U.S. patent application number 16/063983 was filed with the patent office on 2020-08-27 for method of treating uncured thermosetting resin matrices.
The applicant listed for this patent is Hexcel Composites SAS. Invention is credited to Jimmy Grondin, Esteban Villalon.
Application Number | 20200270408 16/063983 |
Document ID | / |
Family ID | 1000004842694 |
Filed Date | 2020-08-27 |
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United States Patent
Application |
20200270408 |
Kind Code |
A1 |
Villalon; Esteban ; et
al. |
August 27, 2020 |
METHOD OF TREATING UNCURED THERMOSETTING RESIN MATRICES
Abstract
Treating an uncured resin to impart energy to the resin enables
a stable Tg to be achieved whereby the resin may be stored and has
a low tack enabling subsequent processing and handling. The
invention provides a method of achieving a stable Tg without the
resin starting to cure and a method of determining the treatment
regime by which a resin with a stable Tg may be obtained. The resin
may be fresh or reused uncured resin and may contain fibrous
reinforcement.
Inventors: |
Villalon; Esteban; (Dagneux,
FR) ; Grondin; Jimmy; (Dagneux, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hexcel Composites SAS |
Dagneux |
|
FR |
|
|
Family ID: |
1000004842694 |
Appl. No.: |
16/063983 |
Filed: |
December 22, 2016 |
PCT Filed: |
December 22, 2016 |
PCT NO: |
PCT/EP2016/082440 |
371 Date: |
June 19, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J 5/24 20130101; B29B
13/08 20130101; B29B 11/16 20130101 |
International
Class: |
C08J 5/24 20060101
C08J005/24; B29B 11/16 20060101 B29B011/16; B29B 13/08 20060101
B29B013/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 2015 |
EP |
15202664.7 |
Dec 24, 2015 |
EP |
15202668.8 |
Claims
1. A method of producing a stabilised uncured resin matrix
composition comprising providing an uncured resin matrix
composition having an initial glass transition temperature (Tg) and
subjecting the resin matrix composition to: i. a first regime
comprising imparting energy to the uncured resin matrix composition
to raise the Tg by at least 5% to provide a raised Tg whereby the
residual cure of the resin matrix is reduced by a maximum of 20%,
preferably a maximum of 10% and more preferably a maximum of 5%;
and ii. a second regime comprising storing the uncured resin matrix
composition to provide a stabilised uncured resin matrix
composition wherein the Tg of the stabilised uncured resin matrix
composition is such that it does not increase by more than 10% from
the raised Tg when stored for 14 days.
2. A method according to claim 1 wherein the uncured resin matrix
composition is initially subjected to a method of determining the
treatment regime for stabilising the Tg of the uncured resin matrix
composition comprising: i) providing an uncured resin matrix
composition having an initial Tg and selecting a first regime
comprising an elevated temperature to impart energy to the uncured
resin matrix composition whereby the residual cure of the resin
matrix is reduced by a maximum of 20%, preferably a maximum of 10%
and more preferably a maximum of 5%; ii) imparting energy to the
resin matrix composition in the first regime so as to increase the
Tg of the resin matrix composition; iii) selecting a second regime
comprising storing the resin matrix composition wherein the second
regime is different to the first regime; iv) subjecting the resin
matrix composition to the second regime whereby the residual cure
of the resin matrix is reduced by a maximum of 10% and more
preferably a maximum of 5% the resin matrix composition; v)
measuring the raised Tg of the resin matrix composition prior to or
at commencement of the second regime and measuring the Tg of the
resin matrix composition periodically until over 14 days either: i.
the periodically measured Tg does not increase by more than 10%
from the raised Tg thereby determining the conditions of the first
regime and the second regime; or ii. where the periodically
measured Tg increases by more than 10% from the raised Tg,
modifying the first regime and/or second regime and repeating steps
ii), iv) and v) until the periodically measured Tg does not
increase by more than 10% from the raised Tg.
3. A method according to claim 1 wherein the resin matrix
composition comprises polymer chains and imparting energy to the
uncured resin matrix composition provides a reduction in cure
enthalpy to complete cure which is in the range of from 2% to
20%.
4. A method according to claim 1 wherein the raised Tg is increased
by at least 5% from the initial Tg.
5. A method according to claim 1 wherein the raised Tg is increased
by at least 25% from the initial Tg.
6. A method according to claim 1 wherein the temperature in the
second regime is ambient.
7. A method according to claim 1 wherein energy is imparted to the
uncured resin matrix composition in the first regime by heating the
uncured resin matrix composition to an elevated temperature for a
first period of time and subjecting the resin matrix composition to
pressure.
8. A method according to claim 1 wherein energy is imparted to the
uncured resin matrix composition in the first regime for a period
of 1 to 20 hours.
9. A method according to claim 1 wherein the second regime
comprises storing the resin matrix composition for at least 12
hours at ambient temperature.
10. A method according to claim 1 wherein the second regime
comprises storing the resin matrix composition for a period of at
least 24 hours to 10 weeks at ambient temperature.
11. A method according to claim 1 wherein the uncured resin matrix
composition is impregnated in a fibrous reinforcement material.
12. A method according to claim 14 wherein the fibrous
reinforcement material pre-impregnated with an uncured resin matrix
composition comprises an unused or uncured composite.
13. A method according to claim 1 wherein the uncured resin matrix
composition is in the form of discrete elements.
14. A method according to claim 1 wherein the stabilised uncured
resin matrix composition comprises discrete elements having a tack
in the range of from 0.1 to 0.6 as measured using the method as
disclosed in the description of this application.
