U.S. patent application number 10/642325 was filed with the patent office on 2005-02-24 for curable compositions for advanced processes, and products made therefrom.
This patent application is currently assigned to HENKEL LOCTITE CORPORATION. Invention is credited to Lehmann, Stanley L., Li, Wei Helen, Wong, Raymond S..
Application Number | 20050042961 10/642325 |
Document ID | / |
Family ID | 34193644 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050042961 |
Kind Code |
A1 |
Lehmann, Stanley L. ; et
al. |
February 24, 2005 |
Curable compositions for advanced processes, and products made
therefrom
Abstract
Curable compositions, such as benzoxazine-based ones, are useful
in applications within the aerospace industry, such as for example
as a heat curable composition for use as a matrix resin in advanced
processes, such as resin transfer molding, vacuum assisted transfer
molding and resin film infusion, and their use in such advanced
processes form the basis of the present invention.
Inventors: |
Lehmann, Stanley L.;
(Martinez, CA) ; Li, Wei Helen; (San Ramon,
CA) ; Wong, Raymond S.; (San Ramon, CA) |
Correspondence
Address: |
HENKEL LOCTITE CORPORATION
1001 Trout Brook Crossing
Rocky Hill
CT
06067
US
|
Assignee: |
HENKEL LOCTITE CORPORATION
|
Family ID: |
34193644 |
Appl. No.: |
10/642325 |
Filed: |
August 18, 2003 |
Current U.S.
Class: |
442/172 ;
106/38.22; 264/35; 442/175; 442/178; 442/179; 442/180 |
Current CPC
Class: |
C08G 12/08 20130101;
C08L 65/00 20130101; Y10T 442/2992 20150401; C08G 59/4014 20130101;
C08G 59/5046 20130101; C08L 2666/02 20130101; C08L 65/00 20130101;
Y10T 442/2951 20150401; Y10T 442/2926 20150401; Y10T 442/2984
20150401; C08G 61/12 20130101; Y10T 442/2975 20150401; Y10T 442/20
20150401 |
Class at
Publication: |
442/172 ;
264/035; 106/038.22; 442/175; 442/178; 442/179; 442/180 |
International
Class: |
B32B 017/02; B32B
017/04 |
Claims
What is claimed is:
1. A resin transfer molding process, steps of which comprise: (a)
providing a heat curable composition into a closed mold containing
a preform; (b) exposing the interior of the mold to a first
elevated temperature and elevated pressure sufficient to wet the
preform with the heat curable composition; and (c) curing the heat
curable composition-impregnated preform within the mold at a second
elevated temperature to form a resin transfer molded product,
wherein the heat curable composition comprises (i) a benzoxazine
component.
2. The resin transfer molding process of claim 1, wherein the heat
curable composition further comprises (ii) a toughener component
comprising acrylonitrile-butadiene co-polymer having secondary
amine terminal groups.
3. The resin transfer molding process of claim 1, wherein the heat
curable composition further comprises: (ii) an epoxy or episulfide
component; (iii) optionally, one or more of an oxazoline component,
a cyanate ester component, a phenolic component, and a thiophenolic
component; (iv) optionally, an acrylonitrile-butadiene co-polymer,
a polyimide component, and a polyimide/siloxane component; and (v)
optionally, a curative.
4. The resin transfer molding process of claim 1, wherein the heat
curable composition has a viscosity in the range of 10 to 3000
centipoise at the resin injection temperature.
5. The resin transfer molding process of claim 1, wherein the time
within which the viscosity of the heat curable composition
increases by 100% under the process conditions is in the range of 1
to 10 hours at the injection temperature.
6. The resin transfer molding process of claim 1 wherein the
plurality of fabric plies or unidirectional plies comprises fibers
selected from glass, carbon, aramid and ceramics.
7. A resin transfer molded product made by the process of claims
1-6.
8. A resin transfer molding preform comprising: (a) a plurality of
fabric plies or unidirectional plies and (b) a heat curable binder
composition, tacked to the plurality of fabric plies or
unidirectional plies, wherein the heat curable binder composition
comprises (i) a benzoxazine component.
9. The resin transfer molding preform of claim 8, wherein the heat
curable binder composition further comprises (ii) a toughener
component comprising acrylonitrile-butadiene co-polymer having
secondary amine terminal groups.
10. The resin transfer molding preform of claim 8, wherein the heat
curable binder composition further comprises: (ii) an epoxy or
episulfide component; (iii) optionally, one or more of an oxazoline
component, a cyanate ester component, a phenolic component, and a
thiophenolic component; (iv) optionally, an acrylonitrile-butadiene
co-polymer, a polyimide component, and a polyimide/siloxane
component; and (v) optionally, a curative.
