Note: Descriptions are shown in the official language in which they were submitted.
i~26~7~
This invention relates to damage tolerant structural
-~ composites comprising high strength filaments in à cross-
linked epoxy resin matrix. This invention, more particu-
larly, relates to improvements in the crosslinked epoxy resin
matrix (and methods of achieving such improvements) which
provide the structural composites with high post impact
. ~
compressive strength while maintaining such other desirable
- attributes of epoxy composites as good high temperature
performance and processing characteristics.
Composites comprising high strength filaments in a resin
~- matrix are well known materials; they are being proposed for
` use in more and more weight sensitive applications such as
aircraft structural components. Recently, there has been keen
interest in increasing the "damage tolerance" of these compos-
ites. A criteria used for quantifying the "damage tolerance"
is the measured compressive strength exhibited by the compos-
ite, layed-up in certain fashion, after it has received an
impact typically in the range of 1,500 inch - pounds per inch
- thickness of the composite, such criteria referred to herein
as post impact compression or post impact compressive strength
~both abbreviated as PIC) or residual compressive strength
after impact (abbreviated as CAI).
Thermoplastics have been proposed as matrix materials to
increase damage tolerance of composites. Thermoplastics are
extremely tough materials when they are free of fiber or other
solid additives, i.e. as neat resins. Thermoplastics, how-
ever, require high processing temperatures in providing pre-
pregs (comprised fi'laments and the resin) and forming the
`~ prepregs into composites.
1~26.17~
-- 2 --
Epoxy resins, on the other hand, are thermosetting
resins and may be processed into prepregs at low temperatures.
In addition, composites made using epoxy resins traditionally
have exhibited good high temperature properties. However, the
damage tolerance oE composites having a crosslinked epoxy
resin matrix has been generally much less than that of the
b~tter thermoplastic materials.
One approach proposed for increasing the damage tolerance
of composites made ~rom epoxy resins has focused on increasing
the toughness of the cured epoxy resin used as the matrix
material in the composites. Inclusion of polysulfones to
lower cross-link density have been suggested ~or this purpose.
(See, for example, EPO 0130270, Union Carbide EPO 0761576,
Sumitomo Chemical Company: and US 4,656,207 and US 4,656,208,
both in the names of Chu, Jabloner and Swetlin.l Another
recent effort along these lines is illustrated by the Diamant
and Moultan paper antitled "Development of ResinS For Damage
Tolerant Composites - A Systematic Approach", Pages 422-436,
29th National Sampe Symposium, April i-5, 1984. Certain
rubber polymers are shown in this paper to enhance toughness
of cured epoxy resins. The rubber polymee in the cured epoxy
resins discussed by Diamant and Mou`ltan is said to be
dispersed in particles 0.5-1 microns in size, independent of
the molecular weight oE the polymer. Included among the
rubber polymers examined by Diamant and Moultan for use in
epoxy composites are butadiene acrylonitrile rubbers ~aving
carboxy functionality, e.g. Hycar 1472.
Use of rubber polymers in epoxy resin composites is also
shown in the following Vnited States Patents: 3,837,904,
3,926,903 and 3,926,904. The use of polysulfone resins in
combination with rubber polymers has been disclosed in the
following United States Patents: 4,187,347: 4,195,113;
4,220,686: 4,222,918 and 4,264,655.
Still anothee approach in making damage tolerant
3S composites is described in United States Patent 4,539,253.
* Denotes Trade Mark
, ' ~' ' : .
, ' . ,- , ',
' ~
-- 3
1326~76
The approach in this patent is to make a "discrete, integral resin
interleaf layer" of an epoxy resin comprising a "rubbery vinyl
addition polymer." The interleaf layer is supported by a fibrous
mat or carrier and is introduced between layers (plies) of high
strength filament that comprise a different epoxy resin.
Although progress has been achieved in increasing the
`- damage tolerance of epoxy resin composites made using conventional
processing temperatures and techniques, damage tolerant composites
with good high temperature performance damage and processing
characteristics have not been heretofore available.
It is an object of this invention to provide improvementq
in the damage tolerance of composites comprising high strength
filaments in a crosslinked epoxy resin matrix, such composites
also having a good high temperature performance and processing
characteristics.
s It is an object of this invention to provide a prepreg
comprising high strength filaments and a crosslinkable epoxy resin
composition wherein the prepreg cures into a damage tolerant
composite.
It is an object of this invention to provide an epoxy
resin composltion which may be used in making damage tolerant
composites.
It is an object of this invention to provide a method of
manufacturing epoxy resin compositions which may be used in making
damage tolerant composites.
-
These and other objects have been accomplished in
practice of this invention which is described in the following
1326~76
- 3A -
disclosure.
In one broad aspect, the present invention relates to a
prepreg useful in making damage tolerant structural
composites, said prepreg comprising one or more high strength
filament tows or bundles that is impregnated with a
thermosettable epoxy resin composition that phase separates
into crosslinked glassy phases upon cure, the improvement
wherein said impreqnation provides a portion of said epoxy
resin composition contained within said tows or bundles and a
portion of said epoxy resin composition atop a surface of said
tows or bundles as a resin surface of said prepreg, said
thermosettable epoxy resin comprising infusible glass, rubber
or ceramic particles having a median size between 10 microns
and 75 microns, and a lower modulus than the epoxy resin
composition, said infusible particles distributed in said
thermosettable resin such that the number of said particles
having a dimension greater than 10 microns is greater than
that part of said resin composition closer to said surface
than contained within said tows or bundles.
In another broad aspect, the present invention relates to
a method of making a prepreg suitable for making damage
tolerant composites, said method comprising: forming an epoxy
resin composition compri~ing infusible particles (a)
respectively comprising an amount of a rubber polymer and (b)
having a median size between about 10 and 75 microns and a
lower modulus than said epoxy resin composition, said resin
composition curing into a crosslinked epoxy thermoset that is
- 3B - 132~ 7 6
phase separated and has a KiC above about 1 MPa~; combining
together said epoxy resin composition and high strength
filaments in the form of one or more filament bundles such
that at least 50% of said particles having a dimension greater
~` than 10 microns are dispersed in that part of said prepreg
which is closer to a resin surface thereof than contained
within said bundles.
This invention relates to the discovery that
composites compr~sing high strength filaments and a tough,
phase separated, crosslinked epoxy resin matrix are made
exceptionally damage tolerant when infusible particles having
a median particle size in excess of ten microns are
incorporated as part of the epoxy resin composition used in
forming the composite. The composition of the infusible
particles
- ~ - 132617~
pre~erably comprises a rubber polymer but other mateeials
such as glass and ceramic are also use~ul as the infusible
particles above or together with other such particulate.
The epoxy resin compositions used in making the damage
tolerant composites comprise a polyepoxide component, a
reactive aromatic oligomer component, a curing agent and a
component that either becomes incorporated in the infusible
particles (preferably during manufacture o~ the resin) or
otherwise constitutes the predominant material o~ infusible
particles. The epoxy resin composition may be in the form o~
a film for impregnating bands of high strength filaments, a
mass of material that can be rendered molten by heat and
spread on bands of high strength filaments or a dissolution
product that can impregnate high strength filaments in dipping
operations. The epoxy resin compositions, when cured in neat
form, have a KIC (critical stress intensity factor) greater
than 1 MPa~,
The polyepoxide component comprises an epoxide compound
having a glass transition temperature preferably between -100
and 20C and can assist in providing tack to the prepregs
made with the resin composition. The polyepoxide component
contains on average more than one epoxide group per molecule
and preferably at least 2 epoxide groups per molecule. The
term epoxide group as used herein refers to the simplest
epoxide group which is the three-membered ring, C ~ CH2.
The terms of ~-epoxy (or epoxide), 1,2-epoxy (or epoxide),
vicinal epoxy (or epoxide) and oxirane group are also art
recognized terms for this epoxide group.
Polyepoxide compounds having between 2 and about 4
epoxide groups per molecule and a glass transition
temperature below 5C are particularly pre~erred. Suitable
aromatic polyepoxide compounds are resorcinol diglycidyl
ether (or 1,3-bis-(2,3- epoxypropoxy)benzene) marketed, for
example, by Wilmington Chemical as HELOXYR 69: diglycidyl
ether of bisphenol A (or 2,2-bis[p-(2,3-epoxypropoxy)phenyl]-
-
"' ;. ' '' ' . ' : .
