U.S. patent application number 09/905264 was filed with the patent office on 2003-05-01 for quick cure carbon fiber reinforced epoxy resin.
This patent application is currently assigned to Toray Composites (America), Inc.. Invention is credited to Li, Wei (Helen), Miwa, Kishio.
Application Number | 20030082385 09/905264 |
Document ID | / |
Family ID | 25420515 |
Filed Date | 2003-05-01 |
United States Patent
Application |
20030082385 |
Kind Code |
A1 |
Li, Wei (Helen) ; et
al. |
May 1, 2003 |
Quick cure carbon fiber reinforced epoxy resin
Abstract
An epoxy composition including an epoxy resin, a latent amine
curing agent, and a specific catalyst. Preferably, the epoxy resin
includes two epoxide groups per molecule, and the latent amine
curing agent is a dicyanopolyamide, most preferably, dicyandiamide.
The specific catalyst is preferably 2,4-toluene bis dimethyl urea.
A prepreg employing the epoxy composition of the present invention
can achieve a 95% cure in about one half of the time required by a
prepreg that differs only in the catalyst employed. Furthermore,
prepregs employing the epoxy composition of the present invention
have glass transition temperatures higher than the curing
temperatures when cured at a temperature range from about
80.degree. C. to about 150.degree. C., enabling cured prepregs to
be removed from molds without being cooled. Use of the prepregs of
the present invention thus enables composite component
manufacturers to substantially increase production rates without
requiring the use of additional molds.
Inventors: |
Li, Wei (Helen); (Puyallup,
WA) ; Miwa, Kishio; (Shiga, JP) |
Correspondence
Address: |
LAW OFFICES OF RONALD M ANDERSON
600 108TH AVE, NE
SUITE 507
BELLEVUE
WA
98004
US
|
Assignee: |
Toray Composites (America),
Inc.
|
Family ID: |
25420515 |
Appl. No.: |
09/905264 |
Filed: |
July 13, 2001 |
Current U.S.
Class: |
428/417 |
Current CPC
Class: |
C08G 59/686 20130101;
C08G 59/4021 20130101; C08L 63/00 20130101; C08L 63/00 20130101;
Y10T 428/31511 20150401; Y10T 428/31525 20150401; C08L 2666/04
20130101 |
Class at
Publication: |
428/417 |
International
Class: |
B32B 027/38 |
Claims
The invention in which an exclusive right is claimed is defined by
the following:
1. A resin matrix composition comprising: (a) an epoxy resin having
more than one epoxide group per molecule; and (b) a catalyst
consisting of 2,4-toluene bis dimethyl urea, wherein a transition
glass temperature of said resin matrix composition is higher than
about 140.degree. C. after being heated to 150.degree. C. for as
little as 3 minutes.
2. The resin matrix composition of claim 1, further comprising at
least one latent curing agent.
3. The resin matrix composition of claim 2, wherein said at least
one latent amine curing agent comprises a dicyanopolyamide.
4. The resin matrix composition of claim 2, wherein at least one
latent amine curing agent comprises dicyandiamide.
5. The resin matrix composition defined by claim 1, further
comprising a thermoplastic additive.
6. The resin matrix composition of claim 5, wherein said
thermoplastic additive is at least one selected from the group
consisting of polyvinylfluorides (PVFs), polymethylmethacrylates
(PMMAs), polyarylethersulfones (PESs), polysulfone (PSF),
polyimides (PIs), polyetherimides (PEIs), and polyethylene oxide
(PEO).
7. The resin matrix composition of claim 1, wherein said epoxy
resin comprises least one epoxy resin selected from the group
consisting of: bisphenol A based epoxy resins, bisphenol F based
epoxy resins, epoxy phenol novolacs, trifunctional epoxy resins,
tetrafunctional epoxy resins, and halogenated derivatives
thereof.
8. The resin matrix composition of claim 7, wherein said bisphenol
A based epoxy resin has an epoxide equivalent weight of from about
170 to about 1400.
9. The resin matrix composition of claim 7, wherein said bisphenol
A based epoxy resin is a blend of a first, bisphenol A based epoxy
resin having an epoxy equivalent in the range of from about 180 to
about 195 and a second, bisphenol A based epoxy resin having an
epoxy equivalent in the range of from about 1200 to about 1400, the
amount and the molecular weight of said second epoxy resin being
such that the blended bisphenol A based epoxy resin has a number
average molecular weight in the range of from about 200 to about
300.
10. The resin matrix composition of claim 1, wherein an amount of
said catalyst ranges from about 0.5 to about 10 phr.
11. The resin matrix composition of claim 10, wherein said amount
ranges from about 2 to about 5 phr.
12. The resin matrix composition of claim 1, wherein said
composition is more than 95% cured after being heated to about
150.degree. C. for about five minutes.
13. The resin matrix composition of claim 1, wherein said
composition is more than 95% cured after being heated to about
120.degree. C. for about 20 minutes.
14. A resin matrix composition comprising: (a) an epoxy resin
having more than one epoxide group per molecule; and (b) a catalyst
consisting of 2,4-toluene bis dimethyl urea, wherein a transition
glass temperature of said resin matrix is higher than about
100.degree. C. after being heated to 80.degree. C. for as little as
5 hours.
15. The resin matrix composition of claim 14, further comprising at
least one latent curing agent.
16. The resin matrix composition of claim 15, wherein said at least
one latent amine curing agent comprises a dicyanopolyamide.
17. The resin matrix composition of claim 15, wherein at least one
latent amine curing agent comprises dicyandiamide.
18. The resin matrix composition defined by claim 14, further
comprising a thermoplastic additive.
19. The resin matrix composition of claim 18, wherein said
thermoplastic additive is at least one selected from the group
consisting of polyvinylfluorides (PVFs), polymethylmethacrylates
(PMMAs), polyarylethersulfones (PESs), polysulfone (PSF),
polyimides (PIs), polyetherimides (PEIs), and polyethylene oxide
(PEO).
20. The resin matrix composition of claim 15, wherein said epoxy
resin comprises at least one epoxy resin selected from the group
consisting of: bisphenol A based epoxy resins, bisphenol F based
epoxy resins, epoxy phenol novolacs, trifunctional epoxy resins,
tetrafunctional epoxy resins, and halogenated derivatives
thereof.
21. The resin matrix composition of claim 20, wherein the bisphenol
A based epoxy resin has an epoxide equivalent weight of from about
170 to about 1400.
22. The resin matrix composition of claim 20, wherein the bisphenol
A based epoxy resin is a blend of a first, bisphenol A based epoxy
resin having an epoxy equivalent in the range of from about 180 to
about 195 and a second, bisphenol A based epoxy resin having an
epoxy equivalent in the range of from about 1200 to about 1400, the
amount and the molecular weight of said second epoxy resin being
such that the blended bisphenol A based epoxy resin has a number
average molecular weight in the range of from about 200 to about
300.
23. The resin matrix composition of claim 14, wherein an amount of
said catalyst ranges from about 0.5 to about 10 phr.
24. The resin matrix composition of claim 23, wherein said amount
ranges from about 2 to about 5 phr.
