U.S. patent application number 14/982057 was filed with the patent office on 2016-06-30 for benzoxazines and compositions containing the same.
This patent application is currently assigned to Cytec Industries Inc.. The applicant listed for this patent is Cytec Industries Inc.. Invention is credited to Paul Mark Cross, Ram B. Gupta, Mark Edward Harriman.
Application Number | 20160185908 14/982057 |
Document ID | / |
Family ID | 56163443 |
Filed Date | 2016-06-30 |
United States Patent
Application |
20160185908 |
Kind Code |
A1 |
Harriman; Mark Edward ; et
al. |
June 30, 2016 |
BENZOXAZINES AND COMPOSITIONS CONTAINING THE SAME
Abstract
A curable composition containing more than 80% by weight of a
blend of benzoxazines, wherein the blend includes (A) one or more
multifunctional benzoxazines and (B) a liquid, non-halogenated
monofunctional benzoxazine. This composition has been found to be
stable at high temperatures, e.g. 180.degree. C.-250.degree. C.,
and suitable for making composite materials using conventional
techniques such as prepregging and liquid resin infusion.
Inventors: |
Harriman; Mark Edward;
(North Yorkshire, GB) ; Cross; Paul Mark; (York,
GB) ; Gupta; Ram B.; (Stamford, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cytec Industries Inc. |
Woodland Park |
NJ |
US |
|
|
Assignee: |
Cytec Industries Inc.
Woodland Park
NJ
|
Family ID: |
56163443 |
Appl. No.: |
14/982057 |
Filed: |
December 29, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62097280 |
Dec 29, 2014 |
|
|
|
Current U.S.
Class: |
428/114 ;
156/180; 264/257; 442/59; 524/876; 525/420; 528/210 |
Current CPC
Class: |
C08J 5/04 20130101; C07D
265/16 20130101; C08J 2361/34 20130101; B29C 39/003 20130101; B29C
43/003 20130101; C08K 5/357 20130101; C08L 61/34 20130101; C08G
73/0233 20130101; C08G 14/06 20130101; C08J 5/24 20130101; C08J
5/18 20130101; C08L 61/34 20130101; C08L 61/34 20130101 |
International
Class: |
C08G 73/02 20060101
C08G073/02; C08J 5/24 20060101 C08J005/24; C08J 5/18 20060101
C08J005/18 |
Claims
1. A curable composition comprising more than 80% by mass of a
benzoxazine blend, said benzoxazine blend comprising: (A) a
non-halogenated, benzoxazine compound in liquid form at temperature
range of 20.degree. C.-30.degree. C. and selected from the
following Structure 1 ##STR00011## and (B) a multifunctional
benzoxazine component comprising one or more benzoxazine compounds
with functionality of 2 or greater.
2. The curable composition of claim 1, wherein the mass ratio of
(A) to (B) is from about 50:50 to about 10:90.
3. The curable composition of claim 1, wherein the composition
exhibits an uncured T.sub.g of room temperature (20.degree.
C.-30.degree. C.) or lower as measured by Differential Scanning
calorimetry (DSC).
4. The curable composition of claim 1, wherein the composition has
viscosity of 5 Pas or less, preferably 1 Pas or less, at processing
temperature in the range of 100.degree. C.-150.degree. C.
5. The curable composition of claim 1, wherein the multifunctional
benzoxazine component (B) is a di-functional benzoxazine, and the
weight ratio of monofunctional benzoxazine to difunctional
benzoxazine is about 30:70.
6. The curable composition of claim 1, wherein the benzoxazine
blend comprises the liquid benzoxazine compound of Structure 1 and
a trifunctional benzoxazine compound, and the mass ratio of liquid
benzoxazine to trifunctional benzoxazine is from about 50:50 to
about 10:90.
7. The curable composition of claim 1, wherein the multifunctional
benzoxazine component (B) comprises a combination of a difunctional
benzoxazine compound and a trifunctional benzoxazine compound, and
the tri-functional benzoxazine compound is present in an amount of
no more than 25% by weight based on the total weight of the
benzoxazine blend.
8. The curable composition of claim 5, wherein the difunctional
benzoxazine compound is selected from: ##STR00012##
9. The curable composition of claim 6, wherein the trifunctional
benzoxazine compound is selected from: ##STR00013##
10. The curable composition of claim 1, wherein the multifunctional
benzoxazine component (B) comprises a combination of m-substituted
difunctional benzoxazine compound and m-substituted trifunctional
benzoxazine trifunctional benzoxazine compound, and the
trifunctional benzoxazine is at maximum 15% by weight based on the
total weight of the benzoxazine blend.
11. The curable composition of claim 1, wherein the curable
composition is void of or contains less than 5% by weight, based on
the total weight of the composition, of any thermosettable resin
selected from epoxy, cyanate ester, bismaleimide, and
phenol-formaldehyde.
12. The curable composition of claim 1, wherein the curable
composition is void of any organic solvent.
13. The curable composition of claim 1, wherein the curable
composition is thermally stable a temperature in the range of about
180.degree. C. to about 250.degree. C.
14. A continuous resin film formed from the curable composition of
claim 1.
15. A composite material comprising reinforcement fibers
impregnated or infused with the curable composition of claim 1.