1326176
,
propane) triglycidyl p-aminophenol (or 4-(2,3-epoxypropox~)
-N,N-bis(2,3-epoxypropyl)aniline): diglycidyl ether o~
bromobisphenol A (or 2,2-bis[4-(2,3-epoxypropoxy)3-bromo-
phenyl]propane; diglycidylether o~ bisphenol F (or
2,2-bis[p-(2,3-epoxypropoxy)phenyl]methane) triglycidyl
ether of meta-aminophenol (or 3-(2,3-epoxypropoxy)
N,N-bis(2,3-epoxypropyl)aniline) tetraglycidyl methylene
dianiline (or N,N,N',N'-tetra(2,3-epoxypropyl) 4,4~diamino-
diphenyl methane), polyglycidyl ethers of phenol-formaldehyde
novalcs (e.g~ DEN 431,438 of Dow Chemical Company); and poly-
glycidyl ether of orthocresol-novalac (available from Ciba
Geigy or, for example, ECN 1235 or 1273). Combinations of
two or more polyepoxide compounds can be used as the poly-
epoxide component. Preferred combinations include mixtures
of diepoxides comprising diglycidyl ether of bisphenol F,
resorcinol diglycidyl ether and the triglycidylaminophenols
or tetraglycidyl methylene dianiline, and mix`tures of the
triglycidylaminophenols and the diglycidyl ether of butanediol
- (or 1,4-bis~2,3-epoxypropoxy]-butane) or the diglycidyl ethers
- 20 of polypropylene glycol, particularly tri- or tetra-(~-propy-
lene glycol) di-(2,3-epoxypropyl) ether. Particularly pre-
ferred are polyepoxide components which comprise aromatic
polyepoxide compounds and up to about 50% of one or more
aromatic or aliphatic diepoxide compounds, and which have
glass transition temperatures between about -100C and about
20-C.
The reactive aromatic oligomer contains functional
groups which are reactive with the polyepoxide component
and/or the amine hardener of the composition. In one pre-
ferred embodiment the oligomer is epoxy-reactive (i.e. reacts
with epoxide groups) and has at least 1.4 epoxy-reactive
groups per molecule. In another embodiment the oligomer is
epoxy-functional, i.e. it contains epoxide groups. The reac-
tive aromatic oligomer preferably contains divalent aromatic
groups such as phenylene, diphenylene or naphthalene groups
linked by the same or different divalent non-aromatic linking
- 6 - ~3261 7 6
groups. Exemplarl linking ~3rou?s ~re ~x~ ) sllltolyl-
(-SO2-) divalent sulfur (-S-), oxyalKylene or oxyal~ylene-
oxy(-OR- or -ORO- ~herein ~ is lower alkyLene pre~era~ly ~it
1-3 carbon atoms); lower alkylene or alkylidene (-R- or
-R(Rl)y -~herein R ~n~ Rl are independently lower
alkylene and y is 1 or 2); ester groups suci- as -(R
XCOO(R2)y- wherein Rl and ~2 a~e independently lowe~
alkylene prefer~bly with 1 to 3 carbons and x and y are
independently 7ero or 1: and
oxaalkylene, i.e.
RlC R2 where Rl and R2 are inde-
pendently lower alkylene or a valence bond. The aromatic
units can ~e substituted with non-in~erfering substituents
such as chlo~ine, lower alkyl, phenyl etc. Generally, at
least twenty-five percent of the total number of carbon atoms
in the reactive aromatic oligomer will be in aromatic struc-
tures, and preferably at least about 50% of the total carbon
ato~s are in aromatic structures.
The preferred reactive aromatic oligomers are preferably
polyethers, polysulfones, polyethersulfones, polyethersulfone-
polythioethersulfones and more preferably contain sulfone
bridged diphenylene units or ketone bridged diphenylene units.
Other types of units which can be present in these preferred
oligomers are aromatic or cycloaliphatic units that are not
bridged (e.g., naphthalene) or are bridged by groups which
are essentially nonpolar, examples of which are alkylidene
such as isopropylidene bridges. Particularly preferred
reactive oligomers contain sulfone bridge diphenylene units
and bisphenol units, a portion of the latter units optionally
being replaced by divalent sulfur (-S-) to provide a reactive
oligomer of the formula:
NH2R -O-~R-R )m-(R-S)n-R-O-R'~NH2
wherein R~ is 3,4-phenylene or 4,4'phenylene; R is the
residuum of a dihalodiphenylsulfone such as 4,4'dichloro-
diphenylsulfone or a dihalogendiphenyl ketone, R' is theresiduum of a dihydroxy or dithiol aromatic compound such as
" .
~ '
`,
`` ~:
::
-- 7 --
~ 32~17~
bisphenol A, dihydroxy benzene biphenol and quinoline, ~ is
divalent oxygen, S is divalent sulfur and m plus n averages
between 8 and 25 and m is preferably at least 2.
The reactive aromatic oligomers preferably have reactive
groups that are terminal groups on the oligomer backbone and
more preferably are reactive groups at the ends of oligomeric
backbones which have little or no branching. The preferred
reactive groups of the reactive aromatic oligomer are primary
amine t-NH,), hydroxyl (-OH), carboxyl (-COOA where A is
hydrogen or an alkali metal), anhydride, thiol, secondary
amine and epoxide groups. Especially preferred are reactive
aromatic oligomers having at least about 1.7 reactive groups
per molecule and having at least about 70~ of the total number
of reactive groups present as primary amine, secondary amine,
hydroxyl and/or epoxide groups.
The preferred reactive aromatic oligomers are made, for
example, ~y reacting a molar excess of a sulfone such as
dichlorodiphenylsulfone with a dihydroxy aromatic compound or
compounds suc~ as bisphenol A or 2,7 naphthalenediol so as to
yield a chloro-terminated oligomer and then reacting this
chloro-terminated oligomer with an alkali metal salt of a
hydroxy amine compound such as para or meta aminophenol to
provide the reactive groups on the ends of the oligomer.
Suitable sulfones for this procedure are meta, and para
dichlorodiphenylsulfones. Among the 6uitable dihydroxy
aromatic compounds for use in this procedure are bisphenol A,
bisphenol F, naphthalenediols and biphenyl diols. More
detailed procedural steps appear in Canadian Patent
Application No. 501,9g6, dated February 17, 1986, which issued
as Canadian Patent No. 1,250,996 on March 7, 1989~ Other
procedures for producing oligomers having reactive end groups
are disclosed in U.~. Patent 3,895,064 to Brode and Kawakami
and U.S. Patent 3,563,951 to Radlman and Nischk, the latter
patent using a procedure which involves forming nitro
terminated oligomers and then reducing the nitro groups to
amines.
An advantageous route for making the preferred amine
terminated aromatic oligomers comprises: (a) dehydrating a
132617~
-- 8 --
dihydroxy aromatic compound or a combination o~ di~dco~
compounds with an amount of alkali ~etal h~droxide that pro-
vides slightly less than one equivalent of alkali metal for
each equivalent of hydroxyl in the dihydroxy compound or
combination thereo~, the dehydration being in the presence of
an organic liquid and an alkali metal carbonate in an amount
which is at least equivalent to the hydroxyl excess: (b)
reacting a molar excess of dihalogen diphenylsul~one bearing
about two replacable halogens per molecule with the dehydrated
product of (a) in the presence of an organic solvent and an
alkali metal carbonate; (c) dehydrating a phenol bearing
epoxy-reactive functionality such as p-aminophenol, m-amino-
phenol or combinations thereof with alkali metal hydroxide in
an amount that provides slightly less than one alkali metal
equivalent for each hydroxy equivalent in the aminophenol and
an amount o~ an alkali metal carbonate at least equal to the
deficiency of alkali metal hydroxide and (d) reacting the
dehydrated products of (c~ with the condensed product of (b).
Amine terminated polysulfone oligomers made in this manner
have at least about 70~ of the end groups amine terminated and
contain little or no organic chlorine substituents. Epoxide
terminated aromatic oligomers can be prepared by the same
route by reacting the condensed product of (d) with an amount
of a polyepoxide compound sufficient to provide at least one
epoxide per equivalent of active hydrogen of (b) or (d).
Preferably an excess of epoxide groups will be present and
more preferably the epoxide : hydrogen equivalence ratio will
be bet~een about S:l and about 30:1. Generally the tempera-
ture of the reaction mixture will be maintained at about 50C
or above to ensure reaction in a reasonable period of time.
The preferred temperature range is about 80 to 150C.