11. The resin transfer molding preform of claim 8, wherein the heat
curable binder composition further comprises optionally, a spacer
selected from the group consisting of particles constructed of
thermoplastics, rubbers, metals, carbon, core shell, ceramics and
combinations thereof.
12. The resin transfer molding preform of claim 8, wherein the
plurality of fabric plies or unidirectional plies comprises fibers
selected from glass, carbon, aramid and ceramics.
13. A binder composition comprising a solid benzoxazine component,
which is partially cured by exposure to elevated temperature
conditions over time sufficient to increase the melting point
higher than the temperature at which a matrix resin composition is
to be infused into a preform and lower than the point at which the
partially cured binder composition and the matrix resin composition
are miscible.
14. The binder composition of claim 13, further comprising a spacer
selected from the group consisting of particles constructed of
thermoplastics, rubbers, metals, carbon, core shell, ceramics and
combinations thereof.
15. The binder composition of claim 13, further comprising a
toughener component comprising acrylonitrile-butadiene co-polymer
having secondary amine terminal groups.
16. The binder composition of claim 13, further comprising: an
epoxy or episulfide component; optionally, one or more of an
oxazoline component, a cyanate ester component, a phenolic
component, and a thiophenolic component; optionally, an
acrylonitrile-butadiene co-polymer, a polyimide component, and a
polyimide/siloxane component; and optionally, a curative.
17. A vacuum assisted resin transfer molding process, steps of
which comprise: (a) providing a preform into a mold; (b) providing
a heat curable composition into the mold under a first elevated
temperature and under vacuum for a time sufficient to allow the
composition to wet the preform; and (c) exposing the mold
containing the composition wetted-preform to a second elevated
temperature while under vacuum sufficient to cure the heat curable
composition-wetted preform within the mold to form a resin transfer
molded product, wherein the heat curable composition comprises (i)
a benzoxazine component.
18. The vacuum assisted resin transfer molding process of claim 17,
wherein after providing the preform a dispersing medium is provided
thereover.
19. The vacuum assisted resin transfer molding process of claim 17,
wherein the heat curable composition further comprises (ii) a
toughener component comprising acrylonitrile-butadiene co-polymer
having secondary amine terminal groups.
20. The vacuum assisted resin transfer molding process of claim 17,
wherein the heat curable composition further comprises: (ii) an
epoxy or episulfide component; (iii) optionally, one or more of an
oxazoline component, a cyanate ester component, a phenolic
component, and a thiophenolic component; (iv) optionally, an
acrylonitrile-butadiene co-polymer, a polyimide component, and a
polyimide/siloxane component; and (v) optionally, a curative.
21. The vacuum assisted resin transfer molding process of claim 17,
wherein the heat curable composition has a viscosity in the range
of 10 to 2000 centipoise at transfer molding temperature.
22. The vacuum assisted resin transfer molding process of claim 17,
wherein the time within which the viscosity of the heat curable
composition increases by 100% under the process conditions is in
the range of 1 to 10 hours at the resin transfer temperature.
23. The vacuum assisted resin transfer molding process of claim 17,
wherein the preform comprises fibers selected from glass, carbon,
aramid and ceramics.
24. A vacuum assisted resin transfer molded product made by the
process of claims 17-23.
25. A vacuum assisted resin transfer molding preform comprising:
(a) a plurality of fabric plies or unidirectional plies and (b) a
heat curable binder composition, tacked to the plurality of fabric
plies or unidirectional plies, wherein the heat curable binder
composition comprises (i) a benzoxazine component.
26. The vacuum assisted resin transfer molding preform of claim 25,
wherein the heat curable binder composition further comprises (ii)
a toughener component comprising acrylonitrile-butadiene co-polymer
having secondary amine terminal groups.
27. The vacuum assisted resin transfer molding preform of claim 25,
wherein the heat curable binder composition further comprises: (ii)
an epoxy or episulfide component; (iii) optionally, one or more of
an oxazoline component, a cyanate ester component, a phenolic
component, and a thiophenolic component; (iv) optionally, an
acrylonitrile-butadiene co-polymer, a polyimide component, and a
polyimide/siloxane component; and (v) optionally, a curative.
28. The vacuum assisted resin transfer molding preform of claim 25,
wherein the heat curable binder composition further comprises
optionally, a spacer selected from the group consisting of
particles constructed of thermoplastics, rubbers, metals, carbon,
core shell, ceramics and combinations thereof.
29. The vacuum assisted resin transfer molding preform of claim 25,
wherein the plurality of fabric plies or unidirectional plies
comprises fibers selected from glass, carbon, aramid and
ceramics.