25. The resin matrix composition of claim 14, wherein a transition
glass temperature thereof is higher than about 118.degree. C. after
being heated to 80.degree. C. for 5 hours.
26. An article resulting from curing the resin matrix composition
of claim 1, said resin matrix composition further comprising a
reinforcing agent.
27. The article of claim 26, wherein said reinforcing agent
comprises at least one selected from the group consisting of glass
fibers, aramid fibers, and graphite fibers, and wherein said fibers
comprise at least one of woven fibers, matted fibers, and
unidirectional fibers.
28. An adhesive film resulting from curing the resin matrix
composition of claim 1, said resin matrix composition further
comprising a supporting material.
29. The adhesive film of claim 28, wherein said supporting material
comprises at least one selected from the group consisting of
polyester and nylon.
30. A prepreg comprising: (a) an epoxy composition including: (i)
an epoxy resin having more than one epoxide group per molecule; and
(ii) a catalyst consisting of 2,4-toluene bis dimethyl urea,
wherein a transition glass temperature of said epoxy composition is
higher than about 140.degree. C. after being heated to 150.degree.
C. for as little as 3 minutes; (b) a plurality of reinforcing
fibers.
31. The prepreg of claim 30, wherein said plurality of reinforcing
fibers comprise at least one type of reinforcing fiber selected
from the group consisting of glass fibers, aramid fibers, graphite
fibers, woven fibers, matted fibers, and unidirectional fibers.
32. The prepreg of claim 30, further comprising at least one latent
curing agent.
33. The prepreg of claim 32, wherein said at least one latent amine
curing agent comprises a dicyanopolyamide.
34. The prepreg of claim 32, wherein said at least one latent amine
curing agent comprises dicyandiamide.
35. The prepreg of claim 30, further comprising a thermoplastic
additive.
36. The prepreg of claim 35, wherein said thermoplastic additive
comprises at least one thermoplastic additive selected from the
group consisting of polyvinylfluorides (PVFs),
polymethylmethacrylates (PMMAs), polyarylethersulfones (PESs),
polysulfone (PSF), polyimides (PIs), polyetherimides (PEIs), and
polyethylene oxide (PEO).
37. The prepreg of claim 30, wherein said epoxy resin comprises at
least one epoxy resin selected from the group consisting of:
bisphenol A based epoxy resins, bisphenol F based epoxy resins,
epoxy phenol novolacs, trifunctional epoxy resins, tetrafunctional
epoxy resins, and halogenated derivatives thereof.
38. The prepreg of claim 37, wherein the bisphenol A based epoxy
resin has an epoxide equivalent weight of from about 170 to about
1400.
39. The prepreg of claim 37, wherein the bisphenol A based epoxy
resin is a blend of a first, bisphenol A based epoxy resin having
an epoxy equivalent in the range of from about 180 to about 195 and
a second, bisphenol A based epoxy resin having an epoxy equivalent
in the range of from about 1200 to about 1400, the amount and the
molecular weight of said second epoxy resin being such that the
blended bisphenol A based epoxy resin has a number average
molecular weight in the range of from about 200 to about 300.
40. The prepreg of claim 30, wherein an amount of said catalyst
ranges from about 0.5 to about 10 phr.
41. The prepreg of claim 40, wherein said amount ranges from about
2 to about 5 phr.
42. The prepreg of claim 30, wherein said prepreg is more than 95%
cured after being heated to about 150.degree. C. for less than five
minutes.
43. The prepreg of claim 30, wherein said prepreg is more than 95%
cured after being heated to about 120.degree. C. for less than 20
minutes.
44. A prepreg comprising: (a) an epoxy composition including: (i)
an epoxy resin having more than one epoxide group per molecule; and
(ii) a catalyst consisting of 2,4-toluene bis dimethyl urea,
wherein a transition glass temperature of said epoxy composition is
higher than about 100.degree. C. after being heated to 80.degree.
C. for as short as 5 hours; and (b) a plurality of reinforcing
fibers.
45. The prepreg of claim 44, wherein said plurality of reinforcing
fibers comprise at least one type of reinforcing fiber selected
from the group consisting of glass fibers, aramid fibers, graphite
fibers, woven fibers, matted fibers, and unidirectional fibers
46. The prepreg of claim 44, further comprising at least one latent
curing agent.
47. The prepreg of claim 46, wherein said at least one latent amine
curing agent comprises a dicyanopolyamide.
48. The prepreg of claim 46, wherein at least one latent amine
curing agent comprises dicyandiamide.
49. The prepreg defined by claim 44, further comprising a
thermoplastic additive.
50. The prepreg of claim 49, wherein said thermoplastic additive
comprises at least one thermoplastic additive selected from the
group consisting of polyvinylfluorides (PVFs),
polymethylmethacrylates (PMMAs), polyarylethersulfones (PESs),
polysulfone (PSF), polyimides (PIs), polyetherimides (PEIs), and
polyethylene oxide (PEO).
51. The prepreg of claim 44, wherein said epoxy resin comprises at
least one epoxy resin selected from the group consisting of:
bisphenol A based epoxy resins, bisphenol F based epoxy resins,
epoxy phenol novolacs, trifunctional epoxy resins, tetrafunctional
epoxy resins, and halogenated derivatives thereof.
52. The prepreg of claim 51, wherein the at bisphenol A based epoxy
resin has an epoxide equivalent weight of from about 170 to about
1400.
53. The prepreg of claim 51, wherein the bisphenol A based epoxy
resin is a blend of a first bisphenol A based epoxy resin having an
epoxy equivalent in the range of from about 180 to about 195 and a
second, bisphenol A based epoxy resin having an epoxy equivalent in
the range of from about 1200 to about 1400, the amount and the
molecular weight of said second epoxy resin being such that the
blended bisphenol A based epoxy resin has a number average
molecular weight in the range of from about 200 to about 300.
54. The prepreg of claim 44, wherein an amount of said catalyst
ranges from about 0.5 to about 10 phr.
55. The prepreg of claim 54, wherein said amount ranges from about
2 to about 5 phr.
56. The prepreg of claim 44, wherein a transition glass temperature
thereof is higher than about 118.degree. C. after being heated to
80.degree. C. for 5 hours.
57. A method to enable a thermosetting epoxy resin formulation to
rapidly reach a 95% cure, said method comprising the steps of: (a)
providing an epoxy composition including an epoxy resin having more
than one epoxide group per molecule, and a latent amine curing
agent; (b) mixing at least 0.5 phr of a catalyst in said epoxy
composition, said catalyst reducing the time required to reach a
95% cure and consisting of 2,4-toluene bis dimethyl urea; and (c)
heating said epoxy composition with said catalyst to at 150.degree.
C. for at least 3 minutes, said catalyst substantially decreasing
the time required to reach a 95% cure.
58. The method of claim 57, wherein a glass transition temperature
of the epoxy composition is from about 140.degree. C. to greater
than 150.degree. C.
59. The method of claim 57, wherein said epoxy composition further
comprises a plurality of reinforcing fibers.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to single part epoxy
resin compositions, and more specifically, to quick cure and low
temperature cure epoxy resin formulations suitable for use in
prepregs, composites, and adhesive films.