15. A method of determining a treatment regime for stabilising the
glass transition temperature (Tg) of a curable resin matrix
composition comprising: i. providing a resin matrix composition
wherein the resin matrix composition may be uncured having an
initial Tg and selecting a first regime comprising an elevated
temperature to impart energy to the uncured resin matrix
composition whereby the residual cure of the resin matrix is
reduced by a maximum of 20%, preferably a maximum of 10% and more
preferably a maximum of 5%; ii. imparting energy to the resin
matrix composition in the first regime so as to increase the Tg of
the resin matrix composition; iii. selecting a second regime
comprising storing the resin matrix composition wherein the second
regime is different to the first regime; iv. subjecting the resin
matrix composition to the second regime whereby the residual cure
of the resin matrix is reduced by a maximum of 10%; vi) measuring
the Tg of the resin matrix composition periodically until over a
selected period of time ranging from 12 hours to 144 hours or
periods thereof either: a. the periodically measured Tg does not
increase by more than 1%, or 2%, or 4%, or 5% or 10% from the
raised Tg thereby determining the conditions of the first regime
and the second regime; or b. where the periodically measured Tg
increases by more than 1%, or 2%, or 4%/o, or 5% or 10% from the
raised Tg, modifying the first regime and/or second regime and
repeating steps ii), iv) and v) until the periodically measured Tg
does not increase by more than 1%, or 2%, or 4%, or 5% or 10% from
the raised Tg.
16. A treated uncured or unused resin matrix composition having a
stable glass transition temperature (Tg) at ambient temperature
wherein the uncured resin matrix composition has a raised Tg after
being treated and the Tg of the treated uncured resin matrix
composition remains within 10% of the initial raised Tg when stored
for at least 1 day.
17. A treated uncured resin matrix composition according to claim
16 wherein the Tg of the treated uncured resin matrix composition
remains within 10% of the raised Tg when stored for at least 1
week.
18. A treated uncured resin matrix composition according to claim
16 wherein the Tg of the treated uncured resin matrix composition
remains within 10% of the raised Tg when stored for at least 1
month.
19. A treated uncured resin matrix composition according to claim
16 in the form of discrete elements.
20. A treated uncured resin matrix composition according to claim
19 wherein the discrete elements have a tack F/Fref of not more
than 0.1 to 0.45 at ambient temperature where Fref=28.19N and F is
the maximum debonding force.
21. (canceled)
22. (canceled)
Description
[0001] This invention relates to a method of producing a stabilised
uncured thermosetting resin matrix and to a method of determining a
treatment regime for stabilising the glass transition temperature
(Tg) of an uncured thermosetting resin matrix and to a stabilised
uncured thermosetting resin matrix.
[0002] Curable thermosetting resin matrices or resin matrix
compositions are employed in a range of applications including in
composites which comprise fibrous reinforcement materials
impregnated with the cured resin matrix and in so-called "prepregs"
which comprise fibrous reinforcement materials impregnated with the
uncured resin matrix which may then be processed to form a
reinforced composite material. Such composite materials are
typically lightweight and of high strength and are used in many
structural applications such as in the automobile and aerospace
industries and in industrial applications such as wind turbine
components such as spars and the shells used to make the blades.
Such applications typically require the prepreg and composite to
comply with stringent requirements, often stipulated by the
manufacturer of products for such applications, as regards
handling, processing and storage of the materials especially where
safety considerations are paramount. The thermosetting resin matrix
composition (in short "matrix") comprises at least one resin
polymer component and at least one curative. The curative enables
the resin component to form an interpolymer network upon curing.
Curing is achieved by imparting energy to the resin matrix
composition, preferably the energy is in the form of heat.
[0003] Prepregs may be produced by a range of methods which
typically involve impregnation of a moving fibrous web with a
liquid, molten or semi-solid uncured thermosetting resin matrix
composition. The thermosetting resin matrix may be cast on a
substrate before it is applied to the reinforcement material or
alternatively, the thermosetting resin matrix composition may be
applied directly to the fibrous reinforcement material (direct
impregnation). Prepregs may also be manufactured by exposing the
fibrous reinforcement to a solvated thermosetting resin matrix
composition which is then followed by flashing off of the
solvent.
[0004] Prepreg is typically shipped to end-users on a roll. The
end-user invariably cuts the prepreg to a desired shape and lays
this up in relation to a mould to form curable stacks. These are
then cured to form composite parts.
[0005] The lay-up of prepreg inevitably results in sections of
unused prepreg (off cuts). Also, the production process of the
prepreg may result in unused sections or volume of resin
matrix.
[0006] Also, the production and the use of prepreg result in a list
of excess material types such as selvedge, end of rolls and off
cuts all being at uncured state. As generated unintentionally
through a production process, those materials can be identified as
by-products. In this application we will refer to the unused resin
matrix composition (or resin matrix) and the unused prepreg as
"by-product".
[0007] Due to safety considerations and stringent specification
relating to handling, processing and storage of thermosetting
resins matrices and prepregs, re-use of by-products has been
problematic. Furthermore, this activity has not proved economically
viable to date. Whilst recycle and re-use of dry carbon fibre waste
is known on a commercial scale, the costs and technical
difficulties of "recycling" prepregs by pyrolysis (thermal
degradation) and solvolysis (chemical dissolution) of the resin
matrix has presented difficulties due to high costs and energy
requirements to process the resin and in the case of prepregs, to
remove the resin from the fibrous reinforcement together with waste
product not necessarily being suitable for re-use in the supply
chain for products which are subject to stringent performance and
safety specifications.
