U.S. patent application number 11/168971 was filed with the patent office on 2006-12-28 for resin compositions with high thermoplatic loading.
Invention is credited to Cary Joseph Martin.
Application Number | 20060292375 11/168971 |
Document ID | / |
Family ID | 37567809 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060292375 |
Kind Code |
A1 |
Martin; Cary Joseph |
December 28, 2006 |
Resin compositions with high thermoplatic loading
Abstract
Uncured thermosetting resins are loaded with relatively high
amounts of solid thermoplastic resin particles to form a resin
precursor. The resin precursor is heat treated so as to produce an
uncured resin composition wherein the thermoplastic resin particles
become substantially dissolved in the thermosetting resin without
causing cure of the resin mixture. Heat treatment of highly loaded
thermosetting resins in accordance with the present invention
provides uncured resin compositions that are well suited for use in
fabricating composite structures and particularly prepreg for use
in lightning protection surface coatings.
Inventors: |
Martin; Cary Joseph;
(Livermore, CA) |
Correspondence
Address: |
HEXCEL CORPORATION
11711 DUBLIN BOULEVARD
DUBLIN
CA
94568
US
|
Family ID: |
37567809 |
Appl. No.: |
11/168971 |
Filed: |
June 28, 2005 |
Current U.S.
Class: |
428/413 ;
428/297.4; 525/523; 525/528 |
Current CPC
Class: |
B32B 27/38 20130101;
B32B 15/14 20130101; B32B 2605/18 20130101; B32B 2307/202 20130101;
C08G 59/3227 20130101; C08L 63/00 20130101; Y10T 428/24994
20150401; C08G 59/4021 20130101; C08L 2205/02 20130101; B32B
2307/558 20130101; C08L 81/06 20130101; B32B 2307/718 20130101;
C08L 81/00 20130101; B32B 27/04 20130101; B32B 5/28 20130101; B32B
15/02 20130101; C08L 63/00 20130101; B32B 27/08 20130101; B32B
15/08 20130101; Y10T 428/31511 20150401; B32B 2260/021 20130101;
B32B 2274/00 20130101; B32B 2260/046 20130101 |
Class at
Publication: |
428/413 ;
428/297.4; 525/523; 525/528 |
International
Class: |
B32B 27/38 20060101
B32B027/38; B32B 27/04 20060101 B32B027/04; C08L 63/00 20060101
C08L063/00 |
Claims
1. An uncured resin composition comprising: a thermosetting resin
component comprising one or more thermosetting resins; a curing
agent for said thermosetting resin component; and a thermoplastic
resin component comprising one or more thermoplastic resins wherein
said thermoplastic resin component is combined with said
thermosetting resin component by adding said one or more
thermoplastic resins to said one or more thermosetting resins to
form a resin precursor wherein at least one of said thermoplastic
resins is initially in the form of thermoplastic resin particles
and wherein said resin precursor is heated to a sufficient
temperature for a sufficient time to substantially dissolve said
thermoplastic resin particles without curing said thermosetting
resin to thereby form said uncured resin composition.
2. An uncured resin composition according to claim 1 wherein said
thermosetting resin component comprises one or more resins selected
from the group consisting of epoxy, bismaleimide and cyanate ester
resins.
3. An uncured resin composition according to claim 1 wherein said
resin particles comprise micronized or densified thermoplastic
resins that have a glass transition temperature that is above
200.degree. C.
4. An uncured resin composition according to claim 3 wherein said
resin particles comprise thermoplastic resins selected from the
group consisting of micronized polethersulfone, densified polyether
sulfone, micorized polyetherimide and densified polyetherimide.
5. An uncured resin composition according to claim 1 wherein said
thermoplastic resin component comprises one or more of said
thermoplastic resins that is substantially dissolved in said
thermosetting resin prior to heating of said resin precursor.
6. An uncured resin composition according to claim 5 wherein said
one or more thermoplastic resins that is substantially dissolved in
said thermosetting resin prior to heating of said resin precursor
comprises a thermoplastic resin selected from the group consisting
of polyethersulfone, polyetherimide and polyimide.
