Note: Descriptions are shown in the official language in which they were submitted.
MULTIELECTROLYTE SHEAR TREATMENT OF CARBON FIBERS
FIELD OF THE INVENTION
This invention relates to a process for
electrolytically treating the surface of carbon
fibers to improve mechanical properties,
particularly when the fibers are combined with a
resin matrix to form a composite. The invention
further relates to the improved carbon fibers per se
and to composites comprising the improved fibers in
a bis-maleimide matrix resin.
BACKGROUND OF THE INVENTION
Electrolytic treatments of carbon fibers to
improve adhesion between the fibers and a matrix
resin when forming composite materials are known.
Strength properties and their permanence in
composite ~aterials, particularly in an adverse
environment, depend on the interfacial bonding of
the composite, that is on the strength of the
bonding between the carbon fiber and the resin
matrix, Thus the development of various processes
to increase interfacial bonding has been a prime
goal of composites research, as evidenced by the
prior art.
U,S. patent 3,671,411 to Ray et al.
discloses subjecting a carbon or graphite fiber to
an electrolytic reaction in an ag~leous electrolyte
whereby negative ions are attracted to the surface
of the fiber acting as anode, thereby modifying the
fiber surface. The patentees state that subsequent
bonding to plastics and resins is improved to such
an extent that the shear strengths are increased in
~.'
D-15422
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many cases to more than double the values obtained
wlthout this particular pretreatment with llttle or
no loss in tensile strength.
U.S. patent 4,401,533 to Saito et al.
discloses electrolytically surface treating carbon
fibers in an aqueous solution of a sulfuric acid
salt while passing 8 current through the fiber at a
specified range of current density, a specified
range for the product of current density, voltage,
and processing time, ~nd while continuously moving
the carbon fiber as an anode in the aqueous
electrolytic solution. The patentees state that
their method produces carbon fibers having good
adhesive properties to resins and high tensile
strength and heat-oxidation resistanoe.
U.S. patent 3,832,297 to Paul, Jr.
discloses an electrolytic process for surface
treating graphite fibers wherein the improvement
resides in using organic and inorganic ammonium
compounds dissolved in wster which compounds will
decompose substantially completely to gaseous
products on heating at temperatures below about
250C. Illustrative ammonium compounds are stated
to include ammonium hydroxide, ammonium carbonate,
ammonium bicarbonate, ammonium cPrbamate, ammonium
benzoate, ammonium dithionate, ammonium
hydrosulfide, ammonium sulfite, ammonium
thiosulfate, and ammonium tartrate.
No prior art known to the inventors
discloses an electrolytic ~reatment of carbon fibers
in a particular sequence of electrolytic baths. The
present invention employs sequential electrolytic
D-15422
- 3 -
treatments which provide carbon fibers useful in
making composites having excellent mechanical
properties, for example, edge delamination strength
(EDS). EDS is a measure of toughness in carbon
fiber composites which indicates the tendency of a
composite to crack around rivet holes, the test for
which is well known to the art.
a~T O~ D~r l~r!~
This invention provides a method of surface
treating carbon fibers to improve the mechanical
properties of composites comprising said fibers
reinforcing a bis-maleimide matrix resin, comprising
the steps of:
moving said fiber, as anode, through a
first aqueous electrolytic bath containing an
ionized acid, base, or neutral salt, followed by
moving said fiber, as anode, through a
second aqueous electrolytic bath containing an
ammonium salt, said bath having a pH of at least
about 8.
The term "carbon fiber" as used herein is
intended to be generic to both carbon and graphite
fibers and includes fibers prepared by heating
fibrous polymeric materials such as
polyacrylonitrile, polyvinyl alcohol, pitch, natural
and regenerated cellulose and the like to
carbonizing or graphitizing temperatures. Generally
the fibers, which are composed of individual
filaments too thin to have any practical mechanical
ruggedness, are conveniently treated in
multi-filament bundles well known in the art as
tows. Other physical arrangements of fibers such as
woven or non-woven mats are also possible.