30. A binder composition comprising a solid benzoxazine component,
which is partially cured by exposure to elevated temperature
conditions over time sufficient to increase the melting point
higher than the temperature at which a matrix resin composition is
to be infused into a preform and lower than the point at which the
partially cured binder composition and the matrix resin composition
are miscible.
31. The binder composition of claim 30, further comprising a spacer
selected from the group consisting of particles constructed of
thermoplastics, rubbers, metals, carbon, core shell, ceramics and
combinations thereof.
32. The binder composition of claim 30, further comprising a
toughener component comprising acrylonitrile-butadiene co-polymer
having secondary amine terminal groups.
33. A resin film infusion process, steps of which comprise: (a)
providing a preform into a closed mold containing a heat curable
composition in film form; (b) exposing the interior of the mold to
a first elevated temperature and optionally vacuum, while the
exterior of the mold is exposed to an elevated pressure, for a time
sufficient to infuse the preform with the heat curable composition;
and (c) curing the heat curable composition-infused preform within
the mold at a second elevated temperature to form a resin transfer
molded product, wherein the heat curable composition comprises (i)
a benzoxazine component.
34. The resin film infusion process of claim 33, wherein the heat
curable composition further comprises (ii) a toughener component
comprising acrylonitrile-butadiene co-polymer having secondary
amine terminal groups.
35. The resin film infusion process of claim 33, wherein the heat
curable composition further comprises: (ii) an epoxy or episulfide
component; (iii) optionally, one or more of an oxazoline component,
a cyanate ester component, a phenolic component, and a thiophenolic
component; (iv) optionally, an acrylonitrile-butadiene co-polymer,
a polyimide component, and a polyimide/siloxane component; and (v)
optionally, a curative.
36. The resin film infusion process of claim 33, wherein the heat
curable composition has a viscosity in the range of 10 to 5000
centipoise at the infusion temperature.
37. The resin film infusion process of claim 33, wherein the time
within which the viscosity of the heat curable composition
increases by 100% under the process conditions is in the range of 1
to 10 hours at the infusion temperature.
38. The resin film infusion process of claim 33, wherein the
preform comprises fibers selected from glass, carbon, aramid and
ceramics.
39. A resin film infused product made by the process of claims
33-38.
40. The resin transfer molding process of claim 1, wherein the
benzoxazine of the heat curable composition comprises 8wherein o is
1-4, X is selected from the group consisting of a direct bond (when
o is 2), alkyl (when o is 1), alkylene (when o is 2-4), carbonyl
(when o is 2), thiol (when o is 1), thioether (when o is 2),
sulfoxide (when o is 2), and sulfone (when o is 2), R.sub.1, is
selected from the group consisting of hydrogen, alkyl and aryl, and
R.sub.4 is selected from hydrogen, halogen and alkyl.
41. The vacuum assisted resin transfer molding process of claim 15,
wherein the benzoxazine of the heat curable composition comprises
9wherein o is 1-4, X is selected from the group consisting of a
direct bond (when o is 2), alkyl (when o is 1), alkylene (when o is
2-4), carbonyl (when o is 2), thiol (when o is 1), thioether (when
o is 2), sulfoxide (when o is 2), and sulfone (when o is 2),
R.sub.1 is selected from the group consisting of hydrogen, alkyl
and aryl, and R.sub.4 is selected from hydrogen, halogen and
alkyl.
42. The resin film infusion process of claim 25, wherein the
benzoxazine component of the heat curable composition comprises
10wherein o is 1-4, X is selected from the group consisting of a
direct bond (when o is 2), alkyl (when o is 1), alkylene (when o is
2-4), carbonyl (when o is 2), thiol (when o is 1), thioether (when
o is 2), sulfoxide (when o is 2), and sulfone (when o is 2),
R.sub.1 is selected from the group consisting of hydrogen, alkyl
and aryl, and R.sub.4 is selected from hydrogen, halogen and
alkyl.
43. The resin transfer molding process of claim 1, wherein the
benzoxazine of the heat curable composition comprises one or more
of 11wherein X is selected from the group consisting of a direct
bond, CH.sub.2, C(CH.sub.3).sub.2, C=0, S, S.dbd.O and
O.dbd.S.dbd.O, and R.sub.1, R.sub.2 and R.sub.3 are the same or
different and are selected from the group consisting of hydrogen,
alkyl and aryl.
44. The vacuum assisted resin transfer molding process of claim 15,
wherein the benzoxazine component of the heat curable composition
comprises one or more of 12wherein X is selected from the group
consisting of a direct bond, CH.sub.2, C(CH.sub.3).sub.2, C=0, S,
S.dbd.O and O.dbd.S.dbd.O, and R.sub.1, R.sub.2 and R.sub.3 are the
same or different and are selected from the group consisting of
hydrogen, alkyl and aryl.