[0008] US2015/0151454 describes a method and system for recycling
uncured composite offcuts comprising reinforcing fibres and uncured
polymer matrix material by mixing the uncured composite material in
a mixing device to blend the fibres and matrix material into a
generally homogeneous mixture and feeding the mixture from the
mixing device to form a component or a semi-finished product. The
offcuts are fed into the mixing device directly without
pre-treatment of the offcuts.
[0009] Unused resin and prepregs may be stored in a wide range of
ambient conditions from sub-zero to high temperature and humidity
depending on the prevailing climate in the storage location and may
undergo changes in properties, particularly in Tg. Where such
materials are processed into a prepreg or composite product and
waste resin material is generated, re-use of such material may not
be possible in applications where it is necessary to be able to
guarantee the conditions under which the resin has been stored
prior to use. A need remains for uncured resins to be suitable for
use in the forming prepregs and composite products irrespective of
the prior storage conditions under which the properties of the
resin may have varied.
[0010] The invention aims to obviate or at least mitigate the above
described problems and/or to provide improvements generally.
[0011] According to the invention there is provided a method or
process and a composition as defined in any one of the accompanying
claims.
[0012] We have now found that by treating an uncured resin to
impart energy to the resin matrix without advancing the cure of
resin matrix composition to a value above 60% of its total cure
enthalpy, preferably above 50% of its total cure enthalpy and more
preferably above 40% of its total cure enthalpy, or more preferably
above 30% of its total cure enthalpy or more preferably above 20%
or above 10% of its total cure enthalpy, the Tg of the resin may be
stabilised such that it does not change significantly over an
extended period. The uncured resin may then be suitable for
processing to form a prepreg or composite having the properties
required for a particular application.
[0013] The glass transition temperature or Tg is determined in
accordance with ASTM D3418 using Digital Scanning Calorimetry
(DSC).
[0014] The unused resin matrix and/or unused prepreg may have a
residual cure of greater than 5% of their total cure enthalpy, or
greater than 10% of their total cure enthalpy, or greater than 15%
of their total cure enthalpy, or greater than 20% of their total
cure enthalpy, or greater than 30% of their total cure enthalpy, or
greater than 40% of their total cure enthalpy. In this context,
"unused" or "uncured" as used interchangeably in this application
is thus defined by the residual cure available in the unused resin
matrix composition or unused prepreg.
[0015] Digital Scanning Calorimetry is utilized to determine % cure
and reaction enthalpy. The total heat or reaction enthalpy detected
during the DSC measurement is identified as the heat released by
the curing reaction when the resin matrix composition is heated
from a starting temperature of typically 10.degree. C. (or room
temperature of 21.degree. C.) to a temperature at which cure is
anticipated to be completed. For fast cure epoxy resins the
temperature at which cure is anticipated to be fully completed is
typically 100 to 225.degree. C., preferably from 100 to 160.degree.
C. and the ramp rate for the temperature is typically set at
10.degree. C./s or faster rate.
[0016] Once the total heat enthalpy has been established, the
residual cure of any subsequent test sample of the resin which has
been subjected to a particular cure can then be analysed by
exposing the test sample to the same heat up rate and the remaining
reaction enthalpy is determined using DSC. The degree of cure of
the test sample is then given by the following formula: cure
%=(.DELTA. Hi-.DELTA. He)/.DELTA. Hi.times.100 where .DELTA.Hi is
the heat generated by the uncured resin heated from the starting
temperature up to the anticipated fully cured temperature (in the
present invention typically 150.degree. C.) and .DELTA.He the heat
generated by the test sample heated up after initial cure to it
being fully cured at 150.degree. C. (so .DELTA.He represents the
residual enthalpy which is released following complete curing of
the sample following on from the initial cure schedule).
[0017] The invention provides in a first aspect a method of
producing a stabilised unused resin matrix composition comprising
providing a resin matrix composition having an initial Tg and
subjecting the resin to: [0018] I. a first regime comprising
imparting energy to the resin matrix composition to raise the Tg by
at least 5.degree. C. to provide a raised Tg without substantially
curing the resin; and [0019] II. a second regime comprising storing
the resin matrix composition to provide a stabilised resin matrix
composition wherein the Tg of the stabilised uncured resin is such
that it does not increase by more than 10.degree. C. from the
raised Tg when stored for at least 24 hours at room temperature
(21.degree. C.).
[0020] In Step I. "without substantially curing" means that the
residual cure of the resin matrix is reduced by a maximum of 20%,
preferably a maximum of 10% and more preferably a maximum of 5%. In
Step I the imparting of energy without substantially curing of the
matrix composition results in a reduction of residual cure enthalpy
in the range of from 1 to 20%, preferably from 2 to 15% and more
preferably from 5% to 10% and/or combinations of the aforesaid
ranges.
[0021] The curing reaction of the resin matrix composition
progresses more rapidly during the step of imparting of energy but
this is arrested or reduced to a very low rate in Step II when the
resin matrix composition is stored at a temperature below room
temperature or at room temperature (21.degree. C.)
respectively.
[0022] The duration of step I is selected so minimize the impact on
the residual cure enthalpy of the resin matrix composition. The
duration is in the range of from 72 hours to 30 mins, preferably
from 48 hours to 1 hour, more preferably from 24 hours to 4 hours,
more preferably from 18 hours to 6 hours and/or combinations of the
aforesaid ranges.
[0023] Step I of the process of the invention is sometimes referred
to as "staging".
[0024] To determine whether curing commences and so to determine
the conditions to be applied in treating the resin, methods known
in the art may be employed, for example FTIR. In this respect we
refer to "Applications of FTIR on Epoxy Resins--Identification,
Monitoring the Curing Process, Phase Separation and Water Uptake",
M Gonzalez Gonzalez, J C Cabanelas, J Baselga, as published in
"Infrared Spectroscopy--Materials Science, Engineering and
Technology", Edited by Prof. Theophanides Theophile, 2012 In a
preferred embodiment, energy is imparted to the resin matrix
composition by heating.