Epoxidè terminated polysulfone oligomers made in this manner
` can contain up to 12 epoxide groups depending upon the epoxide
functionality of the polyepoxide compound.
The glass transition temperature of the reactive
aromatic oligomer preferably ranges between 150 and 250C.
A more preferred range is between 160 and 190C. The
-: ~ - .
,.
` 1326176
g
molecular weight (number average) o~ the reactive aromatic
oligomer preferably ranges between 2500 and 5000. Pre~erably,
the reactive aromatic oligomer has a polydispersity (Mw/
Mn) of between about 2.0 and 4.0 where Mn is number
average molecular weight and M is weight average molecular
weight.
The curing agent o~ the preferred epoxy resin composi-
tions is preferably an amine hardener, more preferably an
aromatic diamine having a ~olecular weight below 750 and still
more preferably is a compound of the formula
~12~1~X)~ ~2
where Rl, R2, R3 and R4 are independently hydrogen,
halogen or an alkyl or alkoxy group with 1 to 12 carbon atoms
and X is O, S, SO2, alkylene, alkylidene, and oxoalkylene
and m is 0 or 1, a phenylene diamine or a heterocyclic
diamine. A particularly preferred aromatic diamine is
3,3'diaminodiphenylsulfone, Other aromatic diamines include
a diaminodiphenyl sulfide; a methylenedianiline such as
4,4'-metbylene-dianiline: a diaminodiphenylether; a diamino-
benzophenone; benzidine: 4,4'thiodianiline; 4-methoxy-6-m-
phenylenediamine 2,6-diaminopyridine 2,4-toluenediamine;
and dianisidine. Still other aromatic diamines such as the
di(aminophenoxy)diphenyl ethers or sulfones can be employed
if desired. Alicylic amines such as menthane diamine may
also be employed. In some cases aliphatic amines such as
secondary alkylamines which are normally ~ast reacting
hardeners can be used alone or in combination with other'
amine hardeners provided the concentration and/or curing
'` temperature are sufficiently low to permit control of the
curing rate. Other fast reacting hardeners which can be
.
1326176
- 10 --
employe~ ~or ma~ing the epoxy resins of the invention ~re
dicyandiamide, boron trifluoride/amine complexes and the like.
The hardener is present in the composition in an amount
sufficient to crosslink or cure the composition and pre~er-
ably is present in an amount which provides (together withthe reactive aromatic oligomer) from 0.6 to 1.5 equivalents
and more preferably ~rom 0.8 to 1.2 equivalents of active
hydrogen atoms per one equivalent of epoxide groups in the
composition.
The epoxy resin compositions hereof in preferred
embodiments contain a rubber polymer, The rubber polymer is
insoluble in the polyepoxide compounds used in making the
epoxy resin compositions. An amount of this polymer is
contained in infusible particles that are dispersed through-
out the epoxy resin composition. The rubber polymer
preferably is crosslinkable having functionality such as
carboxyl groups. Carboxy functional butadiene acrylonitrile
polymers are preferred. An example of this latter polymer is
Hycar 1472 marketed by B. F~ Goodrich~ A description of
carboxy functional rubber polymers appears in the article
`'Crosslinking Reactions of Carboxylic Elastomers" by Harold
P~ Brown in Rubber Chemistry and Technology 36(4), 931 - 62
~1963). A catalyst is preferably employed with carboxy or
other functional polymer~ An example of such a catalyst is
an aryl phosphonium halide catalyst such as ethyltriphenyl-
phosphonium iodide available from Morton-Thiokol.
In other embodiments, the infusible particle comprises
glass, ceramic or ground rubber particles. In these embodi-
ments of this invention, glass beads or the like, ground
rubber or ceramic are dispersed in the epoxy resin composi-
tion during or after its formation~ The rubber particles
comprise natural or synthetic rubber and may be ground
cryrogenically to desired particle sizes.
The infusible particles have a median particle size
(i.e~ half are bigger and half are smaller) ranging between
10 and 70 microns. The particles may be evenly distributed
in the epoxy resin composition but are segregated according
, .
:
1326176
-- 11 --
- to size during prepreg manu~acture, discussed below. As an
alternative the particles may be dispensed directly on the
prepreg during its manufacture.
The infusible particles may take a variety of shapes
including cylindrical, mostly round and spherical. The
particles are infusible insofar as they resist deformation
and agglomeration during manufacture of the epoxy resin
composition and prepregs thereof. The infusible particles
also preferably have a lower modulus than the remainder of
the crosslinked epoxy rèsin matrix.
A preferred route in making epoxy resin compositions of
this invention which contain particles comprising a rubber
polymer involves forming the infusible particles in situ. By
"in situ" is meant forming tbe particles during manufacture of
the epoxy resin composition. The particles formed in this
manner are stable and resist deformation, agglomeration and
solubilization during manufacture of the epoxy resin
composition.
Manufacture of the epoxy resin compositions using the
preferred in situ process comprises admixing a portion e.g.,
between 40 and 60% by weight of the polyepoxide component,
together with the reactive oligomer component at elevated
temperature, e.g., between 30 and 90C, to dissolve the
oligomer component in the epoxy compounds. A crosslinkable
rubber polymer preferably in the form of a solution which has
betwcen about 10 and 20% of the polymer and between 90 and
80% of low boiling solvent is added. The solvent is then
distillèd under vacuum to provide a resin premix having less
than 5% by weight solvent, more preferably 3% or less solvent.
- 30 Then the catalyst and other ingredients such as antioxidant
are added. Mixing continues at this temperature permitting
continuèd reaction of the crosslinkable rubber polymer in
completing the formation of the infusible particles. Alterna-
tively, a crosslinkable rubber polymer may be dissolved in a
portion of the polyepoxide component using a low-boiling
solvent, the solvent driven off, and the polyepoxide com-
pound(s~ containing the dissolved rubber polymer added at
132617~
- 12 -
elevated temperature to a mixture of the amine terminated
polyarylene polyether sul~one and another portion oE the
polyepoxide component. The catalyst is added permitting an
accelerated completion of the reaction forming the in~usible
particles, as desired.
In still another procedure, the polyepoxide component
and the oligomer component are mixed in a sealed mixer Ind
then the rubber polymer, dissolved in solvent, is added
together with or followed by addition of the catalyst and
antioxidant as desired. The sealed mixer is maintained at
elevated temperature causing the infusible particles of
appropriate size to form. The resulting epoxy resin composi-
tion may be used to form prepregs using a bath that is
agieated ~o keep the infusible particles dispersed during
15 impregna~ion of fiber passing through the bath.
The curing agent of the epoxy resin composition is
preferably added after formation or addition of the infusible
particles. Dispersion of the curing agent in the intermediate
epoxy resin composition may be accomplished without deforma-
tion of the infusible particles.
Table A below provides the general and preferred ranges,as parts by weight, for the polyepoxide polymee component,
reactive aromatic oligomer, hardener and in~u~ible particles
present in the thermosetting epoxy resin compositions of this
invention:
- TABLE A
General More Preferred
Polyepoxide Component 100 100
Reactive Oligomer 10 to 200 20 to 60
` 30 Hardener (curing agent) 15 to 100 20 to 60
Infusible Particlesla) 1 to 15~b) 4 to 12(b)
,
(a) E.g. carboxy ~unctional rubber polymer.
(b) By weight, per hundred parts of the epoxy resin
composition.
.
,
~32~176
- ~3 -
Other ingre~ients such as ca~lyst, anti~xida~t,
processing aids and ti~e li'~e are incl~de~ in ti~e e;Joxl r~sin
compositions in minor ~mounts.
The pre~erred cured, i.e., crosslinked resins produced
from the compositions oE this invention have a multiphase
morphology comprising glassy phases and a phase i.e. the
infusible particle phase, that is distri~uted in certain
fashion within the thermoset composite, The domains of t~e
dispersed discontinuous glassy phase preferably are between
about 0.05 and 10 microns and more preferably between 0.1 and
5 microns in largest dimension~ The domains are generally
spherical or ellipsoidal in shape but may take other shapes
particularly around the filaments in the matrix. The
particles containing rubber polymer are dispersed in the
glassy phases and have a size and distribution as previously
discussed. The particles containing the rubber polymer are
preferably of lower modulus than the remainder of the
crosslinked epoxy resin matrix comprising the glassy phases.