7. A prepreg designed for application to a surface of a body to
provide a surface finish for said body, said prepreg comprising: a)
an outer finish layer consisting essentially of a an uncured resin
comprising a thermosetting resin component, a curing agent for said
thermosetting resin component and a thermoplastic resin component
comprising one or more thermoplastic resins wherein said
thermoplastic resin component is combined with said thermosetting
resin component by adding said one or more thermoplastic resins to
said one or more thermosetting resins to form a resin precursor
wherein at least one of said thermoplastic resins is initially in
the form of thermoplastic resin particles and wherein said resin
precursor is heated to a sufficient temperature for a sufficient
time to substantially dissolve said thermoplastic resin particles
without curing said thermosetting resin to thereby form said
uncured resin composition; and b) a fiber layer comprising a
plurality of fibers that are impregnated with a matrix resin.
8. A prepreg according to claim 7 wherein a layer of electrically
conducting material is located between said outer finish layer and
said fiber layer.
9. A prepreg according to claim 8 wherein said electrically
conducting material is in the form of a mesh.
10. A composite material comprising a prepreg according to claim 7
that has been heated at a sufficient temperature for a sufficient
time to cure said uncured resin composition to form said composite
material.
11. A method for forming a surface finish on a body comprising the
steps of applying an uncured resin composition to the surface of
said body and curing said uncured resin composition to form a
surface finish on said body, said uncured resin composition
comprising: a thermosetting resin component comprising one or more
thermosetting resins; a curing agent for said thermosetting resin
component; and a thermoplastic resin component that comprises one
or more thermoplastic resins wherein said thermoplastic resin
component is combined with said thermosetting resin component by
adding said one or more thermoplastic resins to said one or more
thermosetting resins to form a resin precursor wherein at least one
of said thermoplastic resins is initially in the form of
thermoplastic resin particles and wherein said resin precursor is
heated to a sufficient temperature for a sufficient time to
substantially dissolve said thermoplastic resin particles without
curing said thermosetting resin to thereby form said uncured resin
composition.
12. A method for forming a surface finish on a body according to
claim 11 wherein said thermosetting resin component comprises one
or more resins selected from the group consisting of epoxy,
bismaleimide and cyanate ester resins.
13. A method for forming a surface finish on a body according to
claim 11 wherein said resin particles comprise micronized or
densified thermoplastic resins that have a glass transition
temperature that is above 200.degree. C.
14. A method for forming a surface finish on a body according to
claim 11 wherein said thermoplastic resin component comprises one
or more of said thermoplastic resins that is substantially
dissolved in said thermosetting resin prior to heating of said
resin precursor.
15. A method for forming a surface finish on a body according to
claim 11 which includes the additional step of making said surface
finish electrically conductive by combining an electrically
conducting material with said uncured resin composition.
16. A method for forming a surface finish on a body according to
claim 12 wherein said electrically conducting material is a
metal.
17. A method for forming a surface finish on a body according to
claim 12 wherein said electrically conducting material is in the
form of a mesh.
18. A method for forming a surface finish on a body according to
claim 11 wherein said uncured resin composition is in the form of a
prepreg.
19. A method for forming a surface finish on a body according to
claim 18 wherein said prepreg comprises a layer of electrically
conducting mesh that is located between an outer finish layer and a
fiber layer wherein said electrically conducting mesh is
impregnated with said uncured resin.
20. A method for forming a surface finish on a body according to
claim 11 wherein said body is located on an aircraft.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally thermosetting resin
compositions that include varying amounts of one or more
thermoplastic resins, which provide elastomeric toughening of the
resin. More particularly, the present invention involves
compositions and methods wherein the amount of thermoplastic resin
in uncured thermosetting resin compositions is maximized to provide
desired levels of resin toughening. These relatively high levels of
thermoplastic loading are achieved without increasing the viscosity
and/or tack of the uncured composition to levels that would render
them unsuitable for handling and processing.
[0003] 2. Description of Related Art
[0004] Thermosetting resins are popular materials that are used in
the fabrication of a wide variety of composite materials. Epoxy
resins, bismaleimide resins and cyanate ester resins are examples
of popular thermosetting resins. Composite materials typically
include one or more resins that are combined with fibers or other
support materials to form relatively lightweight structures that
are relatively strong. In addition to their wide spread use as a
matrix material in composites, thermosetting resins have also been
used to provide a surface layer or finish coating on the exterior
surface of composite materials. Composite materials and surface
coatings or layers that utilize thermosetting resins have been
widely been used in the aerospace industry where their combination
of lightweight and structural strength is particularly
desirable.