D-15422
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The electrolytes which may be used in the
first aqueous electrolytic bath (herein also
referred to as "oxygen bath") include any
electrolyte which electrolytically generates oxygen
at the surface of the anode, i.e. the carbon fiber
being treated, whereby oxygen functionalities are
generated on the fiber surface. Preferred are
mineral acids and bases such as aqueous solutions of
phosphoric acid, nitric acid, sulfuric acid, and
alkali metal hydroxides including sodium and
potassium hydroxide, and the like. Also preferred
are neutral salts (i.e. which, when dissolved in
water, yield a pH between about 4 and about 8) such
as sodium sulfate, lithium sulfate, sodium
perchlorate, and sodium tetrafluorobornate. For
practical applications concentrations of electrolyte
generally in the range of 0.05 to 20 weight percent,
preferably in the range of 1 to 10 weight percent,
are preferred.
In the second electrolytic bath (herein
also referred to as an "ammonium bath") any ammonium
salt which dissolves in water to yield a pH of at
least about 8 may be employed. Preferred are
ammonium hydroxide and ammonium bicarbonate. The
ammonium compound is believed to improve composite
properties through modifying the carbon fiber
surface with -NH2 functionalities. The
concentration of ammonium salt can be any desired
concentration sufficient to impart -NH2
functionality to the carbon fiber surface such that
mechanical properties in the,composite are improved
as measured, for example, by edge delamination
D-15422
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strength. Generally such concentration will fall in
a range of about 0.02 Molar (M) to about 5M,
preferably about O.OSM to about 3M.
An auxiliary electrolyte such as any of the
neutral salts or alkali metal hydroxides noted as
suitable for use in the oxygen bath may be used to
increase conductivity in the ammonium bath.
Generally the concentration of such auxiliary
electrolytes will range between about O.OlM and
about 0.5M.
The voltage is not narrowly critical and
can be adjusted generally to give a current density
between about O.S and 5 milliamperes per square
centimeter (mA/cm2) of fiber surface area.
Generally, the voltages employed in each bath will
range between about 5 and 80 volts.
Bath temperatures are not narrowly cri~ical
and will generally be in the range of about 5~C to
50C, the prevailing ambient (room) temperature or
below being most preferably employed.
Voltage, current density, and residence
time can be advantageously manipulated to expose the
fiber to a total charge of from about 4 to 100
coulombs/gm, preferably about 7 to about 20
coulombs~gm. Using the general ranges of current
density and voltage noted above, residence times
between about 0.05 and about 1 minute are generally
sufficient to achieve exposure to a charge within
these ranges. Depending on practical bath lengths
through which the tows are fed, usually a length
between abou~ 1 and about 15,feet, line speeds of up
to about 4~ ft/min. are entirely feasible.
D-15422
- 6 ~ 9
The present invention provides increased
mechanical properties in thermosetting resin
composites beyond that which can be ascribed to
either of the baths alone or to their additive
contributions. This result is surprising since
electrolytically treating carbon fibers in the
reverse bath sequence to that stipulated in the
claims results in no improvement or, sometimes, even
less improvement than that which results from using
an oxygen bath alone.
Thermosetting bis-maleimide resins suitable
for use in this invention are widely known in the
art and, generally, are made by reacting a
N,N'-bis-maleimide with a reactive comonomer capable
of being copolymerized therewith. The general
formula for suitable bis-maleimides includes those
compounds of the formula
o o
h 11
/c \ /C\
y
~C \C/
b 11
O O
wherein
Y represen~s a divalent r~dical of at least
2 carbon atoms, preferably 2 to 6 carbon atoms,
containing a carbon-carbon double bond. Y may, for
example, be of the formula
H \ C / C 3\ / CH3 \ / H2C ~ /
Il 11 .~ Il I
H / \ CH / \ H/ \ H2C
D-15422
- 7 - ~3~.~5~
The preferred structure for Y is
H
H,,C~
Y may, for exsmple, be derived from ~cids or
anhydrides such as maleic, citraconic
tetrshydrQphthalic, and the like.
Z is ~ divalent r~dic~l which can be the
residuum of Q diamine containing ~t lesst 2 carbon
atoms and generally not more than ~bout 20 csrbon
atoms. "Reslduum", o~ course, refers to that
portion of a diamine excluslve of the two amino
groups. Z can, for exsmple~ be
alkylene of 2 to 20 carbons stoms;
cycloslkylene of 5 or 6 carbon atoms;
heterocyclic of 4 or 5 carbon ~toms and at
lesst one nitrogen, sulfur, or oxygen fltom in the
heterocyclic ring; or
~ t least two mono-or dicarbocyclic ~romatic
or cycloallcylene groups which ~re llnked to each
other by a direct carbon-to-carbon bond or through a
divalent linking group such as
O-- .