The volume of the discontinuous glassy phases preferably
constitutes at least about 15%, more usually between 30% and
65% of the total volume of the cured resin. The total volume
of the cured resin (Vr) is defined as the volume of the
continuous phase(s) (Vc) and the volume of the discontinuous
phase(s) (Vd) combined. In determining the volume o~ the
' 25 discontinuous phase(s), a micrograph of a microtomed section
of the cured resin or composite is made and the area (or an
area fraction) of the micrograph occupied by the continuous
phase(s) (Ac~, discontinuous phase(s) (Ad) and filament or
` fiber (Af) may be determined visually or instrumentally, using
commercial devices such as a digitizer or image analyzer. In
certain composites of this invention, the disperse phase may
be continuous in certain portions of the composite and vice-
versa. The amine functional polyarylene polyether sulfone
may exist in either of the glassy phases and has been shown
in certain instances as residing as well in the infusible
partlcles that comprise a ceosslinkable rubùer.
,. . . - .
''` ` ' ............................ ;. ,
~ '' ~ , .
- l~ 132~7~
The prepre9s o~ this invention are made ~ combining tne
epoxy cesin compositions and high strength ~ilaments usi~
conventional techniques. For example, the e2oxy resin
composition can be made into a film on a sheet of release
paper in a film process. Film carried by upper and lower
release papers are pressed into bands or sheets of high
strength filaments in making prepreg by this process.
Alternatively, a "hot bead`' process may be used wherein the
epoxy resin composition is rendered molten and pressed into
the bands or sheets of high strength filaments. Still another
route is by dispersing the epoxy resin composition in solvent,
passing the high strength filaments through a bath containing
the solvent and then driving off the solvent to provide the
prepreg. In this latter technique, the bath is advantageously
agitated to keep the infusible particles dispersed therein.
In all of the aforementioned techniques of making pre-
preg, the large infusible particles are trapped by the fila-
ment tows or bundles thereby providing in a prepreg that has
these particles on its surface rather than between filaments
in the bundle or tows of filaments~ The prepregs may be
s}mply layed on one another in making the damage tolerant
components of this invention.
Figure 1 shows a photomicrograph of a damage tolerant
composite of the invention. The carbon fiber appears as
`~25 white streaks ~0, i.e. parallel to the horizontal axis of
the micrograph), white ovals (+/- 45, i.e. diagonal to the
-horizontal axis of the micrograph) and white circles (90,
i.e. perpen~icular to the plane of the micrograph). The
crosslinked epoxy resin matrix appears grayish in the micro-
graph with the particles comprising rubber polymer generally
being circular black dots. The damage tolerant composite
exhibited a 52.2 Ksi (thousand of pounds per square inch)
post impact compressive strength (PIC) at an impact of 1500
inch pounds per inch thickness using the lay-up described in
the Examples. (All PIC values of the composites in the draw-
ings were determined at 1500 inch pounds per inch thickness
using the procedures of the Examples.)
`:
`:
32~76
Figure 2 shows other micrographs oE the dainage tol~rant
co~posite like that of Figure 1 [Figures 2(a) and 2 (D) ]
together with a crosslinked epoxy resin cured without ~iber
[Figures 2(c) and 2(d)]. The crosslinked epoxy resin of
Figures 2(c) and 2(d) is made with the same formulation of
the composite of Figures 1, 2(a) and 2(b). The cured resin
`' of Figure 2(a), (b) and ~c) has been washed with methylene
chloride (CH2C12) to improve phase contrast.
Figures 3, 4 and 5 respectively show photomicrographs of
three damage tolerant composites. The composites were made
using the same nominal formulation. The composite of Figures
3la). (b) and (c) had a post impact compressive strength (PIC)
of 48.5. The composite of Figure 4 had a post impact compres-
sive (PIC) strength of 43.5. The PIC ;trength of the compos-
ites of Figure 5 was ~8.3.
Figure 6 shows a photomicrograph of a cured epoxy resinwherein the resin formulation includes an oligomer which is
different from those of Figures 1 - 5.
This invention has particular applicability to damage
tolerant composites which are made from materials commonly
referred to as '`prepregs.`' Prepregs comprise resin and high
strength filaments which are in the form of filamentary
bun~les (often called "rovings" or "tows") comprising a
~` multitude of the filaments. Each tow of carbon fiber, for
example, typically bundles between about 500 and 20,000
filaments. A plurality of filamentary bundles are aligned or
~: woven together in making a prepreg in sheet form, a preferred
form according to this invention. Alternately, the prepreg
may be in the form of a single bundle of filaments impregnated
with resin. This later prepreg form finds use in processes
such as filament winding and pultrusion.
The preferred high strength filaments are carbon fiber
filaments made, for example, by carbonizing polyacrylonitrile,
rayon or pitch. ~Carbon fiber is also called "graphite fiber"
by some and the terms "carbon fiber" and "graphite fiber" are
interchangeable as used herein.) Examples of preferred high
" strength filaments are AS-4, IM-6 and IM-7 carbon fiber
16 1~26176
marketed by l~ercules Incorporated. Other higi) strengtn ~ila-
ments preferably having a diameter between 3 and 9 microns
can also be employed.
The prepregs hereof comprise euoxy resin composition
that permit the prepreg to cure into damage tolerant
composites. The epoxy resin compositions when cured without
any high strength filaments have a KIC of greater than
1 MPa~i. This high degree of toughness, coupled with the
action of the infusible particles pro~ides composites that
include the infusible pàrticles and high strength filaments
with post impact compression values in excess of 45,000 ~si
at 1,500 inch pounds per inch thickness of the composite.
Figures 1 - 5 are copies of photomicrographs of sections
taken of damage tolerant composites of this invention. As can
be seen in viewing these Figures, the distribution of infus-
ible particles ~black or darker dotsl is such tbat the larger
particles generally reside between the fiber plies whereas the
smaller particles tend to be trapped between filaments within
` the plies. ~ comparison of the photomicrographs of Figures 5
(a composite having a measured post impact compression
strength (PIC) of 38) with the photomicrographs of Figure~ 1
` and 2 (a~ and ~b) (composites having a measured post impact
compressive strength of 52.2 and 54 respectively) shows a
relationship between the size of infusible particles in the
matrix and high PIC values of the damage tolerant composites.
The damage tolerant composites of Figures 1 - 5 are made
using epoxy resin compositions all having the same nominal
formula`tion. The composites having the higher post impact
`; compression values are made from epoxy resin compositions
having infusible particles with a higher median particle size;
and such larger particles can be seen as generally residing in
that portion of the crosslinked epoxy resin matrix between the
plies of filaments.
The epoxy resin compositions used in making the compos-
ites illustrated in Figures 1 - 5 comprise infusible particles
of similar size and shape as appear in Figures l - 5. Com-
pare, for example, the infusible particles in the neat resin
- 17 - 1326176
of Figures 2(c~ and 2(d~ with the in~usi31e particles o~ tne
damage tolerant composites in Figures 2(a~ and 2~b~. A n~mber
of these particles, pre~erably more than half, have a dimen-
: sion that is greater than 10 microns. Composites with highestdamage tolerability as measured in post impact compressiontests generally comprise infusible particles having a mean
dimension at least about 15 microns. More preEerably, the
median particle size of the infusi~le particles is between
about 25 and 75 microns.
The following Examples illustrate pra :ice of this
invention and are not intended as a limitation thereof. All
parts and percentages in the Examples are parts and percent-
ages by weight and all temperatures are in degrees centigrade
unless otherwise noted~
Example 1
The formulation in Table 1 set forth below was ùsed in
preparing prepreg made of an epoxy resin composition and tows
of carbon fibers ùsing procedures described hereinafter.
~`
'```
;~
,.~
.
"
~ - 18 - 132 617 6
TABLE 1
Ingredient Parts bv Weight
Diglycidyl Ether of Bisphenol-Fl 13.12
Triglycidyl p-amino phenol2 13.12
Amine functional polyarylene
polyether sulfone3 13.65
3,3'-Bis(aminophenyl)sulfone- 12.86
Carboxy-functional hutadiene
acrylonitrile polymer5 2.09
Ethyltriphenylphosphonium iodide6O.Q368
Polymerized 1,2-dihydro-2,2,4-trimethyl
quinolinQ7 0.1052
-
1. Epiclon 830*, a product of Dainippon Ink and Chemicals,
Inc. having an epoxy equivalent of about 180, viscosity of
about 3000 cps (at ~5C) and specific gravity of about 1.18
(at 25~c).
2. MY 0510*, a product of Ciba Geigy, said to be a reaction
product of three molar parts of epichlorohydrin and one
molar part o~ p-aminophenol, and have an epoxy equivalent
of about 99.