[0005] In many situations it is desirable to modify thermosetting
resins by adding one or more thermoplastic resins to the
thermosetting resin mix. The use of thermoplastic resins provides
an additional degree of flexibility or elasticity to the
thermosetting resin which increases the toughness of the final
cured resin product. Such thermoplastic toughened resins have been
used both as resin matrix materials in combination with fibers and
as coatings where a particularly tough resin is desired. Typical
thermoplastic resins that have been used as toughening agents
include polyethersulfone, polyetherimide and certain types of nylon
and other thermoplastic polymers that can be dissolved in the
thermosetting resin prior to ultimate cross-linking and cure.
[0006] In general, the degree of elastomeric toughening provided by
the thermoplastic resin is related directly to the amount of
thermoplastic resin that is incorporated into the thermosetting
resin mixture. Accordingly, it is desirable in many situations to
add as much thermoplastic resin as possible to achieve maximum
toughening of the final cured resin. High thermoplastic loading is
particularly desirable for thermosetting resins that are used as
surface coatings on aircraft structures where extremely smooth and
strong surfaces are desired in order to enhance the aerodynamics
and appearance of the structure.
[0007] The amount of thermoplastic resins that can be added to
thermosetting resin mixtures is limited by a number of practical
considerations relating to processing of the uncured resin. For
example, the viscosity of the uncured toughened resin must be kept
low enough that the resin can be fabricated into thin films and/or
used to impregnate or coat various materials. In addition, the tack
of the resin must also be kept within certain limits that vary
depending upon the particular fabrication process. For example, the
resin cannot be fabricated into films or handled during fabrication
of multi-component structures if the uncured resin is too tacky.
High viscosity and high tack is a particular problem when uncured
toughened resins are used in the fabrication of surface coatings.
High viscosity and high tack cause handling problems that lead to
surface imperfections that have a deleterious effect on appearance
and may an adverse effect on aerodynamics. As a result, the amount
of thermoplastic resin that is loaded into thermosetting resins for
use in surface coatings is typically below 25 weight percent.
[0008] The thermosetting and thermoplastic resins that are used to
make composite materials do not conduct electricity. The most
common fibers used in composite materials (such as glass, ceramics
and graphite) are not good conductors of electricity. This is a
particular problem for aircraft because they operate in an
environment where they may be exposed to lightning. It is well
known that a lightning strike on an aircraft that includes
substantial amounts of composite material may result in
catastrophic failure of the aircraft. In order to protect against
such catastrophic events, the composite material used in many
aircraft are modified to include "lightning protection". Lightning
protection typically involves adding one or more layers of
conductive material to the composite materials used to make the
aircraft. The conductive layers are generally located on or near
the exterior surfaces of the composite portions of the aircraft.
The conductive materials used for lightning protection are usually
thin films of metal (or other conductive material) or metallic mesh
or fabric that is relatively lightweight.
[0009] There are many different ways to add lightning protection to
the surface of a composite structure. A common procedure involves
preparing a "prepreg" that is lightning protected and incorporating
the prepreg into the surface of the composite structure. "Prepreg"
is a term used in the composite industry to describe a composite
precursor wherein one or more layers of fabric have been
impregnated with uncured resin. The resulting pre-impregnated
structure is typically stored for later use in fabricating the
final cured composite structure. The preparation and use of
prepregs is particularly desirable in the fabrication of aircraft
and other critical structures because it allows the manufacturer to
carefully control the amount of resin that is combined with a given
amount of fabric. As a result, the final properties of the cured
composite structure can be carefully controlled. Prepreg that is
suitable for use as a lightning protection surface coating will
typically include an electrically conductive layer located between
a layer of surface finish resin and a supporting layer of fabric
that has been pre-impregnated with resin. Examples of lightning
protection prepreg and composites are set forth in the following
U.S. Pat. Nos. 5,225,265; 5,470,413; 5,370,921 and 5,397,618.