BACKGROUND OF THE INVENTION
[0002] Advanced composites are increasingly used as reinforcing
components in aircraft, automotive, and sporting goods
applications. Typically, these composites comprise a strengthening
component, such as carbon fibers, embedded in a thermosetting resin
matrix. Components fabricated of such carbon fiber reinforced resin
composites are produced by impregnating oriented carbon fibers (in
the form of woven carbon cloth, or continuous carbon filaments)
with thermosetting resins, and arranging the filaments of carbon
fibers to form prepregs. Generally, prepregs include a paper
backing onto which the fiber reinforcement is laid, and the
selected resin is then forced into the fibers.
[0003] Thermosetting resins, which normally include a latent curing
agent that is activated by increasing the temperature of the resin
over a minimum cure temperature, are often preferred over two part
resin systems that cure very quickly once the two parts are mixed.
This preference arises from the ease of handling of thermosetting
prepregs during the manufacture of components. Thermosetting
prepregs can be produced in quantity with consistent properties,
and stored at cold temperatures for a considerable length of time
before use. Most of these thermosetting prepregs are provided as
large rolls of material that include the paper backing and the
epoxy impregnated fibers. To use this material, the desired portion
is simply cut from the roll. In contrast, two part resin mixtures,
which admittedly often have desirable properties, such as a rapid
cure time, must be used immediately after being produced. Thus,
component manufacturers can only produce small batches of composite
material, and must then use each batch immediately after it is
mixed. Furthermore, the chance that a bad batch of composite
material will be produced on a manufacturer's production line is
considerably higher than in a chemical plant where the focus is on
the single task of producing a prepreg. The ease of use of prepregs
is such that even though the curing performance of two part resin
systems is generally better than that of thermosetting resins,
prepregs are almost universally preferred for fabricating composite
reinforcing components.
[0004] To fabricate a reinforcing component from prepregs,
manufacturers generally apply multi-layer laminates of these
prepregs over existing molds. To generate a rod or shaft, the
prepreg is wound around a mandrel. Once a sufficient number of
laminations have been achieved, the mold is heated to the cure
temperature required to activate the latent curing agent in the
thermosetting resin, using an oven or autoclave. Generally, a
higher temperature results in a shorter cure time, while a lower
temperature requires a longer cure time.
[0005] Suitable thermosetting epoxy resins generally have more that
one epoxide group per molecule. In addition to the latent curing
agent, which is often a functional amine, state-of-the-art epoxy
matrix resin systems used in advanced composites often employ a
catalyst, which helps to reduce cure times. It should be noted that
cure times are important to end users of prepregs, especially when
prepregs are used in conjunction with molds. Molds can range from
the simple to the complex, depending on the component being
produced. To ensure a high level of production quality, a
manufacturer must spend considerable time and effort to ensure that
each mold is identical. Furthermore, each mold must be able to be
heated to activate the prepreg, thus increasing the equipment
required for each mold. For example, in a golf shaft manufacturing
process, commonly used prepregs need to be cured for more than 20
minutes at 150.degree. C. in order to be removed from the mold or
mandrel without changing shape. If a manufacturer can obtain a
prepreg with a cure time that is one half that of a presently used
product, then the manufacturer can double production without
providing additional molds. It would therefore be desirable to
provide an advanced epoxy resin system that substantially reduces
cure time, to enable manufacturers to increase production without
providing additional molds.
[0006] Because prepregs are often used to form reinforcing
components, such as parts for airplanes, the resulting components
must meet high quality standards. It is desirable that any
reduction in cure time not negatively effect the physical
properties, such as tensile strength, of such composite
components.
[0007] In addition to preferring prepregs that have shorter cure
times, composite component manufacturers also desire prepregs that
cure at lower temperatures, particularly manufacturers who
fabricate large scale composite components, such as those that
might be employed in aviation or marine applications (boat hulls,
for example). Low temperature curing prepregs are desirable for
large parts manufacturing because such low temperatures require
less sophisticated heating systems, and much reduced energy costs,
which can be significant for large scale parts. Note that one major
manufacturer of prepregs, Hexcel Corporation of Dublin, Calif.,
currently offers a low temperature curing prepreg (M34.TM.), which
cures at 65.degree. C. (for 16 hours) or 75.degree. C. for 8 hours.
It would be desirable to provide an advanced epoxy resin system
that substantially reduces cure time below that of currently
available prepregs, particularly at low cure temperatures.
[0008] Many different types of epoxy resins systems are known in
the art. Different combinations of epoxy resins, curing agents, and
catalysts (also known as accelerators) have been formulated. A
balance of desirable properties for prepregs include the following:
(1) a tacky, dough-like consistency prior to curing; (2) low
reactivity at room temperature; and, (3) a high degree of cure
after heating for no more than 2 hours at nor more than 180.degree.
C. As noted above, the provision of a prepreg with a reduced cure
time will offer component manufacturers significant efficiency
advantages. Accordingly, there is an ongoing effort within the
prepreg industry to produce a prepreg that has the desired
consistency and low reactivity at room temperature, yet also
exhibits reduced cure time at relatively low temperatures.
[0009] While certainly not an exhaustive compilation, the following
patents provide examples of thermosetting resin compositions known
in the art. International Patent Publication No. WO 99/36484
describes a composite system that includes an epoxy resin having
two or more epoxide groups per molecule, a latent hardener, and at
least one solid organic acid that is substantially insoluble in the
resin formulation. U.S. Pat. No. 3,759,914 (Simms) discloses an
epoxy resin formulation including a polyepoxide having a plurality
of epoxide groups, a latent amine curing agent, and an accelerator
having a defined formula. U.S. Pat. No. 3,386,956 (Nawakowski)
describes an epoxy resin formulation including a dicyandiamide
(DICY) curing agent and an accelerator to increase the cure rate at
low temperatures (less than 187.degree. F.). The disclosed
accelerator is a bis-urea having a specifically defined formula. A
similar epoxy formulation is disclosed in U.S. Pat. No. 3,386,956
(Harrison), which employs a polyamine curing agent and a phenyl
urea based accelerator (see also U.S. Pat. No. 3,988,257 for
related methods). U.S. Pat. No. 3,956,237 (Doorakian) describes an
epoxy resin formulation including a latent amine curing agent and a
latent accelerator. A number of latent accelerators are disclosed,
including a specific blend of different isomers of toluene bis
dimethyl urea. U.S. Pat. No. 3,386,956 (Nawakowski) describes low
temperature curable epoxy resin compositions comprising a
polyepoxide, a curing agent selected from bis-ureas, polyureas, and
a promoter. The bis-ureas described include 2,4-toluene bis
dimethylurea. U.S. Pat. No. 4,569,956 discloses a rapid, low
temperature curing epoxy resin adhesive composition comprising a
polyepoxide, a catalytic amount of HBF.sub.4, a finely divided
filler (preferably an acidic filler), and, optionally, a
polyalkylene ether glycol. Yet another epoxy formulation is
disclosed in U.S. Pat. No. 4,783,518 (Goel), which teaches a rapid
curing epoxy composition including a polyepoxide, a latent amine
curing agent, a novel thiocyanate salt of the reaction product of
an alkylene polyamine (such as ethylene diamine), and a bicyclic
amide acetal. U.S. Pat. No. 5,407,978 (Bymark), which employs a
dihydric bisphenol curing agent and a immidazole based accelerator
to increase the cure rate. As a final example, U.S. Pat. No.