3. A product made by reacting a molar excess of dichlorodi-
phenylsulfone with the potassium double salt of Bisphenol-A
followed by reaction with the potassium salt of amino-
p~enol. Product has molecular weight (number average)
between about 3500 and 5500 and ~etween about 85-95~ of the
end groups are amine groups with the remainder of the end
groups comprising hydroxyl groups. Procedures for making
this polyether sulfone are described in detail in the
examples of Canadian Patent Application No. 501,966 dated
February 17, 1986, which issued as Canadian Patent No.
1,250,996 on March 7, 1989.
4. Air milled from sumitomo Chemical, Alva Chemical or Aceto
Chemical companies.
5. Hycar 1472*, a product of B. F. Goodrich, said to be
nitrile rubber made from butadiene and acrylonitrile, in
the form of a rubber crumb.
6. Catalyst sold by Morton-Thiokol.
7. Agerite Resin D* sold by R. T. Vanderbilt, antioxidant.
* Denotes Trade Mark
1326176
~. ,
The carbo~y-~unction31 butadiene acrylonitrile pollmec In
the form of a crumb is added to methylethylketone at a ~eight
ratio of 1~ parts crumb to eighty five pa~ts methylethyl-
ketone. The mixture is stirred to form a homogeneous solution
which is called ~Rubber Solution~ in this Example.
A Meyer's vacuum mixer having a five gallon capacity is
used in the preparation of the epoxy resin composition. The
mixer is equipped with a thermometer and fast and slow mixing
blades: it is heated by oil circulation and can be evacuated
by a vacuum pump using a solvent trap.
The vacuum mixer is cleaned with solvent and then first
set to have a temperature between 60C and 100C to drive o~
the cleaning solvent. The triglycidyl p-aminophenol epoxy
resin (13.12 parts) and diglycidyl ether of Bisphenol F epoxy
` 15 resin (2.62 parts) are added together and mixed in the vacuum
mixer while heated to about 60C. To these preheated, mixed
epoxy resins is added the amine functional polyarylene poly-
ether sulfone (13.65 parts) in particulate form. Methylethyl-
ketone (~.658 parts) is used to wash the polysulfone ether
powder from the sides of the mixer during the mixing opera-
tion. The lid on the mixer is then closed and the temperature
of the mixture increased to about 60C. The high speed mixer
blades are set at about 1400 RPM. After the temperature of
about 60C is reached and the amine functional polyarylene
polyether sulfone is dissolved, the mixer is opened and the
Rubber Solution (13.91 parts) added. The mixer is closed and
the temperature set for about 120C. The mixer blades are
set at low speed and mixing continued until the reflux temper-
ature (80) is reached. The vacuum pump is then started. The
vacuum in the mixer is maintained at a level no higher than
13-15 centimeters Hg up to a temperature o~ 85C. (Should
the resin foam up, the vacuum is released slowly until foaming
~decreases to a position below the top of the mixing blades at
a pressure of about 13 centimeters Hg.)
Table 2, set forth below, shows the relationship between
temperature and maximum vacuum that can be employed in heating
the resin mixture:
- 20 - ~32617
r~ E 2
~esin Temperatur~ (c) ~c~lu~ (c~)
up to 85 13 - 1
8, 22.9
88 30.,
91 35.5
93.5 45.7
102 +/- 3 ;-~
When the tem~erature of the resin mixture reaclles
102 +/- 3C, the vacuum is released and the ethyltriphenyl
phosphonium radical catalyst (0.0368 parts) and ~olymerized
1,2-dihydro-2,~,4 trimethyl quinoline antioxidant (0.1052
` parts) are added to the mixer.
With the mixer closed, mixing is continued at low speeds
for about 50 minutes at 105 ~/- 3C. After the mixing has
continued for 5 minutes, vacuum is applied and maintained at
about 51-52 centimeters Hg for 30 minutes. After this 30
minute period, a full vacuum is applied for the remainder of
the 50+/- 5 minute mixing period. The vacuum is released and
the temperature is set for about 70C. A sample of the resin
~"~ mixture is then taken through a port in the mixer and the
sample heated to drive off the solvent. If the heating
reveals that the sample had more than 3~ volatiles by weight,
the vacuum and heating is again applied to the resin mixture
in the vacuum mixer. If there is less than a 3% weight
difference between the sample of the resin mixture and its
heated ~i.e. devolatilized~ product, then the remainder of
the diglycidyl ether of Bisphenol F (10.5 parts) is added to
the vacuum mixer. Mixing is continued while the resin mixture
is cooled. When the mixture reaches 98~C, the 3,3'-bis(amino-
phenol)sulfone (12.86 parts) is added through a port in the
mixer. After the powdery 3,3-bis(aminophenol) sulfone is
fully dispersed, the mixer is raised and the walls scraped
down. The temperature is set to 77~C, the mixer closed with
mixing continued at full vacuum for about 15 minutes. The
132617~
- 21 -
mixer is opened and the contents are poured into small
containers which are stored at 0 C for further processing Oe
the epoxy resin composition thereof into prepreg.
The frozen epoxy resin composition of Part A is slowly
brought to a temperature of about 50C. The warmed e~oxy
resin composition co~prises the uncured epoxy resin composi-
tion and distinct particles which contain the butadiene
acrylonitrile polymer. The warmed epoxy resin composition
containing the infusible particles is spread on a sheet of
release paper. The sheet of release paper having the film of
the epoxy resin composition is rolled up and stored at about
lO~C or below for further processing.
Tows of carbon fiber lIM-7 carbon fiberl available
from Hercules Incorporated, Magna, Utah) are formed into a
band, Two different bands are prepared. The first band has
an areal weight (i.e. weight per unit area) o~ about 145
grams per square meter and the second band has an areal
weight of about 190 grams per ~quare meter. The first band
is impregnated with the epoxy resin composition of this
Example by passing it between a pair of rollers which press
the band and upper and lower filmed epoxy resin composition
~ parts together as they pass between the rollers. The rollers
i are kept about 75C and the resultant prepreg is between
about 33 and 37~ by weight resin. Similaely, the second band
is made into prepreg by pressing the second band of carbon
fiber and a further amount of the filmed resin together be-
~` tween rollers kept at a temperature above 75C. The resultant
prepreg made from the 190 gm per square centimeters areal
weight carbon fiber is between about 33 and 37~ by weight
resin.
1 Approximately 12,000 filaments per tow. Filament
physical characteristics include filament diameter 5
microns round cross section. The modulus of the carbon
fiber is about 44 million psi and the tensile strength
about 750 thousand psi, these modulus and strength values
measured using tow tests.
- ~ 13261~
- 22 -
In an alternate procedure (not bead) tne e~oxy resin is
heated to about 7~C and spread on a sheet o~ release paper.
The tows of car~on f iber are then pressed into the molten
resin carried on the release paper in making the prepreg. The
resultant prepreg has between about 33 and 37~ by weight
resin.
The prepreg, prepared as above, is made into rolls of
prepreg in which the preQreg in each of the rolls is sepa-
rated by a sheet of release paper.
Twenty five grams of epoxy resin compositions prepared
using the procedures of Part A of this Example 1 were placed
in a two hundred fifty milliliter beaker and mixed with 100
milliliters of tetrahydrofuran (THF) until the resin composi-
tion in which the infusible particles were dispersed was
dissolved, The dissolution product was then filtered through
pre-weighed Whatman #41 filter paper. The beaker and stir
`` bar were rinsed with the THF until the filter paper was white.
The filter paper was allowed to air dry and then placed in an
oven at 75C. The filter paper was cooled to room temperature
in a desicator and weighed. This procedure was repeated using
different batches of the epoxy resin composition. The parti-
cles on the filter paper are found using these procedures to
j weigh in a range between ~ and ~% by weight of the respective
epoxy resin compositions.