[0010] Prepregs that are intended for use in providing lightning
protection for composite structures should have certain desirable
characteristics. The prepreg should be as light as possible to
avoid adding unnecessary weight to the aircraft. The prepreg should
be compatible with the underlying prepregs or other pre-cure
composite materials used to make the final composite structure. The
prepreg should also be relatively easily to handle and the surface
finish provided by the cured prepreg should be relatively free of
surface flaw or imperfections.
SUMMARY OF THE INVENTION
[0011] In accordance with the present invention, methods and
compositions are provided wherein uncured thermosetting resins are
initially loaded with relatively high amounts of solid
thermoplastic resin particles to form resin precursors. These resin
precursors are then heat treated so as to produce uncured resin
compositions wherein the thermoplastic resin particles become
substantially dissolved in the thermosetting resin without causing
cure of the resin mixture. It was discovered that the heat
treatment of highly loaded thermosetting resins in accordance with
the present invention provides uncured resin compositions that are
well suited for use in fabricating composite structures and
particularly prepreg for use in lightning protection surface
coatings.
[0012] The uncured resin compositions of the present invention
include a thermosetting resin component that is made up of one or
more thermosetting resins, a curing agent for the thermosetting
resin(s) and a thermoplastic resin component that includes one or
more thermoplastic resins. The thermoplastic resin component is
combined with the thermosetting resin component by adding the
thermoplastic resin(s) to the thermosetting resin(s) to form an
uncured resin precursor. As a feature of the present invention, at
least one of the thermoplastic resins is initially in the form of
thermoplastic resin particles that are substantially dissolved in
the thermosetting resin by heating the resin precursor for a
sufficient time to dissolve the particles without causing curing of
the resin precursor. The resulting uncured resin composition is
highly loaded with thermoplastic resin while still retaining
viscosity and tack properties that are appropriate for use in
manufacturing prepreg and other composite materials.
[0013] The resin precursor may include thermoplastic resins that
are only in particulate form or the precursor may include
combinations of thermoplastic resin particles and thermoplastic
resins that have been dissolved in the thermosetting resin. As a
feature of the present invention, the viscosity and loading levels
of the resin precursor can be controlled by varying the
combinations of particulate and dissolved thermoplastic resins that
are present in the resin precursor.
[0014] The uncured resin compositions in accordance with the
present invention may be used in the fabrication of a wide variety
of composite structures. The uncured resin compositions are well
suited for use in fabricating surface finishes for composite
structures where light weight, high toughness and good surface
finishes are required. The uncured compositions are particularly
well suited for use in fabrication prepreg and other uncured
composite structures that are used to form surface finishes that
also provide lightning protection.
[0015] The above-described and many other features and attendant
advantages of the present invention will become better understood
by reference to the following detailed description when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
[0016] The drawing is a diagrammatic representation an exemplary
method for making a lightning protected composite material using an
exemplary prepreg in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The uncured resin compositions of the present invention
basically include a thermosetting component, a curing agent and a
thermoplastic component. The thermosetting component preferably
includes one or more resins belonging to the group of thermosetting
resins that are widely used in the aerospace industry. Exemplary
thermosetting resins include epoxy, cyanate ester, and bismaleimide
resins. Exemplary epoxy and cyanate ester resins include
glycidylamine type epoxy resins, such as triglycidyl-p-aminophenol,
tetraglycidyldiaminodiphenyl-methane; glycidyl ether type epoxy
resins, such as bisphenol A type epoxy resins, bisphenol F type
epoxy resins, bisphenol S type epoxy resins, phenol novolak type
epoxy resins, cresol novolak type epoxy resins and resorcinol type
epoxy resins; cyanate esters, such as 1,1'-bis(4-cyanatophenyl)
ethane (AroCy L-10, available from Huntsman, Inc., Brewster, N.Y.),
1,3-Bis (4-cyanateophenyl-1-1-(1-methylethylidene) benzene (RTX366,
available from Huntsman, Inc., Brewster, N.Y.). Epoxy resins are
preferred.