[0025] This may occur in a number of ways: by heat transfer,
radiation heating, ultrasound, microwave radiation, or infrared
light.
[0026] Suitably, upon imparting energy to the resin matrix and
following step I of the process of the invention, the raised Tg of
the resin is at least 5.degree. C., preferably at least 20.degree.
C., desirably at least 30.degree. C. and especially greater than
50.degree. C. The raised T.sub.g is preferably not increased beyond
a value greater than preferably at least 40.degree. C., desirably
at least 60.degree. C. and especially greater than 80.degree. C. in
comparison to its original T.sub.g before the start of the process
of the invention.
[0027] The resin suitably has a Tg above the ambient temperature
under which it is likely to be used or stored thereby reducing the
likelihood of the uncured resin being tacky and being susceptible
to agglomeration which may present processing difficulties. Most
fundamentally, given that Tg is linked to polymer backbone
mobility, a Tg higher than ambient decreases the likelihood that
the resin matrix will exhibit enough mobility to undergo continuing
cross-linking reactions. The resin having a stabilised Tg may
advantageously be handled and cut without problems occurring due to
its tackiness or its flow (such as gumming and adherence)
[0028] A resin matrix composition treated according to the
invention which has a Tg in the range of from 5.degree. C. to
20.degree. C., desirably from 10 to 30.degree. C., more preferably
from 15.degree. C. to 50.degree. C., and even more preferably from
20.degree. C. to 80.degree. C. and/or combinations of the aforesaid
ranges. The invention provides storage over an extended period at
ambient temperature without there being significant clustering or
agglomeration of the resin when in the form of discrete elements
irrespective of whether the storage temperature is regulated.
Advantageously, this allows resins to be stored in a range of
ambient conditions without the need to provide refrigeration or
cooling areas to ensure the stored resin remains usable in
downstream processes.
[0029] Energy may be imparted to the uncured resin in the first
regime by any suitable means, for example heating, pressure and
microwave, holding the resin matrix composition at room
temperature. Preferably, energy is imparted to the uncured resin
matrix composition by heating to an elevated temperature for a
first period of time. The resin may be subjected to pressure to
impart energy to the resin. Suitably, the resin matrix composition
is heated to an elevated temperature from 30.degree. C. up to a
temperature below the temperature at which the resin commences
curing, preferably from 30 to 70.degree. C. Suitably, energy is
imparted to the resin matrix composition in the first regime for a
period of 1 to 100 hours, preferably the first regime has a
duration in the range of from duration is in the range of from 72
hours to 30 mins, preferably from 48 hours to 1 hour, more
preferably from 24 hours to 4 hours, more preferably from 18 hours
to 6 hours and/or combinations of the aforesaid ranges.
[0030] Once energy has been imparted to the resin matrix
composition in the first regime, the resin matrix will have a
raised Tg and is then suitably subjected to a second regime under
which the raised Tg may increase. The uncured resin is subjected to
that regime until the Tg remains stable in that it does not
increase by more than 10%, preferably more than 8%, or 6% or 5% or
2% or 1% from the raised Tg when stored for at least 1 day or 2
days or 4 days or 5 days or 7 days or 14 days and/or combinations
of the aforesaid percentages and durations.
[0031] Preferably the temperature in the second regime is ambient.
In the second regime the resin is suitably stored for at least 12
hours at ambient temperature or a temperature which is below
ambient. Preferably the second regime comprises storing the resin
for a period of at least 24 hours to 10 weeks at ambient
temperature.
[0032] Different resin matrix compositions may require different
conditions to impart sufficient energy to the resin to provide a
stable Tg whilst not commencing curing. Where the resin matrix
composition has been previously used in the formation of a prepreg
or composite, the conditions under which the resin matrix
composition has been stored or processed may also influence the
particular stabilising treatment regime required in order to
provide an uncured resin matrix composition having a stabilised Tg.
Suitably the conditions of the first regime and the second regime
in the method for providing a stabilised uncured resin matrix
composition are determined by subjecting an uncured resin matrix
composition of a particular type of from a particular source to a
method of determining the treatment regime for stabilising the
glass transition temperature (Tg) of that uncured resin matrix
composition.
[0033] In a second aspect, the invention provides a method of
determining a treatment regime for stabilising the glass transition
temperature (Tg) of a curable resin matrix composition comprising:
[0034] i) providing an uncured or unused resin matrix composition
having an initial Tg and selecting a first regime comprising an
elevated temperature and residence time to impart energy to the
uncured or unused resin matrix composition whereby the residual
cure of the resin matrix is reduced by a maximum of 20%, preferably
a maximum of 10% and more preferably a maximum of 5%; [0035] ii)
imparting the selected energy over the selected residence time so
as to increase the Tg of the resin matrix composition; [0036] iii)
selecting a second regime comprising storing the resin matrix
composition at a selected second temperature and second residence
time wherein the second regime is different to the first regime,
the selected temperature and residence time being selected so that
the Tg does not increase by more than 10%, preferably more than 8%,
or 6% or 5% or 2% or 1% .degree. C. from the raised Tg when stored
for at least 1 day or 2 days or 4 days or 5 days and/or
combinations of the aforesaid percentages and durations; [0037] iv)
subjecting the resin matrix composition to the second regime;
[0038] v) measuring the raised Tg of the resin matrix composition
prior to or at commencement of the second regime and measuring the
Tg of the resin matrix composition periodically until over a
selected period of time ranging from 12 hours to 144 hours or
periods thereof either: [0039] a. the periodically measured Tg does
not increase by more than 1%, or 2%, or 4%, or 5% or 10% from the
raised Tg thereby determining the conditions of the first regime
and the second regime; or [0040] b. where the periodically measured
Tg increases by more than 1%, or 2%, or 4%, or 5% or 10% from the
raised Tg, modifying the first regime and/or second regime and
repeating steps ii), iv) and v) until the periodically measured Tg
does not increase by more than 1%, or 2%, or 4%, or 5% or 10% from
the raised Tg.