16. The composite material of claim 15, wherein the reinforcement
fibers are selected from carbon fibers, glass fibers, and aramid
fibers.
17. The composite material of claim 1, wherein the reinforcement
fibers are in the form of unidirectional fibers, a fabric, or a
preform comprised of an assembly of fibers or fabric plies.
18. A method for forming a prepreg comprising: (i) forming at least
one continuous resin film from the curable composition of claim 1;
and (ii) pressing the continuous resin film onto a layer of
reinforcement fibers with application of heat so as to impregnate
the layer of reinforcement fibers.
19. The method of claim 18, wherein the layer of reinforcement
fibers is in the form of unidirectional fibers.
20. A prepreg produced by the method of claim 18.
21. A method for fabricating a composite part comprising: (i)
providing a preform comprising an assembly of fibers or fabric
plies on a mold surface; (ii) infusing the preform with the curable
composition of claim 4; and (iii) curing the infused preform.
22. A curable composite part produced by infusing a fibrous preform
with the curable composition of claim 4.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/097,280 filed Dec. 29, 2014, the
disclosure of which is incorporated by reference in its
entirety.
[0002] Benzoxazines offer a number of advantages as compared to
other thermosetting resins including relatively long shelf-life,
molecular design flexibility, low cost, high glass transition
temperature (T.sub.g), high modulus, relatively low viscosities,
good flame retardant properties (due to a high phenolic and
tertiary amine content), low moisture absorption, no by-products
released during curing and very low shrinkage upon curing.
Furthermore, benzoxazines are capable of being self-cured upon
heating; i.e. there is no need for an additional curing agent. This
combination of properties means that benzoxazines are potentially
attractive for use in aerospace applications. In particular they
may be useful as the thermosetting matrix in composite materials.
However, currently available multifunctional benzoxazines are
glassy solids at room temperatures making them difficult to process
using standard techniques such as prepregging for the fabrication
of fiber-reinforced resin composites, such as those used for
aerospace applications.
[0003] "Prepregging" refers to the process of impregnating
unidirectionally aligned reinforcing fibers or woven fabric with a
resin matrix to form prepregs in the form of tapes or sheets. These
prepregs are then laid up onto each other in a particular
orientation on a tool to form a laminate. The prepreg lay-up is
then subjected to elevated temperature and pressure to cure and
consolidate the composite part. The method of pressure application
is dependent on the part and configuration, but the use of an
autoclave is most common for high-performance structural parts.
[0004] Resin infusion approach differs from that of conventional
prepregging in that dry structural reinforcement fibers are placed
into a mold cavity or other shaping tool, and a matrix resin is
injected or infused into the structural reinforcement fibers. Resin
infusion covers processing techniques such as Resin Transfer
Molding (RTM), Liquid Resin Infusion (LRI), Resin Infusion under
Flexible Tooling (RIFT), Vacuum Assisted Resin Transfer Molding
(VARTM), Resin Film Infusion (RFI) and the like. Such conventional
techniques require the resins to be of relatively low viscosity and
to be thermally stable at processing temperatures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 shows Thermogravimetric Analysis (TGA) of various
monofunctional liquid benzoxazines for comparison.
[0006] FIG. 2 shows TGA of monofunctional benzoxazines derived from
using different amines: aniline, o-toluidine, m-toluidine, and
p-toluidine.
DETAILED DESCRIPTION
[0007] Neat benzoxazine resins based on multifunctional
benzoxazines are very glass-like at room temperature (20.degree.
C.-30.degree. C.), meaning that they also have very poor
processability characteristics. Liquid monofunctional benzoxazines
can lower uncured resin T.sub.g to room temperature (20.degree.
C.-30.degree. C.) or lower, allowing enhanced processability by
conventional prepregging processes. Some liquid monofunctional
benzoxazines are commercially available, e.g. Huntsman's RDB
2009-008, but they are limited in application as they suffer from
being unstable at temperatures normally used in cure cycles for the
manufacture of aerospace composite structures (180.degree. C. or
higher). Several benzoxazine hybrid formulations based on
epoxy-benzoxazine blends are commercially available (Henkel Loctite
BZ 9703, BZ 9704, BZ 9705.2), but the addition of the epoxy as a
co-reactant negates some of the benefits brought on by neat
benzoxazines, such as modulus and the cured dry-wet T.sub.g
differential.
[0008] Neat benzoxazine resins based on multifunctional
benzoxazines are very viscous in their melt state meaning that they
also have very poor resin infusion processability characteristics.
Liquid monofunctional benzoxazines can decrease viscosity at
typical infusion temperatures, allowing enhanced processability.
Some liquid monofunctional benzoxazines are commercially available,
e.g. Huntsman's RDB 2009-008, but they are limited in application
as they suffer from being very unstable at temperatures normally
used in cure cycles for the manufacture of aerospace composite
structures (180.degree. C. or higher), potentially causing issues
with voiding. Several benzoxazine hybrid formulations based on
epoxy-benzoxazine blends are commercially available (Henkel Loctite
BZ 9110, BZ 9120, BZ 9130), but the addition of the epoxy as a
co-reactant negates some of the benefits brought on by neat
benzoxazines, such as modulus and the cured dry-wet T.sub.g
differential.
