Comparative EXAMPLE CE5
Co~positions were prepared by extrusion compound-
ing o. all conductive fillers and then injection mold-
lO ing. Various levels of aluminum flake and nickel
coated carbon fiber were used demonstrating the need
for at least about 25~ aluminum flake. The formula-
tions and shielding effectiveness are shown in
Table 3.
\
.
`: :
'.
-- ~
~53~C~
- 26 - 8CV-4015
. . r~
r~
U~ ~ CO
r~
. .
o In ~ .
~D r) ~D
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l-) G U~
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,
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124S390
"
- 27 - 8CV-4015
Comparison of CE5 with EY.amples E7-E12 demon-
strate the need for at least about 25~ aluminum flake.
Shieldir.g effectiveness as a whole suffers somewhat
when all insredients are mixed by extrusion. This is
most likely due to breakage of fibers.
EXA~5PLES E13-E15
Polymer blends with poly(l,4-butylene terephthal~
ate) were prepared to demonstrate the present inven-
tions usefulness in such compositions. The formula-
tion and Shielding effectiveness are presented inTahle 4. A comparison of the resul's shows enhance-
ment of shielding effectiveness in the blend over the
strict poly(l,4-butylene terephthalate).
- TABLE 4
E13 E14 ~15
Poly(1,4-butylene terephthalate)a 61.3 46.3 46.3
Aluminum flake 31 31 31
Aluminum fiber 3.4 3.4 3.4
Glass fiber 4.3 4.3 4.3
Poly(ethylene terephthzlate) - 15
Polycarbonate - 15
Shielding effectiveness 40-29 44-30 48-34
(dB) @ 0.5-lOOOMHz
a includes 0.2% by wt. stabilizer
EXAMPLES E16 and E17
Flame retardant and impact modified poly(1,4-
butylene terephthalate) may also be rendered conduc-
tive by the present invention. The formulation znd
results zre shown in Table 5.
, ~
''-
~Z 4S390
- 2& - 8CV-4015
TABLE 5
, i
E16 E17
Poly(1,4-butylene terephthalate)a 46.3 46.3
5 Aluminum flake 31 31
Aluminum fiber 3.4 3.4
Glass fiber 4.3 4.3
Flame retardantb 15
Impact ~.odifierC - 15
Shielding effectiveness 35-29 30-~1
(dB) @ 0.5-lOOOMHz
a. includes 0.2% by wt. stabilizer
b. halogenated bisphenol based polycarbonate flame
retardant in combination with antimony oxide.
c. KM330 core-shell acrylic-styrenic impact modifier
(Rohm & Haas) and ethylene ethylacrylate blend.
EX~PLES E18-E22
A series of compositions comprising different
base polymers with the synergistic combination of
conductive fillers were prepared to demonstrate the
usefulness of the present teaching to other linear
thermoplastic polymers and blends thereof. The
specific formulations and results are presented in
Table 6.
S39~
29
8CV-4015
'`31 ~ ~r I I I I o
i'l ~r
~D ~r o I I ~
er o
~ i`
ol ~D ~ I I o
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a~ I O I I 'I
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-
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o
o
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EiEi R S ` s: ~ tn o
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Ei k ~ ~ o ~ .E~ ~ ~
r ~ I rl ~
~ ~ O O ~1 ~ O S -'
.
~ 5390
- 30 - 8CV-4015
Obviously, other modifications and variations of
the present invention are possible in light of the
above teachingsO For example, these compositions may
further comprise plasticizers, antioxidants, stabil-
izers, flow promoters, mold release agents, UV stabil-
izers, and the like, as necessary. It is therefore to
be understcod that changes may be made in the partic-
ular embodiments of the invention described which are
within the ~ull intended scope of the invention so`
defined by the appended claims.