--S--
alkylene of 1 to 3 carbon stoms, or R group
of the formula
- P(O)R -
D-15422
- 8 - ~ 3 ~
Rl '
I
--I; -- , ' .
C--NH
in which Rl, which is alkyl of 1 to 5 carbon
atoms, need not be the same within those groups
containing more than one Rl.
Suitable N,N,'-bis-maleimides include
1,2-bismaleimido ethane,
1,6-bismaleimido hexane,
1,12-bismaleimido dodecane,
1,6-bismaleimido -(2,2,4-trimethyl) hexane,
1,3-bismaleimido benzene,
1,4-bismaleimido benzene,
4,4'-bismaleimido diphenyl methane,
2,4-bismaleimido toluene,
2,6-bismaleimido toluene,
3,3'-bismaleimido diphenyl sulfone,
4,4'-bismaleimido diphenyl sulfone,
4,4'-bismaleimido diphenyl ether,
4,4'-bismaleimido dicyclohe~yl methane,
4,4'-bismaleimido diphenyl cyclohexane,
4,4'-bismaleimido diphenyl sulfide,
N,N'-m-xylylene bismaleimide,
~,N'~p-xylylene bis~aleimide,
N,N'-m-phenylene bis-citraconimide,
N,N'-4,4'- diphenylene methane
bis-citraconimide,
D-15422
- 9 - 1 31~514
mixtures thereof, and the like. The above compounds
are disclosed, for example, in U.S. patents
4,211,861 to Stenzenberger and 4,351,932 to Street
et al. Other N,N'-~ismaleimides and their
preparation are disclosed in U.S. patents 3,562,223,
3,627,780 and 3,839,358, and 4,269,966.
Also suitable for use herein are ether
bis-maleimides having the formula
co R2 R6 R4
\co ~ ~ 17 ~ 5 ~ \ /
wherein R2, R3, R4 and R5 are independently
hydrogen, lower alkyl having 1 to 6 carbon atoms,
lower alkoxy having 1 to 6 carbon atoms, chlorine or
bromine; R6 and R7 are independently hydrogen,
methyl, ethyl, trifluoromethyl, or trichloromethyl;
and D is an ethylenically unsaturated divalent group
containing 2 to 24 carbon atoms. Particularly
preferred is the following ether bis-maleimide
,, o
C \ CH
\ C ~ C~3 ~ \ c /
.. ..
o o '~
D-15422
1314~4
- 10 -
which c~n be made by reactlng 2,2-bis
[4-(4-sminophenoxy)phenyl~ propane with malelc
anhydride ln acetone. These ether bls-maleimides,
lncluding the pre~erred compound, ~nd their
prepsration sre disclosed in U.S. patent 4,460,783
to Nlshikawa et 81.
Preferred bis-malelmides include
(a) 4,4'-bismaleimido diphenyl methane,
(b) 1,6-bismaleimldo-(2,2,4-trimethyl)hexsne,
(c~ eutectic mixtures of (8) and (b) with
2,4-bism~leimido toulene.
Any of the bis-maleimldes disclosed in
commonly ~ssigned copending cpplic~tion Serlal No.
564,400 filed December 22, 1983, now U.S. Patent No.
4,691,025, which corresponds to Canadian Patent No.
1,236,466, may also be used in this invention.
The liquid coreactants sultable for use in
this invention for reacting with bis-maleimides to
make bis-maleimide resins include 0,0,-
diallybisphenol A which has the structure
H2C=CH-CH2 CH2-CH=CH2
HO~ C~ ~H
D-15422
~ r ~ ~
N-vinyl-2-pyrrolidinone, ethylene glycol
dimethacrylate, diethylene glycol dimethacrylate,
trimethylolpropane triacrylate, trimethylolpropane
trimethacrylate, pentaerythritol tetraacrylate,
pentaerythritol tetramethacrylate, triallyl
isocyanurate, diallyl phthalate, triallyl
trimellitate, divinyl benzene, dicylcopentadienyl
dienyl acrylate, dicyclopentadienyl oxyethyl
acrylate, vinyl cyclohexene monoepoxide,
1,4-butanediol divinyl ether,
1,4-dihydroxy-2-butene, styrene, alpha methyl
styrene, chlorostyrene, p-phenyl styrene, t-~utyl
styrene, phenyl vinyl ether, unsaturated polyesters,
vinyl ester resins, and the like.