[0009] To address the issues relating to process-ability of
benzoxazine resins, a benzoxazine-based composition containing a
blend of one or more multifunctional benzoxazines having
functionality of 2 or greater and a liquid, non-halogenated
monofunctional benzoxazine is disclosed herein. The blend of
benzoxazines is making up for more than 80% by weight of the
curable composition. According to one embodiment, the
benzoxazine-based composition can be formulated to have an uncured
T.sub.g of 15.degree. C. to 22.degree. C., viscosity below 2 Pas at
about 30.degree. C. and be stable at high temperatures within the
range of 180.degree. C.-250.degree. C. In another embodiment, the
composition is formulated to have an uncured T.sub.g of 20.degree.
C. to 30.degree. C. for the purpose of fabricating prepreg
therefrom. The uncured T.sub.g as discussed herein is measured by
Differential Scanning calorimetry (DSC). In yet another embodiment,
the composition is formulated to have a viscosity of less than 5
Pas at injection temperature for resin infusion, for example, in
the range of about 100.degree. C. to about 150.degree. C.
[0010] As used herein, "monofunctional benzoxazine" refers to a
compound which does not have more than one benzoxazine unit, or a
compound which is substantially a reaction product of monohydric
phenol and monofunctional amine, and "multifunctional benzoxazine"
refers to a compound having more than one benzoxazine unit. The
benzoxazine unit being referred herein includes an oxazine ring
pendant to a benzene ring).
Non-Halogenated Monofunctional Benzoxazine
[0011] The non-halogenated, monofunctional benzoxazine compound of
the present disclosure is represented by the following Structure
1:
##STR00001##
[0012] It has been discovered that other monofunctional benzoxazine
compounds having similar structures (Structures 2-10 below) are
unstable at the same temperature range. This shows the
unpredictable nature of monofunctional benzoxazine compounds.
##STR00002## ##STR00003##
[0013] The non-halogenated, monofunctional benzoxazine compound of
Structure 1 is in liquid form at temperature between 20.degree.
C.-30.degree. C., particularly, 20.degree. C.-25.degree. C. and has
a viscosity of 5 Pas at about 30.degree. C. It remains in its
liquid state for a long period of time, at least 4 years. Moreover,
it is thermally stable at temperatures within the range of
180.degree. C.-250.degree. C. "Thermally stable" means that the
benzoxazine does not decompose, i.e. liberate volatile species
either during or after cure in the temperature range of up to
250.degree. C., and shows weight loss of less than 15% at this
temperature range as determined by Thermogravimetric Analysis
(TGA). FIG. 1 shows the TGA analysis of the monofunctional
benzoxazine compounds of Structures 1-10 for comparison.
[0014] In one embodiment, the non-halogenated monofunctional
benzoxazine could be synthesized by reacting m-cresol, aromatic
amine, and paraformaldehyde. The reaction is depicted below with
3,5-xylidine as the representative aromatic amine.
##STR00004##
The stoichiometry for m-cresol, paraformaldehyde, and aromatic
amine is 1:2:1 molar ratio.
[0015] The temperature stability discussed above is unusual for
non-halogenated, liquid benzoxazines. While not wanting to be bound
by any theory, it is believed that this temperature stability is
due to the favouring of a specific reaction site on the molecule by
judicious choice of substituents on the aniline.
[0016] The liquid, monofunctional benzoxazine of the present
disclosure may be blended with difunctional and/or trifunctional
benzoxazines to improve the process-ability of these
multifunctional benzoxazines, which are normally solid at room
temperature. The presence of liquid monofunctional benzoxazine
improves the process-ability of the benzoxazine-based resin
composition by reducing the viscosity and reducing T.sub.g of the
uncured composition, making it suitable for resin-film impregnation
of reinforcement fibers to form prepregs by lowering the uncured
T.sub.g and/or suitable for liquid resin infusion of dry fibrous
preform, e.g., via RTM, by lowering the viscosity.