[0018] The epoxy may be composed of trifunctional epoxy,
difunctional epoxy and a wide variety of combinations of
trifunctional and difunctional epoxies. Tetrafunctional epoxies may
also be used. Especially preferred epoxy blends include a mixture
of trifunctional epoxy and a difunctional bis-F epoxy. Exemplary
trifunctional epoxy include triglycidyl p-aminophenol and
N,N-Diglycidyl-4-glycidyloxyaniline (MY-0510 or MY-0500 available
from Huntsman, Inc., Brewster, N.Y.). Exemplary difunctional
epoxies which may be used in the resin include Bis-F epoxies, such
as GY-281, LY-9703 and GY-285 which are available from Huntsman,
Inc., Brewster, N.Y.). Bis-A epoxies, such as GY-6010 (Huntsman,
Inc., Brewster, N.Y.) and DER 331 (Dow Chemical, Midland, Mich.)
are suitable Bisphenol-A type epoxies and may also be used. An
exemplary tetrafunctional epoxy is tetraglycidyl diaminodiphenyl
methane (MY-721, MY-720 and MY-9512 available from Huntsman, Inc.,
Brewster, N.Y.).
[0019] Other suitable epoxies include phenol novolak type epoxy,
cresol novolak epoxy and resorcinol type epoxy. Preferred bis-F
epoxies include GY281 and GY285 which are available from Huntsman,
Inc., Brewster, N.Y.
[0020] The curing agent is preferably an amine curing agent.
Exemplary curing agents include dicyandiamide,
3,3-diaminodiphenylsulfone (3,3-DDS), amino or glycidyl-silanes
such as 3-amino propyltriethoxysilane, CuAcAc/Nonylphenol (1/0.1),
4,4'-diaminodiphenylsulfone (4,4'-DDS),
4,4'-methylenebis(2-isopropyl-6-methylaniline), e.g., Lonzacure
M-MIPA (Lonza Corporation, Fair Lawn, N.J.),
4,4'-methylenebis(2,6-diisopropylaniline), e.g., Lonzacure M-DIPA
(Lonza Corp., Fair Lawn, N.J.). Dicyandiamide and 3,3-DDS are
preferred curative agents. Especially preferred are combinations of
3,3-DDS and dicyandiamide.
[0021] The thermoplastic component preferably includes one or more
thermoplastic resins. The thermoplastic resins are added to the
thermosetting resin and curing agent to form a resin precursor
wherein at least one of the thermoplastic resins is in the form of
thermoplastic resin particles. The resin precursor will have
various initial properties, including viscosity, tack, and drape,
heat of reaction and uncured glass transition temperature. The
uncured resin composition is formed by heating the resin precursor
to a dissolution temperature for a sufficient time to substantially
dissolve all of the resin particles without curing the
thermosetting resin(s). An important aspect of the present
invention is that the heating times and dissolution temperatures be
selected to provide an uncured resin composition where substantial
dissolving of the thermoplastic resin particles has taken place
without curing of the thermosetting resin(s).
[0022] For the purposes of this specification, particles that have
lost at least 80 weight percent of their original particle weight
are considered to be substantially dissolved. Preferably, the
particle will have lost at least 90 weight percent of the original
particle weight. Most preferred is where 95 weight percent or more
of the particle has dissolved. The term "without curing the
thermosetting resin(s)" means that resin precursor and the
resulting uncured composition are maintained under conditions such
that the heat of reaction, and other measures of curing, such as
the number of functional groups per mass or mole of resin, do not
change to any appreciable degree. In general, the change in these
properties that reflect the degree of curing should not change by
more than 10-15 percent during the dissolution step.
[0023] A relatively small amount of curing is acceptable, but to
the extent possible, the dissolution temperature that the resin
precursor is subjected to should be sufficiently high to dissolve
the thermoplastic particles, while at the same time being
sufficiently below the cure temperature of the thermosetting resin
to avoid curing. It should be noted that the properties of the
resin precursor, such as viscosity and tack, will usually change
significantly during the heat treatment step without any curing of
the thermosetting resin taking place. For example, during the heat
treatment step, the tack of the resin precursor can be
substantially reduced such that the resulting uncured composition
is essentially tack-free. The color of the resin precursor will
typically change from an opaque white to a translucent amber-brown.
In addition, the viscosity of the resin precursor will
substantially increase during the heat treatment step. Accordingly,
it is preferred that the resin precursors be formed into films or
combined with fibers to form prepregs or other structures prior to
the heat treatment step.