45. The resin film infusion process of claim 25, wherein the
benzoxazine component of the heat curable composition comprises one
or more of 13wherein X is selected from the group consisting of a
direct bond, CH.sub.2, C(CH.sub.3).sub.2, C=0, S, S.dbd.O and
O.dbd.S.dbd.O, and R.sub.1, R.sub.2 and R.sub.3 are the same or
different and are selected from the group consisting of hydrogen,
alkyl and aryl.
46. The resin transfer molding process of claim 1, wherein the
benzoxazine of the heat curable composition comprises 14wherein p
is 2, Y is selected from the group consisting of biphenyl (when p
is 2), diphenyl methane (when p is 2), diphenyl isopropane (when p
is 2), diphenyl sulfide (when p is 2), diphenyl sulfoxide(when p is
2), diphenyl sulfone (when p is 2), and diphenyl ketone (when p is
2), and R.sub.4 is selected from hydrogen, halogen and alkyl.
47. The vacuum assisted resin transfer molding process of claim 15,
wherein the benzoxazine of the heat curable composition comprises
15wherein p is 2, Y is selected from the group consisting of
biphenyl (when p is 2), diphenyl methane (when p is 2), diphenyl
isopropane (when p is 2), diphenyl sulfide (when p is 2), diphenyl
sulfoxide(when p is 2), diphenyl sulfone (when p is 2), and
diphenyl ketone (when p is 2), and R.sub.4 is selected from
hydrogen, halogen and alkyl.
48. The resin film infusion process of claim 25, wherein the
benzoxazine component of the heat curable composition comprises
16wherein p is 2, Y is selected from the group consisting of
biphenyl (when p is 2), diphenyl methane (when p is 2), diphenyl
isopropane (when p is 2), diphenyl sulfide (when p is 2), diphenyl
sulfoxide(when p is 2), diphenyl sulfone (when p is 2), and
diphenyl ketone (when p is 2), and R.sub.4 is selected from
hydrogen, halogen and alkyl.
48. The resin transfer molding process of claim 1, wherein the
benzoxazine of the heat curable composition comprises one or more
of 17
49. The vacuum assisted resin transfer molding process of claim 15,
wherein the benzoxazine component of the heat curable composition
comprises one or more of 18
50. The resin film infusion process of claim 25, wherein the
benzoxazine component of the heat curable composition comprises one
or more of 19
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Curable compositions, such as benzoxazine-based ones, are
useful in applications within the aerospace industry, such as for
example as a heat curable composition for use as a matrix resin in
advanced processes, such as resin transfer molding, vacuum assisted
transfer molding and resin film infusion, and their use in such
advanced processes form the basis of the present invention.
[0003] 2. Brief Description of Related Technology
[0004] Epoxy resins with various hardeners have been used
extensively in the aerospace industry, both as adhesives and as
matrix resins for use in prepreg assembly with a variety of
substrates.
[0005] Blends of epoxy resins and benzoxazines are known. See e.g.
U.S. Pat. No. 4,607,091 (Schreiber), 5,021,484 (Schreiber),
5,200,452 (Schreiber), and 5,445,911 (Schreiber). These blends
appear to be potentially useful in the electronics industry as the
epoxy resins can reduce the melt viscosity of benzoxazines allowing
for the use of higher filler loading while maintaining a
processable viscosity. However, epoxy resins oftentimes undesirably
increase the temperature at which benzoxazines polymerize.
[0006] Ternary blends of epoxy resins, benzoxazines and phenolic
resins are also known. See U.S. Pat. No. 6,207,786 (Ishida), and S.
Rimdusit and H. Ishida, "Development of new class of electronic
packaging materials based on ternary system of benzoxazine, epoxy,
and phenolic resin," Polymer, 41, 7941-49 (2000).
[0007] Resin transfer molding ("RTM") is a process by which a
resin--conventionally and predominately, epoxy-based resin systems
and maleimide-based systems--is pumped at low viscosities and under
pressure into a closed mold die set containing a preform of dry
fabric. The resin infuses into the preform to make a
fiber-reinforced composite article. The RTM process can be used to
produce at low cost composite parts that are complex in shape.
These parts typically require continuous fiber reinforcement along
with inside mold line and outside mold line controlled
surfaces.
[0008] Fiber-reinforced composite articles may be manufactured from
vacuum assisted resin transfer molding ("VaRTM"), like RTM. In
contrast to RTM, VaRTM employs an open mold and places the system
under a vacuum to assist the resin infusion process.