Difunctional Benzoxazines
[0017] The difunctional benzoxazines that are suitable for the
purposes herein include those represented by the following Formula
I:
##STR00005##
where
[0018] Z.sup.1 is selected from a direct bond,
--C(R.sup.3)(R.sup.4)--, --C(R.sup.3)(aryl)-, --C(O)--, --S--,
--O--, --S(O)--, --S(O).sub.2--, a divalent heterocycle and
--[C(R.sup.3)(R.sup.4)].sub.x-arylene-[C(R.sup.5)(R.sup.6)].sub.y--,
or the two benzyl rings of the benzoxazine moieties may be fused;
and
[0019] R.sup.1 and R.sup.2 are independently selected from alkyl
(preferably C.sub.1-8 alkyl), cycloalkyl (preferably C.sub.5-7
cycloalkyl, preferably C.sub.6 cycloalkyl) and aryl, wherein the
cycloalkyl and aryl groups are optionally substituted, for instance
by C.sub.1-8 alkyl, halogen and amine groups, and preferably by
C.sub.1-8 alkyl, and where substituted, one or more substituent
groups (preferably one substituent group) may be present on each
cycloalkyl and aryl group;
[0020] in one embodiment, Z.sup.1 is selected from a direct bond,
--C(R.sup.3)(R.sup.4)--, --C(R.sup.3)(aryl)-, --C(O)--, --S--,
--O--, a divalent heterocycle and
--[C(R.sup.3)(R.sup.4)].sub.x-arylene-[C(R.sup.5)(R.sup.6)].sub.y--,
or the two benzyl rings of the benzoxazine moieties may be
fused;
[0021] R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are independently
selected from H, C.sub.1-8 alkyl (preferably C.sub.1-4 alkyl, and
preferably methyl), and halogenated alkyl (wherein the halogen is
typically chlorine or fluorine (preferably fluorine) and wherein
the halogenated alkyl is preferably CF.sub.3); and
[0022] x and y are independently 0 or 1;
[0023] where Z.sup.1 is selected from a divalent heterocycle, it is
preferably 3,3-isobenzofuran-1(3h)-one, i.e. wherein the compound
of formula (I) is derived from phenolphthalein;
[0024] where Z.sup.1 is selected from
--[C(R.sup.3)(R.sup.4)].sub.x-arylene-[C(R.sup.5)(R.sup.6)].sub.y--,
then the chain linking the two benzoxazine groups may further
comprise one or more arylene group(s) and/or one or more
--C(R.sup.7)(R.sup.8)-- group(s) where R.sup.7 and R.sup.8 are
independently selected from the groups defined hereinabove for
R.sup.3.
[0025] In a preferred embodiment, the arylene group is phenylene.
In one embodiment, the groups attached to the phenylene group may
be configured in para- or meta-positions relative to each other. In
a preferred embodiment, the aryl group is phenyl.
[0026] The group Z.sup.1 may be linear or non-linear, and is
typically linear. The group Z.sup.1 is preferably bound to the
benzyl group of each of the benzoxazine moieties at the
para-position relative to the oxygen atom of the benzoxazine
moieties, as shown in formula (I), and this is the preferred
isomeric configuration. However, the group Z.sup.1 may also be
attached at either of the meta-positions or the ortho-position, in
one or both of the benzyl group(s) in the bis-benzoxazine compound.
Thus, the group Z.sup.1 may be attached to the benzyl rings in a
para/para; para/meta; para/ortho, meta/meta or ortho/meta
configuration. In one embodiment, the difunctional benzoxazine
resin component comprises a mixture of isomers, preferably wherein
the major portion of the mixture is the para/para isomer shown in
Formula I and preferably this is present in at least 75 mol %,
preferably at least 90 mol %, and preferably at least 99 mol %, of
the total isomeric mixture.
[0027] In a preferred embodiment, the difunctional benzoxazine is
selected from compounds wherein Z.sup.1 is selected from
--C(CH.sub.3).sub.2--, --CH.sub.2-- and
3,3-isobenzofuran-1(3H)-one, i.e. benzoxazine derivatives of
bisphenol A, bisphenol F and phenolphthalein.
[0028] In another embodiment, the difunctional benzoxazine is
selected from compounds wherein R.sup.1 and R.sup.2 are
independently selected from aryl, preferably phenyl. In one
embodiment, the aryl group may be substituted, preferably wherein
the substituent(s) are selected from C.sub.1-8 alkyl, and
preferably wherein there is a single substituent present on at
least one aryl group. C.sub.1-8 alkyl includes linear and branched
alkyl chains. Preferably, R.sup.1 and R.sup.2 are independently
selected from unsubstituted aryl, preferably unsubstituted
phenyl.
[0029] The benzyl ring in each benzoxazine group of the
di-functional benzoxazine compounds defined herein may be
independently substituted at any of the three available positions
of each ring, and typically any optional substituent is present at
the position ortho to the position of attachment of the Z.sup.1
group. Preferably, however, the benzyl ring remains
unsubstituted.
[0030] An alternative Formula II for the difunctional benzoxazines
is represented below:
##STR00006##
wherein
[0031] Z.sup.1 is selected from a direct bond,
--C(R.sup.3)(R.sup.4)--, --C(R.sup.3)(aryl)-, --C(O)--, --S--,
--O--, --S(O)--, --S(O).sub.2--, a divalent heterocycle and
--[C(R.sup.3)(R.sup.4)].sub.x-arylene-[C(R.sup.5)(R.sup.6)].sub.y--,
or the two benzyl rings may be fused; and
[0032] R.sup.1 and R.sup.2 are independently selected from
hydrogen, alkyl (preferably C.sub.1-8 alkyl), cycloalkyl
(preferably C.sub.5-7 cycloalkyl, preferably C.sub.6 cycloalkyl)
and aryl, wherein the cycloalkyl and aryl groups are optionally
substituted, for instance by C.sub.1-8 alkyl, halogen and amine
groups, and preferably by C.sub.1-8 alkyl, and where substituted,
one or more substituent groups (preferably one substituent group)
may be present on each cycloalkyl and aryl group;
[0033] in one embodiment, Z.sup.1 is selected from a direct bond,
--C(R.sup.3)(R.sup.4)--, --C(R.sup.3)(aryl)-, --C(O)--, --S--,
--O--, a divalent heterocycle and
--[C(R.sup.3)(R.sup.4)].sub.x-arylene-[C(R.sup.5)(R.sup.6)].sub.y--,
or the two benzyl rings may be fused;
[0034] R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are independently
selected from H, C.sub.1-8 alkyl (preferably C.sub.1-4 alkyl, and
preferably methyl), and halogenated alkyl (wherein the halogen is
typically chlorine or fluorine (preferably fluorine) and wherein
the halogenated alkyl is preferably CF.sub.3); and x and y are
independently 0 or 1;
[0035] where Z.sup.1 is selected from a divalent heterocycle, it is
preferably 3,3-isobenzofuran-1(3h)-one, i.e. wherein the compound
of formula (II) is derived from phenolphthalein;
[0036] where Z.sup.1 is selected from
--[C(R.sup.3)(R.sup.4)].sub.x-arylene-[C(R.sup.5)(R.sup.6)].sub.y--,
then the chain linking the two benzoxazine groups may further
comprise one or more arylene group(s) and/or one or more
--C(R.sup.7)(R.sup.8)-- group(s) where R.sup.7 and R.sup.8 are
independently selected from the groups defined hereinabove for
R.sup.3, provided that the or each substituted or unsubstituted
methylene group is not adjacent to another substituted or
unsubstituted methylene group.