[0024] The thermoplastic resins may be added to the thermosetting
resin to form resin precursors that include varying degrees of
particulate and dissolved thermoplastic resin. It is not required
that all of the thermoplastic resin in the resin precursor be
present in particulate form. The presence of some dissolved
thermoplastic resin in the resin precursor is preferred. The amount
of dissolved thermoplastic resin in the resin precursor should be
about 30 percent or less by weight of the overall resin precursor
and preferably between 5 and 25 percent by weight with 10 to 20
weight percent being most preferred. The amount of particulate
thermoplastic should preferably be between 15 and 50 weight
percent. The amount of total thermoplastic loaded into the resin
precursor will range from 20 to 60 weight percent.
[0025] Exemplary thermoplastic resins that are for dissolution in
the initial resin precursor include thermoplastic polyetherimides
such as ULTEM.RTM. 1000 P which is available from General Electric
(Pittsfield, Mass.); micronized polyethersulfone such as 5003 P,
which is available from Sumitomo Chemical Co., Ltd. (Osaka, Japan);
HRI-1, which is available from Hexcel Corp. (Dublin, Calif.); and
polyimide MATRIMID.RTM. 9725 or 5218, which are available from
Huntsman, Inc. (Brewster, N.Y.). ULTEM.RTM. 1000 P and micronized
PES are preferred. Micronized PES is especially preferred.
Micronized PES refers to PES particles which have a rough surface
configuration which is produced by grinding the particles or other
abrasive techniques of manufacture which are known in the art.
Micronized PES particles may also be made by spraying and drying
procedures which are also known in the art. Micronized PES
particles are preferably less than 120 microns in size. Especially
preferred are particles under 50 microns in size with a range of 10
to 25 microns being particularly preferred.
[0026] Densified polyethersulfone (PES) and densified
polyetherimide particles may be used as suitable thermoplastic
particles. Densified PES particles are preferred. The densified
polyethersulfone (PES) particles are preferably made in accordance
with the teachings of U.S. Pat. No. 4,945,154, the contents of
which is hereby incorporated by reference. The average particle
size of the PES particles range from 1 to 150 microns. Average
particle sizes of 1 to 50 microns are preferred and average
particle sizes of 10 to 25 microns are particularly preferred. It
is preferred that the glass transition temperature (Tg) for the
particles be above 200.degree. C.
[0027] The amount and type of thermoplastic particles that are
added to the epoxy resin mixture and the order in which they are
added may be varied provided that the viscosity of the final resin
precursor is between 20,000 and 100,000 poise when said viscosity
is measured at 30.degree. C. The preferred viscosity range is
30,000 to 90,000 poise. In a preferred embodiment, the micronized
thermoplastic particles are added first and dissolved. Then,
densified thermoplastic particles are added to form a resin
precursor that includes both dissolved and particulate
thermoplastic. As mentioned above, overall thermoplastic loading
(dissolved and particulate) of the resin precursor should be
between 20 and 60 weight percent. The viscosity of the heat-treated
resin precursor increases substantially during the heat treatment
process. The precise amount of increase in viscosity depends upon
the particulars of the formulation.
[0028] In a preferred exemplary procedure, the uncured resin is
made by first mixing the epoxy components together and then slowly
adding the desired amount of micronized thermoplastic resin
particles. Micronized polyetherimide or micronized PES particles
are preferred. The resulting mixture is heated to around
130.degree. C. and mixed for a sufficient time to substantially
dissolve the micronized thermoplastic particles. Once the
micronized thermoplastic particles are dissolved, the mixture is
cooled to around 75.degree. C. A suitable aromatic amine curing
agent and the desired amount of densified PES particles are then
added to the mixture to form the resin precursor. The resin
precursor should be kept at temperatures below about 70-75.degree.
C. while the curative agent and densified PES particles are being
mixed into the resin.
[0029] Once formed, the resin precursor may be impregnated into
fabric/fibers to form prepreg, used to form films or applied to any
number of surfaces or structures. The resin precuror is then heated
at the dissolution temperature for a sufficient time to dissolve
the densified PES particles and form an uncured resin. Typical
dissolution temperatures are from 110 to 140.degree. C. with
dissolution temperatures of about 125.degree. C. being preferred.