[0009] Resin film infusion ("RFI"), like RTM, infuses a resin into
a preform placed in a mold. Here, however, the resin is in the form
of a film, which is placed in the mold together with the preform.
U.S. Pat. No. 5,902,535 speaks to RFI molds and processes, and is
expressly incorporated herein by reference.
[0010] The matrix resin used in the RTM and VaRTM advanced
prossesses should desirably have a low injection viscosity to allow
complete wetting and infusion of the preform.
[0011] Bismaleimide-based resins for RTM and RFI processes are
known, and examples of which are described in U.S. Pat. Nos.
5,955,566 and 6,313,248.
[0012] And, two component epoxy resin compositions have been used,
where the epoxy resin and the hardener components are combined
immediately prior to use. One component epoxy resin compositions
oftentimes must be stored at controlled low temperatures to prevent
premature cross-linking reactions and to extend storage life.
Otherwise, the viscosities of such one component epoxy resin
compositions would build far too quickly, thus rendering their
working life unsuitable (or at least not desirable) from a
commercial standpoint.
[0013] Notwithstanding the state of the technology, there is a need
for other resin systems to be used in these advanced processes,
particularly a resin system with improved performance properties.
And to date there has been no disclosure, teaching or suggestion to
prepare a heat curable composition either as a matrix resin or in
film form based on benzoxazine-containing compositions for these
advanced processes.
SUMMARY OF THE INVENTION
[0014] The present invention relates to a process for producing
composite articles in advanced processes, such as RTM, VaRTM and
RFI systems, using a benzoxazine-containing heat curable
composition.
[0015] The present invention thus provides in one aspect thereof a
RTM process, steps of which include:
[0016] (a) providing a heat curable composition into a closed mold
containing a preform;
[0017] (b) exposing the interior of the mold to a first elevated
temperature and elevated pressure sufficient to wet the preform
with the heat curable composition; and
[0018] (c) curing the heat curable composition-impregnated preform
within the mold at a second elevated temperature to form a RTM
product.
[0019] In another aspect, there is provided a VaRTM process, steps
of which include:
[0020] providing a preform into a mold;
[0021] providing a heat curable composition into the mold under a
first elevated temperature and under vacuum for a time sufficient
to allow the composition to wet the preform; and
[0022] exposing the mold containing the composition wetted-preform
to a second elevated temperature while under vacuum sufficient to
cure the heat curable composition-wetted preform within the mold to
form a VaRTM product.
[0023] In yet another aspect, there is provided a RFI process,
steps of which include:
[0024] providing a preform into a closed mold containing a heat
curable composition in film form;
[0025] exposing the interior of the mold to a first elevated
temperature and optionally vacuum, while the exterior of the mold
is exposed to an elevated pressure, for a time sufficient to infuse
the preform with the heat curable composition; and
[0026] curing the heat curable composition-infused preform within
the mold at a second elevated temperature to form a RFI
product.
[0027] In each of these processes, the heat curable composition
comprises (i) a benzoxazine component.
[0028] Of course, the invention provides products made by these
advanced processes.
[0029] In still another aspect, the invention provides a binder
composition, which is useful in both the RTM and VaRTM processes.
The inventive binder composition is partially cured by exposure to
elevated temperature conditions over time sufficient to increase
the melting point higher than the temperature at which a matrix
resin composition is to be infused into a preform and lower than
the point at which the partially cured binder composition and the
matrix resin composition are miscible.
[0030] The present invention will be more fully understood by a
reading of the following detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] As noted above, provides in one aspect thereof a RTM
process, steps of which include:
[0032] (a) providing a heat curable composition into a closed mold
containing a preform;
[0033] (b) exposing the interior of the mold to a first elevated
temperature and elevated pressure sufficient to wet the preform
with the heat curable composition; and
[0034] (c) curing the heat curable composition-impregnated preform
within the mold at a second elevated temperature to form a RTM
product.
[0035] In another aspect, there is provided a VaRTM process, steps
of which include:
[0036] (a) providing a preform into a mold;
[0037] (b) providing a heat curable composition into the mold under
a first elevated temperature and under vacuum for a time sufficient
to allow the composition to wet the preform; and
[0038] (c) exposing the mold containing the composition
wetted-preform to a second elevated temperature while under vacuum
sufficient to cure the heat curable composition-wetted preform
within the mold to form a VaRTM product.
[0039] In yet another aspect, there is provided a RFI process,
steps of which include:
[0040] (a) providing a preform into a closed mold containing a heat
curable composition in film form;
[0041] (b) exposing the interior of the mold to a first elevated
temperature and optionally vacuum, while the exterior of the mold
is exposed to an elevated pressure, for a time sufficient to infuse
the preform with the heat curable composition; and
[0042] (c) curing the heat curable composition-infused preform
within the mold at a second elevated temperature to form a RFI
product.