A series of composite test panels are made from prepregs
prepared following the foregoing procedures. The prepregs
were layed up and cured and the cured composite panel tested
to determine the post impact compression test values. The
panels tested were 10 centimeters wide and 15 centimeters
long. The panels were thirty two plies thick, each ply con-
taining carbon fiber filaments extending in a single direc-
tion. The panels were quasi-isotropic according to the
~following scheme: (+45/90/~45/0) 4s' (The 4S in the
lay-up means the lay-up had a total of thirty two (32) plies
layed up as follows: a set of four plies was layed at the
recited angles four times (i.e. sixteen plies in all) starting
each time with a +45 ply followed by laying a set of four
132~17~
- 23 -
plie~ ~our ti~e~ in ~-v~r~e or~er (i.e. sixteen ~
starting each tim~ with a ~ ply. The la~-~p was cure~ 3t
177C for t-.~o hours. Tne cure~ ~anels were i;n~acte~ ~it- an
impact ener~y of 1,50~ incn - lbs/inch thickness while sus-
pended over a 3 x , incn o;~ening. The com~ressive strengti-
of the impacted panels was determined using the test procedure
of NASA publication 109~, modified as above. Portions of tl~e
impacted panels were examined microscopically for ~hase sepa-
ration in the epoxy thermoset matrix. Also, ti~e size of the
rubbery particles in sections of the impacted samples were
measured and counted. Table 3, below, snows the results o~
the post impact compression (PIC~ test together with the
~` results of the particle size measùrements.
As can be seen from Table 3, the size and distribution
of the rubber particles have a correlation with the post
impact compression ~PIC) test results the larger particle
distributions generally give higher post impact compression
results~ Also as is seen from Table 3, the cured laminates
having high PIC values exhibit a `~phase separation." By
"phase separation`' is meant that there exists distinct epoxy
-~ phases in addition to the rubbery or other particulate phase.
1326176
-- 24 --
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- 25 - ' 1326176
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- ~6 - 132~7 6
x~ple 2
This ex~mple descri~ea a labora.ory ~reparation of ~n
epoxy resin co~p~sition o~ this invention .~i~icn does ~Ot
requice solvent removal after addition o~ the polyarylene
polyether ~ulfone. ~n initi~l step in thia ~reparation w~a
forming a solution of carbox~-Eunctional butadiene acrylo-
nitrile polymerl and :ne~hyle~hylketorle at 20% ~y wei~t-t o~
the polymer. Four hundred parts of this solution were mixed
with 500 parts of dicylcidyl ether of Bisphenol F2 at roo~
temperature. Tn~ mixt~re was strip~ed of ;nethyIetl-yl~etone
until its volatile content was below 2% by weight. Another
step in this procedure began with heating 5~0 parts of tri-
glycidyl aminophenol3 to oOC in a separate vessel. Then,
520 parts of amine functional polyarylene polyether sulfone4
` 15 were added slowly to the triglycidyl aminophenol with mixing
and the temperature increased to 107C. Mixing continued
~`
uneil the polyether sulfone dissolved. Five hundred eighty
parts of the mixture of carboxy functional butadiene nitrile
polymer and diglycidyl ether of Bisphenol F (less than 2% by
weight volatiles) were heated to 100C in an oven and added
at 110C to the solution of triglycidyl aminophenol and poly-
ether sulfone to provide a reaction mixture that is held at
about 107~C for forty-five minutes. Antioxidant5 (4
parts) and catalyst6 (1.4 parts) were then added to the
reaction mixture. The temperature of the reaction mixture
was then cooled to 80C and 490 parts of 3,3'diaminodiphenyl-
sulfone7 added and dispersed into the mixture.
A prepreg was made from the epoxy resin composition
prepared as shown above in Part A. The high strenyth
filaments used in preparing this prepreg were tows of IM-7
carbon fiber8 of Hercules Incorporated. The prepreg had a
fiber volume of 55%. The prepreg was made into panels using
the lay-up procedures of Example 1. The panels were tested
also using the procedures of Example 1 and determined to have
the following compressive strengths at 1500 inch pounds per
inch thickness impacts: 50.6 thousand pounds per square
inch; 52.9 thousand pounds per square inch and 51.1 thousand
.
27 - 1326~ 7 6
pounds per syuare inch. ~lso, nQat reil- sai~?le, ~ere
exa~ined micros_o~ically and Eound to i~ave s~nerical parti-
cles compring .he butadiene acrylonitrile ~ol~eL ranging in
size between ~.4 microns a;ld 81.4 micLons, which were
generally spherical in shape. The medi~n size of the parti-
cles was judged eo be much greater t~an 10 ~,icrons.
1, 2, 3~ 4, 5 , 6, 7 and 8 - See E~amæle 1 Eor source
and fuller desceiption.
~xample 3
This Example illustraees use of epoxy resin compositions
in making single tows oE carbon Eiber impregnated with resin.
The carbon fiber used in making the tow-preg was I~1-7 carbon
`~ fiber available from Hercules Incor~orated. Tows of this
carbon fiber have approximately 12,000 filaments and no twist
The cross sectional area of the tow is about 0.25 millimeter
with each filament having a diameter of 5 microns and a
smooth, round cross-section.
An epoxy resin composition prepared according to the
procedures of Example is admixed with three levels of
methylethylketone as shown in Table 4. The resin solutions
were placed in resin coating baths which were agitated during
passage of tows of the IM-7 carbon fiber through the bath.
The tows were passed through the bath under a roller fixed in
the bath and then out of the bath to an '`S-bar" apparatus.
The tow passed over a first bar and then under a second bar
in traveling an S-shaped path. This path permitted wiping
both sides of the tow-preg and was judged to give a uniform
distribution of the particles Oe rubber polymer.
A stirring motor was used for take up of the tow-preg.
A tow speed of about 4 feet per minutes was used. The pulley
was high enough that a four-foot length of ~et tow-prep could
pull and cut off. Th}s section was dried in air for about 10
minutes at room tempecature and then in an oven at 93C for
five minutes. This drying was determined to reduce volatiles
to less than 3% by weight.
Volatiles content was determined by weighing a length of
tow, drying it at 350F (133C) for 15 minutes and reweighing
- 28 - 1326~76
Resin content was determined by extracting a weighed length of
tow with tetrahydrofuran (THF), drying the extracted tow and
reweighing. Insoluble rubber content was determined by
filtering the THF extract through a weighed filter paper,
drying and reweighing the filter paper. Distribution of
rubber particles on the tow was determined by visual
examination.
The following Table 4 provides information for three
10 preparations of tow-preg prepared and tested as discussed
above.
TABL~ 4
Resin Con- Volatiles Resin Con- Rnbber
pes. centration ContenttS.D.) tent ~S.D.) Content
g493-12-1 50~ 3.0% (0.1) 46.3% (1.05) 3.3
9493-12-2 35% 3.1% (0.5~ 34.4% (1.12) 3.2%
~493-12-3 30% 3.2% (0.6) 32.1% (1.34) 2.8%
Example 4
A concentrate of particles comprising rubber polymer in
an epoxy resin admixture is made as follows: Ten parts of
diglycidyl ether of Bisphenol F (Epicon 830* from Dainippon
Ink and Chemicals) and 10 parts triglycidyl p-aminopbenol (~G
0510* from Ciba Geigy) were heated to 70 C. Twenty parts of
amine functional polyarylene polyether sulfone were added to
- t~e epoxy resins and a slurry was formed. The slurry was
heated to 105'C and held for 40 minutes whereby the amine
functional polyarylene polyether sulfone was dissolved. The
product was then cooled to about 75 C and fifteen parts of
methyl ethyl ketone added. Then eight parts of carboxy
` functional butadiene acrylonitrile (Hycar 1472*, B.F.
Goodrich) rubber was added as a 15% by weight solution in
methylethylketone. The mixture was heated to about 107 C for
fifteen minutes. The resultant epoxy resin concentrate was
cooled to room temperature.
An initial step in formulating an epoxy resin composition
of this invention from the concentrate of Part A, above, was
forming a slurry of the triglycidyl p-aminophenol
* Denotes Trade Hark
X
. .
.
- 29 - i326~7 6
(~o parts), digl~cii~latl~er Oc ais~he~ol F (~ ~arts) an~
amine function~l polyaeylene polyethec (3 ?arts). T~e ~lurr
was heated to 105C and held at that temperatur~ ~or ~0
minutes to dissolve the polyether sul~one and ~orm a resin
S solution. The concentrate (~ parts) at r~oin temperature Wda
combined with the resin solution held at 1~5C. Then tnis
combination was cooled to 70~ and antivxi~ant (0.4 parts,
Agerite Resin D, polymerized 1,2-dihydro-2,2,4-trimethyl
quinoline, from R. T. Vanderbilt), catalyst (0.1~ parts
ethyltriphenyl phosphon`ium iodide fcom ~lorton-Thiokol and
3,3'-bis(aminopnenyl) sulfone (49 parts, available froln
Example 1~ were added and mixing continued for ten minutes to
; provide the epoxy resin composition.