[0037] In a preferred embodiment, the arylene group is phenylene.
In one embodiment, the groups attached to the phenylene group may
be configured in para- or meta-positions relative to each other. In
a preferred embodiment, the aryl group is phenyl.
[0038] The group Z.sup.1 may be linear or non-linear, and is
typically linear. The group Z.sup.1 may be attached at the
meta-positions, the para-positions or the ortho-position, in one or
both of the benzyl group(s) in the bis-benzoxazine compound. Thus,
the group Z.sup.1 may be attached to the benzyl rings in a
para/para; para/meta; para/ortho, meta/meta or ortho/meta
configuration. In one embodiment, the thermoset benzoxazine resin
component (A) comprises a mixture of isomers, preferably wherein
the major portion of the mixture is the para/para isomer shown in
structure IV, and preferably this is present in at least 75 mol %,
preferably at least 90 mol %, and preferably at least 99 mol %, of
the total isomeric mixture.
[0039] In a preferred embodiment, the di-functional benzoxazine is
selected from compounds wherein Z.sup.1 is selected from
--C(CH.sub.3).sub.2--, --CH.sub.2-- and
3,3-isobenzofuran-1(3H)-one
[0040] In another embodiment, the difunctional benzoxazine is
selected from compounds wherein R.sup.1 and R.sup.2 are
independently selected from aryl, preferably phenyl. In one
embodiment, the aryl group may be substituted, preferably wherein
the substituent(s) are selected from C.sub.1-8 alkyl, and
preferably wherein there is a single substituent present on at
least one aryl group. C.sub.1-8 alkyl includes linear and branched
alkyl chains. Preferably, R.sup.1 and R.sup.2 are independently
selected from unsubstituted aryl, preferably unsubstituted
phenyl.
[0041] The benzyl ring in the di-functional benzoxazine compounds
defined herein may be independently substituted at any of the three
available positions of each ring, and typically any optional
substituent is present at the position ortho to the position of
attachment of the Z.sup.1 group. Preferably, however, the benzyl
ring remains unsubstituted.
[0042] Specific examples of suitable di-functional benzoxazines
include:
##STR00007##
[0043] In a preferred embodiment, the di-functional benzoxazine is
meta-substituted difunctional (or bis-) benzoxazine or
di-meta-substituted difunctional benzoxazine.
##STR00008##
Tri-Functional Benzoxazines
[0044] Suitable tri-functional benzoxazines include compounds
derived from reacting aromatic triamines with monohydric or
polyhydric phenols in the presence of formaldehyde or alkyl
formcel. Specific examples of suitable trifunctional benzoxazines
include:
##STR00009##
Curable Compositions
[0045] The non-halogenated monofunctional benzoxazine compound of
Structure 1 may be combined with one or more multifunctional
benzoxazine compounds to form a blend. Curable compositions may be
formulated such that the benzoxazine blend constitutes more than
80% by weight, preferably, at least 85% by weight of the total
weight of the composition. The curable compositions containing the
benzoxazines disclosed herein are formulated to remain thermally
stable (i.e., not degraded) at temperatures equal to or above
180.degree. C., e.g. 180.degree. C.-250.degree. C.
[0046] According to one embodiment, a curable composition is
formulated to contain more than 80% by weight, preferably, at least
85% by weight of a benzoxazine blend, which contains the
non-halogenated monofunctional benzoxazine compound of Structure 1
and at least one di-functional benzoxazine. The weight ratio of
monofunctional benzoxazine to difunctional benzoxazine may be from
40:60 to 10:90, in some cases, 50:50 to 10:90.
[0047] According to another embodiment, the curable composition
contains more than 80% by weight, preferably, at least 85% by
weight of a benzoxazine blend, which contains the liquid
benzoxazine compound of Structure 1 and at least one trifunctional
benzoxazine compound, wherein the mass ratio of liquid benzoxazine
to trifunctional benzoxazine is from about 50:50 to about
10:90.