Preferred liguid coreactants include
0,0'-diallylbisphenol A, N-vinyl-2-pyrrolidone,
triallyl isocyanurate, divinyl benzene, and ethyl~ne
glyco} dimethacrylate.
Other liguid coreactants include epoxy
resins containing one or more epoxy groups having
the following formula:
/o\
The epoxy groups can be terminal epoxy groups or
internal epoxy groups. The epoxides are of two
general types: polyglycidyl compounds or products
derived f rom epoxidation of dienes or polyenes.
Polyglycidyl compounds conta~n a plurality of
1,2-epoxide groups derived from the reaction of a
D-15422
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131~
polyfunctional active hydrogen containing compound
with an excess of an epihalohydrin under basic
conditions. When the active hydrogen compound is a
polyhydric alcohol or phenol, the resulting epoxide
resin contains glycidyl ether groups. A preferred
group of polyglycidyl compounds are made via
condensation reactions with
2,2-bis(4-hydroxyphenyl)propane, also known as
bisphenol A, and have structures such as I:
~2C \ f ~ 2 ~ C ~ ~ - ~ C~2
l - C~
~ 3
. CH3 ~
where n has a value from about O ~o about 15. These
epoxides are bisphenol-A epoxy resins. They are
available commercially under the trade names such as
"Epon 82~," "Epon 1001", and ''Epon 1009" fro*m Shell
Chemical Co., and as "DER 331", and "DER 334" from
Dow Chemical Co. The most preferred bisphenol A
epoxy resins have an "n" value between O and 10,
Polyepoxides which are polyglycidyl ethers
of 4,4'-dihydroxydiphenyl me~hane,
4,4'-dihydroxydiphenyl sulfone, 4,4'-biphenol,
* Trademark
D-15422
- 13 - 1~1451~
4,4`-dihydroxydiphenyl sulfide, phenolphthalein,
resorcinol, 4,2'-biphenol, or tris(4-hydroxyphenyl)
methane and the like, are useful in this invention.
In addi~i~n, EPON 1031 (~ tetia~lycidyl derivative
of 1,1,2,2-tetrakis(hydroxyphenyl)ethane from Shell
Chemical Company), and Apogen 101, (a methylolated
bisphenol A resin from Schaefer Chemical Co.) may
also be used~ Halogenated polyglycidyl compounds
such as D.E.R. 542*(a brominated bisphenol A epoxy
resin from Dow Chemical Company) are also useful.
other suitable epoxy resins include polyepoxides
prepared from polyols such as pentaerythritol,
glycerol, butanediol or trimethylolpropane and an
epihalohydrin.
Polyglycidyl derivatives of
phenol-formaldehyde novolaks such as II where n = .
0.1 to 8 and cresol-formaldehyde novolaks such as
III where n - 0.1 to 3 are also usable.
R8~ à ~ 8
II R8- H
III R~ CH3
;
The former are commercially available as D.E.N 431,
D.E.N. 438, and D.E.N. 485 from Dow Chemical
Company. The la~ter are avai~able as, for example,
ECN 1235, ECN 1273, and ECN 1299 (obtained from
* Trademark
D-15422
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131~
Ciba-Geigy Corporation, Ardsley, NY). Other
epoxidized novolaks such as SU-8 ~obtained from
Celanese Polymer Specialties Company, Louisville,
KY) are also suitable.
Other polyfunctional active hydrogen
compounds besides phenols and alcohols may be used
to prepare the polyglycidyl adducts useful as
reactive comonomers in this invention. They include
amines, aminoalcohols and polycarboxylic acids.
Adducts derived from amines include
N,N-diglycidyl aniline, N,N-diglycidyl toluidine,
N,N,N',N'-tetraglycidylxylylene diamine, (i.e., IV)
N,N,N',N'-tetraglycidyl-bis (methylamino)
cyclohexane (i.e. V) , N,N,N',N'-tetraglycidyl-
4,4'-diaminodiphenyl methane, (i.e. YI)
N,N,N',N'-tetraglycidyl-3,3'-diaminodiphenyl
sulfone, and N,N'-dimethyl-N,N'-diglycidyl-
4,4'-diaminodiphenyl methane. Commercially
available resins of this type include Glyamine 13S*
and Glyamine 125 (obtained from F.I,C. Corporation,
San ~rancisco, CA,), Araldite MY-720 (obtained from
Ciba Geigy Corporation~ and PGA-X and PGA-C
(obtained from The Sherwin-Williams Co., Chicago,
Illinois).