5,599,629 (Gardner) describes an epoxy resin formulation including
a resin with at least three epoxide groups per molecule and a
specific aromatic amine latent curing agent, the aforementioned
formulation being specifically employed to produce prepregs.
[0010] While the above-cited references all assert that a
functional formulation having desirable properties is achieved,
composite component manufacturers still desire a prepreg material
having faster cure times, and/or lower cure temperatures. It would
be desirable to provide an epoxy formulation differing than those
described in the prior art, that is adaptable to being employed as
a prepreg, and which provides shorter cure times and lower cure
temperatures than existing prepregs provide.
[0011] It should be noted that several different methods can be
used to fabricate prepregs, including a solventless, hot melt
impregnation method, and a solvent method. In a typical hot melt
impregnation process, continuous sheets of resin matrix film
supported by release paper are impregnated into fiber sheets under
heat, pressure, and tension. The matrix has to have a certain
viscosity at impregnation temperature so that the resin can wet-up
the fiber. Furthermore, specific tack, drape, and shelf-life
characteristics are required when utilizing the hot melt method. In
contrast, a solvent-diluting impregnation method does not have such
strict requirements. However, a superior prepreg is often achieved
by the hot melt method, because micro-voids, caused by off gassing
of volatile solvent, are often observed in prepregs prepared by the
solvent-diluting impregnation method. It would be desirable to
provide an advanced epoxy resin system adaptable to be employed to
produce a prepreg, that substantially reduces cure time, that can
be used with either the hot melt impregnation method, or the
solvent based impregnation method.
[0012] In addition, it should be noted that the time required for a
prepreg to cure is not always the limiting factor determining when
the cured prepreg can be removed from a mold. For example, a
commonly utilized prepreg material is produced from an epoxy
formulation including epoxy resin A (a diglycidyl ether of
bisphenol A having an epoxide equivalent weight of 176), epoxy
resin B (a diglycidyl ether of bisphenol A having an epoxide
equivalent weight of 1200-1400), a thermoplastic additive (PVF
powder), a DICY curing agent, and a catalyst
(3,4-dichlorophenyl-N,N-dimehtylurea, available as DYHARD
UR200.TM., made by SKW Trostberg). Depending on the specific
proportions of the above ingredients employed, it is possible to
produce a prepreg whose glass transition temperature (T.sub.g) is
significantly lower (20.degree. C.) than the optimal cure
temperature. For instance, manufacturers of composite shafts
frequently employ mold temperatures of 300.degree. F.-310.degree.
F. (147.degree. C.-153.degree. C.) to obtain rapid cure times.
However, such temperatures are generally above the T.sub.g of the
resin component, and while the resin component is fully cured, it
will be too soft to be removed from the mold. In such cases, a
manufacturer must cool the mold below the T.sub.g before removing
the cured component from the mold. This cooling step is an
additional, undesirable step, which increases the time required to
produce a component, lowers the number of components that can be
produced by a mold during a work cycle, and undesirably increases
costs. It would therefore be desirable to provide an epoxy resin
formulation, suitable for making prepregs, that exhibits reduced
cure times, and having a cure temperature that is either less than
or about (within 10.degree. C. of) the T.sub.g of the cured prepreg
material. While high temperature curing resin systems are known,
which have a cure temperature that is less than the T.sub.g of the
cured resin, such resin systems require long (in excess of two
hours) cure times. The prior art does not teach or suggest a rapid
curing epoxy resin formulation whose cure temperature is
sufficiently close to the T.sub.g of the cured resin so that
cooling of the mold is not required.
[0013] It would further be desirable to provide an epoxy resin
formulation that is not only suitable for making prepregs, which
can also be beneficially employed to fabricate thermosetting resin
adhesive film products by coating a relatively thin layer of resin
onto a backing material, such as paper or film. Such a
thermosetting resin adhesive film product will desirably have good
workability at room temperature, and be activated by exposure to an
appropriate temperature condition.
SUMMARY OF THE INVENTION
[0014] In accord with the present invention, a resin matrix
composition is defined that includes an epoxy resin having more
than one epoxide group per molecule, and a catalyst consisting of
2,4-toluene bis dimethyl urea, wherein a viscosity of said
composition is less than about 20,000 poise at about 40.degree. C.
Preferably, the composition also includes at least one latent
curing agent. In at least one embodiment, the at least one latent
curing agent is a dicyanopolyamide, most preferably DICY.
[0015] In at least one embodiment, the composition further includes
a thermoplastic additive. Preferably the thermoplastic additive is
at least one selected from of the group consisting of
polyvinylfluorides (PVFs), polymethylmethacrylates (PMMA),
polyarylethersulfones (PES), polysulfone (PSF), polyimides (PIs),
polyetherimides (PEIs), and polyethylene oxide (PEO).
[0016] Preferably the epoxy resin utilized in the composition
includes diglycidyl ethers of bisphenols, examples of which are
bisphenol A, bisphenol F, epoxy phenol novolacs, trifunctional
epoxy resins, tetrafunctional epoxy resins, and halogenated
derivatives thereof. More preferably, the diglycidyl ethers have an
average of not more than two vicinal epoxy groups per molecule.
When the epoxy resin is bisphenol A, it preferably has an epoxide
equivalent weight from about 170 to about 1400. Alternatively, the
bisphenol A that is employed is a blend of a first, bisphenol
A-type epoxy resin having an epoxy equivalent in the range of from
about 180 to about 195, and a second, bisphenol A-type epoxy resin
having an epoxy equivalent in the range of from about 1200 to about
1400, the amount and the molecular weight of the second epoxy resin
being such that the blended bisphenol A-type epoxy resin has a
number average molecular weight in the range of from about 200 to
about 300.
[0017] Preferably, an amount of the catalyst included in the
composition ranges from about 0.5 to about 10 phr (i.e., parts per
hundred of epoxy resin). Most preferably, the amount ranges from
about 2 to about 5 phr.
[0018] In at least one embodiment, the composition of the present
invention is 95% cured after being heated to 150.degree. C. for
five minutes, and/or 95% cured after being heated to 120.degree. C.
for 20 minutes. Preferably, after being cured at 150.degree. C.,
the composition has a T.sub.g that is higher than 140.degree. C.,
such that the composition does not need to be cooled before being
removed from a mold.
[0019] Another aspect of the present invention is directed to an
article resulting from curing a composition like that described
above, which also includes a reinforcing agent. Preferably the
reinforcing agent is at least one selected from the group
consisting of glass fibers, aramid fibers, graphite fibers, woven
fibers, matted fibers, and unidirectional fibers. Another aspect of
the present invention is directed to a resin matrix composition
that includes an epoxy resin made from a diglycidyl ether of
bisphenol, which has an average molecular weight in the range of
from about 200 to about 300. The matrix composition also includes a
latent amine curing agent, and a catalyst consisting of 2,4-toluene
bis dimethyl urea.