[0048] According to yet another embodiment, the curable composition
contains more than 80% by weight, preferably, at least 85% by
weight of a benzoxazine blend, which contains the liquid
benzoxazine compound of Structure 1, at least one di-functional
benzoxazine, and at least one tri-functional benzoxazine, wherein
the trifunctional benzoxazine is at maximum 25% by weight based on
the total weight of the benzoxazine blend. According to yet another
embodiment, a curable composition is formulated to contain the
non-halogenated monofunctional benzoxazine compound of Structure 1,
at least one di-functional benzoxazine, specifically m-substituted
bis-benzoxazine, and at least one tri-functional benzoxazine,
specifically m-substituted tris-benzoxazine. It is preferred that
the combination of monofunctional and difunctional benzoxazine is
at a minimum of 85% by weight based on the total weight of the
benzoxazine blend, and the trifunctional benzoxazine is at maximum
15% by weight based on the total weight of the benzoxazine
blend.
[0049] The curable compositions discussed above may further include
additional components, such as tougheners and catalysts, but the
total amount of all benzoxazines in the composition is equal to or
greater than 80% by mass.
[0050] Unlike many conventional benzoxazine-based compositions, the
benzoxazine-based composition of the present disclosure does not
require the presence of a solvent. Although it is possible to add a
minor amount of solvent to further enhance film-formation.
[0051] For prepregging, the T.sub.g of the curable composition may
be adjusted by the appropriate proportions of monofunctional and
multifunctional benzoxazines to enable the formation of continuous
resin films, which are subsequently used to impregnate
reinforcement fibers.
[0052] For resin infusion, the viscosity of the curable composition
may be adjusted by the appropriate proportions of monofunctional
and multifunctional benzoxazines to a maximum of 5 Pas and a
preferred viscosity of 1 Pas or less at processing temperature, for
example, within the range of 100.degree. C.-150.degree. C.
[0053] As used herein, a "curable composition" refers to a
composition prior to curing. Upon curing, the monofunctional and
multifunctional benzoxazines readily polymerize via ring opening
polymerization. Such polymerization may be initiated cationically
(using cationic initiators) or thermally.
[0054] The addition of catalysts/accelerators is optional, but the
use of such additives may increase the cure rate and/or reduce the
cure temperatures. Suitable catalysts/accelerators for the
benzoxazine-based resin composition include, but are not limited
to, Lewis acids, such as phenols and derivatives thereof, strong
acids, such as alkylenic acids, methyl tosylate, cyanate esters,
p-toluenesulfonic acid, 2-ethyl-4-methylimidazole (EMI),
2,4-di-tert-butylphenol, BF.sub.3O(Et).sub.2, adipic acid, organic
acids, phosphorous pentachloride (PCl.sub.5).
[0055] Toughening agents (or tougheners) may be added to produce a
toughened resin matrix suitable for manufacturing advanced
composite structures. Suitable toughening agents include, but are
not limited to, thermoplastic toughening agents such as
polyethersulphone (PES), co-polymer of PES and
polyetherethersulphone (PEES), elastomers, including liquid rubbers
having reactive groups, particulate toughening agents such as
thermoplastic particles, glass beads, rubber particles, and
core-shell rubber particles.
[0056] Functional additives may also be included to influence one
or more of mechanical, rheological, electrical, optical, chemical,
flame resistance and/or thermal properties of the cured or uncured
resin composition. Examples of such functional additives include,
but are not limited to, fillers, color pigments, rheology control
agents, tackifiers, conductive additives, flame retardants,
ultraviolet (UV) protectors, and the like. These additives may take
the form of various geometries including, but are not limited to,
particles, flakes, rods, and the like.
Composite Materials
[0057] To form composite materials, the reinforcing fibers are
impregnated or infused with the curable resin composition using
conventional processing techniques such as prepregging and resin
infusion. After resin impregnation or infusion, curing is carried
out at elevated temperature up to 250.degree. C., preferably in the
range of 160.degree. C. to 220.degree. C., more preferably at about
180.degree. C.-200.degree. C., and with the use of elevated
pressure to restrain deforming effects of escaping gases, or to
restrain void formation, suitably at pressure of up to 10 bar,
preferably in the range of 3 to 7 bar abs. Suitably the cure
temperature is attained by heating at up to 5.degree. C./min. for
example 2.degree. C. to 3.degree. C./min and is maintained for the
required period of up to 9 hours, preferably up to 6 hours, for
example 3 to 4 hours. Temperature may be reduced by cooling at up
to 5.degree. C./min. for example up to 3.degree. C./min.
Post-curing at temperatures in the range of 190.degree. C. to
250.degree. C. may be performed, at atmospheric pressure, employing
suitable heating rates to improve the glass transition temperature
of the product or otherwise.
[0058] To fabricate prepregs, a resin film may be formed from the
curable resin composition by, for example, roll-coating, extrusion,
compression moulding, extrusion, melt-casting or belt-casting,
followed by laminating such film to one or both opposing surfaces
of a layer of reinforcement fibers in the form of, for example, a
non-woven mat of relatively short fibers, a woven fabric of
continuous fibers, or a layer of unilaterally aligned fibers (i.e.,
fibers aligned along the same direction), at temperature and
pressure sufficient to cause the resin film to soften and
impregnate the fibers. Alternatively, the prepreg may be fabricated
by providing the curable resin composition in liquid form, and
passing the layer of fibers through the liquid resin composition to
infuse the layer of fibers with the heat curable composition, and
removing the excess resin from the infused fibrous layer.