* ~rademark
D-15422 ::
-- 15
~'C H2 C~l--CH2
O
C~z
~ ~CH--c~2
C}~2 t'~
C~ f H2
IV
O
~ ~2 ~ H;~
C~2--~
C~2 ~ 2
~\ C~2 C~--~2
C1~2--N~
CH--e~ 2
V
C~ H2
2' c)~-cH2 / Z
\~CH2--~ ~cNz-cN~N2 '
~JI
D-15422
-- 16 - 13~4~14
Suitable polyglycidyl adducts derived from
amino alcohols include O,N,N-triglycidyl-4-amino-
phenol, available as Araldite 0500 or Araldite 0510
(obtained from Ciba Geigy Corporation) and O,N,N-
triglycidyl-3-aminophenol (available as Glyamine 115
from F.I.C. Corporation),
Also suitable for use as reactive
comonomers are the glycidyl esters of carboxylic
acids. Such glycidyl esters include, for example,
diglycidyl phthalate, diglycidyl terephthalate,
diglycidyl isophthalate, and diglycidyl adipate,
There may also be used polyepoxides such as
triglycidyl cyanurates and isocyanurates,
N,N-diglycidyl oxamides, N,N'-diglycidyl derivatives
of hydantoins such as "XB 2793" ~obtained from Ciba
Geigy Corporation), diglycidyl esters of
cycloaliphatic dicarboxylic acids, and polyglycidyl
thioethers of polythiols.
Other reactive epoxy-containing materials
are copolymers of acrylic acid esters of glycidol
such as glycidyl acrylate and glycidyl methacrylate
with one or more copolymerizable vinyl compounds.
Examples of such copolymers are 1:1 styrene-glycidyl
methacrylate, 1:1 methyl methacrylate-glycidyl
acrylate and 62.5:24:13.5 methyl methacrylate~ethyl
acrylate:glycidyl methacrylate.
Silicone resins containing epoxy
functionality, e.g., 2,4,6,8,10-pentakis
[3-(2,3-epoxypropoxy)propyl]-2,4,6,3,10-pentamethyl-
cyclopentasiloxane and the diglycidyl ether of
1,3-bis-(3-hydro~ypropyl)tetramethyldisiloxane) are
also usable.
* Trademark
D-15422
17 - ~ 31~51~
The second group of epoxy resins i~
prepared by epoxidation of dienes or polyenes.
Resins of this type include bis(2,3
epoxycyclopentyl) ether, VII,
~0~ ~0~
VII VIII
reaction products of VII with ethylene glycol which
are described in U.S, Patent 3,398,102,
5(6)-qlycidyl-2-(1,2-epoxyethyl)bicyclo[2.2.1]
heptane, VIII, and dicyclopentadiene diepoxide.
Commercial examples of these epoxides incl*ude
vinylcyclohexene dioxide, e.g., "ERL-4206" (obtained
from Union Carbide Corp.), 3,4-epoxycyclohexylmethyl
3,4-epoxycyclohexane carboxylate, e.g., "ERL-4221"
(obtained from Union Carbide Corp.), 3,4-epoxy-6-
methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexane
carboxylate, e.~., "ERL-4201'i (obtained from Union
Carbide Corp.), bis(3,4-epoxy-6-methylcyclo-
hexylmethyl) adipate, e.g., "ERL-4289" (obtained
from Union Carbide Corp.), dipentene dioxide, e.g.,
"ERL-4~69'~ (obtained from Union Carbide Corp.)
2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclo-
hexanemetadioxane, e.g., "ERL-42~4" (obtained from
Union Carbide Corp.) and epoxidized poly-butadiene,
e.q., "Oxiron 2001" (obtained from FMC Corp.)
D-15422
* Trademark
1 4 5 1 ~1
Other suitable reactive cycloaliphatic
epoxides include those described in U.S. Patents
2,750,395; 2,~90,194; and 3,318,822 and the
following:
~~
~B
O ~c O ~
C - - O--~
O ~ ` .