[0020] Yet another aspect of the present invention is directed to a
resin matrix composition that includes an epoxy resin, a latent
amine curing agent, and 2,4-toluene bis dimethyl urea, which is
used as a catalyst. The epoxy resin of such a composition
preferably is made from a mixture of a diglycidyl ether of
bisphenol A having an epoxide equivalent weight (EEW) of 176, and
diglycidyl ether of bisphenol A having an epoxide equivalent weight
(EEW) of 1200-1400.
[0021] Still another aspect of the present invention is directed to
a resin matrix composition that includes an epoxy resin made from a
mixture of a diglycidyl ether of bisphenol A having an epoxide
equivalent weight (EEW) of 176, a diglycidyl ether of bisphenol A
having an epoxide equivalent weight (EEW) of 1200-1400, and an
epoxy phenolic novalac resin with a functionality of above 3.6,
having an epoxide equivalent weight (EEW) of 174-180. Such a matrix
composition also includes a latent amine curing agent, and a
catalyst consisting of 2,4-toluene bis dimethyl urea.
[0022] Yet another aspect of the present invention is directed to a
resin matrix composition that includes an epoxy resin made from a
mixture of a diglycidyl ether of bisphenol A having an epoxide
equivalent weight (EEW) of 176, a diglycidyl ether of bisphenol A
having an epoxide equivalent weight (EEW) of 1200-1400, and a
tetra-functional epoxy having an epoxide equivalent weight (EEW) of
117-134. The matrix composition preferably also includes a latent
amine curing agent, and a catalyst consisting of 2,4-toluene bis
dimethyl urea.
[0023] Still another aspect of the present invention is a prepreg
that includes an epoxy composition and a reinforcing fiber. The
epoxy composition includes an epoxy resin having more than one
epoxide group per molecule, a latent amine curing agent, and a
catalyst consisting of 2,4-toluene bis dimethyl urea. In at least
one embodiment, the epoxy composition further includes a
thermoplastic additive selected from the group consisting of PVFs,
PMMAs, PESs, PSF, PIs, PEIs, and PEO.
[0024] A different aspect of the present invention is a prepreg
whose epoxy composition includes an epoxy resin having more than
one epoxide group per molecule, a latent amine curing agent, a
catalyst consisting of 2,4-toluene bis dimethyl urea, and a
polyvinyl formal dissolved into the epoxy composition. The
reinforcing fiber of such a prepreg can include at least one of
glass fibers, aramid fibers, graphite fibers, woven fibers, matted
fibers, and unidirectional fibers.
[0025] Yet another prepreg of the present invention includes an
epoxy composition including an epoxy resin having more than one
epoxide group per molecule, a latent amine curing agent, a catalyst
agent for reducing a cure time provided by the latent amine curing
agent; and a reinforcing fiber. Prepregs according to this aspect
of the invention have a gel time of less than 1.5 minutes at
150.degree. C., and a glass transition temperature of no less than
140.degree. C. when heated to a temperature of 150.degree. C. Such
prepregs reach a 95% cure after less than five minutes when heated
to a temperature of 150.degree. C., reach a 95% cure after less
than 20 minutes when heated to a temperature of 120.degree. C.
Preferably, these prepregs employ a catalyst consisting of
2,4-toluene bis dimethyl urea.
[0026] Still another aspect of the present invention is a prepreg
whose epoxy composition includes an epoxy resin having more than
one epoxide group per molecule, a latent amine curing agent, and a
catalyst agent for reducing a cure time provided by the latent
amine curing agent. Such prepregs also include a reinforcing fiber.
These prepregs are characterized by requiring no more than three
minutes to reach a 95% cure at 150.degree. C. Further, such
prepregs have a glass transition temperature of no less than
142.degree. C. when heated to a temperature of 150.degree. C. such
prepregs also preferably employ a catalyst consisting of
2,4-toluene bis dimethyl urea.
[0027] A further aspect of the present invention is a prepreg whose
glass transition temperature, when 95% cured, is such that the
cured prepreg does not need to be cooled before being removed from
a mold. Such a prepreg includes an epoxy resin having more than one
epoxide group per molecule, a latent amine curing agent, a catalyst
agent for reducing a cure time provided by the latent amine curing
agent, and a reinforcing fiber. Preferably, the catalyst consists
of 2,4-toluene bis dimethyl urea.
[0028] A different aspect of the present invention is a method for
decreasing a time required to reach a 95% cure for a thermosetting
epoxy resin formulation. The method steps include providing an
epoxy composition having epoxy resin with more than one epoxide
group per molecule, and a latent amine curing agent. The method
requires adding at least 0.5 phr of a catalyst to the epoxy
composition, the catalyst reducing the time required to reach a 95%
cure. The catalyst consists of 2,4-toluene bis dimethyl urea. The
resulting mixture is then heated to a curing temperature, and the
presence of the catalyst reduces the time required to reach a 95%
cure. Preferably, the step of heating includes selecting a curing
temperature such that a glass transition temperature of the epoxy
composition when 95% cured and at the curing temperature enables a
95% cured epoxy composition to be removed from a mold without
requiring the 95% cured epoxy composition to be cooled before being
removed from that mold. More preferably, the glass transition
temperature is either greater than the curing temperature, or no
more than 10.degree. C. less than the curing temperature.
Generally, the epoxy composition also includes a reinforcing
fiber.
[0029] Yet another aspect of the present invention is directed at a
carbon fiber reinforced epoxy resin article, superior in mechanical
properties, resulting from curing of the prepregs described
above.
[0030] Still another aspect of the present invention is directed to
an adhesive film, superior in handling and curing properties,
resulting from depositing a thin layer of the epoxy resin
formulation described above onto a substrate.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0031] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
becomes better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0032] FIGS. 1A-1C (Prior Art) illustrate the chemical structures
of exemplary epoxy curing accelerators;
[0033] FIG. 1D (Prior Art) illustrates the chemical structure of a
preferred catalyst used in the present invention;
[0034] FIG. 2 is a graph showing the relationship between gel time
and catalyst content when preferred resin compounds are mixed with
the preferred catalyst of FIG. 1D in accord with the present
invention;
[0035] FIG. 3 is a graph showing the relationship between gel time
and curing temperature, comparing a resin formulation embodiment of
the present invention with a prior art resin formulation;
[0036] FIG. 4 is a graph showing the relationship between glass
translation temperature and curing temperature, comparing a resin
formulation embodiment of the present invention with a prior art
resin formulation; and
[0037] FIG. 5 is a graph showing the relationship between glass
translation temperature and curing temperature, comparing a first
resin formulation embodiment of the present invention with a second
resin formulation embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] Overview of the Present Invention
[0039] The present invention defines a thermosetting epoxy
composition including an epoxy resin, a latent amine curing agent,
and a specific catalyst. The epoxy composition of the present
invention offers significantly reduced cure time compared to the
cure time of epoxy resin compositions described in the prior art.