[0059] To fabricate a composite part from prepregs, plies of
impregnated reinforcing fibers are laid up on a tool and laminated
together by heat and pressure, for example by autoclave, vacuum or
compression moulding, or by heated rollers, at a temperature above
the curing temperature of the resin composition.
[0060] The resulting multi-ply layup may be anisotropic in which
the fibres are continuous and unidirectional, orientated
essentially parallel to one another, or quasi-isotropic in which
the fibres in a ply are orientated at an angle, e.g. 45.degree.,
30.degree., 60.degree. or 90.degree., relative to those in the
plies above and below. Orientations intermediate between
anisotropic and quasi-isotropic, and combination thereof, may also
be provided. Woven fabrics are an example of quasi-isotropic or
intermediate between anisotropic and quasi-isotropic. Suitable
layup contains at least 4, preferably at least 8 plies. The number
of plies is dependent on the application for the layup, for
example, the strength required, and layups containing 32 or even
more, for example several hundred, plies may be desirable to form
large composite parts. There may be provided toughening interleaf
or toughening particles, in the interlaminar regions between
plies.
[0061] To fabricate a composite part through resin infusion, e.g.
RTM or VaRTM processes, the first step is to form a dry fiber
preform in the shape of the desired structural part. The preform
generally includes a number of fabric layers or plies made from dry
reinforcement fibers that impart the desired reinforcing properties
to a resulting composite part. Nonwoven veils, for example,
nonwoven thermoplastic veils composed of randomly oriented
thermoplastic fibers, may be interleaved between adjacent fabric
plies as toughening materials. After the fiber preform has been
formed, the preform is placed in a mold. The curable resin
composition is injected/infused directly into fiber preform, and
then the resin-infused preform is cured.
[0062] The reinforcement fibers for forming composite materials and
parts may take the form of whiskers, short fibers, continuous
fibers, filaments, tows, bundles, sheets, plies, and combinations
thereof. Continuous fibers may further adopt any of unidirectional,
multi-directional, non-woven, woven, knitted, stitched, wound, and
braided configurations, as well as swirl mat, felt mat, and
chopped-fiber mat structures. The composition of the fibers may be
varied to achieve the required properties for the final composite
structure. Exemplary fiber materials may include, but are not
limited to, glass, carbon, graphite, aramid, quartz, polyethylene,
polyester, poly-p-phenylene-benzobisoxazole (PBO), boron,
polyamide, graphite, silicon carbide, silicon nitride, and
combinations thereof.
EXAMPLES
Example 1
[0063] The following synthesis was used for the reaction of
m-cresol, 3,5-xylidine and paraformaldehyde to form a substantially
monofunctional benzoxazine: [0064] 1. 18.68 g m-cresol, 20.94 g
3,5-xylidine and 20.76 g paraformaldehyde were added to a 250 ml
glass jar. [0065] 2. The mixture was then mixed at room temperature
(.about.20.0.degree. C.) for 20 minutes. [0066] 3. The jar was
immersed in an oil bath, the temperature of the oil bath was
increased to 115.degree. C., and the mixture was stirred for a
further 40 minutes. A colour change occurred at this stage. [0067]
Sandy brown/cream Orange/Brown [0068] Opaque.fwdarw.Transparent
[0069] Low Viscosity Low Viscosity [0070] 4. The oil bath was
increased in temperature to 120.degree. C. (took approximately 2
minutes to reach temperature) and the mixture was mixed for a
further 20 minutes. [0071] 5. The glass jar was removed from the
oil bath and allowed to cool for approximately 5 minutes. The
reaction product containing benzoxazine was then slowly added to 10
ml diethyl ether whilst stirring. This mixture was then stirred for
a further 20 minutes at room temperature (.about.20.0.degree. C.).
[0072] 6. Once stirred, the resulting benzoxazine-ether mixture was
washed 3 times with 2.0 M NaOH solution in water, in 100 ml
portions, in a separating funnel. [0073] 7. A further water wash
was carried out to neutralise the pH (pH7) after the addition of
the NaOH. [0074] 8. This mixture was left overnight and then
magnesium sulphate drying agent added to mixture and dried for 4
hours. [0075] 9. Residual ether was removed on a rotary evaporated
under vacuum for 15 minutes at 50.degree. C. [0076] 10. The final
product was dried under vacuum at 60.degree. C. in a vacuum oven
for 2 hours, resulting in a non-halogenated liquid benzoxazine
(labeled as "L-BOX") containing m-cresol, 3,5-xylidine benzoxazine
as a major component.
[0077] Rheological analysis at 30.degree. C. shows that the
viscosity of the non-halogenated liquid benzoxazine was 5 Pas.
[0078] A resin blend containing meta-Bisphenol-A benzoxazine and
the non-halogenated liquid benzoxazine L-BOX was prepared as
follows (meta-Bisphenol A benzoxazine 70:30 liquid benzoxazine, in
mass ratio).