[0041] The temperature and duration to which the resin matrix
composition is subjected in the first regime may be selected having
regard to the temperature at which the resin matrix composition
commences curing or proceeds through to full cure or proceeds to
cure at a high rate. The particular resin matrix composition which
is to be treated may be heated and analysed using known methods of
determining Tg known in the art to determine this temperature.
Suitably, a temperature below that level will be appropriate to
provide a means of imparting energy to the resin matrix composition
without curing commencing. Desirably, the resin matrix composition
is heated to an elevated temperature from 30.degree. C. up to a
temperature below the temperature at which the resin matrix
composition commences curing, preferably from 30 to 110.degree. C.
Suitably, energy is imparted to the uncured resin matrix
composition in the first regime for a period of 1 to 144 hours,
preferably in the range of from duration is in the range of from 72
hours to 30 mins, preferably from 48 hours to 1 hour, more
preferably from 24 hours to 4 hours, more preferably from 18 hours
to 6 hours and/or combinations of the aforesaid ranges.
[0042] Once energy has been imparted to the resin matrix
composition in the first regime, the resin matrix composition will
have a raised Tg. This Tg, referred to as the "raised Tg" of the
resin matrix composition is suitably measured using methods known
in the art, preferably differential scanning calorimetry (DSC). The
resin matrix composition is then suitably subjected to a second
regime under which the Tg of the uncured resin matrix composition
is measured periodically to determine any change, particularly an
increase in Tg. Where the Tg of the resin matrix composition does
not increase by more than 10% from the initial Tg following the
energy imparting step and preferably by not more than 5% from the
raised Tg following the energy imparting step over a period of 1
day, the resin matrix composition may be considered as having a
stable Tg. If the Tg continues to vary outside these bounds, the
resin matrix composition is not considered as having a stable Tg
and the method repeated using the same or a different sample of the
resin matrix composition.
[0043] In this case, the conditions of the first regime should be
altered by increasing the temperature and/or period under which
energy is imparted to the resin matrix composition and the same
sample or a different sample of the uncured resin matrix
composition subjected to the first and second regime with the Tg of
the resin matrix composition being periodically determined in the
second regime.
[0044] With knowledge of the present method of determining a
treatment regime for stabilising the glass transition temperature
(Tg) of a curable resin matrix composition, the skilled person will
be able to modify the conditions of the first regime to determine
the conditions under which the resin matrix composition may be
treated to provide a stabilised Tg. The treatment regime, as
determined by this method using samples of a particular resin
matrix composition from a particular source may then be employed to
stabilise a resin matrix composition of that type and from the same
source in a method according to the first aspect of the
invention.
[0045] We have found that by employing a method of stabilising an
uncured resin matrix composition according to a first aspect of the
invention, a treated uncured resin matrix composition having a
stable glass transition temperature (Tg) at ambient temperature may
be provided. The stabilised uncured resin matrix composition has a
raised Tg after being treated and the Tg of the treated uncured
resin matrix composition remains within 10% of the raised Tg when
stored for at least 1 day.
[0046] The resin matrix composition having a stabilised Tg may then
be stored and used in a downstream process of forming a prepreg
comprising a fibrous reinforcement and the uncured resin matrix
composition having a stabilised Tg.
[0047] Suitably, the treated uncured resin matrix composition has a
Tg which remains within 10% or 5% of the raised Tg following the
energy imparting step when stored for at least 1 week, preferably
for at least 1 month.
[0048] Preferably, the treated uncured resin matrix composition is
in the form of discrete elements. Preferably, the discrete elements
have a tack F/Fref of not more than 0.1 to 0.45 at ambient
temperature (21.degree. C.) where Fref=28.19N and F is the maximum
debonding force as defined with reference to WO2013087653 A1 and
DUBOIS ET AL.: `Experimental analysis of prepreg tack`
LAMI)UBP/IFMA 5 Mar. 2009 and as summarized below.
[0049] Tack measurement is performed using the probe tack test as
disclosed in the above Dubois etal. paper. A 1 kN Instron 5543
universal testing machine (Norwood, Mass., USA) is used. The upper
grip of the machine is replaced by an aluminium cylindrical probe
of 10 mm diameter mounted on the moving crosshead of the machine,
via a 50 N capacity load cell. The probe can be heated with a
flexible heater. A PT100 temperature sensor linked to a
Proportional-Integral-Derivative (PID) temperature controller
regulates the temperature. Test samples are applied on the lower
support. The probe, which is surrounded by a heater, is set at a
given temperature, and then the probe is brought into contact with
the sample, and the maximum reading of the load cell was recorded
for each test. The test procedure used for the tack measurement is
as follows: 1. Test strips of prepreg or resin matrix material are
cut to meet the probe. Samples were then put in a climatic chamber
for a given time at controlled temperature and Relative Humidity;
2. Before each run, the contact surface of the probe and the
support are cleaned with acetone; 3. Contact time, contact force
and debonding rate are set for the mechanical cycle; 4. The
temperature of the probe was set by regulator; 5. Once the
temperature of the probe reached the set point and was
equilibrated, the sample was removed from the climatic chamber and
was positioned on the support. It should be noted that the side of
the sample protected by a release paper, i.e. the tackiest side,
was applied without pressure on the lower grip. The release paper
was then removed; and 6. The value given by the load cell was reset
and the test started. Time, force and crosshead displacement were
then measured.