This reduction in cure times is achieved across a wide range of
temperatures, such that the present invention can be employed in a
low temperature (i.e., less than 85.degree. C.) cure environment,
as well in high temperature cure environments (i.e., greater than
140.degree. C.). The epoxy composition of the present invention is
suitable for use as a prepreg composition. When used as a prepreg,
reinforcing fibers as well as specialty fillers can be included to
enhance the physical properties of the cured resin. Significantly,
a glass transition temperature of a 95% cured resin composition
produced in accord with the present invention is sufficient that
even during high temperature, fast cure applications, the 95% cured
resin does not need to be cooled prior to being removed from a
mold. Thus, the use of the prepregs formed in accord with the
present invention enables composite component manufacturers to
increase production rates without requiring additional molds be
provided, by offering reduced cure times as well as eliminating the
need to cool a cured resin component prior to removing it from a
mold.
[0040] Preferably the epoxy resin includes two epoxide groups per
molecule, and the latent amine curing agent is a dicyanopolyamide,
most preferably (DICY). It should be noted that diaminodiphenyl
sulfone (DDS) can also be beneficially employed as a latent amine
curing agent, as well as mixtures of DICY and DDS. The specific
catalyst is 2,4-toluene bis dimethyl urea. While other resin
compositions are known in which 2,4-toluene bis dimethyl urea is
employed alone or in conjunction with additional catalysts, the use
of 2,4-toluene bis dimethyl urea with the specific epoxy resins
disclosed below provides a startling and unexpected reduction in
the curing time for prepregs. For example, a prepreg employing the
epoxy composition of the present invention can achieve a 95% cure
in about one half of the time required by a prepreg that differs
only in the catalyst employed.
[0041] The prepregs used in the present invention are most
preferably prepared by the solventless, hot-melt impregnation
method to avoid the formation of microvoids caused by residual
volatile solvent, which are sometimes observed in prepregs prepared
by the solvent-diluting impregnation method. However, the present
invention can be implemented in accord with the solvent-diluting
method, as well.
[0042] Suitable resin compositions for the prepreg material of the
present invention can be selected from among those discussed below.
However, the resin compositions that can be used for the prepreg
material are not limited to those specifically noted. Generally
suitable epoxy resins have more than one epoxide group per
molecule. Such resins include, for example, diglycidyl ethers of
bisphenols, such as bisphenol A, bisphenol F, epoxy phenol
novolacs, trifunctional epoxy resins, tetrafunctional epoxy resins,
as well as the halogenated derivatives thereof. Chlorine and
bromine are the most common halogens used to form such derivatives.
Brominated epoxy can add anti-flammability to the composition.
Preferred epoxy resins include diglycidyl ethers having an average
of not more than two vicinal epoxy groups per molecule.
[0043] As noted above, the preferred latent curing agent is DICY,
which is employed in amounts from about 4 to about 8 phr, most
preferably in amounts from about 5 to about 7 phr. A key element of
the present invention is the use of a specific urea-based catalyst
or accelerator. It should be noted that the term catalyst and
accelerator are both employed in the art to describe an ingredient
that reduces curing time. While the latent amine curing agent is
still responsible for the curing process, the presence of small
amounts of catalysts or accelerators can significantly reduce cure
times. Thus, it should be understood that the terms "catalyst" and
"accelerator," as used herein and in the claims that follow, refer
to a chemical agent that reduces a cure time achievable with a
curing agent alone. The specific urea catalyst employed in the
present invention to achieve the previously unexpected reduction in
curing time is 2,4-toluene bis dimethyl urea. This catalyst is
employed in amounts of about 0.5 to about 10 phr, more preferably
in amounts from about 2 to about 5 phr, and most preferably in
amounts from about 3 to about 5 phr.
[0044] Also as noted above, suitable thermoplastic additives can be
added to prepregs made from the resin composition of the present
invention. Such thermoplastic additives can include any one or more
of PVFs, PMMAs, PESs, PSF, PIs, PEIs, PEO. More preferred
thermoplastic additives include PVFs and PESs. The most preferred
thermoplastic additives include PVFs. The thermoplastic additives
are employed in amounts ranging from about 0 to about 8% by weight
(based upon the weight of total blended composition). More
preferred amounts range from about 1 to about 4%, and most
preferred amounts range from about 2.5 to about 3.5% by weight.
[0045] It should also be noted that elastomeric additives can be
added to prepregs made from the resin composition of the present
invention. Such elastomeric additives can include any one or more
of natural latex rubbers, synthetic latex rubbers, silicones, and
other elastomers. The elastomeric additives are generally employed
in amounts of less than 10% by weight (based upon the weight of
total blended composition).
[0046] It is anticipated that a particularly useful prepreg can be
obtained by adding to the resin composition of the present
invention a reinforcing material. Suitable reinforcing materials
can be in the form of fabric, unidirectional fibers, and the like.
These reinforcing materials can be prepared from glass fibers,
aramid fibers, carbon fibers, and the like.
[0047] As noted above, it is known in the prior art to employ
urea-based catalysts to reduce the curing time achievable with
latent amine curing agents alone. FIG. 1A illustrates a chemical
structure 10 representing one such urea based catalyst, 2,6-toluene
bis dimethyl urea. The use of this catalyst is described in U.S.
Pat. No. 3,956,237, entitled "EPOXY RESIN COMPOSITIONS COMPRISING
LATENT AMINE CURING AGENTS AND NOVEL ACCELELATORS," filed Jul. 8,
1974. In addition to describing the use of 2,6-toluene his dimethyl
urea as a catalyst that is used alone, this patent also discloses
employing a combination of both 2,6-toluene bis dimethyl urea and
2,4-toluene bis dimethyl urea as a catalyst. The reference teaches
using 35-100% 2,6-toluene bis dimethyl urea, and 0-65% of
2,4-toluene bis dimethyl urea as a catalyst. FIG. 1B shows such a
catalyst mixture, including a chemical structure 20 of 2,4-toluene
bis dimethyl urea, as well as a chemical structure 10 for
2,6-toluene bis dimethyl urea, and the disclosed percentages.
Significantly, however, the '237 patent does not disclose the use
of 100% 2,4-toluene bis dimethyl urea as a catalyst.
[0048] FIG. 1C illustrates a chemical structure 40 for another
catalyst known in the prior art, 100%
3,4-dichlorophenyl-N,N-dimethyl urea (DCMU). This catalyst, which
is sold under the name of DYHARD UR200.RTM. by SKW Trostberg,
(Trostberg, Germany) was used to fabricate a control sample
identical to a test batch of the preferred embodiment of the
present invention except for the catalyst employed. As the
following examples will show, the present invention provides both
high temperature and low temperature cure times that are about one
half of the cure times achieved when DCMU is employed as a
catalyst.
[0049] FIG. 1D illustrates the chemical structure of the preferred
catalyst in the present invention, 100% 2,4-toluene bis dimethyl
urea. This catalyst is sold as OMICURE U-24.TM. by CVC Specialty
Chemicals, Inc. U.S. Pat. No. 3,386,956, entitled "LOW TEMPERATURE
CURABLE EPOXY RESIN ADHESIVE COMPOSITIONS WITH LONG STORAGE
STABILITY," discloses the use of 2,4-toluene bis dimethyl urea as a
catalyst, combined with DICY and polyepoxides to provide a resin
formulation that reaches a 76% cure after 90 minutes at temperature
of 187.degree. F. (87.degree. C.). Significantly, however, this
patent does not teach or suggest that employing 2,4-toluene bis
dimethyl urea as a catalyst will provide a fast curing epoxy resin
formulation at elevated temperatures (in excess of 87.degree. C.).