[0043] In each of these process the heat curable composition
comprises (i) a benzoxazine component.
[0044] Of course, the invention provides products, such as RFI, RTM
and VaRTM products, made by these advanced processes.
[0045] In still another aspect, the invention provides a binder
composition, which is useful in both the RTM and VaRTM processes.
The inventive binder composition is partially cured by exposure to
elevated temperature conditions over time sufficient to increase
the melting point higher than the temperature at which a matrix
resin composition is to be infused into a preform and lower than
the point at which the partially cured binder composition and the
matrix resin composition are miscible.
[0046] Complex three dimensional part geometries may be molded in
the advanced processes described herein as a single piece unit.
RFI, for instance, is particularly useful for molding large
composite parts, as it defines the entire geometry of the part in a
single process cycle, thereby eliminating any subsequent assembly
or bonding processes. In the aerospace industry, for one, it is not
uncommon for parts to be up to 100 feet in length and up to 30 feet
in width, located on lofted surfaces with integral stiffening and
attachment details. Using these advanced processes to form such
large parts, assembly and tooling costs normally associated with a
mechanically fastened or bonded structure may be reduced. In
addition, narrow engineering tolerances may be realized using these
advanced processes to enable assembly of a large aircraft structure
with minimal shimming, typically associated with non-monolithic
components constructed from sub-assemblies.
[0047] In an RFI process, a resin film molding tool is ordinarily
used, which includes an outer mold tool, which includes a facing
sheet supported by a support structure. A resin film prepared from
a benzoxazine is positioned on the facing sheet, and a preform is
positioned on the resin film. The preform is designed in the shape
of a desired article to be fabricated from compositing materials,
such as fibers made from carbon, aramid, ceramic and the like. The
preform may include a preform skin, as described in U.S. Pat. No.
5,281,388, the disclosure of which is hereby expressly incorporated
herein by reference.
[0048] RTM systems are well known, such as those described in U.S.
Pat. Nos. 5,369,192, 5,567,499, 5,677,048, 5,851,336, and
6,156,146, which are incorporated herein by reference. VaRTM
systems are also well known, such as those described in U.S. Pat.
Nos. 5,315,462, 5,480,603 and 5,439,635, which also expressly are
incorporated herein by reference.
[0049] RTM systems produce composite articles from resin
impregnated preforms. The preform is placed in a cavity mold. A
benzoxazine-containing heat curable composition is then injected
into the mold to wet and infuse the fibers of the preform. In an
RTM process, the benzoxazine-containing heat curable composition is
introduced into the cavity mold under pressure. The
benzoxazine-containing heat curable composition-infused preform is
cured under elevated temperature. The resulting solid article may
be subjected to post curing operations to produce a final composite
article, though this is not required.
[0050] Thus, with the RTM process, the preform is placed, within
the mold. The preform used in the RTM process may include a
benzoxazine-containing heat curable binder composition, tacked to
the fibers which make up the preform.
[0051] In an RTM process, therefore, the mold is then closed and
the benzoxazine-containing heat curable composition is introduced,
and allowed to infuse the preform. This introduction may occur
under mildly elevated temperature conditions to improve flow
characteristics of the benzoxazine-containing heat curable
composition for a time sufficient to allow wetting of the
preform.
[0052] The interior of the mold is then heated to and maintained
at, a temperature (ordinarily within the range of 250.degree. F. to
350.degree. F.) which is sufficient to cure the
benzoxazine-containing heat curable composition, for a time
sufficient to cure the heat curable composition. This time is
ordinarily within the 60 to 180 minute range, depending of course
on the precise constituents of the heat curable composition. After
cure is complete, the temperature of the mold is allowed to cool
and the RTM product made by the process is removed.
[0053] In a VaRTM process, after providing the preform, a
dispersing medium may be disposed thereover. The dispersing medium
is positioned on the surface of prefrom in an envelope within the
mold. The dispersing medium is oftentimes an open weave fabric. The
vacuum is applied to collapse the dispersing medium against the
preform and assist in the introduction of the
benzoxazine-containing heat curable composition into the mold to
wet and infuse the preform.
[0054] The benzoxazine-containing heat curable composition is
injected into the mold, and allowed to wet and infuse the preform.
This injection may again occur under a mildly elevated temperature,
this time through and under vacuum for a period of time sufficient
to allow the composition to wet and infuse the preform.