[0050] The Dubois etal method allows tack to be measured
objectively and repeatably by using the equipment as described
above and by measuring the maximum debonding force for a probe
which is brought in contact with the sample structure at an initial
pressure of 30N at a constant temperature of 30.degree. C. and
which is subsequently displaced at a rate of 5 mm/min. For these
probe contact parameters, the tack F/Fref for the tack material is
in the range of from 0.1 to 0.6 or from 0.1 to 0.45 at room
temperature (21.degree. C.) where Fref=28.19N and F is the maximum
debonding force.
[0051] By having a low tack, suitably at ambient temperature, the
discrete elements may be readily processed and are less susceptible
to agglomeration. This facilitates cutting and handling at room
temperature (21.degree. C.) for example when using the treated
unused or uncured resin matrix composition in the formation of a
prepreg and may reduce process downtime by reducing the requirement
for servicing or cleaning process apparatus for example when
forming a prepreg.
[0052] Alternatively, the discrete elements may be cooled to a
temperature below ambient to reduce their tack prior to and/or
during cutting and processing to enhance their processability.
Typically the temperature could be reduced to -18.degree. C.
[0053] Suitably, the treated uncured resin matrix composition
comprises discrete elements which have a torque peel (T Peel) of
less than 10N/10 mm and desirably less than 5N/10 mm at 20.degree.
C. T Peel is preferably determined by a method as set out in the
below Examples.
[0054] The present invention may be employed with a wide-range of
curable resin matrix compositions. One preferred family of resin
matrix compositions contains curable epoxy resin components. The
resin matrix composition may comprise other components for example
thermoplastics or rubbers in the epoxy resin matrix composition.
The epoxy resin material component or epoxy resin polymer or in
short, epoxy resin may be selected from any of the commercially
available diglycidylethers of Bisphenol-A either alone or in
combination, typical materials in this class include GY-6010
(Huntsman Advanced Materials, Duxford, UK), Epon 828 (Resolution
Performance Products, Pemis, Netherlands), and DER 331 (Dow
Chemical, Midland, Mich.).
[0055] The Bisphenol-A epoxy resin component preferably constitutes
from 30 to 50% w/w (weight % of the component based on the total
weight of the composition containing the component) of the total
resin matrix and the remainder may be a thermosetting resin
component material and/or a thermoplastic material.
[0056] Preferred epoxy resins have an Epoxy Equivalent Weight (EEW)
in the range from 150 to 1500 preferably a high reactivity such as
an EEW in the range of from 200 to 500 and the resin composition
comprises the resin and an accelerator or curing agent. Suitable
epoxy resins may comprise blends of two or more epoxy resins
selected from monofunctional, difunctional, trifunctional and/or
tetrafunctional epoxy resins.
[0057] Suitable difunctional epoxy resins, by way of example,
include those based on: diglycidyl ether of bisphenol F, diglycidyl
ether of bisphenol A (optionally brominated), phenol and cresol
epoxy novolacs, glycidyl ethers of phenol-aldelyde adducts,
glycidyl ethers of aliphatic diols, diglycidyl ether, diethylene
glycol diglycidyl ether, aromatic epoxy resins, aliphatic
polyglycidyl ethers, epoxidised olefins, brominated resins,
aromatic glycidyl amines, heterocyclic glycidyl imidines and
amides, glycidyl ethers, fluorinated epoxy resins, glycidyl esters
or any combination thereof.
[0058] Difunctional epoxy resins may be selected from diglycidyl
ether of bisphenol F, diglycidyl ether of bisphenol A, diglycidyl
dihydroxy naphthalene, or any combination thereof.
[0059] Suitable trifunctional epoxy resins, by way of example, may
include those based upon phenol and cresol epoxy novolacs, glycidyl
ethers of phenol-aldehyde adducts, aromatic epoxy resins, aliphatic
triglycidyl ethers, dialiphatic triglycidyl ethers, aliphatic
polyglycidyl amines, heterocyclic glycidyl imidines and amides,
glycidyl ethers, fluorinated epoxy resins, or any combination
thereof. Suitable trifunctional epoxy resins are available from
Huntsman Advanced Materials (Monthey, Switzerland) under the
tradenames MY0500 and MY0510 (triglycidyl para-aminophenol) and
MY0600 and MY0610 (triglycidyl meta-aminophenol). Triglycidyl
meta-aminophenol is also available from Sumitomo Chemical Co.
(Osaka, Japan) under the tradename ELM-120.
[0060] Suitable tetrafunctional epoxy resins include N,N,
N',N'-tetraglycidyl-m-xylenediamine (available commercially from
Mitsubishi Gas Chemical Company under the name Tetrad-X, and as
Erisys GA-240 from CVC Chemicals), and
N,N,N',N'-tetraglycidylmethylenedianiline (e.g. MY0720 and MY0721
from Huntsman Advanced Materials). Other suitable multifunctional
epoxy resins include DEN438 (from Dow Chemicals, Midland, Mich.)
DEN439 (from Dow Chemicals), Araldite ECN 1273 (from Huntsman
Advanced Materials), and Araldite ECN 1299 (from Huntsman Advanced
Materials).
[0061] The epoxy resin compositions used preferably also comprises
one or more urea based curing agents and it is preferred to use
from 0.5 to 10 wt % based on the weight of the epoxy resin of a
curing agent, more preferably 1 to 8 wt %, more preferably 2 to 8
wt %. Preferred urea based materials are the range of materials
available under the commercial name Urone.RTM.. In addition to a
curing agent, a suitable accelerator such as a latent amine-based
curing agent, such as dicyanopolyamide (DICY).