Other suitable epoxides include:
~ ~ ,.
g;~)D ~)n
where n is 1 to 4, m is (5-n), and R9 is H,
halogen or Cl to C4 alkyl.
The preferred epoxy resins are
bis(2,3-epoxycyclopentyl)ether,
N,N,N',N'-tetraglycidyl xylylenediamine,
N,N,N',N'-tetraglycidyl methylene dianiline,
O,N,N-triqlycidyl-4-aminophe~ol, and .-
O,N,N-triglycidyl-3-aminophenol.
D-15422
19- ~3~
If epoxy resins are used, it may be
desireable to add an aromatic diamine to the
formulation. The diamine should have a low level of
reactivity with the epoxy resin and the
bis-maleimide at room temperature. Suitable
polyamine hardeners for use in epoxy resin systems
include 4,4'-diaminodiphenyl sulfone,
3,3'-diaminodiphenyl sulfone,
3,4'-diaminobenzophenone, m-phenylene diamine,
4,4'-methylene dianiline, diethylene triamine, and
the like. A stoichimetry of 0.3 to 2.0, preferably
O.5 to 1.5 equivalents of -NH per equivalent of
1,2-epoxide group can be used.
The epoxy resin system may additionally
contain an accelerator to increase the rate of cure
of the epo~y plus amine reation. Accelerators which
may be used herein include Lewis acid; amine
complexes such as BF3.monoethylamine,
BF3.piperdine, BF3.2-methylimidazole; amines,
such as imidazole and its derivatives such as
4-ethyl-2-methylimidazole, l-methylimidazole,
2-methylimidazole; N,N-dimethylbenzylamine; acid
salts of tertiary amines, such as the p-toluene
sulfonic acid:imidazole complex, salts of trifluoro
me~hane sulfonic acid, such as FC-520 ~obtained from
3M Company), organophosphonium halides and
dicyandiamide. If used, the accelerator may be from
1 to 6 percent by weight of the epoxy component.
The thermosetting resins may also contain
compounds with one or more cyanate ester groups.
By cyanate ester is meant a compound having
at least one cyanate group in its molecule. The
cyanate ester is represented by the formula
D-15422
~ 20 ~
Rl_(O_c~N)g i
wherein R10 is a residue derived from an aromatic
hydrocarbon selected from the group consis~ing of
benzene, biphenyl and naphthalene, or a residue
derived from a compound in which at least tow
benzene rings are bonded to each other by a bridging
member selected from the group consisting of
--C--
R12
wherein Rll and R12 are the same or different
and each represents a hydrogen atom or an alkyl
group containing 1 to 4 carbon atoms,
-O- -CH OCH -, -S-, -C-, -O-C-O-.
Il 11
O O
O O
-S-, -S-, -O-P-O and -O-P-O-;
Il 11 ~I 11
O O O O
said aromatic residue R10 may be optionally
substituted by a substituent selected from the group
consisting of alkyl groups containing 1 to 4 carbon
atoms, alkoxy groups containing 1 to 4 carbon atoms,
chlorine and bromine; ~ is an~integer of 1 to 5, and
the cyanate group is always directly bonded to the
aromatic nucleus.
D-15422
~ 3 ~
- 21 -
Examples of the cyanate ester include
cyanatobenzene, dicyanatobenzene;
1,3,5-tricyanatobenzene;
1,3-, 1,4-, 1,6-, 1,8-, 2,6- or
2,7-dicyanatonaphthalene;
1,3,6-tricyanatonaphthalene;
4,4'-dicyanatobiphenyl; bis(4-cyanatophenyl)methane;
2,2-bis(4-cyanatophenyl)propane;
2,2-bis~3,5-dichloro-4-cyanatophenyl)propane;
2,2-bis(3,5-diblomo-4-dicyanatophenyl)propanei
bis(4-cyanatophenyl)ether;
bis(4-cyanatophenyl)thioether;
bis(4-cyanatophenyl)sulfone;
bis(4-cyanatophenyl)phosphite;
bis(4-cyanatophenyl)phosphate;
bis(3-chloro-4-cyanatophenyl)methane; cyanated
novolak derived from novolak cyanated disphenol type
polycarbonate oligomer derived from bisphenol type
polycarbonate oligomer and mixtures thereof.
Mixtures of bis-maleimides, epoxy resin
systems, and compounds with one or more cyanate
ester groups may be employed in this invention.