[0055] The benzoxazine-containing heat curable composition is
introduced under vacuum into the envelope to wet and infuse the
preform. The vacuum is applied to the interior of the envelope via
a vacuum line to collapse the flexible sheet against the preform.
The vacuum draws the benzoxazine-containing heat curable
composition through the preform and helps to avoid the formation of
air bubbles or voids in the finished article. The
benzoxazine.-containing heat curable composition cures while being
subjected to the vacuum.
[0056] The mold is then exposed to an elevated temperature,
ordinarily within the range at 250.degree. F. to 350.degree. F.,
while remaining under vacuum, for a period of time sufficient to
cure the heat curable composition-wetted preform within the mold.
This time period again is ordinarily within the 60 to 180 minute
range. The vacuum also draws off any fumes produced during the
curing process. After cure is complete, the temperature of the mold
is allowed to cool and the VaRTM product made by the process is
removed.
[0057] For these advanced processes, the benzoxazine-containing
heat curable composition has a viscosity in the range of 10 to 5000
cps at resin injection temperature (10 to 3000 cps for RTM or
VaRTM; 10-5000 cps for RFI). In addition, the time within which the
viscosity of the heat curable composition increases by 100% under
the process conditions is in the range of 1 to 10 hours.
[0058] The resulting solid article so made by the VaRTM process may
be subjected to post curing operations to produce a final composite
article.
[0059] The first step in either of the RTM/VaRTM processes is thus
to fabricate a fiber preform in the shape of the desired article.
The preform generally includes a number of fabric layers or plies
made from these fibers that impart the desired reinforcing
properties to a resulting composite article. Once the fiber preform
has been fabricated, the preform is placed in a mold.
[0060] The benzoxazine of the heat curable composition may be
embraced by the following structure: 1
[0061] where o is 1-4, X is selected from a direct bond (when o is
2), alkyl (when o is 1), alkylene (when o is 2-4), carbonyl (when o
is 2), thiol (when o is 1), thioether (when o is 2), sulfoxide
(when o is 2), and sulfone (when o is 2), R.sub.1 is selected from
hydrogen, alkyl and aryl, and R.sub.4 is selected from hydrogen,
halogen and alkyl.
[0062] More specifically, the benzoxazine may be embraced by the
following structure: 2
[0063] where X is selected from of a direct bond, CH.sub.2,
C(CH.sub.3).sub.2, C=0, S, S.dbd.O and O.dbd.S.dbd.O, and R.sub.1
and R.sub.2 are the same or different and are selected from
hydrogen, alkyl, such as methyl, ethyl, propyls and butyls, and
aryl.
[0064] Representative benzoxazine include: 3
[0065] where R.sub.1 and R.sub.2 are as defined above.
[0066] Alternatively, the benzoxazine may be embraced by the
following structure: 4
[0067] where p is 2, Y is selected from the group consisting of
biphenyl (when p is 2), diphenyl methane (when p is 2), diphenyl
isopropane (when p is 2), diphenyl sulfide (when p is 2), diphenyl
sulfoxide(when p is 2), diphenyl sulfone (when p is 2), and
diphenyl ketone (when p is 2), and R.sub.4 is selected from
hydrogen, halogen and alkyl.
[0068] Though not embraced by structures I, II or III additional
benzoxazines are within the following structures: 5
[0069] where R.sub.1 are R.sub.2 are as defined above, and R.sub.3
is defined as R.sub.1 or R.sub.2.
[0070] Examples of these benzoxazines therefore include: 6
[0071] The benzoxazine component may include the combination of
multifunctional benzoxazines and monofunctional benzoxazines.
Examples of monofunctional benzoxazines may be embraced by the
following structure: 7
[0072] where R is alkyl, such as methyl, ethyl, propyls and butyls,
or aryl, and R.sub.4 is selected from hydrogen, halogen and
alkyl.
[0073] The benzoxazine component should be present in an amount in
the range of about 10 to about 99 percent by weight, such as about
25 to about 75 percent by weight, desirably about 35 to about 65
percent by weight, based on the total weight of the
composition.
[0074] In one version of the heat curable composition, the
benzoxazine component may also include (ii) a toughener component
comprising acrylonitrile-butadiene co-polymer having secondary
amine terminal groups.
[0075] This toughener component should be present in an amount in
the range of about 1 to about 90 percent by weight, such as about
10 to about 70 percent by weight, desirably about 15 to about 30
percent by weight, based on the total weight of the
composition.
[0076] In another version of the heat curable composition; the
benzoxazine component may also include
[0077] (ii) an epoxy or episulfide component;
[0078] (iii) optionally, one or more of an oxazoline component, a
cyanate ester component, a phenolic component, and a thiophenolic
component;
[0079] (iv) optionally, acrylonitrile-butadiene co-polymer, a
polyimide component, and a polyimide/siloxane component; and
[0080] (v) optionally, a curative.