[0062] Another suitable product comprising resin which may be
employed in the present invention is the product available from
Hexcel Composites Ltd as HexMC.RTM. or HexForm.RTM. which also
comprises fibres. Examples of preferred resins for use in this
invention include those employed in multifunctional epoxy resin
matrix compositions which are commercially available under the
following trade names Hex MC.RTM. M21, HexMC.RTM.M77, HexMC.RTM.
M78, HexMC.RTM. M81 and HexMC.RTM. M92 and 8552 (all as supplied by
Hexcel Corporation).
[0063] Other suitable resins for use in the present invention
include polyester resins and bismaleimide resins.
[0064] In a preferred embodiment, the uncured resin matrix
composition is impregnated in a fibrous reinforcement material. The
fibrous reinforcement material pre-impregnated with an uncured
resin matrix composition may comprise a by-products of uncured
composite which has previously been subjected to processing and has
been discarded as an offcut in that prior process.
[0065] Exemplary fibres include glass, carbon, graphite, boron,
ceramic and aramid. Preferred fibres are carbon and glass fibres.
Hybrid or mixed fibre systems may also be envisaged. The use of
cracked (i.e. stretch-broken) or selectively discontinuous fibres
may be advantageous to facilitate lay-up of the product according
to the invention and improve its capability of being shaped.
Although a unidirectional fiber alignment is preferable, other
forms may also be used. Typical textile forms include simple
textile fabrics, knit fabrics, twill fabrics and satin weaves. It
is also possible to envisage using non-woven or non-crimped fiber
layers.
[0066] The invention is illustrated by the following non-limiting
examples and with reference to the accompanying drawings in
which
[0067] FIG. 1 presents a diagrammatic view of a lay-up of a resin
matrix composition according to an embodiment of the invention
using a vacuum bag;
[0068] FIG. 2 presents a diagrammatic view of gripping layers of a
sample according to another embodiment of the invention; and
[0069] FIG. 3 presents a diagram showing the relationship between
peel torque (in N/10 mm) in relation to Tg (in .degree. C.).
EXAMPLE 1
[0070] Several batches of pre-preg products comprising uncured
resin matrix composition and carbon fibres were subjected to T Peel
testing. The pre-preg product was as follows:
[0071] 3 batches of M21E/34%/UD 194/IMA-12K: [0072] Batch 1: N23C14
02A [0073] Batch 2: N14302 12A [0074] Batch 3: N14205 05A
[0075] 1 batch of M21E/34%/UD 268/IMA-12K: [0076] Batch 1*:
N22A1801A
[0077] Stabilizing T.sub.g
[0078] Five samples from each batch were subjected to a first
regime by heating in an oven at 50.degree. C. under a dry
atmosphere for following periods: 24 h, 72 h, 144 h, 152 h and 200
h. For each batch, a sample of fresh material was kept without
being subjected to the first regime. And referred to as T0 below.
After the first regime, the samples were held in a freezer at
-18.degree. C. (0.degree. F.). Furthermore, each specimen was
analyzed by DSC.sup.1 test just after the first regime and prior to
the second regime to determine Tg. The Tg results are shown in
Table 1. .sup.1Differential scanning calorimetry
[0079] The DSC cycle used for analysis consisted of a ramp of
10.degree. C./min from -60.degree. C. (-76.degree. F.) to
315.degree. C. (600.degree. F.); samples comprised 7 mg of resin
matrix composition (approximately 20 mg of prepreg). The Tg value
measured is the "midpoint" temperature. Unless otherwise stated,
DSC measurements may be carried out using this method.
TABLE-US-00001 TABLE 1 Tg for each batch T0 24 h @ 50.degree. C. 72
h @ 50.degree. C. 144 h @50.degree. C. 152 h@50.degree. C. 200
h@50.degree. C. BATCH 1 -0.99.degree. C. 1.1.degree. C.
7.39.degree. C. 17.63.degree. C. 18.19.degree. C. 29.74.degree. C.
BATCH 2 -2.degree. C. 0.97.degree. C. 6.24.degree. C. 16.6.degree.
C. 19.33.degree. C. 26.13.degree. C. BATCH 3 -0.84.degree. C.
2.91.degree. C. 9.19.degree. C. 15.41.degree. C. 23.04.degree. C.
27.39.degree. C. BATCH 1* -0.24.degree. C. 2.63.degree. C.
8.15.degree. C. 17.41.degree. C. 19.71.degree. C. 27.91.degree.
C.
Storage Simulation
[0080] The samples were subjected to a process to simulate storage
of resin matrix composition chips in a bulk quantity in a storage
bag under harsh conditions of storage. This simulation increased
the chance that clustering or agglomeration of chips might occur A
temperature of 60.degree. C. to mimic bright sunlight and a
pressure of 1 bar (14.5 psi) was applied, corresponding to the
higher pressure that a chip could perceive at the bottom of a
storage bag. The storage conditions were performed by using a
"vacuum bag" method as set out below and with reference to FIG.
1.
[0081] The apparatus for the vacuum bag method is shown in FIG. 1
which shows a tool 1 upon which is mounted a vacuum bag 2 having a
first side 2a and a second side 2b sealed with mastic 2c and a
sandwich arrangement comprising two layers of Teflon coated glass,
referred to as "breathers", 3a, 3b, layers of resin matrix
composition product 4a and 4b and a Teflon coated glass primer 5
(length 50 mm) with which to commence the T Peel test.