The heat treatment times will vary depending upon the dissolution
temperature, particular thermoplastics and thermosets being used as
well as the amount of pariculate loading. The amount of time
required to convert a specific resin precursor to the uncured resin
can be determined by routine experimentation. In general, heat
treatment times on the order of a few minutes up to 1 hour are
sufficient. The final uncured resin, along with any fabric/fiber or
other supporting component is then cooled to room temperature. The
final uncured resin, whether it is in the form of a film or the
resin matrix in a prepreg or as part of some other structure, can
then be stored for later use. Alternatively, the uncured resin and
associated components, if any, may be used immediately by applying
the uncured resin to a desired structure, if necessary, and then
curing the uncured resin in accordance with conventional curing
procedures for thermosetting resins that are loaded with
thermoplastic material.
[0030] An exemplary method for making an electrically conductive
composite material using the precursor resin in accordance with the
present invention is shown diagramatically in the drawing. The
composite is initially composed of a layer of precursor resin 12,
which is located on top of a layer of electrically conductive
material 14, such as expanded aluminum foil, wire mesh or other
type of film that is used for lightning protection of composites.
If the electrically conductive material 14 is porous, as in the
case of fine wire meshes, it is preferred that the conductive
material in layer 14 be impregnated with or otherwise include the
precursor resin.
[0031] The electrically conductive layer 14 is in turn located on a
prepreg layer 16 that includes fibers and a resin matrix. The resin
matrix in layer 16 is preferably composed of the precursor resin,
but may be another compatible type of resin, if desired. The fibers
that are used in the prepreg layer 16 can be any of the fiber
materials that are used to form composite laminates. Exemplary
fiber materials include glass, aramid, carbon, ceramic and hybrids
thereof. The fibers may be woven, unidirectional or in the form of
random fiber mat. Woven carbon fibers are preferred, such as plain,
harness satin, twill and basket weave styles that have areal
weights from 80-600 grams per square meter (gsm), but more
preferably from 190-300 gsm. The carbon fibers can have from
1,000-40,000 filaments per tow, but more preferably 3,000-12,000
filaments per tow. All of which are commercially available. Similar
styles of glass fabric may also be used with common types being
6080 and 7781 glass fabric. When unidirectional constructions are
used, typical ply-weights are 150 gsm for carbon and 250 gsm for
glass.
[0032] In accordance with the present invention, the composite
structure 10 is heat-treated for a sufficient time and at a
sufficient dissolution temperature, as previously described, to
form an uncured electrically conductive resin composite 20 which
includes a layer of uncured resin 22, a layer of lightning
protection material 24 that may also include uncured resin in
accordance with the present invention and a prepreg layer 26 that
includes fibers and an uncured resin matrix. The uncured composite
20 can be stored for final application and curing at a later time,
if desired.
[0033] An exemplary use for the uncured composite 20 is shown in
the drawing where the uncured composite 20 is placed on a structure
30 and then cured in accordance with known procedures for curing
thermosetting resins that are loaded with thermoplastic material to
form the final cured composite as shown at 40. The final cured
composite 40 includes a cured outer resin layer 42, lightning
protection layer 44, cured prepreg layer 46 and the underlying
structure 50. The underlying structure 50 can be a prepreg or other
uncured structure that is cured simultaneously with the uncured
resin in layers 22, 24 and 26. The uncured structure 30 (cured
structure 50), on which the electrically conductive uncured
composite 20 (cured composite 40) is located, is shown as a single
layer for simplicity. Typically, structure 30 is only the surface
layer of an underlying structure, such as an aircraft wing, tail
section and/or fuselage.
EXAMPLES OF PRACTICE ARE AS FOLLOWS
Example 1
[0034] A resin precursor was made having the following
formulation:
[0035] 27.0 weight percent MY-0510
(N,N-Diglycidyl-4-glycidyloxyaniline)
[0036] 24.9 weight percent GY285 (bis-F epoxy)
[0037] 15.8 weight percent 3,3'-Diaminodiphenylsulfone
[0038] 1.3 weight percent Dicyandiamide
[0039] 13.5 weight percent micronized Polyethersulfone (PES)
[0040] 17.5 weight percent densified Polyethersulfone (PES)
[0041] Precursor resin formulations in accordance with this example
may also be made wherein the amounts of MY-510, GY281 and 3,3-DDS
are varied by up to .+-.15%. Also, the amounts of both types of PES
may be varied by as much as .+-.40%. The amount of dicyandiamide
may be varied by up to .+-.50%. The densified PES was made from PES
5003 P, which is available from Sumitomo Chemical Co. Ltd. (Osaka,
Japan). The PES was densified in accordance with U.S. Pat. No.