Preferred mixtures are (i) bis-maleimide resin/epoxy
resin system mixtures (ii) epoxy resins/cyanate
ester compounds, and (iii) bis-maleimide
resins/cyanate ester compounds.
The composites of this invention may
optionally contain a small amount of a thermoplastic
polymer. These materials have beneficial effects on
the viscosity and film strength characteristics of
the bismaleimide/reactive comonomer mixture.
D 15422
- 22 - ~~4
The thermoplastic polymers used in this
invention include polyarylethers of formula IX which
are described in U.S. Patents 4,108,837 and
4,175,175,
~O R~ Rl~
IX
wherein R13 is a residuum of a dihydric phenol
such as bisphenol A, hydroquinone, resorcinol,
~,4-bi~henol, 4,4'-dihydroxydiphenyl sulfone,
4,4'-dihydroxy-3,3' 5,5'-tetramethyldiphenyl
sulfide, 4,4'-dihydroxy-3',3',5,5'-
tetramethyldiphenyl sulfone and the like.. R14 is
a residuum of a benzenoid compound susceptible to
nucleophilic aroma~ic substitution reactions such as
4,4'-dichlorodiphenyl sulfone,
4,4'-difluorobenzophenone, and the like. The
average value of n is from about 8 to about 120.
Other suitable polyarylethers are described
in U.S. Patent 3,332,2D9.
Also suitable are polyhydroxyethers of the
formula:
(O - RlS - CH2 CH CH2
OH
where R15 is a cycloaliphatic or aromatic divalent
hydrocarbon radical and the average value of n is
between about 8 and about 300; and polycarbonates
such as those based on bisphenol A, tetramethyl
bisphenol A, 4,4'-dihydroxydipher.yl sulfone,
4,4'-dihydroxy-3,3',5,5'tetramethyl- diphenyl
sulfone, hydroquinone, resorCinol,
4,4'-dihydroxy-3,3',5,5'-tetramethyl diphenyl
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sulfide, 4,~'biphenol, 4,4'-dihydroxydiphenyl
sulfide, phenolphthalein, 2,2,4,4-tetramethyl-1,3-
cyclobutane diol, and the like. Other suitable
thermoplastics include poly (~-caprolactone);
polybutadiene; polybutadiene/acrylonitrile
copolymers, including those optionally containing
amine, carboxyl, hydroxy, or -SH groups; polyesters,
such as poly(butylene terephthalate); poly(ethylene
terephthalate); polyetherimides such as the Ultem
resins (obtained from ~he General Electric Company);
acrylonitrile/ butadiene~styrene copolymers,
polyamides such as nylon 6, nylon 6,6, nylon 6,12,
and Trogamid T (obtained from Dynamit Nobel
Corporation); poly(amide imides) such as Torlon
poly(amide imide) (obtained from Amoco Chemical
Corporation, Napierville, IL); polyolefins,
polyethylene oxide; poly(butyl methacrylate);
impact-modified polystyrene; sulfonated
polyethylene; polyarylates such as those derived
from bisphenol A and isophthalic and terephthalic
acid; poly(2,6- dimethyl phenylene oxide); polyvinyl
chloride and its copolymers; polyacetals;
polyphenylene sulfide and the like.
Poly(vinyl acetate) and copolymers of vinyl
acetate with other vinyl and acrylic monomers can
also be used. Thermoplastics such as low profile
additives, for example, LP-40A, may also be used.
The bismaleimide thermosetting resin
composition should contain between about l and about
99 weight percent, preferably 20-98 percent of
bismaleimide; l to about 60 weight percent,
preferably 3 to 40 percent of the liquid coreactant
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or mixture of coreactants comprising molecules with
one or more amino, epoxy, or cyanate groups and the
like, as described above; 1 to about 40 percent,
preferably 2 to 30 percent Gf other additives such
as thermoplastic polymers.
The amount of carbon fiber in the composite
is between about 10 and about 90 percent by weight,
preferably between about 20 and about 85 percent by
weight.
Additional components in the composition
can include initators for vinyl polymerization such
as di-t-butyl peroxide, dicumyl peroxide, l,l-bis
t-butyl peroxy cyclohexane, azo bis isobutyronitrile
and the like. The initiator comprises from 0 to 3
percent by weight of the total composition.