Furthermore, while the patent discloses that many types of
polyepoxide resins can be employed for the resin component portion
of the formulation containing a polyepoxide resin, DICY and a
2,4-toluene bis dimethyl urea catalyst, no specific class of
epoxies are identified that are known or expected to provide a more
rapidly curing epoxy formulation.
[0050] The present invention arises from a discovery that epoxy
resin formulations comprising polyepoxide resin, DICY and a
2,4-toluene bis dimethyl urea catalyst can be employed to provide a
fast curing resin at higher temperatures than reported in the art,
and that specific blends of polyepoxides enable a substantial
improvement over the 90 minute, 74% cure rate reported in the prior
art to be achieved. As will be detailed below, one embodiment of
the present invention is an epoxy resin formulation comprising a
specific blend of polyepoxides, DICY, and a 2,4-toluene bis
dimethyl urea catalyst that obtains a 95% cure at 130.degree. C. in
19 minutes, and a 95% cure at 150.degree. C. in as little as 3
minutes.
[0051] The resin composition of the present invention can be cured
at 150.degree. C. for 3 to 120 minutes and reach a translation
glass temperature of higher than 140.degree. C., more preferably
for 3 to 60 minutes, and most preferably for 3 to 20 minutes.
[0052] The resin composition of the present invention can be cured
at 80.degree. C. for 5 to 16 hours and reach a translation glass
temperature of higher than 100.degree. C., more preferably for 5 to
12 hour, and most preferably for 5 to 8 hours. Furthermore, one
unique aspect of the present invention is the ability to produce
prepreg formulations that can be cured at high temperatures, which
are very close to the glass transition temperature (T.sub.g) of the
formulation. In some prior art formulations, the high temperatures
required for a rapid cure time have been so much higher (greater
than 13.degree. C.) than the T.sub.g of the prior art formulations
that such resin compositions normally required cooling before being
removed from a mold. As the examples provided below show, the
present invention yields a faster curing resin (about 3 minutes
instead of about 7 minutes required using a conventional resin that
employs DCMU as a catalyst), with a smaller difference between
T.sub.g and the cure temperature. Thus, it is not necessary to
first cool a component fabricated from the cured resin of the
present invention before removing the component from a mold.
[0053] It is anticipated that the rapid curing/high temperature
curing resin composition and prepregs of the present invention can
be used to produce sporting goods, automobile components, aerospace
components, and marine components. Such uses, and the following
examples are illustrative of specific applications of the present
invention, but are not to be construed as limiting its scope. It is
further anticipated that the known epoxy resin formulation
disclosed in the prior patent referenced above (which discloses the
use of 2,4-toluene bis dimethyl urea as a catalyst, combined with
DICY and polyepoxides) can be employed at higher temperatures with
reduced cure times than the 76% cure after 90 minutes (at
temperature of 187.degree. F./87.degree. C.) disclosed in this
prior art patent.
[0054] The following epoxy resins are employed in the examples
discussed below. It should be noted that these specific blends of
epoxy resins are not suggested by the prior art, and empirical data
indicates that these specific blends provide surprisingly faster
cure times than suggested by the prior art in regard to epoxy
compositions employing different epoxy resin components.
Furthermore, the resin formulations identified below are expected
to have viscosity's that are less than 20,000 poise. Epoxy
formulations of less than 20,000 poise are preferred, having
favorable properties such as tackiness, which is useful for
compositions to be employed as prepregs or adhesive films. It is
anticipated that other epoxy formulations than those specifically
enumerated below can be beneficially employed in the present
invention, if such formulations have a viscosity of less 20,000
poise. In addition to having a particular viscosity, it is also
preferred for formulations in accord with the present invention to
have an average molecular weight of around 200-300. To achieve this
desired range, a quantity of a relatively high molecular weight
resin (i.e., a molecular weight over 1,000) will be mixed with an
appropriate quantity of a relatively low molecular weight resin
(i.e., a molecular weight less than 200).
[0055] Epoxy resin A is a diglycidyl ether of bisphenol A having an
epoxide equivalent weight (EEW) of 176. It is anticipated that
diglycidyl ethers of bisphenol A having EEW of 170-195 can also be
beneficially employed.
[0056] Epoxy resin B is a diglycidyl ether of bisphenol A having an
epoxide equivalent weight (EEW) of 1200-1400.
[0057] Epoxy resin C is an epoxy phenolic novalac resin with a
functionality of above 3.6, having an EEW of 174-180.
[0058] Epoxy resin D is a tetra-functional epoxy having an EEW of
117-134.
[0059] Thermoplastic additive is PVF powder.
[0060] Curing agent is DICY.
[0061] Catalyst is 2,4-toluene bis dimethyl urea (sold as OMICURE
U-24.TM., made by CVC Specialty Chemicals, Inc.).
[0062] Catalyst in the control resin composition is
3,4-dichlorophenyl-N,N-dimehtylurea (sold as DYHARD UR200.TM., made
by SKW Trostberg).
Exemplary Epoxy Compositions 1-6
[0063] Epoxy resin compositions described in Examples 1-6 were
prepared by blending 100 parts of epoxy resin A and B (divided as
shown in Table 1), 3.4 parts of PVF, and 5 parts of DICY with 0.5,
1, 2, 3, 4, and 5 parts of U-24, respectively. The gel time of each
composition was determined by a gel machine at 150.degree. C. Resin
samples of each composition were cured at 150.degree. C. for 15
minutes in an oven. The cured resin T.sub.g was determined by
dynamic mechanic analysis (DMA) on a TA Instruments machine, Model
2980.
1 TABLE 1 Composition No./Amount (parts) 1 2 3 4 5 6 Epoxy Resin A
76.4 76.4 76.4 76.4 76.4 76.4 Epoxy Resin B 23.6 23.6 23.6 23.6
23.6 23.6 PVF 3.4 3.4 3.4 3.4 3.4 3.4 DICY 5.0 5.0 5.0 5.0 5.0 5.0
U24 0.5 1 2 3 4 5 Gel Time @ 150.degree. C. (min.) 6.4 3.3 2.2 1.8
1.6 1.3 Tg by DMA G' (.degree. C.) 119 130 140 145 141 140
[0064] FIG. 2 illustrates a graph showing the relationship between
U-24 content and gel time.
Exemplary Epoxy Composition 7
[0065] An epoxy resin composition having the following formulation
was prepared by blending 100 parts of epoxy A and B (in the
relative amounts shown in Table 2), 3.4 parts of PVF, 5 parts of
DICY, with 4.2 parts of U-24. The viscosity of the resin or resin
mixture was determined by a Rheometric Model ARES plate rheometer
running from about 40.degree. C. to about 160.degree. C. at
2.degree. C./minute temperature ramp, and at a 10 rpm frequency.
The heat stability was determined by the viscosity increase versus
the time at 70.degree. C. The gel time was determined by a gel
machine. Digital Scanning Calorimetry was utilized to monitor the
time to reach 95% cure. The total heat detected during the DSC
measurement is identified to the heat evolved by the curing
reaction when resin was heat from 10.degree. C. to 225.degree. C.
at 10.degree. C./min rate. The degree of curing was given by 1 cure
% = ( Hi - He ) Hi .times. 100
[0066] where .DELTA.Hi is the heat generated by the uncured resin
heated from 10.degree. C. up to fully cured at 225.degree. C. and
.DELTA.He the heat generated by the certain degree cured resin
heated up to fully cured at 225.degree. C.