[0082] Two layers of the sample resin matrix composition are
mounted in the apparatus and the assembly was placed in an oven for
15 hours at 60.degree. C. and a pressure of 1 bar was applied using
a vacuum pump.
[0083] Samples Preparation and T Peel Test (in Accordance with ASTM
D1876)
[0084] Once the samples had been subjected to the Storage
Simulation the samples were prepared for use in T Peel tests. The T
Peel test allows the adhesion strength between two layers of a
sample bonded to each other to be determined using a tensile
machine. An average strength of debonding between layers is
measured and a "Peel torque" is determined. The "Peel torque" is
equal to the average strength normalized to a 10 mm width. For each
batch and each treatment, 3 samples were tested according to T Peel
test ISO11339. The samples were cut to the following dimensions:
[0085] Width: 30 mm [0086] Length: 300 mm [0087] Depth: 2 plies
[0088] Orientation: 0.degree.
[0089] The two layers of the sample were gripped respectively in a
fixed jaw and a mobile jaw as shown in FIG. 2. The two layers of
the sample are then separated by moving the mobile jaw away from
the fixed jaw in the direction shown. The force applied in the test
to separate the layers and its variation is measured using software
in accordance with ASTM D1876, from which an average value of
debonding strength is calculated. The Peel torque value is
determined by the climbing drum peel test to determine the peel
resistance of adhesive bonds in accordance with ASTM D1781. This
test consists of peeling a thin strip of metal from a thick strip
of resin matrix material by winding the thin strip around a drum.
Torque is applied to the drum by pulling down on straps wrapped
around the drum. The thin strip of metal is wound on the drum at a
smaller radius than the straps. The difference in radius (i.e.
moment arm) results in a large torque being applied to the drum
compared with that applied on the thin strip. The resultant upward
motion causes the thin strip to peel from the thicker strip. The
average peel torque T can be calculated as follows:
T=(Ro-Ri).times.(Fp-Fo)/b
where Ro is the flange radius, Ri is the drum radius, Fp is the
average load required to bend and peel adherend (including load
required to overcome the torque resistance of the drum), Fo is the
load required to overcome the torque resistance of the drum and b
is the specimen width. Both Ro and Ri account for one half the
loading strap thickness. The upward motion of the drum causes the
thin strip to be peeled from the thicker resin matrix material
resulting in bond failure.
[0090] The results of the T Peel tests are set out in Tables 2 to
5. For each batch three samples were tested under each regime and
the results are the mean value of the three tests.
TABLE-US-00002 TABLE 2 Average deboning Average Peel BATCH 1
Strength .sup.2(N) torque .sup.3(N/10 mm) T0 34.8 11.6 24 h @
50.degree. C. 38.7 12.9 72 h @ 50.degree. C. 2.2 0.7 144 h
@50.degree. C. 0.1 0.0 152 h@50.degree. C. 0.4 0.2 200 h@50.degree.
C. 0.2 0.1
TABLE-US-00003 TABLE 3 Average deboning Average Peel BATCH 2
Strength .sup.4(N) torque .sup.5(N/10 mm) T0 34 11.3 24 h @
50.degree. C. 43.2 14.4 72 h @ 50.degree. C. 2.1 0.7 144 h
@50.degree. C. 0.4 0.1 152 h@50.degree. C. 0.2 0.1 200 h@50.degree.
C. 0 0
TABLE-US-00004 TABLE 4 Average deboning Average Peel BATCH 3
Strength .sup.6(N) torque .sup.7(N/10 mm) T0 40.2 13.4 24 h @
50.degree. C. 47.1 15.7 72 h @ 50.degree. C. 1.5 0.5 144 h
@50.degree. C. 0.9 0.3 152 h@50.degree. C. 0.2 0.1 200 h@50.degree.
C. 0.3 0.1
TABLE-US-00005 TABLE 5 Average deboning Average Peel BATCH 4
Strength .sup.8(N) torque .sup.9(N/10 mm) T0 42.0 14.0 24 h @
50.degree. C. 41.4 13.8 72 h @ 50.degree. C. 15.5 5.1 144 h
@50.degree. C. 1.7 0.6 152 h@50.degree. C. 1.6 0.5 200 h@50.degree.
C. 1.4 0.5
[0091] A plot of the T Peel value versus Tg midpoint value for each
batch was plotted and is shown in FIG. 3. .sup.2Mean value
calculated from 3 specimens results.sup.3Mean value calculated from
3 specimens results.sup.4Mean value calculated from 3 specimens
results.sup.5Mean value calculated from 3 specimens results
[0092] For batches 1, 2 and 3 adhesion decreases significantly
around 5.degree. C. of Tg and debonding occurs at approximately
15.degree. C. A slight difference is noticed with results of batch
1* in that the adhesion decreases less abruptly than with the other
batches and debonding occurs at around a Tg of 20.degree. C. The
batch 1* plies were thicker than the batches 1, 2 and 3 plies which
may contribute to the tailing effect observed for batch 1*.
.sup.6Mean value calculated from 3 specimens results.sup.7Mean
value calculated from 3 specimens results.sup.8Mean value
calculated from 3 specimens results.sup.9Mean value calculated from
3 specimens results
[0093] For every batch debonding is reduced where the Tg is
5.degree. C. and debonding occurs completely where the Tg value is
above 20.degree. C. for chips which have been treated according to
the method of the invention and subjected to a simulation of harsh
storage conditions.
[0094] In summary, a resin matrix composition material which is
staged so that it has a Tg over 20.degree. C. is suitable for
storage over an extended period at ambient temperature without
exhibiting clustering or agglomeration irrespective of whether the
storage temperature is regulated.
* * * * *