Inhibitors for vinyl polymerizations can
also be used. They include, hydroquinone, t-butyl
hydroquinone, bentoquinone, f-methoxyphenol, and
4-nitro-m-cresol. Inhibitors are present in amounts
of from 0 to 2 percent by weight of the total
composition.
By reacting a suitable reactive comonomer
with any one or a mixture of ~he above-described
bis-maleimides a prepregable matrix resin can be
obtained and combined with carbon fibers surface
treated according to the invention to make a
preimpregnated reinforcement.
Preimpregnated reinforcement can be
prepared by several techniques known in the art,
such as wet winding or hot melt. In one method of
making impregnated tow or undirectional tape, the
fiber is passed into a bath of the resin mixture. A
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non-reactive, volatile solvent such as methyl ethyl
keto~e may be optionally included in the resin bath
to reduce viscosity. After impregnation, the
reinforcement is passed through a die to xemove
excess resin, sandwiched between plies of release
paper, passed through a set of heated rollers,
cooled, and taken up on a spool. It can be used
within a few days or may be stored for months at 0F.
Composites may be prepared by curing
preimpregnated reinforcement using heat and,
optionally, pressure. Vacuum bag/autoclave cures
work well with these compositions. Laminates may
also be prepared via wet layup followed by
compression molding, resin transfer molding, or by
resin injection, as described in European Patent
Application 0019149 published November 26, 1980.
Typical cure temperatures are 100F to soOF,
preferably 1&0F to 450F.
The composites of this invention may be
used as aircraft parts such as wing skins,
wing-to-body fairings, floor panels, flaps, radomes;
as automotive parts such as driveshafts, bumpers,
and springs; and as pressure vessels, tanks and
pipes. They are also suitable for protective armor
on military vehicles and sporting goods applications
such as golf shafts, tennis rackets, and fishing
rods.
In addition to structural fibers, the
composition may also contain particulate fillers
such as talc, mica, calcium carbonate, aluminum
trihydrate, glass microballoo,ns, phenolic
thermospheres, and carbon black. Up to half of the
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weight structural fiber in the composition may be
repl~ced by filler. Thixotroplc ~gents such as
fumed silica may also be used.
ExamPle 1
Unsized and unshear treated carbon fiber
samples commercially ~vailable in tows having about
1200~ fibers/tow from Union Csrbide Corporstion
under the trsde desi~nstion T-300 were
electrolytically treated in a nitric acid bath
(conc. 0.5M) and/or an ammonium hydroxide bath
(conc. 2.65M) except for control fiber which was not
treated in a bath. The degree of shear treatment
was evaluated by ESCA of the unsized fiber and by
composite EDS testing using ~ bis-maleimide matrix
resin consisting of a mixture of 54 parts by weight
of methylene dianiline bismalelmide and 46 parts by
weight of 0,0-disllylbisphenol A. The polarity in
each bath was the same. The composites were made by
laying up ten plies of prepreg msde by a hot melt
process. The ~our centermost plies contained T-300
carbon ~iber having R fiber area weight of about 145
gm/m2. The other six outer plies (three on each
side of the four center plies) were made with T-40
carbon fiber ~available from Union Carbide
Corporation ) having 8 fiber area weight of about
136 gm/m2. All composites were sutoclave cured
and the resln WQS bled to give a nominal cured
composite fiber volume loading of 60%.
The ESCA and EDS results are given in Table
I, along with the line speeds snd bath current
va~ues. ln the column designated "Electroylte", a
"+" indicates two separate baths.
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Tabl e I
T-300 12k Shear Treatment
Tre~tment Level Line Speed Current ESCA EDS (ksi )
~lectrolyt~(coul./g~ (ft~minl L~e~ O N As Made Dr~'
None ~ --- 4.2 2.321.5 18.7
HN03 9.8 5 0.210.9 1.940.1 33.3
NH40H16.4 2 0.36.8 3.840.1 38.6
HN03 4.9 10 0.28.2 1.8
+ NH40H8 . 2 4 0 . 3 7 . 2 4 . 6 44 . 4 42 .1
HN03 9.8 S û.212.0 1.0
~ NH40H16.4 2 0.37.8 7.647.7 40.0
# Indicated the polarity of the electrodes in the bath.
~2 Dried overnight at 180~F.
_ _ _
Those skilled in the art will readily
appreciate that many modifications are possible in
the above exemplary em~odiments without materially
departing from the novel teachings and advantages of
this invention.
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