[0067] The value of T.sub.g was determined by dynamic mechanic
analysis (DMA) on an Alpha Technologies Model APA 2000.
[0068] A resin sample was degassed and poured into a mold
consisting of two 13 in..times.13 in..times.0.125 in. (330
mm.times.330 mm.times.3.175 mm) polished steel plates, separated by
0.125 in (3.175 mm) silicone rubber spacers. The case mixtures were
allowed to cure at about 120.degree. C. for about 120 min. After
cooling, the cast sheet was demolded and prepared for testing by
the following methods: ASTM D-638 (tensile); ASTM D-790 (flexural);
and ASTM D-5045 (fracture toughness).
Control Epoxy Composition 7
[0069] An epoxy resin composition having the following composition
was prepared by blending 100 parts of epoxy A and B (in the
relative amounts shown), 3.4 parts of PVF, 5 parts of DICY, with
4.2 parts of UR200. The resins and resin mixtures and results of
the experiments are given in Table 2.
2 TABLE 2 Composition 7 Control Composition 7 Epoxy resin A parts
76.4 76.4 Epoxy resin B parts 23.6 23.6 PVF parts 3.4 3.4 DICY
parts 5.0 5.0 U24 parts 4.2 UR200 parts 4.2 Total parts 112.6 112.6
Gel time (min.) @ 130.degree. C. 3.9 6.0 @ 150.degree. C. 1.5 3.0
Time to reach 95% cure (min) @ 130.degree. C. 19 50 @ 150.degree.
C. 3 10 Tg (.degree. C.) (Max G") Cured at 130.degree. C. for 60
min 142 125 Tensile Ult. Strength, ksi 12.2 10.8 Modulus, msi 0.46
0.43 Elongation, % 5.0 3.9 Flexure Yield Strength, ksi 19.2 18.1
Modulus, msi 0.46 0.45 Compression Yield Strength, ksi 16.3 15.2
Modulus, msi 0.45 0.45 K.sub.1c (ksi-in.sup.1/2) 1.16 0.83
Properties of Exemplary Epoxy Composition 7 and Control Epoxy
Composition 7
[0070] The resin compositions of Exemplary Epoxy Composition 7 and
Control Epoxy Composition 7 were tested for isothermal cure
properties at 176.degree. F. (80.degree. C.), 212.degree. F.
(100.degree. C.), 230.degree. F. (110.degree. C.), 250.degree. F.
(121.degree. C.), 270.degree. F. (132.degree. C.), and 300.degree.
F. (149.degree. C.). All tests were done on the ALPHA Technologies
APA 200 equipped with parallel plate pies. FIGS. 3 and 4 show the
gel time and T.sub.g of these resins (Exemplary Epoxy Composition 7
and Control Epoxy Composition 7) cured at the afore mentioned
temperatures.
[0071] Next, a frozen resin block of Exemplary Epoxy Composition 7
was heated at 70.degree. C. for a short time and coated onto a
releasing paper to obtain a resin film. This resin film was set in
a prepreg machine and impregnated into a sheet of unidirectional
arranged carbon fiber (Type T600S, commercially available from
Toray Industries, Inc.) to obtain a prepreg having a resin content
Wr of 42%.
[0072] Exemplary Prepreg 1 (prepared from Exemplary Epoxy
Composition 7) was cured at 135.degree. C. for 2 hours and tested
for mechanical properties. Exemplary Prepreg 2 (also prepared from
Exemplary Epoxy Composition 7) was cured at 80.degree. C. for 5
hours and tested for mechanical properties. Table 3 reveals the
cure characteristics of these two prepreg examples.
3 TABLE 3 Cured at Cured at 135.degree. C./2 hr 80.degree. C./5 hr
0.degree. Tensile Strength (ksi) 377 367 Modulus (msi) 19.9 20.1
Strain (%) 1.8 1.8 90.degree. Tensile Strength (ksi) 8.2 6.7
0.degree. Compression Strength (ksi) 201 220 ILSS (ksi) 11.7 12.2
0.degree. Flexure Strength (ksi) 254 282 Modulus (ksi) 20.8 20.2
+/- 45.degree. IPS Strength (ksi) 18.5 16.1 T.sub.g by DMA G'
(.degree. C.) 144 118
[0073] The resin composition and prepregs of the present invention
can cure about twice as fast as the control materials, and have a
T.sub.g that is higher than the cure temperature when used as a
250.degree. F. cure system. Their shelf life and work life (heat
stability) are as good as the slow cured control materials.
Furthermore, the resin composition and prepregs of the present
invention can also be used in low temperature curing application
such as at curing at 80.degree. C.
Exemplary Epoxy Compositions 8 and 9
[0074] Epoxy resin compositions 8 and 9 were prepared by blending
100 parts of epoxy A, B and C or A, B and D (in the relative
amounts shown in Table 3), 3.4 parts of PVF, 5 parts of DICY, with
4.2 parts of U-24. The resin compositions 8 and 9 were tested for
isothermal cure properties at 176F (80.degree. C.), 250F
(121.degree. C.), 270F (132.degree. C.), and 300F (149.degree. C.).
All tests were done on the ALPHA Technologies APA 200 equipped with
parallel plate pies. The value of T.sub.g was determined by dynamic
mechanic analysis (DMA) on an Alpha Technologies Model APA
2000.
4 TABLE 4 Composition 8 Composition 9 Epoxy resin A parts 37.5 63.5
Epoxy resin B parts 23.6 23.6 Epoxy resin C parts 38.9 Epoxy resin
D parts 12.9 PVF parts 3.4 3.4 DICY parts 5.0 5.0 U24 parts 4.2 4.2
Total parts 112.6 112.6
[0075] FIG. 5 shows the T.sub.g of these resins cured at the
previously mentioned temperatures.
[0076] It should be noted that there exist several different
methods of measuring and reporting T.sub.g. For example, when
storage modulus (G'), loss modulus (G"), and Tan Delta versus
temperature curves are plotted for a polymer, the T.sub.g can be
generally identified by the portion of the curve that has a
pronounced change in slope. How that slope is interpreted results
in differences in reported T.sub.g values. For example, T.sub.g
values can be expressed as onset G' values, mid-point on G' slope
values, Max G" values, and Max Tan Delta values, each representing
a different portion of the heat versus temperature curve. The
selected value is generally based on some preference of the user,
or a default employed by a specific analytical unit. It should be
noted that the T.sub.g values listed in Table 1 are the mid-point
on G' slope values, while the T.sub.g values listed in Table 2 and
FIGS. 4 and 5 are Max G" values.
[0077] Although the present invention has been described in
connection with the preferred form of practicing it, those of
ordinary skill in the art will understand that many modifications
can be made thereto within the scope of the claims that follow.
Accordingly, it is not intended that the scope of the invention in
any way be limited by the above description, but instead be
determined entirely by reference to the claims that follow.
* * * * *