[0081] The epoxy or episulfide component should be present in an
amount in the range of about 5 to about 60 percent by weight, such
as about 10 to about 50 percent by weight, desirably about 15 to
about 35 percent by weight, based on the total weight of the
composition.
[0082] The oxazoline component, the cyanate ester component, the
phenolic component, and the thiophenolic component should be
present in an amount in the range of about 5 to about 60 percent by
weight, such as about 10 to about 50 percent by weight, desirably
about 15 to about 35 percent by weight, based on the total weight
of the composition.
[0083] The acrylonitrile-butadiene co-polymer, polyimide component,
and the polyimide/siloxane component should be present in an amount
in the range of about 1 to about 50 percent by weight, such as
about 5 to about 35 percent by weight, desirably about 10 to about
25 percent by weight, based on the total weight of the
composition.
[0084] The curative should be present in an amount in the range of
about 0.01 to about 40 percent by weight, such as about 0.5 to
about 20 percent by weight, desirably about 1 to about 15. percent
by weight, based on the total weight of the composition.
[0085] The binder composition, which may be used in the RTM or
VaRTM process, includes a solid benzoxazine component, which is
partially cured by exposure to elevated temperature conditions over
time sufficient to increase the melting point higher than the
temperature at which a matrix resin composition is to be infused
into a preform and lower than the point at which the partially
cured binder composition and the heat curable composition are
miscible. The binder composition may also include a spacer selected
from particles constructed of thermoplastics, rubbers, metals,
carbon, core shell, ceramics and combinations thereof.
[0086] Like the heat curable composition, the binder composition
may include a toughener component comprising an
acrylonitrile-butadiene co-polymer component (such as
acrylonitrile-butadiene co-polymer having secondary amine terminal
groups), polyimide component, and a polyimide/siloxane component;
and/or an optional, epoxy resin or episulfide resin component; an
optional, one or more of an oxazoline component, a cyanate ester
component, a phenolic component, and a thiophenolic component; and
an optional curative.
EXAMPLE
[0087] In this example, a formulation suitable for use as a thick
film in an RFI process (such as 0.20 pounds/ft.sup.2 areal weight
or 30 mils thickness), or as a resin for VaRTM and RTM is
illustrated.
[0088] The formulation included an approximate 1:1 mixture of
benzoxazines based on bisphenol F and thiodiphenol at a 68 weight
percent; cycloaliphatic epoxy resin (CY 179, commercially available
from Vantico) at a 23 weight percent; and ATBN (1300X16,
commercially available from Noveon, Cleveland, Ohio) at a 9 weight
percent, based on the total formulation. The components can be
added to one another in any convenient order, and mixed at room
temperature for a time sufficient to generate a substantially
homogenous mixture.
[0089] The formulation so formed may be used in an RTM process, for
instance, as follows:
[0090] Preheat the formulation to a temperature of 160.degree.
F.
[0091] Insert a perform into a closed mold
[0092] Preheat the mold to a temperature of 250.degree. F.
[0093] Apply vacuum to the mold for a period of time of 1 hour to
remove any volatiles from the preform
[0094] Preheat resin injector to a temperature of 235.degree.
F.
[0095] Add the preheated formulation to the injector
[0096] When the formulation equilibrates at a temperature of
250.degree. F., apply full vacuum for a period of time of 15
minutes to remove air
[0097] Release the vacuum
[0098] Inject the formulation at about the rate of 5 to 200 cc per
minute using about 20 psi injection pressure, which may be
increased, if desired throughout the injection to maintain the
desired flow rate
[0099] When the perform is fully impregnated, close the mold resin
exit ports
[0100] Pressurize the tool to 100 psi and hold at that pressure for
a period of time of about 10 minutes
[0101] Ramp the mold temperature to 350.degree. F. at 3.degree. F.
per minute
[0102] When the formulation has gelled, remove the applied
pressure
[0103] Hold the temperature at 350.degree. F. for a period of time
of 3 hours
[0104] Cool to a temperature of 120.degree. F.
[0105] Open the mold and remove the cured part.
[0106] The properties of the so formed cured part in the form of a
panel were observed as follows using Toray T-300 3K 70 plain weave
woven carbon fabric:
1 Glass transition temperature, hot/wet, .degree. F. 354 Open hole
compressive strength @ 75.degree. F., ksi 43 Open hole compressive
modulus @ 75.degree. F., msi 7.1 Open hole compressive @
180.degree. F., wet, .degree. F. 36 Compression after impact @
75.degree. F., ksi 33
* * * * *