4,945,154. Average particle size was 10-25 microns with no more
than 13 weight percent smaller than 5 microns and no more than 4
weight percent greater than 40 microns.
[0042] 24.9 parts by weight of GY285 and 6.0 parts by weight of
MY0510 were mixed in a resin kettle and heated, with stirring, to
65.degree. C. Once this temperature is attained, 13.5 parts by
weight micronized PES 5003 P is added to the resin kettle. The
mixture is then heated to 128.+-.2.degree. C. and held at this
temperature for 75 minutes. At the end of 75 minutes, heating is
removed and 21 parts by weight of MY0510 is added to the kettle.
Stirring is continued as the mixture cools to 65.degree. C. Then,
15.8 parts of 3,3-DDS is added and mixed for 15 minutes. 1.3 parts
of dicyandiamide is then added and the mixture stirred for 5
minutes at 65.degree. C. Finally, 17.5 parts of densified PES is
added and stirred in for 10 minutes to form the resin precursor.
The resin precursor was heated to 74.degree. C. and coated on
release paper by reverse-roll coater at about to form a film
containing 245 gsm. The film was then heated for 3 minutes at
125.degree. C. to form the uncured resin composition. During this
time, the densified PES completely dissolved, resulting in an
uncured resin film containing about 31 weight percent dissolved
PES. This dissolution resulted in a color change from opaque white
to translucent amber-brown. The tack was also substantially reduced
to an essentially tack free state after the heat treatment and the
viscosity increased substantially.
Example 2
[0043] The same combination of thermosetting resins and curing
agents as set forth in Example 1 were used to make resin precursors
that contained 25, 37.5 and 50 weight percent PES. The PES was
added in the same manner as Example 1 except that the differences
in overall PES loading was accounted for by varying the amount of
densified PES that was added. The amount of micronized PES that was
initially dissolved was kept constant at 13.5 weight percent. Films
of resin precursor were made in the same manner as Example 1. The
films were subjected to the same heat treatment step with the same
dissolution process being observed. The resulting uncured resin
films underwent the same color change from opaque white to
translucent amber-brown. The tack of the uncured resin films was
also substantially less than the resin precursor films and the
final viscosity of the uncured resin films was substantially
higher.
Example 3
[0044] A three layer uncured electrically conductive composite
material as shown in the drawing was made as follows:
[0045] A resin precursor resin film 12 was prepared according to
Example 1. The film 12 was combined with an expanded aluminum foil
14 and a prepreg 16 that was composed of 6080-glass fabric (48 gsm)
and resin precursor (32 gsm) that was prepared as described in
Example 1. The resulting lay-up 10 was heat treated for 5 minutes
at 110.degree. C. in order to substantially dissolve the PES
particles without curing the 1-up. The resulting uncured
electrically conductive composite structure 20 had substantially
reduced tack.
[0046] The uncured composite structure 20 was applied as a
surfacing layer to a number of composite structures that were each
composed of 8 plies of unidirectional prepreg. The unidirectional
prepreg contained unidirectional carbon fibers in an uncured epoxy
resin matrix. The orientation of the unidirectional plies was -45,
90, 45 and 0. Upon final curing at 179.degree. C. for 120 minutes,
the uncured composite structure 20 was found to provide a good
(i.e. smooth and defect free) surface finish. For comparison,
lay-ups 10 that were not heat treated in accordance with the
present invention were applied directly as a surfacing layer to the
same composite structures and cured under the same conditions. The
resulting surface finish was more pitted than the surface finish
obtained using the heat-treated precursor resin film in accordance
with the present invention.
[0047] Having thus described exemplary embodiments of the present
invention, it should be noted by those skilled in the art that the
within disclosures are exemplary only and that various other
alternatives, adaptations and modifications may be made within the
scope of the present invention. Accordingly, the present invention
is not limited by the above-preferred embodiments, but is only
limited by the following claims.
* * * * *