Example 5
In this example, a number of uncured epoxy resin
compositions and cured epoxy resin compositions were analyzed
relative particle size (Table 5) and viscosity ~Table 6).
The epoxy resin compositions were made generally according to
the procedures of Example 1. The results reported in Table 5
were gathered by making a photomicrograph of the uncured resin
composition and then using an image analyzer with a computer-
ized `'mouse`' to determine particle size ~rom the photomicro-
graph. The image analyzer was set to establish particle size
within 10 micron increments.
:. :
. "' ` , `"~
, ` , ,. '
1 3 2 ~ 1 7 ~
- TABLE;
PA~TICLE SIZE A~IALYSIS
UNCU2~D ¦ ~E~T ) R~S I ~
~lean Range 10 90-100
Lot Nl (microns) (mi_ron~) (microns)3 (~icr~n~)4
S005A51 51.7 10 - 90
SQ05B66 ~ 10 - 100
~ S005C55 39.2 10 - 100
- S005D55 48.9 10 - 90
10 S005E74 47.8 10 - 90
SOOSF65 ~7.2 1 - 100 2
S005G40 67.0 20 - 100 4
S005H45 41.9 1 - 100 4 3
S005I29 42.6 1 - iOO 2
15 S005J47 46.7 1 - 100 1 2
` S005K78 36~0 1 - 100 4 2
- S005L124 33.2 1 - 100 10 5
S005M99 35.7 10 - 90
~- S005N76 3B.5 10 - 70
20 S005077 38.1 1 - 80 3
S005P70 34.9 1 - 100 4
SOQSS97 33.2 1 - 90 3
` S005T88 38.0 10 - 70
S005U66 36~7 1 - 90 4
25 S005X118 28.8 1 - 90 6
~- SOOSQ104 36.4 N.D. N.D. N.D.
S005R74 39.2 N.D. N.D. N.D.
S005G89 44.3 10 - 100
S005W136 29.2 1 - 80 6
30 S005X78 37.4 1 - 80
S005Y109 35.2 1 - 80 5
S005Z175 24.6 1 - 80 22
` S005AA119 34.9 1 - 100 17 2
; S005AB42 5~8.9 1 - 100 5
`~ 35 S005AC49 47.2 1 - 100 7
S005AD35 63.5 1 - 80
S005AE59 48.6 1 - 100 9
SOOSAF50 42.5 1 - 100 10
::;
"
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1326176
- 3~ -
TA3LE ~
PAI~TICLE SIZE A~ALYSIS
UNCURD (N~AT) RESI;~
(Continued)
S ~-lean Range 10 90-lOV
Lot ~ (microns) (microns) (microns)3 (microns)~
S005AG61 51.3 1 - 100 7 2
S005AJb3 45.9 N.D. N.D. N.D.
S005AI40 50.6 1 - 80
. .
10 S005AK75 36.6 1 - 60 7
S005AL117 31.3 1 - 70 16
SOQ5-S00~ 102 32.7 1 - 70 14
_
Average 2997 38.7 171 30
(6.20~) (1-09%)
1 N means number of particles counted.
2 N.D. means not determined,
3 Number in 10 micron range.
4 Number in 90-100 micron range.
; .: - . , : ,
, ' , :. - . '; ; ~
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- 32 - 132617~
Table 6 shows melt flow rheology on eleven batches of
resin compositions made according to Example 1. Table 7 shows
the initial viscosity at 60C for these samples, the minimum
viscosity, the temperature at which the minimum viscosity
occurs, the dynamic gel temperature (DGT) and heating rate.
All scans reported in Table 6 were run at similar conditions
of 50 mm diameter parallel plates, 0.5 mm gap, lQ
radiansJsecond frequency, S0% strain and cure mode. The
temperatures at which minimum viscosity and DGT occur are
fairly constant while the viscosities are scattered but not
out of line with other resin systems. The DGT for the epoxy
resin compositions was determined to be about 156C when
heating at 0.851 c/minute; 176 c when heating at 1.857C/
minute; 186-C when ~eating at 2.8s7oc/minute and 199C when
heating at 4.273C/minute.
TABLE 6 - ~SIN VI~GOSITY
Initial 60 C Minimum Viscosity Heating
n* n~ Temp. DGT Rate
(poise) ~poise) (C) (-C) (-C/min)
Rç~in 4505 21.1 ~37 174 1.~21
SX005C 3510 15.1 142 175 1.937
~ SX005F 3215 13.3 137 174 1.889
- SX005G 3605 11.6 144 176 1.729
SX005I 4955 33.7 135 175 1.765
SX005~ 7585 22.8 145 173 1.691
SX005~ 6965 20.0 143 176 1.857
SX005P 4670 10.0 143 176 1.933
SX005S 6780 20.0 149 177 2.035
SX006A 5565 16.4 143 175 1.828
SX006C 6035 22.6 141 1?4 1.~17
X(n=ll) 5217 18.8 142 175 1.864
1493 6.6 4 1 0.103
Cv (%) 28.62 35.27 2.86 0.68 5.51
Table 7 shows the glass transitions of thirteen coupons
made from an epoxy resin composition prepared as in Example 1.
~he existence of more than one glass transition temperature in
these samples as shown in Table 7 indicates the presence of
~ore than one crosslinked epoxy phase.
:
,~
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_33_ I3 2 61 76
TABLE 7 - CO~lPOSITE T~
T~ ' Tg Tg
Panel No. Lot No. (C) #1 (C) ~2 (C)
40025 3-831i3161 181 203
40026 3-83191~2 1~1 202
40027 3-8322 1~ 181 203
40030 3-83211~1 181 202
40033 3-~33231~ 181 207
40034 3-8323~ 1~0 180 197
40087 3-834~15~ 173 195
40118 3-83~9159 181 193
40137 3-8353160 181 203
40220 3912-2161 185 199
40328 3-8390135 158 17~
`15 40337 3-8391160 180 200
40341 3-8395160 178 20
X (n~13) 159 179 199
8 7 7
Cv (%) 4.72 3.76 3.65
.
.
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3~. ~326176
Exa~ple 5
In this Ex~mple, particle sizes of ul-lcured e~oxy resin
compositions (?repare~ accor~i~g to ~xam~le L) co.~osition,
are compare~ with the particle size and post i~pact comptes-
sion values obtai~ed Ero~ ~repregs la~ed-u~ and cure~ u~in~
the procedures of Example 1~
The uncure~ e~oxy resin col~positons were analyzed as
follows: A one half gr~m ~approximate) sam~le was taken ~rom
each batch of the epoxy resin compositiona and placed on a
glass slide. The slides were then each heated on a hot plate
having a temperature setting of 11~C. The resin sample was
then smeared into a thin film across the slide and allowed to
further heat at 118C for ~ive (5) minutes. The sample slide
was then cooled and examined on a polarizing microscope
equipped with a transmitting light source and a Polaroid
camera. A photomicrograph was taken of the sample at a
magnification of 156x.
The photomicrograph was visually examined and those
samples having at least about 75% of the particles which were
round and non-agglomerated were selected for further
processing.
The pbotomicrographs were then Eurther evaluated on an
image analyzer set at 10 micron steps. A computerized "mouse~
was used in measuring the long axis of each particle. When
all particles in the sample were measured, the computer was
used to generate a histogram and print out the number of
particles counted, the median particle size, the range and
the stàndard deviation.
The size of the particles in the cured composites were
`` 30 determined similarly. The particles measured in the cured
composites were those in the boundary (essentially fiber
fill) of resin between the plies of cured resin. The lay-up
was the same as in Example 1 except for sample D shown in
`Table 8 below. Sample D had the lay-up [45/0/-45/~0]3S
which qives a 24 ply laminate. As can be seen from Table 8
the particles remain about the same size during processing of
the epoxy resin compositions into cured composites.
~ 35 ~ 132617 ~
3 L G ;3
Composite ~leat Re~in
Median ~ledi~n Post
Particle Particle Impact
Diameter Di~meter ~om~re~sion 2esin
(Microns) (Microns) (PIC) Lot Nos
A 31 33 5~.5 XS005 L
B 3~.2 36 50.0 XS005 K
C 35.3 3~ 52.5 XSOOS rl
10 D 39.9 36 48.5 XS005 M
E 30.8 29 54.4 XS005 ~
F 37.9 35 50.6 XS005 AA
G 36.8 35 50.0 XS005 Y
H 41.4 47 52.8 XS005 AC
lS I 41.1 42 54.1 XS005 AF
J 32.8 31 51.7 XS005 AL
Example 7
In this Example, epoxy resin compositions are made on a
larger than laboratory scale using the procedures of Example
2 except for the following. The dissolution product of amine
functional polyether sulfone and triglycidyl aminophenol was
cooled to 90C and the mixture oE carboxy functional butadiene
nitrile polymer and diglycidyl ether of Bisphenol F was added
at 55C thereto.