[0079] 1. 12.0 g of liquid benzoxazine and 28.0 g of
meta-Bisphenol-A benzoxazine were degassed separately in a vacuum
oven at 110.degree. C. for 90 minutes.
[0080] 2. 9.0 g of the degassed liquid benzoxazine and 21.0 g of
the degassed meta-Bisphenol-A benzoxazine were added to a 250 ml
glass jar.
[0081] 3. The blend of materials was immersed in an oil bath at
90.degree. C. for 30 minutes and then stirred at 90.degree. C. for
45 minutes.
[0082] 4. The blend was removed from the oil bath and poured into
aluminum dishes.
[0083] 5. The dishes of blended benzoxazine were degassed in a
vacuum oven at 110.degree. C. for 90 minutes.
[0084] The degassed benzoxazine blends were cured using the
following cure cycle: 25.degree. C. to 180.degree. C. at 1.degree.
C. min.sup.-1, held for 2 hr, 180.degree. C. to 200.degree. C. at
1.degree. C. min.sup.-1, held for 2 hr, 200.degree. C. to
25.degree. C. at 2.degree. C. min.sup.-1.
[0085] The lower viscosity of the non-halogenated monofunctional
benzoxazine provided significant improvement in processing of a
70:30 meta-Bisphenol-A benzoxazine to monofunctional benzoxazine
formulation relative to neat meta-Bisphenol-A benzoxazine. This has
been observed in both resin filming for prepregging and also when
the films were applied to a carbon fabric. Resin filming was
carried out using a conventional knife over plate coating tool onto
a silicon based release paper.
[0086] Resin films were produced using the benzoxazine resin blend
discussed above. The resin films showed no signs of resin loss from
the release paper during the filming process. Some tack was
observed at room temperature and the resin film could be folded and
bent with none of the resin breaking away from the release
paper.
[0087] This compared favourably to when neat bisphenol-A
benzoxazine was filmed under the same conditions. With bisphenol-A
benzoxazine the film was lost from the silicon treated release
paper under roll-up of the film. This means that any prepreg
manufactured from the film would be of poor and inconsistent
quality.
Example 2
[0088] The following four monofunctional benzoxazines were prepared
by reacting phenol, paraformaldehyde and an amine selected from
aniline, o-toluidine, m-toluidine, and p-toluidine.
##STR00010##
[0089] The physical state of the synthesized benzoxazines at room
temperature (-25.degree. C.) was found as follows: [0090] 1.)
Aniline-based Liquid with some solid particles appearing on the
side of the glass jar after one month. [0091] 2.) o-toluidine-based
Liquid [0092] 3.) m-toluidine-based Liquid but solidified after 7.5
weeks. [0093] 4.) p-toluidine-based Liquid but solidified after
drying in vacuum oven during preparation.
[0094] FIG. 2 shows the TGA analysis of these benzoxazines.
P-toluidine-based and o-toluidine-based benzoxazines were not
stable in the temperature range of 180.degree. C. to 250.degree.
C.
[0095] Blends of Bisphenol-A benzoxazines and each of the
synthesized monofunctional benzoxazines were prepared according to
the weight ratio of 30:70 monofunctional benzoxazine to bisphenol-A
benzoxazine. A 30:70 blend of the liquid monofunctional benzoxazine
L-BOX prepared in Example 1 and bisphenol-A benzoxazine was also
prepared. The resin samples were then cured according to the
following curing cycle: heating to 180.degree. C. at 1.degree.
C./min, held for 2 hr, 180.degree. C. to 200.degree. C. at
1.degree. C./min, held for 2 hr. The T.sub.g of the cured resin
samples were measured by a Dynamic Mechanical Analysis (DMA) method
and are reported in Table 1.
TABLE-US-00001 TABLE 1 Monofunctional benzoxazine (30) Bis-A
benzoxazine (70) T.sub.g (.degree. C.) L-BOX 187 Aniline-based 161
o-toluidine-based 153 m-toluidine-based 174 p-toluidine-based
159
[0096] As can be seen from Table 1, cured T.sub.g of the resin
sample containing L-BOX is higher than that of other resin samples.
This means that L-BOX can be utilized at higher temperatures after
curing. Also, it was found that p-toluidine-based and
o-toluidine-based benzoxazines were not stable during cure cycle,
and showed weight loss of more than 15% at this temperature range
as determined by TGA. As such, they are not suitable for forming
prepregs and composite structures.
[0097] Ranges disclosed herein are inclusive and independently
combinable, and is inclusive of the endpoints and all intermediate
values within the ranges. For example, the range of "1% to 10%"
includes 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% as well as
intermediate values such as 1.1%, 1.2%, 1.3%, etc.
[0098] While various embodiments are described herein, it will be
appreciated from the specification that various combinations of
elements, variations of embodiments disclosed herein may be made by
those skilled in the art, and are within the scope of the present
disclosure. In addition, many modifications may be made to adapt a
particular situation or material to the teachings of the
embodiments disclosed herein without departing from essential scope
thereof. Therefore, it is intended that the claimed invention not
be limited to the particular embodiments disclosed herein, but that
the claimed invention will include all embodiments falling within
the scope of the appended claims.
* * * * *