A series of prepregs were made from these eyoxy resin
compositions . The prepregs were made by first making a film
; of the resin. The highest temperature used in making the film
was about 70~C. The prepregs were made by pressing either
145 grams per meter areal weight IM-7 carbon fiber or 190
grams per meter areal weight IM-7carbon fiber into the film.
The resulting prepregs were about 35% (Grade 145) or 42~
(Grade 1901 by weight resin. Portions of the prepreg on each
spool were layed up, cured and tested according to the proce-
dures of Example 1. The particle size in the boundary resin
layer (between plies) in the cured laminate was determined to
the extent of determining dimensions of the largest and small-
est particles thereof. In addition, the shape of the parti-
, . - -
"- ~ ' .
~326176
- 36 -
cles in eacil cured s~m~le w~s j~dged viau~ '?ne .e~lts ~.
this testing are shown below in Table 9~. Tnese results sho~
that more dense la~ers o~ fi~er (i.e. areal weight 19u gral1là
per centimeter) can be used to filter particles ~rom the epox~
resin compositions. This filtration causes these larger
particles to lie on the surface of the ~repreg and thereafter
reside in the boundary r~sin layer that is between plies
(layers) of ~ilaments. Presence of these larger particles
between plies of filaments provides, as ~an be seen from the
results in Table 9A, grèater post impact compressive strength
to the resulting composites.
TABLE 9
GRADE 1901
;- PIC PARTICLE SIZE
15 SPOOL (KSI) PARTICLE SHAPE SMALLEST LARGEST
1 48.5 SPHERICAL 4 25
3 46.8 IRREGULAR 2.5 20
4 46.7 IRREGULAR ,1.25 25
49.4 IRREGULAR 1.25 15
6 45.7 ROUND 2.5 55
7 51.3 ROUND 5 35
~ GRADE 1452
'` PIC PARTICLE SI2E3
RUN ~ (KSI) PARTICLE SHAPE SMALLEST LARGEST
25 3-8522 38.3 SMALL SPHERICAL 1.25 10
3-8210 42.6 SMALL SPHERICAL 1.25 10
`` 3-8230 41.1 SMALL SPHERICAL 1.25 7.5
3-8232 43.4 NOT SPHERICAL 0.6 7.5
3-8237 41.5 NOT SPHERICAL 1.25 10
,1
1 IM-7 carbon fiber having an areal weight of 190 grams
per square meter.
- 2 IM-7 carbon fiber having an areal weight of 145 grams
per square meter.
3 Microns.
.
- 37 - ~32~17~
The proce~ur~s ~. tllia ~.Yampl a ~ere re~eate~ ~cept tl-
~the epoxy resin composition waa made accor~ing to t:le proce-
dures of Example 1. The average pacticle was determine~ Cro;~
the neat epoxy resin composition using the pr~cedureâ of
Example ;. Table 9B sets fortll the results.
Tf~BLE 9B
Prepreg Spool Areal Wei~ht Particle PIC
Run No. No~~9m,/m2) ~ize3 ('~si)
X3995-4 2X lg~ 33 51.4
x3987-4 2A 190 35 49.
X ~995--4 7A 145 3 3 ~8 . 3
X4048-4 3B 145 3~ 48.6
X3997-4 2B 135 34 48.1
X3997-~ 183 135 31 43.~
Table 9B illustrates that the particle size of the neat
resin is generally associated with high toughness levels.
Example 8
An epoxy resin composition like that described in
Example l is prepared using a different reactive aromatic
oligomer. This different reactive aromatic oligomer is made
- by replacing an amount o~ the bisphenol A used in manufacture
of the oligomer with sodium sulfide to yield an amine func-
tional polyarylene polyethersulfone polythioethersulfone (see
formula I in the SpeciEication). The level o the ingredients
in the epoxy resin composition was the same as in Table l and
the mixing procedure of Example 1 followed.
Photomicrographs of the cured epoxy resin composition
are taken and copies thereof are shown in Figure 6. The large,
darker circles are the infusible particles of rubber polymer.
(A portion of certain oE the infusible particles has been cut
away during sample preparation.) The other portions of the
crosslinked epoxy resin matrix exhibit phase separation yield-
; ing glassy ceosslinked phases.
. . .
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,
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- 38 _ ~ 32~
~xam;~le 9
In tnis example, an epoxy resin composition .nade
using the ~rocedures of Example 1 was made into a preprey
using IM-7 carbon fibers of Hercules Incorporated. The pre-
preg was layed up and cured into composite test samples. The
samples were tested to deter.nine various mechanical properties
as compared to composites ;nade using the thermoplastic resin
- APC-2 and AS-4 carbon fibers available from Hercules
Incorporated (Column ~). The results are reported in Table 1
below, the data in Table 10 being normalized to 57% fiDer
volume.
,
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_ 3~ _ ~32~7~
TABLE 10
~lEC'~ANI~AL ~ATA 8U~ Y
A B
IM7 AS~
Property X* X*
RT** Tensile Stren~th (ksi)400 315
RT Tensile Modulus (Plsi) 23.00 21.0
0 Com~ression Stren~th (ksi)
RT 235 230
180F 200 205
180F - Wet 160 170
2QOF 185 180
200~F - Wet 180
Short Beam Shear (ksi)
RT 14~5 15.5
180F 11.; 12.3
180F - Wet 10.3 12.4
250F 10.0 9.5
250F - ~et 8.2 7.3
`~` Open Hole Tensile (ksi)
RT 75 60
180F 69
Open Hole Compression (ksi)
RT 42 44
180F 37 38
180'F - Wet 36
CAI***(ksi) 50 44
*Average value; normalized 60% Fiber Volume.
`~ **RT - room temperature.
Compression After Impact 6.67 J/~l Impact Level.
. ~ ~
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: .
_ 4o _ 132617 g
Table 11, s~t ~orth below, sho~1s exe;~ular~ pco~erties o~
a composite o~ this invention (column A), a co~posite made
from a standard co,~ercially available epoxy resin (colu;nn ~)
and a composite made usiny the thermoplastic APC-2 (column C).
The data in column ~ of Table 11 represents values o~tained
from the composites of this invention where the epoxy resin
composition is made using procedures generally descri~ea in
Example 1~
TABLE 11
` A B C
Processing 350F Cure 350F Cure 720F Molding
T G' (C) Wet,'Dry 120/163 130/187
GIC in-lb/in2
~composite) 2.6 1,12 13.7
Gel Times (minutes
at 350F) 8-15 6-12 --
Minimum Viscosity
(poise)l 15 (139C) 6-10 (114C) --
Dynamic Gel
Temperature (F)* 340 (171C) 347 (175C) --
" Post Impact
-~ Compression (ksi)
`-~ at 1500 in-lb/in
thicknesses 532 22 45
Absorbed Moisture
(%~ 1.3 1.3 0.2
.
.
1 Varies upon heating rate (these tested at 2F/min.).
2 IM-7 carbon fiber.
Example 10
A number of epoxy resin compositions were made and
various infusible particles mixed into the compositions. The
SBR, EPDM, natural and silicone rubber particles were made by
cryrogenically freezing the rubber, grinding and then seiving
to desired particle size. The epoxy resin compositions were
,
(
1326176
- 41 -
~ormulated to provide an equal approximate voln~e of
particles and tnen used to make prepreys containiu~ carbon
fiber in the form of a plurality of tows each comprising a
multitude o~ filaments. The prepregs were layed up and cured
in the manner deascribed in Part C of Example l. The cured
samples were then tested with the results shown in Table 12
below. The thermosets all exhibited phase separated behavior.
.
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1326176
^ 42 -
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1326176
-- 43 --
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` I 1326176
-- 45 --
. ~
~o r ` oo ~D ~ CO
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`; :` , ` ` . : :
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1326~7~
- 46 -
It is especially interestiny to note tnat the inter-
laminer Eracture GIC energy is ;nuch higher for the thermo-
plastic resin as compared to the cured neat resin of this
invention but that the damage tolerance of the composites of
this invention are at least comparable to (if not higl~er
than) the damage tolerance of the thermoplastic composite.
~X
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